FIRE PROTECTION HANDBOOK Nineteenth Edition VOLUMES I & II
Arthur E. Cote, P.E. Editor-in-Chief John R. Hall, Jr., Ph.D. Associate Editor
Pamela A. Powell Managing Editor
Casey C. Grant, P.E. Consulting Editor
Robert P. Benedetti, P.E. Guy R. Colonna, P.E. Mark T. Conroy Arthur E. Cote, P.E.
Rita Fahy, Ph.D. Casey C. Grant, P.E. Raymond A. Grill, P.E. John R. Hall, Jr., Ph.D. Milosh T. Puchovsky, P.E.
Dena E. Schumacher Gary O. Tokle Robert J. Vondrasek, P.E. Gregory E. Harrington, P.E.
Section Editors
National Fire Protection Association Quincy, Massachusetts
Editor-in-Chief: Associate Editor: Managing Editor: Consulting Editor: Senior Developmental Editor: Developmental Editor: Project Editor: Permissions Editors: Additional Readings Editor: Editorial-Production Services: Interior Design: Cover Design: Manufacturing Manager: Printer:
Arthur E. Cote, P.E. John R. Hall, Jr., Ph.D. Pamela A. Powell Casey C. Grant, P.E. Robine J. Andrau Dana A. Richards Irene F. Herlihy Josiane B. Domenici and Janet I. Provost Nora H. Jason Omegatype Typography, Inc. Omegatype Typography, Inc. Cameron, Inc. Ellen J. Glisker Courier/National
Copyright © 2003 National Fire Protection Association, Inc. One Batterymarch Park Quincy, Massachusetts 02269
All rights reserved. No part of the material protected by this copyright may be reproduced or utilized in any form without acknowledgment of the copyright owner, nor may it be used in any form for resale without written permission from the copyright owner. Notice Concerning Liability: Publication of this work is for the purpose of circulating information and opinion among those concerned for fire and electrical safety and related subjects. While every effort has been made to achieve a work of high quality, neither NFPA nor the authors and contributors to this work guarantee the accuracy or completeness of or assume any liability in connection with the information and opinions contained in this work. The NFPA and the authors and contributors in no event shall be liable for any personal injury, property, or other damages of any nature whatsoever, whether special, indirect, consequential, or compensatory, directly or indirectly resulting from the publication, use of, or reliance upon this work. This work is published with the understanding that the NFPA and the authors and contributors to this work are supplying information and opinion but are not attempting to render engineering or other professional services. If such services are required, the assistance of an appropriate professional should be sought.
The following are registered trademarks of the National Fire Protection Association: National Electrical Code® and NEC® National Fire Codes® Life Safety Code® and 101® National Fire Alarm Code® and NFPA 72® Learn Not to Burn® Risk Watch® Sparky® NFPA 5000™ and Building Construction and Safety Code™
NFPA No.: FPH1903 ISBN: 0-87765-474-3 Library of Congress Control No.: 2002105867
Printed in the United States of America 03
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Dedication In recognition of those who suffered from the tragedies of September 11, 2001, this Handbook is dedicated to all who have given their lives in an effort to make this world a safer place.
Contents
Preface xv Introduction xvii
SECTION 1 Safety in the Built Environment 1.1 1.2 1.3
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1–1
Challenges to Safety in the Built Environment ■ John R. Hall, Jr. Fundamentals of Safe Building Design ■ Martin W. Johnson Codes and Standards for the Built Environment ■ Arthur E. Cote and Casey C. Grant
SECTION 2 Basics of Fire and Fire Science 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9
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1–3 1–33 1–51
2–1
An Overview of the Fire Problem and Fire Protection ■ John R. Hall, Jr., and Arthur E. Cote Fundamentals of Fire-Safe Building Design ■ John M. Watts, Jr. Chemistry and Physics of Fire ■ D. D. Drysdale Dynamics of Compartment Fire Growth ■ Richard L. P. Custer Theory of Fire Extinguishment ■ Raymond Friedman Fundamentals of Fire Detection ■ Richard L. P. Custer and James A. Milke Basics of Passive Fire Protection ■ Marc L. Janssens Explosions ■ Robert Zalosh Environmental Issues in Fire Protection ■ Jane I. Lataille
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2–5 2–37 2–51 2–73 2–83 2–97 2–103 2–119 2–133
viii ■ Contents
SECTION 3 Information and Analysis for Fire Protection 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13
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Fire Loss Investigation ■ Richard L. P. Custer Fire Data Collection and Databases ■ Marty Ahrens, Stan Stewart, and Paul L. Cooke Use of Fire Incident Data and Statistics ■ Marty Ahrens, Patricia Frazier, and Jim Heeschen Introduction to Fire Modeling ■ Craig Beyler and Philip J. DiNenno Deterministic Computer Fire Models ■ William D. Walton, Douglas J. Carpenter, and Christopher B. Wood Probabilistic Fire Models ■ John M. Watts, Jr. Fire Hazard Analysis ■ Richard W. Bukowski Fire Risk Analysis ■ John R. Hall, Jr. Simplified Fire Growth Calculations ■ Edward K. Budnick, David D. Evans, and Harold E. Nelson Simple Fire Hazard Calculations ■ Morgan J. Hurley and James R. Quiter Simplified Fire Risk Calculations ■ John M. Watts, Jr. Applying Models to Fire Protection Engineering Problems and Fire Investigations ■ Richard L. P. Custer Performance-Based Codes and Standards for Fire Safety ■ Milosh T. Puchovsky Overview of Performance-Based Fire Protection Design ■ Frederick W. Mowrer Formats for Fire Hazard Inspecting, Surveying, and Mapping ■ Thomas R. Wood
SECTION 4 Human Behavior in Fire Emergencies 4.1 4.2 4.3
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Human Behavior and Fire ■ John L. Bryan Calculation Methods for Egress Prediction ■ Rita F. Fahy Concepts of Egress Design ■ James K. Lathrop
SECTION 5 Fire and Life Safety Education 5.1 5.2 5.3 5.4
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Fire and Life Safety Education: A Measure of Fire Department Excellence ■ Meri-K Appy and Dennis Compton Using Data for Public Education Decision Making ■ John R. Hall, Jr. Fire and Life Safety Education: Theory and Techniques ■ Edward Kirtley Reaching High-Risk Groups ■ Sharon Gamache
3–1 3–5 3–15 3–33 3–69 3–83 3–97 3–105 3–115 3–131 3–147 3–161 3–169 3–181 3–197 3–207
4–1 4–3 4–33 4–57
5–1 5–3 5–17 5–31 5–45
Contents
5.5 5.6 5.7 5.8
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Understanding Media: Basics for the Twenty-First Century ■ Dena E. Schumacher Evaluation Techniques for Fire and Life Safety Education ■ Karen Frush and John R. Hall, Jr. Campus Fire Safety ■ Ed Comeau Juvenile Firesetting ■ Paul Schwartzman
SECTION 6 Fire Prevention 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9 6.10 6.11 6.12 6.13 6.14 6.15 6.16 6.17 6.18 6.19 6.20 6.21 6.22 6.23 6.24 6.25 6.26 6.27 6.28 6.29 6.30 6.31 6.32 6.33
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Electrical Systems and Appliances ■ Robert M. Milatovich Control of Electrostatic Ignition Sources ■ Don R. Scarbrough and Thomas H. Pratt Lightning Protection Systems ■ John M. Caloggero Emergency and Standby Power Supplies ■ George W. Flach Heating Systems and Appliances ■ Peter J. Gore Willse Boiler Furnaces ■ Shelton Ehrlich Heat Transfer Fluids and Systems ■ John A. LeBlanc Industrial and Commercial Heat Utilization Equipment ■ Raymond Ostrowski Oil Quenching and Molten Salt Baths ■ Raymond Ostrowski Stationary Combustion Engines and Fuel Cells ■ James B. Biggins Metalworking Processes ■ Paul G. Dobbs Automated Processing Equipment ■ John F. Bloodgood Fluid Power Systems ■ Paul K. Schacht Welding, Cutting, and Other Hot Work ■ August F. Manz Woodworking Facilities and Processes ■ John M. Cholin Spray Finishing and Powder Coating ■ Don R. Scarbrough Dipping and Coating Processes ■ John Katunar III Plastics Industry and Related Process Hazards ■ George Ouellette Chemical Processing Equipment ■ Richard F. Schwab Manufacture and Storage of Aerosol Products ■ David L. Fredrickson Storage of Flammable and Combustible Liquids ■ Anthony M. Ordile Storage of Gases ■ Theodore C. Lemoff and Carl Rivkin Storage and Handling of Chemicals ■ John A. Davenport Storage and Handling of Solid Fuels ■ Kenneth W. Dungan Storage and Handling of Records ■ Thomas Goonan Storage and Handling of Grain Mill Products ■ James E. Maness Grinding Processes ■ Delwyn D. Bluhm Refrigeration Systems ■ Henry L. Febo, Jr. Lasers ■ Yadin David Semiconductor Manufacturing ■ Roger Benson and Heron Peterkin Waste Handling and Control ■ Lawrence G. Doucet Hazardous Waste Control ■ Gary R. Glowinski Housekeeping Practices ■ L. Jeffrey Mattern
5–63 5–79 5–95 5–107
6–1 6–7 6–55 6–65 6–79 6–85 6–133 6–147 6–153 6–175 6–187 6–193 6–201 6–207 6–211 6–221 6–237 6–249 6–261 6–273 6–287 6–297 6–315 6–321 6–337 6–347 6–361 6–381 6–393 6–401 6–407 6–417 6–441 6–457
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SECTION 7 Organizing for Fire and Rescue Services 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 7.10 7.11 7.12 7.13 7.14 7.15 7.16 7.17 7.18 7.19 7.20 7.21 7.22 7.23
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Fire Department Administration and Operations ■ Robin Paulsgrove Evaluation and Planning of Public Fire Protection ■ John Granito Fire Department Information Systems ■ Brian P. Duggan Fire Service Legal Issues ■ Maureen Brodoff Fire Service Occupational Safety, Medical, and Health Issues ■ Stephen N. Foley Pre-Incident Planning for Industrial and Commercial Facilities ■ Michael J. Serapiglia Wildland Fire Management ■ Dan W. Bailey and Richard E. Montague Public Fire Protection and Hazmat Management ■ Michael S. Hildebrand and Gregory G. Noll Managing the Response to Hazardous Material Incidents ■ Charles J. Wright Organizing Rescue Operations ■ Richard Wright Effect of Building Construction and Fire Protection Systems on Fire Fighter Safety ■ Francis L. “Frank” Brannigan Fire Loss Prevention and Emergency Organizations ■ Thomas F. Barry and Larry Watrous Emergency Medical Services ■ James O. Page Fire Prevention and Code Enforcement ■ Ronald R. Farr and Steven F. Sawyer Training Fire and Emergency Services ■ Douglas P. Forsman Fire Department Facilities and Fire Training Facilities ■ Nicholas J. Cricenti Public Emergency Services Communication Systems ■ Evan E. Stauffer Fire Department Apparatus and Equipment ■ Robert Tutterow Fire and Emergency Services Protective Clothing and Protective Equipment ■ Bruce W. Teele Fire Streams ■ Michael A. Wieder Planning Fire Station Locations ■ Robert C. Barr and Anthony P. Caputo Alternate Water Supplies ■ Donald C. Freyer and Laurence J. Stewart Fireground Operations ■ Bernard J. Klaene and Russell Sanders
SECTION 8 Materials, Products, and Environments 8.1 8.2
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Fire Hazards of Materials ■ Frederic B. Clarke Combustion Products and Their Effects on Life Safety ■ Gordon E. Hartzell
7–1 7–5 7–29 7–51 7–67 7–73 7–85 7–95 7–111 7–129 7–159 7–169 7–187 7–207 7–211 7–225 7–237 7–251 7–263 7–283 7–299 7–311 7–319 7–333
8–1 8–5 8–13
Contents
8.3 8.4 8.5 8.6 8.7 8.8 8.9 8.10 8.11 8.12 8.13 8.14 8.15 8.16 8.17 8.18
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Wood and Wood-Based Products ■ John M. Cholin Fire-Retardant and Flame-Resistant Treatments of Cellulosic Materials ■ James R. Shaw Fibers and Textiles ■ Salvatore A. Chines and Jeffrey O. Stull Flammable and Combustible Liquids ■ Orville M. Slye, Jr. Gases ■ Theodore C. Lemoff Medical Gases ■ Guy R. Colonna Oxygen-Enriched Atmospheres ■ Coleman J. Bryan and Joel M. Stoltzfus Plastics and Rubber ■ Guy R. Colonna Pesticides ■ Greg Moerer, Larry Thompson, and Matthew Woody Explosives and Blasting Agents ■ Lon D. Santis Deflagration (Explosion) Venting ■ Richard F. Schwab Explosion Prevention and Protection ■ Erdem A. Ural and Henry W. Garzia Dusts ■ Richard F. Schwab Metals ■ Robert W. Nelson Upholstered Furniture and Mattresses ■ Vytenis Babrauskas Air-Moving Equipment ■ Jane I. Lataille
SECTION 9 Detection and Alarm 9.1 9.2 9.3 9.4 9.5 9.6 9.7 9.8 9.9
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Fire Alarm Systems ■ Wayne D. Moore Automatic Fire Detectors ■ James C. Roberts Notification Appliances ■ Robert P. Schifiliti Fire Alarm System Interfaces ■ Fred Leber Fire Alarm Systems: Inspection, Testing, and Maintenance ■ John M. Cholin Household Fire Warning Equipment ■ Richard W. Bukowski Fire Protection Surveillance and Fire Guard Services ■ Lawrence Wenzel Gas and Vapor Detection Systems and Monitors ■ John M. Cholin Carbon Monoxide Detection in Residential Occupancies ■ Art Black
SECTION 10 Water-Based Suppression 10.1 10.2 10.3 10.4
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Characteristics and Hazards of Water and Water Additives for Fire Suppression ■ John A. Frank Fixed Water Storage Facilities for Fire Protection ■ William E. Wilcox Water Distribution Systems ■ Gerald R. Schultz Water Supply Requirements for Public Supply Systems ■ Lawrence J. Wenzel
8–29 8–47 8–61 8–87 8–101 8–123 8–133 8–149 8–173 8–183 8–193 8–201 8–221 8–233 8–243 8–269
9–1 9–5 9–17 9–35 9–43 9–55 9–79 9–89 9–97 9–111
10–1 10–7 10–19 10–37 10–59
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10.5 10.6 10.7 10.8 10.9 10.10 10.11 10.12
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Hydraulics for Fire Protection ■ Kenneth W. Linder Determining Water Supply Adequacy ■ Gerald R. Schultz Stationary Fire Pumps ■ J. D. Jensen Power Supplies and Controllers for Motor-Driven Fire Pumps ■ James S. Nasby and Milosh T. Puchovsky Principles of Automatic Sprinkler System Performance ■ Russell P. Fleming Automatic Sprinklers ■ Kenneth E. Isman Automatic Sprinkler Systems ■ Milosh T. Puchovsky Sprinkler Systems for Storage Facilities ■ James E. Golinveaux and Joseph B. Hankins Hanging and Bracing of Water-Based Fire Protection Systems ■ Russell P. Fleming Residential Sprinkler Systems ■ Daniel Madrzykowski and Russell P. Fleming Water Spray Protection ■ Christopher L. Vollman Ultra-High-Speed Suppression Systems for Explosive Hazards ■ Robert M. Gagnon Water Mist Fire Suppression Systems ■ Jack R. Mawhinney Standpipe and Hose Systems ■ Jeffrey M. Shapiro Care and Maintenance of Water-Based Extinguishing Systems ■ James M. Fantauzzi and David R. Hague Water Supplies for Sprinkler Systems ■ Wayne M. Martin Microbiologically Influenced Corrosion in Fire Sprinkler Systems ■ Bruce H. Clarke and Anthony M. Aguilera
SECTION 11 Fire Suppression without Water 11.1 11.2 11.3 11.4 11.5 11.6 11.7
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Halogenated Agents and Systems ■ Gary M. Taylor Direct Halon Replacement Agents and Systems ■ Philip J. DiNenno Carbon Dioxide and Application Systems ■ Thomas J. Wysocki Chemical Extinguishing Agents and Application Systems ■ James D. Lake Foam Extinguishing Agents and Systems ■ Joseph L. Scheffey Fire Extinguisher Use and Maintenance ■ Mark T. Conroy Extinguishing Agents and Application Techniques for Combustible Metal Fires ■ Robert W. Nelson
Building and Site Planning for Fire Safety ■ Building Construction ■ Richard J. Davis
10–129 10–159 10–171 10–185 10–213 10–235 10–247 10–265 10–275 10–301 10–351 10–369 10–391 10–403
11–1
SECTION 12 Confining Fires 12.1 12.2
10–71 10–97 10–111
11–3 11–21 11–65 11–77 11–91 11–119 11–141
12–1 Albert M. Comly, Jr.
12–5 12–17
Contents
12.3 12.4 12.5 12.6 12.7 12.8 12.9 12.10 12.11 12.12 12.13 12.14 12.15
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Interior Finish ■ Donald W. Belles Structural Integrity during Fire ■ Peter J. Gore Willse Confinement of Fire in Buildings ■ Harold D. Hicks, Jr. Smoke Movement in Buildings ■ James A. Milke and John H. Klote Venting Practices ■ Gunnar Heskestad Structural Fire Safety in One- and Two-Family Dwellings ■ Richard A. Morris Ventilation of Commercial Cooking Operations ■ David P. Demers Special Structures ■ Wayne D. Holmes Evaluating Structural Damage ■ David J. Hammond and Paul R. De Cicco Building Transportation Systems ■ Edward A. Donoghue Fire Hazards of Construction, Alteration, and Demolition of Buildings ■ Richard J. Davis Miscellaneous Building Services ■ John E. Kampmeyer Air-Conditioning and Ventilating Systems ■ William A. Webb
SECTION 13 Systems Approaches to Property Classes 13.1 13.2 13.3 13.4 13.5 13.6 13.7 13.8 13.9 13.10 13.11 13.12 13.13 13.14 13.15 13.16 13.17 13.18 13.19 13.20
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Assessing Life Safety in Buildings ■ John M. Watts, Jr. Occupancies in Special Structures and High-Rise Buildings ■ Wayne D. Holmes Assembly Occupancies ■ Gregory E. Harrington Mercantile Occupancies ■ Ed Schultz Business Occupancies ■ Brian L. Marburger Educational and Day-Care Occupancies ■ Catherine L. Stashak Detention and Correctional Facilities ■ Thomas W. Jaeger Healthcare Occupancies ■ Daniel J. O’Connor Board and Care Facilities ■ Philip R. Jose Lodging Occupancies ■ April Leyla Berkol and Thomas G. Daly Apartment Buildings ■ Kenneth Bush Lodging or Rooming Houses ■ Alfred J. Longhitano and Mario A. Antonetti One- and Two-Family Dwellings ■ Harry L. Bradley Manufactured Housing and Recreational Vehicles ■ A. Elwood Willey and Walter P. Sterling Storage Occupancies ■ Bruce W. Hisley Cultural Resources ■ Danny L. McDaniel Warehouse and Storage Operations ■ Jeffrey Moore Materials-Handling Equipment ■ Richard E. Munson Industrial Occupancies ■ David P. Demers Motion Picture and Television Studios and Soundstages ■ Raymond A. Grill
12–43 12–61 12–93 12–113 12–127 12–145 12–151 12–165 12–183 12–197 12–211 12–221 12–237
13–1 13–5 13–15 13–29 13–41 13–49 13–59 13–67 13–77 13–95 13–103 13–113 13–125 13–129 13–135 13–147 13–159 13–183 13–201 13–213 13–223
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13.21 13.22 13.23 13.24 13.25 13.26 13.27 13.28 13.29
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Food Processing Facilities ■ Jane I. Lataille Solvent Extraction ■ C. Louis Kingsbaker Protection of Wastewater Treatment Plants ■ James F. Wheeler Fire Protection of Laboratories Using Chemicals ■ Ray H. Richards Fire Protection of Telecommunications Facilities ■ Ralph E. Transue Protection of Electronic Equipment ■ Robert J. Pearce Electric Generating Plants ■ Leonard R. Hathaway Nuclear Facilities ■ Wayne D. Holmes Mining and Mineral Processing ■ Larry J. Moore
SECTION 14 Transportation Fire Safety 14.1 14.2 14.3 14.4 14.5 14.6 14.7 App A App B App C
App D App E App F
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Index
Motor Vehicles ■ Larry Strawhorn Alternative Fuels for Vehicles ■ Carl H. Rivkin Fixed Guideway Transit and Passenger Rail Systems ■ Frank J. Cihak Rail Transportation Systems ■ James P. Gourley, Arthur Candenquist, and Scott Gorton Aviation ■ Thomas J. Lett Marine Vessels ■ Randall Eberly and Guy R. Colonna Fire Protection for Road Tunnels ■ Arthur G. Bendelius Tables and Charts ■ Vytenis Babrauskas SI Units and Conversion Tables ■ Robert P. Benedetti What Time Has Crystallized into Good Practice: The Fire Protection Handbook from 1896 to 2003 ■ Gordon P. “Mac” McKinnon Global Organizations with Fire Protection Interests ■ Richard Candee Organizations with Fire Protection Interests in the United States ■ Robine Andrau Official NFPA Documents (Complete List as of July 19, 2002) ■ Leona Attenasio Nisbet
13–229 13–237 13–245 13–259 13–267 13–279 13–287 13–295 13–305
14–1 14–3 14–17 14–41 14–51 14–75 14–91 14–127 A–1 B–1
C–1 D–1 E–1 F–1
I–1
Preface
Pam Powell Managing Editor
T
he Fire Protection Handbook—there is no other fire protection reference quite like it. Its history stretches back more than a century, and this 19th edition honors the traditions of thoroughness and accuracy that make the Handbook so central to any fire protection library. At the same time, this 19th edition has much that is new and expanded. The most obvious change is the new, two-volume format and new interior design. These changes are in response to reader suggestions to make the Handbook physically easier to handle and the pages easier to read. More substantive changes include • Our list of authors has grown from 232 in the 18th edition to our current 247. • The organization has been refined to add new sections on “Safety in the Built Environment,” “Human Behavior in Fire Emergencies,” “Fire Suppression Without Water,” and “Transportation Fire Safety.” • Case studies and a new feature called “Worldview” have been added. • Chapter summaries highlight the chapter’s main points.
These and many other changes to the Handbook share a simple goal: to help readers with their important work of making our world a bit safer. From time to time during the last 30 months, I imagined the reader using the Fire Protection Handbook. You need a fact, a crucial piece of information, and the Handbook is the source you can count on. Today, I visualize and thank the team that created and produced the Handbook for the reader. In my mind’s eye, I see the authors working on their chapters at night or on the weekend, while “real” work piled up, messages became more insistent, the boss grew impatient, and the people at home wondered why that chapter was so important. There are 247 of these authors and coauthors. They worked hard to meet two sets of high standards—ours and their own—and usually managed to do it cheerfully. I’m particularly awed by the efforts of John Cholin, Richard Custer, John Hall, and Jack Watts, who each wrote four chapters, and of Jane Lataille, Milosh Puchovsky, and Richard Schwab, the authors of three chapters each. I see the 13 section editors, those responsible for the technical quality of the Handbook. They recruited authors, reviewed their material, and resolved technical differences. Sounds simple . . . until you think about doing those tasks for as many as 33 chapters. Special places in heaven are reserved for my colleagues Robine Andrau, John Hall, and Dana Richards. They faced a 10,000-page manuscript, a messy stack of paper almost four feet (roughly 1.3 m) high. As senior developmental editor and developmental editor, respectively, Robine and Dana checked facts, found art, wrote chapter summaries and “Worldviews,” and performed organizational miracles on tables, figures, subheads, and references. As associate editor, John read every chapter with his usual keen eye for old data, untested assumptions, and statements that rested on soft ground. Very quietly, these three people challenged authors and the section editors alike—and the Handbook is better for it. Many other people contributed to this Handbook in large and small ways. If I somehow neglected to thank you before, I thank you now.
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Introduction
Arthur E. Cote, P.E. Editor-in-Chief
S
ince its first edition more than a century ago, the Fire Protection Handbook has endeavored to fulfill the needs of the fire protection community for a single-source handbook on the state of the art in fire protection and fire prevention practices. It was originally known as the Handbook of the Underwriter’s Bureau of New England and was first published in 1896, the same year that the National Fire Protection Association was founded. The original author, Everett U. Crosby, was manager of the Underwriter’s Bureau of New England, and one of the stock fire insurance company executives who came together to develop a consistent set of sprinkler rules in 1895 that led to the formation of NFPA. He also became the first secretary of NFPA, serving from 1896 to 1903, and chairman of the NFPA executive committee from 1903 to 1907. His father, Umberto C. Crosby, was the first chairman of the NFPA executive committee, serving in 1896 and 1897, and the second president of NFPA, serving from 1897 to 1900. Henry A. Fiske joined Crosby as coeditor of the 2nd edition in 1901, and the Handbook later became known as the Crosby-Fiske Handbook of Fire Protection. H. Walter Forster joined the editorial team in 1918, and in 1935, Crosby, Fiske, and Forster donated all rights to their handbook to the NFPA. NFPA has published all successive editions since that 8th edition to this 19th edition. The history of the Handbook from 1896 to 1996 can be found in Appendix C, “What Time Has Crystallized into Good Practice,” by Gordon P. (Mac) McKinnon. The Fire Protection Handbook has changed significantly in the past 100 years. While the body of knowledge in the field of fire protection has proliferated, the Handbook has kept pace, expanding from 183 pages in the first edition to over 3200 pages in this 19th edition. As the most pressing concerns of fire protection have evolved, from property protection concerns of citywide conflagrations in the late 1800s, through life safety concerns for public occupancies at the beginning of the 1900s, to an overall systems approach in use today, the number of subjects covered by the Handbook has increased greatly. This is evidenced by the expansion of the text from the short, running commentary that made up the first edition to material organized into 200 chapters and for the first time two volumes. Today, there are more chapters than there were pages in 1896! The Handbook is organized around the six major strategies that are the building blocks of a systems approach to fire safety through balanced fire protection: • • • • • •
Prevention of ignition Design to slow early fire growth Detection and alarm Suppression Confinement of fire Evacuation of occupants
Production of the Fire Protection Handbook through 19 editions and 107 years has involved literally thousands of fire protection experts from within and outside NFPA. However, in addition to its founders over the past three quarters of a century, a handful of individuals have been especially responsible for establishing the Handbook as the “reference of record” of fire protection practitioners. • Robert S. Moulton, late NFPA technical secretary, who, during his 40 years of service, edited the 9th, 10th, and 11th editions;
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• George H. (Hitch) Tryon, late NFPA assistant vice president, who edited the 12th and 13th editions; • Richard E. Stevens, late NFPA vice president and chief engineer, who, during his 35 years with the Association, contributed to five editions of the Handbook and served as chief technical consultant for the 14th and 15th editions; • Gordon P. (Mac) McKinnon, retired NFPA editor-in-chief, who was directly involved in the preparation of five editions of the Handbook over a quarter century. He served as editorial coordinator of the 12th edition, managing editor of the 13th edition, editor of the 14th and 15th editions, and consulting editor for the 16th edition; • Jim L. Linville, managing editor of the 16th, 17th, and 18th editions; • John R. Hall, Jr., who devised the current organization of the Handbook around the systems approach to fire protection beginning with the 17th edition, and served as associate editor for this 19th edition; • Pamela A. Powell, managing editor for this 19th edition. I am especially proud to have had the privilege of acting as editor-in-chief for the 16th, 17th, 18th, and this 19th edition. In offering this edition of the Fire Protection Handbook, the editors solicit suggestions for improvements in the interest of making future editions increasingly useful to all concerned. Every effort has been made to ensure that the text is consistent with the best available information on current fire protection practices. However, the National Fire Protection Association, as a body, is not responsible for the contents, as there has been no opportunity for the membership to review the Handbook before its publication. If readers discover errors or omissions, the editors would appreciate those shortcomings being called to their attention.
SAFETY IN THE BUILT ENVIRONMENT
I
n recent years the term built environment has come into widespread use to describe all human-made components of our civilized world. The entire Fire Protection Handbook and not just Section 1 is focused on the built environment either in whole or in part. The built environment, as the term suggests, includes more than simply land-based buildings. It includes all manmade structures, whether or not they are intended for human habitation. Furthermore, the structures are not limited to fixed structures; they include transport vehicles such as automobiles, railway transport, surface ships, submarines, aircraft, and spacecraft. Nor are they limited to the relatively conventional structures found in cities but include facilities that can present unique safety challenges, such as underground mines, petrochemical refineries, nuclear power plants, and genetic research laboratories. Many safety challenges exist with today’s built environment, and these challenges are growing daily as we introduce more exotic variations to our urban habitat and related environment. From a general sense, we have different ways of approaching the built environment, and that is the focus of this section. The first step in addressing the safety-related challenges of today’s built environment is to clarify and define the issue. Chapter 1, “Challenges to Safety in the Built Environment,” provides statistical information on the long-term trends in safety-related problems and short-term trends and patterns that help to show the relative status and importance of various strategies to mitigate these safety-related problems. Chapter 2, “Fundamentals of Safe Building Design,” focuses on current building design, concentrating on safety-related issues within the context of the critical building design phase of a property’s life. Much present-day activity centers on the safe design of buildings and other structures; this chapter outlines the approaches being used to properly address these challenges. Chapter 3, “Codes and Standards for the Built Environment,” provides an overview of building codes and standards, from their origins nearly 4000 years ago in the time of Hammurabi of Babylon to the documents that form the foundation of today’s civilization. This overview includes an explanation of the differences between codes, standards, and other regulatory documents and how these documents differ around the world. Also look for these: Sections 2 through 13 of this handbook concentrate on fire safety in structures. Section 14, “Transportation Fire Safety,” deals with fire protection in a nonstructural portion of the built environment.
1–1
SECTION
1
Art Cote
1–2 SECTION 1 ■ Safety in the Built Environment
Chapter 1
Challenges to Safety in the Built Environment
Defining the Challenges to Safety Types of Harm Relevant Major Societal Trends Major Databases Thermal-Related Hazards Objects in Motion Water or Storms Hazardous Environment Summary Bibliography Chapter 2
1–3 1–3 1–4 1–4 1–5 1–6 1–9 1–17 1–23 1–29 1–30
Fundamentals of Safe Building Design 1–33
Challenges to the Built Environment Design Loads and Forces Basic Building Systems and Components
1–33 1–34 1–42
Fundamental Design Concepts Basic Design Methodology Summary Bibliography Chapter 3
Codes and Standards for the Built Environment
History of Regulations for the Built Environment Concepts of Safety versus Risk Role of Codes in the Built Environment Role of Standards in the Built Environment in the United States International Arena Enforcement of Codes and Standards Code Sets for the Built Environment Summary Bibliography
1–46 1–47 1–49 1–50
1–51 1–51 1–52 1–53 1–54 1–56 1–58 1–61 1–64 1–64
CHAPTER 1
SECTION 1
Challenges to Safety in the Built Environment John R. Hall, Jr.
W
or better understanding of the factors driving perilous events and the performance of the built environment to the challenges those events represent.
e ask a great deal of our built environments. We ask that they protect us from hazards arising from objects we bring into the environments. We ask that they protect us from hazards arising from the components of the built environment, that is, the structure itself. We ask that the built environment itself not be harmful. And we ask that our built environments provide a protective envelope to protect us from harm arising outside the built environment. We expect all this from our built environments, in addition to functionality, attractive appearance, affordability of construction and operation, and a host of other nonsafety goals and objectives. The first step in evaluating the challenges to safety in the built environment is to classify the types of harm encountered. This chapter examines the data on which such an evaluation can be based.
Options for Data Natural disasters—including major wildfires, but excluding other major fires—involve probabilistically occurring natural-event triggers, whose probabilities vary by location and by characteristics (e.g., soil conditions) that themselves vary by location. Therefore, risk assessment for these hazards can be set up using risk maps for the triggering events, and codes can control design choices by specifying building performance in response to specified severities of these triggering events (analogous to fire scenarios as used in performance-based design). The actual data on these natural disasters—and the losses they cause, which reflect both the event severity and the building performance in resisting damage from the event—are what we track in order to gain insight into both the challenges to buildings and the performance of different building materials and designs in response to those challenges. In the area of fire safety, the instances of harm occur in well-defined incidents, most of which lead to an encounter with an official body (e.g., a fire department) and the creation of an official record (i.e., an incident report). These reported incidents are represented by the large or small samples of incidents captured by one or another national database. At least in the United States, these databases provide a baseline for surveillance of the magnitude of the harm proper design is intended to prevent or reduce. These databases provide not only information on the size of the problem but also considerable detail on the nature of the problem, answering many, but far from all, of the questions we have about the effect of design choices and code language on resulting harm. It is true that the database encompasses instances where other parties are far more responsible than the builders and managers of built environments for the harm, instances that could not have been prevented or mitigated by even the most expansive of design standards. Nevertheless, the overall database can be used to identify candidate areas for targeted safety improvement, to estimate the magnitude of improved safety achievable by proposed design changes, and to monitor the changes in loss magnitudes associated with implementation of design changes. The databases available for monitoring, tracking, and surveillance of other types of harm within the built environment are
DEFINING THE CHALLENGES TO SAFETY Any harm that occurs inside a built environment could conceivably have been prevented or mitigated, at least in some very small way, by some feasible modification to the built environment. But that definition of challenges to safety is far too sweeping to be useful. A built-in visual and motion monitoring system might provide enough surveillance to reduce the fraction of heart attacks or strokes that prove fatal, but if our purpose is to track the effectiveness of our current, typical code and design choices, it would not be helpful to have a tracking statistic dominated by the large number of heart attacks, simply because it is technically feasible to build a structure that would help on some of them. Any harm that occurs as a direct result of some failure in the built environment under conditions anticipated by the code is the type of event that should be tallied as an indicator of performance. But that definition of challenges to safety is far too narrow to capture what good design can accomplish in the way of preventing or reducing harm. The narrow definition is more appropriate for assigning legal liability than for evaluating overall effectiveness and impact. Also of concern is any harm that occurs as a result of conditions that were not anticipated by the code but that should have been, and would have been, anticipated with better information John R. Hall, Jr., Ph.D., is assistant vice president for fire analysis and research at the NFPA.
1–3
1–4 SECTION 1 ■ Safety in the Built Environment
not so well developed, except for major natural disasters, which are sufficiently few in number that they can be individually documented in great detail. For other instances of harm that do not involve fire or a natural disaster, there is less ability to develop statistics by type of harm and physical object creating the hazard (thereby distinguishing between those that are part of the built environment structure and those that are not). What is needed is data that can support a comprehensive analysis of all forms of harm associated with built environments, leading to a more focused analysis of options for action to address that harm, and supported after actions are taken by followup monitoring of the impact of those actions in practice. This sequence corresponds to what is sometimes called program analysis and, after actions are taken, program evaluation. Engineers and economists both apply something they call “risk assessment,” which includes these steps as well, even though “risk” sometimes means something different to engineers than to economists.
Questions Involved in Safety Decisions Whatever name is given to the analysis in support of safety decisions, questions like the following tend to be involved: • Is this a problem big enough to worry about? Using readily available data and rough groupings into major categories, is this problem one of the larger ones? Does it seem to be increasing or decreasing, and if so, slowly or sharply? This is sometimes called “risk estimation.” Consider this the first triage phase, where we identify problems important enough to justify further examination. • What are the details of this problem? Describe the circumstances of the more likely or more serious examples of this problem, so that we can develop an understanding of how it arises and begin to determine the potential impact of candidate strategies. This is sometimes called “risk factor identification.” Consider this the second triage phase, where we identify which of the important problems appear to be tractable. • What are our options for dealing with this problem? Identify candidate strategies, considering one or more options within each of several general approaches, such as prevention (make it less likely), mitigation (make it less serious if it occurs), and separation (reduce exposure if you can’t make the event itself less severe). The options may be called “interventions,” “programs,” or “risk control techniques.” Consider this the treatment selection phase, where we consider and select one or more ways to address a problem we have decided is important enough to focus on and tractable enough to change. • What is our best way of implementing the strategy? Consider this the service delivery strategy phrase, where we address the cost-effectiveness of our strategy for implementing one or more of the strategies that shows promise for addressing an important, tractable problem. The goal of this chapter is to provide readily available information that bears on the first question—is this a problem big
enough to worry about?—but not much on the subsequent questions. This chapter therefore represents more of a starting point than a full overview of challenges to safety in the built environment. A structure will be provided, and details will be filled in to the extent possible. It is the author’s intention that this starting point will be just that—a first step in the development of more complete databases, providing answers to a wider and wider range of safety questions about our built environments.
TYPES OF HARM Table 1.1.1 provides a first level classification of types of harm to people (deaths, injuries, illnesses) and to property (including potentially business interruption or other interference with mission continuity, cultural or historical value damage, and environmental damage). Direct harm and indirect harm are both of interest. Fire has been combined with other thermal forms of harm, including explosions, lightning, electric shock, scalds, and other burns. The awkwardly phrased “objects in motion” ranges from fall injuries to structural collapse to seismic events. Water and storm harm ranges from plumbing mishaps to catastrophic or everyday storm events. Note that each type of harm listed in Table 1.1.1 arises from a peril that may occur naturally or as a result of human action or error. The degree of harm depends on exposure (which may depend considerably on the location chosen for the built environment) and on the relative vulnerability of the built environment to harm from a particular peril. The term harmful environment refers to whatever is left, including harm that is able to elude or pass through the structure’s protective envelope. (A protective envelope is a set of barriers designed to keep harmful substances that are outside—water, germs, fast-moving air, and so on— from reaching and harming people and property located inside the envelope.) The categories in Table 1.1.1 are not taken from any published source and are not in general use. They are proposed only as a basis for organizing the material in the chapter. Some performance issues for the built environment are excluded from this typology, including all issues of amenities and issues of access, such as those addressed by the Americans with Disabilities Act (ADA). Vehicles and outdoor settings not involving structures are excluded from consideration here, even though most of those environments can be regarded as built.
RELEVANT MAJOR SOCIETAL TRENDS For every form of fatal injury in a built environment, except for poisonings by solids or liquids and unintentional firearms injuries, older adults are at higher risk.1 This part of the population is also the fastest growing segment of the population, not only in the United States but throughout the economically developed world.2 Consider two countries from opposite ends of the spectrum. In Afghanistan, the death rate is high (18.0 per 1000 population in 2000), but the birth rate is much higher (41.8 per 1000 popu-
CHAPTER 1
TABLE 1.1.1
■
Challenges to Safety in the Built Environment
1–5
Typology of Types of Harm to People and Property in the Built Environment
Peril Causing Harm
Harm to Propertya
Harm to People
Thermal-related effects, principally fires
Thermal injury Injury from inhaled toxic products, or oxygen deprivation resulting from fire Injury from structural failure resulting from fire Electric shock Burns from hot surfaces, steam, or other hot objects Explosions
Direct harm from thermal or corrosive effects of fire Damage from structural failure resulting from fire Lightning damage
Objects (including people) in motion
Fall injuries Injuries due to objects falling on people Injuries due to contact with people or objects not involving anything or anyone falling
Earthquake Structural collapse
Water or storms
Drowning Structural collapse or loss of protective envelope resulting from water or wind
Damage due to wind, water, or storm loads (e.g., snow or hail)
Harmful environment
Poisoning by solid, liquid, or gas Mechanical suffocation Water-borne or airborne diseases Adverse health effects of excessive heat or cold, insufficient or poor lighting, excessive noise or vibration, or radiation exposure (e.g., radon)
Corrosive or other damaging effects of moisture Damage due to heat or cold Damage due to noise or vibration Radiation damage
a
Includes business interruption, other functionality damage, and damage to heritage.
lation in 2000). Annual population growth from 1990 to 2000 was 5.6 percent, and older adults represent only 2.8 percent of the population. Afghanistan faces a challenge of finding buildings to house a rapidly growing population, but it does not face much of a problem, proportionally, in dealing with its older adults.2 In Italy, by contrast, the death rate is low (10.0 per 1000 population in 2000), but the birth rate is even lower (9.1 per 1000 population in 2000). Annual population growth from 1990 to 2000 was 0.2 percent and is likely to go negative in the near future. Older adults represent 18.1 percent of Italy’s population. Italy does not need many more buildings, but they are in the forefront of countries faced with a rapidly growing older-adult share of the population and a need to reshape the nation’s built environment to deal with their special needs.2 In between is the United States, whose very low death rate (8.7 per 1000 population in 2000) is lower than its also low birth rate (14.2 per 1000 population in 2000). Annual population growth from 1990 to 2000 was 1.0 percent, and older adults represent 12.6 percent of the total population. The United States must deal with both a need for more buildings to house a growing population and a need to remake the building stock to address the special needs of a rapidly growing older population. In the process of adding more people, the United States has also been adding more people specifically in those regions where the likelihood of certain natural disasters is higher. Although population growth in coastal communities nationwide has actually been slower than in the rest of the country,3 the state of Florida ranked third highest in number of people added in the 1990s, and Florida has by far the highest frequency of hurricane
incidence of any state.4,5 The state that added the largest number of people was California, which also has by far the most people living in areas of frequent seismic activity.4,5 Whether growth in high-risk areas is disproportionately large or only proportional to growth elsewhere, it means the same perilous event will cause more deaths and damage more value in property, unless the increased exposure has been offset by improvements in protection.
MAJOR DATABASES Even though 90 to 95 percent of all unwanted fires are unreported to fire departments, the ones that are reported number nearly 2 million a year, and they represent most of the deaths and property damage.6 For every other type of harm, there is no analogous database with comparable breadth of scope and detail. Major individual incidents, involving multiple deaths or millions of dollars of loss, are more likely to be extensively documented, and the more severe the harm caused by an incident, the more likely it is that a “case study” report on the incident will be published. It is therefore possible to develop lists and pattern analyses of these incidents. However, these large incidents generally account for only a small fraction of total harm to people, either deaths or nonfatal injuries. Such large incidents may account for a large share of damage to property, but for many forms of harm, like fire, they do not. The national database of death certificates provides useful detail on deaths due to injury.7 Illnesses are generally not coded
1–6 SECTION 1 ■ Safety in the Built Environment
to indicate the involvement of or relevance of components of the built environment. This is an important gap, because it means we cannot readily isolate and identify relevant illnesses, such as waterborne illnesses due to backflow or cross-connections in the plumbing, Legionnaire’s disease due to cultivating of bacteria or viruses in poorly designed or poorly operating air-handling systems, and the kind of airborne illnesses associated with indoor air pollution (sometimes referred to by the label “sick building”). Therefore, the statistics presented in this chapter will describe fatal and nonfatal injuries but not illnesses. In the database of death certificates, deaths due to injury are coded as E800 to E999. Deaths where the injury was intentional (e.g., homicide, suicide) or where it was unknown whether the injury was intentional or unintentional (codes E950 to E999) are largely excluded from this chapter. Deaths involving transportation or vehicles (codes E800 to E849) are excluded from this chapter as being outside the definition of the built environment. Also excluded are injuries arising from medical problems (e.g., poisonings by drugs, complications, adverse effects, medical misadventures), as these (codes E850–E859, E870–E879, and E930–E949) are also deemed to be outside the realm of even the hazardous environment definition of issues within the built environment. Finally, the statistics presented here exclude unintentional firearms injuries (E922), radiation (E926), overexertion (E927), and late effects (E929), even though a case could be made that each of these includes some cases that a built-environment choice could have prevented or mitigated. Deaths due to noise or vibration (E928) would have been included, but there have been no such deaths in the latest 5-year period (1994–1998). Excluding radiation probably does not omit useful data on such problems as radon, because chronic illness due to long-term exposure to radiation is unlikely to be captured in E926. Nonfatal injuries are not routinely captured, but there are three exceptions (in addition to the injury component of the fire incident databases). Occupational injuries are captured by the U.S. Department of Labor, if they meet a severity threshold.8 Injuries involving a trip to a hospital emergency room and associated with a consumer product are the subject of a U.S. Consumer Product Safety Commission database.9 (Recent changes mean that all emergency-room injuries will be captured in the near future.) And the injuries people suffer that go unreported to any medical or other entity are tracked through an in-home sample survey as part of the National Health Interview Survey.10 The database on occupational injuries uses approximately the same structure as the death-certificate E-codes, though with additional detail in some places. The other two databases do not have a counterpart to the E-codes at present. Apart from individual natural disasters and fires, property damage is tracked only by the insurance industry and, for storms, the National Weather Service.11,12 Their published information has some useful detail, and it is possible that their unpublished, coded data will in time permit more detailed analysis. Many issues in building codes and other codes for the built environment have historically been addressed not on the basis of numbers, rates, or percentages of fires or statistically derived indicators such as risk values, but rather on the basis of individual
major incidents that indicate a specific type of hazard or type of built-environment performance problem not previously encountered. For example, the Northridge earthquake of 1994 showed some problems with brittle fracture of structural steel that, while not necessarily significant in the loss in that incident, were nevertheless unexpected, leading to new research and code-change proposals. For this reason, this chapter includes not only statistics but also lists of deadliest or costliest incidents, where such lists are meaningful and potentially useful. There is an extended discussion in Section 2, Chapter 1 of the past century of progress in fire safety, by major occupancy type, where trigger events were often individual fires but progress could be measured statistically.
THERMAL-RELATED HAZARDS Fires Because fire loss experience—its magnitude, its trends, and its patterns—is extensively discussed in Section 2, Chapter 1 (which was previously the first chapter of this handbook), it will not be extensively addressed here. Instead, a few statistics are provided for context with the other hazards, and then nonfire thermal-related hazards are addressed at greater length. Tables 1.1.2 and 1.1.3 provide overviews of U.S. fire deaths and related property damage, respectively. Table 1.1.2 compares fire deaths as estimated by the NFPA survey with those recorded by the primary fire-related E-codes in the national death certificate database. The latter excludes transportation and vehicle-related fires, which is why those statistics track more closely with NFPA survey data on structure fires alone, which are also provided in Table 1.1.2. Death certificate counts from these E-codes can also exclude some incendiary fire deaths, but should do so only if the fatal injury was itself known to have been intended, in which case it qualifies as a homicide or suicide and is classified there for primary categorization. It appears that few such fire deaths are so classified.
TABLE 1.1.2
Tracking U.S Fire Deaths
Based on NFPA Survey Year
Total
Structure Fire Only
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
5,410 5,195 4,465 4,730 4,635 4,275 4,585 4,990 4,050 4,035
4,655 4,400 3,765 3,940 3,980 3,590 3,985 4,220 3,510 3,420
Based on Death Certificate Coding E890–E899 Only 4,723 4,181 4,126 3,966 3,914 3,999 3,768 3,748 3,502 3,263
Source: NFPA survey, National Center for Health Statistics (NCHS) data provided by U.S. Consumer Product Safety Commission (CPSC).
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CHAPTER 1
TABLE 1.1.3
Tracking U.S. Property Loss to Fire
Year
Based on NFPA Survey (in Billion Dollars)
Estimated by Insurance Services Office (in Billion Dollars)
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
8.655 7.818 9.467 8.295 8.546 8.151 8.918 9.406 8.525 8.629
9.514 9.495 11.302 13.588 11.331 12.778 11.887 12.544 12.940 11.510
Note: NFPA survey figures are estimates by fire officers, sometimes with the benefit of information on insurance estimates. ISO estimates include actual insurance claims and estimates of losses in uninsured or underinsured properties. Sources: NFPA survey; The I. I. I. Insurance Fact Book 2000, Insurance Information Institute, New York, 2000.
The NFPA survey can miss deaths occurring outside a reported fire. Clothing ignitions are the classic example, but the death certificate database tracks clothing ignition deaths separately, and they total less than 200 a year, some of which will be reported to fire departments. The NFPA survey is also subject to some sampling variation. The estimate of total fire deaths, for example, is subject to a 95 percent confidence band of plus or minus just under 400 deaths, which is more than the typical difference between the structure fire death estimate and the deathcertificate tally. Similarly, there are a number of possible reasons for the modest but growing gap between the NFPA estimates of direct property damage and the Insurance Services Office estimates of fire loss, as shown in Table 1.1.3. The insurance industry estimate may include indirect losses (e.g., reimbursement for temporary housing or business interruption) and may overadjust for losses in uninsured or underinsured properties. The firedepartment-based NFPA estimate will miss losses in unreported fires even if they result in insurance claims. The insurance industry estimate is a mix of detailed observations by highly trained loss appraisers and self-reported losses as adjusted in response to comments from appraisers who have not personally observed the fire scene. It is hard to say whether such estimates will be higher or lower, more or less accurate, than estimates by fire officers, who lack the same loss-estimation training but sometimes have access to insurance appraisals of the same fires and experience in other occupations (e.g., construction), which give them insight into what things cost. Although the NFPA survey estimates are the best measures of fire loss, when fire is considered by itself, the available statistics on other hazards and types of harm are most comparable to the death certificate data and the insurance industry estimates for fire.
Challenges to Safety in the Built Environment
1–7
Other Thermal Injuries Table 1.1.4 provides available information on total US burn injuries, based on in-home sample surveys conducted by the U.S. Department of Health and Human Services. The samples are sufficiently small that the estimates of burn injuries are subject to considerable uncertainty. (For example, the estimate of a quarter million bed-disabling burn injuries per year in 1980–1981 is subject to a relative error of more than 30 percent.) This uncertainty is also the reason why published analyses of the survey data do not always address burns and, when they do, use two- or three-year averages to reduce error to an acceptable level. The principal finding of Table 1.1.4 is that total U.S. burn injuries declined from roughly 2 million in 1980–1981 (and for at least two decades prior) to roughly 1 million in 1991–1993. Table 1.1.5 provides a 10-year trend for the available components of deaths due to unintentional injury by electrical current. The largest share of fatal injuries due to electrical current falls into the “other or unknown” category. Within that category, the “other” (i.e., unclassified) injuries slightly outnumber those of unknown type.
TABLE 1.1.4 U.S. Burn Injuries Based on Responses to National Health Interview (In-Home) Survey Measure Burn injuries (per year) Burn injuries per 100 population (per year) Medically attended burn injuries Restricted-activity burn injuries Bed-disability burn injuries Average number of days of per restricted-activity burn injury Average number of days of beddisability per beddisability burn injury a
1980– 1981
1985– 1987
1991– 1993
2,130,000
1,735,000
1,129,000
1.0
0.7
0.4
1,615,000
1,614,000
1,073,000
1,213,000
810,000
445,000
399,000
124,000
6.1
8.8
NAb
5.7
8.1
NA
244,000a
Relative standard error of estimate exceeds 30 percent. NA—Not available or not yet available. Sources: Types of Injuries and Impairments Due to Injuries— United States, Series 10, No. 159, 1986; Types of Injuries by Selected Characteristics, 1985–87, Series 10, No. 175, 1990; and advance data from John Gary Collins, U.S. Department of Health and Human Services, author of all analyses shown here. b
1–8 SECTION 1 ■ Safety in the Built Environment
TABLE 1.1.5
Unintentional-Injury Deaths by Electrical Current Deaths Coded on U.S. Death Certificates
Year
Lightninga
Total Electric Current
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
75 89 75 53 57 84 76 63 58 63
702 670 626 525 548 561 559 482 488 548
Home Equipment
Industrial Equipment
Generating Plants or Distribution
Other or Unknown
143 100 82 66 82 84 88 66 53 59
61 54 74 37 46 42 26 15 27 27
143 160 132 139 142 144 158 135 139 144
355 356 338 338 278 291 287 266 269 318
a
Not included in total. Source: National Safety Council, Accident Facts and Injury Facts, 1992–2000 editions, National Safety Council, Itasca, IL, 1992–2000; 1998 data from the CDC/NCHS website.
Injuries involving home or industrial equipment have been declining substantially. Those involving generating plants or distribution equipment have not. As a result, deaths from electric current associated with generating plants or distribution now routinely outnumber those associated with home equipment, and by a large margin. This was not true as recently as the 1980s. Tables 1.1.6 and 1.1.7 provide, respectively, a 10-year trend table on explosions excluding pressure vessel explosions and a 5-year trend table on pressure vessel explosions. Note that gas cylinders are a category under pressure vessels. This can point to a rough separation of natural gas (gas explosion excluding pressure vessels) and LP-gas (gas cylinder explosion), although each of these is part of a category that can include other situations and other types of gases. Within the “other or unknown-type,” there is a roughly even split that tilts somewhat toward the unknowns. Table 1.1.8 provides a 10-year trend table on deaths due to injuries from hot objects. Figure 1.1.1 indicates that threefourths of those fatal injuries involve steam or other hot liquid or vapor. Figure 1.1.2 provides an overview of the rates of deaths per million population, by age group, for deaths due to injury by steam or other hot liquid or vapor. These rates are a measure of the differences in risk of death from this type of harm, for different age groups. As with fire deaths, the very young and the TABLE 1.1.7
TABLE 1.1.6 1989–1998
Accidental Deaths Involving Explosions,a
Year
Fireworks
Gas Explosion
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
5 5 4 2 10 4 2 9 8 13
101 98 64 79 59 50 62 49 57 60
Other or Unknown-Type Explosion 132 99 114 108 109 104 106 72 84 79
a
Does not include explosion of pressure vessel. Source: National Safety Council, Accident Facts and Injury Facts, 1992–2000 eds., National Safety Council, Itasca, IL, 1992–2000; 1998 data from the CDC/NCHS website.
older adults are the two high-risk age groups, but unlike fire, the very young are not that much more at risk than the all-ages average, and the older adults have risks much higher than those for the very young.
Unintentional-Injury Deaths Due to Explosion of Pressure Vessel Deaths Coded on U.S. Death Certificates
Year
Total Explosions of Pressure Vessels
Explosion of Boiler
Explosion of Gas Cylinder
Other Explosion of Pressure Vessel
Unknown-Type Explosion of Pressure Vessel
1994 1995 1996 1997 1998
30 36 27 33 31
2 2 3 5 2
10 11 6 11 5
15 16 16 15 22
3 7 2 2 2
Source: CDC/NCHS website.
CHAPTER 1
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TABLE 1.1.8 Unintentional-Injury Deaths Involving Contact with Hot Objects or Substances, 1989–1998 Total
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
142 131 125 131 130 107 97 104 111 108
Note: Includes corrosive substances and steam. Sources: National Safety Council, Accident Facts and Injury Facts, 1992–2000 eds., National Safety Council, Itasca, IL, 1992–2000; 1998 data from CDC/NCHS website.
5–9
0.0
10–14
0.0
15–19
0.0
20–39 40–64
0.1 0.2
65–74
0.6
75–84
1.6
86 and older All ages
1–9
0.5
Under 5
Age
Year
Challenges to Safety in the Built Environment
4.1 0.3 Deaths per million population
FIGURE 1.1.2 Deaths Due to Steam or Other Hot Liquid or Vapor, by Age, 1994–1998 Unintentional Injury Deaths (Source: Data from CDC/NCHS website)
Steam or other hot liquid or vapor (74 percent)
Caustic or corrosive substance (7 percent)
Unknown type (3 percent)
Unclassified (15 percent)
FIGURE 1.1.1 Deaths Due to Hot Object, by Type of Object, 1994–1998 Unintentional Injury Deaths (Source: Data from CDC/NCHS website)
OBJECTS IN MOTION Falls Falls are by far the most common type of fatal injury in the built environment. Table 1.1.9 provides a 10-year trend table for deaths due to falls and for the major types of falls. Within the “other or unknown-type” category, the deaths split roughly twoto-one between unclassified and unknown-type falls versus unknown-type fractures. Falls from or on Stairs or Steps. Note that deaths due to falls from or on stairs or steps—the major category of falls most
clearly linked to the design of the built environment—have been increasing over the period analyzed and are up by about 20 percent in the most recent decade analyzed. This is a larger increase than can be explained by the growth in total population, but might be better explained by an age-adjusted analysis, which would factor in not only the growth in the total population but also the growth in the older-adult share of the population. Figure 1.1.3 provides an overview of deaths per million population, by age, for fatal falls from or on stairs or steps. The risk is negligible for children, even children under age 5, but rises rapidly among older adults. Half of all deaths from falls from or on stairs or steps are people age 75 or older. The risk for adults ages 85 or older is roughly 14 times the all-ages risk and 65 times the risk for young adults. This helps explain the prominent attention given to falls among the elderly in multihazard safety programs, such as NFPA’s Remembering When. Falls from or on stairs or steps are subdivided within the database only into falls on or from escalators and everything else. Those involving escalators are typically about 0.2 percent of the total, which means that separating them from the total provides little insight into what remains. Falls from or on Ladders or Scaffolding. Table 1.1.10 separates deaths from falls from or on ladders or scaffolding into the two parts. Falls involving ladders dominate by about 4 to 1. Figure 1.1.4 provides an overview of deaths per million population for fatal falls from or onto ladders, by age of victim. Again, the risk is highest by far for older adults. In fact, a majority (55 percent) of the deaths are adults ages 65 or older. Falls out of Structures. Figure 1.1.5 provides an overview of deaths per million population for fatal falls out of a building or structure, by age of victim. There has been considerable publicity surrounding preschool children falling out of buildings, resulting in a recent push for bars on windows, which can, if installed incorrectly, provide a deadly barrier preventing safe
1–10 SECTION 1 ■ Safety in the Built Environment
TABLE 1.1.9
Unintentional-Injury Deaths Due to Falls, Deaths Coded on U.S. Death Certificates
Year
Total
Falls on or from Stairs or Steps
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
12,151 12,313 12,662 12,646 13,141 13,450 13,986 14,986 15,447 16,274
1,163 1,148 1,202 1,197 1,087 1,163 1,241 1,239 1,295 1,389
Falls on or from Ladders or Scaffolding
Falls from out of Building or Structure
Falls into Holes or Other Openings in Surface
332 316 317 298 301 327 352 369 368 352
557 615 607 513 509 477 467 444 549 550
77 84 104 99 107 93 94 88 70 95
Other Falls from One Level to Another
Falls on Same Level from Slipping, Tripping, or Stumbling
Falls on Same Level from Collision, Pushing or Shoving
933 1,031 1,061 984 1,156 1,066 1,145 1,129 1,106 1,187
471 491 466 477 520 600 491 688 726 740
5 8 8 6 9 4 8 3 4 6
Other or UnknownType Falls 8,613 8,620 8,897 9,072 9,452 9,920 10,188 11,026 11,329 11,955
Source: National Safety Council, Injury Facts and Accident Facts, National Safety Council, Itasca, IL, 1992–2000; 1998 statistics from the CDC/NCHS website.
Under 5
0.4
5–9
0.1
10–14
0.0
15–19
0.1
20–39
1.1
Under 5
0.0
5–9
0.0
10–14
0.0
40–64
Age
Age
15–19 20–39 40–64
0.1 0.4 1.4
3.7 65–74
65–74
3.9
13.0 75–84
75–84
5.9
35.2 86 and older
86 and older
All ages All ages
4.5
71.7 1.2
5.2 Deaths per million population Deaths per million population
FIGURE 1.1.3 Deaths Due to Falls on or from Stairs or Steps, By Age (Source: Data from CDC/NCHS website, 1994–1998 unintentional injuries)
TABLE 1.1.10 Unintentional Injury Deaths Due to Falls from Ladders versus Scaffolding, Deaths Coded on U.S. Death Certificates
Year
Total Falls on or from Ladders or Scaffolding
Falls on or from Ladders
Falls on or from Scaffolding
1994 1995 1996 1997 1998
327 352 369 368 352
268 294 299 301 284
59 58 70 67 68
Source: CDC/NCHS website.
FIGURE 1.1.4 Deaths Due to Falls on or from Ladders (Source: Data from CDC/NCHS website, 1994–1998 unintentional injuries)
escape from a fire in the building. But as with every other type of fatal fall examined so far, the higher risks are faced by older adults. The risk for adults ages 85 and over is five times the allages risk. Falls into Openings. Table 1.1.11 subdivides deaths due to falls into holes or other openings in surfaces into their component parts. A separate figure showing deaths per million population by age group is not provided because the numbers are small, but preschool children have higher risk than other children but lower risk than most adults. Older adults are again the highest-risk group, but variations in risk by age are much less than for other types of fatal falls. These patterns also apply if the focus is narrowed to fatal falls into wells, storm drains, or man-
CHAPTER 1
Under 5 5–9
0.2
10–14
0.2
15–19 Age
0.6
1.0 2.6
20–39
2.0
40–64
3.0
65–74
4.7
75–84
10.5
86 and older 2.0
All ages
Deaths per million population
FIGURE 1.1.5 Deaths Due to Falls out of Building or Structure (Source: Data from CDC/NCHS website, 1994–1998 unintentional injuries)
holes, although these do not fall within the bounds of what this chapter is addressing as the built environment. The largest component that is well defined is deaths due to jumping or diving into water. Except for swimming pools, this activity also does not involve the built environment.
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Falls from One Level to Another. Table 1.1.12 provides a breakdown of the different types of fatal falls from one level to another. Falls from playground equipment are a negligible share of the total. Falls from cliffs are an important component, but one that has been declining sharply. Neither playgrounds nor cliffs are part of what this chapter is focusing on as the built environment. Falls from chairs or beds are the largest identified component, and those deaths have not been declining. Figure 1.1.6 shows that differences in this risk by age are the largest yet seen in this chapter. Adults ages 85 or older have more than 30 times the all-ages risk of suffering a fatal fall from a chair or bed. This age group accounted for roughly half (49.0 percent) of all deaths from this type of fall. Again, young children have a higher risk than older children but much less risk than older adults. The category of “other” falls from one level to another shows a very different age profile than that for falls from chairs and beds. The age profile more closely resembles that for deaths due to falls involving jumping from cliffs. This means it would be inappropriate and possibly misleading to treat these underspecified falls as if they were like falls from chairs and beds. Their age profile looks more like one might expect from falls off roofs, but it seems unlikely that that specific scenario would account for such a large death toll. This is an area where in-depth research would be useful, and a literature review might be a good place to start.
TABLE 1.1.11 Unintentional-Injury Non-Fire Deaths Due to Falls into Holes or Other Openings in Surface, Deaths Coded on U.S. Death Certificates
TABLE 1.1.12 Certificates
Year
Total Falls into Holes or Other Openings in Surface
Falls from Diving or Jumping into Water
Falls into Wells
Falls into Storm Drains or Manholes
Falls into Other Holes or Other Openings in Surface
1994 1995 1996 1997 1998
93 94 88 70 95
54 62 49 41 57
4 3 3 2 2
3 1 0 0 0
32 28 36 27 36
Unintentional Injury Deaths Due to Other Falls from One Level to Another, Deaths Coded on U.S. Death
Year
Total Other Falls from One Level to Another
Falls from Playground Equipment
Falls from Cliffs
Falls from Chairs or Beds
Other Falls from One Level to Another
1994 1995 1996 1997 1998
1066 1145 1129 1106 1187
4 2 3 6 2
107 113 91 64 63
429 516 485 501 508
526 514 550 535 614
Age
1–12 SECTION 1 ■ Safety in the Built Environment
Under 5
0.4
5–9
0.1
10–14
0.1
15–19
0.1
20–39
0.2
40–64
0.5
65–74
TABLE 1.1.13 Rates per Million Population of Unintentional-Injury Deaths Due to Falls (Average of Available 1986–1995 Rates)
Country
2.8
75–84
12.3
86 and older All ages
Average Death Rate Due to Falls
North America Canada Mexico USA
78 51 50
South America Venezuela Argentina Chile
43 33 30
Asia/Pacific New Zealand Australia Japan
73 57 35
63.5 2.0 Deaths per million population
FIGURE 1.1.6 Deaths from Falls from Chairs or Beds (Source: Data from CDC/NCHS website, 1994–1998 unintentional injuries)
For the few deaths from falls where the victims stays on the same level and the fall is due to collision, pushing, or shoving, nearly half occur in sports (44 percent of 1994–1998 deaths) and the rest involve other or unknown-type events. International Perspective on Falls. Table 1.1.13 has an international perspective. It gives averages of available 1986–1995 fatal fall rates for different countries. Unlike the case with fire deaths, the U.S. rate of fall deaths per million population is one of the lowest, with only Spain having a lower rate among the many European countries listed. Rates in South America are lower still. An analysis of the international differences would need to begin with an examination of differences in age distributions, which could make a large difference in light of the enormous differences in risk of death from falls among age groups. Also, it would be useful to know how much variation in heights of surfaces normally encountered by people exist from place to place. Certainly, high-rise buildings are more common in some countries than in others, but it is unlikely that this is a major factor in the overall statistics. Other differences, such as the average heights of beds or sleeping surfaces (e.g., futons), might exist, however, and might be important. Differences in contributing risk factors, such as the use of alcohol, could be important. And the possibility of differences in definitions used in practice or in data collection should also be considered. Nonfatal Falls. Table 1.1.14 moves away from fatal falls to nonfatal falls, based on responses to the government’s in-home survey of health problems. The nonfatal injuries in Table 1.1.14 outnumber the fatal fall injuries in Table 1.1.9 by nearly a thousand to one. The relative importance of different types of falls is different, reflecting in part the fact that some types of falls—for example, from or on stairs or steps, out of a building or structure— are more likely to be fatal than some of the other types of falls.
Europe Hungary Czech Republic Norway Slovenia France Austria Finland Italy Croatia Sweden Belgium Poland Netherlands Portugal Ireland United Kingdom Bulgaria Greece Russia Spain
309 291 225 195 193 173 167 163 146 134 125 115 103 81 77 75 60 55 52 29
Note: Listings are limited to countries with rates available for at least 7 of the 10 years. Source: National Safety Council, International Accident Facts, 2nd edition, Itasca, IL: National Safety Council, 1999.
Table 1.1.15 is an overview of 1998 injuries reported to hospital emergency rooms, organized by leading consumer products involved. The injuries involved are not all falls or any other type of injury involving objects in motion, but the leading consumer products involved (i.e., stairs or steps, floors or flooring materials) are products for which falls are the type of injury one would expect to dominate. Tables 1.1.16 to 1.1.18 provide a breakdown of 1999 injuries reported to hospital emergency rooms and involving any of five building-product groups of consumer products. Three of these
CHAPTER 1
TABLE 1.1.14 U.S. Nonfatal Fall Injuries Based on Responses to National Health Interview (In-Home) Survey Type of Fall Total fall episodes Total types of falls mentioneda Onto floor or level ground From or onto stairs or steps From or onto curb or sidewalk From or onto chair, bed, sofa, or other furniture From or onto playground equipment From ladder or scaffolding Into hole or other opening From or onto escalator, building or other structure, tree, toilet, bathtub or pool Unreported type Refused to give type or did not know
Estimated 1997 Injuries 11,306,000 12,285,000 4,158,000 1,296,000 1,162,000 807,000 493,000 447,000 382,000 610,000 2,793,000 135,000
a More fall types are mentioned than there were fall episodes, because respondents could specify up to two types. Note: Sum may not equal total because of rounding error.
TABLE 1.1.15 Leading Product Groups Resulting in Injuries Reported to Hospital Emergency Rooms Based on Estimates From National Electronic Injury Surveillance System Consumer Product Stairs or stepsa Floors or flooring materialsa Knives Beds Doors other than glass doors or garage doorsb Tables, excluding TV tables or stands or baby-changing stations Chairs Ceilings or walls Household cabinets, racks, or shelves Household containers or packaging Nails, screws, tacks, or bolts Bathtubs or showers Ladders Windows Porches, balconies, or open-side floors Sofas, couches, or related furniture Fences or fence posts Tableware or flatware, excluding knives Rugs or carpets
Estimated 1998 Injuries 989,977 986,093 454,246 437,980 342,302 316,733 286,020 251,722 242,078 202,252 183,068 181,837 157,219 143,138 138,123 124,258 124,202 122,306 117,588
a Handrails, railings, or banisters accounted for 39,136 injuries, and ramps or landings accounted for 16,811 injuries. b Glass doors accounted for 40,721 injuries, and door sills or frames accounted for 42,984 injuries. Source: NEISS data estimates by CPSC, as analyzed and grouped by National Safety Council, Injury Facts 2000, National Safety Council, Itasca, IL, 2000.
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Challenges to Safety in the Built Environment
1–13
groups—stairs and steps; floors and flooring materials; and handrails, railings, and banisters—involve products where falls are the type of injury one would expect to see. The other two are two categories of doors, which are included for insight into other nonfatal injuries involving components of the built environment.
Events Other Than Falls Table 1.1.19 moves away from falls to other deaths due to other examples of objects in motion. Earthquakes and volcanic eruptions are directly cited in relatively few deaths each year. The same cannot be said for some other countries, which is partly a reflection of variations in the incidence of major events, partly a reflection of relative success in keeping buildings out of highvulnerability zones of exposure, and partly a reflection of differences in the vulnerability of the buildings when built. Falling Objects. Deaths due to falling objects are the kinds of deaths that might include a significant share that can be related to design and operating decisions of the built environment. They are also numerous enough to justify more in-depth analysis. Unfortunately, the coding provides no detail on the kinds of falling objects involved. Whatever the objects may be, the death toll from falling objects has shown little decline. Striking or Being Struck by Falling Objects. Deaths due to people striking against or being struck by objects (e.g., walking into a door), presumably involving a more lateral movement since falling is not involved, jumped significantly in 1997 and 1998. No obvious explanation presents itself. Within the category of people striking against or being struck by objects, it is possible to distinguish deaths due to people striking other people in a crowd, as in a panic evacuation or when a crowd presses someone against an unmoving barrier. There have been no such deaths in the most recent 5-year period analyzed. However, instances that might fit here might also be coded somewhere else, if, for example, a crowd-crushing situation were considered not to fit the “struck by” label. Table 1.1.20 provides a breakdown of 1996 occupational injuries and illnesses by event or exposure (equivalent for the most part to E-code categories for fatal injuries), overall and for each of three groups of objects that are entirely or mostly recognizable as components of the built environment—floors, walkways, and ground surfaces; furniture and fixtures; and machinery.
Earthquakes This section wraps up by looking at the deadliest and costliest incidents in history, specifically for earthquakes.13 Deadliest U.S. Earthquakes. Table 1.1.21 lists the ten deadliest U.S. earthquakes of all time, leading with the 1906 San Francisco earthquake/fire, which is also considered the source of the costliest U.S. fire of all time. Six of the 10 earthquakes occurred in California, and two others were offshore earthquakes near Alaska that produced most of their deaths due to resulting
TABLE 1.1.16 Injuries Reported to Hospital Emergency Rooms Involving Selected Consumer Products Used in the Built Environment, by Age of Victim Based on 1999 Injuries Reported to NEISS A. Numbers and Percentages of Injuries Floors or Flooring Age of Materials Stairs or Steps Victim
1–14
Under 5 5–14 15–24 25–44 45–64 65 and over Unknown Total
Handrails, Railings or Banisters
Glass Doors
Doors Other Than Glass Doors
Porches, Balconies, or Open Side Floors
Windows
102,170 111,044 146,051 317,828 185,130 166,783
(9.9%) (10.8%) (14.2%) (30.9%) (18.0%) (16.2%)
165,300 109,629 66,515 133,239 127,803 421,210
(16.1%) (10.7%) (6.5%) (13.0%) (12.5%) (41.1%)
5,705 9,985 5,731 8,978 4,744 4,364
(14.4%) (25.2%) (14.5%) (22.7%) (12.0%) (11.0%)
4,527 10,745 9,397 7,990 3,411 2,686
(11.7%) (27.7%) (24.2%) (20.6%) (8.8%) (6.9%)
70,378 81,966 46,512 66,915 34,122 35,278
(21.0%) (24.4%) (13.9%) (20.0%) (10.2%) (10.5%)
11,200 23,299 36,754 39,076 12,872 6,007
(8.7%) (18.0%) (28.4%) (30.2%) (10.0%) (4.6%)
14,369 18,857 17,621 41,839 24,577 21,770
(10.3%) (13.6%) (12.7%) (30.1%) (17.7%) (15.6%)
412 1,029,418
(0.0%) (100.0%)
746 1,024,522
(0.1%) (100.0%)
68 39,574
(0.2%) (100.0%)
0 38,755
(0.0%) (100.0%)
86 335,257
(0.0%) (100.0%)
68 129,275
(0.1%) (100.0%)
72 139,105
(0.1%) (100.0%)
B. Injury Rates per 10,000 Population Age of Victim
Stairs or Steps
Floors or Flooring Materials
Handrails, Railings or Banisters
Glass Doors
Doors Other Than Glass Doors
Windows
Porches, Balconies, or Open Side Floors
Under 5 5–14 15–24 25–44 45–64 65 and over All Ages
53.9 28.1 38.7 38.4 31.3 48.3 37.8
87.3 27.8 17.6 16.1 21.6 121.9 37.6
3.0 2.5 1.5 1.1 0.8 1.3 1.5
2.4 2.7 2.5 1.0 0.6 0.8 1.4
37.2 20.8 12.3 8.1 5.8 10.2 12.3
5.9 5.9 9.7 4.7 2.2 1.7 4.7
7.6 4.8 4.7 5.1 4.2 6.3 5.1
Source: Special analysis of NEISS data by CPSC.
TABLE 1.1.17 Injuries Reported to Hospital Emergency Rooms Involving Selected Consumer Products Used in the Built Environment, by Body Part Injured Based on 1999 Injuries Reported to NEISS Part of Body
Stairs or Steps
Floors or Flooring Materials
Handrails, Railings or Bannisters
Glass Doors
Doors Other Than Glass Doors
1–15
Leg and foot Ankle Knee Foot Toe Lower leg
460,830
Head and neck Head Face
208,311
Trunk Lower trunk Upper trunk Shoulder
204,554 120,484
Arm and hand Finger Hand Lower arm Wrist
139,274
Internal and multiple parts
12,866
(1.2%)
37,167
(3.6%)
162
(0.4%)
439
(1.1%)
980
(0.3%)
3,583
(0.3%)
5,545
(0.5%)
107
(0.3%)
76
(0.2%)
221
1,029,418
(100.0%)
1,024,522
(100.0%)
39,574
(100.0%)
38,755
(100.0%)
335,257
Unknown Total
(44.8%)
228,168 79,722 75,746
179,686
(17.5%)
5,244
(13.3%)
4,737
(12.2%)
48,261
(14.4%)
Windows 9,976
(7.7%)
Porches, Balconies or Open Side Floors 58,480
(42.0%)
26,301 8,559 12,316
69,740 20,245
7,128 (20.2%)
357,415
(34.9%)
(19.9%)
283,522 203,032
(35.8%)
6,512 5,353
190,454 123,806
100,498 76,723
14,182
(27.7%)
8,778 2,582
7,078
(18.3%)
641
(24.0%)
(1.7%)
15,664
15,572
(12.0%)
(4.7%)
7,599
28,191
(20.3%)
13,821 9,900
6,944
31,595 40,650
2,571 3,812 (22.2%)
80,342
(5.9%)
27,542 13,941
(19.8%)
7,321
3,582 2,507 (13.5%)
161,186
(15.7%)
11,100
(28.0%)
2,912 2,544 2,388
Note: Specific body parts are shown if they account for at least 5% of total injuries. Source: Special analysis of NEISS data by CPSC.
25,784
(66.5%)
189,790
(73.8%)
23,083
(16.6%)
515
(0.4%)
1,278
(0.9%)
(0.1%)
257
(0.2%)
532
(0.4%)
(100.0%)
129,275
(100.0%)
139,105
(100.0%)
(56.6%)
27,132 28,682 20,350 14,761
132,062 34,211
6,795 5,490 7,537 4,245
95,356
TABLE 1.1.18 Injuries Reported to Hospital Emergency Rooms Involving Selected Consumer Products Used in the Built Environment, by Injury Diagnosis Based on 1999 Injuries Reported to NEISS Diagnosis
1–16
Strain or sprain Contusion or abrasion Fracture Laceration Internal injury Dislocation Concussion Hematoma Dental injury Avulsion (i.e., tearing of body part) Puncture Other Unknown Total
Stairs or Steps
Floors or Flooring Materials
Handrails, Railings or Banisters
Glass Doors
Doors Other Than Glass Doors
Windows
Porches, Balconies or Open Side Floors
345,604
(33.6%)
153,512
(15.0%)
5,375
(13.6%)
677
(1.7%)
20,124
(6.0%)
4,187
(3.2%)
37,707
(27.1%)
238,763
(23.2%)
277,006
(27.0%)
9,646
(24.4%)
4,855
(12.5%)
105,364
(31.4%)
15,429
(11.9%)
31,680
(22.8%)
202,240 109,099 32,140
(19.6%) (10.6%) (3.1%)
235,390 169,180 48,195
(23.0%) (16.5%) (4.7%)
6,343 10,161 1,911
(16.0%) (25.7%) (4.8%)
1,765 28,234 714
(4.6%) (72.9%) (1.8%)
45,330 101,280 7,085
(13.5%) (30.2%) (2.1%)
6,621 91,573 1,803
(5.1%) (70.8%) (1.4%)
29,477 19,178 3,811
(21.2%) (13.8%) (2.7%)
13,291 8,908 8,295 2,341 2,027
(1.3%) (0.9%) (0.8%) (0.2%) (0.2%)
13,172 15,415 11,160 2,437 975
(1.3%) (1.5%) (1.1%) (0.2%) (0.1%)
503 334 463 286 310
(1.3%) (0.8%) (1.2%) (0.7%) (0.8%)
0 193 459 5 113
(0.0%) (0.5%) (1.2%) (0.0%) (0.3%)
2,005 1,438 8,892 387 10,742
(0.6%) (0.4%) (2.7%) (0.1%) (3.2%)
394 300 1,010 82 1,105
(0.3%) (0.2%) (0.8%) (0.1%) (0.9%)
1,326 1,184 1,080 254 225
(1.0%) (0.9%) (0.8%) (0.2%) (0.2%)
1,611 59,246 5,855
(0.2%) (5.8%) (0.6%)
2,423 89,744 5,336
(0.2%) (8.8%) (0.5%)
468 3,357 417
(1.2%) (8.5%) (1.1%)
228 1,352 161
(0.6%) (3.5%) (0.4%)
786 30,595 1,229
(0.2%) (9.1%) (0.4%)
717 5,784 271
(0.6%) (4.5%) (0.2%)
1,151 11,299 735
(0.8%) (8.1%) (0.5%)
1,029,418
(100.0%)
1,024,522
(100.0%)
39,574
(100.0%)
38,755
(100.0%)
335,257
(100.0%)
129,275
(100.0%)
139,105
(100.0%)
Source: Special analysis of NEISS data by CPSC.
CHAPTER 1
TABLE 1.1.19 Other Deaths Due to Objects in Motion Deaths Coded on U.S. Death Certificates
Year
Due to Cataclysmic Earth Movement or Eruption
Struck by Falling Object
Struck by People or against Object
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
10 13 10 24 17 46 25 42 20 24
766 797 799 712 714 739 656 732 727 723
229 215 218 179 187 207 198 171 247 336
Sources: National Safety Council, Injury Facts and Accident Facts, National Safety Council, Itasca, IL, 1992–2000; 1998 statistics from CDC/NCHS website.
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Challenges to Safety in the Built Environment
1–17
quakes in 1811–1812 were the most severe events on land (an estimated 8.7 on the Richter scale) in U.S. history. An offshore earthquake near Alaska in 1964 was more severe (9.2 on the Richter scale), but only six people died in the remote, sparsely populated area affected by the event. There are about 5000 earthquakes a year of sufficient magnitude to be felt by people in the area.14 Unlike the case with fire and water, most loss in cases of earth movement occurs in the small handful of most-severe incidents.
WATER OR STORMS Most of the deaths in the water or storms group do not involve catastrophic events. They involve drownings or submersions in more everyday situations, typically associated with swimming or diving. Table 1.1.24 provides an overview of these water- and storm-related fatal injuries.
Bathtub Drownings tsunamis. This geographic concentration of events is evidence of the value of seismic risk maps as a tool for quantifying the risk of earthquake by location, although such maps are also useful by showing that the areas that have experienced the most severe events are not the only areas at high risk for such events. The two incidents near Alaska are included here because they originated as earthquakes, even though the proximate cause of harm was water, that is, tsunami. Other lists may split these multiperil incidents differently. For example, hurricanes that cause most of their damage through flooding rather than wind appear on some lists of the worst hurricanes and some lists of the worst floods (and may be absent from some lists because they are on the other lists). Deadliest Earthquakes Worldwide. Table 1.1.22 lists the 10 deadliest world earthquakes of all time, seven of which occurred in China or Japan and all of which were estimated to have killed at least 100,000 people (with the possible exception of the 1908 Messina, Italy, incident, for which the range of estimates is unusually wide). Costliest U.S. Earthquakes. Table 1.1.23 lists the 10 costliest U.S. earthquakes of all time, based on adjustment to 1999 dollars. The 1994 Northridge, CA, earthquake and the 1989 Loma Prieta earthquake lead the list by a substantial margin, with the 1906 San Francisco earthquake ranking third, itself having more than double the loss (in inflation-adjusted dollars) of any other event. All but one of the 10 costliest earthquakes occurred in California. Reliable death tolls are hard to come by for older events, and property loss totals are even more rare, regardless of reliability. Therefore, it is possible that some of these incidents do not belong on the lists and other events, no longer even cited in the general references, do belong. But as noted earlier, the environment has also changed. In a given small area, there tend to be more people and more valuable objects than ever before. The New Madrid, Missouri, earth-
Within this group, drownings in bathtubs come closest to involving design options for the built environment. Figure 1.1.7 shows that this risk targets the very young and the very old, much as fire does. Children under age 5 have roughly three times the all-ages risk, a higher relative risk than the same age children have for death from fire. Older adults show a lower relative risk for drowning in bathtubs than they do for death from fire.
Storms Storm data collected by the National Weather Service12 show significant annual averages of property damage (excluding crop damage) in 1996–2000 from five types of storms: • Hurricanes. $1.9 billion per year, but varying from near zero to $4.2 billion from year to year • Tornadoes. $1.1 billion per year, but varying from $0.4 billion to $2.0 billion from year to year • Hail storms. $0.6 billion per year ($0.8 billion per year if crop damage is included), but varying from $0.2 billion to $1.3 billion from year to year • Thunderstorms (including wind). $0.5 billion per year ($0.6 billion per year if crop damage is included), but varying from $0.2 billion to $1.4 billion from year to year • Winter storms. $0.2 billion per year, but varying from $0.1 billion to $0.5 billion from year to year Note that loss data from 2000 was considered incomplete. Four other types of storms or storm effects—lightning, coastal storms, tsunamis, and ice storms—are not shown above because they each averaged much less property damage per year in 1996–2000.
Floods Johnstown, Pennsylvania, Flood. Moving to major events, Table 1.1.25 lists the 10 deadliest U.S. floods of all time. The well-known Johnstown, Pennsylvania, flood of 1889 has by far the highest death toll on this list. Death tolls for each of these
1–18 SECTION 1 ■ Safety in the Built Environment
TABLE 1.1.20 Nonfatal Private-Industry Occupational Injuries or Illnesses Involving Days Away from Work, by Event or Exposure and by Selected Objects Providing Source of Injury or Illness 1996 Injuries and Illnesses per 10,000 Full-Time Workers Event or Exposure
Total
Floors, Walkways, or Ground Surfaces
Furniture or Fixtures
Machinery
Contact with Object or Equipment Struck against object Struck by object Falling object Flying object Swinging or slipping object Rolling or sliding object Unclassified or unknown-type object Caught in or compressed by object or equipment Caught in or crushed in collapsing materials Excavation or cave-in Collapsing structure Unclassified or unknown type Rubbed or abraded by friction or pressure Rubbed, abraded, or jarred by vibration Unclassified or unknown-type
58.7 15.2 28.4 11.4 2.8 8.1 0.9 5.2 9.5
1.0 0.7 0.1 — — — — — —
3.5 1.8 1.4 0.9 — 0.1 — 0.3 0.3
9.9 2.8 2.2 0.8 0.1 0.4 0.2 0.7 4.6
0.1
—
—
—
— — — 3.6
— — — 0.1
— — — —
— — — —
0.4
—
—
0.1
1.6
—
—
0.2
Falls Fall to lower level Down stairs or steps From floor, deck, or ground level Through existing floor opening Through floor surface From loading dock From ground level to lower level Unclassified or unknown type From ladder From piled or stacked material From roof Through existing roof opening Through roof surface Through skylight From roof edge Unclassified or unknown type From scaffold or staging From building girders or other structural steel From nonmoving vehicle Unclassified or unknown type Jump to lower level Fall on same level To floor, walkway, or other surface Onto or against objects Unclassified or unknown type Unclassified or unknown type
39.4 11.7 2.7 0.7 0.1 0.1 0.1 0.3 0.3 3.0 0.1 0.4 — — — 0.2 0.1 0.5 —
34.2 10.4 2.6 0.6 0.1 — 0.1 0.3 0.2 2.5 0.1 0.3 — — — 0.2 0.1 0.5 —
0.8 — — — — — — — — — — — — — — — — — —
0.5 0.1 — — — — — — — — — — — — — — — — —
2.3 2.0 0.9 26.1 22.4 3.3 0.4 0.6
2.0 1.7 0.7 22.6 22.3 — 0.3 0.4
— — — 0.7 — 0.7 — —
— — — 0.3 — 0.3 — —
Bodily reaction or exertion Bodily reaction—slip, trip, or loss of balance, without fall
98.0 7.1
1.0 0.5
3.9 —
3.5 —
CHAPTER 1
TABLE 1.1.20
■
Challenges to Safety in the Built Environment
1–19
Continued 1996 Injuries and Illnesses per 10,000 Full-Time Workers Total
Floors, Walkways, or Ground Surfaces
Furniture or Fixtures
Machinery
10.4
—
—
0.5
0.5 0.1
— —
— —
0.1 —
0.2
—
—
—
— —
— —
— —
— —
— 0.1 3.5 3.2 0.1 5.4
— — — — — —
— — — — — —
— — 0.3 0.3 — —
— 0.6 0.6 — 0.2
— — — — —
— — — — —
— 0.1 0.1 — —
—
—
—
—
Transportation incidents
9.2
—
—
0.2
Fires or explosions
0.5
—
—
—
Assault or violent act
2.9
—
—
—
Unclassified or unknown type
4.8
—
—
—
Event or Exposure Exposure to harmful substances or environments Contact with electrical current Of appliance, tool, or other equipment Of wiring, transformer or other electrical distribution equipment Of overhead power lines Of underground or buried power lines From lightning Unclassified or unknown type Contact with temperature extremes Hot objects Exposure to air pressure changes Exposure to caustic, noxious, or allergenic substances Exposure to noise Exposure to radiation Welding light Unclassified or unknown type Exposure to traumatic or stressful event Unclassified or unknown type
Note: Sums may not equal totals due to rounding error. Source: Table R36, Case and Demographic Resource Tables, from http//www.osha.gov/oshstats.
events often vary widely depending on the source. Part of the reason for the variation is that major flooding exerts effects over enormous areas and for periods of months or even years. Databases may have limits on breadth of capture, and these limitations may be significant in generating an estimate of total impact. Rapid City, South Dakota, Flood. The most recent flood to appear on this list was the 1972 Rapid City, South Dakota, flash flood. Like the classic Johnstown flood and one other on this list, a dam collapse was a critical event in the large loss. The other floods primarily involved rising waters swollen by rain and are more in keeping with the use of flood plain maps as a device for quantifying risk by location. (As with earthquakes and other natural disasters, though, a map showing high-risk areas typically will not be limited to areas that have recently experienced a major event.) Half the floods on this list involved the Mississippi River valley.
Deadliest Floods Worldwide. Table 1.1.26 lists the five deadliest floods of all time worldwide. All of them occurred in China. Two of the incidents, occurring three centuries apart, were initiated or severely worsened by deliberate acts in a wartime setting. One involved the destruction of river dikes by rebels, and the other involved flooding of crops already ravaged by destruction by troops. In general, lists in this handbook of deadliest or costliest incidents exclude wartime incidents, which would account for many of the deadliest fires and avalanches of all time, to name just two examples. The exception is made here only because there are so few incidents known to involve death tolls on the scale of the incidents in Table 1.1.26 that the alternative to include these incidents would probably have been to shorten or exclude this list. Costliest U.S. Floods. Table 1.1.27 lists the 10 costliest U.S. floods of all time. Even though all loss figures have been adjusted
1–20 SECTION 1 ■ Safety in the Built Environment
TABLE 1.1.21
Deadliest U.S. Earthquakes of All Time
Location (Richter scale severity)
Year
Estimated Deaths
1. San Francisco, CA (8.3) 2. Alaska earthquake causes tsunami, which hits California and Hawaii 3. Long Beach, CA (6.2) 4. Anchorage, AK (9.2) Deaths due mostly to tsunami 5. San Fernando, CA (6.6) 6. San Francisco, CA (7.1) 7. Northridge, CA (6.8) 8. Owens Valley, CA 9. Charleston, SC 10. Hebgen Lake, MT
1906 1946
452 173
1933 1964
120 117
1971 1989 1994 1872 1886 1959
64 62 61 60 27–100 28
Note: The earthquake on land in the United States with the highest severity was in New Madrid, MO, in 1811–1812 (8.7), but it occurred in a remote and underpopulated area, so it resulted in only six deaths. Sources: National Safety Council, Injury Facts 2000, National Safety Council, Itasca, IL, 2000; World Almanac 1998, New Jersey: K-III Reference Corporation, 1997; James Cornell, The Great International Disaster Book, Pocket Books, New York, 1979; Lee Davis, Natural Disasters, Facts on File, New York, 1992.
TABLE 1.1.22
World’s Deadliest Earthquakes of All Time
Location (Estimated Richter scale severity)
Year
Estimated Deaths
1. 2. 3. 4. 5. 6. 7.
1556 1976 1737 526 1927 1920 1923
820,000–830,000 255,000–655,000 300,000 250,000 200,000 180,000–200,000 140,000–143,000
1730 1857
137,000 107,000
1908
83,000–160,000
Shaanxi Province, China Tangshan, China (8.0) Calcutta, India Antioch, Syria Nanshan, China (8.3) Gansu, China (8.6) Tokyo and Yokohama, Japan (8.3) Deaths were nearly all due to fire. 8. Hokkaido, Japan 9. Tokyo, Japan Deaths were mostly due to fire. 10. Messina, Italy (7.5)
Sources: National Safety Council, Injury Facts 2000, National Safety Council, Itasca, IL, 2000; World Almanac 1998, New Jersey: K-III Reference Corporation, 1997; James Cornell, The Great International Disaster Book, Pocket Books, New York, 1979; Lee Davis, Natural Disasters, Facts on File, New York, 1992.
for inflation, half of the listed floods are from the last decade of the twentieth century. The costliest incident of all resulted in as much loss as the next two costliest floods combined. Four of the 10 floods involved the Mississippi River valley. The last three floods on the list were due in whole or in part to rivers swollen by melting snow, a scenario that did not contribute to any of the 10 deadliest floods.
TABLE 1.1.23
Costliest U.S. Earthquakes of All Time Estimated Total Property Damage (Billion Dollars)
Location (Richter scale severity) 1. Northridge, CA (6.8) 2. Loma Prieta and San Francisco Bay area, CA 3. San Francisco, CA (8.3) Damage caused primarily by fire. 4. Anchorage, AK (9.2) Damage caused primarily by tsunami. 5. San Fernando, CA (6.6) 6. Southern California 7. Long Beach, CA (6.2) 8. Kern County, CA 9. Southern California 10. Northern California
Year
In Year of Occurrence
In 1999
1994
13.0–20.0
1989
7.0
14.6– 22.5 9.4
1906
0.35
6.5
1964
0.5
2.7
1971
0.6
2.3
1987 1933
0.4 0.04
0.5 0.5
1952 1992 1992
0.06 0.09 0.07
0.4 0.1 0.1
Source: Insurance Information Institute, The I.I.I. Insurance Fact Book 2001, Insurance Information Institute, New York, 2001. Consumer price index data used to adjust loss data.
Table 1.1.28 provides an overview of death tolls and losses from U.S. floods for the five most recent years available, based on the storm data tracking done by the National Weather Service of the U.S. National Oceanic and Atmospheric Administration. Note that flash floods always dominate river floods as causes of deaths and in most years also dominate as causes of property loss, but the damage caused by river floods in the exceptional years is more than enough to dominate the multiyear statistics.
Hurricanes Deadliest U.S. Hurricanes. Table 1.1.29 lists the 10 deadliest U.S. hurricanes of all time. Some very deadly hurricanes are not listed because their death tolls were not high enough when deaths outside the 50 states and the District of Columbia are excluded. The seven deadliest hurricanes all occurred before the convention of assigning names to hurricanes, which began after World War II. Poorer record-keeping prior to the twentieth century and the fact that some hurricanes wiped out all life on isolated or island communities may mean that some hurricanes with true death tolls high enough to justify inclusion are not recognized as such. This also explains the considerable variation in estimated death tolls for some of these storms from one source to another. The most recent hurricane to appear on the list of the 10 deadliest was Hurricane Audrey in 1957. The list of the 10
CHAPTER 1
TABLE 1.1.24
■
Challenges to Safety in the Built Environment
1–21
Deaths Due to Drownings, Submersions, Storms, or Floods Deaths Coded on U.S. Death Certificates
Year
Cataclysmic Storms or Floodsa
Total Drownings and Submersions
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
70 138 70 81 96 107 74 93 136 204
3,967 3,979 3,967 3,524 3,807 3,404 3,790 3,488 3,561 3,964
Drownings in Bathtub
Other or UnknownType Drowning during Sport or Recreation
Drowning or Submersion Including Swimming or Diving Not for Sport or Recreation
312 318 312 345 306 301 281 330 329 337
814 843 814 677 858 694 822 645 648 685
2,841 2,818 2,841 2,502 2,643 2,409 2,687 2,513 2,584 2,942
a
Not included in total drownings and submersions. Note: Excluded from table are water transport accidents, suicides, homicides, and incidents where it could not be determined whether injury was intentional or unintentional. Source: National Safety Council, Accident Facts and Injury Facts, 1992–2000 editions, National Safety Council, Itasca, IL, 1992–2000; 1998 data from CDC/NCHS website.
3.8
Under 5 5–9
0.5
10–14
0.5
Age
15–19 20–39 40–64 65–74
0.6 1.1 0.9 1.2 2.9
75–84
4.8
86 and older All ages
1.3 Deaths per million population
FIGURE 1.1.7
Deaths Due to Drowning in Bathtub, by Age
costliest hurricanes is quite different, with 9 of the top 10 hurricanes occurring after 1957. As will be seen, much improved technologies and procedures for advance warning and effective evacuation in advance of severe hurricanes are among the reasons for the greatly reduced death tolls of equally severe or more severe storms. Deadliest Hurricanes Worldwide. Table 1.1.30 lists the five deadliest hurricanes of all time worldwide. Four of the five occurred on the Indian subcontinent, and the deadliest one of all— the 1970 hurricane in what was then East Pakistan—triggered the most extreme response to ineffective emergency response in world history, namely, the creation of the breakaway nation of Bangladesh.
Costliest U.S. Hurricanes. Table 1.1.31 lists the 10 costliest U.S. hurricanes of all time. The oldest such storm was in 1955, which may reflect the absence of comprehensive recordkeeping on some of the older, costly storms. Hurricane Andrew in 1992, the costliest hurricane on the list, involved higher costs than the next two costliest hurricanes combined did. Coming only three years after Hurricane Hugo, the third costliest storm on the list, which itself came after more than a decade without such costly storms, Hurricane Andrew had a devastating effect on the insurance industry, which had not contemplated a storm of this magnitude in its risk calculations. As with other major disasters, Hurricane Andrew revealed hitherto unrecognized vulnerabilities in the existing building stock, such as inadequately secured roofing on much of the southern Florida housing stock. This is an example of how loss experience can lead to proposals for code changes, if the vulnerabilities had not been addressed, or enforcement practices, if the vulnerabilities had been addressed in the code but not effectively addressed in actual practice.
Tornadoes Table 1.1.32 lists the number of tornadoes and associated deaths for the most recent 10 years with available data. Table 1.1.33 lists the 10 deadliest U.S. tornado incidents of all time, most involving more than one tornado in a short period of time and in a contiguous region. The three single-tornado incidents on the list all occurred in the nineteenth century. Tornado incidents rarely produce combined property losses in excess of $1 billion and, possibly for that reason, there were not enough tornado incidents with document high property losses to justify preparing a list of the 10 costliest tornado incidents. The same scarcity of data accounted for the absence of lists for avalanches and mudslides in the section on objects in motion, and for hailstorms in this section.
1–22 SECTION 1 ■ Safety in the Built Environment
TABLE 1.1.25
Deadliest U.S. Floods of All Time
TABLE 1.1.26
Flood
Year
Estimated Deaths
1. Johnstown, PA South Fork dam collapsed 2. Scioto, Mad, Miami, and Muskingum River Valleys, OH, IN, and IL Rain-swollen waters bridged levees 3. San Fransicquito Canyon, CA St. Francis dam collapsed 4. Ohio and Mississippi River Valleys Rain-swollen waters bridged levees 5. Willow Creek, OR Flash flood due to fast, heavy storm 6. Mississippi River Valley Rain-swollen waters bridged levees 7. Rapid City, SD Flash flood due to heavy rain and dam collapse 8. Mississippi River Valley Rain- and snow-melt-swollen waters flooded banks 9. Mississippi River Valley Snow-melt-swollen waters bridged levees 10. Kansas City, MO and Lower Mississippi, Missouri, Kansas and Des Moines River Valleys Rain-swollen waters flooded banks
1889
2,209
1913
732
1928
450
1937
380
1903
325
1927
313
1972
236
1874
200–300
1912
200–250
1903
200
Sources: National Safety Council, Injury Facts 2000, National Safety Council, Itasca, IL, 2000; World Almanac 1998, K-III Reference Corporation, New Jersey, 1997; James Cornell, The Great International Disaster Book, Pocket Books, New York, 1979; Lee Davis, Natural Disasters, Facts on File, New York, 1992.
Winter Storms Available references do not cite a sufficient number of very costly individual winter storms, ice storms, hail storms, or freezes to generate comparable lists. It also is not clear how much of the reported loss for such storms is relevant to assessments of impact on the built environment. Crop damage and snow removal costs would not be relevant to such an assessment, for example. Damage due to snow loading is not separately tabulated in any published data, and that would be the most relevant form of damage. It can be noted that the highest U.S. property loss discovered for a winter storm was the 1993 blizzard dubbed the “Storm of the Century,” with losses estimated at $3 to $6 billion, including $1.75 billion in insured loss. In the 1990s, however, at
World’s Deadliest Floods of All Time Flood
1. Huane He (Yellow) River, China 2. Huang He (Yellow) River, China 3. Kaifeng, China River dikes were destroyed by rebels. 4. Northern China Crops flooded and also destroyed by government, causing famine. 5. Chang Jiang (Yangtze) River, China
Year
Estimated Deaths
1931 1887 1642
3,700,000 900,000 300,000
1939
200,000
1911
100,000– 200,000
Sources: National Safety Council, Injury Facts 2000, National Safety Council, Itasca, IL, 2000; World Almanac 1998, K-III Reference Corporation, New Jersey, 1997; James Cornell, The Great International Disaster Book, Pocket Books, New York, 1979; Lee Davis, Natural Disasters, Facts on File, New York, 1992.
least three European winter storms, code named Daria, Lothar, and Vivian, each accounted for at least $4 billion in insured losses. The Storm of the Century also would rank second on a list of the 10 deadliest U.S. winter storms, accounting for an estimated 200 to 270 deaths, second only to an 1888 storm in the northeast, where 400 to 800 people were estimated to have died. A 1956 winter storm in Europe had the highest worldwide death toll identified, at 1,000 killed.
Estimating Property Loss Table 1.1.34 represents an attempt to estimate property loss not limited to catastrophes for major sources of such loss. The table is limited to insured loss and to loss covered under homeowner policies. The table combines published data on shares of premium dollars that go toward compensation for losses with published data on the share of losses accounted for by each of several major hazard groups. The fire and lightning losses in Table 1.1.34 should be comparable to NFPA statistics on property damage in home fires, and, in fact, the figures are reasonably close. This encourages optimism that the figures on wind and hail and on water damage and freezing are also reasonable. It has already been noted that fire losses in individual largeloss fires do not dominate total property losses due to fire. In the majority of the years shown in Table 1.1.34, losses due to hurricanes—the large-loss windstorms—would dominate total property damage due to wind and hail. However, losses due to major flood events do not appear to dominate the total water damage and freezing. In any event, most home insurance policies exclude damage due to major floods from coverage. (This is why the Federal Emergency Management Agency’s national flood insurance program was created.) The plumbing failures and ordinary rainstorms that probably account for most or all of the loss under water damage and freezing should constitute challenges that design for the built environment is meant to address.
CHAPTER 1
■
Challenges to Safety in the Built Environment
1–23
Costliest U.S. Floods of All Time
TABLE 1.1.27
Estimated Loss (in Billion Dollars) Flood
Year
In Year of Occurrence
In 1999
1. Mississippi River Valley Rain-swollen waters bridged levees. 2. Connecticut River Valley Rain-swollen waters were due to Hurricanes Connie and Diana, but without storm surge or wind factors. 3. Kansas River Basin Rain-swollen waters bridged levees 4. Mississippi and Missouri River Valleys 5. Texas, Oklahoma, Louisiana, and Mississippi Flooding with hail and tornadoes caused damage. 6. Willow Creek, OR Flash flood due to fast, heavy storm 7. Mississippi River Valley Rain-swollen waters flooded banks. 8. California Flooding was due to snow melt. 9. Northeast to Mid-Atlantic U.S. Flooding was due to snow melt after blizzard. 10. Northwestern US states Snow melt and heavy rain led to flooding.
1993
15.0–20.0
17.3–23.1 11.2
1955
1.8
1951
1.0+
6.4+
1947 1995
0.85 5.0–6.0
6.3 5.5–6.6
1903
0.25–0.325
4.6–6.0
1937
0.30+
3.5+
1995
3.0
3.3
1996
3.0
3.2
2.0–3.0
1996– 1997
2.1–3.1
Sources: National Safety Council, Injury Facts 2000, National Safety Council, Itasca, IL, 2000; World Almanac 1998, K-III Reference Corporation, New Jersey, 1997; James Cornell, The Great International Disaster Book, Pocket Books, New York, 1979; Lee Davis, Natural Disasters, Facts on File, New York, 1992.
TABLE 1.1.28
Losses Due to Floods According to Storm Data Compiled by U.S. National Weather Service
A. Deaths
B. Property Damage (Billion Dollars) Excluding Crop Damage
Year
Total
Flash Floods
1996 1997 1998 1999 2000a
131 118 136 68 37
94 86 118 60 29
River Floods
Small Stream or Urban Flood
31 29 14 5 3
6 3 4 3 5
Year 1996 1997 1998 1999 2000a
Total
Flash Floods
River Floods
Small Stream or Urban Flood
Combined Crop Damage
2.1 6.9 2.3 1.4 1.2
1.1 0.9 0.9 1.2 0.7
1.0 6.0 1.4 0.2 0.5
0.0 0.0 0.0 0.0 0.0
0.4 0.1 0.3 0.4 0.7
a
Data incomplete. Note: Sums may not equal totals because of rounding error. Source: U.S. National Weather Service website.
HAZARDOUS ENVIRONMENT Carbon Monoxide and Other Poisonings by Gases and Vapors Table 1.1.35 gives a 10-year overview of trends in poisonings by gases and vapors. The two major components are motor vehicle exhaust gas and other utility gas or carbon monoxide.
Table 1.1.36 provides a five-year trend overview of the latter, for which half the deaths are attributed to carbon monoxide, with no other details reported. The two largest components with details known are LP-Gas from mobile containers, for which deaths appear to be declining, and carbon monoxide from incomplete combustion of domestic fuels, for which no clear trend is apparent. Tables 1.1.37 and 1.1.38 provide eight-year trends of carbon monoxide associated with unvented releases from heating
1–24 SECTION 1 ■ Safety in the Built Environment
TABLE 1.1.29
Deadliest U.S. Hurricanes of All Time Location
Hurricane 1. No name Deaths due primarily to storm surge wave. 2. No name Entire island wiped out. 3. No name 4. No name 5. No name
6. No name 7. No name 8. Hurricane Diane 9. Hurricane Audrey 10. No name
Galveston, TX
Year 1900
1841
St. Jo, FL
Southern, FL Louisiana Islands off Georgia and North and South Carolina New York and New England Florida Keys New England Louisiana
1928 1893 1893
North Carolina to New England
Estimated Deathsa
4,000
1,833 1,800 1,000+
1938
657
1935 1955 1957
409 400 395
1944
389
Estimated Deaths
Storm
Year
1. East Pakistan The lack of timely, substantial relief from the government led to the breakaway creation of Bangladesh. 2A. Bengal, India 2B. Haiphong, Vietnam 4. Bangladesh 5A. Bengal, India 5B. Bombay, India
1970
200,000– 1,000,000
1737 1881 1991 1876 1882
300,000 300,000 139,000 100,000+ 100,000+
6,000
a Several hurricanes had higher death tolls but not when non-U.S. deaths are excluded. Also, a 1915 Louisiana hurricane had 275 estimated deaths in two sources and 500 in the other two sources. Sources: National Safety Council, Injury Facts 2000, National Safety Council, Itasca, IL, 2000; World Almanac 1998, K-III Reference Corporation, New Jersey, 1997; James Cornell, The Great International Disaster Book, Pocket Books, New York, 1979; Lee Davis, Natural Disasters, Facts on File, New York, 1992.
TABLE 1.1.31
TABLE 1.1.30 World’s Deadliest Cyclones, Hurricanes, and Typhoons of All Time
Sources: National Safety Council, Injury Facts 2000, National Safety Council, Itasca, IL, 2000; World Almanac 2001, K-III Reference Corporation, New Jersey, 2000; James Cornell, The Great International Disaster Book, Pocket Books, New York, 1979; Lee Davis, Natural Disasters, Facts on File, New York, 1992.
and cooking equipment, respectively. Gas-fueled heating equipment dominates these figures, particularly in recent years. Deaths from carbon monoxide from charcoal grills include, and probably are dominated by, deaths from the improper indoor use of these grills. For context, Table 1.1.39 provides statistics on suicide deaths due to gas or vapor and on related deaths where it was not determined whether the death was intentional or not. Suicides are far more numerous than unintentional-injury deaths by the same mechanism of gas or vapor. Note that all these death tolls have been declining significantly, with the possible exception of suicide by gas or vapor other than motor vehicle exhaust.
Costliest U.S. Hurricanes of All Times Estimated Loss (in Billion Dollars)
Hurricane (Category strength) 1. Hurricane Andrew (4) 2. Hurricane Agnes 3. Hurricane Hugo (4) 4. 5. 6. 7.
Hurricane Diane Hurricane Betsy Hurricane Camille Hurricane Floyd (2)
8. Hurricane Fran (3) 9. Hurricane Alicia (3) 10. Hurricane Georges (2)
Location
Year
In Year of Occurrence
In 1999
Florida and Louisiana Mid-Atlantic states North and South Carolina, Puerto Rico, and Virgin Islands New England Florida and Louisiana Gulf Coast states North Carolina and lesser damage to 11 other states North Carolina and Virginia Texas Gulf Coast regions of Alabama, Florida, Louisiana, and Mississippi
1992 1972 1989
27.0 4.5 9.0+
32.1 17.9 12.1
1955 1965 1969 1999
1.6–1.8 1.42 1.5 6.0
10.0–11.2 7.5 6.8 6.0
1996 1983 1998
5.0 3.0 3.0–4.0
5.3 5.0 3.1–4.3
Sources: National Safety Council, Injury Facts, 2000 edition, National Safety Council, Itasca, IL, 2000; World Almanac; 1998 edition, K-III Reference Corporation, New Jersey, 1997; James Cornell, The Great International Disaster Book, Pocket Books, New York, 1979; Lee Davis, Natural Disasters, Facts on File, New York, 1992; National Climatic Data Center, Statistical Abstract of the United States 2000, U.S. Census Bureau, Washington, 2000, Table 406. Consumer price index used to adjust loss totals.
CHAPTER 1
TABLE 1.1.32 Tornadoes and Deaths Due to Tornadoes in the United States Year
Number of Tornadoes
Deaths
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
856 1,133 1,132 1,297 1,173 1,082 1,234 1,173 1,148 1,424
50 53 39 39 33 69 30 25 67 130
Source: U.S. National Weather Service, as cited in Insurance Information Institute, The I.I.I. Insurance Fact Book 2001, Insurance Information Institute, New York, 2001. Consumer price index data used to adjust loss data.
Other Fatalities Involving a Hazardous Environment The broader notion of a hazardous environment is that, as people move about within the built environment, they are exposed in some manner to hazards with the potential to cause harm. An atmosphere contaminated by deadly carbon monoxide is an obvious example, and that was the subject of the preceding several paragraphs. Most other examples of hazardous environments involve hazards that are less pervasive and more avoidable. Table 1.1.40 provides a 10-year overview of other hazardous-environment deaths involving specific objects. The first three columns are for poisonings by various solids or liquids. Cleaners and paints are shown separately because that category includes substances that might be encountered in components of the built environment. Fumes from cleaners and flaked-off lead paint are examples. Corrosives and caustics are shown separately
TABLE 1.1.33
5. 6. 7. 8. 9. 10.
Challenges to Safety in the Built Environment
1–25
because they also have the potential, although probably less than with cleaners and paints, to be encountered after application of the substances to components of the built environment. More often, these substances cause fatal poisonings because they are accessed in stored form and then ingested. The separately listed cleaners, paints, corrosives, and caustics are a very small part of the overall category of poisonings by solids and liquids, as the third column demonstrates. Most of this category consists of alcohol products. The fourth column tabulates deaths occurring when someone is caught in or between two objects. The fifth tabulates deaths involving machinery, more than half of which involve agricultural machinery, pointing to the high risks involved in farming. And the sixth column tabulates deaths caused by cutting or piercing instruments and objects. Almost none of the deaths shown in Table 1.1.40 can be said to arise from hazards of the built environment. However, there may be significant indirect effects. Specifically, the design of the built environment may make access to hazardous products, by small children or other people with reduced capacity to make sound risk judgments, more or less difficult. The design, through ergonomics or a lack thereof, may make interaction with machinery or other large objects more or less likely to cause injury. More likely, Table 1.1.40 is relevant in setting priorities and tracking progress for more general safety programs, as opposed to choices involving the built environment. The same is true of Table 1.1.41, which provides a 10-year overview of deaths due to suffocation or a inhaling foreign object. Only mechanical suffocation has identified components that could relate to the built environment, and they are shown in detail in the 5-year overview of Table 1.1.42. Suffocation in a bed or cradle accounts for hundreds of deaths annually, and a bed is a sufficiently large piece of furniture that it can be treated as part of the specification of a built environment, even though codes for the built environment rarely set requirements for contents and furnishings, particularly in private homes, which is where most of the suffocation deaths in beds and cradles probably occur. Nevertheless, Figure 1.1.8 provides an
Deadliest U.S. Tornado Incidents of All Time Location
1. 2. 3. 4.
■
Southeastern U.S. Illinois, Indiana and Missouri South Carolina Alabama, Arkansas, Georgia, Mississippi, North Carolina, and Tennessee Mississippi Alabama, Georgia, Kentucky, Ohio and Tennessee Missouri Illinois, Indiana, Michigan, Ohio and Wisconsin Alabama Arkansas, Missouri, and Tennessee
Number of Tornadoes
Dates
Estimated Deaths
60+ 8 1 3+
February 19, 1884 March 18, 1925 September 10, 1811 April 4–7, 1936
800+ 606 500+ 402
1 148 1 37–40 20 31
May 7, 1840 April 3–4, 1974 May 27, 1896 April 11, 1965 March 21, 1932 March 21–22, 1952
317 307 306 272 268 229
Sources: National Safety Council, Injury Facts 2000, National Safety Council, Itasca, IL, 2000; World Almanac 1998, K-III Reference Corporation, New Jersey, 1997; James Cornell, The Great International Disaster Book, Pocket Books, New York, 1979; Lee Davis, Natural Disasters, Facts on File, New York, 1992.
1–26 SECTION 1 ■ Safety in the Built Environment
TABLE 1.1.34 Estimated Insured Property Damage under Homeowners Multiple-Peril Policiesa Estimated Loss (in Billion Dollars)
Year
Fire, Lightning and Debris Removal
Wind and Hail
Water Damage and Freezing
1994 1995 1996 1997 1998
5.2 5.9 5.4 6.7 6.5
2.0 4.0 5.0 3.2 6.3
4.7 2.9 3.6 3.1 3.3
a Published data for 1994–1998 from the Insurance Services Office indicates total homeowners policy premiums and percentage of homeowners insured loss accounted for by five types of property damage and three types of liability. Published data also indicates the percentage of premiums accounted for by insured loss for homeowners loss for homeowners for 1998 (77 percent) and 1997 (69 percent) and for all policies for 1997 (73 percent), 1995 (79 percent), and 1994 (81 percent). For this analysis, the 1997 data is used to infer that the homeowner percentage is typically 4 percentage points lower than the all-policies percentage, and the missing 1996 percentage was set equal to 75 percent, given that three of the other four percentages were estimated to fall in the range of 75 to 77 percent. Source: The I.I.I. Insurance Fact Book 2001, Insurance Information Institute, New York, 2001.
TABLE 1.1.35 Nonfire Unintentional-Injury Deaths Due to Poisoning by Gases and Vapors Coded on U.S. Death Certificates
Year
Total
Gas from Pipeline
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
921 748 736 633 660 685 611 638 576 546
48 33 20 21 14 24 27 23 13 15
Motor Vehicle Exhaust Gas
Other Utility Gas or Carbon Monoxide
355 293 278 223 245 246 234 219 208 190
353 289 316 281 290 307 272 283 251 254
Other 165 133 122 108 111 108 78 113 104 87
Source: National Safety Council, Accident Facts and Injury Facts, 1992–2000 editions, National Safety Council, Itasca, IL, 1992–2000; 1998 data from the CDC/NCHS website.
TABLE 1.1.36 Nonfire Unintentional-Injury Deaths Due to Utility Gas or Carbon Monoxide, Excluding Motor Vehicle Exhaust Gas and Gas From Pipeline Deaths Coded on U.S. Death Certificates
Year
Total
LP Gas from Mobile Container
1994 1995 1996 1997 1998
307 272 283 251 254
59 57 57 39 37
Carbon Other and Unspecified Utility Gas
Monoxide from Incomplete Combustion of Domestic Fuels
Other Carbon Monoxide
Unknown Type Carbon Monoxide
11 13 18 25 11
59 44 52 50 60
25 18 10 14 18
153 140 146 123 128
Source: CDC/NCHS website.
TABLE 1.1.37
Unintentional-Injury Nonfire Deaths Due to Carbon Monoxide, by Type of Heating Device, 1990–1997
Year
Central Heating Unit (Furnace) NaturalGas-Fueled
Water Heater Gas-Fueled
Space Heater or Furnace LpGas-Fueled
Any Device Liquid-Fueleda
Any Device Solid-Fueledb
1990 1991 1992 1993 1994 1995 1996 1997
28 76 40 43 64 55 35 61
17 13 6 11 7 5 8 8
86 76 79 83 93 90 99 55
19 22 8 15 12 7 21 12
43 10 12 10 8 8 10 6
a
Principally oil-fueled furnaces and portable kerosene heaters. Includes coal-fueled furnaces, wood stoves, and fireplaces. Notes: Statistics shown here include proportional allocation of deaths and injuries involving gas-fueled heating equipment with unknown type of gas fuel for 1993–1997 and unknown-fueled heating equipment with unknown type of equipment for 1990–1997. These allocations do not appear in the source reports. Source: Mah, J. C., “Non-Fire Carbon Monoxide Deaths and Injuries Associated with the Use of Consumer Products,” US Consumer Product Safety Commission, October 2000, Table 1. Additional information from previous reports in this series. Statistics no longer reported separately for liquid-fueled or solid-fueled heating devices. The 1997 report presented data for 1994 and reanalyzed data for 1990–1993. b
CHAPTER 1
TABLE 1.1.38 Unintentional-Injury Nonfire Deaths Due to Carbon Monoxide, by Type of Cooking Device, 1990–1997 Year
Range, Stove, or Oven Gas-Fueled
Grill Charcoal
1990 1991 1992 1993 1994 1995 1996 1997
10 14 13 6 9 5 15 5
21 25 27 27 15 14 19 23
Challenges to Safety in the Built Environment
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TABLE 1.1.39 Deaths Due to Poisoning by Gases and Vapors, 1989–1998
Year 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
*No gas-fueled grill incidents were reported. Source: Mah, J. C., “Non-Fire Carbon Monoxide Deaths and Injuries Associated with the Use of Consumer Products,” US Consumer Product Safety Commission, October 2000, Table 1, and previous reports in this series. The 1997 report presented data for 1994 and reanalyzed data for 1990–1993.
TABLE 1.1.40
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Suicide— Suicide— Undetermined Whether Other Motor Unintentional Gas or Unintentional Vehicle or Deliberate Vapor Exhaust Injury 1,814 1,877 1,833 1,706 1,670 1,618 1,659 1,508 1,367 1,329
921 748 736 633 660 685 611 638 576 546
414 404 397 351 422 426 436 499 451 397
127 112 102 120 107 84 107 118 77 82
Source: National Safety Council, Accident Facts and Injury Facts, 1992–2000 editions, National Safety Council, Itasca, IL, 1992–2000; 1998 statistics from CDC/NCHS website.
Other Hazardous Environment Deaths Coded on U.S. Death Certificates
Year
Poisoning by Cleaner or Paint
Poisoning by Corrosive or Caustic
Other and UnknownType Poisoning by Solids or Liquidsa
Caught in or between Objects
Caused by Machineryb
Caused by Cutting or Piercing Instrument or Object
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
9 15 5 11 21 13 10 10 14 10
9 12 10 8 13 14 10 9 8 5
550 522 468 479 461 454 441 422 466 402
91 99 89 119 91 83 90 71 85 118
1,179 1,184 1,073 1,037 999 970 986 926 1,055 1,018
119 108 116 132 108 103 118 97 104 121
a Includes alcohol or petroleum products, agricultural products, chemical or pharmaceutical products, and foods or plants. Alcohol products dominate. b Majority of deaths caused by machinery are caused by agricultural machinery.
TABLE 1.1.41
Deaths Due to Suffocation or Foreign Object Coded on U.S. Death Certificates
Year
Total Suffocation or Foreign Object
Suffocation or Respiratory Tract Obstruction Due to Food
Suffocation or Respiratory Tract Obstruction Due to Object Other Than Food
Mechanical Suffocation (i.e., something external blocking air)
Foreign Body Entering Other Bodily Orifice
1994 1995 1996 1997 1998
4,161 4,274 4,338 4,437 4,608
1,110 1,088 1,126 1,095 1,147
1,955 2,097 2,080 2,180 2,368
1,078 1,062 1,114 1,145 1,070
18 27 18 17 23
Source: CDC/NCHS website.
1–28 SECTION 1 ■ Safety in the Built Environment
TABLE 1.1.42
Deaths Due to Mechanical Suffocation, Coded on U.S. Death Certificates
Year
Total Mechanical Suffocation
In Bed or Cradle
By Plastic Bag
Due to Lack of Air in Closed Space
Due to Falling Earth or Other Substance
Unclassified
UnknownType
1994 1995 1996 1997 1998
1,078 1,062 1,114 1,145 1,070
227 207 219 236 247
50 37 40 44 27
9 14 15 21 13
58 59 57 54 55
375 406 436 451 400
359 339 347 339 328
Source: CDC/NCHS website.
9.3
Under 5 0.2
Age
5–9 10–14
0.1
15–19
0.1
20–39
0.1
40–64
0.1
65–74 75–84
0.3 0.8 3.0
86 and older All ages
0.9 Deaths per million population
FIGURE 1.1.8 Deaths Due to Suffocation in Bed or Cradle, by Age
overview of differences in risk of such suffocation by age of victim. Crib deaths of very young children clearly dominate. Table 1.1.43 completes the overview of unintentionalinjury deaths not specifically excluded from consideration at the outset. The fatal hazards shown here are mostly natural hazards and, apart from deaths due to animals or plants (e.g., animal bites or stings), they do not involve objects. Deaths due to excessive heat or cold vary considerably from year to year. Death certificate data shown for 1994–1998 in Table 1.1.43 show that, in most years, cold is the dominant killer. Storm data for 1996–2000, collected by the National Weather Service, shows just the opposite, with excessive heat the leading killer in four of the five years, usually by a wide margin. When detailed circumstances are known and reported, most of the death-certificate excessive-temperature deaths are specifically attributed to weather as the cause of the extreme temperatures. Excessive heat or cold, as a cause of death that can be essentially eliminated by a properly designed and operated building, provides the connection to the built environment, although mostly indirectly. Homelessness creates exposure to these potentially lethal conditions, as does an absence of effective and affordable
TABLE 1.1.43 Deaths Due to Natural or Environmental Factors, Excluding Lightning, Storms, Floods, Earth Movement or Eruption, Coded on U.S. Death Certificates
a
Year
Excessive Heat
Excessive Cold
Hunger, Thirst, Exposure or Neglect
Animal or Plant
Other Natural or Environmental Factora
1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
200 300 200 155 299 221 716 249 182 375
588 596 588 558 641 633 553 685 501 420
145 132 145 167 243 221 203 224 224 252
186 161 186 180 176 152 159 175 170 157
18 24 18 14 13 10 15 19 25 26
Specifically, these were due to high, low, or changing air pressure; travel; or motion. Note: Several heat waves with drought in 1980 and 1988 each killed thousands of people. Sources: National Safety Council, Injury Facts and Accident Facts, National Safety Council, Itasca, IL, 1992–2000; 1998 statistics from the CDC/NCHS web site.
CHAPTER 1
Hunger (50 percent)
Exposure to weather (45 percent)
Thirst Neglect (1 percent) (4 percent)
FIGURE 1.1.9 Deaths Due to Hunger, Thirst, Exposure, or Neglect, by Cause (Source: Data from the CDC/NCHS website)
climate control, principally heat for the winter. These problems are not really problems in the design of a building—although the cost of heating and the extent of natural cooling can vary considerably as a function of design—but are always problems arising from our efforts to live in environments of our own making. Figure 1.1.9 provides a breakdown of the deaths due to hunger, thirst, exposure, or neglect. Nearly half involve exposure to harsh weather, so they belong with the deaths shown on Table 1.1.43 as due to excessive heat or excessive cold.
SUMMARY If we are guided by the relative magnitude of real harm done to real people—either direct harm to people or damage to their property—then the statistics presented here would appear to give us four priority areas for future attention, aimed at improved safety: • Falls
• Fires
• Water
• Natural disasters
based on deaths, because falls are by far the number one cause of deaths due to unintentional injury occurring in a building because no other single cause of harm in buildings is a major cause of both harm to people and harm to property because of billions of dollars of property damage per year, apparently due to plumbing problems and damage from the incursion of rain from everyday storms, not from natural disasters because of property damage rather than deaths, and referring to earthquakes, floods, hurricanes, and other storms
Except for natural disasters, these four priority areas primarily center around harm occurring in homes—dwellings, duplexes,
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manufactured homes, and apartments—which are traditionally the places where strict control by codes stops. Even if you allow for the fact more time is spent at home than anywhere else, the risks of falls, fires, and water are higher at home than elsewhere. In terms of the first triage question—is this a big enough problem to worry about?—the answer for these four is yes. The next question is, how much of a difference can we make through changes in our built environments? And for the answer to that question, it helps to distinguish among the four types in terms of the relative safety focus each has received in recent decades. Fire has been the focus of NFPA for more than a century. Natural disasters are the focus of emergency managers at all levels of government and have been a focus of much of the insurance industry for some time. Water damage due to plumbing problems has been a focus of plumbing codes for some time. Falls are the odd group, in that they so clearly dominate any characterization of deaths in the built environment (and always have, although have recently done so even more) but have never been the primary focus of any major national organization or government agency. Fatal falls can be made less likely through three distinct elements of design in the built environment. First, a variety of design decisions can make footing either more or less precarious. The dimensions of steps and stairs have long been controlled through codes, but there are other design elements, such as flooring angles, that may not have received as much attention. Also, the “slipperiness” of various surfaces, ranging from the aptly named “throw rug” or highly polished wood floor at one extreme to thick carpet or grooved concrete at the other extreme, has a bearing on the probability that a fall will occur. Second, there is the effect of the surface’s ability to absorb the impact of a fall without causing harm, or at least not fatal harm. Different flooring products certainly vary in this regard, but there is also a potential influence from lower walls, hard corners, protruding sharp or hard edges, and so forth. Finally, there is the presence or absence, effectiveness or ineffectiveness, of physical aids to stabilization, such as handrails. These are all the design elements that compensate for the dangers created by the walking surfaces or that permit an incipient fall to be interrupted or minimized in impact. With so many opportunities to intervene via design in the number one cause of unintentional-injury deaths in the built environment, it is remarkable that falls have not emerged previously as a point of focus. The broad interpretation of the goals of NFPA’s Life Safety Code has provided a limited basis for focus on falls by some of the volunteers working with NFPA. More recently, the U.S. Centers for Disease Control and Prevention has identified falls by older adults as a priority focus for their work, and NFPA’s Center for High Risk Outreach has given preventive education regarding falls attention in the Remembering When program. And falls among children ages 14 and under are one of the risk areas addressed in NFPA’s school-based injury prevention program, Risk Watch®. Notwithstanding these serious and worthwhile programs, there is still a niche to be filled in focusing on code provisions to shape design of the built environment to reduce fatal falls.
1–30 SECTION 1 ■ Safety in the Built Environment
BIBLIOGRAPHY References Cited 1. National Safety Council, Injury Facts (previously known as Accident Facts), National Safety Council, Itasca, IL, published annually. 2. U.S. Census Bureau, Statistical Abstract of the United States 2000, 120th ed., US Government Printing Office, Washington, DC, Dec. 2000, Tables 1352 and 1353. 3. U.S. Census Bureau, Statistical Abstract of the United States 2000, 120th ed., US Government Printing Office, Washington, DC, Dec. 2000, Tables 30. 4. U.S. Census Bureau, Statistical Abstract of the United States 2000, 120th ed., US Government Printing Office, Washington, DC, Dec. 2000, Tables 21. 5. National Geographic Society, Natural Hazards of North America, National Geographic Society, Washington, DC, May 1988. 6. Audits and Surveys, Inc., “1984 National Sample Survey of Unreported Residential Fires: Final Technical Report,” prepared for U.S. Consumer Product Safety Commission, Contract No. C-831239, Audits and Surveys, Inc., Princeton, NJ, June 13, 1985. 7. The website of the National Center for Health Statistics with detailed death-certificate data, the same data in Injury Facts, is, for the year 1998 (and similarly constructed for earlier years): http://www.cdc.gov/nchs/data/gmwkl_98.pdf. 8. The website of the US Occupational Safety and Health Administration can be accessed for statistics on workplace injuries and illnesses, by going to the BLS Workplace Injury, Illness and Fatality Statistics section of http://www.osha.gov/oshstats. 9. Estimates of consumer-product-related injuries reported to hospital emergency rooms, based on reports to the National Electronic Injury Surveillance System (NEISS), are available through the National Injury Information Clearinghouse, Office of Information Services, US Consumer Product Safety Commission, Washington, DC 20207 or (301) 504-0424 X 1180. 10. Series 10 reports from the U.S. Department of Health and Human Services include analyses of injury experience taken from the National Health Interview Survey. 11. Insurance Information Institute, The I.I.I. Insurance Fact Book, Insurance Information Institute, New York, published annually. 12. The website of the National Oceanic and Atmospheric Administration, National Weather Service, Office of Climate, Water, and Weather Services, has sections with statistics on storm losses, at http://www.nws.noaa.gov/om/hazstats.htm. 13. In addition to the sources listed above, there are a number of references with loss information on historically large natural disasters, although the loss information often varies widely from one source to another. The two sources that appear to have done the most comprehensive job of gathering other references and providing a best-evidence overview are used as the principal sources in this chapter: James Cornell, The Great International Disaster Book, Pocket Books, New York, 1979; and Lee Davis, Natural Disasters, Facts on File, New York, 1992. 14. Insurance Information Institute, The I.I.I. Insurance Fact Book 2001, Insurance Information Institute, New York, 2001, p. 99.
Additional Readings and Resources Falls and Other Injuries—Research Centers and Technical Journals American Public Health Association: http://www.apha.org; and the APHA Injury Control Section: http://www.icehs.org. Center for Injury Research and Control (CIRCL), University of Pittsburgh, 200 Lothrop Street, Suite B400-PUH, Pittsburgh, PA 15213. http://www.injurycontrol.com/icrin. Their own website is http://www.circl.pitt.edu. Colorado Injury Control Research Center, jointly sponsored by Colorado State University, University of Colorado, and Colorado Department of Public Health Education. http://www.colostate.edu/Orgs/CICRC.
Emory Center for Injury Control, Rollins School of Public Health, Emory University, Atlanta, GA. http://www.sph.emory.edu/CIC. Journal of Safety Research. Sponsored by the National Safety Council. http://www.nsc.org. Morbidity and Mortality Weekly Report and NCHS Advance Data. The U.S. Centers for Disease Control and Prevention. http://www.cdc.gov. Safety Science Monitor (previously Journal of Occupational Accidents). Jointly sponsored by Institute for Human Safety and Accident Research (IPSO Australia), the Scientific Committee on Accident Prevention of the International Commission on Occupational Health, and the Safety Institute of Australia. http://www.ipso.asn.au. Southern California Injury Prevention Research Center (SCIPRC), UCLA, Los Angeles, CA. http://www.ph.ucla.edu/sciprc. TraumaLink, Children’s Hospital of Philadelphia, PA. http://www.traumalink.chop.edu. Trauma Foundation, San Francisco General Hospital, San Francisco, CA. http://www.tf.org. University of Iowa Injury Prevention Research Center, University of Iowa, Iowa City, IA. http://www.pmeh.uiowa.edu/IPRC. Natural Disasters—Research Centers and Institutes Center for Earthquake Research and Information (CERI), University of Memphis, 3892 Central, Memphis, TN 38152. http://www.ceri.memphis.edu. Center for Technology, Environment, and Development (CENTED), Clark University, 950 Main Street, Worcester, MA 01610. Centre for Research on Epidemiology of Disasters (CRED), Unit of Epidemiology, EPID 30-34, School of Public Health, Catholic University of Louvain 30, Clos Chappelle-aux-Champs, B-1200 Brussels, Belgium. Coastal Hazards Assessment and Mitigation Program, Department of Civil Engineering, Clemson University, Clemson, SC 29634-0911. Disaster Management and Mitigation Group (DMMG), Oak Ridge National Laboratory, PO Box 2008, Building 4500 North, Mail Stop 6206, Oak Ridge, TN 37831-6206. http://stargate.ornl.gov/StarGate/DMMG/dmmg.html. Disaster Preparedness Resources Centre, 4th floor, 2206 East Mall, University of British Columbia, Vancouver, BC, Canada V6T 1Z3. Disaster Research Center (DRC), University of Delaware, Newark, DE 19716. http://www.udel.edu/nikidee/drc.htm. Earthquake Engineering Research Center (EERC), ATTN: National Information Service for Earthquake Engineering (NISEE), University of California at Berkeley, 1301 South 46th Street, Richmond, CA 94804-4698. http://nisee.ce.berkeley.edu. Earthquake Engineering Research Institute (EERI), 499 14th Street, Suite 320, Oakland, CA 94612-1902. http://www.eeri.org. Earthquake Preparedness Center of Expertise (EQPCE), Resource Center, U.S. Army Corps of Engineers, ATTN: CESPD-CO-Q (Richard Cook), 211 Main Street, Room 302, San Francisco, CA 94105-1905. Institute for Crisis and Disaster Management, Research and Education, Gelman Library, Room 637, George Washington University, Washington, DC 20052. Institute for Disaster Research, Civil Engineering Department, Texas Tech University, Box 40123, Lubbock, TX 79409-1023. Institute for Business and Home Safety (formerly Insurance Institute for Property Loss Reduction) (IBHS), 1408 North Westshore Boulevard, Suite 208, Tampa, FL 33607. http://www.ibhs.org. International Center for Disaster-Mitigation Engineering (INCEDE), Institute of Industrial Science, University of Tokyo, 7-22-1, Roppingi Minato-ku, Tokyo 106, Japan. http://incede.iis. u-tokyo.ac.jp/Incede.html. International Center for Hurricane Damage and Mitigation Research, Florida International University, Miami, FL 33199. John A. Blume Earthquake Engineering Center, Department of Civil Engineering, Stanford University, Stanford, CA 94305-4020. http://blume.stanford.edu.
CHAPTER 1
National Center for Earthquake Engineering Research (NCEER), Information Service, 304 Capen Hall, Science and Engineering Library, State University of New York, Buffalo, NY 14260-2200. http://nceer.eng.buffalo.edu. National Laboratory of Resource and Environmental Information Systems (LREIS), Institute of Geography, Chinese Academy of Sciences, Beijing 100101, China. Natural Hazards Mitigation Group, Earth Sciences, University of Geneva, 13 Rue des Maraichers, 1211 Geneva 4, Switzerland. http://www.unige.ch/hazards. Natural Hazards Research and Applications Information Center, IBS #6, Campus Box 482, University of Colorado, Boulder, CO 80309-0482. http://adder.colorado.edu/~hazctr/Home.html.
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Natural Hazards Research Centre, School of Earth Sciences, Macquarie University, New South Wales 2109, Australia. Southern California Earthquake Center (SCEC), Department of Earth Sciences, University of Southern California, University Park, Los Angeles, CA 90089-0742. http://www.usc.edu/dept/earth/quake. Wind Engineering Research Center, Civil Engineering Department, Texas Tech University, Box 41023, Lubbock, TX 79409-1023.
CHAPTER 2
SECTION 1
Fundamentals of Safe Building Design Martin W. Johnson
E
ngineers sometimes joke that structural design is “the art of molding materials we do not wholly understand, into shapes we cannot precisely analyze, to withstand forces we cannot really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance.” Although overstated, this saying contains truth. The structure design and construction process contains many inherent uncertainties. Despite these uncertainties, it is possible to provide relatively uniform levels of safety and reliability through the application of building codes, industry standards, and construction quality assurance. Building codes define minimum permissible strengths to resist floor loads and other forces such as wind, snow, and earthquake. They also limit building configuration, construction techniques, and the quality of materials. Industry standards define material strengths, properties, and specific design methods that can be used by engineers with reasonable safety. Some minimum standards for construction quality are also specified in building codes. Design and construction professionals are held accountable through enforcement of professional registration standards and the civil litigation system. If the engineering process were not a part of building design, many buildings would be unsafe and others would go to the opposite extreme and be quite expensive. The structural engineer’s role is to optimize the design in such a manner that the building will provide acceptable levels of safety and serviceability while being economical to construct. One approach to “optimum” building design says that if a structure is loaded to the slightest fraction beyond its strength limit, all elements should simultaneously fail and the entire structure collapse. This approach is seldom used. Instead, most structures are designed such that if they are overloaded, they will be able to deform and give some warning to occupants prior to failure, so that evacuation and perhaps shoring can occur.
Each year, lives and property are lost due to building failures. Mostly, these building failures are precipitated by hurricanes or high winds, earthquakes, floods, and other dramatic events. (See Section 1, Chapter 1, “Challenges to Safety in the Built Environment.”) Much less often, failures are precipitated by minor
CHALLENGES TO THE BUILT ENVIRONMENT The total complex of houses, factories, offices, schools, etc. in which we live and work is referred to as the “built environment.”
Martin W. Johnson is a group manager with the EQE Structural Engineers Division of ABS Consulting, Inc., in Irvine, California. He has an MS degree in engineering and has been a practicing structural engineer for almost 30 years.
1–33
W o r l d v i e w Building codes in well-developed countries, such as Canada, Japan, New Zealand, and countries in Europe, resemble American codes to varying degrees, with differences resulting from the differing opinions of researchers and local variations in construction practices. In less-developed countries, building codes are often derived from older editions of U.S. or European codes, which are sometimes as much as 10 to 20 years behind current editions. The primary difference with regard to building codes in less-developed countries is the degree to which local codes and inspection requirements are applied, enforced, or circumvented. In some areas, builders construct significant structures without the knowledge of any building official or design professional. Also, builders sometimes replace construction details shown on design drawings with more convenient or less expensive ones without the knowledge of designers or building officials. Education and training of design professionals is generally good, although usually limited to the control of behavior up to the point of initial mechanisms, without consideration of providing a controlled sequence of failure mechanisms. The skills of building officials vary considerably, and in some areas corruption may be common. Materials used for building construction also vary considerably. In the United States and other developed countries, the cost of labor tends to be greater than the cost of materials, so that design tends to favor ease of construction rather than the minimization of materials. In less-developed or more populous countries, the opposite is true. Design tends to favor minimization of any expensive materials. In these areas, construction tends to use stone, brick, cheap concrete, and similar materials that are readily available but might require considerable effort to place, while avoiding the use of steel or wood materials that may be scarce.
1–34 SECTION 1 ■ Safety in the Built Environment
events or even ordinary loads and conditions because inadequate design and construction, simple neglect, or decay removed the building’s ability to function under even a minor challenge. Although building codes are intended to protect lives, clearly there are instances where they have not done so. Problems occur for both existing buildings and new construction.
Existing Buildings Modern construction materials are very different from those used in the past. In some respects, they are better and in others worse. However, the methods and details that are used to combine these materials into finished buildings have improved significantly with time. Building codes and construction methods change with time, to not only incorporate new materials and methods of construction but also incorporate “lessons learned” from various failures induced by disasters such as fires, earthquakes, and hurricanes. Because of continual improvements in building codes, most buildings designed and constructed today are considered to be safer and more reliable than buildings that were designed using older building codes. In most communities, building construction in any year represents less than 2 percent of the total number of buildings.* Given the 2 percent rate of new buildings, at any time, at least 50 percent of the building population is likely to be more than 30 years in age. For many communities, this percentage is actually much greater. Because of the continual improvements in codes and building technology, older buildings designed to the standards and codes of 30 or more years ago are by some measures considered unsafe in comparison against current standards. Therefore, it is likely that every community contains a significant number of buildings that could be unsafe if exposed to local conditions or events that newly constructed buildings could easily survive. Existing buildings are typically replaced only when either a better financial use is found for the property or because the physical condition of the building becomes so poor as to preclude further use. Once a building is constructed, and an occupancy permit issued, building codes contain few restrictions on the building’s continued use. In general, the following apply: • The owner is required to meet certain zoning restrictions in terms of types of use or contents. • Major additions, alterations, or changes in use may trigger improvements to meet newer building codes. However, these requirements may be circumvented by physical separation of the new and existing construction or by other negotiated or political means. • If the local building official becomes aware of an obviously unsafe condition, the official has the power to condemn a building. However, such actions are quite rare and typically occur only after a damaging event or failure. • Some codes, like the NFPA 101®, Life Safety Code®, and some regulations, like the Americans with Disabilities Act, *The conservative estimate of 2 percent is based on assessor’s data for the county of Orange, California, an area of high growth. The annual development in Orange County between 1972 and 1994 added an average of 3 percent to the cumulative number of developed parcels.
impose requirements on existing buildings, and some of these provide for enforcement. As a result, many existing buildings contain latent risks due to deterioration, deferred maintenance, or basic details of construction that would not be permitted by newer construction.
New Buildings Every building is somewhat unique and without prototype. To be safe and serviceable, it is important that the construction be correct. This requires that all parties involved in the construction process—code writers, owners, architects, engineers, building officials, contractors, and construction workers—each exercise skill and responsibility to make certain that their part of the project is done in conformance with the intended requirements, while still meeting the limitations of project schedules and budgets. A common challenge to this process is communication— for contractors and building officials to be able to correctly interpret from drawings and specifications the intent of designers, and for the designers to be able to interpret the intent of code writers from building codes. Another challenge of new construction is for designers and code writers to predict the types and magnitudes of forces and events that a building may experience during its existence, and to define design loading conditions within building codes that will be sufficient to withstand those conditions, without undue financial penalties.
DESIGN LOADS AND FORCES Basic Load and Force Types Building codes define the following basic types of loads and forces, as a basis for structural design. Dead Load. This is the weight of the building itself. It includes the weight of all permanent fixed items such as floor framing, walls, ceilings, roofing, and major fixed service equipment, but excludes loads from variable items such as furnishings, people, traffic, and equipment that will change constantly throughout the building’s life. This load is the easiest to predict and can be known with the most certainty, although there can still be some variation between dead load estimated by the designer and the actual as-constructed weight. Live Load. This is the weight of items such as furnishings, people, traffic, and equipment related to the use or occupancy of the building, and which varies over time. This weight is generally known with little certainty, as it can vary even by the time of day. Building codes include tables of minimum required design live loads for various occupancy types, which are sometimes posted on signs within buildings. These design live loads represent reasonable maximum bounds on the amount of weight from these variable items that may be placed on a floor or roof during its life. It is extremely unlikely, except in certain types of occupancies such as warehouses, that all areas of floors and
CHAPTER 2
roofs would simultaneously be loaded to the design levels at the same time. Hence, building codes include “live load reduction factors” that account for the low likelihood of simultaneous heavy loading of large portions of the building and allow the design load to be reduced for building elements that support larger areas. Thus, an individual floor beam might be designed to support a larger floor load (on a pounds per square foot basis) than a column that supports many beams. Snow and Ice Loads. These are the design weights required by building codes to be considered for accumulation of snow and ice. Building codes define snow load in terms of “ground snow loads” that represent a weight of snow having a 2 percent annual probability of being exceeded (50 year mean recurrence).1 This means that it would be anticipated that such heavy loads would occur only every 50 years or so. The building codes include maps that specify minimum design snow loads for various regions of the country. However, snow depths can be highly variable, particularly within mountainous regions, where local building officials often specify “standard” ground snow loads within their jurisdictions that are different than those indicated in the maps. The ground snow load, contained on building code maps and enforced by building officials, is not the same load that is actually used to design buildings. Design snow loads are calculated based on the ground snow load, but require modifications to account for the effects of roof slope, thermal conditions (heated versus unheated), wind conditions that can cause snow to drift across roofs, and building shape or geometry conditions which may cause drifts or snowfalls from adjacent higher roofs to accumulate. Design standards are used to translate the basic ground snow loads into specific design weights that vary geographically over the roof surface. Wind Forces. Design wind forces are determined using horizontal wind pressures associated with a design wind velocity that is specified for a location. Just as with snow loads, building codes include maps of design wind velocity values for most areas (Figures 1.2.1–1.2.4). However these maps exclude some “special wind regions” in which local terrain conditions produce occasional high wind conditions. In those areas, the building official is required to specify the design wind velocity. The definition of design wind velocity has changed in recent years. Prior to 1998, the standard definition of design wind velocity was based on the “fastest-mile” wind speed, which was the wind speed based on the time required for a mile-long sample of air to pass a fixed point. Around 1998, U.S. building codes redefined the design wind velocity as the mean wind speed averaged over 3 seconds, measured at 33 feet above grade, over relatively open terrain.1 The resulting wind velocity maps are generally based on a 50-year wind speed.1 However, in hurricane-prone regions, wind velocity maps have been adjusted to include an adjusted value based on both hurricane simulation techniques and 500-year wind speed records. This “3-s gust” method is an improvement over the earlier method in that the fastest mile did not account as well for the effect of short duration gusts. Also, the older codes did not include the more severe winds anticipated in hurricane-prone regions.
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However, the net effect of the change in design maps for wind (other than by the addition of hurricane effects) is not significantly different than it was with older codes. Mapped wind velocity is not directly used to design buildings. The mapped wind values are modified depending on terrain conditions, elevation, and topographic effects such as hills or ridges that can cause local high-velocity conditions to occur. The design forces are calculated from these site-modified wind velocities, considering the building’s shape, its flexibility, the quantity of openings that can allow fluctuating wind pressures to enter the building, and the total building area that may be subjected to locally varying wind gust pressures. Building standards provide guidance to designers in how to determine appropriate pressures to design building components for relatively regular and normal looking buildings. Buildings that are very tall, flexible, or unusual in shape sometimes require special wind-tunnel testing, using scale models in order to determine appropriate design wind pressures. Earthquake Forces. Earthquakes do not directly exert forces on buildings. Rather, they produce ground accelerations and deformations that vary with time. The response of the building to these ground movements results in stresses and deformations throughout the building. The severity of these effects depends on the event magnitude, its distance from the structure, local soil conditions, and the weight and stiffness characteristics of the building structure itself. Building codes provide procedures that allow engineers to determine design forces. These are calculated as pseudo-inertial forces equal to the building mass times specified design accelerations. These design accelerations are determined from mapped values of design ground accelerations found in building codes, modified to account for the building’s structural characteristics (Figure 1.2.5, p. 1-40). As with wind loads, the definition of the design ground acceleration used in building codes has changed in recent years. Until 1991, building codes included maps that presented design ground motions in the form of seismic zones. The seismic zones covered broad geographic regions, often encompassing several states. Within each seismic zone, the building codes specified earthquake acceleration values that approximately represented the most severe shaking likely to occur in any 500-year period— in statistical terms, having a 10 percent chance of being exceeded in 50 years. The use of broad geographic seismic “zones” resulted in these accelerations being very approximate. Starting in 1991, codes began to abandon seismic zones and present design ground motions on maps in the form of ground motion “contours” that more precisely presented the likely levels of ground motion at any given site. Using these maps, each site location has a unique value of design ground acceleration depending on its location relative to known faults and seismic source zones. The newer mapped earthquake acceleration contours also represent a more unlikely event, approximately corresponding to a 2500-year event, or one having a 2 percent chance of being exceeded in 50 years. This rather rare event is more appropriate for sites in the eastern United States, for example, where large earthquakes occur infrequently, and does not significantly increase the hazard in the Western United States where destructive ground shaking occurs more often. The intent
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FIGURE 1.2.1
Basic Wind Speed (Source: NFPA 5000™)
of the newer building code regulations is to avoid structural collapse for these 2500-year events. However, actual design is based on providing a less severe level of damage for design ground accelerations taken as two-thirds of the mapped values. In regions with moderate or strong earthquake potential, design ground acceleration values are so large that designers can-
not economically design ordinary buildings to resist the full acceleration values without also permitting some degree of damage. Only very special, acute-hazard structures such as nuclear power plants, or very important facilities such as hydroelectric dams or long-span bridges, are designed in this manner. Instead, most buildings are designed to crack and yield when affected by
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90(40) 100(45)
110(49)
120(54)
90 (40)
130(58) 140(63)
130(58) 140(63) 140(63)
140(63)
150(67)
150(67)
Special Wind Region 90(40) 100(45)
130(58)
110(49) 120(54)
Location Hawaii Puerto Rico Guam Virgin Islands American Samoa
V mph 105 145 170 145 125
(m/s) (47) (65) (76) (65) (56)
Notes: 1. Values are nominal design 3-second gust wind speeds in miles per hour (m/s) at 33 ft (10 m) above ground for Exposure C category. 2. Linear interpolation between wind contours is permitted. 3. Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area. 4. Mountainous terrain, gorges, ocean promontories, and special wind regions shall be examined for unusual wind conditions.
FIGURE 1.2.1
design level shaking, but hold together and not collapse. The intent of the code earthquake provisions for ordinary buildings is to protect “life safety” but not protect property investments. In order to accomplish this, design forces are calculated using special reduction factors R that reduce the predicted ground accelerations into artificial design values. These R values are specified in the building codes, based on the type of structural system used and the historical performance of various systems.
Continued
In addition to specification of minimum design forces, building code provisions for earthquake resistance also include prescriptive detailing requirements intended to provide sufficient toughness to hold buildings together as they deform. The prescriptive provisions regulate the types of connections and reinforcements that are used in different types of construction and also the configuration (geometric shape) of the building and its elements. In addition, in locations where stronger accelerations
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140(63)
140(63)
150(67)
Special Wind Region Notes: 1. Values are nominal design 3-second gust wind speeds in miles per hour (m/s) at 33 ft (10 m) above ground for Exposure C category. 2. Linear interpolation between wind contours is permitted. 3. Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area. 4. Mountainous terrain, gorges, ocean promontories, and special wind regions shall be examined for unusual wind conditions.
90(40) 100(45)
130(58)
110(49) 120(54)
FIGURE 1.2.2
Basic Wind Speed—Western Gulf of Mexico Hurricane Coastline (Source: NFPA 5000™)
130(58) 140(63)
Special Wind Region 90(40)
100(45) 110(49) 120(54) 130(58)
130(58)
150(67)
140(63) 140(63) 150(67)
Notes: 1. Values are nominal design 3-second gust wind speeds in miles per hour (m/s) at 33 ft (10 m) above ground for Exposure C category. 2. Linear interpolation between wind contours is permitted. 3. Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area. 4. Mountainous terrain, gorges, ocean promontories, and special wind regions shall be examined for unusual wind conditions.
FIGURE 1.2.3 Basic Wind Speed—Eastern Gulf of Mexico and Southeastern U.S. Hurricane Coastline (Source: NFPA 5000™)
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90(40)
100(45)
110(49)
120(54)
Special Wind Region
Notes: 1. Values are nominal design 3-second gust wind speeds in miles per hour (m/s) at 33 ft (10 m) above ground for Exposure C category. 2. Linear interpolation between wind contours is permitted. 3. Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area. 4. Mountainous terrain, gorges, ocean promontories, and special wind regions shall be examined for unusual wind conditions.
FIGURE 1.2.4
Basic Wind Speed—Mid and Northern Atlantic Hurricane Coastline (Source: NFPA 5000™)
may occur, some types of construction such as unreinforced masonry are not permitted. Other Loads. Building codes and design standards also include provisions for other common types of loading, including lateral earth pressures against retaining walls and forces caused by thermal expansion and contraction or impact. However, building codes have either very limited provisions or no provisions at all for some very unusual types of loads such as those induced by tornadoes or by blasts or explosions. Industry-specific design standards such as those developed by the military or the Department of Energy are typically used for the design methods of structures that must resist such load conditions. Combining Design Loads. Once the individual design forces have been determined, they must be combined to consider the effects of simultaneous application, for example, the simultaneous occurrence of high wind loads and occupancy-related loads such as furnishings and equipment. When combining loads of different types, the probability that loads will occur simultaneously is considered and loads that occur infrequently are typically not combined together. For instance, a full design snow load would not be combined with a full design wind or earth-
quake event, although some portion of the design snow might be considered. Building codes include equations for required combinations of loading that must be considered in building design. Some special types of structures also use load combinations defined in industry-specific standards, for example, tanks that are designed for earthquake inertial forces in conjunction with forces caused by earthquake-induced sloshing of tank contents.
Actual versus Design Loads Building codes deal with the uncertainties associated with predicting design loads by the use of probability and statistics. For example, building codes define a 50-year wind, or a 2500-year earthquake event. However, the design maps that result represent only a statistical representation of the probabilities, based in part on the historical record and also, in part, on the experience and judgment of the code developers. Because neither can completely predict the future, it is possible that code-specified design loads will be exceeded. For example, earthquakes sometimes occur on previously undiscovered fault lines, or changes in global climatic patterns can result in increased wind or snow hazards, that are not accounted for by the building codes.
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125° 50° 120° 115° 110° 105°
100°
95°
45°
40°
35°
30°
DISCUSSION The acceleration values contoured are the random horizontal components. For design purposes, the reference site condition for the map is to be taken as NEHRP sire class B. Regional maps should be used when additional detail is required.
25°
REFERENCES Building Seismic Safety Council 1998, NEHRP Recommended Provisions for Seismic Regulations for New Buildings and other Structures, FEMA 302. Frankel, A, Mueller, C., Barnhard, T., Perkins, D., Leyendecker, E. V., Dickman, N., Hanson, S., and Hopper, M., 1996, National Seismic-Hazard Maps: Documentation June 1996: U.S. Geological Survey Open-File Report 96-532, 110 p. Frankel, A, Mueller, C., Barnhard, T., Perkins, D., Leyendecker, E. V., Dickman, N., Hanson, S., and Hopper, M., 1996, National Seismic-Hazard Maps for the Conterminus United States, Map F- Horizontal Spectral Response Acceleration for 0.2 Second Period with 2% Probability of Exceedance in 50 Years. U.S. Geological Survey Open-File Report 97-131-F; sale 1:7,000,000.
Index of detailed regional maps at larger scales
Petersen, M., Bryant, W., Cramer, C., Cao, T., Reichle, M., Frankel, A., Lienkaemper, J., McCrory, P., and Schwartz, D, 1996 Probabilistic Seismic Hazard Assessment for the State of California: California Division of Mines and Geology Open-File Report 96-08, 66 p., and U.S. Geological Survey Open-File Report 96-706, 66p.
105° 100°
Map prepared by U.S. Geological Survey.
FIGURE 1.2.5 Maximum Considered Earthquake Ground Motion for U.S. Lower 48 States (Source: American Society of Civil Engineers)
95°
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65°
50°
70° 75° 80° 85° 90° 95°
45°
40°
Explanation Contour intervals, % g 200 175 150 125 100 90 80 70 60 50 40 35 30 25 20 15 10 5 0
Note: contours are irregularly spaced. Areas with a constant spectral response acceleration of 150% g Point value of spectral response acceleration expressed as a percent of gravity
10 10
Contours of spectral response acceleration expressed as a percent of gravity. Hachures point in direction of decreasing values.
75° Scale 1:13,000,000
80° 85° 95°
100
0
100
200
300
400
500
600 MILES
90° 100
FIGURE 1.2.5
0
Continued
100
200
300
400
500
600 KILOMETERS
1–41
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External versus Internal Forces Building codes define loads and forces such as dead, live, and snow loads and wind or earthquake forces that are considered externally applied, in that they act upon the structure. When these forces and loads are applied on a structure, they result in movement (deflection) of the structure and also the development of internal forces or stresses within the individual structural elements. Structural elements such as floors, beams, columns or walls that the building structure is made of are designed to control the magnitude of these deflections and stresses. Design engineers must therefore use the external forces specified by the building code to calculate the distribution of internal forces and deflections in each building element. Although such calculations can be performed using manual methods, today, elaborate computer programs are commonly used to assist the engineer in this task. Internal forces calculated in individual elements include tension, compression, shearing, and bending forces (or bending “moments”). After the design engineer determines these forces, they are compared against maximum permitted material strengths that are defined in building code standards to verify the adequacy of each proposed design.
BASIC BUILDING SYSTEMS AND COMPONENTS Basic Building Systems Basic building systems include the building envelope system, the structural system, the foundation system, the plumbing system, mechanical systems (such as heating, ventilating, and air conditioning systems), and the electrical system. Other critical building systems include the fire protection system and the security system, for example. This chapter focuses on the building envelope system and the structural system and also briefly addresses the foundation system. The building envelope and structural systems enable buildings to withstand the loads and forces placed on it. Stated another way, the building envelope and structural systems keep the building intact and standing; the skin and skeleton fulfill similar functions in human anatomy.
Building Envelope System The building envelope has been described as being composed of “several building components that work together to protect the building’s structure and its contents from the elements.”2 The building envelope consists of building elements such as windows, precast or similar nonstructural wall panels, and like elements that enclose and protect the building and create the finished appearance.
Basic Structural Systems To resist both vertical loads such as dead weight and snow, and lateral forces such as those produced by winds or seismic effects, any building or structure that is stable requires two distinct structural systems: a vertical support system and a lateral forceresisting system. Each system consists of a series of structural
components (beams, columns, walls, etc.) that combine to provide resistance against either vertical or lateral loading. These structural components can consist of individual elements, such as columns, or they may consist of combinations of elements, which connect to produce subsystems, such as shear walls, moment-frames, braced frames, and so on. Vertical Support System. Basic structural components that combine to form the vertical support system include roof and floor framing systems, columns, bearing walls, and foundations. All structures must have complete and sound vertical load-supporting systems or they would collapse under their own weight and that of their contents. This is in contrast to structures with missing or inadequate lateral force-resisting systems that could conceivably stand indefinitely, because extreme lateral loading events (high winds and earthquakes, for example) are quite rare. Lateral Force-Resisting System. Basic structural components that provide lateral force-resistance include shear walls, braced frames, and moment-resisting frames, as well as diaphragms (such as roof decks, floor slabs, or horizontal bracing systems) and foundations. Depending on the type, use, and geometry of the structure in each application, these components can be combined to form a structural system. Comparison of Vertical Support and Lateral-Force Resisting Systems. Frequently, there is little visible difference between the frames, bearing walls, and so on, used to provide vertical support, and the similar frames, shear walls, and so on, used to resist lateral forces. The basic distinction that exists between vertical support and lateral-force-resisting systems arises from the following factors: • All loads applied to a structure tend to be resisted first by the structural components that have the greatest rigidity (relative to other components) in the direction of load. Thus, vertical loads supported by an elevated floor slab tend to be borne by the closest adjacent columns. On the other hand, lateral forces applied against a floor diaphragm may span entirely past interior support columns (which provide little or no lateral rigidity) and be resisted by more distant (but very rigid) walls or braced frames. • The connections used to fasten components must provide adequate strength to resist the imposed forces and deflections. In addition, the various components that form a structure must be designed considering the likely deflection and rigidity of adjacent elements. Where design assumptions require a rigid or inflexible link between lateral load resisting components, the connection must impart rigidity, whereas where independent motion is more appropriate, it must provide adequate flexibility to accommodate structure deformations without impact or binding. Structures must be able to resist forces that are imposed from any direction. Most structures are therefore designed with two separate lateral-force-resisting systems, one for each of two orthogonal axes of the building. When forces are applied about either orthogonal axis of the structure, some of the resisting elements will be aligned parallel to the forces. Wall and bracing elements have high relative rigidity in-plane, and thus provide
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substantial lateral support. However, walls or bracing systems have low relative strength and rigidity when aligned perpendicular to the direction of load, and thus must be properly attached to and supported by structural components that are parallel to the forces.
footings, and mats. Piles, piers, and caissons are deep foundation systems designed to support heavy buildings on soft, compressible surface soils. Spread footings and mats are shallow foundation systems designed to support light buildings or heavier buildings on stiffer, stronger surface soils (Figure 1.2.6).
Types of Basic Structural Systems. Building codes define certain standard structural systems, called basic structural systems. In essence, basic structural systems are those that resist vertical and lateral (i.e., horizontal) loads. These basic structural systems are
Basic Building Components
• Bearing Wall System: Any structure in which vertical walls and/or diagonally braced frames simultaneously support both the weight of the structure (vertical loads) and resist lateral loads. • Building Frame System: Systems in which the weight of the structure is completely supported by beams and columns. Resistance to lateral loads is independently provided either by walls, termed shear walls, and/or diagonally braced frames. • Moment-Resisting Frame System: These structures are composed of beams and columns that are rigidly interconnected into moment-resisting frames to provide resistance to both vertical loads and lateral forces, without assistance from walls or diagonal braces. • Dual System: Systems that provide two independent lateral-force-resisting systems, each capable of resisting all or part of the total lateral design forces. One system must always be a moment-frame system; the other can consist of either reinforced shear walls or braced frames that are added at selected locations. • Special Systems: Special systems include base-isolated systems or guyed systems, which do not fit the above descriptions. A base-isolated system is a special type of seismic-resistant construction in which the structure is mounted on rubber bearing or sliding steel plates. A guyed system is a structure that is braced by guy wires, such as a radiotransmission tower. Diaphragm Systems. Diaphragms are horizontal-spanning systems that tie vertical walls and columns together, provide stability to walls and other vertical elements, prevent excessive torsional (plan) deformations, and transfer forces to shearwalls or frames below. Lateral forces resisted by diaphragms originate from wind forces applied against exterior walls, from seismic inertial forces or from forces transmitted from shearwalls or frames above. The use of building floor and roof systems as diaphragm systems can be very efficient, since most of the structural elements required for diaphragm action are also required for these systems. Horizontal bracing systems provide diaphragm-like performance for applications where solid-surface construction cannot be used or is not required.
Basic structural components that collect loads from roof and floor levels and transfer them to foundations include moment-resisting frames, vertical walls, diagonally braced frames, and diaphragms and horizontal bracing. These underlying structures are surrounded and protected from the environment by the building envelope. Critical structural design considerations for the building envelope include resistance to lateral pressure or impact, accommodation of transient building movements, and accommodation of long-term building movement. Resistance to Lateral Pressure or Impact. Exterior walls, windows, and doors provide the primary protection against wind pressures and small stones and missiles thrown up by wind. Windows must be designed to resist design wind pressures while still maintaining moisture protection at surrounding gaskets. In special hurricane-prone areas, limited missile protection may be required as well. Near grade and around entrances, missile or impact resistance may also be required for protection against small stones thrown up by lawnmowers or attempted forced entries. Walls must have adequate shear and bending strengths and strong enough connections to resist code-defined wind pressures and earthquake inertial forces. Accommodation of Transient Building Movements. The structure that supports the building will sway and drift during wind storms or earthquakes. The attached building components P
De B (a)
(c) Dowels or anchor bolts as required by column above Cap Shaft 24 in. (.61 m) diameter Bell Rock or hard stratum
Building Foundation Systems Foundation systems are used to transfer vertical and horizontal loads from the aboveground structure into the underlying soils. Common foundation types include piles, piers, caissons, spread
(b)
(d)
FIGURE 1.2.6 Common Types of Foundation Systems: (a) Spread Footing; (b) Mat; (c) Pile; and (d) Pier or Caisson
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must be designed to accommodate these movements without damage. Frequently, these movements are accommodated by adding jointing and special connection details that allow structural movements without binding against cladding or window elements. In relatively flexible buildings, glass panels may need to be able to rock within their frames to accommodate building sway without binding. Accommodation of Long-Term Building Movements. After construction completion, all buildings experience some degree of long-term movements as the building adjusts to its environment. Building components can experience some shrinkage or expansion. Foundations can slightly settle. Over the long term, some of this movement may continue in the form of thermal cycling or perhaps continuing foundation movements due to moisture-related expansive soil conditions. These movements often cause slight cracking and distress that can be observed in many buildings. Although not specifically a code-regulated issue, the details of building construction used should attempt to minimize both the amount of such movement that occurs and the damage sustained as a result of such movements. Moment-Resisting Frames. Moment frames rely on bending forces developed at the connections of the beams to the columns to resist lateral forces. Because moment frames tend to be much more flexible than either shear walls or braced frames, lateral deflections of moment-frame structures will be much greater. The ratio between relative story deflection and story height is called the story drift ratio. Moment frames that permit too much story drift during wind storms or earthquakes may permit an excessive amount of damage to nonstructural components, such as siding, partitions, and contents. Critical design elements of moment-resisting frames include beams and columns and the beam-column connection. • Beams and Columns: Frame elements must be designed to resist internal bending and shear forces. Optimum performance is gained when the members selected are stronger in shear than in bending and when the building’s columns are stronger in bending than its beams. This provides a controlled damage mode under very large loads and forces and, in multistory frames, increases the total energy dissipation capability of the frame. • Beam-Column Connection: The stability of the frame is dependent on the rigidity and strength of the beam-column connection. Adequate strength and toughness must be provided in the connection to permit repeated cycling of stresses without a loss of integrity. Connections can be made of bolted or welded components, or a combination of bolted and welded elements. Since the toughness of welded joints is highly dependent on the workmanship, special quality control measures are often required in the most critical welds. Shear Walls. The shear wall is designed as a vertical beam element. As shown in Figure 1.2.7, critical design considerations for shear walls include the following: • In-Plane Shear: The wall acts as a web, or shear membrane, to resist in-plane shear forces. Adequate anchorage
Wall deformation
Force
(a)
Wall deformation
Force
(b)
Applied force (pressure
Wall deformation
(c)
FIGURE 1.2.7 Types of Wall Deformation: (a) In-Plane Shear Deformation; (b) In-Plane Bending Deformation; (c) Bending from Forces Perpendicular to Wall
must be provided along the top and bottom edges of the web to transfer the shearing forces into, and out of, the web. • In-Plane Bending: To resist bending stresses due to overturning moments, structural elements, called chords or boundary elements, are concentrated at the vertical edges of the wall. Chords are tension-only elements, which resist the tension component of bending forces. Boundary elements are tension-compression elements, which resist tension forces as well as extremely large compression strains (large
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enough to cause crushing of unconfined concrete) due to bending and vertical loads. Boundary elements are required by building codes only in high-seismic zones. Both chord and boundary elements must be anchored into a foundation that is capable of transferring the vertical components of overturning forces into the ground. • Bending from Forces Perpendicular to Wall: Adequate bending strength and anchorage must be provided to resist inertia loads and wind pressures applied perpendicular to the plane of the wall. Diagonally Braced Frames. Braced systems rely on the axial rigidity of vertical and diagonal elements to resist lateral forces. The configuration of diagonal elements within the bracing can vary, and some configurations have better seismic performance than others. Commonly encountered types of bracing systems, in order of relative performance when subjected to overload or damaging conditions (best to worst), include 1. Eccentric-Braced Frame (EBF): A special type of bracing system that is designed to provide a high degree of overload resistance by permitting controlled overstresses within a short, ductile beam segment. 2. Tension-Compression Bracing: Diagonal elements are provided either singly or paired in an “X” pattern to resist forces both in tension and compression. 3. Chevron Bracing: Arranged in either a “V” or inverted “V” configuration, the diagonal elements resist lateral forces by sharing the load between tension and compression elements. Bracing in this configuration also will resist vertical loads applied to the beam, although building codes require that the beam be designed to resist vertical loads as if the bracing did not exist. This configuration can experience problems when overstressed because buckling of the diagonal undergoing compression creates a force imbalance that increases bending forces on the beam. 4. Tension-Only Bracing: Similar to tension-compression bracing, except that the diagonal elements, by being very slender, are assumed to buckle at very low compression forces. This configuration can experience a loss of strength under repeated tension-compression cycles. In regions subject to significant ground shaking, tension-only bracing is limited to structures of less than two stories in height. 5. K-Bracing: This system provides the poorest overload performance. Overstresses in the diagonal elements can lead to buckling of the diagonal undergoing compression. The resulting force imbalance creates a lateral force on the column, which could possibly lead to a general collapse of the system. Building codes include several restrictions on the use of this type of bracing. As shown in Figure 1.2.8, critical design elements of bracing systems include the following: • Diagonal Elements: Designed to resist lateral (story shear) forces. Because bracing connections often tend to have brittle modes of failure, for some loading conditions the connections must be designed to be stronger than the braces themselves.
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Horizontal elements (beams)
Vertical elements (columns)
Diagonal elements (braces)
FIGURE 1.2.8 Diagonal Elements, Vertical Elements, and Horizontal Elements
• Vertical Elements: Designed to resist overturning forces. • Horizontal Elements: Designed as axial struts to collect and transfer tension and compression forces into the diagonal elements. The strut system can be sloped, such as when pitched roof elements are used as struts. Diaphragms and Horizontal Bracing Components. Diaphragms are generally designed as beams that span between the vertical-resisting elements (frames, walls, braced frames, etc.). Critical design elements of diaphragm systems include the following: • Shear Membrane: The floor or roof acts as a web, or shear membrane, to resist shear forces. The web is assumed to resist shear forces only (no tension or compression). • Chords and Boundary Elements: Located at the extreme edges of the diaphragm, the chords resist tension forces caused by bending in the diaphragm, in a manner similar to the flanges of an I-beam. When compressive stresses warrant, boundary elements may also be required to resist the compressive forces caused by bending. • Collectors: Also called drag struts, collectors are used to resist axial tension and compression forces within the diaphragm by • Collecting shear forces from the diaphragm and transferring them to the vertical resisting elements (walls, braces, or frames) • Redistributing chord forces at diaphragm offsets and gathering loads and distributing them to intersecting walls, braces, or frames • Redistributing diaphragm shear forces and local chord forces around openings within the diaphragm • Distributing points of concentrated force into the diaphragm, such as from heavy roof-top equipment Foundation Components. Critical design issues for foundation systems include bearing strength, overturning resistance, sliding resistance, and ground hazards. • Bearing Strength: The foundation system must have sufficient strength to transfer the weight of the structure to the surrounding soils without adverse settlements.
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• Overturning Resistance: Piles must have sufficient compressive and tensile capacity to resist overturning loads; spread footings must be massive enough and/or support adequate soil surcharge to counteract uplift. • Sliding Resistance: Either passive soil pressure, friction, or a factored combination of both may be used, depending on the soil type and foundation geometry. • Bending and Shearing Strength: The foundation system must have adequate strength to transmit loads without failure or excessive deflections. • Ground Hazards: Some sites are susceptible to special hazards that can occur within the site itself, such as excessive settlement, potential slope failures, water-induced scour or shaking-induced-liquefaction. In some instances, the risk of these hazards can be reduced by conducting site improvements prior to construction, such as by soil densification or by removal of unsuitable materials. In other instances, the site itself may not be fundamentally unsuitable for the structure.
FUNDAMENTAL DESIGN CONCEPTS Load-Path Concept The load-path concept involves the provision of a continuous system of interconnected elements throughout the structure, adequately connected to transfer applied loads and forces from the points of origin or application, to the final points of resistance. As an example, columns are used to transfer loads from roof beams to foundations. While providing a continuous load path is an obvious design requirement for vertical loads, a continuous load path is sometimes overlooked or not completely developed when designing for lateral force resistance. The failure to review all members and connections for each combination of load can lead to weak links in the load path. Building codes require a continuous load path as a fundamental requirement. Important aspects of developing, designing, and detailing the lateral load path include • Considering all likely conditions of load. In addition to the basic design loads such as gravity forces, forces caused by thermal expansion or contraction, and outside events such as wind or earthquakes, the possible directions of application of these forces must be considered. • Providing means of collecting load or force from one element (such as roof sheathing) and transferring it to another (such as a wall). • Ensuring stiffness compatibility of load-resisting elements acting in parallel (before and after yield). For example, welding cannot be used to “increase” the strength of a connection using bolts, because slight movement or slip within the bolted connection may cause the more rigid weld to bear all of the force and fail. • Considering eccentric loading or attachment conditions. Many times it is not physically possible to attach parts together in a concentric manner and some eccentricity must be permitted in order to make the attachment. This eccentricity will cause additional bending and deformation forces
in the local area around the connection that the structure must be designed to resist. These local forces are often referred to as secondary. However, they can be very large and often cause failures if not adequately considered in the design. • Considering transfer of design loads through the foundation system into the surrounding soil. Inadequate consideration may result in portions of a structure sliding about in the soil or in local foundation settlements due to high bearing pressures.
Structure Geometry Although it is typically the structural engineer’s responsibility to determine the actual details of structural resistance, the architect and other design team members can also greatly affect the ultimate resistance of the structure by controlling the configuration of the structure, and the distribution of weight. These issues of configuration can have significant impact on the way a structure behaves when subjected to extreme loads. Although architectural design has a significant impact on structural configuration, local geographic, cultural, and climatalogic conditions can also dictate many aspects of building geometry. In coastal flood zones, for example, structures may need to be elevated on columns or piers above potential storm surge or flood heights. In inner-city areas, local planners often promote street-level plazas or parking into the design of tall buildings, which redefines the building geometry in lower levels. A simple, symmetrical, and regular structural geometry tends to result in better performance of structures subjected to extreme loads such as earthquakes or blasts. Buildings with significant irregularities in geometry, mass, or stiffness tend to twist or deform unevenly as the building is overloaded, resulting in local areas of high stress concentration. Although irregular features often create pleasing aesthetic affects, such areas can also become early damage initiation points that can rapidly degrade structural integrity and result in poor performance, unless additional attention is given to them during design and construction. It is the mutual responsibility of the architect and structural engineer to identify and resolve geometry problems early in the design process. The challenge to the design team is to create a building with a structural system that is reasonably regular and yet still retains the intended form and function. Poor geometry can result in poor performance, unless special attention is given during the design process (often at increased design and construction cost).
Designing Structures to Resist Overstress Traditionally, the possibility of overload or overstress has not often been considered in structural design except in regions of active seismicity. Structures designed without such consideration of inadvertent overload could potentially collapse when subjected to moderate overloads or an inadvertent failure of a single member. Structures designed for resistance of strong earthquakes or large blast pressures, however, are typically detailed with toughness and redundancy. Tough and redundant
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structures may have the same strength and general appearance as other structures, but contain a reliable method of resisting possible overloads without collapse. Although buildings are designed to resist most load conditions without damage, unpredicted overload conditions can occur, and for some design load conditions, overstress and damage are permitted to occur. When these conditions occur, structures can experience undesirable failure modes. Undesirable failure modes include those resulting in total collapse of the structure, such as caused by progressive column failures, and those involving sudden failure, such as a buckling or brittle (e.g. shear) failure. During severe overload conditions, structural materials that are overstressed may crack, buckle, or yield. Once such behavior, often termed nonlinear behavior, occurs, the load-deformation characteristics of the element, that is, its ability to resist loading without adverse deflection, will change substantially. When nonlinearity occurs, structural elements will either behave in a brittle manner, in which rapid loss of load carrying capacity occurs, or in a ductile manner, in which the element can continue to carry load, but may have substantially increased deformation and deflection. The difference between brittle and ductile behavior can be demonstrated by the following example. If a piece of chalk is bent, the chalk will quickly break, as the bending stress exceeds the tensile strength of the chalk. On the other hand, if a metal paper clip is bent, the metal will deform and refuse to break unless bent back and forth many times. The chalk is brittle; the metal paper clip is ductile. A structure can be designed to resist overstresses in a ductile manner. Important features of ductile design include (1) selecting ductile materials and member configurations, (2) assuring that connections are stronger than the elements they connect, (3) providing redundancy or backup systems, and (4) controlling damage modes. Ductility is a material property that exists only for nonbrittle materials such as steel. It is a measure of the material’s ability to undergo nonlinear deformation without fracture (breaking). Nonlinear behavior can be safely accommodated in structures that use ductile materials (such as steel) either as the primary structural element or as reinforcing for more brittle materials. For example, plain concrete is a brittle material, but properly reinforced concrete (and masonry) can behave in a ductile manner and produce structures that exhibit satisfactory seismic performance. Conversely, although steel is an inherently ductile material, proper proportioning of members and design and detailing of connections is necessary to assure ductile behavior of the overall structural system. Redundancy in a structural system allows for redistribution of internal loads around local areas of overstress or failure. Redundancy effectively provides a backup system for protection against collapse when localized failures occur. As an example, a cantilever is a nonredundant structural system and will collapse when yielding occurs at the base of the cantilever. Some elements will behave in a ductile manner if subjected to one type of loading and in a brittle manner if subjected to other types of loading. For example, reinforced concrete or masonry beams will generally behave in a ductile manner when
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Fundamentals of Safe Building Design
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overloaded in bending, but will behave in a brittle manner when overloaded in shear. Careful design practice can control the actual failure mechanism by proportioning the beam to be stronger in shear than it is in bending, so that the more ductile mode then controls the behavior.
BASIC DESIGN METHODOLOGY In building design, there are three basic approaches. These are the allowable stress design approach, load and resistance factor design (LRFD), and performance-based design.
Allowable Stress Design Allowable stress design is the simplest and most common design method used for building design. Fundamentally, it requires that the applied forces or stresses on any element not exceed the strength of that element, divided by a factor of safety. The factor of safety used generally varies from 1.5 to 3.0, depending on the reliability or variability of the data on which the value of strength is determined and also the consequences of failure. Forces in individual elements are calculated using the various design loads and forces prescribed by the building code. Element strengths are calculated in accordance with procedures specified by standards published by institutes and associations supported by the several materials industries. EXAMPLE: A steel beam is made from material with a specified minimum yield strength of 36,000 lb/sq. in. (248,000 kPA). Building codes require a minimum factor of safety of 1.5 for simple gravity (dead plus live) loads. Thus, the beam must be designed for this condition using a maximum “allowable stress” of 36,000/1.5 = 24,000 lb/sq. in. (248,000/1.5 ≈ 165,000 kPa).
One drawback associated with the allowable stress design method is that the factors of safety used are generally independent of the certainty inherent in the definition of the applied loading. Structures that support basically nothing other than self-weight are designed using the same factor of safety as structures that support highly variable and unpredictable types of loading, such as vehicular traffic, although it would be more appropriate to provide a greater margin of safety when the loading is uncertain.
Load and Resistance Factor Design (LRFD) The load and resistance factor design method is an alternative procedure that provides several improvements over the allowable stress design method. These include the following: • Load and resistance factor design separates the factor of safety into components that are separately applied to the types of loading experienced, and the types of elements used. Hence, the factor of safety in any structure or element varies, based on the uncertainty in both the expected loading and the predictability of the element strength. • The procedures for calculating the strength of structural sections more realistically estimate the likely value than those
1–48 SECTION 1 ■ Safety in the Built Environment
used in allowable stress design procedures. This provides the opportunity to compare the strengths of any element relative to another, so that the path of failure due to overload becomes more transparent. By calculating the expected strength of each component, the designer gains the opportunity to proportion the structure in a manner so that overload conditions are less likely to result in catastrophic failures. Although the load and resistance factor design method offers many improvements over the allowable stress design method, many building designers regard the method as more complex and confusing. Hence, both methods are commonly used. Although load and resistance factor design is common for concrete elements, allowable stress design has been common for the design of steel, timber, and masonry elements. The design profession is slowly moving toward universal adoption of LRFD procedures.
A Third Approach Although both the allowable stress and load and resistance factor design methods incorporate a finite probability of structural failure, this may be misunderstood by the public, who may believe that there is no possibility of failure of a code-conforming structure. For example, owners of relatively new buildings may be upset to learn following relatively moderate earthquakes that their damaged building had performed within the intent of the building code. The expected response after a hurricane may be similar. Normal buildings designed in accordance with building codes are intended to provide good and serviceable performance for load conditions commonly encountered, resist relatively rare load conditions with moderate but repairable damage, and provide protection against collapse for very rare events. For some hazards such as tornadoes, very little protection is provided. Essential facilities such as hospitals and fire stations are designed with expectations of somewhat better performance. Specifically, the minimum permissible design loads for such structures are increased relative to those for ordinary occupancy structures. However, the extent that the actual performance of these essential facilities is improved is not quantifiable. Although very special structures such as nuclear power plants can be and have been designed to resist all kinds of extreme events without damage, the added cost of design and construction and the required limitations on architectural freedom have limited building codes to providing lower levels of protection. Sophisticated owners of very valuable or important facilities have sought better quantification of the risks associated with extreme events, to permit them to make better business decisions and tradeoffs between paying added initial costs for better building construction and avoiding the future costs of insurance protection, damage repair, and potential business interruption. This has led to the development of a third design methodology called performance-based design.
Performance-Based Design The essence of performance-based design procedures is that rather than following prescriptive requirements contained in the
building codes, the design professional directly develops a design that is capable of achieving specific performance goals or objectives. Performance-based procedures intended to assure adequate fire/life safety protective features in buildings have been under development for a number of years. Recently, structural engineers have also begun to develop performance-based design procedures, primarily for application to earthquake-resistant design. For the structural engineer, performance-based design means the application of a predictive procedure, in which the damage or behavior anticipated of a structure’s design to design events is estimated and compared against preselected objectives. The design is revised until the predictive methodology indicates that acceptable performance can be obtained. Predictive methods can include calculation procedures as well as the construction and laboratory testing of prototype designs. Performance-based design is beneficial in that it allows owners to understand how their buildings may be expected to perform if they are subjected to various design events. It also allows them to determine the levels of performance that will be acceptable, given how much they are willing to invest to obtain this performance. Building owners have three basic interests in relation to building performance: 1. Preservation of safety 2. Preservation of capital 3. Preservation of function Some building owners may not be particularly interested in either preservation of the capital invested in a building or in maintaining its function, feeling that the probability of a damaging event is low and that insurance is available and sufficiently inexpensive to provide protection against these rare unexpected events. For other building owners, performance-based structural design is an attractive alternative approach that provides financial justification for providing better performance than what is defined in the building code, where this makes sense. Building Importance Defined in Building Codes. The basic reason that municipalities adopt building codes is to protect the public safety, and the primary goal of building codes is, therefore, to protect life safety for the most severe events (fire, wind, earthquake, etc.) likely to affect the structure during its life. In effect, codes deem some buildings more important than others. For some types of buildings, structural failure could result in greater loss of life than other types or could result in the loss of vital disaster recovery services. Greater protection is warranted for such buildings. To assist with the assignment of appropriate levels of safety to buildings with different intended occupancies and uses, building codes define several standard occupancy categories. An abbreviated summary of these occupancy categories follows: • Occupancy Type I. This category includes structures such as sheds or agricultural buildings that are normally unoccupied. The failure of such buildings is unlikely to result in significant probability of life loss. Therefore, relatively little protection is required for such structures, and it is considered acceptable if they collapse during a rare event.
CHAPTER 2
• Occupancy Type II. This category includes most types of buildings, including most commercial, residential, and institutional structures. It is literally defined in the building codes as all buildings except those specifically included in other categories. Under extreme loading these structures are expected to be heavily damaged but not collapse. • Occupancy Type III. This category includes important buildings that accommodate a large number of people, that provide important public services (such as utilities), or that house occupants with limited mobility such as schools or detention facilities. It also includes facilities that house moderately hazardous substances such as certain chemicals or petroleum products. Greater protection against collapse is warranted for these structures for rare events, and less damage is acceptable for more moderate events. • Occupancy Type IV. This category includes buildings that are deemed to be essential to the public welfare such as hospitals; fire, rescue, and police stations; and essential communication, transportation, and water storage facilities. It is highly desirable that these facilities be capable of functioning following even a rare event. Benchmark Damage Levels. In recent years, a series of standard definitions of tolerable damage levels, termed performance levels, have been developed. Standard definitions are found in NFPA 5000 ™, Building Construction and Safety Code™. • Serviceability Performance. The serviceability level of performance is a state in which structural elements and nonstructural components have not sustained detrimental cracking or yielding, or degradation in strength, stiffness, or fire resistance requiring repair, that is troubling to occupants or disruptive of building function. Nonstructural components and permanent fixtures and features have also not become displaced or dislodged. • Immediate Occupancy Performance. The immediate occupancy level of performance is a state in which minor, repairable cracking, yielding, and permanent deformation of the structure and nonstructural elements may have occurred. Although repair may be required, the structure would not be considered unsafe for continued occupancy. • Collapse Prevention Performance. Under this level of performance, the building may experience substantial damage to structural and nonstructural elements, with some failures occurring. However, collapse is avoided and emergency responders can effect occupant rescue and building evacuation. Quantification of Risk. The fundamental improvement that the performance-based design method offers is a quantification of the degree of risk of damage associated with load events that are likely to occur, might possibly occur, and could conceivably occur during the existence of a structure. The benefit of this approach is that it produces a (1) structure that is unlikely to experience unwanted damage and (2) quantification of risk that can be directly used in financial analysis when evaluating the cost/benefit of increased performance versus future insurance payments and risk of loss (Figure 1.2.9).
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Fundamentals of Safe Building Design
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Performance Level Loading Frequency Frequent <50 yr Occasional 50–200 yr Rare >200 yr
Serviceability
Immediate occupancy
Oc
cup
anc yT cup ype a I ncy Oc cup Typ anc e II Oc y Typ cup e II anc I yT y p Not e IV required Oc
Collapse prevention Not permitted
FIGURE 1.2.9 Performance Objectives for Building Occupancy Types
For the basic occupancy types that are defined in building codes, risk levels for various types of transient loading are defined to be consistent with the performance objectives outlined in Figure 1.2.9. Criteria to Confirm Compliance. To assess the damage level associated with any risk level of loading, design procedures must present criteria for determining the strength or deformation resistance of each building element at each damage level. ASCE/FEMA 356 “Prestandard for the Seismic Rehabilitation of Buildings” and Appendix G of the SEAOC “Recommended Lateral Force Criteria and Commentary” provide criteria that may be used to determine these values.
SUMMARY The combination of building codes, industry standards, and the engineering process provides a reasonably standard process and uniform factor of safety to building design. Building codes provide a uniform, statistically derived standard to define the vertical loads and lateral forces to which buildings may be subjected, as well as uniform standards for margins of safety in design. Industry standards define uniform means to determine the usable strengths of building components. The engineering process provides a rational method to determine the minimum levels of strength and toughness in individual building components and also a measure of warning to permit occupants to evacuate if overload conditions occur. Various methodologies used to design building components in the engineering process include the allowable stress, load-and-resistance factor, and performancebased design methods. There are many challenges to safe building design. Each building is unique, in geometry, use, construction, and condition. Because building codes, materials, and methods of construction change with time, and uncorrected deterioration may reduce the strength or safety of buildings with time, many buildings exist that would be considered substandard relative to “current” building standards. Even in new construction, mistakes or misunderstandings during either the design or construction process can result in building defects. In addition, design standards contained in building codes cannot define with certainty
1–50 SECTION 1 ■ Safety in the Built Environment
the actual ranges of loading or exposure to snow, wind, or other extreme events to which any building may be subjected throughout its existence.
BIBLIOGRAPHY References Cited 1. ASCE 7-98. Minimum Design Loads for Buildings and Other Structures, Commentary Section C6.5.40, American Society of Civil Engineers, Reston, VA, 1998. 2. Natural Hazard Mitigation Insights, February 2000, The Institute for Business and Home Safety, Boston, MA.
NFPA Codes, Standards, and Recommended Practices NFPA 101®, Life Safety Code® NFPA 5000™, Building Construction and Safety Code™
Additional Readings American Concrete Institute, ACI 530, Building Code Requirements for Masonry Structures, ACI, 1999. American Concrete Institute, ACI 530.1, Specifications for Masonry Structures and Commentaries, ACI, 1999.
American Concrete Institute, ACI 318, Building Code Requirements for Structural Concrete, ACI, 2002. American Forest and Paper Association, AF&PA Allowable Stress Design Manual, AF&PA, Washington, DC, April 2002. American Forest and Paper Association, AF&PA Load Resistance Factor Design Manual, AF&PA, Washington, DC, 1996. American Forest and Paper Association, AF&PA Wood Frame Construction Manual, AF&PA, Washington, DC, 2002. American Iron and Steel Institute, ASD Manual of Steel Construction, 9th ed. American Institute of Steel Construction, LRFD Manual of Steel Construction, 3rd ed. American Society of Civil Engineers, “Specification for the Design of Cold-Formed Stainless Steel Structural Members,” ASCE 8, ASCE, Reston, VA, 1990. American Society of Civil Engineers, “Air Supported Structures,” ASCE 17, ASCE, Reston, VA, 1996. American Society of Civil Engineers, “Structural Applications of Steel Cables for Buildings,” ASCE 19, ASCE, Reston, VA, 1996. American Society of Civil Engineers, “Specifications for Structural Steel Beams with Web Openings,” ASCE 23, ASCE, Reston, VA, 1997. American Society of Civil Engineers, “Flood resistance Design and Construction,” ASCE 24, ASCE, Reston, VA, 1998.
CHAPTER 3
SECTION 1
Codes and Standards for the Built Environment
Revised by
Arthur E. Cote Casey C. Grant
T
hroughout history there have been building regulations for preventing fire and restricting its spread. Over the years, these regulations have evolved into the codes and standards developed by committees concerned with safety. In many cases, a particular code dealing with a hazard of paramount importance may be enacted into law.
HISTORY OF REGULATIONS FOR THE BUILT ENVIRONMENT King Hammurabi, the famous law-making Babylonian ruler who reigned from approximately 1955 to 1913 B.C., is probably best remembered for the Code of Hammurabi, a statute primarily based on retaliation. The following decree is from the Code of Hammurabi: In the case of collapse of a defective building, the architect is to be put to death if the owner is killed by accident; and the architect’s son if the son of the owner loses his life. Today, society no longer endorses Hammurabi’s ancient law of retaliation but seeks, rather, to prevent accidents and loss of life and property. From these objectives have evolved the rules and regulations that represent today’s codes and standards for the built environment.1
Early Building and Fire Laws The earliest recorded building laws apparently were concerned with the prevention of collapse. During the rapid growth of the Roman Empire under the reigns of Julius and Augustus Caesar, the city of Rome became the site of a large number of hastily constructed apartment buildings—many of which were erected to
Arthur E. Cote, P.E., is executive vice president and chief engineer at NFPA. Casey C. Grant, P.E., is NFPA’s assistant chief engineer and secretary of the NFPA Standards Council.
considerable heights. Because building collapse due to structural failure was frequent, laws were passed that limited the heights of buildings—first to 70 ft (21 m) and then to 60 ft (18 m). Later in history there evolved many building regulations for preventing fire and restricting its spread. In London, during the fourteenth century, an ordinance was issued requiring that chimneys be built of tile, stone, or plaster; the ordinance prohibited the use of wood for this purpose. Among the first building ordinances of New York City was a similar provision, and among the first legislative acts of Boston was one requiring that dwellings be constructed of brick or stone and roofed with slate or tile (rather than being built of wood and having thatched roofs with wood chimneys covered with mud and clay similar to those to which the early settlers had been accustomed in Europe). The intention of these building ordinances was to restrict the spread of fire from building to building in order to prevent conflagrations. As an inducement for helping to prevent fires, a fine of 10 shillings was imposed on any householders who had chimney fires. This fine encouraged the citizenry to keep its chimneys free from soot and creosote. Thus was the first fire code in America established and enforced. In colonial America, the need for laws that offered protection from the ravages of fire developed simultaneously with the growth of the colonies. The laws outlined the fire protection responsibilities of both homeowners and authorities. Some of these new laws were planned to punish people who put themselves and others at risk of fire. For example, in Boston no person was allowed to build a fire within “three rods” (about 49.5 ft or about 15.5 m) of any building, or in ships that were docked in Boston Harbor. It was illegal to carry “burning brands” for lighting fires except in covered containers, and arson was punishable by death. Regardless of such precautions, in Boston and in other emerging communities, fires were everyday occurrences. Therefore, it became necessary to enact more laws with which to govern building construction and to make further provisions for public fire protection. There emerged a growing body of rules and regulations concerning fire prevention, protection, and control. From these small beginnings, various codes and types of codes have evolved in this country, ranging from the most meager of ordinances to comprehensive handbooks and volumes of codes and standards on building construction and fire safety.
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Development of Building and Fire Regulations The rapid growth of early North American cities inspired much speculative building, and the structures usually were built close to one another. Construction often was started before adequate building codes had been enacted. For example, the year before the great Chicago fire of 1871, Lloyd’s of London stopped writing policies in Chicago because of the haphazard manner in which construction was proceeding. Other insurance companies had difficulty selling policies at the high rates they had to charge. Despite these excessively high rates, many insurance companies suffered great losses when fire spread out of control. The National Board of Fire Underwriters [NBFU; later the American Insurance Association (AIA) and now the American Insurance Services Group (AISG)], organized in 1866, realized that the adjustment and standardization of rates were merely temporary solutions to a serious technical problem. This group began to emphasize safe building construction, control of fire hazards, and improvements in both water supplies and fire departments. As a result, the new tall buildings constructed of concrete and steel conformed to specifications that helped limit the risk of fire. These buildings were called Class A buildings. In 1905 the National Board of Fire Underwriters published the first edition of its Recommended Building Code [later the National Building Code (NBC)]. This was a first and very useful attempt to show the way to uniformity. In San Francisco in early 1906, although there were some new Class A concrete and steel buildings in the downtown section, most of the city consisted of fire-prone wood shacks. Concerned with such conditions, the National Board of Fire Underwriters wrote that “San Francisco has violated all underwriting traditions and precedents by not burning up.” On April 18 of that same year, the city of San Francisco experienced a conflagration—started by an earthquake—that
FIGURE 1.3.1
killed 452 people and destroyed some 28,000 buildings. Total financial loss was $350 million, which is over $6.7 billion in estimated 2000 dollars. Although the contents of many of the new Class A buildings were destroyed in the San Francisco fire, most of the walls, frames, and floors remained intact and could be renovated (Figure 1.3.1). Following analysis of the fire damage caused by the San Francisco disaster and other major fires, the National Board of Fire Underwriters became convinced of the need for more comprehensive standards and codes relating to the design, construction, and maintenance of buildings. With this increasing recognition of the importance of fire protection came more knowledge about the subject. Engineers started to accumulate information about fire hazards in building construction and in manufacturing processes, and much of this information became the basis for the early codes and standards. Several chapters in this handbook have a bearing on the provisions of building codes and their enforcement. Of particular interest is Section 12, Chapter 2, “Building Construction,” which contains information on the various types of construction and how they are classified in building codes as a basis for fire protection requirements.
CONCEPTS OF SAFETY VERSUS RISK There are two broad categories of voluntary codes and standards: (1) safety codes and standards and (2) product standards. These documents are not solely a matter of science, especially safety codes and standards.2 Codes and standards embody value judgments as well as facts and sometimes must use empirical evidence on judgment to compensate for gaps or limits in the relevant science. (Also see the SFPE Handbook of Fire Protection Engineering.3) Codes and standards oriented toward safety tend to be more complicated and extensive than product standards.
The Great Earthquake and Ensuing Conflagration That Devastated San Francisco in 1906
CHAPTER 3
Furthermore, safety codes and standards are often adopted with the power of law and, thus, require more extensive technical advisory support. Safety is the inverse or opposite of risk, so greater safety means the reduction or elimination of some risk to people or property or some other vulnerable entity of concern. Risk can never be entirely eliminated, and so safety is never absolute. Even short of absolute safety, any relative increase in safety will not have unlimited value. Individual, organizational, or societal decision makers must decide whether a particular increase in safety (i.e., reduction in risk) is worth more to them than what they must pay in order to achieve that safety increase. Because financial resources are the most obvious sacrifice required to decrease risk, the trade-off involved is often called “willingness to pay.” The lower risk becomes, the more it typically costs to achieve each additional constant increase in safety. In addition, part of the cost of risk elimination is the reduction of freedom. Many aspects of safety systems or materials standards have this effect, as they come to bear on the establishment of an “acceptable level” of risk. Assessments of levels of risk are also needed with respect to cost of use of the codes and standards themselves, including complex calculations or other costs of information. If tolerance limits are exceeded, codes and standards will be modified in practice or ignored. Also, the more onerous and costly compliance becomes, the more carefully critics will examine the “degree of contribution to a safe environment” that the code or standard will bring about. The many effects of codes and standards on what people value bring into play an aggregation of complex factors—social, economic, political, legal, business-competitive, and others—that affect how much people value safety and how much they value what may be sacrificed for safety. No solely economic, engineering, or public health approach can do justice to all these factors, many of them unavoidably or even intrinsically subjective. One of the strengths of the voluntary consensus codes- and standards-development system in the United States is that the deliberative committee structure, which comprises a balanced representation of all affected interests, including users, consumers, manufacturers, suppliers, distributors, labor, testing laboratories, enforcers, and federal, state, and local government officials, can consider all of the diverse factors at hand and develop a consensus on an acceptable level of standardization. It has been observed that “this may be one of the greatest strengths of the present private standards-writing system, insofar as it truly represents variety, and one of the greatest insufficiencies of a governmental system.”4
ROLE OF CODES IN THE BUILT ENVIRONMENT A code is a law or regulation that sets forth minimum requirements and, in particular, a building code is a law or regulation that sets forth minimum requirements for the design and construction of buildings and structures. These minimum requirements, established to protect the health and safety of society, attempt to represent society’s compromise between optimum
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1–53
safety and economic feasibility.5 Although builders and building owners often establish their own requirements, the minimum code requirements of a jurisdiction must be met. Features covered include, for example, structural design, fire protection, means of egress, light, sanitation, and interior finish. There are two general types of building codes. Specification or prescriptive codes spell out in detail what materials can be used, the building size, and how components should be assembled. Performance codes detail the objective to be met and establish criteria for determining if the objective has been reached; thus, the designer and builder are free to select construction methods and materials as long as it can be shown that the performance criteria can be met. Performance-oriented building codes still embody a fair number of specification-type requirements, but provisions exist for substitution of alternate methods and materials (“trade-offs”), if they can be proven adequate. The requirements contained in building codes are generally based on the known properties of materials, the hazards presented by various occupancies, and the lessons learned from previous experiences, such as fire and natural disasters. The promulgation of modern building codes in the United States began with the disastrous conflagrations that occurred in the late nineteenth and early twentieth centuries. For a number of years, building codes dealt mainly with structural safety under fire or earthquake conditions. Since then, codes have grown into documents prescribing minimum requirements for structural stability, fire resistance, means of egress, sanitation, lighting, ventilation, and built-in safety equipment. Typically, more than half of a modern building code usually refers in some way or another to fire protection. Building codes usually establish fire limits or fire districts in certain areas of a municipality. Only specific types of construction are allowed within the fire limits. Such a restriction is said to reduce the conflagration potential of the more densely populated areas. Use of a given type of building construction alone, however, is not necessarily a sufficient guard against conflagration. Outside the fire limits, the restriction of certain construction types is relaxed, due to such factors as decreased building density (i.e., increased spacing between buildings). Unfortunately, as areas outside the fire limits are developed, building density increases and the fire limits frequently must be extended. In addition, without construction restrictions, areas outside the fire limits invite the erection of large buildings despite public protection that is weak or lacking. Another example of the impact of building codes on fire protection and prevention is the establishment of height and area criteria. The criteria establish the maximum height and area of a particular building, based on its intended use. These requirements have typically varied considerably from one type of occupancy to the next. The types of building construction are important factors in establishing height and area limitations. Other requirements found in building codes that directly relate to fire protection include (1) enclosure of vertical openings such as stair shafts, elevator shafts, and pipe chases; (2) provision of exits for evacuation of occupants; (3) requirements for flame spread of interior finish; and (4) provisions for automatic fire suppression systems. Exit requirements found in most building codes are based on requirements in NFPA 101®, Life Safety Code®.
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Inasmuch as a building code is actually a law, various state and local jurisdictions write their own codes. Because of the complexities of modern building code development, several organizations develop model building codes for use by jurisdictions, which can then adopt the model codes into law.
ROLE OF STANDARDS IN THE BUILT ENVIRONMENT IN THE UNITED STATES Many requirements found in building codes are excerpts from, or based on, the standards published by nationally recognized organizations. The most extensive use of the standards is their adoption into building codes by reference, thus keeping the building codes to a workable size and eliminating much duplication of effort. Such standards are also used by specification writers in the design stage of a building to provide guidelines for the bidders and contractors. Numerous NFPA standards are referenced by model building codes and, thus, obtain legal status where these model codes are adopted. Notable examples of such referenced NFPA standards are those that deal with extinguishing systems, flammable liquids, hazardous processes, combustible dusts, liquefied petroleum gas, electrical systems, and fire tests. The model building codes contain appendices that list standards published by many organizations, including standards-making organizations, professional engineering societies, building materials trade associations, federal agencies, and testing agencies. The appendices are prefaced with a statement indicating that the standards are to be used where required by the provisions of the code or where referenced by the code.
Fundamentals of Voluntary Consensus The voluntary standards development system in the United States is efficient, cost-effective, highly productive, and results in the promulgation of thousands of quality standards each year. A diverse, decentralized network of private-sector entities develops U.S. voluntary standards. Many different organizations are involved, and this is a feature that is one of the great strengths of the system. Based on information compiled in 1996, the U.S. standardization community currently maintains approximately 93,000 standards in active status.6 The number of U.S. standards at any given moment in time, however, is difficult to identify. Today, it is assumed that the number 93,000 is still a relatively valid estimate, since various newly created standards tend to offset a trend of the largest U.S. producer of standards, the U.S. Department of Defense, to retire more standards each year than it generates. Standards exist for virtually all industries and product sectors. The oldest standards-developing organization in the United States is the U.S. Pharmacopoeial Convention, which published standards for 219 drugs in 1820. Today, the U.S. federal government supports the overall approach used in the United States through Public Law 104-113, which indicates that the federal government will support and (as needed) participate in the development of private, voluntary consensus documents, or if not, then to justify otherwise.
For a variety of reasons, data on the number of standards must be treated with caution. These reasons include (1) uncertainty on whether to consider as a standard a product description, specification, definition of a term, or description of a procedure; (2) the distinction between a single standard with many sections and a series of separate but related standards may be arbitrary; (3) the influence and impact of various standards on the economy can vary dramatically; (4) many documents become technologically obsolete but remain in a technically active status; (5) information on the number of state and local government standards is extremely limited and fragmented; and (6) statistical information typically does not include de facto standards (i.e., unsponsored and unwritten yet usually widely accepted standards, such as the configuration of typewriter and computer keyboards). The 93,000 standards in the United States generally comprise 49,000 private-sector standards and approximately 44,000 federal government standards. Furthermore, private-sector standards can be further subdivided based on the type of sponsoring organization: standards-developing organizations, scientific and professional societies, and industry associations. Table 1.3.1 provides a summary of this information.5 In comparison to most systems, the institutional structure of the U.S. voluntary consensus standards system is highly decentralized. Approximately 700 standards developers exist in the United States, with approximately 620 engaged in ongoing standards-setting activities that are mostly organized around an academic discipline, profession, or a given industry. The remainder of the aforementioned 620 organizations typically have a small number of standards that were developed in the past, which may or may not be occasionally updated. It is interesting to note that, of the 620 private-sector standards developers in the United States, the 20 largest developers account for a little more than 70 percent of all privatesector development. Table 1.3.2 indicates the number of TABLE 1.3.1
U.S. Standards and Their Developers Number of Standards
Percentage
17,000
18%
16,000 14,000
17% 15%
3,000
3%
49,000
53%
Department of Defense (DOD) General Services Administration (GSA) Other
34,000 2,000
37% 2%
8,000
8%
Subtotal of Federal Government
44,000
47%
Overall Total
93,000
100%
Private Sector Standards-Developing Organizations Trade Associations Scientific and Professional Societies Developers of Informal Standards Subtotal of Private Sector Federal Government
CHAPTER 3
TABLE 1.3.2 Number of U.S. Standards-Developing Organizations Number of Standards
Percentage
Private Sector Standards-Developing Organizations Scientific and Professional Societies Trade Associations Developers of Informal Standards Subtotal of Private Sector
40
6%
130
19%
300 150
43% 21%
620
89%
Federal Government Department of Defense (DOD) General Services Administration (GSA) Other
4 1
1% 1%
75
10%
Subtotal of Federal Government
80
11%
700
100%
Overall Total
Note: Numbers are rounded to the nearest 10, except for components of the federal government.
standards organizations by sector for the U.S. standards-development community.5
American National Standards Institute (ANSI) The significant private-sector standards-development system in the United States is largely self-regulated, with oversight and coordination provided by ANSI, a federation of U.S. codes and standards developers, company organizations, and government users of those standards. Originally known as the American Engineering Standards Committee, its first meeting was held on January 17, 1917, by the following founding organizations: American Institute of Electrical Engineers, American Institute of Mining Engineers, American Society of Civil Engineers, American Society of Mechanical Engineers, and the ASTM. The government Departments of War, Navy, and Commerce were soon involved, along with NFPA and other organizations. One of the first documents that was accepted and registered under the established rules as an “American Standard” was the 1920 edition of NFPA 70, National Electrical Code®. In 1928 the name of the American Engineering Standards Committee was changed to the American Standards Association. This organizational title was used until 1968 when the organization became known briefly as the United States of America Standards Institute (USASI) before adopting the current title of American National Standards Institute. Organizational membership in ANSI fluctuates, but as of 1996 it is comprised of approximately 265 U.S. professional, technical societies, and trade associations, along with 1100 U.S.
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companies. ANSI is able to fulfill its coordinating role for the voluntary standards system in the United States because of the support it receives from those actively involved in standards work. NFPA is an ANSI-accredited codes and standards organization, with “audited-designator status,” and this results in ANSI accreditation for virtually all NFPA codes and standards. As of 1996, approximately 11,180 standards approved by ANSI were designated as “American National Standards.” ANSI coordinates and harmonizes private-sector standards activity in the United States. In order for a document to be designated an American National Standard, the principles of openness and due process must have been followed in its development, and consensus among those directly and materially affected by the standard must have been achieved. ANSI also represents the interests of the United States in the international standardization activities of the International Electrotechnical Commission (IEC) and the International Organization for Standardization (ISO). The ANSI arrangement is unique in the ISO/IEC arena, since most countries are represented by a single organization that is either fully or partially funded by that country’s national government. The United States, however, is represented by a single private organization (ANSI) that further represents the interests of numerous organizations, including private standardsdevelopment organizations (e.g., ASTM, IEEE, NFPA, etc.). This results in a complex legal and business environment involving international copyright. Further complicating this situation is that U.S. standards developers do not limit their activities to only U.S. constituents and typically have members involved from other countries. It is not unusual for the U.S. representation or secretariats in IEC and ISO standards-developing activities to be true international standards developers in their own right. Under ANSI procedures, all American National Standards must be reviewed and reaffirmed, modified, or withdrawn no less frequently than every five years—a requirement that ensures that voluntary standards in the United States keep pace with developing technology and innovations. Thus, the voluntary system produces quality standards that do not become outdated.
Standards-Developing Organizations (SDOs) in the United States Authority and technical expertise in the U.S. standards-developing system is highly decentralized and linked to specific industry sectors. This has evolved based on the development of a wide range of consensus standards processes in many different standards-developing organizations (SDOs). The basic common principles of consensus codes and standards development are, thus, applied in different ways, with procedures and objectives specific to the needs of a particular industry or professional community. Three types of organizations generally develop standards handled and administered by the private sector, as follows:7 Standards-Developing Organizations. These organizations typically have the development of codes and standards as one of their central activities or missions. Membership-oriented codes and standards-developing organizations are the most prominent of these organizations, and they tend to have the most diverse
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membership among all SDOs, since they are not limited to a particular industry or profession. These membership organizations have a notable number of international members, which is a feature of many U.S. SDOs in general, and makes the U.S. codes and standards-developing system somewhat distinct among the rest of the world. Codes and standards-developing membership organizations, because of their diverse membership, tend to have the strictest due-process requirements. Aside from membership organizations, standards development is also a key activity of certain testing and certification organizations, such as Underwriters Laboratories Inc. or the American Gas Association. Two examples of standards-developing organizations are ASTM and NFPA, both of which are membership based. ASTM has a membership of approximately 32,000. The 132 ASTM technical committees are responsible for more than 9,900 standards, and approximately one-third of ASTM’s sales of standards are to international users. NFPA, for sake of comparison, has about 75,000 members. The 235 consensus technical committees of NFPA are responsible for about 300 safety-oriented documents, which are dramatically fewer than ASTM. This difference in committee structure provides some indication of the distinction between product standards handled by ASTM and safety codes and standards handled by NFPA. Furthermore, despite NFPA having substantially fewer documents than ASTM and some other standards developers, the total number of pages generated by NFPA (because they are mostly safety-oriented documents rather than product oriented) is often comparable and, in some cases, clearly more. As noted earlier, safety standards tend to be more complex, which leads to greater length. The number of published standards is not necessarily an absolute indicator of overall activity level or significance, and a vivid example of this concept is the Boiler and Pressure Vessel Code administered by ASME. Although it is considered a single standard, it is approximately 12,000 pages in content and far exceeds the size of almost all other standards that are more commonly only several pages in length. In a similar fashion, any of the model building codes and similar safety-related documents for the built environment far exceed most other standards in terms of page count. In fact, neither numbers nor page counts are as valid indicators of impact as would be numbers of users by document and numbers of lives and dollars affected, but both of these measures are very hard to develop. Scientific and Professional Societies. These societies are a refined form of membership organizations that support the practice and advancement of a particular profession. The most recognized of these societies involve the engineering disciplines. A unique characteristic of these societies is that the participants, as part of their standards-development processes, typically function as individual professionals and not as specific representatives of their sponsoring organization or industry. Prominent examples of scientific and professional societies include the American Society of Mechanical Engineers (ASME) and the Institute of Electrical and Electronics Engineers (IEEE). ASME has an international membership of more than 125,000.
The ASME standards process has more than 700 committees responsible for 600 codes and standards. ASME has responsibility for the Boiler and Pressure Vessel Code, which comprises some 12,000 pages and is one of the most prominent single documents in the U.S. standards-development arena and in the world. IEEE has a worldwide membership of more than 315,000 engineering professionals. The approximately 680 standards published by IEEE focus specifically on areas of electrotechnology. Industry Associations. Industry or trade associations are organizations of manufacturers, service providers, customers, suppliers, and others that are active in a given industry. The development of technical standards is specifically intended to further the interests of their particular industry sector. The Association for the Advancement of Medical Instrumentation (AAMI) is an example of a trade organization that develops standards. Approximately 2,000 health care professionals support their activities and include representatives from industry, health care facilities, academia, research centers, and government agencies, such as the Food and Drug Administration (FDA). Industry association SDOs are likely to be more openly responsive to commercial market concerns than other types of SDOs. Other examples of industry associations include the American Petroleum Institute (API) and the National Electrical Manufacturers Association (NEMA).
INTERNATIONAL ARENA Basics of International Standards Development In the common lexicon of codes and standards development, and especially in the various international arenas, the term “standards” is most commonly used to characterize all the various types of standardizing documents (i.e., codes, standards, guides, policies, etc.). A quick review of the language of these documents is helpful for this discussion. As mentioned previously, the entities that administer these standardizing activities are generally known throughout the world as “standards-developing organizations” and are commonly referred to by the acronym SDO. (The term “SDO” has been expanded in the last few years to address those SDOs that have activities or a basis in more than one country, and these are now being recognized as international SDOs, or ISDOs.8) “One-Country/One-Vote” versus “Full-Consensus.” Arguably the most widely recognized ISDOs today are those of the “one-country/one-vote” design based in Geneva, Switzerland. Most notable among these are the IEC (International Electrotechnical Commission) and the ISO (International Organization on Standardization). These organizations enjoy a casual bureaucratic recognition by various world political organizations that is not readily available to other ISDOs. They are referred to herein as “one-country/one-vote” organizations since the prime mechanism for establishing a position on any particular subject is by a single vote from each participating country.
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Perhaps the most noteworthy contrast to the “one-country/one-vote” processes are those based on principles involving “full consensus.” This is characteristic of the methods used by the ISDOs of North America. Each individual person, regardless of their particular nationality, has the ability to participate directly in the issues under consideration. “Full-consensus” organizations are more democratic in their design in comparison to those organizations based on “one-country/one-vote.” North American Model. In the realm of codes and standards development, the ISDOs located in North America have certain characteristics that make them relatively unique9. The significant private-sector standards-development system in the United States is largely self-regulated, with certain oversight and coordination efforts provided by ANSI (American National Standards Institute), a federation of U.S. codes and standards developers, and corporate and government users of those standards. ANSI provides accreditation for the development of documents that meet their fundamental principles for full consensus. Organizations that meet these requirements typically have elaborate processes involving volunteer committees and utilizing extensive public input. Although federal, state, and local governments usually participate, they do as would any other participant. The resulting documents are referred to as “model documents,” and it is then up to any particular authority to subsequently implement the issued document as it sees fit (i.e., into law, as a specification, etc.). Of all the attributes of the North American ISDOs, of special note is the fact that they are oriented around a particular subject matter, based on a foundation of individual participant involvement. A trademark of North American processes is that they are blind to the geographic roots of their input and, thus, they allow anyone, anywhere to participate on an equal basis. In Search of Alternative ISDO Approaches. The developers of codes and standards based in North America are characterized, depending on the circumstances, as either an SDO or an ISDO. These organizations typically exist with a dual personality, providing for the domestic needs of their constituents, while at the same time not being exclusively dedicated to any particular collection of those constituents (i.e., serving the needs of constituents in multiple countries). It is admittedly a virtue to have participants involved in any process that provides wide representation rather than simply a narrow or limited focus. But is there an outward boundary to such representation, and at what point does the representation become misleading? When does it become “involvement without representation”? At the root of these questions is the effectiveness of processes based on the collective representation of very large entities such as entire nations (i.e., the “one-country/one-vote” design). This is a model that lends itself well to consideration of universal issues of sweeping impact, in which the singular voice of each country is able to speak clearly and contribute decisively to a common good. But is this same model the most appropriate approach, or more importantly, to be considered the only approach, to the
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myriad of technical details on which civilization is built? Although it can be argued that the “one-country/one-vote” model may perhaps lend itself well to certain topics and certain types of standards-development activities, it should not be expected to be the only approach for all standards activities.8 Clearly, alternative approaches exist, and one of these approaches, is the “full-consensus” approach. The “one-country/one-vote” model does not have the flexibility to equitably address detailed technical issues in the same manner as the “full-consensus” approach. It is convenient, of course, when a particular technical topic is used in the same manner in all of the countries of the world, but the many blends of society make such a convenience a true rarity. For example, consider the very common scenario of when a technical standard addresses a focused topic. In particular, consider a case study that has a relatively extreme focus, such as a hypothetical standard addressing harness gear for reindeer. Does it make sense for all the nations of the world to vote equally on this standard? Why should the nations at the equator have an equal vote with the Nordic nations that are clearly more familiar with—and affected by—the topic? The casual assumption that all topics exist equally in all nations, and that the “one-country/one-vote” model is the only approach needed, does not make sense. Regional Nature of ISDOs. Of particular note when discussing SDOs and ISDOs are the regional organizations. These exist today, both in a formal sense and in a less than formal or de facto sense.10 Although many jurisdictions have country-specific SDOs, there is a tendency for them to cluster regionally to assert their collective presence. The boundaries of such regions are not always geographically clear. More commonly, they are generally based on the culture and influence of the primary participants, or at least those participants with the primary control. Various examples exist of formalized regional standards bodies. Fitting this description are organizations such as CEN (European Committee for Standardization) for Europe, COPANT (Pan American Standards Commission) for the Americas, and PASC (Pacific Area Standards Congress) for the Pacific Rim nations. Although organizations such as these are easily distinguished, it is the nonformalized regional developers that are of interest in this discussion. In a unified sense, all the various codes and standards developers of the United States comprise a de facto regional standards body. This is particularly the case based on the coordinating role played by ANSI. Thus, we can observe that the standards-developing organizations of the United States exist independently as SDOs, in a collective sense as a regional organization, and in a practical sense as ISDOs. As a contrast to the North American position, the organizations of the “one-country/one-vote” design based in Geneva, Switzerland, and in particular ISO and IEC, enjoy an informal recognition by various world political organizations that is not readily available to other ISDOs. Despite their international stature, however, are implications that they are a European-based regional organization based on their operating characteristics. For
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example, in late 2000 it was reported that CEN and CEN-affiliated countries (33 in all) have 50 percent or more voting members on 80 percent of all ISO committees.10 Today, as an observation, ISO and IEC are typically considered as ISDOs, while gaining recognition as European regional SDOs. Meanwhile, the standards organizations based in the United States are typically considered as North American regional SDOs, while gaining recognition as ISDOs. World Trade Organization (WTO) and the Technical Barriers to Trade (TBT) Agreement. The World Trade Organization (WTO) is today generally considered the foremost-recognized global organization dealing with the rules of trade between nations.11 Its main function is to ensure that trade flows smoothly, predictably, and freely. The goal is to help producers of goods and services, exporters, and importers conduct their business. The WTO is headquartered in Geneva, Switzerland, with a staff of approximately 500, and is represented by 140 member countries and customs territories (as of November 30, 2000) that account for over 90 percent of world trade. Over 30 other countries are negotiating membership. A its heart are the WTO agreements, negotiated and signed by the bulk of the world’s trading nations and ratified in their parliaments. Technical Barriers to Trade. The WTO’s top-level decisionmaking body is the Ministerial Conference, and reporting to the Ministerial Conference and considered the prime operational entity is the General Council. Three other councils and various committees, working groups, and working parties report to the General Council, but of particular note of these is the Council for Trade in Goods. The Council for Trade in Goods likewise has various committees reporting to it, one of which is the Committee on Technical Barriers to Trade. This committee is responsible for the Agreement on Technical Barriers to Trade (TBT), which tries to ensure that regulations, standards, testing, and certification procedures do not create any unnecessary obstacles. Technical regulations and industrial standards may vary from country to country, and having too many different standards makes life difficult for producers and exporters. If the standards were set arbitrarily, they could be used as an excuse for protectionism. However, the TBT Agreement recognizes that countries have the right to establish protection at levels that they consider appropriate, and they should not be prevented from taking measures necessary to ensure that those levels of protection are met based on the need to fulfill certain legitimate objectives. These legitimate objectives include protection of human health and safety; national security; prevention of deceptive practices; protection of animal or plant life or health; and the environment. International Standards. The TBT Agreement encourages the countries to use international standards where these are appropriate, although it does not require them to change their levels of protection as a result of standardization. As guidance for member countries, Annex 3 to the TBT Agreement provides the Code of Good Practice for the Preparation, Adoption, and Application of Standards, which attempts to ensure that standards do not present an obstacle to international trade.
An obvious question that comes into play when attempting to implement the TBT Agreement is “what is an international standard?” This matter was recently addressed in the Report (2000) of the Committee on Technical Barriers to Trade.12 Included in this particular report is Annex 4, entitled “Decision of the Committee on Principles for the Development of International Standards, Guides and Recommendations with Relation to Articles 2,5 and Annex 3 of the Agreement.” This annex outlines the principles and procedures that should be observed for the preparation of international standards and attempts to ensure the following essential characteristics: (a) (b) (c) (d) (e) (f)
Transparency Openness Impartiality and consensus Effectiveness and relevance Coherence Ability to address the concerns of developing countries
The elements outlined here can be found as inherent traits in the various organizations that exist today that develop codes and standards in the international arena. For example, these elements fit the more commonly recognized international developers like ISO and IEC, but clearly others also meet or exceed these requirements, such as many of the North American codes and standards developers (e.g., NFPA and others). For certain aspects such as openness, impartiality, and consensus, the “fullconsensus” approach used by North American developers arguably does a better job meeting these TBT elements than do those that use the “one-country/one-vote” approach.
ENFORCEMENT OF CODES AND STANDARDS The types of government and the characteristics of governing authorities around the world vary considerably, yet despite the differences, there are some aspects that are common with relation to legislative adoption of codes and standards. For the sake of illustration, the following discussion focuses on this topic, based on a form of government similar to that used in the United States. Today the life and property of every citizen is safeguarded to at least some extent by safety legislation enacted by the Congress of the United States, state legislatures, city councils, town meetings, and many other jurisdictions and levels of government. The implementation and enforcement of this legislation are in the hands of administrative agencies of government, such as federal departments and agencies, state fire marshal offices and other appropriate state agencies, and local fire departments, building departments, electrical inspectors, and so on. In the earlier days of the United States, the protection of citizens from fire was solely the concern of the local community. Present-day fire fighting is carried on by local fire departments. Although most communities have had some type of building code since the beginning of the twentieth century, they have not had fire prevention or life safety codes until more recently. With the need for more detailed, comprehensive standards and codes relating to the construction, design, and maintenance
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of buildings came the knowledge that regulations based on such codes certainly could prevent most incidents of damage to the building, its contents, and the activities therein, and reduce losses in the incidents that did occur. Regulations relating to safety are determined and enforced by different levels of government. Although some functions overlap, federal and state laws generally govern those areas that cannot be regulated at the local level.
Nationally Based Safety Regulations There is a substantial amount of federal regulation pertaining to safety. Under the Constitution in the United States, Congress has the power to regulate interstate commerce. This power has been interpreted to permit Congress to pass laws authorizing various federal departments and agencies to adopt and enforce regulations to protect the public from hazards. Any federal department or agency in the United States can promulgate safety regulations only if authority to do so is granted by a specific act of Congress. These regulations have the force of law, and violations can result in legal action. In general, such federal laws can be enacted to provide (1) that all state laws on the same subject are superseded by the federal law, (2) that state laws not conflicting with the federal law remain
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valid, or (3) that any state law will prevail if it is more stringent than the federal law. Among the federal agencies that have the authority to promulgate fire safety regulations are the Consumer Product Safety Commission (CPSC), the Department of Health and Human Services (HHS), and the Occupational Safety and Health Administration (OSHA). It must be recognized that model codes are only representations of possible regulations, and they do not actually become law until enacted by state and municipal legislatures.13 The general areas of model code adoption and use in the United States can be seen in Figures 1.3.2 through 1.3.5. Although these illustrations are representative of code adoption activities in the United States, a similar approach of using model codes exists in numerous other countries. The world’s most widely adopted code, NFPA 70, is adopted in virtually every state in the United States, Mexico, and numerous other countries.
Regulations of State and Local Government Within the scope of the police power of state government in the United States is the regulation of building construction for the health and safety of the public—a power usually delegated to local governments of the state.
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FIGURE 1.3.2
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Adoption of NFPA 101®, Life Safety Code® (as of 2002)
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FIGURE 1.3.3
Adoption of a Fire Prevention Code (as of 2002)
Building code requirements usually apply to new construction or to major alterations to buildings. Retroactive application of code requirements is very rare. Building code applicability usually ends with the issuance of an occupancy permit or certificate of occupancy. The basic premise that legislation should regulate for the safety of current occupants and for current risk is not generally the province of building codes once a structure is occupied. Then after-occupancy codes or safety maintenance codes apply. Also, this usually is the point at which the authority of the building official ends and the fire official begins. This division of authority, however, does not preclude interaction between the two officials during both a building’s development and its subsequent use. In practice, many jurisdictions assign responsibilities to officials in various departments for codes whose natural “homes” are or are not in their departments. The division of authority varies considerably among communities. In most states in the United States, the principal fire official is the state fire marshal. For the most part, the state fire marshal is the statutory official charged by law with responsibility for the administration and enforcement of state laws relating to safety to life and property from fire. Usually the state fire marshal also has the power to investigate fires and to investigate arson.
The manner in which each state handles the promulgation of building and fire regulations varies widely. In some states, each local government may have its own code, whereas in others the local authority has the option of adopting the state codes. In still others, the state codes establish the minimum requirements, below which the local regulations cannot go. Finally, in some states the local government has no choice and must adopt the state code. These situations have resulted in a plethora of different local codes. Some of the local governments adopt one or more of the model codes or codes based on the model codes. Others draft their own local codes. This lack of uniformity has been criticized by materials producers, building designers, builders, and others, and some years ago prompted the appointment of federal commissions to study the situation and make recommendations to the administration.14–16 The legal procedure for adopting codes and standards into law can also vary from one enforcing jurisdiction to another. Usually, the simplest and best way is to adopt by reference. This method, applicable to public authorities as well as to private entities, requires that the text of the law or rule cite the code or standard by its title and give adequate publishing information to permit its exact identification. The code or standard itself is not
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FIGURE 1.3.4
Adoption of NPFA 70, National Electrical Code® (as of 2002)
reprinted in the law. All deletions, additions, or changes made by the adopting authority are noted separately in the text of the law. Adoption of a current edition of a code or standard obviates outdated editions maintained as law until a new law referencing a new edition is adopted. Where local laws do not permit adoption by reference, a code or standard can be adopted by transcription. This requires that the text of the adopted code or standard be transcribed into the law. Existing material can be deleted and new material added only if such material does not change the meaning or intent of the existing or remaining material. Under adoption by transcription, the code or standard cannot be rewritten, although changes can be made for administrative provisions. Because the text of the code or standard is transcribed into the law, due notice of the copyright of the document’s developer is required. As a result, most code groups copyright their codes or standards to prevent misuse and unlawful use.
CODE SETS FOR THE BUILT ENVIRONMENT Although building codes provide much focus, a variety of other related codes also readily serve the built environment. Specifi-
cally, these codes address distinct interrelated topics that are essential components in structures of all kinds. Topics that are typically addressed include electrical, plumbing, mechanical, fuel gas, energy, and fire prevention. Yet this is not an all-inclusive list, and any particular subject that lends itself to specific and detailed criteria is eligible and, thus, the evolution of “electrical codes,” “plumbing codes,” “mechanical codes,” and so on. Often the reference to “building codes” is intended to include, in a general sense, a reference to all of these related codes for the built environment. Of these different related topics, fire prevention codes are somewhat unique (e.g., construction versus ongoing operation and maintenance). It often is difficult to differentiate between items that should go into a fire prevention code and those best included in a building or other related code. Generally, those requirements that deal specifically with construction of a building are part of a building or similar code administered by the building department. A fire prevention code, on the other hand, includes information on fire hazards in a building and usually is regulated by the fire official. Requirements for exits and fire-extinguishing equipment generally are found in building codes, whereas the maintenance of such items is covered in fire prevention codes. More simply
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FIGURE 1.3.5
Adoption of a Regional Model Building Code (as of 2002)
stated, building and other related codes generally address the original design or major renovation of a building, whereas a fire prevention code usually addresses the building during its useful life after the initial construction or renovation is complete.
Comprehensive Consensus Codes With the exception of the independent operations of some of the largest cities, the business of code development for the built community in the United States is primarily in the hands of the recognized model code organizations. The primary objectives of these organizations are to provide standardization of construction regulations and/or support of the enforcement of these regulations. In the United States, two organizations in particular are coming of age with the establishment of code sets for the built environment. NFPA et al. A coalition of organizations led by NFPA, the International Association of Plumbing and Mechanical Officials (IAPMO), the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE), the Western Fire Chiefs Association (WFCA), and others are developing the only full set of integrated codes and standards for the built environment under a full-consensus process.
In December 1999 NFPA embarked on a project to establish a complete set of consensus codes and standards for the built environment. NFPA had already had at its disposal a number of major codes such as NFPA 1, Fire Prevention Code, NFPA 54, National Fuel Gas Code, NFPA 70, and NFPA 101, among others that could serve as a strong foundation for the basis of this set of consensus codes. Other codes and related standards were not present in the NFPA system in late 1999, but it was recognized from the start that they would be crucial to rounding out the code set. The needed codes included a code that covered structural design issues and other items normally found in a building code. Although major NFPA codes like NFPA 101 covered the most salient building code issues as they relate to fire protection, other items such as general structural design, foundation and roof issues, energy conservation, and accessibility were not covered to any measurable extent in the existing NFPA codes and standards. This led to the development of NFPA 5000™, Building Construction and Safety Code™, with the 2002 edition being the first edition. Other important codes, such as a plumbing code, mechanical code, and energy code, were contributed to the set by partnering organizations. In the setting of this coalition, model codes and standards are developed through a full, open, ANSI-accredited, consensus-based process allowing full participation of all interested
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groups. This has long been the hallmark of the U.S. system of codes and standards development. This unique system relies on the energies and expertise of private citizens brought together by nonprofit organizations like NFPA and its partners to forge consensus over important issues of technology and public safety. The building and construction fields have greatly benefited from this type of codes- and standards-development process. Consensus codes and standards exist today that address almost every aspect of the built environment, from life safety to electrical safety, from fuel gas to energy. The codes and standards processes of NFPA and its partners are accredited by the American National Standards Institute (ANSI), and the features that earned that accreditation make them considerably more accessible to the general public than the processes used by other code organizations. This is also the only coalition that is based on truly national and international organizations and is not an amalgamation of regional (partial U.S.) organizations, each of which have an independent and narrow geographic focus. ICC (International Code Council). In 1995 the International Code Council (ICC) was established. The purpose of the ICC is to combine the codes of the three traditional regional modelbuilding code organizations into a single national model. In a sense, the ICC is coming of age as a national organization and is striving to overcome the challenges of combining three distinctly different regional organizations, each of which have uniquely inherent geographic characteristics. The three regional organizations that comprise ICC are the Building Officials and Code Administrators (BOCA), the International Conference of Building Officials (ICBO), and the Southern Building Code Congress International (SBCCI). BOCA was originally known as the Building Officials Conference of America and published its first building code in 1950. It has traditionally had a regional focus on the Northeast and Great Lakes portions of the United States. ICBO first published its regional building code in 1927. The ICBO code has traditionally been used in the western United States but has been utilized in municipalities as far east as Indiana. Organized in 1940, SBCCI first published its building code in 1945, which has traditionally been used throughout the southern United States. The current documents of the ICC, as well as its three sponsoring regional organizations (i.e., BOCA, ICBO, and SBCCI), are developed in a process that has traditionally been by and for building officials, which restricts involvement and final voting to the building official community. This is in contrast to the codes and standards developed and maintained in an open, full-consensus process that allows widespread involvement, such as those accredited by the American National Standards Institute and used by NFPA. In particular, the documents of NFPA and its partners are developed and maintained in an open, full-consensus process that allows widespread involvement and, thus, provides documents that are more technically balanced and economically fair.
Other Organizations Related to Code Set Activities Wide ranges of organizations provide support, input, or involvement for the codes and standards infrastructure in North
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America. The following paragraphs are intended to provide information for several active groups that have not already been mentioned in earlier sections of this chapter. AISG (American Insurance Services Group). As previously noted, the National Board of Fire Underwriters (NBFU), renamed the American Insurance Association (AIA), and now known as the American Insurance Services Group (AISG), first published the National Building Code in 1905. The code was used as a model for adoption by cities, as well as a basis to evaluate the building regulations of towns and cities for town grading purposes. The code was periodically reviewed by the NBFU staff, revised as necessary, and republished. The last code revision was the 1976 edition. Since then, the AISG has discontinued updating and publishing the National Building Code, and Building Officials and Code Administrators (BOCA) has acquired the right to use the name National Building Code on its regional building code. The AISG also developed a fire prevention code, most recently published in 1976, but has also discontinued the updating and publishing of this document. ANSI (American National Standards Institute). The significant private-sector standards-development system in the United States is largely self-regulated, with oversight and coordination provided by ANSI, a federation of U.S. codes and standards-developers, company organizations, and government users of those standards. ANSI coordinates and harmonizes private-sector standards activity in the United States. In order for a document to be designated an American National Standard, the principles of openness and due process must have been followed in its development, and consensus among those directly and materially affected by the standard must have been achieved. ANSI also represents U.S. interests in the international standardization activities of the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). Association of Major City Building Officials (AMCBO). The Association of Major City Building Officials (AMCBO) was formed in 1974. This group focuses on issues of building codes, administrative techniques, and public safety in buildings. The association has 36 members and provides a national forum of city and county building officials united to discuss topics of mutual interest. AMCBO is affiliated with the National Conference of States on Building Codes and Standards (NCSBCS). The activities of AMCBO include encouraging the development of comprehensive training and educational programs for building code enforcement personnel, providing scientific and technical resources for the improvement of building codes, and enhancing building technology and products to reduce the cost of construction and maintain safety levels. CFPA-I (Confederation of Fire Protection Associations). CFPA-I is a body of leading fire protection organizations from around the world that have joined forces to collectively direct their resources at reducing the global fire problem and increasing life safety. By sharing experience, research, technical knowhow, and fire statistics, the group aims to maximize the
1–64 SECTION 1 ■ Safety in the Built Environment
effectiveness of fire prevention and protection and foster improved international fire safety codes and standards. The CFPAI typically meets in full session every three years at which time some of the more challenging global fire problems are debated. These sessions provide an opportunity to share advanced research and developments that have taken place in specific problem areas. Significant advances have been made in recent years in fire safety and the CFPA-I has provided an exceptional forum to disseminate this knowledge. At this time, one suborganization that exists within CFPA-I is the Confederation of Fire Protection Associations-Europe (CFPA-E), which is comprised of European fire protection associations. National Conference of States on Building Codes and Standards (NCSBCS). NCSBCS is a nonprofit corporation founded in 1967 as a result of Congressional interest in reform of building codes. It attempts to foster increased interstate cooperation in the area of building codes and standards and coordinates intergovernmental code administration reforms. NCSBCS is an executive-branch organization of the National Governors Association and includes as members governorappointed representatives of each state and territorial government. It has a working relationship with the National Conference of State Legislatures and the Council of State Community Affairs Agencies. National Institute of Building Sciences (NIBS). NIBS was authorized by Congress in 1974, under Public Law 93-383, as a nongovernmental, nonprofit organization governed by a 21member board of directors. Fifteen of the board members are elected and six are appointed by the president of the United States, with the advice and consent of the U.S. Senate. The institute is a core organization that serves primarily as an investigative body, offering its findings and recommendations to government and to responsible private-sector organizations for voluntary implementation. It carries out its mandated mission essentially by identifying and investigating national problems confronting the building community and proposing courses of action to bring about solutions to the problems. NIBS’s activities are board based and center around regulatory concerns, technology for the built environment, and distribution of technical and other useful information. Working under its very broad mandate, NIBS has established a Consultative Council, with membership available to representatives of all appropriate private trade, professional, and labor organizations; private and public standards, codes, and testing bodies; public regulatory agencies; and consumer groups. The council’s purpose is to ensure a direct line of communication between such groups and the institute and to serve as a vehicle for representative hearings on matters before the institute. World Organization of Building Officials (WOBO). WOBO was founded in 1984, with the primary objective of advancing education through worldwide dissemination of knowledge in building science, technology, and construction. WOBO was established because of increased participation of nations in the global marketplace; the rapid development of new interna-
tional building technologies and products; and development of international standards that now make it impossible for building officials to confine their concern to activities within their own national boundaries.
SUMMARY Codes and standards serve many purposes but foremost is their contribution to the overall betterment of civilization. Their role is particularly important as we work toward the challenges of a safer and more cost-effective built environment. In many ways, today’s world is complex, and codes and standards provide a point of measurement to simplify our lives. In this sense, codes and standards provide the practical foundation for a better tomorrow.
BIBLIOGRAPHY References Cited 1. Spivak, S. M., & Brenner, F. C., Standardization Essentials: Principles and Practices, Marcel Dekker Publishers, New York, 2001. 2. Cheit, R. E., Setting Safety Standards: Regulations in the Public and Private Sectors, University of California Press, Berkeley, CA, 1990. 3. Meacham, Brian, “Building Fire Safety Risk Analysis,” SFPE Handbook of Fire Protection Engineering, 3rd edition, National Fire Protection Association, Quincy, MA, 2002. 4. Thomas, J., “Time to Take Stock,” ASTM Standardization News, West Conshohocken, PA, Aug. 2000. 5. Project Report on the Second Conference on Fire Safety Design in the 21st Century, “Regulatory Reform and Fire Safety Design in the United States,” Worcester Polytechnic Institute, Worcester, MA, June 9–11, 1999. 6. Toth, R. B., “Standards Activities of Organizations in the United States,” NIST Special Publication 806, National Institute of Standards and Technology, Gaithersburg, MD, 1996. 7. Grant, C. C., “Common Sense and International Standards,” NFPA Journal, Quincy, MA, Jan./Feb. 2002. 8. ANSI, “A National Standards Strategy for the United States,” American National Standards Institute, New York, Aug. 2000. 9. ANSI, “American Access to the European Standardization Process,” American National Standards Institute, New York, Dec. 1996. 10. Thomas, J., “Raising the Bar,” ASTM Standardization News, West Conshohocken, PA, Nov. 2000, p. 5. 11. Liu, V., “The WTO TBT Agreement and International Standards,” presentation at PASC XXIV, Seoul, Korea, April 23, 2001. 12. “Report (2000) of the Committee on Technical Barriers to Trade,” WTO, World Trade Organization, Geneva, Switzerland, G/L/412, November 14, 2000. 13. Horwitz, B., “Codes and Standards: Engineers Wanted,” Consulting—Specifying Engineer, May 2001, pp. 38–42. 14. “Building the American City,” Report of the National Commission on Urban Problems, Superintendent of Documents, U.S. Government Printing Office, Washington, DC, 1968. 15. Building Codes: A Program for Intergovernmental Reform, Advisory Commission on Intergovernmental Relations, Superintendent of Documents, U.S. Government Printing Office, Washington, DC, 1966. 16. “Report of the President’s Commission on Housing,” Superintendent of Documents, U.S. Government Printing Office, Washington, DC, 1982.
CHAPTER 3
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on building and fire codes and standards discussed in this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 1, Fire Prevention Code NFPA 30, Flammable and Combustible Liquids Code NFPA 54, National Fuel Gas Code NFPA 70, National Electrical Code® NFPA 70A, Electrical Code for One- and Two-Family Dwellings and Mobile Homes NFPA 80, Standard for Fire Doors and Fire Windows NFPA 80A, Recommended Practice for Protection of Buildings from Exterior Fire Exposures NFPA 88A, Standard for Parking Structures NFPA 88B, Standard for Repair Garages NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems NFPA 90B, Standard for the Installation of Warm Air Heating and Air-Conditioning Systems NFPA 92A, Recommended Practice for Smoke-Control Systems NFPA 92B, Guide for Smoke Management Systems in Malls, Atria, and Large Areas NFPA 99, Standard for Health Care Facilities NFPA 101®, Life Safety Code® NFPA 105, Recommended Practice for the Installation of Smoke Control Door Assemblies NFPA 203, Guide on Roof Coverings and Roof Deck Constructions NFPA 204, Standard for Smoke and Heat Venting NFPA 220, Standard on Types of Building Construction NFPA 241, Standard for Safeguarding Construction, Alteration, and Demolition Operations NFPA 703, Standard for Fire Retardant Impregnated Wood and Fire Retardant Coatings for Building Materials
Integrated Consensus Code Set for the Built Environment (NFPA and partners) NFPA 1, Fire Prevention Code NFPA 30, Flammable and Combustible Liquids Code NFPA 30A, Code for Motor Fuel Dispensing Facilities and Repair Garages NFPA 54, National Fuel Gas Code NFPA 58, Liquefied Petroleum Gas Code NFPA 70, National Electrical Code® NFPA 101®, Life Safety Code® NFPA 5000™, Building Construction and Safety Code™ Uniform Plumbing Code—IAPMO (NCA/NAPHCC) Uniform Mechanical Code—IAPMO ASHRAE 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings ASHRAE 90.2, Energy Code for New Low-Rise Residential Buildings
Additional Readings ASTM Standards in Building Codes, 27th ed., American Society for Testing and Materials, Conshohocken, PA, 1990. Babrauskas, V., “Designing Products for Fire Performance: The State of the Art of Test Methods and Fire Models,” Fire Safety Journal, Vol. 24, No. 3, 1995, pp. 299–312. Batik, A. L., “A Layman’s View of the Relationship of Standards to Product Liability,” Standards Engineering, Dayton, OH, Jan./Feb. 1990. Baker, D. R., “Meeting High-Rise Requirements for Fire Detection/Alarm/Suppression,” Consulting—Specifying Engineer, Vol. 3, No. 2, 1988, pp. 56–59. Baker, D. R., “Performance by Computer Modeling or Prescription by Model Code,” TR 86-5, Society of Fire Protection Engineers, Boston, MA, 1986.
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Belles, D. W., “History and Use of Wired Glass in Fire Rated Applications,” Journal of Applied Fire Science, Vol. 5, No. 1, 1995/1996, pp. 3–15. Breitenberg, M. A., The ABC’s of Standards-Related Activities in the United States, U.S. Department of Commerce, National Bureau of Standards, Gaithersburg, MD, May 1987. “Brief History of the Standards of Fire Cover,” Fire Research News, Vol. 22, Winter 1999, pp. 2–4. Bukowski, R. W., “History of NBS/NIST Research on Fire Detectors,” Proceedings of 12th International Conference on Automatic Fire Detection “AUBE /01,” March 25–28, 2001, Gaithersburg, MD, National Institute of Standards and Technology, Gaithersburg, MD, NIST SP 965, February 2001, pp. 1–12. Bukowski, R. W., and Babrauskas, V., “Developing Rational, Performance-based Fire Safety Requirements in Model Building Codes,” Fire and Materials: An International Journal, Vol. 18, No. 3, 1994, pp. 173–192. “Code Change B7–97 Will Reduce Conflict between FHAA Objectives and Fire Safety,” Building Official and Code Administrator, Vol. 31, No. 5, 1997, pp. 16–19. Cooke, P. W., A Review of U.S. Participation in International Standards Activities, U.S. Department of Commerce, National Bureau of Standards, Gaithersburg, MD, Jan. 1988. Cooke, P. W., A Summary of the New European Community Approach to Standards Development, U.S. Department of Commerce, National Bureau of Standards, Gaithersburg, MD, Aug. 1988. Cooke, P. W., An Update of U.S. Participation in International Standards Activities, U.S. Department of Commerce, National Institute of Standards and Technology, Gaithersburg, MD, Jan. 1988. Corcoran, D., “Fire Prevention and Building Restoration Activities,” Fire Engineering, Vol. 146, No. 12, 1993, pp. 94–98, 100. Corneo, E., Gallina, G., and Mutani, G., “Fire Safety in a Historical Building: A Case History,” Proceedings of Symposium for ’97 FORUM, Applications of Fire Safety Engineering, October 6–7, 1997, Tianjin, China, 1997, pp. 60–72. Cote, R., Life Safety Code Handbook, 6th ed, National Fire Protection Association, Quincy, MA, 1994. Deakin, A. G., “Fire Safety in Buildings: Standards for 1992’s Europe,” Fire International, No. 121, Feb./Mar. 1990, pp. 15–16. Dixon, R. G., Jr., Standards Development in the Private Sector: Thoughts on Interest Representation and Procedural Fairness, National Fire Protection Association, Quincy, MA, 1978. Duthinh, D., and Carino, N. J., “Shear Design of High-Strength Concrete Beams: A Review of the State-of-the-Art,” National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 5870, Aug. 1996. Finnimore, B., “Need for Atria Fire Codes,” Fire Prevention, No. 205, Dec. 1987, pp. 30–33. Galan, S. A., “History of Underwriters’ Laboratories and Plenum Cable Fire Testing and Materials Evaluation,” Proceedings of Fall Conference, Flame Retardant Polymerics: Electrical/ Electronic Applications, October 4–7, 1998, Newport RI, 1998, pp. 53–62. Gann, R. G., “NIST/NBS Fire Research and FRCA: 25 Years of Progress,” Proceedings of Fire Safety and Technology: Turmoil—Progress—Opportunities—1973–1998–2000, March 22–25, 1998, Atlanta, GA, Fire Retardant Chemicals Association, Lancaster, PA, 1998, pp. 77–84. Green, M., “History of Building Code Regulations for Existing Buildings in the United States,” Proceedings of Pacific Rim Conference and 2nd International Conference on Performance-Based Codes and Fire Safety Design Methods, May 3–9, 1998, Maui, HI, International Code Council, Birmingham, AL, 1998, pp. 39–47. Gross, J. G., “Developments in the Application of the Performance Concept in Buildings,” Proceedings of the CIB-ASTM-ISORILEM 3rd International Symposium, Applications of the Performance Concept in Building, December 9–12, 1996, Tel Aviv, Israel, National Building Research Institute, Haifa, Israel, 1996, Vol. 1, pp. 1/1–11.
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Gross, J. G., “Harmonization of Standards and Regulations: Problems and Opportunities for the United States,” Building Standards, National Institute of Standards and Technologies, Gaithersburg, MD, Mar./Apr. 1990, pp. 32–35. Harvey, C. S., “Flexible Approach to Fire-Code Compliance,” Architectural Record, No. 10, Oct. 1988, pp. 130–135. Heskestad, A., “Survey of Fire Safety Activities in Scandinavia with Regard to the Introduction of Performance-Based Fire Safety Building Codes,” Proceedings of Fire Safety Design of Buildings and Fire Safety Engineering, August 19–20, 1996, Oslo, Norway, Fire Safety Building Codes, 1996, Conference Compendium, pp. 1–2. Hemenway, D., “Industrywide Voluntary Product Standards,” Ballinger Publishing Company, Cambridge, MA. Hosker, H., and Waters, C., “Building Regulations Determined,” Fire Prevention, No. 224, Nov. 1989, pp. 37–38. Hubbard, D. B., and Pastore, T. M., “New Zealand Building Regulations Five Years Later,” University of Canterbury, Christchurch, New Zealand, Fire Engineering Research Report 97/9, Aug. 1997. Johnson, P. F., “International Implications of Performance Based Fire Engineering Design Codes,” Journal of Fire Protection Engineering, Vol. 5, No. 4, 1993, pp. 141–146. Kaufman, S., “1990 National Electric Code—Its Impact on the Communication Industry,” 38th International Wire and Cable Symposium, U.S. Army Communication Electronics Command, Atlanta, GA, 1989, pp. 301–305. Korman, R., and Post, N. M., “The Code System, It Ain’t Pretty. . . But it Works, Codes, ENR,” Construction Weekly, June 22, 1989. Lathrop, J. K., “Life Safety Code Key to Industrial Fire Safety,” NFPA Journal, Vol. 88, No. 4, 1994, pp. 36–46. “Legal Aspects of Code Enforcement: A Report on the 1993 Annual Conference Education Program,” Building Standards, National Institute of Standards and Technologies, Gaithersburg, MD, Vol. 63, No. 1, 1994, pp. 27–30. Lucht, D. A., Kime, C. H., and Traw, J. S., “International Developments in Building Code Concepts,” Journal of Fire Protection Engineering, Vol. 5, No. 4, 1993, pp. 125–133. “Major Changes to the 1995 Codes,” Consensus, Spring 1995, p. 25. Mawhinney, J. R., “Development of Regulations in the 1990 National Fire Code of Canada on Storage of Dangerous Goods,” Fire Technology, Vol. 26, No. 3, 1990, pp. 266–280. McMillen, J., “Guideline for the Fire Design of Shopping Centres,” University of Canterbury, Christchurch, New Zealand, Fire Engineering Research Report 00/16, Nov. 2000. Meacham, B. J., and Custer, R. L. P., “Performance-Based Fire Safety Engineering: An Introduction of Basic Concepts,” Journal of Fire Protection Engineering, Vol. 7, No. 2, 1995, pp. 35–54. Moss, D., “Fire Safety and Compliance of 1992,” FM Journal, Jul./Aug. 1995, pp. 15–19. Murphy, J. J., Jr., “Fire Safety Operations and Code Compliance Concerns. Part 2,” Fire Engineering, Vol. 148, No. 1, 1995, pp. 78–82, 84, 86. Neale, R. A., “When Code Equivalencies Don’t Work,” American Fire Journal, Vol. 48, No. 1, 1996, pp. 20–23. Oey, K. H., and Passchier, E., “Complying with Practice Codes,” Batiment International/Building Research and Practice, Vol. 21, No. 1, 1988, pp. 30–36. Peralta, M., “Statement of the American National Standards Institute Concerning International Voluntary Standardization,” American National Standards Institute, New York, July 25, 1989. “Project 3: Fire Resistance and Non-Combustibility. Part 1. Objectives and Performance Levels for Fire Resistance,” Fire Code Reform Centre Ltd., NSW Australia, October 1996. Richardson, L. R., “Determining Degrees of Combustibility of Building Materials—National Building Code of Canada,” Fire and
Materials: An International Journal, Vol. 18, No. 2, 1994, pp. 99–106. Robertson, J. C., “Development and Enactment of Fire Safety Codes,” Introduction to Fire Prevention, 3rd ed., Macmillan, New York, 1989, pp. 112–132. Sabatini, J., “Ensuring Code Compliance in High-Hazard Buildings,” Plant Engineering, Vol. 44, No. 9, 1990, pp. 57–59. Sanderson, R. L., Codes and Code Administration, Building Officials Conference of America, Inc., Chicago, IL, 1969. Schirmer, C., “Helping Develop the Codes and Standards,” Fire Journal, Vol. 84, No. 3, 1990, p. 44. Solomon, R. E., “Preserving History from Fire. Bridging the Gap Between Safety Codes and Historic Buildings,” Old House Journal, Vol. 28, No. 6, 2000, pp. 40–45. Standards Activities of Organizations in the United States, National Institute of Standards and Technology, U.S. Dept. of Commerce, Washington, DC, 1991. Steiner, V. M., “Building Codes—Bane or Blessing?” Plant Engineering, July 21, 1988. Strength, R. S., “Status Report Model Building Codes 1992, NEC-93 and IEC-89,” Fire Retardant Chemicals Association Fall Conference: Industry Speaks Out on Flame Retardancy: Coatings; Polymers and Compounding; Test Method Development; New Products, Technomic Publishing Co., Lancaster, PA, 1992, pp. 41–46. Stroup, D. W., “Using Performance-Based Design Techniques to Evaluate Fire Safety in Two Government Buildings,” Proceedings of Pacific Rim Conference and 2nd International Conference on Performance-Based Codes and Fire Safety Design Methods, May 3–9, 1998, Maui, HI, International Code Council, Birmingham, AL, 1998, pp. 429–439. Stubbs, M. S., “The Widening Web of Codes and Standards,” AEBO Section Newsletter, Fall 1988, National Fire Protection Association, Quincy, MA, 1988. (Reprinted from Doors and Hardware.) Swankin, D. A., How Due Process in the Development of Voluntary Standards Can Reduce the Risk of Anti-Trust Liability, U.S. Department of Commerce, National Institute of Standards and Technology, Washington, DC, Feb. 1990. Terio, C., Introduction to Building Codes and Standards, The American Institute of Architects, State Government Affairs, Washington, DC, Apr. 1987. Todd, N. W., and Ryan, J. D., “Improving Codes by Predicting Product Performance in Real Fires,” Fire Journal, Vol. 84, No. 2, 1990, p. 64. Traw, J. S., “ICBO Code Interpretation Policy,” Building Standards, Jan.–Feb. 1990. Turner, M., “New Code Governing the Means of Escape for Disabled People,” Fire Prevention, No. 215, Dec. 1988, pp. 36–37. Use of Building Codes in Federal Agency Construction, Building Research Board, National Research Council, Commission on Engineering and Technical Systems, Washington, DC, 1989. VanRickley, C. W., “Survey of Code Officials on Performance-Based Codes and Risk-Based Assessment,” Code Forum, Jan./Feb. 1996, pp. 42–43. Wenzel, A. B., and Janssens, M. L., “Using the Cone Calorimeter to Assess Combustibility of Building Products,” Proceedings of FORUM 2000 Symposium, Fire Research Development and Application in the 21st Century, October 23–24, 2000, Taipei, Taiwan, 2000, pp. 1–26. “World Trade Center Bombing May Bring Code Reviews,” Consulting— Specifying Engineer, Vol. 13, No. 5, 1993, p. 13. “1991 Updated: Legislation and Codes Affecting the Fire Sprinkler Industry,” Sprinkler Age, Vol. 10, No. 11, 1991, pp. 12–15, 17.
BASICS OF FIRE AND FIRE SCIENCE
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s its title states, Section 2 of the Fire Protection Handbook presents the basics about the fire problem, fire protection, fire safety, fire science, and everything else that makes a systematic approach to fire possible. For decades, many users of the Fire Protection Handbook and of the National Fire Codes® have treated these resources as sources of material to be learned through memorization. Yet, understanding why the rules of fire protection and safety are as they are begins with understanding the most basic and general concepts of systems and of physical science related to fire protection. Section 2 is designed to provide the technical foundation and logic for fire protection. Users should, therefore, consider reading these chapter first before turning to the more subject-specific chapters in subsequent sections. Chapter 1 in Section 2 provides statistical information on the long-term trends in fire and on short-term trends and patterns that help to show the relative status and importance of various strategies to reduce that fire problem. This chapter also provides a number of basic organizing principles to help provide unity and understandability to the large, sprawling subject of fire safety and fire protection. These principles and themes are then repeated and used throughout the handbook to help show the connection between subjects.
SECTION
2
Arthur E. Cote John R. Hall, Jr.
Case Study SOCCER STADIUM FIRE, BRADFORD, ENGLAND, MAY 11, 1985 As the fire grew, smoke and heat accumulated in the roof cavity and moved to the rear concourse, influenced by a light breeze coming from the playing field. The continued growth and spread of fire throughout the grandstand was greatly influenced by the roof structure and by the amount and arrangement of available fuels. Filmed documentation of the growth of the fire indicates that the blaze spread the entire 290-ft length of the stand in less than five minutes. Based on the NFPA study of the fire, the following factors contributed significantly to the fire spread and subsequent loss of life:
At approximately 3:40 p.m. on Saturday, May 11, 1985, 56 people died and more than 300 were injured, many severely, as a result of a rapidly spreading fire at an outdoor soccer stadium in Bradford, England, a medium-sized industrial city 171 miles north of London. The fire occurred in the main grandstand, which may have been occupied by as many as 5000 people. The portion of the grandstand in which the fire began consisted of wood bleacher seats and flooring and lightweight wood materials. A double-peaked combustible wood roof consisting of felt insulation and various layers of tar over wood members covered the entire 290-by-55-ft grandstand. A National Inquiry determined that the fire began in accumulated trash beneath the wood bleachers that most likely was ignited by smoking materials. Once ignited, the trash fire spread to and ignited the lightweight materials used in the construction of the wood bleachers. Spectators seated immediately adjacent to the developing fire moved into an aisle and then to the rear concourse, where the grandstand’s main exits were located. Persons in remote sections of the grandstand continued to watch the match, apparently unconcerned about (or perhaps unaware of) the developing fire. No public announcement was made to notify the patrons that there was a fire in the grandstand and that they should leave.
• Ignition of accumulated trash below the wood bleachers • Initial fuel supply provided by the trash and lightweight wood bleacher material • Combustibility of the wood bleachers and roof structure • Influence of the structure on fire spread once flames reached the roof deck • Failure of patrons to perceive the danger of the developing fire in the early stages and begin evacuation • One-direction occupant flow design of aisles and exits • Lack of a sufficient number of open and available exits
Source: Thomas J. Klem, “Investigation Report: 56 Die in English Stadium Fire,” Fire Journal, May 1986, pp. 128–147.
2–1
2–2 SECTION 2 ■ Basics of Fire and Fire Science
Of the postignition strategies, which are collectively known as “fire protection,” Chapter 1 states: “It is important to remember that fire protection requires the development of an integrated system of balanced protection that uses many different design features and systems to reinforce one another and to cover for one another in case of the failure of any one. . . . Success is measured by the extent of usage of effectively designed integrated fire protection systems.” The need to emphasize systems design and systems thinking is developed further in Chapter 2, which presents a systems approach to fire prevention and fire protection. Chapters 3 and 4 address the basics of physical science that determine how fires start and grow. Chapter 3 provides the basic principles of fire chemistry and physics; Chapter 4 provides the most general and important application of those principles, which is the development of fire in a compartment (i.e., a bounded space). Chapters 5 through 7 provide basics tied to fire protection strategies. Whereas the properties of products and materials that allow fires to start (Section 6) or grow (Section 8) are woven into the basic physics and chemistry covered in Chapters 3 and 4, the other strategies have their own specialized bodies of scientific principles. Chapter 5 provides the basics of how fires are extinguished, supporting Sections 10 and 11. Chapter 6 provides the basics of how fires are detected, supporting Section 9. And Chapter 7 provides the basics of how products and features resist fire, supporting Section 12. Sections 4, 5, and 7 contain their own basics chapters, and Sections 13 and 14 are further applications of the material in the earlier sections. Finally, Chapters 8 and 9 provide basics on two specialized topics—explosions and environmental impacts. Also look for these: Section 1 places fire in the larger context of all causes of unintentional injury to people or physical damage to property. Section 1 also provides an overview of codes and standards as the mechanism for expressing our shared values on risk and our best technical knowledge, in the form of effective controls. The early chapters of some of the later sections also present basic scientific material but material specific to one type of strategy and hence to those sections only. Also, every chapter on basics recommends the same source for more detailed information on that aspect of the science underlying fire protection engineering—namely, The SFPE Handbook of Fire Protection Engineering, also published by NFPA.
SECTION 2
Chapter 1
An Overview of the Fire Problem and Fire Protection
U.S. Fire Loss Trends Fire Patterns by Property Class Fire Prevention Fire Protection Materials, Products, and Environments Detection and Alarm Suppression Confining Fires Evacuation of Occupants Systems Approaches for Property Classes A Century of Accomplishment Organizing for Fire Protection Information and Analysis Bibliography Chapter 2
Fundamentals of Fire-Safe Building Design
Design and Fire Safety Fire Safety Design Strategies Summary Bibliography Chapter 3
Chemistry and Physics of Fire
Basic Definitions and Properties Combustion Principles of Fire Heat Measurement Heat Transfer Energy Sources or Sources of Ignition Summary Bibliography Chapter 4
Dynamics of Compartment Fire Growth
Fire Growth Heat Release Rate Fuel Loading Classifications of Fire Effects of Compartment Boundaries on Fire Effects of Fire Location Summary Bibliography
Chapter 5 2–5 2–5 2–11 2–15 2–19 2–19 2–20 2–21 2–22 2–23 2–24 2–26 2–31 2–34 2–34
2–37 2–37 2–39 2–48 2–48 2–51 2–51 2–55 2–57 2–60 2–62 2–65 2–68 2–68
2–73 2–73 2–74 2–74 2–75 2–76 2–80 2–80 2–81
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Basics of Fire and Fire Science
Theory of Fire Extinguishment
The Combustion Process Extinguishment with Water Extinguishment with Aqueous Foams Extinguishment with Water Mist Extinguishment with Inert Gases Extinguishment with Halogenated Agents Extinguishment with Dry Chemical Agents Deep-Seated Fires Special Cases of Extinguishment Summary Bibliography Chapter 6
Fundamentals of Fire Detection
Simplified Fire Development Fire Signatures Summary Bibliography Chapter 7
Basics of Passive Fire Protection
Terminology Stages of Fire Development Materials, Products, and Assemblies Reaction-to-Fire Fire Resistance Exterior Fire Spread Egress Summary Bibliography Chapter 8
2–3
2–83 2–83 2–86 2–87 2–88 2–88 2–90 2–92 2–93 2–93 2–94 2–94 2–97 2–97 2–97 2–99 2–99 2–103 2–104 2–105 2–106 2–107 2–112 2–114 2–115 2–115 2–116
Explosions
2–119
Fundamental Explosion Principles Types of Explosions Summary Bibliography
2–119 2–123 2–129 2–130
Chapter 9
Environmental Issues in Fire Protection
Pollution Control Fire Protection Systems Summary Bibliography
2–133 2–133 2–135 2–138 2–139
CHAPTER 1
SECTION 2
An Overview of the Fire Problem and Fire Protection John R. Hall, Jr. Arthur E. Cote
W
nizational considerations for fire protection organizations, such as fire departments. The next five sections address principal strategies for engineered fire protection. The last two sections provide systems approaches for types of buildings and occupancies and for types of vehicles or elements of transportation. To understand the sequencing of the sections, think of fire protection as a series of opportunities to intervene against a hostile fire, arrayed along a timeline of potential growth in fire severity. First, there are the opportunities to prevent the fire entirely, by education or by changes to products, whether heat sources or combustible materials. Second, there are opportunities to slow the initial growth and spread of fire or to reduce the severity of fires through the design, selection, and handling of materials and products. Third, there are opportunities to detect fire early, permitting effective intervention before damage becomes too severe. Fourth, there are opportunities for automatic or manual suppression. Fifth, there are opportunities to confine the fire in space through compartmentation and other passive fire protection methods. Sixth, there are opportunities to move occupants to safe locations, taking advantage of the extra time provided by the earlier steps to move people from hazardous locations to safety, or to defend them where they are. Before examining each of these fire protection strategies, it is useful to assess the size of the fire problem that faces us and the success achieved in reducing it over the past decades.
hen the first Fire Protection Handbook was published in 1896, it contained no information on the size, trends, or patterns of the U.S. fire problem. Like most scientific and engineering handbooks, especially in years gone by, the first Fire Protection Handbook merely compiled a series of rules, tables, and formulas, which the knowledgeable fire safety professional of that time would find useful. One had to read between the lines to realize that the information provided in that handbook said nothing about hazards to life and limb and little about fire prevention as a strategy to reduce fire loss. (One also saw very little about such related hazards as electrical shock, hazardous materials, and environmental risks, topics that later editions have steadily expanded.) In the century since that first edition appeared, the field of fire protection has grown tremendously. This edition of the Fire Protection Handbook is more than an order of magnitude larger than the original edition. With that growth of information has come an increasing need for context, perspective, and systematic approaches to organizing knowledge. This chapter has two goals. One is to provide a perspective on the size, trends, and patterns of the U.S. fire problem and the global fire problem as well. Special attention has been paid to the incidents that led to changes in codes and standards—and the changes in fire experience that followed those code and standard changes. The other goal is to provide a basic structure for the elements of fire protection—a structure that can be tied to particular measures of the fire problem and that is carried forward in the first-level organization of this handbook. There are 14 major sections in this handbook. The first is new and addresses nonfire hazards and related codes and standards. The second addresses basics of fire and fire science; more detailed treatment of data, information, analysis, and modeling are covered in the third section; and issues of human behavior are covered in the fourth section. The next two sections correspond to education and other strategies of fire prevention. The seventh section addresses orga-
U.S. FIRE LOSS TRENDS Table 2.1.1 and Figures 2.1.1 through 2.1.4 show that the number of fires has declined over the past 2 decades. Civilian fire deaths were stuck around 6000 during 1982 to 1988, but have declined by roughly two-fifths since then. Civilian fire injuries showed no consistent trend up or down, until the mid-1990s, when they began to decline consistently. Direct property damage has risen dramatically, but most of that is due to inflation, although there have been years when individual fires of historic size have driven the total, adjusted for inflation, to new heights. Table 2.1.2 and Figure 2.1.5 provide a longer perspective on U.S. fire deaths by switching to trends in the death-certificate database. (NFPA uses this database only for long-term trend
John R. Hall, Jr., is NFPA’s assistant vice president for fire analysis and research. Arthur E. Cote, P.E., is NFPA’s executive vice president and chief engineer.
2–5
2–6 SECTION 2 ■ Basics of Fire and Fire Science
TABLE 2.1.1 The U.S. Fire Problem, 1977–1999: Fires Reported to U.S. Fire Departments
Year
Fires
Civilian Deaths
1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
3,264,000 2,817,500 2,845,500 2,988,000 2,893,500 2,538,000 2,326,500 2,343,000 2,371,000 2,271,500 2,330,000 2,436,500 2,115,000 2,019,000 2,041,500 1,964,500 1,952,500 2,054,500 1,965,500 1,975,000 1,795,000 1,755,500 1,823,000
7,395 7,710 7,575 6,505 6,700 6,020 5,920 5,240 6,185 5,850 5,810 6,215 5,410 5,195 4,465 4,730 4,635 4,275 4,585 4,990 4,050 4,035 3,570
Civilian Injuries
Direct Property Damagea
31,190 29,825 31,325 30,200 30,450 30,525 31,275 28,125 28,425 26,825 28,215 30,800 28,250 28,600 29,375 28,700 30,475 27,250 25,775 25,550 23,750 23,100 21,875
$4,709,000,000 $4,498,000,000 $5,750,000,000 $6,254,000,000 $6,676,000,000 $6,432,000,000 $6,598,000,000 $6,707,000,000 $7,324,000,000 $6,709,000,000 $7,159,000,000 $8,352,000,000 $8,655,000,000 $7,818,000,000 $9,467,000,000 $8,295,000,000 $8,546,000,000 $8,151,000,000 $8,918,000,000 $9,406,000,000 $8,525,000,000 $8,629,000,000 $10,024,000,000
a Direct property damage figures do not include indirect losses, such as business interruption, and have not been adjusted for inflation. Source: NFPA National Fire Experience Survey.
analysis, where there is no alternative database with as much consistency in methodology. Fires involving postcrash vehicle fires or arson are often excluded or missed from the fire totals in the death-certificate database.)
Fire deaths have fallen by roughly 70 percent in the 76 years since their peak levels around World War I. Fire death rates have fallen by a factor of 9. The decline in fire deaths was fairly irregular until the mid-1960s, in part because individual incidents with death tolls in the hundreds used to occur with some regularity. A few such incidents could significantly affect the total U.S. fire death toll in a given year. From 1955 to the present, there have been only four U.S. incidents with a death toll of 100 or more—the Lexington, Kentucky, restaurant fire in 1977; the Oklahoma City, Oklahoma, office building bombing of 1995; the Florida in-flight fire of 1996; and the terrorist attack on the World Trade Center in 2001. By contrast, the previous 55 years (1900 through 1954) produced 44 incidents involving death tolls of 100 or more, a decline from nearly one fire per year of that severity to less than one per decade.1 “America Burning,”2 the report of the National Commission on Fire Prevention and Control (NCFPC), set a goal in 1973 of reducing the U.S. fire death toll by one-half in a generation, which is usually understood to mean 25 years. With that generation now gone, fire deaths measured by death certificates did fall by more than one-half. Table 2.1.3 provides a longer perspective on property damage in fire, using estimates from the Insurance Services Office (ISO). (NFPA uses this database only for long-term trend analysis, where there is no alternative database with as much consistency in methodology. The database has considerable uncertainty due to its adjustments for uninsured and unreported losses.) Fire losses have grown more than 150 times in the past 120 years, but this reflects a 15- to 16-fold decline in the purchasing power of the dollar and a more than 40-fold increase in the nation’s economy (measured by gross national product [GNP]) after adjustment for those changes in purchasing power. As a fraction of GNP, fire loss has declined by more than 80 percent since the turn of the century, a large decline though not so large as the decline in the fire death rate relative to population. To put the total in another perspective, the property damage caused by fire in 1993 was more than the cost of building 155
2,500,000
2,115,000 2,019,000
2,054,500 2,041,500
1,975,000 1,823,000
1,964,500 1,952,500
1,965,500 1,795,000 1,755,500
1,500,000
1,000,000
Year
FIGURE 2.1.1
U.S. Fire Incident Trend, 1989–1999 (Source: NFPA National Fire Experience Survey)
1999
1998
1997
1996
1995
1994
1993
1992
1991
0
1990
500,000
1989
Number of incidents
2,000,000
CHAPTER 1
■
7,000
5,000
30,475
30,000 5,195 5,410
4,730
4,635 4,585
4,000
4,275
4,050 3,570
2,000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1,000 1989
25,775
24,000
3,000
0
27,250
28,700 28,250
26,000
4,035
4,465
28,600
29,375
28,000
4,990
Year
25,550 23,750
23,100
22,000 Number of injuries
Number of fatalities
6,000
2–7
An Overview of the Fire Problem and Fire Protection
21,875
20,000 18,000 16,000 14,000 12,000 10,000
FIGURE 2.1.2 U.S. Civilian Fire Death Trend, 1989–1999 (Source: NFPA National Fire Experience Survey)
8,000 6,000 4,000
Figure 2.1.6 shows that fire death rates are similar in the United States and Canada and that these two countries have among the highest fire death rates in the Americas. It is possible that the completeness of reporting varies from country to country. As an example, fire statistics jumped in the Russian Federation after the society became more open at the urging of President Boris Yeltsin. This occurred part way through the 1986–1995 period used for Figure 2.1.6. In the last 3 years of this period, Russia’s fire death rate averaged more than 60 deaths per million population.
The highest fire death rate for the 10-year period is not shown in Figure 2.1.6. It belongs to the island nation of Mauritius, off Madagascar, in Africa, which averaged 59 fire deaths per million population. The Asia/Pacific region appears to show the lowest fire death rates, but none of the countries of the Asian
$9.406B
$9.467B $8.295B $8.546B
$7.818B
$8.629B
$8.843B
$8.655B $7.454B 7.00
$8.566B
$8.525B $7.654B $7.789B
$7.925B
$8.145B
$7.382B
$7.353B
$7.511B
1998
8.00
Billions of dollars
$8.918B $8.151B
1997
$8.655B
9.00
6.00 5.00 4.00 3.00
Actual damage 2.00
Adjusted by Consumer Price Index
1.00
Year
FIGURE 2.1.4 U.S. Direct Property Damage Trend, 1989–1999 (Source: NFPA National Fire Experience Survey)
1999
1996
1995
1994
1993
1992
1991
1990
0.00
1989
1999
FIGURE 2.1.3 U.S. Civilian Fire Injury Trend, 1989–1999 (Source: NFPA National Fire Experience Survey)
$10.024B 10.00
1998
1997
1996
1995
1994
1993
1992
1991
Fire around the World
1990
0
1989
2,000
new single-family houses of average cost (which was $152,500 in 1998) each day for 1 year.
2–8 SECTION 2 ■ Basics of Fire and Fire Science
mainland have data available for comparison. In Europe, if entered from its northwest corner, the island nations of Ireland and the United Kingdom have higher fire death rates than the nations across the English Channel. The other original member nations of the European Union have most of the lowest fire death rates in Europe. Fire death rates are higher in the Nordic countries and Eastern Europe, especially in countries where very high rates of alcohol consumption are found. Figure 2.1.7 looks at 2 decades of trend data on fire death rates for four countries where comparable data has been consistently available for this long period. The United States and Canada have tracked together throughout this period, and both have narrowed the gap in fire death rates with Sweden, the United Kingdom, and Japan, passing the latter in the last couple of years. The U.S. and Canadian rates were twice as high in the late 1970s, roughly 50 percent higher in the late 1980s, and nearly the same in the late 1990s. The gap is closing because the United States and Canada have been improving fire safety faster than other countries. Throughout, analysis has shown that the United States does well in holding down the average severity of fire (i.e., deaths per fire) but fares poorly in holding down the fire incident rate (i.e., preventing fires). Figure 2.1.8 shows 1995–1997 property loss to fire as a fraction of gross domestic product, based on the estimates of the World Fire Statistics Centre (WFSC). The WFSC analysts make a number of adjustments to nationally reported loss data, in order to improve comparability. For example, Japan’s percentage based on reported data is nearly 50 percent lower than the
History of U.S. Fire and Burn Fatalities
TABLE 2.1.2
Year
Fire Deathsa
Fire Deaths per 100,000 Population
1913 1918 1923 1928 1933 1938 1943 1948 (old) 1948 (new) 1953 1958 1963 1968 1973 1978 1983 1988 1993 1998
8,900 10,200 9,100 8,400 6,800 6,500 8,700 7,700 6,800 6,600 7,300 8,200 7,300 6,500 6,200 5,000 5,000 3,900 3,000
9.1 9.9 8.1 7.0 5.4 5.0 6.5 5.3 4.7 4.2 4.2 4.3 3.7 3.1 2.8 2.2 2.0 1.5 1.1
a Fire deaths are calculated on the basis of death certificates and are given to the nearest hundred. Fire deaths involving arson or postcollision vehicle fires may be omitted. Classification changes in 1968, 1958, and especially 1948 limit comparability of figures. Source: National Safety Council, Injury Facts, National Safety Council, Itasca, IL, 2000, pp. 38–41.
12,000
10,000
Number of deaths
8,000
6,000
4,000
1999
1996
1992
1988
1984
1980
1976
1972
1968
1964
1960
1956
1952
1948
1945
1941
1937
1933
1929
1925
1921
1917
0
1913
2,000
Year
FIGURE 2.1.5
U.S. Fire and Burn Deaths, 1913–1999 (Source: National Center for Health Statistics, National Safety Council)
CHAPTER 1
TABLE 2.1.3
■
An Overview of the Fire Problem and Fire Protection
2–9
History of U.S. Property Damage in Fire
Year
Property Damage in Millions of Dollarsa
Property Damage in Millions of 1995 Dollarsb
Property Damage per Capita in Dollarsc
Property Damage per Capita in 1995 Dollars
Property Damage as Percentage of GNPd
1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1985 1990 1995
75 109 161 214 448 502 286 649 1,108 2,238 5,579 7,753 9,495 11,887
1,175 1,841 2,937 3,487 3,406 4,581 3,112 4,107 5,698 8,780 10,333 10,968 10,187 11,887
1.49 1.73 2.11 2.32 4.21 4.08 2.17 4.29 6.18 11.01 24.63 32.59 38.06 45.24
23.37 29.20 38.59 37.74 31.99 37.21 23.59 27.15 31.77 43.18 45.61 46.10 40.84 45.24
0.67 0.83 0.86 0.61 0.49 0.56 0.29 0.23 0.22 0.23 0.20 0.19 0.16 0.16
a Insurance Services Office Estimates, including adjustments for estimated uninsured and unreported losses, as reported by Insurance Information Institute, The Fact Book: 1992 Property/Casualty Insurance Facts, Insurance Information Institute, New York, 1992, p. 6, and Insurance Information Institute, The Ill Fact Book 2001, Insurance Information Institute, 2001, p. 100. b Based on Consumer Price Index, as calculated by the U.S. Bureau of Labor Statistics, including estimates for historical times by the U.S. Bureau of the Census. c Based on U.S. residential population. d Based on gross national product estimates by the U.S. Bureau of Economic Analysis, including estimates for historical times by the U.S. Bureau of the Census.
Europe 40
Russia Romania
30
Hungary
25 20
Ireland Finland
18
Bulgaria
16
Norway
15
Greece
14
Croatia
13
UK
12
Czech Republic
11
Portugal
11
Sweden
11
Belgium
10
France
10
Austria
8
Slovenia
8
Italy
7
Spain Netherlands
6 5
North America 17
U.S.A. 14
Canada 10
Mexico
South America 21
Chile 12
Argentina Venezuela
6
Asia/Pacific 10
Japan
9
New Zealand Australia
7
FIGURE 2.1.6 Fire Death Rates around the World—Fire Deaths per Million Population, 1986–1995 (Source: National Safety Council, International Accident Facts, 2nd edition, Itasca, IL: National Safety Council, 1999, p. 57) Note: Countries were included only if they had rates for at least 7 of the 10 years. Rates shown are average of annual rates, not rates for all years combined.
2–10 SECTION 2 ■ Basics of Fire and Fire Science
U.S.A.
40 35
34.7
Deaths per million people
34.4
35.8
Canada
34.7 34.6
35.8 29.2
30
30.7
27.4 28.6 28.7
25
26.0
25.3 23.6
26.0
24.4 24.0
21.9 22.2 21.7 21.8 21.7
20
25.4
20.1
20.8 17.7 18.5 18.0
19.2 19.1
15
16.4
17.4
18.8 15.1
17.0 14.2 14.0 14.2
10
12.7 13.3 12.2 13.5
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1983
1982
1981
1980
1979
1978
0
1977
5
Year U.S.A.
40
Deaths per million people
35
34.4
35.8
Japan
34.7 29.2
30 28.6
26.0
25.3
25
26.0
24.4 24.0
25.4 20.8
22.2
20 15
16.7 16.1
17.8
16.6 16.7
21.9
17.4 15.6 15.3
18.8 18.8 16.6
16.4 17.4
17.2
16.9
15.7 15.1
15.2 14.2 14.8 14.6 15.1 14.8
15.2
14.4
17.7 18.5 18.0
10
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1983
1982
1981
1980
1979
1978
0
1977
5
Year U.S.A.
40
Deaths per million people
35
34.4
35.6
U.K.
34.7
28.6 29.2
30
26.0
25.9
25.3
25
22.2
24.3 23.9
25.3 21.8
20.7
20
17.7 18.5 18.0 19.5
15
16.8
18.4
17.3
15.1
16.3 16.0 15.7
17.3 17.0 16.3 15.8 15.1 14.8 13.9 13.1
10
11.9
16.4
11.0
17.4
18.8 15.1
12.6 12.1 12.3
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1983
1982
1981
1980
1979
1978
0
1977
5
Year
FIGURE 2.1.7 Fire Death Rates in Four Countries, 1977–1997 (Source: NFPA Survey, annual reports from Association of Canadian Fire Marshals and Fire Commissioners, U.K. Home Office, Japan Fire Defense Agency, Swedish Fire Protection Association) Note: Swedish figures include fire fighters killed at fires.
CHAPTER 1
■
An Overview of the Fire Problem and Fire Protection
U.S.A.
40
Deaths per million people
35
2–11
Sweden
34.0 35.1 34.1 29.5
30
26.3
29.0
26.3
25.6
25
24.6 24.2
25.7 21.0
22.5
20 15
17.0
22.2
17.9 18.7 18.1
16.7
17.6
18.9 15.3
18.4 16.7
15.5 15.9 15.9 16.0
15.4
13.9
10
13.9
12.7 12.6
15.5 15.3 13.3
11.4 12.2 12.0
12.1
13.1
10.5
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1983
1982
1981
1980
1979
1978
0
1977
5
Year
FIGURE 2.1.7
percentage shown in Figure 2.1.8. The United States has one of the lowest ratios of property loss due to fire versus gross domestic product, in stark contrast to its ranking in fire death rates. Comparable data on fire loss are not readily available outside North America, Europe, and Japan. It would be especially difficult to interpret from nations with command economies, such as China.
FIRE PATTERNS BY PROPERTY CLASS The patterns of fire by property class can be examined using a property classification procedure first used in NFPA’s longrange planning exercises, as follows.
Homes and Garages. This category includes dwellings, duplexes, mobile homes, apartments, townhouses, condominiums, and detached dwelling garages. American Community. This category includes all public assembly properties; all educational, health care, or correctional facilities; and stores and offices. It also includes any residential properties that do not qualify as homes, such as hotels and motels, rooming or boarding houses, dormitories, fraternity and sorority houses, and barracks. This revised definition of the American Community also incorporates the Our American Heritage property class, which consists of historically important places and objects. Its direct fire loss is quite small, but it deserves and receives special attention because losses in this property class may be quite literally irreplaceable.
0.29
Italy Norway
0.24
Denmark
0.23
France
0.23
Sweden
0.23
Canada
0.21
Netherlands
0.20
Germany
0.18
Austria
0.17
Poland
0.13
U.K.
0.13
U.S.A Japan
Continued
0.13 0.10
FIGURE 2.1.8 Property Loss to Fire around the World— Direct Property Damage as a Fraction of Gross Domestic Product, 1995–1997 (Source: World Fire Statistics Centre Bulletin #14, Geneva, Switzerland: The Geneva Association, September 1998, Table 1) Note: Countries were included only if they had data for all 3 years. Estimates by WFSC involve changes for consistency and may differ substantially from nationally reported figures.
Industrial Environment. This category includes all industrial, manufacturing, defense, and utility properties, and all storage facilities other than dwelling garages. Other Structures. This category includes all buildings or structures that are vacant or under construction, demolition, or renovation. It also includes all structures that are not buildings, such as bridges and tunnels. Mobile Environment. This category includes all vehicles. Outdoor. This category includes all wildlands, forests, brush, grass, timber, and crops. It also includes outdoor trash, such as dumpsters or litter. Note that the statistics used here capture only fires reported to local fire departments; therefore, national, state, and private forests and parks may be significantly underrepresented. Other. This category includes all other and unclassified properties. It is needed for completeness but is a factor only for fire incidents, not for human or property losses.
2–12 SECTION 2 ■ Basics of Fire and Fire Science
Figures 2.1.9 through 2.1.12 summarize the patterns of fire loss in these seven property categories in recent years. The Outdoor category accounts for the largest share of reported fires. Fire deaths, and to a lesser degree fire injuries, are overwhelmingly concentrated in the Homes and Garages category. The three other building and structure categories combined (i.e., American Community, Industrial Environment, and Other Structures) account for a fire death toll one-third to one-half the size of the death toll in the Mobile Environment, which is itself only one-sixth the death toll in Homes and Garages. The majority of these vehicle fire deaths are due to fires following surviv-
Other (7.7%)
Outdoor and other Mobile (5.7%) environment (9.3%)
Other structures (1.1%)
Homes and garages (72.8%)
Industrial environment (3.2%)
American community (7.8%)
Homes and garages (22.0%)
American community (3.7%)
Industrial environment (2.1%)
Other structures (1.8%)
FIGURE 2.1.11 Civilian Fire Injuries by Property Use, 1994–1998 (Source: National estimates based on NFIRS and NFPA survey data)
Outdoor (2.0%) Mobile environment (14.2%)
Other (0.7%)
Homes and garages (51.3%)
Other structures (3.8%)
Mobile environment (21.2%)
Outdoor (41.4%)
FIGURE 2.1.9 Reported Fire Incidents by Major Property Class, 1994–1998 (Source: National estimates based on NFIRS and NFPA survey data)
Mobile environment (13.4%)
Other structures (1.7%)
Outdoor and other (1.3%) Homes and garages (80.1%)
Industrial environment (0.8%) American community (2.8%)
FIGURE 2.1.10 Civilian Fire Deaths by Property Use, 1994–1998 (Source: National estimates based on NFIRS and NFPA survey data)
Industrial environment (14.9%)
American community (13.0%)
FIGURE 2.1.12 Direct Property Damage by Major Property Use, 1994–1998 (Source: National estimates based on NFIRS and NFPA survey data)
able crashes in people’s personal cars or trucks. The U.S. fire death problem therefore is not a matter of large death tolls in large buildings, although these incidents dominate the news. Most people who die in fire die in ones or twos in the very places where they feel safest—their own homes and vehicles. Home and garage fires also lead the dollar loss due to fire, although here the share for other buildings is much larger than it is for deaths and injuries. Most of the visibility of the U.S. fire problem and a large share of the public’s fear and concern centers on very large fires. The relative importance of the different property classes can be very different, as is shown in Tables 2.1.4 through 2.1.7. Tables
CHAPTER 1
2.1.4 and 2.1.5 list the 10 deadliest U.S. fires and explosions of all time (through 1999) and those from 1990 to 1999, respectively, whereas Tables 2.1.6 and 2.1.7 list the 10 costliest U.S. fires and explosions of all time (through 1999) and those from 1990 to 1999, respectively. TABLE 2.1.4 The 10 Deadliest U.S. Fires and Explosions in History through 1999 Number of Deaths 1. S.S. Sultana steamship boiler explosion 1,547 and fire, Mississippi River, April 27, 1865 2. Forest fire, Peshtigo, WI, and environs, 1,152 October 8, 1871 3. General Slocum excursion steamship fire, 1,030 New York, NY, June 15, 1904 4. Iroquois Theater, Chicago, IL, 602 December 30, 1903 5. Forest fire, northern MN, October 12, 1918 559 6. Cocoanut Grove nightclub, Boston, MA, 492 November 28, 1942 7. S.S. Grandcamp and Monsanto Chemical 468 Company plant, Texas City, TX, April 16, 1947 8. Monongah Mine coal mine explosion, 361 Monongah, WV, December 6, 1907 9. North German Lloyd Steamship, Hoboken, 326 NJ, June 30, 1900 10. Explosion of two ammunition ships at depot, 322 Port Chicago, CA, July 18, 1944 Source: NFPA’s Fire Incident Data Organization and other NFPA fire incident records.
TABLE 2.1.5 1990–1999
The 10 Deadliest U.S. Fires and Explosions, Number of Deaths
1. Office building bombing, Oklahoma City, OK, April 19, 1995 2. Airplane in flight, near Miami, FL, May 11, 1996 3. Social club, New York, NY, March 25, 1990 4. Religious group complex, Waco, TX, April 19, 1993 5. Chicken processing plant, Hamlet, NC, September 3, 1991 6. Oakland Hills (forest) fire storm, Oakland, CA, October 20, 1991 7. Airplane loading passengers struck by falling flaming debris from mid-air collision, Fort Bragg, NC, March 23, 1994 8. Two-airplane collision on runway, Los Angeles, CA, February 1, 1991 9. Hotel, Chicago, IL, March 16, 1993 10. Chemical plant, Houston, TX, July 5, 1990 Note: Excludes nonfire deaths in incidents with both. Source: NFPA’s Fire Incident Data Organization.
169 110 87 47 25 25 24
22 20 17
■
An Overview of the Fire Problem and Fire Protection
2–13
TABLE 2.1.6 The 10 Largest U.S. Fire Losses in History through 1999 (in 1999 dollars) Loss in Year Fire Occurred (in million) 1. Earthquake and fire, San Francisco, CA, April 18, 1906 2. Great Chicago Fire, Chicago, IL, October 8–9, 1871 3. Oakland Hills (forest) fire storm, Oakland, CA, October 20, 1991 4. Great Boston Fire, Boston, MA, November 9, 1872 5. Polyolefin plant, Pasadena, TX, October 23, 1989 6. Baltimore conflagration, Baltimore, MD, February 7, 1904 7. Civil disturbance, Los Angeles, CA, April 29–May 1, 1992 8. Power plant, Dearborn, MI, February 1, 1999 9. “Laguna Fire” forest fire, Orange County, CA, October 27, 1993 10. Textile mill, Methuen, MA, December 11, 1995
Adjusted Loss (in million)
350
6,468
168
2,329
1,500
1,836
75
1,039
750
1,009
50
924
567
674
650
650
528
609
500
547
Note: The list is limited to fires for which some reliable dollar-loss estimate exists, is limited to fires occurring in or over the United States, and includes direct property damage only. Source: 1984 Fire Almanac, NFPA Fire Incident Data Organization, and Consumer Price Index, including the U.S. Bureau of the Census estimates of the index for historical times.
The 10 deadliest fires and explosions through 1999 include 5 from the Mobile Environment, 2 that began in the Outdoor Environment, and 1 from the Industrial Environment. Only 2, the Iroquois Theater and the Cocoanut Grove nightclub, involved the American Community, which people tend to think of as the area of greatest risk of multiple-death fires. In the 101 fires and explosions from 1900 through 1999 that killed at least 50 people, similar results, which may surprise the fire community, were found.1 The leading category was the Industrial Environment with 68 incidents, 59 of them being mine fires or explosions. The American Community had 22, the Mobile Environment had 8, the Outdoor Environment had 2, and the San Francisco earthquake and fire is hard to tie to any single environment. Even in the period from 1990 to 1999, the 10 deadliest fires and explosions include 3 from the Mobile Environment, 2 from the Industrial Environment, and 1 that started in the Outdoor Environment, in contrast with 4 from the American Community.
2–14 SECTION 2 ■ Basics of Fire and Fire Science
TABLE 2.1.7
The 10 Largest U.S. Fire Losses, 1990–1999
1. Oakland Hills (forest) fire storm, Oakland, CA, October 20, 1991 2. Civil disturbance, Los Angeles, CA, April 29–May 1, 1992 3. Power plant, Dearborn, MI, February 1, 1999 4. “Laguna Fire” forest fire, Orange County, CA, October 27, 1993 5. Textile mill, Methuen, MA, December 11, 1995 6. Cargo plane in-flight fire, near Newburgh, NY, September 5, 1996 7. High-rise office building, Philadelphia, PA, February 23, 1991 8. “Paint Fire/Goletta” forest fire, Santa Barbara, CA, June 27, 1990 9. Warehouse fire, New Orleans, LA, March 21, 1996 10. “Cleveland Fire” forest fire, Placerville, CA, October 1, 1992
Loss in Year Fire Occurred (in million dollars)
Adjusted Loss (in million dollars)
1,500
1,835
567
674
650
650
528
609
500
547
395
420
325
398
237
303
280
298
500
547
Note: The list is limited to fires for which some reliable dollar-loss estimate exists, is limited to fires occurring in or over the United States, and includes direct property damage only. Source: NFPA Fire Incident Data Organization and Consumer Price Index.
From 1948 through 1999, only 6 building fires in the United States resulted in 80 or more deaths—the Winecoff Hotel fire (119), the Our Lady of the Angels School fire (95), the Beverly Hills Supper Club fire (165), the MGM Grand Hotel fire (85), the Happy Land Social Club fire (87), and the Oklahoma City bombing of an office building (168). Compare these 6 building fires in 52 years (1948–1999) to 14 building fires and explosions of comparable severity in the previous 48 years (1900–1947). As previous comparisons in this chapter also have shown, any threshold of severity chosen demonstrates the tremendous progress made in the first half-century in reducing the rate of loss of life in fire, both in general and especially in major lifeloss fires. Later in this chapter is a more extended discussion of the “century of accomplishment” in fire safety that has been the legacy of NFPA’s first century. Another statistic may help to further explain this pattern. During the period from 1989 to 1994 in structure fires outside of
homes, 61 percent of all persons killed had been familiar with the building they died in for more than a year. More than 84 percent had been familiar with the building for more than a week. This statistic suggests a fire fatality problem that affects employees (and possibly some long-term patients) far more than customers. (Long-term guests or tenants are not the answer because the percentage of fatal victims with long-term familiarity goes up if all residential properties are excluded.) In other words, the number one fear of Americans—a fatal fire in strange surroundings—has been reduced to a minority share of a shrinking problem, even if homes are excluded. All these patterns underline the fact that life safety is a major issue everywhere—in homes and vehicles where most deaths occur, in locations that are part of the American Community where public concerns are highest, and in U.S. workplaces where significant risk of fire death still exists. Conversely, Figure 2.1.12 shows that the Industrial Environment category, which is typically considered the focus of potential property loss, actually contributes about the same property damage as the American Community category. In short, the dangers of fire to people and property are everywhere, and so strategies of design, fire protection, and other programs must also reach everywhere. Tables 2.1.4 and 2.1.5 also deliver a very encouraging message, and that is the progress made in reducing gigantic deadly fires. Tables 2.1.6 and 2.1.7 tell a slightly different tale for property damage. Note that the 5 costliest fires of the period from 1990 to 1999 were also 5 of the 10 costliest fires of all time. In fact, 6 of the 10 costliest incidents of all time came in 1989 or later, whereas the other 4 all occurred in 1906 or earlier. Despite the dramatic progress in reducing fire loss relative to the size of the U.S. economy, recent years have seen a resurgence of individual fires with historic-size losses, particularly California forest fires, which account for 4 of the 10 costliest incidents of 1990 to 1999. Tables 2.1.6 and 2.1.7 also show how much the character of large, costly fires has changed. Five of the 10 costliest fires of all time were fires that engulfed huge parts of cities, whereas only 1 of the 10 costliest fires of the period from 1990 to 1999—the Los Angeles civil disturbance fires—could be similarly described, and it was not a conflagration like the others. Except for the wildland/urban interface, the risk of conflagration has declined significantly from the pattern of a century ago. Conflagration, group fire, and city fire (the last term used in Japan) lack fully standardized definitions. The definitions used to code death certificates use the term conflagration to mean any building fire. More often, conflagration is used colloquially to mean any large fire with significant flame showing outside. NFPA generally uses the term conflagration to describe a fire with major building-to-building flame spread over some distance. Significant building-to-building fire spread within a complex or among adjacent buildings is typically called a group fire. Table 2.1.8 describes four different types of conflagrations, or group fires, and gives recent examples of each. The first type listed is also the most common conflagration scenario in recent years, which is the forest fire or brush fire that spreads to nearby buildings in what is called the urban/wildland interface. The classic conflagration scenario of the last century, involving nar-
CHAPTER 1
TABLE 2.1.8 Fires
Illustrative Recent Conflagrations and Group
1. Urban/Wildland Interface, Malibu, CA, 1987 A fire of incendiary origin with multiple points of origin was driven by Santa Ana winds gusting over 60 mph. The fire moved 12 mi in 10 hours, entering Malibu, where it damaged or destroyed 74 dwellings and mobile homes and 54,000 acres of property. Losses were estimated at nearly $9 million. Two of the 10 costliest U.S. fires and explosions of all time are recent California conflagrations of this type, both shown in Table 2.1.7. 2. Congested, Combustible District, Chelsea, MA, 1973 The fire began in a yard area of a congested district of combustible buildings, including multifamily housing and storage properties. The heavy fuel load inside and outside the buildings, and the narrow separations between buildings, created an ideal environment for rapid multibuilding fire growth. The wind was strong, gusting up to 48 mph. The water supply was inadequate to support master streams, and some sprinklered properties had broken piping that depleted the water supply without fighting the fire. Eventually, hundreds of buildings over 17 blocks were destroyed. Damage was estimated at $4 million. 3. Untreated Wood Shingles, Anaheim, CA, 1982 A fire initially reported as a tree fire spread over several blocks. Untreated wood shingles provided a ready source of secondary ignitions and firebrands, which were transported by high winds, gusting up to 60 mph. These hot, dry Santa Ana winds spread damage to 53 structures, for total estimated damages of $50 million. More than any other fire in recent history, this illustrates the devastating potential hazard of untreated wood shingles. Other major fires involving untreated wood shingles as significant factors include a 1983 apartment complex fire in Dallas ($5.4 million damage), a 1985 brush fire in and near Los Angeles ($11.2 million damage), a 1985 office building fire in San Antonio ($4.2 million damage), and a 1988 home and hotel fire in Lihue, HI ($5.5 million damage). 4. Group Fire—Commercial or Industrial Complex, Fall River, MA, 1987 A boiler flue pipe ignited wood components in a ceiling/floor space of a manufacturing plant. Multiple penetrations of the fire wall helped the fire spread into the main area of the plant, where it overwhelmed the plant’s complete-coverage sprinkler system. Once the first building was fully involved, high winds (35 mph) helped spread fire to the other five buildings in the complex. Total damages were estimated at $50 million. Other group fires include a 1987 Lowell, MA, fire ($30 million damage), exacerbated by a shut-off sprinkler system and oil-soaked wood floors, and a $70 million fire that damaged or destroyed 20 buildings in Lynn, MA, in 1981. Source: NFPA Fire Incident Data Organization.
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2–15
row streets and closely packed buildings, is now comparatively rare. The 1973 Chelsea, Massachusetts, conflagration is the only major example in recent decades. The construction and density conditions for such fires are largely confined to the old manufacturing areas of some old cities, particularly in the Northeast. A more common problem, particularly in the Southwest, is the phenomenon of conflagrations driven by strong, hot, dry winds and untreated wood shingles. This problem has been around for as long as NFPA has been collecting information on major fires. Finally, the group fire scenario, in which fire extends to most or all of the buildings of the complex, also continues to occur. The conditions for these fires also are most common in the old manufacturing areas of old cities.
FIRE PREVENTION Every hostile fire requires an initial heat source, an initial fuel source, and something to bring them together. That something nearly always has a human component, usually an immediate act or omission that brings heat and fuel together or sometimes the delayed effects of an error in design or installation. Fire also requires oxygen and sustainable chemical chain reactions, both of which can be useful points of attack for some suppression systems. Nevertheless, the three components of heat, fuel, and human error are central to nearly all fires and can be used as a framework for thinking about fire prevention, without much fear of oversimplification. It is important to remember that prevention can occur through successful action on the heat source, the fuel source, or the behavior that brings them together. No one line of attack is clearly preferable to the other, and success is most likely to come if all three components are treated as real options at all times. Product redesign is the means by which a heat source or a fuel source is changed. Such a change can come about in several ways: (1) regulation, (2) design to a set of voluntary, consensus codes and standards, (3) a voluntary industry-wide program to change product designs, not driven by laws or codes, and (4) product redesign in response to consumer demand. Changing behavior means education, which also may be done by targeting a variety of audiences. Schoolchildren are a group that can be reached when they are ready and able to learn substantial quantities of information. NFPA’s Learn Not to Burn®3 and Risk Watch® curricula are designed for this audience. Manufacturers’ labels and instructions reach consumers when they may be most disposed to learn rules for the fire-safe use of products. Product advertisements and public service announcements (PSAs), such as the NFPA Learn Not to Burn PSAs, have the potential to reach large audiences. Brochures, educational kits, community meetings, and the like can reach small, motivated audiences that may act as change agents. And Fire Prevention Week, of which NFPA is the originator and a sponsor, provides heightened attention to fire safety each October. “America Burning,” the report of the U.S. National Commission on Fire Prevention and Control, stated in 1973:2 Indifferent to fire as a national problem, Americans are similarly careless about fire as a personal threat. It
2–16 SECTION 2 ■ Basics of Fire and Fire Science
takes the careless or unwise action of a human being, in most cases, to begin a destructive fire. In their home environments, Americans live their daily lives amid flammable materials, close to potential sources of ignition. Though Americans are aroused to issues of safety in consumer products, fire safety is not one of their prime concerns. This is an understandable perception for people who work for fire safety full time and give it the very highest priority. But more than 2 decades later, it can be seen that this view is at least overstated. Many people do tend to believe that fire “only happens to the other guy,” and that view ironically is strongest in populations with above-average fire risk. But many people probably come to these views out of a lack of understanding of the risks of what they do and, even more, a lack of perspective on how they can achieve greater safety without unacceptably high costs or other sacrifices of things that also matter to them. People can be educated and motivated if approached in the right way. Addressing people effectively may involve nothing more than emphasizing what to do rather than what not to do. This is why an important milestone of the late 1970s was the introduction into the nation’s schoolrooms of fire safety education based on sound behavioral principles and good learning techniques. NFPA’s Learn Not to Burn3 campaign, which includes both a curriculum and a public information program, is a good example of a thoughtfully prepared educational campaign with specific, far-reaching goals. The Learn Not to Burn curriculum, in particular, seeks to teach schoolchildren key fire safety behaviors that can be retained for a lifetime. Product design strategies need to be carefully examined and not treated as simple technological quick fixes. Many design improvements can be undone by product users if the users have not also been educated to the importance of fire-safe product usage. Some product design proposals have high costs relative to the problem they address, and some involve the loss of other significant product performance features, even nonfire safety features. And with any product design strategy, except one driven by consumer demand, there should be concern over the loss of freedom of choice. Educational programs have concerns, too. NFPA’s Learn Not to Burn curriculum is estimated to be in use in roughly 5 percent of U.S. schools. Although many more schools have some fire safety education, there is a danger that brief exposure to fire safety slogans will be considered an adequate means of teaching fire-safe behavior. This is not the case. Also, in any fire prevention program, the highest-risk groups tend to be the hardest to reach. The poor may not be able to afford safer products. Small rural communities are too scattered to be reached efficiently by targeted means of communications. Preschool children are harder to reach with curriculum programs. Elderly people may resist changes in products and practices. This means that a program with less-than-national coverage is likely to miss a disproportionate number of those most in need. The challenge to fire prevention is to recognize this danger and design programs that reach everyone. It can be done. For example, universal fire safety education, particularly in the schools but also in neighborhoods, seems to be a crucial factor in the still lower fire death rates in western Europe and Japan.
Leading Causes of Fire As noted, hostile fire requires an initial heat source, an initial fuel source, and usually a behavioral error. Therefore, causes can be defined and ranked in terms of any of these three components, as is done in Table 2.1.9 for structure fires. The cause categories shown are those that accounted for the largest number of civilian deaths per year in structure fires from 1994 through 1998. Many of these categories overlap. For example, “abandoning or discarding something” usually means smoking materials, and most open flame fires involve incendiary or suspicious causes or a child playing. Grouping choices also makes a difference. If the related behaviors of abandoning something, falling asleep, and leaving something unattended were combined, they would account for 980 deaths a year, nearly the largest total in Table 2.1.9. Homes and Garages. Table 2.1.10 provides a ranking of major fire causes for Homes and Garages. Smoking materials are the number one cause of civilian fire deaths, accounting for nearly one-fourth of deaths, and most begin with ignition of upholstered furniture, mattresses, or bedding. The ignitability of these items by lighted tobacco products has been declining for some time, due to a federal law restricting mattress construction and a voluntary program by the upholstered furniture industry. Incendiary or suspicious causes (i.e., arson and suspected arson) are the number one cause of property damage for home and garage fires, accounting for one of every five dollars lost. More than half of all the people arrested for arson are juveniles. Cooking equipment is the leading cause of home fires and home fire injuries, and is involved in the majority of unreported home fires. Unattended cooking is the principal behavioral factor. Heating equipment is the second leading cause of home fire incidents. Most involve portable or other space heaters; however, the current size of the heating fire problem is much smaller than the peak it reached shortly after the rapid growth in usage of portable and other space heaters in the 1970s and early 1980s. Child fire play, typically involving matches or lighters, accounts for only 1 of every 12 fire deaths, but it is the leading cause of preschooler fire deaths, accounting for more than 2 of every 5 such deaths. Electrical distribution system equipment accounts for a much smaller share of the home fire problem than many people realize, ranking no higher than fourth among the 12 major cause categories for any measure of loss, except for property damage, where it ranks second, reflecting the fact that many such fires are in concealed spaces and are hard to attack. The widespread use and enforcement of NFPA 70, National Electrical Code®, is probably the primary reason why electrical systems are not among the leading causes of fire. Moreover, even a fire cause such as this, which seems so totally an equipment problem, usually involves human error. One benchmark study found that 61 percent of home electrical fires involved code violations, particularly the general workmanship provisions.4 Exposed elements, such as cords, are even more subject to abuse by occupants. American Community. Arson and smoking dominate the ignition scenarios of fatal fires in the American Community, as Table 2.1.11 shows. Together, they accounted for half of all fire
CHAPTER 1
TABLE 2.1.9
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2–17
Major Causes of U.S. Structure Fires Reported to Fire Departments, 1994–1998 annual average Civilian Deaths
Cause
Civilian Injuries
Direct Property Damage (in million dollars)
Fires
Defined by Heat Source Smoking material (i.e., lighted tobacco product) Electric-powered equipment Open flame (e.g., match, lighter, torch, candle) Fueled equipment
990 970 820 640
2,540 7,670 5,550 3,580
430 2,484 1,563 1,149
35,400 208,900 106,000 119,300
Defined by Equipment Involved Heating equipment Electrical distribution system Cooking equipment
490 350 330
1,910 1,670 5,120
839 1,028 560
75,700 58,100 116,300
Defined by First Ignited Item Upholstered furniture Mattress or bedding Structural member or framing
640 540 320
1,670 2,890 880
272 373 1,111
15,000 29,700 48,700
Defined by Material in First Ignited Item Fabric, textile, or fur Wood or paper Flammable or combustible liquid
1,570 920 300
6,490 3,580 2,160
1,077 2,947 505
89,700 174,100 30,000
Defined by Behavior or Event Mechanical or electrical failure Incendiary or suspicious causes Abandoning something (e.g., cigarette) Child playing
670 640 610 300
3,700 2,530 1,960 2,170
2,078 1,680 374 284
158,300 94,500 35,300 23,500
Source: National estimates based on NFIRS and NFPA survey data.
TABLE 2.1.10
Major Fire Causes for Homes and Garages, 1994–1998 annual average Average Loss per Year
Major Cause Cooking equipment Heating equipment Incendiary or suspicious causes Other equipment Electrical distribution system Appliance, tool, or air conditioning Smoking materials Open flame Child playing Exposure (to other hostile fire) Other heat source Natural causes Total
Fires
Civilian Deaths
Civilian Injuries
Direct Property Damage (in million dollars)
92,500 59,700 53,600 44,200 39,100 29,600
22.0% 14.2% 12.7% 10.5% 9.3% 7.0%
330 460 580 270 350 130
9.3% 13.2% 16.4% 7.6% 10.0% 3.8%
4,610 1,630 1,950 1,580 1,360 970
25.3% 8.9% 10.7% 8.6% 7.4% 5.3%
397.3 557.8 829.8 522.8 622.5 255.1
8.9% 12.5% 18.5% 11.7% 13.9% 5.7%
21,900 20,800 19,300 18,100 13,400 8,700 420,900
5.2% 5.0% 4.6% 4.3% 3.2% 2.1% 100.0%
810 110 290 30 140 10 3,510
22.9% 3.2% 8.3% 0.9% 4.1% 0.3% 100.0%
1,990 720 2,070 170 1,090 130 18,260
10.9% 4.0% 11.3% 0.9% 6.0% 0.7% 100.0%
255.4 222.9 243.2 233.1 169.3 165.5 4,474.7
5.7% 5.0% 5.4% 5.2% 3.8% 3.7% 100.0%
Note: This ranking uses a hierarchical sorting procedure developed by analysts at the U.S. Fire Administration, which focuses on heat sources and behavioral causes. Results will be affected by the sorting rules used and the sequence in which unknown-cause fires are proportionally allocated to known causes and results by the property-use class are aggregated. Fires are expressed to the nearest hundred, deaths and injuries to the nearest ten, and property damage to the nearest hundred thousand dollars. Source: National estimates based on NFIRS and NFPA survey data.
2–18 SECTION 2 ■ Basics of Fire and Fire Science
deaths in these property classes from 1994 to 1998. Incendiary and suspicious fires (i.e., arson and suspected arson) are the leading cause for all four measures of fire loss specified in the table. Electrical distribution system components are also significant contributors to property damage due to fire in these properties. Cooking fires are a major problem in all properties where food or drink is served. They account for two out of every five fires in TABLE 2.1.11
eating and drinking establishments, but, even so, incendiary and suspicious fires account for the largest share of property loss. Industrial Environment. The many types of specialized equipment used in industry collectively accounted for the largest share of 1994 through 1998 structure fires and associated losses in the Industrial Environment, as Table 2.1.12 indicates. Incendiary and
Major Fire Causes in the American Community, 1994–1998 Average Loss per Year
Major Cause Incendiary or suspicious causes Cooking equipment Electrical distribution system Other equipment Appliance, tool, or air conditioning Heating equipment Smoking materials Open flame Exposure (to other hostile fire) Other heat source Natural causes Child playing Total
Fires 15,800 11,100 9,600 7,700 7,100 5,400 4,700 4,000 2,200 1,400 1,400 800 71,100
Civilian Deaths
22.3% 15.6% 13.5% 10.8% 10.0% 7.5% 6.6% 5.6% 3.1% 2.0% 1.9% 1.2% 100.0%
32 6 9 17 2 9 31 11 1 5 0 1 125
25.9% 4.4% 7.5% 13.5% 1.5% 7.1% 24.6% 9.1% 1.1% 4.2% 0.0% 1.1% 100.0%
Civilian Injuries 21.3% 13.7% 10.4% 12.1% 10.6% 6.5% 11.4% 7.0% 0.4% 3.3% 1.7% 1.5% 100.0%
420 270 200 240 210 130 220 140 10 70 30 30 1,970
Direct Property Damage (in million dollars) 341.4 67.0 169.0 143.0 53.9 86.9 42.1 74.0 59.5 56.8 38.3 5.5 1,137.4
30.0% 5.9% 14.9% 12.6% 4.7% 7.6% 3.7% 6.5% 5.2% 5.0% 3.4% 0.5% 100.0%
Note: This ranking uses a hierarchical sorting procedure developed by analysts at the U.S. Fire Administration, which focuses on heat sources and behavioral causes. Results will be affected by the sorting rules used and the sequence in which unknown-cause fires are proportionally allocated to known causes and results by the property-use class are aggregated. Fires are expressed to the nearest hundred, deaths and injuries to the nearest ten, and property damage to the nearest hundred thousand dollars. Source: National estimates based on NFIRS and NFPA survey data.
TABLE 2.1.12
Major Fire Causes in the Industrial Environment, 1994–1998 Average Loss per Year
Major Cause Other equipment Open flame Incendiary or suspicious causes Electrical distribution system Exposure (to other hostile fire) Natural causes Heating equipment Appliance, tool, or air conditioning Other heat source Child playing Smoking materials Cooking equipment Total
Fires 9,700 6,300 6,000 4,000 3,000 2,900 2,700 1,300 1,200 1,100 900 700 39,800
24.2% 15.8% 15.0% 10.1% 7.5% 7.3% 6.8% 3.2% 3.0% 2.8% 2.4% 1.8% 100.0%
Civilian Deaths 9 7 3 5 0 3 2 1 1 1 0 1 33
26.1% 22.5% 9.0% 16.2% 0.9% 9.9% 6.3% 1.8% 3.6% 1.8% 0.0% 1.8% 100.0%
Civilian Injuries 310 120 40 80 10 70 50 30 30 20 20 20 800
38.9% 15.3% 5.5% 10.1% 1.1% 9.0% 5.8% 4.2% 3.7% 2.2% 1.9% 2.2% 100.0%
Direct Property Damage (in million dollars) 383.7 156.0 283.6 151.1 50.0 86.6 74.3 27.7 27.1 8.9 27.3 26.2 1,302.7
29.5% 12.0% 21.8% 11.6% 3.8% 6.7% 5.7% 2.1% 2.1% 0.7% 2.1% 2.0% 100.0%
Note: This ranking uses a hierarchical sorting procedure developed by analysts at the U.S. Fire Administration, which focuses on heat sources and behavioral causes. Results will be affected by the sorting rules used and the sequence in which unknown-cause fires are proportionally allocated to known causes and results by the property-use class are aggregated. Fires are expressed to the nearest hundred, deaths and injuries to the nearest ten, and property damage to the nearest hundred thousand dollars. Source: National estimates based on NFIRS and NFPA survey data.
CHAPTER 1
suspicious fires ranked third in fire incidents and second on direct property damage. It is important to note, however, that these properties also had significant problems with open-flame fires (e.g., torches), electrical distribution systems, and heating equipment. Exclusive concentration on the more exotic hazards of any one industrial setting would be a mistake. Effective prevention requires a broad view encompassing all potential ignition scenarios. Other Properties. Postcollision fires and arson or suspected arson are the leading causes of fires and associated losses in vehicles, particularly for deaths, where they collectively account for more than half the total. Electrical system fires also are significant, as are overheated objects, such as tires, brakes, or exhaust pipes. Arson and suspected arson also is far and away the leading cause of outdoor fires in general and wildland fires in particular. Debris burning, careless handling of smoking materials, lightning, and children playing are other leading causes of wildland fires.
FIRE PROTECTION Recognizing that prevention will never be 100 percent successful, it is necessary to plan and design so as to mitigate damages when fire occurs. The various strategies to do this constitute what is usually called fire protection. It is important to remember that fire protection requires the development of an integrated system of balanced protection that uses many different design features and systems to reinforce one another and to cover for one another in case of the failure of any one. Defense in depth and engineered redundancy are concepts that also are relevant here. The process of achieving that integration, balance, and redundancy to attain fire safety objectives is the essence of fire protection engineering, including codes and standards. This means that success is not measured by the extent of use of any one technology or system or code. Success is measured by the extent of usage of effectively designed, integrated fire protection systems. No one system should be considered disposable, and no one system should be considered a panacea. Once fire has started, the first opportunity to reduce its impact comes in the design of burnable items, that is, the choice of materials and products and their environments. Both the growth of the fire from small to large and its spread along vertical or horizontal surfaces may be slowed through such design. Active fire protection systems provide the next opportunity. Automatic detection systems will tend to activate first, followed by automatic sprinklers or other automatic suppression systems, although this will vary depending on the design of the detection and suppression systems. Passive fire protection provides the final opportunity to stop the fire and smoke but also plays an essential role in providing automatic systems with a manageable fire to act on. Passive protection is designed to confine fire and smoke in zones, a concept called compartmentation. Special attention is given to protection of the building’s structural integrity and the spaces through which occupants will move to safety. Occupant evacuation depends on effective detection and a system to alert occupants, along with a total fire safety design that will defend the occupants where they are or provide protected routes to safe refuges, inside or outside the building. Evacuation also depends on the knowledge of the occupants.
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An Overview of the Fire Problem and Fire Protection
MATERIALS, PRODUCTS, AND ENVIRONMENTS If prevention fails, the first opportunity to reduce fire damage comes in the design of materials, products (including assemblies), and environments so as to slow down the growth and spread of fire. Tables 2.1.13 through 2.1.15 show that most structure fires never grow beyond the first involved room, but most deaths and property damage occur in the one-fourth of fires that do. This pattern holds for homes and for structures other than homes. Clearly, then, a fire that can be slowed in its growth
TABLE 2.1.13 Extent of Flame Damage Confined to room Beyond room, confined to floor Beyond floor Total
Sizes of Structure Fires, 1994–1998
Fires
Civilian Deaths
Civilian Injuries
Property Damage
70.4%
20.0%
59.1%
19.7%
4.6%
11.7%
10.5%
9.0%
25.1% 100.0%
68.3% 100.0%
30.4% 100.0%
71.3% 100.0%
Source: National estimates based on NFIRS and NFPA survey data.
TABLE 2.1.14 Extent of Flame Damage Confined to room Beyond room, confined to floor Beyond floor Total
Sizes of Home Fires, 1994–1998
Fires
Civilian Deaths
Civilian Injuries
Property Damage
72.7%
19.6%
57.2%
21.4%
5.3%
12.1%
11.3%
10.9%
22.2% 100.0%
68.3% 100.0%
31.5% 100.0%
67.6% 100.0%
Source: National estimates based on NFIRS and NFPA survey data.
TABLE 2.1.15 Sizes of Fire in Structures Other Than Homes, 1994–1998 Extent of Flame Damage Confined to room Beyond room, confined to floor Beyond floor Total
Fires
Civilian Deaths
Civilian Injuries
Property Damage
64.3%
26.2%
70.2%
17.0%
2.8%
5.4%
5.8%
6.0%
32.9% 100.0%
68.3% 100.0%
24.0% 100.0%
77.0% 100.0%
Source: National estimates based on NFIRS and NFPA survey data.
2–20 SECTION 2 ■ Basics of Fire and Fire Science
mable and Combustible Liquids Code. Unusually hazardous environments, such as oxygen-enriched atmospheres, also receive special attention.
so that it can be discovered and controlled before fire leaves the first room is likely to result in far less damage to people and property. (Injuries are something of an exception, as they are almost as likely to occur in small fires as in large ones.) The following are some of the fire protection approaches that may be taken under this overall strategy:
DETECTION AND ALARM
1. Restrict materials used in contents and furnishings.
The impact of automatic detection and alarm systems has been particularly great in the Homes and Garages environment. From less than 5 percent of homes having smoke alarms in 1972, the United States has risen to a position where 94 percent of homes had at least one smoke alarm in 19975 (Figure 2.1.13). Smoke alarms cut the risk of dying in a home fire nearly in half, and they do this despite the fact that one-fifth of smoke alarms—and one-third of smoke alarms in homes that have fires—are nonoperational (primarily because of dead or missing batteries), and many homes with smoke alarms do not have all the smoke alarms they need for code-compliant, every-level protection. Nevertheless, thousands of lives have been saved through the widespread use of home smoke alarms. This success has been achieved in several stages. The initial surge in smoke alarm usage was driven primarily by manufacturer advertising of an attractive, affordable product and secondarily by public service announcements promoting home smoke alarms. Since then, state and local laws have come along to help complete the process of equipping U.S. homes with smoke alarms, which is important, because more than 40 percent of reported home fires occur in the tiny fraction of homes without smoke alarms. In 1977, most states had no home smoke alarm requirements of any kind. By 1983, most states had a home smoke alarm law, but most states still did not cover existing single-family homes, by far the largest segment of the population. By 1988, most states had laws that extended to all homes, new or existing, but most still did not mandate codecompliant, every-level coverage. The trend in state laws is
• Reduce the heat release rate. • Reduce the smoke generation rate. • Prevent unusual toxic hazard relative to quantity of smoke generated. 2. Add fire retardant to materials. • Slow the growth of the heat release rate. 3. Use fire-resistive barriers. • Slow the spread of fire to large secondary items. 4. Restrict total fuel load. • Limit contents based on total fuel potential. 5. Restrict linings of rooms to prevent rapid flame spread. • Restrict wall coverings. • Restrict ceiling coverings. • Restrict floor coverings. 6. Restrict materials in concealed spaces. • Restrict concealed combustibles. • Restrict concealed space linings. 7. Require safe handling of large quantities of potential fuel. With regard to the last point, large quantities of combustible or flammable liquids or gases are the most obvious examples of materials that could make a small fire huge very quickly. It is important to handle and store these materials safely, following procedures such as those in NFPA 54, National Fuel Gas Code; NFPA 58, Liquefied Petroleum Gas Code; and NFPA 30, Flam-
100
Percent of households
90 80
74 67
70
77
81
90
93
94
93
92
88
85
82
76
86
67
60
50
50 40 30
22
20
Year
FIGURE 2.1.13 Growth in Detector Coverage, 1970–1997 (Sources for homes with detectors: 1977, 1980, and 1982 estimates from sample surveys by the U.S. Fire Administration; 1983–1995 estimates from “The Prevention Index,” a Louis Harris survey for Prevention Magazine; 1997 estimate from an NFPA fire awareness survey)
1997
1996
1995
1994
1992
1990
1988
1986
1984
1982
1980
1978
1976
1974
1972
0
1970
10
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An Overview of the Fire Problem and Fire Protection
100 90
82
Percentage of homes
80
74 67
70
76
77
85
88
90
86
71
70
69
92
2–21
93
81
67
73
76
60
60
55 50
50
45
46
55
48
40 29
30
22
U.S.A.
20
Sweden
16
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1983
1982
1981
1980
1979
1978
1977
0
1976
10
Year
FIGURE 2.1.14 Home Smoke Alarms, United States and Sweden (Source: Sweden Fire Protection Association)
clear—more complete and more thorough laws—but the process is still far from complete. As noted, nonoperational smoke alarms typically are that way because of dead or missing batteries. Frustration over nuisance alarms, which typically outnumber real fire alarms by an order of magnitude, may be a factor in battery removal. Sensitivity drift, which is a gradual shift in the range of fire effects that will activate the smoke alarms, is an example of the problems that can affect older units. Smoke alarms more than 10 years old should be replaced, and this affects tens of millions of units now in use. Figure 2.1.14 shows that the adoption of home smoke alarms in Sweden is proceeding at a pace about a decade behind the adoption pattern in the United States. The latest data are from the mid-1990s, when three-fourths of Swedish homes had at least one smoke alarm. The only other country with comparable data is the United Kingdom, which also lags behind the United States by roughly a decade. Three-fourths of U.K. homes had smoke alarms as of 1997. The success of smoke alarms in the home—and the importance of completing the job of providing complete coverage by operational smoke alarms in all homes—should not obscure the fact that automatic detection and alarm systems are an important part of an integrated system of fire protection in any property class. Major life-loss fires frequently cite problems with detection or alarm as significant contributing factors. Among the frequently cited problems in major fires with large loss of life are (1) the absence of needed systems, (2) misapplication, that is, using equipment or systems that were not appropriate for the property, (3) lack of maintenance, and (4) improper response by occupants to notification of the fire. In too many property classes, the majority of fires occur in facilities with no detectors. This is true, for example, for the majority of fires in public assembly properties, for two-thirds of store or office properties, and for two-thirds of industrial properties.
SUPPRESSION Automatic sprinklers are highly effective elements of fire protection systems design for buildings. When sprinklers are present, the chances of dying in a fire and property loss per fire are cut by one-half to two-thirds, compared to fires reported to fire departments where sprinklers are not present.6 Furthermore, this simple comparison understates the potential value of sprinklers, because it lumps together all sprinklers, regardless of type, coverage, or operational status. If unreported fires could be included, and complete, well-maintained, properly installed and designed systems could be isolated, sprinkler effectiveness would be seen as even more impressive. When sprinklers do not produce satisfactory results, the reasons usually involve one or more of the following: (1) partial, antiquated, poorly maintained, or inappropriate systems; (2) explosions or flash fires that overpower the system before it can react; and (3) fires very close to people who can be killed before a system can react. Except for health care facilities, hotels and motels (especially high rise), department stores, high-rise office buildings, and industrial sites, sprinkler usage is rare in properties with large potential for life loss. Sprinkler usage is growing in these properties, but most fires still occur in properties without sprinklers. Most reported fires in storage properties—even in generalpurpose warehouses—also occur in properties where sprinklers were reported as absent. There is considerable potential for expanded use of sprinklers to reduce the loss of life and property to fire. In recent years, particular attention has gone to quickresponse residential sprinklers for the home. The evidence of their potential for substantial reductions in loss of life and property is clear, but usage is still quite limited. Several communities have adopted requirements for these new sprinklers in new housing developments, and their experience provides the principal
2–22 SECTION 2 ■ Basics of Fire and Fire Science
real-world proof to date of the tremendous fire protection value such systems deliver. The suppression strategy for fire protection involves much more than home sprinklers or even sprinklers in general. Portable fire extinguishers are in use in roughly half of all homes and in many other properties, as well. Specialized, non-waterbased suppression systems, using alternative suppression agents or other design characteristics adapted to the special needs of a particular property class, also exist. In the second half of the 1980s, the world became aware of and concerned about the potentially adverse environmental impacts of suppression systems using halogenated agents (the so-called halon/ozone problem). This development has led to research on alternative fire protection technologies and new agents for critical electronic facilities. It also serves to underline the importance of considering major nonfire factors in any fire protection design.
CONFINING FIRES The design of building features to contain fires and their effects effectively is one of the most technically complex aspects of fire protection and is certainly the most difficult to evaluate statistically. In all the other phases—prevention, detection, suppression, evacuation—systems thinking also is essential, but it is at least possible to focus attention on one set of products or systems or occupants. But in fire confinement, systems thinking is both essential and unavoidable, because one must deal with every facet of building design and operation. One must consider not only the direct effects of wall assemblies, ceiling/floor assemblies, door assemblies, and the like on fire confinement but also their effectiveness in creating the design conditions assumed by every other part of the overall fire protection system. The effectiveness of detectors and sprinklers can be demonstrated to some degree by comparisons of fire experience in buildings that have these systems to buildings that do not. Unfortunately, however, every building has walls, floors, ceilings, and doors, and the various types of assemblies have proved too diverse to be routinely documented in the national fire databases. The best analysis possible with existing statistics shows that, for many property classes, the proportion of fires confined to the room of origin rises as the type of construction becomes TABLE 2.1.16
more fire protective, from unprotected wood frame to fire resistive. Problems with building in effective fire confinement tend to be more subtle, too. For detectors and sprinklers, the leading problem is turning off or disabling the equipment—a clear-cut, yes/no change that is easy to document. For fire confinement features, the problems tend to be more a matter of degree, that is, barriers partially breached for utility networks, some but not all doors blocked open, and so forth. Setting the context for this important strategy therefore must be approached in other ways. One is to point out the strong correlation between fire damage, that is, to life and property, and fire spread, as was done in Tables 2.1.13 through 2.1.15. Table 2.1.16 provides more evidence on this point, as it shows that the majority of fatal fire victims, including roughly 40 percent of the victims of fatal fires in structures other than homes, are located away from the room of fire origin. More than 25 percent of the victims are on another floor from the point of fire origin. What these figures indicate is that there are still many fatal victims of fire who might be saved by strategies that block or delay the passage of fire and smoke between rooms and floors—strategies of fire protection design for fire confinement. Patterns are quite different in the United Kingdom. Whereas a substantial majority of fatal U.S. fire victims are located outside the room of fire origin, a clear majority of fatal U.K. fire victims are located in the room of fire origin. Part of the reason may be that U.K. dwellings typically use a less open floor plan, with more separation of rooms by walls and doors. By keeping these doors closed to lower heating costs, U.K. households would also be expected to reduce the spread of fire and smoke beyond the room of origin, thereby reducing the number and share of fatal victims outside the room of fire origin as well. Some of the options available for fire confinement are the following: 1. Use construction barriers to block fire spread between zones. • • • • •
Wall assemblies Ceiling/floor assemblies Barriers between occupied and concealed spaces Firestopping in concealed spaces Exterior barriers to vertical spread between floors
Locations of Fatal Victims of Structure Fires, 1994–1998 Victim Location Relative to Fire
Intimate with ignition Not intimate, but in same room Not in room, but on same floor Not on same floor, but in building Outside building of origin Unclassified and other known Total
Structures 2,506 3,773 4,710 4,046 146 164 18,719
16.3% 24.6% 30.7% 26.4% 1.0% 1.1% 100.0%
Source: National estimates based on NFIRS and NFPA survey data.
Homes 2,271 3,524 4,546 3,879 127 151 17,492
15.7% 24.3% 31.4% 26.8% 0.9% 1.0% 100.0%
Structures Other Than Homes 235 249 164 167 19 13 1,227
27.7% 29.4% 19.4% 19.7% 2.2% 1.5% 100.0%
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2. Design doors and windows to block fire spread between zones.
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An Overview of the Fire Problem and Fire Protection
the design of programs. But the fight for American fire safety will largely be won or lost in these areas.
• Fire door assemblies • Window restrictions to block spread between buildings 3. Separate buildings enough to prevent fire spread between buildings. 4. Regulate design and operations of ducts to permit shutoff of air movement in fires. 5. Regulate design and operation of systems for heating, venting, and air conditioning to prevent their serving as mechanisms to transfer smoke and gases into uncontaminated, occupied areas. Barriers around concealed spaces are of importance for two reasons. First, fires in concealed spaces cannot hurt people until smoke or flames break out into occupied spaces. Second, fires in occupied spaces may spread faster if they break into concealed spaces because many interior barriers do not extend into concealed spaces. For example, fire may spread vertically through concealed wall spaces if they are not firestopped at each floor or horizontally through concealed floor/ceiling spaces if the walls do not extend past the suspended ceilings that many buildings have below their main ceilings. Exterior flame spread can occur in several ways, all of which must be addressed. Flying brands or heat from other fires can ignite exterior materials. Flames from one floor can “lap” up the exterior walls to ignite combustible materials on other floors by radiation from flame fronts. Large losses of life or property are virtually unknown in buildings that comply with the fire protection requirements of modern codes. This is clear evidence of their effectiveness. Nevertheless, large losses continue to occur because so many buildings are not in compliance with modern codes. A major reason is the frequent exclusion of existing buildings from many requirements by “grandfathering” or a lack of retroactive application of codes. Even where good codes are on the books, enforcement may be hurt by a scarcity of resources in overburdened building and fire departments. And some communities do not routinely update their codes, which can create areas of vulnerability. Sustained, consistent attention to fire safety is key to the long-term success of an integrated system design for fire protection. Furthermore, universal application is essential to make a substantial impact on the fire problem. Balanced fire protection really works, but there are no simple, one-time quick fixes. The installed system must be maintained every day. If this is done, however, such systems will virtually eliminate large losses of life or property. In fact, very large fires usually involve multiple major failures of fire protection design, but sometimes one or two deficiencies can be enough to produce disaster in a building with many excellent features. Remember that fire protection succeeds or fails as a system and is therefore only as sound as its weakest link. Universality means, in simple terms, that any successful program must go where the fires are, including poor neighborhoods, rural communities, big-city neighborhoods, preschoolers, the elderly, and existing buildings. These are among the hardest groups to reach and the most frequently overlooked in
2–23
EVACUATION OF OCCUPANTS Most fire protection strategies are designed to slow or divert the movement of smoke and fire, not stop it, so key questions are whether, where, and how to move the occupants. The occupant evacuation strategy, which includes defending in place and safe interior refuges as possibilities, involves both building design principles and behavioral/educational elements. The building design principles include the following: 1. 2. 3. 4.
Two ways out from any location Adequate numbers, sizes, and spacing of exits Adequate capacity of all escape route parts Protection for escape paths • • • • •
Mark exit paths clearly and light them. Restrict fuel loads and finishes in exit paths. Enclose stairways. Use construction barriers to keep fire out. Use smoke control methods to protect atmosphere in exit paths. • Ensure structural integrity of exit path. 5. Escape to outside or to protected places, or adequate defense of places where occupants should remain 6. Avoidance of makeshift security systems Protection of the exit paths begins with construction barriers to separate hallways from other rooms where fire may begin. Stairways need to be enclosed to separate them from all other spaces. Exits from any room or area must be adequate for the number of people those exits will serve. This dictates minimum numbers and sizes of exits. Multiple exits from a room must be sufficiently separate to provide two distinct paths from the room to the outside so that escape will still be possible if one escape route is blocked. The paths themselves must not involve long distances, which dictates maximum distances from any occupied room to a stairway access or to access to some other protected area. Restrictions on the fuel loads and finishes in areas that serve as parts of exit paths also are needed to prevent rapid spread of fire into and through these paths. Once the building is designed for safe evacuation, the occupants have to be educated about the principles of escape behavior: 1. Know whether to escape and where to go (e.g., stay in place, go to safe refuge, go outside). 2. Know two ways out. 3. Get out fast. 4. Practice escape. 5. Check paths for safety before proceeding (e.g., feel the door). 6. Crawl low under the smoke. It is worth emphasizing the need for practice. Learning the rules of safe escape as slogans is not enough. (That is why it is a matter of concern that in 1999 three-fourths of U.S. households had not developed and rehearsed an escape plan.) If fire
2–24 SECTION 2 ■ Basics of Fire and Fire Science
occurs, one doesn’t have time to make the mistakes that typically occur during learning. To use an analogy, suppose one has read about driving a car and even passed the state’s written test. One does not want the first time behind the wheel to be a drive to the hospital emergency room. The lack of learned confidence in the key behavior could cost time when it can be least afforded. Most people have not seen a real hostile fire. They have no idea how fast fire can grow or how bad it can get. They are not familiar with the phenomenon of flashover. Therefore, they spend time they cannot afford confirming that there is a fire or gathering up valuables. They also tend to try to leave by their customary route, even in the face of serious fire hazard. Rehearsing safe behaviors is the only way to be sure that they will be used when necessary. Special mention should be made of the problems posed by unusually vulnerable groups. Small children will need help to escape and are likely, on their own, to think hiding makes them safe. People who are elderly, handicapped, or impaired by substance abuse are likely to have physical or mental limitations that may present a need for help in escaping. Patients in health care facilities and inmates of confinement facilities present the largest problem, as they are large groups that cannot evacuate on their own. Specific plans need to be developed and rehearsed to address these situations.
SYSTEMS APPROACHES FOR PROPERTY CLASSES In applying the general principles of fire protection, it usually becomes clear that particular property classes have special considerations that must be understood for an effective systems approach. Some of these special considerations are briefly summarized next.
Homes and Garages Fire death rates in the biggest cities are 25 to 50 percent higher than in the small cities, but fire death rates in rural communities of less than 2500 population are triple the rates in the smallest cities. The unusually high fire risk in rural communities is one of the hidden parts of the U.S. fire problem. The peak rates in very small and very large communities are explained by the fact that poverty rates are highest in these two sizes of communities. The South has the highest fire death rates in the United States (25 percent above the national average in the period from 1995 through 1999). This is in large part because that region has proportionally more rural poverty than any other U.S. region. However, the South has been closing that gap. Several of the states in the South have been pursuing statewide fire safety initiatives as ambitious as anything undertaken anywhere in the United States, and the results are only just starting to appear in lower fire death rates. Fire death rates are highest for preschool children and older citizens. Preschool children have more than twice the fire death rate of the population as a whole. At the other end, fire death rates begin climbing at age 50 and climb higher and higher as people age. People age 65 and over have fire death rates twice the national average. People age 75 and over have fire death
rates three times the national average. People age 85 and over have fire death rates four times the national average. Because fire deaths occur primarily in Homes and Garages, patterns like these are true for those fire deaths and for all fire deaths, as well.
American Community Community activities often concentrate large numbers of people, creating the risk of large loss of life should a fire occur in the properties that make up the American Community. For this reason, properties in the American Community are generally subject to legally binding codes, such as NFPA 101®, Life Safety Code®. Historically, fires resulting in a major loss of life have resulted in important changes in building and fire codes and in standard fire protection or prevention practices. In the early 1900s, four building fires—the Iroquois Theatre in Chicago (1903), the Rhoades Opera House in Boyertown, Pennsylvania (1908), the Lakeview Grammar School in Collinwood, Ohio (1908), and the Triangle Shirtwaist Factory in New York City (1911)—were largely responsible for the appointment in 1913 of the NFPA Committee on Safety to Life. The opening summary of the “Origin and Development of 101” in the current NFPA 101®, Life Safety Code®, states: For the first few years of its existence, the Committee devoted its attention to a study of the notable fires involving loss of life and in analyzing the causes of this loss of life. This work led to the preparation of standards for the construction of stairways, fire escapes, etc., for fire drills in various occupancies, and for the construction and arrangement of exit facilities for factories, schools, etc., which form the basis of the present Code. The 1937 fire at the Consolidated School in New London, Texas, tragically pointed out the need for state laws to protect public buildings not subject to municipal ordinance and inspection. Then, in the 1940s, a series of multiple-death fires—including those at The Rhythm Club; The Cocoanut Grove; and the La Salle, Canfield, and Winecoff Hotels—focused national attention on the need for adequate exits and other fire safety features in hotels and public buildings. These fires resulted in major changes to the Building Exits Code (as NFPA 101, Life Safety Code, was then known) over a period of almost 2 decades. NFPA 102, Standard for Grandstands, Folding and Telescopic Seating, Tents, and Membrane Structures (included in NFPA 101 since 1994), was the result of still another multiple-death fire of the 1940s—the 1944 Hartford, Connecticut, circus tent fire in which 168 people were killed. Three hospital fires—St. Anthony’s in Effingham, Illinois, in 1949 (74 killed); Mercy Hospital in Davenport, Iowa, in 1950 (41 killed); and Hartford Hospital, Hartford, Connecticut, in 1961 (16 killed)—moved hospital administrators and fire prevention officials across the nation to assess the quality of construction and fire protection systems in hospitals. The Our Lady of the Angels School fire in Chicago on December 1, 1958, probably resulted in the swiftest action in the wake of any major fire since World War II. Within days of the
CHAPTER 1
fire, state and local officials throughout the nation ordered fire inspections of schools, and within 1 year, it was reported that major improvements in life safety had been made in 16,500 schools across the country. Improvements in the frequency and quality of exit drills and inspections, in the storage of combustible supplies, and in the disposal of waste materials were also reported in almost every community where schools were surveyed. This fire and the 1961 Hartford Hospital fire, which killed 16 people, also focused attention on the hazards of combustible ceiling finishes. During a 4-year period from 1970 to 1973, there were eight care-of-aged facility fires, each killing at least 10 people and collectively killing 112 people. This rapid succession of catastrophic fatal fires stimulated action in a way that the deadliest nursing-home fire of all time, which occurred in isolation at the Golden Age Nursing Home of Fitchville, Ohio, on November 23, 1963, and killed 63 people the day after President John F. Kennedy was assassinated, could not. A pattern was found of insufficient fire protection and sprawling, undivided construction based on adding extensions to aging, converted farmhouses. Codes were reexamined, and the new Medicare program provided clout by tying reimbursement eligibility to code compliance with NFPA 101. During the period from 1976 through 1985, attention shifted to boarding homes, spurred by a rash of major fatal fires in those facilities in 1979 through 1981. Six severe fires, causing 114 deaths in all, with the first three fires all occurring in the same month, commanded attention. During the period from 1979 to 1984, boarding home residents had a risk of dying in a multiple-death fire that was five times the risk for residents of other residential properties. Analysis of these incidents and other smaller fatal fires showed that many of the residents had characteristics of age or chronic mental illness that should have received ongoing medical attention that the facilities were not licensed or equipped to provide. This gap between the fire protection and other features of the facilities and the needs of their occupants was a more difficult problem than the one posed by the nursing home fires because there were fewer mechanisms to enforce codes. The factors in what came to be called the “board-and-care” home fire problem were all too familiar and can be summarized as an overall lack of basic fire protection provisions. Contributory factors include inadequate means of egress, combustible interior finishes, unenclosed stairways, lack of automatic detection or sprinkler systems, and lack of emergency training for the staff and residents. Many of the facilities were either licensed as something other than a boarding home (such as a hotel) or were unlicensed, “underground” boarding homes. None of the facilities was provided with automatic sprinkler protection. There is no particular mystery about how to reduce these risks, either. Enclosed stairs, providing two ways out, avoiding the use of combustible interior finishes, compartmentation, providing automatic detection and sprinkler systems, and training staff and residents in emergency procedures all would greatly reduce the risk of multiple deaths if fire occurs. These analyses and others (such as an NFPA study of 2 decades of hotel fires causing 10 or more deaths, done for Congressional testimony) consistently point to the difficulty of de-
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An Overview of the Fire Problem and Fire Protection
2–25
livering fire protection to and enforcing codes and standards on the facilities that cater to the poorest and most vulnerable populations. Simply creating and adopting good codes and standards is not enough. State and local authorities must adopt them and enforce them, being sure to pay attention to existing buildings, or this knowledge will lack practical impact where it is most needed. But although fire safety professionals stay aware of the difficulties and challenges still to be met, it is useful to look back at what has been accomplished, which is considerable. The next major section of this chapter, entitled “A Century of Accomplishment,” does just that. Our American Heritage. Special mention also should be made of the small part of the American Community referred to as Our American Heritage. Our American Heritage includes historic buildings, museums, art galleries, and memorial structures. Such structures often attract large numbers of visitors. Because many of these structures are owned and operated by nonprofit charitable organizations, funds for fire protection are often limited. In addition, many historic structures are located in remote areas where public protection is minimal at best. Museums and art galleries incorporate the special hazards of workrooms for restoration and storage. Also, many properties that are not wholly devoted to historical preservation contain major areas of historical importance. The large-loss fire in the Los Angeles Central Library in 1986 was a recent reminder of this point, as a number of unique collections were destroyed, damaged, or endangered. There is a tendency to forget the vulnerability to fire of these vestiges of Our American Heritage that were so important to our ancestors and will be important to future generations. The small share of total dollar loss they typically represent does not begin to capture what the real loss of fires in such facilities can mean to U.S. culture. The actual loss sustained when artifacts and ancient structures burn cannot be measured in dollars alone. Since 1980, fires damaged or destroyed many historic buildings. Included are the Paul Revere house in Boston, Massachusetts; the Wayside Inn in Sudbury, Massachusetts; Sutter’s Mill in Sacramento, California; the Daniel Boone dwelling in Defiance, Missouri; the Franklin Roosevelt home in Hyde Park, New York; the Legislative Office Building in Concord, New Hampshire; the John C. Calhoun mansion in Clemson, South Carolina; Hundred Oaks Castle in Winchester, Tennessee; the Confederate Memorial Building in Greenwood, Mississippi; the Benbow Hall dormitory of Oak Ridge Military Academy in Greensboro, North Carolina; a barn on President Dwight D. Eisenhower’s farm in Gettysburg, Pennsylvania; a historic lace mill in Patchogue, New York; the Phoenix Opera House of Rushville, Illinois; the Atlanta, Georgia, home where Margaret Mitchell wrote Gone with the Wind; the Santa Fe Railroad depot of Emporia, Kansas; and the Wingfield Mansion of Reno, Nevada.
Mobile Environment The principal point of interest about the Mobile Environment fire problem is how large it is, relative to every other environment but Homes and Garages. As Figure 2.1.10 shows, the Mobile Environment fire death toll dwarfs all other properties
2–26 SECTION 2 ■ Basics of Fire and Fire Science
combined, excluding the roughly 80 percent in Homes and Garages. Figure 2.1.11 shows the Mobile Environment fire injury toll is second only to Homes and Garages, and Figure 2.1.12 shows the Mobile Environment fire damage total is comparable to the structure environments other than Homes and Garages. Fire safety programs and requirements for the Mobile Environment have been almost entirely delegated, by NFPA and others, to the federal government. The majority of vehicle fire deaths occur in postcrash fires, and the death toll is far less than in the crashes themselves, so the difference may be understandable. Nevertheless, the mission of fire safety must encompass vehicles, which are a large, and increasingly large, share of the total. Some special issues and trends pertain to the Mobile Environment. One development of the past 2 decades has been an increased use of recreational vehicles, such as campers and trailers for travel, and tents for lodging. This increased usage creates a potential for increased fire hazard in these recreational-type properties, but so far the actual fire experience has been small by comparison to other road vehicles. For example, of the 302,210 passenger road vehicle fires per year that occurred during the period from 1993 to 1997, 2450 involved motor homes (not mobile or manufactured homes, which typically stay in one place), 2400 involved all types of all-terrain vehicles (including motorcycles, golf carts, dune buggies, and snowmobiles), and 1250 involved travel or camping trailers. Collectively, they represented roughly 1 out of every 50 passenger road vehicle fires. (Tents and other similar outdoor sleeping quarters contributed at most 60 fires a year to the structure fire total.) Another concern that is so far based more on changing activity patterns than on confirmed fire problems is the increasing use of automobile fuels other than gasoline and diesel (e.g., LPgas, LNG, and CNG). These new fuels introduce hazards with which the public and authorities are not totally familiar. Changes in transportation preference, such as the growing use of public transportation, have opened up new problems for fire protection. The fire potential problems of public transportation center on equipment design and materials, as well as the growing dependency on automation. Transportation of raw materials and finished goods throughout the nation and in U.S. coastal waters by common carriers represents the potential for substantial economic loss if fire destroys the materials transported or the vehicles in which they are being moved. This type of transportation at the interstate level is subject to federal regulation. Another key area is hazardous materials. This problem not only poses the potential for costly loss, but, more importantly, carries with it substantial risk to public safety. Hazardous materials often are transported over land, even through highly congested urban communities. The fire record shows an abundance of examples of disastrous accidents involving hazardous materials transportation. Air transportation also is regulated by the federal government, with regard to the level of fire safety in aircraft design and fire potential following ground impact. Other fire protection concerns associated with air transportation include fuel servicing, aircraft maintenance, design of airport facilities, and aircraft rescue and fire-fighting techniques.
Outdoor Environment A significant part of our great heritage is that created by nature. Forests and wildlands represent resources that have been recognized nationally in legislation as a part of our American heritage only since the days of Theodore Roosevelt’s presidency (1901–1909). Forests and open lands provide raw materials, recreational facilities, and scenic breaks from the urban sprawl. Great portions of the U.S. landscape, including wildlands, forests, and deserts, are under the control of the U.S. Department of Agriculture. Bureaus of this federal agency have their own regulations, which include fire prevention and suppression programs. Wildland fires are once again much in the news. Environmental trends have produced a succession of years that are among the hottest and driest on record in the United States. These weather conditions have combined with the expanded scale of activity in the wildland/urban interface to produce a number of very large property-loss fires, as seen in Tables 2.1.6 and 2.1.7. These major wildfires have also taken a toll in fire fighters’ lives, most notably in 1994 when more than 30 fire fighters died on duty at or while responding to, or returning from, wildland-related incidents, roughly a third of the total on-duty fire fighter death toll for that year. These figures point to a devastating toll of life and property that deserves the increased level of attention it has recently received through federal/private cooperative efforts, such as the Wildland/Urban Interface Program.
A CENTURY OF ACCOMPLISHMENT NFPA has been a force for fire protection and fire safety for the past 100 years. In that time, most of NFPA’s influence has come through its codes and standards, which have changed the rules that guide building specifications and operations and, in that way, have changed the environments in which people live. As in past editions of the Fire Protection Handbook, this edition cites examples of major NFPA code changes that responded to needs demonstrated in major fire incidents. This section describes several of the most dramatic examples of fire experience that responded favorably to changes in codes or to changes in the extent of compliance with codes. The literally hundreds of thousands of people who have been part of the NFPA “family” since 1896 have helped to save untold lives from the scourge of unwanted fire. What follows is some of the clearest evidence available of that good work. Because most codes and standards focus on the risk of large fire losses outside the home, this section focuses on major incidents outside the home involving multiple loss of life. In particular, NFPA’s fire incident record-keeping is best for incidents in which 10 or more people died, and these incidents are used here as the principal tracking mechanism for the impact of codes, standards, and other fire protection requirements. In keeping with the normal approach used by NFPA’s statisticians, most incidents are cited anonymously, to keep the emphasis on statistical patterns. In general, only incidents involving 50 or more deaths are given specific identifiers.
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Schools and Hospitals Since NFPA was founded in 1896, NFPA’s fire incident records show a total of nine school fires in which at least 10 people died. Two of these are among the 10 deadliest single-building fires in U.S. history. The first of the nine was also the only one not to involve grades K–12. It was a 1903 university building fire in which 11 people died. NFPA files indicate the building had no fire exits and escape was cut off. The second incident, in 1908, was also the second deadliest school fire in history. Inadequate fire escapes, inadequate fire drills, and a building layout that created bottleneck exit paths all contributed to the death toll of 176 at the Lakeview Grammar School in Collinwood, Ohio. A parochial school fire in 1915 was the third of the nine fires and cost 21 people their lives. After the fact, the exits were deemed inadequate, even though they complied with existing laws. Again, the failure to include all exits in fire drills made those drills inadequate and proved critical in this fire, as many exits were not used when they could have made a difference. The first of three incidents in the 1920s was a 1923 fire that killed 77 people. Fleeing occupants jammed the only stairway serving the Cleveland School of Beulah, South Carolina, and it collapsed during the evacuation. A 1924 fire in a one-room schoolhouse spread rapidly from its origin in a Christmas tree. The fire department’s report of the fire said, “the struggling crowd became wedged in the doorway, which was only 3 ft (0.9 m) wide.” A total of 33 people died. Finally, a 1927 incident led to 46 deaths when a “crazed farmer” used dynamite to bomb a school. The deadliest school incident in history stemmed from a gas explosion; 294 people died in the Consolidated School of New London, Texas, in 1937. The next school incident killing at least 10 people came in 1954, when a faulty heating system led to a gas buildup in the attic of a school. Ignition by an undetermined heat source produced a flash fire in an unoccupied area. Delayed discovery allowed the fire to spread into occupied areas, and 15 people died. The last three incidents took place over 2½ decades, from 1927 to 1954, and all three involved rapidly developing situations—two explosions and a flash fire—that were unlike the earlier incidents. Officials might have been forgiven for believing that the older school fire problem, consisting of too many ordinary combustibles and insufficient or inadequate exits, was essentially under control. If so, that belief proved illusory when the 1958 Our Lady of the Angels School fire occurred in Chicago, Illinois, killing 95 people, 92 of them children. The reaction to that fire was more rapid, more sweeping, and arguably more effective than the reaction to any other single fire in U.S. history. NFPA codes and standards were quickly revisited, and stricter requirements for interior finish and exiting were established. An April 1959 issue of the Journal of American Insurance caught the mood of the country at the enforcement end, noting in an article subhead: “U.S.A., aroused by Chicago lesson, is overhauling its school buildings as never before.” In the nearly 4 decades since Our Lady of the Angels fire, there has never been another school fire killing 10 or more peo-
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ple. In recent years, no incident has even come close. In the period from 1994 through 1998, grades K–12 averaged one civilian fire death per year—a typical annual death toll for schools since at least 1980. Detailed examination of fatal school fires by NFPA analysts indicates that the few deaths that do occur are all or nearly all adults (e.g., maintenance workers) or juvenile firesetters fatally injured by the fires they set. Innocent children are no longer the victims in school fires. Few lessons have been learned as thoroughly as the ones from the Our Lady of the Angels incident appear to have been learned. A similar story applies to U.S. hospitals. There were a similar number of incidents in which 10 or more people died, including a 1929 fire that killed 125 people in the Cleveland Clinic Hospital of Cleveland, Ohio, and a 1949 fire that killed 74 people in St. Anthony’s Hospital of Effingham, Illinois. The last hospital fire to kill 10 or more people was the Hartford Hospital fire of 1961, in which 16 people died in Hartford, Connecticut. Reports on the fire focused on combustible ceiling tile that led to rapid flame spread down a corridor, delayed reporting to the fire department, and the fact that all the deaths involved doors left open to the corridor. Closed doors meant survival in every case. The NFPA Building Exits Code of 1961 already mandated complete sprinkler systems for hospitals for many combinations of height and construction. The next edition after the Hartford Hospital fire was the 1963 edition, which extended this requirement to even more combinations of height and construction. The 1966 edition changed the name of the document to a wordier version of today’s NFPA 101 signaling right from the cover that this code was not just about exits, as it had not been for some time. By 1980, when NFPA first developed its nationally representative statistics on the use of sprinklers in buildings that had fires, nearly half (43.5 percent) of all fires in facilities that care for the sick were in properties with sprinklers. This undoubtedly meant that most hospitals were sprinklered by then, because it is known from occasional special studies on sprinkler usage that reported fires are more likely to occur in unsprinklered properties. By 1997, the latest year for which statistics are available, 71.7 percent of fires in facilities that care for the sick were in properties with sprinklers, and 91.8 percent were in properties with automatic fire detectors. This equipment was making a measurable difference. For example, statistics from 1988 through 1997 indicated that sprinklers cut the chances of dying in a fire by 64 percent in facilities that care for the sick. Since hospitals are required to comply with NFPA 101 to receive reimbursement under Medicare and Medicaid, other provisions of NFPA 101 are undoubtedly also in nearly universal use. This helps explain why, in the latest available statistics, hospitals averaged fewer than seven civilian fire deaths per year between 1989 and 1993. As in the case of schools, the characteristics of the people who still die in hospital fires underline the extent to which NFPA codes have solved the type of hospital fire problem they targeted decades ago. About four of every five hospital fire deaths involve a victim who is so close to the start of the fire as to be described as “intimate with ignition.” Smoking and incendiaries dominate
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the causes of fatal fires in facilities that care for the sick. These circumstances involve very rapid fatal injuries, often too rapid to be reliably prevented by even the best fire protection provisions. Fire prevention strategies are needed and, indeed, the past decade has seen widespread adoption of more aggressive controls and prohibitions on smoking.
Hotels and Motels From 1900 to the present, 4 of the 101 U.S. fires and explosions that killed at least 50 people involved hotels or motels. This compares to 8 in industrial settings, 5 that involved ships, 2 that involved industrial settings and nearby ships, 8 that involved places of assembly, 4 in schools, and 59 in mines. (The other 11 were 2 forest fires, 2 hospital fires, 2 nursing home fires, 1 prison fire, 1 missile silo incident, 1 office building bombing, 1 in-flight aircraft fire, and 1 postearthquake fire.) Three of the 4 hotel fires occurred in a 4-year period, 1943 through 1946—the Gulf Motel fire in Houston, Texas, in 1943, which killed 54 people; the LaSalle Hotel fire in Chicago, Illinois, in 1946, which killed 61 people; and the Winecoff Hotel fire in Atlanta, Georgia, in 1946, which killed 119 people. National conferences on hotel fire safety were convened in early 1947, one by NFPA and another by President Harry Truman; the result included significant change to the hotel section of NFPA’s Building Exits Code and model legislation for hotel fire safety, prepared by the Fire Marshals Association of North America, NFPA’s member section for fire marshals. A third of a century later, the 1980 MGM Grand Hotel fire, in Las Vegas, Nevada, inspired an industry response that combined unprecedented widespread code compliance with fire safety provisions that often ran ahead of code requirements. The result has been a dramatic change both in the fire death toll in hotels and motels and in the use of proven fire protection systems in that industry. In 1981, NFPA published an overview of hotel and motel fire experience leading up to the 85 deaths in the MGM Grand Hotel fire. In the 2 decades from 1961 through 1980, NFPA documented 53 hotel or motel fires that each killed at least five people. (In those days, the threshold for a multiple-death fire was 3 deaths in any property; today, it is 5 deaths in residential properties.) With more than two fires a year causing at least 5 deaths apiece, chronic public concern over fire safety when traveling was understandable. The MGM Grand Hotel fire was not the only fire that shaped public concerns at this time. Certainly, the MGM Grand Hotel fire ran counter to the conventional industry wisdom that fire problems were primarily a matter of older or poorer facilities. MGM Grand was neither. But the MGM Grand fire also was not an isolated incident. Two months after the MGM Grand fire, a second Las Vegas, Nevada, hotel, this one part of a national chain, had a fire that killed 8 people. Then, the year after that, 12 more people died in a fire in another hotel of the same chain. A second chain lost 10 people in each of two fires during each of the 2 years preceding the MGM Grand Hotel fire. All these events combined to create a picture of an industry in need of improvement. Led by strong industry associations and fire safety–conscious professionals at the major chains, the industry began to respond.
In 1980, the year of the MGM Grand Hotel fire, sprinklers were reported present in only one of every nine hotel or motel fires reported to U.S. fire departments. Detectors were reported present in just over one-fourth of reported hotel or motel fires. By 1997, sprinklers were reported present in one-third of hotel and motel fires and in two-thirds of high-rise hotel fires. An industry-sponsored study of sprinkler usage in 1988 found sprinklers present in roughly half of all properties, suggesting the percentage today is much higher still. By 1997, detectors were reported present in three-fourths of all hotel or motel fires. And for both detectors and sprinklers, it is reasonable to assume that the new level of built-in fire protection had much to do with the dramatic drop in the number of hotel and motel fires since 1980. NFPA statistics from 1988 through 1997 indicated that sprinklers cut the chances of dying in a given fire by 91 percent and also reduced the average property loss per fire by 56 percent. In terms of the deadliest fires, beginning in 1983, only two hotel or motel fires have killed 10 or more people, and each of them was on the outer fringes of the industry. A 1984 fire killed 15 people in a facility that called itself a rooming house but was classified as a hotel by NFPA because it had too many occupants to qualify as a rooming or boarding house. This facility also included a number of de-institutionalized former mental patients among its occupants, raising questions about the health care needs of the occupants versus the fact that no such care was provided by the facility. A 1993 fire killed 20 people in a facility licensed for, and principally run for, long-term residents; yet the fire began in, and most deaths occurred in, a section housing transient guests. In terms of the more familiar names in the lodging industry and the bulk of the facilities in operation, the changes of the past 15 years have moved the fire experience picture in hotels and motels to roughly the same position as nursing homes and hospitals. That is, a steadily shrinking number of fatal victims tend more and more to be people who die in fires they caused or that began very close to them. In the period from 1993 through 1997, for example, half of all hotel and motel fire deaths resulted from fires started by smoking materials or associated lighting implements (i.e., matches, lighters). As with schools and hospitals, so with hotels and motels: the past century has seen dramatic accomplishments—a clear sequence from major fires to major code changes to major changes in the practices in the concerned facilities to major declines in the loss of life due to fire.
Places of Assembly Seven of the 11 deadliest single-building fires and explosions in U.S. history have involved places of assembly. (The other 4 were 2 school fires discussed above, 1 prison fire, and the 1995 bombing of an Oklahoma City, Oklahoma, office building.) They include the Brooklyn Theater fire of 1876, which killed 285 people and preceded NFPA’s founding. Both the Iroquois Theater fire of 1903, which killed 602 people in Chicago, Illinois, and the Rhoades Opera House fire of 1908, which killed 170 people in Boyertown, Pennsylvania, occurred early in NFPA’s life and led to an early focus on the dangers posed by inadequate exiting provisions and the kinds of combustible loads that make rapid fire development likely.
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From 1909 through 1939—a period of more than 3 decades—three incidents killed 10 or more people in places of assembly, one of which involved an explosion. A 1919 Louisiana restaurant and dance hall fire led to 25 deaths when relatives rushing into the building to try to save occupants collided with occupants fleeing onto the only exit stairway, leading to the collapse of that stairway. A 1928 dance hall incident started by ignition of gasoline fumes, and killed 38 people. A 1929 nightclub fire spread rapidly via the decorations, and many of the 22 who died took refuge in rooms with no way out. In 5 years, from 1940 to 1944, three of the worst fires in U.S. history occurred, all involving places of assembly. More than one-fourth of the 746 occupants of the Rhythm Club in Natchez, Mississippi, died in a 1940 fire. Overcrowding, inadequate exits, and highly combustible decorations were all cited as factors in the 207 deaths. Nearly half of the more than 1000 occupants of the Cocoanut Grove nightclub in Boston, Massachusetts, died in a 1942 fire. Overcrowding, inadequate exits, and highly combustible decorations again were cited as key factors in the 492 deaths, with roughly 200 trapped behind one revolving door alone. And 168 of the roughly 7000 patrons at the Ringling Brothers Barnum & Bailey Circus in Hartford, Connecticut, died in a 1944 fire, many of them children. These three incidents, particularly Cocoanut Grove, the sixth deadliest fire or explosion in U.S. history, are credited with inspiring a rush of tougher codes, focusing on exiting provisions and the use of combustible materials, but also pushing a more comprehensive and appropriate definition of places of assembly. Incredibly, many jurisdictions excluded eating and drinking places from the classification “place of assembly” prior to Cocoanut Grove. In the half-century since 1944, no incident in a place of assembly has matched the death toll in any of these three incidents, and only one incident came close—the 1977 Beverly Hills Supper Club fire in Kentucky, which killed 165 people. This fire, the third deadliest U.S. fire or explosion of the past 50 years (after the 1995 Oklahoma City, Oklahoma, bombing and the 2001 attack on the World Trade Center), echoed many of the problems of the 1940s incidents. The 165 victims represented less than 10 percent of the 2400 to 2800 occupants reportedly on site, but those occupants represented two to three times the facility’s capacity, indicating severe overcrowding. All types of exiting problems were also recorded. In terms of accomplishments, the post–Cocoanut Grove code changes worked. Large-loss-of-life fires have not occurred where code compliance has been observed, except for rapidonset situations, such as explosions. But large-life-loss incidents do continue to occur—less severe individually but still too large and too frequent to be acceptable—because of spotty enforcement. One type of incident, most dramatically embodied in the Happy Land social club fire of 1990, in New York City, has occurred in each of the last 5 decades and is worthy of special attention: an arson fire using accelerants started in a location that interferes with normal exiting. The first of these incidents is also the least well documented. In NFPA’s sixth decade, 1946 through 1955, a 1947 gambling hall fire began when a gallon of gasoline was thrown on the floor and ignited. The exiting provisions are not known,
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but 15 people died in the fire. In NFPA’s seventh decade, 1956 through 1965, a 1965 restaurant fire began when an arsonist poured gasoline at the main entrance. The 40 to 50 occupants may have encountered a security delay at the rear exit, which also was too narrow; 13 people died, or roughly one-fourth to one-third of the number present. The succeeding fires involved even worse exiting problems and death tolls that accounted for even larger fractions of the total occupants. In NFPA’s eighth decade, 1966 through 1975, a 1973 lounge fire was set in the stairway of the lounge’s normal exit. The second exit was poorly marked, and the windows were blocked or barred. The death toll of 32 people represented roughly half of the occupants present. In NFPA’s ninth decade, 1976 through 1985, a 1976 fire was set in the only exit of a New York City social club, leaving only windows for escape. The death toll of 25 represented roughly half of the occupants present. In NFPA’s tenth decade, 1986 through 1995, a 1990 arson fire was set in the main exit of New York City’s Happy Land social club. There were no other marked exits, nor were the windows useable for escape. Only 6 of the 93 occupants survived, 5 by going out an obscure, normally locked door that one of them had a key to, and the sixth by literally running through the fire at the entrance, sustaining critical burns. None of these properties had complete sprinkler systems or sprinklers in the area of the fire, so they emphasize the value of such systems. But taken together, they also illustrate how the consequences become worse as the deviation from code-compliant exiting provisions becomes worse. If there is literally nowhere to go, everyone will die. Finally, consider what it will take to accomplish even more in terms of life safety from fire, in any of the types of properties discussed thus far. People who die in fires, do so in either the kinds of fires that codes do not reach or the kinds of properties that codes do not reach due to lack of adoption or lack of enforcement. For schools and hospitals, codes reach nearly everywhere. These properties are tightly controlled. Nursing homes and the lodging industry are not quite so tightly controlled, but are very broadly compliant. Both have active industry associations that have broad membership and are sensitive to fire safety. Both industries have difficulty primarily in exerting control over properties on the fringes of the industry, such as board-and-care homes. Notwithstanding the emergence in recent years of legitimate board-and-care homes that provide only personal care to residents who need nothing more, a sizable group of facilities, long referred to as board-and-care homes, provides only lodging to residents who legitimately need health care as well. Places of assembly have the problem of widespread noncompliance far more than do hotels or nursing homes. Proportionally fewer properties belong to national chains, which in other industries often lead the move to greater fire safety. Industry associations have less of a track record as leaders in fire safety and, more importantly, capture a smaller proportion of their industry’s operating facilities. There is more, and more frequent, turnover in these facilities, which also hampers enforcement efforts, because educating owners and managers about fire safety is a gradual, incremental process, which has to start all over whenever an existing facility “goes under” and a new facility takes its place.
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Despite all this, the deadliest fires (i.e., 50 or more deaths) in places of assembly are less frequent and less deadly than they were a half-century ago, which suggests that enforcement and sensitivity to fire safety is better among at least the largest facilities. This is an achievement worth building upon.
Manufacturing Facilities Manufacturing properties are worthy of note because they also include a significant single incident that led to dramatic changes in NFPA codes. The 1911 Triangle Shirtwaist Company fire in New York City still ranks as the deadliest manufacturing facility fire (excluding explosions) in U.S. history. NFPA code requirements for the workplace, particularly exiting provisions, were substantially changed as a result of that fire. Since NFPA’s founding, according to NFPA records, 38 fires or explosions in manufacturing facilities have caused 10 or more deaths. Of these, 30 involved explosions, 2 involved flash fires, and 1 involved a large spill of burning fuel from a crashed aircraft; therefore, only 4 are truly comparable to the Triangle Shirtwaist Company fire. One such fire took place only 2 years after the Triangle Shirtwaist Company fire and also involved a New York State clothing manufacturer. The death toll in that fire reached 35 because an external fire escape was engulfed in flames early in the incident. More than 40 years later, two more garment factory fires, one like the Triangle Shirtwaist Company located in New York City, occurred in 1957 and 1958, killing 15 and 24 people, respectively. In the former, one stairway was open and filled early with smoke, and one fire escape was enveloped in flames and collapsed. In the latter, fire filled a key stairway early when the door to the stairway was wedged open. In 1991, a North Carolina food processing plant fire killed 25 people. NFPA investigators and the U.S. Occupational Safety and Health Administration (OSHA) both pointed to the similarities between this incident and the Triangle Shirtwaist Company fire, in terms of grossly inadequate exiting provisions. With the North Carolina fire still so recent in memory, it is particularly difficult to declare any kind of century of accomplishment for manufacturing facility fires. Major fires of the Triangle Shirtwaist Company variety were never particularly common, so there is no particular evidence of a statistical trend. NFPA codes for fire safety in the workplace are certainly stricter today, but there is no clear way to demonstrate with existing fire incident data that actual industrial practices are markedly better than they were a century ago. One exception is in the use of sprinklers, where manufacturing properties have shown some improvement (up from 45 percent of reported fires being in sprinklered properties in 1980 to 51 percent in 1997) and significant impact (civilian deaths per fire were 49 percent lower in 1988 through 1997 when sprinklers were present in manufacturing facilities). Within the manufacturing group, food product manufacturing facilities—the type of facility involved in the 1991 North Carolina fire—had the lowest percentage of reported fires with sprinklers present. However, a battle for life safety in manufacturing facilities is still being fought with respect to explosions, which involve a number of different NFPA codes. During the 5 decades from 1916 through 1965, the United States averaged just over four
manufacturing facility explosions per decade that each killed 10 or more people. During the 3 decades of 1966 through 1995, the average was just under three such incidents per decade. It is on the thin reed of one fewer incident per decade, on average, that a claim can be made for “a century of accomplishment” in manufacturing facility fire safety. As with fire safety in places of assembly, but even more so, an undeniable century of accomplishment in writing safer codes has been undercut by far less clear-cut progress in achieving code compliance. OSHA and the U.S. labor movement, both strong champions of a safer industrial workplace in years gone by, have been substantially weakened in recent years. Perhaps they can still be part of a revitalized coalition, with NFPA, concerned state and local authorities, and the thousands of responsible fire safety–conscious owners and managers of the better manufacturing sites, to improve a situation that still has much room for improvement.
Mines Mining is cited here to end this section on a true high note, even though NFPA had little input into what has been one of the most remarkable centuries of accomplishment in any class of properties. Most of the 101 U.S. fires and explosions that have killed 50 or more people since 1900 to 1999 have been in mining, specifically coal mining. (Only 3 of the 59 mining incidents were not coal mines; they were metal mines.) In the first decade that NFPA tracked, from 1900 through 1909, 15 of the 59 mining incidents occurred, killing a total of 2286 people. At the start of the second decade, from 1910 through 1919, the U.S. Bureau of Mines was formed (in 1910). In that second decade, there were 18 incidents, killing a total of 1882 people. Sometime in the second and third decades, the U.S. Bureau of Mines began issuing rules and guidelines, because by the end of the third decade (1929), they were publishing summaries of what they issued. In the third decade, from 1920 through 1929, there were a total of 14 incidents, killing a total of 1407 people. In the fourth decade, from 1930 through 1939, during the Great Depression, there were only two incidents, killing a total of 136 people. NFPA 493, Spontaneous Heating and Ignition of Coal and Other Mining Products, was first issued in 1936, but, by then, the big decline in the frequency of serious incidents had already occurred. In the fifth decade, from 1940 through 1949, which includes the wartime demands of World War II, there were seven incidents, killing a total of 533 people. The next 3 decades had one incident each, killing a total of 288 people. The decades from 1980 through 1989 and 1990 through 1999 have had no such incidents. A natural question, which also applies to the fire experience of garment manufacturing facilities discussed previously, is how much the reduction in fire deaths reflects a reduction in economic activity and associated exposure. Employment in coal mining peaked around the end of the second decade of the twentieth century and declined dramatically until about 1970, when it rose sharply for about a decade, then began declining again to its present levels, the lowest in this century. The decline in mining incidents killing 50 or more people and in the number of people killed in those incidents has been even steeper than the decline in employment in the industry, but both have been so steep that one
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will be used effectively and safely. Protecting the community and protecting themselves are dual responsibilities of a fire department, and both are more likely when planning and preparation are fully used. Table 2.1.17 gives a brief overview of the resource base of local fire departments. Only 11 percent of local fire departments are composed entirely or mostly of career fire fighters, but they protect 59 percent of the population, and 26 percent of all local fire fighters are career fire fighters. The majority of volunteer fire fighters serve in small, rural communities of less than 2500 population. Figure 2.1.15 shows that the workload for fire departments nearly doubled from 1980 to 1999, led by a 128 percent increase in emergency medical calls, which constitute more than half of all fire department calls (Figure 2.1.16). Since some communities still do not offer emergency medical service, those that do may find medical calls running at 80 to 90 percent of their calls. Fires now constitute only 1 of every 11 fire department calls, depending on how mutual-aid calls are categorized (see Figure
has to consider both the reduction in exposure and increased safety among those exposed as major factors in the trends. What makes these two property groups different, then, is that their century of accomplishment in fire safety, which has been dramatic and has involved changes in both the adequacy of the rules and the breadth of enforcement, has been overshadowed by nearly a century of decline in activity.
Implications for NFPA’s Second Century Of the many property classes that had tremendous risk of death in fire when NFPA was born, several have nearly eliminated life loss from fire and have achieved nearly all that can be achieved by fire protection after ignition occurs. Others have moved a long way in that direction but still have pockets where code compliance remains spotty. Still others have accomplished the development of adequate codes for fire safety but have major gaps in enforcement and compliance that still leave thousands, even millions, of people at risk. For the first group of properties, the next century’s agenda will be principally fire prevention and maintaining the gains in fire safety already won. For the other properties, to varying degrees, the next century’s agenda will be finding ways to extend effective fire safety practices throughout.
TABLE 2.1.17 Selected U.S. Local Fire Department Resources, 1999 • • • • • • •
ORGANIZING FOR FIRE PROTECTION Fire department organization is a critically important element of fire protection. The effectiveness of the organization and management of U.S. fire departments determines whether the more than $20 billion (1998 dollars) in annual expenditures for local fire protection are spent well or badly. More important, it also determines whether the roughly one million U.S. fire fighters
279,900 career fire fighters 785,250 volunteer fire fighters $20.3 billion in total public expenditures (in 1998) 30,400 fire departments 52,100 fire stations 69,000 pumper trucks (at least 500 gpm) 6300 aerial apparatus
Source: NFPA National Fire Experience Survey, NFPA Fire Service Inventory, U.S. Bureau of the Census.
20,000,000
19,667,000 18,753,000
19,000,000
17,957,500
18,000,000 17,503,000
17,000,000
16,391,500
12,000,000
16,127,000
14,684,500 13,707,500
13,308,000
15,318,500
14,556,500 10,548,000 10,819,000
11,070,000
11,890,000
10,000,000
10,594,500
10,933,000
1983
11,888,000
1981
Number of calls
16,000,000 14,000,000
13,409,500
12,237,500
8,000,000 6,000,000 4,000,000
1999
1998
1997
1996
1995
1994
1993
1992
1991
1990
1989
1988
1987
1986
1985
1984
1982
1980
2,000,000 0
Year
FIGURE 2.1.15
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Fire Department Emergency Calls, 1980–1999 (Source: NFPA National Fire Experience Survey)
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2.1.16). But fire calls demand the majority of fire department resource utilization, including stress on people and equipment. The potential to overload a department’s total resources still comes primarily from fires. Hazardous materials calls are a small fraction of the total but a growing one, and they also can involve a lot of resources per incident. False alarms today are more often nonemergency activation of automatic detection systems and less often the malicious box-alarm activations that were of so much concern in the 1960s and 1970s. The increasingly diverse responsibilities of the modern fire department are both an opportunity and a challenge. On the one hand, more duties mean more value delivered to the community. On the other hand, more duties mean a greater chance of overloading the system with simultaneous major calls. Since the rapid rise in calls for service has occurred during a period of generally declining or level staffing, the risk of overload is real. A more subtle challenge comes from the need to design an emergency response system to cope with different types of emergencies having very different patterns. Emergency medical calls require swift response with a minimum of equipment and personnel. Fire calls require swift response with a large complement of equipment and personnel and may tend to occur in different parts of the community than those where emergency medical calls are concentrated. These competing bases for decision-making require sophisticated planning. In many major cities, fire fighters are now required to be trained also as paramedics or emergency medical technicians (EMTs).
Organizing before Fire Occurs Preparing for fire begins with the promotion of fire prevention and built-in fire protection, which fire departments can do in a variety of ways.
Hazardous materials (1.5%) Fires (9.3%) Other hazardous conditions (2.8%)
Medical aid (58.4%)
Other (13.4%)
Mutual aid (4.2%)
False alarms (10.4%)
FIGURE 2.1.16 Fire Department Calls, 1999 (Source: NFPA National Fire Experience Survey)
First, fire departments typically are involved as inspectors and sometimes as certifiers for a wide range of fire-related regulations. Sometimes fire departments support building inspectors in their reviews of building code requirements for new and remodeled buildings. More often, fire departments handle ongoing fire code requirements for commercial buildings. Various permit requirements, from the general ones, such as occupancy permits and business licenses, to specific permits for hazardous materials and processes, also may be handled by fire departments. Smoke alarm laws are among the few examples where existing homes may be covered by these activities. These code and permit inspections not only empower fire departments to control fixed hazards, but also provide an excellent opportunity to educate and motivate occupants on general rules of fire safety. Research has shown this educational effect can reduce the frequency of fire significantly. Second, fire departments investigate the causes of fires and pass on what they learn to a community whose attention is focused by the immediacy of a recent tragedy. Support for prosecution of arson cases is the most obvious example of the effect investigations can have. Changes in codes and standards can result from these findings, too. The fire department is also the one constant in local programs to educate the public about fire safety, even though other groups may have primary authority for some programs. Fire departments can serve as catalysts for, and participants in, programs to counsel juvenile firesetters or to teach fire safety to schoolchildren. Fire departments often arrange for extensive programs of fire safety speeches to community groups, increasing community attention to the special programs of Fire Prevention Week in October. Fire departments can circulate fire safety messages by promoting local media use of fire safety public service announcements and by pointing out lessons from news coverage of local fires. Some fire departments are able to pursue even more ambitious programs, such as home fire inspections, using their own resources or acting as change agents to enlist a group of volunteers to do the job. In summary, the fire department is central to local fire prevention and protection, and fire prevention and protection is central to the duties of the modern fire department. With regard to preparing for nonfire emergencies, fire departments are increasingly called on to serve as the local agents for enforcement of federal and state laws to achieve “cradle-tograve” control of hazardous materials. This enforcement may involve regulations on storage, use, and transportation. In many communities, fire department resources for gathering, processing, and acting on information in this new area are severely lacking. Control of hazardous materials is one of the areas in which local fire departments are most in need of help to do the new jobs that are now expected of them.
Organizing Effectively at Fires Effective fire suppression requires clear policies and objectives, with tactics that follow logically from those policies. A suppression policy or objective is a concise description of priorities for the use of resources available at a fire. Particularly in properties with large numbers of people, containment of fire and pro-
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Pre-incident planning can range from the review and rehearsal of strategy and tactics for a single facility to the elaborate planning required to prepare for natural disasters or civil defense emergencies. Large-scale planning of the latter type may involve the development and maintenance of multi-agency coordination systems and large-scale incident command and control systems.
tection of large numbers of people outside the fire-involved zone may need first priority, ahead of any efforts to save people and property in areas already involved in fire. Some losses, such as injury or even death of occupants in the room of fire origin, occur so early in a fire that they cannot be consistently prevented by any suppression strategy of the fire department alone. Objectives imply tasks, such as forcible entry, rescue, application of water, ventilation, and salvage. And each task implies needs for staffing, equipment, the water delivery system, and response time. These needs are also affected by the level of on-site prevention and protection the community or the particular building has adopted. For example, suppose a building has a certain size and a set of on-site hazards associated with the kind of business or use at the property. These imply a potential fire size for planning purposes. The potential fire size implies a required number of gallons per minute (L/min) of water that would be needed to control and suppress that fire. The gallons-per-minute (L/min) requirement, in turn, implies needs for water pressure and pipe sizes serving the nearest hydrants and for hose sizes and pumping capacity in the fire department apparatus that respond. All these requirements also imply a certain staffing level to handle all the needed fireground activity, including (1) forcing entry if necessary, (2) finding and evacuating or protecting any occupants in certain zones of the building, (3) ventilating as necessary, (4) carrying the needed hoses to the potentially distant fire location, and (5) applying water there until the fire is controlled and extinguished. This process is a task analysis of suppression resources and their use. Implicitly or explicitly, such an analysis should underlie all resource decisions. It should be clear from this example that on-site sprinkler protection or limitations on quantities of burnable materials on site can change the potential fire size, which might permit longer response times or smaller personnel complements. However, if anything and everything is permitted on site, the fire department must plan for the worst, and if they lack the resources to do so, disaster is there, just waiting to happen.
138
140
136 127
120
Protecting Fire Fighters Fire fighter deaths on duty have generally been declining, though the trend has been far from steady (Figure 2.1.17). The high death tolls up to the early 1980s were led by career fire fighters, but the death tolls since then have been dominated by volunteers. These totals reflect both immediate and delayed effects of acute injuries or illnesses but do not reflect deaths due to long-term chronic illnesses, such as cancer. In a typical year, nearly half of all fire fighter deaths in the line of duty involve heart attacks. These deaths are nearly always limited to older fire fighters, at least 38 years of age, and are particularly prevalent in volunteer fire departments, where older fire fighters are more likely to serve. A large fraction of these heart attack deaths involve fire fighters with serious preexisting health conditions, including arteriosclerosis, hypertension, and previous heart attacks. Since nearly half of all fire fighter deaths involve heart attacks, physical fitness is one of the most important elements of an occupational health and safety program. In a typical year, one-fourth of on-duty fire fighter deaths occur during response to, or return from, an emergency call. Vehicular collisions and heart attacks while operating vehicles are both major causes. This scenario affects volunteers more than career fire fighters. Driver training is needed to prevent vehicle accidents. Safe passenger practices must be emphasized because falls from vehicles are also a major cause of fire fighter deaths. Careful attention to the safety of the vehicles themselves, including inspection, maintenance, and repair, is needed, too.
136 118 107 108
120 113
100
112
104
96 97 97
75
78
1993
80
1992
Number of deaths
119
131
128
91
60 40
1999
1998
1997
1996
1995
1994
1991
1990
1989
1988
1987
1986
1985
1984
1983
1982
1981
1980
20 0
Year
FIGURE 2.1.17
2–33
U.S. Fire Fighter Death Trend, 1980–1999 (Source: NFPA FIDO)
2–34 SECTION 2 ■ Basics of Fire and Fire Science
Fire fighter safety on the fireground depends on good equipment. Protective clothing for fire fighters is sometimes referred to as the “protective envelope.” Many of the advances in this equipment in recent years have come about as a result of a program of research in the late 1970s and early 1980s, under the name Project FIRES, sponsored by the U.S. Fire Administration. NFPA maintains and regularly updates standards for each type of protective clothing and equipment, including those needed for special environments, such as hazardous material incidents or airplane crash fire rescue. Fire fighter injuries on duty had been stuck at about 100,000 a year until the mid-1990s when they declined to just below 90,000, where they stuck for 4 years. Injuries at the scene of a fire emergency have declined from 65 percent of the total in 1981 to 52 percent in 1999. One reason the total remained so high was that injuries at the scene of a nonfire emergency have been increasing, from 9 percent of the total in 1981 to 16 percent in 1999.
INFORMATION AND ANALYSIS Fire protection is becoming increasingly scientific. The advent of sophisticated new databases, measurement techniques, and computer-based models has produced a pace of change unlike anything seen before. The Fire Protection Handbook has reflected this acceleration of knowledge, as dozens of whole chapters simply did not exist as recently as two editions ago. There is an increasing demand for hard evidence of the effectiveness and the cost effectiveness of fire protection features, systems, codes, and standards. New technologies judged by old standards may be admitted too slowly or too quickly to the marketplace. The old “build and burn” approach to gathering information on the fire performance of materials, products, assemblies, buildings, systems, and features is very expensive and is increasingly seen as wasteful when valid alternatives exist. Validity is the key, however. Fire protection engineers will find themselves having to deal with and control change in the content of their discipline at an ever-increasing rate. Use of unvalidated tests or models can bring dire consequences, but so can a failure to adapt to new techniques. Much of the material within this section, as well as the scientific fundamentals that underline new methods, receives more elaborate treatment in the SFPE Handbook of Fire Protection Engineering, published jointly by NFPA and the Society of Fire Protection Engineers.7
BIBLIOGRAPHY References Cited 1. Fire Analysis Division, “The Deadliest Fires and Explosions of the 1900s,” Fire Journal, Vol. 82, No. 3, 1988, pp. 48–54. 2. NCFPC, “America Burning,” report of the U.S. National Commission on Fire Prevention and Control, 1973, U.S. Government Printing Office, Washington, DC. 3. Learn Not to Burn® and Risk Watch® curricula and public service announcements, National Fire Protection Association, Quincy, MA, 2002. 4. Hall, J. R., Jr., Bukowski, R., and Gombey, A., “Analysis of Electrical Fire Investigations in Ten Cities,” NBSIR 83-2803,
Dec. 1983, National Bureau of Standards, Center for Fire Research, Gaithersburg, MD, p. 56. 5. Ahrens, M., “U.S. Experience with Smoke Alarms,” National Fire Protection Association Fire Analysis and Research Division, Quincy, MA, Sept. 2001. 6. Rohr, K. D., “U.S. Experience with Sprinklers,” National Fire Protection Association Fire Analysis and Research Division, Quincy, MA, Sept. 2001. 7. Society of Fire Protection Engineers and National Fire Protection Association, SFPE Handbook of Fire Protection Engineering, 2nd ed., SFPE and NFPA, Quincy, MA, 1995.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices provide further information on the elements of fire protection discussed in this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 30, Flammable and Combustible Liquids Code NFPA 54, National Fuel Gas Code NFPA 58, Liquefied Petroleum Gas Code NFPA 70, National Electrical Code® NFPA 101®, Life Safety Code® NFPA 102, Standard for Grandstands, Folding and Telescopic Seating, Tents, and Membrane Structures
Additional Readings The NFPA Fire Analysis and Research Division, through its “OneStop Data Shop” program, offers more than a hundred reports and packages that elaborate on the points in this chapter. Most are updated annually. “1994 Learn Not to Burn Champions,” NFPA Journal, Vol. 88, No. 3, 1994, pp. 67–69. Almond, G. H., “Fire and Crime,” Fire Chief, Vol. 42, No. 8, 1998, p. 122. “Arson Fire Kills 87 in Worst Mass Slaying in U.S. History,” Fire Control Digest, Vol. 16, No. 4, 1990, pp. 1–4. Brannigan, F. L., “Managing the Fire Problem,” Fire Chief, Vol. 40, No. 10, 1996, pp. 51–54. Brushlinsky, N. N., et al., “Russia’s 1993 Fire Statistics,” Fire Technology, Vol. 30, No. 4, 1994, pp. 458–467. Catchpole, L., “Fires in the Food Industry,” Fire Prevention, No. 285, Dec. 1995, pp. 21–25. Christian, D., “Study to Identify the Incidence in the United Kingdom of Long-Term Sequelae Following Exposure to Carbon Monoxide,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications, Ltd., London, UK, 2001, pp. 253–262. Clarke, F. B., “Contribution of Brominated Flame Retardants to Life Safety in the United States,” Proceedings of the Fire Risk and Hazard Assessment Research Application Symposium. Research and Practice: Bridging the Gap, San Francisco, CA, June 25–27, 1997, National Fire Protection Research Foundation, Quincy, MA, 1997, pp. 51–77. Collier, P., and Watson, L., “Summary Fire Statistics, United Kingdom, 1996,” Home Office Statistics Bulletin, No. 1/98, Jan. 21, 1998, pp. 1–83. Collier, P., and Watson, L., “Fire Statistics United Kingdom, 1997,” Home Office Statistical Bulletin, No. 25/98, Nov. 3, 1998, pp. 1–91. Corneo, E., Gallina, G., and Mutani, G., “Fire Safety in a Historical Building: A Case History,” Proceedings of the Applications of Fire Safety Engineering, Symposium for ’97 FORUM, FORUM for International Cooperation on Fire Research, Tianjin Fire Research Institute and Shanghai Yatai Fire Engineering Co., Ltd., Tianjin, China, 1997, pp. 60–72.
CHAPTER 1
Damant, G. H., and Nurbakhsh, S., “Christmas Trees—What Happens When They Ignite?” Fire and Materials: An International Journal, Vol. 18, No. 1, 1994, pp. 9–16. DePoortere, M., Schonback, C., and Simonson, M., “Fire Safety of TV Set Enclosure Materials: A Survey of European Statistics,” Fire and Materials, Vol. 24, No. 1, 2000, pp. 53–60. “Fire Statistics United Kingdom, 1993,” Home Office, London, UK, Sept. 1995. “Fire Statistics: Summary of Major Fires, 1992,” Fire Protection, Vol. 20, No. 4, 1993, pp. 24–25. Goddard, G., “Summary Fire Statistics, United Kingdom, 1996,” Home Office Statistical Bulletin, Vol. 19, No. 97, 1997, pp. 1–7. Green, M., “History of Building Code Regulations for Existing Buildings in the United States,” Proceedings of the Pacific Rim Conference and the 2nd International Conference on Performance-Based Codes and Fire Safety Design Methods, International Code Council and the Society of Fire Protection Engineers, Maui, HI, May 3–9, 1998, International Code Council, Birmingham, AL, 1998, pp. 39–47. Hall, J. R., Jr., “Brief History of Home Smoke Alarms (Abridged),” Proceedings of the Research and Practice: Bridging the Gap Fire Suppression and Detection Research Application Symposium, Orlando, FL, February 7–9, 2001, National Fire Protection Research Foundation, Quincy, MA, 2001, pp. 258–281. Hall, J. R., Jr., “Manufactured Home Fires: Fewer but Deadlier,” NFPA Journal, Vol. 90, No. 2, 1996, pp. 55–58. Hall, J. R., Jr., “Other Way Cigarettes Kill,” NFPA Journal, Vol. 92, No. 1, 1998, pp. 52–62. Hall, J. R., Jr., “Total Cost of Fire in the United States through 1993,” National Fire Protection Association, Quincy, MA, Oct. 1995. Hall, J. R., Jr., “U.S. Arson Trends and Patterns, 1990,” National Fire Protection Association, Quincy, MA, Oct. 1991. Hall, J. R., Jr., “U.S. Fire Problem Overview Report through 1990. Leading Causes and Other Patterns and Trends,” National Fire Protection Association, Quincy, MA, Feb. 1992. Hall, J. R., Jr., “U.S. Fire Problem Overview Report through 1994. Leading Causes and Other Patterns and Trends,” National Fire Protection Association, Quincy, MA, Apr. 1996. Hall, J. R., Jr., Taylor, K. T., and Sullivan, M. J., “Large-loss Fires Top $2.6 Billion in Damage in 1991,” NFPA Journal, Vol. 86, No.6, 1992, pp. 40–47, 74, 80. Hasemi, Y., “Fire Safety and Industrial Development: Fire Research Strategies for Asia in the First Decade of the 21st Century,” Proceedings of the 4th Asia-Oceania Symposium on Fire Science and Technology, Tokyo, Japan, May 24–26, 2000, co-organized by Asia-Oceania Association for Fire Science and Technology (AOAFST) and Japan Association for Fire Science and Engineering (JAFSE), 2000, pp. 63–66. Holmes, W. D., and Barry T. F., “FPEQRA: Fire Protection Engineering Quantitative Risk Assessment. A Risk Reduction/Return on Investment Approach to Designing for Industrial Fire Protection,” Proceedings of the Fire Risk and Hazard Assessment Symposium, Research and Practice: Bridging the Gap. San Francisco, CA, June 26–28, 1996, National Fire Protection Research Foundation, Quincy, MA, 1996, pp. 430–442. Hough, E., “ ‘On a Thin Red Line’: Solving South Africa’s Fire Problem,” Fire International, No. 174, March 2000, pp. 11–12. Hurley, M. J., “Research Agenda for Fire Protection Engineering,” National Institute of Standards and Technology, Gaithersburg, MD, NIST-GCR-99-791, June 2000, pp. 53. Hurley, M., and O’Connor, D. J., “Integrating Human Behavior in Fires into Fire Protection Engineering Design,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications, Ltd., London, UK, 2001, pp. 403–409. Jerome, I., “Update on Arson Fires, 1990,” Fire Prevention, No. 242, Sept. 1991, p. 16.
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Johnson, P., “Shattering the Myths of Fire Protection Engineering,” Fire Protection Engineering, Premier Issue, 1998, pp. 18–20. Karter, M. J., Jr., “1996 U.S. Fire Loss,” NFPA Journal, Vol. 91, No. 5, 1997, pp. 76–83. Karter, M. J., Jr., “Fire Loss in the U.S.,” NFPA Journal, Vol. 92, No. 5, 1998, pp. 72–76. Karter, M. J., Jr., “Fire Loss in the United States during 1990,” Fire Journal, Vol. 85, No. 5, 1991, pp. 36–38, 40–42, 44–46, 48. Karter, M. J., Jr., “Fire Loss in the United States, 1998,” NFPA Journal, Vol. 93, No. 5, 1999, pp. 88–95. Karter, M. J., Jr., “U.S. Fire Experience by Region: 1986–1990,” National Fire Protection Association, Quincy, MA, Jan. 1992. Karter, M. J., Jr., “U.S. Fire Experience by Region: 1989–1993,” National Fire Protection Association, Quincy, MA, Mar. 1995. Kirby, R. N., “Research Topics in the Field of Fire Detection and Alarm for Fire Protection Engineering Students,” Proceedings of the Fire Suppression and Detection Research Application Symposium, Research and Practice: Bridging the Gap, Orlando, FL, February 12–14, 1997, National Fire Protection Research Foundation, Quincy, MA, 1997, pp. 264–269. Koffel, W. E., “How Can We Solve the Residential Fire Problem?,” NFPA Journal, Vol. 95, No. 2, 2001, p. 32. Komaniya, K., “Changes in the Industry and the Disaster in Postwar Japan,” Proceedings of the 4th Asia-Oceania Symposium on Fire Science and Technology, Tokyo, Japan, May 24–26, 2000, co-organized by Asia-Oceania Association for Fire Science and Technology (AOAFST) and Japan Association for Fire Science and Engineering (JAFSE), 2000, pp. 115–127. Lataille, J. I., “Discipline of Fire Protection Engineering,” Fire Protection Engineering, No. 3, Summer 1999, pp. 40–42. Louderback, J., “Arverne Conflagration of 1992: 141 Structures Destroyed in the Rockaways Section of Queens, New York,” Firehouse, Vol. 18, No. 1, 1993, pp. 67, 69. Lun, S., “Getting to Grips with China’s Fire Problems,” Fire International, No. 172, Jan. 2000, p. 15. McCarthy, R. S., “Catastrophic Fires of 1999,” NFPA Journal, Vol. 94, No. 5, 2000, pp. 52–54. McCarthy, R. S., “Catastrophic Fires of 2000,” NFPA Journal, Vol. 95, No. 5, 2001, pp. 71–80. Meacham, B. J., “Application of Risk Concepts in Performance-Based Fire Protection Engineering,” Proceedings of the International Conference on Engineered Fire Protection Design, Applying Fire Science to Fire Protection Problems, San Francisco, CA, June 11–15, 2001, National Institute of Standards and Technology, Gaithersburg, MD and Society of Fire Protection Engineers, Bethesda, MA, 2001, pp. 122–131. Meacham, B. J., “Identifying and Addressing Uncertainty in Fire Protection Engineering,” Proceedings of the 2nd International Conference on Fire Research and Engineering (ICFRE2), Gaithersburg, MD, August 3–8, 1997, National Institute of Standards and Technology, Gaithersburg, MD, and Society of Fire Protection Engineers, Boston, MA, 1998, pp. 238–251. Miller, A. L., and Tremblay, K. J., “342 Die in Catastrophic Fires in 1991,” NFPA Journal, Vol. 86, No. 4, 1992, pp. 62–73. “National Fire Loss 1994,” Fire Protection, Vol. 22, No. 2, 1995, pp. 12–22. Nolan, D. P., “Statistical Review of Fires and Explosion Incidents in the Gulf of Mexico 1980–1990,” Journal of Fire Protection Engineering, Vol. 7, No. 3, 1995, pp. 99–105. Ohlemiller, T. J., “Flammability of Real Objects: A Progress Report,” Proceedings of the 13th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Gaithersburg, MD, March 13–20, 1996, K. A. Beall (Ed.), National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6030, 1997, pp. 107–114. Pagni, P. J., “Causes of the 20 October 1991 Oakland Hills Conflagration,” Fire Safety Journal, Vol. 21, No. 4, 1993, pp. 331–340. Queen, P. R., “Conflagration in Oakland!” American Fire Journal, Vol. 43, No. 12, 1991, pp. 12–15.
2–36 SECTION 2 ■ Basics of Fire and Fire Science
Quiter, J. R., “Research Agenda for Fire Protection Engineering,” Proceedings of the Conference on Technical Basis for Performance Based Fire Regulations, A Discussion of Capabilities, Needs and Benefits of Fire Safety Engineering, San Diego, CA, January 7–11, 2001, G. Cox (Ed.), United Engineering Foundation, Inc., New York, 2001, pp. 9–10. Randall, J., and Jones, R. T., “Teaching Children Fire Safety Skills,” Fire Technology, Vol. 29, No. 4, 1993, pp. 268–280. Rollman, D. J., “Fire Protection Engineering: A Best Kept Secret!,” Fire Protection Engineering, No. 3, Summer 1999, pp. 28–29. Rosenberg, T., “Statistics for Fire Prevention in Sweden,” Fire Safety Journal, Vol. 33, No. 4, 1999, pp. 283–294. Runyan, C. W., et al., “Risk Factors for Fatal Residential Fires,” Fire Technology, Vol. 29, No. 2, 1993, pp. 183–193. Schofield, R., “Fire Statistics, Estimates United Kingdom, 1999,” Home Office Statistical Bulletin, No. 13/00, Aug. 9, 2000, pp. 1–14. Sekizawa, A., “Fire Death Trends and Fire Deaths Pattern for Vulnerable People in Fire in Japan,” Proceedings of the 14th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Tsukuba, Japan, 1998, pp. 273–284. Scoones, K., “Fires in Hotels during 1990,” Fire Prevention, No. 249, May 1992, pp. 11–12. Scoones, K., “FPA Large Loss Analysis for 1993,” Fire Prevention, No. 286, Jan./Feb. 1996, pp. 42–50. Scoones, K., “Serious Fires in Educational Establishments during 1993,” Fire Prevention, No. 283, Oct. 1995, pp. 35–37. Scoones, K., “Serious Fires in Manufacturing Industries in 1993,” Fire Prevention, No. 285, Dec. 1995, pp. 31–33. Scoones, K., “Serious Fires in the Leisure/Retail Industry during 1992,” Fire Prevention, No. 272, Sept. 1994, pp. 17–18. Sekizawa, A., “Statistical Analysis on Fatalities Characteristics of Residential Fires,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, London, UK, 1991, pp. 475–484. Taylor, K. T., and Sullivan, M. J., “Large Loss Fires in the United States in 1990,” NFPA Journal, Vol. 85, No. 6, 1991, pp. 28–32, 34, 70, 92–98.
Torvi, D., “Teaching Fire Science and Fire Protection Engineering to Building Engineering Students,” Proceedings of the Fire Information in the New Millennium: Challenges and Opportunities Conference, Ottawa, Canada, May 9–12, 2000, International Network of Fire Information Reference Exchange, 2000, pp. 1–10. Tremblay, K. J., “Catastrophic Fires and Deaths Drop in 1992,” NFPA Journal, Vol. 87, No. 5, 1993, pp. 56–62, 64, 66–69. Tremblay, K. J., “Catastrophic Fires of 1994,” NFPA Journal, Vol. 89, No. 5, 1995, pp. 48–54, 56–58, 60, 62, 64, 66–68, 70. Trembley, K. J., “Catastrophic Fires of 1995,” NFPA Journal, Vol. 90, No. 5, 1996, pp. 86–94. Trembley, K. J., “1996 Catastrophic Fires,” NFPA Journal, Vol. 91, No. 5, 1997, pp. 46–56. Trembley, K. J., and Fahy, R. F., “Catastrophic Fires,” NFPA Journal, Vol. 92, No. 5, 1998, pp. 42–46. Trembley, K. J., “Catastrophic Fires of 1998,” NFPA Journal, Vol. 93, No. 5, 1999, pp. 59–64. Watson, L., and Gamble, J., “Fire Statistics United Kingdom, 1998,” Home Office Statistical Bulletin, No. 15/99, Sept. 8, 1999, pp. 1–91. Watson, L., Gamble, J., and Schofield, R., “Fire Statistics United Kingdom, 1999,” Home Office Statistical Bulletin, No. 20/00, Nov. 8, 2000, pp. 1–91. Wilmot, R. T. C., “United Nations Fire Statistics Study,” World Fire Statistics Center, London, UK, Bulletin No. 12, June 1996, pp. 1–6. Wilmot, R. T. C., “United Nations Fire Statistics Study,” World Fire Statistics Center, London, UK, Bulletin No. 13, Sept. 1997, pp. 1–6. Wilmot, R. T. C., “United Nations Fire Statistics Study,” World Fire Statistics Center, London, UK, Bulletin No. 14, Sept. 1998, pp. 1–6. Wilmot, R. T. C., “United Nations Fire Statistics Study,” World Fire Statistics Center, London, UK, Bulletin No. 15, Sept. 1999, pp. 1–6.
CHAPTER 2
SECTION 2
Fundamentals of FireSafe Building Design Revised by
John M. Watts, Jr.
B
uilding design and construction practices have changed significantly during the past century. A little over 100 years ago, structural steel was unknown, reinforced concrete had not been used in structural framing applications, and the first high-rise building had just been built in the United States. The design professions have also advanced significantly during the past century. The practice of architecture has changed markedly, and techniques of analysis and design that were unknown a century or even a generation ago are available to engineers today. Building design has become a very complex process, with many skills, products, and technologies integrated into its system. Fire protection has made developmental strides in the building industry similar to those of other professional disciplines. At the turn of the twentieth century, conflagrations were a common occurrence in cities. In later years, increased knowledge of fire behavior and building design enabled buildings to be constructed in such a manner that a hostile fire could be confined to the building of origin rather than to the block or larger areas. Progress has continued in the field of fire protection so that, at the present time, knowledge is available that enables a hostile fire to be confined to the room of origin or even to smaller spatial subdivisions in a structure. The material in this chapter identifies the components of a complete fire safety system. The organizational structure follows the NFPA fire safety concepts trees as described in NFPA 550, Guide to the Fire Safety Concepts Tree. This approach may be used as a basis on which to design fire safety in both new and existing buildings.
DESIGN AND FIRE SAFETY Much activity is taking place today regarding fire-safe building design. The general thrust is directed toward quantification procedures and identification of a rational design methodology to parallel or supplement the traditional “go or no go” specifications approach. Knowledge in the field of fire protection is un-
John M. Watts, Jr., Ph.D., is director of the Fire Safety Institute, a not-for-profit information, research, and educational corporation located in Middlebury, Vermont. He also serves as editor of NFPA’s quarterly technical journal, Fire Technology.
dergoing development and reorganization that will enable buildings to be designed for fire safety more rationally and efficiently. The SFPE Engineering Guide to Performance-Based Fire Protection Analysis and Design of Buildings1 describes this process in more detail. This chapter deals with a field that is changing dynamically in its analysis and design capabilities. “America Burning,” the report of the National Commission on Fire Prevention and Control,2 identifies several areas in which building designers create unnecessary hazards, often unwittingly, for the building occupants. In some cases, these unnecessary hazards are the result of oversight or insufficient understanding of the interpretations of test results. In other cases, they are due to a lack of knowledge of fire safety standards or to failure to synthesize an integrated fire safety program. The Commission’s report cites the frequent minimal attention paid by the designer of conscious incorporation of fire safety into buildings. Furthermore, building designers and their clients are often content only to meet the minimum safety standards of the local building code. They both may assume incorrectly that the codes provide completely adequate measures rather than minimal ones, as is actually the case. Building owners and occupants may also see fire as something that will never happen to them, as a risk that they will tolerate because fire safety measures can be costly, or as a risk adequately balanced by the provisions of fire insurance or availability of public fire protection. Conditions arising from these attitudes need not continue. Information is available for design professionals to incorporate better fire protection into their designs. Use of this information requires that the various members of the building design team recognize that fire conditions are a legitimate element of their design responsibilities. This requires a greater understanding of the special loadings that fire causes on building features and of the countermeasures that can be incorporated into designs.
Systems Approach The problem of fire safety in buildings is overwhelming both in the number of variables and in the subsequent difficulty of obtaining detailed data. The established approach of specification codes and standards has limitations for many modern structures and for older buildings of historic significance. An alternative approach to dealing with this kind of situation is a systems approach. In the broadest sense, a systems approach or systems analysis is simply the methodical study of an entity as a whole.
2–37
2–38 SECTION 2 ■ Basics of Fire and Fire Science
The objective of a systems approach is to define a credible process for making the best decision from among the alternatives. Fire safety can be incorporated into building design using three different methods: 1. Mandate that design and construction conform to prescriptive requirements in specification-oriented building codes and standards. Such requirements are based on fire experiences and are generally strict. 2. Use performance codes to overcome the inflexibility of specification codes. A present limitation of performancebased fire safety is that it is an evaluation procedure, not a design procedure. Once a design has been formulated, performance measures can be used to evaluate fire safety but the approach does not provide direct guidance on how to develop design concepts. 3. Use a systems approach that shows how various protection strategies can be used to meet fire safety objectives. Buildings can be designed with a systematic approach and then evaluated using either prescriptive or performance criteria or an appropriate combination of both. This approach to fire safety can require a high level of professional expertise; however, it allows greater flexibility and can achieve a greater level of cost effectiveness.
Fire Safety Concepts Tree The NFPA fire safety concepts tree, as described in NFPA 550 and shown in Figure 2.2.1, uses a branching diagram to show relationships of fire prevention and fire damage control strategies. Fire safety features such as construction type, combustibility of contents, protection devices, and characteristics of occupants traditionally have been considered independently of one another. This can lead to unnecessary duplication of protection. On the other hand, gaps in protection can exist when these pieces do not come together adequately, as evidenced by the fire losses that continue to occur. The distinct advantage of the fire safety concepts tree is its systems approach to fire safety. The fire safety concepts tree provides an overall structure with which to analyze the potential impact of fire safety strategies. Fire safety objective(s)
Prevent fire ignition
Control heat-energy source(s)
Control source-fuel interaction
Manage fire impact
Control fuel
= OR gate
FIGURE 2.2.1 Concepts Tree
Manage fire
Manage exposed
= AND gate
Principal Branches of the Fire Safety
The tree can identify gaps and areas of redundancy in fire protection strategies as an aid in making fire safety design decisions. The fire safety concepts tree shows the elements that must be considered in building fire safety and the interrelationship among those elements. The tree enables a building to be analyzed or designed by progressively moving through the various concepts in a logical manner. The tree’s degree of success depends on how completely each level is satisfied. Lower levels on the tree, however, do not represent a lower level of importance or performance; they represent a means for achieving the next higher level. Rather than considering each feature of fire safety separately, the fire safety concepts tree examines all of them and demonstrates how they influence the achievement of fire safety objectives.
Objectives of Fire-Safe Design The conscious process of design for building fire safety must be integrated, if it is to be effective and economical, into the complete architectural process. All members of the traditional building design team should incorporate, as an integral part of their work, design for emergency fire conditions. The earlier in the design process that fire safety objectives are established, alternative methods of accomplishing those objectives are identified, and engineering design decisions are made, the more effective and economical the final results. As the first step in the process, setting objectives is part of clearly identifying the specific needs of the client with regard to the function of the building. After the building functions and client needs are understood, the designer must consciously ascertain both the general and the unique conditions that influence the level of fire safety that is acceptable for the building. The acceptable levels of safety and the focus of the fire safety analysis and design process objectives are concentrated in the following five areas: 1. 2. 3. 4. 5.
Life safety Property protection Continuity of operations Environmental protection Heritage conservation
It is difficult to ascertain the level of risk that will be tolerated by the owner, occupants, and community. Often it is necessary to put a conscious effort into recognizing the sensitivity of the occupants, contents, and mission of the building to the products of combustion. Consequently, fire safety criteria often are not identified in a clear, concise manner that enables the designer to provide appropriate protection for the realization of the design objectives. Unfortunately, it is impossible to provide more than general guidelines that must be considered in building design to assist in the identification of the fire safety objectives in this handbook. Specific objectives must be developed for each individual building. Life Safety. Adequate life safety design for a building is often related only to compliance with the requirements of local building regulations. This may or may not provide sufficient occupant
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protection, depending on the particular building function and occupant activities. The first step of life safety design is to identify the occupant characteristics of the building. What are the physical and mental capabilities of the occupants? What are the range of their activities and locations during the 24-hour, 7-day-a-week periods? Are special considerations needed for certain periods of the day or week? In short, the designer must anticipate the special life safety needs of occupants during the entire period in which they inhabit the building. The identification of life safety objectives is usually not difficult, but it does require a conscious effort. In addition, it requires an appreciation of the time and extent to which the products of combustion can move through the building. The interaction of the building response to the fire and the actions of its occupants during the fire emergency determines the level of risk that the building design poses. Consideration for the safety of fire-fighting personnel responding to a building fire also can be taken into account. Property Protection. Specific items of property that have a high monetary or other value must be identified in order to protect them adequately in case of fire. In some cases, specially protected areas are needed. In other cases, a duplicate set of vital records in another location may be adequate. The establishment of the fire safety objectives should ascertain whether the user of the building has property that requires special fire protection. In modern buildings, the value of the contents of a single room may be extremely high. This value may be due to the cost of equipment or records, or to the high cost of business interruption. The sensitivity of equipment and data to the effects of heat, smoke, gases, or water must be addressed. In any event, the designer should protect the especially sensitive rooms from products of a fire originating either inside or outside the room. Continuity of Operations. The maintenance of operational continuity after a fire is the third major design concern. The amount of “downtime” that can be tolerated before revenues begin to be seriously affected must be identified. Frequently, certain functions or locations are more essential to the continued operation of the building than others. It is important to recognize those areas particularly sensitive to building operations so that adequate protection is provided for the vital business operations conducted in them. Often, these areas need special attention that is not required throughout the building. Environmental Protection. Another important objective considers the impact of a fire on the environment. Problems such as runoff of chemicals housed in the building that may dissolve in fire department water applications need to be addressed. Waterborne or airborne products of combustion, produced in buildings that house certain chemicals, can affect the environment significantly. Heritage Conservation. The preservation of our heritage from destruction by fire is gaining worldwide importance. Heritage conservation involves providing a reasonable level of fire
Fundamentals of Fire-Safe Building Design
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protection against damage to and loss of historic structures, their unique characteristics, and their contents. Preservation objectives require a design to minimize damage to historic structures or materials from fire and fire suppression while maintaining and preserving original space configurations and minimizing alteration, destruction, or loss of historic fabric or design. Substantial renovation or modification to a historic building is often challenging. Historic buildings, and spaces within such buildings, have a hierarchy of significance. Particularly for those historic buildings of higher significance, extraordinary attempts should be made to minimize alteration to the original space configurations and the historic design. Fire safety and fire protection features should be designed, implemented, and maintained so as to preserve the original qualities and character of the building, structure, or site.
FIRE SAFETY DESIGN STRATEGIES The fire safety concepts tree provides the logic required to achieve fire safety; that is, it provides conditions whereby the fire safety objectives can be satisfied, but it does not provide the minimum condition required to achieve those objectives. Thus, according to the tree, the fire safety objectives can be met if fire ignition can be prevented or if, given ignition, the fire can be managed. This logical OR function is represented by the symbol + under fire safety objectives in Figure 2.2.1. Evaluating a design for building fire safety represents a systematic approach to the principal fire safety strategies identified in Section 2, Chapter 1, “An Overview of the Fire Problem and Fire Protection.” These strategies can be identified as follows: • • • • • • •
Prevent fire ignition. Control the combustion process. Control fire by construction. Detect fire early and provide notification. Automatically suppress fire. Manually suppress fire. Manage the exposed.
Prevent Fire Ignition The first opportunity to achieve fire safety in a building is through fire (ignition) prevention, which involves separating potential heat sources from potential fuels. Table 2.2.1 lists common factors in fire prevention and identifies major candidate heat sources and ignitable materials, common factors that bring them together, and practices that can affect the success of prevention. Most building fires are started by heat sources and ignitable materials that are brought into the building, not built into it. This means the design of the building, from the architect’s and builder’s standpoints, provides limited potential leverage on the building’s future fire experience. The building’s owners, managers, and occupants, however, will have numerous opportunities to reduce fire risks through prevention, and they should be urged to do so. For design purposes, fire prevention is enhanced by careful observance of codes and standards in the design and installation of the electrical and lighting system, the heating system, and any other major built-in equipment, such as cooking, refrigeration,
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TABLE 2.2.1
air conditioning, and clothes washing and drying. Venting systems need to be designed carefully to carry carbon monoxide and potential fuels along protected paths. These venting systems need to be inspected and cleaned regularly. Protection from lightning and exposure fires affects the external design of the building, particularly in certain parts of the country, such as areas near wildlands. A fire in one building creates an external fire hazard to neighboring structures by exposing those structures to heat by radiation, and possibly by convective currents, as well as to the danger of flying brands of the fire. Any or all of these sources of heat transfer may be sufficient to ignite the exposed structure or its contents. When considering protection from exposure fires, there are two basic types of conditions: (1) exposure to horizontal radiation, and (2) exposure to flames issuing from the roof or top of a burning building in cases where the exposed building is higher than the burning building. Radiation exposure can result from an interior fire where the radiation passes through windows and other openings of the exterior wall. It can also result from the flames issuing from the windows of the burning building or from flames of the burning facade itself. NFPA 80A, Recommended Practice for Protection of Buildings from Exterior Fire Exposures, provides guidelines and data on exposure protection. Inside the building, design features may make incendiarism, arson, or other human-caused fires more or less likely by making security and housekeeping easier or harder to perform. The interaction of the design with these critical support activities should be thought through and planned into the design from the outset. In the fire safety concepts tree, the prevent fire ignition branch of Figure 2.2.2 essentially represents a fire prevention code. Most of the concepts described in this branch require continuous monitoring for success. Consequently, the responsibility
Fire Prevention Factors
1. Heat Sources a. Fixed equipment b. Portable equipment c. Torches and other tools d. Smoking materials and associated lighting implements e. Explosives f. Natural causes g. Exposure to other fires 2. Forms and Types of Ignitable Materials a. Building materials b. Interior and exterior finishes c. Contents and furnishings d. Stored materials and supplies e. Trash, lint, and dust f. Combustible or flammable gases or liquids g. Volatile solids 3. Factors That Bring Heat and Ignitable Material Together a. Arson b. Misuse of heat source c. Misuse of ignitable material d. Mechanical or electrical failure e. Design, construction, or installation deficiency f. Error in operating equipment g. Natural causes h. Exposure 4. Practices That Can Affect Prevention Success a. Housekeeping b. Security c. Education of occupants d. Control of fuel type, quantity, and distribution e. Control of heat energy sources
Prevent fire ignition
+ Control source-fuel interactions
Control heat-energy source(s)
Control fuel
+ Eliminate heat-energy source(s)
+ Control rate of heat-energy release
Control heat-energy transfer processes
Control heat-energy source transport
Control fuel transport
+ Provide separation
Control fuel ignitibility
+ Provide barrier
Control conduction
Control convection
= OR gate
FIGURE 2.2.2
Eliminate fuel(s)
Control radiation
Provide barrier
+ Provide separation
Control fuel properties
= AND gate
Components of the Prevent Fire Ignition Branch of the Fire Safety Concepts Tree
Control the environment
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According to the logic of the tree, the impact of the fire can be managed either through the manage fire or manage exposed branches (see Figure 2.2.1). The OR (+) gate indicates that the objectives may be reached through either or both design branches, as long as the avenue selected completely satisfies the fire safety objective. Naturally, it is acceptable to do both, which increases the likelihood of success over using one branch only. Through the manage fire branch, the fire safety objectives can be achieved by managing the fire itself. Figure 2.2.3 shows that this can be accomplished by (1) controlling the combustion process, (2) suppressing the fire, or (3) controlling the fire by construction. Again, any one of these branches of the tree will satisfy the manage fire concept. For example, in some fires success is achieved where the building construction controlled the fire. In
for satisfactorily achieving the goal of fire prevention is essentially an owner/occupant responsibility. The designer, however, may be able to incorporate certain features into the building that may assist the owner/occupant in preventing fires.
Manage Fire Impact It is not practical to prevent completely the ignition of fires in a building. Therefore, to reach the overall fire safety objective, from a building design viewpoint, a high degree of success in the manage fire impact branch of the fire safety concepts tree is important. Essentially, the manage fire impact branch of the fire safety concepts tree may be considered a building code by the design team. After ignition occurs, all considerations shift to the manage fire impact branch to achieve the fire safety objectives.
Manage fire
+ Control combustion process
Control fire by construction
+
Control fuel properties
Control fuel
Control the environment
Control movement of fire
+
+
+
Limit fuel quantity
Control fuel distribution
Control physical properties of environment
Control chemical composition of environment
Vent fire
Provide structural stability
Confine/ contain fire
Suppress fire
+ Automatically suppress fire
Detect fire
Apply sufficient suppressant
= OR gate
FIGURE 2.2.3
Manually suppress fire
Detect fire
Communicate signal
Decide action
Respond to site
= AND gate
Components of the Manage Fire Branch of the Fire Safety Concepts Tree
Apply sufficient suppressant
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other fires success is achieved by controlling the combustion process, either through control of the fuel or the environment.
Control Combustion Process The control combustion process is concerned with slowing the fire to provide other fire safety measures with sufficient time to be effective. A systematic design for this purpose should address the possible ways that hazards can grow rapidly, for example, flame spread, rapid growth in rate of heat release or rate of mass release, unusually toxic gases, unusual corrosivity, quantity of fuel available to feed the fire, and so forth. Each of these can be evaluated separately in terms of the threat to exposed people, property, and mission of the building. The building design should provide effective countermeasures to rapid fire growth. In a building fire, the most common hazard to humans is from smoke and toxic gases. Most building-related fire deaths are directly related to these products of combustion. Death often results from oxygen deprivation in the bloodstream, caused by the replacement of oxygen in the blood hemoglobin by carbon monoxide. In addition to the danger of carbon monoxide, many other toxic gases that are present in building fires cause a wide range of symptoms, such as headaches, nausea, fatigue, difficult respiration, confusion, and impaired mental functioning. Smoke, in addition to accompanying toxic and irritant gases, contributes indirectly to a number of deaths. Dense smoke obscures visibility and irritates the eyes and can cause anxiety and emotional shock to building occupants. Consequently, the occupant may not be able to identify escape routes and use them. Although heat injuries do not compare in quantity to those caused by inhalation of smoke and toxic gases, they are painful, serious, and cause shock to victims. In addition to deaths from thermal products of combustion, the pain and disfigurement caused by nonfatal burns can result in serious, long-term complications. Property also is affected by the thermal and nonthermal products of combustion, as well as by extinguishing agents. Smoke may damage goods located long distances from the effects of the heat and flames. Fires that are not extinguished quickly often result in considerable water damage to the contents and the structure, unless special measures are incorporated to prevent that damage. It should be noted, however, that the water damage caused from extinguishing a fire rarely exceeds the fire damage resulting from a fire that is not suppressed. Fast flame spread over finish materials or building contents and vertical propagation of fire are serious concerns. The ability of the fire service to contain or extinguish a fire is diminished significantly if the fire spreads vertically to two or more floors. With a given potential for fire growth, the prevention of vertical fire spread is influenced principally by architectural and structural decisions involving details of compartmentation, which are discussed in the section on controlling fire by construction on page 2-43.
Designing Countermeasures to Fire Growth The building fire safety system can be organized around fire growth and its resulting products of combustion, that is,
flame/heat and smoke/gas. The ease of generation and movement of these products is influenced by the countermeasures provided by the building. The effectiveness of the building fire safety systems determines the speed, quantity, and paths of movement of these products of combustion. The speed and certainty of fire growth and development in rooms can vary greatly. The contents and interior finish in some rooms are quite safe, and, for this type of situation, it is unlikely that, once ignited, a fire can grow to full involvement of the room. On the other hand, the interior design of other rooms poses a high hazard, which, if an ignition were to occur, could lead to an almost certain full-room involvement. The traditional method of describing the fire growth hazard has been through fuel loads (the amount of combustible material present) reflected in use and occupancy classifications. Building types, rather than rooms within buildings, have been grouped with regard to their relative hazard. For example, residential and educational occupancies are considered low hazard because they normally contain relatively low fuel loads in the rooms. Mercantile buildings are normally a moderate hazard whereas certain industrial and storage buildings may be considered a high hazard because they contain a high fuel load. This type of classification is a basis for building and fire code requirements, and, historically, it has been quite useful. However, a more detailed look at the fire growth potential within the rooms of a building can be a valuable part of a detailed fire safety design. The fire growth hazard potential, which identifies the speed and relative likelihood of a fire reaching full room involvement, is a useful base on which to design suppression interventions and to evaluate life safety problems. For example, situations in which fast, severe fires occur may call for automatic sprinkler protection even though that protection may not be required by a building or fire code. The combustion characteristics in a room form the basis for a fire growth hazard analysis. The main factors that influence the likelihood and speed with which full room involvement occurs are • Fuel load (i.e., the quantity, type of materials, and their distribution) • Interior finish of the room • Air supply • Size, shape, and construction of the room Fire development in a room is neither uniform nor a guaranteed progression from ignition to full room involvement. Fires develop through several stages, called realms. Table 2.2.2 provides guidance on descriptions of the realms. Within any realm a fire may continue to grow or it may be unable to sustain continued development and die down. Table 2.2.2 includes a rough guide to the approximate flame sizes that may be used to describe the fire size of the realms. The table also describes the major factors that influence growth within a realm. Absence of a significant number of the factors indicates that the fire would self-terminate rather than continue to develop. Different rooms pose different levels of risk regarding the likelihood of reaching full room involvement and the time in which fire development takes place. The factors in Table 2.2.2 provide a general guide to the important types of factors.
CHAPTER 2
TABLE 2.2.2
Realm
Major Factors Influencing Fire Growth Approximate Ranges of Fire Sizes
Major Factors That Influence Growth
1. Preburning
Overheat to ignition
Amount and duration of heat flux, surface area receiving heat, material ignitability
2. Initial burning
Ignition to radiation point (254 mm[10 in.-] high flame)
Fuel continuity, material ignitability, thickness, surface roughness, thermal inertia of the fuel
3. Vigorous burning
Radiation point to enclosure point (254 mm- to 1.5 mhigh flame [10 in. to 5 ft])
Interior finish, fuel continuity, heat feedback, material ignitability, thermal inertia of the fuel, proximity of flames to walls
4. Interactive burning
Enclosure point to ceiling point (1.5 m- [5 ft-] high flame to flame touching ceiling)
Interior finish, fuel arrangement, heat feedback, height of fuels, proximity of flames to walls, ceiling height, room insulation, size and location of openings, HVAC operation
5. Remote burning
Ceiling point to full room involvement
Fuel arrangement, ceiling height, length/width ratio, room insulation, size and location of openings, HVAC operations
A single event that might be used to represent the relative level of hazard posed by the contents and interior finish in a room is the ability of flames to reach the ceiling. The arrangement of contents and types of fuels where it would be difficult for a fire to grow to touch the ceiling poses a relatively low fire growth hazard potential. On the other hand, where furniture combustibility and density allow a fire to develop to ceiling height, or when combustible interior finish is present, the fire growth hazard potential usually is comparatively high.
Control Fire by Construction Barriers, such as walls, partitions, and floors, separate building spaces. These barriers also delay or prevent fire from propagating from one space to another. In addition, barriers are important features in any fire-fighting operation because they dictate the size of the fire. The effectiveness of a barrier depends on its inherent fire resistance; the details of its construction; and its penetrations, such as doors, windows, ducts, pipe chases, electrical raceways, and grilles. Although the hourly ratings of fire endurance do not al-
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ways represent the actual time that the barrier can withstand a building fire, unpenetrated rated barriers seem to perform rather well. This may be due to the rather large factor of safety inherent in the codes. On the other hand, it is quite common for rated barriers to fail because of inattention to penetrations. For example, the fire resistance of a rated floor-ceiling assembly can be compromised because of large or numerous poke-throughs. Also, the fire resistance of a rated partition is lost when a door is left open. Fire resistance requirements imposed by the regulatory system often have comparatively little meaning because of inattention to the functional and construction details. To predict field performance of barriers, the penetrations and details of construction must be considered, in addition to the fire endurance of the base construction. The major function of barriers is to prevent heat and flame spread from causing an ignition in an adjacent room or floor. It is useful to classify barrier failure in two categories. One is a massive barrier failure, which would occur when part of the barrier collapses or when a large penetration, such as a door or large window, is open. When a massive failure occurs, the adjacent room can become fully involved in a short period of time. The second type of failure is a localized penetration failure, which occurs when flames or heat penetrates small poke-throughs or small windows. A localized penetration failure causes a hot spot to occur. If fuel is present and ignition occurs, this could lead to a full room involvement by the normal fire development progression. Smoke and gases move through a building much faster and more easily than flames and heat. The time from ignition until a building space is untenable is an important aspect of fire safety, and the loss of tenability may be due to smoke and gases more often than flames and heat. Therefore, barriers need to be designed and considered as barriers to the spread of smoke and fire gases, too. In addition to its value as means of containing fire, compartmentation also addresses specific needs for protection, such as structural integrity of the building and escape routes. The collapse of structural building elements can be a serious life safety hazard. Although statistically structural collapse has not resulted in many deaths or injuries to building occupants, it is a particular hazard to fire fighters. A number of deaths and serious injuries to fire fighters occur each year because of structural failure. Although some of these failures result from inherent structural weaknesses, many are the result of renovations to existing buildings that materially, though not obviously, affect the structural integrity of the support elements. A building should not contain surprises of this type for fire fighters. The potential for structural collapse must be determined. Building codes address this aspect through construction classification requirements. The relationship between fire severity and fire resistance to collapse is the principal factor in the potential for structural collapse. Collapse can occur when the fire severity exceeds the fire endurance of the structural frame. However, this is comparatively rare. Structural collapse is more commonly associated with deficiencies in construction. These deficiencies are not evident under normal, everyday use of the building. They become a problem when the fire weakens supporting members, triggering a progressive collapse.
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In the fire safety concepts tree, when considering the control fire by construction concept, structural integrity must be provided, and the movement of the fire itself must be controlled. As shown in Figure 2.2.3, this can be accomplished either by venting, confining, or containing the fire.
Fire Detection and Alarm Fire detection is needed so that automatic or manual fire suppression will be initiated, any other active fire protection systems will be activated (e.g., automatic fire doors for compartmentation and protection of escape routes), and occupants will have time to move to safe locations, typically outside the building. One reason for concern over any rapid initial fire growth is that it can shrink the time available after detection for these life- and property-saving responses. Therefore, detection provisions must be designed systematically to reflect the building’s other features, its occupants, and its other fire safety features. For example, smoke is often the first indicator of fire, so a system of automatic detection based on smoke detectors often makes sense. In certain properties or areas, however, detectors based on heat or rate of increase in heat may be more appropriate because of the types of fires likely to occur in those areas or because of the potential for nonfire activations in those areas. Whatever type of detection system is chosen, it is important that, for each area of the building, a realistic assessment be made of the implications for response time after the fire is detected and before a lethal or other high-hazard condition develops. Alarm provisions need not be linked to the detection sensor locations, but should be designed systematically to tell occupants what they need to do, based on where they are and their ability to respond. This would include the possible use of central annunciator panels and monitors to inform responsible staff, voice messages to provide instructions on occupant movements, and direct remote alarms to supervised stations or fire departments. All these options have an impact on the time available for some type of response and, possibly, on the efficiency of that response. A timeline can be constructed to provide a quantitative analysis for design of this and related building fire safety features.
Automatic Suppression From the fire safety concepts tree, the suppress fire event and its branches are shown in Figure 2.2.3. In this figure, the sym• represents a logical AND gate, and signifies that all the bol 䊊 elements in the level immediately below the gate are necessary to achieve the concept above the gate. To accomplish automatic suppression, for example, both concepts, that is, detecting the fire and applying sufficient suppressant, are necessary. Similarly, to suppress the fire manually, five concepts must occur. The omission of any single concept is sufficient to break the chain and cause the failure of suppression to manage the fire. For nearly a century and a half, automatic sprinklers have been the most important single system for automatic control of hostile fires in buildings. Many desirable aesthetic and functional features of buildings that might offer some concern for fire safety because of the fire growth hazard potential can be protected by the installation of a properly designed sprinkler system.
An automatic sprinkler system has been the most widely used method of automatically controlling a fire. Among the advantages of automatic sprinklers is the fact that they operate directly over a fire and are not affected by smoke, toxic gases, and reduced visibility. In addition, much less water is used because only those sprinklers fused by the heat of the fire operate, particularly if the building is compartmented. The major elements for determining the effectiveness of an automatic sprinkler system are (1) its presence or absence; (2) if present, its reliability; and (3) if reliable, its design and extinguishing effectiveness. Although automatic sprinkler systems have a remarkable record of success, it is possible for them to fail. Often failure is due to a feature that could have been avoided if appropriate attention had been given at the time of the system’s design, installation, or maintenance. Table 2.2.3 describes common failure modes and their causes. During the design stages, these factors should be addressed to increase the probability of successful extinguishment by the sprinkler system. Other automatic extinguishing systems, for example, carbon dioxide, dry chemical, clean (halon replacement) agents, and high-expansion foam, may be used to provide protection for certain portions of buildings or types of occupancies for which they are particularly suited.
Manual Suppression The protection offered by a community fire department has an important influence on building fire design. Some buildings are designed in a manner that helps the fire department extinguish fires while they are small; others are designed in a manner that hinders a fire department. Rarely does the designer consciously design the building for emergency operations. The following discussion provides some guidelines for building design to enhance the building’s ability to allow the fire department to extinguish a fire with minimal threat to life and property. Ideally, a building is designed so that should a fire occur, it can be attacked before it extends beyond the room of origin. If that is not possible, the building design and construction features should retard fire spread so that the fire department encounters a relatively small, easily controllable fire. The major aspects of this part of building design include (1) fire department notification, (2) initial agent application, (3) fire extinguishment, (4) ventilation, (5) water supply and use, (6) water removal, and (7) barrier effectiveness (control of fire by construction). These aspects are discussed briefly to provide guidance for incorporating features into the building that enable fire departments to be more effective and less harmful to the building. Fire Department Notification. Part of every building fire safety design should be the following complete chain of events: (1) detection of the fire, (2) decision to inform the fire department, (3) sending of the message, and (4) correct receipt of the information by the fire department. Fire department notification should be consciously designed, rather than left to chance. The time durations for completing the events through agent application are very dependent on the speed of the fire spread. Buildings have been lost because of insufficient attention to the method of notifying the local fire department.
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TABLE 2.2.3
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Fundamentals of Fire-Safe Building Design
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Common Automatic Sprinkler Failure Modes Potential Causes
Failure Mode Water supply valves are closed when sprinkler operates.
Valve supervision is inadequate. Owner’s attitude is lackadaisical. Maintenance policies are not effective.
Water does not reach sprinkler.
Dry pipe accelerator or exhauster malfunctions. Preaction system malfunctions. Maintenance and inspection are inadequate.
Nozzle fails to open when expected.
Fire rate of growth is too fast. Response time and/or temperature of link are inappropriate for the area protected. Sprinkler link is protected from heat. Sprinkler link is painted, taped, bagged, or corroded. Sprinkler skips.
Water cannot contact fuel. (Note: The intent of this failure mode is to ensure that discharge is not interrupted in a manner that will prevent fire control by a sprinkler.)
Fuel is protected. High-piled storage is present. New construction (walls, ductwork, ceilings) obstructs water spray.
Water discharge density is not sufficient.
Discharge needs are insufficient for the type of fire and the rate of heat release. Change in combustible contents occurs. Number of sprinklers open is too great for the water supply. Water pressure is too low. Water droplet size is inappropriate for the fire size.
Not enough water continues to flow.
Water supply is inadequate because of original deficiencies, changes in water supply, or changes in the combustible contents. Pumps are inadequate or unreliable. Power supply malfunctions. System is disrupted.
Agent Application. The next critical event is fire department application of agent to the fire, which involves three distinct events for its success: (1) arrival at the site, (2) nozzle entrance into the room, and (3) water discharge from the nozzle. Each of these events can be affected by site or building access considerations in the design. Ideal exterior accessibility occurs where a building can be approached from all sides by fire department apparatus, which is not always possible. In congested areas, only the sides of buildings facing streets may be accessible. In other areas, topography or constructed obstacles can prevent effective use of apparatus in combating the fire. Buildings located some distance from the street may make the approach of apparatus difficult. If obstructions or topography prevent apparatus from being located close enough to the building for effective use, fire-fighting equipment, that is, aerial ladders, elevating platforms, and water tower apparatus, are rendered useless. Valuable labor must be expended to hand-carry hose lines or ground ladders long distances. The matter of access to buildings has become far more complicated in recent years, especially in light of the movement to secure buildings against possible terrorist attacks. The build-
ing designer must consider this important aspect in the planning stage. Inadequate attention to site details can place the building in an unnecessarily vulnerable position. If preventing adequate fire department access compromises its fire defenses, the building must compensate with more complete internal building protection. The arrival at the site is only a part of the agent application evaluation. The fire fighters then must be able to enter the building, reach the floor of the fire, and find the involved room or rooms. This is often a time-consuming, difficult task. Considerable attention must be given to the problem of finding the fire and getting fire fighters and equipment to the fire. Access to the interior of a building can be greatly hampered where large areas exist and where buildings have blank walls, false facades, solar screens, or signs covering a high percentage of exterior walls. Obstacles that prevent ventilation allow smoke to accumulate and obscure fire fighters’ vision. Lack of adequate interior access also can delay or prevent fire department rescue of trapped occupants. Windowless buildings and basement areas present unique fire-fighting problems. The lack of natural ventilation openings, such as windows, contributes to the buildup of dense smoke and
2–46 SECTION 2 ■ Basics of Fire and Fire Science
intense heat, which hamper fire-fighting operations. Fire fighters must attack fires in these spaces despite heat and smoke, which can result in lengthy times for fire extinguishment and greater damage by the products of combustion. Fire Extinguishment. After the time-consuming and sequential events of notification and initial agent application have transpired, the fire department is ready to fight the fire. The size of fire that is present at the time of initial agent application determines the fire-fighting strategy and likelihood of success of the operation. Broadly speaking, the following three categories of fire conditions may be expected: • Comparatively small fires may be extinguished by direct application of water. • When the fire is larger than can be directly extinguished, the building may be opened (ventilated), and the hose streams can drive the fire, heat, and smoke out of the building. • Fires that are too large for this operation must be surrounded. All available techniques of ventilation and heat absorption by water evaporation are used; however, the fire area is lost. The main purpose of this strategy is to protect exposures, both external and internal. Ventilation. Ventilation is an important fire-fighting operation. It involves the removal of smoke, gases, and heat from building spaces. Ventilation of building spaces performs the following important functions: • Life is protected by removing or diverting toxic gases and smoke from locations where building occupants must find temporary refuge. • The environment in the vicinity of the fire is improved by removal of smoke and heat. This enables fire fighters to advance close to the fire to extinguish it. • The spread or direction of fire is controlled by setting up air currents that cause the fire to move in a desired direction. In this way, occupants or valuable property can be more readily protected. • Unburned, combustible gases are provided release before they develop into a flammable mixture, thus avoiding a backdraft or smoke explosion. The building designer should be conscious of these important functions of ventilation and provide effective means of facilitating venting practices whenever possible. This may involve access panels, movable windows, skylights, or other means of readily opened spaces in case of a fire emergency. Emergency controls on the mechanical equipment or inclusion of an engineered smoke-control system may also be an effective means of accomplishing the functions of fire ventilation. Each building has unique features, and, consequently, a unique solution should be incorporated into each building design. Water Supply and Use. Water is the principal agent used to extinguish building fires. Although other agents may be employed occasionally (e.g., carbon dioxide, dry chemical, foams and surfactants, and clean halon replacement agents), water remains the primary extinguishing agent of the fire service. Con-
sequently, the building designer should anticipate the needs of both the fire department and automatic extinguishing systems and make sure adequate supply of water is provided at adequate residual pressure. Water normally is supplied to the building site by mains that are part of the water distribution system. Few cities can supply a sufficient amount of water at required pressures to every part of the city. Consequently, water supplied to hydrants, standpipes, or pumps located on fire department apparatus or in the buildings themselves must boost sprinklers. Buildings that do not have an adequate, reliable water source for fire fighting must either provide supplemental water or incorporate other fire defense measures to compensate for this deficiency. Careful attention must be given to water supply, distribution, and pressure for emergency fire conditions. High-rise buildings are particularly sensitive in this respect because the water pressures that are required depend on building height. The water supply needs of large buildings must also be given careful attention. Fire conditions that require operation of a large number of sprinklers or use of a large number of hose streams can reduce pressure in standpipe and sprinkler systems to the point where residual pressures in the distribution system are adversely affected. Fire department connections for sprinkler and standpipe systems are important components of building fire defenses. The building designer must carefully consider installation details of fire department connections to make sure they will be easily located, readily accessible, and properly marked. Locations should be approved by the local fire department. Water Removal. Watertight floors are important in water removal. Salvage efforts can be greatly affected by the integrity of the floors. Of greater importance is the number and location of floor drains. If interior drains and scuppers are available, salvage teams can effectively remove water with minimum damage to the structure.
Managing the Exposed As shown in Figure 2.2.4, from the fire safety concepts tree, fire impact can be lessened by managing the “exposed,” that is, people, property, operations, environment, or heritage, depending on the design aspects being considered. The manage exposed branch is successful either by limiting the amount exposed or by safeguarding the exposed. For example, the number of people as well as the amount or type of property in a space may be restricted. Often, this is impractical. If this is the case, the objectives can still be met by incorporating design features to safeguard the exposed. The exposed people or property may be safeguarded either by moving them to a safe area of refuge or by defending them in place. For example, people in institutionalized occupancies, such as hospitals, nursing homes, or detention and correctional facilities, must generally be defended in place. To do this, the defend exposed in place branch shown in Figure 2.2.4 would be considered. On the other hand, alert, mobile individuals, such as those expected in offices or schools, could be moved to safeguard them from fire exposure on either a short-term or long-range basis, de-
CHAPTER 2
■
Fundamentals of Fire-Safe Building Design
2–47
Manage exposed
+ Limit amount exposed
Safeguard exposed
+ Defend exposed in place
Move exposed A
Restrict movement of exposed
Defend the place
Maintain essential environment
Cause movement of exposed
Provide movement means
Provide safe destination Go to A
Defend against fire product(s)
Provide structural stability
Detect need
Signal need
Provide instructions
= OR gate
FIGURE 2.2.4
Provide capacity
= AND gate
Provide route completeness
Provide protected path
Provide route access
Go to A
Components of the Manage Exposed Branch of the Fire Safety Concepts Tree ( . = transfer/entry point)
pending on other key design elements. Figure 2.2.4 illustrates the concepts that must be achieved if fire safety objectives are to be met when managing the exposed property and people. The design for life safety may involve one or a combination of the above concepts: (1) evacuation of the occupants, (2) defending the occupants in place, or (3) providing an effective area of refuge. These alternatives can be evaluated on the likelihood that the building spaces will be tenable for the period of time necessary to achieve the expected level of safety. The criteria for tenability, therefore, become an important part of the design. Evacuation. The design for building evacuation involves two major components: (1) the availability of an acceptable path or paths for egress, and (2) the effective alerting of the occupants in sufficient time to allow egress before segments of the path of egress become untenable. Alerting occupants to the existence of a fire is a vital part of the life safety design. A useful performance objective could be to identify that occupants should have adequate time to escape from fire before the escape route becomes blocked. To accomplish this, the designer either must ensure that the fire and the movement of its products of combustion will be slow enough to provide that time, or incorporate special provisions into the building to achieve that objective. Defending in Place. The second life safety design alternative is to defend the individual in place. This may be appropriate for
occupancies such as hospitals, nursing homes, detention and correctional facilities, and other institutions. It may be an appropriate alternative for other buildings when the size or design may show that evacuation has an unacceptably low likelihood of success. Defend-in-place design also uses performance criteria of time and tenability levels. The performance criteria relating to time might state that the building space should be tenable for a sufficient period of time after the start of the fire. This duration could be longer than the duration of any expected fire. The definition of tenability may be quite different from that acceptable for evacuation because of the influence of both time and the products of combustion. Refuge. The third alternative is to design for an area of refuge. This involves occupant movement through the building to specially designed refuge spaces. This type of design is more difficult than either of the other two alternatives because it involves the major design aspects of each. In certain types of buildings this may be a reasonable alternative. However, an evaluation of the effectiveness of the area of refuge design and its likelihood of success are extremely important. Life safety design for a building is difficult. It involves more than a provision for emergency egress. Life safety design must also address the population who will be using the building and what they will be doing most of the time. Consideration must then be given to communication, the protection of escape routes, and temporary or permanent areas of refuge for a
2–48 SECTION 2 ■ Basics of Fire and Fire Science
reasonable period of time for the building occupants to achieve safety. Even occupants familiar with their surroundings often experience difficulty in locating means of egress. The problem is compounded for transients and occasional visitors to the building. Architectural layout and normal circulation patterns are important elements in emergency evacuation. For example, many large office buildings are a maze of offices, storage areas, and meeting rooms. Clearly marked emergency travel routes can enhance life safety features in all buildings.
SUMMARY The fire safety concepts tree can be employed effectively in building design. If the architect incorporates the tree during the preliminary planning phase of design, many important decisions and alternatives can be defined more effectively. For example, decisions can be made regarding evacuation versus temporary refuge, including the implications of each on the functions of the building. Specific needs with regard to design decisions can then be recognized. The fire safety concepts tree also provides for the separation of the functions of fire prevention and building design. In this way, the responsibilities of the owner/occupant can be differentiated from those of the building design team. Those concepts that are eventually incorporated into the design can be identified with a specific member of the building design team. This chapter describes in general terms the concepts required to create such a design. More specific guidance requires joining the general concepts described here with the more detailed guidance in later chapters on specific fire safety strategies. NFPA codes and standards are important factors in building design, and the fire safety concepts tree should not supersede them. Rather, the tree enables those documents to be interrelated and, consequently, used more effectively.
BIBLIOGRAPHY References Cited 1. Society of Fire Protection Engineers, SFPE Engineering Guide to Performance-Based Fire Protection Analysis and Design of Buildings, National Fire Protection Association, Quincy, MA, 2000. 2. “America Burning,” report of the National Commission on Fire Prevention and Control, 1973, Superintendent of Documents, U.S. Government Printing Office, Washington, DC.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on the fundamentals of firesafe building design discussed in this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 1, Fire Prevention Code NFPA 13, Standard for the Installation of Sprinkler Systems NFPA 14, Standard for the Installation of Standpipe, Private Hydrant, and Hose Systems
NFPA 22, Standard for Water Tanks for Private Fire Protection NFPA 24, Standard for the Installation of Private Fire Service Mains and Their Appurtenances NFPA 70, National Electrical Code® NFPA 72®, National Fire Alarm Code® NFPA 80A, Recommended Practice for Protection of Buildings from Exterior Fire Exposures NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems NFPA 92A, Recommended Practice for Smoke-Control Systems NFPA 92B, Guide for Smoke Management Systems in Malls, Atria, and Large Areas NFPA 101®, Life Safety Code® NFPA 101A, Guide on Alternate Approaches to Life Safety NFPA 220, Standard on Types of Building Construction NFPA 221, Standard for Fire Walls and Fire Barrier Walls NFPA 232, Standard for the Protection of Records NFPA 241, Standard for Safeguarding Construction, Alteration, and Demolition Operations NFPA 286, Standard Methods of Fire Tests for Evaluating Contribution of Wall and Ceiling Interior Finish to Room Fire Growth NFPA 550, Guide to the Fire Safety Concepts Tree NFPA 909, Code for the Protection of Cultural Resources NFPA 914, Code for Fire Protection of Historic Structures NFPA 1142, Standard on Water Supplies for Suburban and Rural Fire Fighting NFPA 1600, Standard on Disaster/Emergency Management and Business Continuity Programs
Additional Readings Alamdari, F., and Kumar, S., “Environmental and Fire Safety Design Assessment Methods,” Fire Safety Engineering, Vol. 6, No. 3, June 1999, pp. 12–15. Bak, D. N., and Simmons, R. J., “Assessing Risk: What Every Member of the Fire and Life Safety Community Will Have to Face,” Proceedings of the Engineered Fire Protection Design . . . Applying Fire Science to Fire Protection Problems, June 11–15, 2001, San Francisco, CA, Society of Fire Protection Engineers, Bethesda, MD, and National Institute of Standards and Technology, Gaithersburg, MD, 2001, pp. 107–121. Beck, V., and Zhao, L., “CESARE-RISK: An Aid for PerformanceBased Design. Some Results,” Proceedings of the 6th International Symposium on Fire Safety Science, July 5–9, 1999, Poitiers, France, International Association of Fire Safety Science, Boston, MA, 2000, pp. 159–170. Beller, D., “Performance-Based Fire Safety: An Engineering Perspective,” Proceedings, Fire Risk and Hazard Assessment: Research Application Symposium. Research and Practice: Bridging the Gap. June 25–27, 1997, San Francisco, CA, National Fire Protection Research Foundation, Quincy, MA, 1997, pp. 19–32. Cooke, G. M. E., “Sandwich Panels for External Cladding: Fire Safety Issues and Implications for the Risk Assessment Process,” Fire Engineers Journal, Vol. 61, No. 210, 2001, pp. 31–36. Corneo, E., Gallina, G., and Mutani, G., “Fire Safety in a Historical Building: A Case History,” Proceedings, Applications of Fire Safety Engineering, Symposium for ’97, FORUM for International Cooperation on Fire Research, Applications of Fire Safety Engineering, October 6–7, 1997, Tianjin, China, Tianjin Fire Research Institute and Shanghai Yatai Fire Engineering Co., Ltd., 1997, pp. 60–72. Ferguson, A., and Law, M., “International Conference on Performance-Based Codes and Fire Safety Design Methods Case Study: Project Summary,” Proceedings, Pacific Rim Conference and 2nd International Conference on Performance-Based Codes and Fire Safety Design Methods, May 3–9, 1998, Maui, HI, International Code Council, Birmingham, AL, 1998, pp. 486–497. Iliaskos, C., Beever, P., Williams, C., Marchant, R., Collins, M., and England, P., “Role of the Fire Services in a Performance Based
CHAPTER 2
Regulatory Environment,” Proceedings, Building Tomorrow’s Future (BTF) Conference 2001, April 9–11, 2000, Australia, Standards Australia, BRANZ, Australian Window Association, Australian Greenhouse Office, Building Center of Japan, Plantation Timber Association, Master Buildings, Australian Building Energy Council, Quantas, IRCC, 2001, pp. 1–8. Kandola, B. S., “Risk Based Approach to Fire Safety Engineering,” Fire Engineers Journal, Vol. 57, No. 188, 1997, pp. 21–26. Magnusson, S. E., Frantzich, H., and Harada, K., “Evacuation Design Based on Calculation Methods for Life Safety Analysis: A Comparison between the Safety Index and Pra-Methodologies,” Proceedings, 1st European Symposium on Fire Safety Science, Session I: Risk, August 21–23, 1995, Zurich, Switzerland, 1995, pp. 1–24/65–66. Mathews, M. K., Darydas, D. M., and Delichatsios, M. A., “Performance-Based Approach for Fire Safety Engineering: A Comprehensive Engineering Risk Analysis Methodology, a Computer Model, and a Case Study,” Proceedings, International Associa-
■
Fundamentals of Fire-Safe Building Design
2–49
tion of Fire Safety Science 5th International Symposium, March 3–7, 1997, Melbourne, Australia, International Association of Fire Safety Science, Boston, 1997, pp. 595–606. Mehaffey, J. R., “Performance-Based Design for Fire Resistance in Wood-Frame Buildings,” 8th Proceedings, INTERFLAM ’99, June 29–July 1, 1999, Edinburgh, UK, Interscience Communications, Ltd., London, UK, 1999, Vol. 1, pp. 293–304. O’Neill, J. G., and Bowman, A. B., “Fire Protection of a Landmark Historic Building: Performance Based Life Safety Analysis,” Proceedings, Research and Practice: Bridging the Gap, Fire Suppression and Detection Research Application Symposium, February 23–25, 2000, Orlando, FL, Fire Protection Research Foundation, Quincy, MA, 2000, pp. 180–203. Walsh, C. J., “National Fire Safety Engineering Approach to the Protection of People with Disabilities in or near Buildings during a Fire, or Fire Related Incident,” Proceedings, Human Behavior in Fire, 1st International Symposium, August 31–September 2, 1998, Belfast, UK, Textflow, Ltd., UK, 1998, pp. 341–352.
CHAPTER 3
SECTION 2
Chemistry and Physics of Fire Revised by
D. D. Drysdale
T
his chapter presents basic definitions of some physical properties and chemical terms applicable to the chemistry and physics of fire; it also discusses combustion, the principles of fire, heat measurement, heat transfer, and heat energy sources (i.e., sources of ignition). The material contained in this chapter does not attempt to offer a comprehensive course of instruction on the subject, but is intended to present basic background reference material applicable to this and other sections of this handbook.
BASIC DEFINITIONS AND PROPERTIES Atoms and Molecules Atom. Atoms are the basic particles of chemical composition. They form the basis of all matter with which we are familiar. Each atom has a dense, positively charged nucleus, or core, which comprises protons (positively charged) and neutrons (no charge), and around which negatively charged electrons swarm in a regularly structured pattern. The number of protons and electrons is equal, ensuring that the atom is electrically neutral. The precise structure of the electron “swarm” (or “cloud”) determines the chemical nature and reactivity of the atom. Atomic Number of an Element. The atomic number is the number of protons in the nucleus of the atom of an element. It determines the position of that element in the Periodic Table (Table 2.3.1), which reveals the underlying regularity in the properties of the elements. Atomic Weight of an Element. The atomic weight of an element is proportional to the weight of its atom. The “scale” is based arbitrarily on the carbon-12 isotope (the isotope of carbon containing six protons and six neutrons). The mass of C-12 corresponding to 12 g contains 6.022 ? 1023 atoms (known as Avogadro’s number). The atomic weights of the elements are given in Table 2.3.2. Element. Elements are substances that are composed of only one type of atom (e.g., pure carbon, C; nitrogen, N2; bromine, Br2).
D. D. Drysdale, Ph.D., is professor of fire safety engineering, School of Civil and Environmental Engineering, University of Edinburgh, Scotland.
Isotope. Atoms that contain the same number of protons but different numbers of neutrons are called isotopes. Most elements have more than one isotope (e.g., C-12 and C-13 contain six protons, but they have six and seven neutrons, respectively). Molecule. Molecules are groups of atoms combined in fixed proportions. Substances composed of molecules that contain two or more different kinds of atoms are called compounds. The molecules of a single compound are identical. Chemical Formula. A chemical formula represents the number of atoms of the various elements in a molecule. For example, water is H2O (two atoms of hydrogen and one of oxygen) whereas propane is C3H8, where C stands for carbon (see Table 2.3.2 for symbols of other elements). A formula may be written to indicate the arrangement of the atoms in the molecule. Thus, propane is CH3CH2CH3. Molecular Weight of a Compound. The molecular weight of a compound is the sum of the atomic weights of all atoms in its molecule. For example, from its chemical formula, the molecular weight of propane (C3H8) is (3 ? 12) = (8 ? 1) C 44. The gram molecular weight of a substance is the mass of the substance equal to its molecular weight in grams. Mole. A mole of an element or compound is the amount that corresponds to the gram molecular weight. Thus one mole of propane has mass of 44 g. One mole of any element or compound contains 6.022 ? 1023 molecules (see definition of atomic weight).
Chemical Reactions Chemical Reaction. A chemical reaction is a process by which reactants are converted into products. More often than not, the equation that is used to describe a chemical reaction hides the details of the mechanism by which the change takes place. Thus, the equation for the oxidation of propane is written conventionally as C3H8 = 5 O2 C 3 CO2 = 4 H2O However, the mechanism is very complex and involves highly reactive species called free radicals. Free radicals include atomic hydrogen and oxygen, the hydroxyl radical (OH), and many more. The conversion of propane to carbon dioxide and water involves hundreds of intermediate steps (elementary
2–51
2–52 SECTION 2 ■ Basics of Fire and Fire Science
TABLE 2.3.1
Periodic Table
alkali metals 1A
Period
1
1
H 1.01
2 Period
3 Period
4 Period
5 Period
6 Period
7
2
nonmetals
alkaline earth metals II A
3
4
III A 5
Li
Be
B
C
Hydrogen
Period
noble gases O
He 4.00
IV A 6
VA 7
VI A 8
VII A 9
Helium
N
O
F
Ne
10
6.94
9.01
10.81
12.01
14.01
16.00
19.00
20.18
Lithium
Beryllium
Boron
Carbon
Nitrogen
Oxygen
Fluorine
Neon
11
12
13
14
15
16
17
18
Na
Mg
Al
Si
P
S
Cl
Ar
transition metals
22.99
24.31
Sodium
Magnesium
19
20
III B 21
IV B 22
VB 23
VI B 24
VII B 25
K
Ca
Sc
Ti
V
Cr
50.94
52.00
II B 30
26.96
28.09
30.97
32.07
35.45
39.95
Aluminum
Silicon
Phosphorus
Sulfur
Chlorine
Argon
28
IB 29
31
32
33
34
35
36
Co
Ni
Cu
Zn
Ga
Ge
As
Se
Br
Kr
55.85
58.93
58.70
63.55
65.39
69.72
72.61
74.92
78.96
79.90
83.80
Iron
Cobalt
Nickel
Copper
Zinc
Gallium
Germanium
Arsenic
Selenium
Bromine
Krypton
26
VIII 27
Mn
Fe
54.95
39.10
40.08
44.96
47.88
Potassium
Calcium
Strontium
Titanium
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
Rb
Sr
Y
Zr
Nb
Mo
Tc
Ru
Rh
Pd
Ag
Cd
In
Sn
Sb
Te
I
Xe
95.94
(98)
Vanadium Chromium Manganese
85.47
87.62
88.91
91.22
91.91
101.07 102.91
106.4
Rubidium
Strontium
Yttrium
Zirconium
Niobium Molybdenum Technetium Ruthemium Rhodium
Palladium
Silver
Cadmium
Iridium
Tin
Antimony
Tellurium
Iodine
55
56
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
Cs
Ba
Lanthanide series (see below)
Hf
Ta
W
Re
Os
Ir
Pt
Au
Hg
Tl
Pb
Bi
Po
At
Rn
207.2
208.98
(209)
(210)
(222)
Lead
Bismuth
Polonium
Astatine
Radon
132.91 137.33 Cesium
Barium
87
88
Fr
Ra
(223)
226.03
Francium
Radium
(261)
180.94 183.85 188.21 190.23 192.22 195.08 196.97 200.59 204.38
Hafnium
Tantalum
Tungsten
Rhenium
104 105 106 107 Actinide series (see (261) (262) (263) (264) below) Rutherfordium Dubnium Seaborgium Bohrium
Rf
rare earth elements—Lanthanide series
Df
Sg
Bh
Osmium
Iridium
Platinum
Gold
Mercury
108
109
110
111
112
114
116
118
Hs
Mt (269)
(272)
(277)
(281)
(289)
(293)
(265)
(266)
Hassium
Meiterium
Thallium
Xenon
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
La
Ce
Pr
Nd
Pm
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
(145)
150.4
138.91 140.12 140.91 144.24 Lanthanum
Actinide series
107.87 112.41 114.82 118.71 121.74 127.60 126.90 131.29
Cerium
Praesodymium Neodymium Promethium Samarium
151.96 157.25 158.93 162.50 164.93 167.26 168.93 173.04 174.97 Europium Gadolinium
Terbium Dysprosium Holmium
Erbium
Thulium
Ytterbium
Lutetium
103
89
90
91
92
93
94
95
96
97
98
99
100
101
102
Ac
Th
Pa
U
Np
Pu
Am
Cm
Bk
Cf
Es
Fm
Md
No
Lr
(244)
(243)
(247)
(247)
(251)
(252)
(257)
(258)
(259)
(260)
227.03 232.04 231.04 238.03 237.05 Actinium
Thorium Protactinium Uranium
Neptunium Plutonium Americium
reactions), which create a chain reaction. Typical elementary reactions are C3H8 = H C C3H7 = H2 C3H8 = OH C C3H7 = H2O C3H7 = O2 C C3H6 = HO2 The radicals are highly reactive and very short lived. The reaction of H atoms with molecular oxygen is particularly important because it leads to chain branching: H = O2 C OH = O C3H8 = O C C3H7 = OH in which one free radical (the H atom) is replaced by three (two OH and one C3H7). At high temperatures, the H = O2 reaction begins to dominate and the conversion rate (propane to products) increases dramatically. If species that remove hydrogen atoms (e.g., halons, dry powder) are added to a flame, then the conversion rate (i.e., the rate of burning) falls dramatically. Stoichiometric/Stoichiometry. A stoichiometric mixture of fuel and air is one in which there is an exact equivalence of fuel
Curium
Berkelium Californium Einsteinium Permium Menelevium Nobelium Lawrencium
and oxygen (in the air) so that after combustion all fuel has been consumed and no oxygen is left. The equation for the oxidation of propane (see p. 2-49) defines the stoichiometric propane/oxygen mixture as 1:5 (by volume). As oxygen is approximately 21 percent of normal air, the stoichiometric propane/air mixture would be 1:(5/0.21), that is, 1:23.8 (by volume). (This corresponds to a ratio of 1:15.7 by mass.) Heat of Reaction. The heat of a chemical reaction is the energy that is absorbed or released when that reaction takes place. Exothermic reactions release energy when they occur whereas energy is absorbed when an endothermic reaction takes place. Combustion reactions are exothermic—the products are more stable than the reactants. Endothermic reactions include the pyrolysis of solid fuels, as well as the decomposition processes that occur in concrete when chemically bound water is released at high temperature.
Physical Properties Density. The density of a substance is the ratio of its mass to volume (expressed as g/cm3, kg/m3, or lb/ft3).
CHAPTER 3
TABLE 2.3.2 Element Actinium Aluminum Americium Antimony Argon Arsenic Astatine Barium Berkelium Beryllium Bismuth Boron Bromine Cadmium Calcium Californium Carbon Cerium Cesium Chlorine Chromium Cobalt Copper Curium Dysprosium Einsteinium Erbium Europium Fermium Fluorine Francium Gadolinium Gallium Germanium Gold Hafnium Helium Holmium Hydrogen Indium Iodine Iridium Iron Krypton Lanthanum Lawrencium Lead Lithium Lutetium Magnesium Manganese Mendelevium
■
Chemistry and Physics of Fire
2–53
The Chemical Elements Symbol
Atomic No.
Atomic Weight
Ac Al Am Sba Ar As At Ba Bk Be Bi B Br Cd Ca Cf C Ce Cs Cl Cr Co Cu Cm Dy E Er Eu Fm F Fr Gd Ga Ge Au Hf He Ho H In I Ir Fe Kr La Lr Pb Li Lu Mg Mn Md
89 13 95 51 18 33 85 56 97 4 83 5 35 48 20 98 6 58 55 17 24 27 29 96 66 99 68 63 100 9 87 64 31 32 79 72 2 67 1 49 53 77 26 36 57 103 82 3 71 12 25 101
(227) 226.98 (243) 121.75 39.95 74.92 (210) 137.34 (247) 9.01 208.98 10.81 79.90 112.40 40.08 (251) 12.01 140.13 132.91 35.45 52.00 58.93 63.55 (247) 162.50 (254) 167.26 151.96 (257) 19.00 (223) 157.20 69.72 72.59 196.97 178.49 4.00 164.93 1.01 114.82 126.91 192.20 55.85 83.80 38.91 (257) 207.20 6.00 174.97 24.31 54.94 (256)
Element Mercury Molybdenum Neodymium Neon Neptunium Nickel Niobium Nitrogen Nobelium Osmium Oxygen Palladium Phosphorus Platinum Plutonium Polonium Potassium Praseodymium Promethium Protoactinium Radium Radon Rhenium Rhodium Rubidium Ruthenium Samarium Scandium Selenium Silicon Silver Sodium Strontium Sulfur Tantalum Technetium Tellurium Terbium Thallium Thorium Thulium Tin Titanium Tungsten Uranium Vanadium Xenon Ytterbium Yttrium Zinc Zirconium
Symbol
Atomic No.
Atomic Weight
Hg Mo Nd Ne Np Ni Nb N No Os O Pd P Pt Pu Po K Pr Pm Pa Ra Rn Re Rh Rb Ru Sm Sc Se Si Ag Na Sr S Ta Tc Te Tb Tl Th Tm Sn Ti W U V Xe Yb Y Zn Zr
80 42 60 10 93 28 41 7 102 76 8 46 15 78 94 84 19 59 61 91 88 86 75 45 37 44 62 21 34 14 47 11 38 16 73 43 52 65 81 90 69 50 22 74 92 23 54 70 39 30 40
200.59 95.94 144.20 20.18 237.05 58.71 92.91 14.01 (254) 190.20 16.00 106.40 30.97 195.09 (244) (210) 39.10 140.91 (145) 231.04 226.03 (222) 186.20 102.91 85.47 101.07 150.40 44.96 78.96 28.09 107.87 22.99 87.62 32.06 180.95 98.91 127.60 158.93 204.37 232.04 168.93 118.69 47.90 183.80 238.03 50.94 131.30 173.04 88.91 65.38 91.22
Note: Based on the assigned relative atomic mass of the carbon-12 isotope equal to 12.00. Most elements consist of isotope mixtures. Elements with atomic weights in parentheses are unstable isotopes. a In some cases, the symbol bears no relationship to the English name of the element. These symbols are derived from the Latin names, thus: Ag (Silver, or Argentum), Au (Gold, or Aurum), Fe (Iron, or Ferrum), Hg (Mercury, or Hydrargyrum), K (Potassium, or Kalium), Na (Sodium, or Natrium), Pb (Lead, or Plumbum), Sn (Tin, or Stannum), and Sb (Antinomy, or Stibium).
2–54 SECTION 2 ■ Basics of Fire and Fire Science
Specific Gravity. Specific gravity is the ratio of the mass of a solid or liquid substance to the mass of an equal volume of water. (Note that most commonly used hydrometers are based on a specific gravity of 1 for water at 4°C. At this temperature, water is at its most dense. At 15°C, 1 cm3 weighs 1 g.) Gas Specific Gravity. Gas specific gravity is the ratio of the mass of a gas to the mass of an equal volume of dry air at the same temperature and pressure. It is equal to its molecular weight divided by 29, where 29 is the effective molecular weight of dry air (approximately 21% oxygen = 79% nitrogen). This is a direct consequence of the ideal gas law (see below). Buoyancy. Buoyancy is the upward force exerted on a body or volume of fluid by the ambient fluid surrounding it. If the volume of a gas has positive buoyancy, then it is lighter than the surrounding gas and will tend to rise. If it has negative buoyancy, it is heavier and will tend to sink. The buoyancy of a gas depends on both its molecular weight (see gas specific gravity) and its temperature. If a flammable gas with a gas specific gravity greater than 1 leaks relatively slowly from its container, it will tend to sink to a low level. If the conditions are right, it can travel considerable distances and may be ignited by a remote source of ignition. If propane (C3H8, MW 44) leaks from a cylinder, it will accumulate and spread at ground level with little dilution. In a confined space, such as a basement or a boat with poor ventilation, this presents a serious hazard. The density of a gas decreases as its temperature is increased. Thus, hot products of combustion rise. On the other hand, immediately following a spillage of liquefied natural gas (LNG, mainly methane), the vapor is heavier than air because it is at a very low temperature (the boiling point of methane is –161.5°C). As with propane at ambient temperature, LNG spills can be very dangerous because the vapor can spread over a wide area. However, the gas specific gravity of methane is only 0.55 (16/29) so that at ambient temperature the gas rises and disperses. In an enclosed area, it can create an explosion hazard very rapidly.
The Ideal Gas Law The ideal gas law gives the relationship between pressure, temperature, and volume for a gas and may be expressed as PV C nRT where P C pressure (Pa) V C volume (m3)
its constituent gases, and the “permanent gases” (H2, He) obey this law closely, although higher molecular weight species tend to deviate from “ideal behavior.” The easiest way of distinguishing between a gas that is likely to behave “ideally” and one that does not is to consider its boiling point. Gases that are close to their condensation temperature (i.e., just above the boiling point of the liquid) are likely to deviate strongly from ideal behavior: such gases are more properly described as “vapors.” Nevertheless, this equation is widely used in fire safety engineering calculations. In most cases, the extent of dilution of fire gases is so great that they consist mainly of air. The above equation is a satisfactory approximation to real behavior.
Vapor Pressure and Boiling Point Because molecules of a liquid are always in motion (the amount of motion depending on the temperature), molecules are continually escaping from the free surface of the liquid to the space above. Some molecules remain in this space whereas others, due to random motion, collide with the liquid surface and are “recaptured.” If the liquid is in a closed container (e.g., a can half full of gasoline), equilibrium will be reached when an equal number of molecules are returning to the liquid from the gaseous phase as are leaving (evaporating) from the liquid. In the equilibrium state, the pressure exerted by the vapor is the saturation vapor pressure. It is measured in kiloPascals (kPa) or pounds per square inch absolute (psia)* and increases as the temperature of the liquid is raised. If the liquid is in an open container, molecules in the vapor state continuously diffuse away from the surface and the liquid evaporates. The rate of evaporation increases with temperature and is also influenced by air movement and (to a lesser extent) by pressure. The liquid boils when the saturation vapor pressure equals atmospheric pressure (101.3 kPa). Vapor–Air Specific Gravity (vasg). Vapor–air specific gravity is the ratio of the weight of a vapor–air mixture (resulting from the vaporization of a liquid at equilibrium temperature and pressure) to the weight of an equal volume of air under the same conditions. The specific gravity of a vapor–air mixture thus depends on the vapor pressure and the molecular weight of the liquid. At temperatures well below the boiling point, the vapor pressure of the liquid may be so low that the vapor–air mixture, consisting mostly of air, has a density that approximates that of pure air, that is, the vapor–air specific gravity is approximately 1. As the temperature of the liquid increases, the rate of vaporization increases and the local vapor pressure increases. Close to the boiling point of the liquid, the vapor–air specific gravity approaches the specific gravity of the pure vapor.
T C temperature (K) R C the ideal gas constant (8.314 J/K-mol) n C the number of moles of gas involved This shows that for a given quantity of gas (n is constant), pressure is inversely proportional to volume at constant temperature (Boyle’s law). For a sealed container (constant n and V), pressure is directly proportional to temperature (Charles’ law). Air,
*Absolute pressure is the total force exerted against a unit of area. It is measured in Pascals (Pa, or N/m2) or in pounds per square inch (psi). It often is expressed in fractions or multiples of atmospheric pressure, or in terms of the height of a column of liquid (usually mercury, Hg) that balance the absolute pressure. In situations where pressure gages are used, absolute pressure is obtained by adding gauge pressure to atmospheric pressure. Normal atmospheric, or ambient, pressure equals 101.3 kPa, 14.7 psia, 760 mm Hg, or 30 in. Hg.
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A vapor–air mixture with a density significantly above that of air at the ambient temperature seeks lower levels and can travel some distance from the source. The vapor–air specific gravity of a substance at ambient temperature may be calculated as follows: Let P equal the ambient pressure, p the vapor pressure of the liquid at ambient temperature, and s the specific gravity of the pure vapor. Then, vasg C
p? s P>p = P P
p? s , is the contribution of the vapor to the speP P>p cific gravity of the mixture; the second term, , is the conP tribution of air. The first term,
EXAMPLE: Find the vapor–air specific gravity at 38°C and atmospheric pressure for a flammable liquid whose vapor specific gravity is 2, and whose vapor pressure at 38°C is 10.1 kPa, or one-tenth of atmospheric pressure.
vsag C
10.1 ? 2 101 > 10.1 = C 0.2 = 0.9 C 1.1 101 101
COMBUSTION Combustion is an exothermic, self-sustaining reaction involving a solid, liquid, and/or gas-phase fuel. The process is usually (but not necessarily) associated with the oxidation of a fuel by atmospheric oxygen. Some solids can burn directly by glowing combustion or smoldering, but in flaming combustion of solids and liquid fuels, vaporization takes place before burning. It is necessary to distinguish between two types of flaming: (1) premixed, in which gaseous fuel is mixed intimately with air before ignition, and (2) diffusive, in which combustion takes place in the regions where the fuel and air are mixing. If premixed burning takes place in a confined space, a rapid pressure rise occurs, giving rise to an explosion.
Oxidation Reactions Fire involves oxidation reactions that are exothermic, that is, heat is generated. The reactions are complex and are not understood in their entirety, although certain generalizations can be made. For an oxidation reaction to take place, a combustible material (fuel) and an oxidizing agent must both be present. Fuels include innumerable materials that, due to their chemistry, can be oxidized to yield more stable species, such as carbon dioxide and water; thus, for example, C3H8 = 5 O2 C 3 CO2 = 4 H2O Hydrocarbons, such as propane (C3H8), consist entirely of carbon and hydrogen and may be regarded as “prototype fuels.” All common fuels, whether solid, liquid, or gaseous, are based on the element carbon, with significant proportions of hydrogen, and may also contain oxygen (e.g., wood, polymethylmethacrylate [PMMA]), nitrogen (e.g., wool, nylon), chlorine (e.g., polyvinyl chloride [PVC]), and so on.
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In the present context, the most common oxidizing agent is molecular oxygen (O2) in the air, which consists approximately of one-fifth oxygen and four-fifths nitrogen. However, certain chemicals are powerful oxidizing agents, such as sodium nitrate (NaNO3) and potassium chlorate (KClO3), which, if intimately mixed with a solid or liquid fuel, produce highly reactive mixtures. Thus, gunpowder is a physical mixture of carbon and sulfur (the fuel) with sodium nitrate as the oxidizer. If reactive groups, such as the nitrate group, are incorporated chemically into a fuel, such as in cellulose nitrate or trinitrotoluene (TNT), the resulting species can be highly unstable and will decompose violently under appropriate conditions. There are circumstances involving reactive species in which combustion may take place without oxygen being involved. Thus, hydrocarbons may “burn” in an atmosphere of chlorine, whereas zirconium dust can be ignited in pure carbon dioxide. Ignition (Piloted Ignition and Autoignition). Ignition is the process by which self-sustaining combustion is initiated. Considering first a flammable gas– or vapor–air mixture (see below), piloted ignition can be achieved by the introduction of an ignition source, such as a flame or spark. However, if the temperature is raised sufficiently, the mixture undergoes autoignition, in which the onset of combustion is spontaneous. In general, for the combustion process to become selfsustaining, the molecules of fuel and oxygen must be excited to an activated state, which results in the formation of highly reactive intermediate species (free radicals). These initiate rapid, branched chain reactions that convert fuel and oxygen into products of combustion, with the release of heat (energy). The chain reaction will be self-sustaining for as long as the rate of production of the radicals equals (or exceeds) their natural rate of removal (decay). Once ignition has occurred, combustion will continue until all the available fuel or oxidant has been consumed, or until the flame is extinguished. In general, a selfsustained ignition can occur only in those situations that are capable of supporting self-sustained combustion. For example, if the ambient pressure (or ambient oxidant concentration) is insufficient for sustaining combustion, it also will be insufficient for ignition. For combustible liquids and solids, the initiation of flame occurs in the gas phase. Thermal energy (heat) must first be supplied to convert a sufficient part of the fuel to vapor, thus creating a flammable vapor–air mixture in the vicinity of the surface. For most liquid fuels, this is simply a process of evaporation, but almost all solid fuels must undergo chemical decomposition before vapor is released. One can usually identify a minimum liquid or solid temperature that is capable of generating a flammable mixture close to the fuel surface. For liquid fuels, this is defined in terms of the bulk liquid temperature, and is called the flashpoint. The same phenomenon can be observed for combustible solids, but must be defined as a surface temperature. Note that these are piloted ignition temperatures, because an external pilot is needed to ignite the mixture and only the flammable vapor–air mixture will burn. A slightly higher temperature—the fire point—must be achieved if the liquid (or solid) fuel is to continue burning after the flammable mixture has been consumed.
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In practice, the piloted ignition temperatures of solids and liquids can be influenced by the rate of airflow (oxidant), the rate of heating, and the size and shape of the fuel bed. As a result, reported piloted ignition temperatures, particularly for solids, depend somewhat on the specific test methods. In general, piloted ignition of a gas– or vapor–air mixture is affected by composition, ambient pressure, and the dimensions of the containing vessel, as well as the nature and energy of the pilot. For a given fuel–air mixture, there is a minimum pressure below which ignition does not occur. As the temperature increases, less and less pilot energy is required to ignite the mixture until, at a sufficiently high temperature, the mixture ignites spontaneously. This temperature is referred to as the autoignition (or spontaneous ignition) temperature (AIT). The autoignition temperature of a gaseous fuel also depends on composition and pressure, but it is particularly sensitive to the size and shape of the vessel in which the measurement is made. Differences in test apparatus can lead to significant differences in the results; for example, different values of AIT have been reported in the literature for the same vapor (Tables 2.3.3 and 2.3.4). (The same comments are relevant to the measurement of AIT for solid fuels.)
Limits of Flammability The limits of flammability define the range of concentrations of flammable gas (or vapor) in air that ignite if an ignition source (e.g., a flame, an electrical spark, etc.) is introduced into the mixture (Table 2.3.5). For example, at 25°C, methane/air mixtures are flammable only between 5 percent (the lean, or lower flammability limit) and 15 percent (the rich, or upper flammability limit) by volume. Below 5 percent, the mixture is too lean to burn, whereas above 15 percent it is too rich. The limits for hydrogen are much wider (4% and 74% respectively). When the
TABLE 2.3.3 Variation of Autoignition Temperature with Mixture Composition
% Propane in Air 1.50 3.75 7.65
Autoignition Temperature °F
°C
1018 936 889
548 502 476
TABLE 2.3.4 Variation of Autoignition Temperature for Carbon Disulphide (CS2) with Vessel Size Autoignition Temperature
Volume cm3
in.3
°F
°C
200 1000 10000
12 61 610
248 230 205
120 110 96
TABLE 2.3.5 and Vapors1
Hydrogen Methane Propane n-Octane Ethene Acetylene Methanol Ethanol Acetone
Flammability Limits for Typical Gases Lower Flammability Limit
Upper Flammability Limit
% by Volume
g/m3
% by Volume
g/m3
4.0 5.0 2.1 0.95 2.7 2.5 6.7 3.3 2.6
3.6 36 42 49 35 29 103 70 70
75 15 9.5 — 36 (100) 36 19 13
67 126 210 — 700 — 810 480 390
temperature of the mixture is increased, the flammability range widens, and when the temperature is reduced, the range narrows (Figure 2.3.1). An increase in temperature can cause a nonflammable mixture to become flammable by placing it within the flammability range associated with the higher temperature (see Figure 2.3.1). Flashpoint—Closed Cup. The closed cup flashpoint of a liquid fuel is the temperature at which its vapor pressure corresponds to the lower flammability limit of the vapor (see the section on vapor pressure). The closed cup ensures that equilibrium exists between the liquid and the vapor. When an ignition source is introduced into the enclosed vapor space above the liquid surface, a flash of flame is observed to propagate through the mixture, momentarily consuming all the fuel vapor. It may be measured in the Pensky-Martens Closed Cup Apparatus.2 The term lower flashpoint is sometimes used to distinguish it from the rarely quoted upper flashpoint—the bulk liquid temperature above which the vapor pressure is above the upper flammability limit (see Figure 2.3.1). This is relevant to low lower flashpoint liquid fuels: they can be stored quite safely at ambient temperatures if they are above the upper flashpoint because the vapor–air mixture inside the container is too rich to burn. Gasoline in a partially full gasoline tank is the prime example of this. In contrast, the lower alcohols (methanol and ethanol) lie between the two flashpoints at ambient temperatures (15–20°C). With these fuels, the vapor–air mixture will burn, rendering hazardous any container that is partially full of these liquids. (There have been several serious fires caused by the ignition of alcohol vapor when a flambé lamp has been topped up from a container before the flame has extinguished.) It should be noted that flashpoint decreases as the atmospheric pressure decreases—this has relevance to the fuel tanks of aircraft. Flashpoint—Open Cup. The open cup flashpoint of a liquid fuel is measured under conditions where fuel vapor can diffuse away from the surface of the liquid. It is the lowest bulk liquid temperature at which a flash of flame is observed when an ignition source is present at the rim of the container. All the fuel
Nonflammable
pre
mit
Rich li
or dv ap tur ate
Mists
Sa
Combustible concentration
ssu
re
line
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(Saturated vapor–oxidant mixtures) Flammable
Lean lim
it
Nonflammable Lower and upper flashpoints Temperature
FIGURE 2.3.1 Diagram Showing the Limits of Flammability of Fuel Vapor–Air Mixtures and How They Vary with Temperature. The sloping vapor pressure line shows the saturation limit.
vapor within the flammability limits is consumed momentarily and flame does not persist. It may be measured in the Cleveland Open Cup Apparatus.3
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Once ignition has occurred, flame propagates through the unburnt mixture until all the flammable mixture has been consumed. The fuel may be in the form of gas or vapor, or a suspension of droplets (e.g., a mist) of a combustible liquid, or solid particles of an explosible dust.
Catalysts and Inhibitors Catalyst. A catalyst is a substance that greatly affects the rate of a chemical reaction but is not changed by the reaction itself. For example, platinum in the catalytic converter of a car causes residual fuel to burn without consuming the platinum catalyst. Inhibitors. Inhibitors, also called stabilizers, are chemicals that may be added in small quantities to an unstable material to prevent a vigorous reaction. For example, premature polymerization of styrene monomer is inhibited by the addition of at least 10 ppm (parts per million) of tertiary-butyl-catechol (TBC). Flame-retardant chemicals usually act as inhibitors. For example, the addition of relatively small quantities of chlorineor bromine-containing compounds to a plastic material can increase its resistance to ignition and reduce its ability to support the spread of small flames. However, flame-retardant chemicals are, in general, not effective once a fire has become large.
Stable and Unstable Materials Fire Point. The fire point of a liquid is normally measured in an open cup (e.g., the Cleveland Open Cup Apparatus). It is the lowest bulk temperature at which ignition of the fuel vapors is followed by sustained flaming of the liquid. As a general rule, closed cup flashpoint A open cup flashpoint A fire point. (For n-decane, these temperatures are 46°C, 56°C, and 64°C, respectively.) At or above the fire point, vapors are being evolved at a rate that can sustain a flame. For typical fuels, the minimum rate of vaporization required to support combustion is of the order of 2 g/m2Ýs. It should be emphasized that, if a source of ignition has been established, fires can spread over liquids whose temperatures are considerably below their (lower) flashpoints. In such situations, the ignition source or fire itself heats the liquid surface locally so that its temperature rises above the fire point. Flame can then spread over the surface, aided by surface-tension driven flows.
Explosions In general, explosions occur in situations where the fuel and oxidant have been allowed to mix intimately before ignition. As a result, the combustion reaction proceeds very rapidly without being delayed by the need for first mixing fuel and oxidant. If premixed gases are confined, their tendency to expand on burning can cause a rapid pressure rise or explosion. This is in contrast to fires in which fuel and oxidant are initially separate and the combustion rate is controlled by the rate at which they are able to mix. As a result, the burning rate per unit volume of flame is much lower for fires, and the very rapid increase in pressure characteristic of explosions is not encountered. For ignition of a fuel that has been premixed with air, the fuel concentration must lie within the limits of flammability.
Stable Materials. Stable materials have the capacity to resist changes in normal environmental exposure to air, water, heat, shock, or pressure. Most combustible materials can be classified as stable, although, of course, they can be made to burn. Unstable Materials. Unstable materials may polymerize, decompose, condense, or become self-reactive when exposed to air, water, heat, shock, or pressure. For example, pure gaseous acetylene, hydrazine, and ethylene oxide can all decompose violently, resulting in damaging explosions.
PRINCIPLES OF FIRE Considerable technical knowledge exists concerning the ignition, burning, and fire spread characteristics of combustible materials (solids), liquids, and gases. However, most of the knowledge about combustible solids is for simple geometric arrangements and is inadequate for predicting ignition and fire (flame) spread in realistic situations. Nevertheless, insight can be gained from an understanding of these simple situations. Perhaps the simplest combustion process is the burning of premixed, gaseous fuel–air mixtures involved in explosions. Premixed flames have been the subject of much experimental research. Flammability limits and burning velocities have been catalogued for most of the common gases and vapors.1 It is now possible to calculate the burning rates for the simplest hydrocarbon fuel–air mixtures from the rates of the individual intermediate (elementary) reactions.4 Other scenarios for which burning rates may be calculated include fuel droplets and small samples of certain plastics. In such
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situations, combustion takes place in the gas-phase (diffusion flame) and the rate of burning is controlled by the rate of supply of fuel vapor. In contrast to explosions, fires involve situations in which fuel vapor and oxidant (air) are initially unmixed. Their burning rates are restricted primarily by the supply of fuel vapor and oxidant (air) to the flames rather than the rates of the elementary chemical reactions within the flames. In fires, the basic gasphase combustion process usually occurs along thin flame sheets—the diffusion flame—that separate regions rich in fuel vapor from regions rich in oxidant. Fuel vapor and oxidant diffuse toward each other from opposite sides of the flame sheet where they combine to produce combustion products and heat, which in turn diffuse away from the flame sheet. When diffusion flames are small, for example, from a burning match or candle, they typically appear quite smooth and steady. They are called laminar diffusion flames. If the fire is allowed to grow (e.g., by spreading over an extended surface), the flames become unstable, evidenced as a characteristic flickering. Eventually, they become fully turbulent when the fire diameter exceeds 300 mm to 500 mm. Scientists have obtained a relatively clear understanding of small fires involving laminar diffusion flames. For example, they can calculate the rate of flame spread over solid surfaces,5 and steady burning rates6 in terms of basic combustion properties for a variety of simple geometries (e.g., smooth flat surfaces, cylinders, etc.). In these situations, the burning rates are controlled by the convective heat transfer from the flame to the solid fuel which, in response, gasifies and supplies fuel vapors to the flames. The oxidant (air) is supplied to the flames by the upward flow induced by the buoyant hot combustion products. The buoyant flow also may enhance the convective heat transfer from the flames to the solid fuel. In the case of a spreading flame, the spread rate is governed by the forward heat transfer from the flames to the as yet uninvolved fuel, which must be preheated before it can provide fuel vapors to the flames. (A review of flame spread is given by Quintiere.5) Larger fires involving turbulent diffusion flames are less well understood because of difficulties in describing the turbulent gas motion, and the flame radiation, which is usually the dominant form of heat transfer for larger fires (fuel bed diameters greater than 500 mm to 1000 mm). Experience and measurements have shown that this enhanced role of flame radiation in larger fires can alter the relative flammability ranking of fuels in comparison to their small-scale flammability rankings. The study of these larger (hazardous) scale fires is at the forefront of current fire research. During the past decade, new laboratory tests have been developed that are capable of providing data relevant to full-scale fire behavior.7 Furthermore, a number of different computer programs are now available that are capable of modeling various aspects of fire development, from ignition and flame spread, to full room involvement (flashover), propagation to adjacent rooms, and possibly even to other buildings (see for example the review by Cox8). However, these programs should still be regarded as research tools. Great care is required if they are to be used as predictive tools although some are used regularly as aids to the engineering design process.
Ignition and Combustion To illustrate the many physical and chemical processes involved in fires, it is convenient to first discuss the ignition, burning, and eventual extinction of a wood slab in a typical situation, such as a fireplace.9 1. Suppose the wood slab is initially heated by thermal radiation. As its surface temperature approaches the boiling point of water, gases (principally steam) slowly evolve from the wood. These initial gases have little, if any, combustible content. As the slab temperature increases above the boiling point of water, the “drying” process penetrates deeper into the wood. 2. With continued heating, the wood surface begins to discolor when the surface temperature exceeds 250°C. This discoloring is visible evidence of pyrolysis, the chemical decomposition of matter through the action of heat. When wood pyrolyzes, it releases combustible gases* while leaving behind a black, carbonaceous residue called char. This pyrolysis process penetrates deeper into the wood slab as the heating continues. 3. Soon after active pyrolysis begins, combustible gases begin to evolve rapidly enough to support gas-phase combustion. However, combustion occurs only if a pilot flame or some other source of energy sufficient to ignite the vapors is present. If no such pilot is present, the wood surface must be heated to a much higher temperature before spontaneous ignition occurs. 4. Once ignition occurs, a diffusion flame rapidly covers the pyrolyzing surface. Once the diffusion flame is established, little oxygen will reach the pyrolyzing surface. Meanwhile, the flame heats the fuel surface and causes an increase in the rate of pyrolysis. If the original radiant heat source is withdrawn at ignition, the burning will continue provided that the wood slab is thin enough (less than 19 mm, although this depends on how long the slab has been heated). Otherwise, the flames will go out because the surface is losing too much heat by conduction into the interior of the slab and by thermal radiation to the surroundings. If an adjacent, parallel wood surface (or insulating material) is facing the ignited slab, some surface radiation loss is returned as the adjacent surface heats up and begins to radiate back. Under these circumstances, the ignited slab can continue burning even after the withdrawal of the initial heat source. This explains why one cannot burn a single large log in a fireplace, but instead must use several logs to capture the radiant heat losses. 5. As the burning continues, a char layer builds up. This char layer, which is a good thermal insulator, restricts the flow of heat to the wood interior, and consequently the rate of
*The pyrolysis of wood is complex, involving two distinct mechanisms. At low temperatures (c. 250–300°C), the formation of char predominates and the fuel vapors are mainly CO2 and H2O, with low combustible content. At higher temperatures, less char is formed and the vapors are of higher combustible content. Flame retardants such as phosphates and borates promote the char-forming mechanism, trapping a substantial proportion of the combustible material as char while releasing vapor of low flammability.
CHAPTER 3
pyrolysis tends to reduce. The pyrolysis rate will also decrease when the supply of unpyrolyzed wood runs out. When the pyrolysis rate decreases to the point of not being able to sustain gas-phase combustion, oxygen will diffuse in sufficient amounts to the char surface, permitting it to undergo direct glowing combustion (provided that the radiant heat losses are not too large). 6. This scenario presumes an ample (but not excessive) supply of air (oxidant) for combustion. If there were insufficient oxidant to burn the available fuel vapor, the excess vapors would travel with the flow and possibly burn where they eventually would find sufficient oxidant. For example, this happens when fuel vapors emerge and burn outside a window of a fully involved but underventilated room fire. Generally, underventilated fires produce large amounts of smoke and toxic products, dominated by carbon monoxide. If, on the other hand, one imposed an airflow over the pyrolyzing surface, the oxidant supply may exceed that required for complete combustion of the fuel vapors. In this case, the excess oxidant can cool the flames sufficiently to suppress their chemical reaction and extinguish them, as happens, for example, when one blows out a match. In the case of larger fires with ample supply of fuel vapors, imposing a forced draft on them simply increases their rate of burning by increasing the flame-to-fuel surface heat transfer, which in turn enhances the fuel supply rate. 7. Following the ignition of a certain portion of our wood slab, the flames may spread over the entire fuel array. Flame spread can be thought of as a continuous succession of piloted ignitions where the flames themselves provide the heat source. One commonly observes that upward flame spread on a vertical surface is much more rapid than downward or horizontal flame spread. This is because flames and hot gases travel upward and contribute their heat over a greater area in an upward direction. Thus, each successive “upward ignition” adds a much greater burning area to the fire than a corresponding “downward,” or “horizontal,” ignition. Generally, materials that ignite easily (rapidly) also propagate flames rapidly. The ignitability of a material is controlled by its resistance to heating (thermal inertia) and by the temperature rise required for it to begin to pyrolyze. Materials with low thermal inertia, such as foamed plastics or balsa wood, heat rapidly when subjected to a given heat flux. These materials are often easy to ignite and can cause very rapid flame spread. On the other hand, dense materials, such as the hardwoods oak and ebony, tend to have relatively high thermal inertias and are difficult to ignite. The burning rates of larger, more hazardous fires are principally governed by the radiant heat transfer from the flames to the pyrolyzing fuel surface.9 This flame radiation comes primarily from the luminous soot particles in the flames. Combustibles that tend to produce copious amounts of soot or smoke, such as polystyrene, also tend to support more intense fires, despite the fact that their fuel vapors burn less completely, as evidenced by their higher smoke output. Well-ventilated fires generally release less smoke than poorly ventilated ones. In well-ventilated fires, the surrounding
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air can gain speedy access to the unburned fuel vapors and soot before the fuel vapors cool down by radiation. Poorly ventilated fires can release copious amounts of smoke and products of incomplete combustion, such as carbon monoxide. In poorly ventilated fires, fuel vapors have insufficient air to burn completely before cooling off and leaving the fire area. Fires occurring in oxygen-enriched atmospheres have higher flame temperatures, increased fractions of heat release by radiation, and increased burning rates per unit fuel area. These higher flame temperatures generally cause a much greater conversion of fuel vapors into soot, resulting in significantly increased smoke release rates. For example, a well-ventilated methanol fire typically burns with a blue (i.e., soot-free) flame in normal air. However, a similarly well-ventilated methanol fire can burn with a brightly luminous smoky flame in an oxygenenriched atmosphere. This sensitivity to ambient oxygen concentration significantly increases the flame radiation, burning rates, and resultant fire hazard.
Flammability Properties of Solid Combustibles and High Fire Point Liquid Fuels The previous discussion can be amplified by identifying a number of materials factors that are important in contributing to fire hazards in typical fires. Heat of Combustion. Heat of combustion is a measure of the maximum amount of heat that can be released by the complete combustion of unit mass of combustible material (units of measurement kJ/kg). (See section on heat energy sources.) Stoichiometric Oxidant. The mass of oxidant required for complete combustion of a unit mass of combustible is called the stoichiometric oxidant requirement. Oxidation of propane proceeds according the following formula: C3H8 = 5 O2 C 3 CO2 = 4 H2O This means 44 g of propane (1 mole) requires 160 g of oxygen (5 moles) for a reaction that yields 3 moles of carbon dioxide and 4 moles of water. This also means 1 g propane requires 3.64 g oxygen. If the oxidant is air, then the stoichiometric oxidant requirement would be (5/0.21) ? (29/44) C 15.7, where 29 is the average molecular weight of air. Combustibles with large stoichiometric oxidant requirements often produce large flame heights, which in turn present greater fire spread hazards. The stoichiometric oxidant requirements for typical (organic) combustibles is approximately proportional to their heat of combustion, so that organic combustibles all release approximately the same amount of heat per unit mass of consumed oxidant. Thus, it is found that 13 kJ of energy is released for every gram of oxygen consumed in the combustion of most common materials. This fact is the basis for the measurement of heat release in the cone calorimeter. (This can also be expressed as 3 kJ/g of air, assuming that all the oxygen is consumed.) Heat of Gasification. The heat required to vaporize a unit mass of combustible material that is initially at ambient temperature is
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called the heat of gasification. This quantity is very important because it determines the amount of combustible vapor supplied to a fire in response to a given supply of heat to the pyrolyzing surface. The fire hazard of some plastics can be reduced by adding inert fillers, such as alumina trihydrate, which increase their effective heats of gasification. Ignitability (Piloted). Ignitability, or ease of ignition, is inversely proportional to the time it takes for a given applied heat flux to raise the surface temperature of a material to its piloted ignition (fire point) temperature. This property is important both for ignition and fire spread although its measurement is highly sensitive to the method of determination. Char Formation. Char is a black, carbonaceous residue, formed during the pyrolysis of some materials, for example, wood, wood products, and some thermosetting plastics. The insulating properties of the resulting char layer can lead to reduced burning rates by restricting the flow of heat to the unpyrolyzed material below. When exposed to heat, intumescent paints mimic the formation of a char layer by charring at the same time as releasing a “blowing agent,” thus producing a char layer of low density and excellent insulating properties. Note that thermoplastics, such as polypropylene, tend not to char, but soften, melt, and flow instead. Soot Formation. Soot consists of minute solid carbonaceous particles formed as a result of incomplete combustion and pyrolysis in the fuel-rich regions of diffusion flames. Combustibles whose flames produce significant amounts of soot are generally more hazardous because the soot increases flame radiation, which in turn increases the burning rate. Soot is also the source of the particulate matter in smoke that is produced by fires. (Note that “smoke” also contains other [gaseous] fire products that are progressively diluted as the smoke spreads to points remote from the fire.) Flame Retardants. The addition of relatively small amounts of certain chemicals to the combustible solid or the oxidant can inhibit gas-phase flame reactions. Such inhibitors can be effective in retarding ignition and flame spread associated with small fires. Flames can also be inhibited by introducing additives to solid combustibles that promote char formation and cause fuel vapors of lower combustible content to be released (see footnote on p. 2-56). Melting. Combustibles that tend to melt are often more hazardous than those that do not. This is because the molten material can flow to form a pool, thus increasing the area of pyrolyzing surface and spreading the fire. The molten material itself also can be a hazard. Toxicity. Carbon monoxide usually is the principal toxicant produced by a fire. It is present in all fire gases and indicates that combustion has not been completed. Materials containing other elements such as chlorine and nitrogen can produce other toxicants such as hydrogen chloride (from polyvinyl chloride) or hy-
drogen cyanide (from wool and polyurethane), respectively (see Section 8, Chapter 2, “Combustion Products and Their Effects on Life Safety”). Geometry. Last, but not least, the geometry of a material strongly influences its flammability. In general, thin materials ignite more readily and spread flame more rapidly than do thick materials. Upward flame spread is more rapid than downward or horizontal flame spread. In particular, geometric arrangements that promote rapid spread, such as the vertical flues within high rack storage, which are well ventilated (i.e., there is ample air) and provide shielding to reduce radiative and convective heat losses, are usually the most hazardous.
General Principles The underlying science of fire protection engineering rests on the following principles: 1. An oxidizing agent, a combustible material, and an ignition source are essential for combustion. (The exception is spontaneous combustion, which does not require an independent ignition source. Spontaneous combustion is discussed in the section on spontaneous heating on p. 2-63.) 2. The combustible material must be heated to its piloted ignition temperature before it can be ignited or support flame spread. 3. Subsequent burning of a combustible material is governed by the heat feedback from the flames to the pyrolyzing or vaporizing combustible. 4. The burning will continue until one of the following happens: a. The combustible material is consumed. b. The oxidizing agent concentration is lowered to below the concentration necessary to support combustion. c. Sufficient heat is removed or prevented from reaching the combustible material, thus preventing further fuel pyrolysis. d. The flames are chemically inhibited or sufficiently cooled to prevent further reaction. All the material presented in this handbook for the prevention, control, or extinguishment of fire is based on these principles.
HEAT MEASUREMENT The temperature of a material is the condition that determines whether it will transfer heat to or from other materials. Heat always flows from higher to lower temperatures. Temperature is measured in degrees.
Temperature Units Celsius. A Celsius (or centigrade) degree (°C) is 1/100 of the difference between the temperature of melting ice and boiling water at 1 atmosphere pressure. On the Celsius scale, zero (0°C) is defined as the melting point of ice, and 100°C is the boiling point of water. The Celsius unit is approved by the International System (SI) of units.
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Kelvin. A Kelvin degree or Kelvin (K) is the same size as the Celsius degree but the zero on the Kelvin scale is –273.15°C (–459.67°F). Zero on the Kelvin scale is the lowest achievable temperature, known as “absolute zero”; thus the Kelvin scale provides us with so-called absolute temperatures. The Kelvin is an approved SI unit. Fahrenheit. A Fahrenheit degree (°F) is 1/180 of the difference between the temperature of melting ice and boiling water at 1 atmosphere pressure. On the Fahrenheit scale, the melting point of ice (0°C) is taken as 32°F; thus 212°F is the boiling point of water (100°C). Rankine. A Rankine degree (°R) is the same size as the Fahrenheit degree, but on the Rankine scale, zero is –459.67°F (–273.15°C). The Rankine scale also provides an absolute temperature. Fahrenheit and Rankine degrees are not approved SI units, and their use is greatly discouraged.
Temperature Measurement Devices that measure temperature depend on physical change (expansion of a solid, liquid, or gas), change of state (solid to liquid), energy change (changes in electrical potential energy, i.e., voltage), or changes in thermal radiant emission and/or spectral distribution. The principles of operation of the more common temperature measuring devices are discussed next. Liquid Expansion Thermometers. These thermometers consist of a tube partially filled with a liquid. The tube measures expansion and contraction of the liquid by changes in temperature. The tube is calibrated to permit reading the level of the liquid in degrees of a temperature scale. The most common example is the mercury-in-glass thermometer. Bimetallic Thermometers. Bimetallic thermometers contain strips of two metals that are laminated together and have different coefficients of expansion. As the temperature changes, the two metals expand or contract to different extents, causing the strip to deflect. The amount of deflection is measured on a scale that is calibrated in degrees of temperature. Thermocouples. Thermocouples consist of a pair of wires of different metals or alloys welded together at a point to form a junction. A voltage is generated across this junction, the magnitude of which depends on the nature of the metals and the temperature. The magnitude is compared with a compensating junction at 0°C, and the voltage difference is calibrated to give the temperature in degrees. Pyrometers. Pyrometers measure the intensity of radiation from a hot object. Because intensity of radiation depends on temperature, pyrometers can be calibrated to give readings in degrees of temperature. Optical pyrometers measure the intensity of a particular wavelength of radiation.
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Heat Units Joule (J). Conventionally, the Joule is defined as the energy (or work) expended when unit force (1 Newton) moves a body through unit distance (1 m). The Joule is the most convenient unit of energy to use and can be related to the calorie, which is defined in terms of the heat energy required to raise the temperature of unit mass of water by 1°. The Joule is an approved SI unit. Watt (W). The Watt is a measure of power, or the rate of energy release. One Watt is equal to 1 Joule per second (1W C 1 J/s). The rate of heat release from a fire can be expressed in kilowatt (kW) or megawatt (MW) units that are familiar to the electrical engineer. Calorie. The amount of heat required to raise the temperature of 1 g of water 1°C (measured at 15°C [59°F]) is called a calorie. One calorie equals 4.183 J. British Thermal Unit (Btu). The amount of heat required to raise the temperature of 1 lb of water 1°F (measured at 60°F [15.5°C]) is called the British thermal unit. One Btu equals 1054 J (252 calories). Btu and calories are not approved SI units. Heat energy has quantity, as well as potential (intensity). For example, consider the following analogy. Two water tanks stand side by side. If the first tank holds twice as many gallons as the second, then the first tank can hold twice the quantity of water as the second. But if the level of water in the two tanks is equal, then their pressures or potentials are equal. If the two tanks are joined by a pipe at low level, water will not flow from one to the other because both tanks have the same equilibrium pressure. In a similar manner, one body may hold twice the quantity of heat energy (measured in Joules or Btu) as a second body. However, if the potentials or temperatures of the bodies are equal, no heat energy will flow from one body to the other when they are brought into contact because the bodies are at equilibrium. If a third body at a lower temperature were brought into contact with the first body, heat would flow from the first to the third until both body temperatures became equal. The amount or quantity of heat flowing until this equilibrium is reached depends on the heat retention capacities of each body involved. (Note that, essentially, ignition involves the addition of sufficient heat [by heat transfer, q.v.] to raise the temperature to the appropriate value. On the other hand, extinction may be accomplished by the removal of heat. “Chemical” extinguishment works by another mechanism, i.e., by interrupting chemical reactions that are important in the combustion process.)4
Specific Heat The specific heat of a substance defines the amount of heat it absorbs as its temperature increases. It is expressed as the amount of thermal energy required to raise unit mass of a substance 1 temperature degree and is measured in J/kg(°C) or Btu/lb(°F). Water has a specific heat of 4200 J/kg(°C) (1 Btu/lb°F). (Note:
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for simplicity, it is common practice to use K for Kelvin instead of °C as the symbol for degrees when specifying the units of a quantity such as specific heat: this can be written J/kgÝK.) Specific heats vary over a considerable range, from 460 J/kgÝK for steel to 2400 J/kgÝK for oak. Values of specific heat are relevant to fire protection because they define the amount of heat required to raise the temperature of a material to a point of danger, or the quantity of heat that must be removed to cool a burning solid to below its fire point. One reason for the effectiveness of water as an extinguishing agent is that its specific heat is higher than that of most other substances (4200 J/kgÝK).
Latent Heat A substance absorbs heat when it is converted from a solid to a liquid, or from a liquid to a gas. This thermal energy is called latent heat. Conversely, heat is released during conversion of a gas to a liquid or a liquid to a solid. Latent heat is the quantity of heat absorbed by a substance passing between liquid and gaseous phases (latent heat of vaporization), or between solid and liquid phases (latent heat of fusion). It is measured in Joules per unit mass (J/kg). The latent heat of fusion of water (normal atmospheric pressure) at the freezing or melting point of ice (0°C) is 333.4 kJ/kg; the latent heat of vaporization of water at its boiling point (100°C) is 2257 kJ/kg (970.3 Btu/lb). The large heat of vaporization of water is another reason for the effectiveness of water as an extinguishing agent. It requires 3 MJ (million Joules) to convert 1 kg of ice at 0°C to steam at 100°C. The latent heats of most other common substances are substantially less than that of water. Thus, the heat absorbed by water evaporating from the surface of a burning solid is a major factor in reducing its temperature and thus reducing the rate of pyrolysis and preventing flame spread to adjacent hot surfaces.
HEAT TRANSFER Transfer of heat governs all aspects of fire, from ignition through to final extinguishment. Heat is transferred by one or more of three mechanisms: (1) conduction, (2) convection, or (3) radiation.
Conduction Heat transfer through a solid (e.g., from a heated surface to the interior of the solid) is the process called conduction. The rate at which heat (energy) is transferred by conduction through a body is a function of the temperature difference and the conductance of the path involved. Conductance depends on the thermal conductivity, the cross-sectional area normal to the flow path and the length of flow path. The rate of heat transfer is simply the quantity of heat transferred per unit time whereas the heat “flux” (normally given the symbol qg) is the quantity of heat transferred per unit time per unit cross-sectional area (the dot over q specifies per unit time and the double prime indicates per unit surface area). qg C
k !T L
where !T C temperature difference L C path length k C thermal conductivity of the material (the heat flux resulting from a unit temperature gradient [falloff of 1 degree per unit of distance]) The units of thermal conductivity are J/(mÝs°C), that is, W/mÝK. The conduction of heat through air or other gases is independent of pressure within the usual pressure range. It approaches zero only at very low pressures. No heat is conducted in a perfect vacuum. Solids are much better conductors of heat than are gases. The best commercial insulators consist of fine particles or fibers that have spaces between the particles that trap air (e.g., fiberglass insulation). Heat conduction cannot be completely stopped by any heatinsulating material. Thus, the flow of heat is unlike the flow of water, which can be stopped by a solid barrier. Heat-insulating materials have low thermal conductivities, but no matter how thick the insulation may be between the source of heat and a combustible material, it may still be insufficient to prevent ignition. If the rate of heat conduction through the insulating material is greater than the rate of dissipation from the combustible material, the temperature of the latter may increase to the point of ignition. For this reason, there should always be an air gap or some other means by which heat may be carried away by convection, rather than relying solely on insulating materials for protection. For heat conduction, the most important physical properties of a material are thermal conductivity (k), density (:), and specific heat (C). The last two quantities are usually listed separately, although it is their product (:C) that is of interest. The product :C is a measure of the amount of heat necessary to raise the temperature of unit volume of the material by 1° K. The units would be J/m3ÝK (Joules per cubic meter per degree [Kelvin]) and could be called the thermal capacity per unit volume. Thermal conductivity and thermal capacity per unit volume are rarely of much importance individually. The solution to heat conduction problems is very complex and cannot be adequately presented here. However, one or two interesting features must be mentioned. A most useful quantity is the time constant of a given thickness (x) of a material. Thus, if the surface of a material is suddenly increased to an elevated temperature, then the temperature at a depth (x) within the material will begin to change significantly after a certain time, t (s): tC
x 2:C k
It is seen that the dimensions of the expression are seconds (s): m2 Ý (J/m3 Ý K) J mÝsÝK C m2 3 Cs J/(mÝsÝK) m ÝK J meters (m), Joules (J), and degrees Kelvin (K) cancel out, leaving the result of the dimension in seconds, that is, time. This is a time constant; thus, the higher the number, the slower the transfer. It can be seen that the time required for a thermal wave to penetrate a body increases with the square of its thickness. This expression contains the quantity thermal diffusivity, k/:C,
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which occurs in many time-dependent heat transfer equations. Another important quantity is the thermal inertia, k:C. This quantity determines how rapidly the temperature of a surface increases when exposed to a heat flux (convection or radiation— see discussion below). It is particularly relevant to the ignition of combustible solids. Materials with low thermal inertia, such as polyurethane foam, can be ignited very easily in comparison with solids such as wood or PMMA. This is very clearly shown in Figure 2.3.2 in which the surface temperature of very thick (“semi-infinite”) solids of different materials exposed to convective heat transfer is plotted as a function of time. Chemically, oak and fiber insulation board (FIB) are very similar, but the thermal inertia of oak is almost 40 times greater than that of FIB: consequently the surface of FIB heats up much more rapidly than the surface of an oak sample.
Convection Convection involves the transfer of heat by a circulating fluid— either a gas or a liquid. Thus, heat generated in a stove is distributed throughout a room by heating the air in contact with the stove (by conduction across the stationary boundary layer in contact with the surface of the stove). The hot, buoyant air then rises, setting up convection currents that transfer heat to distant objects in the room. Heat is transferred from the air to these distant objects again by conduction across the boundary layer. Air currents can be made to carry heat by convection in any direction by use of a fan or blower. Note that the term convective heat transfer is commonly used to describe the mode of heat transfer between a fluid and a solid surface. The corresponding convective heat transfer coefficient (h) is defined by the expression qg C h!T
1.0 PUF 950
FIB 20 × 103
TS – T0 θs /θ∞ = ———– T∞ – T0
Asbestos 90 × 103
0.5 Oak 780 × 103
Steel 1.6 × 108 0
5 Time (min)
10
FIGURE 2.3.2 The Effect of Thermal Inertia (k:C) on the Rate of Temperature Rise at the Surface of a “Semi-Infinite” Solid. The figures are values of k:C in units W 2s/m4K 2. See Chapter 2, “Heat Transfer,” in An Introduction to Fire Dynamics.10 FIB C fiber insulation board; PUF C polyurethane foam.
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where qg is the rate of heat transfer per unit surface area (W/m2), and !T is the temperature difference (K) between the fluid and the surface.
Radiation Radiation is a form of energy that travels across a space without the need for an intervening medium, such as a solid or a fluid. It travels as electromagnetic waves, similar to light, radio waves, and X-rays. In a vacuum, all electromagnetic waves travel at the speed as light (3 ? 1010 m/s). If these waves are directed onto the surface of a body, they can be absorbed, reflected, and/or transmitted. Visible light consists of wavelengths between 0.4 ? 10>6 to 0.7 ? 10>6 m, corresponding to the blue and the red end of the visible spectrum. Thermal radiation (emission) from combustion processes occurs principally in the infrared region (wavelengths greater than red wavelengths). Our eyes see only the tiny fraction of the total radiation that happens to be emitted within the visible region. The distinction between radiation and convection can be illustrated by reference to a candle flame. The air that is required for combustion of the fuel vapors is drawn into the flame from the surrounding atmosphere by a process known as entrainment. The hot gases rise vertically upwards as a plume that carries with it most of the heat (70%–90%) released in the combustion process, depending on the fuel. The rest of the heat is lost from the flame by radiation. This can be detected if a hand is held near the side of the flame. The sensation of warmth is caused by radiant heat transfer, that is, radiation. If, instead, the hand is held over the flame, it will sense much more heat. Most of the heat radiated from a diffusion flame arises from minute particles of soot (solid carbonaceous particles) formed in the complex series of reactions that occur within the flame.11 These particles are the source of the characteristic yellow luminosity: they are radiating over a wide range of wavelengths, mainly in the infrared, and we see only that part of the emission that lies in the visible region (A0.7 5m). Some radiation also comes from the gaseous combustion products H2O and CO2. These gases emit radiation within narrow wavelength bands in the infrared part of the spectrum so that fuels that do not produce soot (such as methyl alcohol and polyoxymethylene) have nonluminous flames. As a rough guide, less than 10 percent of the heat of combustion is lost from the flame by radiation in these cases. However, larger fires involving “ordinary” fuels may release 30 to 50 percent of the total amount of energy as radiation, exposing nearby surfaces to high levels of radiant heat transfer. Radiation travels in straight lines. We would expect intuitively that the heat received from a small area source would be less than that received from a large radiating surface, provided the sources were at comparable distances and were emitting comparable energies per unit area (Figure 2.3.3). Thermal radiation passes freely through gases that consist of symmetrical diatomic molecules, such as oxygen (O2), and nitrogen (N2) (the principal constituents of air), but is absorbed in narrow wavelength bands by water vapor (H2O), carbon dioxide (CO2) and other asymmetrical molecules such as carbon monoxide (CO) and sulfur dioxide (SO2). Although their concentrations
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H
H H H
H
FIGURE 2.3.3 A Comparison of Heat Absorption by Surfaces of Similar Area from a Pinpoint Source (Left) and a Large Radiating Surface (Right)
are low, the presence of carbon dioxide and water vapor in the normal atmosphere prevents radiation in narrow bands in the vicinity of 2.8 5m (microns) and 4.4 5m (in particular) from reaching the surface of the earth. Advantage is taken of this fact in the development of infrared flame detectors, some of which are designed to be blind to solar radiation by responding only to 2.8 5m or 4.4 5m. These wavelengths are emitted strongly by molecules of water and carbon dioxide in flames. On the same principle, water vapor and carbon dioxide in the atmosphere are responsible for the absorption of appreciable amounts of thermal radiation emitted from large fires: the effect is appreciable only at significant distances from such fires. This absorption helps to explain why forest fires or large LNG fires are (relatively) less hazardous on days when humidity is high. Also, because water droplets absorb almost all the incident infrared radiation, mists or water sprays are effective attenuators of radiation. This property is used by firefighters for their protection. (It should be noted that suspended smoke particles absorb thermal radiation selectively, but transmit a sufficient proportion to allow infrared cameras to “see” hot objects through smoke.) When two bodies face each other and one body is hotter than the other, a net flow of radiant energy from the hotter body to the cooler body will ensue until thermal equilibrium is achieved. The ability of the cooler body to absorb radiant heat depends on the nature of the surface. If the receiving surface is shiny or polished, it will reflect most of the radiant heat away, whereas if it is black or dark in color, it is likely to absorb most of the heat. The absorptivity of the surface is simply the fraction of the incident radiant heat that is absorbed by the surface. A surface with an absorptivity of 1.0 (the maximum value) is called a black surface. Most nonmetallic materials are effectively “black” to infrared radiation, despite the fact that they may appear light or colored to the naked eye (i.e., visible radiation). Some substances, such as pure water and glass, are transparent to visible radiation and allow it to pass through them with minimal absorption; however, both liquid water and glass are opaque to most infrared wavelengths. Glass greenhouses and solar panels operate on the principle of being transparent to the sun’s visible radiation while at the same time being opaque to the infrared radiation attempting to escape from the greenhouse or solar panel. Shiny metallic materials are excellent reflectors of radiant energy and have low absorptivities (perhaps as low as 0.1). For
example, aluminum foil often is used together with fiberglass in building insulation. Sheet metal is often used beneath stoves or on heat-exposed walls. The Stefan-Boltzmann law states that the radiation emitted per unit area from a hot surface is proportional to the fourth power of its absolute temperature. The law can be expressed by the formula qg C .;T 4 kW/m2 where qg C the radiant emission per unit surface area . C the surface emissivity (which is 1.0 for a black body or black surface) ; C the Stefan-Boltzmann constant (equal to 56.7 ? 10>12 kW/m2ÝK4) T C the absolute temperature expressed in Kelvin It should be noted that the numerical values of emissivity and the absorptivity of a surface are equal. To appreciate the importance of the fourth power dependence, consider the following situation. EXAMPLE: A heater is designed to operate safely with an external surface temperature of 260°C. What is the increase in radiation if the external surface temperature is allowed to increase by 100°C to 360°C, and by 240°C to a maximum of 500°C? SOLUTION:
First, it is necessary to convert the temperatures from degrees Celsius to degrees Kelvin by adding 273: thus 260°C becomes 533 K, 360°C becomes 633 K and 500°C becomes 773 K. Next, if we assume that the surface is black (. C 1.0), the radiant emission per unit area of the external surface (its “emissive power”) for safe operation at 260°C is q C .;T 4 C 1.0 ? 56.7 ? 10>12 ? (533)4 C 4.6 kW/m2
The corresponding emissive powers at the higher temperatures are q C .;T 4 C 1.0 ? 56.7 ? 10>12 ? (633)4 C 9.1 kW/m2 q C .;T 4 C 1.0 ? 56.7 ? 10>12 ? (773)4 C 20.2 kW/m2 Thus, it can be seen that, by increasing the stove temperature by 100°C, the emissive power is approximately doubled from 4.6 to 9.1 kW/m2. If amount of heat radiated was only a function of the first power of the absolute temperature (qg ä T), then it would increase by only about 20 percent if the absolute temperature was increased from 533 to 633 K. Finally, if one were so careless as to allow the stove to reach 500°C, it would emit 20 kW/m2, this is sufficiently high to lead to ignition of many typical home furnishings that were in close proximity to the stove. Because residential coal or wood stoves can sometimes undergo a temperature “runaway” if given too much air, it is important to keep all nearby furnishings well away from the stove to ensure that the maximum received radiant heat transfer is kept to safe levels. The radiant energy transmitted from a pointlike source to a receiving surface will vary inversely, as the square of their separation distance. If a stove is small relative to its distance from nearby objects, then it behaves like a point source; doubling its separation distance will decrease the incident radiant heat (per unit area) by a factor of 4. However, if the nearby
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object is close to the stove, the stove appears like a large surface, and small changes in separation will have only a small effect on the intensity of radiation falling on the receiving surface (e.g., a large stove located within a few centimeters of a combustible wall; see Figure 2.3.3). In this case, one must protect the wall by some means such as a noncombustible board faced with a reflecting material (low absorptivity). Generally, we have a good understanding of radiant heat transfer between solid surfaces.12 It is also possible to carry out reliable estimates of radiant heat absorbed or emitted by gases of a known composition and temperature. However, it is more difficult to estimate the amount of heat radiated from flames. This is because most of it is emitted by soot particles in the flames, the concentration of which is difficult to measure and even more difficult to predict. Moreover, this lack of data prevents an accurate estimate of the burning rate of a fire to be made. There is, however, one useful rule of thumb: the total radiant output from flames from fires burning on a fuel bed of diameter more than approximately 0.3 to 0.5 m is usually about 30 to 40 percent of the maximum heat output, assuming complete combustion.9 A comparable amount of energy leaves by convection, with the remaining fraction accounted for by incomplete combustion (carbon monoxide, soot, etc.).
ENERGY SOURCES OR SOURCES OF IGNITION Because fire prevention and extinguishment depend on the control of heat, it is important to be familiar with the more common ways in which heat energy can be produced. Four sources of heat energy are (1) chemical, (2) electrical, (3) mechanical, and (4) nuclear.
Chemical Energy Oxidation reactions produce heat. They are the source of the heat that is of primary concern to fire protection engineers. Heat of Combustion. The heat of combustion is the amount of heat released during the complete oxidation of unit mass of a combustible substance to stable products (carbon dioxide and water in the case of most common fuels). Heat of combustion is also referred to as calorific or fuel value and depends on the types and numbers of atoms as well as their arrangement in the molecule. Calorific values are commonly expressed in Joules per gram (J/g) but are sometimes reported in calories/g or Btu/lb (1 Btu/lb C 2.32 J/g; and 1 cal/g C 4.18 J/g). In the case of fuel gases, calorific values are commonly reported in MJ/m3 or Btu/ft3. Calorific values are used in calculating fire loading, but do not necessarily indicate relative fire hazard because the fire hazard depends on the rate of heat release in a fire (rate of burning), which is determined more by the distribution of fuel than by the total amount of heat (potentially) available. In almost all accidental fires, not all of the heat is released because the combustion process is incomplete and only partial oxidation of some species occurs. For all compounds of carbon and hydrogen, and of carbon, hydrogen, and oxygen (this in-
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cludes substances of vegetable and petroleum origin), the heat released during combustion, whether complete or partial, depends on the amount of oxygen consumed. For these common substances (e.g., wood, coal, natural gas, common plastics, oils, wood, cotton, sugar, and vegetable and mineral oils), the heat released corresponds to approximately 3 kJ/g of air consumed (or alternatively 13 kJ/g oxygen consumed). Spontaneous Heating. Spontaneous heating is the process whereby a material increases in temperature without drawing heat from its surroundings. Spontaneous heating is normally associated with large accumulations of porous, char-forming materials such as coal and sawdust at ambient temperatures, but reactive oils absorbed onto porous material also present a hazard (e.g., linseed oil–soaked rags). Spontaneous heating also occurs if a material is stored hot (e.g., fiber insulation board stacked hot directly from the production line, or hospital linen removed from an industrial tumble drier and stored in large bins or skips without allowing it to cool first). Spontaneous heating occurs because all organic substances, which are capable of combination with oxygen, release heat as they oxidize. At ambient temperature, the rate of reaction of oxygen at the surface is so low as to be imperceptible and no temperature rise is detected because the heat that is generated is immediately lost to the surroundings (e.g., the perishing of rubber is exothermic but can take many years before it becomes significant). However, if the heat cannot escape (for example, at the center of a very large pile of coal), the temperature will rise and cause the rate of the chemical reaction to increase. As a rule of thumb, the rate of a reaction doubles for every 10°C rise in temperature. If the conditions are right, a runaway process occurs and the temperature within the mass of material rises, uncontrolled, until the onset of smoldering combustion occurs. (Flaming does not normally occur until the smolder has propagated to the surface of the pile.) The key factor is that heat is being produced at a rate that is greater than it can be lost to the surroundings. The risk can be greatly reduced or even eliminated by ensuring that the accumulation (pile) of material can lose heat rapidly. Keeping the surface area to volume ratio as great as possible allows the material to lose heat rapidly because it is through the surface that heat is lost. Thus, many small piles are safer than 1 large pile. It is safer to store 1000 m3 of coal as 10 separate piles each containing 100 m3 than as 1 pile containing 1000 m3. (Note that some materials react so rapidly with air even at normal temperatures that spontaneous ignition [to flame] occurs with only small quantities. The oxidation of powdered zirconium in air is one such example.) The other requirement for spontaneous heating (and combustion) to occur is that sufficient air must be available within the pile to permit oxidation, yet not so much that the heat is carried away by convection as rapidly as it is formed. A rag soaked with a drying oil (such as linseed oil) may heat spontaneously if crumpled and left at the bottom of a wastebasket, but would not do so if stretched out and hung on a clothesline where air movement would remove any heat released. Whether or not it would heat up if wrapped up tightly in a bale of rags would depend on the porosity of the bale. Because of the increased porosity (better access for air and the insulating effect of the bale), a loosely
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packed bale might provide ideal conditions for self-heating. Many factors determine whether spontaneous combustion will occur and it is almost impossible to predict with certainty whether a material will heat spontaneously. However, materials that are prone to self-heating (and hence could lead to spontaneous combustion) have been identified: the attention of the reader is drawn to Table A.10, “Materials Subject to Spontaneous Heating,” and to the references by Bowes and Gray. Another cause of self-heating is to be found in agricultural produce as a result of microbiological activity that generates heat. A pile of fresh grass cuttings will self-heat in the same way. The moisture content of these materials is known to have an influence on self-heating by bacteria. Wet or improperly cured hay is very likely to heat in barn lofts. Experience has indicated that such heating may result in ignition within a period of 2 to 6 wk after storage. Because most bacteria cannot live at elevated temperatures (some are believed to survive up to 70°C), continued heating of such materials to produce spontaneous combustion requires the oxidation processes to become significant at these elevated temperatures. Alfalfa meal that has been exposed to rain and then stored in bins or piles is very susceptible to spontaneous heating. Soybeans stored in bins have been known to sustain what is called “bin burn,” that is, the beans next to the bin walls are charred due to the moisture condensation on the inside surfaces of the wall and the self-heating of the beans. Other agricultural products susceptible to spontaneous heating are those with a high content of oxidizable oils, such as cornmeal feed, linseed, rice bran, and pecan meal (see Table A.10). Heat of Decomposition. The heat of decomposition is the heat released by the decomposition of compounds that have been formed from their elements by endothermic reactions. Such compounds are intrinsically unstable, and when decomposition is started, such as by heating the substance above a critical temperature, decomposition continues with the liberation of heat. Acetylene and cellulose nitrate are well known for their tendency to decompose, with the liberation of dangerous quantities of heat. The chemical action responsible for this effect in many commercial and military explosives (the so-called high explosives) is the rapid decomposition of an unstable compound. Most of these can be regarded as consisting of molecules in which fuel and oxidizer are in the same molecule. An example is trinitrotoluene, which is a substituted toluene molecule (C7H8), three of the hydrogen atoms being replaced by nitrate groups (NO3), which are powerful oxidizers. Heat of Solution. The heat of solution is the heat released when a substance is dissolved in a liquid. Most materials release heat when dissolved, although the amount of heat is usually not sufficient to have any significant effect on fire protection. In the case of some chemicals, for example, concentrated sulfuric acid, the heat evolved may be sufficient to be dangerous. The chemicals that react with water in this manner are not themselves combustible, but the liberated heat may be sufficient to ignite nearby combustible materials. In contrast to most materials, ammonium nitrate absorbs heat when dissolved in water. (It is said to have a negative heat of solution.) Some first-aid products, for use where cold is rec-
ommended, consist of dry ammonium nitrate in watertight packages. These packages become cold when water is added. Heat of Reaction. It is appropriate to mention other reactions in which the heat generated is capable of initiating combustion. One example is the reaction of the alkali metal potassium (K) with water. Hydrogen is evolved and will ignite spontaneously as it mixes with air because the temperature is very high. Lithium and sodium also react with water (see Table 2.3.1), but the hydrogen does not ignite. On the other hand, cesium (Cs) and francium (Fr) react much more vigorously with water than does potassium.
Electrical Energy When a current flows through a conductor, electrons are effectively passing from atom to atom within the conductor. The better conductors, such as copper and silver, have the most easily removed outer electrons, so that the potential difference or voltage required to establish or maintain any unit electric current (or electron flow) through the conductor is less than for substances composed of more tightly bound electrons. The electrical resistance of any substance depends on its atomic (or molecular) characteristics; the electrical resistance is proportional to the energy required to move a unit quantity of electrons through the substance against the forces of electron capture and collision. This energy expenditure appears in the form of heat. Resistance Heating. Resistance heating is characterized by the rate of heat generation that is proportional to the resistance and the square of the current. Because the temperature of the conductor resulting from resistance heating depends on the rate of heat loss to the surroundings, bare wires can carry more current than insulated wires, without heating dangerously, and single wires can carry more current than closely grouped wires, or wires bundled into a cable of equivalent cross-sectional area. Provided that the current rating of a wire or cable is not greatly exceeded, resistance heating of straight runs of cable are very unlikely to cause a problem. It is a different matter if the cable is used when it is tightly coiled on a cable drum as heat will build up within the coil. Resistance heating is most likely to occur at locations where the resistance is high, particularly at poor electrical connections. This scenario is more likely to act as an ignition source than elsewhere in an electrical circuit. The heat generated by incandescent and infrared bulbs is due to resistance heating of the filaments in the bulbs. Material of very high melting point is used for the “white-hot” filaments of incandescent lamps. Destruction of the filament by oxidation is prevented by partial evacuation of the bulb and by removal of oxygen. The filaments of infrared lamps operate at a much lower temperature (a “red” heat); the most efficient infrared lamp reflectors are gold because gold is one of the best reflectors of infrared radiation. Dielectric Heating. When a poor electrical conductor is subjected to an alternating electric potential gradient from an external source, heat is generated within the material as a result of the
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motion of the electrons. The heating is uniform and the method is used for drying timber and curing the glue used to bond plywood sheets together. In general, very high frequencies are required. Induction Heating. Whenever a conductor is subject to the influence of a fluctuating or alternating magnetic field, or whenever a conductor is in motion across the lines of force of a magnetic field, potential differences develop in the conductor. These potential differences result in the flow of current, with attendant resistance heating in the conductor. For rapidly changing or alternating potentials, energy is expended and appears as heat energy. This type of heating increases with the frequency of the alternating field. Food in a microwave oven, for example, is heated by the molecular friction induced by absorbed microwave energy. Passing a high-frequency alternating current through a coil surrounding the material to be heated creates a useful form of induction heating. An alternating current passing through a wire can induce a current in another wire parallel to it. If the wire in which a current is induced does not have adequate current-carrying capacity for the size of the induced current, resistance heating occurs. In this example, the heating is due primarily to resistance to flow, and only in a small degree to molecular friction. Leakage Current Heating. Because all available insulating materials are imperfect insulators, there is always some current flow when the insulators are subjected to substantial voltages. This flow is commonly referred to as a leakage current and is usually not important from the standpoint of heat generation. However, if the insulating material is not suited for the service, or the material is too thin (for reasons of economy, space saving, or attempts to attain the maximum capacity in a condenser), leakage currents may exceed safe limits, resulting in heating of the insulator with consequent deterioration of the material and ultimate breakdown. Leakage currents may also occur when current “tracks” across the surface of the insulator, where mechanical damage or a build-up of contaminant has occurred. Heat from Arcing. Arcing occurs when an electric circuit that is carrying current is interrupted either intentionally, as by a knife switch, or accidentally, as when a contact or terminal becomes loosened. Arcing is especially severe when motor or other inductive circuits are involved. The temperatures of arcs are very high, and the heat released may be sufficient to ignite combustible or flammable material in the vicinity. In some instances, the arc may melt the conductor and scatter molten metal. Because an arc does not draw a high current, the fault that causes it may not blow a fuse. One requirement of an intrinsically safe electrical circuit is that arcing, due to accidental current interruption, does not release sufficient energy to ignite the hazardous atmosphere in which the circuit is located. Static Electricity Heating. Static electricity (sometimes called frictional electricity) is an electrical charge that accumulates on the surfaces of two materials that have been brought together and then separated. One surface becomes charged positively, the other negatively. If the substances are not bonded
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or grounded, they eventually accumulate sufficient electrical charge so that a spark may occur. Static arcs are ordinarily of very short duration and do not produce sufficient heat to ignite ordinary combustibles, such as paper. Static sparks, however, are capable of igniting flammable vapors and gases, and clouds of explosible dust. Hydrocarbon fuel (e.g., gasoline) flowing in a pipe can generate static electricity of sufficient energy to ignite a flammable vapor. Heat Generated by Lightning. Lightning is the discharge of an electrical charge from a cloud to an opposite charge on another cloud or on the ground. Lightning passing between a cloud and the ground can develop very high temperatures in any material of high resistance in its path, such as wood or masonry.
Mechanical Energy Heat generated mechanically is responsible for a significant number of fires each year. Frictional heat is responsible for most of these fires, although there are a few notable examples of ignition by the mechanical energy released by compression. Frictional Heat. The mechanical energy used in overcoming the resistance to motion when two solids are rubbed together is known as frictional heat. Any friction generates heat. The danger depends on the available mechanical energy, the rate at which the heat is generated, and its rate of dissipation. An example of frictional heating is caused by friction of a slipping belt against a pulley. Friction Sparks. Friction sparks include the sparks that result from the impact of two hard surfaces. In most cases, at least one of the materials is metal. Some examples that have been reported as responsible for fires are sparks from dropping steel tools on a concrete floor; from falling tools striking machinery or piping; from tramp metal in grinding mills; and from shoe nails on concrete floors. Friction sparks are formed in the following manner: heat, generated by impact or friction, initially heats the particle that breaks away from the surface. The maximum temperature is usually determined by the lowest melting point of the materials involved, but with some metals, the freshly exposed surface of the particle may oxidize at the elevated temperature, with the heat of oxidation increasing the temperature until the particle is incandescent. Although the temperatures necessary for incandescence vary with different metals, in most cases they are well above the ignition temperatures of flammable materials, for example, the temperature of a spark from a steel tool approaches 1400°C; sparks from copper–nickel alloys with small amounts of iron may be well above 3000°C. However, the ignition potential of a spark depends on its total heat content; thus, the particle size has a pronounced effect on spark ignition. The practical danger from mechanical sparks is limited by the fact that usually they are very small and have a low total heat content, even though each spark may have a temperature of 1100°C or higher. Mechanical sparks cool quickly and start fires only under favorable conditions, for example, when they fall into loose dry cotton, combustible dust, or explosive
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materials. Larger particles of metal, able to retain their heat longer, usually are not heated to dangerous temperatures. Although the hazard of ignition of flammable vapors or gases by friction sparks is often overemphasized, it is best to avoid the use of grinding wheels and other sources of mechanical sparks in areas where any flammable liquids, gases, or vapors are, or may be, present. The possibility of ignition due to some unusual condition should not be overlooked. One unusual condition that is well documented is the impact between aluminium and rusty iron. Aluminium reacts with ferric oxide (Fe2O3) to produce aluminium oxide and iron, a highly exothermic process known as the thermite reaction. The sparks that are produced are highly incendive, achieving temperatures up to 3000°C as they burn. Nickel, Monel metal™, and bronze have a very slight spark hazard; stainless steel has a much lower spark hazard than ordinary tool steel. Special tools of copper–beryllium and other alloys are designed to minimize the danger of sparks in hazardous locations. Such tools cannot, however, completely eliminate the danger of sparks because a spark may be produced under several conditions. Little or no benefit is gained by using nonsparking hand tools in place of steel to prevent explosions of hydrocarbons.13 Leather, plastic, and wood tools are, however, free from the friction spark hazard. Heat of Compression. When a gas is compressed suddenly, the temperature rises, a fact that is known to everyone that has used a pump to inflate bicycle tires. This is also known as the diesel effect and has found practical application in diesel engines in which heat of compression eliminates the need for spark ignition. Air is first compressed in the cylinder and a spray of oil is injected into the hot, compressed air. The heat released during compression of the air is sufficient to cause ignition of the oil.
Nuclear Energy Nuclear energy is released when the nucleus of an unstable isotope of an element (e.g., uranium 235) undergoes fission (splitting apart) to yield two smaller nuclei, the sum of whose masses is imperceptibly less than the original nucleus. The “lost mass” (m) is converted to energy (E), according to Einstein’s formula E C mc 2 where c is the velocity of light. The amounts of energy are huge, although the rate of release is extremely small for naturally occurring radioactive isotopes. The higher rates necessary to generate nuclear power are only achieved when higher concentrations of certain isotopes of uranium and plutonium are produced that have the property of undergoing chain reactions in which neutrons released from the fission process cause a cascade of fission reactions in other atoms of these unstable isotopes. The energy released by these nuclear processes is vastly greater than the energy released by ordinary chemical reactions. The instantaneous release of a large quantity of nuclear energy manifests itself as an atomic explosion. Controlled release of nuclear energy is a source of heat for everyday use (i.e., the source of energy for the production of high-pressure steam for the generation of electricity in power stations).
SUMMARY Fire is a complex phenomenon. To gain an understanding of fire behavior, it is necessary to have at least a basic knowledge of a range of subjects, including chemistry, physics, heat and mass transfer, and fluid dynamics. In this chapter, some of the chemistry and physics required to explain the most important aspects of fire behavior is presented. The relevant terminology is explained in detail and an attempt has been made to place the individual terms in context. It is important to use terminology that is consistent with scientific and engineering disciplines.
BIBLIOGRAPHY References Cited 1. Zabetakis, M. G., “Flammability Characteristics of Combustible Gases and Vapors,” Bulletin 627, 1965, Bureau of Mines, U.S. Department of Interior, Washington, DC. 2. ASTM D93, Standard Test Methods for Flash-Point by PenskyMartens Closed Cup Tester, American Society for Testing and Materials, West Conshohocken, PA, 2000. 3. ASTM D92, Standard Test Method for Flash and Fire Points by Cleveland Open Cup, American Society for Testing and Materials, West Conshohocken, PA, 1998. 4. Westbrook, C. K., and Dryer, F. L., “Chemical Kinetics and Modeling of Combustion Processes,” Eighteenth Symposium (International) on Combustion, Combustion Institute, Pittsburgh, PA, 1981. 5. Quintiere, J. G., “Surface Flame Spread,” in SFPE Handbook of Fire Protection Engineering, 3rd ed., P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 2002, pp. 2-246–2-257. 6. Kim, J. S., de Ris, J., and Kroesser, F. W., “Laminar FreeConvective Burning of Fuel Surfaces,” 13th Symposium (International) on Combustion, Combustion Institute, Pittsburgh, PA, 1971, pp. 949–961. 7. Babrauskas, V., “The Cone Calorimeter: A Vertical Bench-Scale Tool for the Evaluation of Fire Properties,” in New Technology to Reduce Fire Losses and Costs, S. J. Grayson and D. A. Smith (Eds.), Elsevier, London, UK, 1986, pp. 78–87. 8. Cox, G., “Compartment Fire Modelling,” in Combustion Fundamentals of Fire, G. Cox (Ed.), Academic Press Limited, London, UK, 1995, pp. 329–404. 9. Browne, F. L., “Theories of the Combustion of Wood and Its Control,” Report No. 2136, 1958, Forest Products Laboratory, U.S. Department of Agriculture, Madison, WI. 10. Drysdale, D. D., An Introduction to Fire Dynamics, 2nd ed., John Wiley and Sons, Chichester, UK, 1999. 11. deRis, J., “Fire Radiation—A Review,” 17th Symposium (International) on Combustion, Combustion Institute, Pittsburgh, PA, 1979, pp. 1003–1016. 12. Tien, C. L., Lee, K. Y., and Stretton, A. J., “Radiation Heat Transfer,” in SFPE Handbook of Fire Protection Engineering, 3rd ed., P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 2002, pp. 1-73–1-89. 13. NFPA, “Friction Spark Ignition of Flammable Vapors,” NFPA Quarterly, Vol. 53, No. 2, 1959, pp. 155–157.
Additional Readings Alpert, R. L., and de Ris, J., “Prediction of Fire Dynamics,” Final and Fourth Quarterly Report, National Institute of Standards and Technology, Report: NIST-GCR-94-642, June 1994, 36 pages. Andersson, B., Babrauskas, V., Holmstedt, G., Sardqvistt, S., and Winter, G., “Scaling of Combustion Products: Initial Results from the TOXFIRE Study,” Proceedings of the Industrial Fires III Workshop, Major Industrial Hazards, Riso, Denmark, Sep-
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tember 17–18, 1996, European Commission, Brussels, 1996, pp. 65–74. Angel, S. M., “In situ Flame Chemistry by Remote Spectroscopy,” Fire Resistant Materials: Progress Report, R. E. Lyon (Ed.), Department of Transportation, Federal Aviation Administration, Atlantic City, NJ, DOT/FAA/AR-97/100; AAR-422, 1998, pp. 259–265. Atreya, A., and Abu-Zaid, M., “Effect of Environmental Variables on Piloted Ignition,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, London, UK, 1991, pp. 177–186. Atreya, A., Everett, D. A., Agrawal, S., and Anderson, M. K., “Radiation Temperature and Extinction of Transient Gaseous Diffusion Flames in Microgravity,” Proceedings of the 4th Workshop on Microgravity Combustion, Cleveland, OH, May 19–21, 1997, National Aeronautics and Space Administration, Lewis Research Center, NASA Conference Publication 10194, 1997, pp. 63–68. Babrauskas, V., “Assessment of the Dietenberger Model,” CBUF: Fire Safety of Upholstered Furniture, Final Report on the CBUF Research Program, European Commission Measurements and Testing Report EUR 16477 EN, Appendix A9, London, UK, Interscience Communication Ltd., B. Sundstrom (Ed.), 1996, pp. 377–384. Babrauskas, V., “Fire Modeling Tools for FSE: Are They Good Enough?” Journal of Fire Protection Engineering, Vol. 8, No. 1, 1996, pp. 87–96. Babushok, V. I., Tsang, W., Burgess, D. R. F., Jr., and Zachariah, M. R., “Numerical Study of Low- and High-Temperature Silane Combustion,” Proceedings of the 27th International Symposium on Combustion, Boulder, CO, August 2–7, 1998, Combustion Institute, Pittsburgh, PA, 1998, Vol. 2, pp. 2431–2439. Bertelli, G., et al., “Structure—Char Forming Relationship in Intumescent Fire Retardant Systems,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, London, UK, 1991, pp. 537–546. Blevins, L. G., and Gore, J. P., “Computed Structure of Low Strain Rate Partially Premixed CH4/Air Counterflow Flames: Implications for NO Formation,” Combustion and Flame, Vol. 116, 1999, pp. 546–566. Blevins, L. G., Renfro, M. W., Lyle, K. H., Laurendeau, N. M., and Gore, J. P., “Experimental Study of Temperature and CH Radical Location in Partially Premixed CH4/Air Flames,” Combustion and Flame, Vol. 118, Sept. 1999, pp. 684–696. Bowes, P. C., Self-Heating: Evaluating and Controlling the Hazard. HMSO, London, UK, 1984. Brehob, E. G., and Kulkarni, A. K., “Time-dependent Mass Loss Rate Behavior of Wall Materials Under External Radiation,” Fire and Materials: An International Journal, Vol. 17, No. 5, 1993, pp. 249–254. Butcher, E. G., “Nature of Fire Size, Fire Spread and Fire Growth,” Fire Engineers Journal, Vol. 47, No. 144, 1987, pp. 11–14. Carty, P., and White, S., “Smoke/Char Relationships in PVC Formulations,” Journal of Fire Sciences, Vol. 13, No. 4, 1995, pp. 289–299. Chen, Y., et al., “Effects of Fire Retardant Addition on the Combustion Properties of a Charring Fuel,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, London, UK, 1991, pp. 527–536. Cox, G. (Ed.), Combustion Fundamentals of Fire, Academic Press Limited, London, UK, 1995. Damant, G. H., “Cigarette Ignition of Upholstered Furniture,” Journal of Fire Sciences, Vol. 13, No. 5, 1995, pp. 337–349. DeHaan, J. D., Kirk’s Fire Investigation, 4th ed., Upper Saddle River, NJ, Brady Fire Sciences Series, Prentice Hall, Inc., 1997. Delichatsios, M. A., “Fire Physics: A Personal Overview,” Proceedings of the 4th Asia-Oceania Symposium on Fire Science and Technology, Tokyo, Japan, May 24–26, 2000, co-organized by Asia-Oceania Association for Fire Science and Technology (AOAFST) and Japan Association for Fire Science and Engineering (JAFSE), 2000, pp. 151–153.
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de Ris, J., “A Scientific Approach to Flame Radiation and Material Flammability,” Proceedings of the 2nd International Symposium on Fire Safety Science, Hemisphere Publishing Corporation, New York, 1989, pp. 29–48. Delichatsios, M. A., “Basic Polymer Material Properties for Flame Spread,” Journal of Fire Sciences, Vol. 11, No. 4, 1993, pp. 287–295. Delichatsios, M. A., et al., “Flame Radiation Distribution from Fires,” Proceedings of the 4th International Symposium on Fire Safety Science, International Association for Fire Safety Science, 1994, pp. 149–160. Di Blasi, C., “On The Influence of Physical Processes on the Transient Pyrolysis of Cellulosic Samples,” Proceedings of the 4th International Symposium on Fire Safety Science, International Association for Fire Safety Science, 1994, pp. 229–240. Drysdale, D. D., and Thomson, H. E., “The Ignitability of Flame Retarded Plastics,” Proceedings of the 4th International Symposium on Fire Safety Science, International Association for Fire Safety Science, 1994, pp. 195–204. Emmons, H. W., “The Ceiling Jet in Fires,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, London, UK, 1991, pp. 249–260. Fallon, G. S., Chellish, H. K. and Linteris, G. T., “Chemical Effects of CF3H in Extinguishing Counterflow CO/Air/H2 Diffusion Flames,” Proceedings of the 26th International Symposium on Combustion, Napoli, Italy, July 28–August 2, 1996, Combustion Institute, Pittsburgh, 1996, pp. 1395–1403. Fan, W., and Zhong, M., “Review on Modelling of Fire Physics and Risk Assessment,” Proceedings of the 4th Asia-Oceania Symposium on Fire Science and Technology, Tokyo, Japan, May 24–26, 2000, co-organized by Asia-Oceania Association for Fire Science and Technology (AOAFST) and Japan Association for Fire Science and Engineering (JAFSE), 2000, pp. 165–178. Fan, W. C., and Wang, J., “Predictions of Unsteady Burning of a Fuel Bed,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, London, UK, 1991, pp. 325–334. Floyd, J. E., Baum, H. R., and McGrattan, K. B., “Mixture Fraction Combustion Model for Fire Simulation Using CFD,” Proceedings of the International Conference on Engineered Fire Protection Design, Applying Fire Science to Fire Protection Problems, San Francisco, CA, 2001, co-organized by the Society of Fire Protection Engineers, Bethesda, MD, and National Institute of Standards and Technology, Gaithersburg, MD, 2001, pp. 279–290. Fredlund, B., “Modeling of Heat and Mass Transfer in Wood Structures During Fire,” Fire Safety Journal, Vol. 20, No. 1, 1993, pp. 39–70. Friedman, R., Principles of Fire Protection Chemistry and Physics, 3rd ed., National Fire Protection Association, Quincy, MA, 1998. Friedman, R., “Some Unresolved Fire Chemistry Problems,” Proceedings of the 1st International Symposium on Fire Safety Science, Hemisphere, 1986, pp. 349–359. Gann, R. G., et al., “Cigarette Ignition of Soft Furnishings,” Proceedings of the 2nd International Symposium on Fire Safety Science, Hemisphere Publishing Corporation, New York, 1989, pp. 77–86. Glassman, I., Combustion, 2nd ed., Academic Press, Orlando, FL, 1987. Griffiths, J. F., and Barnard, J. A., Flame and Combustion, Blackie Academic & Professional, London, UK, 1995. Hasemi, Y., and Nishihata, M., “Fuel Shape Effect on the Deterministic Properties of Turbulent Diffusion Flames,” Proceedings of the 2nd International Symposium on Fire Safety Science, Hemisphere Publishing Corporation, New York, 1989, pp. 275–284. Heat Release in Fires, Babrauskas, V., and Grayson, S. J. (Eds.), Elsevier Science Publishers, Ltd., London, UK, 1992. Hirano, T., “Physical Aspects of Combustion in Fires,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, London, UK, 1991, pp. 27–44. Horrocks, A. R., and Price, D. (Eds.), Fire Retardant Materials, Woodhead Publishing Ltd, Cambridge, UK, 2001.
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Hull, T. R., Price, D., Carman, J. M., and Purser, D., “Studies of Carbon/Oxygen Chemistry under Different Fire Conditions, Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, Edinburgh, UK, June 29–July 1, 1999, Interscience Communications Ltd., London, UK, 1999, pp. 189–199. Hwang, C. C., and Litton, C. D., “Ignition of Combustible Dust Layers on a Hot Surface,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, London, UK, 1991, pp. 187–196. Iqbal, N., and Quintiere, J., “Flame Heat Fluxes in PMMA Pool Fires,” Journal of Fire Protection Engineering, Vol. 6, No. 4, 1994, pp. 153–163. Janssens, M., “A Thermal Model for Piloted Ignition of Wood Including Variable Thermophysical Properties,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, London, UK, 1991, pp. 167–176. Jones, W. W., “State of the Art Zone Modeling of Fires,” Proceedings of the 9th International Fire Protection Seminar, Engineering Methods for Fire Safety, Munich, Germany, May 25–26, 2001, Vereinigung zur Forderung des Deutschen Brandschutzes e. V., 2001, pp. A.4/89–126. Joulain, P., “Fire Research in France: An Overview,” Proceedings of the 6th International Symposium for Fire Safety Science, Poitiers, France, July 5–9, 1999, M. Curtat (Ed.), International Association for Fire Safety Science, Boston, 2000, pp. 41–58. Karpov, A. I., and Bulgakov, V. K., “Prediction of the Steady Rate of Flame Spread Over Combustible Materials,” Proceedings of the 4th International Symposium on Fire Safety Science, International Association for Fire Safety Science, 1994, pp. 373–384. Kashiwagi, T., Omori, A., and Brown, J. E., “Effects of Material Characteristics on Flame Spreading,” Proceedings of the 2nd International Symposium on Fire Safety Science, Hemisphere Publishing Corporation, New York, 1989, pp. 107–118. Kennedy, L. A., and Cooper, L. Y., “Before the Smoke Clears—Heat and Mass Transfer in Fires and Controlled Combustion,” Mechanical Engineering, Vol. 109, No. 4, 1987, pp. 62–67. Kokkala, M. A., “Experimental Study of Heat Transfer to Ceiling from an impinging Diffusion Flame,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, London, UK, 1991, pp. 261–270. Kumar, S., and Cox, G., “Radiation and Surface Roughness Effects in the Numerical Modeling of Enclosure Fires,” Proceedings of the 2nd International Symposium on Fire Safety Science, Hemisphere Publishing Corporation, New York, 1989, pp. 851–860. Kumar, S., Gupta, A. K., and Cox, G., “Effects of Thermal Radiation on the Fluid Dynamics of Compartment Fires,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, London, UK, 1991, pp. 345–354. Law, M., “Behavior of a Fire,” Proceedings of the International Conference on the Design of Structures Against Fires, Elsevier, NY, 1986, pp. 15–20. Lazzarini, A. K., Krauss, R. H., Chelliah, H. K., and Linteris, G. T., “Extinction Conditions of Nonpremixed Flames with Fine Droplets of Water and Water-NaOH Solutions,” Proceedings of the 28th International Symposium on Combustion, Edinburgh, UK, July 20-August 4, 2000, S. Candel, J. F. Driscoll, A. R. Burgess and J. P. Gore (Eds.), Combustion Institute, Pittsburgh, PA, 2000, pp. 2930–2945. Lee, K. Y., Cha, D. J., Hamins, A., and Puri, I. K., “Heat Release Mechanisms in Inhibited Laminar Counterflow Flames,” Combustion and Flame, Vol. 104, No. 1–2, 1996, pp. 27–40. Levine, R. S., and Pagni, P. J. (Eds.), Fire Science for Fire Safety, Gordon and Breach, New York. Lewis, M. J., Rubini, P. A., and Moss, J. B., “Field Modelling of NonCharring Flame Spread,” Proceedings of the 6th International Symposium for Fire Safety Science, Poitiers, France, July 5–9, 1999, M. Curtat (Ed.), International Association for Fire Safety Science, Boston, MA, 2000, pp. 683–694.
Li, S. C. and Williams, F. A., “Experimental and Numerical Studies of Two-Stage Methanol Flames,” Proceedings of the 26th International Symposium on Combustion, Napoli, Italy, July 28–August 2, 1996, Combustion Institute, Pittsburgh, PA, 1996, pp. 1017–1024. Linteris, G. T., Rumminger, M. D., Babushok, V. I., and Tsang, W., “Flame Inhibition by Ferrocene and Blends of Inert and Catalytic Agents,” Proceedings of the 28th International Symposium on Combustion, Edinburgh, UK, July 20–August 4, S. Candel, J. F. Driscoll, A. R. Burgess and J. P. Gore (Eds.), 2000, Combustion Institute, Pittsburgh, PA, 2000, pp. 2965–2972. Lyons, J. W., Fire, Scientific American Books, New York, 1986. Marlair, G., Bertrand, J. P., and Brohez, S., “Use of the ASTM E2058 Fire Propagation Apparatus for the Evaluation of Under-Ventilated Fires,” Proceedings of the 7th International Conference and Exhibition, Fire and Materials 2001, San Antonio, TX, January 22–24, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 301–313. McDonough, J. M., Garzon, V. E., and Saito, K., “Porous Medium Model for Large-Scale Forest Fires,” Proceedings of 2nd International Symposium on the Scale Modeling, Lexington, KY, June 23–27, 1997, University of Kentucky, Lexington, KY, 1997, pp. 33–45. Mikkola, E., “Charring of Wood Based Materials,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, London, UK, 1991, pp. 547–556. Miller, J. A., “Theory and Modeling in Combustion Chemistry,” Proceedings of the 26th International Symposium on Combustion, Napoli, Italy, July 28–August 2, 1996, Combustion Institute, Pittsburgh, PA, 1996, pp. 462–480. Most, J. M., Bellin, B., and Sztal, B., “Interaction between Two Burning Vertical Walls,” Proceedings of the 2nd International Symposium on Fire Safety Science, Hemisphere Publishing Corporation, New York, 1989, pp. 285–294. Najm, H. N., Wyckoff, P. S., and Knio, O. M., “Semi-Implicit Numerical Scheme for Reacting Flow. Part 1. Stiff Chemistry,” Journal of Computational Physics, Vol. 143, 1998, pp. 381–402. Ohlemiller, T., et al., “Assessing the Flammability of Composite Materials,” Journal of Fire Sciences, Vol. 11, No. 4, 1993, pp. 308–319. Ohlemiller, T. J., “Smoldering Combustion Propagation on Solid Wood,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, London, UK, 1991, pp. 565–574. Ohtani, H., Maejima, T., and Uehara, Y., “In-Situ Heat Release Measurement of Smoldering Combustion of Wood Sawdust,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, London, UK, 1991, pp. 557–564. Pagni, P. J., “Fire Physics—Promises, Problems, and Progress,” Proceedings of the 2nd International Symposium on Fire Safety Science, Hemisphere Publishing Corporation, New York, 1989, pp. 49–66. Parker, W. J., “Prediction of the Heat Release Rate of Douglas Fir,” Proceedings of the 2nd International Symposium on Fire Safety Science, Hemisphere Publishing Corporation, New York, 1989, pp. 337–343. Pitts, W. M., and Blevins, L. G., “Investigation of Extinguishment by Thermal Agents Using Detailed Chemical Kinetic Modeling of Opposed-Flow Diffusion Flames,” Proceedings of the Fall Technical Meeting, Combustion Institute/Eastern States Section, Raleigh, NC, October 10–13, 1999, pp. 184–187. Quintiere, J. G., Fire Growth and Development, Center for Fire Research, Gaithersburg, MD, 1989. Quintiere, J. G., and Cleary, T. G., “Heat Flux from Flames to Vertical Surfaces,” Fire Technology, Vol. 30, No. 2, 1994, pp. 209–231. Reinelt, D., and Linteris, G. T., “Experimental Study of the Inhibition of Premixed and Diffusion Flames by Iron Pentacarbonyl,” Proceedings of the 26th International Symposium on Combustion,
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Napoli, Italy, July 28-August 2, 1996, Combustion Institute, Pittsburgh, PA, 1996, pp. 1421–1428. Rumminger, M. D., and Linteris, G. T., “Role of Particles in the Inhibition of Premixed Flames by Iron Pentacarbonyl, Combustion and Flame, Vol. 123, No. 1–2, 2000, pp. 82–94. SFPE Handbook of Fire Protection Engineering, “Section 1,” 2nd ed., National Fire Protection Association, Quincy, MA, 1995. Skocypec, R. D., and Peterson, C. W., “DOE Programs in Fire and Materials,” Proceedings of the 41st International SAMPE Symposium and Exhibition, Materials and Process Challenges: Aging Systems, Affordability, Alternative Applications, Anaheim, CA, March 24–28, 1996, C. Schmitt, J. Bauer, C. H., Magnurany, and C. Hurley (Eds.), Vol. 41, Book 1, Society for the Advancement of Material and Process Engineering, 1996, pp. 361–369. Smyth, K. C., “NO Production and Destruction in a Methane/Air Diffusion Flame,” Combustion Science and Technology, Vol. 115, 1996, pp. 151–176. Suzuki, T., et al., “Polyurethane Foam Smoldering Supported by External Heating,” Proceedings of the 4th International Symposium on Fire Safety Science, International Association for Fire Safety Science, 1994, pp. 397–408. Suzuki, M., Kushida, H., Dobashi, R., and Hirano, T., “Effects of Humidity and Temperature on Downward Flame Spread Over Filter Paper,” Proceedings of the 6th International Symposium for Fire Safety Science, Poitiers, France, July 5–9, 1999, M. Curtat (Ed.), International Association for Fire Safety Science, Boston, MA, 2000, pp. 661–670. Syoboda, Z., “Convective-Diffusion Equation and Its Use in Building Physics,” International Journal on Architectural Science, Vol. 1, No. 2, 2000, pp. 68–79. Tewarson, A., and Macaione, D. P., “Polymers and Composites—An Examination of Fire Spread and Generation of Heat and Fire Products,” Journal of Fire Sciences, Vol. 11, No. 5, 1993, pp. 421–441. Tewarson, A., “Flammability Parameters of Materials: Ignition, Combustion, and Fire Propagation,” Journal of Fire Sciences, Vol. 12, No. 4, 1994, pp. 329–356. Tewarson, A., Chu, F., and Jiang, F. H., “Combustion of Halogenated Polymers,” Proceedings of the 4th International Symposium on Fire Safety Science, International Association for Fire Safety Science, 1994, pp. 563–574. Torero, J. L., Fernandez-Pello, A. C., and Kitano, M., “Downward Smolder of Polyurethane Foam,” Proceedings of the 4th International Symposium on Fire Safety Science, International Association for Fire Safety Science, 1994, pp. 409–420. Tuovinen, H., “Modeling of Laminar Diffusion Flames in Vitiated Environments,” Proceedings of the 4th International Symposium on Fire Safety Science, International Association for Fire Safety Science, 1994, pp. 113–124. Watt, S. D., Staggs, J. E. J., McIntosh, A. C. and Brindley, J., “Theoretical Explanation of the Influence of Char Formation on the Ignition of Polymers,” Fire Safety Journal, Vol. 36, No. 5, 2001, pp. 421–436. Weast, R. C. (Ed.), Handbook of Chemistry and Physics, 69th ed., CRC Press, Boca Raton, FL, 1988.
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Chemistry and Physics of Fire
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Wen, J. X., Huang, L. Y., Amin, E. M. and Nolan, P., “Modeling Sooting Jet Fires in a Large-Scale Offshore Compartment,” Proceedings of the 27th International Symposium on Combustion, Boulder, CO, August 2–7, 1998, Combustion Institute, Pittsburgh, PA, 1998, Vol. 2, pp. 2881–2886. Wighus, R., “Empirical Model for Extinguishment of Enclosed Fires with a Water Mist,” Proceedings of the Halon Options Technical Working Conference, HOTWC-98, Albuquerque, NM, May 12–14, 1998, sponsored by the University of New Mexico, 3M Co., Fire Suppression Systems Assoc., Great Lakes Chemical Corp., Halon Alternative Research Corp., Hughes Associates, Inc., Kidde International, Modular Protection, Inc., National Association of Fire Equipment Distributors, Inc., Next Generation Fire Suppression Technology Program, 1998, pp. 482–489. Williams, F. A., “Mechanisms of Fire Spread,” Sixteenth Symposium (International) on Combustion, Combustion Institute, Pittsburgh, PA, 1977, pp. 1281–1294. Yang, B., and Pope, S. B., “Treating Chemistry in Combustion with Detailed Mechanisms—in situ Adaptive Tabulation in Principal Directions—Premixed Combustion,” Combustion and Flame, Vol. 112, No. 1–2, 1998, pp. 85–112. Yang, J. C., Bryant, R. A., Huber, M. L., and Pitts, W. M., “Experimental Investigation of Extinguishment of Laminar Diffusion Flames by Thermal Agents,” Proceedings of the Halon Options Technical Working Conference, HOTWC 2000,Albuquerque, NM, May 2–4, 2000, sponsored by the University of New Mexico, Fire Suppression Systems Assoc., Fire and Safety Group, Great Lakes Chemical Corp., Halon Alternative Research Corp., Hughes Associates, Inc., Kidde Fenwal, Inc., Kidde International, Modular Protection, Inc., National Association of Fire Equipment Distributors, Inc., Next Generation Fire Suppression Technology Program, Sandia National Laboratories, Summit Environmental Corp., Inc., and 3M Specialty Materials, 2000, pp. 444–446. Zdanowski, M., Teadorczyk, A., and Wojcicki, S., “A Simple Mathematical Model of Flashover in Compartment Fires,” Fire and Materials, Vol. 10, 1986, p. 145. Zhou, L., and Fernandez-Pello, A. C., “Turbulent Burning of a Flat Fuel Surface,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, London, UK, 1991, pp. 415–424. Zimberg, W. J., Frankel, S. H., Gore, J. P., and Sivathanu, Y. R., “Study of Coupled Turbulent Mixing, Soot Chemistry, and Radiation Effects Using the Linear Eddy Model,” Combustion and Flame, Vol. 113, No. 3, 1998, pp. 454–469. Zukoski, E. E., “Mass Flux in Fire Plumes,” Proceedings of the 4th International Symposium on Fire Safety Science, International Association for Fire Safety Science, 1994, pp. 137–148. Zukoski, E. E., et al., “Combustion Processes in Two-Layered Configurations,” Proceedings of the 2nd International Symposium on Fire Safety Science, Hemisphere Publishing Corporation, New York, 1989, pp. 295–304.
CHAPTER 4
SECTION 2
Dynamics of Compartment Fire Growth Richard L. P. Custer
O
ver the past twenty years, research scientists and engineers have worked to develop an understanding of the factors and physical processes that enter into and control the growth and spread of fire and its products. Much of the work has focused on two general types of fire scenarios: (1) the pool fire and (2) the compartment fire. Research on pool fires has developed an understanding of energy production from a burning surface and the dynamics of the plume of hot gases and other products of combustion that rise from the surface. Understanding of compartment fire, in part, is built on the work involving pool fires in order to define the characteristics of a simplified fire environment without the effects that compartment boundaries (such as walls and ceilings) and compartment openings or vents (such as doors and windows) have on the development of the growth rate of the fire. Other work has produced literally hundreds of test fires in compartments with varying fire sources, physical dimensions and materials of construction, and venting arrangements. As a result of this work, it is now possible to quantify many aspects of pool and compartment fires in order to predict their effect for use in hazard analysis, analysis and design of fire protection systems, and fire reconstruction. Fire spread and growth in the context of this chapter is limited to the compartment of origin and the fuel packages within it. The purpose of this chapter is to provide the reader with a basic understanding of the concepts involved in modern-day applied fire dynamics as the basis for using the calculation methods described elsewhere in this handbook. See Section 3, “Information and Analysis for Fire Protection,” for more information. This chapter is intended to introduce the general concepts of fire growth in a compartment and not to focus on the detailed mathematics involved. References to other chapters of this handbook and to the published literature will be provided, as needed, to guide the reader to sources of information for additional study. For the purposes of this chapter, the discussion will deal with fire growth from the time of established burning to the time
Richard L. P. Custer, M.Sc., is associate principal and technical director at ARUP Fire in Westborough, Massachusetts. Mr. Custer is a fellow of the Society of Fire Protection Engineers.
when the fire involves the entire compartment and is controlled by airflow out of and into the compartment vents. Established burning is defined as the point in fire development when the size of the flame is sufficiently large so that flaming combustion will continue without an independent external ignition source and the fire will grow to the extent permitted by the fuel or oxygen present. The flame height at established burning is frequently considered to be approximately 10 in. (254 mm) on a horizontal fuel surface. It is suggested that, at this point, there is sufficient energy feedback from the flame to the fuel so that there will be adequate production of fuel vapors and the flame will not go out without external influences.
FIRE GROWTH The following discussion assumes that ignition has taken place and the fire has reached the point of established burning. Beginning with the first materials ignited, the early stages of a fire provide the driving force for growth and spread, both within the compartment and to other portions of the building. The fire serves not only as a source of energy providing flame and heated gases for the spread of fire, but also the source of the smoke particulate and the toxic and corrosive gases that form the products of combustion. The rate and amount of energy produced by the initial fire in a compartment will frequently determine whether or not the fire will spread beyond that compartment. The fuel available for fire growth and spread can be characterized in two ways: (1) the rate at which it burns and releases energy into the compartment environment and (2) the total energy available that could be released from the fuel. Each of these characteristics is used to describe fire hazard or potential fire severity. Rate of burning is commonly described using the term heat release rate (HRR), which is quantified in terms of the kilowatts (Btu per second) released instantaneously at a given point in time during the fire. The HRR describes how fast the energy is being released. The concept of potential hazard or fire severity is expressed as fire loading or fuel loading and is based on the amount of energy that would be available if all the fuel were to be consumed regardless of how long it would take. Fire or fuel load is generally expressed in terms of kilograms of fuel per square meter
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(pounds per square foot) of floor area of the space being evaluated. Fuel load can also be expressed in energy terms as Mega Joules (MJ) per square meter or Btu per square foot. Fuel loading does not consider the speed at which the fuel burns or the rate at which the fire grows, but rather addresses the issue of how long a fire might burn until the fuel is consumed. These concepts are discussed in detail in the following sections.
HEAT RELEASE RATE The amount of heat released by a fire per unit of time (HRR) depends on its heat of combustion (which is the amount of energy produced for each unit of mass burned), the mass of fuel consumed per unit of time, and the efficiency of the combustion process. The HRR is then determined by multiplying the mass loss rate (mass consumed/unit of time) by the heat of combustion (energy available/unit of mass) and the combustion efficiency (fraction of the mass converted to energy) to yield the HRR, Qg , in units of energy produced per unit time. Various units are used, such as kilowatts (kW), Btu/s, or J/s. The kilowatt (1055 Btu/s) is the most common unit. The HRR is important during the growth phase of the fire, when air for combustion is abundant and the characteristics of the fuel control the burning rate. During this phase, the instantaneous HRR increases over time. Equation (1) describes this relationship between the HRR, mass loss (mg ), and heat of combustion (!hc). Qg C mg !hc
(1)
Energy released from burning fuel is both convective and radiative. Radiation is the transfer of energy from a hot surface to a cooler surface by electromagnetic waves. Convection is the transfer of energy by the movement of heated gases and liquids from the source of heat to a cooler part of the environment. The amount of radiation (the radiative fraction) varies somewhat depending on the chemistry of the fuel and the combustion efficiency. Generally, the radiative fraction is considered to be 30 percent, with the remaining 70 percent released as convective energy. The burning rate of a given fuel is controlled both by its chemistry and by its form. Fuel chemistry refers to its composition, for example, cellulosic versus petrochemical. Cellulosic materials include wood, paper, cotton, fabric, and so on. Petrochemical materials, in general, refer to plastics that are largely composed of formulations derived from petroleum. The form of the material, that is, its size, shape, and arrangement, also has an effect on the burning rate. Table 2.4.1 provides some examples of burning rates. One way of looking at the form of fuel is in terms of the surface area available to burn compared to the mass of the material, which is called the surface area to mass ratio. In the case of cellulosic materials, for example, a solid block of wood weighing 2.2 lb (1 kg) will burn more slowly than will the same mass if converted into thin sheets of paper, and may burn explosively if converted into very fine wood dust and dispersed throughout a compartment volume. Another example of form that is, in part, related to chemistry deals with the differences between foam plastic and rigid plastic. Foam plastic, in general, burns more rapidly than a sim-
TABLE 2.4.1 Representative Peak Heat Release Rates (Unconfined Burning) Fuel (lb)
Peak HRR (kW)
Wastebasket, small (1.5–3) Trash bags, 11 gal with mixed plastic and paper trash (2½–7½) Cotton mattress (26–29) TV sets (69–72) Plastic trash bags/paper trash (2.6–31) PVC waiting room chair, metal frame (34) Cotton easy chair (39–70) Gasoline/kerosene in 2 ft2 (0.61 m2) pool Christmas trees, dry (14–16) Polyurethane mattress (7–31) Polyurethane easy chair (27–61) Polyurethane sofa (113)
4–18 140–350 40–970 120–290 120–350 270 290–370 400 500–650 810–2630 1350–1990 3120
Sources: Values are from the following publications: Babrauskas and Krasny, Fire Behavior of Upholstered Furniture. NFPA 72®, National Fire Alarm Code®, 1996 ed., B.2.2.2.1. Lee, B. T. Heat Release Rate Characteristics of Some Combustible Fuel Sources in Nuclear Power Plants, NBSIR 85-3195, National Bureau of Standards, Gaithersburg, MD, 1985.
ilar formulation in rigid form. Two examples are (1) flexible urethane versus rigid urethane and (2) Styrofoam™ versus rigid styrene. The flexible or foam form is of low density and generally has a higher HRR than the rigid material does. Another difference in physical characteristics related to burning characteristics of plastics is whether or not the plastic melts when it burns. Those plastics that change shape or form when heated are referred to as thermoplastics, and may melt and release their energy more rapidly than those plastics that remain rigid when heated. The latter are referred to as thermosetting plastic materials. Thermosetting materials generally tend to form a char layer and burn more slowly. Although this is not an exhaustive discussion of fuel burning characteristics, it does represent some factors that the reader might consider in assessing the potential HRR or growth rate of a fire, given certain types of fuels. More detailed discussions of individual fuels are found in the appropriate chapters of this handbook.
FUEL LOADING The concept of fuel loading is a way of characterizing the hazard of a compartment fire or building fire in terms of the length of time the building would be expected to burn, based on the total amount of fuel available and the total energy produced. Fuel loading is determined by adding up all fuel present and dividing it by the area of the compartment or fire space. The fuel load is expressed as a mass of fuel equivalent to wood. When plastics or other materials are present, multiplying the number of pounds (kilograms) of plastic or other materials by the heat of combustion for those materials and dividing by the heat of combustion for wood provides a conversion. This conversion produces an equivalent number of pounds (kilograms) of wood to plastics or other materials.
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CHAPTER 4
CLASSIFICATIONS OF FIRE It is frequently useful to classify fires in order to simplify communication regarding certain common characteristics. Fires have been characterized in four general ways: (1) type of combustion process, (2) growth rate, (3) ventilation, and (4) fire stage.
Classification by Type of Combustion Process Perhaps the simplest description of a fire classification would be to divide the fire into three regimes: (1) precombustion, (2) smoldering combustion, and (3) flaming combustion. No sequence is necessarily implied by this classification. Precombustion is the process of heating fuels to their ignition point, during which time vapors and particulates are released from the fuel. Smoldering is defined as glowing combustion on the fuel surface and may or may not be related in any way to the oxygen content in the vicinity of the smoldering process. What is implied here is that the fuel vapor production rate and temperatures involved may not be sufficient to support flaming combustion. Flaming combustion is almost self-explanatory in that the production of sufficient energy and fuel vapors in the combustible range is the condition that underlies and supports the presence of flame. These conditions of burning may exist simultaneously within a given fire. As flames spread from one point to another on a given item of fuel or within the building, the precombustion or preignition situation will exist at the perimeter of the fire. The presence of both smoldering and flaming, even in the same compartment, is quite common as the fire spreads through different types of fuels by different mechanisms.
Classification by Rate of Growth Fires may also be classified on the basis of growth. Growth can be either positive (increasing growth rate) or negative (decreasing growth rate). A fire that increases its instantaneous energy output or heat release rate over time is said to be a growing fire. Typically, growing fires have more air available than is needed for combustion of the fuel gases being generated and will continue to grow until limited either by the amount of fuel available or the amount of air for combustion. A second category based on growth rate is the steady-state fire. Under steady-state conditions, the fire’s heat output or heat
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release rate remains relatively constant over time. This is not to say that there will not be variations, but there is no rapid continuing increase or continuing decrease in energy release rate. An example of this phenomenon might be a flammable liquid pool fire of fixed diameter where, once the entire surface is involved in flame, the amount of energy produced is controlled by the surface area and will be essentially constant until the fuel is exhausted. Another example would be the production of energy from a fire becoming limited due to air supply. A third category is the burnout or decay condition, where there is plenty of air for combustion but the HRR is decreasing, due to fuel consumption. See Figure 2.4.1 for a graphical representation of growing fire, steady-state fire, and decay. Growth rate or the speed at which growth accelerates is another way to classify fires. These are considered “timedependent” fires. Typical fires in buildings such as residences and offices have been determined to grow as a function of the square of time and are referred to as “t-squared” fires. The t-squared fire can be characterized by Equation 2.1 Qg C *t 2
(2)
where Qg C heat release rate at a given time * C fire growth constant t C time
Classification on the Basis of Ventilation Fires may also be classified based on whether the fire is dominated by the fuel available to burn or by the oxygen or air available for the combustion process to continue. When a fire is burning in the open, or is in the early stages of development within a compartment where there is excess air for combustion, this fire is said to be a fuel-controlled fire. In a compartment fire with sufficient fuel available, the window or door openings may ultimately serve to control the amount of air available for
1500 Growing fire Heat release rate (kW)
Fuel loading is related to the expected length of time a fire will burn once it is controlled by the amount of air available for the fuel to burn. The air that is supplied through openings, such as doors and windows, controls the amount of heat produced by a fire during this time. For fire duration analysis, all doors and windows are generally assumed to be open. A fire burning at a constant HRR burns fuel mass at a constant rate as well. Given the mass of material being burned per minute and the amount of material available to be burned, it is possible to estimate the total burning time.
Dynamics of Compartment Fire Growth
Steady-state fire
1000
Decay (burnout)
500
0 0
FIGURE 2.4.1 Growth Rate
100
200
300 Time (s)
400
Categories of Fire Growth, Based on
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combustion within the compartment. Once the fire develops to a point where it produces more fuel vapors than can be consumed in the compartment with the available air, it is considered to be a ventilation-controlled fire. The effect of ventilation on HRR is related to the dimensions of the ventilation opening as shown in Equation 3.2 ‚ Qg ä A h (3) where Qg C heat release rate A C area of the opening
Plume
Q fire Air entrainment
A Note: A = source of fire.
FIGURE 2.4.2
h C height of the opening
Classification by Fire Stage The fire service has typically classified the course of a fire in three stages: (1) incipient, (2) free burning, and (3) smoldering.3 The first stage or phase, called the incipient, is related to the start of the fire during which time there is no active flaming. The fire may be smoldering for several hours. The second phase or stage, called the free burning or flame production period, is accompanied by increased fuel consumption and heat generation. The third phase or stage, called smoldering, is characterized by reduced oxygen in the compartment and rapidly decreasing heat production. In discussions of the three phases or stages of fire, it is generally pointed out that, although these are typically the steps in which a fire progresses, fires may, because of changes in ventilation, return to phase two and continue to free burn in the flame production stage. This classification of fire types by stages has been useful in the past in describing general conditions of burning, but should not be relied on as a rigorous description of the sequence of events involved in ignition and in fire growth and spread.
EFFECTS OF COMPARTMENT BOUNDARIES ON FIRE The presence of compartment boundaries, such as walls and ceilings, can have a significant influence on the manner in which a fire grows and spreads by affecting and controlling heat losses and the HRR.
Air entrainment
Fire in the Open
about the center of the fire. The action of the hot gases rising due to buoyancy causes air to flow in from the surrounding air at the base of the fire and along the boundaries between the plume and the surrounding air. This process is called entrainment. The temperature in the plume decreases with height due to the cooling effects of the entrained air. When the temperature in the plume reaches the temperature of the surrounding air, the gases and smoke stop rising. This phenomenon is frequently observed, particularly on a calm day when smoke from a chimney rises to a certain level and suddenly stops and begins to spread out horizontally. This is the result of the equalization of temperature of the smoke in the plume with the surrounding air. These conditions can develop in tall spaces, such as atria, resulting in stratification of the smoke and hot gases. This phenomenon may result in delayed operation of sprinklers or detectors.
Fire Under a Ceiling (Far from Walls) When a ceiling is located above a fire plume, the rising hot gases and combustion products impinge on the ceiling and begin to flow outward away from the plume centerline. On a smooth, flat (nonsloping) ceiling, this flow would ideally be equal in all directions. Figure 2.4.3 shows the general effects of a ceiling. When a ceiling interposes the plume, the flow can be considered in two regions: (1) the plume region and (2) the ceiling jet region. The temperature and velocities that can be estimated
Losses to ceiling
C L
Losses to ceiling
Fire in the Open The simplest arrangement of a fire is in the open where it is unaffected by either walls or ceilings. A fire in the open is considered a free-burning fire and is generally fuel controlled. Figure 2.4.2 shows a steadily burning fire in the open, with no confining ceiling or walls. This situation can either represent a fire outdoors or a small compartment fire that has not grown to the size where the compartment boundaries may have an influence. Directly above the fire shown in Figure 2.4.2, a column of hot gases and combustion products rises into the air. This column is referred to as the plume and forms a narrow inverted cone-shaped column of rising heated combustion products and smoke. Under stable conditions, the plume will be symmetrical,
Turning region
Q fire Air entrainment
Air entrainment
A Note: A = source of fire.
FIGURE 2.4.3
Fire Under Ceiling, Far from Walls
CHAPTER 4
within the plume and the ceiling jet are strongly dependent on location, with respect to radial distance from the centerline. Research has shown that one set of relationships holds for the immediate area of the impingement point where the plume turns to flow out horizontally underneath the ceiling. This area is known as the turning region. In this region, the flow gas is buoyancy dominated, and the temperatures and velocities are a function primarily of the height of the ceiling above the base of the fire, since the height affects the amount of entrainment. Although the actual temperature above the plume is related to the heat release rate of the fire (Qg ), for any given fire it can be shown that the temperature along the centerline of the plume decreases with increasing height. A general relationship for this phenomenon is given in the Equation 4.4 !T C 16.9
Qg 2/3 H 5/3
for
r D 0.18 H
(4)
where !T C temperature rise above ambient Qg C heat release rate H C height of ceiling above fire The temperature of the ceiling jet outside of the turning region is a function of the distance or radius from the plume. Temperatures will decrease as the radius increases, due to heat losses to the ceiling and to the entrainment of cooler air from the surroundings. A general relationship for this phenomenon is given in Equation 5.4 !T C 5.38
(Qg /r)2/3 H 5/3
for
r B 0.18 H
(5)
Flow rate outside the turning radius is dominated more by momentum (the force of the moving mass of gas) than by buoyancy (the force due to temperature differences between hot and cool gases).1
■
Dynamics of Compartment Fire Growth
Fire in a Compartment Away from Walls Figure 2.4.4 represents the early stages of a compartment fire with a single vent where there is no effect of the compartment. There are two items in the compartment: A and B. A is the source of the fire, and B is an initially unignited target sufficiently far from A that it cannot be ignited directly.5 A thin layer of hot gases and smoke begins to accumulate at the ceiling. As the fire in object A increases in intensity, the gases accumulating at the ceiling spread out and become trapped at the soffit of the door. As the fire continues to produce smoke and hot gases, the layer at the ceiling will thicken and begin to flow out under the soffit into the next compartment, which may be either another room or a hallway, for example (Figure 2.4.5). If the fire stops growing or become steady state at this time, the thickness of the upper layer in the fire compartment will become essentially constant, with the excess combustion products leaving the compartment at a constant rate. However, if the fire continues to increase in heat release rate and the opening is too small to carry away the combustion products at the rate at which they are generated, the upper layer will continue to increase in thickness and descend to the floor, even though there is a vent (Figure 2.4.6). At this time, it is useful to take a look at the various component parts of the compartment fire “system.” A simple conceptual model for this compartment fire system consists of a plume of hot gases above the initially burning object or objects, a heated upper gas layer, and a cool layer below. This model is commonly referred to as a zone created by the hot gases inside and the cool gases outside (Figure 2.4.7). This results in a positive pressure in the hot gases leaving the compartment, relative to the outside of the compartment, and a negative pressure in the cool gases relative to the inside. The resulting airflow is shown in Figure 2.4.8, along with the ceiling layer and plume. In the doorway, there will be a boundary layer between the outflowing hotter gases (resulting from the positive pressure) and the inflowing cooler gases (resulting from the negative pressure). This
Thin ceiling layer
A
B
Note: A = source of fire. B = target fuel.
FIGURE 2.4.4
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Initial Ceiling Effect
2–78 SECTION 2 ■ Basics of Fire and Fire Science
A
B
Note: A = source of fire. B = target fuel.
Initial Smoke Discharge from Compartment of Origin
FIGURE 2.4.5
A
B
Note: A = source of fire. B = target fuel.
FIGURE 2.4.6
Increasing Fire Size and Layer Depth
Q cond loss Q conv loss
Upper zone—hot layer
Q radiation loss Q radiation loss Q fire Lower zone—cool layer Plume A
B
FIGURE 2.4.7
Compartment Fire Zones and Heat Transfer
CHAPTER 4
■
Dynamics of Compartment Fire Growth
2–79
Ceiling layer Pressure (+)
Outflow Neutral plane
Plume Inflow
A
Pressure (–)
B
FIGURE 2.4.8
Compartment Fire Pressure and Airflow
boundary layer or boundary zone is commonly referred to as the neutral plane, i.e., neutral or equal with respect to pressure inside and outside the room. Figure 2.4.7 can also be used to discuss the general heat balance within the zones of a compartment fire. Energy is generated in the combustion region of the fire. The plume acts as a pump to provide combustion products and hot gases to the upper layer. This is the Qfire in Figure 2.4.7. Energy in the hot upper layer is lost in a number of ways. Heat is lost by radiation from the hot gases to the cool area below and by convection of hot gases out the door. Heat is lost to the wall and the ceiling materials by conduction from the hot gas layer. If the fire is burning at a constant heat output, the layer thickness and the losses through the door or vent and to the compartment boundaries will remain constant after some period of time to establish an equilibrium between the heat generated and the heat lost. If the fire continues to grow, conditions will change. Temperatures in the upper layer will continue to rise, and the thickness of the upper layer will continue to increase. The increasing layer temperature and the decreasing distance of the layer from the floor results in greater radiation heat transfer to unignited objects elsewhere in the compartment. The development of the ceiling layer plays a significant role in compartment fire growth. In addition to acting as a radiator to heat other objects in the room, radiation from the layer also increases the burning rate of the items already ignited.6 Typically, as the fire continues to grow in the compartment, with a corresponding increase in the thickness and temperature of the upper gas layer, a transition will occur from a fire that is dominated by the first materials ignited to a fire that is dominated by the burning materials throughout all of the room. This transition is called flashover. Ventilation at flashover becomes controlled by the size of the room openings and the position of the layer in the opening. As the layer descends, the effective ventilation area of the opening is decreased. The triggering conditions7 for the flashover transition are reached when (1) the upper gas layer is approximately 600°C and (2) the radiant flux on unignited materials in the room is approximately 20 kW/m2. Figure 2.4.9 represents flashover, the
transition stage between preflashover and the fully involved compartment fire (called full-room involvement). Full-room involvement, as shown in Figure 2.4.10, is characterized by the production of excess fuel vapors that cannot be consumed within the compartment with the combustion air available. This results in flame extension through vent openings into adjacent compartments or out of windows, should they fail. Window failure generally occurs shortly before or after flashover conditions are reached and can provide additional ventilation area. The HRR needed for flashover is related to the vent openings of the compartment and can be generally predicted using Equations 6 and 7.2 ƒ Babrauskas’ equation: Qg f o C 750A0 H0 (6) ƒ g Thomas’ equation: Qf o C 7.8AT = 378A0 H0 (7) where Qg f o C heat release for flashover (kW) A0 C area of vent opening (m2) H0 C height of venting (m) AT C total area of compartment enclosing surfaces (m2) Flashover is not an inevitable result of a compartment fire. In the event that the fuel is limited or that there is a sufficiently large ventilation opening, the ceiling layer may not develop adequately to make the transition through flashover to full room involvement. Application of suppression agents, either automatically or manually, can also interrupt the process at or prior to flashover. It should be noted that some research indicates that the heat release rate of burning objects, such as mattresses, can be increased by a factor of 2 in a postflashover room fire.6 Once the transition from flashover to full-room involvement begins, the fire approaches ventilation control. Smoke from under the neutral plane is frequently recirculated back toward the fire, along with smoke that may be accumulating in adjacent compartments in the hallway. This process, called vitiation, reduces the oxygen available for combustion, causing a reduced heat release rate. Under these conditions, the fire approaches steady-state burning.
2–80 SECTION 2 ■ Basics of Fire and Fire Science
o
Upper layer — 600 C
20 kW/m2 A
B
FIGURE 2.4.9
Flashover—Transition to Full-Room Involvement
Recirculating smoke A
B
FIGURE 2.4.10
Full-Room Involvement (Postflashover)
EFFECTS OF FIRE LOCATION Under some circumstances, the location of the fire in a room can have an effect on the rate of growth of the fire, in terms of ceiling jet temperature velocity.4 When a fire is burning in a room far from walls, air is free to be entrained into the plume from all directions (Figure 2.4.11). If the fire is close to a wall or in a corner, the amount of air entrainment into the plume is decreased, and adjustments can be made for heat release rate in the correlations used to calculate temperature and velocity. For fires adjacent to a wall, 2Q is substituted for Q; for a fire in a 90° corner, Q is multiplied by 4 in the correlations. It should be noted, however, that experiments have shown that if a circular burner is placed so that only one point is in contact with the wall, the fire behaves almost identically to a fire away from the wall.8
SUMMARY This discussion was presented to provide the reader with an overview of the processes involved in fire growth and spread in
Direction of airflow
FIGURE 2.4.11
Effect of Fire Location on Air Entrainment
and beyond the compartment. The reader is encouraged to study the equations and relationships discussed elsewhere in this handbook, and is directed to the additional reading provided at the end of this chapter.
CHAPTER 4
BIBLIOGRAPHY References Cited 1. Evans, D., “Ceiling Jet Flows,” SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno (Ed.), National Fire Protection Association, Quincy, MA, 1995. 2. Walton, W. D., and Thomas, P. H., “Estimating Temperatures in Compartment Fires,” Section 3/Chapter 6, SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno (Ed.), National Fire Protection Association, Quincy, MA, 1995. 3. Layman, L., Attacking and Extinguishing Interior Fires, National Fire Protection Association, Quincy, MA, 1995, pp. 12–15. 4. Alpert R., and Ward, E., “Evaluation of Unsprinklered Fire Hazards,” Fire Safety Journal, Vol. 7, No. 2, 1984. 5. Babrauskas, V., “Will the Second Item Ignite,” Fire Safety Journal, Vol. 4, No. 4, 1982, pp. 281–292. 6. Babrauskas, V., “Burning Rates,” SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno (Ed.), National Fire Protection Association, Quincy, MA, 1995. 7. Drysdale, D. D., Introduction to Fire Dynamics, John Wiley and Sons, New York, 1985. 8. Zukowski, E. E., Kubuta, T., and Cetegen, B., “Entrainment in Fire Plumes,” Fire Safety Journal, Vol. 3, No. 2., 1981, p. 107.
Additional Readings Bishop, S. R., et al., “Nonlinear Dynamics of Flashover in Compartment Fires,” Fire Safety Journal, Vol. 21, No. 1, 1993, pp. 11–45.
■
Dynamics of Compartment Fire Growth
2–81
Bishop, S. R., and Drysdale, D. D., “Fires in Compartments: The Phenomenon of Flashover,” Philosophical Transactions: Mathematical, Physical and Engineering Sciences, Series A, Vol. 1748, No. 356, 1998, pp. 2855–2872. Chow, W. K., and Ng, Y. S., “Experimental Studies of Compartment Fire,” Journal of Applied Fire Science, Vol. 4, No. 1, 1994–1995, pp. 17–30. Cooper, L. Y., “Compartment Fire-Generated Environment and Smoke Filling,” P. J. DiNenno (Ed.), SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995. Luochan, S., Jianping, Y., and Jianren, F., “Numerical Study of the Compartment Fire with Transient Developing Source,” First Asian Conference on Fire Science and Technology (ACFST), October 9–13, 1992, Hefei, China, International Academic Publishers, China, 1992, pp. 330–334. Parkes, A. R., “Under-Ventilated Compartment Fires: A Precursor to Smoke Explosions,” University of Canterbury, Christchurch, New Zealand, Fire Engineering Research Report 96/5, Dec. 1997. Thomas, P. H., “Two-Dimensional Smoke Flows from Fires in Compartments: Some Engineering Relationships,” Fire Safety Journal, Vol. 18, No. 2, 1992, pp. 125–137. Williams, F. W., Scheffey, J. L., Hill, S. A., Toomey, T. A., Darwin, R. L., Leonard, J. T., and Smith, D. E., “Post-Flashover Fires in Shipboard Compartments Aboard ex-USS SHADWELL. Phase 5. Fire Dynamics. Final Report,” Naval Sea Systems Command, Washington, DC, NRL/FR/6180-99-9902, May 31, 1999.
CHAPTER 5
SECTION 2
Theory of Fire Extinguishment Raymond Friedman
O
ne or more of the following mechanisms—more often, several of them simultaneously—can be used to extinguish fire:
• Physically separating the combustible substance from the flame • Removing or diluting the oxygen supply • Reducing the temperature of the combustible or of the flame • Introducing chemicals that modify the combustion chemistry For example, when water is applied to a fire of a solid combustible burning in air, several extinguishing mechanisms are involved simultaneously. The solid is cooled by contact with water, causing its rate of pyrolysis, or gasification, to decrease. The gaseous flame is cooled, causing a reduction in heat feedback to the combustible solid and a corresponding reduction in the endothermic pyrolysis rate. Steam is generated, which, under some confined conditions, may prevent oxygen from reaching the fire. Water in the form of fog may block radiative heat transfer. As another example, consider the application of a blanket of aqueous foam to a burning pool of flammable liquid. Several mechanisms may be operative. The foam prevents the fire’s radiant heat from reaching the surface and supplying the needed heat of vaporization. If the fire point of the flammable liquid is higher than the temperature of the foam, the liquid is cooled and its vapor pressure decreases. If the flammable liquid is water soluble, such as alcohol, then, by a third mechanism, it will become diluted by water from the foam, and the vapor pressure of the combustible will be reduced. As yet another example, when dry chemical is applied to a fire, the following extinguishing mechanisms may be involved: • • • •
Chemical interaction with the flame Coating of the combustible surface Cooling of the flame Blocking of radiative energy transfer
Ideally, any fully successful theory of fire extinguishment should be able to predict the quantity and rate of application of the extinguishing agent needed for a given fire. Such a theory
Dr. Raymond Friedman was vice president in charge of fire research for the Factory Mutual Research Corporation from 1969 to 1987. Now semiretired, he is a consultant and author.
would be better than empirical measurements that yield the same information, because the empirical data would be fully reliable only in circumstances identical to those employed in the empirical testing. Furthermore, the theory would provide guidance toward improvement of extinguishment performance. Unfortunately, the agents mentioned above—water, foam, and dry chemical—each work by a combination of several mechanisms, and the relative importance of the various contributions varies with circumstances. The degree of complexity resulting from this situation, as well as other problems, has up to now prevented completion of a quantitative fundamental theory of extinguishment action. However, much is known about the various extinguishment modes, and this knowledge is outlined herein. A more detailed treatment can be found in Friedman.1
THE COMBUSTION PROCESS Much scientific information has been developed about the combustion process, the understanding of which is central to the understanding of fire extinguishment. For details, one may refer to the texts by Friedman, which is rather elementary; Drysdale2 and Glassman,3 which are more advanced; or Strehlow,4 which is the most advanced. Only some simple, basic concepts of combustion especially relevant to fire extinguishment are presented in this chapter. The term combustion usually refers to an exothermic, or heat-producing, chemical reaction between some substance and oxygen. Chemical analysis of combustion products shows the presence of certain molecules involving combinations of oxygen atoms with other types of atoms, such as CO2, H2O, SO2, NO2, Al2O3, or SiO2. A slow reaction is a reaction between some substance and oxygen that requires weeks or months to complete. Such a reaction, which is not combustion, releases heat so slowly that the temperature never increases more than a degree or so above the temperature of the surroundings. One example of this process is the rusting of metal. The difference between a slow oxidative reaction and a combustion reaction is that the latter occurs so rapidly that heat is generated faster than it is dissipated, causing a substantial temperature rise of at least hundreds of degrees, and often several thousand degrees. Very often, the temperature is so high that visible light is emitted from the combustion reaction zone.
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2–84 SECTION 2 ■ Basics of Fire and Fire Science
The concern in fire protection is generally with combustion reactions between various materials and the oxygen of the air. A flame is a gaseous oxidation reaction that (1) occurs in a region of space much hotter than its surroundings and (2) generally emits light. Familiar examples include the yellow flame of a candle and the blue flame of a gas burner. When a solid such as a match or candle burns, a portion of the heat of the gaseous flame is transferred to the solid, causing the solid to vaporize (Figure 2.5.1). This vaporization can occur with or without chemical decomposition of the molecules. If chemical decomposition occurs, the process is called pyrolysis. There is another mode of combustion that does not involve any flame. It is called smoldering, glowing, or nonflaming combustion. A cigarette burns in this way. Upholstered furniture containing cotton batting or polyurethane foam can also smolder. A large pile of wood chips, sawdust, or coal can smolder for weeks or even months. Smoldering is generally limited to porous materials that can form a carbonaceous char when heated. The oxygen in the air slowly diffuses into the pores of the material, and there is a glowing reaction zone within the material, even though the glow might not be visible from outside. These porous materials are poor conductors of heat, so even though the combustion reaction occurs slowly, enough heat is retained in the reaction zone to maintain the elevated temperature needed to sustain the reaction. It is not uncommon for a piece of upholstered furniture, once ignited, to smolder for several hours. During this time, the reaction zone spreads only 2 or 4 in. (50 or 100 mm) from the ignition point, and then, suddenly, the furniture can burst into flames. The rate of burning during flaming combustion is many times greater than the rate of burning during smoldering combustion.
Inverted beaker is trapping carbon dioxide combustion products from flame
Inverted beaker is lowered, bringing carbon dioxide down on burning wax flame
Combustion requires a high temperature, and the chemical reactions must proceed fast enough at this high temperature to generate heat as fast as it is dissipated, so that the reaction zone will not cool down. If anything is done to upset this heat balance, such as introducing a coolant, it is possible that the combustion will be extinguished. It is not necessary for the coolant to remove heat as fast as it is being generated, because the combustion zone in a fire is already losing some heat to the cooler surroundings. In some cases, only a modest additional loss of heat is needed to tip the balance toward extinguishment (see Figure 7.3 in Friedman1). Extinguishment can be accomplished by cooling either (1) the gaseous combustion zone or (2) the solid or liquid combustible. In the latter case, the cooling prevents the production of combustible vapors. This is probably the primary mode of action when a wood fire is extinguished by applying water. As an alternative to removing heat from the combustion zone to slow the reactions, it is also possible to reduce the temperature of the flame by modifying the air that supplies the oxygen that feeds the flame. Air is 21 percent oxygen by volume, the remainder being almost entirely the inert gas nitrogen. The nitrogen, which is drawn into the flame along with the oxygen, absorbs heat, with the result that the flame temperature is much lower than it would be in a fire burning in pure oxygen. If additional nitrogen or some other chemically unreactive gas, such as steam, carbon dioxide, or a mixture of combustion products, were to be added to the air entering the flame, the heat absorbed by these inert molecules would cause the flame temperature to be even lower. The flame temperature is so important because the rate of a key combustion reaction (H = O2 ó OH = O) is very sensitive to temperature. A small decrease in temperature causes a disproportionately large decrease in the rate of this reaction, according to Arrhenius’ law, which states that chemical reaction rates vary exponentially with temperature. The symbol H denotes a free hydrogen atom, as contrasted with the ordinary stable form of hydrogen, H2. Combustion consists of rapid chain reactions involving these hydrogen atoms and other active species, hydroxyl free radicals OH, and free oxygen atoms O. Figure 2.5.2 shows a sequence of reactions occurring in the hydrogen–oxygen flame. Figure 2.5.2 shows that a single H atom, when introduced into an H2–O2 mixture at an elevated temperature, will be transformed by a sequence of rapid reactions, requiring a fraction of a millisecond, to form two molecules of H2O and three new H atoms. Each of these new H atoms can immediately initiate the same sequence, resulting in a branching chain reaction, which continues until the reactants are consumed. Then, the remaining H, O, and OH species recombine according to the reactions H = O ó OH and H = OH ó H2O
Freely burning candle
Self-extinguished candle
FIGURE 2.5.1 Flaming Combustion (Left) and Extinguishment (Right) by Its Own Combustion Products of a Wax Candle
Similar chain reactions occur in flames of any hydrogencontaining species. Hydrogen is present in the vast majority of combustibles, except for metals and pure carbon. The ability of hydrogen atoms to multiply rapidly in a flame depends, then, on the prevailing temperature in the flame,
■
CHAPTER 5
+O2
OH + O
+H2 OH + H +H2
+H2 H2O + H
H2O + H Net result: H + 3H 2 + O2
2H2O + 3H
FIGURE 2.5.2 Chain Reaction Mechanism in the Hydrogen–Oxygen Flame
which is modified by heat loss or by inert gases, thus leading to extinguishment. Hydrogen atoms or other active species may also be removed from the flame by purely chemical means, that is, by introducing a species capable of chemical inhibition, which will be discussed later in this chapter. Accordingly, there are two fundamental ways of reducing combustion intensity in a flame and ultimately causing extinguishment:
2–85
ious flames has not been fully established yet. For practical purposes, the measured flammability limits can be relied on. Notice also from Figure 2.5.3 that a 9.5 percent methane– air–nitrogen mixture can be made nonflammable by adding not only nitrogen but also additional air or additional methane. Such additions would produce an excess of one of the reactants and, therefore, a dilution and reduction of flame temperature. The foregoing discussion of flammability limits applies to premixed combustion, or combustion of a uniform mixture of fuel and air and possibly a third component. This is often the case for explosions, but fires are generally diffusion flames rather than premixed flames. That is, a solid or liquid combustible is vaporizing, and air approaches the vapor cloud from the sides. The flame burns at the interface of the interdiffusing combustible vapors and air. The hot combustion products then rise because of buoyancy. A diffusion flame is clearly more complex than a premixed flame, but much the same principles apply to its extinguishment. If more inert gas is added to the air feeding a diffusion flame, extinguishment will occur when the flame temperature is reduced to about 1200°C or 1300°C. However, another important way of extinguishing a diffusion flame over a solid or liquid is to cool 16
14
Consider the effect of adding additional nitrogen to a fuel vapor–air mixture. Suppose the fuel vapor is methane, CH4. Figure 2.5.3 shows that if more than about 35 percent additional nitrogen is added to a 9.5 percent methane–air mixture at 25°C, the resulting mixture is nonflammable. This nonflammability is caused by the reduction of flame temperature from about 1900°C to about 1200°C, since the added nitrogen absorbs heat. But why is the flame unable to burn when its temperature is below 1200°C? This is not fully understood. If we had an ideal flame, burning in a place with no gravitational field (e.g., a space station), and also with negligible radiative heat loss, it is believed that there would still be a flammability limit, caused by the competition between chain-branching and chain-breaking chemical reactions. Chain-branching reactions are known to be much more temperature-sensitive than chain-breaking reactions; therefore, below a critical temperature, chain-breaking reactions will dominate and the flame can no longer burn. However, a real flame, on earth, will be in a gravitational field, and when the dilution of the flame reduces the burning velocity to a value lower than the free-convective motions (buoyancy) of the burning region surrounded by colder gases, then the burning surface will be “strained” and disrupted, and extinguishment will result. Another effect is the radiative heat loss from the flame to the surroundings, which can cause instability when the rate of heat loss becomes a sufficient fraction of the rate of heat generation. The relative importance of the various effects for var-
12
Methane (volume percent)
1. Reducing the flame temperature 2. Adding a chemical inhibitor to interfere with the chain reaction
Nonflammable
10
Fla mm abl e
H
Theory of Fire Extinguishment
8
Sto ich iom etr ic
mix tur es
6
Nonflammable 4
2
% CH4 + % Air + % N2 = 100%
0 0
10
20
30
40
50
Added nitrogen (volume percent)
FIGURE 2.5.3 Limits of Flammability of Various Methane–Air–Nitrogen Mixtures at 25°C and 1 atm (Source: Zabetakis5)
2–86 SECTION 2 ■ Basics of Fire and Fire Science
EXTINGUISHMENT WITH WATER One might suppose that water is the most widely used extinguishing agent because of its low cost and ready availability, relative to other liquids. However, quite aside from cost and availability, water is superior to any other known liquid for fighting the majority of fires. Water has a very high heat of vaporization per unit mass, at least four times higher than that of any other nonflammable liquid. It is also outstandingly nontoxic; even a chemically inert liquid, such as liquid nitrogen, can cause asphyxiation. Water can be stored at atmospheric pressure and normal temperatures. Its boiling point (100°C) is well below the 250°C to 450°C range of pyrolysis temperatures for most solid combustibles, and therefore evaporative cooling of the pyrolyzing surface is efficient. No other liquid, regardless of cost, can match these properties. However, water is not an absolutely perfect extinguishing agent. It does freeze below 0°C. It does conduct electricity. It can irreversibly damage some items, although, in many cases, it is practical to salvage water-damaged items. Water may not be effective for flammable liquid fires, especially flammable liquids that are insoluble in water and float on water, such as hydrocarbons. Water is not compatible with certain hot metals or certain chemicals. With fires in these materials, other agents, for example, aqueous foam, inert gases, halons (with specific limitations due to atmospheric concerns), and dry chemical, are preferred. Water may extinguish a fire by a combination of mechanisms—cooling the solid or liquid combustible; cooling the flame itself; generating steam that prevents oxygen access; and as fog, blocking radiative transfer. Although all these mechanisms may contribute to extinguishment, probably the most important is cooling a gasifying combustible. For a solid to burn, a portion of the solid must be at a high enough temperature so that pyrolysis occurs at a sufficient rate to maintain the flame. For most solids, this temperature is 300°C to 400°C, and the pyrolysis rate must be a few grams per square meter per second. If even a small amount of liquid water, with its high heat of vaporization, can reach this region, the solid can be cooled sufficiently to reduce or stop the pyrolysis, and the flame will be extinguished. Even deep-seated fires can be suppressed in this way. Accordingly, water is the obvious agent of choice for burning solids. The two most common means of applying water are by (1) a solid stream or spray from a hose and (2) spray from automatic sprinklers. The practical aspects of manual fire fighting and the use of sprinklers are discussed elsewhere in this handbook. From a scientific viewpoint, studies reviewed by Heskestad6 and Rasbash7 have investigated the minimum rate of water application to a burning solid surface that will cause extinguishment. In an important paper by Magee and Reitz,8 burning slabs of various plastics, horizontal and vertical, were simultaneously heated with radiant heaters and cooled with controlled water
sprays. Extinguishment conditions were then determined. Figure 2.5.4 shows a linear relationship between the radiative heating rate and the water application rate required for extinguishment. The reciprocal of the slope of the line is found to be approximately the heat of vaporization of water, as theory would predict. To extinguish burning polymethyl methacrylate (Lucite®, Plexiglas®, Perspex®), enough water must be applied to reduce the burning rate to less than about 4 g/m2Ýs. Depending on the intensity of the externally imposed radiative flux—up to 18 kW/m2—a water application rate of 1.5 g/m2Ýs to 8 g/m2Ýs was required. This is a very small application rate of water. For extinguishment with no external radiative flux, it was only necessary to spray enough water so that the heat absorbed by its vaporization was 3 percent of the heat of combustion. Experiments with other plastics and with wood cribs have given similar results; only a few grams per square meter per second of water must be applied to the burning surface to cause extinguishment, and the rate of heat absorption by the water is only a few percent of the rate of heat generation by the fire before water application. The reason for this high efficiency is well understood. Consider a horizontal slab of polymethyl methacrylate, 0.3 m ? 0.3 m, which is burning steadily on its top surface. Measurements1 have shown that only about 12 percent of the energy released by combustion is transferred back to the surface. Of this energy arriving at the surface, primarily by radiation from the flame above, about 40 percent is reradiated from the hot surface to the surroundings, and only 60 percent of 12 percent, or 7 percent of the available combustion energy, is used to decompose and gasify the plastic. It is only necessary to apply enough water to the surface to drain off a substantial portion of this 7 percent of the combustion en-
8
Critical water application rate (g/m2 – s)
the solid or liquid enough to interrupt the gasification process. If the gasification rate can be reduced to less than a few grams per square meter per second, the flame becomes unstable and can no longer sustain itself.
7 6
5
4
3
2
1 0 0
5
10 External radiative flux
15
20
(kW/m2)
FIGURE 2.5.4 Water Application Rate Needed to Extinguish a Fire on a Vertical Polymethyl Methacrylate Sheet
CHAPTER 5
ergy, and the rate of burning is then reduced to a point at which the flame can no longer sustain itself. Of course, the evaporation of the water produces steam that dilutes the flame and reduces the flame temperature, causing some reduction in the rate of burning, but this effect is generally small and need not be considered in a first-approximation model of the extinguishment process. It is interesting to note that in ignition experiments, a solid surface is progressively heated, with a gradual increase in the rate of pyrolysis, or gaseous decomposition, but it is not possible to ignite the vapors to obtain a selfsustaining flame until the pyrolysis rate reaches a certain minimum value. This is roughly the same value to which the pyrolysis rate must be reduced when water is applied to a burning surface to accomplish extinguishment. In practical fire fighting, water must be applied at 10 to 100 times the rates used in the research described above because of the difficulty of delivering the water directly to the burning surface. In the case of fire suppression by use of sprinklers at the ceiling, it is possible to calculate the fraction of the water droplets able to penetrate the fire plume and arrive at the burning surface beneath. Such a calculation is complex.9 It is necessary to know the heat release rate of the fire, the location of the fire relative to the nearby ceiling sprinklers, and the distribution of drop sizes of the water. The calculation takes into account the aerodynamic drag on the downward-moving droplets encountering the upward-moving fire gases, and calculates the change in motion of the fire gases because of the downward momentum of the water spray. Droplet evaporation and cooling of the fire gases are included in the calculation. The drop-size distribution of the water depends not only on the sprinkler design but also on the pressure drop across the sprinkler. The mean drop size varies inversely with the cube root of the pressure drop. The drop size also depends on the surface tension of the water, which could be modified with additives. In some cases—for example, a purely gaseous fire—water may extinguish the fire by cooling the flame rather than the source of the fuel vapor. The theory of this action has been discussed previously. For a pool fire of a flammable liquid with a high flashpoint (e.g., diesel oil), water can be effective by reducing the temperature of the liquid below its flashpoint. However, water impinging on the flammable liquid with high velocity can cause burning liquid to be scattered, increasing the fire intensity. Water applied as a foam or as a fine mist avoids this situation.
EXTINGUISHMENT WITH AQUEOUS FOAMS Aqueous foam agents are principally used for fighting flammable liquid fires. If the flammable liquid is lighter than water and is insoluble in water, then application of water would simply result in the liquid floating on it and continuing to burn. If the flammable liquid is an oil or fat, the temperature of which is substantially above the boiling point of water, then the water will penetrate the hot oil, turn into steam below the surface, and cause an eruption of oil that will accelerate the burning rate and possibly spread the fire.
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Theory of Fire Extinguishment
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Foams are the primary tools for fighting fires that involve substantial quantities of petroleum products, such as those found at refineries, tankers, and storage areas. If the flammable liquid is water soluble, such as alcohols, then the addition of sufficient water will dilute the liquid to the point where it is no longer flammable. If there is a deep pool of water-soluble flammable liquid rather than a shallow spill, however, the time required to obtain sufficient dilution might be so great that an aqueous foam would be a better extinguishing agent. If the nature of a liquid is unknown, aqueous foam might be chosen instead of the direct application of water. Another important application of aqueous foam agents is on liquids or solids that are burning in difficult-to-access spaces, such as a room in a basement or the hold of a ship. The foam is used to flood the compartment completely. Fire-fighting foam is a mass of bubbles formed by various methods from aqueous solutions of specially formulated foaming agents. Because foam is much lighter than any flammable liquid, it floats on the liquid, producing an air-excluding, cooling, continuous layer of vapor-sealing, water-bearing material that can halt or prevent combustion. Fire-fighting foams are formulated in several ways for fireextinguishing action. Some foams are thick and viscous, forming tough heat-resistant blankets over burning liquid surfaces and vertical areas. Other foams are thinner and spread more rapidly. Some foams are capable of producing a vapor-sealing film of surface-active water solution on a liquid surface, and some are meant to be used as large volumes of wet gas cells for inundating surfaces and filling cavities. There are various methods for applying foams, which are fully described in Section 11 of this handbook. The use of foam for fire protection requires attention to its general characteristics. Foam breaks down and vaporizes its water content when under attack by heat and flame. Therefore, it must be applied to a burning surface in sufficient volume and rate to compensate for this loss and to provide an additional amount to guarantee a residual foam layer over the extinguished portion of the burning liquid. Before starting to apply foam to a large fire, a sufficient amount of foam concentrate to do the job must be accumulated. Nothing will be accomplished by putting out only part of a fire and then running out of foam, because the fire will build back to its original intensity. Foam is an unstable air–water emulsion and can be broken down easily by physical or mechanical forces. Certain chemical vapors or fluids can destroy foam quickly. When certain other extinguishing agents are used in conjunction with foam, severe breakdown of the foam can occur. Turbulent air or violently uprising combustion gases can divert light foam from the burning area. There is no theoretical basis available to serve as a guide to the needed rates of application of the various types of foams in different situations. The guidelines come from experience or from empirical tests. One useful laboratory measure of foam effectiveness is to fill a graduated cylinder with foam and observe the time required for a certain fraction of the water in the cylinder to drain to the bottom. The more stable the foam, the slower it will drain.
2–88 SECTION 2 ■ Basics of Fire and Fire Science
Clearly, the time for collapse of a foam layer should be greater than the time required to coat the entire surface of a large spill with foam. Thus, a basis is available for calculating the necessary rate of application. Of course, fire causes foam to break down at a greater rate than indicated by the drain test in a cylinder; therefore, empirical information is still needed. Another laboratory tool useful for formulating film-forming foams is the measurement of surface tension of the foam solution, F, the flammable liquid, L, and the interfacial tension between the two liquids, FL. The film will spread over the surface only if F plus L is greater than FL.
EXTINGUISHMENT WITH WATER MIST There has been recent interest in developing equipment for applying a fine mist of water to a fire as an alternative to halogenated agents. The following three methods can be used to distribute water mist: 1. Fixed installation, in which a fine mist is used to inert a compartment in which a fire may occur, perhaps in a concealed and unpredictable location 2. Fixed spray nozzles positioned around the site of an anticipated fire 3. A portable extinguisher using a fine spray or mist Three mechanisms by which a fine water mist might extinguish a flame are as follows: 1. The mist droplets, while evaporating, remove heat, either at the surface of the combustible or within the gaseous flame. This cooling can cause extinguishment, as discussed previously. 2. The fine droplets evaporate in the hot environment even before reaching the flame, generating steam that dilutes the oxygen percentage in the air approaching the flame, thus causing extinguishment by a mechanism similar to that of an inert gas, for example, carbon dioxide. 3. The mist blocks radiative heat transfer between the fire and the combustible. In those tests in which mists have successfully extinguished fires, some combination of the above effects appears to have occurred in each case. In regard to mechanism 1, it is much easier for a large drop to reach a burning surface than for a very fine drop (mist), which would tend to be blown away from the surface by the pyrolysis gases, if indeed the fine drop could get through the flame to the vicinity of the underlying surface, in the first place. This difficulty disappears when the fine mist is directed at the burning surface with high momentum. In regard to cooling the flame gases rather than the burning surface, a sufficiently high concentration of water mist in the approaching air must be achieved. This is estimated to be at least 15 percent water mist by weight in air. This can be achieved if the mist is sprayed directly at the flame, but if the mist is sprayed in some random direction into a compartment, the buildup to a high concentration is hampered by the settling of some mist droplets to the floor of the compartment. Table 2.5.1 shows settling times of water droplets of various sizes. The settling rate is
TABLE 2.5.1
Settling Velocities of Water Drops
Diameter (microns) 5 10 20 50
Time (s) to Settle 0.305 m (1 ft) 391 99 25 4
Source: Friendlander, S., Smoke, Dust, and Haze, Wiley, New York, 1977.12
negligible (assuming the goal is extinguishment in a few tens of seconds) for droplets finer than about 10 microns diameter. However, it is very difficult to produce droplets this fine. Mawhinney et al.10 classify mists as Class 1 sprays (at least 10 percent of the spray less than 100 microns) or Class 2 sprays (at least 10 percent of the spray less than 200 microns). The bulk of the droplets in sprays just meeting the Class 1 requirement settle out in a very few seconds, according to Table 2.5.1; thus, it is very difficult to build up an adequate concentration in the compartment. The blockage of radiation by a mist will often be effective in reducing the intensity or spread rate of a fire, but will rarely be sufficient in itself to extinguish a fire. In summary, the effectiveness of a fine mist depends on (1) the momentum and direction of the spray relative to the fire and (2) the compartment geometry. Further discussion of water mists can be found in Mawhinney et al.,10 and the International Conference on Water Mist Fire Suppression Systems.11
EXTINGUISHMENT WITH INERT GASES Water acts to extinguish fires primarily by cooling, although the formation of steam helps to dilute the concentration of oxygen. On the other hand, inert gases act to extinguish a fire primarily by dilution. Carbon dioxide is the most commonly used inert gas, although nitrogen or steam could be used. Theoretically, helium, neon, or argon could be used, but they are expensive, and there is no reason to use them except in certain special cases, such as magnesium fires. Table 2.5.2 presents the minimum proportions of carbon dioxide or nitrogen gas that if added to air will form an atmosphere in which various vapors will not burn. On a volume basis, carbon dioxide is substantially more effective than nitrogen. Note, however, that a given volume of carbon dioxide is 1.57 times as heavy as nitrogen (44 to 28 molecular weight ratio), so the two gases have nearly equal effectiveness on a weight basis. Either gas in sufficient quantity will prevent the combustion of anything except certain metals or unstable chemicals such as pyrotechnics, solid rocket propellants, hydrazine, and so on. If available, steam also can be used as an inert extinguishing agent. The percentage by volume required is intermediate between that required for carbon dioxide and for nitrogen. Table 2.5.2 shows that the required addition of either carbon dioxide or nitrogen reduces the oxygen level to a point at which exposed humans will suffer undesirable effects. In the
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TABLE 2.5.2 Minimum Required Volume Ratios of Carbon Dioxide or Nitrogen to Air That Will Prevent Burning of Various Vapors at 25°C
CO2/Air
% O2
Extra N2/Air
% O2
Carbon disulfide Hydrogen Ethylene Ethyl ether Ethanol Propane Acetone n-Hexane Benzene Methane
1.59 1.54 0.68 0.51 0.48 0.41 0.41 0.40 0.40 0.33
8.1 8.2 12.5 13.9 14.2 14.9 14.9 15.0 15.0 15.7
3.00 3.10 1.00 0.97 0.86 0.78 0.75 0.72 0.82 0.63
5.2 5.1 10.5 10.6 11.3 11.8 12.0 12.2 11.5 12.9
Source: Friedman.1
case of carbon dioxide, an additional serious physiological effect will occur at the concentrations required to extinguish a fire. Table 2.5.2 refers only to vapors, but the data are relevant to liquids or solids because they burn only by vaporizing or pyrolyzing. Accordingly, application of an inert gas can extinguish the flame over a liquid or solid. However, if the inert gas dissipates after several minutes, because, for example, the enclosure is not airtight, it is possible that a glowing ember or hot metal could reignite the fire. Reignition is common for a deep-seated fire, such as what might occur in upholstered furniture or in a carton of documents. Some explanation of the physical forms of carbon dioxide is appropriate. Carbon dioxide is unusual in that it can exist only as a gas or solid at normal atmospheric pressure, but not as a liquid. Figure 2.5.5 shows the phase diagram of carbon dioxide. The solid form of carbon dioxide, commonly known as dry ice, at atmospheric pressure, exists only below –79°C, at which temperature it undergoes sublimation directly to vapor, without melting. However, liquid carbon dioxide can exist at elevated pressures, as long as the temperature is above –57°C and the pressure is above 5.2 atm. This temperature and pressure condition is known as the triple point of carbon dioxide because it is the only condition at which solid, liquid, and vapor can coexist. Liquid carbon dioxide can be kept in a pressure vessel at any temperature between –57°C and +31°C (the critical temperature). Above the critical temperature, there will no longer be a liquid–gas interface in the pressure vessel; therefore, the fluid in the vessel would be a gas. A pressure vessel at 21°C containing liquid carbon dioxide would be at a pressure of 58 atm, which is the vapor pressure of carbon dioxide at that temperature. This pressure is used to expel liquid carbon dioxide from a cylinder in fire fighting. The cylinder normally would contain an internal dip tube reaching to the bottom so that liquid rather than vapor would be discharged. As the liquid droplets emerge from a nozzle into the lower-pressure environment, instantaneous evaporation occurs, with evaporative cooling of the residual liquid in each drop. This process causes solidification of the residual portion into dry ice particles at –79°C. If the liquid was
– 80
– 40
0
+ 40
+ 80
+ 120
100
Nitrogen
Vapor
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Theory of Fire Extinguishment
Temperature (°F) –120
Liquid Critical point
30 Pressure (Atm; log scale)
Carbon Dioxide
■
10 Solid Vapor 3
Triple point
1 Atm
1 – 80
– 40
0
+40
Temperature (°C)
FIGURE 2.5.5
Phase Diagram of Carbon Dioxide
originally at 21°C, about 75 percent of the discharged liquid would have evaporated and about 25 percent would have been converted to dry ice particles. Some of the dry ice particles might impinge on a combustible surface and have a cooling effect. However, because the heat of sublimation of carbon dioxide is only about one-fourth the heat of vaporization of water and because only about onefourth of the carbon dioxide discharged is converted to dry ice, the cooling effect on a hot surface is only about one-sixteenth that produced by water discharged at an equal rate (on a mass basis). In comparing carbon dioxide and nitrogen, carbon dioxide has the advantage that it can be stored in a cylinder as a liquid at a relatively moderate pressure of 58 atm at 21°C, while nitrogen at the same temperature must be stored as a gas, usually at about 140 atm. A given size of cylinder at 21°C and these pressures could hold about three times as large a volume of carbon dioxide as nitrogen (measured after expansion, at atmospheric conditions). Nitrogen also could be stored for short periods more compactly as a cryogenic liquid at –196°C and 1 atm. However, long-term storage results in continuous loss of nitrogen. As a result of these factors, carbon dioxide is used more commonly than nitrogen as an inerting gas. Semipermeable membranes are being developed that can inexpensively separate the oxygen and nitrogen of the air. When and if such systems become cost-effective, it might be practical to provide permanent nitrogen-inerting of hazardous spaces that do not require human presence. A reduction of the oxygen percentage in the air from 21 percent to 10 percent by volume
2–90 SECTION 2 ■ Basics of Fire and Fire Science
would make fires and explosions impossible, except for a few special gases, for example, hydrogen, acetylene, or carbon disulfide, which would require greater dilution.
EXTINGUISHMENT WITH HALOGENATED AGENTS Halogenated agent extinguishing systems are a relatively recent innovation in fire protection, but despite this they already face extinction. As of January 1, 1994, the global production of fireprotection halons in many countries ceased. The reason halon production has come to a halt has nothing to do with its effectiveness as an extinguishing agent. Halon production has ceased because halons have a deleterious effect on the environment. Scientific evidence has strongly linked halons and chlorofluorocarbons (CFCs) to the depletion of the earth’s stratospheric ozone layer, which protects us from the sun’s harmful ultraviolet radiation. Depletion of the ozone layer may reduce its effectiveness, leading to potentially significant health and environmental problems. The halogenated extinguishing agents, or halons, are chemical derivatives of methane (CH4) or ethane (CH3–CH3), in which some or all of the hydrogen atoms have been replaced with fluorine, chlorine, or bromine atoms, or by some combination of these halogen elements. These agents are liquids when stored in pressurized tanks at normal temperatures, but most of them are gases at atmospheric pressure and normal temperatures. Halogenated agents can be used for fire applications such as those discussed previously for carbon dioxide. For example, they can be used on electrical fires, in cases where water or dry chemicals would cause damage, or for inert-gas flooding of compartments. Halogenated agents have two principal advantages over carbon dioxide: 1. Certain halogenated agents are effective in such low volumetric concentrations that sufficient oxygen remains in the air after compartment-flooding for comfortable breathing. 2. For several halogenated agents, only partial vaporization occurs initially during projection from a nozzle, and the liquid can be projected farther than carbon dioxide. The drawbacks of using halogenated agents have to do with the toxicity and corrosivity of their decomposition products and with the detrimental effect halogenated compounds have on the earth’s ozone layer. Of the various halons, Halon 1301 (bromotrifluoromethane) is by far the most commonly used in fire protection because it has the lowest toxicity as well as the highest effectiveness on a weight basis. Among the highly effective halons, it has the highest volatility, which is desirable for flooding applications. If a halon liquid is needed for direct application to a burning surface to accomplish cooling as well as inerting of the nearby region, however, a less volatile halon, such as Halon 1211 (bromochloro-difluoromethane) or Halon 2402 (dibromotetrafluoroethane), would be preferred. Table 2.5.3 gives the physical properties of these three halons. They are all liquids at normal temperatures when stored
in pressurized tanks. They can be stored under high-pressure nitrogen if the liquid must be expelled from the tank more rapidly than under the vapor pressure of the halon alone. The use of nitrogen for pressurization is especially important for outdoor storage in the winter. The inerting capabilities of Halon 1301 and Halon 1211 are shown in Table 2.5.4. If methane in any proportion is combined with a mixture containing 5.4 volumes of Halon 1301 and 100 volumes of air, at 25°C, then no combustion can result. By contrast, a mixture containing 33 volumes of carbon dioxide and 100 volumes of air is required to obtain the same result. This suggests that a molecule of Halon 1301 is 6.1 (33/5.46) times as effective as a molecule of carbon dioxide. Note, however, that the molecular weight of Halon 1301 is 149, whereas that of carbon dioxide is 44, so the ratio of molecular weights is 3.39 (149/44). Accordingly, on a weight basis, Halon 1301 is only 1.8 (6.1/3.39) times as effective as carbon dioxide for methane fires. Table 2.5.4 shows that the inerting proportion of halon needed varies somewhat, depending on the nature of the combustible, and substantially more halon is needed for hydrogen, carbon disulfide, or ethylene fires than for most other com-
TABLE 2.5.3 Physical Properties and Chemical Formulas of Three Halon Extinguishing Agents Halon 1301 (CF3Br)
Property Boiling point (°C) Liquid density at 20°C (g/cc) Latent heat of vaporization (J/g) Vapor pressure at 20°C (atm)
Halon Halon 1211 2402 (CF2CIBr) (C2F4Br2)
–58.00
–4.00
+47.00
1.57
1.83
2.17
117.00
134.00
105.00
14.50
2.50
0.46
TABLE 2.5.4 Minimum Required Volume Ratios of Halons to Air at 25°C that Will Prevent Burning of Various Vapors Halon 1301
Halon 1211
Vapor
1301/air
% O2
1211/air
% O2
Hydrogen Carbon disulfide Ethylene Propane n-Hexane Ethyl ether Acetone Methane Benzene Ethanol
0.290
16.2
0.430
14.7
0.150 0.130 0.073 — 0.070 0.059 0.054 0.046 0.045
18.2 18.5 19.5 — 19.6 19.8 19.9 20.0 20.0
— 0.114 0.065 0.064 — 0.054 0.062 0.052 —
— 18.8 19.7 19.7 — 19.9 19.7 19.9 —
Source: Calculated from tabulations by Kuchta.13
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bustibles. Table 2.5.4 also shows that Halon 1301 and Halon 1211 have similar effectiveness on a volume basis for most combustibles. On the basis of molecular weights, a molecule of Halon 1211 is 1.11 (165.5/149) times as heavy as a molecule of Halon 1301. Table 2.5.4 is based on experiments in which a strong ignition source is applied to a uniform combustible–air–halon mixture, and the occurrence or nonoccurrence of a propagating flame is noted. A somewhat smaller quantity of halon would be needed to cause an existing flame on a burner to become unstable and then extinguish itself; the quantity of halon needed will depend on the details of the burner. A flame burning on a solid is even more easily extinguished. Grant14 found that flames on most solids could be extinguished with 4 to 6 percent by volume of Halon 1301 in the surrounding atmosphere. Still, the discussion in the previous section about problems with extinguishment of deep-seated fires by carbon dioxide or nitrogen is equally valid when a halon agent is used. Unless a sufficient quantity of the halon in liquid form can reach the seat of the fire and cool all the solid sufficiently, reignition can occur after the agent has dissipated. If the halon reaches the combustible as a gas via compartment-flooding, then no such cooling can occur, and the effect of the halon is to extinguish the gaseous flame without affecting the pyrolysis or smoldering. Table 2.5.4 also shows that the addition of Halon 1301 or 1211 needed in the air will only reduce the oxygen percentage from 21 percent to about 19 percent for most combustibles, whereas the required amount of carbon dioxide would have reduced the oxygen level to 14 percent or 15 percent. Furthermore, the physiological effects of carbon dioxide on humans at the concentrations needed for inerting are greater than those of Halon 1301. In recent years, it has been found that halons and other chemicals work their way into the earth’s upper atmosphere, where they appear to act as catalysts for the conversion of ozone, O3, to normal oxygen, O2. The ozone in the upper atmosphere plays a valuable role in filtering out the far-ultraviolet radiation of the sun, which would otherwise damage plant and animal life on the earth’s surface. Destruction of the ozone layer also affects the world’s weather. Accordingly, there has been international activity directed toward eliminating the production of halons and/or the release of halons into the atmosphere. The stratospheric ozone layer depletion issue is a problem confronting the global community unlike any other. Late in 1987, the United States and 24 other countries (including the European Economic Community) signed the Montreal Protocol to protect stratospheric ozone. Originally, the protocol restricted the consumption of ozone-depleting CFCs to 50 percent of the 1986 use levels by 1998, and halon production was to be frozen in 1993 at 1986 production levels. But the November 1992, the Copenhagen revision to the Montreal Protocol accelerated this restriction, such that all production of the chemicals ceased worldwide as of January 1, 1994. The Montreal Protocol was based on unprecedented trade restrictions and was the first time nations of the world joined forces to address an environmental threat in advance of fully established effects. The trade restrictions concern nations that did not participate in the agreement (the nonsignatories).
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Halons used in fire protection make up only a small fraction of the total current halogenated hydrocarbon use, which includes refrigerants, blowing agents for foamed plastics, solvents, and propellants for aerosol products in cans, such as hair sprays or deodorants. For these nonfire uses, substitute fluids are available, and a changeover is occurring in various countries. The regulation of Halon 1301 under the Montreal Protocol has generated tremendous research and development efforts across the world in a search for replacements and alternatives. Over the past several years, several total flooding, clean agent alternatives to Halon 1301 have been commercialized, and development continues on others. In addition to clean total flooding gaseous alternatives, new technologies, such as water mist and fine solid particulate, are being introduced. It would, of course, be highly desirable if chemists discovered a substitute for Halon 1301 or Halon 1211 that provided both fire protection and breathability qualities and did not attack the ozone layer. In considering this possibility, a review follows of what is known about why the CF3Br and CF2C1Br molecules are so effective. Figure 2.5.6 shows a methane–air flammability limit diagram as modified by various volumetric proportions of bromotrifluoromethane or carbon dioxide. The enormous difference is obvious. It has been established that carbon dioxide acts by absorbing heat and reducing the flame temperature from about 1900°C for a stoichiometric fuel–air mixture to about 1200°C to 1300°C. Below these temperatures, most flames can no longer burn. If nitrogen were added to a stoichiometric fuel–air mixture instead of carbon dioxide, a somewhat larger volume of inert agent would be needed because the heat capacity of the nitrogen molecule is less than that of the carbon dioxide molecule. Similarly, if argon were added—argon has an even lower heat capacity per molecule—an even larger volume of argon would be needed for inerting. In each case, the flame would go out when the temperature dropped below 1200°C to 1300°C. However, if a small volume of bromotrifluoromethane were added to a flame, so that the temperature dropped to only about 1500°C, the flame would be extinguished. Clearly, the mechanism is different. The important chemical reactions in flames involve the free atoms H and O and the free radical OH, which undergo chain reactions with the fuel and oxygen. In particular, the branching chain reaction H = O2 ó OH = O is very important. It is believed that the CF3Br molecule decomposes in the flame to form HBr, and HBr then acts to remove H atoms and OH radicals by the following two combustion reactions: HBr = H ó H2 = Br and HBr = OH ó H2O = Br HF and HCl cannot react as rapidly with H or OH as can HBr, so bromine appears to be essential to the inerting molecule. It has been found that hydrogen iodide, HI, is about as effective as HBr, but iodine is more expensive and heavier than bromine as well as quite toxic, and so iodine offers no advantage over bromine for flame extinguishment. In addition to the destruction
2–92 SECTION 2 ■ Basics of Fire and Fire Science
20 % Air = 100 – % Methane – % Added inert
18
Methane (volume percent)
16 14 Carbon
Halon 1211
12
dioxide
Halon 1301
Nonflammable
10 Flammable 8 6 4 2 0
0
2
4
6
8
10
12
14
16
18
20
22
Added inert (volume percent)
FIGURE 2.5.6
Flammability Limits for Methane–Air Mixtures with Added Inerting Agents (Source: Kuchta13)
of chain carriers, it has been speculated that a secondary contribution of halons to flame extinguishment comes from the extreme sootiness of halogen-containing flames. The more sooty or luminous the flame, the greater the radiative heat loss and the lower the temperature. The role of the fluorine in halogenated agents is twofold. First, fluorine atoms replace hydrogen atoms in methane or ethane, thereby reducing the flammability of the inerting agent itself. Second, the toxicity of the agent is reduced. For example, CH3Br is much more toxic than CF3Br, and, again, CH2C1Br is much more toxic than CF2C1Br. This current degree of understanding about why CF3Br is such a good inerting agent for flames does not provide clear guidance as to how other equally effective gaseous agents might be found. The vast majority of known molecules are liquids or solids, not gases, at room temperature and 1 atm. The known gaseous molecules have all been considered for inerting effectiveness, but no practical substitute as effective as CF3Br has yet emerged.
EXTINGUISHMENT WITH DRY CHEMICAL AGENTS Dry chemicals provide an alternative to carbon dioxide or the halons for extinguishing a fire without the use of water. These powders, which are 10 to 75 microns in size, are projected by an inert gas. Of the five types of dry chemicals in use, only one, monoammonium phosphate, is effective against deep-seated fires because of a glassy phosphoric acid coating that forms over the combustible surface. All forms of dry chemical act to suppress the flame of a fire. One reason that dry chemical agents other than monoammonium phosphate are popular is corrosion. Any chemical powder can produce some degree of corrosion or other damage, but monoammonium phosphate is acidic and cor-
rodes more readily than other dry chemicals, which are neutral or mildly alkaline. Furthermore, corrosion by the other dry chemicals is stopped by a moderately dry atmosphere, while phosphoric acid has such a strong affinity for water that an exceedingly dry atmosphere would be needed to stop corrosion. Application of any dry chemical agent on electrical fires is safe, from the viewpoint of electric shock, for fire fighters. However, these agents, especially monoammonium phosphate, can damage delicate electrical equipment. For the special case of kitchen fires involving hot cooking oil, monoammonium phosphate is not recommended because it does not create a foam layer (saponification) on the surface of the oil. An alkaline dry chemical, such as sodium bicarbonate, is preferred. Table 2.5.5 lists the chemical names, formulas, and popular or commercial names of various dry chemical agents. In each case, the particles of powder are coated with an agent, such as zinc stearate or a silicone, to prevent caking and to promote free flowing. The effectiveness of any of these agents depends on the
TABLE 2.5.5
Dry Chemical Agents
Chemical Name
Formula
Sodium bicarbonate Sodium chloride Potassium bicarbonate Potassium chloride Potassium sulfide Monoammonium phosphate Urea + potassium bicarbonate
NaHCO3 NaCl NHCO3 KCl K2SO4 (NH4)H2PO4 NH2CONH2 + KHCO3
Popular Name(s) Baking soda Common salt “Purple K” “Super K” “Karate Massiv” “ABC” or Multipurpose “Monnex”
CHAPTER 5
particle size: the smaller the particles, the less agent is needed, as long as particles are larger than a critical size.15 The reason for this is believed to be that the agent must vaporize rapidly in the flame to be effective.16 However, if an extremely fine agent were used, it would be difficult to disperse and apply to the fire. It is difficult to compare precisely the effectiveness of one dry chemical with another because a comparison to reveal chemical differences would require that each agent have identical particle size, which is difficult to achieve. Furthermore, gaseous agents can be compared by studying the flammability limits of uniform mixtures at rest. If particles were present, however, they would settle out unless the mixtures were agitated, thus modifying the combustion behavior. It seems clear that the effective powders act on a flame by some chemical mechanism, presumably forming volatile species that react with hydrogen atoms or hydroxyl radicals. However, the precise reactions have not been established firmly. Although the primary action is probably removal of active species, the powders also discourage combustion by absorbing heat; by blocking radiative energy transfer; and, in the case of monoammonium phosphate, by forming a surface coating. The potassium-bicarbonate-based agent, often referred to as “Purple K,” is about twice as effective on a pound-per-pound basis as ordinary sodium-bicarbonate-based dry chemical.
DEEP-SEATED FIRES As was previously mentioned, combustion may occur in a smoldering, rather than a flaming, mode. Extinguishment of such fires is usually quite difficult. Application of water or foam to the surface of a smoldering fire is not always effective, because the water cannot penetrate the hot interior where the combustion is occurring. Surrounding the smoldering material with an inert gas or a halon gas will only be effective if such an atmosphere can be maintained for the extensive time required for the interior to cool. If the smoldering object can be sealed for a long time to prevent access of oxygen, the combustion will eventually cease. However, the pyrolysis and combustion product gases being generated in the interior of the porous material will generate pressure, which will tend to break through any sealant applied. One practical approach is to remove the smoldering object from the building and either let it burn outside or submerge it in water for a long time. If the smoldering occurs in a large outdoor pile, extinguishment will generally require digging into the pile and extinguishing the hot material with water as it is exposed. Much research has been done on the theory of the smoldering process, but this has not yet led to new practical techniques for extinguishment.
SPECIAL CASES OF EXTINGUISHMENT Three-Dimensional Gas Fires Extinguishment of a fire involving a continuously flowing combustible gas is often very difficult. The best tactic is to shut off the flow of gas. If extinguishment is accomplished while the gas is still flowing inside a building, then the danger of filling the
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building with an explosive gas mixture is introduced. In some cases, it might be preferable to let the flame continue to burn if the flow of combustible gas cannot be stopped. If it is not possible to shut off the gas supply, fire fighting by any of several techniques is possible. One approach is to attack the base of the flame with a dry chemical nozzle, or carbon dioxide, or steam, or a halon. Whichever agent is used, it should be projected in the same general direction as the burning jet or plume. When this tactic is used, it is advisable to cool any hot metal in the vicinity and to remove or de-energize any other ignition sources before attacking the fire itself. Otherwise, reignition is likely to occur after temporary extinguishment, and the supply of agent could be depleted by that time.
Metal Fires Water is usually the wrong agent for fires involving metals because a number of metals can react exothermically with water to form hydrogen, which, of course, burns rapidly. Furthermore, violent steam explosions can result if water enters molten metal.17 As an exception, extinguishment has been accomplished when large quantities of water were applied to small quantities of burning magnesium, in the absence of pools of molten magnesium. Table 2.5.6 lists extinguishing agents used for various metal fires. In general, metal fires are difficult to extinguish because of the very high temperatures involved and the correspondingly long cooling times required. Note that certain metals react exothermically with nitrogen; therefore, the only acceptable inert gases for these metals are helium and argon. Halons should not be used on metal fires.
Chemical Fires In addition to metals, certain inorganic chemicals are not compatible with water. For example, alkali and alkaline earth carbides, of which the best known is calcium carbide, react with water to form acetylene, which is highly flammable. Lithium hydride, sodium hydride, or lithium aluminum hydride react with water to produce hydrogen. Peroxides of sodium, potassium, barium, and strontium react exothermically with water. Cyanide salts react with acidified water to form a highly toxic gas, hydrogen cyanide. Even if these chemicals are not combustible themselves, they could be packed in combustible cartons and thus become involved in a fire or they could be stored in racks above combustible items. Certain organic peroxides used as polymerization catalysts in plastics manufacturing are so unstable that they are stored under refrigeration to avoid exothermic heating. If water at normal room temperature were to be applied, it would provide heat to the peroxide and promote its exothermic decomposition. A problem in applying water to fires involving toxic chemicals, such as pesticides, is associated with the runoff of contaminated water, which could cause groundwater pollution. In cases where no other agent but water is available or practical, the only alternatives might be to use the minimum quantity of water possible or to allow a building to burn, thus producing downwind air pollution if the fire does not completely destroy the toxic chemicals.
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TABLE 2.5.6
Extinguishing Agents for Metal Fires Main Ingredients
Agent Powders “Pyrene” G-1 or “MetalGuard”
Used On
Graphitized coke + organic phosphate NaCl + Ca3 (PO4)2 Mixed chlorides + fluorides Graphite + additives (NH4)2H(PO4) + NaCl KCl + NaCl + BaCl2 SiO2 NaCl Na2CO3 LiCl ZrSiO4
Mg, Al, U, Na, K
Liquids “TMB”
Trimethoxyboroxine
Mg, Zr, Ti
Gases Boron trifluoride Boron trichloride Helium Argon Nitrogen
BF3 BCl3 He Ar N2
Mg Mg Any metal Any metal Na, K
“Met-L-X” Foundry flux “Lith-X” “Pyromet” “T.E.C.” Dry sand Sodium chloride Soda ash Lithium chloride Zirconium silicate
Na Mg Li, Mg, Zr, Na Na, Ca, Zr, Ti, Mg, Al Mg, Na, K Various Na, K Na, K Li Li
Source: Prokopovitsh17
SUMMARY The fundamentals of combustion science, which relate to fire extinguishment, are briefly reviewed and references are provided to more detailed treatments. Limits of flammability are discussed. Chemical chain reactions and the possibility of inhibiting these reactions are reviewed. Details of how water extinguishes a fire or a burning solid are presented. The role of aqueous foams in fighting flammable liquid fires is discussed in terms of extinguishment mechanism. Discussion is provided of extinguishment by mists, by inert gases, by halogenated agents, and by dry chemical agents. Deepseated fires, three-dimensional fires, metal fires, and chemical fires are mentioned. Reference is made to the textbook Principles of Fire Protection Chemistry and Physics for more information. A list of references and items for additional reading is provided.
BIBLIOGRAPHY References Cited 1. Friedman, R., Principles of Fire Protection Chemistry and Physics, 3rd ed., National Fire Protection Association, Quincy, MA, 1998. 2. Drysdale, D., An Introduction to Fire Dynamics, J. Wiley, New York, 1999.
3. Glassman, I., Combustion, 2nd ed., Academic Press, New York, 1987. 4. Strehlow, R. A., Combustion Fundamentals, McGraw-Hill, New York, 1984. 5. Zabetakis, M. G., “Flammability Characteristics of Combustible Gases and Vapors,” Bulletin 627, U.S. Bureau of Mines, Washington, DC, 1965. 6. Heskestad, G., “The Role of Water in Suppression of Fire,” Fire and Flammability, Vol. 11, 1980, pp. 254–259. 7. Rasbash, D. J., “The Extinction of Fire with Plain Water: A Review,” Fire Safety Science—Proceedings of the 1st International Symposium, Hemisphere, New York, 1986, pp. 1145–1163. 8. Magee, R. S., and Reitz, R. D., “Extinguishment of RadiationAugmented Plastic Fires by Water Sprays,” 15th Symposium (International) on Combustion, Combustion Institute, Pittsburgh, PA, 1975, pp. 337–347. 9. Alpert, R. L., “Numerical Modeling of the Interaction between Automatic Sprinklers Sprays and Fire Plumes,” Fire Safety Journal, Vol. 9, Nos. 1–2, 1985, pp. 157–163. 10. Mawhinney, J. R., Dlugogorski, B. Z., and Kim, A. K., “A Closer Look at the Fire Extinguishing Properties of Water Mist,” Fire Safety Science—Proceedings of the 4th International Symposium, National Institute for Standards and Technology, Gaithersburg, MD, 1994, pp. 47–60. 11. International Conference on Water Mist Fire Suppression Systems, Swedish National Testing and Research Institute, Boras, Sweden, Nov. 1993. 12. Friedlander, S., Smoke, Dust, and Haze, Wiley, New York, 1977. 13. Kuchta, J. M., “Investigation of Fire and Explosion Accidents in the Chemical, Mining, and Fuel-Related Industries—A Manual,” Bulletin 680, U.S. Bureau of Mines, Washington, DC, 1985. 14. Grant, C., “Halon Design Calculations,” SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995, Section 4, pp. 123–144. 15. Ewing, C. T., Faith, F. R., Hughes, J. T., and Carhart, H. W., “Flame Extinguishment Properties of Dry Chemicals,” Fire Technology, Vol. 25, 1989, pp. 134–149. 16. Iya, K. S., Wollowitz, S., and Kaskan, W. E., “The Mechanism of Flame Inhibition by Sodium Salts,” 15th Symposium (International) on Combustion, Combustion Institute, Pittsburgh, PA, 1975, pp. 329–336. 17. Prokopovitsh, A. S., “Combustible Metal Agents and Application Techniques,” Fire Protection Handbook, 16th ed., National Fire Protection Association, Quincy, MA, 1986, pp. 49–54.
Additional Readings Almgren, L. E., “Designing for Fire and Explosion Safety,” Proceedings of the National Meeting of the American Institute of Chemical Engineers, American Institute of Chemical Engineers, NY, 1988, p. 10. Andersson, P., Arvidson, M., and Holmstedt, G., “Small Scale Experiments with Theoretical Aspects of Flame Extinguishment with Water Mist,” Lund University, Sweden, LUTVDG/TVBB-3080SE, May 1996. Andersson, P., and Holmstedt, G., “Limitations of Water Mist as a Total Flooding Agent,” Journal of Fire Protection Engineering, Vol. 9, No. 4, 1999, pp. 31–50. Application Guide for Explosion Suppression Systems, Fenwal Inc., Ashland, MA, Nov. 1979. Back, G. G., III, Beyler, C. L., and Hansen, R., “Capabilities and Limitations of Total Flooding, Water Mist Fire Suppression Systems in Machinery Space Applications,” Fire Technology, Vol. 36, No. 1, 2000, pp. 8–23. Back, G. G., III, Beyler, C. L., and Hansen, R., Quasi-Steady-State Model for Predicting Fire Suppression in Spaces Protected by Water Mist Systems,” Fire Safety Journal, Vol. 35, No. 4, 2000, pp. 327–362. Barsamian, C., Gameiro, V. M., and Hanna, M., “Local Application Water Mist Fire Protection Systems,” Proceedings of the Halon
CHAPTER 5
Options Technical Working Conference, May 2–4, 2000, Albuquerque, NM, University of New Mexico, HOTWC 2000, 2000, pp. 204–214. Beeson, H. D., Forsyth, E. T., and Hirsch, D. B., “Total Water Demand for Suppression of Fires in Hypobaric Oxygen-Enriched Atmospheres,” Proceedings of the 8th Volume, Flammability and Sensitivity of Materials in Oxygen-Enriched Atmospheres, American Society for Testing and Materials, Philadelphia, ASTM STP 1319, 1997, pp. 17–24. Bill, R. G., Jr., and Ural, E. A., “Water Mist Protection of Combustion Turbine Enclosures,” Proceedings of the 6th International Symposium on Fire Safety Science, International Association for Fire Safety Science (IAFSS), July 5–9, 1999, Poitiers, France, International Assoc. for Fire Safety Science, Boston, 2000, pp. 457–468. Blouquin, R., and Joulin, G., “On the Quenching of Premixed Flames by Water Sprays: Influences of Radiation and Polydispersity,” Proceedings of the 27th International Combustion Institute Symposium, August 2–7, 1998, Boulder, CO, Combustion Institute, Pittsburgh, PA, 1998, pp. 2829–2837. Bodurtha, F. T., Industrial Explosion Prevention and Protection, McGraw-Hill, New York, 1980. Bruderer, R. E., “Design Example: Explosion Protection Selected for a Spray Drying Installation,” Plant/Operation Progress, Vol. 8, No. 3, 1988, pp. 141–146. Bruyninckx, E., and Andries, M., “Fire Protection Concept for Chemical Plants, Refineries and Terminals,” Journal of Applied Fire Science, Vol. 5, No. 4, 1995/1996, pp. 285–297. Burgan, B., “Engineering Safety,” Fire Prevention, No. 331, Apr. 2000, pp. 28–30. Capraro, M. A., and Strickland, J. H., “Preventing Fires and Explosions in Pilot Plants,” Plant/Operation Progress, Vol. 8, No. 4, 1989, pp. 189–194. Delichatsios, M. A., “Critical Mass Pyrolysis Rates for Extinction in Fires over Solid Materials,” National Institute of Standards and Technology, Gaithersburg, MD, NIST GCR 98-746, Apr. 1998. DesJardin, P. E., Gritzo, L. A., and Tieszen, S. R., “Modeling the Effect of Water Spray Suppression on Large-Scale Pool Fires,” Proceedings of the Halon Options Technical Working Conference, May 2–4, 2000, Albuquerque, NM, University of New Mexico, HOTWC 2000, 2000, pp. 262–273. DeVries, H., “Foam Follows Function: The Tremonia and Wattenscheid Trials,” Fire Chief, Vol. 43, No. 8, 1999. Dow’s Fire and Explosion Index: Hazard Classification Guide, 6th ed., American Institute for Chemical Engineers, NY, 1987. Dunn, M. H., “Full-Scale Testing of Fire Suppression Agents on Unshielded Fires,” University of Canterbury, Christchurch, New Zealand, Fire Engineering Research Report 98/2, June 1998. Eckhoff, R. K., “Role of Powder Technology in Understanding Dust Explosions,” Proceedings of the 3rd International Hazards, Prevention, and Mitigation of Industrial Explosions Symposium, October 23–27, 2000, Tsukuba, Japan, pp. 6–21. Gann, R. G., “Fire Suppression Research in the United States: An Overview,” Proceedings of the 15th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, March 1–7, 2000, San Antonio, TX, National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6588, Nov. 2000, pp. 230–235. Gottuck, D. T., Williams, F. W., and Farley, J. P., “Development and Mitigation of Backdrafts: A Full-Scale Experimental Study, Proceedings of the 5th International Symposium on Fire Safety Science, March 3–7, 1997, Melbourne, Australia, International Association for Fire Safety Science, Boston, 1997, pp. 935–946. Gravestock, N., “Full-Scale Testing of Fire Suppression Agents on Shielded Fires,” University of Canterbury, Christchurch, New Zealand, Fire Engineering Research Report 98/3, June 1998. Grosshandler, W. L., “Trend of Research and Technology of Sensing and Extinguishing Building Fires in the U.S.A.,” Proceedings of the NRIFD 50th Anniversary Symposium, Fire Detection, Fire
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Extinguishment and Fire Safety Engineering, June 1, 1998, Tokyo, Japan, 1998, pp. 31–38. Hadjisophocleous, G., Cao, S., and Kim, A., “Modelling the Interaction between Fine Water Sprays and a Fire Plume,” Proceedings of the 4th International Conference on Advanced Computational Methods in Heat Transfer, Udine, Italy, 1996. Hansen, R., and Back. G. C., “Fire Water Mist: Design Considerations,” Proceedings of the Fire Suppression and Detection Research Application Symposium, Research and Practice: Bridging the Gap, February 24–26, 1999, Orlando, FL, National Fire Protection Research Foundation, Quincy, MA, 1999, pp. 233–239. Harvie, D. J. E., Novozhilov, V., Kent, J. H., and Fletcher, D. F., “Experimental Study of Wood Crib Extinguishment by a Sprinkler Spray,” Journal of Applied Fire Science, Vol. 8, No. 4, 1998/1999, pp. 283–299. International Progress in Fire Safety, Fire Retardant Chemicals Association, Technomic, Lancaster, PA, 1987. Isman, K. E., “Hydraulic Calculation Theory. Part 1,” Sprinkler Quarterly, No. 113, Winter 2000, pp. 35–37. Khan, M. M., “Flame Extinction of Water Miscible Flammable Liquid/Water Solutions,” Proceedings of the Fire Suppression and Detection Research Application Symposium, Research and Practice: Bridging the Gap, February 12–14, 1997, Orlando, FL, National Fire Protection Research Foundation, Quincy, MA, 1997, pp. 142–149. Kim, A. K., Liu, Z., and Su, J. Z., “Water Mist Fire Suppression Using Cycling Discharges,” Proceedings of the 8th International INTERFLAM Conference, June 29–July 1, 1999, Edinburgh, UK, Interscience Communications, London, UK, 1999, pp. 1349–1354. Liu, Z., Kim, A. K., and Su, J. Z., “Examination of the Extinguishment Performance of a Water Mist System Using Continuous and Cycling Discharges,” Fire Technology, Vol. 35, No. 4, 1999, pp. 336–361. Liu, Z., and Kim, A. K., “Review of Water Mist Fire Suppression Systems: Fundamental Studies,” Journal of Fire Protection Engineering, Vol. 10, No. 3, 2000, pp. 32–50. Madrzykowski, D., “Water Additives for Increased Efficiency of Fire Protection and Suppression,” Proceedings of the NRIFD 50th Anniversary Symposium, Fire Detection, Fire Extinguishment and Fire Safety Engineering, June 1, 1998, Tokyo, Japan, 1998, pp. 1–6. Makhviladze, G. M., Roberts, J. P., Yakush, S. E., and Agavonov, V. V., “Study of Fire Suppression in Enclosure by an Extinguishing Powder,” Journal of Applied Fire Science, Vol. 6, No. 4, 1996/1997, pp. 339–356. Maranghides, A., Sheinson, R. S., Williams, B. A., and Black, B. H., “Water Spray Cooling System: A Gaseous Suppression System Enhancer,” Proceedings of the 8th International INTERFLAM Conference, June 29–July 1, 1999, Edinburgh, UK, Interscience Communications, London, UK, 1999, pp. 627–637. Mawhinney, J. R., and Back, G. G., III, “Bridging the Gap between Theory and Practice: Protecting Flammable Liquid Hazards Using Water Mist Fire Suppression Systems,” Proceedings of the Fire Suppression and Detection Research Application Symposium, Research and Practice: Bridging the Gap, February 25–27, 1998, Orlando, FL, National Fire Protection Research Foundation, Quincy, MA, 1998, pp. 11–173. Mawhinney, J. R., and Darwin, R., “Protecting against Vapor Explosions with Water Mist,” Proceedings of the Halon Options Technical Working Conference, May 2–4, 2000, Albuquerque, NM, University of New Mexico, HOTWC 2000, 2000, pp. 215–226. Mawhinney, R. N., Grandison, A. J., Galea, E. R., Patel, M. K., and Ewer, J., “Development of a CFD Based Simulator for Water Mist Fire Suppression Systems: The Development of the Fire Submodel,” Journal of Applied Fire Science, Vol. 9, No. 4, 1999/2000, pp. 311–345. McGrattan, K. B., Hamins, A., and Forney, G. P., “Modeling of Sprinkler, Vent and Draft Curtain Interaction,” Proceedings of the 6th International Symposium on Fire Safety Science, International
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Association for Fire Safety Science (IAFSS), July 5–9, 1999, Poitiers, France, International Assoc. for Fire Safety Science, Boston, 2000, pp. 505–516. Moore, T. A., and Yamada, N., “Nitrogen Gas as a Halon Replacement,” Proceedings of the Halon Options Technical Working Conference, May 12–14, 1998, Albuquerque, NM, University of New Mexico, HOTWC-98, 1998, pp. 330–338. Morita, M., Kikkawa, A., and Watanabe, Y., “Oil Fire Extinguishment by Using Water Mist,” Proceedings of the NRIFD 50th Anniversary Symposium, Fire Detection, Fire Extinguishment and Fire Safety Engineering, June 1, 1998, Tokyo, Japan, 1998, pp. 57–65. Najario, F. N., “Preventing or Surviving Explosions,” Chemical Engineering, Aug. 15, 1988. Novozhilov, V., Fletcher, D. F., Moghtaderi, B., and Kent, J. H., “Numerical Simulation of Enclosed Gas Fire Extinguishment by a Water Spray,” Journal of Applied Fire Science, Vol. 5, No. 2, 1995/1996, pp. 135–146. Novozhilov, V., Hartvie, D. J. E., Kent, J. H., Apts, V. B., and Pearson, D., “Computational Fluid Dynamics Study of Wood Fire Extinguishment by Water Sprinkler,” Fire Safety Journal, Vol. 29, No. 4, 1997, pp. 259–282. Novozhilov, V., Moghtaderi, B., Kent, J. H., and Fletcher, D. F., “Solid Fire Extinguishment by a Water Spray,” Fire Safety Journal, Vol. 32, No. 2, 1999, pp. 119–135. Novozhilov, V., “CFD Modeling of Thermoplastic Fire Behavior under Suppression Conditions,” Journal of Applied Fire Science, Vol. 9, No. 3, 1999/2000, pp. 217–235. Novozhilov, V., and Kent, J. H., “Flashover Control with Water-Based Fire Suppression Systems,” Proceedings of the 4th Asia-Oceania Symposium on Fire Science and Technology, May 24–26, 2000, Tokyo, Japan, 2000, pp. 339–350. Pepi, J. S., “Water Mist System Performance Trade-Offs with Flammable Liquid Hazards,” Proceedings of the Fire Suppression and Detection Research Application Symposium, Research and Practice: Bridging the Gap, February 24–26, 1999, Orlando, FL, National Fire Protection Research Foundation, Quincy, MA, 1999, pp. 219–232. Pitts, W. M., Yang, J. C., Huber, M. L., and Blevins, L. G., “Characterization and Identification of Super-Effective Thermal Fire Extinguishing Agents. First Annual Report,” National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6414, 1999. Pucci, W. E., “Hot Software for the Fire Protection Community,” NFPA Journal, Vol. 91, No. 1, 1997, pp. 51–56. Saito, N., Ogawa, Y., Saso, Y., Liao, C., and Sakei, R., “Flame Extinguishing Concentrations and Peak Concentrations of N2, Ar, CO2 and Their Mixtures for Hydrocarbon Fuels,” Fire Safety Journal, Vol. 27, No. 3, 1996, pp. 185–200. Sardquist, S., and Holmstedt, G., “Correlation between Firefighting Operation and Fire Area: Analysis of Statistics,” Fire Technology, Vol. 36, No. 2, 2000, pp. 109–130. Stull, D. R., Fundamentals of Fire and Explosion, Monograph Series, No. 10, Vol. 73, American Institute of Chemical Engineers, New York, 1977.
Su, J., Kim, A., Liu, Z., and Crampton, G., “Fire Suppression Testing of Inert Gas Agents in a 120 m3 Enclosure,” Proceedings of the Fire Suppression and Detection Research Application Symposium, Research and Practice: Bridging the Gap, February 24–26, 1999, Orlando, FL, National Fire Protection Research Foundation, Quincy, MA, 1999, pp. 196–206. Swift, I., “Design of Deflagration Protection Systems,” Journal of Loss Prevention in the Process Industries, Vol. 1, 1988, pp. 5–15. Swift, I., “Developments in Explosion Protection,” Plant/Operation Progress, Vol. 7, No. 3, 1988, pp. 159–167. Tuhtar, D., Fire and Explosion Protection: A Systems Approach, Halsted Press, New York, 1989. Wighus, R., “Empirical Model for Extinguishment of Enclosed Fires with a Water Mist,” Proceedings of the Halon Options Technical Working Conference, May 12–14, 1998, Albuquerque, University of New Mexico, HOTWC-98, 1998, pp. 482–489. Wrenn, C., “Inerting for Fire Safety,” Plant/Operations Progress, Vol. 5, No. 4, 1986, pp. 225–227. Yamashita, K., “On the Applicability of Aerial Fire Fighting Approach in Preventing the Spread of Fires in Urban Areas: A Large Scale Field Experiment and Its Implications,” Proceedings of the NRIFD 50th Anniversary Symposium, Fire Detection, Fire Extinguishment and Fire Safety Engineering, June 1, 1998, Tokyo, Japan, 1998, pp. 15–22. Yang, J. C., Boyer, C. I., and Grosshandler, W. L., “Minimum Mass Flux Requirements to Suppress Burning Surfaces with Water Sprays,” National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 5795, 1996. Yang, J. C., Bryant, R. A., Huber, M. L., and Pitts, W. M., “Experimental Investigation of Extinguishment of Laminar Diffusion Flames by Thermal Agents,” Proceedings of the Halon Options Technical Working Conference, May 2–4, 2000, Albuquerque, University of New Mexico, HOTWC 2000, 2000, pp. 433–446. Yang, X., Han, F., and Yang, X., “Deploying Fire Trucks and Water Sources,” Fire Technology, Vol. 35, No. 2, 1999, pp. 179–185. Zalosh, R., “Explosion Protection,” SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995, pp. 312–329. Zalosh, R., “Suppression of Asphalt Based Material Fires Using Water Sprays and Water Films,” Proceedings of the Honors Lecture Series, Engineering Seminars: Fire Protection Design for High Challenge or Special Hazard Applications, May 20–22, 1996, Boston, Society of Fire Protection Engineers, Boston, MA, 1996, pp. 37–42. Zegers, E. J. P., Williams, B. A., Sheinson, R. S., and Fleming, J. W., “Water Mist Suppression of Methane/Air and Propane/Air Counterflow Flames,” Proceedings of the Halon Options Technical Working Conference, May 2–4, 2000, Albuquerque, University of New Mexico, HOTWC 2000, 2000, pp. 251–261. Zhang, B. L., and Williams, F. A., “Effects of the Lewis Number of Water Vapor on the Combustion and Extinction of Methanol Drops,” Combustion and Flame, Vol. 112, No. 1/2, 1998, pp. 113–120.
CHAPTER 6
SECTION 2
Fundamentals of Fire Detection Richard L. P. Custer James A. Milke
A
ny fire, no matter how large it may become, begins as a small fire. Small fires, if detected, are easily controlled manually or by fixed fire suppression systems. The earlier a fire is detected, the more likely building occupants are to escape with little or no impact from exposure to fire products. Furthermore, the earlier a fire is detected, the sooner suppression methods can be brought to bear on the fire, thereby reducing damage to property and the environment. Section 9 of this Handbook addresses the technology of fire detection.
SIMPLIFIED FIRE DEVELOPMENT In the earliest stages of fire development, fuel materials are heated by an ignition source even before smoldering (i.e., glowing combustion) occurs. Large numbers of extremely small invisible particles are produced and distributed into the surrounding atmosphere. At this point in fire development (prepyrolysis), very little energy is produced to distribute these particles, and they are generally transmitted with the existing air movement. Smoldering fires produce large particles and gases such as carbon monoxide (CO) and carbon dioxide (CO2). Following the development of flame, a column of hot gases rises as a plume.1 As the plume rises, uncontaminated air is drawn or “entrained” into the plume, increasing its volume. As a result of dilution of the hot gases in the plume by the entrained cool air, the buoyancy of the plume is reduced. For any space, there is a minimum fire size necessary to provide sufficient energy to the plume to enable it to reach the ceiling. Until the smoke reaches the ceiling, ceiling-mounted smoke and thermal detectors are not able to respond.2 Entrainment of air is discussed in the Section 12, Chapter 6, “Smoke Movement in Buildings.” In some tall atria and indoor sports arenas, the fire size needed to drive the smoke to the ceiling is substantial. This situation is made worse if a hot layer is present before the start of the fire, as in cases in which a solar heat load is present at the ceiling. In such cases, the smoke may stop rising at a point below
Richard L. P. Custer, M.Sc., is associate principal and technical director at ARUP Fire in Westborough, Massachusetts. Mr. Custer is a fellow of the Society of Fire Protection Engineers. Dr. James A. Milke is associate professor of fire protection engineering at the University of Maryland in College Park, Maryland.
the ceiling. This situation is referred to as “intermediate stratification.”3 In these situations, the response of ceiling-mounted detectors is delayed until the fire grows large enough to provide sufficient buoyancy to the plume to force its way through the hot air layer. This may cause a substantial time delay if ceilingmounted detectors are the only initiating devices present. If there is a ceiling above the fire, the vertically rising plume will be deflected, and the gases will travel horizontally across the ceiling. The upward movement of the hot gases is accomplished by a mechanism commonly referred to as convection. Convection is a combination of heat transfer between the air molecules and the motion of the air resulting from buoyancy.4 The horizontal movement of air just below the ceiling is caused by momentum and forms what is called a ceiling jet.5 The plume and ceiling jet transport the smoke particles or aerosols from their point of generation to a detector. Generally, ceilingmounted detectors respond to heat or smoke transported vertically by convection and horizontally by the ceiling jet. As the fire progresses, a layer of hot gases forms at the ceiling, descending over time and spreading to adjacent spaces through open doorways. For a more detailed discussion of compartment fire dynamics, see Section 2, Chapter 4, “Dynamics of Compartment Fire Growth.”
FIRE SIGNATURES Characteristics of Fire Signatures Custer and Bright first proposed the concept of fire signatures in 1974.6 From the very beginning, a fire produces a variety of changes in the surrounding environment. Any product or result of a fire that changes the ambient condition is referred to as a fire signature and has the potential for use in detection. Production of smoke particles, for example, results in a decrease in light transmission. Not all fire signatures, however, are practical for fire detection purposes. To be useful, a fire signature should generate a measurable change in ambient conditions. In addition, the magnitude of the change must be greater than normal background variations. For example, a sudden increase in temperature could be due to either a fire or normal start-up of a heating appliance. The magnitude of change in the ambient condition is the signal from a fire signature; the background level, with its normal variations, is referred to as the noise. All other factors, such as hazard level at detection and hardware costs, being equal, the
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preferred fire signature will be one that can generate the highest signal-to-noise ratio at the earliest time in the fire’s development. The best signatures for most applications are those associated exclusively with fire and found in a wide variety of fuels. Fuel-specific signatures, such as the release of hydrogen chloride from polyvinyl chloride (PVC) wire insulation, may be particularly valuable in telecommunications facilities, but they may be of little use for general-purpose applications. Individual signatures are discussed below.
Aerosol Signatures The process of combustion produces very large numbers of solid and liquid particles, ranging from 5 ? 10>4 to 10 microns (5m). These particles, suspended in air, are called aerosols. The characteristics of smoke aerosols produced in a fire depend on the composition of the fuel, the combustion state (smoldering or flaming), and the amount of air available. Aerosols resulting from fire actually represent two different fire signatures: invisible and visible. Particles less than 0.3 5m do not scatter light efficiently and are therefore classified as invisible. The larger particles do scatter light and are classified as visible aerosols. Smoke aerosols may change with respect to their particle size distribution. Smoke particles or droplets can collide and adhere to each other. Smoke may coagulate, become deposited on surfaces, and settle out by sedimentation over time. Invisible aerosols are among the earliest appearing fire signatures and are produced at very low energy levels from the fire. Invisible aerosols can be detected through air sampling systems such as VESDA (very early smoke detection apparatus) or incipient fire detection systems.6 Larger smoke aerosols can be detected by light-scattering, photoelectric, or ionization detectors. For a discussion of the operating principles of these detectors, see Section 9, Chapter 2, “Automatic Fire Detectors,” and the National Fire Alarm Code® Handbook.7 Additional information on smoke aerosols can be found in the SFPE Handbook of Fire Protection Engineering.8
Energy Release Signatures There are two types of energy release signatures: radiative and convective thermal release. Radiative Energy Release Signatures. Throughout its course, fire continuously releases energy into the surrounding environment, producing several detectable signatures. The earliest detectable energy signature is radiated energy. Radiation is emitted across a wide range of wavelengths: • Ultraviolet (0.10–0.35 5m) • Visible (0.35–0.75 5m) • Infrared (0.75–22.00 5m) The specific wavelength of radiation from a heated material is highly dependent on the characteristics of the material itself. Ultraviolet fire signatures appear in flames as emission from hydroxyl (OH) ions, CO2, and CO in the 0.27–0.29 5m range.9 Devices often respond to both ultraviolet and infrared
signatures. Video fire detection systems are being developed that block visible light and only pass infrared to the video camera. The detection principle is based on an increase in the area emitting infrared versus time. Curves have been developed such that fires involving different fuels can be recognized.10 Infrared emissions from hydrocarbon fuels (with the exception of acetylene and other highly unsaturated hydrocarbons) are particularly strong in the 4.4-5m region due to CO2 and in the 2.7-5m region due to water vapor.11 Infrared detectors employ sensors designed to respond to infrared over narrow ranges associated with these frequencies. Radiant energy sensing devices are generally limited to line-of-sight applications with a field of vision generally represented by a cone.* The size of fire that can be detected is a function of the distance between the detector and the radiant energy source. Because radiation intensity decreases as the square of the distance from the source, detectors generally need to be placed relatively close to the area being protected. Convective Thermal Release Signatures. Convected thermal energy from a fire rises toward the ceiling, resulting in increased air temperature at ceiling-mounted heat detectors. The response time for heat detectors depends on the heat release rate of the fire, the distance between the fire and the ceiling, and the thermal response characteristics of the detector. The thermal response characteristics relate to the time that it takes for the detector to reach the temperature of the surrounding hot gases. This time is called thermal lag. Detectors having low mass and high surface area respond to a given fire more quickly than detectors with high mass and low surface area. Detectors designed to respond to convected thermal energy may activate at a fixed temperature or a specified rate of rise in temperature.
Gas Signatures A fire may produce several different gases. The type and production rate of gases produced in fires depends on the fuel composition, fire size, ventilation conditions, and burning mode. Carbon-containing fuels produce CO and CO 2 . Wellventilated, flaming fires involving such fuels generally yield 100 to 1000 times more CO2 than CO. Conversely, for underventilated or smoldering fires of carbonaceous fuels, the amount of CO2 and CO produced may be similar. In addition to CO2 and CO, hydrocarbon fuels also produce a variety of gases containing carbon, hydrogen, and oxygen, such as formaldehyde (HCHO) and acrolein (CH2CHCHO). Other gases produced by carbonaceous fuels depend on the presence of other elements in the fuel. For example, fuels that contain chlorine, such as polyvinyl chloride (PVC), produce hydrogen chloride (HCl) and chlorine gas (Cl2). Fuels that contain nitrogen, such as wool and polyurethane, produce hydrogen cyanide (HCN), ammonia (NH3), and nitrogen oxide com-
*Infrared sensors, however, may respond to surfaces that are heated by fires not in the direct line of sight.
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pounds (NOx). Sulfur-containing fuels produce sulfur dioxide (SO2) and hydrogen sulfide (H2S). The mass of a particular gas that is produced in a fire per unit mass of fuel consumed is referred to as the yield of the gas. Yields of CO, CO2, and other selected gases in fires are provided by Tewarson.12 Most of the data available in this and other references applies to flaming, well-ventilated fires. In addition to the ventilation and burning mode, the rate of production of any particular gas in a fire is affected by the size of the fire, expressed in terms of the heat release rate of the fire. In general, the rate of production of a particular gas from a wellventilated, flaming, 500-kW fire is five times that from a wellventilated, flaming, 100-kW fire. Currently, gas sensors are used primarily for industrial safety applications, that is, to detect the release of a particular chemical. Some manufacturers have considered incorporating CO and CO2 sensors in fire detectors.
Other Fire Signatures Although the human body is well designed to feel heat and smell smoke, some evidence suggests that sounds associated with a burning fire can be the first cues received. Sounds caused by fire arise from a variety of causes such as nonuniform expansion of heated materials, boiling of trapped moisture, and bursting of gas bubbles. Experiments have been conducted to demonstrate the feasibility of using acoustic signatures of fire as the bases for fire detection.13,14 The human nose recognizes an odor of smoke by detecting a group of airborne gases and particles and associating that array of gases with a particular source. Some individuals are able to distinguish between different fuels producing the smoke, for example, burning leaves versus burning electrical insulation. Currently, artificial noses are used in some industrial process control applications, such as to determine when coffee beans have been sufficiently roasted or to detect spoiled food. However, current efforts to develop an artificial nose for fire detection are limited to research activities.15
Multiple Signature Detection An emerging technology addresses the problem of unwanted alarms and improving response time to unwanted fires. Chemical sensors, for example, are being investigated to detect fire precursors.16 Considerable research has been conducted on using combined gas/fire signatures for fire detection. Combining CO and CO2 sensors and evaluating the CO/CO2 ratio has been shown to be an effective means for detection of fire.17 Additionally, CO/CO2 concentrations have been used to discriminate between smoldering and nuisance fires.18 Experiments have also been conducted using light obscuration; temperature; CO, CO2, and O2 concentrations; and signals from metal oxide sensors. By employing neural network and statistical methods, a system was developed to distinguish between fire and nonfire sources. Flaming and nonflaming fires could also be differentiated.19,20 Additional work has been carried out for residential fire detectors combining smoke and CO sensors.21 Work has also been reported of combined optical, thermal, and CO sensors.22
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SUMMARY A variety of technologies exist for detecting the products of combustion generated at different stages of fire growth and spread. These technologies are based on detecting one or more unique fire signatures and have been growing in sophistication as the fire community becomes more adept at measuring fire and its effects.
BIBLIOGRAPHY References Cited 1. Heskestad, G., “Fire Plumes,” SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995. 2. Milke, J. A., “Smoke Management in Covered Malls and Atria,” SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995. 3. Schifiliti, R. P., Meacham, B. J., and Custer, R. L. P., “Design of Detection Systems,” SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995. 4. Atreya, A., “Convective Heat Transfer,” SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995. 5. Evans, D. D., “Ceiling Jet Flows,” SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995. 6. Custer, R., and Bright, R. W., Fire Detection: The State-of-theArt, NBS Technical Note 839, National Bureau of Standards, Gaithersburg, MD, 1974. 7. Bunker, M. W., and Moore, W. D., “Initiating Devices,” National Fire Alarm Code Handbook, National Fire Protection Association, Quincy, MA, 1999. 8. Mulholland, G., “Smoke Production and Properties,” SFPE Handbook of Fire Protection Engineering, 3rd ed., National Fire Protection Association, Quincy, MA, 2002. 9. Mauordineanu, R., and Boiteaux, H., Flame Spectroscopy, John Wiley and Sons, Inc., New York, 1965. 10. Chen, X., Wu, J., Yuan, X., and Zhou, H., “Principles for a Video Fire Detection System,” Fire Safety Journal, Vol. 33, No. 1, 1999, pp. 57–69. 11. Comerford, J. J., “The Spectral Distribution of Radiant Energy of a Gas-Fired Radiant Panel and Some Diffusion Flames,” Combustion and Flame, Vol. 18, 1972, pp. 125–132. 12. Tewarson, A., “Generation of Heat and Chemical Compounds in Fires” SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995. 13. Grosshandler, W. L., and Jackson, M., “Acoustic Emission of Structural Materials Exposed to Open Flames,” Fire Safety Journal, Vol. 22, 1994, pp. 209–228. 14. Grosshandler, W. L., and Braun, E., “Early Detection of Room Fires Through Acoustic Emission,” Fire Safety Science— Proceedings of the 4th International Symposium, Ottawa, Canada, 1994, pp. 773–784. 15. Okayama, Y., “Approach to Detection of Fires in Their Very Early Stage By Odor Sensors and Neural Net,” Fire Safety Science—Proceedings of the 3rd International Symposium, Edinburgh, UK, 1991. 16. Riches, J., Chapman, A., and Beardon, J., “Detection of Fire Precursors Using Chemical Sensors,” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, Edinburgh, UK, 1999, pp. 155–166. 17. Gottuk, D. T., Petrus, M. J., Roby, R. J., and Beyler, C. L., “Advanced Fire Detection Using Multi-Signature Alarm Algorithms,” Fire Suppression and Detection Research Application
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18.
19.
20. 21.
22.
Symposium, Research and Practice: Bridging the Gap, National Fire Protection Research Foundation, Orlando, FL, Feb. 1999, pp. 140–149. Shaner, D. L., and Milke, J. A., “Discrimination Between Smoldering and Nuisance Sources Using Gas Signatures,” Proceedings of the 2nd International Conference on Fire Research and Engineering, Gaithersburg, MD, 1997, pp. 500–511. Milke, J. A., and McAvoy, T. J., “Analysis of Fire and Non-Fire Signatures for Discriminating Fire Detection,” Fire Safety Science, Proceedings of the Fifth International Symposium, Melbourne, Australia, 1997, pp. 819–828. Hagen, B., and Milke, J. A., “Use of Gaseous Fire Signatures as a Means to Detect Fires,” Fire Safety Journal, Vol. 34, No. 1, 2000, pp. 55–67. Cleary, T. J., and Ono, T., “Enhanced Residential Fire Detection by Combining Smoke and CO Sensors,” International Conference on Automatic Fire Detection, AUBE ’01, 12th NIST SP 965, National Institute of Standards and Technology, Gaithersburg, MD, 2001, pp. 346–357. Oppelt, U., “Measuring Results of a Combined Optical, Thermal, and CO Detector in Real Sites and Classifying the Signals,” International Conference on Automatic Fire Detection, AUBE ’01, 12th NIST SP 965, National Institute of Standards and Technology, Gaithersburg, MD, 2001, pp. 390–402.
Additional Readings Barrett, R., “CO Fire Detection: A Useful Technique?,” Fire Safety Engineering, Vol. 7, No. 4, 2000, pp. 20–23. Chen, Y., Serio, M. A., and Sathyamoorthy, S., “Development of a Fire Detection System Using FT-IR Spectroscopy and Artificial Neural Networks,” Proceedings of the 6th Fire Safety Science Symposium, International Association for Fire Safety Science (IAFSS), July 5–9, 1999, Poitiers, France, International Association for Fire Safety Science, Boston, 2000, pp. 791–802. Cleary, T. G., and Donnelly, M. K., “Aircraft Cargo Compartment Fire and Nuisance Source Test in the FE/DE,” Proceedings of the 12th International Conference on Automatic Fire Detection AUBE ’01, March 25–28, 2001, Gaithersburg, MD, National Institute of Standards and Technology, Gaithersburg, MD, NIST SP 965, Feb. 2001, pp. 689–700. Cleary, T. G., and Grosshandler, W. L., “Survey of Fire Detection Technologies and System Evaluation/Certification Methodologies and their Suitability for Aircraft Cargo Compartment,” National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6356, July 1999. Cleary, T. G., Grosshandler, W. L., and Chernovsky, A., “Smoke Detector Response to Nuisance Aerosols,” Proceedings of the 11th International Conference on Automatic Fire Detection AUBE ’99, March 16–18, 1999, Duisburg, Germany, 1999, pp. 42–51. Cleary, T. G., Grosshandler, W. L., Nyden, M. R., and Rinkinen, W. J., “Signatures of Smoldering/Pyrolyzing Fires for Multi-Element Detector Evaluation,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 497–506. Clery, T. G., and Ono, T., “Enhanced Residential Fire Detection by Combining Smoke and CO Sensors,” Proceedings of the 12th International Conference on Automatic Fire Detection, AUBE ’01, March 25–28, 2001, Gaithersburg, MD, National Institute of Standards and Technology, Gaithersburg, MD, NIST SP 965, February 2001, pp. 346–357. Gandhi, P., Patty, P., and Sheppard, D. T., “Investigation into the Early Stages of a Fire for Development of Multi-Point Smoke Detectors,” Proceedings of the Fire Suppression and Detection Research Application Symposium, Research and Practice: Bridging the Gap, February 12–14, 1997, Orlando, FL, National Fire Protection Research Foundation, Quincy, MA, 1997, pp. 42–58. Gottuck, D., Rose-Pehrsson, S., Shaffer, R., and Williams, F., “Early Warning Fire Detection via Probabilistic Neural Networks and
Multi-Sensor Arrays,” Proceedings of the Fire Suppression and Detection Research Application Symposium, Research and Practice: Bridging the Gap, February 23–25, 2000, Orlando, FL, National Fire Protection Research Foundation, Quincy, MA, 2000, pp. 365–369. Grosshandler, W. L., “Nuisance Alarms in Aircraft Cargo Areas and Critical Telecommunications Systems,” Proceedings of the 3rd NIST Fire Detector Workshop, December 4–5, 1997, Gaithersburg, MD, National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6146, 1998. Harms, M., and Goschnick, J., “Early Detection and Distinction of Fire Gases with a Gas Sensor Microarray,” Proceedings of the 12th International Conference on Automatic Fire Detection, AUBE ’01, March 25–28, 2001, Gaithersburg, MD, National Institute of Standards and Technology, Gaithersburg, MD, NIST SP 965, February 2001, pp. 416–431. Hart, S. J., Hammond, M. H., Rose-Pehrsson, S. L., Shaffer, R. E., Gottuk, D. T., Wright, M. T., Wong, J. T., Street, T. T., Tatem, P. A., and Williams, F. W., “Real-Time Probabilistic Neural Network Performance and Optimization for Fire Detection and Nuisance Alarm Rejection: Test Series 1 Results. Memorandum. February 1, 2000–May 3, 2000,” Naval Research Laboratory, Washington, DC, NRS/MR/6110-00-9480, Aug. 31, 2000. Kozeki, D., “Smoldering Fire Detection by Image-Processing,” Proceedings of the 12th International Conference on Automatic Fire Detection, AUBE ’01, March 25–28, 2001, Gaithersburg, MD, National Institute of Standards and Technology, Gaithersburg, MD, Feb. 2001, pp. 71–78. Lloyd, A. C., Zhu, Y. J., Tseng, L. K., Gore, J. P., and Sivanthanu, Y. R., “Fire Detection Using Reflected Near Infrared Radiation and Source Temperature Discrimination,” National Institute of Standards and Technology, Gaithersburg, MD NIST GCR 98747, Apr. 1998. Mengel, R. K., “Earlier Detection of Smoldering Fires in Residential Applications,” Proceedings of the Fire Suppression and Detection Research Application Symposium, Research and Practice: Bridging the Gap, February 23–25, 2000, Orlando, FL, National Fire Protection Research Foundation, Quincy, MA, 2000, pp. 242–247. Milke, J. A., “Discriminating Fire Detection with Multiple Sensors and Neural Networks,” Proceedings of the Fire Suppression and Detection Research Application Symposium, Research and Practice: Bridging the Gap, February 12–14, 1997, Orlando, FL, National Fire Protection Research Foundation, Quincy, MA, 1997, pp. 12–26. Milke, J. A., and McAvoy, T. J., “Analysis of Fire and Non-Fire Signatures for Discriminating Fire Detection,” Fire Safety Science— Proceedings of the 5th International Symposium, International Association for, Fire Safety Science, March 3–7, 1997, Melbourne, Australia, International Association for Fire Safety Science, Boston, MA, 1997, pp. 819–828. Milke, J. A., and McAvoy, T. J., “Multivariate Methods for Fire Detection,” Proceedings of the 13th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, March 13–20, 1996, Gaithersburg, MD, National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6030, 1996, pp. 411–418. Milke, J. A., and McAvoy, T. J., “Neural Networks for Smart Fire Detection. Final Report,” National Institute of Standards and Technology, NIST GCR 96-699, Dec. 1996. Nohmi, T., and Fenn, J. B., “Early Detection of Fire by Analysis of Smoldering Odor,” Proceedings of the 4th Asia-Oceania Symposium on Fire Science and Technology, May 24–26, 2000, Tokyo, Japan, 2000, pp. 399–410. Pfister, G., “Multisensor/Multicriteria Fire Detection: A New Trend Rapidly Becomes State of the Art,” Fire Technology, Vol. 33, No. 2, 1997, pp. 115–139. Qualey, J. R., III, Desmarais, L., and Pratt, J. W., “Fire Test Comparisons of Ion and Photoelectric Smoke Detector Response Times,” Proceedings of the Fire Suppression and Detection Research Ap-
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plication Symposium, Research and Practice: Bridging the Gap, February 7–9, 2001, Orlando, FL, National Fire Protection Research Foundation, Quincy, MA, 2001, pp. 385–424. Riches, J., Chapman, A., and Beardon, J., “Detection of Fire Precursors Using Chemical Sensors,” Proceedings of the 8th International INTERFLAM conference, INTERFLAM ’99, June 29–July 1, 1999, Edinburgh, UK, Interscience Communications Ltd., London, UK, 1999, pp. 155–166. Rose-Pehrsson, S. L., Hart, S. J., Shaffer, R. E., Gottuk, D. T., Wong, J. T., Tatem, P. A., and Williams, F. W., “Analysis of MultiCritical Fire Detection Data and Early Warning Fire Detection Prototype Selection. Final Report,” Naval Research Laboratory, Washington, DC, NRL/MR/6110-00-8484, Sept. 18, 2000. Spearpoint, M. J., and Smithies, J. N., “Practical Comparison of Domestic Smoke Alarm Sensitivity Standards,” Proceedings of the
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11th International Conference on Automatic Fire Detection, AUBE ’99, March 16–18, 1999, Duisburg, Germany, 1999, pp. 576–587. Wittkopp, T., Hecker, C., and Opitz, D., “Cargo Fire Monitoring System (CFMS) for the Visualization of Fire Events in Aircraft Cargo Holds,” Proceedings of the 12th International Conference on Automatic Fire Detection, AUBE ’01, March 25–28, 2001, Gaithersburg, MD, National Institute of Standards and Technology, Gaithersburg, MD, Feb. 2001, pp. 665–676. Wright, M. T., Gottuk, D. T., Wong, J. T., Pham, H., Rose-Pehrsson, S. L., Hart, S. J., Hammond, M., Williams, W. F., Tatem, P. A., and Street, T. T., “Prototype Early Warning Fire Detection System: Test Series 2 Results, April 25–May 5, 2000,” Naval Research Laboratory, NRL/MR/6180-00-8506, Oct. 23, 2000.
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SECTION 2
Basics of Passive Fire Protection Marc L. Janssens
A
n acceptable level of fire protection is accomplished in the design stage of a building through compliance with local regulations, which are typically based on national model building codes. Fire protection of buildings addresses all aspects of fire safety and consists of a combination of active and passive measures. Active fire protection devices require manual, mechanical, or electrical power for their operation. For example, a sprinkler system requires sprinklers to open and a water supply at a sufficient flow rate and pressure after activation to be delivered through the system. A smoke control system relies on a mechanical system to operate when a fire is detected. A detection and alarm system requires electric power to operate. Passive fire protection does not require any external power. This chapter deals with passive fire protection. There are essentially three types of passive fire protection measures: 1. Rate of Fire Growth. The rate of fire growth in a room can be controlled to some extent by using interior finishes with specific ignition, flame spread, and heat release characteristics. A slow-growing fire leaves more time for safe egress of building occupants, and generally results in reduced property damage at the time of manual or automatic suppression. 2. Compartmentation. Should the fire grow to full involvement of the room of origin, the next step is to contain the fire within a limited area, at least for a certain time. Thus, fire spread to other parts of the building or adjacent buildings is delayed or prevented. This containment process is referred to as compartmentation. It is accomplished by providing fire-resistive floor, wall, and ceiling assemblies and by protecting openings and penetrations through room boundaries. Compartmentation also involves protecting structural elements and assemblies to avoid or delay partial or total collapse in the event of fire. 3. Emergency Egress. The third type of passive fire protection measure pertains to emergency egress. Escape corridors, doors, and stairways have to be wide enough to accommodate the flow of people in case of emergency evacuation. Occupants must have access to a sufficient
Dr. Marc L. Janssens is director of the Department of Fire Technology at Southwest Research Institute in San Antonio, Texas. Dr. Janssens has more than 20 years experience in fire standards development, fire testing and research, and computer fire modeling.
number of emergency exits within a maximum allowable distance so that they can reach a safe area before conditions become untenable. This chapter provides a discussion of model building code provisions that pertain to passive fire protection. These provisions have traditionally been prescriptive, meaning that they consist of specific requirements for building materials, products, and elements that are based on performance in a test. Model building codes also include prescriptive provisions to establish adequate means of egress. Fire safety objectives are not explicitly stated in traditional building codes, and it is assumed that an acceptable level of fire safety is obtained if the prescriptive code requirements are fulfilled. The main objective of building codes is life safety of building occupants and fire fighters. The protection of neighboring property is secondary. The model building codes do not directly provide for property conservation. However, any fire protection features that contribute to meeting the primary objective are also likely to reduce property and indirect fire losses. Sometimes it is not possible to meet the passive fire protection requirements in the model building codes. For example, changing the use of a building may lead to a new set of fire protection requirements that cannot be accomplished through retrofitting. Another common example is when the architect wants to use an innovative system that cannot be tested according to the accepted procedures. All model building codes have a clause that allows the authority having jurisdiction (AHJ) to accept a noncompliant design. A technical rationale or engineering analysis, or both, usually has to be presented to demonstrate that the level of fire safety of the proposed design is at least as good as that of a comparable code-compliant building. This process is referred to as code equivalency. New types of building codes, known as performance-based codes, have emerged in recent years. These codes are concerned with the performance of a building as a whole and require that specific fire safety goals and objectives be met. No specific methods are mandated to demonstrate compliance. The performance-based, or code-conforming design process involves an engineering analysis, often supported by standard or ad-hoc fire test data and fire statistics. Increased design flexibility and opportunities for cost savings are the main advantages of performance-based codes over the traditional prescriptive approach. (See Section 3, Chapter 13, “Performance-Based Codes and Standards for Fire Safety,” for more information.)
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This chapter focuses primarily on the test and design procedures that serve as the basis for passive fire protection requirements in the model building codes. Alternate methods that demonstrate prescriptive code equivalency or performancebased code compliance are also discussed. First, however, some important terminology is defined and an overview is provided of the different stages of fire growth and factors that affect fire spread.
TERMINOLOGY Active Fire Protection. Active fire protection devices require manual, mechanical, or electrical power for their operation. For example, a sprinkler system requires sprinklers to open and a water supply at a sufficient flow rate and pressure after activation to be delivered through the system. A smoke control system relies on roof vents that open or a mechanical system to operate when a fire is detected. A detection and alarm system requires electric power to operate. Code Equivalency. Code equivalency is the process of demonstrating compliance with the intent of prescriptive code provisions through technical reasoning or engineering analyses, or both. Compartmentation. Large buildings are typically segmented into smaller compartments with fire-resistive boundaries and protected openings through the boundaries. The objective of compartmentation is to confine a fire to a limited area for a specified time and thus slow down fire spread through a building, to leave more time for safe evacuation of the building, and to reduce property and indirect losses. Fire Endurance. Fire endurance is a measure of the elapsed time during which a building element continues to exhibit fire resistance. It is usually determined on the basis of a furnace test, in which the element is exposed to a standard fire for a specified duration. Fire endurance is expressed in the form of an hourly rating corresponding to the time to failure in the furnace test. Failure criteria are based on thermal penetration, integrity, or structural collapse. Fire Resistance. The fire resistance of a building element characterizes its ability to confine a fire or to continue to perform a given structural function, or both. Flaming Combustion. Heat transferred to the surface of a burning fuel results in the formation of combustible volatiles through vaporization if the fuel is a liquid, or thermal decomposition if the fuel is a solid. Thermal decomposition of a solid fuel is also referred to as pyrolysis. The fuel volatiles mix with oxygen in the air and burn in a hot luminous region referred to as the flame. Flashover. Flashover is a relatively rapid (typically less than one minute) transition from a localized growing fire to a fully de-
veloped stage in which all combustibles in the room are involved. When flashover occurs, it is no longer possible to survive in the fire compartment and the fire becomes a major threat beyond the room of origin. Commonly used criteria for the onset of flashover are a hot smoke layer temperature of 1100°F (600°C) and an incident heat flux at floor level of 1.8 Btu/sÝft2 (20 kW/m2). Heat Flux. Heat is a form of energy that is transferred from a body at a high temperature to a body at a lower temperature. There are three modes of heat transfer: conduction, convection, and radiation. Conduction involves either the transfer of energy from molecules that have a higher kinetic energy to adjacent molecules with a lower kinetic energy, or the flow of free electrons in metals. When a fluid flows over a solid surface, heat is transferred between the fluid and the solid, provided they are at different temperatures. This mode of heat transfer is referred to as convection. Thermal radiation is the transmission of thermal energy by electromagnetic waves. Radiation is the only possible mode when a vacuum exists between the hot and the cold body. Radiation is the dominant mode of heat transfer in fires because its rate is proportional to the fourth power of absolute temperature whereas the rate of conduction and convection heat transfer are (approximately) linear functions of temperature. The rate of heat transfer expressed per unit area perpendicular to the direction of the heat flow is referred to as the heat flux. Heat flux is a measure of the potential for damage. For example, most common combustibles ignite when exposed to a heat flux of 0.9–1.8 Btu/sÝft2 (10–20 kW/m2). The latter at floor level is a commonly used criterion for the onset of flashover. Heat Release Rate. The heat release rate of a fire is the rate at which heat is released in the combustion reactions. Heat release rate is typically expressed in kilowatts (kW) or megawatts (MW). A kilowatt is 1000 watts (W), and a megawatt is 1,000,000 watts. To put things in perspective, a typical light bulb consumes 40 W. The heat output from a fire of a small wastepaper basket peaks at approximately 40 kW, which is equivalent to the energy consumed by one thousand 40-W light bulbs. The heat release rate of planar surface products is often expressed on a per-unit-area basis, typically in kW/m2. Limited Combustible. Materials with a potential heat of 3500 Btu/lb (8.2 MJ/kg), determined according to NFPA 259, Standard Test Method for Potential Heat of Building Materials, are defined as limited combustible. Model Building Code. Local building codes and regulations are based on national model codes that are developed by a consensus process. The model code groups in the United States are BOCA (Building Officials and Code Administrators International), ICBO (International Conference of Building Officials), ICC (International Code Council), NFPA (National Fire Protection Association), and SBCCI (Southern Building Code Congress International). Some jurisdictions have adopted a model code verbatim, either by reference or by transcription whereas others have made significant amendments. The extent of changes that can be made at the local level varies from state to state.
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Noncombustible. Materials that produce a negligible amount of heat when exposed to a thermal environment representative of a postflashover fire are referred to as noncombustible. Some inert materials such as steel and concrete are recognized as being noncombustible without testing. Other materials need to be qualified on the basis of performance in a test. ASTM E136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750°C, is a small-scale furnace test that is used in the United States for this purpose. Opposed-Flow Flame Spread. Opposed-flow flame spread occurs when flames spread in the opposite direction of the surrounding airflow. An example is the flame spread in the downward direction over a vertical solid fuel surface, against the air entrained into the flame. Opposed-flow flame spread is typically very slow (T1 mm/s), and is therefore also referred to as creeping flame spread. Passive Fire Protection. Passive fire protection does not require any external power but relies instead on specific construction features and the use of materials, products, and building elements that meet well-defined fire performance requirements. Performance-Based Code. Performance-based codes are concerned with the performance of the building as a whole and require that specific fire safety goals and objectives be met. No specific methods are mandated to demonstrate compliance. The code-conforming design process involves an engineering analysis, often supported by standard or ad-hoc fire test data and fire statistics. A detailed discussion of the steps involved in such a design process is provided in the SFPE Engineering Guide to Performance-Based Fire Protection. Increased design flexibility and opportunities for cost savings are the main advantages of performance-based codes over the traditional prescriptive approach. Prescriptive Code. Model building codes and other fire safety regulations are largely prescriptive and consist of specific requirements for building materials, products, and elements that are based on performance in a test. They also include prescriptive provisions to establish adequate means of egress. The fire safety objectives are not explicitly stated, and it is assumed that an acceptable level of fire safety is obtained if the prescriptive requirements are fulfilled. Pyrolysis. Flaming combustion of solid fuels takes place in the gas phase. Fuel vapors mix and react with air in a luminous zone referred to as the flame. Fuel vapors are generated by decomposition of the fuel molecules into smaller and lighter molecules that escape from the surface. This process is referred to as pyrolysis. Reaction-to-Fire. Ignition, surface flame spread, and heat and smoke release rate determine how a product reacts when exposed to thermal conditions that are representative of a preflashover fire. These characteristics collectively describe the reaction-to-fire of the product.
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Smoldering Combustion. Smoldering is a slow exothermic surface reaction between a solid fuel and oxygen in the air. Oxygen is needed to support smoldering combustion, but it is consumed at a much smaller rate than in flaming fires. Smoldering fires involve a low rate of mass loss per unit time, but a larger share of lost mass is released as products of incomplete combustion, in particular carbon monoxide (CO), than in flaming fire conditions. Ventilation-Limited Fire. Flashover leads to the fully developed stage of a compartment fire. The supply of air in the postflashover stage is usually below what is needed to burn all fuel volatiles inside the compartment. The fire is ventilation limited under these conditions and some fuel volatiles burn outside the compartment; in other words, flames emerge from doors and windows. Wind-Aided Flame Spread. Wind-aided flame spread occurs when flames spread in the same direction as the surrounding airflow. An example is the flame spread in the upward direction over a vertical solid fuel surface, concurrent with the surrounding natural airflow. The rate of wind-aided flame spread is typically one or two orders of magnitude higher than that of opposed-flow flame spread, and is therefore of much greater concern.
STAGES OF FIRE DEVELOPMENT Flaming Combustion Development in a Compartment A distinction has to be made between flaming combustion and smoldering combustion. The latter is a slow combustion process that involves oxygen and a solid fuel, and is discussed later in this section. Flaming combustion (or a flaming fire) is more common in fires. The main difference between smoldering combustion and flaming combustion is that flaming combustion takes place in the gas phase. Flaming combustion takes place when heat that is transferred to the fuel surface results in the formation of combustible volatiles through vaporization if the fuel is a liquid, or thermal decomposition if the fuel is a solid. Thermal decomposition is also referred to as pyrolysis. The fuel volatiles mix with oxygen in the air and burn in a hot luminous region referred to as the flame. Flaming combustion is much more rapid than smoldering combustion, and is of greater concern in terms of fire protection. Flaming compartment fires typically consists of three stages: preflashover stage, flashover, and postflashover stage. Preflashover Stage. Following ignition, a fire remains limited in size for some time, during which only one item or a small area is involved. A single person could easily extinguish the fire with a portable extinguisher, but the fire may not be detected at this time. The environment inside the compartment is not yet affected, and there is no major threat to occupants. The fire may be detected shortly thereafter, when flames are large enough to
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be visible or when smoke or heat is produced in sufficient quantities to activate a detector. As the fire grows, a hot smoke layer accumulates beneath the ceiling and temperatures gradually increase. If automatic sprinklers protect the compartment, the suppression system will activate when the smoke layer temperature at the ceiling is high enough to melt the fusible link in a sprinkler. The sprinkler system will control and possibly extinguish the fire. A fire in a compartment that is not protected by automatic sprinklers will be uncontrolled, which can lead to a sequence of events described next. Conditions may become untenable when the heat flux to the lower part of the compartment exceeds a critical level, or when people become exposed to the hot toxic smoke. At this point it is no longer possible to control the fire with a portable extinguisher. Flashover. When heat fluxes to the lower part of the compartment are high enough to ignite common combustible materials, a rapid transition occurs to a fully developed fire. This transition usually takes less than a minute and is referred to as flashover. When flashover occurs, it is no longer possible to survive in the fire compartment. All exposed combustible materials become involved in the fire. Commonly used criteria for the onset of flashover are a hot smoke layer temperature of 1100°F (600°C) and an incident heat flux at floor level of 1.8 Btu/sÝft2 (20 kW/m2). Postflashover Stage. Flashover leads to the fully developed phase of a fire in which all exposed combustibles in the compartment are involved. The temperatures and heat fluxes in the compartment and the types of combustible materials that are present control the generation rate of fuel volatiles. Typical temperatures in a fully developed fire are 1500–1800°F (800–1000°C), and corresponding incident heat fluxes range from 6.6–13.2 Btu/sÝft2 (75–150 kW/m2). The flow rate of air into the compartment is primarily determined by the size and shape of the ventilation openings. The supply of air in a fully developed fire is usually below what is needed to burn all fuel volatiles inside the compartment. The fire is therefore ventilation limited and some fuel volatiles burn outside the compartment; in other words, flames emerge from doors and windows. Once a fire reaches the postflashover stage, it becomes a threat to the entire building. Occupants remote from the fire compartment may be affected and evacuation of the entire building is necessary to avoid casualties. Flames can propagate to other compartments through interior or exterior pathways, and smoke may travel over long distances and pose a threat to occupants in remote parts of the building. Radiation through unprotected openings or from flames that emerge from windows can heat exterior surfaces or combustible contents of neighboring buildings and result in ignition and fire spread to those buildings. Without intervention, the fire eventually decays and burns out when all combustibles in the compartment are consumed.
Smoldering Combustion Smoldering combustion is a slow exothermic surface reaction between a solid fuel and oxygen in the air. Oxygen is needed to support smoldering combustion, but it is consumed at a much
smaller rate than in flaming fires. Smoldering fires involve a low rate of mass loss per unit time, but a larger share of lost mass is released as products of incomplete combustion, in particular carbon monoxide (CO), than in flaming fire conditions. A smoldering upholstered chair fire in a closed room can cause untenable conditions in approximately 1 to 2 hours, depending on the size of the room.1 (Note that in the United States, most upholstered furniture fires begin in rooms, like living rooms, that are almost never closed.) The heat produced by smoldering fires is usually insufficient to activate a sprinkler. Smoldering fires often make a transition to flaming combustion. It is difficult to predict if and when this transition will occur, but it usually happens after conditions near the fire’s point of origin have already become untenable due to the elevated concentration of carbon monoxide. A significant number of fire fatalities in the United States are attributed to fires that have a lengthy initial smoldering phase. The most common smoldering ignitions in homes involve upholstered furniture or a mattress ignited by a cigarette.
MATERIALS, PRODUCTS, AND ASSEMBLIES Materials form the basic ingredients of the components and contents of structures. Materials are combined into products in a form that is suitable for practical application. For example, gypsum, paper, glass fibers, and other fillers are combined in the form of sheets that are used as protective membranes in the construction of fire-rated wall and ceiling assemblies. One or more products are used in the construction of assemblies. For example, wood-frame wall assemblies consist of wood studs that are protected on one or both sides by a membrane such as gypsum board or plywood, and the cavities between the studs may be filled with thermal insulation. Reaction-to-fire requirements usually apply to products, whereas fire-resistance requirements pertain to assemblies. There are also some material requirements as described in the next few paragraphs. One approach to accomplish a high level of fire safety is the exclusive use of materials that produce a negligible amount of heat when exposed to a thermal environment representative of a postflashover fire. These materials are referred to as noncombustible. Fires initiated by a malfunction of heating, cooking, or electrical equipment would then not be able to spread. It is not practical to apply such an approach to an entire building, but it may be appropriate to require the exclusive use of noncombustible materials for some areas or components of a building. Model building codes explicitly recognize inert materials, such as steel and concrete, as noncombustible. Other materials must be tested and meet specific criteria. ASTM E136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750°C, is the test procedure that is used in the United States to determine whether a material is noncombustible.2 The apparatus used in the ASTM E136 test consists of a small tubular furnace, with an inside diameter of 3 in. (76 mm) and a height of 8½ to 10 in. (210 to 250 mm) (Figure 2.7.1). The air temperature in the furnace is at 1382°F (750°C). A controlled flow of ambient air is supplied at the bottom of the apparatus. A speci-
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men, 1½ in. × 1½ in. × 2 in. (38 mm × 38 mm × 51 mm), is inserted into the furnace from the top. ASTM E136 provides recommended pass/fail criteria based on the specimen center temperatures not rising more than 30°C (54°F). Additional requirements are that specimen mass loss does not exceed 50 percent, and flaming combustion is not observed after the first 30 seconds. If the mass loss exceeds 50 percent, no flaming is permitted at all and additional temperature criteria apply. NFPA 101®, Life Safety Code®, makes a distinction between noncombustible and limited combustible materials. NFPA 101 refers to NFPA 220, Standard on Types of Building Construction, for a description of the different types of construction. In turn, NFPA 220 refers to ASTM E136 for noncombustible materials, and specifies a maximum potential heat of 3500 Btu/lb (8.2 MJ/kg) for limited combustible materials as determined by NFPA 259, Standard Test Method for Potential Heat of Building Materials. According to NFPA 259, the potential heat of a material is determined as the difference between the gross heat of combustion of the material measured with an oxygen bomb calorimeter and the gross heat of combustion of its residue after heating in a muffle furnace at 1382°F (750°C) for 2 hr.
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Furnace and oxygen bomb methods to assess combustibility have serious limitations. The most significant limitations are that materials cannot be evaluated in their end-use configuration, that test conditions are not representative of real fire exposure conditions, and that the test results do not provide a realistic measure of the expected heat release rate. These limitations led to the idea of exploring the use of small-scale heat release calorimeters to assess material combustibility. Extensive work has been done in this area over the past 15 years, in particular the use of the Cone calorimeter3 for measuring combustibility of materials4 has been explored. Despite this research, model building code organizations have not yet been convinced to adopt the use of small-scale heat release calorimeters.
REACTION-TO-FIRE This section describes test and design procedures pertinent to model building code requirements that are intended to control fire growth in the preflashover stage. The design procedures determine how a product reacts to thermal exposure conditions that are representative of a preflashover fire; that is, they characterize the reaction-to-fire of a product in terms of ignition, surface flame spread, and heat and smoke release rate.
Surface Finishes and Contents Model building code requirements pertaining to the reaction-tofire of products are largely restricted to interior finishes, that is, wall and ceiling linings and floor coverings. There are several reasons why contents such as upholstered furniture, mattresses, and so on, are not regulated by building codes. First, contents are not a fixed part of the building. Building occupants are free to bring in whatever they like, as long as it does not change the hazard classification of the building. Active suppression systems, such as sprinkler systems, are required in many types of occupancies to control fires that involve the building contents. Second, interior finishes cover large surfaces. A wall lining that is easily ignitible and releases heat at a high rate will support rapid flame spread when exposed to a small or moderate size ignition source. This is illustrated by the following example. Consider a room that is 10 ft (3 m) wide, 14 ft (4.2 m) long, and 8 ft (2.4 m) high, with a doorway that is 30 in. (0.8 m) wide and 80 in. (2 m) high in one of the vertical walls. The floor, walls, and ceiling are lined with thick redwood paneling. The heat release rate necessary to achieve flashover in this room can be calculated according to the following equation (discussed in more detail in Section 3, Chapter 9): ƒ ‰ Qg f o C 610 hkAsAo Ho 1/2 (1) where Qg f o C heat release rate at flashover (kW)
FIGURE 2.7.1 ASTM E136 Furnace (Source: Southwest Research Institute)
hk C enclosure conductance (kW/m2ÝK) As C total enclosure area excluding vent area (m2) Ao C area of the vent opening (m2) Ho C height of the vent opening (m)
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Because the room is lined with thick redwood paneling, the enclosure conductance follows from the following equation: ˆ ˆ ‡ ‡ k:cp ‡ † 0.187 † V C 0.025 kW/m2ÝK (2) hk C t 300 The numerical values used here are based on the thermal inertia, k:cp, for redwood5 and the assumption that the time to flashover is 300 s. The total enclosure area is equal to the sum of the areas of the floor, ceiling, and four walls, or the areas of six rectangles, minus the area of the door and window openings. The floor and ceiling areas are given by the length times the width; two walls have areas equal to height times length; and the other two walls have areas equal to height times width. The area of the doorway, Ao, is also equal to height, Ho, times width. Therefore, As is equal to 2 ? [3 ? 4.2 = 3 ? 2.4 = 4.2 ? 2.4] > 2 ? 0.8 C 58.16 m2. Thus, the heat release rate at flashover is estimated from Equation 1 as ‰ ‚ Qg fo C 610 0.025 ? 58.16 ? 1.6 ? 2 1/2 C 1106 kW (3) The surface area of redwood that is needed to generate a heat release rate of 1106 kW is between 95 ft2 and 238 ft2 (8.6 m2 and 22.1 m2). The low and high estimates are based respectively on the peak and average heat release rates measured in the Cone calorimeter at an incident heat flux of 25 kW/m2.5 This heat flux is representative of that from a thin wall flame.1 Thus, the fraction of the total enclosure area that contributes at flashover is somewhere between 15 percent and 38 percent. Because the fire performance of untreated wood products is better than that of many other types of products, it is clear that the use of surface finishes with poor fire performance could have disastrous consequences. To put things in perspective, it is interesting to note that, based on the heat release data in Figure 3.9.2, a single chair may be sufficient to create flashover conditions in the example room.
Flame Spread In the previous section it was demonstrated that involvement of a relatively small fraction of the interior finishes can lead to flashover. It is therefore essential to control the flame spread characteristics of interior finishes so that flashover can be delayed and sufficient time can be made available for evacuation. Flames can spread over a solid surface in two modes. The first mode is referred to as wind-aided flame spread. In this mode, flames spread in the same direction as the surrounding airflow. The second mode is referred to as opposed-flow flame spread, which occurs when flames spread in the opposite direction to the surrounding airflow. These two modes are illustrated for flame spread over a vertical surface in Figure 2.7.2. Flame spread in the upward direction is concurrent with the surrounding airflow and is therefore wind aided. Flame spread in the downward direction is against the entrained airflow and is of the opposed-flow type. The height of the region that is heated by the flame above the pyrolyzing region, -f,u, is much greater than the height of the heated region below the pyrolyzing region, -f,d . The former is comparable to the height of the pyrolyzing region, -p, and is typically of the order of 3 ft (1 m). The latter is only a few millimeters (1/16 in.) at most. The result is that up-
Wind-aided flame spread
Wall flame δf,u
δp
Entrained airflow δf,d Opposed-flow flame spread
FIGURE 2.7.2 Fuel Surface
Modes of Flame Spread over a Vertical
ward or wind-aided flame spread is much faster that downward or opposed-flow flame spread. It is obvious from the previous paragraph that reaction-tofire requirements should focus on the wind-aided flame spread mode. That is the primary intent of the Steiner tunnel test, which is the most common reaction-to-fire test method prescribed by U.S. model building codes. The Steiner tunnel test is described in ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials,6 and NFPA 255, Standard Method of Test of Surface Burning Characteristics of Building Material. The apparatus, as shown in Figure 2.7.3, consists of a long tunnel-like enclosure measuring 25 ft ? 1½ ft ? 1 ft (8.7 m ? 0.45 m ? 0.31 m). The test specimen is 24 ft (7.6 m) long and 1.67 ft (0.51 m) wide, and is mounted in the ceiling position. It is exposed at one end, designated as the burner end, to a 5000 Btu/min (79 kW) gas burner. There is a forced draft through the tunnel from the burner end with an average initial air velocity of 240 ft/min (1.2 m/s). The measurements consist of flame spread over the surface and smoke obscuration in the exhaust duct of the tunnel. Test duration is 10 min. A flame-spread index (FSI) is calculated on the basis of the area under the curve of flame tip location versus time. The FSI is 0 for an inert board, and is normalized to approximately 100 for red oak flooring. Albert Steiner developed the first prototype of the tunnel test in 1922 at Underwriters Laboratories Inc. The tunnel test was used initially to evaluate the effectiveness of fire retardant (FR) paint, and later to investigate FR-treated lumber. During World War II there was a growing interest in reducing combustibility of commonly used products. Consequently, the tun-
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FIGURE 2.7.3 ASTM E 84/NFPA 255 Tunnel Test Apparatus (Source: Southwest Research Institute)
nel was reinvestigated, and a surface burning characteristics classification scale similar to the present FSI was introduced. The current physical design was completed in 1948. A tentative ASTM specification E84–50T was published in 1950 and a full standard became available in 1961. The current calculation and classification method were implemented in 1980. The tunnel test was introduced into the model building codes following several catastrophic fires in the 1940s, such as the Cocoanut Grove nightclub fire in Boston in 1942; the Winecoff, LaSalle, and Canfield hotel fires in 1946; and the St. Anthony Hospital fire in 1949. The objective was to eliminate the use of materials with very high flame spread potential in public buildings. The classification of linings in the model building codes is based on the FSI. There are three classifications: Class A, or I, for products with FSI D 25, Class B, or II, for products with 25 A FSI D 75, and Class C, or III, for products with 75 A FSI D 200. Class A, or I, products are generally permitted in enclosed vertical exits. Class B, or II, products can be used in exit access corridors, and Class C, or III, products are allowed in other rooms and areas. The tunnel test was originally developed for wood products. Such products do not melt or drip, do not have an excessively low thermal inertia, stay in place during a test, and are usually sufficiently thick so that the substrate and adhesive do not affect the test results. This explains why there is a good correlation between the FSI classification of FR-treated and untreated wood products and the time to flashover in a full-scale room test.7 However, the fact that the specimen is mounted on the ceiling often causes practical problems in testing certain products, in particular products that melt or soften when heated. To support specimens of such products, ASTM and NFPA standards describe various optional mounting methods (rods, bars, netting, etc.) that may have a pronounced effect on the results. Significant inconsistencies have been found between the FSI classification and real fire performance of certain products such as plastic foams and textile wall coverings. The high thermal insulation of plastic foams traps the heat inside a room, which results in higher temperatures and accelerated fire growth. This effect is not captured in the flow-through environment of the tunnel test.8 Carpetlike textile coverings on walls and ceil-
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ings have been recognized as a major contributing factor in many fires. Research conducted by the Fire Research Laboratory of the University of California at Berkeley and the American Textile Manufacturers Institute indicated that consideration of only tunnel test performance might not reliably predict the fire behavior of textile wall coverings.9 To address these inconsistencies, the model building codes now require that plastic foams and textile wall coverings for use in unsprinklered spaces pass a room/corner test such as UBC 26-3, Room Fire Test for Interior of Foam Plastic Systems,10 or NFPA 265, Standard Methods of Fire Tests for Evaluating Room Fire Growth Contribution of Textile Wall Coverings. The room/corner test apparatus consists of a room measuring 12 ft (3.6 m) deep by 8 ft (2.4 m) wide by 8 ft (2.4 m) high, with a single ventilation opening (doorway) measuring approximately 30 in. (0.8 m) wide by 80 in. (2 m) high in the front wall. The back wall, both side walls, and the ceiling are lined for tests according to UBC 26-3. For tests according to NFPA 265, the interior surfaces of all walls (except the front wall) are covered with the test product. The product is exposed to a wood crib (UBC 26-3; Figure 2.7.4) or propane burner (NFPA 265) ignition source, located on the floor in one of the rear corners of the room opposite the doorway. Pass/fail criteria are based primarily
FIGURE 2.7.4 UBC 26-3 Room/Corner Test (Source: Southwest Research Institute)
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on the extent of fire growth. NFPA 286, Standard Methods of Fire Test for Evaluation Contribution of Wall and Ceiling Interior Finish to Room Fire Growth, provides a more recent room/corner test that is very similar to NFPA 265, and that is used to evaluate vinyl and other nontextile wall coverings. Although wind-aided flame spread is the dominant mode in most fire scenarios involving interior finishes, there are some cases for which opposed-flow flame spread needs to be considered. The National Bureau of Standards (NBS, currently the National Institute of Standards and Technology, or NIST) conducted a series of full-scale fire tests in the 1970s to investigate the fire hazard of floor coverings. The main concern was flame spread from a fire room to a connected corridor. This work resulted in the development of the radiant flooring panel test. This test is described in ASTM E648, Standard Test Method for Critical Radiant Flux of Floor Covering Systems Using a Radiant Heat Energy Source,11 and NFPA 253, Standard Method of Test for Critical Radiant Flux of Floor Covering Systems Using a Radiant Heat Energy Source. The apparatus consists of an air–gas-fueled radiant heat panel inclined at 30° to and directed at a horizontally mounted floor covering system specimen (Figure 2.7.5). The radiant panel generates a heat flux distribution along the 40-in. (1-m) length of the test specimen from a nominal maximum of 1 W/cm2 (10 kW/m2) to a minimum of 0.1 W/cm2 (1 kW/m2). The test is initiated by open-flame ignition from a pilot burner. The heat flux at the location of maximum flame propagation is reported as critical radiant flux. Recent studies conducted in Europe identified fire scenarios that are controlled by wind-aided flame spread over floor coverings.12 These scenarios are not addressed by the radiant flooring panel test. The test method described in ASTM E16213 also evaluates opposed-flow flame spread characteristics of a product, and is referred to in regulations that pertain to various modes of transportation.
Smoke and Toxicity Fires generate particulate matter, which reduces the intensity of light transmitted through smoke. The distance at which an exit
FIGURE 2.7.5 Radiant Flooring Panel Test Apparatus (Source: Southwest Research Institute)
sign can be seen through a smoke layer is a direct function of the concentration of particulates in the smoke.1 The model building codes do not permit interior finishes that produce excessive amounts of light-obscuring smoke. Products that have to be tested according to the tunnel test must have a Smoke Developed Index (SDI) of 450 or less. The SDI is equal to 100 times the ratio of the area under the curve of light absorption versus time for the 10-min test duration to the area under the curve for red oak flooring. Thus, the SDI of red oak flooring is 100, by definition. The light absorption is measured in the exhaust duct of the tunnel test apparatus with a smoke photometer, which consists of a white light source on one side of the duct and a photocell on the opposite side of the duct. UBC 26-3 also specifies limitations to smoke, but the acceptance criteria are qualitative and based on visual observations. The more recent room/corner test procedures, NFPA 265 and NFPA 286, include quantitative measurements of the smoke production rate. Test methods have been developed specifically to measure smoke obscuration. The prime example is the NBS smoke chamber. This method is described in ASTM E662, Standard Test Method for Specific Optical Density of Smoke Generated by Solid Materials,14 and NFPA 258, Recommended Practice for Determining Smoke Generation of Solid Materials. The apparatus consists of a 3-ft (0.914-m) wide, 3-ft (0.914-m) high, and 2-ft (0.61-m) deep enclosure. A 3-in. ? 3-in. (75-mm ? 75-mm) specimen is exposed in the vertical orientation to an electric heater (Figure 2.7.6). Tests can be conducted with or without small pilot flames impinging at the bottom of the specimen. A white light source is located at the bottom of the enclosure, and a photomultiplier tube is mounted at the top to measure obscuration and optical density of the smoke as it accumulates inside the enclosure. The procedure specifies that tests be conducted in triplicate at a heat flux of 25 kW/m2 under the following conditions: with the pilot flames and without the pilot flames. These conditions are referred to as the flaming and nonflaming modes, respectively. The latter is misleading because specimens often ignite spontaneously, leading to flaming combustion without the pilot flames. The model building codes do not specify requirements based on performance in the NBS smoke chamber, but fire safety regulations for various modes of transportation (air, maritime, and rail) do. The test has been subjected to criticism because the smoke generated by the specimen accumulates inside the chamber and eventually affects combustion. The test conditions, therefore, are not well controlled and partly depend on the burning behavior of the product itself. Fires also generate toxic products of combustion, primarily in gaseous form. There are two types of toxic gases: narcotic gases, such as carbon monoxide (CO) and hydrogen cyanide (HCN), and irritant gases, such as hydrochloric acid (HCl) and hydrogen bromide (HBr). There are two schools of thought as far as smoke toxicity is concerned. Some experts feel that if fire growth is adequately controlled, smoke toxicity becomes a nonissue. The model building codes seem to adhere to this philosophy because they do not have specific requirements to control the toxic potency of materials or products. The New York City building code is an exception.
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FIGURE 2.7.6 NBS Smoke Chamber Heater Calibration (Source: Southwest Research Institute)
FIGURE 2.7.7 University of Pittsburgh Toxicity Test Apparatus (Source: Southwest Research Institute)
Other experts think that smoke toxicity needs to be addressed separately. Traditionally, this involved product testing that exposes animals to the effluents from a sample heated under well-defined thermal exposure conditions. Mice, rats, and primates have been used for this purpose. Under pressure from animal rights groups and the general public, bioassay methods have fallen out of favor and have largely been replaced with assessments based on analytical measurements. An exception to this is the University of Pittsburgh (UPitt), method, which is used to demonstrate compliance with the requirement in the New York City building code that no product shall be more toxic than wood. A small sample of the product is heated in a muffle furnace, and four mice are exposed to the products of combustion diluted with air (Figure 2.7.7). The furnace temperature is ramped at a rate of 5°C/min. The test is terminated after 30 min. The objective is to find the quantity in grams of the product that results in 50 percent mortality of the test animals. A product meets the requirements if this quantity, referred to as the LC50, is equal to or greater than 19.5 g (the value generically assigned to wood). Attempts in the 1980s to develop a consensus standard of the UPitt method failed, primarily because the exposure conditions are not representative of real fires, the sample is not representative of the product’s end-use conditions, and anomalies were found in the performance of certain types of products. The test procedure described in ASTM E1678, Standard Test Method for Measuring Smoke Toxicity for Use in Fire Hazard Analysis,15 and NFPA 269, Standard Test Method for Developing Toxic Potency Data for Use in Fire Hazard Modeling, minimizes the number of animal tests. In this test procedure, a specimen is exposed to a radiant heat flux of 50 kW/m,2 and the products of combustion are collected in a 0.2 m3 (7 ft3) chamber. Test duration is 30 min. Additional tests are performed with specimens of different size to find the exposed area that is expected to result in 50 percent mortality of test animals exposed over the 30-min test duration to the atmosphere in the chamber. To verify the results, a final test is conducted with a specimen of that area and six rats exposed to the gases in the chamber. A mathematical correction is made to the analytical measurements to account for the increase in CO production in underventilated postflashover fires. This is important because the majority of
U.S. fire deaths occur remote from the fire room, overall and especially for fires that have proceeded past flashover.16 A wide range of techniques is used to measure toxic gas concentrations in fire tests, ranging from simple qualitative sorption tube methods to sophisticated spectroscopy techniques. ASTM E800, Standard Guide for Measurement of Gases Present or Generated During Fires,17 describes the most common analytical methods and sampling considerations for many gases. Fourier Transform InfraRed (FTIR) Spectroscopy has emerged in recent years as the method of choice for real-time continuous analysis of fire gases18 (Figure 2.7.8).
Computer Fire Modeling Evolutions in fire science and technology and computing have resulted in a growing number of powerful mathematical models that are used in support of fire safety engineering design and analysis. The most commonly used computer fire models simulate the consequences of a fire in an enclosure. Zone models as well as field (CFD) models are used for this purpose. Zone models are based on the observation that gases inside a fire room generally accumulate in two distinct layers: a hot smoke layer
FIGURE 2.7.8 Fourier Transform Spectrometer for Analysis of Toxic Gases in Fire Effluents (Source: Southwest Research Institute)
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the North American standard temperature-time curve in the early 1900s.25 It is representative of a moderately severe fully developed enclosure fire, and is similar to the international curve used in most other countries (see Figure 2.7.9). The fire endurance of a building element is determined on the basis of a furnace test (Figure 2.7.10). Wall and floor/ceiling assemblies, roof structures, doors, windows, cable penetrations, and joint systems are mounted in a vertical or horizontal frame. The frame is placed against an open wall furnace or on top of an open ceiling furnace, and is exposed to the standard fire (Figure 2.7.11). Failure criteria for separating elements are based on thermal penetration and integrity. Thermal penetration is measured with thermocouples attached to the unexposed side of the
1200 ISO curve 1000 Temperature rise (°C)
beneath the ceiling and a layer of relatively cool air above the floor. The temperature and composition of both layers are assumed to be uniform, which greatly simplifies the equations to be solved. CFD models subdivide the room in thousands of small elements and solve the conservation equations of mass, momentum, and energy for each element. CFD models are therefore much more detailed than zone models, but require powerful computational resources. Enclosure fire models have been extended to simulate the spread of fire and smoke through multiroom structures. A second category of computer fire models predicts how materials, systems, or people respond when exposed to specific fire conditions. Models that simulate how a product performs in a fire test fall in this category. Several correlations and mathematical models have been developed to calculate performance in the tunnel test.8,19–22 However, these predictions are restricted to specific classes of products and have limited accuracy. Extensive research has been conducted over the past 2 decades to explore the use of small-scale fire test data in conjunction with correlations and models to predict room/corner test performance.23 The primary application of calculation methods that predict tunnel or room/corner test performance is for product development. Such calculations may also be used to demonstrate code equivalency and in support of performance-based design.
ASTM curve 800
600 400
FIRE RESISTANCE 200
Fire Endurance Testing Despite the active and passive fire protection measures affecting the growth stage, fires often develop beyond flashover. The objective of passive measures is then to contain the fire to a limited area for a specified duration. This is accomplished by subdividing buildings into smaller compartments that are separated from each other by fire-resistive wall and floor/ceiling assemblies. Openings in the separations, such as doors and cable penetrations, need to be protected to avoid or delay fire spread from one compartment to another. Fires can spread from the fire compartment to a neighboring compartment if the heat transfer results in a temperature rise that is high enough to ignite common combustibles on the side not exposed to the fire, or if cracks or fissures develop that allow the passage of flames and hot gases. Load-bearing assemblies need to fulfill their function for the specified duration because premature collapse allows fire spread to a larger area. Moreover, failure of structural assemblies and elements could adversely affect life safety of building occupants and fire fighters and could dramatically increase property loss and indirect fire costs. ASTM E176, Standard Terminology of Fire Standards,24 defines the fire resistance of a building element as its ability to confine a fire or to continue to perform a given structural function, or both. Fire endurance is a measure of the elapsed time during which a building element continues to exhibit fire resistance. The fire resistance of a building element is a function of the severity of the fire. To provide a uniform basis for measuring fire endurance, a standard fire has been defined. This fire is expressed in the form of a temperature-time curve (Figure 2.7.9). An ASTM committee chaired by Ira Woolson developed
0
0
60
120 Time (min)
180
240
FIGURE 2.7.9 Standard Temperature–Time Curves Used for Fire Endurance Testing
FIGURE 2.7.10 Standard Fire Endurance Wall Furnace (Source: Southwest Research Institute)
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element. Typically, the average temperature rise above the initial temperature is limited to a maximum of 250°F (139°C). The integrity of an element is maintained as long as there is no passage of flames and gases hot enough to ignite cotton waste on the unexposed side. Structural assemblies and beams must have sustained the applied load, which typically is equal to the design load. Columns are generally not tested under load, and failure is based on a critical temperature of the structural steel at which it starts to yield. Columns and beams can be tested with full or partial exposure of the perimeter. Beams, floor/ceiling assemblies, and roof structures can be tested under restrained or unrestrained conditions. The former uses a stiff frame that resists the forces due to thermal expansion of structural steel. Testing under restrained conditions is required for building elements that are part of a structure that is capable of resisting substantial thermal expansion throughout the range of anticipated elevated temperatures. Structural timber and wood assemblies do not need to be tested under restrained conditions because thermal expansion is negligible. Procedures for measuring the fire endurance of wall and floor/ceiling assemblies, roof structures, beams, and columns are described in ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials,26 and NFPA 251, Standard Methods of Tests of Fire Endurance of Building Construction and Materials. Variants of these basic standards have been developed to provide specific details for fire endurance testing of doors, windows, and other types of building elements that are not
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covered by the general standard. Table 2.7.1 gives an overview of the various ASTM and NFPA fire endurance standards. All ASTM and NFPA fire endurance test standards, except ASTM E1725, Standard Test Methods for Fire Tests of FireResistive Barrier Systems for Electrical System Components,29 prescribe a supplemental hose stream test procedure to evaluate the ability of the construction to resist disintegration under adverse conditions. The hose stream test is either performed after termination of the fire endurance test, or on a duplicate specimen that has been exposed to the standard fire for half the duration of the desired fire endurance classification. A hose stream test is not required for columns, floor/ceiling assemblies, and roof structures; wall assemblies with a fire endurance rating of less than 1 hr; and 20-min rated door assemblies. The hose stream requirement is unique to North America. North American fire endurance test standards have traditionally not specified the furnace pressure. However, the furnace pressure can have a pronounced effect on the performance and design of fire doors and, to a lesser extent, fire-resistive window assemblies. An extensive research program resulted in recent changes to the fire endurance test standards for doors and windows so that these tests now have to be conducted under slightly positive pressure.27,28,31 Fire endurance testing under positive pressure has been common practice in other parts of the world for a very long time. Fire endurance is determined on the basis of the time that one of the failure criteria for thermal penetration, integrity, and/or structural performance is first exceeded. The fire endurance time is rounded down to 20 min, ½ hr, 1 hr, 1½ hr, 2 hrs, 3 hrs, 4 hrs, and so on. Fire endurance requirements in the building codes were established with the objective that fire-resistive elements be able to survive complete burnout of a compartment. Each type of occupancy has an associated hazard that is quantified in terms of its fire load. Ingberg developed a relationship between the fire load and the time to burnout of a fully developed compartment fire.25 Ingberg also performed a series of room fire tests to establish a relationship between the standard fire and actual fires, and introduced the equal-area concept.25 According to this concept, the duration of standard fire exposure of equivalent severity to an actual burnout fire can be determined on the basis of equal areas under the temperature-time curve. The fire endurance requirements in the model building codes are still largely based on the concepts and data developed by Ingberg in the 1920s. TABLE 2.7.1 Standards
FIGURE 2.7.11 Fire Endurance Test on Wall Assembly (Source: Southwest Research Institute)
Basics of Passive Fire Protection
ASTM and NFPA Fire Endurance Test
ASTM Designation
NFPA Designation
E11926 E207427 E201028 E172529
255 252 257 —
E81430
—
Subject General test requirements Door assemblies Window assemblies Barriers for electrical system components Through-penetration firestops
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Analytical Methods A number of analytical methods have been developed in North America32 and other parts of the world33 on the basis of years of experience and extensive fire endurance testing. These calculation methods are accepted by the model building codes in lieu of test results. However, the scope of these methods is limited to relatively simple concrete, masonry, steel, and wood construction. Analytical methods for concrete slabs and columns specify the thickness of concrete cover that is needed to limit the reinforcing or prestressing steel temperatures. The fire endurance of clay and concrete masonry walls is specified as a function of the thickness of the wall. The fire endurance of steel columns and beams is a function of the area to heated perimeter ratio, and the thermal characteristics and thickness of protective materials (gypsum board, sprayed-on fireproofing, etc.). The component additive method estimates the fire endurance rating of a light wood-frame wall, floor/ceiling, or roof assembly on the basis of times assigned to the individual components of the assembly, that is, the protective membrane(s), thermal insulation, structural members, and so on. Analytical methods for heavy timber beams and columns estimate the reduction of the load-bearing cross section of the member as a function of time on the basis of experimental charring rate data for wood obtained under standard fire conditions. The estimated fire endurance corresponds to the time when the remaining section is no longer able to support the load.
Fire Endurance Modeling Finite difference or finite element conduction heat transfer models are also used to predict the temperature distribution in building elements exposed to fire.34 Some of these models have been coupled with strength and stiffness calculations to predict structural performance under fire conditions.35 The acceptance of this type of computer fire modeling is not as widespread as that of the analytical methods described in the previous section. However, it is a useful tool to demonstrate code equivalency or to support performance-based design. One of the main problems is that accurate thermal and mechanical material properties are needed at elevated temperatures. Such property data are often not available and are difficult to measure. A major advantage of this approach is that the exposure conditions are not limited to the standard fire conditions. Predictions can be made for real fire exposure conditions. These exposure conditions can be based on experimental measurements or on predictions obtained with a fully developed compartment fire model such as COMPF2.36
EXTERIOR FIRE SPREAD Upward Fire Spread over Facades Exterior Insulation Finish Systems (EIFS) are very common in the construction of exterior walls for high-rise buildings. Because the systems typically consist of plastic foam insulation and other combustible components, the potential exists for rapid upward flame spread over facades to stories above the fire room.
NFPA 285, Standard Method of Test for the Evaluation of Flammability Characteristics of Exterior Non-Load-Bearing Wall Assemblies Containing Combustible Components Using the Intermediate-Scale, Multistory Test Apparatus, describes a test method intended to evaluate the capability of such wall assemblies to resist vertical and, to some extent, lateral flame propagation over the exterior and interior faces and within the core of the assembly. The test structure consists of two stories. The interior dimensions of the first and second floor rooms are identical and equal to 10 ft (3.05 m) wide by 10 ft (3.05 m) deep by 7 ft (2.13 m) high. Both rooms are constructed of concrete block walls and concrete slabs, and are fully enclosed except for the front side. The interior surfaces of the bottom room are protected with gypsum board and ceramic fiber insulation. The test assembly is mounted against the front of the test structure and covers both stories. There is a window opening of 78 in. (1.96 m) wide by 30 in. (0.76 m) high at 30 in. (0.76 m) from the floor of the first floor room. The main burner is located inside the first floor burn room, and is supplied with gas so that its heat output increases according to a prescribed regime from approximately 700 kW at the start of the test to approximately 900 kW at the end of the 30-min test. A second burner is located inside the window opening so that flames hit the window soffit, which is the most vulnerable part of the exterior wall assembly for flame penetration into the core. The heat output of the window burner increases from 0 kW at the start of the test to approximately 400 kW at the end of the 30-min test duration. Acceptance criteria are based on visual observations of flame propagation over the exterior surface, and temperature measurements above and at a lateral distance from the window opening.
Ignition of Exterior Claddings Model building codes address the problem of fire spread from one building to an adjacent building due to radiant ignition of combustible exterior facades by specifying a minimum distance to the property line. This distance is based on the assumption that the exterior cladding is wood. The commonly accepted threshold for piloted ignition of wood is 1.10 Btu/ft2Ýs (12.5 kW/m2). However, many different types of exterior wall claddings are now available in the marketplace. To ensure that the model building code provisions are adequate for these products, it is necessary to verify that their ignition threshold is equal to or higher than that for wood. NFPA 268, Standard Test Method for Determining Ignitability of Exterior Wall Assemblies Using a Radiant Heat Energy Source, describes a test method that can be used to perform this verification. The apparatus consists of a vertical 0.91-m × 0.91-m propane-fire radiant panel that exposes the 4-ft (1.22-m) wide by 8-ft (2.44-m) specimen to a radiant heat flux that is equal to approximately 12.5 kW/m2 over a central 1-ft ? 1-ft (0.3-m ? 0.3-m) region (Figure 2.7.12). A spark igniter is mounted on the vertical centerline of the test specimen at a point 18 in. (0.46 m) above its horizontal centerline, and at 5/8 in. (15.9 mm) from its surface. A product passes if ignition does not occur during the 20-min test exposure.
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Basics of Passive Fire Protection
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FIGURE 2.7.13 Burning Brand Test on Roof Covering (Source: Southwest Research Institute)
EGRESS Code Provisions for Establishing Means of Egress
FIGURE 2.7.12 Radiant Panel Test to Measure Ignitability of Exterior Wall Claddings (Source: Southwest Research Institute)
Ignition and Fire Spread over Roof Structures Other possible mechanisms of fire spread involve burning brands landing on a roof surface or flames propagating over a roof covering. ASTM E108, Standard Test Methods for Fire Tests of Roof Coverings,37 and NFPA 256, Standard Methods of Fire Tests of Roof Coverings, describe a procedure to measure the relative fire characteristics of roof coverings under simulated fire originating outside the building (Figure 2.7.13). The roof covering is mounted on a 40-in. (1-m) wide by 52-in. (1.3-m) long deck at the required incline. The procedure involves three different tests: an intermittent flame exposure test, a spread of flame test, and a burning brand test. Only the spread of flame test is required for roof coverings mounted on a noncombustible deck. For each test there are three levels of exposure (severe, moderate, and light), leading to Class A, B, and C respectively. Additional flying brand tests are required for roof coverings that are prone to generating flying brands. Rain tests are required when the fire-retardant characteristics of the roof covering or construction may be adversely affected by water.
The ability of building occupants to quickly and efficiently exit the building is often the difference between life and death. Model building codes, therefore, have detailed provisions that address emergency egress. The means of egress that are needed depend primarily on the number of people who can occupy the space. The model building codes have tables that specify the number of square feet per person based of the use of a space. Every compartment is usually required to have at least two independent exits that are far enough apart, so that one exit is available if the second one is inaccessible by the fire. More than two exits may be required, depending on the size of the compartment, so that travel distances are limited. Longer travel distances are acceptable in buildings that are protected with automatic sprinklers. Finally, each component of the means of egress (doorways, exit corridors, stairways, etc.) must meet minimum size requirements so that the flow of evacuating occupants can be accommodated.
Egress Modeling A number of computer models have been developed to simulate human behavior and evacuation under fire and other emergency conditions. These models are very useful as part of engineering analyses in support of fire investigation and reconstruction and performance-based design. However, the human behavior and egress problem has long been neglected and there is an urgent need for more work in this area.
SUMMARY Fire protection of buildings addresses all aspects of fire safety and consists of a combination of active and passive measures. Active fire protection devices require manual, mechanical, or electrical power for their operation. Passive fire protection does not require any external power. This chapter deals with passive fire protection.
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There are essentially three types of passive fire protection measures. The first type consists of requirements for the reaction-to-fire of interior finishes. The main objective of these requirements is to slow down fire growth and delay the onset of flashover. The second type of passive fire protection measures pertains to the fire resistance of building elements. The intent is to confine the fire to a limited area and to ensure structural integrity of the building and its components through burnout. The third type of passive fire protection measures addresses emergency egress and consists of construction features such as the number, size, and location of exits needed for safe evacuation of the building occupants. An overview is given of standard test procedures, calculation methods, and design practices that pertain to the three types of passive fire protection measures.
15.
16. 17.
18.
BIBLIOGRAPHY
19.
1. Quintiere, J., Principles of Fire Behavior, Delmar Publishers, Albany, NY, 1997. 2. ASTM E136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750°C, Annual Book of Standards, Vol. 04.07, American Society of Testing and Materials, West Conshohocken, PA, 2001. 3. ASTM E1354, Standard Test Method for Heat and Visible Smoke Release Rates Using an Oxygen Consumption Calorimeter, Annual Book of Standards, Vol. 04.07, American Society of Testing and Materials, West Conshohocken, PA, 2001. 4. Janssens, M., and Wenzel, A., “Using the Cone Calorimeter to Assess Combustibility of Building Products,” Fire Technology, in press. 5. Janssens, M., Thermophysical Properties of Wood and Their Role in Enclosure Fire Growth [Ph.D. Thesis], University of Ghent, Belgium, 1991. 6. ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials, Annual Book of Standards, Vol. 04.07, American Society of Testing and Materials, West Conshohocken, PA, 2001. 7. Gardner, W., and Thomson, C., “Flame Spread Properties of Forest Products—Comparison and Validation of Prescribed Australian and North American Flame Spread Test Methods,” Journal of Fire and Materials, Vol. 12, 1988, pp. 71–85. 8. Quintiere, J., “Some Factors Influencing Fire Spread over Room Linings and in the ASTM E84 Tunnel Test,” Journal of Fire and Materials, Vol. 9, 1985, pp. 65–74. 9. Belles, D., Fisher, F., and Williamson, R. B., “How Well Does the ASTM E84 Predict Fire Performance of Textile Wallcoverings?” Fire Journal, Vol. 82, 1988, p. 24. 10. UBC 26-3, Uniform Building Code, Vol. 3, ICBO, Whittier, CA, 1997. 11. ASTM E648, Standard Test Method for Critical Radiant Flux of Floor Covering Systems Using a Radiant Heat Energy Source, Annual Book of Standards, Vol. 04.07, American Society of Testing and Materials, West Conshohocken, PA, 2001. 12. Van Hees, P., and Vandevelde, P., “Mathematical Models for Wind-Aided Flame Spread on Floor Coverings,” Proceedings of the 5th International Symposium, March 3–7, 1997, Melbourne, Australia, International Association of Safety Science, Boston, 1997, pp. 321–332. 13. ASTM E162, Standard Test Method for Surface Flammability of Materials Using a Radiant Heat Energy Source, Annual Book of Standards, Vol. 04.07, American Society of Testing and Materials, West Conshohocken, PA, 2001. 14. ASTM E662, Standard Test Method for Specific Optical Density of Smoke Generated by Solid Materials, Annual Book of Stan-
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24. 25. 26.
27.
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dards, Vol. 04.07, American Society of Testing and Materials, West Conshohocken, PA, 2001. ASTM E1678, Standard Test Method for Measuring Smoke Toxicity for Use in Fire Hazard Analysis, Annual Book of Standards, Vol. 04.07, American Society of Testing and Materials, West Conshohocken, PA, 2001. Gann, R., Babrauskas, V., Peacock, R., and Hall, J., “Fire Conditions for Smoke Toxicity Measurement,” Journal of Fire and Materials, Vol. 18, 1994, pp. 193–199. ASTM E800, Standard Guide for Measurement of Gases Present or Generated During Fires, Annual Book of Standards, Vol. 04.07, American Society of Testing and Materials, West Conshohocken, PA, 2001. Orvis, A., and Janssens, M., “Trends in Evaluating Toxicity of Fire Effluents,” Fire and Materials ’99, Sixth International Conference and Exhibition, February 22–23, 1999, San Antonio, TX, Interscience Communications Ltd., London, UK, 1999, pp. 95–106. Janssens, M., “Modeling the E84 Tunnel Test for Wood Products,” Fire and Materials, First International Conference, September 24–25, 1992, Arlington, VA, Interscience Communications Ltd., London, 1992, pp. 33–42. Stevens, M., Voruganti, V., and Rose, R., “Correlation of Small Scale Fire Tests to ASTM E-84 Tunnel Performance for Thermoset Resin Systems,” Fourth International Fire and Materials Conference and Exhibition, November 15–16, 1995, Crystal City, VA, Interscience Communications Ltd., London, UK, 1995, pp. 319–327. Sheppard, D., and Gandhi, P., “Estimating Smoke Hazard from Steiner Tunnel Smoke Data,” Fire Technology, Vol. 32, 1996, pp. 65–75. Stevens, M., “Cone Calorimeter as a Screening Test for ASTM E-84 Tunnel Test,” Fifth International Fire and Materials Conference, February 23–24, 1998, San Antonio, TX, Interscience Communications Ltd., London, UK, 1998, pp. 147–151. Janssens, M., “A Survey of Methods to Predict Performance of Wall Linings in the Room/Corner Test,” Third International Symposium on Computer Applications in Fire Safety Engineering, September 11–12, 2001, Baltimore, MD, Society of Fire Protection Engineers, Bethesda, MD, 2001. ASTM E176, Standard Terminology of Fire Standards, Annual Book of Standards, Vol. 04.07, American Society of Testing and Materials, West Conshohocken, PA, 2001. Babrauskas, V., and Williamson, R. B., “Historical Basis of Fire Resistance Testing, Parts 1 and 2,” Fire Technology, Vol. 14, 1978, pp. 184–194, 304–316. ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials, Annual Book of Standards, Vol. 04.07, American Society of Testing and Materials, West Conshohocken, PA, 2001. ASTM E2074, Standard Test Method for Fire Tests of Door Assemblies, Including Positive Pressure Testing of Side-Hinged and Pivoted Swinging Door Assemblies, Annual Book of Standards, Vol. 04.07, American Society of Testing and Materials, West Conshohocken, PA, 2001. ASTM E2010, Standard Test Method for Positive Pressure Fire Tests of Window Assemblies, Annual Book of Standards, Vol. 04.07, American Society of Testing and Materials, West Conshohocken, PA, 2001. ASTM E1725, Standard Test Methods for Fire Tests of FireResistive Barrier Systems for Electrical System Components, Annual Book of Standards, Vol. 04.07, American Society of Testing and Materials, West Conshohocken, PA, 2001. ASTM E814, Standard Test Method for Fire Tests of ThroughPenetration Fire Stops, Annual Book of Standards, Vol. 04.07, American Society of Testing and Materials, West Conshohocken, PA, 2001. van Geyn, M., “National Fire Door Fire Test Project. Positive Pressure Furnace Fire Tests,” and Gandhi, P., and Sheppard, D.,
CHAPTER 7
32. 33.
34. 35. 36. 37.
“National Fire Door Fire Test Project. Positive Pressure Room Burn Tests,” National Fire Protection Research Foundation, Quincy, MA, 1995. “Guidelines for Determining Fireresistance Ratings of Building Elements,” Third Printing, Building Officials and Code Administrators International, Country Club Hills, IL, 1997. Kruppa, J., “Development of Standards for Structural Fire Design: Eurocodes,” INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 563–572. “FIRES-T3: A Guide for Practicing Engineers,” Society of Fire Protection Engineers, Bethesda, MD. Lie, T., Structural Fire Protection, ASCE Manuals and Reports on Engineering Practice No. 78, American Society of Civil Engineers, New York, 1992. Babrauskas, V., “COMPF2: A Program for Calculating PostFlashover Compartment Fire Temperatures,” National Bureau of Standards, Technical Note TN 991, Gaithersburg, MD, 1979. ASTM E108, Standard Test Methods for Fire Tests of Roof Coverings, Annual Book of Standards, Vol. 04.07, American Society of Testing and Materials, West Conshohocken, PA, 2001.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on the elements of fire protection discussed in this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 101®, Life Safety Code® NFPA 220, Standard on Types of Building Construction NFPA 251, Standard Methods of Tests of Fire Endurance of Building Construction and Materials NFPA 252, Standard Methods of Fire Tests of Door Assemblies NFPA 253, Standard Method of Test for Critical Radiant Flux of Floor Covering Systems Using a Radiant Heat Energy Source NFPA 255, Standard Method of Test of Surface Burning Characteristics of Building Materials NFPA 256, Standard Methods of Fire Tests of Roof Coverings NFPA 257, Standard on Fire Tests for Window and Glass Block Assemblies NFPA 258, Recommended Practice for Determining Smoke Generation of Solid Materials NFPA 259, Standard Test Method for Potential Heat of Building Materials NFPA 265, Standard Methods of Fire Tests for Evaluating Room Fire Growth Contribution of Textile Wall Coverings NFPA 268, Standard Test Method for Determining Ignitability of Exterior Wall Assemblies Using a Radiant Heat Energy Source NFPA 269, Standard Test Method for Developing Toxic Potency Data for Use in Fire Hazard Modeling NFPA 285, Standard Method of Test for the Evaluation of Flammability Characteristics of Exterior Non-Load-Bearing Wall Assemblies Containing Combustible Components Using the Intermediate-Scale, Multistory Test Apparatus NFPA 286, Standard Methods of Fire Tests for Evaluating Contribution of Wall and Ceiling Interior Finish to Room Fire Growth
Additional Readings Barnes, G. J., “Sprinkler Trade Off Clauses in the Approved Documents,” University of Canterbury, Christchurch, New Zealand, Fire Engineering Research Report 97/1, 1997. Buchanan, A. H., Structural Design for Fire Safety, Wiley, Chichester, UK, 2001. Chow, W. K., “Discussion on Applying the American Fire Safety Evaluation System for Business Occupancies in Hong Kong,” International Journal on Engineering Performance-Based Fire Codes, Vol. 3, No. 2, 2001, pp. 92–97.
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Chow, W. K., Wong, L. T., Chen, K. T. Fong, N. K., and Ho, P. L., “Fire Safety Engineering: Comparison of a New Degree Programme with the Model Curriculum,” Fire Safety Journal, Vol. 32, No. 1, 1999, pp. 1–15. Custer, R. L. P., and Meacham, B. J., Introduction to PerformanceBased Fire Safety, National Fire Protection Association, Quincy, MA, 1997. Diamantes, D., Fire Prevention: Inspection and Code Enforcement, Delmar, Albany, NY, 2002. Dowling, V. P., and Blackmore, J. M., “Fire Performance of Wall and Ceiling Linings, Final Report,” Commonwealth Scientific and Industrial Research Organization, Melbourne, Australia, Project 2, Stage A, July 1998. Galvez, R., “Smothering Smoke Sources,” Consulting-Specifying Engineer, Vol. 27, No. 1, 2000, pp. 46–48. Hirschler, M. M., “How to Assess the Effect of an Individual Product on the Fire Hazard in a Real Occupance,” Proceedings of the 8th Conference, Flame Retardants ’98, London, UK, February 3–4, 1998, sponsored by the Interscience Communications Ltd., and British Plastics Federation, Association of Plastics Manufacturers, European Flame Retardant Association, Fire Retardant Chemicals Association, 1998, pp. 226–240. Hirschler, M. M., “Use of Heat Release Rate to Predict Whether Individual Furnishings Would Cause Self Propagation Fires,” Fire Safety Journal, Vol. 32, No. 3, 1999, pp. 273–296. Hovde, J., “Needs for Service Life Prediction of Passive Fire Protection Systems,” INTERFLAM ’99, Proceedings of 8th International Conference, Edinburgh, UK, Interscience Communications Ltd., London, UK, June 29–July 1, 1999, pp. 477–488. Hsiung, K. H., “Study on the Alternative Fire Control Performance Between the Interior Finishing and Sprinkler System Based on Equivalency Concept,” Proceedings of the FORUM 2000 Symposium, Fire Research Development and Application in the 21st Century, Taipei, Taiwan, 2000, organized by Architectural and Building Research Institute (ABI), MOI, and FORUM for International Cooperation in Fire Research, 2000, pp. 1–20. Janssens, M. L., An Introduction to Mathematical Fire Modeling, CRC Press, Boca Raton, FL, 2000. Murrell, J., and Fritz, T. W., “Engineering Approach to Satisfying Code Requirements in China,” Proceedings of the 5th International Conference, Fire and Materials ’98, San Antonio, TX, February 23–24, 1998, Interscience Communications Ltd., London, UK, 1998, pp. 89–97. Nelson, H. E., “Elements of Fire Hazard Analysis for Fire Safety Design,” Proceedings of the Pacific Rim Conference and 2nd International Conference on Performance-Based Codes and Fire Safety Design Methods, Maui, HI, May 3–9, 1998, International Code Council, Birmingham, AL, 1998, pp. 347–356. O’Connor, D. J., “New Concepts Keep Smoke in Check,” ConsultingSpecifying Engineer, Vol. 19, No. 1, 1996, pp. 30–33. Proceedings of the 2nd International Symposium on Human Behavior in Fire, March 26–28, 2001, MIT, Cambridge, MA, Interscience Communications, London, UK, 2001. Royle, F., “Passive Fire Protection,” Fire Safety Engineering, Vol. 7, No. 2, 2000, pp. 24–25. Trew, P., “Putting Panels to the Test,” Fire Prevention, No. 308, Apr. 1998, pp. 11–13. Weiger, P. R., “Adapting Tests for Interior Finishes,” NFPA Journal, Vol. 95, No. 2, 2001, pp. 53–55. White, D. A., Gewain, R. G., and Hamer, A. J., “Semiconductor Fabrication Facilities: Alternative Design using Performance-Based Engineering Methods,” Proceedings of the Fire Risk and Hazard Assessment Symposium. Research and Practice: Bridging the Gap, San Francisco, CA, June 26–28, 1996, National Fire Protection Research Foundation, Quincy, MA, 1996, pp. 443–450. Wu, S., “Fire Safety Design of Apartment Buildings,” University of Canterbury, Christchurch, New Zealand, Fire Engineering Research Report 01/10, Mar. 2001.
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SECTION 2
Explosions Robert Zalosh
T
FUNDAMENTAL EXPLOSION PRINCIPLES The amount of energy released determines the strength of the blast wave, that is, the pressure disturbance, at a given distance far away from the energy release site. The peak pressure (i.e., the maximum pressure) at the explosion site itself depends on the energy released per unit volume. However, a more complete understanding of both the damage potential and various explosion protection alternatives also requires knowledge of the approximate time duration of the energy release. Therefore, it is helpful to characterize the various types of explosions in terms of their peak pressures, energies, and energy release durations.
Peak Pressure, Energy, and Energy Release Duration Figure 2.8.1 shows a very rough plot of the peak pressures and energy release durations in various types of explosions. Nuclear
Robert Zalosh is professor of fire protection engineering at Worcester Polytechnic Institute in Worcester, Massachusetts, and a consultant with expertise in industrial fire and explosion issues and incident investigations.
Nuclear Explosives 100,000
Peak pressure (psig)
he Random House Dictionary of the English Language defines explosion as a violent expansion or bursting with noise. The violent expansion is due to a sudden release of energy or an energy transformation that causes a region of high pressure and/or temperature, which propagates away from the source as a blast wave. Therefore, a more scientific definition for explosion would be a sudden, rapid release of energy that produces potentially damaging pressures. One way to categorize various types of explosions is in terms of the energy source. Fire protection professionals are familiar with combustion energy sources that cause gas explosions and dust explosions when the fuel and air are premixed and confined before being ignited. Other energy sources that can be released or transformed rapidly enough to produce explosions include condensed phase explosives, chemical reactions other than combustion, nuclear energy, potential energy due to compression, and extremely rapid vaporization. This chapter discusses the fundamental nature of various types of explosions, beginning with a brief overview of the energies released and the associated peak pressures produced. A general discussion of blast waves and primary and secondary fragments is also provided.
10,000
Closed vessel detonations Steam explosions
1,000
Closed vessel deflagrations
100
1 1E–6
Vapor cloud explosions
Pressure vessel Building bursts deflagrations
10
1E–5
1E–4
1E–3
1E–2
1E–1
1E+0
Time scale(s) for energy release
FIGURE 2.8.1 Peak Pressures and Energy Release Time Scales in Various Types of Explosions
explosions release by far the greatest amount of energy per unit volume, and therefore generate the highest peak pressures, which are of the order of many millions of pounds per square inch (psi). This pressure is generated within a millionth of a second (microsecond) as the fission or fusion products and expanding bomb debris compress and heat the air at the release site.1 Condensed Phase Explosives. Commercial and military condensed phase explosives are usually divided into two categories: high explosives and low explosives. High explosives tend to detonate, that is, to have a reaction propagation speed greater than the speed of sound in the reacting material. High explosives can generate peak pressures in the range 104–106 psi. The energy release time-scale for a high explosive is equal to the length of the explosive material divided by its detonation speed. For example, the detonation propagation speed of dynamite is approximately 16,000 ft/s (4900 m/s), so that a 1-ft-long stick would release its energy in 1/16th of a millisecond (ms). Detonation speeds for other high explosives are in the range of 2000 to 8200 m/s.2 Low explosives tend to deflagrate, that is, to have a reaction propagation speed that is less than the speed of sound in the reacting material. The actual speeds can vary from hundreds of meters per second down to millimeters per hour.3 Peak pressures
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E burst C
(Pb > Pa)V ,>1
(1)
where Pb C vessel pressure at the time of bursting Pa C pressure of ambient air (1 atmosphere C 14.7 psia C 101 kPa at sea level) V C vessel volume , C ratio of specific heats for the gas in the vessel (, C 1.4 for air) Using Equation 1, one can calculate the burst energy for a 10-m3 vessel that ruptures when it is filled with air at a pressure of 1000 psia (6890 kPa). At sea level, (Pb > Pa) C 6890 > 101 C 6789 kPa. For a vessel filled with air, (, > 1) C 1.4 > 1 C 0.4. Therefore, Eburst C 6789 ? 103 Pa)(10 m3)/0.4 C 172 ? 106 J, which is equivalent to 172/4.2 C 41 kg (90 lb) of TNT. Gas Explosions. Gas explosions can be either deflagrations or detonations, depending on whether the flame speed is less than or greater than sound speed in the unburned fuel-air mixture. (Sound speed is approximately equal to 335 m/s if the fuel concentration is small compared to the air concentration.) Peak pressures and the form of the pressure-time loading are fundamentally different for deflagrations and detonations. Separate discussions of deflagrations and detonations are provided later in the chapter. For now, it is sufficient to say that the peak pressures generated in detonations are at least twice as large as those in deflagrations, and the time scale is often at least an order of magnitude smaller, as indicated in Figure 2.8.1. Pressures generated in gas or dust deflagrations in buildings are often of the order of 1 psig because most building structures will fail at pressures of that order of magnitude. The
structural failure, either planned (deflagration venting) or unplanned, releases the confined burned and unburned gases and usually prevents further pressure rise even though the fuel continues to burn. Deflagrations in process equipment often lead to higher pressures than in buildings because the equipment can withstand higher pressures prior to failure and because there is more likely to be a flammable mixture throughout the enclosure volume. The energy release time-scale is shown smaller for equipment than for buildings because the smaller volumes allow for more rapid rates of pressure rise. Vapor Cloud Explosions. Vapor cloud explosions refer to external deflagrations of very large clouds of flammable gas or vapor in a highly obstructed or partially confined area. Peak pressures in vapor cloud explosions are of the same order of magnitude as those in building deflagrations, but the energy release times are usually longer because the flammable clouds are usually much larger than those that form inside buildings.
Blast Waves Pressure disturbances propagating into the atmosphere away from the energy release region are called blast waves. The propagation of a blast wave that started as a detonation wave is shown in Figure 2.8.2 as a series of pressure versus distance profiles at six different times. In all six profiles, a shock wave (sudden discontinuous increase in pressure) occurs as the leading edge of the pressure wave, and the pressure decays behind the shock wave. As the blast wave propagates away from the energy release site, the amplitude of the shock wave decreases, and the time duration of the pressure disturbance increases. It eventually develops a characteristic N wave shape at time t 6, that is, in the far field at distances far from the explosion site. The parameters used to characterize far-field blast waves are identified in Figure 2.8.3. The shock wave amplitude is denoted as Ps0, and the area between the pressure curve and the ambient pressure, P0, is called the specific impulse, is. Because there is a portion of the blast wave in which pressures are smaller than P0, there is a positive specific impulse and a negative spe-
t1 Overpressure
produced by low explosives are orders of magnitude lower than those of high explosives. The current UN/U.S. DOT classification system for explosives consists of six categories, depending on their propensity to detonate in their entirety and their susceptibility to accidental initiation (NFPA 495). Standardized testing and classification procedures are described in 49 CFR, Part 173.57. Energies released by condensed phase explosives and military weapons are often quoted in terms of the TNT (trinitrotoluene) equivalent weight. One kilogram of TNT has an explosive energy of 4.2 ? 106 Joules (J), so that one kiloton of TNT is equivalent to 4.2 ? 106 kJ. Most condensed phase high explosives have an explosive energy per unit mass that is similar to that of TNT. For example, the explosive energy of pentolite (50/50) is 5.1 ? 106 J/kg, and that of RDX is 5.4 ? 106 J/kg. The corresponding TNT equivalent of pentolite is 5.1/4.2 C 1.2 kgpentolite/kg-TNT, and that of RDX is 5.4/4.2 C 1.3 kg-RDX/kgTNT.2,4 A burst pressure vessel releases its energy of compression in the time it takes for a crack to propagate sufficiently far to allow the metal shell to split open. This is typically on the order of 10 5s. The peak pressure is approximately equal to the vessel pressure at the time of bursting, Pb. The isentropic expansion energy, Eburst, for an ideal gas released during the vessel burst is4
t2 t3 t4 t5 t6
Distance from explosion
FIGURE 2.8.2 Blast Wave Propagation Away from Detonation Site
CHAPTER 8
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Explosions
2–121
Pso
Pressure
Positive specific impulse, i s Negative specific impulse, i s–
Ps
Pso–
t A + t o + t o–
tA + to
tA
Ambient, Po 0
Positive phase duration
Negative phase duration
Ps–
t o–
to
Time after explosion
FIGURE 2.8.3
Pressure-Time Variation for a Far-Field Blast Wave (Source: DOD TM5-1300)
cific impulse. The blast wave damage and injury potential depends on the magnitudes of the shock pressure, Ps0, and the positive is. Various correlations and theoretical models of ideal blast waves (produced from instantaneous, point source releases of energy) have shown that Ps0 can be correlated with an energyscaled distance of the following form:
1000
100
z z or 1/3 E 1/3 WT NT
Pso, psi
where z C distance from the explosion site E C blast wave energy
10
WTNT C the TNT equivalent weight for the same blast wave energy z
1/3 Figure 2.8.4 shows the correlations between Ps0 and WTNT z 1/3 1/3 (in ft/lb ) for a condensed phase exand between is and WTNT plosion at ground level. Criteria for blast wave damage and injuries generally involve considerations of both pressure (Ps0) and impulse (is). However, at large distances from the explosion site, the impulse is usually large enough that structural damage depends primarily on Ps0. Table 2.8.1 shows the consequences of representative values for overpressure and the associated TNT equivalentscaled distance. The scaled distances in Table 2.8.1 were developed from correlations of explosions at various altitudes and from the incident blast wave pressures at the various types of targets listed in the table. One complication in using this data is that explosions at ground level produce hemi-spherically expanding blast waves, whereas elevated explosions produce spherically expanding blast waves that are reflected off the ground. The usual way of accounting for the reflection effect is to use double the blast wave energy when applying the correlations for spherically expanding blast waves to ground level explosions. This doubling of the blast wave energy would be needed in using the scaled
I s, psi–ms/lb1/3 1.0 1.0
10 Scaled distance, Z g, ft/lb1/3
100
FIGURE 2.8.4 Decay of Blast Wave Pressure and Specific Impulse with Distance from Explosion Site (Source: Reference 5)
distances in Table 2.8.1, whereas the correlations in Figure 2.8.4 do not need any corrections because they come directly from ground level explosions. Consider the previous example of the 10-m3 pressure vessel burst as an example of the how to use Table 2.8.1 and Figure 2.8.4. Suppose we want to find the distance from the vessel to the location at which Ps0 would be 1 psig, in other words, to the blast wave distance at which personnel would be knocked down, windows shattered, and thin sheet metal panels buckled, according to Table 2.8.1. If we use the scaled distance in Table
2–122 SECTION 2 ■ Basics of Fire and Fire Science
TABLE 2.8.1
High Explosives Overpressure Constants and Consequences
Scaled Distance Z (ft/kg1/3)
Overpressure (psi)
Consequences
3000–890 420–200 200–100 82–41 44–32 44–28 44–24 28–20 20–16 20–16 16–12 16–12 11–10 15–9 14–11 14–11 6.7–4.5 3.8–2.7 2.4–1.9
0.01–0.04 0.1–0.2 0.2–0.4 0.5–1.1 1.0–1.5 1.0–1.8 1.0–2.2 1.8–2.9 2.9–4.4 2.9–4.4 4.4–7.3 4.4–7.3 10.2–11.6 5.1–14.5 5.8–8.7 5.8–8.7 29.0–72.5 102–218 290–435
Minimum damage to glass panels Typical window glass breakage Minimum overpressure for debris and missile damage Windows shattered, plaster cracked, minor damage to some buildings Personnel knocked down Panels of sheet metal buckled Failure of wooden siding for conventional homes Failure of walls constructed of concrete blocks or cinder blocks Self-framing paneled buildings collapse Oil storage tanks ruptured Utility poles broken off Serious damage to buildings with structural steel framework Probable total destruction of most buildings Eardrum rupture Reinforced concrete structures severely damaged Railroad cars overturned Lung damage Lethality Crater formation in average soil
Source: Reference 6.
2.8.1 of 44 ft/kg1/3, the blast wave distance is calculated as follows: (44 ft/kg1/3)(2 * 41 kg)1/3 C 191 ft If we use the correlation for Ps0 in Figure 2.8.4 extrapolated slightly to 1 psig, the calculated distance is (45 ft/lb1/3)(90 lb)1/3 C 202 ft Thus, the distance would be approximately 200 ft in both cases. However, if we are evaluating blast damage potential for a structural surface that directly faces the explosion, we would have to account for the reflected blast wave pressures. The ratio of reflected blast wave pressure to incident pressure is approximately 2 for values of Ps0 less than about 2 psig. Thus, if the exposed persons and structures are facing the pressure vessel at the time of rupture, the corresponding effects could be experienced at a value of Ps0 as low as 0.5 psig, corresponding to a TNTequivalent scaled distance of 82 ft/kg1/3, as per Table 2.8.1.
Primary and Secondary Fragments Casualties from explosions are often caused by projectile fragments, either from the exploding container (primary fragments) or from structures damaged by the explosion blast wave (secondary fragments). Fragmentation of the exploding container depends on the type of container or explosive case, and is usually approached via statistical analysis of test and accident data. High explosives and weapons usually produce a large number of casing fragments, whereas burst pressure vessels produce relatively few, but larger, fragments.
Primary fragment statistical correlations for condensed phase explosives are described by Baker et al.7 Calculations for burst pressure vessels involve first estimating the number and size of fragments and then using the results of projectile calculations to determine how far the fragments can fly. This procedure is explained in References 7 and 8. Primary fragment projectile distances often determine the safe standoff distance for a pressure vessel exposed to a fire. Correlations shown in the Guidelines for Consequence Analysis show approximately 80 percent of the fragments from LP-Gas BLEVEs land within about 1000 ft from the vessel; however, one fragment in a Mexico City incident traveled about 3000 ft. In the case of horizontal cylindrical vessels, more fragments are projected in the axial direction than in the lateral direction, but emergency responders need to be wary of the danger of fragments in all directions. Two volunteer firefighters in Iowa were killed in 1998 when they were about 100 ft from the side of an LP-Gas vessel that eventually failed as a BLEVE and projected fragments in all directions.9 Secondary fragment hazards have been documented and generalized through analyses of damage and casualties at major explosions. Oswald et al.10 conducted such an analysis for five buildings damaged in the 1995 Oklahoma City bombing. The 4000-lb ammonium nitrate fuel oil explosion in that incident had an estimated TNT equivalence of 3400 lb. Using data from that and other incidents, Oswald et al. developed a correlation for the percentage of building occupants that are expected to experience life-threatening injuries due to glass shard projectiles, building roof damage, and wall damage. Implementation of the Oswald et al. model requires calculations of blast wave impulse at the lo-
CHAPTER 8
TYPES OF EXPLOSIONS Flammable Gas and Vapor Deflagrations Ignition of a gas–air mixture usually results in a deflagration, that is, a flame propagation at subsonic speed away from the ignition site. The pressure developed in the enclosure depends on the extent of flame propagation, the temperature and composition of the burned gas, and the size and location of any vent area. If the flame has propagated throughout an unvented enclosure, the ratio of the deflagration pressure to the initial pressure in the enclosure can be obtained from the ideal gas equation as it applies to the postdeflagration and predeflagration gas-air mixtures, both of which occupy the same enclosure volume. Thus, Pm nT C b b P0 n0T0
(2)
where Pm C pressure developed at the completion of a closed vessel deflagration P0 C initial pressure in the enclosure nb C number of moles of burned gas at the completion of the deflagration n0 C number of moles of gas–air mixture initially in the enclosure Tb C temperature of the burned gas at the completion of the deflagration T0 C initial temperature of the gas-air mixture Conservative estimates of burned gas temperature and composition can be obtained using the assumption that there is no heat loss from the flame to the enclosure walls. Assuming there is no heat loss or venting, various computer codes are available to calculate the burned gas temperature, composition, and pressure at the completion of the deflagration. Calculations obtained with the STANJAN code are shown in Figure 2.8.5 for the closed vessel deflagration pressures for methane-air, propaneair, and hydrogen-air mixtures of varying concentration. The fuel concentration used in Figure 2.8.5 is the equivalence ratio, defined as the fuel-to-air ratio divided by the stoichiometric fuelto-air ratio. In terms of the fuel volume fraction, x, the equivax (1 > x ) lence ratio is equal to xst (1 > stx) where x st is the stoichiometric volume fraction of fuel. The stoichiometric fuel volume fraction for methane-air is 0.095, for propane-air 0.040, and for hydrogen-air 0.296. The maximum pressures for each flammable gas occur at fuel equivalence ratios in the range 1.1 to 1.2, that is, at slightly richer than stoichiometric concentrations. These worstcase deflagration pressures are in the range of 8 to 9.6 atm absolute (118 to 140 psia) for an initial pressure of 1 atm, that is, the ratio Pm/P0 is 8 to 9.6. Experimental measurements of closed vessel deflagration pressures agree well with the theoretical values of Pm at near-stoichiometric concentrations, but are significantly less than the theoretical values at concentrations near the
Explosions
2–123
lower and upper flammable limits because of incomplete flame propagation and heat losses for marginally flammable mixtures. Similar Pm/P0 pressure ratios occur for closed-vessel deflagrations initiated at other initial pressures. One example of a deflagration initiated at a lower initial pressure is the Center Wing Tank explosion that occurred during the TWA 800 flight on July 17, 1996. The flammable vapor in the Center Wing Tank of the Boeing 747 on that flight came from a small quantity of Jet A fuel in the tank. Although the composition of Jet A is complicated, many of the volatile constituents have flame temperatures and deflagration pressures similar to those of methane and propane. As the fuel was heated from air conditioning equipment under the Center Wing Tank, and the partial pressure of tank air was reduced as the Boeing 747 climbed after takeoff, the fuel–air equivalence ratio increased well into the flammable range. Ignition occurred at an altitude of 14,000 ft, at which the ambient pressure is 0.585 bar (8.6 psia). A deflagration pressure ratio of 6 at that initial pressure would correspond to a Pm of 6 (8.6 psia) C 52 psia, and Pm > P0 C 43 psi. This pressure difference was significantly higher than the strength of the Center Wing Tank structures, leading to a massive breakup of the Boeing 747. The rate of pressure rise in a gas or vapor deflagration is a crucial factor in determining the effectiveness of protection measures such as deflagration venting and suppression. Flame speeds, enclosure volume, and the value of Pm are the primary parameters governing the rate of pressure rise. Theoretical models described in the chapter on explosion protection of the SFPE Handbook of Fire Protection Engineering11 allow the transient pressure rise to be calculated for any gas-air mixture with a known burning velocity (rate of flame propagation relative to the unburned gas velocity). Calculated pressure histories for three different sets of conditions are shown in Figure 2.8.6. During the early stages of the deflagration, the pressure rise varies as (Sut/a)3 , where Su is the mixture burning velocity and a is the radius of a sphere with the same volume as the enclosure. The burning velocities of 45 cm/s and 300 cm/s used for the calculations represent laminar burning velocities for near-stoichiometric propane-air mixtures and hydrogen-air mixtures, respectively. Flame speeds are often
Closed Vessel Deflagration Pressures 10 Propane
9 Pmax (atm)
cation of the exposed building as well as specifications of the type of building wall and roof construction.
■
8 Methane
7
Hydrogen
6 5 4 0
0.2
0.4
0.6
0.8 1 1.2 Equivalence ratio
1.4
1.6
1.8
FIGURE 2.8.5 Calculated Adiabatic, Constant Volume Pressures as a Function of Equivalence Ratio
2
2–124 SECTION 2 ■ Basics of Fire and Fire Science
0.5 m radius, 45 cm/s burning velocity 1 m radius, 300 cm/s burning velocity 20 18 16
Pressure (psig)
14 12 10 8 6 4 2 0
0
0.1
0.2 Time (s)
0.3
0.4
FIGURE 2.8.6 Calculated Pressure versus Time during the Early Stages of Three Different Deflagrations
significantly higher than the burning velocities because they include the velocity of the unburned gas as it is compressed by the expanding burned gases behind the flame front. The curve in Figure 2.8.6 for a 1-m radius enclosure containing a gas–air mixture with a burning velocity of 45 cm/s shows the pressure rising to 2 psig in about 0.2 s. If the damage threshold for the enclosure is 2 psig, deflagration venting or suppression would have to be actuated within 0.2 s of ignition to prevent damage in this case. The pressure developed in a vented or suppressed deflagration is denoted by Pred . Methods and guidelines for determining Pred are discussed elsewhere in this Handbook, and in NFPA 68, Guide for Venting of Deflagrations, and NFPA 69, Standard on Explosion Prevention Systems. If the deflagration pressure causes the enclosure to open (because of either deflagration venting or structural failure), a blast wave will exert pressure loads on adjacent structures. Blast waves emitted from vented deflagrations are very different than those discussed earlier from condensed phase explosives and burst pressure vessels. The blast wave energy is difficult to define and locate because the combustion energy is released both inside and outside the enclosure. Correlations discussed by Forcier and Zalosh12 indicate that the blast wave pressure is proportional to Pred/d, where d is the line-of-sight distance from the enclosure vent.
Gas Detonations A detonation is an explosion in which the flame propagates at supersonic speeds through the unburned fuel. Detonations are fundamentally different than the closed vessel deflagrations described in the previous section of this chapter. As flames in a deflagration propagate at speeds well below the speed of sound, whereas pressure disturbances propagate at sound speed, the pressure increase during a deflagration occurs virtually uni-
formly throughout the enclosure as the explosion evolves. In contrast, the pressure rise during a detonation is highly nonuniform and occurs virtually instantaneously as the shock wave propagates through the gas-air mixture. If the flame speed is slightly lesser than the speed of sound, such that the pressure rise is nonuniform but shock waves do not occur, the explosion is called a quasi-detonation. The practical significance of this fundamental difference between detonations and deflagrations is that they require different approaches to explosion protection. The sudden, spatially nonuniform pressure rise during a detonation or quasi-detonation precludes the use of explosion venting or explosion suppression systems. Furthermore, the high-peak, short-duration detonative pressure loads warrant special considerations in the evaluation of structural resistance. Methods for designing and analyzing detonation resistant structures are discussed in Reference 5. Peak pressure during a detonation can be calculated from the classical Chapman-Jouguet theory, which is a combination of thermochemical equilibrium and gas dynamic conservation equations across the detonation front. Figure 2.8.7 shows calculated detonation pressures as a function of fuel concentration for seven different flammable gases. A good approximation to the Chapman-Jouguet detonation pressure, PCJ , is PCJ C 2Pm, that is, twice the closed vessel deflagration pressure. This approximation represents a much simpler alternative to the Chapman-Jouguet theory of calculating detonation pressures. As indicated in Figure 2.8.7, PCJ for a near-stoichiometric gas-air mixture initially at atmospheric pressure is in the range 16 to 20 atmospheres. The different pressure loads during deflagrations and detonations produce characteristically different structural failure modes on equipment and structures. The slower pressure loadings in deflagrations usually cause ductile metals to fail by bulging out and stretching. The rapid impulsive loads in detonations often cause sharp fractures of metal, plastic, and wood structures. Photographs of the detonation fracture patterns on the fragments of a large reactor vessel are included in the Jacobs et al. paper describing the detonation that destroyed a large petroleum refining unit in Indiana.13
Ethylene oxide
25
Vinyl chloride
Butadiene Detonation pressure, Bars
1 m radius, 45 cm/s burning velocity
20
15
10 Propane
Ammonia
Ethylene
5 Methane 0
0
5
FIGURE 2.8.7 Pressures
10
15 20 % by Volume Fuel
25
30
35
Calculated Chapman-Jouguet Detonation
■
CHAPTER 8
What is the likelihood of a detonation occurring rather than a deflagration? Most accidental explosions are deflagrations. However, detonations can occur in very flammable gas mixtures if there is an exceptionally strong or large ignition source (flame jet ignition for example), a highly elongated geometry, or an exceptionally high level of turbulence to promote flame acceleration. In the case of a weak (typical accidental) ignition source in a pipe or some other elongated enclosure, the deflagration-todetonation transition (DDT) distance depends on the following parameters: • Mixture reactivity. The more reactive the mixture, the more rapid the flame acceleration to DDT. • Enclosure or pipe wall roughness and the presence of obstruction. The rougher the pipe interior surface or the more obstructions present, the shorter the transition length to DDT. • Enclosure or pipe diameter. The larger the enclosure or pipe diameter, the shorter the transition to DDT. • Initial pressure and temperature. The higher the initial temperature and pressure, the shorter the transition length to DDT. • Initial turbulence level. The more turbulence or initial gas velocity in the enclosure, the shorter the DDT transition length. In the absence of any obstructions and initial turbulence, data reviewed in Reference 11 indicate that length-to-diameter
TABLE 2.8.2
Explosions
ratios greater than 100 are needed for DDT in most hydrocarbon-air mixtures. Thus, detonations are much more likely to occur in large piping systems rather than in building explosions or process vessel explosions. This demonstrates the importance of preventing long propagation lengths by using the various deflagration isolation systems described in NFPA 69.
Combustible Dust Deflagrations Clouds of combustible dust in an enclosure also produce deflagrations when they are ignited while the dust concentration is greater than the minimum explosive concentration (MEC) for a particular material. The MEC depends on dust particle size as well as material composition, with smaller particles having smaller MECs than larger particles have. Typical lower explosive limits for dusts with characteristic particle sizes less than about 100 5m are in the 30–60 g/m3 range. Some examples for representative dusts and particle sizes are shown in Table 2.8.2.14 The other parameters shown in Table 2.8.2 are the maximum deflagration pressure in a closed vessel, Pmax , and the Kst parameter defined as follows: ‹ Kst C
dP dt
V 1/3
Activated carbon Aluminum Ascorbic acid Calcium stearate Coal, bituminous (high volatility) Corn starch Epoxy resin Fructose Methyl cellulose Milk powder Napthalene Paper tissue dust Phenolic resin Polyethylene, l.d. Polyethylene, l.d. Polyvinylchloride Rubber Silicon Sugar Zinc
(3)
max
where (dP/dt)max C maximum rate-of-pressure rise measured in a test vessel of volume V.
Explosibility Data for Representative Powders and Dusts
Material
2–125
Median Particle Size (5m)
Minimum Explosive Concentration (g/m3)
Pmax (bar g)
KST (bar-m/s)
18 <10 39 <10
60 60 60 30
8.8 11.2 9.0 9.2
44 515 111 99
4 <10 26 200 37 165 95 54 <10 <10 150 25 80 <10 10 <10
60 — 30 60 30 60 15 30 15 30a 125 125 30 125 60 250
9.1 10.2 7.9 7.0 10.1 8.1 8.5 8.6 9.3 8.0 7.4 8.2 8.5 10.2 8.3 6.7
59 128 129 28 209 90 178 52 129 156 54 42 138 126 75 125
a This value was measured in a 1.2-L vessel; all other values were measured in either a 20-L vessel or a 1-m3 vessel. Source: Dust Explosions in the Process Industries, by Rolf K. Eckhoff. Reprinted by permission of Butterworth-Heinemann.
2–126 SECTION 2 ■ Basics of Fire and Fire Science
Laboratory tests are usually conducted in a 20-L spherical vessel per the ASTM E1226 standard. The magnitude of Kst depends on the dust reactivity, the particle size, and the level of turbulence used to generate the dust cloud. Higher turbulence levels produce higher rates of pressure rise. Larger the Kst value, more difficult it is to achieve effective deflagration venting or suppression. Thus, Kst for dusts plays a similar role as the burning velocity, Su, does for flammable gases. Dust cloud concentrations above the MEC values are experienced routinely in process equipment such as dust collectors, blenders, dryers, pulverizers/grinders, conveying systems, and silos/bunkers. Tabulations of dust explosions in Germany from 1965 to 1985 indicate that 78 percent of all dust explosions originate in this equipment. Ignition sources that have occurred in dust explosions in Germany and in U.S. grain elevator explosions are shown in Table 2.8.3. The most frequent ignition source reported in the German dust explosions is mechanical sparks, presumably, impact or friction sparks. Impact sparks are often attributable to tramp metal in either conveying systems or pulverizers/grinders. The most frequent ignition source in U.S. grain elevator explosions investigated by Kauffman15 is mechanical heating/friction of belt drives in bucket elevators. Electrostatic discharges have been responsible for initiating explosions of dusts and powders, such as tantalum, with high resistivities and low ignition energies.16 Guidance on eliminating these dust explosion ignition sources is provided in NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids. Most of the damage and casualties in destructive dust explosions occurs as a result of secondary explosions. A secondary dust explosion is caused by dust layers on floors, equipment, and structures being dispersed by the blast wave of the primary explosion, and then being ignited by the flame emitted from the primary explosion. This process, illustrated in Figure 2.8.8, is particularly destructive when it occurs in confined and occupied
TABLE 2.8.3
Ignition Sources in Dust Explosions
Ignition Source Mechanical sparks Smoldering nests Mechanical heating, friction Electrostatic discharges Fire Spontaneous ignition Hot surfaces Cutting/welding Electrical equipment Unknown/Others a
Percentage of Dust Explosions in Germanya
Percentage of Dust Explosions in U.S. Grain Elevatorsb
26.2 11.3
4.6 13.6
9.0 8.7 7.8 4.9 4.9 4.9 2.8 19.5
22.7 0 9.1 0 9.1 6.8 15.9 18.2c
Based on Table 1.7 of Reference 14. Based on data reported in Reference 15. c Includes 13.6 percent gas explosion initial events. b
Primary explosion
Blast wave
Dust layer is entrained and dust cloud formed.
(a)
Extensive secondary explosion can result. (b)
FIGURE 2.8.8 Secondary Dust Explosion Schematic (Source: Reference 14)
areas. Accounts of 14 grain dust explosions investigated in Reference 15 indicate that 17 of 20 fatalities, 58 of 65 injuries, and $36 million of the $37 million in property damage were due to the secondary explosions in these incidents. Prevention of these secondary explosions requires using effective protection measures for the primary explosion and minimizing dust accumulations in surrounding areas. However, this is a major challenge because dust layers as thin as 1 mm can generate an average dust cloud concentration of 100 g/m3 (above the MEC for most combustible dusts) when dispersed throughout a 5-m high room.14 Partial dispersal over a lesser height can generate a still larger concentration, with correspondingly increased damage potential.
Chemical Reaction Explosions Uncontrolled chemical reactions can cause explosions in two ways. First, they can produce gaseous reaction products that can overpressurize vessels that are not equipped with an adequate relief vent area. Second, runaway exothermic reactions can generate sufficient heat to rapidly increase the pressure of the existing gases and vapors in the vessel and possibly vaporize other materials. Fire protection personnel are familiar with hydrocarbon combustion reactions, which produce carbon dioxide and water vapor as complete reaction products. There are also several other types of generic chemical reactions that can occur as fast as or faster than hydrocarbon combustion reactions at elevated temperatures, and can also produce multiple gaseous reaction products. These reactions include decompositions and polymerizations of inherently unstable compounds, rapid oxidation-reductions, nitrations, diazotizations (formation of a salt containing two nitrogen atoms and an aromatic hydrocarbon group), and hydration of waterreactive materials. Several of these reactions are autocatalytic in the sense that reaction products catalyze the reaction of the remaining reactants. Recent examples of chemical reaction explosions are shown in Table 2.8.4. The last two incidents in Table 2.8.4 have some remarkable similarities. They were both multiple fatality incidents caused by the detonative decomposition of hydroxylamine (NH2OH). In
CHAPTER 8
TABLE 2.8.4 Date
■
Explosions
2–127
Recent Chemical Reaction Explosions Location
Chemicals
Cause of Accident
Casualties
Reference
March 11, 1997
Tokai, Japan
Asphalt, sodium nitrate, sodium nitrite, sodium carbonate, and sodium bicarbonate
Excessive concentration of sodium bicarbonate lowered the reaction onset temperature
37 people received some radioactive contamination
17
March 26, 1997
Haskell, Oklahoma
Printing ink solvents and oxidizers
Mixing of incompatible chemicals
1 fatality, 2 injuries
18
April 8, 1998
Patterson, New Jersey
Ortho-nitrochlorobenzene, 2-ethylhexylamine
Delayed cooling of reactor, Inadequate emergency vent
9 injuries
19
October 13, 1998
South Baltimore, Maryland
Powdered aluminum, aluminum chloride, and water
Excessive steam addition rate produced uncontrolled reaction with aluminum.
5 injuries
20
February 19, 1999
Hanover Township, Pennsylvania
Hydroxylamine
Excessive concentration of unstable material
5 fatalities, 14 injuries
21
June 10, 2000
Gunma, Japan
Hydroxylamine
Excessive concentration of unstable material, High concentration of iron from coated steel tube
4 fatalities, 58 injuries
22
both cases, the aqueous solution hydroxylamine concentration was significantly higher than the normal recommended practice (A50% HA). Laboratory tests have shown that these high concentrations, together with trace contaminants, can lead to particularly violent decomposition reactions, often in the form of a detonation. How can chemists and regulatory authorities recognize the potential for chemical reaction explosions and take appropriate actions to prevent them? The AIChE Center for Chemical Process Safety has published guidelines23,24 to answer this question. These guidelines call for a combination of the following: 1. Reviewing lists of unstable materials (e.g., Reference 25) and potentially dangerous reactive combinations of materials 2. Using software to help identify incompatible chemicals (e.g., Reference 26) and to characterize the reaction energy associated with unstable chemicals (e.g., Reference 27) 3. Conducting reactivity laboratory screening tests to determine reaction onset temperatures, concentrations, and sensitivities 4. Having experts review the material storage/handling/processing conditions and results of screening tests, literature review, and software calculations The design of process controls and emergency vents to accommodate these hazardous reactions requires scale-up calculations based on the reaction chemistry, material thermodynamic properties, expected heat transfer rates, and the possible presence of two-phase vent flow regimes.28 After the design is completed, on-site audits are necessary in view of the reported poor record of many facilities in properly installing and maintaining pressure relief devices.29
Steam Explosions: Melt-Water Explosive Interactions A steam explosion is a physical explosion caused by the extremely rapid vaporization of water due to heat transfer from a second liquid that is at a temperature far in excess of the water boiling point and in direct contact with the water. As the second liquid is usually either molten metal or some other melt, a steam explosion is a violent melt-water interaction. If the water is replaced with some other liquid that has a much lower boiling point than the hot liquid, the more general term is vapor explosion. Steam explosions only occur if certain thermodynamic and hydrodynamic conditions are satisfied. The thermodynamic condition is that the liquid–liquid contact surface temperature, Tcon, must be greater than the spontaneous nucleation temperature, Tsn, for water, that is, the temperature at which vapor bubbles first appear in the absence of any heated surfaces. The equation for Tcon follows:30 ƒ TH = TC (k:c)c /(k:c)H ƒ Tcon C (4) 1 = (k:c)c /(k:c)H where TH C hot liquid temperature TC C cold liquid temperature k:c C product of thermal conductivity, density, and specific heat for either the hot liquid or cold liquid, depending on the subscript
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For example, if molten copper at a temperature of 1400°C is immersed in 20°C water, the interfacial contact temperature as per Equation 4 is 1341°C. If molten cuprous oxide at a temperature of 1330°C is immersed in 20°C water, the calculated interfacial contact temperature is 954°C.31 In both cases, the contact temperature is substantially higher than the spontaneous nucleation temperature for water, which is very sensitive to surface tension changes due to additives or contaminants, but can be as high as 270°C. Thus, molten copper interactions with water can indeed be explosive. Similar results are observed with many other molten metals and with kraft smelt immersions into water. The latter have been associated with black liquor recovery boiler accidents at paper mills. The liquid temperature criterion is a necessary, but not sufficient, condition for the occurrence of steam explosions. For the vaporization to occur rapidly enough and in sufficient volume to generate potentially damaging pressures, it is necessary to have ample liquid–liquid interfacial contact area. The consensus among steam explosion researchers32 is that a large-scale steam explosion also requires premixing of the liquids, triggering of vapor film collapse, and rapid propagation of vapor zone collapse subsequent to triggering, as illustrated in Figure 2.8.9. The upper left diagram in Figure 2.8.9 shows numerous drops of melt falling through water, which is the required premixing. The upper right sketch shows that each melt drop is surrounded by a water vapor film associated with film boiling of water around the perimeter of the drop. The lower right-hand diagram shows the vapor film being penetrated by a small jet of melt, thus triggering film collapse. The lower middle diagram shows the interaction continuing via the fragmentation of the original drop into numerous jet fragments. As the jet fragments are propelled into the surrounding water, they explosively vaporize the water in a rapidly expanding region shown in the lower left-hand corner of Figure 2.8.9. This rapid vaporiza-
Water Melt
tion/expansion provides the energy needed to drive a shock wave through the liquid and the adjacent area. Our current limited understanding of the phenomena illustrated in Figure 2.8.9 does not allow a priori predictions of all the conditions that may result in steam explosions as opposed to less violent vaporization interactions. On the other hand, there have been several interesting empirical studies to help us anticipate the kinds of melts, containers, and mixing conditions that are more likely to lead to steam explosions. For example, Nelson33 reports that smelt-water explosions do not occur when the water temperature is greater than 187°F (86°C), and Zyskowski31 reports that molten tin–water explosions do not occur at water temperatures above 60°C. Long34 did some pioneering experiments that showed how the bottom surface of the water container influences the likelihood of an explosion when molten aluminum was poured into the container. A rusty container base would promote steam explosions, whereas a greased or oil-coated or painted container base would prevent such explosions. These surface treatments change the wettability of the surface and the probability of a water film being trapped beneath a molten aluminum puddle. Later experiments have confirmed that molten aluminum–water explosions will not occur without either a wetted solid wall or high-velocity injection of one liquid into the other.30 Other experiments have shown how water additives can change the likelihood of molten metal–water or smelt–water explosions by altering the water viscosity or surface tension. When a steam explosion does occur, it often produces peak pressures in the range of 30 to 1000 psig, with pressure rise times of the order of a millisecond. Significantly lower pressures have also been observed under marginal conditions that produce rapid vaporization in the absence of shock waves. Vapor explosions have also been observed during at least some mixing conditions with the following pairs of liquids: Freon-22 and heated mineral oil, water and liquid nitrogen, liquid ethane and water,30 molten nuclear reactor fuel and water, and molten zirconium oxide and water.32
Vapor Cloud Explosions Water vapor
Melt
A vapor cloud explosion is a combustion explosion that follows the release of a large quantity of flammable gas or vapor in an outdoor area with conditions that promote rapid flame speeds and associated pressure increases. The following conditions promote rapid flame speed:
Melt Melt
Melt
Melt
Premixing of melt and water
ck wave propagatio n Sho
Melt
Rapidly expanding vapor
FIGURE 2.8.9
Melt fragmentation
Vapor film penetration
Steam Explosion Phenomena
• Turbulent jet releases • Partial confinement due to large structures or buildings in the release area • Repeated obstructions usually due to congested process equipment and piping • Ignition delays that allow the formation of large clouds with vapor-gas concentrations above the lower flammable limit Flame speeds needed to generate potentially damaging overpressures in a virtually unconfined area are of the order of 100 m/s. As the level of confinement increases, the required flame speeds decrease. The levels of turbulence or obstructions and the size of the cloud needed to generate such flame speeds depend on the reac-
CHAPTER 8
tivity of the flammable gas or vapor. Highly reactive gases or vapors with large laminar burning velocities, and those more prone to flame accelerations are more likely to be involved in vapor cloud explosions. Some of the vapors that have been involved in large numbers of vapor cloud explosions include propane, propylene, ethylene, and various aromatic hydrocarbons. Table 2.8.5 lists the vapor cloud explosion incidents described in the CCPS Guidelines.35 The gas or vapor and quantity released, and the numbers of reported casualties are shown in the table. The large number of fatalities in the 1948 Ludwigshafen incident was due to the release occurring in a populated area. The large number of fatalities in the 1989 Ufa incident was due to the cloud being ignited as two passenger trains were passing each other. These incidents, and the Flixborough and Pasadena incidents, demonstrate that vapor cloud explosions can be the most catastrophic of all accidental explosions. The same conclusion can be drawn from considerations of property damage. Lenoir and Davenport36 have provided a much more extensive compilation of vapor cloud explosion incidents. A better understanding of how vapor cloud explosions differ from nonexplosive ignitions of large vapor clouds can be obtained from a review of the flame acceleration factors in these incidents. The Ludwgshafen, Raunheim, Flixborough, Pasadena, and Kuwait incidents all occurred in petrochemical processing facilities with highly obstructed processing areas containing pipe racks, process columns, tanks, and so on. The Kuwait incident is particularly interesting because there were eight separate processing areas, each one corresponding to a blast center with damage caused by relatively high pressures. According to Reference 35, the Port Hudson explosion was ignited inside a concrete block warehouse, and then propagated outside into a rural area. The Ufa explosion was ignited by one of two passing trains. Trees in a heavily forested area around the tracks may have also contributed to the flame acceleration in the Ufa explosion. Predictions of pressure damage from vapor cloud explosions consist of two parts. In the vicinity of the cloud, pressures depend on estimated flame speed and level of confinement. Theoretical calculations performed by Strehlow et al.37 and described in the CCPS Guidelines show how the pressure generated in the cloud varies with flame speed. Guidance on estimating flame speeds
TABLE 2.8.5
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and confinement for vapor cloud explosion predictions have been developed by Baker et al.,7 and the resulting method is called the Baker-Strehlow method. Predictions of blast wave pressures outside the cloud entail using curves of shock pressure, Pso, versus an energy-scaled dimensionless distance, defined as follows: RC
rP01/3 E 1/3
[5]
where r C distance from the blast epicenter P0 C atmospheric pressure E C combustion energy that contributes to the blast wave The computation of E involves estimating the amount of flammable vapor released and the yield, that is, the fraction of the theoretical combustion energy contributing to the blast wave. An essential part of the Baker-Strehlow method is the choice of an appropriate yield value for gases or vapors of various reactivity classes. Another important step in the method is the selection of the appropriate flame speed or Mach number curve to use. The effect of using the Baker-Strehlow curves, or similar curves generated by other researchers, is that the blast wave pressure at a given energy-scaled distance is higher than what would be predicted using the curve shown in Figure 2.8.3, which was based on correlations for blast pressures produced by condensed phase explosives. Thus, vapor cloud explosions represent a more extensive damage and injury potential for a given blast wave energy. This is consistent with the observed areas of destruction in many of the large vapor cloud explosion incidents.
SUMMARY An overview of explosion fundamentals is provided in terms of the relationship between peak pressure and energy release magnitude and duration for various types of explosions. Ideal blast wave propagation and scaling relations are also discussed along with a brief summary of primary and secondary fragmentation
Noteworthy Vapor Cloud Explosion Incidents
Date
Location
July 28, 1948 January 16, 1966 December 9, 1970 June 1, 1974 March 26, 1980 June 3, 1989 1989 July 2000
Ludwigshafen, Germany Raunheim, Germany Port Hudson, Missouri Flixborough, UK Enschede, The Netherlands Ufa, Russia Pasadena, Texas Kuwait
Source: Reference 35 and NTSB Report PAR-72-1, 1972.
Flammable Gas or Vapor Dimethyl ether Methane Propane Cyclohexane Propane Natural gas liquids Ethylene C3 + C4 Hydrocarbon condensate
Quantity Released (kg)
Deaths
Injuries
30,400 500 23,000 30,000 750 ? ? ~80,000
207 1 0 28 0 645 25 7
3818 5 10 36 0 >1000 ? ~3
Casualties
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effects. The following specific types of explosions are briefly described: flammable gas and vapor deflagrations, gas detonations, combustible dust deflagrations, chemical reaction explosions, steam explosions, and vapor cloud explosions.
BIBLIOGRAPHY References Cited 1. Glasstone, S., and Dolan, P., The Effects of Nuclear Weapons, 3rd ed., 1977, for sale by Government Printing Office (see sections 2.03 and 2.115). 2. Wharton, R., Formby, S., and Merrifield, R., “Airblast TNT Equivalence for a Range of Commercial Blasting Explosives,” Journal of Hazardous Materials, Vol. A79, 2000, pp. 31–39. 3. Cruice, W., “Explosions,” Fire Protection Handbook, 18th ed., NFPA, Quincy, MA, 1997. 4. Strehlow, R., “The Characterization and Evaluation of Accidental Explosions,” NASA CR 134779, 1975. 5. U.S. Department of Defense, Structures to Resist the Effects of Accidental Explosions, TM5-1300, 1992. 6. Kinney, G., and Graham, K., Explosive Shocks in Air, 2nd ed., Springer-Verlag, 1985. 7. Baker, W., Cox, P., Westine, P., Kulesz, J., and Strehlow, R., Explosion Hazards and Evaluation, Elsevier, New York, 1983. 8. CCPS, Guidelines for Consequence Analysis of Chemical Releases, AFCGE, 1999. 9. Chemical Safety Board, “Propane Tank Explosion (2 Fatalities, 7 Injuries),” Investigation Report No. 98-007-I-IA, 2000. 10. Oswald, C., and Baker, Q., “Vulnerability Model for Occupants of Blast Damaged Buildings,” Proceedings of the AIChE Loss Prevention Symposium, Paper No. 3C, 2000. 11. Zalosh, R., “Explosion Protection,” SFPE Handbook of Fire Protection Engineering, 3rd ed., SFPE, NFPA, 2002. 12. Forcier, T., and Zalosh, R., “External Pressures Generated by Vented Gas and Dust Explosions,” Journal of Loss Prevention in the Process Industries, Vol. 13, 2000. 13. Jacobs, R. B., Bulkley, W. L., Rhodes, J. C., and Speer, T. L., “Gaseous Detonation,” Chemical Engineering Progress, Vol. 53, 1957, pp. 565–573. 14. Eckhoff, R., Dust Explosions in the Process Industries, Butterworth-Heinemann, 1991. 15. Kauffman, C. W., “Recent Dust Explosion Experiences in the U.S. Grain Industry,” Industrial Grain Explosions, ASTM STP 958, 1986. 16. Matsuda, T., and Yamaguma, M., “Tantalum Dust Deflagration in a Bag Filter Dust-Collecting Device,” Journal of Hazardous Materials, Vol. A77, 2000, pp. 33–42. 17. Hasegawa, K., and Li, Y., “Explosion Investigation of AsphaltSalt Mixtures in a Reprocessing Plant,” Journal of Hazardous Materials, Vol. A79, 2000, pp. 241–267. 18. EPA, “Prevention of Reactive Chemical Explosions,” EPA 550F00-001, Apr. 2000. 19. Chemical Safety Board, “Investigation Report Chemical Manufacturing Incident (9 Injured),” Report No. 1998-06-I-NJ, 2000. 20. Chemical Safety Board, “Management of Change,” Safety Bulletin No. 2001-04-SB, Aug. 2001. 21. Chemical Safety Board, “The Explosion at Concept Sciences: Hazards of Hydroxylamine,” Case Study No. 1993-13-PA, Feb. 2002. 22. Tamura, M., “Accidental Explosion of Hydroxylamine,” Presented at the OECD-IGUS-EOS Meeting, Mar. 2001. 23. AIChE Center for Chemical Process Safety, Guidelines for Safe Storage and Handling of Reactive Materials, 1995. 24. AIChE Center for Chemical Process Safety, Guidelines for Chemical Reactivity Evaluation and Application to Process Design, 1995.
25. Fire Protection Guide to Hazardous Materials, 12th ed., National Fire Protection Association, Quincy, MA, 1997. 26. NOAA/EPA, “Chemical Reactivity Worksheet,” Version 1.2, National Oceanographic and Atmospheric Administration, 2000. 27. CHETAH Version 7.2, ASTM Computer Program for Chemical Thermodynamic and Energy Release Evaluation, ASTM DS51C, 1997. 28. Fauske, H., “Properly Size Vents for Nonreactive and Reactive Chemicals,” Chemical Engineering Progress, Feb. 2000, pp. 17–29. 29. Berwanger, P., Kreder, R., and Lee, W-S., “Analysis Identifies Deficiencies in Existing Pressure Relief Systems,” Process Safety Progress, Vol. 19, 2000, pp. 166–172. 30. Henry, R., and Fauske, H., “Nucleation Processes in Large Scale Vapor Explosions,” Journal of Heat Transfer, Vol. 101, 1979, pp. 280–287. 31. Zyszkowski, W., “Study of the Thermal Explosion Phenomenon in Molten Copper-Water System,” International Journal of Heat Mass Transfer, Vol. 19, 1976, pp. 849–868. 32. Bankoff, S., Cho, D., Cronenberg, A., Fauke, H., Henry, R., Hutcherson, M., Marciniak, T., Reid, R., and Thomas, G., “Steam Explosions—Their Relationship to LWR Safety Assessments,” NUREG/CP-0027, 1983, pp. 1388–1398. 33. Nelson, W., “A New Theory to Explain Physical Explosions,” Combustion, May 1973, pp. 31–36. 34. Long, G., “Explosions of Molten Aluminum in Water—Cause and Prevention,” Metal Progress, Vol. 71, 1957, pp. 107–112. 35. AIChE Center for Chemical Process Safety, Guidelines for Evaluating the Characteristics of Vapor Cloud Explosions, Flash Fires, and BLEVEs, 1994. 36. Lenoir, E. M., and Davenport, J. A., “A Survey of Vapor Cloud Explosions: Second Update,” Process Safety Progress, Vol. 12, 1993, pp. 12–33. 37. Strehlow, R., Luckritz, R., Adamcyk, A., and Shimpi, S., “The Blast Wave Generated by Spherical Flames,” Combustion and Flame, Vol. 35, 1979, pp. 297–310.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on explosions discussed in this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 68, Guide for Deflagration Venting NFPA 69, Standard on Explosion Prevention Systems NFPA 495, Explosive Materials Code NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids.
Additional Readings Allen, N., “Business is Booming,” Fire Prevention, No. 308, Apr. 1998, pp. 18–19. Bradish, J. K., “Explosions Rock Burning Chemical Plant in Michigan,” Firehouse, Vol. 22, No. 12, 1997, p. 64. Bradish, J. K., “Firefighter Among 5 People Killed in 1970 Refinery Fire,” Firehouse, Vol. 21, No. 7, 1996, pp. 85–86. Brown, R. J., “Classification for Dusts: An Update,” Power Engineering Journal, Vol. 14, No. 5, 2000, pp. 234–237. Cuzzillo, B. R., and Pagni, P. J., “Myth of Pyrophoric Carbon,” Proceedings of the 6th International Symposium, Fire Safety Science, International Association for Fire Safety Science (IAFSS), July 5–9, 1999, Poitiers, France, International Association Fire Safety Science, Boston, MA, 2000, pp. 301–312. Dahoe, A. E., Lemkowitz, S. M., Zevenbergen, J. F., Pekalski, A. A., and Scarlett, B., “Effect of Burning Velocity, Flame Thickness, and Turbulence on Dust Explosion Severity,” Proceedings of the 3rd International Symposium, Hazards, Prevention, and Mitiga-
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tion of Industrial Explosions, October 23–27, 2000, Tsukuba, Japan, 2000, pp. 60–65. DeHaan, J. D., Kirk’s Fire Investigation, 4th ed., Brady Fire Sciences Series, Prentice Hall, Inc., Upper Saddle River, NJ, 1997. Eckhoff, R. K., “Role of Powder Technology in Understanding Dust Explosions,” Proceedings of the 3rd International Symposium, Hazards, Prevention, and Mitigation of Industrial Explosions, October 23–27, 2000, Tsukuba, Japan, 2000, pp. 6–21. Fowler, A., and Hazeldean, J., “Catalogue of Errors,” Fire Prevention, No. 311, 1998, pp. 22–24. Gann, R. G., “FY2000 Annual Report. Next Generation Fire Suppression Technology Program (NGP),” National Institute of Standards and Technology, Gaithersburg, MD, NIST TN 1437, March 2001. “Gas Explosions,” Fire Findings, Vol. 6, No. 4, 1998, pp. 7–9. Gottlieb, J., “2 in 3 UCI Buildings Have No Sprinklers,” Los Angeles Times, July 26, 2001, pp. 1–5. Gottlieb, J., and Cholo, A. B., “Explosion in UC Irvine Science Lab Caused Less Damage than Feared,” Los Angeles Times, July 25, 2001, pp. 1–5. Gottlieb, J., and Cholo, A. B., “Orange County: UCI Fire Damage Less Than Feared,” Los Angeles Times, July 25, 2001, pp. 1–6. “Grain Elevator Explosion, Haysville, Kansas, June 8, 1998,” National Fire Protection Association, Quincy, MA, NFPA Fire Investigation Report, 1999. Haldane, D., and Martelle, S., “Lab Work Touches Off Blast, Fire in UC Irvine,” Los Angeles Times, July 24, 2001, pp. 1–4. Haldane, D., and Martelle, S., “Explosion, Fire Shake UCI Lab, Injuring Three,” Los Angeles Times, July 24, 2001, pp. 1–4. Ho, H. S., Hwan, K. J., and Woo, L. C., “Explosion Hazard of AirBorne Carbon Black Dust by Hartman’s Apparatus,” Journal of Applied Fire Science, Vol. 9, No. 1, 1999/2000, pp. 91–101. Ho, H. S., Hwan, K. J., Woo, L. C., and Hyung, K. W., “Explosion Hazard of Airborne Activated Carbon,” Journal of Applied Fire Science, Vol. 8, No. 3, 1998/1999, pp. 219–227. Kosanke, B., and Kosanke, K., “Physics and Chemistry of Pyrotechnic Explosives: A Primer,” Fire and Arson Investigator, Vol. 49, No. 1, 1998, pp. 54–57. Matsuda, T., Yashima, M., Nifuku, M., and Enomoto, H., “Some Aspects in Testing and Assessment of Metal Dust Explosions,” Proceedings of the 3rd International Symposium, Hazards,
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Prevention, and Mitigation of Industrial Explosions, October 23–27, 2000, Tsukuba, Japan, 2000, pp. 92–97. Mittal, M., and Guha, B. K., “Study of Ignition Temperature of a Polyethylene Dust Cloud,” Fire and Materials, Vol. 20, No. 2, 1996, pp. 97–105. Mniszewski, K. R., and Campbell, J. A., “Analytical Tools for Gas Explosion Investigations,” Proceedings of the 3rd International Conference on Fire Research and Engineering (ICFRE3), October 4–9, 1999, Chicago, IL, Society of Fire Protection Engineers, Boston, MA, 1999, pp. 339–350. Nifuku, M., and Enomoto, H., “Evaluation of the Explosibility of Malt Grain Dust Based on Static Electrification During Pneumatic Transportation,” Proceedings of the 3rd International Symposium, Hazards, Prevention, and Mitigation of Industrial Explosions, October 23–27, 2000, Tsukuba, Japan, 2000, pp. 166–171. Nifuku, M., and Katoh, H., “Incendiary Characteristics of Electrostatic Discharge for Dust and Gas Explosion,” Proceedings of the 3rd International Symposium, Hazards, Prevention, and Mitigation of Industrial Explosions, October 23–27, 2000, Tsukuba, Japan, 2000, pp. 240–245. Pierre, M., Philippe, G., and Isabelle, S., “Loss Prevention in France: An Overview of the Political and Administrative Organization as well as the Research Activities Related to Dust and Gaseous Explosions,” Proceedings of the 3rd International Symposium, Hazards, Prevention, and Mitigation of Industrial Explosions, October 23–27, 2000, Tsukuba, Japan, 2000, pp. 37–44. Tamanini, F., “DUSTCALC: A Computer Program for Dust Explosion Venting,” Proceedings of the Technical Symposium, Computer Applications in Fire Protection Engineering, June 20–21, 1996, Worcester, MA, pp. 35–40. Tamanini, F., “Scaling Parameters for Vented Gas and Dust Explosions,” Proceedings of the 3rd International Symposium, Hazards, Prevention, and Mitigation of Industrial Explosions, October 23–27, 2000, Tsukuba, Japan, 2000, pp. 80–85. Waft, J., “Major Explosion and Blaze Hits Avonmouth Chemical Complex,” Fire, Vol. 89, No. 1101, 1997, pp. 19–21. Wenzel, B. J., “Kansas Grain Dust Explosion,” Fire Engineering, Vol. 151, No. 11, 1998, pp. 65–66.
CHAPTER 9
SECTION 2
Environmental Issues in Fire Protection Jane I. Lataille
A
lmost all human activity can harm the environment. Manufacturing products, storing and using chemicals, burning fuel, and discarding wastes can cause pollution. More often than not, efforts made to protect the environment from these activities have raised new fire protection concerns. Likewise, many fire protection measures have added to environmental problems. Therefore, whenever attempts are made to reduce pollution or to protect a structure or a process from fire, the interrelationship between fire protection and the environment must be considered. This chapter presents an overview of the environmental issues related to fire protection. It is not an exhaustive review of environmental incidents that have affected or been affected by fire protection system design. For more specific information, see the bibliography at the end of this chapter. The first part of this chapter—pollution control—describes fire protection concerns introduced by pollution control measures. The second part of this chapter—fire protection systems— describes environmental problems that are related to fire protection systems and methods. The chapter summary explores the impact these interrelationships have on fire protection engineers.
General building ventilation systems use filters to remove particles from both fresh and recirculated air. If the filters burn, a ventilation system can spread smoke throughout a building. Because ventilation systems are enclosed, fires in them are difficult to locate and extinguish. Therefore, ventilation system filters should always be noncombustible, with the lowest possible smoke generation ratings. Ventilation systems also can be arranged to exhaust those portions of a building in which smoke has been detected and to pressurize adjacent areas simultaneously to prevent smoke leakage into them. An extreme case of controlling air quality is seen in today’s cleanrooms. The massive amounts of filters used in cleanroom air-handling systems make fire protection crucial. Although the filters may be noncombustible, the materials the filters collect can burn, causing damage to expensive cleanroom equipment and materials. Products of combustion from coated wiring and other plastics materials also can do extensive damage when circulated through the cleanroom air-handling system. Carefully designed air-handling systems with fast smoke detection and flexible air control are necessary parts of the fire protection design.
POLLUTION CONTROL
Vapors. One way to control air pollution is to collect vapors from vapor-producing processes. Collected vapors are then converted, incinerated, or recycled (recovered). Each of these three options for treating vapors needs protection. Catalytic conversion can involve enclosed vessels, high temperatures, and fluidized beds. The hazards needing protection include heated combustible materials, fuel-fired equipment, and the presence of ignitable vapors in enclosed spaces. Process monitoring and control are also important to safe operation. Incineration is done in flare stacks, in fuel-fired equipment designed primarily for incineration, or in fuel-fired equipment designed for some other purpose and modified to burn waste liquids or vapors. Incineration by flare often is used with emergency venting systems to burn off emergency discharges. Incineration by flare also is used when the nonemergency venting of vapors is not frequent enough to warrant their recovery. A flare stack is just a tall stack into which vapors are piped to be burned in a pilot flame at the top of the stack. The flame normally is monitored with a closed-circuit television camera or with thermal sensors. Stacks also must be monitored for safe air flows and oxygen levels so the stack gas mixture does not become explosive. Other than the protective measures normally taken for fuelfired equipment, incineration requires proper design of burners
Pollution may be classified as air, water, land, thermal, or noise pollution. Air, water, and land pollution generally imply pollution by substances. Thermal pollution is most often associated with water, and noise pollution with air. Efforts to control any type of pollution may raise fire protection concerns. These fire protection concerns can include ordinary combustible materials, flammable liquids, fuel-fired equipment, and other hazards that are inherent in pollution control systems.
Air Pollution Particles. Process-generated particles, such as dust, ash, or fibers, must be removed from the air to keep it clean. Such particles are removed with dry or wet dust collectors, or with electrostatic precipitators. Particle collection equipment can involve combustible dusts, heat- and friction-producing mechanical equipment, combustible filters, combustible collection bags, transformers, and other electrical equipment—all of which require protection. Jane I. Lataille, P.E., ARM, has over 25 years experience working in fire protection and loss prevention.
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and combustion safeguard logic to account for the different physical and chemical properties of the materials to be burned. Sometimes, this design includes the ability to switch from fuel to fuel or to burn different fuels simultaneously. Solvent recovery systems, as well as recycling solvents, reduce pollution. Recycling is now more common because laws require collection of vapors that were previously released to the atmosphere. Most solvent recovery systems have vapor collection ductwork, condensers, and liquid storage tanks. Activated carbon recovery systems absorb solvent that is then collected by steaming it out of the carbon. In some cases, collected solvent must be filtered, scrubbed, or distilled before it can be reused. Often, both “clean” and “dirty” solvent storage tanks are needed in a solvent recovery system. Each tank, piece of equipment, and process involving a solvent requires proper fire protection. Plastic ductwork often is used to collect vapors that corrode metal. The interior of this ductwork is a combustible concealed space that requires sprinkler protection. In addition, burning plastics emit dense, acidic smoke, so fire response must include actions that minimize corrosion of exposed equipment. Fluorocarbon Gases. The ozone level in Earth’s upper atmosphere is depleted when normally stable fluorocarbon molecules are broken down by ultraviolet radiation. Fluorine atoms thus freed from the fluorocarbon molecules then combine with single oxygen atoms from oxygen molecules that also have been broken down by ultraviolet radiation. These single oxygen atoms would normally combine with oxygen molecules to make ozone if the fluorine atoms were not present. Bromine and chlorine have the same effect as fluorine. As early as the 1970s, it was suspected that fluorocarbons had detrimental effects on the environment. International action to study these effects took place during the early 1980s and led to the Vienna Convention of 1985, when 27 countries signed an agreement to protect the ozone layer. Research continued, and in 1987, the Montreal Protocol was signed. This protocol froze the production of most fluorocarbons to 1986 levels by July 1989. It also called for further cuts in 1993 and 1998. After the Montreal Protocol was enacted, scientists determined that the ozone depletion problem was even more serious than previously thought. The London Amendments of 1990 mandated no fluorocarbon production by the year 2000. The Copenhagen Amendments of 1992 prohibited halon production as of January 1, 1994. (Halon is any bromine-containing fluorocarbon.) The Montreal Amendments of 1997 and the Beijing Amendments of 1999 set further restrictions on other fluorocarbons. In the United States, the U.S. Environmental Protection Agency (EPA) implemented measures to comply with the Montreal Protocol on a chemical-by-chemical basis, starting with the chemicals with the highest ozone depletion potentials. See the EPA website, at www.epa.gov, for information on chemical phase-out schedules and other information. Also see the United Nations environmental site, at www.unep.org. Fluorocarbons are used as refrigerants and propellants. To safeguard the environment, these fluorocarbons are being replaced by much more hazardous materials, such as hydrocarbons, alcohol, or ammonia. Use of the replacement substances
creates new fire protection problems. Fluorocarbons are also used as extinguishing agents. Other Gases. Any gas that is not normally present in Earth’s atmosphere may present a pollution problem if it gets into the atmosphere. The same is true of gases normally found in the atmosphere that are present in concentrations higher or lower than usual. Changes in the composition of the atmosphere affect its complex chemical balance and cause many other changes, the most well known of which is global warming. Gases believed to contribute to global warming are called greenhouse gases. Greenhouse gases warm Earth by reflecting back to Earth’s surface sunlight, which would otherwise have escaped the atmosphere. CO2 is the greenhouse gas that has received the most publicity. The greatest source of excess CO2 in the atmosphere comes from the combustion of fossil fuel. The cleanest-burning fossil fuel–fired equipment, which may release no conventional pollutants, releases water and CO2 as products of complete combustion. This process puts more CO2 into the atmosphere than is present naturally. Fossil fuel–burning equipment includes industrial boilers and furnaces; motor vehicles; and household appliances, such as furnaces, lawn mowers, leaf blowers, and snow blowers. It also includes the very large utility boilers used to generate the massive amounts of electricity used today. It is unlikely that the amount of excess CO2 entering the atmosphere will be reduced, but attempts can be made to control the increase. Two ways of controlling greenhouse gas emissions that may raise fire protection concerns are (1) changing chemical processes, which may add an unknown hazard while removing a known one, or (2) running fired equipment intermittently that once ran continuously, which increases the number of startups and shutdowns.
Water Pollution Building floors were once commonly sloped to holes called scuppers to allow water and other liquids to flow out of the building. Scuppers are no longer allowed in buildings. Now, all liquids must be contained and treated before they are released. Even large fire department training grounds are now built with thick, underground clay liners to contain all water discharged from practice fire fighting. This practice keeps Earth’s water from becoming (more) polluted. It also introduces an additional hazard if any pooled liquids are combustible or flammable. Polluted water is now treated with various types of chemicals. These chemicals can neutralize the water, react with harmful substances to inert them, or cause contaminants to settle out of the water. Fire protection must be considered when storing and using treatment chemicals that are hazardous. Sometimes, pollutants removed from the water are hazardous. A good example of this is oil spilled into the ocean by a tanker. Appropriate fire protection measures must be taken during collection and storage of such materials. Mixed pollutants may have to be separated further after removal because they may have different disposal requirements. Separation and other treatment equipment must be designed and arranged to handle the materials safely.
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The need to clean up Earth’s water affects more than the water being treated. Chemicals that were once allowed to be dumped into rivers and streams must now be collected and stored. Fire protection measures appropriate for storage and handling of hazardous materials must then be taken for these chemicals.
groundwater monitoring, and liquid level alarms. As an option to double walls, fiberglass tanks or tanks of other nonmetallic materials may be used. These tanks require especially careful installation because they crack or break much more easily than metal tanks, resulting in a higher potential for leaks.
Land Pollution
Thermal and Noise Pollution
Waste disposal is increasing due to the rising world population and industrial growth. Dumps and landfills are ravaging the land and contaminating groundwater, which serves as the source of public water supplies. Recycling helps restore the land, but recycling systems often entail more fire protection concerns. Recycling is an industry of its own, with many plants that do nothing else. These plants need basic fire protection and risk management programs, just as any other industry does. They must also deal with the hazards unique to their recycling processes. Plastics recycling involves grinding, melting, and extruding processes, as well as warehousing. Due to the burning characteristics of plastics, fire protection systems for their storage and handling must be designed carefully. Process equipment must be designed with due regard for the capacity of plastics to hold static charges. A fast-emerging recycling industry is the so-called trashto-cash business. In this industry, municipal waste is collected, separated, shredded, and burned to generate electric power. The hazards inherent in the generation of electrical power must be protected, as well as those unique to the storage of large amounts of combustible waste inside buildings and to the processing and burning of this waste. Unique protection problems include the large distance between the combustible waste and roof sprinklers, because of the need for large cranes or other materialshandling systems, and the special design of systems that safely burn waste with varying chemical content. Other materials now commonly recycled are glass, metal, paper, and wood. In each case, protection must be provided for the buildings, materials, and processes associated with recycling materials that used to be buried in the land and forgotten. Another strategy to eliminate sources of land pollution is to replace underground liquids storage tanks, especially those for gasoline and oil, with aboveground tanks. This strategy reverses the 1960s policy of burying tanks to reduce their fire protection problems, except now there are even more problems. To contain leaks from aboveground tanks, the tanks are provided with dikes sized to hold the contents of the largest tank within the dike. To keep spills from seeping into the ground, the surfaces of diked areas must be nonporous. If there is a spill, the ground must be dug up and tested. Contaminated ground must then be removed and treated as hazardous waste. Rainwater that collects in the dike must be tested before it can be released. If there are any contaminants, the water must be treated as hazardous waste. Although this treatment greatly reduces the chance of pollution, it increases the amount of fire protection needed. If underground tanks are necessary, they must be designed to minimize the potential for leakage. Design features include proper preparation of the tank bed, anchoring the tank, careful backfilling, using double walls on the tank, leak detection,
Concern for the environment rests mainly with the addition of physical pollutants to the air, water, and land. However, the need to control heat and sound also has had an effect on the fire protection engineer. For example, even pure water should not be dumped into a stream if it raises the temperature of the stream enough to affect its ecology. Elevated water temperatures can cause excessive algae growth and can be harmful to fish and other water life. Cooling towers reprocess cooling water to help alleviate thermal pollution of waterways and to help preserve Earth’s water. Because cooling towers are often of combustible construction or have combustible fill, they need fire protection systems. Heat preservation is good for global ecology. Heat preservation is also economical because fuel and fuel-burning equipment are expensive to buy and maintain. Insulating is a common way to preserve heat, but it introduces fire protection concerns in that many of the materials with good insulating properties are combustible and can emit toxic and acidic products of combustion when burning. The problem increases when such insulation is installed inside inaccessible spaces, such as closed-off attics and crawl spaces. Noise control requires careful design and placement of process equipment, as well as the use of soundproofing. Soundproofing materials introduce the same concerns that insulating materials do. They may be combustible, they may release toxic and acidic products of combustion when burning, and they may be installed in inaccessible places, such as inside air-handling ducts or process equipment.
FIRE PROTECTION SYSTEMS All fire protection system extinguishing agents can affect the environment. Of primary concern are halons. Like refrigerants and propellants, fire protection halons are fluorocarbons. The relationship between the fire protection halons and depletion of the ozone layer has drawn much attention. The most damaging halon is considered to be Halon 1301, which is the most common fluorocarbon used for fire protection. Although much attention is focused on halons, fire protection engineers must be aware of other sources of potential harm to the environment, such as other extinguishing agents.
Halons and the Ozone Layer Research has found that Halon 1301 has the highest ozone depletion potential of all the fluorocarbons, at least 10 times higher than the four most common fluorocarbon refrigerants. As a result, the fire protection community has had to move quickly to work out ways of acceptably controlling loss potential while minimizing the use of this previously well-accepted extinguishing agent.
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Full-flooding halon acceptance tests are now often replaced with pressure and puff tests to prove the integrity of the piping, and with door fan tests to prove room tightness. Pressure tests of piping can find leaks, which are usually caused by incorrectly fastened fittings. Puff tests confirm that there are no serious piping blockages. If properly done, a door fan test gives an accurate measure of expected extinguishing agent leakage. Procedures and calculations for door fan testing are now well developed and information on them can be found in NFPA 12A, Standard on Halon 1301 Fire Extinguishing Systems, and NFPA 2001, Standard on Clean Agent Fire Extinguishing Systems. These alternative methods of testing eliminate the dumping of halon into the environment from extinguishing systems testing. Halon release can be reduced further by carefully designing detection systems to suit the occupancies they protect, and by periodically inspecting, testing, and maintaining halon systems so that inadvertent discharge does not occur. Recovery of halon discharged from cylinders during hydrostatic testing is another way to reduce the amount of halon released into the environment. Figure 2.9.1 shows storage containers for FM 200, one of the clean agents. According to current U.S. EPA regulations, existing Halon 1301 systems may be kept in service; existing Halon 1301 reserves may be maintained; and Halon 1301 reserves may even be used in new systems when handled by qualified contractors. However, new Halon 1301 systems should be discouraged. One of many alternative protection methods should be appropriate for the hazard being protected. Two methods to consider immediately are (1) conventional sprinklers and (2) CO2 protection.
Alternative gaseous agents to Halon 1301, sometimes called clean agents, have also been developed. NFPA 2001, Standard on Clean Agent Fire Extinguishing Systems, addresses the use of these agents in extinguishing systems. Table 2.9.1 lists clean agents addressed by NFPA 2001, all of which are acceptable to the U.S. EPA. Another possible alternative to Halon 1301 systems is specially designed water mist systems. These are water-based systems that produce very fine mist and use much less water than conventional water-based systems. Water mist systems have long been used aboard ships but have only recently been developed for industrial use. At this time, only a few preengineered-type water mist systems have been listed for specific applications, such as enclosed machine rooms and turbine enclosures. The technology for these systems is still in its infancy. See NFPA 750, Standard on Water Mist Fire Protection Systems, and Section 10, Chapter 17 of this work for more information on water mist systems.
Other Special Extinguishing Agents Substances that get into the ground can contaminate groundwater. These substances include agents used in special extinguishing systems, such as dry and wet chemicals, fire protection foams, and the antifreezes sometimes added to wet-pipe sprinkler systems. It is becoming more common to enclose or dike areas protected with these agents so that they may be cleaned up after discharge. Sometimes, areas protected with these agents are drained to a suitably sized holding tank for later disposal (Figure 2.9.2).
TABLE 2.9.1 Agent FC-2-1-8 FC-3-1-10 HCFC Blend A
HCFC-124 HFC-125 HFC-227ea HFC-23 HFC-236fa FIC-13I1 IG-01 IG-100 IG-541
FIGURE 2.9.1 FM 200 Storage Containers (Source: GE GAP Services and Fenwal Protection Systems)
IG-55
Clean Agent Alternatives to Halon 1301 Chemical Name Perfluoropropane Perfluorobutane Dichlorotrifluoroethane HCFC-123 (4.75%) Chlorodifluoromethane HCFC-22 (82%) Chlorotetrafluoroethane HCFC-124 (9.5%) Isopropenyl-1methylcyclohexene (3.75%) Chlorotetrafluoroethane Pentafluoroethane Heptafluoropropane Trifluoromethane Hexafluoropropane Trifluoroiodide Argon Nitrogen Nitrogen (52%) Argon (40%) Carbon dioxide (8%) Nitrogen (50%) Argon (50%)
Formula C3F8 C4F10 CHCl2CF3 CHClF2 CHClFCF3
CHClFCF3 CHF2CF3 CF3CHFCF3 CHF3 CF3CH2CF3 CF3I Ar N2 N2 Ar CO2 N2 Ar
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FIGURE 2.9.2 Foam Storage Tank (Source: GE GAP Services and Rockwood Swendeman)
One of the early fire protection agents was carbon tetrachloride. This liquid, a precursor of the halogens, was known to be an effective extinguishing agent. Carbon tetrachloride was either put into pressurized containers with sprinklerlike operating mechanisms at the bottom, or it was sealed into glass bulbs for manually throwing at a fire, as shown in Figure 2.9.3. These containers or bulbs were once commonly placed in unsprinklered dead records storage rooms and in other small rooms. Carbon tetrachloride is no longer used because of its high toxicity. It has been replaced with alternative extinguishing agents, all of which must now be reviewed for their effects on the environment. Carbon dioxide is a nontoxic, relatively inert gas that is found naturally in the atmosphere. Carbon dioxide extinguishes fire by displacing the oxygen required for combustion and, therefore, poses a suffocation hazard. Careful system design with appropriate safety interlocks is used to mitigate this danger to people. Otherwise, carbon dioxide is an ideal extinguishing agent for protecting many hazards. However, the warming of Earth through the greenhouse effect is thought to be aggravated by excessive carbon dioxide. So now, even the use of this agent must be considered carefully.
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There have been many incidents in which sprinkler discharge has carried hazardous materials and posed a contamination hazard to drinking water. In a May 1987 paint plant fire in Dayton, Ohio, sprinkler discharge spread flammable liquids near potable water sources. There have also been incidents in which fire protection discharge contributed to air pollution. In these cases, chlorine gas was released from stored swimming pool chemicals when the chemicals were wetted by sprinklers. Two well-known incidents of this type occurred, one in June 1988 in Springfield, Massachusetts, and one in August 1988 in Glendale, Arizona. The effects of fire protection discharge must therefore be considered in the design of a protected facility and its site. Even if a facility existed that had no possible contaminants, the sprinkler system fed by a public water supply could still pose an environmental threat—that is, contamination of the public water supply through backflow. Pollutants can pass from the sprinkler system to the water supply through the normal backflow permitted by check valves. The pollutants come from the water pumped into the sprinkler system through the fire department connection. This water could be contaminated if a fire department used a nonpotable auxiliary source, such as a pond, or if the water in the fire department tankers was treated with anticorrosion chemicals. To keep sprinkler system water from contaminating public water supplies, many states and municipalities have passed laws pertaining to the arrangement of sprinkler systems. Some states and municipalities do not permit connections to the public supply if the fire protection system includes a suction or gravity tank. Others do not permit booster pumps. Antifreeze systems may not be allowed. In some cases, systems with tanks or pumps may be connected to the public water supply if double check valves are used.
Water-Based Fire Protection With most extinguishing agents posing some sort of environmental threat, an obvious solution is to use water-based extinguishing systems, such as sprinklers, water spray, deluge, and so on, wherever water is a suitable extinguishing agent. However, even water-based protection presents environmental concerns. Indeed, it is likely that discharge from water-based systems will be one of the biggest fire protection concerns of the coming century. When a sprinkler system operates, the water flows over whatever is burning and over anything else that is in the area of the sprinkler discharge. The water then collects and flows even farther, carrying potential contaminants that seep into the ground unless the protected area has been designed to contain the sprinkler discharge.
FIGURE 2.9.3 Old-Style Carbon Tetrachloride Extinguisher (Source: GE GAP Services)
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A requirement that is becoming more common for sprinkler systems is the installation of a reduced-pressure-principle backflow preventer wherever the potential for contamination of the public water supply exists (Figure 2.9.4). Interpretation of where a potential for contamination exists is often left to a state or municipality. Examples of the potential for contamination are the presence of a fire department connection on a sprinkler system, the proximity of a nonpotable suction source, or the addition of anticorrosion chemicals to fire department tanker water. The reduced-pressure-principle backflow preventer uses two check valves, two taps for pressure sensing, and a diaphragmoperated dump valve (Figure 2.9.5). The dump valve releases pressure in the backflow preventer’s zone of reduced pressure, which prevents backflow when the first check valve is closing. Although reduced-pressure-principle backflow preventers prevent backflow better than double check valves, they have many disadvantages, including high cost and excessive friction loss. Backflow preventers also can rob water from the sprinkler system, if the dump valve fails to close when it should. Manual fire-fighting efforts introduce the same environmentcontaminating potential that automatic fire protection systems do. Any water used to extinguish a fire can carry hazardous materials that were in the area of the fire. These materials can seep into the groundwater. Therefore, even unprotected facilities need careful site layout.
Fire Protection Measures Many measures have been taken for protection from fire, beyond installing automatic-extinguishing systems. Not surprisingly, these measures, too, are a source of environmental concern. PCBs (polychlorinated biphenyl) were used to replace most transformer dielectric fluids due to their low fire and explosion hazard compared with the formerly used combustible oils. Unfortunately, it was later learned that the stability that made PCBs safe from a fire protection standpoint also caused serious pollution problems—that is, PCBs are poisons that do not break down. PCB and PCB-contaminated transformers now must be retrofitted or replaced. PCBs also are found in capacitors, large circuit breakers (usually over 1000 V), and isolating switches.
Check valve no. 1 Normal flow
Zone of reduced pressure
Check valve no. 2
Inlet
Outlet
Reverse flow
Sensing lines
Differential relief valve
FIGURE 2.9.5 Reduced-Pressure-Principle Backflow Preventer System Diagram (Source: Cla-Val)
Structural steel members of buildings or process structures often are fireproofed to withstand the heat of possible fires. The materials used in fireproofing formulations can be hazardous to the environment. Asbestos is a primary example of such a material. Application of spray-on fireproofing can result in overspray. After application, any fireproofing can crumble when fire protection hose streams are applied. Therefore, fireproofing materials must be reviewed for their contamination potential. Fire-retardant chemicals are used to reduce the flamespread of plastics, wood, and other materials. When a treated product is used outside, the fire-retardant chemicals can leach due to harsh weather and get into the soil. Both inside and out, these chemicals escape into the air. Like all chemicals, the fire retardants must be reviewed for their potential to contaminate the environment, both before their use and after they have become part of the finished product. To keep the bottom of a steel suction tank from rusting, a specified thickness of the sand under the tank is saturated with No. 2 fuel oil. This practice, required by NFPA 22, Standard for Water Tanks for Private Fire Protection, must now be reviewed, and environmentally acceptable alternatives must be developed.
SUMMARY Recently, the PCB, landfill, ozone, and oil spill problems have focused more attention on the environment. So, too, have incidents of groundwater contamination by fire protection discharge. Many new laws have been passed to protect and preserve the environment, and there are more to come. Every fire protection engineer must be aware of these laws and must apply them properly when designing and installing fire protection systems. Among the fire protection engineer’s present and future concerns are the following: FIGURE 2.9.4 Reduced-Pressure-Principle Backflow Preventer (Source: IRI and Cla-Val)
1. Backflow preventers may have to be installed. Sprinkler system hydraulics must then take backflow preventer fric-
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3.
4.
5.
6.
tion loss into account. Testing and maintenance of backflow preventers will have to be added to fire protection equipment inspection programs. Where the preventers are not used, careful analysis of the potential for contamination will have to be made. The use of halon systems must be reviewed very carefully. All other options for extinguishing agents and types of protective systems must be considered. Emergency operating procedures and disaster recovery plans must be developed and tested. A thorough business interruption analysis is necessary to develop emergency plans and to specify the appropriate protection. Underground tanks must be designed and installed carefully. Proper tank bed preparation, tank anchoring, and backfilling are critical. Double-walled tanks with leak detection between the walls often are required. The quality of groundwater around the tank must be monitored. Aboveground tanks will become more common, and fire protection engineers will have to decide where to install such tanks on crowded sites and how to protect the tanks and their exposures. For every fire protection system installed, consideration must be given to how the discharge from that fire protection system will be contained, handled, and disposed of. If fire protection discharge is found to have contaminants, the discharge must be handled as hazardous waste. Any places on a site where rainwater collects, such as sumps, catch tanks, and dikes, will have to be monitored for the presence of contaminants, and, if any are found, this water must be treated as hazardous waste. Increased storage of hazardous chemicals will become more common. Every environmentally hazardous substance used in manufacturing facilities will have to be recovered to comply with the new laws. Fire protection engineers will have to decide where to place that storage and how to protect it.
Fire protection engineers have begun to plan fire protection systems with concern for the environment, but there is still much to be done. The fire protection discipline must be coordinated with the civil, structural, mechanical, and electrical disciplines to ensure a total facility design that preserves the environment while allowing the most economical and effective fire protection possible. High cost and much effort will be involved, but this is necessary because an environment safe from fire and explosion is of little value if one cannot live in it in good health.
BIBLIOGRAPHY NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on environmental issues in fire protection discussed in this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 11, Standard for Low-Expansion Foam NFPA 11A, Standard for Medium- and High-Expansion Foam Systems NFPA 12, Standard on Carbon Dioxide Extinguishing Systems NFPA 12A, Standard on Halon 1301 Fire Extinguishing Systems
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NFPA 13, Standard for the Installation of Sprinkler Systems NFPA 15, Standard for Water Spray Fixed Systems for Fire Protection NFPA 16, Standard for the Installation of Foam-Water Sprinkler and Foam-Water Spray Systems NFPA 17, Standard for Dry Chemical Extinguishing Systems NFPA 17A, Standard for Wet Chemical Extinguishing Systems NFPA 20, Standard for the Installation of Stationary Pumps for Fire Protection NFPA 22, Standard for Water Tanks for Private Fire Protection NFPA 24, Standard for the Installation of Private Fire Service Mains and Their Appurtenances NFPA 30, Flammable and Combustible Liquids Code NFPA 33, Standard for Spray Application Using Flammable or Combustible Materials NFPA 34, Standard for Dipping and Coating Processes Using Flammable or Combustible Liquids NFPA 45, Standard on Fire Protection for Laboratories Using Chemicals NFPA 54, National Fuel Gas Code NFPA 58, Liquefied Petroleum Gas Code NFPA 75, Standard for the Protection of Electronic Computer/Data Processing Equipment NFPA 230, Standard for the Fire Protection of Storage NFPA 232, Standard for the Protection of Records NFPA 329, Recommended Practice for Handling Releases of Flammable and Combustible Liquids and Gases NFPA 434, Code for the Storage of Pesticides NFPA 471, Recommended Practice for Responding to Hazardous Materials Incidents NFPA 703, Standard for Fire Retardant Impregnated Wood and Fire Retardant Coatings for Building Materials NFPA 750, Standard on Water Mist Fire Protection Systems NFPA 850, Recommended Practice for Fire Protection for Electric Generating Plants and High Voltage Direct Current Converter Stations NFPA 2001, Standard on Clean Agent Fire Extinguishing Systems
Additional Readings General Dungan, K. W., “Fire Protection and the Environment,” The Locomotive, Vol. 67, No. 7, 1991, pp. 163–167. Hazardous Waste: A Guide to RCRA Requirements, National Fire Protection Association, Quincy, MA, 1986. HSB Professional Loss Control, “Fire Protection and Chemical Recycling,” Fire and Current Technologies, Vol. 2, No. 1, 1993, pp. 1–2. Hall, J. R., Jr., “Fire Protection and the Future,” NFPA Journal, May/June 1991, pp. 38–53. Holmes, W. H., “Converting Waste to Energy,” Plant Engineering, Mar. 21, 1991, pp. 120–122. Mitchell, Jr., J. M., “Carbon Dioxide and Future Climate,” Weatherwise, Aug./Sept. 1991, pp. 17–23. “Significant New Alternatives Policy,” The Federal Register, May 12, 1993. Teague, P. E., “Fire Protection and the Environment,” NFPA Journal, Jan./Feb. 1991, pp. 34–43. Air Quality ASME Research Committee on Industrial and Municipal Waste, “Rotary Kiln Incinerators: The Right Regime,” Mechanical Engineering, Sept. 1989, pp. 78–81. “Controlling Particulate Emissions from Utility and Industrial Boilers,” Power Special Report, Vol. 124, No. 6, 1980, pp. S-1–S-20. Corcoran, E., “Cleaning up Coal,” Scientific American, May 1991, pp. 106–116. Elliott, T. C., “Coal Handling and Preparation,” Power, Jan. 1992, pp. 17–32. Gordon, V. R., and Holness, P. E., “Human Comfort and Indoor Air Quality,” Heating/Piping/Air Conditioning, Feb. 1990, pp. 43–52.
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Mawhinney, J. R., P.E., “Tire Fire Pollutes the Environment,” NFPA Journal, Jan./Feb. 1991, pp. 50–58. McKee, B. A., “Yearning to Breathe Free,” Nation’s Business, Feb. 1990, pp. 46–47. Backflow Prevention AWWA, “Recommended Practice for Backflow Prevention and CrossConnection Control,” AWWA M14, American Water Works Association, Denver, CO, 1980. Backflow Protection for Fire Sprinkler Systems, National Fire Sprinkler Association, Inc., Patterson, NY, 1988. Ballanco, J. E., P.E., “Automatic Fire Sprinkler Backflow Protection,” Heating/Piping/Air Conditioning, Mar. 1992, pp. 87–88. “Protecting Drinking Water Systems from Backflow,” ConsultingSpecifying Engineer, Nov. 1989, p. 64. “Recommended Practice for Backflow Prevention and CrossConnection Control,” AWWA M14, American Water Works Association, Denver, CO, 1980. Fire Retardants “Fire-Resistant Plywood—Hot Topic for Builders,” Engineering News Record, Nov. 30, 1989, p. 17. Fluorocarbons and Their Substitutes “An Inside Look at How CFCs Affect Your Life,” ASHRAE Journal, Nov. 1989, p. 42. Anderson, S. O., “Halons and the Stratospheric Ozone Issue,” Fire Journal, Vol. 81, No. 3, 1987, p. 56. Blatt, M. H., “Electric Chillers: Cost-Effective Choice for the Future,” Heating/Piping/Air Conditioning, Mar. 1993, pp. 75–82. Chines, S. A., “Halon, Ozone, and the Environment,” The Sentinel, Third Quarter 1989, p. 3. Cohn, B. M., “Laboratory Halon Systems: Rehab, Replace or Remove?,” Journal of Applied Fire Science, Vol. 5, No. 1, 1995/1996, pp. 45–54. “Controlling Fire Protection Halon Emissions,” Fire Technology, Feb. 1988, p. 70. DiNenno, P. J., Hanauska, C. P., and Forssell, E. W., “Design and Engineering Aspects of Halon Replacements,” Process Safety Progress, Jan. 1995, pp. 57–62. “Final Report of the Halon-Technical Options Committee of the United Nations Environmental Programme,” Montreal Protocol Assessment Technology Review, Aug. 11, 1989. (Available from ICF Inc., 9300 Lee Highway, Room 1171, Fairfax, VA, 220311207.) Gallup, J. G., P.E., “Ozone Fears Limit Halon Use,” Plant Engineering, Sept. 6, 1990, pp. 92–93. Gilkey, H. T., P.E., “The Coming Refrigerant Shortage,” Heating/ Piping/Air Conditioning, Apr. 1991, pp. 41–63. Grant, C. C., “Controlling Fire Protection Halon Emissions,” Fire Technology, Feb. 1988, pp. 70–78. Grant, C. C., “Fire Protection Halons and the Environment,” Fire Technology, Feb. 1988, pp. 63–64. Grant, C. C., “Halons and the Ozone Layer: An Overview,” Fire Journal, Vol. 83, No. 5, 1989, p. 59. Grant, C. C., “Life Beyond Halon,” Fire Journal, Vol. 84, No. 3, 1990, pp. 52–59. Halon Alternatives Research Corporation, “EPA Releases List of Acceptable Alternatives,” HARC NEWS, Vol. 3, No. 1, 1993, pp. 1–2. Halon Alternatives Research Corporation, “President Announces Accelerated Phaseout of Ozone-Depleting Substances,” HARC NEWS, Vol. 2, No. 1, 1992, p. 1. Harrington, J. L., “The Halon Phaseout Speeds Up,” NFPA Journal, Mar./Apr. 1993, pp. 38–42. Industrial Risk Insurers, “Clean Agent Halon Replacements,” IRInformation, IM.13.6.0, Dec. 1997. Industrial Risk Insurers, “Clean Agent Systems—NFPA 2001-1994,” IRInformation, IM.13.6.1, Dec. 1995. Industrial Risk Insurers, “Clean Agent Systems—NFPA 2001–2000,” IRInformation, Mar. 2001.
Industrial Risk Insurers, “Door Fan Testing for Enclosure Integrity,” IRInformation, IM.13.0.5.2, Mar. 2001. Isman, K. E., “New Standard for Backflow Prevention,” Sprinkler Quarterly, Winter 1990, p. 64. Makansi, J., “Ammonia: It’s Coming to a Plant Near You,” Power, May 1992, pp. 16–22. Mauzerall, D. L., “Protecting the Ozone Layer: Phasing out Halon by 2000,” Fire Journal, Vol. 84, No. 5, 1990, pp. 22–31. McCon, P., “Replacements for Halogenated Fire Extinguishing Agents in Fixed Systems—Where We Stand,” Professional Safety, Apr. 1996, pp. 22–26. Moore, T., “Refrigerants for an Ozone-Safe World,” EPRI Journal, Jul./Aug. 1992. Nadel, B., “Ozone-Friendly Cooling,” Popular Science, Jul. 1990, pp. 57–59. Stamm, R. H., “The CFC Problem: Bigger than You Think,” Heating/ Piping/Air Conditioning, Apr. 1989, p. 51. Stoecker, W. F., “Opportunities for Ammonia Refrigeration,” Heating/ Piping/Air Conditioning, Sept. 1989, pp. 93–108. Stouppe, D. E., P.E., “CFCs, the Law and You!” The Locomotive, Vol. 68, No. 3, 1992, pp. 51–56. Stouppe, D. E., P.E., “Taxes Help the Ozone Layer,” The Locomotive, Vol. 67, No. 1, 1990, pp. 11–13. Su, J. Z., Kim, A. K., and Mawhinney, J. R., “Review of Total Flooding Gaseous Agents as Halon 1301 Substitutes,” Journal of Fire Protection Engineering, Vol. 8, No. 2, 1996, pp. 45–64. Willey, A. E., “Conference on Halons and the Environment Held in Switzerland,” Fire Journal, Vol. 82, No. 6, 1988, p. 47. Wojdon, W., and George, M., “How to Replace CFC Refrigerants,” Hydrocarbon Processing, Aug. 1994, pp. 107–112. Ziemba, J., and Waters, S., “Halon: The Search for Alternatives,” Firewatch!, Vol. 30, No. 3–4, 1993, pp. 6–7. Ziffer, F. E., “Managing Refrigerants in a CFC-Free Era,” Plant Engineering, Sept. 3, 1992, pp. 53–56. Zimmer, C., “Unintended Consequences,” Discover, Mar. 1995, pp. 32–33. Zurer, P., “Fate of CFC Alternatives Remains up in the Air,” C&EN, Jul. 16, 1990, pp. 5–6. PCBs McPartland, B. J., “PCBs . . . Time Is Running Out,” Electrical Construction and Maintenance, Sept. 1988, p. 62. “PCBs and PCB-Containing Equipment—Disposal and Treatment Options,” Environmental Contractor Magazine, Nov. 1989, p. 73. Spills and Fire Protection Discharge Andrews, R. C., Jr., P.E., “The Environmental Impact of Firefighting Foam,” Industrial Fire Safety, Nov./Dec. 1992, pp. 26–31. Constantine, P., “Lining up against Oil,” Civil Engineering, Jan. 1990, p. 70. “Foam-Water Sprinkler Protection for Flammable Liquids,” Plant Operations Progress, Oct. 1989, p. 218. “Guidelines for Safe Handling and Storage of Calcium Hypochlorite and Chlorinated Isocyanurate Pool Chemicals,” Monsanto-OlinPPG; St. Louis, MO; Cheshire, CT; Pittsburgh, PA; 1989. Industrial Risk Insurers, “Dry Chemical Extinguishing Agents— Corrosive and Contaminating Effects,” IRInformation, IM.13.1.3, Feb. 1990. Isner, M. S., “$49 Million Loss in Sherwin-Williams Warehouse Fire,” Fire Journal, Vol. 83, No. 2, 1989, p. 65. Isner, M. S., Flammable Liquids Warehouse Fire, Dayton, Ohio, May 27, 1987, Investigation Report, National Fire Protection Association, Quincy, MA, 1987. PVI Industries, “HVAC Technology Speeds Alaskan Oil Cleanup,” Engineered Systems, Jan./Feb. 1990, pp. 26–32. Underground Tanks Donovan, B. C., and O’Connor, P., “Underground Storage Tank Update,” Plant Engineering, June 22, 1989, p. 60.
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EPA—LUST, Locating Underground Storage Tanks [Video], U.S. Environmental Protection Agency, Office of Underground Storage Tanks, Washington, DC, 1985. Gellop, J. G., “Ozone Fears Limit Halon Use,” Plant Engineering, Sept. 6, 1990, pp. 92–93. “Government Regs Force Loss Prevention Changes,” Sentinel, Vol. 47, No. 4, pp. 3–7. Gross, R. A., “Preventing Contamination of the Earth,” The Sentinel, Third Quarter 1989, p. 8. Hazardous Waste: From Cradle to Grave [Video, 40 min], distributed by National Fire Protection Association, Quincy, MA, 1986. Hazardous Waste: Small Quantities, Big Challenges [Video, 27 min], distributed by National Fire Protection Association, Quincy, MA, 1985. Henry, M. F., “Update on the Underground Leakage Problem,” Fire Journal, Vol. 80, No. 1, 1986, pp. 26–27 and 86. Murarka, I. P., “MOSES: Mineral Oil Spill Evaluation System,” EPRI Journal, Jul./Aug. 1991, pp. 46–48.
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Silveria, V., “Basic UST Leak Detection Systems,” Plant Engineering, Aug. 13, 1992, pp. 74–76. Smalley, J. C., “Underground Storage Tanks: Rest in Peace,” Fire Command, Mar. 1986, pp. 40–42. Underground Storage Tanks: A Guide to Installation, National Fire Protection Association, Quincy, MA, 1988. Underground Storage Tanks: A Question of When [Video, 37 min], distributed by National Fire Protection Association, Quincy, MA, 1988. Underground Storage Tanks: Close to Home [Video, 9 min], distributed by National Fire Protection Association, Quincy, MA, 1988. Underground Storage Tanks: In Your Own Backyard [Video, 26 min], distributed by National Fire Protection Association, Quincy, MA, 1988. Underground Storage Tanks: Rest in Peace [Video, 30 min], distributed by National Fire Protection Association, Quincy, MA, 1986.
INFORMATION AND ANALYSIS FOR FIRE PROTECTION
F
rom a conceptual standpoint, fire protection is achieved through a series of coordinated decisions, which is to say, actions based on processed information. There are decisions in design, construction or manufacture, purchase, installation, maintenance, education, response to emergency, and so forth. Every decision is as good as the information it is based on, and so every aspect of fire protection stands to benefit from better sources of information and better methods of analyzing and interpreting the available information. One of the most exciting developments of recent years has been the rapid evolution of analytical tools to provide better information to support decisions and to coordinate them in a systematic approach to fire safety. Section 3 covers these tools. Chapters 1 and 2 discuss information gathering in connection with individual fires, either in-depth investigation, in Chapter 1, or routine incident reporting, in Chapter 2. Chapter 3 then discusses the techniques used to analyze this material—to turn raw data into useful statistics, facts into information, observations into knowledge. Chapters 2 and 3 have been substantially expanded and revamped to provide guidance and help for those who work on or with the principal U.S. fire incident database, which is the U.S. Fire Administration’s National Fire Incident Reporting System (NFIRS). Chapter 4 provides an introduction to the various types of mathematical modeling. Modeling relies on data—fire incident data produced in Chapters 1–3, fire-test-response data from laboratory tests, and other data on parameters and variables ranging from equipment specifications to room and building geometries to patterns of product usage to reliability statistics for fire
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John R. Hall, Jr.
Case Study KING’S CROSS UNDERGROUND STATION FIRE, NOVEMBER 18, 1987, LONDON, ENGLAND The King’s Cross Station fire became the subject of one of the most extensive applications to date of fire modeling, specifically computational fluid dynamics (CFD) modeling, for both practical value and theoretical insight. Modeling results were requested by the British authorities and used by them to help determine responsibility of various factors and parties for the fire’s severity. These results were also used to identify and prioritize changes needed in the entire British underground system to prevent another such incident. The research provided a new understanding of the potential for rapid fire spread in a space that can be described as an inclined trench. (See P. J. Woodburn and D. D. Drysdale, “Fires in Inclined Trenches: The Dependence of the Critical Angle on the Trench and Burner Geometry,” Fire Safety Journal, Vol. 31, No. 2, 1998, pp. 143–164.)
The King’s Cross underground station is one of the three busiest of London’s complex underground railway system, with five separate subway lines served on three different levels. At approximately 7:30 p.m. on November 18, 1987, a fire occurred just as rush hour was tapering off. The incident began when a small fire was reported on one of the three wooden escalators between the ticket concourse and the station immediately below. At 7:45 p.m. the fire erupted up into the ticket concourse, creating severe conditions likened to that of a flashover, with thick black smoke emerging from the station entrances at the street level. The fire burned for several hours. Thirty-one people died, including a London Fire Brigade officer, and more than fifty people were injured, several with severe burns. Most fatalities were located around the perimeter of the ticket concourse.
Source: Richard L. Best, “Fact Sheet—King’s Cross Station Fire,” Fire Command, January 1988; and Paul Grimwood, “The King’s Cross Fire 1987, London, England,” http:///www.firetactics.com/KINGSCROSS.htm.
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protection systems. Chapter 5 provides more details on deterministic fire models; Chapter 6 provides more details on probabilistic fire models. Chapters 7 and 8 lay out the essential elements of fire hazard analysis and fire risk analysis, two very general methodologies for combining diverse technical measurements into summary characterizations of the overall fire danger posed by some object of analysis, whether they be products, buildings, or something else. These two analytical methods are at the top end of the hierarchy of fire-related models in terms of scope. The fire models described in Chapter 5 form the core of the broader, more ambitious calculations in fire hazard models, which in turn form the core of fire risk models, in combination with the models described in Chapter 6. Much of the work of fire safety science and fire protection engineering is now explicitly designed to fill gaps or improve accuracy or flexibility in some comprehensive fire hazard or fire risk model. Chapters 9 through 11 provide simplified modeling and analysis techniques. Performancebased codes and standards and related design and assessment activities involve large numbers of calculations. Short cuts can make analysis more affordable and manageable, and these chapters provide a road map to those methods. Chapter 12 shows how modeling can be applied to fire-safety design, fire investigations, and other fire protection engineering problems. Chapters 13 and 14 describe the use of models in performance-based fire codes and standards, in combination with the models described in Chapter 6. Design to achieve performance produces greater design flexibility and greater clarity on how much safety is being achieved, all while providing latitude for cost savings. Finally, Chapter 15 examines the special topics of inspecting, surveying, and mapping. Also look for these: Most of the subjects in this section also are examined in much more detail in the SFPE Handbook of Fire Protection Engineering, an indispensable reference for anyone wishing to go further in the use of advanced calculation methods as applied to fire protection. This part of the field is changing so fast that the serious practitioner should also keep abreast of new developments in the technical literature through such publications as the SFPE Journal of Fire Protection Engineering and NFPA’s Fire Technology. By the time material of this kind reaches book form, there often are exciting new developments already in use.
Chapter 1
Fire Loss Investigation
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Organizations Involved in Fire Loss Investigation The Reconstruction and Failure Analysis Process Organization for Fire Investigation Education and Training of Fire Investigation Personnel Summary Bibliography
3–5 3–6 3–10
Chapter 2
Fire Data Collection and Databases
History of NFIRS NFIRS—A Three-Tiered System NFIRS Definitions Getting to NFIRS 5.0 Computers and NFIRS Getting the Big Picture on Fires Other Sources of Data Summary Bibliography Chapter 3
3–11 3–11 3–12 3–15 3–16 3–16 3–21 3–22 3–26 3–27 3–28 3–30 3–30
Using Data in Program and Strategy Analysis Comparing Estimates Using Different Databases or Analytic Approaches Summary Bibliography Chapter 4
Introduction to Fire Modeling
Physical Fire Models Mathematical Fire Models Trends Summary Bibliography Chapter 5
Deterministic Computer Fire Models
Enclosure Fire Models Special-Purpose Models Combined Models Wildland Fire Models Summary Bibliography
3–64 3–66 3–67 3–67 3–69 3–69 3–70 3–74 3–76 3–76 3–83 3–83 3–88 3–90 3–92 3–92 3–92
Use of Fire Incident Data and Statistics 3–33
Using Data to Characterize the Fire Problem Basic Tools for NFIRS Analysis Data Source Issues Approaches to Fire Data Analysis
3–34 3–36 3–36 3–44
Chapter 6
Probabilistic Fire Models
Probability Probability Models and Modeling Networks
3–97 3–97 3–98 3–99
SECTION 3
Statistical Models Simulation Summary Bibliography Chapter 7
Fire Hazard Analysis
Hazard versus Risk Performing an FHA Summary Bibliography Chapter 8
Fire Risk Analysis
What Is Fire Risk Analysis? What Is and Is Not Risk Analysis? Uses of Data from Real Fires Risk Estimation and Risk Evaluation Overview of a Risk Analysis Conceptual Framework General Characteristics and Fire Types Decision Model Ignition Initiation Model Postignition Model Loss Evaluation Model Cost Model Cost-Benefit Comparison Model Summary Bibliography Chapter 9
Simplified Fire Growth Calculations
Ignitability of Solids Energy Release Rate Flame Heights Plume Centerline Temperature and Velocity Calculating the Hypothetical Virtual Origin (Zo) Radiant Heat Flux to a Target Preflashover Temperature Estimates Prediction of Flashover Postflashover Temperature Estimates Equivalent Fire Duration Smoke-Filled Gas Production Rate Enclosure Smoke Filling Buoyant Gas Head Thermal Fire Detector Response Ordinary Sprinkler Fire Suppression Summary Bibliography Chapter 10
Simple Fire Hazard Calculations
Hazard Assessment Process Developing Fire Scenarios and Design Fire Scenarios Quantification of Design Fire Scenarios Summary Bibliography
3–100 3–103 3–103 3–103 3–105 3–105 3–105 3–110 3–110 3–115 3–115 3–117 3–118 3–119 3–119 3–120 3–121 3–121 3–122 3–124 3–126 3–127 3–127 3–128 3–131 3–131 3–132 3–133 3–134 3–134 3–135 3–136 3–137 3–137 3–137 3–138 3–139 3–139 3–140 3–141 3–142 3–143 3–147 3–147 3–151 3–153 3–157 3–157
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Chapter 11
Simplified Fire Risk Calculations
Fire Risk Assessment Event Trees Probability Assessment Risk Calculations Summary Bibliography Chapter 12
Applying Models to Fire Protection Engineering Problems and Fire Investigations
Definition of Fire Growth Models Types of Models Model Applications Computer Modeling in Fire Investigation Some Additional Considerations Summary Bibliography Chapter 13
Performance-Based Codes and Standards for Fire Safety
Performance-Based versus Prescriptive-Based Regulations The Performance-Based Design Process The Role of Codes and Standards in the Performance-Based Design Process Precedents for Performance-Based Codes and Standards Future NFPA Codes and Standards Pursuing Performance-Based Regulations Summary Bibliography Chapter 14
3–161 3–161 3–162 3–164 3–166 3–167 3–167
3–169 3–169 3–169 3–171 3–172 3–175 3–176 3–176
3–181 3–181 3–183 3–188 3–190 3–190 3–190 3–190 3–191
Overview of Performance-Based Fire Protection Design 3–197
What Is Performance-Based Design? The Performance-Based Fire Protection Design Process Time as a Performance-Based Design Parameter Deterministic Hazard versus Probabilistic Risk Assessment Summary Bibliography Chapter 15
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Formats for Fire Hazard Inspecting, Surveying, and Mapping
Inspection or Surveying Mapping Summary Bibliography
3–197 3–198 3–202 3–204 3–204 3–205
3–207 3–207 3–209 3–210 3–216
CHAPTER 1
SECTION 3
Fire Loss Investigation Richard L. P. Custer
D
Information about the dynamics of fire spread and growth can be found in Section 2, Chapter 4 (“Dynamics of Compartment Fire Growth”); Section 8, Chapter 2 (“Combustion Products and Their Effects on Life Safety”); Section 8, Chapter 17 (“Upholstered Furniture and Mattresses”); Section 3, Chapter 9 (“Simplified Fire Growth Calculations”); and Section 3, Chapter 12 (“Applying Models to Fire Protection Engineering Problems and Fire Investigations”).
ata gathered during a fire loss investigation have several applications, ranging from filling out the fire department incident report to creating a detailed engineering reconstruction and failure analysis of the incident. Understanding the fire origin and cause of a fire can lead to targeted inspection, public education programs, or, perhaps, proposed code changes. An engineering reconstruction and failure analysis can reveal factors concerning the fuel, building, and fire suppression that resulted in the ultimate extent of flame and smoke movement. Building codes and fire safety design standards involved would be included in this analysis, as would construction, operation, and maintenance practices. Results of a failure analysis provide input to insurance loss adjustment and underwriting, improved design practice, and civil and criminal litigation. Failure analysis can also result in changes to codes and standards. In most fires, origin and cause are expressed in terms of the area of fire origin, the heat of ignition, the materials involved, and the factors that brought them together. (See NFPA 921, Guide for Fire and Explosion Investigations.) In the past, only fires that resulted in large loss of life or property received the attention of a complete investigation. In these cases, the engineering reconstruction and failure analysis was often conducted months or years after the fire, when only fragmentary evidence, if any, remained. In these situations, the depth and accuracy of the fire department report can be critical. Recently, insurance claims, subrogation activities, and greatly increased litigation have been concerned with smaller and smaller losses. Thus, more detailed examination is needed of all fires that result in a loss, almost regardless of the extent of the loss. This chapter discusses fire loss investigation by examining organizations that are involved in fire loss investigations and the reconstruction and failure analysis process. Two other pertinent chapters in this section are Chapter 2 (“Fire Data Collection and Data Bases”) and Chapter 3 (“Use of Fire Incident Data and Statistics”). A discussion of a fault tree for managing fire risk can be found in Section 2, Chapter 2 (“Fundamentals for Fire Safe Building Design”), and fire-resistive construction information can be found in Section 7, Chapter 11 (“Building Construction Concerns of Fire Departments”).
ORGANIZATIONS INVOLVED IN FIRE LOSS INVESTIGATION Organizations involved in fire investigation can be separated into two types: (1) public agencies, or those required by law to investigate fires at the local, state, and federal levels, and (2) private sector organizations.
Local and State Of the public agencies, the local fire department generally has the primary responsibility to document a fire and to provide an initial determination of the origin and cause. If the department uses NFPA 901, Standard Classifications for Incident Reporting and Fire Protection Data, as the basis of a reporting system such as the National Fire Incident Reporting System, factors that affected the ultimate course of the fire, such as fire and smoke spread and the performance of fire protection features, may be included. When a fire department investigation determines that the fire may have been of incendiary origin, in other words, deliberately set, other organizations may be assigned the legal responsibility for determining fire cause and for the investigation pursuant to suspect identification and possible criminal action. In much of the United States and in all Canadian provinces, the state or provincial fire marshal’s office is responsible for investigating incendiary fires. In states or jurisdictions where this is not the case, the local fire marshal or the local police or fire department may have investigative responsibility, either directly by statue or by delegation from the state.
Federal U.S. Federal agencies are also involved in investigating fires. These agencies are generally charged with investigating incidents to determine compliance with federal regulations and to
Richard L. P. Custer, M.Sc., is associate principal and technical director at ARUP Fire in Westborough, Massachusetts. Mr. Custer is a fellow of the Society of Fire Protection Engineers.
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provide input for the regulatory process to reduce human and property losses. For example, the National Transportation Safety Board (NTSB) conducts complete reconstruction and failure analysis of accidents, including fire-related incidents, which involve air, rail, and highway transportation. Investigations of pipeline incidents and maritime fires are under the authority of the Department of Transportation (DOT). Other federal agencies involved in fire investigations include the Occupational Safety and Health Administration (OSHA) of the Department of Labor; the Bureau of Mines (BoM) of the Department of the Interior; the Federal Bureau of Investigation (FBI); the Bureau of Alcohol, Tobacco, and Firearms (ATF) of the Department of Justice; the Consumer Product Safety Commission (CPSC); the Nuclear Regulatory Commission (NRC); and the National Institute of Standards and Technology (NIST) of the Department of Commerce. The Federal Emergency Management Agency (FEMA) conducts detailed investigations of fire and hazardous materials incidents and prepares reports that can be obtained through the U.S. Fire Administration. Other agency reports are available from the National Technical Information Service (NTIS) in Atlanta, Georgia. In addition to investigating fires under their jurisdiction, these federal agencies may serve as resources for lab analysis and technical information for state and local fire officials. Committees of the U.S. House of Representatives and the Senate are often very interested in the results of these investigations, particularly when the incidents under investigation deal with timely public policy topics, such as standards for elderly care facilities and prison fire safety.
Private Sector Organizations Most of the complete reconstruction and failure analyses of fires other then those that fall under government jurisdiction are conducted by private sector organizations for education, improved design, insurance, and litigation purposes. NFPA. The National Fire Protection Association’s (NFPA) fire investigations program is a long-standing data collection and engineering analysis activity. The purpose of the program is to collect, analyze, and report detailed fire experience data through on-site investigations. This activity assists NFPA in analyzing and documenting facts about fires for technical or educational value; distributing the information to the fire protection community to help prevent future similar fire losses; publishing of investigation reports as individual reports, as well as in the NFPA Journal and on the NFPA home page; providing technical assistance to state and local officials as an integral service of the NFPA investigation process; determining important “lessons learned” for input to NFPA technical committees and technical programs; and contributing to an increasing fire incident data base for analysis purposes. Several NFPA fire investigations have included or been supplemented by analysis of human behavior patterns, where the discovery of the fire and subsequent evacuation occurred in sufficient time to permit analysis. Human behavior studies have been conducted through on-site interviews with survivors or
mailed surveys and have generally been carried out by NFPA staff in combination with leading authorities on human behavior in fire. NFPA frequently works with fire departments and code organizations during the on-scene investigation. Results of most of these investigations are published as special studies or as reports in various fire protection periodicals. Insurance Industry. The insurance industry often investigates and reconstructs a fire incident to evaluate the merits of claims submitted or to identify parties for possible subrogation action. Reconstruction may be conducted by insurance company personnel, by an adjustment bureau, or by a consultant. Individual consultants or consulting firms perform reconstruction and failure analysis for a variety of clients, including property owners, industrial organizations, criminal prosecution and defense and the insurance industry. Consultants are also retained for litigation purposes by law firms to evaluate fire origin and cause, code compliance, conformance with applicable design standards, and other technical aspects of fire loss. When major financial consequences are linked to investigators’ conclusions, it is not uncommon for two or more parties to retain investigators and for two or more theories of fire origin and development to be presented. The need to resolve such disputes is a major reason for the increasing interest in applying state-of-the-art scientific methods and computer fire models, analytical procedures, and test results to fire investigations.
THE RECONSTRUCTION AND FAILURE ANALYSIS PROCESS The complete reconstruction and failure analysis process involves developing a time history for the incident, identifying the location of the fire origin and establishing the factors that led to ignition and that increased or lessened the severity of the loss. The reconstruction includes prefire history, as well as “transfire” events, or those that occur from the point of established burning to extinguishment. Failure analysis is concerned with the design, construction, and performance aspects of the incident. It is also important in the reconstruction to document the successes. For example, did fire protection features inhibit the spread of fire within a portion of the building? Time is the framework for reconstruction and failure analysis, and it can be viewed in two scales: the macro scale, where time is measured in increments of days, weeks, and years, and the micro scale, where the increments are in seconds, minutes, and hours. Macro time is prefire, whereas micro time may apply to both pre- or transfire events. The best way to organize reconstruction and failure analysis information is through the use of timelines or event sequences. In constructing a timeline, it is important to establish benchmark events. A benchmark1 event can be described as an event that is well documented in time and space and that serves as a point of reference because it can be assumed to have created a set of specific conditions or initiated a sequence of actions that had a significant impact on the fire. The issuance of a building permit or the time of arrival of the fire department apparatus are
CHAPTER 1
good examples of benchmark events. Using time of arrival as a reference event, other events for which the time of occurrence is unknown can be placed approximately in time either before or after arrival of the fire department apparatus. Other examples of typical benchmark events are explosions and the collapse of walls or roofs or calling for multiple alarm response. A single timeline can be adequate for fires in which only a few events occurred. For more complex situations, separate timelines on the same scale can be used for the history of the building, the evolution of the “model codes,” the installation and maintenance history of a suppression system, human activity, or any other time-related aspect of the incident. STEP (sequentially timed events plotting) procedures have been developed to deal with complex accident situations such as major fires.* Prefire timeline information can be obtained from building permits, plans and specifications, inspection reports, fire and building codes, and fire research and engineering literature. Sources of information for use in the development of transfire timelines include the fire department incident report, recordings of fire department radio transmissions during the incident, photographs and video footage shot during the event by news media, private citizens or fire department personnel, and interviews with fire fighters and other witnesses. It should be pointed out that, in many cases, only parts of the reconstruction and failure analysis process are carried out. Many different organizations may be involved in the investigation, often at different times. Because people may have to rely on information gathered by others, an understanding of the whole process makes it easier to obtain the most complete and accurate data at each step. The basic steps of overall reconstruction and failure analysis are examination of the scene, collection of background data, testing, incident reconstruction, and specific failure analysis. Many of these steps are outlined in NFPA 921.
Examination of the Scene Examining the fire scene is critical to the entire reconstruction and analysis process. It is here that the physical and photographic evidence is gathered and the fire damage is documented. As many photographs as possible should be taken at the scene, and each photograph should be documented on a diagram with a description of the direction of view and contents of the photograph. The techniques of fire-scene photography have been well reported and can be applied to reconstruction and failure analysis.2–4 Color photography is recommended. In addition, maps and diagrams should be prepared that include dimensions and interior layout of the building, the location and degree of fire damage, the location and types of fuel materials, and the locations of victims. The location of fire protection features, such as firewalls, detectors, and suppression systems, should also be noted. It is also helpful to determine the prefire *Any event for which the actual time of occurrence is known is a “benchmark” event. A “hard time” timeline has benchmarks for each event. A “soft time” or “relative time” timeline has the sequence of events known, relative to each other, but not all of the actual times. Benchmark events are exceptions in a relative time timeline, and their known times of occurrence often can set bounds on the times of other events.
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location and nature of fuel items as well as the prefire location and activities of fire victims. Often, buildings will be modified considerably over their lifetimes, and an individual reviewing the original plans could receive a false impression of the building at the time of the fire. Thus, it is important to record the architectural, construction, and fire protection features of a structure, both as built and at the time of the fire. When fire suppression systems are present, the positions of valves, the locations of discharge nozzles, and the locations and types of detectors used to operate the system should be noted. It may also be necessary to evaluate the water supply in order to determine if it was adequate. With special systems, such as those that use halon, CO2, or dry chemicals, agent storage tanks should be checked to determine whether the system discharged as designed. It is important to interview or review the interviews of fire department responders to determine what actions they took on the scene. Some of the damage may have occurred during fire fighting and overhaul and not as a direct result of the fire. For example, ventilation of a building to facilitate fire suppression activities may result in an increased burning rate at the area of venting thus increasing the damage at that point. A careful study of the damage patterns, combined with onsite interviews and a knowledge of the ignition sources, location of fuel materials present immediately before the fire, and fire dynamics, should be used by an investigator to determine the area of origin. If possible, the source and form of heat of ignition and the type and form of the materials first ignited should be determined. Burn patterns, such as a “V,” low burns, and multiple “points of origin,” can often be misleading and should only be used to establish origin and cause when they are unambiguous or are supported by other physical evidence. The investigator should collect evidence, develop hypotheses or theories about the origin and cause, and test these theories to see which the evidence supports. The investigator should keep in mind that the burn patterns seen after a fire represent the total burning history of the event, including damage that may have occurred during extinguishment and overhaul. As a rule, patterns observed in fires that are extinguished early in their development are more meaningful and useful than those remaining after the near-total destruction of a building or a portion of a building. Indicators, such as depth of char, should be used with care. The burning rate of wood traditionally has been calculated as approximately 1.4 in. in 60 min (0.6 mm/min). This figure has been used to estimate the time of burning and to detect the presence of flammable liquids. Research has shown that the traditional calculation varies substantially, depending on the radiant heat flux and ventilation. The rate of burning can be as high as 10 in./hr (4.3 mm/min).5 Investigators should also be careful not to assume that certain burn patterns can be used as sole proof of the presence of flammable liquids. Factors such as ventilation, room flashover, floor clutter, room contents, fire duration, fire-fighting activities, and overhaul can affect the patterns seen by investigators. Corroborative evidence, such as pertinent chemical traces or the detected absence of an appropriate prefire fuel load, is needed to
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establish the presence of flammable liquids. The color of observed smoke is not necessarily evidence of the presence of flammable liquids. A number of recent studies have been carried out to identify some of the patterns that can develop from different ignition and ventilation scenarios.6–8 In visualizing conditions in the area of origin, it is often helpful to reconstruct the scene physically by replacing the carpet, furniture, and other items in their original locations. Although interviews are conducted at many different times in the reconstruction and failure analysis process, those taken at or close to the time of the incident also can be very useful, particularly in describing the course of the fire. Whenever possible, events described in interviews should be related to benchmark events. Private sector investigators are often not called in to evaluate a fire scene until well after the incident. Frequently, the scene has been disturbed, or, in some cases, the building has been restored or removed. In these situations, the investigator should review physical evidence collected and photographic evidence. Examination of photographs using 7- to 10-power binocular microscopy can often reveal details, particularly when low-speed film has been used. If possible, copies of all photos and videotapes taken of the scene should be obtained. Grouping them for study, chronologically and by area depicted, is useful in documenting the amount of scene disturbance over time. Fire, police, and autopsy reports, as well as witness statements, should be reviewed. Although an actual on-scene investigation of a fire is most desirable, careful analysis of a well-documented fire can lead to reliable conclusions or assessment of conflicting opinions regarding the origin and cause of many fires, as well as provide information for failure analysis. The effectiveness of a delayed investigation and analysis depends on the extent of the fire, as well as the degree of documentation. In some cases where there has been total or near-total destruction, neither an on-scene welldocumented investigation nor subsequent delayed analysis can establish origin or cause.
Collection of Background Data Although some of the background data, such as accounts of activities immediately before the fire, can be gathered at the scene very soon after the fire, much of the information needed for the investigation will be gathered later. Building plans, permits, and the codes in effect at the time of approval should be obtained, along with the specifications and drawings for the building fire protection features. If any major modifications were made to the building or its fire protection systems or if there was a change of occupancy, the codes, plans, and permits should be obtained as well. These materials should be reviewed as part of the reconstruction process, because the changes may have influenced the course of the fire. Other background data include instruction or training manuals, maintenance records, data on construction and interior finish materials, the previous fire history of the building or equipment involved, the amount of any previous fire damage, the location of contents, and the physical and burning characteristics of the contents. Maintenance records can often reveal
problems with equipment that might have been part of the cause of a fire. This step also involves obtaining detailed statements from the building occupants to determine the circumstances leading up to ignition and established burning.
Testing Three types of tests are involved in reconstruction and failure analysis: (1) standard tests of flammability properties, (2) standard analysis to identify unknown materials, and (3) special tests designed to establish burning behavior under conditions related to a specific fire scenario. The volume and pressure of the water supply could also be tested. Properties of flammability that may be determined by test include flame spread of materials, fabric flammability, flash point, and rate of heat release, among others.9–16 Analysis of unknowns is performed by analytical laboratories using techniques such as gas chromatography and mass spectroscopy to identify unknown materials, particularly possible accelerants. Such analysis should be conducted in accordance with the following appropriate ASTM standards: ASTM E1385, Standard Practice for Separation and Concentration of Ignitable Liquid Residues from Debris Samples by Steam Distillation; ASTM E1386, Standard Practice for Separation and Concentration of Ignitable Liquid Residues from Fire Debris Samples by Solvent Extraction; ASTM E1387, Standard Test Method for Flammable or Combustible Liquid Residues in Extracts from Samples of Fire Debris by Gas Chromatography; ASTM E1388, Standard Practice for Sampling of Headspace Vapors from Fire Debris Samples; and ASTM E1389, Standard Practice for Cleanup of Fire Debris Sample Extracts by Acid Stripping. Other useful analysis techniques for unknown materials include FTIR (Fourier transfer infrared) analysis, EDS (energy dispersive spectroscopy), and metallurgical or X-ray analysis. In collecting samples for testing, it is important to know the sizes and/or amounts of the sample needed for each test, as well as the conditions under which the samples should be transported. This information can be obtained from a testing laboratory or by reviewing a copy of the test method. Although special tests, sometimes called “demonstrations,” can often be extremely revealing in understanding the course of a particular fire, results of these demonstrations can be misleading because the test may not be truly representative of the actual event. Factors such as ventilation, arrangement of the fuel, or even the point of ignition can have a significant effect on the outcome of the test. In other words, a great deal needs to be known about the specific conditions at the time of the fire, and these conditions must be reasonably reproduced in the demonstration. Special tests or demonstrations should be conducted by personnel familiar with full-scale fire testing under laboratory conditions to permit control of such variables as ambient temperature, relative humidity, and wind effects.
Reconstruction and Analysis Fire reconstruction is an organized, step-by-step portrayal of the most likely course of the fire under study, from the ignition se-
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quence through established burning to the limits of flame and smoke movement at the time of extinguishment. Fire reconstruction is based on the facts developed through on-scene investigation, background studies, and testing. The reconstruction should explain the speed and direction of fire growth and smoke spread within the compartment or area of origin and beyond. It also should explain the effects of barriers and automatic suppression systems on fire spread and growth and the effects of manual extinguishment. The reconstruction should also evaluate the performance of the building’s life safety features relative to injury or loss of life. In sorting through the facts to develop the reconstruction, it is often useful to apply the system safety techniques of failure modes and effects analysis (FMEA) and fault tree analysis.17 These methods help identify alternative sequences of events that could have led to the observed fire situation, such as the development of room flashover or fire breaching a fire wall. The alternatives can then be evaluated against the evidence to determine the most likely scenario. These techniques are particularly valuable where complex or interrelated machinery, buildings, or human activities are involved. Computer modeling techniques can also be used to predict the outcome of a series of possible fire causes and growth scenarios. The model results can be compared to actual events to narrow down the likely scenarios for a given event or to evaluate the possible effects that fire protection equipment, such as detectors or sprinklers, might have had on the outcome of a fire. The analyses of the DuPont Plaza and the First Interstate Bank fires are examples of model applications.18,19 Analysis of the ignition sequence (fire cause) is concerned with three specific items: (1) size, nature, and source of the ignition energy; (2) physical and chemical fire properties of the materials ignited; and (3) circumstances, either human or mechanical, that brought the energy in contact with the fuel. In selecting the most likely ignition source, the energy available from a candidate source must be compared with the ignition energy requirements of the fuel in its given form. For example, given the same material and heat source, ignition is more likely if the material is present in a finely divided form than if it is in a solid mass. Energy available at the source, such as temperature and thermal radiation, distance from the fuel to the energy source, and time of exposure to the source of energy, is also a factor that needs to be considered in ignition sequence analysis. The term competent ignition source is used to describe a source that has sufficient energy and temperature to raise a particular fuel to its ignition temperature during the postulated exposure time. For example, an electric arc may be at a temperature well above the ignition temperature of a particular fuel but be of short duration and not provide enough total energy to result in ignition. Circumstances that result in ignition generally involve human factors or equipment failure. Careless welding, poor housekeeping, and improper selection or misuse of materials are examples of human factors. Valve rupture and combustion control failure could be considered equipment failures. Ultimately, most equipment failures can be traced to design, manufacturing, installation, or maintenance problems or to misuse. If established burning is achieved after ignition, it must be determined why the fire continued to grow to full room involve-
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ment—that is, flashover, or, in the absence of compartmentation, such as that in a warehouse or industrial building, why it reached a certain extent. In providing answers, a number of factors must be evaluated, including the rates of heat release of the fuels, continuity of the fuels (i.e., the proximity of fuel packages to each other) and location of fuels relative to walls, compartment ceiling height, ventilation, and interior finish. Heat release rate is one of the more important factors in analysis. In many instances, a fire reported to have grown or spread “unusually fast” is characterized as suspicious or incendiary when, in fact, the growth rate may have been due to a combination of the burning properties of the materials and the nature of the compartment in which the fire burned. A number of studies have been carried out to characterize the burning rates of materials and furnishings. Data can be found in NIST reports and in Appendix B-2.2 of NFPA 72®, National Fire Alarm Code®.16,20–23 The roles of heat release rate, fire location, and ceiling height in fire development have also been reported.24 Alpert’s work includes methods to estimate ceiling temperatures and ceiling gas velocities. Guidance on estimating the likelihood that a given fire size and room ventilation combination can develop flashover also is provided in NIST reports and the SFPE Handbook of Fire Protection Engineering.25–27 The performance of automatic suppression systems in controlling the growth and spread of the fire also must be evaluated in the reconstruction process. Here, the factors to be reviewed include the appropriateness of the agent being used; the system response time, as related to the detection devices used, relative to ceiling height and fire growth rate; location of the agent discharge nozzles relative to the source of the fire; agent availability, including rate of discharge, pressure, and adequacy of supply; and conformance of the system design and installation with NFPA standards, industry design, and installation manuals. For example, a sprinkler system may have failed to control a fire due to a very high ceiling that delayed the response time, combined with low water pressure that could not produce the needed water flow rate. Another component of the reconstruction is barrier performance. Barrier performance evaluation focuses on the nature of the barrier, whether rated or not rated; barrier construction; the thermal stresses to which it was exposed; and the manner in which the barrier failed. Barriers can fail by passage of flame or hot gases through a small opening, by a hot spot failure, by movement of flame and hot gases through open doors, or by barrier collapse, resulting in a massive failure. Failure of opening protection, poor construction practices, modifications to the barrier after construction, and fire stresses that exceed those assumed in the design can be significant transporters of products of combustion beyond design limits. Manual suppression activities, whether by a municipal fire department or a plant fire brigade, can have a significant effect on the outcome of a fire. In the absence of fire suppression systems, the response time of the fire department for a given fire will influence the size of the fire at the time of agent application. For ease of analysis, the response time can be broken down into the following segments: detection time, alarm transmission time, dispatch time, travel time, and time from the arrival of fire suppression personnel to agent application. Problems resulting in
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delays in any of the above time segments will extend the limits of flame and smoke travel. Examples of factors that could cause delays are the absence of automatic detectors, the absence of people in the building, or an improperly designed detection system. Equipment failure or out-of-service fire apparatus can also delay response time. Weather, terrain, traffic, and the condition of apparatus can extend travel time to the incident. Frozen hydrants, blocked access, and shortage of personnel are also examples of factors that could delay application of fire suppression agents. The reconstruction process must also consider the performance of the building life safety system. This includes the detection and alarm system, the building egress system, and the smoke control system. In addition to the factors discussed above that affect detector response, the audibility of alarms plays a role in life safety. Guidance on this topic can be found in work by Nober,28 in NFPA 72, and in the SFPE Handbook of Fire Protection Engineering.29 Building egress factors include the capabilities of the occupants and the number, capacity, and protection of the egress routes. The movement of smoke in buildings is related to the temperature of the fire gases; differences between inside and outside temperatures, or the stack effect; effects of the building’s heating and air conditioning systems; and effects of wind.
Failure Analysis In a fire safety context, failure can be defined as a fire that results in personal injury, death, or property or monetary losses, or in conditions that prevent buildings or mechanisms from functioning as designed. In fire failure analysis, the objective is to use on-site and background data, testing results, and reconstruction to identify the primary and contributing causes of the failures and their sources. The sources of failures include basic design, material or equipment selection, material or equipment defects, construction or assembly, testing, postconstruction modifications, service conditions, and unanticipated conditions or abuse. The analysis is made by comparing the causes of failures with codes, standards, design practices, and the state-of-the-art technology present at the time of the fire. In the analysis, it is important to identify noncompliance with the standard practices, but it is even more important to note where compliance with the standards failed to provide the expected or needed degree of fire safety. In either event, failure analysis should provide recommendations for how the failures could have been prevented or how the knowledge gained can be applied to preventing similar failures in the future.
ORGANIZATION FOR FIRE INVESTIGATION It is a good idea to be prepared in advance for the investigation of a fire. The preparation may range from identifying an individual or company to hire as needed to the organization of a permanent fire investigation unit complete with full-time staffing, vehicles, and a laboratory. The level of organization selected de-
pends on the size of the organization, the frequency of need, the resources available, and the legal or statutory requirements. One other factor to be considered is whether or not the organization is in the public sector—the fire department, police department, state and federal government, and so on—or in the private sector—insurance company, product manufacturer, major hotel chain, and so on. Frequently, public sector needs will include more than just the ability to conduct a fire scene investigation. Should it be determined that the possibility of arson exists, the likelihood of criminal or civil action often requires the involvement of the police or persons trained in the legal aspects of arson and fraud investigation.
Public Sector In the public sector, the fire department personnel responding to the scene carry out most initial investigations. If the cause is easily determined and does not appear to be of a potentially criminal nature, the investigation ends at that level. When the cause cannot be determined, a fatality is involved, or arson is suspected, additional help is generally dispatched. In a small fire department, the local police or the county or state fire marshal’s office may be contacted. In some jurisdictions, the assistance may come from the country or state police. In large cities, a fire investigation unit is usually formed. The unit may be made up of fire department personnel and be wholly within the fire department, or the unit may be within the police department. Regardless of where the unit is placed organizationally, it is generally recommended that both fire investigation and police functions be represented in the background and training of personnel. This objective is often accomplished by selecting individuals from both departments to serve in the fire investigation unit. In some jurisdictions, an investigations unit is established in the local criminal prosecutor’s office. Such a unit will usually have arson detection and prosecution as its major focus where the caseload is high. A special prosecutor is often assigned specifically for arson, and that individual frequently is trained in fire investigation techniques. In many instances, fire investigation units in both the fire and police departments are called arson investigation units. Determination of arson can usually come only after a thorough fire investigation in which other possible causes are ruled out and physical evidence of an incendiary fire is established. This provision should be stressed to investigative personnel so they do not come to believe that their role is to find arson. The term fire investigation is more appropriate to the work that is done than arson investigation. If arson is a major problem in a community, special arson task forces can be established to identify arsonfor-profit groups, associating real estate buying and selling and insurance patterns with arson and arson prevention activities. This work is less concerned with actual fire scene investigation, and deals more with the establishment of motivation, insurance manipulation, and patterns of arson occurrence. Some federal agencies, such as the General Services Administration or the military services, have personnel who investigate fires involving their facilities. These personnel are generally assigned fire investigation in addition to other functions
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such as facility safety or fire protection design. In the event of a major fire, an agency may conduct its own investigation or use an outside consultant to assist its own personnel.
tigation skills. The specialist in arson investigation will need education and experience in the legal aspects of civil or criminal investigations, or possibly both.
Private Sector
Education
In the private sector, large insurance companies may have investigative units that conduct fire scene investigations and perform arson and fraud detection and control functions. Some companies employ adjustment bureaus or private investigators to make the initial cause determination, and follow up with their own personnel if it appears that arson or fraud is involved or if there is a particularly large loss. Small companies may rely exclusively on outside investigation services. A number of large industrial companies also maintain a fire investigative capability, often located in their risk management or loss prevention groups. These groups or individuals may investigate fires in company facilities or fires involving products or systems designed, manufactured, supplied, or installed by the company. These investigations may be for the purpose of future loss prevention or plant safety programs, or they may be carried out in response to actual or potential litigation. An important function of this type of investigation is the identification of the causative factors in the fire that could lead to improved design, manufacturing, installation, or operating practices. Organizations such as NFPA and the U.S. Fire Administration also investigate fires in order to determine “lessons learned.” Small companies may not be able to afford their own investigation staffs. In such cases, an appropriate outside capability should be identified in advance for use if the need arises. The individual or firm selected should either have or be given some knowledge of the specific products, facilities, or operations that are likely to be involved.
In the past decade, a great deal of data regarding the nature of the ignition process and the forces that control fire spread and growth has emerged. Research by university, government, and insurance laboratories has developed information that can explain much of the evidence remaining after a fire has been extinguished and assist in determining origin and cause. To determine adequately the origin and cause of a fire, the modern investigator needs a basic knowledge of physics and chemistry, preferably at the post-secondary-school level. The investigator should also be familiar with the concepts of heat release rate, fire plume and ceiling layer development, compartment flashover, and full room involvement. All fire investigators should also have some knowledge of the legal aspects of investigations, such as how to gain access to a scene, how to take and handle evidence, and how to question witnesses. Fire science courses offered at many postsecondary schools today can provide much of the needed background. Where such facilities are not available, basic science courses supplemented by study using the additional reading at the end of this chapter can be employed. In some areas of the country, the U.S. Fire Administration’s Open Learning Program is also available through selected local colleges and universities. In fire investigation units to which both police and fire personnel are assigned, personnel should be cross-trained in basic fire science and law enforcement. Departments that become familiar with each other’s technology and terminology benefit from enhanced communication, more complete and thorough investigations, and more successful prosecutions. Advanced education might include college-level courses in such areas as forensic science, industrial safety, insurance, accident investigation, and fire protection engineering.
EDUCATION AND TRAINING OF FIRE INVESTIGATION PERSONNEL The nature and extent of education, training, and experience needed by investigators obviously varies greatly with the specific goals and objectives for fire investigations set by the organization where they are employed and by budget resources. Some basic performance requirements for fire investigators are provided in NFPA 1033, Standard for Professional Qualifications for Fire Investigator. The level of knowledge needed by a fire ground officer faced with a residential fire extinguished early in its development will be less than that needed by an investigator from the department’s fire investigation unit. This investigator will have to deal with fires extinguished in more advanced stages, where the evidence of cause is often much less clear. In addition, this investigator will have to deal with fires in the full range of occupancies found in the unit’s jurisdiction. This could include residences, office structures, warehousing, manufacturing, and heavy industry. The private sector investigator employed by a petrochemical company may need a degree in chemistry or chemical or fire protection engineering in addition to the basic fire scene inves-
Training All investigators should be trained in the basics of fire scene investigation, which include adequate documentation of the scene, origin determination, and cause determination. Specific emphasis should be placed on techniques for debris removal and scene reconstruction. Although much of this knowledge can be gained by studying text materials, there is no substitute for field experience. Even limited hands-on work can be of great value in relating the text materials to “the real world.”
SUMMARY Fire loss investigation ranges in complexity from completing a fire incident report to detailed engineering reconstruction and failure analysis. Once rare, fire loss reconstruction and failure analysis is becoming more common. As described in this chapter, that process may include examination of the fire scene, collection of
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background data, testing, and the organized, step-by-step portrayal of the most likely course of the fire under study. The complexity of the fire loss investigation dictates the complexity of training needed to conduct the investigation. NFPA 1033 prescribes minimum basic competencies. In addition, a basic knowledge of physics and chemistry is needed. College-level study in areas such as forensic science, insurance, accident investigation, and fire protection engineering is needed for the successful and credible investigation and reconstruction of complex fires.
BIBLIOGRAPHY References Cited 1. Hendrick, K., and Benner, L., Investigating Accidents with STEP, Marcel Deckker, New York, 1987. 2. Lyons, P. R., Techniques of Fire Photography, National Fire Protection Association, Quincy, MA, 1978. 3. Kodak, Using Photography to Preserve Evidence, Pamphlet M-2, Eastman Kodak Company, Rochester, NY, 1976. 4. Kodak, Fire and Arson Photography, Pamphlet M-67, Eastman Kodak Company, Rochester, NY, 1977. 5. Drysdale, D., Introduction to Fire Dynamics, John Wiley & Sons, New York, 1985. 6. Putorti, A. D., Flammable and Combustible Liquid Spill/Burn Patterns, NIS Report 604-00, National Institute of Justice, Washington, DC, March 2001. 7. Putorti, A. D., Full Scale Room Burn Pattern Study, NIS Report 601-97, Publication 169 281, National Institute of Justice, Reference Service, Washington, DC, 1997. 8. Shanley, J. M. et al., USFA Burn Pattern Tests FA-178, U.S. Fire Administration, Emmitsburg, MD, July 1997. 9. ASTM E162, Standard Test Method for Surface Flammability of Materials Using a Radiant Heat Energy Source, American Society for Testing and Materials, W. Conshohocken, PA, 1994. 10. ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials, American Society for Testing and Materials, W. Conshohocken, PA, 1995. 11. Standard for the Flammability of Clothing Textiles (CS-191-53), 16CFR1610, Code of Federal Regulations, 1953. 12. Standard for the Flammability of Children’s Sleepwear: Sizes 0 Through 6X (FF3-71) 16CFR1615, Code of Federal Regulations, 1981. 13. ASTM D92, Standard Test Method for Flash and Fire Points by Cleveland Open Cup, American Society for Testing and Materials, W. Conshohocken, PA, 1990. 14. ASTM D56, Standard Test Method for Flash Point by Tag Closed Tester, American Society for Testing and Materials, W. Conshohocken, PA, 1993. 15. ASTM E906, Standard Test Method for Heat and Visible Smoke Release Rate for Materials and Products, American Society for Testing and Materials, W. Conshohocken, PA, 1983. 16. Babrauskas, V. et al., Upholstered Furniture Heat Release Rates Measured with a Furniture Calorimeter, NBSIR 82-2604, National Bureau of Standards, Gaithersburg, MD, 1982. 17. Henley, E. J., and Kumamoto, H., Reliability Engineering and Risk Assessment, Prentice Hall, Englewood Cliffs, NJ, 1981. 18. Nelson, H. E., Engineering Analysis of the Early Stages Fire Development—The Fire at the DuPont Plaza Hotel and Casino— December 31, 1986, NBSIR 87-3560, National Institute of Standards and Technology, Gaithersburg, MD, 1987. 19. Nelson, H. E., Engineering View of the Fire of May 4, 1988, in the First Interstate Bank Building, Los Angeles, California, NISTR 89-4061, National Institute of Standards and Technology, Gaithersburg, MD, 1989.
20. Babrauskas, V., Combustion of Mattresses Exposed to Flaming Ignition Sources Part I: Full-Scale Tests and Hazard Analysis, NBSIR 77-1290, National Bureau of Standards, Gaithersburg, MD. 21. Babrauskas, V., Full-Scale Burning Behavior of Upholstered Chairs, NBSTN 1003, National Bureau of Standards, Gaithersburg, MD, 1979. 22. Lee, B. T., Heat Release Rate Characteristics of Some Combustible Fuel Sources in Nuclear Power Plants, NBSIR 85-3195, National Bureau of Standards, Gaithersburg, MD, 1985. 23. Walton, W. D., and Twilley, W. H., Heat Release and Mass Loss Rate for Selected Materials, NBSIR 84-2960, National Bureau of Standards, Gaithersburg, MD, 1984. 24. Alpert, R. L., and Ward, E. J., Evaluation of Unsprinklered Fire Hazards, Technology Report 83-2, Society of Fire Protection Engineers, Boston, 1983. 25. Babrauskas, V., “Estimating Room Flashover Potential,” Fire Technology, Vol. 16, No. 2, 1980, p. 94. 26. Babrauskas, V., “Will the Second Item Ignite?” Fire Safety Journal, Vol. 4, 1981–1982, p. 281. 27. Walton, W. D., and Thomas, P. H., “Estimating Temperatures in Compartment Fires,” SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno et al. (Eds.), National Fire Protection Agency, Quincy, MA, 1995, pp. 3–134 to 3–147. 28. Nober, E. H., et al., “Waking Effectiveness of Household Smoke and Fire Detection Devices,” NBSGCR-80-284, National Bureau of Standards, Gaithersburg, MD, 1984. 29. Schifiliti, R. P., Meacham, B. J., and Custer, R. L. P., “Design of Detection Systems,” SFPE Handbook of Fire Protection Engineering, P. J. DiNenno et al. (Eds.), National Fire Protection Agency, Quincy, MA, pp. 4–21 to 4–29.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information about fire and arson investigation. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 72®, National Fire Alarm Code® NFPA 422, Guide for Aircraft Accident Response NFPA 901, Standard Classifications for Incident Reporting and Fire Protection Data NFPA 902, Fire Reporting Field Incident Guide NFPA 903, Fire Reporting Property Survey Guide NFPA 904, Incident Follow-up Report Guide NFPA 921, Guide for Fire and Explosion Investigations NFPA 1033, Standard for Professional Qualifications for Fire Investigator
Additional Readings “Arson Fire Kills 87 in Worst Mass Slaying in U.S. History,” Fire Control Digest, Vol. 16, No. 4, 1990, pp. 1–4. “Arson Fires Leave Few Clues,” Fire and Flammability Bulletin, Nov. 1993, pp. 5–6. Andersson, H., “Swedish Investigation of Arson,” Fire Technology, Vol. 29, No. 4, 1993, pp. 350–373. Babrauskas, V., “Burning Rates,” SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 1995. Barber, K., et al., “Social Issues and Juvenile Arson,” Insurance Committee for Arson Control, 1992 National Arson Forum, September 9–10, 1992, Arlington, VA, 1992, pp. 1–2. Beale, R., “Arson: The Problem of Proof,” Fire Prevention, No. 244, Nov. 1991, pp. 30–31. Brannigan, V., “Arson and the Fourth Amendment,” Fire Chief, Vol. 37, No. 4, 1993, pp. 22–24. Burnett, G. E., Jr., “Checklist for Investigating the Arson-for-Profit Scheme,” Fire and Arson Investigator, Vol. 42, No. 4, 1992, pp. 14–16.
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Carlsson, G., and Wistedt, I., “Analysis of Arson Accelerant Residues by ATD 400,” SKL-National Laboratory of Forensic Science, Linkoping, Sweden, Report 26, Mar. 15, 1993. Catchpole, L., “Counselling Your Arsonists,” Fire Prevention, No. 273, Oct. 1994, pp. 25–27. Chubb, M., “High Temperature Accelerant (HTA) Arson Fires,” USFA Fire Investigation Technical Report Series, TriData Corp., Arlington, VA, Federal Emergency Management Agency, Washington, DC, Report 065, 1992. Corry, R. A., and Golembeski, J. K., “Solving an ‘Impossible’ Arson Case,” Fire and Arson Investigator, Vol. 41, No. 1, 1990, pp. 36–37. deHaan, J. D., Kirk’s Fire Investigation, 4th ed., Prentice Hall, Upper Saddle River, NJ, 1997. Eisner, H., “Arson Wave Strikes Lawrence, Massachusetts (MA),” Firehouse, Vol. 17, No. 8, 1992, pp. 36–37. Eisner, H., “Lawrence, Massachusetts: Arson Hits City as Cutbacks Decrease Fire Protection,” Firehouse, Vol. 19, No. 6, 1994, pp. 32–35, 116. Factory Mutual Engineering, “Prevention of Arson Fires,” Factory Mutual Engineering, Norwood, MA, P9213, March 1995; Factory Mutual Engineering, Business Under Fire! A Manager’s Guide to Fire Prevention Programs, 1995, pp. 1–4. Federal Emergency Management Agency, “Arson Forum Report and Analysis and Recommendations for Federal Arson Policy and Priorities,” FA-134, Federal Emergency Management Agency, Washington, DC, June 1993. Federal Emergency Management Agency, “Arson in America: A Profile of 1989 NFIRS,” USFA Fire Investigation Technical Report Series, Special Report, TriData Corp., Arlington, VA, Federal Emergency Management Agency, Washington, DC, 1991. Federal Emergency Management Agency, “Arson Resource Directory,” FA-74, Federal Emergency Management Agency, Washington, DC, Apr. 1993. Federal Emergency Management Agency, “Fire/Arson Investigation Training Resource Catalog,” FA-131, Federal Emergency Management Agency, Emmitsburg, MD, Mar. 1993. Ferry, T. S., Modern Accident Investigation and Analysis, 2nd ed., John Wiley & Sons, New York, 1990. Few, E. W., “Tracking Arsonists in America’s National Forests,” Firehouse, Vol. 15, No. 8, 1990, pp. 34–35, 83. Friedman, R., Principles of Fire Protection Chemistry and Physics, 3rd ed., National Fire Protection Association, Quincy, MA, 1998. Governors Special Arson Task Force, California State Fire Marshals Office and California District Attorneys Association, “Arson Investigation . . . A Team Approach,” Governors Special Arson Task Force, CA, State Fire Marshals Office, CA, District Attorneys Assoc., CA, Team Approach, 1994. Hall, J. R., Jr., U.S. Arson Trends and Patterns [Annual], National Fire Protection Association, Fire Analysis and Research Division, Quincy, MA. Higgins, S. E., “Complex Arson: A Specialty of ATF Labs,” Firehouse, Vol. 18, No. 9, 1993, pp. 50–51. Higgins, S. E., “Portrait of a Serial Arsonist. The Newest Tool in the War against Arson,” Firehouse, Vol. 15, No. 8, 1990, pp. 54–57. Icove, D. J., and Horbert, P. R., “Serial Arsonists: An Introduction,” Police Chief, Dec. 1990, pp. 46–47. Icove, D., “Arson Awareness,” Federal Fire Forum on Engineering Aspects of Fire Investigations, April 5, 1990, Gaithersburg, MD, 1990. “Incendiary Devices: Information and Guidance. Fire Safety Data Arson Dossier AR4,” AR41, Fire Protection Assoc., London, UK, 1990. Investigator, Vol. 40, No. 3, 1990, pp. 50–52. Keltner, N., et al., “Investigation of High Temperature Accelerant Arsons,” Proceedings of the Extended Abstracts of the Society of Fire Protection Engineers Engineering Seminars on Large Fires: Causes and Consequences, November 16–18, 1992, Dallas, TX, Society of Fire Protection Engineers, Boston, 1992, pp. 20–22; Proceedings of the 6th International Fire Conference on Fire
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Safety, INTERFLAM ’93, March 30–April 1, 1993, Oxford, UK, Interscience Communications Ltd., London, UK, 1993, pp. 607–620; Proceedings of the 18th International Conference on Fire Safety, Vol. 18, January 11–15, 1993, Millbrae, CA, Product Safety Corp., Sunnyvale, CA, 1993, pp. 393–399. Kennedy, P. M., “The Crisis in Fire Investigation Education,” Fire Journal, Vol. 83, No. 6, 1989, p. 13. Kinard, W. D., and Midfiff, C. R., Jr., “Arson Evidence Container Evaluation. Part 2. New Generation Kapak Bags,” Fire and Arson Investigator, Vol. 43, No. 1, 1992, pp. 22–26. Klem, T. J., “Los Angeles High-Rise Bank Fire,” Fire Journal, Vol. 83, No. 3, 1989, p. 72. Klem, T. J., Investigation Report on the Dupont Plaza Hotel Fire, National Fire Protection Association, Quincy, MA, 1987. Madrzykowski, D., and Vettori, R. L., “Simulation of the Dynamics of the Fire at 3146 Cherry Road NE, Washington, DC, May 30, 1999,” NISTIR 6510, National Institute of Standards and Technology, Gaithersburg, MD, April 2000. Matthews, D. B., “Identification of Flammable Liquids in Arson Evidence,” Proceedings of the 18th International Conference on Fire Safety, Vol. 18, January 11–15, 1993, Millbrae, CA, Product Safety Corp., Sunnyvale, CA, 1993, pp. 133–139. Midkiff, C. R., Jr., “Spalling of Concrete as an Indicator of Arson— Let’s Look at the Concrete before We Decide,” Fire and Arson Investigator, Vol. 41, No. 2, 1990, pp. 42–44. National Volunteer Fire Council, “National Volunteer Fire Council Meets with FBI on Firefighter Arson,” Firefighter Arson Special Rpt., National Volunteer Fire Council, Washington, DC, Aug. 1994. Nelson, H. E., “Science in Action: An Engineering View of the Fire at the First Interstate Bank Building,” Fire Journal, Vol. 83, No. 4, 1989, p. 28. “New York—Bronx Social Club Arson Claims 87 Lives. On the Job,” Firehouse, Vol. 15, No. 6, 1990, pp. 46–48. Payne, B., “Arson Attacks on Places of Worship,” Fire Prevention, No. 284, Nov. 1995, pp. 26–27. Pengra, A. G., “Partial System Not Enough: Arson Fire in Partially Sprinklered Motel Kills Four, Injures Others,” Sprinkler Age, Vol. 15, No. 3, 1996, pp. 20–21. Sapp, A. D., et al., “Report of Essential Findings from a Study of Serial Arsonists,” Central Missouri State Univ., Warrensburg, Federal Bureau of Investigation, Quantico, VA, Bureau of Alcohol, Tobacco and Firearms, Washington, DC, 1994. “Scene Reconstruction: Prefire Positioning Can Furnish Important Clues,” Fire Findings, Vol. 9, No. 1, 2001, pp. 12–13. Shriver, K., “Financial Records Investigation Assist in Conviction of Arsonist: One Case Study,” Fire and Arson Investigator, Vol. 45, No. 4, 1995, pp. 19–20. Skelley, M. J., “An Experimental Investigation of Glass Breakage in Compartment Fires,” NIST-JCR-90-578, National Institute of Standards and Technology, Gaithersburg, MD, 1990. Stambaugh, H., “Grems Case: How an Arson Case Was Solved and Prosecuted in Colorado,” USFA Fire Investigation Technical Report Series, Report 047, TriData Corp., Arlington, VA, Federal Emergency Management Agency, Washington, DC, 1991. Strube, D., “Fire Investigations Involving Motor Loads and Conductor Overcurrent Protection,” Fire Journal, Vol. 83, No. 5, 1989, p. 83. Tobin, W. A., “What Collapsed Springs Really Tell Arson Investigators,” Fire Journal, Vol. 84, No. 2, 1990, pp. 24–27. Tobin, W. A., and Monson, K. L., “Collapsed Springs in Arson Investigations: A Critical Metallurgical Evaluation,” Fire Technology, Vol. 25, No. 4, 1989. Trimpe, M. A., “What the Arson Investigator Should Know about Turpentine,” Fire and Arson Investigator, Vol. 44, No. 1, 1993, pp. 53–55. Williams, H. E., Pavllsin, M. J., and Kightlinger, S. M., “Understanding and Effectively Utilizing the Arson Reporting Immunity Laws,” Fire and Arson Investigator, Vol. 42, No. 2, 1991, pp. 23–31.
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SECTION 3
Fire Data Collection and Databases
H
ow do we know what we know about fire? Where do the statistics come from? Although some tests can be done in laboratories, laboratory tests don’t explain what causes the largest number of fires or how often fire kills people. In this chapter, several real-world data sources for fire analysis are described. Most of this chapter will focus on the U.S. National Fire Incident Reporting System (NFIRS), the largest and most detailed fire incident database in the world and the source of most of what we know about fire. NFIRS provides a standard format for data collection, enabling aggregation of and comparisons across stations, communities, and states. NFIRS was designed to meet the needs of both the people collecting the data and the people who use it. NFIRS has been widely used since 1980 and has added and dropped data elements at several times in different versions. A few areas began implementing Version 5.0 in 1999. Between one-third and one-half of the states were at least accepting Version 5.0 incidents during 2000. Version 5.0 of NFIRS is being implemented at various speeds in fire departments around the country. NFIRS 5.0 was designed to give local fire officers greater ability to document their department’s activities and experiences and represents a major departure from the structure of earlier versions. NFPA’s annual fire department survey, the source of the fire problem’s “big picture,” and scaling ratios to be used with NFIRS will also be discussed in some detail. Additional information will be provided on the following: • NFPA’s Fire Incident Data Organization (FIDO), an anecdotal database • The death certificate database • The National Electronic Injury Surveillance System (NEISS), a system that tracks injuries treated at emergency rooms • The FBI’s Uniform Crime Reporting System (UCR), the source for data on arson arrests • Some fire incident data collection systems elsewhere in the world and international fire data collection efforts
Marty Ahrens is a fire analysis specialist at NFPA. Stan Stewart works as a computer specialist within the U.S. Fire Administration’s National Fire Data Center. Paul L. Cooke is director of Colorado’s Division of Fire Safety and president of the National Fire Information Council (NFIC).
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Revised by
Marty Ahrens Stan Stewart Paul L. Cooke
W o r l d v i e w In some countries, fire data collection is a government function; in others, it is done by the insurance industry. Definitions vary from country to country, so comparisons should be made with caution. • Canada: In Canada, as in the United States, the system is three-tiered. Local fire departments report their data to the provinces. However, the provinces report the totals, not the incidents themselves, to the Association of Canadian Fire Marshals and Fire Commissioners. • Australia: The Australian Fire Incident Reporting System (AFIRS) is structured similarly. Fire brigades in the Australian Assembly of Fire Authorities collect data on each incident. This incident is then entered into a database at CSIRO. Although the Australian states had been collecting data for several years, AFIRS first requested data from the states for fiscal year 1989–1990. While most states had been using the Australian Standard AS 2577, 1983 edition, Collection of Data on Fire Incidents, as the basis for their reporting, the fire services in each state had modified some elements to meet their own needs. They have been working on ensuring standardization. The data classification system for AFIRS is very similar to NFIRS. • Sweden: In Sweden, the insurance industry collects fire data. Only fire deaths are reported to the government. When the insurance industry collects the data, it is likely that fires in uninsured properties or fires that do not trigger a claim will be underreported. • United Kingdom: Fire brigades (departments) in the United Kingdom report their fires directly to the Home Office in London. In addition, the British Crime Survey includes questions about fire experience and provides some information about fires that were never reported. The federal government manages these databases. However, the government does not collect dollar loss information; that task is left to the insurance industry. The British fire databases are described in Fire Statistics—A User Guide for Research.1 • Japan: Fire departments in Japan also report their fires directly to a national government office.
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The use of fire data and the implications of NFIRS Version 5.0 for fire data analysis are discussed in Section 3, Chapter 3, “Use of Fire Incident Data and Statistics.”
HISTORY OF NFIRS The need to collect aggregated fire data was realized and identified in 1972 when President Nixon’s Commission on Fire Prevention and Control issued a report called “America Burning.”2 Among other things, the report documented the fact that the United States had one of the highest fire death rates at that time in the industrialized world. As a result of the report, it had become painfully obvious that we had a big fire problem in the United States, yet we knew very little about its exact nature. This alarming fact led directly to the National Fire Prevention and Control Act, Public Law (P.L.) 93-498 in 1974. The act directed the formation of the U.S. Fire Administration (originally called the National Fire Prevention and Control Administration) in order to initiate a national focus on the fire problem. Section 9 of the act established the National Fire Data Center to “provide an accurate, nationwide analysis of the fire problem, identify major problem areas, assist in setting priorities, determine possible solutions to problems, and monitor the effectiveness of programs to reduce fire losses.” The National Fire Data Center established the National Fire Incident Reporting System to meet their charter. Early data collection efforts varied throughout the country. In the past, local fire departments used their own systems of documentation. For many small fires, the department log was the only documentation that an incident occurred. Other departments had developed their own reports and even their own coding system, but most reports were simply narratives of the incident and actions taken to manage it. Pulling meaningful information or even simple statistics from narratives, however, is an exercise in frustration at the local level and nearly impossible at the state and national levels. Fire service leaders and the NFPA had recognized this as a problem for a long time. By 1969, the NFPA had already identified data elements and developed standardized classifications for recording and reporting fire incidents. NFPA 901, Uniform Coding for Fire Protection, provided the classification system for the then new National Fire Incident Reporting System. (Some data elements in the standard are not included in NFIRS.) The 1976 edition of the incident and civilian casualty codes, and the 1981 edition of fire service casualty codes were used until the recent release of NFIRS 5.0. The first Fire in the United States report was published by the U.S. Fire Administration’s National Data Center in December 1978. The authors noted that better fire data were needed: “The most detailed data on fire causes were available for a full year for only two states—California and Ohio. A few other states had detailed data, but not in a form that was easily comparable. The limited State data available this year were supplemented by data from seven cities (in other states) with compatible data systems.”3 California’s data were for 1975, and Ohio’s data were for 1976. The second Fire in the United States was published in 1982.4 This report looked at fires in 1978 and included full-year
data for 15 states. Other volumes have appeared since then, usually on an annual basis. By April 1981, 38 states and the District of Columbia were either participating in NFIRS or preparing to participate. In the late 1970s and early 1980s, the USFA provided states with funding and other resources to help implement NFIRS in their states. One of the long-term goals of NFIRS is to promote local fire incident reporting. Because of fiscal, technical, or personnel issues, some participating states have had years in which they were unable to submit data. Consequently, it is hard to precisely define which states are or are not participating in the national system.
NFIRS—A THREE-TIERED SYSTEM Local fire departments, state fire agencies, and the federal government all play critical roles in collecting NFIRS data.
NFIRS at the Local Level Fire officers and firefighters at the local level provide the basis of the system. Without their efforts, this system could not work. By completing a fire report, a fire officer does three important things. First, he or she is making a legal public record that documents the incident. Second, the fire officer’s report provides information to senior officers and fire department managers so that they are kept informed about what is happening within their areas of responsibility. This allows them to evaluate the performance of their units at the incident and to talk intelligently about the incident to the media and others. Good information about a fire can motivate change in fire protection approaches in a community or even the nation (e.g., the MGM Grand Hotel fire in Las Vegas, Nevada, in 1980 helped to trigger a wave of improvements in fire safety). Finally, the report provides data on the fire problem to fire service management so that they can track trends, gauge the effectiveness of fire prevention and fire suppression measures currently in practice, evaluate the impact of new methods, and indicate those areas that may require further attention. For the first two purposes, the report format may vary considerably. The report may be as brief as a basic fact statement or as lengthy as an extensive discussion of the fire, supported by photographs, witness statements, laboratory test results, and physical evidence. The length and complexity of the report will depend on the size and nature of the fire, the local fire service manager’s need for specific data, and the resources available for obtaining information and completing reports. They also depend on the training and motivation of the person filling out the report. A fire report should include, at some level of detail, a timestaged description of the circumstances related to the initiation, discovery, growth, and termination of the fire, along with a description of the casualties or the damage resulting from the incident. This report should be in the words of the fire officer and
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must be complete so that people who were not at the fire scene can understand what happened. A standardized format is required before statistics can be extracted to meet the third purpose. Statistics can reveal patterns or trends, enable comparisons across jurisdictions, and play an important part in service and program evaluations. NFIRS provides a format to make it possible to obtain these statistics. Fire officers who use NFIRS to document incidents are simultaneously collecting and providing data on the time of the incident, the occupancy, the area where a fire started, what caught fire, what started the fire, property damage, casualties, whether sprinklers and detectors were present, and whether they worked. Using the NFIRS structure and codes, these fire officers provide data on what worked to keep small fires from growing in addition to documenting what went wrong at big fires. The reports may be handwritten, typed, or entered directly into a computer. The older systems were built around paper formats, although the data may have been entered directly into a computer. Version 5.0 was designed as a modular, computer-based system in which the user will be shown the questions that must be answered. Paper forms may be used but will appear cumbersome because they must provide for different circumstances. Figure 3.2.1 shows an example of a NFIRS report form. All the data in the National Fire Incident Reporting System originally come from local fire officers and firefighters. Approximately 14,000, or almost half, of the nation’s public fire departments report at least one fire to NFIRS each year. More and more fire departments see NFIRS as a tool for local use. As computers have become more powerful and software easier to use, the NFIRS system has become a vital management tool. A fire chief can see which companies are busiest, what the leading fire problems were last year, and how many incidents of each type occurred. Some departments use the statistics to justify budgets or apply for grants. Departments seeking funds under the 2001 Assistance to Firefighters Federal Grant Program must participate in NFIRS. Some departments integrate NFIRS data with information concerning other department activities to create a comprehensive management information system (MIS). Some systems transfer computer-aided dispatch (CAD) information directly into the appropriate incident report fields. NFIRS Reports Beginning as Local Records. Although analysts think of NFIRS as a tool for research about fire, at the local level it is first a systematic record-keeping system. The incident report describes where and when the incident occurred, the resources used, and the services performed. It provides the framework to collect information about how the fire started, how fire protection systems worked, and the nature of any injuries. These reports are public records. At times, the needs of the researcher for details and the needs of the fire service for efficiency conflict; the needs of the fire service will take priority. At times, coding practices may violate NFIRS rules but make perfect sense. The field “item first ignited” (“form of material first ignited” in older versions of NFIRS) describes the shape or form as the object or substance is customarily used, such as upholstered furniture, fuel, or clothing. The field “type of material first
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ignited” captures information about the composition of the object or substance, such as cotton, sawn wood, or gasoline. Under these rules, it is inconsistent to see a fire in which the form of material first ignited was upholstered furniture and the type of material was gasoline. However, from a documentation standpoint, this may be a very accurate description of an incendiary fire. In the old days of paper forms, a fire officer might write in, “Gasoline poured on chair cushion.” NFIRS training should encourage consistency between these two fields and further explanation of specific circumstances in the narrative. Cause and Origin Skills Essential Parts of Local NFIRS. The persons responsible for reporting the data should be trained and capable of investigating a fire to determine the origin, cause, and circumstances of the fire. Their determinations become the data used by the system. Weaknesses here can undermine the validity of the data and of any analyses performed on the data. The fire department should have certain standards that apply to all its record-keeping operations. Such standards will help make the data more uniform from report to report and application to application. Standardization aids all users of the data, makes analysis more accurate, and is essential if data is to be automated. Some areas where department standards should be developed include the following: • Methods of entering the names of persons and businesses on records. NFIRS 5.0 provides a clear system for people’s names, but businesses are trickier. • Recording addresses of buildings with multiple or ambiguous addresses, as well as nonstructure locations, such as those on highways or at street intersections • Designating apparatus. Should it be done by company assigned? Serial number? Shop number? • Designating employees. Should it be done by name? Badge number? Social Security Number? • The common abbreviations that are acceptable to use. Updating incident reports is crucial to a fire data system. The updating of incident reports as better or more complete information becomes available is often not done. This is a major problem in the quality of information available. The lack of updates is especially common for fatal fires and large-loss fires, for which the initial incident report is left incomplete pending an investigation but does not get updated after the investigation is complete. Each department should have detailed written procedures explaining how to perform each step in report compilation. These procedures should address such issues as how the reports are to be edited, processed, and filed; within what time frame; and how they are to be corrected or updated. Everyone responsible for completing any portion of the report should understand the procedures and schedule for completing, correcting, and forwarding the data. Delays in submitting data will result in delays in assembling the complete report and in making it available for use. Record Retention. Local fire officials must obtain or develop a record retention schedule for all their records.
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FIGURE 3.2.1
Example of NFIRS Report Form
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FIGURE 3.2.1
Continued
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3–20 SECTION 3 ■ Information and Analysis for Fire Protection
There should be a written policy that details the length of time a report is to be retained in the active files, the length of time it should be kept in inactive storage, and when it can be discarded. The city attorney’s office can help to determine legal requirements for retaining records; that office should review the final written policy before its implementation. Obviously, paper records require storage space, and storage space costs money. As the files become more voluminous, the likelihood that material will be lost or misfiled also increases. The costs for electronic data storage have decreased in recent years. There may be different retention requirements for computerized records, which require less space and are useful for multiyear analysis. Ongoing changes in the computer industry pose challenges for record retrieval. As new technology and programs replace old, will the older electronic records be accessible? It is now hard to find a machine that can read data on a 5¼ inch floppy disk. Because the media can deteriorate, duplicate copies of archived records are advised. Before discarding old software, users should confirm that a new version or system can retrieve old records in an acceptable format. Motivation to Complete Reports. Better data come from fire fighters who see, use, and understand the compiled statistics. Although far more fire fighters will complete the forms than actually access the data, data quality will improve if the fire fighters collecting the data understand how it is analyzed. Training officers and command staff are encouraged to share reports describing activities at their own department, their state’s annual reports, and statistical reports produced by the USFA and NFPA with their fire fighters to ensure that they know their completed reports are used.
NFIRS at the State Level States generally provide the forms or form layout used by local departments. Some states use the standard NFIRS forms without modification. Some have added a few additional data elements or changed the format slightly. A few states have modified the NFIRS data classification to meet their own needs. These states convert the data back to the standard format before forwarding the data. New computer technology has made the system more efficient, but it introduces complications besides quality control issues. Getting data electronically cuts costs and saves time. However, the data have to be in a format that the state computer can process. In most states that have mandatory incident reporting, the state authority also dictates the form the reports will take. Most states plan to at least accept Version 5.0 by 2001, but some may not. Some states collect additional information. Vendors selling NFIRS software in a state must check with the state authority to be sure that their software collects all the information the state requires. Local departments should also check with the state before making a purchase. State fire agencies administer NFIRS in a variety of ways. In some states, one person has primary responsibility for the whole system, the training, quality control, entry, analysis, and report writing. In others, these responsibilities are divided among several individuals or divisions.
NFIRS at the Federal Level Periodically, after the NFIRS data have been entered and checked for errors, state NFIRS administrators send the compiled data from each incident or release the incidents to the USFA via the federal server. The power of NFIRS at the national level comes from having the details of individual incidents as opposed to a collection of state totals. It is impossible to predict all of the questions that will arise. Although a few fields are not forwarded, most are. This makes it possible to run new queries on specific items. The USFA provided states with the basic software to run NFIRS at the state level. Initially, this was mainframe software and then DOS-based PC software modeled after that used on the mainframe. Local departments were able to purchase a version of this software at a nominal cost. However, it had none of the bells and whistles of the newer commercial software. The National Fire Data Center processes the data that the states submit. It periodically publishes Fire in the United States and other analyses. After the data are compiled nationally, other users, such as the NFPA, the U.S. Consumer Product Safety Commission (CPSC), and private entities, may obtain the data for their own analyses.
National Fire Information Council (NFIC) and NFIRS The National Fire Information Council (NFIC) is a nonprofit, volunteer organization. From its beginning of six states in 1975, the Council now encompasses 45 states and 33 metropolitan jurisdictions. The NFIC is a unique partnership of federal, state, and local participants. The USFA funds the NFIC through a series of cooperative agreements. The NFIC comprises representatives from participating state fire agencies, the District of Columbia and metropolitan departments that protect populations of at least 500,000. It is the umbrella organization for NFIRS. It provides specialized training and the opportunity to learn from other people doing the same work. The NFIC provides technical assistance to states on request and answers coding questions that stump state program managers. The NFIC has been working with the USFA on the development of the new NFIRS. State and metropolitan representatives bring to the process the concerns of firefighters out in the field; they share ideas, discuss common problems, and network to avoid reinventing the wheel. The USFA and NFIC work together to manage NFIRS and promote fire incident reporting. The NFIC identifies states that are having problems with their reporting systems. Its members provide each other with specific technical assistance. The USFA, through the National Fire Academy (NFA), and NFIC jointly sponsor a NFIRS Program Management course twice a year at the NFA. The course enables participants to promote, support, and manage NFIRS data collection. The content includes data collection, processing, analysis, and presentation of useful, timely, and accurate information about fire department activities. It is designed for new and experienced state, metropolitan, and fire department NFIRS program managers. As in NFIC, participants learn from both structured classes and from each other.
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NFIRS DEFINITIONS One of the benefits of NFIRS or any systematic data collection effort is the standardization of terminology. However, this means taking the time to examine terms or words that are familiar in everyday usage but have very specific meanings in the system’s context.
Defining Fire The American Heritage Dictionary, Third Edition, 1994, gives two relevant definitions for the word fire: (1) “A rapid, persistent chemical change that releases heat and light and is accompanied by flame, esp. the burning of a combustible substance and (2a) burning fuel or (2b) A destructive burning.”5 Yet fires in NFIRS include only those fires that are considered “hostile.” Appendix C—Glossary and Abbreviations in the NFIRS 5.0 Reference Guide defines fire as “Any instance of destructive and uncontrolled burning, including explosion, of combustible solids, liquids, or gases.” Fire does not include the following, except when they cause fire or occur as a consequence of fire: • Lightning or electrical discharge • Rupture of a steam boiler, hot water tank, or other pressure vessel due to internal pressure and not to internal combustion • Explosion of munitions or other detonating material • Accident involving ship, aircraft, or other vehicle • Overheat condition.6 Fire department responses to someone burning with a permit or unauthorized burning would not be considered hostile fires and would not be counted as fires at all unless they got out of control.
What Is a Structure Fire? Structures include buildings but are not limited to them. Tents, storage tanks, tunnels, and covered walkways would all be considered structures but not buildings. In older versions of NFIRS, any fire inside a structure whether it involved the structure or not or any fire under or touching a structure that involves the structure would be considered a structure fire. This is still true in Version 5.0, with one notable exception. In older versions, a vehicle burning inside a structure was considered contents of, or the equipment involved in, a structure fire. Judging from the large number of vehicle fires that occurred at parking garages, it is clear that this convention was not always observed. Under the Version 5.0 rules, a vehicle burning inside a structure would be considered a vehicle fire unless the structure became involved. At that point, the incident becomes a structure fire, but vehicle information can be picked up in the mobile property section. Under the rules established for Version 5.0, abbreviated reporting is allowed for certain types of confined structure fires, including fires confined to cooking vessels, chimneys, incinerators, fuel or oil burners or boilers, trash compactors, and trash or rubbish with no flame damage to the structure or its contents. This means that only the Basic Module would be completed. States and local fire department officials may elect to require full reports on all of these fires. Because no causal information
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would be collected on abbreviated reports, full reports are suggested when incidents might be incendiary.
Civilian and Fire Service Casualties Distinctions are generally made in discussing civilian and fire service injuries and deaths. Civilians include anyone, including the police or other emergency personnel, who is not a member of the fire service. Different data collection systems have defined fire deaths somewhat differently. According to NFIRS, fire deaths include anyone who dies as a result of the fire within one year of the fire. Although smoke inhalation and burns are the most common causes of fire deaths, a person would be considered a fire fatality if fatally injured while jumping out of a burning building or if a fatal heart attack struck during a fire. In some cases, particularly vehicle fires that were caused by collisions, it may be necessary to obtain autopsy results to determine whether an individual should be counted as a fire fatality. People who died immediately of trauma would not be counted. NFPA uses death certificates to compare fire death rates among the states.7 Death certificates track where the victim died, not the state in which the fatal injury occurred. Death certificates may list fire deaths caused by collisions simply as motor vehicle accidents. Self-immolations may be counted as simply suicides, and some arson-related deaths are counted as homicides. When a body is found at an arson scene, it is necessary to determine whether the victim died before or as a result of the fire. The NFPA and USFA track fire fighter fatalities individually and do not place a time limit on the death.
Equipment Involved in Ignition “Equipment involved in ignition” refers to the equipment that provided the heat that started the fire. This does not mean that the equipment malfunctioned in any way. Even if the equipment was misused, if it provided the heat, it should be documented. An upholstered chair may be too close to a space heater. An iron may have been left on. Also, fixed wiring inside the wall should be considered a type of equipment.
Arson, Incendiary, Suspicious, and Intentional Many people are interested in arson. Older versions of NFIRS had two categories of ignition factors that, for statistical purposes, were generally lumped together as arson. Incendiary was used when a legal decision had been made or physical evidence indicated that a fire was deliberately set. Suspicious was used when circumstances indicated that the fire may have been deliberately set, multiple ignitions were found, or there were suspicious circumstances and no natural or unintentional cause could be found. Although suspicious was not appropriate as a final cause following an investigation, many fires were not fully investigated, and this cause could serve as a flag. Intentional replaces the terms incendiary and suspicious on the Fire Module cause categories of Version 5.0. (Incendiary is still a choice on the Wildland Module.) When older data is
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converted to Version 5.0, incendiary and suspicious will convert to intentional. None of these terms correspond exactly to the term arson, and this distinction will need to be explained. Because Version 5.0 can capture data about the age of the person involved, it is quite possible to see a fire intentionally set by a five-year-old. This would be below the age of responsibility in most, if not all, states. The fire module is not required for certain confined structure fires, including a contained trash or rubbish fire, or for outside rubbish fires. If these forms are not voluntarily completed when a fire appears incendiary, the level of information gathered may be insufficient to pursue an investigation. Substantial shares of these fires were considered incendiary or suspicious under older versions of NFIRS. Dropping the suspicious choice and required causal coding for certain incidents is likely to result in an artificial drop in arson incidents. This will make reliable trend analysis of the subject extremely difficult during the transition.
GETTING TO NFIRS 5.0 The previous material alluded to some of the changes in Version 5.0. What other changes have been made? Who decided what would change? On the basis of feedback from state program managers and departments in the late 1980s, the USFA began entertaining the possibility of a revision of the NFIRS 4.1 version. Although the initial plan was for an incremental change to version 4.1, it soon became apparent from user feedback that nothing less than a sweeping revision would be acceptable. The Fire Administration, through its cooperative partnership with the National Fire Information Council (NFIC), sponsored a series of workgroups made up of fire departments, NFIRS state program managers, national data users, and fire software vendors whose charter was to examine every aspect of the way data were being collected in previous versions, apply the lessons learned, and develop consensus requirements for a new NFIRS system. The process took seven years to complete and included input from users of the system and its data at all levels. The results were some dramatic changes in the NFIRS system. The USFA and NFIC began working on the new NFIRS in 1989. NFIC members surveyed fire departments of different sizes to see what they liked and didn’t like about the existing system. NFIRS consumers, such as the NFPA, the Consumer Product Safety Commission (CPSC), the National Highway Traffic Safety Administration (NHTSA), and private industry groups, were consulted about their data needs.
The Choosing of Data Elements All agreed that the data requested must be (1) reportable, that is, something that could be described in a codable or quantifiable manner, (2) collectable—the information must be readily available without spending an excessive amount of time to obtain it and users must be willing to report it, and (3) usable. Code developers want very specific information, but sometimes it is more detail than fire fighters can be expected to provide. Even if the data can be collected, if that particular information is not
used, it’s a waste of time to collect it. Fire fighters also indicated that they had difficulty with certain data elements and questioned the reliability of those elements. For example, it was difficult to accurately determine whether all openings were protected, a critical piece of information in determining the type of construction. Consequently, the field “construction type” has been dropped from Version 5.0. Fire fighters also resented filling out the same information on many of their minor fires. By expanding the situation found (incident type in Version 5.0) to three digits, specific codes could be assigned for confined food on stove fires and confined chimney fires. For certain types of confined structure fires and for outdoor rubbish fires, fire fighters will complete little more than basic dispatch information. Table 3.2.1 summarizes the changes in NFIRS 5.0.
Different Circumstances Triggering Different Modules NFIRS 5.0 is modular in design and uses only the modules necessary to describe the incidents. Identifying and dispatch data such as dates, times, incident type and occupancy, are collected for all incident types in the Basic Module. Local authorities may also require owner and occupant information and narratives. That is the extent of the information required by the NFIRS for nonfire incidents, confined structure fires and outside rubbish fires. More detailed information is collected in other modules to further describe specific circumstances of an incident. The modules used by NFIRS 5.0 are as follows: • • • • • • • • • • • • •
Basic Module (mandatory) Fire Module (mandatory) Structure Fire Module (mandatory) Civilian Casualty Module (mandatory) Fire Service Casualty Module (mandatory) EMS Module HazMat Module Wildland Fire Module Apparatus or Resources Module Personnel Module Arson Module Juvenile Firesetter Module Supplemental Module
Basic Module. The modules identified as mandatory must be used when triggered by incident type or casualty data entries in the Basic Module. Fire Module. For nonconfined fires in their jurisdiction, fire fighters must complete the Fire Module that collects information about property details and on-site materials, fire causes, any equipment or mobile property involved, the area of origin, material first ignited, human factors, and any fire suppression factors. A broad cause category has been introduced that contains the following choices: 1. Intentional 2. Unintentional
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TABLE 3.2.1
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Summary of Changes in NFIRS 5.0 New Structure Fire Data
New Basic or Fire Data
Elements Dropped in Version 5 Method of alarm
Three-digit incident types
Type of detector, sprinkler
Method of extinguishment Extent of smoke damage Avenue of smoke travel Type of material generating most smoke Form of material generating most smoke Construction type
Expanded mutual aid data
Fire fighter injury equipment unless a factor in injury
On-site materials
Sprinkler and detector effectiveness Sprinkler heads operating Reason for detector or sprinkler failure Structure status (vacant, occupied, under renovation) Number of stories above and below ground Material contributing to flame spread Number of stories by flame damage
Reduction in property use codes Abbreviated reporting for certain confined structure fires, outside trash fires Suppression factors
Broad causal factor categories including preand post-investigation undetermined Human factors
Other New Data Optional Modules: EMS, Wildland, HazMat, Arson, Juvenile Firesetter, Personnel, Resources, Supplemental
Mobile property identified only if involved in ignition Multiple actions taken, factors contributing to ignition Pre-incident property value Separate loss fields for contents and structure Expanded, more specific equipment involved in ignition Separate fields for equipment portability, power Numeric entries for number of units, buildings, acres burned Codes on basic form for minor hazardous releases Incident types indicate fires in mobile buildings
3. 4. 5. U.
Failure of equipment or heat source Act of nature Cause under investigation Cause undetermined after investigation
Code 5, Cause under investigation, makes it possible to identify reports that might need revisions. Local departments must have procedures to update these records when new information becomes available. This causal data are not required for the specified confined structure fires or outside rubbish fires. The field “Factors contributing to ignition” provides the opportunity to document more specific causal factors. Structure Fire Module. The Structure Fire Module is completed for building fires. Only the question on structure type is
completed for structures other than enclosed or portable or mobile structures. This includes tents, open platforms, fences, and the like. The Structure Fire Module captures information on building status and size, the floor or story of fire origin, the extent of and material contributing to flame spread, and detection and automatic suppression system performance. Civilian and Fire Service Casualty Modules. The Civilian Casualty Module is required for and used only for civilian fire injuries. It captures information such as the cause of injury, the victim’s location, and factors contributing to injury. Race and ethnicity will now be captured in this casualty module. Several fields have been added to the civilian casualty module that will be of particular interest to those dealing with performance-based codes. These include the story or floor of the
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injured occupant, first, at the time of ignition and, second, at the time of injury, if different. In addition to location at ignition, information is now required on the location at time of injury. Severity gradations of minor, moderate, severe, life-threatening, and death are now provided, instead of just injury or death, the choices in older versions. Human and other factors contributing to the injury are also captured. The victim’s name, age, and gender and the cause, activity at time, and the nature and severity of injury are captured on both types of casualty modules. The Fire Service Casualty module is used for all fire service injuries, including those resulting from events other than fires. This module captures information about whether the victim was a career or volunteer fire fighter, lost time injuries, type of location at injury, and the nature of any protective equipment failures that contributed to the injury. The Basic, Fire, Structure Fire, Civilian Casualty, and Fire Service Casualty are the mandatory modules associated with NFIRS. State or local authorities may require completion of the new Emergency Medical Services (EMS), Hazardous Material, Wildland Fire, Arson, and Juvenile Firesetter Modules when appropriate. EMS Module. In its infancy, fire department activity reporting was limited to fires only, at least on a national level. Little recognition was given to the other activities that fire departments were performing on a daily basis. As fire department management became more responsive to the budgetary concerns and restrictions of fiscal policy, the need to justify all activities and expenditures grew. Many local fire departments began to collect data on their own, using the NFIRS program to attempt to gather management information concerning all of those other activities and stretching the program in directions that were never anticipated. Recognizing that emergency medical services (EMS) activities represent a significant portion of what fire departments are currently doing, an EMS reporting module was included in NFIRS 5.0. The starting point for development of the EMS Module was the Final Report of the 1993 Uniform Pre-Hospital Emergency Medical Services (EMS) Data Conference sponsored by the National Highway Traffic Safety Administration (NHTSA). This document contains the 80 EMS data points, and their definitions as agreed upon by the participants of the conference as being “essential” or “desirable” for EMS data systems. Upon review of the NHTSA data elements, the NFIRS 5.0 development team concluded that many of the data elements did not pass the test for collectable, reportable, or usable. As a result, patient care reports and EMS data forms from fire departments and state EMS agencies across the country were assembled and compared for data elements that were universally being collected and reported. As much as was practical, NHTSA codes and definitions were retained to provide linkage to databases that employ these codes. The EMS Module is not intended to replace or otherwise interfere with state or local EMS patient care reporting requirements, nor is it intended to be a comprehensive EMS patient care report. Instead, the data elements in this module should be viewed as “core elements” around which a complete patient care report can be built.
HazMat Module. The HazMat (hazardous material) Module captures the substance, container size, amount released, cause and circumstances of release and mitigation, evacuation information, and disposition for HazMat incidents. Multiple substances and associated containment activities may be documented in this module. Common, minor releases (such as gasoline leaking from a vehicle fuel tank or propane gas escaping from a grill cylinder) that do not require specialized resources can be documented in the Basic Module. Wildland Fire Module. The Wildland Fire Module may, if local or state authorities permit or require, be used to document brush, grass, forest, crop, or other vegetation fires, as well as incidents of unauthorized, controlled, or prescribed burning. Unauthorized, controlled, and prescribed burning incidents are not counted as hostile fires. This module allows for alternative forms of incident location, such as latitude and longitude or township. Area type, property ownership type, fire causal data, weather information, number of buildings ignited or threatened, crops burned, National Fire Danger Rating System (NFDRS) fuel model at origin, and fire behavior are collected in this module. If an identified person was involved in the ignition, the age, gender, and activity data are also collected. Apparatus or Resource and Personnel Modules. The NFIRS 5.0 system includes the optional Apparatus or Resource Module and Personnel Module. After completing an incident report, an officer can identify the apparatus and personnel that were dispatched and how they were used to handle the incident. This provides the means to examine resource needs and deployment, something that could not be done with previous versions of NFIRS. These modules are generally for local use and completed at the discretion of the local authority. Arson and Juvenile Firesetter Modules. The Arson Module captures motivational factors, group involvement, and specific circumstances of the crime. The Juvenile Firesetter Module captures information about the child, family, and risk factors. Disposition is captured on both of these modules. Names of individuals are not part of these modules or the EMS module. Supplemental Module. Information about additional persons or entities involved, special studies, and remarks are captured in the Supplemental Module.
Legacy Data Because many fire departments and states will continue to collect data using the older version, the data they collect for the dropped data elements (construction type, method of alarm, method of extinguishment, extent of smoke damage, avenue of smoke travel, and form and type of material generating most smoke) will still be included as legacy data in the national database.
Better Documentation of Nonfire Incidents Anyone involved with the fire service or fire protection knows that fires are only part of the story. As was mentioned previously,
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earlier versions of NFIRS provided limited ability to track nonfire incidents. With the exception in recent years of some hazardous material incidents, nonfire incidents were not compiled by the USFA. This changes with Version 5.0. The fire service will obtain more detailed information about EMS type calls and other nonfire emergencies. They will also be better able to track calls by station and mutual or automatic aid incidents.
Fire Protection Systems The three-digit incident type provides specific information about false alarms and indicates whether the detector was heat, smoke, or carbon monoxide. The fire protection community has been plagued by a lack of information about sprinkler systems. Incident type codes in the Basic Module will indicate sprinkler activations due to unintentional tripping or malfunctions. Data from the Structure Fire Module indicate whether an automatic extinguishing system was present in the fire area, the type of system present (wet, dry pipe, dry chemical, foam, halogen, or carbon dioxide), whether it was effective, how many heads operated, and the reason if the system was not effective. Similar detailed information is collected on fire detection systems, including detector type (smoke, heat, combination smoke and heat, sprinkler with waterflow detection, more than one type present, and other), detector power supply, detector operation, detector effectiveness in terms of alerting occupants, and failure reason if the detector failed to operate.
Occupancy Groups or Fixed Property Use The number of property use codes has been dramatically reduced. Residential occupancies include codes for one- and twofamily dwellings, multifamily dwellings, rooming houses, hotels or motels, residential board and care, sorority or fraternity houses, barracks or dormitories, other dormitory type residences, and other residential. A separate entry documents the number of units in each. (When older property use data are converted forward, a midpoint value is generally assigned.) Similar reductions have been made in the mercantile, basic industrial, manufacturing, and storage categories. Code 700 now covers all manufacturing or processing. The specifics are captured by documenting on-site materials and indicating whether these materials were used in or stored as (1) bulk storage or warehousing, (2) processing or manufacturing, (3) packaged goods for sale, or (4) repair or service. Up to three on-site materials may be listed. The general property use classification is captured in the Basic Module. The Fire Module captures details about number of units and on-site materials.
Structure Status The Structure Fire Module also collects information about the status of the structure. In the older versions of NFIRS, separate occupancy or fixed property use codes identified vacant buildings or buildings under renovation or demolition. However, many were still coded according to their intended use. Every fire fighter knows that fighting a fire in an abandoned mill is different from fighting one in a vacant dwelling. Separate codes indicate whether the structure was under construction, occupied and
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operating, idle, under major renovation, vacant and secured, vacant and unsecured, or being demolished.
Property Damage Direct property damage provides one of the measures of fire problem severity. In older versions of NFIRS, when this field was left blank, the dollar loss was assumed to be zero. A checkbox in Version 5.0 indicates that there was no loss. While the information is required when known, presumably the field will be left blank if unknown. Property damage estimates are provided by the fire service. Sometimes they have input from insurance adjusters; in many cases, they do not. Loss figures are estimates on the basis of the expected replacement cost of the property damaged. Property damage for the property and its contents are now separated into two fields. Pre-incident property and contents values are optional. Caution should be used when comparing these values. In many cases, it would be inappropriate to claim credit for saving all of the nondamaged property. These data are collected in the Basic Module. One of the frustrations with older versions of NFIRS was the inability to accurately gauge the severity of a fire. Dollar loss was influenced by the value of the property. When extent of flame damage was confined to the structure, the damage might have been to just one exterior wall. Version 5.0’s Structure Fire Module captures data on the number of stories with minor (1–24%), significant (25–49%), heavy (50–74%), and extreme (75–100%) damage. The extent of flame damage field is still present, although the code for confined to part of room or area of origin was dropped. The size or dimensions of the main floor are now required.
Direct Entry of Numeric Data Users of NFIRS data from the older systems were often frustrated by fields in which numeric values, such as number of stories or fire fighter responses before injury, were coded. Too often, it was unclear whether the individual completing the form was using the codes or using the raw numbers. In Version 5.0, these are direct entries. Version 5.0 also captures the number of stories above and below grade.
More Specific Choices for Equipment Involved The equipment involved in ignition (or release) field has far more specific choices than in older versions. In addition, portability is now a separate field. A portable space heater might be coded as a heater, excluding catalytic and oil-filled (code 141), and in the portability box, portable would be checked. In the past the fuel or power source for equipment was generally found in the “form of heat of ignition” field. That field has been functionally divided into two: “heat source” and “equipment power.”
Suppression Factors Up to three suppression factors may be entered in the Fire Module. Suppression factors are circumstances that contributed to
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the growth or spread of the fire. These include specific building construction or design factors; an act or omission, such as blocking a fire door; the building contents or fuel load; delays; problems with protective equipment such as water supply, suppression systems, or fire protection assembly; egress or exit factors, such as overcrowding, window type, or occupant characteristics; and natural conditions.
Human Factors Life safety educators are very happy to see the ability to capture data about human factors in the Version 5.0 Fire Module. Some of these factors could be captured for civilian casualties in older versions but not for fires that didn’t result in casualties. Human factors include asleep, possibly impaired by alcohol or drugs, unattended (or unsupervised) person; possibly mentally disabled; physically disabled; multiple persons involved; and age was a factor with a block to indicate the age. An additional field captures the gender of the principal person involved when age was a factor. Similar data are captured on the casualty report for any civilians injured by fire.
Factors Contributing to Injury A new field in the Civilian Casualty Module, “Factors Contributing to Injury,” allows up to three entries. These include the following: • Various egress problems, such as crowd situations with limited exits, locked exits, or security bars • The fire pattern itself, such as trapped above or below, vision impaired by smoke, clothing igniting while escaping, or exits blocked by flame or smoke • Escape difficulties, such as choosing inappropriate exit route or reentered building • Collapse of the roof, floor, or wall • Vehicle related factors • Equipment related factors such as unvented heating equipment or improper use of heating or cooking equipment • Other factors, such as clothing burning before the individual tried to escape
Other Differences and Options In some cases, similar data are collected in different modules. Either the state or local fire department will determine whether the Wildland Module or the Fire Module will be completed for forest fires. These modules use the same codes for some fields, but the broad cause codes are different. If the Juvenile Firesetter module is completed, a juvenile’s age may not be recorded on the Fire Module. Because different jurisdictions have different data needs, and because many information needs cannot be anticipated, Version 5.0 has the ability to generate “plus one” codes by adding an extra character to the codes in each field. These extra codes will not be a part of the national database. Local fire departments should check with their state authorities before implementing their own plus one codes to ensure that no conflict exists between the state and local needs.
Several fields in the Supplemental Module have been set aside for special studies. Fire officers must know what the codes cover.Version 5.0 has the ability to provide much more detailed documentation and data about fires. However, this can happen only if the fire fighters who complete the forms know that the new codes exist. The developers of 5.0 worked hard to make the system easier for and more responsive to the fire service. A danger exists that, in this era of pull-down menus, individuals may not even know that a particular optional field is relevant or that a certain code exists in that field. Dry as the material is, anyone who completes NFIRS forms should occasionally thumb through the coding manual or quick reference guide as a reminder of the type of information collected in each field.
Difficulty of Change The transition to NFIRS 5.0 involves changes in what and how data are recorded, in data and editing specifications, in computer systems, training, manuals, and analysis. With such a major overhaul, the transition has sometimes been difficult. The USFA established the NFIRS Support Center with a 24-hour toll-free number (1-888-382-3827) and on-line e-mail capability at http://www.usfa.fema.gov/nfdc/nfirs-help.htm to facilitate the process and enable fire fighters to quickly obtain answers to their NFIRS questions. Version 5.0 of NFIRS is being implemented at various speeds across the country. NFIRS 5.0 brings major changes in the underlying logic of the system. It will also provide significant new data in terms of expanded incident types, human factors, and fire protection systems. Implementation practices vary by state and reflect the state’s needs and priorities. Consequently, the national NFIRS database and many state databases will contain data collected in Version 5.0 and data collected in older versions that has been converted to Version 5.0. Although a conversion program is available, the conversion is not exact because data definitions and data elements in the two systems are not identical. Consequently, an understanding of both Version 5.0 and the older systems is required for accurate analyses of merged data.
COMPUTERS AND NFIRS Computers have made it easier to enter and use the data. Onscreen look-ups assist the fire officer in choosing the correct classification.
Quality Control Quality control issues can become more complicated with computer-generated reports. Most programs do some error checking for allowable values, and some checks to see whether the data make sense. Computers, however, have no common sense. As long as the data meet the criteria, they will pass through the system. It is often easier to spot inconsistencies or patterns of problems through a visual scan of paper forms than by working with coded electronic data. A detailed narrative is more important than ever with an automated or paper checkbox system. Before checkboxes and computers, a fire officer would
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write words describing the event seen. In many cases, one code covers multiple items such as “portable appliance designed to produce heat, other” or “storage area, tank or bin.” “Electric blanket” or “500-gallon propane tank” would be more specific. If that information is not entered elsewhere, it will be lost. At least one vendor provides users with the ability to generate a preliminary narrative based on the coded information in the incident report. To be meaningful, this narrative must be supplemented with the specifics of an incident. To protect the integrity and data quality of the information collected from departments, standard NFIRS edits checks exist and are documented in the NFIRS 5.0 Design Documentation maintained by the USFA. The edits consist of both normal and relational edit checks and must be implemented in a standard way by all developers of NFIRS 5.0 data collection software. System edits prevent many common data entry errors such as transposing the incident alarm time and the time that the department arrived at the incident scene. Software edit checks are typically done at the time of data entry, and the corrections are made at the department level. Incidents that fail validation are either corrected by the state NFIRS program manager or returned to the department for correction and resubmission.
NFIRS Software The USFA has developed bare-bones software for Version 5.0 to enable states to manage their systems. If the state authority permits, local fire departments may also use this software. However, the state authority, not the USFA, is expected to provide the support, and many do not feel they have the resources to do so. Some states have purchased software or licenses for their fire departments from commercial vendors.
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usefulness of the standard reports is greatly extended. For example, the standard Tally report counts the frequency of occurrence for each code within a data field. Running this report on the Incident Type field with no data filter results in a count for each type of run done by the department. By using a data filter, the department can also limit the report output to just fires, just arson fires, or just fires in single-family homes started with a candle. In this way, multiple questions can be answered with the same canned report. More information on data analysis can be found in Section 3, Chapter 3, “Use of Fire Incident Data and Statistics.”
NFIRS Support Materials on USFA Web Site The USFA’s Web site (http://www.usfa.fema.gov/nfdc/nfirs.htm) has downloadable coding manuals for NFIRS 4.1 and 5.0, active vendors and procedures, and other relevant information.
GETTING THE BIG PICTURE ON FIRES NFIRS can provide a great deal of information, but it is important to remember what it cannot do. Because of the time lag in compiling data, some time will pass before a new problem can be identified. NFIRS by itself cannot be used to determine risk. Denominators such as prevalence in the population are needed. As was mentioned earlier, different states have different reporting policies. NFIRS is not a census of all fires; it is not even a full listing of all fires reported to fire departments. Such a listing does not exist. How do we tell how big the fire problem is in the United States?
NFPA’s Annual Fire Department Survey Data Retrieval and Analysis In many fire-reporting systems, a great deal of effort is devoted to data collection, and then very little effort is given to making good use of the data. Data analyses should be of two kinds: (1) routine, periodic reports that summarize the fire problem and that provide management data and (2) special reports that answer queries about particular problems or evaluate programs, support budget requests, and the like. Data analysis can begin with a simple tally of incident types or other data element. Data analysis should also consider the interrelationship between various data elements or various databases. For example, relating fire data to socioeconomic data by census tract shows the population groups that are most affected. Comparing fire losses over the years to inflation rates and increasing property values may show that fire protection is currently more effective, even though in raw numbers the total loss is greater. Nearly all NFIRS reporting software comes with a suite of canned reports. Since getting answers from raw data can be difficult for those not trained in data analysis, canned reports ensure standard and accurate answers to commonly asked questions about the data. Many incident reporting software packages also include powerful data-filtering features so that the
Each January, NFPA sends its survey to all fire departments protecting 100,000 or more and a random sample, stratified by population, of the smaller departments. In 1999, NFPA sent out almost 14,000 surveys and received a total of 2,725 back, a response rate of 20%, higher response rates being from the larger communities. The departments that did respond protect about 37% of the U.S. population.8 The data are used to develop national estimates of the fire problem. A press release about the number of fires and fire deaths is issued each August. An abbreviated version of the full report “Fire Loss in the United States” is published in the September issue of NFPA Journal. NFPA’s survey is not terribly detailed. It asks about fires by type and broad occupancy class, incendiary and suspicious structure and vehicle fires, and civilian and fire fighter deaths and injuries. NFIRS has far more detail, although it usually lags substantially behind the survey in terms of timeliness. By comparing the totals from NFPA’s survey to corresponding totals in NFIRS, analysts estimate what fraction of total U.S. fires, deaths, injuries, and lost dollars were captured by the NFIRS sample. These fractions are inverted into ratios that are used to “scale up” the NFIRS numbers on specific fire problems to “national estimates” of the total size of these problems. Different ratios are used for residential structure fires, nonresidential structure fires, vehicle fires, and other fires. Within each group,
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Because of the large number of fires reported to NFIRS, reliable analyses can be done on most common types of problems even though many jurisdictions are not included. Difficulties arise, however, with unusual circumstances, such as non-home fire deaths or fires in specific nonresidential occupancies. For example, the states of North Carolina and Pennsylvania were not participating in NFIRS during the 1990s. National estimates based on NFIRS and the NFPA survey showed no fatalities in college dormitories or fraternity houses in the five-year period from 1993 through 1997, yet we knew from our Fire Incident Data Organization (FIDO) (see below) that two fires in these properties had claimed five lives in each state. NFPA was aware of six other fatal fires in these properties during that time.10 However, statistical projections can be footnoted, but not adjusted, on the basis of anecdotal data. Similarly, a fire with an unusually large dollar loss or number of casualties can also skew the data when projections are made. These problems are not unique to fire data and are typical of any type of data collection effort. Even the U.S. Census Bureau considered using statistical projections to control for areas where undercounting was expected to be a problem.
analysts use different ratios for fires, injuries, deaths, and direct property damage.9 Many fire fighters have wondered why, if they faithfully complete their fire incident reports, they are also asked to complete NFPA’s survey. The reason is that because different states have different reporting practices, NFIRS cannot estimate the total number of reported fires per year. Analysts need to use the survey results and NFIRS together to develop national estimates. In the older versions of NFIRS, nonfire responses (except for hazardous material incidents in Version 4.1) were not forwarded to the USFA. Until all fire departments around the country report using NFIRS 5.0 to states that are processing all incidents, the NFPA survey is the only national source of this data. Because the survey is completed by June each year, it can produce numbers about a year earlier than NFIRS.
What Is Not Included in the Statistics Neither the survey nor NFIRS captures data on fires that were not reported to fire departments. Consequently, fires that are handled by private brigades or individuals will not be counted. The NFPA survey samples only municipal fire departments, including career and volunteer departments. Fires reported to wildland fire agencies or military agencies will also not be captured. Figure 3.2.2 illustrates how fires in communities protected by municipal fire departments are or are not captured in the data. If a fire is handled privately, with no fire department notification, as far as these two databases are concerned, it never happened. If the fire department responded but did not complete a report, the fire will not be counted. If the report was completed but not sent forward to the state, it will not become part of the state or national NFIRS database. If a fire report has a serious or fatal error or inconsistency, it will also be excluded from the NFIRS database. If the fire department was in the NFPA sample and it responded, then the fire will be counted by the survey. If the state does not collect or forward NFIRS data to the USFA, then that state’s communities generally will not be in the NFIRS database. Exceptions have been made for large metropolitan fire departments reporting directly to the USFA with state permission.
Fire department called
No fire department response
OTHER SOURCES OF DATA NFIRS and NFPA’s annual fire department experience survey provide national estimates of fires reported to local fire departments. Other sources are needed to provide more detailed narrative accounts, international data, and arrest and injury data.
NFPA’s Fire Incident Data Organization (FIDO) NFPA designed and maintains the Fire Incident Data Organization (FIDO) to provide examples and details of specific types of fires. News clips, word of mouth, and other sources are used to identify fires of interest. Additional information is then sought from fire departments, insurance companies, and other federal and state safety agencies. FIDO is the source for the fires pro-
Report completed
Sent to state
Report not completed
Not sent to state
Not included in statistics
Not included in NFIRS, may be captured by NFPA survey
Not sent to USFA, not in NFIRS
Not included in statistics
FIGURE 3.2.2
Sent to USFA, in NFIRS
How a Fire Gets Counted
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filed in NFPA Journal’s “Firewatch” column. Because every effort, including surveying state fire marshals’ offices, is made to track down reports of multiple death fires, large loss incidents, and fire fighter fatalities, we are confident of the completeness of the data and use FIDO as the source for these reports. Unsolicited fire department reports of fires with lessons learned are very welcome. Most of the fires in FIDO are more serious than the usual. They show what can happen, not what is likely to happen. Anecdotal data such as FIDO cannot be the basis for statistical analysis. Incidents in FIDO have been entered by using codes very similar to the older versions of NFIRS, but additional fields have been added to capture other significant issues. NFPA does not release identifying information about a specific fire without the fire department’s permission.
Uniform Crime Reporting System (UCR) The Uniform Crime Reporting System (UCR) of the Federal Bureau of Investigation (FBI) collects standardized reports about crimes and offenders from law enforcement agencies around the country. Most contributing agencies are local police departments, but other agencies, including state fire marshal’s offices, also make arrests. Agencies protecting about 90% of the U.S. population submit at least some reports, but reports over the full year come from agencies protecting roughly half the country’s population. As with NFIRS, UCR has a goal of complete participation. Different rates of participation by communities of different sizes are likely and may introduce some systematic bias in national totals.11 The UCR data provide information about the ages and genders of the arrestees. The FBI regularly publishes crime statistics in the Crime in the United States series.
ATF Arson and Explosives National Repository Branch In 1996, Congress enacted Title 18 USC 846 (b), which authorized the Department of the Treasury Bureau of Alcohol, Tobacco and Firearms (ATF) to establish a national repository of information on incidents involving the crimes of arson and the criminal or suspected criminal misuse of explosives. Title 18 USC 846 (b) requires all federal agencies having information (internal or external) concerning such incidents to report the information to the ATF Arson and Explosives National Repository. Currently, ATF, the FBI Bomb Data Center (BDC), and the USFA (National Fire Incident Reporting System (NFIRS)) provide arson and bombing incident data to the ATF Arson and Explosives National Repository Branch (AENRB). A primary goal of the AENRB is to make the data from the Arson and Explosives Incident System (AEXIS), BDC, UCR, and NFIRS available to federal, state and local arson and bombing investigators for the purpose of pursuing multijurisdictional violent offenders. The data available through the AENRB will also be used to provide summary data to describe the scope and nature of arson and bombing incidents at national, regional, and local levels. Summary data are currently available to the general public from the AENRB via the ATF Web site at http://www.atf.treas.gov/.
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National Electronic Injury Surveillance System (NEISS) Through its National Electronic Injury Surveillance System (NEISS), the U.S. Consumer Product Safety Commission (CPSC) tracks injuries that were treated in a selected sample of emergency rooms. This information has been used to develop projections of injuries caused by products and to identify unsafe products or practices when using the products. Together with the Centers for Disease Control’s (CDC’s) National Center for Injury Prevention and Control, they have been expanding the scope of NEISS to include all types of injuries. Originally, only injuries involving consumer products were included, but in 2000, the system expanded to include all injuries treated at emergency rooms. Historically, it has been difficult to find information about nonfatal injuries, and it is hoped that this system will help alleviate that problem. The CPSC also maintains a death certificate database about deaths associated with consumer products. Victim data are removed before these data are released. Additional information may be obtained on the Web site for the National Injury Information Clearinghouse at http://www.cpsc.gov/about/clrnghse.html. Phone: (301) 504-0424 Fax: (301) 504-0025
Injury Facts The National Safety Council compiles reports about deaths caused by unintentional injuries. Injury Facts (formerly Accident Facts) is published annually. This report provides data on death causes by age, state, home, vehicle or work, and long-term trends. A similar report, International Accident Facts, is updated less often but provides international comparisons from up to 50 countries.
International Fire Data Collection Efforts NFPA is aware of two organizations engaged in collecting international fire data. Because each country collects data independently and has their own criteria for what is collected, it is difficult to make accurate comparisons. World Fire Statistics Centre. The Geneva Association’s sponsors the World Fire Statistics Centre. Each year, the Centre collects data from about 20 nations on fire deaths, direct property damage, indirect fire losses, costs of fire-fighting organizations, costs of fire insurance administration, and costs of fire protection to buildings. When applicable, the data are presented as a percentage of the gross domestic product (GDP) or as per capita rates. Its annual report is presented each year to the U.N. Committee on Human Settlements. The FEU and the Centre organized a June 2000 seminar “European Fire Strategy—The Part of Statistics” that was held in Augsburg, Germany. The League of Augsburg 2000 was formed at that meeting to develop proposals for a European fire statistical database. Input is being sought from the fire service, fire protection associations, academia, government, business and industry, insurance companies, and fire equipment suppliers.12
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CTIF. The International Technical Committee for the Prevention and Extinction of Fire (CTIF) was formed in Russia in 1995. Its 200013 report contains information collected from more than 50, or almost one-third, of the world’s countries with about two-thirds of the world’s population. They collect information on the number of fires, structure fires, vehicle fires, arsons, false calls, and fire department staffing and equipment. They have also begun to collect data from the world’s largest cities and national capitals. Their data include many of the former Soviet republics and other countries from Eastern Europe as well as elsewhere.
SUMMARY The data provided by NFIRS and other detailed national and international databases make it possible to monitor progress in fire prevention and protection. Almost all of the data come originally from fire services. Researchers must remember that completing incident reports is a small part of a fire officer’s responsibilities and certainly not why someone joined the fire service. However, most fire officers understand that statistics can help them to manage a department more effectively, prepare and defend a budget proposal, and determine what types of fire problems their community faces. Data collection will improve as the fire service uses the data itself and better understands the role of the data it provides in decisions elsewhere. Fire data analysis is more accurate when the analysts understand the system used and the conditions under which the data was collected. When a fire officer completes an incident report, he or she is contributing data to a huge research effort in addition to preparing a local record of the event. NFIRS provides the ability to collect many specific details about a wide variety of incidents. NFIRS 5.0 provides the means for fire departments to document more of the concerns and activities of today’s fire service. Modern computer technology makes it easier to complete and process the reports. When incident reports are compiled, the local department, the state, and the country can analyze the data to identify trends, new problems, progress solving old ones, and the effectiveness of different protective features. Between onethird and one-half of the fires reported to municipal fire departments are reported to NFIRS each year. Projections about the total numbers of fires, fire casualties, direct property damage, and fire department calls are made from NFPA’s annual fire department experience survey. Because it is smaller in scope, the results are available more quickly. Each September, NFPA Journal runs “Fire Loss in the United States During. . . .” for the previous year. The sample-based survey collects summary data and lacks most of the detail collected by NFIRS. However, national estimates of specific fire problems can be obtained by developing scaling ratios from the relationship of the NFIRS totals to the totals from the NFPA survey. Most of what we know about a country’s fire experience, both in the United States and elsewhere, is based on reports filed by a fire officer. These reports are a small fraction of their responsibilities, but the data provided are critical to policy makers, regulators, life safety educators, inventors, the media, and others.
BIBLIOGRAPHY References Cited 1. Fire Statistics—A User Guide for Research, Home Office, London, UK, January 1998. Available at http://www.homeoffice.gov.uk/rds/pdfs/inforev1.pdf. 2. America Burning, National Commission on Fire Prevention and Control, Federal Emergency Management Agency, Washington, DC, 1973. 3. Fire in the United States, National Fire Data Center, Washington, DC, 1978, page iii. 4. Fire in the United States, U.S. Fire Administration, Washington, DC, 1982. 5. The American Heritage Dictionary Office Edition, 3rd ed., Houghton Mifflin, Boston, MA, 1994, p. 317. 6. NFIRS 5.0 Reference Guide, National Fire Data Center, Washington, DC, 1999, p. C-3. 7. Hall, J. R., Jr., U.S. Fire Death Patterns by State, NFPA, Quincy, MA, 2001. 8. Karter, M., Jr., Fire Loss in the United States During 2000, NFPA, Quincy, MA, 2000, p. 30. 9. Hall, J. R., Jr., and Harwood, B., “The National Estimates Approach to U.S. Fire Statistics,” Fire Technology, Vol. 25, No. 2, 1989, pp. 99–113. 10. Rohr, K. D., School, College and University Dormitories, and Fraternity and Sorority House Fires in the United States, NFPA, Quincy, MA, June 2000. 11. Hall, J. R., Jr., U.S. Arson Trends and Patterns, NFPA, Quincy, MA, 2001, p. 63. 12. Wilmot, T. (Ed.), World Fire Statistics: International Bulletin of the World Fire Statistics Centre, The Geneva Association, International Association for the Study of Insurance Economics, Oct. 16, 2000, ISSN: 1605-8283. Available at http://www.genevaassociation.org/ world_fire_statistics_bulletin.htm. 13. Brushlinsky, N., Sokolov, S., and Wagner, P., World Fire Statistics at the end of XX Century, Report No. 6 of Fire Statistics of CTIF, Brushlinsky, Sokolov, and Wagner, Moscow and Berlin, 2000.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on fire data collection and databases discussed in this chapter. NFPA 901, Uniform Coding for Fire Protection, 1976 and 1981 editions NFPA 901, Standard Classifications for Incident Reporting and Fire Protection Data, 2001 edition
Additional Readings Ahrens, M., “All Fired Up—How We Know What We Know about Fire,” NFPA Journal, May/June 1998, pp. 80–89. Ahrens, M., The U.S. Fire Problem Overview Report, Leading Causes and Other Patterns and Trends, National Fire Protection Association, Quincy, MA, June 2001. Burris, K. O., Jr., “NFIRS: Better Data for Better Decisions,” Fire Engineering, Vol. 153, No. 5, 2000, pp. 107–108. Campbell, C. A., “Furor over 5,” Fire Chief, Vol. 45, No. 3, 2001, pp. 40–42. Carter, H. R., “Community Fire Defense Plan: Analyze Before You Organize,” Firehouse, Vol. 22, No. 6, 1997. Fahy, R. F., and LeBlanc, P. R., “Report on 2000 Firefighter Fatalities,” NFPA Journal, July/Aug. 2001, pp. 66–75. “Fire in the United States,” 12th ed., Report FA-216, TriData Corp., Arlington, VA, Federal Emergency Management Agency, Emmitsburg, MD, Aug. 2001. “Fire Risks for the Mobility Impaired,” U.S. Fire Administration, Washington, DC, Oct. 1999.
CHAPTER 2
Hall, J. R., Jr., Burns, Toxic Gases and Other Hazards Associated with Fires: Deaths and Injuries in Fire and Non-Fire Situations, National Fire Protection Association, Quincy, MA, Mar. 2001. Hall, J. R., Jr., “Special Data Information Package: High-Rise Fatal Fires, Apartment Buildings,” National Fire Protection Association, Special Data Information Package, Aug. 1999. Hall, J. R., Jr., The Total Cost of Fire in the United States, National Fire Protection Association, Quincy, MA, Mar. 2001. “Heating Fires in Residential Structures,” U.S. Fire Administration, Washington, DC, Topical Fire Research Series, Vol. 2, No. 5, 2001, pp. 1–4. Krakeel, J. J., “Incident Reporting System Needs to Include EMS,” Fire Chief, Vol. 45, No. 4, 2001, pp. 16–17. Mah, J., “Residential Fire Loss Estimates, 1998, U.S. National Estimates of Fires, Death, Injuries and Property Losses from NonIncendiary, Non-Suspicious Fires,” U.S. Consumer Product Safety Commission, Washington, DC, 1999. National Fire Data Center, National Fire Incident Reporting System—Version 5.0 Design Documentation, Jan. 2001. Available at http://www.nfirs/fema.gov/design.htm. National Fire Data Center, National Fire Incident Reporting System— Version 5.0 Design Documentation, July 2000. National Safety Council, Injury Facts, 2000 edition, Itasca, IL, 2000.
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National Safety Council, International Accident Facts, 2nd ed., Itasca, IL, 1999. “NFIRS Analysis: Investigating City Characteristics and Residential Fire Rates,” Report FA-179, TriData Corp., Arlington, VA, U.S. Fire Administration, Washington, DC, Apr. 1998. “NFPA’s One-Stop Data Shop. Fire Data and Statistics Reports and Services from the NFPA Fire Analysis and Research Division,” NFPA, Quincy, MA, May 2001. “Profile of the Rural Fire Problem in the United States,” Report FA-181, Federal Emergency Management Agency, Washington, DC, Aug. 1998. “Profile of the Urban Fire Problem in the United States,” Report FA-190, Federal Emergency Management Agency, Washington, DC, May 1999. Smith, L. E., Greene, M. A., and Sing, H. A., “Fires Caused by Children Playing with Lighters. An Evaluation of the CPSC Safety Standards for Cigarette Lighters,” U.S. Consumer Product Safety Commission, Washington, DC, Sept. 2000. Tri-Data Corporation, Uses of NFIRS: The Many Uses of the National Fire Incident Reporting System, June 1997. Worley, S. T., “The New National Fire Incident Reporting System,” Fire Engineering, Vol. 152, Issue 4, April 1999, pp. 111–114.
CHAPTER 3
SECTION 3
Use of Fire Incident Data and Statistics
T
he previous chapter, Section 3, Chapter 2 (“Fire Data Collection and Databases”) provided a description of the sources used for analyses of fire experienced in the real world, as opposed to laboratory studies. In the United States, the key database for such analysis is the National Fire Incident Reporting System (NFIRS). The rules for analysis will soon change in many ways to accommodate the most extensive changes to the coding structure since its inception, NFIRS 5.0. Implementation of NFIRS 5.0 began in 1999 and is expected to take several years. This means that the national database will include data collected in older versions and converted to NFIRS 5.0 as well as data collected in the 5.0 format. Responsible data analysis requires the analyst to understand what is and is not included in the data and the impact of system upgrades on the data itself. The text in this chapter will be more meaningful if readers have a working knowledge of NFIRS or have at least read the previous chapter. This chapter explores how data source issues impact the analysis process. Particular attention is paid to reporting policies and practices, differences between NFIRS 5.0 and earlier versions of NFIRS, and to issues that arise with data converted from older NFIRS. Several approaches to fire data analysis are also described, including top-down and topic-driven analysis. This portion includes discussions of analysis by specific data elements; U.S. Fire Administration’s (USFA’s) cause hierarchy; handling fires with unknown causal factors; issues faced when working with small data-sets; location-based fire data analysis; rates and measures of risk; trend analysis; and of data use for program and strategy analysis. The chapter concludes with a discussion of issues encountered when using data from different databases or analytic approaches. Descriptions of and sample results from the older version of NFIRS are provided. Suggestions for comparable analysis with NFIRS 5.0 data are included. NFIRS 5.0 data and data converted from 4.1 to 5.0 were not available at the time this chapter was written. Consequently, the material presented here is based on our best understanding of currently available information.
Marty Ahrens is a fire analysis specialist at NFPA. Patricia Frazier is director, Center for Data Analysis at TriData Corporation. She is lead data analyst and specializes in fire-related data. Jim Heeschen is a statistician at the Federal Emergency Management Agency/U.S. Fire Administration’s National Fire Data Center.
Revised by
Marty Ahrens Patricia Frazier Jim Heeschen
For those familiar with the state of fire experience data prior to the late 1970s, it is still remarkable to see how much the quantity and quality of fire data available for analysis have grown since then. In the early 1970s, even the best fire departments typically had fire incident records only in narrative form. Neither the method of storage (in file cabinets, by incident number) nor the method of description (phrases selected by fire officers, without standardized coded descriptions or even a standard list of characteristics to be documented) facilitated analysis of the community’s leading fire problems. At the state level, very few states had any fire experience database. At the national level, the National Fire Protection Association (NFPA) prepared estimates of U.S. incidents, deaths, injuries, and losses from its annual survey, and provided analyses of fire causes and other detailed factors from its Fire Incident Data Organization (FIDO) database. The Fire Reporting Committee of NFPA had developed NFPA 901, Uniform Coding for Fire Protection (now Standard Classifications for Incident Reporting and Fire Protection Data),1 a standard fire incident reporting format, but few fire departments were using it. In 1977, NFPA modified its survey techniques to take account of modern statistical design principles and, in the process, greatly improved estimates of the size of the national fire problem. Also in the 1970s, the new National Fire Prevention and Control Administration [now the U.S. Fire Administration (USFA), a branch of the Federal Emergency Management Agency (FEMA)] launched the National Fire Incident Reporting System (NFIRS). Based on NFPA 901, the NFIRS system provided the framework for a large-scale, truly national fire experience database. Since 1980, NFIRS has had the participation, in whole or in part, of the majority of states and now receives standardized reports on between one-third and one-half of all fire incidents. (As sources of the principal fire databases, NFPA and FEMA also have helped each other over the years, with FEMA providing financial support and technical suggestions on NFPA databases and NFPA providing developmental work and analysis services on NFIRS for FEMA.) Other countries, such as Australia and Canada, have adopted their own versions of NFIRS, making possible much more valid international comparisons. A parallel development has enlarged the capacity for analysis of the newly generated fire data. The advent of powerful micro and personal computers and the increasing affordability and flexibility of computer power in general have made it increasingly possible for the fire service and other fire data users
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to perform meaningful analyses. Most readers of this handbook now have access to valid national or local databases in forms suitable for analysis, and to the equipment and skills required to analyze that data. See Table 3.3.1 for a sample of the many potential data users and uses. TABLE 3.3.1
USING DATA TO CHARACTERIZE THE FIRE PROBLEM Table 3.3.2 lists 10 major findings on the nature of the fire problem that have emerged from analyses of the past decades. Many
Typical Users and Uses of Fire Experience Results Use
User Fire protection engineers
Supporting data needs of performance-based codes and standards Defining and quantifying fire scenarios Estimating probabilities of fire incidence and fire protection performance Evaluating fire protection alternatives
Technical fire safety standards committees
Supporting data needs of performance-based codes and standards Identifying needs for standards Keeping standards current Monitoring the performance of standards Analyzing the benefits and costs of standards
Local and state fire service
Showing value of proposed fire safety and fire protection programs and legislation Targeting fire prevention and suppression programs Backing up budget requests Enacting and enforcing fire codes Developing community fire safety education program Monitoring progress
Fire protection planners at national and state levels
Showing value of proposed fire safety and fire protection programs and legislation Comparing fire to other problems competing for resources Planning the most effective deployment of resources to make the greatest impact on the fire problem Monitoring fire protection progress
Communicators/educators
Reporting of fire problems Educating for fire safety
Committees developing fire fighter safety standards, individuals, fire departments working to improve fire fighter safety
Identifying reasons for fire fighter deaths and injuries Developing safety and training programs Designing protective equipment
Researchers
Establishing fire safety research priorities Designing research programs
Insurers
Loss prevention Risk selection and underwriting
Industry
Worker safety Loss prevention
Product developers
Identifying needed products and markets Modifying products to improve fire safety
Building designers, architects, managers
Ensuring a firesafe design
Legislators, regulators, enforcers, courts
Effective and equitable fire safety laws and regulations
CHAPTER 3
TABLE 3.3.2
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Ten Major U.S. Data-Based Findings of Recent Years
1. U.S. and Canadian fire death rates were, in the 1970s and 1980s, among the highest in the developed world. The gap had been steadily closing. In the late 1970s, U.S. fire death rates were double the rates in the United Kingdom, Japan, and Sweden. In the mid-1980s, U.S. fire death rates were roughly 50 percent higher. In the early 1990s, U.S. fire death rates were only one-fourth to one-third higher. Fire death rates in Sweden, the United Kingdom, and Japan leveled off in the nineties, whereas the rates in the United States and Canada continued the downward trend.2 2. Within the United States, the states of the Old South still tend to have the highest fire death rates, but the gap is closing; for some years, the South is not the highest region. In the early 1980s, fire death rates in the South were typically around 50 percent higher than those in the Northeast and North Central regions and double the rates in the West. In 1989 and 1991, the South fell to second highest region. In 1997, the South and Northeast had identical death rates. On average, during 1994–1998, the South’s fire death rates have been one-fourth to one-third higher than the rates in the North Central and Northeast regions, respectively. The West continues to do substantially better than any other region, having an average death rate half that of the South.3 3. Almost half (44% percent) of the 25 U.S. fires with the largest property loss occurred in the 1990s. NFPA maintains a list of the 25 costliest fires and explosions of all time, based on loss values adjusted for inflation. The list is headed by the 1906 San Francisco earthquake fire, with involved losses estimated at $350 million at the time, worth more than $6.5 billion today. Eleven of these 25 fires occurred in the 10-year period from 1990 to 1999. This list includes the Oakland fire storm, the third costliest of all times, and four other California fires, three of them wildfires. Three of the top 25 fires occurred in the 1980s, one in the 1970s, one in the 1960s, three in the 1940s, and the remaining six before 1920.4 4. Fire death rates in rural communities (population under 2500) are more than twice the rate found in communities with a population of more than 250,000 and three times the rate in communities with populations between 25,000 and 100,000. Although the magnitude of the difference varies somewhat, these patterns have been seen consistently ever since the fire statistics were first formatted in a way to make this type of analysis possible. In recent years, the gap between big cities and towns has narrowed, whereas the difference between towns and rural areas has grown. Rural areas of the United States have the highest fire death rates, and that gap may be widening. During 1984–1988, fire death rates in rural communities (population less than 2500) were more than double the rates in small cities (population 25,000 to 50,000) and more than 50 percent higher than rates in large cities (population of 500,000 or more). During 1995–1999, fire death rates in rural communities were triple the rates in small cities and more than double the rates in large cities. A caution is needed here because even with 5 years of data, fire death rates for rural areas tend to be volatile and subject to substantial estimation uncertainty and
year-to-year variation. Nevertheless, there are signs that the steady, significant declines in fire death rates taking place in communities of all larger sizes have not been taking place as consistently in rural communities.5 5. Usage of automatic sprinkler systems continues to grow, and their fire safety value remains dramatic. The last 10 years of fire experience statistics indicate that sprinklers reduce both the rate of deaths in fires and the average property loss per fire by one-half to two-thirds. Enough data have now accumulated to extend this statement to American homes, as sprinklers are increasingly proving themselves in the places where most people die in fires. In 1980, only one hotel in nine having a reported fire was found to have sprinklers; by 1997, that had risen to one in three, and, according to the American Hotel and Motel Association’s 1988 article “Fire Protection in the Lodging Industry,” the overall rate of sprinkler usage in hotels, regardless of whether they had fires, was over half. In 1980, fewer than half the facilities caring for the sick that reported a fire were found to have had sprinklers; by 1997, almost three-fourths had sprinklers.6 6. Home smoke alarms are nearly universal, but many aspects of the national use of home smoke alarms still need attention. According to a 1997 Fire Awareness survey done for the NFPA, 94 percent of U.S. homes had at least one smoke alarm,7 a remarkable change from 30 years earlier, when almost no one had these devices. The 6% percent of homes without detectors experienced nearly two-fifths of the reported fires and half of the fire deaths.8 In 1992, the U.S. Consumer Product Safety Commission (CPSC) studied smoke alarms in all types of homes—not just those that had fires—and found that in 20% percent of the households with at least one smoke alarm present, none were operational.9 In about 30% percent of the homes that reported fires and had smoke alarms, smoke alarms did not work.8 Only 16% percent of households had escape plans that they had rehearsed, so the extra warning time provided by detectors may often be wasted in real fires.7 7. Children playing with fire, principally matches and lighters, is still the leading cause of fire death among preschoolers, despite a 44% percent decline from 1994 to 1998. Total fire deaths fell 16% percent during that same period. The U.S. Consumer Product Safety Commission’s requirement for child-resistant lighters took effect in 1994. Since that time, child-play deaths involving lighters and matches declined by roughly equal percentages.10 8. Juvenile firesetters became even more dominant as the leading share of the arson problem. In the early 1980s, juveniles (those under age 18) typically accounted for around 40 percent of those arrested for arson, according to data from the Federal Bureau of Investigation’s Uniform Crime Reports. Since 1994, at least 50 percent of those arrested were under 18. During the same time, there was a growing recognition that many of the child-playing fires involved psychological or environmental problems similar to
(continued)
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TABLE 3.3.2
Continued
those common among juvenile firesetters classified as arsonists. These findings supported greatly expanded programmatic attention to the juvenile firesetter problem, which was reflected in fire safety initiatives in the 1990s.11 9. Steep declines in the number of heating equipment fires dropped heating out of first place among causes of home structure fires. NFPA statistical analysis had tracked the sharp rise in home-heating fires, driven by growth in the usage of portable and fixed space heaters, which account for the largest share of home heating fires and associated losses. After peaking in the early 1980s, this heightened home-heating fire problem began declining steeply, as the use of portable and fixed space heaters leveled off, and as widespread public education and public awareness
of these analyses could not have been conducted without the new and refined databases that emerged in the late 1970s. This list is not arranged in any order of priority, nor is it necessarily a list of what everyone would consider the 10 most important data-based findings. The list does, however, illustrate the ability of data and analysis to identify emerging problems, describe those problems in ways that can help the design of corresponding programs, and track the impact of those programs.
BASIC TOOLS FOR NFIRS ANALYSIS Before attempting to analyze fire data, it is important to have the right tools and an understanding of what is in and not in the data. The following items will be needed in some or all circumstances.
Version 4.1 Coding Manual Codes for the incident report, civilian casualty report and firefighter casualty report are available from the USFA, and may be downloaded from the web at http://www.usfa.fema.gov/nfdc/ codes.htm. National data for 1998 were collected and released according to this coding structure. If the database contains converted data, it is important to know how the data were collected originally.
Version 5.0 Reference Guide and/or Quick Reference Guide These are the coding manuals for the new system and may be downloaded from http://www.nfirs.fema.gov/refguide.htm. The longer reference guide provides completion directions, form samples, and expanded definitions. Because many—if not most—of the people completing reports in NFIRS 5.0 will be using pull-down menus instead of a coding manual, the analyst should check either the Quick Reference Guide or the Data Dictionary in the Version 5.0 Design Documentation Manual to see the code descriptions seen by the people completing the form. The longer definitions found in the Reference Guide provide greater specificity about what should and should not be included in a specific code. People who use computer look-ups or the Quick Reference Guide may miss these distinctions. The analyst
campaigns, coupled with the use of applicable codes and standards, took hold. By the early 1990s, heating had fallen to second place, behind cooking, among causes of home fires, and had fallen to third place among causes of structure fires. These rankings remained through 1998, although the impact of surging fuel prices in 1999 and 2000 is not yet known. Statistics for these years were not available when this chapter was prepared.12 10. The number of firefighter on-duty fatalities has generally been declining. From an annual death toll over 150 in the late 1970s, fire fighter fatalities occurring due to injuries or illnesses suffered while on duty fell below 100 on average in the 1990s. (These fatalities did spike to a 10-year peak in 1999, when 112 firefighters lost their lives.)13
should be guided by the definitions used by the fire service, the people who provide the data.
Version 5.0 Design Documentation The Version 5 Design Documentation Manual contains conversion tables, record layouts, edit checks, and the data dictionary. The data dictionary contains the standard codes plus codes used only for conversion of older data. These conversion-only codes are not listed in the Version 5.0 Reference Guide or Quick Reference Guide, so that users will not consider them valid. However, they are essential to analysts working with a database that contains any converted data. This document may be downloaded from http://www.nfirs.fema.gov/design.htm. Conversion tables and Version 5.0 forms may also be downloaded separately from the same site. Anyone who is working with the national fire database or who wishes to use national numbers in his/her own analysis should be familiar with the article “The National Estimates Approach to U.S. Fire Statistics” by Hall and Harwood.14 A free copy of this article may be obtained from NFPA’s One-Stop Data Shop [Tel: (617) 984-7450; e-mail:
[email protected]]. The results of NFPA’s annual survey of fire department experience can be found in Mike Karter’s report “Fire Loss in the United States,”5 an abbreviated form of which is published each year in the September/October issue of the NFPA Journal®. This information is also available from NFPA’s One-Stop Data Shop.
DATA SOURCE ISSUES NFIRS is not a complete census of reported fires. When people are interested in the size of the national fire problem, they must look beyond NFIRS. Because NFIRS at the national level is not a complete census and not a random sample, it cannot by itself answer questions such as “How many fires were reported last year?” or “How many people died as a result of last year’s fires?” NFPA’s annual survey of fire department experience, described in the last chapter, is based on a stratified random sample. This allows projections to be made on the “big picture” numbers of fires, residential or home fires, fire deaths and fire injuries. When the NFIRS totals are compared to the results of
CHAPTER 3
the survey, scaling ratios are derived that can be applied to NFIRS to develop estimates of the national fire problem. The procedures are described in Reference 14.
Reporting Policies and Practices Voluntary State Participation in NFIRS. Each state may set its own requirements. Some states require all runs to be reported, some only require fires, some have a dollar loss threshold, and, in some states, reporting is voluntary. Different communities within each state may have different practices or interpretations of the requirements. NFIRS was designed to capture fires reported to fire departments. If the fire department did not respond, no NFIRS report was generated. When fire reporting is voluntary or based on loss criteria, there may be differences in deciding which fires are worth reporting or should be reported. Influence of Reporting Requirements on NFIRS Data. Different states have different reporting requirements for NFIRS. These differing requirements impact the data in ways that cannot fully be controlled. States may differ not only in what reporting they require, but also in what incident types they will accept. These differences pose larger issues with NFIRS 5.0 as the USFA now accepts all types of incidents in its database. For example, in older versions of NFIRS data, it was possible to identify fires in which smoke alarms and sprinklers operated. With the expanded incident types of 5.0, it is now possible to identify incidents in which smoke alarms or sprinklers were unintentionally activated. This would help in cost/benefit analyses. However, if several states are not routinely capturing nonfire incidents, the projection or estimation rules will need to compensate for that fact, or the number of unintentional activations will appear artificially low. Even when complete reporting is required, a dislike of paperwork has occasionally influenced how incidents were coded. In the past, fire officers had to complete the full form for structure fires, but provide nothing or only basic information for smoke scares. This may have resulted in some minor fires being called “smoke scares.” These problems may have resulted in the undercounting of some minor incidents. Even on the NFPA fire experience survey, the fire department can only report incidents it has documented. Consequently, minor fires and nonfire incidents may not be documented if the state does not require the department to do so. Many departments understand that they need to know the nature of their fire problems and activities, and therefore document all incidents regardless of what is required. NFIRS software programs facilitate documenting and reporting by making the process easier. However, there is no systematic way to control for underreporting or changes in reporting practices. Comparing Data from Different Jurisdictions. Any comparison of fire department experience across jurisdictions must begin with a detailed evaluation of each jurisdiction’s reporting practices and policies. Because of the variations described earlier, results may be misleading. To avoid misleading results, each jurisdiction’s reporting practices and policies should be reconciled with one another. If the study is to use existing data, then a dataset of common as-
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Use of Fire Incident Data and Statistics
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sumptions may be constructed through inclusion/exclusion of specific types of incidents. For example, if a jurisdiction that reports all incidents wishes to compare itself with another jurisdiction that employs threshold reporting, then the all-incident department may exclude incidents that would not have been reported by the threshold reporting department for comparison purposes. This is true regardless of the NFIRS version. Similar issues pertain to location-based analysis outlined later in this chapter. Intercity comparisons should only be made when each entity adheres to similar geocoding data quality standards. If Department A maintains a 95 percent valid location rate for all incidents, and Department B’s and C’s are only at 80 percent, there will be a bias toward higher location specific rates for Department A’s reporting areas than the others for comparison purposes. Although this might not greatly affect percentage distribution of types of fires (unless there is a bias among nongeocoded incidents), rates of fires per capita would be affected. Converting Data to Standard NFIRS—States’ Unique Versions. Some states and cities use different data systems and convert their data back to standard NFIRS. Because of the implementation process for NFIRS 5.0, this means that an area’s data, collected in an older system, might be first converted to the standard version of the older NFIRS and then converted again to NFIRS 5.0. This will be true for California. California’s CFIRS is significantly different from the versions of NFIRS used elsewhere. In addition to using a different coding system, California’s CFIRS also did not collect certain elements, such as age of casualty, which were collected elsewhere. If California or another area doing something similar differed significantly from the rest of the country on an element they do not collect, that could be missed. Although conversion programs are carefully developed, it is possible that unexpected results could be caused by the conversion. If unexpected results are encountered, it behooves the analyst to determine what the data might have been converted from or what, if any, portions of the data were excluded. Optional NFIRS 5.0 Modules. Version 5.0 requires the use of five modules under specific circumstances: Basic, Fire, Structure Fire, Civilian Fire Casualty, and Fire Service Casualty. The other modules, including EMS (emergency medical services), HazMat (hazardous materials), Wildland Fire, Arson, Juvenile Firesetter, Apparatus or Resources, Personnel, and Supplemental, may or may not be required or even accepted at the state or local level. According to NFIRS, either the Fire Module or the Wildland Fire Module may be used for grass, crop, and wildland fires. NFIRS 5.0 Wildland Fire Module. It might seem logical to assume that the number of wildland forms received by NFIRS equals the number of wildland fires in the reporting areas. This is not the case. Departments using earlier versions of NFIRS will not use the Wildland Fire Module. According to the NFIRS 5.0 Reference Guide, “The purpose of the Wildland Fire Module is to document REPORTABLE wildland fires. Generally speaking, a reportable wildland fire is any fire involving vegetative fuels that occurs in the wildland or urban-wildland interface areas, including those which threaten or consume structures.” The module may, depending on state or local policy, be used for brush, forest or grass fires, fires on cultivated land or unauthorized, controlled
3–38 SECTION 3 ■ Information and Analysis for Fire Protection
or prescribed burning. Normally, only hostile fires are counted as fires. This means that Wildland Module forms may be present for incidents that are not counted as part of the fire problem. It is generally good practice to restrict queries by incident types, and this holds true here. Some states, such as Kansas, require the Wildland Module for outside vegetation fires in communities with populations under 50,000. Some of these fires would not normally be considered wildland. Cause Categories in the NFIRS 5.0 Wildland Fire Module. The fields in the Wildland and Fire Modules overlap, but there are differences in the broad cause categories. See Table 3.3.3. Although the Wildland Fire Module was designed to document reportable wildland fires, local and state authorities may require its use with fires of specific incident types that have not reached the status of what would normally be called “wildland fires.” If an analysis of NFIRS 5.0 data of intentionally set fires is based only on the causes from the Fire Module, incendiary fires documented on the Wildland module will be omitted. Although similar, the cause “Failure of Equipment or Heat Source” on the Fire Module, and the cause “Equipment” on the Wildland Module are not exactly equivalent. If a lantern placed on the ground ignited some leaves or pine needles, the equipment played a role, and “Equipment” might reasonably be listed as the cause. However, if the Fire Module was completed instead, “Unintentional” would probably be the more appropriate code because the equipment did not really fail, except in the terms of not protecting against likely misuse. “Equipment” on the Wildland module includes equipment that was operating properly as well as defective equipment. Consequently, the “Equipment” causes on the two modules cannot confidently be combined. Impact of Abbreviated Reporting. With the older versions of NFIRS, some states allowed abbreviated reporting of the socalled no-loss outside fires—the brush, rubbish, or grass fires and the outside trash, rubbish, or waste fires. Abbreviated reporting generally captured dispatch-type information and the occupancy class or fixed property use. Ignition factor was requested, but often left blank or coded as undetermined because cause investigation was not a priority in these incidents.
TABLE 3.3.3 Fire Modules
Cause of Ignition Codes in Fire and Wildland Wildland Fire Cause
Fire Module Cause 1. Intentional 2. Unintentional 3. Failure of equipment or heat source 4. Act of nature 5. Cause under investigation U. Cause undetermined after investigation
1. 2. 3. 4. 5. 6. 7. 8. U.
Natural Source Equipment Smoking Open/outdoor fire Debris/vegetation burn Structure (exposure) Incendiary Misuse of fire Undetermined
Source: Adapted from NFIRS-2, Fire Module, Revision 1/19/99 and NFIRS-8 Wildland Fire Module, Revision 2/12/99.
For analysis, the uncollected fields were treated as “unknowns.” Abbreviated Reporting and the Analysis of Structure Fires. Abbreviated reporting for structure fires was generally not allowed in the older versions of NFIRS. Items such as area of origin, fire cause, and detector and sprinkler performance were always required fields. This has changed and requires a new approach. Version 5.0 allows for abbreviated reporting of certain confined structure fires (and outside rubbish fires), including fires confined to the chimney, incinerator, trash receptacle, fuel burner, or food on the stove. It was believed that causal factors were so similar for these types of incidents that it was redundant to ask for completion of the fire and structure fire module. This data will be present for these types of incidents when fires from the older versions are converted. However, the older incidents will not have the specific incident type codes. In some jurisdictions, abbreviated reporting will not be allowed. Fire officers have also been advised to complete the fire and structure fire module when a confined fire is believed to be intentional. This will pose interesting challenges to the assumptions about the distribution of unknown’s. This is likely to be an issue chiefly with rubbish container fires. National analysts have agreed among themselves that certain codes can, in the absence of other information, be inferred for abbreviated reports for area of origin, equipment involved in ignition, and material ignited. Table 3.3.4 shows the inferences that analysts agreed upon for area of origin, item first ignited, equipment involved in ignition, and cause from the traditional USFA cause hierarchy. It also indicates new codes that NFPA will add for its own analyses. Possibility of Artificial Increase in Fires. The ease of recording these incidents is likely to lead to an artificially created statistical increase in these types of incidents and of their share of the total fire problem. It will be necessary to carefully examine the breakdown of incident types to determine if the increase is real or a result of the new reporting system. Many states will continue to accept older versions of NFIRS from at least some of their departments for a number of years. This means that systemdriven changes in the data will continue for a number of years. Number of Expected Entries per Data Element. Analysts working with Version 5.0 data need to understand which combinations of data elements must be completed under which circumstances. Certain data elements allow multiple entries. For example, two entries are allowed for “factors contributing to ignition.” This means, in effect, that two fields must be queried for one data element. This is also an issue for other data elements such as actions taken, human factors, on-site materials, and fire suppression factors. Because only the Basic Module is required for specific confined structure fires and outside rubbish fires, data collected from the Fire or Structure Fire Module may not be captured.
NFIRS Versions and Converted Data Analyses are cleaner when working with data collected in only one version of NFIRS. However, this is not possible for trend
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TABLE 3.3.4
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Use of Fire Incident Data and Statistics
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Confined Structure Fires and Inferred Codes or Causes Codes to Be Inferred or Assigned
Type of Confined Fire 113—Cooking fire, confined to container
Area of origin = 24 (kitchen) Item first ignited = 76 (cooking materials, including edible materials) Equipment involved = 640 (a new code defined as cooking equipment of unknown type) This will sort these fires into “Cooking” among the 12 major causes in the hierarchical sort.
114—Chimney or flue fire, confined to chimney
Area of origin = 57 (chimney, conversion code only) Item first ignited = 95 (Film, residue, included are paint, resin and chimney film or residue or residue and other films and residues produced as a by-product of an operation. Creosote was coded as rubbish, trash or waste in older versions of NFIRS.) Equipment involved = 129 (a new code defined as chimney or flue of unknown type) This will also sort these fires into “Heating” among the 12 major causes in the hierarchical sort.
115—Incinerator overload or malfunction
Area of origin = 64 (incinerator area) Item first ignited = 96 (rubbish, trash, or waste) Equipment involved = 352 (incinerator) This will also sort these fires into “Other Equipment” among the 12 major causes in the hierarchical sort.
116—Fuel burner/boiler malfunction
Area of origin = 62 (Heating room or area or water heater area) Item first ignited = 69 (a new code for flammable or combustible liquid of unknown type) Equipment involved = 130 (a new code for boiler, furnace, or central heating unit of unknown type) This will also sort these fires into “Heating” among the 12 major causes in the hierarchical sort.
117—Commercial compactor, confined to rubbish
Area of origin = 46 (chute or container for trash, rubbish, or waste) Item first ignited = 96 (rubbish, trash, or waste) Equipment involved = 812 (trash compactor) This will sort these fires into “Appliances” among the 12 major causes in the hierarchical sort
118—Trash or rubbish fire, contained
Area of origin = UUU (unknown) Item first ignited = 96 (rubbish, trash, or waste) Equipment involved = NNN (none) This will sort these fires into the residual “Unknown Category” of the hierarchical sort.
Source: P. A. Frazier et al., Memorandum dated September 25, 2000, “Revised Proposed Analysis Rules for Fire Incident Data in NFIRS 5.0 Format.”
analyses or analysts who must work with data collected in two or more systems. The differences between Version 3, 4.0, and 4.1 were not that extreme. A few new fields, such as the number of stories, were added to Version 4.0. The fire fighter casualty report was also added, and required conversion of fire fighter injury reports collected on the old injury report. In Version 4.0 and 4.1, the original injury report was used for civilian and nonfirefighter injuries only. None of the fields in the fire incident report required conversion. Version 4.1 added the Hazardous Material Module,
but did not change any of the elements on the other forms. With the advent of NFIRS 5.0 with its new coding scheme and data structure, the issue of converted data becomes prominent. As mentioned earlier, conversion issues also arise when states that use their own data collection systems convert their data to NFIRS 4.1, which, in turn, is converted to NFIRS 5.0. Comparing Version 5.0 with Older Versions of NFIRS. The structure and the coding system of NFIRS 5.0 are significantly
3–40 SECTION 3 ■ Information and Analysis for Fire Protection
different from those of Versions 3, 4.0, and 4.1. Conversion tables were developed, but the conversion is not one to one. Code definitions differ between the systems, and conversions are often not exact. For some analyses, it would be prudent to exclude converted data. Data collected in the older versions will be converted to the Version 5.0 format. A field will identify the version the data was collected in, enabling analysts to include or exclude the older data. (Legacy data, the elements collected in Version 4.1 but dropped from 5.0, will be maintained.) In some cases, greater detail was sought. However, it is impossible to accurately specify greater detail than was collected originally. For example, the older Form of Heat of Ignition codes for solid-burning equipment will convert to Heat Source “Other solid fuel” because there is no way to know which of the following three codes would be most appropriate: wood or paper; coal or charcoal; or chemicals. If the analyst were unaware of the conversion, and queried on wood or paper fuel only, none of the older version’s fires would be captured. In older versions, a two-digit Situation Found code captured what is now called Incident Type. Incident Type has expanded to three digits. Situation Found 11 identified a structure fire in earlier versions. Table 3.3.5 shows the categories of structure fires in Version 5.0 and the required modules for that incident type. Mobile properties used as a structure are captured in the 120s. In older versions, these properties were identified by a mobile property type code to identify a mobile structure and the fixed property use that identified the occupancy. With the exception of fires in which mobile property was used as a structure, the Situation Found 11s will convert to a
TABLE 3.3.5
conversion-only incident type code of 110. When NFIRS 5.0 was implemented, conversion-only codes were documented in only the data dictionary and not the coding manuals to prevent their use in coding. Table 3.3.6 lists some of the conversion codes and their uses. (The data dictionary is found in the Design Documentation.) Beginning with the 1999 NFIRS data, which will probably be released to analysts in 2002, the entire national database will be converted to Version 5.0. A group of fire analysts from the NFPA, USFA, U.S. Consumer Product Safety Commission (CPSC), TriData Corporation, and the National Fire Information Council (NFIC) have been working together to determine the best way to analyze the Version 5.0 data. Nationally, the NFPA annual fire department survey will face the earliest impact from the new system. Fire departments or vendors offering the NFPA survey as an output report need to know what combination of coded values should be used to categorize and count types of fires, and specific types of fire fighter injuries as discussed below. Structure and Vehicle Fires. These Version 5.0 analysts agree that structure fires include all the fires in the 110 and 120 series. Vehicle fires, formerly identified by Situation Found 13, are captured in the 130 series in Version 5.0. However, the NFPA will drop the distinction between highway and other vehicles, as the older Situation Found 13 will convert to Incident type 130, “Other mobile property or vehicle fire.” In Version 5.0, code 131 identifies passenger vehicle fire, and 132 identifies road freight or transport vehicle fire. Residential Fires. In older versions of NFIRS, the 400’s series of fixed property use defined residential fires. The 400’s se-
Version 5.0 Structure Fires and Required Modules
Code
Description
Comments
110
Conversion code only for older structure fires (Situation Found 11), excluding those with mobile property used as a structure Building fire Fires in structures other than buildings Cooking fire, confined to container Chimney or flue fire, confined to chimney or flue Incinerator overload or malfunction Fuel burner/boiler malfunction, fire confined Commercial compactor fire, confined to rubbish Trash or rubbish fire, contained
Associated data will be converted or incomplete
111 112 113 114 115 116 117 118
121 122 123 120
Fire in mobile home used as fixed residence Fire in motor home, camper, recreational vehicle (used as fixed structure) Fire in portable building with a fixed location Fire in mobile property used as a fixed structure, other
Basic, Fire and Structure Fire Modules Basic, Fire and part of Structure Fire Module Abbreviated report okay Abbreviated report okay Abbreviated report okay Abbreviated report okay Abbreviated report okay Abbreviated report okay, but full report encouraged when fire may have been intentionally set Basic, Fire and Structure Fire Modules Basic, Fire and Structure Fire Modules Basic, Fire and Structure Fire Modules Basic, Fire and Structure Fire Modules
Source: Incident Type/Module Rules by USFA and National Fire Incident Reporting System Version 5.0 Design Documentation Specification, Release 2001.2, July 2001.
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TABLE 3.3.6
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Use of Fire Incident Data and Statistics
Conversion-Only Codes Definition
Code
Used for
Basic Module 110
Incident Type Structure fire, other
Structure fires (situation found 11) and mobile property was not used as a structure (mobile property < > 17)
320
Emergency medical service, other
Emergency medical calls (situation found 32)
UUU
Undetermined incident type
Situation found undetermined—code 00
UU
Actions Taken Undetermined
Action taken undetermined—code 0
Fire Module 57
Area of Origin Chimney
UU
Mobile Property Type Undetermined
Chimney—Area of origin 57 Confined chimney fires are identified by incident type 114 (abbreviated report). If a fire breaks out of the chimney, the area of origin would be the room or space in which the fire breaks into. Mobile property undetermined (code 00)
Civilian Casualty Module N
Cause of Injury None
Cause of injury not applicable (code 8)
U
Affiliation Undetermined
Other emergency personnel (code 2)
U
Primary Area of Body Injured Undetermined
' Primary part of body undetermined (Code 00)
UU
Factors Contributing to Injury Undetermined
Condition preventing escape undetermined (code 0)
Fire Service Casualty 30 60 70
Primary Area of Body Injured Thorax, other Upper extremities, other Lower extremities, other
UU
Protective Equipment Item Undetermined
NN
None
Unclassified or unknown part of trunk (code 20, 29) Unclassified or unknown part of arm or hand (code 30, 39) Unclassified or unknown type leg or foot (code 40, 49) Protective equipment worn or protective equipment problem undetermined None in protective equipment worn or protective equipment problem fields
HazMat Module 10 20 40 50 60 90
DOT Hazard Classification Class 1 Explosives, other Class 2 Gases, other Class 4, Flammable solids other Class 5-Oxidizers and organic peroxides, other Class 6—Toxic or infectious material or substance, other Miscellaneous dangerous goods, other
Explosives and blasting agents (Code 1) Gases (compressed, liquefied, or dissolved under pressure) (Code 2) Flammable solids (Code 4) Oxidizers and organic peroxides (Code 5) Poisonous and infectious substances (Code 6) Other regulated materials (Code 9)
Source: National Fire Incident Reporting System Version 5.0 Design Documentation Specification, Release 2001.2, July 2001.
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3–42 SECTION 3 ■ Information and Analysis for Fire Protection
ries of property use will likewise define residential fires in Version 5.0. The NFPA and some other organizations separate homes from other residential properties. Homes include oneand two-family dwellings, apartments and manufactured housing, captured in older versions of NFIRS with fixed property use 410–429, and now captured property use 419, one- or twofamily dwelling, manufactured home, mobile home or duplex, and 429, multifamily dwelling, including apartments, condominiums, townhouses, row houses and tenements. Outside and Other Fires. Outside and other fires were said to include outside fires involving property of value; brush, tree, grass, or forest fire; outside rubbish or trash fires; explosions with no after-fire; outside spill or leak with ensuing fire; unclassified fires; and unknown-type fires (situation found 12, 14, 15, 16, 17, 19, and 10, respectively). In Version 5.0, an explosion that does not result in a fire (incident type 240s series) is no longer grouped with fires or counted as a fire. Exposure Fires. Older analyses of NFIRS counted each exposure as a separate incident. Unless otherwise specified, the USFA’s output reports for NFIRS will count the losses from exposures as part of the original incident. However, they will remain separate in the database. To check the results of an original query against a standard output report, it may be necessary to subtract the exposure fire and loss totals from the query results. Incendiary, Suspicious, and Intentional Fires. For statistical purposes, analysts generally grouped Ignition Factors for incendiary and suspicious together as arson, much to the chagrin of many fire investigators who concur with NFPA 921, Guide for Fire and Explosion Investigations, which does not consider suspicious to be a valid cause. Although there is broad consensus that “suspicious” is never a valid final cause determination after investigation, it was considered appropriate for fires that are likely to never be fully investigated or for reports that may not have been updated after an investigation. The Ignition Factors of incendiary and suspicious will both convert to the Cause of Intentional, so the distinction between the two will be lost. Incendiary and suspicious both imply an illegal act; “intentional” does not carry that implication as strongly. For example, a crisis-type juvenile firesetter may be below the age of legal responsibility but may intentionally start a fire. Ignition Factor Information Collected Under Human Factors. The field “Human Factors” is new and of considerable interest to many, particularly those working in life safety education. Some aspects of Ignition Factor are now captured under Human Factors. For example, a “Factor Contributing to Ignition” code covers “playing with heat source,” but it is no longer confined to children. The older Ignition Factor codes “child playing with heat of ignition” and “child playing with material ignited” both convert to Cause “unintentional,” Factor Contributing to Ignition “playing with heat source,” Human Factor “age was a factor” and age equals nine. This conversion will artificially increase the portion of nine year olds shown in the results. The old Ignition Factor “unconscious, mental or physical impairment, or drug or alcohol stupor” converts to Cause “unintentional” and Human Factor “possibly impaired by alcohol
or drugs.” Although other Human Factors include “physically disabled” and possibly “mentally disabled,” it was necessary to do a direct conversion. This conversion will artificially increase the portion of alcohol and drug-impaired fires. Age Reporting in NFIRS 5.0. When age is a factor in a fire, the age may be captured in one or two of the following three modules: the Fire Module which records age only when it is entered as a Human Factor; the Wildland Module, which records age or date of birth for the person responsible, whether the fire was intentional or not; and the Juvenile Firesetter Module, which documents age on fires set by juveniles, again whether intentional or not. Either the Fire Module or the Wildland Module is required for fires that are not confined or are not outside rubbish fires. Fire fighters have been told that if they document the age on the Juvenile Firesetter Module, it does not need to be documented on the Fire Module, but that it might make analysis easier if they did so. To answer questions about how many fires occurred in which a young age was a factor, it would be necessary to do an “or” query, asking how many cases were recorded in each module. Again, there are subtle differences in underlying definitions. Age is one of a number of “Human Factors Contributing to Ignition” in the Fire Module, and it implies that were the individual not that age, the ignition would not have occurred. Age might be listed as a factor when a latch-key child unintentionally starts a fire while cooking. The age would not be documented when an absent-minded middle-aged adult does the same thing. It probably would be documented for an 80 year old. Age is documented for all known responsible parties on the Wildland Module. Fire Fighter Injury Definitions. Version 5.0 adds a new severity code, “Report only, including exposures” for fire fighter injuries. While the NFPA survey will ask for a distinction to be made for exposures, the other “report only” injuries will be included. Since historically, many firefighters injury reports indicate that no treatment was received, this is not a change. However, before comparing fire fighter injury rates (or civilian rates, for that matter) across jurisdictions, it is necessary to determine what criteria the different departments used in deciding when an injury report was warranted. The NFIRS 5.0 Reference Guide states “An injury is physical damage to a person that requires either: (a) treatment by a practitioner of medicine within one year of the incident, or (b) at least one day of restricted activity immediately following the incident.” Analysts who examine trends or work with combined data need to familiarize themselves with the conversion tables found in the NFIRS Version 5.0 Design Documentation Manual. Several samples of additional conversion issues are included to demonstrate this point. Fire Alarm Information. Although the abbreviated reports have a check box to indicate that the smoke alarm alerted occupants, presence and operational status is collected only on the structure fire module. In Version 5.0, fire detectors are considered present only if they are in the area of the fire. Older versions had two codes indicating that detectors were not in the room or space of origin and they did or did not work. The conversion
CHAPTER 3
program will convert the working detectors outside of the area of origin to present, but the detectors that were not in the room or space of origin and did not operate will convert to “not present.” This conversion will cause the results to show a decrease in the number of fires in which detectors were present and an increase in the percentage of detectors that worked when detectors were present. Since information on detector type, power supply, and effectiveness in terms of alerting occupants were not collected, these fields will be left blank or undetermined. Automatic Extinguishing Systems. Several fields on Automatic Extinguishing System replace the Sprinkler Performance found in older versions. While sprinkler presence is consistently tracked, sprinkler performance has become more specific by asking about effectiveness. In Version 5.0, fire officers are given two choices for operating systems: “operated and effective” or “operated and not effective” in the field Automatic Extinguishment System Operated. The simple “Equipment operated” from the older Sprinkler Performance cannot be broken down in this
TABLE 3.3.7 Version 5.0
Use of Fire Incident Data and Statistics
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manner; so the operating sprinklers in the older system convert to “undetermined” in Version 5.0. Unclassified detector and sprinkler performance in the older versions convert to “present” in Version 5.0, with the secondary questions undetermined or blank. Equipment Involved in Ignition. In older versions of NFIRS, the codes for equipment involved were only two characters long. The field has been expanded to three characters, with a corresponding increase in number of choices. A separate field indicates if the equipment was portable or stationary. These added details will provide much more specific information and should be particularly helpful in examining nonresidential fires. However, some of the choices may be so specific that the meaning is not clear to the fire fighters completing the incident reports or to the analyst trying to capture the same type of information as previously obtained. Table 3.3.7 shows the codes for heating equipment in Versions 4.1 and 5.0 and how the old codes are converted to Version 5.0.
Heating Equipment Codes from Equipment Involved in Ignition in NFIRS Versions 3, 4.0, and 4.1 and in Versions 3, 4.0, 4.1
11 12 13 14 15 16 17 18 19 10
■
Central heating unit Water heater Fixed, stationary local heating unit Indoor fireplace Portable heater Chimney or gas vent flue Chimney connector or vent connector Heat transfer system Unclassified heating equipment Unknown-type heating equipment
132 151 131 120 141 120 125 152 100 100
Converts to in Version 5.0
Portability
Furnace, central heating unit Water heater Furnace, local heating unit, built-in Other chimney or fireplace Heater, excluding catalytic and oil-filled heaters Other chimney or fireplace Chimney connector or vent connector Steam line, heat pipe, hot air duct Other heating, ventilation or air conditioning equipment Other heating, ventilation or air conditioning equipment
S S S S P S S S
Version 5.0 121 122 123 124 125 126 127 120 131 132 133 141 142 143 144 145 151 152 100
Masonry fireplace Factory-built fireplace Fireplace, insert/stove Stove, heating Chimney connector or vent connector Chimney—brick, stone or masonry Chimney, metal, including stovepipe or flue Other chimney or fireplace Furnace, local heating unit, built-in Furnace, central heating unit Boiler (power, process, heating) Heater, excluding catalytic and oil-filled heaters Heater, catalytic Heater, oil-filled Heat lamp Heat tape Water heater Steam line, heat pipe, hot air duct Other heating, ventilation or air conditioning equipment
Source: National Fire Incident Reporting System Version 5.0 Design Documentation Specification, Release 2001.2, July 2001 and NFPA 901, Uniform Coding for Fire Protection, 1976 edition.
3–44 SECTION 3 ■ Information and Analysis for Fire Protection
APPROACHES TO FIRE DATA ANALYSIS The discussion to this point has focused on how the data and the data collection system impacts analysis. The remainder of the chapter will focus on approaches to fire data analysis. Most of the examples with real data will be taken from analyses of Version 4.1 NFIRS. National data from Version 5.0 was not available when this chapter was prepared. Possible approaches for analysis with NFIRS 5.0 data are included.
Top-Down and Topic-Driven Analysis Most characterizations of the fire problem begin with some measures of the problem’s size. Why? Implicit in these measurements is the idea that fire is a problem big enough to justify concern and attention. Each year, fire kills thousands of people, injures tens of thousands more, and destroys billions of dollars of property. When the fire community wishes to pursue a program that requires the cooperation of others, that community must first attract their attention. The big numbers on fire—incidents, deaths, injuries, and property damage—accomplish this. Top-down analysis is an approach that begins with a summary of the big numbers, then subdivides the totals into their major parts. A top-down analysis might begin with the number of runs. Several types of subsections are possible, including types of runs, that is, fires, EMS, false calls, and so on. These subsections may be broken down further: for example, separate profiles can be created for each time period, occupancy class, or fire cause. At the local level this breakdown might also include profiles by station or company. A top-down look at U.S. fire department runs over the past 20 years reveal a steady drop in fire calls, but an increase in false alarms. Although the decrease in fires is encouraging, the total of reported fires and fire calls has averaged about 3.6 million since 1980. Through most of the 1990s, the total was above this average. In 1999, the combined total was at its highest point since 1980.15 These statistics are shown in Figure 3.3.1. Fire
Fire departments cannot presume a call is a false alarm and must respond as they would to a fire. If only the statistics for fires were examined, this pattern would be missed. The top-down approach provides the broadest perspective on the overall fire problem or a fire department’s activity. It differs from topic-driven analysis, which begins with interest in certain issues involving only certain types of fires. For example, a top-down analysis of fires in residences might identify smoking materials as the leading factor in civilian fatalities in homes, accounting for roughly one-fourth of the fires for which the cause was reported. On the other hand, a topic-driven analysis focused on smoking-material fires—for example, a study of the likely impact of a self-extinguishing cigarette or of a public education program aimed at smokers—would involve more than just homes. Although both topic-driven and top-down analyses might be interested in the role of smoking-related fires in home fire deaths, topic-driven analysis might also be interested in the involvement of smoking materials in non–home fire fatalities or in property damage in home fires. Even though smoking-related fires do not account for the largest shares of the latter two problems (incendiary and suspicious causes lead in both cases), they are still part of the overall smoking-related fire problem; any change that affects the smoking-fire problem may affect all smoking-related fires. In a top-down analysis, the basic rule is to look for the biggest parts of the problem. Why bother subdividing the problem? Resources usually are too limited to permit an attack on the whole problem and choices must be made. At times, important pieces of information are missed if only totals are examined. For example, home structure fires account for only one-fifth of reported fires, but four-fifths of all fire deaths. The use of data to identify the largest manageable parts of the problem is the first step in making those choices. Whereas totals are used to show the overall size of the problem, percentages are used to indicate the largest parts. Use of percentages to identify the largest parts of the fire problem is not as easy as it sounds. Judgment is involved in se-
False alarm
4.5 4
Incidents (in millions)
3.5 3 2.5 2 1.5 1 0.5 0
80
81
82
83
84
85
86
87
88
89 90 Year
91
92
93
94
95
96
97
FIGURE 3.3.1 Reported Fires and False Alarms,1980–1999 (Source: The U.S. Fire Problem Overview Report: Leading Causes and Other Patterns and Trends)
98
99
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Use of Fire Incident Data and Statistics
atively little risk, accounts for more than one-fourth of all fire fighter deaths. Figure 3.3.3 implicitly demonstrates that as fire fighter age increases, the leading share of deaths dramatically shifts to heart attacks.13 Such patterns have direct implications for targeting of physical fitness programs.
Analysis by Fire Cause and Property Type The dimensions most frequently chosen for top-down and topicdriven analyses are fire cause and property type, because most fire prevention strategies are structured along those lines. “Analysis by cause” actually refers to a variety of analyses addressed to different aspects of the ignition factors. The question of how to
Other on-duty 9% Nonfire emergencies 9% Fireground 50%
Training 4%
Responding to or returning from alarms 29%
FIGURE 3.3.2 Fire Fighter Fatalities in 1999 by Type of Duty (Source: Fahy, R. F., and LeBlanc, P. R., “Report on 1999 Firefighter Fatalities,” NFPA Journal, July/Aug. 2000, Vol. 94, No. 4, p. 49)
Non–heart attack Heart attack
25 20 Number of deaths
8
15
7
10
2 6 11
5 0
5 0
5 1
0
8 11
5 2
4
4
12 9
9
3
16 –2 0 21 –2 5 26 –3 0 31 –3 5 36 –4 0 41 –4 5 46 –5 0 51 –5 5 56 –6 0 O ve r6 0
lecting the categories for which percentages will be calculated. For example, suppose an analysis showed the biggest subgroup of a particular occupancy group’s fire problem consisted of fires involving electrical short circuits. This finding does not fit well into most strategies for attacking the fire problem. If one is going to examine every piece of equipment that could be subject to short circuits, one might as well also check for other electrical faults in that equipment. The available strategy may dictate a broader category, covering fires involving all electrical equipment faults. Or maybe it is easier to design strategies around particular types of electrical equipment (e.g., fixed wiring, heating systems, ranges, and ovens) and address all fires involving such equipment, whether the equipment or the user were at fault. Take another example. Which of the following findings is more useful: (1) 31 percent of all home fires begin in the kitchen; or (2) 23 percent of home fires involve cooking equipment?15 The latter finding identifies a smaller part of the problem and uses a completely different categorization (equipment involved in ignition vs. area of origin), but it locates the problem much more specifically. In a kitchen, there could be dozens of fire hazards to check out; with cooking equipment, most homes have only a few. Finally, suppose a categorization includes equipment involvement, material ignited, and the human elements that brought them together. Such a categorization will produce detailed scenarios, but the “leading” category might account for only 2 to 4 percent of all fires. It would be necessary to develop strategies for several dozen scenarios in order to make any noticeable impact on the total fire problem. If that is so, it may make more sense to select scenarios that fit together logically and can be addressed by variations of the same strategy (i.e., use of less specific categories) than to select several dozen distinct scenarios and tackle each one separately. To put it another way, the scenario technique of analyzing several fire characteristics simultaneously is most useful as a second-stage analysis, performed after one characteristic has been used to establish basic clustering. Therefore, in selecting categories for calculating percentages, it is important to match the structure of the categories to the structure of the strategies available to attack the fire problem. Remember that the size of the problem being attacked is no more or less important than the anticipated leverage on the problem; for example, a 7 percent reduction in a problem that causes 500 deaths a year is worth just as much as a 70 percent reduction in a problem that causes 50 deaths a year. (This is discussed at greater length later in this chapter under the heading “Using Data in Program and Strategy Analysis.”) So be sure when you pick out the biggest parts of the problem that they collectively account for a sizable share of the total, but also remember that some parts of the problem may be much more preventable than others. Figures 3.3.2 and 3.3.3 illustrate the effective use of percentages (some implicitly presented through the display of numbers) to describe patterns in the 1999 fire fighter fatality problem. (These figures also illustrate the effective use of graphics to bring summarize numerical data in a more comprehensible manner.) In Figure 3.3.2, which shows the percentage of firefighter deaths by type of duty,13 the fact that fireground activity is the leading type of duty is not as interesting as the fact that it accounts for only half of the deaths. Response/return from alarm, which should involve only controllable dangers and rel-
■
FIGURE 3.3.3 Fire Fighter Fatalities in 1999 by Age and Cause of Death (Source: Fahy, R. F., and LeBlanc, P. R., “Report on 1999 Firefighter Fatalities,” NFPA Journal, July/Aug. 2000, Vol. 94, No. 4, p. 50)
3–46 SECTION 3 ■ Information and Analysis for Fire Protection
categorize, already discussed in general terms, becomes especially difficult in analyses of cause-related information. Even the question of how to refer to cause-based descriptions can be a problem. For example, suppose one observes that roughly one-fourth of all civilian fire fatalities in homes with fire cause reported were smoking related. Does this mean that cigarettes (the principal smoking material involved, by far) were to blame for all those deaths? Not necessarily. If the smokers in question had been careful not to smoke in bed and always to place cigarettes in sturdy ashtrays, few of the deaths would have occurred. Or if the bedding, mattresses, pillows, and upholstered furniture that are the first items ignited in most fatal smoking-related fires had been more ignition resistant, many or most of the deaths would have been avoided. If the cigarettes used had been designed to selfextinguish more quickly, many or most of the deaths might have been prevented. A decision on which dimension to use in categorizing fire causes—the source of heat, items ignited, or the behaviors that brought them together—should be made in a way that supports analyses of workable prevention strategies. Assessments of blame are tasks for lawyers or philosophers; they do not help in the search for ways to reduce fire problems. Fire incident data coded according to NFPA 901 format, which is used in most major fire databases (a modified version is used in NFIRS 5.0), contains five fire-cause-related elements of information: (1) the heat source; (2) equipment involved in ignition, if any; (3) the form of material ignited (e.g., chair, floor covering, structural beam) (this data element is called “item first ignited” in NFIRS 5.0); (4) type of material ignited (e.g., wood, plastic, fabric); and (5) ignition factor (“factors contributing to ignition” in NFIRS 5.0)—the human or equipment failures that brought together the ignition heat and ignited material. Together, these five dimensions and their subsections can define billions of distinct fire-cause categories, a clearly unworkable partitioning of the problem. In the face of all this detail, several approaches have been developed to extract major patterns. These approaches include the following: • • • • • •
Emphasis on intentional versus unintentional Emphasis on equipment Emphasis on behavior Emphasis on heat source Emphasis on item ignited Emphasis on hierarchical approach (cause)
Table 3.3.8 presents examples of how different approaches can affect the description of “leading cause” with the data available from Version 4.1 when this chapter was written. A similar analysis done on Version 5.0 data would be somewhat more complicated. Differences between versions are noted below each approach. Analyzing by One Data Element. Any one of the causal dimensions can be used to describe the fires. Because coding structure used for many data elements is generally grouped into “decades” and “centuries,” one can use the first digit alone to create 10 categories, or two digits to create nearly 100 categories for each dimension. This approach often proves frustrating, however, because the structure of the coding elements often does not coincide with the issues to be analyzed.
For example, suppose the ignition-factor dimension is used in an analysis of NFIRS 4.1 data. Incendiary and suspicious fires would be easy to identify (codes 10–29). Fires caused by children playing, however, involve two code values (36 and 48) that do not have the same first digit and therefore do not fall into a natural common grouping. Also, an analysis using ignition factors will produce a sizable number of entries under “abandoned, discarded material.” A novice analyst might not recognize that most of these are smoking-related fires and can best be characterized in this manner. Analysis on this dimension will be more complicated in NFIRS 5.0. “Intentional” (“incendiary” in the Wildland Fire Module) is a Cause of Ignition. The field Factors Contributing to Ignition must be completed for fires in which the cause is unintentional, a failure of the equipment or heat source, or an act of nature. However, an entry of none is valid. Taken together, the fields of Cause of Ignition and Factors Contributing to Ignition are equivalent to the older Ignition Factor. The Ignition Factor categories for children playing have been replaced with “playing with heat source” without regard to age. Child involvement would be identified when age was noted as a Human Factor Contributing to Ignition and the age was less than 18 or some other locally determined limit. If the ignition-factor dimension has problems when used by itself, what about the other dimensions? Problems arise here because incendiary and suspicious fires are not isolated. Under the category of “heat of ignition,” arson fires set with matches (the most common type) are indistinguishable from unintentional fires involving matches. Scenario Groupings. A third approach has been to use scenarios based on two or three of the causal dimensions. This avoids the tendency, in the one-dimensional scenario, for major problems to be mixed together (e.g., arson and unintentional match fires) or disguised (e.g., smoking-related fires listed as discarded or abandoned material). The use of even two dimensions of NFPA 901, however—or the use of three dimensions with the first digit only—creates thousands of cause categories, and again one is faced with the likelihood that even the largest parts of the total will not represent a very large share of the total. Broad Cause Categories. The fourth approach has been to use a small number of major, easily recognizable categories based on the causal data elements, but not necessarily grouped along the lines laid out in the NFPA 901 or NFIRS coding structure. The most widely used scheme based on this approach is a set of 13 categories developed at the U.S. Fire Administration (USFA). This scheme uses a hierarchical process to sort fires into categories. For example, one will start with ignition factor or cause and remove the incendiary, suspicious and intentional fires, and then the child playing or playing with heat source and young age fires. Then the analyst (or computer program) may switch to heat of ignition and use it to separate fires involving smoking materials. Criticisms of this or any other hierarchical sorting approach focus on the reasonableness of the sorting priorities and the usefulness of the categories produced. If a fire is caused by a child playing with cigarettes, should that be categorized as a children-
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3–47
TABLE 3.3.8 How “Leading Causes of Fire” Depend on How Data Are Sorted in NFIRS 3.0–4.1 and How This Will Change with NFIRS 5.0 NFIRS 3.0–4.1
NFIRS 5.0
Emphasis on intentional vs. unintentional Based on ignition factor Unintentional 75% 6% Suspicious 5% Incendiary 15% Unknown
Based on the Cause of Ignition field (E1 Note that “intentional” may not be “incendiary.” Also, a causal determination cannot be inferred for some types of on the Fire Module) confined fires, particularly rubbish fires. “Incendiary” and Unintentional “suspicious” fires from older versions of NFIRS will convert Intentional to “intentional.” Failure of equipment or heat source Act of nature Cause under investigation Cause undetermined after investigation
NFIRS 3.0–4.1
NFIRS 5.0
Emphasis on equipment Based on Equipment Involved in Ignition in Fire Module or Wildland Fire Module
Based on equipment involved in ignition No equipment Cooking equipment Heating equipment Electrical distribution equipment Appliance or tool Other known equipment Unknown equipment
36% 17% 14% 8% 5% 6% 14%
For simplicity’s sake, one could use the category titles with Version 5.0 data, although they do not match exactly. None Inferences can be made about equipment for Kitchen and cooking equipment most types of confined structure fires. Heating, ventilation and air conditioning Confined cooking fires would be counted Electrical distribution, lighting and power under kitchen and cooking equipment. transfer Confined chimney or flue fires and confined Shop tools and industrial equipment fuel burner or boiler malfunction would fall Commercial and medical equipment under heating, ventilation and air conditioning; Garden tools and agricultural equipment confined incinerator fires would be counted Electronic and other electrical equipment with shop tools and industrial equipment; Personal and household equipment confined trash compactor fires would fall Other known equipment under personal and household equipment. It Undetermined could be assumed that no equipment was involved in contained trash or rubbish fires.
NFIRS 3.0–4.1
NFIRS 5.0
Emphasis on behavior Like unintentional vs. intentional, this is based on ignition factor 28% Mechanical failure or malfunction (e.g., short circuit) 14% Misuse of heat of ignition (e.g., abandoned material) Operational deficiency (e.g., something left unattended) 15% 11% Incendiary or suspicious causes Misuse of material ignited (e.g., combustible placed too 8% close to heat source) 5% Design, construction, or installation deficiency 5% Other known ignition factor 15% Unknown ignition factor NFIRS 3.0–4.1
The field “Factors Contributing to Ignition” when combined with the Cause field is roughly comparable to Ignition Factor. There are some important differences. One, two or no contributing factors may be reported. These factors supplement and expand on, but do not replicate, the Cause field. Because two entries are allowed, analysts must query two fields although it appears to be only one. Because of these issues, it is difficult to determine the appropriate denominator to use when calculating percents.
NFIRS 5.0
Emphasis on heat source Data extracted from the “Form of Heat of Ignition” field Electrically powered equipment Fueled equipment Open flame source involved (e.g., match) Lighted tobacco product involved (e.g., cigarette) Exposure (to other hostile fire) Other known heat source Unknown heat source 28%
29% 19% 13% 4% 4% 10% 19%
In Version 5.0, Form of Heat of Ignition has been split into two fields: “Heat Source” and Equipment Power Source.” The broad categories under “Heat Source” are Operating equipment Hot or smoldering object Explosives Other open flame or smoking material Chemical or natural heat source Heat spread from another fire Other heat source
Equipment Power Source categories include: Electrical Gas fuels Liquid fuels Solid fuels Other
(continued)
3–48 SECTION 3 ■ Information and Analysis for Fire Protection
TABLE 3.3.8
Continued
NFIRS 3.0–4.1
NFIRS 5.0
Emphasis on item ignited Data extracted from Form of Material First Ignited
Specific choices in these categories allow distinctions to be made between natural gas and LP-gas and between gasoline, and diesel or fuel oil. Entries below show correspondence for form of Material First ignited in Older Versions with Item First Ignited and inferences from confined fires.
Cooking materials (e.g., spilled food or grease) Trash or waste (including creosote build-up)
12% 8%
Structural member or framing Electrical wire or cable insulation
8% 7%
Mattress, pillow, or bedding Unclassified item Interior wall covering Exterior sidewall covering Clothing (worn and not worn) Multiple items Fuel
5% 5% 4% 4% 3% 3% 3%
Upholstered furniture Other known item Unknown form of item
2% 23% 14%
Cooking materials, except utensils (May be inferred for incident type 113— confined cooking fire) Trash or waste (Residues such as creosote are not included. Trash may be inferred as item first ignited for Incident type 115—confined incinerator overload or malfunction; 117—confined commercial compactor fire and 118—contained trash or rubbish fire.) Structural member or framing Electrical wire or cable insulation (Full manual advises that insulation should only be entered when no other materials were in the immediate area. This advice is not on screen look-ups.) Mattress, pillow or bedding Unclassified item Interior wall covering Exterior sidewall covering Clothing (worn and not worn) Multiple items Fuel (For incident type 116—fuel burner or boiler malfunction, a flammable or combustible liquid fuel may be inferred. NFPA will add a code for its analysis, or this may be considered generic fuel.) Upholstered furniture Other known item Unknown form of item
Emphasis on hierarchical sorting approach The major cause categories are based on a hierarchy developed by the U.S. Fire Administration. Cooking equipment 16% Heating equipment 15% Incendiary or suspicious causes 10% Electrical distribution system 9% Other equipment 9% Appliance, tool, or air7% conditioning Open flame source 5% Child playing with fire 4% Smoking materials 4% Exposure (to other hostile fire) 3% Other known cause 5% Unknown cause 12%
A hierarchy using the old categories is being developed as this chapter is being prepared. It is expected that a second broad cause hierarchy will be developed that takes advantage of the additional data collected by NFIRS Version 5.0.
Note: Figures in some groupings may not sum to 100 percent because of rounding errors. Source: National Fire Incident Reporting System Version 5.0 Design Documentation Specification, Release 2001.2, July 2001; and P. A. Frazier, et al., Memorandum dated September 25, 2000, “Revised Proposed Analysis Rules for Fire Incident Data in NFIRS 5.0 Format.”
playing fire or a smoking-related fire? Is it useful to have a category called “open flame” that combines matches, bonfires, undoused embers, and cutting and welding torches? For most of the categories, the number of fires falling into each category is not
greatly dependent on the sorting order. The most striking exception is match-related fires, which are scattered among the incendiary/suspicious, children-playing, and open-flame categories. As for usefulness, the categories that seem to be most
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mixed are, for the most part, categories that account for relatively little of the fire problem in residential properties, the setting for which the categories were designed. For nonresidential properties, particularly manufacturing and industry, the usefulness of the categories is questionable. Note the category called “Other
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3–49
Equipment” in Table 3.3.9. In nonresidential properties, this includes all kinds of specialized industrial equipment, which may be a leading part of the fire problem. In residential properties, however, these fires tend to be fires reported as involving equipment, but with no details on the type of equipment.
TABLE 3.3.9 Causes of Fires and Direct Property Damage in Industrial and Manufacturing Structure Fires, 1994–1998 Annual Averages Unknown-Cause Fires Allocated Proportionally Cause
Fires
Property Damage (in millions of dollars)
Other equipment Working or shaping machine Unclassified or unknown-type processing equipment Furnace, oven or kiln Unclassified or unknown-type special equipment Heat treating equipment Separate motor or generator Waste recovery equipment Casting, molding, or forging equipment Conveyor
6,600 (39.1%) 1,000 (5.6%) 900 (5.5%)
277.4 (35.1%) 21.0 (2.7%) 65.5 (8.3%)
900 (5.4%) 500 (2.9%)
26.4 (3.3%) 31.3 (4.0%)
300 (1.8%) 300 (1.7%) 300 (1.6%) 300 (1.5%) 200 (1.1%)
11.0 (1.4%) 6.2 (0.8%) 4.4 (0.6%) 14.9 (1.9%) 13.1 (1.7%)
Open flame, ember or torch Torch Open fire Rekindle or reignition
2,300 (13.8%) 1,400 (8.2%) 300 (1.6%) 200 (1.2%)
101.0 (12.8%) 75.3 (9.5%) 2.4 (0.3%) 2.6 (0.3%)
Electrical distribution Fixed wiring Light fixture, lamp holder, ballast or sign Power switch gear or overcurrent protection device
1,700 (10.3%) 500 (2.9%) 200 (1.3%) 200 (1.2%)
86.6 (11.0%) 29.1 (3.7%) 12.0 (1.5%) 11.1 (1.4%)
Heating equipment Fixed area heater Central heating unit
1,200 (7.1%) 300 (1.7%) 200 (1.2%)
32.3 (4.1%) 10.5 (1.3%) 6.8 (0.9%)
Natural causes Spontaneous ignition or chemical reaction Lightning
1,100 (6.6%) 700 (4.1%)
40.6 (5.1%) 23.7 (3.0%)
300 (1.5%)
9.0 (1.1%)
Incendiary or suspicious
1,000 (6.1%)
158.6 (20.1%)
Appliance, tool or air conditioning Dryer
800 (4.8%) 300 (1.8%)
21.5 (2.7%) 3.9 (0.5%)
Other heat source
700 (3.9%)
16.2 (2.1%)
Cooking equipment
500 (2.9%)
24.1 (3.1%)
Exposure (to other hostile fire)
500 (2.7%)
17.1 (2.2%)
Smoking materials
400 (2.1%)
13.1 (1.7%)
Child playing
100 (0.5%)
1.1 (0.1%)
Total
16,900 (100.0%)
789.6 (100.0%)
Note: These are fires reported to U.S. municipal fire departments and so exclude fires reported only to Federal or state agencies or industrial fire brigades. Fires are expressed to the nearest hundred and property damage is rounded to the nearest hundred thousand dollars. Property damage figures have not been adjusted for inflation. The 12 major cause categories are based on a hierarchy developed by the U.S. Fire Administration. Sums may not equal totals due to rounding errors. Source: National estimates based on NFIRS and NFPA National Fire Experience Survey.
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These standard cause categories used in many analyses of older NFIRS data did not distinguish between unintentional and failure of equipment. When fires were said to be caused by cooking or heating equipment, it was understood that human error, such as leaving the equipment unattended or putting combustible materials too close, was frequently to blame. Top-Down Refinement Along Causal Factors. The last approach, which can be used as a refinement of any of the others, applies the top-down approach to one dimension, such as cause. Start with an initial sorting of fires based on either a single dimension of NFPA 901 or NFIRS 5.0, a scenario structure, or a hierarchically based structure. Then, for each category of the initial sort that has a sufficient number of fires to be worthy of further analysis, use another dimension of the system to provide more detail. Table 3.3.9 shows this top-down or nesting approach applied to 1994–1998 structure fires in industrial and manufacturing properties. Nesting represents the top-down approach at its best—it provides usable levels of detail without sacrificing an overview of the largest parts of the total.
Recreating USFA’s Hierarchical Sorting of Major Causes Early on, the USFA created a set of hierarchical sorting rules based on Ignition Factor, Equipment Involved in Ignition, and Form of Heat of Ignition (plus Exposure Number) to create a hierarchical sorting of all fires into 35 priority (hierarchical) cause codes. These priority cause codes were then regrouped into 12 major cause categories plus a residual unknown-cause group. This framework has proved enormously useful to analysts over the years. The old hierarchical cause sequencing rules are shown in Table 3.3.10. Fires are assigned to a cause category based on a set of rules. Fires that do not meet the criteria are then available for cause assignment from the next rule. Anything left at the end is declared “Unknown.” In some cases, there seemed to be gaps or typographical errors in the statement of the old sorting rules, which are noted. These hierarchical groups are then grouped together to form the 13 major cause groups that fire analysts currently use. The cause grouping is shown in Table 3.3.11. In the single-digit Cause codes used in NFIRS 5.0, a distinction is made between “cause under investigation” and “cause undetermined after investigation.” Some “cause under investigation” are unknown for our purposes, and there is a possibility that a high portion of “cause under investigation” are intentional. All “cause undetermined after investigation” incidents are unknown for our purposes. In practice, the “cause under investigation,” if not updated, may also be considered unknown. Several additional codes are suggested for implementation to complete the range of possibilities for this cause matrix and for other analyses. These codes, shown in Table 3.3.12, can in many cases be inferred from the abbreviated fire reports, may be used in an analytic database. Table 3.3.13 shows the proposed “crosswalk” for to assign the same type of priority cause sequence coding for NFIRS 5.0.
CPSC uses a similar top-down approach to provide more specific information on Equipment Involved in Ignition. The existing NFIRS dataset, based on the 1976 edition of NFPA 901, does not provide enough specific information to identify some electrical equipment, such as microwave ovens, coffee makers, electric blankets, etc. By selecting incidents based on a group of equipment involved in ignition codes that might have been used, searching the text-based make and model fields for identifiable products and classifying them, the CPSC derived national estimates for the role of these products in residential fires.16 A report by the U.S. General Accounting Office (GAO) raised a number of issues about the analysis of fire statistics concerning upholstered furniture.17 Because of that report, the CPSC has excluded fires in which the ignition factor was incendiary or suspicious. For its analyses, NFPA generally includes these fires but performs further analyses when necessary to identify ignition factors or the number of incendiary or suspicious fires associated with a particular product.
Handling Fires with Unknown Causal Factors Another matter to consider when analyzing fire data by cause is how to handle incidents for which the cause was unknown or unreported. A sizable share of fires are reported without causal information. This is particularly true for severe fires involving deaths or significant property loss. Note that several points in this section have been illustrated with the observation that roughly one-fourth of all civilian fire fatalities in homes with known cause involved smoking materials. About one-sixth of all civilian fire fatalities in homes were coded as involving smoking materials. A calculation of percentages based only on cases where cause was reported implicitly assumes (in the absence of contrary evidence) that the cause profile of the fires reported without known cause would look the same (if those causes were known) as the cause profile of the fires reported with known causes. (The two types of percentages are sometimes referred to as causes based on “allocating unknowns over known causes” and causes based on “unallocated unknowns.”) This assumption was made for Table 3.3.9. Why is it desirable to allocate unknowns? Suppose two neighboring states have relative cause profiles that look the same, except that fire deaths due to unknown causes appear as 10 percent in one state and 40 percent in the other. Table 3.3.14 shows the results. State B seems to be doing better than State A with respect to every known cause, but if unknowns are allocated, both states have the same problems to the same degree. If it is necessary or desirable to compare two groups, differences in the proportions of the unknowns need to be taken into consideration. Why is it difficult to allocate unknowns? There are many reasons. One reason is that no one particular method of allocating the unknowns has been shown to be the “best.” Fire data analysts have generally chosen to allocate unknowns over known causes as it is a simple solution to this potentially difficult problem. And, in the absence of another methodology, it has been generally accepted as reasonable. A study underway by the
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TABLE 3.3.10
Equipment Involved in Ignition
Form of Heat of Ignition
Type of Material Ignited
Ignition Factor
“and”
“or”
“or”
“or”
“or”
10–19
<>11, 12, 21, 22 <>11, 12, 21, 22
20–25 >00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 a
Use of Fire Incident Data and Statistics
70–79 63, 64a 60, 61, 65b 30–39 10–19 20–29 30–39 40–49 50–54, 56–59 55, 60–65, 67–69 70–79 87 80–86, 88–89 66, 96c
11, 12, 21, 22 36, 48 84
28, 54
41–43
32, 35
47 40–43, 49 51, 52 53, 55 50, 58, 59d 80–89 Blank, ?? 00, 97, 99
54, 55
Gas flag
Gas flag
02
Flammable liquid flag
Flammable liquid flag
03 04
Exposure Incendiary, suspicious
05 06 07 08
Exposure 1 Incendiary, suspicious Children playing Natural Fireworks Explosives
09 10 11 12 13 14 15
Smoking Not used in structures Heating Cooking Air conditioning Electrical distribution Appliances
Smoking
16
Special equipment
Other equipment
17
Processing equipment Torches Service equipment
Other equipment
Other equipment
30 31 32
Vehicles, engine Not used in structures Not used in structures Not used in structures Not used in structures Unclassified fuelpowered equipment Unclassified electrical malfunction Matches, candles, lighters Open fire Other open flame, spark Friction, hot material Ember, rekindle Other hot object
33 34 35
Exposure 2 Unknown 1 Unknown 2
Exposure Unknown Unknown
18 19
26 27 28 29
65
Assigned to
Description
01
20 21 22 23 24 25
10–19
20–29, 56, 57 44–46
Priority Code
Children playing Natural Other heat, flame, spark Other heat, flame, spark
Heating Cooking Appliances, air conditioning Electrical distribution Appliances, air conditioning
Open flame, ember, torch Other equipment
Unknown
Unknown Matches, candles, lighters Open flame, ember, torch Other heat, flame, spark Other heat, flame, spark Open flame, ember, torch Other heat, flame, spark
Code 62 was mistakenly included in the original. Code 64 was mistakenly included in and 62 was mistakenly omitted from the original. c Original mistakenly read 69–96 instead of 66, 96. d Code 54 was mistakenly included in the original. Source: National Fire Incident Reporting System, System Documentation Manual, Version 4.1, January 1990. b
3–51
Pre-NFIRS 5.0 Priority Cause Sequence Coding
Exposure Number
00 00 00 00 00 00 00
■
3–52 SECTION 3 ■ Information and Analysis for Fire Protection
TABLE 3.3.11
Pre-NFIRS 5.0 Cause Groupings
Cause Assignment
Cause Grouping Name
1 2 3 4 5 6 7
Incendiary, suspicious Children playing Smoking Heating Cooking Electrical distribution Appliances, air conditioning Open flame, ember, torch Other heat, flame, spark Other equipment Natural Exposure Unknown Flammable liquid Gas
8 9 10 11 12 13 14 15
Priority Cause Sequences 4 5 9 11 12 14 13, 15 18, 27, 28, 31 7, 8, 29, 30, 32 16, 17, 19, 20 6 3, 33 34, 35, 25, 26 2 (Flag) 1 (Flag)
Source: National Fire Incident Reporting System, System Documentation Manual, Version 4.1, January 1990.
USFA to investigate the causes of unknown-cause fatal fires may shed light on the validity of this method of allocation. Moreover, this methodology is not without its detractions as some fire data analysts maintain that there is often enough information provided by the data to make other equally reasonable assumptions on how to allocate the unknown: time of day, size of fire, and property type are examples of data items that can be used to allocate the unknown across causes. Some knowledgeable individuals believe that assessments of probable cause are subject to biases, although no substantive analyses have supported this belief. Regardless of the method of allocation, it is the analyst’s responsibility to both specify the allocation scheme and support the rationale behind it. A further observation on allocation is offered: Cause is most difficult to assess in the largest fires as more of the evidence of fire origin is destroyed. Known-cause fires indicate that cause profiles are different for larger vs. smaller fires. For ex-
TABLE 3.3.12
ample, incendiary/suspicious and electrical-distribution-system fires tend to have greater loss per fire, and incendiary/suspicious and smoking-related fires are more likely than other fires to result in deaths. Therefore, if unknowns are to be allocated, the allocation should take into account the cause profiles for fires of comparable size. This is another fire data analysis issue around which no consensus has yet formed. The ideal solution would be to find ways to reduce the rate of unknowns, but there also may be better ways to arrive at estimates in the face of the unknowns that do exist. Unknowns are a data problem for many other fire characteristics, not just cause and property type. Each data element has a portion of the entries that are either not reported or designed as “undetermined.” For some data elements, the allocation of unknowns is less problematic. Analyses by property use, for example, are reasonably straightforward. Most analyses are concerned with distinctions covered by the “fixed or specific property use” or “mobile property type” categories of NFPA 901 or NFIRS. In older versions of NFIRS, the only major property class requiring use of both scales is manufactured homes, and there is little difficulty with unknown or unreported property types. (Manufactured housing fires are identified by incident type in NFIRS 5.0. However, confined fires in these properties may be completed using incident types for confined fires. Mobile property type is not required and the fixed property use will be indistinguishable from other one- or two-family dwelling confined fires.) In addition to the unknowns associated with fire characteristics, there is a second category of unknowns: Many questions analysts would like to have answered on all reported fires have not been asked at all, such as whether weather was a compounding factor in fire spread. NFIRS 5.0 has added a field on fire suppression factors and a field on factors contributing to injury. Up to three entries are allowed on each, although “none” is also acceptable. Because these fields cover a wide variety of conditions that are not asked individually, the absence of a specific mention does not mean that the factor was not a problem. Other questions are not asked or answered, such as whether a victim was involved in the ignition of the fire or whether the victim was intoxicated, because of potential privacy or litigation issues.
Proposed Codes for Use in NFIRS 5.0 Cause Hierarchy and Other Analyses
Field
Proposed Codes
Equipment Involved Equipment Involved Equipment Involved
640 129 130
Heat Source
60
Area of Origin Item First Ignited
57 69
Assigned to Cause
Proposed Code Definition Cooking equipment of unknown-type Chimney or flue of unknown-type Boiler, furnace, or central heating unit of unknown type Change definition to “Other heat from open flame.” This would be a change to the code definitions themselves. Chimney (already a conversion code) Flammable or combustible liquid of unknown type
Cooking Heating Heating Open flame (existing code, modify to exclude smoking materials) Heating —
Source: P. A. Frazier et al., Memorandum dated September 25, 2000, “Revised Proposed Analysis Rules for Fire Incident Data in NFIRS 5.0 Format.”
TABLE 3.3.13
Inc. Type
& or
Exp #
NFIRS 5.0 Priority Cause Sequence Coding
& or
Area Origin
& or
Heat Source
—
& or
TMI
& or
Cause of Ignition
10– 15 20– 27
—
& or
Factors Contrib to Ignition
&
not = 1
1
Gas
&
not = 1
2
Flammable liquid
& or
Age on NFIRS11 < 10a —
&
&
5
&
1
&
&
1 or 2
&
70–79d
0
&
54e
0
&
or
0 0
or
0
& & & &
50–59 (× 54) 61–63f
0
&
or
& or
2 4
19 60–69 (× 66)
Remaining causes left after above incidents removed from testing sequence " " " " "
120– 152 63xd, 64xd, 654g 111–117, 445, 652, 655–656
Children < 10a
— —
Children < 10a Adult > 64b
— 3 5
Adult > 64b Exposure Children playing
4
Suspicious
4
Incendiary
5
Children playing ( juvenile firesetter)c
5 6
Playing (any age) Natural
7
Fireworks
8
Explosives
9 11
Smoking Heating
12
Cooking
13
Air conditioning
(continued)
3–53
& &
not 7, or 7 & age > 10 7 & age < 10a
—
Use of Fire Incident Data and Statistics
0 0
7 & age < 10a
Description
■
114, 116 113
19
Old Inc Priority Type Code
CHAPTER 3
Arson report submitted
EII
7 & age > 64b
Age on NFIRS11 > 64a >0 & & 0
0
& or
7 & age < 10a
—
Arson report submitted
Human Factors
Continued
Factors Contrib Cause to & & Human & Inc. & Exp & Area & Heat & of & Type or # or Origin or Source or TMI or Ignition or Ignition or Factors or
11xd
&
0 0
& &
" "
0
&
"
0
&
"
0 0
& &
" "
0 0
& Mobile Property Involved (MPI) = 2, 3 " & " 11 &
13
or
0
&
64–66
or
"
0 0 0 0 0 0 0
& & & & & & &
" " " " " " "
0
&
67 60f, 69 41, 42 or 43 40 or 8xd blank, invalid 00, 97, UU
37
13
&
or
2xxa (× 228–229) 31x (× 317), 345, 611–612, 621–623, 651, 653, 73x–75xd, 81x–86xd, 871, 872 w/equip power <> 20–22 or 30–33, 874–876, 881–883, 891–897 34xd (× 345), 361, 372–374, 376–377, 41xd, 42xd, 431–432, 44x (× 445), 5xxd, 71xd, 72xd 317, 32xa, 351, 353, 355–358, 371 331–334 228–229, 352, 354, 362–365, 433–434
not 51
30–36
"
or
EII
72 71
Old Inc Priority Type Code
Description
14 15
Electrical dist. Appliances
16
Special equip.
17
Processing equip.
18 19
Torches Service equip.
20 25 200
26
872 (equip power = 30 (butane)) 873
27
Vehicle, engines Unclassified fuel powered equip. Unclassified elec malfunction Matches, candles
28 29 30 31 32 33 34
Open fire Other open flame, spark Friction, hot material Ember, rekindle Other hot object Exposure 2 Unknown 1
35
Unknown 2
a The age used to differentiate between arson and child play is hazy; different locales use different ages. We need to follow up on this and come to an “educated” agreement on what this age will be for NFIRS. Under 10 was chosen to be compatible with age-related population data. Recommendation: The specific age cutoff should be a local option. b Over 64 was chosen as a reasonable age delineation of the older adult and to be compatible with age-related population data. Recommendation: The specific age cutoff should be a local option. c An option to replace “Children Playing” as a cause; age coding of firesetter in 5.0 is strongly encouraged. d When decade incomplete, included entire decade IF current decade members reflect consistent type of item. e Changed from 4.1 code which included blasting (4.1 FMI 62) and did not include party caps; 5.0 Heat Source 54 is more appropriate. f Requires Heat Source 60 to be changed: delete “or smoking materials.” g Includes grease hood/duct exhaust fan in addition to heat-generating cooking appliances as in 4.1.
3–54 SECTION 3 ■ Information and Analysis for Fire Protection
TABLE 3.3.13
CHAPTER 3
TABLE 3.3.14 The Problem of Comparisons with Unallocated Unknown Cause Fires Percentage of Home Fire Deaths Cause Category Smoking Heating Incendiary/suspicious Other known Unknown
State A
State B
36 18 18 18 10
24 12 12 12 40
Analysis of Small Data Sets A problem can arise in the size of the database available for analyses aimed at particular property uses. In 1999, according to NFPA, all nonresidential structures combined accounted for 140,000 fires, 120 civilian deaths, 2100 civilian injuries, and $3.4 billion in property damage.5 Typically, roughly half of all fires are represented in the NFIRS, which has individual incident reports and can be used to analyze patterns by specific property use. The older versions of NFIRS had several hundred separate categories of nonresidential properties. NFIRS 5.0 data rely on on-site materials and their use category to determine specific occupancy hazards for retail, manufacturing, and storage properties. The net result in either case is that for some data elements, the available data is spread across many categories. This spread can result in data sets that are very small and present unique problems for analysis. A topic-driven analysis focused on one property use from Version 4.1 or one property use and a specific set of on-site materials from Version 5.0 might be able to draw upon only a few dozen incidents per year, which is not enough to generate statistical confidence in the results. An analyst who discovers that there is a very small database available on the property use of interest should do two things. One is to keep the analysis of these fires fairly limited; if each fire represents 2 to 3 percent of the total number of fires being analyzed, there may be no point in conducting fire structure analysis. The other is to reconsider the appropriateness of focusing on this particular property use or extending the time period considered. It may make sense to look at 10-year annual averages or include a broader range or properties or similar materials. The issue of small numbers is not limited to property use or to national analyses. In many cases, a question can be expanded to include other properties or similar causal factors. The property use classification in Version 5.0 will almost force this, as all manufacturing properties will be coded simply as 700—manufacturing or processing property. Some fluctuations occur normally; one large incident can artificially inflate the casualties or dollar loss. It may seem logical to use the number of fire deaths as a measure of success for a public fire education program. However, the numbers at the state and local level are generally not big enough to do this with confidence. To minimize the year-to-year variability, NFPA produces five-year annual averages for most analyses. (As of this writing, national data from NFIRS 5.0 is not yet available.
■
Use of Fire Incident Data and Statistics
3–55
The transition will cause changes in some practices, at least temporarily.)
Introduction to Location-Based Fire Data Analysis As mentioned earlier in this chapter, the increase in power of desktop PCs has enabled sophisticated analysis of fire incident data at the local level, in ways that would have been impractical, if not impossible, just a few years ago. One of the most exciting new approaches now accessible to many jurisdictions is the use of geographical information systems (GIS) for location-based analysis. Previous efforts at a more targeted, location-based description of the fire situation have centered on fire station or district level groupings of data. However, this tends to blur differences among neighborhoods of differing characteristics. By geocoding fire incident data, one is able to examine groups of incidents at the census tract (approximately 500–3500 people), block group, or even block (X population) levels. What is meant by geocoding data? For our purposes, geocoding is the process of assigning an absolute location to a fire incident report. This information could be as simple as street address or zip code, or as detailed as high-resolution latitude/longitude. This location can then be associated with a variety of other location-based datasets, including census tracts, fire districts, or political boundaries. The process of geocoding incidents is fairly straightforward. For most structure fires, simply an accurately entered address will be all the information needed for processing with off-the-shelf geocoding software. The software will assign any of a number of attributes to the incident, including latitude/longitude and census tract/block group data. The types of data could include demographics such as age distribution, race/ethnicity, education level, income, residential occupancy rates, and information on the housing stock. Once this has been accomplished, we can count the number of fires, types of fires, casualties, and any type of incident that you collect for each census area. Grouping these data at various levels will paint different pictures of your city’s fire experience. Combined with the allincident reporting of NFIRS 5.0, location-based, rather than fire station–based, reporting may be of great interest. With wellscrubbed data, local analysis as fine as the census block may be possible. By doing this, area-specific trends and issues can be identified. Are false alarms a problem in a neighborhood? Is one area of the city experiencing a higher rate of arson? What is the expected rate of fire for a particular city? How does it vary across the city? How do neighborhoods of certain demographic attributes compare with other neighborhoods within the city, and even across different cities? It is possible to identify high densities of at-risk populations, such as the very young and very old. Limited prevention resources can be targeted at the areas where they will do the most good, instead of a shotgun approach to public education. Although many of these issues are intuitively obvious, in the current arena of backing dollars with facts, it is imperative that the fire service quantify the needs for its services, both for
3–56 SECTION 3 ■ Information and Analysis for Fire Protection
response and prevention. This approach makes it possible to say more than, “Arson is a problem in poor areas of the city.” The data could justify or refute statements such as “People in these sections of the city are at twice the risk for residential arson as the rest of the city. . . .” For this approach to work, it is necessary to implement and maintain quality control procedures when entering location data. Some departments have location data (latitude/longitude) automatically associated with each dispatch. This simplifies matters greatly and facilitates analysis of nonstructure incidents for which there might not be suitable address data. Resources necessary for location-based fire data analysis: • • • • •
Fire incident data (good) Census data GIS application Locally produced datasets Good PC/spreadsheet-type skills
Many municipalities have GIS shops already working in offices such as transportation, planning, and zoning. It may be possible to dovetail fire-location-based analysis with existing GIS efforts. Otherwise, a reasonably literate computer user can be trained on introductory level GIS skills in about a week.
Rates and Measures of Fire Risk The use of rates is another means to provide a context or make comparisons across groups or time. A rate is a ratio consisting of a measure of the size of a fire problem divided by a measure of the size of the group affected by that problem. In 1999, the United States suffered 13 civilian fire deaths in the home per million population. That is a rate consisting of the number of fire deaths divided by the number of people who live in the United States (the so-called resident population) divided by one million. In 1999, the average fire-related property loss in rural communities was $61 per person per year.5 That is a ratio consisting of the total property damage in rural communities divided by the number of people living in those communities. Rates provide measures of relative fire risk. They can be used, therefore, in any analysis where the size of the group affected by a problem may change. For example, as has been said, the United States suffered 13 civilian fire deaths in the home per million persons in 1999. Because the total population growth adds about 2 million people to the population each year, the number of civilian fire fatalities will be about 66 deaths higher each year, unless increased fire safety lowers the rate. Along similar lines, the National Safety Council’s estimates of fire deaths show total deaths declining by 48 percent from 1979 to 1999, whereas the fire death rate per million population declined 59 percent in the same period.18 Increased fire safety is best measured by the decline in the fire death rate; population growth produced a smaller decline in the death toll. Risk measures do the best job of bringing the fire problem down to a personal level. Rural communities do not account for a majority of the country’s fire deaths, but they have by far the highest fire death rates compared to those that communities of larger size have.5 Person for person, their citizens are in the most danger from fire. Occupants of manufactured homes suffer a
substantially higher rate of fire fatalities per million population than do occupants of conventional one- and two-family dwellings. Because there are comparatively few manufactured homes, deaths there do not constitute a large share of the total fire fatality problem, but the individuals living in older manufactured homes are more at risk than their counterparts elsewhere and should be concerned.19 An individual wants to know his or her own risk, not the risk to an average American. Barring that, he or she wants to know the risk for people as much like him or her as possible. Risk measured for specifically defined groups provides that information. Risk measured by rates is of particular interest if there is the potential for large-scale shifts from one group to another of substantially higher or lower risk. In the early 1980s, analysts determined that solid-fueled heating devices, principally wood-burning stoves, accounted for an unusually high risk; that is, there was a high ratio of fires involving those devices divided by homes using those devices.12 At the time, it appeared that the generation-long decline in use of these devices was about to be reversed, under the pressure of higher prices for oil and natural gas. This was an ideal opportunity to use data to guide action; at a time when decisions were being made, most people did not know the unusual dangers posed by their choices. As an example of risk moving in the other direction, analysts using fire incident data from the early growth years of smoke-alarm usage were able to demonstrate that the rate of deaths per home fire was just over half as great for homes with smoke alarms as for homes without them.8 Here again, decisions with substantial impact on risk were being made regarding equipment; therefore it was possible to get people’s attention and encourage the move toward smoke alarms. Getting Information Needed to Calculate Rates. For some analyses, it may be difficult or impossible to obtain the information needed to construct the appropriate rate. One example is an analysis comparing the dangers of firefighting with risks of other professions. The ratio should be number of on-duty fire service deaths to number of hours of exposure by fire fighters. The latter number cannot be easily calculated, however, because no one has national statistics on how many hours volunteer fire fighters serve. Also, differences in workweek need to be considered for career fire service personnel. Another example is a comparison of fire fatality risks in homes versus those in hotels. Numbers of persons cannot be used for both, because length of stay is obviously much shorter for hotels than for homes. Numbers of units might work better if one could obtain that data and if occupancy rates could be addressed by a single parameter estimate. The problems of selecting the right denominator and obtaining data for it usually can be solved to some degree of acceptability, but the process is often complex and challenging. Another problem in constructing rates can occur if the group of interest is defined too narrowly. A household, for example, might like to be able to calculate a risk index that reflects its smoking and drinking habits, its number of children, the ages of its members, its types of equipment and how they are fueled or powered, and many other characteristics. Today this would pose an insoluble problem. There is not enough data to calculate
CHAPTER 3
the numbers of households with all those characteristics (so there can be no denominator), and the list of descriptors defines a class so narrow that the number of fires experienced by households of that precise type would be very small and subject to considerable statistical uncertainty. One could separately measure the effects of some of these characteristics and then combine the results, but such a calculation would involve modeling assumptions that are already known to be false. Considerable statistical modeling and research will be needed to make progress on questions of this type. Risk of Fires by Occupancy. Many analyses focus on fires or incidents in specific types of occupancies, i.e., homes, health care, educational, manufacturing, etc. By combining NFIRS data with the NFPA survey, an estimate for the number of fires in these occupancies can be obtained. These sources do not, however, reveal anything about the risk of fires in these occupancies. A denominator, based on the number of units or establishments, is required to calculate risk. NFIRS users from outside the fire service may be more familiar with the North American Industry Classification System (NAICS) codes, released in 1997, or the older Standard Industrial Classification (SIC) codes.20 Data on the number of establishments of a certain occupancy type would most likely be collected according to the NAICS codes. Table 3.3.15 shows the sectors that are included. Each sector is further divided into subsectors, industry groups, the NAICS industry, and the national industry. Challenges abound when two data sources are combined, and the users must remember the differences in original goals. The property use codes in NFIRS describe the setting the fire department encountered; the NAICS codes describe businesses or related entities. Consequently, many of the codes will not line up neatly with each other, particularly when one business has multiple property uses, such as a parking lot, storage shed, and an office building. Analysts calculating risk trends by occupancy will need to remember that the older SIC code data has been converted, to the extent possible. With conversions in both the numerator and denominator, analysts should proceed cautiously.
Using Data to Identify Trends Although most of the analyses described above provide a “snapshot” of the fire problem, some questions need a “moving picture.” Is a part of the fire problem getting better or worse? Is the character of the fire problem changing? If changes are occurring, do they track with corresponding changes in product use, property use, fire service practices, fire prevention activities, codes and regulations, or other elements of the environment? (For this last question, one may need a full-fledged strategy or program analysis, as described later in this chapter, under “Using Data in Program and Strategy Analysis.”) All trend analyses must address the question of whether or not the past is a consistent guide to the present, let alone the future. It would be nice to be able to say that a trend indicates whether fire risk is going up or coming down. However, a simple trend calculation may not provide this information if the base of comparison has been shifting during the years covered. For
■
Use of Fire Incident Data and Statistics
3–57
example, start with a calculation of the number of fire deaths per year in manufactured homes. If the number dropped over time, that might mean that manufactured homes were becoming safer or it might mean that fewer people were choosing to live in manufactured homes. A trend calculation based on the number of fire deaths per million people living in manufactured homes would factor out the latter possibility and do a better job of showing whether manufactured homes were becoming safer. Another problem in trend calculations might be a shift in the sampling technique used to create the database. Suppose that while analyzing fire deaths per million population, as in the previous paragraph, the state of Alaska was added to the database in the middle of the trend period. The increase in the number of persons would not by itself bias the results because, all other things being equal, numbers of deaths and persons would rise together. But in this case, all other things are not equal. Alaska has an unusually large percentage of households living in manufactured homes, which exerts a sizable influence on the results, and Alaska presents some additional problems, including a severe climate and above-average rates of alcoholism, that differ from those of other states. There would be no way to know how much of any change was due to changes in manufactured home fire safety and how much was due to the addition of Alaska to the database. As mentioned previously, trend analysis involving data collected by NFIRS 5.0 and earlier versions may be misleading. The change from SIC codes to the NAICS codes affects some of the establishment counts. These changes necessitate extreme caution in occupancy class risk analysis. Trends in Fire Fatalities and the Protection of Life. Figure 3.3.4 shows the trend in NFPA’s estimates of civilian fire deaths, starting with 1977 when the NFPA survey was upgraded. The National Safety Council (NSC) has been using a consistent estimating procedure based on state health department records of death certificates for a longer period, although their definition includes nonfire burn deaths and excludes some fire deaths, most notably those involving vehicle accidents, arson, or selfimmolations. Their longer trend line (seen in Figure 3.3.5) shows an even longer decline, although there were periods of backsliding. Figure 3.3.6 shows the steady decline in the rate of fire deaths per million population from both sources. The cumulative drop in the death rate since NSC’s methods changed in 1968 is more than two-thirds, and other NSC figures, using slightly different estimating methods, suggest that since 1913 the rates may have dropped by more than four-fifths.18 The NSC figures, like NFPA’s, indicate that the steady decline in the fire death toll, and to a lesser degree the fire death rate, was interrupted by a plateau that lasted from the early 1980s to the late 1980s, during which fire death rates showed no consistent trend up or down. Table 3.3.16 shows another approach to tracking by way of the deadliest of the big fires. Not being a graph, it lacks visual impact. Instead, the sense of progress is stated more subtly, as the table shows how much less severe the worst fires of the decade have become. Figure 3.3.7 shows this relationship graphically with death counts from each of the three fires marked. Although the 1990s were the worst decade in the second half of the century, the total for the top three fires is still only two-thirds that of the lowest decade sum in the first half of the century.
3–58 SECTION 3 ■ Information and Analysis for Fire Protection
TABLE 3.3.15
NAICS Codes Compared to NFIRS Property Use Codes
NAICS Sector
NAICS Name
NFIRS Code
NFIRS Property Use
11
Agriculture, forestry, fishing, and hunting
655 659 669
Crop or orchard Livestock production Forest, timberland, woodland
21
Mining
679
Mine or quarry
22
Utilities
610 614
Other energy production plant Steam or heat generating plant Electric generating plant Electrical distribution Water utility Other utility or distribution system
615 642 647 640 31–33 Manufacturing
42
a
700 984
Wholesale trade
44–45 Retail trade
51
NAICS Name
NFIRS Code
NFIRS Property Use
Transportation and warehousing (cont.)
922 941a 972 973 974 982
Tunnel Open waters, including portsa Aircraft runway Aircraft taxiway Aircraft loading area Pipeline, powerline, or other utility right of waya
Information
151 183 185 186
Library Movie theater Radio or television studio Film or movie production studio Other studio or theater Computer center, including computer laboratories Communications center Manufacturing (e.g., printing and publishing)
180a 635
a
Manufacturing or processing Industrial plant yard area not used for storage
639 700a
No separate category for wholesale—see retail 500a 511 519 529 539a 549 559 569a
571 579a 581 580 48–49 Transportation and warehousing
NAICS Sector
171 173 174 170 596a 644 645 816 819 839 849a 891 899a 800a 921
Other mercantile or businessa Convenience store Food and beverage sales Textile or wearing apparel sales Household goods, sales, repairsa Specialty shop Recreational stores Sale of specialized professional supplies, art supplies, home maintenance servicesa Service or gas station Motor vehicle or boat sales, services or repaira Department or discount store Other general retail Airport passenger terminal or heliport Bus station Rapid transit station Other passenger terminal Post office or mailing firma Gas distribution or pipeline Flammable liquid distribution or pipeline Grain elevator or silo Livestock or poultry storage Refrigerated storage Outside storage tanka Warehouse Residential or self-storage unitsa Other storagea Bridge or trestle
52
Finance and insurance
592a 599a
Bank, including ATMs when not part of other structurea Business officea
53
Real estate and rental and leasing
599a
Business officea See also Retail section 500–580a
54
Professional, scientific and technical services
593a 599 629a
Veterinary or research office Business officea Laboratory or science laboratory
55
Management of companies and enterprises
592a 599a
Bank, including ATMs when not part of other structurea Business officea
56
Administrative and support and waste management and remediation
599a 648 919
Business officea Sanitation utility Dump or sanitary landfill
61
Educational services
213
Elementary school, including kindergarten Middle, junior and high school Other nonadult school Adult education center or college classroom Other educational
215 210 241 200a 62
Healthcare and social assistance
211 254 255 256
Preschool, not in same facility with other grades Day care in commercial property Day care in residential property, licensed Day care in residential property, unlicensed
CHAPTER 3
TABLE 3.3.15 NAICS Sector
Use of Fire Incident Data and Statistics
3–59
Continued
NAICS Name Healthcare and social assistance (cont.)
NFIRS Code
NFIRS Property Use
200a 311 321
Other educationala Licensed nursing homes 24-hour mental retardation/ development disability facility 24-hour alcohol or substance abuse center Mental institution Medical or psychiatric hospital Hospice Clinic or clinic-type infirmary Doctor, dentist or oral surgeon’s office Hemodialysis unit Other clinic, doctor’s office or hemodialysis unit Other healthcare, detention or correctiona Residential board and care, long-term care or half-way house Laboratory or science laboratory
322 323 331 332 341 342 343 340 300a 459
a
629 71
■
Arts, entertainment, and recreation
111 112 113 114 115 116 110 121 122
123
124 129
120 141 142 143 144
Bowling establishment Billiard center or pool hall Electronic amusement center Indoor or outdoor ice rinks Indoor or outdoor roller skating rinks Swimming facility Other fixed use recreation place Ballroom or gymnasium Large open hall without fixed seats, including convention halls, exhibit halls and field houses Fixed seating in large area, including ball parks, stadiums, grandstands and race tracks Playground or outdoor area with fixed equipment Indoor or outdoor amusement center, excluding video arcades Variable use amusement or recreation place Athletic club Clubhouse associated with country club Yacht club Casino, gambling club or bingo hall
NAICS Sector
NAICS Name Arts, entertainment and recreation (cont.)
NFIRS Code
NFIRS Property Use
140 152
Other club Museum or art gallery, planetarium or aquarium Memorial structure, monument or statue Legitimate theater Auditorium or concert hall Other studio or theatera Beach Graded and cared for plot of land, including parks, cemeteries, golf courses and residential yardsa
154 181 182 180a 937 938a
72
Accommodation and food services
161 162 160 439 449 462 464 460 935
81
Other services (except Public administration)
131 134 130 419b 429b 539a 557
564
569a
579a
700a 881b
Restaurant or cafeteria Bar, nightclub, tavern or pub Other eating or drinking place Rooming or boarding house Hotel or motel Sorority or fraternity Barracks, dormitory Other dormitory type residence Campsite with utilities Church, temple, mosque or other religious facility Funeral parlor or crematorium Other place of worship or funeral parlor Detached one- or twofamily dwellingb Multi-family dwellingb Household goods, sales, repairsa Personal service, including barber and beauty shops Laundry or dry-cleaning, including self-service facilities Sales of specialized professional supplies, art supplies, home maintenance services, including linen supply servicesa Motor vehicle or boat sales, services, or repaira Manufacturing (such as photo finishing)a Residential vehicle storageb (continued)
3–60 SECTION 3 ■ Information and Analysis for Fire Protection
TABLE 3.3.15 NAICS Sector
NAICS Name
NFIRS Property Use
NFIRS Code
Other services (except Public administration) (cont.) 92
By focusing on specific fires, Table 3.3.16 can also serve as an introduction to the kind of extended discussion of turning-point fires, i.e., incidents that triggered changes in our approach to fire safety that significantly and permanently altered our loss experience, provided in Section 2, Chapter 1 (“An Overview of the Fire Problem and Fire Protection”). From a statistical standpoint, it is striking that in every decade the deadliest fires tend to include fires that are not building fires, ranging from the ship fires at the start of the century to the airline fires at the end of the century, with forest fires and mine fires occurring throughout the century. Remember that the purpose of statistics is to answer important questions that will help indicate what is needed for fire safety. An interest in major fires is justified by the view that fire codes and standards ought to be able to prevent any really large incidents from occurring. This is what leads to the phenomenon of one bad fire leading by itself to a set of code changes, because it only takes one fire of sufficient severity to indicate that an objective as stringent as preventing all very large fires has not been met. This sequence of events is especially likely to occur if the one bad fire occurs in a place or under circumstances never previously associated with really bad fires, because, in that case, the one bad fire will serve as a sign to many that a particular class of properties, equipment, or activities is not as safe as everyone thought it was. Because this kind of logic is so common and seems so plausible, it is useful to introduce some cautions. First, fire protection engineering may be thought of as deterministic solutions for a probabilistic world. To put it another way, risk can never be reduced to zero, and it is important that realistic fire safety designs recognize that even the most determined enforcement of the most stringent requirements will not eliminate all possibility of a serious fire.
Continued
Public administration
882b 880b 965b 155 150 361 363 365 300a
631 888
General vehicle parking garageb Other vehicle storageb Vehicle parking areab Courthouse or courtroom Other public or government Jail or prison (not juvenile) Reformatory or juvenile detention center Police station Other healthcare, detention or correctiona Defense or military installation Fire station
Note: NFIRS property uses that did not have an obvious conversion are not included in this table. a May be found in more than one NAICS category. b NAICS tracks economic entities. Private households are counted when they employ others; parking facilities are counted when they charge for the service. Source: NFIRS 5.0 Reference Guide, North American Industry Classification System, United States, 1997.
9000 8000
Civilian fire deaths
7000 6000
7,710
7,575
7,395
6,700 6,505
5000
5,920 6,020
6,185
6,215
5,850 5,810
5,240
5,195 5,410
4,730 4,635 4,585 4,465
4000
4,990 4,035
4,275
4,050 3,570
3000 2000 1000 0 77 78 79 80
81 82 83 84 85 86 87
88 89 90 91 92 93 94 95
96 97 98 99
Year
FIGURE 3.3.4 National Estimates of Civilian Fire Deaths (Source: NFPA National Fire Experience Survey)
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12000
Number of deaths
10000
8000 Year of 1948 6000
4000
2000
13
17
21
25
29
33
37
41
45
51
55 59 Year
63
67
71
75
79
83
87
91
95
99
FIGURE 3.3.5 Estimates of Unintentional Injury Fire Deaths per Year. Note: Two figures are given for 1948 to reflect old and new methodologies. These are reflected by a break in the graph. Other methodology changes occurred in 1958 and 1968, but different numbers were not provided. (Source: National Safety Council,18 pp. 38–39) 12000
Death certificate data NFPA survey data
10000
Death rate
8000
6000 Year of 1948 4000
2000
13
17
21
25
29
33
37
41
45
51
55 59 Year
63
67
71
75
79
83
87
91
95
99
FIGURE 3.3.6 Fire Death Rates per Million Population. Two figures are given for 1948 to reflect old and new methodologies. These are reflected by a break in the graph. Other methodology changes occurred in 1958 and 1968, but different numbers were not provided. (Source: National Safety Council Death Certificates and NFPA National Fire Experience Survey,18 pp. 440–441)
Second, most fire deaths and other fire losses do not occur in big fires or even in the kinds of places and situations where big fires occur. Big multiple-death fires occur in high-occupancy places, such as hotels or dormitories or nightclubs, while most fire deaths occur in low-occupancy places, such as dwellings or individual apartment units. Big multiple-death fires involve high-occupancy vehicles such as commercial airliners or large ships, whereas most fire deaths, excluding those occurring in homes, occur in small private vehicles such as cars and trucks.
Finally, it should be obvious from a casual glance at the deadliest fires of recent years that the problem often is not that the codes are not tough enough but rather that the adoption is not universal or the enforcement is not effective. Event-driven changes in fire codes primarily involve the fire community. However, getting those changes adopted into law and backing the law with strong enforcement programs require the cooperation of elected officials and the public, who are concerned about many subjects in addition to fire. Recognizing this, some
3–62 SECTION 3 ■ Information and Analysis for Fire Protection
TABLE 3.3.16
Deadliest U.S. Fires and Explosions of the Past Century, 1900–1999 Fire 1990–1999 1. Alfred P. Murrah Federal Building, Oklahoma City, OK (April 19, 1995) 2. ValuJet Airlines DC-9 passenger jet, Miami, FL (Everglades) (May 11, 1996) 3. Happy Land social club, New York, NY (March 25, 1990) 1980–1989 1. MGM Grand Hotel, Las Vegas, NV (November 21, 1980) 2. Galaxy Airlines #203, Reno, NV (January 21, 1985) 3. United Airlines #232, Sioux City, IA (July 19, 1989) 1970–1979 1. Beverly Hills Supper Club, Southgate, KY (May 28, 1977) 2. Silver mine, Kellogg, ID (May 2, 1972) 3. Capital International chartered airliner, Anchorage, AK (November 28, 1970) 1960–1969 1. Coal mine, Farmington, WV (November 20, 1968) 2. Indiana State Fairgrounds Coliseum, Indianapolis, IN (October 10, 1963) 3. Golden Age Nursing Home, Fitchville Township, OH (November 23, 1963) 1950–1959 1. Coal mine, West Frankfort, IL (December 21, 1951) 2. USS Bennington aircraft carrier, off RI coast (May 26, 1954) 3. Our Lady of the Angels Grade School, Chicago, IL (December 1, 1958) 1940–1949 1. Cocoanut Grove Night Club, Boston, MA (November 28, 1942) 2. SS Grandcamp and Monsanto Chemical Plant, Texas City, TX (April 16, 1947) 3. Munitions ships and depot, Port Chicago, CA (July 17, 1944) Plus 5 other incidents that each killed at least 100 people. 1930–1939 1. Ohio State Penitentiary, Columbus, OH (April 21, 1930) 2. Consolidated School, New London, TX (March 18, 1937) 3. SS Morro Castle, off NJ coast (September 8, 1934)
Number Killed 168 110 87 85 42 38 165 91 47
78 75 63
119 103 95 492 468 322
320 294 135
1920–1929 1. Coal mine, Mather, PA (May 19,1928) 2. Coal mine, Castle Gate, UT (March 8, 1924) 3. Cleveland Clinic, Cleveland, OH (May 15, 1929) Plus 2 other incidents that each killed at least 100 people.
273 171 125
1910–1919 1. Forest fire, northern MN (October 12, 1918) 2. Coal mine, Dawson, NM (October 22, 1913) 3. Aetna Chemical Company, Oakdale, PA (May 18, 1918) Plus 7 other incidents that each killed at least 100 people.
559 263 193
1900–1909 1. SS General Slocum steamship, New York, NY (June 15, 1904) 2. Iroquois Theater, Chicago, IL (December 30,1903) 3. Coal mine, Monongha, WV (December 6,1907) Plus 13 other incidents that each killed at least 100 people.
1030 602 361
Source: NFPA archive files, NFPA Fire Incident Data Organization, NFPA 1984 Fire Almanac, and The Great International Disaster Book by James Cornell, Pocket Books, New York, 1976.
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2500
Fire deaths
2000
1500 1000
500
0 1900– 1909
1910– 1919
1920– 1929
1930– 1939
1940– 1949 Year
1950– 1959
1960– 1969
1970– 1979
1980– 1989
1990– 1999
FIGURE 3.3.7 Sum of Fire Deaths from Three Largest U.S. Fatal Fires per Decade (Source: NFPA archive files, NFPA Fire Incident Data Organization, NFPA 1984 Fire Almanac, and The Great International Disaster Book by James Cornell, Pocket Books, New York, 1976)
fire chiefs have prepared legal packages targeted at particular problems in advance, holding them in reserve until a major fire provides the visibility and sense of urgency required for adoption. In view of this strategy, it is worth noting that “newsworthiness” is not always synonymous with incident severity. Two examples will suffice. The third most deadly fire of the decade 1960–1969 was the Golden Age Nursing Home fire, which killed 63 persons; it occurred, however, on the day after President John F. Kennedy was assassinated. This coincidence of timing sharply reduced the visibility of the fire. By contrast, the 1937 Hindenburg zeppelin fire killed “only” 36 persons, a death toll barely a fourth the size of even the third-largest fire of that decade and only one-eighth the size of the New London, Texas, school fire in the same year. The zeppelin fire, however, was broadcast “live” and occurred in full view of newsreel cameras, and therefore it was probably the most widely heard and seen fatal U.S. fire until the Challenger space shuttle explosion in 1986. It meant the end of the rigid-airship industry. These examples also have a lesson for analysis of trends in fire deaths, injuries, or incidents. For fires as severe as those discussed in the last few paragraphs, only decade-by-decade comparisons suffice to separate real trends from random ups and downs. For total U.S. civilian fire deaths, year-to-year tracking is generally meaningful. For a single large city, however, yearto-year tracking of fire deaths will be subject to considerable statistical noise; for town and rural areas, there is no good way to track fatality trends except as part of a larger aggregation, such as the state or the rural portion of the entire region. Trends in Property Damage Due to Fire. The first fire protection standards promulgated by NFPA were directed principally at property protection, reflecting the association’s founding by men in the business of insuring property against loss due to fire. Assessments of the success of strategies for property protection are more difficult than for life protection, however, because data on fire damage is subject to several gaps and quirks that do not affect data on fire deaths. While all indicators of fire— incidents, deaths, injuries, and property damage—are clouded by
the absence of information on fires not reported to local fire departments, property damage is the only indicator of severity that is left unreported in a significant minority of reported fires. Estimates of property damage involve more guesswork than estimates of people killed or injured. Some very-large-loss fires are never reported to local fire departments, because the affected firms are able to handle them with on-site resources. No comparable omissions occur among multiple-death fires. Trend analysis must take into account the effect of inflation. Table 3.3.17 shows NFPA’s estimates for total national property damage due to fire during 1989–1999, both as published and as recalculated in terms of 1989 dollars, using the U.S. Bureau of Labor Statistics’ Consumer Price Index to remove the effects of inflation.21 When inflation is not removed, the loss totals show a 16 percent increase in property damage from 1989 to 1999. When inflation is removed, the loss totals show a 14 percent decrease in property damage. Also significant is the effect of changes in the number of fires, because total damage figures involve the total number of fires and the average dollar loss per fire. From 1989 to 1999 the average loss per fire rose 34 percent, but the average loss per fire adjusted for inflation was virtually unchanged. This inflation makes it difficult to compare large-loss experience over several years. In the early 1930s, the NFPA defined a large-loss fire as one involving at least $250,000 in direct property damage. In 1978, a large-loss fire was redefined as one involving at least $500,000, and in the early 1980s the amount became at least $1,000,000 in direct property damage. Each minimum represented the cutoff point for the largest several hundred fires of its time. In the late 1980s, it was further decided to shift the large-loss study to a more detailed treatment of a smaller number of fires, and therefore the threshold was raised to $5,000,000. Tables 3.3.18 and 3.3.19 list the 20 largest-loss fires of 1990–1999, first on the basis of their published losses, and then on the basis of losses adjusted for inflation. Note that Table 3.3.17 adjusts backward for inflation, putting all losses in terms of dollars for the earliest year or the period (1989 within 1989–1999), whereas Table 3.3.19 adjusts forward, putting all
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TABLE 3.3.17 U.S. Trends in Property Damage Due to Fire, 1989–1999 Year 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
Total Estimated Damage (Billion Dollars)
Adjusted to1989 (Billion Dollars)21
8.66 7.82 9.47 8.30 8.55 8.15 8.92 9.41 8.53 8.63 10.02
8.66 7.42 8.61 7.33 7.33 6.82 7.25 7.44 6.59 6.57 7.45
losses in terms of dollars for the latest year in the period (1999 within 1990–1999). Either approach is valid, and, in fact, the year chosen need not even be part of the range of events. (All losses could be converted to 1900 dollars, for example.) Backwardadjusting works well with graphs, because it shows two trend lines emerging from a common starting point, whereas forwardadjusting would show them converging to a common end-point, which looks less natural. In a table, however, as in any display covering a very long timeline, forward-adjusting comes closest to showing what things would cost today. It also yields the largest numbers, which makes the most dramatic impression. Note how the adjustment for inflation changes the list, as older fires rise and more recent fires fall. For example, the loss associated with the Los Angeles riots ranked third on the first list but second when the losses were adjusted for inflation. Each list has one fire the other does not have. From an interpretation standpoint, note that California fires account for one-third of the fires on the second list, for a total in 1999 dollars of more than $4 billion. Difficulties in comparison become more pronounced when points even further back in history are considered. The 1947 chemical plant fire in Texas City, Texas, had a reported loss of $67 million. Using the Consumer Price Index, that translates into $500 million in 1999. The 1906 earthquake and fire in San Francisco had a reported loss of $350 million. That means $6.5 billion today—or more than half the loss attributed to all reported fires in the United States in a typical year. At this point, comparisons can become very sensitive to assumptions. Was the property lost in the Texas City fire sufficiently similar to the items covered by the Consumer Price Index? Or should a more industry-specific price index be used? Were the estimates of loss for the San Francisco fire made to the nearest $10 million or even the nearest $50 million? Then the 1999 version of that loss might be accurate to only the nearest $185 million or $925 million, which would mean its range of uncertainty would be higher than the total loss of almost any recent fire.21,22 The lesson in all this is that trend analysis of loss figures can be very tricky and needs to be done with an eye toward the effects of inflation and population growth (which also affects
TABLE 3.3.18 Largest Loss U.S. Fires Reported to NFPA, 1990–1999 Reported Dollars Loss (million dollars)
Place
Date
1. Wildland firestorm, Oakland, CA 2. Power plant (auto manufacturing complex), Dearborn, MI 3. Civil disturbance, Los Angeles, CA 4. “Laguna” wildfire, Orange, CA 5. Textile mill, Methuen, MA 6A. Cargo plane—in-flight fire, Near Newburgh, NY 6B. Wildland fire, FL
October 20, 1991 February 1, 1999
1500
April 29, 1992 October 27, 1993 December 11, 1995 September 5, 1996 May–June 1998 February 23, 1991 July 5, 1999 March 21, 1996 March 25, 1999 October 1, 1992 June 27, 1990 February 26, 1993 November 2, 1993 January 31, 1995 February 17, 1999 April 19, 1995 October 16, 1999 October 12, 1994
567
8. High-rise office building, Philadelphia, PA 9. Aluminum plant, Gramercy, LA 10. Warehouse fire, New Orleans, LA 11. Refinery, CA 12. “Cleveland” wildfire, Placerville, CA 13. “Paint fire/Goleta” wildfire, Santa Barbara, CA 14. High-rise office building bombing, New York, NY 15. “Malibu/Old Topanga” wildfire, Los Angeles CA 16. Carpet Manufacturing, La Grange, GA 17. Power plant, Kansas City, MO 18. Office building, Oklahoma City, OK 19. Wildlands, Redding, CA 20. Methanol plant, Pasadena, TX
650
528 500 395 395 325 300 280 247 246 237 230 219 200 196 136 121.4 116
trends in numbers of fires, deaths, and injuries). Keep in mind that loss trends have a tendency to look bad even if real progress is being made.
USING DATA IN PROGRAM AND STRATEGY ANALYSIS Earlier in this chapter, techniques were described for using data to analyze the present (size and characteristics of the fire prob-
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TABLE 3.3.19 Largest Loss U.S. Fires Reported to NFPA, 1990–1999 Adjusted to 1999 Dollars 21
Place 1. Wildland firestorm, Oakland, CA 2. Civil disturbance, Los Angeles, CA 3. Power plant (auto manufacturing complex), Dearborn, MI 4. “Laguna” wildfire, Orange, CA 5. Textile mill, Methuen, MA 6. Cargo plane in-flight fire, Near Newburgh, NY 7. Wildland fire, FL 8. High-rise office building, Philadelphia, PA 9. “Paint fire/Goleta” wildfire, Santa Barbara, CA 10. Aluminum plant, Gramercy, LA 11. Warehouse fire, New Orleans, LA 12. “Cleveland” wildfire, Placerville, CA 13. High-rise office building bombing, New York, NY 14. “Malibu/Old Topanga” wildfire, Los Angeles CA 15. Refinery, CA 16. Carpet Manufacturing, La Grange, GA 17. Power plant, Kansas City, MO 18. Office building, Oklahoma City, OK 19. Methanol plant, Pasadena, TX 20. Chemical plant, Monroe, LA
Date October 20, 1991 April 29, 1992 February 1, 1999 October 27, 1993 December 11, 1995 September 5, 1996 May–June 1998 February 23, 1991 June 27, 1990 July 5, 1999 March 21, 1996 October 1, 1992 February 26, 1993 November 2, 1993 March 25, 1999 January 31, 1995 February 17, 1999 April 19, 1995 October 12, 1994 May 1, 1991
Loss (million dollars) 1835 674 650
609 547 420 404 398 303 300 298 292 265 253 247 219 196 149 131 128
Source: NFPA’s Fire Incident Data Organization (FIDO).
lem) and the past (trends in the size and nature of the fire problem). Program and strategy analysis is the most decision-relevant use of data because it tries to project the future, and, in particular, the ways in which the future will be different if a particular program or strategy is or is not adopted. The most fundamental question to be answered in using data for program or strategy analysis is whether past fire experience is a good guide to future fire problems. Sometimes it is;
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sometimes it is not. However, intelligent use of data with other sources of information is an essential part of the best possible projection of the future. After all, what will we use if not data? Models are tied to reality by validation, which is based on experience of the past. Expert judgment is formed, at least in part, by the experience of the past. The issue is not whether to use the past as a guide; it is how best to characterize the important changes that will occur in the future. Often the most important aspect of the future will be a different mix of the elements already in place in the present. For example, home smoke-detector usage has grown at a phenomenal rate in the past 25 years, with most of the growth occurring in or after 1976. Fire incident data from the early years of growth in detector usage showed that smoke detectors reduce by nearly half the risk (measured by the number of deaths per 1000 fires) that a person will die if he or she has a fire. At that point, there were uncertainties about the applicability of this finding to the future. Would the life-saving impact of detectors remain the same when detectors were installed in poorer households with less-educated occupants?23 The answer turned out to be yes, although there was some erosion in the estimated benefit from detectors that coincided with adverse trends in the estimated fraction of detectors that were operational.8 But the form of the question shows how data can be used intelligently to try to project the future. Start with the future predicted by a simple projection of recent trends. Using judgment, creativity, and brainstorming, try to identify what aspects of the present environment might be changing in ways that would modify the simple projection. Try to obtain data on the speed of those changes. Try to analyze the fire data in hand to determine the sensitivity of your conclusions to those changes. Combine these results to produce a revised projection. Most analyses to date have found that environmental changes relevant to fire occur slowly and so produce relatively modest changes in what are called baseline projections, i.e., projections of the size and character of the fire problem if no new strategies are adopted. For example, the average age of the U.S. population is rising. This means a drop in the percentage of the population in the high-death-rate years of infancy, a rise in the percentage in the high-death-rate elderly years, and other shifts along the age spectrum. By the end of the century the cumulative effect will be large, but on a year-to-year basis it produces only a small predicted change in the national fire death rate. An analysis of the projected impact of a strategy or program involves the following five steps: 1. Identify the part of the fire problem that the strategy can affect and measure the size of that problem. For example, a change in the flame resistance of upholstered-furniturecovering materials would affect only fires involving those materials. Keep in mind the need to address both fires that begin with upholstered furniture and fires that begin elsewhere and become severe primarily because of spread to upholstered furniture. A change to self-extinguishing cigarettes would affect only fires whose form of heat of ignition was cigarettes, and so on. 2. Estimate the likely percentage reduction in this target fire problem if the strategy or program were adopted, and prepare
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estimates for each of the measures of fire severity (deaths, injuries, property loss) because the impact probably will be different for each measure. If the strategy or program is already in use (as was true for smoke detectors), then fire incident data analysis may produce these estimates. If the strategy or program is not in use or is in very limited use, as is true for home sprinklers, then some combination of modeling, laboratory tests, and expert judgment will be needed to produce the estimates. In either case, it makes sense to develop a range of estimates, from optimistic to pessimistic. 3. Estimate how much of the target population will adopt the program or strategy, and how quickly. This typically is a marketing question, and the results can be surprising. Most analyses of the growth in smoke alarm coverage were too pessimistic on both how much and how fast. At the same time, most analyses were too optimistic about the installation of smoke alarms in homes most likely to have fires. While 94 percent of U.S. households had these devices in 1997 (1997 Fire Awareness Survey for NFPA), only twothirds of the home fires that year were reported to occur in homes with smoke alarms. This discrepancy is not unusual for strategies that work through the marketplace. The first purchasers tend to be more affluent and better educated; these people traditionally have lower fire rates than the rest of the population do. Also, speed of adoption will reflect the normal life of a product. Changes in cigarettes can be implemented for all cigarettes in months, while changes in the upholstered furniture ignited by cigarettes may take decades to work their way through the whole population. 4. Estimate how often the strategy will be defeated in practice. For example, what proportion of smoke-alarm-equipped homes will have their smoke alarms out of service because worn-out batteries were not replaced or removed? Note that if the method in step (2) involved the use of actual fire incident data, the estimate already may include the effects of defeating or attenuation. (The latter is a term that does not have the connotation of deliberate sabotage that defeating may have for some people.) 5. Combine the measures of fire problem size from step (1) and the percentages from steps (2) through (4) to produce estimates of the net percentage reduction in the fire problem and of the new size of the fire problem. With these results, decide how valuable this strategy or program would be and whether to press for its adoption. In some forums, this decision will require a parallel calculation of the cost of the strategy or program, followed by some kind of comparison of the costs and loss reductions. The important point is the use of analysis to narrow the target of a program or strategy in order to maximize impact and conserve scarce program resources. Another consideration in analysis is the need to identify clearly which of many important objectives are to be given priority. For example, is it more important to reduce the fire loss actually being suffered, thereby targeting properties where most loss now occurs? Or is it more important to reduce the potential for catastrophic fire loss, thereby targeting properties with sizable numbers of lives or property value at risk, even if their actual loss has been relatively
small? Also, is it most important to reduce numbers of fires, numbers of deaths and injuries, or numbers of dollars in direct property loss? In home fires, for example, a focus on fires might mean targeting cooking and heating-related fires, a focus on deaths might mean targeting smoking-related fires, and a focus on property loss might mean targeting incendiary and suspicious fires. Finally, remember that tracking analysis continues to be useful even after a decision has been made and a strategy or program has been implemented. As noted earlier, most of the estimates used in an analysis involve uncertainty; therefore, it may be useful to see whether the future unfolds as projected. If not, some further refinements in the design of a strategy or program may be warranted. Even early termination of a program might be indicated.
COMPARING ESTIMATES USING DIFFERENT DATABASES OR ANALYTIC APPROACHES The previous chapter “Fire Data Collection and Databases” details how NFIRS, the NFPA fire experience survey, NFPA’s Fire Incident Data Organization, and other databases not exclusively dedicated to fire, such as the death certificate database, collect and categorize fires. Occasionally a situation arises for which two different numbers exist, derived from different sources or different analytical approaches. For nonanalysts who may not know the source of either number, such a situation can prove frustrating and can encourage a cynical attitude about the arbitrariness of all fire statistics. Even analysts familiar with the sources of both numbers may have difficulty pinning down the precise reasons for any discrepancies and deciding how important the differences are and which number is best. It is very important, therefore, for all data users—and others who expect to confront arguments based on fire statistics—to understand how and why estimates can differ. For the most part, variations involve the ways different data sources and estimates deal with the inevitable gaps in coverage that affect all sources of fire incident information. No fire database can possibly capture all instances of unwanted fires. Few databases—and none of the three discussed in this section—cover fires that are not reported to fire departments. (Special studies, such as one done on residential fires for the CPSC in 1984,24 do provide one-time estimates of the size and composition of the unreported fire problem.) No fire database even captures all the fires reported to fire departments, but some databases, notably the NFPA survey, are built on samples designed to be representative of all fire departments. By their nature, fire databases are biased in favor of “failures” rather than “successes.” The fire that is controlled so quickly that it does not need to be reported to a fire department is not captured by the databases that cover reported fires. Analyses of the impact of devices and procedures that provide early detection or suppression also need to allow for the phenomenon of missing “success” stories. Moreover, databases such as FIDO, which provide the most detail on building features and their performance, are limited to the largest of the reported fires.
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There is also the issue of quality control for a database. For databases with limited depth of detail (e.g. the NFPA survey) or limited breadth of coverage (e.g., FIDO, which is confined mostly to large fires), it is possible to invest considerable effort in ensuring that each report is as complete and accurate as possible. Follow-up calls can be used to fill gaps and check possible odd answers. For a database with the depth and breadth of NFIRS, however, the same level of quality control effort has not been possible. Consequently, NFIRS is missing more entries and has more that are dubious. The trade-off between data quality and data quantity is never easy; an analyst needs to be aware of the strength and dependability of the sources before conducting an analysis. Two examples indicate how differences in databases and assumptions can produce different results. The U.S. Department of Justice estimates the size of the nation’s arson problem through its Uniform Crime Reports (UCR) based on reports from law-enforcement agencies. NFPA, through its annual survey of fire departments, estimates the size of the nation’s fire problem due to incendiary or suspicious causes. For 1998, the UCR estimate of the arson problem in structures was 167 fires per million population. For the same year, NFPA estimates were 264 incendiary or suspicious structure fires per million population and 159 structure fires per million population for incendiary fires alone.11 The UCR arson estimate and the NFPA incendiary fire estimate differ by about 5 percent, which is within the range of statistical uncertainty for an estimate based on a survey the size of NFPA’s. Several points are illustrated by this example. First, the UCR estimate is close to the NFPA incendiary-only estimate, because the UCR definition of arson approximates NFPA’s definition of incendiary. NFPA and other fire organizations, however, traditionally regard the combination of incendiary and suspicious fires as the best indicator of the nation’s problem with intentionally set fires. The UCR and NFPA systems produce roughly the same estimates where they are attempting to measure the same thing. However, because they differ on how to handle the more ambiguous fires, the “arson” numbers they release may appear significantly different to the casual reader or listener. The fire death statistics, discussed earlier, provide another example of differing results. NFPA’s estimates are sample-based statistical projections derived from the fire department survey. Fire deaths from all types of fires, including arson, self-immolations and vehicle fires, are included. In the death certificate database, fire deaths resulting from these three causes might be classified as homicide, suicide, and vehicle accidents, respectively. The NFPA uses the death certificate database to compare fire deaths by state. However, a death certificate is issued in the state an individual dies, not in the state in which the injury occurred. Because of these differences, discrepancies will occur. However, the trends and patterns are consistent.25
SUMMARY As this book goes to press, the analysis of fire data is in transition. NFIRS 5.0 is significantly different from earlier versions in
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its structure and in much of the data collected. For at least the next several years, the national NFIRS database will contain a mixture of data from different versions, and trend analyses will need to compensate for the changes in the data itself. The data users—fire service, insurers, industry planners, educators, and policy makers—still need the same types of information they had in the past as well as the new information that will become available. Analysts must be sensitive to the differences introduced by changes in the data collection system, but the techniques for analysis remain the same. This chapter has illustrated several techniques for analysis with data collected by either or both systems. These techniques include the selection of appropriate data elements for consideration, the combination of data elements, dealing with unknown or missing data, trend analysis, and determining when and how risk of fire can be calculated. Geocoding and the use of other databases with NFIRS were also discussed.
BIBLIOGRAPHY References Cited 1. NFPA 901, Uniform Coding for Fire Protection, 1976 edition (used in most fire databases) and 1991 edition. 2. Hall, J., International Comparison Reports: USA vs. Canada, Japan, UK, Sweden, NFPA, Quincy, MA, 1999 and 2000. 3. Karter, M., U.S. Fire Experience by Region, NFPA, Quincy, MA, 2000. 4. “The 25 Largest Fire Losses in U.S. History,” One-Stop Data Shop, NFPA. Copies are available upon request (Tel. 617-9847450; e-mail:
[email protected]). 5. Karter, M., Fire Loss in the United States, NFPA, Quincy, MA, 2000. 6. Rohr, K., U.S. Fire Experience with Sprinklers, NFPA, Quincy, MA, 2000. 7. 1997 Fire Awareness Survey done for NFPA. 8. Ahrens, M., U.S. Experience with Smoke Alarms and Other Fire Alarms, NFPA, Quincy, MA, 2000. 9. Smith, C., Smoke Detector Operability Survey Report on Findings, U.S. Consumer Product Safety Commission, Bethesda, MD, 1993. 10. Hall, J., Children Playing with Fire, NFPA, Quincy, MA, 2000. 11. Hall, J., U.S. Arson Trends and Patterns, NFPA, Quincy, MA 2001. 12. Hall, J., U.S. Home Heating Patterns and Trends, NFPA, Quincy, MA, 2001. 13. Fahy, R., and LeBlanc, P. “Report on 1999 Firefighter Fatalities,” NFPA Journal, July/Aug. 2000. 14. Hall, J. R., Jr., and Harwood, B., “The National Estimates Approach to U.S. Fire Statistics,” Fire Technology, Vol. 25, No. 2, 1989, pp. 99–113. 15. Ahrens, M., The U.S. Fire Problem Overview Report: Leading Causes and Other Patterns and Trends, NFPA, Quincy, MA, 2001. 16. Mah, J., 1998 Residential Fire Loss Estimates: U.S. National Estimates of Fires, Deaths, Injuries and Property Loss from NonIncendiary and Non-Suspicious Fires, U.S. Consumer Product Safety Commission, Washington, DC, 2001. 17. U.S. General Accounting Office Report to Congressional Committees, Consumer Product Safety Commission: Additional Steps Needed to Assess Fire Hazards of Upholstered Furniture, Washington, DC, 1999. 18. National Safety Council, Injury Facts, 2000 Edition, Itasca, IL, 2000.
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19. Hall, J. R., Jr., Manufactured Home Fires in the U.S., NFPA, Quincy, MA, 2001. 20. Executive Office of the President, Office of Management and Budget, North American Industry Classification System United States, 1997, 1998. 21. U.S. Census Bureau, “Table No. 767, Purchasing Power of the Dollar: 1950 to 1999” Statistical Abstract of the United States: 2000, 120th ed., Washington, DC, 2000. 22. U.S. Census Bureau, “Series E 135–166, Consumer Price Indexes (BLS)—All Items, 1800 to 1970, and by Groups, 1913 to 1970.” Historical Statistics of the United States, 1975. 23. Hall, J. R., Jr., “A Decade of Detectors: Measuring the Effect,” Fire Journal, Vol. 66, No. 3, 1985, pp. 38–39. 24. Audits & Surveys, Inc., 1984 National Survey of Unreported Residential Fires: Final Technical Report, Prepared for U.S. Consumer Product Safety Commission, Contract No. C-83-1239, Audit & Surveys, Inc., Princeton, NJ, June 13, 1985. 25. Hall, J. R., Jr., U.S. Fire Death Patterns by State, NFPA, Quincy, MA, 2001.
Additional Readings Carter, H. R., “Community Fire Defense Plan: Analyze before You Organize,” Firehouse, Vol. 22, No. 6, 1997, pp. 118–120. Damant, G. H., “Developing an Open-Flame Ignition Standard for Residential Mattresses,” Proceedings, New Developments and Key Market Trends in Flame Retardancy, Fall Conference, October 15–18, 2000, Ponte Vedra, FL, Fire Retardant Chemicals Association, Lancaster, PA, 2000, pp. 5–36.
Fire in the United States, 1986–1995, 10th ed., U.S. Fire Administration, Emmitsburg, MD, 1998. Fire in the United States, 1987–1996, 11th ed., U.S. Fire Administration, Emmitsburg, MD, 1999. Hall, J., and Ahrens, M., “Data for Engineering Analysis,” SFPE Handbook for Fire Protection Engineering, 3rd ed., Society of Fire Protection Engineers, Boston, 2002, Section 5, Chapter 5. McEwen, T., and Miller, C., Fire Data Analysis Handbook, U.S. Fire Administration, Emmitsburg, MD, 1993. Available at http://www.usfa.fema.gov/pdf/usfapubs/fdah.pdf. NFIRS Analysis: Investigating City Characteristics and Residential Fire Rates, FA-179, U.S. Fire Administration, Emmitsburg, MD, Apr. 1998. NFPA’s “One-Stop Data Shop” program in the Fire Analysis and Research Division produces dozens of reports on fire experience each year, most of them distributed directly through the division and not published in books or periodicals. A listing of reports that may be ordered is available free. Smith, L. E., Greene, M. A., and Singh, H. A., Fires Caused by Children Playing with Lighters. An Evaluation of the CPSC Safety Standard for Cigarette Lighters, Consumer Product Safety Commission, Washington, DC, 2000. Uses of NFIRS. The Many Uses of the National Fire Incident Reporting System, FA-171, U.S. Fire Administration, Emmitsburg, MD, June 1997.
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SECTION 3
Introduction to Fire Modeling Craig Beyler Philip J. DiNenno
M
odeling is an inherent part of research in science and engineering, and its application to fire is as old as scientific research into fire behavior itself. The first book devoted solely to modeling in fire research was published in 1960.1 Modern fire research, coupled with the ever-increasing power of computers, has given rise to highly complex models that can only be implemented as computer fire models. While computer fire models have popularized fire modeling, these computerbased models do not differ substantially from earlier fire models; they just are more complex and possess greater capabilities. The importance of modeling, in its application to fire safety design, has grown in the past decade; with this widespread application comes a critical need for detailed understanding and appropriate use of models relative to the problem under consideration. Models can be classified into two broad classes: (1) physical models and (2) mathematical models. Physical models attempt to reproduce fire phenomena in a simplified physical situation. Scale models are a very widespread form of modeling, as full-scale experiments are expensive, difficult, and sometimes wholly infeasible. Insights can often be gained by studying fire phenomena at reduced physical scale. Mathematical models are sets of equations that describe the behavior of a physical system. Very often, the goal of physical models is to uncover laws governing the behavior of physical/chemical systems. The resulting mathematical model can then be used to predict the behavior of real physical systems. Thus, physical and mathematical models are interrelated and complementary.
PHYSICAL FIRE MODELS Physical modeling does not simply mean conducting experiments at reduced physical scale; that is, reducing the linear dimensions of a physical situation and conducting experiments with the reduced-scale model is not sufficient. In addition to geometric scaling, it is necessary to maintain mechanical, thermal, and chemical similarity in the reduced-scale model. The scaling laws required to maintain these similarities can be determined from dimensional analysis or from the fundamental equations describing the physical/chemical phenomena.
Dr. Craig Beyler is technical director, Hughes Associates, Inc., and section editor of the SFPE Handbook of Fire Protection Engineering. Philip J. DiNenno, P.E., is president, Hughes Associates, Inc., and editor-in-chief of the SFPE Handbook of Fire Protection Engineering.
The most widespread physical scaling laws in fire are known as “Froude modeling,” which is applicable to buoyant flows associated with fires. Froude modeling requires that the ratio of buoyant forces to inertia forces be maintained. The Froude number, Fr, can be expressed as ‚ Fr T Q2/5/D T V/ D where Q is the fire heat release rate, D the physical scale of the experiment, and V the characteristic velocity. Thus, if a half-scale experiment is to be performed, the heat release must be reduced to 18 percent of the full-scale heat release to maintain the same Fr number and thus ensure that the flow velocities scale in geometrically similar locations in the half-scale and full-scale models. The velocities themselves scale as the square root of the scale at constant Fr. ‚ VT D Froude modeling has been used successfully to understand plume flows, ceiling jet flows, and flame heights. Flame-height correlation models based on Froude modeling have been successful over a wide range of physical scales. An example is shown in Figure 3.4.1, which was developed by McCaffrey.2 The flame height to fire source diameter, L/D, is shown as a function of the ƒ Fr. The correlation is successful over 12 decades of Fr, an amazingly wide range of applicability for any correlation or model. Because different fire phenomena scale differently, it is not generally possible to study complex fire situations in small scale. This limits the use of scale modeling principles. It is notably difficult to scale convective flows and radiation at the same time. Thus, Froude modeling cannot be applied readily to fire problems where radiation is important, for instance. Scale modeling using Froude scaling laws has been most successful in addressing smoke movement issues. Two techniques have found important applications: (1) reduced-scale gasphase modeling and (2) saltwater modeling. The principles of these modeling techniques have been reviewed by Quintiere.3 Saltwater modeling uses the discharge of high-density salt water into fresh water as an inverse simulation of buoyant flows. This technique has been used successfully in both compartments4 and multiple-compartment enclosures.5 Reduced-scale modeling has been used in a wide range of flow situations.6 An excellent example of the use of reduced-scale modeling is given by Quintiere and Dillon,7 and describes smoke movement in an atrium fire. The use of scale modeling in the design of smoke management systems is embraced by NFPA 92B,
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10 3
10 2
Steward L/D
Becker
10 1 Zukoski
You & Faeth 10 0 10 -3
10 -2
10 -1
10 1
10
10 2
10 3
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Flame–Height Correlation Model Based on Froude Modeling. (Source: McCaffrey 2)
Guide for Smoke Management Systems in Malls, Atria, and Large Areas. Physical modeling does not always involve major reductions in physical scale. Physical models may simply seek to simplify complex phenomena into a manageable and understandable problem. Examples of this type of physical modeling can be found as far back as the ASTM E119 fire-resistance test. The ASTM E119 time–temperature curve shown in Figure 3.4.2 was selected as a representative time–temperature curve for testing structural assemblies. The E119 fire-resistance test is a form of physical modeling. The furnace environment is intended to model the fire environment experienced by structural members in a fire. The portions of the building structure exposed in an E119 furnace are intended to model the fire behavior of the building structure in a fire. No single time–temperature exposure can represent all fires, and testing portions of building structures does not fully represent the behavior of the structure, but the results of the simplified E119 test are useful nonetheless. Over the decades the value and the limitations of this widespread physical model have been learned. All standard fire tests are physical models of fire behavior. The adequacy of these physical models varies widely. There is a trend in the development of modern fire test methods to consider explicitly the adequacy of the test method as a physical model of actual fire behavior and response to fire.
1200
1000 Average gas temperature (°C)
FIGURE 3.4.1
Standard curve
800
600
400
200
0
0
10
20
30 40 Time (min)
50
60
FIGURE 3.4.2 Representative Time–Temperature Curve (Source: ASTM E119)
els presume that, given a well-defined physical situation, fire growth and behavior is entirely determined. Both approaches are valuable in understanding fire.
MATHEMATICAL FIRE MODELS Mathematical fire models can be classified as either probabilistic or deterministic. Probabilistic models attempt to deal with the random nature of fire behavior, whereas deterministic mod-
Deterministic Fire Models Deterministic fire models can range from simple one-line correlations of data to highly complex models requiring hours of
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L/D C 0.2 (Q2/5/D) where length units are in meters and heat release rate is in kW. (For U.S. Custom Units, 1 m C 39.37 in.; 1 kW C 1.655 BTU/s.) This equation is the result of applying Froude modeling principles. Other equations are available that are applicable at even lower values of L/D. At the other end of the scale of complexity are models that describe the behavior of fire in one or more rooms. These models may be complex because they include many physical/chemical processes or because a few processes are modeled in great detail. These complex models can be broadly classified as zone models and computational fluid dynamics (CFD) models, also called field models. Perhaps the most important attribute of computer fire models is their ability to predict accurately and realistically the relevant fire behavior within their stated limitations. The predictive capability of a model depends on both the underlying scientific understanding of the processes being modeled and the translation of that understanding into some calculation scheme. There remain substantial shortcomings in the scientific understanding of fire and related processes. This knowledge shortfall, however, will not necessarily slow the development of calculations with enhanced predictability. It is not necessary to understand a phenomenon fully in the pure scientific context in order to exploit a lower level of understanding for design and practice purposes. In fact, current models take great advantage of “imperfect” knowledge to yield acceptable results. More general discussions of the state of related fire science can be found in the research of Emmons, Pagni, and Friedman.8–10
Zone Fire Models Fire environment in a room is quite complex. Major insights into fire behavior have been achieved by a simple conceptual construct called zone modeling. In essence, a zone model assumes that the compartment may be idealized as consisting of two regions: (1) an upper region, filled with hot combustion gases, and (2) a lower region, filled with essentially cool air. Each region or zone is idealized to have uniform temperatures and gas concentrations. The plane dividing the two zones is the hot layer interface that may move vertically during a fire. Figure 3.4.3 shows a comparison of the temperature profile in a room fire with the idealized zone model equivalent. In one case, the zone model concept matches reality quite well; in the other, differences are clearly seen. Gas concentrations are idealized in the same way.
Introduction to Fire Modeling
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200
160
Temperature (°C)
computing time using mainframe computers. The unifying aspect of these models is that the course of a fire is fixed by the variables that establish the environment in which it occurs. The physical conditions that determine the progress and outcome of the fire are called the fire scenario. The fire scenario includes fuels involved, arrangement of the fuels, characteristics of the building and its fire protection systems, location of the ignition, location and capabilities of occupants, and any other variables that affect the fire’s outcome. Thus, for all deterministic fire models, formulation of the fire scenario is of critical importance. An example of a very simple mathematical model is an equation describing the relationship shown in Figure 3.4.1.
■
120
80
40
0.4
0.8
1.2
1.6
0.4
0.8
1.2
1.6
2.0
Height (m)
FIGURE 3.4.3 Comparison of the Temperature Profile in a Room Fire with the Idealized Zone Model Equivalent
The zone model concept simplifies the room fire thermal environment to two temperatures and an interface height, rather than a three-dimensional temperature field. Major simplifications are realized both mathematically and computationally. These simplifications have made many fire problems tractable and have allowed significant progress to be made. Of course, additional components are needed to specify fully the fire environment. Vent flows, plume entrainment, heat transfer, and combustion models are needed. Even if each of the component submodels is fairly simple, the result when coupled together is a complex model requiring computers for efficient, practical calculations. Zone models by definition will always be approximate. The key is whether the predictions are “close enough” to yield significant insight for the situation under study. Zone modeling yields useful insight into many fire problems. The real question is under what conditions these models yield acceptably accurate results. This question has been largely unanswered. There is a reasonable amount of validation test data available for comparison to models with single or with up to six compartments with length scales of 10 ft (3.05 m) connected via a corridor and modest (less than 1000 kW) 1055 BTU/s, well-characterized fire.11–24 The extent to which zone models can be effectively applied in large open areas or tall structures is uncertain. The twozone paradigm does not preclude their use in large or tall structures per se, but rather stretches the assumption of uniform properties within a zone. An excellent summary of the underlying assumptions of zone modeling is given by Quintiere.25 Further discussions of the status and limitations of zone modeling are given elsewhere.26–29 While the number of zone fire models is very large, Friedman has reviewed the most available model,30 and Beard has reviewed a few of the most widely used models.31 The status of zone modeling as a predictive tool can be evaluated with acceptable confidence as follows. For a relatively small room [approximately 100 sq ft (9.3 m2)] with a welldescribed, well-ventilated fire source, the temperature, layer position, and gas concentrations can be estimated with acceptable accuracy. Within the limitations of zone modeling, smoke filling a corridor and then adjacent rooms can also be adequately described. This case does not imply that, for conditions outside
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this narrow description, modeling is inaccurate or unacceptable but rather that the results must be carefully evaluated in the context of what level of prediction is required as well as independent experimental evidence. Beyond the comparisons of predictions with experimental data in validation studies in References 11–24 discussed above, the issues involved in the evaluation of fire models have begun to receive attention in the technical fire community.29,32–36 ASTM has developed guides to documenting and evaluating fire models, and SFPE is beginning to take on the task of providing guidance documents on the use of fire models. ISO TC 92 SC 4 has international groups of experts who are also developing guidance on validation and verification of models. Although these efforts are tentative first steps, they reflect recognition of the need within the fire community to understand the applicability, limitations, and accuracy of fire models that are being used in hazard analysis and design. The following discussions attempt to briefly describe the current status and near-term possibilities for modeling some important phenomena. No one model is assumed; rather, the discussion summarizes the integrated capability of the HARVARD/FIRST and CFAST zone models.37,38 Ignition. Both piloted and unpiloted ignition due to radiative heating can be approximated and if the ignition temperature is known, alternative small-scale ignition test data can be used (ASTM E1354). Burning Behavior. The burning behavior of a single fuel item cannot currently be predicted. The treatment of this obviously important subphenomenon in models is done through empirical correlations and/or large-scale test data. Approximations using small-scale tests are possible.39 A more fundamental treatment is unlikely in the near term. Empirical methods, small-scale and large-scale data, and “design basis” fire assumptions will continue to form the basis of zone models. Flame Spread. Flame spread modeling on interior surfaces has recently been a very active area of model development.40–47 Flame spread models use the inputs from small-scale tests such as the cone calorimeter and the LIFT apparatus to predict the spread of flame and heat release rate in wall and corner fires. These models are beginning to be incorporated as submodels into zone fire models.48 It is expected that the concepts developed in this work will be used in tackling the more difficult problems of flame spread and heat release rate prediction for individual fuel items. Compartment Effects Energy Balance. Zone-type approximations are being improved with the inclusion of plumes or ceiling jets as subzones. Heating of a ceiling in the vicinity of a flame or plume can be calculated. Enhanced radiation levels can be estimated, but it is not possible to predict the general effect on burning behavior. Walls and Corners. Current methods used to approximate the impact of walls and corners on plumes, flame heights, and ceil-
ing jets are suspect. Some modest development work is needed before these submodels can be appreciably improved. Oxygen Starvation. Currently treated by use of heuristics in conjunction with limited-oxygen index for energy release rate. Multiple Room Fire and Smoke Spread. There are several models that treat smoke spread through multiple compartments using the standard two-zone smoke “filling” approximation. Depending on the problem under analysis, this approach may yield acceptable results. Limited empirical studies on smoke flow in corridors could be integrated near term with uncertain results. Flows in shafts, stairs, and through horizontal vents are more problematic. Some experimental work is required.50,51 It is expected that useful approximations will be available in the near term. Fire spread is currently limited to remote ignition of remote objects by heating from flames and the hot layer. Fire spread to multiple compartments is in principle predictable. Unknown effects of multiple compartments burning along a single corridor in close proximity may be important. Fire spread by ignition of a hot layer is currently unresolved. Forced Ventilation. Several models have attempted to treat forced ventilation under simple vent configurations.52 There appear to be major unresolved technical issues in the full understanding of forced vents and fires, which precludes effective modeling for many cases. Postflashover Predictions. The onset of flashover in a compartment poses a difficult prediction problem. Major unresolved technical problems include prediction of a radiation-enhanced burning rate; prediction of CO production in underventilated conditions; ignition of hot layers; burning at vents; and flame spread down corridors.53 There is one area where postflashover fires are very well characterized. The prediction of temperature as a function of time for calculating the fire resistance of a structure is very well developed. Design approaches using postflashover models are accepted alternatives to prescriptive fire resistance requirements in several countries. However, these successes are in single-zone models. Two-zone models, such as CFAST, tend to overpredict temperatures in postflashover compartment fires, especially for large vent openings.54 The model is capable of producing predicted layer temperatures in excess of any experimentally measured layer temperature found in the literature. Detection System Activation. Procedures exist for estimating the response of ceiling-mounted heat detectors via heating by a plume or ceiling jet. These calculations have been relatively well established for flat, smooth ceilings, with more limited validation for compartments with high ceiling heights or nonsmooth, nonflat ceilings. Methods also exist for estimating smoke detector response. These have not been generally used due to the unavailability of the necessary detector-specific parameters. Calculation methods exist for detector activation where a layer has formed, although
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the procedures have not been adequately verified. No procedures currently exist for estimating the activation of detectors in situations where the detector responds before a well-developed plume or ceiling jet forms or where mechanical ventilation appreciably perturbs the flow. Incremental progress is expected in this area in the near and moderate term. Suppression Modeling. Fire suppression with a total-flooding gas system and with a water mist system has been successfully modeled.55,56 Although there is research effort in modeling the suppression of fires by water application,57 no generally applied design or analysis procedures are expected in the near future. Fire Effects Modeling Heat Damage. If the temperature threshold of a piece of equipment or material is known, standard heat transfer calculations can be used in conjunction with fire models to estimate the time dependence or degree of damage. Smoke Damage. Estimates of smoke damage that reflect the sensitivity of the equipment exposed and type of smoke or fire involved are not generally available. Such calculations involve uncertainties associated with cold smoke transport and deposition, prediction of smoke production and properties, wide variability of smoke properties, and sensitivity of equipment to this wide variation of smoke types. Human Interaction Visibility. Limited experimental data on visibility combined with small-scale constant-yield smoke concentration and optical property measurements enable rough estimates of human visibility in smoke. Using the results of computer models for smoke, layer depth, and smoke properties, approximate visibility estimates can be made. Temperature/Radiation. Effects of heat and radiation can be estimated using empirical human tenability data. Toxicity. Toxic effects of CO, CO2, HCN, and oxygen depletion can be reasonably predicted using N-gas modeling approaches.49,58 The effects of gases such as HCl, HF, or HBr can be estimated, but with a lower level of confidence. Bioassay methods can be used to screen for so-called paper-toxicant fire products, where their existence is suspected. The legitimate application of models to problems outside of the relatively narrow ranges discussed above is possible and occurs frequently. If the results of the calculations do not require great accuracy (e.g., ±50 percent), the important physics of the problem is reflected in the model, and/or the results are used for approximate comparative purposes, these tools can be approximately used in a much broader range of problems.
Computational Fluid Dynamics (CFD) Models Computational fluid dynamics (CFD) models avoid the simplifications inherent in zone models. The temperature, velocity, and
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gas concentrations are calculated as three-dimensional fields. The compartment is descretized into thousands of computational cells, and the temperatures, velocities, and concentrations are found for each of the thousands of cells throughout the room. The model is a complex fluid mechanical model of turbulent flow. Although empirical modeling is required even in these very complex models, empiricisms are made at a more fundamental level. Although simple CFD model calculations can be made on the fastest PCs available, larger computers are desirable from a practical standpoint and are often essential. To date, CFD models have not progressed to the point where they can include the wide range of physical/chemical processes phenomena included in zone models. Far more detailed knowledge is required for CFD models, but it is only a matter of time until CFD models can accommodate a wide range of phenomena.59,60 Despite their limited scope, CFD models are making important contributions to fire safety today. The application of CFD to fire problems has been dramatically increasing. The ready availability of commercial CFD packages with increasing sophistication enables more widespread applications. The vast majority of uses of these programs have nothing to do with fire problems but are concerned with fluid flow in pipes, convective flow in enclosures, cooling of electronic packages, etc.61 In general, there have not been critical evaluations of these methods relative to their use in fire problems. Since the basic mass-energy and momentum-conservation equations are identical for all problems, these codes have potentially dramatic revolutionary impact on fire modeling. The difficulties in CFD modeling of fires lie in two areas. First, no direct simulation of turbulent diffusion flames (i.e., a fire) is currently possible; hence, the fire source itself must be approximated. Other major phenomena that can only be approximated include turbulence, particularly large eddies associated with strong plumes and flames, and thermal radiation interchange between soot, gases, and solid surfaces. Second, the capability of these codes to handle specific phenomena important in fire modeling varies widely. This has given rise to the development of CFD models specifically for fire applications.62–64 Significant focus has been placed on modeling flame spread and fire development.65–70 Although the general problem of flame spread cannot yet be predicted with existing CFD models, significant progress has been made. At this time, modeling of combustion and the resulting heat fluxes seems to be the most difficult remaining problem. The programs require substantial computational effort, although most are available in PC versions. More importantly, they require sophisticated users due to the complexity of defining initial and boundary conditions. CFD modeling programs have direct and immediate potential application problems driven largely by fluid mechanics. Such problems include far-field smoke flow, details of flow and heat transfer to complex geometries (e.g., sprinkler links), and impact of fixed ventilation flows on bouyancy-driven flows. Applications of CFD models to fire problems have included aircraft terminals and atria, air-supported structures, electronic generating stations, aircraft cabins, tunnels, hospital wards, and shopping malls.71–79
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Most CFD models use empirical models of turbulence. An alternative approach, known as large eddy models, is being developed and applied and large-scale turbulence is directly modeled.80 While computationally intensive, the method has shown great promise. LES modeling has had success in modeling buoyant flows and interaction of fire flows with sprinkler sprays.80–85 While validation of models as detailed as CFD models is an arduous task, papers have begun to appear in the literature in which experimental data and CFD model predictions are computed.86–91 Evaluation of CFD results for a particular application poses particular challenges. The sheer quantity of output data, the importance of the computational grid size, and subtleties in the internal model treatment of important physics require substantial effort to critically evaluate and ensure reliability of the results. For example, the differences between traditional turbulence approximations and real fire-induced fluid mechanics can give rise to modeling problems for even simple plume flows.92 Efforts are ongoing to include the interaction of sprinkler sprays and fire-induced flow fields.93–98 These models focus solely on the fluid mechanics aspects of the interaction and do not deal with the effect of water on combustion.
tion models regard fires as deterministic once the fire is fully defined. However, the inputs to the models are assumed to follow probabilistic models. Thus, the inputs to the deterministic model are treated as random variables. Such variables might include which furniture item is ignited or how far open the door is when the fire starts. A large series of runs is performed by selecting inputs from the probabilistic models, and the range and frequency of different outcomes are examined. Such modeling combines elements of both probabilistic and deterministic models.99 Probabilistic models are taking on increased importance in the fire community in the assessment of risk. Various risk-based methods are under continuing development, most notably in Australia and Canada.100–103 These have been applied to building classes, individual buildings, and ships.
Probabilistic Models
Although progress has been made, the predictive capability of computer models is limited. It is not known with confidence to what limits these models can be applied. It is equally clear that ongoing research and development efforts aimed at resolving some of these uncertainties will result in improved predictive capability. The use of heuristics to aid in simplifying particularly difficult problems will continue. Confidence in the capabilities of models will increase with improved validation and careful use.
Probabilistic fire models can be categorized into three classes: (1) network, (2) statistical, and (3) simulation. Each of these deals with the uncertainties associated with fire growth processes. Network models are fire growth models in which the transition from one fire stage to another and the effectiveness of fire suppression systems, manual fire fighting, passive fire protection, and so on are governed by user-assigned probabilities that are based on historical data, or engineering evaluations, or both. In some cases, these probabilities are single values, and in other models, the probabilities are time dependent. Statistical models represent the probability of an occurrence as it is determined from historical data. A classic example of a statistical model is the occurrence of fire alarms. Fire alarms are random events that are, within certain constraints, uniform in nature. That is, a fire or fire alarm might occur at any time with equal probability. Clearly, one of the constraints on this behavior is that the time of day must be controlled. It is well known that fires are a function of the time of day, and so one must restrict attention to a single time of day. The probability of k fire alarms occurring over the period s is given by P (k) C
(4s)k >4s e k!
where 4 is the mean frequency of fire alarms. This statistical model describes the probability of a given number of alarms, k, occurring during a specified period of time, s. Such a statistical model can be very useful in fire protection resource planning. Simulation methods try out different sets of conditions to see how they affect the outcome. Probabilities are often used to weigh outcomes for each set of conditions and produce and overall expected outcome. Simulation models may predict outcomes for a given set of conditions by using other physical, probabilistic, or deterministic models. In the latter case, simula-
TRENDS Having briefly discussed the current and near-term capabilities of models to predict fire effects, we will now focus on observable trends and the possibilities for the future of modeling.
Predictive Capability
Applications Applications of modeling have included fire litigation and reconstruction, hazard analysis of building materials and contents, and the evaluation of building code exceptions or equivalencies. Computer models and other analytical tools have not, however, been integrated into fire protection engineering design practice. Several case studies of “reconstructed” fire incidents using computer models have been published.104–108 They generally demonstrate how a computer model used as part of a more general engineering analysis is a powerful tool. One lesson of these case studies is that the state of the art is not such that one sets up a reasonable input file and the computer describes how the fire evolved. Rather, the models are more appropriately used to evaluate in approximate terms the time sequence of the event or to establish in more detail the reasonableness of one or another ignition growth and spread scenarios. These programs are also used to pose “what if” questions related to the contribution of a particular material, furnishing item, etc. versus one of greater or lesser combustibility, energy release rate, and so on. Most modeling applications occur today, and have occurred in the recent past, in fire litigation circumstances. Most of these applications are never published. The use of modeling in litigation and fire investigation will expand. The problem of fire reconstruction lends itself readily to modeling tools.
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Applications outside of litigation are often associated with the evaluation of the fire hazard posed by a product or material.109–113 Modeling received a major boost in the context of predicting the “toxic hazard” posed by materials. The combination of deterministic models with risk assessment methods into integrated hazard assessment schemes has begun.114,115 The method enables one to integrate ignition, flammability, and toxicity properties with the end use of the material under varying scenarios to estimate the outcome. As always, the quality of these applications is driven by the methods, data, approximations, and assumptions used. Additional applications that reflect the increasing use of models112 for a range of applications can be found in work by Bukowski, Bengston and Hagglund,116 and Hagglund and Wickstrom.117 While current applications are somewhat limited in terms of “routine” use, the trend has been for a relatively rapid increase in the application of models across all aspects of fire protection. Clearly, the use of models in fire investigations and litigation will continue, and their application to special facilities and problems not directly dealt with in codes and standards will also increase. Applications of CFD modeling to unique facilities and problems should dramatically increase. There is currently widespread use of modeling in the design and evaluation of fire safety of buildings and facilities. These applications often arise in the context of “code equivalency” or “performance-based” approach to fire safety. There are relatively few fire safety problems for which direct comparison or equivalency, based on the prediction of fire growth or smoke spread alone, is possible. There are almost always probabilistic, risk, economic, and political factors involved. Computer models are still helpful, however, given the almost nascent state of development, in that they provide the ability to approximately compare expected fire conditions across a range of scenarios. The potential impact of various intervention strategies can also be evaluated in a relatively crude fashion. Although there are significant limitations in the treatment of important physics in widely used models, the primary difficulties arise in the overall context of the model’s use. Appropriate selection of expected or worst case input parameters, consensus on the safety factors or margins of safety to be applied and, more fundamentally, the lack of clear design objectives remain important areas of concern. Significant differences in the results of modeling analyses of fire safety appear to arise more from these external factors than from the limitations of any particular model. A major question exists on the application of these models in fire safety design relative to building codes and fire safety standards. The primary determinants in this area will likely be the degree to which relatively prescriptive codes and standards can be harmonized with more performance-based design and engineering methods. This is, of course, more complicated than it sounds, given the legal, social, and political realities under which buildings are approved. An additional prerequisite for the general use of modeling in building design is the need to deal with the inherently probabilistic nature of fire events and the “reliability” of various construction features and fire safety systems. Several generic approaches have been suggested to integrate deterministic modeling with probabilistic problems.100–103,118,119 This chal-
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lenge also poses the greatest opportunity. The tremendous potential of this significant technological advance for improved fire safety will be recognized and exploited.
Hardware It has become relatively safe to forecast that more powerful, easy-to-use computer hardware will continue to emerge. The past decade has seen a revolution in computing capacity available to individuals. This has eliminated most computational speed problems with respect to zone models. The computational requirements of CFD models have been reduced, but will continue to be a challenge. Developments in hardware should also appreciably extend the range and utility of these calculation methods, perhaps into the “real time” world of the fire incident commander. The use of these models in conjunction with interactive video training and simulation will likely result in “fire simulators” becoming widely available to fire departments.120 Longer-term hardware developments in the area of intelligent sensors integrated with software derived from fire modeling may revolutionize fire detection. The “smart” building will include fire protection.
Acceptance The trend toward increased acceptance of predicted results in resolving fire safety questions will continue and likely accelerate. A decade of continued progress in modeling, with the increase in the number of published application studies in the NFPA Journal and other widely read fire literature, has led to a more open approach to the subject by building and fire officials. Progress related to integration of these methods into the design of facilities is more problematic.
Validation Numerous validation studies of computer fire models have been undertaken. Most have been in relatively small [approximately 100 sq ft (9.3 m2)] compartments with well-defined fire sources (cribs, pool fires, or gas burners). In general, the best agreement that can be expected is ±20 percent in terms of smoke layer temperature and depth. It is unlikely given funding and prioritization realities that any significant systematic and complete validation will ever be performed on any model. It is arguable that complete validation is an impractical objective. Given this, models will be evaluated and the results accepted in a relatively slowly evolving time frame. The obligation that this lack of independent validation places on users and approving authorities is obvious. Particular attention must be paid to using these programs within their stated limits and, perhaps more importantly, to searching out experimental data for cases similar to the problem being evaluated. The dearth of validation studies should not be taken as rationale for rejecting the use or results of a model in any particular case. The validation picture could improve dramatically if it became clear that the lack thereof was a significant barrier to more widespread use.
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Material Flammability Testing The development of small-scale fire test methods, which in principle enables the extrapolation of the results to “real” fires, was essential to the development of modeling. Some of these test methods have been standardized by ASTM and NFPA. The input data required by models, which describes the burning behavior, energy release rate, smoke properties, and combustion gas yields of materials, comes largely from these small-scale test methods. It is expected that the availability of this data for a wider range of products and materials will increase. The availability will accelerate dramatically if these relevant test methods are referenced in buildings codes and fire standards in lieu of or in conjunction with more traditional methods. Since models form the basis for extrapolating this flammability data to full-scale performance, increased use of models in this context is expected. In many ways, this particular class of applications may be ideal for the direct integration of modeling into building design standards.
SUMMARY Fire modeling is an old and well-developed field, though much remains to be done. Physical models and mathematical models have made and are making important contributions to fire safety and fire protection. These fire models are an important and growing part of fire protection engineering. Computer fire models are simply the most recent and complex engineering models of fire. Their use requires knowledge of the underlying fire science and fire protection engineering principles. It is no longer a question of whether modeling will be used in the solution of fire safety problems but rather to what extent. The degree to which scientifically based engineering models can impact fire safety will be driven largely by their application to design practice. This requires some integration with building codes and fire safety standards. Without such integration, incremental progress in predictive capability and applications can be expected. If fire safety engineering methods and codes are successfully integrated, the forecast will be on of rapid, revolutionary change in all aspects of modeling as well as building design.
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sium, International Association for Fire Safety Science, 1997, pp. 619–630. Zhao, L., and Beck, V., “The Definition of Scenarios for the CESARE-RISK Model,” Fire Safety Science—Proceedings of the 5th International Symposium, International Association for Fire Safety Science, 1997, pp. 655–666. Bukowski, R., “Fire Models: The Future Is Now,” National Fire Protection Association Journal, Mar./Apr. 1991, p. 60. Nelson, H. E., “An Engineering Analysis of Fire Development in the Hospice of Southern Michigan, December 15, 1985,” Fire Safety Science—Proceedings of the 2nd International Symposium, Hemisphere Publishing Corporation, New York, 1989. Levine, R. S., and Nelson, H. E., Full-Scale Simulation of a Fatal Fire and Comparison of Results with Two Multiroom Models, NISTIR 90-4268, National Institute of Standards and Technology, Gaithersburg, MD, 1990. Alvares, N., “Defining Fire and Smoke Spread Dynamics in the DuPont Plaza Fire of 31 December 1986,” Proceedings of the International Conference on Fire Research and Engineering, Society of Fire Protection Engineers, Boston, MA, September 10–15, 1995. Bukowski, R. W., and Spetzler, R. C., “Analysis of the Happyland Social Club Fire with HAZARD I,” Journal of Fire Protection Engineering, Vol. 4, No. 4, 1992. Clarke, F., and DiNenno, P. J., “Computer-Based Analysis of the Fire Hazard of Furniture Materials,” Proceedings of the SPI 28th Annual Technical Conference, San Antonio, TX, 1984. Clarke, F., and DiNenno, P. J., “Fire Safety of Wire and Cable Materials, Part III,” Proceedings of the International Wire and Cable Symposium, Reno, NV, November 1984. DiNenno, P. J., “Mathematical Fire Modeling—Toward the Rational Integration of Fire Safety Features,” BVD/SPI Conference on Fire Protection Concepts, March 1984. Bukowski, R., “Toxic Hazard Evaluations of Plenum Cables,” Fire Technology, Vol. 21, No. 4, 1985, pp. 252–266. Peacock, R. D., and Bukowski, R. W., “A Prototype Methodology for Fire Hazard Analysis,” Fire Technology, Vol. 26, No. 1, 1990, p. 15. Clarke, F. B., Bukowski, R. W., Stiefel, S. W., Hall J. R., and Steele, S. A., “A Method to Predict Fire Risk: The Report of the National Fire Protection Research Foundation Risk Project,” Report to the National Fire Protection Research Foundation (NFPRF), Quincy, MA, 1990. Hall, J. R., and Sekizawa, A., “Fire Risk Analysis: General Conceptual Framework for Describing Models,” Fire Technology, Vol. 27, No. 1, 1991, pp. 33–53. Bengston, S., and Hagglund, B., “The Use of Zone Model in Fire Engineering Applications,” Fire Safety Science—Proceedings of the 1st International Symposium, Hemisphere Publishing Corporation, Washington, DC, 1986, pp. 667–675. Hagglund, B., and Wickstrom, U., “Smoke Control in Hospitals—A Numerical Study,” Fire Safety Journal, Vol. 16, 1990, pp. 53–63. Ling, W. C., and Williamson, R. B., “Using Fire Tests for Quantitative Risk Analysis,” Fire Risk Assessment, ASTM STP 762, American Society for Testing and Materials, W. Conshohocken, PA, 1982. Wakamatsu, T., “Development of Design System for Building Fire Safety,” Fire Safety Science—Proceedings of the 2nd International Symposium, Hemisphere Publishing Corporation, New York, 1989. “From Burns to Bytes,” NFPA 100 Years, Fire Service Overview, supplement to the NFPA Journal, 1996, pp. 31–32.
NFPA Codes, Standards, and Recommended Practices References to the following NFPA codes, standards, and recommended practices will provide further information on fire modeling discussed in
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this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 92B, Guide for Smoke Management Systems in Malls, Atria, and Large Areas
Additional Readings Alamdari, F., and Kuman, S., “Environmental and Fire Safety Design Assessment Methods,” Fire Safety Engineering, Vol. 6, No. 3, 1999, pp. 12–15. Bailey, J. L., Jones, W. W., Tatem, P. A., and Forney, G. P., “Development of an Algorithm to Predict Vertical Heat Transfer through Ceiling/Floor Conduction,” Fire Technology, Vol. 34, No. 2, 1998, pp. 139–155. Beck, V., Yung, D., He, Y., and Simathipala, K., “Experimental Validation of a Fire Growth Model,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 653–662. Beller, D., “Validating Fire Models: FPETOOL, CFAST, WPI/FIRE,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 959–963. Beyler, C. L., Hunt, S. P., Iqbal, N., and Williams, F. W., “Computer Model of Upward Flame Spread on Vertical Surfaces,” Proceedings of the 5th International Symposium, Fire Safety Science, International Association for Fire Safety Science (IAFSS), March 3–7, 1997, Melbourne, Australia, Intl. Assoc. for Fire Safety Science, Boston, MA, 1997, pp. 197–308. Birk, A. M., “Study of Fire Heating of a Propane Tank Located Near a Burning Building,” Journal of Applied Fire Science, Vol. 9, No. 2, 1999/2000, pp. 173–199. Bjorkman, J., and Keski-Rahkonen, O., “Full-Scale Experiments with Different Smokes,” VTT Technical Research Center of Finland, Espoo, VTT Publications 332, 1997. Blake, D., Domino, S., Gill, W., Gritzo, L., and Williams, J., “Initial Development of Improved Aircraft Cargo Compartment Fire Detection Certification Criteria,” Proceedings of the 12th International Conference on Automatic Fire Detection, AUBE ’01, March 25–28, 2001, Gaithersburg, MD, National Institute of Standards and Technology, Gaithersburg, MD, NIST SP 965, 2001, pp. 615–629. Bukowski, R. W., “Application of FASTLite,” Proceedings of Technical Symposium, Computer Applications in Fire Protection Engineering, June 20–21, 1996, Worcester, MA, 1996, pp. 59–66. Cappuccio, J. A., “Pitfalls of Building Fire Performance Evaluation,” Proceedings of the Fire Risk and Hazard Assessment Symposium. Research and Practice: Bridging the Gap, June 26–28, 1996, San Francisco, CA, National Fire Protection Research Foundation, Quincy, MA, 1996, pp. 416–421. Carpenter, D. J., Investigation into the Validity of Modeling PostFlashover Fires and Flame Extension from Openings with the Fire Field Model JASMINE [Thesis], Worcester Polytechnic Inst., MA, Aug. 1996. Cohn, B. M., “Characterization and Use of Design Basis Fires in Performance Codes,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 581–588. Cooper, L. Y., and Steckler, K. D., “Methodology for Developing and Implementing Alternative Temperature-Time Curves for Testing the Fire Resistance of Barriers for Nuclear Power Plant Applications,” National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 5842, May 1996. Cox, G., “Capability of CFD Fire Simulation Models,” Proceedings of the 9th International Fire Protection Seminar, Engineering Methods for Fire Safety, May 25–26, 2001, Munich, Germany, 2001, pp. 3/71–88.
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Crockett, J., “Perusing Performance Based Design,” ConsultingSpecifying Engineer, Vol. 27, No. 5, 2000, pp. 50–52. Damant, G. H., “Flammability and Materials Trends in the Furnishings Industry,” Proceedings of Fire Retardants—101: Basic Dynamics—Past Efforts Create Future Opportunities, Spring Conference, March 24–27, 1996, Baltimore, MD, Fire Retardant Chemicals Assoc., Lancaster, PA, 1996, pp. 181–194. Dey, M., “Proposed International Collaborative Project to Evaluate Fire Models for Nuclear Power Plant Applications,” Proceedings of the International Collaborative Project to Evaluate Fire Models for Nuclear Power Plant Applications: Summary of Planning Meeting, October 25–26, 1999, College Park, MD, U.S. Nuclear Regulatory Commission, Washington, DC, NUREG/CP-0170, 1999, pp. 1–11. Dolph, B. L., “Modeling Fires on Ships,” Proceedings of Technical Symposium, Computer Applications in Fire Protection Engineering, June 20–21, 1996, Worcester, MA, 1996, pp. 1–4. Elton, S., and Staples, R., “Use of Modelling in Burn Injury Evaluation beneath Clothing Layers,” Fire and Materials, Vol. 23, No. 5, 1999, pp. 217–221. Evans, D. D., “Use of Fire Simulation in Fire Safety Engineering and Fire Investigation.” Proceedings of the 15th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, March 1–7, 2000, San Antonio, TX, National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6588, 2000, Vol. 2, pp. 441–448. Fahy, R. F., “EXIT89: High-Rise Evaluation Model—Recent Enhancements and Example Applications,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 1001–1005. Fleming, J. M., “Code Official’s View of Performance-Based Codes,” Code Official, Vol. 33, No. 1, 1999, pp. 18–30. Floyd, J., Wolf, L., and Krawisc, J., “Evaluation of the HDR Fire Test Data and Accompanying Computational Activities with Conclusion from Present Code Capabilities. Volume 1. Test Series Description for T51 Gas Fire Test Series,” National Institute of Standards and Technology, Gaithersburg, MD, NIST GCR 97727, 1997. Floyd, J., Wolf, L., and Krawisc, J., “Evaluation of the HDR Fire Test Data and Accompanying Computational Activities with Conclusion from Present Code Capabilities. Volume 2. CFAST Validation for T51 Gas Fire Test Series,” National Institute of Standards and Technology, Gaithersburg, MD, NIST GCR 97-731, 1997. Floyd, J., Wolf, L., and Krawisc, J., “Evaluation of the HDR Fire Test Data and Accompanying Computational Activities with Conclusion from Present Code Capabilities. Volume 3. Test Series Description and CFAST Validation for HDR T51 Wood Crib Fire Test Series,” National Institute of Standards and Technology, Gaithersburg, MD, NIST GCR 99-778, 1999. Floyd, J., Wolf, L., and Krawisc, J., “Evaluation of the HDR Fire Test Data and Accompanying Computational Activities with Conclusion from Present Code Capabilities. Volume 4. Test Series Description and CFAST Validation for HDR T52 Oil Pool Fire Test Series,” National Institute of Standards and Technology, Gaithersburg, MD, NIST GCR 01-809, 2000. Galea, E. R., “General Approach to Validating Evacuation Models with an Application to EXODUS,” Journal of Fire Sciences, Vol. 6, No. 6, 1998, pp. 414–436. Galea, E. R., “Validation of Evacuation Models,” University of Greenwich, London, UK, Paper No. 97/IM/22, 1997. Gandhi, P. D., Sheppard, D., and Steppan, D., “Role of Component and Large-Scale Testing in the Evaluation of Design of Sprinklers,” Proceedings of the Fire Risk and Hazard Assessment Symposium. Research and Practice: Bridging the Gap, February 25–27, 1998, Orlando, FL, National Fire Protection Research Foundation, Quincy, MA, 1998, pp. 211–217. Grandison, A. J., Mawhinney, R. N., Galea, E. R., Patel, M. K., Keramida, E. P., Boudouvis, A. G., and Markatos, N. C., “FIREDASS (FIRE Detection And Suppression Simulation
Model), University of Greenwich, London, UK, Paper No. 98/IM/43, 1998. Gritzo, L. A., Moya, J. L., and Murray, D., “Fire Characterization and Object Thermal Response for a Large Flat Plate Adjacent to a Large JP-4 Fuel Fire,” Sandia National Labs., Albuquerque, NM, SAND97-0047, Feb. 1997. Gwynne, S., Galea, E. R., Lawrence, P. J., Owen, M., and Filippidis, L., “Further Validation of the Building EXODUS Evacuation Model,” University of Greenwich, London, UK, Paper No. 98/IM/31, 1998. Gwynne, S., Galea, E. R., Lawrence, P. J., Owen, M., and Filippidis, L., “Systematic Comparison of Model Predictions Produced by the Building EXODUS Evacuation Model and the Tsukuba Pavilion Evacuation Data, Journal of Applied Fire Science, Vol. 7, No. 3, 1997/1998, pp. 235–266. Hadjisophocleous, G. V., Benichou, N., and Tamim, A. S., “Literature Review of Performance-Based Fire Codes and Design Environment,” Journal of Fire Protection Engineering, Vol. 9, No. 1, 1998, pp. 12–40. Hasemi, Y., “Performance-Based Fire Tests of Materials Japan Overview,” Proceedings of the 14th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, May 28–June 3, 1998, Tsukuba, Japan, 1998, pp. 88–97. Hoover, J. B., and Tatem, P. A., “Application of CFAST to Shipboard Fire Modeling. Part 1. Development of the Fire Specifications,” Naval Research Laboratory, Washington, DC, NRL/MR/618000-8466, June 26, 2000. Hoover, J. B., and Tatem, P. A., “Application of CFAST to Shipboard Fire Modeling. Part 3. Guidelines for Users. Final Report. 1998–2000,” Naval Research Laboratory, Washington, DC, NRL/MR/6180-8550, Apr. 23, 2001. Ierardi, J. A., Computer Model of Fire Spread from Engine to Passenger Compartments in Post-Collision Vehicles [Thesis], Worcester Polytechnic Inst., MA, 1999. “International Collaboration Project to Evaluate Fire Models for Nuclear Power Plant Applications: Summary of 2nd Meeting,” U.S. Nuclear Regulatory Commission, Washington, DC, NUREG/CP0173, 2000. Janssens, M. L., “Computer Fire Model Selection and Data Sources,” Proceedings of ASTM’s Role in Performance-Based Fire Codes and Standards, December 8, 1998, Nashville, TN, American Society for Testing and Materials, ASTM STP 1377, 1999, pp. 74–86. Jones, W. W., “Modeling Fires—The Next Generation of Tools,” Proceedings of Technical Symposium, Computer Applications in Fire Protection Engineering, June 20–21, 1996, Worcester, MA, 1996, pp. 13–18. Jones, W. W., “Progress Report on Fire Modeling and Validation,” Proceedings of the 13th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, March 13–20, 1996, Gaithersburg, MD, National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6030, Vol. 2, 1997, pp. 7–14. Jones, W. W., Bailey, J. L., Tatem, P. A., and Forney, G. P., “Comparison of CFAST Predictions to Real Scale Fire Test,” Proceedings of Fire Safety Conference on Performance Based Concepts, October 15–17, 1996, Zurich, Switzerland, 1996, pp. 25/1–14. Kassawara, R. P., and Jajafi, B., “Evaluation of Fire Models for Nuclear Power Plant Applications,” Proceedings of the International Collaborative Project to Evaluate Fire Models for Nuclear Power Plant Applications: Summary of Planning Meeting, October 25–26, 1999, College Park, MD, U.S. Nuclear Regulatory Commission, Washington, DC, NUREG/CP-0170, 1999, pp. 1–7. Lewis, D., “Fire Design of Steel Members,” University of Canterbury, Christchurch, New Zealand, Fire Engineering Research Report 00/7, March 2000, 171 pp. Liu, Z., and Kim, A. K., “Review of the Research and Application of Water Mist Suppression Systems,” National Research Council of Canada, Ottawa, Ontario, Internal Report No. 736, 1997.
CHAPTER 4
Madrzykowski, D., “Society of Fire Protection Engineers’ Evaluation of DETACT-QS,” Proceedings of the 14th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, May 28–June 3, 1998, Tsukuba, Japan, 1998, pp. 65–69. Matsuyama, K., Wakamatsu, T., and Harada, K., “Systematic Experiments of Room and Corridor Filling for Use in Calibration of Zone and CFD Fire Models,” Proceedings of the 15th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, March 1–7, 2000, San Antonio, TX, National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6588, 2000, Vol. 2, pp. 321–327. McCormick, P., “Future Trends in Fire Modeling,” American Fire Journal, Vol. 53, No. 3, 2000, pp. 16–17. Miles, S. D., Kumar, S., and Cox, G., “Comparisons of ‘Blind Predictions’ of a CFD Model with Experimental Data,” Proceedings of 6th International Symposium, Fire Safety Science, International Association for Fire Safety Science (IAFSS), July 5–9, 1999, Poitiers, France, Intl. Assoc. for Fire Safety Science, Boston, MA, 2000, pp. 543–554. Mitler, H. E., “Input Data for Fire Modeling,” Proceedings of the 13th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, March 13–20, 1996, Gaithersburg, MD, National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6030, Vol. 1, 1997, pp. 187–199. Newman, D. G., Rhodes, N., and Locke, H. A., “Simulation versus Code Methods for Predicting Airport Evacuation,” Proceedings of 1st International Symposium, Human Behavior in Fire, August 31–September 2, 1998, Belfast, UK, Textflow Ltd., UK, 1998, pp. 519–528. Pagni, P. J., and Woycheese, J. P., “Modular Model for Post-Earthquake Fire Growth,” Proceedings of the 14th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, May 28–June 3, 1998, Tsukuba, Japan, 1998, pp. 149–156. Peacock, R. D., Reneke, P. A., Bukowski, R. W., and Babrauskas, V., “Defining Flashover for Fire Hazard Calculations,” Fire Safety Journal, Vol. 32, No. 4, 1999, pp. 331–345.
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Peacock, R. D., Reneke, P. A., Davis, W. D., and Jones, W. W., “Quantifying Fire Model Evaluation Using Functional Analysis,” Fire Safety Journal, Vol. 33, 1999, pp. 167–184. Reiss, M. H., and Cappuccio, J. A., “Computer Fire Modeling: A Building Design Tool,” Consulting-Specifying Engineer, Vol. 23, No. 5, 1998, pp. 34–36. Richardson, J. K., Richardson, L. R., Mehaffey, J. R., and Richardson, C. A., “What Users Want Fire Model Developers to Address,” Fire Protection Engineering, No. 6, Spring 2000, pp. 23–25. Robertson, D. C., “Appraisal of Existing Room-Corner Fire Models,” University of Canterbury, Christchurch, New Zealand, Fire Engineering Research Report 97/6, May 1997. Sheppard, D. T., and Meacham, B. J., “Acquisition, Analysis and Reporting of Fire Plume Data for Fire Safety Engineering,” Proceedings of 6th International Symposium, Fire Safety Science, International Association for Fire Safety Science (IAFSS), July 5–9, 1999, Poitiers, France, Intl. Assoc. for Fire Safety Science, Boston, MA, 2000, pp. 195–206. Skocypec, R. D., and Peterson, C. W., “DOE Programs in Fire and Materials,” Proceedings of 41st International SAMPE Symposium and Exhibition, Materials and Process Challenges: Aging Systems, Affordability, Alternative Applications, March 24–28, 1996, Anaheim, CA, Society for the Advancement of Material and Process Engineering (SAMPE), Vol. 41, Book 1, 1996, pp. 361–369. Taylor, S., Galera, E., Patel, M., Petridis, M., Knight, B., and Ewer, J., “SMARTFIRE: An Intelligent Fire Field Model,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 671–680. Walker, A. M., “Uncertainty Analysis of Zone Fire Models,” University of Canterbury, Christchurch, New Zealand, Fire Engineering Research Report 97/8, May 1997. Wang, Z., Jia, F., Gelea, E. R., Patel, M. K., and Ewer, J., “Simulating One of the CIB W14 Round Robin Test Cases Using the SMARTFIRE Fire Field Models,” University of Greenwich, London, UK, Paper No. 00/IM/53, Jan. 2000. Yung, D., and Hadjisophocleous, G. V., “Cost-Effective Fire Safety Designs for Highrise Office Buildings,” Proceedings of the ’98 International Symposium, Fire Protection of High-Rise Buildings, November 3–6, 1998, Shanghai, China, 1998, pp. 164–170.
CHAPTER 5
SECTION 3
Deterministic Computer Fire Models
C
omputer models are simply computer programs that model or simulate a process or phenomenon. Computer models have been used for some time in the design and analysis of fire protection hardware. The use of computer models, commonly known as design programs, has become the industry’s standard method for designing water supply and automatic sprinkler systems. These programs perform large numbers of tedious and lengthy calculations and provide the user with accurate, cost-optimized designs in a fraction of the time required for manual procedures. In addition to the design of fire protection hardware, computer models may be used to evaluate the effects of fire on people and property. These computer fire models can provide a faster and more accurate estimate of the impact of a fire and the measures used to prevent or control the fire than many of the methods previously used. Although manual calculation methods provide good estimates of specific fire effects (e.g., prediction of time to flashover), they are not well suited for comprehensive analyses involving the time-dependent interactions of multiple physical and chemical processes present in developing fires. In recent years, increasing attention has been given to the development and use of computer fire models. They have been used by engineers and architects for building design, building officials for plan review, the fire service for prefire planning, investigators for postfire analysis, groups writing fire codes, materials manufacturers, fire researchers, and educators. Although these models are not a replacement for building and fire codes, they still can be valuable tools for the fire professional. The state of the art in computer fire modeling is changing rapidly. Understanding of the processes involved in fire growth is improving, and thus the technical basis for the models is improving. The capabilities, documentation, and support for a given model can change dramatically over a short period of time. In addition, computer technology itself (both software and hardware) is advancing rapidly. In the past, a large mainframe computer was required to use most of the computer fire models.
William D. Walton, P.E., is a research fire protection engineer in the Building and Fire Research Laboratory of the U.S. National Institute of Standards and Technology, Gaithersburg, Maryland. Douglas J. Carpenter is a vice president and principal engineer with Combustion Science & Engineering, Inc., based in Columbia, Maryland. Christopher B. Wood is the leader of the Fire Science and Forensic Services Group of Arup, based in Westborough, Massachusetts.
William D. Walton Douglas J. Carpenter Christopher B. Wood
Today, almost all of the models can be run on personal computers. Therefore, rather than providing an exhaustive discussion of rapidly changing state-of-the-art available computer models, the following discussion will focus on a representative selection. The reader should refer to the bibliography at the end of this chapter for in-depth reviews of particular models. In general, computer models for fire hazard prediction can be grouped into two categories: (1) enclosure fire models and (2) special-purpose fire models.
ENCLOSURE FIRE MODELS Major advancements have occurred in the development of computational models structured to predict the interaction of multiple fire processes involving heat transfer, fluid mechanics, and combustion chemistry occurring at the same time in an enclosure. These models provide estimates of particular elements of hazard development such as fire growth, temperature rise, and smoke generation and transport. Some models are able to address multiple rooms. Others are confined to the room of fire origin. Generally, the large number of mathematical expressions to be solved simultaneously in any of these models necessitates the use of a computer. There are two general classes of computer models for analyzing enclosure fire development: (1) probabilistic and (2) deterministic.
Probabilistic Models Probabilistic models treat fire growth as a series of sequential events or states. These models are sometimes referred to as state transition models. Mathematical rules are established to govern the transfer from one event to another (e.g., from ignition to established burning). Probabilities are assigned to each transfer point on the basis of analysis of relevant experimental data and historical fire incident data. These models do not normally make direct use of the physical and chemical equations describing the fire processes.
Deterministic Models In contrast, deterministic models represent the processes encountered in a compartment fire by interrelated mathematical expressions based on physics and chemistry. These models may also be referred to as room fire models, computer fire models, or
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mathematical fire models. Ideally, such models represent the ultimate capability, which means that discrete changes in any physical parameter could be evaluated in terms of the effect on fire hazard. Although the state of the art in understanding fire processes will not yet support the ultimate model, a number of computer models are available that provide reasonable estimates of selected fire effects.1,2
Zone Models The most common and widely used type of physically based compartment fire model in North America is the zone or control volume model, which solves the conservation of mass and energy equations for distinct regions (control volumes). A number of zone models exist, varying to some degree in detailed treatment of fire phenomena. The dominant characteristic of this class of models is that they divide the room(s) into two distinct regions: a hot upper layer and a cool lower layer. Conditions in both layers are assumed to be uniform with a sharp interface between the two. The model calculations provide estimates of key conditions for each of the layers as a function of time.3 Zone models have proved to be a practical method for providing firstorder estimates of fire processes in enclosures.
Computational Fluid Dynamics (CFD) Models The other general type of deterministic model is the computational fluid dynamics (CFD) model. This type of model solves
FIGURE 3.5.1
the fundamental equations of mass, momentum, and energy at each element in a compartment space that has been divided into a grid of small elements. Imagine an enclosure filled with a three-dimensional grid of tiny cubes; a CFD model will calculate the physical conditions in each cube as a function of time. The CFD model program uses an iterative solver to calculate the physical changes in the cube at the current time step, as a result of physical changes in the surrounding cubes from the previous time step. Depending on the size of the cubes, this model permits the user to determine the conditions at almost any point in the compartment. Figure 3.5.1 shows an example of a CFD model prediction for the gas velocity in a compartment fire. The figure shows the cross section of a compartment with the door to the right of center and a fire near the floor to the left. The arrows represent the predicted gas velocity, with the arrows pointing in the direction of gas flow and the speed of the flow indicated by the length of the arrows. The prediction shows air entering the lower level of the compartment to the right, rising in the fire, and flowing under the soffit as it leaves the compartment. In the past, the computational demands and memory requirements of CFD modeling necessitated the use of workstations, minicomputers, or mainframe/supercomputers for use in practical applications. Advances in computer technology over recent years have significantly increased computational speed and available resources. For example, to model an industrial rack storage fire with a commercial CFD model running on an early 1990s generation workstation using approximately 514,000 cells and a time step of 0.2 s required 18 days of
CFD Model Prediction of Gas Velocity in a Compartment Fire
CHAPTER 5
computer time.4 That same computation with today’s generation workstation would require four days of computer time and represents an order of magnitude increase in computational speed. Although in the past, CFD models were intractable for personal computers, the new power and configurations of personal computers are making quick inroads into the area of CFD models. Although these types of problems are still best run on workstations and larger machines, today’s large memory configurations (B500MB RAM), high-speed hard disk drives (10,000 RPMs), and high-speed CPUs (1–2 GHz) available on PCs make tackling CFD models within the realm of solvable problems on this type of machine. In addition, advances in approaches to the numerical methods and available computer software mathematical libraries have greatly increased the efficiency of CFD modeling. Although the combination of improvements in techniques and hardware have greatly reduced the amount of time required to run on PC-sized systems, run times are more often than not on the order of days rather than hours for typical fire-modeling applications. As improvements in the availability of computer fire modeling software and hardware continue, the demand for more detailed fire hazard and fire reconstruction analyses have evolved. CFD models have been used successfully to evaluate a wide range of fire problems, including the well-known effort to simulate the King’s Cross fire.5 Several efforts to validate specific CFD models against limited experimental data have been performed.6–8 An attempt to validate the accuracy of the commonly used k-e turbulence model to predict velocity and temperature CFDs in buoyant flows demonstrated the need to modify significantly the default values of physical constants, such as the turbulent viscosity constant of proportionality and the turbulent Prandtl number, to obtain reasonable agreement with experimental measurements.9 Empirical constants were adjusted for the numerical simulation of thermal plumes and might not be appropriate for other types of turbulent flows associated with fire. These constants should be used with caution and only to model phenomena similar to that of the validation/calibration study used to refine the constants.
■
TABLE 3.5.1 Model Name
Deterministic Computer Fire Models
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Enclosure Zone Fire Models Author(s)
Maintaining Organization
Special Features
ASET
L. Y. Cooper D. W. Stroup
NIST
Single room
ASET-B
W. D. Walton
NIST
Single room
BRI2
K. Harada D. Nii T. Tanaka S. Yamada
Building Research Institute, Japan
Multiroom, mechanical ventilation
CCFM— VENTS
L. Y. Cooper G. P. Forney
NIST
Multiroom, multilevel
UCLA
Single room, developed for nuclear power facilities
COMPBRN N. Siu V. Ho III
COMPF2
V. Babrauskas
NIST
Single room, postflashover
FAST/ CFAST
R. D. Peacock P. A. Reneke W. W. Jones R. W. Bukowski G. P. Forney
NIST
Up to 30 compartments, 30 ducts, and 5 fans
FIRST
H. W. Emmons H. E. Mitler
NIST
Single room, burning item
WPI/FIRE
D. B. Satterfield WPI J. R. Barnett
Single room, ceiling vents
Table 3.5.1 lists a number of zone-type enclosure fire models that are widely used. A more detailed description of each model is also given in this section.
ASET-B. ASET-B is a program for calculating the temperature and position of the hot smoke layer in a single room with closed doors and windows.11 ASET-B is a compact version of ASET designed to run on personal computers. The required program inputs are a heat loss fraction, the height of the fire, the room ceiling height, the room floor area, the maximum time for the simulation, and the rate of heat release of the fire. The program outputs are the temperature and thickness of the hot smoke layer as a function of time. Species concentrations and time to hazard and detection calculated by ASET are not calculated in the compact ASET-B version.
ASET. ASET (Available Safe Egress Time) is a program for calculating the temperature and position of the hot smoke layer in a single room with closed doors and windows.10 ASET can be used to determine the time to the onset of hazardous conditions for both people and property. The required program inputs are the heat loss fractions, the height of the fuel above the floor, criteria for hazard and detection, the room ceiling height, the room floor area, a heat release rate, and a species generation rate of the fire (optional). The program outputs are the temperature, thickness, and (optional) species concentration of the hot smoke layer as a function of time and the time to hazard and detection. ASET can examine multiple cases in a single run.
BRI2. BRI2 is a multiroom, two-zone model for predicting smoke transport, temperature, and layer height.12 The model can consider both natural and mechanical ventilation, including horizontal and vertical flows. BRI2 includes a number of submodel and other refinements. BRI2 performs a balance on the lower layer so that it predicts the lower layer conditions as well as the upper layer. BRI2 uses the depth of smoke layer for vertical vents so that it predicts the extent to which mass is entrained from the lower layer rather than just entraining mass entirely from the hot gas layer. BRI2 also employs a species yield model based on the equivalence ratio. Heat conduction through thermally thin elements provides a source term for development of
Overview of Selected Zone Models
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a convected hot layer in an adjoining compartment without hot gas flow. CCFM (Version VENTS). CCFM (Consolidated Compartment Fire Model) (version VENTS) is a two-layer zone-type compartment fire model computer code.13–16 It simulates conditions caused by user-specified fires in a multiroom, multilevel facility. The required inputs are a description of room geometry and vent characteristics (up to nine rooms and 20 vents), initial state of the inside and outside environments, fire energy release rates as functions of time (up to 20 fires), and a user-specified heat loss fraction. If simulation of concentrations of products of combustion is desired, then product release rates must also be specified (up to three products). Vents can be simple openings between adjacent spaces (natural vents) or fan/duct-forced ventilation systems between arbitrary pairs of spaces (forced vents). For forced vents, flow rates and direction can be user-specified or included in the simulation by accounting for user-specified fan and duct characteristics. Wind and stack effects can be taken into account. The program outputs for each room are pressure at the floor, layer interface height, upper/lower layer temperature, and (optionally) product concentrations. CCFM (version VENTS) is supported by four-part documentation. COMPBRN III. COMPBRN III has been generally used in conjunction with probabilistic analysis for the assessment of risk in the nuclear power industry.17 The model is based on the assumption of a relatively small fire in a large space or fire involving large fuel loads early during the preflashover fire growth period. The model’s emphasis is on the thermal response of elements within the enclosure to a fire within the enclosure and on modeling simplicity. The temperature profile within each element is computed, and an element is considered ignited or damaged when its surface temperature exceeds the user-specified ignition or damage temperature. The model outputs include the total heat release rate of the fire, the temperature and depth of the hot gas layer, the mass burning rate for individual fuel elements, the surface temperatures, and the heat flux at user-specified locations. COMPF2. COMPF2 is a computer program for calculating the characteristics of a post-flashover fire in a single building compartment, based on fire-induced ventilation through a single door or window.18 It is intended both for performing design calculations and for the analysis of experimental burn data. Wood, thermoplastic, and liquid fuels can be treated. A comprehensive output format is provided that gives gas temperatures, heat flow terms, and flow variables. The documentation includes input instructions, sample problems, and a listing of the program. FAST/CFAST. CFAST (Consolidated Model of Fire Growth and Smoke Transport) is a multiroom fire model that predicts the conditions resulting from a user-specified fire within a structure.19 CFAST version 3.1.6 can accommodate up to 30 compartments with multiple openings between the rooms and to the outside. The required program inputs are the geometrical data describing the rooms and connections; the thermophysical properties of the ceiling, walls, and floors; the fire as a rate of mass
loss; and the generation rates of the products of combustion. The program outputs are the temperature and thickness of, and species concentrations in, the hot upper layer and the cooler lower layer in each compartment. Also given are surface temperatures, heat transfer, and mass flow rates. CFAST has mechanical ventilation capabilities (up to 30 ducts and five fans) and can accommodate up to 30 fires and multiple sprinklers and detectors. FAST provides the data-editing and reporting tools for the CFAST model.20 The distribution software includes graphic and text report generators, a plotting package, and a system for comparing results from multiple simulations. FIRST. FIRST (FIRe Simulation Technique) is the direct descendant of the HARVARD V program developed by Howard Emmons and Henri Mitler.21 The program predicts the development of a fire and the resulting conditions within a room, given a user-specified fire or user-specified ignition. It predicts the heating and possible ignition of up to three targets. The required program inputs are the geometrical data describing the room and openings, and the thermophysical properties of the ceiling, walls, burning fuel, and targets. The generation rate of soot must be specified, and the generation rates of other species may be specified. The fire may be entered either as a user-specified time-dependent mass loss rate or in terms of fundamental properties of the fuel. Among the program outputs are the temperature and thickness of, and species concentrations in, the hot upper layer and also in the cooler, lower layer in the compartment. Also given are surface temperatures, and heat transfer and mass flow rates. WPI/FIRE. WPI/FIRE is a direct descendant of the HARVARD V and FIRST programs.22 It includes all of the features of the HARVARD program, Version 5.3, and many of the features of the FIRST program. WPI/FIRE also includes the following features: improved input routine, momentum-driven flow through ceiling vents, two different ceiling jet models for use in detector activation, forced ventilation for ceiling and floor vents, and an interface to a finite difference computer model for the calculation of boundary surface isotherms and hot spots.
Overview of Selected CFD Models Table 3.5.2 provides a list of available CFD models. Selected models from this list are described in this section. ALOFT-FT. ALOFT-FT (A Large Outdoor Fire plume Trajectory model - Flat Terrain) is a computer-based model to predict the downwind distribution of smoke particulate and combustion products from large outdoor fires.23 It uses a CFD modeling approach that has been optimized to solve the fundamental fluid dynamic equations quickly on a personal computer.24 Program inputs include the fire area (up to five fires), fuel properties, combustion product release rates, wind speed and fluctuation, and atmospheric temperature profile. ALOFTFT contains a built-in, user-modifiable database and correlations to aid in generating data input and automatically compute grid cells and computation parameters associated with the CFD modeling. Program outputs include graphical presentations of
CHAPTER 5
TABLE 3.5.2 Model Name
■
Deterministic Computer Fire Models
3–87
CFD Fire Models Author(s)
Maintaining Organization
Applications and Special Features
ALOFT-FT
W. D. Walton K. B. McGratten
NIST (U.S.)
Smoke plumes from outdoor fires
CFX-4
AEA Technology
AEA Technology
General purpose computational fluid dynamics (CFD) code
FDS
K. McGratten H. Baum R. Rehm A. Hamins G. Forney
NIST (U.S.)
3-D Large Eddy Simulation (LES) model for fires in multicompartments with sprinkler suppression capabilities
FISCO-3L
V. Scheider J. Hoffmann
INTELLEX, FR (Germany) SINTEF (Norway)
Single room treatment of fire development
JASMINE
G. Cox S. Kumar
Fire Research Station (U.K.)
Analysis of smoke movement
KAMELEON FIRE E-3D
B. F. Magnussen
NTH/SINTEF (Norway)
Single room fire growth model for pool fires
KAMELEON II
B. F. Magnussen
NTH/SINTEF (Norway)
Multiroom fire and smoke spread
KOBRA-3D
INTELLEX
INTELLEX (Germany)
3-D CFD model for determining hydrodynamical flow in a single fire compartment
PHOENICS
D. B. Spalding
CHAM, Ltd. (U.K.)
A general-purpose 3-D transient fluid dynamics code
RMFIRE
G. Hadjisophocleous National Research Council of Canada (Canada)
SPLASH
A. J. Gardiner
South Bank Polytechnic (U.K.)
A quasi-CFD model describing the interaction of sprinkler sprays with fire gases
STAR*CD
D. Gossman R. Issa
Computational Dynamics (U.K.)
General-purpose computational fluid dynamics (CFD) code
the plume concentration profiles in the downwind, crosswind, and horizontal planes. CFX-4. CFX-4 (formally known as CFDS-FLOW3D) is a general-purpose computational fluid dynamics (CFD) code. The code includes mesh generation and postprocessing, and is capable of time-dependent or steady-state heat and mass transfer, and twoor three-dimensional coordinate systems. Model features include body-fitted coordinates, moving and adaptive grids, heat transfer in solid regions, porous media approximation, turbulence modeling, compressibility, scalar transport equations, and discrete particle transport. An optional feature is multifluid modeling. Additional information can be obtained from AEA Technology. FDS. The Fire Dynamics Simulator (FDS), Version 1.0.0, allows for “Direct Numerical Simulation” or “Large Eddy Simulations (LES)” of fire.25,26 The LES approach most readily lends itself to solving the types of fire problems typically found in fire engineering design and forensic applications. LES uses a low Mach number approximation for the Navier-Stokes equations. Under the LES mode, the user inputs the parameters of the fire in terms of heat release rate and species generation. The fire is
A 2-D CFD model for transient calculations of smoke movement in a room fire
modeled as Langrangian particles that release heat. FDS calculates the temperature, pressure, species concentrations, and flow field in relation to the prescribed fire. FDS provides for calculating the activation of heat detectors and sprinklers. In addition, the sprinklers can dispense droplets, which yield evaporative cooling and prewetting. The model supports prediction of multiple sprinkler activations. The geometry is rectilinear with description of the overall computational domain. Within the computational domain, sections can be delineated as walls or vents. Heat transfer is treated as one-dimensional and is calculated by using thermally thin or thermally thick elements, but heat is not conducted through wall portions to other parts of the domain. The model also supports heat-activated vents that “open,” allowing flow through the vent. Smokeview27 is the companion software that is designed to visualize the numerical predictions generated by FDS. FISCO-3L. FISCO-3L is a three-dimensional single-room CFD model for unsteady and compressible buoyant heat flow.28 Fire can be simulated under both natural and forced ventilation. An option is available for simulating fire suppression by water sprinklers. The program is menu-driven with a graphical user
3–88 SECTION 3 ■ Information and Analysis for Fire Protection
interface and a real-time system for graphical display of results. The algorithms used to calculate turbulence, flame region effects, and combustion processes are simplified in order to reduce computation demands. The model is copyright restricted. JASMINE. JASMINE uses PHOENICS, a CFD code for computation of fluid motion, and provides full three-dimensional solutions for heat and mass transfer.29 It solves the full partial differential equations describing the conservation of mass, momentum, energy, and species, using a two-equation model for turbulence together with simple radiation models. Primary input requirements include a description of the fire source, the thermal properties of the structure, structure geometry, and ventilation conditions. Use of the code is through the Fire Research Station (U.K.). KAMELEON FIRE E-3D. KAMELEON FIRE E-3D is a three-dimensional CFD model for transient calculation of pool fires in a single enclosure.30 The model can be applied to problems involving multiple natural or forced vents. The fire source is characterized by either a predetermined leakage rate or a pool fire (liquid hydrocarbons only). Turbulence is modeled by k-e, and combustion and soot by eddy dissipation. Radiation is included. SINTEF (Norway) provides modeling services using this model, but the model is not directly available commercially. KAMELEON II. KAMELEON II is an enhanced CFD model that is optimized for vector performance.30 It has a graphical preprocessor that allows the user to generate input simply by making drawings. The postprocessor provides color graphics of any cross section and any variable in the calculation domain. The model predicts the spread of smoke and exhaust gases in complex multienclosure geometries and open configurations. Turbulence is modeled by k-e, and combustion and soot by eddy dissipation. Radiation is also modeled. A key input is the burning rate of the fire to be modeled. SINTEF (Norway) will perform customer calculations, but the code is not available commercially. KOBRA-3D. KOBRA-3D is a three-dimensional CFD model for calculating the unsteady and compressible heat flow in a natural- or forced-ventilated compartment. The development of a fast-converging iteration procedure for solving the hydrodynamic equations allows for effective use on a high-performance personal computer. The fire source can be defined by semiempirical relations or by defining constant or time-dependent heat release rates. Turbulence modeling is not included. The model is embedded in a menu-driven user surface combined with databases for fuel and room geometry input data. On-line graphic displays of temperature and velocity contours are possible. Additional information can be obtained from the developer, INTELLEX (Germany). PHOENICS. PHOENICS is a computational fluid dynamics (CFD) code that includes calculation routines for turbulence effects, heat transfer, chemical reaction, multiphase behavior of fluids, and complex geometries.31 Output displays include perspective views, contour mapping, vector diagrams, and gradi-
ents. Several CFD models developed for fire hazard applications rely on this code to perform the fluid dynamics processes. It is commercially available. RMFIRE. RMFIRE is a two-dimensional CFD model developed for analysis of unsteady smoke movement and heat transfer in a fire compartment.7 The governing equations are solved in boundary-fitted coordinate systems that allow compartments with complex geometries to be evaluated. Inputs include boundary conditions, initial conditions, and the fire heat release rate history. Output includes temperature contours, as well as velocity and pressure values within the compartment. This model will become available at a later date. Currently, NRCC (Canada) will perform the calculations. SPLASH. SPLASH is a quasi-CFD model describing the interaction of sprinkler sprays with fire gases in corridors. Inputs include detailed sprinkler parameters, corridor geometry, and smoke layer characteristics.32 The model provides information on the effects of the spray on the smoke layer conditions, variation in heat transfer and drag to buoyancy ratio in the spray volume, the thermal and physical histories of individual droplets in the spray, and the water delivery pattern on the floor. STAR*CD. STAR*CD is a general-purpose computational fluid dynamics (CFD) code.33 STAR*CD is designed to solve a wide range of flow phenomena, including steady and transient, laminar and turbulent (from a choice of turbulence models), incompressible and compressible, heat transfer (convection, conduction, and radiation), mass transfer and chemical reaction (including combustion), porous media, and multiple fluid streams and multiphase flows.
SPECIAL-PURPOSE MODELS Special-purpose deterministic computer models include computer models designed for special-purpose analyses, such as structural fire resistance, prediction of response time of heat detectors and automatic sprinklers, the design of sprinkler systems, and performance of smoke-control or ventilation systems. These models may require or permit coupling with other special-purpose models or with a more general enclosure fire development model. Table 3.5.3 lists a number of special-purpose deterministic fire models that are widely used. A more detailed description of each model follows Table 3.5.3. ASCOS. ASCOS (Analysis of Smoke COntrol Systems) is a program for steady air-flow analysis of smoke-control systems.34 This program can analyze any smoke control system that produces pressure differences with the intent of limiting smoke movement in building fire situations. The input consists of the outside and building temperatures, a description of the building flow network, and the flows produced by the ventilation or smoke control system. The output consists of the steady-state pressures and flows throughout the building.
CHAPTER 5
TABLE 3.5.3 Model Name
■
Deterministic Computer Fire Models
3–89
Special-Purpose Models Author(s)
Maintaining Organization
Model Type
Applications and Special Features
ASCOS
J. H. Klote
NIST
Smoke control
Steady-state network flow model for smoke control evaluation, no fire condition
BREAK1
A. A. Joshi P. J. Pagni
U. C. Berkeley
Glass breakage
Calculates glass breakage for window exposed to a compartment fire
CONTAMW
W. S. Dols G. N. Walton K. R. Denton
NIST
Smoke management and tenability analysis
Predicts building airflow and contaminant concentration
DETACT-T2
D. W. Stroup
NIST
Thermal device activation
Calculates actuation time for heat detectors and sprinklers, time-squared fires
NIST
Thermal device activation
Calculates actuation time for heat detectors and sprinklers, user-defined fires
Structural heat transfer
Three-dimensional heat transfer through structural assemblies
DETACT-QS D. D. Evans FIRES-T3
U. C. Berkeley R. H. Idling B. Bresler Z. Nizamuddin
JET
W. D. Davis
NIST
Ceiling jet, detector activation
Calculates detector and sprinkler activation with a smoke layer
LAVENT
W. D. Davis L. Y. Cooper
NIST
Thermal device activation
Calculates actuation time for sprinklers and linkactuated vents with draft curtains
BREAK1. BREAK1 (Berkeley algorithm for BREAKing window glass in a compartment fire) is a program that calculates the temperature history of a glass window exposed to userdescribed fire conditions.35 The calculations are stopped when the glass breaks. The inputs required are the glass thermal conductivity, thermal diffusivity, absorption length, breaking stress, Young’s modulus, thermal coefficient of linear expansion, thickness, emissivity, shading thickness, half-width of window, the ambient temperature, numerical parameters and the time histories of flame radiation from the fire, hot layer temperature and emissivity, and heat transfer coefficients. The outputs are temperature history of the glass normal to the glass surface and the window breakage time. CONTAMW. CONTAMW is a multizone indoor air quality and ventilation analysis computer program designed to predict airflows, that is, infiltration, exfiltration, and room-to-room airflows in building systems driven by mechanical means; wind pressures acting on the exterior of the building; and buoyancy effects induced by the indoor and outdoor air temperature difference.36 It can also predict the dispersal of airborne contaminants transported by these airflows and the exposure of occupants to airborne contaminants. Although CONTAMW was developed primarily for indoor air quality purposes, it has been used to analyze the performance of smoke control systems, including stairwell pressurization systems, and to aid in the performance of tenability (occupant safety) analysis.37 Inputs include building geometry, airflow paths, air-handling systems, ducts, contaminant sources and sinks, occupants, weather conditions, wind
pressure profiles, and type of simulation (steady state, transient, and cyclical). Outputs include airflows, pressures, contaminant concentrations, and occupant exposure results. CONTAMPP is the CONTAMW postprocessor designed to simplify the process of analyzing CONTAM simulation results. CONTAMW is an update of the CONTAM96 program. DETACT-T2. DETACT-T2 (DETector ACTuation-Time squared) is a program for calculating the actuation time of thermal devices below unconfined ceilings.38 It can be used to predict the actuation time of fixed-temperature and rate-of-rise heat detectors and of sprinkler heads subject to a user-specified fire that grows as the square of time. DETACT-T2 assumes that the thermal device is located in a relatively large area; that is, only the fire ceiling flow heats the device, and there is no heating from the accumulated hot gases in the room. The required program inputs are the ambient temperature, the response time index (RTI) for the device, the activation and rate-of-rise temperatures of the device, the height of the ceiling above the fuel, the device spacing, and the fire growth rate. The program outputs are the time to device activation and the heat release rate at activation. DETACT-QS. DETACT-QS is a program for calculating the actuation time of thermal devices below unconfined ceilings.39 It can be used to predict the actuation time of fixed-temperature heat detectors and sprinkler heads subject to a user-specified fire. DETACT-QS assumes that the thermal device is located in a relatively large area; that is, there is no accumulated hot gas
3–90 SECTION 3 ■ Information and Analysis for Fire Protection
layer in the room so only the fire ceiling flow heats the detection device. The required program inputs are the height of the ceiling above the fuel, the distance of the thermal device from the axis of the fire, the actuation temperature of the thermal device, the response time index (RTI) for the device, and the rate of heat release of the fire. The program outputs are the ceiling gas temperature at the device location and the device temperature both as a function of time and the time required for device actuation. FIRES-T3. FIRES-T3 (FIre REsponse of Structures—Thermal 3-dimensional version) is a finite-element computer model designed to analyze heat transfer through structural assemblies.40 A wide variety of structural assemblies can be examined with FIRES-T3, including columns, walls, beams, floor/ceiling assemblies, and roof/ceiling assemblies. The structural assembly may be solid or include air cavities. The input requirements include a description of the structural assembly and the fire exposure. The information necessary to describe the column assembly includes geometric factors (dimensions, shape of assembly) and material property values (thermal conductivity, specific heat, and density) as a function of temperature. The fire exposure is characterized in terms of the temperature of the surrounding media and appropriate heat-transfer coefficients. The output is a tabulation of the temperatures within the structural assembly as a function of time. JET. JET is a model for the prediction of detector activation and gas temperature in the presence of a smoke layer.41 JET is a two-zone, single-compartment computer model designed to predict the plume centerline temperature, the ceiling jet temperature, and the ceiling jet velocity produced by a single fire plume. The impact on the upper layer due to the presence of draft curtains, ceiling vents, and thermal losses to the ceiling is included in the model. Ceiling-mounted fusible links and link-actuated ceiling vents can be included in the model calculations. Inputs include the room geometry, ceiling properties, fire properties, forced ventilation, link characteristics (which may be used to open vents or may represent sprinklers or detectors), and vent characteristics. Outputs include plume centerline, layer, link and ceiling jet temperatures, ceiling jet velocity, and link activation times. The zone model JET evolved from the computational platform used for the zone model LAVENT and therefore contains many of the features found in LAVENT. The major differences between JET and LAVENT include the ceiling jet temperature and velocity algorithms, the fusible link algorithm, and the use of a variable radiative fraction as a function of fire size and type. LAVENT. LAVENT (Link-Actuated VENT) is a program developed to simulate the environment and the response of sprinkler links in compartment fires with draft curtains and fusible-link-actuated ceiling vents.42 The model used to calculate the heating of the fusible links includes the effects of the ceiling jet and the upper layer of hot gases beneath the ceiling. The required program inputs are the geometrical data describing the compartment, the thermophysical properties of the ceiling, the fire elevation, the time-dependent energy release rate of the fire, the fire diameter or energy release rate per area of the fire,
the ceiling vent area, the fusible-link response time index (RTI) and fuse temperature, the fusible-link positions along the ceiling, the link assignment to each ceiling vent, and the ambient temperature. A maximum of five ceiling vents and ten fusible links are permitted in the compartment. The program outputs are the temperature, mass and height of the hot upper layer, the temperature of each link, the ceiling jet temperature and velocity at each link, the radial temperature distribution along the interior surface of the ceiling, the radial distribution of the heat flux to the interior and exterior surfaces of the ceiling, the fuse time of each link, and the vent area that has been opened.
COMBINED MODELS A new category of deterministic fire models has emerged that can be called combined models or model suites. The purpose of these combined models is to move beyond calculations of individual phenomena to chained calculation routines that can perform all or many of the calculations required to predict the effect of fire on people or property for a specified scenario. The first of these were FIREFORM43 and HAZARD I.44–46 The combined models contain several models under the control of a single program. The individual models may include fire effects models typically zone models), egress models, active fire protection system activation and effect formulas, formulas for fire effects on people or property, and other engineering calculations. The combined models may include fire models that are available in stand-alone form or fire models that are only available as part of the combined model. Some combined models are themselves components in larger fire risk assessment methods, in which they are combined with scenario probability estimation routines. Table 3.5.4 lists a number of combined deterministic fire models that are widely used. A more detailed description of each model follows Table 3.5.4. ASKFRS. ASKFRS is a collection of fire safety engineering routines.47 The routines include fire heat release rate, flame height, fire plume calculations, plume rise, compartment hot gas layer temperature, flashover, smoke filling time, roof venting calculations, egress, and toxic threat. ASMET. ASMET (Atria Smoke Management Engineering Tools) consists of a set of equations and a zone fire model for analysis of smoke management systems for large spaces, such as atria, shopping malls, arcades, sports arenas, exhibition halls, and airplane hangars.48 Routines calculate the height of the smoke layer during atrium filling from a steady or an unsteady fire, and the atrium filling time for a steady or an unsteady fire. Routines also calculate the plume mass flow rate, centerline temperature, and average temperature with or without a virtual origin correction. ASMET also contains a C language version of the ASET-B program. FIRECALC. FIRECALC was developed from the original FPETOOL and is a collection of fire safety engineering routines.49,50 About half of the routines in FIRECALC are the same as routines found in FPETOOL. FIRECALC also contains rou-
CHAPTER 5
TABLE 3.5.4
■
Deterministic Computer Fire Models
3–91
Combined Models Model Name
Maintaining Organization
Author(s)
Special Features
ASKFRS
R. Chitty G. Cox
FRS
Collection of fire safety engineering routines
ASMET
J. H. Klote
NIST
Collection of routines for smoke management in large spaces
FireCalc
V. O. Shestopal S. J. Grubits
CSIRO
Collection of fire safety engineering routines
FPETOOL
H. E. Nelson S. Deal
NIST
Collection of fire safety engineering routines
HAZARD I
R. D. Peacock W. W. Jones R. W. Bukowski C. L. Forney
NIST
Predicts hazards to building occupants from fire for a defined scenario (includes CFAST, EXITT, and DETACT-QS)
FireWind
V. O. Shestopal
Fire Modeling & Computing, Australia
Collection of fire safety engineering routines
tines for steel beam load-bearing capacities, atrium smoke temperature, plume flow and temperatures, smoldering fires, smoke control with a common plenum, fire resistance time, and thermal radiation. FIRECALC has a one- and two-room hot layer model and a one-room natural ventilation model. FPETOOL. FPETOOL is the descendant of the FIREFORM program.51 It contains a computerized selection of relatively simple engineering equations and models that are useful in estimating the potential fire hazard in buildings. The calculations in FPETOOL are based on established engineering relationships. The FPETOOL package addresses problems related to fire development in buildings and the resulting conditions and response of fire protection systems. The subjects covered include smoke filling in a room, sprinkler/detector activation, smoke flow through (small) openings, temperatures and pressures developed by fires, flashover and fire severity predictions, fire propagation (in special cases), and simple egress estimation. The largest element in FPETOOL is a zone fire model called FIRE SIMULATOR. FIRE SIMULATOR is designed to estimate conditions in both preflashover and postflashover enclosure fires. The inputs include the geometry and material of the enclosure, a description of the initiating fire, and the parameters for sprinklers and detectors being tracked. The outputs include the temperature and volume of the hot smoke layer; the flow of smoke from openings; the response of heat-actuated detection devices, sprinklers and smoke detectors; oxygen, carbon monoxide, and carbon dioxide concentrations in the smoke; and the effects of available oxygen on combustion. FPETOOL also contains a routine to predict the characteristics of a moving smoke wave in a corridor and a routine that predicts smoke conditions developing in a room and the subsequent reduction in human viability resulting from exposure to the conditions. HAZARD I. HAZARD I is a method for predicting the hazards to the occupants of a building from a fire therein.44–46 Within
prescribed limits, HAZARD I allows one to predict the outcome of a fire in a building populated by a representative set of occupants in terms of which people successfully escape and which are killed, including the time, location, and likely cause of death for each. HAZARD I is a set of procedures combining expert judgment and calculations to estimate the consequences of a specified fire. These procedures involve four steps: (1) defining the context, (2) defining the scenario, (3) calculating the hazard, and (4) evaluating the consequences. Steps 1, 2, and 4 are largely judgmental and depend on the expertise of the user. Step 3, which involves use of the extensive HAZARD I software, requires considerable expertise in fire safety practice. The heart of HAZARD I is a sequence of procedures implemented in computer software to calculate the development of hazardous conditions over time, calculate the time needed by building occupants to escape under those conditions, and estimate the resulting loss of life based on assumed occupant behavior and tenability criteria. These calculations are performed for a specified building and set of fire scenarios of concern. HAZARD I consists of a three-volume report and a set of computer disks containing the software necessary to conduct hazard analyses of products used in residential occupancies. The HAZARD I software is used to make detailed predictions of the fire-generated environment within a building; the evacuation process of occupants as they interact with the building, the fire, and each other; and the fate of the occupants as they either successfully escape or are killed. The underlying science—including a detailed presentation of the equations, constants, and assumptions contained in each of the programs—and a set of worked example cases are contained in the Technical Reference Guide. The Software User’s Guide includes detailed instructions on use of the software and an extensively illustrated learning section that walks the user through a worked example. Specific applications depend on the user, but some include material/product performance evaluation, fire reconstruction and litigation, evaluation of code changes or variances, fire department preplanning, and extrapolation of fire test data to additional physical configurations.
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FireWind. FireWind is an update to the previous FireCalc model created for the Commonwealth Scientific and Industrial Research Organization (CSIRO). This collection package of 18 programs runs under Microsoft Windows, including Windows NT. The package includes a one/two-room model, sprinkler activation, evacuation, and heat radiation calculations. The numerical model also includes a “slower-speed” solver for improved convergence. FireWind is licensed software available through Fire Modeling & Computing (Australia); a demonstration version is available on the World Wide Web.
WILDLAND FIRE MODELS Wildland fire models used in the United States began as a series of charts, tables, and formulas that were computerized to speed their use.52 Initially, these were implemented as custom chips for programmable calculators and later as computer programs. These deterministic models are used for prefire planning like other fire models, but unlike other models they are also used real-time during the fire to aid in fire management. Table 3.5.5 lists two wildland fire models, the first of which is widely used and the second of which represents the next generation of programs. A more detailed description of each model is also given in this section. BEHAVE. BEHAVE is a collection of wildland fire behavior modules in an interactive program.53,54 In some cases, output from one of the modules may be used as input to another module. Typical module inputs include fuel description parameters, moisture content, slope, wind speed, temperature, and mode of attack. The modules and their principal output features include CONTAIN—containment time and final fire size; DIRECT—rate of spread, flame height, fireline intensity, and direction of maximum spread; DISPATCH—automatic linking of DIRECT, SIZE, and CONTAIN for containment time and fire size; IGNITE—probability of ignition; MAP—map spread and spotting distance; MOISTURE—fuel level, temperature, wind speed, and relative humidity; MORTALITY—fuel mortality level and crown volume torch; RH—relative humidity; SCORCH—crown scorch height; SITE—rate of spread, flame height, fireline intensity, and direction of maximum spread; SIZE—area, perimeter, width, forward spread distance, and backing spread distance; SLOPE—slope and horizontal distance; and SPOT—maximum spot fire distance.
TABLE 3.5.5 Model Name
Wildland Fire Models Author(s)
Maintaining Organization
Special Features
BEHAVE
P. L. Andrews C. H. Chase
U.S. Forest Service
System of modules for a wide range of wildland fire predictions
FARSITE
M. A. Finney
U.S. Forest Service
GIS Interface
FARSITE. FARSITE (Fire Area Simulator) is a model for simulating the spread and behavior of wildland fires under conditions of heterogeneous terrain, fuels, and weather.55 The model requires the support of a geographic information system (GIS) to generate, manage, and provide data for fuels, elevation, slope, topographic aspect, and canopy cover. Outputs include fire area, fire perimeter, fireline intensity, flame length, rate of spread, heat release per unit area, and time of arrival. FARSITE also includes spotting and crown fire routines. FARSITE simulates fire growth as a spreading elliptical wave. The fire is propagated over a finite time step using many small ellipses at points that define the flame front. The boundary formed by the small ellipses, calculated on the original flame front, becomes the new flame front. FARSITE supports graphical display of the input data and the model calculations.
SUMMARY The development of deterministic fire models is a very active area. The above review is intended to offer the reader a perspective on what is currently available. One should also recognize that the information in this chapter is not exhaustive. Papers listed in the reference section provide additional information on the topic. Before using any fire model, the user should be aware of the assumptions and limitations for that model. The brief descriptions provided in this chapter should not be used as the basis for the selection of a model for a particular application. Further, the range of validity for an individual computer fire model is difficult to determine and is the topic of a significant amount of continuing research. Before using any model, the user should study the comparisons of model predictions with experimental data to aid in determining if the use of the model is appropriate.
BIBLIOGRAPHY References Cited 1. Friedman, R., An International Survey of Computer Models for Fire and Smoke, 2nd ed., Factory Mutual Research Corporation, Norwood, MA, Mar. 1990. 2. Friedman, R., “An International Survey of Computer Models for Fire and Smoke,” Journal of Fire Protection Engineer, Vol. 4, No. 3, 1992, pp. 83–92. 3. Quintiere, J. G., “Compartment Fire Modeling,” SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 1995, pp. 3-125–3-133. 4. Hamer, A., and Beyler, C. L., “Modeling the Activation of DryPipe Sprinklers in High-Rack Storage,” Proceedings of the International Conference on Fire Research and Engineering, Society of Fire Protection Engineers, Boston, MA, 1995, pp. 65–70. 5. Simcox, S., Wilkes, N. S., and Jones, I. P., “Computer Simulation of the Flows of Hot Gases from the Fire at King’s Cross Underground Station,” Fire Safety Journal, Vol. 18, No. 1, 1991, p. 4973. 6. Stroup, D. W., “Using Field Modeling to Simulate Enclosure Fires,” SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 1995, pp. 3-152–3-159. 7. Hadjisophocleous, G. V., and Cacambouras, M., “Computer Modeling of Compartment Fires,” Journal of Fire Protection Engineer, Vol. 5, No. 2, 1993, pp. 39–52.
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8. Mawhinney, R. N., Galea, E. R., Hoffmann, N., and Patel, M. K., “A Critical Comparison of a Phoenics-Based Fire Field Model with Experimental Compartment Fire Data,” Journal of Fire Protection Engineer, Vol. 4, No. 3, 1992, pp. 81–92. 9. Nam, S., and Bill, R. G., “Numerical Simulation of Thermal Plumes,” Fire Safety Journal, Vol. 21, 1993, pp. 231–256. 10. Cooper, L. Y., and Stroup, D. W., “ASET—A Computer Program for Calculating Available Safe Egress Time,” Fire Safety Journal, Vol. 9, 1985, pp. 29–45. 11. Walton, W. D., ASET-B: A Room Fire Program for Personal Computers, NBSIR 85-3144, National Bureau of Standards, Gaithersburg, MD, 1985. 12. Harada, K., Nii, D., Tanaka, T., and Yamada, S., “Revision of Zone Fire Model BRI2 for New Evaluation System,” Fifteenth Meeting of the UJRN Panel on Fire Research and Safety, Sheilda L. Bryner (Ed.), NISTIR 6588, March 1–7, 2000, Vol. 2., p. 381–388. 13. Cooper, L. Y., and Forney, G. P., The Consolidated Compartment Fire Model (CCFM) Computer Code Application CCFM. VENTS—Part I: Physical Basis, NISTIR 4342, National Institute of Standards and Technology, Gaithersburg, MD, July 1990. 14. Cooper, L. Y., and Forney, G. P., The Consolidated Compartment Fire Model (CCFM) Computer Code Application CCFM. VENTS—Part II: Software Reference Guide, NISTIR 4343, National Institute of Standards and Technology, Gaithersburg, MD, July 1990. 15. Cooper, L. Y., and Forney, G. P., The Consolidated Compartment Fire Model (CCFM) Computer Code Application CCFM. VENTS—Part III: Catalog of Algorithms and Subroutines, NISTIR 4344, National Institute of Standards and Technology, Gaithersburg, MD, July 1990. 16. Cooper, L. Y., Forney, G. P., and Moss, W. F., The Consolidated Compartment Fire Model (CCFM) Computer Code Application CCFM. VENTS—Part IV: User Reference Guide, NISTIR 4345, National Institute of Standards and Technology, Gaithersburg, MD, July 1990. 17. Ho, V., Siu, N., and Apostolakis, G., “COMPBRN III—A Fire Hazard Model for Risk Analysis,” Fire Safety Journal, Vol. 13, Nos. 2 and 3, pp. 137–154, 1988. 18. Babrauskas, V., COMPF2—A Program for Calculating PostFlashover Fire Temperatures, NBS TN 991, National Bureau of Standards, Gaithersburg, MD, 1979. 19. Peacock, R. D., Forney, G. P., Reneke, P., Portier, R., and Jones, W. W., CFAST, the Consolidated Model of Fire Growth and Smoke Transport, NIST Tech. Note 1299, National Institute of Standards and Technology, Gaithersburg, MD, Feb. 1993. 20. Peacock, R. D., Reneke, P. A., Jones, W. W., Bukowski, R. W., and Forney, G. P., A User’s Guide for FAST: Engineering Tools for Estimating Fire Growth and Smoke Transport, NIST SP921, National Institute of Standards and Technology, Gaithersburg, MD, October 1997. 21. Mitler, H. E., and Rockett, J. A., User’s Guide to FIRST, a Comprehensive Single-Room Fire Model, CIB W14/88/22, National Bureau of Standards, Gaithersburg, MD, 1987. 22. Satterfield, D. B., and Barnett, J. R., User’s Guide to WPI/FIRE Version 2 (WPI-2)—A Compartment Fire Model, Worcester Polytechnic Institute, Center for Fire Safety Studies, Worcester, MA, 1990. 23. Walton, W. D., and McGrattan, K. B., ALOFT-FT A Large Outdoor Fire Plume Trajectory Model—Flat Terrain, NIST SP924, CD-ROM, National Institute of Standards and Technology, Gaithersburg, MD, 1998. 24. McGrattan, K. B., Trelles, J. J., Baum, H. R., and Rehm, R. G., Smoke Plume Trajectory over Two-Dimensional Terrain, NISTIR 5904, National Institute of Standards and Technology, Gaithersburg, MD, October 1996. 25. McGrattan, K., Baum, H., Rehm, R., Hamins, A., and Forney, G., Fire Dynamics Simulator—Technical Reference Guide, NISTIR 6467, National Institute of Standards and Technology, Gaithersburg, MD, January 2000.
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26. McGrattan, K., and Forney, G., Fire Dynamics Simulator— User’s Manual, NISTIR 6469, National Institute of Standards and Technology, Gaithersburg, MD, January 2000. 27. Forney, G. P., and McGrattan, K. B., User’s Guide for Smokeview Version 1.0: A Tool for Visualizing Fire Dynamics Simulation Data, NISTIR 6513, National Institute of Standards and Technology, Gaithersburg, MD, May 2000. 28. Scheider, V., and Hoffmann, J., Modelluntersuchung von Offshore-Kohlenwasserstaff-Branden Feldmodellierung von Loschversuchen, Intellex, Frankfort am Main, Germany. 29. Cox, G., and Kumar, S., “Field Modeling of Fire in ForcedVentilation Enclosures,” Combustion Science and Technology, Vol. 52, 1987, pp. 7–23. 30. Magnussen, B. F., NTH/SINTEF, Trondheim, Norway, 1990. 31. Markatos, N. C., Malin, M. R., and Cox, G., “Mathematical Modeling of Buoyancy-Induced Smoke Flow in Enclosures,” International Journal of Heat and Mass Transfer, Vol. 25, 1982, pp. 63–75. 32. Gardiner, A. J., “The Mathematical Modeling of the Interaction Between Sprinkler Sprays and the Thermally Buoyant Layers of Gases from Fires” [Ph.D. Thesis], South Bank Polytechnic, London, UK, 1988. 33. Computational Dynamics, “STAR*CD Version 2.2 Methodology—Part 1, Mathematical Modeling,” Computational Dynamics, London, UK, 1993. 34. Klote, J. H., Computer Program for Analysis of Smoke Control Systems, NBSIR 82-2512, National Bureau of Standards, Gaithersburg, MD, 1982. 35. Joshi, A. A., and Pagni, P. J., User’s Guide to BREAK1, The Berkeley Algorithm for Breaking Window Glass in a Compartment Fire, NIST GCR 91-596, National Institute of Standards and Technology, Gaithersburg, MD, October 1991. 36. Dols, W. S., Walton, G. N., and Denton, K. R., CONTANW 1.0 User Manual, Multizone Airflow and Contaminant Transport Analysis Software, NISTIR 6476, National Institute of Standards and Technology, Gaithersburg, MD, June 2000. 37. Klote, J. H., and Milke, J. A., Design of Smoke Management Systems, American Society of Heating, Refrigerating and AirConditioning Engineers, Inc., Atlanta, GA, 1992. 38. Evans, D. D., Stroup, D. W., and Martin, P., Evaluating Thermal Fire Detection Systems (SI Units), NBSSP 713, National Bureau of Standards, Gaithersburg, MD, April 1986, p. 549. 39. Evans, D. D., and Stroup, D. W., “Methods to Calculate the Response Time of Heat and Smoke Detectors Installed Below Large Unobstructed Ceilings,” Fire Technology, Vol. 22, No. 1, 1986, pp. 54–65. 40. Iding, R. H., Nizamuddin, Z., and Bresler, B., FIRES T3—A Computer Program for the Fire Response of Structures— Thermal Three-Dimensional Version, UCB FRG 77-15, University of California, Berkeley, Oct. 1977. 41. Davis, W. D., Zone Fire Model JET: A Model for the Prediction of Detector Activation and Gas Temperature in the Presence of a Smoke Layer, NISTIR 6324, National Institute of Standards and Technology, Gaithersburg, MD, May 1999. 42. Cooper, L. Y., “Estimating the Environment and the Response of Sprinkler Links in Compartment Fires with Draft Curtains and Fusible-Link-Actuated Ceiling Vents Theory,” Fire Safety Journal, Vol. 16, 1990, pp. 137–163. 43. Nelson, H. E., FIREFORM—A Computerized Collection of Convenient Fire Safety Computations, NBSIR 86-3308, National Bureau of Standards, Gaithersburg, MD, 1986. 44. Peacock, R. D., Jones, W. W., Bukowski, R. W., and Forney, C. L., Software User’s Guide for the HAZARD I Fire Hazard Assessment Method, Version 1.1, Volume II, NIST HB-146/II, National Institute of Standards and Technology, Gaithersburg, MD, June 1991. 45. Peacock, R. D., Jones, W. W., Bukowski, R. W., and Forney, C. L., Technical Reference Guide for the HAZARD I Fire Hazard Assessment Method, Version 1.1, Volume I, NIST HB-146/I,
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National Institute of Standards and Technology, Gaithersburg, MD, June 1991. Peacock, R. D., Jones, W. W., Forney, G. P., Portier, R., Reneke, P., Bukowski, R. W., and, Klote, J. H., An Update Guide for HAZARD I, Version 1.2, NISTIR 5410, National Institute of Standards and Technology, Gaithersburg, MD, May 1994. Chitty, R., and Cox, G., ASKFRS: An Interactive Computer Program for Conducting Fire Engineering Estimations, Fire Research Station, Borehamwood, UK, 1988. Klote, J. H., Method of Predicting Smoke Movement in Atria with Application to Smoke Management, NISTIR 5516, National Institute of Standards and Technology, Gaithersburg, MD, Nov. 1994. FIRECALC Version 2.3 User’s Manual, Commonwealth Scientific and Industrial Research Organization, Division of Building Construction and Engineering, Sydney, Australia, 1993. Shestopal, V. O., and Grubits, S. J., “Computer Program for an Uninhibited Smoke Plume and Associated Computer Software,” Fire Technology, Vol. 29, No. 3, 1993, pp. 246–267. Deal, S., Technical Reference Guide for FPETOOL Version 3.2, NISTIR 5486, National Institute of Standards and Technology, Gaithersburg, MD, August 1994. Rothermel, R. C., How to Predict the Spread and Intensity of Forest and Range Fires, INT 143, U.S. Forest Service, U.S. Department of Agriculture, Forest Service, Washington, DC, June 1983. Andrews, P. L., BEHAVE: Fire Behavior Prediction and Fuel Modeling System—BURN Subsystem, Part 1, General Technical Report INT-194, Ogden, UT, U.S. Department of Agriculture, Forest Service, Intermountain Research Station, 1986, p. 130. Andrews, P. L., and Chase, C. H., BEHAVE: Fire Behavior Prediction and Fuel Modeling System—BURN Subsystem, Part 2, General Technical Report INT-260, U.S. Department of Agriculture, Forest Service, Intermountain Research Station, Ogden, UT, 1989, p. 93. Finney, M. A., FARSITE Users’ Guide and Technical Documentation, Systems for Environmental Management, Missoula, MT, 1995.
Additional Readings Alpert, R. L., “Improvement of the FSG Fire Spread Computer Model Through Use of Data from Large-Scale Experiments in Japan and Canada,” U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, 12th Joint Panel Meeting, October 27–November 2, 1992, Tsukuba, Japan, Building Research Inst., Ibaraki, Japan, 1994, pp. 14–15. Babrauskas, V., “Fire Modeling Tools for FSE: Are They Good Enough?” Journal of Fire Protection Engineering, Vol. 8, No. 2, 1996, pp. 87–96. Bailey, J. L., Jones, W. W., Tatem, P. A., and Forney, G. P., “Development of an Algorithm to Predict Vertical Heat Transfer through Ceiling/Floor Conduction,” Fire Technology, Vol. 34, No. 2, 1998, pp. 139–155. Barbu, G., “Fires in Railway Passenger Vehicles: The Feasibility of Computer Simulation,” European Railway Review, 1999, pp. 71–75. Beard, A., “Evaluation of Fire Models—Report 1, ASET: Qualitative Assessment; Report 2, ASKFRS: Qualitative Assessment; Report 3, HAZARD I: Qualitative Assessment; Report 4, FIRST: Qualitative Assessment; Report 5, JASMINE: Qualitative Assessment; Report 6, ASET: Quantitative Assessment; Report 8, HAZARD I: Quantitative Assessment; Report 9, FIRST: Quantitative Assessment; Report 6, JASMINE: Quantitative Assessment; Report 11, Overview; Unit of Fire Safety Engineering, University of Edinburgh, UK, 1990. Beard, A. N., “Fire Models and Design,” Fire Safety Journal, Vol. 28, No. 2, 1997, pp. 117–138. Beard, A., “Limitations of Computer Models,” Fire Safety Journal, Vol. 18, No. 4, 1992, pp. 375–391.
Beard, A. N., “Limitations of Fire Models,” Journal of Applied Fire Science, Vol. 5, No. 3, 1995/1996, pp. 233–243. Birk, D. M., Introduction to Mathematical Fire Modeling, Technomic Publishing Co., Inc., Lancaster, PA, 1991, p. 267. Bishop, S. R., and Drysdale, D. D., “Fires in Compartments: The Phenomenon of Flashover,” Philosophical Transactions: Mathematical, Physical and Engineering Sciences, Series A, Vol. 1748, No. 356, 1999, pp. 2855–2872. Brani, D. M., and Black, W. Z., “Two-Zone Model for a Single-Room Fire,” Fire Safety Journal, Vol. 19, Nos. 2–3, 1992, pp. 189–216. Bressington, P., “Tunnel Vision: Setting the Fire Engineering Scene,” Fire Engineers Journal, Vol. 61, No. 213, 2001, pp. 20–23. Bukowski, R. W., “Review of International Fire Risk Prediction Methods,” U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, 12th Joint Panel Meeting, October 27–November 2, 1992, pp. 232–240. Charters, D. A., Gray, W. A., and McIntosh, A. C., “Computer Model to Assess Fire Hazards in Tunnels (FASIT),” Fire Technology, Vol. 30, No. 1, 1994, pp. 134–154. Chow, W. K., “Approach for Evaluating Fire Zone Models,” Journal of Fire Sciences, Vol. 16, No. 1, 1998, pp. 25–31. Chow, W. K., “Atrium Smoke Filling Process in Shopping Malls of Hong Kong,” Journal of Fire Protection Engineering, Vol. 9, No. 4, 1999, pp. 18–30. Chow, W. K., “Fire Hazard Assessment in a Big Hall with the MultiCell Zone Modelling Concept,” Journal of Fire Sciences, Vol. 15, Jan./Feb. 1997, pp. 14–28. Chow, W. K., “Multi-Cell Concept for Simulating Fires in Big Enclosures Using a Zone Model,” Journal of Fire Science, Vol. 14, No. 3, 1996, pp. 186–198. Chow, W. K., “Possibility of Using a Time Constant in Fire Codes for Smoke Management in Atria,” Journal of Fire Sciences, Vol. 18, No. 2, 2000, pp. 130–150. Chow, W. K., and Li, J., “Simulation on Natural Smoke Filling in Atrium with a Balcony Spill Plume,” Journal of Fire Science, Vol. 19, No. 4, 2001, pp. 258–283. Chow, W. K., “Study of Flashover Using a Single Zone Model,” Journal of Applied Fire Science, Vol. 8, No. 2, 1998/1999, pp. 159–175. Chow, W. K., “Study on the Flashover Criteria for Compartmental Fires,” Journal of Fire Sciences, Vol. 15, No. 2, 1997, pp. 95–107. Collier, P., “Modeling Fire in Large Spaces,” BUILD, Aug./Sept. 1997, pp. 38–39. Collier, P. C. R., “Fire in a Residential Building: Comparisons between Experimental Data and a Fire Zone Model,” Fire Technology, Vol. 32, No. 3, pp. 195–218. Cooper, L. Y., “VENTCF2: An Algorithm and Associated Fortran 77 Subroutine for Calculating Flow through a Horizontal Ceiling/Floor Vent in a Zone-Type Compartment Fire Model,” Fire Safety Journal, Vol. 18, No. 3, 1997, pp. 253–287. Cooper, L. Y., and Franssen, J. M., “Basis for Using Fire Modeling with 1-D Thermal Analyses of Barriers/Partitions to Simulate 2D and 3-D Barrier Partition Structural Performance in Real Fires,” Fire Safety Journal, Vol. 33, No. 2, 1999, pp. 114–128. Davis, W. D., Notarianni, K. A., and Tapper, P. Z., “Algorithm for Estimating the Plume Centerline Temperature and Ceiling Jet Temperature in the Presence of a Hot Upper Layer,” Journal of Fire Protection Engineering, Vol. 10, No. 3, 2000, pp. 23–31. Duong, D. Q., “The Accuracy of Computer Fire Models: Some Comparisons with Experimental Data from Australia,” Fire Safety Journal, Vol. 16, No. 6, 1990, pp. 415–431. Fan, W. C., and Weng, W. G., “Fire modeling: An Effective Study Method of Deterministic Law in Fire Study,” Proceedings of the FORUM 2000 Symposium, Fire Research Development and Application in the 21st Century, Taipei, Taiwan, October 23–24, 2000, organized by Architectural and Building Research Institute (ABRI), MOI, and FORUM for International Cooperation in Fire Research, 2000, pp. 1–18. Fu, Z., and Fan, W., “Zone-Type Model for a Building Fire and its Sensitivity Analysis,” Fire and Materials, Vol. 20, No. 5, 1996, pp. 215–224.
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Fu, Z., and Hadjisophocleous, G., “Two-Zone Fire Growth and Smoke Movement Model for Multi-Compartment Buildings,” Fire Safety Journal, Vol. 34, No. 3, 2000, pp. 257–285. Gautier, B., Pages, O., and Thibert, E., “MAGIC: Global Modelling of Fire into Compartments,” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, Edinburgh, UK, June 29–July 1, 1999, London, UK, Interscience Communications Ltd., 1999, pp. 1217–1222. Hadjisophocleous, G. V., and Cacambouras, M., “Computer Modeling of Compartment Fires,” Journal of Fire Protection Engineering, Vol. 5, No. 2, 1993, pp. 39–52. Hadjisophocleous, G. V., and Fu, Z., “Modeling Smoke Conditions in Large Compartments Equipped with Mechanical Smoke Exhaust Using a Two-Zone Model,” International Journal on Engineering Performance-Based Fire Codes, Vol. 1, No. 3, 1999, pp. 162–167. Hara, T., “Required Performance of CFD Based on Analysis of Smoke Movement Prediction with Zone Model,” Bulletin of Japan Association for Fire Science and Engineering, Vol. 49, No. 2, 1999, pp. 9–21. He, Y., and Beck, V., “Smoke Spread Experiment in a Multi-Story Building and Computer Modeling,” Fire Safety Journal, Vol. 28, No. 2, 1997, pp. 139–164. Hokugo, A., Yung, D., and Hadjisophocleous, G. V., “Experiments to Validate the NRCC Smoke Movement Model for Fire Risk-Cost Assessment,” International Association for Fire Safety Science, Proceedings, 4th International Symposium, July 13–17, 1994, Ottawa, Ontario, Canada, pp. 805–816. Hyde, S. M., and Moss, J. B., “Field Modelling of Carbon Monoxide Production in Fires,” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, Edinburgh, UK, June 29–July 1, 1999, London, UK, Interscience Communications Ltd., 1999, pp. 951–962. Janssens, M. L., “Critical Analysis of the OSU Room Fire Model for Simulating Corner Fires,” American Society for Testing and Materials, Fire and Flammability of Furnishings and Contents of Buildings, ASTM STP 1233, ASTM, Philadelphia, PA, 1992, pp. 169–185. Klote, J. H., “Overview of Atrium Smoke Management,” Fire Protection Engineering, No. 7, Summer 2000, pp. 24–25. Levine, R. S., and Nelson, H. E., “Full-Scale Simulation of a Fatal Fire and Comparison of Results with Two Multiroom Models,” NBSIR 90-4268, National Bureau of Standards, Gaithersburg, MD, 1990. Luo, M., “One Zone or Two Zones in the Room of Fire Origin During Fires? The Effect of the Air-Handling System,” Journal of Fire Sciences, Vol. 15, No, 3, 1997, pp. 240–260. Luo, M., and He, Y., “Verification of Fire Models for Fire Safety System Design,” Journal of Fire Protection Engineering, Vol. 9, No. 2, 1998, pp. 1–13. Luo, M., He, Y., and Beck, V., “Application of Field Model and TwoZone Model to Flashover Fires in a Full-Scale Multi-Room Single Level Building,” Fire Safety Journal, Vol. 29, No. 1, 1997, pp. 1–25. Luo, M., He, Y., and Beck, V., “Comparison of Existing Fire Model Predictions with Experimental Results from Real Fire Scenarios,” Journal of Applied Fire Science, Vol. 6, No. 4, 1996/1997, pp. 357–382. Mathews, M. K., Darydas, D. M., and Delichatsios, M. A., “Performance-Based Approach for Fire Safety Engineering: A Comprehensive Engineering Risk Analysis Methodology, a Computer Model, and a Case Study,” Proceedings of the 5th International Symposium, Fire Safety Science, International Association for Fire Safety Science, Melbourne, Australia, March 3–7, 1997, Y. Hasemi (Ed.), International Society for Fire Safety Science, Boston, MA, 1997, pp. 595–606. Mitler, H. E., “Comparison of Several Compartment Fire Models: An Interim Report,” NBSIR 85-3233, Oct. 1985, National Bureau of Standards, Gaithersburg, MD. Mowrer, F. W., and Gautier, B., “Comparison of Four Zone Models used in Nuclear Safety Studies,” Proceedings of the 8th Interna-
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tional INTERFLAM Conference, INTERFLAM ’99, Edinburgh, Scotland, UK, June 29–July 1, 1999, London, UK, Interscience Communications Ltd., 1999, pp. 1093–1104. Nelson, H. E., “FPETOOL: Fire Protection Engineering Tools for Hazard Estimation,” NISTIR 4380, National Institute of Standards and Technology, Gaithersburg, MD, 1990. Notarianni, K. A., and Davis, W. D., “Use of Computer Models to Predict the Response of Sprinklers and Detectors in Large Spaces,” Society of Fire Protection Engineers and Worcester Polytechnic Institute, Computer Applications in Fire Protection, Proceedings, June 28–29, 1993, Worcester, MA, 1993, pp. 27–33. Nyankina, K., Turan, O. F., He, Y., and Britton, M., “One-Layer Zone Modelling of Fire Suppression: Gas Cooling and Blockage of Flame Spread by Water Sprinklers,” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, Edinburgh, UK, June 29–July 1, 1999, London, UK, Interscience Communications Ltd., 1999, pp. 1081–1092. Peacock, R. D., Jones, W. W., and Bukowski, R. W., “Verification of a Model of Fire and Smoke Transport,” Fire Safety Journal, Vol. 21, No. 2, 1993, pp. 89–129. Peacock, R. D., Reneke, P. A., Davis, W. D., and Jones, W. W., Quantifying Fire Model Evaluation Using Functional Analysis,” Fire Safety Journal, Vol. 33, 1999, pp. 167–184. Pietrzak, L. M., and Dale, J. J., “User’s Guide for the Fire Demand Model: A Physically Based Computer Simulation of the Suppression of Post-Flashover Compartment Fires,” NIST-GCR-92612, National Bureau of Standards, Gaithersburg, MD, 1992. Reneke, P. A., Peatross, M. J., Jones, W. W., Beyler, C. L., and Richards, R., “Comparison of CFAST Predictions to USCG Real-Scale Fire Tests,” Journal of Fire Protection Engineering, Vol. 11, No. 1, 2001, pp. 43–68. Rho, J. S., and Ryou, H. S., “Numerical Study of Atrium Fires Using Deterministic Models,” Fire Safety Journal, Vol. 33, No. 3, 1999, pp. 213–229. Rockett, J. A. “Zone Model Plume Algorithm Performance,” Fire Science and Technology, Vol. 17, Special Issue, 1997, pp. 28–39. Schneider, V., Loffler, S., Steinert, C., and Wilk, E., “Application of the Compartment Fire CFD Model KOBRA-3D in Fire Investigations,” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, Edinburgh, UK, June 29–July 1, 1999, London, UK, Interscience Communications Ltd., 1999, pp. 977–987. Soares, C. G., and Teixeira, A. P., “Probabilistic Modelling of Offshore Fires,” Fire Safety Journal, Vol. 34, No. 1, 2000, pp. 25–45. Tubbs, J. S., and Barnett, J. R., “Modeling the NIST High-Bay Fire Experiment with JASMINE,” National Institute of Standards and Technology, and Society of Fire Protection Engineers, International Conference on Fire Research and Engineering, Proceedings, September 10–15, 1995, Orlando, FL, pp. 383–388. Van Hess, P., “Tuovinen, H., Persson, B., and Geysen, W., “Use of Zone and Fire Models for the Fire Investigation of the Switel Hotel Fire (Antwerp 1994),” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, Edinburgh, UK, June 29–July 1, 1999, London, UK, Interscience Communications Ltd., 1999, pp. 245–256. Wade, C., BRANZFIRE: Engineering Software for Evaluating Hazard of Room Lining Materials,” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, Edinburgh, UK, June 29–July 1, 1999, London, UK, Interscience Communications Ltd., 1999, pp. 1147–1152. Walton, W. D., and Notarianni, K. A., “Comparison of Ceiling Jet Temperatures Measured in an Aircraft Hangar Test Fire with Temperatures Predicted by the DETACT-QS and LAVENT Computer Models,” NISTIR 4947; Jan. 1993. Wang, Y, C., “Effects of Structural Continuity on Fire Resistant Design of Steel Columns in Non-Sway Multi-Story Frames,” Fire Safety Journal, Vol. 28, No. 1, 1997, pp. 101–119. Webb, W. A., “Using FPETOOL to Evaluate Fire Safety of a FourLevel Shopping Mall,” National Institute of Standards and
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Technology and Society of Fire Protection Engineers, International Conference on Fire Research and Engineering, Proceedings, September 10–15, 1995, Orlando, FL, pp. 365–370. Wing, T. T. H., Kowok, W. C., Chung, J. M. Y., and Graham, T. L., Zone Modeling of Tunnel Fire Development,” Fire Engineers Journal, Vol. 58, No. 194, 1998, pp. 11–13. Xi Juan, L., and Hong, X., “Extraction Modes in Performance-Based Design of Smoke Control System in Shopping Malls,” Journal of Applied Fire Science, Vol. 8, No. 2, 1998/1999, pp. 133–146. Yao, J., Fan, W., Kohyu, S., and Daisuke, K., “Verification and Application of Field-Zone-Network Model in Building Fires,” Fire Safety Journal, Vol. 33, No. 1, 1999, pp. 35–44.
Yaping, H., Fernando, A., and Luo, M., “Determination of Interface Height from Measured Parameter Profile in Enclosure Fire Experiments,” Fire Safety Journal, Vol. 31, 1998, pp. 19–38. Yung, D., Hadjisophocleous, G. V., and Proulx, G., “Description of the Probabilistic and Deterministic Modelling used in FIRECAM,” International Journal on Engineering PerformanceBased Fire Codes, Vol. 1, No. 1, 1999, p. 18–26. Ziesler, P. S., and Gunnerson, F. S., “Live Fire Comparisons of the CFAST Code,” National Institute of Standards and Technology and Society of Fire Protection Engineers, International Conference on Fire Research and Engineering, Proceedings, September 10–15, 1995, Orlando, FL, pp. 346–349.
CHAPTER 6
SECTION 3
Probabilistic Fire Models John M. Watts, Jr.
A
s indicated Section 3, Chapter 5 (“Deterministic Computer Fire Models”), several excellent deterministic models have been developed to describe fire behavior. So an accurate picture of fire growth seems possible if the needed data are available and if the initial and boundary conditions are given. However, it is unlikely that the described result is the most probable fire, which is really required for fire risk assessments. This chapter presents information on probabilistic models of fire behavior and other aspects of fire protection. It begins with a brief introduction to probability theory and modeling concepts. It then discusses three basic forms of probabilistic models: (1) networks, (2) statistical models, and (3) simulation. Additional information relating to the material discussed in this chapter can be found in Section 2, Chapter 2 (“Fundamentals of Fire Safe Building Design”); Section 3, Chapter 4 (“Introduction to Fire Modeling”); and Section 3, Chapter 8 (“Fire Risk Analysis”).
PROBABILITY Because it plays such a big part in daily life, most people have some idea of what probability is about. They know it involves weighing the chances, or likelihood, that something or other will take place. They often hear, or make statements, such as, “It is likely a fire will start here”; “We have a better chance of controlling the fire if we can ventilate”; “Sprinklers have a very good probability of success.” Such statements refer to situations in which the outcome is not certain, but in which one has some degree of confidence that the statement will be correct. The theory of probability provides a mathematical framework for such statements. Occurrence of fires, aspects of fighting fires, and sprinkler performance are repetitive operations, repeated often under similar circumstances. The percentage of times a certain outcome occurs, under the same conditions, will always remain approximately unchanged, only rarely deviating significantly from some average figure. It can, therefore, be said that this average figure is a characteristic measure of the given repetitive operaJohn M. Watts, Jr., Ph.D., is director of the Fire Safety Institute, a not-for-profit information, research, and educational corporation located in Middlebury, Vermont. He also serves as editor of NFPA’s quarterly technical journal, Fire Technology.
tion, under prescribed conditions. Knowledge of such measures is very important as it enables us not only to describe the outcome of repetitive operations that have already occurred, but also to predict the outcome in the future.
Probability Defined The term repetitive operation refers to the recurrence of a large number of similar individual operations, such as fires. Of specific interest is a well-defined result of individual operations, such as fire control, and the number of such results in some repetitive operation, such as how many fires are controlled. The percentage, or fractional part, of “successful” outcomes of a repetitive operation is called the probability of this result. It is important to realize that the probability of an event, or result, has meaning only under the precisely defined conditions in which the repetitive operation takes place. Each significant variation of these conditions can cause a change in the probability of the event under consideration. If the repetitive operation is such that event A, a success, is observed on the average a times in n individual operations, then the probability of event A under the given conditions is a/n. It can then be said that the probability of a successful result for any individual operation is the ratio of the number of “successful” results observed to the total number of individual operations constituting the prescribed repetitive operation. Probability of success
Number of outcomes with “successful” result Total number of equally likely outcomes
In reference to fires, it might be sometimes more appropriate to talk about “unsuccessful” results. In the theory of probability, however, it is conventional to refer to the event of interest as a success. There are more sophisticated definitions of probability that vary according to application. A more detailed treatment can be found in the SFPE Handbook of Fire Protections Engineering1 and in basic texts on probability such as References 2 and 3.
Evaluating Probabilities The probability of an event is always a positive number, ranging from zero to one. The number cannot be greater than one because in the fraction above, by which it is defined, the numerator cannot be greater than the denominator. The number of successful operations cannot be greater than the number of
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operations undertaken. Neither the numerator nor the denominator can be negative, so probability cannot be less than zero. Thus, when probability is measured, a “scale” that runs from zero to one is used. If denotes the probability of event A, then there is the requirement:
The larger is, the more often event A occurs; for example, the greater the probability that a sprinkler system controls the fire, the more fires that are successfully suppressed by sprinklers, relative to the number of fires that occur. If the probability of an event is very small, then it occurs rarely. If then the event either never occurs, or it occurs so rarely that, in practice, it is considered to be impossible; for example, the probability that the item first ignited is a reinforced concrete wall. In contrast, if is close to 1, then the fraction by which the probability is expressed has a numerator close to the denominator, and the overwhelming majority of operations are successful. If then event A occurs always or almost always so that, in practice, it can be assumed that its occurrence is certain; for example, in a room containing a functional smoke detector and an alert person, it might be assumed the probability of discovering a fire is 1. If then event A occurs in approximately half of all cases, or successful operations are observed approximately as often as unsuccessful ones. The classic example is a coin toss. If then event A occurs more frequently than it does not occur; for the reverse is true. How small the probability of an event must be before it can be assumed to be impossible depends on how important the event is. If 5 percent of smoke detectors manufactured are not sold due to quality control procedures, 0.05 might appear to be a small number. A manufacturer may be able to accept this cost. If 5 percent of smoke detectors sold are defective, however, 0.05 is a very large number. A manufacturer may find it hard to accept this cost knowing that one out of twenty new installed smoke detectors will not work. In every individual problem, it must be established in advance, based on practical considerations, how small the probability of an event ought to be, so it can be considered to be impossible and of insignificant consequence.
Assigning Probabilities In applications of probability to fire problems, the assignment of measures and the analysis of logical possibilities may, at times, depend on masses of data that are best obtained, analyzed, and interpreted by professional statisticians. At other times, the task depends more on qualitative knowledge and judgment of facts with which the fire protection professional is most familiar, and is therefore the person best qualified to assign measures and analyze logical possibilities. Very often, a combination of objective fact and subjective judgment is the best source of information in assigning probabilities.4 Having a measure for probability is important to be able to deal with situations involving chance or uncertainty. There are many cases when knowing the probabilities of certain events, it is useful to find the probabilities of more complicated ones. It would
be inconvenient to search for a particular method of solution for each new problem of this sort that is encountered. Science tries to form general rules, the knowledge of which would readily permit one to solve mechanically, or almost mechanically, individual problems that are similar to one another. In the area of repetitive phenomena, the science that takes upon itself the formulation of such general rules is called the theory of probability. Probability is a branch of mathematics, and, therefore, involves precise reasoning and uses formulas, tables, diagrams, and so on as its tools.
PROBABILITY MODELS AND MODELING The word model has several different meanings. Even when descriptors are added, such as in the phrase “fire model,” it is not always clear what is meant. As the word model appears more frequently in fire protection literature, it becomes more important that its several meanings are appreciated.
Analytical Models Classifications of models place them into various groups in an effort to avoid confusion over the term. An important distinction exists between exemplary models and analytical models. An exemplary model is a pattern or design, or otherwise serves as an example for imitation, such as a model code. An analytical model is a tool used to study some aspect of the world so as to make a decision about it. Not all models are easily classified. A scale model may be exemplary, or analytical, or neither. An analytical model is a description of some part of the environment formulated in a way to make it convenient for analysis. It is an efficient means of viewing a problem. The model may not describe every characteristic of a situation, but only those features that are deemed important. This may, at times, make it difficult to recognize the “real” world in a model description. For example, the Arabic numerals 1, 2, 3 are more abstract, or unlike what they represent, than their Roman counterparts I, II, III. However, Arabic numerals are much more efficient to use in mathematics.
Mathematical Models Another way to classify models is by whether they are physical or symbolic. Model trains are physical models, as they look like the thing being modeled. Most analytical models are symbolic, using symbols to represent the real world. Thus, a pie chart is a symbolic model of how something is divided up. Flow charts and fault trees are also models that use pictures, or graphic symbols. Mathematical models are also symbolic. They use numbers and other mathematical symbols to represent various parameters, or conditions, that influence a situation. Einstein’s theory of relativity, is a mathematical model of the relationship between energy and mass in the universe.
Dealing with Uncertainty Depending on how mathematical models deal with uncertainty, they may be either deterministic or probabilistic. If, for a specific set of input values, there is a uniquely determined output,
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the model is deterministic. Such models have fixed values for the input variables, and, therefore, have fixed outputs. On the other hand, a model dealing explicitly with the uncertainty inherent in fire is a probabilistic model. Fire protection is a discipline in which there is significant uncertainty associated with most decisions. The concept of safety itself is one of uncertainty. There is no such thing as absolute safety; therefore human activity will always, and unavoidably, involve risks. The concept of fire is also uncertain. Unwanted combustion is the least predictable common physical phenomenon. Reliability of manufactured, or fabricated, systems for suppression and confinement is another source of uncertainty. Reliability analysis is itself a concentrated area of study that uses probabilistic models such as fault trees to quantify the timedependent failure of a system (e.g., see Reference 5). Probabilistic models recognize variables as having a degree of randomness, which is usually more accurate than simple deterministic models, and is especially useful when evaluating fire risk, since risk, by definition, includes the uncertainty of loss. Probabilistic models can yield a numeric measure of risk. There are many forms of probabilistic models. Complex models may involve both deterministic and probabilistic components. The remaining sections of this chapter introduce three types of probabilistic models that can be used independently or as part of a more comprehensive fire risk analysis. They are networks, statistical models, and simulation.
NETWORKS A network model is a graphic representation of paths, or routes, by which objects, energy, information, or logic may flow, or move, from one point to another. Network models are useful for minimizing the time or distance of travel from point to point and have many applications in solving complex problems. The connected points in a network are called nodes. The connections themselves are called links, arcs, or branches. The simplest network is two nodes connected by a single link (Figure 3.6.1). A path is a sequence of links connecting two nodes and usually passing through other nodes. In driving from Los Angeles to New York, for instance, one might go through Denver and St. Louis. The cities could be considered nodes, and the roads between them links. Then one path from Los Angeles to New York would consist of the links connecting the intermediate cities. A significant advantage of a graphic model like a network is the qualitative representation of the structure of the problem, or system. Such a diagram functions as a visual aid to help convey an intuitive understanding of the process for obtaining and using probabilities.
Link
Subsequently, the probabilities for each similar outcome can be summed and results obtained that indicate that the fire will be discovered 82 percent of the time—and that it will not be discovered 18 percent of the time. Using this model, it is relatively easy to see the effect of a smoke detector on the discovery of such a fire.
Fault Trees According to Haimes,6 fault tree analysis (FTA) was first conceived in 1961 by H. A. Watson of Bell Telephone Laboratories. The technique was popularized by the Boeing Company in its application to the Minuteman Ballistic Missile Program7 and was subsequently made famous by the Rasmussen report on safety of nuclear power plants.8 FTA uses an event tree-like diagram to describe and analyze the undesired or “top” event, so-called because it is at the top of the diagram, with “branches” of the tree extending downward from it. These branches connect the events or conditions that cause the top event to happen. Relationships of these causative
Fire department called No
Controlled by sprinklers
Network Components
Very large consequence
Yes No
Large consequence
Yes No
Medium consequence
B Yes
Small consequence
Node
FIGURE 3.6.1
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The term tree is used to describe a special type of network in which there is only one path connecting any two nodes. The simplest probability model, and one of the most powerful, is the event tree. An event tree is a model of the sequence of possible states of a system and of corresponding events that lead to those states. Nodes represent events, and the links between them show how one event leads to another. Figure 3.6.2 shows a simple event tree. The event tree proceeds chronologically, left to right, showing events as they occur in time. By assigning probabilities to the outcome of events, an event tree can be used to calculate the probability of the consequences. Figure 3.6.3 is an event tree that represents the likelihood of discovery of a fire caused by a cigarette in an upholstered chair. Three intermediate events that affect discovery are (1) someone home, (2) a responsible person awake, and (3) a functional smoke detector. Probabilities of these events are shown on the tree. For each path, a probability of the final outcome can be calculated. Assuming the events are independent, the probabilities along each path are multiplied. Thus, looking at the uppermost path, the probability of this path is
Fire Node
Probabilistic Fire Models
Event Trees
Extinguished by occupant A
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FIGURE 3.6.2
Event Tree
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Ignition source
Is someone home?
Is a responsible person awake?
Is there a functional smoke detector?
Is fire discovered before leaving chair? Discovered
Functional 0.05
1.00 Not discovered
Awake
0.00 Discovered
0.80 Not functional
0.95 Not discovered
0.95 Home
0.05 Discovered
0.95 Functional
0.83
Not discovered
0.05 Not awake
0.17 Discovered
0.20 Not functional
Cigarette
0.50 Not discovered
0.95
0.50 Discovered Functional 0.05
0.02 Not discovered
Not home
0.98 Discovered
0.05 Not functional 0.95
0.01 Not discovered 0.99
FIGURE 3.6.3
Event Tree for Cigarette Ignition of Upholstered Chair (numbers illustrative only)
events are shown by the connecting lines going through one of two basic “logic gates”: (1) the AND gate and (2) the OR gate. The AND gate shows that a “fault” will occur when all the causative events happen simultaneously. If any single one of a group of events can produce the fault, then they are inputs to an OR gate. Figure 3.6.4 shows a fault tree for fire accidents involving elevator cars stopping at fire-involved floors. The plus and dot symbols used for OR gates and AND gates are standard symbols for these logic operations used in electronic circuit diagrams and Boolean algebra. They are derived from the algebra of probabilities. For example, consider the flip of a coin. If one wants to calculate the probability of a head OR a tail, then add the probability of a head (1/2) to the probability of a tail (1/2), i.e., 1/2 = 1/2 C 1. Thus, the symbol for an OR operation is a plus sign. Now suppose one flips the coin twice and wants to calculate the probability of getting a head AND then a tail. This is found by multiplying probabilities, i.e., 1/2 Ý 1/2 C 1/4, provided the two events are independent. Thus the symbol for an AND gate is a dot signifying multiplication. Some additional examples of these logic gates and their corresponding Venn diagrams are shown in Figures 3.6.5 and 3.6.6. Fault trees are based on setting down a specific failure and examining the systems in a logical, well-organized way to learn what can go wrong to produce the failure. Alternatively, one can consider a desirable top event. A success tree is based on analysis of requirements and alternatives to achieve a specified goal or objective. The NFPA fire safety concepts tree is a success-type tree.9 (See Figures 2.2.1–2.2.3 in Section 2, Chapter 2 of this handbook.) Use of fault tree analysis requires close knowledge of the systems being analyzed. It is often time consuming but, if
thorough, revealing. A fault tree can lead to discovery of combinations of factors that otherwise might not have been recognized as causative of the event being analyzed. The tree also becomes a record of the thought process of the analyst and serves as an excellent visual aid for communication with designers and management. More detailed descriptions of fault trees and analysis can be found in cited References 10 and 11. Network models have been used in a wide variety of fire safety applications, such as those portrayed in References 12 and 13. These model forms and others are explained more fully in textbooks on the subject. (See, for example, References 14 and 15.)
STATISTICAL MODELS The fields of probability and statistics are closely linked. Most statistical concepts, such as sampling and hypothesis testing, have their basis in probability theory. Statistical modeling involves the description of random phenomena by an appropriate probability distribution.
Probability Distributions A probability distribution may be thought of as a mathematical function that defines the probability of an event. For example, the probability distribution that describes the roll of a die is P (x) C 1/6 where x C 1, 2, 3, 4, 5, or 6. All the possible outcomes, one through six, have an equal probability of 1/6. This is called a uniform distribution.
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Probabilistic Fire Models
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Accident occurrence
Presence of fire in elevator lobby
Fuel load
Ignition source
Elevator “called” to fire floor Lack of automatic detection system to prevent elevator response to fire floor
Spread of fire and smoke
Activation of call button of fire floor
Elevator response to occupant of car
Activation due to stimulus of fire effects Control variables: sensitivity adjustment, humidity, oils and foreign substances on the buttons, effect of multiple calls
Fire at a distance
Light exposure (ultraviolet)
Thermal exposure (infrared)
FIGURE 3.6.4
Lack of automatic detection system to prevent the elevator from stopping at a fire-involved floor Elevator stops at fire floor
Elevator response to automatic programming
Elevator response to occupant of the involved floor
Fire impingement
Flame associated phenomenons, ionic radicals, flame flicker frequently
Combustion products (smoke or ion products)
Capacitance effect
Fire Accidents Involving Elevator Cars Stopping at Fire-Involved Floors
AND GATE
OR GATE
A
A
B1
B2
B1
BN
B2
Barriers
Limitation of fire characteristics
B1
B1
B2
BN
BN
Structural integrity
Occupancy
FIGURE 3.6.5 Diagram
Example of OR Logic Gate, with Venn
B2
Thermal resistance
Completeness
Suppression
Construction
BN
FIGURE 3.6.6 Diagram
Example of AND Logic Gate, with Venn
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35 30 25 Number of days
Another example of a uniform distribution is the outcome of a spin of a roulette wheel, which can be modeled mathematically as This equation indicates that the probability of any possible outcome, n (the numbers 1 through 36 plus 0 and 00), is 1/38 or 0.0263158. All models have underlying assumptions. In the roulette model, a perfectly fair wheel was assumed. If one chooses not to accept this assumption, then it becomes necessary to collect a lot of statistical information about the roulette wheel to calculate the individual probability of each outcome.
20 15 10
Poisson Distribution There are many different probability distributions used to describe many different types of random events. An example is shown in the data on fire calls in Table 3.6.1. The first column shows the number of calls that might be received in any one day, and the second column shows the number of days with that many calls. The data are from a four-month period consisting of a total of 443 calls in 123 days.16 Charting the data, as shown in Figure 3.6.7, reveals a trend. The frequency starts out low, increases rapidly, decreases rapidly, and then tails off toward higher numbers of calls. If more data were collected, this trend would be “smoother.” A Poisson distribution can mathematically describe the shape of this trend. The Poisson distribution is widely used to describe random events having a large opportunity to occur, but a small likelihood that any one of these opportunities will actually result in an occurrence. This very accurately fits the description of fire incidents.
Other Distributions
5
0
1 2 3
4
5 6 7 8 9 10 11 12 13 14 15 16 17 Number of calls for service
FIGURE 3.6.7 Distribution of Public Service Calls16 (Source: National Bureau of Standards)
and IQ. It also applies to characteristics such as shoulder width and walking speed to exits. The lognormal distribution is skewed like the Poisson distribution (Figure 3.6.9). It has been shown to describe fire load in offices.17 The exponential distribution has been suggested as a model of fire growth,18 and the extreme value distribution is used to characterize fire loss.19 More sophisticated probabilistic models use principles of the probability theory to combine probability distributions of two or more random variables.20,21
Other probability distributions used to model aspects of fire protection include the familiar normal distribution and the less familiar lognormal distribution. The normal distribution (Figure 3.6.8) finds wide application in describing biological phenomena, such as human height
TABLE 3.6.1 Number of Days Having a Specified Number of Calls for Service16 Number of Calls for Service Per Day (n)
Number of Days Having (n) Public Service Calls
0 1 2 3 4 5 6 7 8 9 10 11
6 8 24 22 31 14 7 8 0 0 1 0
FIGURE 3.6.8
Normal Distribution
0
FIGURE 3.6.9
Lognormal Distribution
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More details of probabilistic modeling can be found in basic texts2,3 and in the SFPE Handbook of Fire Protection Engineering.22
SIMULATION Often, the relevant variables in a decision problem are too numerous, or the interactions too complex, to be handled mathematically. One way to handle such problems is by computer simulation. Simulation models try out different sets of conditions to see how they affect the outcome. This is what happens in a flight simulator when an airplane pilot tries various maneuvers to see which work and which do not without risking life or the loss of an airplane. The operation of an airplane is “simulated” by the electromechanical training device.
Monte Carlo Simulation A computer simulation uses mathematical models to predict the range of outcomes from probabilistic situations. For a roulette wheel, letting the computer select a random number from 1 to 38 would simulate a spin of the wheel. Using the computer, the wheel can be “spun” thousands of times in a fraction of a second. A roulette wheel analogy can be used to describe a computer simulation of fire scenarios. First, the wheel is divided like a pie chart so that a likely ignition source, such as smoking materials, has a big slice covering several numbers and a less likely ignition source, such as spontaneous combustion, has fewer or only one number. Then, spinning the wheel simulates the first part of an ignition sequence, the heat source. Next, a second wheel is divided according to the most common materials first ignited. Spinning the second wheel will complete the ignition simulation. A refinement would be to provide a different second wheel for each heat source, thereby modeling the observed situation that some materials are more likely to be ignited by some heat sources than by others. Subsequent stages of fire growth can also be included in the simulation. Fire development could be represented by a state transition model, a type of model that describes a progression from one defined state to another. In a fire, these “transitions” are determined by parameters, or variables of the fire area, such as flame spread, fire load, ventilation, and so on. Now, more roulette wheels should be added to represent these varying state transitions and to allow the computer to “spin” all these wheels hundreds of times. This is referred to as a Monte Carlo simulation model.
Applications Because of the flexibility of simulation modeling, and the complex nature of fire problems, there is a wide range of applications. One area where simulation is used extensively is in the modeling of building evacuation.23 Computer simulations of emergency egress range from simple travel time models to detailed representations of human decision-making. Other areas of application include fire growth and development,24,25 and emergency response.26,27 Additional information on fire safety applications of computer simulation can be found in Reference 28.
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SUMMARY This chapter presents information on probabilistic models of fire behavior and other aspects of fire protection. It provides a brief introduction to probability theory, including information on evaluating and assigning probability, and then covers modeling concepts, including descriptions of analytical models, mathematical models, and dealing with uncertainty. This chapter concludes with a discussion of three basic forms of probabilistic models: (1) networks, (2) statistical models, and (3) simulation.
BIBLIOGRAPHY References Cited 1. Hall, J. R., Jr., “Probability Concepts,” Section 1, Chapter 11, SFPE Handbook of Fire Protection Engineering, 3rd ed., National Fire Protection Association, Quincy, MA, 2002. 2. Ang, A. H.-S., and Tang, W. H., Probability Concepts in Engineering Planning and Design: Volume 11—Decisions, Risks, and Reliability, John Wiley, New York, 1984. 3. Benjamin, J. R., and Cornell, C. A., Probability, Statistics, and Decision for Civil Engineers, McGraw-Hill, New York, 1970. 4. Noonan, F., and Fitzgerald, R., “On the Role of Subjective Probabilities in Fire Risk Management Studies,” Fire Safety Science: Proceedings of the 3rd International Symposium, G. Cox and B. Langford (Eds.), Elsevier, New York, 1991, pp. 495–504. 5. Modarres, M., and Joglar-Billoch, F., “Reliability,” Section 5, Chapter 3, SFPE Handbook of Fire Protection Engineering, 3rd ed., National Fire Protection Association, Quincy, MA, 2002. 6. Haimes, Y. Y., Risk Modeling, Assessment, and Management, John Wiley, New York, 1998. 7. Rogers, W. P., Introduction to System Safety Engineering, John Wiley, New York, 1971. 8. Reactor Safety Study: An Assessment of Accident Risks in U.S. Commercial Nuclear Power Plants, WASH-1400 (NUREG75/014), U.S. Nuclear Regulatory Commission, Washington, DC, 1975. 9. NFPA 550, Guide to the Fire Safety Concepts Tree, National Fire Protection Association, Quincy, MA, 2002. 10. Vesely, W. E., Goldber, F. F., Roberts, N. H., and Hasl, D. F., Fault Tree Handbook (NUREG-0492), U.S. Nuclear Regulatory Commission, Washington, DC, 1981. 11. Crosetti, P. A., Reliability and Fault Tree Analysis Guide, DOE 76-45/22, U.S. Department of Energy, 1982. 12. Connolly, R. J., and Charters, D. A., “Use of Probabilistic Networks to Evaluate Passive Fire Protection Measures in Hospitals,” Fire Safety Science—Proceedings of the 5th International Symposium, Y. Hasemi (Ed.), International Association for Fire Safety Science, Boston, MA, 1997, pp. 583–593. 13. Ling, W.-C. T., and Williamson, R. B., “The Use of Probabilistic Networks for Analysis of Smoke Spread and the Egress of People in Buildings,” Fire Safety Science—Proceedings of the 1st International Symposium, Hemisphere, New York, 1986, pp. 953–962. 14. Ball, M., Magnanti, T. L., Monma, C., and Nemhauser, G. L., “Network Models,” Handbook of Operations Research and Management Science, Vol. 7, Elsevier, New York, 1995. 15. Ford, L. R., and Fulkerson, D. R., Flows in Networks, Princeton University Press, New Jersey, 1962. 16. Nilsson, E. K., and Swartz, J. A., Jr., Application of Systems Analysis to the Alexandria, Virginia Fire Department, NBS Report 10 454, National Bureau of Standards, Washington DC, Feb. 1972. 17. Watts, J. M., Jr., A Theoretical Rationalization of a GoalOriented Systems Approach to Building Fire Safety, NBS-GCR79-163, National Bureau of Standards, Gaithersburg, MD, Feb. 1979, pp. 70–92.
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18. Ramachandran, G., “Stochastic Model of Fire Growth,” Section 3, Chapter 15, SFPE Handbook of Fire Protection Engineering, 3rd ed., National Fire Protection Association, Quincy, MA, 2002. 19. Ramachandran, G., “Extreme Value Theory,” Section 5, Chapter 8, SFPE Handbook of Fire Protection Engineering, 3rd ed., National Fire Protection Association, Quincy, MA, 2002. 20. Watts, J. M., Jr., “A Probability Model for Fire Safety Tree Elements,” Hazard Prevention, Journal of the Systems Safety Society, Vol. 19, No. 6, 1983, pp. 14–15. 21. Gross, D., “Aspects of Stochastic Modeling for Structural Fire Safety,” Fire Technology, Vol. 19, No. 2, 1983, pp. 103–114. 22. Hall, J. R., Jr., “Statistics,” Section 1, Chapter 12, SFPE Handbook of Fire Protection Engineering, 3rd ed., National Fire Protection Association, Quincy, MA, 2002. 23. Watts, J. M., Jr., “Computer Models for Evacuation Analysis,” Fire Safety Journal, Vol. 12, 1987, pp. 237–245. 24. Berlin, G. N., “A Simulation Model for Assessing Building Fire Safety,” Fire Technology, Vol. 18, No. 1, 1982, pp. 66–76. 25. Fahy, R. F., “Building Fire Simulation Model,” Fire Journal, Vol. 77, No. 4, 1983, pp. 93–95, 102–104. 26. Ignall, E. J., “The Fire Operations Simulation Model,” Chapter 13, Rand Fire Project, Fire Department Deployment Analysis, North Holland, New York, 1979. 27. Simulation (special issue on emergency planning), Society for Computer Simulation, San Diego, CA, Sept. 1989. 28. Phillips, W. G. B., Beller, D. K., and Fahy, R. F. “Computer Simulation for Fire Protection Engineering,” Section 5, Chapter 9, SFPE Handbook of Fire Protection Engineering, 3rd ed., National Fire Protection Association, Quincy, MA, 2001.
Additional Readings Barbagallo, S., Henwood, H., and Moss, T. J., “Case Study: Estimation of Fire Protection System Failure Probability,” Paper B4, The Warren Center for Advanced Engineering, Sydney University, Australia, 1986. Charters, D. A., Barnett, J. R., Shannon, M., Harrod, P., Shea, D., and Morin, K., “Assessment of the Probabilities that Staff and/or Patients Will Detect Fires in Hospitals.” Fire Safety Science— Proceedings of the 5th International Symposium, Y. Hasemi (Ed.), International Association for Fire Safety Science, Boston, MA, 1997, pp. 747–758. Clancy, P., Beck, V. R., and Leicester, R. H., “Time Dependent Probability of Failure of Wood Frames in Real Fire,” Fire and Materials; 4th International Conference and Exhibition. Proceedings, Interscience Communications, London, UK, 1995, pp. 85–94. Elms, D. G., Buchanan, A. H., and Dusing, J. W., “Modeling Fire Spread in Buildings,” Fire Technology, Vol. 20, No. 1, 1984. Hall, J. R., Jr., “How to Tell whether What You Have Is a Fire Risk Analysis Model,” Fire Risk Assessment, ASTM STP 1150, M. M. Hirschler (Ed.), American Society for Testing and Materials, Philadelphia, 1990, pp. 121–135.
Hasofer, A. M., and Beck, V. R., “Probability of Death in the Room of Fire Origin: An Engineering Formula,” Journal of Fire Protection Engineering, Vol. 10, No. 4, 2000, pp 19–26. Hognon, B., and Zini, M., “Probabilistic Approach to the Analysis of Fire Safety in Hotels: MOCASSIN,” Fire Safety Science— Proceedings of the 3rd International Symposium, G. Cox and B. Langford (Eds.), Elsevier, New York, 1991, pp. 505–513. Karydas, D. M., “Probabilistic Methodology for the Fire and Smoke Hazard Analysis of Electronic Equipment,” Interflam’93, C. A. Franks (Ed.), Interscience Communications, London, UK, 1993, pp. 509–517. Kazarians, M., and Apostolakis, G. E., “Some Probabilistic Aspects of Fires,” American Nuclear Society Transactions, Vol. 27, 1977, pp. 636–637. Naveda, O. A., Durbetaki, P., and Wulff, W., “Probability of Fabric Ignition under Given Exposure,” Fire Safety of Combustible Materials International Symposium, University of Edinburgh, 1975, pp. 325–332. Pape, R., and Waterman, T., “Semistochastic Approach to Predicting the Development of a Fire in a Room from Ignition to Flashover,” NBS GCR 77–112, National Bureau of Standards, Gaithersburg, MD, August 1976. Platt, D. G., Elms, D. G., and Buchanan, A. H., “Probabilistic Model of Fire Spread with Timber Effects,” Fire Safety Journal, Vol. 22, No. 2, 1994, pp. 367–398. Ramachandran, G., “Non-Deterministic Modelling of Fire Spread,” Journal of Fire Protection Engineering, Vol. 3, No. 2, 1991, pp. 37–48. Ramachandran, G., “Probability-Based Building Design for Fire Safety, Part 1,” Fire Technology, Vol. 31, No. 3, 1995, pp. 265–275. Ramachandran, G., “Probability-Based Building Design for Fire Safety, Part 2,” Fire Technology, Vol. 31, No. 4, 1995, pp. 355–368. Ramachandran, G., “Stochastic Modelling of Fire Growth,” Fire Safety Science and Engineering, ASTM STP 882, T. Z. Harmathy (Ed.), American Society for Testing and Materials, Philadelphia, 1984, pp. 122–144. Ramachandran, G., “Trade-Offs between Fire Safety Measures: Probabilistic Evaluation,” Fire Surveyor, Vol. 19, No. 2, 1990, pp. 4–13. Ramachandran, G., “Probabilistic Approach to Fire Risk Evaluation,” Fire Technology, Vol. 24, No. 4, 1988, pp. 204–226. Ramachandran, G., “Probability-Based Fire Safety Code,” Journal of Fire Protection Engineering, Vol. 2, No. 3, 1990, pp. 75–91. Rutsein, R., and Clarke, M. B. J., “Probability of Fire in Different Sectors of Industry,” Fire Surveyor, Vol. 8, No. 1, 1979, pp. 20–23. Watts, J. M., Jr., “Dealing with Uncertainty: Some Applications in Fire Protection Engineering,” Fire Safety Journal, Vol. 11, 1986, pp. 127–134.
CHAPTER 7
SECTION 3
Fire Hazard Analysis Revised by
Richard W. Bukowski
H
istorically, most fire safety regulation has been on the basis of fire hazard analysis, in which such assessments were based on the judgment of “experts.” Today formal, scientifically based fire hazard analysis (FHA) is common and increasingly being required as a means to avert certain outcomes, regardless of their likelihood. This chapter discusses the differences between hazard and risk analysis, the process of performing an FHA, and resources available to assist in this process.
ture itself. It would then be necessary to determine the maximum exposure to heat and combustion products that these items can tolerate before unacceptable damage occurs.
PERFORMING AN FHA Performing an FHA is a fairly straightforward, engineering analysis. The steps include the following: 1. Selecting a target outcome 2. Determining the scenario(s) of concern that could result in that outcome 3. Selecting an appropriate method(s) for prediction 4. Evacuation calculation 5. Analyzing the impact of exposure 6. Examining the uncertainty
HAZARD VERSUS RISK The goal of an FHA is to determine the expected outcome of a specific set of conditions called a scenario. The scenario includes details of the room dimensions, contents, and materials of construction; arrangement of rooms in the building; sources of combustion air; position of doors; numbers, locations, and characteristics of occupants; and any other details that have an effect on the outcome of interest. This outcome determination can be made by expert judgment, by probabilistic methods using data on past incidents, or by deterministic means such as fire models. The trend today is to use models whenever possible, supplemented if necessary by expert judgment. Although probabilistic methods are widely used in risk analysis, they find little direct application in modern hazard analyses. Hazard analysis can be thought of as a component of risk analysis. That is, a risk analysis is a set of hazard analyses that have been weighted by their likelihood of occurrence. The total risk is then the sum of all of the weighted hazard values. In the insurance and industrial sectors, risk assessments generally target monetary losses, since these dictate insurance rates or provide the incentive for expenditures on protection. In the nuclear power industry, probabilistic risk assessment has been the basis for safety regulation. Here they most often examine the risk of a release of radioactive material to the environment, from anything ranging from a leak of contaminated water to a core meltdown. FHAs performed in support of regulatory actions generally look at hazards to life, although other outcomes can be examined as long as the condition can be quantified. For example, in a museum or historical structure, the purpose of an FHA might be to avoid damage to valuable or irreplaceable objects or to the struc-
Selecting a Target Outcome The target outcome that is most often specified is to avoid fatalities of occupants of a building. Another might be to ensure that fire fighters are provided with protected areas from which to fight fires in high-rise buildings. The U.S. Department of Energy (DOE) requires that FHAs be performed for all DOE facilities.1 Their objectives for such FHAs, as stated in DOE 5480.7A, include the following: • Minimizing the potential for the occurrence of fire • No release of radiological or other hazardous material to threaten health, safety, or the environment • An acceptable degree of life safety to be provided for DOE and contractor personnel and no undue hazards to the public from fire • Critical process control or safety systems that are not damaged by fire • Vital programs that are not delayed by fire (mission continuity) and • Property damage that does not exceed acceptable levels ($150 million per incident) In Boston, the Office of the Fire Marshal2 has established a set of objectives for FHAs performed in support of requests for waivers of the prescriptive requirements of the applicable code. These include the following:
Richard W. Bukowski, P.E., FSFPE, is senior research engineer at the NIST Building and Fire Research Laboratory, Gaithersburg, Maryland.
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• Limit the probability of fatalities or major injuries to only those occupants intimate with the fire ignition.
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• Limit the probability of minor injuries to only those in the dwelling unit of origin. • No occupant outside of the dwelling unit of origin should be exposed to the products of combustion in a manner that causes any injury. • Limit the probability of flame damage to the dwelling unit of fire origin (this includes taking into account the possibility of flame extension up the exterior of the building). • Limit the probability of reaching hazardous levels of smoke and toxic gases in the dwelling unit of fire origin before safe egress time is allowed. At no time during the incident should the smoke conditions in any compartment, including the compartment of origin, endanger people in those compartments or prevent egress through those compartments. • Limit the incident to one manageable by the Boston Fire Department without major commitment of resources or excessive danger to fire fighters during all phases of fire department operation, that is, search and rescue, evacuation, and extinguishment.
feel that the resulting losses are not catastrophic or otherwise unacceptably severe. If nothing else, such assumptions can help to identify the factors that mean the difference between an incidental fire and a major disaster so that appropriate backups can be arranged. Scenarios must be translated into design fires for fire growth analysis and occupant assumptions for evacuation calculation.
An insurance company might want to limit the maximum probable loss to that which is the basis for the insurance rate paid by the customer; a manufacturer wants to avoid failures to meet orders resulting in erosion of its customer base; and some businesses must guard their public image of providing safe and comfortable accommodations. Any combination of these outcomes may be selected as appropriate for an FHA, depending on the purposes for which it is being performed.
Growth. The primary importance of the appropriate selection of the design fire’s growth is in obtaining a realistic prediction of detector and sprinkler activation, time to start of evacuation, and time to initial exposure of occupants. In 1972, Heskestad first proposed that for these early times, the assumption that fires grow according to a power law relation works well and is supported by experimental data.4 He suggested fires of the form
Selecting Design Fire(s) Choosing a relevant set of design fires with which to challenge the design is crucial to conducting a valid analysis. The purpose of the design fire is similar to the assumed loading in a structural analysis; that is, to answer the question of whether the design will perform as intended under the assumed challenge. Keeping in mind that the greatest challenge is not necessarily the largest fire (especially in a sprinklered building), it is helpful to think of the design fires in terms of their growth phase, steady-burning phase, and decay phase (Figure 3.7.1).
Q C *t n
Determining the Scenario(s) of Concern where
Q C rate of heat release (kW) * C fire intensity coefficient (kW/sn) t C time (s) n C 1, 2, 3 Later, it was shown that for most flaming fires (except flammable liquids and some others), n C 2, the so-called t-squared growth rate.5 A set of specific t-squared fires labeled slow, medium, and fast, with fire intensity coefficients (*) such that the fires reached 1055 kW (1,000 Btu/s) in 600, 300, and 150 s,
Growth phase of fire
Flashover Temperature rise
Once the outcomes to be avoided are established, the task is to identify any scenarios that may result in these undesirable outcomes. Here, the best guide is experience. Records of past fires, either for the specific building or for similar buildings or class of occupancy, can be of substantial help in identifying conditions leading to the outcome(s) to be avoided. Statistical data from the National Fire Incident Reporting System (NFIRS) on ignition sources, first items ignited, rooms of origin, and the like can provide valuable insight into the important factors contributing to fires in the occupancy of interest. (See also Section 3, Chapter 3, “Use of Fire Incident Data and Statistics.”) Anecdotal accounts of individual incidents are interesting but might not represent the major part of the problem to be analyzed. Murphy’s law (if anything that can go wrong, it will) applies to major fire disasters; that is, all significant fires seem to involve a series of failures that set the stage for the event. Therefore, it is important to examine the consequences of things not going according to plan. In DOE-required FHAs, one part of the analysis is to assume both that automatic systems fail and that the fire department does not respond. This is used to determine a worst-case loss and to establish the real value of these systems. The 2000 edition of NFPA 101®, Life Safety Code®,3 includes a performance-based design option containing a basic set of design fire scenarios. Scenario 8 is a common fire that starts while the fire alarm system and then the sprinkler system (in turn) is rendered ineffective. Given the normal high reliability of these systems, it is not required for the performance objectives to be met fully under these conditions, but the stakeholders should
Fully developed fire Growth Ignition Decay Time
FIGURE 3.7.1
Design Fire Structure
CHAPTER 7
respectively, were proposed for design of fire detection systems.6 Later, these specific growth curves and a fourth called “ultrafast,”7 which reaches 1055 kW in 75 s, gained favor in general fire protection applications. This set of t-squared growth curves is shown in Figure 3.7.2. The slow curve is appropriate for fires involving thick, solid objects (e.g., solid wood table, bedroom dresser, or cabinet). The medium growth curve is typical of solid fuels of lower density (e.g., upholstered furniture and mattresses). Fast fires are thin, combustible items (e.g., paper, cardboard boxes, draperies). Ultrafast fires are some flammable liquids, some older types of upholstered furniture and mattresses, or other highly volatile fuels. In a highly mixed collection of fuels, selecting the medium curve is appropriate as long as no especially flammable item is present. It should also be noted that these t-squared curves represent fire growth starting with a reasonably large, flaming ignition source. With small sources, there is an incubation period before established flaming, which can influence the response of smoke detectors (resulting in an underestimate of time to detection). This can be simulated by adding a slow, linear growth period until the rate of heat release reaches 25 kW. This specific set of fire growth curves has been incorporated into several design methods, such as that for the design of fire detection systems in NFPA 72®, National Fire Alarm Code®, 1999 edition.8 They are also referenced as appropriate design fires in several international methods for performing alternative design analyses in Australia and Japan, and in a product fire risk analysis method published in this country.9 Although in the Australian methodology the selection of growth curve is related to the fuel load (mass of combustible material per unit floor area), this is not justified, since the growth rate is related to the form, arrangement, and type of material and not simply its quantity. Consider 22 lb (10 kg) of wood arranged in a solid cube, as sticks arranged in a crib, and as a layer of sawdust (Figure 3.7.3). These three arrangements would have significantly different growth rates while representing identical fuel loads.
Corrugated cardboard cartons 4.6 m (15 ft) high various contents
Wood pallets 1.5 m (5 ft) high
Cotton/polyester innerspring mattress
Full mail bags 1 m (3 ft) high
Thin plywood wardrobe Methyl alcohol pool
Upholstered Furniture
Solid wood cabinetry
Heat release rate (k/W)
6000 Ultra fast
5000
Slow
Fast
4000
Medium
3000 2000 1000
0
0
200
400
600
800
Time from ignition (s)
FIGURE 3.7.2
Set of T-squared Growth Curves
Solid cube
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Fire Hazard Analysis
Sticks (crib)
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Sawdust
FIGURE 3.7.3 Dependence of Fire Growth on Fuel Form and Arrangements
Steady Burning. Once all of the surface area of the fuel is burning, the heat release rate goes into a steady burning phase. This may be at a subflashover or a postflashover level; the former will be fuel controlled, and the latter will be ventilation controlled. It should be obvious from the model output (for oxygen concentration or upper layer temperature) in which condition the fire is burning. Most fires of interest will be ventilation controlled; this is a distinct advantage, since it is easier to specify sources of air than details of the fuel items. This makes the prediction relatively insensitive to both fuel characteristics and quantity, since adding or reducing fuel simply makes the outside flame larger or smaller. Thus for ventilation-controlled situations, (1) the heat release rate can be specified at a level that results in a flame out the door, and (2) the heat released inside the room will be controlled to the appropriate level by the model’s calculation of available oxygen. If the door flame is outside, it has no effect on conditions in the building; if it is in another room, it will affect that and subsequent rooms. For the much smaller number of fuel-controlled scenarios, values of heat release rate per unit area at a given radiant exposure10 can be found in handbooks and used with an estimate of the total fuel area. Decay. Burning rate declines as the fuel is exhausted. In the absence of experimental data, an engineering approximation specifies this decline as the inverse of the growth curve; this means that fast-growth fuels decay fast and slow-growth fuel decay slowly. It is often assumed that the time at which decay begins is when 20% of the original fuel is left. Although these are assumptions, they are technically reasonable. This decay will proceed even if a sprinkler system is present and activated. A simple assumption is that the fire immediately goes out; but this is not conservative. A recent National Institute of Standards and Technology (NIST) study documents a (conservative) exponential diminution in burning rate under the application of water from a sprinkler (Figure 3.7.4).11 Since the combustion efficiency is affected by the application of water, the use of values of soot and gas yields appropriate for postflashover burning would represent the conservative approach in the absence of experimental data.
Selecting an Appropriate Method(s) for Prediction Fire Models. A survey12 documented 62 models and calculation methods that could be applied to FHA. Thus the need is to
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Fraction of initial HRR
1
0.4 0.3
0.2
0.1 0
200
400
600
800
Time (s) e [-0.0023(t-t act )] Secretarial desk fuel package Office II fuel package Sofa fuel package Workstation II fuel package
FIGURE 3.7.4
Paper cart fuel package Executive desk fuel package Office I fuel package Workstation I fuel package Wood cribs fuel package
Decay Rates for Various Fuels
determine which ones are appropriate to a given situation and which are not. The key to this decision is a thorough understanding of the assumptions and limitations of the individual model or calculation and how these relate to the situation being analyzed. Fire is a dynamic process of interacting physics and chemistry; so predicting what is likely to happen under a given set of circumstances is daunting. The simplest of predictive methods are the (algebraic) equations. Often developed wholly or in part from correlations to experimental data, they represent, at best, estimates with significant uncertainty. Yet under the right circumstances, they have been demonstrated to provide useful results, especially when used to assist in setting up a more complex model. For example, Thomas’s flashover correlation13 and the McCaffrey/Quintiere/Harkleroad upper layer temperature correlation14 are generally held to provide useful engineering estimates of whether flashover occurs and peak compartment temperatures. Where public safety is at stake, it is inappropriate to rely solely on such estimation techniques for the fire development/ smoke-filling calculation. Here, only fire models (or appropriate testing) should be used. Single-room models are appropriate where the conditions of interest are limited to a single, enclosed space. Where the area of interest involves more than one space and especially where the area of interest extends beyond a single floor, multiple-compartment models should be used. This is because the interconnected spaces interact to influence the fire development and flows. Many single-compartment models assume that the lower layer remains at ambient conditions (e.g., ASET).15 Since there is
little mixing between layers in a room (unless there are mechanical systems), these models are appropriate. However, significant mixing can occur in doorways, so multiple-compartment models should allow the lower layer to be contaminated by energy and mass (Figure 3.7.5). The model should include the limitation of burning by available oxygen. This is straightforward to implement (based on the oxygen consumption principle) and is crucial to obtaining an accurate prediction for ventilation-controlled burning. For multiple-compartment models, it is equally important for the model to track unburned fuel and allow it to burn when it encounters sufficient oxygen and temperature. Without these features, the model concentrates the combustion in the room of origin, overpredicting conditions there and underpredicting conditions in other spaces. Heat transfer calculations take up a lot of computer time, so many models take a shortcut. The most common is the use of a constant “heat loss fraction,” which is user-selectable (e.g., ASET or CCFM16). The problem is that heat losses vary significantly during the course of the fire. Thus in smaller rooms or spaces with larger surface-to-volume ratios where heat loss variations are significant, this simplification is a major source of error. In large, open spaces with no walls or walls made of highly insulating materials, the constant heat loss fraction may produce acceptable results, but in most cases, the best approach is to use a model that does proper heat transfer. Another problem can occur in tall spaces, for example, atria. The major source of gas expansion and energy and mass dilution is entrainment of ambient air into the fire plume. It can be argued that in a very tall plume, this entrainment is constrained; but most models do not include this. This can lead to an underestimate of the temperature and smoke density and an overestimate of the layer volume and filling rate—the combination of which may give predictions of egress times available that are either greater or less than the correct value. In the model CFAST,17 this constraint is implemented by stopping entrainment when the plume temperature drops to within 1° (Kelvin) of the temperature just outside the plume, where buoyancy ceases.
Smoke layer mixing at doorway
Tµ,j
Tµ,i Doorjet
Tl,j
Plume
Tl,j
FIGURE 3.7.5 Assumption of Zone Models That Fire Gases Collect in Internally Uniform Layers
CHAPTER 7
Input Data. Even if the model is correct, the results can be seriously in error if the data that are input to the model do not represent the condition being analyzed. Proper specification of the fire is the most critical and is addressed in detail in the subsection on selecting the design fire(s). Next in importance is specifying sources of air supply to the fire, that is, not only open doors or windows, but also cracks behind trim or around closed doors. Most (large) fires of interest quickly become ventilation controlled, making these sources of air crucial to a correct prediction. The most frequent source of errors by novice users of these models is to underestimate the combustion air and to underpredict the burning rate. Two other important items of data are (1) ignition characteristics of secondary fuel items and (2) the heat transfer parameters for ceiling and wall materials. In each case, the FHA should include a listing of all data values used, their source (i.e., what apparatus or test method was employed and what organization ran the test and published the data), and some discussion of the uncertainty of the data and its result on the conclusions. The National Institute of Standards and Technology’s (NIST) Web site contains a section of well-documented data for use in calculations, called Fire on the Web (http://fire.nist.gov). A much larger database, called FASTDATA, is available from NIST on a CD-ROM (see the URL above for information). (See also the subsection entitled “Accounting for Uncertainty” later in this chapter.)
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Models. The process of emergency evacuation of people follows the general concepts of traffic flow. There are a number of models that perform such calculations that may be appropriate for use in certain occupancies. Most of these models do not account for behavior and the interaction of people (providing assistance) during the event. This is appropriate in most public occupancies where people do not know each other. In residential occupancies, family members will interact strongly; and in office occupancies, people who work together on a daily basis would be expected to interact similarly. The literature reports incidents of providing assistance to disabled persons, again especially in office settings.22 If such behavior is expected, it should be included, as it can result in significant delays in evacuating a building. Another situation in which models (e.g., Fahy’s EXIT8923) are preferred to hand calculations is with large populations where congestion in stairways and doorways can cause the flow to back up. However, this can be accounted for in hand calculations as well. Crowded conditions, as well as smoke density, can result in reduced walking speeds.24 A person’s walking speed decreases in dense smoke until he or she moves as if blindfolded (Figure 3.7.6). Care should be exercised in using models relative to how they select the path (usually the shortest path) over which the person travels. Some models are optimization calculations that give the best possible performance. These are inappropriate for a code equivalency determination unless a suitable safety factor was used. 1.5 Irritating smoke Nonirritating smoke
1.0
0.5
Walking speed of blindfolded person
Performing an Evacuation Calculation The prediction of the time needed by the building occupants to evacuate to a safe area is performed next and compared to the time available from the previous steps. Whether the evacuation calculation is done by model or hand calculation, it must account for several crucial factors.
Fire Hazard Analysis
First, unless the occupants see the actual fire, time is required for detection and notification before the evacuation process can begin. Next, unless the information is compelling (again, they see the actual fire), it takes time for people to decide to take action. Finally, the movement begins. All of these factors require time, and that is the critical factor. No matter how the calculation is done, all of the factors must be included in the analysis to obtain a complete picture. Excellent discussion of this topic is found in Pauls’s19 and Bryan’s20 chapters in the SFPE Handbook of Fire Protection Engineering, and in Proulx’s Supplement 4 in the National Fire Alarm Code® Handbook.21
Walking speed (m/s)
Documentation. Only models that are rigorously documented should be allowed in any application involving legal considerations, such as in code enforcement or litigation. It is simply not appropriate to rely on the model developer’s word that the physics is proper. This means that the model should be supplied with a technical reference guide that includes a detailed description of the included physics and chemistry, with proper literature references; a listing of all assumptions and limitations of the model; and estimates of the accuracy of the resulting predictions, based on comparisons to experimental data. Public exposure and review of the exact basis for a model’s calculations, internal constants, and assumptions are necessary for it to have credibility in a regulatory application. ASTM publishes a Standard Guide for Documenting Computer Software for Fire Models, ASTM E1472-92.18 Documentation for any model used in a regulatory application should comply with this guide. Although it may not be necessary for the full source code to be available, the method of implementing key calculations in the code and details of the numerical solver utilized should be included. This documentation should be freely available to any user of the model, and a copy should be supplied with the analysis as an important supporting document.
■
0 0
0.2
0.4
0.6
0.8
1.0
1.2
Extinction coefficient, α (1/m)
FIGURE 3.7.6 Reduced Walking Speeds Resulting from Crowded Conditions and Smoke Density
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Hand Calculations. Evacuation calculations are sometimes simple enough to be done by hand. The most thorough presentation on this subject (and the one that is most often used in alternate design analysis) is that of Nelson and MacLennen.25 Their procedure explicitly includes all of the factors discussed previously, along with suggestions on how to account for each. They also deal with congestion, movement through doors and on stairs, and other related considerations.
The FHA report should include a discussion of uncertainty. This discussion should address the representativeness of the data used and the sensitivity of the results to data and assumptions made. If the sensitivity is not readily apparent, a sensitivity analysis (i.e., varying the data to the limits and seeing whether the conclusions change) should be performed. This is also a good time to justify the appropriateness of the model or calculation method.
Analyzing the Impact of Exposure
Final Review
In most cases, the exposure will be to people, and the methods used to assess the impacts of exposure of people to heat and combustion gases involve the application of combustion toxicology models. The HAZARD I software package contains the only toxicological computer model, called TENAB,26 that is based on research at NIST on lethality to rats27 and by Purser28 on incapacitation of monkeys. These methods can also be applied in hand calculations, utilizing the material by Purser28 and the equations found in Reference 25. TENAB accounts for the variation in exposure to combustion products as people move through a building, by reading the concentrations from the fire model in the occupied space during the time the person is in that space. If the person moves into a space with a lower concentration of carbon monoxide, the accumulated dose actually decreases. Details such as these ensure that the results are reasonable. It is important that these details be observed in hand calculations as well. Assessing the impact of exposure to sensitive equipment is more difficult, since little data exist in the literature on the effects of smoke exposure on such equipment. Of particular importance here is the existence of acid gases in smoke, which are known to be corrosive and especially harmful to electronics. Fuels containing chlorine (e.g., polyvinyl chlorides) have been studied. However, unless the equipment is close to the fire, acid gases, especially HCl, deposit on the walls and lower the concentration to which the equipment may be exposed. CFAST in the HAZARD I package contains a routine that models this process and the associated diminution of HCl concentration.
If a model or calculation produces a result that seems counterintuitive, there is probably something wrong. Cases have been seen in which the model clearly produced a wrong answer (e.g., the temperature predicted approached the surface temperature of the sun), and there have been others in which it initially looked wrong but was not (e.g., a dropping temperature in a space adjacent to a room with a growing fire was caused by cold air from outdoors being drawn in an open door). Conversely, if the result is consistent with logic, sense, and experience, it is probably correct. This is also a good time to consider whether the analysis addressed all of the important scenarios and likely events. Were all the assumptions justified and were uncertainties addressed sufficiently to provide a comfort level similar to that obtained when the plan review shows that all code requirements have been met?
SUMMARY Quantitative fire hazard analysis is becoming the fundamental tool of modern fire safety engineering practice and is the enabling technology for the transition to performance-based codes and standards. (For more information on performance-based codes, see Section 3, Chapter 13, “Performance-Based Codes and Standards for Fire Safety.”) The tools and techniques described in this chapter provide an introduction to this topic and the motivation for fire protection engineers to learn more about the proper application of this technology.
Accounting for Uncertainty Uncertainty accountability refers to dealing with the uncertainty that is inherent in any prediction. In the calculations, this uncertainty is derived from assumptions in the models and from the representativeness of the input data. In evacuation calculations, there is the added variability of any population of real people. In building design and codes, the classic method of treating uncertainty is with safety factors. A sufficient safety factor is applied such that, if all of the uncertainty resulted in error in the same direction, the result would still provide an acceptable solution. In the prediction of fire development/filling time, the intent is to select design fires that provide a worst likely scenario. Thus a safety factor is not needed here, unless assumptions or data are used to which the predicted result is very sensitive. In present practice for the evacuation calculation, a safety factor of 2 is generally recommended to account for unknown variability in a given population.
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7. Stroup, D. W., and Evans, D. D., “Use of Computer Models for Analyzing Thermal Detector Spacing,” Fire Safety Journal, Vol. 14, 1988, pp. 33–45. 8. NFPA 72, National Fire Alarm Code®, 1993. 9. Bukowski, R. W., “A Review of International Fire Risk Prediction Methods, Interflam ’93,” in Fire Safety 6th International Fire Conference, March 30–April 1, 1993, Oxford England, C. A. Franks (Ed.), Interscience Communications, Ltd., London, UK, 1993, pp. 437–466. 10. Standard Test Method for Heat and Visible Smoke Release Rates for Materials and Products Using an Oxygen Consumption Calorimeter, ASTM E1354, American Society for Testing and Materials, West Conshohocken, PA, 1994. 11. Madrzykowski, D., and Vettori, R. L., Sprinkler Fire Suppression Algorithm for the GSA Engineering Fire Assessment System, NISTIR 4833, National Institute of Standards and Technology, Gaithersburg, MD, 1992. 12. Friedman, R., Survey of Computer Models for Fire and Smoke, 2nd ed., Factory Mutual Research Corporation, Norwood, MA, 1991. 13. Thomas, P. H., “Testing Products and Materials for Their Contribution to Flashover in Rooms,” Fire and Materials, Vol. 5, 1981, pp. 103–111. 14. McCaffrey, B. J., Quintiere, J. G., and Harkeleroad, M. F., “Estimating Room Temperatures and the Likelihood of Flashover Using Fire Testing Data Correlations,” Fire Technology, Vol. 17, 1981, pp. 98–119. 15. Cooper, L. Y., and Stroup, D. W., Calculating Available Safe Egress Time (ASET)—A Computer User’s Guide, NBSIR 822578, National Bureau of Standards, Gaithersburg, MD, 1982. 16. Cooper, L. Y., and Forney, G. P., The Consolidated Compartment Fire Model (CCFM) Computer Code Application CCFM. VENTS—Part 1: Physical Basis, NISTIR 4342, National Institute of Standards and Technology, Gaithersburg, MD, 1990. 17. Peacock, R. D., Forney, G. P., Reneke, P., and Jones, W. W., CFAST, the Consolidated Model of Fire Growth and Smoke Transport, NIST Technical Note 1299, National Institute of Standards and Technology, Gaithersburg, MD, 1993. 18. ASTM E1472, Standard Guide for Documenting Computer Software for Fire Models, American Society for Testing and Materials, West Conshohocken, PA, 1998. 19. Proulx, G., “Movement of People,” in SFPE Handbook of Fire Protection Engineering, 3rd ed., Section 3, Chapter 13, P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 2002. 20. Bryan, J. L., “Behavioral Response to Fire and Smoke,” The SFPE Handbook of Fire Protection Engineering, 3rd ed., Section 3, Chapter 12, P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 2002. 21. Proulx, G., “Supplement 4, Occupant Response to Fire Alarm Signals,” in National Fire Alarm Code® Handbook, M. Bunker and W. Moore (Eds.), National Fire Protection Association, Quincy, MA, 1999. 22. Julliet, E., “Evacuating People with Disabilities,” Fire Engineering, Vol. 146, No. 12, 1993. 23. Fahy, R., “An Evacuation Model for High-Rise Buildings,” in Interflam ’93, Fire Safety 6th International Fire Conference March 30–April 1, 1993, Oxford, England, C. A. Franks (Ed.), Interscience Communications, Ltd., London, UK, 1993, pp. 519–523. 24. Jin, T., “Visibility Through Fire Smoke,” Report of Fire Research Institute of Japan, Vol. 2, No. 33, 1971, pp. 12–18. 25. Nelson, H. E., and MacLennen, H. A., “Emergency Movement,” in SFPE Handbook of Fire Protection Engineering, 3rd ed., Section 3, Chapter 14, P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 2002. 26. Peacock, R. D., Jones, W. W., Bukowski, R. W., and Forney, C. L., Technical Reference Guide for HAZARD I Fire Hazard Assessment Method, Version 1.1, NIST Hb 146, Vol. 2, National In-
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Additional Readings Almond, G., “Commonwealth Games 2002: Public Safety Planning,” Fire Engineers Journal. Vol. 61, No. 211, 2001, pp. 20–23. Anderson, C. P., “Methodology for the Use of HAZARD I in Residential Fire Investigation” [Thesis], Worcester Polytechnic Institute, MA, Dec. 14, 1990. Angulo, R. A., “Crew Development Tips for the Company Officer,” Fire Engineering, Vol. 153, No. 9, 2000, pp. 48–51. Aronstein, J., “Fire Hazard Due to High Resistance Connections,” Consultant, Poughkeepsie, NY, 1990. Babrauskas, V., “Effective Measurement Techniques for Heat, Smoke, and Toxic Fire Gases,” Fire Safety Journal, Vol. 17, No. 1, 1991, pp. 13–26. Babrauskas, V., and Peacock, R. D., “Heat Release Rate: The Single Most Important Variable in Fire Hazard,” Fire Safety Journal, Vol. 18, No. 3, 255–272, 1992. Babrauskas, V., “Toxic Fire Hazards: Control by Limiting Toxic Potency or Control by Limiting Burning Rate?,” Flame Retardants ’94, Sixth International Conference, January 26–27, 1994, London, UK, Interscience Communications Ltd., London, UK, 1994, pp. 239–250. Babrauskas, V., “Toxicity, Fire Hazard and Upholstered Furniture,” Third European Conference on Furniture Flammability (EUCOFF ’92), November 1992, Brussels, Interscience Communications Ltd., London, UK, 1992, pp. 125–133, 1992. Becker, W. H. K., “Assessment of Fire Hazards Related to Exterior Walls and Facades,” First International Conference on Fire and Materials, September 24–25, 1992, Arlington, VA, 1992, pp. 13–19. Bjorkman, J., and Keski-Rahkonen, O., “Fire Safety Risk Analysis of a Community Center,” Journal of Fire Sciences, Vol. 14, No. 5, 1996, pp. 346–352. Boyt, A., “Saunas: Is There a Fire Hazard?,” Fire Prevention, No. 261, July/Aug. 1993, pp. 13–15. Braun, E., et al., “Performance of School Bus Seats: A Fire Hazard Assessment,” Fire Safety Developments and Testing: Toxicity— Heat Release—Product Development—Combustion Corrosivity, Oct. 21–24, 1990, Ponte Vedra Beach, FL, Fire Retardant Chemicals Assoc., Lancaster, PA, 1990, pp. 105–125. Brown, J. R., Fawell, P. D., and Mathys, Z., “Fire-Hazard Assessment of Extended-Chain Polyethylene and Aramid Composites by Cone Calorimetry,” Fire and Materials, Vol. 18, No. 3, 1994, pp. 167–172. Bukowski, R. W., “Toxic Hazard Evaluating Plenum Cables,” Fire Technology, Vol. 21. No. 4, 1985, pp. 252–266. Bukowski, R. W., “Fire Hazard Prediction: HAZARD I and Its Role in Fire Codes and Standards,” ASTM Standardization News, Vol. 18, No. 1, 1990, pp. 40–43. Bukowski, R. W., “On the Central Role of Fire Calorimetry in Modern Fire Hazard Assessment,” National Institute of Standards and Technology, Gaithersburg, MD, DOT/FAA/CT-95/46, AAR-423; National Institute of Standards and Technology, Fire Calorimetry, Proceedings, July 27–28, 1995, Gaithersburg, MD, 1995. Bukowski, R. W., et al., “Technical Reference Guide for the HAZARD I Fire Hazard Assessment Method. Version 1.1. Volume 2,” National Institute of Standards and Technology, Gaithersburg, MD, NIST Handbook 146/II, June 1991.
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Fire Risk Analysis John R. Hall, Jr.
F
ire risk analysis is the most comprehensive form of analysis that can be applied to any fire safety choice. It looks at all the types of fires that may be affected by the choice, for example, of product, of building design, of anything potentially affecting fire safety, not just one fire or a few selected fires. It provides a flexible framework for estimating the impact of any type of fire safety program or strategy in terms of actual reductions in losses—deaths, injuries, and property damage—and in terms that can be compared to the costs of those programs and strategies. There is no other method as well suited for the analysis of strategic options affecting large numbers of properties and their occupants. Product development, related research and marketing, and regulatory decisions can benefit from fire risk analysis, as can any program to manage and oversee fire safety from a financial point of view.* Fire risk analysis is unusual because the overall framework that it uses is taken not from the hard sciences of physics, chemistry, biochemistry, and engineering, which underlie the rest of fire safety research, but from statistical decision theory, which is based on the fields of economics and operations research. Because fire risk analysis comes from a setting with which much of the fire community may be unfamiliar, this chapter will focus on a discussion of basic concepts, definitions, and approaches.
WHAT IS FIRE RISK ANALYSIS? Risk is very generally defined as a probability distribution function over the space of all possible fire scenarios, together with one or more severity or consequence functions also defined over that space. Summary measures can be defined on these functions and this space, and it is not unusual for one of these summary measures to be given as the definition of “fire risk” of interest. In particular, the two most common summary measures are the expected value of the consequence function and the probability of consequences exceeding a defined threshold of acceptable severity.
*Much of the material in this chapter was first developed for an inhouse concept paper at the National Bureau of Standards, Center for Fire Research (NBS/CFR). The author expresses his appreciation for the valuable support accorded this work by NBS/CFR. John R. Hall, Ph.D., is NFPA’s assistant vice president for fire analysis and research.
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W o r l d v i e w FIRE RISK ANALYSIS METHODS AROUND THE WORLD CESARE-Risk is a probability-weighted hazard analysis modeling package that is probably the most fully developed and documented package in the field of fire risk assessment. It was developed in Australia under a multidisciplinary, multiorganization team headed first by Professor Vaughan Beck of Victoria University of Technology and more recently by Professor Ian Thomas. Significant work has been done on the integrative framework and components of all types, from fire development models to model of human behavior.1,2 Development of CESARE-Risk was done for many years in active collaboration with the National Research Council of Canada, whose team was headed by Dr. David Yung. NRCC’s own modeling package derived from this effort is called FiRECAM (Fire Risk Evaluation and Cost Analysis Model).3,4 Some of the further development, with some significant differences in component models and classes of occupancies chosen for developmental application, has been done under the model name of FIERA, under a team headed by Dr. George Hadjisophocleous. In the United Kingdom, Dr. Jeremy Fraser-Mitchell of the Building Research Establishment has headed development of CRISP, Computation of Risk Indices by Simulation Procedures. The framework for CRISP is classical simulation methodology, which resembles both event tree risk models and probability-weighted hazard analysis but also has some important differences in details and overall feel.5,6 In Sweden, at Lund University, Professor Hakan Frantzich and Sven Erik Magnusson have developed a body of work on fire risk assessment using a single curve for probability vs. severity as the foundation.7,8 The Nuclear Regulatory Commission (NRC) has sponsored some of the best work in the field, but it is highly specialized to the problems of nuclear power plants and may need more work to translate to other settings.9,10 Individual fire risk analyses have appeared in materials prepared as background for regulatory decisions,11 but these also tend to be highly specialized.
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W o r l d v i e w FIRE RISK ANALYSIS METHODS AT NFPA NFPA 550, Guide to the Fire Safety Concepts Tree, 1995 edition, is a widely recognized, broadly generic, unquantified fault tree representation for analysis of a building design. Fault trees do not directly use deterministic calculations at any point. They can use deterministic calculations indirectly, particularly if the tree is constructed so that at many points, either success or failure is nearly certain under the indicated conditions. Fault trees tend to emphasize the relevant reliability probabilities and possibly the ignition probabilities. NFPA’s Building Fire Simulation Method (BFSM) from the late 1970s is among the few fire risk analysis methods designed along the lines of the generic risk analysis models used in all other major fields of risk analysis. State transition models use an event tree structure that estimates a timeline of fire, of the building or product being evaluated, and of the exposures (e.g., people or property), all based on chains of conditional probabilities. Probabilities in the BFSM are derived primarily from fire incident date bases, and consequences of scenarios are also calculated as loss-per-fire rates from historic fire incidents. The Fire Protection Research Foundation’s FRAMEworks (Fire Risk Assessment MEthod) is a fire risk analysis framework approach that uses probability-weighting of several calculations from HAZARD, the modeling package developed by the National Institute of Standards and Technology. It involves thousands to millions of individuals scenarios. It calculates hazard (severity, consequence) for a list of scenarios, weights each one by its probability, and sums the results to produce an expected value of loss. HAZARD provides a fire-effects development model (e.g., a two-zone model), an occupant behavior model (e.g., an evaluation behavior model with a premovement front end), and a model of fire effects on people (e.g., a fractional effective dose model of toxic and heat impact). All three component models are stated as functions of time, which allows them to be combined to produce an estimate of total deaths for each scenario. Even within a primarily deterministic approach to estimating severity, these models need to develop heuristic or judgment-based approaches to calculate consequences for scenarios for which conventional deterministic methods are insufficient (e.g., fire development in concealed spaces, fire effects on victims who are “intimate with ignition”). Documentation on FRAMEworks is limited to an overview, a user’s manual, and specifics on four developmental cases. It does not yet exist in a turnkey version, ready for use. In 2000, NFPA launched a new Technical Committee on fire risk assessment methods. Several of the task groups and publications of the Society of Fire Protection Engineers have addressed or will address guidance on best fire risk assessment methods, and NFPA has supported and will support broad dissemination and use of this guidance.
Because the space of all scenarios is infinite, scenarios must be either grouped or sampled for calculation, and it is not unusual for risk measures to be developed from a very small, or at least manageable, number of scenarios. The more valid approach is to partition the space into a set of exclusive, exhaustive sets of largely homogeneous scenarios so that meaningful probabilities can be calculated on the sets and consequences can be calculated on a single representative scenario from each set. A measure of fire risk therefore always has three parts: (1) a measure of consequence or severity, (2) a probability distribution, and (3) a scenario structure for managing the infinite number of possible fires and conditions that may challenge the product, building, or other object to be analyzed. Specification of the severity measure is not only a matter of deciding what kind of harm—such as deaths, injuries, property damage, or business interruption—is of concern. Sometimes, the most appropriate measure is not a simple count of how much harm is of concern. For example, suppose harm to people is clearly of concern. Are all kinds of injuries of concern or only fatal injuries? Are injuries of concern if they are not discovered until hours or days after the fire? Are injuries of concern if they are never recognized as such, as can be the case for some symptoms of carbon monoxide poisoning? Are all injuries or deadly events of equal concern, regardless of how many people are injured or killed? Or is a count of the number of injuries and deaths more appropriate? Are all injuries relevant, or are people disproportionately, or even exclusively, concerned about injuries in fire that can be attributed to the actions or deficiencies of strangers? Is there any level of user misuse—or of other contributions to ignition or to the degree of harm that followed—that would disqualify the resulting injuries from being counted, or being fully counted, in the severity measure of a risk analysis of a product or building? Or suppose the scale was dollars of damage. A severity measure of the number of dollars of damage would set the stage for a risk analysis on expected loss or average loss, the most common approach. Alternatively, one could set the severity measure equal to 1 if damage exceeded $100,000,000 and 0 otherwise. This would set the stage for a risk analysis focusing on large losses, which might be more useful for an insurance company that worries less about ordinary claims than about a single loss so large that the company cannot cover it. The probability distribution gives a probability for each value the severity measure can take. Most often, a probability distribution is specified first for every type of fire. Then one can derive a probability distribution on the severity measure or simply work with the scenarios. In general, the fire risk analyst will specify a scenario structure, which is a set of classification rules for dividing the range of possible fires into a manageable number of relatively homogenous groups. Then probabilities can be calculated or estimated for each scenario (a group of like fires), and a severity measure can be calculated or estimated for the average fire in each scenario, usually by detailed examination of a typical or representative fire from each scenario. The abstract nature of this explanation so far may lead people to ask a simple question: What good is fire risk analysis? Perhaps the best response is that the practical value of fire risk
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analysis emerges as these general-purpose measures are calculated under specified real or potential conditions. In any fire risk analysis, there will be a certain set of assumptions about key conditions in the environment of interest: some or all of the buildings have sprinklers or detectors, some or all of the mattresses were built to a certain ignition-resistance standard, some or all of the occupants have been regularly trained in fire-safe behavior, and so forth. Fire risk analysis refers to a systematic examination of how measures of fire risk change as the assumptions change. It may be done in conjunction with a parallel examination of changes in costs. On the one hand, if no smoke alarm is present, a household can expect to experience fires with a certain probability, and these fires will have a certain expected severity in terms of deaths, injuries, and property damage. On the other hand, if a smoke alarm is present, the household will pay purchase and maintenance costs that are not paid by the household without smoke alarms, but the smoke alarm household can expect on average to achieve lower severities of losses—and in particular, fewer deaths per fire. Risk analysis is used to quantify the expected size of the reductions in deaths, injuries, and damage. One can then determine whether these risk reductions are great enough to justify the cost. This is an analysis of cost versus risk reduction benefits in which the risk portion is measured explicitly.
WHAT IS AND IS NOT RISK ANALYSIS? Other kinds of analysis are also sometimes labeled “risk analysis.” Three key elements of the fire risk analysis approach are (1) explicit treatment of probability, (2) well-defined measures of severity, and (3) explicit consideration of uncertainty. Some modeling approaches that are called risk analysis omit one or more of these key elements. In particular, the explicit consideration of uncertainty is easily the most difficult step, and the one that is most often given abbreviated treatment in even the better fire risk analyses, but it is essential to sound interpretation of data and separation of meaningful, significant differences from artifacts of statistical “noise.” For example, the term fire risk analysis has sometimes been used to refer to an exercise of listing locations under the jurisdiction of the analyst that present the greatest potential for fire damage or for demand on fire suppression resources. Such an exercise lacks most or all of the key elements of a true fire risk analysis. There is no consideration of probabilities or uncertainty at all, and even the severity measures that are implicit in the definition of potential damage or demand may not be explicitly defined, let alone measured. Other commonly used analysis approaches present subtler problems. Fire protection engineers often focus on alternative means for dealing with fires after fire has begun. It might seem natural to construct a fire risk analysis that takes established burning as given but measures the probability of performance for all building features and systems that operate after the fire. Assuming that it makes sense to write off fire prevention, there still will be a need to address explicitly different types of initial fires. A fast, accelerant-driven fire or an initial explosion will challenge the built-in fire protection in different ways than an or-
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dinary flaming or smoldering fire. A concealed-space fire will present different problems than a fire in a room, and both will differ from fires that start in a means of egress. If each of these fires is analyzed separately, if the analysis leans on physics and chemistry, and if the focus is on preventing major fire extent as an either-or proposition, than the subject is more properly termed a hazard analysis. Although the terminology is not standardized, hazard analysis is best used to describe analyses that do not treat most probabilities explicitly, particularly probabilities of ignition and probabilities of occupant characteristics and behaviors. Risk analysis should be reserved for analyses that address all relevant probabilities. Concern over the computational burden is one reason why analysts sometimes conduct fire risk analyses using a very small number of scenarios (e.g., only three alternatives for where and how fire begins). There may also be concern over the shakiness of the available data and a desire to minimize the number of different terms supported by expert judgments. In a situation like that, it is essential to understand what is being implicitly assumed by the use of a stripped-down scenario structure. One way or another, the scenarios that are modeled explicitly are being treated as representative of the far larger number of scenarios that are not modeled explicitly. If only a few scenarios are modeled explicitly, then each one is implicitly required to be representative of a much larger and more varied collection of other scenarios. There may be no good evidence to support this. Is it better, for example, to examine the different types of flaming fires individually or to assume that they all behave like a burning wood crib ignited by a lighter? The variability and uncertainty are there either way; the only choice is how much to examine explicitly and how much to handle by assumption (Figure 3.8.1). At the same time, either probability or severity can be estimated subjectively and/or categorically. A matrix analysis of high versus low probability and high versus low severity is still a risk analysis, although it will be more difficult to demonstrate its essential validity. Risk analysis can be done by using a curve to express the probability/severity trade-off, in which the shape or type of the curve is specified (and presumably validated), while the choice of a particular curve from the family of curves is done subjectively. These approaches have all the essential elements of fire risk analysis, even if their estimates are not all firmly rooted in external, objective, scientific measurement. Even risk analysis frameworks with more elaborate structures and with parameters and variables that are measurable in principle are likely to rely, in whole or in part, on subjective, “expert” judgments for estimation. Also, risk analysis usually measures deaths, injuries, and property damage rather than stopping with measures of how many rooms or square feet (or square meters) reached a particular temperature or had smoke or gas levels over a particular threshold. In most situations in which risk analysis is used, it is important to address whether people and property are actually damaged, which means implicit or explicit attention to the locations, decisions, movements, and vulnerabilities of occupants—actual, not just potential—and the damageability of property. Risk analysis also requires estimation of the factors that contribute to reliability of systems, such as the probability
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Probability is the single element that separates fire risk analysis from other forms of analysis. Given its importance, there is surprising depth of disagreement as to what probability is. The “frequentist” school regards any probability as the estimated frequency of occurrence of an event in an infinite series of experiments. The “subjective” school regards any probability as an expression of degree of belief in the occurrence of an event. Adherents of the frequentist school recognize that many necessary probabilities involve experiments that are not even theoretically possible. The combination of circumstances that precede a fire’s ignition, for example, can never be precisely duplicated. Many more probabilities involve multiple real-life experiments, very similar if not identical, but that cannot be observed, or, at best, are not being recorded. For all these reasons, a frequentist will acknowledge that subjective estimation is necessary, even pervasive, in probability specification for risk analysis. Treating probability as a degree of belief, as the subjectivists purport to do, raises the question of why anyone should attach any credibility to anyone else’s estimate of probability. It suggests that everyone is free to select their own probability and that there is no point of comparison to revise or challenge those selections. For this reason, a pure subjectivist is rare, and a convincing fire risk analysis openly based on pure subjectivism is even more rare. A more broadly credible version of subjectivism holds that a probability estimate is an expression of all the knowledge one has regarding the underlying process that leads to the event or does not. Bayesian analysis provides a flexible mathematical framework for uniting the two schools. A prior probability distribution is set by the analyst both to capture his or her knowledge (or beliefs) about the process and to specify how much or how little experimentation would be required to substantially revise the prior. A prior probability distribution is obtained by adjusting the prior in light of empirical evidence in the form of a series of experiments. FIGURE 3.8.1
Frequentist versus Subjectivist Probability
of features and systems being rendered inoperative or ineffective owing to human error or negligence; hazard analysis does not always address field reliability in all its aspects. To put this another way, fire risk analysis requires several types of probabilities: • Probabilities of fire ignition. In most cases, the specification of the initiating fire is the whole of the definition of a scenario. These probabilities are easier than others to base on data from real fires because these are the factors that are routinely documented. • Probabilities of fire development from one stage to another. In most cases, these probabilities are not needed because fundamentally grounded physics models of fire development can be used. • Probabilities of various environmental conditions affecting fire development. Even if physics models are available, the calculations will depend on such environmental conditions as the dimensions of the room or space in which fire begins, the initial fire’s proximity to barriers and surfaces, ventilation conditions, openings to other spaces and their configuration and sizes, and the thermal properties of the linings of the room or space of origin. Although some of these may take on standard values in most settings, others can and will vary significantly and create the need for probabilistic treatment. • Probabilities of numbers, locations, and characteristics of occupants. These conditions, which will vary considerably,
can influence both the course of fire development and the degree of harm caused by the fire. • Reliability probabilities. Both active fire protection systems and passive fire protection features can vary from their ideal or nominal statuses. Those variations constitute issues of reliability and will also affect the severity of a fire. Hazard analysis addresses the core concerns of fire development, smoke spread, and sometimes toxicity; it often does so in far greater detail than risk analysis. Risk analysis includes victim decisions, locations, and characteristics; ignition factors; and reliability of systems and building features. To be this broad, fire risk analysis cannot always make use of the full power and sensitivity to detail of the hard-science models of hazard analysis; the only models that can be used are those that can be fitted into the complete risk analysis framework. Thus hazard analysis has the advantage of being able to examine details of design that fire risk analysis cannot now handle. In the long term, however, work is proceeding on model integration techniques that are capable of combining the breadth of fire risk analysis with the depth of hazard analysis.
USES OF DATA FROM REAL FIRES Because real fires reflect all the factors that affect ignition probability and fire severity, fire risk analysis usually begins with calculations from databases on actual fires. (Nearly two million
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fires are reported to the fire service each year.) For most analyses of classes of properties, then, one can identify initial databases of historical fires that will give statistically meaningful probabilities and severities of fires. Many situations, however, may dictate going beyond incident databases in performing a fire risk analysis. First, in analyzing new strategies, products, or systems, there will be no database of fires reflecting the influence of these innovations. Second, there may be interest in so many product or building characteristics that the database does not have enough fires to cover all possible combinations. Third, more detail may be needed than is available in the typical database. If available fire experience data are insufficient, a fire risk analysis will begin to look more like a hazard analysis, with tree diagrams to capture alternative sequences of events, probabilities for the various possible starting conditions, and probabilities for transitions from one stage to the next in a fire. What is measured and in how much detail may differ from a hazard analysis in the ways noted earlier.
RISK ESTIMATION AND RISK EVALUATION Fire risk analysis can sometimes be separated into (1) risk estimation, the estimation and analysis of the measures of severity and probability and their associated uncertainties, and (2) risk evaluation, the additional steps required to decide on the importance of a particular value of risk or a change in risk. A fire risk analysis that includes risk evaluation may be called a fire risk assessment to underline the fact that the analysis will support value judgments. Risk evaluation should be familiar to anyone who has had to make business decisions because it essentially involves using analysis to determine whether you will get what you pay for. The most common approach to risk evaluation is cost-benefit analysis, a technique in which all benefits of risk reduction are translated into monetary equivalents. This technique permits a proposed new product or fire suppression system to be assessed in terms of its net profit or loss, total cost plus loss, or ratio of profit to loss. In such a context, “profit” means saved lives, avoided injuries, and reduced property damage, all combined in one monetary scale, and “loss” means the cost—both initial and ongoing—of the new product or system. A variation is costeffectiveness analysis, in which the benefits of risk reduction are translated into a single nonmonetary scale. For example, it is possible to derive the cost per life saved for a new system or product. Cost-benefit and cost-effectiveness analyses require the explicit estimation or derivation of some controversial parameters. Examples include the value of reduced risk of death or injury and the discount rate by which future consequences are compared to present consequences (both discussed in more detail later in this chapter). Because these parameters are controversial, risk evaluation sometimes uses methods that downplay the role of these parameters. Acceptable risk is a term that is used when the method of risk evaluation involves treating risk as a constraint. This method may seem attractive because it refuses to consider costs until or
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unless a sufficient degree of fire safety has been provided. In an acceptable risk approach, a certain level of risk is defined as acceptable; then all alternatives meeting that level are evaluated strictly on the basis of cost. This approach can produce unsatisfactory results. If risk is greater than the acceptable level by even a small fraction, no cost is too great to reach acceptable risk. If risk is already acceptably low, not a nickel more should be spent, no matter how much more fire safety could be purchased for very little money. This means that the selected level of acceptable risk is often set with an eye toward affordability and may be reset if technology changes. In effect, this makes the acceptable risk approach a kind of backdoor cost-benefit analysis and runs counter to most approaches to decision making in business. When acceptable risk is not defined in terms of affordable risk, it is often defined in terms of (1) historically acceptable risk (i.e., anything in use for a long time is all right), which may be overturned if public understanding of the magnitude of the risk changes dramatically, or (2) unavoidable risk, such as the use of background radiation levels as a guide for acceptable exposure to medical X-rays. In fire protection, acceptable risk has sometimes been inferred from provisions of NFPA codes and standards. The most extreme version of an acceptable risk approach is a minimum risk approach, in which cost is not considered unless all feasible safety improvements have been made. A logical complement to the acceptable risk approach would be an acceptable cost approach, in which the greatest risk reduction available within the fixed cost budget (but no more) would be sought. Although this approach is rarely mentioned in the literature, it almost certainly describes the way some decisions are made. Note that the acceptable risk and acceptable cost approaches both can be very sensitive to the initial selection of a single key parameter. If these approaches are used, it is necessary to conduct a sensitivity analysis to see how conclusions would be changed if the reference level of acceptable risk or acceptable cost were different. Sensitivity analysis of key parameters is essential to all other forms of risk analysis as well and is one way in which the uncertainty surrounding estimates can be addressed systematically.
OVERVIEW OF A RISK ANALYSIS CONCEPTUAL FRAMEWORK Figure 3.8.2 provides an overview of the kind of conceptual framework used to identify necessary models and necessary data in risk analysis. The major aspects to be modeled can be grouped into six models, as shown in the ovals: (1) decision model, (2) ignition initiation model, (3) postignition model, (4) loss evaluation model, (5) cost model, and (6) cost-benefit comparison model. The rectangles indicate numbers, either inputs or outputs, derived from the models. These numbers may in turn be supplied as inputs to other models later in the modeling sequence. The model refers to a “proposed change,” which is a general term for anything that might be modeled: a new sprinkler system, increased compartmentation requirements, no-smoking areas, mandatory self-extinguishing cigarettes, a training program for staff, or any
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General characteristics of building(s) and occupants
Decision model
Fire scenarios
Ignition initiation model
Postignition model
Fault tree
Event tree
Probabilities of fire, by fire scenario, with and without proposed change
Expected losses per fire, by type of loss and fire scenario, with and without proposed change
Expected losses per year, by type of loss, with and without proposed change
Loss evaluation model
Cost model
Annual cost of proposed change
Expected change in losses per year due to proposed change, expressed in monetary terms
Costbenefit comparison model
Measure of attractiveness of proposed change
FIGURE 3.8.2
A Risk Analysis Conceptual Framework
other change that could make fires more or less likely or more or less severe. A decision model is used to describe what the building and its occupants would look like if a proposed change were or were not made. An ignition initiation model is used to estimate the probabilities of occurrence per year for each fire scenario, and a postignition model is used in parallel to estimate the expected losses per fire, for each fire scenario and each type of loss (i.e., deaths, injuries, property damage). The fire scenarios are defined by the requirements of the two models. For example, if the postignition model uses different parameters for smoldering and flaming fires, then that distinction must be reflected in the separation of fires into scenarios for the ignition initiation model. When the outputs of these two models are combined, they produce estimates of expected losses per year by type of loss and for all fire scenarios. Then a loss evaluation model is used to convert all types of loss to a common scale and produce year-by-year projections of overall expected loss, with and without the proposed change. Meanwhile, on the right side of the framework, the purchase, installation, maintenance, inspection, operating, replacement, and other costs of the new system are combined by a cost model into year-by-year figures of the cost impact of the proposed change. Finally, a cost-benefit comparison model produces a measure of attractiveness for the proposed change. This is simply a
comparison of annualized costs and benefits, the benefits consisting of changes in risk. The discussion that follows will address the six component models in more detail. With respect to two terms introduced earlier, risk estimation involves the decision model, the ignition initiation model, and the postignition model, and risk evaluation covers the other three models. Much more detailed guidance on the specification of fire risk analysis models can be found in Section 5, Chapter 1, “Product Fire Risk”; Chapter 12, “Building Fire Risk Analysis”; and Chapter 13, “Quantitative Risk Assessment in Chemical Process Industries,” the third edition of The SFPE Handbook of Fire Protection Engineering. That handbook also has guidance on the basics of the mathematical methods used in fire risk analysis, particularly probability theory and statistical analysis, and much more detail on the treatment of uncertainty and reliability.
GENERAL CHARACTERISTICS AND FIRE TYPES Before the models shown in Figure 3.8.2 come into play, there must be an initial structure to the problem that describes the type of building, the characteristics of its occupants, and the types of
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fires to be studied. Probability distributions may be needed for any of these factors. Even if only a single building is being analyzed, that building’s behavior with respect to fire may vary as a function of randomly varying conditions such as the positions of doors and windows (open or closed) or of forced air heating and cooling systems (on or off). Occupant locations and conditions also may vary in random or patterned ways. It is also useful in setting up a problem to be aware of any factors that cannot be explicitly addressed. This helps in interpreting the results. The most important point to remember in defining types of fires is that all possible fire ignitions must be covered. Fires may have to be grouped into classes that are not entirely homogeneous, but it is not sound practice to exclude certain categories of fires. In the likely event that the postignition model requires each fire type to be specified in great detail (e.g., location and heat release rate of first material ignited), one will be left to choose between an unmanageably large computational burden from a large number of fire scenarios or some uncomfortable groupings of very different types of fires into a small number of fire scenarios. The classification scheme should distinguish among fire scenarios that are affected differently by the systems or strategies being studied. Suppose fast-response sprinklers are being evaluated for possible home use. Then the key properties of fires affecting their response to sprinklers might be identified by answering these questions: Which areas of origin would not be accessible to sprinklers (e.g., the outside of the house, concealed spaces, unsprinklered living areas such as bathrooms)? Could the fire ignition energy best be characterized as smoldering, flaming, or fast-flaming/high energy? The distinction among smoldering, flaming, and fast-flaming fires might be made to recognize the fact that fire growth (which activates the sprinkler) and smoke spread (which is the principal cause of death) do not develop in the same way for all fires.
DECISION MODEL In addition to defining types of fires and specifying general building and occupant characteristics, it is necessary to specify all the differences that would occur if the proposed change were made. If the change involves new built-in smoke detection systems, for example, specifications for the systems would be needed. If the systems were available in two or more versions (e.g., ionization and photoelectric smoke detectors), the probability of each version being used should be estimated (e.g., from data on usage patterns or projected shares of market). Probabilities also would be needed for the variations in status of a system (e.g., fully operational, operational but blocked in one room, turned off, or removed). These specifications dictate precisely what fire protection and fire-related features would be in place to influence the course of fire if one occurs. If the proposed change involves training staff or educating occupants, similar questions would be asked: What are the specifics of the program(s)? What is the likelihood that each version of the program would be used? If fire occurs, what would be the status of the program (e.g., everyone was trained and acted accordingly, some missed the training, some forgot, some panicked)?
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It is sometimes useful to separate the parts of the decision model into those characteristics that were selected by a building owner or manager (e.g., a sprinkler was installed) and those that came into play after the selection (e.g., the sprinkler was installed incorrectly). The latter parts are sometimes collectively referred to as the implementation model. The implementation model isolates those factors that are hardest to control, either because they require continued alertness (e.g., without scheduled testing and maintenance, a sprinkler system’s reliability will decrease) or because they are not directly under the control of the building owner or manager (e.g., a manager can order a sprinkler system but has to work through others to make sure it is installed properly). Neither the implementation model nor the larger decision model needs every bit of information on the proposed changes. The models need only those details that will affect the likelihood of having a fire, the development of that fire, or the reactions of people and property to the fire. For example, some factors will incapacitate the system so that the fire will develop as if no system were present, and that is all the information needed. Some factors will degrade system performance but still permit some impact on fire development; it may be possible to model such reduced impact as simple modifications to the impact expected if the system were fully functional.
IGNITION INITIATION MODEL The ignition initiation model is needed to produce estimates of the probability of ignition per year, by type of fire, given a structure of fire scenarios and fire-relevant characteristics of the building and its occupants. The ignition initiation model is a device for combining known probabilities to infer unknown probabilities. A simple example will illustrate the kinds of calculations that are possible and desirable. Suppose there are n brands of cigarettes. Define pi as the share of total product usage contributed by product i; in this case pi is the share of all cigarettes smoked that are brand i. Let r i be the proportion of brand i cigarettes discarded each year in such a way as to make a fire possible. Let qi be the probability of ignition given such an exposure for brand i; qi is a measure of the relative self-extinguishing tendencies of brand i, but it can be affected by changes in the ignitability of materials that are typically ignited. Let F be the number of cigarette-related fires per year, and let N be the number of cigarettes smoked per year. Then FC
n }
Npi r i qi
iC1
Note that there are three ways to cut down on fires from brand i cigarettes: (1) see that almost no one buys them (reduce pi), (2) see that the people who buy them almost always dispose of used cigarettes properly (reduce r i), and (3) see that discarded cigarettes usually self-extinguish (reduce qi). This model can be used to examine several different types of strategies. A ban on all cigarettes that do not meet a selfextinguishment standard would change the pi values, because
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the prohibited brands would have their pi values cut to zero and the pi values of all the other brands would rise to fill the gap in the market. A campaign to educate the public not to discard cigarettes would lower the r i values, and a requirement to reduce the flammability of couches would lower all the qi values, because more cigarettes would self-extinguish if couches were harder to ignite. To perform the analysis, one must set initial values for the parameters. The purpose of this example is to show how to derive values for the parameters through a combination of direct measurement, reasonable assumptions, and mathematical inference. The values of pi might be measured through sales records or a survey of product users. The values of qi might be measured in laboratory tests. The most elusive will be the r i values, the measures of how often cigarettes are being discarded, whether or not fires result. If it is assumed or can be proven that all types of cigarettes are equally likely to be discarded, then there is only one common r i value, and it can be solved for. Or if data can be obtained on numbers of cigarette fires per year by brand of cigarette, then individual r i values can be solved for. In a more complex case, suppose the analyst had at least as many years of fire data as there were brands of cigarettes. Also suppose that it can be assumed or shown that year-to-year variations in fire experience were due solely to changes in market share. (This is equivalent to assuming that neither behavior in discarding cigarettes nor the propensity of each brand to start fires if discarded has changed over the years.) Then if pi values (market shares) could be obtained for each year, it would be possible to solve for the r i values using the years of fire data as a set of n equations in n unknowns. These diverse approaches illustrate a general point. To estimate unknown probabilities, it is necessary to (1) find direct
data sources for the unknowns (e.g., survey of couch usage), (2) develop reasonable assumptions as to the values of the unknowns (e.g., why the r i might all be equal), (3) find valid formulas relating the unknowns to other variables about which there are sufficient data to make inferences back to the unknown probabilities, or (4) fill the gaps with expert estimates. A full ignition initiation model needs to combine far more factors than were used in the simple illustration and to accommodate a multitude of logical and probabilistic interdependencies among the variables. There may be many different factors, none necessary for fire to occur and none sufficient to cause fire except in combination with certain other factors. The standard format for constituting such models is the fault tree or success tree, which is discussed in more detail under the more general name of fire safety concepts tree in Section 2, Chapter 2, “Fundamentals of Fire-Safe Building Design.” A more generic flowchart of the steps needed to estimate probabilities is shown in Figure 3.8.3.
POSTIGNITION MODEL The postignition model is used for estimating the severity of specified types of fires, given specified building and occupant characteristics and the status of all systems, features, products, and other changes being analyzed. The methodology for tracking the development and final consequences of a specified fire under specified building and occupant conditions may be deterministic, probabilistic, or, more likely, a mix of the two. Fire protection engineers are aware of the rapid growth in computer-based deterministic models for analyzing the development of a fire and its effects under specified conditions. There
Compilation and review of generic historical fire incident data Review and evaluation of historical data specific to what is being studied (e.g., building, product)
Yes
Edited database on relevant historical fires
Are historical data sources sufficient to estimate probabilities?
Evaluation of data applicability: What is different or has changed between now and the time of the historical fires regarding what is being studied?
No
Estimate probabilities using • Bayes law • Fault tree analysis • Nonfire data (e.g., reliability) • External events analysis
Calculate probabilities
Document/justify data, engineering judgments, and accuracy of values (degree of uncertainty)
Needed probabilities
FIGURE 3.8.3
General Procedure for Estimating Needed Probabilities
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are two special requirements for the postignition model component of a fire risk analysis that constrain the use of existing deterministic models: (1) It cannot accommodate a more finely divided typology of fires than can be handled by the ignition initiation model (i.e., for every distinct type of fire whose development and final impact is modeled, it must also be possible to estimate the likelihood of that type of fire); and (2) it should produce not only physical descriptions of flame, gas, and smoke extent, but also measures that are useful as end measures of impact, such as deaths, injuries, and dollar-value property damage. The postignition model—a model of fire development and outcomes—consists of a set of linked time functions of fire characteristics and their effects. For example, the model might need to specify, at each time, the extent of flame, smoke, and gases by type, the status of fire protection systems and other building characteristics, the locations of occupants, the tenability of various locations, and the like. No existing model can do all this. To develop a practical version of the model, one must ask (1) how many of these characteristics need be known to develop reasonably good estimates of deaths, injuries, and damage from a given fire and (2) at which moments in time the development of a particular type of fire will change as a result of the different input values to be modeled (e.g., different initial statuses of fire protection systems). In other words, one must identify a limited number of fire descriptors to track and a limited number of points in time at which to check them. One type of model to do this is called an event tree, the standard modeling format of statistical decision theory. In an event tree, each point in time is characterized by a set of events. These events indicate all the states in which the fire might be at given points in time (with the states defined by the limited number of fire descriptors previously cited). Then, for each event, one must specify the probabilities that—starting from that event—the fire will develop into each of the possible states (or events) that could characterize the fire at the next point in time. Event trees work well if all the factors being analyzed operate at relatively well-defined moments in time or stages of the fire. Experience in using these models indicates that the performance of most fire protection systems and features can be tied to events, which are themselves defined by characteristics of the fire. Figure 3.8.4 is a simple but still practical and useful example. Figure 3.8.5 shows a fire risk analysis that includes a more integrated system of fire and smoke growth models and treats fire development deterministically rather then probabilistically. An event tree (see Figure 3.8.4), like any tree model, consists of nodes and arcs. Each node represents an event or stage in the development of the fire—typically a point where a particular system or feature will activate if it is operational or where the speed of the fire changes dramatically (e.g., flashover). The condition of the fire at extinguishment is captured by the outcome events, which are the various terminal events of the tree. Each outcome event is assigned values of expected losses per fire (i.e., average severity—deaths, injuries, property damage) that are the estimated losses if the fire ends in the way described by the outcome event. However, the only losses covered by these values are those that occur during the final stage of the fire or are otherwise correlated with the ultimate size of the fire. For com-
Do alarms function?
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Do sprinklers function?
Branch probability
Branch consequence
Success probability P3
P1 × P3
Minor fire damage
Failure probability P4
P1 × P4
Moderate fire damage
Success probability P5
P2 × P5
Moderate to heavy fire damage
Failure probability P6
P2 × P6
Major fire damage
Success probability P1
Fire
Failure probability P2
FIGURE 3.8.4 Event Tree (Source: © Factory Mutual Insurance Co. Reprinted with permission. All rights reserved.)
putational reasons, deaths and some other losses that take place early in the fire may have to be associated with the stage of the fire at which they occur. For example, suppose the first event in a fire is ignition and the second is the point at which a fastresponse sprinkler would activate. Fatal injuries occurring before that second event (e.g., due to clothing ignitions) would be captured in a loss-per-fire figure assigned to that second critical event and would be understood to occur no matter how the fire does or does not grow after that event. These losses are sometimes referred to as tolls because any fire that passes through the event acquires those losses, just as a car pays a toll on an express highway. At each event (except outcome events), there will be two or more directions in which the fire may subsequently develop, and there will be transitional probabilities associated with each of these directions. All transitional probabilities from an event add up to 1. They are conditional probabilities that a fire will reach a particular event, given that it has already reached the immediately preceding event. A path is a possible sequence of events for the fire from the first event (ignition) to one of the outcome events. Each path describes the growth and extinguishment of the fire with as much detail as the model can provide. A path probability is the probability of a complete path, calculated as the product of the transitional probabilities for all the events along the path. Because several outcome events often are identical
3–124 SECTION 3 ■ Information and Analysis for Fire Protection
Start
Design fire model
Fire growth model
Smoke movement model
Fire detection model
Occupant warning and response model
Boundary element model
Yes
Flashover fire?
Smoke hazard model
No
Fire brigade action model
Evacuation duration model
Fire spread model
Egress model Probability of property loss model
Probability of life loss model
Economic model
Expected number of deaths model
No
All scenarios analyzed?
Yes
Expected risk-to-life model
Fire cost expectation model
Stop
FIGURE 3.8.5
Risk-Cost Assessment Model
except for the paths used to reach them, it is sometimes useful to compute an outcome probability. This is the probability of a set of similar outcome events and is equal to the sum of the path probabilities for the paths ending in those outcome events. The expected loss per fire is calculated by multiplying transitional probabilities for branches leading to outcomes by the losses associated with those outcomes, then assigning those losses to the events from which the branches originated and adding any tolls associated with those events. This process is repeated (and is called “rolling back the tree”) until an expected loss figure has been computed for the first event (ignition). That value then becomes the expected loss for the event tree.
LOSS EVALUATION MODEL The explicit or implicit assignment of monetary values to lives saved and injuries averted is the key element of this model. It is a difficult step that many people find distasteful or even immoral. The first and most important point to make is that individuals are not being asked to name a price for which they would be willing to die or suffer crippling injury. Instead, they are being asked to name a price they would be willing to accept to allow their current low risk of incurring death or injury in fire to increase or what they would pay to make that risk still smaller. With a resident population of about 260 million and an annual fire death toll in the range of 4000–5000, an average U.S. citizen has less than
one chance in 50,000 each year of dying in a fire. Even for the highest-risk groups, the risk is probably less than one chance in 5000 each year or less than one chance in 65 over an entire lifetime. A person could rationally attach a price to a 10% or 50% change in such a risk and still be consistent in believing that life (i.e., the certainty of losing it) is beyond price. A rational person would pay much more to reduce the probability of dying from 1.0 to 0.8 than he or she would pay to cut that risk from 0.3 to 0.1. If that point is made, the next task is identifying what particular figures should be used for the value of life and the value of injury when considering alternatives that change risks in the range characteristic of fire risk. In the 1960s and earlier, the value of life was generally calculated on the basis of discounted forgone future earnings. This approach implicitly assigned no value to the lives of retired people and full-time homemakers and negligible value to the lives of older workers and young children. Such distinctions were philosophically objectionable. Even for prime wage earners, the methodology did not afford any guarantee that the value obtained would match the price people wanted to pay for risk reduction. In recent years, this approach has been largely abandoned in favor of calculations of willingness to pay to reduce risk of death. Practically speaking, the shift in approach roughly tripled the standard values of life.12 For all the philosophical disagreements, the actual values attached to lives saved, however calculated, tend to be concentrated within two orders of magnitude. Most studies estimate the value of life in hundreds of thousands of dollars or millions of
CHAPTER 8
dollars. Some of the higher values are taken from jury awards that compensate deaths. Few estimates go as high as tens of millions of dollars or as low as tens of thousands of dollars. It is difficult to set up fully persuasive methodologies to assess a popular consensus on value of life because people do not like to think about death. If asked about the value of a whole life, they refer to the sanctity of life and say that the value is infinite. If asked about the value of a shift in the risk of dying, they find it difficult to relate to such a choice. If presented with forced-choice situations that contain implicit values of life, they give answers that can reflect the way the questions were posed. Nevertheless, a 1988 study of assessments used in evaluating a wide range of proposed federal regulations concluded that “there has recently been some convergence around a figure of $1 to $2 million per statistical life.”13 Another alternative is to use a value per year of life saved. A large number of regulatory cases were examined, and the ranking of alternatives found was not drastically affected by the use of life-year value versus life value.12 However, use of lifeyear value tends to give more credit to saving children (by up to double, since their expected life spans are about double those of the population at large) and less credit to saving older adults (by a factor of four or more). Fire safety in schools would be boosted and fire safety in nursing homes might be gently scaled back if life-year value calculations were used. Even after deciding to use willingness to pay as the standard for value of life, some difficult technical problems remain. One is the question of whether to calculate separately the willingness to pay for each individual (or each major group) affected by a proposed change. In an analysis aimed at the individual property owner or manager, such differentiation is unavoidable and should be an explicit, or at least implicit, part of any analysis of the market for a new product, system, or approach. There also have been several studies of factors that affect willingness to pay. Willingness to pay is lower for poor, older Americans, the seriously ill or handicapped, and risk takers. For the poor, of course, ability to pay is lower, too. For older Americans and the seriously ill, the lower value given to life seems to reflect the fact that the quantity (for the older American) or the quality (for the sick) of life remaining is well below the national norm. However, all these groups with lower willingness to pay also tend to have relatively high risks of becoming fire fatalities. They are precisely the groups to target if total lives saved were the criterion of choice. Conversely, the people who are most willing to pay—affluent, healthy, risk-averse, young heads of families—are the ones least likely to benefit because their current risks of dying in fire are already below average. Another reason for variations in the willingness to pay involves the nature of the risks rather than the characteristics of those who experience these risks. Risks that are voluntary, nonessential, occupational, or results of product misuse are deemed less serious than risks that are involuntary, essential, public, or results of normal product use. A risk of death to someone who lives near a nuclear reactor is valued more highly than an equal risk of death to someone who works in a coal mine. The difference is based on the assumption that occupational risks are more likely to be voluntary and more likely to be financially compensated. (Both of these assumptions are questionable.
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Workers in hazardous occupations such as mining may have few realistic occupational alternatives, while residents of hazardous areas, such as like floodplains, may have many alternative places to live and may have received financial compensation in the form of lower housing costs that at least equal any financial benefits received by the workers.) Similarly, risks of death associated with voluntary nonessential activities, such as smoking and hang gliding, are valued less than equal risks associated with voluntary but essential activities, such as driving a car. In fire risk, this argument appears in the debate over the fairness of imposing flame resistance standards (and accompanying costs) on all mattresses to protect people who choose to smoke in bed. Deaths that occur in major multifatality incidents are valued differently—and generally more highly—than deaths that occur in smaller incidents. Major incidents are termed dread hazards in the risk analysis literature; it is the factor of dread—the greater fear of death occurring in a major incident—that inflates the value of risk in such cases. The effect of major incidents on families and communities has been used to argue for both higher and lower weighting of such deaths—higher because familial bloodlines may be extinguished, lower because multiple deaths in one family mean fewer survivors to mourn per fatality.14 Dread incidents constitute an especially dramatic example of the phenomenon of risk aversion. For example, most people feel that if loss A is ten times as great as loss B but only onetenth as likely, losses A and B still are not equally onerous. The general public tends to be more concerned about fire scenarios that may kill, say, 100 people once every three years than they are about fire scenarios that kill one person at a time every week, year after year. Technical adjustments can be made to incorporate some risk aversion into a benefit calculation. Such adjustments will have less effect on dwelling fire risk calculations, in which really large incidents are impossible, than on risk calculations for large residential (e.g., hotel), institutional, or public assembly properties. Values for injuries avoided can be estimated more directly than values for fatalities avoided because direct costs such as medical expense and lost wages seem more appropriate as indicators of value. A survey was used to estimate direct injuryrelated costs for residential fires.15 Based on their figures, after adjusting for inflation and for the fact that their cost-per-injury figures are dominated by very small injuries from unreported fires, an estimate of $5,000 might be obtained for actual costs per injury received in a reported fire. Willingness to pay to avoid an injury is greater because of pain and suffering considerations, so economists at the U.S. Consumer Product Safety Commission16 derived a figure of $35,000 in the late 1980s. This average is based on a highly skewed distribution. The vast majority of injuries can be valued in the low hundreds of dollars or less, but a small number of serious burn injuries each year—considerably fewer than the corresponding number of fire fatalities—can cost hundreds of thousands or even millions of dollars in medical expenses. These few injuries account for most of the overall cost average. This suggests that analyses of expected impacts of new systems or programs on injuries should, if possible, separate serious and nonserious injuries when average values are used, to make sure that the average values are not understated as typical values.
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For property damage, the losses probably will already have emerged from the postignition model expressed in monetary terms, but that is not necessarily so, and even if it is, some conversions may still be necessary. If fire growth and smoke spread models have been used, property damage may have been calculated in such terms as rooms exposed to fire or smoke for various lengths of time or areas where structural integrity has been lost. Converting such descriptions to monetary equivalents would require data and models that do not now exist, despite repeated efforts to develop them.17 Even if damage is expressed in dollars, one might wish to take account of the fact that the loss faced by the property owner may be mediated by such things as insurance. In that case, it would be necessary to estimate the likely reduction in out-ofpocket, uninsured damage plus insurance premiums, rather than the likely reduction in total direct damage achievable. Another consideration in the loss evaluation model is whether to include an adjustment for indirect loss—such items as lost wages, costs of a temporary location, and lost revenue for days that a business is closed. These losses can be very large in individual cases, such as the 1980 MGM Grand Hotel fire, but the best studies indicate that in the aggregate they tend to be an order of magnitude smaller than the direct losses.18
COST MODEL Costs may be divided into (1) initial costs of the proposed changes being studied, (2) the ongoing costs of these changes once they have been made, and (3) the ripple effects on other costs, such as the need to increase the water supply to support a sprinkler system. The last could involve cost increases or cost reductions, including calculation of costs for many years into the future. To make this task manageable, the analysis can be set up in terms of the normal periods of maintaining, repairing, and replacing the items being analyzed. This is called life-cycle costing. An overview of major components of each of these three types of costs is shown below. These lists are not exhaustive, but they indicate the need to estimate the effects of different decisions and assess their cost impacts.
Initial Costs of Changes Being Studied Equipment Costs. For new products, it may be necessary to estimate what costs will be when mass production is under way. In many cases, the mass production cost continues to drop as further development occurs. (Smoke detectors have shown this pattern, for example.) Installation Costs. Estimation of costs of installation may require an analysis of the steps required for installation, because the person-hours and skills required for those steps may be higher or lower than for comparable products already in use. (For example, plastic pipe may be faster to install than iron pipe, and it may require less time-consuming effort to protect carpets and furniture from soiling during installation.) Labor costs per hour may vary considerably from one place to another, as may overhead rates; these variations argue in favor of a serious effort to collect representative data.
Financing Costs. These will be relevant if the systems are financed through time-payment plans (e.g., as part of what is covered by the building mortgage). Permit/License Costs. There may be some one-time fees required to install the systems. Some Costs Offset in Resale. If the new systems and features add to the resale value of the property, this will partially offset the initial costs.
Ongoing Costs of Changes Being Studied Operating Costs. A new system or product may need labor, power, or some other continuing input to operate. These costs need to be included. Inspection and Testing Costs. Many systems require periodic inspection and testing after installation. These costs should be included. Labor usually will be the main cost element, but some tests (such as sprinkler tests) may involve materials costs, and other tests may require destruction of a sample of system components that would need replacement. Repair, Maintenance, and Replacement Costs. Most systems will require repair and maintenance, and if the study period is long enough, periodic replacement will need to be considered. Costs of Nonfire Damage Caused by the Systems. An example of nonfire damage caused by a system would be water damage due to accidental discharge of a sprinkler. Permit/License Costs. An example of a permit or license cost would be the standby water charge levied in some jurisdictions on buildings equipped with sprinklers. Salvage Revenues for Cost Offsets. Equipment that is replaced may be resellable. If so, salvage revenues help to reduce net system costs.
Ripple Effects on Other Building Costs Costs of Supporting Systems. Many new products may require replacement, modification, or addition of critical supporting systems (e.g., extra water supply for home sprinkler system in a rural area). The equipment and installation costs of these changes in supporting systems need to be identified and included. So do any changes in operating costs, repair and maintenance costs, inspection and testing costs, and the like, for the modified supporting systems and any changes in these ongoing costs for unmodified supporting systems. Special Incentives or Credits. Insurance premium reductions that reflect the expected reduction in direct loss should be counted in the loss evaluation model. Extra reductions offered as inducements to buy systems, as well as incentives or credits in property or income taxes, should be counted here. Property Value and Tax Impacts. Changes in property taxes reflecting changed property value assessments should be con-
CHAPTER 8
sidered. There may be tax consequences if the features add value to the property. Changes in Land Costs or Required Building Features. Added safety features may permit trade-offs in the form of increased density or reduced requirements for other building features. These need to be accommodated as costs, and any trade-offs in other safety features need to be addressed in the loss evaluation models as well. Changes in Costs of Public Fire Protection. If buildings in a group receive similar modifications, it may be possible to accept longer response times or reduced sizes of fire suppression teams, resulting in reduced costs of public fire protection.
COST-BENEFIT COMPARISON MODEL The cost model and loss evaluation model produce time streams of costs and risk-reduction benefits—that is, year-by-year estimates of costs and of reductions in fire deaths, injuries, and property damage, the latter being expressed as total monetized losses. To compare the costs to the benefits, the two time streams need to be combined into a single, manageable, indicator of net benefits. To compare future and present costs and benefits, it is necessary to decide what the future costs and benefits are worth in the present. This involves the concept of opportunity cost. Suppose $20 were spent now on a fire safety system and $20 were received back 10 years later in the form of reduced property damage in a fire. This would not be a break-even proposition because alternative investments could pay interest over that period. Assumptions about the attractiveness of such investments are reflected in an assumed discount rate—a proportion between 0 and 1 used to reduce the value of future costs and benefits. Most fire risk reducing strategies involve greater costs than benefits in the near years and greater benefits than costs in the later years; this makes the discount rate a critical factor in overall assessment of whether the benefits justify the costs. Also, even if opportunity costs were not involved, there would be a cost associated with delayed consumption. All other things being equal, people usually prefer to have goods and services now rather than later, and a discount rate reflects that fact. If a cost is incurred 10 years from now, for instance, the discount rate must be applied 10 times to translate that cost into a figure that is comparable with today’s costs. This figure is called the present value of a future cost or benefit. It is calculated as the discount rate raised to a power equal to the number of years in the future when the cost or benefit will occur, then multiplied by the value of that cost or benefit. A reasonable discount rate can be assumed for the purpose of analysis or can be calculated as the discount rate required just to balance benefits and costs. If the latter is done, the derived discount rate is called the internal rate of return. It can be used to compare alternatives in the same way that a benefit-cost ratio can be used. The two principal objections to discounting of future safety benefits are (1) the possibility of very large, perhaps even irreversible, effects at a remote point in the future and (2) the cumulative effects of the short-term biases induced by rigorous
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application of discounted assessments. The first objection is not a great concern for fire risk problems because fire does not produce irreversible effects on the scale contemplated by this argument. At most, several small towns could be wiped out by a wildfire (ignoring, for the moment, the possibility of wartime firestorms). Nevertheless, as a technical matter, it is worth considering the possibility that discount rates undervalue the real value people assign to events beyond the next decade or so. For example, most people would regard benefits in 105 years as equal to benefits in 100 years; but under constant discounting of, say, 10%, the former would be only 59% of the latter.19 As for the cumulative problems of short-term bias, this has been discussed more in the context of business research, development, and innovation in general than in regard to safety innovations in particular. In business, investments are expected to balance benefits and costs within three to seven years, but many analysts believe that such requirements are too demanding and tend, over time, to choke off truly dramatic breakthroughs. The result, in business, can be the eventual loss of competitive edge to a competitor that is willing to take a longer view. One pertinent article20 was particularly forceful on this point, arguing that the implied opportunity cost model underlying a short payback period requirement assumes a standard reference alternative investment that, contrary to the model’s assumptions, is not itself immune to the cumulative effects of a stream of choices driven by short-term considerations. The fallacy, then, is in assuming that there always is an alternative investment that pays back in three to seven years; the short-term-driven decisions may have the cumulative effect of eroding all such alternatives. The technical approach to addressing this concern is to check the sensitivity of any conclusions to the use of a lower discount rate. Any innovation that year by year, after the initial cost period, produces more benefits than costs can be made to look attractive through the selection of a sufficiently low discount rate. It is risky, however, to use too low a discount rate, because that will give a misleading picture of what people will be willing to pay. Other approaches, such as using a higher discount rate for costs than for benefits, can produce perverse results. For example, such an approach could mean that an attractive safety program would seem even more attractive if its implementation were delayed. In this way, a program can be made to seem attractive but may never be implemented because further delay will always make it seem even more attractive.21
SUMMARY Fire risk analysis is a technique that can pull together, reduce, and provide perspectives on large quantities of data from many sources. Recent rapid advances in the size and quality of fire-related databases and in the power and affordability of computers have helped to turn fire risk analysis into a practical tool for individual decision making and especially for large-scale decision making by governments and companies. The accelerating pace of development of computerized models of fire development and occupant behavior will eventually produce integrated deterministic/probabilistic models, providing even more powerful tools for fire risk analysis.
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Step 1 Definition of risk assessment objectives
3.
Step 2 Hazard identification
4. Step 3 Scenario development Step 4 Severity analysis
5.
Step 5 Probability analysis
6.
Step 6 Risk presentation Step 7 Risk reduction analysis
7. No
Is the risk acceptable?
8.
Yes
9. Risk monitoring
FIGURE 3.8.6
Fire Risk Assessment Steps
10. 11.
At present, there are only a few abbreviated published examples of fire risk analysis,22–25 but other more elaborate examples, providing more detailed illustrations and more broadly applicable models, are in progress. Until better materials are available to demonstrate the specific analytic techniques of fire risk analysis, it is useful to recognize the essence of fire risk analysis: creation of the simplest possible framework for identifying the available choices and estimating their consequences. Whether the estimates consist of nothing more than a series of guesses or are the result of an elaborate network of sophisticated models, laboratory tests, and fire experience, the framework in principle remains the same. Its purpose is to assemble all the information available, however slight or extensive, and focus that information on how and how much things would change as a result of the choices made. (See Figure 3.8.6 for a simple fire risk assessment flowchart that focuses specifically on the crucial step of presenting all this information to set up decisions and choices.) Identifying choices, predicting consequences, evaluating those consequences, and finally making choices—those are the steps of fire risk analysis. However complicated the methods used, the purpose is always to perform these familiar tasks that are the basics of rational decision making.
12. 13. 14. 15. 16.
17. 18. 19. 20. 21. 22.
BIBLIOGRAPHY References Cited 1. Beck, V., et al., Fire Safety and Engineering Project Report, The Warren Center for Advanced Engineering, University of Sydney, Sydney, Australia, 1989. 2. Beck, V. R., “Performance-Based Fire Engineering Design and Its Application in Australia,” Invited Lecture, in Fire Safety Science—
23. 24.
Proceedings of the 5th International Symposium, IAFSS, Bethesda, MD, 1997, pp. 23–40. Beck, V. R., and Yung, D., “The Development of a Cost-Effective Risk-Assessment Model for the Evaluation of Fire Safety in Buildings,” in Fire Safety Science—Proceedings of the 4th International Symposium, IAFSS, Boston, MA, 1994, pp. 817–828. Yung, D., Hadjisophocleous, G. V., and Proulx, G., “Modeling Concepts for the Risk-Cost Assessment Model FIRECAM and Its Application to a Canadian Government Office Building,” in Fire Safety Science—Proceedings of the 5th International Symposium, IAFSS, Bethesda, MD, 1997, pp. 610–630. Fraser-Mitchell, J., “An Object-Oriented Simulation (CRISP II) for Fire Risk Assessment,” in Fire Safety Science: Proceedings of the 4th International Symposium, IAFSS, Bethesda, MD, 1994, pp. 793–803. Fraser-Mitchell, J., “Risk Assessment of Factors Related to Fire Protection in Dwellings,” in Fire Safety Science—Proceedings of the 5th International Symposium, IAFSS, Bethesda, MD, 1997, pp. 631–642. Frantzich, H., Uncertainty and Risk Analysis in Fire Safety Engineering, Report LUTVDC/(TVBB-1016), Lund University, Lund, Sweden, 1998. Magnussen, S. E., “Risk Assessment,” Invited Lecture, in Fire Safety Science—Proceedings of the 5th International Symposium, Bethesda, MD, 1997, IAFSS, pp. 41–58. Apostolakis, G., “Fire Risk Assessment and Management in Nuclear Power Plants,” Fire Science and Technology, Vol. 13, Supplement, 1993, pp. 12–39. Siu, N., and Apostolakis, G. (1988). “Uncertain Data and Expert Opinions in the Assessment of the Unavailability of Fire Suppression Systems,” Fire Technology, Vol. 24, 1998, pp. 138–162. Hall, J. R., Jr., and Stiefel, S. W., Decision Analysis Model for Passenger-Aircraft Fire Safety with Application to Fire-Blocking of Seats, NBSIR 84-2817, National Bureau of Standards, Washington, DC, March 1984. Graham, J. K., and Vaupel, J. W., “Value of a Life: What Difference Does It Make?,” Risk Analysis, Mar. 1981, pp. 89–95. Gillette, C. P., and Hopkins, T. D., Federal Agency Valuations of Human Life, Report to the Administrative Conference of the United States, unpublished, Apr. 1988. Starr, C., and Whipple, C., “Risks of Risk Decisions,” Science, June 6, 1980, pp. 1114ff. Munson, M. J., and Ohls, J. C., Indirect Costs of Residential Fires, FA-61, Federal Emergency Management Agency, Washington, DC, April 1980. Hall, J. R., Jr., Expected Changes in Fire Damage from Reducing Cigarette Ignition Propensity, Final Report to Technical Study Group of Cigarette Safety Act of 1984, National Fire Protection Association, Quincy, MA, July 16, 1987. Hall, J. R., Jr., “Reduce Fire Loss Guesstimates,” Fire Service Today, Nov. 1982, pp. 11–13. Hall, J. R., Jr., The Total Cost of Fire in the United States Through 1988, NFPA Fire Analysis and Research Division, Quincy, MA, Nov. 1990. Whipple, C., “Energy Production Risks: What Perspective Should We Take?,” Risk Analysis, Mar. 1981, pp. 29–35. Hayes, R. H., and Garvin, D. A., “Managing as If Tomorrow Mattered,” Harvard Business Review, May–June 1982, p. 70ff. Keller, E. B., and Cretin, S., “Discounting of Life-Saving and Other Non-Monetary Effects,” Management Science, 1983, pp. 300–306. Ruegg, R. T., and Fuller, S. K., A Benefit-Cost Model of Residential Fire Sprinkler Systems, NBS Technical Note 1203, National Bureau of Standards, Gaithersburg, MD, November 1984. Helzer, S. G., et al., Decision Analysis of Strategies for Reducing Upholstered Furniture Fire Losses, NBS Technical Note 1101, National Bureau of Standards, Washington, DC, June 1979. Hall, J. R., Jr., “A Fire Risk Analysis Model for Assessing Options for Flammable and Combustible Liquid Products in Storage and Retail Occupancies,” Fire Technology, Vol. 31, No. 4, 1995, pp. 291–306.
CHAPTER 8
25. Bukowski, R. W., et al., Fire Risk Assessment Method: Description of Methodology, NISTIR 90-4242, National Institute of Standards and Technology, Gaithersburg, MD, National Fire Protection Association, Quincy, Mass., Benjamin/Clarke Associates, Inc., Kensington, MD, National Fire Protection Research Foundation, Quincy, MA, May 1990.
Additional Readings Barry, T. F., “An Introduction to Quantitative Risk Assessment in Chemical Process Industries,” SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 1995. Barry, T. F., “Fire and Explosion Risk Assessment. Part 1,” Industrial Fire Safety, Vol. 2, No. 5, 1993, pp. 49–53. Barry, T. F., “Fire and Explosion Risk Assessment. Part 2. Procedures and Major Issues,” Industrial Fire Safety, Vol. 2, No. 6, 1993, pp. 30–37. Barry, T. F., “Fire and Explosion Risk Assessment. Part 3. Hazard Identification and Scenario Development,” Industrial Fire Safety, Vol. 3, No. 1, 1994, pp. 32–39. Barry, T. F., “Fire and Explosion Risk Assessment: An Integral Part of Safety Analysis Reports,” Fire and Current Technologies (FACTs), Vol. 3, No. 1, 1994, pp. 1–2, 4–7. Beck, V. R., “Fire Safety System Design Using Risk Assessment Models: Developments in Australia,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, New York, 1991, pp. 45–59. Beck, V. R., and Yung, D., “Cost-Effective Risk-Assessment Model for Evaluating Fire Safety and Protection in Canadian Apartment Buildings,” Journal of Fire Protection Engineering, Vol. 2, No. 3, 1990, pp. 65–74. Brandyberry, M. D., and Apostolakis, G. E., “Fire Risk in Buildings: Frequency of Exposure and Physical Model,” Fire Safety Journal, Vol. 17, No. 5, 1991, pp. 339–361. Brandyberry, M. D., and Apostolakis, G. E., “Fire Risk in Buildings: Scenario Definition and Ignition Frequency Calculations,” Fire Safety Journal, Vol. 17, No. 5, 1991, pp. 363–386. Brannigan, V., and Meeks, C., “Computerized Fire Risk Assessment Models: A Regulatory Effectiveness Analysis,” Journal of Fire Sciences, Vol. 13, No. 3, 1995, pp. 177–196. Bukowski, R. W., “Review of International Fire Risk Prediction Methods,” Sixth International Fire Conference on Fire Safety, Interflam ’93, March 30–April 1, 1993, Oxford, UK, Interscience Communications Ltd., London, UK, 1993, pp. 437–446. Hadjisophocleous, G. V., and Yung, D., “Fire Risk and Protection Cost Assessment Model for Highrise Apartment Buildings,” National Research Council of Canada, Ottawa, Ontario, ASTM STP 1150; American Society for Testing and Materials, Fire Hazard and Fire Risk Assessment, Sponsored by ASTM Committee E-5 on Fire Standards, ASTM STP 1150, Dec. 3, 1990, San Antonio, TX, ASTM, Philadelphia, PA, 1990, pp. 224–233. Hall, J. R., Jr., “How to Tell Whether What You Have Is a Fire Risk Analysis Model,” National Fire Protection Association, Quincy,
■
Fire Risk Analysis
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MA, ASTM STP 1150; American Society for Testing and Materials, Fire Hazard and Fire Risk Assessment, Sponsored by ASTM Committee E-5 on Fire Standards, ASTM STP 1150, Dec. 3, 1990, San Antonio, TX, ASTM, Philadelphia, PA, 1990, pp. 131–135. Hall, J. R., Jr., “Product Fire Risk,” SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 1995. Hall, Jr., Jr., “Key Distinctions in and Essential Elements of Fire Risk Analysis,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, New York, 1991, pp. 467–474. Kazarians, M., Siu, N., and Apostolakis, G., “Risk Management Application of Fire Risk Analysis,” Proceedings of the 1st International Symposium on Fire Safety Science, Hemisphere, 1986, pp. 1029–1038. Parkes, T., and Caldwell, C., “Risk-Based Fire Engineered Alternative Solution for Nursing Homes. A Case Study in New Zealand,” Fire Protection Engineering, Vol. 6, Spring 2000, pp. 29–30. Pate-Cornell, E., “Managing Fire Risk Onboard Offshore Platforms: Lessons from Piper Alpha and Probabilistic Assessment of Risk Reduction Measures,” Fire Technology, Vol. 31, No. 2, 1995, pp. 99–119. Raiter, S., Risk Analysis and Risk Management: A Selected Bibliography, Vance Bibliographies, Monticello, IL, 1987. Ramachandran, G., “Probabilistic Approach to Fire Risk Evaluation,” Fire Technology, Vol. 24, No. 3, 1988, p. 204. Ramsay, G. C., Horasan, M. B. N., and Taylor, P. T., “Does Performance Based Fire Engineering Lead to Safer Designs for Hospitals?” Proceedings of 3rd International Conference on Fire Research and Engineering (ICFRE3), October 4–8, 1999, Chicago, IL, Society of Fire Protection Engineers, Boston, MA, 1999, pp. 123–134. Respondek, J., “Performance-Based Fire Safety Design Approach: Current Developments in Switzerland,” Proceedings of Fire Suppression and Detection Research Application Symposium, Research and Practice: Bridging the Gap, February 7–9, 2001, Orlando, FL, National Fire Protection Research Foundation, Quincy, MA, 2001, pp. 576–595. Rowe, W. D., An Anatomy of Risk, reprint, R. E. Krieger, Malabar, FL, 1988. Watts, J. M., “Fire Risk Rankings,” SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 1995. Yung, D., and Beck, V. R., “Application of a Risk-Cost Assessment Model for the Evaluation of Fire Safety in Buildings,” Proceedings of the 1st International Conference on Fire Science and Engineering, ASIAFLAM ’95, March 15–16, 1995, Kowloon, Hong Kong, 1995, pp. 51–62. Yung, D., and Beck, V. R., “Building Fire Safety Risk Analysis,” SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 1995.
CHAPTER 9
SECTION 3
Simplified Fire Growth Calculations
A
s part of a fire protection analysis, it is often desirable to estimate the burning characteristics of selected fuels and their effects in enclosures. Also important for many analyses is the estimation of when fire protection devices such as heat detectors or automatic sprinklers will activate for specific fire conditions. Equations are available, based principally on experimental correlations, which permit the user to estimate these effects. In this chapter, a brief introduction to enclosure fire effects is presented, along with equations that can be evaluated using hand calculators to provide estimates of particular effects. Generally, the equations presented are well documented and are widely used for such estimates. However, the user is cautioned that most of the equations were developed based on data from experiments that were conducted for very specific, and sometimes idealized, conditions. Therefore, some judgment must be exercised when applying these equations to complex conditions occurring in enclosure fires of general interest. The equations in this chapter are primarily intended to be used in evaluating fire conditions in enclosures during the preflashover fire growth period. Most of the methods presented do not apply to fully developed room fires, such as postflashover conditions. In addition, these shorthand calculations apply only to the room of fire origin and to a single burning fuel package such as a contiguous grouping of combustibles like an upholstered chair and ottoman or a bookcase full of books. More complicated methods are available for multiroom analysis, but they are beyond the scope of this chapter; see Section 3, Chapter 5, “Deterministic Computer Fire Models.” For some of the effects, more than one equation is presented. In these cases, one equation may be preferred over the other, based on the best match of the experimental basis for the equation to the specific case of interest. Material properties, such as heat of combustion (!hc), are listed in this handbook in Appendix A, Tables and Charts. For additional information on material properties or the topics in-
Edward K. Budnick David D. Evans Harold E. Nelson
troduced in this chapter, refer to Section 3 of The SFPE Handbook of Fire Protection Engineering.1 All calculations in this chapter are presented in SI units. For U.S. customary units, see Table 3.9.1. Also, if TK is the temperature in degrees Kelvin, then the same temperature in degrees Celsius or Centigrade (T°C) is given by T°C C TK = 273.15. The same temperature in degrees Fahrenheit (T°F) is given by T°F C 1.8T°C = 32.
IGNITABILITY OF SOLIDS Ignition is a complex phenomenon, dependent on physical and chemical properties of the materials, the environment in which the material exists, and the source(s) of heat exposing the material. A quantitative description of the physical and chemical processes associated with ignition of heated solids can be found in Reference 2. Closed form solutions for ignition of solids are developed by Kanury2 for specific applications. Nelson and Forssell3 develop an approach for prediction of ignition of solids that relies on material properties and data from a cone calorimeter or similar heat release rate test. The ignition time (tign) for a material exposed to a constant heat flux, as in the cone calorimeter, is estimated using empirical correlations and available test data. For “thermally thick” materials, that is, materials that have sufficient thickness such that the time to ignition is less than the thermal penetration time through the solid, a “trial and error” fit is used to estimate the ignition time. Such an approach is outside the scope of this chapter; therefore, the reader is referred to References 2 and 3 for a detailed discussion of this approach. A somewhat less complicated problem involves estimates of ignition time for “thermally thin” materials. These are solids that are so thin or so highly conductive that temperature gradients are essentially nonexistent within the material slab, and the temperature of the material is dependent only on the exposure time to the TABLE 3.9.1
Edward K. Budnick, P.E., is a senior engineer and vice president at Hughes Associates, Inc., in Baltimore, Maryland. David D. Evans, P.E., Ph.D., is a research engineer at the Building and Fire Research Laboratory, National Institute of Standard and Technology, U.S. Department of Commerce, Gaithersburg, Maryland. Harold E. Nelson, P.E., is a senior research engineer at Hughes Associates, Inc., in Baltimore, Maryland.
3–131
Conversion Factors
To Convert from SI Units
To U.S. Customary Units
Multiply by
Kilograms Kilojoules Kilowatts Meters
Pounds (avdp.) Btu Btu/hour Feet
2.2046226 0.948608 3414.99 3.2808399
3–132 SECTION 3 ■ Information and Analysis for Fire Protection
source of heating. Under such conditions the heating can be treated as a bulk heating process, using the following expression:2 Œ hst ign TS > TSO C 1 > exp (1) (iO /h) = Tã > TSO :S CSV
•
Mass loss rate (kg/s)
Unsteady m
If convective losses are assumed to be zero (i.e., h ó 0), then Equation 1 can be further simplified to :S CSV (TS > TSO) C1 iO st ign
(2)
•
Steady m
where CS C specific heat of the solid [(kJ/kg)K] s C surface area (m2) TS C temperature of the solid (K) TSO C initial temperature of the solid (K) Tã C ambient temperature (K) V C volume (m3) h C heat transfer coefficient (kW/m2K) iO C absorbed exposure irradiance (W/m2) t ign C ignition time (s) :s C density of the solid (kg/m3) Caution is recommended in using the formulas provided here for estimating ignition times. As stated earlier, ignition is a complex phenomenon and the limitations associated with the use of these expressions are important. The reader is encouraged to review the more detailed discussions in References 2 and 3.
Time (s)
FIGURE 3.9.1
Steady and Unsteady Burning Rates
by a series of constant energy release rate fires. This approach can require a great deal of calculation time, depending upon the desired accuracy. Such analysis is generally more suited to computer simulation. For the complete combustion of a fuel, energy release rate and mass loss rate are related by the equation Qg C !hc Ý mg
(3)
where Qg C energy release rate (kJ/s or kW) !hc C heat of combustion (kJ/kg) mg C mass loss rate (kg/s)
ENERGY RELEASE RATE Calculation procedures for fire effects in enclosures require knowledge of the energy release rate of the burning fuel. The term energy release rate is frequently used interchangeably with heat release rate, and it is usually expressed in units of kilowatts (kW) and symbolized by Qg . Currently, no broadly accepted methods exist for prediction of energy release rates based solely on basic measurements of material properties. Recent efforts in this area show promise.2 However, it is expected that generalized methods will not be available for some time. In addition, in any enclosure fire, the actual rate of heat release is dependent not just on the burning fuel, but also on the fire environment, the manner in which the fuel is volatilized, the efficiency of the vapor combustion, and other physical and chemical effects. Therefore, for the immediate future one must rely on available laboratory test data for the specific or similar fuels. In addition, knowledge of the complete energy release rate history may be required for many situations. This is particularly desirable where the fuel package exhibits unsteady burning (Figure 3.9.1). For those cases where only limiting conditions or worst-case analysis is required, it may be reasonable to assume that the fuel is burning at a constant rate, which simplifies the calculation considerably. For the equations presented here, the more simplified condition of constant energy release rate is generally assumed. However, techniques are available that represent a growing fire
(The heat of combustion is a material property and is tabulated for selected materials in Appendix A, Tables and Charts. The mass loss rate is typically found experimentally.) It should be recognized that most enclosure fires of interest do not exhibit constant energy release rates. Rather, as illustrated in Figure 3.9.2 for selected items of furniture, the mass loss rate, and therefore the energy release rate, varies over time. Depending on the detail required, one might select a constant mass loss rate, such as a peak value or an average value as the basis for analysis. Data on mass loss rates for selected fuel packages are available in several publications.1,4–7 Most information available on fuel package burning rates is reported for “free burn” conditions—that is, the data are collected for items burning in the open rather than in an enclosure. Although enclosure effects are of little importance in evaluating early fire growth, they are important in fully developed room fires. The effects of most importance are those related to radiation feedback to the fuel from the hot smoke and enclosure linings and those related to the ability of the fire to obtain sufficient air for combustion. When fire conditions reach a stage where the smoke and heated room linings approach 932°F (500°C), the radiant feedback normally increases the burning rate above that observed in a free burn situation. The difference between the free burn rate and the radiation-enhanced burning rate increases as the room temperature and resulting radiant impact on the fuel package increase. Once flashover conditions are reached, rates greater than double the free burn rate are not unusual.
CHAPTER 9
Rate of heat release (kW)
Simplified Fire Growth Calculations
3–133
tions have been established. Section 3, Chapter 1, in The SFPE Handbook of Fire Protection Engineering1 provides a detailed discussion of the prediction of burning rates for liquid pool fires. Detailed discussions of energy release rates for specific fuels are available elsewhere.8,9
3000
F32 (sofa) 2000
■
F31 (loveseat)
FLAME HEIGHTS F21 (single chair)
Axisymmetric Flames 1000
0
200
400
600 Time (s)
800
Estimates of flame height L can be important in determining exposure hazards associated with a burning fuel (Figure 3.9.3). Experimentally determined “mean” flame heights have been correlated by several researchers. A simple correlation for flame heights for pool or horizontal burning fuels has been developed by Heskested:10
1000
L C >1.02 = 15.6N 1/5 D
FIGURE 3.9.2 Free Burn Heat Release Rates for Selected Furniture Items
(5)
where The second enclosure effect is the availability of oxygen for combustion. If the air in the space, plus that drawn in through openings, plus that provided to the space by HVAC systems or other means is insufficient to burn all the combustible products driven from the fuel package, only that amount of combustion supportable by the oxygen available in the air will burn within the room or other space involved. This situation is referred to as ventilation-limited burning. When ventilation-limited burning occurs, the combustible products driven from the fuel package and not burned in the room often burn when they combine with air outside the room and appear as flame extensions from the room. The following equation for stoichiometric fuel pyrolysis can be used to estimate the mass loss rate at which these effects begin to dominate: mg st C
ƒ 1 Ý 0.5A= h= rs
(4)
L C mean flame height (m) D C diameter of fire source (m) N C nondimensional parameter ¹ N C¹ ¹ Ÿ
º Qg 2 º º D5
(6)
where Cp C specific heat of air at constant pressure [(kJ/kg)K] Tã C ambient temperature (K) g C acceleration of gravity (9.81 m/s2) :ã C ambient air density (kg/m3) !hc C heat of combustion (kJ/kg) rs C stoichiometric air/fuel mass ratio Qg C total heat release rate (kJ/s) or (kW)
where mg st C stoichiometric mass loss rate (kg/s)
CpTã 3 Œ 2 !hc g:ã rs
A= C area of ventilation opening (m2)
For noncircular fuel packages, an effective D can be estimated by Π1/2 Af DC2 (7) 9
h= C height of ventilation opening (m)
where
r s C stoichiometric air/fuel mass ratio
For wood fuel, rs C 5.7. An estimate of the maximum burning rate possible for an enclosure with a particular opening can be determined from Equation 4. If the mass loss rate for a particular fuel package is less than this value, the condition is referred to as fuel-controlled, and results from Equation 3 provide a reasonable estimate of the energy release rate. If the free burn mass loss rate is higher than the stoichiometric rate from Equation 4, then the rate determined for stoichiometric conditions should be used for combustion within the room. A more rigorous treatment of energy release rates is available for selected material types such as wood cribs, wood and plastic slabs, and liquid pool fires where experimental correla-
D C effective diameter (m) Af C area of fire (m2) For a broad range of experimental conditions, !hc /rs is nearly constant, representing the heat liberated per unit mass of air entering the combustion reaction. Assuming !hc /rs C 3100 kJ/kg and atmospheric conditions (Tã C 293 K and p C 760 mm Hg), Equation 5 can be simplified to L C >1.02D = 0.23Qg 2/5
(8)
Since flames are unsteady, the mean flame height L is generally taken to be the height above the fire source where the flame tip is observed to be at or above this point 50 percent of the time.
3–134 SECTION 3 ■ Information and Analysis for Fire Protection
The above correlation is considered suitable for pool fires or for horizontal surface burning. In addition, the correlation will produce negative values for L at small heat release rates. The available experimental data indicate that the most reliable region of application is where Q2/5/D is greater than 16.5. For more detail on flame height calculations, the reader is referred to Beyler11 and the SFPE Handbook of Fire Protection Engineering.1
Fire plume centerline
L (mean flame height)
Wall and Line Fires Equations have also been developed for elongated fires that are either (1) against a wall so that air is entrained from one side only (i.e., wall fires) or (2) sufficiently in the open so that air is entrained along both of the longitudinal sides (i.e., line fires).12 In these equations, the flame height is based on the rate of heat release per meter of length of the fire source.
Zo
Virtual origin
FIGURE 3.9.3
Wall Fire Flame Height L C 0.034Qg 2/3
(9)
Line Fire Flame Height L C 0.017Qg 2/3
(10)
modate large density deficiencies present in fire plumes. These equations do not apply to fire plumes with small temperature rises, such as !To/Tã H 1. For normal atmospheric conditions, for example,
where Qg C length of heat release per meter length of the fire source
PLUME CENTERLINE TEMPERATURE AND VELOCITY The plume centerline excess temperature and velocity at elevations above the mean flame height can be estimated from the following equations13 (Figure 3.9.3): ¡ ¢1/3 T >5/3 (11) !To C 9.1 £ 2ã 2 ¤ Qg 2/3 c (Z > Z o) gCp pã Œ
g Uo C 3.4 Cp pã Tã
1/3 >1/3 Qg 1/3 c (Z > Z o)
Flame and Fire Plume Characteristics
(12)
where !To C excess centerline mean temperature (Tg > Tã)(K) Tg C gas temperature (K) Tã C ambient temperature (K) g C acceleration of gravity (9.81 m/s2) Cp C specific heat of air at constant pressure [(kJ/kg)/K] pã C ambient air density (kg/m3) Qg c C convective heat release rate (kJ/s or kW) Z C elevation above burning fuel fire source (m) Z o C location of virtual fire source (m) Uo C centerline mean velocity (m/s) Equations 11 and 12 are based on extensive experimental data and are known as strong plume correlations, which accom-
T C 293 K g C 9.81 m/s2 C C 1.00 [(kJ/kg)/K] : C 1.2 kg/m3 Equations 11 and 12 can be simplified to >5/3 !To C AQg 2/3 c (Z > Z o)
(13)
>1/3 Uo C BQg 1/3 c (Z > Z o)
(14)
where A C 25.0 Km5/3 kW–2/3 B C 1.03 m4/3 s–1 kW–1/3 While methods exist to calculate excess temperature and velocities at locations other than along the plume centerline, the highest confidence is placed on centerline estimates. The reader is referred to DiNenno,1 Beyler,11 and Heskestad13 for a detailed discussion of noncenterline temperature and velocity estimates. The use of centerline excess temperature and velocity for evaluating exposure conditions is conservative since the centerline values are the highest values at any elevation. The estimates are sensitive to values for the convective heat release rate, Qg c, which can vary from 60 to 80 percent of the total heat release rate, depending on the type and arrangement of the burning fuel.
CALCULATING THE HYPOTHETICAL VIRTUAL ORIGIN (Zo) In order to estimate the plume centerline mean temperature and velocity, one must first determine the virtual origin. The virtual origin is the hypothetical location or elevation associated with a
CHAPTER 9
substitution of a point source fire for the actual fire in question (Figure 3.9.3). The consideration of virtual origin is most important for evaluating centerline conditions near the fire. As the distance above the fire increases, the impact of the discrepancy that results from neglecting the virtual origin decreases. It is common practice to ignore virtual source considerations for calculations where the distance above the fire is many times the diameter of the fire. For centerline elevations near the fire, however, a more accurate estimate of the position of the virtual source is necessary. The following expression, limited to pool fires and horizontal burning, provides an estimate of the location of the virtual source:10 Z o C >1.02D = 0.083Qg 2/5
(15)
where Z o C location of virtual fire source (m) D C diameter of burning fuel surface (m) Qg C total heat release rate (kJ/s) or (kW)
RADIANT HEAT FLUX TO A TARGET For many fires, it is of interest to estimate the radiation transmitted from a burning fuel array to a target located some distance from the fire. Fairly sophisticated methods for such estimates exist in the literature.14 These methods are derived primarily from correlations of experimental flammable liquid pool fire data. The simplified methods provided here are to be used primarily as screening methods.
Lawson and Quintiere Method Lawson and Quintiere9 developed a simple hemispheric model based on correlations of available experimental data (Figure 3.9.4). The following expression was developed, based on these correlations, to estimate the radiant heat flux from a fire to a target positioned normal to the radial distance: ?rQg P 2 V 49Ro 49Ro2
(16)
where
qgo C incident radiation on the target (kW/m2)
Ro C distance to target fuel (m) P C total radiative power of the flame (kW) ?r C radiative fraction Qg C total heat release rate (kJ/s or kW) The radiative fraction ?r, varies from 0.2 to 0.4, depending on the fuel type and pool diameter. The experimental measurements relied upon indicate that Equation 16 has good accuracy for Ro B4 R
Simplified Fire Growth Calculations
3–135
Hemisphere Target fuel element oriented normal to RO
Flame
RO
R
FIGURE 3.9.4
Radiant Heat Transfer to a Target
where R (in meters) is the radius of the base of the fire. At values of Ro/R A 4, the method tends to underpredict the incident heat flux.
Shokri and Beyler Correlation
The virtual source can be at, above, or below the base of the burning fuel.
qgo C
■
An alternative approach to the Lawson and Quintiere method is the Shokri and Beyler Correlation,14 which was developed from large-scale pool fire data. This simple correlation can be used to estimate the heat flux to a vertically oriented surface (i.e., target) at ground level. The incident heat flux is given by “ —>1.59 L qgo C 15.4 (17) D where D C diameter of the pool fire (m) L C distance from the center of the pool fire to the target (m) Noncircular pool fires with length to width ratios of approximately one (e.g., square surfaces) can be evaluated based on the use of an equivalent diameter, De. De is given by ˆ ‡ † 4A (18) De C 9 where A C the surface area of the noncircular pool. This correlation is based largely on liquid fuels that have pool diameters ranging from 1 m to 50 m, and that produce luminous flames. Further, the data used were limited to values of L/D that were greater than the range of 0.7 to 15. Uses of this correlation for L/D values less than 0.7 will under predict the estimates of radiant heat flux. This correlation provides realistic predictions of incident heat flux levels. Shokri and Beyler14 recommend the use of a safety factor of two for general design applications.
Point Source Method The point source method14 is based on a simple relationship that varies as the inverse square of the distance (D) to the target (Figure 3.9.5). It is useful for estimates of incident radiant fluxes that are less than or equal to 5 kW/m2. The incident radiant flux is given by Qg cos 1 qgo C r 2 (19) 49R
3–136 SECTION 3 ■ Information and Analysis for Fire Protection
Qg C total heat release rate (kJ/s or kW)
Point source (P )
g C acceleration of gravity (m/s)
Flame
Cp C specific heat of air at constant pressure [(kJ/kg)/K] R
:ã C density of air (kg/m3)
Target
As C total surface area of enclosure interior excluding vent area (m2)
θ
A= C vent area (m2)
D
FIGURE 3.9.5 Point Source Heat Transfer to a Target Fuel (Source: Society of Fire Protection Engineers, “Assessing Flame Radiation to External Targets from Pool Fires,” Engineering Guide, June 1999)
where Qg r C total radiative energy output of the fire (kJ/s or kW) 1 C angle between the normal to the target and the line of sight from the target to the point source location
h= C vent height (m) hk C effective enclosure conductance [(kW/m)/K] ƒ The terms hkAs and A= h= should be summed in Equation 21 for multiple structural materials and openings, respectively. In addition, although it is recognized that the enclosure gas temperature varies within the compartment, this equation is based on the assumption that an average upper-layer temperature and an average lower-layer, or ambient, temperature reasonably approximate temperature conditions in the enclosure. By substituting values for ambient conditions for key variables in Equation 21,
R C distance from the point source to the target (m)
Cp C 1.0 (kJ/kg)/K, at one atmosphere
The location of the equivalent point source with identical total radiative power, P, is at the center of the pool fire and at the mid-height of the flame. The flame height can be estimated using Equation 8. Qg r can be estimated similarly to Lawson and Quintiere by
:ã C 1.18 kg/m3, density of ambient air
Qg r C ?rQg C (0.21 > 0.0034D)Qg
PREFLASHOVER TEMPERATURE ESTIMATES Several researchers have developed correlations for predicting temperature rise in developing enclosure fires before. McCaffrey et al. suggest the following expression for naturally ventilated fires, based on correlation of an extensive number of enclosure experiments:15 ¡ ¢2/3 ¡ ¢>1/3 g h A Q !T k s ƒ ¤ £ ƒ ¤ C 1.63 £ (21) Tã Cp:ãTã A= gh= Cp:ã A= gh= !T C temperature rise of upper gas (K) T C gas temperature (K) Tã C ambient air temperature (K)
g C 9.81 m/s2 gravitational constant A simplified expression can be provided of the form ¡ ¢1/3 g2 Q ƒ ¤ (22) !T C 6.85 £ hk As A= h=
(20)
Qg can be estimated using Equation (3). The point source method assumes that the pool fire is circular or nearly circular. The point source configuration factor assumption is more appropriate at larger distances from the fire; that is, where L/D is greater than 2.5. At closer locations, this method underpredicts the incident heat flux. Because this method is limited to prediction of incident heat fluxes at or below 5 kW/m2 (due to limited data), it is not suitable for use in estimating the potential for ignition of combustibles. However, reasonable estimates of lower heat fluxes associated with damage to electronics or other thermally sensitive equipment as well as the onset of burns can be expected.
where
Tã C 295 K, ambient air temperature
where Œ
k:cp hk C t
1/2 for t D t p
and hk C
k -
for t B t p
where k C thermal conductivity of enclosure surface material [(kW/m)/K] : C density of enclosure materials (kg/m3) cp C specific heat of enclosure material [(kJ/kg)/K] - C enclosure material thickness (m) t C time (s) ‹ :cp - 2 tp C , thermal penetration time (s) k 2 For an enclosure lined with gypsum board, key variable values are cp C 1.1 (kJ/kg)/K : C 960 kg/m3 k C 0.0017 (kW/m)/K - C 0.016 m
CHAPTER 9
Thus, 1/2
hk C (0.18/t)
for t D t p, (0.00017/-) for t B t p
where t p C 400 s for 16-mm (5/8-in.) thickness of gypsum board. For the case of completely forced ventilation conditions, a correlation for enclosure temperature rise has been developed by Foote et al.16 0.72 Œ >0.36 Œ hk As Qg !T C 0.63 (23) mg =Cp Tã mg =CpTã where mg = C compartment forced mass ventilation rate (kg/s). For detailed discussions of methods that address multiple vents as well as forced ventilation, the reader is referred to DiNenno, Foote, et al., and Deal and Beyler.1,16,17
PREDICTION OF FLASHOVER A critical point in room fire growth is an event often referred to as flashover. Although a universal definition does not exist, this event is generally associated with rapid transition in fire behavior from localized burning of fuel to involvement of all the combustibles in the enclosure. Experimental work indicates that this transition can occur when upper room temperatures are between 750 and 1100°F (400 and 600°C).18 Using a value of 932°F (500°C), Equation 15 may be solved for the heat release rate necessary to achieve flashover in a naturally ventilated enclosure.9 The resulting equation is Š ƒ "1/2 (24) Qg fo C 610 hk As A= h= where Qg fo C heat release rate at flashover (kJ/s or kW) 2
hk C enclosure conductance [(kW/m )/K] 2
As C total enclosure area (m ), excluding vent area
■
Simplified Fire Growth Calculations
3–137
but they were extended by Law20 through the evaluation of extensive preflashover room fire data. The results indicate that the predictions reasonably, but not exactly, predict the temperatures reported in the test fires. The equation does not consider variations in the thermophysical properties of room linings. Most of the tests used to justify the equation-involved rooms lined with gypsum board or concrete block. Caution should be exercised in applying these equations to rooms lined with highly insulating materials, such as fiberglass or foamed materials, or rooms in which major portions of the lining are of thermally thin materials such as steel or glass. Forced ventilation is considered to occur when significant air is supplied by a ventilation system. The natural ventilation equation assumes that, at the time of peak temperature, all of the air for combustion will be drawn into the room through the vent openings and that these same openings will vent the product gases. This results in a natural sharing of the opening by the incoming air and out flowing gases that obey the laws of conservation of mass. The forced ventilation equation assumes that enough air is supplied to ensure that the fire will be free burning. It should be used only when the rate of air supply is sufficient to ensure such burning. Where forced ventilation is not enough to ensure free burning but is sufficient to cause concern that the assumed conservation in the natural venting equation has not been preserved, the peak temperature is expected to lie between the predictions of the two approaches. The expression for natural ventilation conditions is ” ˜ (1 > e>0.100 !Tmax C 6000 (1 > e>0.05@) (26) (0)1/2 where !Tmax C peak temperature rise (K) 0 C [As /A= (h=)1/2 ]
A= C area of vent opening (m2)
@ C Lf /(A= As)1/2
h= C height of vent opening (m)
As C total surface area of enclosure interior interior excluding vent area (m2)
Assuming that an enclosure has been heated thoroughly before flashover, that is, t B t p, Equation 24 can be simplified to* ’ ƒ –1/2 Qg fo (min) C 610 (k/-)As A= h= (25) where k C thermal conductivity of enclosure material [(kW/m)/K] - C enclosure material thickness (m)
POSTFLASHOVER TEMPERATURE ESTIMATES An alternative approach to estimating peak enclosure temperature was originally developed by Thomas,19 and extended by Law20 to include both natural and forced ventilation. The correlations were based initially on postflashover enclosure fire data,
*For 13-mm (1/2-in.) thickness of gypsum board enclosure liner, k/- C 0.014. For 16-mm (5/8-in.) thick gypsum, k/- C 0.011.
A= C vent area (m2) h= C height of vent opening (m) Lf C total enclosure fire load (equivalent weight of wood) (kg) The expression for forced ventilation conditions is !Tmax C 1200 (1 > e>0.04@)
(27)
EQUIVALENT FIRE DURATION Equivalent fire duration or fire severity is an approximation of the potential destructive impact of the burnout of all the available fuel in a room or space with at least one opening. The correlation presented here was developed by Law.21 The results predict the potential impact of a postflashover fire in terms of equivalent exposure in a fire-endurance furnace fired to follow the European equivalent exposure of the ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials, (NFPA 251, Standard Methods of Tests of Fire Endurance of Building
3–138 SECTION 3 ■ Information and Analysis for Fire Protection
Construction and Materials) standard time-temperature curve. Law based her correlation on data developed through an international research program carried out under the auspices of the Conseil International du Batiment (CIB). The results of this CIB effort are reported by Thomas and Heselden.22 All of the tests were conducted with wood crib fuel sources. Law reports about 20 percent variation, depending on the porosity of the fuel. In wood cribs, porosity is defined by the ratio of open volume between the sticks of the crib and the total volume of the crib, the greater fire severity being experienced with the more loosely packed cribs. Law extended the crib analysis to show that data from burnout tests using a range of fuel types in normal size rooms could be correlated by Equation 28. This correlation is not appropriate for rooms that do not have openings for ventilation. Although no precise minimum can be stated, it is suggested that this equation not be used unless the area of the opening is at least greater than that of a typical residential window. The equation also assumes that virtually all of the potential energy in the fuel is released in the involved room. This holds true for the wood cribs used in the CIB tests. This assumption may not hold true where there are large surface areas, such as in rooms having combustible linings or in rooms that contain extensive materials with low thermal inertia, such as foam plastics. In these cases, the generation of pyrolized fuel may significantly exceed the combustion ability of the air drawn through the ventilation openings into the fire room. When this occurs, some of the fuel leaves the room in the vented gases. This often burns in the expelled gases causing the extension of flame from the room. In such cases, Equation 28 should be expected to over predict the equivalent fire duration by an amount approximately proportional to the portion of the fuel that does not burn in the room being evaluated. ¡ ¢ Lf ¤ t C 60 £ ƒ (28) AsA= where
Cp C specific heat of air at constant pressure [(kJ/kg)/K] Tã C ambient air temperature (K) g C acceleration of gravity (m/s2) Y C distance from the virtual point source for the fire to bottom of smoke layer (m) Assuming an ambient air temperature of 293 K (20°C), Equation 29 can be reduced to mg s C 0.065Qg 1/3Y 5/3
(30)
When the flame height exceeds Y in Equation 30, Equation 30 tends to overpredict gas production. Equation 30 does not apply to elevations in the flame region. However, McCaffrey24 has investigated gas temperatures and velocity distributions within the flame and intermittent flame regions for fire up to 250 kW. Under these conditions, the mass flow rate of combustion products was found to correspond to the following expression: mg s C 0.055Qg 1/2Y
(31)
Equations 30 and 31 are based on the assumption that the fire can be reasonably approximated as a circular pool fire. Experiments have shown that reasonable results will be obtained with fires that are not circular, provided that the aspect ratio of length to width is relatively small. The equations are not suitable for conditions where entrainment is restricted (e.g., the fire is against a wall) or if the fire is long and narrow (e.g., a line fire). An alternative approach to predicting smoke production rates in enclosures has been developed by Butcher and Parnell,25 based on the size of the fire perimeter and vertical distance to the smoke layer. This approach assumes a constant heat release rate. Based on this approach, smoke production rate can be expressed as 1/2 ΠTo 3/2 mg s C 0.096P:oy g (32) Tf l where
t C fire severity (s) As C surface area of enclosure interior surfaces, excluding vent area (m2) A= C vent area (m2)
The rate of smoke-filled gas produced by a fire is nearly equal to the rate of air entrained into the rising fire plume; therefore, the mass production rate of smoke-filled gas can be estimated as equal to the mass flow rate of gas in the fire plume. This mass flow rate into a plume above the visible flame height may be estimated using an expression developed by Zukoski.23
mg s C rate of smoke-filled gas production (kg/s) Qg C total heat release rate (kJ/s or kW) 3
:ã C density of air (kg/m )
y C distance from floor to bottom of smoke layer (m) Tf l C flame temperature (K)
SMOKE-FILLED GAS PRODUCTION RATE
where
P C perimeter of fire (m) To C ambient temperature (K)
Lf C wood fuel mass (kg)
>1/3 >1/3 1/3 5/3 mg s C 0.18Qg 1/3:2/3 Tã g Y ã Cp
mg s C rate of smoke production (kg/s)
(29)
po C density of ambient air (kg/m3) g C gravitational acceleration (9.81 m/s2) Since the expression assumes a constant or steady burning rate, its application has limitations. Yet it will provide a reasonable estimate of smoke generation rate for many enclosure configurations of practical interest. This expression can be further simplified, based on value assignments for selected parameters. That is, for :o C 1.22 kg/m3 at 17°C To C 290 K Tf l C 1100 K g C 9.81 m/s2
CHAPTER 9
Equation 32 is reduced to mg C 0.188Py
3/2
(33)
Figure 3.9.6 provides graphical results based on the calculation of the smoke-filled gas mass production rate in Equation 32 for selected values of P and y.25 The mass rate of smoke-filled gas production can be changed to a volume rate by dividing by the density of air at the appropriate gas temperature.
ENCLOSURE SMOKE FILLING Smoke from a fire begins to fill an enclosure as it accumulates below the ceiling. The rate of smoke filling depends on the amount of smoke produced and the size and location of vents. The mass rate of smoke flow at any distance above a fire of known heat release rate can be calculated using Equation 29. The rate at which a smoke-filled layer descends toward the floor depends on the plan area of the enclosure, the distance of the lower edge of the smoke layer above the fire, and the temperature of the layer. For an enclosure vented in the lower layer, the upper layer descends with a velocity given by Ut C
mg s :lAp
(34)
where Ut C rate of layer descent (m/s) mg s C mass rate of smoke production (kg/s) :l C density of smoke layer (kg/m3) Ap C enclosure floor area (m2) The lower limit for the velocity of descent is obtained by using Equation 28 and the ambient density :ã. Fires in enclosures in which the upper layer is vented can stabilize at a constant-depth smoke layer. Venting can occur nat200
10
9
8
7
6
150 4 100 3
50
Height of clear layer (m)
Mass of smoke produced (kg/s)
5
40 60 Size of fire perimeter (m)
80
3–139
urally through openings, such as doors and windows, or it can be forced by mechanical smoke control systems. For the case of a known vent flow rate, the height of the bottom of the smoke layer stabilizes above the fire at the position where smoke mass inflow from the fire plume equals vent outflow. This is calculated using a known vent mass flow rate, mg s=, and solving Equation 30 for position Y= as Y= C 1.9Qg >1/5mg 3/5 s=
(35)
This shows that the height at which a smoke layer may be stabilized by venting depends mostly on the vent capacity and is relatively insensitive to changes in the fire heat release rate.
BUOYANT GAS HEAD During a fire, a pressure differential develops between the fireheated areas and other spaces. Essentially, expressions for pressure differential are derived from the basic hydrostatic equation. The equations in this section resulted from rearrangement of terms and simplification based on assumed values for selected variables. These expressions are useful in evaluating a range of enclosure effects caused by pressure differentials. Examples include potential for smoke flow to overcome normal air flow, the pressure loading on a door due to the fire, and the uplift pressure on ceiling tiles. The pressure calculated by these equations results from the difference between the density of a heated gas column from the fire and the density of the surrounding environment. A pressure surge can also result from the expansion of heated gases in those situations where the rate of fire development is fast and the space is not vented sufficiently to relieve the resultant increase in gas volume. The equations given below, however, address only the pressure difference caused by the heated gas column condition. The equations are universal to any heated gas column and can apply to buoyant gas heads caused by building stack effects or other temperature differential effects, including, but not limited to, those caused by fire. The equations, as presented, assume that the entire column of heated gas is at the same temperature. This is a reasonable approximation in many fires but is not exact and would be inappropriate for a fire where the condition consisted of a plume freely entraining cooling air over an extensive portion of its length or any other condition where a significant temperature gradient existed in the heated gas column being appraised. The general equation can be expressed as (36)
where
2
20
Simplified Fire Growth Calculations
!P C (:o > :c)gh !P C pressure difference (Pa)
:o C gas (air) density outside the heated gas column (kg/m3)
1 0
■
100
FIGURE 3.9.6 Smoke-Filled Gas Production Rate for Steady Fires at Various Distances (m) from Virtual Origin to Bottom of Smoke Layer
:c C gas (smoke or flame) density of the heated gas column (kg/m3) g C gravitational constant (m/s2) h C distance above point where gas column density is same as density outside the heated column. [In a fire, this is normally the base of the hot gas column (m).]
3–140 SECTION 3 ■ Information and Analysis for Fire Protection
If it is assumed that the outside atmosphere and the gas column are predominantly air at standard atmospheric pressure, the equation can be expressed as: Œ 1 1 !P C 3460 > h (37) Tã Tc where !P C pressure difference (Pa) Tã C absolute temperature of air outside the heated gas column (K) Tc C temperature of the heated gas column (K) h C height of the portion of interest of the hot gas column (m)
[Tm(plume)] set equal to the activation temperature of the thermal device. In this form, Equation 38 becomes Qg C 0.0144 (Tm(plume) > Tã)3/2 ? h5/2
Based on cases where the hot gases have begun to spread under a ceiling located above the fire, Equation 39 also applies for a small radial distance, r, from the impingement point (Figure 3.9.7). Over this distance, up to r/h C 0.18, where the gas is turning to flow out under the ceiling, the highest temperature in the flow remains equal to the value at the impingement point directly over the fire, calculated using Equation 38. At radial distances greater than r/h C 0.18, the maximum temperature in the ceiling jet flow depends on the distance from the impingement point, according to
For further discussion, see Klote and Milke.26
Tm(jet) C 5.38
THERMAL FIRE DETECTOR RESPONSE
(Qg /r)2/3 = Tã h
(40)
where
Computer programs have been developed to calculate the response time of heat detectors and sprinklers installed below ceilings in large rooms.27,28 These programs can determine the time to operation for a user-specified fire energy release rate history. They are convenient to use because the tedious repetitive calculations needed to analyze a growing fire can be avoided. However, the same calculations can be performed easily with a scientific hand calculator for steady fires that have a constant energy release rate. In cases where a more detailed analysis of a fire that has important changes in energy release rate over time is required, the fire may be represented as a series of steady fires occurring immediately after one another. A useful calculation directly related to thermal detection is to find the plume temperature at positions directly above the flame produced by burning materials. This can be done using the centerline plume temperature correlation or the following simplified correlation.29 Qg 2/3 Tm(plume) C 16.9 5/3 = Tã h
(39)
(38)
h C distance above fuel surface (m) Qg C fire energy release rate [(kJ/s) or (KW)] r C radial distance from plume centerline to device (m) Tm(jet) C temperature of ceiling jet (K) Tã C ambient room temperature (K) Correlations are also available for maximum velocities in the ceiling jet flow, Um, under a ceiling. As with the temperature correlations, there are two regions: (1) one close to the impingement point where velocities are nearly constant and (2) the other farther away where velocities vary with radial position. The two correlations are expressed as follows: Œ 1/3 Qg Um C 0.096 for r/h A 0.15 (41) h and Œ
Qg 1/3h1/2 Um C 0.195 r 5/8
1/3 for r/h B 0.15
(42)
where r C radial distance from plume centerline to device (m)
where h C distance above fuel surface (m) Qg C fire energy release rate [(kJ/s) or (kW)] Tm(plume) C plume gas temperature above fire (K)
Um C gas velocity (m/s) Equations 39 and 40 can be used to determine whether the temperature of the fire-driven gas flow past a detection device is
Tã C ambient room temperature (K) This equation was developed from analysis of experiments with large-scale fires having energy release rates from 670 kW to 100 MW.29 For example, using Equation 38, the plume gas temperature [Tm(plume)] 5 m (h) above the fuel surface of a 500 kW (Qg ) fire is found to be 366 K (93°C) for an ambient room temperature (Tã) of 293°K (20°C). For the case of fixed-temperature detectors, the minimum fire energy release rate, Qg , needed to operate a fixed-temperature detection or suppression device located directly above the fire can be estimated using Equation 38, solving for Qg with
r h
FIGURE 3.9.7 Parameters h and r Both Related to Calculation of Sprinkler or Heat-Detector Actuation Time
CHAPTER 9
high enough to operate the device. However, more information is needed to calculate the amount of time needed to heat the detector or sprinkler-sensing element to the operating temperature. Often, these elements are made of metal, such as the ordinary solder-type fusible link used in the link and lever sprinklers, or they are liquid-filled glass vials, such as those used in bulb-type sprinklers. Both of these sensing elements require some time to absorb the heat transferred from the hot gas flowing around the device. For steady fires, the time required to heat the sensing element of a thermal detection or suppression device from room temperature to operation temperature is given by Œ Tm > Tã RTI toperation C ƒ loge (43) Tm > Toperation Um where RTI, the response-time index, is a measure of the ease of heating thermal elements in heat detectors and sprinklers. The larger the RTI value, the greater the lag in heating the sensing element. RTI values for sprinklers have been measured30 in the range of 15 m1/2s1/2 to 400 m1/2s1/2. In the previous example, it was found using an earlier equation that a 500-kW (Qg ) fire would produce a gas temperature of 366 K [Tm(plume)] at 5 m (h) above the fuel surface in a room with 293 K (Tã) ambient temperature. From Equation 41, the gas velocity at this position would be 4.4 m/s (Um). For a sprinkler with an RTI of 200 m1/2s1/2 and operation temperature of 347 K (Toperation), the time to operation in response to the steady fire can be calculated from Equation 43 as ‹ 200 93 > 20 ƒ loge C 128 s toperation C 93 > 74 4.4 The measurement of thermal lag for sprinkler is a topic of current research investigations and validation.31,32 Recent progress has included means to account for the effects of heat loss due to conduction.33 It has been found that, for cases when the gas temperature does not substantially exceed the activation temperature for the sprinkler, significant error can occur in the prediction for activation time. In these cases it is possible for small changes in predicted gas temperatures to result in large changes in predicted operation time.31 In the case of constant or slowly varying gas temperatures this effect may be important where Tm > Toperation 1 A Tm > Tã 4
(44)
Another factor that contributes to the inaccuracy of predicted results, using Equation 43 under low gas temperatures and gas velocities and also for low RTI values, is that no means is included to account for loss of heat from sensing element, either link or glass bulb, to the sprinkler frame and piping by conduction. Heskestad and Bill33 and Ingason34 have studied means to account for the effects of conduction loss, and measured values for it for sprinkler hardware. Following Heskestad and Bill,33 Equation 43 can be modified to account for the conduction losses to the frame and piping, which are assumed to be at constant temperature equal to the initial ambient temperature (Tã) as
toperation C
■
Simplified Fire Growth Calculations
3–141
¹ º Tm > Tã º ¢ loge ¹ ¹ º C Ÿ ƒ ƒ T > T > (T ) C m operation operation>T £ ¤ ã Um 1 = ƒ Um Um ¡ RTI
(45) where C is a conduction loss parameter with units (m/s)1/2 obtained by measurement.33,34 A realistic range of values for the conduction loss parameter is 0.5 to 1.6 (m/s)1/2, the expected operation time for the sprinkler in the example would increase to 190 s as predicted using Equation 45, which is over 1 min slower than the prediction of 128 s (using Equation 43 or Equation 45 with C C 0). At a value of C B 0.74 (m/s)1/2, the heat loss would be great enough to prevent sprinkler operation even though the gas temperature was sustained above the indicated operating temperature of the sprinkler. All calculations in use today for determining times to operation only consider the convective heating of sensing elements by the hot fire gases. They do not account explicitly for any direct heating by radiation from the flames. Research is continuing to evaluate and improve calculations of operation for heat-activated devices, such as sprinklers.
ORDINARY SPRINKLER FIRE SUPPRESSION Fire suppression with water is an extremely complex physical, thermal, and chemical problem. Recently, work has been performed to aid in the design and analysis of sprinkler fire suppression experiments using fire modeling to predict the heat release rate of a fire after sprinkler operation.35 Often, all that is needed is to gain some insight into the probable conservative bounds for time needed for suppression of fires. In that regard, a limited series of experiments has been conducted to measure the heat release rate during suppression for a series of light hazard occupancy fires involving furnishings. Data from these experiments have been correlated and bounded by a simple expression that permits hand calculations of the rate of heat release from fires during suppression by sprinklers. Figure 3.9.8 shows the results of measured heat release rate for furnishing and wood cribs normalized to the rate of heat release rate at the time of sprinkler operation. As expected, there is a wide range of behaviors. Some furnishing fires are more easily suppressed than others. The heat release rate from the sofa fire decreases rapidly—less than 10 percent of its initial value in about 20 s. The more complex Office I Fuel Package takes about 500 s to decrease by the same percentage. The regular array of wood sticks that make up a wood crib presents both exposed and hidden burning surfaces that are difficult to extinguish. Over 800 s of sprinkler water spray is needed to reduce the heat release rate of the wood cribs tested by 90 percent. All of this test data were collected using a water spray density of 0.07 mm/s (0.1 gal/min/ft2).36
3–142 SECTION 3 ■ Information and Analysis for Fire Protection
per unit of exposed surface area of the crib, the data from experiments using two different height cribs could be collapsed into a single correlation. The wood crib fire suppression was analyzed in the same way as furniture fires have been analyzed previously. Results showed that for water spray densities varying from 0.03 mm/s to 0.13 mm/s, at flow rates below the minimum, no substantial effect on heat release rate was measured. Although the data was scattered, as is common with suppression experiments, results38 showed that for water spray densities varying from 0.03 mm/s to 0.13 mm/s the time constant for the exponential decay in heat release rate varied as
1
Q (t – tact) /Q (tact)
e–(t – tact)/410
•
0.4
•
0.3
t e C 3.0 (mw)>1.85
0.2
(47)
where mw 0.1
0
200
400
600
At flow rates below the minimum, no substantial effect on heat release rate was measured. Using Equation 47, the conservative estimate for exponential decay in heat release rate for furnishing fires suppressed with a water spray density of 0.07 mm/s (0.1 gal/min/ft2) is
800
t – tact Paper cart fuel package
t e C 3.0 (0.07)>1.85 C 410 s
Executive desk fuel package Office II fuel package
(48)
Using this time constant, the predicted values of the normalized heat release rate during suppression appear along the straight line in Figure 3.9.8. This provides a conservative upper bound for almost all of the data. Using the correlation (Equation 47), Equation 46 may be rewritten for water spray densities varying from 0.03 mm/s to 0.13 mm/s as
Office I fuel package Sofa fuel package Work station I fuel package Work station II fuel package Average of two tests (crib type 38.1 × 6 × 16 × 18)
FIGURE 3.9.8 Heat Release Reduction During Suppression of Furnishing Fires with Ordinary Sprinklers (Data for spray density of 0.07 mm/s [0.1 gal/min/ft2]). (Source: A Sprinkler Fire Suppression Algorithm for the GSA Engineering Fire Assessment System, NISTIR 4833)
An upper bound for the data can be constructed by drawing a straight line of the semilog plot. This line results in an expression for the conservative bound (meaning least expected reduction in heat release rate) for suppression of a furnishing fire. This line represents the heat release rate during suppression as a decaying exponential function of time as follows: Qg (t > t act)/Qg (t act) C exp (t > t act)/t e
C water spray density (mm/s)
(46)
where Qg C rate of heat release t C time (s) tact C time spray suppression begins (s) t e C time constant for exponential decay (s) A limited experimental study of wood crib fire suppression was conducted by Walton37 and analyzed by Evans.38 Using the results of an earlier study39 that showed the time to extinction of wood crib fires was proportional to the water application rate
Qg (t > t act)/Qg (t act) C exp [(>1/3)(t > t act)(mw)1.85 ] (49) Equation 49 is used in the current FPEtool version 3.240 and CFAST version 3.1.641 to estimate the reduction in heat release rate for fires due to the effect of water spray from sprinklers. Although far from a general prediction of fire suppression, Equation 49 provides the user with means to demonstrate the minimum effect expected from the application of water from ordinary sprinklers in suppressing light hazard fires.
SUMMARY This chapter provides equations that can be evaluated using hand calculators to estimate fire conditions in enclosures. Predominately the chapter deals with fire during the preflashover fire growth period in which fire detection and sprinklers may be activated by the fire. The methods presented were developed from systematic studies of data from experiments that were conducted for very specific, and sometimes idealized, conditions. Therefore judgment must be used in applying the methods to particular complex fire conditions. Means to estimate ignitability of solids, flame heights, plume temperatures, radiant heat flux to targets, enclosure temperatures, fire duration, smoke-filled gas production rate, thermal fire detector response, and sprinkler fire suppression are given.
CHAPTER 9
BIBLIOGRAPHY References Cited 1. DiNenno, P. J., et al. (Eds.), SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995. 2. Kanury, A. M., “Flaming Ignition of Solid Fuels,” SFPE Handbook of Fire Protection Engineering, P. J. DiNenno (Ed.), National Fire Protection Association, Boston, MA, 1991. 3. Nelson, H. E., and Forssell, E. W., “Use of Small-Scale Test Data in Hazard Analysis,” Proceedings of the 4th International Symposium, International Association for Fire Safety Science, 1994, pp. 971–982. 4. Babrauskas, V., and Krasny, J. F., “Fire Behavior of Upholstered Furniture,” NBS Monograph, National Bureau of Standards, Gaithersburg, MD, 1985. 5. Lawson, J. R., et al., “Fire Performance of Furnishings as Measured in the NBS Furniture Calorimeter, Part 1,” NBSIR 832787, National Bureau of Standards, Gaithersburg, MD, Jan. 1984. 6. Alpert, R. L., and Ward, E. J., “Evaluating Unsprinklered Fire Hazards,” SFPE TR 83-2, Society of Fire Protection Engineers, Boston, MA, 1983. 7. Babrauskas, V., et al., “Upholstered Furniture Heat Release Rates Measured with a Furniture Calorimeter,” NBSIR 82-2604, National Bureau of Standards, Gaithersburg, MD, 1982. 8. Babrauskas, V., “Free-Burning Fires,” Proceedings, SFPE Symposium: Quantitative Methods for Fire Hazard Analysis, University of Maryland, College Park, MD, 1985. 9. Lawson, J. R., and Quintiere, J. G., “Slide-Rule Estimates of Fire Growth,” NBSIR 85-3196, National Bureau of Standards, Gaithersburg, MD, 1985. 10. Heskestad, G., “Virtual Origins of Fire Plumes,” Fire Safety Journal, Vol. 5, No. 109, 1983. 11. Beyler, C. L., “Fire Plumes and Ceiling Jets,” Fire Safety Journal, Vol. 11, No. 53, 1986. 12. Delischatsios, M., “Flame Heights in Turbulent Wall Fire with Significant Flame Radiation,” Combustion Science and Technology, Vol. 39, 1984, p. 195. 13. Heskestad, G., “Luminous Heights of Turbulent-Diffusion Flames,” Fire Safety Journal, Vol. 7, No. 25, 1984. 14. SFPE, Engineering Guide, “Assessing Flame Radiation to External Targets from Pool Fires,” Society of Fire Protection Engineers, Bethesda, MD, June 1999. 15. McCaffrey, B. J., Quintiere, J. G., and Harkleroad, M. F., “Estimating Room Temperatures and the Likelihood of Flashover Using Fire Test Data Correlations,” Fire Technology, Vol. 17, No. 2, 1981, p. 98. 16. Foote, K. L., Pagni, P. J., and Alvares, N. J., “Temperature Correlations for Forced-Ventilated Compartment Fires,” Proceedings of the 1st International Symposium, International Association for Fire Safety Science, New York, Hemisphere Publishing, 1986, pp. 139–148. 17. Deal, S. D., and Beyler, C. L., “Correlating Preflashover Room Fire Temperatures,” Journal of Fire Protection Engineering, Vol. 2, No. 2, 1990, pp. 33–48. 18. Thomas, P. H., “Testing Products and Materials for Their Contribution to Flashover in Rooms,” Fire and Materials, Vol. 5, No. 3, 1981, pp. 103–111. 19. Thomas, P. H., Fire in Model Rooms, CIB Research Program, Building Research Establishment, Borehamwood, Hertfordshire, UK, 1974. 20. Law, M., “Fire Safety of External Building Elements—The Design Approach,” AISC Engineering Journal, Second Quarter, American Institute of Steel Construction, 1978. 21. Law, M., “Prediction of Fire Resistance,” Proceedings, Symposium No. 5: Fire-Resistance Requirements for Buildings—A
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New Approach, Joint Fire Research Organization, H. M. Stationery Office, London, UK, 1973. Thomas, P. H., and Heselden, A. J. M., Fully Developed Fires in Single Compartments, A Co-operative Research Programme of the Conseil International du Batiment, Joint Fire Research Organization Research Note No. 923, H. M. Stationery Office, London, UK, 1972. Zukoski, E. E., “Development of a Stratified Ceiling Layer in the Early Stages of a Closed-Room Fire,” Fire and Materials, Vol. 2, No. 2, 1978, pp. 54–62. McCaffrey, B. J., “Purely Buoyant Diffusion Flames: Some Experimental Results,” NBSIR 79-1910, National Bureau of Standards, Gaithersburg, MD, 1979. Butcher, E. G., and Parnell, A. C., Smoke Controling Fire Safety Design, E. and F. N. Spon, Ltd., London, UK, 1979. Klote, J. H., and Milke, J. A., Design of Smoke Management Systems, American Society of Heating, Refrigerating, and AirConditioning Engineers, Atlanta, GA, 1992. Evans, D. D., and Stroup, D. W., “Methods to Calculate the Response Time of Heat and Smoke Detectors Installed Below Large Unobstructed Ceilings,” Fire Technology, Vol. 22, No. 1, 1985, pp. 54–65. Walton, W. D., and Notarianni, K. A., “Comparison of Ceiling Jet Temperatures Measured in an Aircraft Hanger Test Fire with Temperatures Predicted by the DETACT-QS and LAVENT Computer Models,” NISTIR 4947, National Institute of Standards and Technology, Gaithersburg, MD, 1993. Alpert, R. L., “Calculation of Response Time of CeilingMounted Fire Detectors,” Fire Technology, Vol. 8, 1972, pp. 181–195. Heskestad, G., and Smith, H., “Investigation of a New Sprinkler Sensitivity Approval Test: The Plunge Test,” FMRC Serial No. 22485, Factory Mutual Research Corporation, Norwood, MA, 1976. Madrzykowski, D., “Evaluation of Sprinkler Actuation Prediction Methods,” Proceedings of the 1st International Asiaflam Conference 1995, March 15–16, 1995, Kowloon, Hong Kong, InterScience Communications Limited, London, UK, pp. 211–218. Notarianni, K. A., and Davis, W. D., “The Use of Computer Models to Predict Temperature and Smoke Movement in High Bay Spaces,” NISTIR 5304, National Institute of Standards and Technology, Gaithersburg, MD, 1993. Heskestad, G., and Bill, R. G., “Quantification of Thermal Responsiveness of Automatic Sprinklers Including Conduction Effects,” Fire Safety Journal, Vol. 14, Nos. 1–2, 1988, pp. 113–125. Ingason, H., “Thermal Response Models for Glass Bulb Sprinklers, An Experiment and Theoretical Analysis,” SP Report 1992: 12, 1992, Swedish National Testing and Research Institute, Boras, Sweden. McGrattan, K. B., Hamins, A., and Evans, D. D., “Sprinkler, Vent and Draft Curtain Interaction—Modeling and Experiment,” Fire Suppression and Detection Research Application Symposium, Proceedings, February 25–27, 1998, Orlando, FL, National Fire Protection Research Foundation, Quincy, MA 1998, pp. 98–106. Madrzykowski, D., and Vettori, R. L., “A Sprinkler Fire Suppression Algorithm for the GSA Engineering Fire Assessment System,” NISTIR 4833, NIST/BFRL, Gaithersburg, MD, 1992. Walton, W. D., “Suppression of Wood Crib Fires with Sprinkler Sprays: Test Results,” NISTIR 88-3696, NIST/BFRL, Gaithersburg, MD, 1988. Evans, D. D., “Sprinkler Fire Suppression Algorithm for HAZARD,” NISTIR 5254, NIST/BFRL, Gaithersburg, MD, 1993. Tamanini, F., “The Application of Water Sprays to the Extinguishment of Crib Fires,” Combustion Science and Technology, Vol. 14, 1976, pp.17–23. Deal, S., “Technical Reference Guide for FPEtool Version 3.2,” NISTIR 5486-1, NIST/BFRL, Gaithersburg, MD, 1995.
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41. Jones, W. W., Forney, F. P., Peacock, R. D., and Reneke, P. A., “A Technical Reference for CFAST: An Engineering Tool for Estimating Fire and Smoke Transport,” NISTTN 1431, NIST/BFRL, Gaithersburg, MD, 2000.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on the elements of fire protection discussed in this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 251, Standard Methods of Tests of Fire Endurance of Building Construction Materials
Additional Readings ASTM E906, Standard Test Method for Heat and Visible Smoke Release Rates for Materials and Products, American Society for Testing and Materials, W. Conshohocken, PA, 1993. Babrauskas V., “A Closed-Form Approximation for Post-Flashover Compartment Fire Temperatures,” Fire Safety Journal, Vol. 4, 1981, pp. 63–73. Babrauskas, V., “Applications of Predictive Smoke Measurements,” Journal of Fire and Flammability, Vol. 12, 1981, p. 51. Babrauskas, V., “Burning Rates,” The SFPE Handbook of Fire Protection Engineering, 2nd Edition, Section 3/Chapter 1, National Fire Protection Association, Quincy, MA, 1995, pp. 3/1–3/15. Babrauskas, V., “Estimating Room Flashover Potential,” Fire Technology, Vol. 16, 1980, pp. 94–103, 112. Babrauskas, V., “Free Burning Fires,” Proceedings, SFPE Symposium: Quantitative Methods for Fire Hazard Analysis, University of Maryland, College Park, MD, 1985. Babrauskas, V., and Krasny, J. F., “Fire Behavior of Upholstered Furniture,” NBS Monograph, National Bureau of Standards, Washington, DC, 1985. Babrauskas, V., and Peacock, R. D., “Heat Release Rate: The Single Most Important Variable in Fire Hazard,” Fire Safety Journal, Vol. 18, No. 3, 1992, pp. 255–272. Battaglia, F., Rehm, R. G., and Baum, H. R., “Fluid Dynamics of Fire Whirls: An Inviscid Model,” National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6427, Feb. 2000. Baum, H. R., “Large Eddy Simulations of Fires: From Concepts to Computations,” Fire Protection Engineering, No. 6, 2000, pp. 36–38. Baum, H. R., McGrattan, K. B., and Rehm, R. G., “Large Eddy Simulations of Smoke Movement in Three Dimensions,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 189–198. Baum, H. R., McGrattan, K. B., and Rehm, R. G., “Three Dimensional Simulations of Fire Plume Dynamics,” Proceedings of the 5th International Symposium, International Association for Fire Safety Science, March 3–7, 1997, Melbourne, Australia, International Association for Fire Safety Science, Boston, MA, 1997, pp. 511–522. Baum, H. R., and Mell, W. E., “Radiative Transport Model for LargeEddy Fire Simulations,” Combustion Theory and Modelling, Vol. 2, 1998, pp. 405–422. Baum, R. T., McGrattan, K. B., and Nyden, M. R., “Examination of the Applicability of Computed Tomography for the Measurement of Component Concentrations in Fire-Generated Plumes,” Combustion and Flame, Vol. 113, No. 3, 1998, pp. 358–372. Chow, W. K., “Better Parameter for Specifying the Requirement of Smoke Control System in Atria,” Proceedings of Safety Conference 1997, Hong Kong Engineers: Engineering for Public Safety, April 23, 1997, Hong Kong, 1997, pp. 1–17. Chow, W. K., “On the Minimum Smoke Extraction Rate for Basement Required in the Local Fire Codes,” International Journal on Engineering Performance-Based Fire Codes, Vol. 2, No. 3, 2000, pp. 77–80.
Chow, W. K., “Predictability of Flashover by Zone Models,” Journal of Fire Sciences, Vol. 16, No. 5, 1998, pp. 335–350. Chow, W. K., “Study of Flashover Using a Single Zone Model,” Journal of Applied Fire Science, Vol. 8, No. 2, 1998/1999, pp. 159–175. Chow, W. K., and Cui, E., “Plume Equations for Studying SmokeFilling Process in Atria with a Zone Model,” Fire and Materials, Vol. 21, No. 5, 1997, pp. 235–244. Chow, W. K., and Mok, W. K., “CFR fire simulations with four turbulence models and their combinations,” Journal of Fire Sciences, Vol. 17, No. 3, 1999, pp. 209–239. Cooper, L. Y., “Simulating Smoke Movement Through Long Vertical Shafts in Zone-Type Compartment Fire Models,” Fire Safety Journal, Vol. 31, No. 2, 1998, pp. 85–99. Cooper, L. Y., “Simulating the Opening of Fusible-Link-Actuated Fire Vents,” Fire Safety Journal, Vol. 34, No. 3, 2000, pp. 219–255. Curtat, M. R., and Bodart, X. E., “Simple and Not So Simple Models for Compartment Fires,” Proceedings of the 1st International Symposium of Fire Safety Science, New York, Hemisphere, 1986, pp. 637–646. Delichatsios, M. A., “Fire Growth Rates in Wood Cribs,” Combustion and Flame, Vol. 27, 1976, pp. 267–278. Drysdale, D., An Introduction to Fire Dynamics, John Wiley & Sons, New York, 1985. Evans, D. D., “Calculation of a Fire Plume in a Two-Layer Environment,” Fire Technology, Vol. 20, No. 3, 1984, p. 39. Fujita, T., Yamaguchi, J., and Tanaka, T., “Investigation into Travel Time of Buoyant Fire Plume Fronts,” Proceedings of the 1st International Symposium on Engineering Performance-Based Fire Codes, September 8, 1998, Hong Kong, 1998, pp. 220–228. Ghojel, J. I., “New Approach to Modeling Heat Transfer in Compartment Fires,” Fire Safety Journal, Vol. 31, No. 3, 1998, pp. 227–237. Gross, D., “Data Sources for Parameters Used in Predictive Modeling of Fire Growth and Smoke Spread,” NBSIR 85-3223, National Bureau of Standards, 1985, Gaithersberg, MD. Hasofer, A. M., and Beck, B. R., “Stochastic Model for Compartment Fires,” Fire Safety Journal, Vol. 28, No. 3, 1997, pp. 207–225. Heskestad, G., “Modeling of Enclosure Fires,” 14th International Symposium on Combustion, Combustion Institute, Pittsburgh, PA, 1973, p. 1021. Huggett, C., “Estimation of Rate of Heat Release by Means of Oxygen Consumption Measurements,” Fire and Materials, Vol. 4, 1980, pp. 61–65. Ingason, H., “Plume Flow in High Rack Storage,” Fire Safety Journal, Vol. 36, No. 5, 2001, pp. 437–457. Ingason, H., and deRis, J., “Flame Heat Transfer in Storage Geometries,” Fire Safety Journal, Vol. 31, 1998, pp. 39–60. Karlsson, B., and Quintiere, J. G., Enclosure Fire Dynamics, CRC Press, Boca Raton, FL, 2000. Kawagoe, K., and Sekine, T., Estimation of Fire Temperature-Time Curve for Rooms, Japanese Ministry of Construction Building Research Institute, June 1963. Krasner, L. M., Burning Characteristics of Wooden Pallets as a Test Fuel, Factory Mutual Research Corporation, Norwood, MA, 1968. Law, M., “A Relationship Between Fire Grading and Building Design and Contents,” Fire Research Note 877, British Fire Research Station, 1971. Law, M., “Notes on the External Fire Exposure Measured at Lehrte,” Fire Safety Journal, Vol. 4, 1981/82, pp. 243–246. Log, T., and Heskestad, G., “Temperatures of Restricted Turbulent Fire Plumes,” Fire Safety Journal, Vol. 31, No. 2, 1998, pp. 101–115. Lovatt, A., “Comparison Studies of Zone and CFR Fire Simulations,” University of Canterbury, Christchurch, New Zealand, Fire Engineering Research Report 98/5, June 1998. Makhvaladze, G. M., Roberts, J. P., Yakush, S. E., and Agavonov, V. V., “Study of Fire Suppression in Enclosure by an Extinguishing Powder,” Journal of Applied Fire Science, Vol. 6, No. 4, 1996/1997, pp. 339–356. Makhviladze, G. M., Roberts, J. P., Melikhov, V. I., and Melikhov, O. I., “Numerical Modeling and Simulation of Compartment
CHAPTER 9
Fire Extinction by a Sprinkler Water Jet,” Journal of Applied Fire Science, Vol. 8, No. 2, 1998/1999, pp. 93–115. Matsuyama, K., Fujita, T., Kaneko, H., Ohmiya, Y., Tanaka, T., and Wakamatsu, T., “Simple Predictive Method for Room Fire Behavior,” Fire Science and Technology, Vol. 18, No. 1, 1998, pp. 23–32. McGrattan, K. B., “Smoke Plume Trajectory from in situ Burning of Crude Oil: Complex Terrain Modeling,” Proceedings of the 20th Arctic and Marine Oilspill Program (AMOP) Technical Seminar, June 11–13, 1997, Alberta, Canada, 1997, pp. 723–734. McGrattan, K. B., Baum, H. R., and Rehm, R. G., “Large Eddy Simulations of Smoke Movement,” Fire Safety Journal, Vol. 30, No. 2, March 1998, pp. 161–178. McGrattan, K. B., Baum, H. R., and Rehm, R. G., “Large Eddy Simulations of Smoke Plumes,” Proceedings of the 2nd International Symposium on Scale Modeling, June 23–27, 1997, Lexington, KY, 1997, pp. 59–72. McGrattan, K. B., Baum, H. R., Rehm, R. G., Hamins, A., and Forney, G. P., “Fire Dynamics Simulator: Technical Reference Guide,” National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6467, January 2000. McGrattan, K. B., Baum, H. R., Walton, W. D., and Trellies, J. J., “Smoke Plume Trajectory from in situ Burning of Crude Oil in Alaska: Field Experiments and Modeling of Complex Terrain,” National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 5958, January 1997, pp. 723–734. Modak, A. T., “Thermal Radiation from Pool Fires,” Combustion and Flame, Vol. 29, 1977, pp. 177–192. Modak, A. T., and Croce, P. A., “Plastic Pool Fires,” Combustion and Flame, Vol. 30, 1977, pp. 251–265. Naruse, T., and Hasemi, Y., “Wind Effect on Fire Behavior in Compartment,” Proceedings of the 15th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, March 1–7, 2000, San Antonio, TX, National Institute of Standards and Technology, NISTIR 6588, 2000, pp. 399–405. Naruse, T., and Sugahara, S., “Study on the Deterministic Properties of Fire Plumes,” Bulletin of Japanese Association of Fire Science and Engineering, Vol. 44, No. 1/2, 1996, pp. 25–37. Novozhilov, V., Fletcher, D. F., Moghtaderi, B., and Kent, J. H., “Numerical Simulation of Enclosed Gas Fire Extinguishment by a Water Spray,” Journal of Applied Fire Science, Vol. 5, No. 2, 1995/1996, pp. 135–146. Nyankina, K., Turan, O. F., He, Y., and Britton, M., “One-Layer Zone Modelling of Fire Suppression: Gas Cooling and Blockage of Flame Spread by Water Sprinklers,” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, June 29–July 1, 1999, Edinburgh, UK, Interscience Communications Ltd., London, UK, 1999, pp. 1081–1092. Peacock, R. D., Davis, S., and Lee, B. T., “An Experiment Data Set for the Accuracy of Room Fire Models,” NBSIR 88-3752, National Bureau of Standards, Gaithersburg, MD, Apr. 1988. Poreh, M., and Garrad, G., “Study of Wall and Corner Fire Plumes,” Fire Safety Journal, Vol. 34, No. 1, 2000, pp. 81–98. Poreh, M., and Morgan, H. P., “On Power Laws for Describing the Mass Flux in the Near Field of Fires,” Fire Safety Journal, Vol. 27, 1996, pp. 159–178. Poreh, M., and Trebukov, S., “Wind Effects on Smoke Motion in Buildings,” Fire Safety Journal, Vol. 35, No. 4, 2000, pp. 257–273. Porterie, B., Morvan, D., Loraud, J. C., and Larini, M., “Cross Wind Effects on Fire Propagation Through Heterogeneous Media,” Proceedings of the 6th International Symposium, International Association for Fire Safety Science (IAFSS), July 5–9, 1999, Poitiers, France, International Association for Fire Safety Science, Boston, MA, 2000, pp. 707–716. Quintiere, J. G., and Grove, B. S., “Unified Analysis for Fire Plumes,” Proceedings of the 27th International Symposium on Combustion, August 2–7, 1998, Boulder, CO, Combustion Institute, Pittsburgh, PA, 1998, pp. 2757–2766.
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Quintiere, J. G., “A Simple Correlation for Predicting Temperature in a Room Fire,” NBSIR 83-2712, National Bureau of Standards, Washington, DC, 1983. Quintiere, J. G., “Smoke Measurements: An Assessment of Correlations Between Laboratory and Full-Scale Experiments,” Fire and Materials, Vol. 6, Nos. 3 and 4, 1982. Quintiere, J. G., and Grove, B. S., “Unified Analysis for Fire Plumes,” Proceedings of the 27th International Symposium on Combustion, August 2–7, 1998, Boulder, CO, Combustion Institute, Pittsburgh, PA, 1998, pp. 2757–2766. Quintiere, J. G., and Rhodes, B., “Fire Growth Models for Materials. Final Report. June 1992–Dec. 1993,” Maryland University, College Park, National Institute of Standards and Technology, Gaithersburg, MD, NIST-GCR-94-647, June 1994. Quintiere, J., “A Perspective on Compartment Growth,” Combustion Science and Technology, Vol. 39, 1984, pp. 11–54. Ramachandran, G., “Exponential Model of Fire Growth,” Proceedings of the First International Symposium on Fire Safety Science, New York, Hemisphere, 1986, pp. 657–666. Tanaka, T., “Current State of Two-Layer Zone Models,” Proceedings of the Discussion of Capabilities, Needs and Benefits of Fire Safety Engineering Conference, January 7–11, 2001, San Diego, CA, United Engineering Foundation, Inc., New York, NY, 2001, pp. 58–62. Tanaka, T., Fukuda, T., and Wakamatsu, T., “Experiments on Smoke Behavior in Cavity Spaces. Part 3. In Case of the Cavity Space Which Has an Opening at the Bottom,” Proceedings of the 13th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, March 13–20, 1996, Gaithersburg, MD, National Institute of Standards and Technology, NISTIR 6030, June 1997, pp. 91–103. Tanaka, T., Fujita, T., and Yamaguchi, J., “Investigation into Rise Time of Buoyant Fire Plume Fronts,” International Journal on Engineering Performance-Based Fire Codes, Vol. 2, No. 1, 2000, pp. 14–25. Thomas, P. H., Morgan, H. P., and Marshall, N., “Spill Plume in Smoke Control Design,” Fire Safety Journal, Vol. 30, No. 1, February 1998, pp. 21–46. Trelles, J. J., McGrattan, K. B., and Baum, H. R., “Smoke Dispersion from Multiple Fire Plumes,” AIAA Journal, Vol. 37, No. 12, 1999, pp. 1588–1601. Trelles, J. J., McGrattan, K. B., and Baum, H. R., “Smoke Transport by Sheared Winds,” Combustion Theory and Modelling, Vol. 3, 1999, pp. 323–341. Tuovinen, H., and Simonson, M., “Incorporation of Detailed Chemistry into CFD Modelling of Compartment Fires,” SP Swedish National Testing and Research Institute, Boras, Sweden, SP Report 1999:03, 1999. Williams, F. A., “Mechanisms of Fire Spread,” 16th International Symposium on Combustion, Pittsburgh, PA, Combustion Institute, 1976, pp. 1281–1294. Woycheese, J. P., and Pagni, P. J., “Combustion Models for Wooden Brands,” Proceedings of the 3rd International Conference on Fire Research and Engineering (ICFRE3), October 4–8, 1999, Chicago, IL, Society of Fire Protection Engineers, Bethesda, MD, 1999, pp. 53–71. Wu, Y., and Bakar, M. Z. A., “Control of Smoke Flow in Tunnel Fires Using Longitudinal Ventilation Systems: A Study of the Critical Velocity,” Fire Safety Journal, Vol. 35, No. 4, 2000, pp. 363–390. Yamashika, S., and Kurimoto, H., “Burning Rate of Wood Cribs,” Report of the Fire Research Institute of Japan, Tokyo, No. 41, March 1976, pp. 8–15. Yii, E. H., “Exploratory Salt Water Experiments of Balcony Spill Plume Using Laser Induced Fluorescence Technique,” University of Canterbury, Christchurch, New Zealand, Fire Engineering Research Report 98/7, June 1998. Zdanowski, M., Teadorczyk, A., and Wojcicki, S., “A Simple Mathematical Model of Flashover in Compartment Fires,” Fire and Materials, Vol. 10, 1986, p. 145.
CHAPTER 10
SECTION 3
Simple Fire Hazard Calculations Morgan J. Hurley James R. Quiter
A
vailable methods to estimate the potential impact of fire can be divided into two categories: risk based and hazard based. Both types of methods estimate the potential magnitude of a given scenario. Risk-based methods also analyze the likelihood of the scenario occurring, whereas hazard-based methods do not. Fire risk analysis is described more fully in Section 3, Chapter 8, and Section 3, Chapter 11 provides simple fire risk calculation methods. Typically, when the potential impact of fire was estimated, a hazard basis was used. When probabilities or frequencies were considered, it was usually in the context of determining whether or not a scenario was sufficiently likely to warrant further analysis. Hazard analysis can be used for one of two purposes. One is to determine the hazards that are present in an existing or planned facility. The other use is for design, where trial design strategies are evaluated to determine whether they achieve a set of fire safety goals. Available fire hazard calculation methods range from relatively simple equations that can be performed with a hand calculator to complex methods that require powerful computers, and many methods that fall between. Examples of fire hazard calculation methods include flame height and compartment gas temperature correlations, hydraulic flow models, detector activation models, zone fire models, and computational fluid dynamics models. Each of these calculation methods predicts the conditions resulting from a given scenario.
HAZARD ASSESSMENT PROCESS The SFPE Engineering Guide to Performance-Based Fire Protection Analysis and Design of Buildings1 identifies a hazard assessment process for using a performance-based approach in the design and assessment of building fire safety. This process (Figure 3.10.1) includes defining the project scope, identifying goals, defining objectives, developing performance criteria, developing design fire scenarios, developing and evaluating trial designs, and developing documentation. Hazard assessment is primarily used in two steps of the performance-based process: development and quantification of deMorgan J. Hurley, P.E., is the technical director of the Society of Fire Protection Engineers. James R. Quiter, P.E., is a principal with Arup Fire.
sign fire scenarios, and evaluation of trial designs. Additionally, hazard analysis might be used outside of the design process, for example, to gain an understanding of the hazards that are presented by an existing or planned facility. However, in this context, the hazard analysis process would still be similar to that which would be used in the development and quantification of design fire scenarios.
Define Project Scope The project scope is an identification of the portion of a building, structure, or facility that will be analyzed and the conditions that could affect the analysis. The project scope could include specific fire protection system components, such as sprinkler systems and fire alarm systems; a subset of a building or structure, for example, a room or building wing; an entire building or structure; or several buildings. Also, some characteristics of the building, facility, or structure, such as ceiling heights, could affect performance in the event of a fire. To the extent possible, all available information regarding the construction and operation of the building and the types of people who might use the building should be determined.
Identify Goals Goals are qualitative statements of the expected fire safety performance of a building, facility, or structure. Goals are typically stated in terms that are easily understood by people who are not fire protection engineers. Fire safety goals can be divided into four categories: life safety, property protection, protection of continuity of operations, and protection of the environment from the effects of fire. Examples of goals in these areas include the following: • Minimize fire-related injuries and prevent undue loss of life • Minimize fire-related damage to the building, its contents, and its historical features and attributes • Minimize undue loss of operations due to fire-related damage • Limit environmental impact of fire Goals can come from a code or standard, or from a stakeholder in the building design. In the case of a performance-based code or standard, goals are typically explicitly stated (see examples above). In the case of a prescriptive-based code or standard, goals can be inferred based on the interpretation of specific
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Define project scope
Identify goals Design brief Define objectives
Develop performance criteria
Develop fire scenarios
Develop trial design(s)
Evaluate trial design(s)
Modify design or objectives
No
Selected design meets performance criteria Yes Select final design
Prepare design documents
Performance-based design report Plans and specifications, operations and maintenance manuals
FIGURE 3.10.1 Performance-Based Analysis and Design Process (Source: SFPE Engineering Guide to Fire Protection Analysis and Design of Buildings)
provisions. Stakeholders may also provide goals. For example, a building owner or tenant may desire a fire protection design that provides more property protection or protection of continuity of operations than compliance with code or standard provides. The next steps in the process facilitate the translation of goals into measurable values, called performance criteria, which can be predicted using fire modeling tools and methods.
Define Objectives An objective is a requirement of the fire, building, system, or occupants that needs to be obtained in order to achieve a fire safety goal. Objectives are stated in more specific terms than goals. In general, objectives define a series of actions necessary for the achievement of a goal. Objectives are divided into two categories: stakeholder objectives and design objectives. Stakeholder objectives provide more detail than fire protection goals,
and they are often stated in terms of acceptable or sustainable loss. The key differentiation between goals and stakeholder objectives is the quantification of the maximum tolerable extent of loss. By developing stakeholder objectives, a fire protection engineer can help other stakeholders (building owners, insurers, authorities having jurisdiction, etc.) focus on determining exactly how much loss they would be willing to accept. Examples of stakeholder objectives include the following: • Provide adequate time for those people not intimate with the first materials burning to reach a place of safety without being overcome by the effects of fire and fire effluents. • Limit fire-related damage to a maximum of $500,000. • Limit the development and spread of fire such that the maximum fire-related process downtime is no greater than 24 hr. • Ensure that there is no groundwater contamination by fire suppression water runoff.
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To undertake an engineering analysis, stakeholder objectives must first be translated into values that can be quantified in fire protection engineering terms. The process of developing quantifiable design objectives should focus on the target that is being protected to meet a specific stakeholder objective. For example, targets might be the occupants of the facility (for a life safety fire protection objective), products or valuable equipment in a warehouse (for a property protection objective), a critical production or manufacturing process (for a continuity of operations objective), or water supply and wetlands (for an environmental objective). Fire protection engineers typically develop design objectives based on the stakeholder objectives. Examples of design objectives include the following: • Prevent flashover in the room of fire origin • Prevent fire spread beyond the room of fire origin • Limit the smoke exposure to less than would result in unacceptable damage to the target • Provide a suitable means for capturing fire protection water runoff
Develop Performance Criteria Performance criteria are threshold values, ranges of threshold values, or distributions that are used to evaluate the acceptability of trial designs. Performance criteria are established from the design objectives. The design objectives are stated in engineering terms, but lack the full specificity required to allow comparison with the results of hazard and/or risk assessment. The performance criteria must be crafted to reflect the intent of the objectives while being quantitative measures of the consequences of fire that need to be avoided to meet the goals. As such, performance criteria generally take the form of damage indicators. The means of preventing the damage need not be known at this stage, but a complete understanding of the acceptable limits of damage and injury must be well understood. Some performance criteria might also be set by performancebased codes. Performance criteria might include temperatures of materials, gas temperatures, smoke concentration or obscuration levels, carboxyhemoglobin (COHb) levels, and radiant flux levels. For example, performance criteria might include values for thermal radiation exposure (kW/m2) or gas (air) temperature. Other types of performance criteria include concentration of toxic gases (ppm), distance of the smoke layer above the floor (m), visibility (m), or other measurable or calculable parameters. Example of performance criteria include the following: • Visibility greater than 7 m • Upper layer temperature not greater than 200°C • HCl not greater than 5 ppm
Develop Design Fire Scenarios The SFPE Engineering Guide to Performance-Based Fire Protection Analysis and Design of Buildings provides a three-step process for developing design fire scenarios. The first step involves “brainstorming” qualitative descriptions of fire scenarios
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that could occur. The second step involves developing the design fire scenarios, which are a subset of the fire scenarios. Finally, the design fire scenarios are quantified. Identifying Qualitative Descriptions. Each fire scenario is described by three components: building characteristics, occupant characteristics, and fire characteristics. Building characteristics describe the physical features, contents, and ambient environment of the building. Occupant characteristics describe the factors that could affect how people respond to a fire. Occupant factors include number, distribution, activities, alertness, commitment, focal point, physical and mental capabilities, role, familiarity, social affiliation, and physical and mental condition. Fire characteristics describe the history of a fire scenario, such as ignition source, growth, full development, and extinction or decay. Developing Design Fire Scenarios. Design fire scenarios, the fire scenarios that will be used in the fire analysis, can be developed from fire scenarios by either probabilistic or deterministic means. (Probabilistic methods are discussed in Section 3, Chapter 6, “Probabilistic Fire Models”; Section 3, Chapter 8, “Fire Risk Analysis”; and Section 3, Chapter 11, “Simplified Fire Risk Calculations.”) Some scenarios will be less severe than, or “bounded” by other scenarios. This is an important consideration in deterministic analysis, because scenarios that are bounded by others do not need to be further analyzed. For more detailed information, see the section on bounding conditions later in this chapter. Although probabilities are not explicitly treated in a deterministic analysis, they can be used to develop the set of design fire scenarios. Scenarios that are accepted by the stakeholders as being too unlikely can be eliminated from further analysis. However, it is important to recognize that when a scenario is eliminated from further analysis because it is considered to be too unlikely, an implied risk is accepted that in the event that the scenario does occur, the performance criteria might be exceeded. Quantifying Design Fire Scenarios. Following their selection, design fire scenarios are quantified. Depending on the scope of the analysis, quantification could involve any or all of the components of the design fire scenario: building characteristics, occupant characteristics, and fire characteristics. For an existing building or facility, quantification of the building characteristics involves determining relevant aspects of the building as it was constructed, such as ceiling heights and travel distances. In the case of a planned building or facility, the quantification of building characteristics might come from a prescriptive-based design option (if they are not part of the performance-based design); from other disciplines, such as mechanical, electrical, architectural or interior design; or quantified as part of a trial design. Occupant characteristics are the factors that affect human behavior in fire. These factors include gender, age, physical capabilities, sensory capabilities, familiarity with the building, social and cultural roles, presence of others, and commitment to activities. In the case of an existing building, occupant characteristics can be determined by observing the operation of the
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building and the types of people that use it. For a planned building, the types of occupants that might use the building can be determined from the stakeholders, and occupant characteristics can be determined by referencing the literature (e.g., Section 4, Chapter 1, “Human Behavior in Fire”). Quantification of the fire characteristics typically involves development of a design fire curve. A design fire curve describes the heat release rate history of the fire, and is a graphical representation of heat release rate versus time (see Figure 3.9.2). Design fire curves can be developed through testing or be developed through calculations, and provide the basis for modeling and other engineering analysis.
Develop Documentation
Develop Trial Designs
Fire Protection Engineering Design Brief. The objective of the fire protection engineering design brief is to review the architectural proposals, identify potential fire hazards, and define the fire safety problems in qualitative terms, suitable for detailed analysis and quantification. By reaching agreement on the design approach prior to beginning analysis, the engineer ensures that effort is not expended on any designs or evaluation methods that will not be acceptable to one or more stakeholders.
In a performance-based design process, trial designs would be developed as possible methods of achieving the performance criteria in the design fire scenarios. The development of trial designs is beyond the scope of this chapter; for more information refer to Section 3, Chapter 7, “Fire Hazard Analysis”; Section 3, Chapter 14, “Overview of Performance-Based Fire Protection Design”; or Chapter 9 of the SFPE Engineering Guide to Performance-Based Fire Protection Analysis and Design of Buildings.
Evaluate Trial Designs Evaluation is the process of determining if a trial design is expected to achieve the performance criteria in the design fire scenarios. Evaluation may be on either a probabilistic or a deterministic basis. Probabilistic analysis is beyond the scope of this chapter; for more information refer to Section 3, Chapter 6, “Probabilistic Fire Models”; Section 3, Chapter 8, “Fire Risk Analysis”; Section 3, Chapter 11, “Simplified Fire Risk Calculations”; or to Chapter 10 of the SFPE Engineering Guide to Performance-Based Fire Protection Analysis and Design of Buildings. The trial designs are tested against each design fire scenario. The intent is to demonstrate that in the design fire scenario, the performance criteria will not be exceeded. If a trial design is found successful, any remaining trial designs might be evaluated as necessary. If a trial design is not found to be successful, the trial design might be modified and reevaluated, or it might be dismissed. After the selected trial designs have been tested, a final design is selected from among those found successful. If there are no trial designs that are found successful, the engineer should ensure that the trial designs considered all possible mitigation strategies. If, after considering all possible mitigation strategies, there still are not any trial designs that are found successful, the stakeholder objectives and performance criteria should be revisited. For a trial design to be successful, each performance criteria must be met in each of the design fires accounting for uncertainties due to known variations and unknown effects. Factors that might introduce uncertainty into the analysis include material variations, installation unknowns, system and component variability, unanticipated use of systems, and unpredictable future human actions.
Proper documentation is critical for others to understand the performance-based analysis or design. Proper documentation also ensures that all parties involved understand what is necessary for the design implementation, maintenance, or continuity of the fire protection design. The documentation can be divided into four categories: the fire protection engineering design brief, the performance-based design report, the detailed specifications and drawings, and the building operations and maintenance manual. Depending on the scope of the project, several or all of the forms of documentation might be used.
Performance-Based Design Report. The performance-based design report is a complete documentation of the entire analysis and design process. Due to the importance of the design report, it is critical that it be a thorough, clear, and unambiguous document. Many stakeholders might review this report, including the authority having jurisdiction (AHJ) and his or her staff, an appeals board, the building owner, the building insurer, the building operator, a future building purchaser, or a forensic team after a fire in the building has occurred. Since some of these reviewers might have limited technical or fire protection training, the design report should be prepared for a general audience. The report should convey the expected hazards, risks, and system performance over the entire building lifecycle (i.e., construction, operation, renovation, and demolition). Specifications and Drawings. The specifications and drawings convey to building and system designers and installing contractors how to implement the performance design. Specifications and drawings might include required sprinkler densities, hydraulic characteristics and spacing requirements, the fire detection and alarm system components and programming, special construction requirements including means of egress and location of fire resistive walls, compartmentation, and the coordination of interactive systems. The detailed specifications are the implementation document of the performance design report. The specifications are derived from the calculations and results within the report. Building Operations and Maintenance Manual. The fire protection operations and maintenance manual (O&M Manual) clearly states the requirements of the building operator to ensure that the components of the performance design are in place and operating properly. The O&M Manual also describes the commissioning requirements and the interaction of the different systems interfaces. All fire protection systems are identified in the O&M Manual and inspection and testing regimes and schedules
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are created for it. Of primary concern is the documentation of the restrictions placed on the building operations necessary to ensure continued validity of the analysis or design. These limiting factors might include critical fire load, sprinkler design requirements, building use and occupancy, and reliability and maintenance of systems. Whatever components of the design are critical to achieve the goals must be maintained, and a maintenance plan for those components must be developed. The O&M Manual also gives instructions on proper function of interactions of fire protection systems.
DEVELOPING FIRE SCENARIOS AND DESIGN FIRE SCENARIOS Determining the fire source is one of the most important parts of performing a fire hazard analysis. To determine the fire source, a design fire scenario must be developed. The design fire scenario is based on a fire that has a reasonable likelihood of developing from a series of fire scenarios. Fire scenarios need to be based on reality, and should be developed accordingly. For example, the occupancy, the purpose for which the design fire is being developed, the fuel load, potential changes in the property, the presence of sprinklers and fire detection, and the presence of alarm and notification systems, should be considered. Design fire scenarios differ by occupancy, and should be based on reasonably expected fires and worst-case fires. Although this chapter deals with hazard-based approaches, some risk must be included in the analysis when developing design fire scenarios. For instance, though a fire may be technically plausible, if it is extremely unlikely, that fire may not be necessary to be included as a design fire. It may be a fire scenario is discarded because it is so unlikely. The context of the evaluation must be considered when developing a design fire scenario. For instance, if one were to deal with fire scenarios in a school, the common causes of fire are playing with matches and incendiary fires. The incendiary fire is a much larger initial fire source, but will likely not occur when the property is occupied. Therefore, if the design goals include property protection, the incendiary fire would certainly be one of the design fire scenarios that needs to be considered. However, if the goals include only life safety, the incendiary fire would be much less likely because they generally occur when the school is unoccupied. Therefore, the selection of design fire scenarios must relate back to the goals and objectives, in order to determine which fire scenarios establish reasonable design fire scenarios.
NFPA 101 ® Design Fire Scenarios NFPA 101®, Life Safety Code®,2 provides eight design fire scenarios that should be considered in the development of a performance-based design. Briefly, these design fire scenarios are as follows: 1. An occupancy-specific design fire scenario that is representative of a typical fire for the occupancy. 2. An ultrafast developing fire in the primary means of egress, with interior doors open at the start of the fire.
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3. A fire that starts in a normally unoccupied room that may endanger large numbers of occupants. 4. A fire that originates in a concealed wall or ceiling space adjacent to a large occupied room. 5. A slowly developing fire, shielded from fire protection systems, in close proximity to a high occupancy area. 6. The most severe fire resulting from the largest possible fuel load characteristic of the normal operation of the building. 7. An outside exposure fire. 8. A fire originating in ordinary combustibles with each passive or active fire protection system independently rendered ineffective. An exception allows the engineer to avoid some of these failure calculations where it can be shown that the level of reliability and the design performance in the absence of the system are acceptable to the authority having jurisdiction. While only eight scenarios are listed in the performance option of NFPA 101, for most building designs, more than eight scenarios will be developed and analyzed. For example, there will usually be far more than a single scenario that is representative of a typical fire in a given occupancy.
Applying NFPA 101 Design Fire Scenarios For a typical building, what happens when each of these eight general scenarios is applied to what might occur as a reasonable design fire in that building? For the purposes of this illustration, a multistory hotel building with some meeting rooms on lower floors is considered. The following fires might be used as design fires in meeting the eight-scenario criteria of NFPA 101. 1. A typical fire based on the occupancy might include a patron smoking in bed, or a sterno-initiated fire in a meeting room or restaurant area. 2. An ultrafast fire in a primary means of egress would likely mean a flammable liquid fire in the corridor near one of the exit doors. 3. Fire in a normally unoccupied room would likely include a fire in a janitor’s closet, due to oily rags or ignition of some cleaning fluid. 4. Fire in a concealed space, particularly if the hotel were of combustible construction, might occur in the drop ceiling above the bathroom. This would likely be an electrical fire. 5. A shielded fire near occupied space may be in a maid’s cart, or under a display table in a meeting room. 6. The most severe fire from the largest fuel load typical to the building could occur during remodeling, or might occur due to storage of furniture in one room or storage of chairs in a meeting room. 7. The outside exposure fire could include other buildings, skylights in the roof of a low-rise building nearby, or wildland fire. This fire would be specific to the occupancy and building being considered. 8. Failure of a system would need to include looking at rated walls, rated floors, as well as sprinkler and fire alarm systems. When looking at these systems, one should consider what might fail rather than failure of the entire system. For instance, failure of a sprinkler system might mean failure of
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the entire water supply or it might mean failure of a single sprinkler to react when expected. By providing redundancy into water supply and fire pumps, and monitoring main valves, failures can be limited as a part of this evaluation.
Bounding Conditions During development of the fire scenarios and design fire scenarios, the allowable changes in the facility must also be considered. The extent of the changes that are considered by the design become bounding conditions for the analysis and subsequent use of the building. One can expect that the design fire scenario is not exactly what will happen, and that the building as originally designed and anticipated will not remain exactly as built. Therefore, as one develops design fire scenarios and one calculates the expected fire response, some amount of change in those scenarios must also be considered. Examples of bounding condition might include a hotel room floor becoming a meeting room floor, a meeting room area that becomes an exposition center, occupant loads that are greater than expected or calculated, movable walls that create simultaneous use when nonsimultaneous use was expected, or the space between a ballroom ceiling and the floor above suddenly being used for storage. All of these events are reasonably foreseeable, but some may fall outside of the bounding conditions. Bounding conditions must clearly be identified because changes in the building may occur. Other things that might occur on a more general basis, for any occupancy, include the response of a fire department and cutbacks in fire department funding, or unwanted alarms causing deactivation of a system. Some of these bounding assumptions can be addressed specifically, for instance, maximum fuel load or occupant load, whereas others might have to be covered more generally.
Implied Risk Although this chapter addresses hazard calculations, there is some implied risk in any such calculation. The primary risk factors involved are included in the design fire development. The design fires described for the hotel building did not include such accidents as gasoline tanker trucks crashing into the side of the building or bombs ignited at the base of the building. There is always the risk that this might happen, but the engineer must evaluate the likelihood of such an event. For example, buildings are typically not designed to survive the impact and issuing fire of a missile strike. If this were to occur, achievement of the design goals and objectives might not be expected. Similarly, it is conceivable that simultaneous fires could occur, although the prescriptive building codes do not anticipate such an event. These might be limitations that are described in the fire strategy report so that it is clear what is covered and what is not. When proposing to exclude a scenario from further consideration, it is important to ensure that the stakeholders understand the implications of excluding the scenario. For example, if the fire scenario associated with a gasoline tanker truck crashing into the side of the building is dismissed, and the building is located on a highway leading to a major oil refinery, the stake-
holders would need to understand and accept that if a gasoline tanker truck did crash into the side of the building, the goals and objectives might not be met.
Data Sources In development of the design fire scenarios, it is useful to have data on which to base future quantification. Members of the NFPA 101 Technical Committee for Safety to Life developed the design fire scenarios. The committee looked at statistical analyses prepared by the NFPA Fire Analysis and Research Division, and also at past fires that have occurred in different occupancy types. The NFPA One Stop Data Shop provides much information regarding fire statistics and results. Other locations for typical fires in occupancies might include Factory Mutual data, state data gathering for various occupancies, the National Fire Incident Reporting System, or examples of fires that can be found in the NFPA Journal. Other information that might be used include fire test results, many of which can be found on the National Institute of Standards and Technology Fire Internet site, manufacturers data regarding specific materials and their fire performance, listings of materials by recognized test labs, or actual fire testing of the proposed situation. One thing that can be reasonably expected is that the amount of data to develop a design fire will not be sufficient to be able to exactly predict what will happen. The user will only be able to determine boundaries of fires that may occur.
Overall Example The following example develops scenarios for a large exhibit hall at a convention center, and describes some of the work that might be done using the scenarios that have been developed. The first step is to investigate potential fires that might be used in a scenario, so that the design fire scenarios can be chosen. Again, using the scenarios from NFPA 101, the scenarios that might be examined for a typical convention center would be as follows: 1. The occupancy-specific design fire scenario might include a fire in an exhibit booth or a fire in auditorium seating. 2. The ultrafast fire might involve a fire in a plastic boat display located near the main exit. 3. A fire in a normally unoccupied room could occur in the storage of stacked chairs in an exhibit hall next to the exhibit hall being considered. The show could be going on in one exhibit hall with large numbers of people, and the one next door might be used as temporary storage during that event. 4. A fire in a concealed space is unlikely in Type 1 construction, but could occur in electrical or insulation areas. 5. A shielded fire could occur in the plastic boat that was previously mentioned or in a covered exhibit space. More and more jurisdictions are requiring automatic sprinklers in covered exhibit spaces, but that is not yet universal. 6. The most severe fire to be considered would likely be the boat fire that was previously mentioned.
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7. An outside exposure fire would typically not be considered for this occupancy since convention centers are generally surrounded by parking lots, etc. However, if the loading dock is considered as an outside fire, the scenario might involve fire in a truck waiting to unload to the convention center. 8. A typical fire with failure might include failure of the sprinkler or fire alarm system, or perhaps failure of the smoke control system. Since the purpose of the example is to perform timed exiting, the worst-case fire may be all that is necessary for evaluation. The worst-case fire would likely be the shielded boat fire at peak rate of heat release. To quantify the fire, the users might look at the fuel load and estimate the rate of burning, they might look at plastic fires and extrapolate, they might look at fast or ultrafast fires and peak the fire at the estimated fire response point, they might assume the fire is shielded on the inside of the boat and so not peak the fire at the estimated sprinkler response point, or they might specify sprinklers inside the boat and limit the fire size. The user would likely try a combination of these factors to see the effects. Once the fire scenario is developed, smoke-filling calculations can be performed to determine the clear height of smoke over time. Those calculations would be compared to the timed evacuation analysis. Both calculations would likely start without suppression or smoke control to see whether the evacuation can occur without those two systems. If so, the analysis is simplified. Finally, the user would identify bounding conditions via a sensitivity analysis. For instance, is the size of the boat important? How about the materials of the boat? Has the fuel been removed from the boat? If smoke control is necessary to make the calculation work, that smoke control needs to be identified as a bounding condition. Similarly, the occupant load, the exit sizes, the numbers of disabled, and the availability of an alarm system as well as its audibility must all be considered in the sensitivity analyses. Once all of these factors have been considered and dealt with, the simple hazard-based analysis is complete. The documentation of the analysis is the next important part and cannot be omitted from any fire hazard analysis, whether simple or complex. The assumptions, bounding conditions, scenarios considered, and limitations should be identified to the authorities having jurisdiction, the owner, and other interested parties.
QUANTIFICATION OF DESIGN FIRE SCENARIOS Quantification of design fire scenarios involves two steps. The first step is to develop the design fire curve for the design fire scenario or portion of the design fire scenario of interest. Once the design fire curve is estimated, it is then possible for the second step, predicting the fire effects.
Design Fire Curves The design fire curve can be divided into four phases: ignition, growth, full development, and decay. As there is not a single
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framework for developing the entire design fire curve, each step is typically developed separately, and then brought together as a single curve.3 It is not always necessary to quantify each phase of a design fire curve, depending on the goals of the analysis. For example, for prediction of when a fire detection or suppression system would activate, it might only be necessary to quantify the growth phase. For sizing a smoke control system, only the maximum heat release rate might be needed. A structural analysis might only need the peak burning rate and the duration of peak burning. Performing an evacuation analysis might require quantification of the growth and fully developed stages. Ignition. The design fire curve starts at ignition. A simple approach to developing a design fire curve is to assume that an ignition source of sufficient intensity is available to instantaneously ignite the initial fuel package to established burning. However, if the heat transfer to a combustible object or the temperature of the object is known, calculations can be performed to predict whether the object will ignite. Calculations to determine whether ignition occurs depend on the state of the fuel: solid, liquid, or gas. Ignition can be divided into two categories: piloted and nonpiloted. In the case of piloted ignition, a “pilot” such as a spark or flame initiates flaming. For nonpiloted ignition, flaming occurs spontaneously.4 Except for piloted ignition of gases and liquids that are at a temperature above their flashpoint, all materials must first be heated before ignition can take place.4 Solids. With the exception of smoldering combustion, for a solid to ignite it must first be heated sufficiently to release flammable vapors. Flammable vapors can be given off either by pyrolization or by melting and subsequent vaporization. Pyrolization occurs when a material is heated and decomposes, releasing vapors known as pyrolyzates. Unlike melting and vaporization, in which no molecular changes occur, the vapors given off are different from the material that was originally heated.5 The process of pyrolization can be viewed as “cracking,” in which larger molecules are broken into smaller molecules. Piloted ignition occurs if the concentration of pyrolyzed gases is above the lower flammable limit and a “pilot” is present. For nonpiloted ignition to occur, the pyrolizated gases must be above the lower flammable limit and they must be above the autoignition temperature. Because of this, it requires less energy for piloted ignition to occur than for nonpiloted ignition.5 Methods of predicting ignition of solid materials exposed to thermal radiation differ depending on whether a solid is thermally thin or thermally thick. A thermally thick material is one in which a temperature rise will not be perceived on the unexposed surface when the material is heated. Wood is a typical example of a thermally thick material, whereas paper is a good example of a thermally thin material. Reference 5 contains six methods for predicting the ignition of solid materials as follows.
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For thermally thin materials, the method of Mikkola and Wichman can be used: t ig C :L0c
(Tig > T0) (qgr > qgcrit)
(1)
where Tig C ignition temperature (C) T0 C initial temperature (C) t ig C time to ignition (s) : C density of the material (kg/m3) c C specific heat of the material (kJ/kgÝC) L0 C thickness of the material (m) qg C external heat flux (kW/m2) r
qgcrit C critical heat flux for ignition (kW/m2) For thermally thick materials, the following methods can be used:
cient vapor is given off to form an ignitable mixture with air, near the surface of the liquid or within the vessel used.”6 A number of methods can be used to measure the flash point of a liquid. Flash point is not a physical property, and is instead a model of physical phenomena associated with vaporization of a sufficient quantity of fuel to establish a gaseous mixture that is at the flower flammable limit at a distance above the fuel surface.4 Since methods for measuring flashpoints differ, they also predict differing flashpoints for individual liquids. Ignition of a liquid at its flashpoint is analogous to piloted ignition of a solid, in that for ignition to occur, a pilot must be present. The analogy for nonpiloted ignition of liquids would be ignition at the autoignition temperature. Values for flashpoints and autoignition temperatures for some common materials can be found in NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas.
• Mikkola and Wichman t ig C
(Tig > T0)2 9 k:c 4 (qgr > qgcrit)2
(2)
where k C thermal conductivity (W/mÝK). • Tewarson t ig C
9 (TRP)2 )2 4 (qgr > qgmin
(3)
where TRP C thermal response parameter (kWÝs1/2/m2), and qgmin C minimum heat flux for ignition (kW/m2). • Quintiere and Harkleroad 2 Œ qgmin t ig C b Ý qgr
for t D t m
(4)
–1/2
where b C a constant related to k:c (s ), and t m C characteristic time to reach thermal equilibrium (s). • Janssens
¡
¢Œ
Gases. For ignition of a flammable gas to occur, it must be mixed with a sufficient quantity of oxygen for a reaction to take place. Concentrations where this occurs are represented by a flammability range, which corresponds to gas/air concentrations that are at or above the lower flammable limit, and not exceeding the upper flammable limit. Flammability limits for a variety of gases can be found in NFPA 497. For mixtures of flammable gases, Le Chatelier’s principle can be used to determine lower flammable limit.4 Le Chatelier’s law states that
where
100 Lm C } Pi L i i
(7)
Lm C lower flammability limit of the mixture Pi C volume fraction of gas i Li C lower flammable limit of gas i
See Reference 5 for additional information on applying these methods.
Growth. Following ignition, a fire might grow as it develops on the first item ignited or spreads to additional items. To determine whether spread would occur to adjacent items, the problem can be approached from the perspective of whether or not the item would ignite. For growth involving a single item, the fire could spread to unignited portions of the item. This could either lead to the entire item burning, or earlier ignited portions might burn out before the fire spreads to involve the entire item, such that the entire burning item is never fully involved. Estimation of the heat release rate for a single item can be made by using existing fire test data for the item ignited or items that are similar to the item ignited, by commissioning a fire test where an exemplar item is burned, or by the use of simplified correlations, such as a power law function. For further information on power law growth, refer to Section 3, Chapter 7, “Fire Hazard Analysis.”
Liquids. For a liquid to ignite, it must be at a temperature that is equal to or greater than its flash point. NFPA 30 defines “flash point” as “the minimum temperature of a liquid at which suffi-
Full Development. Fire growth might continue until the fire is either fuel limited or ventilation limited. If there is sufficient ventilation, then the peak burning rate will be a function of the
>1.83 k:c ¤ qgr £ t ig C 0.563 >1 h2ig qgcrit
(5)
where hig C heat transfer coefficient at ignition, which incorporates both the radiative and convective components (W/m2 ÝC) • Toal, Silcock, and Shields t ig C
(FTPn) (qgr > qgcrit)n
(6)
where FTPn C flux time product and n C flux time product index E 1.
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item(s) burning. However, for fires in compartments, ventilation might limit combustion, and flashover could occur. There are three methods available to predict the minimum heat release rates necessary to cause flashover in a compartment.7 • Babrauskas
ƒ Qg C 750A0 H0
(8)
where Qg C minimum heat release rate required for flashover (kW)
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heat flux to a structural member. An evacuation analysis might require quantification of all of the hazards listed above. Radiant Heat Flux. The radiant heat flux from a single burning item can be predicted as a function of the distance from the item in accordance with equation 16 of Section 3, Chapter 9, “Simplified Fire Growth Calculations.” For radiant heat fluxes resulting from fire gases, such as in a compartment fire, the radiant heat flux can be calculated if the gas temperature and the temperature of the target object are known by applying the following equation:
A0 C Area of opening into compartment (m2)
Qg r C .; (T14 > T24)
H0 C height of opening into compartment (m) • McCaffrey, Quintiere and Harkleroad ƒ Qg C 610 (hkAT A0 H0)1/2
(9)
(11)
where Qg r C rate of radiant heat transfer (kW) . C emissivity of gas (0–1) (—) ; C Stephan-Boltzmann constant (5.67 ? 10>11 kW/m2ÝK4)
where k k C thermal conductivity of compartment surface (kW/mÝK)
hk C
- C thickness of compartment surface (m) AT C Total area of compartment surfaces (m2). • Thomas
ƒ
Qg C 7.8AT = 378A0 H0
(10)
Decay. Because the hazards posed during the decay phase are typically insignificant in comparison to the hazards posed during the fully developed phase, decay is typically omitted from analysis. A fire can decay for one of three reasons. The available fuel could be consumed, oxygen depletion, or suppression. Where test data is available, it might include decay. In the case of suppression by sprinklers, Section 3, Chapter 7, “Fire Hazard Analysis,” provides an algorithm for estimating the heat release rate.
Prediction of Hazards Once the design fire curve has been developed, it is then possible to predict the hazards that would result. The types of hazards that might be of interest include • • • • •
Simple Fire Hazard Calculations
T1 C temperature of gas (K) T2 C temperature of target (K) Equation 11 is only applicable for instantaneous calculations, as the temperature of the target will rise as a function of the thermal radiation that it receives. Smoke Production. When calculating smoke production rates, “smoke” is usually defined as the products of combustion and the air entrained into the fire plume. Therefore, the amount of smoke produced is a function of the height above the fire. Section 3, Chapter 9, “Simplified Fire Growth Calculations,” provides a number of equations that can be used to predict smoke production. Fire Plumes and Ceiling Jet Temperatures and Velocities. A fire will produce a ceiling jet that will rise, and contact the ceiling of a compartment, forming a ceiling jet. The temperature and velocity of a plume can be calculated as described in Section 3, Chapter 9, “Simplified Fire Growth Calculations.” Similarly, the temperature and velocity of a ceiling jet can be calculated in accordance with the following equations:8 16.9Qg 2/3 H 5/3 5.38 (Qg /r)2/3 r For B 0.18 !T C H H Œ 1/3 Qg r U C 0.96 For 0.15 E H H For 0.18 E
Radiant heat flux Smoke production Fire plume and ceiling jet temperatures and velocities Species production Depth of upper layer
As was the case with the stages of design fire curves, it is not always necessary to quantify all of the hazards that result from a design fire scenario. The hazards that are quantified are a function of the goals of the analysis. For example, if the purpose of the analysis is to determine whether a thermally activated detection or suppression system activates, only the plume and ceiling jet temperatures and velocities might be determined. For analysis of a smoke control system, only the smoke production rate might be determined. A structural analysis might only require information on compartment temperatures to determine
For
r H
r B 0.15 H
!T C
UC
0.195Qg 1/3H 1/2 (r/H)5/6
where !T C temperature rise over ambient (C) U C ceiling jet velocity (m/s) H C height above fire (m) r C horizontal distance from fire centerline (m) Qg C heat release rate (kW)
(12) (13) (14) (15)
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When using these equations, it must be cautioned that they are only valid for horizontal, unobstructed ceilings where there is no smoke layer present. In cases where a layer forms, higher temperature rises can be expected. Species Production. Fires can create a number of products of combustion, including carbon dioxide (CO2), water vapor (H2O), carbon monoxide, and many others that vary with the fuel and burning conditions. Species production rates can be calculated from the following equation:9 Qg Gg j C yj !Hc
(16)
where Gg j C smoke production rate of species j (kg/s) yj C yield fraction of species j (–) Qg C heat release rate (kW) !Hc C heat of combustion of fuel (kJ/kg) Yield fractions for several fuels are available in Reference 9. Depth of Upper Layer. As smoke is produced in a compartment, it forms a layer that descends as a function of time. This is analogous to filling a bowl of water. Section 3, Chapter 9, “Simplified Fire Growth Calculations,” provides an equation that can be used to estimate the velocity of decent of the smoke layer. However, when applying this equation, it should be noted that the mass production rate of smoke is not constant, since as the layer descends, the smoke production rate decreases due to the reduced vertical distance available to entrain air. (See the equations for predicting smoke production rate in the same chapter.)
Simple Analytical Solution Techniques Simple computer programs and spreadsheets can be used to perform simple fire hazard calculations. In the case of the equations listed above or referenced in other chapters, this is a relatively straightforward task. However, many fires and fire effects are not steady state. For example, consider smoke filling within an enclosure. The smoke production rate is a function of the smoke layer height, so the rate of smoke layer descent is not constant. In such instances, spreadsheets can be used to develop solutions to differential equations for which developing an exact solution is non trivial. Consider a differential equation of the following form: dy C f (y, t) dt where the initial value y (t C 0) C y0. The Euler method is a numerical technique for solving differential equations of this form, and can be stated as yn= 1 C yn = hf (yn, t n) where yn C value of equation y at time step n yn= 1 C value of equation y at time step n = 1 h C time step size
This process can be iterated over the desired length of time to obtain the desired solution. Since the Euler method determines the value of equation y at time step n = 1 based on the value at time step n and the slope of the tangent to y at time step n, errors can be introduced based on the non-linearity of equation y. There are methods available to reduce this error, such as the improved Euler method. However, another method of reducing the error is to reduce the time step, recognizing that as the size of the time step approaches zero, the difference between the predicted value of y and the actual value of y also approaches zero. The computational power offered by modern computers allows very small time steps to be used and to still get a solution rapidly. It should be noted that the default for many spreadsheets is to not permit iterative calculations. (The spreadsheet views the “circular reference” as an error.) With spreadsheets where this is the case, they would need to be configured to allow iteration. Consult the spreadsheet’s user’s manual or help function for assistance. Example. Thermal detector response can be used to illustrate application of the Euler method to a fire protection problem. This example uses an algorithm similar to that used by the computer fire model DETACT-QS10 to predict the time to activation of a thermal detector for a heat release rate that follows a power law curve. Two calculations will be performed. First, the instantaneous ceiling jet velocities are calculated in accordance with Equations 12-15. A quasi-steady assumption is made, which means that transport delays from the fire to the detector are ignored. Then, based on the temperature and velocity of the ceiling jet, the temperature change at the detector will be calculated. The change in temperature of the detector can be expressed as11 ƒ Ug (Tg > Td) dTd C (17) dt RTI where Td C temperature of detector (C) Ug C ceiling jet velocity at detector (m/s) Tg C ceiling jet temperature at detector (C) t C time (s) RTI C detector response time index (m1/2 ? s1/2) A Euler solution to this expression can be expressed as ƒ Ug (Tg > Tdn) Tdn= 1 = Tdn = !t (18) RTI where Tdn= 1 C temperature of detector at time step n = 1 (C) Tdn C temperature of detector at time step n (C) !t C size of time step (s) The above equation could easily be programmed into a spreadsheet or simple computer program, along with the ceiling jet temperature and velocity correlations expressed in Equations 12–15 to calculate Ug and Tg. It is also necessary to include a method of calculating the heat release rate at each time step.
CHAPTER 10
The following example illustrates the use of this method in estimating thermal detector response. A heat detector is located on a 3-m high ceiling, 2 m away from a fire located on the floor with a constant heat release rate of 1000 kW. The room has an ambient temperature of 20°C and is sufficiently large that a smoke layer will not form quickly. The heat detector has a temperature rating of 75°C and an RTI of 50 m1/2 s1/2. When would the detector operate? Using Equation 18 and Equations 12–15, the following solutions are obtained when different time steps are used: Time Step (s)
Predicted Activation Time (s)
1 0.1 0.01 0.001
24 24.2 24.23 24.229
SUMMARY Predicted fire hazards are a function of the design fire scenarios analyzed. Therefore, when performing a fire hazard analysis, it is important to select design fire scenarios that are challenging enough to represent a realistic “worst case,” but not so challenging that the likelihood of occurrence is too remote. There are many fire hazard calculations that can be performed with a hand calculator, a simple spreadsheet, or a computer program. In some cases, these simple methods would not be sufficient, for example, in cases where compartment geometry is complex, where it is desired to optimize cost/benefit, or where predicted hazard values are very close to acceptable limits. However, even in these types of cases, simple methods can be used for initial predictions or as a reality check of results from more complex models. In any engineering analysis, it is incumbent upon the user to understand the application and limitation of any methods used. This chapter has outlined a number of simple fire hazard calculation methods, but the applicability and limitations of the methods were not included. Users are referred to the reference documents identified in the text for information regarding the applications and limitations of any of the methods included in this chapter.
BIBLIOGRAPHY References Cited 1. SPFE Engineering Guide to Fire Protection Analysis and Design of Buildings, National Fire Protection Association, Quincy, MA, 2000. 2. NFPA 101®, Life Safety Code®, NFPA, Quincy, MA, 2000 edition. 3. Engineering Guide: Design Basis Fires, Society of Fire Protection Engineers, Bethesda, MD, in process. 4. Drysdale, D., An Introduction to Fire Dynamics, 2nd ed., Wiley, Chichester, 1998. 5. Engineering Guide: Piloted Ignition of Solid Materials Under Radiant Exposure, Society of Fire Protection Engineers, Bethesda, MD, 2002. 6. NFPA 30, Flammable and Combustible Liquids Code, NFPA, Quincy, MA, 2000 edition.
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7. Walton, W., and Thomas, P., “Estimating Temperatures in Compartment Fires,” SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995. 8. Evans, D., “Ceiling Jet Flows,” SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995. 9. Tewarson, A., “Generation of Heat and Chemical Compounds in Fires,” SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995. 10. Evans, D. D., and Stroup, D. W., “Methods to Calculate the Response Time of Heat and Smoke Detectors Installed Below Large Unobstructed Ceilings,” NBSIR 85-3167, Building and Fire Research Laboratory, U.S. Department of Commerce, Gaithersburg, MD, 1985. 11. Evaluation of the Computer Fire Model DETACT-QS, Society of Fire Protection Engineers, Bethesda, MD, in process.
Additional Readings Babrauskas, V., “Wall Insulation Products: Full-Scale Tests Versus Evaluation from Bench-Scale Toxic Potency Data,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 257–274. Beller, D., “Performance-Based Fire Safety: An Engineering Perspective,” Proceedings of the Fire Risk and Hazard Assessment Research Application Symposium, Research and Practice: Bridging the Gap, June 25–27, 1997, San Francisco, CA, 1997, pp. 19–32. Bjorkman, J., and Keski-Rahkonen, O., “Fire Safety Risk Analysis of a Community Center,” Journal of Fire Sciences, Vol. 14, No. 5, 1996, pp. 346–352. Bruyninckx, E., and Andries, M., “Fire Protection Concept for Chemical Plants, Refineries and Terminals,” Journal of Applied Fire Science, Vol. 5, No. 4, 1995/1996, pp. 285–297. Bukowski, R. W., “Hazard II: Implementation for Fire Safety Engineering,” Proceedings of Fire Safety Design of Buildings and Fire Safety Engineering Conference Compendium, Session 3: Fire Safety Engineering Tools, August 19–20, 1996, Oslo, Norway, 1996, pp. 1–7. Bukowski, R. W., Peacock, R. D., Reneke, P A., Averill, J. D., and Markos, S. H., “Development of a Hazard-Based Method for Evaluating the Fire Safety of Passenger Trains,” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, June 29–July 1, 1999, Edinburgh, UK, Interscience Communications Ltd., London, UK, 1999, pp. 853–864. Castino, T., “Apollo 13 Had a Plan: We Need One Too,” Proceedings of the Fire Risk and Hazard Assessment Research Application Symposium, Research and Practice: Bridging the Gap, June 26–28, 1996, San Francisco, CA, 1996, pp. 1–11. Chow, W. K., “Preliminary Discussion on Engineering PerformanceBased Fire Codes in the Hong Kong Special Administrative Region,” International Journal on Engineering Performance-Based Fire Codes, Vol. 1, No. 1, 1999, pp. 1–10. Chubb, M., “Outline of a New Regulatory Approach for Fire Hazard Abatement and Fire Prevention,” Proceedings of the Fire Risk and Hazard Assessment Research Application Symposium, Research and Practice: Bridging the Gap, June 25–27, 1997, San Francisco, CA, 1997, pp. 284–293. Clarke, F. B., “Firesafety of Cables in Air-Handling Plenums,” Proceedings of the Fire Risk and Hazard Assessment Research Application Symposium, Research and Practice: Bridging the Gap, June 24–26, 1998, San Francisco, CA, 1998, pp. 95–99. Corneo, E., Gallina, G., and Mutani, G., “Fire Safety in a Historical Building: A Case History,” Proceedings of the Symposium for ’97 FORUM, Applications of Fire Safety Engineering, FORUM for International Cooperation on Fire Research, October 6–7, 1997, Tianjin, China, 1997, p. 60–72. Custer, R. L. P., “Hazard Analysis and Risk Assessment Techniques with Applications to Performance-Based Fire Safety Design,” Proceedings of the Fire Risk and Hazard Assessment Research
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Application Symposium, Research and Practice: Bridging the Gap, June 26–28, 1996, San Francisco, CA, 1996, pp. 140–146. Custer, R. L. P., and Meacham, B. J., Introduction to PerformanceBased Fire Safety, Society of Fire Protection Engineers, Boston, MA, PBFS-97, 1997. Davis, D., “Intervention Strategies: When Systems Fail,” Fire Engineers Journal, Vol. 61, No. 215-20, 2001, pp. 21–24. Frantzich, H., “Fire Safety Risk Analysis of a Hotel,” Lund University, Sweden, LUTVDG/TVBB-3091-SE, February 1997. Frantzich, H., “Fire Safety Risk Analysis of a Hotel: How to Consider Parameter Uncertainty,” Proceedings of the Pacific Rim Conference and 2nd International Conference on Performance-Based Codes and Fire Safety Design Methods, May 3–9, 1998, Maui, HI, International Code Council, Birmingham, AL, 1998, pp. 265–278. Frantzich, H., “Risk Analysis and Fire Safety Engineering,” Fire Safety Journal, Vol. 31, No. 4, 1998, pp. 313–329. Frantzich, H., “Uncertainty and Risk Analysis in Fire Safety Engineering,” Lund University, Sweden, LUTVDG/TVBB-1016, 1998. Giziakis, K., and Giziski, E., “Analysing the Risk of Fires in Shipping,” Proceedings of the 1st International Fire Safety Conference, May 24–25, 1996, Santorini, Greece, 1996, pp. 123–135. Hakkinen, P., “How to Achieve the Fire Resistant Engine Room,” Fire Europe, Vol. 91, No. 1122, 1998, pp. 19–20. Hall, J. R., Jr., “Fire Risk Analysis Model for Assessing Options for Flammable and Combustible Liquid Products in Storage and Retain Occupancies,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 591–600. Hall, J. R., Jr., “Progress Report on Design, Risk, Hazard and Performance-Based Codes,” Proceedings of the 13th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, March 13–20, 1996, Gaithersburg, MD, National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6030, Vol. 1, June 1997, pp. 7–13. Hall, J. R., Jr., “Risk Analysis Data and Tools,” Proceedings of the Discussion of Capabilities, Needs and Benefits of Fire Safety Engineering, January 7–11, 2001, San Diego, CA, United Engineering Foundation, Inc., New York, NY, 2001, pp. 141–146. He, Y., Horasan, M., Tayor, P., Ramsay, C., and Lai, D., “Probabilistic Fire Safety Engineering Assessment of a Refurbished High Rise Office Building,” Proceedings of the International Conference, Engineered Fire Protection Design . . . Applying Fire Science to Fire Protection Problems, June 11–15, 2001, San Francisco, CA, 2001, pp. 211–228. Hoover, J., Caudill, L., Chapin, T., and Clarke, F., “Full-Scale Fire Research on Concealed Space Communication Cables,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 295–304. Hume, B., “Fire Models Training for Fire Safety Officers. Volume 3: HAZARD-I,” Home Office Fire Research and Development Group, London, UK, FRDG Publication Number 7/98, 1998. Jonas, G. H., “Development of a National Multihazard Mitigation Council,” Proceedings of the Pacific Rim Conference and 2nd International Conference on Performance-Based Codes and Fire Safety Design Methods, May 3–9, 1998, Maui, HI, International Code Council, Birmingham, AL, 1998, pp. 61–74. Jonsson, R., and Lundin, J., “Swedish Case Study: Different Fire Safety Design Methods Applied on a High Rise Building,” Proceedings of the Pacific Rim Conference and 2nd International Conference on Performance-Based Codes and Fire Safety Design Methods, May 3–9, 1998, Maui, HI, International Code Council, Birmingham, AL, 1998. Kidder, R. C., “Progress Being Made in Fire Safety Directives in Europe Covering Construction Products and Upholstered Furniture,” Proceedings of the Fire Risk and Hazard Assessment Research Application Symposium, Research and Practice: Bridg-
ing the Gap, June 26–28, 1996, San Francisco, CA, 1996, pp. 166–175. Krasny, J. F., Parker, W. J., and Babrauskas, V., Fire Behavior of Upholstered Furniture and Mattresses, William Andrew Publishing, LLC, Norwich, NY, 2001. Lawless, M., and Suzedell, B., “Fire Risk Valuation Issues and Methods: A Cost Benefit Perspective,” Proceedings of the Fire Risk and Hazard Assessment Research Application Symposium, Research and Practice: Bridging the Gap, June 25–27, 1997, San Francisco, CA, 1997, pp. 294–314. Lynch, A., “Partnership and Risk Approach in Fire Safety Across Europe,” Fire, Vol. 93, No. 1140, 2000, pp. 13–13. Mathews, M. K., Darydas, D. M., and Delichatsios, M. A., “PerformanceBased Approach for Fire Safety Engineering: A Comprehensive Engineering Risk Analysis Methodology, a Computer Model, and a Case Study,” Proceedings of the 5th International Symposium, Fire Safety Science, March 3–7, 1997, Melbourne, Australia, International Association for Fire Safety Science (IAFSS), Boston, 1997, pp. 595–606. Meacham, B. J., “Assessment of the Technological Requirements for the Realization of Performance-Based Fire Safety Design in the United States. Final Report,” National Institute of Standards and Technology, Gaithersburg, MD, NIST GCR 98-763, Nov. 1998. Meacham, B. J., “Concepts of a Performance-Based Building Regulatory System for the United States. Report of the 1996 Activities of the SFPE Focus Group on Concepts of a Performance-Based System for the United States,” National Institute of Standards and Technology, Gaithersburg, MD, NIST GCR 98-762, Nov. 1998. Meacham, B. J., “Evolution of Performance-Based Codes and Fire Safety Design Methods,” National Institute of Standards and Technology, Gaithersburg, MD, NIST GCR 98-761, Nov. 1998. Meacham, B. J., “Introducing Risk-Informed Decision-Making into Performance-Based Building and Fire Code Development,” Proceedings of the Fire Risk and Hazard Assessment Research Application Symposium, Research and Practice: Bridging the Gap, June 24–26, 1998, San Francisco, CA, 1998, pp. 62–77. Meacham, B. J., “Introduction to Performance-Based Fire Safety Design,” Proceedings of the Fire Risk and Hazard Assessment Research Application Symposium, Research and Practice: Bridging the Gap, June 26–28, 1996, San Francisco, CA, 1996, pp. 127–139. Meeks, C. B., and Brannigan, V. M., “Performance Based Codes: Economic Efficiency and Distribution Equity,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 573–580. Morrey, E. L., “Identification and Mechanisms for Reduction of Hazards from Combusted Polymer Composite Materials in Primary Structural Transport Applications,” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, June 29–July 1, 1999, Edinburgh, UK, Interscience Communications Ltd., London, UK, 1999, pp. 1205–1210. Munday, J. W., and Griffith, S. J., “Post-Fire Safety and the Investigative Process,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 1033–1036. Nelson, H. E., “Elements of Fire Hazard Analysis for Fire Safety Design,” Proceedings of the Pacific Rim Conference and 2nd International Conference on Performance-Based Codes and Fire Safety Design Methods, May 3–9, 1998, Maui, HI, International Code Council, Birmingham, AL, 1998, pp. 347–356. Nelson, H. E., “Performance Based Fire Safety,” Fire Science and Technology, Vol. 17, Special Issue, 1997, pp. 49–54. Nelson, H. E., and Forssell, E. W., “Use of Small-Scale Test Data in Hazard Analysis,” Proceedings of the 4th International Symposium, Fire Safety Science, July 13–17, 1994, Ottawa, Canada, International Association for Fire Safety Science (IAFSS), Boston, MA, 1994, pp. 971–982.
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Novozhilov, V., “Mathematical Modelling in Fire Science: Current Role and Perspective,” Proceedings of the 4th Asia-Oceania Symposium on Fire Science and Technology, May 24–26, 2000, Tokyo, Japan, 2000, pp. 131–136. Papaionnou, K. K., Malhotra, H. L., and Log, T., “Fire Safety in Engineering in Historic Buildings,” Proceedings of the 1st International Fire Safety Conference, May 24–25, 1996, Santorini, Greece, 1996, pp. 239–250. Peacock, R. D., Bukowski, R. W., Reneke, P. A., Averill, J. D., and Markos, S. H., “Development of a Fire Hazard Assessment Method to Evaluate the Fire Safety of Passenger Trains,” Proceedings of the 7th International Conference and Exhibition, Fire and Materials 2001, January 22–24, 2001, San Antonio, TX, Interscience Communications Ltd., London, UK, 2001, pp. 67–78. Pink, R., “Steps Needed to Take Fire Safety Forward in the New Millennium,” Record, Vol. 92, No. 1137, 2000. Puchovsky, M., “Creating Performance-Based Documents at the NFPA,” Proceedings of the Fire Risk and Hazard Assessment Research Application Symposium, Research and Practice: Bridging the Gap, June 26–28, 1996, San Francisco, CA, 1996, pp. 46–56. Puchovsky, M., “Performance-Based Regulations: What Role Will They Play?” Proceedings of the Fire Risk and Hazard Assessment Research Application Symposium, Research and Practice: Bridging the Gap, June 25–27, 1997, San Francisco, CA, 1997, pp. 259–267. Purser, D. A., Rowley, J. A., Fardell, P. J., and Bensilum, M., “Fully Enclosed Design Fires for Hazard Assessment in Relation to Yields of Carbon Monoxide and Hydrogen Cyanide,” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, June 29–July 1, 1999, Edinburgh, UK, Interscience Communications Ltd., London, UK, 1999, pp. 1163–1169. Rahikainen, J., and Keski-Rahkonen, O., “Determination of Ignition Frequency of Fires in Different Premises in Finland,” Fire Engineers Journal, Vol. 58, No. 197, 1998, pp. 33–37. Richardson, J. K., Yung, D., and Hadjisophocleous, G. V., “What Is Risk Assessment and Why Is It Important Anyway?” Proceedings of the Fire Risk and Hazard Assessment Research Application Symposium, Research and Practice: Bridging the Gap, June 24–26, 1998, San Francisco, CA, 1998, pp. 1–6. Sekizawa, A., “Study on Potential Alternative Approach to Fire Death Reduction,” Proceedings of the 6th International Symposium, Fire Safety Science, July 5–9, 1999, Poitiers, France, International Association for Fire Safety Science (IAFSS), Boston, MA, 2000, pp. 171–181. Soderbom, J., “Roof Fire Testing Technology,” CBUF: Fire Safety of Upholstered Furniture. Final Report on the CBUF Research Program, European Commission Measurements and Testing Report EUR 16477 EN, Chapter 4, 1996, Interscience Communications Ltd., London, UK, 1996, pp. 93–118. Strength, R. S., “Fire Safety of Fabrics in Building Furnishings,” Proceedings of the Fire Risk and Hazard Assessment Research Application Symposium, Research and Practice: Bridging the Gap, June 25–27, 1997, San Francisco, CA, 1997, pp. 78–121. Sullivan, P. D., “Existing Building Performance-Based Firesafety Design,” Proceedings of the Pacific Rim Conference and 2nd International Conference on Performance-Based Codes and Fire Safety Design Methods, May 3–9, 1998, Maui, HI, International Code Council, Birmingham, AL, 1998, pp. 49–60. Sundstrom, B., “Fire Safety Design of Upholstered Furniture: Application of the CBUF Project,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 3–12.
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CHAPTER 11
SECTION 3
Simplified Fire Risk Calculations John M. Watts, Jr.
T
his chapter provides an overview of fire risk assessment used to make risk reduction decisions. This assessment can help to identify the uncertainty that exists concerning the probability of fire events, the magnitude of their consequences, and the determination of cost-effective risk reduction measures. The process described in this chapter is normally a part of a comprehensive risk management decision-making process. Usefulness and credibility of this information for management decision-makers will depend largely on methodology, procedures, documentation, and quality assurance controls integrated into the application.
FIRE RISK ASSESSMENT A critical component of fire safety decision-making is fire risk assessment. Yet there is little guidance that addresses the specific concerns of most facilities. A great deal of practiced fire risk analysis is ad hoc and undocumented. The subject of fire risk analysis in general is in a nascent stage.1,2 There is recognition of the need for fire risk analysis, but there is a large gap between the scientific aspects and their application. This gap is not likely to be fully bridged in the near future. What we can provide is an approach that will reduce the gap and give stakeholders more confidence in the fire risk decisions that they must continually make. As is the case with a great deal of useful science, most descriptions of risk are qualitative rather than quantitative. However, one of the reasons for assessing risk is to gain a sense of proportion. We want to know what differences in risk are big enough to pay attention to and what differences are so trivial that they can be ignored. To do this we need to quantify, to measure, and to have approximate numbers, such as probabilities of fire incidents. If these numbers are relevant and accurate, then we can predict with accuracy and will be able to make accurate assessments of risk. If the figures are relevant, but not very accurate, we will still be able to make useful comparisons of fire safety strategies. Fire risk analysis is strongest in the areas of potentially hazardous processes, such as nuclear facilities and chemical pro-
cessing plants. Techniques have evolved from roots in the aerospace and electronic industries of the 1960s. The most extensive assessments have been carried out where exposure of the public to potential harm has generated immense government investment in data collection and analysis.
Fire Hazard and Fire Risk Fire hazard is defined as any situation, process, material, or condition that, on the basis of applicable data, may cause a fire or explosion or provide a ready fuel supply to augment the spread or intensity of the fire or explosion and that poses a threat to life or property.3 To assess the risk associated with a fire hazard, we first need to measure two variables: probability (or frequency) and consequence (or severity). Figure 3.11.1 is a simplified representation of the risk assessment process, which illustrates the relationships of hazard and risk and of probability and consequence. In all cases, the first step is identification of the hazards that can lead to risk. Then we need to consider the two aspects of hazard, the probability of that the hazard will manifest itself into an event or a fire scenario that leads to a consequence, and the potential magnitude of the consequence or loss resulting from the manifestation of the hazard. In fire protection engineering, consequence modeling has evolved as fire hazard analysis. Deterministic fire growth models can predict the spread of fire and products of combustion, although impact analysis is still largely subjective. This chapter is focused on the probability analysis that can be combined with the consequence analysis to produce a risk assessment.
John M. Watts, Jr., Ph.D., is director of the Fire Safety Institute, a not-for-profit information, research, and educational corporation located in Middlebury, Vermont. He also serves as editor of NFPA’s quarterly technical journal, Fire Technology.
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Hazard identification
Probability analysis
Consequence analysis
Risk assessment
FIGURE 3.11.1
Risk Assessment Process
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Risk Matrix
Frequent
A simple qualitative risk assessment can help illustrate the relationship of these variables. This approach was developed in the 1960s as a systems safety technique for military systems and is presently documented as MIL-STD882D.4 In this approach, each hazard is assigned a probability level and a severity category. Tables 3.11.1 and 3.11.2 are adapted from corresponding tables in MIL-STD882D. Probability levels and severity categories can then be used to represent the axes of a two-dimensional risk matrix, such as shown in Figure 3.11.2. The matrix indicates that improbable hazards with negligible consequences represent a low risk and frequently occurring hazards with greater consequences represent high risk levels. There are many other forms of this risk matrix approach, including the SFPE Engineering Guide to Performance-Based Fire Protection.5 The risk matrix approach is not limited to analyzing hazards per se, but is equally applicable to specific events or fire scenarios.
Probable
Occasional
Remote
Improbable
Negligible
Marginal
Critical
Catastrophic
Key
TABLE 3.11.1 Frequent Probable Occasional Remote Improbable
Probability (p) Levels Likely to occur frequently, experienced ( p > 0.1) Will occur several times system life ( p > 0.001) Unlikely to occur in a given system operation ( p > 10–6) So improbable it can be assumed this hazard will not be experienced ( p < 10–6) Probability of occurrence cannot be distinguished from zero ( p ~ 0.0)
TABLE 3.11.2
Severity Categories
Negligible
The impact of loss is so minor that it has no discernible effect on the facility or its operations. The loss has a noticeable impact on the facility. The facility may have to suspend some operations briefly. Some monetary investments may be necessary to restore to full operations. May cause minor personal injury. The loss will cause personal injury or substantial economic damage. Loss would not be disastrous, but the facility would have to suspend at least part of its operations. The loss produces death or multiple death or injuries, or the impact on operations are disastrous, resulting in long-term or permanent closing. The facility ceases to operate immediately after the fire occurred.
Marginal
Critical
Catastrophic
(Risk) Low
Moderate
High
Risk Matrix
FIGURE 3.11.2
Risk Calculations Assessment of risk involves identification of all possible fire scenarios. The scenarios are produced by examination of event trees. A consequence is calculated for each scenario, and an estimate of the relative likelihood of each fire scenario is made. The fire risk in terms of the expected loss for a protection strategy is the sum of the expected losses incurred from each fire scenario that is applicable to that strategy. } Risk C Pi Ci i
Where Pi is the likelihood of scenario i, and Ci is the consequence or damage level for scenario i. The resulting risk assessment provides information that can help focus attention on important aspects of fire safety decision-making. Briefly, fire risk is measured in terms of both the probability of an event (fire) and the consequence of that event (fire damage). The use of event trees is the technique by which these two modeling components are joined together.
EVENT TREES An event tree is a visual representation of all the events that can occur in a system. As the number of events increases, the picture fans out like the branches of a tree. The goal of an event tree is to determine the probability of an event based on the outcomes
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of each event in the chronological sequence of events leading up to it. The event tree displays the sequences of events involving success and/or failure of the system components. By analyzing all possible outcomes, one can determine the percentage of outcomes that lead to the desired result. To make a model as complete as possible, the tree must represent all possible events as accurately as possible. Event trees can be used to analyze systems in which all components are continuously operating or for systems in which some or all of the components are in standby mode. In the case of standby systems and, in particular, safety and missionoriented systems, the event tree is used to identify the various possible outcomes of the system following a given initiating event, which is generally a fire. The initiating event is what starts the sequence of events detailed in the event tree. All subsequent events stem from the initiating event. In standby systems, the events must be analyzed in chronological order since the operation of one component depends on the success or failure of other components. As a simplistic example, an event tree can be constructed to analyze the possible outcomes of a fire. The system has two strategies components designed to handle this event: manual intervention by staff and an automatic suppression system. If the fire is too large to be controlled by staff, it will be mostly contained by the suppression system. If the suppression system fails as well, the loss is unacceptable. The event tree shown in Figure 3.11.3 can be constructed to model these events.
Is the release instantaneous?
Is there immediate ignition?
Yes
■
Simplified Fire Risk Calculations
Manual Intervention
Failure Fire
Success Success
Event tree No fire
FIGURE 3.11.3
Simplified Event Tree
More events can be added to this tree, such as the detection and alarm system that alerts staff or the event that the fire department will respond to help control major fires. The event tree can grow significantly as more events are taken into consideration. For very large trees, there are techniques for reducing the necessary number of branches. In many applications a truncated or reduced event tree is sufficient. Figure 3.11.4 is an example of a more detailed event tree. Once the event tree is constructed, the frequency or probability of each outcome, or consequence, can be determined. In the example above, the calculations are done to determine the likelihood or frequency of the system incurring major destruction from failure of both strategies (consequence 1), partial damage with successful activation of the suppression system (consequence 2), and minimal damage with successful manual
Does a pool form?
Does the pool ignite?
Assess fire damage Yes
Adiabatic expansion Yes Yes
Pool fire
Assess pollution. Use gas event trees to model gas behavior
No
No
No
Jet flame
Assess fire damage
Yes No
No
FIGURE 3.11.4
Use gas event tree to model gas behavior
Pool fire
Estimate duration. Calculate release rate
Assess fire damage
Calculate spread and evaporation
No
Yes
Automatic Suppression Failure
Fireball
Release case
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Calculate spread and evaporation
Yes
Assess fire damage
No
Assess pollution. Use gas event trees to model gas behavior Use gas event tree to model gas behavior
Flammable Liquid Event Tree (Source: Center for Chemical Process Safety6)
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intervention (consequence 3). The probability of occurrence of each path is the product of the given event probabilities since they all must occur for the given outcome to occur. The total for each outcome is then the summation of all the probabilities leading to that outcome. For example, the probabilities of the top two branches of an event tree are P (Pn) C R1 ? R2 ? ß ? Rn P (Pn>1) C R1 ? R2 ? ß ? Rn>1 ? Qn where P (Pn) C probability of occurrence of path n R C reliability of the event Q C unreliability of the event This analysis represents the usual assumption for event trees that all events are completely independent from one another. Event trees show all possible event options and chance events with a branching structure. They proceed chronologically, left to right, showing events as they occur in time. All outcomes along with the values and probabilities associated with them can be shown directly on the tree. There is very little ambiguity as to the possible outcomes and events the tree represents; any node gives all possible outcomes resulting from the node and the events that follow. The advantages of event tree analysis (ETA) include, but are not limited to, the following: • Event trees are easy to draw once the sequence of events is established. • Event trees are easy to understand. • It is easy to compute probabilities. The disadvantages of ETA include, but are not limited to, the following: • It may be difficult to identify all consequences. • The event tree can become very large. ETA is a comprehensive tool for modeling all possible outcomes of a sequence of events. Event trees are used to model the selected fire scenarios. They provide a framework for the utilization of probability data associated with the events that make up the fire scenario.
PROBABILITY ASSESSMENT Probability assessments must be made using a team approach. The team assembled to support the fire risk analyst generally will include members experienced in process design and instrumentation, reliability engineering, safety and environmental concerns, and team members from the plant knowledgeable in the specific facility hazards and operations. Sometimes, the services of a statistician may be required to analyze data from insurance reports and injury logs. In selecting fire and explosion event frequencies and probabilities, an experienced risk assessment team will initially use failure frequencies and probabilities based on generic industry wide data. The team will need to provide supporting rationale for cases in which frequencies in other ranges are used. These variations or adjustments from generic industry wide data must often be made
to reflect specific experience at a facility or the quality of the facility’s loss prevention and safety management programs. Two basic approaches are commonly employed in fire and explosion risk assessments to estimate initiating event frequencies and conditional probabilities: 1. Use of relevant historical data. 2. Synthesis of event frequencies and probabilities using techniques, such as fault trees, human reliability analysis, and expert engineering judgment. References 7 and 8 provide information on these methods. Often the two approaches are used complementarily to provide an independent check on one another and to increase the validity and confidence in the results. The first approach examines (1) relevant historical data to assess the frequency with which these events have occurred in the past and (2) the likelihood of their occurrence in the future. Where sufficient relevant past data is available, historically based frequencies may be adequate in making a reasonable assessment of fire and explosion risks. However, frequencies derived in this way represent only average values and are most applicable to simple systems where few variables (i.e., propagation and mitigation factors) can significantly change the results. In actual application, assessments of potential fire and explosion risks at a specific facility will usually require adjustments to historical data to reflect the particular facility management and protection deviations. When evaluating the relevance of historical data for use in a specific facility or process risk assessment, the following factors should be taken into account: 1. For many types of hazardous industrial operations historical data to make confident predictions about consequence likelihoods are limited or not available. 2. The general distribution between the primary causes leading to fire and explosions shows that human error is the leading cause. • Human factors (e.g., management controls, human operator errors): 70 to 85 percent • Equipment failures: 10 to 20 percent • External factors (e.g., earthquakes, floods): 10 to 20 percent As most causes are associated with human factors, it is expected that most risk research would be in this area; however, the quantification of the human element is very difficult and much work still needs to be done. 3. Fire prevention and protection technology is continually being expanded and updated based on new codes, standards, and industry practices developed after loss occurrences, and continued fire and explosion research efforts. Considering these factors, the fire risk analyst must take a systematic approach to first determine the best approach for estimating frequencies and probabilities based on available data and specific plant conditions.
Historical Accident Data An important part of fire and explosion risk assessment is a review of the history of loss incidents similar to the hazard being
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analyzed. A review of the available information on loss incidents or the available loss trending data provides 1. A relative breakdown of consequential effects, as to type of fire or explosion or as to resulting damage (can generally be used for estimating conditional event probabilities) 2. Identification of representative or dominant failure modes (equipment related, human error, systems related) that have led to fire or explosion accidents 3. Identification of ignition sources and fire propagation factors 4. Information concerning the duration of the fire and the general effect of loss mitigation factors 5. Information to support the generation of credible fire and explosion incident loss scenarios and the structuring of event tree analysis. Databases are the information foundation of hazard analysis and risk assessment. One of the most effective ways to learn TABLE 3.11.3
■
Simplified Fire Risk Calculations
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if a system has a fire or explosion potential is to review past loss incident records. Accident data from specific plant operations (if available) are usually the best source and probably more accurate for specific equipment and operations, since the data reflect the operating and maintenance practices of the specific facility. Fire records of NFPA and the American Petroleum Institute (API) provide fire loss incident data for many processes, plants, and types of equipment. Federal and state agencies also collect a variety of data related to safety and loss prevention issues. A few loss incident data sources are listed in Table 3.11.3.
Equipment Failure Data Sources An excellent source of generic equipment failure data is Guidelines for Process Equipment Reliability Data, with Data Tables, developed by the Center for Chemical Process Safety (CCPS).8 Failure data can also be obtained as a computerized database on
Some Sources of Information for Use in Fire Risk Assessments Source
Nature of Information
NFPA (National Fire Protection Association) Fire Analysis and Research Division 1 Batterymarch Park, P.O. Box 9101 Quincy, MA 02269-9101
Fire incident data FIDO (Fire Incident Data Organization) NFIRS (National Fire Incident Reporting System-Based Analysis) Various occupancy reports, research, statistics
National Transportation Safety Board (NTSB) U.S. DOT Washington, DC
Accident reports A detailed report is produced for transportation accidents involving hazardous materials Hazardous materials accident spill maps These give a map showing the location of the spill, any airborne plume, site of fatalities, and injured people, at one or more times after the start of the incident
American Petroleum Institute (API) Publications and Distribution 1220 L Street, NW Washington, DC 20005
Annual summaries of petroleum industry loss incidents Loss incidents
Association of American Railroads/Federal Railroad Administration (AAR/FRA)
Railroad facts (annual editions) Accident/incident bulletins (annual)
U.S. Environmental Protection Agency (EPA) 401 M Street, SW Washington, DC 20460
Reports on various aspects of hazardous material release incidents
U.S. Department of Transportation (DOT) Research and Special Programs Administration Office of Pipleline Safety Washington, DC
Pipeline leak reports for onshore gas transmission and gathering lines, and liquid lines
Gas Research Institute (GRI) 8600 West Bryn Mawr Avenue Chicago, IL 60631
Failure rate data for 21 system categories, including cryogenic valves, heat exchangers, fire protection primarily associated with LNG facilities
American Institute of Chemical Engineers (AIChE) 345 East 47th Street New York, NY 10017
Guidelines for Process Equipment Reliability Data with Data Tables, and other excellent books on risk assessment
National Technical Information Service (NTIS) U.S. Department of Commerce P.O. Box 100955 Atlanta, GA 30384
Excellent source for out-of-print documents, government documents, and foreign articles and documents
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a diskette. This handbook provides a listing and general description of all the data sources used to construct the CCPS generic failure rate database. It is essential for the fire risk analyst to understand the sources of this data, the limitations and applicability to the particular environment, and management controls for the specific facility being assessed. This reference provides a good summary of these concerns.
• • • • • •
Type of systems Quality of human engineering of controls and displays Motivation Level of perceived psychological stress Skill and training Presence and quality of written instructions and methods
Fire Suppression Failure Probability Human Error Probability Human failure rate data are very limited; however, some data have been developed on the reliability of human judgment.7,9,10 Data show that the reliability of human judgment is greatly influenced by the stress level that accompanies the decisionmaking process. At very low stress levels, the probability of human failure is high because the operator may be bored and inattentive. At very high stress levels, the probability of failure is also high because fear and anxiety interfere with the operator’s judgment. Human failure rates are lowest when the task is sufficiently interesting to keep the operator alert and when the operator does not feel endangered. Table 3.11.4 provides a generalized range of human error potential based on some human reliability data. The general procedure in applying human error probabilities includes the following: • Select the human error probability range from relevant data sources • Select and justify a probability within that range based on plant-specific knowledge and engineering evaluation of the facility and the human operation factors that can include • Types of tasks • Environmental conditions • System elements and characteristics
TABLE 3.11.4
Fire suppression system assessment involves evaluation of three factors: availability, reliability, and effectiveness. Failure to consider these aspects leads to lack of confidence or incorrect decisions. Typical problems in many fire risk assessments result from two major mistakes: 1. System suppression success is only associated with the system being available. This approach assumes perfect operational reliability and perfect suppression effectiveness— neither of these conditions is realistic. 2. Time is not properly integrated into fire suppression success probability. This includes the time at which damage starts versus time at which system automatically operates, and time delays involving manually actuated suppression systems or manual application of an extinguishing agent.
RISK CALCULATIONS Fire risk in terms of the expected loss for a protection strategy is the sum the expected losses incurred from each fire scenario that is applicable to that strategy. Risk C
Some Typical Human Operator Error Rates
Activity
Error Rate
Error of omission/item embedded in procedurea Simple arithmetic error with self-checkinga Inspector error of operator oversighta General rate/high stress/dangerous activitya Checkoff provision improperly used Error of omission/10-item checkoff list Carryout plan policy/no check on operator Select wrong control/group of identical, labeled, controls
3 × 10–3 3 × 10–2 10–1
}
PiCi
i
where Pi is the likelihood of scenario i and Ci is the consequence or damage level for scenario i. As an example, refer to the event tree of Figure 3.11.3. The tree indicates that there are three basic fire scenarios (the three possible outcomes from a fire event). These scenarios are listed in Table 3.11.5 along with hypothetical consequences. In a real example, the consequences can be calculated using procedures of fire hazard analysis in the previous chapter. Next, we need to estimate the probabilities of the events shown in the tree in Figure 3.11.3. These probabilities are determined from information as described in the previous section
0.2 – 0.3 TABLE 3.11.5 0.1 – 0.9 (0.5 avg.) 0.0001 – 0.005 (0.001 avg.)
Number
Description
Consequence
1
Failure of both manual intervention and automatic suppression Failure of manual intervention and success of automatic suppression Success of manual intervention
10.0
0.005 – 0.05 (0.01 avg.) 0.001 – 0.01 (0.003 avg.)
a WASH-1400 (NUREG-75/014), “Reactor Safety Study—An Assessment of Accident Risks in U.S. Commercial Nuclear Power Plants,” 1975.
Example Fire Scenarios
2
3
3.0
2.0
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of this chapter. Table 3.11.6 identifies the events from Figure 3.11.3 and assigns them hypothetical probabilities. For each event the probabilities associated with each outcome must sum to unity. P(event occurs) = P(event does not occur) C 1 This means that if we estimate the probability of an event occurring, the probability of the event not occurring is 1 minus the estimated probability. P(event does not occur) C 1 > P(event occurs) For example, if we estimate the probability of success of automatic suppression as 0.9, then the probability of failure is calculated to be 1 > 0.9 C 0.1. To further simplify the example calculations, the fire is ignored and the relative risk of alternative fire protection strategies calculated.
Simplified Fire Risk Calculations
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Manual Intervention The fire damage consequence of successful manual intervention is estimated by the outcome of scenario 3 in Table 3.11.5. The risk associated with the scenario is then given by PMIC3, where PMI is the probability of success of manual intervention and the computed consequence of scenario 3. Therefore, the relative risk of scenario 3 is (0.7)(2.0) C 1.4. If there is no automatic suppression system present, then the consequence of a failure of manual intervention is the same as scenario 1, identified as C1. The relative risk for the fire safety strategy of manual intervention can be calculated as follows: RMI C PMIC3 = (1 > PMI)C1 where PMI is the probability of success of manual intervention and Ci the computed consequence of scenario i. Thus, RMI C (0.7)(2.0) = (0.3)(10) C 4.4
Automatic Suppression Assume there is no manual intervention strategy. Then fire scenarios 1 and 2 in Table 3.11.5 represent the consequences of interest, C1 and C2. The probability of scenario 2 is the probability of success of automatic suppression, PAS, and the consequence of scenario 2 is denoted as C2. Then the risk associated with scenario 2 is given by (PAS)(C2). From Tables 3.11.5 and 3.11.6, PAS C 0.9 and C2 C 3.0; thus the relative risk associated with scenario 2 is (0.9)(3.0) C 2.7. The probability of scenario 1 is the probability of failure of automatic suppression. This value is calculated as 1.0 minus the probability of success or (1.0 > PAS). Then the risk associated with scenario 1 is given by (1.0 > PAS)(C1). From Tables 3.11.5 and 3.11.6, PAS C 0.9 and C1 C 10.0; thus the relative risk associated with scenario 1 is (1.0 > 0.9)(10.0) C 1.0. Now the relative risk for the automatic suppression strategy, RAS, is given by }
■
Combined Strategies Consider the risk for a protection system that includes both strategies. If manual intervention is not successful, then the automatic suppression system will be called upon to operate. To do | this, the basic equation of Risk C i PiCi is used and all three fire scenarios included. Thus, Risk C (1 > PMI)(1 > PAS)C1 = (1 > PMI)(PAS)C2 = (PMI)C3 where PMI C the probability of success of manual intervention PAS C the probability of success of automatic water suppression Ci C the computed consequence of scenario i Using the hypothetical values of the variables in this equation, Risk C (0.3)(0.1)(10.0) = (0.3)(0.9)(3.0) = (0.7)(2.0) C 2.5
PiCi
i
where Pi is the probability of scenario i and Ci is the consequence for scenario i, for i equals 1 and 2. Therefore, RAS C (1.0 > PAS)(C1) = (PAS)(C2) where PAS C the probability of success of manual intervention and Ci C the computed consequence of scenario i. Thus, RAS C (0.1)(10.0) = (0.9)(0.3) C 3.7
TABLE 3.11.6
SUMMARY Fire risk assessment is a critical component of fire safety decision-making. As described in this chapter, the fire risk assessment process can help stakeholders identify the uncertainty that comes with probability of fire and the magnitude of the consequences of fire. Fire risk assessment can also help stakeholders determine cost-effective risk reduction measures. This chapter defines fire hazard, fire risk, probability, and consequence, and presents an overview of some of the tools used in fire risk assessment, including the risk matrix, the event tree, and risk calculations.
Example Event Probabilities Event
Probability
Value
Fire Success of manual intervention Success of automatic suppression
PF PMI PAS
10–5 0.7 0.9
BIBLIOGRAPHY References Cited 1. Hall, J. R., Jr., “Fire Risk Analysis,” Section 3, Chapter 8, Fire Protection Handbook, 19th ed., National Fire Protection Association, Quincy, MA, 2003.
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2. Watts, J. M., Jr., and Hall, J. R., Jr., “Introduction to Fire Risk Analysis,” Section 5, Chapter 1, SFPE Handbook of Fire Protection Engineering, 3rd ed., National Fire Protection Association, Quincy, MA, 2001. 3. NFPA 1, Fire Prevention Code, National Fire Protection Association, Quincy, MA, 2000, p. 15. 4. MIL-STD-882D, Standard Practice for System Safety, U.S. Department of Defense, 10 February 2000. 5. Society of Fire Protection Engineers, SFPE Engineering Guide to Performance-Based Fire Protection, National Fire Protection Association, Quincy, MA, 2000. 6. Center for Chemical Process Safety, Guidelines For Chemical Process Quantitative Risk Analysis, American Institute of Chemical Engineers (AIChE), New York, NY, 1989. 7. Center for Chemical Process Safety (CCPS), Guidelines for Hazard Evaluation Procedures with Examples (Second Edition), American Institute of Chemical Engineers (AIChE), New York, NY, 1992. 8. Center for Chemical Process Safety, Guidelines For Process Equipment Reliability Data, with Data Tables, AIChE, New York, NY, 1989. 9. Meister, D., “Human Factors in Reliability,” Reliability Handbook, W. G. Ireson (Ed.), McGraw-Hill, New York, 1966, pp. 12.2–12.37. 10. Swain, A. D., and Guttmann, H. E., Handbook of Human Reliability Analysis with Emphasis on Nuclear Power Plant Applications, Report NUREG/CR-1278 (draft), United States Nuclear Regulatory Commission, Washington, DC, 1983.
Additional Readings American Petroleum Institute, Recommended Practice 750, Management of Process Hazards, 1st ed., Washington, DC, 1990. Benichou, N., Yung, D., and Dutcher, C., “Model for Calculating the Probabilities of Flame Spread from Fires in Multi-Storey Buildings,” Proceedings of the Building Envelope Systems and Technologies International Conference (ICBEST-2001), June 2001, Ottawa, Canada, 2001, pp. 407–411. Brandyberry, M. D., and Apostolakis, G. E., “Fire Risk in Buildings: Frequency of Exposure and Physical Model,” Fire Safety Journal, Vol. 17, No. 5, 1991, pp. 339–361. Brandyberry, M. D., and Apostolakis, G. E., “Fire Risk in Buildings: Scenario Definition and Ignition Frequency Calculations,” Fire Safety Journal, Vol. 17, No. 5, 1991, pp. 363–386. Covello, V. T., Sandman, P. M., and Slovic, P., Risk Communication, Risk Statistics, and Risk Comparisons: A Manual for Plant Managers, Chemical Manufacturers Association, Washington, DC, 1988. Fraser-Mitchell, J. N., “Modelling Human Behavior within the Fire Risk Assessment Tool ‘CRISP’,” Fire and Materials, Vol. 23, No. 6, 1999, pp. 349–355. Gann, R. G., “Research Program to Determine When and How to Include Sublethal Effects of Smoke in Fire Safety Decisions,” Proceedings of the 15th Joint Panel Meeting, U.S./Japan
Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, March 1–7, 2000, San Antonio, TX, National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6588, November 2000, pp. 127–134. Ghosh, B., and Fraser-Mitchell, J., “Fire Risk Assessment CRISP a Calculation Tool,” Fire Safety Engineering, Vol. 6, No. 4, 1999, pp. 11–13. Hall, J. R., “Fire Risk Analysis Model for Assessing Options for Flammable and Combustible Liquid Products in Storage and Retain Occupancies,” Proceedings of the 7th International INTERFLAM Conference, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 591–600. Hall, J. R., Jr., “Progress Report on U.S. Research in Fire Risk, Hazard, and Evacuation,” National Fire Protection Association, Quincy, MA, NISTIR 4449; Eleventh Joint Panel Meeting of the U.S./Japan Government Cooperative Program on Natural Resources (UJNR) on Fire Research and Safety, October 19–24, 1989, Berkeley, CA, 1990, pp. 2–4. Hall, J. R., Jr., “Key Distinctions in and Essential Elements of Fire Risk Analysis,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, New York, 1991, pp. 467–474. Noonan, F., and Fitzgerald, R., “On the Rold of Subjective Probabilities in Fire Risk Management Studies,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, New York, 1991, pp. 495–504. Reynolds, C., and Pedroza, J., “Fire Cover Modelling for Brigades,” FRDG Publication Number 6/98, Home Office Fire Research and Development Group, London, UK, 1998. Society of Fire Protection Engineering, SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995. Systems Safety Analysis Handbook, System Safety Society, Albuquerque, NM, 1993. White, D. A., Gewain, R. G., and Hamer, A. J., “Semiconductor Fabrication Facilities: Alternative Design Using Performance-Based Engineering Methods,” Proceedings of the Fire Risk and Hazard Assessment Symposium, Research and Practice: Bridging the Gap, June 26–28, 1996, San Francisco, CA, National Fire Protection Research Foundation, Quincy, MA, 1996, pp. 443–450. Yashiro, Y., Ebihara, M., and Notake, H., “Fire Safety Design and Fire Risk Analysis Incorporating Staff Response in Consideration of Fire Progress Stage,” Proceedings of the 15th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, March 1–7, 2000, San Antonio, TX, National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6588, November 2000, pp. 135–143. Zhao, L., “New Approach for Modeling the Occupant Response to a Fire in a Building,” Journal of Fire Protection Engineering, Vol. 10, No. 1, 1999, pp. 28–38.
CHAPTER 12
SECTION 3
Applying Models to Fire Protection Engineering Problems and Fire Investigations Revised by
Richard L. P. Custer
S
tarting in the 1980s, computerized fire growth models were developed and applied to fire safety problems. In general, these models estimate changes to a building or space within a building and its environment, based on user input data for an assumed fire in that structure. For the most part, these models do not model the fire directly but use the input data selected by the user to predict the impact of the selected fire. A more extensive discussion of computer fire models and their elements is covered in other chapters in this section. (See Section 3, Chapter 4, “Introduction to Fire Modeling,” and Section 3, Chapter 5, “Deterministic Computer Fire Models.”) The purpose of this chapter is briefly to advise the user on some of the types of applications where modeling can be of assistance and provide some guidance for users to establish criteria for selection of the model chosen and the input data used. As an outgrowth of the major advances in understanding the dynamics of fire and its effects on the operation of fire protection devices, workers in the field have developed a number of predictive models. These models range from prediction of upper layer gas temperature in a compartment fire1,2 and the time of sprinkler head operation3,4 to human response to the heat and toxic species produced.5 Many of the models have, in turn, been assembled into larger consolidated models and hazard assessment tools6–11 that provide a wide capability for the calculation and assessment of the predicted effects of fire using today’s state-of-the-art personal computers. (See Section 3, Chapter 7, “Fire Hazard Analysis”; Section 3, Chapter 9, “Simplified Fire Growth Calculations”; Section 3, Chapter 10, “Simplified Fire Hazard Calculations”; and Section 3, Chapter 11, “Simplified Fire Risk Calculations.”) Computer fire modeling is used extensively in performance-based fire engineering design. (See Section 3, Chapter 14, “Overview of Performance-Based Fire Protection Design.”)
Richard L. P. Custer, M.Sc., is associate principal and technical director at ARUP Fire in Westborough, Massachusetts. Mr. Custer is a fellow of the Society of Fire Protection Engineers.
DEFINITION OF FIRE GROWTH MODELS The term model can be applied to many physical and mathematical procedures designed to simulate reality. For the purpose of this chapter, fire growth models are defined as mathematical procedures developed to estimate the change in the environment of a space or building caused by the existence of a fire in that space that varies in intensity and/or area of involvement with time. All of these models predict the temperature of the smoke layer produced by that fire. Most fire growth models also predict the depth of the smoke layer. In addition, many models predict other variables such as the oxygen, carbon monoxide, carbon dioxide, and other gas species concentrations in the smoke; the rate of flow of smoke, gases, and unburned fuel from one space to another; and the temperatures of the walls, ceiling, floor, and air not yet drawn into the fire. Some models also predict the time of smoke and heat detector activation (including sprinkler heads) and the effects of opening or closing doors, breakage of windows, or other physical events that take place during a fire. Some models are limited to the room of fire involvement, others can track the flow of fire products through a series of rooms, and a few follow the spread of fire outside the room of origin. Typically, the models involve the simultaneous solution of two or more differential equations. The more sophisticated models involve the simultaneous solution of such equations for many variables and use sophisticated techniques to obtain the results. The range of complexity and sophistication is wide, but all models follow the basic conservation principles of mass, energy, and momentum.
TYPES OF MODELS As discussed more thoroughly in Section 3, Chapters 4 and 5, prediction models can generally be classed into the two categories of zone models that solve the basic conservation equation for distinct regions (control volumes), and computational fluid dynamic (CFD) or field models that solve the fundamental equations of mass, momentum, and energy in a space that has been divided into a grid of small-volume cells.
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Most of the fire growth models in common use are zone models. These usually divide each room into two spaces or zones: (1) an upper zone that contains the hot gases produced by the fire, and (2) a lower zone that contains a space beneath the upper zone that is the source of the air for combustion. Zone sizes change during the course of the fire. The upper zone can expand to occupy virtually all the space in the room. In zone models, any changes to the conditions in the upper layer occur instantly throughout the layer.
Computational Fluid Dynamics (CFD) Models In the past, CFD models usually required large-capacity computer workstations or mainframe computers. Advances in memory space and operating speed now allow CFD models to run off high-end PCs. Small compartments and simple geometries can now be run in a few hours, whereas large complicated problems may take days or weeks. By dividing the space into many small cells (frequently hundreds of thousands of millions), CFD models can examine much greater detail than zone models. For example, CFD can represent the actual variation in thickness and temperature gradients in the upper layer and depict flows around obstructions and through openings. If such detail is needed, it is often necessary to use the sophistication of a CFD model. In general, however, CFD models are much more expensive to use, require more time to set up and run, and often require a high level of expertise to make the decisions required in setting up the problem and interpreting the output produced by the model. The use of CFD models in fire protection problems, however, is increasing. CFD models are particularly well suited for situations where the space or fuel configuration is irregular, turbulence is a critical element, or very fine detail is sought. CFD is particularly valuable in complex smoke management system evaluation and design.
Predictive Capability of Models The reality of accidental fire is more varied and complex than can be exactly described by any existing collection of equations and data. Users should not expect that the model will produce an exact duplication of reality. Rather, the results of models should be considered as engineering estimates, valid to the degree that the physical relationships being calculated are those that actually dominate the situation and that the data entered into the model is accurate. Figures 3.12.1 through 3.12.6 demonstrate the type of approximation that should be expected. In Figure 3.12.1, four different models and one simple correlation were used in an attempt to reproduce the results from a well-documented test of a fire in a room.* In Figure 3.12.1, the curve using the letter x to indicate data points plots the average upper layer temperature computed from thermocouple readings during the test. The other curves graph the predictions by the various models. The complexity of the models varied widely in this exercise. The simplest model was a single correlation equation, whereas the most complex involved the coordination of almost a hundred variables. In the case of this test, the most sophisticated model was the most
accurate, but other much less sophisticated models grouped in the same range. Figure 3.12.2 is a reproduction of the actual data obtained in the burn test. Figure 3.12.2 reports the actual measured temperatures detected by a thermocouple tree near the center of the room but away from the fire plume. Every third thermocouple is plotted. Each of the lines depicts the temperature recorded by one of the thermocouples. The thermocouples were mounted with one near the ceiling and the others at 6-in. (0.15-m) intervals, with the bottom thermocouple located about 6 in. (0.15 m) above the floor. Figure 3.12.3 plots the same information as Figure 3.12.2, but rearranges the data to show the temperature profile from floor to ceiling as 1-min intervals through the first 6 min of the test. All of the models used to produce the results in Figure 3.12.1 are classed as zone models; that is, they predicted a single “upper layer” (smoke) temperature. As shown in Figures 3.12.2 and 3.12.3, an upper layer or “zone” of hot fire gases with an approximately equal temperature did exist. Although the type of approximation produced by these models is often more accurate than previous methods of estimation, the results must still be recognized as an engineering approximation. Figure 3.12.4 plots the smoke layer interface calculated by the models with that observed by the investigators. Figure 3.12.5 compares the oxygen concentration measured in the smoke in the test to concentrations calculated by the models. Figure 3.12.6 compares the measured mass flow through the vent opening with the same flow as calculated by the models. These four measures (i.e., temperature, smoke layer interface, oxygen concentration, and mass flow through the vent opening) were chosen to represent the full range of model outputs.
700 Average layer temperature (°c)
Zone Models
600 500 400 300 200 100
= Observed in test
0 0
100
200 Time (s)
300
400
FIGURE 3.12.1 Predicted Layer Temperature by Zone Models versus Test Measurements (°F °C 9/5 32)
*The fire test used for this comparison is test PRC17W4-¼. This was one of a series of compartment fire tests conducted under the sponsorship of the Product Research Committee. Test PRC17W4-¼ was conducted in a room 2.18 m2 and 2.41 m high. The room had a single vent opening 0.19 m wide and 2 m high. The fuel for this test consisted of four wood cribs having a total weight of approximately 14 kg located near the center of the room12 (1 ft 0.305 m; 1 sq ft 0.0929 m2; and 1 lb 0.4536 kg).
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Applying Models to Fire Protection Engineering Problems and Fire Investigations
600
21
500
18 Oxygen (% by volume)
Temperature (° C)
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400 300 200 = ceiling = 12 in. = 24 in.
100
= 36 in. = 48 in. = 90 in.
60
120
180
240 300 Time (s)
360
= Observed in test
15 12 9 6 3
0 0
3–171
0
420
0
100
200
300
400
Time (s)
FIGURE 3.12.2 Actual Temperature Plots at Various Distances below Ceiling (°F °C 9/5 32; 1 in. = 25.4 mm)
FIGURE 3.12.5 Prediction of Oxygen Concentration by Zone Models versus Test Measurements
0.28 0.24
2.1
0.20
1.8
Flow (g/s)
Thermocouple height (m above floor)
2.4
Hot layer
1.5 1.2
0.12 0.08
0.9
0.04
0.6
= 1 min = 2 min = 3 min
0.3
= 4 min = 5 min = 6 min
0
100
200
300
400
500
= Observed in test
0 0
0 600
Thermocouple temperature (°C)
FIGURE 3.12.3 Actual Temperature Profile at 1-min Intervals, Showing Hot Layer (“zone”) (°F °C 9/5 32; 1 m 3.28 ft)
Smoke layer interface (m above floor)
0.16
100
200
300
400
Time (s)
FIGURE 3.12.6 Prediction of Mass Flow through Vents by Zone Models versus Test Measurements (1 g/s .0022 lb/s)
When using models for fire engineering or forensic investigation applications, it is important to be aware of the differences between actual and predicted fire effects as demonstrated above. The literature contains many model validation studies comparing full-scale fire test results with model predictions.12–19 If, for example, a model overpredicts the temperature of the hot gas layer at the ceiling, the estimated time of a heat detector operation would be faster than the actual response. This would give the impression of earlier warning than would occur in reality. If the time to performance of a rated ceiling was being evaluated, the failure would be predicted to occur earlier and actually provide a conservative estimate.
2.4 = Observed in test
2.1 1.8 1.5 1.2 0.9 0.6
MODEL APPLICATIONS
0.3 0
100
200
300
Time (s)
FIGURE 3.12.4 Prediction of Smoke Layer by Zone Models versus Test Measurements (1 m 3.28 ft)
400
In the broadest sense, a fire growth model can be applied as a tool in the solution of any fire protection problem where the fireproduced conditions inside a building or space or the response of fire protection devices in that space are needed as input to the
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decision. The following are some typical examples of application classes.
Predicting a Hazard In this case, hazard is defined as the expected fire-produced conditions. To start, a set of circumstances that represents a specific scenario, such as the maximum expected fire, is postulated. All of the conditions are fixed and the model is run to make a prediction of the rise in smoke (upper layer) temperature, the volume or depth of that smoke, the response of fire protection devices, the onset of serious conditions such as flashover, smoke gases or toxicity, or other items of concern. Often, this type of analysis searches for the most serious case and is used to answer questions such as, “How serious are the fire-produced conditions that can occur in this space?” Frequently, a number of scenarios will have to be run to establish the most serious case. For example, consider an analysis of the hazard of a hotel room that contains a type of bed that fire tests indicate will grow, if ignited, at a moderate rate, eventually reaching a fire size of 2 megawatts (MW); a chair having a very fast fire-growth rate if ignited but a maximum rate of energy of less than 1 MW; and a number of pieces of furniture that would not be expected to be points of ignition but could join a fire at a later state. Discovery of the worst case might require a series of computer runs in which the ignition source was placed first on the bed and then on the chair, runs where the distance between the bed and the chair were varied, runs with the door open and the door closed, and other possible variations.
Sensitivity Analysis In all of the above examples, it is frequently necessary to answer the question, “What if a change were made?” Models provide excellent tools for such parametric or sensitivity studies. Most frequently, the changes would involve the change of a material (construction, finish, furnishings), a change of an arrangement (door opened or closed, air conditioner on or off, spacing variations between fuel packages), or the presence or absence of a protection system such as smoke detectors or sprinklers. Variations in design parameters of fire protection systems can also be evaluated, such as detector or sprinkler spacing or sprinkler operating temperature and response time index (RTI). Using the example of the hotel room, typical questions might include the change in hazard or risk that would occur should the mattress be changed from a moderate-burning mattress to one that is fast burning or one that is treated to burn at a very slow rate. A similar question might relate to the use of a combustible wall material. In the case of a fire analysis, questions might relate to the difference in the situation had there been an ordinary versus a fast response sprinkler in the space or had the door been equipped with a door closer. A first-order approximation of the contribution of an item of furnishing or a material can be made by exercising the model with and without that material present and noting the differences.
Reconstruction of a Fire Fire models can be useful in reconstructing incidents that occur during a fire or testing suggested hypotheses or fire cause sce-
narios. Ideally, there will be enough physical evidence, data available on conditions at the time of the fire, and reliable witness statements to produce all of the information necessary as input to run the selected model. In actual practice, only part of the necessary information is usually available, and running the model may in itself involve some assumptions as to what the conditions were most likely to have been. Often, running the model will help demonstrate which assumptions are plausible and which are not. In the case of the example of the hotel room, the comparison of the known data to the various scenarios may demonstrate that some would not resulted in the growth and spread of the fire and the consequences that actually occurred. In some cases, a single dominant fire scenario will emerge. The use of computer modeling in fire reconstruction and failure analysis is of particular interest to many fire protection practitioners, and papers have begun to appear in the literature.13,14 This topic is discussed in more detail below.
Computer Modeling in PerformanceBased Fire Protection Design The application of computer fire models to performance-based design requires that the user understand the limitations and intended uses of the models selected. Several sources are available to provide guidance.20,21 Valuable guidance can also be found in published case studies of performance-based designs found in the literature. Examples are provided in the Additional Readings.
COMPUTER MODELING IN FIRE INVESTIGATION Among the applications that have evolved for computer modeling has been the analysis of actual fire incidents after the fact to determine the most likely fire scenario or group of scenarios that could have produced the end result—a process called fire reconstruction or failure analysis. (See Section 3, Chapter 1, “Fire Loss Investigation.”) Often, reconstruction includes an analysis of the role played by building fire protection features and how the fire might have progressed had additional fire protection measures been present, particularly when none existed at the time of the fire. Failure analysis22 involves identification of the primary and contributing factors that caused the loss. Examples of factors that may result in failure include design, material or equipment selection, maintenance, and postconstruction modifications. Traditionally, these activities have been carried out by field investigators, based on physical evidence, witness statements, and the investigator’s knowledge and experience, but with limited analytical tools.
Application to Reconstruction and Failure Analysis One of the early attempts at application of the emerging analytical tools was carried out by Fleming,23 who focused on the role that sprinklers might have played had they been present in the Haunted Castle of the Great Adventure Six Flags Amusement Park, Jackson Township, New Jersey. Fleming employed a com-
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bination of modeling and results of a variety of full-scale tests of manufactured home and compartment fires in reaching his conclusions. Since that time, a number of analyses have been carried out of major fires using progressively more sophisticated tools and approaches24–31 in fire reconstruction and failure analysis modeling. Since each fire incident will be different, there will be no “standard” set of models and techniques to apply. The purpose of this section is to outline the process of collecting the necessary data and setting up the modeling “experiments.” The reader is encouraged to study the referenced reports as examples for specific fires. Before a modeling effort can begin, a great deal of information needs to be obtained about the incident, beginning with an accurate layout of the building at the time of the fire. One also needs to know about the location and position of doors and windows, the type of heating, ventilating, and air-conditioning (HVAC) system, and the size and location of stairways and other vertical openings between floors. Although it may not be possible, a visit to the scene is valuable. Photos of the building during and after the fire should be studied if available. Often, news videos can be obtained. Information needs to be gathered about the materials of construction, including the interior finishes and the furnishings and their distribution. Sources for this information include building occupants or their relatives, building owners or managers, contractors, interior decorators, or others who may have been involved in the construction, renovation, or operation of the building. Figure 3.12.7 is a form that may prove helpful in gathering the type of data needed to use compartment models or similar analytical methods. Where there are fire victims, important information, such as location and severity of burn injuries or blood chemistry, can be obtained from hospital or autopsy reports. Since fire growth and the effect of fire on the building and its systems and occupants is largely time dependent, it is essential to obtain as much information as possible regarding the timing of events leading up to ignition (prefire events), during the fire (trans-fire events), and after the fire (postfire events).22 The best way to organize this information is through the use of timelines or event sequences. Benchmark events, those for which the time is known and not merely relative to a known event, are important to establish. If there are only a few events, a single timeline may suffice; otherwise, multiple timelines or event sequences32 on the same scale may be useful. The timelines are then used for comparison with the results of the modeling experiments. Once the data have been gathered and organized, a modeling plan should be developed based on the objectives of the study. The objective may be to assess the validity of a given hypothesis for the origin and cause of a fire or to develop new alternative hypotheses. In this case, the following questions are to be answered: • Would the fuels, fire location, ventilation conditions, and building and occupant characteristics hypothesized results in the actual fire conditions?
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• Which scenarios, given the range of available fuels, possible ventilation conditions, and building characteristics, could result in the actual fire conditions? Another objective might be to determine whether or not someone might have been injured had a detector been in use. In this case, the question to be answered could be: For the set of scenarios that could result in the actual fire conditions, what conditions would the potential victim be exposed to, given the range of initial locations of the victim relative to the fire, the conditions at the time of operation of the detector, and the actions and route taken during an escape attempt? Using the questions as a guide, a list of scenarios to be modeled and the associated variable can be prepared and perhaps arrayed as a “test matrix.” For the detector case above, the matrix could be multidimensional and very large. The matrix can be pruned by eliminating highly unlikely scenarios and by starting with the most conservative scenarios, that is, those that place the occupant at greatest risk. For example, • • • •
Fire remote from the detector Fire between occupant and detector Occupant impaired Fuel has highest heat-release rate
Once the matrix has been developed, it will probably be noted that there are not enough facts to provide all the needed model inputs. If the initial fuel package is furniture, and the construction materials and design characteristics are not known, a database for several items that bound the actual item might be used. If the characteristics are known, an exemplar might be tested. If nothing is known about door position, this becomes a variable, as would the starting position of victims. Most models are driven by a heat-release curve (Figure 3.12.8) input by the user. The user may apply one of several “standard” fires (slow, medium, fast, or ultra fast33) or develop a curve more specific to the fire under investigation. The closer the rate of the heat-release curve is to the actual occurrence, the more accurate the results. If “standard” fires are used, it is incumbent on the user to justify their appropriateness. Developing a casespecific heat-release curve is one of the more difficult tasks in a reconstruction. One begins with the first item ignited, if this is known. If the first item is not known, part of the reconstruction will be to experiment with several possible “first items.” Next, the ignition of nearby items is determined and the heat-release curve(s) added to that of the first item, making adjustments for the radiation effects from the burning first item, as necessary. It has been shown34 that the developing hot layer in a compartment fire increases the burning rate of items before the onset of flashover. Adjustments must be made to reflect this phenomenon.26 Considerable data and reference material on heat-release rates for a variety of items and materials are available to assist in the development of case-specific heat-release curves.35,36 Once a fire curve has been developed, one way to prune the matrix is to plan a set of experiments to test the sensitivity of the results to the unknowns. If, for example, the HVAC has little or no effect on the time to flashover, it may be ignored, but it may have a major effect on tenability in an area remote from the fire,
3–174 SECTION 3 ■ Information and Analysis for Fire Protection
Data for Compartment Fire Modeling Room Number _______________
Use ___________________________________________________________
Size (use diagrams if possible)
Wall/Floor/Ceiling Construction
Length _____________________
_______________________________________________________________
Width
_______________________________________________________________
_____________________
Height _____________________ _______________________________________________________________ Lining Materials (that represent over 10 percent of room lining) (Include thickness, density, and other material characteristics, if known) Wall Material
% of walls or area involved
_________________________________________________
______________________________________________
_________________________________________________
______________________________________________
_________________________________________________
______________________________________________
Ceiling Material _________________________________________________
______________________________________________
_________________________________________________
______________________________________________
Floor or Floor Covering Material _________________________________________________
______________________________________________
_________________________________________________
______________________________________________
Doors, windows and other openings [Enter all heights as distance above floor. If door sill is at floor enter zero (0).] Opening
To
Top
Sill
Width
Changed During Fire (How?)*
_________
___________
_________
_________
________
______________________________________
_________
___________
_________
_________
________
______________________________________
_________
___________
_________
_________
________
______________________________________
_________
___________
_________
_________
________
______________________________________
_________
___________
_________
_________
________
______________________________________
Heating ventilating and air conditioning (HVAC) Include air flows from HVAC systems. Give rates and positions of supply and return or exhaust in this room. Also sizes and types of ducts/diffusers. ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ ___________________________________________________________________________________________________ Tightness of walls, closed windows, door fits, etc. (Unless fit is very loose, classify fit as tight, average, or loose. If fit is very loose try to get size, number & location of cracks, etc.) Doors _________________________________________________________________________________________ Windows ______________________________________________________________________________________ Inside walls ____________________________________________________________________________________ Exterior walls ___________________________________________________________________________________ *For example: “window broke at 10:33” or “door was closed until opened by escaping occupant, then left open—Exact time
10:30.”
FIGURE 3.12.7
A Sample Compartment Fire Modeling Data Form
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Applying Models to Fire Protection Engineering Problems and Fire Investigations
Rate of heat release (kW)
3000
Large Hood Tests F32 (sofa)
2000
F31 (loveseat)
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delay the transport of smoke to a detector. If the model being used for detector operation relies on temperature rise above ambient, the “ambient” used should be that of the hot layer, not the temperature lower in the compartment or outside the building. When there are open windows, the effects of wind should be considered in modeling the effects of low-energy fires (i.e., smoldering or small flaming fires).
F21 (single chair)
Cautions on the Use of Computer Models in Fire Reconstruction and Failure Analysis
1000
0
200
400
600 Time (s)
800
1000
FIGURE 3.12.8 Typical Upholstered Chair Heat Release Rates (Source: Philip J. DiNenno et al. (Eds.), SFPE Handbook of Fire Protection Engineering, 2nd ed., Quincy, MA: National Fire Protection Association, 1995. Fig. 3-1.6.)
in which case HVAC would need to be included. Keeping detailed records of the modeling experiments is important. It is very easy to “check a few things out” at the keyboard and not remember what the results were. Keep a “lab” notebook. It is suggested that a file-naming convention be used that tracks the scenario number as well as the key variables. It is clear that many, many runs will be necessary for even the most straightforward analysis. It is not the intent of this chapter to thoroughly examine all aspects of modeling for fire construction and failure analysis. However, a number of guidelines should be observed: 1. Know the limitations of the models used. ASET,2 for example, assumes no vent and the data is questionable after flashover. ASET also requires that the user assign an arbitrary heat loss factor to the space being evaluated. Most models do not consider the effect of radiation from the upper layer on the heat release of the burning items.17 Heat detector models may not include the transit time for heated gas to reach the sensor. This can be a consideration for lowheat output fires (weak plumes) or high ceilings. The importance of transport time may be evaluated using a technique proposed by Mowrer.37 2. Use more than one model. For example, different models use different correlations for plumes38 and for preflashover layer temperature.39 3. Where possible, check the model against actual experiments40 or test data that was collected under similar conditions. 4. Use ranges of values for variables to which the model is sensitive, unless the value is known to be correct. For example, the heat of combustion of materials with generic names, such as “polyurethane,” can vary from product to product. Modeling with both upper and lower bounds will give a range of results that brackets the problem. 5. Consider the ambient conditions. For example, the hot layer formed under a metal deck roof on a blistering hot day will
One should always keep in mind that there are some situations where a real-world fire situation is so complicated that the use of models at the present level of sophistication to analyze the entire event may not be valid. However, parts of the event, particularly the early stage of growth within the compartment or on the floor of origin, may be studied. The use of fire models for forensic applications is expanding, and some are being used as “black boxes.” For fire models to gain credibility in the forensic arena, they must be applied with care, keeping in mind their limitations.
SOME ADDITIONAL CONSIDERATIONS Fire models are engineering tools. Like engineering handbooks, they are available to all persons, regardless of competence. Unlike engineering handbooks, however, many models have been made user-friendly and can be executed by persons who may not understand their capabilities, limitations, or the impact of the choices made in setting up the problems. When decisions produced by a model impact on the safety of life and property, one of the two following cases must hold. 1. Users must understand what the model is doing and how it is achieving the results, thereby treating it as an engineering tool. In such cases, the users are as responsible for the results as they would be had they gone to the engineering handbooks and extracted the equations themselves. Engineers are encouraged to use models, understand them, and become fluent with them. They will become an excellent tool under their control, or 2. Users must ascertain the limits to which the model has been demonstrated as rational and restrain their use within these bounds. If the occasion necessitates exceeding these bounds, the user should obtain the advice and/or service of individuals competent to examine the model and determine its appropriateness for the use desired. Many models require that the user provide inputs beyond a simple description of the space and its contents. Some of these inputs can greatly affect the result. The user may or may not have the data available or an understanding of the impact of his or her decision. Some models provide information to assist users; others do not. It is important that users exercise the model, find the variables required, and ensure that they can properly assign these before using the model. An important thing to remember is that many models include default values for the variables. A default value is one that has been included in the model
3–176 SECTION 3 ■ Information and Analysis for Fire Protection
and will be used by the model unless changed by the user. Usually, the values are ones felt to be reasonable by the model developer. However, they may or may not be appropriate for the case involved. The user must examine and responsibly accept or alter the default values as is appropriate for the case at hand. The sophistication or detail of a model may or may not be related to its accuracy for the case involved. A general principle is to use the simplest model that meets the user’s needs for the type and quality of information desired and the information required to run the model. Many of the more sophisticated models provide masses of detail that are not available in the simpler version. Conversely, some of the very simple models omit important fire phenomena. The balance between ensuring that the necessary phenomena are modeled and maintaining the sophistication of the model is best achieved by frequent use and examination of the models of interest. Finally, many computer fire models undergo regular review and possible adjustments. Users should try to stay abreast of updates, revisions, or other changes to models they use. They should be wary of models that are not being maintained and adjusted as needed by a competent organization.
SUMMARY Fire growth models are tools used to solve fire protection problems. This chapter provides general guidance on the types of applications in which computerized fire growth models might be useful. For example, fire growth models may be used to predict a hazard, to reconstruct a fire, or to analyze how changing the parameters of a fire might affect its outcome. This chapter also provides specific information on the predictive capability of models and on types of models, including zone models and CFD models.
BIBLIOGRAPHY References Cited 1. Cooper, L. Y., and Stroup, D. W., “Calculating Safe Egress Time from Fires,” NBSIR 82-2587, National Bureau of Standards, Gaithersburg, MD, 1982. 2. Walton, W. D., “ASET-B, A Room Fire Program for Personal Computers,” NBSIR 85-3144, National Bureau of Standards, Gaithersburg, MD, 1985. 3. Alpert, R. L., “Calculations of Response Time of CeilingMounted Fire Detectors,” Fire Technology, Vol. 8, No. 3, 1972. 4. Evans, D. D., and Stoup, D. W., “Methods to Calculated the Response Time of Heat and Smoke Detectors Installed Below Large Unobstructed Ceilings,” NBSIR 85-3167, National Institute of Standards and Technology, Gaithersburg, MD, 1985. 5. Purser, D. A., “Toxicity Assessment of Combustion Products,” SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 1995. 6. Mittler, H. E., “Guide to FIRST, A Comprehensive Single-Room Fire Model,” NBSIR 87-3595, National Institute of Standards and Technology, Gaithersburg, MD, 1987. 7. Jones, W. W., and Peacock, R. D., “Technical Reference Guide for FAST Version 18,” NIST Technical Note 1262, National Institute of Standards and Technology, Gaithersburg, MD, 1989. 8. Nelson, H. E., FPETOOL: “Fire Protection Engineering Tools for Hazard Estimation,” NISTIR 4380, National Institute of Standards and Technology, Gaithersburg, MD, 1990.
9. Satterfield, D. B., and Barnett, J. R., “User’s Guide for WPI/Fire Version 2, Compartment Fire Model,” Worcester Polytechnic Institute, Worcester, MA, 1990. 10. Bukowski, R. W., Peacock, R. D., Jones, W. W., and Forney, C. L., “Technical Reference Guide for the HAZARD I Fire Hazard Assessment Method, Handbook 146, Volume II,” National Institute of Standards and Technology, Gaithersburg, MD, 1991. 11. Peacock, R. D., Jones, W. W., Forney, G. P., Renke, P., and Portier, R., “CFAST, the Consolidated Model of Fire and Smoke Transport,” NIST Technical Note 1299, National Institute of Standards and Technology, Gaithersburg, MD, 1992. 12. Nelson, H. E., and Deal, S., “Comparing Compartment Fire Tests with Compartment Fire Models,” Fire Safety Science— Proceedings of the 3rd International Symposium, International Association for Fire Safety Science, July 8–12, 1991, Edinburgh, UK, Elsevier Applied Science, New York, 1991, pp. 719–728. 13. Quintiere, J. G., and McCaffery, B. J., “The Burning of Wood and Plastics in an Enclosure—Volumes 1 and 2,” NBSIR 802054, National Institute of Standards and Technology, Gaithersburg, MD, Nov. 1980. 14. Dembsey, N. A., Pagni, P. J., and Williamson, R. B., “Compartment Fire Experimental Data: Comparison to Models,” International Conference on Fire Research and Engineering, Orlando, FL, September 10–15, 1995, SFPE, Boston, 1995, pp. 350–358. 15. Zeigler, P., and Gunnerson, F. S., “A Live Fire Comparison of the CFAST Code,” International Conference on Fire Research and Engineering, Orlando, FL, September 10–15, 1995, SFPE, Boston, 1995, pp. 346–349. 16. Pherson, R., and Barnett, J. R., “Prediction of Fire Growth on Furniture Using CFD,” Third International Conference on Fire Research and Engineering, Chicago, IL, October 4–8, 1999, SFPE, Boston, 1999, pp. 15–26. 17. Lougheed, G. D., et al., “Smoke Movement in Egress Routes in a High Rise Building,” Third International Conference on Fire Research and Engineering, Chicago, IL, October 4–8, 1999, SFPE, Boston, 1999, pp. 27–38. 18. Wong, D. Q., “Accuracy of Computer Fire Models: Some Comparisons with Experimental Data from Australia,” Fire Safety Journal, Vol. 16, No. 6, 1990, pp. 415–431. 19. Peacock, R. F., Jones, W. W., and Bukowski, R. W., “Verification of a Model of Fire and Smoke Transport,” Fire Safety Journal, Vol. 21, No. 2, 1993, pp. 89–129. 20. Custer, R. L. P., and Meacham, B. J., Introduction to PerformanceBased Fire Safety, Chapter 7, National Fire Protection Association, Quincy, MA, 1997. 21. ASTM E1355-97, Standard Guide for Evaluating Predictive Capability of Models, American Society for Testing and Materials, West Conshohocken, PA, 2000. 22. Custer, R. L. P., “Computer Modeling in Fire Reconstruction and Failure Analysis,” Proceedings of the SFPE Symposium on Computer Applications in Fire Protection Engineering, Society of Fire Protection Engineers and Worcester Polytechnic Institute, Worcester, MA, June 28–29, 1993, SFPE, Boston, 1993. 23. Fleming, R. P., Analysis of Potential Fire Sprinkler Performance in the Great Adventure Fire, May 11, 1984, National Fire Sprinkler Association, Patterson, NY, 1985. 24. Nelson, H. E., “An Engineering Analysis of the Early Stages of Fire Development—The Fire at the DuPont Plaza Hotel and Casino—December 31, 1986,” NBSIR 87-3560, National Institute of Standards and Technology, Gaithersburg, MD, 1987. 25. Nelson, H. E., “Engineering Analysis of Fire Development in the Hospice of Southern Michigan,” Proceedings of the International Association for Fire Safety Science, and International Symposium, June 13–17, 1988, Tokyo, Japan, Hemisphere Publishing Corporation, New York, 1989, pp. 927–938. 26. Nelson, H. E., “Engineering View of the Fire of May 4, 1988, in the First Interstate Bank Building, Los Angeles, California,” NISTIR 89-4061, National Institute of Standards and Technology, Gaithersburg, MD, 1985. 27. Nelson, H. E., “Engineering Analysis of the Fire Development in the Hillhaven Nursing Home Fire, October 5, 1989,” NISTIR
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28. 29. 30.
31.
32. 33. 34.
35. 36. 37. 38. 39. 40.
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4665, National Institute of Standards and Technology, Gaithersburg, MD, 1991. Moodie, K., and Jagger, S. F., “The Technical Investigation of the Fire at London’s King’s Cross Station,” Journal of Fire Protection Engineers, Vol. 3, No. 2, 1991. Bukowski, R. W., and Spetzer, R. C., “Analysis of the Happyland Social Club Fire with HAZARD I,” Journal of Fire Protection Engineers, Vol. 4, No. 4, 1992. Mowrer, F. W., Williamson, R. B, and Fisher, F. L., “Analysis of Early Fire Development at the MGM Grand Hotel,” Second International Conference on Fire Research and Engineering, National Institute of Standards and Technology and Worcester Polytechnic Institute, Gaithersburg, MD, August 10–15, 1997, SFPE, Boston, 1997, pp. 49–60. Senez, P. L., and Mehaffey, J. R., “A Forensic Analysis of a Montreal Building Fire,” Third International Conference on Fire Research and Engineering, Society of Fire Protection Engineers, National Institute of Standards and Technology, and International Association of Fire Safety Science, Chicago, IL, October 4–8, 1999, SFPE, Boston, 1997, pp. 243–254. Hendrick, K., and Benner, L., Investigating Accidents with STEP, Marcel Deckker, New York, 1987. Evans, D. D., “Ceiling Jet Flows,” SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 1995. Parker, W., Tu, K., Nurbakhsh, S., and Damant, G., “Furniture Flammability: An Investigation of the California Bulletin 133 Test. Part III: Full-Scale Chair Burns,” NISTIR 4375, National Institute of Standards and Technology, Gaithersburg, MD, 1990. Babrauskas, V., “Burning Rates,” SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 1995. Babrausks, V., and Grayson, S. J. (Eds.), Heat Release in Fires, Elsevier Applied Science, New York, 1992. Mowrer, F., “Lag Timer Associated with Fire Detection and Suppression,” Fire Technology, Vol. 26, No. 3, 1990. Beyler, C. L., “Fire Plumes and Ceiling Jets,” Fire Safety Journal, Vol. 11, pp. 53–75, 1986. Deal S., and Beyer, C. L., “Correlating Preflashover Room Fire Temperatures,” Journal of Fire Protection Engineers, Vol. 2, No. 2, 1990. Nelson, H. E., “Computer Models in Fire Reconstruction,” Proceedings of the SFPE Symposium on Computer Applications in Fire Protection Engineering, Society of Fire Protection Engineers and Worcester Polytechnic Institute, June 28–29, 1993, Worcester, MA, SFPE, Boston, 1993.
Additional Readings Alamdari, F., and Kumar, S., “Environmental and Fire Safety Design Assessment Methods,” Fire Safety Engineering, Vol. 6, No. 3, 1999, pp. 12–15. Allan, H., Grubits, S., and Quaglia, C., “Predicting Smoke Movement in a Multi-Storey Shopping Center With Interconnecting Voids Using a Zone Model,” Proceedings of the Society of Fire Protection Engineers (SFPE) Honors Lecture Series, May 20, 1996, Engineering Seminars: Fire Protection Design for High Challenge or Special Hazard Applications, May 20–22, 1996, Boston, MA, 1996, pp. 43–48. Andersson, P., and Holmstedt, G., “CFD-Modelling Applied to Fire Detection: Validation Studies and Influence of Background Heating,” Proceedings of the 10th International Conference on Automatic Fire Detection, AUBE ’95, [Internationale Konferenz uber Automatischen Brandentdeckung]. April 4–6, 1995, Duisburg, Germany, 1995, pp. 429–438. Beard, A., “Limitations of Computer Modelling,” Fire Safety Modelling and Building Design, Proceedings of the One-Day Conference to Review the Potential and Limitations of Fire Safety Models for Building Design, March 29, 1994, Salford, UK, 1994, pp. 10–26. Beard, A., “Limitations of Computer Models,” Fire Safety Journal, Vol. 18, No. 4, 1992, pp. 375–391.
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Beard, A. N., “Reliability and Computer Models,” Journal of Applied Fire Science, Vol. 3, No. 3, 1993/1994, pp. 273–279. Beard, A. N., Drysdale, D. D., and Bishop, S. R., “Non-Linear Model of Major Fire Spread in a Tunnel,” Fire Safety Journal, Vol. 24, No. 4, 1995, pp. 333–357. Beller, D., and Till, R., “Computer Fire Model Validation: FPETOOL, CFAST, WPI/FIRE,” Proceedings of the International Conference on Fire Research and Engineering, September 10–15, 1995, Orlando, FL, SFPE, Boston, 1995, pp. 341–345. Bilger, R. W., “Computational Field Models in Fire Research and Engineering,” Proceedings of the 4th International Symposium on Fire Safety Science, International Association for Fire Safety Science, Boston, MA, 1994, pp. 95–110. Blount, K., “Regulatory Implications of Fire Safety Modelling,” Fire Safety Modelling and Building Design, Proceedings of the OneDay Conference to Review the Potential and Limitations of Fire Safety Models for Building Design, March 29, 1994, Salford, UK, 1994, pp. 27–35. Bowman, A., “Performance-Based Analysis of an Historic Museum. Arts and Industrial Building: A Case Study,” Fire Protection Engineering, No. 8, 2000, pp. 36–38. Brescianini, C., Liu, X., Blackmore, J., and Delichatsios, M. A., “Investigation and Analysis Using Fire Modeling Techniques of Events Leading to the Fire Destruction of a Factory,” Proceedings of the International Conference on Engineered Fire Protection Design . . . Applying Fire Science to Fire Protection Problems, June 11–15, 2001, San Francisco, CA, 2001, pp. 85–96. Bukowski, R. W., “How to Evaluate Alternative Designs Based on Fire Modeling,” NFPA Journal, Vol. 89, No. 2, 1995, pp. 68–70, 72–74. Chow, W. K., “Short Note on the Simulation of the Atrium Smoke Filling Process Using Fire Zone Models,” Journal of Fire Sciences, Vol. 12, No. 6, 1994, pp. 506–515. Chow, W. K., “Simulation of Car Park Fires Using Zone Models,” Journal of Fire Protection Engineering, Vol. 7, No. 3, 1995, pp. 65–74. Chow, W. K., “Use of Zone Models on Simulating Compartmental Fires With Forced Ventilation,” Fire and Materials, Vol. 19, No. 3, 1995, pp. 101–108. Chow, W. K., and Cheung, K. C., “Industrial Fire Simulation With Zone Models and Review on the Current Regulations,” Hong Kong Polytechnic University, Hong Kong, ISBN 0-9516320-9-4; Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 601–620. Chow, W. K., and Cheung, Y. L., “Simulation of Sprinkler-Hot Layer Interaction Using a Field Model,” Fire and Materials, Vol. 18, No. 6, 1994, pp. 359–379. Cohn, B. M., “Characterization and Use of Design Basis Fires in Performance Codes,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 581–588. Cooper, L. Y., “VENTCF2: An Algorithm and Associated FORTRAN 77 Subroutine for Calculating Flow Through a Horizontal Ceiling/Floor Vent in a Zone-Type Compartment Fire Model,” National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 5470, Aug. 1994. Crockett, J., “Perusing Performance Based Design,” ConsultingSpecifying Engineer, Vol. 27, No. 5, 2000, pp. 50–52. Custer, R. L. P., “Computer Modeling in Fire Reconstruction and Failure Analysis,” Proceedings of Computer Applications in Fire Protection, June 28–29, 1993, Worcester, MA, 1993, pp. 69–74. Custer, R. L. P., “Selecting and Using Computer Fire Models,” Worcester Polytechnic Institute, MA, Society of Fire Protection Engineers and WPI Center for Firesafety Studies, Proceedings of the Technical Symposium on Computer Applications in Fire Protection Engineering, Final Program, June 20–21, 1996, Worcester, MA, 1996, pp. 7–11. Davis, W. D., Notarianni, K. A., and Tapper, P. Z., “Modelling of Smoke Movement and Detector Performance in High Bay Spaces,” Proceedings of the International Conference on Fire
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Research and Engineering, September 10–15, 1995, Orlando, FL, SFPE, Boston, 1995, pp. 307–311. Deubler, J. F., “How to Review a Computer Modeling Report,” Schirmer Engineering Corporation, Arlington, VA, Society of Fire Protection Engineers and WPI Center for Firesafety Studies, Proceedings of the Technical Symposium on Computer Applications in Fire Protection Engineering, Final Program, June 20–21, 1996, Worcester, MA, 1996, pp. 67–72. El-Rimawi, J. A., Burgess, I. W., and Plank, R. J., “Modelling the Behavior of Steel Frames and Subframes With Semi-Rigid Connections in Fire,” University of Sheffield, UK, TNO Building and Construction Research, Third CIB/W14 Workshop, Proceedings of the Fire Engineering Workshop on Modelling, January 25–26, 1993, Delft, the Netherlands, 1993, pp. 152–168. Evans, D. D., “Large Fire Experiments for Fire Model Evaluation,” National Institute of Standards and Technology, Gaithersburg, MD, ISBN 0-9516320-9-4; Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 329–334. Evans, D. D., “Use of Fire Simulation in Fire Safety Engineering and Fire Investigation,” Proceedings of the 15th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, San Antonio, TX, March 1–7, 2000, S. L. Bryner (Ed.), National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6588, November 2000, pp. 441–448. Fahy, R. F., “EXIT89: High-Rise Evacuation Model—Recent Enhancements and Example Applications,” National Fire Protection Association, Quincy, MA, National Institute of Standards and Technology, Gaithersburg, MD, ISBN 0-9516320-9-4; Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 1001–1005. Galea, E. R., Owen, M., and Lawrence, P. J., “Emergency Egress from Large Buildings under Fire Conditions Simulated Using the EXODUS Evacuation Model,” University of Greenwich, London, England, ISBN 0-9516320-9-4; Proceedings of the Seventh International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 711–720. Gandhi, P. D., Sheppard, D., and Steppan, D., “Role of Component and Large-Scale Testing in the Evaluation and Design of Sprinklers,” Proceedings of the Fire Suppression and Detection Research Application Symposium, Research and Practice: Bridging the Gap, February 25–27, 1998, Orlando, FL, National Fire Protection Research Foundation, Quincy, MA, 1998, pp. 211–217. Griffith, S. J., and Munday, J. W., “Legal Implications of Real Fire Data Collection and Computer Modelling,” Metropolitan Police Forensic Science Laboratory, London, UK, ISBN 0-9516320-9-4; Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 1027–1031. Hadjisophocleous, G. V., and Knill, K., “CFD Modelling of Liquid Pool Fire Suppression Using Fine Watersprays,” National Research Council of Canada, Ottawa, Ontario, Advanced Scientific Computing, Ltd., Ontario, Canada, NISTIR 5499, Sept. 1994; National Institute of Standards and Technology, Annual Conference on Fire Research: Book of Abstracts, October 17–20, 1994, Gaithersburg, MD, 1994, pp. 71–72. Hagglund, B., Fransson, C., and Bengtson, S., “Use of Zone and Field Model to Recommend Fire Protection Measures in New Stores of the Royal Library in Stockholm,” National Defence Research Establishment, Sundbyberg, Sweden, FOA Report C20981-2.4, June 1994. Hoover, J. B., and Tatem, P. A., “Application of CFAST to Shipboard Fire Modeling. Part 3. Guidelines for Users. Final Report, 1998–2000,” Naval Research Laboratory, Washington, DC, NRL/MR/6180-01-8550, Apr. 23, 2001.
Janssens, M. L., “Computer Fire Model Selection and Data Sources,” Proceedings of ASTM’s Role in Performance-Based Fire Codes and Standards, December 8, 1998, Nashville, TN, American Society for Testing and Materials, ASTM STP 377, 1999, pp. 74–86. Jones, W. W., and Forney, G. P., “Programmer’s Reference Manual for CFAST, the Unified Model of Fire Growth and Smoke Transport,” National Institute of Standards and Technology, Gaithersburg, MD, NIST TN 1283, Nov. 1990. Karlsson, B., “Models for Calculating Flame Spread on Wall Lining Materials and the Resulting Heat Release Rate is a Room,” Fire Safety Journal, Vol. 23, No. 4, 1994, pp. 365–386. Kasahara, I., and Hara, T., “Life Safety Design of an Atrium and an Air Dome With an Applied Zone Model,” Taisei Corporation, Tokyo, Japan, CIB W14/96/1 (J); Mini-Symposium on Fire Safety Design of Buildings and Fire Safety Engineering, June 12, 1995, Tsukuba, Japan, 1995, pp. VIa/1–3. Kassawara, R. P., and Najafi, B., “Evaluation of Fire Models for Nuclear Power Plant Applications,” Proceedings of the International Collaboration Project to Evaluate Fire Models for Nuclear Power Plant Applications: Summary of Planning Meeting, October 25–26, 1999, College Park, MD, U.S. Nuclear Regulatory Commission, NUREG/CP-0170, 1999, pp. 1–7. Kerrison, L., et al., “Comparison of Two Fire Field Models with Experimental Room Fire Data,” Proceedings of the 4th International Symposium on Fire Safety Science, International Association for Fire Safety Science, Boston, MA, 1994, pp. 161–172. Kerrison, L., et al., “Comparison of a FLOW3D Based Fire Field Model with Experimental Room Fire Data,” Fire Safety Journal, Vol. 23, No. 4, 1994, pp. 387–411. Kumar, S., and Yehia, M., “Application of JASMINE to the Modelling of Vehicle Fires in a Channel Tunnel Shuttle Wagon,” Proceedings of the 2nd International Conference on Safety in Road and Rail Tunnels, April 3–6, 1995, Granada, Spain, 1995, pp. 321–328. Lewis, K., “Fire Design of Steel Members,” University of Canterbury, Christchurch, New Zealand, Fire Engineering Research Report 0/7, March 2000. Lygate, J. F., “Value of Fire Tests in Fire Investigation,” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, Edinburgh, UK, June 29–July 1, 1999, Interscience Communications Ltd., London, UK, 1999, pp. 221–232. Macey, P., and Cordey-Hayes, M., “Computer-Based Simulation and Risk-Assessment Model for Investigation of Airliner Fire Safety,” Proceedings of the AGARD Conference, Aircraft Fire Safety, Propulsion and Engineering Panel (PEP) Symposium, Dresden, Germany, October 14–17, 1996, Advisory Group for Aerospace Research and Development (AGARD), 1996, pp. 4/1–11. Madrzykowski, D., and Vettori, R. L., “Simulation of the Dynamics of the Fire at 3146 Cherry Road, NE, Washington, DC, May 30, 1999,” National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6510, April 2000. Mawhinney, R. N., et al., “Critical Comparison of a Phoenics Based Fire Field Model With Experimental Compartment Fire Data,” Journal of Fire Protection Engineering, Vol. 6, No. 4, 1994, pp. 137–152. Mitler, H. E., and Steckler, K. D., “SPREAD: A Model of Flame Spread on Vertical Surfaces,” NISTIR 5619, National Institute of Standards and Technology, Gaithersburg, MD, Apr. 1995. Mowrer, F. W., Williamson, R. B., and Fisher, F. L., “Analysis of the Early Fire Development at the MGM Grand Hotel,” Proceedings of the 2nd International Conference on Fire Research and Engineering (ICFRE2), Gaithersburg, MD, August 3–8, 1997, Society of Fire Protection Engineers, Boston, 1998, pp. 49–60. Notarianni, K. A., and Davis, W. D., “Use of Computer Models to Predict the Response of Sprinklers and Detectors in Large Spaces,” Proceedings of Computer Applications in Fire Protection, June 28–29, 1993, Worcester, MA, 1993, pp. 27–33. Ogle, R. A., and Schumacher, J. L., “Application of Fire Testing and Modeling in a Forensic Investigation,” Proceedings of the 2nd International Conference on Fire Research and Engineering
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(ICFRE2), Gaithersburg, MD, August 3–8, 1997, Society of Fire Protection Engineers, Boston, 1998, pp. 539–550. Opstad, K., and Magnussen, B. F., “Algorithm for Thermal Flame Spread on Solid Surfaces by the Use of Cone Calorimeter Fire Test Data in a CFD-Model” [Thesis], University of Trondheim, Norway, Norwegian Institute of Technology, Norway, May 1995; Modelling of Thermal Flame Spread on Solid Surfaces in LargeScale Fires, 1995, pp. 1–15. Pagni, P. J., and Woycheese, J. P., “Modular Model for PostEarthquake Fire Growth,” Proceedings of the 14th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, May 28–June 3, 1998, Tsukuba, Japan, 1998, pp. 49–156. Peacock, R. D., Davis, S., and Babrauskas, V., “Data for Room Fire Model Comparisons,” Journal of Research of the National Institute of Standards and Technology, Vol. 96, No. 4, 1991, pp. 411–462. Peacock, R. D., et al., “CFAST, The Consolidated Model of Fire Growth and Smoke Transport,” NIST TN 1299, National Institute of Standards and Technology, Gaithersburg, MD, Feb. 1993. Peacock, R. D., Jones, W. W., and Bukowski, R. W., “Verification of a Model of Fire and Smoke Transport,” Fire Safety Journal, Vol. 21, No. 2, 1993, pp. 89–129. Reiss, M. H., and Cappuccio, J. A., “Computer Fire Modeling: A Building Design Tool,” Consulting-Specifying Engineer, Vol. 23, No. 5, 1998, pp. 34–36. “Report from the Reconstruction Committee Fire at 3146 Cherry Road, N.E., Washington, DC, May 30, 1999,” Fire and Emergency Medical Serices Dept., Washington, DC, 2000. Rockett, J. A., Howe, J. M., and Hanbury, W. L., “Modeling Fire Safety in Multi-Use, Domed Stadia,” Journal of Fire Protection Engineering, Vol. 6, No. 1, 1994, pp. 11–22. Schifiliti, R. P., and Pucci, W. E., “Fire Detection Modeling: State of the Art,” R. P. Schifiliti Associates, Inc., Reading, MA; Performance Consultants, Holland, MA; Fire Detection Institute, Bloomfield, CT; State of the Art Report, May 6, 1996, 57 pages; Society of Fire Protection Engineers and WPI Center for Firesafety Studies, Proceedings of the Technical Symposium on Computer Applications in Fire Protection Engineering, Final Program, June 20–21, 1996, Worcester, MA, 1996, pp. 19–27. Schneider, V., Loffler, S., Steinert, C., and Wilk, E., “Application of the Compartment Fire CFD Model KOBRA-3D in Fire Investi-
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gations,” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, Edinburgh, UK, June 29–July 1, 1999, Interscience Communications Ltd., London, UK, 1999, pp. 977–987. Sheppard, D. T., and Meacham, B. J., “Acquisition, Analysis and Reporting of Fire Plume Data for Fire Safety Engineering,” Proceedings of the 6th International Symposium on Fire Safety Science, July 5–9, 1999, Poitiers, France, International Association for Fire Safety Science, Boston, 2000, pp. 195–206. Stroup, D. W., “Using Computer Fire Models to Evaluate Equivalent Levels of Fire and Life Safety,” Proceedings of Computer Applications in Fire Protection, June 28–29, 1993, Worcester, MA, 1993, pp. 21–26. Stroup, D. W., and Madrzykowski, D., “Modeling Smoke Flow in Corridors,” Proceedings of the International Conference on Fire Research and Engineering, September 10–15, 1995, Orlando, FL, SFPE, Boston, MA, 1995, pp. 377–382. Taylor, S., Galea, E., Patel, M., Petridis, M., Knight, B., and Ewer, J., “SMARTFIRE: An Intelligent Fire Field Model,” University of Greenwich, London, UK, ISBN 0-9516320-9-4; Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 671–680. Thompson, P. A., and Marchant, E. W., “Testing and Application of the Computer Model ‘SIMULEX’,” Fire Safety Journal, Vol. 24, No. 2, 1995, pp. 149–166. Van Hees, P., Tuovinen, H., Persson, B., and Geysen, W., “Use of Zone and Field Models for the Fire Investigation of the Switel Hotel Fire (Antwerp 1994),” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, June 29–July 1, 1999, Edinburgh, UK, Interscience Communications Ltd., London, UK, 1999, pp. 245–256. Van Hees, P., Tuovinen, H., Persson, B., and Geysen, W. J., “Simulation of the Switel Hotel Fire,” Swedish National Testing and Research Institute, Boras, Sweden, SP Report 1998:04, 1998. Yung, D., and Hadjisophocleous, G. V., “Cost-Effective Fire Safety Designs for Highrise Office Buildings,” Proceedings of the International Symposium, Fire Protection of High-Rise Buildings, November 3–6, 1998, Shanghai, China, 1998, pp. 164–170.
CHAPTER 13
SECTION 3
Performance-Based Codes and Standards for Fire Safety Milosh T. Puchovsky
O
ver the past century, the basic question concerning fire safety design for the built environment has been this: Does the building comply with the code? More recently, however, other resources for providing fire safety are gaining exposure and acceptance. The emergence of computer fire models, design guides and other tools, as well as a maturing fire engineering profession, is changing the landscape.1 The availability of these new resources prompts a host of new questions about fire safety. While traditional questions concerning fire safety design center on code compliance, new ones focus on measurement and calculation. The principal argument is that fire safety can be accomplished more effectively by quantifying the level of safety required, and verifying that the entire fire safety package delivers that level of safety. The conventional approach of providing fire safety through the direct application of prescribed solutions embodied in traditional codes and standards faces increasing challenges. The new approach in fire safety is commonly referred to as performance-based design and its success hinges on the effective utilization of relatively new calculation or verification methods, many of which are packaged as computer models. It is these models that embody the scientific principles that allow for the calculation of fire related phenomena such as the spread of fire effects, the response of fire protection systems and the reaction of building occupants. These models serve as the tools for engineers and other qualified professionals for evaluating fire safety solutions not prescribed by codes or standards. Performance-based design can offer a number of advantages over traditional prescriptive-based methods. The overall intent aims at providing more effective and efficient fire safety designs and building construction practices. By allowing greater freedom in the design process, proponents argue that the overall outcome results in an optimal level of fire safety at reduced construction costs. In an effort to realize these benefits, a number of nations have enacted efforts to better support performance-based design
Milosh T. Puchovsky, P.E., is a senior fire engineer for Arup Fire based in Westborough, Massachusetts, and a principal member of NFPA’s Safety to Life Technical Committee on Fundamentals.
and remove existing barriers to its broader application.2 The lack of quantifiable fire safety goals, as well as a tangible interface between regulations and the relevant tools and data needed to conduct performance-based design, present such barriers. A key activity across the globe, that is still ongoing, focuses on the development and implementation of performance-based building and fire codes. With few exceptions, most codes and standards were developed in a manner that did not accommodate or support the use of calculation methods and other resources. Furthermore, many current computer models were developed and distributed without an established link to the codes and standards that have dictated fire safety design over the past century. A direct path for the application of these tools in combination with fire safety regulations needs to be made more readily apparent.
PERFORMANCE-BASED VERSUS PRESCRIPTIVE-BASED REGULATIONS Ideally, a performance-based code or standard explicitly states its fire safety goals and clearly defines the desired level of safety.3 Any solution that meets or exceeds the fire safety goals would be permitted. Fire safety would be designed for a specific use or application, rather than for a generic occupancy. Means to achieve compliance with the code begins with a scientific understanding of fire safety, followed by the application of proven engineering methods. Most fire safety codes and standards used today are considered to be prescriptive. Prescriptive-based documents provide fire safety in a generic fashion by prescribing a combination of specific requirements, such as construction materials, limiting dimensions, or protection systems, but without referring to how these measures achieve a desired level of safety or outcome. Even most documents that require measurement of performance through a test or calculation procedure do not state their goals or objectives in terms of these performance measures nor indicate how to connect the goals and objectives to performance as it is measured. In fact, a measurable level of safety is usually neither stated nor defined as a goal or objective. Usually there is only one way of providing the specified fire safety—the prescribed way.4 Concerns about the reliability of systems and features, as well as other uncertainties of performance, are addressed
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W o r l d v i e w Major initiatives to increase the greater acceptance of performance-based methods have been initiated around the world.1,2 Since the 1980s, governments in a number of nations have been urging the reform of their entire building construction industries and encouraging the use of performance-based design methods. This has prompted the development and implementation of new performance-based building codes in the United Kingdom, New Zealand, and Australia, with similar codes in preparation for the United States and Canada. In addition, regulations have been presented to introduce competition and third-party review into the plans approval process.3 The primary incentives for pursuing a new performance-based building code for the United Kingdom and Australia were within the context of more global regulatory reform rather than an attempt to address specific fire safety concerns.4 Many government officials believed that the level of protection prescribed by the old building codes could be achieved by more cost-effective solutions, resulting in increased economic growth and international competitiveness. Overall, the governments believed that market forces should rule as much as possible and that regulatory interference should be minimized. New regulations were written to increase technology transfer, and to promote innovation, flexibility, and deregulation with regard to building design. Revised regulations in the United Kingdom and New Zealand call for simplified building codes identifying only major fire and life safety goals for an adequate and reasonable level of safety for persons within and in the vicinity of the building, as well as referencing design practices to achieve these goals.5,6 Designers have been given the freedom to choose any method to demonstrate compliance. To provide guidance in achieving these goals, engineering design practices and “approved documents” are being presented in New Zealand and the United Kingdom.7,8 “Approved documents” are essentially user-friendly versions of the prescriptive traditional codes and other standards. Currently, compliance with “approved documents” virtually guarantees design acceptance; the use of other practices or methods does not. The creation of new
through redundancies, often in the form of requirements for two or more independent safety provisions, each designed to be sufficient by itself to provide safety. This crude, unquantified approach to redundancy can mean excessive and costly over design if the systems and features have high reliability individually. Prescriptive codes find their roots in the nineteenth century when major conflagrations created the need for specific building provisions.4–6 Revisions to the codes resulted primarily from other significant fires that revealed deficiencies. To prevent recurrence of such disasters, changes were incorporated into the codes. However, these changes were often instituted without ef-
performance-based building codes has encouraged and promoted the development of engineering-based documents and methods for the support of performance-based design. Most notable, the Society of Fire Protection Engineers has initiated technical projects aimed at developing engineering design guides and other resources in this regard.9 Overall, it has been reported that the revised regulations in the United Kingdom and New Zealand allow the design team and the enforcement authorities to work more as a team to develop acceptable solutions. Building officials are more willing to recognize calculation methods, alternative designs, and trade-offs, as the new rules have removed many of the constraints placed on their professional judgment. Increased training programs have also been a factor. 1 Meacham, B. J., “International Development and Use of Performance-Based Building Codes and Fire Safety Design Methods,” SFPE Bulletin, March 1995, p. 7. 2 Snell, J. E., Babrauskas, V., and Fowell, A. J., “Elements of a Framework for Fire Safety Engineering,” Proceedings—Interflam ’93, Interscience Communications Limited, London, UK, 1993, p. 447. 3 Lovegrove, K., “Private Certification in Australia,” Proceedings—Pacific Rim Conference of Building Officials, Darwin, Australia, May 1995. 4 Lucht, D. A., Kime, C. H., and Traw, J. S., “International Developments in Building Code Concepts,” Journal of Fire Protection Engineering, Vol. 5, No. 4, 1993, p. 141. 5 Law, M., “Fire Safety Design Practices in the United Kingdom—New Building Regulations,” Ove Arup Partnership, London, UK, 1991. 6
Hunt, J., “A Performance-Based Code at Work—The New Zealand Experience,” 1995 Annual Meeting, National Fire Protection Association, Quincy, MA, May 1995. 7 Buchanan, A. H., Fire Engineering Design Guide, Center for Advanced Engineering, University of Canterbury, Christchurch, New Zealand, 1994. 8 Warrington Fire Research Consultants, Draft British Standard Code of Practice for the Application of Fire Safety Engineering Principles to Fire Safety in Buildings, Warrington, UK, 1993. 9 “Update on SFPE Engineering Task Group Activities,” SFPE Bulletin, Society of Fire Protection Engineers, Fall, 1997.
fectively evaluating their adequacy, excessiveness, or conflicts with other requirements. This has created regulations that are based on empiricism and experience, rather than on a scientific understanding of fire. Many advances in fire safety have been made in recent time, but they are not being incorporated into everyday fire safety practice partly because of the prescriptive nature of our current codes and standards. Some believe that this lack of technology transfer has allowed fire safety to fall behind other engineering disciplines, such as structural design, which is thought of as relying more heavily on scientific and engineering principles.
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Performance-Based Codes and Standards for Fire Safety
THE PERFORMANCE-BASED DESIGN PROCESS General Concepts Although many groups in many countries have independently developed their approaches to performance-based design, the underlying framework for conducting performance-based design varies little.7,8 Performance-based design is an iterative process that requires the completion of a series of tasks, each of which must be properly documented. The process is graphically depicted in Figures 3.13.1 and 3.13.2. Although the entire process is quite involved, the following three general concepts are employed in most performance-based design frameworks. 1. Establish fire safety goals. Goals indicate the overall outcome to be achieved with regard to fire. Because these desired outcomes must be quantified in some manner, goals are usually expressed as a series of requirements that begin
with general statements about fire safety and conclude with measurable performance criteria (e.g., temperatures, energy levels, concentration of fire products). 2. Specify design parameters. Design parameters define the conditions under which the proposed fire safety goals are to be achieved. They include details and assumptions about the fire challenges to be considered, the people and property to be protected, the characteristics of the building in question and ultimately the proposed fire safety solution. 3. Verify proposed solutions. Assessment methods, computer models and physical tests are employed to verify that the fire safety goals have been achieved for the design parameters specified. This entails an iterative process in which those aspects of the design parameters pertaining to or affecting the proposed fire safety features are revised and refined until the fire safety goals are satisfied. Regardless of the verification method used—a computer model that calculates occupant movement, a calculation method
Defining project scope
Identifying goals Developing a fire protection engineering design brief
Defining stakeholder and design objectives
Developing performance criteria
Developing design fire scenarios
Developing trial designs
Evaluating trial designs
Modifying design or objectives
No
Selected design meets performance criteria? Yes Selecting the final design
Preparing design documentation
FIGURE 3.13.1
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Performance-based design report
Specifications, drawings, and operations and maintenance manual
Steps in the Performance-Based Analysis and Design Procedure
3–184 SECTION 3 ■ Information and Analysis for Fire Protection
Fire safety code or standard
Project team fire protection goals
Fire safety goals
General code or standard requirements
Specific code or standard requirements
Building purpose and aesthetic goals
Proposed building design (including fire protection design)
Fire safety objectives Occupant characteristic
Assumptions
Scenario data
Building characteristics
Design specifications
Fire safety criteria Proposed building design modification
Input
Verification methods
Safety factor
Output
Acceptable?
No
Yes
Finish
FIGURE 3.13.2
Performance-Based Design Process
that determines time to flashover, or a fire test that measures smoke movement—all require specific input data and knowledgeable users to produce effective results. Input data consists of information contained within the design parameters. Those aspects of the design parameters not entered directly into the verification methods will be retained as assumptions in the design process. Depending on the method used, specific information about the fire, occupants, building, and fire protection features will be required. For example, the sprinkler/detector response model used in FPEtool would require the heat release rate of a specified fire, the distance between the sprinkler and the fire, the sprinkler’s activation temperature, and thermal sensitivity and other data as input.9
Another example is Fire Dynamics Simulator (FDS), which can be used to predict sprinkler activation time as well as the effects of sprinkler activation on a fire compartment.10 However, FDS requires more detailed input than does the sprinkler/detector response model in FPEtool. In order to make these predictions, FDS requires that the user input the full geometry of the space in which the sprinklers will be installed, including all obstructions and vents, as well as surface properties of all obstructions. A fire must be specified using such parameters as the heat release rate per unit area or the heat of vaporization of a fuel. Specific sprinkler properties, including the response time index (RTI), activation temperature, operating pressure, and C-factor, as well as the sprinkler’s location in the space, are input and
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allow FDS to predict when the sprinkler will activate. Additionally, a sprinkler’s K-factor can be specified and water flow from the sprinkler into the fire domain can be modeled. The verification method’s output will likely be produced in engineering terms such as time, temperature, or heat release. This output, in combination with the assumptions and decisions employed in the design process, will be evaluated against the performance criteria to determine whether the fire safety goals have been achieved for the design parameters specified. It is important to note that more than one verification method will likely be used to verify the various aspects of a fire safety solution.
Fire Safety Goals, Performance Objectives, and Performance Criteria Fire Safety Goals. Fire safety goals are the overall outcomes to be achieved with regard to fire.11,12 They should be nonspecific and expressed on a qualitative basis. Fire safety goals should be stated in terms of conditions that are intrinsically desirable and do not rely on any assumptions. Goals should be further stated in terms that are potentially measurable, even if the precise measurement scale is not specified. Thus, they would typically be expressed in terms of impact on people or property, business interruption, or environmental impact. For example, a fire safety goal stated in terms of impact on people might be to maintain that the risk of death due to fire is not higher than the current level for similar properties or not higher than x per 100,000 people exposed. Another example of a fire safety goal in terms of impact on people might be to increase the likelihood that anyone capable of self-evacuation and not intimate with ignition can safely escape. An example of a fire safety goal stated in terms of impact on property might be to limit fire damage to x square feet (m2) of building space. More specifically, the goal of a sprinkler system installation standard might be to provide for a system that will aid in the detection and control of residential fires and reduce the likelihood of injury and loss of life due to fire. Performance Objectives. In order to assess the degree of achievement of a particular fire safety goal, intermediate measures, such as performance objectives and performance criteria, also need to be defined. Performance objectives can be described as the requirements of the fire, building, or occupants that need to be obtained in order to achieve a fire safety goal.13 These objectives define a series of actions necessary to make the achievement of a goal much more likely. Performance objectives are stated in more specific terms than goals and are measured on a more quantitative basis. For example, a performance objective for a sprinkler system might be that the system be designed, installed, and maintained to prevent instantaneous or cumulative exposure to conditions that exceed a certain survivability criteria, or that the sprinkler system prevent flashover in the room of origin for the period of time necessary for occupant evacuation. Objectives could also include statements that call for prevention of structural damage, no life loss in the room of fire origin, the separation of occupants from fire effects for a specified length of time, or the containment of the fire to the room of origin.
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Performance Criteria. Performance criteria can be described as performance objectives for individual products, systems, assemblies, or areas that are further quantified and stated in engineering terms.12 Engineering terms can include temperatures, radiant heat flux, or levels of exposure to fire and products of combustion. Performance criteria provide threshold values that are treated as data for calculations used to develop a proposed solution. For example, performance criteria for occupant survivability might be that at a distance of 5 ft (1.5 m) above the floor that following conditions are met: 1. Temperature does not exceed 150°F (65.5°C) 2. Instantaneous carbon monoxide concentration does not exceed 10,000 ppm 3. Cumulative carbon monoxide concentration does not exceed 25 percent carbon monoxide hemoglobin level 4. Oxygen concentration is maintained at 14 percent or greater Criteria with regard to the prevention of flashover might be 1. Upper layer temperature does not exceed 1100°F (or the threshold might be stated as 600°C, which is roughly the same) 2. Radiant heat flux at the floor does not exceed 20 kW/m2 (or the threshold might be stated as 1.75 Btu/s/sq ft, which is roughly the same).
Characteristics of and Assumptions about Occupants, Contents, and Building Features It is unlikely that any proposed solution, performance-based or prescriptive-based, will be able to achieve the fire safety goals for everyone and everything under all possible conditions. This is due primarily to limitations and uncertainty with available technology and science in combination with society’s unwillingness to accept the restrictions and costs associated with attempting to achieve zero risk. Therefore, details about who or what is intended to be protected and under what conditions needs to be specified.13 An evaluation of the characteristics of the occupants, contents, and building features is needed. All assumptions about who or what is being protected and all other factors that could invalidate the proposed solution need to be identified as part of the design parameters. For example, a proposed solution may only be valid for occupants who are capable of self-rescue and who have an unobstructed means of egress available to them, or for occupants who are familiar with their egress routes. The effectiveness of the proposed solution for occupants who fall outside the scope of these assumptions or characteristics would be much less certain.
The Fire Challenge—Fire Hazards and Scenarios The potential for ignition and development of a fire that presents a threat to building occupants or contents exists in virtually all locations. The conditions under which these hazards exist and
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their likelihood of occurring in a given location need to be considered. An analysis of some type, preferably of the risk variety, will identify the hazards that are intended to be protected against. The specific hazards to be guarded against need to be precisely defined through a set of fire scenarios and included in the design parameters. Fire scenarios specify the fire conditions under which a proposed solution is expected to meet the fire safety goals. A fire scenario can be considered as the “fire load” that an occupant or building would likely be subjected to. It poses the challenge that the fire safety systems must overcome. The fire scenario describes factors critical to the outcome of the fire, such as the ignition source, initial fuel package, the location of initial fire development, aspects of the building arrangement, and the available fuel load. Fire scenarios describe the specifications needed for a fire test, and can serve as direct input for a fire-modeling run. The number of fire scenarios for any given space can be quite large; therefore, fire scenarios will need to be grouped into categories for manageable analysis.13 Those scenarios representing the most severe case of each category could be included in the design parameters if a conservative, hazard analysis approach were used. A typical case for each category would be used if a fire risk approach were employed. Or, possibly best of all, a hybrid approach could be used. For example, a set of fire scenarios might include those scenarios that are common (i.e., high probability) for the facility type in question and those that are general-purpose high-challenge scenarios but less likely to occur (i.e., likely to result in rapid, early onset of severe fire conditions). With regard to a single-family residence, a set of scenarios might include that described in Table 3.13.1. (Obviously certain terms, such as free-burning fire, would need to be more explicitly defined.) The design parameters for a single-family dwelling might specify, among other conditions, that the fire safety goals be met for all of the six identified fire scenarios. Any proposed solution that demonstrates success would be permitted. For example, a residential sprinkler system designed and installed in accorTABLE 3.13.1
dance with a specific sprinkler system standard might be presented as the proposed solution. However, the sprinkler system alone might not be sufficient, as typical sprinkler systems are not intended to protect against fires in areas that are not sprinklered (high-challenge scenario No. 2) or fires that enter the dwelling from outdoors (common scenario No. 3); additional fire safety features, such as a smoke detection system and certain construction materials, would likely be needed.
Design Specifications Design specifications refer to the physical design arrangement intended to achieve the goals under the fire scenarios, assumptions, and other conditions specified. Design specifications include details about the protection systems to be employed, whether the systems are active or passive, manual or automatic. They comprise that portion of the design parameters that allow for the most design flexibility and serve as another input for a verification method, either directly or as a retained assumption.
Safety Factors The proposed solution needs to be expressed in terms that make it possible to assess whether the fire safety goals have been achieved. The proposed solution also needs to address how reliably it can achieve the fire safety goals. This will include addressing the reliability of the individual components and subsystems of the buildings overall fire safety system as well as the system in its entirety. In addition to relying on testing and maintenance of the system and its components to ensure reliability, safety factors should also be applied. Safety factors can be considered as adjustments to various elements of the design process, such as performance criteria, or to the overall proposed solution. Safety factors reflect conservatism due to the uncertainty in the methods and assumptions employed in calculating or measuring performance. A safety factor does not reflect a ratcheting up of the
Possible Set of Fire Scenarios for a Single-Family Residence
Scenario
Initial Fuel
Ignition Source
Room or Location of Fire Origin
Fire Type
Common No. 1
Ordinary combustibles
Small open-flame source such as a match or cigarette lighter
Principally occupied rooms such as living room and bedroom
Free burning fire
Common No. 2
Upholstered furniture
Cigarette
Principally occupied rooms such as living room and bedroom
Smoldering fire
Common No. 3
Ordinary combustibles
Small open-flame source such as a match or cigarette lighter
Structural area such as an attic
Free burning combustibles
High Challenge No. 1
Ordinary combustibles
Small open-flame source such as a match or cigarette lighter
Entryway of a principally occupied room of the dwelling
Free burning fire
High Challenge No. 2
Ordinary combustibles
Small open-flame source such as a match or cigarette lighter
Small unprotected room such as a bedroom closet
Free burning area
High Challenge No. 3
Ordinary combustibles
Small open flame source or cigarette
Principally occupied rooms such as living room and bedroom
Shielded room-corner fire with a substantial initial smoldering period
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safety goals or objectives. To aid in its assessment, the proposed solution needs to identify all fire models, assumptions, and safety factors employed. Suppose the safety objective was for everyone to egress the building in less time than is required for fire effects such as toxic smoke to reach them. Then there are two time measures—time required for egress and time required for fire effects to reach occupied areas—and each time measure requires calculations using uncertain data, assumptions, and simplified models. A safety factor to reflect all these uncertainties could be doubling the estimated time for egress or halving the estimated time for fire effects to reach occupied areas, or both. Safety factors should reflect the actual magnitude of uncertainties.
Verification Methods—Calculation Methods, Computer Fire Models, Fire Tests Calculation methods, computer fire models, and fire tests serve as tools that help verify whether the fire safety goals have been achieved for the design parameters.14–16 Due to the complex nature of the principles involved and the numerous calculations required, models are often packaged as computer software. However, hand calculations that can model certain aspects of a fire event are available.17,18 All associated relevant input data, assumptions, limitations, and safety factors needed to properly implement the verification method should be provided. It is important to note that verification methods do not provide the final solution, but rather help in the evaluation of a performance-based design. This fundamental concept is often misunderstood. The verification methods account for the physics that describe the fire phenomenon, occupant response, fire safety system performance, and their interaction, and quickly perform the necessary calculations, making performance-based design much more likely. The ultimate fire safety decisions lie with the designer’s and the authority having jurisdiction’s (AHJ’s) or regulator’s interpretation of the methods’ results. Fire protection engineers appear eager to apply performancebased methods and fire modeling to their projects as a means of validating noncode prescribed solutions.19,20 Currently, these approaches are primarily used in special applications, such as fire reconstructions, in the development of unique design arrangements not addressed by current codes and standards, and to demonstrate that an alternative means of protection meets or exceeds code requirements. Performance-based design requires increased time and effort by fire protection engineers and creates the potential for increased design costs.11 Although many fire models can generate results with a reasonable degree of accuracy when properly employed by knowledgeable individuals, skepticism remains with regard to their routine use for designing fire safety. Overall a good deal of uneasiness exists due to the potential for misuse. Some of the reasons for this include a lack of available input data such as the burning characteristics of materials, a lack of understanding of the model’s purpose and limitations, and the improper interpretation of the model’s output. These concerns are valid and efforts to resolve them have been initiated.21 The increased application of performance-based design approaches and computer fire modeling warrants a higher level of
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scrutiny than required for prescriptive-based design. Calculation methods have limitations that may not be identified or known by their developers or users. Misuse of these methods and misinterpretation of their results can have a detrimental effect on safety and overall fire protection. Guidance is needed for users and AHJs so that they either understand or are aware of a verification method’s assumptions, limitations, and proper application.22,23 Further issues exist, as many models have not been validated to show under what conditions their results are valid, and much of the input data needed to run the models is not available. Although the development of calculation methods and fire models continues, more and improved versions are needed if a more complete performance-based design option is to be truly realized. Additional scientific research and testing are necessary for the development of new models and their input data. Existing models and methods do not provide all that is needed. However, it can be argued that fire models can become more effective once codes and standards explicitly state their fire safety goals and provide a direct connection to their application.
Verification—The Role of the AHJ and Regulators In summary, verification is confirmation by the AHJ that a proposed solution meets the established fire safety goals under the conditions specified.13 Verification can be thought of as a process similar to that used for the approval of traditional code prescribed solutions. However, unlike prescriptive-based methods, the proposed solution developed through performance-based design cannot be easily confirmed by visual inspection for compliance with code requirements near the completion of the design process. The AHJ needs to be brought into the process early on and remain involved throughout. A partnership is required and a “cookbook” mentality does not properly serve performancebased design. A solid understanding and/or confidence level with the fire protection engineering design concepts employed by all involved is essential. Verification involves several steps not currently required under current prescriptive-based methods as follows: 1. Verification that the proposed solution shows the building will meet the fire safety goals under the conditions established 2. Verification during construction that the building as built fits the design and data used in the proposed solution 3. Verification that the development of the proposed solution was completed by an individual or group qualified to perform such a task 4. Verification that the proposed solution implemented appropriate models, test methods, and other calculation procedures, and that they were used in an appropriate manner 5. Verification that the assessment used appropriate data, and that it was used in an appropriate manner Verification confirms that the building is constructed as intended to a design that will achieve the intended goals, and that the building’s ability to achieve the stated goals has been demonstrated by qualified people using appropriate methods applied to correct data. Unfortunately, a means to accomplish all the
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necessary steps of the verification process to everyone’s satisfaction does not yet exist. As a result, the confidence level with performance-based design is not where it needs to be on a routine basis. Additional efforts, especially with gaining acceptance of calculation methods and fire models, establishing qualifications for model users, providing input data and training of both AHJ and designers, need to be and are currently being undertaken. However, that fact that voids exist should not be reason to completely disregard current performance-based designs. Our traditional approaches do not provide all the answers either. Current performance-based designs should be considered carefully and within their proper scope.
THE ROLE OF CODES AND STANDARDS IN THE PERFORMANCE-BASED DESIGN PROCESS Value Judgments and Fire Safety Goals If verification indicates failure of a proposed solution, what can be changed to achieve success? One response might be to alter the fire safety goals. Lower the bar and success requires less effort. However, the establishment of fire safety goals represents one means by which society expresses its desires about safety. Goals set by society represent value judgments and cannot be compromised, even by those responsible for verifying their compliance. However, the building owner might also require certain goals be achieved. Unlike the goals of society, a degree of latitude exists for those goals set by the building owner or his representatives provided that they do not conflict with those of society. Goals, whether those set by society or the building owner, must be written in a way that those responsible for verifying that they have been achieved can do so (i.e., the complete fire safety goal from the general statements about safety to the quantifiable performance criteria need to be clearly stated in fire safety regulations and the project brief). This is especially important, as the enforcing authority will be asked to verify a proposed solution that is based largely on the output produced by verification methods, that is, computer models and calculation methods. The verification process becomes more workable when the terms used to measure the performance of a proposed solution (i.e., model output) resemble those used to quantify the fire safety goals (i.e., performance criteria).
Value Judgments and Design Parameters The design parameters identify all the conditions about the fire, people, property, building, and protection features under which the fire safety goals are to be achieved. The severity and types of fire challenges considered as well as the condition and location of the occupants and the layout of the building impacts the ability of a proposed solution in achieving the fire safety goals. If the fire scenarios encompassed within the design parameters are relatively undemanding, then a lesser degree of fire protection is necessary to achieve the fire safety goals. A given building could be considered unsafe if it is required to meet stringent fire safety goals for a set of fire scenarios that
does not adequately represent the associated fire risks. For example, it would be less challenging for a sprinkler system in a rack storage warehouse to prevent fire spread across storage aisles if the fire load represented paper products instead of plastic commodities. The fire challenge associated with the combustion of plastics is relatively more severe than those of paper. A similar situation might arise if the results of an egress model indicate that building occupants will not be able to evacuate to an area of safe refuge before untenable conditions arise. Would it be acceptable to change the condition of the occupants so that their speed of movement is increased so that success could be achieved? A comparable condition would also arise if the fire safety solutions for a hotel did not consider occupants who are asleep when a fire occurs. As in the specification of fire safety goals, the determination of the design parameters particularly in the description of the applicable fire scenarios and character of the occupants and property also embodies value judgments about fire safety, and therefore certain details about them need to remain fixed regardless of the specific project. The details pertaining to value judgments need to be captured by codes and standards and cannot be subject to modification by the building owner. Without this information, those responsible for verification would be much less certain about which fire scenarios and what occupant characteristics the building owner must evaluate to demonstrate that the level of safety demanded by society has been achieved.
Value Judgments and Retained Assumptions While portions of the design parameters contain details that must remain fixed to meet the needs of society, they also include those details that can be modified to fit the needs of the building owner. The question about what aspects of the design parameters need to be fixed by fire safety regulations remains. Details about the building and the potential protection features fall to the bottom of the list. After all, the intent of performance-based design is to provide for greater freedom in building design. Greater flexibility in designing fire safety in terms of the building’s layout, construction materials, and protection features is the essence of performance-based design. Specifying this information in codes and standards would result in a practice no different than what has been done for the past 100 years. Codes and standards used in conjunction with performancebased design, therefore, would not specify details about the building, but rather identify those characteristics about the building and the occupants that need to be defined by the building owner. For example, the 2000 edition of the NFPA 101®, Life Safety Code®, requires details pertaining to the building’s dimensions, construction materials, furnishings, spatial geometry, number and size of openings, and other facts that serve as input for specific calculation methods or models.24 For the most, part regulations should provide as much flexibility as possible in the layout of the building and the design of the protection features. However, there comes a point where the scale used to weigh design flexibility against practical design becomes unbalanced. It is at this point that decisions pertaining to fire safety design can impact value judgments, and this is
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where it becomes appropriate for codes and standards to set limits. Therefore, codes would need to further require that certain assumptions be made about any proposed solutions. Such assumptions might be include • Compliance with the fire safety goals shall not depend solely on any single safeguard. • For life safety purposes, a minimum of two means of egress shall be provided unless it can be demonstrated that fire or smoke cannot block the occupants’ egress from a single exit. • Safeguards that comprise the proposed solution must be continuously exercised and maintained in accordance with specified requirements so that the safeguards remain properly operational for the life of the building.
Regulations and Their Impact on the Fire Challenge The fires that will challenge the proposed solutions need to be specified. This includes a qualitative description of the types of fires to be considered as well as a conversion of this description into quantifiable terms that can be used as input for a computer model. The selection of fires to be considered embodies value judgments, as more stringent fires require more substantial safety measures that in turn raise the overall level of safety. By providing a qualitative description of applicable fires, regulations begin to frame and scope the conditions under which a proposed solution is intended to perform. This caps the range of potential fires to be examined and makes the design process more workable by all involved. This also provides a reference for the enforcement authority when verifying a proposed solution, and limits the possibilities of engineers having to prove the impossible. Examples of the type of scenario data to be specified by regulations include the following: • A single fire source is assumed. • An ultrafast-developing flammable liquids fire, in the primary means of escape, with interior doors open at the start of the fire. • A fire originating in a concealed wall or ceiling space adjacent to a large occupied room. • A fire, starting in a normally unoccupied room that can potentially endanger a large number of occupants in a large room or other area. Because fire conditions largely depend on the characteristics of a given building, codes and standards are limited in the type of information they can provide about them. For instance, the building’s contents, dimensions, and so on, will dictate the growth and spread of potential fires. Additionally, because the fire conditions must be presented in quantifiable form, the final details about them need to be established by the owner through the application of pertinent data sources. As with the fire safety goals, the building owner may require that fire conditions in addition to those specified by the regulations be considered and other appropriate measures would need to be implemented in this regard.
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Regulations and Their Impact on Occupant and Property Characteristics Characteristics and qualities about the occupants or property to be protected will be required as this information is critical to the outcome of a fire. Certain details about the occupants or property would be used as input data for computer models or be retained as key assumptions throughout the design process. Codes and standards need to require that specific information be provided about the occupants, such as their sensibility, reactivity, mobility, and susceptibility. The building owner would need to provide specific information in this regard. However, the code might also require that specific assumptions be made about the occupants, such as • In every normally occupied room or area, at least one person shall be located at the most remote point from the exits. • In every normally occupied room or area, the average maximum density of occupancy shall be present. Additional details or other assumptions about the people or property exposed might be project specific and the details about these would be the responsibility of the building owner.
How Much Performance to Be Measured Performance-based design should not include the blind application of calculation methods and computer models. Performancebased design embodies a new way of thinking about and conducting fire safety design for the built environment. It is an approach that needs to be implemented from the start of a project and continued to its completion even if all the tools and data needed for measurement and quantification are unavailable. As in the past, certain assumptions based on knowledge, judgment, and experience will be needed to fill the gaps and this will result in a combination of prescriptive- and performance-based solutions in many cases. For example, an egress plan developed largely through the application of a computer model is likely to rely upon existing provisions for stair tread size and egress path lighting. Another example considers the installation of sprinklers under a ceiling with varying elevations. NFPA 13, Standard for the Installation of Sprinkler Systems, requires that sprinklers be positioned not more than a certain distance below the ceiling to ensure that the sprinklers will activate in a timely manner.25 However, where a ceiling contains many changes in elevation or deep pockets, the application of the positioning rules becomes awkward as a sprinkler would be required in each pocket and this could result in the installation of more sprinklers than would be needed to protect the hazard. Modeling could be conducted to determine the length of time it takes for the pockets to fill with hot gases and activate the sprinklers at the lower ceiling elevation. This information could be used to determine if sprinklers are necessary in each pocket. Although the modeling in this example might provide positioning rules that differ from that of the standard, the other prescriptive installation rules of NFPA 13 would need to be followed unless other similar analyses are conducted. It is important to note that though prescriptive methods are often characterized as overly burdensome, the push to
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performance-based design is not a result of their failure. Prescriptive methods still provide good results even though they may not be the most efficient.
PRECEDENTS FOR PERFORMANCEBASED CODES AND STANDARDS Although considered to be a relatively new concept, various versions of performance-based design have been and are currently being performed. Many building and fire safety codes and standards provide an option to develop alternative means of protection, provided the level of safety prescribed by the document is not lowered.26,27 Primary examples include the development of fire safety for unique architectural or functional features not anticipated by current codes and standards, or the development of alternative means of protection to existing code requirements. Many of the principles of performance-based design are also employed in the preparation of fire reconstructions. Unfortunately, all the pieces needed to properly support this process are not in place. Performance-based approaches today require a major undertaking by both the designer and AHJ. Current codes and standards do not serve performance-based design well. Any performance-based design attempted today must demonstrate a level of safety equivalent to the existing prescriptive standards. However, many existing codes and standards typically do not explicitly state their fire safety goals, nor do they identify the assumptions and fire scenarios under which the prescribed fire safety solution is to be effective. The task of determining what the code is intending to achieve, for whom, and under what conditions can prove to be difficult as each concerned individual typically may have a differing opinion of what is intended. To further complicate matters, current codes and standards do not reference computer models or calculation methods that have been demonstrated to be effective for the design and assessment of a proposed solution. Efforts to validate models, qualify their input data, and train or certify their users need to be increased. In addition, the current level of technology cannot produce the calculation methods and models that will properly address all of the relevant concerns. As a result, the necessary confidence level with these methods does not yet exist. Once performance-based approaches and their supporting pieces undergo an acceptable level of standardization, for example, product listings and installation standards, as other fire safety technologies have, they will enjoy greater acceptance overall. What primarily exist are general provisions allowing something vague called “equivalency,” and a collection of experts, models, data bases, and other resources that may lead to better solutions if used properly. What are needed are better definitions and procedures that allow the concerned parties to agree more explicitly on the goals against which equivalence is defined and how to demonstrate equivalence.
scriptive-based methods work, although their solutions might not be as effective or efficient as desired in certain situations. It can also be said that prescriptive-based methods present a more straightforward design approach that requires less of an initial effort to implement. In addition, prescriptive-based codes are more easily enforced. Because of the inherent advantages, future NFPA codes and standards will be revised to include both performance-based and prescriptive-based options as appropriate.12 In essence a dual track approach will be advocated such that either the performance-based or prescriptive-based option could be applied to achieve the safety goals and objectives specified by the code or standard. This arrangement provides an option for either method, as one method might be better suited over the other for a certain project. The dual-track approach also connects the two design methods and supports the philosophy that performancebased options are the next level of sophistication for codes and standards. NFPA’s overall approach in this regard is documented in the NFPA Primer for Performance-Based Codes and Standards Preparation.28 It is intended that future NFPA codes and standards provide the needed level of standardization for the pieces necessary to employ performance-based design. A more formalized arrangement better supports the overall performance-based design and verification process by explicitly identifying the fire safety goals and by providing guidance with regard to the determination and use of specific fire safety criteria, assumptions, fire scenarios, and calculation methods. The overall outcome should result in greater application and acceptance of performance-based design methods by both design engineers and AHJs. It is also hoped that future NFPA codes and standards will provide a better direction for research efforts, improve the transfer of technology, and encourage prescriptive-based requirements to be based more on science and technology.
PURSUING PERFORMANCE-BASED REGULATIONS Over the past several years NFPA has been pursuing the development of performance-based codes and standards. While a number of initiatives are underway, including the development of a formalized performance-based option for the soon to be published NFPA Building Code, a major milestone was reached in the Fall of 1999 when the NFPA membership voted to approve the 2000 edition of NFPA 101®, Life Safety Code®. NFPA 101 has become the first performance-based code in wide use across North America and follows the “dual track” approach. Specific life safety goals and objectives are stated and guidance is provided with regard to the determination of performance criteria, fire scenarios, design assumptions and occupant characteristics.
SUMMARY FUTURE NFPA CODES AND STANDARDS Although the application of performance-based methods will continue to increase, it is unlikely that performance-based approaches will entirely replace prescriptive-based methods. Pre-
The performance-based design concept for fire safety continues to gain momentum on a global scale. Governments encourage the use of engineering approaches. Fire protection engineers are increasing the application of nontraditional methods in their de-
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signs. An increasing number of code and fire officials are being asked to make decisions about fire safety designs based upon performance-based approaches. Researchers continue to improve and develop new tools and data. But what is performancebased design really about? Is it about minimizing the cost for fire safety in buildings and increasing design flexibility? Is it about addressing voids in current regulations? Or is it about embracing new technologies? In part, the performance-based concept encompasses all these themes. However, it must also extend beyond them. The creation of more functional buildings at reduced cost is certainly a desirable goal. However, fire safety is about safety. Cost savings and design flexibility should be considered valuable byproducts in the application of calculation methods and other information. The application of new technologies should produce more effective and reliable fire safety solutions. Developing regulations that better support performancebased design is only a starting point. Implementation of performance-based design into everyday practice requires more than a rewrite of existing codes and standards. Major efforts to standardize fire models, test methods, and the qualifications of model users and practitioners are essential, as are efforts with legal issues, and education.29 Success requires cooperation and coordination by all concerned interests. In the end, performance-based design should provide more answers than questions about safety. Once a performance-based design has been implemented and the building has been built, will the building owner and the broader community feel more confident about the building’s safety features? More importantly, how will they know?
BIBLIOGRAPHY References Cited 1. Richardson, J. K., “The Toolbox for Fire Protection Engineers,” Fire Protection Engineering, Premier Issue, 1998, pp. 4–8. 2. Lucht, D. A., Strategies for Shaping the Future—A Report on the Conference on Fire Safety Design in the 21st Century, Worcester Polytechnic Institute, Worcester, MA, 1991. 3. Buchanan, A. H., “Fire Engineering for a Performance-Based Code,” Proceedings—Interflam ’93, Interscience Communications Limited, London, UK, 1993, p. 457. 4. Lucht, D. A., “Changing the Way We Do Business,” Fire Technology, Vol. 28, No. 3, 1992. 5. Richardson, J. K., “Moving Toward Performance-Based Fire Codes,” NFPA Journal, May 1994, p. 70. 6. Nelson, H. E., “History of Fire Technology,” Conference on Fire Safety Design in the 21st Century—Pre-Conference Papers, Worcester Polytechnic Institute, Worcester, MA, 1991, p. 180. 7. “NFPA’s Future in Performance-Based Codes and Standards— Report of the NFPA In-House Task Group,” NFPA International, Quincy, MA, July 1995. 8. “The SFPE Engineering Guide to Performance-Based Fire Protection Analysis and Design,” Society of Fire Protection Engineers, Bethesda, MD, 2000. 9. Deal, S., “Technical Reference Guide for FPEtool Version 3.2,” U.S. Department of Commerce, National Institute for Standards and Technology, Building and Fire Research Laboratory, Apr. 1995, pp. 57–60. 10. McGrattan, K. B., et al., “Fire Dynamics Simulator—Technical Reference Guide, U.S. Department of Commerce, National Institute of Standards and Technology, Jan. 2000, p. 11.
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11. Custer, R. L. P., “Selection and Specification of the Design Fire for Performance-Based Fire Protection Design,” PerformanceBased Fire Safety Engineering, Society of Fire Protection Engineers, Boston, MA, 1993, p. 17. 12. Bukowski, R. W., and Babrauskas, V., “Developing Rational, Performance-Based Fire Safety Requirements in Model Building Codes,” Fire and Materials, Vol. 18, 1994, p. 173. 13. “NFPA’s Future in Performance-Based Codes and Standards— Report of the NFPA In-House Task Group,” NFPA International, Quincy, MA, July 1995. 14. Friedman, R., “An International Survey of Computer Models for Fire and Smoke,” Journal of Fire Protection Engineering, Vol. 4, No. 3, 1992, p. 81. 15. Cote, A. E., “The Computer and Fire Protection Engineering— 25 Years of Progress,” Fire Technology, Vol. 26, No. 3, 1990, p. 195. 16. Emmons, H. W., “Fire Safety Science—The Promise of a Better Future,” Fire Technology, Vol. 26, No. 1, 1990, p. 5. 17. SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 1995. 18. Drysdale, D., An Introduction to Fire Dynamics, John Wiley & Sons, New York, 1985. 19. Koffel, W. E., private communication, 1993. 20. Maddox, J. A., private communication, 1993. 21. “Update on SFPE Engineering Task Group Activities,” SFPE Bulletin, Fall 1997. 22. Lavine, R. S., “User’s Needs in Fire Models—Proceedings of the Ad Hoc Mathematical Fire Modeling Working Group,” Fire Technology, Vol. 24, No. 2, 1988, p. 163. 23. Bukowski, R. W., “Fire Models—The Future Is Now!,” NFPA Journal, Mar. 1991, p. 61. 24. NFPA 101®, Life Safety Code®, NFPA International, Quincy, MA, 2000. 25. NFPA 13, Standard for the Installation of Sprinkler Systems, NFPA International, Quincy, MA, 1999. 26. Mawhinney, J. R., “Evaluating Equivalencies to Building Code Requirements,” National Research Council of Canada, Ottawa, Canada, 1991. 27. Bukowski, R. W., “How to Evaluate Alternative Designs Based on Fire Modeling,” NFPA Journal, Mar. 1995, p. 68. 28. “Performance-Based Primer for Codes and Standards Preparation, Revision 1.0,” NFPA International, Quincy, MA, January 2000. 29. Richardson, J. K., “Regulatory System Changes Needed to Gain Acceptance of Fire Safety Engineering Methods,” Issues in International Fire Protection Engineering Practice, Society of Fire Protection Engineers, Boston, MA, 1993, p. 37.
Additional Readings Anderson, R. C., “New Requirements in Building Codes,” Special Conference on Recent Advances in Flame Retardancy of Polymeric Materials—Materials, Applications, Industry Developments, Markets, May 15–17, 1990, Stamford, CT, 1990, pp. 1–7. Ashe, B., and Shields, J., “Analysis and Modelling of the Unannounced Evacuation of a Large Retail Store, Fire and Materials, Vol. 23, No. 6, 1999, pp. 333–336. Babrauskas, V., “Designing Products for Fire Performance: The State of the Art of Test Methods and Fire Models,” Fire Safety Journal, Vol. 24, No. 3, 1995, pp. 299–312. Barnett, C. B., and Simpson, M. R., “Fire Code Review: New Zealand’s Performance Based Fire Code,” Proceedings of the 1st International Conference on Fire Science and Engineering, ASIAFLAM ’95, March 15–16, 1995, Kowloon, Hong Kong, 1995, pp. 27–40. Beck, V. R., “Performance Based Fire Safety Design: Recent Developments in Australia,” Fire Safety Journal, Vol. 23, No. 2, 1994, pp. 133–158. Beller, D., “Decision Support System for Performance-Based Design Evaluation,” Proceedings of the Pacific Rim Conference and 2nd
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International Conference on Performance-Based Codes and Fire Safety Design Methods, May 3–9, 1998, Maui, HI, International Code Council, Birmingham, AL, 1998, pp. 249–258. Brannigan, V., “Performance-Based Codes: No Panacea,” Fire Chief, Vol. 40, No. 4, 1996, pp. 31–32, 34. Brannigan, V. M., and Lehner, P., “Performance Based Fire Safety Codes: A Regulatory Effectiveness Analysis,” Proceedings of the International Conference on Fire Research and Engineering, September 10–15, 1995, Orlando, FL, SFPE, Boston, MA, 1995, pp. 181–186. Brannigan, V., Smidts, C., and Kilpatrick, A., “Regulatory Requirements for Performance Based Codes Using Mathematical Risk Assessment,” Maryland University, College Park, Caledonian University, Glasgow, Scotland, National Institute of Standards and Technology, Gaithersburg, MD, ISBN 0-9516320-9-4; Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 621–630. Buchanan, A. H., “Fire Engineering for a Performance Based Code,” Fire Safety Journal, Vol. 23, No. 1, 1994, pp. 1–16. Bukowski, R. W., “International Activities for Developing PerformanceBased Fire Codes,” National Institute of Standards and Technology, Gaithersburg, MD, CIB W14/96/1 (J); Mini-Symposium on Fire Safety Design of Buildings and Fire Safety Engineering, June 12, 1995, Tsukuba, Japan, 1995, pp. IV/1–3. Bukowski, R. W., “Setting Performance Code Objectives: How Do We Decide What Performance the Codes Intend?,” National Institute of Standards and Technology, Gaithersburg, MD, ISBN 0-9516320-9-4; Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 555–561. Bukowski, R. W., and Tanaka, T., “Toward the Goal of a Performance Fire Code,” Fire and Materials, Vol. 15, No. 4, 1991, pp. 175–180. Bukowski, R. W., and Babrauskas,V.,“Developing Rational, PerformanceBased Fire Safety Requirements in Model Building Codes,” Fire and Materials: An International Journal, Vol. 18, No. 3, 1994, pp. 173–192. Butcher, E. G., and Parnell, A. C., “Fire Safety Engineering: What Performance Standard Is Acceptable and What Does It Mean?,” Fire Safety, Vol. 3, No. 3, 1996, pp. 29–30. Cohn, B. M., “Characterization and Use of Design Basis Fires in Performance Codes,” Bert Cohn Associates, Inc., ISBN 0-95163209-4; Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 581–588. Cohn, B. M., “Synthesis of a Goal-Oriented Building Code,” Journal of Applied Science, Vol. 1, No. 4, 1990–1991, pp. 301–314. Crowley, M. A., “Performance Based Smoke Exhaust Systems for High Piled Storage: A Case Study,” Proceedings of the Society of Fire Protection Engineers (SFPE) Honors Lecture Series, Engineering Seminars: Fire Protection Design for High Challenge or Special Hazard Applications, May 20–22, 1996, Boston, MA, 1996, pp. 55–58. Custer, R. L. P., “Progress on Computer Modeling in PerformanceBased Detection System Design in the United States,” Worcester Polytechnic Institute, MA, European Society for Automatic Alarm Systems (EUSAS), European Platform for Promoting Security and Fire Protection Engineering, Newsletter, Number 5, June 1994, pp. 17–26. Custer, R. L. P., “Selection and Specification of the ‘Design Fire’ for Performance-Based Fire Protection Design,” Proceedings of the Society of Fire Protection Engineers Engineering Seminars on Performance-Based Fire Safety Engineering, November 15–17, 1993, Phoenix, AZ, SFPE, Boston, MA, 1993, pp. 17–22. Custer, R. L. P., Meacham, B. J., and Wood, C. B., “PerformanceBased Design Techniques for Detection and Special Suppression Applications,” Proceedings of the Technical Symposium on
Halon Alternatives, June 27–28, 1994, Knoxville, TN, 1994, pp. 17–32. Dolph, B. L., “Ship Fire Safety Engineering Methodology: A Performance Based Fire Safety Analysis,” Third International Conference and Exhibition on Fire and Materials, October 27–28, 1994, Arlington, VA, 1994, pp. 199–206. Emmons, H. W., “Strategies for Performance Codes in the U.S.,” Harvard University, Cambridge, MA, Worcester Polytechnic Institute, Conference on Firesafety Design in the 21st Century, Part 1, Conference Report, Part 2, Conference Papers, May 8–10, 1991, Worcester, MA, 1991, pp. 166–179. Feld, J. M., “Developing a Performance Based Sprinkler System Standard,” Proceedings of the Society of Fire Protection Engineers Engineering Seminars on Performance-Based Fire Safety Engineering, November 15–17, 1993, Phoenix, AZ, SFPE, Boston, MA, 1993, pp. 31–38. Finucane, M., “Adoption of Performance Standards in Offshore Fire and Explosion Hazard Management,” Fire Safety Journal, Vol. 23, No. 2, 1994, pp. 171–184. Frantzich, H., “En Modell for Dimensionering av Forbindelser for Utrymning Utifran Funktionsbaserade Krav [Model to Design Escape Routes in a Building Based on Performance Based Requirements],” Lund University, Sweden, LUTVDG/TVBB-1011SE, Dec. 1994. Fraser, R. J., “Performance-Based Codes: The New Zealand Experience,” Proceedings of the Society of Fire Protection Engineers Engineering Seminars on Performance-Based Fire Safety Engineering, November 15–17, 1993, Phoenix, AZ, SFPE, Boston, MA, 1993, pp. 1–7. Fryer, R., “Building Regulations Are Barrier to Performance Testing of Fire Doors,” Fire International, No. 138, 1993, p. 28. Gradinscak, M., Beck, V., Brennan, P., and Horasan, M., “2D Computer Modelling and Human Response,” Fire and Materials, Vol. 23, No. 6, 1999, pp. 389–393. Groner, N. E., and Chubb, M. D., “Latent Human Error Is the Principal Threat to the Adoption and Use of Performance-Based Fire Safety Requirements,” Proceedings of the International Conference on Fire Research and Engineering, September 10–15, 1995, Orlando, FL, SFPE, Boston, MA, 1995, pp. 203–208. Gross, J. G., “Codes, Standards, and Institutions—Pressures for Change,” Journal of Professional Issues in Engineering Education and Practice, Vol. 117, No. 2, 1991, pp. 75–87. Hotta, H., “Example of Performance-Based Design for Fire Protection System: New Sprinkler System,” Bosai Consultants Corporation, Tokyo, Japan, CIB W14/96/1 (J); Mini-Symposium on Fire Safety Design of Buildings and Fire Safety Engineering, June 12, 1995, Tsukuba, Japan, 1995, pp. VII/1–20. Johnson, P. F., and Timms, G. R., “Performance Based Design of Shopping Center Fire Safety,” Proceedings of the 1st International Conference on Fire Science and Engineering, ASIAFLAM ’95, March 15–16, 1995, Kowloon, Hong Kong, 1995, pp. 41–49. Johnson, P. F., Beck, V. R., and Horasan, M., “Use of Egress Modelling in Performance-Based Fire Engineering Design: A Fire Safety Study at the National Gallery of Victoria,” Proceedings of the 4th International Symposium on Fire Safety Science, International Association for Fire Safety Science, Boston, MA, 1994, pp. 669–680. Johnson, P. F., “International Implications of Performance Based Fire Engineering Design Codes,” Journal of Fire Protection Engineering, Vol. 5, No. 4, 1993, pp. 141–146. Karlsson, B., and Kokkala, M. A., “New Developments in Performance Based Test Methods for Fire Safety Assessment of Products,” Lund University, Sweden, VTT-Technical Research Center of Finland, Espoo, CIB W60 Workshop on New Developments in Performance Test Methods, April 10–11, 1995, Horsholm, Denmark, 1995, pp. 1–16. Karydas, D. M., and Delichatsios, M. A., “Risk Assessment Methodology for Fire Safety Factors in Performance-Based Design of Buildings,” Factory Mutual Research Corporation, Norwood,
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MA, NISTIR 5499, Sept. 1994; National Institute of Standards and Technology, Annual Conference on Fire Research: Book of Abstracts, October 17–20, 1994, Gaithersburg, MD, 1994, pp. 43–44. Kilpatrick, A., “Performance Based Fire Safety Codes: The UK Model?,” Proceedings of the International Conference on Fire Research and Engineering, September 10–15, 1995, Orlando, FL, SFPE, Boston, MA, 1995, pp. 193–194. Koffel, W., “Model Codes—New Directions” [VHS Video Tape], Federal Fire Forum, Interaction of Fire Safety with Building Design, Conducted in Conjunction with “Safety/Survivability 2000,” May 1, 1991, Washington, DC, 1991. Koffel, W. E., “Are We Ready for Performance Codes?,” NFPA Journal, Vol. 84, No. 3, 1992, p. 20. Koffel, W. E., “Ready or Not: Designing for Performance Codes,” NFPA Journal, Vol. 89, No. 5, 1995, p. 20. Koffel, W. E., “Who Sets Performance-Based Codes?,” NFPA Journal, Vol. 88, No. 6, 1994, pp. 16, 102. Kujime, M., Matsushita, T., and Tanaka, T., “Hand Calculation Method for Air Supply Rates in Vestibule Pressurization Smoke Control System,” International Journal on Engineering Performancebased Fire Codes, Vol. 1, No. 1, 1999, pp. 27–40. Larsen, G. P., “Nordic Model: Performance Building Code,” Nordic Fire Safety Engineering Symposium, Development and Verification of Tools for Performance Codes, August 30–September 1, 1993, Espoo, Finland, 1993, pp. 1–6. Lathrop, J. K., and Birk, D., “Building Life Safety with Codes,” NFPA Journal, Vol. 84, No. 3, 1992, pp. 42–46, 48, 50, 52. Lathrop, J. K., “Life Safety Code Key to Industrial Fire Safety,” NFPA Journal, Vol. 88, No. 4, 1994, pp. 36–46. Lippiatt, B., “Cost-Effective Compliance with Performance-Based Life Safety Codes” [VHS Video Tape], National Institute of Standards and Technology, Gaithersburg, MD, Federal Fire Forum, Providing Fire Safety for Equipment Use in Buildings. [This Forum Will Also be a Part of the BFRL Building Technology Symposia Series.], June 6, 1994, Gaithersburg, MD, 1994. Lucht, D., “What Is Meant by Performance-Based Design” [Video], Worcester Polytechnic Institute, MA; Federal Fire Forum, Performance-Based Design Issues of Concern to the A/E Community, November 6, 1995, Gaithersburg, MD, 1995. Lucht, D. A., Kime, C. H., and Traw, J. S., “International Developments in Building Code Concepts,” Journal of Fire Protection Engineering, Vol. 5, No. 4, 1993, pp. 125–133. Magnusson, S. E., “Performance Based Codes,” 6th International Fire Conference on Fire Safety, INTERFLAM ’93, March 30–April 1, 1993, Oxford, UK, Interscience Communications Ltd., London, UK, 1993, pp. 413–425. Magnusson, S. E., et al., “Determination of Safety Factors in Design Based on Performance,” Proceedings of the 4th International Symposium on Fire Safety Science, International Association for Fire Safety Science, Boston, MA, 1994, pp. 937–948. McCormick, J. W., “Building Code Applications Using the Emerging Technology: A Challenge Requiring a Strategy,” Journal of Applied Science, Vol. 1, No. 4, 1990/1991, pp. 321–330. McDowell, J. L., and Burton, G. C., “Forensic Engineering Application of Computer Modeling Techniques in the Determination of Human Response in Fire,” Proceedings of the 1st International Symposium, Human Behavior in Fire, August 31–September 2, 1998, Belfast, UK, Textflow Ltd., UK, 1998, pp. 753–758. Meacham, B. J., “Assessment of the Technological Requirements for the Realization of Performance-Based Fire Safety Design in the United States. Final Report,” NIST GCR-98-763, National Institute of Standards and Technology, Gaithersburg, MD, Nov. 1998. Meacham, B. J., “Concepts of a Performance-Based Building Regulatory System for the United States. Report of the 1996 Activities of the SFPE Focus Group on Concepts of a Performance-Based System for the United States,” NIST GCR 98-762, National Institute of Standards and Technology, Gaithersburg, MD, Nov. 1998.
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Meacham, B. J., “Evolution of Performance-Based Codes and Fire Safety Design Methods,” NIST GCR 98-761, National Institute of Standards and Technology, Gaithersburg, MD, Nov. 1998. Meacham, B. J., “International Development and Use of PerformanceBased Building Codes and Fire Safety Design Methods,” SFPE Bulletin, Mar./Apr. 1995, pp. 7–16; Selected Readings in Performance-Based Fire Safety Engineering, 1995, Boston, MA, Society of Fire Protection Engineers, Boston, 1995, pp. 64–84. Meacham, B. J., “Performance-Based Codes and Fire Safety Engineering Methods: Perspectives and Projects of the Society of Fire Protection Engineers,” Society of Fire Protection Engineers, Boston, ISBN 0-9516320-9-4; Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 545–553. Meacham, B. J., and Lucht, D. A., “Performance-Based Fire Safety Design in the United States: An Update from the Society of Fire Protection Engineers,” SFPE Bulletin, Fall 1995, pp. 6–9. Meacham, B. J., and Lucht, D. A., “Performance-Based Fire Safety Design in the United States: An Update From the Society of Fire Protection Engineers,” Society of Fire Protection Engineers, Boston, MA, Center for Fire Safety Studies, Worcester, MA, ISBN 0-9527398-3-6; Institution of Fire Engineers, University of Sunderland, Fire Research Station, CIB W14, Tyne and Wear Metropolitan Fire Brigade, Fire Safety by Design, Conference Proceedings, Volume 3, Research Papers, July 10–12, 1995, UK, 1995, pp. 9–14. Meacham, B. J., and Custer, R. L. P., “Performance-Based Fire Safety Engineering: An Introduction of Basic Concepts,” Journal of Fire Protection Engineering, Vol. 7, No. 3, 1995, pp. 35–54. Meeks, C. B., and Brannigan, V., “Performance Based Codes: Economic Efficiency and Distribution Equity,” University of Georgia, Athens, Maryland University, College Park, National Institute of Standards and Technology, Gaithersburg, MD, ISBN 0-9516320-9-4; Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 573–580. Mehaffey, J. R., “Performance-Based Design for Fire Resistance in Wood-Frame Buildings,” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, June 29–July 1, 1999, Edinburgh, UK, Interscience Communications Ltd., London, UK, 1999, pp. 293–304. Milke, J. A., “Performance-Based Design of Fire Resistant Assemblies,” Proceedings of the Society of Fire Protection Engineers (SFPE) Honors Lecture Series, Engineering Seminars: Fire Protection Design for High Challenge or Special Hazard Applications, May 20–22, 1996, Boston, MA, 1996, pp. 13–18. Milke, J. A., “Providing a Performance-Based Design Method for Smoke Management Systems in Atria and Covered Malls,” SFPE Bulletin, May/June 1992, pp. 6–8. Nakaya, I., “Our Activities Toward Performance Based Fire Regulation in Japan,” Nordic Fire Safety Engineering Symposium, Development and Verification of Tools for Performance Codes, August 30–September 1, 1993, Espoo, Finland, 1993, pp. 1–5. National Fire Protection Association, “Making of Codes and Standards,” National Fire Protection Association, Quincy, MA, Video, 1991. Neale, R. A., “When Code Equivalencies Don’t Work,” American Fire Journal, Vol. 48, No. 1, 1996, pp. 20–23. Nelson, H. E., “Performance-Based Smoke Movement Design,” Hughes Associates, Inc., Baltimore, MD, Video; Federal Fire Forum, Performance-Based Design Issues of Concern to the A/E Community, November 6, 1995, Gaithersburg, MD, 1995. Newman, D. G., Rhodes, N., and Locke, A., “Simulation Versus Code Methods for Predicting Airport Evacuation,” Proceedings of the 1st International Symposium, Human Behavior in Fire, August 31–September 2, 1998, Belfast, UK, Textflow Ltd., UK, 1998, pp. 519–528.
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Oleszkiewicz, I., “Transition to a Performance-Based NBC,” NBC/NFC News, No. 136, Fall 1993, pp. 2–3. Pauls, J., “Egress Time and Safety Performance Related to Requirements in Codes and Standards,” Hughes Associates, Inc., Columbia, MD, Building Officials and Code Administration International, Inc. (BOCA) and OBOA, Workshop Landout, June 1990, Ontario, Canada, 1990, pp. 1–10. Peacock, R. D., Reneke, P. A., Bukowski, R. W., and Babrauskas, V., “Defining Flashover for Fire Hazard Calculations,” Fire Safety Journal, Vol. 32, No. 4, 1999, pp. 331–345. Puchovsky, M., “Developing Performance-Based Documents One Step at a Time,” NFPA Journal, Vol. 90, No. 1, 1996, pp. 46–49. Puchovsky, M., “From Start to Finish Performance-Based Design,” NFPA Journal, Vol. 94, No. 1, 2000, pp. 76–80. Puchovsky, M., “Performance Based Design in the United States,” Proceedings of the International Conference on Fire Research and Engineering, September 10–15, 1995, Orlando, FL, SFPE, Boston, 1995, pp. 187–192. Puchovsky, M., “Supplementing NFPA’s Codes and Standards with Performance-Based Provisions,” National Fire Protection Association, Quincy, MA, ISBN 0-9516320-9-4; Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 945–949. Quiter, J., “How Today’s Fire Codes Impact Building Construction,” Consulting/Specifying Engineer, Vol. 9, No. 5, 1991, pp. 46–48, 50, 52. Ramachandran, G., “Probability-Based Building Design for Fire Safety. Part 1,” Fire Technology, Vol. 31, No. 3, 1995, pp. 265–275. Ramachandran, G., “Probability-Based Building Design for Fire Safety. Part 2,” Fire Technology, Vol. 31, No. 4, 1995, pp. 355–368. Ramachandran, G., “Probability-Based Fire Safety Code,” Journal of Fire Protection Engineering, Vol. 2, No. 3, 1990, pp. 75–91. Reiss, M. H., and Cappuccio, J. A., “Computer Fire Modeling: A Building Design Tool,” Consulting-Specifying Engineer, Vol. 23, No. 5, 1998, pp. 34–36. Richardson, J. K., “Moving Toward Performance-Based Codes,” NFPA Journal, Vol. 88, No. 3, 1994, pp. 70–72, 77–78. Richardson, J. K., “Performance Codes and the Fire Marshal,” National Research Council of Canada, Ottawa, Ontario, IRCORAL-88; National Fire Protection Association, Fire Marshal’s Forum, October 28, 1944 [sic], 1994, pp. 1–22. Richardson, J. K., “Practice of Fire Protection Engineering in a Performance-Based Regulatory Environment,” Selected Readings in Performance-Based Fire Safety Engineering, 1995, Boston, MA, Society of Fire Protection Engineers, Boston, 1995, pp. iii–iv. Richardson, J. K., Oleszkiewicz, I., and Yung, D., “Toward a Performance-Based Code in Canada,” Nordic Fire Safety Engineering Symposium, Development and Verification of Tools for Performance Codes, August 30–September 1, 1993, Espoo, Finland, 1993, pp. 1–5. Rosenbaum, E. R., “Using Performance Based Analysis to Assess Fire Hazard and Develop Governing Criteria for a Combustible Fuel Package in Facilities,” Proceedings of the Society of Fire Protection Engineers Engineering Seminars on Performance-Based Fire Safety Engineering, November 15–17, 1993, Phoenix, AZ, SFPE, Boston, 1993, pp. 57–61. Scherfig, S., “Development of a Performance Fire Code and a Design System for Fire Safety in Buildings,” Nordic Fire Safety Engineering Symposium, Development and Verification of Tools for Performance Codes, August 30–September 1, 1993, Espoo, Finland, 1993, pp. 1–10. Scholten, N. P. M., “Performance Based Building Regulations: Modelling of Works in Relation to Fire and Smoke Compartments and Means of Escape,” TNO Building Construction Research Delft, the Netherlands, TNO Building and Construction Research, Third CIB/W14 Workshop, Proceedings of the Fire Engi-
neering Workshop on Modelling, January 25–26, 1993, Delft, the Netherlands, 1993, pp. 232–234. Snell, J. E., “Status of Performance Fire Codes in the USA,” Nordic Fire Safety Engineering Symposium, Development and Verification of Tools for Performance Codes, August 30–September 1, 1993, Espoo, Finland, 1993, pp. 1–9. Sober, G., “Acceptance of Performance-Based Design by the Authority Having Jurisdiction” [Video]; Federal Fire Forum, Performance-Based Design Issues of Concern to the A/E Community, Nov. 6, 1995, Gaithersburg, MD, 1995. Strength, R. S., “Status Report Model Building Codes 1992, NEC-93 and IEC-89,” Fire Retardant Chemicals Association Fall Conference: Industry Speaks Out on Flame Retardancy: Coatings; Polymers and Compounding; Test Method Development; New Products, Technomic Publishing Co., Lancaster, PA, 1992, pp. 41–46. Sullivan, P. D., “Recent Applications of Computers in Performance Design of Buildings,” Robert W. Sullivan, Inc., Boston, MA, Society of Fire Protection Engineers and WPI Center for Firesafety Studies, Proceedings of the Technical Symposium on Computer Applications in Fire Protection Engineering, Final Program, June 20–21, 1996, Worcester, MA, 1996, pp. 87–92. Sullivan, P. D., World’s First Performance-Based Building Code “The New Zealand Experience” [Thesis], Worcester Polytechnic Institute, MA, December 14, 1993. Talbert, J. H., “Application of Performance-Based Techniques for the Design of Fire Safety in Buildings,” Proceedings of the International Conference on Fire Research and Engineering, September 10–15, 1995, Orlando, FL, SFPE, Boston, MA, 1995, pp. 475–480. Tanaka, T., “Concept and Framework of a Performance Based Fire Safety Design System for Buildings,” Journal of Applied Fire Science, Vol. 3, No. 4, 1993/1994, pp. 335–358. Tanaka, T., “Concept of a Performance Based Design Method for Building Fire Safety,” Building Research Institute, Ibaraki-Ken, Japan, NISTIR 4449, 1990; Eleventh Joint Panel Meeting of the U.S./Japan Government Cooperative Program on Natural Resources (UJNR) on Fire Research and Safety, October 19–24, 1989, Berkeley, CA, 1990, pp. 23–31. Tanaka, T., “Performance Based Design Method for Fire Safety of Buildings,” Building Research Institute, Ibaraki-ken, Japan, NISTIR 4449; Eleventh Joint Panel Meeting of the U.S./Japan Government Cooperative Program on Natural Resources (UJNR) on Fire Research and Safety, October 19–24, 1989, Berkeley, CA, 1990, pp. 269–291. Tanaka, T., “State of Art: Development of Performance-Based Fire Safety Design Methods of Buildings in Japan,” Building Research Institute, Ibaraki-ken, Japan, CIB W14/96/1 (J); MiniSymposium on Fire Safety Design of Buildings and Fire Safety Engineering, June 12, 1995, Tsukuba, Japan, 1995, pp. II/1–7. Taylor, P., Timms, G., and Johnson, P., “Performance Based Approach to Fire Safety Design of Cardboard Box Manufacturing Plant,” Proceedings of the Society of Fire Protection Engineers (SFPE) Honors Lecture Series, Engineering Seminars: Fire Protection Design for High Challenge or Special Hazard Applications, May 20–22, 1996, Boston, MA, 1996, pp. 49–54. Todd, N. W., and Ryan, J. D., “Improving Codes by Predicting Product Performance in Real Fires,” Fire Journal, Vol. 84, No. 2, 1990, pp. 64–68, 70–72, 93–94. VanRickley, C. W., “Survey of Code Officials on Performance-Based Codes and Risk-Based Assessment,” Codes Forum, 1996, pp. 42–43, 45–46. Watts, J. M., Jr., “Performance-Based Codes. Editorial,” Fire Technology, Vol. 30, No. 4, pp. 385–386. White, D. A., Beyler, C. L., and DiNenno, P. J., “Performanced-Based Engineering of Industrial Facilities,” Hughes Associates, Inc., Columbia, MD, Society of Fire Protection Engineers and Worcester Polytechnic Institute, Proceedings of Computer Applications in Fire Protection, June 28–29, 1993, Worcester, MA, 1993, pp. 51–55.
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Woolley, D., “Developments in the UK to Support Performance Based Codes,” Nordic Fire Safety Engineering Symposium, Development and Verification of Tools for Performance Codes, August 30–September 1, 1993, Espoo, Finland, 1993, pp. 1–12. Yamada, T., and Harada, K., “Progress and Overview of Fire Engineering Tools in Japan,” Proceedings of the 14th Joint Panel Meeting, U.S./Japan Government Cooperative Program on National Resources (UJNR), Fire Research and Safety, May 28–June 3, 1998, Tsukuba, Japan, 1998, pp. 44–51. Yung, D., Hadjisophocleous, G. V., and Yager, B., “Case Study: The Use of FIRECAM™ to Identify Cost-Effective Fire Safety Design Options for a Large 40-Storey Office Building,” Proceedings of the Pacific Rim Conference and 2nd International
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Conference on Performance-Based Codes and Fire Safety Design Methods, May 3–9, 1998, Maui, HI, International Code Council, Birmingham, AL, 1998, pp. 249–258. Code Council, Birmingham, AL, 1998, pp. 441–452. Yung, D., Hadjisophocleous, G. V., and Proulx, G., “Description of the Probabilistic and Deterministic Modelling used in FIRECAM™,” International Journal on Engineering Performancebased Fire Codes, Vol. 1, No. 1, 1999, pp. 18–26. Yung, D., “Development of a Tool to Support the Introduction of Performance-Based Codes in Canada,” National Research Council of Canada, Ottawa, Ontario, IRC-Oral-93; National Fire Protection Association, Fall Meeting, November 13–16, 1994, Toronto, Canada, 1994, pp. 1–25.
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Overview of Performance-Based Fire Protection Design Frederick W. Mowrer
E
ngineering design is the process of selecting and orienting basic design elements to serve functional performance objectives within the constraints imposed by cost, technology, and safety. Design elements may include materials, components, products, assemblies, systems, or subsystems, depending on the application. The suitability of a design element for a particular application is determined by analysis. Different analyses use different properties or attributes of design elements to measure expected performance. Design elements selected for use must demonstrate acceptable performance based on the different analyses. In this context, all engineering design is, by definition, performance-based. The concept of performance-based fire protection design is at least as old as the discipline of fire protection engineering. When the first sprinkler systems were developed in the mid1800s, they were designed to meet the performance objective of automatic fire suppression in buildings with the constraints that such systems be installed at reasonable cost using technology available at the time. As with many engineered systems, these early sprinkler systems were redesigned, largely through trial and error as well as adverse loss experience, to improve their efficiency as well as their reliability. Other fire safety systems have similar development histories, as do most engineered systems. Although the concept of performance-based fire protection design has been around for a long time, the term performancebased has taken on a more specific meaning within the fire safety community in recent years. The term performance-based has become widely used internationally to distinguish emerging scenario-based methods of quantitative fire hazard analysis and fire risk assessment from traditional “prescriptive” regulatory approaches to fire safety. Within a performance-based design framework, desired outcomes are normally expressed in terms of specific fire safety goals, objectives, and performance criteria to be achieved. Within the traditional prescriptive framework, the analysis and design of building fire safety occur largely within
the context of building code compliance, which does not explicitly demonstrate achievement of fire safety goals, objectives, or performance criteria. Over the past two decades, considerable progress has been made in the areas of performance-based fire protection analysis, design, and regulation. A number of guidance and regulatory documents have been published internationally that address the performance-based fire protection design process. Some of these documents include the following:
Frederick W. Mowrer is an associate professor in the Department of Fire Protection Engineering at the University of Maryland. At the time this chapter was prepared, Professor Mowrer was the President-elect of the Society of Fire Protection Engineers and the immediate past chair of the Technical Steering Committee of the SFPE.
Before considering the performance-based fire protection design process, it is useful to consider what distinguishes performancebased design from other design approaches. The SFPE Engineering Guide to Performance-Based Fire Protection Analysis
• Comprehensive Fireproof Building Design Methods, Volume 1, Regulations for Comprehensive Design for Fire Prevention, published by the Architectural Center of Japan in 19891 • Fire Engineering Design Guide, published by the Centre for Advanced Engineering at the University of Canterbury in Christchurch, New Zealand, in 19942 • Fire Engineering Guidelines, published by the Fire Code Reform Centre in Australia in 19963 • Fire Safety Engineering in Buildings, Part 1: Guide to the Application of Fire Safety Engineering Principles, Document DD240, published by BSI in the United Kingdom in 19974 • Fire Safety Engineering—Parts 1 through 8, ISO/TR 13387, published by the International Organization for Standardization in Geneva, Switzerland, in 19995–12 • SFPE Engineering Guide to Performance-Based Fire Protection Analysis and Design of Buildings, published jointly by the Society of Fire Protection Engineers and the National Fire Protection Association in the United States in 200013 These documents present similar processes for the performance-based design of building fire safety. This chapter takes advantage of the processes documented in these publications to present an overview of performance-based fire protection design.
WHAT IS PERFORMANCE-BASED DESIGN?
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and Design of Buildings (hereafter referred to as the SFPE PBD Guide) defines performance-based design as follows: An engineering approach to fire protection design based on (1) established fire safety goals and objectives; (2) deterministic and probabilistic analysis of fire scenarios; and (3) quantitative assessment of design alternatives against the fire safety goals and objectives using accepted engineering tools, methodologies, and performance criteria. [Emphasis added] In comparison with prescriptive design, performance-based fire protection design has the following distinguishing features: • Performance-based design is based on the specification of quantitative and physically meaningful performance criteria that can be used to evaluate the achievement of fire safety goals and objectives. • Performance-based design is based on analysis of the dynamics of anticipated fire scenarios. • Performance-based design is based on quantitative assessment of fire scenarios using accepted engineering tools and methodologies, which typically include some form of enclosure fire model. Ultimately, the goal of performance-based fire protection design is to demonstrate, through appropriate engineering analyses, that an acceptable level of fire safety will be achieved under a comprehensive set of anticipated or foreseeable conditions of use. The adequacy and reliability of performance-based design depend in large part on the adequacy of the performance criteria selected, the comprehensiveness of the fire scenarios anticipated, and the accuracy of the engineering tools and methodologies used for analysis.
THE PERFORMANCE-BASED FIRE PROTECTION DESIGN PROCESS The process of performance-based fire protection design can be considered in terms of a number of distinct steps. The SFPE PBD Guide outlines these steps in the flowchart illustrated in Figure 3.14.1.
Define Project Scope The first step in the performance-based design process is to define the scope of a project. The SFPE PBD Guide identifies the following issues associated with defining the scope of a project: • Constraints on the design and project schedule • The stakeholders associated with project • The proposed building construction and features desired by the owner or tenant • Occupant and building characteristics • Intended use and occupancy of the building • Applicable codes and regulations The various stakeholders must understand and agree upon these issues at the outset to ensure that a performance-based de-
sign (PBD) meets their needs and interests. A stakeholder is an individual or other representative who has an interest in the successful completion of a project for financial, safety, or other reasons. Possible stakeholders include, but are not necessarily limited to, the following: • Building owners, managers, and operations and maintenance personnel • Tenants and other occupants • Design team • Construction team—construction managers, general contractors, subcontractors • Authorities having jurisdiction (AHJ)—fire, building, insurance • Accreditation agencies • Emergency responders Because the scope of many projects is limited, it is essential that the project boundaries be clearly defined and documented during this step so that all stakeholders clearly understand what will, and what will not, be addressed by the PBD. A clear definition of project scope is particularly important for the designer undertaking a PBD to avoid the potential for future misunderstandings and liabilities that might arise during the construction and use of a building.
Identify Fire Safety Goals Once the project scope has been defined, the next step in the PBD process is for the various stakeholders to identify and for the fire protection engineer to document the fire safety goals of the design. These are the general goals to be achieved by the performance-based design. Fire safety goals may include levels of protection for people and property, or they may provide for continuity of operations, historical preservation, or environmental protection, among others. Fire protection generally has the following four interrelated fundamental fire safety goals: 1. Provide life safety for the public, for employees and other occupants, and for fire fighters; minimize fire-related injuries and prevent undue loss of life. 2. Protect property, minimizing damage to property from fire and fire protection measures (e.g., protect building, contents, and historical features from fire and exposure to and from adjacent buildings.) 3. Provide for continuity of operations (i.e., protect the organization’s ongoing mission, production, or operating capability), minimizing undue loss of operations and business-related revenue due to fire-related damage. 4. Limit the environmental impact of fire and fire protection measures. Not all of the above goals are relevant to all projects; the relevance depends on the scope of the project. One purpose of identifying fire safety goals is to help focus stakeholders on the overall fire protection concepts being developed so that all stakeholders are clear on what goals are and, of equal importance, are not being addressed by a given design. Another purpose is simply to document the fire safety goals to be achieved by the design. Although fire safety goals serve this important purpose,
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Overview of Performance-Based Fire Protection Design
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Define project scope
Identify goals Fire protection engineering design report
Define stakeholder and design objectives
Develop performance criteria
Develop design fire scenarios
Develop trial designs
Evaluate trial designs
Modify design or objectives
No
Selected design meets performance criteria? Yes Select final design
Prepare design documentation
Performancebased design report
Plans and specifications, operations and maintenance manuals
FIGURE 3.14.1 Steps in the Performance-Based Fire Protection Design Process. (Source: SFPE Engineering Guide to Performance-Based Fire Protection, 2000, Figure 3-2)
they do not provide sufficient detail to evaluate whether specific fire safety objectives will be achieved by a proposed design. This determination requires a more detailed description of objectives and performance criteria.
Define Stakeholder and Design Objectives and Develop Performance Criteria The evaluation of fire safety objectives generally requires the specific stakeholder and design objectives to be defined and detailed performance criteria to be developed. Performance crite-
ria are quantitative measures, usually in the form of threshold damage or injury levels, that reflect the intent of the design objectives. In general, some criteria address life safety while other criteria address damage thresholds for property. Life safety criteria generally address tenability and survivability of fire-induced atmospheres in terms of thermal effects, toxicity, and visibility through smoke. Property criteria may include thermal damage thresholds, structural integrity, smoke damage, and fire spread, among others. Some examples of fire safety goals and associated stakeholder objectives, design objectives, and performance criteria are provided in Table 3.14.1 for each of the fire safety goals described above.
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TABLE 3.14.1
Examples of Fire Protection Goals, Stakeholder Objectives, Design Objectives, and Performance Criteria
Fire Protection Goals
Stakeholder Objectives
Design Objectives
Performance Criteria
Minimize fire-related injuries and prevent undue loss of life.
No loss of life outside of the room or compartment of fire origin
Prevent flashover in the room of fire origin
COHb level not to exceed 12% Visibility greater than 7 meters (23 ft)
Minimize fire-related damage to the building, its contents, and its historical features and attributes
No significant thermal damage outside of the room or compartment of fire origin
Minimize the likelihood of fire spread beyond the room of fire origin
Upper layer temperature no greater than 200°C (390°F)
Minimize undue loss of operations and businessrelated revenue due to firerelated damage
No process downtime exceeding 8 hours
Limit the smoke exposure to less than would result in unacceptable damage to the target
HCl no greater than 5 ppm Particulate no greater than 0.5 g/m3
Limit environmental impacts of fire and fire protection measures
No groundwater contamination by fire suppression water runoff
Provide a suitable means for capturing fire protection water runoff
Impoundment capacity at least 1.20 times the design discharge
Source: SFPE Engineering Guide to Performance-Based Fire Protection, 2000, Table B-3.
Develop Design Fire Scenarios After the performance criteria have been established, the next step in the performance-based design process is to develop design fire scenarios. In this context, a fire scenario is a set of conditions that defines the development of a fire and the spread of combustion products through a building. The fire, building, and occupant characteristics at the time of a fire need to be considered in order to define different fire scenarios because these characteristics all interact with each other and influence a fire scenario. The fire characteristics describe the history of anticipated fire development and generally include consideration of the following: • • • • •
Ignition sources and materials first ignited Incipient fire development Flame spread and fire growth Flashover and fully developed fire conditions Fire burnout, decay, and extinction
Fire development in buildings is strongly dependent on enclosure and ventilation effects as well as on the installed fire protection features, so the building characteristics must be considered as part of the fire scenario development. Building Characteristics. The building characteristics describe the physical features, contents, and ambient environment of a building. The building characteristics of interest for fire safety include the following: • • • • • • •
Architectural features, including space layout Structural features Building services and processes Operational characteristics Fire protection systems Emergency response characteristics Environmental factors
These building characteristics affect the growth and spread of fire as well as the movement of combustion products, so they need to be considered in the identification of possible fire scenarios. With respect to fire development, the primary building features influencing a fire scenario include the following: • Floor area and volume of the fire enclosure • Flammability properties of room lining materials, furnishings, and other contents • Number, type, and location of natural ventilation pathways • Type and operating characteristics of mechanical HVAC systems • Type and operating characteristics of automatic fire detection and suppression systems • Thermophysical properties of enclosure boundaries and the fire endurance characteristics of enclosure boundaries and structural elements Occupant Characteristics. Occupant activities can also influence fire development; therefore they need to be considered in the development of fire scenarios as well. Occupants can influence fire development in a number of ways, including the following: • Occupants can accidentally or intentionally contribute to the ignition of fires. • Occupants can open or close doors and windows to influence the potential for fire and smoke spread. • Occupants can detect and suppress fires, particularly during the incipient stage of development. Occupant characteristics also influence how occupants are affected by a fire and how they respond to fire-induced conditions. Some of the important characteristics influencing human behavior in fire include the following: • Number and distribution of occupants • Alertness, physical and mental capabilities
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• Physical and physiological condition • Role, commitment, familiarity, and social affiliation Some of these occupant characteristics relate to the decision-making capabilities of occupants, some to their mobility, and some to their susceptibility to smoke. Design Fire Curves. One of the most important factors to recognize and consider in the development and evaluation of fire scenarios is the transient nature of building fires. Because fire is a transient process, it affects a building and its occupants and operations in different ways at different stages. Differences of minutes or even seconds can mean the difference between the success or failure of a fire protection strategy. Consequently, in a performance-based design analysis, time is always one of the key design parameters. With respect to the development of design fire scenarios, this time dependency is normally addressed by the development of one or more design fire curves that describe the anticipated heat and smoke release rate histories of the design fire scenarios. Design fire curves typically have some or all the stages illustrated in Figure 3.14.2. The initiating event is ignition. Following ignition, there may or may not be an incipient period of little or no growth, depending largely on the type and intensity of the ignition source and on the nature of the first fuel ignited. For example, a smoldering fire ignited by a cigarette in upholstered furniture may exhibit a relatively long incipient period, while a flaming fire involving the same upholstered furniture may not. Following ignition and the incipient period, if it occurs, most fires of any consequence undergo a period of growth to a maximum size. To a large extent, the rate of fire growth and the peak heat release rate distinguish relatively hazardous fire scenarios from less hazardous scenarios. Once the fire reaches its peak heat release rate, it may continue to burn at approximately this rate for some period of time, depending on how much fuel is available to burn. This period of relatively steady burning is frequently called the fully developed stage. The final period, typically called the decay stage, occurs when the available fuel starts to become depleted. Some fires are already starting to burn out by the time they reach their peak heat release rate; these fires tend to exhibit heat release rates with distinct peaks, rather than plateaus. The area under the design fire curve represents the total energy released by the fire (see Figure 3.14.2).
Growth
Heat release rate (kW)
Incipient
Fully developed
Total energy released Q (kJ)
Decay
Design fire curve
Ignition
FIGURE 3.14.2
Time
Stages of Design Fire Curves
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In many respects, construction and quantification of design fire curves make up the most difficult, as well as the most important, aspect of the performance-based design process. Design fire curves are important because they govern the rate of hazard development as well as the ultimate magnitude of hazard development. Selection of a design fire curve that does not accurately portray the expected fire development will result in predictions of fire-induced conditions that are either too severe or too mild. This can result in designs that are either inadequate or uneconomical. Ideally, actual fire test data representative of the design fire scenario would be available and would be used to develop design fire curves, but in most cases such specific data are not available. In these cases, engineering judgment is needed to characterize and select appropriate design fire curves based on the types, quantities, and configuration of available fuels, including initial and secondary fuels. It is important for all stakeholders to understand the bases for the selection of design fire curves and agree to the selection. To the extent that this selection may impose a need for administrative controls on the potential fuels within a building, these administrative controls need to be documented and enforced.
Develop and Evaluate Trial Designs The steps of developing and evaluating trial designs are intended to consider how the various fire protection features (fire safety subsystems) will interact to provide the desired level of fire safety in a building. The fire safety subsystems considered in the SFPE PBD Guide include the following: • • • • • •
Fire initiation and development Spread, control, and management of smoke Fire detection and notification Fire suppression Occupant behavior and egress Passive fire protection
These categories for fire safety subsystems are not unique; they are similar to the categories used to describe fire safety subsystems in a number of the international performance-based fire protection design guides listed at the beginning of this chapter. Fire Initiation and Development. The fire initiation and development subsystem addresses the probability that ignition will occur as well as the rate of fire development and smoke release if ignition does occur. This subsystem is related directly to the design fire scenario and the design fire curves addressed in the previous section. Treating fire initiation and development as one of the fire safety subsystems helps to emphasize that the selection and placement of interior finishes and contents are an important part of the overall fire safety of a building. This aspect of fire protection design, controlling the fire source through product selection, is too often overlooked in favor of other fire protection strategies, such as fire detection and suppression, rather than being considered in conjunction with these other strategies. Spread, Control, and Management of Smoke. The smoke management subsystem addresses the hazards resulting from the production and movement of smoke and the methods that can be
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used to control these hazards. These methods generally include the reduction of smoke generation through the control of materials that produce large quantities of smoke or by suppression, the extraction of smoke by natural or mechanical ventilation, and the containment of smoke by construction, often in combination with mechanical pressurization. Fire Detection and Notification. The fire detection and notification subsystem addresses both the means used to detect a fire and the means used to notify building occupants and emergency responders of the presence and location of a fire. The fire detection element addresses the response of humans and automatic detection devices to the various fire signatures released during a fire. Fire Suppression. The fire suppression subsystem addresses the means used to extinguish or control a fire. This includes automatic suppression systems, such as automatic sprinkler systems, as well as manual suppression systems, including fire department suppression operations. The impact of suppression systems and activities on fire development would be considered part of this subsystem. Occupant Behavior and Egress. The occupant behavior and egress subsystem addresses the means used to protect occupants from the harmful effects of fire. In general, this means the design of an egress system that permits occupants to evacuate a building before untenable conditions develop. Passive Fire Protection. The passive fire protection subsystem addresses the structural stability of a building as well as the fire resistance of enclosure boundaries to prevent the spread of fire between rooms of a building.
to evaluate trial designs. The PBD report is intended to thoroughly document the performance-based design and its bases; the O&M manual is intended to help ensure that all the components of a PBD are in place and operating properly. Of central importance is documentation of the changes in use, occupancy, or operation of a building that should trigger a reevaluation of the building’s fire safety.
TIME AS A PERFORMANCE-BASED DESIGN PARAMETER As was noted previously, time is a key parameter in performance-based fire protection design. Most meaningful fire parameters are functions of time. For example, the physical hazards of fires are measured in terms such as fire growth rates, flame spread rates, heat release rates, smoke release rates, heat fluxes, and burning duration—all functions of time. Similarly, the response of buildings, occupants, and fire protection systems to different fire scenarios can be considered in terms such as fire endurance periods, evacuation times, and fire detection and suppression response times. Consequently, time is an appropriate parameter to use for the quantitative evaluation of different fire scenarios and fire protection strategies. There are two competing time scales that need to be considered, one associated with hazard development and the other with hazard mitigation. In this context, a successful fire protection strategy is one in which the time to the onset of unacceptable hazardous conditions is longer than the time to successful hazard mitigation for all relevant fire scenarios. This concept is illustrated in Figure 3.14.3. The hazard development time scale shown in Figure 3.14.3 denotes two relevant times: t (Qg crit) and t (Qcrit). The first of these, t (Qg crit), represents the time when a critical heat release
Develop Documentation One of the most important aspects of performance-based fire protection design is documentation. Documentation is needed for the decisions made and analyses developed during the design process as well as for the duties and responsibilities of the stakeholders to ensure the ongoing conformance of the building’s operation with the performance-based design basis. The SFPE PBD Guide identifies the following types of documentation:
Heat release rate (kW) Time–release rate curve Fire scenario without automatic suppression •
Q crit
Fire scenario with automatic suppression
•
• • • •
Plans and specifications Fire protection engineering design brief Performance-based design (PBD) report Operations and maintenance (O&M) manual
Plans and specifications are basically the same in performance-based design as in other design methods; they are intended to communicate important design information, particularly geometric data and information regarding acceptable materials and methods of construction, to the owner’s representatives, to contractors, to AHJs, and to other stakeholders. The other three types of documentation are somewhat specific to performance-based design. The design brief is intended to summarize the performance criteria and analysis methods to be used
Q crit •
Qsup •
Q det •
t (Q crit )
Hazard development
Hazard mitigation
t det
t sup
•
t (Q crit )
tFR
Time scales
FIGURE 3.14.3 Time Scales Associated with Fire Hazard Development and Mitigation
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Overview of Performance-Based Fire Protection Design
rate is achieved. For example, this might be the heat release rate needed to cause flashover of an enclosure. The second relevant time, t (Qcrit), represents the time when a critical total quantity of heat or smoke has been released. For example, this might be when sufficient carbon monoxide has been released to develop an untenable atmosphere. The time to critical hazard development will be based on the fire scenario and the design fire curve. The hazard mitigation time scale shown in Figure 3.14.3 denotes three relevant times: t det, t sup, and t FR. The detection time, t det, denotes the time when a fire will be detected. The detection time will depend on the fire scenario, the design fire curve, and the types and locations of fire detection devices. The suppression time, t sup, denotes the time when fire suppression is initiated. The suppression time will be equal to the detection time plus the time needed to initiate suppression once the fire is detected. For a wet-pipe sprinkler system, the suppression lag should be nil, and the suppression time will be the same as the detection time. For a dry-type sprinkler system, the suppression lag may be as much as 60 seconds for systems conforming to the requirements in NFPA 13, Standard for the Installation of Sprinkler Systems, 1999 edition. For manual suppression, the suppression lag may be tens of minutes because the suppression lag includes the times needed for alarm verification and for fire department notification, response, and setup at the fire scene. The fire resistance time, t FR, is the fire endurance period for the enclosure boundaries under the fire exposure conditions. For successful fire confinement, the fire resistance time must be longer than the duration of fully involved fire conditions. To make practical use of this concept, the stakeholders need to agree on the performance criteria to be used and the design fire scenarios to be considered in order to evaluate when unacceptable hazard conditions are expected to develop. All unwanted fires cause some damage and present some hazard. To permit quantitative assessment of fire mitigation strategies, a threshold level of tolerable or acceptable damage or hazard must be established. The time to the onset of unaccept-
able damage or hazard for a particular fire scenario depends on the following two factors: 1. The susceptibility to damage of the target being evaluated 2. The rate of development of the hazardous environment at the location of the target If these two factors can be assessed quantitatively, they can yield either a time-dependent scale of damage or a critical time to damage onset. Damage to some targets may be related primarily to the total quantity of a fire signature, such as heat or smoke, released during a fire. This damage is represented as the area under the time–release rate curve (see Figure 3.14.3). Other targets may be damaged once a critical release rate is reached. The relevant time scales to be compared depend on the type of fire safety analyses being performed. For life safety, the available safe egress time (ASET) must be greater than the required safe egress time (RSET). The available safe egress time is the time from ignition until the specified tenability criteria are exceeded at the location of interest. The required safe egress time is the time from ignition until the building or location of interest has been evacuated. Normally, a safety factor is added to the required egress time to provide for a margin of error. This concept is illustrated in Figure 3.14.4, which compares available safe egress time (ASET) and required safe egress time. Note that the required safe egress time includes a number of intermediate periods, including the time from ignition to detection, the time from detection to alarm notification, the time from alarm notification to recognition that an emergency exists, the time from recognition until movement begins, and, finally, the travel time for the exposed population to exit to a safe location. Each of these time periods needs to be evaluated through appropriate engineering analyses for each design fire scenario. Time lines similar to the one shown in Figure 3.14.4 can be constructed to evaluate the performance of structural elements, fire barriers, and other targets that may be of interest for a particular application.
ASET
∆t esc Escape time
∆t evac Evacuation time
∆t pre ∆ ta
∆t trav Travel time
Pre-movement time
∆t del Recognition time
Ignition
Response time
Detection Alarm time
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Evacuation Tenability complete limit
FIGURE 3.14.4 Example Time Line for Evaluation of Available versus Required Safe Egress Times (Source: Fire Safety Engineering in Buildings, Part 1: Guide to the Application of Fire Safety Engineering Principles, Document DD20, BSI, 1997, Figure 2)
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DETERMINISTIC HAZARD VERSUS PROBABILISTIC RISK ASSESSMENT Performance-based design is predicated on the specification of design fire scenarios and the evaluation of design alternatives. Two general approaches are available for this process: deterministic and probabilistic. Deterministic analyses consider only the consequences of specified fire scenarios, while probabilistic analyses consider the likelihood as well as the consequences of different fire scenarios. For example, a deterministic analysis could be used to assess the expected outcomes for a scenario with and without a properly operating sprinkler system but not the likelihood of each alternative. In a deterministic analysis, a given set of input conditions always results in the same output predictions. Most fire dynamics and enclosure fire modeling calculations are deterministic. For most designs based on deterministic analysis, more than one fire scenario will be considered, even though the likelihood of the different scenarios is not explicitly addressed. For example, the performance-based option in the 2000 edition of the NFPA 101®, Life Safety Code®, specifies eight required design fire scenarios without consideration of the likelihood of any of the specified scenarios. In a probabilistic analysis, frequencies of occurrence are associated with design fire scenarios to yield the expected losses associated with each scenario. In this way, appropriate weights can be associated with different scenarios and different system reliabilities. A number of risk assessment tools can be used to aid the probabilistic analysis. Because time is a key parameter in fire scenarios, the event tree is a particularly useful tool for evaluating different possible outcomes at each stage of a fire scenario. The example fire event tree shown in Figure 3.14.5 illustrates the stages in fire development and typ-
ical factors that contribute to the probabilities at each stage of development. The event tree shown in Figure 3.14.5 illustrates the concept of “defense in depth,” which is widely used for building fire safety, particularly in the nuclear power industry. The defensein-depth concept is based on the premise that the fire safety of a building should not rely exclusively on a single fire protection subsystem but should be based on a combination of subsystems in case one of the subsystems fails. The defense-in-depth concept has been used historically in building fire safety regulations, for example, through requirements for both automatic suppression and fire-resistive construction. With probabilistic assessment the costs and benefits associated with defense-in-depth applications can be appraised and optimized. Analysis of the dynamics of different fire scenarios is not likely to differ significantly between deterministic and probabilistic approaches, but expression of performance objectives and criteria is likely to differ. For example, in a deterministic analysis the design objective may be to prevent flashover, while in a probabilistic analysis the design objective may be to demonstrate that the likelihood of flashover will not exceed 10–6, or some other very small likelihood, per year. Conceptually, the risk-based probabilistic approach is more satisfying, but statistics are not always available to justify the probabilities needed for its application.
SUMMARY The concept of performance-based fire protection design is not new. Fire protection engineers have been designing systems and subsystems to meet fire protection performance objectives and criteria within the constraints imposed by cost, technology,
Fire confined to:
Fire ignites
First item
Area of origin
Room of origin
Floor of origin
Building of origin
Block of origin
P (fi) P (ig)
P (bl)
Very small Small Medium Large Very large Major
1–P (bl)
Very low
Conflagration
P (ro) 1–P (ao)
P (fo) 1–P (ro)
P (bu) 1–P (fo)
Expected event outcome
Very high High Med.–high Medium Med.–low Low
P (ao) 1–P (fi)
Desired event frequency
1–P (bu) Typical contributing factors at each stage: Control of energy sources / fuels Flammability of fuels / early detection Early detection / automatic suppression Automatic suppression / fire resistance Fire resistance / fire department operations Building construction / fire department operations P = probability Fire department operations
FIGURE 3.14.5
Example Fire Event Tree
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and safety for as long as such systems and subsystems have existed. In recent years, however, the term performance-based fire protection has taken on the more specific meaning associated with the design process outlined in this chapter. This process entails the quantitative assessment of different fire scenarios using appropriate computational methods and tools to determine whether specified performance objectives and criteria will be met by a proposed design. The application of performance-based fire protection design demands a higher level of knowledge about building fire dynamics and fire protection system operating characteristics on the part of stakeholders than does traditional prescriptive design. Although this increased demand can impose additional costs on the design and review processes, it will also produce tangible and intangible benefits. One of these benefits is a better understanding of the expected consequences of fires in a building; another benefit, in many cases, will be reduced costs for fire protection. Whether the benefits of performance-based fire protection design will outweigh the costs depends on the particular application. In closing this overview of performance-based fire protection design, it is important to emphasize that building fires are complex events, involving the interactions of the fire with the building and the people within the building. The range of potential interactions among the fire, the building, and the people gives rise to a large number of possible fire scenarios. It is not generally practical to evaluate every possible fire scenario, but it is important that the most significant scenarios, from either a hazard or a risk standpoint, are identified and evaluated.
BIBLIOGRAPHY References Cited 1. Comprehensive Fireproof Building Design Methods, Volume 1, Regulations for Comprehensive Design for Fire Prevention, Architectural Center of Japan, Tokyo, Japan, 1989. 2. Fire Engineering Design Guide, Centre for Advanced Engineering at the University of Canterbury, Christchurch, New Zealand, 1994. 3. Fire Engineering Guidelines, Fire Code Reform Centre, Melbourne, Australia, 1996. 4. Fire Safety Engineering in Buildings, Part 1: Guide to the Application of Fire Safety Engineering Principles, Document DD240, BSI, London, UK, 1997. 5. Fire Safety Engineering—Part 1: Application of Fire Performance Concepts to Design Objectives, ISO/TR 13387-1:1999, International Organization for Standardization, Geneva, Switzerland, 1999. 6. Fire Safety Engineering—Part 2: Design Fire Scenarios and Design Fires, ISO/TR 13387-2:1999, International Organization for Standardization, Geneva, Switzerland, 1999.
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7. Fire Safety Engineering—Part 3: Assessment and Verification of Mathematical Fire Models, ISO/TR 13387-3:1999, International Organization for Standardization, Geneva, Switzerland, 1999. 8. Fire Safety Engineering—Part 4: Initiation and Development of Fire and Generation of Fire Effluents, ISO/TR 13387-4:1999, International Organization for Standardization, Geneva, Switzerland, 1999. 9. Fire Safety Engineering—Part 5: Movement of Fire Effluents, ISO/TR 13387-5:1999, International Organization for Standardization, Geneva, Switzerland, 1999. 10. Fire Safety Engineering—Part 6: Structural Response and Fire Spread Beyond the Enclosure of Origin, ISO/TR 13387-6:1999, International Organization for Standardization, 1999. 11. Fire Safety Engineering—Part 7: Detection, Activation and Suppression, ISO/TR 13387-7:1999, International Organization for Standardization, Geneva, Switzerland, Geneva, Switzerland, 1999. 12. Fire Safety Engineering—Part 8: Life Safety—Occupant Behaviour, Location and Condition, ISO/TR 13387-8:1999, International Organization for Standardization, Geneva, Switzerland, 1999. 13. SFPE Engineering Guide to Performance-Based Fire Protection Analysis and Design of Buildings, Society of Fire Protection Engineers and National Fire Protection Association, 2000.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on the performance-based fire protection design. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 13, Standard for the Installation of Sprinkler Systems, 1999 edition. NFPA 101®, Life Safety Code®, 2000 edition.
Additional Readings Appleton, R. G., “Fire Code Reform Program of Australia,” Proceedings of the 3rd International Symposium, Applications of the Concept in Buildings, Tel Aviv, Israel, December 9–12, 1997, National Building Research Institute, 1996, Vol. 2. Beyler, C. L., “Fire Safety Challenges in the 21st Century,” Journal of Fire Protection Engineering, Vol. 11, No. 1, 2001, pp. 4–15. Budkley, G., Bradborn, W., Edwards, J., Marchant, R., Terry, P., and Wise, S., “Fire Brigade Intervention Model,” Proceedings of the 6th International Symposium, International Association for Fire Safety Science (IAFSS), Poitiers, France, July 5–9, 1999, M. Curtat (Ed.), Society of Fire Protection Engineers, Boston, MA, 2000, pp. 183–194. Gemeny, D., and Reiss, M., “Up to Snuff,” Consulting-Specifying Engineer, Vol. 29, No. 5, 2001, pp. 26–28. Sims, J., “Occupant Response,” Fire Safety Engineering, Vol. 8, No. 1, 2001, pp. 14–18. Yang, K. H., and Wang, S. H., “Performance-Based Design and Analysis of Smoke Management System for Large Open Space Buildings,” Proceedings of the FORUM 2000 Symposium, Fire Research Development and Application in the 21st Century, Taipei, Taiwan, October 23–24, 2000, organized by Architectural and Building Research Institute (ABRI), MOI, and FORUM for International Cooperation in Fire Research, 2000, pp. 1–10.
CHAPTER 15
SECTION 3
Formats for Fire Hazard Inspecting, Surveying, and Mapping Revised by
Thomas R. Wood
T
he reasons for inspecting a property are (1) to evaluate the danger to life from fire and associated hazards, (2) to evaluate and determine ways to minimize fire danger to buildings and contents, (3) to prepare prefire plans to familiarize responding emergency personnel with the existing fire protection and fire-fighting challenges associated with the property, and (4) to make recommendations to correct deficiencies or unsafe conditions. Inspections are made by fire protection engineers, fire and building officials, insurance representatives, and others similarly qualified. To properly evaluate the existing or needed protection for a property or specific hazard, an inspection or survey of the premises must be made. Three essential results of this evaluation should be: 1. A precise and complete narrative report describing the fire protection features and fire hazards of the property 2. A plan indicating the physical characteristics and layout of the premises 3. Recommendations for improvement if necessary Functions performed during an inspection or survey and the compilation of the narrative report are discussed in detail in the NFPA Inspection Manual.1 This chapter provides (1) a checklist of the important features to observe when inspecting or surveying a property; (2) guidelines for drawing (mapping) a site or building plan; (3) a chart of standard symbols used on architectural, engineering, and shop drawings and fire risk and loss analysis diagrams; (4) prefire planning symbols; and (5) a legend of standard abbreviations. All are key items that contribute to or are part of the narrative report.
INSPECTION OR SURVEYING There are many different routes to choose from in conducting an inspection or survey. A particular route is selected according to Thomas R. Wood is the deputy fire chief of Boca Raton Fire Rescue Services Department, Boca Raton, Florida, and chair of NFPA’s Technical Committee on Fire Safety Symbols.
the layout of the property, personal preference of the inspector, and convenience. It is important for the inspector to pass through the building and surrounding site systematically, without leaving any space uncovered. The following checklist provides a general outline of key items that should be addressed in the written report. By formulating similar checklists, the inspector will be assured of being prepared for the survey and of having all the necessary information to prepare a detailed sketch afterwards. Using such checklists to make rough, hand-drawn sketches of every individual section, floor, building, or site reduces the difficulty in preparing a finished plan. Checklist I. Property Identification A. Name and address B. Building identification C. Date of construction D. Date of report E. Name of inspector II. Property Use A. General property use(s) (e.g., educational, mercantile, industrial, warehouse) B. Specific uses; state each principal use and its location; for storage areas, identify the product(s)2 stored C. Names of tenants in a building or site of multiple occupancy, including their location and amount of space occupied III. Site Information A. Fire department access B. Streets, roadways, parking, and traffic C. Natural barriers D. Bodies of water E. Fences F. Exposures: type and separation distances 1. Other buildings or structures 2. Outside storage or processes 3. Natural exposures (e.g., forest, grass, brush) 4. Railways, highways, and runways IV. Construction A. Dimensions
3–207
3–208 SECTION 3 ■ Information and Analysis for Fire Protection
1. Area 2. Height and number of stories 3. Ceiling heights B. Classification of building construction—Types I, II, III, IV, and V. (See NFPA 220, Standard on Types of Building Construction, 1999 edition.) For mixed construction, a table may be shown to report the location of each type. C. Compartmentation 1. Locations and ratings of fire areas, fire walls, and fire partitions 2. Locations and ratings of vertical openings (e.g., atria, stairways, elevators, shafts, chutes) 3. Protection of openings (e.g., fire doors, fire windows, fire dampers, firestopping) 4. Concealed spaces and voids D. Building exterior 1. Doors 2. Windows 3. Loading docks V. Life Safety A. Exit facilities 1. Number and arrangement 2. Occupant load capacity 3. Door hardware, special locking arrangements, and security B. Exit marking, illumination, and emergency lighting C. Interior finish 1. Furnishings 2. Decorations D. Evacuation plans and drills VI. Water Supply and Distribution A. General description including adequacy, deficiencies, and reliability 1. Fire flow requirements versus existing conditions, as determined by tests 2. Storage requirements versus existing conditions B. Storage tanks—gravity, suction, pressure 1. Capacity 2. Construction 3. Location and dimensions 4. Pipe arrangement to yard mains or fire pump(s) 5. Percent of capacity for fire protection C. Public and private water distribution systems 1. Type of system—gravity, direct pumping, or a combination of both 2. Size of water mains and arrangement in relation to the property 3. Type of pipe (e.g., cement lined, cast iron, etc.) 4. Connection arrangement to all supply sources available D. Other water storage methods (e.g., rivers, ponds, streams, harbors, wells) E. Hydrants 1. Locations of public and private hydrants 2. Types—dry barrel or wet barrel
F. Location and types of check valves and water meters G. Fire pumps 1. Location of pump and control valves 2. Rated capacity [L/min, kPa (gpm, psi)] 3. Types—split case, horizontal end suction, in-line, or vertical shaft turbine 4. Name of manufacturer 5. Type of motor drive—diesel, electric, gas, gasoline, or steam 6. Suction pressure, head, or lift [m (ft)] 7. Starting mechanism—automatic, manual, or both H. Inspections, maintenance, and tests VII. Extinguishing Systems and Devices A. Automatic sprinkler systems 1. Types—wet pipe, wet pipe with antifreeze, dry pipe, deluge, preaction 2. Area covered by type 3. Coverage, occupancy classification, and spacing of sprinklers 4. Riser location and size 5. Temperature rating of sprinklers 6. Control valves for water supplying sprinklers— location, size, type, and status if normally shut 7. Fire department connections—location, size, and area covered 8. Inspection, maintenance, and tests B. Standpipe and fire hose systems 1. Classification—Classes, I, II, or III 2. Types—wet, dry 3. Outside systems 4. Inspections, maintenance, and tests C. Special hazard systems 1. Types (e.g., carbon dioxide, foam, dry chemical, wet chemical, clean agent) 2. Hazard protected 3. Location and capacity of storage containers 4. Inspection, maintenance, and tests D. Portable extinguishers 1. Types of coverage 2. Inspections and maintenance VIII. Fire Alarm and Detection Systems A. Location and manufacturer of main control panel B. Monitoring and fire department notification C. Audible and visual device types (e.g., bells, horns, speakers, strobes, etc.) D. Products of combustion detection 1. Heat detectors (e.g., rate of rise, fixed temperature, rate compensation, pneumatic line type) 2. Smoke detectors (e.g., photoelectric, ionization, air sampling) 3. Gas detectors 4. Flame detectors (e.g., ultraviolet, infrared) E. Water-flow detection on sprinkler risers F. Trouble and supervisory indications G. Power supplies H. Inspection, maintenance, and tests
CHAPTER 15
■
Formats for Fire Hazard Inspecting, Surveying, and Mapping
IX. Electrical Systems A. Condition of conduit, raceways, cables, conductors, and cords B. Clear space around switchboards and panelboards C. Grounding D. Overcurrent protection E. Ground-fault circuit-interrupters F. Motors G. Hazardous (classified) locations H. Transformers—capacity, protection, liquids, and cutoffs I. Lightning protection X. Heating, Ventilation, and Air-Conditioning (HVAC) Systems A. Location of equipment B. Smoke control systems C. Inspection, maintenance, and tests XI. Fire Prevention A. Common hazards 1. Heat, light, power, and air-conditioning 2. Housekeeping, brush, and grass 3. Ordinary combustibles 4. Electrical appliances 5. Smoking B. Building inspection program 1. Frequency 2. Scope 3. Records C. Employee fire safety training 1. Adequacy and frequency of training 2. Reference materials 3. Records D. Fire brigade program 1. Type of brigade 2. Training 3. Special equipment provided 4. Records XII. Special Hazards and Equipment A. Flammable liquids B. Flammable gases C. Chemicals and hazardous materials D. Tanks and cylinders—location, size, contents, and construction E. Finishing processes F. Industrial processes G. Welding and cutting H. Cooking I. Shops J. Materials handling K. Waste removal—incinerators, chutes, dumpsters, compactors, recycling L. Tunnels M. Electronic equipment N. Dust collectors O. Boilers and furnaces P. Water-cooling towers Q. Chimneys—location, construction, and height R. Silos
3–209
S. Cranes T. Conveyers XIII. Construction, Demolition, and Modifications A. Fire protection—water supply, fire department access B. Fire prevention—control of debris and combustibles, welding and cutting, roofing operations, fire watches, and storage and handling of hazardous materials C. Life safety, temporary or alternative means of egress
MAPPING Once the necessary information has been collected, a site plan can be drawn readily. A practical approach is to split the preparation into three parts: 1. Building sketch 2. Addition of fire protection equipment 3. Detailing occupancy and specific processes or hazards The initial step is to outline the shape of the building, using an appropriate architect/engineer scale on an adequately sized sheet of paper. Once the shell is complete, the other important construction features referenced in the preceding section on inspection or surveying should be added, and various construction materials should be labeled. The inspector should draw sufficient sectional views to show all vertical areas of the facility or building. Figure 3.15.1 illustrates what a typical, simple site sketch looks like when completed. The second step is to plot the fire protection facilities and equipment on the finished building sketch. Two important points should be noted. First, water supplies—public or private (yard) mains—are continuous from a point of origin to the individual automatic sprinkler risers. Conversely, the automatic sprinkler systems within the buildings are not entirely shown. (Note: Sprinkler occupancy classification and spacing are referred to in the body of the narrative inspection report.) Second, when space limitations prohibit drawing all the equipment on the plan at approximate actual locations (owing to size, quantity of symbols, or labeling requirements), a small side sketch (not drawn to scale) can be used effectively. The last step in completing the plan is to label the internal occupancy or processes of each area of the facility or building, and any yard storage or processes of interest. The symbols and plans in Figures 3.15.1 and 3.15.2 will enable any inspector to develop a building plan in accordance with widespread convention. These symbols are based on NFPA 170, Standard for Fire Safety Symbols, 1999 edition. However, many organizations use their own, slightly different set of symbols and layouts. When trying to take information from a plan developed from another source, it is essential to refer to the legend of symbols used by that organization to interpret the information accurately. Occasionally, the use of a symbol alone will not sufficiently describe the situation. In that case, it is also necessary to label
3–210 SECTION 3 ■ Information and Analysis for Fire Protection
COMPR on ST DK STOCK STG ON STEEL RACKS
100,000 GAL STEEL WATER TANK 25 FT DIAM x 27 FT HIGH NOT TO SCALE
1000 GPM 100 PSI ELEC CENT AUTO
PUMP HOUSE 1 ST CONC 1972 NOT TO SCALE
COMPR ON RC MANUFACTURING OF WIDGETS
BOILER ROOM
SECTION A – A
10 IN. CI FROM TANK
COMPR ON WD OFFICE OFFICE
4 2 IN. OUTLETS
SECTION B – B
8 IN,
TYPE I CONST. 10 FT
N
CI TO TANK WOODS
8 IN. CI
6 IN.
8 IN. CI A 6 IN.
6 IN.
40 FT BR 5000 GAL LACQUER DIP TANK WITH DRY CHEMICAL EXTINGUISHING SYSTEM 1958
1966 TYPE I CONSTRUCTION
TYPE I CONSTRUCTION 75 FT TO 1 ST TYPE II STORAGE BLDG.
6 IN.
1
CONC
CONC 25 FT
1
LOADING DOCK
MANUFACTURING
PRODUCT STORAGE
PARKING AND OPEN LAND 200 FT
6 IN. TYPE II CONST.
ACC. CB 16 FT
1
8
IN
.C
B
I
A
6 IN. TYPE III CONST. 1968 BR OFFICES 30 FT 2 B
ACE MANUFACTURING CO. 1626 MAIN STREET ANYTOWN, WA JULY 24, 1999 SCALE:
8 IN. CI
6 IN.
6 IN.
STOCK STGE 1972
4 IN.
8 IN. VALVE 2 EA 8 IN. CHECKS 8 IN. VALVE 16 IN. CI
CEMENT-LINED
MAIN STREET 2 EA 2-IN. x 4 IN. NST
FIGURE 3.15.1
Typical Site Sketch Showing Fire Protection Facilities and Equipment
that point on the plan. Table 3.15.1 gives a list of standard abbreviations that can be used. Although brief, the list nevertheless provides all of the abbreviations commonly needed. Abbreviations for Use on Drawings and in Text, prepared by the American National Standards Institute,2 lists additional, less commonly used abbreviations. At one time, colors were used to describe the type of construction materials used for walls. Today, color-coded plans are being replaced by black-and-white drawings to facilitate preparation and for economic reasons, so construction type is being noted narratively. Table 3.15.2 identifies colors that should be used if the plan is to be in color. To avoid confusion on compli-
cated plans, construction materials can be labeled in accordance with the abbreviations in Table 3.15.1.
SUMMARY Agencies that conduct quality hazard inspection, surveying, and mapping (1) identify the danger to life from fire and associated hazards, (2) determine ways to minimize fire danger to buildings and contents, (3) familiarize responding emergency personnel with existing fire protection and fire-fighting challenges associated with the property, and (4) recommend corrections to deficiencies and/or unsafe conditions.
CHAPTER 15
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Formats for Fire Hazard Inspecting, Surveying, and Mapping
3–211
SYMBOLS FOR SITE FEATURES Bodies of water. Rivers, lakes, etc., are outlined.
Buildings. 1. The exterior walls of buildings are outlined in single thickness lines if other than fire-rated and double thickness lines if fire-rated.
K CREE POND
2. The perimeter of canopies, loading docks, and other open-walled structures are shown by broken lines. Fences. Fences are shown by lines with "x's" every in. (25.4 mm). Gates are shown.
LOADING
SHED
x
Railroad tracks. Railroad tracks are shown by a single line with crossed dashes.
x
x
x
x
Property lines
Streets. Streets are shown, usually at property lines. Fire department access 10 12-14 Downing Street
F.D.
SYMBOLS FOR BUILDING CONSTRUCTION Types of building construction. Types of construction are shown narratively. FIRE RESISTIVE CONST. (TYPE I)
Floor openings, wall openings, roof openings, and their protection
WOODFRAME CONST. (TYPE V)
Height. Indicate number of stories above ground, number of stories below ground, and height from grade to eaves. C 1=2 24 ft 3 40 ft 1B 20 ft 1 D 1 E B
A
F
G Three stories, no basement, 40 ft to eaves.
B
One story with basement, 20 ft to eaves.
C
One equals two stories, no basement, 24 ft to eaves. One-story open porch or shed.
E
One-story addition.
F
Thirteen stories with basement.
G
Underground structure.
(Includes copyrighted material of Insurance Services Office with its permission. Copyright, Insurance Services Office 1975.)
Wall Smoke barrier
2-hr fire-rated
1/2-hr fire-rated
2-hr fire-rated/ smoke barrier
1/2-hr fire-rated/ smoke barrier 3/4-hr fire-rated
3-hr fire-rated
3/4-hr fire-rated/ smoke barrier 1-hr fire-rated
3-hr fire-rated/ smoke barrier
1-hr fire-rated/ smoke barrier
4-hr fire-rated/ smoke barrier
S
S
S
S
S
Stairs in firerated shaft
Elevator in combustible shaft.
E
Stairs in open shaft
Elevator in noncombustible shaft.
E
Skylight
SL
Horizontal tank, above ground.
Chimney. Describe height and construction.
Vertical tank, above ground. Horizontal tank, below ground.
S
S
S
Boiler
S
S
S
S
Stairs in combustible shaft
Miscellaneous features. For tanks, indicate type, dimensions, construction, capacity, pressurization, and contents.
S S S
S
Escalator
4-hr fire-rated
Parapets. The symbol for parapets utilizes one cross for each 6 in. (152 mm) that the parapet extends above the roof. The cross is drawn through an extension of the wall line for the parapeted wall (in plan view).
S
Rated fire door in wall (less than 3 hr). Indicate floors.
E
Roof, floor assemblies. These symbols indicate features in cross sections. Descriptive notes are often required. Fire-resistive Floor/ceiling or floor or roof roof/ceiling assembly. Details indicated as necessary. Wood joisted floor or roof Floor on ground Other floors or roofs. (Steel deck on Note steel joists) Truss roof. construction. Note construction.
Walls. Indicate construction.
S
Opening hoistway
Fire door in wall (3-hr rated). Indicate floors.
13B UNDERGROUND
A
D
Opening in wall. Indicate floors.
S
Fire escape
Symbol used to note wall ratings and parapets on life safety plans and risk analysis plans/cross sections.
FIGURE 3.15.2
Standard Drawing Symbols
(continued)
3–212 SECTION 3 ■ Information and Analysis for Fire Protection
SYMBOLS RELATED TO MEANS OF EGRESS Emergency lights. Indicate if light head (lamp) is remote from battery.
Exit signs. Indicate direction of flow for each face. Illuminated exit sign, single face
Emergency light, battery powered, one lamp Combined battery powered emergency lights and illuminated exit signs, two lamps
Illuminated exit sign, double face Emergency light, battery powered, three lamps SYMBOLS FOR WATER SUPPLY AND DISTRIBUTION Valves. Indicate valve size. Mains, pipe. Indicate pipe size and material. Valves Float (general) valve Water main under Public water main building OS&Y valve Valve in Private water main Suction pipe (outside screw and pit yoke, rising stem) PostHydrants. Indicate size, type of thread, or connection. Symbol indicator Indicating butterfly valve element may be utilized in any combination to fit the type of hydrant. valve Private hydrant, one hose outlet
Thrust block
Public hydrant, two hose outlets
Wall hydrant, two hose outlets
Keyoperated valve
Nonindicating valve (nonrising-stem valve)
Pressureregulating valve
Backflow preventer— double-check type
Pressurerelief valve
Backflow preventer— reduced pressure zone (RPZ) type
Fire department connections. Indicate size and type. Single fire department connection
Siamese fire department connection
Public hydrant, two hose outlets and pumper connection
Private housed hydrant, two hose outlets
Free-standing siamese fire department connection
Fire pump. For test headers. Indicate number and size of outlets.
Others: Riser
Fire pump with drives
Freestanding test header
Meter
Wall-mounted test header
Screen/ strainer
SYMBOLS FOR SPRINKLER SYSTEMS Alarm/supervisory devices Flow detector/ Dry-pipe valve switch (flow with quick opening alarm) device (accelerator Pressure detector/ or exhauster) switch (Specify type
Piping, valves, control devices. Indicate size. Sprinkler riser Check valve, general (Arrow indicates direction of flow)
Alarm check valve
Deluge valve
—water, low air, high air, etc.)
Preaction valve
Water motor alarm/water motor gong
Level detector/ switch Tamper detector or tamper switch Valve with tamper detector/ switch
(shield optional)
Dry-pipe valve
Bell (gong) SYMBOLS FOR FIRE SPRINKLERS
Upright sprinkler Note "DP" on drawing and/or in specifications where dry pendent sprinklers are employed.
Pendent sprinkler
Sprinkler, with guard
Upright sprinkler, nippled up
Outside sprinkler Upright sprinkler head shown
Pendent sprinkler, on drop nipple
Specify type, orifice size, for example: Open sprinkler (window or cornice).
Sidewall sprinkler
Note "DP" on drawing and/or in specifications where dry pendent sprinklers are employed.
SYMBOLS FOR PIPING, VALVES, CONTROL DEVICES, AND HANGERS Sprinkler piping and branch line
Pipe hanger
Indicate pipe size.
This symbol is a diagonal stroke imposed on the pipe that it supports.
FIGURE 3.15.2
Continued
Angle valve (angle hose valve)
CHAPTER 15
■
Formats for Fire Hazard Inspecting, Surveying, and Mapping
3–213
SYMBOLS FOR EXTINGUISHING SYSTEMS† For fires of all types, except metals
Water-based systems
Automatically actuated
Wet (charged) system Automatically actuated
Manually actuated
Systems utilizing a gaseous medium Carbon dioxide system
Dry system Automatically actuated
Manually actuated
Manually actuated
Automatically actuated
Manually actuated
Foam system Automatically actuated
Manually actuated
Halon or clean agent extinguishing system Automatically actuated
Dry chemical systems for liquid, gas, and electrical-type fires Automatically actuated
Manually actuated
Supplementary symbols
Manually actuated
Nonsprinklered space
NS
Partially sprinklered space
AS
Water mist extinguishing system Automatically actuated
Fully sprinklered space
AS
Water spray system
WS
†
Manually actuated
These symbols are intended for use in identifying the type of installed system protecting an area within a building. SYMBOLS FOR FIRE-FIGHTING EQUIPMENT, INCLUDING STANDPIPE AND HOSE SYSTEMS
Hose station, charged standpipe
CO2 reel station
Hose station, dry standpipe
Dry chemical reel station
Monitor nozzle, dry Foam reel station Monitor nozzle, charged SYMBOLS FOR SPECIAL HAZARD SYSTEMS
SYMBOLS FOR FIRE EXTINGUISHERS
Agent storage container. Specify type of agent and mounting. Carbon dioxide
Foam
FO
Clean agent
Halon
HL
Dry chemical extinguisher for fires of all types, except metals CO2 extinguishers
Water extinguisher
CO2 CL
Dry chemical Water mist
DC
Foam extinguisher
WM
Dry chemical extinguishers for fires of liquid, gas, electrical types
Special spray nozzle. Specify type, orifice, size, other required data (shown here on pipe).
Halon extinguishers Extinguisher for metal fires
SYMBOLS FOR FIRE ALARMS, DETECTION, AND RELATED EQUIPMENT Control panels
Manual stations
Fire alarm control panel
FCP
Fire alarm communicator
FAC
Foam
Halon F
Fire system annunciator FSA Fire alarm transponder or transmitter
FTR
Elevator status/recall
ESR
Halon control panel
HCP
Control panel for heating, HVA ventilation, air conditoning, exhaust stairwell pressurization, or similar equipment
Fire service or emergency telephone station
H
Clean agent
CA
Wet chemical
W
Carbon dioxide
C
Water mist
WM
Pull station
P
Dry chemical
D
Deluge sprinkler
DL
Indicating appliances M
Mini-horn Accessible
Jack A
Abort switch Halon Carbon dioxide
CO2
Bell (gong)
J
Dry chemical HL
Hand-set
Foam Wet chemical
H
DC
Clean agent
CA
FO
Water mist
WM
WC
Deluge sprinkler
DL
FIGURE 3.15.2
Speaker/horn (electric horn) Horn with light as separate assembly
Continued
Horn with light as one assembly Light (lamp, signal light, indicator lamp, strobe) Related equipment Door holder
•
(continued)
3–214 SECTION 3 ■ Information and Analysis for Fire Protection
Smoke detector
Heat detector (thermal detector) Combination — rate of rise and fixed temperature
Rate of rise only
R
R/F
Rate compensation
Gas detector R/C
Fixed temperature F Line-type detector (heat-sensitive cable)
Flame detector (flicker detector) Indicate UV, IR, or visible radiation type
Beam receiver
Photoelectric products of combustion detector
P
Ionization products of combustion detector
I
Beam transmitter
BR
Smoke detector in duct
BT
SYMBOLS FOR SMOKE/PRESSURIZATION CONTROL Purge controls
Dampers
Manual control
Ventilation openings (Orient as required for intake or exhaust.)
Pressurized stairwell
Fire
Fire/smoke S
(Orient as required for base or head injection.)
Fans General
Roof
Duct
Wall
Smoke
Barometric
MISCELLANEOUS SYMBOLS
Fusible link
Fusible link with electronic feature
Specify degrees.
SOV
Solenoid valve ETL
Specify degrees.
SYMBOLS FOR PREFIRE PLANNING Triangle symbols can point at a specific location or direction.
Circle symbols are used for all piping system appendatures, such as valves, since most pipes are round.
Diamond symbols identify a specific location by touching a wall.
Square symbols are used for all room designations, as they represent most rooms having four sides.
Detector/extinguishing equipment
Access features, assessment features, ventilation features, and utility shutoffs
Access features
Duct detector
DD
Heat detector
HD
Smoke detector
SD
Flow switch (water)
FS
Manual pull station
PS
Tamper switch
TS
LPG
Halon system
HL
NG
Dry chemical system
DC
Utility shutoffs
Fire department access point
FD
Fire department key box
K
Roof access
RA
Assessment features
Electric shutoff
E
Domestic water shutoff
W
Gas shutoff
G
Specific variations
Fire alarm annunciator panel
AP
Fire alarm reset panel
RP
Fire alarm voice communication panel
CP
LP gas shutoff Natural gas shutoff
Smoke control and pressurization panel
SP
Sprinkler system water flow bell
WB
Ventilation features Sky light Smoke vent
SL
SV
FIGURE 3.15.2
CO2 system
CO2
Wet chemical system
WC
Foam system
FO
Clean agent system
CA
Beam smoke detector
BSD
Continued
■
CHAPTER 15
Formats for Fire Hazard Inspecting, Surveying, and Mapping
Equipment rooms .
Water flow control valves and water savers Post-indicator valve
PIV
Riser valve
RV
Sprinkler zone valve
ZV
Hose cabinet or connection
HC
Wall hydrant
WH
Test header (fire pump)
TH
Inspector's test connection
TC
Fire hydrant
FH
Fire department connection
FDC
Drafting site
DS
Water tank
WT
FIGURE 3.15.2 TABLE 3.15.1
3–215
Air-conditioning equipment room Air-handling units (AHUs)
AC
Elevator equipment room
EE
Emergency generator room
EG
Fire pump room
FP
Telephone equipment room
TE
Boiler room
BR
Electrical/transformer room
ET
Continued
Legend of Common Abbreviations*
Above Accelerator Acetylene Aluminum Asbestos Asphaltprotected metal Attic Automatic Automatic fire alarm Automatic sprinklers Avenue Basement Beam Board on joist Brick Building Cast iron Cement Centrifugal fire pump Cinder block Composition roof Concrete Construction Corrugated iron Corrugated steel Diameter Diesel engine Domestic Double hydrant Dry-pipe valve East Electric motor driven Elevator Engine Exhauster
ABV ACC ACET AL ASB APM A AUTO AFA AS AVE B BM BDOJ BR BLDG CI CEM CFP CB COMPR CONC CONST COR IR COR ST DIA D ENG DOM DH DPV E EMD ELEV ENG EXH
Feet Fiber board Fire escape Fire department pumper connection Fire detection units Products of combustion Rate of heat rise Fixed temperature Fire pump Floor Frame Fuel oil (label with grade number) Gallon Gallons per day Gallons per minute Galvanized iron Galvanized steel Gas, natural Gasoline Gasoline engine driven Generator Glass Glass block Gypsum Gypsum board High voltage Hollow tile Hose connection Hydrant Inch, inches Iron Iron clad Iron pipe Joist, joisted Liquid
FT FBR BD FE FDPC
FDU POC RHR FTEP FP FL FR FO #_____ GAL GPD GPM GALVI GALVS GAS GASOLINE GED GEN GL GLB GYM GYM BD HV HT HC HYD IN IR IR CL IP J LIQ
Liquid oxygen Manufacture Manufacturing Maximum capacity Mean sea level Metal Mezzanine Mill use Normally closed Normally open North Number Open sprinklers Outside screw and yoke valve Partition (label composition) Plaster Plasterboard Platform Pound (unit of force) Pressure Unit of pressure (psi) Protected steel Private Public Railroad Reinforced concrete Reinforcing steel Reservoir Revolutions per minute Roof Room Slate shingle roof Space South Stainless steel Steam fire pump Steel
LOX MFR MFG MAX CAP MSL MT MEZZ MU NC NO N No OS OS&Y PTN (e.g., WD PTN) PLAS PLAS BD PLATF LB PRESS PSI PROT ST PRIVATE PUB RR RC RST RES RPM RF RM SSR SP S SST SFP ST
Steel deck Stone Story Street Stucco Suspended acoustical plaster ceiling Suspended acoustical tile ceiling Suspended plaster ceiling Suspended sprayed acoustical ceiling Tank (label capacity in gallons) Tenant Tile block Timber Tin clad Triple hydrant Truss Under Vault Veneer Volts (indicate number of) Wallboard Wall hydrant Water pipe West Wire glass Wire net Wood Wood frame Yard
ST DK STONE STO STREET STUC SAPL
SATL
SPC SSAL
TK
TEN TB TMBR TIN CL TH TR UND VLT VEN 450V WLBD WLH WP W WGL WN WD WD FR YD
Note: For SI units: 1 gal = 3.785 L; 1 psi = 6.895 kPa/1 lb (force) = 4.448 N. a Some words that have a common abbreviation, e.g., “ST” for “street,” are spelled out fully to avoid confusion with similar abbreviations used herein for other terms. See Reference 1.
3–216 SECTION 3 ■ Information and Analysis for Fire Protection
TABLE 3.15.2 Color Code for Denoting Construction Materials for Walls Color Brown Red Yellow Blue Gray
Interpretation Fire-resistive protected steel Brick, hollow tile Frame-wood, stucco Concrete, stone, or hollow concrete block Noncombustible (sheet metal or metal lath and plaster) unprotected steel
BIBLIOGRAPHY References Cited 1. NFPA Inspection Manual, 7th ed., National Fire Protection Association, Quincy, MA, 1994. 2. ANSI, Abbreviations for Use on Drawings and in Text, ANSI Y1.1, American National Standards Institute, New York, 1989.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on formats for fire hazard inspection, surveying, and mapping. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 170, Standard for Fire Safety Symbols NFPA 220, Standard on Types of Building Construction
Additional Readings Brannigan, F. L., “Preplanning Public Hazards,” Fire Engineering, Vol. 153, No. 6, 2000, p. 120.
Brown, P., “Garages and NFPA 13D; Some Communities Extend 13D Requirements with Local Ordinances,” Sprinkler Age, Vol. 18, No. 6, 1999, pp. 13–14. Clyde, J. E., Construction Inspection, Wiley, New York, 1983. Collier, P. C. R., “Fire in a Residential Building: Comparisons between Experimental Data and a Fire Zone Model,” Fire Technology, Vol. 32, No. 3, 1996, pp. 195–218. Electrical Inspection Illustrated, 2nd ed., National Safety Council, Chicago, IL, 1984. Gustin, W., “Search and Rescue in Single Family Dwellings, Part 1,” Fire Engineering, Vol. 151, No. 8, 1998, pp. 73–74. Gustin, W., “Search and Rescue in Single Family Dwellings, Part 1,” Fire Engineering, Vol. 151, No. 9, 1998, pp. 51–52. Gustin, W., “Search and Rescue in Single Family Dwellings, Part 1,” Fire Engineering, Vol. 151, No. 10, 1998, pp. 81–88. McCormick, P., “Industrial and Commercial Prevention and Protection, Part 1,” American Fire Journal, Vol. 52, No. 4, 2000, pp. 14–17. McGill, R. J., “The Important Pre-Plan,” Health & Safety, Vol. 10, No. 2, 1999, p. 3. Naylis, G. J., “How to “COPE” on the Fireground,” Fire Engineering, Vol. 151, No. 11, 1998, p. 26. Palmer, O. J., “Seven-Story, Non-Fireproof, Multiple Dwelling— Communication Problems,” WNYF, Vol. 59, No. 2, pp. 28–29. Pilborough, L., Inspection of Industrial Plants, 2nd ed., Gower Technical, Brookfield, VT, 1989. Robertson, J. C., “Fire Safety Inspection Procedures,” Introduction to Fire Prevention, 3rd ed., Macmillan, New York, 1989, pp. 154–181. Stromberg, P. T., “Wildland Fire Defense: Wisconsin’s Hazards Identification System, Voice, Vol. 26, No. 9, 1997, pp. 7–8. “Study: Fire Protection Inadequate in Capitol and House Buildings,” Fire Engineering, Vol. 152, No. 3, 1999, pp. 50–51.
HUMAN BEHAVIOR IN FIRE EMERGENCIES
M
ost of the fire prevention and protection strategies addressed in subsequent sections are tied directly to the timeline of fire growth and development. Whether the system element is fire prevention; control of materials, products, and environments; suppression; or fire confinement, the aim is to slow down or stop the fire and its potentially devastating effects. However, life safety also depends on using the extra time provided by a delayed fire to
SECTION
4
Rita Fahy
Case Study RESIDENTIAL HIGH-RISE BUILDING, NORTH YORK, ONTARIO, CANADA, JANUARY 6, 1995 munication system, so it was not used during the initial stages of the fire. When the emergency voice alarm communication system was used at some point later in the fire, many residents did not hear or could not understand the messages. Without guidance that could be communicated through the use of the emergency voice alarm communication system or information from other sources, residents made decisions based on their personal knowledge, experience, and the cues they were receiving. Once aware of the fire, some residents attempted to evacuate early in the incident and were successful. Other residents who attempted to exit minutes later were unable to do so. Some residents moved through worsening smoke conditions only to be forced to abandon their attempted escape and seek refuge in apartments. Many residents who sought refuge in their apartments or in apartments of other residents were able to stay safely in the apartments where they were rescued by fire department personnel. Some residents moved from the apartments to their balconies. In many instances, the people who remained in their apartments or moved to the balconies were exposed to less risk to their safety than those who attempted to escape. Based on the NFPA’s investigation and analysis of this fire, the following factors were considered as having contributed to the loss of life and property:
At approximately 5 a.m. on Friday, January 6, 1995, a fire in a North York, Ontario, residential high-rise building resulted in the deaths of six residents. All were found on upper stories in exit stairways. The fire appeared to have been ignited by the improper disposal of smoking materials and initially involved a couch in a fifth-floor apartment. The fire caused severe damage to the apartment and to an exit access corridor. The loss was estimated at $1 million, Canadian ($730,000, U.S.). After unsuccessfully attempting to extinguish the fire, the occupant in the apartment of fire origin left without closing the dwelling unit door to the corridor. Fire and smoke passed through the open door into the exit access corridor and made that corridor untenable for many fifth-floor residents. The residents who did not escape early in the incident stayed in their apartments until they were rescued by fire fighters. The combination of closed doors and noncombustible walls prevented untenable conditions and deaths from occurring in other fifth-floor apartments. The door to one of the building’s two exit stairways was heavily damaged by the fire, and the door to the other exit stairway was held open by a fire department hose line used during the fire suppression operations. As a result, smoke entered both stairways. Natural stack effect moved the smoke vertically through the stairways, elevator shafts, and heating, ventilation, and air-conditioning ducts. On the upper floors, the smoke passed through open doors and seeped past closed doors. As a result, smoke accumulated to varying degrees in exit access corridors and in apartments. In many instances, the smoke spreading through the building made occupants aware of the fire. It also, however, made the exit stairways untenable, prevented residents from escaping, and caused the death of six residents. The communication of information to residents in the building was not effective in this incident. No one in the building was trained to use the emergency voice alarm com-
• Lack of automatic sprinkler protection • Lack of door self-closing devices on apartment entrance doors • Vertical smoke movement due to stack effect • Staff who were not trained with respect to managing fire emergencies in the building for which they were responsible • Lack of fire safety training for building residents • Voice communication equipment that could not transmit messages understandable to residents
Source: Michael S. Isner, NFPA.
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move occupants out of harm’s way. Effective evacuation involves understanding and using the latest knowledge regarding human behavior in fires—how people tend to react and how that affects how they be can be trained to react—and building design features that can accommodate or shape occupant behavior toward effective action. This section covers these essential bodies of knowledge. A section on human behavior, entitled “Evacuation of Occupants,” first appeared in the 18th edition of the Fire Protection Handbook. In the current edition the section has been expanded by one chapter and retitled “Human Behavior in Fire Emergencies.” This new section title more accurately describes the range of occupant behavior that includes many complex actions—such as alerting others, seeking refuge, and forming convergence clusters—that are not necessarily related to evacuation. Chapter 1, “Human Behavior and Fire,” covers what we know about human behavior and fire. Forget about panic. When the term is used precisely, such behavior very rarely occurs, even in the most severe fire conditions. Chapter 1 presents basic information that is as fundamental to fire protection as fire behavior. It also addresses the means by which people investigate “ambiguous threat cues” and decide that there really is a fire—namely, recognition, validation, definition, evaluation, commitment, and reassessment. This chapter is a must read for all fire protection professionals. Chapter 2, “Calculation Methods for Egress Prediction,” contains information and techniques of vital importance to design professionals, especially those involved in performancebased design. Chapter 3 reviews concepts that underlie the provisions of NFPA 101®, Life Safety Code®. These include the sizes of people and other key factors in flow speed. They also include characteristics of the building that can protect or threaten means of egress, such as interior finish that promotes rapid flame spread. Also look for these: Chapters 3-12, 3-13, and 3-14 of the SFPE Handbook of Fire Protection Engineering provide more detailed treatment of the science of human behavior in fire and the modeling of people movement. In the Fire Protection Handbook, the entirety of Section 5 on fire and life safety education will be of interest. Section 12 is germane because the building design principles for confining fire and for protecting egress routes need to be considered together. Special evacuation requirements for specific property-use classes, if needed, are addressed in the appropriate chapters of Section 13.
Chapter 1
Human Behavior and Fire
Awareness of the Fire Decision Processes of the Individual Behavior Actions of Occupants Handicapped or Impaired Occupants Fire Exit Drills Summary Bibliography Chapter 2
Calculation Methods for Egress Prediction
Components of Evacuation Time Estimating Evacuation Time Calculation Methods for Travel Time Computer Simulation and Modeling of Egress Design Summary Bibliography
4–3 4–4 4–5 4–9 4–21 4–26 4–28 4–28
4–33 4–33 4–34 4–40 4–47 4–49 4–49
Chapter 3
Concepts of Egress Design
Fundamentals of Design Life Safety Code Influences on Egress Definition of the Term “Means of Egress” Capacity of Exits Exit Facilities and Arrangements Exit Lighting and Signs Alarm Systems Emergency Egress and Relocation Drills Maintenance of the Means of Egress Summary Bibliography
4–57 4–57 4–60 4–62 4–65 4–69 4–71 4–76 4–77 4–77 4–77 4–77 4–77
CHAPTER 1
SECTION 4
Human Behavior and Fire Revised by
John L. Bryan
H
role of human behavior research being primarily applicable to the educational aspects of fire prevention. During the 1970s the National Bureau of Standards, through the Center for Fire Research, and the National Fire Protection Association were the primary sources for funding studies on human behavior in fire in the United States. Thus, studies resulted in an examination and development of the methods for investigating behavior of the occupants in fire situations in both the United States and United Kingdom. Funding was also provided for the formation with Japan of the United States and Japan Natural Resource Panel on Fire Research and Safety, which included the study area of human behavior in fire.7–15 The emphasis of the studies in human behavior in fire during this period was on defining the behavioral actions of the occupants in fire situations, the examination of the then popular concept of “panic behavior,” and an emphasis on the study of the evacuation process as it occurred in high-rise building fires. Characteristics of the behavior of people individually and within groups have been determined primarily by research studies in which individuals were interviewed by fire department personnel at the time of the fire.8,15 It must be recognized that an individual’s behavior in a fire is affected by the variables of the building in which the fire occurs and by the appearance of the fire at the time of detection. For example, the occupants’ response will vary if they smell smoke rather than see flames or dark, acrid smoke completely obscuring a corridor. Variables of the fire protection provided for the building may also be critical to the individual’s perception of the threat involved. Obviously, the most important individual decisions and behavior in lifethreatening situations occur before the arrival of the fire department, in the early stages of the fire. Studies of healthcare facilities have indicated the importance of this early behavior:
ow one reacts during a fire is related to the role assumed, previous experience, education, and personality; the perceived threat of the fire situation; the physical characteristics and means of egress available within the structure; and the actions of others who are sharing the experience. Postevent analysis of behavior has described actions as adaptive or nonadaptive, participative or inhibited, and altruistic or individualistic. Detailed interview and questionnaire studies over the last half century have established that instances of nonadaptiveor panic-type behavior are rare, occurring under specific conditions. Most behavior in fires is determined by information analysis, resulting in cooperative and altruistic actions. The earliest documented studies on human behavior in the United States involved capacity counts of the velocity of pedestrian movement for the New York city design of the Hudson Terminal Building in 1901.1 The first edition of the National Fire Protection Association’s Building Exits Code in 1927 was developed from evacuation studies conducted during the decade since 1917.2 Classical evacuation studies involving railway terminals, subway stations, theaters, department stores, and federal government office buildings with both “normal” exiting flows and “fire-drill” exiting flows were conducted in the early 1930s and published in 1935.1 In England, the London Transit Board and other evacuation studies were conducted.3,4 In the United States, during the 1940s and the 1950s, a lack of interest in studies on human behavior in a fire was prevalent, even in fires that resulted in large loss of life, such as the Cocoanut Grove fire, in which dedicated human behavior studies of the activities of the occupants were not conducted. An exception was the interview study of selected occupants of the Arundel Park fire in 1956, which verified the process of reentry behavior by members of family groups.5 The most productive period for research and publications in the United States on human behavior appeared to be from 1970 through the mid-1980s. The five-year study and report of the National Commission on Fire Prevention and Control, entitled America Burning, in 1973 provided a federal government focus on the national fire problem.6 This report resulted in new and enhanced federal financial support for all facets of fire research including human behavior, even though the report envisioned the
In the process of investigating these case studies we have come to believe that the period between detection of the fire and the arrival of the fire department is the most crucial lifesaving period in terms of the first compartment (the area in direct contact with the room of origin and the fire).12 Thus, the behavior of the individuals intimately involved with the initiation of the fire is critical not only for themselves but often for other occupants of the building. It should be recognized that the altruistic behavior observed in most fires with the interaction of the occupants and the fire environment in a deliberate, purposeful manner appears to be the general mode of
John L. Bryan is professor emeritus of the Department of Fire Protection Engineering, College of Engineering, University of Maryland, and currently a consultant in Frederick, Maryland.
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reaction. The nonadaptive flight or panic-type of behavioral reaction is apparently unusual in fires.
AWARENESS OF THE FIRE Obviously, the way in which an individual is alerted to the presence of a fire may determine the degree of threat perceived. With vocal alerting systems in buildings, variations in voice quality, pitch, or volume, as well as the content of the message, tend to provide threat cues.16 Proulx and Sime17 in their study involving evacuation drills in an underground rapid transit station found the use of directive public announcements with an alerting alarm bell most effective in creating an immediate effective evacuation. Ramachandran in his review of the research on human behavior in fires in the United Kingdom since 1969 summarized the effectiveness of alarm bells as awareness cues: “The response to fire alarm bells and sounders tends to be less than optimum. There is usually skepticism as to whether the noise indicated a fire alarm and if so, is the alarm merely a system test or drill?”18 Ramachandran19 indicated that the development of “informative fire warning systems,” which use a graphic display with a computer-generated message and a high-pitched alerting tone, has reduced the observed delay times in the initiation of practice evacuations. Cable20 in his study of the response times of staff personnel to the fire alarm signal in veterans administration hospitals found the greatest delay in response time with the coded alarm-bell type systems. Kimura and Sime21 in a study of the evacuation of two lecture halls with college students found that the lecturer’s verbal instructions were the determining factor in the students choosing to use the fire exit over the normal entrance and exit. Research literature developed from practice evacuations indicates that the use of verbal directive informative messages may be most effective in reducing delay in evacuation initiation. However, note that if verbal directive messages conflict with other awareness cues, such as the odor or sight of smoke, occupants may question the credibility of the message and disregard the information. One of the few documented cases of this type of situation occurred in the South Tower of the World Trade Center on April 17, 1975. Lathrop22 reported that the fire occurred in a trash cart in a storage area on the fifth floor, adjacent to an open stairway door that allowed smoke to infiltrate the ninth through twenty-second floors at approximately 9:04 a.m. Occupants of these floors moved into the core area of the building, and the building communications center monitoring the core lobby areas verbally directed the people in these areas to remain calm and return to their office areas at 9:10 a.m. Despite this announcement, occupants remained in the core lobby areas and became more concerned about smoke conditions. Thus, with occupants on the affected floors becoming more anxious, an evacuation message was announced at 9:16 a.m. As Burns23 reported, simultaneous occupant evacuations occurred in the explosion and fire of February 26, 1993, which severely affected both towers and the Vista Hotel of the World Trade Center. The explosion disrupted the Center’s communications center, and the occupants, having experienced within minutes the explosion, loss of power and smoke infiltration of the
floors areas, evacuated without the established verbal directional announcements used in previous practice evacuations. Fahy and Proulx24 in their questionnaire study of 382 trained fire warden personnel located in both towers of the World Trade Center at the time of the explosion and fire of February 26, 1993, found these personnel were alerted primarily in the following manner:24 Respondents mentioned the following cues, either singly or in combination that something was occurring: hearing or feeling the explosion, loss or flickering of lights or telephones, smoke or dust, sirens and alarms, information from others, and people movement. Most of the participants in residential occupancy studies were alerted initially to the fire by the odor of smoke. When the two categories “notified by family” and “notified by others” are combined, however, personal notification becomes the most frequently reported means of initial perception of fire, as indicated in Table 4.1.1.8 The category “noise” includes noise from persons moving downstairs and through corridors, plus miscellaneous noise sources, including the breaking of glass and the arrival of fire apparatus. Table 4.1.2 compares the means of awareness from participants of a British study15 and those of a U.S. study.8 The number of stimuli was reduced because the British study had fewer categories, and the U.S. responses have been adapted to the British categories. There was only one significant difference in the means of awareness between the two groups: 15 percent of the British participants became aware of the fire upon observing flame, contrasted with 8.1 percent of the U.S. participants. A study of the NFPA-recommended smoke detector noise level of 75 dBA indicates that individuals with hearing impairments, those taking sleeping pills, or those on medication may require a detector noise level exceeding 100 dBA25 (see NFPA 72®, National Fire Alarm Code®). Flashing or activated lights are effective fire signals in occupancies populated primarily by hearing-impaired persons.26 The 1981 edition of NFPA 101®, Life Safety Code® for the first time permitted flashing of exit signs along with activation of an audible fire alarm system.
TABLE 4.1.1 Means of Awareness of the Fire Incident (United States Studies) Means of Awareness
Participants
Percent
Smelled smoke Notified by others Noise Notified by family Saw smoke Saw fire Explosion Felt heat Saw/heard fire department Electricity went off Pet
148 121 106 76 52 46 6 4 4 4 2
26.0 21.3 18.6 13.4 9.1 8.1 1.1 0.7 0.7 0.7 0.3
569
100.0
N = 11
CHAPTER 1
Means of Awareness
Saw flame 15.0 Smelled smoke 34.0 Heard noises 9.0 Heard shouts and was told 33.0 Heard alarm 7.0 Other 2.0
N=6
2193
U.S. (percent, P2) P1 – P2
Human Behavior and Fire
4–5
their behavior in public places. The performance of naive subjects in the passive-confederate situation was reported as follows:
TABLE 4.1.2 Comparison of British and United States Study Results Relative to Means of Awareness of a Fire Incident British (percent, P1)
■
SEPa 1 – P2
CR b
8.1
6.9
1.64
4.21c
35.1
1.1
2.27
0.48
11.2
2.2
1.41
1.56
34.7
1.7
2.25
1.20
7.4 2.8
0.4 0.8
1.23 0.70
0.33 1.14
569
a
Standard error. Critical ratio. c Critical ratio (CR) significant at or above the 1 percent level of confidence. b
A study of 24 male subjects that was designed to determine whether they were awakened by a smoke detector’s audible alarm signal and could identify fire cues found that the subjects slept through the alarm signals at a signal-to-noise ratio of 10 dBA and consistently failed to identify the awakening cue or radiant heat and smoke odor cues as fire warnings.27 Other researchers have indicated that the alarm-signal-to-noise ratio is attenuated by physical surroundings.28 A signal passing through a ceiling or a wall may be reduced by 40 dBA, whereas a signal passing through a door may be reduced by 15 dBA; in addition, the signal could be masked by a typical residential air conditioner noise level of 55 dBA. The acknowledgment of ambiguous threat cues as signaling an emergency may be inhibited by presence of other people. Recognition of this phenomenon resulted in an experiment involving college students.29 While the students were completing a written questionnaire, the experimenter introduced smoke into the room through a small vent in the wall. If the students left the room and reported the smoke, the experiment was terminated. If the students did not report the presence of the smoke within 6 min from the time they first noticed, the experiment was considered complete. Students alone in the room reported the smoke in 75 percent of the cases. When two passive, noncommittal persons joined each student, only 10 percent of the students reported the smoke. When the experimental group consisted of three naive subjects, one individual reported the smoke in only 38 percent of the groups. Of the 24 persons involved in the eight naive-subject groups, only one reported the smoke within the first 4 minutes of the experiment. In the single-subject situation, 55 percent of the subjects reported the smoke within 2 min and 75 percent in 4 min. The study reported that reaction to smoke was apparently delayed by the presence of other persons, with the median being 5 s for single subjects but 20 s in both the group conditions. These results undoubtedly reflect constraints that people accept regarding
The other nine stayed in the waiting room as it filled up with smoke, doggedly working on their questionnaires, and waving the fumes away from their faces. They coughed, rubbed their eyes, and opened the window but did not report the smoke.29 It has been suggested that while trying to interpret the emergency potential of ambiguous threat cues, an individual is influenced by the reactions of others. Should these others remain passive and seem to interpret the situation as a nonemergency, the individual tends to modify his or her own interpretation according to this inhibiting social influence.29 This behavioral experiment may help explain the reported tendency of people to disregard threat cues or interpret them as nonthreatening when they occur in places where there are many other people, such as restaurants, movie theaters, or department stores. These results may help explain the calls received by fire departments minutes or even hours after an incident is first detected. In the report of the Arundel Park fire,5 several of the sample population indicated that when they entered the hall after observing the fire from outside the building, they warned their friends and suggested they leave but were laughed at, their warnings apparently disregarded. Social inhibition, diffusion of responsibility, and mimicking have been indicated to be primarily responsible for the inhibition of adaptive and assistance behavior in emergencies. The inhibition of behavior in the early stages of a fire, when the cues are relatively ambiguous, may lead to nonadaptive flight behavior because the time available for evacuation has been expended. It is sometimes difficult to get the occupants of a building to evacuate because of social inhibition and diffused responsibility. The tendency to adopt cues for behavior from others is well documented in fires in restaurants, other public assembly occupancies, and hotels.
DECISION PROCESSES OF THE INDIVIDUAL Seven processes have been identified that an individual may use in trying to structure and evaluate situational threat cues.30 Six of these—recognition, validation, definition, evaluation, commitment, and reassessment—are presented in Figure 4.1.1. The seventh, a lattice involving the failure of successive defensives and a hierarchy of defenses, is not relevant to the decision process in fires.
Recognition Recognition occurs when the individual perceives cues that indicate a threatening fire. The cues may be very ambiguous and not clearly indicative of a severe fire. However, the clues usually are continuous, with an increasing intensity due to the dynamics of flame, heat, and smoke production. It was also reported that an individual is predisposed to recognize threat cues in terms of the most probable occurrences, usually in relation to past experience and in the form of an optimistic wish. The optimistic wish aspect
4–6 SECTION 4 ■ Human Behavior in Fire Emergencies
Validation
Recognition
Definition
deprivation of the threat, and the time context. The individual’s stress and anxiety appear to be most severe before he or she has determined the situation’s structure or meaning, although it is apparent that the situation requires interpretation. The individual’s role (described at the end of the Evaluation section) is one of the critical factors in the situation, relative to the personalization of the threat and the physical environment. The most important physical aspects in the definition process are the generation, intensity, and propagation of the smoke, flames, and thermal exposure.
Individual
Evaluation Reassessment
Evaluation
Commitment
FIGURE 4.1.1
Decision Processes of the Individual in a Fire
of the response may be a direct result of the individual’s concept of his or her personal invulnerability.30 Threat recognition is important for fire protection. The adaptive action involved in the initiation of the fire alarm, the evacuation of building occupants, and the suppression of the fire may be delayed or postponed if individuals do not perceive the cues as indicative of a fire. The ambiguous nature of threat cues indicates that individuals who do not have specialized fire prevention or fire protection education and experience recognize only large amounts of smoke or sudden and threatening flames as indicative of a threatening fire.
Validation Validation consists of attempts by an individual to determine the seriousness of the threat cues, usually by reassurance of the mild nature of the threat and its improbability. When the cues are significantly ambiguous, however, the individual tries to obtain additional information. In other words, the person is aware that something is happening but is not sure exactly what. This process of validation may be conducted by questioning other nearby individuals. Studies of the explosion of a fireworks plant in Houston, Texas, found that of the 139 persons interviewed, 85 individuals (or 61 percent of the population) obtained information on the source and nature of the explosion and smoke from someone they saw or from someone who telephoned and told them.31 The presence of others during the threat recognition and validation process was found possibly to inhibit or influence the behavioral responses of the individual.
Definition Definition essentially consists of an attempt by the individual to relate the information concerning the threat to some of the variables, such as the qualitative nature of the threat, the magnitude of
Evaluation may be described as the cognitive and psychological activities required for the individual to respond to the threat. The individual’s ability to reduce his or her stress and anxiety levels becomes the essential psychological factor. In the threat situation created by a fire, evaluation is the process involved in the decision to react by fight or flight. With evaluation, an initial decision to make an overt behavioral response is completed. Because of the time context of the generation and propagation of the fire, the mental processes up to and including the process of evaluation may have to be accomplished within several seconds. Sime32 emphasized the importance of the individual’s perception of the time available for evacuation or to reach a refuge area as being the individual’s estimation of the fire threat. He indicates that the “perceived time available” depends upon the information and communication provided to the occupants concerning the fire’s location and development. Variables of the physical environment are an important source of information for individuals involved in formulating adaptation, escape, or defense plans. Additional determinants may be the location of the individual relative to the egress routes, other people, the untenable effects of the fire, and the behavior of other individuals. During evaluation, an individual may decide to leave the building—flight—or to use a portable fire extinguisher—fight. During this time, he or she is particularly susceptible to the actions and communications of others. Thus, the individual may mimic the behavioral reactions of observed individuals, resulting in mass adaptive or nonadaptive behavior rather than selective, individualized behavior. The following situation at an auto sales and service agency in 1971 demonstrates what may have been an instance of mimicked behavior becoming normative group behavior:33 About 10 pm, the fire department received an alarm from a street fire alarm box. When fire fighters arrived, the 150 by 200 ft (46 by 61 m), one- and two-story building of wood frame and hollow block construction was well alight and nearly 300 spectators were watching the fire in 10°F (–12°C) weather. An investigation revealed the fire had been burning for about 90 minutes before the fire department was notified. In studies of nonadaptive group behavior, the concept that this mode of behavior depends directly on the individual’s perception of the reward structure of a situation has been developed.34 People in a building who are confronted with a fire would probably initially perceive a reward structure that would encour-
CHAPTER 1
age cooperative and adaptive behavior; in such cases, everyone should be able to reach and proceed through the available exits. However, the reward structure perceived by some individuals more remote from the egress routes could result in competitive behavior. Such individuals would perceive that cooperative behavior would make it impossible for them to reach an exit in time to escape the fire. Once the pattern of competitive behavior is initiated, the behavior pattern of the group may become one of intense individual competition for the escape routes. In the evaluation process, an individual’s cultural influences and assumption of a particular role may be very important in formulating defense or escape plans. It is believed that an individual playing a familiar role that is also suitable for the threat situation experiences less anxiety and responds with more adaptive behavior than an individual in an unfamiliar role confronted with an unfamiliar threat. Jones and Hewitt35 conducted detailed interviews with 40 occupants of a 27-story office building who had evacuated the building during a fire. It should be noted the fire occurred at 9:00 p.m. when the fire management plan was not in effect due to the building’s reduced occupancy. In this situation it appeared that leadership and evacuation group formation were related to the occupants’ fire training and their normal roles. The investigators found that relationship of the occupancy roles and normal or emergent leadership of occupants were critical factors in successful evacuation, with the following variables: The social and organizational characteristics of the occupancy, including what a person knows (or believes) of the situation, whether the person is alone or part of a group, the normal roles that people hold within the occupancy, and the organizational structure or framework. One factor that appears to be related to the chosen evacuation strategy of an occupant is the presence of leadership and the form which that leadership takes. Horiuchi, Murozaki, and Hokugo36 reported on a questionnaire study of 458 occupants of an eight-story office building involved in a fire incident. The researchers found significant differences between occupants who were familiar with the building and occupants attending training sessions who were unfamiliar with the building, relative to their actions, selection of evacuation routes, and effectiveness in exiting. The regular occupants of the building engaged in fire-fighting actions and alerted or assisted other occupants, while occupants unfamiliar with the building primarily engaged in evacuation.
Commitment Commitment consists of the mechanisms the individual uses to initiate the behavioral activity required to fulfill the defense plans conceptualized in the evaluation process. This overt response to the threat of fire results in success or failure. If the response fails, the individual immediately becomes involved in the next process of reassessment and commitment. If the action succeeds, the anxiety and stress aspects of the situation are reduced and relieved, although the severity of the general fire situation may have increased.
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Human Behavior and Fire
4–7
Reassessment Reassessment and overcommitment are the most stressful of the individual’s processes because previous attempts to adjust to the threat have failed. Thus, more intense effort goes into the behavioral reactions and the individual tends to become less selective in the choice of response. Encountering successive failures, the individual becomes more frustrated. The possibility of injury and risk increases with a greater activity level and with less probability of success, as was demonstrated in the Arundel Park fire. There, the number of those who selected windows as a means of escape increased as people became involved in their second escape attempts.5 In analyzing the behavior of an individual involved in the processes of recognition, validation, definition, evaluation, commitment, and reassessment, it must be remembered that these are dynamic processes. They are constantly being modified in relation to their magnitude, velocity, and intensity. A person’s usual psychological and physiological activities will probably be below normal during the recognition process, when he or she is concentrating on perceiving the threat cues. During the process of validation and definition of the threat, adjacent members of the threatened population communicate overtly. The period of hyperactivity appears to occur initially during the process of commitment and to become intense during the process of reassessment and recommitment. Stress increases with each successive stage, as the primary motivation of the behavioral activity is stress reduction. Appearance, proximity, propagation, time, and toxic gases of the fire threat also tend to predispose the individual to a higher level of behavioral activity, again depending upon the individual’s perception of these threat variables. During the process of reassessment and recommitment, the individual’s activity level may assume the hyperactive mode of frantic activity, or it may be expressed in the catastrophic state of complete physical immobility with a loss of ability to communicate coherently. These individuals appear to perceive the threat as above their level of adaptability. The stress is too severe, and they give up completely. Thus, they cease to make any attempt at an adaptive behavior and retreat totally from the situation through the mechanism of psychological withdrawal. These behavioral dynamics are presented in Figure 4.1.2. A conceptual model of the individual’s decision processes similar to some concepts previously discussed has been developed. Instead of the six processes described, only three have been used: (1) recognition/interpretation; (2) behavior, with either action or inaction; and (3) the outcome of the action, which involves the evaluation and long-term effect of the behavior.7 Behavior evaluation is similar to the process of reassessing the decision model. Both the recognition/interpretation concept and the behavior concept involve factors critical to the decision processes. Experience and immediate circumstances have an impact on the recognition/interpretation concept. It has been emphasized that individuals in a fire may not know right away that they are involved in a fire and may not know where, in relation to their location, the fire is developing or where the egress routes are. A concept of a heuristic (i.e., experimental or provisional) systems model is presented in Figure 4.1.3.
4–8 SECTION 4 ■ Human Behavior in Fire Emergencies
Threat Low Probability Mild Nature Deprivation Property Indefinite Time Assured Escape
First Loop High Severe Life Immediate Doubtful High Reassessment
ity tiv c la ra io Commitment v ha Evaluation Be Definition
PS Ambiguous information
Second Loop
Stress
FIGURE 4.1.2 Individual
Fear
Stress cern -con self
Ambiguous irrelevant information
Stress rt effo
Ambiguous irrelevant information
Input 2 Past experience
Recognition interpretation
Behavior (action/no action)
Input 3 Current state factors
Input 2 Social factors
PS Worry
Extreme Fifth Loop
Input 1 Environmental factors
limite d time dang er
Ambiguous information
Dynamics of Behavioral Activity of the
Input 1 Factors immediately arising
Uncertainty Stress PS
Third Loop
Validation Recognition
Mild
Control low stress
PS
Ambiguous information
Fourth Loop Low
avoid ance
PS
fatigue
inef ficie ncy
Confusion
Stress
PS = Processing system
FIGURE 4.1.4
Outcome (evaluation longterm effect)
FIGURE 4.1.3 Preliminary Heuristic Systems Model of Behavior in Fires
The conceptual model just described has been modified into one involving three phases: (1) detection of cues, (2) definition of the situation, and (3) coping behavior. In addition, tentative determinants of the behavior have been developed, which increase the probability of detection and of fire suppression.37 Proulx38 developed a stress model to demonstrate various levels of stress generation within an individual involved in the decision process during a fire incident. Figure 4.1.4 illustrates this stress model, which should be compared with the behavioral activity dynamics of the individual in a fire incident presented in Figure 4.1.2. The left side of Figure 4.1.4 indicates the information the individual must process; the right side indicates the emotional state that results. Proulx describes the five loops in the stress model as follows: 1. The first loop starts with the perception of ambiguous information. This information is decoded in the processing system (PS in the figure) for interpretation. Given that the
2.
3.
4.
5.
Stress Model of People in a Fire Situation
available information may not allow for a straightforward assessment of the situation, people will at first minimize or deny the situation. These defensive strategies of avoidance lead to an absence of reaction. Although individuals may vary considerably in their appraisal of the same event, the repeated perception of ambiguous information will eventually generate a state of uncertainty, which will then induce a feeling of stress. Some time can be spent going repeatedly through the second loop. The third loop is related to the interpretation of the situation as an emergency. The thicker line around the processing system expresses the pressure of the overload of information with which the person tries to deal at once. The fear felt by the person is a manifestation of a specific appraisal of the environment. The fourth loop relates to the person’s processing of irrelevant information and is represented by the very thick line around the processing system. This irrelevant information creates worry and more stress. The irrelevant information, created by the person, is caused by concern for his or her own performance in coping with the situation. Perceived feelings of arousal and fear, uncertainties regarding how to proceed with the problem, difficulties in interpreting what exactly is going on, and self-estimation of the efficiency of already applied actions become additional information to process. The fifth loop supposes an investment of more mental effort to master the problem, momentarily reducing the pressure
CHAPTER 1
on the processing system, but resulting in fatigue and inefficiency manifested in a state of confusion. Proulx indicates that definitive, valid, and directive information provided to occupants of a building in a fire incident most effectively reduces stress and thus tends to minimize response delays created in the first and second loops of the stress model. Chubb39 proposes that the model of the decision processes that fire department officers use in the incident command procedure be adopted as the decision process of building occupants in a fire situation. The decision model was developed from the theory of naturalistic decision making, which evolved from studies of decision makers in complex, time-critical situations. The critical variables of naturalistic decision-making theory appear to share many environmental and psychological features of fire situations involving building occupants. Chubb identified these critical variables: • • • • • • • • •
Ill-defined goals and ill-structured tasks Uncertainty, ambiguity, and missing data Shifting and competing goals Dynamic and continually changing conditions Real-time reactions to changed conditions Time stress High stakes Organizational goals and norms Experienced decision makers
■
Human Behavior and Fire
4–9
BEHAVIOR ACTIONS OF OCCUPANTS A study involving 952 fires and 2193 individuals interviewed by fire department personnel at the scenes of fires in England found that the most frequent responses to fire involved evacuating the building, fighting or containing the fire, and alerting other individuals or the fire brigade.15 An identical broad behavior categorization was found in a similar study, which involved interviewing 584 participants in 335 fire incidents in the United States. Interviews were conducted by fire department personnel, who used a structured questionnaire at the scene of the fires.8 Examination of initial actions to fire is presented in Table 4.1.3. Behavior of the individuals also varied by sex: males were predominately active in fighting the fire, whereas females predominately concerned with alerting and helping others leave the building.
Comparison of the First Actions of British and U.S. Study Populations It should be noted that there were 10 statistically significant differences between the British and U.S. study populations. The U.S. study population was more likely to report five categories of first actions: “notified others,” “got dressed,” “got family,” “left area,” and “entered the building.” A higher percentage of the British population reported as first actions “fought fire,” “went to fire area,” “closed door to fire area,” “pulled fire alarm,” and “turned off appliances.”
Figure 4.1.5 illustrates the Recognition-Primed Decision (RPD) model developed by Klein40 from studies of fire department officers. Chubb correctly indicated this model’s limitation when applied to building occupants: They lack the dynamic abilities—suitable training and previous experience—in building fires that fire officers have. Static abilities relative to building occupants’ mental and physical capabilities also appear to be more varied and limited than those of fire officers’. Chubb indicates that successful recognition-primed decision making depends on occupant training and practice of fire safety plans, with the decision support system in the building consisting of egress signs, emergency lighting, and vocal communication systems.
Comparison of the Behavior of the British and U.S. Study Populations The general classification of the three early actions for the British and the U.S. study populations alike were categorized as “evacuation,” “reentry,” “fire fighting,” “moved through smoke,” and “turned back” behavior. Comparison of the two populations is presented in Table 4.1.4. There was a statistically significant difference between British and U.S. populations in every category except “moved through smoke.”
Summary of the First, Second, and Third Actions of the Occupants
Dynamic Abilities Present Sensory Input
Future RPD
Response
Static Abilities
FIGURE 4.1.5
Recognition-Primed Decision Model
An interesting aspect of the U.S. study involves variation in the first, second, and third actions reported by participants. Table 4.1.5 presents the three actions for the group, totaling 584 individuals. “Notifying others” accounted for 15 percent of the first actions, but by the time of the third actions, it accounted for only 5.8 percent. A similar reduction in frequency can be observed for “searching for the fire.” This activity decreases from 10.1 percent as the first action to 0.8 percent as the third action. The actions “got dressed” and “got family” also reduced in frequency with the progression from the first to the third action as time passed during the fire. In contrast, “left building,” “fought fire,” and “called fire department,” increased in frequency from the first to the third actions. Canter, Breaux and Sime41 developed a decomposition diagram of the acts of 41 persons in 14 domestic fires. This study,
4–10 SECTION 4 ■ Human Behavior in Fire Emergencies
TABLE 4.1.3
Comparison of the First Actions of a British and U.S. Study Population
Action
British (percent, P1)
U.S. (percent, P2)
P1 – P2
SEPa 1 – P2
CR b
Notified others Searched for fire Called fire department Got dressed Left building Got family Fought fire Left area Nothing Had others call fire department Got personal property Went to fire area Removed fuel Entered building Tried to exit Closed door to fire area Pulled fire alarm Turned off appliances
8.1 12.2 10.1 2.2 8.0 5.4 14.9 1.8 2.1 2.8 1.2 5.6 1.2 0.1 1.6 3.1 2.7 4.1
15.0 10.1 9.0 8.1 7.6 7.6 10.4 4.3 2.7 2.2 2.1 2.1 1.7 1.6 1.6 1.0 0.9 0.9
6.9 2.1 1.1 5.9 0.4 2.2 4.5 2.5 0.6 0.6 0.9 3.5 0.5 1.5 0.0 2.1 1.8 3.2
1.38 1.51 1.40 0.85 1.27 1.11 1.63 0.70 0.69 0.76 0.55 1.01 0.53 0.30 0.00 0.76 0.70 0.85
5.00 c 1.39 0.79 6.94 c 0.31 1.98d 2.76 c 3.57 c 0.87 0.79 1.64 3.47 c 0.94 5.00 c 0.00 2.76 c 2.57d 3.20 c
2193
580
N = 18 a
Standard error. Critical ratio. c Critical ratios significant at or above the 1 percent level of confidence. d Critical ratios significant at or above the 5 percent level of confidence. b
conducted in the United Kingdom, covers home fires, as do the studies by Wood15 and Bryan8 discussed previously. Figure 4.1.6 presents this decomposition diagram and should be compared with Tables 4.1.3 through 4.1.5. The sequence of the first, second, and third actions of the U.S. study population are generally similar to the sequence of actions in the decomposition diagram.
ence of cultural roles is probably indicated explicitly in the concern for other family members—11 percent of the females “got family” as the first action, whereas only 3.4 percent of males engaged in this as an initial action. It should be noted that the second and third prevalent male actions of “searched for fire” and “got extinguishers” were equated to the female actions of “called fire department” and “got family.”8 This behavior has also been observed in healthcare and educational fires.
Summary of the First Actions of the Occupants, According to Sex
Behavior in Hotel Fires
Differences between the first actions of the participants according to their sex have been examined. Table 4.1.6 presents the reported initial actions of the U.S. study population relative to the sex of the participants. Statistical differences between males and females are significant in the categories “searched for fire,” “called fire department,” “got family,” and “got extinguishers.” Male participants more frequently reported investigation and fire-fighting activities. For example, 14.9 percent of the males “searched for fire,” as opposed to 6.3 percent of the females; 6.9 percent of the males “got extinguishers,” as opposed to 2.8 percent of the females. Females more frequently reported warning and evacuation activities. For example, 11.4 percent of the females “called fire department” as their initial action, as opposed to 6.1 percent of the male participants. In relation to evacuation behavior, 10.4 percent of the females reported “left building” as the first action, contrasted with 4.2 percent of the male participants. The influ-
Fire protection of high-rise buildings and their occupants was tested severely by the MGM Grand Hotel fire in Clark County, Nevada, on November 21, 1980,42 and by the subsequent fire at the Las Vegas Hilton Hotel on February 10, 1981.43 Both these hotel fires resulted in injuries and fatalities among guests. NFPA conducted an intensive questionnaire study of the guests registered in the MGM Grand Hotel on the evening of November 20–21, 1980.44 The MGM Grand Hotel fire was discovered by a hotel employee who entered the unoccupied deli-restaurant located on the casino level of the hotel at approximately 7:10 a.m. on November 21, 1980. As instructed, the hotel telephone operator immediately notified the Clark County Fire Department at approximately 7:18 a.m. The telephone operators were forced from their switchboard by the smoke immediately after they had made an announcement over the public address system, at approximately 7:20 a.m., to evacuate the casino area. The fire
CHAPTER 1
9.84
2.68
3.13
17 Wait for person to return
8.88 2.12 3
Feel concern
10
22
0
3.58
Fight fire
18
1.34 Go to neighbors or return to house
1.79
0.89
1.72
0.45
1.79 3.90
0.45
15 0.89
19
16
Encounter difficulties in smoke
20 Close door
13
8
0.45
3.58 Warn (phone fire brigade)
Instruct/ reassure
Enter room of fire origin
21
2.24
1.34
0.89
1.34
1.79
Dress
Encounter smoke/fire
4–11
6.26
Misinterpret 4 (ignore) Hear strange 2 4.02 noises 0.89 0.97 5.81 0.55 5 0.97 12 Informed (discuss) 2.46 Investigate
1.84
14
Human Behavior and Fire
Pre-event activity (typically sleeping)
1
0.89
■
Rescue attempt Search for person in smoke
Evasive
6
14.3 4.47
4.47 Leave house
25
Meet fire brigade on arrival Note: Numbers on lines indicate strength of association between two acts linked by arrow.
FIGURE 4.1.6
TABLE 4.1.4
2.24
4.47 24
9.39
End of involvement
*
Decomposition Diagram—Domestic Fires
Comparison of the Behavior of the British and U.S. Study Populations
Behavior
British (percent, P1)
U.S. (percent, P2)
P1 – P2
SEPa 1 – P2
CR b
Evacuation Reentry Fire fighting Moved through smoke Turned back
54.5 43.0 14.7 60.0 26.0
80.0 27.9 22.9 62.7 18.3
25.5 15.1 8.2 2.7 7.7
2.30 2.30 1.74 2.29 2.01
11.09 c 6.51c 4.71c 1.18 3.83c
2193
584
a
Standard error. Critical ratio. c Critical ratios significant at or above the 1 percent level of confidence. b
4–12 SECTION 4 ■ Human Behavior in Fire Emergencies
TABLE 4.1.5 Summary of the First, Second, and Third Actions of the Occupants Action (percent) First
Second
Third
15.0 10.1 9.0 8.1 7.6 7.6 4.6 4.6 4.3 3.1 2.7 2.2
9.6 2.4 14.6 1.8 20.9 5.9 5.7 5.3 2.8 0.0 0.0 4.0
5.8 0.8 12.7 0.3 35.9 1.4 11.5 1.6 1.1 0.0 0.0 4.1
2.1 2.1 1.7 1.6 1.6 1.6 1.2 1.2 1.0 0.9 0.9 0.9 0.0
3.8 1.0 1.0 0.8 2.4 1.8 0.6 1.8 0.2 0.6 0.6 1.4 1.0
0.8 0.0 1.1 1.1 0.5 1.1 1.1 1.9 0.3 0.5 0.3 0.5 3.6
0.2 0.0
0.8 0.0
2.7 1.6
0.2 3.9
0.4 8.0
1.1 6.6
N = 29
100.0
100.0
100.0
Range
0–87
0–106
0–131
Percent of participant population
99.3
86.6
62.9
Notified others Searched for fire Called fire department Got dressed Left building Got family Fought fire Got extinguisher Left area Woke up Nothing Had others call fire department Got personal property Went to fire area Removed fuel Entered building Tried to exit Went to fire alarm Telephoned others Tried to extinguish Closed door to fire area Pulled fire alarm Turned off appliances Checked on pets Awaited fire department arrival Went to balcony Removed by fire department Opened doors/windows Other
quickly reached flashover in the deli, immediately spread from east to west through the main casino area, and extended out the west portico doors on the casino level immediately following the arrival of the first fire department personnel. An addition to the hotel was being constructed adjacent to the west end of the building, and construction workers helped warn and evacuate guests and assisted in fire fighting. The heat and smoke rapidly extended from the casino area through the seismic joints, elevator shafts, and stairways throughout the 21 residential floors of the hotel. The heat was intense enough on the 26th floor, a top floor, to activate automatic sprinklers in the lobby adjacent to the elevator shafts.
Due to the rapid early evacuation of the telephone staff, guests were not alerted by the hotel public address system or the local fire alarm system. Guests warned early in the fire, and those already awake and dressed, were able to escape before the smoke became untenable on the upper floors. Guests alerted later remained in their rooms or moved to other rooms, usually with other occupants. The fire itself did not extend above the casino level, except in a rather minor nature, into two guest rooms on the fifth floor. The fire resulted in 85 fatalities and injured 778 guests and 7 hotel employees. Seventy-nine body locations were documented: 18 on the casino level, 25 in guest rooms, 22 in corridors and lobbies, 9 in stairways, and 5 in elevators. The victims were found on the casino level and on the 16th and floors above, with the majority between the 20th and the 25th floors. Figure 4.1.7 is a diagram of the guest floor of the MGM Grand Hotel that was used in the engineering study conducted by NFPA.42 Of the 9 victims found in the stairways, 2 were in stairway 1 at the extreme south end of the south wing on the 17th floor; 6 were between the 20th and 23rd floor in stairway 2 at the central end of the south wing; and 1 was found at the groundfloor level of stairway 4 at the extreme west end of the west wing. There are various estimates of the number of guests and fire department personnel who suffered injuries at the MGM Grand Hotel fire. Morris indicated that 619 people were taken to hospitals, and another 150 were treated at the Las Vegas Convention Center, where the survivors were transported from the hotel.45 The MGM Grand Hotel tragedy was a unique fire, especially from two aspects: (1) it was the second most serious hotel fire in U.S. history, surpassed only by the Winecoff Hotel fire in Atlanta, Georgia, on December 7, 1946, which killed 119; and (2) it was the first high-rise fire in the United States in which helicopters evacuated large numbers of people. About 300 were evacuated in this manner; the fire department rescued approximately 900 people by other means. Shortly after the MGM Grand Hotel fire, NFPA prepared a four-page, 28-item questionnaire that included the floor plan of the guest rooms. A total of 1960 questionnaires were mailed, and 554, or approximately 28 percent, of these were returned. Of the respondents, 455 indicated a willingness to be interviewed. The age of the questionnaire population ranged from 20 to 84 years, with an average age of 45. The population consisted of 331 males and 222 females; one respondent did not indicate a sexual classification. One-hundred and three guests indicated that they were alone at the time they became aware of the fire in the hotel. The presence of other people, especially if they belong to the individual’s primary group, appears to be a determinant of the response of many individuals in residential fires.8 The initial five actions reported by the 554 guests, as elicited from the NFPA questionnaire study, are presented in Table 4.1.7. Notice that the five most frequent first actions were “dressed,” “opened door,” “notified roommates,” “dressed partially,” and “looked out window.” Guests reporting these actions were predominately engaged in determining the degree of threat to themselves. Only 7.9 percent of the study population began or tried to begin their own evacuation with such actions as “attempted to exit,” “went to exit,” and “left room.” A total of 16 in-
CHAPTER 1
TABLE 4.1.6
■
Human Behavior and Fire
4–13
First Actions of the Occupants, According to Sex of Occupant
First Action
Male (percent, P1)
Female (percent, P2)
P1 – P2
SEPa 1 – P2
CR b
Notified others Searched for fire Called fire department Got dressed Left building Got family Fought fire Got extinguisher Left area Woke up Nothing Had others call fire department Got personal property Went to fire area Removed fuel Entered building Tried to exit Went to fire alarm Telephoned others Tried to extinguish Closed door to fire area Pulled fire alarm Turned off appliances Checked on pets Other
16.3 14.9 6.1 5.8 4.2 3.4 5.8 6.9 4.6 3.8 2.7 3.4 1.5 1.9 1.1 2.3 1.5 1.1 0.8 1.9 0.8 1.1 0.8 0.8 6.5
13.8 6.3 11.4 10.1 10.4 11.0 3.8 2.8 4.1 2.5 2.8 1.3 2.5 2.2 2.2 0.09 1.6 0.19 1.6 0.6 1.3 0.6 0.9 0.9 2.5
2.5 8.6 5.3 4.3 6.2 7.6 2.0 4.1 0.5 1.3 0.1 2.1 1.0 0.3 1.1 1.4 0.1 0.8 0.8 1.3 0.5 0.5 0.1 0.1 4.0
2.98 2.51 2.41 2.30 2.22 2.22 1.77 1.77 1.70 1.45 1.38 1.23 1.17 1.20 1.08 1.02 1.05 1.02 0.91 0.91 0.87 0.75 0.79 0.79 1.70
0.83 3.43 c 2.19 d 1.87 2.79 c 3.42 c 1.13 2.31d 0.29 0.90 0.72 1.71 0.85 0.25 1.02 1.37 0.09 0.78 0.87 1.43 0.57 0.66 0.12 0.12 2.35d
262
318
N = 25 a
Standard error. Critical ratio. c Critical ratios significant at or above the 1 percent level of confidence. d Critical ratios significant at or above the 5 percent level of confidence. b
dividuals, or 2.9 percent of the population, initiated actions to improve the room as an area of refuge: “wet towels for face” and “put towels around door.” The actions of the guests could be classified, in general, as evacuation actions or refuge processes. Actions relating to evacuation behavior appeared to be initiated early if the egress passages were clear of smoke or if the smoke was not perceived as personally threatening. If the smoke was heavy, however, the guests apparently decided to stay in their rooms or other rooms and to initiate actions to prevent smoke migration into the rooms of refuge. Further examination of Table 4.1.7 shows that the five actions most frequently reported by guests as their second actions were “opened door,” “dressed,” “went to exit,” “dressed partially,” and “secured valuables.” Approximately 19 percent of the study population reported dressing before initiating evacuation or refuge procedures. The third actions of guests in the study population generally progressed to evacuation, attempted evacuation, and notification. Approximately 25 percent of this population was involved in evacuation actions, and approximately 10 percent attempted evacuations, as identified by the third actions of “attempted to
exit” and “returned to room.” The alerting and notification actions are identified as “notified occupants” and “notified other room.” The fourth actions of the guests in the study population indicate a progression to evacuation, attempted evacuation, and self-protection or room refuge actions. The most frequently reported fourth action was “went to exit”; approximately 16 percent of the population indicated that they did this. However, when one combines the guests involved in this action with those who “went down stairs,” “went to another exit,” “left hotel,” and “left room,” a total of 151 guests, or approximately 30 percent of the fourth action guest population, were involved in evacuation actions. The process of forming convergence clusters was noted in this hotel fire. This action involved individuals clustering together in rooms they considered areas of refuge with individuals they usually characterized as strangers before the fire. The fourth actions of “went to other room” and “went to other room/others” are explicit indicators of the formation of convergence clusters.46 The fifth actions of the guests were primarily for selfprotection and included improving the room as an area of refuge
4–14 SECTION 4 ■ Human Behavior in Fire Emergencies
Stairway W2
MGM Grand Hotel — Longview Sketch
1
1 2
1
Stairway W1
1
Stairway S2
1 5 7
1 1 1 1
3
4
1
2 1
4
6 1
1
7 6
1
Stairway S1 Eighty percent (49 victims) of the 61* high-rise tower fatalities in this zone. Stairway E1
1
*Not all victim locations were documented.
Stairway E2
FIGURE 4.1.7 Grand Hotel
Residential Floor Diagram of the MGM
and evacuation behavior. The evacuation actions were “went downstairs,” “left to exit,” and “went to another exit.” Involved in these evacuation actions were 175 individuals, or approximately 40 percent of the study population. Those unable to evacuate, and thus vitally concerned with refuge procedures, reported the fifth actions of “went to other room/others,” “wet towels for face,” “put towels around door,” “broke window,” “returned to room,” “went to other room,” “offered refuge in room,” and “went to balcony.” Approximately 40 percent of the fifthaction study population was involved in refuge procedures and self-protection actions.
Convergence Clusters The phenomenon of convergence cluster formation was first noticed in a study of occupant behavior in a high-rise apartment building fire in 1979.47 The clusters appear to involve occupants
of the building who converged into specific rooms they perceived as areas of refuge. In the MGM Grand Hotel fire, guests tended to select rooms on the north side of the east and west wings and rooms on the east side of the south wing. In addition, guests reported that people had converged in the rooms with balconies and doors leading out to the balconies because of the ventilation, reduced smoke, improved visibility, and communication that the balconies offered. Guests who reported this behavior either estimated the number of persons in the room or connecting rooms, or they indicated only that “others” or “other persons” were present. Table 4.1.8 lists the rooms identified by guests as areas of refuge for numerous persons other than the original occupants. This table also presents estimates of the length of time that the clusters were maintained in the rooms—usually until the individuals were evacuated, or until the occupants were notified by fire or rescue personnel that evacuation was possible. Numbers in the two right-hand columns indicate the total number of persons in the clusters for the total number of rooms identified on the floor. The smallest number of people identified as a cluster was 3, and the largest was 35. The greatest number of rooms used by convergence clusters and the largest population participating in convergence clusters were located on the 17th floor of the hotel. No convergence clusters were identified by guests on the 6th, 21st, or 26th floors. The clusters appear to serve as an anxiety- and tension-reducing mechanisms for individuals confronted with a threatening situation. The action of “offered refuge in room,” previously identified in the discussion of the fifth actions, is a positive indication of the occurrence of a convergence cluster. In addition to the detailed human behavior study of the MGM Grand Hotel fire,48 NFPA conducted a questionnaire study of guests’ behavior in the Westchase Hilton Hotel fire in Houston, Texas, on March 6, 1982, in which 12 people died.49 Figure 4.1.8 presents the decomposition diagram for eight multiple occupancy fires covering the actions of 96 persons.41 These multiple occupancy fires in the United Kingdom involved hotel occupancies. A comparison of Figure 4.1.8 with Table 4.1.7 shows similarities between the five actions of the guests in the MGM Grand Hotel fire and the occupants’ behavior in the British study. The classic types of nonadaptive behavior in a fire ignore adaptive actions that might facilitate the evacuation of others or limit the propagation of smoke, heat, or flame. Nonadaptive behavior ranges from the single act of leaving a room of fire origin without closing the door, thus allowing the fire to spread throughout the structure and endanger the lives of all the occupants, to the more generalized behavior of fleeing from a fire without regard for others and perhaps injuring others in what is often termed “panic.” Nonadaptive behavior may be an omission, such as forgetting to close a door, or it may involve an action that, although well meaning, results in negative consequences. When the results of behavior are extinguishing the fire and eliminating the threat, the behavior may be said to be adaptive. However, the same behavior may be ineffective because the fire was more severe than was first perceived. In such cases, the time spent try-
CHAPTER 1
TABLE 4.1.7
■
Human Behavior and Fire
4–15
First Five Reported Actions of Guests in the MGM Grand Hotel Fire Action (percent of population) First
Second
Third
Fourth
Fifth
Dressed Opened door Notified roommates Dressed partially Looked out of window Got out of bed Left room Attempted to phone Went to exit Put towels around door Felt door for heat Wet towels for face Got out of bath Attempted to exit Secured valuables Notified other rooms Returned to room Went down stairs Left hotel Notified occupants Went to another exit Went to other room Went to other room/others Looked for exit Broke window Offered refuge in room Went upstairs to roof Went to balcony Other
16.8 15.9 11.6 10.1 9.7 4.5 4.3 3.4 2.5 1.6 1.3 1.3 1.1 1.1 — — — — — — — — — — — — — — 14.8
11.6 11.7 3.0 7.5 5.7 — 5.4 3.6 10.3 2.5 2.3 3.7 — 3.0 6.8 3.4 — — — — — — — — — — — — 19.5
6.5 6.7 — 4.5 — — 8.1 — 9.5 3.0 — 6.3 — 5.8 4.3 2.2 3.9 3.9 3.4 3.0 — — — — — — — — 28.9
— 3.4 — — — — 2.4 2.8 16.1 6.8 — 4.6 — 4.3 — — 8.4 5.4 2.6 — 3.6 3.6 3.4 2.4 — — — — 30.2
— — — — — — 2.0 — 6.7 7.7 — 7.9 — — — — 4.1 21.3 2.0 — 4.8 3.6 8.7 — 4.3 1.8 2.9 1.8 20.1
Total (percent) No. of guests
100.0 554
99.1 549
96.9 537
90.6 502
79.6 441
ing to extinguish it might have been used more effectively to warn others and to notify the fire department. Thus, some behavior that appears to be nonadaptive really is behavior that would have seemed most adaptive if it had been successful. Injuries people suffer in relation to a fire may be cues to their nonadaptive or risk behavior.
Panic Behavior One concept always discussed following a fire in which multiple fatalities occur, such as the Beverly Hills Supper Club fire,50 is panic behavior. One classic definition of panic is A sudden and excessive feeling of alarm or fear, usually affecting a body of persons, originating in some real or supposed danger, vaguely apprehended, and leading to extravagant and injudicious efforts to secure safety.51 According to this definition, panic is a flight or fleeing type of behavior that involves extravagant and injudicious effort and
is likely not to be limited to a single individual, but to be transmitted to and adopted by a group of people. From simulation experiments, a panic-type behavior reaction has been defined in the following manner: “A fear-induced flight behavior which is nonrational, nonadaptive, and nonsocial, which serves to reduce the escape possibilities of the group as a whole.”52 The concept of panic is often used to explain the occurrence of multiple fatalities in fires even when there is no physical, social, or psychological evidence showing that competitive, injudicious flight behavior actually took place. The media and public officials often label various types of fire behavior as panic. The evidence accumulated from interviews with participants in the Beverly Hills Supper Club fire, and questionnaires completed by occupants, provided no evidence of the classic group-type of panic behavior with competitive flight for the exits.53 It has been said that panic as a concept is primarily a description rather than an explanation of behavior. The concept is used to support the introduction of requirements in fire and building laws or ordinances to provide for the fire safety of
4–16 SECTION 4 ■ Human Behavior in Fire Emergencies
TABLE 4.1.8
Summary of Rooms, Time Duration, and Number of Guests Reported in Convergence Clusters Persons
Total Range a
Floor
Room Number(s)
Time (hr)
Number
Percent
7 8 9 10 11 12 14 15 16 17 18 19 20 22 23 24 25
731 827, 840 927 1009A, 1025, 1034, 1060 1129, 1115 1261, 1225, 1233A 1433A, 1461A, 1451, 1416A 1501, 1533A, 1510 1643, 1625, 1633, 1629, 1627, 1615 1725, 1775, 1731, 1719, 1762, 1756, 1733A 1819, 1802, 1850 1929, 1919, 1962A, 1962, 1964, 1925 2027, 2013, 2030 2213, 2221, 2229 2329, 2314, 2342, 2331, 2308, 2340 2446 2512, 2509A
0.6 1.5–1.75 2.5 1–2 1.5–2 2–3 1.5–2 2–3 2–3.5 2–2.5 2–3 2–3.5 2.5–3.5 2–3 2.5–3.25 3.5 3.5
3 14a 5 53 30a 53 8a 38a 35a 84 20 13a 25 13 20a 4
0.7 3.3 1.2 12.7 7.2 12.7 1.9 9.1 8.4 20.1 4.8 3.1 6.0 3.1 4.8 0.9 0
57 1–7
0.6–3.5
17 7–25
a
418 3–84
100.0 0–20.1
Persons indicated only as “others.”
occupants. There also has been shown to be a difference between use of the concept to describe other persons’ behavior in a fire and the use by someone engaged in the behavior to indicate his or her own state of concern and anxiety.54 Just because an individual identifies behavior as associated with panic does not necessarily identify the behavior as the classic panic-type response. The outcome of the behavior, as previously discussed, affects its labeling: the behavior of people in a fire is most likely to be misinterpreted when the outcome of the fire has been unfortunate. The use of the concept of panic must be separated from use of the terms “anxiety” or “fear.” The concept of self-destructive or animalistic panic responses to stimuli, such as the presence of smoke, has not been supported by the research on human behavior in fires. As has been pointed out, it is rare to have panic behavior in which the flight is characterized by competition among the participants, with resultant personal injuries.8,15,16,54–56 In an interview study of 100 participants in single-family dwelling fires, no instances of panic behavior were found; primarily altruistic, helpful behavior was found instead.56 Ramachandran18 in his review of studies of human behavior in fires in the United Kingdom came to this conclusion about nonadaptive behavior: In the stress of a fire, people often act inappropriately and rarely panic or behave irrationally. Such behavior, to a large extent, is due to the fact that information initially available to people regarding the possible existence of a fire and its size and location is often ambiguous or inadequate.18
Reentry Behavior The study of the 1956 Arundel Park fire was the first to document the phenomenon of reentry behavior.5 Some older codes and regulations affecting design of the means of egress appear to have been based on the assumption that pedestrian traffic only moves away from a fire and away from the area or floor of the building involved. However, the Arundel Park study indicated that approximately one-third of the survivors interviewed had reentered the building. Thus, it has become apparent that doors, stairways, and corridors will be often subjected to two-way movement of occupants and others. The occupant who, after leaving the building safely, turns around and reenters is often completely aware of the fire in the building and of the specific portions of the building involved in fire and smoke propagation. Based on interviews with 61 persons, Table 4.1.9 presents the number of participants who reentered Arundel Park during the fire. Note the reasons for the reentry behavior and that those who reentered were predominately male. The Arundel Park fire occurred in an assembly occupancy being used for a church-sponsored oyster roast, a family-type affair. Thus, the primary group cultural role of father or husband was apparently a critical variable in the reentry behavior of the population interviewed and may have resulted in the fact that the reentry participants were mostly male. It can reasonably be argued that reentry behavior is not a nonadaptive behavior, since it is often used to assist or rescue persons remaining or believed to be remaining in the building. This type of behavior is often used by parents whose children are missing during a fire. The
CHAPTER 1
24.70 5.20 2.68
3.09
5 Misinterpret (ignore) 4.02 2.68
0.34 Note persistance of noise 17
3.20
5.36
1.81 Seek information/investigate 6 1.96 .38 1 11.21 See smoke/glow 3 2.96 Encounter . smoke with 4 92 difficulties 0.84
4
Close doors
1.73
8.05
Warn others
4.02 9
1.57
18 2.60
Dress/ gather valuables
6.70
3.57
4.85 1.34 . 1 78 15 Seek/receive 6.37 assistance
24
Leave immediate area
4.92
11.77
23 Out of fire
20 25.49
6.70
Note: Numbers on lines indicate strength of association between two acts linked by arrow.
FIGURE 4.1.8
10
4.92
11
14
Duty related (cleaning up, checklists, postfire actions)
4.02
1.78
2.23
Cope (open window)
Evasive
7
4.47
Receive instructions
16
Assess fire state
2.91
6.37
3.13
4–17
1.78 Re-enter room
12
Receive warning
Human Behavior and Fire
Pre-event (typically sleeping)
1
Hear strange 2 noises 14.75
■
*
End of involvement
Decomposition Diagram for Multiple Occupancy Fires
behavior is often undertaken in a rational, deliberate, and purposeful manner, without the emotional anxiety and self-doubt usually associated with nonadaptive behavior. However, reentry behavior has been considered nonadaptive, since people going back into a burning building often hinder the efficient and effective evacuation of others through the same means of egress. The reasons elicited from participants in reentry behavior in the Project People study8 in the United States are presented in Table 4.1.10. It would seem that 162 people from the total study population of 584, or 27.9 percent, engaged in reentry behavior. The most popular reason given was to “fight fire,” followed by “obtain personal property,” “check on fire,” “notify others,” “assist fire department,” and “retrieve pets.” These six reasons accounted for approximately 73 percent of this reentry behavior.
Table 4.1.11 compares the reentry behavior of the British and U.S. study populations. Note that all the reasons were significantly different, with the exception of the item “save personal effects.” The reentry reasons of the U.S. population were predominantly “save personal effects,” “call fire department,” “rescue pets,” “notify others,” “assist fire department,” and “assist evacuation.” The British population’s reentry reasons were predominantly “fight fire,” “observe fire,” “shut doors,” “await fire department,” and “fire not severe.”
Occupant Fire-Fighting Behavior Occupants who engaged in fire fighting behavior were predominately male, and this behavior now appears to be a culturally
4–18 SECTION 4 ■ Human Behavior in Fire Emergencies
TABLE 4.1.9 Behavior of Occupants Who Reentered in the Arundel Park Fire, Relative to Sex and Reentry Reasons Reentered Reentered and Left by and Left by Same Exit Different Exit
Sex M M M M M M M&1F
1 1 3 1 2 2
1
3 2 5
21 M & 1 F 10
Stated Reason for Reentrance Turn off kitchen stoves Tell people to leave To help Assist people Find wife Assist fire fighting No stated reason
12
determined and expected aspect of the male role. However, it should be noted that, in the Project People8 study of 335 U.S. fires, approximately 23 percent of the study population of 584 individuals was involved in occupant fire fighting behavior. Of these, 37.3 percent were female. Of the 134 individuals who participated in fire fighting behavior, 50 were female and 84 male. They ranged from a 7-year-old girl to an 80-year-old man. Distribution of the participants by sex and age is presented in Table 4.1.12. Most of those involved in fire fighting behavior, or approximately 30 percent of the fire fighting behavior population, were between 28 and 37 years old. A higher proportion of males than females reported “got extinguisher” and “fought fire,” and this difference is statistically significant (Table 4.1.13). Approximately 15 percent of the male population reacted by obtaining extinguishers. Similarly, approximately 26 percent of the male population fought the fire when they became aware of it, as contrasted with approximately 10 percent of the female participants. A higher proportion of
TABLE 4.1.11
TABLE 4.1.10
Reasons for Reentry of Occupants Participants
Reason
Number
Percent
Fight fire Obtain personal property Check on fire Notify others Assist fire department Retrieve pets Call fire department Assist evacuation To be taken to hospital Turn power back on Rescue from balcony Help injured family member Turned off gas Open windows Close door No apparent danger Entered nondanger area Job responsibility Due to fire Told to by others Not reported
36 28 18 13 12 12 9 4 3 2 1 1 1 1 1 1 1 1 1 1 16
22.2 17.2 11.0 8.0 7.4 7.4 5.5 2.5 1.8 1.2 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 9.8
163
100.0
N = 21 Range = 1–36
Percent of participant population = 27.9
women notified the fire department: 33 percent of the females, compared with 26 percent of the males, reacted to the fire by notifying the fire department, as indicated in Table 4.1.13, but this difference is not statistically significant.
Comparison of Reasons for Reentry Behavior of British and U.S. Study Populations
Reason
British (percent, P1)
U.S. (percent, P2)
P1 – P2
SEPa 1 – P2
CR b
Fight fire Observe fire Save personal effects Shut doors Await fire department Call fire department Rescue pets Fire not severe Notify others Assist fire department Assist evacuation
36.0 19.0 13.0 10.0 9.0 2.0 2.0 5.0 0.0 0.0 0.0
22.2 11.0 17.2 0.6 0.0 5.5 7.4 1.2 8.0 7.4 2.5
13.8 8.0 4.2 9.4 9.0 3.5 5.4 3.8 8.0 7.4 2.5
4.02 3.25 2.91 2.38 2.26 1.32 1.40 1.74 0.92 0.80 0.54
3.43 c 2.46 d 1.44 3.95 c 3.98 c 2.65 c 3.86 c 2.18 d 8.69 c 8.41 c 4.63 c
943
163
N = 11 a
Standard error. Critical ratio. c Critical ratios significant at or above the 1 percent level of confidence. d Critical ratios significant at or above the 5 percent level of confidence. b
CHAPTER 1
Participants Percent
84 50
62.7 37.3
Total
134
100.0
Age 7–17 18–27 28–37 38–47 48–57 58–67 68–80 Unknown
8 31 41 27 16 2 3 6
5.9 23.1 30.6 20.1 11.9 1.5 2.2 4.7
Total
134
100.0
Sex Male Female
Percent of participant population = 22.9
Occupant fire-fighting behavior appears most prevalent in occupancies in which the individuals are emotionally and economically involved—that is, in their homes or where such behavior is an assigned role as a result of training.57 At some time during the fire, 285 individuals engaged in one of the six actions defined as fire-fighting behavior and 252 individuals partici-
TABLE 4.1.13
Human Behavior and Fire
4–19
pated in one of the four actions defined as notifying the fire department. In the study of residential fire incidents in Berkeley, California, 180 persons were involved in extinguishing and firefighting behavior. This study surveyed a population different from that of Project People, since the 1411 Berkeley households, with 208 fires, included fires not reported to the fire department; these accounted for approximately 80 percent of the total 208 fires. The majority of the unreported fires were extinguished by the occupants alone or with the help of neighbors.58 Six percent of these fires self-extinguished, and 52 percent were extinguished by the individual who had started the fire. Thus, it appears that only the fires in the Project People study that were judged uncontrollable by the occupants resulted in notification to the fire department. Similarly, approximately 85 percent of the fires in the National Fire Prevention and Control Administration National Household Survey59 were not reported to the fire department. In the Project People study, 107 of the 584 participants did not leave the building voluntarily after becoming aware of the fire. Their reasons for staying in the building are presented in Table 4.1.14. Fifty-two of the participants, or approximately 49 percent of the population, who stayed in the building reported that they remained because they wished to engage in fire control or fire-fighting activities. The other most frequent reasons were to notify others of the fire or because the occupant’s way out of the building was blocked by smoke.
TABLE 4.1.12 Age and Sex of the Occupants Engaged in Fire-Fighting Behavior
Number
■
Occupants’ Movement Through Smoke Often related to fire-fighting behavior, and a definite component of evacuation behavior in many fires,8,15 is the movement of
Sexual Differences of the Occupants Engaging in Fire Fighting and Notifying the Fire Department Male (percent, P1)
Female (percent, P2)
P1 – P2
SEPa 1 – P2
CR b
Searched for fire Got extinguisher Fought fire Removed fuel Tried to extinguish Went to fire area
17.2 15.6 25.6 3.4 5.3 3.1
9.1 6.0 9.7 3.1 2.8 2.8
8.1 9.6 15.9 0.3 2.5 0.3
4.23 3.95 4.83 2.17 2.49 2.07
1.91 2.43 d 3.29 c 0.14 1.00 0.14
Total
70.2
33.5
36.7
6.01
6.11 c
N
184
101
Called fire department Had others call fire department Went to fire alarm Pulled fire alarm
25.6 9.2 3.8 1.9
33.0 7.5 3.8 1.6
7.4 1.7 0.0 0.3
5.83 3.27 0.00 1.65
1.27 0.52 0.0 0.18
Total
40.5
45.9
5.4
6.31
0.85
N
106
146
Action
a
Standard error. Critical ratio. c Critical ratios significant at or above the 1 percent level of confidence. d Critical ratios significant at or above the 5 percent level of confidence. b
4–20 SECTION 4 ■ Human Behavior in Fire Emergencies
TABLE 4.1.14 Reasons Elicited from Occupants for Not Leaving the Fire Building Participants Reason
Number
Percent
Fight fire Notify others Blocked by smoke Blocked by fire Overcome by smoke Search for fire Needed help Secure property Afraid of fire spread No fire in area Help others Does not know No response to fire department Home Return to area Not reported
52 7 7 5 5 3 2 2 2 1 1 1 1 1 1 16
48.7 6.5 6.5 4.7 4.7 2.8 1.9 1.9 1.9 0.9 0.9 0.9 0.9 0.9 0.9 15.0
107
100.0
N = 15 Range = 1–52
Percent of participant population = 15.6
occupants through smoke. The principal variables influencing an occupant’s decision to move through smoke appear to be recognition of the location of the exit and thus of the travel distance, the appearance of the smoke, the smoke density, and the presence or absence of heat.48,49 To achieve evacuation, occupants have moved through smoke, even for extended distances under conditions of extremely limited visibility at personal risk, and sometimes have been forced to turn back without completing the evacuation.8,15,48,49 Jin and Yamada60 reported on a study involving 31 subjects (14 males and 17 females) traveling a maximum distance of 10.5 m in a corridor while exposed to smoke from smoldering cedar crib chips. The smoke extinction coefficient varied from 0.1 to 1.2 (m–1). Subjects were also exposed to increasing heat from radiant heaters at the end of the corridor, where the mean temperature was 82°C. At five points in the corridor the subjects stopped and were asked mental arithmetic questions. Both walking speed in the corridor and mental arithmetic capability decreased as smoke density and radiant heat exposure increased. Proulx and Fahy24 in their questionnaire study of 382 employees in the1993 World Trade Center explosion and fire found that 94 percent of the respondents in Tower 1 and 70 percent of the respondents in Tower 2 moved through smoke. In addition, the study reported that approximately 75 percent of these individuals turned back during their evacuation because of smoke, crowding, locked doors, breathing difficulty, fear, and poor visibility. It was also reported that some occupants continued to move through smoke, even when they perceived the smoke to be worsening and believed that they may have been moving toward the fire.
Table 4.1.15 compares the distance moved through smoke for the 1316 persons in the British study and the 322 persons in the U.S. study. Sixty percent of the British study population and 62.7 percent of the Project People participants reported that they moved through smoke. It is thus apparent that building occupants will move through smoke in an evacuation process. An important variable may be the smoke density or the visibility distance of the occupants during the evacuation process. Table 4.1.16 presents the visibility distance reported by the British and U.S. occupants as they moved through smoke while evacuating a fire building. They reported their movement
TABLE 4.1.15 Comparison of the Distance Moved through Smoke for British and U.S. Populations Distance Moved (ft) 0–2 3–6 7–12 13–30 31–36 37–45 46–60 60+
British (percent, P1)
U.S. (percent, P2)
P1 – P2
SEaP1 – P2
CR b
3.0 18.0 30.0 19.0 5.0 4.0 5.0 15.0
2.3 8.4 17.1 45.5 2.0 4.1 11.0 9.6
0.7 9.6 12.9 26.5 3.0 0.1 6.0 5.4
1.02 2.23 2.71 2.62 1.25 1.19 1.47 2.10
0.69 4.30 c 4.76 c 10.11 c 2.40 d 0.08 4.08 c 2.57 d
1316
322
a
Standard error. Critical ratio. c Critical ratios significant at or above the 1 percent level of confidence. d Critical ratios significant at or above the 5 percent level of confidence. b
TABLE 4.1.16 Comparison of the Visibility Distance for the British and U.S. Populations When Moved through Smoke Visibility Distance (ft) 0–2 3–6 7–12 13–30 31–36 37–45 46–60 60+
a
British (percent, P1)
U.S. (percent, P2)
P1 – P2
SEaP1 – P2
12.0 25.0 27.0 11.0 3.0 3.0 3.0 17.0
10.2 17.2 20.2 31.7 2.2 3.7 7.4 7.4
1.8 7.8 6.8 21.7 0.8 0.7 4.4 9.6
1.99 2.65 2.73 2.24 1.03 1.08 1.21 2.24
1316
322
Standard error. Critical ratio. c Critical ratios significant at or above the 1 percent level of confidence. d Critical ratios significant at or above the 5 percent level of confidence. b
CR b 0.90 2.94 c 2.49 d 9.69 c 0.78 0.65 3.64 c 4.20 c
CHAPTER 1
through smoke under relatively high smoke density conditions, with visibility under 12 ft (3.7 m) for 64 percent of the British population and for 47.6 percent of the U.S. population. Visibility distance for the British and U.S. populations at the time participants were forced to turn back is presented in Table 4.1.17. Comparison with Table 4.1.16 reveals that very few participants turned back when they could see more than 31 ft (9.4 m). The greater percentage of participants turned back at shorter visibility distances. When the visibility distance was below 12 ft (3.7 m), 91 percent of the British study population and 76.4 percent of the U.S. study population turned back (see Table 4.1.17). Proulx61 in the study of the occupants’ response to a fire in a 25-story high-rise apartment building received 137 questionnaires returned, with 68 percent of the occupants over 60 years of age. Of the occupants, 114, or 83 percent, attempted to evacuate during the fire and 96, or 84 percent, of those attempting to evacuate moved through smoke. Forty-five percent of those moving through through smoke indicated they could see “nothing at all” or “little,” and 30 percent said they could see 12–15 m in the corridor. Of the 114 occupants who attempted to evacuate, 61, or 54 percent, were successful and 53, or 46 percent, were unsuccessful due to the smoke conditions in the stairs or corridors. Relative to the 53 unsuccessful occupants, 29, or 55 percent, returned to their own apartments and 24, or 45 percent, sought refuge in other apartments. Heskestad and Pederson62 have reported on five large “escape through smoke” experiments involving more than 300 persons with various wayguidance systems. In all of these experiments, the visibility was less than 3 m due to the induced smoke conditions. Two of the experiments involved the test situation modeled on a ship staircase and a ship or hotel corridor. One of these experiments involved an emergency training mockup, one experiment used a corridor in a healthcare facility, and
TABLE 4.1.17 Comparison of the Visibility Distance for the British and U.S. Populations Relative to the Turn Back Behavior Visibility Distance (ft) 0–2 3–6 7–12 13–30 31–36 37–45 46–60 60+
a
British (percent, P1)
U.S. (percent, P2)
P1 – P2
SEPa 1 – P2
29.0 37.0 25.0 6.0 0.5 1.0 0.5 1.0
31.8 22.3 22.3 17.6 1.2 0.0 4.7 0.0
2.8 14.7 2.7 11.6 0.7 1.0 4.2 1.0
5.31 5.57 5.02 3.07 0.90 1.10 1.16 1.10
570
85
Standard error. Critical ratio. c Critical ratios significant at or above the 1 percent level of confidence. b
CR b 0.53 2.64 c 0.54 c 3.78 c 0.77 0.91 3.62 c 0.91 c
■
Human Behavior and Fire
4–21
one experiment used portions of a passenger ferry. Variables measured during the experiments were the occupants time to travel through the experimental facility with the number of incorrect decisions made during the travel. These experiments found that tactile and audible wayguidance systems appear to be as suitable as the visible systems in assisting the individuals movement through smoke. Jin63 has reported on numerous studies involving the effectiveness of guidance sign systems with human subjects in smoke environments. Improvements resulting from these experiments include a pictorial exit sign, flashing exit lights, and a flashing row of lights at floor level indicating the direction of egress travel. The flashing row of lights was effective in a smoke level of 1.01/m with the spacing of the lights at 0.5 m.
HANDICAPPED OR IMPAIRED OCCUPANTS Fire problems involving occupancies designed for permanently or temporarily disabled persons, such as nursing homes and hospitals, appear to be matched on the basis of building design, adequate staff training, and ability to protect the occupants in place until evacuation is possible. An extensive study of human behavior in healthcare facilities57 indicated that the nursing staff performed their professional roles toward their patients even when they were at risk. The few fires studied involving handicapped persons in occupancies other than healthcare facilities have primarily been in residential occupancies. In two of these cases, handicapped individuals were helped by other occupants to evacuate successfully. One instance involved a wheelchair user48 and the other a blind person.64 Handicapped people may have a variety of limitations that increase their risk in a fire: sensory problems, such as deafness and blindness; mobility problems that may entail the need for a wheelchair; and intellectual problems, such as mental retardation. Many handicapped persons with mobility problems also are concerned about their personal risk in high-rise office and residential buildings where the use of elevators is not allowed in a fire. In such situations, adequate areas of refuge must be provided for handicapped, as well as nonhandicapped, occupants.65 In their reports of the explosion and fire in the World Trade Center on February 26, 1993, Isner and Klem66,67 indicated that when the explosion occurred at approximately 12:18 p.m., normal power was lost and the emergency generators failed about 20 min later; all remaining power to the World Trade Center complex was disconnected at approximately 1:32 p.m. Thus, the simultaneous evacuations of both able and disabled occupants from Towers 1 and 2 were conducted in darkness with varying smoke conditions in the stairways. These simultaneous evacuations may have involved the largest number of occupants and the longest evacuation times of any fire-induced evacuations of buildings in the United States. Juillet,68 in one of the first documented studies of this type, reported on the interview study of 27 occupants with disabilities who were evacuated from one of the two towers in the World
4–22 SECTION 4 ■ Human Behavior in Fire Emergencies
Trade Center during the explosion and fire of February 26, 1993. The impairments of the interviewees included 14 with mobility impairments, 3 with sight or hearing impairments, 3 who were pregnant, 2 with cardiac conditions, and 7 with respiratory conditions. Juillet68 indicated that the total disability population in both Towers 1 and 2 at the time of the incident was believed to be between 100 and 200 persons, approximately 100 of whom had been previously identified. The average evacuation time of the 27 study participants was 3.34 hr, with evacuation times reportedly ranging from 40 min to over 9 hr. The predominant means of evacuation was through the stairs with assistance from other evacuees or emergency personnel. The altruistic behavior seen in many fire incidents with large populations47,48,69 appeared to have been exhibited in this fire incident in relation to the disabled occupants as reported by Juillet. However, in the absence of communications by authorities, they gladly accepted assistance—from colleagues and even from complete strangers—in evacuating. These caring groups of people who assisted the disabled protected their ‘charges’ until they were safely evacuated and moved away from the building.68 The Fire Safety Engineering Research and Technology (SERT) Centre at the University of Ulster has completed the most extensive and detailed analytical and experimental studies of the evacuation capabilities of impaired individuals. Boyce, Shields, and Silcock conducted a series of studies in Northern Ireland to determine the number and characteristics of impaired persons who may be expected to frequent public buildings and to determine the capabilities of these persons to complete an evacuation. The initial study determined the number and types of impaired persons expected to occupy public assembly occupancies.70 This study found that 12 percent of the mobile population of Northern Ireland out in public are impaired persons and
2 percent of these impaired persons require assistance. Table 4.1.18 presents the number of impaired adults and children by their degree of mobility expressed as a percentage of the total mobile population. Table 4.1.19 illustrates the impaired persons in public who have experienced evacuation difficulties as percentages of the total mobile population. Table 4.1.20 indicates the involvement of impaired persons in social and recreational occupancies relative to their degree of mobility. Additional data presented in this study involved the frequency with which impaired persons go out in public. The prevalence of the type of impairment among the impaired population attending theaters, concert halls, motion picture theaters, sports stadiums, leisure centers, hotels, and lodging occupancies was reported. In addition, data was presented relative to the types of impairment among impaired adults who live in communal facilities and go out for meals and drinks, and for adults who are employed. The perceived value of this information and data relative to the application of performance codes was stated in the following manner: The information provided in this analysis has important implications for characterizing building occupancies. It establishes that public buildings are frequented by a significant number of disabled people and that the nature of their disabilities and how well they can be expected to evacuate without assistance during an emergency will be a function of the use of the building or part of the building. Characterizing buildings and characterizing occupants as required by performance-based codes, are not mutually exclusive activities a fact that has not yet percolated through the design professions.71 The second study by Boyce, Shields, and Silcock72 involved experimental observations and measurement of the movement of impaired persons on a horizontal corridor, inclined
TABLE 4.1.18 Number of Disabled Adults and Children Who Go Out by Degree of Mobility, Expressed as Percentages of the Total Mobile Population, i.e., Able-Bodied People and Mobile Disabled People, N. Ireland Adults
Children
Total (adults and children)
Assisted
Total
Unassisted
Assisted
Total
6.0 0.05 8 0.13 1.27 3.99 1.8 2.2 2.0 0.02 4.2 0.1
1.6 0.09 8
7.6 0.14
1.52
6.91
0.8 0.9 0.9 0.05 0.8 0.1
2.6 3.0 2.9 0.06 5.0 0.1
0.2 — — — — 0.0 0.1 0.04 0.0 0.1 0.0
0.1 — — — — 0.0 0.0 0.04 0.0 0.1 —
0.3 — — — — 0.1 0.1 0.2 0.01 0.2 0.0
2.0
0.7
2.7
0.3
0.2
0.4
Disability
Unassisted
Locomotion Wheelchair users Zimmer/rollator user Walking stick/crutch No aid Reaching and stretching Dexterity Seeing Blind Hearing Deaf Mental Behavioral
Assisted
Total
6.2 0.05 8 0.13 1.27 3.99 1.8 2.2 2.1 0.02 4.3 0.1
1.7 0.09 8
7.9 0.14
1.52
6.91
0.8 0.9 0.9 0.05 0.9 0.1
2.6 3.1 3.0 0.07 5.2 0.1
2.3
0.9
3.2
Unassisted
Note: Percentages for each disability do not sum to percent provided of the mobile population since many individuals have more than one disability. Percentages for wheelchair users and walking aid users do not sum to total since some data is missing. Source: K. E. Boyce, T. J. Shields, and G. W. H. Silcock, “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Prevalence, Type, and Mobility of Disabled People,” Fire Technology, 35, 1, 1999, p. 41.
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Human Behavior and Fire
4–23
TABLE 4.1.19 Number of Disabled Adults Who Go Out and Experience Difficulty, Expressed as Percentages of Total Mobile Population of N. Ireland Go Out Unassisted Degree of Difficulty
Assisted Degree of Difficulty
Total Degree of Difficulty
Action
Some
Great
Impossible
Some
Great
Impossible
Some
Great
Impossible
Go up and down stairs Climb outside steps Cross door saddles Go through doors Turn door knobs
2.4 1.5 0.1 0.1 0.3
1.1 0.8 0.1 0.03 0.1
0.2 0.2 0.03 0.01 0.03
0.2 0.3 0.2 0.1 0.2
0.6 0.4 0.1 — 0.07
0.2 0.2 0.01 0.01 0.05
2.59 1.81 0.32 0.15 0.43
1.69 1.14 0.13 0.03 0.13
0.43 0.40 0.04 0.02 0.08
Note: Since these percentages are based on adults only, the actual percentages of the mobile population in N. Ireland who experience difficulty may be higher. Source: K. E. Boyce, T. J. Shields, and G. W. H. Silcock, “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Prevalence, Type, and Mobility of Disabled People,” Fire Technology, 35, 1, 1999, p. 42.
TABLE 4.1.20 Extent of Involvement of Disabled Adults and Children in Various Social and Recreational Activities by Degree of Mobility Adults
Children Total
Unassisted
Assisted
All
387 (7.3)
1,415 (11.3)
10,784 (6.9)
2,901 (9.5)
13,685 (7.3)
153 (81.0) 3,205 (44.0)
53 (28.0) 1,084 (20.5)
206 (75.7) 4,289 (3.4)
2,235 (79.6) 16,366 (10.5)
1,330 (23.5) 2,090 (6.8)
3,565 (42.1) 18,456 (9.9)
8,950 (5.1) 44,657 (25.6)
— — — —
— — — —
— — — —
8,052 (5.4) 40,220 (25.7)
898 (3.6) 4,437 (14.5)
8,950 (5.1) 44,657 (23.9)
3,350 (40.9) 19,125 (11.0) 350 (0.2) 316 (0.2)
— — — — 0 (0.0) 0 (0.0)
— — — — 0 (0.0) 0 (0.0)
— — — — 0 (0.0) 0 (0.0)
1,277 (45.5) 18,896 (12.1) 350 (0.2) 316 (0.2)
2,032 (35.8) 229 (0.7) 0 (0.0) 0 (0.0)
3,350 (39.6) 19,125 (10.2) 350 (0.2) 316 (0.2)
Activity
Unassisted
Assisted
Total
Unassisted
Participates in theatre, i.e., opera, musicals, ballet, cinema Goes shoppinga
9,756 (6.5)
2,514 (9.6)
12,270 (7.0)
1,028 (14.0)
1,532 (58.5) 13,161 (8.9)
2,233 (40.0) 1,006 (4.0)
3,765 (40.1) 14,167 (8.1)
8,052 (5.4) 40,220 (27.0)
898 (3.6) 4,437 (17.6)
1,318 (50.3) 18,896 (12.7) 350 (0.2) 316 (0.2)
2,032 (36.4) 229 (0.9) 0 (0.0) 0 (0.0)
Participates indoor sport/ spectates sport Attends ordinary social club Stayed in hotel/ other holiday accommodation Goes out for meals/drinksa Is employed Attends ordinary school Attends college of further education
Totals
Assisted
a
Asked of disabled persons living in communal establishments only. Source: K. E. Boyce, T. J. Shields, and G. W. H. Silcock, “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Prevalence, Type, and Mobility of Disabled People,” Fire Technology, 35, 1, 1999, p. 44.
ramps, and stairs. Observations included the velocity of movement, rest periods required, assistance required, and the physical aids used relative to their degree of mobility impairment. One hundred seven persons (54 males and 53 females, ages 20 to 85) completed the horizontal corridor without assistance. The velocity of this population relative to the mobility impairment is presented in Table 4.1.21. Sixteen of the manual wheelchair
users needed assistance to traverse the 50-m long corridor at the 90° turn, 8 m from the starting point. Only 34 individuals were capable of participating in the stair movement studies involving ascent and descent travel, with 30 of these without assistance and 4 with assistance, including three blind persons. In general the movement velocity was slightly faster in descent travel on ramps, while on the stairs the ascent movement
4–24 SECTION 4 ■ Human Behavior in Fire Emergencies
TABLE 4.1.21 Ambulant
Speed (m/s) on Horizontal by Presence/Absence of Locomotion Disability and Walking Aid—Unassisted
Subject Group
Mean (m/s)
Standard Deviation (m/s)
Range (m/s)
Interquartile Range (m/s)
All disabled (n = 107)
1.00
0.42
0.10–1.77
0.71–1.28
With locomotion disability (n = 101) No aid (n = 52) Crutches (n = 6) Walking stick (n = 33) Walking frame or Rollator (n = 10)
0.80 0.95 0.94 0.81 0.57
0.37 0.32 0.30 0.38 0.29
0.10–1.68 0.24–1.68 0.63–1.35 0.26–1.60 0.10–1.02
0.57–1.02 0.70–1.02 0.67–1.24 0.49–1.08 0.34–0.83
Without locomotion disability (n = 6)
1.25
0.32
0.82–1.77
1.05–1.34
Source: K. E. Boyce, T. J. Shields, and G. W. H. Silcock, “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capabilities of Disabled People Moving Horizontally and on an Incline,” Fire Technology, 35, 1, 1999, p. 54.
was faster, as indicated in a comparison of Table 4.1.22 and Table 4.1.23. These authors indicated the following findings from these experiments: The abilities of disabled people cover a wide spectrum with respect to movement on horizontal and inclined planes. Given the significant differences in the capabilities of those using different mobility aids and the inherent differences in their spatial requirements, it is suggested that, for evacuation and modeling purposes, they be considered separately. Escape times are usually determined from characteristic travel speeds coupled with premovement times. From this study it is apparent that, for some disabled people, it may also be necessary to include periods of rest and time to negotiate changes in direction. This paper’s findings should help designers derive characteristic times for disabled people traversing any typical escape route. The detailed observations made during the movement studies suggest that, in designing accessible escape routes, more attention needs to be focused on the real, rather than the perceived needs of disabled people. Consideration should be given to the nature and position of support systems such as handrails, and the positioning of doors in escape routes, since these will influence the progress and the flight behaviors of some disabled occupants.73
TABLE 4.1.22
The third study by Boyce, Shields, and Silcock74 was an experimental study of door operation and egress. One hundred four mobility-impaired persons (54 male and 50 female, ages 25 to 85) participated in this study. Impairments of the participants involved 5 using crutches, 28 using a walking stick, 8 using a walker, and 63 using no mobility aids. The time to negotiate a standard singleleaf door with a clear width opening of 750 mm for these individuals is presented in Table 4.1.24 with the type of door operation and the closer force on the door leaf. In addition to the mobility impairments, other critical impairments for this action involved 45 persons with a minor reaching and stretching impairment and 58 persons with a dexterity impairment. Table 4.1.25 presents the failure rates and the time to negotiate the door for the seven manual wheelchair users. The manual wheelchair users in general took more time to push the door open than to pull the door open. It also took these wheelchair users three to four times longer than the mobility impaired persons to negotiate the door. The fourth study by Boyce, Shields, and Silcock75 was an experimental study to determine the ability of impaired persons to locate and read three types of exit signs: nonilluminated, internally illuminated, and light-emitting diode (LED) signs. The signs were placed in a clear atmosphere in a room, 2.3 m from the floor with a maximum viewing distance of 85 m. The distance which participants were able to read the exit signs was measured. A total of 118 impaired persons participated in this study, including 25 persons with a sight impairment. Table 4.1.26 presents the distance at which the participants could read the signs.
Speed (m/s) on Stairs (Ascent) by Presence/Absence of Locomotion Disability—Unassisted Ambulant
Subject Group
Mean (m/s)
Standard Deviation (m/s)
Range (m/s)
Interquartile Range (m/s)
With locomotion disability (n = 30) No aid (n = 19) Crutches (n = 1) Walking stick (n = 9) Rollator (n = 1)
0.38 0.43 0.22 0.35 0.14
0.14 0.13 — 0.11 —
0.13–0.62 0.14–0.62 0.13–0.31 0.18–0.49 —
0.26–0.52 0.35–0.55 0.26–0.45
Without disability (n = 8)
0.70
0.24
0.55–0.82
0.55–0.78
—
Source: K. E. Boyce, T. J. Shields, and G. W. H. Silcock, “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capabilities of Disabled People Moving Horizontally and on an Incline,” Fire Technology, 35, 1, 1999, p. 64.
CHAPTER 1
TABLE 4.1.23
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Human Behavior and Fire
Speed (m/s) on Stairs (Descent) by Presence/Absence of Locomotion Disability—Unassisted Ambulant
Subject Group
Mean (m/s)
Standard Deviation (m/s)
Range (m/s)
Interquartile Range (m/s)
With locomotion disability (n = 30) No aid (n = 19) Crutches (n = 1) Walking stick (n = 9) Rollator (n = 1)
0.33 0.36 0.22 0.32 0.16
0.16 0.14 — 0.12 —
0.11–0.70 0.13–0.70 — 0.11–0.49 —
0.22–0.45 0.20–0.47 — 0.24–0.46 —
Without disability (n = 8)
0.70
0.26
0.45–1.10
0.53–0.90
Source: K. E. Boyce, T. J. Shields, and G. W. H. Silcock, “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capabilities of Disabled People Moving Horizontally and on an Incline,” Fire Technology, 35, 1, 1999, p. 65.
TABLE 4.1.24
Time (s) to Negotiate Door for Each Door Setting by Mobility Aid—Ambulant Disabled No Aid (n = 63)
Mean (s)
Standard Deviation (s)
Push 21 30 42 51 60 70
3.0 3.5 3.7 4.1 4.0 4.3
Pull 21 30 42 51 60 70
3.3 3.2 3.7 3.8 4.1 4.6
Closing Force (N )
Crutch Users (n = 5)
Walking Stick Users (n = 28)
Walking Frame/Rollator Users (n = 8)
Range
Mean (s)
Standard Deviation (s)
Range (s)
Mean (s)
Range
3.7 3.0 3.8 3.6 3.8 3.9
3.6–3.8 2.5–3.2 2.9–5.2 3.1–3.9 3.6–4.1 3.3–4.6
3.7 3.8 4.0 4.3 3.7 4.6
1.5 1.5 1.6 2.4 1.5 2.1
2.3–7.4 2.5–7.3 2.3–7.5 1.5–10.7 1.7–7.9 2.5–11.1
7.9 6.3 5.2 7.9 5.2 6.2
2.0–12.8 2.2–10.5 2.1–10.3 2.0–14.3 2.0–10.3 1.7–11.2
2.8 — 4.0 3.6 3.6 4.6
2.2–4.0 — 2.9–6.3 2.5–4.6 2.7–4.7 2.6–4.7
3.6 3.2 3.9 4.6 4.1 4.9
1.4 0.9 1.4 2.2 1.7 2.3
1.8–7.6 1.8–4.9 1.9–6.8 1.5–9.5 1.4–7.4 2.1–9.7
5.7 5.2 4.7 6.3 8.9 3.2
2.0–8.2 4.3–6.0 2.6–6.9 2.5–11.2 1.9–17.0 1.9–6.7
Range
Mean (s)
0.8 2.2 1.5 2.4 1.9 2.0
1.7–4.5 1.9–15.0 1.6–10.2 1.0–14.3 1.3–13.0 1.7–11.2
1.5 1.0 1.8 1.6 1.9 2.2
1.5–7.6 1.5–5.2 1.4–12.6 1.5–10.2 1.5–11.4 1.5–12.6
Source: K. E. Boyce, T. J. Shields, and G. W. H. Silcock, “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capabilities of Disabled People to Negotiate Doors,” Fire Technology, 35, 1, 1999, p. 73.
The LED signs appeared to be the most visible and legible by the impaired persons with and without a sight impairment. In a related study, Shields76 observed that wheelchair users and mobile participants did not impede each other in evacuation progress and wheelchair persons did not impede each other. Mobility-impaired persons with walkers did impede wheelchair users. Klote, Alvord, Levin, and Groner77 examined the design considerations needed to enable elevators in tall buildings to be utilized for the evacuation of disabled occupants. In the World Trade Center explosion and fire of 1993, the loss of power in both Towers 1 and 2 (including emergency power) trapped occupants in elevators in both buildings. Burns23 indicated Tower 1 had 99 elevator cars, many of them occupied. When one 6 ft ? 8 ft (1.8 m ? 2.4 m) car was opened, nine occupants were found unconscious. It was esti-
mated that they had been exposed to the smoke in the shaft for approximately 2 hr at the ninth floor. Sherwood78 reported that one 9 ft ? 12 ft (2.7 m ? 3.6 m) elevator car was stuck for 6 hr at the 41st floor of Tower 2 with 72 occupants (62 elementary school children and 10 adults). NFPA 1012 in the 1991 edition of the Code permitted the use of elevators with fire fighter service from areas of refuge which were also specified in this edition. In 1997 the Life Safety Code permitted the use of a fire fighter service elevator with special features to be used as a second means of egress from towers with specifications on the occupant load of the tower, the provision of automatic sprinklers, the egress arrangement, and capacity. A study of a number of evacuation drills in high-rise office buildings in Canada indicated that approximately 3 percent of the occupants were unable to use the stairs due to permanent or temporary conditions limiting their mobility.79 The study
4–26 SECTION 4 ■ Human Behavior in Fire Emergencies
TABLE 4.1.25
Percentage Failure and Time (s) to Negotiate Door for Each Door Setting—Manual Wheelchair Users No. of Failures (percent)
No. successful (percent)
Mean (s)
Median (s)
Range
Push (n = 7) 30 42 51 60 70
1 (14.3) 1 (14.3) 2 (28.6) 2 (28.6) 2 (28.6)
6 (85.7) 6 (85.7) 5 (71.4) 5 (71.4) 5 (71.4)
13.1 13.3 10.0 10.5 11.6
7.4 10.7 7.4 10.5 6.7
3.6–39.0 3.6–36.0 3.6–20.5 3.5–17.4 3.6–26.3
Pull (n = 7) 30 42 51 60 70
2 (28.6) 3 (42.9) 3 (42.9) 5 (71.4) 5 (71.4)
5 (71.4) 4 (57.1) 4 (57.1) 2 (28.6) 2 (28.6)
13.5 12.8 10.5 4.2 4.3
11.3 6.8 7.0 4.2 4.3
3.7–34.0 3.8–34.0 3.8–24.0 2.8–4.6 3.7–5.0
Closing Force Leading Edge (N )
Source: K. E. Boyce, T. J. Shields, and G. W. H. Silcock, “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capabilities of Disabled People to Negotiate Doors,” Fire Technology, 35, 1, 1999, p. 74.
TABLE 4.1.26
Distance (m) at Which Subjects Can Read Exit Signs by Presence/Absence of Seeing Disability
Type of Sign and Subject Group
Mean (m)
Median (m)
Standard Deviation (m)
Range (m)
Interquartile Range (m)
13.3 11.4 13.7
15.0 12.0 15.0
3.1 4.0 2.7
1.0–15.0 1.0–15.0 6.0–15.0
12.0–15.0 9.7–15.0 15.0–15.0
14.2 12.9 14.5
15.0 15.0 15.0
2.7 4.6 1.8
1.0–15.0 1.0–15.0 6.0–15.0
15.0–15.0 15.0–15.0 15.0–15.0
14.6 14.0 14.7
15.0 15.0 15.0
1.6 2.6 1.2
5.0–15.0 5.0–15.0 7.0–15.0
15.0–15.0 15.0–15.0 15.0–15.0
Non-illuminated exit sign All disabled (n = 105) With seeing disability (n = 25) Without seeing disability (n = 80) Illuminated exit sign All disabled (n = 118) With seeing disability (n = 25) Without seeing disability (n = 93) LED sign All disabled (n = 83) With seeing disability (n = 23) Without seeing disability (n = 60)
Source: K. E. Boyce, T. J. Shields, and G. W. H. Silcock, “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capabilities of People with Disabilities to Read and Locate Signs,” Fire Technology, 35, 1, 1999, p. 83.
population included occupants with heart conditions and individuals recovering from surgery, other illnesses, and accidents.
FIRE EXIT DRILLS Well-marked exits do not ensure life safety during a fire. Exit drills are necessary so that occupants will know how to make an efficient and orderly escape according to NFPA 101, which contains detailed information on exit drills in individual occupancies. Exit drills are required in schools, board and care facilities, and healthcare facilities, and are common in industries with high hazards. Employee training and drills are required in assembly, hotel, mercantile, and large business occupancies. Some form of exit drill should be conducted wherever or whenever possible to avoid
confusion and ensure the evacuation of all occupants during a fire.80 Personnel should be assigned to check exits for availability, search for stragglers, count occupants once they are outside the fire area, and control reentry into the building before it is safe. This reentry behavior for rescue purposes of persons involved in fire incidents should be noted. In a study of 335 fire incidents involving 584 persons, it was found that 163 persons, approximately 28 percent of the study population, reentered the fire buildings following evacuation.8 Approximately 10.5 percent of those persons who reentered the buildings did so to alert or assist other persons. Determining when and what area to evacuate is probably the most important decision in a fire emergency. Any area at all affected by heat, flame, or smoke should be evacuated; in case of doubt, the entire building should be evacuated.
CHAPTER 1
The fire loss prevention and control management staff are responsible for planning exit drills. Plans should be discussed with both middle and line management to ensure understanding and cooperation. If there is no fire loss prevention and control manager, the plant, facility, or building manager should assume this responsibility or assign it to a staff member. All employees should recognize the evacuation signal and know the exit route they are to follow.81 Upon hearing the signal, they should shut off equipment and report to a predetermined assembly point. Primary and alternative routes should be established, and all employees should be trained to use either route.80,82 The problem with audible evacuation signals is the conditioning of the population within the occupancy to ignore the signal due to numerous false alarms. An investigation of an apartment building fire found that the alarm system actuation to initiate evacuation behavior was ignored by many of the building occupants due to the conditioning effect of numerous prior false alarms: 44 percent of the building occupants believed the alarm signal was a false alarm.83 When employees are assembled, the manager or supervisor of each area should account for all personnel. Missing employees should be immediately reported to the fire loss prevention and control manager and responding fire department personnel so that search and rescue efforts can be initiated. Only trained fire-fighting search and rescue personnel with adequate protective equipment should be permitted to reenter an evacuated area. After each exit drill, a meeting of the responsible managers should be held to evaluate the success of the drill and to solve any problems that may have arisen. One significant improvement to the traditional concept of fire drills in educational occupancies was suggested by a study of fire drills conducted in such occupancies.84 The concept of smoke drills has been established, whereby the occupants are instructed to move through the simulated smoke areas in a crouched position. Students have transferred the smoke drill concept to fire incidents in residential occupancies, with effective results. Obviously, the utilization of smoke drill training may be effective in a fire incident and should be used where applicable. The timing of drills depends upon the nature of the operation in the facility. Generally, drills conducted a few minutes before the lunch break have been found to minimize loss of time and production. The frequency of drills should be determined by the degree of hazard present and by the complexity of shutdown or evacuation procedures. If a facility does not maintain a security organization that is responsible for daily inspection of emergency exits and designated evacuation routes, one employee in each area should be assigned this task. Maintenance of doors, panic hardware, exit lights, and emergency illumination should be given high priority, and repairs must be made without delay. Research has found that for multistory office buildings, a trained group of floor wardens is the most effective means of monitoring the evacuation of occupants.80 Adequate training for floor wardens or other personnel is necessary and must be specifically developed to include the procedures of the emergency evacuation plan for the facility.
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Human Behavior and Fire
4–27
The lecture method has been used to convey the essential features of the emergency plan to employees in healthcare facilities.82 However, it was also found that the emergency plan in the facility studied was too general and ambiguous. The most serious problem with using building monitors is the turnover of personnel due to employee transfers, reassignments, or resignations. Effective evacuation planning and preparation should assign specific responsibilities to staff positions (rather than individuals) within an organization. This ensures continuity of performance despite personnel changes. A content and time evaluation of fire drill behavior by staff in six nursing homes concluded that a training program of the most modest type can produce changes in both knowledge and behavior of evacuation and fire emergency procedures.85 A total of 339 nursing home staff participated in the study that matched a group of 37 persons receiving the training with a control group of 49 persons not receiving the training. The high rate of personnel turnover, which appears to be rather typical in nursing home facilities, was noted. Following the presentation of the training program, staff members were evaluated by a written knowledge test, and their behavior was observed during the conduct of a drill of the emergency plan. The evacuation signal should be familiar to all employees. Vocal alarm systems (VAS)80,81 reduce the need for employee perception and recognition of a signal, because the system provides vocal communication to the areas designated for evacuation. NFPA 101 first recommended the use of the VAS in assembly occupancies in 1981. An evaluation of VAS systems in nine buildings found that familiarity with the system or initial activation did not significantly affect the egress behavior of populations.80 In addition, the investigation determined the evacuation drills were valuable because they gave floor or area wardens an opportunity to rehearse their procedures. The use of an alerting tone in the frequency range of 2000–4000 Hz for the VAS is recommended prior to the verbal announcement, which should be specific for the audience and the facility.80,86
Healthcare Facilities Drills Fire drills in healthcare institutions are usually conducted as a part of the orientation program for new employees. Later, the drills are supplemented with in-service training for the staff personnel, including the emergency procedures. Fire drills in many facilities are conducted once a month on each shift. The training for the drills typically involves instruction and practice for the staff personnel in the various means of moving nonambulatory patients, procedures for alerting the facility staff, and the method of notifying the fire department. Once or twice a year, many facilities have fire departments provide training in the operation of portable fire extinguishers. Some fire departments actually provide staff personnel with experience in the operation of extinguishers on external fires. However, most healthcare facilities prefer to train their personnel. Most adopt the philosophy that it is the staff’s responsibility to ensure the safe evacuation of patients initially to an area of refuge and then to the exterior if necessary. The control of the
4–28 SECTION 4 ■ Human Behavior in Fire Emergencies
fire is limited to preventing the spread of heat and smoke by closing doors. This protects the occupants and inhibits or restricts the propagation of the smoke and heat throughout the facility. Staff personnel have effectively evacuated numerous patients under fire conditions or have protected the patients in their rooms by closing doors.87 Thus, the evacuation process may be considered in four sequential phases: (1) the personnel supply phase, (2) the patient preparation phase, (3) the patient removal phase, and (4) the rest and recovery phase.88 This approach focuses on the occupants in the fire-threatened area and the patients in or adjacent to the fire area. Removing immediately threatened patients and closing doors to the room of fire origin and to adjacent patient rooms would be compatible with this four-phase approach to evacuation. A detailed report on the fire evacuation organization, training, and drills involved in a 502-bed acute-care teaching hospital with 2500 employees has been published.89 In 1985, NFPA 101 included a new chapter devoted to the fire protection and life safety requirements for board and care facilities. That chapter requires the evaluation and classification of the population of the facility, according to their evacuation capability.
Evaluating Fire Drill Plans The ultimate evaluation of fire drill and emergency plans has two factors: (1) performance of the occupants in a fire incident, and (2) effectiveness of the behaviors used in accordance with the fire drills or the fire emergency plan. In a World Trade Center fire incident report,22 building occupants tended to attempt to verify their beliefs about the threat of fire by physical clues, primarily smoke in the occupants’ area. The report also indicated public address messages were not sufficient to alleviate spontaneous evacuations when occupants saw smoke on their floor. Further, occupant evacuation was reported (9th through 22nd floors) due to the perception and concern that a valid fire threat existed. In actuality, the fire did not require such an extensive evacuation. Successful evacuation of personnel from the two floors above and below a fire in a 28-story high-rise college dormitory has been reported.90 To allow free evacuation flow of the occupants down the stairways and allow fire department personnel to move up the stairs, stairs have been marked for occupant and fire department movement. The fire department movement stair has a red circle, 6 in. (152 mm) in diameter, on the door, and is also utilized for ventilation. The occupant stair is marked with a 6-in. (152-mm) green circle. In the safe evacuation during a high-rise hotel fire with 190 guests, 110 guests were assisted by the fire department. The success of the evacuation was made possible by the hotel employees’ fire safety education and practice of evacuation procedures.91
SUMMARY Behavior in fires can be understood as a logical attempt to deal with a complex, rapidly changing situation in which minimal information upon which to act is available. It is suggested that the goals of codes should be “reoriented to increase the likelihood
of informed decisions being made by people in fires.”92 Examination of behavior in the Beverly Hills Supper Club fire led to the recommendation that “fire safety education should consider and be based on people’s erroneous conceptions about distance being related to safety, and the time needed to escape from a fire emergency.”93 More than a decade of detailed systematic research on human behavior in fires has resulted in the following consensus54 on the behavior of most persons: Despite the highly stressful environment, people generally respond to emergencies in a “rational,” often altruistic manner, insofar as is possible within the constraints imposed on their knowledge, perceptions, and actions by the effects of the fire. In short, “instinctive panic” type reactions are not the norm. The relationship between the physical and social environment in which behavior occurs is complex. The situation is complicated by the individual’s perception of ambiguous fire cues, which is primarily influenced by the person’s relevant training and previous fire experience, if any. It must be recognized that fire cues are a product of a rapidly changing dynamic process that is constantly altering the decisions of the building occupant. This dilemma has been summarized: “What is an appropriate action at one stage may be quite inappropriate a minute later.”
BIBLIOGRAPHY References Cited 1. National Bureau of Standards, Design and Construction of Building Exits, Washington, DC, 1935. 2. National Fire Protection Association, NFPA 101®, Life Safety Code®, Quincy, MA, 2000. 3. London Transit Board, Second Report of the Operational Research Team on the Capacity of Footways, London, UK, 1958. 4. Melnick, S. J., and Booth, S., An Analysis of Evacuation Times and the Movement of Crowds in Buildings, Fire Research Station, Borehamwood, Hertforshire, UK, 1975. 5. Bryan, J. L., A Study of the Survivors’ Reports on the Panic in the Fire at Arundel Park Hall, Brooklyn, Maryland, on January 29, 1956, Fire Protection Curriculum, University of Maryland, College Park, MD, 1957. 6. National Commission on Fire Prevention and Control, America Burning, U.S. Government Printing Office, Washington, DC, 1973. 7. Breaux, J., Canter, D., and Sime, J., Psychological Aspects of Behavior of People in Fire Situations, University of Surrey, Guilford, UK, 1976. 8. Bryan, J. L., Smoke as a Determinant of Human Behavior in Fire Situations, Department of Fire Protection Engineering, University of Maryland, College Park, MD, 1977. 9. Canter, D., and Matthews, R., The Behavior of People in Fire Situations: Possibilities for Research, Fire Research Station, Borehamwood, UK, 1976. 10. Canter, D., Studies of Human Behavior in Fire: Empirical Results and Their Implications for Education and Design, Building Research Establishment Report L61, Borehamwood, UK, 1985. 11. Keating, J. P., and Loftus, E. F., People Care in Fire Emergencies—Psychological Aspects 1975, Society of Fire Protection Engineers, Boston, 1975. 12. Lerup, L., Conrath, D., and Liu, J. K. C., Human Behavior in Institutional Fires and Its Design Complications, NBS-GCR-7793, Center for Fire Research, National Bureau of Standards, Washington, DC, 1978.
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13. Loftus, E. F., and Keating, J. P., The Psychology of Emergency Communications, University of Washington, Seattle, 1974. 14. Stahl, F. I., Crosson, J. J., and Margulis, S. T., Time-Based Capabilities of Occupants to Escape Fires in Public Buildings: A Review of Code Provisions and Technical Literature, National Bureau of Standards, Washington, DC, 1982. 15. Wood, P. G., The Behavior of People in Fires, Fire Research Note 953, Fire Research Station, Borehamwood, UK, 1972. 16. Keating, J. P., and Loftus, E. F., “The Logic of Fire Escape,” Psychology Today, 15, June 1981, pp. 14–19. 17. Proulx, G., and Sime, J. D., “To Prevent Panic in an Underground Emergency: Why Not Tell People the Truth?” Fire Safety Science—Proceedings of the 3rd International Symposium, Elsevier Applied Science, New York, 1991, pp. 843–852. 18. Ramachandran, G., “Human Behavior in Fires—A Review of Research in the United Kingdom,” Fire Technology, Vol. 26, No. 2, 1990, pp. 149–155. 19. Ramachandran, G., “Informative Fire Warning Systems,” Fire Technology, Vol. 27, No. 1, 1991, pp. 66–81. 20. Cable, E. A., “Cry Wolf Syndrome: Radical Changes Solve the False Alarm Problem,” Department of Veterans Affairs, Albany, NY, Jan. 1994. 21. Kimura, M., and Sime, J. D., “Exit Choice Behavior during the Evacuation of Two Lecture Theatres,” Fire Safety Science— Proceedings of the 2nd International Symposium, Hemisphere Publishing Corporation, Washington, DC, 1989, pp. 541–550. 22. Lathrop, J. K., “Two Fires Demonstrate Evacuation Problems in High-Rise Buildings,” Fire Journal, Vol. 70, No. 1, 1976, pp. 65–70. 23. Burns, D. J., “The Reality of Reflex Time,” WNYF, Vol. 54, No. 3, 1993, pp. 26–29. 24. Fahy, R. F., and Proulx, G., “Collective Common Sense: A Study of Human Behavior during the World Trade Center Evacuation,” NFPA Journal, Vol. 87, No. 2, 1995, p. 61. 25. Berry, C. H., “Will Your Smoke Detector Wake You?” Fire Journal, Vol. 72, No. 4, 1978, pp. 105–108. 26. Cohen, H. C., “Fire Safety for the Hearing Impaired,” Fire Journal, Vol. 76, No. 1, 1982, pp. 70–72. 27. Kahn, M. J., “Human Awakening and Subsequent Identification of Fire-Related Cues,” Fire Technology, Vol. 20, No. 1, 1984, pp. 80–86. 28. Nober, E. H., et al., “Waking Effectiveness of Household Smoke and Fire Detector Devices,” Fire Journal, Vol. 75, No. 4, 1981, pp. 86–91, 130. 29. Latane, B., and Darley, J. M., “Group Inhibition of Bystander Intervention in Emergencies,” Journal of Personality and Social Psychology, Vol. 10, No. 3, 1968, pp. 215–221. 30. Withey, S. B., “Reaction to Uncertain Threat,” Man and Society in Disaster, G. W. Baker and D. W. Chapman (Eds.), Basic Books, New York, 1962, pp. 93–123. 31. Killian, R. M., et al., “A Study of Response to the Houston, Texas, Fireworks Explosion,” Disaster Study No. 2, Publication 391, National Academy of Science, Washington, DC, 1956. 32. Sime, J. D., “Perceived Time Available: The Margin of Safety in Fires,” Fire Safety Science—Proceedings of the 1st International Symposium, Hemisphere Publishing Corporation, Washington, DC, 1986, pp. 561–570. 33. National Fire Protection Association, “Bimonthly Fire Record,” Fire Journal, Vol. 65, No. 3, 1971, p. 51. 34. Mintz, A., “Nonadaptive Group Behavior,” Journal of Abnormal and Social Psychology, Vol. 46, 1951, pp. 150–159. 35. Jones, B. K., and Hewit, J. A. “Leadership and Group Formation in High-Rise Building Evacuations,” Fire Safety Science— Proceedings of the 1st International Symposium, Hemisphere Publishing Corporation, Washington, DC, 1986, pp. 513–522. 36. Horiuchi, S., Murozaki, Y., and Hokugo, A., “A Case Study of Fire and Evacuation in a Multi-Purpose Office Building,” Osaka, Japan, Fire Safety Science—Proceedings of the 1st International Symposium, Hemisphere Publishing Corporation, Washington, DC, 1986, pp. 523–532.
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37. Bickman, L., Edelman, P., and McDaniel, M., “A Model of Human Behavior in a Fire Emergency,” NBS-GCR-78-120, National Bureau of Standards, Washington, DC, 1977. 38. Proulx, G., “A Stress Model for People Facing a Fire,” Journal of Environmental Psychology, Vol. 13, 1993, pp. 137–147. 39. Chubb, M., Human Factors Lessons for Public Fire Educators: Lessons from Major Fires, National Fire Protection Association, Education Section, Phoenix, AZ, 1993. 40. Klein, G. A., and Klinger, D., Naturalistic Decision Making, CSERIAC Gateway, Crew System Ergonomics Information Analysis Center, Wright-Patterson AFB, 1991, pp. 1–4. 41. Canter, D., Breaux, J., and Sime, J., “Domestic, Multiple Occupancy and Hospital Fires,” Fires and Human Behavior, D. Canter (Ed.), John Wiley & Sons, New York, 1980, pp. 117–136. 42. Best, R., and Demers, D. P., “Fire at the MGM Grand,” Fire Journal, Vol. 76, No. 1, 1982, pp. 19–37. 43. Demers, D. P., “Investigation Report on the Las Vegas Hilton Hotel Fire,” Fire Journal, Vol. 76, No. 1, 1982, pp. 52–57. 44. Bryan, J. L., “Human Behavior in the MGM Grand Hotel Fire,” Fire Journal, Vol. 76, No. 2, 1982, pp. 37–41, 44–48. 45. Morris, G. P., “Preplan Was the Key to MGM Rescue as EMS Helped Thousands of Hotel Fire Victims,” Fire Command, Vol. 48, No. 6, 1981, pp. 20–21. 46. Bryan, J. L., “Convergence Clusters: A Phenomenon of Human Behavior Seen in Selected High-Rise Building Fires,” Fire Journal, Vol. 74, No. 6, 1985, pp. 27–30, 86–90. 47. Bryan, J. L., and DiNenno, P. J., “An Examination and Analysis of the Dynamics of the Human Behavior in the Fire Incident at the Georgian Towers on January 9, 1979,” NBS-GCR-79-187, National Bureau of Standards, Washington, DC, 1979. 48. Bryan, J. L., An Examination and Analysis of the Dynamics of the Human Behavior in the MGM Grand Hotel Fire, revised edition, National Fire Protection Association, Quincy, MA, 1983. 49. Bryan, J. L., An Examination and Analysis of the Dynamics of the Human Behavior in the Westchase Hilton Hotel Fire, National Fire Protection Association, Quincy, MA, 1983. 50. Best, R. L., “Tragedy in Kentucky,” Fire Journal, Vol. 72, No. 1, 1978, pp. 18–35. 51. English, H. B., and English, A. C., A Comprehensive Dictionary of Psychological and Psychoanalytical Terms, Longmans, Green and Company, New York, 1948. 52. Schultz, D. P., Contract Report NR 170-274, University of North Carolina, Charlotte, 1968. 53. Kentucky State Police, Investigative Report to the Governor, Beverly Hills Supper Club Fire, 1977, Frankfort, KY. 54. Sime, J. D., “The Concept of Panic,” Fire and Human Behavior, D. Canter (Ed.), John Wiley & Sons, New York, 1980, pp. 63–81. 55. Quanrantelli, E. L., Panic Behavior in Fire Situations: Findings and a Model from the English Language Research Literature, Disaster Research Center, Ohio State University, Columbus, 1979. 56. Keating, J. P., “The Myth of Panic,” Fire Journal, Vol. 76, No. 3, 1982, pp. 57–61, 147. 57. Bryan, J. L., DiNenno, P. J., and Milke, J. A., The Determination of Behavior Response Patterns in Fire Situations, Project People II, Final Report—Incident Reports, Aug. 1977 to June 1980, NBS-GCR-80-297, National Bureau of Standards, Washington, DC, 1980. 58. Crossman, E. R., Zachary, W. B., and Pigman, W., FIRRST: A Fire Risk and Readiness Study of Berkeley Households, UCBFRG/WP 75-5, University of California, Berkeley, 1975. 59. U.S. Department of Commerce, Highlights of the National Household Fire Survey, National Fire Prevention and Control Administration, United States Fire Administration, Washington, DC, 1976. 60. Jin, T., and Yamada, T., “Experimental Study of Human Behavior in Smoke Filled Corridors,” Fire Safety Science—Proceedings of the 2nd International Symposium, Hemisphere Publishing Corporation, Washington, DC, 1989, pp. 511–519.
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61. Proulx, G., “The Impact of Voice Communication Messages During a Residential Highrise Fire,” Human Behavior in Fire Proceedings of the 1st International Symposium, Fire SERT Centre, University of Ulster, 1998, pp. 265–274. 62. Heskestad, A. T., and Pederson, K. S., “Escape through Smoke: Assessment of Human Behavior and Performance of Wayguidance Systems,” Human Behavior in Fire: Proceedings of the 1st International Symposium, Fire SERT Centre, University of Ulster, 1998, pp. 631–638. 63. Jin, T., “Studies on Human Behavior and Tenability in Fire Smoke,” Fire Safety Science—Proceedings of the 5th International Symposium, International Association for Fire Safety Science, 1997, pp. 3–21. 64. Bryan, J. L., DiNenno, P. J., and Milke, J. A., An Examination and Analysis of the Dynamics of the Human Behavior in the Fire Incident at the Taylor House on April 11, 1979, NBS-GCR-80200, National Bureau of Standards, Washington, DC, 1979. 65. Levin, B. N., and Nelson, H. E., “Firesafety and Disabled Persons,” Fire Journal, Vol. 75, No. 5, 1981, pp. 35–40. 66. Isner, M. S., and Klem, T. J., Fire Investigation Report World Trade Center Explosion and Fire, New York, New York, February 26, 1993, National Fire Protection Association, Quincy, MA, 1993. 67. Isner, M. S., and Klem, T. J., “Explosion and Fire Disrupt World Trade Center,” NFPA Journal, Vol. 87, No. 6, 1993, pp. 91–104. 68. Juillet, E., “Evacuating People with Disabilities,” Fire Engineering, Vol. 126, No. 12, 1993, pp. 100–103. 69. Juillet, E., personal communication, January 18, 1994. 70. Boyce, K. E., Shields, T. J., and Silcock, G. W. H., “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Prevalence, Type and Mobility of Disabled People,” Fire Technology, Vol. 35, No. 1, 1999, pp. 35–50. 71. Ibid., p. 48. 72. Boyce, K. E., Shields, T. J., and Silcock, G. W. H., “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capability of Disabled People Moving Horizontally and on an Incline,” Fire Technology, Vol. 35, No. 1, 1999, pp. 51–67. 73. Ibid., pp. 66–67. 74. Boyce, K. E., Shields, T. J., and Silcock, G. W. H., “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capability of Disabled People to Negotiate Doors,” Fire Technology, Vol. 35, No. 1, 1999, pp. 68–78. 75. Boyce, K. E., Shields, T. J., and Silcock, G. W. H., “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capability of People With Disabilities to Read and Locate Exit Signs,” Fire Technology, Vol. 35, No. 1, 1999, pp. 79–86. 76. Shields, T. J., Fire and Disabled People in Buildings, Building Research Report 231, Building Research Establishment, UK, 1993. 77. Klote, J. H., Alvord, D. M., Levin, B. M., and Groner, N. E., Feasibility and Design Considerations of Emergency Evacuation by Elevators, NISTIR 4870, NIST, Building and Fire Research Laboratory, Gaithersburg, MD, 1992. 78. Sherwood, J., “Darkness and Smoke,” WNYF, Vol. 54, No. 3, pp. 56–60. 79. Pauls, J. L., “Movement of People in Building Evacuations,” Human Response to Tall Buildings, D. J. Conway (Ed.), Dowden, Hutchinson and Ross, Stroudsburg, PA, 1977. 80. Keating, J. P., et al., An Evaluation of the Federal High-Rise Emergency Evacuation Procedures, Department of Psychology, University of Washington, Seattle, 1978. 81. Keating, J. P., and Loftus, E. F., Vocal Emergency Alarms in Hospitals and Nursing Facilities: Practice and Potential, NBSGCR-77-102, Center for Fire Research, Gaithersburg, MD, 1977. 82. Herz, E., Edelman, P., and Bickman, L., The Impact of Fire Emergency Training on Knowledge of Appropriate Behavior in Fires, NBS-GCR-78-137, Center for Fire Research, Gaithersburg, MD, 1978.
83. Scanlon, J., Human Behavior in a Fatal Apartment Fire— Research Problems and Findings, Emergency Communications Research Unit, Carleton University, Ottawa, Canada, 1978. 84. Phillips, A. W., To Keep Them Safe, National Smoke, Fire and Burn Institute, Inc., Brookline, MA, 1979. 85. Bickman, L. E., et al., An Evaluation of Planning and Training for Fire Safety in Health Care Facilities—Phase Two, NBSGCR-79-179, Center for Fire Research, Gaithersburg, MD, 1979. 86. Shavit, G., “Evacuation: Testing the Effect of Voice-Message Formats,” ASHRAE Journal, Vol. 20, 1978, pp. 38–41. 87. Bryan, J. L., and DiNenno, P. J., “Human Behavior in a Nursing Home Fire,” Fire Journal, Vol. 73, No. 3, 1980, pp. 82–87, 126–127, 141–143. 88. Archea, J., The Evacuation of Non-Ambulatory Patients from Hospital and Nursing Home Fires: A Framework for a Model, NBSIR 79-1906, Center for Fire Research, Gaithersburg, MD, 1979. 89. Elliott, S., and Scheidt, J., “Hospital and Fire Department Unite to Design New Code Red Program,” Fire Journal, Vol. 73, No. 4, 1983, pp. 47–54. 90. Nygren, R. G., “Alarm Signaling and Evacuation in a High-Rise University Resident Hall,” Fire Journal, Vol. 66, No. 2, 1972, pp. 5–6, 11. 91. Timoney, T., “Howard Johnson’s Hotel Fire, Orlando, Florida,” Fire Journal, Vol. 78, No. 5, 1984, pp. 37–45, 88. 92. Canter, D., Human Behaviour in Fires, Department of Psychology, University of Surrey, Guildford, UK, 1978. 93. Pauls, J. L., and Jones, B. K., “Research in Human Behavior,” Fire Journal, Vol. 74, No. 3, 1980, pp. 35–41.
References Bryan, J. L., Human Behavior Factors and the Fire Occurrence in Buildings, International Fire Protection Engineering Institute, Department of Fire Protection Engineering, University of Maryland, College Park, 1971. Holton, D., “Boarding Homes—The New Residential Fire Problem?” Fire Journal, Vol. 47, No. 2, 1981, pp. 53–56. Paulsen, R. L., “Human Behavior and Fires: An Introduction,” Fire Technology, Vol. 20, No. 2, 1984, pp. 15–27. Swartz, J. A., “Human Behavior in the Beverly Hills Fires,” Fire Journal, Vol. 73, No. 3, 1979, pp. 73–74, 108.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on human behavior and fire discussed in this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 72®, National Fire Alarm Code® NFPA 101®, Life Safety Code®
Additional Readings Ballast, D. K., Egress from Buildings in Emergencies: A Bibliography, Vance Bibliographies, Monticello, IL, 1988. Beck, K. H., “A Canonical Correlation of Fire Protective Behaviors and Beliefs,” Fire Technology, Vol. 25, No. 1, 1989, pp. 41–50. Bodamer, M., “How People Behave in Fires,” Fire Prevention, No. 224, Nov. 1989, pp. 20, 22–23. Booker, C. K., Powell, J., and Canter, D., “Understanding Human Behavior during Fire Evacuation,” Chapter 6, Council on Tall Buildings and Urban Habitat, Fire Safety in Tall Buildings. Tall Building Criteria and Loading, Committee 8A, McGraw-Hill, Inc., Blue Ridge Summit, PA, 1992, pp. 93–104. Bryan, J. L., “Behavioral Response to Fire and Smoke,” SFPE Handbook of Fire Protection Engineering, 3rd ed., National Fire Protection Association, Quincy, MA, 2002, pp. 3-315–3-341.
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Canter, D., Fires and Human Behavior, 2nd ed., Fulton, London, UK, 1988. Chalmet, L. G., et al., “Network Models for Building Evacuation,” Management Science, Vol. 28, No. 1, 1990, pp. 86–105. Collins, B. L., Dahir, M. S., and Madrzykowski, D., “Visibility of Exit Signs in Clear and Smoky Conditions,” Fire Technology, Vol. 24, No. 2, 1993, pp. 154–182. Cooper, L. Y., and Stroup, D. W., “ASET: A Computer Program for Calculating Available Safe Egress Time,” Fire Safety Journal, Vol. 9, 1985, p. 29. Cote, R. (Ed.), Life Safety Code Handbook, 8th ed., National Fire Protection Association, Quincy, MA, 2000. Frantzich, H., “Evacuation Capability of People,” Lund Univ., Sweden, TNO Building and Construction Research, CIB/W14 Workshop, Proceedings of the 3rd Fire Engineering Workshop on Modelling, Jan. 25–26, 1993, Delft, the Netherlands, 1993, pp. 224–231. Fraser-Mitchell, J. N., and Pigott, B. B., “Modelling Human Behavior in the Fire Risk Assessment Model ‘CRISP II,’” Fire Research Station, Borehamwood, UK, University of Ulster and Fire Research Station. CIB W14: Fire Safety Engineering, International Symposium and Workshops Engineering Fire Safety in the Process of Design: Demonstrating Equivalency, Part 3, Symposium: Engineering Fire Safety for People with Mixed Abilities, September 13–16, 1993, Newtownabbey, UK, 1993, pp. 1–10. Fruin, J. J., Pedestrian Planning and Design, revised edition, Elevator World, Mobile, AL, 1987. Golton, C. J., Golton, B. J., and Hinks, A. J., “Human Behavior in Fire: A Background Review for Modelling,” Fire Safety Modelling and Building Design, Proceedings of the One-Day Conference to Review the Potential and Limitations of Fire Safety Models for Building Design, March 29, 1994, Salford, UK, 1994, pp. 48–62. Jin, T., and Yamada, T., “Experimental Study on Human Emotional Instability in Smoke Filled Corridor. Part 2,” Journal of Fire Sciences, Vol. 8, No. 2, 1990, pp. 124–134. Keating, J. P., “Human Resources during Fire Situations: A Role for Social Engineering,” General Proceedings Research and Design, American Institute for Architects Foundation, Washington, DC, 1985. Kendik, E., “Methods of Design of Means of Egress: Towards a Quantitative Comparison of National Code Requirements,” Proceedings of the 1st International Symposium of Fire Safety Science, Hemisphere, Washington, DC, 1986. Kisko, T. M., and Francis, R. L., “EVACNET+, A Computer Program to Determine Optimal Building Evacuation Plans,” Fire Safety Journal, Vol. 9, No. 2, 1985, pp. 211–220. Klevan, J. B., “Modeling of Available Egress Time from Assembly Spaces or Estimating the Advance of the Fire Threat,” SFPE TR 82-2, Society of Fire Protection Engineers, Boston, May 1982. Ling, W. C. T., and Williamson, R. B., “Use of Probabilistic Networks for Analysis of Smoke Spread and Egress of People in Buildings,” Proceedings of the 1st International Symposium for Fire Safety Science, Hemisphere, New York, 1986, pp. 953–962. Maclennan, H. A., “Towards an Integrated Egress/Evacuation Model Using an Open Systems Approach,” Proceedings of the 1st Inter-
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national Symposium on Fire Safety Science, Hemisphere, 1986, pp. 581–590. Magawa, M., Kose, S., and Moushita, Y., “Movement of People on Stairs during a Fire Evacuation Drill—Japanese Experience in a High-Rise Office Building,” Proceedings of the 1st International Symposium on Fire Safety Science, Hemisphere, Washington, DC, 1986. Ozel, F., Way Finding and Route Selection in Fires, School of Architecture, New Jersey Institute of Technology, Newark, NJ, 1986. Pauls, J., “Development of Knowledge about Means of Egress,” Fire Technology, Vol. 20, No. 2, 1984, pp. 28–40. Pauls, J., Gatfield, A. J., and Juillet, E., “Elevator Use for Egress: The Human-Factors Problems and Prospects,” National Research Council of Canada, Ottawa, Ontario, National Task Force on Life Safety and the Handicapped American Society of Mechanical Engineers, Council of American Building Officials and National Fire Protection Association, Elevators and Fire, February 19–20, 1991, Baltimore, MD, 1991, pp. 63–75. Paulsen, R. L., “Human Behavior and Fires: An Introduction,” Fire Technology, Vol. 20, 1984, pp. 15–27. Poon, L. S., and Beck, V. R., “Numerical Modelling of Human Behavior during Egress in Multi-Storey Office Building Fires Using EvacSim—Some Validation Studies,” Proceedings of the 1st International Conference on Fire Science and Engineering, ASIAFLAM ’95, March 15–16, 1995, Kowloon, Hong Kong, 1995, pp. 163–174. Predtechenskii, V. M., and Milinskii, A. I., Planning for Foot Traffic Flow in Buildings, Amerind Publishing Co., New Delhi, India, 1978. Proulx, G., “Human Factors in Fires and Fire Safety Engineering,” SFPE Bulletin, Winter 1995, pp. 13–15. Proulx, G., “Movement of People: The Evacuation Timing,” SFPE Handbook of Fire Protection Engineering, 3rd ed., National Fire Protection Association, Quincy, MA., 2002, pp. 342–366. Robertson, J. C., “Instilling Proper Public Fire Reaction,” Introduction to Fire Prevention, 3rd ed., Macmillan, New York, 1989, pp. 219–248. Rubadiri, L., Ndumu, D. T., and Roberts, J. T., “Predicting the Evacuation Capability of Mobility-Impaired Occupants,” Fire Technology, Vol. 33, No. 1, 1997, pp. 32–53. Shields, J. (Ed.), Human Behaviour in Fire Proceedings of the First International Symposium, Fire SERT Centre, University of Ulster, 1998. Shields, J. (Ed.), 2nd International Symposium on Human Behaviour in Fire, London Interscience Communications, Cambridge, MA, 2001. Takahashi, K., and Tanaka, T., “An Evacuation Model for the Use in Fire Safety Designing of Buildings,” 9th Joint Panel Meeting of the UJNR Panel on Fire Research and Safety, NBSIR 88-3753, National Bureau of Standards, Gaithersburg, MD, Apr. 1988. Van Bogaert, A. F., “Evacuating Schools on Fire,” Proceedings of the 1st International Symposium on Fire Safety Science, Hemisphere, 1986, pp. 551–560. Weinroth, J., “An Adaptable Microcomputer Model for Evacuation Management,” Fire Technology, Vol. 25, No. 4, 1989, pp. 291–307.
CHAPTER 2
SECTION 4
Calculation Methods for Egress Prediction Revised by
Rita F. Fahy
T
he evaluation of an engineered design requires a balanced comparison of predicted fire conditions and realistic evacuation predictions. Over the past several years, fire safety engineers have worked with, and developed confidence in, a range of calculation methods for the prediction of fire conditions. Researchers working in the area of human behavior in fire have begun to make real progress in recent years in the collection of data necessary for this analysis and in the development of predictive tools that will be comparable to those used to predict the growth and spread of fire and its effects. Performance building and fire codes allow designers to use innovative building materials and concepts often not encouraged or even permitted in existing prescriptive codes, which can result in more cost-effective and creative designs. But this openness to innovation requires the designer to then demonstrate that the design is safe. For a design to be shown to be “safe,” the designer must demonstrate that the time needed to move people to a safe location will be less than the time predicted when fire effects will have a potentially lethal impact on any occupant. Time available to escape B Time needed to escape Fire safety design is a two-sided problem that requires fire safety engineers and the enforcement community to have knowledge in the use of both fire models and egress and human behavior models. Currently, fire safety engineers are very well trained in predicting fire growth and the spread of fire effluents in a structure. The focus of a fire safety design appears to favor this component of the fire safety problem. But it is crucial that the complexity and importance of the egress/behavior component never be underestimated or short-changed and that a balance between both components be maintained. For their part, building and fire officials (the enforcement community) will need to evaluate designs presented in their jurisdictions that will use various computer models or other calculation methods to demonstrate both the time necessary and the time available for occupant evacuation. They may need guidance on how to judge the appropriateness of methods, data, and assumptions used in these evaluations, particularly in the egress portion of analyses. Members of both user groups must balance the two sets of escape time calculations in order to produce a meaningful result. Rita F. Fahy is manager of NFPA’s fire databases and systems.
COMPONENTS OF EVACUATION TIME The evacuation time for an individual is the entire span of time that elapses from the ignition of the fire until the occupant emerges from the building or arrives at a location of safety. It consists of four components, all of which must be taken into consideration: • • • •
Time to notification Reaction time Preevacuation activity time Travel or movement time
The first three components are often grouped together and referred to as “delay time” or “premovement time.” Evacuation time C Delay time = Travel time C Time to notification = Reaction time = Preevacuation activity time = Travel time It is very important that engineers not underestimate the contribution that delay time can make to total evacuation time. Studies of evacuation drills in apartment buildings have shown that, on average, travel time makes up less than 25 percent of the average total time to evacuate.1 In office evacuations, however, delay times can be extremely short, and the largest proportion of total evacuation time is accounted for by travel time. Therefore, the selection, estimation, or calculation of premovement times is extremely important to obtain valid results.
Time to Notification In the evaluation of an engineered building design, evacuation time begins when ignition occurs. Some period of time, the time to notification, will elapse before conditions develop to the point where an alarm sounds or where people begin to sense the cues of the fire itself. The fire cues that reach occupants can be the sight or smell of smoke, heat, the sight of flames, the sound of glass breaking, or the sound of an alarm signal from a smoke alarm, a heat detector, or a sprinkler system. The time to notification can be modeled, or it could be estimated if necessary using expert judgment. Fire growth and smoke transport models can be used with detector/sprinkler activation models to estimate this period
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of time. Some models that can be used include ASET,2 which estimates the temperature and position of the smoke layer in the room of fire origin; DETACT,3 which models heat detection and sprinkler activation; or BREAK1,4 which estimates time until glass breaks.*
Reaction Time Reaction time is the time it takes an occupant to perceive the alarm or fire cue and decide to take action. For example, if a person is asleep when the smoke alarm sounds, it will take some period of time for the person to wake up, to identify the sound as the smoke alarm, and to decide to leave. There is currently no generally accepted modeling technique available for reaction time. The time used in an analysis may depend on observations (data) or expert judgment. An appropriate reaction time will depend on whether the person is awake or asleep, on his or her hearing ability, mental capacity, age (baby/child/adult), and so on.
Preevacuation Activity Time Preevacuation activity time includes the time that elapses while the occupant is preparing to leave or seek refuge. Preevacuation activities involve all of the activities in which an occupant will engage from the time when he or she makes the decision to leave until the time he or she actually starts to travel toward an exit or an area of refuge. These activities may vary by occupancy. For example, hotel occupants might stop to pack their bags before they leave their rooms, whereas office workers may take time to shut off equipment and lock files. In an industrial setting, there may be a procedure that must be followed to safely shut down the plant’s operations. To some degree, preevacuation activities can be reduced or eliminated through education or training. As with reaction time, there are no generally accepted modeling techniques available for preevacuation activity time, and the time used in an analysis may depend on observations (data) or expert judgment. In reality, reaction time and preevacuation activity time are often considered together. In data collection exercises, it is generally not possible to separate the two time components, and the results will be reported as a single, combined time from notification to the time that movement toward the exit begins. Some of the data on preevacuation delays that has been obtained from postfire behavior studies and evacuation drills will be presented later in this chapter.
Travel Time Travel time is the final component in the calculation of evacuation time. It is defined here as the time to move to a location of safety. There are various calculation or estimation techniques available for travel time. Some simple calculation methods can *The mention of these models does not represent or imply an endorsement of the models or the organizations that developed them.
be found in FPEtool,5 which is available from the National Institute for Standards and Technology (NIST) in the United States. These are based on some of the hand calculation methods described later in this chapter.
ESTIMATING EVACUATION TIME For evacuation modeling, several types of data are needed, either as model inputs or as considerations for the designer in setting up an analysis of a building design. A major data category that overarches the components of evacuation is occupant factors. Occupant factors include the characteristics of the people who would be expected to populate a building, whether on a permanent or transient basis. These factors include age, agility, commitment to the task at hand, familiarity with the building, level of training in what to do in emergencies, and many others. More specifically, to calculate evacuation time, data is needed on delay times and travel times for a range of occupancy types. What types of delays should be expected, and how long they may last, is very often a function of the characteristics of the occupants. Likewise, travel times will be impacted by the characteristics of the occupants.
Factors Related to Delay Times Delay times, also referred to as premovement time, initial response time, or time to start, can last from a few seconds to several minutes or more. It is important to remember that during this period of delay, people might be simply ignoring available cues, or they might be engaged in preevacuation activities as discussed earlier. As described previously, delay time includes time to notification, reaction time, and preevacuation activity time. Several factors can result in variations in delay times. These factors, which are also related to the characteristics of the occupants, include • Effectiveness of different cues • Effectiveness or training • Time of day, weather, and so on Alarm devices use different sounds and, as a result, there can be confusion among building occupants as to what the sound is that they are hearing. And the alarm itself does not give people information as to what actions they should take. When building occupants hear an alarm, will they know if it is a burglar alarm or a fire alarm? Will they know if they should evacuate, or wait for further instructions? Voice communication systems, on the other hand, can convey information to building occupants and can decrease delay times by telling people what the situation is and what they are expected to do and how they should do it. Training has been shown in studies to decrease delay times.6 Trained building occupants can be expected to know where the closest exits are, should be able to recognize the alarm signal and know what to do, and could be expected to have shorter delay times. In buildings such as theaters and shopping
CHAPTER 2
centers, where the building occupants are not expected to be familiar with the alarms and exits, trained staff can reduce delay times significantly by directing occupants to the nearest exits immediately on hearing an evacuation signal. Time of day and weather can have an impact on premovement delays. People may be reluctant to leave a building during a storm, in cold weather, or during the night. People may need extra time in winter to dress themselves and small children warmly. Various characteristics of the occupants can also impact delay times. People with hearing impairments may not hear or interpret the sound of an alarm as quickly as people without impairments. People with mobility impairments may be slower to prepare themselves to evacuate or move to another location in the building. People who are engrossed in an activity may be too preoccupied to hear an alarm or warnings from other occupants, and then may be reluctant to leave what they are doing to take any protective actions.
Available Data on Delay Times There are two principal sources of data on delay times: postfire survey questionnaires and videotaped observations from drills. Each method of data collection has its own advantages and disadvantages. Postfire survey questionnaires provide a method to collect information from real fires. However, it is very difficult for people to accurately estimate time lines for events in the past, particularly for traumatic events. Another problem is the subjectivity of the observations. For example, when people are asked to describe the thickness of smoke they traveled through or the duration of events, there is often a wide disparity in the descriptions among people who were in the same space at the same time. Videotaped observations allow the collection of very precise timelines, occupant densities, and travel flows in corridors and through doorways; however, the building occupants are not operating under any threat, and it is not clear to what degree observations from a fire drill will provide a good estimate of delay times or travel speeds in real fires. A third alternative method that has been mentioned recently is the use of video recordings from security cameras operating during a fire incident. Although the existence of such recordings has been mentioned, no data from the tapes has been reported yet in the literature. Until behavioral models exist that can accurately predict the activities and behaviors of occupants before they begin to leave a building, it will be necessary for a designer evaluating an engineered design to provide an estimate of the duration of time those activities will require. Although a database of “accepted values” does not yet exist, there are summaries of delay times observed in several evacuation drills and actual fires available in the literature.7 One such summary report is based on five case studies that involved two sets of evacuation drills in apartment buildings, one set of office building drills, an actual apartment building fire and a fire in a megastructure complex.8 The five case studies are part of an ongoing data collection project that is part of the development of the National Research Council of Canada’s fire
■
Calculation Methods for Egress Prediction
4–35
risk model. These studies uncovered a broad range in the delay times that can occur and provided an indication of some of the factors that can result in delays. The times observed in these studies cannot be taken at face value as the “correct” times a designer should use, but they do provide an indication of the range of times that exist in real-life situations. The main factor influencing delay times in the evacuation drills was the audibility of the alarm system. The evacuation drills in apartment buildings took place during two research projects and involved seven mid- and high-rise buildings. In the two mid-rise apartment buildings where the performance of the alarm systems was described as “good,” the average time for occupants to begin evacuation was 2.82 min. For the two mid-rise apartment buildings with alarm system performance described as “bad,” the average delay time increased to 8.92 min. Alarm system performance in two of the high-rise apartment buildings was described as “good,” but the average delay time in those evacuations was quite different: 2.80 min in one and 5.32 min in the other. This discrepancy pointed out another factor that can significantly influence delay time—the weather. Since it was snowing at the time of one of the high-rise evacuation drills, the occupants took the time to dress warmly before leaving their apartments, adding approximately 2.50 min to the mean delay time. Overall in the apartment drills, the shortest average delay time for a building was 2.50 min and the longest was 9.70 min. Clearly, then, the delay time selected by a designer in the calculation of total evacuation time can greatly impact the final result and must be chosen with care. The short delay times observed in the two office building evacuation drills demonstrated the combined effect of “good” alarms, training of occupants, and the use of fire wardens to assist in the evacuation. The delay times in the two drills averaged 0.60 min and 1.05 min. The activities most frequently reported in postdrill questionnaires were gathering valuables, getting dressed, and notifying others. To these activities, the participants in the residential drills had added: looking in the corridor, finding children, finding pets, and moving to the balcony. A building designer must be cautious when using delay time data from evacuation drills as input to an evacuation model, as drills might underestimate the amount of time an occupant will delay. Although one might expect that occupants will move more quickly in an actual fire, it often takes longer, while the occupants attempt to sort through ambiguous cues and determine whether or not they really need to act.9 The postfire human behavior study provided important evidence that evacuation might take longer in an actual fire than in a drill. The fire started on the fifth floor of a 30-story building at approximately 5:00 a.m. on a winter morning. Six building occupants died in two stairwells while attempting to evacuate. The building occupants who participated in this study filled out questionnaires 2 to 3 wk after the fire. Because of the time that elapsed between the fire and the survey, the occupants often rounded off the times they reported, but the study still provided important information on the range of time between various activities and events. Although the respondents in this study reported delays in beginning evacuation that ranged from 0 to
4–36 SECTION 4 ■ Human Behavior in Fire Emergencies
12 hr, close to half of the occupants attempted to leave within the first hour of becoming aware of the fire. And because no one above the fire floor who started evacuating after 5:30 a.m. was able to reach ground level on his or her own, the activities of the occupants in the first hour are of most interest. The average delay time for occupants who started to evacuate in the first hour was 10.50 min. The human behavior study of the megastructure complex involved the explosion and fire that impacted the two 110-story World Trade Center towers in New York City in 1993. Building occupants had been trained, as had the occupants in the office drills mentioned previously, but in this case they were trained to wait on their respective floors for instructions. Since the emergency control center was destroyed in the explosion, the fire alarm system did not sound and no messages were transmitted. Occupants were forced to rely on ambiguous cues to alert them to the incident. Since the explosion was closer to the base on one tower, cues in that tower were somewhat less ambiguous than in the other. The delay times reported for the tower closer to the blast ranged from 0 to 4.08 hr, with a mean time of 11.03 min and a median time of 5.00 min. For the other tower, the delay times ranged from 0 to 3.08 hr, with a mean time of 25.40 min and a median time of 10.00 min. Additional data need to be collected before a database exists that will provide precise estimates suitable for use, directly, in evacuation modeling. This set of studies illustrates, however, the variation that exists among different types of occupancies, between occupancies of the same type and between drills and actual incidents, as well as the role of alarm effectiveness, training, and weather. It is important to mention that the delay times described here are mean times. The distribution of delay times shown in Figure 4.2.1 is typical, with most times relatively short, but with a long tail that can stretch to infinity (representing building oc-
cupants who never leave the building during the incident). The data in Figure 4.2.1 comes from a fire drill in a one-story department store.6 A fire safety engineer or building designer must take into consideration the actual distribution of delay times in evaluating an engineered design. As mentioned earlier, some of the data collected has been summarized in a recent paper that proposed a database of travel speed and delay time data.7 The delay time data from that paper can be found in Table 4.2.1. The studies represented in this table involved hotels, office buildings, department stores, and a training facility. The user is cautioned to refer to the source documents for the full context of the experiments and incidents before applying the data to his or her application, otherwise, important differences between the evacuations that were the source of the data and the design being evaluated will be missed, and the resulting analysis could be completely invalid.
Factors Related to Travel Time Travel time is a function of travel speed and distance to the exit and will vary among occupants. Evacuation models handle the calculation of travel time in various ways. Some evacuation models require the user to set a travel speed that will apply to all occupants throughout the evacuation, but this method does not take into account the effect of crowdedness, which will slow the travel speed of the occupants and increase their travel and total evacuation time. Another problem is that a uniform travel speed does not take into consideration the differing abilities of the building’s occupants. Travel time is to some degree a function of exit choice, because exit choice will determine travel distance. Buildings can be designed with multiple exits in the hope that people will use the closest exit in an emergency, and thereby reduce their evacuation
14
12
Frequency
10
8
6
4
2
0
0
0.5
1.0
1.5
2.0
2.5
Time (min)
FIGURE 4.2.1
Experimental and Theoretical Premovement Times in a Department Store Evacuation
CHAPTER 2
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Calculation Methods for Egress Prediction
4–37
TABLE 4.2.1 Delay Times (Minutes) Derived from Actual Fires and Evacuation Exercises Reported in the Referenced Literature Event Description
N
Min
1st Q
Median
3rd Q
Max
Mean
High-rise hotel10
536
0
3.3
60.0
130.9
290
n/aa
High-rise hotel11
47
0
2.0
5.0
17.5
120
n/a
High-rise office building12
85
0
2.0
5.0
10.0
245
11.3
High-rise office building12
46
0
4.5
10.0
31.5
185
28.4
High-rise office building13
107
1.0
1.0
1.0
1.0
High-rise office building14
12
0.5
n/a
1.0
Mid-rise office building15 Mid-rise office building15 One-story department store16,17
92
0
0.4
0.6
0.8
<4
0.6
161
0
0.5
0.9
1.4
<5
1.1
95
1
0.2
0.3
0.5
122
0.05
n/a
n/a
122
0.07
n/a
71
0.03
n/a
219
Three-story department store17 One-story department store17 One-story department store17 High-rise apartment building18
n/a
~6.0
2.3
n/a
1.2
0.9
0.4
n/a
1.6
0.6
n/a
n/a
1.7
0.5
n/a
n/a
n/a
1.0
0.4
0
n/a
n/a
n/a
n/a
10.5
0
n/a
187.8
n/a
720
190.8
High-rise apartment building19 High-rise apartment building19 High-rise apartment building13
33
0.3
0.8
1.3
4.4
10.2
2.8
93
0.4
1.5
3.6
6.9
18.6
5.3
27
1.0
2.0
8.0
14.0
>20
Mid-rise apartment building20 Mid-rise apartment building20 Mid-rise apartment building20 Mid-rise apartment building20 Training facility21
42
0.6
1.0
1.4
3.0
>14
2.5
55
>0.5
1.6
4.4
13.5
>21
8.4
77
>0.3
1.9
7.7
19.1
>24
9.7
80
>0.3
1.2
2.5
3.7
>12
3.1
566
<0.2
0.7
1.1
1.5
>5
a
n/a: not reported.
n/a
n/a
Factors MGM Grand Hotel fire, no alarm notification, grouped data from questionnaires Westchase Hilton Hotel fire, no alarm in early stages, grouped data from questionnaires World Trade Center explosion and fire, no alarm notification (building closer to explosion) World Trade Center explosion and fire, no alarm notification (building further from blast) Fire incident, no alarms, data from interviews with occupants of four floors of building (11 interviewees were trapped) Unannounced drill on three floors; data for first person to reach each of four stairwell doors to wait for voice instruction; trained staff; data from video recordings Unannounced drill, good alarm performance; fire wardens; warm day Unannounced drill, good alarm performance; fire wardens; cool day Unannounced drill; trained staff; data here derived from grouped data for 95 participants Unannounced drill; trained staff; times distilled from analysis of videotapes Unannounced drill; trained staff; times distilled from analysis of videotapes Unannounced drill; trained staff; times distilled from analysis of videotapes Forest Laneway fire; for occupants who attempted to evacuate in the first hour, based on questionnaire responses Forest Laneway fire, for all occupants Unannounced drill; good alarm performance Unannounced drill; good alarm performance; heavy snow during drill Fire incident in early morning, alarm functioned, fewer than half the occupants evacuated Unannounced drill; good alarm performance Unannounced drill; poor alarm performance Unannounced drill; poor alarm performance Unannounced drill; good alarm performance Testing sleeping subjects at a training facility
4–38 SECTION 4 ■ Human Behavior in Fire Emergencies
time. It has been shown time and again, however, that people tend to use the exit with which they are familiar, even if there is a closer emergency exit.22 Without training, or instructions from trained staff, it may not be appropriate to assume that people will take the shortest route out of a building. Other occupant characteristics impact both delays and travel time, but until very recently much of the necessary data to calculate their effects was not available. One important characteristic for which data has not been readily available is mobility, but a series of papers on the characterization of occupants of buildings, with particular emphasis on disabled occupants, was recently published. The series of papers covered the following: • Prevalence, type, and mobility of disabled people • Capability of disabled people to move horizontally or on an incline • Capability of disabled people to negotiate doors • Capability of disabled people to read and locate exit signs The first paper documents a study that was done in Northern Ireland to estimate the number of disabled people who leave their homes and should be expected to use a variety of public buildings.23 The study also looked at what percentage of the mobile population consists of the mobility-impaired as well as to what degree those who use public places are disabled, concentrating on disabilities that would influence a person’s ability to escape a fire. According to this study, almost 8 percent of the total mobile population has a mobility impairment of some sort and 0.14 percent use a wheelchair. The study also looked at the use of public buildings by people with disabilities and found that approximately 40 percent of mobility-impaired adults frequent theaters and sports facilities, almost 60 percent stay in hotels, almost 30 percent are employed, and approximately 50 percent frequent eating and drinking establishments. The paper also presents detail on the frequency of use of public spaces and degree of mobility (whether or not they require assistance). A design team should be able to calculate, using the data presented in the paper, the proportion of building occupants likely to have a mobility impairment. Other types of disabilities that impact the ability to evacuate are also detailed, including dexterity, reaching and stretching, seeing, hearing, and mental abilities. The second paper in the series provides important data on the travel speed of a mobility-impaired population on horizontal paths, ramps, and stairs, with and without assistance.24 For those traveling without assistance on horizontal paths, the mean speed for the mobility-impaired group was 2.62 ft/s (0.80 m/s), compared to 4.10 ft/s (1.25 m/s) for those not mobility impaired. The mean travel speed for the mobility impaired varied by type of aid required, from 1.87 ft/s (0.57 m/s) for walker users to 3.12 ft/s (0.95 m/s) for those who did not use an aid. Electric wheelchair users had a mean travel speed of 2.92 ft/s (0.89 m/s) whereas manual-wheelchair users had a mean speed of 2.26 ft/s (0.69 m/s). Travel speed data is also presented in the paper for movement on ramps, up and down stairs and around corners. Information on the study participants’ use of travel paths included observations on the amount of space used by people as they
made their way along corridors or on stairs, the use of handrails, and difficulties negotiating stairway landings. An important added consideration covered in this paper is the rest time that many participants required while negotiating the 164-ft (50-m) paths, and the recovery time required by those who completed the 164 ft (50 m) distance without stopping. The third paper in the series looks at the ability of disabled people to use doors.25 The data in the paper include the percentage of mobility-impaired participants who could not negotiate doors with various closing forces and the time needed to negotiate doors of various closing forces, overall and by type of aid used. The authors conclude in this paper that the travel times predicted for disabled building occupants must include the time needed to negotiate doors. The fourth and final paper in the series looks at the ability of disabled people to locate and read exit signs.26 The study evaluated three types of exit signs—nonilluminated signs, internally illuminated signs, and light emitting diode (LED) signs. The paper presents data on the distances required by those with and without vision disabilities to locate and read exit signs and concludes that LED signs are the most visible and legible. The study did not, however, evaluate the ability of the participants to locate and read signs in the presence of distractions such as contrasting colors and smoke. When an engineered design is being developed for public assembly properties, the design team must consider the characteristics of a population that accurately reflects the expected user population. This set of papers describes research on disabled groups in Northern Ireland. Whether or not it is reasonable to extrapolate the results to the rest of the world, this research provides data that begin to answer critical questions about the population at risk in public places. Similar data must be collected for the full range of occupancy types. A great deal of data on travel speeds has been collected and reported in the literature for a long time. To put the reported data into the correct context, it is important to note the factors that can result in variations in movement speed. These include crowd density; the mobility, age and other characteristics of the occupants; the presence of family groups; the presence of smoke; and lighting and other design features. As the density of the crowd increases, the ease and speed of movement decreases until the crowd is moving at a shuffling pace. Family groups will attempt to stay together and will move at the speed of the slowest person. The presence of smoke can slow people down, or it can cause them to change directions or ultimately to stop their evacuation. Low lighting can slow people, particularly on stairs, and the evenness of the exit path and the roughness or smoothness of the walls along the exit path can also impact travel speeds. Some of the data on travel speeds that has been collected has been summarized in a recent paper.7 The data collected include the following types of occupancies: transport terminals, apartment buildings, assembly properties, industrial buildings, and hotels. Data for both able-bodied and mobility-impaired subjects are also available. The summary data from that paper are shown in Table 4.2.2. Again, the user is cautioned to refer to the source documents for the full context of the experiments and incidents before applying the data to his or her application.
CHAPTER 2
TABLE 4.2.2
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Calculation Methods for Egress Prediction
4–39
Travel Speeds Reported in the Referenced Literature
Type of Situation
Measured Travel Speeds
A. Where Density Was Reportedly Not a Factor Transport terminals27 Average under “normal conditions”28
265 ft/min on walkways (1.35 m/s) 60 m/min (1.0 m/s)
Experiment with disabled subjects29 On horizontal (m/s) All disabled subjects With locomotion disability No aid Crutches Cane Walker/rollator Without locomotion disability Unassisted wheelchair Assisted ambulant Assisted wheelchair
Min
1st Q
3rd Q
Max
Mean
0.10 0.10 0.24 0.63 0.26 0.10 0.82 0.85 0.21 0.84
0.71 0.57 0.70 0.67 0.49 0.34 1.05 — 0.58 1.02
1.28 1.02 1.02 1.24 1.08 0.83 1.34 — 0.92 1.59
1.77 1.68 1.68 1.35 1.60 1.02 1.77 0.93 1.40 1.98
1.00 0.80 0.95 0.94 0.81 0.57 1.25 0.89 0.78 1.30
On upward incline All disabled With locomotion disability No aid Crutches Cane Walker/rollator Without locomotion disability Unassisted wheelchair Assisted ambulant Assisted wheelchair
0.21 0.21 0.30 0.35 0.21 0.30 0.70 0.70 0.23 0.53
0.42 0.42 0.48 — 0.38 — — — 0.42 0.70
0.74 0.72 0.87 — 0.70 — — — 0.70 1.05
1.32 1.08 1.08 0.53 1.05 0.42 1.32 — 0.72 1.05
0.62 0.59 0.68 0.46 0.52 0.35 1.01 — 0.53 0.89
On downward incline All disabled With locomotion disability No aid Crutches Cane Walker/rollator Without locomotion disability Unassisted wheelchair Assisted ambulant Assisted wheelchair
0.10 0.10 0.28 0.42 0.18 0.10 0.70 1.05 0.42 0.70
0.42 0.42 0.45 — 0.35 — — — 0.52 0.96
0.70 0.70 0.94 — 0.70 — — — 0.86 1.05
1.83 1.22 1.22 0.53 1.04 0.52 1.83 — 1.05 1.05
0.60 0.58 0.68 0.47 0.51 0.36 1.26 — 0.69 0.96
Mid-rise apartment drill20 Mid-rise apartment drill20 Mid-rise apartment drill20 High-rise apartment drill19 High-rise apartment drill19
0.47 m/s on stairs (ranged from 0.34 to 1.08 m/s among various adult age groups; one visually impaired person traveled 0.31 m/s) 0.44 m/s on stairs (ranged from 0.32 to 0.56 m/s among various adult age groups) 0.41 m/s on stairs (ranged from 0.30 to 0.47 among various adult age groups) 1.05 m/s (ranged from 0.57 to 1.20 m/s among various adult age groups) 0.95 m/s (ranged from 0.56 to 1.12 m/s among various adult age groups)
B. Where Density Was a Factor Public places27 Public places28 Theaters and educational28 Industrial buildings28 Transport terminals28 Descending stairs28
100–250 ft/min on walkways (0.51–1.27 m/s) 70–150 ft/min on stairs (0.36–0.76 m/s) 17 m/min minimum on horizontal (0.28 m/s) 11–16 m/min downstairs (0.18–0.27 m/s) 15–20 m/min (0.25–0.33 m/s) max 2.33 m/s 25–30 m/min (0.42–0.56 m/s) max 2.33 m/s 20–25 m/min (0.33–0.83 m/s) max 2.10 m/s 20–25 m/min (0.33–0.42 m/s) max 1.28 m/s
(continued)
4–40 SECTION 4 ■ Human Behavior in Fire Emergencies
TABLE 4.2.2
Continued
High-rise office building drill14 Stair with full lighting Stair with reduced lighting Stair with photoluminescent material (PLM) installation and reduced lighting Stair with PLM only Mid-rise office building drill15 Mid-rise office building drill15 Hotel exercise—along corridor (m/s)30 Daytime scenario 1 Able-bodied participants Wheelchair users Walking disabled Daytime scenario 2 Able-bodied participants Wheelchair users Walking disabled Nighttime scenario Able-bodied participants Wheelchair users Walking disabled a
Mean Speed
Density
0.61 m/s 0.70 m/s
1.30 persons/m2 1.25 persons/m2
0.72 m/s 0.57 m/s
1.00 persons/m2 2.05 persons/m2
0.78 m/s down stairs 0.93 m/s down stairs
Min
1st Q
Med
3rd Q
Max
Mean
0.6 0.2 0.1
1.1 — —
1.3 — —
1.8 — —
4.0 1.2 —
1.5 0.8 —
0.3 0.4 0.7
0.9 — —
1.1 — —
1.3 — —
1.6 0.7 —
1.1 0.6 —
0.5 0.5 2.4a
1.1 — —
1.3 — —
1.7 — —
3.8 0.9 —
1.5 0.7 —
This person traveled at this speed for a distance of 4.9 m.
CALCULATION METHODS FOR TRAVEL TIME Calculating the travel time for an individual alone is a fairly straightforward exercise: travel time will be the product of travel distance and walking speed. Calculating the travel time for a crowd of occupants is more complex. There are three fundamental characteristics of crowd movement: density, speed, and flow. Density of a crowd is defined as the number of persons per unit area (e.g., 2.0 persons/m2). Density can also be expressed as the area per person (e.g., 0.5 m2/person). Speed is the time rate of motion of the occupants, usually expressed in meters per second. Flow is the rate at which people pass a particular point, such as a doorway per unit of time (e.g., 2.0 persons/s). Along with path width, the three characteristics of crowd movement are related as follows: flow C speed ? density ? width As mentioned in the previous section, speed is a function of density. The more people there are in a space, the slower they move, until eventually they reach the point where they are at a shuffling speed. Flow and density have a more complex relationship. At low densities, the rate of flow is small, as there are few people in the stream. Flow rates again are slow at high densities where there is little movement. Optimal flow is achieved at a density of approximately 2.0 persons/m2. For details on the derivation of this value, the reader is referred to the SFPE Handbook of Fire Protection Engineering.31
There are several different approaches to calculating egress time. Flows through doors or corridors can be calculated. Walking speeds can be calculated or can be used as input to models to calculate evacuation time. These methods can be simple enough to do by hand, or can be carried out by computer models that may incorporate other behavioral factors.
Empirically Based Evacuation Time Equations Figure 4.2.2 presents a comparison of observed evacuation times for tall buildings with derived equations for the prediction of total evacuation time.32–34 Pauls’s data34 is based on measurements obtained from 29 evacuation drills, primarily in office buildings ranging from 8 to 21 stories high. Pauls observed evacuation times varying from approximately 10 s/story for buildings with small populations to approximately 20 s/story for buildings with large populations. The evacuation equations indicated in Figure 4.2.2 were developed from these observed evacuation times. The first equation, T C 0.70 = 0.0133p is to be applied to predict evacuation times in buildings with large populations exceeding 800 persons/m2 of effective stair width. T is the minimum time (min) to complete an uncontrolled total evacuation by stairs and p is the actual evacuation population/m of effective stair width, measured immediately above the discharge level of the stair.
CHAPTER 2
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Calculation Methods for Egress Prediction
4–41
28 24 Total evacuation time (min)
22 20 18 16 Observed times in Canadian evacuations
14 12 10
T = 0.70 + 0.0133p
8
T = 2.00 + 0.0117p
6
Melinek & Booth 11 & 21 stories 17
4
Galbreath 11 stories 16
2 0
0
200
400
600
800
1000 1200 1400 1600 1800 2000
Evacuation population/persons/meter of effective stair width
Evacuees’ speed down stairs (meters per second)
26 Spot measurement
1.0
Case average
0.5
S = 1.08 - 0.29d
Fruin (1971)
0 0
1
2 3 Density (persons/m2)
4
5
FIGURE 4.2.3 Relation between Speed and Density on Stairs in Uncontrolled Total Evacuations
FIGURE 4.2.2 Predicted and Observed Total Evacuation Times for Tall Office Buildings
It should be recognized that “effective stair width,” as used by Pauls, is defined in the following manner.34 This empirically based model describes flow as a linear function of a stair’s effective width—the width remaining once the edge effects are deducted (150 mm or 6 inches from each wall boundary and 90 mm or 3.5 inches from each handrail centerline). It takes into account the propensity of people to sway laterally—especially when walking slowly in a crowd—and therefore to arrange themselves in a staggered traditional unitwidth model based on presumed static dimensions of people’s shoulders. The second equation in Figure 4.2.2, T C 2.00 = 0.0117p is to be applied when the population/m of effective stair width is less than 800 persons. Pauls34 also examined the relationship between the speed of evacuation and the density on the stairs during the uncontrolled total evacuation, as indicated in Figure 4.2.3. It should be remembered that this movement would be in the vertical, downward direction.
Hydraulic Flow Calculations The estimation of modeled evacuation time uses a series of expressions that relate data acquired from tests and observations to a hydraulic approximation of human flow.35 Although the expressions indicate absolute relationships, there is considerable variability in the data. Figure 4.2.2 shows a typical relationship between the source data and the derived equation. The equations and relationships presented in the following paragraphs can be used independently or collectively to solve a complex egress problem. Such a coordinated collection of equations is demonstrated in the sample problem.
Effective Width, We. Persons moving through the exit routes of a building maintain a boundary layer clearance from walls and other stationary obstacles they pass. This clearance is needed to accommodate lateral body sway and assure balance. Discussion of this crowd movement phenomena is found in the works of Pauls,36 Fruin,37 and Habicht and Braaksma.38 The useful (effective) width of an exit path is the clear width of the path less the width of the boundary layers. Figures 4.2.4 and 4.2.5 depict effective width and boundary layer. Table 4.2.3 is a listing of boundary layer widths. The effective width of any portion of an exit route is the clear width of that portion of an exit route less the sum of the boundary layers. Clear width is measured 1. 2. 3. 4.
From wall to wall in corridors or hallways As the width of the treads in stairways As the actual passage width of a door in its open position As the space between the seats along the aisles of assembly arrangement 5. As the space between the most intruding portions of the seats (when unoccupied) in a row of seats in an assembly arrangement The intrusion of handrails is considered by comparing the effective width without the handrails, and the effective width using a clear width from the edge of the handrail. The smaller of the two effective widths then applies. Using the values in Table 4.2.3, only handrails that protrude more than 2.5 in. (6 cm) need to be considered. Minor midbody height or lower intrusions such as panic hardware are treated in the same manner as handrails. Where an exit route becomes either wider or narrower, only that portion of the route has the appropriate greater or lesser clear width. Density, D. Density is the measurement of the degree of crowding in an evacuation route and is usually expressed in persons/unit area. The calculations in this chapter are based on density expressed in persons/ft2 (or persons/m2).
4–42 SECTION 4 ■ Human Behavior in Fire Emergencies
Handrail centerlines 3.5 in. (8.9 cm)
Wall
Open side
Wall
Nominal stair width Recessed passenger queue
Boundary layer
3.5 in. (8.9 cm)
Effective design width
Railing
Effective width 6 in. (15.2 cm)
Departure lounge
6 in. (15.2 cm) Viewing area
Suspended TV display flight information
Area of tread use Stair tread (A)
Effective design width Wastebasket
Nominal aisle stair width 3.5 in. (8.9 cm)
Center aisle handrail
Bench
Telephones Floor-standing display
Half aisle Effective width
Half aisle Effective width
Wastebasket
Chair Effective design width
Wall
Aisle stair tread (48 in. preferred) (122 cm)
FIGURE 4.2.5
Public Corridor Effective Width
(B)
FIGURE 4.2.4 Measurements of Effective Width of Stairs in Relation to Walls, Handrails, and Seating
Unless information on the dispersion of occupants indicates otherwise, the density of the first exit element (aisle, corridor, ramp, etc.) is based on all of the served occupants. This will demonstrate the capacity limits of the route element and produce a value representing the maximum capacity of the element. However, if the egressing population is widely dispersed, in terms of reaching the exit route element, the calculation is based on an appropriate time step. At each time increment, the density of the exit route is based on those who have entered the route minus those who have passed from it. The density factors in subsequent portions of the egress system are determined by calculation. The calculation methods involved are contained in the section on transitions. Speed of Exiting Individuals, S. The evacuation speed of a group is a function of the population density. The relationships presented in this section have been derived from Fruin,37 Pauls,36 and Predtechenskii and Milinskii.39 If the population density is less than about 0.05 persons/ft2 (0.54 persons/m2) of exit route (20 ft2/person; 1.85 m2/person), in-
TABLE 4.2.3
Boundary Layer Widths Boundary Layer
Exit Route Element
in.
cm
Stairways—walls or side of tread Railings, handrailsa Theater chairs, stadium benches Corridor, ramp walls Obstacles Wide concourses, passageways Door, archways
6 3.5 0 8 4 Up to 18 6
15 9 0 20 10 46 15
a Where handrails are present, use the value if it results in a lesser effective width.
dividuals will move at their own pace, independent of the speed of others. If the population density exceeds about 0.35 persons/ft2 (3.8 persons/m2), no movement will take place until enough of the crowd has passed from the crowded area to reduce the density. Between the density limits of 0.05 and 0.35 persons/ft2 (0.54 and 3.8 persons/m2), the relationship between speed and density can be considered as a linear function. The equation of this function is S C k > akD
(1)
CHAPTER 2
where
■
4–43
TABLE 4.2.5 Conversion Factors for Relating Line of Travel Distance to Vertical Travel for Various Stair Configurations
S C speed along the line of travel D C density (persons/unit area) k C constant, as shown in Table 4.2.4, where k C k 1 and a C 2.86 when calculating speed in feet per minute and density in persons per square foot k C k 2 and a C 0.266 when calculating speed in meters per second and density in persons per square meter Table 4.2.4 shows evacuation speed constant. Figure 4.2.6 is a graphic representation of the relationship between speed and density. The speeds determined from Equation 2 are along the line of movement; for stairs this is along the line of the treads. Table 4.2.5 provides convenient multipliers for converting vertical rise of a stairway to a distance along the line of movement. The travel on landings must be added to the values derived from Table 4.2.5. The maximum speed occurs when the density is less than 0.05 persons/ft2 (0.54 persons/m2). These maximum speeds are listed in Table 4.2.6.
TABLE 4.2.4
Calculation Methods for Egress Prediction
Constants for Equation 2, Evacuation Speed
Exit Route Element
k1
ks
275
1.40
Stairs Riser [in. (mm)]
Tread [in. (mm)]
Conversion Factor
7.5 (190) 7.0 (178) 6.5 (165) 6.5 (165)
10.0 (254) 11.0 (279) 12.0 (305) 13.0 (330)
1.66 1.85 2.08 2.22
Within the range listed in Tables 4.2.4 through 4.2.6, the evacuation speed on stairs varies approximately as the square root of the ratio of tread width to tread height. There is not sufficient data to appraise the likelihood that this relationship holds outside this range. Specific Flow, Fs . Specific flow, Fs, is the flow of evacuating persons past a point in the exit route/unit of time/unit of effective width, We, of the route involved. Specific flow is expressed in persons/min/ft of effective width (if the value of k C k 2, from Table 4.2.4) or persons/s/m of effective width (if the value of k C k 2, from Table 4.2.4). The equation for specific flow is Fs C SD
(2)
where Corridor, Aisle, Ramp, Doorway Stairs Riser (in.)
Tread (in.)
7.5 7.0 6.5 6.5
10 11 12 13
Fs C specific flow D C density
196 212 229 242
1.00 1.08 1.16 1.23
Note: 1 in. = 25.4 mm.
S C speed of movement Fs is in persons/min/ft2 when density is in persons/ft2 and speed is in ft/min; Fs is in persons/s/m2 when density is in persons/m2 and speed is in m/s. Combining Equations 1 and 2 produces Fs C (1 > aD)kD
.5
3.5
4 1.5
250
Movement speed (ft/min)
Density (persons/m²) 1.5 2 2.5 3
1
where k is as listed in Table 4.2.4. The relationship of specific flow to density is shown in Figure 4.2.7. In each case the maximum specific flow occurs when the density is 0.175 persons/ft2 (1.9 persons/m2) of exit route
Corridor, ramp, aisle, doorway
1.25
200
1
150
.75
100
.5 Various stairs
50
.25
0 0
.05
.1
.15 .2 .25 Density (persons/ft²)
Movement speed (m/s)
300
0
(3)
.3
.35
.4
0
FIGURE 4.2.6 Evacuation Speed as a Function of Density. S = k – akD, where D = density is persons/ft 2 and k is given in Table 4.2.4. Note that speed is along line of travel.
TABLE 4.2.6
Maximum (Unimpeded) Exit Flow Speeds Speed—Along Line of Travel
Exit Route Element
ft/min
m/s
Corridor, Aisle, Ramp, Doorway
235
1.19
167 187 196 207
0.85 0.95 1.00 1.05
Stairs Riser [in. (mm)]
Tread [in. (mm)]
7.5 (190) 7.0 (178) 6.5 (165) 6.5 (165)
10 (254) 11 (279) 12 (305) 13 (330)
4–44 SECTION 4 ■ Human Behavior in Fire Emergencies
.5
TABLE 4.2.7
Density (persons/m2) 1.5 2 2.5 3
1
3.5
Specific flow (persons/min-ft effective width)
25 Corridor, ramp, aisle, doorway
20
1.20 1.00
15
0.80 0.60
10
Various stairs 0.40
5 0.20 0.00
0 0
.05
FIGURE 4.2.7
.1
.15 .2 .25 Density (persons/ft2)
.3
.35
.4
Specific Flow as a Function of Density
space. Maximum specific flows are associated with each type of exit route element; these are listed in Table 4.2.7. Calculated Flow, Fc. The calculated flow, Fc, is the predicted flow rate of persons passing a particular point in an exit route. The equation for actual flow is Fc C FsWe
(4)
where
Maximum Specific Flow Exit Route Element [in. (mm)] 7.5 (190) 7.0 (178) 6.5 (165) 6.5 (165)
Persons/min/ft of Effective Width
Persons/s/m of Effective Width
17.1 18.5 20.0 21.2
0.94 1.01 1.09 1.16
10 (254) 11 (279) 12 (305) 13 (330)
aisle that serves other sources of exiting population. It is also the point of entrance into a stairway serving other floors (Figure 4.2.8). 2. The point where a corridor enters a stairway. There are actually two transitions: one occurs as the egress flow passes through the doorway; the other as the flow leaves the doorway and proceeds onto the stairs. 3. Any point where an exit route becomes wider or narrower. For example, a corridor may be narrowed for a short distance by an intruding service counter or similar element. The calculated density, D, and specific flow, Fs, differ before reaching, while passing, and after passing the intrusion (Figure 4.2.9). The following rules apply to determining the densities and flow rates following the passage of a transition point: 1. The flow after a transition point is a function, within limits, of the flow(s) entering the transition point. 2. The calculated flow, Fc, following a transition point cannot exceed the maximum specific flow, Fsm, for the route element involved multiplied by the effective width, We, of that element.
Fc C calculated flow Fs C specific flow We C effective width Combining Equations 3 and 4 produces Fc C (1 > aD)kDWe
Maximum Specific Flow, Fsm
4 Specific flow (persons/s-m effective width)
0
(5)
Fc is in persons/min when k C k 1 (from Table 4.2.4), D is in persons/sq ft2, and We in ft. Fc is in persons/s when k C k 2 (from Table 4.2.4), D is in persons/m2, and We in m.
2
Time for Passage, Tp. Time for passage, Tp, that is, time for a group of persons to pass a point in an exit route, can be expressed as Tp C P/Fc
(6)
where Tp is time for passage (Tp is in minutes where Fc is persons/min; Tp is in seconds where Fc is persons/s. P is population in persons. Combining Equations 5 and 6 yields Tp C P/(1 > aD)kDWe
3
(7)
Transitions. Transitions are any point in the exit system where the character or dimension of a route changes or where routes merge. Typical examples of points of transition include the following: 1. The point where two or more exit flows merge. For example, the meeting of the flow from a cross aisle into a main
1
FIGURE 4.2.8
Merging Egress Flows
CHAPTER 2
1
Transition in Egress Component
3. Within the limits of rule 2, the specific flow, Fs, of the route departing from a transition point is determined by the following equations: (a) For cases involving one flow into and one flow out of a transition point: Fs (out) C Fs (in)We(in)/We(out)
Calculation Methods for Egress Prediction
4–45
4. Where the calculated specific flow, Fs, for the route(s) leaving a transition point, as derived from the equations in rule 3, exceeds the maximum specific flow, Fsm, a queue will form at the incoming side of the transition point. The number of persons in the queue will grow at a rate equal to the calculated flow, Fc, in the arriving route minus the calculated flow leaving the route through the transition point. 5. Where the calculated outgoing specific flow, Fs (out), is less than the maximum specific flow, Fsm, for that route(s), there is no way to predetermine how the incoming routes will merge. The routes may share access through the transition point equally, or there may be total dominance of one route over the other. For conservative calculations, assume that the route of interest is dominated by the other route(s). If all routes are of concern, it is necessary to conduct a series of calculations to establish the bounds on each route under each condition of dominance.
2
FIGURE 4.2.9
■
(8a)
where Fs (out) C specific flow departing from a transition point
EXAMPLE: This example uses stairs of U.S. conventional size and is therefore presented in English units. Consider an office building (Figure 4.2.10) with the following features:
Fs (in) C specific flow arriving at a transition point We(in) C effective width prior to a transition point
1. There are nine floors, 300 ft ? 80 ft. 2. Floor-to-floor height is 12 ft. 3. There are two stairways, located at ends of building (no dead ends). 4. Each stair is 44 in. wide (tread width) with handrails protruding 2.5 in. 5. Stair risers are 7 in. wide; treads are 11 in. high. 6. There are two 4 ft ? 8 ft landings per floor of stairway travel. 7. There is one 36 in. clear width door at each stairway entrance and exit. 8. The first floor does not exit through stairways. 9. Each floor has a single 8-ft wide corridor extending the full length of each floor. Corridors terminate at stairway entrance doors. 10. There is a population of 300 persons/floor.
We(out) C effective width after passing a transition point (b) For cases involving two incoming flows and one outflow from a transition point, such as that which occurs with the merger of a flow down a stair and the entering flow at a floor: 2» ½ Fs (out) C Fs (in)-1We(in)-1 » ½6 (8b) = Fs (in)-1We(in)-2 /We(out) where the subscripts (in-1) and (in-2) indicate the values for the two incoming flows. (c) For cases involving other merger geometries, the following general relationship applies: » ½ » ½ Fs (in-1)We(in-1) = ß = Fs (in-n)We(in-n) » » ½ ½ (8c) C Fs (out-1)We(out-1) = ß = Fs (out-n)We(out-n)
SOLUTION A—FIRST ORDER APPROXIMATION
1. Assumptions. The prime controlling factor will be either the stairways or the door discharging from them. Queuing will occur; therefore, the specific flow, Fs, will be the maximum specific flow, Fsm. All occupants start egress at the same
where the letter n in the subscripts (in-n) and (out-n) is a number equal to the total number of routes entering (in-n) or leaving (out-n) the transition point.
Example building typical floors 2 through 9 Office space 150 occupants
80 ft (24 m) Office space 150 occupants
300 ft (80 m)
FIGURE 4.2.10
Floor Plan for Example
4–46 SECTION 4 ■ Human Behavior in Fire Emergencies
2.
3.
4.
5.
time. The population will use all facilities in the optimum balance. Estimate flow capability of a stairway. From Table 4.2.3, the effective width, We, of each stairway is 44 > 12 C 32 in. (2.66 ft). Also, the effective width, We, of each door is 36 > 12 C 24 in. (2 ft). The maximum specific flow, Fsm, for the stairway (from Table 4.2.7) is 18.5 persons/min/ft effective width. Specific flow, Fs, equals maximum specific flow, Fsm. Therefore, using Equation 4, the flow from each stairway is limited to 18.5 ? 2.66 C 49.2 persons/min. Estimate flow capacity through a door. Again from Table 4.2.7, the maximum specific flow through any 36-in. door is 24 persons/min/ft effective width. Therefore, using Equation 4, the flow through any door is limited to 24 ? 2 C 48 persons/min. Since the flow capacity of the doors is less than the flow capacity of the stairway served, the flow is controlled by the stairway exit doors (48 persons/stairway exit door/min). Estimate the speed of movement for estimated stairway flow. From Equation 1, the speed of movement down the stairs is 212 > (2.86 ? 212 ? 0.175) C 105 ft/min. The travel distance between floors (using the conversion factor from Table 4.2.5) is 12 ? 1.85 C 22.2 ft on the stair slope plus 8 ft travel on each of the two landings, for a total floor-to-floor travel distance of 22.2 = (2 ? 8) C 38.2 ft. The travel time for a person moving with the flow is 38.2/105 C 0.36 min/floor. Estimate building evacuation time. If all of the occupants in the building start evacuation at the same time, each stairway can discharge 48 persons/min. The population of 2400 persons above the first floor will require approximately 25 min to pass through the exit. An additional 0.36 min travel time is required for the movement from the second floor to the exit. The total minimum evacuation time for the 2400 persons located on floors 2 through 9 is estimated at 25.4 min.
SOLUTION B—MORE DETAILED ANALYSIS
1. Assumptions. The population will use all exit facilities in the optimum balance; all occupants start egress at the same time. 2. Estimate flow density, D, speed, S, specific flow, Fs , effective width, We , and initial calculated flow, Fc , typical for each floor. Divide each floor in half to produce two exit calculation zones, each 150 ft long. Determine the density, D, and speed, S, if all occupants try to move through the corridor at the same time; that is, 150 persons moving through 150 ft of an 8-ft wide corridor. Density, D C 150 persons/1200 ft2 corridor area C 0.125 persons/ft2. From Equation 1, speed, S C k > akD. From Table 4.2.4, k C 275. S C 275 > (2.86 ? 275 ? 0.125) C 177 ft/min. From Equation 3, specific flow, Fs C (1 > aD)kD. Fs C [1 > (2.86 ? 0.125)] ? 275 ? 0.125 C 22 persons/ft effective width/min.
From Table 4.2.7, the specific flow, Fs, is less than the maximum specific flow, Fsm1; therefore, Fs is used for the calculation of calculated flow. From Table 4.2.3, the effective width of the corridor is 8 > (2 ? 0.5) C 7 ft. From Equation 5, calculated flow, Fc C (1 > aD)kDW Fc C [1 > (2.86 ? 0.125)] ? 275 ? 0.125 ? 7 C 154 persons/min. Note: At this stage in the calculation, calculated flow, Fc, is termed “initial calculated flow” for the exit route element (i.e., corridors) being evaluated. This is because the calculated flow rate can be sustained only if the discharge (transition point) from the route can also accommodate the indicated flow rate. 3. Estimate impact of stairway entry doors on exit flow. Each door has a 36-in. clear width. From Table 4.2.3, effective width, We, is 30 > 12 C 24 in. (2 ft). From Table 4.2.7, the maximum specific flow, Fsm, is 24 persons/min/ft effective width. From Equation 8, Fs(door) C [Fs(corridor)We(corridor)]/We(door)Fs(door) C (22 ? 7)/2 C 77 persons/min/ft effective width. Since Fsm is less than the calculated Fs, the value of Fsm is used. Therefore, the effective value for specific flow is 24. From Equation 4 the initial calculated flow, Fc C FsWe C 24 ? 2 C 48 persons/min through a 36-in. door. Since Fc for the corridor is 154 whereas Fc for the single exit door is 48, queuing is expected. The calculated rate of queue buildup will be 154 > 48 C 106 persons/min. 4. Estimate impact of stairway on exit flow. From Table 4.2.3, effective width, We, of the stairway is 44 > 12 C 32 in. (2.66 ft). From Table 4.2.7, the maximum specific flow, Fsm, is 18.5 persons/ft effective width. From Equation 8, the specific flow for the stairway, Fs(stairway), is 24 ? 2/2.66 C 18.0 persons/ft effective width. In this case, Fs is less than Fsm, and Fs is used. The value of 18.0 for Fs applies until the flow down the stairway merges with the flow entering from another floor. Using Figure 4.2.6 or Equation 3 and Table 4.2.4, the density of the initial stairway flow is approximately 0.146 persons/ft2 of stairway exit route. From Equation 1, the speed of movement during the initial stairway travel is 212 ? (2.86 ? 212 ? 0.146) C 123 ft/min. From Solution A, the floor-to-floor travel distance is 38.2 ft. The time required for the flow to travel one floor level is 38.2/123 C 0.31 min (19 s). Using Equation 4, the calculated flow, Fc, is 18.0 ? 2.66 C 48 persons/min. After 0.31 min, 48 ? 0.31 C 15 persons will be in the stairway from each floor feeding to it. If floors 2 through 9 exit all at once, there will be 15 ? 8 C 120 persons in the stairway. After this time, the merging of flows between the
CHAPTER 2
flow in the stairway and the incoming flows at stairway entrances will control the rate of movement. 5. Estimate impact of merger of stairway flow and stairway entry flow on exit flow. From Equation 9, Fs(out-stairway) C {[Fs(door) ? We(door)] = [Fs(in-stairway) ? We(in-stairway)]}/We(out-stairway) C [(24 ? 2) = (18 ? 2.66)]/66 C 36 persons/ft effective width. From Table 4.2.7, Fsm for the stairway is 18.5 persons/min/ft effective width. Since Fsm is less than the calculated Fs, the value of Fsm is used. 6. Track egress flow. Assume all persons start to evacuate at time zero. Initial flow speed is 177 ft/min. Assume that congested flow will reach the stairway in 30 s. At 30 s, flow starts through stairway doors. Fc through doors is 48 persons/min for the next 19 s. At 49 s, 120 persons are in each stairway, and 135 are waiting in a queue at each stairway entrance door. Note: Progress from this point on depends on which floors take dominance in entering the stairways. Any sequence of entry may occur. To set a boundary, this example estimates the result of a situation where dominance proceeds from the highest to the lowest floor. The remaining 135 persons waiting at each stairway entrance on the 9th floor enter through the door at the rate of 48 persons/min. The rate of flow through the stair is regulated by the 48 persons/min rate of flow of the discharge exit doors. The descent rate of the flow is 19 s/floor. Thus, at 218 s (3.6 min) All persons have evacuated the 9th floor. at 237 s (4.0 min) The end of the flow reaches the 8th floor. at 401 s (6.7 min) All persons have evacuated the 8th floor. at 420 s (7.0 min) The end of the flow reaches the 7th floor. at 584 s (9.7 min) All persons have evacuated the 7th floor. at 603 s (10.1 min) The end of the flow reaches the 6th floor. at 767 s (12.8 min) All persons have evacuated the 6th floor. at 786 s (13.1 min) The end of the flow reaches the 5th floor. at 950 s (15.8 min) All persons have evacuated the 5th floor. at 969 s (16.2 min) The end of the flow reaches the 4th floor. at 1133 s (18.9 min) All persons have evacuated the 4th floor. at 1152 s (19.2 min) The end of the flow reaches the 3rd floor. at 1316 s (21.9 min) All persons have evacuated the 3rd floor.
■
Calculation Methods for Egress Prediction
at 1335 s (22.3 min) at 1499 s (25.0 min) at 1518 s (25.3 min)
4–47
The end of the flow reaches the 2nd floor. All persons have evacuated the 2nd floor. All persons have evacuated the building.
COMPUTER SIMULATION AND MODELING OF EGRESS DESIGN Simulation modeling may be appropriate for problems that would otherwise require costly, time-consuming, and tedious manual effort; those that cannot be solved through experimentation because of high costs or unacceptable risks to human participants; and for which past experience, intuition, or available data do not provide the proper insight.40
Types of Evacuation Models Three types of evacuation models are currently available: • Single-parameter estimation models • Movement models • Behavioral simulation models Single-Parameter Estimation Models. Single-parameter estimation models are generally used for simple estimates of movement times. They can be hand calculations or simple computer models (e.g., flow times based on widths of exit paths or travel times based on distances). Movement Models. Movement models generally handle large numbers of people in a network flow. This type of model treats occupants like water in a pipe or ball bearings in a chute. They tend to optimize occupant behavior, with all occupants moving at the same speed, with perfect knowledge of the building’s layout and exit routes. Such models can be useful in benchmarking designs; if the calculated exit times using this type of model are insufficient for safe evacuation, then the actual evacuation time in a real fire will certainly be insufficient. Behavioral Simulation Models. Behavioral simulation models consider more of the variables related to occupant movement and behavior. They treat occupants as individuals with unique characteristics. Occupants can move at different speeds, in reaction to the conditions in their surroundings. Because they are tracked individually, their exposure and reaction to toxic conditions while evacuating can be estimated by some of these models or by tenability or toxicity models that analyzed the simulation results. This type of model allows a more realistic simulation, but there are concerns with their use related to the lack of available data that would allow the prediction of human behavior in fire. In choosing a model, the user has to understand the underlying assumptions and be sure that those assumptions are appropriate to the analysis at hand. Computer simulation and modeling have become important tools in designing adequate means of egress under a variety of
4–48 SECTION 4 ■ Human Behavior in Fire Emergencies
occupancy and structural conditions. Evacuation modeling has become particularly important in recent years since standardsmaking organizations around the world have developed performance-based options for fire protection design. An essential element in the evaluation of an engineered design is a comparison of the results of the modeling of a range of fire scenarios, and the subsequent fire effects that can be expected, with the results of an evacuation model that will predict where and for how long people will be dispersed throughout a structure.
History of Evacuation Modeling Evacuation modeling has a long history. In one study of the critical variables for fire safety in relation to buildings used to house the elderly, the problem of fire development and evacuation as a time-structured problem was considered.41 This study analyzed the variables related to the occurrence and spread of fire relative to the population’s ability to reach an area of refuge from the effects of the fire. The study established the variables for the fire on a continuum of a “critical time” and the parameters for the survival of the occupants on a continuum of a “reaction time.” The definition adopted for critical time is the time elapsed from the start of the fire to the attainment of intolerable levels. The definition for reaction time is reported as the amount of time used by the occupant to react to the fire and to achieve safety by evacuating the fire area or by obtaining a place of refuge from the effects of the fire. Thus, within the framework of these definitions, both the parameters of the problem of the human behavior factors involved in a fire in a building and the variables of the problem are considered. This conceptualization of a critical time for fire development within a building and of the reaction time required for occupants to perceive and respond to the fire threat, either by evacuation or movement to an area of refuge, has been studied thoroughly. It resulted in multiple computer models of this essential egress behavior since Caravaty and Haviland’s study in 1967.41 A computer model that simulated the movement of people during evacuation through the floor of fire origin was developed in the mid-1970s.42 This Markov-based model focused on the movement of people through a fire floor from the time of alarm until their safe exit or until they became casualties of the fire. Six variables affecting their movement were identified: 1. Objective location of the threatening stimuli in time and space 2. Occupants’ prior knowledge of effective egress routes 3. Occupants’ perception of the location and severity of the threat 4. Occupants’ perception of available alternatives 5. Occupants’ threat-reducing experiences prior to the current movement decision 6. The interjection of sudden interpretations to the occupants’ goal-directed behavior A modeling technique was developed in the early 1980s that appeared to have potential for comparing the evacuation behavior of occupants assisted by trained personnel with evacuation without assistance.43 This model determined the escape potential
from an area of a building based on a deterministic approach with a computer algorithm, and it evaluated the effects of fire growth and smoke movement on occupants as they try to egress. Occupant evacuation was simulated with evaluation of the effects of the egress design, the density of the occupants in the means of egress, the congestion at door or other restrictions, and the effects of the combustion products on occupants. The concepts of critical time and reaction time as originally formulated by Caravaty and Haviland41 were adapted into a determination of the available safe egress time (ASET) model.2 This model is a mathematical procedure for simulating of the conditions that develop between the time of fire ignition and the onset of untenable conditions for human occupancy. It was developed to evaluate the evacuation plans and procedures within a specific building.2 This model required input data on the physical dimensions of the building areas, the means of egress, and the specified evacuation routes with the number and location of the occupants. The model provided an estimated average evacuation time and an estimated total evacuation time. Building network evacuation models similar to the model of O’Leary and Gratz44 were developed that evaluate the egress environment within the building and the characteristics of the population relative to density and location.45 The models predicted evacuation flows and times, and identified queueing problems. The model was validated with evacuation data from high-rise federal office buildings and college dormitories. An analytical queueing network model (QNM) was also developed to be used in the analysis of a building design relative to the suitability of the egress system.46 This model provided estimates of the evacuation times, the average queue lengths along egress routes, potential impairments, and total egress probability. The improvement and use of computer models for evacuation analysis in the late 1980s was examined and reviewed by Watts.47 During the 1990s, development of evacuation models accelerated. Fahy48 developed a FORTRAN model called EXIT89 to predict evacuation times for high-rise buildings. This evacuation model was designed to work with two of the subprograms of HAZARD I,49 FAST, and TENAB to estimate the hazard to the occupants from the modeled fire incident. It calculates the occupants’ movement along the shortest evacuation routes or user-defined “familiar” routes, and the queuing of the occupants along these routes. The walking speeds in this model are derived from the occupant densities values developed by Predtechenskii and Milinskii.39 The model has been further developed over the following decade to incorporate a range of real-life features, such as the presence of disabled occupants, premovement delays, choices in exit route selection, and so on.50 In recent years, improvements in computer technology have allowed a new generation of computer models that take advantage of the power of computers today and the sophistication of newer software tools. Many of these models are analogous to the CFD models of fire development. Rather than using network-node descriptions of a building, these models describe the building space as a mesh, or grid, and use complex spatial analysis and computer-generated route finding techniques. Rather than jump from node to node, as simulated occupants will ap-
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pear to do in a network model, occupants will move from “tile” to “tile” in the grid that overlays the floor plan. This allows a more precise location of occupants throughout spaces. The current generation of model all include the phenomena that EXIT89 sought to address. Some of the new models also include additional phenomena, but there are always tradeoffs between the completeness and detail of the models and the implied magnitude of data requirements. It is not clear that the net predictive power or accuracy is improved if simplified representations requiring limited data with moderate uncertainty are replaced by elaborate, highly sophisticated representations requiring enormous databases with large associated uncertainty and a heavy reliance on subjective estimation to compensate for a lack of field data. In short, the range of choices has expanded greatly over the past several years, but the value of more simple models has not been diminished. Due to the variation in techniques used for modeling evacuation, it is not possible to present the equations used. For that level of detail, the reader is referred to the documentation for the particular model of interest. And, as the available list of evacuation models grows, it would not be feasible to list the models here. No truly objective comparison has been undertaken of the range of evacuation models currently available, but a brief overview of many of the currently available programs can be found in the literature.51–53 The degree to which behavior is simulated varies extensively among available models. Care must be taken in choosing a model. The complexity of some models implies a greater predictive capability, but the scarcity of data available on behavior means that a great number of assumptions are imbedded in the models, and the appropriateness of those assumptions is critical in evaluating the validity of a model’s results. Chapter 3–14 of the SFPE Handbook of Fire Protection Engineering, “Emergency Movement,” includes guidance on the selection of evacuation models. A list of questions the user should be able to answer about the model selected for analysis is provided.
SUMMARY It is critically important in estimating the time to evacuate a building that attention be paid to more than the travel time necessary to clear spaces. The total time to evacuate a building, or to bring occupants to a location of safety, must include delay times before movement or refuge actions begin. Whether the calculations are based on data or on calculations, and regardless of whether the calculations are done by hand or by computer, a valid time estimate cannot be made without consideration of time to start. The characteristics of the building occupants and of the building itself will govern the choice of appropriate delay time estimates, as well as the calculation of travel times.
BIBLIOGRAPHY References Cited 1. Proulx, G., “Evacuation Time and Movement in Apartment Buildings,” Fire Safety Journal, Vol. 24, No. 3, 1995, pp. 229–246.
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2. Cooper, L. Y., “A Mathematical Model for Estimating Available Safety Egress Time in Fires,” Fire and Materials, Vol. 6, Nos. 3 & 4, 1982, pp. 135–144. 3. Evans, D. W., and Stroup, D. W., Methods to Calculate the Response Time of Heat and Smoke Detectors Installed below Large Unobstructed Ceilings, NBSIR 85-3167, National Bureau of Standards, Washington, DC, 1985. 4. Joshi, A. A., and Pagni, P. J., Users’ Guide to BREAK1, the Berkeley Algorithm for Breaking Window Glass in a Compartment Fire, NIST-GCR-91-596, National Institute of Standards and Technology, Gaithersburg, MD, 1991. 5. Nelson, H. E., FPETOOL—Fire Protection Engineering Tools For Hazard Estimation, National Institute of Standards and Technology, Washington, DC, 1990. 6. Shields, T. J., Boyce, K. E., and Silcock, G. W. H., Unannounced Evacuation of Marks & Spencer Sprucefield Store, Unpublished Report, University of Ulster Fire SERT, Carrickfergus, Jan. 1997. 7. Fahy, R. F., and Proulx, G., “Toward Creating a Database on Delay Times to Start Evacuation and Walking Speeds for Use in Evacuation Modeling,” Proceedings of the 2nd International Symposium on Human Behaviour in Fire 2001, Interscience Communications Ltd., London, UK, 2001, pp. 175–183. 8. Proulx, G., and Fahy, R. F., “The Time Delay to Start Evacuation: Review of Five Case Studies,” Proceedings of the 5th International Symposium on Fire Safety Science, International Association for Fire Safety Science, 1997, pp. 783–794. 9. Donald, I., and Canter, D., “Behavioural Aspects of the King’s Cross Disaster,” Fires & Human Behaviour, 2nd ed., David Fulton Publishers, London, UK, pp. 15–30. 10. Bryan, J. L., An Examination and Analysis of the Human Behavior in the MGM Grand Hotel Fire, revised report, National Fire Protection Association, Quincy, MA, 1983. 11. Bryan, J. L., An Examination and Analysis of the Dynamics of the Human Behavior in the Westchase Hilton Hotel Fire, revised edition, National Fire Protection Association, Quincy, MA, March 1983. 12. Fahy, R., and Proulx, G., Unpublished Analysis of World Trade Center Data, National Fire Protection Association, Quincy, MA, Oct. 1994. 13. Brennan, P., “Timing Human Response in Real Fires,” Proceedings of the 5th International Symposium on Fire Safety Science, Y. Hasemi (Ed.), International Association for Fire Safety Science, 1997, pp. 807–818. 14. Proulx, G., Tiller, D., Kyle, B., and Creek, J., Assessment of Photoluminescent Material During Office Occupant Evacuation, Internal Report 774, National Research Council of Canada, Ottawa, ON, Apr. 1999. 15. Proulx, G., Kaufman, A., and Pineau, J., Evacuation Time and Movement in Office Buildings, Internal Report No. 711, National Research Council of Canada, Ottawa, ON, Mar. 1996. 16. Shields, T. J., Boyce, K. E., and Silcock, G. W. H., Unannounced Evacuation of Marks & Spencer Sprucefield Store, Unpublished Report, University of Ulster Fire SERT, Carrickfergus, Jan. 1997. 17. Shields, T. J., and Boyce, K. E., “A Study of Evacuation from Large Retail Stores,” Fire Safety Journal, Vol. 35, No. 1, 2000, pp. 25–49. 18. Proulx, G., and Fahy, R. F., “The Time Delay to Start Evacuation: Review of Five Case Studies,” Proceedings of the 5th International Symposium on Fire Safety Science, Y. Hasemi (Ed.), International Association for Fire Safety Science, 1997, pp. 783–794. 19. Proulx, G., Latour, J. C., McLaurin, J. W., Pineau, J., Hoffman, L. E., and Laroche, C., Housing Evacuation of Mixed Abilities Occupants in Highrise Buildings, Internal Report No. 706, National Research Council of Canada, Ottawa, ON, Aug. 1995. 20. Proulx, G., Latour, J., and MacLaurin, J., Housing Evacuation of Mixed Abilities Occupants, Internal Report No. 661, National Research Council of Canada, Ottawa, ON, July 1994.
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21. Nakano, M., and Hagiwara, I., “Experimental Study on Starting Time of Evacuation in Sleeping Condition,” Presented at the Fourth Asia-Oceania Symposium on Fire Science and Technology, Waseda University, Tokyo, Japan, May 25, 2000. 22. Pauls, J., “Movement of People,” SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1996, pp. 3-263–3-285. 23. Boyce, K. E., Shields, T. J., and Silcock, G. W. H., “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Prevalence, Type, and Mobility of Disabled People,” Fire Technology, Vol. 35, No. 1, 1999, pp. 35–50. 24. Boyce, K. E., Shields, T. J., and Silcock, G. W. H., “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capabilities of Disabled People Moving Horizontally and on an Incline,” Fire Technology, Vol. 35, No. 1, 1999, pp. 51–67. 25. Boyce, K. E., Shields, T. J., and Silcock, G. W. H., “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capability of Disabled People to Negotiate Doors,” Fire Technology, Vol. 35, No. 1, 1999, pp. 68–78. 26. Boyce, K. E., Shields, T. J., and Silcock, G. W. H., “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capability of People with Disabilities to Read and Locate Exit Signs,” Fire Technology, Vol. 35, No. 1, 1999, pp. 79–86. 27. Fruin, J. J., Pedestrian Planning Design, Metropolitan Association of Urban Designers and Environmental Planners, Inc., New York, 1971. 28. Predtechenskii, V. M., and Milinskii, A. I., Planning for Foot Traffic Flow in Buildings, Amerind Publishing Company, Inc., New Delhi, India, 1978. 29. Boyce, K. E., Shields, T. J., and Silcock, G. W. H., “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capabilities of Disabled People Moving Horizontally and on an Incline,” Fire Technology, Vol. 35, No. 1, 1999, pp. 51–67. 30. Shields, T. J., Fire and Disabled People in Buildings, Report BR 231, Building Research Establishment, Garston, 1993. 31. Proulx, G., “Movement of People: The Evacuation Timing,” Section 3, Chapter 13, SFPE Handbook of Fire Protection Engineering, 3rd ed., National Fire Protection Association, Quincy, MA, 2002, p. 3-342. 32. Galbreath, M., “Time of Evacuation by Stairs in High Buildings,” Ontario Fire Marshal, Vol. 5, No. 2, 1969. 33. Melinek, S. J., and Booth, S., “An Analysis of Evacuation Times and the Movement of Crowds in Buildings,” CP 96175, 1975, Building Research Establishment, Fire Research Station, Borehamwood, UK. 34. Pauls, J. L., “Calculating Evacuation Times for Tall Buildings,” Fire Safety Journal, Vol. 12, No. 3, 1987, pp. 213–236. 35. Nelson, H. E., and MacLenna, H. A., “Emergency Movement,” SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995, pp. 3-285–3-295. 36. Pauls, J. L., “Effective-Width Model for Evacuation Flow in Buildings,” Proceedings of the Engineering Applications Workshop, 1980, Society of Fire Protection Engineers, Boston. 37. Fruin, J. J., Pedestrian Planning Design, Metropolitan Association of Urban Designers and Environmental Planners, Inc., New York, 1971. 38. Habicht, A. T., and Braaksma, J. P., “Effective Width of Pedestrian Corridors,” Journal of Transportation Engineering, Vol. 110, No. 1, 1984, pp. 80–93. 39. Predtechenskii, V. M., and Milinskii, A. I., Planning for Foot Traffic in Buildings (translated from the Russian), Russian publication, Stroizdat Publishers, Moscow, 1969; English translation published for the National Bureau of Standards and the National Science Foundation, Washington, Amerind Publishing Co. Pvt., Ltd., New Delhi, India, 1978.
40. Stahl, F. I., “BFIRES II: A Behavior-Based Computer Simulation of Emergency Egress During Fires,” Fire Technology, Vol. 18, No. 1, 1982, p. 63. 41. Caravaty, R. D., and Haviland, D. S., “Life Safety from Fire, A Guide for Housing the Elderly,” Architectural Standards Division, Federal Housing Administration, Washington, DC, 1967. 42. Stahl, F. I., “Simulating Human Behavior in High-Rise Building Fires: Modeling Occupant Movement Through a Fire Floor from Initial Alert to Safety Egress,” NBS-GCR-77-92, 1975, Center for Fire Research, National Bureau of Standards, Washington, DC. 43. Berlin, G. N., “A Simulation Model for Assessing Building Fire Safety,” Fire Technology, Vol. 18, No. 1, 1982, pp. 66–75. 44. O’Leary, T. J., and Gratz, J. M., “An Analysis of Fire Evacuation Procedures Using Simulation,” Fire Journal, Vol. 76, No. 3, 1982, pp. 119–121. 45. Chalmet, L. G., et al., “Network Models for Building Evacuation,” Fire Technology, Vol. 18, No. 1, 1982, pp. 90–113. 46. Smith, J. M., “An Analytical Queuing Network Computer Program for the Optimal Egress Problem,” Fire Technology, Vol. 18, No. 1, 1982, pp. 18–33. 47. Watts, J. M., “Computer Models for Evacuation Analysis,” Fire Safety Journal, Vol. 12, No. 3, 1987, pp. 237–245. 48. Fahy, R. F., “EXIT89: An Evacuation Model for High-Rise Buildings,” Fire Safety Science—Proceedings of the 3rd International Symposium, Elsevier Applied Science, New York, 1991, pp. 815–823. 49. Bukowski, R. W., et al., HAZARD I—Volume I: Fire Hazard Assessment Method, NBSIR 87-3602, July 1987, NIST, Center for Fire Research, Gaithersburg, MD. 50. Fahy, R. F., “Verifying the Predictive Capability of EXIT89,” Proceedings of the 2nd International Symposium on Human Behaviour in Fire, Interscience Communications Ltd., London, UK, 2001, pp. 53–64. 51. Gwynne, S., et al, “A Review of the Methodologies Used in the Computer Simulation of Evacuation from the Built Environment,” Human Behaviour in Fire—Proceedings of the 1st International Symposium, University of Ulster, Belfast, UK, 1998, pp. 681–690. 52. Human Behaviour in Fire—Proceedings of the 1st International Symposium, University of Ulster, Belfast, UK, 1998. 53. Proceedings of the 2nd International Symposium on Human Behaviour in Fire, Interscience Communications Ltd., London, UK, 2001.
Additional Readings Ashe, B., and Shields, J., “Analysis and Modelling of the Unannounced Evacuation of a Large Retail Store,” Fire and Materials, Vol. 23, No. 6, 1999, pp. 333–336. Beck, V., and Zhao, L., “CESARE-RISK: An Aid for PerformanceBased Fire Design, Some Preliminary Results,” Fire Safety Science—Proceedings of the 6th International Symposium, July 5–9, 1999, Poitiers, France, International Association of Fire Safety Science, Boston, MA, 2000, pp. 159–170. Beller, D. K., and Watts, J. M., Jr. “Human Behavior Approach to Occupant Classification,” Proceedings of the 1st International Symposium Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 83–92. Bennetts, I. D., and Thomas, I. R., “Performance Design of Shopping Centers for Fire Safety,” Proceedings of the International Conference, Engineered Fire Production Design, Applying Fire Science to Fire Protection Problems, San Francisco, CA, June 11–15, 2001, Society of Fire Protection Engineers, Bethesda, MD, 2001, pp. 42–53. Bodamer, M., “How People Behave in Fires,” Fire Prevention, No. 224, Nov. 1989, pp. 20, 22–23. Booker, C. K., Powell, J., and Canter, D., “Understanding Human Behavior during Fire Evacuation,” Chapter 6, Council on Tall
CHAPTER 2
Buildings and Urban Habitat, Fire Safety in Tall Buildings. Tall Building Criteria and Loading, Committee 8A, McGraw-Hill, Inc., Blue Ridge Summit, PA, 1992, pp. 93–104. Boyce, K., Fraser-Mitchell, J., and Shields, J., “Survey Analysis and Modelling of Office Evacuation Using the CRISP Model,” Proceedings of the 1st International Symposium on Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 691–702. Boyce, K. E., Shields, T. J., and Silcock, G. W. H., “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capability of Disabled People Moving Horizontally and on an Incline,” Fire Technology, Vol. 35, No. 1, 1999, pp. 51–67. Brennan, P., “Impact of Social Interaction on Time to Begin Rvacuation in Office Building Fires: Implications for Modelling Behavior,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, Cambridge, UK, March 26–28, 1996, C. A. Franks and S. Grayson (Ed.), Interscience Communications Ltd., London, UK, 1996, pp. 701–710. Brennan, P., “Modelling Cue Recognition and Pre-Evacuation Response,” Proceedings of the 6th International Symposium on Fire Safety Science (IAFSS), Poitiers, France, July 5–9, 1999, M. Curtat (Ed.), Intl. Assoc. for Fire Safety Science, Boston, MA, 2000, pp. 1029–1040. Brennan, P., “Successful Evacuation in Smoke: Good Luck, Good Health or Good Management?” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, Edinburgh, UK, June 29–July 1, 1999, Interscience Communications Ltd., London, UK, 1999, pp. 697–706. Brennan, P., “Victims and Survivors in Fatal Residential Building Fires,” Fire and Materials, Vol. 23, No. 6, 1999, pp. 305–310. Brennan, P., and Thomas, I., “Predicting Evacuation Response and Fire Fatalities,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 321–332. Brennan, P., and Thomas, I., “Victims of Fire? Predicting Outcomes in Residential Fires,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 123–134. Bruck, D., and Brennan, P., “Recognition of Fire Cues during Sleep,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 241–251. Bryan, J. L., “Behavioral Response to Fire and Smoke,” SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1995. Bukowski, R. W., “Applications of FASTLite,” Proceedings of Technical Symposium, Computer Applications in Fire Protection Engineering, June 20–21, 1996, Worcester, MA, Society of Fire Protection Engineers, Boston, MA, 1996, pp. 59–66. Bukowski, R. W., “HAZARD II: Implementation for Fire Safety Engineering,” Proceedings of Fire Safety Design of Buildings and Fire Safety Engineering, August 19–20, 1996, Oslo, Norway, Session 3: Fire Safety Engineering Tools, 1996, Conference Compendium, pp. 1–7. Caldwell, C. A., “Ballantynes Department Store Performance Fire Design,” Proceedings of International Conference, Engineered Fire Protection Design, Applying Fire Science to Fire Protection Problems, June 11–15, 2001, San Francisco, CA, Society of Fire Protection Engineers, Bethesda, MD, 2001, pp. 54–65. Caldwell, C. A., and Palmer, D. L., “Human Behavior and the Practising Fire Engineer,” Proceedings of the 1st International Symposium Human Behavior in Fire, Belfast, UK, August 31– September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 93–103.
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Canter, D., Fires and Human Behavior, 2nd ed., Fulton, London, UK, 1988. Capucio, J., “PathFinder: A Computer-Based Timed Egress Simulation,” Fire Protection Engineering, No. 8, Fall 2000, pp. 11–12. Chalmet, L. G., et al., “Network Models for Building Evacuation,” Management Science, Vol. 28, No. 1, 1990, pp. 86–105. Charters, D., Holborn, P., and Townsend, N., “Analysis of the Number of Occupants, Detection Times and Pre-Movement Times,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 197–207. Chien, S. W., and Lin, B. W., “Evaluation of the Evacuation Performance of the Mass Rapid Transit Station Based on the Prescriptive Code,” Proceedings of FORUM 2000 Symposium, Fire Research Development and Application in the 21st Century, October 23–24, 2000, Taipei, Taiwan, 2000, pp. 1–23. Chitty, R., and Kuman, S., “Development of an Integrated Fire Modelling Environment for the Study of Smoke-Egress Interactions,” Proceedings of the 1st International Symposium Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 649–659. Christian, D., “Study to Identify the Incidence in the United Kingdom of Long-Term Sequelae Following Exposure to Carbon Monoxide,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 197–207. Cohn, B. M., “Characterization and Use of Design Basis Fires in Performance Codes,” Proceedings of 7th INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 581–588. Collins, B. L., Dahir, M. S., and Madrzykowski, D., “Visibility of Exit Signs in Clear and Smoky Conditions,” Fire Technology, Vol. 24, No. 2, 1993, pp. 154–182. Cooper, L. Y., and Stroup, D. W., “ASET: A Computer Program for Calculating Available Safe Egress Time,” Fire Safety Journal, Vol. 9, 1985, p. 29. Cote, R. (Ed.), Life Safety Code Handbook, 6th ed., National Fire Protection Association, Quincy, MA, 1994. Daysh, R., and Exley, A., “Using the Net Worth Method to Prove Illicit Income,” Fire and Arson Investigator, Vol. 51, No. 4, 2001, p. 41–44. Ebihara, M., Notake, H., and Yashiro, Y., “Fire Risk Assessment Method for Building Under Consideration of Actions of Security Staff Using an Idea of Fire Phase,” Proceedings of the 1st International Symposium Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 421–428. Fahy, R. F., “EXIT 89: High-Rise Evacuation Model—Recent Enhancements and Example Applications,” Proceedings of 7th INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 1001–1005. Fahy, R. F., “High-Rise Evacuation Modeling: Data and Applications,” Proceedings of the 13th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, Gaithersburg, MD, March 13–20, 1996, National Institute of Standards and Technology, Gaithersburg, MD, NISTIR 6030, June 1997, pp. 35–42. Fahy, R. F., “Practical Example of an Evacuation Model for Complex Spaces,” Proceedings of the 1st International Symposium Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 421–428. Fahy, R. F., “Toward Creating a Database on Delay Times to Start Evacuation and Walking Speeds for Use in Evacuation Modeling,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001,
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Interscience Communications Ltd., London, UK, 2001, pp. 175–183. Fahy, R. F., “Verifying the Predictive Capability of EXIT89,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 53–64. Fahy, R. F., and Proulx, G., “Human Behavior in the World Trade Center Evacuation,” Proceedings of the 5th International Symposium on Fire Safety Science, Melbourne, Australia, March 3–7, 1997, Y. Hasemi (Ed.), Intl. Assoc. for Fire Safety Science, Boston, MA, 1997, pp. 713–724. Fahy, R. F., and Proulx, G., “Study of Occupant Behavior During the World Trade Center Evacuation,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, Cambridge, UK, March 26–28, 1996, C. A. Franks and S. Grayson (Eds.), Interscience Communications Ltd., London, UK, 1996, pp. 793–802. Fahy, R. F., and Sapochetti, J. I., “Human Behavior Modeling as Part of an Engineered Design,” Proceedings of the 8th International INTERFLAM Conference, INTERFLAM ’99, Edinburgh, UK, June 29–July 1, 1999, Interscience Communications Ltd., London, UK, 1999, pp. 747–756. Feinberg, W. E., and Johnson, N. R., “Primary Group Size and Fatality Risk in a Fire Disaster,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 11–22. Fire Engineering Guidelines, 1st ed., Fire Code Reform Center Limited, Sydney, New South Wales, Australia. Fleming, J. M., “Code Official’s View of Performance-Based Codes,” Code Official, Vol. 33, No. 1, 1999, pp. 18–30. Frantzich, H., “Evacuation Capability of People,” Lund Univ., Sweden, TNO Building and Construction Research, CIB/W14 Workshop, Proceedings of the 3rd Fire Engineering Workshop on Modelling, Jan. 25–26, 1993, Delft, the Netherlands, 1993, pp. 224–231. Frantzich, H., “Occupant Behavior and Response Time: Results from Evacuation Experiments,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 159–165. Fraser-Mitchell, J. N., “Modelling Human Behaviour within the Fire Risk Assessment Tool ‘CRISP’,” Human Behaviour in Fire— Proceedings of the 1st International Symposium, University of Ulster, 1998, pp. 447–457. Fraser-Mitchell, J., “Simulated Evacuations of an Airport Terminal Building, Using the CRISP Model,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 89–100. Fraser-Mitchell, J. N., and Pigott, B. B., “Modelling Human Behavior in the Fire Risk Assessment Model ‘CRISP II’,” Fire Research Station, Borehamwood, UK, University of Ulster and Fire Research Station. CIB W14: Fire Safety Engineering, International Symposium and Workshops Engineering Fire Safety in the Process of Design: Demonstrating Equivalency, Part 3, Symposium: Engineering Fire Safety for People with Mixed Abilities, September 13–16, 1993, Newtownabbey, UK, 1993, pp. 1–10. Fruin, J. J., Pedestrian Planning and Design, revised edition, Elevator World, Mobile, AL, 1987. Galea, E. R., Lawrence, P. J., and Filipidis, L., “Extending the Capabilities of the Building EXODUS Evacuation Model to Cater for Hospital Evacuations,” Proceedings of the 3rd International Conference on Fire Research and Engineering (ICFRE3), Chicago, IL, October 4–8, 1999, Society of Fire Protection Engineers, Boston, 1999, pp. 39–50.
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CHAPTER 2
Hadjisophocleous, G. V., Torvi, D. A., Fu, Z., and Yager, B., “FIERAsystem: A Computer Model for Fire Evaluation and Risk Assessment”, Proceedings of 18th International Conference, Offshore Mechanics and Arctic Engineering (OMAE), July 11–16, 1999, St. Johns, Newfoundland, Canada, American Society of Mechanical Engineers, 1999, OMAE99/S&R-6016, pp. 1–8. Hartzell, G. E., “Engineering Analysis of Hazards to Life Safety in Fires: The Fire Effluent Toxicity Component,” Proceedings of the 1st International Symposium on Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 621–629. Hayes, A., and Marchant, E., “People Watching,” Fire Prevention, No. 347, Aug. 2001, pp. 16–19. Heskestad, A. W., and Meland, O. J., “Determination of Evacuation Times as a Function of Occupant and Building Characteristics and Performance of Evacuation Measures,” Proceedings of the 1st International Symposium on Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 673–680. Horasan, M. B. N., “Occupant Evacuation and Orientation Problems in Large Halls: An Exhibition Building Case Study,” Fire and Materials, Vol. 23, No. 6, 1999, pp. 369–373. Hsu, F. K., “Study of Occupants’ Behavior in Industrial/Commercial Fire Incidents: Case Study,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 471–475. Hurley, M. J., “New Tools for Engineered Fire Protection Design,” Proceedings of the International Conference, Engineered Fire Production Design, Applying Fire Science to Fire Protection Problems, San Francisco, CA, June 11–15, 2001, Society of Fire Protection Engineers, Bethesda, MD, 2001, pp. 12–19. Hurley, M. J., and O’Connor, D. J., “Integrating Human Behavior in Fires into Fire Protection Engineering Design,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 403–409. Jin, T., and Yamada, T., “Experimental Study on Human Emotional Instability in Smoke Filled Corridor. Part 2,” Journal of Fire Sciences, Vol. 8, No. 2, 1990, pp. 124–134. Jones, W. W., “Evolution of HAZARD, the Fire Hazard Assessment Methodology,” Fire Technology, Vol. 33, No. 2, 1997, pp. 167–182. Jonsson, R., and Lundin, J., “Swedish Case Study: Different Fire Safety Design Methods Applied to a High Rise Building,” Proceedings of 2nd International Conference, Performance-Based Codes and Fire Safety Design Methods, May 5–9, 1998, Maui, HI, 1998. Keating, J. P., “Human Resources During Fire Situations: A Role for Social Engineering,” General Proceedings Research and Design, American Institute for Architects Foundation, Washington, DC, 1985. Kendik, E., “Methods of Design of Means of Egress: Towards a Quantitative Comparison of National Code Requirements,” Proceedings of the 1st International Symposium of Fire Safety Science, Hemisphere, Washington, DC, 1986. Keski-Rahkonen, O., “Probability of Multiple Deaths in Building Fires According to an International Fire Statistics Study,” Proceedings of the 1st International Symposium on Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 381–391. Kisko, T. M., and Francis, R. L., “EVACNET+, A Computer Program to Determine Optimal Building Evacuation Plans,” Fire Safety Journal, Vol. 9, No. 2, 1985, pp. 211–220. Klevan, J. B., “Modeling of Available Egress Time from Assembly Spaces or Estimating the Advance of the Fire Threat,” SFPE TR 82-2, Society of Fire Protection Engineers, Boston, May 1982.
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31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 461–468. Owen, M., Galea, E. R., and Lawrence, P., “Advanced Occupant Behavioral Features of the buildingEXODUS Evacuation Model,” Proceedings of the 5th International Symposium on Fire Safety Science, Melbourne, Australia, March 3–7, 1997, Y. Hasemi (Ed.), Intl. Assoc. for Fire Safety Science, Boston, 1997, pp. 795–806. Owen, M., Galea, E. R., and Lawrence, P. J., “The EXODUS Model,” Fire Engineers Journal, Vol. 56, No. 183, 1996, pp. 26–30. Owen, M., Galea, E. R., Lawrence, P. J., and Filippidis, L., “AASK: Aircraft Accidents Statistics and Knowledge: A Database of Human Experience in Evacuation, Derived from Aviation Accident Reports,” Proceedings of the 1st International Symposium on Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 509–518. Ozel, F., Way Finding and Route Selection in Fires, School of Architecture, New Jersey Institute of Technology, Newark, NJ, 1986. Pauls, J., “Development of Knowledge About Means of Egress,” Fire Technology, Vol. 20, No. 2, 1984, pp. 28–40. Pauls, J., Gatfield, A. J., and Juillet, E., “Elevator Use for Egress: The Human-Factors Problems and Prospects,” National Research Council of Canada, Ottawa, Ontario, National Task Force on Life Safety and the Handicapped American Society of Mechanical Engineers, Council of American Building Officials and National Fire Protection Association, Elevators and Fire, February 19–20, 1991, Baltimore, MD, 1991, pp. 63–75. Paulsen, R. L., “Human Behavior and Fires: An Introduction,” Fire Technology, Vol. 20, 1984, pp. 15–27. Peacock, R. D., Reneke, P. A., Jones, W. W., Bukowski, R. W., and Forney, G. P., “User’s Guide for FAST: Engineering Tools for Estimating Fire Growth and Smoke Transport,” NIST SP 921, National Institute of Standards and Technology, Gaithersburg, MD, Mar. 2000. Poon, L. S., and Beck, V. R., “Numerical Modelling of Human Behavior during Egress in Multi-Storey Office Building Fires Using EvacSim—Some Validation Studies,” Proceedings of the 1st International Conference on Fire Science and Engineering, ASIAFLAM ’95, March 15–16, 1995, Kowloon, Hong Kong, 1995, pp. 163–174. Portier, R. W., Peacock, R. D., and Reneke, P. A., “FASTLite: Engineering Tools for Estimating Fire Growth and Smoke Transport,” NIST SP 899, National Institute of Standards and Technology, Gaithersburg, MD, 1996. Predtechenskii, V. M., and Milinskii, A. I., Planning for Foot Traffic Flow in Buildings, Amerind Publishing Co., New Delhi, India, 1978. Proulx, G., “As of Year 2000, What Do We Know about Occupant Behavior in Fires?” Proceedings of the United Engineering Foundation Conference, Technical Basis for Performance Based Fire Regulations. A Discussion of Capabilities, Needs and Benefits of Fire Safety Engineering, San Diego, CA, January 7–11, 2001, G. Cox (Ed.), New York, United Engineering Foundation, 2001, pp. 127–129. Proulx, G., “Few Findings Resulting from a Study of Occupant Behavior Following a Residential Highrise Fire,” Canadian Fire Chief, Vol. 3, No. 3, 1999, pp. 49–50. Proulx, G., “Highrise Evacuation: A Questionable Concept,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 221–230. Proulx, G., “Human Factors in Fires and Fire Safety Engineering,” SFPE Bulletin, Winter 1995, pp. 13–15. Proulx, G., “Impact of Voice Communication Messages during a Residential Highrise Fire,” Proceedings of the 1st International Symposium on Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 265–274.
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CHAPTER 2
Shields, T. J., and Boyce, K. E., “Study of Evacuation from Large Retail Stores,” Fire Safety Journal, Vol. 35, No. 1, 2000, pp. 25–49. Shields, T. J., Boyce, K. E., and Silcock, G. W. H., “Towards the Characterization of Large Retail Stores,” Fire and Materials, Vol. 23, No. 6, 1999, pp. 325–331. Shields, T. J., Smyth, B., Boyce, K. E., and Silcock, G. W. H., “Evacuation Behaviours of Occupants with Learning Difficulties in Residential Homes,” Proceedings of the 1st International Symposium on Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 369–377. Sime, J. D., “Occupant Response,” Fire Safety Engineering, Vol. 8, No. 1, 2001, pp. 14–18. Sime, J. D., “Advancing Human Behavior Theory: Visual Access and Occupancy Resarch, Modeling and Applications,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 37–40. Sinclair, R., and Horasan, M., “Emergency Evacuation of the Gaming Rooms of a Large Casino Complex: Occupant and Management Related Issues,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 349–360. Stroup, D. W., “Using Performance-Based Design Techniques to Evaluate Fire Safety in Two Government Buildings,” Proceedings of Pacific Rim Conference and 2nd International Conference on Performance-Based Codes and Fire Safety Design Methods, May 3–9, 1998, Maui, HI, International Code Council, Birmingham, AL, 1998, pp. 429–439. Takahashi, K., and Tanaka, T., “An Evacuation Model for the Use in Fire Safety Designing of Buildings,” 9th Joint Panel Meeting of the UJNR Panel on Fire Research and Safety, NBSIR 88-3753, National Bureau of Standards, Gaithersburg, MD, Apr. 1988. Taylor, B., Manifold, T., and Lodge, J., “Towards Developing a Picture of Those Most at Risk of Death by Fire,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 333–339. Thomas, G., “Capital E: A Refurbishment Case Study,” Proceedings of Pacific Rim Conference and 2nd International Conference on Performance-Based Codes and Fire Safety Design Methods, May 3–9, 1998, Maui, HI, International Code Council, Birmingham, AL, 1998, pp. 411–427. Thompson, B., “Wayfinding to Escape in Complex Buildings,” Fire International, No. 170, Sept. 1999, p. 31. Thompson, P., et al., “Simulex 3.0: Modelling Evacuation in MultiStorey Buildings,” Proceedings of the 5th International Symposium of Fire Safety Science, Y. Hasemi (Ed.), International Association for Fire Safety Science, Melbourne, 1997, pp. 725–736.
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CHAPTER 3
SECTION 4
Concepts of Egress Design Revised by
James K. Lathrop
M
eans of egress and their design should be based upon an evaluation of a building’s total fire protection system and an analysis of the population characteristics and hazards to the occupants of that building. The means of egress design should be treated as an integral part of the total system that provides reasonable safety to life from fire. This chapter covers the fundamental concepts of good egress design that are the basis for NFPA 101®, Life Safety Code®, and NFPA 5000™, Building Construction and Safety Code™. NFPA 101 governs good practices to provide life safety features in existing buildings and structures and features that can be designed as integral parts of new construction to provide reasonable safety to occupants in fires. NFPA 5000 addresses new construction only, but covers life safety from many hazards in addition to fire. The components of good means of egress are discussed in some detail, with their functions and relationships in the total concept of proper egress design. Computer modeling and simulation to assist the egress design process also are discussed.
FUNDAMENTALS OF DESIGN The approach to designing means of egress first requires a familiarity with the reaction of people in fire emergencies. These reactions can differ widely, depending upon the physical and mental capabilities and conditions of building occupants. The psychological and physiological factors affecting the use of exits during emergencies are being identified and measured in research studies. Dr. John L. Bryan discusses in detail behavioral response to fire and smoke in Section 3, Chapter 12 of the SFPE Handbook of Fire Protection Engineering, third edition.1 Patterns of movement of people, singly and in crowded conditions, must also be understood. In buildings used as schools or theaters housing highly mobile occupants, for example, there are certain reproducible flow characteristics from persons exiting the buildings. These predictable flow characteristics have fostered computer simulation and modeling to aid the
James K. Lathrop is a vice president in the firm Koffel Associates of Ellicot City, Maryland, and Niantic, Connecticut. He is a member of the Technical Committee on Fundamentals; Board and Care Occupancies; the NFPA Uniform Fire Code; and an alternate on the Technical Committee on Means of Egress. He is chair of the Technical Committee on Residential Occupancies.
egress design process. However, no number of practical exit facilities can prevent injury or loss of life if the occupant egress flow is inhibited or prevented by the building itself, by personnel, or by fire and smoke conditions. An in-depth review of movement of people by Pauls can be found in Section 3, Chapter 13 of the SFPE Handbook of Fire Protection Engineering,2 as well as in “Emergency Movement” by Nelson and MacLennon in Section 3, Chapter 14 of the same document.3
Human Factors The design and capacity of passageways, stairways, and other components in the total means of egress are related to the physical dimensions of the human body. The tendency of people to avoid bodily contact with others should be recognized as a major factor in determining the number of persons who will occupy a given space at any given time. Given a choice, people usually automatically establish “territories” to avoid bodily contact with others. Studies have shown that most adult men measure less than 20.7 in. (520 mm) across at the shoulder, with no allowance for additional thicknesses of clothing.4 A “body ellipse” concept is used to develop the design of pedestrian systems. The major axis of the body ellipse measures 24 in. (609 mm), whereas the minor axis is 18 in. (457 mm). This ellipse equals 2.3 sq ft (0.21 m2), which is assumed to help determine the maximum practical standing capacity of a space. The movement of persons results in a swaying action that varies from male to female and, depending upon the type of motion, varies with movement on stairs, on level surfaces, or in dense crowds. Body sway has been observed to range 1½ in. (38 mm) left and right during normal free movement. Where movement is reduced to shuffling in dense crowds and to movement on stairs, a total sway range of almost 4 in. (101 mm) has been observed. In theory, this indicates that a total width of 30 in. (762 mm) would be required to accommodate a single file of pedestrians traveling up or down stairs.5 Crowding people into spaces where less than 3 sq ft (0.28 m2) of space per person is available under nonemergency conditions may create a hazard. When the average area occupied per person is reduced to 2¾ sq ft (0.25 m2) or less, contact will be unavoidable. Needless to say, under the psychological stresses imposed during a fire, such crowding and contact could contribute to crowd pressures, resulting in injuries. When a
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4–58 SECTION 4 ■ Human Behavior in Fire Emergencies
Factors Affecting Movement of People There are several factors that determine how quickly people may pass through the means of egress. In level walkways an average walking speed of 250 ft/min (76 m/min) is attained under free-flow conditions, with 25 sq ft (2.3 m2) of space available per person. Speeds below 145 ft/min (44 m/min) show shuffling, which restricts motion. Figure 4.3.1, adapted from Research Report No. 95 of the London Transport Board,6 shows the rate of speed reduction for space concentrations of less than 7 sq ft (0.65 m2) per person. Speeds of less than 145 ft/min (44 m/min) result in shuffling, and, finally, a jam point is reached with one person every 2 sq ft (0.18 m2). The possibility of a significant nonadaptive behavior exists whenever egress movement is restricted, and the problem becomes urgent under fire exposure conditions, especially when there is more than one person every 3 sq ft (0.28 m2). Calculations of flow rates using velocity [ft/min (m/min)] and density [persons/sq ft (m3)] will reveal flow [persons/min/ft (m) of width], which increases as the pedestrian area decreases. The flow increases will continue until forward movement becomes restricted to the point that the flow begins to drop. Interestingly, observations of flow rates in one study noted the same flow rate sometimes occurred even though walking speeds of people were significantly different. Investigation revealed that the rate of decrease in speed, accompanied by an increase in density, results in uniform flow rates over a wide range of conditions. A study of footways indicates that for passageways over 4 ft (1.2 m) wide, flow rates are directly proportional to width. The London Transport Board Research Report No. 956 determined the flow rate in level passages to be 27 persons/min/ft (0.30 m) of width. Travel down stairways was determined at 21 persons/min/ft (0.30 m) of width, whereas upward travel was reduced to 19 persons/min/ft (0.30 m) of width. Where the width Speed (mph) (fpm) 4
(m/min) (kph)
(352)
(106)
6.4
Natural flow 3
(264)
ng wi Slo
wn do
(176)
2
Flow imagined to be artificially impeded to bring passengers to a stop
Sh u
(80)
(53)
3.2
(27)
1.6
fflin g
(88)
1
Jam point concentration (measured) 0
20
10 7
4.8
5.0 3.33 2.25 Concentration (sq ft per person)
of a footway is less than 4 ft (1.2 m), the flow rate depends upon the number of possible traffic lanes. Absolute maximum flow rates occur when approximately 3 sq ft (0.28 m) is occupied per person, which is applicable to both level walkways and stairs. In observed and measured evacuations, however, it has been empirically determined that the maximum flow rates down stairs in high-rise buildings occur when from 4 to 5 sq ft of space (0.37 to 0.46 m2) is occupied per person, as shown in Figure 4.3.2.5 When flow in opposite directions takes place in a passageway up to the point where the two flows are of equal magnitude, there is no significant reduction in total flow below that which would be predicted on the basis of unidirectional flow in the same passageway. Further, flow can be 50 percent greater in short passageways less than 10 ft (3.05 m) long than through a long passageway of the same width. Minor obstructions within a passageway do not appear to have a significant effect on flow. Within a 6 ft (1.82 m) wide passageway, there is no effect on flow rates when a 1-ft (0.45-m) projection is introduced. A 2-ft (0.61-m) projection resulting in a 33 percent reduction in width reduces the flow rate by approximately 10 percent. A major obstruction, though, such as that which occurs at a ticket booth or turnstile, may interrupt the movement of people and reduce flow rates. Corners, bends, and slight grades up to 6 percent are apparently not factors in determining flow rates. A slight reduction in speed does occur, but the flow rate is maintained by an increased concentration of persons. A center handrail or mullion, which may divide a passageway into narrower sections, can further reduce the capacity of the passageway. The observed capacity of a 6 ft (1.82 m) wide stairway reveals a reduction from 130 to 105 persons/min after installation of a center handrail. Except for the very young and the very old, age does not appear to be a significant factor in determining travel speed. Studies have shown a significant reduction in walking speeds for persons
50
Mean flow per 22 in. (559 mm) stairway width persons/minute
queue occurs because of an artificial, temporary situation or because of some permanent design feature, crowd control becomes difficult, and the well-being of individuals is threatened.
40
30
20
10
0 0 2.0
FIGURE 4.3.1 Speed in Level Passageways (SI units; 1 ft/min = 0.305 m/min; 1 sq ft = 0.093 m2)
0.1
0.2
0.3
0.4
0.5
Mean density stairway, person/sq ft
FIGURE 4.3.2 Effect of Density on Flow Down Exit Stairways in Evacuations of High-Rise Office Buildings5 (SI units: 1 sq ft = 0.032 m2)
CHAPTER 3
7.5 in. (190 mm) riser, 10 in. (255 mm) tread (A)
The Capacity Method. This method is based on the theory that sufficient numbers of stairways should be provided in a building to adequately house all occupants of the building without requiring any movement, or flow, out of the stairways. In theory, assuming a stairwell provides a safe and protected area for all occupants within the protective barrier created by the stairway enclosure, evacuation of the building may then be more leisurely, permitting people to travel at a rate within their physical ability. The capacity method recognizes that evacuation from high-rise buildings is physically very demanding. Further, evacuation of a healthcare facility is likely to be slow. Thus, design criteria are established to permit holding occupants within exits or areas of refuge.
Application The capacity and flow methods may both be applied to efficient egress design, depending upon specific circumstances. Where people are expected to be physically or mentally sick, aged, asleep, or incapacitated in any way, evacuation and use of the flow method is unwise. Therefore, the capacity method, which provides a place for everyone within an area of refuge, is the appropriate method. There is little time between an alert and the use of an exit in assembly occupancies, and maximum flow rates that cause reductions in the area used by each person may result in reduced traffic flows. On the other hand, the control of children in an educational setting, coupled with their familiarity with the surroundings, their presumed high physical capabilities, and their
(B)
0.25 6
Two units of exit width/150 persons
5
4
0.20
0.15
3 220 seconds
2
0.10
W/P, Effective stair width per person (in.)
Traditional capacity reference: Two units of exit width/120 persons
7 W/P, Effective stair width per person (mm)
The Flow Method. This method uses the theory of evacuating a building within a specified maximum period of time. Flow rates have traditionally been set at 60 persons per 22 in. (559 mm) width/min through level passageways and doorways. In older editions of NFPA 101 this 22 in. (59 mm) width was referred to as 1 “unit” of exit width. Credit was given only for whole units or ½ unit, a ½ unit being 12 in. The flow method may be applied in assembly occupancies, such as theaters, and educational occupancies where people are alert, awake, and assumed to be in good physical condition. Figure 4.3.3 illustrates the flow time in seconds relative to the effective stair width per person and the units of width. Pauls’s7 effective stair width concept advocates the consideration of only the portion of the stair used in effective movement by the occupants, as observed in functional and practice evacuations. This width is established with 6-in. (150-mm) clearance from each side wall of the stair.
8 0.30
Methods of Calculating Exit Width Two major principles are used to determine the necessary exit width. They are based on anticipated population characteristics identified with a specific occupancy.
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Concepts of Egress Design
6.5 in. (165 mm) riser, 13 in. (330 mm) tread 7.0 in. (180 mm) riser, 11 in. (280 mm) tread
185 seconds
over 65 years of age. Studies have further revealed that a 40 percent increase is possible in the normal walking speed, which tends to discount this factor as a major influence on flow rates.4 For additional information see Section 3, Chapter 13, of the SFPE Handbook of Fire Protection Engineering.
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0.05
1
0 0
100
200
300 400 Flow time (s)
500
0 600
FIGURE 4.3.3 Relationship between Effective Stair Width and Units of Exit Width per Person and Flow Time for Three Stair Geometries7
experience with a program of drills should allow rapid evacuation times. The flow method appears to have its application in those occupancies where people are considered to be alert, awake, and of normal physical ability. Pauls has reviewed the historical and current literature relative to the principles of people movement, exit width determination, and the design of the means of egress.8
Design of Means of Egress Designing a means of egress involves more than numbers, flow rates, and densities. Safe exit from a building requires a safe path of escape from the fire environment. The path is arranged for ready use in case of emergency and should be sufficient to permit all occupants to reach a safe place before they are endangered by fire, smoke, or heat. Proper egress design permits everyone to leave the fire-endangered areas in the shortest possible time with efficient exit use. If a fire is discovered in its incipient stage and the occupants are alerted promptly, effective evacuation may take place. Evacuation travel distances are related to the content fire hazard. The higher the hazard, the shorter the travel distance to an exit. Depending upon the physical environment of the structure, the characteristics of the occupants, and the fire detection and alarm facilities, fire or smoke may prevent the use of one means of egress. Therefore, at least one alternative means of egress remote from the first is essential. Provision of two separate means of egress is a fundamental safeguard, except where a building or
4–60 SECTION 4 ■ Human Behavior in Fire Emergencies
room is small and arranged so that a second exit would not provide an appreciable increase in safety. There are fewer or no advantages to separate means of egress if there is travel through a common space or use of common structural features that result in the loss of the two distinct and physically separate means of egress. One example of a “common” structure is a multistory building where scissors stairs are used. These are two stairs enclosed within a common shaft, separated by a partition common to both stairs. Scissors stairs are sometimes used to provide the required exit capacity while minimizing the loss of valuable floor space. Where a set of scissors stairs is the only means of egress when two remote exits are required, however, the fundamental principle of two separate means of egress design may be violated. If the common partition between the stairs fails, it would result in the simultaneous loss of both exits during a fire, leaving no alternative means of egress. With scissors stairs, the validity of the two separate means of egress, therefore, depends upon the design characteristics and construction of the common partition (Figure 4.3.4).
X
In some proposed egress designs, all the exits discharge through a single lobby at street level, even though this procedure results in egress travel through a common space. This design philosophy presumes that the lobby may be considered a safe area for all future egress needs during the life of the building. Where two remote means of egress are required, this type of egress design is unsuitable. NFPA 101 limits openings in exit enclosures to those necessary for access to the enclosure from normally occupied spaces and for egress from the enclosure. Penetration of enclosures by ducts or other utilities constitutes a point of weakness and may result in contamination of the enclosure during a fire and should not be permitted. Furthermore, it is not good practice to use exit enclosures for any purpose that could interfere with their value as exits. For example, exit stair enclosures should not be used for storage or any other use not associated with egress or areas of refuge for mobility impaired persons. The removal of handicapped persons is an important consideration in the design of an emergency means of egress from a building. A 32-in. (813-mm) doorway is considered the minimum width to accommodate a person in a wheelchair. Since handicapped employees or visitors may be found in all types of buildings, special life safety considerations are indicated. The 2000 edition of NFPA 101 contains several additional provisions to protect mobility impaired individuals.
LIFE SAFETY CODE
X
FIGURE 4.3.4 Advantages and Disadvantages of Scissors Stairs versus Conventional Stairs. This set of scissors stairs provides the same degree of remote exit or entrance doors as the circled stairs shown by dotted lines—travel distance for all occupants is the same, even if the dotted exit stairs were located at opposite corners as denoted by the cross marks. Space is saved; however, the integrity of the separation of the two scissors stairs may remain in question.
NFPA 101, introduced in 1927 and revised and reissued in successive editions, is developed by several committees under the oversight of the Technical Correlating Committee on Safety to Life, a representative group dedicated to safety of life from fire. NFPA 101 is primarily concerned with the control of conditions that threaten the lives of individuals in building fires. This objective is different from fire protection provisions in building codes, which are concerned with the preservation of property, in addition to the preservation of life. In 2000, NFPA announced its intent to write a building code: NFPA 5000™, Building Construction and Safety Code™, first edition, due to be published in 2003. The provisions for means of egress in NFPA 5000™ are written by the same committees that write NFPA 101. Because of this, the discussion here will address NFPA 101. It is equally applicable to NFPA 5000™ when dealing with new construction. Adequate means of egress alone are not a guarantee of life safety from fire. They do not protect an individual whose own carelessness causes a threat to life, such as setting his or her own clothes on fire. Neither do sufficient means of egress alone provide adequate protection in occupancies such as hospitals, nursing homes, prisons, assisted living facilities, and mental institutions, where occupants are confined or are physically or mentally unable to escape without effective and immediate assistance. NFPA 101 does recognize such situations and provides life safety measures, including low-flame-spread and reduced-smokeproducing materials for interior finish. In addition, automatic sprinkler and smoke management systems called for by NFPA 101 are designed to restrain the spread of fire and smoke and thus help to defend the occupants within an area of refuge until they are able to use the exits or until the fire has been extinguished.
CHAPTER 3
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In general, saving building occupants from a fire requires the following, all of which are identified in NFPA 101: 1. Sufficient number of properly designed, unobstructed means of egress of adequate capacity and arrangement. 2. Provision of alternative means of egress for use if one means of egress is blocked by fire, heat, or smoke. 3. Protection of the means of egress against fire, heat, and smoke during the egress time determined by the occupant load, travel distance, and exit capacity. 4. Subdivision of areas by proper construction to provide areas of refuge in those occupancies where total evacuation is not a primary consideration. 5. Protection of vertical openings to limit the operation of fire protection equipment to a single floor. 6. Provision of detection or alarm systems to alert occupants and notify the fire department in case of fire. 7. Adequate illumination of the means of egress. 8. Proper marking of the means of egress, and the indication of directions. 9. Protection of equipment or areas of unusual hazard that could produce a fire capable of endangering the egressing occupants. 10. Initiation, organization, and practice of effective drill procedures. 11. Provision of instructional materials and verbal alarm systems in high-density and high-life-hazard occupancies to facilitate adaptive behavior. 12. Use of interior finish materials that prevent a high flame spread or dense smoke production that could endanger egressing occupants. Figure 4.3.5 illustrates some of the principles of exit safety. NFPA 101 recognizes that full reliance cannot be placed upon any single safeguard, since any single protective feature may not function due to mechanical or human failure. For this reason, redundant safeguards, any one of which will result in a reasonable level of life safety, should be provided. NFPA 101 also recommends the special protection of hazardous areas and specifies where automatic sprinkler, detection, and other protective systems are required. NFPA 101 is used widely as a guide to good practice and as a basis for local laws or regulations. It differs from building codes since it generally provides little distinction among the different classes of building construction. However, where total evacuation of a building is not practical, due either to the occupant characteristics or the building environment, the construction type becomes an important variable and should be considered. NFPA 101 also recognizes that all habitable buildings contain sufficient quantities of combustible contents to produce lethal quantities of smoke and heat.9,10 In addition, casualty studies have established that the toxic properties of smoke are the principal hazard to life,11 and this hazard is recognized in NFPA 101. NFPA 101 is intended to be applied to both new and existing buildings and is designed to provide a reasonable level of life safety from fire in both types of buildings. The Authority Having Jurisdiction is given considerable latitude in achieving conformance with existing buildings. Each existing building represents a special situation that requires individual attention
Concepts of Egress Design
4–61
At least two ways out remote from each other Evacuation drills well planned frequently practiced
Additional exits according to number of persons and relative fire danger
Exit available in reasonable travel distance
Exit paths marked, unobstructed, well lighted This way out
Exit
FIGURE 4.3.5
Not an Exit E xit
Principles of Exit Safety
for the most effective and economical method of achieving a reasonable level of life safety. The argument that buildings constructed many years ago according to all the legal requirements are sufficiently safe now should not necessarily be accepted. If the economic cost of reasonable life safety is judged to be prohibitive, the occupancy or the structure should be changed or prohibited because there is no justification for subjecting building occupants to an unreasonable level of peril from a fire. There may be a variety of differing opinions as to what constitutes reasonable life safety from a fire in any given case. It is not possible to guarantee occupants 100 percent life safety from a fire; beyond certain conditions, a building becomes hazardous to the life safety of the occupants in a fire. How should the Authority Having Jurisdiction establish the minimum conditions? NFPA 101 provides guidance for such decisions with the help of studies of major-loss-of-life fires,12,13 fire development research,10,14 personnel evacuation,15–17 and human behavior.18,19 NFPA 101 examines the various occupancy populations according to their perceived life safety hazard, which includes psychological and sociological variables, in addition to the physiological and environmental factors. These occupancy classifications are assembly, educational, daycare, healthcare, ambulatory healthcare, detention/correctional, residential, residential board and care, mercantile, business, industrial, and storage. Additional provisions for special-purpose and high-rise structures are also included.
4–62 SECTION 4 ■ Human Behavior in Fire Emergencies
Separate and distinct means of egress provisions are made for each occupancy classification, with the various occupancy subgroups included. These classifications, based on the perceived hazard to life safety from a fire, often differ from older building code occupancy classifications. For example, mercantile and office occupancies were often grouped together in previous editions of building codes. However, there appears to be an increased hazard to life in mercantile properties, resulting from the displays of combustible merchandise, the greater density of the population, and the transient character of most of the occupants. These factors are not usually found in office and educational buildings, which have a relatively low combustibility content, a lower population density, and normally alert occupants who are in the building daily and presumably have the opportunity to familiarize themselves with the means of egress through functional use and evacuation drills.
INFLUENCES ON EGRESS Influence of Hazard of Contents An evaluation of the hazard of the building contents must take into account the relative probability of the ignition of combustibles, the spread of flames and heat, the probable smoke and gases expected to be generated by the fire, and the possibility of a fire-related explosion or other structural failure endangering occupants. The degree of hazard is usually determined by the flammability or toxicity of the contents and by the processes or operations conducted in the building. Most NFPA 101 requirements are based on the exposure created by contents with an ordinary hazard. Special requirements for areas with high-hazard contents usually consist of special protection systems, isolation of the hazard area via fire-rated construction, reduced travel distances, and additional means of egress. To assist in evaluating the contents hazards, NFPA 101 establishes three classifications of contents: (1) low-, (2) ordinary-, and (3) high-hazard. They are discussed next. These should not be confused with the classifications established by NFPA 10, Standard for Portable Fire Extinguishers, or NFPA 13, Standard for the Installation of Sprinkler Systems, nor with those established by some model building codes. Low-Hazard Contents. These are contents of such low combustibility that no self-propagating fire can occur in them. Consequently, the only probable danger requiring the use of emergency exits will be from smoke or from fire from some external source. These are extremely unusual. The storage of sheet metal without combustible packing is one example. Ordinary-Hazard Contents. These are contents that are liable to burn with moderate rapidity and to give off a considerable volume of smoke. This class includes most buildings and is the basis for the general requirements of NFPA 101. High-Hazard Contents. These are contents that are liable to burn with extreme rapidity or from which explosions are to be feared in the event of fire. Examples are occupancies in which
flammable liquids or gases are handled, used, or stored; in which combustible dust explosion hazards exist; in which hazardous chemicals or explosives are stored; in which combustible fibers are processed or handled in a manner that produces combustible flyings; and similar situations.
Influence of Building Construction and Design A building of fire-resistance-rated construction is designed to permit a burnout of contents without structural collapse. Fireresistance-rated design does not ensure the life safety of the occupants of such buildings.12,18 However, the ability of a structural frame to maintain building rigidity under fire exposure is important to the maintenance of the fire-resistance protection of exit enclosures. Where a 2-hr fire-rated exit enclosure is required, a fire-resistance-rated structural frame capable of withstanding stresses imposed by fire for a similar period is also necessary. It is inconsistent to provide a 2-hr exit enclosure in a building with a structural frame rated at less than 1 hr, for example, unless special construction precautions are taken to prevent structural failure of the building from adversely affecting the protective construction of the exit enclosures. The protection of vertical openings is one of the most significant factors in the design of multistory buildings, from the standpoint of life safety and exit design. Because of the natural tendency of fire to spread upward in a building, careful attention to details of design and construction are required to minimize this effect. One of the greatest hazards to life safety results from fires that start below the occupants and the means of egress, such as in basements or on the level of exit discharge. Similarly, fires in multistory buildings may result in smoke spread into enclosed exits before evacuation.12,13,18 Conversely, escape from fires that occur above the occupants is relatively simple, provided sufficient warning is given and adequate means of egress are available. The influence on the life safety of the occupants by the materials used in building construction depends primarily upon whether the materials will propagate flame, support combustion, or create dense amounts of smoke when exposed to a fire initially involving the building contents. Some materials used as insulation, for example, could contribute to rapid flame development and dense smoke production spread. Masonry walls enclosing a wood-frame interior provide no increased occupant life safety compared with a total wood-frame structure. Exit requirements are based on buildings of conventional design. Unusual buildings, such as those without windows or those with unopenable windows, call for special consideration. Windows provide a number of advantages in a fire. Persons at openable windows have access to fresh air, can see fire department rescue operations in progress, are able to communicate verbally and visually with rescue personnel, and may thus be less subject to stress and anxiety. Windows provide a means of escape and accessibility to the building by the fire department for rescue and fire fighting. Automatic sprinklers are considered a primary requirement for life safety in windowless buildings, buildings with unopenable windows, and underground structures.
CHAPTER 3
Influence of Interior Finish, Furnishings, and Decorations The rapid spread of flame over the surface of walls, ceilings, or floor coverings may prevent occupant use of the means of egress. In general, NFPA 101 limits the flame-spread index classification of interior finish materials on walls and ceilings to a maximum of 200, based on the results of tests conducted in accordance with NFPA 255, Standard Method of Test of Surface Burning Characteristics of Building Materials, also known as ASTM E84. Lower ratings are prescribed for the interior finish materials used in exits and in exit accesses. Materials classified as having a lower flamespread index are also required in certain areas in individual occupancies. A fire-retardant coating may be used on existing interior finish materials to reduce the rate of flame spread. In areas protected with automatic sprinklers, the use of materials with higher flame-spread index classifications sometimes is permitted. Table 4.3.1 summarizes the interior finish requirements contained in NFPA 101 for the various occupancy classifications. NFPA 101 also recognizes a new test method: NFPA 286, Standard Methods of Fire Tests for Evaluating Contribution of Wall and Ceiling Interior Finish to Room Fire Growth. Any nontextile material that passes this test, based on the pass-fail criteria contained in NFPA 101, can be used anywhere in a building. The flame spread of floor coverings is evaluated by NFPA 101, through the use of NFPA 253, Standard Method of Test for Critical Radiant Flux of Floor Covering Systems Using a Radiant Heat Energy Source, also known as ASTM E648. Two classes of floor coverings are established: (1) Class I finishes, with a minimum critical radiant flux of 0.45 W/cm2; and (2) Class II finishes, with a minimum critical radiant flux of 0.22 W/cm2. Furnishings and decorations—particularly furnishings— play an increasingly important role in loss of life by fire. Decorations can be treated with a flame retardant. Furnishings, on the other hand, are difficult to control and regulate as a fire hazard, since they are not attached to, or part of, the building construction or of the interior finish materials. Furnishings are moved, refurbished, and replaced. However, there are now test procedures for measuring the combustibility of upholstered furniture and its susceptibility to ignition.19 Two NFPA standards address furniture combustibility: NFPA 260, Standard Methods of Test and Classification System for Cigarette Ignition Resistance of Components of Upholstered Furniture; and NFPA 261, Standard Method of Test Determining Resistance of Mock-Up Upholstered Furniture Material Assemblies to Ignition by Smoldering Cigarettes. NFPA 267, Standard Method of Test for Fire Characteristics of Mattresses and Bedding Assemblies Exposed to Flaming Ignition Source, assesses heat release of mattresses and bedding. The “Operating Features” of each occupancy chapter of NFPA 101, 2000 edition, specifies that if new upholstered furniture or mattresses are introduced, they must meet the requirements of NFPA 260, 261, or 267. The “Operating Features” portion of each occupancy chapter of NFPA 101, 2000 edition, specifies if new upholstered furniture or mattresses are introduced, they must meet the requirements of NFPA 260, 261, or 267. The U.S. Consumer Products Safety Commission (CPSC) also has a standard for evaluating the ignitibility of mattresses.20 A number of fires have been docu-
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Concepts of Egress Design
4–63
mented in which severe conditions resulted from fire involvement of only a few furnishing items.9,10,14
Influence of Psychological and Physiological Factors on Egress The psychological and physiological conditions of the occupant population must be considered, in addition to the physical configuration factors of the building, in planning means of egress. Studies indicate people usually behave adaptively and often altruistically in the stress of a fire.21,22 A heterogeneous collection of persons under the influence of alcohol or drugs, as may be present in an assembly occupancy, may pose a greater probability of nonadaptive group behavior, with a competitive flight, panic-type behavior the likely result. Historically, this type of nonadaptive behavior has been documented, although studies indicate that the phenomenon is rare and depends upon unique, predetermined conditions involving both the population and the physical environment of the structure.21–23 In some cases, evacuation procedures and the creation of areas of refuge within high-rise buildings encourage occupant movement upward within the building. The effectiveness of this concept has not been completely validated in actual fires. Because of the orientation of some people toward total evacuation and escape from the building, it is possible that they may attempt to evacuate a building in the conventional “down and out” approach despite instruction to the contrary.22 Evacuation procedures in federal high-rise office buildings, as directed by vocal alarm systems, have continually obtained the selective movement of personnel in both upward and downward directions.15 In both of two serious high-rise office building fires in São Paulo, Brazil, the occupants moved upward to the roof when their downward movement was inhibited by smoke and heat.12 In the MGM Grand Hotel fire in Las Vegas, Nevada, in November 1980, there also was upward movement to areas of refuge in the stairways to the roof and to rooms on upper floors when downward travel was made untenable by smoke and heat.13,21 All exits need to be conspicuously marked, because people are likely to be unfamiliar with the various exits from an area under fire conditions and thus to neglect alternate means of egress. It is also important that the means of egress from a building be used as a matter of daily routine, so the occupants will be familiar with their location and operation. NFPA 101 requires that the main exit of assembly occupancies, which also serves as the entrance, be sized to handle at least one-half of the total occupant load of the building. There are three critical parameters in the effective use of the zoned evacuation of personnel to areas of refuge within a building.24 1. Proper construction to provide compartmented areas that are protected from the effects of fire and smoke. 2. An effective verbal alarm system giving clear and comprehensive instructions, with provision for originating onscene instructions from the fire department.15 3. Effective evacuation drills to familiarize the occupants with the way the system functions.
4–64 SECTION 4 ■ Human Behavior in Fire Emergencies
TABLE 4.3.1
Summary of Life Safety Code Requirements for Interior Finishings Exits
Occupancy Assembly—New > 300 occupant load < 300 occupant load Assembly—Existing > 300 occupant load < 300 occupant load Educational—New Educational—Existing Daycare Centers—New Daycare Centers—Existing Group Daycare Homes—New Group Daycare Homes—Existing Family Daycare Homes Healthcare—New (sprinklers mandatory) Healthcare—Existing Detention and Correctional—New Detention and Correctional—Existing 1- and 2-Family Dwellings, Lodging or Rooming Houses Hotels and Dormitories—New Hotels and Dormitories—Existing Apartment Buildings—New Apartment Buildings—Existing Residential Board and Care— See Chapters 32 and 33 Mercantile—New Mercantile—Existing Class A or Class B Mercantile—Existing Class C Business and Ambulatory Health Care—New Business and Ambulatory Health Care—Existing Industrial Storage
Access to Exits
Other Spaces
A A
A or B A or B
A or B A, B, or C
A A A
A or B A or B A or B
A A I or II A or B A or B A or B A or B A or B
A or B Aa I A or Ba I or II A, B, or C
A or B A I or II A or B A or B A, B, or C A, B, or C A or B, C on lower portion of corridor walla A or B Aa I A or Ba I or II A, B, or C
A or B A, B, or C A or B, C on low partitionsa A, B, or C A or B NR A or B A, B, or C A, B, or C A, B, or C A or B, C in small individual roomsa A or B A, B, or C
A I or II A or B I or IIa A I or IIa A or B I or IIa
A or B I or II A or B I or IIa A or B I or IIa A or B I or IIa
A, B, or C
A or B A or B
A or B A or B
A, B, or C A or B I or II A or B
A, B, or C A or B I or II A or B
A or B Ceilings—A or B, walls—A, B, or C A, B, or C A, B, or C
A or B A or B
A, B, or C A, B, or C
A, B, or C A, B, or C
A, B, or C A, B, or C A, B, or C
A, B, or C A, B, or C A, B, or C
NR: No requirement. Notes: 1. Class A interior wall and ceiling finish—flame spread 0–25, (new) smoke developed 0–450. 2. Class B interior wall and ceiling finish—flame spread 26–75, (new) smoke developed 0–450. 3. Class C interior wall and ceiling finish—flame spread 76–200, (new) smoke developed 0–450. 4. Class I interior floor finish—critical radiant flux, not less than 0.45 W/cm2. 5. Class II interior floor finish—critical radiant flux, not less than 0.22 W/cm2 but less than 0.45 W/cm2. 6. Automatic sprinklers—where a complete standard system of automatic sprinklers is installed, interior wall and ceiling finish with flame spread rating not exceeding Class C is permitted to be used in any location where Class B is equired and with rating of Class B in any location where Class A is required; similarly, class II interior floor finish is permitted to be used in any location where Class I is required, and no critical radiant flux rating is required where Class II is required. These provisions do not apply to new health care facilities. 7. Exposed portions of structural members complying with the requirements for heavy timber construction are permitted. a See corresponding chapters for details. Source: NFPA 101 ®, Life Safety Code ®, 2000, pp. 101–306 and 101–307.
CHAPTER 3
It has been advocated that occupants in fire-resistant, compartmented buildings used as hotels, motels, apartments, dormitories, hospitals, and other healthcare facilities should stay in their rooms rather than evacuate, since the rooms are the most adequate area of refuge.25 This method has not been adopted by NFPA 101 or by the model building codes. However, the concept of areas of refuge has been used by NFPA 101 extensively in occupancies such as healthcare and detention and correctional facilities for many years and, more recently, to protect occupants with mobility impairments in all occupancies.
Influence of Fire Protection Equipment It is unsuitable to rely totally on manual or automatic fire extinguishing systems in place of adequate means of egress, since fire extinguishing systems are subject to both human and mechanical failure. In addition, building areas may become untenable for human occupancy before the fire extinguishing systems are effective. Under no condition can manual or automatic fire suppression be accepted as a substitute for the provision and maintenance of proper means of egress. Where a complete standard system is installed, automatic sprinklers are sufficiently reliable to have a major influence on life safety. In addition to providing an automatic alarm of fire, they quickly discharge water on the fire before smoke has spread dangerously. While automatic sprinklers should never be used in place of adequate means of egress, they are recognized in various ways by NFPA 101. When total automatic sprinkler protection is provided, NFPA 101 permits increased travel distance to exits, the use of interior finish of greater combustibility, reductions in corridor requirements, and, in some occupancies, the use of combustible construction in situations where it would otherwise be prohibited. Provisions for areas of refuge are significantly easier to comply with in buildings protected throughout by automatic sprinklers. Sprinklers are particularly valuable in dealing with problems in existing buildings. Automatic fire detection, or fire alarm, systems are valuable in notifying building occupants of a fire so they may evacuate promptly. Automatic fire detection systems only provide a warning of fire and do nothing themselves to suppress or limit the spread of fire and smoke. An automatic fire detection system is not a substitute for adequate means of egress. Smoke detection systems can be useful to help mitigate problems in existing buildings. They can be especially useful where earlier egress may help solve problems, such as existing excessive common paths of travel, dead ends, and travel distance.
DEFINITION OF THE TERM “MEANS OF EGRESS” NFPA 101 and most of the U.S. model building codes use the term “means of egress.” A means of egress is a continuous path of travel from any point in a building or structure to a public way that is in the open air outside at ground level. Egress consists of three separate and distinct parts: 1. The exit access. Portion of a means of egress that leads to the entrance of an exit.
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Concepts of Egress Design
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2. Exit. Portion of a means of egress that is separated from the area of the building from which escape is to be made by walls, floors, doors, or other means that provide the protected path necessary for the occupants to proceed with reasonable safety to the exterior of the building. An exit may comprise vertical and horizontal means of travel, such as exterior doors, protected stairways, ramps, and exit passageways. 3. Exit discharge. Portion of a means of egress between the termination of the exit and a public way. Figure 4.3.6 illustrates the relationship among these three parts of an exit in a building.
The Exit Access The exit access may be a corridor, aisle, balcony, gallery, room, porch, or roof. The length of the exit access establishes the travel distance to an exit, an extremely important feature of a means of egress, since an occupant might be exposed to fire or smoke during the time it takes to reach an exit. The average recommended maximum travel distance is 200 ft (61 m), but this distance varies with the occupancy, depending upon the fire hazard and the physical ability and alertness of the occupants (Table 4.3.2). The travel distance must be measured from the most remote point in a room or floor area to an exit. In most cases, the travel distance can be increased up to 50 percent if the building is completely protected with a standard supervised automatic sprinkler system.
A1
D1
E1
A2
D2
E2
FIGURE 4.3.6 Examples of Exit Access, Exit, and Exit Discharge. To the occupant of the building at the discharge level, the doors at A1, A2, E1, and E2 are exits, and the path denoted by dashes is the exit access. To the person emerging from the exit enclosures or from doors A1, A2, or E2 the paths denoted by dotted lines are the exit discharge. Doors D1 and D2 are exit discharge doors. Solid lines are within the exit.
4–66 SECTION 4 ■ Human Behavior in Fire Emergencies
TABLE 4.3.2
Common Path, Dead-End, and Travel Distance Limits (by occupancy) Common Path Limit
Type of Occupancy
Dead-End Limit
Travel Distance Limit
Unsprinklered [ft (m)]
Sprinklered [ft (m)]
Unsprinklered [ft (m)]
Sprinklered [ft (m)]
Unsprinklered [ft (m)]
Sprinklered [ft (m)]
20/75 (6.1/23)a,b 20/75 (6.1/23)a,b
20/75 (6.1/23)a,b 20/75 (6.1/23)a,b
0/20 (0/6.1)b
0/20 (0/6.1)b
150 (45)c
200 (60)c
0/20 (0/6.1)b
0/20 (0/6.1)b
150 (45)c
200 (60)c
75 (23) 75 (23)
100 (30) 100 (30)
20 (6.1) 20 (6.1)
50 (15) 50 (15)
150 (45) 150 (45)
200 (60) 200 (60)
75 (23) 75 (23)
100 (30) 100 (30)
20 (6.1) 20 (6.1)
50 (15) 50 (15)
150 (45)d 150 (45)d
200 (60)d 200 (60)d
NR NR
NR NR
30 (9.1) NR
30 (9.1) NR
NA 150 (45)d
200 (60)d 200 (60)d
75 (23)e 75 (23)e
100 (30)e 200 (30)e
20 (6.1) 50 (15)
50 (15) 50 (15)
150 (45)d 150 (45)d
200 (60)d 200 (60)d
50 (15)
100 (30)
50 (15)
50 (15)
150 (45)d
200 (60)d
50 (15) 50 (15)f
100 (30) 100 (30)f
20 (6.1) NR
20 (6.1) NR
150 (45)d 150 (45)d
200 (60)d 200 (60)d
NR
NR
NR
NR
NR
NR
NR
NR
NR
NR
NR
NR
35 (10.7)g,i 35 (10.7)g
50 (15)g,i 50 (15)g
35 (10.7)i 50 (15)
50 (15) 50 (15)
175 (53)d,h 175 (53)d,h
325 (99)d,h 325 (99)d,h
35 (10.7)g 35 (10.7)g
50 (15)g 50 (15)g
35 (10.7) 50 (15)
50 (15) 50 (15)
175 (53)d,h 175 (53)d,h
325 (99)d,h 325 (99)d,h
NR NR 110 (33)
NR 125 (38)i 160 (49)
NR NA 50 (15)
NR 50 (15) 50 (15)
NR NA 175 (53)d,h
NR 325 (99)d,h 325 (99)d,h
75 (23) 75 (23) NR
100 (30) 100 (30) NR
20 (6.1) 50 (15) 0 (0)
50 (15) 50 (15) 0 (0)
100 (30) 150 (45) NR
200 (60) 200 (60) NR
75 (23) 75 (23)
100 (30) 100 (30)
20 (6.1) 50 (15)
50 (15) 50 (15)
100 (30) 150 (45)
400 (120) j 400 (120) j
Assembly New Existing Educational New Existing Daycare New Existing Healthcare New Existing Ambulatory healthcare New Existing Detention and correctional New—Use conditions II, III, IV New—Use conditions V Existing—Use conditions II, III, IV, V Residential One- and two-family dwellings Lodging or rooming houses Hotels and dormitories New Existing Apartments New Existing Board and care Small, new and existing Large, new Large, existing Mercantile Class A, B, C New Existing Open air Covered mall New Existing
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CHAPTER 3
TABLE 4.3.2
Concepts of Egress Design
4–67
Continued Common Path Limit
Type of Occupancy
Dead-End Limit
Travel Distance Limit
Unsprinklered [ft (m)]
Sprinklered [ft (m)]
Unsprinklered [ft (m)]
Sprinklered [ft (m)]
Unsprinklered [ft (m)]
Sprinklered [ft (m)]
75 (23)k 75 (23)k
100 (30)k 100 (30)k
20 (6.1) 50 (15)
50 (15) 50 (15)
200 (60) 200 (60)
300 (91) 300 (91)
50 (15) 50 (15) 0 (0) 50 (15)m
100 (30) 100 (30) 0 (0) 50 (15)m
50 (15) 50 (15) 0 (0) 50 (15)m
50 (15) 50 (15) 0 (0) 50 (15)m
200 (60)n 300 (91) 75 (23) note n
250 (75)l 400 (122) 75 (23) note n
50 (15)m
50 (15)m
50 (15)m
50 (15)m
75 (23)
75 (23)
NR 50 (15) 0 (0) 50 (15) 50 (15) 50 (15)m
NR 100 (30) 0 (0) 50 (15) 50 (15) 100 (30)m
NR 50 (15) 0 (0) 50 (15) 50 (15) 50 (15)m
NR 100 (30) 0 (0) 50 (15) 50 (15) 50 (15)m
NR 200 (60) 75 (23) 300 (91) 150 (45) note n
NR 400 (122) 100 (30) 400 (122) 200 (60) note n
50 (15)m
75 (23)m
50 (15)m
50 (15)m
75 (23)
75 (23)
50 (15)m
100 (30)m
50 (15)m
100 (30)m
200 (60)
400 (122)
Business New Existing Industrial General Special purpose High hazard Aircraft servicing hangars, ground floor Aircraft servicing hangars, mezzanine floor Storage Low hazard Ordinary hazard High hazard Parking garages, open Parking garages, enclosed Aircraft storage hangars, ground floor Aircraft storage hangars, mezzanine floor Underground spaces in grain elevators
NA: Not applicable. NR: No requirement. a 20 ft (6.1 m) for common path serving >50 persons: 75 ft (23 m) for common path serving < 50 persons. b Dead-end corridors not permitted: 20 ft (6.1 m) dead-end aisled permitted. c See Chapters 12 and 13 for special considerations for smoke-protected assembly seating in arenas and stadia. d This dimension is for the total travel distance, assuming incremental portions have fully utilized their permitted maximums. For travel distance within the room, and from the room exit access door to the exit, see the appropriate occupancy chapter. e See business occupancies Chapters 38 and 39. f See Chapter 23 for special considerations for existing common paths. g This dimension is from the room/corridor or suite/corridor exit access door to the exit; thus, is applies to corridor common path. h See appropriate occupancy chapter for special travel distance considerations for exterior ways of exit access. i See appropriate occupancy chapter for requirement for second exit access based on room area. j See Sections 36.4 and 37.4 for special travel distance considerations in covered malls considered pedestrian ways. k See Chapters 38 and 39 for special common path considerations for single tenant spaces. l See Chapter 40 for industrial occupancy special travel distance considerations. m See Chapters 40 and 423 for special requirements if high hazard. n See Chapters 40 and 423 for special requirements on spacing of doors in aircraft hangars. Source: NFPA 101 ®, Life Safety Code ®, 2000, pp. 101–296 and 101–297.
A dead end is an extension of a corridor beyond an exit or an access to exits that forms a pocket in which occupants may be trapped. Since there is only one direction of travel to an exit from a dead end, a fire in a dead end between the exit and an occupant prevents the occupant from reaching the exit. Another problem with dead ends is that while traveling toward an exit in a smoky atmosphere, an occupant may pass by the exit and walk into the dead end. This requires return travel, which adds distance, and therefore time, to reach the exit. In good egress designs, dead-end corridors are not used. However, NFPA 101 permits dead ends in most occupancies, within reasonable limits (see Table 4.3.2). Two dead-end corridors are illustrated in Figure 4.3.7.
Elevators
FIGURE 4.3.7
Two Types of Dead-End Corridors
4–68 SECTION 4 ■ Human Behavior in Fire Emergencies
The width of an exit access should be at least sufficient for the number of persons it must accommodate. In some occupancies, the width of the access is governed by the character of activity in the occupancy. One example is a new hospital, where patients may be moved in beds or in gurneys. The corridors in the patient areas of the hospital must be 8 ft (2.4 m) wide to allow for a bed to be wheeled out of a room and turned 90º. A fundamental principle of exit access is the provision of a free and unobstructed way to the exits. If the access passes through a room that can be locked or through an area containing a fire hazard more severe than is typical of the occupancy, the principles of free and unobstructed exit access are violated. The floor of an exit access should be level. If this is not possible, small differences in elevation may be overcome by a ramp and large differences by stairs. Where only one or two steps are necessary to overcome differences in level in an exit access, a ramp is preferred, because people may trip in a crowded corridor and fall on the stairs if they do not see the steps or notice that those in front of them have stepped up.
2-hr wall
2-hr wall
10 ft (3 m) min. distance to unprotected window opening
Not less than width of exit door 20-min door
1½-hr door
Min. 72 in. (183 cm)
Open to outside min. 16 ft2 (1.5 m2)
Plan A
1½-hr door Guard rails
Plan B
2-hr wall
The Exit
Shaft for mechanical ventilation
2-hr wall
Exit
Se fire lf-clo do sing or
Up
Exit
2-hr Fire barrier
20-min door 20-min door 1½-hr door
Min. 72 in. (183 cm) Plan C
Open to outside min. 16 ft2 (1.5 m2)
Min. 72 in. (183 cm)
1½-hr door
Plan D
FIGURE 4.3.9 Four Variations of Smokeproof Towers. Plan A has a vestibule opening from a corridor. Plan B shows an entrance by way of an outside balcony. Plan C could provide a stair tower entrance common to two areas. In Plan D, smoke and gases entering the vestibule would be exhausted by a natural or induced draft in the open air shaft. In each case, a double entrance to the stair tower with at least one side open or vented is characteristic of this type of construction. Pressurization of the stair tower in the event of fire provides an attracted alternate for tall buildings and is a means of eliminating the entrance vestibule.
e Fir r o do
Down
Au se tom lf-c at lo ic fire sing - or do or
The types of permissible exits are doors leading directly outside at ground level or through a protected passageway to the outside at ground level, smokeproof towers, protected interior and outside stairs, exit passageways, enclosed ramps, and enclosed escalators or moving walkways in existing buildings. Elevators are not accepted as exits; however, they can be used to provide a way of removing mobility impaired individuals from areas of refuge. NFPA 101 also recognizes elevators for very limited use as a second exit for limited access towers such as FAA control towers. See Figures 4.3.8 and 4.3.9 for illustrations of some common types of exit arrangements.
1-hr door
Enclosed stairway
Horizontal exits
FIGURE 4.3.8 Plan Views of Types of Exits. Stair enclosure prevents a fire on any floor from trapping the persons above. A smokeproof tower is better, as it opens to the air at each floor, largely preventing the chance of smoke in the stairway. A horizontal exit provides a quick refuge and lessens the need for a hasty flight down stairs. Fire-rated doors must be arranged to be self-closing or automatic-closing by smoke detection.
The specific placement of exits is a matter of design judgment, given the specifications of travel distance, allowable dead ends, common path of travel, and exit capacity. NFPA 101 states that exits must be remote from each other, thus providing two separate means of egress so located that occupants can travel in either of two opposite directions to reach an exit. This concept is important when it is necessary for occupants to leave a fire or smoke-contaminated area and move toward an exit. If occupants have no choice but to enter the fire area to reach an exit, it is doubtful whether they will be able or willing to do so.
CHAPTER 3
The Exit Discharge Ideally, all exits in a building should discharge directly to the outside or through a fire-resistance-rated passageway to the outside of the building. NFPA 101 permits a maximum of 50 percent of the exit stairs to discharge onto the street floor. The obvious disadvantage of this arrangement is that if a fire occurs on the streetlevel floor, it is possible for people using the exit stairs discharging to that floor to be discharged into the fire area. If any exits discharge to the street floor, NFPA 101 therefore requires that such exits discharge to a free and unobstructed way to the outside of the building, that the street floor be protected by automatic sprinklers, and that the street floor be separated from any floors below by construction having a 2-hr fire resistance rating. Discharging an exit to the outside is not necessarily discharging to a safe place. If the exit discharges into a courtyard, an exit passageway must be provided from the courtyard through the building so that the occupants can get away from the building. If the exit discharges into a fenced yard, the occupants must be able to get out of the yard to get away from the building. If the exit discharges into an alley, the alley must be of sufficient width to accommodate the capacity of all the exits discharging into it, and any openings in the building walls bordering the alley should be protected to prevent fire exposure to the occupants proceeding through the alley. When exit stairs from floors above the street floor continue on to floors below the street floor, occupants evacuating the building may miss the exit discharge door to the street level, continue down the stairway, and enter a floor below the level of exit discharge. Therefore, NFPA 101 requires a physical barrier or other effective means at the street floor landing to prevent evacuees from passing the level of exit discharge.
CAPACITY OF EXITS The capacity of exits is calculated using a capacity factor provided in NFPA 101. This capacity factor is given as in./person and varies with the occupancy (Table 4.3.3). The total exit capacity for each component of the means of egress, such as doors, stairs, ramps, corridors, and so on, is calculated based on its clear width. For example, one 34-in. clear-width door in an office occupancy would have an exit capacity of 170 persons (34 in. ÷ 0.2 in./person 170 persons [86 cm ÷ 0.5 cm/person 172 persons]). The reason for these variations in exit capacity factors is to establish a consistent total evacuation time in different occupancies, based on the physical ability, mental alertness, age, and sociological roles of the occupants. In occupancies where people are housed for care, the time taken to reach exits will be greater than in some other occupancies, and so the exits must be sufficiently wide to allow nonambulatory occupants to egress and to prevent any waiting to get into the exit. The capacity of exits was traditionally used to establish a consistency of evacuation time on the basis of the rate of travel through a door of 60 persons/min and down a stairway of 45 persons/min/22 in. (558.8 mm) of exit width, respectively. These figures were established by evacuation counts conducted primarily in federal office buildings.26 More recent studies of evacuations in
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Concepts of Egress Design
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high-rise office buildings indicate peak flows of 30 persons/min and mean flows of 24 persons/min/22 in. (558.8 mm) of exit width down stairways.5,16,17
Occupant Load Occupant load, or the number of people to be expected in a building or an area within a building at any time for whom exits must be provided, is determined by the actual anticipated occupant load but not less than that number obtained by dividing the gross area of the building or the net area of a specific portion of the building by the area in sq ft (m2) projected for each person. The amount of floor area projected for each person varies with the occupancy (Table 4.3.4). These figures are based on actual counts of people in buildings and on reviews of architectural plans. In some situations, the maximum number of people in a building above the calculated occupant load can be determined at the design stage, in which case this number should be used in the design of the exits. A typical example is an assembly occupancy in which fixed seating is installed. Counting the number of seats provided, and calculating the standing or waiting areas by the occupant load factor, would obviously give a more accurate figure than multiplying a sq ft (m2)/person figure by the net floor area.
Computing Required Egress Width To compute the minimum required egress widths from the individual floors of a building, it is necessary to 1. Calculate the floor area, either net or gross, whichever is applicable 2. Determine from NFPA 101 the estimated number of sq ft (m2)/person, or occupant load factor 3. Divide the number of sq ft (m2)/person (occupant load factor) into the floor area to determine the minimum number of people for whom exits must be provided for that floor 4. Measure the clear width of each component in the means of egress 5. Determine the capacity factor from NFPA 101 for each exit component for the appropriate occupancy 6. Divide the clear width of each exit component by the capacity factor to determine the exit capacity for each component 7. Determine the most restrictive component in each egress system 8. Determine the total egress capacity for the floor 9. Ensure that the total egress capacity equals or exceeds the total occupant load. In multistory buildings, the exit capacity for each floor is calculated separately. In other words, the capacity of the stairs need only be wide enough to serve each floor, but it must not be less than the minimum width required by NFPA 101. It must also be noted that the required egress capacity cannot be decreased in the direction of egress travel. Street-floor exits may require special treatment, depending upon the occupancy. Some occupancies require that street-floor exits be sized to handle not only the occupant load of the street floor but also the occupant load of the exits discharging to the
4–70 SECTION 4 ■ Human Behavior in Fire Emergencies
TABLE 4.3.3
Occupant Load Factor a
a
ft2 (per person)
m2 (per person)
Assembly Use Concentrated use, without fixed seating Less concentrated use, without fixed seating Bench-type seating Fixed seating Waiting spaces Kitchens Library stack areas Library reading rooms Swimming pools Swimming pool decks Exercise rooms with equipment Exercise rooms without equipment Stages Lighting and access catwalks, galleries, gridirons Casinos and similar gaming areas Skating rinks
7 net 15 net 1 person/18 linear in. Number of fixed seats See 12.1.7.2 and 13.1.7.2 100 100 50 net 50—of water surface 30 50 15 15 net 100 net 11 50
0.65 net 1.4 net 1 person/45.7 linear cm Number of fixed seats See 12.1.7.2 and 13.1.7.2 9.3 9.3 4.6 net 4.6—of water surface 2.8 4.6 1.4 1.4 net 9.3 net 1 4.6
Educational Use Classrooms Shops, laboratories, vocational rooms
20 net 50 net
1.9 net 4.6 net
Daycare Use
35 net
3.3 net
Healthcare Use Inpatient treatment departments Sleeping departments
240 120
22.3 11.1
Detention and Correctional Use
120
11.1
Residential Use Hotels and dormitories Apartment buildings Board and care, large
200 200 200
18.6 18.6 18.6
Industrial Use General and high hazard industrial Special purpose industrial
100 NAb
9.3 NAb
Business Use
100
9.3
Storage Use (other than mercantile storerooms)
NAb
NAb
30 40 30 60 See business use. 300
2.8 3.7 2.8 5.6 See business use. 27.9
Per factors applicable to use of spacee
Per factors applicable to use of spacee
Use
Mercantile Use Sales area on street floorcd Sales area on two or more street floorsd Sales area on floor below street floord Sales area on floor above street floord Floors or portions of floors used only for offices Floors or portions of floors used only for storage, receiving, and shipping, and not open to general public Covered mall buildings a
All factors expressed in gross area unless marked “net.” Not applicable. The occupant load shall not be less than the maximum probable number of occupants present at any time. For the purpose of determining occupant load in mercantile occupancies where, due to differences in grade of streets on different sides, two or more floors directly accessible from streets (not including alleys or similar back streets) exist, each such floor shall be considered a street floor. The occupant load factor shall be one person for each 40 ft2 (3.7 m2) of gross floor area of sales space. d In mercantile occupancies with no street floor, as defined in 3.3.196, but with access directly from the street by stairs or escalators, the principal floor at the point of entrance to the mercantile occupancy shall be considered the street floor. e The portions of the covered mall, where considered a pedestrian way and not used as a gross leasable area, shall not be assessed an occupant load based on this table. However, means of egress from a covered mall pedestrian way shall be provided for an occupant load determined by dividing the gross leasable area of the covered mall building (not including anchor stores) by the appropriate lowest whole number occupant load factor from Figure 7.3.1.2 of NFPA 101. Each individual tenant space shall have means of egress to the outside or to the covered mall based on occupant loads figured by using the appropriate occupant load factor from this table. Each individual anchor store shall have means of egress independent of the covered mall. b c
CHAPTER 3
TABLE 4.3.4
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Concepts of Egress Design
4–71
Summary of NFPA 101®, Life Safety Code®, Provisions for Occupant Load and Exit Capacity
Occupancy Assembly Less concentrated use without fixed seating Concentrated use without fixed seating Fixed seating Educational Classrooms Shops and vocational Care centers Healthcare Sleeping departments Treatment departments Residential Board and care Mercantile Street floor and sales basement Multiple street floors—each Other floors Storage—shipping Malls Business Industrial Detention and correctional
Level Components (Doors, Corridors, Horizontal Exits, Ramps)
Stairs
15 net (1.4) 7 Net (.65) Actual number of seats
0.2
0.3
0.2
0.3
0.2
0.3
20 Net (1.9) 50 Net (4.6) 35 Net (3.3)
0.2
0.3
0.2
0.3
0.2
0.3
Occupant Load sq ft (m2) per person
120 Gross (11.1) 240 Gross (22.3) 200 Gross (18.6) 200 Gross (18.6) 30 Gross (3.7) 40 Gross (3.7) 60 Gross (5.6) 300 Gross (27.9) See Code 100 Gross (9.3) 100 Gross (9.3) 120 Gross (11.1)
NAS 0.5
AS 0.1
NAS 0.6
AS 0.3
0.5
0.2
0.6
0.3
0.2
0.3
0.2
0.4
0.2
0.3
0.2
0.3
0.2
0.3
0.2
0.3
0.2 0.2
0.3 0.3
0.2
0.3
0.2
0.3
Note: NAS = nonsprinklered; AS = sprinklered. See NFPA 101 for additional Occupant Load factors.
street floor from floors above and below. In addition, in those occupancies where floors above and/or below the street floor are permitted to have unenclosed stairs and escalators connecting them with the street floor, the exits must be sufficient to provide simultaneously for all the occupants of all communicating levels and areas. In other words, all communicating levels in the same fire area are considered a single floor area for the purposes of determining the required exit capacity. This identical, single fire area factor can have a considerable effect on the sizing of the street-floor exits. Should two or more exits converge into a common exit, the common exit should never be narrower than the sum of the width of the exits converging into it.
Generally, the minimum number of exits is two. In certain limited situations, however, one exit may be permitted in some occupancies if there is a very low occupant load, low fire hazard, and a limited travel distance.
EXIT FACILITIES AND ARRANGEMENTS The following exit facilities are covered in NFPA 101.
Doors Doors should be side-hinged or pivoted swinging type and should swing in the direction of exit travel, except in small
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rooms. Horizontal sliding, vertical, or rolling doors are recognized for use as means of egress in some occupancies. In assembly occupancies and in schools, panic hardware should be installed on all egress doors equipped with latches that serve rooms with an occupant load of 100 or more. Where doors protect exit facilities, as in stairway enclosures and horizontal exits, they normally must be kept closed to limit the spread of smoke. If open, they must be closed immediately in case of fire. Although ordinary, fusible-link-operated devices to close doors in case of fire are designed to close in time to stop the spread of fire, they do not operate soon enough to stop the spread of smoke and are not permitted by NFPA 101. At relatively low temperatures, smoke accumulation could continue and could reach untenable levels long before the fusible link melts, allowing the door to close. Sometimes, people keep self-closing doors open with hooks or with wedges under the door. Doors also can be blocked open to provide ventilation, for the convenience of building maintenance personnel, or to avoid the accident hazard of swinging doors. The following measures have been provided in the NFPA 101 to alleviate this undesirable situation: 1. Doors that are normally kept open can be equipped with door closers and automatic hold-open devices that release the door and allow them to close when an automatic sprinkler system, the fire alarm system, an automatic fire detection system, and smoke or other products of combustion detection devices operate. 2. Doors that are normally closed can be equipped to open electrically or pneumatically when a person approaches the door, as long as precautions are used to prevent the door from automatically opening when there is smoke in the area. 3. Doors that normally are closed can be opened and held open manually by monitors, as in schools. 4. Use of smokeproof towers that protect against smoke, even if the doors are open. Qualifications and limitations are applicable to each of these measures. One is that, in the event of electrical failure, the door must close and remain closed unless it is opened manually for egress purposes. Another major maintenance difficulty with exit doors is the exterior door that is locked to prevent unauthorized access or for other reasons. NFPA 101 specifies that when the building is occupied, all doors must be kept unlocked from the side from which egress is made. NFPA 101 allows a delayed releasing device on some egress doors, provided this is permitted by the requirements of the occupancy in question. Where the devices are allowed, the following provisions apply: 1. The building must be protected throughout by an approved and supervised automatic fire detection system or automatic sprinkler system. 2. The release devices are installed only in low- or ordinaryhazard areas. 3. The devices must unlock when the fire detection system or automatic sprinkler system operates.
4. The devices must unlock upon loss of power. 5. The devices must initiate an irreversible process that will free the latch within 15 sec whenever a force of not more than 15 lb (6.8 kg) is applied to the releasing device, and the door must not relock automatically. Operation of the releasing device must actuate a signal near the door. 6. A sign must be placed adjacent to the door that reads: PUSH UNTIL ALARM SOUNDS. DOOR CAN BE OPENED IN 15 SECONDS! 7. Emergency lighting must be provided at the door. NFPA 101 also provides “Access Controlled Egress Doors.” The code spells out several limitations for these. One of the limitations included is that when an occupant approaches the door, a sensor must unlock it. Locks on a door that let people exit but not enter are satisfactory, but even this type of lock may not be satisfactory for security purposes. Possible measures to prevent unauthorized use of exit doors include 1. An automatic alarm that rings when the door is opened 2. Visual supervision such as wired-glass panels, closedcircuit television, and mirrors, which may be used where appropriate 3. Automatic photographic devices to provide pictures of users So-called exit locks, with a break-glass unit actuated by striking a handle with the hand, are not permitted by NFPA 101 unless installed in conjunction with panic bars. Otherwise, they do not comply with the NFPA 101 provision that reads: “A latch or other fastening device on a door shall be provided with a releasing device having an obvious method of operation and that is readily operated under all lighting conditions.” Other types of break-glass locks and electrical controls for releasing exits from a central point are not permitted by NFPA 101. The exception is an occupancy where controls may be necessary, as in healthcare, and detention and correctional occupancies. A single door in a doorway should not be less than 32 in. (813 mm) wide in new buildings and 28 in. (711 mm) in existing buildings. To prevent tripping, the floor on both sides of the door should have the same elevation for the full swing of the door.
Panic Hardware Egress doors in assembly and educational occupancies, such as schools or movie theaters, normally are equipped with panic hardware. Basically, panic hardware devices are designed to facilitate the release of the latching device on the door when a pressure not to exceed 15 lb (6.8 kg) is applied in the direction of exit travel. Such releasing devices are bars or panels extending not less than one-half of the width of the door and placed at a height not less than 30 in. (762 mm) or more than 44 in. (1.1 m) above the floor. Panic hardware that has been tested and listed for use on fire-protection-rated doors is termed “fire exit hardware.” If panic hardware is needed on fire-protection-rated doors, only fire exit hardware is to be used.
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Panic hardware is available for use on single and double doors, with variations for rim-mounted hardware and mortise or vertical rod devices.
Horizontal Exits A horizontal exit is a means of egress from one building to an area of refuge in another building on approximately the same level, or a means of egress through a 2-hr fire barrier to an area of refuge at approximately the same level in the same building that affords safety from fire and smoke. With a horizontal exit, it is obvious that space must be provided in the area or building of refuge for the people entering the refuge area. NFPA 101 recommends 3 sq ft (0.28 m2) of space per person, with the exception of healthcare and detention and correctional occupancies, where 6 to 30 sq ft (0.56 to 2.79 m2) of space is recommended. Horizontal exits cannot comprise more than one-half the total required exit capacity, except in healthcare facilities, where horizontal exits may comprise two-thirds of the total required exit capacity, and in detention and correctional facilities, where horizontal exits can comprise 100 percent of the total exit capacity. Horizontal exits have been applied universally in healthcare facilities where the evacuation of patients over stairs is slower and more difficult than taking them through a horizontal exit to a safe area of refuge. A horizontal exit arrangement within a single building and between two buildings is illustrated in Figure 4.3.10. A swinging door in a fire wall provides a horizontal exit in one direction only. Two openings, each with a door swinging in the direction of exit travel, are needed to provide horizontal exits from both sides of the wall. Where property protection requires fire doors on both sides of the wall, a normally open, automatic, fusible-link-operated, horizontally sliding fire door may be used on one side, with a swinging fire door on the other.
Stairs Exit stairs are arranged to minimize the danger of falling, because one person falling on a stairway may result in the complete blockage of an exit. Stairs must be wide enough for two persons to descend side by side, thus maintaining a reasonable rate of evacuation, even though aged or infirm persons may slow the travel on one side. There must be no decrease in the width of the stair along the path of travel, since this may create congestion.
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Steep stairs are dangerous. Stair treads must be deep enough to give good footing. NFPA 101 specifies a minimum 11 in. (279 mm) tread and a maximum 7 in. (178 mm) riser for new stairs. Landings should be provided to break up any excessively long individual flight. Continuous railings are now recommended for new stairs. New stairs more than 60 in. (1.5 m) wide should have one or more center rails. Two classes of stairs are permitted in NFPA 101 for existing buildings, with a single class of stairs for new stairs. There are Class A and Class B stairs for existing buildings. The requirements for each class are given in Table 4.3.5. Stairs can serve as exit access, exit, or exit discharge. When used as an exit, they must be in an enclosure that meets exit enclosure requirements or outside the building and properly protected. Exit access stairs that connect two or more stairs are vertical openings and must be protected as a vertical opening. Stairways may be inside the building where the NFPA 101 generally specifies protective enclosures. They also may be outside if they comply with the requirements for exterior stairs and are arranged so that persons who fear heights will not be reluctant to use them, are not exposed to fire conditions originating in the building, and, where necessary, are shielded from snow and ice. Exterior stairs should not be confused with fire escape stairs (Figure 4.3.11). This method has application in many types of occupancies, such as schools, motels, small professional buildings, and so on. Note that there are two means of egress, remote from each other, from the second-story balcony. Construction details of stair enclosures involve the principles of limiting fire and smoke spread. Doors on openings from each story are essential to prevent the stairway from serving as a flue. In general, stairway enclosures should include not only the stairs, but also the path of travel from the bottom of the stairs to the exit discharge, so that occupants have a protected, enclosed passageway all the way out of the building. The stair enclosure should be of 1-hr construction when connecting three or fewer floors and of 2-hr construction when connecting four or more floors.
Smokeproof Towers Smokeproof towers provide the highest protected type of stair enclosure recommended by NFPA 101. Access to the stair tower is only by balconies open to the outside air, vented vestibules, or mechanically pressurized vestibules, so that smoke, heat, and flame will not spread readily into the tower even if the doors are accidentally left open (see Figure 4.3.9).
Refuge side when fire side
Ramps Fire side to refuge side
A
B
Refuge side when fire side X Fire side to refuge side
Two-way horizontal exit in an open-plan building. Self-closing fire doors required in fire separation.
FIGURE 4.3.10
One-way horizontal exit from building A to building B. Selfclosing or automatic-closing fire doors and protected passage required.
Types of Horizontal Exits
Ramps, enclosed and otherwise arranged like stairways, are sometimes used instead of stairways where there are large crowds and to provide both access and egress for nonambulatory persons. To be considered safe, exits ramps must have a very gradual slope.
Exit Passageways A hallway, corridor, passage, tunnel, or underfloor or overhead passageway may be designated an exit passageway, providing it
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TABLE 4.3.5
Requirements for New and Existing Building Stairs Existing Stairs New Stairs
Minimum width clear of all obstructions except projections not exceeding 3½ in. (0.89 mm) at and below handrail height on each side Maximum height of risers Minimum height of risers Minimum tread depth Minimum headroom Maximum height between landings Minimum dimension of landings in direction of travel
Doors opening immediately on stairs, without landing at least width of door
Class A
Class B
44 in. (1.12 m) 44 in. (1.12 m) 44 in. (1.12 m) 36 in. (0.91 m) 36 in. (0.91 m) 36 in. (0.91 m) where total occupant load where total occupant load of all floors of all floors served by served by stairways is less than 50. stairways is less than 50. 8 in. (203 mm) 7½ in. (191 mm) 7 in. (178 mm) — — 4 in. (102 mm) 9 in. (229 mm) 10 in. (244 mm) 11 in. (279 mm) 6 ft 8 in. (2.03 m) 6 ft 8 in. (2.03 m) 6 ft 8 in. (2.03 m) 12 ft (3.7 m) 12 ft (3.7 m) 12 ft (3.7 m) Stairways and intermediate landings shall continue with no decrease in width along the direction of exit travel. In new buildings every landing shall have a dimension, measured in direction of travel, equal to the width of the stair. Such dimension need not exceed 4 ft (1.22 m) when the stair has a straight run. No No No
Ordinary glass windows
FIGURE 4.3.11 Outside Stairs Providing Direct Exits to the Outside for All Rooms in a Multistory Building. There are no interior corridors through which smoke and flame could spread.
is separated and arranged according to the requirements for exits. The use of a hallway or corridor as an exit passageway introduces some unique considerations. The use of these spaces for purposes other than exiting may violate fundamental design considerations. In an industrial situation, for example, the use of a gasoline-powered forklift in a corridor designated as an exit passageway would violate the principles of exit design. NFPA 101 specifies that an exit enclosure should not be used for any purpose that could interfere with its value as an exit and is strictly limited by the code. Furthermore, penetration of the enclosure by ducts and other utilities may violate the protective enclosure.
Each opening in an exit enclosure introduces a point of weakness that could allow fire contaminants to spread into the exit and prevent its use. The typical corridor used as an exit with numerous door openings could result in fire contamination of the enclosure if a door fails to close and latch. The door openings in exit enclosures should be limited to those necessary for access to the enclosure from normally occupied spaces. Therefore, doors and other openings to spaces such as boiler rooms, storage spaces, trash rooms, and maintenance closets are not allowed into an exit passageway. An exit passageway should not be confused with an exit access corridor. Exit access corridors do not have as stringent construction protection requirements as do exit passageways, since they provide access to an exit rather than being an extension and component of the exit. In Figure 4.3.6 the passage between E and D is an exit passageway.
Fire Escape Stairs Fire escapes should be stairs, not ladders. Fire escapes are, at best, a poor substitute for standard interior or exterior stairs. NFPA 101 only permits existing fire escapes in existing buildings. The same principles of design apply to fire escapes that apply to interior stairs, though requirements for width, pitch, and other dimensions are generally less strict. NFPA 101 gives the following criteria for fire escape stair design. Fire escape stairs ideally extend to the street or to ground level. When sidewalks would be obstructed by permanent stairs, swinging stair sections designed to swing down under the weight of a person may be used for the lowest flight of the fire escape stairs. The area below the swinging section must be kept unobstructed so the swinging section can reach the ground. A counterweight of the type that balances on a pivot should be pro-
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vided for swinging stairs; cables should not be used. Fire escapes that end on balconies above the ground level and provide no way to reach the ground, except by portable ladders or jumping, are unsafe. Many persons who fear heights are reluctant to use fire escapes. As far as possible, design should provide a sense of security, as well as suitable railings and other details actually needed for safety. Fire escapes must be well anchored to building walls and kept painted to prevent rust. Preferred access to fire escapes is through doors leading from the main building area or from corridors, never through rooms that may have locked doors except where every room or apartment has separate access to a fire escape. Although preferred access to fire escapes is by doors, windows may be used, in which case sills should not be too high above the floor. Windows should be of ample size, and, if insect screens are installed, they should be of a type that can be opened or removed quickly and easily. Decorative grilles or security bars should not be installed over windows that provide access to fire escapes. Fire escapes can create a severe fire exposure to people if flames come out windows beneath them (Figure 4.3.12). The best location for fire escapes is on exterior masonry walls without exposing windows, with access to fire escape balconies by exterior fire doors. Where window openings expose fire escapes, fixed wired-glass in metal sashes should be used. Where there is a complete standard automatic sprinkler system in the building, the fire exposure hazard to personnel on fire escapes is minimized. In northern climates, outside fire escapes may be obstructed by snow and ice.
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they would qualify as exits, and it is common to find escalator installations with unprotected floor openings. Escalators are not recognized as an acceptable component in a means of egress in new construction. Moving walkways also may be used as means of egress if they conform to the general requirements for ramps, if inclined, and for passageways, if level. Elevators are not recognized as exits. However, elevators are permitted to be used, under limited conditions, to serve areas of refuge for the mobility impaired. The Life Safety Code also recognizes elevators, under very limited conditions, as the second exit from limited access towers such as FAA control towers.
Areas of Refuge Since 1991, NFPA 101 has listed “areas of refuge” as a specific means of egress element. Although they are beneficial to all people, their primary purpose is for people with difficulty using stairs. All new buildings must address the issue of “accessible means of egress.” In most new nonsprinklered multistory buildings, this will require some form of area of refuge. Figures 4.3.13 and 4.3.14 illustrate two methods for providing areas of refuge in non-sprinklered buildings.
Ropes and Ladders Ropes and ladders generally are not recognized in codes as a substitute for standard exits from a building. This is proper since there is no excuse for permitting their use except possibly in
Escalators, Moving Walkways, and Elevators In some occupancies, escalators may be recognized as exits in existing buildings if they have enclosures similar to exit stairs and meet the requirements for stairs as to tread width and riser height. However, they are seldom installed in such a way that
FIGURE 4.3.13
Exit Stair Used as an Area of Refuge
E
FIGURE 4.3.12 The Makeshift, Often Dangerous Aspect of Fire Escapes. Fire may make fire escapes useless as this picture, drawn from a photograph of an actual fire, shows.
FIGURE 4.3.14 Construction
Areas of Refuge in Nonsprinklered New
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existing one- and two-family dwellings where it is economically impractical to add a secondary means of escape. In this case, a suitable rope or chain ladder or a folding metal ladder may be suitable. However, the homeowner should recognize that aged, infirm, very young, and physically handicapped persons cannot use ladders and that, if the ladder passes near or over a window in a lower floor, flames from the window can prevent the use of the ladder.
Windows Windows are not exits. They may be used as access to fire escapes in existing buildings if they meet certain criteria concerning the size of window opening and the height of the sill from the floor. Windows may be considered a means of escape from certain residential occupancies. Windows are required in school rooms subject to student occupancy, unless the building is equipped with a standard automatic sprinkler system, and in bedrooms in one- and two-family dwellings that do not have two separate means of escape. These windows are for rescue and ventilation and must meet the criteria for size of opening, method of operation, and height from the floor.
EXIT LIGHTING AND SIGNS Exit Lighting In buildings where artificial lighting is provided for normal use, the illumination of the means of egress is required to ensure that occupants can evacuate the building quickly. The intensity of the illumination of the means of egress should be not less than 1 footcandle (10.77 lu/m2) measured at the floor. It is desirable that such floor illumination be provided by lights recessed in the wall and located approximately 1 ft (30.5 cm) above the floor because such lights are then unlikely to be obscured by the smoke that might occur during a fire. In auditoriums and other places of public assembly where movies or other projections are shown, NFPA 101 permits a reduction in this illumination for the period of the projection to values of not less than 1/5 footcandle (2.2 lu/m2).
Emergency Lighting NFPA 101 requires emergency power for illuminating the means of egress in many occupancies. For example, emergency lighting is required in assembly occupancies; in most educational buildings; in healthcare facilities; in detention and correctional facilities; most hotels and apartment buildings; in Class A and B mercantiles; in business buildings based on occupant load and number of stories; in most industrial and storage buildings; and in underground or windowless structures subject to occupancy by more than 100 persons. Well-designed emergency lighting using a source of power independent from the normal building service automatically provides the necessary illumination in the event of an interruption of power to normal lighting. The failure of the public utility or other outside electric power supply, the opening of a circuit breaker or fuse, or any manual act, including accidental opening
of a switch controlling normal lighting facilities, should result in the automatic operation of the emergency lighting system. Reliability of the exit illumination is most important. NFPA 70, National Electrical Code®, details requirements for the installation of emergency lighting equipment. Battery-operated electric lights and portable lights normally are not used for primary exit illumination, but they may be used as an emergency source under the restrictions imposed by NFPA 101. Luminescent, fluorescent, or other reflective materials are not a substitute for required illumination, since they are not normally sufficiently intense to justify recognition as exit floor illumination. Where electric battery-operated emergency lights are used, suitable facilities are needed to keep the batteries properly charged. Automobile-type lead storage batteries are not suitable because of their relatively short life when not subject to frequent recharge. Likewise, dry batteries have a limited life, and there is a danger that they may not be replaced when they have deteriorated. If normal building lighting fails, well-arranged emergency lighting provides necessary floor illumination automatically, with no appreciable interruption of illumination during the changeover. Where a generator is provided, a delay of up to 10 seconds is considered tolerable. The normal procedure is to provide such emergency lighting for a minimum period of 1½ hr. Most healthcare occupancies have self-contained electric generating plants for emergency power supplies, not only for exit lighting but also for use in the event of failure of the public utility. Where such emergency electric facilities are provided, they may supply power for emergency exit lighting, as well as other critical areas of such buildings.
Exit Signs All required exits and access ways must be identified by readily visible signs where the exit or the way to reach it is not immediately visible to the occupants. Directional “EXIT” signs are required in locations where the direction of travel to the nearest exit is not immediately apparent. The character of the occupancy will determine the actual need for such signs. In assembly occupancies, hotels, department stores, and other buildings with transient populations, the need for signs will be greater than in a building with permanent or semi-permanent populations. Even in permanent residential-occupancy buildings, signs are needed to identify exit facilities, such as stairs, that are not used regularly during the normal occupancy of the building. It is just as important that doors, passageways, or stairs that are not exits but are so located or arranged that they may be mistaken for exits be identified by signs with the words “NO EXIT.” Signs should be so located and of such size, color, and design as to be readily visible. Care should be taken not to locate decorations, furnishings, or other building equipment so as to obscure the visibility of these signs. NFPA 101 does not make any specific requirement for sign color but requires that signs be of a distinctive color. Some local codes do specify exit sign color. NFPA 101 specifies the size of the sign, the dimensions of the letters, and the levels of illumination for both externally and internally illuminated signs. Improvement in the physical marking of exits in an office occupancy with point-source, red or green strobe lights has been
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suggested. Placing corridor illumination on the walls close to the floor to provide effective illumination under smoke conditions, as is the practice in Japan, is a technique worthy of research.27
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routes should be varied from drill to drill. Occasional drills should be held that simulate conditions of an exit blocked by fire or smoke. All drills should simulate the fire department notification procedure. For a more detailed discussion of fire exit drills, see Chapter 1 of this section.
ALARM SYSTEMS Fire alarm systems to alert occupants to leave the building are normally operated manually. The alarm-sounding devices themselves should be distinctive in pitch and tone quality from all other sounding devices, and the use of these devices should be restricted to evacuation notification. Vocal alarm systems have been developed and installed in many high-rise buildings.14 NFPA 101 mandates voice alarm and communication systems in high-rise buildings. It is, of course, very important that all alarm system devices be distributed throughout a building so as to be heard effectively in every room above all other sounds. Visible, as well as audible, alarm devices are sometimes used in buildings. NFPA 101 permits flashing the exit signs with the activation of the fire alarm system. In new construction, visible alarms must be provided in addition to audible alarms in most instances. The proper maintenance of alarm systems is most important. Alarm systems should be supervised by a responsible person who will make the proper tests at specified intervals and will take charge of all alterations and additions to the systems.
EMERGENCY EGRESS AND RELOCATION DRILLS Emergency exit and relocation drills are essential in schools and are desirable in every type of occupancy to ensure familiarity with the exits and their operation. In occupancies such as hospitals, nursing homes, hotels, and department stores, drills are usually limited to employee participation, without alarming patients, guests, or customers. Drills should be planned to get everyone out of the building or to an area of refuge in an orderly manner, as promptly as possible. Fire fighting is always secondary to life safety, and, in general, fire-fighting operations should not be started until the evacuation is completed, except in cases where trained fire departments conduct rescue and firefighting operations simultaneously. Drills should be held at least once a month or more often, but not at regularly scheduled periods. Drills should occur on all shifts in an occupancy operated 24 hours a day. They should simulate typical fire conditions for the occupancy. Drills, both with and without warning, are beneficial. School emergency egress and relocation drills are an exercise in discipline, not speed, though reasonably prompt evacuation of a building is important. Students and staff should not be permitted to stop to put on coats. No individuals should be permitted to remain in the building, and no one should be excused from participating in the drill. The drill should include a roll call by class at designated assembly areas outside the building to make sure that no one has been left behind. There also should be an established routine for a complete check of the entire building, including toilets, to make sure that no one has been left behind. All exits should be used in drills, but
MAINTENANCE OF THE MEANS OF EGRESS The provision of a standard means of egress with adequate capacity does not guarantee the safety of the occupants in the event of an evacuation of any building. Means of egress that are not properly maintained can mean loss of life in a fire. Property managers usually assign definite responsibility for maintenance of mechanical and electrical equipment but may fail to do the same for the means of egress. As a result inspection authorities may find otherwise safe stairways used as storage for materials during peak sales or manufacturing periods. In apartment buildings, rubbish, baby carriages, and other obstructions are often found in stairway enclosures. Exit doors may be found locked or hardware in need of repair. Doors blocked open or removed from openings into stairway enclosures may permit rapid spread of smoke or hot gases throughout the building. Loose handrails and loose or slippery stair treads offer the dangerous probability that persons evacuating a building will fall in the path of others seeking escape. Maintaining the means of egress in safe operating condition at all times is as important to the prevention of loss of life as the proper construction of the building and the elimination of fire hazards.
SUMMARY Providing adequate means of egress is a key fire safety issue in both new buildings and in existing facilities. NFPA 101 provides in-depth coverage for providing adequate means of egress. For new construction, many of the issues are also covered in building codes, including the new NFPA 5000. This chapter only introduces the subject. To more completely understand the subject, both the NFPA Life Safety Code® Handbook and the SFPE Handbook of Fire Protection Engineering should be consulted.
BIBLIOGRAPHY References Cited 1. Bryan, J. B., “Behavioral Response to Fire and Smoke,” SFPE Handbook of Fire Protection Engineering, National Fire Protection Association, Quincy, MA, 2002. 2. Proulx, G., “Movement of People: The Evacuation Timing,” SPFE Handbook of Fire Protection Engineering, National Fire Protection Association, Quincy, MA, 2002. 3. Nelson, H. E., and Mowrer, F. W., “Emergency Movement,” SPFE Handbook of Fire Protection Engineering, National Fire Protection Association, Quincy, MA, 2002. 4. Fruin, J. J., Pedestrian Planning and Design, Metropolitan Association of Urban Designers and Environmental Planners, Inc., New York, 1977. 5. Pauls, J. L., “Movement of People in Building Evacuations,” Human Response to Tall Buildings, Dowden, Hutchinson and Ross, Inc., Stroudsburg, PA, 1977.
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6. “Second Report of the Operational Research Team on the Capacity of Footways,” Research Report No. 95, London Transport Board, London, UK, 1958. 7. Pauls, J. L., “Calculating Evacuation Times for Tall Buildings,” Fire Safety Journal, 1987, pp. 213–236. 8. Pauls, J. L., “The Movement of People in Buildings and Design Solutions for Means of Egress,” Fire Technology, Vol. 20, No. 1, 1984, pp. 27–47. 9. Abbott, J. C., “Fire Involving Upholstery Materials,” Fire Journal, Vol. 65, No. 4, 1971, p. 88. 10. Lathrop, J. K., et al., “In Osceola: A Matter of Contents,” Fire Journal, Vol. 69, No. 3, 1975, pp. 20–26. 11. Hall, J. R., Burns, Toxic Gases, and Other Hazards Associated with Fires, National Fire Protection Association Fire Analysis and Research Division, Quincy, MA, 1996. 12. Sharry, J. A., “South America Burning,” Fire Journal, Vol. 68, No. 4, 1974, pp. 23–33. 13. Best, R., and Demers, D. P., “Fire at the MGM Grand,” Fire Journal, Vol. 76, No. 1, 1982, pp. 19–37. 14. Powers, W. R., “New York Office Building Fire,” Fire Journal, Vol. 65, No. 1, 1971, pp. 18–23, 87. 15. Keating, J. P., et al., An Evaluation of the Federal High Rise Emergency Evacuation Procedures, Department of Psychology, University of Washington, Seattle, 1978. 16. Pauls, J. L., “Evacuation and Other Fire Safety Measures in High-Rise Buildings,” Research Paper No. 648, National Research Council of Canada, Division of Building Research, Ottawa, Canada, 1975. 17. Pauls, J. L., “Management and Movement of Building Occupants in Emergencies,” Research Paper No. 788, National Research Council of Canada, Division of Building Research, Ottawa, Canada, 1978. 18. Phillips, A. W., “You and the High-Rise Building Fire,” Technology Report 74-1, Society of Fire Protection Engineers, Boston, 1974. 19. Krasny, John F., et al., “Development of a Candidate Test Method for the Measurement of the Propensity of Cigarettes to Cause Smoldering Ignition of Upholstered Furniture and Mattresses,” NBSIR 81-2363, Center for Fire Research, National Bureau of Standards, Washington, DC, 1981. 20. CFR Part 1623, Standard for the Flammability of Mattresses and Mattress Pads, FF-4-72, 40 FR 59940, U.S. Consumer Product Safety Commission, Washington, DC, 1972. 21. Bryan, J. L., “Human Behavior in the MGM Grand Hotel Fire,” Fire Journal, Vol. 76, No. 2, 1982, pp. 37–41, 44–48. 22. Keating, J. P., and Loftus, E. F., “The Logic of Fire Escape,” Psychology Today, 1981, pp. 14–19. 23. Keating, J. P., “The Myth of Panic,” Fire Journal, Vol. 76, No. 3, 1982, pp. 57–61, 147. 24. Sharry, J. A., “Real-World Problems with Zoned Evacuation,” Fire Journal, Vol. 77, No. 2, 1983, pp. 32–33, 55. 25. Macdonald, J. N., Non-Evacuation in Compartmented FireResistive Buildings Can Save Lives and Makes Sense, 88th NFPA Annual Meeting, New Orleans, LA, May 23, 1984. 26. “Design and Construction of Building Exits,” Miscellaneous Publication M51, 1935, National Bureau of Standards, Washington, DC, pp. 30–37. (Out of print) 27. Cohn, B. M., Study of Human Engineering Considerations in Emergency Exiting from Secure Spaces, Gage-Babcock & Association, Inc., Chicago, 1978.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on concepts of egress design discussed in this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 13, Standard for Installation of Sprinkler Systems NFPA 70, National Electrical Code® NFPA 101®, Life Safety Code®
NFPA 101A, Guide on Alternative Approaches to Life Safety NFPA 253, Standard Method of Test for Critical Radiant Flux of Floor Covering Systems Using a Radiant Heat Energy Source NFPA 255, Standard Method of Test of Surface Burning Characteristics of Building Materials NFPA 260, Standard Method of Tests and Classification System for Cigarette Ignition Resistance of Components of Upholstered Furniture NFPA 261, Standard Method for Determining Resistance of Mock-Up Upholstered Furniture Material Assemblies to Ignition by Smoldering Cigarettes NFPA 267, Standard Method of Test for Fire Characteristics of Mattresses and Bedding Assemblies Exposed to Flaming Ignition Source NFPA 286, Standard Methods of Fire Tests for Evaluating Contribution of Wall and Ceiling Interior Finish to Room Fire Growth NFPA 5000™, Building Construction and Safety Code™
Additional Readings Bachman, E. G., “Residential Preincident Intelligence,” Fire Engineering, Vol. 154, No. 8, 2001, pp. 71–72. Ballast, D. K., Egress from Buildings in Emergencies: A Bibliography, Vance Bibliographies, Monticello, IL, 1988. Bamford, G. J., and Kandola, B., “AEA EGRESS: A New Approach to Evacuation Modelling,” NISTIR 5499, Sept. 1994; National Institute of Standards and Technology, Annual Conference on Fire Research: Book of Abstracts, October 17–20, 1994, Gaithersburg, MD, 1994, pp. 29–30. Beck, V., and Zhao, L., “CESARE-RISK: An Aid for PerformanceBased Fire Design. Some Preliminary Results,” Proceedings of the 6th International Symposium on Fire Safety Science, Poitiers, France, July 5–9, 1999, M. Curtat (Ed.), Intl. Assoc. for Fire Safety Science, Boston, 2000, pp. 159–170. Beller, D. K., and Watts, J. M., Jr., “Occupancy Classification for Performance-Based Life Safety,” Fire and Materials, Vol. 23, No. 6, 1999, pp. 281–289. Boyce, K. B., Shields, T. J., and Silcock, G. W. H., “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capability of People with Disabilities to Read and Locate Exit Signs,” Fire Technology, Vol. 35, No. 1, 1999, pp. 79–86. Boyce, K. B., Shields, T. J., and Silcock, G. W. H., “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capability of Disabled People to Negotiate Doors,” Fire Technology, Vol. 35, No. 1, 1999, pp. 68–78. Boyce, K. B., Shields, T. J., and Silcock, G. W. H., “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Capability of Disabled People Moving Horizontally and on an Incline,” Fire Technology, Vol. 35, No. 1, 1999, p. 51–67. Boyce, K. B., Shields, T. J., and Silcock, G. W. H., “Toward the Characterization of Building Occupancies for Fire Safety Engineering: Prevalence, Type, and Mobility of Disabled People,” Fire Technology, Vol. 35, No. 1, 1999, pp. 35–50. Bruniges, B., “No Place Like Dome,” Fire Prevention, No. 330, Mar. 2000, pp. 19–21. Bryan, J. L., Smoke as a Determinant of Human Behavior in Fire Situations (Project People), Department of Fire Protection Engineering, University of Maryland, College Park, June 30, 1977. Bryan, J. L., An Examination and Analysis of the Dynamics of the Human Behavior in the Westchase Hilton Hotel Fire, National Fire Protection Association, Quincy, MA, Mar. 28, 1983. Bryan, J. L., An Examination and Analysis of the Dynamics of the Human Behavior in the MGM Grand Hotel Fire, revised edition, National Fire Protection Association, Quincy, MA, Apr. 1983. Bryan, J. L., “Convergence Clusters: A Phenomenon of Human Behavior Seen in Selected High-Rise Building Fires,” Fire Journal, Vol. 79, No. 6, Nov. 1985, pp. 27–30, 86–90. Bryan, J. L., “Behavioral Response to Fire and Smoke,” SFPE Handbook of Fire Protection Engineering, National Fire Protection Association, Quincy, MA, 1988.
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Bukowski, R. W., “HAZARD II: Implication for Fire Safety Engineering,” Proceedings of the Fire Safety Design of Buildings and Fire Safety Engineering Conference Compendium, Session 3: Fire Safety Engineering Tools, Oslo, Norway, August 19–20, 1996, pp. 1–7. Bukowski, R. W., Peacock, R. D., and Jones, W. W., “Sensitivity Examination of the airEXODUS Aircraft Evacuation Simulation Model,” Proceedings of the International Aircraft Fire and Cabin Safety Rescue Conference, Atlantic City, NJ, November 16–20, 1998, pp. 1–14. Cadwell, C., Fleischmann, C., Parkes, A. R., and Henderson, A., “Case Study Building Specifications: A New Zealand Approach,” Proceedings of the Pacific Rim Conference and 2nd International Conference on Performance-Based Codes and Fire Safety Design Methods, Maui, HI, May 3–9, 1998, International Code Council, Birmingham, AL, 1998, pp. 453–469. Caldwell, C. A., “Ballantynes Department Store Performance Fire Design,” Proceedings of the International Conference on Engineered Fire Protection Design, Applying Fire Science to Fire Protection Problems, San Francisco, CA, June 11–15, 2001, Society of Fire Protection Engineers, Bethesda, MD, 2001, pp. 54–65. Canter, D., Fires and Human Behavior, 2nd ed., Fulton, London, UK, 1988. Cappucio, J., “Pathfinder: A Computer-Based Timed Egress Simulation,” Fire Protection Engineering, No. 8, Fall 2000, pp. 11–12. Cherry, A., “Fire Safety Design and Construction: Approved Document B2000,” Fire Safety Engineering, Vol. 7, No. 2, 2000, pp. 9–10. Chien, S. W., and Lin, H. W., “Evaluation of the Evacuation Performance of the Mass Rapid Transit Station Based on the Prescriptive Code,” Proceedings of the Fire Research Development and Application in the 21st Century FORUM 2000 Symposium, Taipei, Taiwan, October 23–24, 2000, pp. 1–23. Chow, W. K., and Lui, G. C. H., “On Evaluating Building Fire Safety for Business Occupancies,” International Journal on Engineering Performance-Based Fire Codes, Vol. 3, No. 1, 2001, pp. 16–24. Clerico, M., Coppola, L., and Gecchele, G., “Non-Conventional Evaluation of Escape Behavior Factors and Design Parameters in Fire Buildings Evacuation,” Proceedings of the 1st International Symposium on Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 115–124. Cohn, “Characterization and Use of Design Basis Fires in Performance Codes,” Proceedings of the International INTERFLAM Conference, INTERFLAM ’96, Cambridge, UK, March 26–28, 1996, C. A. Franks and S. Grayson (Eds.), Interscience Communications Ltd., London, UK, 1996, pp. 581–588. Collins, B. L., “Overview of Exit Sign Research” [Video], CFR Video Seminar, National Institute of Standards and Technology, Gaithersburg, MD, Sept. 20, 1990. Collins, B. L., and Goodin, P. J., “Visibility of Exit Directional Indicators,” NISTIR 4532, National Institute of Standards and Technology, Gaithersburg, MD, National Electrical Manufacturers Assoc., Washington, DC, Mar. 1991. Collins, B. L., Dahir, M. S., and Madrzykowski, D., “Evaluation of Exit Signs in Clear and Smoke Conditions,” NISTIR 4399, National Institute of Standards and Technology, Gaithersburg, MD, Aug. 1990. Cooke, G. M. E., “Assisted Means of Escape of Disabled People from Fires in Tall Buildings,” BRE IP 16/91, Fire Research Station, Borehamwood, UK, Nov. 1991. Cooper, L. Y., “A Concept for Estimating Available Safe Egress Time in Fires,” Fire Safety Journal, Vol. 5, 1983, p. 135. Cooper, L. Y., and Nelson, H. E., “Life-Safety Implementation through Designed Safe Egress,” Chapter 8, Council on Tall Buildings and Urban Habitat, Fire Safety in Tall Buildings. Tall Building Criteria and Loading, Committee 8A, McGraw-Hill, Inc., Blue Ridge Summit, PA, 1992, pp. 113–125.
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Coppola, L., and Gecchele, G., “Fire Safety for Historical Buildings and Performance Criteria for Their Use,” Proceedings of the 2nd International Symposium on Human Behavior in Fire: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Interscience Communications Ltd., London, UK, 2001, pp. 451–458. Crawford, E., “Effect of Safety Factors on Timed Human Egress Simulations,” Fire Engineering Research Report 99/3, University of Canterbury, Christchurch, New Zealand, Mar. 1999. Donegan, H. A., Pollock, A. J., and Taylor, I. R., “Egress Complexity of a Building,” Proceedings of the 4th International Symposium on Fire Safety Science, Intl. Assoc. for Fire Safety Science, Boston, MA, 1994, pp. 601–612. Donegan, H. A., and Taylor, I. R., “How Complex is the Egress Capability of Your Design?” Proceedings of the 1st International Symposium on Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 601–608. Donegan, H. A., Taylor, I. R., Christie, G., and Livesey, G., “Illustrating Some Rule Based Algorithms of Egress Complexity Using Simple Case Studies,” Journal of Applied Fire Science, Vol. 8, No. 3, 1998/1999, pp. 243–258. Ebihara, M., Notake, H., and Yashiro, Y., “Assessment of Clarity of Egress Route in Buildings,” Proceedings of the 13th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, Gaithersburg, MD, March 13–20, 1996, K. A. Beall (Ed.), NISTIR 6030, National Institute of Standards and Technology, Gaithersburg, MD, 1997, pp. 43–51. Evans, D. H., Weber, R. D., and Quiter, J. R., “Luxor Hotel and Casino: An Application of Performance-Based Fire Safety Design Methods,” Proceedings of the Pacific Rim Conference and 2nd International Conference on Performance-Base Codes and Fire Safety Design Methods, Maui, HI, May 3–9, 1998, International Code Council, Birmingham, AL, 1998, pp. 393–410. Fahy, R. F., “EXIT89: An Evacuation Model for High-Rise Buildings—Recent Enhancements and Example Applications,” Proceedings of the International Conference on Fire Research and Engineering, Sept. 10–15, 1995, Orlando, FL, SFPE, Boston, 1995, pp. 332–337. Fahy, R. F., “Practical Example of an Evacuation Model for Complex Spaces,” Proceedings of the 1st International Symposium on Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 743–751. Fahy, R. F., “Verifying the Predictive Capability of EXIT89,” Proceedings of the 2nd International Conference on Human Behavior in Fire 2001, March 26–28, 2001, Cambridge, MA, Interscience Communications Limited, London, UK, 2001, pp. 53–64. Fahy, R. F., and Proulx, G., “Human Behavior in the World Trade Center Evacuation,” Proceedings of the 5th International Symposium of the International Association for Fire Safety Science, Melbourne, Australia, March 3–7, 1997, Y. Hasemi (Ed.), Intl. Assoc. for Fire Safety Science, Boston, 1997, pp. 713–724. Fahy, R. F., and Proulx, G., “Study of Occupant Behavior during the World Trade Center Evacuation,” Proceedings of the International INTERFLAM Conference, INTERFLAM ’96, Cambridge, UK, March 26–28, 1996, C. A. Franks and S. Grayson (Eds.), Interscience Communications Ltd., London, UK, 1996, pp. 793–802. Fahy, R. F., and Sapochetti, J. I., “Balancing Fire Protection and Egress Prediction,” Proceedings of the 3rd International Conference on Fire Research and Engineering (ICFRE3), Chicago, IL, October 4–8, 1999, Society of Fire Protection Engineers, Boston, 1999, pp. 135–145. Feng, P., and Hajisophocleous, G. V., “Equations and Theory of the Simple Correlation Model of FIERAsystem,” Internal Report 779, National Research Council of Canada, Ottawa, Ontario, Feb. 2000. Fiameni, C., Gallina, G., and Mutani, G., “Fire Safety Performance Based Approach Applied to LaFenice Theatre in Venice (Italy),”
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Proceedings of the Fire Research Development and Application in the 21st Century FORUM 2000 Symposium, Taipei, Taiwan, October 23–24, 2000, pp. 1–19. Foley, M., “Fire Engineering of the Superdome for the 2000 Olympics,” Fire Australia, May 2000, pp. 4–8. Francis, R. L., “Network Models of Building Evacuation: Development of Software Systems,” NBS-GCR-85-489, National Bureau of Standards, Gaithersburg, MD, Mar. 1985. Fruin, J. J., Pedestrian Planning and Design, revised edition, Elevator World, Mobile, AL, 1987. Galea, E., “Design on the Mind,” Fire Prevention/Fire Engineers Journal, No. 344, May 2001, pp. 3–39. Galea, E. R., Blake, S. J., and Larence, P., “airEXODUS Evacuation Model and Its Application to Aircraft Safety,” Paper No. 01/IM/78, University of Greenwich, London, UK, Aug. 2001. Galea, E. R., Gwynne, S., and Lawrence, P., “Using Computer Simulation to Predict the Evacuation Performance of Passenger Ships,” Paper No. 00/IM/61, University of Greenwich, London, UK, Apr. 2000. Galea, E. R., Owen, M., and Lawrence, P. J., “Emergency Egress from Large Buildings under Fire Conditions Simulated Using the EXODUS Evacuation Model,” ISBN 0-9516320-9-4; Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, March 26–28, 1996, Cambridge, UK, Interscience Communications Ltd., London, UK, 1996, pp. 711–720. Gibson, G. A., and Locke, H. A., “Performance-Based Approach to Exiting of the Proposed Vancouver Convention and Exhibition Centre Utilizing Fire Modelling,” Proceedings of the International Conference on Engineered Fire Protection Design, Applying Fire Science to Fire Protection Problems, San Francisco, CA, June 11–15, 2001, Society of Fire Protection Engineers, Bethesda, MD, 2001, pp. 400–411. Gwynne, S., Galea, E. R., Lawrence, P. J., Owen, M., and Filippidis, L., “Further Validation of the buildingEXODUS Evacuation Model Using the Toukuba Dataset,” Paper No. 98/IM/31, University of Greenwich, London, UK, 1998. Gwynne, S., Galea, E. R., Lawrence, P. J., Owen, M., and Filippidis, L., “Systematic Comparison of Model Predictions Produced by the buildingEXODUS Evacuation Model and the Tsukuba Pavillion Evacuation Data,” Journal of Applied Fire Science, Vol. 7, No. 3, 1997/1998, pp. 235–266. Hagiwara, I., “Evaluation Method of Egress Safety,” Proceedings of the 15th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, San Antonio, TX, March 1–7, 2000, S. L. Bryner (Ed.), NISTIR 6588, National Institute of Standards and Technology, Gaithersburg, MD, 2000, pp. 161–165. Hagiwara, I., and Tanaka, T., “International Comparison of Fire Safety Provisions for Means of Escape,” 12th Joint Panel Meeting of the U.S./Japan Government Cooperative Program on Natural Resources (UJNR) on Fire Research and Safety, October 27– November 2, 1992, Tsukuba, Japan, Building Research Inst., Ibaraki, Japan, Fire Research Institute, Tokyo, Japan, 1992, pp. 224–231; Proceedings of the 4th International Symposium on Fire Safety Science, International Association for Fire Safety Science, 1994, pp. 633–644. Hagiwara, I., Tanaka, T., and Mimura, Y., “Consideration on Common Path Length and Single Stairway,” Proceedings of the 5th International Symposium of the International Association for Fire Safety Science, Melbourne, Australia, March 3–7, 1997, Y. Hasemi (Ed.), Intl. Assoc. for Fire Safety Science, Boston, 1997, pp. 759–770. Hock, D. S. C., “Fire Safety Design of the World’s Tallest Twin Towers,” Fire Engineers Journal, Vol. 57, No. 191, 1997, pp. 12–16. Hung, W. Y., and Chow, W. K., “Review of Fire Regulations for New High-Rise Commercial Buildings in Hong Kong and a Brief Comparison with Those in Overseas,” International Journal on Engineering Performance-Based Fire Codes, Vol. 3, No. 1, 2001, pp. 25–51. Ikahata, Y., Ebihara, M., Notake, H., and Ohmiya, Y., “Assessment Method for Evacuation Safety under Consideration of Uncertainty of Human Behavior and Fire,” Proceedings of the 1st In-
ternational Symposium on Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 429–437. Jin, T., “Evaluation of Fire Exit Sign in Fire Smoke,” ’93 Asian Fire Seminar, October 7–9, 1993, Tokyo, Japan, 1993, pp. 167–175. Jin, T., and Yamada, T., “Experimental Study on Effect of Escape Guidance in Fire Smoke by Travelling Flashing of Light Sources,” Proceedings of the 4th International Symposium on Fire Safety Science, Intl. Assoc. for Fire Safety Science, Boston, MA, 1994, pp. 705–714. Jin, T., et al., “Evaluation of the Conspicuousness of Emergency Exit Signs,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, New York, 1991, pp. 835–841. Johnson, P. F., Beck, V. R., and Horasan, M., “Use of Egress Modelling in Performance-Based Fire Engineering Design: A Fire Safety Study at the National Gallery of Victoria,” Proceedings of the 4th International Symposium on Fire Safety Science, Intl. Assoc. for Fire Safety Science, Boston, MA, 1994, pp. 669–680. Jones, B. K., and Hewitt, J. A., “Leadership and Group Formation in High-Rise Building Evacuations,” Proceedings of the 1st International Symposium on Fire Safety Science, Hemisphere, 1986, pp. 513–522. Jonsson, R., and Lundin, J., “Swedish Case Study: Different Fire Safety Design Methods Applied on a High Rise Building,” Report LUTBDG/TVBB-3099-SE, Lund University, Sweden, Mar. 31, 1998. Kakegawa, S., Yashiro, Y., and Ebihara, M., “Life Safety Evaluation of Large Populations with Mixed-Abilities,” Proceedings of the 13th Joint Panel Meeting, U.S./Japan Government Cooperative Program on Natural Resources (UJNR), Fire Research and Safety, Gaithersburg, MD, March 13–20, 1996, K. A. Beall (Ed.), NISTIR 6030, National Institute of Standards and Technology, Gaithersburg, MD, 1997, pp. 27–34. Kendik, E., “Assessment of Escape Routes in Buildings and Design Method for Calculating Pedestrian Movement,” TR 85-4, Society of Fire Protection Engineers, Boston, 1985. Kendik, E., “Methods of Design of Means of Egress: Towards a Quantitative Comparison of National Code Requirements,” Proceedings of the 1st International Symposium of Fire Safety Science, Hemisphere, Washington, DC, 1986. Kisko, T. M., and Francis, R. L., “EVACNET+, A Computer Program to Determine Optimal Building Evacuation Plans,” Fire Safety Journal, Vol. 9, No. 2, 1985, pp. 211–220. Kisko, T. M., and Francis, R. L., “Network Models of Building Evacuation: Development of Software Systems,” NBS-GCR-85-489, National Bureau of Standards, Gaithersburg, MD, 1985. Klevan, J. B., “Modeling of Available Egress Time from Assembly Spaces or Estimating the Advance of the Fire Threat,” SFPE TR 82-2, Society of Fire Protection Engineers, Boston, 1982. Klote, J. H., “Elevators as a Means of Fire Escape,” NBSIR 82-2507, National Bureau of Standards, Gaithersburg, MD, May 1982. Koffel, W. E., “Evaluating Occupant Load for Egress,” NFPA Fire Journal, Vol. 88, No. 1, 1994, pp. 14, 93. Koffel, W. E., “Exiting Safely,” NFPA Journal, Vol. 95, No. 5, 2001, p. 36. Koffel, W. E., “When Security Systems Affect Life Safety,” NFPA Journal, Vol. 93, No. 6, 1999, p. 26. Kostreva, M., “Optimization Models for Fire Egress Analysis” [Video], BFRL Video Seminar, Clemson Univ., SC, Aug. 20, 1991. Kostreva, M. M., “Mathematical Modeling of Human Egress from Fires in Residential Buildings,” NIST-GCR-94-643, Fire Technology, Vol. 30, No. 3, June 1994, pp. 338–340. Ling, W. C. T., and Williamson, R. B., “Use of Probabilistic Networks for Analysis of Smoke Spread and Egress of People in Buildings,” Proceedings of the 1st International Symposium for Fire Safety Science, Hemisphere, New York, 1986, pp. 953–962. Lo, S. M., “Use of Designated Refuge Floors in High-Rise Buildings: Hong Kong Perspective,” Journal of Applied Fire Science, Vol. 7, No. 3, 1997/1998, pp. 287–299.
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Lo, S. M., and Deng, Z. M., “Study on the Exit Requirements in Karaoke Establishments,” Journal of Applied Fire Science, Vol. 8, No. 1, 1998/1999, pp. 61–71. Lo, S. M., Lam, K. C., Yuen, K. K., and Fang, Z., “Pre-Evacuation Behavioral Study for the People in High-Rise Residential Buildings under Fire Situations,” International Journal on Architectural Science, Vol. 1, No. 4, 2000, pp. 143–152. Lo, S. M., and Will, B. F., “View to the Requirement of Designated Refuge Floors in High-Rise Buildings in Hong Kong,” Proceedings of the 5th International Symposium of the International Association for Fire Safety Science, Melbourne, Australia, March 3–7, 1997, Y. Hasemi (Ed.), Intl. Assoc. for Fire Safety Science, Boston, 1997, pp. 737–745. MacLennan, H. A., “Towards an Integrated Egress/Evacuation Model Using an Open Systems Approach,” Proceedings of the 1st International Symposium on Fire Safety Science, Hemisphere, 1986, pp. 581–590. MacLennan, H. A., Regan, M. A., and Ware, R., “Engineering Model for the Estimation of Occupant Pre-Movement and or Response Times and the Probability of Their Occurrences,” Fire and Materials, Vol. 23, No. 6, 1999, pp. 255–263. Marchant, R., “Some Discussions on Egress Calculations: Time to Move,” International Journal on Engineering PerformanceBased Fire Codes, Vol. 1, No. 2, 1999, pp. 81–95. McClintock, T., Shields, T. J., Rutland, T. R., and Leslie, J., “Dishabituation and Stimulus Equivalence Could Make All Emergency Fire Exits Familiar,” Journal of Applied Fire Science, Vol. 9, No. 2, 1999/2000, pp. 125–134. Mongeau, E., “Building a Fire-Safe Dorm,” NFPA Journal, Vol. 93, No. 1, 1999, pp. 60–64. Mongeau, E., “Life Safety at the Baltimore Convention Center,” NFPA Journal, Vol. 93, No. 3, 1999, pp. 138–144. Murosaki, Y., Hayashi, H., and Nishigaki, T., “Effects of Passage Width on Choice of Egress Route at a T-Junction in a Building,” Proceedings of the 1st International Symposium on Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 593–600. Notake, H., Ebihara, M., and Yashiro, Y., “Assessment of Legibility of Egress Route in a Building from the Viewpoint of Evacuation Behavior,” Proceedings of the 1st International Symposium on Human Behavior in Fire, Belfast, UK, August 31– September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 553–562. Ouellette, M. J., “Exit Signs in Smoke: Design Parameters for Greater Visibility,” Lighting Research and Technology, Vol. 20, No. 4, 1988, pp. 155–160. Ouellette, M. J., “Visibility of Exit Signs,” Institute for Research in Construction, Canada, Construction Practice, 1994. Owen, M., Galea, E. R., Lawrence, P. J., and Filippidis, L., “Numerical Simulation of Aircraft Evacuation and Its Application to Aircraft Design and Certification,” Paper No. 97/IM/28, University of Greenwich, London, UK, 1997. Ozel, F., Way Finding and Route Selection in Fires, School of Architecture, New Jersey Institute of Technology, Newark, NJ, 1986. Pauls J., “Development of Knowledge About Means of Egress,” Fire Technology, Vol. 20, No. 2, 1984, pp. 28–40. Pauls, J., “Calculating Evacuation Times for Tall Buildings,” Fire Safety Journal, Vol. 12, No. 3, 1987, pp. 213–236. Pauls, J., “Egress Time and Safety Performance Related to Requirements in Codes and Standards,” Hughes Associates, Inc., Columbia, MD, Building Officials and Code Administration International, Inc. (BOCA) and OBOA, Workshop Landout, June 1990, Ontario, Canada, 1990, pp. 1–10. Pauls, J., “Movement of People,” SFPE Handbook of Fire Protection Engineering, 2nd ed., National Fire Protection Association, Quincy, MA, 1988, pp. 3-263–3-285. Pauls, J., Gatfield, A. J., and Juillet, E., “Elevator Use for Egress: The Human-Factors Problems and Prospects,” National Research Council of Canada, Ottawa, Ontario, National Task Force on Life Safety and the Handicapped American Society of Mechanical Engineers, Council of American Building Officials and Na-
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Stevens, R. E., “Scissors Stairs as Exits,” Fire Journal, Vol. 59, No. 1, Jan. 1965, p. 40. Stevens, R. E., “What Is an Exit?” Fire Journal, Vol. 59, No. 6, Nov. 1965, pp. 44–45. Stevens, R. E., “Smokeproof Towers,” Fire Journal, Vol. 60, No. 1, Jan. 1966, pp. 54–55. Takahashi, K., and Tanaka, T., “An Evacuation Model for the Use in Fire Safety Designing of Buildings,” 9th Joint Panel Meeting of the UJNR Panel on Fire Research and Safety, NBSIR 88-3753, National Bureau of Standards, Gaithersburg, MD, Apr. 1988. Tanaka, T., “Study for Performance Based Design of Means of Escape in Fire,” Proceedings of the 3rd International Symposium on Fire Safety Science, Elsevier Applied Science, New York, 1991, pp. 729–738. Templer, J., The Staircase: Studies of Hazards, Fills and Safer Design, MIT Press, Cambridge, MA, 1992. Teo, A., “Validation of an Evacuation Model Currently under Development,” Fire Engineering Research Report 01/7, University of Canterbury, Christchurch, New Zealand, Mar. 2001. Thompson, P., Wu, J., and Marchant, E., “Simulex 3.0: Modelling Evacuation in Multi-Story Buildings,” Proceedings of the International INTERFLAM Conference, INTERFLAM ’96, Cambridge, UK, March 26–28, 1996, C. A. Franks and S. Grayson (Eds.), Interscience Communications Ltd., London, UK, 1996, pp. 725–736. Van Bogaert, A. F., “Evacuating Schools on Fire,” Proceedings of the 1st International Symposium on Fire Safety Science, Hemisphere, 1986, pp. 551–560.
Wade, C. A., “Means of Escape in Multi-Storey Buildings. Study Report,” BRANZ Study Report SR38, Building Research Association of New Zealand, Judgeford, July 1991. Walsh, C. J., “Rational Fire Safety Engineering Approach to the Protection of People with Disabilities in or Near Buildings during a Fire, or Fire Related Incident,” Proceedings of the International INTERFLAM Conference, INTERFLAM ’96, Cambridge, UK, March 26–28, 1996, C. A. Franks and S. Grayson (Eds.), Interscience Communications Ltd., London, UK, 1996, pp. 341–352. Watts, J. M., Jr., “Angle of Exit Remoteness. Technical Note,” Fire Technology, Vol. 32, No. 1, 1996, pp. 76–82. Webber, G., and Hallman, P., “Photoluminescence for Aiding Escape,” Fire Surveyor, Vol. 17, No. 6, 1988, pp. 17–29. Weinroth, J., “An Adaptable Microcomputer Model for Evacuation Management,” Fire Technology, Vol. 25, No. 4, 1989, pp. 291–307. Yoshida, Y., “Evaluating Building Fire Safety Through Egress Prediction: A Standard Application in Japan,” Fire Technology, Vol. 31, No. 2, 1995, pp. 158–174. Yung, D., Hadjisophocleous, G. V., and Yager, B., “Case Study: The Use of FIRECAM™ to Identify Cost-Effective Fire Safety Design Options for a Large 40-Story Office Building” Proceedings of the Pacific Rim Conference and 2nd International Conference on Performance-Based Codes and Fire Safety Design Methods, Maui, HI, May 3–9, 1998, International Code Council, Birmingham, AL, 1998, pp. 441–482.
FIRE AND LIFE SAFETY EDUCATION
F
ire and life safety education is a cornerstone for preventing injuries and deaths and for minimizing loss due to direct and indirect property damage as the result of fire. With so much riding on the outcome of fire and life safety initiatives, it is imperative for fire protection professionals to have a working knowledge of the critical components of fire and life safety education. Section 5 provides an overview of the discipline of fire and life safety education and describes approaches and techniques that compose it. Focusing on specific elements of program development and effectiveness for fire and life safety education, each of the eight chapters contains vital information essential to building a comprehensive fire and life safety education program. Chapter 1, “Fire and Life Safety: A Measure of Fire Department Excellence,” provides an overview of community public education strategy and operation theory with emphasis on the trend toward agencies working hand in hand to deliver fire and life safety education. Chapter 2, “Using Data for Public Education Decision Making,” focuses on using data to target resources effectively. Chapter 3, “Fire and Life Safety Education: Theory and Techniques,” applies the knowledge base of teaching children and adults to specialized topics of fire and life safety education. Chapter 4, “Reaching High-Risk Groups,” provides updated and critical information on identifying and designing programs for groups with high risk of fire, burn injury, or related hazard. Chapter 5, “Understanding Media: Basics for the Twenty-First Century,” provides guidance on working with the media to convey public information and educational messages to broadbased audiences. Chapter 6, “Evaluation Techniques for Fire and Life Safety Education,” provides a brief review of evaluation techniques for fire and life safety education. Using Risk Watch® as an example of successful evaluation technique, the author assists fire and life safety educators to perform the basic program evaluation functions necessary for planning future events. Chapter 7, “Campus Fire Safety,” and Chapter 8, “Juvenile Fire Setter Intervention,” are new chapters that discuss interventions and process to specific targeted groups.
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Dena E. Schumacher
Also look for these: Several chapters in other sections in this handbook contain information that relates to fire and life safety education. For example, Section 2, Chapter 4, “Dynamics of Compartment Fire Growth,” can be considered the underpinning of the need for prompt action during fire. Section 4, Chapter 1, “Human Behavior and Fire,” and Section 8, Chapter 2, “Combustion Products and Their Effects on Life Safety,” should be considered required reading for fire and life safety educators.
Case Study VEGREVILLE, ALBERTA, CANADA, OCTOBER 24, 1999 teries the night before so steam from the shower wouldn’t activate the smoke alarms and wake her husband up. The fire prevention captain said he believed that if Melanie had not acted as quickly and calmly as she had, the whole family would have been overcome with smoke. The family had developed and practiced a home escape plan with Melanie’s eight-year-old brother Paul, who was taught the Learn Not to Burn® program at his school. As a result, seven lives were saved.
On the morning of October 24, 1999, a fire broke out at 10year-old Melanie’s home. The fire started when the family’s furnace malfunctioned and ignited a pile of clothes in the basement. Melanie awoke to find smoke rising from a vent in her bedroom. Finding the hallway filled with smoke, she quickly and calmly crawled low under the smoke to alert her sleeping family. Using their home escape plan, the family exited safely and reported to their outside meeting place, where they called the fire department. Although the home did have smoke alarms, Melanie’s mother had disconnected the batSource: NFPA.
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Chapter 1
Fire and Life Safety Education: A Measure of Fire Department Excellence
Importance of Fire and Life Safety Education A Systems Approach to Fire and Life Safety Role of Fire Departments in Public Education Engineering to Support Engineering Strategies Summary Appendix A Appendix B Bibliography Chapter 2
Using Data for Public Education Decision Making
What Is the Problem? Differences in Fire Risks around the World Type of Property What Is the Strategy? Who Is the Target Audience? Was the Target Audience Reached? Did the Strategy Work? Were Lives Saved or Losses Reduced? Available Data and Analysis Resources Bibliography Chapter 3
Fire and Life Safety Education: Theory and Techniques
Education Theory for Fire and Life Safety Educators Characteristics of Learning Education Techniques for Fire and Life Safety Educators Bibliography Chapter 4
Reaching High-Risk Groups
Preschool Children Older Adults The Disadvantaged Native Populations Special Issue: Home Security and Fire Safety National Programs in the United States Programs on the International Level Summary Bibliography Chapter 5
Understanding Media: Basics for the Twenty-First Century
Defining Terms Fire Department’s Communication Goals and Objectives
5–3 5–3 5–6 5–8 5–10 5–10 5–11 5–12 5–14
5–17 5–18 5–19 5–20 5–23 5–25 5–27 5–27 5–27 5–29 5–30
5–31 5–31 5–31 5–37 5–43 5–45 5–45 5–48 5–52 5–57 5–58 5–59 5–60 5–60 5–61
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Understanding Community Media Services Matching the Medium with the Message Providing Practical Publicity Providing Public Information at a Fire/Emergency Scene Evaluating Efforts Exploring Legal Issues Communication Technologies Summary Bibliography Chapter 6
Evaluation Techniques for Fire and Life Safety Education
The Evaluation Process A Hierarchy of Evaluation Measures Formative Evaluation Process Evaluation Impact Evaluation Outcome Evaluation Handling Uncontrollable Factors Summary Bibliography Chapter 7
Campus Fire Safety
On-Campus Residences Off-Campus Residences History PODS Strategy PODS Prevention PODS Occupant Awareness PODS Detection PODS Suppression Fire Department Strategy Solutions Summary Bibliography Chapter 8
Juvenile Firesetting
Terminology Magnitude of the Problem Characteristics of Children Involved in Firesetting Behavior Motivation for Firesetting Behavior Response to Juvenile Firesetting Pitfalls Training Information Resources Summary Bibliography
5–67 5–69 5–74 5–74 5–75 5–75 5–77 5–77 5–78
5–79 5–79 5–82 5–83 5–84 5–84 5–87 5–91 5–94 5–94 5–95 5–95 5–96 5–98 5–98 5–99 5–100 5–101 5–102 5–103 5–103 5–105 5–105 5–107 5–107 5–108 5–108 5–109 5–111 5–118 5–118 5–119 5–119 5–120
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Fire and Life Safety Education: A Measure of Fire Department Excellence Meri-K Appy Dennis Compton
U
IMPORTANCE OF FIRE AND LIFE SAFETY EDUCATION
nintentional injuries, including those caused by fire, are the leading cause of death in the United States for people aged 1–34.1 Each year, more than 90,000 people die in the United States as a result of unintentional injuries. During an average year in the United States, unintentional injuries account for more than a million emergency room visits.2 For children under the age of 14 throughout the United States and Canada, the number-one health risk is not disease, violence, or suicide3—it’s injuries. A landmark 1985 study by the Committee on Trauma Research, Injury in America: A Continuing Public Health Problem,4 documented the magnitude of the injury problem and set forth a research agenda, calling upon Congress to establish a center for injury control within the federal government. Reviewing the progress made since 1985, the National Committee on Injury Prevention and Control, appointed by the Institute of Medicine in March 1997, concluded that although injury in the United States remains a major public health problem, significant progress has been achieved since the mid-1980s:
Fire departments have played a strong—though underrecognized—role within this “community of interest” by providing prevention, education, and response programs directed at reducing fire losses. This contribution has resulted, at least in part, in an impressive track record. Fire deaths in the United States and Canada have each fallen by roughly half in the past 25 years and fire deaths relative to population by even more. North Americans made great strides in both safety technology and the safe use of technology. As of 1997, for example, 94 percent of homes in the United States had at least one smoke alarm, the highest rate of home smoke alarm usage in the world. Changes have been made in the United States and many other countries in the design of products ranging from upholstered furniture to mattresses to lighters to space heaters to manufactured homes. And the well-established systems by which model codes and standards are developed, adopted into law by reference, and enforced by national, state and local authorities ensure that engineering achievements involving products, structures, vehicles, processes, and systems tend to move fairly rapidly into programmatic achievements at the grass-roots level. But on the level of human behavior, including the basic ignorance and carelessness that are involved in so many unwanted fires, much remains to be done. And with most fire departments now also responsible for providing emergency medical services to their communities, a fire department’s role in prevention education has expanded to encompass a much broader range of issues. Public fire and life safety education may be defined as “comprehensive community fire and injury prevention programs designed to eliminate or mitigate situations that endanger lives, health, property, or the environment.”6 This definition from NFPA 1035, Standard for Professional Qualifications for Public Fire and Life Safety Educator, illustrates that fire and life safety education is multihazard education. In other words, fire and life safety educators often teach bicycle safety, pedestrian safety, poisoning prevention, cardiopulmonary resuscitation
One of the most impressive achievements over the past two decades has been a “political” one—through communication, advocacy, and constituency building, a national “community of interest” in promoting safety and preventing injury has emerged. . . . Future advances in the injury field depend on the continued development of the infrastructure of the field through public and private partnerships.5
Meri-K Appy is vice president of public education at NFPA. She has 25 years of experience in developing and managing fire and life safety programs designed to increase people’s knowledge and practice of injury prevention. Dennis Compton is the retired chief of the Mesa, Arizona, Fire Department and serves on the NFPA Board of Directors.
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(CPR) and other emergency medical procedures, safe babysitting techniques, electrical safety, and water safety, as well as the more traditional subjects of fire and burn prevention.
History of Fire and Life Safety Education In one form or another, fire and life safety education has existed since at least the early 1900s. Five factors have been especially significant in shaping fire and life safety education to its present form: • Publication of America Burning.7 • Evolution of positive educational messages. • Availability of incident data for program planning and evaluation. • Utilizing a public health framework to address fire prevention and control as one aspect of comprehensive injury prevention and mitigation. • Increasing participation of fire departments in broad-based injury prevention coalitions that include educators, public health professionals, law enforcement officers, and other community leaders. The Impact of America Burning. With rare exceptions, fire and life safety education activities were occasional and fragmented until the 1970s. However, in 1968, President Lyndon B. Johnson signed the Fire Research and Safety Act, which created the National Commission on Fire Prevention and Control. By 1973, the Commission had completed a nationwide series of fact-finding hearings and delivered its final report to President Richard M. Nixon. The Commission’s report, America Burning, included strong recommendations for comprehensive public education activities. According to America Burning, Among the many measures that can be taken to reduce fire losses, perhaps none is more important than educating people about fire. Americans must be made aware of the magnitude of fire’s toll and its threat to them personally. They must know how to minimize the risk of fire in their daily surroundings. They must know how to cope with fire, quickly and effectively, once it has started. Public education about fire has been cited by many Commission witnesses and others, as the single activity with the greatest potential for reducing losses.7 Fire service advocates cited statements such as the one above to persuade fire departments (and others) to support education programs. Fire departments, in turn, cited America Burning in budget requests and in convincing schools to extend the teaching of fire and life safety skills beyond Fire Prevention Week. America Burning became a rallying point for those who advocated continuous and comprehensive fire and life safety education programs. Most recently, in a report entitled America at Risk: America Burning Revisited,8 a group commissioned in 2000 by the Federal Emergency Management Agency called for increased measures to educate the public in fire and life safety behaviors. In one specific finding, the commission suggested that the most effective way to reduce loss of life is through a multihazard mitigation process that addresses all the hazards faced by a community rather than each hazard in isolation.
Positive Educational Messages. Shortly after the publication of America Burning, several organizations began research on how to make fire and life safety education messages more effective. For example, NFPA commissioned opinion research in 1973 on how the public felt about fire and education. The unpublished research by Strother Associates of Cambridge, Massachusetts, included the following findings: 1. People are aware of the threat of fire, but fear (unless continually maintained) has little long-term, positive effect on behavior. Although concerned about fire safety, the public often does not know what to do about fire safety. 2. The public wants to take clear, concise, and positive actions for fire safety.9 A 1991 study by Dr. Rocky Lopes of the American Red Cross (on whether seeing slides of natural disasters encouraged people to take more or less action to prepare for disasters) confirmed the earlier research. According to the Red Cross study, seeing graphic images of disasters did not encourage people to take action to prepare for a disaster. In fact, seeing images of disasters confused people and actually discouraged them from taking action.10 As a result of research such as this, fire and life safety education acquired a new tone and a new look by the late 1970s. Messages became less preachy and far less prone to discuss what people should not do. Instead, fire and life safety focused more on teaching positive, proactive behaviors. At the same time, images of burned buildings and injured, perhaps scarred, children were replaced with, for example, diagrams of how and where to install home smoke alarms and how to conduct a home fire drill. Following the publication of America Burning, NFPA created Learn Not to Burn®,11 the nation’s first comprehensive fire safety curriculum for school-aged children. With its emphasis on the need for smoke alarms and home escape plans and drills, Learn Not to Burn was an important tool for fire departments and school systems to use in teaching children and their families to survive a home fire. Through its use, 554 lives have been saved in 202 documented instances as of September 2001. Learn Not to Burn established some of the basic tenets of effective fire and life safety education in North America considered as “best practice” today. It pioneered the use of positive, nonthreatening lessons to help children understand what to do to be safe from fire. It targeted impressionable young children in an effort to instill positive values about fire safety from an early age and organized the lessons according to each student’s age and developmental level. Learn Not to Burn also encouraged partnerships among local fire departments, classroom teachers, and parents and caregivers to reinforce and support the educational messages with sufficient repetition for children to understand and embrace the concepts—at home, at school, and in the community. It was the only fire safety curriculum to advocate the routine use of evaluation tools to measure student knowledge gain and behavior changes as a means of guiding program implementation. With the 1998 launch of Risk Watch®,12 a complete fire and life safety education curriculum for school-based delivery throughout North America, NFPA reaffirmed its commitment to the educational principles exemplified in Learn Not to Burn. The scope of Risk Watch® was much larger, incorporating all the
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Fire and Life Safety Education: A Measure of Fire Department Excellence
leading causes of unintentional childhood injury and death. In the design of the Risk Watch® module, whether adapted from existing components such as Learn Not to Burn for fire and burns or assembled from less developed materials, the Learn Not to Burn principles of using sound data, developmentally appropriate educational methods, and broad-based community support were maintained and reinforced. Data for Program Planning. America Burning provided motivation for fire and life safety education, and the use of positive images became a fundamental technique. Improved access to fire incident data was the third factor that shaped the state-ofthe-art of fire and life safety education. The development of the National Fire Incident Reporting System (NFIRS) by the U.S. Fire Administration (with work beginning in 1974 and data available starting in 1980) and userfriendly reports produced by NFPA, the USFA, TriData Corporation, and others influenced the day-to-day practice of fire and life safety education at the community level. Using data, educators could identify the causes of, for example, fatal home fires and target educational resources at those causes. Also, through the use of data, educators could compare their community’s loss experience with that of other communities. The impact of widely available and understandable data had a profound impact on fire and life safety education. Data became a planning and evaluation tool for the educator. For more information on this vital subject, see Section 5, Chapter 2, “Using Data for Public Education Decision Making,” and Section 3, Chapter 3, “Use of Fire Incident Data and Statistics.” Utilizing a Public Health Framework to Address Fire Prevention and Control. The increase in home smoke alarm usage in the last quarter of the twentieth century, supported by widespread public education efforts, has clearly played a major role in reducing the fire problem in North America. But the United States and Canada are still at or near the top of the list of Western industrialized nations with the highest fire death rates per capita, and the U.S. and Canada rates of total unintentional injuries per capita from a variety of causes to which fire departments respond also remain intolerably high. Progressive fire service leaders understand the fire problem as part of the larger picture of injury—not just as a safety issue, but as one facet of a severe public health challenge that exacts an enormous toll of disability and premature death, draining healthcare dollars and undermining a nation’s productive capacity. This conceptual shift requires us to move from a traditional paradigm of “accident prevention” to embrace the full range of proven public health tools and perspectives and apply them using rigorous and well-evaluated methodology for comprehensive injury control. Modern approaches to injury prevention and control are grounded in a public health framework. The National SAFE KIDS Campaign’s comprehensive approach is based on an established public health model, which SAFE KIDS refers to as the “five Es.” Updating the traditional “three Es” of injury prevention (enforcement, environmental change, and education), the National SAFE KIDS Campaign® cites five primary strategies: education, empowerment, environment, enactment, and evaluation (Figure 5.1.1). While SAFE KIDS focuses on children 0–14 years of age, the five Es can be applied to all age groups:
5–5
• Education Increasing knowledge and changing behavior through public awareness and school-based initiatives • Empowerment Encouraging people and communities to take responsibility for safety through grassroots organizing, community events, and safety device distribution • Environment Enhancing the design, development, and distribution of safety products, and by improving the environments where people live, work, and play • Enactment Working to pass, strengthen, and enforce laws, and encourage the development of voluntary safety standards and guidelines to protect people • Evaluation Emphasizing research, data collection, and surveillance to guide programs and determine the most effective behavior-changing strategies.13 These five injury-prevention strategies are closely linked and most effective when used together. For example, in the area of preventing injuries caused by children playing with lighters and matches, • Education includes teaching young children to tell a grownup if they see a match or a lighter • Empowerment includes efforts to convince parents and other caregivers to use child-resistant lighters and to keep all lighters and matches locked away out of the sight and reach of children • Environment includes the manufacture of child-resistant lighters or the installation of smoke alarms and automatic home fire sprinklers • Enactment includes a U.S. Consumer Product Safety Commission (CPSC) standard requiring that disposable lighters sold in the United States be child-resistant • Evaluation tracks the impact of these interventions on the problem and reveals ways to improve their delivery for greater effectiveness. Progressive fire and life safety educators understand the need to design and implement programs that draw on all these injury control strategies. This view is clearly demonstrated in the 2000 David and Lucile Packard Foundation report entitled “The
Education
Evaluation
Comprehensive Injury Control Strategies Enactment
Empowerment
Environment
FIGURE 5.1.1 Relationship of the Five Injury-Prevention Strategies: Education, Empowerment, Environment, Enactment, and Evaluation
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Future of Children: Unintentional Injuries in Childhood.” In its preface, editor Richard E. Behrman, M.D., calls on those in the field to go beyond education alone and to address preventable childhood injury through a multifaceted public health approach: . . . the most effective injury prevention efforts are often those that focus on public policy change, reinforced through legislation or regulations. Public policies—such as requirements that young children be restrained in car seats, that prescription medications have child-resistant caps, and that children’s sleepwear be flame retardant— save the lives of thousands of children each year. Yet there are many more opportunities to reduce childhood injuries through policy change that have not been seized. Uniform statewide requirements that children and teen bicyclists wear helmets, fences that enclose swimming pools on all sides, and environmental changes that slow the speed and density of traffic in residential areas are just a few strategies that could further reduce childhood injuries if widely implemented.14 Dr. Behrman concludes his statement of purpose with an important caveat: These public policy strategies have a greater likelihood of being implemented and enforced if they are coupled with community-wide efforts to change social norms about the acceptability of safety behaviors, and adequate financial resources to ensure the availability of safety devices. The Fire Department’s Role in Community-Based Coalitions. Research indicates that community-based programs are most successful when they use multiple strategies, integrated into the community and adapted to meet unique community characteristics. Multiple strategies are likely to need multiple participants. This is just one reason for actively involving community stakeholders in the development and delivery process. Ongoing evaluation to document measurable outcomes and improve program effectiveness is likely to confirm that multiple strategies are needed to address the whole injury problem, further reinforcing the value of a broad and diverse coalition. National model programs such as Risk Watch® and Learn Not to Burn already incorporate multiple strategies and reflect contributions from broad and diverse coalitions at the national level. But national model programs do not teach themselves. They require effective, committed teachers and advocates. By participating in a national model program through a communitybased approach, a community gives itself a stronger reason for that commitment and an opportunity to boost effectiveness by incorporating unique local strengths. With a demonstrated track record in reducing fire death and injury in the last two decades and a high degree of public trust and approval, the fire service has a legitimate leadership role to play in the injury control arena. But the fire service cannot succeed in isolation from other safety professionals and other stakeholders. Injury is a community problem that deserves and rewards support and involvement from the whole community. The challenge is to articulate a clear and compelling vision of a safer society and attract others in the community to work in cohesive, collective action toward that ideal.
Because no fire department—or any single agency, for that matter—can possibly amass the breadth of talent needed to tackle such a complex set of tasks, the future of public safety lies in successful coalition building and management. In addition to fire departments, public health professionals, law enforcement, educators, parents and caregivers, faith leaders, private sector and nonprofit partners, the city managers, and many others have a vested interest in safety and well-being of the community. Harnessing the energy and resources of diverse partners into a comprehensive strategic action plan can be very challenging. Turf issues may arise. Yet whether the fire department emerges as the lead agency for the coalition or as a valued contributor to the team, there are many advantages to multiagency collaboration. These include gaining access to a wider audience, combined strengths of a broader and more diverse talent pool, better data, more resources, and more efficient service delivery, all of which contribute to greater impact on the injury problem.
A SYSTEMS APPROACH TO FIRE AND LIFE SAFETY Overview Society relies on a basic infrastructure that gives shape to the quality of life in a community. Transportation, utilities, code enforcement, school, and recreational systems are but a few examples of the diverse parts of this infrastructure that allow community residents to make individual choices in an interactive social context. Policy makers understand that weaknesses in these infrastructure systems can result in performance failures at a given point in time, that is, everyone will get less of what they want. Plans that are developed today revolve around design and maintenance of “system” components rather than simply addressing programs and issues separately without considering the impact of decisions on overall system performance. In other words, every problem is considered in a broad systems context, and special care is taken to maintain the infrastructure components that allow systems solutions to work most effectively in a dynamic environment. Any systems approach begins by laying out the infrastructure of organizations, technologies, incentives, laws, and internal arrangements that seek to give structure to those interactions, so that needless inefficiency and disruption is minimized. Fire departments and other fire service organizations should address fire and life safety more holistically in terms of community infrastructure and systems approaches, rather than as separate programs that may at times appear disconnected from each other.
Systems Management and Leadership Model A fire and life safety system describes basic components required to protect life and property in a community, as illustrated in Figure 5.1.2. The components may be programs or groups or the infrastructure that allows them to work together effectively towards solutions. There is not one single program or intervention strategy that will address the many ways that people can be killed or injured and property destroyed as a result of fire and
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Fire and Life Safety Education: A Measure of Fire Department Excellence
Management of Finances and Human Resources
Leadership
Prevention through Consensus Codes and Built-In Protection
5–7
Management of Physical Resources and Technology
Emergency Response
All Risk Public Education (i.e., Risk-Watch ®)
Emergency Management
Community Partnerships, Relationships, and Politics
Management
Preparing Members to Perform Their Roles
= Line Services = Staff Services
Program Integration
FIGURE 5.1.2 Systems Management and Leadership Model (Fire and Life Safety Infrastructure) (Source: © Chief Dennis Compton, Mesa, Arizona)
other causes. Furthermore, every program strategy is affected by many groups, whether it is designed to include them or not. A system describes the component parts of a whole and their interactions. Each piece depends upon the others for overall system effectiveness. Within a fire service organization, its components of this fire and life safety system can be divided into line and staff responsibilities as follows: Line Services. Line services are mission-driven and include prevention activities, all-risk public education programs, and emergency response and emergency management. • Prevention through consensus codes and built-in protection. These codes for prevention and mitigation govern structures, hazardous facilities and contents, as well as built-in protection, such as automatic fire sprinklers, and so on. Code-related services also include fire investigation, inspection, and enforcement activities. • All-risk public education programs designed to teach people how to prevent harmful situations and to survive should a situation occur. • Response to emergency incidents such as fires, medical emergencies, hazardous materials events, or technical rescues. This would include nonemergency service requests answered by emergency responders and the area of emergency (disaster) management.
• Management of finances and human resources. Support for the members who actually provide the line and staff services externally and internally. This includes issues such as adequate compensation, policy direction, definitive planning, safety issues, humane treatment, and other areas related directly to making people as effective as possible. • Community partnerships, relationships, and politics. This includes maintaining positive, productive relationships internally and externally; an appreciation for (and understanding of) the importance of developing effective strategic alliances; and functioning effectively in the political arena with policy makers. • Management of physical resources and technology. This means building and maintaining the infrastructure and equipment necessary to be effective. This includes management of facilities, the fleet, dispatch and communications systems, and other nonhuman resources.
Staff Services. Staff services are in place to support the primary mission and are provided to internal customers. Too often, public education has been considered a support program to the emergency response system. However, public education is a line service as its customers are outside the fire department. Like any service provided within the mission of the organization, public education requires adequate staff support to be successful.
These represent the component parts of the fire and life safety infrastructure. The mission is delivered effectively to the extent that these are brought together and managed in a systems approach. Failure of any of the individual parts of the system can result in failure of the mission in a given situation. A three-legged stool represents another way to picture the fire and life safety system (Figure 5.1.3). Think of the stool as being only as strong as the people within the organization. The people form the very fiber of the seat, legs, and braces. The fire and life safety mission of the fire department rests on the seat of the stool. The stool must be strong enough to support the weight of the mission. The three legs of the stool represent the three line services provided by fire departments. They are of equal importance and each saves lives and property in given situations. They are
• Prepare members to perform their roles. This includes training the people in the organization to perform in their assigned roles within all areas.
• Fire Prevention (Codes) • Public Education (i.e., Risk Watch® and Remembering When) • Emergency Response
5–8 SECTION 5 ■ Fire and Life Safety Education
The braces represent the staff functions that are required to effectively support the delivery of the mission. These functions are of equal importance as well, and each contributes to the strength and stability of the stool (the “system”). They are • • • •
Training and Preparation Members and System Support Partnerships, Relationships, and Politics Infrastructure and Equipment
The three-legged stool clearly illustrates the components of this systems approach to delivering the mission of the fire department. Every member of the organization is responsible for playing his or her part in keeping each leg and brace as strong and effective as possible. A weak leg or brace can result in system failure during a particular event or in a given situation. The stool concept illustrates how public education fits within the system and is just as important to the fire and life safety infrastructure as any other component. Public education is critical to the mission. It prevents harm and it modifies human behavior in a way that saves lives. Public education is one of the keys to protecting our customers.
ROLE OF FIRE DEPARTMENTS IN PUBLIC EDUCATION Executive Level Commitment It is almost impossible for any program to be successful without the support and commitment of the Chief Executive Officer of the organization. Programs that function in spite of the “Chief” struggle every day. Be it fire suppression, health and safety, labor relations, fire prevention, media relations, fire and life
safety education, EMS, training, or special operations—without the visible, active support of the chief, the program results will usually be mediocre at best. Public education programs that have full executive level support within the organization are effective, meaningful components of the service delivery system. This executive level support is demonstrated by such actions as • Representing public education’s importance inside and outside the organization • Describing how public education integrates into the mission • Identifying public education as a section within the organizational structure • Assigning responsibility and accountability for public education to a specific manager • Ensuring a public education voice in decision making and planning processes • Providing adequate personnel and other resources dedicated to public education programs • Supporting the ongoing professional development of public educators by allocating funds to attend regional and national meetings and trainings or conferences • Including public education in strategic and operational plans, as well as budget packages • “Opening doors” for public education staff inside the organization and within the community Public education, like any other program, is successful in fire departments where the chief and other leaders want it to be successful and consistently act that out. It is treated and represented as a key organizational responsibility and a critical component of the fire and life safety infrastructure of a community.
Knowing the Business
Fire & Life Safety Mission
(C tio n rev en eP
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Fir
Ris
Members & System Support
n( h®
e tur ruc ent t s m ra Inf quip &E
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P lati ar tn e on shi rship ps, s &P , olit ic
ca
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Emergency Response
Training & Preparation
FIGURE 5.1.3 Key Concepts of a Fire and Life Safety System (Source: © Chief Dennis Compton, Mesa, Arizona)
Many progressive fire departments have accepted the concept of identifying those who receive their services as “customers.” They measure the quality of services in terms of customer satisfaction, as well as other output and outcome-based measurements. Many of these customers who have received emergency services from their fire departments say that the day they had to call the fire department was either the worst day of their life or one of the worst days of their life. This describes the unique relationship fire departments have with their customers, and may also tend to describe the business fire departments are really in—the “worst day of their life” business. Our role is to prevent their “worst day” from happening; teach people how to survive that day should it happen to them; or to respond quickly, skillfully, and in a way that demonstrates a caring attitude when a customer calls 9-1-1. Public education plays a key role in this “business” because the information and behaviors that are taught have been proven to prevent dangerous situations in the first place, and help people survive them should they happen. Public education is a key component of a community’s fire and life safety infrastructure. It is an investment in the future of people, one that could save someone’s life immediately, months later, or even years later. Public education offers fire departments a highly visible way to connect with all people in the community, not just those
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who require help in an emergency. The familiarity and trust that develop through meaningful, ongoing contact between fire departments and the citizens they serve can strengthen public support for fire service priorities. It also provides an important way to deliver information and training and create opportunities to practice new skills. Together, these can help to modify behavior and save lives and property. To achieve measurable results, community fire and life safety education must be well targeted, comprehensively delivered, and sustained over time. One example of a systematic delivery system for injury prevention education is NFPA’s successful Champion Model, currently being used to implement the Risk Watch® program in schools throughout the United States and Canada.
The NFPA Champion Model of School-Based Delivery The NFPA has identified several fundamental qualities that appear to correlate with long-term success in implementing school-based public education programs. Together, they comprise the NFPA Champion Model of implementation. The Champion Model relies on 10 components or “Cs to Success” and these qualities can be used as a checklist to assess a community’s readiness to initiate, evaluate, and institutionalize a comprehensive public safety program in the school environment and the community at large. The “Ten Cs” were originally developed to guide schoolbased programs, but their application could benefit any public education initiative. They provide a framework for success, proven to be effective in establishing and delivering messages and lessons that modify behavior, reduce injuries, and save lives. A checklist of questions to help assess your program’s strength in each of these 10 areas is provided in the Appendix. The 10 “C’s to Success” are coalition, champion, careful planning, compelling case, credentials, collaboration, continuity, creativity, camaraderie, and commitment. Coalition. For reasons discussed earlier, NFPA has concluded that the most effective way to reduce unintentional injuries is to work through a community coalition. That coalition should include (at a minimum) a representative from each of the following organizations: the fire department; the police department or local law enforcement agency; a health organization (hospital, health department, school nurse, or local SAFE KIDS representative); a school administrator (principal or curriculum director); and a classroom teacher from a school where the program will be implemented. Champion. Every coalition needs to select a leader (or “Champion”) who will be responsible for the coalition’s efforts, from planning and implementation, to evaluation and expansion of the public education project. Long-term success depends on the Champion’s ability to think strategically, to motivate and coach others toward common goals, and to document and communicate program results to key decision-makers, coalition members, teachers, other participants, and the public.
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Careful Planning. Successful coalitions need to develop a written strategic plan outlining a clear set of written goals, measurements, and timeframes. While each participating organization will have its own individual priorities, successful coalitions will be able to come to consensus on an achievable number of objectives toward which every member can make a contribution. The strategic plan will assign responsibility for each of the following areas: program development; training and implementation; support, promotion and communication; strategic alliance building and fundraising; and research and evaluation. Progress needs to be documented. As the coalition develops, the plan must be updated and the leadership structure redefined. Compelling Case. By analyzing the incidence of unintentional injuries in a community and focusing first on those neighborhoods or areas at highest risk, a Champion coalition can achieve dramatic results early in the program and use that momentum to gain support for further expansion. Start small, document the team’s progress, and use concrete examples of the program’s effectiveness to justify expansion. The extent to which a coalition can articulate an urgent need and define the tangible benefits of its program will largely determine the level of media attention, funding, and community involvement the program receives. To learn more about how to reach those at highest risk to fire, see the chapter “Reaching High Risk Groups.” Credentials. A program’s reputation will be determined by the quality of the materials used and the manner in which they are delivered. A coalition should select an established curriculum that has been thoroughly evaluated by independent researchers. Put professional educators in the lead role of teaching the core subject matter, since they have the necessary training and consistent access to guide student learning. Seek the participation of wellqualified, highly respected experts to serve on the coalition with the common goal of supporting the classroom teachers. Strive to enhance professional development and keep informed of new trends and innovations in the injury control field. Collaboration. Successful public education initiatives are those that enjoy a high level of commitment from the community: the board of education, teachers, the fire department, the police department, and other agencies that have a specific mission to prevent childhood injuries. After teachers have introduced the core safety lessons to their students, local safety experts can then visit classrooms and reinforce lessons with their “real-world” perspective. NFPA suggests giving experts a copy of key lesson points to ensure consistency and accuracy of messages delivered by outside experts. Continuity. Because people learn best through repetition and practice, the most effective way to teach injury prevention skills is through repeated, age-appropriate learning opportunities extended over a period of years. A successful program will target each age group in the program with messages they can understand. Injury risks to children change as they grow older; therefore, safety messages should become more comprehensive and
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complex as students mature. Also, growth brings the ability to understand and absorb more complex information and associated behaviors, and so safety messages should be tailored to a child’s development, finding the right time to teach them all they will need to know throughout their lives. Creativity. Communities are encouraged to supplement public education programs with elements (such as performance experiences) designed to address local needs. The creative use of safety trailers, clowns and puppets, coloring and comic books, and so on helps customize the program and provides an important sense of ownership. Creative reinforcement techniques can also enhance student knowledge gain and retention, so long as the information presented does not replace or conflict with the program’s core messages. “Educational” programs delivered infrequently and with insufficient student preparation and reinforcement have not been shown to yield positive results. Camaraderie. NFPA always makes time for “fun” during its public education training workshops. And the same concept can be applied in any community coalition. Sharing meals, attending planning retreats together, even playing an “ice-breaker” game before meetings can help build strong, trusting relationships and keep everyone on the team coming back for more. Commitment. Successfully implementing a public education program is a major initiative for any community, regardless of its size or available resources. It requires hard work, the commitment of individuals and community organizations, and, most importantly, persistence. While your initiative may be filled with challenges, there will also be rewards, including knowing that fewer children are being injured and that your community is a safer place to live, work, and play.
ENGINEERING TO SUPPORT ENGINEERING STRATEGIES As vital as fire and life safety education is to the creation of a safer society, the community cannot rely on it exclusively to achieve that goal. Engineered changes are needed, too, and there have been many over the past quarter century. Upholstered furniture and mattresses have been built to resist cigarette ignition since the mid-1970s. Lighters have been built to resist operation by small children since the mid-1990s. The risk of dying if fire occurs is cut nearly in half by the use of home smoke alarms, and even more when educated occupants know how to keep the smoke alarms operational.15 Sometimes education strategies reinforce engineered strategies by shaping people’s behavior in using, purchasing, replacing, or maintaining products. Nearly all fire safety programs include guidance on choosing, locating, testing, and maintaining home smoke alarms, for example. Sometimes, education strategies reinforce engineered strategies by shaping people’s behavior to take advantage of anticipated product performance. Think of the linkage between home escape plans and home smoke alarms. Sometimes education strategies are needed to persuade the target audience to adopt an engineered safer technology. In such
cases, the line between education and advocacy is nearly erased, but so long as the goal is behavior change to achieve greater safety based on greater knowledge, the program is very definitely educational in the truest sense of the word. NFPA, the American Fire Sprinkler Association (AFSA), and the National Fire Sprinkler Association (NFSA) in 1996 formed the Home Fire Sprinkler Coalition (HFSC). HFSC focuses its efforts on sprinkler installation in new one- and two-family homes, but it also targets those who can influence consumers, builders, sprinkler installers, insurance companies, and realtors. The HFSC has developed educational materials that can be useful for the various “stakeholders” involved in the residential new construction process. These materials dispel common myths about fire sprinklers, such as the belief that when one head discharges, the entire system activates. The materials also illustrate the speed with which fire can spread through a home, visually reinforcing the value of built-in fire suppression. They explain that with sprinklers, 90% of fires are contained or extinguished by the operation of just one sprinkler located nearest the fire, thereby addressing the myth of intolerable water damage. Statistics from past applications demonstrate the magnitude of savings in lives and property, addressing any belief that other strategies leave no fire problem still to be addressed. And concerns about affordability are addressed through information on costs and on insurance credits. In summary, the educational strategy provides all the information needed to support a well-informed choice about an engineered product that promotes safety. The Home Fire Sprinkler Coalition supports a grass-roots campaign in targeted states and provinces. As it introduces the program in new markets, HFSC works primarily with the local fire service. Once fire departments and their partners become familiar with available tools and technical assistance, HFSC helps them identify local resources that can play a role in designing and installing home fire sprinkler systems and then supports them in mounting an aggressive consumer education campaign. In 2001, HFSC formed an alliance with Habitat for Humanity, working in the target states with individual Habitat affiliates and their local resources to supply the material, labor, and technical support needed to install residential fire sprinkler systems in low-income homes. Since low-income households are at the greatest risk of fire death, it is very important to channel the right technology, education, and community support into targeted high-risk homes and neighborhoods (Figure 5.1.4). But home fire sprinklers, combined with early warning and escape plans, represent a safety net that can include everyone. The Home Fire Sprinkler Coalition and its members are in the forefront of a significant breakthrough in fire safety.
SUMMARY NFPA recommends a multifaceted, coordinated process at the community level to address local safety needs. Safety advocates must first use data to define the local injury problem, collaborate with others to develop a program based on these findings, select a mix of interventions that reflects the state-of-the-art in injury
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control, and evaluate the program’s achievement of process and outcome objectives. Fire departments can serve a vital role in the concerted effort to reduce the national incidence of preventable injury and death. The public safety needs of communities increasingly place fire department personnel in the role of emergency responders—first on the scene not only in a fire emergency, but in medical emergencies as well. With a proven record in educating the public to prevent and respond effectively to fire emergencies, fire safety advocates often have the credibility and expertise to organize their communities around broader safety issues. Increasingly, fire and life safety advocates view such incidents as traffic injuries, drownings, firearm injuries, falls, and poisonings; that is, not random accidents, but predictable events that, with proper education, are largely preventable. Most fire department leaders are encouraging their members to get more involved in their communities to strengthen organizational credibility and influence. There are a variety of ways this can be accomplished, and public education is the program that provides perhaps the greatest opportunity.
FIGURE 5.1.4 Construction of a Sprinklered Home as Part of the HFSC Alliance with Habitat for Humanity (Source: Chicago Tribune file photo)
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APPENDIX A Fire and Life Safety Education History 1909
NFPA’s Franklin Wentworth begins sending fire prevention bulletins to correspondents in 70 cities, with the hope that local newspapers will publish the bulletins as news articles.
1911
Fire Marshals Association of North America proposes the October 9 anniversary of the Great Chicago Fire as a day to observe fire prevention.
1912
NFPA publishes Syllabus for Public Instruction in Fire Prevention—fire safety topics for teachers to use in the classroom.
1916
NFPA and the National Safety Council establish a Committee on Fire and Accident Prevention. Communities nationwide organize Fire Prevention Day activities.
1920
President Woodrow Wilson signs first presidential proclamation for Fire Prevention Day.
1922
President Warren G. Harding signs first Fire Prevention Week proclamation.
1923
Twenty-three states have legislation requiring fire safety education in schools.
1927
NFPA begins sponsoring the national Fire Prevention Contest.
1942
New York University publishes Fire Prevention Education.
1946
U.S. government publishes Curriculum Guide for Fire Safety.
1947
Hartford Insurance Group begins the Junior Fire Marshal Program, perhaps the first nationally distributed fire safety program for children.
1948
American Mutual Insurance Alliance publishes first edition of Tested Activities for Fire Prevention Committees, based on Fire Prevention Contest entries.
1950
In October, 7000 newspapers receive the ad “Don’t Gamble with Fire—The Odds are Against You,” developed by the Advertising Council and NFPA.
1951
Ted Royal of the Advertising Council creates Sparky® the Fire Dog as NFPA’s fire safety mascot.
1965
Fire Journal begins a regular column on “Reaching the Public.”
1966
“Wingspread Conference” highlights the need for public education.
1973
• The National Commission on Fire Prevention and Control publishes its report, America Burning. • The Fire Department Instructors’ Conference offers its first presentation on fire and life safety education, delivered by Cathy Lohr of North Carolina.
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1974
• NFPA and the Public Service Council release the first television Learn Not to Burn®, public service announcements, starring the actor Dick Van Dyke. • The Fire Prevention and Control Act establishes the National Fire Prevention and Control Administration.
1975
The National Fire Prevention and Control Administration holds its first national fire safety education conference.
1977
• NFPA 1031, Standard for Professional Qualifications for Fire Inspector, Fire Investigator, and Fire Prevention Education Officer, is published. • National Fire Prevention and Control Administration releases Public Fire Education Planning: A Five-Step Process. • National Fire Prevention and Control Administration launches the national smoke detector campaign.
1979
• J. C. Robertson’s Introduction to Fire Prevention is published by Glencoe Press. • Learn Not to Burn Curriculum is published by NFPA. • International Fire Service Training Association (IFSTA) releases IFSTA 606, Public Fire Education.
1981
NFPA establishes its Education Section.
1985
• The National Education Association recommends the Learn Not to Burn Curriculum. • NFPA publishes Firesafety Educator’s Handbook.
1986
Learn Not to Burn Foundation is incorporated.
1987
• The first edition of NFPA 1035, Standard for Professional Qualifications for Public Fire Educator, encourages civilians to become public fire educators in the fire department. • TriData Corporation publishes Overcoming Barriers to Public Fire Education.
1994
• TriData Corporation releases Proving Public Fire Education Works. • NFPA launches Learn Not to Burn Champion Award Program.
1996
Learn Not to Burn Foundation integrated into NFPA Public Education Division as the NFPA Center for HighRisk Outreach.
1998
• NFPA launches Risk Watch® Program. • NFPA publishes Remembering When: A Falls and Fire Prevention Program for Older Adults, developed in partnership with the National Center for Injury Prevention and Control, Centers for Disease Control.
2000
®
• Longitudinal study of Risk Watch initiated. • NFPA creates the Risk Watch® Champion Management Team program to support state and provincial level implementation.
This timeline was originally prepared for IFSTA’s Fire and Life Safety Educator, based on information from Pam Powell’s “Firesafety Education: It’s Older than You Think” (Fire Journal, May 1986) and information provided by Nancy Trench, Oklahoma State University.
APPENDIX B Ten “C’s” Checklist16
1. Coalition Are there at least four loyal members of your Risk Watch® Coalition representing (at a minimum) fire, law enforcement, health, and the local or state/province educational system? Yes No What other strong community partners and advocates have you been able to recruit? Do you meet at least quarterly and preferably more often? Yes No Does someone take and issue meeting notes and keep track of action items? Yes No
2. Champion Does your Risk Watch® Coalition have a designated lead agency (not necessarily the fire department)? Yes No Do you or the person identified as team leader have the needed leadership, communications, and organizational skills to function well in the role? If not, can these skills be acquired or provided by another member of the team? Yes No Is the team leader able to devote sufficient time and attention to the Risk Watch® project? Yes No
3. Careful Planning Does your Coalition have a written plan for the growth of Risk Watch® in your community? Yes No Is your Coalition well-positioned to provide needed support to all Risk Watch® participants, such as teacher in-service and community expert training, promotion and communications, funding, and evaluation? If not, what areas need strengthening and how are you planning to do this? Yes No
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4. Compelling Case Are you tracking the results of your Risk Watch® program? Yes No Have you identified reliable sources of data? Yes No
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by Interwest Applied Research in the communities of Palm Beach County, FL; Champaign, IL; Brockville, ON; Portland, OR; Philadelphia, PA; and Plano, TX? Yes No Have you and your Coalition members enhanced your own Risk Watch® credentials by striving to keep on top of new information, technologies, and best practices? (e.g., Packard Report, automatic fire sprinklers, booster seats, etc.) Yes No
Are you constantly soliciting feedback from teachers and community partners to document evidence of risk reduction, behavioral/engineering/ environmental changes that have occurred as a direct result of Risk Watch®? Yes No
Are you expanding the skill set represented in your Coalition by learning from your partners and by mentoring others? Yes No
Have you shared these results with NFPA in the form of a Risk Watch® “Save” or “Success” as soon as you became aware of them? Yes No
7. Continuity
Have you publicized your results at every opportunity in your own community? Yes No What promotional strategies have worked best?
Is Risk Watch® fully established in every pre-K through grade eight classroom in your community? If not, have you made significant progress towards that goal? Yes No Is the program becoming fully institutionalized throughout the school system and at all levels throughout all participating agencies? Yes No
5. Collaboration Are your teachers happy with Risk Watch®? Yes No Has the number of classroom teachers actively teaching Risk Watch® increased steadily since the launch of the program? Yes No Does every teacher have his/her own module? Yes No Have you instituted effective ways to encourage and recognize their efforts? Yes No Has the number of community experts available to reinforce classroom lessons increased and is it sufficient to meet the demand of teachers? Yes No
8. Creativity Do the “creative elements” of your Risk Watch® program extend the classroom experience or overshadow it? Yes No Are the messages “creatively” communicated by all supplemental materials and methodologies 100 percent consistent with those recommended by NFPA? Yes No Is the balance between substance and style appropriate to support the educational and behavior modification goals of the program (are you spending too much time on things that will not make a measurable difference)? Yes No
9. Camaraderie 6. Credentials Are you aware of the positive results from the independent evaluation process being conducted
As challenging as it is to get Risk Watch® institutionalized in your community, are you still enjoying the process? Are your partners still having fun with it, too? Yes No
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Have you been able to build strong relationships with your Coalition members and other partners? Yes No Have these new friends and colleagues helped you to advance other personal, professional, organizational, or community objectives besides Risk Watch®? Yes No
12. Risk Watch®, National Fire Protection Association, Quincy, MA, 1998. 13. 2000 Annual Report, National SAFE KIDS Campaign, Washington, DC, 2001. 14. The David and Lucile Packard Foundation, The Future of Children (ISSN 1054-8289), Vol. 10, No. 1, inside cover. 15. Ahrens, M., U.S. Experience with Smoke Alarms, NFPA Fire Analysis and Research Division, January 2000. 16. Trench, N., Fire Service Training.
NFPA Codes, Standards, and Recommended Practices
10. Commitment If the results of this self-examination indicate changes are needed to improve the health of your Risk Watch® program, are you prepared to tackle them? Yes No NFPA’s commitment to Risk Watch® and to our Champion communities is as strong as ever—is yours? If yes, what ideas can you share to help others maintain and build commitment? If not, what can NFPA and your Champion colleagues do to help? Yes No
BIBLIOGRAPHY References Cited 1. CDC National Center for Health Statistics (NCHS), National Mortality Data, 1997, NCHS, Hyattsville, MD, 1998. 2. Burt, C. W., and Fingerhut, L. A., “Injury Visits to Hospital Emergency Departments: United States, 1992–95,” Vital Health Statistics, Vol. 13, No. 131, 1998. 3. SAFE KIDS, www.safekids.org. 4. Committee on Trauma Research, Commission on Life Sciences, National Research Council, and the Institute of Medicine, Injury in America: A Continuing Public Health Problem, National Academy Press, Washington, DC, 1985. 5. Institute of Medicine, Committee on Injury Prevention and Control, Division of Health Promotion and Disease Prevention, Reducing the Burden of Injury: Advancing Prevention and Treatment, National Academy Press, Washington, DC 1999, p. 14. 6. NFPA 1035, Standard for Professional Qualifications for Public Fire and Life Safety Educator, NFPA, Quincy, MA, 1993. 7. America Burning, Report of the National Commission on Fire Prevention and Control, U.S. Government Printing Office, Washington, DC, May 1973. 8. America Burning Recommissioned Commission, America at Risk: Findings and Recommendations on the Role of the Fire Service in Prevention and Control of Risks in America, Emmitsburg, MD, U.S. Fire Administration, Federal Emergency Management Agency, 2000. 9. Powell, P. A., “Learn Not to Burn®: A Decade of Progress,” Fire Journal, Vol. 79, No. 2, 1985, p. 8. 10. Lopes, R., “Public perceptions of disaster preparedness presentation using disaster damage images,” NFPA Education Section Newsletter, Fall/Winter 1992, NFPA, Quincy, MA. 11. Learn Not to Burn® Curriculum, National Fire Protection Association, Quincy, MA, 1979.
Reference to the following NFPA codes, standards, and recommended practices will provide further information on concepts of fire and life safety education discussed in this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 1035, Standard for Professional Qualifications for Public Fire and Life Safety Educator
Additional Readings “1994 Learn Not to Burn Champions,” NFPA Journal, Vol. 88, No. 3, 1994, pp. 67–69. “ ‘Alarming’ Day,” Fire Fighting in Canada, Vol. 39, No. 8, 1995, pp. 14–15. Bahls, M., “German Solution to Child Fire Education,” Fire International, No. 180, Oct. 2000, pp. 20–21. Barber, D., “New Zealand’s Youth Fire Safety Plan,” Fire International, No. 180, Oct. 2000, p. 19. Cooper, E., “Top of the Ops for Fire Safety,” Fire Prevention, No. 313, Oct. 1998, pp. 8–9. “CPSC Advance Notice of Proposed Rulemaking on Children’s Sleepwear Standards [58 FR 4111, January 13, 1993],” Product Safety and Liability Reporter, Jan. 27, 1993, pp. 87–91. “Curious Kids Set Fires. Fire Safety Program,” Federal Emergency Management Agency, Washington, DC, 1991. Damant, G. H., and Nurbakhsh, S., “Christmas Trees—What Happens When They Ignite?,” Fire and Materials: An International Journal, Vol. 18, No. 1, 1994, pp. 9–16. “Directory of National Community Volunteer Fire Prevention Program. Community-Based Fire Prevention Education Initiatives, 1984–1992,” National Criminal Justice Assoc., Washington, DC, Federal Emergency Management Agency, Emmitsburg, MD, FA-92, April 1993. “Essentials of Public Education,” Fire Chief, Vol. 45, No. 10, 2001, pp. 38–45. “Fire Departments and Communities: Partners in Prevention,” Fire Engineering, Vol. 148, No. 6, 1995, pp. 101–110. “Fire Safety Program Covers All the Bases,” Fire Fighting in Canada, Vol. 41, No. 5, 1997, pp. 28–29. Gamache, S., Porth, D., and Diment, E., “Development of an Education Program Effective in Reducing the Fire Deaths of Preschool Children,” Proceedings of the 2nd International Symposium on Human Behavior in Fire: Understanding Human Behavior for Better Fire Safety Design, Boston, MA, March 26–28, 2001, Intersciences Communications Ltd., London, UK, 2001, pp. 309–320. Gaull, E. S., “Show Me the Results,” Fire Chief, Vol. 41, No. 5, 1997, p. 74. Gustin, B., “Working Cooperatively with Law Enforcement,” Fire Engineering, Vol. 149, No. 8, 1996, pp. 93–94. Hall, J. R., Jr., “Children Playing with Fire: U.S. Experience, 1980– 1993,” National Fire Protection Association, Quincy, MA, August 1995. Hayashi, T., “Disaster Protection for the Aged,” Firesafety Frontier ’94, International Fire Conference and Exhibition in Tokyo, Creating a Safe Tomorrow, October 18–22, 1107-112, Tokyo, Japan, 1994, pp. 277–280.
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Henricsson, L., “Measures for the Safety of the Lives of the Elderly and the Physically Handicapped,” Firesafety Frontier ’94, International Fire Conference and Exhibition in Tokyo, Creating a Safe Tomorrow, October 18–22, 1107-112, Tokyo, Japan, 1994, pp. 281–286. Hines, K., “How Do You Teach Safety? It’s Elementary,” Fire Chief, Vol. 41, No. 5, 1997, pp. 57–60. Jones, R. T., and Randall, J., “Rehearsal–Plus: Coping with Fire Emergencies and Reducing Fire-Related Fears,” Fire Technology, Vol. 31, No. 4, 1994, pp. 432–444. Kakegawa, S., et al., “Evaluation of Fire Safety Measures in Care Facilities for the Elderly by Simulating Evacuation Behavior,” Proceedings of the 4th International Symposium for Fire Safety Science, Intl. Assoc. for Fire Safety Science, Boston, MA, 1994, pp. 645–656. Larson, R. D., “From Ashes to Education,” Firehouse, Vol. 18, No. 1, 1993, pp. 44, 46. Lerner, N. D., and Huey, R. W., “Residential Fire Safety Needs of Older Adults,” Thirty-Fifth Annual Meeting of the Human Factors Society, Part 1 of 2, September 2–6, 1991, San Francisco, CA, Human Factors Society, Inc., Santa Monica, CA, 1991, pp. 172–176. “Let’s Retire Fire. A Fire Safety Program for Older Americans,” Federal Emergency Management Agency, Washington, DC, 1990. Marchone, M. K., “It’s Not Just Fire Safety Education Anymore,” Fire Chief, Vol. 41, No. 5, 1997, pp. 53–55. McCloe, D., “Outreach Team Teaches Seniors to Be Fire and Life Safety Aware,” American Fire Journal, Vol. 49, No. 11, 1997, pp. 18–19. McDonald, T., “Department Showpiece,” Fire Chief, Vol. 42, No. 8, 1998, p. 46. Millsap, S., “Planning for Disasters in Your Community,” Fire Engineering, Vol. 147, No. 12, 1994, pp. 28–33. O’Rourke, J. J., “Woodstock ’94: Fire Planning for Large Public Events. Part 1: Fire Safety Preparations,” Fire Engineering, Vol. 148, No. 1, 1995, pp. 74–78. Penney, G., “Schooling Seniors in Safety,” Fire Chief, Vol. 41, No. 5, 1997, pp. 67–70. Perrault, M. E., “Home Security and Fire Safety Meeting Report, August 14–15, 1994, Quincy, Massachusetts,” National Fire Protection Assoc., Quincy, MA, Meeting Report, December 1994.
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Perroni, C., “ ‘Get Alarmed, South Carolina’ Lessons Learned from Its Success,” USFA Fire Investigation Technical Report Series, Special Report, Federal Emergency Management Agency, Washington, DC, 1991. Phillips, H., “South Africa Moves toward Safer Citizens,” Fire International, No. 185, Apr. 2001, p. 21. Porth, D., “ ‘Preventhink’ Paves the Path for Prevention Programs,” American Fire Journal, Vol. 48, No. 10, 1996, pp. 16–17. Powell, P. A., and Custer, R. L. P., “Fire and Life Safety Education: Bridging the Gap between Human Behavior and PerformanceBased Design,” Proceedings of the 1st International Symposium on Human Behavior in Fire, Belfast, UK, August 31–September 2, 1998, J. Shields (Ed.), Textflow Ltd., UK, 1998, pp. 125–134. Randall, J., and Jones, R. T., “Teaching Children Fire Safety Skills,” Fire Technology, Vol. 29, No. 4, 1993, pp. 268–280. Rubin, D. L., “Wingspread IV: A Practical Look,” Firehouse, Vol. 22, No. 3, 1997, p. 42. Runyan, C. W., et al., “Risk Factors for Fatal Residential Fires,” Fire Technology, Vol. 29, No. 2, 1993, pp. 183–193. Sabbeth, M. G., “Elementary Ethics,” Fire Chief, Vol. 44, No. 7, 2000, pp. 46–48. Semenchuk, M., “Laying Down the Law,” Fire Prevention, No. 319, Apr. 1999, pp. 26–27. Teague, P. E., “1992 FPW Offers ‘Sound’ Advice,” NFPA Journal, Vol. 86, No. 5, 1992, pp. 68–71. Thomas, J., “California Still Has Lessons to Learn,” Fire International, No. 143, May 1994, pp. 37, 40, 42. Walker, B. L., et al., “Short-Term Effects of a Fire Safety Education Program for the Elderly,” Fire Technology, Vol. 28, No. 2, 1992, pp. 134–162. Walker, B. L., “The Effects of a Burn Prevention Program on ChildCare Providers,” Fire Technology, Vol. 31, No. 3, 1995, pp. 244–264. Whitaker, D. A., “Austin’s Public Education Program Evolves into Multi-Tiered Success,” Firehouse, Vol. 25, No. 6, 2000, pp. 90–92. Wolf, A., “Fire Safety in the Navajo Nation,” NFPA Journal, Vol. 91, No. 2, 1997, pp. 74–82. Wood, B., “Childrens Fire Setting Behavior,” Fire Engineers Journal, Vol. 55, No. 179, 1995, pp. 31–35.
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Using Data for Public Education Decision Making John R. Hall, Jr.
S
uccessful fire and life safety education begins with good decisions by the managers of fire and life safety education—decisions that identify the major fire problems and target audiences, design a program best able to address those problems with that audience, and deliver the right program to the right people. At every stage of this process, good decisions depend on the proper use of good data. As a fire and life safety education program is developed and applied, questions needing data arise and may be grouped into the following six sections, which will be used to organize this chapter. • • • • • •
What is the problem to be addressed? What is the strategy to address the problem? Who is the target audience? Was the target audience reached by the strategy? Did the strategy change the target audience as intended? Did the fire problem decline?
The first three question groups give the design for the program. The second three question groups indicate what was accomplished. Because most programs are not one-time affairs, the lessons learned regarding accomplishments will then feed into the next cycle of program redesign decisions. This chapter addresses matching the right data with the questions posed, interpreting that data correctly, and eventually using data and all other available resources to save lives and property. Many of the issues and themes of this chapter have counterpoints elsewhere in the Fire Protection Handbook. The reader is particularly encouraged to read Section 3, Chapter 3, “Use of Fire Incident Data and Statistics,” which provides additional guidance on techniques of data interpretation for fire safety not limited to public education; Section 5, Chapter 6, “Evaluation Techniques for Fire and Life Safety Education,” which provides more detailed guidance on questions four through six than will be provided
Dr. John R. Hall, Jr., is assistant vice president for fire analysis and research at the National Fire Protection Association. He has been involved in studies of fire experience patterns and trends, models of fire risk, and studies of fire department management since 1974 at NFPA, the National Bureau of Standards, the U.S. Fire Administration, and the Urban Institute.
W o r l d v i e w In the increasingly global fire safety community, the transfer of fire and life safety education programs from one community to another or from one state to another has now been joined by transfer from one nation to another and one continent to another. Language and cultural differences are pervasive, but it is also important to note that the fire problem to be solved is often different in different countries (see “Differences in Fire Risks Around the World”).
here; and Section 5, Chapter 4, “Reaching High-Risk Groups,” which provides more information for those (common) occasions when the target audience includes a number of high-risk groups. This chapter—and this author—do not propose that analysis of readily available data is necessary or sufficient to answer all questions in the design and evaluation of public fire and life safety education programs (or any other kind of program). It is claimed that answers are sounder when they reflect the best data available and are ill-advised if they contradict, without engaging, the best data analysis. Use data to challenge assumptions, even the ones that seem most obvious. If the data isn’t strong enough or detailed enough to dictate the specific answer needed, then use the data to reduce the range of possibilities before applying judgment to make the final choices. Do not be afraid to use data to support choices and persuade third parties; however, do not confuse that exercise with the use of data to shape and assess choices. Decisionmaking and advocacy of decisions are both essential, and both can be done better with data analysis. For advocacy purposes, representative statistics may be less effective than more specific examples that allow people to put a human face on the fire losses and the program activities. Match appropriate data to the target audience. Supervisors, managers, local legislative officials, and budget officials tend to want hard numbers, although even they will have an easier time grasping the need and the plan with examples. The general public, the press, and organizations outside the fire safety arena may relate
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primarily to the examples. The resources cited in the last part of this chapter, particularly the NFPA (National Fire Protection Association) “One-Stop Data Shop,” can help locate accurate statistics and relevant stories.
WHAT IS THE PROBLEM? This first stage requires the fire safety education team to define the objectives explicitly. What aspects of the fire problem should be addressed? What scales measuring fire loss are the team willing to use to measure success and hold the team accountable for results? The answer may appear obvious—save lives and prevent injuries, for example—but here, and at every other stage in the data use process, the team will learn a great deal about real objectives as it wrestles with the problem of setting performance criteria that are measurable, meaningful, and realistically achievable. Start with the basics. Is the team comfortable being judged by changes in the size of the fire problem? If so, they will be taking responsibility for outcomes that are not totally under their control. Fire safety or risk is affected by both the behaviors people learn and the products and other physical aspects of their environment. Education directly affects only the former. On the other hand, if success is measured only by the number of children taught or the fraction of all children reached, then the team can guarantee success, given sufficient resources. But reaching children does not necessarily mean teaching children, and learning does not necessarily mean safety. The following three examples are different ways to fail, relative to the only criterion that ultimately matters—are people safer? And yet each of these examples of unequivocal failure would be judged a success by some, even many, methods of evaluation. 1. To take an extreme example, an educator can stand in front of a class full of sight- or hearing-impaired or non-Englishspeaking children and deliver a standard fire safety education program. Although this may add 20 to 25 children to the tally of people reached, one can say with confidence, based on the mismatch between the standard medium of delivery and the special needs of these audiences, that the behaviors of this target audience will not change at all. 2. Or, an educator can deliver a program to a classroom of children who pass the test at the end of the day with “flying colors” but who forget everything they learned by the start of the next day’s classes. 3. Or, an educator can teach a program that stays with the children for the rest of their lives, changing their behaviors as intended, but that somehow misses the behaviors that will prove to be most important in coping with the fire hazards they will face as adults. Why address evaluation/success at this early stage? Because the design of a program—and the data appropriate to help design the program—should anticipate the way it will be evaluated. That is, at the very end, when evaluating whether the “problem” was reduced, it should be the same “problem” identified at the outset that inspired the design of the program.
Type of Loss There are four principal measures of fire loss: (1) fire incidents (count each fire once), (2) deaths, (3) injuries, and (4) monetary loss. In some settings, other measures may be of value, such as environmental impact, continuity of operations and protection of cultural resources. The latter two measures are increasingly important in commercial settings. If a particular education effort leads to, for example, presenting a training session at the local chemical plant that employs a large number of the community’s people and provides a large part of the community’s tax base, then the educator may be less concerned about preventing a “typical” $10,000 fire at the plant than at preventing a catastrophic fire that might put thousands out of work and release a vapor cloud that could force evacuation of thousands more. Which is the right measure to use? Most fire and life safety educators have a principal concern with saving lives, so deaths should be a measure of fire loss of concern to them. But should it be the only measure used? Injuries are another measure of loss often targeted by fire safety educators. Injuries are several times more common than deaths, and some injuries are extraordinarily expensive, painful, and tragic. Most people value reducing the risk of death much more highly than reducing the risk of injury. However, injuries are more common, which means that injury statistics can provide significant, hard evidence of a program’s positive effects much sooner. For that reason, measuring success by fire incidents, regardless of severity, also has advantages. In the end, decisions must be made on which measure(s) of loss will be used. For each measure of loss, there needs to be an explicit rationale for the measure, which will provide guidance on how to interpret it and how much importance to attach to it. Different measures of loss will yield different priorities and multiple measures of loss can pull in different directions. For example, child-playing and smoking fires are major contributors to deaths and injuries, but only minor contributors to fire incidents (Table 5.2.1). Cooking fires are major contributors to fire incidents and injuries, but much less so to deaths. Smoke alarms have major impact on the risk of death but very minor impact on the risk of injury. And so on. Design the education program to produce results on the measures that matter most, not the measures that will show results the soonest. For example, suppose the team chooses to measure fire incidents as early evidence of program success and fire deaths the measure of the real objective. Then they should design the program not for its leverage on the rate of fire incidents but only for its leverage on fire deaths. Even after a measurement scale is chosen, more decisions are needed to select a specific measure. For example, suppose fire deaths are chosen as a measure of fire loss. This can be translated into four very different specific measures: (1) deaths in fires, (2) fatal fires, (3) multiple-death fires, or (4) deaths in multiple-death fires. Counting fatal fires rather than total deaths reduces the emphasis on deaths occurring in multiple-death fires. Under what circumstances might this make sense? Imagine a fire and life safety education manager in Las Vegas in the early 1980s. The MGM Grand Hotel fire caused more deaths in one fire than the city experienced in all other fires combined in many years. In
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TABLE 5.2.1
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Using Data for Public Education Decision Making
5–19
Major Causes of 1994–1998 Home Structure Fires Unknown Cause Fires Allocated Proportionally National Estimates—Annual Averages
Major Cause Cooking equipment Heating equipment Incendiary or suspicious Electrical distribution Other equipment Appliance, tool or air conditioning Smoking materials Open flame, ember or torch Child playing Exposure (to other hostile fire) Other heat source Natural causes Total
Fires 91,700 (22.6%) #1 59,100 (14.5%) #2 49,000 (12.1%) #3 38,400 (9.4%) #5 42,800 (10.5%) #4 29,400 (7.2%) #6 21,200 (5.2%) #7 19,700 (4.8%) #8 18,200 (4.5%) #9 15,500 (3.8%) #10 13,000 (3.2%) #11 8,400 (2.1%) #12 406,400 (100.0%)
Civilian Deaths 327
(9.3%) #5 468 (13.4%) #3 568 (16.2%) #2 352 (10.1%) #4 264 (7.6%) #7 133 (3.8%) #9 798 (22.8%) #1 112 (3.2%) #10 289 (8.3%) #6 33 (0.9%) #11 142 (4.1%) #8 13 (0.4%) #12 3,498 (100.0%)
Civilian Injuries 4,607
Direct Property Damage (in Millions) $394.8
(9.0%)
(25.5%) #1 (8.8% #5 (10.6%) #4 (7.4%) #7 (8.6%) #6 (5.3%) #9 (11.0%) #3 (3.9%) #10 (11.4%) #2 (0.9%) #11 (6.0%) #8 (0.7%) #12
12.6%) #3 $803.2 (18.3%) #1 $614.2 (14.0%) #2 $509.8 (11.6%) #4 $253.4 (5.8%) #6 $252.0 (5.7%) #7 (214.2 (4.9%) #10 $239.6 (5.5%) #8 $224.1 (5.1%) #9 $165.9 (3.8%) #11 $162.6 (3.7%) #12
18,092 (100.0%)
$4,384.3 (100.0%)
1,592 1,923 1,343 1,554 962 1,983 706 2,056 164 1,078 124
#5 $550.6
Note: Major cause classes are based on a hierarchy developed by the U.S. Fire Administration. Fires are expressed to the nearest hundred, deaths and injuries to the nearest ten, and property damage to the nearest hundred thousand dollars. Totals under “Total” may not equal sums because of rounding errors. Note: Each entry shows the estimated number, percent share of total in parenthesis, and rank among the twelve major cause groups below. Percentages are calculated on the actual estimates, so two figures with the same rounded-off estimates may have different percentages. Fires in which the cause was unknown have been allocated proportionally among fires of known causes. “Homes” include one- and two-family homes, manufactured housing and apartments. The values in this table represent the sum of the data for a) fires in one- and two-family dwellings and manufactured housing, and b) fires in apartments. Source: National estimates based on NFIRS and NFPA survey. Updated 2/01.
that kind of situation, counting deaths individually—and targeting programs accordingly—will mean devoting all educational resources to ensuring that the city never has another fire like the MGM Grand Hotel fire. This is a worthy goal, but it is not the only worthy goal. How many lives would be worth losing in ordinary home fires in order to ensure, say, that the odds against another MGM Grand-sized fire were a billion to one instead of only a hundred million to one? Alternatively, the team could decide up front to concentrate exclusively on multiple-death fires. The public often seems to be far more upset by one fire that kills five people than by five fires that kill one person each. If the intention is not so much to increase safety as to increase feelings of safety or to reduce public distress over gaps in safety, then the team might devote more attention to boosting the safety factors of programs that prevent large fires rather than programs more likely to save people in the circumstances where deaths are actually occurring.
DIFFERENCES IN FIRE RISKS AROUND THE WORLD In Japan young children are not a distinctively high-risk group for fatal fires. Their rate of fire deaths per million population is nearly the same as the rates for their parents and for older children. By contrast, in the United States, preschool children face a risk of dying in fire that is considerably more than double the risk for everyone else. At the other end of the age spectrum, however, Japan faces a much more severe problem than does the United States. The gap between fire risks for older adults and those for everyone else is much wider in Japan than in the United States. For example, the oldest of the older adults—those aged 81 or older—have about three times the average fire risk in the United States but about five times the average fire risk in Japan. The gap is so large—and the rate of growth in population so disproportionately
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large in the oldest age groups—that Dr. Ai Sekizawa of Japan has forecast that Japan’s slowly declining fire death rates will begin rising in the near future, driven by the fast-growing older population. This is one of the situations where there may be lessons to be learned in both directions. Child-rearing and child-supervision approaches in Japan may deserve some credit for their better experience in protecting the youngest of their people, while the better experience in protecting older people in the United States may reflect some of the distinctive U.S. practices. Only in-depth research can establish a credible link between differences in practices and differences in outcomes, because usually there are more than enough of the former to explain the latter. In Russia and much of eastern Europe, fire death rates overall are higher than they are in North America (the United States and Canada, in particular), Western Europe, and the Pacific Rim (particularly Japan). An obvious explanation is that the use and abuse of alcoholic beverages appears to be higher in Russia and Eastern Europe as well, to the extent that available statistics can be trusted to quantify such behavior. Two-fifths to one-half of U.S. adults who die in fire each year are legally intoxicated at the time; therefore there is no doubt that abuse of alcohol is associated with elevated risk of fire death. The use of smoking materials is also a point of distinction. In Europe, the percent of the adult population who smoke—and the range of places where smoking routinely occurs—is much larger than it now is in North America and is in fact reminiscent of the 1950s in North America. Coupled with better European success in preventing or mitigating many other types of fires, this distinctive behavior with regard to smoking is, not surprisingly, associated with a much higher percentage of fire deaths being attributed to smoking materials. As a last example, consider the differences between the United States and the United Kingdom in typical fatal fire size and victim location. In the United States, the majority of fatal victims of home fires are killed while in another room than the fire by a fire that has had flames spread beyond the room of origin, a development that is the best indication of transition to flashover, when the quantity of toxic smoke produced increases sharply and the heat pressure to distribute that smoke also rises substantially. In the United Kingdom, by contrast, a typical fatal victim is killed in the room of fire origin by a fire that remains largely confined to that room. As with the Japanese versus U.S. age differences, there are a number of possible explanations for the United States versus United Kingdom fire size and victim location differences. What is not debatable is the need to reflect such differences in the selection and evaluation of fire and life safety education programs. Smoke alarms and sprinklers, for example, though still highly effective safety approaches, may produce less leverage on a fire problem like the one in the United Kingdom than they have produced on a fire problem like the one in the United States. The UK fire problem may need more outright prevention of fire ignition for success. As around the globe, so within the United States, local differences in the problem to be solved should be identified early and incorporated into the design of an appropriate fire safety program.
TYPE OF PROPERTY A similar set of choices arises in choosing the properties of interest. Suppose the concern is with fire deaths, and the community, like most, suffers 80 percent of its fire deaths in home fires. This clearly argues for special attention to homes. But should the team target all homes and should homes be the only target? If not all homes, which homes should be targeted? If not exclusively homes, what other properties should be targeted? Data on the fire problem will indicate where to target programs if targeting is done, but the same data will indicate the high price paid for targeting of any kind. Targeting based on fire problem data will mean targeting high-risk places and people. However, targeting the highest-risk places and people may mean giving up in advance any chance of reducing the large share of the fire problem cumulatively accounted for by places and people having less than the highest risk. It may be that 1 percent of the community accounts for 20 percent of fire deaths, for example, but if that group is targeted exclusively, then 80 percent of fire deaths will be left untouched, even if the program works perfectly on its targeted group. In addition, there are other legitimate concerns, many of which also have data, that can be used in choosing the types of properties to target. For example, there are costs involved in delivering the program. If there is need to travel to selected sites (e.g., schools, homes) to deliver the program (e.g., school-based fire safety education, home inspections), then those costs are likely to be sensitive to the scatter of locations of targeted properties. It will cost much less, for example, to go to the highestrisk block in the city than to go to the 25 highest-risk households in the city (Table 5.2.2 for an example of a data analysis technique for prioritizing and targeting parts of a community). Also, the program itself needs to have multiple parts if it is to address several very different property types. After homes, the property class that accounts for, by far, the largest share of TABLE 5.2.2 Using Data to Target by Part of Community— An Illustration from a Dallas Anti-Arson Program District Number
Number of Arson Incidents
Percent of Total Arson Incidents
Cumulative Percentage
5 6 4 3 1
94 79 70 69 66
16.7 14.0 12.4 12.2 11.7
16.7 30.7 43.1 55.3 67.0
Setting priorities is a matter of drawing a line on this table at a point where resources available for the program will be exhausted or where the value of adding one more district drops sharply. The city drew that line here. 2 10 9 8 7 Total
42 40 38 33 33 564
7.4 7.1 6.7 5.9 5.9 100.0
74.4 81.5 88.2 94.1 100.0 100.0
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Trend versus Current Size Another point to examine in data analysis to define the fire problem is the question of trends. From a national perspective, for example, total fire deaths have been declining, and the risk of death from fire relative to the size of the population has been declining even faster. Trends for fire deaths involving particular fire causes, however, have shown different trends. In 1980 the top two major fire causes, in terms of home fire deaths, were (1) smoking and (2) heating. Since then, these two causes have been among the fastest declining, so that, in 1992, both accounted for smaller shares of fire deaths than they had in 1980 (Figure 5.2.1, which shows the trend over time in percent of home fire deaths with known cause attributable to each of four causes, using a hierarchical-sorting approach to grouping major causes as developed by analysts at the U.S. Fire Administration). Confirmed and suspected arson declined in terms of fire deaths, but not so steadily and not so steeply, and it moved past heating as the second leading cause of home fire deaths. Childplaying fire deaths rose in terms of share of fire deaths, ranking fourth in 1993 behind smoking, arson and suspected arson, and heating. In 1993, child-playing fire deaths increased so much that the total represented an absolute increase in deaths, not just percentage share of deaths, over 1980. With the help of the new child-resistant lighter standard, introduced in 1994, however,
40
Smoking Incendiary/suspicious Heating Child playing
35
Percentage
30.5%
25
22.7%
20 15
14.9%
17.5%
15.0% 10
11.0%
8.1%
6.5%
5 0
1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 Year
FIGURE 5.2.1
5–21
tory of fire deaths? Or places with unusually vulnerable populations (e.g., schools, nursing homes, hospitals), even if their actual fire history has been extremely low? Or places with high occupancy (e.g., arenas, high-rise buildings), just because of the number of people potentially exposed to fire? Or places with unusual hazards, because the complex knowledge and behaviors required for their fire safety are the furthest from simple common sense? Should only buildings be targeted? Are other agencies or organizations being implicitly expected to address the fire safety needs of places not targeted?
fire deaths is road vehicles. But the fire problems of cars and trucks are far different from those of homes. An educational program designed for homes would be much easier to adapt to other residential properties—or to any group of buildings—than to vehicles, where the educator might as well start over from scratch. In fact, it is difficult to find any fire safety educational program designed for vehicles, and this brings up another problem. Data analysis may do more than help choose among alternative educational programs. It may indicate a need to go beyond education in designing an effective prevention or mitigation program, for example, through codes and standards or other means for changing the physical characteristics of an engineered environment. Public priorities do not always follow patterns of risk, either. The public wants most of all to be protected from fire risks associated with strangers, even though they are much more at risk from themselves and their families and friends. Risks are less acceptable when they are unfamiliar or involuntary, hence, the tendency to focus on strangers.1 Homes and private vehicles account for more than 90 percent of all fire deaths, but they account for much less than 90 percent of people’s exposure, as measured by, say, time.2 The public worries about fire risks to children, even though school-age children are the lowest-risk age group in the population. Much of the public worries about fire risks to people like themselves more than they worry about fire risks to people in other social groups.3 Hence, programs targeted on the comparatively small high-risk groups may draw less public support than programs that make people with average-to-low risk even safer. This may seem like a purely philosophical or ethical question, but most fire safety educators are able to operate only because other people decide to give them funding and other resources. A program designed with an eye to the special concerns of the people who control the resources is more likely to obtain the resources it needs to succeed. All of this needs to be considered, and all of it can be reduced to data. Should the educator target properties with a his-
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Trends in Four of the Leading Causes of Home Fire Deaths
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child-playing fire deaths plunged. By 1998, child playing ranked only seventh among the 12 major causes. Which cause should a new educational program target first? Should it be smoking, which is still, as far as the most current statistics indicate, the leading cause of fire deaths? Should it be arson and suspected arson, which could be the leading cause in a few years if trends continue? Should it be heating, which of all these four causes involves behaviors that are easiest to change through education and so might still produce the most lifesaving value for a given level of effort? Or should it be cooking, which rose to third leading cause of fire deaths in 1998, as heating continued to decline? There is no one best answer to these questions. Any declining problem that is given priority in a new program may turn out to be a case of overkill. Any increasing problem that is given priority may turn out to have been varying around a constant or even declining trend line; that is, the “increase” may turn out to have been an artifact of when and how the baseline statistics were analyzed. Then again, any problem not given priority may suddenly “take off” and, once increasing, may lead to considerable loss and suffering before it can be controlled. For example, heating fire losses increased from the late 1970s to the early 1980s before intensified educational efforts, combined with other factors, brought that fire problem back under some degree of control.
Putting It All Together The previous paragraphs were heavier on questions and issues than on answers. For those who prefer answers and guidance, the following tips may provide a reasonable way forward. Design the program to reduce the risk of fire death among the people whose safety is the responsibility of the educator’s team, which may be a community, an age group, a company’s employees, an organization’s members, etc. Treat every death as equally important and potentially preventable. Although fire deaths should not be the only measure, because they take too long to show statistically significant effects, deaths should be regarded as the primary measure of success. As an example of how long it takes to show success, measured by fire deaths, however, consider the Louisville, Kentucky, home smoke alarm campaign of the 1980s (Figure 5.2.2). Louisville fire officials properly used a 5-year baseline that stretched back before the program began. The average fire death toll in that period was 15, including a declining trend in the last three years of the baseline. The first year of the program showed a death toll of 10, well below any year in the baseline and even below the improved level one might have computed from the baseline trend. However, a prudent program manager would want to see multiple years of data in order to see whether the excitement surrounding the program had produced a first-year improvement that couldn’t be sustained or whether some other fluke or normal variation asserted itself. With four years of postprogram data, it seemed clear that a substantial (more than onequarter) decline in fire deaths had occurred. But suppose the 1987 death toll of 16 had occurred in 1985. That would have presented a real blow to the program and might
Program started
Year
# Deaths
80 81 82 83 84
14 13 19 15 13
average = 15
85 86 87 88
10 9 16 8
average = 11
FIGURE 5.2.2 Louisville, Kentucky, Fire Deaths and a Home Smoke Alarm Program (Source: Philip Schaenman et al., Proving Public Fire Education Works, Arlington, VA: TriData Corporation, 1990, pp. 92–93)
have prematurely aborted it, even though time would show that it was a fluke. Or, suppose someone put forward a theory based on changes already in the works in 1982–1984 and claimed that the 1985–1988 success was only a continuation of that earlier trend and not a result of the program. It might have taken much more analysis or more years of data to sort out these conflicting claims. As it is, the substantial difference between 15 deaths a year in 1980–1984 and 11 deaths a year in 1985–1988 is not yet statistically significant. The difference between the two averages (15 and 11) is about 1.2 standard deviations, if the entire nine years is treated as one set of years with death tolls randomly chosen from what is assumed to be a constant risk of fire death, subject to variation. Statisticians usually look for at least 12/3 standard deviations for significance in a one-sided test. A trend line analysis might look better, given that three of the four lowest years came after the program was begun, but it would still probably take quite a few additional years of progress to satisfy a classical test of statistical significance. This illustrates the special challenge involved in focusing on fire deaths as an outcome measure. When extending the scope to include injuries, property damage, or some other objective, treat all such objectives as secondary to the risk of fire death. That is, design the program to achieve a reduction in the fire death toll, and only then, if some latitude in the design of the program exists (i.e., room for a few more behaviors to be taught), look for program design features that will address the other objectives. The reason for this is that, even though other kinds of losses are more frequent, deaths are preemptively more important. Use at least a 5-year baseline of the community’s or organization’s fire experience for analysis as they did in Louisville. More years will be needed if the community or organization has fewer than 100,000 people. If the target population is closer to 10,000, or even less, the community or organization’s own data will comprise too small a base to analyze or track success by the fire death toll in any reasonable period of time. In that event, use historical national fire death data—or, if obtainable, state data or data on a group of similar communities—for analysis to design the program.
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Using Data for Public Education Decision Making
5–23
341 298
315 283 280 Number of fires
245
257
239
243
210
186
175 140
Program starts
144
157
166
143
133
105
115 96
70 35 0
1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 Year
FIGURE 5.2.3 Waterford, Connecticut, Fires (Excluding Vehicles) and a SchoolBased Education Program (Source: Philip Schaenman et al., Proving Public Fire Education Works, Arlington, VA: TriData Corporation, 1990, pp. 39–41)
Many fire safety education programs are aimed primarily at fire prevention, as opposed to mitigation after fire starts, as is true for programs based on home smoke alarms or sprinklers. If so, it is appropriate to use fire incidents, rather than fire deaths, as the primary outcome measure. Since fires are 50 to 100 times as common as fire deaths, a shift from deaths to fires greatly improves the analyst’s ability to quickly confirm statistically significant program impacts. See Figure 5.2.3 for an example of such a tracking, in which a Waterford, Connecticut, schoolbased education program covering several fire safe behaviors was used to reduce the number of reported fires (excluding vehicle fires, which were considered outside the range of impact of the behaviors included in the program). Note, too, that there is still room for interpretation and debate. The program in Waterford was introduced at the end of a two-year period of increases in the number of reported fires, which followed a two-year period of decreases. The program appears to have been successful. An immediate and substantial drop in the number of fires occurred, followed by an even larger decline the next year. These gains have been largely sustained through the seven years that followed. But as with the other examples, one could make the case that the 1976–1978 decline was the real long-term trend, that the 1978–1980 increase was a temporary fluke, and that the 1980–1989 declines were therefore more attributable to a resumption of the already established declining trend and not so much to the new program. In a situation like this, where the data is not conclusive, the obvious, simple interpretation is also the one that favors the program, and a positive impact from the program is what everyone would have expected. Nevertheless, if there were already some well-defined programs underway in the mid-1970s and a good case could be made that their full effect had not yet been achieved, one would want to make sure that the older programs were kept in force alongside the new program, thereby assuring
that the favorable impact on fire rates continues, no matter what the principal factors in the trend might really be. Analyze the historical data base for major patterns that will be useful in selecting or refining programs or in targeting or reaching selected audiences. (See the following two sections.) Do a “snapshot” analysis of the baseline, i.e., one that ignores trends. Then, only after the initial conclusions have been set, look at major trends and consider making a few adjustments based on the trends. Minimizing use of any apparent trend information other than major trends will (1) avoid the dangers of over-reacting to statistical fluctuations that aren’t real trends and (2) avoid the temptation to change the program before it has finished “doing its job” (which is analogous to stopping the antibiotics as soon as symptoms improve).
WHAT IS THE STRATEGY? The purpose of data analysis is to set the stage for design or selection of a program that will reduce the fire problem as defined. However, many programs already exist; so do not “reinvent the wheel”—or any other parts of the car. This means the analysis will be most useful if it identifies patterns in the fire problem that favor some strategies and programs or help to set specifications for the selected strategies and programs. For example, if the education team has data on fire deaths by home smoke alarm status (e.g., how many fires were in homes with no smoke alarms, how many in homes where smoke alarms were not working, how many in homes with an insufficient number of smoke alarms, how many in homes with smoke alarms in the wrong place) or related variables (how many in homes where there was no escape plan), then they will have a much better idea whether to build the program around home smoke alarms, and if so, what specific points the education should address. Some of the data cited in this example will be retrievable from a typical
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state or local fire department data base on fire incidents. Other data might require a survey. The analysis done will depend on the data available. If data specific to the target audience is not available, analysis based on national data may be available and used. Fire cause data is similarly of interest because each cause corresponds to specific fire prevention behaviors that may be emphasized if the cause is a major concern. A key danger at this stage lies in committing oneself too early to a particular approach. For example, if fires are analyzed by cause—and only by cause—this may lead to an education emphasis on prevention, to the exclusion of the kind of education that can save lives even when fire occurs. It is far better to develop at the outset a comprehensive view of all the programs one could pursue, then let the specifics of those programs guide the selection of analyses that will help decide the best programs and refine them to best fit the team’s particular circumstances.
Keys to Program Success—Reach and Effectiveness The central point to remember when setting priorities is that success requires substantial leverage, which comes from two equally important sources: 1. The educational program has to be effective enough to make a major difference in the fire risks faced by everyone the program reaches. 2. The program has to reach most of the people, representing most of the existing fire risk, or else even a highly effective program will have little effect on the size of the total fire problem. People cannot be saved if they are not reached or if they are reached by a program that makes little or no difference. Frequently, the need to reach a large audience and the need to be effective with those reached will compete with one another. One can affordably reach many people with billboards and radio public service announcements, but it is not clear that such media, by themselves, make much difference. The educator can dramatically reduce the fire risk to people by using a comprehensive fire safety curriculum, for example, NFPA’s Learn Not to Burn® Curriculum, but it takes significant resources to do so, and even then, such a program directly reaches only school-age children. A full unintentional-injury curriculum, like NFPA’s Risk Watch®, provides high effectiveness over a wider range of injuries, but it poses the same challenges in achieving reach to the full target population. Effectiveness, in turn, can only be assessed against a clearly stated objective, and a single program may be used to achieve many distinct objectives. What are the objectives with a schoolbased program, for example? (1) Is the program objective to teach the school children how to be more fire-safe during their school-age years? (2) Is the program objective to teach them fire safety for the rest of their lives? (3) Is the program objective to have them deliver fire safety to their families? The first program objective involves a narrow reach (only the students and only for a limited time), but a high degree of effectiveness that can be readily measured. The second objective involves a wider reach (only the students but for their entire
lives), but a lesser degree of effectiveness (many will forget what they have learned without practice) or a need to expand the program (how can fire safety refresher training be given to adults who learned fire safety in schools as children?). The third objective involves the widest reach (potentially everyone who knows a school-age child), but the least effectiveness (a lot will be lost in translation before the students can pass on their knowledge to their families). To evaluate the impact of a program, a baseline is needed that addresses all the objectives. If the educator intends only to teach the school children while they are present, only a pretest and a posttest are needed to check gains in knowledge, what fraction of the class learned all behaviors, and so on. However, if the goal is to teach children for life, methods must be found to test adults five, ten, and so on, years out of school, to determine their retention levels. And if the goal is to teach families through their children, then pre- and post-tests are needed for family members as well as for school children. Selection and refinement of the program using data analysis requires application of the data collection protocols that support the kinds of evaluation implied by the objectives set.
Programs Implement Broad Strategies At this stage, consider the difference between the strategy and the program. For an educational program, the strategy is to impart specific knowledge and change specific behaviors for a designated target audience. The program includes the materials used to accomplish that end, the people taught, and the people they teach, together with the materials they have to use. For example, the city of Portland, Oregon, won a national fire safety award for a program that involved targeting high-risk neighborhoods by working through respected, trusted neighborhood groups.4 The fire department taught the church leaders who took the lead in teaching the neighborhood. Fire code inspection programs are also education programs. NFPA research conducted in the 1970s indicated that the successful fire code inspection programs are the ones that have nearly universal reach and that educate and motivate building occupants to make changes, even when the inspector is not there.5 Most fires and losses involve behaviors and transitory hazards that may not show up in an annual inspection. Unless the occupant has been convinced to act as a year-round inspector, which means education, the value of the inspection wears off very fast, even if the inspector is very thorough and enforcement is very effective.
Six General Approaches to Prevent Fire Loss During development of the initial list of candidate educational programs, for which objectives will be assigned and reach and effectiveness assessed, it may be useful to use the following set of categories, introduced in Section 2, Chapter 1, of this handbook: (1) prevention, (2) slowing the rate of growth of initial fire, (3) early detection, (4) early suppression, (5) preventing unusually rapid spread of fire or its effects, and (6) evacuation.
CHAPTER 2
Each of these categories has engineering and educational approaches, which ideally should work together. And each can be pinpointed as a possible priority through data analysis. Analysis of fire deaths by major causes, defined in terms of behaviors and heat sources, can identify a number of possible priorities for prevention education. Most educational programs include a number of prevention-oriented behaviors and so can benefit from an analysis by major causes. Bear in mind, however, that conventional educational techniques are of limited or unproven effectiveness in dealing with most of the leading causes of fatal fires, for example, smoking, arson, and children playing with fire. Make sure the program is designed to succeed with these causes before assigning a high effectiveness to the prevention education part. The child-playing fire problem has been dropping since 1994, when the U.S. Consumer Product Safety Commission implemented a standard for child-resistance in lighters. The unexpected aspect of that change has been that child-playing fires and losses plummeted, not just for lighters but for matches and everything else fire play may involve. It is difficult to explain this broad effect as anything other than a breakthrough in public awareness and education. For this chapter, the lesson is that sometimes a program’s impact exceeds even the most ambitious projections of direct impact. Sometimes, the unintended side effects are positive. If analysts see effects like this emerging, they can retailor the program to reinforce this favorable trend. But doing so begins with an openness to possibilities and a correspondingly broad and imaginative approach to data analysis. Analysis of fire deaths by the first burnable item ignited may shed some light on the problem of rapid early fire growth. Flammable and combustible liquids and gases can promote such rapid growth, as can large pieces that are ordinary combustibles, like upholstered furniture. Most educational programs contain some guidance on storage of such materials, on limiting quantities, or on the use of potential heat sources near them, but the educator might also consider guidance on selecting items to reduce risk (e.g., choosing upholstered furniture made to the industry’s voluntary standard on resistance to cigarette ignition) and on positioning items (e.g., how close are furniture pieces to walls and to each other?) Analysis of fire deaths by detector performance will always show the value of home smoke alarms and of keeping them operational. National statistics show smoke alarms cut the chances of dying when fire occurs in a home nearly in half.6 So will analysis by sprinkler performance, which should be included as an option in any fire safety program. Sprinklers reduce the chances of dying and the average property loss per fire by onehalf to two-thirds.7 Analysis of fire deaths by extent of flame damage—and, in particular, whether or not fire is confined to the room of fire origin—will always show the importance of blocking fire spread. For an educational program, the analysis will be enough to justify including guidance on the need to avoid creating avenues of rapid flame spread (e.g., untreated wood paneling on walls, especially on stairway or corridor walls). Analysis of fire deaths by the victim’s condition before fire began and activity at time of fatal injury will give some insight
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into the importance of evacuation issues. Typically, most victims never get as far as trying to escape. They were asleep, impaired by drugs or alcohol or disability, or too young or too old to act effectively. Every such finding translates into a point for education, but be realistic about what can be achieved. The educator probably cannot convince people not to get drunk—and certainly cannot change disabilities or the limitations associated with various ages—but he/she may be able to convince people to develop and practice escape plans that are tailored to their circumstances. Note that in each of these cases, NFPA has conducted analyses of national fire data that can be used both to make the general points that help sell the importance of particular behaviors to key third parties and to demonstrate formats for analyses that can be done on the community’s or organization’s fire experience data.8
Putting It All Together Assemble and brainstorm a list of promising educational programs. Include any available evidence on their track record of effectiveness. Lacking such evidence, try to develop some estimates, for example, by asking for quantitative estimates from a variety of national experts and others familiar with the programs. Set up a flow chart showing how specific actions will lead to changes in and actions by other parties, and from them to changes in the target audience, and from those changes to reductions in fire deaths and other forms of fire loss and risk. Fill in anticipated effects of changes at each stage and how effective the changes will be, based on the predicted effects. Based on a review of available resources (and other considerations in the following section), rough out how large a version of each program can be launched. Translate that into an estimate of reach, that is, the fraction of the target audience that can probably be reached. Despite the emphasis on data analysis throughout this exercise, it is important to think qualitatively more than quantitatively. Look for big differences in likely impact, and don’t be too wrapped up in small percentages. It should be obvious by now that much of the information will involve best guesses. Pay particular attention to any points in the flow chart where there is a real risk that the whole program will go “off track” if some key group does not do their part. For programs that still look attractive after this analysis, use data analysis of fire experience to specify program details (e.g., which prevention behaviors will be emphasized?). Based on these details, estimate what fraction of the total fire problem the program will target.
WHO IS THE TARGET AUDIENCE? Most public education programs target one of the following four groups: (1) the general population, (2) high-risk populations, (3) school children, or (4) people where they work. The first two are targeted because they represent all or a large share of the total fire problem, which gives the program a large reach. The second two are targeted because they find people under circumstances where they can and will spend significant time in an
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ideal learning environment, able to listen to lessons, practice behaviors, and be tested for what they learn. Conversely, the first group is hard to reach in ways that are highly effective, and the second group is just hard to reach. The last two groups have below-average fire risk to begin with, which may mean that high impact requires extending the reach of the program. For programs aimed at the general population, serious questions have to be asked at the outset as to how effective the program will be. It is almost impossible to devise a program for the general population in which the participants practice fire-safe behaviors. Can the program even ensure that everyone will read or hear the lessons? Mailed materials and materials dropped off by people on rounds will often be discarded without being read. Billboards and public service announcements are within viewing range of only a fraction of the population and will be ignored by many of those. Cost alone is usually enough to force a program to target only a fraction of the general population, in which case the program should be targeted at high-risk populations. If forced instead to target a partial program based on greatest ease or lowest cost, the education will almost inevitably, albeit inadvertently, end up targeting low-risk populations, the people who need the program least. The safest neighborhoods for home inspections, the most receptive neighborhoods for community meetings, the participants in fraternal organizations and other social groups, and the best and most receptive schools, all tend to favor the more affluent, better educated, and lower fire-risk people. It takes a great deal of work to hit the target of high-risk populations, so much so that Section 5, Chapter 5, of this handbook is devoted to that topic alone. Once the decision to target high-risk populations is made, they must be identified and creative ways must be determined to reach them. If high-risk populations are defined by where people live, use actual fire history to find parts of the community where fire rates and fire death rates, relative to population, are unusually high. This will lead naturally to programs that deliver fire safety within those neighborhoods. (High-risk areas can easily have rates several times the community-wide average. Again, do not focus too much on small differences, such as slightly above-average fire rates.) At this stage, effectiveness considerations, already discussed, will become as important as extent of coverage, or reach. Door-to-door programs offer more potential for substantial learning but are very resource-intensive. How many can the program afford to reach in this fashion? Assembling people through the guidance of some community group is more cost-effective but permits less individualized teaching and therefore may not result in as much practice of behaviors by the entire target audience. Such programs also tend to draw disproportionately from the lower-risk occupants of even a high-risk neighborhood. Mailing or dropping off materials is even more affordable and even less likely to change behavior. Use available data on effectiveness with estimates of projected numbers of people reached to compare different programs. High-risk populations need not be defined by neighborhood or community, however. Older adults are a high-risk population, for example. Use data analysis to check every assumption for these programs.
For example, in 1997, there were 1.6 million resident patients in nursing homes, compared to a total of more than 34 million United States residents who were age 65 or older.9 That is, there were about 20 older adults living at home for every one living in a nursing home; therefore, any program intending to target older adults as a high-risk population would only “scratch the surface” by targeting the nursing home population. Further, older adults living in nursing homes already have much lower fire risk than older adults living at home, because of the much greater built-in fire protection and supervision afforded in nursing homes. The population ratio may have been roughly 15:1, but the ratio of fire deaths in the same period was more like 80:1. Therefore, within the high-risk older adult population, the people living in nursing homes need additional fire safety least. With creativity, an educator might try to target a program for older adults in homes but without ignoring nursing homes altogether. For example, nursing homes or like facilities could be used as magnets to draw in older adults from homes throughout the community? The need for data analysis lies in the need to check assumptions, because assumptions are an inevitable part of crafting a fire and life safety education program to fit within limited resources. The example just discussed started with a (presumed) fact: It is not affordable to target everyone in the population, and so limited program resources should be applied where they will do the most good. That means large-reach and/or high effectiveness. Targeting high-risk populations gives the most reach (in terms of share of the fire problem) per population reached. First assumption: Older adults are a high-risk population. Data confirms this; they have more than twice the fire death rate of the general population. Second assumption: Nursing homes are a compact, efficient way to reach older adults. Data disproves this, as shown. Third assumption: A program can be devised with enough effectiveness to produce high impact when targeted to older adults. Data can best address this only after the program is specified (targeting nursing homes didn’t work) and alternative programs are specified, against which to compare the older-adult program. If targeting nursing homes had proved to be a good idea, it would still be necessary to be creative, challenge assumptions, and analyze data to specify details of a program. For example, should the educational program target the patients or the staff? Both are possibilities, and both types of programs may have data on effectiveness. Or would a mixed program, targeting both groups, be best (where “best” takes account of affordability, too)? In fact, every fire-related characteristic can be examined as a basis for identifying high- versus low-risk populations, and, hence, for targeting fire and life safety education programs. Smoking material fires lead the list of causes of fatal fires. How about an educational program that works through points of sale of cigarettes? Heating equipment fires still rank fairly high. How about educational materials distributed where portable or space heaters are sold, serviced, or maintained? These are examples of what can be an iterative process, wherein data helps in design and selection of existing educational programs but also suggests unmet needs that may spark ideas for entirely new kinds of educational programs. Data analysis can be a stimulus to that kind of creativity as well as a reality check on assumptions about what will work and who most needs attention.
CHAPTER 2
Targeting schools or workplaces presents its own set of questions, similar in form but different in specifics. Does the program provide that participants will practice fire-safe behaviors, or (less effective) take a written or oral test after being taught about fire-safe behaviors, or (even less effective) be lectured on fire safety with no testing or interaction, or (least effective) be notified of the availability of materials on fire safety? Note the variations implied by this question. After a target audience and a set of information to be used in an educational program are specified, success (effectiveness) in getting the audience to learn, know, and be able (and likely) to act on the information may depend on the manner and intensity of the interaction. The easier it is for the audience to “drop out” of the exchange, by ignoring the materials or even by not examining them at all, the more likely it will be that many people will not be educated. And reach takes many forms. Do all classrooms in the school, all schools in the system, all areas in the workplace, and all facilities in the industry participate? Or do only the most motivated, self-selected ones, who probably have the lowest fire risk already, participate?
WAS THE TARGET AUDIENCE REACHED? At this stage, data is used not to design or select the program but to evaluate its impact. That evaluation may lead to some redesign, in which case it is necessary to move back to an earlier point, as appropriate. This first step in evaluation corresponds to the first effects the educator can hope to measure. It relies on activity measures—measures of the work already done. The third section called for estimating the likely reach of programs and strategies as a basis for choosing those to be implemented. After program implementation, it is necessary to measure the reach that was actually achieved. To do this, begin with data on people and groups to whom the program was delivered. For example, which schools were sent materials? Usually, the materials will not have been sent directly to the target audience, and so it will be necessary to survey the addressees to determine how many of them passed on the materials, and to what fraction of the target audience members within their organization. Then it may be necessary to survey those individuals to determine how many of them used the materials. Take the school materials example again. The program data will indicate which schools were sent the materials, but the educator will need to survey the principals to determine which classrooms took the materials, then survey the teachers from those classrooms to determine which ones used the materials and to what extent, and finally survey the teachers or the students to determine how many students in the classrooms participated in the exercise (e.g., omitting students who were sick or excused for other reasons). Whatever method is used to build up the data base, the goal is to estimate the fraction of the original target audience that was actually reached. Therefore, count people, not some more convenient distribution unit, such as classrooms, schools, workplaces, and so on.
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This evaluation needs to be this thorough so that a realistic view of what was achieved can be obtained. There are many steps in a program where targeted people may be missed, and so any such step not evaluated is a place where one might inadvertently overestimate the effective reach of the program.
DID THE STRATEGY WORK? This is the evaluation step that corresponds to the design step that specified the strategy. It usually involves pre- and posttests of knowledge or learned behaviors for the target audience. This step calls for change measures—the most direct measures possible of the difference the program has made. Table 5.2.3 summarizes types of evaluation measures. This comes later in the time sequence because, for most programs, the program objectives will imply a goal of long-term learning. The educator needs to ensure that the program has effects that last past the end of the program. This means, ideally, a sequence of post-tests, for example, immediately after the program, one year out, five years out, and so on. In time, enough may be known about patterns of retention of fire safety knowledge that it will no longer be necessary to conduct elaborate posttesting regimens for specific programs; but, at present, such information is quite useful. Even at this stage, look primarily for changes that are substantive and closely linked to how lives are saved. Measure changes in knowledge (pre- and posttests) and behavior (by surveys, interviews, and other sample observation techniques). It may be interesting to note, for example, that school officials and fire officials are working together more now than before or that they enjoyed participating in the program or that they believe it made a difference; but these kinds of changes are too far removed from the hard evidence of program impact to deserve much emphasis in the evaluation. They may even reflect a mistaken notion of how success occurs. A study of workplace teams found that successful teams rarely sought consensus and that consensus was not a precondition for team success. An evaluation that assumed consensus was valuable in itself or that consensus was a good indicator of task success and program impact would be off the mark.
WERE LIVES SAVED OR LOSSES REDUCED? This is the ultimate measure of benefit and impact—and the only one that truly matters. It is the evaluation counterpart to the design step that asked what the problem was. It involves comparing fire death rates and other fire loss rates after the program to those before the program. This step calls for outcome measures. These are change measures, too, but they are measures of the intrinsically valuable changes to which all the work was meant to lead. If people learn more or know more, that is valuable only if they have fewer fires and fewer of them die [or are injured or whatever the chosen loss measure(s) for the objectives may have been]. At the same time, these change measures may be affected by more than just the program. Time has passed since the baseline period. People may have gotten poorer or richer, smarter or
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TABLE 5.2.3 Type of Measure
Types of Evaluation Measures for Public Fire and Life Safety Education Programs Purpose
Timing
Examples
Activity measure
Determine whether the target population was reached with something.
Measure can be calculated based on plans and scheduled activity, before or during program delivery.
1. Number of school children contacted. Weak measure because it doesn’t indicate fraction of total reached, any bias in selection of children reached, or possibly even whether contact stopped short of program delivery. 2. Percentage of school children taught, overall and by school, by grade, by part of community (distinguished by high vs. low fire risk). Strong measure because it indicates relative achievement of goal and checks for bias. 3. Breakdown of above measures by different risk populations (e.g., by income, gender, ethnic or cultural grouping). Measures are to look for differential input and reasons for it.
Change measure
Of the people reached, determine whether learning occurred or whether behavior changed as a result.
Measure of learning can be calculated at end of program but should also be calculated 6–12 months later to check for decay in learning. Measure of behavior change takes time to measure but can also be calculated just after the end of the program and 6–12 months later.
1. Percent correct answers on post-test. Weak measure because it shows knowledge other than learning. 2. Percent correct on post-test minus percent correct on pre-test. Better measure but still needs to be calibrated or interpreted by how much learning was needed. 3. One minus [(percent correct on post-test) / (percent correct on pre-test)]. Measure addresses learning achieved, calibrated by learning needed. May still be misleading if very little learning was required, and form of the measure is sufficiently unfamiliar and complex that it will take educators a while to get comfortable with it. 4. Analogous measures can be applied to behavior, if a system can be established to observe representative samples of behavior. For example, bicycle-helmetwearing behavior in school can be checked unobtrusively before and after program. 5. Breakdown of above measures by different risk populations (e.g., by income, gender, ethnic or cultural grouping). Measures are to look for differential input and reasons for it.
Outcome measure
Determines whether enough people at risk were reached by a program with enough effectiveness or the knowledge, skills, and behaviors most important to that risk, resulting in reduced human losses (i.e., deaths and injuries)
Statistically significant data will require years to accumulate. Even more time will be required if analysis focuses on deaths and injuries involving the specific skills, knowledge, and behaviors targeted by the program.
1. Number of deaths and injuries among the target population, baseline vs. after program. Good measure of what the program is intended to affect, but not calibrated for program reach or effectiveness. 2. Number of deaths and injuries among the population taught vs. target population not reached, baseline vs. after program. Better measure calibrates for reach but not for effectiveness. Also useful to use population not reached as a control group. 3. Breakdown of measure #2 for deaths and injuries involving knowledge, skills, and behaviors targeted by program vs. deaths and injuries not involving those. Measures are not to gauge impact but to sort out reasons for impact or lack of impact. Does the program have limited impact or limited reach (among target population, among critical behaviors and risk factors) or both? 4. Breakdown of above measures by different risk populations (e.g., by income, gender, ethnic or cultural grouping). Measures are to look for differential input and reasons for it.
CHAPTER 2
less knowledgeable, more mature or more impaired by advanced age. And other groups will have been conducting programs, some directly and deliberately focusing on fire safety, others not intending to address fire safety but having some impact on it nevertheless. Therefore, while these measures are more directly indicative of the program objectives, their changes or lack of changes may reflect more than the program under scrutiny. Therefore, it is useful to apply experimental techniques that can isolate the fire safety program from other influences. Some common phenomena should be checked, as described below. Fire loss rates, including death rates, will vary randomly over time, often significantly. If the educator introduces a program at a time when those variations have pushed loss rates up to historically high levels, then significant reduction relative to that baseline can be expected, even if the program itself has no effect. Loss rates will return to “normal” levels or trends, and that return will look like an improvement. Since a random variation pushing up loss rates looks the same as a problem “spinning out of control,” in need of immediate special attention, it is not unusual for programs to be launched at the top of one of these artificial peaks. Consider that possibility when interpreting data. Consider, too, the Hawthorne effect. First noted in studies of industrial productivity, the “Hawthorne effect” refers to the tendency of populations to do better just because someone is paying more attention to them. Just being in a fire and life safety program may inspire participants to be more fire-conscious, and so more fire-safe, even if they really haven’t learned anything more. These motivational effects rarely outlast the program, or even the experimental phase of the program when publicity is most intense, so this possibility is another reason to check for effects over the long term. (It also can be checked by running a “placebo” program that has no educational content but delivers to a control group all the attention of being part of a program.) Analyze data not just for how much impact a program produces but for how the program achieves its impact. It is not unusual for a successful program to produce effects differently than expected. This is important for design choices when moving from pilot programs to full-scale programs or from experimental programs to institutionalized programs, because it is important to emphasize those features that actually produced success. One classic example was a fire department home inspection program whose introduction coincided with a large decline in home fire rates.5 Detailed analysis, however, showed the decline often preceded the arrival of inspectors in a particular neighborhood, suggesting that the fire safety effects were produced more by the motivational effects of the program’s introduction and the desire to “look good” for the inspectors when they arrived. This had implications for the program, because it suggested a need to emphasize mass-media publicity in support of the program on a continuing basis and to look for ways to encourage people to “clean up for the inspectors” rather than relying on the inspectors to find hazards on the spot and have them corrected. See Section 5, Chapter 6, “Evaluation Techniques for Public Education,” for more detailed guidance on measurement techniques and guidelines for interpretation of these last three sections. Also, there is extensive guidance on evaluation in NFPA’s Learn Not to Burn Curriculum and Risk Watch® materials.
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AVAILABLE DATA AND ANALYSIS RESOURCES Much of the design and evaluation work needs to be based on local data; this includes data specific to the team’s program, community or organization, and target audiences. But a fair amount of the design work can be done on the basis of existing national data analysis, and even the evaluation can take advantage of existing data analysis already done on similar programs. Guidance on analysis methods is given in Section 3, Chapter 3, “Use of Fire Incident Data and Statistics.” For more details on sophisticated statistical analysis and modeling techniques, consult The SFPE Handbook of Fire Protection Engineering, published by NFPA.10 The most important caution to keep in mind regarding methods is this: The key weakness in most data bases is not the quality of the reporting but the representativeness of the coverage. Data bases do not have to be complete to be comprehensive; if they are properly representative, statistical methods will allow valid projection of totals from samples. Data bases do not have to be totally accurate within each record to be very accurate for statistical analysis; errors usually balance each other out, as one person’s miscoding is offset by an opposite miscoding by someone else. (See Section 3, Chapter 3, “Use of Fire Incident Data and Statistics.”) The best national data for public education program design consists of what are called national estimates based on two national fire-department-based data bases—the U.S. Fire Administration’s National Fire Incident Reporting System (NFIRS) and NFPA’s annual fire experience survey. Through the “OneStop Data Shop,” NFPA maintains a listing of dozens of reports covering all aspects of the home fire problem, including patterns, trends, comparative risk factors, major causes, victim patterns, and detection and suppression equipment roles in fire safety. NFPA encourages educators to seek this support. The U.S. Fire Administration’s National Fire Data Center (NFDC) is another valuable data analysis resource. In addition to its role in maintaining and distributing NFIRS to all fire data users, the NFDC has done more than any other organization to develop analyses at the state and local levels. NFIRS is not a complete data base, having data on about half of all reported U.S. fires each year, so analyses below the national level are not possible for all areas; however, the NFDC is an excellent resource. Another major source of fire data analysis at the national level is the U.S. Consumer Product Safety Commission (CPSC). In addition to a wide range of national estimate analyses focused on home fires—and a key role working with NFPA analysts in standardizing the methods used for making national estimates— CPSC is the nation’s leading organization for special data collection and analysis projects applicable to home fires. Watershed analyses of home electrical fires and smoke alarm usage and problems are only two of the best known examples. Their Hazard Analysis Group conducts these analyses and can describe what is available. The best compilation of data-based evaluations of fire safety education programs is in a report by TriData Corporation. Anyone interested in evaluation of fire safety education programs
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should read Proving Public Fire Education Works, TriData Corporation, 1990.11 Finally, the roughly 30,000 communities in the United States are resources for each other. Remember that, when creating programs or analyzing data for programs, it is likely that some other community has done so already and learned some useful lessons. NFPA’s Champions program is building a network of leading-edge communities that have not only successfully demonstrated fire safety education programs but also committed themselves to sharing their knowledge and methods with others. Contact NFPA Public Education for more on the Champions network.
BIBLIOGRAPHY References Cited 1. Slovic, P., Fischoff, B., and Lichtenstein, S., “Rating the Risks,” Readings in Risk, T. S. Glickman and M. Gough (Eds.), Resources for the Future, Inc., Washington, DC, 1990. 2. Karter, M. J., Jr., Fire Loss in the United States, Fire Analysis & Research Division, National Fire Protection Association, Quincy, MA, annually; and interval estimates of average percentages of time spent in various locations, done by John R. Hall, Jr., National Fire Protection Association, 1996. 3. This is an example of people’s tendency to show concern with situations where benefits go to others and costs or risks go to “us.” See M. W. Merkhofer, A Complete Evaluation of Quantitative Decision-Making Approaches, Final Report, SRI Project 2102, National Science Foundation, Apr. 1983, Washington, DC. 4. Teague, P. E., “Member Profile: Jim Crawford,” NFPA Journal, Sept./Oct. 1993, p. 23. 5. Hall, J. R., Jr., et al., Fire Code Inspections and Fire Prevention: What Methods Lead to Success?, National Fire Protection Association and the Urban Institute, Boston, MA, 1979.
6. Ahrens, M., U.S. Experience with Smoke Alarms, Fire Analysis & Research Division, National Fire Protection Association, Quincy, MA, January 2000. 7. Rohr, K. D., U.S. Experience with Sprinklers, Fire Analysis & Research Division, National Fire Protection Association, Quincy, MA, January 2000. 8. A listing of reports and a description of analyses that can be done may be obtained from the “One-Stop Data Shop,” National Fire Protection Association, 1 Batterymarch Park, Quincy, MA 02296-9101. Phone: (617) 984-7450; fax (617) 984-7478; e-mail
[email protected]. Guidance on how to analyze state or local data bases in the same way can be obtained from NFPA’s analysts at the same address. 9. Statistical Abstract of the United States 2000, Bureau of the Census, Washington, DC, 2000, Tables 208 and 13. 10. The SFPE Handbook of Fire Protection Engineering, 2nd ed., P. J. DiNenno et al. (Eds.), National Fire Protection Association, Quincy, MA, 1995. 11. Schaenman, P.S., et al., Proving Public Fire Education Works, Arlington, VA, TriData Corporation, 1990.
Recommended Reading NFPA, Learn Not to Burn® Curriculum, National Fire Protection Association, Quincy, MA.
Additional Resources NFPA Champions Network, NFPA Public Education, National Fire Protection Association, Quincy, MA. Phone: (617) 984-7285. NFPA, “One-Stop Data Shop,” National Fire Protection Association, Quincy, MA. Phone: (617) 984-7450. U.S. Consumer Product Safety Commission (CPSC), Hazard Analysis Group. Phone: (301) 504-0470. U.S. Fire Administration’s National Fire Data Center (NFDC), 16825 S. Seton Ave., Emmitsburg, MD 21727. Phone: (301) 447-1272.
CHAPTER 3
SECTION 5
Fire and Life Safety Education: Theory and Techniques Revised by
Edward Kirtley
P
ublic fire and life safety education may be defined as “comprehensive community fire and injury prevention programs designed to eliminate or mitigate situations that endanger lives, health, property, or the environment.”1 Organizations whose personnel conduct fire and life safety education programs include fire departments, state or provincial fire agencies, schools, burn prevention and treatment organizations, city health departments, and corporate safety offices. Fire and life safety educators blend and apply seven distinct areas of expertise in their professional practice: (1) education theory, (2) education techniques, (3) methods of coalition building, (4) presentation skills, (5) working with the media, (6) education program planning, and (7) education program evaluation. This chapter will focus on education theory and techniques. For further information, see the following chapters in Section 5: Chapter 2, “Using Data for Public Education Decision Making”; Chapter 4, “Reaching High-Risk Groups”; Chapter 5, “Understanding Media: Basics for the Twenty-First Century”); Chapter 6, “Applying Evaluation Techniques to Risk Watch®”; and Chapter 7, “Campus Fire Safety.”
Information is facts, knowledge, or data. Information is the raw material of the new skills of education and the change of learning. For example, a presentation for the chamber of commerce on how to develop an occupant emergency plan for the workplace is an educational activity. It teaches a skill (i.e., how to develop an occupant emergency plan). Later, when the participants actually do their plans, a change has happened, that is, learning has taken place. A presentation to the same group about how the community’s Insurance Services Office (ISO) rating is set is a public information activity. Interesting facts have been shared. But the participants do not have any new skills, such as how to use an ISO grading schedule.
CHARACTERISTICS OF LEARNING For the practicing fire and life safety educator, the complex field of learning theory can be summarized in a few points.2
EDUCATION THEORY FOR FIRE AND LIFE SAFETY EDUCATORS What Is Learning? The terms learning, education, and information are related, but there are important differences between these three concepts. Learning is knowledge gained through observation and study, resulting in a change of attitude or behavior.2 Stated another way, learning cannot take place without change. Education is the process of training, teaching, or instructing students in new skills. Training, teaching, and instruction all deal with preparing students for some kind of action or activity, such as driving a car, operating a machine, or testing a smoke detector. “How to do” something is at the core of education. Edward Kirtley, M.A., is the fire chief of the Guymon Oklahoma Fire Department and former training director of the Colorado Springs Colorado Fire Department. He is the chair of the NFPA 1035 standard committee and is well known internationally in the area of fire and life safety education.
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1. Learning is a life-long activity. Learning does not stop when school ends. 2. Because learning causes a change in attitude or behavior, learning can be stressful. For example, it is uncomfortable to change a fire and life safety attitude from “My kids would never play with fire” to “I need to be more careful about where I put my cigarette lighter.” 3. People learn at different rates and in different ways. How people learn is not related to intelligence. 4. Learning must be reinforced to be effective. This characteristic argues against once-a-year fire and life safety education programs, but is a strong argument for ongoing activity. 5. Effective learning requires support from the people who influence or control the students. In the workplace, supervisors should support an employee’s new interest in keeping exits clear. Parents need to support a child’s pressure to install more smoke detectors. 6. Learning is enhanced when multiple senses are stimulated. Students need to hear words and see illustrations. Through props (such as burned items from a house fire) students touch and even smell the effects of fire. This characteristic of learning applies to adults as well as children, although
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great care should be taken in the use of potentially threatening props with children. 7. Learning is most effective when it is focused. In focused learning, the fire and life safety educator begins with an overview (e.g., “This morning, we will learn what to do in case your clothes catch fire”) and then explains the individual actions (e.g., how to “stop, drop, and roll”; how to cool a burn; and when to get medical attention).
Motivation and Learning3 Motivation is an essential step in the learning process. Educators have long realized the importance of motivation when attempting to create behavioral and attitudinal changers of the learner. Although several different models describe learner motivation, there are some common elements in all the models. First, the educator must establish a strong connection between the topic and the needs of the learner. This is commonly called the relevance of the topic. The learners must be able to see that the topic applies to their world. For fire and life safety topics the learners must understand that the risk applies to them. For example, an educator is delivering a presentation to parents (the target audience) of young children about the need for bicycle helmets. The educator must convince the parents that their children who ride bicycles, skate boards, etc. are at risk from injury if they crash without a helmet. This can be accomplished through the use of personal testimonies, injury statistics, anecdotes, or local news stories about a child being injured without a bike helmet. Next, the educator must explain the benefit to the target audience of acting on the information. In other words, the target audience must believe they will benefit from changing their behavior or their beliefs about the topic. In the example above involving bicycle helmets, the parents must understand and believe they and their children will benefit from wearing the helmets, that is, their children will avoid a head injury from a bicycle crash. This can be accomplished with personal testimony, statistics, medical information, and so on. As with relevance, the greater the benefit for the learner the stronger the motivation to learn about the fire or life safety education topic. A final component of motivation is the ability to act on the information, especially for adult learners. The learners must be able to take personal action with the information to be motivated to change. If they believe there is no way to act on the recommendations, they will not act. For example, consider the example of the bike helmets already discussed. Suppose that the target audience was low-income parents who could not afford bike helmets or who might not have access to them. The parents may clearly understand the need for helmets, and the benefits from them, but cannot act because of the monetary issue. In this case, the educator must provide a way for the learner to take action, for example, by providing the helmets to the children at little or no cost. These two motivational issues must be addressed with every audience, regardless of age, if motivation for the topic is to be created. With younger children this will require a simple approach using basic language that is positive and does not frighten or intimidate the children. For adults, the educator must draw on the experiences of the audience and an understanding of their needs to create the motivation.
TABLE 5.3.1
Education Needs and Learning Domains
Target Domain
Audience Needs
Audience Situation
Affective Cognitive Psychomotor
Motivation Information Skills
Does not value something Does not know something Cannot do something
The Domains of Learning Education is not based solely on fundamental human needs, such as those described by Maslow. Education is also based on audience needs. Audience needs are often described according to three domains of learning: 1. The affective domain involves how people feel about a situation and is the realm of values and opinions (e.g., whether or not they worry that their cigarette may have started a grass fire; whether they care about damage to wildlands). 2. The cognitive domain involves what people understand (e.g., how fast a grass fire is likely to grow). 3. The psychomotor domain deals with what people can do (e.g., how to dispose of smoking materials properly). Each domain can be related to specific kinds of educational needs (Table 5.3.1). As discussed later in this chapter, the domains of learning are very important to the process of writing educational objectives.
The Learning Process3 To be effective with creating behavior and attitude change in the learner, the educator must approach educational presentations with a sound understanding of how people learn—that is, the learning process (Figure 5.3.1). By understanding the learning process educators can appropriately apply all the educational tools available to them. While the learning process is basically the same for all audiences, the tools used will vary greatly based
Sensory input
Repetition of message Short-Term Memory (6 or 7 bits of information)
Link to information in LTM Long-Term Memory
Application of knowledge and skills Transfer of learning
FIGURE 5.3.1
The Learning Process
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on the topic, the age of the learner, and amount of life experiences of the learner. The first step in the learning process is for the learner to receive information about the topic. The information is received by learners through the senses—what they see, what they hear, what they touch and experience. The more senses that are involved in this step the greater the likelihood that learning will occur. Part of this first step is also creating the initial motivation to learn about the topic. This has previously been discussed. It is important to remember that young or old, without the motivation, learning will not occur. This means the first few minutes of a presentation, when communication is initiated with the learner, are critical to the success of the overall learning experience. The second step in the learning process is the transfer of the information into short-term memory (STM). STM is an area where information is initially sorted. It has a limited storage capacity, approximately six or seven bits of information or one “chunk” of information. When the information arrives in shortterm memory, the learner’s mind immediately begins searching for a connection with knowledge the learner already possesses that is similar to the new information. If a connection, or link, is made with existing knowledge, the information is then transferred to long-term memory. If the information is not connected, it is lost as more new information comes into STM, since STM can hold only six or seven individual bits of information. The third step in the learning process is the transfer of information from STM to long-term memory (LTM). LTM memory is the storage area for all knowledge and skills the learner possesses. LTM is similar to a computer memory in that information is stored based on similar characteristics. These storage areas are called “cells.” There may be a cell for colors, one for automobiles, one for birds, and so on. The more life experiences the learner has, the greater the number of cells that exist in LTM. As discussed above, a link must be established between the new information and a cell that already exists. If a cell does not exist, the educator must create a new cell for that type of information. This is especially important with presentations to preschool children. In all cases, the educator must actively and thoughtfully create the link for the learner through examples, stories, experiences, and so on. The fourth step in the learning process is application of new information so that transfer of learning occurs. Transfer of learning is the ultimate goal of the learning process. When transfer of learning occurs, the learner is able to apply the new information—skills, knowledge, and attitude—to situations in their lives. Transfer of learning occurs through application of the new information or skills. In other words, transfer of learning occurs after the new information or skill has been practiced. For young children this means performing the behavior—for example, fire or life safety behavior—until it is mastered. For adults this can be accomplished through questions or activities and may even require actual practice with some skills, such as donning a bicycle helmet or placing a child in a car safety seat. The amount of application required to achieve transfer of learning is determined by several factors. First, the developmental stage of the learner will influence the amount of application required. Young children will require more time for practice than will adults, in most cases. Another factor is the life
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experience of the learner. Someone who has had experience with a fire or life safety behavior, for example, the use of a fire extinguisher, will require less practice. Finally, the quality of the educational experience will affect the amount of application required. A high-quality experience that utilizes appropriate presentation techniques and applies learning theory will result in quicker transfer of learning. It is important to understand that learners may know the correct action to take, but without transfer of learning, they may not be able to actually perform the action when the time comes. For example, children may know that if their clothes catch on fire, they are to “Stop, Drop and Roll.” However, if they have never applied or practiced “Stop, Drop and Roll,” they may not be able to do so if their clothes actually catch on fire. There are several essential elements from the learning process the educator must apply in every presentation to enhance transfer of learning: 1. The educator must present information so that all the learner’s senses are used. This means adding at least visual and kinesthetic components so the learner sees, hears, and experiences the new information. 2. The educator must explain the relevance and benefit of the new information at the beginning of the presentation and reemphasize them throughout the remainder of the presentation, when appropriate. The educator’s job is more than just presenting good information; it involves connecting with and, if necessary, changing the learner’s personal values about fire and life safety. This way means that the educator must overcome existing beliefs about safety, especially with learners who have extensive life experiences. This values change can be accomplished only when the learner clearly understands the need to change (motivation), a process that begins with understanding the relevance and benefit of the new information. 3. The educator must present information in small amounts, six or seven bits of information or one psychomotor skill, and must then apply the information. This process of “present—apply” ensures that no information is lost between short-term and long-term memory. It also helps ensure that transfer of learning occurs. 4. The educator must create strong links between the new information or skills and the learner’s current knowledge, skills, or experiences. This is a planned process by the educator and is never left to chance. If that link is not created, the information or skill will be lost from short-term memory and the learning process stalled. 5. The educator should minimize the stress in the learning environment. This is especially critical for younger children. The educator should always use positive behaviors, should avoid the use of “don’t,” and should never scare or frighten the learner, as this closes their minds to learning.
Lifelong Learning People learn from cradle to grave. How people learn, on the other hand, changes throughout life. The twin factors of “development stage” and age determine how people learn throughout
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their lives. Generally, people pass through six development stages, as outlined in Table 5.3.2.4 Aging happens automatically, whereas psychological development happens only when the person is ready and when environmental factors (such as family, friends, school, and work situation) are right.
Age and Learning The second factor that influences learning is age. Preschoolers, elementary school children, adolescents, adults, and seniors all learn very differently. In learning, age combines the influences of psychological/social/personal development with the effects of motor ability and communication skills. Being aware of how people learn at different ages is the first step in making sure that education programs and materials are “age appropriate.” Preschool Children. Children ages 3 to 5 grow and change more rapidly than any other fire safety audience. Some basic facts, though, will be true throughout the preschool years. 1. Children ages 3 to 5 will learn fire and burn safety the same way they learn everything else—by seeing and doing.5 What young children do will have a more lasting effect than what they see. For example, an adult will remember how to “stop, drop, and roll” after seeing a demonstration. A preschool child must practice before learning happens. 2. What young children see is more influential than what they hear. A child will watch an adult find a lighter, but will not remember the adult saying: “Always tell me when you find a lighter. Never touch a lighter.”
TABLE 5.3.2
3. Young children love repetition. Fire and life safety educators will need far fewer programs and activities for this group than for other audiences. 4. Young children have a very limited view of the world. Using the right approaches with this audience is critical, because the wrong approach may be dangerous. Children’s Television Workshop (the producers of Sesame Street) studied how preschoolers would interpret fire and burn safety messages on television. Their findings also apply to nontelevised programs. Their findings include6 1. Showing a dangerous activity, even while warning against it, is not recommended for preschoolers. Children respond more to what they see than to what they hear. 2. The extremely limited vocabulary of preschool children limits the fire and burn safety concepts that can be presented. “Hot” and “fire” will be understood, but “scald,” “avoid,” “prevent,” “appliance,” and “boil” are beyond preschoolers. 3. Young children have difficulty relating one event to another. “If/then” thinking or making choices (e.g., “If the door is hot, don’t open it” or “Use your second way out”) is simply more than many preschool children can do. 4. Young children view the world unpredictably. They may focus on one part of a program or story, but ignore the rest. It is difficult for them to link the beginning and end of even the simplest story. Preschoolers do not necessarily link a problem and its solution. Findings such as these have very practical implications for fire and life safety educators. For example, “All fire safety mes-
Developmental Stages and Implications for Education
Stage
Characteristics
Educational Implications
Stage 0, Blind trust
Develops only biologically; does not interact with surroundings
Too early for education
Stage 1, Focused on self
Responds out of fear; recognizes and begins to interact with surroundings; bases decisions on authority, obedience, and punishment
Wants to avoid the pain of burns; may fear punishment for fireplay
Stage 2, “Me and Thee”
Responds out of need for personal gain; will satisfy needs of others for personal gain; bases decisions on “What’s in it for me?”
Wants approval of others: for children, approval of fire fighters, teachers, and parents is important. Adults will seek approval of individuals who matter to them.
Stage 3, Group stage
Responds from a need for belonging and loyalty; accepts group rules as price for being part of the group; tries to meet group expectations
Responds to pressure from peers (whether children, adolescents, or adults) for fire safety; may respond to group pressure to be fearless
Stage 4, Group focus stage
Makes groups more abstract, does things “for the good of the order”; values social stability; accepts group rules for the good of other people
Responds to fire safety rules (such as bans on outdoor burning) and ordinances (such as smoke detector codes)
Stage 5, Interactive and independent stage
Regulates own behavior; negotiates for what the individual thinks is best
Will be fire safe only if it personally matters; may ignore rules that “don’t apply to me”
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sages should involve the two basic techniques by which preschoolers actually gain knowledge. By seeing an image, it is implanted; by doing, the action is learned. These two principles should guide fire safety messages for the preschool audience.”6 Clearly, special care is needed in teaching safety to preschool children. Rather than develop their own, fire and life safety educators may prefer to rely on programs and materials such as the Learn Not to Burn: Preschool Program,7 those available from Oklahoma State University, and the Sesame Street Fire Safety Resource Book.8 Elementary School Children. The elementary school years are marked by steady physical, mental, and emotional growth. Considering physical growth, for example, “There are some marvelous happenings going on in the body, such as the shedding and erupting of teeth, the body’s changing proportions. Along with the increase in height and weight, the internal organs—heart, kidneys, and liver—are increasing in their ability to function.”9 Children ages 5 to 11 are probably the most frequent audience for fire and life safety education programs. Two strong trends in elementary education relate directly to fire and burn prevention: (1) developmental learning and (2) comprehensive education. Fire and life safety educators may need to tailor their approach and techniques to conform to these educational trends in elementary schools. Developmental Learning.10 University of Chicago educator Robert Havighurst identifies nine major groups of “developmental tasks” for elementary school children. Several of these tasks relate directly to fire and burn safety. 1. Physical skills. Children become much more coordinated so that tasks that were impossible or difficult a short time ago—such as lighting a match—become possible or easy. 2. Self-attitudes. Children develop strong attitudes about themselves: their adequacy, personal hygiene and appearance, vulnerability, or their safety. 3. Social skills. By elementary school age, children learn to get along with others, to make friends. Courtesy and other rules (including safety behavior) become important to them. 4. Social roles. Boys and girls become more interested in gender differences. Children this age are curious about—and want to follow—what society perceives as masculine and feminine roles. 5. Academic skills. Elementary school children learn a fantastic array of academic skills. In the mid-elementary years, abstract learning begins; speed reading, spelling, cursive writing, and higher math skills follow. 6. Living concepts. Concepts of everyday living (such as social, work, and civic issues) are included here. 7. Values. With the development of a conscience, children learn to distinguish between good and bad, right and wrong. 8. Independence. Between the ages of 5 and 11, children realize that adults are imperfect. As children spend more time away from their home, peers become more important. 9. Social attitudes. Feelings about home, religion, government, and other groups develop.
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Fire and life safety programs that actually teach bigger areas, such as Havighurst’s developmental tasks have a far better chance of being taught in the classroom than a stand-alone fire safety effort. For example, 1. Fire and burn safety helps children develop positive selfattitudes. 2. A fire station tour teaches social skills (how the fire fighters live and work together), social roles (both men and women can be fire fighters), and living concepts (the fire service as a career), in addition to self-attitudes (learning about safety). Comprehensive Education. The education trend of the 1990s is toward comprehensive education and away from categorical education. Rather than being taught as a stand-alone subject, fire and burn safety can be taught as part of a larger safety program or as part of a comprehensive health education program. In many ways, fire and life safety education has been comprehensive education for many years. For example, for years fire departments have conducted babysitter programs that teach first aid and child care along with fire safety. Many fire safety educators include electrical safety, water safety, and citizen cardiopulmonary resuscitation (CPR) in their presentations. Many fire departments teach emergency response to hurricanes, earthquakes, or other natural disasters. The Phoenix Fire Department adopted the idea of comprehensive education when it developed the Urban Survival Program.11 In addition to fire and burn safety, the program’s 32 modules cover how to • • • • • • • • • • • • •
Be a safe pedestrian Understand firearm safety Practice transportation safety Practice basic electrical safety Practice water safety Identify poisons and harmful substances Protect your pet Understand desert survival Be a happy latchkey child Practice outdoor recreation safety Avoid confined spaces and dangerous workplaces Identify the need for CPR training Understand basic first aid
Adolescents.12 Knowing how adolescents develop and learn helps make the job of teaching them easier. [Adolescents] live in the present and seem reluctant, even fearful, of looking too far beyond next weekend. Taking precautions in advance or being too concerned about the possible dangers that could harm them are not considered very important by most young people. This may be in part because teenagers characteristically have an it-can’t-happen-to-me attitude, but the underlying reason may have more to do with appearing “babyish” or “nerdlike” to their friends than to any real sense of invulnerability.12
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Of all the characteristics of adolescence, fire and life safety educators especially need to understand their developmental tasks and how adolescents learn. Developmental Tasks. Adolescence is a bridge between childhood and adulthood. Becoming an adult is much more than going through puberty, learning how to drive, and deciding what to do after high school. Adolescence involves several developmental tasks that H. D. Thornburg listed in his 1975 book, Development in Adolescence. The tasks are to 1. 2. 3. 4. 5. 6. 7.
Develop conceptual thinking and problem-solving skills Form more mature relationships with peers of both sexes Achieve a masculine or feminine social role Prepare for marriage and family life Prepare for a career Acquire a set of ethics to guide behavior Develop civic competence and responsible community behavior
A major challenge for fire safety educators is to find ways to fit their message into the big picture of adolescent development. For example, a discussion about knowing who is pulling false alarms can be presented as ethics. The role of smoking in residential fire death can be taught in terms of responsibility toward others. How Adolescents Learn. Adolescents have their own distinct learning style, especially when it comes to learning behaviors and attitudes (rather than facts). Ways that adolescents learn include the following: 1. Direct experience. Although direct experience with a fire or burn must be avoided, adolescents can have indirect experience with a fire or burn through fire department “ridealong” programs, serving coffee and donuts at the fire scene, or by volunteering at a burn unit or burn camp. 2. Hypothetical projection. Adolescents might think about how a fire would destroy their clothes or stereo or about how a burn injury would change their appearance. 3. Role model emulation. This involves following the attitudes and actions of role models. For example, young adolescents will observe whether their heroes smoke and how they dispose of their smoking materials. 4. Instruction/demonstration. This technique is particularly effective in teaching skills, such as changing a smoke detector battery or CPR. 5. Rehearsal. Through simulation, adolescents practice their response to emergencies. 6. Teaching “best practice” to others. For example, showing younger adolescents the safe use of flammable liquids is a good test of how well the “teacher” can perform and gives a sense of competence. Adults.3 life.
Adults as students reflect the many roles they have in
They are parent, spouse, employer, employee, homeowner, renter, community worker, volunteer, child to
their parents, hero to their children, and emotional and financial provider. . . . They are expected to face the trials of the very young, the confusion of the teenager, the responsibility of adjusting to a changing world, and, somehow, balance their own desires and needs for relaxation and happiness. Adults appreciate the need for training and education for professional purposes. They also invest untold amounts of money and time in leisure activities. The task of the educator is to make fire safety just as worthy of their time, interest, and effort.13 When it comes to learning, adults are not simply “grownup children.” Instead, adults learn in specific ways. General principles of how adults learn include the following: 1. Adults can and do learn. The old saying “You can’t teach an old dog new tricks” does not apply to people. In fact, the ability to learn through comprehension and synthesis is far greater in adults than in children. Adults are especially skilled at informal learning (e.g., figuring out how to use a new VCR) and they also learn through “learning projects” (e.g., researching consumeroriented publications to find top-rated compact disk players, or mastering a new computer program). 2. Adults need to know why they must learn something. Establishing a need to know is the cornerstone of teaching adults. For the most part, adults feel that they need to know practical, nuts-and-bolts-type information. Being able to perform some task better is usually a strong motivator for the adult learner. 3. Adults need to be self-directing. Adults like to control their lives and make their own decisions. Similarly, adults like to control what and how they learn. In other words, adults are participatory—not passive—learners. Instructional methods that encourage participation include role play, debate, problem-solving discussion, demonstration, case discussion, coaching others, and skillspractice exercises. 4. Adult learners bring their total life experiences into the learning environment. Instructional methods that encourage participation take advantage of the experiences and knowledge of adult learners. However, adults may have already made up their minds about how fire safe they are— or want to be. Brainstorming exercises or group discussion may help keep minds open. 5. Adults are task-centered learners. Adults tend to center their learning around completing tasks, solving problems, or handling the way they live. Adults are, for example, much more interested in “writing better business letters” than in diagramming sentences, or in “doing my time sheet right” than in addition. 6. Adults have external and internal motivators to learn. External motivators to learning include objectives such as getting promoted, getting a raise, or finding a job with better working conditions. For the most part, external motivators are visible or measurable. Internal motivators are related to the hierarchy of needs. They are usually invisible and impossible to measure.
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Older Adults.14 Older adults, senior citizens, seniors, the elderly, elders—perhaps no other group has so many names. Older adults are an important audience for fire and life safety education for two reasons: (1) older adults are the fastest growing segment of the population, and (2) older adults have an unusually high risk of fire and burns. When planning fire and life safety programs for older adults, remember to 1. Allow plenty of time. Like anyone else, older adults may get anxious if time appears short. 2. Count on a talkative audience, and include a question-andanswer session. 3. Watch out for too much sunlight or glare in a room. 4. Darken the room, as possible, when using audiovisuals. 5. Keep the room at a steady, warm temperature. 6. Limit programs to 30 minutes. 7. Keep a low-pitched voice; speak slowly and clearly. 8. Use or design simple handouts. Avoid “busy” materials and fancy typography. Look for double-spaced materials. For more guidance on working with older adults, see Section 2, Chapter 5, “Reaching High-Risk Groups.”
Different Audiences Require Different Messages Fire safety messages even on a single subject will have very different forms and be taught quite differently to different age groups. For example, education messages on smoking and fire safety will change with the age of the audience (Table 5.3.3).
Positive Messages Are Effective There has been surprisingly little research about what kinds of messages motivate people to be firesafe. The research that does exist, though, gives clear direction to fire and life safety educators. A Study of Motivational Psychology Related to Fire Preventive Behavior in Children and Adults,15 commissioned by the NFPA and completed in 1974, states: There is ample evidence that fear and threats of violence, unless continually maintained, have little longterm positive effect on behavior. People tend to tune out or suppress information which is disturbing or contrary to their belief or inclinations. TABLE 5.3.3 Audience Age
Age and Message Message
Preschoolers
“Hot things hurt.” “Tell a grownup when you find matches or lighters.”
Elementary school children
“A match is a tool.” “Smokers need watchers.”
Adolescents, adults, and older adults
“Keep matches and lighters where children can’t reach them.”
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People under threat or tension will seek to reduce that tension. Some will seek new information in order to act effectively. Others will block out that which is creating the tension. Therefore, fire prevention information should be directed toward positive motives which already exist within the recipient of the message.15 The Motivational Psychology15 study shifted the tone of fire and life safety education from negative to positive. Messages such as “stop, drop, and roll” began replacing negative messages, such as “don’t run if your clothes catch fire.” The study also contributed to the development of the National Fire Protection Association’s Learn Not to Burn programs. That study challenged the conventionally held view of the public’s apathy about fire safety by concluding that people do care about fire safety, even though they might not know how to prevent or respond to fires. Based on interviews with people who had and had not experienced a fire, the study noted that “awareness of a fire as a powerful and potentially tragic force is not deeply buried in most people’s consciousness.” For both those who had and had not experienced a fire, “fire prevention awareness is increased when a person is responsible for others.” The Association’s research also included questions about how the public wanted fire safety information presented. The messages from the public were clear: Teach, don’t preach. Do not scare us to death, but make us think about fire safety. Give us information and if you can’t make it interesting, at least make it short.16 A 1991 study by the American Red Cross about whether people took action to prepare for natural disasters after seeing slides of disasters reached conclusions that were similar to the Strother study.15 Highlights from the American Red Cross report are as follows: 1. People remember more when they see disaster damage images in presentations. 2. Seeing disaster images does not encourage people to take action to get ready for a natural disaster. 3. Seeing disaster images discourages people from taking action. 4. After seeing disaster images, people were confused about what to do. 5. Avoiding or denying something unpleasant caused people not to take action, among those who saw disaster images. 6. “Just not getting around to it” caused people not to take action, among those who did not see the disaster images.17
EDUCATION TECHNIQUES FOR FIRE AND LIFE SAFETY EDUCATORS This part of the chapter will cover curriculum development, as well as two special topics: (1) questioning techniques and (2) managing the learning environment.
Curriculum Development There are seven basic steps to curriculum development: (1) write educational objectives, (2) develop a course outline, (3) develop a lesson plan, (4) select instructional methods, (5) choose
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instructional materials, (6) develop testing tools, and (7) allocate time. Write Educational Objectives. Educational objectives are sometimes called instructional objectives, behavioral objectives, or learning objectives. Regardless of what they are called, objectives answer the question: “What will happen as a result of the education program?” Increasingly, objectives focus on what people can do after education, not on what they will know after education. For example, “the student will show how to change the battery in a home smoke detector” rather than “the student will describe how to change the battery in a home smoke detector,” or “the student will appreciate the importance of changing the battery in a home smoke detector.” Objectives need to be realistic and measurable. Making objectives realistic is the responsibility of the educator. Making objectives measurable—so that students and programs can be evaluated—is also necessary. A standardized language and format for educational objectives help make them measurable. Objectives are often written in a standardized format, originally developed by Robert F. Mager in his landmark book, Preparing Instructional Objectives.18 This standardized format has three components: 1. The performance or behavior component of the objective describes what learners must be able to do to demonstrate what they have learned. 2. The condition component of the objective describes the conditions and resources available to the learner. 3. The standard or criterion component describes how well the action must be performed.19 Table 5.3.4 presents sample objectives for the affective, cognitive, and psychomotor domains of learning. Note that the affective objective deals with values (i.e., what is important). The cognitive objective covers understanding or knowledge. The psychomotor objective describes what the participant will be able to do. These three sample objectives are measurable. Develop a Course Outline. The course outline is developed to meet the educational objectives and may be as straightforward as determining the sequence for teaching several lessons. For these instances, fire safety educators teach a single audience a single lesson, and developing a course outline is not necessary. Develop a Lesson Plan. A series of steps, known as the “fivestep method of instruction,” comprises the act of “teaching.” The steps are (1) pretest, (2) preparation, (3) presentation, (4) application, and (5) evaluation. The steps of preparation, presentation, application, and evaluation will become part of the written lesson plan. A lesson plan is a step-by-step guide for presenting a lesson. It outlines the material to be taught and the procedures to be followed in teaching the fire safety lesson. The lesson plan helps ensure efficient use of time and accurate coverage of the subject matter. When several fire and life safety educators are involved, the lesson plan helps ensure uniform teaching and helps avoid overlapping instruction.
TABLE 5.3.4 Learning Domain
Educational Objectives and Domains of Sample Objective
Affective (values, feelings, or opinions)
At the conclusion of the 30-min presentation on residential fire safety (condition), the adult participant will be able to state two factors (standard or criterion) that illustrate the importance of testing and maintaining smoke detectors (performance or behavior).
Cognitive (knowledge or understanding)
At the conclusion of the 30-min presentation on residential fire safety (condition), the adult participant will be able to describe three key steps (standard or criterion) in testing and maintaining smoke detectors (performance or behavior).
Psychomotor (skills)
At the conclusion of the 30-min presentation on residential fire safety and given a smoke detector for demonstration purposes (condition), the adult participant will be able to change the smoke detector’s battery (performance or behavior) so that the detector alarms when tested (standard or criterion).
The lesson plan guides how the students and educator spend their class time, but does not dictate what will happen in class minute-by-minute. A lesson plan is not a script. A good lesson plan has some built-in flexibility—which is very valuable if, for example, the pretest reveals that the class already knows what the educator planned to teach, but does not understand what the educator expected the class to already know. Pretest. Pretests determine what the student/participant already knows (and doesn’t know) before the fire safety education program. Pretests allow the public fire educator to customize the presentation to meet the needs of the individual participants. In addition, pretests are useful tools for audience assessment. Some public fire educators use pretests as motivational tools. Pretests can also provide students with an overview of what they will learn. Finally, pretests can serve as learning aids by providing questions for practice quizzes and by guiding individual study and review. The most common type of pretest is the pencil-and-paper written test, although oral or performance tests are also used. Written or oral pretests are somewhat more convenient, simply because the entire class can take part in a written or oral pretest simultaneously. However, written or oral pretests do not assess psychomotor skills; for example, a score of 100 percent on a written pretest about home smoke detectors is no guarantee that the student can actually change the battery. Preparation. In everyday speech, the term “preparation” describes the necessary “homework” that educators do prior to a class or presentation. In educational use and this chapter, the
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term preparation describes how the educator prepares the student to learn. Preparation involves developing a desire in learners for the information being presented. The educator must establish the relevance of the information, that is, how the information applies to their everyday lives. The educator must also explain the benefit of the information to the learner, that is, how this information is going to help them in their everyday life. Both the relevance and benefit to the learner are closely tied to the learner’s development and personal experiences. Regardless of the age or experiences of the learner, the preparation step must be accomplished successfully for every audience. Presentation. Presentation is the actual delivery of instructional materials and ideas. This activity involves explaining information, using supplemental training aids, and demonstrating methods and techniques. Application. During the application step, students use or apply what the instructor has taught. Through application, students practice new techniques and skills. Whenever possible, each student should apply new knowledge by performing the task or solving problems. For example, students could demonstrate how to report a fire, perform the “stop, drop, and roll” technique, or test a smoke detector. The fire and life safety educator should supervise the application step closely, checking key points and correcting errors. Evaluation. During evaluation or testing, the fire and life safety educator finds out whether the educational objectives have been met. Seen another way, evaluation shows whether students can perform a task independently. Select Instructional Methods. Instructional methods and educational materials are the vehicles that carry the fire and life safety education message to the audience. Fire and life safety educators have many types of instructional methods available to them. The challenge is to select the most appropriate instructional method for the educational objective. Types of instructional methods include:
TABLE 5.3.5
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1. Lecture. In a lecture, the fire and life safety educator tells, talks, and explains. Today’s audiences are accustomed to the fast pace, as well as the visual and audio stimulation, of television, computers, and video games. Lectures can bore the audience. For this reason, fire and life safety educators should use the lecture format sparingly—and only for short periods. 2. Illustration. Through the illustration method of instruction, the fire and life safety educator shows the audience something, for example, how an overloaded electrical outlet looks. Unlike a demonstration, illustration does not show the audience how to perform a task. The illustration method relies heavily upon educational materials (such as drawings, posters, photos, slides, overhead transparencies, videotapes or films, models, and diagrams) and props. Illustration is especially helpful in combination with the lecture format. 3. Demonstration. The demonstration method teaches new skills. The educator actually does the task, usually explaining the task step-by-step. The audience may then practice the skill through drills. Safety is always a concern with demonstrations and drills, especially true when live fire is involved. Whenever the safety of a live demonstration is in question, use another method or material. 4. Discussion. Group discussion can be valuable, especially when the audience already has basic knowledge. Types of discussion are guided discussion (an exchange of ideas directed toward a goal), the conference method of discussion (in which the group directs its thinking toward solving a common problem), the case study (the group reviews real or hypothetical events), role-playing (in which the group acts out various scenarios), and brainstorming (where the objective is to identify as many ideas or approaches as possible). Matching Instructional Method and Educational Objective. Selecting the most appropriate instructional method to address a specific educational objective is a critical skill for fire and life safety educators; it is a matter of using the right tool for a particular task. Table 5.3.5 presents examples of matched instructional methods and educational objectives.
Matching Instructional Methods and Educational Objectives
Educational Domain
Sample Educational Objective
Effective Instructional Method
Affective (values, feelings, or opinions)
At the conclusion of the 30-min presentation on residential fire safety, the adult participant will be able to state two factors that illustrate the importance of testing and maintaining smoke detectors.
Group discussion, role play, and case study
Cognitive (knowledge or understanding)
At the conclusion of the 30-min presentation on residential fire safety, the adult participant will be able to describe three key steps in testing and maintaining smoke detectors.
Lecture, illustration, guided discussion, conference discussion, and case study
Psychomotor (skills)
At the conclusion of the 30-min presentation on residential fire safety and given a smoke detector for demonstration purposes, the adult participant will be able to change the smoke detector’s battery so that the detector alarms when tested.
Illustration, demonstration and drills, and role play
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Choose Instructional Materials.20 Educational materials are any material—printed matter, audiovisual materials, or props— that the educator uses to teach new fire and life safety skills to the audience. Through materials, the audience will actually see the effects of fire and burns, as well as the specific steps to take to avoid them. The materials literally give shape and color to the information and skills that the educators are teaching. Effective materials are important tools in getting and keeping the attention of the audience. As important as they are, materials alone do not make an education program. An education program has specific measurable objectives and evaluation instruments, uses instructional methods that match the objectives, and uses materials to reach the objectives and reinforce the methods. Materials are also important from the standpoint of resources. Next to the educator’s time, materials are the most expensive item in the budget. For these reasons, fire and life safety educators must use special care in selecting or creating their materials. Recognizing that materials are tools (rather than a program) and matching the material to the educational objective and to the audience are especially key to selecting educational materials. Kinds of Educational Materials. The three kinds of educational materials are (1) print matter, (2) audiovisual materials, and (3) props. 1. Print materials include brochures (also called flyers or folders), posters, fact sheets, coloring books, activity sheets, display or bulletin boards, educational card or board games, and pretests/posttests. 2. The variety of audiovisual materials is expanding and now includes films and filmstrips, videotapes and audiotapes, 35-mm slides and slide-tape combinations, overhead transparencies (sometimes called “vu-graphs”), and computer simulators. Flip charts and blackboards are also examples of audiovisual materials. 3. Props are artifacts or samples that the audience can see, touch, smell, or hear. A burned object from a home fire, a piece of melted glass, a manual fire alarm pull station, or a smoke detector could each be an effective prop during a fire and life safety presentation. Props are effective teaching aids because they make the subject real. Since they often involve several of the senses, props are an excellent memory aid. Evaluating Educational Materials. There are vast differences in the quality of fire and life safety educational materials. Whether purchased commercially, borrowed or adapted from another educator, or created in-house, all educational materials should be evaluated. At a minimum, educational materials should be evaluated before their first use and should be re-evaluated every year or so. The purpose of the follow-up evaluation is to make sure that what was acceptable initially still is. The techniques for evaluating materials range from asking a few simple questions to sophisticated testing. The amount of evaluation needed depends on (1) how much money the fire and life safety educator is investing, (2) how many people the material is expected to reach, and (3) how long the material will be used.
The kinds of evaluation techniques for educational materials can also vary greatly. For example, qualitative approaches are fairly subjective and rely on the fire and life safety educator’s experience, judgment, and interpretation. Quantitative approaches are likely to be more sophisticated and to involve formal testing. In evaluating educational materials, the key point is to evaluate all materials being considered in the same way. Qualitative Approaches. Evaluating educational materials can be as simple as reviewing the material against a standard checklist. Questions to ask during a review include the following: 1. How well does the material match the specific educational objectives of the fire and life safety program? 2. Is the material technically accurate? Is the material produced by a reputable organization? 3. Is the information clearly understood by members of the potential audience? Answering this question can range from asking several members of the audience to describe or demonstrate skills that the material is trying to teach, to more elaborate testing. 4. Is the material age appropriate? With 3- to 4-year-old children, for example, are stories or activities limited to the 5-minute typical attention span for that age group? For guidance in determining how age-appropriate material is, see Developmentally Appropriate Practice in Early Childhood Programs: Serving Children from Birth Through Age Eight.21 5. Is the material free of bias? Does the material reflect how people in the audience really live and work? The only way to make sure that material is bias-free is to invite (and accept) comments from representative members of the potential audience. These questions essentially call for “yes” or “no” responses. The Pan-Educational Institute has developed a more sophisticated approach to evaluating materials as part of its Practical Criteria and Instruments for Selecting and Implementing Sound Fire and Burn Education Programs in School and Community.22 The package includes worksheets for assessing posters and stand-alone print visuals, written informational materials (brochures, stand-alone handbooks, storybooks, coloring books, and workbooks/worksheets), and audiovisual materials (media campaigns, public service announcements, and audiovisual presentations). When the scoring is done, a material is found to fit one of five categories: (1) limited quality, (2) below average quality, (3) medium quality, (4) high quality, or (5) comprehensive high quality. Quantitative Approaches. Reading ease is a major consideration in selecting written fire and life safety education materials. A seventh to eighth grade reading level is typical for adults in the United States. Daily newspapers are often written at about that reading level. Several readability indexes measure how easy a passage is to read. Commonly used indexes are a passive sentence index (a simple percentage of passive sentences within a passage), Flesch Reading Ease/Flesch Grade-Level Index, and the Gunning Fog Index. The Flesch Index is based on a 100-word passage of the written material and counts the average number of words per
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sentence and the average number of syllables. With the Flesch Index, 17 words per sentence and 147 syllables per 100 words is “standard” reading ease. The Gunning Fog Index, on the other hand, combines the average sentence length and the number of difficult words (three or more syllables). Curriculum specialists with local school departments, or the education and journalism departments of universities, can help fire and life safety educators use these or other readability indexes. These indexes can be used manually and are included in some word-processing programs. Whether the indexes are used manually or through the word processor, the important point is to check whether sample materials are harder or easier to read than some standard that reflects the audience. A highly precise test is not necessary, so long as the fire and life safety educator knows whether written materials are “in the ballpark” for readability. Testing Materials. In some cases, fire and life safety educators may need to test materials before going into full production. Questions to ask when deciding to test materials include the following: 1. Could someone get hurt if the educational message is misunderstood? 2. How widely will the material be distributed? 3. How difficult or expensive will it be to change the material once it is produced? After considering questions such as these, the Learn Not to Burn Foundation decided to test a planned television public service announcement (PSA). The results are published in PreProduction Evaluation of the “Tell a Grown-Up to Put It Away” Public Service Announcement for 3–6 Year Olds.23 In that test, 50 children ages 3 to 6 saw the preproduction version of a 30second PSA twice. The children were then interviewed, one at a time, after each viewing to determine understanding. The PSA was found to be ineffective with the target audience. The test results influenced the Learn Not to Burn Foundation’s decision not to produce the PSA. The Learn Not to Burn Foundation experience offers some lessons for all fire and life safety educators. The preproduction test had a set interview procedure and questions—so the results compared “apples and apples.” The test evaluated how well the target audience responded; for example, if only middle-income children had been in the study, the results would have been different. Perhaps most important, the material was tested when changes were still possible. Create or Purchase Educational Materials? Many fire and life safety educators like to prepare their own educational materials, rather than buy them (from a business or nonprofit organization) or adopt what other educators have already created. The interest in developing materials often is related to saving money (“Those other materials are too expensive for me”) or the desire to give materials a “local flavor.” Before deciding to create their own materials, fire and life safety educators can use the following as a checklist: 1. How much will it really cost to develop materials (including the cost of time spent)? 2. How important is “local flavor”? How can it be added at the lowest possible cost?
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3. What is the motivation to create the materials? Are locally created materials really needed and cost-effective? Or does the educator just prefer to create materials? 4. Does the fire and life safety educator have the technical knowledge, experience, and equipment to create materials? Selecting Audiovisual Materials. Audiovisual materials range from the simple—flip charts, 35-mm slides, and overhead transparencies—to the sophisticated—films and filmstrips, videotapes and audiotapes, slide-tape combinations, and computer simulators. Flip charts, 35-mm slides, and overhead transparencies can be very effective audiovisual educational materials and can be created in-house. The key points are: (1) limit the text, (2) have effective visuals in audiovisual materials, and (3) keep the visual image as simple as possible. Large-size or projected words are simply words. Flip Charts. Flip charts are often used to record ideas from meetings and can also be used as audiovisual educational materials. Flip charts are inexpensive, easy-to-change, and effective with small groups. Although the paper is always white, marking pens come in a wide variety of colors. Flip charts can be reused a few times but will need to be replaced when they get torn, rumpled, or soiled. 35-mm Slides. 35-mm slides are a very popular medium for do-it-yourself audiovisuals. They are far superior to flip charts in illustrating concepts (e.g., the extensive damage caused by a home fire), emotions (e.g., the face of a fire fighter after a rescue), and objects (e.g., the parts of a smoke detector). Personal computers have vastly improved the quality of text slides—making slides of transfer letters obsolete. Slides are also easy to rearrange into different presentations, are effective with large groups, and are more durable than flip charts or overhead transparencies. There are, though, several disadvantages with slides. The lights must be down or off, making eye contact with the audience difficult or impossible. Once the presentation has started, the flexibility to change is gone. The fan on the slide projector may be noisy. Overhead Transparencies. “Overheads” are among the most popular teaching aids of all time—for good reason. They are inexpensive and easy to make, are durable, and can be used in rooms ranging in size from a classroom to an auditorium. They show text and line art to good advantage. The user can mark on them to underscore a point during a presentation. The lights can be on full or almost full. Overheads can be rearranged for use in several presentations. Like flip charts and 35-mm slides, overhead transparencies do have some disadvantages. Photographs do not reproduce particularly well on transparencies. Like the slide projector, the overhead transparency projector fan may be noisy. Digital Slide Shows. Digital slide shows are now commonly used instead of 35-mm slides and overhead transparencies. Digital shows are created on a computer using presentation software. The show can be saved to disk and taken to a remote site
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for a presentation. A presentation does require a digital projector and a computer, which may limit its use. However, as digital technology expands and becomes more cost-effective, the use of digital slide shows will increase. Develop Testing Tools. Testing tools can be pencil-and-paper tests or nonwritten tests, such as practical skills tests. Some fire and life safety materials include testing instruments. Local schools may develop testing tools or help fire and life safety educators develop them. Section 5, Chapter 6, “Applying Evaluation Techniques to Risk Watch®, covers the analysis of test results. Allocate Time. A key part of developing a lesson plan is deciding how much time to spend on various subjects. A basic rule of thumb is to spend time on topics and drills that support the educational objective. Topics and drills that do not support the educational objective should receive little (if any) time in the lesson plan.
Questioning Techniques24 Questioning is an extremely effective educational technique. Questions encourage thinking, the exchange of ideas, and the molding of opinions, attitudes, and values. As a result, what the fire and life safety educator asks the audience may be as important as what the educator tells the audience. Effective questions • Are “open-ended” or require more than a “yes” or “no” answer • Do not suggest the answer • Seek information, but do not make the audience feel uninformed There are four kinds of questions: 1. Direct questions are aimed at one person in the audience. Because direct questions can intimidate the audience, they are not often used with adults. 2. Overhead questions are aimed at the whole group, and anyone is free to respond. Because these questions are particularly helpful in starting thinking or in bringing out ideas and opinions, they are frequently part of a case study or brainstorming discussion. 3. Rhetorical questions are directed at the entire group, but an answer is not expected. A rhetorical question can be an effective “attention-getter.” For example, a fire and life safety educator might open a presentation by saying, “What are the most important things that you and your family can do to protect yourselves from a home fire? By the end of this presentation, you will know how to answer that question.” 4. Relay questions are those that the audience asks, and the educator sends back to the audience. Relay questions are a good technique for opening up discussion. Relay questions should not be used to avoid a question that the educator cannot answer or to force the audience to guess about facts or techniques. It is important to note that the use of questions may be limited with younger children. Preschool children may not understand
the meaning of a “question” and may answer the question with a story. Also, the effective use of questions requires the learner to have some experiences from which to answer the question. This requires the educator to thoughtfully plan his/her questions based on the topic, the developmental stage of the audience, and the experiences of that audience.
Managing the Learning Environment The term learning environment refers to the physical facilities where the learning will take place. The learning environment supports everything that the educator does in the classroom. For this reason, managing the physical learning environment is as important as selecting the best instructional method or educational material. Individual factors that make up the learning environment include the room size, temperature, the level of light, ventilation, background noise, acoustics, the comfort of chairs and tables, and the physical arrangement of the room. Practiced educators inspect the room before arriving for a presentation. It may be possible to move the program to another room or to correct what is wrong with the room. For example, removing extra chairs and rearranging chairs into a circle can make a huge room feel smaller. Videos or films can be shown in rooms with uncurtained windows—if the screen or monitor is placed so that the windows are behind the audience. Rooms can be arranged in several ways, depending on the size of the group and whether or not tables are used. The choice of a room arrangement lies in satisfying three criteria: 1. Can everyone in the audience see and hear the educator and audiovisual materials? 2. Can everyone in the audience see and hear each other? 3. Does the arrangement place as many people as possible as close to the educator as possible? When tables are used for small groups, three common arrangements are (1) a U-shaped setup, (2) a hollow square, and (3) a conference table. The U-shaped arrangement offers eye contact between the educator and audience, as well as among the audience. The fire and life safety educator is able to move around the open U. All participants are able to see a screen or video monitor placed behind the educator’s table. The U-shape can either be flat or long. The flat U-shape lets more members of the audience be closer to the educator and audiovisual material (Figure 5.3.2).
FIGURE 5.3.2
Examples of U-Shaped Arrangements
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FIGURE 5.3.3 Examples of the Hollow Square (left) and Conference Table (right) Arrangements (b) (a)
The hollow square is very similar to the U-shaped room setup. Participants may feel farther away from each other, even though the distance is the same as the U-shaped arrangement. A conference table setup is essentially a solid U-shaped arrangement. This arrangement is more commonly used for meetings but may be used for a class (Figure 5.3.3). For larger groups that need tables, several classroom styles are available. The traditional classroom style setup is the most restrictive and provides little eye contact among participants. The chevron (sometimes called herringbone) or fan-style classroom setups place more members of the audience closer to the educator—and let participants see each other (Figure 5.3.4). The most common way to arrange chairs without tables is the amphitheater or auditorium style. Rearranging the chairs into a slight semicircle provides for better eye contact between the educator and the audience (and among members of the audience). The semicircle also improves the audience’s line of sight to a screen or video monitor (Figure 5.3.5).
(c)
FIGURE 5.3.4 (a) Traditional Classroom Setup; (b) Chevron Arrangement; (c) Fan-Style Classroom. (Note that these same seating arrangements can be used without tables.)
BIBLIOGRAPHY References Cited 1. NFPA 1035, Standard for Professional Qualifications for Public Fire and Life Safety Educator, National Fire Protection Association, Quincy, MA, 2000. 2. Lambert, C., Secrets of a Successful Trainer: A Simplified Guide for Survival, Wiley, New York, 1986. 3. Schunk, D. H., Learning Theories: An Educational Perspective. Macmillan, NY, 1991, pp. 144–160. 4. The National Fire Academy’s course, Developing Fire and Life Safety Strategies, covers the concept of life stages in some detail. 5. For more information on teaching methods for preschool children, see Smalley, T., “Preschool Children,” Fire Safety Educator’s Handbook, National Fire Protection Association, Quincy, MA, 1983, pp. 43–51. 6. Fire Safety on Television for Preschoolers, prepared by the Children’s Television Workshop, under a grant from the U.S. Fire Administration/Federal Emergency Management Agency, FA2A, July 1980; and Sesame Street Fire Safety Resource Book, prepared by the Children’s Television Workshop, under a grant from the U.S. Fire Administration/Federal Emergency Management Agency, Emmitsburg, MD, 1982. 7. Gamache, S., and Powell, P., The Learn Not to Burn® Preschool Program, National Fire Protection Association, Quincy, MA, 1991.
(a)
(b)
FIGURE 5.3.5 (a) Amphitheater or Auditorium; (b) Semicircle 8. Sesame Street Fire Safety Resource Book, Children’s Education Services, Children’s Television Workshop, One Lincoln Plaza, Dept. FS, New York, NY 10023. [Telephone (212) 595-3456.] 9. Gross, C., “Elementary School Children,” Fire Safety Educator’s Handbook, National Fire Protection Association, Quincy, MA, 1983, p. 56. 10. This material is largely based on C. Gross’s chapter, “Elementary School Children,” in Fire Safety Educator’s Handbook, National Fire Protection Association, Quincy, MA, 1983, p. 56.
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11. Pedrotti, D., Urban Survival Program, Phoenix Fire Department, Community Services Division, 520 West Van Buren, Phoenix, AZ 85003, 1991. 12. This material is largely based on J. Sowers’ chapter, “Adolescents,” in Fire Safety Educator’s Handbook, National Fire Protection Association, Quincy, MA, 1983. 13. Gratton, J., “Adults,” Fire Safety Educator’s Handbook, National Fire Protection Association, Quincy, MA, 1983, p. 85. 14. For more information, see R. Lightman’s chapter, “Elderly,” in the Fire Safety Educator’s Handbook, National Fire Protection Association, Quincy, MA, 1983. 15. Strother, R., A Study of Motivational Psychology Related to Fire Preventive Behavior in Children and Adults, National Fire Protection Association, Quincy, MA, 1974. 16. “Learn Not to Burn®: A Decade of Progress,” Fire Journal, March 1985, p. 8. 17. Lopes, R., “Public Perception of Disaster Preparedness Presentation Using Disaster Damage Images,” NFPA Education Section Newsletter, Fall/Winter 1992. 18. Mager, R., Preparing Instructional Objectives, rev. 2nd ed., David S. Lake Publishers, Belmont, CA, 1984. 19. See the Association Education Handbook, p. 30, G. H. Tecker (Ed.), American Society of Association Executives, Washington, DC, 1984. 20. For more information on selecting, creating, and using educational materials, see Public Fire and Life Safety Educator, International Fire Service Training Association, Stillwater, OK, 1997. 21. Bredenkamp, S., Developmentally Appropriate Practice in Early Childhood Programs: Serving Children from Birth through Age Eight, National Association for the Education of Young Children, Washington, DC, 1989. 22. Practical Criteria and Instruments for Selecting and Implementing Sound Fire and Burn Education Programs in School and Community. This document is informally known as “The Stillwater Standard.” The package is available for $19.95 from the PanEducational Institute, 10922 Winner Road, P.O. Box 520347, Independence, MO 64052. [Telephone (816) 461-0201; Fax (816) 461-0210] 23. Pretsfelder, G., Ed.M., Pre-Production Evaluation of the “Tell a Grown-Up to Put It Away” Public Service Announcement for 3 to 6 Year Olds, for the Learn Not to Burn® Foundation, National Fire Protection Association, Quincy, MA, Dec. 1990. 24. Adapted from M. Hunter, Mastery Teaching, TIP Publications, El Segundo, CA, 1982, pp. 85–90.
Additional Readings Comer, D., Developing Safety Skills with the Young Child, Delmar, 1987. DeWitt, W. E., “Teaching Fire-Related Failure Analysis in a PostGraduate Course for Engineers and Technologists,” Proceedings of the 7th International INTERFLAM Conference, INTERFLAM ’96, Cambridge, UK, March 26–28, 1996, C. A. Franks and S. Grayson (Eds.), Intersciences Communications Ltd, London, UK, 1996, pp. 989–993. “Directory of National Community Volunteer Fire Prevention Program. Community-Based Fire Prevention Education Initiatives, 1984–1992,” National Criminal Justice Association, Washington, DC, Federal Emergency Management Agency, Emmitsburg, MD, FA-92, Apr. 1993, 130 pages. Emery, A. F., and Abrous, A., “Use of Finite Elements and PCs in Teaching Heat Transfer,” Proceedings of the National Heat Transfer Conference, 1989, Numerical Heat Transfer with Personal Computers and Supercomputing, Philadelphia, PA, August 6–9, 1989, R. K. Shah (Ed.), ASME, New York, HTD-Vol. 110, 1989, pp. 147–151. “Fire Departments and Communities: Partners in Prevention,” Fire Engineering, Vol. 148, No. 6, 1995, pp. 101–110. Gagné, R. M., The Conditions of Learning, Harcourt Brace, NY, 1996.
Hall, J. R., Jr., “Children Playing With Fire: U. S. Experience, 1980–1993,” National Fire Protection Assoc., Quincy, MA, Aug. 1995. Henricsson, L., “Measures for the Safety of the Lives of the Elderly and the Physically Handicapped,” Firesafety Frontier ’94, International Fire Conference and Exhibition in Tokyo, Creating a Safe Tomorrow, October 18–22, 1107-112, Tokyo, Japan, 1994, pp. 281–286. Jones, R. T., and Randall, J., “Rehearsal—Plus: Coping with Fire Emergencies and Reducing Fire-Related Fears,” Fire Technology, Vol. 31, No. 4, 1994, pp. 432–444. Kakegawa, S., et al., “Evaluation of Fire Safety Measures in Care Facilities for the Elderly by Simulating Evacuation Behavior,” Proceedings of the 4th International Symposium for Fire Safety Science, International Association for Fire Safety Science, Boston, MA, 1994, pp. 645–656. Knowles, M. S., “Adult Learning,” The Training and Development Handbook, 3rd ed., McGraw-Hill, 1987. Lambert, C., Secrets of a Successful Trainer: A Simplified Guide for Survival, Wiley, New York, NY, 1986. “Let’s Retire Fire. A Fire Safety Program for Older Americans,” Federal Emergency Management Agency, Washington, DC, 1990. Lichty, T., Design Principles for Desktop Publishers, Scott, Foresman, Glenview, IL, 1989. Louderback, J., “Learning to Survive in the Bronx,” Fire International, No. 163, July 1998, pp. 21–22. “Making Sense of the Future. A Position Paper on the Role of Technology in Science, Mathematics, and Computing Education,” Office of Educational Research and Improvement (ED), Washington, DC, January 1998. Mata, A. P., “Low-Tech Teaching in a High-Tech World,” Fire Engineering, Vol. 154, No. 19, 2001, pp. 53–54. Millsap, S., “Planning for Disasters in Your Community,” Fire Engineering, Vol. 147, No. 12, 1994, pp. 28–33. O’Rourke, J. J., “Woodstock ’94: Fire Planning for Large Public Events. Part 1: Fire Safety Preparations,” Fire Engineering, Vol. 148, No. 1, 1995, pp. 74–78 Parker, R. C., The Aldus Guide to Basic Design (the developers of PageMaker® desktop publishing software), Aldus Corporation, Seattle, WA, 1987. Parker, R. C., Looking Good in Print, Ventana Press, Chapel Hill, NC, 1988. Peoples, D., Presentations Plus, Wiley, New York, NY, 1988. Perrault, M. E., “Home Security and Fire Safety Meeting Report, August 14–15, 1994, Quincy, Massachusetts,” National Fire Protection Association, Quincy, MA, Meeting Report, December 1994. Randall, J., and Jones, R. T., “Teaching Children Fire Safety Skills,” Fire Technology, Vol. 29, No. 3, 1993, pp. 268–280. Rusbridge, S. J., “Peoples Awareness of Fire,” University of Canterbury, Christchurch, New Zealand, Fire Engineering Research Report 99/14, June 1998. Savia, S. A., “Supervisory Techniques Are for Volunteers, Too,” Fire Engineering, Vol. 153, No. 12, 2000, p. 8. Schappert, R. J., III, “University of Maryland: Maryland Fire and Rescue Institute. A Showcase in Teaching Excellence,” Firehouse, Vol. 18, No. 7, 1993, pp. 94–97. Torvi, D., “Teaching Fire Science and Fire Protection Engineering to Building Engineering Students,” Proceedings of the inFIRE (international network for Fire Information and Reference Exchange) Conference 2000, Fire Information in the New Millennium: Challenges and Opportunities, Ottawa, Canada, May 9–12, 2000, pp. 1–10. Walker, B. L., et al., “Short-Term Effects of a Fire Safety Education Program for the Elderly,” Fire Technology, Vol. 28, No. 2, 1992, pp. 134–162. Walker, B. L., “The Effects of a Burn Prevention Program on Child-Care Providers,” Fire Technology, Vol. 31, No. 3, 1995, pp. 244–264. Wendt, G. A., “Using Adult Learning Techniques in Instruction,” Fire Engineering, Vol. 152, No. 5, 1999, p. 30. “1994 Learn Not to Burn Champions,” NFPA Journal, Vol. 88, No. 3, 1994, pp. 67–69.
CHAPTER 4
SECTION 5
Reaching High-Risk Groups Sharon Gamache
less likely to have received or understand information about fire safety.
Characteristics of This Group Special Fire Risk Characteristics. The fire deaths of preschool children are dominated by fires started by children playing with fire, usually matches or lighters. Children playing with matches and lighters and other fire sources started roughly 91,800 fires per year from 1993 through 1997, which resulted in an estimated 338 deaths and 2624 injuries per year. Preschool children are the most frequent victims of fires started by children playing with matches or lighters.4 Roughly two of every five preschool children killed in home fires are killed by a fire started by a child—the victim or a sibling or playmate—playing with fire. It is not unusual for the firestarter to be a different child, more often a slightly older child. How Preschool Children Learn. An instructive video, From Theories to Play: Providing a “Creative” Developmentally Supportive Environment for Young Children,5 reviews characteristics 80
Civilian fire deaths per million population
C
ertain groups are disproportionately affected by fires. Even though fire deaths in the United States have dropped substantially over the past century and fairly steadily over the past several decades (e.g., from 5685 in 1977 to 2895 in 1999), and even though progress in fire safety has been made across the board, the same groups continue to incur disproportionate rates of fire deaths and deaths from other unintentional injuries.1 In particular, preschool children, older adults, and disadvantaged (by income or education) populations are at highest risk of fire deaths in the United States. The death rate from fires and burns of children 5 years old and younger is roughly twice the rate of the population at large, as is the death rate of adults 65 and older. Adults 75 and older have three times the risk, and those 85 and older have four and a half times the risk (Figure 5.4.1). The two high-risk groups—ages 5 and under and ages 65 and over—have been increasing their domination of home fire deaths. Together they accounted for 38.9 percent of home fire deaths in 1980 and for 40.5 percent in 1998.2 Statistics show that high fire death rates are often associated with key measures of socioeconomic disadvantage, starting with poverty and the lack of a high school education among adults.3 For fire departments to be effective in continuing to reduce deaths, injuries, and fires in their communities, they will need to be sure that their programs at least include and at best focus on those at greatest risk.
PRESCHOOL CHILDREN Children age 5 and younger have a fire death rate more than twice the national average. Each year in the United States until 1995, 700 children age 5 and under died in fires in the home each year. Beginning in 1995, that death toll has dropped sharply and was just under 400 in 1998. Representing more than 20 percent of the home fire deaths from 1994 to 1998, this age group still had a fire risk that was double the national average.2 Preschool-age children are less able than older children to control their environments, are more dependent on adults, and are
70 60.4
60 50 40 32.4
All ages average = 13.2 30
26.2 19.4
20 13.2
10.9
10
5.6
7.6
9.8
0
Sharon Gamache is executive director of the NFPA Center for HighRisk Outreach. She develops and implements programs for those at highest risk to fire and burns. She was formerly manager of community safety programs at the National Safety Council and was a community organizer in St. Paul and Chicago.
5 and 6–9 10–19 20–29 30–49 50–64 65–74 75–84 85 under and Age over
FIGURE 5.4.1 Civilian Fire Rates by Age Group, 1994–1998 Annual Average (Source: NFIRS, NFPA survey, and U.S. Census Bureau 1996 population figures)
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5–46 SECTION 5 ■ Fire and Life Safety Education
of play in an environment for young children. This video can help fire safety instructors with developing or using appropriate safety activities with young children. The following are some general principles discussed in the video: 1. Children need a variety of play environments. They need outdoor and indoor play and a variety of play materials that support sensory/motor, dramatic, and constructive play. Construction materials can range from fluid, such as sand and paints, to more complex materials, such as puzzles or interlocking building blocks. The Learn Not to Burn® Preschool Program,6 created by NFPA’s Learn Not to Burn Foundation (now the NFPA Center for High-Risk Outreach), adopted this general developmental insight into one of its basic approaches when teaching young children: “Don’t scare children. Teach them what to do.” Young children learn in several ways. Lessons to preschoolers should use a variety of activities to get behaviors across. Children learn best when they can use all the senses—through what they see, hear, smell, taste, and touch, as well as how they move. 2. Activities should provide opportunities for children to interact with adults and other children in a language-rich environment. Children should be provided experiences with music, puppets, stories, and dramatic play to enhance language development. 3. Children like to create or recreate dramatic activities in the miniature, using items, such as little characters, building blocks, puppets, and so on, or with activities, such as acting out family scenes with costumes and props. 4. Children at this age have difficulty waiting for turns. Games with rules are inappropriate at this time, as children of this age do not understand win and lose. In a Federal Emergency Management Agency (FEMA) investigation on how children respond to disasters, Children’s Television Workshop (CTW) found that young children ages 3 and 4 look to adults to help interpret their world, whereas children ages 5 through 7 begin to recognize cause and effect in relation to the disaster. This natural dependence on adults is also an opportunity to introduce new adults, such as fire fighters, into the child’s environment, allowing those new adults to assist in interpretation in their special area of expertise, fire safety.7 As noted in Section 5, Chapter 1, “Fire and Life Safety Education: A Measure of Fire Department Excellence,” in this handbook, frightening images do not motivate effective learning of fire safe behaviors in any age group. Such images typically inspire efforts to flee the images, either physically or otherwise, for example, by looking away. The inadvisability of using frightening images is at least as true for young children, which is why another principle of the Learn Not to Burn Preschool Program is “Don’t Scare Children: Teach Them What to Do.” The Learn Not to Burn Preschool Program teaches fire safety awareness and skills in a nonthreatening way. Caregivers do not scare children by showing them burned toys or pictures of burned people. Lessons need to be repeated for reinforcement. Participatory activities do not seem so repetitive even when they (use-
fully, necessarily) are. And embedding lessons in songs can also make repetition more acceptable, and even enjoyable. The Learn Not to Burn Preschool Program’s English language version makes extensive use of songs as aids to learning such behaviors as crawling low under smoke. On your hands and your knees like a dog in a chase, Crawl low under smoke and leave that place; Crawl low under smoke where you can breathe; Crawl low under smoke and leave.
Legislation and Engineering Since children playing with fire represents the single greatest source of their above-average fire risk, it is appropriate that legislative and engineering strategies have focused on this hazard. In 1994 the U.S. Consumer Product Safety Commission (CPSC) enacted legislation making it a requirement that all disposable and some novelty cigarette lighters be child resistant. This legislation specified that 85 percent of children age 2½ years to 4½ years tested must not be able to activate these lighters. Canada enacted its own legislation in 1995, making child-resistant lighters mandatory. The U.S. standard has resulted in a reduction of fires and property loss and, more importantly, of deaths and injuries of children age 5 and younger playing with matches and lighters. CPSC estimated that 70 deaths occurred in residential structure fires caused by children younger than age 5 playing with cigarette lighters in 1998. In the absence of the standard, there would have been an estimated 200 deaths. CPSC reports that the difference of 130 deaths represents deaths prevented during 1998 because of the standard.8 An estimated 480 injuries occurred in residential structure fires caused by children younger than age 5 playing with cigarette lighters in 1998. In the absence of the standard, CPSC estimates that 1430 injuries would have occurred. Again, the difference of 950 represents injuries prevented during 1998 that CPSC attributes to the standard.8 However, a significant number of fires that kill young children are begun by matches.5 It is, therefore, extremely important to get the message to adults and caretakers to keep all lighters and matches away from children.
Reaching Young Children through Others Because preschool children need and rely on adults to learn, a strategy of reaching these high-risk children through adults is not just promising—it is essential. An adult component must be included in a comprehensive safety education program for preschoolers. The NFPA Learn Not to Burn Preschool Program has three letters for educators to send home to parents or caregivers at different times during the course that teach eight key behaviors to young children. 1. The introductory letter tells parents what behaviors the children are learning in school but reminds parents that, although children are learning these fire safety behaviors, fire safety is still the parents’ responsibility. It emphasizes four
CHAPTER 4
points for parents; for example, keep matches and lighters out of the reach of children, preferably in a locked cabinet. 2. A second letter is sent home when the match and lighter lesson is taught. This letter emphasizes that children must be taught to stay away from matches and lighters and to tell a grown-up when they see matches and lighters. It then repeats the information to parents to keep matches and lighters away from children. 3. The third letter describes how to design and practice a fire escape plan and emphasizes the importance of having smoke alarms in the home. Drawings or art activities from preschool programs can also be sent home to parents or caregivers to reinforce understanding of what the children are learning in school. Some parents may not always read information sent home, but some of these are more likely to respond to a video shown at parent meetings or at home. The NFPA Center for High-Risk Outreach produced A Lighter Is Not a Toy™ video9 for the parents of young children. The eight-minute video depicts several scenes of preschool children interacting with their parents or grandparents. It suggests actions that can prevent serious burns and deaths from fires started by children who have access to matches and lighters. Programs to reach preschool children through their parents or other caregivers can be targeted through child care centers, public housing developments, foster care training, Women, Infants, and Children’s (WIC) programs, parenting skill programs, and babysitting classes. Reaching young children in child care settings directly is probably the easiest way to deliver a program. There are child care centers, preschools, and prekindergarten programs in public school systems. Since day care providers are not necessarily linked under one organization, it is often necessary to contact several groups before identifying all day care providers in a community. Many states have programs. These organizations often provide training and are a good resource when working at the state level. In Canada, the Ministry of Social Services and various provincial child care associations help coordinate activities.
Teaching Young Children Fire safety materials must be appropriate for preschoolers. This means that they cannot be simply adapted from materials used to teach children in elementary schools. The developmental limitations of young children mean that fire safety must be taught in an environment providing interaction with adults. This is necessary because, in the absence of a strong adult role, lessons transmitted by television, for example, are likely to be misunderstood, perhaps dangerously so, or simply not understood at all. This conclusion has been reached repeatedly in the history of design of fire safety education for children. In 1979 the U.S. Fire Administration (USFA) asked Children’s Television Workshop (CTW) to explore ways of including burn prevention and fire safety messages in its Sesame Street® programming. Initial research recommended against this course of action.10 Because of the one-way nature of viewing, television presents a difficult challenge especially with regard to
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such serious and important topics. For example, we need to be concerned that if a child viewed (the program) alone, questions could not be answered or clarified by an adult and a dangerous misunderstanding could occur.10 Resulting from this initial research was the USFA-funded Sesame Street fire safety curriculum, one of the first available fire safety programs for preschool children. In 1990 the Learn Not to Burn Foundation concluded that public service advertising to young children with messages on matches and lighters would most likely be ineffective.11 The foundation tested 50 children in day care settings with a video prototype and found that the youngest children (3 and 4 years old) did not understand the safety message well enough to risk putting the public service announcement on television; that is, mere exposure to the message and pictures of matches and lighters without comprehension could have the opposite effect on children, possibly causing them to have more of an interest in playing with or exploring matches and lighters. Because they do not understand “if-then” situations, young children need to act out different scenarios. For example, if preschoolers only learn the behavior “stop, drop, and roll,” they are likely to do that behavior for every fire situation (e.g., when there is fire and smoke in the room; if they burn themselves; etc.). In Follow the Footsteps to Fire Safety, A Prevention Program for Young Children,12 one lesson is dedicated to the topic of “good fires/bad fires.” This lesson introduces the concept of fire and lays the groundwork for the next lesson, which teaches match and lighter safety. The Learn Not to Burn Preschool Program, in English, Spanish, and French versions, has reached more than 200,000 child care centers and schools in the United States, Canada, and Latin America. Much of its success has been in the easy-to-use lessons offering a variety of activities. Another important lesson to teach children is to go to a fire fighter if they are trapped in a fire situation and cannot escape. Messages children might learn are to yell out to the fire fighter and not hide from the fire fighter even though the fire fighter may look or sound different. The Play Safe! Be Safe! Children’s Fire Safety Education Program, for ages 3 to 5,13 includes in its fire safety video a component that introduces the friendly fire fighter and shows the fire fighter acting in different teaching situations, dressing, and explaining the gear. Presentations by fire fighters should not scare children with equipment but rather allow the child to get to know the fire fighter without his or her protective clothing or equipment, followed by a demonstration of the clothing and equipment donned one piece at a time.
Looking to the Future: Evaluation and Innovation Preschool programs should be field-tested and pre- and posttested in their development and implementation. However, one cannot use written tests to evaluate young children’s knowledge gain. Using and documenting one-on-one interviews in which children demonstrate specific behaviors prior to and after the program is one way to access children’s knowledge gain.
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Although it is important to measure the knowledge gain accomplished by a fire safety education program, it is even more important to measure the effectiveness of the program in reducing fire deaths and injuries in the target population. The use of evaluation is well illustrated by the experience of the Portland (Oregon) Fire and Rescue Department, which implemented the use of the Learn Not to Burn (LNTB) Preschool Program and Play Safe! Be Safe!. In fiscal year 1992–1993, the LNTB Preschool Program was delivered to 29 Head Start classrooms in Portland. The primary means of evaluation was a focus on behavioral changes, which would be measured against the history of the juvenile fire problem in Portland. In 1994 and 1995, the Fire Bureau decided to expand the outreach to preschool-age children in group child care facilities, serving 12 or more children in nonresidential settings. The Play Safe! Be Safe! program was used for the children in these settings. In all, more than 200 copies of both programs were distributed into formal learning settings in the Portland area. Some of the positive findings of the evaluation were the following: • In the target age group of 3- to 5-year-olds, the success measure was the reduction in the percentage of children having to be referred to the juvenile fire setting intervention program for reasons of low knowledge and skills. The preprogram referral rate of 6.2 percent was reduced to a low of 1.8 percent by fiscal year 1996–1997. • Prior to the implementation of this program, the city of Portland experienced an average of two deaths a year attributed to child-set fires. Since the implementation, the death rate due to child-caused fires has dropped to one death every six years, on average. • The rate of child-set fires per thousand children in the targeted population, expressed as a fraction of the rate of child-set fires per thousand children in the entire community, has declined by roughly half. Portland Fire and Rescue is convinced that this level of reduction in the different success measures point to education as the key to success.14 More evaluation such as the pre- and posttesting and impact studies such as those done in Portland should be conducted. Too many programs are still in use based only on the reasonableness of their design assumptions and favorable, but unquantified, impressions of them by their lead adopters. The need for more evaluation will only grow as various preschool programs are adapted for international use. Programs should continue to be developed and existing ones improved. It is also important to develop more lab research on how young children learn fire safety behaviors to get a better sense of whether young children understand the message and whether we are giving the right messages and teaching the right behaviors. New programs for caregivers should also be developed and tested. Messages and programs for a variety of cultural groups should be studied and evaluated. New implementation methods should be used to reach children who are not in formal child care settings. Funding to conduct longitudinal, full program, sus-
tained behavior change and impact evaluations should be obtained from groups such as the Centers for Disease Control and Prevention. Even when a strategy emphasizes an engineering change, it needs an educational counterpart for maximum advantage. As an example, consider the standard on child-resistant lighters. Some children will be able to operate child-resistant lighters. Among the children younger than age 5 who ignited cigarette lighters in the CPSC study, about one-third were older than 4 years and 3 months, the oldest age of the children required to be tested by the CPSC standard-testing protocol.8
OLDER ADULTS Older adults are the only one of the high-risk groups that is growing rapidly. In 2000, people age 65 or older represented 12.7 percent (or roughly one-eighth) of the population of the United States. By 2030, older adults will represent a projected 20 percent of the population.15 Internationally the population is also aging rapidly. One can see the increases in certain developed countries, such as Japan and Western Europe. However, even developing countries are seeing an increase. As pointed out by Dr. Alexandre Kalache, chief of aging and health for the World Health Organization, the developed world became rich before it got old, whereas the developing world is going to get old before it gets rich. This has important implications since poorer countries do not have the resources to deal with injuries that are available in the developed world.16 Although only 16.1 percent of persons 65 and older in the United States are minorities, the rate of growth in numbers of minorities is increasing rapidly. By 2030 it is projected that minorities will represent 25.4 percent of the elderly population. Between 1999 and 2030, the white population age 65 and older is projected to increase by 81 percent compared with 319 percent for older minorities, including Hispanics (328%), African Americans (131%), American Indians, Eskimos, and Aleuts (147%), and Asians and Pacific Islanders (285%).15 In targeting programs to reach older adults, it should be noted that older adults vary in their physical and mental abilities and probably in their risk of death from fires and burns. As health care has improved and more is known about exercise and nutrition, people are more active and in good health and involved longer in the community. Also many older people are financially secure and living in good housing. Those age 85 and older or the “vulnerable elderly” have the greatest risk. Not only do they have the highest risk for both fire deaths and fire injuries but also their injury rate is 90 percent higher than the national average. From this, one may infer that this is a different population from those people age 65 to 74 whose risk of home fire injury is actually lower than the all-ages average.2 Putting all this together, fire risk continues to increase as people age, beginning at about age 50. People age 65 and older have about twice the risk of dying in a home fire as the general population. For people age 75 and older, the risk is three times as high, and it is four times as high for people age 85 and older.
CHAPTER 4
Characteristics of This Group For older adults, the principal causes of fatal fires are primarily the same ones as for other adults. They suffer less from childplaying fires and incendiary or suspicious fires, both of which are typically set by children. Older adults have less relative risk from those two causes of fire, probably because they spend less time around children than do other adults. Most fire safety messages for older adults are similar to those for other adults, but there are some variances in patterns that may affect relative emphasis on messages by an educator. Smoking-related fires are the leading cause of fire deaths. Heating equipment fires rank second, but they are a close second only for the oldest adults, accounting for nearly as many deaths among the 85 and older age group as smoking materials.2 Older adults are more likely than others to be intimately involved with the ignition source. For adults 65 and older, more than one-fifth are intimate with the ignition, compared to less than one-sixth of victims of all age groups. More than one-third of adults 65 and older have either specific physical or mental disabilities or the more general limitations captured by the phrase “too old to act.”2 This compares to just over one-fourth for all age groups combined. Older adults are more at risk from cooking fires only to the same extent that they are more at risk from all types of fires. However, there are important differences in the kinds of cooking fires that kill older adults. Of the cooking fire deaths involving victims age 65 and older, 37.0 percent involved ignition of clothing on a person and 26.4 percent involved ignition of cooking materials. Of the cooking fire deaths involving victims under age 65, only 4.0 percent involved clothing on a person as the first item ignited whereas 47.4 percent involved cooking materials.2 Males are a high-risk group compared to females for nearly all age groups. The death rate for males from 1994 to 1998 was 15.6 fire deaths per million population, which was 43 percent higher than the death rate for females at 10.9 fire deaths per million. The second largest difference was for age 85 and over, where the male death rate of 92.2 deaths per million was nearly twice the rate of 47.7 for females.2 Men age 85 and over also had the highest risk of injury from fires of all ages.2 Programs developed for older adults should be appealing to both men and women because men are at higher risk, but women make up a larger portion of the older population. With so many important and distinct causes of injury, programs developed for older adults need to be multifaceted. For example, Remembering When: A Fire and Fall Prevention Program for Older Adults™17 developed by the NFPA Center for High-Risk Outreach and the Centers for Disease Control and Prevention uses three strategies for reaching older adults: group presentations, home visits and smoke alarm installation, and fall intervention.
How Older Adults Learn The Learn Not to Burn Foundation and the American Association of Retired Persons (AARP) collaborated on an instructional piece of educators in the 1995 NFPA prevention week kit18 that gave the following basic principles for reaching older adults.
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Presentations. Educators should make presentations interactive. Older adults have a lot of experience and want to share that experience. Presenters should ask questions, invite input, and look to the older audience frequently for responses. If a video is used, the presenter must make sure everyone can hear and see it clearly. Demonstrations and interactive activities, such as having participants design their own escape plans or having discussions about real fire case studies, are important. Many older people have hearing impairments but may be too embarrassed to tell you that they cannot hear, so it’s important that presenters speak clearly and project their voices without shouting. Although meeting places for all groups of people should be accessible, people are more likely to have a physical disability as they grow older. Therefore, top on the list for someone hosting a safety presentation is to make sure that the meeting room is accessible. In addition, older adults in focus groups conducted by the NFPA Center for High-Risk Outreach and the Centers for Disease Control said that a program should focus on the key safety messages dealing with the major causes of fires and falls and how they can be prevented. To encourage program attendance, respondents said that program leaders should provide transportation for older adults who do not have transportation, provide food, and advertise that they will have food. The majority of those surveyed felt that the ideal time to hold an educational program is about 10 o’clock in the morning.19 Printed Materials. When developing or choosing print materials for the older audience, one should use a sans serif type. Print size should be at least 12 point. Use a one point or larger font for so-called large-print books. Uncoated paper or buff paper is most readable. A designed background may be interesting to the eye, but it will make the copy more difficult to read; therefore, designs and pictures are better kept separate from the actual print. Illustrators should portray older adults in positive, active roles. Stereotypes are likely to make the target audience avoid the message.18 Home Visits. Results indicated that older adults wanted both group presentations and home visits. Older adults thought visits to people in the home should be one-to-one and conducted by someone with whom older adults felt comfortable, such as a fire fighter or someone who already visits the home.19 Respect. Older groups of people are very skeptical, especially when it comes to consumer advertising.20 Avoid talking down. Seniors aren’t newly arrived on planet earth. They may look old, but they were all young once and most of them still have many of the same values and interests. Do not patronize older people. Older people don’t think they are cute and they hate it when you treat them like little dolls. Never forget that they know more about this world than you do. They aren’t waiting for you to give them a badge for still being alive. Although certain aspects of brain power decline with age, it is not as severe as one would expect.
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Don’t simplify to the point of banality. The older brain is packed with gigabytes of information and with advanced age-blessed software, so naturally retrieval time takes longer. It doesn’t mean seniors are stupid, and they will resent it if you fail to appreciate this. Don’t produce advertising that requires rapid information retrieval to be understood.21
Legislation and Engineering Properties designed to provide special care to older adults are covered by the NFPA 101®, Life Safety Code®, other model codes, and related governmental requirements. Many other engineering provisions—for example, to reduce the risk of fall injuries—are contained in guidelines such as those contained in NFPA’s Remembering When. Most older adults, however, live in their own homes, where there is less control and regulation for their safety. However, there are many engineering solutions that can be helpful for older adults. Advancements such as ten-year battery smoke alarms and home fire sprinklers should be installed in homes. Also, advocating for engineered product changes such as fire-safe cigarette legislation and flame-resistant sleepwear should be a priority for those working to reduce deaths and injuries among older adults.
Reaching Older Adults Through Others Many older adults have people who provide them with care or support, but the typical independent older adult does not cede authority to any of these volunteer caregivers. The options available to caregivers of young children do not exist in the same form for caregivers of older adults.
Teaching Older Adults The earlier lessons on how older adults learn can be translated into a concise set of generic guidelines for constructing an effective safety education program for older adults. • Find venues where older adults congregate and are receptive to an educational program. Older adults can be reached through a variety of organizations including senior housing parks, parks and recreation departments, places of worship, nutrition centers, or AARP chapters.18 • Construct interactive presentations focused on specific safety behaviors, so that the interactive participation by the older adults can help to lock in the safety knowledge and serve as a start on practicing the safety behavior. • Tailor the presentation to address potential physical limitations of the audience, but unobtrusively and without overcompensation based on stereotypes. • Use the presentations to set up home visits for followup. Extend the reach of the programs by arranging home visits with additional older adults who may not desire or be able to be involved with organizations that sponsor presentations. • Involve older adults on every facet—from program design to program delivery—to assure that the high level of respect and credibility needed for success is achieved consistently.
Sample Programs for Older Adults Older and Wiser. In response to the disproportionate number of fire deaths that occurred among older adults in the Canadian province of Ontario, the Ontario Fire Marshal’s Public Fire Safety Council organized an older adults task force to reduce fires, injuries, and fire deaths among adults 65 and older. Research into the fires showed several different fire scenarios in which older adults were dying or being injured. To effectively address each scenario, a program had to be developed to address each scenario using a multipronged approach because those dying in fires were either very active in the community or lived on their own and were often isolated in urban and rural areas. The Ontario Fire Marshal’s Public Education Office developed a fire safety resource kit entitled Older and Wiser21 based on the research and testing by the Older Adults Task Force. The kit includes a checklist for friends and families of older adults, a large-print pamphlet with fire safety tips, a highrise pamphlet, a fire safety quiz, a booklet on working with the media, and an instructional booklet entitled “Getting the Community Involved.” Program aids such as a booklet entitled “Planning for Success” and a presentation script help program leaders deliver a presentation to groups of older adults. The Ontario Fire Marshal’s Office also provides a presentation to older adults in PowerPoint, overhead, or slide show formats to fire safety educators.21 Older and Wiser was distributed free of charge to every fire department in Ontario with funding by the City of North York. (North York experienced several fire deaths of older adults in 1997.) Surveys are sent out periodically to determine who is using the program, how it is being used, and to see if there is need of additional resources or tools to educate this group. Some of the most important community partners for Older and Wiser are the home support workers who visit the homes of older or physically and mentally challenged people to assist them with their daily chores. Many support workers test alarms in the homes of their clients. An Older and Wiser checklist was developed and field-tested by home care agencies in Ontario. In some communities fire service personnel train home support workers to conduct basic fire safety checks in the homes they visit. Smoke alarms are installed or replaced, and older adults are taught how to prevent fire and protect themselves if there is a fire. Part of the success of the Older and Wiser program is attributed to the fact that in Ontario public fire safety education is mandatory. Under the Fire Protection Act, municipalities must deliver public education programs based on local needs and circumstances. Because many communities have many older people, a program that provides materials and resources to help reduce fires among this group is often welcomed. Remembering When: A Fire and Fall Prevention Program for Older Adults.17 In 1997 the NFPA Center for High-Risk Outreach had many programs to reach high-risk fire groups but had few materials to use to reach older adults. The center met with representatives from the Centers for Disease Control’s (CDC) Di-
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vision of Unintentional Injury. CDC also had an interest in reducing fires among older adults. Both organizations agreed that a program designed for older adults regarding preventing fires could also include how to prevent unintentional injury from falls. (Fires and falls are the leading cause of unintentional injury in the home among older adults.) Many fire service personnel respond to emergency calls for older people falling as well as fires. Also, since many more older adults had experienced a fall than had been in a fire, the two organizations thought there would be more interest in a program that included both injury areas. Research was conducted at all stages of program development. Because no single agency is responsible for reaching all older adults in a given community or jurisdiction, Remembering When is designed to be implemented by coalitions of local fire departments, public health departments, service clubs, social and religious organizations, area agencies on aging, and other organizations. As a team, coalition members can decide how to best approach the local older population. Once the program was developed, 5000 free copies were made available to fire fighters, public health workers, other professionals serving older adults, hospital workers, and other organizations throughout North America. Some state organizations and corporations funded distribution of Remembering When for each fire department and other organizations in their states. Most people who received the program materials implemented the program without extra outside technical assistance. The NFPA Center for High-Risk Outreach has a corps of diverse
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trainers who provide training on the Remembering When program for state and local conferences of fire safety educators, organizations serving older adults, and public health officials. The Centers for Disease Control and Prevention provided 3-year grants for the implementation of Remembering When in Arkansas, Maryland, Minnesota, North Carolina, and Virginia. For other local groups that want to evaluate the program, the Center for High-Risk Outreach provides a local evaluation packet including questionnaires and a template for a final report to local officials. The Remembering When program focuses on 16 fire and fall prevention messages (Figures 5.4.2 a and b). The program uses the following approaches to reach older adults. • Group Presentations. This section gives steps on reaching older adults through senior centers, high-rise housing, and other places people gather in groups. Three optional lesson plans feature interactive activities such as a trivia game to support the presentations. • Home Visits. This section focuses on reaching older people in their own homes through service providers who already visit the home. It includes several visitation formats, support checklists, and handouts. • Installation and Intervention. This section outlines how to organize a smoke alarm installation and fall intervention program, including the installation of smoke alarms and the distribution of night lights, nonskid bath mats, and other items.
FIGURE 5.4.2 Fire and Fall Prevention Messages from the Remembering When Program (a) Exercising Regularly (b) Planning and Practicing Your Escape from Fire (Continued)
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FIGURE 5.4.2
Looking to the Future: Evaluation and Innovation When the Remembering When program was in development, a formative evaluation was conducted. Hundreds of older adults in the five test sites participated in the group presentations and home visits. Fire departments worldwide need to conduct a sustained effort on reaching older adults. This population will continue to grow rapidly. Training of fire service personnel should include not only the content of the program such as Remembering When but also model sensitivity to older adults and cultural relevancy to the period history of events that older persons have experienced. Also humor and fun activities should be part of all training and programs to overcome possible preconceived ideas many have regarding the target group. Fire and life safety educators who have worked over the years with older adults report enjoying working with this group. Programs should also be targeted to the adult children or nieces and nephews of older adults. This group could benefit by learning more about how they can assist their parents, aunts, and uncles in making their homes safer and can also learn how to design their own homes to be safer as they age and to increase their safety behavior.
THE DISADVANTAGED Today’s urban environment offers challenges to anyone working to improve schools or provide health services, city services,
Continued
crime prevention, or fire and life safety measures. Traditionally programs for fire safety tended to reach those who needed it least. And without concentrated effort to understand the urban or rural poor situations, it is unlikely that programs developed for more affluent communities will be effective. A number of statistical studies, stretching back at least a quarter of a century, have demonstrated that the risk of fire or fire death is higher among disadvantaged populations.22 Many measures of what it means to be disadvantaged have shown this relationship to high risk, but the various conditions all tend to be correlated with each other, so it is probably impossible—and unnecessary—to determine which condition is most critical in creating higher fire risk. Lack of income (poverty) and lack of education are the two conditions that most consistently show a substantial relationship to high risk. Only 65 percent of poor household heads are high school graduates, compared with 81 percent of all household heads.23 The correlation with poverty and low education appears to explain why race and age of housing, by themselves, appear to be factors in high risk. When the effects of poverty and low education are removed, neither race nor age of housing appears to be a good predictor of high risk. Although blacks are overrepresented among the poor, whites make up 67 percent of America’s poor compared with 83 percent of the overall population. Blacks, who represent 13 percent of the population, make up 29 percent of the poor. The black ratio has barely budged since the mid-1960s.23 Similarly, fire risk is highest in large cities and even more in small, rural communities, the two sizes of communities with
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the highest shares of this population living in poverty. And among regions of the United States, the higher incidence of rural poverty, in particular, provides an explanation for the consistently higher fire death rates in the South. A more recent study of deaths and injuries from house fires in the city of Dallas, conducted from 1991 through 1997 and reported in the New England Journal of Medicine, confirmed the previous findings. It found that the rate of injuries was highest among older adults, low-income populations, minorities, and in houses without functioning smoke alarms. Homes with low incomes are less likely to have smoke alarms.24 The study also showed that census tracts with the lowest median incomes had rates of injury 20 times as high as the rates in tracts with high median incomes25 (Table 5.4.1). As noted earlier, older adults account for one-fourth of the population and young children account for one-sixth. The disadvantaged are the smallest part of these high-risk populations, depending on how the condition is measured. More than one of seven Americans live in poverty, including more than one of every five children. This means that people do not earn enough to feed, clothe, and house their families at a level that the federal government considers adequate. The minimum incomes needed to do this are $7363 for singles to $14,763 for a family of four to $29,529 for a family of nine or more.23 Older adults are less likely to be poor than other age groups, thanks in large part to Social Security, Medicare, and Medicaid. In 1999 the poverty rate for persons 65 and older dropped to a historic low of 9.7 percent. Another 6.1 percent of the elderly were classified as “near-poor” (income between the poverty level and 125% of this level.) Older women had a higher poverty rate (11.8%) than older men (6.9%) in 1999. Older persons living alone or with nonrelatives were much more likely to be poor (20.2%) than were older persons living with families (5.2%).
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The highest poverty rate (58.8%) was experienced by older Hispanic women who lived alone.15 Of the elderly white population, 8.3 percent were poor in 1999, compared to 22.7 percent of elderly African Americans and 20.4 percent of elderly Hispanics. Higher than average poverty rates for older persons correlated with living in central cities (11.7%), in rural areas (11.8%), and in the South (11.7%).15 Poor families are not unusually large families. The average poor family receiving Aid to Families with Dependent Children (AFDC) consists of 2.9 people. The typical American family is 3.2 people. Although everyone grows out of the high-risk group of young children and often into the high-risk group of older adults, being disadvantaged is often regarded as a lifelong affliction. This stereotype misses a sizable share of the disadvantaged who do leave the group. Studies show that although about a third of the poor are elderly or disabled and, thus, unlikely to climb out of poverty, one of every five poor people in a given year isn’t poor in the following year. Isabel V. Sawhill, a senior fellow at the Urban Institute think tank, estimates that roughly a third of the nation’s poor remain impoverished only temporarily because of job loss, illness, or divorce.23
Characteristics of This Group Only 9 percent of poor working-age adults work full-time year around compared with 42 percent of all working-age adults; 40 percent of the poor do work part-time or part of the year, compared with 69 percent of all adults.23 It is not true that most of the poor live in inner-city ghettos. Only about one in eight poor Americans lives in census tracts with poverty rates of 40 percent.23 Part of the reason for this is that poor people can be found in most communities that are not poor. A more important reason for this is the large share of poor
TABLE 5.4.1 Rates of House Fires and Injuries Related to House Fires, According to the Median Income of the Census Tract, in Dallas from 1991 to 1997 a
Median Income per Year <$20,000 $20,000– $39,999 $40,000– $59,999 $60,000– $79,999 >$80,000 a
No. of No. of House No. of Fires Houses Injuries Populationb
Injuries per 100,000 Population per Year
Relative Risk (95% CI)c
House Fires per 1000 Houses per Year
Relative Risk (95% CI)c
Injuries per 100 House Relative Risk (95% CI)c Fires
1681
33,411
75
107,944
9.93
8.1 (2.5–32.0)
7.19
2.4 (2.1–2.8)
4.46
4.1 (1.2–16.2)
4085
97,205
121
286,892
6.03
4.9 (1.5–15.4)
6.00
2.0 (1.8–2.3)
2.96
2.7 (0.8–10.7)
800
40,454
17
103,242
2.35
1.9 (0.5–8.2)
2.83
1.0 (0.8–1.1)
2.13
1.9 (0.5–8.4)
340 273
24,104 13,154
7 3
74,810 34,833
1.34 1.23
1.1 (0.3–4.2) 1.0
2.02 2.96
0.7 (0.6–0.8) 1.0
2.06 1.10
1.9 (0.4–9.2) 1.0
Data on the median income of the census tract were missing for 5034 persons and 11 house fires. Population indicates the number of people living in houses, which were defined as nonmobile residential structures with one or two units. c P < 0.001 by the chi-square test for trend for each income category. CI denotes confidence interval. Source: New England Journal of Medicine, Vol. 344, No. 25 (June 21, 2001). Copyright © 2001, Massachusetts Medical Society. All rights reserved. b
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people located in rural communities where census designations are not defined at the tract level. If relative fire rates and fire death rates are any indication, then rural poverty is a greater risk factor than urban poverty. Special Fire Risk Characteristics. One reason that rural poverty is a greater risk factor than urban poverty is the larger number of rural poor who are located in the U.S. south. Here winters tend to be milder, and it is possible to at least attempt to heat whole housing units with portable or fixed space heaters designed for safe use only in smaller spaces. Fire deaths due to heating equipment fires account for a larger share of all fire deaths in the rural South than elsewhere.26 The other fire causes for which the poor have distinctly higher risk than others, at least in large cities, are child-playing fires and incendiary or suspicious fires, which are known to be dominated by juvenile fire setting. A possible explanation for this pattern follows this chain: Most of the poor live in singleparent households headed by women. Just over half of the poor families (52%) in America are headed by single females compared with only 18 percent of all U.S. families.23 Single-parent families have less total person-time available for close supervision of children, which creates more opportunities for children to start fires, as well as reduces the ability of the family to respond quickly and effectively to help children escape any type of fire that may occur. Other factors related to poverty that also contribute to high fire deaths are unattended or unsupervised children; a lack of utilities; the use of safety devices, such as window bars, to prevent crime; a lack of smoke alarms; and older electrical wiring.26 How the Disadvantaged Become Safer. Any effective fire and life safety program targeting the disadvantaged must reflect the limitations that low income and less education impose. Even one single-station smoke alarm with a battery may be beyond the poor family’s budget, let alone annual battery replacement. Reading levels need to be kept low if educational materials are to be readily grasped by a target disadvantaged population. For a number of disadvantaged communities, there may also be language barriers. In most urban and some suburban and rural communities, the fire safety educator must be prepared to provide instruction and information in languages other than English. According to the U.S. Census Bureau, there were 28.4 million foreign-born residents (10.4% of the total U.S. population) in 2000. Among the foreign born, 51 percent were born in Latin America, 25.5 percent were born in Asia, 15.3 percent were born in Europe, and the remaining 8.1 percent were born in other regions of the world.27 Almost half of the foreign born lived in the central city of a metropolitan area (43.1%), compared with slightly more than one-quarter of the native (people born in the United States) population (27.5%). The percentage living outside these large central cities but within a metropolitan area was slightly less for the foreign born than for the native population (48.8% and 51.0%, respectively). The percentage of the foreign born living in nonmetropolitan areas (5.1%) was much smaller than the percentage of natives (20.7%).27
Although a large proportion of immigrants move to the large metropolitan areas, many smaller communities also experience changes in their ethnic makeup. For example, Sioux Falls, a city of about 123,000 in the mostly rural state of South Dakota, is a town that has grown from mostly white to one in which 9 percent of the population picked a race other than white on the 2000 census form compared to 2.5 percent in 1980. Hispanics make up the greatest number at 3087, American Indians at 2627, blacks at 2226, and Asians at 1479.28 The Sioux Falls school system now has 42 different language groups. Challenges to the fire department there include not only reaching families, especially adults who speak a different language, but also reaching people with cultural and socialization issues related to fire, such as teaching people to use stoves with several burners and ovens when they may have cooked on an open fire in their native country and teaching people not to use hibachis or barbecue grills inside their homes.29 The multilingual nature of Canada is growing as a result of increased immigration. In 1996, there were 4.7 million people who reported a mother tongue other than English or French, which was a 15.1 percent increase from 1991. This increase was two and a half times greater than the overall growth rate of the Canadian population (5.7%). The number of people reporting English as their mother tongue increased by only 4.7 percent and those reporting French increased by only 2.3 percent.30 The trend of multilingualism is likely to increase in Canada and the United States. Europe, Australia, and other nations are also experiencing growth in immigrants who speak other native languages. This presents a challenge to public educators as they try to reach people in their communities with safety messages and culturally appropriate programs.
Legislation, Engineering, and Government The principal concern with safety programs for the disadvantaged is that normal program funding dynamics will tend to target away from the disadvantaged rather than toward them. Resources that can be tapped for safety programs anywhere else are likely to be missing in a poor neighborhood or community. One Chicago neighborhood, North Lawndale, according to the Chicago Tribune, has one bank, one supermarket, 48 state lottery agents, and 99 licensed bars and liquor stores. “With only one bank, there are few loans available for home repair; private housing has therefore deteriorated rapidly.”31 In the school system the city often relies on low-paid substitute teachers who represent one-fourth of Chicago’s teaching force. Even substitute teachers are in short supply. On an average morning in Chicago, 5700 children in 190 classrooms come to school to find no teacher.31
Reaching the Disadvantaged Directly and Through Others A Community-Based Fire Safety Education Model. A community-based fire safety education model32 has been de-
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signed to address the challenges of the poor urban areas, for example, working with tight budgets, large numbers of unsupervised children, non-English-speaking residents, and other issues related to social and economic changes. An important concept of the community-based approach is that no two communities are exactly alike. Fire departments must adjust approaches to fire safety education to fit the audience they are trying to reach. The fundamental principles of the community-based approach are geographic targeting, market research, and grassroots community involvement. • Geographic targeting. Identify specific neighborhoods or areas where the fire problem is most severe and concentrate efforts on reaching residents of these high-risk areas. • Market research. Use methods developed by the advertising industry to learn more about the target audience to understand how they get information and what will motivate them to listen and respond to fire safety messages. • Grassroots community involvement. Invite the active participation of as many of the targeted audience as possible in each aspect of the program.32 Community involvement is not just a means for disseminating information but also should be a goal in itself. When people actively participate in a program, they develop a personal stake in fire safety that they bring back to family, friends, and neighbors.33 The following basic steps are the foundation of a successful community-based fire safety education program. • Educators analyze fire data to identify the geographic target areas with the most fires and deaths and to determine the main causes. • A market researcher or other qualified individual conducts focus groups among people in the target area to identify the leaders in the community and determine the best strategies for communicating fire safety messages to residents. • Meetings are held with the leaders of community groups identified during the market research. • Educators implement the program with the cooperation of the community groups. Some programs give free smoke alarms and educational materials as part of each pilot program. Most of the programs include a door-to-door canvass of households in the target area. Fire fighters or trained volunteers install the detectors. • The success of each program is evaluated by documenting citizens’ response and analyzing fire data by comparing the number of fires or fire deaths and injuries before and after the program’s implementation.33 The qualities necessary to be an effective fire and life safety educator in low-income and other communities are very similar to those necessary to be a community organizer trying to improve overall conditions in neighborhoods. The following list identifies qualities needed by fire and life safety educators: • Being able to find leaders in the community • Being able to find the networks and organizations in the community that really work for people
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• Understanding the enlightened self-interest of the person or persons to be motivated • Recognizing differences without stereotyping people • Having imagination or empathy • Being ready to give volunteers and leaders in the community recognition and empowering others to act and lead on their own • Having a sense of humor School-Based Programs. School-based programs have been very popular in reaching children and their parents. Example programs are (1) ones in which the fire department does all the teaching directly to students in their classrooms or in auditoriums, (2) fire safety houses and trainers, and (3) ones that concentrate on training the teacher to teach fire and life safety as part of the ongoing curriculum. The public educator needs to take into account what teachers and administrators are dealing with in schools in urban or rural communities. There are many groups eager to provide their messages to children in these schools; therefore, in order to get fire and life safety on the priority list, the fire and life safety educator must be able to communicate the urgency of the safety issue and provide new resources to the school system. An example of a fire department reaching children in urban schools is the Philadelphia Fire Department. The department implements NFPA’s Risk Watch®34 curriculum in 15 schools in high-risk communities. (Risk Watch® teaches eight safety subjects of motor vehicle safety; fire and burn prevention; choking, suffocation, and strangulation prevention; poison prevention; falls prevention; firearms injury prevention; bicycle and pedestrian safety; and water safety for preschool to grade 8.) The communities were targeted by observing census track information showing low incomes combined with information on areas where there was a greater rate of fire deaths and injuries. Lt. Joseph Flores, the Risk Watch® champion in the Philadelphia Fire Department, supplemented the Risk Watch® materials in order to address the needs of urban children. Some of the subjects for which he wrote supplemental materials were children playing on playgrounds with glass, needles, or crack vials; children playing in abandoned cars or houses; and children opening fire hydrants during the summer to cool off. The department also added information on lead paint and dog bites— other problems in the city. In addition to the Risk Watch® curriculum implementation, a Philadelphia-wide smoke alarm program provides for the installation of free smoke alarms in the homes of any child 12 and younger who does not have a home smoke alarm. The department also installs 10-year battery smoke alarms in homes in high-risk areas.35 Spanish-Language Materials from the NFPA. In response to the dramatic growth of Latinos in the United States (Latinos now make up 12 percent of the U.S. population)36 and the demand for bilingual materials in schools, the NFPA Center for High-Risk Outreach developed its Learn Not to Burn Preschool Program in Spanish. It is entitled Mis primeros pasos en prevención contra incendios®37 or My First Steps to Prevent Fires.
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FIGURE 5.4.3 Children from First Street Elementary School in East Los Angeles Demonstrating Things That Can Get Hot and Singing “Cuidado, Puede Estar Caliente” (“Careful, It May Get Hot”) from NFPA’s Spanish Language LNTB Preschool Program (Mis primeros pasos en prevención contra incendios®)
Project staff not only translated the teacher’s guide into Spanish but also produced eight original Latin songs on a cassette tape to accompany the guide. Each song was written in a different Latin style characteristic of the music in a variety of Latin American countries (e.g., the Cuban cha-cha-cha, the Puerto Rican plena, the Mexican polka norteña, and the Dominican Republic merengue). The words for the new songs were reviewed by a team of Latino fire safety educators to determine that all words were appropriate for Latinos having varied countries of origin (Figure 5.4.3). Individual songs were given to child care providers for Spanish-speaking children. The teachers would try them out over several weeks to determine if the children understood the messages of the songs, whether there were words that children did not recognize, and if the children could sing the songs easily. Changes in the song were made after the feedback was given to the project team. Artists were hired from Mexico to provide new illustrations in a style attractive to the Latino audience. To implement Mis primeros pasos in the United States, the center trained a network of Latino fire fighters from various communities in the United States with a large number of Latinos. A partnership between NFPA and the National Association of Hispanic Firefighters (NAHF) introduced the program to the National Association of Bilingual Educators. “One of the goals of NAHF was to make sure that the Latino community had a culturally relevant education program in their school and community. For many of the children who are immigrants, this is the first time that they have ever received any fire safety education because in the past, public fire safety education was not provided in their mother countries. We want to improve the well-being of the Hispanic community in the communities where Hispanic fire fighters serve,” according to Sal Morales, past president of the National Association of Hispanic Firefighters.38 Fire fighters from other countries began hearing about Mis primeros pasos after its introduction outside the United States at the Mexican Association of Fire Chiefs Conference in Leon, Mexico, in 1997. The center’s four bilingual trainer/consultants
have trained users in Argentina, Mexico, Costa Rica, and Puerto Rico, and comprehensive programs are being conducted in Argentina, Costa Rica, and Puerto Rico. Figure 5.4.4 illustrates one such session. NFPA’s Remembering When program has been translated into Spanish. It is entitled Los Buenos Recuerdos (The Good Memories), and it too will be implemented in the United States and Latin America. Using the program in other countries requires working through the appropriate networks in those countries to keep the program going. Some of the challenges include difficulties in getting materials, lack of money for materials in poor communities, and lack of availability of safety devices such as smoke alarms or child-resistant lighters. Other Resources to Support Foreign-Language Materials. It is essential to use professional translators to create foreign-
FIGURE 5.4.4 Teachers in Sonora, Mexico, Demonstrating the Lesson “Crawl Low Under Smoke” in a Train-the-Trainer Session Run by Rene Alaniz, Representing the NFPA Center for High-Risk Outreach
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language versions of fire safety materials. Professional associations such as the American Translator Association39 can help locate translators. Educators should use an advisory group of people who are native speakers of the language to review the copy. Educators should be sensitive to the audience. Foreignlanguage populations may include some who are not literate in their own spoken language; therefore, the educator may have to rely on illustrations to describe the message. Furthermore, translated materials may be best given to the consumer with one side in English and one side in the foreign language, because household members may be at different levels in their reading skills in English, with some primarily reading English and others primarily reading their mother tongue.
NATIVE POPULATIONS In the United States native populations may be called American Indians, Native Americans, Amerinds, or by the name of a specific nation. In Canada, they may be called the First Nations, aboriginals, First Peoples, or by the name of a specific nation. Many of them qualify as disadvantaged populations. Between 1990 and 1996, the age-adjusted residential fire mortality rate for American Indian/Alaska Natives was 2.6 times greater than the U.S. all-races rate. American Indian and Alaska Native children ages birth to 4 years are at 2.4 times higher risk than the U.S. all-races population.40 In 1999 Indian and Northern Affairs of Canada reported that the average death rate in First Nation communities over a 10-year period including 1999 was 6.81 per 100,000 compared to 1.43 for the Canadian national average or 4.75 times the Canadian average.41
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First Peoples in Canada To help reduce fire deaths and injuries among First Peoples in Canada, the Assembly of First Nations of Canada, in cooperation with the NFPA and the Aboriginal Fire Fighters Association of Canada, obtained funding from the Canada Mortgage and Housing Corporation to develop The Wisdom of the Fire–Learn Not to Burn®,42 an adaptation of NFPA’s Learn Not to Burn Programs for children of First Peoples in grades kindergarten to second grade. The program’s purpose was to blend technical knowledge of fire safety behaviors with First Peoples’ cultural teachings and traditions emphasizing the respectful and constructive use of fire. The program teaches 22 key fire safety behaviors. It employs the use and development of thinking skills and action/doing skills. Each activity is marked with a single eagle for activities for students to do alone and a group of eagles for activities for children to do together. They are designated as follows: Think it out alone; think it out together; try it out alone; or try it out together.42 The program addresses the differences that exist among First Peoples by including blank and completed templates to provide examples of First Peoples’ community profiles; positive fire safety behavior, fire safety words for translation into original languages of First Peoples, and First Peoples’ legends and teachings about fire. The eagle was selected as a generic symbol to represent the culture of First Peoples. “Flying high above the earth, the eagle has been given the gifts of farsightedness, strength, and speed; it watches the movement of all creatures and guards the well-being of others.”42 Children using the curriculum are named Junior Fire Eagles to fit within this theme. About 80 new illustrations by a Navajo artist are used to demonstrate the behaviors for the total curriculum and the pre- and postknowledge tests for kindergarten and first grades. In the illustration in Figure 5.4.5, children are
FIGURE 5.4.5 Artwork by Navajo Artist Irving Toddy, Used in the Knowledge Test for the Wisdom of the Fire—Learn Not to Burn Program
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instructed to circle the part of the illustration that shows what to do if there is smoke in a room.
Navajo Nation The Navajo Nation is the largest American Indian nation in the United States and is about the size of the state of West Virginia. It is located in parts of the states of Arizona, New Mexico, and Utah and is divided into 110 governing chapters. When a manufactured-home fire took the lives of two children and their mother in 1996 in the Navajo Nation, the Navajo Nation Bureau of Indian Affairs Safety Office contacted the NFPA Center for High-Risk Outreach for assistance in establishing a coalition to help reduce fires among the people in the Navajo Nation. The fire was caused by an improperly installed wood stove, a leading cause of home fires on reservations in the winter. About 30 people representing various organizations of the Navajo Nation such as the Navajo Fire Department, the Red Cross, the Indian Health Service, and a Navajo tribe from northern New Mexico and eastern Arizona attended a meeting. At the meeting the group learned that in 1995 there were 93 major home fires that left 400 people homeless in the Navajo Nation. Due to the lack of infrastructure of fire protection services in the Navajo Nation, 82 of the homes involved in these fires were completely destroyed. The group formed the Navajo Nation Fire Safety Coalition and began working on strategies to provide more fire safety programs for the 220,000 residents of the nation. The coalition supported efforts in cooperation with the NPFA Center for High-Risk Outreach through the Learn Not to Burn Program. Ten train-the-trainer sessions were conducted, reaching more than 350 teachers serving 6000 students. The Navajo Coalition and community members installed 670 tenyear battery smoke alarms with hush buttons. These included chapter officials, the Indian Health Service, the Bureau of Indian Affairs Fire Departments, the Navajo Nation Tribal Fire Department, and volunteers from the Kirtland Volunteer and Sanders Fire Departments adjoining the Navajo Nation in 335 homes in Hogback and Window Rock chapters of the Navajo Nation. Sixty Indian Health Service personnel, senior center directors, and their workers were trained on the Remembering When—A Fire and Fall Prevention Program for Older Adults. In 1997 the Center for High-Risk Outreach conducted focus groups among Navajo people from the five major sections of the Navajo Nation: Eastern Navajo, Fort Defiance, Chinle, Western Navajo, and Shiprock. The purpose was to identify the needs, concerns, and cultural beliefs of the Navajo people and to educate attendees about various fire safety issues relevant to the Navajo Nation. Some recommendations resulting from the focus group included the following: 1. Make personal testimonies an important part of the program. House presentations should encourage people to talk about fire experiences and allow sufficient time for discussions. 2. Use public service announcements on KTNN, the reservation-wide Navajo radio station. Because many people do
not have electricity, transistor radios are an important means to receive information. 3. Pair brochures, other written materials, and videos showing nonnative people with other materials depicting Navajos and using the Navajo language in addition to English.42
SPECIAL ISSUE: HOME SECURITY AND FIRE SAFETY People can become at high risk for fire as an inadvertent side effect of actions taken in good faith in response to other problems considered in isolation. A major, recent, emerging example has been the elevated fire risk arising from certain steps taken for home security. One example is entrapment caused by bars on windows and doors installed to keep out intruders. Even though fire deaths in general are going down in the United States, those related to bars on windows and doors are on the rise. An average of less than one fire death per year was attributed to illegal gates or locks for the years 1980 through 1985. The average increased dramatically to nearly 16 deaths a year for the period 1986 through 1991.43 Incidents occurring in recent years show the seriousness of fires when bars prevent people from escaping. In February 1993, seven family members died in a fire in Bruce, Mississippi. Bars on windows kept a grandmother, five grandchildren, and one infant great-grandchild from escaping. During 1996, twelve people died in three incidents in California. Four children perished in a fire in 1997 in Tampa, Florida, a family of five died in a fire in Bessemer, Alabama, and in East Palo Alto, California, nine people were killed in a fire. The Home Security and Fire Safety Task Force of the NFPA Center for High-Risk Outreach has worked on this issue since 1993, focusing on engineering, education, and enforcement approaches: • Make sure windows open easily and fully enough to allow escape. • Make sure all security-barred windows needed for escape have quick-release devices and that everyone can open them. • Make sure locked or barred doors operate quickly and easily and that everyone knows how to open them. • Practice exit drills in the home and use them to identify and correct obstructions of doors and windows needed for escape. • Have working smoke alarms on each level of the house and outside of every sleeping area.43 Several cities have formed coalitions to provide retrofitting of security bars with quick-release devices and community educational programs on fire safety and home security. One of the most comprehensive local programs was organized by Steve Kastner, fire marshal for the city of Ft. Lauderdale. This program was initiated by the combined Fire-Rescue and the Building Departments. The program was composed of public education, financial assistance, and enforcement. The department received $108,000 from a federal Community Development Block Grant
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to pay for the cost of retrofitting one window per bedroom of homes with security bars on the windows. Those grants were available to owner-occupied single-family homes or duplexes for owners with low and moderate incomes. The Fire and Building Department identified a quality contractor to work for the city to retrofit the windows with bars.44 Community inspectors did sidewalk surveys to identify properties that had bars on windows. Building inspectors later visited properties and issued notices of violation. Property owners were given 30 days to initiate action. Since the program’s conception in 1997, over 800 properties were cited. Of these 80 percent went before the Code Enforcement Board and 50 percent had complied by May 2001.44 The education component of this program included the development of an informational brochure on security-bar hazards, code requirements, and how to access financial assistance. This brochure was distributed to homeowner groups and civic associations. Presentations were also given to civic associations, targeted neighborhoods, and the city commission. In order for this program to succeed, the following internal and community partnerships were needed: the mayor, city commission, city manager, fire chief, fire marshal, building official, Council of Civic Associations, individual civic associations, homeowner associations, community service and action organizations, and other city agencies.44
NATIONAL PROGRAMS IN THE UNITED STATES National Center for Injury Prevention and Control (NCIPC) Smoke Alarm Programs One of the best ways that communities can reduce fire deaths and injuries in high-risk communities is by implementing smoke alarm programs. Homes with smoke alarms typically have death rates about 40 to 50 percent less than the rate for homes without alarms.45 To reduce deaths in high-risk communities, the National Center for Injury Prevention and Control (NCIPC) of the Centers for Disease Control and Prevention (CDC) funds 14 states through three-year cooperative agreements with the state health departments to provide fire injury prevention programs. These programs provide installation of smoke alarms and education on fire safety and escape plans. Each state focuses on communities within their state that have fire incidence rates above the state average and mean household income below the poverty line. A total of 30 communities is addressed in the 14-state program. The state health department staff provides oversight and technical assistance to the local program officials and fosters partnerships between local communities and fire safety personnel. From October 1998 to October 2000, more than 112,226 homes have been canvassed through the program; 82,993 smoke alarms installed in high-risk homes, and 5,500,000 people have heard or seen fire safety messages in the 14 states. A docu-
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mented 98 lives have been saved by the early warning provided by the installed smoke alarms in the program homes.46 Successful techniques learned in the CDC projects include: • Partnering with local fire departments in the community (both paid and volunteer) • Partnering with community-based organizations to assist in canvassing homes • Getting support from community leaders • Being flexible in the hours and days of the week that canvassing activities are conducted • Advertising the program through all available media
National Fire Academy Class Several organizations have recognized the need to reach those most vulnerable to fire and burns. In 2000, the United State Fire Administration in cooperation with the NFPA Center for HighRisk Outreach developed a new two-week National Fire Academy Class, Discovering the Road to High-Risk Audiences.47 The course takes an in-depth focus on topics that include the impact of social and economic diversity on the fire problem; fire and life safety for people challenged with disabilities; the aging process and fire risk; and the effect of fire on very young children.47 The class is designed for personnel who have responsibility for public fire and life safety education in their fire departments and who have more than one year in this functional area. The class discusses what factors make the audience vulnerable, ways to reach each group, and how to plan programs for them. Both the urban and rural audiences are woven into the course material. It uses evaluation methods such as small group learning exercises and case studies.
Solutions 2000 and Beyond In April 1999, the North American Coalition for Fire and Life Safety Education* conducted a symposium to examine fire safety challenges for those who cannot take life-saving action in a timely manner in the event of a fire—specifically young children, older adults, and people with disabilities. The symposium brought together more than 70 experts on fire safety and the concerns of preschool-age children, adults over 65, and people with disabilities. In two days participants developed solutions or recommendations to be carried out by collaborative efforts of associations, industries, educators, and individuals working with the fire service. Some of the key recommendations of the symposium were: 1. Develop fire safety programs specifically focused toward children with disabilities.
*Note: The North American Coalition for Fire and Life Safety Education is made up of the American Red Cross, British Columbia, Canada, Fire and Life Safety Advisory Committee, International Association of Fire Marshals, National Association of State Fire Marshals, National Fire Information Council, National Fire Protection Association, National Fire Sprinkler Association, Operation Life Safety, and the United States Fire Administration.
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2. Expedite the development of a “smart stove” designed to shut itself off before the food starts to burn. 3. Educate the fire service and building design community on fire safety considerations for people with disabilities. 4. Improve emergency egress from buildings that house people with disabilities. 5. Promote the installation of home fire sprinklers. Make the costs more affordable and educate the public on the benefits of the sprinkler system in general. 6. Form a coalition that will make fire safety a primary concern by raising our safety expectations for the environments to which young children, older adults, and people with disabilities are exposed.48 With funding from the Federal Emergency Management Agency, a second symposium (Beyond Solutions 2000) was held in April 2001 with a more specific goal “to examine the issues related to egress capability, early warning and fire sprinkler protection for those who may not be able to take life saving action in a timely manner in the event of a fire, specifically: young children, older adults, and people with disabilities.”
PROGRAMS ON THE INTERNATIONAL LEVEL Many innovative fire safety education programs are occurring outside North America in both developed and developing countries. Leaders of these programs have also found the importance of targeting their high-risk populations. A description of two of the initiatives follows.
South Africa The City of Johannesburg Emergency Management Services had experienced fire death patterns familiar to all of us. Causes of fires included cooking, arson, smoking, electrical problems, and open flames. Factors that exist in South Africa that make people at greater risk were also the use of paraffin (kerosene) for cooking and lighting, large number of security bars on windows and doors because of a high crime rate, poor housing construction, lack of fire-safe construction, and poverty. In the past the fire department’s fire safety education program for children consisted of demonstrating fire safety skills to children by showing them how the fire department extinguished a fire.49 To provide a more successful delivery of fire and injury prevention education in the city, a public education division was developed for the Emergency Management Services. The main function of the division is to educate the public, especially children. Several programs are conducted by the public education division. Presently the Emergency Management Services uses the Learn Not to Burn Program to teach key behaviors to young children. Community Emergency Response Teams (C.E.R.T.) were developed to provide fire safety skills as well as to provide instruction on how to extinguish a fire in its earliest stage to people who live in informal settlements with a high incidence of
fires. Participants in the course are trained to identify fire hazards and correct them, detect fire early, evacuate an area, and extinguish a fire with several different readily available extinguishing agents. They are also taught the key safety behaviors to inform their communities and families. A mobile classroom was acquired to take the LNTB Program and C.E.R.T. program on the road and into the community. This allows them to deliver the fire safety programs to schools with limited or substandard classrooms and informal settlements. The mobile classroom contains all the audio-visual aids and media needed to present the fire safety presentations.49 The Emergency Management Services has also acquired a mapping system of the entire city. The plan is to have an injury surveillance program using the map technology to record every fire incident and other incidents to which Emergency Management Services responds. The data will then be used to better target prevention interventions to the major risks in a community and focus on the communities most at risk.49
Australia The 1991 census indicated that there were more than 2.7 million people (17.4%) age 5 and older in Australia whose first language spoken at home was other than English. In the state of Victoria, 22.6 percent of the population fell into this category; in the city of Melbourne in Victoria, 28.8 percent were in this category.50 Fire departments have used a variety of strategies to reach this segment of the population, including translations of printed materials, advertisements, involvement in wider programs sponsored by other organizations, lectures, and use of radio stations targeted to ethnic audiences.50 One unique program implemented jointly by the Melbourne Fire Brigade and the Adult Migration Education Services, in Victoria is Flames—Better English Through Fire Safety Program. Flames is a collection of activities that a teacher can integrate as a subtheme into a broader course in English as a second language. The materials are divided into levels of proficiency and focus on the themes of smoke alarms, escape from fire, fire hazards and prevention, and calling the fire brigade. Some of the materials used in the program are an audiotape with scripts, student worksheets, a reader, a quiz, and a board game.51 A fire fighter visit highlights the program. Fire fighters have been given preparation on how to talk to adults learning English as well as information about students’ levels of English.51
SUMMARY Many mainstream fire and life safety education programs fail to reach those who are at greatest risk. Programs implemented among the general population do not automatically trickle down to those at most risk—preschool children, older adults, the disadvantaged, and those who speak languages foreign to the country they are living in. This chapter presented characteristics of the various highrisk groups that make them at high risk to fire and provided samples of programs and strategies to reach those groups. It pointed
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out societal trends and demographic changes that help to anticipate new needs as communities grow or change. The chapter emphasized not only educational solutions but also samples of engineering and legislative changes that will make the total outreach program more successful.
BIBLIOGRAPHY References Cited 1. Ahrens, M., “The U.S. Fire Problem Overview Report Leading Causes and Other Patterns and Trends,” NFPA Fire Investigation Report, Quincy, MA, June 2001. 2. Hall, Jr., J. R., “Patterns of Fire Casualties in Home Fires by Age and Sex, 1994–1998,” NFPA Fire Investigation Report, Quincy, MA, August 2001. 3. Hall, Jr., J. R., “U.S. Fire Death Patterns, by State,” NFPA Fire Investigation Report, Quincy, MA, March 2001. 4. Hall, Jr., J. R., “Children Playing with Fire,” U.S. Fire Experience, 1990–1997, National Fire Protection Association, Quincy, MA. 5. Phelps, P. C., Ph.D., From Theories in Play: Providing a “Creative” Developmentally Supportive Environment for Young Children [videotape], Diane Wilkins Productions in cooperation with the Creative Center for Childhood Research and Training, Creative Preschool, Tallahassee, FL, 1990. 6. Gamache, S., Powell, P., et al., Learn Not to Burn Preschool Program®, NFPA International, Quincy, MA, 1991. 7. Children’s Television Workshop, “Fire Education for Sesame Street: A Research Study on Mass Media Fire Education.” 8. Smith, L. E., Green, M. A., Greene, and Singh, H. A., “Fires Caused by Children Playing with Lighters, An Evaluation of the CPSC Safety Standard for Cigarette Lighters,” Sept. 2000, U.S. Consumer Product Safety Commission. 9. Smalley, J., Gamache, S., et al., A Lighter Is Not a Toy™ [videotape], Smalley Productions for the NFPA Center for High-Risk Outreach, Quincy, MA, 1997. To obtain a free copy, write the NFPA Center for High-Risk Outreach, NFPA, Quincy, MA. 10. Davis, E. P., Friedman, G. I., and Martin, L., “Community Education and Child-Care Programs,” Educational Research and Development, Vol. 38, No. 4, 1990, pp. 46–50. 11. Pretsfelder, E., and Gary, M., “Pre-Production Evaluation of the ‘Tell a Grown-up to Put It Away’ Public Service Announcement for 3–6 Year Olds,” Dec. 1990, NFPA Center for High-Risk Outreach, Quincy, MA. 12. Peterson, P., and Bergeron, S., Follow the Footsteps to Fire Safety, A Prevention Program for Young Children, Saint Paul Department of Fire and Safety Services, St. Paul, MN, May 1993, pp. 3–9. 13. Fire Proof Children, a division of National Fire Service Support Systems, Inc., and Rowan & Blewitt, Inc., Play Safe! Be Safe! Children’s Fire Safety Education Program, Ages 3–5, BIC Corporation, Milford, CT, 1993. 14. Gamache, S., Porth, D., and Diment, E., “The Development of an Education Program Effective in Reducing the Fire Deaths of Preschool Children,” 2nd International Symposium on Human Behavior in Fire—Understanding Human Behavior for Better Fire Safety Design Conference Proceedings, March 2001, Interscience Communications, London, UK. 15. A Profile of Older Americans: 2000, Administration on Aging, U.S. Department of Health and Human Services, Washington, D.C. 16. Kalache, A., “International Perspective on Health Care for the Aging,” Proceedings of the International Organization for Standardization Workshop, May 1999, International Standards Organization, Geneva, Switzerland. 17. Gamache, S., Dornbusch, S., Beale, H., et al., Remembering When: A Fire and Fall Prevention Program for Older Adults™, National Fire Protection Association, Quincy, MA, 1999.
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18. Gamache, S., and Turner, M., “Reaching Older Adults: Watch What You Heat,” 1995 Fire Prevention Week Kit, October 1995, Department of Public Affairs, National Fire Protection Association, Quincy, MA. 19. Leitner, D., Interwest Applied Research, Beaverton, Oregon, “Senior Safety: Report on the Focus Groups Considering Program Design,” April 1997, NFPA Center for High-Risk Outreach, Quincy, MA. 20. Haller, T., “Older Consumers Don’t Believe You,” Advertising Age, August 14, 1995, p. 14. 21. Gilbert, B., et al., Older and Wiser, A Fire Safety Education Program for Older Adults, Ontario, Canada, 1997. 22. See, for example, Conley, C. J., and Fahy, R. F., “Who Dies in Fires in the United States?” NFPA Journal, May/June 1994, p. 99. 23. Topolnicki, D. M., “No More Pity for the Poor,” Money Magazine, May 1995, p. 123. 24. Ahrens, M., “U.S. Experience with Smoke Alarms,” Sept. 2001, NFPA International, Quincy, MA. 25. Istre, G. R., McCoy, M. S., Osborn, L., et al., “Deaths and Injuries from House Fires,” New England Journal of Medicine, June 2001, pp. 1911–1916. 26. “Burning Issues,” NFPA Journal, Jan./Feb. 1996, p. 104. 27. Lollock, L., “The Foreign Born Population in the United States: March 2000,” Current Population Reports, pp. 20–534, U.S. Census Bureau, Washington, D.C. 28. Olson, C., “Diversity Thrives in Sioux Falls,” Sioux Falls Argus Leader, June 19, 2001. 29. Author interview with Qadir Aware, Executive Director of the Sioux Falls Cultural Center, and David Renli, Inspector, Sioux Falls Fire Department, Sioux Falls, South Dakota, June 2001. 30. “1996 Census: Mother Tongue, Home Language and Knowledge of Languages,” Statistics Canada’s Internet site, www.statcon.ca. 31. Kozol, J., “Other People’s Children,” Savage Inequalities, Children in America’s Schools,” Crown, NY, 1990. 32. Rossomando, C., The Community-Based Fire Safety Education Handbook, National Association of State Fire Marshals, 1995, pp. 1–6. 33. Author interview with Christina Rossomando, president, Rossomando & Associates, August 1995. 34. Appy, M. K., Comoletti, J., et al., Risk Watch®, National Fire Protection Association, Quincy, MA, 1998. 35. Author interview with Lt. Joseph Flores, Philadelphia Fire Department, June 2001. 36. Therrien, M., and Ramirez, R. R., “2000, The Hispanic Population in the United States,” March 2000, Current Population Reports, pp. 20–535, U.S. Census Bureau, Washington, D.C. 37. Gamache, S., Amador, B., Saiz, M., et al., Mis primeros pasos en prevención contra incendios®, NFPA Center for High-Risk Outreach, 1 Batterymarch Park, Quincy, MA, 1997. 38. Author interview with Sal Morales, past president, National Association of Hispanic Firefighters, June 2001. 39. American Translator Association, 1800 Diagonal Rt., Suite 220, Alexandria, VA (703-683-6100). 40. American Indian/Alaska Native mortality tapes, 1990–1996, Centers for Disease Control and Prevention, National Center for Health Statistics, Atlanta, GA, 1996. 41. “Indian and Northern Affairs Canada Fire Loss Report 1999” and distribution letter, Indian and Northern Affairs Canada, EAHG-01-01, Ottawa, Ontario, Canada, 2001. 42. Tremblay, P., et al., Wisdom of the Fire—Learn Not to Burn®, Assembly of First Nations, Ontario, Canada, 1997. 43. Perrault, M. E., “Home Security and Fire Safety Meeting Report,” Dec. 1994, Center for High-Risk Outreach, NFPA, Quincy, MA. 44. Mederos, J., McMullen, J., et al., “Setting Standards and Putting Them into Practice,” presentation at the NFPA World Fire Safety Congress & Exposition, May 2001, Anaheim, California, and author interview with Steve Kastner, Fire Marshal, Ft. Lauderdale, June 2001.
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45. Ahrens, M., “U.S. Experience with Smoke Alarms and Other Fire Alarms,” NFPA Fire Investigation Report, Quincy, MA, Jan. 2001. 46. Author interview with Mark Jackson, public health specialist, National Center for Injury Prevention and Control, CDC, Atlanta, GA, May 2001. 47. “Discovering the Road to High-Risk Audiences” course description, National Fire Academy, U.S. Fire Administration, Emmitsburg, MD, Apr. 2001. 48. TriData Corporation for the U.S. Fire Administration, Emmitsburg, MD, “Solutions 2000: Advocating Shared Responsibilities for Improved Fire Protection,” symposium report, NFPA International, Quincy, MA.
49. Eksteen, R., “Emergency Services and Secondary Prevention Initiatives,” paper presented at SAFECOM International Conference, 2001. 50. “Fire Safety Education Strategy for People of Non English Speaking Backgrounds,” Metropolitan Fire Brigade Fire Prevention Department, January 1997, Melbourne, Australia. 51. Ross, N., Flames: Better English Through Fire Safety, A Joint Initiative of Adult Migration Education Services, Victoria and Metropolitan Fire Brigade Melbourne, Melbourne Fire Prevention Department, Melbourne, Australia, 1997.
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Understanding Media: Basics for the TwentyFirst Century Dena E. Schumacher
A
chievement of the goals of fire and life safety educators require an effective working relationship with the mass media—print, broadcast, and, increasingly, electronic (e.g., the Internet). The media are the gatekeepers to the public, intermediaries to the largest target audience there is. If the goal is to transform safety knowledge and skills of everyone in the community, then the job begins with making contact with the public. Using mass media is a critical means to reach the community as a whole. The goals of fire and life safety educators, however, are not always the goals of the media. The media do not measure success by the knowledge, skills, and losses of their audience. The media often want the facts before educators know what the facts are. The media want details that educators may consider an infringement on privacy. The media want events and issues framed in certain ways, often with an emphasis on drama, conflict, and outrage, rather than on complex truths and constructive learning. None of these conflicts in goals is a reason to avoid the media, because the media are necessary to the success of educators’ goals. Fire and life safety educators need to understand the media—and the educators’ own options for dealing with the media—to best pursue the educators’ goals. That is the goal of this chapter. In an age of global communications—immediate, on-thespot news coverage, fast-paced marketing—fire service information must be provided faster than ever to be considered timely, but it must still be accurate and delivered calmly and courteously, despite the heightened time pressure. To provide information effectively, fire service personnel must understand the workings, the goals, and the changing world of the media: how the media function, how reporters and editors view their jobs, and how the fire service may best utilize ever-changing communication resources.
Often the fire department media liaison or public information officer (PIO) who conveys information to reporters in times of emergency is the fire and life safety educator. The life safety educator also provides public service announcements (PSAs) to local newspapers or radio web sites or speaks on a local talk show about an upcoming bicycle rodeo the department will sponsor. Educators need to understand their distinct roles in dealing with the media. Many large and even small communities have media bureaus to aid in the distribution of information and the design of brochures and ads. Others have no such resources. With the advent of personalized web pages, however, any department may make a name for itself by simply establishing a presence on the World Wide Web of the Internet. Educators need to understand how technology has transformed the mass communications landscape. Books have been written on communications, media, and education. This chapter outlines the basics and aims to provide practical information to aid fire personnel who communicate with the media. It discusses community media services—print as well as broadcast—noting their similarities and differences. The chapter also explores legal issues involved in working with the media and the public. In addition, it describes four proactive as well as reactive situations in which fire and life safety educators engage the media:
Dena E. Schumacher is the fire and life safety educator, public information officer, and juvenile firesetter interventionist with the Champaign Fire Department in Champaign, Illinois. She is a founding member of the Champaign County SAFE KIDS® Coalition. Her national efforts include membership on NFPA 1035, Public Fire and Life Safety Educator; technical committee member for IFSTA Fire and Life Safety Educator; and NFPA Midwest regional representative for Learn Not to Burn®.
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• Breaking News. Fire service personnel most frequently encounter the media during emergency situations, evacuation, and traffic control. To bolster their news stories, reporters approach any available personnel for further information. • News Fire Service Personnel Can Use. Fire service personnel depend on the media to share injury prevention information the community might need—for example, further education about the effectiveness of sprinkler systems, announcements of car seat check-up events, information about bike helmet fittings at fire stations, poisoning or drowning information through public service announcements and news releases. • Public Education via the Media. Fire service personnel work with the media to educate the public through communication technologies and by providing coursework and
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other materials. Educators find it necessary to become acquainted with and adapt to ever-changing vocabulary and technology (e.g., the Internet). • The Media as Attention Getter. By using media resources, the fire service can send messages in practical ways, such as by billboards, newsletters, flyers, and even hot-air balloons.
DEFINING TERMS Public Relations, Public Education, and Public Information The distinctions between public relations, public education, and public information are fine but critical. There are many similarities among these concepts. All require a carefully thought-out planning process, including a solid implementation strategy. All can and should be evaluated for their effectiveness. The goals of communication for each, however, are different. The goal of a public relations strategy is to improve or sustain the positive working relationship between the fire service and the community that supports it.1 The goal of a public education program is to enlighten people, giving them the knowledge and skill to improve their existence.1 The goal of a public information officer is to service requests for information within the unique scope of the department so that listeners see and understand issues the way the department does. Both public education and public information delivery can contribute to good public relations, although that is not their primary goal. Both rely on good public relations for their effectiveness. A public relations professional might describe public relations (PR) as “communicating specific messages at targeted publics as a means of helping to achieve an organization’s goals and objectives.”2 Tim Birr aptly describes PR as “the art of doing something well and getting caught at it.”2 Some departments believe the PIO, who is responsible for disseminating information to the media at disasters and emergency incidents, serves solely as the department’s spokesperson. The International Fire Service Training Association’s Public Information Officer manual,3 however, broadens the definition to include one who may also provide education to the public, promote public safety, and talk about the services the department provides. As a PIO, the ultimate goal is to enhance the public perception of the department.
Communications Communications is the process by which people interact and, thereby, influence each other.4 To communicate is to impart information. However, information is not necessarily knowledge. Information converts most effectively into knowledge when it is needed, useful, and sought. The PIO should keep two points in mind: 1. The audience is always in the driver’s seat in any communications situation. Audience members ultimately decide whether to listen to, accept, reject, or act on any new information.
2. No one—including our audience—has much interest in operating totally within the confines of someone else’s agenda.5 Active listening and using focus groups and community surveys can help with this process of understanding.
Media A medium is defined as the physical environment through which information can be transmitted by controlled variations in that environment. Variations may be ink patterns on paper, electronic patterns in wires or in air, or sound variations in air. Media include radio, television, newspapers, magazines, motion pictures, direct mail, cable television, books, records, tapes,6 e-mail, and web sites. Different media outlets within the community have different advantages and disadvantages, in terms of the messages they send (e.g., short versus long, emotionally stripped versus emotionally laden) and the audiences they reach within the community.
Media Relations Terms The PIO should be familiar with media relations terms. The following definitions clarify several terms commonly used in media relations. Advance. A news story written before an event and held for later release. Also called an “advancer.”4 Fact Sheet. An information handout of one or more pages about a person or event, provided to assist the media.3 The name and telephone number of a contact person should be provided at the top of the front page. Each page ends with a completed paragraph and “more” typed across the bottom of the page if necessary. The last page ends with “-30-” or a number sign (#) typed at the bottom (Figure 5.5.1). News Release. A short, factual description of an event prepared for the media. The terms press release and news release are interchangeable. The first sentence (the “lead”) in a news release summarizes what needs to be conveyed followed by who, what, where, when, why, and how. The PIO should always provide the source of the information, the headline, the date or dates of the event, and whom to contact for additional information. The PIO should use the “inverted pyramid” writing style, with the most important facts presented in the beginning paragraphs, followed by facts of lesser significance. An editor can then decide the article’s value with only a glance. The news release should • • • •
Be doubled-spaced, with 2-inch margins Be printed on only one side of the paper on agency letterhead Carry the date at the top Have “FOR IMMEDIATE RELEASE” inserted when prompt publishing is desired • Have “FOR RELEASE ON (DATE)” on releases that need to be held until a certain date • Be limited to one page whenever possible • If more than one page, have pages numbered, with “more” placed at the bottom of continued pages and “end” or “-30-” or “#” inserted on the final page
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FIGURE 5.5.1
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NFPA Fact Sheet for Fire Prevention Week
Unless an individual has much broadcast experience, providing the news release information in outline form may be more efficient. This lets the news director create the story. When necessary, the PIO should contact media professionals for input and advice. Press Conference. A meeting between members of the press and a newsworthy figure in which statements are made and/or questions are asked.4 Press Kit. A portfolio of news releases, pictures, background information, and so on, distributed to the press for publicity purposes6 (Figure 5.5.2). Public Service Announcements (PSA). Any announcement for which no charge is made and which promotes programs, activities, or services of federal, state, or local governments or programs, activities, or services of nonprofit organizations and other announcements regarded as serving community interests7 (Figure 5.5.3). News stations are not as committed to public service airtime as they once were; however, many stations keep card and computer files of information provided and use them when possible.
FIGURE 5.5.2
NFPA Fire Prevention Week Press Kit
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Organization Name on Letterhead [Heading information can be single-spaced.] For Information Release
Contact:
Date of release
Name, title Phone number
Story by [optional]
Fax Number E-mail address
NEWS RELEASE [Leave about 2 inches before heading.]
Headline [Double-space body copy.] DATELINE—[Insert location for the origin of the release (in capital letters) plus a dash, followed by the first line of the lead.] Lead: [Start with a hard-news lead, particularly on releases for news events or announcements.] Body: [Write tightly. Limit copy to one page if possible, no more than two. If you have two pages, write “more” at the end of the first page and number the pages.] Ending: [As part of the ending, tell where more information is available such as graphics and Web sites.] —30— or ### FIGURE 5.5.3 Format for a Public Service Announcement (Source: Writing and Reporting News,13 p. 253)
FIRE DEPARTMENT’S COMMUNICATION GOALS AND OBJECTIVES Communications within the Fire Department Hopefully the fire department management will have goals for communication within the fire department, but the public educators, public relations officer, and PIO also have goals defined by external audiences. However, these goals usually require assistance and participation by people in the fire department be-
yond the staff dedicated to communications. The goals themselves may be shaped by concerns or information held by others in the department. Therefore, internal fire department communication must include • Employee-to-employee communication • Staff-to-suppression communication • Fire fighter-to-fire chief communication To be effective, fire and life safety educators and PIOs need the backing and support of the fire department before proceeding into the community and introducing themselves to the
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media. They must know which areas the department wishes to highlight, which departmental goals need an explanation, and how the department wishes to address potentially embarrassing situations. They must also know whether other members are willing to be available to the press and whether media representatives are welcome to stop by the department. After devising a plan to work with the media, department members must help prepare campaigns and programs. Fire department administrators need to review news releases prior to dissemination to prepare for reporters’ calls.
Communications outside the Fire Department A second, more obvious, mission includes communicating information to the public, both before an emergency occurs and at the scene of the emergency. Fire service members possess extensive information. Media representatives, on the other hand, are interested in the information educators can provide. The fire service may serve as the reporters’ “eyes and ears”; the media generally serves as the voice to the public. One key to successful media relations is identifying the audience. Identifying a very general audience may ease the communications planning but will complicate all other parts of the process. It results in diluted messages and weak delivery and compromises the timing of messages. It also wastes and time and materials, forcing fire chiefs, fire and life safety educators, and PIOs to send messages to persons who have neither need for nor interest in them.6 The audience should be specifically identified; this greatly increases any program’s potential effectiveness. (Other chapters in this section provide useful information on defining audiences.) Educators or public information officers who define their audience as “everyone” or “the general public” lack a sufficiently clear understanding of whom they are trying to reach— and should not proceed any further until they clarify this.5 Each news station, newspaper, and news outlet claims a particular audience and a particular area as its own. Media outlets within the fire department’s service delivery area can provide information on their particular target audiences.
UNDERSTANDING COMMUNITY MEDIA SERVICES Another key to successful media relations includes understanding the media’s various roles. To do so, educators need to identify local media, establish credibility, and identify key players at each outlet.
Identifying Local Media To create a positive relationship with the media, fire service personnel must take time to understand each media outlet’s responsibilities and target audience. Some fire service personnel may be able to spend the time and effort necessary to become competent professional-level producers in one or more of the various media. Because most fire service personnel cannot do so, the essential issues become: (1) What sort of relationship can
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full-time fire and life safety educators and PIOs develop with local media representatives and (2) How can they work cooperatively with writers, editors, and broadcasters.5 Fire department representatives must make diligent efforts to meet reporters, editors, photographers, and station managers and get to know them and become familiar with their specific job responsibilities. That may be accomplished simply by scheduling appointments with the various media personnel in the area. Perhaps it includes educating future journalists by setting up a time for the local college journalism classes to visit the station, learn about the fire service, and interview the chief. Some departments hold half-day media academies to allow journalists an opportunity to play and interact. Others such as the City of Phoenix Fire Department provide extensive week-long training sessions (Figure 5.5.4). Job turnover occurs regularly in the media business. Reporters and editors move frequently; so getting to know new personnel is a never-ending task. PIOs should keep a contact list and update it regularly. Media sources can be identified in several ways: (1) by checking media directories, (2) by scanning the Yellow Pages of the phone directory, and (3) by talking with other public relations personnel in the community. A wide variety of books, information resources, and services are available to aid fire and life safety educators in identifying local media resources (Figure 5.5.5). PIOs should balance the created media list by including neighborhood ethnic and suburban papers. They should collect and learn the names, titles, phone numbers, and fax numbers of those in charge. An organizational flow chart proves useful in determining whom to contact about a particular project. Figure 5.5.6 shows an example of media quick call list that can be used during an emergency. Pertinent names and telephone numbers are readily accessible to the PIO, whose role is the one
Certified Fire Journalists The City of Phoenix Fire Department invited media to train as certified fire journalists. The fire department held an intensive training academy for members of the media, requiring them to commit to a full 40-hour, 5-day week. The class size was limited to a maximum of 12. The benefit to the media was the loan of protective gear and certification, allowing the graduates inside fire lines to photograph and report closer to the action on both fire and medical emergencies. The training program included fireground operations; fire behavior; fire suppression; search and rescue; hazardous materials; helicopter, trench, and mountain rescue; emergency vehicle driving (a favorite); emergency medical services; flash over/back draft chamber; and stress management. All students took advantage of an optional hour of physical training. The academy ended with the traditional “Barrel Squirt” competition. FIGURE 5.5.4
Certified Fire Journalists
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MEDIA INFORMATION RESOURCES Media Guides and Directories • Ayer Directory of Publications: The publicist’s bible, lists nearly every newspaper and magazine. It includes publisher’s addresses, circulation, topics covered, and maps with coordinates. A subject index helps users identify audiences by interests. A revised edition is published annually. • Bacon’s PR and Media Information Systems: Presents information on every radio and television station in the United States and includes contact names, formats, target audiences, and network affiliations. • Burrelle’s Media Directories: Includes more than half a dozen directories listing minority media and local media contacts in Chicago, New England, New Jersey, New York, Pennsylvania, and the Washington, DC, metropolitan area. Provides contact names, deadlines, and editorial focus. • Gale Directory of Publications and Broadcast Media: An annual guide to publications and broadcast stations, includes newspapers, magazines, journals, radio stations, television stations, and cable systems. Information Resources • Associated Press Stylebook and Libel Manual: 8 Provides a handy reference for writing press releases; arranged alphabetically by subject. • The Advertising Council (261 Madison Avenue, New York, NY, 10016-2303): Obtains media time and space worth $1.2 billion for nonprofit organizations and government agencies. It “ . . . freely counsel[s] leaders in government and private philanthropy who come to us for help, whether or not a Council campaign eventually emerges.” The Council’s four criteria for projects are 1. The project must be noncommercial, nondenominational, nonpartisan politically, and not designed to influence legislation. 2. The purpose of the project . . . [is] such that the advertising methodology can help achieve its objectives. 3. If the organization is a fund-raising one, the Council will take into consideration whether or not it currently meets the standards of public and private accreditation organizations. 4. The project is national in scope, or sufficiently national so that it is relevant to media audiences in communities throughout the nation. • Public Interest Public Relations, Inc. (PIPR 225 W. 34th Street, Suite 1500, New York, NY 10122): Promotes issues and ideas of not-for-profit organizations. • Fire Chief Magazine: Cooksey, P., “Improving On-Scene Releases,” Fire Chief Magazine, Vol. 29, July 1985, pp. 30–33: Provides additional guidance on news releases. FIGURE 5.5.5
Media Information Resources
most likely to be prominent in an emergency. Building call list numbers into the cell phone is also of great use in event of crisis. The PIO should keep copies of the completed form at home, in the office, and in the vehicle generally used in emergencies.
Establishing Credibility and Identifying Key Players Building the fire department’s reputation with the media is critical. Reporters, editors, station managers, and producers can quickly form opinions about a person’s operating style and credibility. To establish credibility, the PIO must (1) understand what
makes news, (2) know what the media need to know, and (3) use imagination and creativity to find new ways to keep the media updated on the fire organization.9 Reporters need to know the latest trends and opportunities, activities, and resources. The PIO should assure them that accurate and timely facts will be provided, promises will be kept, and deadlines will be met. Then the PIO should follow through. Deadlines are critical in broadcasting and journalism; being late is inexcusable. Creating an archive system is an efficient way to keep track of much departmental information and to be prepared for grant requests, media inquiries, and city manager details (Figure 5.5.7). Having information at one’s fingertips may make the dif-
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Contact Person
Understanding Media: Basics for the Twenty-First Century
Phone #
Fax #
5–69
E-mail
Print organizations 1. 2. 3. Notes
Radio 1. 2. 3. Notes
Television 1. 2. 3. Notes
FIGURE 5.5.6
ference between being or not being on the news at 10. Educators must identify key players at local television and radio stations and newspapers and must understand what reporters, station managers, and editors do. In turn, local television and radio station personnel will most likely better understand the fire and life safety educator’s role in the fire service.
MATCHING THE MEDIUM WITH THE MESSAGE All communications channels have distinguishing features. Each situation is different, and each requires a fresh look.4
Broadcast Media Radio. Radio has been called the medium of the mind;9 the absence of pictures allows more room for the listeners’ imagination to be engaged. Radio is also cost-effective, and most of it is local. Over 95 percent of the population 12 years and older listen to radio at least once a week, and two out of three listeners
Quick Call List Form
tune to FM stations, according to Arbitron, a radio rating service.9 Radio appeals to audiences for many reasons. An intimate medium, far less intrusive than television, it demands less concentration than do newspapers. Portable, it can be listened to while doing most anything. Given the way people listen to radio, programs are built on short, self-contained time segments. The medium, therefore, works best when used to notify, remind, or tell easily remembered, uncomplicated stories. Radio messages must be simple and concise. Radio reporters rely on lively interviews to add color to their stories. Broadcasters suggest stories 20, 30, and 60 seconds in length. The station manager (general manager) oversees all operations. The program director oversees news and sports. Fire service personnel work most frequently with the news director. Note, however, that at smaller stations the station manager is often the owner, program director, and chief engineer. Figure 5.5.8 shows the general organization of a radio station. Individual stations vary considerably, depending on their size and programming. The fire department should identify persons in the offices shown, however, and maintain contact with the news
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How to Create an Information Archive System Here are some general suggestions for setting up an Information Archive System for publicity and proposal purposes. Although publicity and proposal needs may be similar, bear in mind that the information you send should “speak” to the audience in their language and fit the purpose. For instance, there are some items of information that may be required for a grant proposal that would not be appropriate if given to the media. What to Include • • • • • • • • • • •
Articles and editorials that mention your program specifically Articles and editorials that relate to or support the work of your program Photographs that were taken for articles or brochures Video tapes of broadcasts of interviews or those that relate to your program Support letters and “nice notes” from various resources Copies of web site printouts that relate to your program Printed listing of web sites of importance to program Current organizational charts, staff and board lists, operational flow chart Documentation of significant fires and statistics for both your site and others of importance Resource needs list of items with value, current operating budget, mission statement Brochures, flyers, and other program specific information
How to Store the Information • You will use an assortment of binders, files, and computer storage for the information. • Newspaper clippings, support and photos are best saved in sheet protectors placed in binders. Put original clipping in its own protector and mark on it “original do not remove.” Make copies for distribution. BE SURE to record publication name and date of clipping on the original and copies. BE SURE to have name of professional photographer on photo for photo credit. • Clippings, photos and other information can be scanned for even more convenient storage. • Computer storage of files, charts, clippings, photos should be maintained in a wellorganized directory. BE SURE to back up this file regularly. • Video tapes and dupes should be well labeled. Master copies should be kept locked from dupes so that they are not given away accidentally. • Keep copies of brochures in file folders or in a binder separate from regular inventory. This ensures that you always have enough for publicity and proposal needs. Where to Store the Information • Keep the information in a central location that is easily accessible to those who need to distribute the information. • Keep files for grant proposals in a special drawer in a file cabinet for easy access. • You may want to consider keeping your Information Archive locked if it is housed in an area where you share space. Maintaining the Information • Establish procedures and train staff so that everyone is on the same wave length when it comes to saving and distributing the information. • Keep information current! You could be disqualified for funding or ruin a media opportunity if information is obviously outdated. • Have program kids assist you in clipping articles and maintaining photo and clipping files. • Keep a master inventory of the types and quantity of information you have on hand so that you always have enough copies. • Keep an inventory sheet in the file to record when an item is removed, who removed it, and what purpose the item was used for. • Pick a regular time once a month or quarter (minimum) to review the files to ensure that they are in order, stocked, and up-to-date. FIGURE 5.5.7 Creating an Information Archive System (Source: © Mary Beth Miller, The Right Steps Resource, www.therightsteps.com)
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porters, as well as the vice president for public affairs and members of the public affairs staff, such as the public service director and the editorial writer. Before approaching a television news department with a story idea, the PIO should know the station’s format and the individual to whom the idea should be pitched. Television reporters believe the best stories have strong visuals that grab and hold a viewer’s interest. With a camera crew in tow, a television reporter is attracted to activities that make exciting or interesting footage and to interview subjects who talk in clear, concise language.9
General Manager
Sales Manager
Program Director
News Director
Promotion Director
Chief Engineer
Advertising Department
Producer
Reporters (2)
Public Affairs Director
Engineer
Announcers (6)
Generalized Organization of a Radio Station
FIGURE 5.5.8
5–71
director and individual reporters, as well as the promotion director and public affairs director. Television. “When nightly television news began in 1948, newscasts were 15 minutes long. In 1963, the first 30-minute newscast was broadcast. Today, CNN, MSNBC and other national and local cable network broadcast news around the clock. Since then, television has become America’s predominant source of news.”10 Just as with radio, understanding the television system helps the fire department receive airplay and may increase its credibility. Key contacts in the television news department include the news director, who oversees news and broadcast staff; the assignment editor, who assigns reporters to stories and ensures coverage of major stories and “beats”; the news producer, who determines which reports will air; and reporters who cover the stories. For information on television public affairs, the PIO should approach the public affairs director or the public service director. Figure 5.5.9 shows the general organization of a television station. Most stations have large staffs, sometimes numbering into the hundreds. Key contacts include the vice president for news, the news director, the assignment editor, and individual re-
Public Access Television. Public access television is another excellent and inexpensive way to provide community education programs. Approximately 2000 public educational or governmental access channels in the United States are either citysupported, member-based, or franchised from the cable company. The community cable company can explain how the system operates locally. Local talk shows also provide an excellent forum for sharing information. Educators should take time to view a segment of a program before agreeing to appear. Television tends to be underutilized for educational purposes. In the emerging information age, when the trend is to move “from institutional help to self-help,” television and videotapes can be the educator’s forum to speak with millions of people in the places where they live, study, work, and play. The equipment is in place. The channels are open. The medium is available and waiting for the message.9
Print Media Print journalism includes daily and weekly newspapers, magazines, and wire services. Print media have space for longer items—long enough to have an educational impact, not just awareness—and their readers are receptive to such longer pieces. Reporters need good sources to inform them about timely, important stories. By understanding how the press operates, how to prepare press releases, and with whom to work, the fire department can provide that good source. They can identify the
General Manager
Vice President, News
Vice President, Programming
Executive Producer
News Director
Executive Producer
Producers (5)
Assignment Editor
Technicians
Camera crews
Vice President, Public Affairs
Public Service Director
Producer
Vice President, Sales
Editorial Writer
Sales Manager
Reporters (20)
FIGURE 5.5.9
Generalized Organization of a Television Station
Advertising Manager
Marketing Director
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types of press available in the area by consulting newsstands, media directories, phone books, and web sites (see Figure 5.5.6). After creating a complete list of print media, educators can determine who is best suited to convey information for a particular campaign. This is a good first step. The second step is to identify the appropriate editors, reporters, and other newspaper and magazine contacts. Doing so increases the likelihood that the copy will be read and professionally handled. As in broadcast media, understanding the print media hierarchy is essential. Most newspapers are staffed similarly with the same general titles; however, the work done under those titles varies from paper to paper, city to city. To better understand this, look at the major divisions in a large daily newspaper. There are generally three: (1) the corporate board and executive committee, (2) the business division, and (3) the editorial division.11 The first two divisions have little to do with the fire department’s publicity and media needs. The editorial and news staffs can provide more assistance. A large daily, for example, the Washington Post, contains many sections. For that reason, it is important for the PIO to identify the sections of the paper most likely to use safety information and the person on the staff best suited to help. When dealing with a medium-sized newspaper, the PIO will likely have contact with the news editor, assistant news editor, features editor, and one or two reporters on the mailing list. Figures 5.5.10 and 5.5.11 show the organization of weekly newspapers. The small weekly has a circulation of about 5000. The medium-sized weekly has a circulation of about 100,000. Editors and reporters of a paper this size can all be used as publicity contacts. Efforts should be made, however, to identify precisely the “beats” or areas for which each editor and reporter is responsible. After identifying the target audience, the fire department must determine what reporters need. All reporters are attracted to a good story, but each has a somewhat different way of covering it. A newspaper or magazine reporter will generally interview sources in person or on the telephone, looking for photographic possibilities or statistics for an eye-catching piece of graphic art.9
Publisher
News Editor
Assistant Editor
Reporters (2)
FIGURE 5.5.10 Weekly
Freelancers
Generalized Editorial Structure of a Small
Publisher
General Manager
News Editor
Assistant News Editor
Editor (Region)
Editor (Metro)
Reporters (5)
Reporters (3)
Features Editor
Reporters (3)
FIGURE 5.5.11 Generalized Editorial Structure of a Medium-Sized Weekly
Public Service Announcements (PSAs) One common way to inform the public is through public service announcements (PSAs). Prepared for radio and television stations, PSAs are short announcements, generally running between 10 and 60 seconds. The Federal Communications Commission (FCC) defines a PSA as “any announcement . . . for which no charge is made and which promotes programs, activities, or services of federal, state, or local governments . . . or the programs, activities, or services of nonprofit organizations . . . and other announcements regarded as serving community interests.”7 PSAs give the listener important information. Generally, the first two-thirds of the copy attracts attention and directs the listener to further information. Much can be said in 20 seconds. Note, however, that stations no longer have a legal obligation to provide a minimum amount of public affairs and public service programs. In a mid-sized market, the educator may deliver PSAs and reasonably expect that they will be used. In major markets, placing PSAs becomes increasingly difficult. Because competition is strong, many stations stylize their newscasts to stand out on the crowded dial. They simply refuse to run anything their competition might have also received. In most large markets, it is best simply to become a news source. Provide information in a regular and timely fashion.9
Understanding What Makes News News may be defined as any piece of information that will affect your head, heart, or pocketbook.9 News reports something new—information that is a break from everyday events. Some news is information that people need in order to make sound decisions about their lives.12 News editors decide if information they receive is indeed newsworthy by checking news values or
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news pegs. These news pegs are the basis for deciding what makes it to print and what does not. From the media’s viewpoint, six factors (i.e., news values) determine an event or an idea’s newsworthiness: 1. Consequence: Does the event affect many people? 2. Interest: Is the event an unusual, rare, odd, or interesting situation? 3. Timeliness: Are the events immediate or recent? 4. Prominence: Does the event involve well-known personalities or institutions? 5. Proximity: Does the event occur within the circulation or broadcast area? 6. Conflict: Does the event show dissent or trouble between people or institutions? At least three-fourths of all news stories fall into the first two general categories of consequence and interest.12 News is relative. Each day, changing dynamics define “news.” These dynamics include how much news occurred that day, the advertising load for the days, the type of audience, and the type of medium. Hard News. “Hard” news must be covered immediately or it becomes stale. Today’s news is not necessarily tomorrow’s news. Fire and emergency disasters are in the category of hard news. If the facts about an emergency emerge slowly, the story may develop longevity while remaining hard news. If the event pushes a larger event into prominence, that larger issue may acquire a life independent of the event and become “soft” news. The basic hard news story for the Web, for print, or for broadcast is written in what is called an inverted pyramid style. The most pertinent details appear at the top of the story; less important details are toward the bottom of the story, allowing the editor who is short on space or time to cut the bottom of the story while still preserving the most important information. Soft News. Many news items do not fit the emergency (hard news) model yet are still newsworthy or educational. “Soft” news is less urgent, more complex, and often has more perspective than hard news. Soft news items that originate as such usually cannot be committed to a specific day; news editors decide how or when to place these items. By identifying an event, writing an appropriate headline, relating how it affects the community, and explaining how this information can help to avoid another accident, an educator can increase the chances of the media using the information. Most local fire service stories lack the inherent news value of a national event; however, ample community interest exists to warrant sharing information. Many fire service activities are considered news, and announcements of them may be locally broadcast and printed. Local media and community members may want to know of meetings, rallies, seminars, and open houses. Workshops, National SAFE KIDS Campaign® activities, bicycle safety demonstrations, and checkpoints can raise citizens’ to safety consciousness. Public statements on local affairs, awards given and received, fund drives, calls for membership, and the appointment and resignation of organization officials can generate consider-
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able interest. Announcements of the availability of free speakers, films for loan, and the findings of reports and surveys conducted by the department have community news value. There is no limit to the activities that can generate publicity—especially for a well-organized, positively focused, energetic group. The PIO should let the media know—in their terms—how fire service information provides their audiences with useful, creative, positive information.
Press Releases and Interviews Online Press Releases. Many news organizations may prefer to receive their press releases in online form. The information does not need to be retyped. That way it can be stored in computers. PIOs should not, however, send unsolicited electronic press releases but should first ask if the news organization wants the material sent electronically. For online releases, the PIO should try to limit the length to two screens and should include any related web sites.13 Today’s reporters often multitask. The radio station may expect a reporter to place broadcast news stories and information on the station’s web site. The television station may post news clips from the 6 p.m. broadcast on its Internet site. This concept, called convergence, is the blending of print, audio, and video to create multimedia news products for television, newspapers, and the Internet. It is the next step in journalism. PIOs should be prepared for changes that will affect how the fire department does business with the media. Educators should remember that messages that destroy do not reflect the intent of educational news, hard news, or practical publicity credibility. They should, therefore, never overstate or distort the significance of an event, inflate serious issue, or be theatrical. Interviewing Tips. An interview is a formal exchange of information. The PIO should know as much as possible about the reporter(s), audience(s), and issue(s) before providing an interview. The interviewer must be aware that the message goes to all readers, listeners, and viewers to whom the interviewing reporter provides information. Communicating clearly and credibly and defining the “headlines” that the audience should see or hear is essential in an effective interview. In addition, when being interviewed, 1. Be prepared. Review all pertinent information before the interview. Anticipate and prepare for questions the interviewer is likely to ask. Have reference notes. 2. Be professional. Dress appropriately. Avoid unnecessary movements and gesture calmly. Move more slowly than you normally would. Avoid chewing gum, smoking, or eating when providing reporters with information. Be confident. Look the reporter in the eye. During an interview, resist the temptation to look straight into the camera or at yourself on the TV monitor. 3. Be newsworthy, factual, and correct. Double-check information before releasing it to the media. 4. Plan points to be made. Present two or three main points as quotable single-sentence summaries. Begin the interview by stating the most important points or conclusions.
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5. Be understood. Use common language; avoid fire fighter jargon and technical terms. When technical terms must be used, explain them. 6. Assume that all is “on the record.” Anything said can and likely will be used. 7. Never say “no comment.” It invites speculation. Rather, say “I don’t have enough information to properly answer that question.” 8. Avoid “traps.” If the reporter’s question contains objectionable words, don’t repeat them in any answer, even to refute them. If a reporter poses a hostile or inaccurate remark, respond by saying, “First let me correct a misperception that was part of your question.” 9. Maintain composure. Some interviewers try to provoke angry responses to get additional information. Always remain calm and courteous. 10. Be prepared to restate your policy or position. Do not attempt to answer hypothetical questions. Refocus the interview on the issue by saying, “Here’s the situation we are focusing on.” 11. Don’t be afraid to say, “I don’t know.” If the answer to a question is not known, say so. Follow with, “As soon as I get the information, I’ll get right back to you.” Make note of the question and get the answer. 12. Stay on track. Don’t digress from the subject. Lead a reporter who starts to wander back to the subject at hand. 13. Be accountable. Never assign blame or criticize. 14. Be available. Offer to answer any follow-up questions a reporter may have and help clarify problems that may arise as the story is being written or edited. 15. Be honest. Never lie or “stretch the truth.” Such tactics rarely work and, when discovered, can have severe consequences. 16. Be patient and willing to teach. Reporters have different professional knowledge and backgrounds. They need education on some fire and life safety issues. 17. Stand up and be counted. Keep records of media calls. See how and if department comments were used. If a serious misinterpretation becomes apparent, call the reporter or editor and ask for a correction. If reporters used comments in an appropriate and effective way, tell them so.
PROVIDING PRACTICAL PUBLICITY Fire and life safety educators must carefully plan how to spend limited money and time. One approach is practical publicity. Practical publicity is used here to mean a program with a substantial public relations front end that is designed to set up a public education campaign with broad reach. First, educators get the public’s attention. Second, they build interest and trust. Finally, they teach. Distributing frisbees shaped like smoke alarms and imprinted with “Test Your Detector” helps provide departmental recognition. More complex examples might include an open house or a mass CPR training. There is no single “best” way to run a publicity campaign. Communities have individual traits and characteristics. Groups within communities have specific needs and interests. However, a three-phase publicity framework from which to build exists; it can also be used as a benchmark for evaluation.11
1. Kick-off phase: This “name recognition” phase explains who the group is—that is, the education division of the fire department, its foundation and origin, and its plans for the future. Billboards, lawn signs, placards, news releases, flyers, and rallies support this phase. 2. Expansion/issue-oriented phase: This phase comes after the public knows what the public education group in the fire department does and believes it to be credible. At this stage, the goal is to acquaint citizens with issues important to the fire department. The key is to emphasize issues, educate, and inform. Providing accurate information maintains credibility. Use seminars and workshops, radio and television editorials, newsletters, PSAs, and news releases. Meet the people face to face.11 Note that this phase is still a public relations activity, but by moving from a broad department focus to an issues focus, it sets the stage for education. 3. Culmination phase: After establishing an identity, informing citizens, and focusing on important issues, the fire department can educate.11 Use local as well as national statistics and data to add credence for a specific campaign; like increased use of sprinkler systems within new residential construction. Begin to work more closely with like-minded agencies such as the National SAFE KIDS campaign, the local police department, park district, water conservation specialist, Cooperative Extension agencies. The more groups there are sending a similar message, the more likely “air time” will come for all involved. Educators could investigate hiring a public relations firm if there is a specific issue that needs to be addressed. They could call on the already informed public if a popular issue, for example passing fireworks reform legislation, arises. Phone “trees” (in which one group of people calls a second group, the second group calls a third group, etc.), newsletters, direct mailings, letters to the editor, letters to politicians, press releases, news releases, citizen editorials, and media coverage are effective after publicity efforts have made issues newsworthy. The effect is an amplification of the group’s plea—a far greater noise than the group could ever make alone.11 Other options for the public relations phase include alternative outlets and campaign strategies, such as • • • • • • • •
Exhibits and displays Newsletters Poster contests Attention-grabbing methods (e.g., hot-air balloons) Instructional slide shows or videos Signs, billboards, and bumper stickers Safety trailers Flyers, brochures, grocery bags, placemat announcements
PROVIDING PUBLIC INFORMATION AT A FIRE/EMERGENCY SCENE The PIO is responsible for gathering, preparing, and providing information to the media. The PIO helps convey the needed story safely, quickly, and efficiently and serves as the contact between the incident commander and the media. The PIO’s goal is to help the media present an accurate, understandable, fact-filled account
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of the emergency and to ensure that reporters are safe and not interfering with those who are attempting to secure the scene. Public information officers link the fire service and the community. The PIO, acting in a professional capacity, assembles as much timely and accurate information as possible and informs reporters so they, in turn, can provide it to their viewers, listeners, and readers. The job of PIO is a “role rather than a rank.”14 The professional PIO does not attempt to stand in the limelight or upstage a fire officer. After gathering information, the PIO streamlines the process of providing reporters with needed information as fire fighters continue their work. Four excellent resources that should be in the library of every PIO are • Birr, Tim, Public and Media Relations for the Fire Service, Fire Engineering Books and Videos, PennWell Publishing Company, Saddle Brook, NJ, 1999, 156 pp. • Charlesworth, Michelle, Public Information Officer, International Fire Service Training Association, Fire Protection Publications, Oklahoma State University, 1999, 104 pp. and disc with forms. • NFPA 1035, Standard for Professional Qualifications for Public Fire and Life Safety Educator. • Riha, Bob, Jr., and David Handschuh, National Media Guide for Emergency and Disaster Incidents, National Press Photographers Association, Durham, NC,1995, 81 pp. As in every other aspect of the fire and life safety educator’s job, the PIO will be more efficient and effective if planning and thought have been put into practice ahead of time,before the inevitable emergency arises.
Creating and Following Standard Operating Procedures (SOPs) Creating standard operating procedures (SOPs) expedites work with news media at an emergency scene or at any other time or place reporters might be contacted. SOPs establish (1) who in the department may speak with the media and (2) how the fire chief wants the matter handled. The PIO provides the bridge between the fire department and the community served. Often the community does not understand the fire department’s day-to-day operations and activities. The community may not know how the modern fire service operates or the various tasks fire personnel perform, despite impressive efforts in evidence. In most jurisdictions, the percentage of citizens who call the fire department for emergency assistance is low. Although the fire service conducts many public education and community service activities, a high percentage of the community learns of these activities only through the media. Providing clear, concise, and timely information to the media benefits everyone.15
PIO Tools When facing reporters at an emergency scene, the PIO needs essential tools: • A radio to communicate with fire command and other suppression personnel.
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• Two pencils, a notepad, and a small tape recorder. Addresses, names of persons injured, telephone numbers, and so on can easily be forgotten in the rush of a large emergency. The PIO should write them down. If the PIO’s style is to include every detail, the conversation should be taped. Taping conversations allows self-critiquing later. If inaccurate reporting becomes a problem, the tape recorder may show reporters that the PIO expects them to provide correct information. • A cellular telephone for updating the news media and communicating with others involved in the situation. • A media quick-call list provides up-to-date phone numbers. The quick-call list is a short version of the media address and phone list. In an escalating emergency, the PIO must be prepared to notify media sources or update them as the situation changes. The list includes essential local broadcast and print media news reporters and personnel (see Figure 5.5.5). • Basic question list—media worksheet, including basic interview tips, fire information, EMS information, hazmat information, and rescue information (Figure 5.5.12).
EVALUATING EFFORTS In any process, the final stage is evaluation. To assess success, PIOs should compare the results of a program with its original objectives. Although it is not this chapter’s purpose to discuss evaluation in depth, PIOs should understand the importance of evaluation and feedback. For example, if the percent of the public aware of bike safety as an issue increases by half after the fire and life safety educator provides three public service announcements and appears on local community calendar talk shows, the value of the effort is evident. If the number of bike-related injuries decreases by half after the educator conducts a school program to teach bike safety, the value is evident. If most of the public is aware of a recent large fire, describe its points accurately, and report that they trust the information provided by the fire department, then PIO efforts have been successful by those measures. From 1988 to 1998, the National SAFE KIDS Campaign worked diligently to reduce unintentional injuries across the nation. Over the past decade, the unintentional injury death rate among children aged 14 and under has declined by 33 percent. Through the campaign’s 300 state and local coalitions, in 50 states and Puerto Rico, over a million bike helmets, 500,000 car seats, and 100,000 smoke alarms have been given away: properly fitted and/or placed.16 Evaluations may be conducted either throughout the program or after completion of the program. If the objectives are met, pertinent information for future planning becomes available. If the objectives are only partially met, reasons for failure can be explored.
EXPLORING LEGAL ISSUES The fire department must be aware of various legal terms and issues. When dealing with the media, PIOs should leave no room for carelessness, misunderstanding, or inaccuracy. Copyright laws, privacy acts, broadcast regulations, and the federal Freedom of Information Act (FOIA) should be understood and
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FIGURE 5.5.12 Department)
Phoenix Fire Department Public Affairs Media Guide (Source: Phoenix Fire
addressed. PIOs should develop a working relationship with the city attorney.
Copyrights Copyright questions arise frequently. Downloading a photo or document from the Internet without permission is a violation of copyright laws. U.S. copyright laws protect everything written the minute the information is offered in “fixed form,” which includes online or print information. Enacted in 1997, the No Electronic Theft Act provides penalties of up to $500,000 and five years in jail for copying software or online materials even if no profit is made. The Digital Millennium Copyright Act of 1998 provides further penalties of up to $1 million for copying online materials for profit.13 The fire department user must receive permission from the author or publisher. Copyright laws dictate that copyright owners
have the exclusive right to reproduce, distribute, and use original works of expression fixed in a tangible medium. NFPA’s Sparky® is an example of a registered trademark. The National Fire Protection Association’s legal office must grant permission before a fire department may use Sparky for any promotion, activity, or brochure. Copyright statutes, revised in 1976, take into account developments in photocopiers, videotapes, motion pictures, broadcasting, cable television, and other technologies developed after the act’s adoption in 1909. To claim a copyright, • Place a copyright notice on the work. This information, written in the upper-right-hand corner of the work, claims the copyright. • Complete a copyright form and pay the designated fee. • Register the work with the copyright office in Washington, DC.
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Further, when using copyright material, include: • The word “copyright,” the abbreviation “Copr.,” or the symbol “©” • The name of the owner of the copyright • The year of publication Registration is not necessary for a valid copyright, but if a suit is brought, the work must be registered. Generally, copyrights last the author’s lifetime, plus fifty years. For copyright information, contact Copyright Office Information and Publications Section, LM-455 Library of Congress Washington, DC, 20559 Publications available include • • • •
Catalogue of materials published Highlights of new copyright law (#R99) Copyright basics (#R1) Trademarks (#R13)
Freedom of Information Act What rules pertain when a citizen asks for access to a private meeting? When must meeting transcripts be released? Freedom of information is defined as the “access to government documents that do not compromise national security or violate privacy rights of individuals.”6 “Sunshine” laws address media access to public meeting records. Varying from state to state, these laws generally cover • • • •
The amount of notice required to hold a public meeting Whether or not a meeting is open to the public Requirements on meeting minutes or transcripts Executive session rules
The federal Freedom of Information Act, a 1966 statute, requires all federal executive and administrative agencies to furnish information to the public when it is requested, unless that information is in one of nine protected categories. The scope of the act was expanded in 1974.4 A model for many state laws, it is designed to make government information available to the public. The government has 10 days to respond to a request and 20 days to respond to an appeal if records are denied.12 Libel and slander laws protect the reputation of a person or institution. Libel is written defamation. It is essentially a false or defamatory attack in written form on a person’s reputation or character. Broadcast defamation is libel because there usually is a written script. Oral or spoken defamation is slander.12 The fire department must be constantly watchful for photographs and statements that might defame or invade another’s privacy.
COMMUNICATION TECHNOLOGIES Today’s PIOs and fire and life safety educators have the world at their fingertips: databases, e-mail, educator groups, and millions of web sites. With a modem, an Internet account, and a computer, they may pick the brains of the best and the brightest
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fire and life safety educators across the globe. The Internet is filled with pages containing hundreds of valuable links. Indeed, advances in computer technology have strengthened the relationship between communications and education. What once seemed impossible is today commonplace. Fire service personnel need to be trained and updated frequently on not only the advances in suppression technologies but also developments in computer technologies. Self-education via online classes and CD-ROM is common today. Bruce Piringer, director of the University of Missouri’s Fire and Rescue Training Institute, believes this fact will change the fire and life safety educator’s position to one of managing, rather than delivering, programs. Personalized educational programs may be found on many departmental web sites today. Pull-down menus allow people to create personal home escape plans, hunts for hazards, or search for specific injury or prevention information. The success of the Internet and online magazines such as www.firehouse.com have made information gathering decidedly more friendly. Up-to-the-minute updates may be found with the click of the mouse. More information and data than a mind can comprehend may be located with that same mouse. In 1998 the All-in-One Search Web page listed more than 400 search engines, databases, indexes and directories that catalogue information on the Internet.10 With the power of PCs doubling every few months, we might soon expect integration of all digital technologies. Computing, publishing, entertainment, communications, and consumer electronic devices will all use and produce digital data. The world is amid an uncharted information environment in which users may copy, move around, and interchange all types of data. This leads to one caution: Everything on the Internet may appear to be official. It is easy to assume it is fact. Often, however, information posted on the Web is incorrect. PIOs should always double-check facts with another source and develop their own tough standards for which sources are reliably accurate and credible. Educating with computer-based media offers numerous possibilities, for example, one-to-one teaching, continuing education, and professional development for fire and life safety educators. Many North American universities use computer-based communication technologies. Among the technological possibilities are audio conferencing, satellite video conferencing, and computer-based audio graphics. Portions of these educational resources are available, at minimal cost, to fire and life safety educators through cooperative extension offices that operate through partnerships with federal and state authorities and through community colleges. The challenges and opportunities for the PIO and fire and life safety educator seem endless. These next few years may see an explosion of media and Internet possibilities. However, the basic and fundamental steps of researching, face-to-face communications, and understanding how the “other side” thinks, will never go out of style.
SUMMARY Honest, forthright communications, data collection, and evaluation sit at the heart of any outstanding public relations/public
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information campaign. Wise administrators recognize the value of training fire personnel in communication skills and marketing techniques. The positive dividends reaped through targeting identified audiences allow citizens to be trained appropriately and money to be spent well. Emphasis and training on public information enhances the positive relationship fire departments worldwide value and enjoy with the citizens they serve.
BIBLIOGRAPHY References Cited 1. Crawford, J., “How to Tell the Difference—What Every Fire Service Leader Should Know about Public Education and Public Relations,” IAFC On Scene, Vol. 6, No. 13, 1992. 2. Birr, T., Public and Media Relations for the Fire Service, Fire Engineering Books and Videos, Saddle Brook, NJ, 1999. 3. Charlesworth, M., Public Information Officer, International Fire Service Training Association, Oklahoma State University, Stillwater, OK, 1999. 4. Evans, J. F., “Education Campaign Planning,” Course reference, University of Illinois at Urbana-Champaign, 1985. 5. Blackburn, D. J. (Ed.), Extension Handbook, Processes and Practices, Thompson Educational Publishing, Inc., Toronto, Canada, 1994. 6. Ellmore, T., NTC’s Mass Media Dictionary, National Textbook Company Business Books, Lincolnwood, IL, 1991. 7. Yale, D. R., The Publicity Handbook, NTC Business Books, Lincolnwood, IL, 1991. 8. Associated Press, Associated Press Stylebook and Libel Manual, Addison-Wesley, New York, 1996. 9. Calvert, P. (Ed.), The Communicator’s Handbook, Techniques and Technologies, Maupin House, Gainesville, FL, 1993. 10. Scanlan, C., Reporting and Writing: Basics for the 21st Century, Harcourt College Publishers, Orlando, FL, 2000. 11. Tedone, D., Practical Publicity, How to Boost Any Cause, Harvard Common Press, Boston, MA, 1983. 12. Mencher, M., News Reporting and Writing, Wm. C. Brown Publishers, Dubuque, IA, 1987. 13. Rich, C., Writing and Reporting News: A Coaching Method, Wadsworth Publishing, Belmont, CA, 2000. 14. Harber, J. B. (Ed.), The Public Information Officer: A Media Relations Training Program for the Fire Service, Action Training Systems, Inc., Vancouver, WA, 1993. 15. Kirtley, E., PIO Training Materials, Colorado Springs Fire Department, 1993. 16. www.safekids.org. Web site, May 30, 2001.
Additional Readings Birr, T., “When the News Hits the Fan: Preparing for the Inevitable,” Fire Engineering, Vol. 152, No. 12, 1998, pp. 63–65. Cavagnaro, E., “Broadcast Media: The Key to Communicating with the Public in Large Scale Disasters,” KCBS Newsradio 74, San Francisco, CA, CIB W14/95/1 (J); Tokyo Fire Department, Firesafety Frontier ’94, International Fire Conference and Exhibition in Tokyo, on Creating a Safe Tomorrow, October 18–22, 1107112, Tokyo, Japan, 1994, pp. 229-232. Clark, E., “Media Frenzy Turned Disaster into a Spectacle,” Fire, Vol. 93, No. 1151, 2001, p. 9. Comeau, E., Ode, M. C., and Duval, R. F., “Office Building Fire, New York, New York, October 10, 1996,” National Fire Protection Association, Quincy, MA, NFPA Fire Investigation Report, 1997. Dunford, D. O., “Electronic Evolution,” Fire Chief, Vol. 40, No. 6, 1996, p. 56. Dunn, V., “13-Point Size-Up of a High-Rise Fire,” Firehouse, Vol. 24, No. 1, 1999, p. 16.
Dunn, V., “Fire Service and the Last Quarter of the 20th Century,” Firehouse, Vol. 26, No. 8, 2001, pp. 96–98. Federal Emergency Management Agency, “Home Fire Safety: Act On It! How the Media Can Promote Public Fire Safety Education,” Media Kit, Federal Emergency Management Agency, Washington, DC, 1992. Federal Emergency Management Agency, “Public Fire Education Today: Fire Service Programs Across America,” Federal Emergency Management Agency, Washington, DC, FA-98, Sept. 1990. Gosnell, R., “Maximizing Media Coverage,” Fire Engineering, Vol. 153, No. 5, 2000, pp. 93–94. Hansen, J., “Working With the Media,” Fire Engineering, Vol. 148, No. 10, Oct. 1995, pp. 116-119. Hansen, O. J., “Protecting Norway’s Newest Airport,” Fire International, No. 168, Mar. 1999, p. 21. Hunt, R., “Why It Is Vital for Brigades to Effectively Investigate when Accidents Occur,” Fire, Vol. 90, No. 1106, 1997, p. 27. Kefalas, J., and Weninger, S., “ICS with a Memory,” Fire Chief, Vol. 45, No. 1, 2001, pp. 37–38. Khan, B., “Phoenix Fire Department Certified Fire Journalist Program,” Fire Engineering, Vol. 152, No. 12, 1998, pp. 60–61. King, K. B., “Buying the Front Page/Media Marketing,” Keller FireRescue, TX, International Association of Fire Chiefs (IAFC), Fire-Rescue International Conference Proceedings, 1993 Annual Conference, August 28–September 1, 1993, Dallas, TX, 1993, pp. 27–33. Knisley, J., “Good, the Bad and the Ugly: Dealing with the Media,” Fire Fighting in Canada, Vol. 42, No. 3, 1998, p. 16. MacOwan, D., “Secure Digital Communications: The Future Comes Closer,” Fire International, No. 185, Apr. 2001, pp. 12–13. McKeever, L. P., “Radio Procedures: A Practical Guide for Fire Departments,” Firehouse, Vol. 22, No. 2, 1997, pp. 36–38. Morris, G., “Capturing the Power of Television,” Fire International, No. 176, May 2000, p. 15. Murphy, J. J., Jr., “McDonald’s and Media Teach Fire Prevention,” Fire Chief, Vol. 35, No. 4, 1991, pp. 70–71. Phillips, K., “Radio Telemetry Trials Show Positive Results,” Fire, Vol. 90, No. 1505, 1997, pp. 25–26. “Radio Problems at Bombing Incidents,” Fire, Vol. 90, No. 1106, 1997, p. 31. Riddet, A., “Replacement Communications Systems: Does This Need to Be a Problem?” Fire Engineers Journal, Vol. 58, No. 194, 1998, pp. 20–24. Sanders, R. E., “Long-Term Answer Is Public Education,” NFPA Journal, Vol. 87, No. 6, 1993, pp. 14, 26. Schaenman, P., et al., Proving Public Fire Education Works, TriData, Arlington, VA, 1990. Stittleburg, P. C., “Making the Media Work for You,” NFPA Journal, Vol. 88, No. 6, 1994, pp. 25, 102. Torres, H. L., “Cooperative Communications,” Fire Chief, Vol. 43, No. 6, 1999, p. 38. United States Fire Administration, “Fire Risks for the Deaf or Hard of Hearing,” Washington, DC, October 1999. Walton, W. D., Bryner, N. P., and Jason, N. H., (Eds.), Proceedings of the Fire Research Needs Workshop, October 20, 1999, Emmitsburg, MD, National Institute of Standards and Technology, NISTIR 6539, July 2000. Walton, W. D., Bryner, N. P., Madrzykowski, D., Lawson, J. R., and Jason, N. H., (Eds.), Proceedings of the Fire Research Needs Workshop, October 13–15, 1999, San Antonio, TX, National Institute of Standards and Technology, NISTIR 6538, July 2000. Werner, C., “New Technology in the Firehouse,” Firehouse, Vol. 26, No. 8, 2001, p. 124. Wilbur, M., “Evaluating Vehicle Pre-Emption Systems,” Firehouse, Vol. 24, No. 5, 1999, p. 32.
CHAPTER 6
SECTION 5
Evaluation Techniques for Fire and Life Safety Education*
Revised by
Karen Frush John R. Hall, Jr.
I
njuries from fire and other causes account for a significant number of deaths in all age groups in the United States, and unintentional injury is the leading cause of death in children aged 1–14.1 In recent years scientists have come to better understand the risk factors involved in injuries and the potential of a wide range of engineering and education measures to successfully reduce injury occurrence or severity.2 Proven interventions, such as smoke alarms, child safety seats, and bicycle helmets, can substantially reduce the number of fatal and nonfatal injuries and decrease the enormous dollar loss associated with these injuries, premature death, or long-term disability.3 However, these measures must be successfully implemented to be effective. Selecting the most effective strategies— or the best strategies one can afford—requires evaluation. Designing a chosen strategy for greatest impact requires evaluation. So does successful implementation. Every reader or user of the Fire Protection Handbook section on fire and life safety education has to make decisions about educational programs. They may be decisions about whether to adopt an educational program in a community or school that has none. They may be decisions about how to modify or reinforce elements of an educational program to reflect the special needs or capabilities of a particular group of students. They may be strategic, tactical, or operational decisions. But in the end, every decision comes down to good information about better versus worse, about more versus less effective. Evaluation refers to any systematic process for gathering information about better versus worse. The term evaluation means different things to different people. That leads to various concepts of how to evaluate a public fire and life safety education program. Some people evaluate *The first version of this chapter appeared in the 18th edition of the Fire Protection Handbook and was largely based on the book Proving Public Fire Education Works published by TriData Corporation in 1990 under the authorship of Philip Schaenman and Paul Gunther. Many of the tables in this chapter originally appeared in that book.
programs based on how well the public education program is accepted and used by teachers, or how well it is liked by the target audience. Others evaluate a public education program from the point of view of features that are thought to constitute a good program, such as whether it has good graphics, is well targeted, and has input from various community groups. Another type of evaluation asks whether a program causes “institutional changes,” such as getting additional funding for public education materials, obtaining additional slots for public fire and life safety educators in the prevention bureau, having public education incorporated in the school curriculum, or stimulating local businesses and service organizations to participate in public safety education. All of these concepts of evaluation are useful. All help indicate the path to program success. But they are several steps removed from being able to prove that public fire and life safety education works in achieving its main purpose: reduction of deaths, injuries, and dollar loss from fire. Many programs have side effects, secondary missions, or even hidden agendas. Public education, for example, can enhance the image of the fire department, demonstrate a caring city administration, and raise or lower public fears. A sophisticated, comprehensive set of measures of effectiveness of a public program would consider such issues, which often are important in the minds of managers under their day-to-day political pressures. But the main purpose of public fire and life safety education is to improve safety, and unless one can demonstrate that a program is achieving this goal, it will be hard to convince decision makers in the long run that the program should be supported. Sooner or later questions will arise about the bottom line. The purpose of this chapter is to present an overview of the evaluation process and a hierarchy of evaluation measures. In addition, the chapter will illustrate the evaluation process and hierarchy through examples based on the NFPA Risk Watch® curriculum.
THE EVALUATION PROCESS Dr. Karen Frush is director of pediatric emergency services and the Injury Prevention Center at Duke University Hospital. Dr. John R. Hall, Jr., is NFPA assistant vice president for fire analysis and research.
Evaluation is the process of determining whether a curriculum, educational program, or community initiative is effective and appropriate, and it may indicate whether a program has unexpected benefits or creates unexpected problems.4,5 Because evaluation
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is a process, it begins early, in the initial stages of program design, and continues throughout the development and implementation of the program. Many injury prevention programs have been developed, but few have been rigorously evaluated and shown to be effective in reducing injuries. Reasons for this may include a lack of funding to support evaluation efforts, a focus on implementation and service delivery rather than evaluation, or a lack of understanding of the importance of evaluation. Target populations may be too small, or the injury event and safety behavior too rare to demonstrate significant effects, and in some cases program developers are simply unaware of evaluation techniques to use.4 When developing a safety program, one must remember that evaluation is an ongoing process: it begins with identification of goals and objectives, and continues throughout the program development cycle. As the program is implemented, final assessment is completed to determine the effectiveness of the program in meeting the stated goals and objectives.
Stages of Evaluation Successful evaluation involves a series of steps, each of which must succeed in order for the goal of fire and life safety education—a changed human being whose behavior produces less risk and more safety—to be achieved. Professional program evaluators have developed a staged approach to evaluation, summarized in Table 5.6.1, which addresses these steps in a logical order. Formative Evaluation. Formative evaluation is qualitative, whereas process, impact, and outcome evaluation are quantitative, that is, they measure. The educational program has to be designed to target the behaviors associated with the most common or severe forms of harm. Teaching everyone how to safely operate a tractor, for example, would be mostly ineffective because most people will never have use for that information. However, teaching everyone how to select safe floor coverings to avoid unusual risks of falling will benefit nearly everyone.
TABLE 5.6.1
The educational program has to be designed to be effective for its intended audience. The key behaviors for the intended audience may not be the same as the key behaviors for the general public. If the audience is a high school in a farm community, for example, teaching them how to safely operate a tractor would be appropriate. If the community included a large population of immigrants from non-English-speaking communities, then an effective program would need to deal with language issues. Process Evaluation. Once the content of the program is selected and evaluated for its potential to make a difference, the next step is to evaluate the program’s effectiveness in reaching its target audience. This step is dependent on program resources and the skill with which they are deployed. There are all kinds of ways of targeting a program to achieve the maximum bang for the buck. But even with these targeting methods, too few bucks will mean too little bang. This is where evaluation of some secondary program goals cited earlier—obtaining additional funding or additional personnel slots, for example—may also be appropriate as part of program evaluation against the primary goal of reducing harm to people. But there are all kinds of reasons other than insufficient resources why a program may fail to reach its audience. Impact Evaluation. If the program has targeted the key behaviors in a manner appropriate to the target audience and has been delivered effectively to that audience, it is now time to ask about direct educational effects. Impact evaluation measures changes in knowledge, attitudes, and beliefs. If those are confirmed, it goes on to measure changes in behavior. As with the earlier stages of evaluation, there are many reasons why a program that has shown nothing but success in the prior stages of evaluation might nevertheless demonstrate serious problems in this stage. The specific educational content might prove ineffective with the audience. The audience might already have a high degree of relevant knowledge but might have deeply ingrained attitudes or beliefs that prove resistant to change. At this point, if not before, it is useful (some would say necessary) to have a model of how people learn and how and why
Stages of Program Evaluation
Stage
Description
When Used
Formative evaluation
The process of testing program plans, messages, materials, strategies, and activities for feasibility, appropriateness, acceptability, and applicability
During development of new program or modification of existing program
Process evaluation
The mechanism of testing whether a program is reaching the target population, such as by counting the number of people or households reached
From the start of program implementation throughout the life of the program; results used to fine-tune a program during implementation
Impact evaluation
The mechanism of measuring changes in the target population’s knowledge, attitudes, beliefs, or behaviors associated with the program
Before program implementation and during and/or following the program
Outcome evaluation
The mechanism of determining how well a program achieves its goal of reducing morbidity and mortality; requires a large study population and analysis of the same data for a similar population that did not receive the program (control group)6,7
Before program implementation and after program completion
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TABLE 5.6.2
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Selected Health Behavior Frameworks Used in Community-Based Interventionsa
Model Type
Description
Health Belief Model8
An individual’s readiness to alter behavior depends on four conditions: • Perceived threat or susceptibility to the condition • Perceived severity of the condition • Perceived benefits of the health action • Perceived barriers or personal costs of the health action
Comments Community-based interventions should be designed to convince the target population of the threat of injury and their risk while simultaneously instilling confidence that a particular action is ineffective in reducing their risk.
Social Learning Theory9
Behavior change occurs within a social context and is influenced by both active involvement in the learning process and identified consequences of the behavior change.
Strategies such as modeling behavior (i.e., having someone physically demonstrate the desired behavior) and promoting external reinforcement (e.g., offering money) or internal reinforcement (e.g., instilling a feeling of pleasure or pride) are key to successful behavior change. The ways in which social groups alter behavior support social learning theory; members change their behavior as a result of modeling or reinforcement by others, or by their own active involvement in the group.
PRECEDE Model (an acronym for Predisposing, Reinforcing, and Enabling Constructs in Educational Diagnosis and Evaluation)10
Predisposing, Reinforcing, and Enabling constructs work together toward behavioral change.
Predisposing factors include attitudes, beliefs, and values of the target population. Reinforcing factors include support for behavioral change, such as support from family, peers, teachers, or healthcare providers. Enabling factors consist of the individual skills necessary to adopt the proposed change, as well as the availability and accessibility of external resources to facilitate change. The educational diagnosis is the examination of predisposing, enabling, and reinforcing factors in the specific context of the proposed behavioral change.
Evaluation is the quantification of the program’s impact. a
See Additional Readings.
they change behavior. Table 5.6.2 describes three widely used and highly general examples. Impact evaluation may also be the stage where the design and implementation of good measures is the most difficult. It is relatively straightforward to segment parts of the fire problem and characteristics of target audiences for formative evaluation, and data on these are often plentiful. It is entirely straightforward to count people reached for process evaluation, even though the information necessary for proper context and indepth examinations can be more challenging. But measuring overall changes in knowledge—based on a brief test with a few questions—can be done in many ways, none of them obviously the best. Measuring changes in attitudes and beliefs is notoriously difficult, because many people are not articulate or even fully aware of all their critical safety-related attitudes and beliefs, and some attitudes and beliefs are known to be widely disapproved and are likely to be concealed. In addition, measuring change in behavior is very difficult outside structured situations, when what is important is behavior in the places and at the times when the choice between safe and unsafe behavior will be done automatically, based on learning, and
not with a heightened and artificial sensitivity to the needs of a test. Outcome Evaluation. If impact evaluation is successful—if it is established that the target audience has received the education, learned new knowledge and new attitudes and beliefs, and modified its behavior—then it is time for the final, decisive stage of evaluation, which is outcome evaluation. Although the basic measures for outcome evaluation are in many ways simpler than those for impact evaluation, proper interpretation of the data can be enormously complex. The measure of a program’s success is not simply the outcomes and events in the lives of its target audience; it is the change in those outcomes and events attributable to the program. Determining success means comparing outcomes to baseline experience prior to the program. It means considering preexisting trends and what they say about how bad or how much better experience would likely have been in the absence of the program, if other changes already underway had simply continued without additional intervention. Or, if simple extrapolation is considered unreliable, it may mean comparison of the educated group and its progress to a control group not exposed to the program.
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Amount of Evaluation Needed By this point, evaluation may sound like a worthy ideal but a practical impossibility. It is true that no evaluation is ever thorough enough to address all questions. It is also true that few, if any, fire and life safety education programs (or for that matter, fire and life safety interventions of any other type, including engineering) have ever been fully evaluated. Yet there is a great deal of evaluative information on some programs, and evaluation is not by any means an all-or-nothing proposition. When choosing an educational program or strategy, it is always better to have some evaluation information than none, it is always better to have more than less, and each successive stage in evaluation adds enormous value to the store of information available to make good educational choices.
A HIERARCHY OF EVALUATION MEASURES Since evaluation is about measures of better versus worse, it can be useful to regard evaluation not only as a sequence of stages of evaluation activities, but also as a hierarchy of evaluation measures keyed to those steps. For example, 1. Outreach (process evaluation). Safety information must be delivered to the target audience and reach enough of the audience to make a difference. 2. Knowledge Gain or Refresh (impact evaluation). The audience must understand the material and must remember it. The information must be relevant and accurate for improving safety. It also must add to what the audience already knows, or remind them of what they know. 3. Behavioral Change or Maintenance (impact evaluation). The target audience must act on the information gained (or refreshed). They have to recall it accurately and be motivated to put it in use. 4. Environmental Change (impact evaluation). Actions taken to improve the safety of the environment need to be done correctly and the changes maintained. 5. End Impact (outcome evaluation). The behavioral or environmental changes must have a significant impact on the types of problems that actually occur and not be overwhelmed by factors beyond control or not addressable by public education. Note that formative evaluation, which is qualitative, is excluded from the hierarchy of evaluation measures. Ideally, a program should prove that it caused the desired end impacts. Where it is not possible to demonstrate such “bottomline” effects directly, look for the next best evidence earlier in the sequence leading to end impacts: were there changes in behavior or environment that are likely to produce a bottom-line effect? For example, did the program change fire and life safety behaviors, for example, get people to maintain or install smoke alarms, practice escape plans, or identify and discuss an outside meeting place with their family? Did the program reduce fire safety hazards that lead to fires, such as defective wiring, dirty chimneys, or wood stoves installed too close to walls? Since people usually have to
change their behavior in order to change the environment, such as doing more maintenance, or hiring someone to clean a chimney, the change in hazards can be considered another way to measure changes in behavior. If a change in behavior or environment cannot be shown, the evaluation can retreat a step further and ask whether a program caused a change in awareness or knowledge of key fire safety information that leads to safer behavior and environment if the knowledge is applied. Examples include knowing what kind of fuel is supposed to go into a kerosene heater, the way to extinguish a grease fire, or the need to crawl low under smoke. Even further back in the chain of proof is the extent to which people are reached by a program, especially when measured in terms of the percent of the target audience that was contacted by the program and the frequency of contacts. Reaching 90 percent of the school children in grade 3 twice a year would be an example of this measure. Table 5.6.3 shows a hierarchy of evaluation measures. Try to use the highest level of proof possible on the list to get as close to evaluating the goals of prevention directly; avoid assumptions that can stand between what is measured and what really was effected. People reached may not learn. People who learn may not act. Acting as instructed does not always work. Therefore, the closer one comes to measuring the end impact, the surer one can be that there really is an end impact. However, showing that only some hierarchy of measures changed is vastly better than doing no evaluation. The intermediate measures also can be excellent proof that the public education program did indeed change things that led to an observed change in the bottom line and that an observed change in end impact did not happen by chance. Intermediate measures can also be diagnostic and help show where in the chain the education process is breaking down if there is no change in the bottom line. Intermediate measures are best used in conjunction with end measures. Sources of data for the measures range from existing, routine data collected by every department to special studies. Approaches to undertaking evaluations of these data measures are discussed in the next section. Outreach data may be obtained by counting attendees at public education presentations, classes, and exhibits, or tallying households visited. For television, radio, and newspapers, information about circulation or audience usually is known and available. When a reasonably significant portion (10 percent or more) of the population is thought to have been reached, a citizen survey can be used, in the form of phone calls to random households or a mail survey. Total population of a target group often is available from U.S. Census data or local planning departments; this forms the denominators for computing the percentage reached. • Knowledge changes are usually measured by before and after tests. • Behavior changes and environment changes can be measured by using telephone or mail surveys, by visiting and inspecting households, or by asking school children about their households. • End impact changes are measured from fire incident and casualty report data or special studies.
CHAPTER 6
TABLE 5.6.3
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Evaluation Techniques for Fire and Life Safety Education
5–83
A Hierarchy of Evaluation Measures for Public Fire and Life Safety Education
Aspect Measured
Examples of Evaluation Measures
End results (strongest proof)
• Number of deaths, injuries, dollar loss, or fires per capita • Anecdotes of saves linked to programs
Behavior or the environment
• Percent of households with a working smoke detector • Percent of households sprinklered • Percent of chimneys cleaned at least annually
Awareness, knowledge
• Percent of public who know how to extinguish a grease fire • Percent of public who know how to use extinguishers • Percent of public aware of need to crawl low in smoke
Extent of program outreach
• Percent of population (or a subgroup) receiving public education materials • Percent of elderly receiving safety lecture • Percent of schoolchildren with x hours of safety instruction each year
Likeableness and usage of programs
• Percent of teachers who think program materials are good and use them
Institutional change
• Introduction of safety curriculum in schools • Addition of service organization to aid dissemination
FORMATIVE EVALUATION Overview of Formative Evaluation Formative evaluation is like a very thorough technical review; formative evaluation is qualitative rather than quantitative. It involves checking embedded assumptions against available relevant data. Are the hazards targeted the leading ones in this community, or are they the equivalent of tractor safety in Manhattan? Is there experience elsewhere with these materials and activities, and does the proposed approach fully incorporate lessons learned in those prior implementations? What are the key characteristics of the target audience, and are those fully reflected in the program’s specific design? Has a diverse group collectively representing all relevant perspectives and types of expertise reviewed the program, and have their comments all been addressed? Are there issues of acceptability for the students, the teachers, or the community?
Formative Evaluation of Risk Watch®: An Example Risk Watch®, designed for students grades pre-K through 8, is the first injury prevention program for children that is comprehensive in scope, addressing eight high-risk areas, including motor vehicle safety, bicycle and pedestrian safety, fire and burns, poisoning, choking, falls, water safety, and firearms safety. Developed in collaboration with injury prevention experts and educators, Risk Watch® is a school-based curriculum designed to be implemented as a community-based injury prevention initiative, emphasizing community participation and involvement. One very important component of Risk Watch®—the use of community volunteers (firefighters, EMS personnel, law enforcement officials, and health care providers) to visit classrooms to present and demonstrate safety messages to children—was the direct result of formative evaluation, in which teachers indi-
cated their strong preference for the direct involvement of community helpers. The benefits of using community volunteers are twofold. First, children are presented important safety messages by front-line community role models.11 Second, volunteers themselves become more involved in promoting the health of the community. Before the Risk Watch® curriculum could be evaluated in terms of impact—that is, effectiveness in improving children’s safety knowledge and behavior—it first had to undergo a formative evaluation to assess core activities and safety messages. If the curriculum could not be easily taught by school teachers, or if the safety messages were inappropriate for the target agegroup of students, then one would not expect to see positive results in terms of knowledge gain or behavior change. The Risk Watch® curriculum had been developed by injury experts, who suggested appropriate safety messages to relay to children, and by developmental specialists, who “translated” these messages into lessons that children of different ages and developmental levels could comprehend. For example, many songs and chants were used for young children grades pre-K through kindergarten, whereas story writing was used for older children in grades 6–8. Focus groups of teachers and educators were formed to discuss the appropriateness of the lessons and messages, and scripted interviews were administered to a large sample of teachers to obtain additional feedback. The information obtained from these studies constituted the formative evaluation and was used by curriculum writers to revise the lessons, clarify safety messages, and assure a user-friendly manual. The next step in the Risk Watch® development cycle was to complete a comprehensive field test of the curriculum. The purposes of the field test were to gather additional formative data (that would allow further “fine-tuning” of the program) and to begin to assess its effectiveness in terms of student knowledge gain. Five geographic test sites were chosen, with several schools participating at each site. A sample of teachers representing all grade levels from each site was trained, as were community
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actions that may bear on the program’s likely acceptance if its target audience is broadened. In other words, the process of delivery of the material needs to be evaluated. Figure 5.6.1 is part of a process evaluation questionnaire for Risk Watch®. The first question, on time allotted per lesson, is one of many that may provide insight into hidden problems with the quality of delivery. The second and third questions, on enthusiasm from the students and teachers respectively, may give insight into sources of resistance down the road or help explain why teaching might occur and learning still not occur.
volunteers who came into classrooms to augment the teachers’ safety lessons. After teaching Risk Watch® lessons, teachers completed surveys with questions relating to acceptability and usability of materials, as well as perceived learning by students. Results of end-of-lesson surveys and end-of-program surveys completed the formative evaluation. Many teacher suggestions and recommendations were incorporated into a new, revised Risk Watch® curriculum.
PROCESS EVALUATION Process evaluation involves more than just counting students taught or households reached. It involves more than comparing such numbers to the size of the target audiences and determining the degree of coverage, penetration, or reach. It involves evaluating the reasons for shortfall and also information on re-
IMPACT EVALUATION Impact evaluation usually proceeds in two successive steps. First is evaluation of changes in knowledge, attitudes, and beliefs. Second is evaluation of changes in behavior.
Representative Teacher Survey Questions 1. On average, how much classroom time do you spend teaching Risk Watch® lesson? (Select only one response) Less than 30 minutes Thirty minutes Forty-five minutes One hour More than one hour 2. How enthusiastic about each lesson were your students? (Please answer on a scale of 1 to 10 with 1 being NOT enthusiastic and 10 being VERY enthusiastic.) Not enthusiastic
Very enthusiastic
Lesson 1: Motor Vehicle Safety
1
2
3
4
5
6
7
8
9
10
n/a
Lesson 2: Fire & Burn Prevention
1
2
3
4
5
6
7
8
9
10
n/a
Lesson 3: Choking, Suffocation, & Strangulation Prevention
1
2
3
4
5
6
7
8
9
10
n/a
Lesson 4: Poisoning Prevention
1
2
3
4
5
6
7
8
9
10
n/a
Lesson 5: Falls Prevention
1
2
3
4
5
6
7
8
9
10
n/a
Lesson 6: Firearms Injury Prevention
1
2
3
4
5
6
7
8
9
10
n/a
Lesson 7: Bike & Pedestrian Safety
1
2
3
4
5
6
7
8
9
10
n/a
Lesson 8: Water Safety
1
2
3
4
5
6
7
8
9
10
n/a
3. Over, how much do you like teaching Risk Watch®? 1
2
3
4
Do not like teaching Risk Watch® FIGURE 5.6.1
5
6
7
8
9
10
Like teaching Risk Watch®
Representative Teacher Survey Questions
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CHAPTER 6
Evaluation Techniques for Fire and Life Safety Education
Measuring Change in Knowledge
Number of students
One of the most common types of evaluations of fire safety education is the classic multiple-choice test. Often such tests are given before a program starts, or at the beginning of the first class, and then repeated at the end of the training using the same test instrument. Sometimes the “after” test uses a slightly different set of questions. The results of the “before” test not only establish a baseline but also give insight into exactly where the group is weak. The “after” test shows the increase in knowledge. Pre- and posttests do not have to be elaborate. Sometimes a few well-chosen questions can suffice. Figure 5.6.2 shows profiles of test scores before and after a class that was conducted over a four-day period. The graphs show the profile of scores for different questions. It is very clear that the class dramatically improved. Although this example was drawn from a class of fire fighters taught about fire safety education, the data could have been for a classroom of children or a group of elderly. In addition to the graphic presentation in Figure 5.6.2, the average score and the range of scores for the pretest versus the posttest describe the change quantitatively. This type of evaluation can be done separately for each class or group of people, or all classes can be lumped together. The separation by class is especially useful when there are differences in the composition of the classes or when the classes are taught by different instructors.
Retention Tests. Giving a posttest immediately at the end of training may reflect only short-term retention, though the test itself may promote retention. It is desirable, therefore, to administer another test several weeks to a year after the last training session. That test would measure retention and present an opportunity for a “booster shot” or reminder of the safety lesson to the students. Practical Tests. Another testing problem is that a paper test may not reflect what a person will remember or do in a crisis. Physical, hands-on training and demonstrations of competence may be better indicators of actual performance. Few people would certify someone as competent in cardiopulmonary resuscitation (CPR) or first aid based solely on a multiple-choice test, yet this can occur in fire safety program evaluation. Different Pre- and Posttests. When the same test is used for pre- and posttesting of the same group, there might be some improvement in the score even if nothing was taught, due to increased familiarity with the questions and discussion of answers among the students. This is not necessarily detrimental—the test itself can be part of the learning experience. But there are ways to circumvent the problem: 1. Slightly different wording of questions can be used in preand posttests, though some of the changes measured might
Pretest score histogram
10 9 8 7 6 5 4 3 2 1 0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
65
70
75
80
85
90
95
100
Number of students
Score
Post-test score histogram
10 9 8 7 6 5 4 3 2 1 0
5
10
15
20
25
30
35
40
45
50
55
60
Score
FIGURE 5.6.2
5–85
Profile of Test Scores Based on Bolitin/Histogram
5–86 SECTION 5 ■ Fire and Life Safety Education
result from differences in the test wording rather than changes in knowledge. 2. Test one group before they are taught the prevention material, and test another group after they are taught the material. If the groups are reasonably similar in composition, the difference in test results will show the effectiveness of the program in improving knowledge, while requiring only one test per class and allowing all students to receive the prevention material. This approach works particularly well when a large number of reasonably similar classes are to be taught the same fire and life safety material, for example, all grade 5 classes. The test might be given to every other class before the material is taught, with the remainder given the posttest. The large number of classes is likely to make the difference between the two groups unimportant. To take the other extreme, one would not want to use this approach on only two classes, especially if one were a “slow” class and the other an honors class.12
Measuring Impact on Knowledge, Attitudes, and Beliefs in Risk Watch®: An Example NFPA worked with an external evaluation firm to conduct a three-year analysis of the impact of Risk Watch® on children’s knowledge of safety behaviors. The field test was designed to gather impact data, and instruments were developed to measure knowledge change in children exposed to Risk Watch®. A pretest/posttest methodology was used, comparing knowledge gain of students exposed to the curriculum (study group) with knowledge gain of students who did not experience Risk Watch® in their classrooms (control group). Pretest/Posttest Methodology. Pretest/posttest exams had to be created with developmental characteristics of the audience in mind, such as children in the youngest classrooms (pre-K–1) who were nonreaders. Teachers in the latter classrooms administered exams verbally and by using pictures, whereas exams for older children consisted of short answer questions and multiplechoice type questions, each of which had three answer choices. After teachers in the pilot site classrooms conducted a pretest of knowledge with students, Risk Watch® was implemented by using the NFPA collaborative model. A team approach was used to deliver course content to students, with representatives from fire and police departments, EMS, and numerous other community resources augmenting the work of teachers in presenting Risk Watch® lessons. After all lessons were completed, a posttest was conducted. A comparison of the pretest and posttest scores was used to indicate knowledge gain within each risk area. This incremental change was then compared to a control group who received the same pretest and posttest as the experimental group did without receiving Risk Watch® lessons. Analyzing Initial Pretest/Posttest Data. NFPA’s evaluation researchers analyzed data from pilot sites, using t-tests from the Statistical Package for the Social Sciences (SPSS) to determine
the equivalence of the Risk Watch® (study site) students and comparison (control site) students in terms of their pretest knowledge.13 This is an important concept to consider when using a pretest/posttest design to measure impact on knowledge, because if pretest scores are very high, students will not be able to show much growth in knowledge from pretest to posttest. This is what occurred with the initial Risk Watch® knowledge tests. Students, even with no exposure to Risk Watch®, got the great majority of test items correct. This makes it almost impossible to demonstrate change, or growth in knowledge, as a result of participating in Risk Watch®. Either the initial tests leaned too much on widely shared safety knowledge, in which case more difficult tests would show the value of Risk Watch® as these initial tests did not, or Risk Watch® was only teaching children what they already knew and was not an effective program. Redesigning Tests. NFPA’s evaluation researchers developed new, more difficult knowledge tests that were administered to children in a pretest/posttest style, as had been done in the field test. Results demonstrated statistically significant gain in knowledge between pretest and posttest scores of children exposed to Risk Watch®. Although comparison (control) group scores also improved, the increases in score were greater for the Risk Watch® students in all grade levels.14 Table 5.6.4 displays the differences between target and control groups, using the redesigned test. There were statistically significant improvements in both the test group and the comparison group. For Risk Watch®, the important result is not the significance of the differences. Rather, it was important that the Risk Watch® student gains were larger, by enough of a margin that it was considered statistically demonstrated that the superiority of the Risk Watch® students over their comparison group was real and not due to chance. However, this also demonstrated that students learning safety outside a structured program, and a less sophisticated evaluation, might well have overestimated the particular contribution of Risk Watch®.
TABLE 5.6.4 Comparison of Risk Watch ® Target and Control Groups Target Group Gain (in items) Gain (in percent) Significance Sample size
Pre-K–K
5–6
3–4
1–2
3.10
1.26
2.0
1.97
9
6
8
8
<.0001 74
<.0001 114
<.0001 83
<.001 78
1.32
1.05
.82
.75
4
5
3
3
<.0001 65
<.0001 135
<.05 67
<.05 71
Control Group Gain (in items) Gain (in percent) Significance Sample size
CHAPTER 6
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Previous studies have suggested a link between knowledge gain and behavior change, and several educational interventions have been shown to increase a safety behavior (use of motor vehicle restraints) of preschool children.14,15 For some safety behaviors, there is also evidence that adoption of the behavior (such as wearing a bicycle helmet) is strongly associated with a decrease in injury rates (such as head injury).16 Several observational studies have reported beneficial effects of increased use of safety practices on childhood injuries.17,18 Nontest data collection strategies have been designed to determine whether student behavior changes as a result of participation in Risk Watch®. This is a difficult undertaking, for although direct observation is a natural technique for identifying behavioral changes, fully half of the topics covered in Risk Watch® are almost impossible to observe. Many of the safety behaviors associated with Risk Watch® do not occur in the school environment, where researchers could easily complete observations of all children. If researchers move off site from the school, they would need to be sure that every child they were observing was exposed to Risk Watch® in the study area, and every child they observed in a control area had not been in a Risk Watch® classroom. With so much cross-over in school populations (i.e., children attending “magnet” schools out of district or attending private school some distance from their homes), this would be difficult. Further, many of the behaviors taught in Risk Watch® occur relatively rarely, making observation of such behaviors difficult. As a simple example, the chance of one student participating in a Risk Watch® evaluation study being involved in a fire during time period of the study is, fortunately, small. The chance that enough students would be involved in fires to allow valid conclusions to be drawn about their response to such an emergency situation is, just as fortunately, nearly infinitesimal. Although no observational studies have yet been completed to evaluate the effect of Risk Watch® on behavior change, several have been designed and can serve as examples of additional evaluation techniques. One such study was designed to include children and households in a rural, high-risk geographic area. The evaluation uses a pretest/posttest design in an intervention community and a control community. Data collection was accomplished by direct observation of the behavior of children in the areas of motor vehicle safety, bicycle safety, and pedestrian safety. In addition, home visits are planned to complete a safety survey. These observations were recorded prior to the implementation of Risk Watch® in all classrooms of the intervention community’s schools. Repeat observations will be completed in both the study county and a control county after the school year has ended to gather postintervention data.
Measuring Impact on Behavior through Inference: An Example Direct observation of natural behavior with safety implications is extraordinarily difficult. In even the best evaluated programs, evaluation is likely to be limited to some behaviors in artificial environments and some other behaviors that lend themselves to unobtrusive observation in a natural setting, but may not be collectively representative of the range of behaviors covered by the educational program.
Evaluation Techniques for Fire and Life Safety Education
5–87
One method of compensating for the lack of direct observational data is inference from established research demonstrating the conditions linking knowledge to behavior change for similar educational programs on other matters of safety or health. The developers of Risk Watch® have used this technique on at least a temporary basis, to strengthen their impact evaluation.
OUTCOME EVALUATION For outcome evaluation, it may be assumed that the general measures of interest are deaths and injuries due to the targeted hazard, that is, fires and falls. The more detailed guidance in this section has to do with techniques and issues in using anecdotes as evaluation evidence, selecting focused outcome measures to better fit the programs, and using basic approaches to making comparisons.
Using Anecdotes One of the favorite means of evaluating public education programs is through anecdotes of survivors who testify that they learned a safety behavior from a public education program, and it saved their own life or that of another. Anecdotes are wonderful human interest stories and can attract the attention of the media. To most people, including decision makers, they are more interesting and more understandable than statistics. But anecdotes alone can be dismissed as weak evidence, especially if there are only one or two. Despite the frequently made statement that “this program is worth it if only one life is saved,” politicians and budget managers do not always see it that way. Nevertheless, anecdotes are a legitimate form of evaluation, especially when used in conjunction with statistics. An anecdote provides insight into a program and proves that at least in one case the program worked. Multiple anecdotes are much stronger evidence than single anecdotes, because one event might be considered a fluke. Anecdotes are most credible when documented in writing by survivors or first-hand witnesses and when they describe not only an appropriate behavior but where that behavior was learned. Preferably the anecdote should be verified by at least a telephone call or second witness. The more anecdotes on a program, the better. NFPA’s Learn Not to Burn Curriculum19 has accumulated more than 202 documented cases where its messages saved lives or reduced injury to 554 people. Similarly, there are 15 Risk Watch® documented incidents in which 31 lives were saved. Anecdotes are also more impressive when at least some of them are fresh (because programs and program delivery change) and when there are a series of anecdotes, indicating consistent, long-term results. Since it is virtually impossible to collect anecdotes for all saves associated with a program, one needs the relevant overview statistics as well. A budget manager is much more likely to continue to fund a public education program where fire deaths decreased by ten over the previous year and anecdotes were used to show that the program was a factor in the decline, than where only the statistics or only the anecdotes are used. Together the picture portrayed is much more convincing. Some people belittle the use of anecdotes because they do not add up to statistical “proof.” But at the local level or even
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nationally it does not take that many anecdotes to drastically change the fire loss picture. If public education programs reached half the people in each community and saved more persons per 100,000 people reached by public education per year than at present, the nation’s fire death rate would be cut in half. (To see this, consider that one out of 100,000 is equivalent to 2500 saves out of 250,000 people and the annual fire death toll per year has been about 5000.)
TABLE 5.6.5 Focuses
Use of smoke detectors
Number of households with detectors Number of reported fires (early detection leads to occupant extinguishment and fewer reports) Number of fire deaths
Selecting Focused Measures
Getting out quickly from residential fires
Number of injuries while attempting fire control in residential fires Number of fire deaths Number of severe injuries
Need to clean chimneys
Number of chimney fires
Careless smoking
Number of fires or deaths involving careless smoking
Safe storage of flammable liquids at home
Number of non-arson fires where flammable liquid was material first ignited
Children playing with lighters or matches
Number of residential fires where heat of ignition was a match (or lighter) and ignition factor was “children playing” Number of children injured in above type of fire
When a fire safety education program is targeted at a particular type of fire, such as grease fires on the stove, Christmas tree fires, or kerosene heater fires, the evaluation, too, should focus on how that type of fire changes over time and how it compares to other types of fires for which there was no current program. Sometimes focusing on one type of fire may raise awareness and have a beneficial effect on many types of fires, and so the overall change in the fire problem needs to be monitored, too. But the primary focus should be on the type of fire that was the target of the program. The same philosophy of targeting the evaluation properly applies to programs aimed at changing people’s response to fire, such as escaping quickly or closing doors or using extinguishment methods properly. Unfortunately, those attempting to undertake evaluations often look for changes only in the larger universe of fires rather than in the target group they were after. They measure the change in all fires when a program was targeted just to residences, or they measure the change in all residential fires when the program was aimed solely at cooking fires, or they look at all cooking fires when the prevention message was targeted solely at grease fires. The chance of detecting results increases if one keeps the focus as narrow as the category the program message addresses. Otherwise, the results are diluted amid a larger pool of fires, and one may not be able to detect them. Table 5.6.5 gives examples of some targeted messages and associated measures of their effects. In each case one also should compare the change in the targeted type of fire to the change in other types of fires, or fires in general, as a control. If cooking fires are targeted and they dropped in number, check whether heating and children-playing fires dropped, too. And check whether cooking fires dropped in nearby communities where there was no program. If there were reductions in other types of fires or in other communities, forces other than the education program may be at work. Or the program may have broader impact than what it targeted. It may be difficult to obtain the data for exactly what one wants to measure. Therefore, it may be necessary either to (1) retreat and find a surrogate measure or (2) measure the impact on the next larger category that includes the type of fire or behavior targeted. For example, one runs a public service announcement (PSA) about sliding a lid on grease fires, but cannot easily measure the number of grease fires; therefore, the number of cooking fires might be used instead. Further, if a school program is focused on the need for children to escape quickly from home fires, but one cannot measure the number of injuries from not escaping quickly, it might still be useful to track the number of injuries to children in home fires.
Sample Measures for Specific Education
Prevention Theme
Examples of Measures to Use
Using Basic Approaches to Making Comparisons This section presents a short, condensed summary of the complex subject of data measure evaluation. A more in-depth treatment on evaluation in general is available from the Urban Institute’s book, Public Program Evaluation.20 Another excellent reference specifically on evaluating public fire education is the National Fire Academy’s fire education evaluation guide.21 Perhaps the most basic concept of an evaluation is to demonstrate that some benefit can come from having a prevention program compared to not having it. There are several approaches to making the desired comparisons. 1. Compare the targeted community’s experiences over time to see if there is a difference after a program started compared to the “baseline” before it started. (Changes in the community that occurred during the period used in the comparison and that could affect the results must be taken into consideration.) 2. Compare one part of the community to another, to see if there is a difference between areas that have public education programs versus other areas that do not yet have the program, or had it for a shorter time or with less intensity. 3. Compare the community to other communities, especially to similar communities that have not had a comparable public education program recently. A variation is to compare like parts of different communities, such as inner-city neighborhoods or high-rise dwellers.
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4. Compare changes in a targeted type of fire or hazard (or safety behavior) to the trend in other types of fires or hazards (or other safety behaviors). For example, consider the change in cooking fires versus the change in heating fires after a campaign that targeted cooking fires. Measuring Change over Time. The most straightforward way to show that a public fire education program has had an impact is to demonstrate improvement after the program started (Figure 5.6.3).22 In some cases, the effects are not immediate, and time must be allowed to observe results. In other cases, the effect is expected to be immediate and wear off with time, in which case speed of measurement is necessary. In yet other cases, the changes result from uncontrollable factors outside the program. All of these issues must be addressed. Although ideally a public education program produces a drop in hazardous events, injuries, or deaths, the impact sometimes may be to reduce the magnitude of an increase, or change the rate of an increase. Data from statewide fire and life safety education programs in South Carolina provide further information (Figure 5.6.4).22
Heating fires per 100,000 population
250
200 Before 150 Program starts 100 After 50
0 1984
1985
1986
1987
1988
1989
1990
Year
15
200 Projected without program
160
120 After 80
40
0 1984
5–89
Often, there are random fluctuations in fire experience; these are especially noticeable when the community is small and the number of fires few. It may be necessary to observe data that zigzags for weeks or years before being able to discern the trend (Figure 5.6.5). There are sophisticated statistical analysis tests that can help. Also, patterns may be more apparent visually if one uses rolling multi-year averages (e.g., 1995–97, 1996–98, 1997–99, 1998–2002). The speed with which a prevention program has impact varies with the fire safety behavior being targeted, the frequency and timing of the message, and the receptiveness of the audience. It also may vary with the size of the audience reached. For example, if one-third of the population of a city is reached by a PSA associated with a popular television show—a very large audience for television—one might expect an immediate drop in the type of fires targeted. If instructions in the PSA were on how to prevent and extinguish a cooking fire, and the city averaged nine reported cooking fires per week, it might be reasonable to expect an average of six or fewer after the broadcast, if the program was designed to reach a broad cross section of households. The behavior change can be immediate for those who saw the PSA. It does not require any accumulation of knowledge over time, because the message is simple. Effects of a program may be delayed when the safety behavior being sought takes time and money to implement. For example, when people are instructed to test their detectors and replace the batteries, it may take some time before they get around to doing the test, then buying the batteries or alarms, and then installing them. In contrast, there is no delay in being able to implement “crawl low under smoke” or “slide a lid on a grease fire.” The speed with which a prevention program has an impact also depends on the nature of the audience. If the audience comprises mostly “safe households” with a low incident injury rate, it may take a while to see any further impact. In contrast, a PSA targeted to areas with disproportionately high fire rates may impact faster, because there is more opportunity to create a larger change. However, if these households tend to ignore safety information, there could be no change. One
Number of cooking fires
Juvenile-set fires per 100,000 juveniles
FIGURE 5.6.3 Hypothetical Example of a Change over Time Showing a Successful Program’s Impact
Evaluation Techniques for Fire and Life Safety Education
Before
Program starts
Average = 9.0 fires/week Average = 6.9 fires/week
10
5
Program starts
0 1985
1986
1987
1988
Year
FIGURE 5.6.4 Hypothetical Example of a Change in the Rate of Increase Showing a Successful Program’s Impact
1
2
3
4
5
6
7 8 Week
9
10
11
12 13 14
FIGURE 5.6.5 Hypothetical Example of a Change in Trend Visible Even with Fluctuating Data
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Increasing Chances for Identifying Changes. Although there are a number of reasons why it may not be easy to see a change in trend as a result of public education, there are several ways to increase the likelihood of detecting a success. One way is to use more sophisticated statistical techniques to see if there is some signal of a change amidst the noisy, erratic data coming from the outside world. Some fire departments have people on their staff or from nearby universities or other organizations who have training in statistical analysis. Modern, easyto-use statistical computer software packages may help too. By all means use them if available. But if it takes extremely sophisticated statistical techniques to identify a change caused by a program, the program is not likely to be having a large effect. That is, if one cannot see the effect of the program looking at the data with the “naked eye,” chances are that the effect is probably not very large. There are exceptions, and even if a change is small, it may be cost effective if only a correspondingly small effort were required to produce it. An easier approach than employing sophisticated techniques is to collect more data over time. Average the data before the program started and compare that to the average after the program starts, as in Figure 5.6.5. The averaging will take out some of the random fluctuations, and some of the problems in-
herent in having only small numbers of deaths, injuries, or fires for smaller areas. Compute the trend lines (Figure 5.6.6). Look at fires, not just deaths, because there are usually about 100 times more fires than deaths. The impact of a program aimed at ignition prevention will show up sooner and more clearly for fires than deaths. If the program is directed toward education about escape or preventing bodily harm after a fire starts, rather than preventing or mitigating the fire itself, look at the number and severity of civilian injuries, and not just deaths. There tends to be about four times more injuries than deaths, and again the effects of a program may be more readily detected. If the targeted community’s population has not remained constant over the period of analysis, look at the data per 10,000 or per 100,000 population. (One also should look at the data on a per capita basis when comparing the community to others.) If the targeted community’s population is increasing but the number of fires or deaths remains approximately the same, the rate per 10,000 people will be going down. That is, when more people are at risk but the community is not experiencing more fires or deaths, that can be an indication of a successful program. Comparing Different Parts of the Community. As an evaluation tool, comparing parts of the community against each other is most useful when a program is introduced to one area of the community and not to the others. Then one can compare the “treated” population to the “untreated” population, as is done in medical research (Figure 5.6.7). For example, an educator might introduce to the schools in one neighborhood a program directed at getting smoke alarms tested and properly installed. The students might be asked to count the number of smoke alarms they have at home and to test them. This can be a homework exercise. Then the students can be taught the importance of maintaining alarms and periodically testing them. Results can be monitored for the next three months by looking at fires in that school area, and determining the percent of fires in which alarms were found working versus how that area did prior to the program, and how it compares to the areas of the community without the program. If the program appeared successful immediately, it could be tried in other areas. If not successful immediately, the material might be repeated and monitoring of results continued. An attempt might also be
Number of cooking fires
needs to consider the status of the audience in assessing program impact, especially when comparing different programs or the same program in different areas. The effects of a program also may be delayed when the target audience is young. For example, teaching students in junior high school to slide a lid on a grease fire may not have its full effect until they begin cooking more for themselves (though they may pass the information to other members of their households or intervene in a fire themselves). Measuring a drop in reported hazardous events as a result of a public education program can be thwarted due to the unpredictable effects publicity can have on people’s likelihood to report a fire. It is known that many fires go unreported. Almost all of the unreported ones are small, though they include fires that injure and that cause hundreds or even thousands of dollars in damages. When a fire and life safety education program brings attention to a fire problem, more of these small fires might get reported than is usual, making it appear to the fire department that the problem is worsening when it actually is not. For example, encouraging people to evacuate their home quickly may cause some who previously would have extinguished their own fire and not reported it to leave and report the fire. The education program thus could cause an upsurge in reporting of fires. As another example, asking people to refer children who set fires to a juvenile firesetter program could encourage reporting of fires that might otherwise have gone unreported because of the perceived futility of reporting them. The only way to know for sure whether a surge in reported fires is due to reporting of previously unreported fires is to periodically survey the population to determine the degree of their underreporting and the reasons for it. Then one can determine whether fires are being shifted from being unreported to being reported or are truly increasing in number.
Initial trend
Program starts
New trend
Time
FIGURE 5.6.6 Noisy Data
Hypothetical Example of Plotting Trends in
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important if all similar areas have been trending in the same direction, and the impact of the program is to reduce the rate of rise or accelerate the drop in fires or casualties. Comparisons among areas are best made over a period of time. Data is needed for each area from before and after the time when a program was first started, to know whether differences between areas result from differences in their characteristics or differences in the program.
Area B, with program Number of fires per capita
Evaluation Techniques for Fire and Life Safety Education
Area A, without program
Program starts Weeks
FIGURE 5.6.7 Hypothetical Example of Comparing Area with Prevention Program to Area without Program
made to determine if any outside factors were causing a counter, that is, negative, impact. As another example, for one year one might equip the schools in a selected neighborhood or district with a fire safety curriculum. Results would then be monitored for the trial neighborhood versus the rest of the community. If the program shows some success, perhaps in a few types of fires such as “children playing,” then it might be implemented in the rest of the community. Chances of getting expanded implementation are much greater if one can show quantitatively that the program really made a difference in the area of the trial. Sometimes a program applied in one area of a community inadvertently may have effects on the whole community. A notable example came from Edmonds, Washington, where a doorto-door home inspection program in the mid-1970s using paid elderly women to make the inspections was found to have had about as much impact in the census tracts that had not been visited by the program as in the census tracts that had been visited. The suspicion was that the publicity attendant to the program caused people to “clean up their act” in anticipation of having a stranger inspecting their house. The program raised awareness of fire safety even in areas that did not receive the door-to-door inspections. If one compared the areas visited by the program to the areas not visited by the program, it could be concluded that the program was not very effective, when in fact the overall impact of the program was a drop in fire incidence by a remarkable two-thirds. The before-and-after comparison for the city as a whole made clear what had most likely happened. It is sometimes politically difficult to run an education program in one area of the community and not in others unless (1) it is clearly labeled a pilot program and (2) a plan exists for subsequently introducing the program everywhere. Nevertheless, whenever possible, introduce a program in one area first, and test the results in that area versus the rest of the city. Even for proven programs this initial test can help the educator make adjustments in the program before introducing it everywhere. When comparing different parts of the community, one should compare like areas, if possible. For example, compare a program in a low-income area against how other low-income areas are doing without the program, or compare a moderateincome area to other moderate-income areas. This is especially
Comparing the Community to Other Communities. Similar in principle to comparing different areas within a community is to compare the community to other communities—especially to other communities that are generally similar to the target community. A variation on this is to compare the community’s experience to that of its state. Comparisons among communities (or areas) should be made on a per capita basis or in terms of percentage changes or trends in the magnitude of the problem. Otherwise, differences observed in the numbers of fires or casualties may be due to differences in the numbers of people protected rather than from the results of the program.
HANDLING UNCONTROLLABLE FACTORS It often is not enough to show that there was a change in knowledge or behavior or in bottom-line measures, such as injuries or dollar loss. One also needs to demonstrate that the observed changes were caused by the education program and not by other factors, such as an unusually warm winter that caused fewer heater fires or a dramatic national fire in the news that raised awareness. Likewise, one needs to check whether positive effects of a program may have been masked by uncontrollable factors, such as a weakening economy that leads to an increase in vandalism and arson fires during the implementation of an arson control program. The sociology of fire is complex. There are many causes of fire and many uncontrollable factors that may affect the environment or behaviors leading to fires. A social scientist or statistician might never be totally satisfied with the degree of rigor of most evaluations that are practical, because it is difficult to account for all of the uncontrollable variables without much effort, and perhaps not even then. Nevertheless, evaluations can be useful if undertaken with a little care, because they generally lead one in the right direction. Table 5.6.6 lists some of the factors that might affect evaluation results. The first column in Table 5.6.6 contains variables that are largely out of the hands of the fire and life safety educator to affect. The most classic examples perhaps are the weather and the economy. The second column has factors that may not be controllable in the short run, though they may be affected by codes and other prevention efforts in the longer run. The third column has the initial conditions that need to be considered, even though they can be affected by public education. Evaluations can be made more meaningful by comparing results for situations in which these external variables are reasonably similar, or at least by acknowledging the possible influence of these variables.
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TABLE 5.6.6
Examples of Factors Affecting Evaluation Results Uncontrollable Factors
Semicontrollable Factors
Starting Conditions
Age profile of population Income distribution of population Education level of population Geographical scatter of population Ethnic groups in population Weather or climate change Economic changes Migration of people in or out of community • Nature of local business and industry • Changes in fire reporting procedures
• Condition of housing • Architecture of the homes • Hazards of new technology
• Severity of fire problem (fire and death rates) • Previous exposures of population to fire safety information • Current level of detector usage and condition
• • • • • • • •
The need to consider uncontrollable variables can cut more ways than one. A modest reduction in the number of woodburning stove fires that would have followed the introduction of an intense education program on the need to clean chimneys might be masked or negated by an unusually severe winter. The colder temperatures might cause a sharp increase in the use of stoves and a corresponding increase in fires that overwhelms the decrease from more people cleaning their chimneys. But the increase might be less than in earlier years when no prevention effort took place, which could be a demonstrable positive impact of the program. If there were a decrease in chimney fires in spite of a particularly cold winter, that would suggest that the program was being extremely effective, not only in reducing the normal toll, but doing so in the face of increased stove use. The reverse situation is also possible: An ineffective public education program might appear to be effective if chimney fires drop because the winter is relatively mild and the use of stoves decreases. That type of external factor has to be considered before one starts claiming success. It should be noted, however, that the chimney fire situation is a somewhat difficult example because relatively mild winter weather can cause people to reduce airflows to the firebox to reduce the intensity of the fire, which in turn can increase creosote buildup and lead to more house fires, instead of fewer. To understand whether changes in fire incidence or casualties is due to the public fire and life safety education program or to climate change, one needs to look at the data on the weather in the period in question, and perhaps some nearby communities that did not change their public safety education programs but had the same weather. Looking at the data averaged across several winters may also reveal whether a program is having an impact independent of fluctuations in climate (unless the climate takes a several-year shift in one direction). Another approach is to compare the data from years when the uncontrollable factor—in this case the climate—was the same. Nebraska’s Forest Service provided a brilliant example of this approach. Fire rates in years of relatively similar dryness were compared with respect to the intensity of the prevention
programs in those years. Comparing results from years with similar weather allowed the impact of the program to stand out. Otherwise the fluctuations in dryness masked the effects of the fluctuation in the intensity of the program. Besides considering factors that are uncontrollable by the fire department, evaluation of public education programs needs to consider the relevant preexisting fire situation in the community. This is especially important to do when effectiveness is compared to resources expended; that is, when productivity is to be measured. Table 5.6.6 includes a list of several starting conditions to consider. The existing level of smoke alarm usage, for example, will affect the apparent effectiveness of a new effort on smoke alarms. It is easier to get the middle 20 percent of households to install smoke alarms than the last “hard-core” 20 percent. It usually is easier to reduce a high fire death rate than it is to further reduce a very low death rate. It is easier to maintain new alarms than old alarms, because the new ones use less expensive batteries, begin with fresh batteries, and are less worn out. Although one may use the change in the percent of households with working smoke alarms as a measure of effectiveness, it must be realized that it gets harder and harder to reach the last ten households. Measuring Change in Juvenile Firesetter Programs: An Example. Juvenile firesetter programs are different in nature from other prevention programs, and their evaluation requires some special considerations. First, juvenile firesetter programs often are aimed both at the curious child and the disturbed or malicious child. The “bottom-line” effect of the program is manifested by whether there is a reduction in (1) children-playing fires and/or (2) arson. Both of these categories need to be monitored, because sometimes fires are simply re-labeled and shifted from one category to the other rather than truly reduced. A “gettough” policy with children can result in labeling fires as arson that previously would have been called “children playing.” Conversely, a more sympathetic attitude toward juvenile firesetters could cause a shift from labeling fires as “arson” to “children playing.” Differences in legal definitions between jurisdictions
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also can muddy intercommunity comparisons if both categories of fires are not considered. Second, a common practice in evaluating juvenile firesetter programs is to consider “recidivism rates,” that it, the rates of repeat fires from children who have been treated by the program. Recidivism rates usually are quite different for the curious firesetter than for the disturbed or malicious firesetter. It is easier to “cure” the curious child than the disturbed child. Rates therefore should be measured separately for these two categories. If not, one program can appear to be more successful than another, simply because one has a greater proportion of the easier-to-cure, curious-child cases. Also, curious firesetters may have a low recidivism even without any program. A truly fair evaluation would consider their recidivism rates, with and without the program. A recidivism rate of 5 percent might appear good at first, but would not be so good if the rate without the program was 4 percent. Statistical Change—Determining Whether Change Is a Fact or a Fluke. The evaluator often must address factors that confound simple statistical approaches. The majority of fire departments do not have a trained statistician, though many departments have someone with some knowledge of formal statistical techniques. Unfortunately, real-world statistical situations often require considerable expertise to be able to say that “with such and such a confidence level” the impact of a program is real. Standard statistical formulas actually may be invalid for many situations, such as when the samples collected are not truly random samples and the assumptions behind the formulas are not met. It is recommended that fire departments seek statistical expertise either from among their own personnel or from outside sources, such as local universities or statistical consultants, to assist in their evaluations. Despite these caveats, some basic idea of statistics can give at least a rough, “ballpark” feel for whether observed changes are likely to be significant. This material is offered later in this chapter, as much to give the reader a feel for the kinds of situations that are not “statistically significant” as they are to be a guide for quoting statistics. What many statisticians do not like to reveal is that, in many cases, common sense and good judgment are needed to say whether a change is likely to be real or not, and not just complex statistical formulas. It is also useful practice to periodically review previous evaluations to see if initial findings about effectiveness or lack of effectiveness held up over time. Sometimes what seemed like a true program impact may appear to be a fluke after a few years of data are collated. Sometimes it goes the other way; a program with little impact initially starts to have a large cumulative impact after a year or two. Another kind of statistical evaluation problem comes when trying to separate the impacts of two or more programs that overlap in time. For example, it is difficult to separate the impact of fire department programs on smoke detector purchases versus the impact of television ads. Comparing communities with and without fire department programs but exposed to the same television ads may give some insight into whether the programs in
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question add anything. Sophisticated statistical techniques can be applied but are virtually unusable without expert statisticians. Suffice it to be flagged as a complex problem here.
Unintentional Impacts The evaluation of a program should include a check for unintentional impacts along with expected desirable results. Some common unexpected side effects are 1. Greater reporting of minor fires that previously went unreported. Encouraging the public to flee a fire and call 9-1-1 instead of trying to put it out can lead to an increase in reported fires. Other positive aspects of a public education program sometimes are partly or entirely masked by this surge. Looking at the number of small fires apart from large fires can be a check on this. 2. Increase in fires set by children. Sometimes raising the subject of fire to children boomerangs and greater curiosity is generated instead of being lessened. 3. Scares, nightmares, and other psychological problems. Young children can have a new fear added unwittingly by a program that is too scary for their age group. Children may become fearful instead of careful. 4. Intrusion into parents’ lives. Getting a child to harass parents to improve home safety or to purchase safety devices the parents feel they cannot afford can lead to complaints by the parents. Usually this is outweighed by positive feedback from parents whose safety consciousness is improved. But complaints should be taken seriously, and the curriculum and instructors reviewed to see if the safety message can be delivered effectively without unwanted side effects.
Proving Effectiveness after a Program Is Terminated Sometimes the value of a program is not evident until after it is gone. Proving that there was a real loss of benefit after a budget cut or reallocation of resources causes the demise of a program is one way to fight for its restoration. It also is a valuable type of hindsight from which the profession can learn. Just as a drop in fires, fire casualties, or dollar loss after a program is initiated can prove it worked, so can a rise in these measures after the program is dropped. Likewise, drops in smoke detector maintenance, drops in fire safety knowledge, and increases in numbers of hazards found per home after a program terminates can all indicate the effectiveness it had. Of special importance after a program ends (or after an initial test of a program in one area) is to see how long the good results last. One might be able to show, for instance, that half of the people exposed to a public service announcement continue to test their detectors for three months after seeing it and then begin to forget and stop testing. Information on how fast the initial effect wears off is highly valuable for identifying the minimum repetition frequency a message needs to have to produce a continuing impact on the majority of those who receive it. This information can be used to optimize the use of scarce prevention resources.
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The problem of unintentional injury is one of the most significant public health issues facing society today, and effective injury prevention programs need to be developed and implemented to address this problem. Evaluation is a key component of any program and should include assessment of the program’s feasibility, cost-effectiveness, and efficacy. Data gathered early in the development cycle can be used to help create better programs, modify implementation strategies, revise interventions, and monitor progress toward goals and objectives. Outcome data can be used by policymakers, funders, and practitioners to expand successful programs to larger populations. Education is an important component of safety and prevention programs, but acquiring knowledge is just one step in reducing injuries. Successful programs use multiple strategies, such as teaching children in schools, involving families and communities, and promoting changes in the home or community environment. Risk Watch® is an example of such a program. Recent reviews have shown that many communities have the commitment, desire, and ability to share the responsibility for reducing unintentional injuries. In consultation with community leaders, future studies should continue to evaluate the effectiveness of well-designed community-based approaches aimed at improving safety behaviors and reducing injuries.
SUMMARY Evaluation is a key component of fire and life safety education programs for two reasons. First, evaluation is a technique for making the most effective use of limited fire and life safety resources. Second, evaluation provides the educator with the feedback needed to know whether fire and life safety education is indeed reducing incidents and preventing incidents. Either reason is a strong argument for the merits of evaluation. Together, the two reasons make a compelling case for undertaking evaluation activities.
BIBLIOGRAPHY References Cited 1. National Safety Council, “Injury Facts: Foreword,” http://www.nsc.org/Irs/statinfo/99forewd.html. Accessed June 12, 2000. 2. Deal, L. W., Gomby, D. S., et al., “Unintentional Injury in Childhood: Analysis and Recommendations,” The Future of Children, Vol. 10, No. 1, 2000, p. 5. 3. Rivara, F. P., “Prevention of Traumatic Deaths to Children in the United States: How Far Have We Come and Where Do We Need to Go?” Pediatrics, Vol. 97, 2000, pp. 791–97. 4. Mallone, S., “Evaluating Injury Prevention Programs: The Oakland City Smoke Alarm Project,” The Future of Children: Unintentional Injuries in Childhood, Vol. 10, No. 1, 2000, pp. 163–174. 5. Deniston, O. L., and Rosenstock, I. M., “Evaluating Health Programs,” Public Health Reports, Vol. 85, 1970, pp. 35–40.
6. Thompson, N. J., and McClintock, H. O., Demonstrating Your Program’s Worth: A Primer on Evaluation for Programs to Prevent Unintentional Injury, Centers for Disease Control and Prevention, National Center for Injury Control and Prevention, Atlanta, Georgia, 1998. 7. Fitz-Gibbon, C. T., and Morris, L. L., How to Design a Program Evaluation, Sage Publications, Newbury Park, CA, 1987. 8. Becker, M. H., and Mainman, L. A., “Socio-Behavioral Determinants of Compliance with Health and Medical Care Recommendations,” Medical Care, No. 13, 1975, pp. 10–21. 9. Haggerty, R. J., “Changing Lifestyles to Improve Health,” Preventive Medicine, No. 6, 1977, p. 289. 10. Green, L. N., Community Health. Times Mirror/Mosby College Publishing, St. Louis, MO, 1990, pp. 81–102. 11. Dixon, M. B., “An Evaluation of Risk Watch, A Comprehensive School-Based Injury Prevention Curriculum in Western North Carolina,” Unpublished Master’s Thesis, Dept. of Maternal Child Health, School of Public Health, University of North Carolina, Chapel Hill, June 2000, p. 7. 12. Klaswer, T. P., et al., “Community-Based Injury Prevention Interventions,” The Future of Children, pp. 83–105. 13. Interwest Applied Research, “Evaluation Report 1: Adequacy of Current Knowledge Tests to Measure Growth,” Nov. 1998, p. 2. 14. Chang, A., Dillman, A. S., Leonard, E., et al., “Teaching Car Passenger Safety to Preschool Children,” Pediatrics, No. 76, 1985, pp. 425–428. 15. Interwest Applied Research, “Evaluation Report 3: Results from the First Year of Risk Watch,” Aug. 1999, p. 5. 16. Bowman, J. A., Sanson-Fisher, R. W., and Webb, G. R., “Interventions in Preschools to Increase the Use of Safety Restraints by Preschool Children,” Pediatrics, No. 79, 1987, pp. 103–109. 17. Klaser, T. P., et al., “Community-Based Injury Prevention Interventions,” The Future of Children, p. 85. 18. DiGuiseppi, L., Atkins, D., Wolf, S., et al., “US Preventive Services Task Force. Counseling to Prevent Motor Vehicle Injuries,” Guide to Clinical Preventive Services, 2nd ed., US Government Printing Office, Washington, DC, 1996, pp. 643–57. 19. Learn Not to Burn Curriculum®, National Fire Protection Association, Quincy, MA. 20. Hatry, H., et al., Public Program Evaluation, 2nd ed., Urban Institute, Washington, DC, 1989. (Note: Many other Urban Institute publications address the art and science of evaluation). 21. Short Guide to Evaluating Local Public Fire Education Programs, U.S. Fire Administration, Emmitsburg, MD, 1991. 22. Schaenman, P., et al., Proving Public Fire Education Works, TriData Corporation, Arlington, VA, 1990.
Additional Readings Institute of Medicine, Reducing the Burden of Injury: Advancing Prevention and Treatment, National Academy Press, Washington, DC, 1998. Thompson, N. J., and McClintock, H. O., “Demonstrating Your Program’s Worth: A Primer on Evaluation for Programs to Prevent Unintentional Injury,” Centers for Disease Control and Prevention, National Center for Injury Control and Prevention, Atlanta, GA, 1998. Wallis, W. A., and Roberts, H. V., Statistics: A New Approach, Free Press, New York, 1960. Weiss, N. A., and Hassett, M. J., Introductory Statistics, 2nd ed., Addison-Wesley, Reading, MA, 1987. www.animatedsoftware.com/statglos/statglos.html.
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Campus Fire Safety Ed Comeau
A
ccording to the U.S. Department of Education, there are 2309 four-year and 1755 two-year colleges (referred to generically as universities in this chapter) in the United States. The facilities of these institutions cover a wide variety of occupancies, including residential occupancies, assembly occupancies (classroom buildings, for example), and health care facilities. Roughly 7.5 million students attended these colleges in 1997/98.1 Approximately 38 percent of the total number of students enrolled, or 2,059,565 students, live in dormitories.1 For many of these students, this will be their first time living away from home, meeting new friends, and having new experiences. They are at an age when they may have a sense of invulnerability—nothing bad can happen to them. Unfortunately, tragedy can strike hard at these young men and women. • A dormitory fire at Seton Hall University claimed the lives of three freshmen. • A fraternity fire at the University of North Carolina in Chapel Hill killed five students. • Double fraternity fire tragedies in Bloomsburg, Pennsylvania, killed eight young men. • Off-campus fires in Berkeley, California; Pittsburgh, Pennsylvania; Morgantown, West Virginia; and New York City, among others, have also killed young men and women preparing to move on with their lives. A number of factors can heighten the risk of a particular campus environment. Students may engage in risky behaviors, such as drinking, and they may indulge in such behaviors for the first time, without either supervision or experience to guide them. Both can contribute to the incidence of fire. On-campus housing facilities tend to be more regulated and monitored, whereas off-campus housing facilities have a lower level of scrutiny and a potentially lower level of fire safety. Because of the fire tragedies at Seton Hall and Bloomsburg, campus fire safety is receiving a higher level of attention than it has in the past. This chapter will address the risk of fire associated with on-campus and off-campus residential occupancies and will describe strategies for minimizing that risk.
Ed Comeau is the principal of writer-tech.com in Belchertown, MA, and the publisher of Campus Firewatch, an electronic monthly newsletter that focuses on campus fire safety.
ON-CAMPUS RESIDENCES Residence Halls Fires in residence halls are of concern because of the large number of people potentially exposed. Residence halls tend to be occupied by younger students, such as freshmen and sophomores. Many students prefer to live off-campus, and many campuses have limited on-campus housing but may restrict the opportunity for off-campus living to older students. As residence halls are under the control of the university, they have more authority to impose conditions that can dramatically improve the level of fire safety in these buildings as opposed to off-campus residential occupancies. These safety measures can include the following: • Regulating the combustibility of contents such as furniture and wall and floor finishes • Regulating the use of appliances such as microwaves and refrigerators • Regulating the use of candles, incense, and smoking Students who live in residence halls are also typically under stricter guidelines regarding their behavior. When students move into a residence hall, they are often provided with information regarding expected behavior, what comprises a violation, and the penalties that can follow. Because of the presence of university staff in these buildings, it is more likely that violators can be identified and either counseled or penalized as necessary. If a student’s actions are serious enough, he/she can be removed from the residence hall altogether. Many residence halls have staff often referred to as resident assistants or RAs assigned to help the students. This staff is generally made up of older students who live in the building and have received training in a variety of different areas. RAs can serve a vital role in fire safety since they live in the building, can identify potential hazards, and help students understand the importance of fire safety and the dangers of tampering with fire protection equipment. The residence hall physical plant can be maintained to a consistent level of fire safety by the university, as opposed to off-campus housing in the community. Dangerous conditions can be corrected properly. The types of residence halls found on campuses can vary tremendously, from wood-frame renovated houses to high-rises.
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Often, the buildings used for residence halls are constructed of non-combustible material. In an analysis conducted in Pennsylvania, 85 percent of the residence halls, housing 86 percent of the on-campus students, were of noncombustible construction among the institutions surveyed.2 By using noncombustible construction, it is possible to reduce the fire load in the building.
500 450 400 350 300
Greek Housing 250
Greek housing may be found on-campus or off-campus. The local “house” may be owned by the national fraternity organization, rented from a local landlord, or owned by the corporation board (alumni or who are responsible for the physical facilities). Greek housing provides an alternative for students who are seeking to move out of a residence hall. Greek housing can range from renovated wood frame structures to noncombustible structures that were built to the same standards, and even by the same people, as the residence halls. The level of fire protection within these occupancies can vary dramatically, too. The North-American Interfraternity Conference (NIC) is the umbrella organization for more than 60 national and international fraternal organizations. These fraternities have chapters on over 800 campuses, with a membership of approximately 350,000 undergraduates. The state with the most fraternity chapters is Pennsylvania, with 454 listed at 55 institutions, which represents 8 percent of all of the chapters listed (Figure 5.7.1). Running a distant second is New York, with 368 fraternities located at 62 institutions, followed by California with 343 chapters at 41 schools. These three states, combined, represent over one-fifth of the fraternity chapters in the country.3 In the Greek system, the fire problem clearly lies within the fraternities rather than the sororities. From 1990 to 2000, there was only one fire fatality in a sorority, compared to 23 within fraternities.4 Because of the recognized problem with fires in Greek occupancies, a number of communities, as well as the state of New Jersey, have passed ordinances and laws requiring that they be equipped with automatic fire sprinklers. Some fraternal organizations are taking it upon themselves to install sprinklers in their properties, nationwide, recognizing the importance and value of these systems.
200 150 100 50 0 PA
NY
CA
TX
FIGURE 5.7.1
OH IL States
VA
MI
NC
IN
Distribution of Fraternities
University-Owned Property Off Campus Because of the lack of existing dormitory space on-campus, some institutions are either building or purchasing apartment complexes off campus to provide student housing. Although these structures may be located off campus, because the institution owns the structures, they are considered the same as residence halls in terms of fire protection.
OFF-CAMPUS RESIDENCES Student off-campus residences are the subject of conflicting expectations. Traditionally, colleges have lacked established authority to oversee these properties and have not always been aggressive in asserting their informal influence. This section will review the risks and gaps in fire protection associated with young people living on their own in ordinary housing and will
Case Study UNIVERSITY-OWNED OFF-CAMPUS HOUSING A fire in a house owned by the University of Dayton killed a student on Sunday, December 10, 2000. Austin Cohen, 21 years old and a senior at the university, died in the fire. There were eight students living in the house at the time of the fire. According to reports, the residents had extinguished an earlier fire at the house. One of the occupants, a University of Dayton student, was later arrested and charged with involuntary manslaughter and arson.
According to fire department officials, the fire alarm system was disconnected at the time of the fire. The building was a two-story, wood frame building that was owned by the University of Dayton. According to fire officials, the university was buying a number of properties to use for student housing.5
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Case Study OFF-CAMPUS GREEK HOUSING On Sunday, May 12, 1996, an accidental fire occurred at the Phi Gamma Delta fraternity house at the University of North Carolina in Chapel Hill. Five occupants were killed and three others were injured. The fire and smoke caused heavy damage, estimated at $475,000, throughout the 70-year-old, three-story-plus-basement building. Local and state fire investigators determined that smoking materials most likely ignited combustible materials underneath an alcohol bar in the basement. The fire then spread to the combustible interior finishes and the furnishings in the basements open area and chapter room. Fire and unburned products of combustion spread up the interior stairway and ignited fires on all levels above the basement. Single-station, battery-powered smoke detectors were installed near the central stairway in the basement and in the corridors on the second and third floors. Portable fire extinguishers were provided throughout the building. Doors to the sleeping rooms were solid, consisting of wood-based composite material. These doors did not have self-closing devices. The following factors significantly contributed to the loss of life in the Chapel Hill fire:
identify some strategies campuses have used to try to assert oversight and improve the situation. According to the U.S. Department of Education, an estimated 3.4 million students who attend four-year institutions, or 62 percent, live off-campus. Universities often do not get involved in fire safety issues for off-campus students. This is considered to be the responsibility of the authority having jurisdiction (AHJ) and beyond the scope of the institution. However, this may be changing. Recently, some universities have begun taking action against students whose off-campus actions result in their being arrested or issued citations. To keep the individual cost of housing low, students frequently share rooms, apartments, or houses. For this reason, there may be a larger number of occupants in a particular occupancy than would otherwise be expected. To obtain some level of privacy, students resort to creative solutions, such as living in attics, walk-in closets, basements, and other areas where sleeping areas would not normally be located. According to the report from Campus Fire Safety Forum I, the participants believed that the number of off-campus fires involving students was a somewhat “hidden” problem because these fires were not identified in the national statistics as involving students. At one university, it was recognized some time ago that the houses and apartments that the students were living in had some serious deficiencies. According to a city official, parents were coming in and saying that they could not believe the condition of the places (where the students were living off-campus). They
• Combustible interior finish materials • An open stairway • Lack of fire-rated construction separating the assembly areas from the residential areas of the building • Lack of automatic fire detection and fire alarm systems throughout the building • Lack of automatic sprinkler protection • Improper use or disposal of smoking materials In the wake of the tragedy in Chapel Hill, the Town Council voted unanimously to work toward a plan that would require sprinklers in fraternity and sorority houses. On June 19, 1996, the state legislature granted the town authorization to enact a retroactive sprinkler law, requiring fraternity and sorority houses in Chapel Hill to comply within five years. The Chapel Hill Fire Department is working with the fraternity and sorority community on retrofit plans. As of April 2000, 17 of Chapel Hill’s 36 fraternity and sorority houses had been retrofitted with sprinkler protection. The vast majority of the remaining chapters have plans underway to complete the installation of sprinkler protection.6
were dumfounded that the university could let them advertise in the newspaper. As a result, the university and city developed a program to try and address this problem. A landlord could request a special annual inspection of their property by the city, which would be done using the criteria in the property maintenance code. Once the landlord passes this inspection, they could advertise their property through the university. The inspector would check each smoke detector, door closers, fire doors, make sure sprinklers were not painted over, that exits are not blocked, and that the fire escapes are in good shape. The only problem was that most of the landlords who did sign up for the program did not have many problems. Unfortunately, it did not hit the people that it needed to because most of the landlords are reluctant to bring in the inspectors. Once a property receives its occupancy permit, there are no subsequent inspections unless a problem is reported. Unfortunately, the program died off because few landlords were taking advantage of the program. Off-campus students are a group that is difficult to reach. Providing the information and education to these students once they move off-campus is a challenge recognized by many fire officials.7 Students living in off-campus residential occupancies tend to be the older students. Because all states have a minimum drinking age of 21, this means that the off-campus student may have more access to alcohol. Furthermore, since there is no oversight, students are more able to drink even if they are underage. AHJs have cited the link between alcohol consumption and
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student behavior, which has led to fires, injuries, and deaths. A number of the fires and the fatalities that have occurred off-campus have happened either following a party or the victim has had a high alcohol level in the blood.6 One of the significant problems that arises is disabling or removing smoke detectors. In a number of fatal home fires, disabled or missing smoke detectors have been significant contributing factors. The behavior of the students living off-campus can be contributing factors to fires. In one case, the students were playing a game of lighting toilet paper on fire and then pushing it under the doors into their roommate’s rooms.8 The fire that ensued destroyed the house. In another instance, the residents were refueling a Halloween decoration on their front porch using camping fuel when it ignited, burning the house down.9
Apartments Apartment houses may have requirements regarding the installation of sprinkler systems and/or smoke detection systems. Since they are multiunit dwellings, the local fire department may have an inspection schedule for these types of occupancies. Apartments may have requirements for hardwired smoke detectors, either in the common corridors or in the units themselves. Depending on the size of the apartment building or complex, the landlord may have a greater presence or maintenance personnel on staff that can monitor the conditions and take corrective action when needed.
TABLE 5.7.1 School, College, and University Dormitories and Fraternity and Sorority House Fires, by Cause Reported to U.S. Fire Departments,3 1994–1998 Annual Averages
Fires
Cause Incendiary or suspicious causes Cooking equipment Smoking material (i.e., lighted tobacco product) Other equipment Other heat source Electrical distribution equipment Open flame, ember or torch Applicance, tool, or air conditioning Heating equipment Child playing Exposure (to other hostile fire) Natural causes Total
Property Damage (in Million Dollars)
490
(31.2%)
1.5
300 180
(18.9%) (11.7%)
0.9 0.4
130 120 110
(8.5%) (7.4%) (7.1%)
0.2 2.3 2.0
80
(5.4%)
0.6
80
(5.4%)
0.4
40 10 10
(2.5%) (0.8%) (0.8%)
0.4 0.2 0.0
10
(0.5%)
0.0
1,570
(100.0%)
9.1
Source: National Estimates based on NFIRS and NFPA survey.
Single-Family Dwellings If a group of students rent a house, it may still be considered a single-family dwelling and therefore may not be under any special constraints regarding built-in fire protection or inspections by the local AHJ.
Like most parts of the U.S. fire problem, the size of the fire problem in dormitories and Greek housing has been declining (Table 5.7.2).10 Although these statistics omit reported fires in off-campus, non-Greek housing and unreported fires, these omissions affect the total size of the problem and not the general documented trend.
HISTORY Fire Incidence The latest data on campus residential fires is available in the NFPA’s report School, College, and University Dormitories, and Fraternity and Sorority House Fires in the United States, 1994–1998 Annual Averages (June 2001), and the following statistics are taken from that report.10
Cooking. Cooking accounts for 19 percent of the fires in campus residential occupancies (on-campus and Greek). These fires have resulted in an average of $900,000 in damage each year.10 Smoking. The third leading cause of fires in residence halls and Greek housing is smoking, which causes 12 percent of the fires each year. Fires started by smoking materials cause an average of $600,000 in damage in a year.10
Fatalities/Injuries From 1994 to 1998, there were an average of 1570 structure fires causing $9.1 million a year in direct damage in dormitories and fraternity and sorority houses. From 1990 to 2000, NFPA has records on 19 fatal incidents that killed 33 people. Eight of these incidents occurred in dormitories, causing the deaths of 10 students. The remaining 11 fires occurred in Greek housing and killed 23 people. These statistics do not include the fires in offcampus, non-Greek housing. The three leading causes of fires in campus residential occupancies are incendiary and suspicious causes, cooking, and smoking (Table 5.7.1).10 Together, they accounted for three of every five fires in these properties.
PODS STRATEGY Dr. Fred Mowrer from the University of Maryland developed a concept to integrate the four components of an effective campus fire safety program. He identified the following four components: • • • •
Prevention Occupant awareness Detection Suppression11
From these four components, he developed the acronym PODS. PODS is a concept that can be compared to a table with four legs.
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TABLE 5.7.2 School, College and University Dormitories and Fraternity and Sorority House Fires, by Year Reported to U.S. Fire Departments3
Year
Fires
Direct Property Damage (in Million Dollars)
1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
2,500 2,400 1,700 1,900 1,900 1,900 1,800 1,900 1,900 2,000 1,500 1,600 1,600 1,600 1,700 1,700 1,500 1,500 1,400
4.8 7.5 7.3 18.7 4.8 6.1 4.6 7.5 5.8 8.7 7.4 15.1 2.8 4.9 10.0 16.7 5.9 7.0 5.9
1,600
9.1
Annual Average 1994–1998
Source: National estimates based on NFIRS and NFPA survey.
An effective campus fire safety program requires all four components, as does a table, to work. Each of these components has a different timeframe associated with it. For an institution that is developing a long-range fire safety concept plan, the components would probably have different implementation timeframes. For example, suppression in the form of sprinklers may require a longer timeframe to acquire the funding, perform the engineering design work, and so on. On the other hand, a very effective prevention program can be implemented almost immediately.
PODS PREVENTION There is a unique challenge in the campus environment to educate and train the students. People of this age may have a sense of invulnerability that can be difficult to overcome. It is therefore important to ensure that the environment is as fire-safe as possible, so that the effects of risk-taking behavior, should fire occur, can be minimized. The prevention techniques used to create a fire-safe environment include evaluating/inspecting the students’ living space with the goal in mind of reducing the fuel load in these spaces and reducing ignition sources. Here, prevention is not used in the traditional sense to refer solely to prevention of ignition, but also refers to built-in passive protection and designed provisions for effective escape.
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There should be sufficient exits, and they should be properly marked and illuminated. If there are fire safety design features, such as fire doors, that are routinely propped open for convenience, then the university or landlord should evaluate strategies to stop this from occurring.
Reducing Fuel Load The fuel load in a fire comprises the structure itself and the contents that are placed inside of the structure. Structure. Many dormitories built today are made of noncombustible materials. This helps to reduce the fire load significantly and also helps to compartmentalize the building, limiting fire spread. However, a number of older buildings, either built as residence halls or converted into residence halls, are made of combustible materials. In this case, steps should be taken to help minimize the potential for the fire rapidly spreading to the building. Finishes. At the Chapel Hill fraternity fire, the wood paneling on the walls was identified as a significant contributing factor to the spread of the fire from the basement to the second floor.6 Universities and landlords should be cognizant of the materials used inside the buildings and how they may contribute to the fire spread. Some students personalize or decorate areas using combustible materials. This can especially be a problem during holidays. At the Providence College fire in 1977 where ten students were killed, the combustible decorations on the corridor walls were identified as a significant factor in the fire spread.12 A Halloween decorating contest at Seton Hall, months after the fatal fire, was stopped by the fire department because of the accumulation of combustible materials in the corridor, including hay.13 Furniture. Furniture represents much of the fuel load in student housing. In an environment where it is possible to control the type of furniture, such as residence halls, flammability and combustibility standards should be established. Clothing, Books, and So On. Personal contents, such as clothes and books that students bring, are not something that can be regulated and should be considered a part of the normal fuel load that will exist in any student housing occupancy.
Reducing Ignition Sources Smoking. Many institutions have implemented no-smoking policies in residence halls. This is often done because of the public health concerns, but also is a safety issue. In a survey conducted for the Pennsylvania state legislature, it was found that 43 percent of institutions surveyed did not allow smoking in individual rooms.2 The fire safety professional should be concerned with students attempting to circumvent these regulations, especially during colder weather when people are not as receptive to going outside to smoke. In order to smoke in their rooms, students may disable smoke detectors.
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Candles and Incense. Information on candle fires is available from the NFPA report Candle Fires in U.S. Homes and Other Occupancies: A Statistical Analysis.14 From 1994 to 1998, candle fires in 140 structure fires a year caused an average of $2.3 million per year in direct damage in dormitories or Greek housing. Overall, candle use and candle fires have been increasing. As with smoking, a number of institutions have banned candles from their residence halls. Others are permitting candles within the rooms, but they cannot be lit. An issue to address is that of religious ceremonies involving candles. Several institutions have continued their outright ban on candles, whereas others make provisions for students using them in religious ceremonies. Some of the conditions that are imposed include the following: • A special permit must be obtained. • The candles must be burned in a specific location, such as a common area. The logic behind this is that there is less of a combustible fuel load in the common areas than might be found in a student’s room. • The candles must rest on a noncombustible surface. • The candles must not be left unattended Electrical. Electrical fires are a significant concern in today’s college environment. Many residence halls, fraternities, and sororities were built prior to the advent of computers, microwave ovens, and before the nearly universal use of stereos, televisions, and other entertainment equipment. This equipment carries some fire hazard itself, but there may be additional hazard to the buildings electrical distribution equipment from the increased power demand. Two problems arise because of the increased electrical needs. A room, house, or facility may not have sufficient electrical capacity to provide the power required, which may cause overloads in the electrical system. If there are ongoing problems, such as tripping circuit breakers, the occupants may try to circumvent the safety features to ensure that power is not interrupted. If there are not enough outlets, then the occupants may use extension cords and power taps (more commonly known as power strips). This creates several problems. • Tripping hazard • Overheating electrical cords that may be coiled or bunched up, creating a potential ignition source • Physical damage to electrical cords run under carpet and around furniture in such a way that they can become damaged or worn, exposing bare conductors • Overload, even though the occupants may be using power strips equipped with individual circuit breakers, the circuit is not adequately protected Halogen torchiere lamps have been a concern in residence halls and Greek housing because of the high temperature of the bulb. Design changes have been made by manufacturers to ensure that combustible materials cannot come into direct contact with the bulb, helping to reduce the potential for ignition. However, this style of light is discouraged by a number of institu-
tions, not only because of the fire hazard, but also because of their high power consumption. A number of utility companies are offering “buy-back” programs, where they will trade a lamp with lower power needs for a halogen lamp. Cooking. Cooking should be permitted only in specifically designated cooking areas. The use of hotplates and other cooking devices should be restricted to minimize the potential for a fire. Cooking in a student room means cooking near more combustibles than would be tolerated in a kitchen, and therefore a higher risk of fire. The use of microwave ovens should be evaluated based on the occupancy and the capacity of the electrical system. To regulate the size of microwave ovens and refrigerators in residence halls, some institutions specify a vendor to provide this equipment to the students, and only this equipment is permitted.
PODS OCCUPANT AWARENESS Education and Training A key component of any fire safety program is to ensure that the occupants understand the importance of fire safety and how their actions can have a direct impact on the level of fire safety in their residence hall, fraternity, sorority, apartment, or house. By providing ongoing education to the students, a higher level of fire safety awareness can be maintained. However, this may be difficult to do because of the ongoing turnover of students in the various occupancies. In today’s society, students are “bombarded” with messages from a wide variety of media, including television, radio, print, and the Internet. Any fire safety program is going to have to compete for attention with all of this activity, which can be a challenge. The fire safety professional may have to be creative and tailor the message to appeal to the student so that it will not become lost or be ineffective. Some examples of strategies that may work include the following. Videos. The U.S. Fire Administration’s video Get Out and Stay Alive is one such program. Fire Academies. The Seattle Fire Department holds an annual one-day Fraternity Fire Academy for Greek students at the University of Washington. This involves a combination of classroom lecture, live fire training, and a mock-up of a fraternity room where they have to identify safety hazards. Fire Drills. At Miami University in Oxford, Ohio, students participating in fire drills are taught the proper actions to be taken should they encounter smoke by being given the chance to pass through a corridor that has been filled with theatrical smoke.
Housekeeping Maintaining an environment that is relatively clean and orderly helps to reduce the amount of combustible fuel load that can potentially be ignited or serve as a fuel load to a fire. The 1996 fire
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in Chapel Hill was fueled in its initial stages by trash that had not been discarded following a party the evening before. This requires ongoing vigilance to ensure that conditions do not change. The residence hall staff should be educated as to what can create unsafe conditions. Recycling has created a new challenge. Recycling containers for paper and cardboard are now being placed in buildings, creating two concerns. The first is that a container with a concentrated combustible fuel load may either be ignited (unintentionally or deliberately) or may serve as a fuel package for an external fire. The second is that these containers may be placed in a means of egress. The philosophy is that corridors, stairways, and so on should be kept clear of any such fuel loads because they may impact on the safety and integrity of the escape route if they should become ignited. Also, these containers may serve as an obstruction along the egress route. Placement of these containers should be carefully monitored and controlled. It is also important that they be emptied on a regular basis to ensure they do not become full, and then the occupants start to place combustible materials outside of the containers.
Alcohol Alcohol consumption has long been connected with college campuses. Although the recent trend is towards educating students in more responsible behavior, the problem continues to exist. The connection among alcohol consumption, student behavior, and the incidence of fires in student housing, both onand off-campus is a serious concern. What is the prevalence of alcohol on campus? This is something that is difficult to quantify. However, some indicators and surveys can provide information in this area. When reviewing this information, it is important to remember that the national drinking age is 21. Under federal law, colleges and universities are required to annually report crime statistics to the United States Department of Education. Among these statistics, they are required to report the number of alcohol-related arrests. According to the June 9, 2000, issue of The Chronicle of Higher Education, in a review of 481 campuses with over 5000 students, arrests for liquor law violations increased to 23,261 in 1998 from 18,708 in 1997, a 24 percent increase. However, increased policing and enforcement may attribute to this increase.15 The Harvard School of Public Health has been measuring alcohol usage on campuses since 1993. College Binge Drinking
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in the 1990s: A Continuing Problem; Results of the Harvard School of Public Health 1999 College Alcohol Study included responses from over 14,000 students at 139 institutions across the country. It focused on what has been classified as binge drinking, which is defined as consuming five drinks in a row for men and four drinks for women. According to the study, there is an increasing polarization occurring on campus, in which both extremes of alcohol-related behavior—binge drinking and total abstention—are growing. The number of frequent binge drinkers, that is, those who binge drinks three or more times within a twoweek period, increased from 23 percent in 1993 to 28 percent in 1999. At the same time, the number of people abstaining from alcohol increased from 15 percent to 19 percent over the same period.16 When looking at the responses, 81 percent of the respondents reported drinking, with 44 percent classifying themselves as either an occasional or a frequent binge drinker (Table 5.7.3). According to a 1999 report by the Educational Resource Information Center (ERIC), the prevalence of binge drinking is higher among Greek residents (Table 5.7.4).17
Fire Protection Features Students may not be fully aware of the fire protection features in the buildings they occupy and may inadvertently bypass them. A common violation is doors that are propped open for easier traffic flow. By doing so, they bypass the fire safety feature of compartmentation and create an avenue for fire spread from beyond the compartment of origin. Students should understand the importance of the fire protection systems and the results of tampering with them. This includes sprinkler systems and fire alarm systems. Smoke detectors and audible devices should not be disabled.
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PODS DETECTION Smoke detection plays a critical role in any fire safety program. A properly installed, operating smoke detector can literally make the difference between the occupants being able to escape from a fire or being trapped by the smoke and flames. However, smoke detectors cannot save lives if they have been disabled or bypassed, a significant problem in all types of residential properties, including campus housing. False or nuisance alarms are a problem in all types of properties, both because they may lead frustrated occupants to disable the detectors and because they may lead residents to ignore all alarms. False or nuisance alarms can occur because of design, installation, or usage problems, including prank activation. TABLE 5.7.3 (1999)
College Student Patterns of Alcohol Use 19% 37% 21% 23%
Abstainer Nonbinge drinker Occasional binge drinker Frequent binge drinker
Source: College Binge Drinking in the 1990s: A Continuing Problem; Results of the Harvard School of Public Health 1999 College Alcohol Study.
TABLE 5.7.4
Students Who Participate in Binge Drinking
Greek residents Non-Greek residents Greeks who became binge drinkers in college Non-Greeks who became binge drinkers in college Source: ERIC Digest.
Men
Women
86% 45% 78%
80% 35% 76%
32%
25%
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Some strategies to help combat this problem include • Severe penalties for students that are caught activating the fire alarm needlessly. • Financial penalties being imposed upon the floor or building where there is an ongoing problem of false alarms. This leads to peer pressure to help reduce the problem. • Cross-zoning smoke detectors so that more than one smoke detector must sense smoke within a given area before the building fire alarm system will be activated. • Using devices that cover the manual pull stations. When the device is lifted, a local alarm sounds, alerting people in the area. However, they do not restrict access to the pull station, which can be activated if necessary. Different fire detection strategies can be employed, depending on the occupancy and the desired level of fire safety. However, the first strategy may lead residents to hesitate before sounding the alarm in a real fire; the second strategy penalizes innocent residents; and the third strategy may also mean delayed notification.
Single Station Alarms Single station smoke alarms are stand-alone units that can be powered by batteries, hardwired, or both. When a single station smoke alarm senses smoke, it activates an alarm at only that detector; any other detectors are not interconnected. These smoke alarms are easy to install and are relatively inexpensive. At the same time, it is relatively easy to defeat them by either removing the battery or removing the entire unit itself. For more information, refer to NFPA 101®, Life Safety Code®.
System Detection When smoke detectors are interconnected, a much higher level of fire safety is achieved. Whenever any one smoke detector senses fire, a signal can be sent to either other interconnected smoke detectors or to a fire alarm control panel. If the design is such that there are other smoke detectors interconnected with each other, each smoke detector will sound an alarm, alerting the occupants. In systems where the smoke detectors are connected to a fire alarm control panel, a series of events may occur, depending on the design of the system. At the minimum, audible and visual devices should be activated in the building to alert the occupants to a fire. Refer to NFPA 101 for more information.
Local Alarms A local fire alarm system will sound an alarm only within the protected building, alerting the occupants. No signal is sent offpremises to any monitoring agencies or companies. These systems certainly serve the purpose of alerting the occupants to the fire and providing them with adequate time to escape the fire. However, unless someone takes the specific action of calling the fire department, a fire will have the opportunity to grow. Many people assume that if a fire alarm system is activated, it automatically notifies either the fire department or some other
agency. If the fire alarm system only sounds a local alarm, the occupants should be made aware of this fact, and procedures should be established to ensure that the fire department is notified of the fire alarm activation. Refer to NFPA 101 for more information.
Supervised Alarms Fire alarm systems can be designed to transmit a signal offpremises to the local fire department, campus police or security, or a commercial alarm monitoring company. In the event that the signal is transmitted to a location other than the fire department, procedures should be in place to notify the fire department of the alarm activation. The signal can be transmitted by either hardwired proprietary systems, telephone lines, or via radio signals. At this time, consideration is being given to approving systems that will transmit signals over packet-switched systems (i.e., the Internet). Refer to NFPA 101 for more information.
PODS SUPPRESSION Two types of suppression can be used to suppress a fire: manual and automatic.
Manual Suppression First responders can manually suppress fire using equipment such as fire extinguishers. Fire fighter first responders can manually suppress fire using hose lines. (See Section 11, Chapter 6, “Fire Extinguisher Use and Maintenance.”)
Automatic Suppression Sprinklers are unquestionably the most effective method of controlling a fire. Sprinklers reduce the chances of dying in fire and the expected loss per fire by one-half to two-thirds.10 (Refer to NFPA 101 for sprinkler requirements.) In the wake of Seton Hall, legislation was introduced across the country calling for the installation of sprinkler systems in residence halls and Greek housing. The most sweeping legislation was enacted in 2000 in New Jersey, which calls for sprinkler systems to be installed within four years. The state is providing funding for this initiative through low-cost/no-cost loans to the institutions. On the local level, sprinkler ordinances have been enacted in Chapel Hill, North Carolina; Boulder, Colorado; Durham, New Hampshire; and Lawrence, Kansas. Despite their outstanding record, there still can be resistance to sprinkler installation, primarily from a cost standpoint. Some of the strategies that are being used or proposed to fund sprinklers include the following. • New Jersey is providing the funding through state funds. • In the 2001/2002 budget, the governor of Pennsylvania proposed underwriting the interest on bonds so that no institution has to pay over 3 percent interest. • Legislation across the nation in 2001 proposed varying amounts of funds for low interest loans, ranging from
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$50,000,000 to $200,000,000. The interest rates varied from 0 percent to 3 percent.
FIRE DEPARTMENT STRATEGY Municipal Fire Department The university should work closely with the municipal fire department in all areas of fire protection. This should include not only the academic and support buildings and residence halls, but also off-campus Greek and private student housing as well. Especially in off-campus housing, the fire department will be a critical component in helping to provide a fire-safe environment for the school’s students. The university should not completely rely on the fire department for all fire safety needs. For example, fire prevention, whether the institution or the AHJ delivers it, is still the responsibility of the institution. Also, the fire department cannot be expected to be able to inspect the residence halls and other buildings for fire safety hazards as frequently as the university staff can. When a fire occurs, time is critically important; the sooner the occupants of the building are alerted to the fire, the better their chances of escape and survival. Also, the sooner the fire department is notified of the fire, the faster it will be able to respond, suppress the fire, and rescue any trapped victims. For this reason, it is important that procedures be in place to notify the fire department promptly whenever a fire alarm is sounding. The university should be familiar with the resources that the fire department has available and the type of department. There are generally three different types of fire departments. 1. Full-Time Firefighters: On duty 24 hours a day and available to respond to incidents from staffed fire stations. 2. Combination: Fire department is made up of a cadre of fulltime firefighters in conjunction with either on-call or volunteer fire fighters. 3. Call or Volunteer Fire Departments: Fire fighters that are not staffing a fire station but are “called in” to respond to an incident when needed. A major consideration between the different fire departments is the response time. Since full-time firefighters are immediately available to respond (assuming that they are available and not on another emergency response), the response time should be relatively low. Call or volunteer fire departments may take longer to assemble the necessary personnel to respond and/or initiate a fire attack. The location of the fire station to the university is also a consideration in terms of response time. The fire-fighting capability of a fire department is only one factor. The university should also evaluate the department’s ability to provide fire prevention services. This can range from providing guidance and assistance to the university to actually conducting fire drills, planing reviews, and providing fire prevention education and training. Depending on the status of the university, the fire department may or may not be legally required to conduct plan reviews. However, it is a good idea to always involve the fire department in any plan reviews of new construction or renova-
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tions. This helps to build a stronger relationship between the university and the fire department, the university can gain some valuable information on a fire-safe design, and the fire department becomes familiar with the different occupancies on campus.
Student or University-Based Fire Departments Some universities have fire departments that are based at the university. These can be staffed by either full-time fire fighters who are university employees, students who volunteer as fire fighters, or a combination. Another option is for a fire department to have students serve as volunteers within the municipal fire department. By having students involved in the local fire department, a stronger rapport can be developed with the local community. These students can also serve as an invaluable resource in helping to provide fire safety education and training to other students because of the “peer-to-peer” connection. The reasoning for having students involved in a fire department varies from institution to institution. In some cases the local fire department is not capable of providing an adequate level of fire protection, so the university has taken it upon itself to provide this service. In some cases, the university provides fire protection to the local community as well as to the university property. At universities where there is a fire science engineering program, a student-based fire company or department provides a real world “laboratory” for these students.
SOLUTIONS Campus fire safety is receiving higher profile and awareness among campus administrators, legislators, parents, and students. Some of the following methods are being used to make campuses safe from fire.
Education and Training Education and training for all levels of students, faculty and staff at universities is a key component to the PODS concept. Because of the changes that occur each semester in campus housing, it is important to provide this training at least semiannually to ensure that all of the students are aware of the importance of fire prevention and the fire protection systems. Those living in the Greek system may be more accessible to receive this training. However, a challenge is reaching out to those thousands of students that are living off-campus in houses and apartments. It may be a bad assumption to think that they are already cognizant of the dangers and the right actions to be taken in the event of a fire. Furthermore, today’s students are being bombarded with messages from a wide variety of sources and different media. Radio, television, newspapers, and the Internet are all competing for their time and attention. For this reason, any fire safety program has to be designed to appeal to them.
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Enforcement Enforcement is an ongoing effort that requires, as one fire chief stated, “constant vigilance.” It is important to ensure that the occupancies both on- and off-campus meet the minimum fire safety codes and standards. In between the inspections, however, conditions can change dramatically. For this reason, it is important to train staff such as resident assistants to identify any hazards that may arise in their area. Similarly, a relationship should be fostered with the Greek system to help identify and resolve any problems that are encountered. It would be worthwhile to know the names and addresses of each of the corporation board. When there is a problem in a Greek residency, the corp board can be notified and asked to participate in the solution.
Engineering Engineering can be used to design buildings with passive fire protection features such as compartmentation. By creating safe fire zones within the building, ensuring that there are adequate means of egress, and using noncombustible building materials, the level of fire safety in structures can be enhanced. Through proper engineering, many of the problems encountered in campus housing relating to false alarms can be minimized, if not eliminated. As with any occupancy, careful consideration must be given to the placement of smoke detectors (not in the vicinity of showers or kitchens, for example). Because of the number of false alarms that can plague some universities, different strategies are employed to help reduce these needless calls. These can include • Cross-zoning smoke detectors • Installing covers on manual pull stations to deter malicious activation • Continuous system maintenance to ensure proper operation It is important to evaluate new construction and renovations with a strong emphasis on fire protection. This may be a challenge when renovating existing structures. It may be necessary to employ the services of a fire protection engineer for these projects to ensure that the fire protection needs are met, or to develop different fire protection strategies, perhaps through performance-based engineering methods.
Town-Gown Relations The relationship between the institution and the community, sometimes referred to as “town-gown,” is an important one. Often, neither one is completely responsible for all aspects of fire safety. The community may be responsible for building and fire code issues or providing emergency response services. The institution may have a staff dedicated to fire prevention, safety, and response to incidents on the campus. Constant education is a key aspect to an effective fire prevention strategy. Highlighting known fire situations may have some impact on student thought process. Repetition, honest di-
alogue, and high expectations of cleanliness all play a role in the education process. The Greek system is of particular concern, especially the fraternities. The community, university, and the Greek system must work together to address concerns in these occupancies. Since statistically the fatal fires have occurred in the fraternities much more often than in the sororities, resources and efforts should be targeted at these occupancies. Solutions in some communities have included • • • • •
Mandatory sprinkler ordinances Semiannual inspections Mandatory alarm monitoring Self-inspection Voluntary inspections prior to parties or functions
It is important to identify the landlord of the property and to work closely with that person or entity to ensure that unsafe conditions are corrected as soon as possible. The national fraternal organization and the university’s Greek affairs office should be involved and made aware of any violations or problems with the local chapter.
Insurance When evaluating what level of fire protection to install into a new or existing occupancy, the possibilities of an insurance reduction should be considered. One insurance company for fraternities estimated that they would offer a 30 percent discount if a property was fully sprinklered. A second company insuring sororities said that the discount would run about 15 percent. According to the representative, the lesser discount occurs because they already have low rates on sorority houses as “preferred properties.” A third company that insures campuses said that it would offer a reduction of about 15 percent to 20 percent if the campus went from nonsprinklered to sprinklered buildings.
Resources A variety of resources available to the fire safety professional may be drawn upon in developing a campus fire safety program. Meeting of the Minds (CD-ROM). Meeting of the Minds is produced by the National Association of State Fire Marshals (NASFM) and contains a wealth of information about campus fire safety, including case studies, enacted legislation, proposed legislation, list of organizations that than provide assistance. A copy of the CD can be obtained by contacting NASFM at P.O. Box 8778, Albany, NY 12208. Campus Firewatch. Campus Firewatch, along with its companion website, is an electronic newsletter that focuses exclusively on the issues surrounding campus fire safety. Some of the information in this newsletter and on the website includes legislation updates, a listing of fire incidents on campuses nationwide, and articles on strategies being used to implement fire
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safety on campuses and in Greek housing. Contact Campus Firewatch at www.campus-firewatch.com. Campus Fire Safety Forums. In 1999, Campus Fire Safety Forum I was held at the NFPA headquarters. This landmark forum, sponsored by the U.S. Fire Administration, brought together campus fire safety professionals from across the country. The report from this forum is available on the USFA website at www.usfa.fema.gov. These forums have become an ongoing annual series of forums held at the NFPA fall meeting. 20 Questions. The following list of 20 questions that every student and parent should ask before renting an apartment or house was prepared by the National Association of State Fire Marshals. 1. Are smoke alarms installed? Working? 2. How old are the smoke alarms? 3. How often are the smoke alarms checked and batteries changed? 4. Are there at least two ways to exit your living space and your building? 5. Do the upper floors have a fire escape or ladder available for each bedroom? (if there are multiple floors) 6. Are the living unit doors rated for fire? 7. Are fire extinguishers available? Working? 8. Were the fire extinguishers inspected within the last year? 9. Is a sprinkler system installed? 10. Is the electrical wiring adequate? 11. Is the building regularly inspected by the local fire department or college emergency management office for safety? 12. What is the owner’s policy and method for correcting safety problems in the building? 13. Has there ever been a fire in this building? If so, identify the cause. 14. Does the residence have a gas or electric stove/oven? 15. Do you know how to use the appliance(s) correctly? 16. Where is the nearest fire hydrant on the street? 17. Who is responsible for keeping it cleared in the winter season? 18. Did the school recommend the unit for student housing? 19. Is the owner a member in good standing in a landlord/tenant association or other housing association? 20. Has the city and/or university received any safety complaints regarding this building? Organizations. A number of organizations are active in various facets of campus fire safety. See the References section of Bibliography for a listing.
SUMMARY Providing effective fire protection in the campus environment is a challenging endeavor. By employing a PODS concept, it is possible to build a comprehensive program that addresses all the facets of fire safety. However, because of the changing environ-
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ment and the constant turnover of students, it is necessary to provide the training on a regular basis, and to monitor the conditions in the residence halls and other buildings regularly. By providing training and building effective lines of communication between the institution and the community, the potential for fire tragedies can be reduced.
BIBLIOGRAPHY References National Fire Protection Association (NFPA), 1 Batterymarch Park, Quincy, MA 02269, www.nfpa.org. United States Fire Administration (USFA), 16825 S. Seton Ave., Emmitsburg, MD 21727, www.usfa.fema.gov. National Association of State Fire Marshals (NASFM), P.O. Box 8778, Albany, NY 12208-0778. National Fire Sprinkler Association (NFSA), Robin Hill Corporate Park, Route 22, P.O. Box 1000, Patterson, NY 12563, www.nfsa.org. Campus Firewatch, PO Box 1046, Belchertown, MA 01007, www.campus-firewatch.com. Campus Safety Health and Environmental Management Association, c/o National Safety Council, 1121 Spring Lake Dr., Itasca, IL 60143, www.cshema.org. North-American Interfraternity Conference (umbrella organization for fraternities), 3901 W. 86th Street, Suite 390, Indianapolis, IN 46268, www.nicindy.org. National Panhellenic Conference (umbrella organization for sororities), 3905 Vincennes Road, Suite 105, Indianapolis, IN 46268, www.npcwomen.org.
References Cited 1. Hung, I., Institutional Characteristics and Fall Enrollment Surveys, 1997–98, U.S. Department of Education, National Center for Education Statistics, Integrated Postsecondary Education Data System (IPEDS), 2000. 2. Firepro, for the Pennsylvania State Legislature, “The Feasibility of Retrofitting High Rises, College Dorms, and Certain Other Buildings with Fire Sprinklers,” Jan. 2001. 3. Interfraternity Directory, North-American Interfraternity Conference, Spring 2000. 4. Rohr, K. D., School, College, and University Dormitories, and Fraternity and Sorority House Fires in the United States, 1994–1998 Annual Averages, NFPA Fire Analysis and Research Division, Quincy, MA, June 2001. 5. Campus Firelog, Campus Firewatch, Dec. 2000, p. 11. 6. Isner, M. S., Fraternity House Fire, Chapel Hill, North Carolina, NFPA Fire Investigations Department. 7. “Off-Campus . . . Out of Sight, Out of Mind?” Campus Firewatch, Oct. 2000, p. 1 8. Campus Firewatch Firelog 2001. 9. Campus Firewatch Firelog 2000. 10. Rohr, K. D., School, College, and University Dormitories, and Fraternity and Sorority House Fires in the United States, 1994–1998 Annual Averages, NFPA Fire Analysis and Research Division, Quincy, MA, June 2001. 11. Mowrer, F. W., Fire Safety Student Housing, A Guide for Campus Administrators, USFA, 1999. 12. Demers, D., “10 Students Die in Providence College Fire,” NFPA Journal, Vol. 72, July 1978, p. 59. 13. Campus Firewatch, Halloween at Seton Hall, Nov. 2000. 14. Ahrens, M., Candle Fires in U.S. Homes and Other Occupancies: A Statistical Analysis, NFPA Fire Analysis and Research Division, Quincy, MA, Mar. 2001. 15. Chronicle of Higher Education, A Look at Campus Crime, June 9, 2000, www.chronicle.com.
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16. Wechsler, H., et al., “College Binge Drinking in the 1990s: A Continuing Problem; Results of the Harvard School of Public Health 1999 College Alcohol Study,” Journal of American College Health, Vol. 48, 2000, pp. 199–210. 17. Kellogg, K., ERIC ED 436110, ERIC Clearinghouse on Higher Education, George Washington University, Washington, DC, 1999.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on assembly occupancies discussed in this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 13, Standard for the Installation of Sprinkler Systems NFPA 72®, National Fire Alarm Code® NFPA 101®, Life Safety Code®
Additional Readings Comeau, E., “Campus Firewatch Newsletter, www.campus-firewatch.com. “Dormitory Fires,” Topical Fire Research Series, Vol. 1, No. 14, 2001, pp. 1–3. “Fraternity and Sorority House Fires,” Topical Fire Research Series, Vol. 2, No. 12, 2001, pp. 1–3.
“Korean Fire Data, 1999,” Korean Fire Protection Association, Seoul, February 2000. Lake, J. D., “Life Safety in Dormitories,” NFPA Journal, Vol. 94, No. 5, 2000, p. 30. “Life Safety Improvements in Greek Houses: Chapel Hill, NC,” American Heat [Video Journal], Vol. 11, No. 12, 1996. Mawhinney, J. R., and Richardson, J. R., “State-of-the-Art Review of Water Mist Fire Suppression Research and Development, 1996,” National Research Council of Canada, Ottawa, Ontario, IC-IR718, June 21, 1996. Mongeau, E., “Building a Fire-Safe Dorm,” NFPA Journal, Vol. 93, No. 1, 1999, pp. 60–64. Mowrer, F. W., “Fire Safe Student Housing: A Guide for Campus Housing Administrators,” Maryland University, College Park, Feb. 1, 1999. Rohr, K. D., “School, College, and University Dormitories, and Fraternity and Sorority House Fires,” National Fire Protection Association, Quincy, MA, Mar. 2000. “School, College, and University Dormitories, and Fraternity and Sorority House Fires,” National Fire Protection Association, Quincy, MA, June 2001. Tracy, J., “Campus Fires: Tactical Considerations,” Fire Engineering, Vol. 154, No. 2, 2001, pp. 117–118.
CHAPTER 8
SECTION 5
Juvenile Firesetting Paul Schwartzman
T
he fire service has known that children are accountable for many fires. In a small city in northern Pennsylvania, a presentation was being made on children and fire. The fire chief wanted to highlight their local fire museum and escorted a group to take a tour. On entering the museum, a fire department–run log from the late 1800s was displayed on a pedestal under a glass cover. The log was open to a handwritten entry describing a house fire with extensive damage. The cause was listed as “children playing with matches.” Prior to the mid-1970s, there were few, if any, programs or even concepts on how to change the behavior of children playing with matches. Some in the fire community took the view that “kids will be kids,” treating firesetting by children as a normal and harmless stage of development. On the other end of the spectrum were those who believed that children who misused fire were psychologically disturbed. This view saw juvenile firesetting as neither normal nor harmless but still as unpreventable. Both views left the fire community with no effective intervention other than effective fire fighting. The mid-1970s brought about major change. The fire service began working with mental health professionals to better understand firesetting behavior and evolve more effective intervention and prevention strategies. The past 25 to 30 years have brought about a much greater understanding of young people’s misuse of fire and what can be done to prevent and minimize further incidents. This chapter highlights many of these findings and procedures that the fire service can implement to reduce fire incidents involving young people.
TERMINOLOGY An important aspect of understanding children and fire is being familiar with the language frequently used to describe this behavior. Different words and phrases are employed depending on perspective and position. Discussions on the standardization of terminology are currently ongoing among fire professionals and Paul Schwartzman is a nationally certified psychotherapist with over 25 years experience working with children and families. In 1981, while on staff at the University of Rochester, he and his colleagues in cooperation with the City of Rochester Fire Department began doing research on children and fire. This research led to the development of a model Juvenile Firesetter Program. He has a private counseling practice and consulting service in Rochester, New York.
others involved in addressing this concern. Common use of terms would facilitate more precise statistics describing the magnitude of the problem as well as directing appropriate prevention and intervention strategies. The primary distinction in labeling behavior is intent. Children who do not understand the consequences of their use and have no specific intent of starting a fire traditionally have had this behavior referred to as “fireplay.” The terms accidental or unintentional have also been used to describe this behavior. These terms have become quite controversial. Associating the concept of play with children’s use of fire has raised concerns. Play is a positive aspect of child development and many have questioned whether using the term fireplay minimizes the risk and normalizes the behavior. The term accidental formally implies a behavior or incident that could not be avoided or prevented. This notion when applied to children’s use of fire also raises concerns because these incidents are not truly accidental. In fact, it is argued that almost no fire cause is “accidental.” Enhanced supervision or storage of ignition materials can usually prevent these incidents. Advocates of these perspectives prefer the terms fire experimentation or fire starting, believing that this phrase is more accurate and better describes the intent. Critics of these alternative terms, however, argue that experimentation and setting imply more conscious intent, deliberation, and knowledge than are typically present. So far, the search for a phrase free of misleading connotations has been unsuccessful. The label of firesetting implies a deliberate effort to start of fire. The term firesetting is often associated with arson. Arson is a legal term that implies a deliberate intent to cause damage or injury. Similar to the concern involving the term play, arson or firesetting carries an ominous tone and raises objections. Some feel that the use of these terms causes avoidance of the issue because of the stigma attached to these terms. Fire fighters are resistant to labeling a young child a firesetter or arsonist. In many jurisdictions, the legal age of accountability precludes young people from being charged and the terms are not applied. Common terminology can go a long way to clarify and facilitate better responses to the problem of children and fire. It is not the intent of this chapter to establish a standard terminology. Doing so will require more dialogue among the various organizations to come to consensus. The terminology used in this chapter will echo common terms currently used in report forms and among fire service officers and line fire fighters.
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MAGNITUDE OF THE PROBLEM Based on fires reported to U.S. fire departments, an average of 85,620 fires was attributed to children playing with fire per year in 1994–1998, the latest years for which data were available. In the same period of time, children’s fireplay resulted in 303 civilian deaths, 2359 civilian injuries, and $276 million per year in direct property loss.1 While this will be further explored later in this chapter, it is clear that a significant portion of fires involving young people goes beyond “child-playing” and is more intentional. Incendiary fires that are intentional can be considered arson. The Federal Bureau of Investigation (FBI) Uniform Crime Report for 1999 indicated that 54 percent of arson arrests were children under the age of 18, the sixth straight year that the juvenile share has been 50 percent or more. Eighty-two percent of juveniles arrested for arson were under 15, and 7 percent were younger than 10 (Figure 5.8.1).2 Arson is the number one cause of all fires (an estimated 447,300 reported U.S. fires in 1998 were incendiary or suspicious) and the second leading cause of fire deaths, behind smoking. In 1998, incendiary or suspicious fires reported to U.S. fire departments resulted in an estimated 639 civilian deaths, 2322 fire injuries, and $1.9 billion in direct property loss. If half of these incidents and losses are assigned to juveniles, it means that 225,000 fires can be attributed to juvenile incendiarism, as can a death toll comparable to that for child-playing fires. This does not include the many fires that never come to the attention of the fire service. Past studies have estimated unreported fires at 10 to 20 times the number of reported fires, although most are small cooking fires. Putting the juvenile share (52%) of 1998 arson arrests together with the estimated total number of reported U.S. fires due to incendiary or suspicious causes, and then adding in the 1998 child-playing fires, the estimated total of reported fires started by children in 1998 is 300,000 fires, 587 civilian deaths, 3212 civilian injuries, and $1.2 billion in direct property loss. Precise numbers will remain elusive, but it is clear that juvenile firesetting remains a significant and dangerous problem. The good news is that the total number of such fires and associated losses have plunged since 1994. Mental health professionals assessing the problem of children and fire believe that a
significant proportion of this reduction is due to the efforts of the fire service systematically addressing juvenile firesetting along with the introduction of a child-resistant requirement for lighters by the U.S. Consumer Product Safety Commission.
CHARACTERISTICS OF CHILDREN INVOLVED IN FIRESETTING BEHAVIOR Age In Rochester, New York, the city fire department tracked fire incidents over a nine-year period to determine youth involvement. The study identified children from 18 months to 18 years of age who had been involved in an incident that required a fire department response. The majority of fire incidents involved youth between the ages of 4 and 9 years.3,4 Additional studies in other cities that systematically respond to fires with youth involvement have paralleled these numbers. Preschool children under age 6 are disproportionately likely to be killed in child-set fires, accounting for more than 66 percent of deaths in child-playing home fires and about 15 percent of deaths in incendiary or suspicious fires, while accounting for only 9 percent of the population. Fireplay remained the leading cause of death among preschoolers. It is not always the children who were playing with fire who die. Very often it was a sibling or playmate. Most of the people killed by child-playing fires are under age 6. The above-mentioned Rochester studies further determined that a third of youth involved in fire incidents were between 10 and 17 years of age, with 98% of these being under age 15. Arson arrest statistics also indicate that firesetting behavior falls off steadily at or after age 15 (Figure 5.8.2).
Gender Firesetting is predominantly a male behavior. Studies tracking youth involved in fire incidents consistently report that young people who come to the attention of the fire service average 85 percent male and 15 percent female. This closely matches the gender breakdown for arson arrestees of all ages. Males tend to
Incidents Over Ten Years
250
20
Percent
15 10 5 0 Under 10–12 13–14 15 10 Age
16
17
FIGURE 5.8.1 Juveniles Arrested for Arson as a Percentage of All Arrests, According to FBI Statistics
200 150 100 50 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Age
FIGURE 5.8.2 Age of Children Involved in Actual Fires, According to the Rochester Study
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be more highly represented in risk-taking and acting-out behaviors of all kinds. Interestingly, a developmental study5 of school-age children looking at behavior with fire found a higher percentage of females. Children in grades 1 through 8 were asked if they ever experimented with fire. In this group, the male to female ratio was 2:1. Therefore, on comparing young people who come to the attention of the fire service because of a fire concern with a general population of school children who have not come to the attention of the fire service, the percentage of female involvement more than doubled (from 15 percent to 33 percent). When asked how they used fire, females stated that they lit matches and lighters, whereas males tended to use such implements to ignite other things, making their experimentation riskier and perhaps more detectable.
Family Type Firesetting occurs in all family types, but is somewhat overrepresented among single-parent households, as is the fire incidence in general. This is believed to be more a factor of increased stress and decreased time for supervision rather than family structure.
Socioeconomic Status Poverty is highly correlated with firesetting. In a longitudinal study examining children who came to the attention of the fire department,3 over 90 percent were found to be on a free or reduced lunch plan in school compared to 35 percent in the district as a whole. This indicates that the family falls below the poverty line. Families living in poverty typically have more difficulty providing structure, appropriate supervision, and effective parenting due to household chaos and chronic stress, evidenced by relationship discord and unemployment. Families in poverty typically have less education and are therefore less likely to possess the awareness and judgment to provide a safe environment. The same lack of effective supervision that makes ignition more likely also makes it more likely that fires will grow large enough to require fire department intervention and become reported fires. The inability of a poor household to readily absorb fire damage as a result of poor construction and high housing density may also make it more likely that their fires will come to the attention of the fire department.
Race and Ethnicity Race and ethnicity are not associated with firesetting behavior, although they appear to be in studies that do not adjust for correlated socioeconomic conditions, such as poverty. Children are represented proportionately to the presence of their race or ethnicity in the general population.
MOTIVATION FOR FIRESETTING BEHAVIOR Fire fascinates us all. Its power, beauty, and functionality parallels few entities existing on our planet. It is therefore natural that people of all ages express curiosity about fire. However, for young people with limited skills and understanding, turning cu-
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riosity into fire play can be deadly. Young people are motivated to use fire for various reasons. This section will present the underlying philosophy of how firesetting behavior develops and describe profiles describing different motivations or goals.
Dynamic-Behavioral Theory At the outset of this chapter, it was mentioned that collaboration between the fire service and mental health community during the mid-1970s brought about new understanding. One of the major outgrowths of this collaboration resulted in a conceptual framework designed to explain firesetting behavior. This framework, known as the Dynamic-Behavioral Theory, was developed primarily by Dr. Kenneth Fineman, a clinical psychologist working closely with the Los Angeles County Fire Service and the United States Fire Administration. The Dynamic-Behavioral Theory views firesetting as an interaction among the individual, the family, social circumstances, and immediate environmental conditions. The major contribution of this theory is that characteristics of firesetting youngsters can be organized and classified by using this conceptual framework and observed and measured. The Dynamic-Behavioral Model is an additive factor model. Models similar to this have been used in all kinds of injury control studies and have wide acceptance. Individual characteristics consist of demographic, physical, emotional, motivational, and psychiatric descriptors. Social circumstances are composed of family, peer, and social descriptors. Environmental conditions refer to events occurring immediately prior, during, and after firesetting. These variables interact to produce firesetting or increase the risk of firesetting. Figure 5.8.3 illustrates the sequence of how these dimensions may evolve to produce firesetting behavior.
Types of Firesetters Many “types” of firesetters are listed in the literature concerning firesetting behavior. Researchers have categorized firesetters by focusing on a variety of personality and other factors, which specify a quality of the personality of firesetters and of their previously set fires. Any attempt to categorize the firesetter should serve the pragmatic purpose of helping describe the firesetter’s risk level for future fire-related dangerous behavior and help guide prevention and intervention efforts. Dangerous in terms of firesetting are behaviors that destroy property or do physical and/or emotional harm. Another concern is the probability that the juvenile will set more fires. It is important to understand that these categories are not exclusive. In fact, a firesetter may have multiple motives for his/her behavior. The following firesetter types focus on the firesetter’s psychological state or diagnostic category, what is set on fire, or whether the fire is set as a function of the firesetter’s need to bring attention to himself or herself or the need to use fire to direct attention elsewhere. Curiosity Type. The most common profile describes children who act primarily out of curiosity and do not developmentally understand the consequences of their behavior. The few studies3,4,6–8 that have examined representative samples of children
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Pre-existing Circumstances That Predispose to Maladaptive Behavior
Firesetting Behavior
Thoughts, Feelings, Sensations That Reward Firesetting
or Current Environmental Factors That Predispose to Maladaptive Behavior Trauma/Crisis
=
ADHD Drinking /Drugs School Issues Illness Depression
Personality and Individual Characteristics
FIGURE 5.8.3
Latch Key Neglect /Abuse Loner Marital Discord
+
Events Occuring Prior During After
+
Family and Social Circumstances
Immediate and Environmental Conditions
The Dynamic-Behavioral Model (Source: Paul Schwartzman and Ken Fineman)
converge on this point. The majority of children who start fires do so out of experimentation and may not have other psychological problems. Children motivated exclusively by curiosity tend to be young, primarily between 5 and 10 years of age, and to be involved in only one reported fire incident. While this curiosity-driven fire play is apparently not pathological, it is nevertheless potentially dangerous and a concern. Individual, family, and environmental factors predict whether children engage in fire play and serve as guides to preventive intervention. Access to ignition materials, momentary lapses in supervision, the perception that they would not be disciplined if they were caught playing with fire, and premature exposure to and responsibility for activities involving fire are all associated with curiosity fire play.5 Children also often have an unrealistic sense of their ability to control a small fire. Teenagers trying to conduct science experiments could fall into this group. Case Example. Jonathan, age 9, lives with his mother and father in a single-family house. One evening at about 7 p.m., Jonathan was in his bedroom while his parents were downstairs watching television. Jonathan’s mother smokes and had left her cigarette lighter on the dresser in her bedroom. Jonathan saw the lighter on the dresser and took it into his room. He lit the cigarette lighter and touched the flame to some school papers he had piled in his room. The papers quickly ignited and Jonathan became frightened and dropped the papers on the floor near his bed. The flame spread to the bedding. Jonathan slapped at the flames with a nearby blanket and yelled for his father. Fortunately, Jonathan was able to put the fire out but not before singeing the bedding. His father arrived dismayed, but glad that Jonathan was not injured and that there was no further damage. Jonathan was very remorseful and frightened. He was crying and apologetic and insisted that he did not mean to start a fire.
Cry-for-Help Type. The cry-for-help type includes children of all ages. These juveniles consciously or subconsciously wish to bring attention to an intolerable life stress. This may be a personal problem such as feelings of depression or anger. It could also be associated with an interpersonal concern such as family stress and dysfunction, stressful life events, separation and divorce, and remarriage. This type of firesetting is more likely to continue without intervention. Physical and sexual abuse and chronic neglect are frequently associated with recidivism.3,4,6–8 Case Example. Mark, age 12, lived with his mother and stepfather. Mark had a younger brother, age 10, who was the birth child of his mother and stepfather. Mark frequently felt left out and believed that his stepfather treated him more harshly than his brother. Mark and his brother would argue frequently. During an argument, Mark’s father became extremely angry and grabbed Mark and pushed him across the room, telling him that he would have to go live elsewhere if he did not stop fighting with his brother. Mark strongly felt that his brother was as responsible as he for these arguments, but his stepfather would not acknowledge this possibility and kept blaming Mark, claiming that he was older and knew better. Mark was sent to his room for the rest of the day. Shortly thereafter, a neighbor reported seeing smoke coming from the eaves outside of Mark’s bedroom window and called the fire department. Delinquent Type. The delinquent type usually involves adolescents between the ages of 11 and 15. Typically their firesetting is part of a larger constellation of conduct and aggression problems. This behavior most often occurs with other juveniles. An interest in vandalism and hate crimes is noteworthy. As juveniles manifesting this type, though frequently showing little empathy for others and little conscience, they usually avoid harming others with fire. Significant property damage is com-
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mon. In this group, firesetting behavior is more easily extinguished than other personality and behavioral problems, which usually accompany the firesetting.3,4,6–8 Case Example. Seven youths under the age of 18 began setting fires in dumpsters, then graduated to setting them in automobiles and vacant buildings. In March 1996, members of this group set a fire in an illegal tire dump beneath an interstate highway, resulting in damages estimated at $8 million to the overpasses. Commuter and interstate traffic was disrupted during the incident and for months during the repair. Various members of this group are linked to intentionally set fires in 18 vacant buildings in the same area. Severely Disturbed Type. The severely disturbed type—the rarest type—includes young people who are suffering from serious mental health problems that may include paranoid and psychotic symptoms. Often, the fire setting may be reinforced because it creates a profound sense of elation or sensory reinforcement. Sensory reinforcement describes those for whom the sensory aspects of the fire are sufficiently reinforcing to cause fires to be frequently set. The reinforcement histories of many suggest an early fixation on fire. A subgroup of this type is the “self-harm” type, whose members use fire to harm or kill themselves. Prognosis is guarded with this severely disturbed group.3,4,6–8 Case Example. Lenny, age 7, was subdued by his parent after he attempted to set fire to his little brother. The police and fire department were immediately dispatched to the scene. The juvenile firesetter intervention specialist began talking to the young boy about his behavior. Lenny explained that he was directed to burn his little brother by the devil. When the fire investigator asked how he communicated with the devil, the boy stated that the devil was present in the room and that they had a regular conversation. Lenny was admitted to the child psychiatric hospital for further observation and treatment. Lenny had several firesetting incidents and was described by others to behave bizarrely. Cognitively Impaired Type. The cognitively impaired type includes the developmentally disabled and the organically impaired types. This group, although tending to avoid intentional harm, lacks good judgment. Significant property damage is common.7 The organic group includes those persons whose cognition ability or ability to control impulses is significantly affected by their neurological or medical state. Also included in this group are persons with severe learning disabilities and those who were affected by the fetal alcohol syndrome or by the drugs taken by their mother during pregnancy. Case Example. Ken, age 14, was referred to the fire department by his parents. The parents were afraid because Ken had started several fires in and around their home. Ken was severely learning disabled and impulsive. He attended a self-contained special education program to assist him with his learning disabilities and impulsive behaviors. Ken was also on several medications to control impulsivity and other behavior concerns. Ken
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had suffered from these behaviors since birth, and his parents stated that he needed constant supervision. Although they worked hard to control the environment and keep ignition materials from him, he was persistent. Ken is a very concrete thinker and when he does understand and accept an idea or concept, he internalizes it. Ken’s parents hoped that the fire department might be able to provide information and education that Ken would find meaningful and effect his behavior. Sociocultural Type (including the uncontrolled mass hysteria type, the attention-to-cause type, the religious type, and the satanic type). This category includes those who set fires in the midst of civil unrest and are either enraged and enticed by the activity of others and follow suit or set fires with deliberation in order to call attention to the righteousness of their cause. Those involved in uncontrolled mass violence frequently lose control and harm others, though initially the intent to do so may not be present.7 Case Example. The Earth Liberation Front is a group of older adolescents and young adults who are currently attempting to bring attention to a cause. This group targeted a ski resort in Vail, Colorado, by burning five buildings and four ski lifts because they believed that the development threatened the lynx. This group has also targeted housing projects in wildland regions because they feel these properties are infringing on nature. They justify their behavior with rhetoric, explaining the injustice imposed on others.
RESPONSE TO JUVENILE FIRESETTING Juvenile firesetting is a community problem. The fire service is in a unique position to address it. Although specific responsibilities can be distributed among different agencies, depending on resources and demographics, the fire service is usually in the best position to manage the community response. Successful program models have been examined for several years. An Office of Juvenile Justice and Delinquency Prevention (OJJDP) and United States Fire Administration (USFA) initiative to assess effective programs addressing juvenile firesetting identified seven critical components.9 A recent review conducted by a group of researchers on behalf of the National Association of State Fire Marshals (NASFM) funded by OJJDP confirmed that these program components remain state of the art.10 The components are as follows: 1. A program management component to make key decisions, coordinate interagency efforts, and foster interagency support. 2. A screening and evaluation component to identify and evaluate children who have been involved in firesetting. 3. An intervention services component to provide primary prevention, early intervention, and/or treatment for juveniles, especially for those who have already set fires or shown unusual interest in fire. 4. A referral component to link the program with the full range of community support agencies that might help identify juvenile firesetters and provide services to them and their families.
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5. A publicity and outreach component to raise public awareness of the intervention program and encourage early identification of juvenile firesetters. 6. A monitoring component to track the program’s identification referrals and treatment of juvenile firesetters. 7. A juvenile justice system component to establish relationships with the juvenile justice agencies that often handle juvenile firesetters.
Program Management Effective programs need structure and standard operating procedures. In most instances, juvenile firesetter intervention (JFSI) programs are incorporated into ongoing department operations such as fire prevention, investigation, or inspection. It is recommended that JFIP efforts be incorporated into the day-to-day responsibilities of these programs, with specific responsibilities assigned to trained individuals. Whether programs are located in a specific department is a matter of philosophy and personnel resources. Some juvenile firesetter specialists recommend locating programs in specific areas. Some propose that programs are better positioned within the investigation units so that fire circumstances can be more carefully reviewed and that the law enforcement aspects are preserved for incidents involving intentionally set fires. Figure 5.8.4 illustrates one way to locate juvenile firesetter programs within the fire department. Other juvenile firesetter specialists propose that the educational aspects of children and fire need to be emphasized due to the primary motivation of curiosity and experimentation and that programs should be situated in fire education units. Both concerns are valid and essential. Most important is that programs include the components just listed and that the response to all concerns regarding children and fire be handled systematically and thoroughly, whether the response is to a big fire or to no fire at all. Figure 5.8.5 illustrates the flow of a well-organized program. Referrals can be initiated from anyone with awareness or concerns regarding firesetting behavior. The process remains the
same whether there is an actual fire or no fire at all. Therefore, a careful information gathering procedure to assess motivation and direct interventions is needed. This is succeeded by a follow-up contact to assess the effectiveness of the intervention and the need for any additional services. For the first time, the 2000 edition of NFPA 1035, Standard for Professional Qualifications for Fire and Life Safety Educators, includes two chapters outlining job performance requirements for Juvenile Firesetter Intervention Specialist I and Juvenile Firesetter Intervention Specialist II.11 The standard is a resource to facilitate development of job responsibilities and procedures. A Juvenile Firesetter Intervention Specialist I is an individual assigned with the day-to-day tasks of conducting a juvenile firesetter intervention program. This individual is responsible for keeping records of contacts, conducting assessment interviews, delivering educational interventions, and making referrals given the direction and feedback of a supervisor, but he or she does not have program management or oversight responsibilities. A Juvenile Firesetter Intervention Specialist II is the program coordinator or manager. His or her responsibilities address key management concerns such as record management, compliance with government regulations, referral procedures, supervision of assessment and intervention personnel, establishment and maintenance of interagency networks, public relations, and program development and evaluation. In a smaller program or department, it is likely that a single individual performs the role of Juvenile Firesetter Specialists I and II. See Table 5.8.1, which is a section of the responsibilities table for Juvenile Firesetter Specialist I and II in the appendix of NFPA 1035.
Screening and Evaluation An essential component of an effective JFSI program is the screening and evaluation procedure to determine primary motivation and potential risk for future firesetting. This component
Reported fires
Parent calls
Other concerned agencies
Fire chief
Deputy chief
Training division
Fire marshal
Juvenile firesetter intervention program Line chief
Code enforcement
Fire investigation
Cause and origin
Juvenile firesetter program
Educational intervention
Mental health intervention
Juvenile justice intervention
Adult investigation
Follow-up and feedback
FIGURE 5.8.4 Sample Organizational Chart of a Juvenile Firesetter Intervention Program within a Fire Department
FIGURE 5.8.5
Referral Flowchart
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TABLE 5.8.1
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Professional Qualifications for Juvenile Firesetter Intervention Specialists I and II Juvenile Firesetter Intervention Specialist I
Juvenile Firesetter Intervention Specialist II
Resources
6-2.4 Apply educational and referral resources, given interagency network list, education program outline, and program guidelines, so that all educational and referral resources are identified and the family can access resources that meet its needs. (a) Requisite Knowledge: Educational resources, interagency members, service program guidelines. (b) Requisite Skills: Evaluate resources.
7-3.4 Establish and maintain an interagency network, given a list of agencies, a sample interagency agreement, and protocol, so that roles and responsibilities are clarified, so that a mission, participation agreements, and a continuum of intervention services are established and maintained for the community, and so that duplication of services is avoided. (a) Requisite Knowledge: Community resources, capability of service providers. (b) Requisite Skills: Facilitate meetings, resolve conflict, build team, relate to others, manage network.
Time Management
6-2.2 Manage personal work schedule, given contact name and requested time, so that all interviews are conducted on time and in a location agreeable to all parties. (a) Requisite Knowledge: Program guidelines. (b) Requisite Skills: Maintain records.
Assessment Process
6-4.1 Review a case file, given a referral, incident report, interview forms, and all related information, so that, before speaking with the child and family, the fire setter specialist becomes familiar with the incident and circumstances of the firesetting. (a) Requisite Knowledge: Program guidelines. (b) Requisite Skills: Review records for completeness. 6-4.2 Initiate contact with the family, given the case file, so that the juvenile firesetter intervention specialist contacts the family; explains the program and its benefits; schedules a time, date, and place for the interview; and advises the family of possible intervention options. (a) Requisite Knowledge: Scope of services provided by given agency. (b) Requisite Skills: Manage personal work time. 6-4.3 Conduct an interview, given interview forms and program guidelines, so that the juvenile firesetter intervention specialist can establish the purpose and limits of the interview, establish rapport, gather relevant information, identify and intervene in any immediate lifethreatening situations, report any suspected abuse and neglect, record and report observations, and summarize findings. (a) Requisite Knowledge: Governing laws, policies, and procedures pertaining to juveniles, firesetting behavior, child development, abuse and neglect, profile of the firesetter and family. (b) Requisite Skills: Conduct an interview.
JPR Group
7-2.3 Determine the intervention for a firesetter’s family, given a case file, interview forms, list of treatment providers, and a list of established educational curricula, so that the firesetting problem is addressed. (a) Requisite Knowledge: Fire behavior, child development, intervention options, profile of the firesetter and family, laws pertaining to the juvenile justice system, interview techniques. (b) Requisite Skills: Analyze and apply information, select intervention.
Source: Adapted from Appendix C, Table C-2, NFPA 1035, Standard for Professional Qualifications for Fire and Life Safety Educators, 2000 Edition.
typically includes structured interviews with the children and parents conducted by a trained juvenile firesetter intervention specialist. Most JFSI programs conduct the initial screening interviews themselves; if additional concern is generated, children are referred to identified specialists to conduct more comprehen-
sive assessments. Some programs prefer to have all assessments initially conducted by an outside agency or professionals who are certified to work with youth and families. The goal of the interview is to obtain background information about the child(ren), family, and fire behavior. Usually, the
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interviewer explains the purpose of the meeting, interviews the children and parents separately, and then reconvenes the family to explain the outcome and recommendations. Different programs based on philosophy and resources conduct this interview either at home or at an approved facility outside the home such as fire department administrative offices. Both procedures have been demonstrated to be effective. There are advantages and disadvantages to each location. In the family home, the interviewer has the opportunity to assess the physical environment and observe the family interaction in their natural setting. However, the interviewer sacrifices an element of control in the home and sometimes children and families are more accountable in an “official” location. The Federal Emergency Management Agency/United States Fire Administration (FEMA/USFA) has supported the development and distribution of manuals and community training materials.12–17 FEMA manuals include copies of structured interview forms18–20 and guidelines for their use. These interview forms were initially developed in the late 1970s by Dr. Fineman and are based on the Dynamic-Behavioral Theory mentioned earlier in this chapter. The manuals and the interview forms were revised in 2000 and are currently available from FEMA/USFA. The revised FEMA manual includes a newly developed “short form,” which is a subset of the complete interview designed to be a preliminary assessment. Figure 5.8.6 displays a page from the full assessment. Many practitioners have advocated a shortened procedure. This abbreviated interview is a new procedure and is undergoing evaluation to determine reliability. The initial caution is that any reduced inventory will possibly miss important information, but that it might provide useful information to make a preliminary decision in the field by less experienced personnel. The FEMA forms are not the only forms available. Wellestablished programs throughout the United States have taken the initial concepts and revised them to meet their own needs and procedures. Many of these programs have worked with local universities and researchers to establish reliability. A few examples of these are the Phoenix Fire Department in Arizona, the Portland Fire Department in Maine, the Rochester Fire Department in New York, and the State Fire Marshal’s Office in Oregon. Most programs are proud of their efforts and welcome inquiries regarding their screening and assessment procedures. The following is an example of the assessment procedure. The FEMA (child, parent, and family) forms are designed to assist in determining risk for additional firesetting behavior. The questions are scored and totaled to indicate the degree of risk. The scale ranges from little risk to extreme risk. The FEMA Juvenile Firesetter Intervention Handbook21 defines the categories of risk as follows.
to be involved in future fire behaviors. They are in need of interventions in addition to educational interventions. The cry for help and delinquent types described earlier typically fall into this category. Extreme Risk. Less than 1 percent of children and adolescents fall into the extreme risk category. The severely disturbed types suffering from severe mental illness are most likely to be of extreme risk.
Interventions Juvenile firesetting is a community problem requiring a community response. A comprehensive program is balanced between prevention and intervention services. This section will sample some fundamental intervention strategies and methods.
Little Risk. Curiosity or experimentation accounts for the majority (60 to 65 percent) of children’s involvement in fire in the little risk category. Most of these children are of little risk of repeating their behavior if they receive the proper supervision and educational intervention.
Primary Prevention. The goal of primary prevention is to reduce the likelihood of children and adolescents engaging in unsupervised activity with fire. As illustrated in Figure 5.8.7, primary prevention is a multifaceted approach based on the prevention triangle and the three E’s: Educate, Engineer (sometimes called Environmental Change), and Enforce. Education is the responsibility of the fire service, parents, teachers, media, community, and neighborhood groups, and many others to provide relevant messages. Education messages that are aimed at children and fire should put emphasis on providing consistent supervision to children and adolescents, restricting access to ignition materials, teaching fire and life safety, and assigning age appropriate responsibility. The developmental study5 mentioned earlier explored the relationship between premature assignment of responsibility for tasks involving fire and subsequent unsanctioned use of fire. Premature assignment of responsibility may be defined as children cooking or building a fire in the fireplace before fully understanding the consequences or responsibilities of this action. Children who perceive their parents approve of this behavior feel a greater sense of control and permission and are more apt to be involved in unsupervised, nonsanctioned use of fire. Effective prevention programs encourage the utilization and creation of products and environments that are engineered to prevent fire use or minimize the consequences from misuse. An excellent example of this is the manufacture of the child-resistant lighter designed to restrict the ability of preschool age children from igniting the flame on a disposable lighter. Additional examples range from the use of sleepwear and bedding with flameretardant fabrics to the installation of residential sprinkler systems. Intervention programs are designed to respond to actual concerns or incidents and can vary depending on the risk level determined in the assessment and the circumstances of the fire. Effective intervention programs have a range of interventions and include educational interventions, mental health counseling, juvenile justice consequences, and child welfare actions. Depending on the motivation and outcome of the risk assessment, one or all of these interventions might be implemented.
Definite Risk. Approximately 30 to 40 percent of children and adolescents fall into the definite risk category and are very likely
Educational Intervention. Educational interventions are recommended for most young people who demonstrate an in-
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C-1
Juvenile Firesetting
C-2
C-3
P-1
P-2
5–115
P-3
BEHAVIOR ISSUES 10. Do you get in trouble frequently at school?
Yes (C-2)
No (C-1)
11. Do you usually not do things you are asked to do?
Yes (C-2)
No (C-1)
12. Have you ever stolen or shoplifted?
Yes (C-2)
No (C-1)
13. Have you ever frequently lied?
Yes (C-2)
No (C-1)
14. Have you ever used drugs, alcohol, or inhalants?
Yes (C-2)
No (C-1)
15. Have you ever beat up or hurt others?
Yes (C-2)
No (C-1)
Behavior Issues Subtotals COMMENTS:
FAMILY ISSUES 16. Do you like going home?
Yes
No
Why? __________________
17. How well do you get along with your mother (female caregiver)? always get along (P-1) usually get along (P-1) sometimes get along (P-2) don't get along very often (P-2) never get along (P-3) 18. Do you fight or argue with your mother? always (P-3) usually (P-2) sometimes (P-1)
rarely (P-1)
never (P-1)
19. Are you afraid of your mother? always (P-3) usually (P-2)
rarely (P-1)
never (P-1)
sometimes (P-1)
20. How well do you get along with your father (female caregiver)? always get along (P-1) usually get along (P-1) sometimes get along (P-2) don't get along very often (P-2) never get along (P-3) 21. Do you fight or argue with your father? always (P-3) usually (P-2) sometimes (P-1)
rarely (P-1)
never (P-1)
22. Are you afraid of your father? always (P-3) usually (P-2)
rarely (P-1)
never (P-1)
sometimes (P-1)
23. Do your mother and father fight? [If the parents fight, have the child elaborate on the fights] always (P-3) usually (P-2) sometimes (P-1) rarely (P-1) never (P-1) 24. Tell me about your brothers and/or sisters. How well do you get along with them? (If there is a variability in the relationship among siblings, rate the most serious.) always get along (P-1) usually get along (P-1) sometimes get along (P-2) don't get along very often (P-2) never get along (P-3) 25. Do you see your mom as much as you'd like?
Yes (P-1)
No (P-2)
26. Do you see your dad as much as you'd like?
Yes (P-1)
No (P-2)
27. What do you do that gets you into trouble at home? _______________________ 28. What happens at home when you get in trouble? grounded him/her (P-1) physical punishment (P-1) or (P-2) nothing (P-2) talked/lectured (P-1) or (P-2) sought outside help (P-1) yelled (P-1) or (P-2) abused (P-2) or (P-3) other (P-1) or (P-2) Explain __________________ 29. Do you get spanked/punished too much? Yes (P-2) No (P-1) If so, by whom ____ Family Issues Subtotals COMMENTS:
FIGURE 5.8.6 Sample FEMA Assessment Form (Source: K. Fineman, “Comprehensive Fire Risk Assessment,” in Poage et al. (Eds.), Colorado Juvenile Firesetter Prevention Program: Training Seminar Vol. 1, Colorado Division of Firesafety, Denver, CO, 1997)
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TABLE 5.8.2
Educational Intervention Objectives
Parents or Caregivers
Ed u
ca te
r ee gin En
Enforce
FIGURE 5.8.7
Fire Prevention Triangle
appropriate interest or use of fire. The majority of presentations are going to be primarily motivated by curiosity. Wellconstructed education programs are effective for changing this behavior. Educational interventions need to be aimed at the youth involved in the incident as well as primary caretakers. Programs traditionally include reactive fire safety behaviors that teach what to do in the event of a fire such as “stop, drop, and roll” and “know two ways out.” This information is clearly essential and saves lives, but it does not address the curiosity and misinformation that empowers young people to experiment with fire. Educational interventions need to be age appropriate. Information should be presented in a concrete manner and without scare tactics. Table 5.8.2 illustrates objectives particularly appropriate for the listed age categories. Providers should feel flexible to amend objectives based on individual needs. The priority for preschool children is to teach them that matches and lighters are for adult use only and that children should tell a grown-up if they discover matches or lighters in their environment. Preschool children are capable of learning basic life safety messages such as “crawl under smoke” and should be taught these skills. Caregivers should be included and encouraged to have children practice these behaviors so that the skills are rehearsed. Many of the objectives are appropriate for adolescents as long as they are adjusted to be age appropriate. Many intervention programs include projects that require young people to create escape plans and home safety drills. Community impact statements have also proved successful in creating empathy and understanding. In a community impact statement, youth are required to complete a project that highlights the impact their actions have had on others. The only exception to providing an educational intervention concerns the timing of the intervention rather than the omission of this procedure. In certain cases, children or adolescents may be of imminent harm to themselves or others or may be in crises and therefore not able to process the information. When the situation stabilizes, it is suggested that an appropriately leveled educational intervention be implemented. Research at the University of Pittsburgh conducted by Dr. David Kolko specifi-
Fire safety Limit access to ignition materials Supervision Age appropriate responsibility Clear rules and consequences
Ages 5–8
Ages 9–11
Power of a single match How quickly fire spreads False sense of control What burns
False sense of control Responsibility and fire Consequences of misuse Personal vulnerability Peer pressure
cally demonstrated the effectiveness of a structured intervention program that incorporates fire safety education for reducing the likelihood of future misuse of fire.22 This was compared to a more casual intervention in which fire fighters make a brief visit to the home to discuss with parents ways to prevent children from using fire and to hand out educational materials. Mental Health Intervention. As indicated in the DynamicBehavioral Theory and the crisis profile type, firesetting behavior is often motivated by the interaction of the individual with his or her family or social circumstances. Frequently, the individual lacks sufficient coping or problem-solving skills. Referral for individual and family counseling is imperative. Counseling juvenile firesetters is not substantially different from interventions with others, but some critical aspects need to be understood and addressed. The specific mental health interventions are beyond the scope of this chapter but are generally built around a case management model, which allows for careful coordination of services and includes focus on the firesetting behavior. Mental health treatment for juvenile firesetters needs to be personalized to the firesetting type, motivation, and circumstances. Treatment tools include individual treatment, family counseling, cognitive techniques, behavior management, empathy and social-skill building, parenting skills, problem solving methods, and relaxation techniques. Referrals should always be made to mental health professionals who have specific understanding of juvenile firesetters. When knowledgeable mental health providers are not available, the fire service should facilitate access to training and information to develop these resources. A comprehensive overview of treatment strategies is available in the National Association of State Fire Marshal’s Juvenile Firesetter Intervention Project Research Report.10 This information is downloadable free of charge at the web site www.firemarshals.org. The section is entitled “Juvenile Firesetter Mental Health Intervention: A Comprehensive Discussion of Treatment, Service Delivery, and Training of Providers,” and comprises areas 1 and 2 of the overall report. The bibliography of the NASFM report references several resources that further address treatment concerns. The references at the end of this chapter also contain additional treatment resources by this author and others. Social Service Intervention. It is well established that a critical predictor of repeat firesetting is documented incidents of ne-
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glect and abuse. In the Rochester study,3,4 recidivism, or repeat firesetting, increased fivefold in families in which children were victims of chronic neglect and physical or sexual abuse. Juveniles who experience this in their lives feel powerless and helpless and sometimes use firesetting because of its power to bring attention to a serious concern in a dramatic way. It is essential that a juvenile firesetter intervention program have an established relationship with the child welfare agency charged with responding to abuse and neglect. Parents and primary caretakers must be held accountable in these cases and children protected from further abuse. Social services agencies can assist with evaluation and help determine the need for placement and mandate services.
Referral Component Juvenile firesetting is not just a fire service problem; it is a community problem. If there is any single aspect that can enhance the likelihood of success, it is the relationship among key stakeholders in a community. Effective intervention demands a comprehensive network of services, clear interagency communication, ongoing support, and follow-through. Many juvenile firesetter intervention programs have established community advisory panels to facilitate the development and maintenance of their program. Perhaps one of the best established advisory panels based on its longevity and influence is the Phoenix Fire Department Community Advisory Panel.23 Figure 5.8.8 displays the organizations represented on the Phoenix Fire Department Community Advisory Panel. The panel meets on a bimonthly basis to help determine actions and services necessary to address juvenile firesetters. The goals of the advisory panel are as follows: • To utilize the members collective resources and expertise to reduce youth firesetting in the community • To identify potential funding sources Behavioral Health Child Protective Services Allstate Insurance Agency Judicial Officer for Juveniles Juvenile Probation Maricopa County Attorney's Office Maricopa County Public Defender's Office
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5–117
• To increase the awareness of the program to its member agencies and to provide training • To encourage ongoing collaboration in the community The panel of community stakeholders is in the best position to help define what entails an appropriate referral to any given agency or service and the procedures to make the referral. Particular attention should be paid to necessary forms, funding, hours, feedback to referring party, availability, and waiting lists. All participants need to be trained in these procedures and kept abreast of any changes. Confidentiality is frequently perceived to be a roadblock to interagency cooperation. This is often interpreted too narrowly. Confidentiality is not intended to deter services. It is critical that agencies serving children and their families share information that enables them to coordinate and provide more effective services. A failure to provide information generally results in fragmentation and duplication of services.24 In all circumstances, information can be shared with the consent of a juvenile’s parent or guardian. A release of information signed by a parent or guardian allows information to be freely shared. Disclosures on a need-to-know basis can also be made when there is immediate need for information to prevent imminent harm to self and others. Children who are at high risk to start fires could be argued to fall under this umbrella. Other arrangements can be made to facilitate communication between agencies. A memorandum of agreement can be established between two agencies that bind the providers in each agency to confidentiality under the regulations of each agency. Information can be provided when a school initiates legal action against a student or when a lawfully issued subpoena is presented. Florida passed legislation designed to facilitate the sharing of information between entities. The state passed legislation to require the State Department of Juvenile Justice to establish an early delinquency intervention program with cooperation of local law enforcement agencies and community service agencies that work with children. Comparable laws exist in other states.25 It is beyond the scope of this chapter to detail all the circumstances in which information can be shared. Communication is facilitated in an environment where there is awareness, trust, and ongoing relationships to clarify how information is to be used. Confidentiality is not intended to hinder effective interventions when trying to help young people.
Publicity and Outreach
Phoenix Fire Department Phoenix Parks, Recreation & Library Raising Arizona Kids Magazine Publisher St. Luke's Behavioral Health Center The Burn Center at Maricopa County Medical Center United Phoenix Firefighters Local 493 Valleywide Fire Departments Washington School District Administrator
FIGURE 5.8.8 Phoenix Fire Department Community Advisory Panel (Source: Phoenix Fire Department 23)
Generally, a program is only as successful as its reputation. Awareness of the program goals and how the public and relevant agencies can access the program should be regularly disseminated. The advisory panel is an excellent body to help distribute information among its members and outside. Public service announcements can be a useful method to reach a broad audience. The United States Fire Administration has developed brochures and videotape-based programs that can be used for presentations to service organizations, schools, and other community groups to increase awareness. Publicity and outreach programs should be designed to fit the profile of the community so that the messages clearly define
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the problem in terms of types of fires, who is at risk, demographics, and cultural influences. Messages should be designed to inform and not frighten the community. More diverse communities should design outreach that is multilingual and fully utilizes the media to maximize exposure. There is plenty of room for creativity to extend reach at low cost. One community in upstate New York arranged to print messages regarding match and lighter safety with program contact information on the grocery bags of a major grocery chain, thus enabling the message to reach thousands without any direct cost to the program.
Monitoring Careful record keeping to measure program utilization and results can help programs survive in environments where resources are highly sought after or scarce. Feedback of this nature also helps programs structure themselves to best meet the needs the community. Programs should monitor at least the kinds of referrals that come into the program, the basic demographics of clientele, types of firesetting behavior, source of referrals, and referral dispositions. It is also recommended that programs document their activities. Keeping track of presentations, interventions, program development activities, and interagency networking, will help to insure that adequate resources both in personnel and moneys are allocated to the maintenance of the program over time. Methods of tracking this data should be carefully considered. It is generally recommended to collect information as individual data points and not in a summary or aggregate form. Data can always be grouped to generate a summary but cannot be unbundled once aggregated. Program managers should decide whether program activities and data will be tracked specific to the program or whether there will be a central system for collecting and storing information within the department. Regardless, data should be easily retrievable. Programs will want to determine whether an individual has had prior contact with the program as well as generate reports for reporting and monitoring systems. Computerized data management systems are commercially available. Many fire departments around the United States have developed custom systems using desktop computers. Some departments have adapted the National Fire Incident Reporting System to store information and some still utilize the old-fashioned method of file folders and index cards. Programs with several years of history and documentation in states such as New York, Oregon,26 Arizona,23 Massachusetts, Indiana, and Illinois27 consistently demonstrate reductions in rates of repeat firesetting among young people who have come to the attention of their programs. Communities that have established primary prevention programs document reductions in the numbers of fires and resulting loss of young lives and property, especially among preschool age children.
perceive that their behavior will have a consequence. The juvenile justice system has a critical role. The juvenile justice system has the power to mandate services and to hold juveniles and their families accountable. The juvenile justice system usually comprises the juvenile unit of the probation department and family court. Family court is designed to address behaviors that would be considered crimes if committed by an adult. The ages of culpability (age at which a child can be held accountable) vary from state to state and typically range from 7 to 16 years of age. Children older than 16 may be treated as adults in many areas of the United States. Given the chaos in the lives of many cry-for-help and delinquent type firesetters and the risk to the community, this power is a pivotal factor in addressing juvenile firesetting. Effective juvenile justice programs maintain graduated sanctions. These sanctions consist of mandated counseling interventions, restitution, accountability, and community service on an initial level; and secure confinement in community settings, training, and aftercare on more severe levels. The juvenile justice system in each community needs to work with the juvenile firesetter intervention program to aggressively support programs that address juvenile problems through a continuum of services and sanctions that consider youth needs, family needs, community safety, and victim restoration.28,29
PITFALLS Clearly, juvenile firesetting is a serious concern requiring a systematic response that is institutionalized and supported. The following comments are intended to highlight common pitfalls that can undermine programs or prevent them from being maximally effective. Too often juvenile firesetter programs are initiated by an individual who appreciates the problem and has a passion to do something to help. While it is true that an individual’s efforts can start something that can make a difference, attempting to maintain a program single handedly threatens the life of the program over time. When a program is generated and maintained by an individual, it is unusual to find replacements that have the same level of energy and ownership to carry on these efforts. Individuals retire, get promoted, reassigned, or simply burned-out and with these changes go the program. Individuals who have a passion to work with juveniles involved with fire will best serve the mission by making a concerted effort to institutionalize the program so that the program’s longevity can be their legacy. Programs need to be recognized and supported from top to bottom within a fire department. It was stated earlier that juvenile firesetting is not just a fire service problem but a community problem. However, when attempting to establish and maintain a program within the fire department, it needs to be acknowledged that this is not just the responsibility of the prevention or investigation unit conducting the program.
Juvenile Justice Children and adolescents need to be accountable for their actions. In the earlier referenced developmental study,5 it was demonstrated that children are less likely to misuse fire if they
TRAINING Training opportunities are widely available. The National Fire Academy in Emmitsburg, Maryland, has established a course
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focusing on juvenile firesetter intervention. The United States Fire Administration has revised and reissued their manual and forms. Statewide coalitions in Oregon and Massachusetts as well as others conduct annual conferences with comprehensive seminars on a wide variety of related topics. The National Fire Protection Association provides training and awareness via the annual World Fire Safety Conference and Exposition in May and the Fall Meeting in November. In addition, several training entities are establishing certification programs based on NFPA 1035. Many of the consultants and providers who helped establish these programs are available to work with individual communities to assist in developing personalized training, program development, and evaluation services. Awareness of the juvenile firesetter issue needs to be incorporated on an ongoing basis at all levels of training and professional development within the fire service. The Rochester, New York Fire Department has its juvenile firesetter intervention specialists present an overview of the issue and the intervention process to every graduating class at their fire fighter training academy. In this way, all new recruits begin their careers with a basic understanding of children and fire. Officer training programs should adopt this model as well. Effective juvenile firesetter intervention depends on suppression, prevention, investigation, and inspection divisions all working together. It is the responsibility of every line fire fighter and officer to be sensitive and alert to the possibility of juvenile involvement and to initiate intervention. Programs that are highly successful have support not only from the hierarchy within the department but from the entire fire service ranks. Oregon established an infrastructure that supports juvenile firesetter intervention statewide. The Oregon State Fire Marshal established a full-time coordinator responsible for supporting juvenile firesetter intervention programs, which includes facilitating all the program elements illustrated earlier. Although the importance of establishing formal programs within the fire service is advocated, it is also important to acknowledge that programs should be designed to meet the demand however large or small. Programs can be undermined when they are underutilized. Program managers need to be sensitive to the size of the community and to the potential number of referrals. Rural communities may not want to put extensive resources into maintaining an individual program, but may want
TABLE 5.8.3
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Juvenile Firesetting
5–119
to combine personnel and resources between a few departments to establish a regional or county-based program. At the opposite end of the continuum, programs that are understaffed will also be undermined. Program credibility will be lost in the community if referrals cannot be responded to in a timely or comprehensive manner. Staff turnover will increase if personnel perceive that they are not able to protect children and their families due to inadequate support or feel they cannot perform their duties competently.
INFORMATION RESOURCES Fire departments can build on the experience of many established programs throughout North America. Technology allows the transfer of information and materials unlike that in any period in our history. Several web sites have been established solely for supporting efforts to address juvenile firesetting. Many of these sites offer links to other sites and provide references for materials, training, and speakers (Table 5.8.3). In addition, several state coalitions and providers have established newsletters and publications that are published regularly. Perhaps the best known is Hot Issues, published by the Oregon State Fire Marshal’s Office for Juvenile Firesetting. The newsletter is published quarterly and features program issues, treatment recommendations, current research, and resources.
SUMMARY The fire service has never been in a better position to be the leader in addressing the problem of juvenile firesetting. Juvenile firesetter intervention programs work. Years of collective experience and research have proven that the fire service is in a unique position to make a critical difference and to do what it has always been recognized for doing—saving lives and protecting property. Our communities are struggling with many complex and frustrating problems and challenges endangering our youth. Clearly there is always room to grow and perfect our understanding, but the problem of children and fire is one that we have considerable knowledge about and the immediate ability to impact.
Juvenile Firesetter Web Sites Organization
URL
National Association of State Fire Marshals
www.firemarshals.org
National Fire Protection Association
www.nfpa.org
Oregon State Fire Marshal—Hot Issues
www.osp.state.or.us/sfm/html/hot-issues.htm
Phoenix Fire Department JFIP
www.ci.phoenix.az.us/FIRE/firesetr.html
SOS Fires Youth Intervention Programs
[email protected]
United States Fire Administration
www.usfa.fema.gov
5–120 SECTION 5 ■ Fire and Life Safety Education
BIBLIOGRAPHY References Cited 1. Hall, J. R., Jr., Children Playing with Fire, National Fire Protection Association, Quincy, MA, June 2001. 2. Hall, J. R., Jr., U.S. Arson Trends and Patterns, National Fire Protection Association, Quincy, MA, 2001. 3. Cole, R., Laurenitis, L., McAndrews, M., McKeever, J., and Schwartzman, P., Juvenile Firesetter Intervention, Report of the Rochester Fire-Related Youth Program Project, Rochester, NY, 1983. 4. Cole, R., Grolnick, W., Laurenitis, L., McAndrews, M., Matkowski, K., and Schwartzman, P., Children and Fire, Rochester Fire-Related Youth Project Progress Report, Rochester, NY, 1986. 5. Grolnick, W. S., Cole, R. E., Laurentis, L., and Schwartzman, P., “Playing with Fire: A Developmental Assessment of Children’s Fire Understanding and Experience, Journal of Clinical Child Psychology, Vol. 19, 1990, pp. 128–135. 6. Fineman, K. R., “Firesetting in Childhood and Adolescence,” Pediatric Clinics of North America, Vol. 3, 1980, pp. 483–500. 7. Fineman, K. R., “A Model for the Qualitative Analysis of Child and Adult Fire Deviant Behavior,” American Journal of Forensic Psychology, Vol. 13, 1995, pp. 31–60. 8. Kolko, D. J., and Kazdin, A. E., “A Conceptualization of Firesetting in Children and Adolescents, Journal of Abnormal Child Psychology, Vol. 4, 1986, pp. 49–61. 9. National Juvenile Firesetter/Arson Control and Prevention Program, Fire Service Guide to a Juvenile Firesetter Early Intervention Program, Federal Emergency Management Agency, U.S. Fire Administration, June 1994. 10. Schwartzman, P., Fineman, K., Slavkin, M., Mieszala, P., Thomas, J., Gross, C., Spurlin, B., and Baer, M., “Juvenile Firesetter Mental Health Intervention: A Comprehensive Discussion of Treatment, Service Delivery and Training of Providers,” Juvenile Firesetter Intervention Research Project Phase I Final Report, National Association of State Fire Marshals, Albany, NY, 2000. 11. NFPA 1035, Standard for Professional Qualifications for Public Fire and Life Safety Educator, National Fire Protection Association, Quincy, MA, 2000. 12. Federal Emergency Management Agency, Preadolescent Firesetter Handbook, Unites States Fire Administration, Washington, DC, 1988. 13. Federal Emergency Management Agency, Interviewing and Counseling Juvenile Firesetters, U.S. Government Printing Office, Washington, DC, 1996. 14. Fineman, K. R., “Adolescent and Family Interview Schedules,” Adolescent Firesetter Handbook: Ages 14–18, J. Gaynor and C. Kartchmer (Eds.), Federal Emergency Management Agency, Washington, DC, 1988. 15. Fineman, K. R., Baizerman, M., Mieszala, P., Day, J. B., Emshoff, B., and Bookbinder, L., Juvenile Firesetter Handbook: Dealing with Children Ages 7–14, Federal Emergency Management Agency, Washington, DC, 1981. 16. Fineman, K. R., Day, J. B., Michaelis, L., Brudo, C., Brudo, E., and Morris, C., Interviewing and Counseling Juvenile Firesetters: The Child Under Seven Years of Age, Federal Emergency Management Agency, Washington, DC, 1979. 17. Fineman, K. R., Day, J. B., Michaelis, L., Brudo, C., Brudo, E., and Morris, C., Preadolescent Firesetter Handbook: Ages 0–7, Federal Emergency Management Agency (FEMA), Washington, DC, 1988. 18. Fineman, K. R., Family Fire Risk Interview Form, FEMA, Washington, DC, 1997. 19. Fineman, K. R., Juvenile Fire Risk Interview Form, FEMA, Washington, DC, 1997.
20. Fineman, K. R., Parent Fire Risk Questionnaire, FEMA, Washington, DC, 1997. 21. Gaynor, J., Juvenile Firesetter Intervention Handbook, FEMA, Washington, DC, 2000. 22. Kolko, D. J., “Efficacy of Cognitive-Behavioral Treatment and Fire Safety Education for Firesetting Children: Initial and Follow-Up Outcomes,” Journal of Child Psychology and Psychiatry and Allied Disciplines, Vol. 42, 2001, pp. 359–369. 23. Phoenix Fire Department, Youth Firesetter Intervention Program, Phoenix Fire Department Corporate Communications Publication Section, Phoenix, AZ, 2001. 24. U.S. Department of Justice, Information Sharing and the Family Educational Rights and Privacy Act, Juvenile Justice Fact Sheet #39, 1996. 25. Sharing Information: A Guide to the Family Educational Rights and Privacy Act and Participation in Juvenile Justice Programs, OJJDP Report, U.S. Department of Justice, June 1997. 26. Porth, D., The Portland Report ’99, Portland Fire and Rescue Department, Portland, OR, 1999. 27. Illinois Juvenile Firesetters Task Force Report, Illinois State Fire Marshal’s Office, 1998. 28. U.S. Department of Justice, Balance and Restorative Justice Project, Juvenile Justice Fact Sheet #42, 1996. 29. U.S. Department of Justice, Serious Habitual Offender Comprehensive Action Program, Juvenile Justice Fact Sheet #35, 1996.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on juvenile firesetting discussed on this chapter. (See the latest version of the NFPA Catalog for availability of the current edition of the following document.) NFPA 1035, Standard for Professional Qualifications for Public Fire and Life Safety Educator
Additional Readings Bills, J., Cole, R., Crandall, R., and Schwartzman, P., Fireproof Children Handbook, National Fire Service Support Systems, Inc., Rochester, NY, 1990. Cole, R., Grolnick, W., and Schwartzman, P., “Fire Setting,” Handbook of Prescriptive Treatments for Children and Adolescents, 2nd ed., R. Ammerman, C. Last, and M. Hersen (Eds.), Allyn & Bacon, Boston, 1999. Federal Emergency Management Agency, Socioeconomic Factors and the Incidence of Fire, United States Fire Administration and National Fire Data Center, Washington, DC, 1995. Kolko, D. J., Dorsett, P. G., and Milan, M. A., “A Total Assessment Approach to the Evaluation of Social Skills Training: The Effectiveness of an Anger Control Program for Adolescent Psychiatric Patients,” Behavioral Assessment, Vol. 3, 1981, pp. 383–402. Schwartzman, P., Fineman, K., and Slavkin, M., Treating Arson: Young People and Adults, Wiley, UK, in press. Schwartzman, P., Stambaugh, H., and Kimball, J., Arson and Juveniles: Responding to the Violence. A Review of Teen Firesetting and Interventions (Federal Emergency Management Agency. United States Fire Administration, United States Fire Administration), Emmitsburg, MD, 1994. Stadolnick, R., Drawn to the Flame: Assessment and Treatment of Juvenile Firesetter Behavior, Professional Resource Press, Sarasota, FL, 2000. U.S. Fire Administration, Arson in the United States, National Fire Data Center, Washington, DC, 2001. U.S. Fire Administration, Children and Fire: The Experience of Children and Fire in the United States, National Fire Data Center, Washington, DC, 1997. U.S. Department of Justice, Juvenile Firesetting and Arson, Juvenile Justice Fact Sheet #51, 1997.
FIRE PREVENTION
P
revention is probably the most effective means for reducing loss due to fire. It can be achieved by changing or controlling the source of heat that leads to ignition, the source of fuel that is first ignited, or the circumstances by which the two are brought together. Section 6 of this handbook (Section 3 in the previous edition) discusses various sources of heat and fuel—some common to most occupancies and operations, others more specific—and the ways in which they can be prevented from causing a fire. Methods of fire prevention that involve educating the general public are covered extensively in Section 5, “Fire and Life Safety Education.” Most fuels first involved in a fire are also important contributors to rapid growth of the fire, and these are discussed in more detail in Section 8, “Materials, Products, and Environments.” The relationship of building design and construction to fire growth is covered in Section 12, “Confining Fires.” Discussion of the fire hazards of particular occupancies is covered in Section 13, “Systems Approaches to Property Classes.” Several major causes of fire, such as careless use of smoking materials and cooking-related fires, are not covered extensively in this handbook but are discussed in detail in NFPA’s Learn Not to Burn® materials. Fire loss investigation is discussed in Section 3, Chapter 1. The purpose of this section is threefold: (1) to discuss particular sources of heat and fuel, including some which may be part of a specific occupancy (discussed in more detail in Section 13); (2) to identify the fire hazards associated with these; and (3) to discuss applicable means of fire prevention. In this latter context, the reader should recognize that certain techniques of fire detection, protection, suppression, and confinement can be successfully applied to several heat and fuel sources. Therefore, there will be common elements among the chapters and sections of the handbook. Chapters 1 through 6 and Chapters 31, 32, and 33 address fire hazards that are common to most occupancies and commercial, institutional, or industrial operations. The remaining chapters focus on specific processes and operations. Chapter 1 covers the electrical system, the leading source of heat that results in property damage in building fires. Chapters 2 and 3 discuss control of static electricity and protection from lightning. Chapter 4 deals with emergency and standby electrical power supplies and their interconnection with the electrical system. Chapter 5 discusses the leading sources of building fire incidents in the United States, heating systems and appliances, which can cause fires because they typically operate above the ignition temperature of many common materials. Chapter 6 addresses boiler furnaces and their fuels. Chapter 7 covers heat transfer fluids and systems using nonwater fluids, which can operate at temperatures above 350°F (177°C). Chapter 8 covers industrial equipment, such as process ovens, dryers, and furnaces. Chapter 9 covers oil quenching and molten salt baths for heat treating and tempering. Chapter 10 discusses stationary combustion engines used as prime movers for standby electrical generators and fire pumps. Other chapters in Section 6 address specific processes or operations. Included are chapters on storage of flammable and combustible liquids, gases, chemicals, and solid fuels in small containers and in tanks and silos at processing plants. Chapter 14 discusses: welding, cutting, and other hot work operations, Chapter 28 covers refrigeration systems, Chapter 31 examines waste handling and control, and Chapter 32 discusses the regulation of hazardous waste.
6–1
SECTION
6
Robert P. Benedetti
6–2 SECTION 6 ■ Fire Prevention
Chapter 1
Electrical Systems and Appliances
Arcing and Overheating in Electrical Systems Origins of Electrical Fires in Buildings Codes and Standards Building Wiring, Design, and Protection Electrical Household Appliances Industrial and Commercial Equipment Electrical Equipment for Outdoor Use Locations Exposed to Moisture and Noncombustible Dusts Signaling and Communications Systems Emergency Systems Special Occupancy Electrical Problems Summary Bibliography Chapter 2
Control of Electrostatic Ignition Sources
Static Electricity Defined Charge Separation Dissipation of Static Electricity Control of Ignitable Mixtures Flammable Liquids Gases Dusts and Fibers Static Detectors Definition of Terms Summary Bibliography Chapter 3
Lightning Protection Systems
Factors in the Need for Lightning Protection Nature of Lightning Traditional Theory of Lightning Protection Property Protection Protection of Persons Summary Bibliography Chapter 4
Emergency and Standby Power Supplies
Power Supply System Code and Standard Energy Sources Engine-Driven Generator Power Systems Miscellaneous Considerations Summary Bibliography Chapter 5
Heating Systems and Appliances
Fuels and Methods of Firing Controls for Fuel Burners Heating Appliances and Their Applications Distribution of Heat by Ducts and Pipes Installation of Heating Appliances Chimney and Vent Connectors Vents Chimneys
6–7 6–7 6–11 6–16 6–17 6–33 6–38 6–41 6–42 6–42 6–42 6–44 6–52 6–52
6–55 6–55 6–56 6–57 6–59 6–59 6–60 6–61 6–61 6–62 6–63 6–63 6–65 6–65 6–67 6–69 6–71 6–76 6–76 6–76
6–79 6–79 6–80 6–81 6–83 6–83 6–83 6–85 6–85 6–93 6–94 6–101 6–103 6–110 6–111 6–121
Fireplaces and Fireplace Stoves Summary Bibliography Chapter 6
Boiler Furnaces
The Combustion Process Fuels Oil- and Gas-Burning Systems Piping and Control Devices Pulverized Coal Systems Fluidized Bed Combustion Special FBC Hazards Boiler-Furnace Hazards Open Register Lightoff and Continuous Purge Procedure Fire and Explosion Protection Special Considerations for Small Boilers Interlocks, Alarms, and Operator Competence Summary Bibliography Chapter 7
Heat Transfer Fluids and Systems
Types of Transfer Fluids Heat Transfer System Components Hazards of Organic Heat Transfer Fluids Safeguards for Heat Transfer Systems Using Organic or Synthetic Heat Transfer Fluids Summary Bibliography Chapter 8
Industrial and Commercial Heat Utilization Equipment
Industrial Heat Utilization Equipment Ovens and Furnaces Class A Ovens and Furnaces Class B Industrial Furnaces Class C Industrial Furnaces Using a Special Processing Atmosphere Class D Vacuum Furnaces Afterburner and Catalytic Combustion Systems Heat Recovery Lumber Kilns Dehydrators and Dryers Summary Bibliography Chapter 9
Oil Quenching and Molten Salt Baths
Oil and Polymer Quenching Quench Tanks Material Transfer Oil Temperature Control Central Oil System Safety Considerations Molten Salt Baths Summary Bibliography
6–129 6–131 6–131 6–133 6–133 6–134 6–134 6–137 6–138 6–140 6–141 6–141 6–144 6–144 6–144 6–144 6–145 6–145 6–147 6–147 6–148 6–149 6–150 6–151 6–151
6–153 6–153 6–154 6–161 6–162 6–163 6–164 6–165 6–167 6–167 6–169 6–172 6–172
6–175 6–175 6–175 6–177 6–177 6–178 6–178 6–179 6–184 6–184
SECTION 6
Chapter 10
Stationary Combustion Engines and Fuel Cells
Stationary Combustion Engines Fuel Cells Summary Bibliography Chapter 11
Metalworking Processes
The Metalworking Process Alternative Means of Machining Fire Hazards Safeguards Summary Bibliography Chapter 12
Automated Processing Equipment
General Considerations Automated Processing Equipment Analysis of the Process Design Solutions Standards Related to Automated Processing Equipment Summary Bibliography Chapter 13
Fluid Power Systems
Fluids under Pressure Fire Characteristics Less Hazardous Hydraulic Fluids Environmentally Acceptable Fluids International Fluid Designations Summary Bibliography Chapter 14
Welding, Cutting, and Other Hot Work
Process Using Electricity Oxyfuel Gas Processes Thermal Spraying (THSP) Safeguards Special Situations and Additional Precautions Summary Bibliography Chapter 15
Woodworking Facilities and Processes
Terms Used in the Forest Products Industry Woodworking Processes Fire Prevention Fire Protection Summary Bibliography Chapter 16
Spray Finishing and Powder Coating
Types of Coatings
6–187 6–187 6–190 6–192 6–192 6–193 6–193 6–197 6–197 6–197 6–198 6–198 6–201 6–201 6–202 6–202 6–203 6–204 6–205 6–205 6–207 6–207 6–208 6–208 6–209 6–209 6–209 6–209
6–211 6–212 6–213 6–215 6–215 6–218 6–219 6–219
6–221 6–221 6–221 6–228 6–231 6–236 6–236
6–237 6–237
■
Fire Prevention
Spray Process Equipment and Components Powder Coating Process Equipment and Components Fluid Spray Process Hazards and Control Powder Coating Process Hazards and Control Summary Bibliography Chapter 17
Dipping and Coating Processes
The Processes Process Hazards Hazard Reduction Fire Protection Summary Bibliography Chapter 18
Plastics Industry and Related Process Hazards
Overview of the Plastics Industry Plastics Processing Raw Materials Production Process Fire Hazards Safeguards Summary Bibliography Chapter 19
Chemical Processing Equipment
Plant Siting Exposure Protection Ignition Sources Control of Spills Hazards of Heat Transfer Stability and Shock Sensitivity Chemical Plant Operations and Equipment Summary Bibliography Chapter 20
Manufacture and Storage of Aerosol Products
The Aerosol Product Classification and Fire Behavior of Aerosols Aerosol Filling Plants Product Storage Summary Bibliography Chapter 21
Storage of Flammable and Combustible Liquids
Tank Storage Other Storage of Flammable Liquids Handling of Flammable and Combustible Liquids Transportation of Flammable and Combustible Liquids Summary Bibliography
6–3
6–238 6–241 6–243 6–245 6–247 6–247 6–249 6–249 6–250 6–252 6–257 6–259 6–259
6–261 6–261 6–261 6–263 6–264 6–268 6–270 6–271 6–271 6–273 6–273 6–277 6–277 6–278 6–279 6–280 6–282 6–283 6–283
6–287 6–287 6–288 6–290 6–290 6–295 6–295
6–297 6–297 6–307 6–309 6–311 6–312 6–312
6–4 SECTION 6 ■ Fire Prevention
Chapter 22
Storage of Gases
6–315
Gas Containers Storage Safety Considerations Summary Bibliography
6–315 6–316 6–319 6–319
Chapter 23
Storage and Handling of Chemicals
Sources of Information Principles of Good Storage Toxicity of Chemicals Oxidizing Chemicals Combustible Chemicals Unstable Chemicals Water- and Air-Reactive Chemicals Corrosive Chemicals Radioactive Material Material Subject to Self-Heating Mixtures of Chemicals Transportation of Chemicals Waste Chemical Disposal Summary Bibliography Chapter 24
Storage and Handling of Solid Fuels
Coal as a Fuel Storage Practices for Coal Gas Generation and Explosions with Coal Coal Handling and Coal Dust Explosions Wood as a Fuel Hazards of Wood Fuels Storage Practices for Wood Fuels Handling Wood Fuels Fire Prevention for Wood Fuels Fire Protection for Wood Fuels Summary Bibliography Chapter 25
Storage and Handling of Records
Storage Options Damageability and Salvage Records Storage Fire Risk Analysis Fire Risk Reduction Automatic Extinguishing Systems Fire Prevention and Emergency Planning Protection Limitations Relevant Fire Experience Summary Bibliography Chapter 26
Storage and Handling of Grain Mill Products
Raw Materials Storage Handling Elevators
6–321 6–321 6–321 6–322 6–322 6–325 6–326 6–328 6–329 6–330 6–331 6–332 6–332 6–332 6–332 6–333 6–337 6–337 6–338 6–340 6–340 6–341 6–341 6–343 6–343 6–343 6–344 6–345 6–345 6–347 6–347 6–349 6–350 6–351 6–352 6–354 6–355 6–355 6–356 6–358 6–358
6–361 6–363 6–363 6–364 6–365
Dust Control The Fire Hazard The Explosion Hazard The Safeguards Summary Bibliography Chapter 27
Grinding Processes
General Characteristics of Dust Explosions Grinding Hazards Grinding Equipment Application of Grinding Equipment Protection against Fires or Explosions Summary Bibliography Chapter 28
Refrigeration Systems
Effects of Regulatory Changes Applications Refrigerant Classifications Basic Operating Principles Types of Systems and Their Basic Hazards Hazard Control and Emergency Response Summary Bibliography Chapter 29
Lasers
Laser Properties and Components Laser Operation Hazard Classification of Lasers Hazards and Control Measures Summary Bibliography Chapter 30
Semiconductor Manufacturing
Preproduction Process Production Process Semiconductor-Related Developments and Guidelines Hazard Control in Semiconductor Manufacturing Fire Hazards Health Hazards Summary Bibliography Chapter 31
Waste Handling and Control
Solid Waste Management Systems Solid Waste Storage Rooms Waste Chutes and Handling Systems Incinerators Waste Compactors Shredders Industrial Waste Systems and Equipment Waste Materials Waste Management Systems
6–367 6–368 6–369 6–374 6–378 6–379 6–381 6–381 6–384 6–386 6–387 6–389 6–390 6–391 6–391 6–393 6–393 6–394 6–394 6–396 6–396 6–398 6–400 6–400 6–401 6–401 6–402 6–403 6–403 6–404 6–405 6–407 6–408 6–408 6–411 6–412 6–413 6–415 6–415 6–416 6–417 6–417 6–417 6–417 6–419 6–423 6–424 6–424 6–425 6–431
SECTION 6
Treatment and Disposal Systems Ultimate Disposal Codes, Regulations, and Standards Summary Bibliography Chapter 32
Hazardous Waste Control
Regulation of Hazardous Waste Sources of Waste Characterization of Waste Collection, Handling, and Disposal of Waste Hazard Prevention and Control Specific Wastes
6–431 6–436 6–436 6–438 6–438 6–441 6–442 6–443 6–443 6–445 6–448 6–449
■
Fire Prevention
Summary Bibliography Chapter 33
Housekeeping Practices
Good Housekeeping Defined Essentials of Good Housekeeping Building Care and Maintenance Floors Occupancy and Process Housekeeping Outdoor Housekeeping Practices Inspections Summary Bibliography
6–5
6–452 6–452 6–457 6–457 6–458 6–459 6–460 6–462 6–464 6–465 6–465 6–466
CHAPTER 1
SECTION 6
Electrical Systems and Appliances Revised by
Robert M. Milatovich
T
An electric arc may not only ignite combustible material in its vicinity, for example, the insulation and covering of the conductor, but may also melt the metal of the conductor. Embers from burning combustible material and splatters of hot metal may fall on combustible material, setting it on fire. When an electrical conductor carries current, heat is generated in direct proportion to the resistance (ohms) of the conductor and to the square of the current (amperage). The resistance of conductors used to convey current to the location in which it is used or to convey it through the windings of a piece of apparatus (except resistance devices and heaters) should be as low as practical. Metals, such as copper and aluminum, are used for this purpose. In other instances, such as in electric heaters, electric cooking equipment, and soldering irons, the heat from the current serves a useful purpose. The heating of electrical conductors is almost never a fire hazard under design conditions. NFPA 70, National Electrical Code®, specifies the ampacity, or the maximum safe current a conductor can carry without overheating (Tables 6.1.1 through 6.1.8). Ampacity depends on size of the conductor; temperature of the environment in which the equipment is installed; type of insulation; and location where the conductors are installed, such as in a raceway, in a cable, in the earth, or in free air. Where the specified current is exceeded, the generation of heat causes deterioration of the electrical insulation and may ignite combustibles in contact with or close to the conductors. Apparatus or appliances that use electric conductors as heating elements or use an electric arc to generate heat (e.g., arc welders) can also be fire hazards if improperly installed and used. The risk of an electrical fire can be reduced by using the proper size conductor for the load, suitable insulation for the environment, and the correct size overcurrent protection (fuse or circuit breaker). Where heat-generating equipment is utilized, the risk of fire can be further reduced by ensuring that sufficient clearances and air circulation are provided to prevent unsafe temperatures and premature breakdown of electrical insulation or ignition of nearby combustibles. All standards governing electrical equipment include requirements intended to prevent fires caused by arcing and overheating and to prevent accidental contact, which may cause an electric shock. These primary sources of electrical hazards should be kept in mind whenever any work is being done on electric equipment.
his chapter discusses electrical systems and appliances. Specific topics include origins of electrical fires; codes and standards; building wiring, design, and protection; electrical household appliances; industrial and commercial equipment; electrical equipment for outdoor use; locations exposed to moisture and dust; signaling and communications systems; emergency systems; and special occupancy installations. Other chapters in this handbook address related building services, most notably Section 6, Chapter 5, “Heating Systems and Appliances”; and Section 12, Chapter 15, “AirConditioning and Ventilating Systems.” Special considerations for the installation of electrical systems can be found elsewhere in this handbook. See Section 6, Chapter 3, “Lightning Protection Systems”; Section 6, Chapter 8, “Industrial and Commercial Heat Utilization Equipment”; Section 8, Chapter 8, “Medical Gases”; and Section 4, Chapter 3, “Concepts of Egress Design.” If properly designed, installed, and maintained, electrical systems are both convenient and safe; otherwise they can be a source of both fire and personal injury. Electricity can cause a fire if an arc occurs or if electrical equipment overheats and can cause injury or death through shocks and burns.
ARCING AND OVERHEATING IN ELECTRICAL SYSTEMS When an electric circuit carrying a current is interrupted either intentionally, as by a switch, or unintentionally, as when a connection at a terminal becomes loosened, arcing at the switch contacts or heating from the high-resistance connection at the terminal is produced. The intensity of the arc and the energy released depend largely on the current and resistance of the contact at the terminal, as well as the voltage and inductance of the circuit load. The temperature may easily be high enough to ignite any combustible material in the vicinity.
Robert M. Milatovich is a supervising inspector for the Clark County Building Department, Las Vegas, Nevada, and the chair of Code Making Panel 20 of NFPA 70, National Electrical Code® (NEC).
6–7
TABLE 6.1.1 Allowable Ampacities of Insulated Conductors Rated 0 through 2000 V, 140° to 194°F (60° to 90°C) Not More Than Three Current-Carrying Conductors in Raceway or Cable or Earth (Directly Buried), Based on Ambient Temperature of 86°F (30°C) Temperature Rating of Conductora
Size
AWG or kcmil
140°F (60°C)
140°F (60°C)
167°F (75°C)
194°F (90°C)
Types TW, UF
Types RHW, THHW, THW, THWN, XHHW, USE, ZW
Types TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN- 2, USE-2, XHH, XHHW, XHHW-2, ZW-2
COPPER
Types TW, UF
Size 167°F (75°C)
194°F (90°C)
Types RHW, THHW, THW, THWN, XHHW, USE
Types TBS, SA, SIS, THHN, THHW, THW-2, THWN-2, RHH, RHW-2, USE-2, XHH, XHHW, XHHW-2, ZW-2
ALUMINUM OR COPPER-CLAD ALUMINUM
AWG or kcmil
18 16 14b 12b 10b 8
— — 20 25 30 40
— — 20 25 35 50
14 18 25 30 40 55
— — — 20 25 30
— — — 20 30 40
— — — 25 35 45
— — — 12b 10b 8
6 4 3 2 1
55 70 85 95 110
65 85 100 115 130
75 95 110 130 150
40 55 65 75 85
50 65 75 90 100
60 75 85 100 115
6 4 3 2 1
1/0 2/0 3/0 4/0
125 145 165 195
150 175 200 230
170 195 225 260
100 115 130 150
120 135 155 180
135 150 175 205
1/0 2/0 3/0 4/0
250 300 350 400 500
215 240 260 280 320
255 285 310 335 380
290 320 350 380 430
170 190 210 225 260
205 230 250 270 310
230 255 280 305 350
250 300 350 400 500
600 700 750 800 900
355 385 400 410 435
420 460 475 490 520
475 520 535 555 585
285 310 320 330 355
340 375 385 395 425
385 420 435 450 480
600 700 750 800 900
1000 1250 1500 1750 2000
455 495 520 545 560
545 590 625 650 665
615 665 705 735 750
375 405 435 455 470
445 485 520 545 560
500 545 585 615 630
1000 1250 1500 1750 2000
CORRECTION FACTORSc Ambent Temp. (°C) 21–25 26–30 31–35 36–40 41–45 46–50 51–55 56–60 61–70 71–80
Ambient Temp. (°F) 1.08 1.00 0.91 0.82 0.71 0.58 0.41 — — —
1.05 1.00 0.94 0.88 0.82 0.75 0.67 0.58 0.33 —
1.08 1.00 0.91 0.82 0.71 0.58 0.41 — — —
1.04 1.00 0.96 0.91 0.87 0.82 0.76 0.71 0.58 0.41
1.05 1.00 0.94 0.88 0.82 0.75 0.67 0.58 0.33 —
NEC Table 310.13. See NEC Section 240.3(D). c For ambient temperatures other than 86°F (30°C), multiply the allowable ampacities by the appropriate factor. Source: NFPA 70–2002, National Electrical Code®. aSee b
6–8
1.04 1.00 0.96 0.91 0.87 0.82 0.76 0.71 0.58 0.41
70–77 78–86 87–95 96–104 105–113 114–122 123–131 132–140 141–158 159–176
TABLE 6.1.2 Allowable Ampacities of Single Insulated Conductors, Rated 0 through 2000 V, in Free Air Based on Ambient Air Temperature of 86°F (30°C) Temperature Rating of Conductor a
Size 140°F (60°C)
AWG or kcmil
Types TW, UF
140°F (60°C)
167°F (75°C)
194°F (90°C)
Types RHW, THHW, THW, THWN, XHHW, ZW
Types TBS, SA, SIS, FEP, FEPB, MI, RHH, RHW-2, THHN, THHW, THW-2, THWN-2, USE-2, XHH, XHHW, XHHW-2, ZW-2
Copper
Types TW, UF
Size
167°F (75°C)
194°F (90°C)
Types RHW, THHW, THW, THWN, XHHW
Types TBS, SA, SIS, THHN, THHW, THW-2, THWN-2, RHH, RHW-2, USE-2, XHH, XHHW, XHHW-2, ZW-2
Aluminum or Copper-Clad Aluminum
AWG or kcmil — — -— 12b 10b 8
18 16 14b 12b 10b 8
— — 25 30 40 60
— — 30 35 50 70
18 24 35 40 55 80
— — — 25 35 45
— — — 30 40 55
— — — 35 40 60
6 4 3 2 1
80 105 120 140 165
95 125 145 170 195
105 140 165 190 220
60 80 95 110 130
75 100 115 135 155
80 110 130 150 175
6 4 3 2 1
1/0 2/0 3/0 4/0
195 225 260 300
230 265 310 360
260 300 350 405
150 175 200 235
180 210 240 280
205 235 275 315
1/0 2/0 3/0 4/0
250 300 350 400 500
340 375 420 455 515
405 445 505 545 620
455 505 570 615 700
265 290 330 355 405
315 350 395 425 485
355 395 445 480 545
250 300 350 400 500
600 700 750 800 900
575 630 655 680 730
690 755 785 815 870
780 855 885 920 985
455 500 515 535 580
540 595 620 645 700
615 675 700 725 785
600 700 750 800 900
1000 1250 1500 1750 2000
780 890 980 1070 1155
935 1065 1175 1280 1385
1055 1200 1325 1445 1560
625 710 795 875 960
750 855 950 1050 1150
845 960 1075 1185 1335
1000 1250 1500 1750 2000
Correction Factorsc Ambent Temp. (°C) 21–25 26–30 31–35 36–40 41–45 46–50 51–55 56–60 61–70 71–80
Ambient Temp. (°F) 1.08 1.00 0.91 0.82 0.71 0.58 0.41 — — —
1.05 1.00 0.94 0.88 0.82 0.75 0.67 0.58 0.33 —
1.08 1.00 0.91 0.82 0.71 0.58 0.41 — — —
1.04 1.00 0.96 0.91 0.87 0.82 0.76 0.71 0.58 0.41
a
1.05 1.00 0.94 0.88 0.82 0.75 0.67 0.58 0.33 —
See NEC Table 310.13. See NEC Section 240.3(D). c For ambient temperatures other than 86°F (30°C), multiply the allowable ampacities by the appropriate factor. Source: NFPA 70-2002, National Electrical Code®. b
6–9
1.04 1.00 0.96 0.91 0.87 0.82 0.76 0.71 0.58 0.41
70–77 78–86 87–95 96–104 105–113 114–122 123–131 132–140 141–158 159–176
6–10 SECTION 6 ■ Fire Prevention
TABLE 6.1.3 Allowable Ampacities of Three Single Insulated Conductors Rated 0 through 2000 V, 302° to 482°F (150° to 250°C), in Raceway or Cable Based on Ambient Air Temperature of 104°F (40°C) Temperature Rating of Conductor a
Size
Size
302°F (150°C)
392°F (200°C)
482°F (250°C)
302°F (150°C)
Type Z
Types FEP, FEPB, PFA
Types PFAH, TFE
Type Z
Nickel or Nickel-Coated Copper
Aluminum or Copper-Clad Aluminum
AWG or kcmil
Copper
AWG or kcmil
14 12 10 8
34 43 55 76
36 45 60 83
39 54 73 93
— 30 44 57
14 12 10 8
6 4 3 2 1
96 120 143 160 186
110 125 152 171 197
117 148 166 191 215
75 94 109 124 145
6 4 3 2 1
1/0 2/0 3/0 4/0
215 251 288 332
229 260 297 346
244 273 308 361
169 198 227 260
1/0 2/0 3/0 4/0
250 300 350 400 500
— — — — —
— — — — —
— — — — —
— — — — —
250 300 350 400 500
600 700 750 800
— — — —
— — — —
— — — —
— — — —
600 700 750 800
1000 1500 2000
— — —
— — —
— — —
— — —
1000 1500 2000
Correction Factorsb Ambient Temp. (°F)
Ambient Temp. (°C) 41–50 51–60 61–70 71–80 81–90 91–100 101–120 121–140 141–160 161–180 181–200 201–225 a
0.95 0.90 0.85 0.80 0.74 0.67 0.52 0.30 — — — —
0.97 0.94 0.90 0.87 0.83 0.79 0.71 0.61 0.50 0.35 — —
0.98 0.95 0.93 0.90 0.87 0.85 0.79 0.72 0.65 0.58 0.49 0.35
0.95 0.90 0.85 0.80 0.74 0.67 0.52 0.30 — — — —
See NEC Table 310.13. For ambient temperatures other than 104°F (40°C), multiply the allowable ampacities by the appropriate factor. Source: NFPA 70-2002, National Electrical Code®.
b
105–122 123–140 141–158 159–176 177–194 195–212 213–248 249–284 285–320 321–356 357–392 393–437
CHAPTER 1
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TABLE 6.1.4 Allowable Ampacities for Single Insulated Conductors Rated 0 through 2000 V, 302° to 482°F (150° to 250°C), in Free Air Based on Ambient Air Temperature of 104°F (40°C) Temperature Rating of Conductora
Size
Size
302°F (150°C)
392°F (200°C)
482°F (250°C)
302°F (150°C)
Type Z
Types FEP, FEPB, PFA
Types PFAH, TFE
Type Z
Nickel or NickelCoated Copper
Aluminum or Copper-Clad Aluminum
AWG or kcmil
AWG or kcmil
Copper
14 12 10 8
46 60 80 106
54 68 90 124
59 78 107 142
— 47 63 83
14 12 10 8
6 4 3 2 1
155 190 214 255 293
165 220 252 293 344
205 278 327 381 440
112 148 170 198 228
6 4 3 2 1
1/0 2/0 3/0 4/0
339 390 451 529
399 467 546 629
532 591 708 830
263 305 351 411
1/0 2/0 3/0 4/0
Correction Factorsb Ambient Temp. (°F)
Ambient Temp. (°C) 41–50 51–60 61–70 71–80 81–90 91–100 101–120 121–140 141–160 161–180 181–200 201–225
0.95 0.90 0.85 0.80 0.74 0.67 0.52 0.30 — — — —
0.97 0.94 0.90 0.87 0.83 0.79 0.71 0.61 0.50 0.35 — —
0.98 0.95 0.93 0.90 0.87 0.85 0.79 0.72 0.65 0.58 0.49 0.35
0.95 0.90 0.85 0.80 0.74 0.67 0.52 0.30 — — — —
105–122 123–140 141–158 159–176 177–194 195–212 213–248 249–284 285–320 321–356 357–392 393–437
a
See NEC Table 310.13. For ambient temperatures other than 104°F (40°C), multiply the allowable ampacities by the appropriate factor. Source: NFPA 70-2002, National Electrical Code®.
b
ORIGINS OF ELECTRICAL FIRES IN BUILDINGS Table 6.1.9 provides an overview of structure fires reported to U.S. fire departments from 1994 through 1998 that were coded as caused by electrical failure. This table is limited to fires coded as involving a short circuit, a ground fault, or another electrical failure, so some relevant incidents are likely not counted. Other causes, some of which may include a mix of electrical failures
with other fires, are not included. Also, these statistics reflect cause determinations by fire officers on the scene, so some errors of inclusion or exclusion may have occurred. Electrically powered equipment is involved in several times this number of fires each year (see Table 6.1.10, for example, for total fires involving electrical distribution equipment), but in nonelectrical failure scenarios, such as installing or using equipment with hot surfaces too close to combustibles. Some of these nonelectrical-failure scenarios involve mechanical failure or
6–12 SECTION 6 ■ Fire Prevention
TABLE 6.1.5 Allowable Ampacities of Insulated Conductors Rated 0 through 2000 V, Not More Than Three Single CurrentCarrying Conductors Supported on a Messenger, Based on Ambient Temperature of 104°F (40°C) Temperature Rating of Conductor a
Size
194°F (90°C)
167°F (75°C)
AWG or kcmil
Types RHW, THHW, THW, THWN, XHHW, ZW
Types MI, THHN, THHW, THW-2, THWN- 2, RHH, RHW-2, USE-2 XHHW, XHHW-2, ZW-2 Copper
Size
167°F (75°C)
194°F (90°C)
Types RHW, THW, THWN, THHW, XHHW
Types TBS, SA, SIS, THHN, THHW, THW-2, THWN-2, RHH, RHW-2, USE-2, XHH, XHHW, XHHW-2, ZW-2
Aluminum or Copper-Clad Aluminum
AWG or kcmil
8 6 4 3 2 1
57 76 101 118 135 158
66 89 117 138 158 185
44 59 78 92 106 123
51 69 91 107 123 144
8 6 4 3 2 1
1/0 2/0 3/0 4/0
183 212 245 287
214 247 287 335
143 165 192 224
167 193 224 262
1/0 2/0 3/0 4/0
250 300 350 400 500
320 359 397 430 496
374 419 464 503 580
251 282 312 339 392
292 328 364 395 458
250 300 350 400 500
600 700 750 800 900 1000
553 610 638 660 704 748
647 714 747 773 826 879
440 488 512 532 572 612
514 570 598 622 669 716
600 700 750 800 900 1000
Correction Factorsb Ambient Temp. (°F)
Ambient Temp. (°C) 21–25 26–30 31–35 36–40 41–45 46–50 51–55 56–60 61–70 71–80 a
1.20 1.13 1.07 1.00 0.93 0.85 0.76 0.65 0.38 —
1.14 1.10 1.05 1.00 0.95 0.89 0.84 0.77 0.63 0.45
1.20 1.13 1.07 1.00 0.93 0.85 0.76 0.65 0.38 —
1.14 1.10 1.05 1.00 0.95 0.89 0.84 0.77 0.63 0.45
See NEC Table 310.13. For ambient temperatures other than 104°F (40°C), multiply the allowable ampacities by the appropriate factor. Source: NFPA 70-2002, National Electrical Code®.
b
70–77 79–86 88–95 97–104 106–113 115–122 124–131 133–140 142–158 160–176
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Electrical Systems and Appliances
6–13
TABLE 6.1.6 Ampacities of Two or Three Insulated Conductors, Rated 0 through 2000 V, Within an Overall Covering (Multiconductor Cable), in Raceway in Free Air Based on Ambient Temperature of 86°F (30°C) Temperature Rating of Conductora
Size
AWG or kcmil 14 12 10 8
140°F (60°C)
167°F (75°C)
194°F (90°C)
Types TW, UF
Types RHW, THHW, THW, THWN, XHHW, ZW
Types THHN, THHW, THW-2, THWN-2, RHH, RWH-2 USE-2, XHHW, XHHW-2, ZW-2
140°F (60°C)
167°F (75°C)
194°F (90°C)
Types TW, UF
Types RHW, THHW, THW, THWN, XHHW, ZW
Types THHN, THHW, THW-2, THWN-2, RHH, RWH-2 USE-2, XHHW, XHHW-2, ZW-2
Copper 16b 20b 27b 36
18b 24b 33b 43
Size
Aluminum or Copper-Clad Aluminum 21b 27b 36b 48
— 16b 21b 28
— 18b 25b 33
— 21b 28b 37
AWG or kcmil 14 12 10 8
6 4 3 2 1
48 66 76 88 102
58 79 90 105 121
65 89 102 119 137
38 51 59 69 80
45 61 70 83 95
51 69 79 93 106
6 4 3 2 1
1/0 2/0 3/0 4/0
121 138 158 187
145 166 189 223
163 186 214 253
94 108 124 147
113 129 147 176
127 146 167 197
1/0 2/0 3/0 4/0
250 300 350 400 500
205 234 255 274 315
245 281 305 328 378
276 317 345 371 427
160 185 202 218 254
192 221 242 261 303
217 250 273 295 342
250 300 350 400 500
600 700 750 800 900 1000
343 376 387 397 415 448
413 452 466 479 500 542
468 514 529 543 570 617
279 310 321 331 350 382
335 371 384 397 421 460
378 420 435 450 477 521
600 700 750 800 900 1000
Correction Factorsc Ambent Temp. (°C) 21–25 26–30 31–35 36–40 41–45 46–50 51–55 56–60 61–70 71–80 a
Ambent Temp. (°F) 1.08 1.00 0.91 0.82 0.71 0.58 0.41 — — —
1.05 1.00 0.94 0.88 0.82 0.75 0.67 0.58 0.33 —
1.04 1.00 0.96 0.91 0.87 0.82 0.76 0.71 0.58 0.41
1.08 1.00 0.91 0.82 0.71 0.58 0.41 — — —
1.05 1.00 0.94 0.88 0.82 0.75 0.67 0.58 0.33 —
See NEC Table 310.13. See NEC Section 240.3(D). c For ambient temperatures other than 86°F (30°C), multiply the allowable ampacities by the appropriate factor. Source: NFPA 70–2002, National Electrical Code®. b
1.04 1.00 0.96 0.91 0.87 0.82 0.76 0.71 0.58 0.41
70–77 79–86 88–95 97–104 106–113 115–122 124–131 133–140 142–158 160–176
6–14 SECTION 6 ■ Fire Prevention
TABLE 6.1.7 Ampacities of Multiconductor Cables with Not More than Three Insulated Conductors, Rated 0 through 2000 V, in Free Air Based on Ambient Temperature of 104°F (40°C) (For Types TC, MC, MI, UF and USE Cables) Temperature Rating of Conductor a Size (AWG or kcmil) 18 16 14 12 10 8
140°F (60°C)
167°F (75°C)
185°F (85°C)
194°F (90°C)
Copper — — 18b 21b 28b 39
— — 21b 28b 36b 50
140°F (60°C)
167°F (75°C)
185°F (85°C)
194°F (90°C)
Aluminum or Copper-Clad Aluminum — — 24b 30b 41b 56
11 16 25b 32b 43b 59
— — — 18b 21b 30
— — — 21b 28b 39
— — — 24b 30b 44
— — — 25b 32b 46
Size (AWG or kcmil) — — — 12 10 8
6 4 3 2 1
52 69 81 92 107
68 89 104 118 138
75 100 116 132 154
79 104 121 138 161
41 54 63 72 84
53 70 81 92 108
59 78 91 103 120
61 81 95 108 126
6 4 3 2 1
1/0 2/0 3/0 4/0
124 143 165 190
160 184 213 245
178 206 238 274
186 215 249 287
97 111 129 149
125 144 166 192
139 160 185 214
145 168 194 224
1/0 2/0 3/0 4/0
250 300 350 400 500
212 237 261 281 321
274 306 337 263 416
305 341 377 406 465
320 357 394 425 487
166 186 205 222 255
214 240 265 287 330
239 268 296 317 368
250 280 309 334 385
250 300 350 400 500
600 700 750 800 900 1000
354 387 404 415 438 461
459 502 523 539 570 601
513 562 586 604 639 674
538 589 615 633 670 707
284 306 328 339 362 385
368 405 424 439 469 499
410 462 473 490 514 558
429 473 495 513 548 584
600 700 750 800 900 1000
Correction Factorsc Ambient Temp. (°C) 21–25 26–30 31–35 36–40 41–45 46–50 51–55 56–60 61–70 71–80
Ambient Temp. (°F) 1.32 1.22 1.12 1.00 0.87 0.71 0.50 — — —
1.20 1.13 1.07 1.00 0.93 0.85 0.76 0.65 0.38 —
1.15 1.11 1.05 1.00 0.94 0.88 0.82 0.75 0.58 0.33
1.14 1.10 1.05 1.00 0.95 0.89 0.84 0.77 0.63 0.44
1.08 1.00 0.91 0.82 0.71 0.58 0.41 — — —
1.05 1.00 0.94 0.88 0.82 0.75 0.67 0.58 0.33 —
1.15 1.11 1.05 1.00 0.94 0.88 0.82 0.75 0.58 0.33
1.14 1.10 1.05 1.00 0.95 0.89 0.84 0.77 0.63 0.44
70–77 79–86 88–95 97–104 106–113 115–122 124–131 133–140 142–158 160–176
a
See NEC Table 310.13. See NEC Section 240.3(D). c For ambient temperatures other than 104°F (40°C), multiply the allowable ampacities by the appropriate factor. Source: NFPA 70-2002, National Electrical Code®. b
some other type of equipment failure. But, in fact, even when equipment failure is a proximate cause, nearly all fires involving electrically powered equipment stem from foreseeable or avoidable human error, such as the following.
Improper Installation Failure to follow manufacturer’s installation instructions or to observe all provisions of the NEC, including the workmanship
CHAPTER 1
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6–15
TABLE 6.1.8 Ampacities of Bare or Covered Conductors in Free Air, Based on 104°F (40°C) Ambient, 176°F (80°C) Total Conductor Temperature, 610 mm/s (2ft/s) Wind Velocity Copper Conductors Bare
AAC Aluminum Conductors Covered
Bare
Covered
AWG or kcmil
Amperes
AWG or kcmil
Amperes
AWG or kcmil
Amperes
AWG or kcmil
Amperes
8 6 4 2 1/0 2/0 3/0 4/0 250 300 500 750 1000 — — — — — — —
98 124 155 209 282 329 382 444 494 556 773 1000 1193 — — — — — — —
8 6 4 2 1/0 2/0 3/0 4/0 250 300 500 750 1000 — — — — — — —
103 130 163 219 297 344 401 466 519 584 812 1050 1253 — — — — — — —
8 6 4 2 1/0 2/0 3/0 4/0 266.8 336.4 397.5 477.0 556.5 636.0 795.0 954.0 1033.5 1272 1590 2000
76 96 121 163 220 255 297 346 403 468 522 588 650 709 819 920 968 1103 1267 1454
8 6 4 2 1/0 2/0 3/0 4/0 266.8 336.4 397.5 477.0 556.5 636.0 795.0 — 1033.5 1272 1590 2000
80 101 127 171 231 268 312 364 423 492 548 617 682 744 860 — 1017 1201 1381 1527
Notes: 1. This table is for Overhead Service and Feeder Drops. 2. AAC Aluminum Conductors are conductors which are All Aluminum 1350- H19 Conductors, not the AA-8000 Aluminum Alloy Conductors referenced in NEC, Section 310.14. Source: NFPA 70-2002, National Electrical Code®.
provisions, can result in equipment being installed in ways that will lead to overloading, damage to equipment, or excessive heating of nearby combustibles. Mismatching of wire gauge size with equipment wattage or overfusing (using a fuse of too high an amperage rating) are examples.
Lack of Maintenance Equipment wears out in service. An example is the deterioration of electrical insulation over time. Deterioration can accelerate due to improper installation, excessive heat, adverse environmental conditions, or physical damage. Even when equipment and systems are properly installed, aging can cause deterioration; therefore, periodic inspection and maintenance of electrical equipment should be performed.
Improper Use Listed equipment that is not installed in accordance with the manufacturer’s instruction for its intended use and for the conditions under which it is used can cause fires or injure personnel. Use of equipment listed for dry locations, but installed in damp or wet locations or general-purpose equipment installed in locations where flammable liquids are used can be sources of ignition. Cords installed in traffic areas or pinched against a wall
can be damaged and lead to overheat fires. Light bulbs with higher wattage than the fixture is rated for can overheat and ignite lamp shades. Many other examples exist.
Carelessness or Oversight Even momentary lapses of caution in the use of equipment can cause fires. Failure to turn off devices (e.g., space heaters) when no longer needed, dropping combustible objects into equipment, and draping combustible materials over operating equipment (e.g., clothes on a lamp) are all examples. Some special studies provide additional insights that go beyond the level of detail in Table 6.1.9, although no other sources of representative national fire statistics exist. These studies include the annual tabulations by the International Association of Electrical Inspectors (IAEI) of fire and shock incidents that come to their attention and the several field studies done by the U.S. Consumer Product Safety Commission (CPSC). These studies appear to support a few qualitative observations: • Many electrical cord fires involve extension cords, as opposed to lamp or other appliance power cords. This indicates that extension cords are probably overused as semipermanent extensions of building wiring systems.
6–16 SECTION 6 ■ Fire Prevention
TABLE 6.1.9 Structure Fires Due to Electrical Failure (Annual Average of 1994 through 1998 Reported Fires)
Equipment Involved in Ignition Heating Equipment Central heating unit Water heater Fixed space heater Portable space heater Cooking Equipment Stove Oven Portable cooking or warming unit Air-Conditioning or Refrigeration Equipment Central air-conditioning or refrigeration equipment Refrigerator Fixed local air-conditioning unit Portable air conditioning or refrigeration unit Electrical Distribution Equipment Fixed wiring Transformer Meter or meter box Power switch or overcurrent protection device (e.g., fuse, circuit breaker) Switch, receptacle, or outlet Light fixture, lampholder, ballast, or sign Cord or plug Lamp or light bulb Unclassified electrical distribution equipment Appliance or Tool Television, radio, or phonograph Dryer Washing machine Separate motor or generator Portable appliance designed to produce controlled heat (e.g., iron, electric blanket) Portable appliance not designed to produce controlled heat (e.g., can opener, electric razor) Unclassified appliance or equipment Special Equipment Electronic equipment (e.g., telephone, computer, x-ray) Other Vehicle No equipment involved Other known equipment involved Unknown equipment involved Total
Average Number of Fires per Year
TABLE 6.1.10 Structure Fires Originating with Specified Electrical Distribution Equipment (Annual Average of 1994 through 1998 Reported Fires)
Equipment Involved in Ignition 1,930 1,280 1,110 850
Average Number of Fires per Year
Fixed wiring Transformer Meter or meter box Power switch gear or overcurrent protection device (e.g., fire or circuit breaker) Switch, receptacle, or outlet Light fixture, lampholder, ballast, or sign Cord or plug Lamp or light bulb
17,800 1,100 1,300 3,000
940
Total
49,700
960 560 540
Notes: These are fires reported to U.S. municipal fire departments and so exclude fires reported only to federal or state agencies or industrial fire brigades. Statistics include a proportional share of fires with equipment involved in ignition unreported or unknown. Numbers rounded to nearest hundred. Source: Kimberly D. Rohr, The U.S. Home Product Report (Appliances and Equipment Involved in Fires), NFPA Fire and Analysis Division, Quincy, MA, January 2002.
1,970 910 600
15,030 750 890 2,520 4,430 4,890 6,360 740 3,370 1,440 2,310 750 690 1,120 550 2,500 620
450 9,770 5,270 5,580 81,670
Notes: These are fires reported to U.S. municipal fire departments and so exclude fires reported only to federal or state agencies or industrial fire brigades. Statistics include a proportional share of fires with ignition factors unknown or unreported. “Electrical failure” defined as Ignition Factor 54 (short circuit or ground fault) or 55 (other electrical failure). Numbers rounded to nearest ten. Sums may not equal totals because of rounding error. Individual types of equipment are shown if they accounted for at least 450 fires per year. Source: National estimates based on NFIRS and NFPA survey.
5,700 8,900 8,000 3,900
• Overcurrent protection device fires appear to involve circuit breakers more often than fuses, both overall and relative to the degree of use of each type of device. This is notable given that fuses are used primarily in much older homes, where deterioration due to age or damage due to system alterations would be more likely, and that fuses are more susceptible to tampering. • Color televisions pose a greater fire hazard than black-andwhite televisions due to differences in the energy usage of the two types.
CODES AND STANDARDS All electrical installations in the United States should be made, used, and maintained in accordance with the NEC and other National Fire Protection Association (NFPA) standards that apply in special situations, for example, NFPA 70E, Standard for Electrical Safety Requirements for Employee Workplaces; NFPA 79, Electrical Standard for Industrial Machinery; NFPA 75, Standard for the Protection of Electronic Computer/Data Processing Equipment; and NFPA 99, Standard for Health Care Facilities. There are also special standards for electrical installations on marine vessels, on aircraft, in hazardous (classified) locations, and in other locations.
National Electrical Code (ANSI/NFPA 70) The NEC provides for the practical safeguarding of persons and property from hazards arising from the use of electricity. The NEC was first issued under its present name in 1897. It is revised every three years by the National Electrical Code Committee.
CHAPTER 1
National Electrical Safety Code (ANSI C2) As interest increased in electrical safety in the United States, a need arose for a code to cover the practices of public utilities and others when installing and maintaining overhead and underground electric supply and communications lines. Accordingly, the first edition of the National Electrical Safety Code (NESC) was completed in 1916. This code is updated and published by the Institute of Electrical and Electronics Engineers (IEEE).
Canadian Electrical Code CSA International (CSA) sponsors and publishes the Canadian Electrical Code (CEC). This code establishes essential requirements and minimum standards for the installation and maintenance of electrical equipment in Canada. It can be adopted and enforced by electrical inspection departments throughout Canada and was prepared with due regard for the NEC and the NESC. Its several parts are the Canadian equivalent of the NEC, the NESC, and the standards of Underwriters Laboratories, Inc. (UL) in the United States. ®
The National Electrical Code Handbook Although not itself a code or standard that can have the force of law, the National Electrical Code® Handbook is a valuable resource in implementing provisions of the NEC. The NEC Handbook contains the entire text of the NEC, supplemented by comments, diagrams, examples,and illustrations that are intended to clarify and explain some of the intricate requirements of the NEC. The NEC Handbook is published by the NFPA; a new edition is published with each new edition of the NEC.
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Electrical Systems and Appliances
6–17
and construction. Other testing laboratories in the United States and Canada that test electric equipment include Factory Mutual Research Corporation (FMRC); U.S. Testing; Applied Research Laboratories; Dash, Straus, and Goodhue; and CSA. Some laboratories stipulate compliance with the NEC in testing equipment. (Where no published standards are available for special equipment, arrangements usually can be made with testing laboratories for field testing on an individual basis.)
BUILDING WIRING, DESIGN, AND PROTECTION This section contains information on various types of building wiring and electrical equipment, including panelboards and overcurrent protection; types of electric conductors; identification of conductors, terminals, and so on; how to calculate loads; and similar subjects.
Service Entrance Good practice requires that service entrance conductors comply in all respects with the detailed requirements of Article 230 of the NEC. Figure 6.1.1 provides typical arrangements of service entrance conductors. The basic requirement is that a building or other structure can be supplied by only one service. Where more than one service is allowed, however, a permanent plaque or directory that describes all the other services to the building and the area served by each is required to be installed at each service drop or lateral or at each service equipment location. This plaque or directory should be sufficiently durable to withstand the ambient environment.
Listed and Labeled Electrical Equipment Manufacturers Publications are available that list the names of companies making electric appliances and materials that have been listed or labeled by nationally recognized testing laboratories, such as UL, Intertek Testing Services, and other testing laboratories. Devices and materials in the product categories listed have been tested for actual field use in accordance with the NEC and against other American National Standards Institute (ANSI) safety standards. The lists are published so that the names of manufacturers of devices that meet test criteria may be readily obtained. UL publishes the Hazardous Location Equipment Directory, the Electrical Appliance and Utilization Equipment Directory, and the Electrical Construction Materials Directory. UL also publishes the Fire Resistance Directory, which includes a number of listed methods of protecting penetration of building assemblies, such as walls or floors. They are all published annually by UL with six-month supplements. Certain types of electrical equipment are covered in other testing laboratory directories, such as the Marine Products Directory. There are sections of the NEC that influence the design and construction of electric equipment. Most testing labs have complete published standards for most electric fittings, materials, and equipment, including specifications for performance under test conditions and in actual service and further details of design
(a)
(b)
FIGURE 6.1.1 (a) Two Sets of Service Entrance Conductors Tapped from One Service Drop, with Meters Mounted on Outside of Building; (b) Set of Main Service Entrance Conductors Connected to Service Drop and Carried through a Trough and through Four Sets of Subservice Entrance Conductors to Each Service Equipment, with Meters Mounted on Outside of Building
6–18 SECTION 6 ■ Fire Prevention
Where separate services are permitted, such as for fire pumps, emergency or legally required standby electrical systems, optional standby electrical systems, or parallel power production systems, six additional switches or circuit breakers are allowed, in addition to the six service disconnects normally allowed. The intent here is that a disruption of the main building service will not interfere with the operation of fire pump equipment, emergency or legally required standby electrical systems, optional standby electrical systems, or parallel power production systems. Special permission is required for the installation of more than one service. Expansion of buildings, shopping centers, or industrial plants often necessitates the addition of one or more new services. It may, for example, be impractical or impossible to install one service for an industrial plant with capacity requirements to compensate for any and all future load requirements. It is also impractical to run feeders for extremely long distances, because of high costs and voltage drop problems. More than one service is allowed for different characteristics, such as different voltages, frequencies, single-phase or three-phase services, or different utility rate schedules. For example, different service characteristics exist between a threewire, 120/240-V single-phase service and a three-phase, four-wire, 480Y/277-V service. For different rate schedules, a second service is allowed to supply a second meter for specific equipment, such as an electric water heater. Parallel underground conductors, 1/0 AWG or larger that are connected together at their supply end and at their load end are considered to be one service lateral. These conductors are permitted to supply up to six service disconnecting means installed at one location in a group, as required by NEC Section 230.71(A). All feeder and branch-circuit conductors must be separated from service conductors. Service conductors are not provided with overcurrent protection where they receive their supply; they are protected against overload conditions at their load end by the service disconnect fuses or circuit breakers. The amount of current that could be imposed upon feeder or branch circuit conductors, should they be in the same raceway and a fault occurs, would be much higher than the ampacity of the feeder or branchcircuit conductors. The NEC requires that means be provided for disconnecting all conductors in the building from the service entrance conductors. The object is to permit disconnection of all conductors of the service at that location with no more than six operations of the hand (Figure 6.1.2). This requirement applies to all of the service disconnecting means located, or grouped, in one place and each disconnect must be marked to indicate the load served. It does not include service disconnecting means for fire pumps, legally required standby services, or optional standby services, which the NEC recognizes as being separate services for specific purposes. These must be sufficiently remote from the one to six service disconnecting means for normal service to minimize the possibility of simultaneous interruption of supply to the building or structure. The disconnecting means can be either outside or inside the building served and must be at a readily accessible location nearest the point of entrance of the service entrance conductors. It cannot be in a bathroom. A remote control device may be used
Multiple disconnect devices & overcurrent protection used as service equipment
Feeders to specific loads or distribution panels One example: To load center panels in apt. house
FIGURE 6.1.2 Means
Typical Layout for Multiple Disconnecting
to actuate the service disconnecting means, if it is located in a readily accessible location. Service entrance conductors must be of sufficient size to carry the calculated load. No maximum distance is specified from the point of entrance of the service conductors to the service disconnecting means. The authority enforcing the NEC has the responsibility for, and is charged with, deciding how far inside the building the service entrance conductors are allowed to travel before reaching the main disconnecting means. The length of service entrance conductors should be kept to a minimum inside buildings, since power utilities provide limited overcurrent protection and, in the event of a “fault,” the service conductors could ignite nearby combustible materials. Some local jurisdictions have ordinances that allow service entrance conductors to run within the building up to a specified length to terminate at the disconnecting means. The authority having jurisdiction (AHJ) may permit service conductors to pass by fuel storage tanks or gas meters to permit the service disconnecting means to be located in a readily accessible location. However, if the authority judges the distance to be excessive, the disconnecting means may be required to be located on the outside of the building or near the building at a readily accessible location that is not necessarily nearest the point of entrance of the conductors. One set of service entrance conductors, either overhead or underground, is permitted to supply two to six service disconnecting means in lieu of a single main disconnect. A singleoccupancy building can have up to six disconnects for each set of service entrance conductors. Multiple-occupancy buildings (residential or other than residential) can be provided with one main service disconnect or up to six main disconnects for each set of service entrance conductors. Multiple-occupancy buildings may also have service entrance conductors run to each occupancy, with each such set of service entrance conductors having from one to six disconnects. Where service entrance conductors are routed outside the building, each set of service entrance conductors is permitted to supply not more than six disconnecting means at each occupancy of a multiple-occupancy building. Conductors are considered outside a building where installed under not less than 2 in. (50 mm) of concrete beneath a building or in a raceway encased by 2 in. (50 mm) of concrete or brick within a building. They are also considered outside the building where installed in a transformer vault (Figure 6.1.3).
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Electrical Systems and Appliances
Multiple occupancy building
6–19
Utility-owned service drop Service conductors
Concrete slab
Service conductors Service point
2 in. (50 mm)
Building service
Brick Fire pump service Concrete slab
Fire pump
FIGURE 6.1.3 Conductors Installed under Concrete beneath a Building or in a Raceway of Concrete or Brick within a Building
Service entrance conductors, overhead or underground, are the supply conductors between the point of connection to the service drop or service lateral conductors and the service equipment. Service equipment is intended to constitute the primary means of controling and disconnecting the electrical supply to the premises wiring system. At this point, an overcurrent device, which usually consists of circuit breakers or a set of fuses, is required to be installed in series with each ungrounded service conductor. The service overcurrent device will not protect the service conductors under conditions of short circuit or ground fault on the line side of the disconnect. A degree of protection under these overcurrent conditions is provided by the special requirements applicable to locating and physically protecting the service conductors. Figure 6.1.4 illustrates the wiring and components of a fire pump circuit designed to comply with the NEC and NFPA 20, Standard for the Installation of Stationary Pumps for Fire Protection. Note that the service head protects the conductors against the entrance of water and that the point of connection of the service entrance conductors is below the level of the service head. The pump motor represented is a 100-hp, 460-V, threephase, squirrel-cage induction type, and its full-load current, taken from NEC Table 430-150, is 124 A. The service conductors, feeder conductors, and branchcircuit conductors are sized for 125 percent of the motor’s fullload current rating (124 A at 125 percent 155 A). According to NEC Table 310.16, the appropriate copper wire size for 155 A is a 2/0 AWG, XHHW conductor, which has an allowable ampacity of 175 A; therefore, all the conductors would be sized at not less than 2/0 AWG, XHHW copper. Where the voltage drop at the controller under starting conditions exceeds 15 percent, conductors with an ampacity greater than 155 A are necessary. The locked-rotor current of the motors in the installations illustrated in Figure 6.1.4 is 725 A, derived from NEC Table 430.151(B). The power supply protection may consist of either fuses or circuit breakers sized to carry locked-rotor current. In either case, the next standard ampere rating for fuses or circuit breakers is 800 A. Most fire pumps rated 100-hp and over would require a disconnecting means rated at 1000 A or more. However, due to the emergency nature of their use, fire pumps are exempt from the following ground-fault provisions.
Main Separated from each other to minimize damage from a fire in the main service.
Utility-owned service drops Service conductors Service conductors Service point
Building service
Fire pump service Fire pump
Main Separated from each other to minimize damage from a fire in the main service.
FIGURE 6.1.4 Methods of Connecting Utility-Owned Service Drop Conductors to the Service Entrance Conductors Supplying the Building and Fire Pump Services
Ground-Fault Protection for Equipment (GFP) Ground-fault protection of equipment (GFP) should not be confused with ground-fault circuit-interrupter protection for personnel (GFCI). Ground-fault protection of equipment on services rated 1000 A or more, operating at 480Y/277 V, was first required in the 1971 NEC because of the unusually high number of burndowns that were reported for this type of service. Alternating current, due to its sine wave characteristics, can be a dangerous source of ignition that can ignite combustibles and start a fire. Where the voltage is greater than 250 V to ground, even though the voltage sine wave decreases to zero, the voltage
6–20 SECTION 6 ■ Fire Prevention
can cause a restrike of the arc, causing continuation of burning at the ground-fault location. Ground-fault protection of services will not protect the conductors on the supply side of the service disconnecting means, but is designed to provide protection from line-to-ground faults that occur on the load side of the service disconnecting means. An alternative to installing ground-fault protection may be to provide multiple disconnects rated less than 1000 A. For instance, up to six 800 A disconnecting means may be used, and, in this case, ground-fault protection would not be required. The second fine print note (FPN) in NEC Section 230.95(C) recognizes that ground-fault protection may be desirable at lesser amperages on solidly grounded systems for voltages exceeding 150 V to ground, but not exceeding 600 V phase-to-phase. The maximum setting for ground-fault sensors is 1200 A; however, there is no minimum, and it should be noted that setting at lower levels increases the likelihood of nuisance tripping. The NEC requirements place a restriction on fault currents greater than 3000 A and limit the duration of the fault to not more than 1 s. This will minimize the amount of damage done by an arcing ground fault, which is directly proportional to the time it is allowed to burn. Where interconnection is made between multiple-supply systems or multiple buildings, care should be taken to ensure that the interconnecting of different systems or buildings does not negate the proper ground-fault sensing by the ground-fault protection equipment. A careful engineering study should be made to ensure that fault currents do not take parallel paths back to the supply system, thereby bypassing the ground-fault detection device.
Installation of such devices serves to minimize damage to solidstate electronic equipment, since such equipment is very sensitive to voltage surges. Each lead-in from an outdoor antenna to a radio or television set or to an amateur radio transmitting station needs protection from lightning. Antenna discharge units should be installed to provide lightning protection for the equipment. Additional protection from power line surges or from connected communications equipment may also be desirable.
Grounding Requirements— Building Wiring Dangerous voltages that constitute a fire hazard and a personal injury (shock) hazard can be imposed on electric distribution systems and equipment by lightning, inadvertent contact between low-voltage conductors and a high-voltage primary system, breakdown of insulation in transformers, surface leakage due to dirt or moisture, or by a wire coming loose from its connection. Grounding one conductor of the electrical system and then grounding all exposed noncurrent-carrying metal parts of the electrical installation that might accidentally come in contact with an ungrounded circuit conductor ensures that a lowresistance path is provided for fault-current to actuate the fuse or circuit breaker. The fault current finds a path through the equipment grounding conductor and can cause the operation of an overcurrent device (fuse or circuit breaker) in the ungrounded circuit conductor, thereby eliminating the dangerous condition. The impedance of the fault path must be low enough to permit sufficient current flow to cause the overcurrent device to operate quickly.
Physical Protection Underground service conductors must be protected against physical damage (Figure 6.1.5). Tables 6.1.11 and 6.1.12 give minimum cover requirements for underground installations. (Cover is defined as the shortest distance in millimeters measured between a point on the top surface of any direct buried conductor, cable, conduit, or other raceway and the top surface of finished grade, concrete, or similar cover.) For circuits over 600 V, there are variations in burial depths shown in Table 6.1.12, under certain circumstances. For example, the burial depth beneath areas subject to vehicular traffic is 24 in. (600 mm). Under airport runways and adjacent areas, the burial depth must be a minimum of 18 in. (450 mm). Lesser burial depths are permitted where access is necessary, or where termination or splicing points are located.
Lightning (Surge) Arresters— Building Wiring Lightning and surge arresters are not required but may be used, particularly where buildings are supplied by an overhead service and where thunderstorms are prevalent in the area. (See NFPA 780, Standard for the Installation of Lightning Protection Systems). Surge arresters are required to be installed on electric and telephone services and on radio and television antenna lead-ins.
Protective sleeve Conduit (pipe) to protect conductors
8 ft (2.4 m) minimum required height of conduit
6 in.(152 mm) minimum below ground
FIGURE 6.1.5 Two Different Configurations Permitted for Connecting to Electric Utility-Owned Service Drops
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TABLE 6.1.11
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Electrical Systems and Appliances
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Minimum Cover Requirements, 0 to 600 V, Nominal, Burial in Inches (Millimeters) Type of Wiring Method or Circuit
Location of Wiring Method or Circuit All locations not specified below In trench below 2-in. (50-mm) thick concrete or equivalent Under a building
Under minimum of 4-in. (102-mm) thick concrete exterior slab with no vehicular traffic and the slab extending not less than 6 in. (152 mm) beyond the underground installation Under streets, highways, roads, alleys, driveways, and parking lots One- and two-family dwelling driveways and outdoor parking areas, and used only for dwelling-related purposes In or under airport runways, including adjacent areas where trespassing prohibited
Column 3 Nonmetallic Raceways Listed for Direct Burial without Concrete Encasement or Other Approved Raceways
Column 4 Residential Branch Circuits Rated 120 Volts or Less with GFCI Protection and Maximum Overcurrent Protection of 20 Amperes
Column 5 Circuits for Control of Irrigation and Landscape Lighting Limited to Not More than 30 Volts and Installed with Type UF or in Other Identified Cable or Raceway
Column 1 Direct Burial Cables or Conductors
Column 2 Rigid Metal Conduit or Intermediate Metal Conduit
in.
mm
in.
mm
in.
mm
in.
mm
in.
mm
24
600
6
150
18
450
12
300
6
150
18
450
6
150
12
300
6
50
6
50
0 0 (in raceway only) 18 450
0
0
0
0
4
100
4
100
0 0 (in raceway only) 6 150 (direct burial) 4 100 (in raceway)
0 0 (in raceway only) 6 150 (direct burial) 4 100 (in raceway)
24
600
24
600
24
600
24
600
24
500
18
450
18
450
18
450
12
300
18
450
18
450
18
450
18
450
18
450
18
450
Notes: 1. Raceways approved for burial only where concrete encased shall require concrete envelope not less than 2 in. (50 mm) thick. 2. Lesser depths shall be permitted where cables and conductors rise for terminations or splices or where access is otherwise required. 3. Where one of the wiring method types listed in columns 1–3 is used for one of the circuit types in columns 4 and 5, the shallower depth of burial shall be permitted. 4. Where solid rock is encountered, all wiring shall be installed in metal or nonmetallic raceway permitted for direct burial. The raceways shall be covered by a minimum of 2 in. (50 mm) of concrete extending down to rock. Source: NFPA 70-2002, National Electrical Code®.
6–22 SECTION 6 ■ Fire Prevention
TABLE 6.1.12
Over 600 V, Minimum Cover Requirements (4) Rigid Metal Conduit and Intermediate Metal Conduit
(1) Circuit Voltage
(2) Buried DirectCables in.
Over 600 V through 22 kV Over 22 kV through 40 kV Over 40 kV
mm
(3) Rigid Nonmetallic Conduit Approved for Direct Burial and Not under a Buildinga
(5) All Locations Not Otherwise Specified
(6) Under a Building (Including Rigid Nonmetallic Conduit Approved for Direct Burial)
(7) Under Minimum of 4-in. (102-mm) Thick Concrete Exterior Slab with No Vehicular Traffic and the Slab Extending Not Less than 6 in. (152 mm) Beyond the Underground Installation (Including Rigid Nonmetallic Conduit Approved for Direct Burial)
(8) Under Streets, Highways, Roads, Alleys, Driveways, and Parking Lots
(9) In or under Airport Runways, Including Adjacent Areas Where Trespassing Is Prohibited
in.
mm
in.
mm
in.
mm
in.
mm
in.
mm
in.
mm
30
750
18
450
6
150
0
0
0
0
24
600
18
450
36
900
24
600
6
150
0
0
0
0
24
600
18
450
42
1000
30
750
6
150
0
0
0
0
24
600
18
450
a
Listed by a qualified testing agency as suitable for direct burial without encasement. All other nonmetallic systems require 2 in. (50 mm) of concrete or equivalent above conduit in addition to above depth. Source: NFPA 70-2002, National Electrical Code®.
The metal enclosures of conductors (metal armor of cables, metal raceways, boxes, cabinets, and fittings) must be grounded. (Article 250 of the NEC contains general requirements for grounding electrical installations.) The NEC also requires grounding of exposed noncurrent-carrying metal parts of equipment likely to become energized, where the equipment is operated by persons standing on the ground or on metal surfaces, or where it is operated at more than 150 V to ground. In some cases, the metal frames of electrically heated appliances should also be grounded. The NEC also specifies grounding of cordand plug-connected appliances. These appliances include refrigerators, freezers, air conditioners, clothes washers and dryers, dishwashers, sump pumps, electric aquarium equipment, and portable hand-held motor-operated tools, for example, hedge clippers, lawn mowers, snow blowers, and wet scrubbers. Appliances may be exempt from grounding if equivalent protection via double insulation is provided. If available on the premises at each building or structure served, each item in (NEC) Section 250.52(A)(1) through (A)(6)
must be bonded together to form the grounding electrode system. Where none of these electrodes is available, one or more of the electrodes specified in (NEC) Section 250.52(A)(4) through (A)(7) must be used. A metal underground water pipe with at least 10 ft (3.0 m) of pipe in direct contact with the earth can be used as the grounding electrode (including any metal well casing effectively bonded to the pipe). Interior metal water piping more than 5 ft (1.5 m) from the point of entrance to the building is not allowed to be used as part of the grounding electrode system or as a conductor to interconnect electrodes that are part of the grounding electrode system. However, a metal underground water pipe grounding electrode must be supplemented by an additional electrode of the type specified in (NEC) Section 250.52(A)(2) through (A)(7), in the event that the metal water pipe is replaced by a nonmetallic pipe, thereby maintaining the integrity of the grounding electrode system. Electrodes permitted for grounding are located in the NEC, Section 250.52(A), and they are (1) metal underground water
CHAPTER 1
pipe, (2) metal frame of the building or structure, (3) concreteencased electrode, (4) ground ring, (5) rod and pipe electrode, (6) plate electrode, and (7) other local metal underground systems or structures. An example of a grounding electrode is shown in Figure 6.1.6. Piping should be inspected to ensure that there are no intervening insulating joints that might isolate it from the earth. Effective bonding jumpers must be provided around any insulated joints and sections and around any equipment that is likely to be disconnected for repairs or replacement. Figure 6.1.6 shows an electrical system service neutral conductor grounded by connection to a metal water pipe and supplemented with a driven ground rod. The metal parts of the service equipment are allowed to be grounded by bonding to the neutral (grounded) conductor. The service enclosure is bonded to the grounded neutral conductor at point “B.” This connection is often a removable strap or green-colored screw. The service raceway (conduit) is grounded through the metal of the panelboard. Since service equipment is not protected by an overcurrent device, a bonding jumper is one of the methods employed to ensure electrical continuity at service equipment; this electrical connection is indicated at “A.” The meter box on the line side of the service equipment is usually grounded by means of the neutral terminal being bonded directly to the meter box and would be required where service-entrance cable is used. The upper portion of the service raceway or cable is grounded through threaded connections to the meter box where metal conduit or electrical metallic tubing is used. The conduit between the meter and panelboard may be grounded by bonding to the
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Electrical Systems and Appliances
6–23
meter enclosure or bonding to the panelboard. The branch circuit equipment grounding conductor is connected to ground through the equipment grounding terminal block, which is grounded at point “C.” This connection is commonly the mounting screw for this terminal block. The grounding connection shown is an underground water piping system. The connection should be as required by the NEC.
Panelboards and Overcurrent Protection— Building Wiring and Equipment Panelboards. A panelboard consists of an assembly that may include switches, fuses, or circuit breakers that are mounted on copper or aluminum bus-bars, whose function is the control and protection of light, heat, or power circuits. The buses are mounted in a cabinet or cutout box, which may be placed in or on a wall and is accessible only from the front. The NEC does not allow a lighting and appliance branch circuit panelboard to have more than 42 overcurrent devices installed in any one cabinet or cutout box. Lighting and appliance panelboards are not allowed to have more than two main circuit breakers or two main sets of fuses to protect the buses in a lighting and branch-circuit panelboard (Figures 6.1.7 and 6.1.8). Figures 6.1.9 and 6.1.10 show exceptions to the general rule for individual protection of panelboards. The arrangement shown Figure 6.1.10 is acceptable only for the service to an existing individual residential occupancy where the panelboard was installed prior to application of the 1981 NEC requirements. Panelboards installed in wet locations need weatherproof cabinets and must be mounted so that there is at least ¼ in. (6 mm) of air space between the cabinet and the wall or other
Feeder Service raceway Meter
150 A
Service raceway Main circuit breaker
Service "LB" conduit body
Neutral terminal block (electrically insulated from enclosure except at "B")
Branch-circuit circuit breakers Nonmetallicsheathed cable Branch circuit conductors
A
B C
Water pipe
Equipment grounding conductor Equipment grounding terminal block
Additional supplemental electrode (may be located elsewhere)
FIGURE 6.1.6 Grounding at a Typical Small Service [ac, Single-Phase, Three-Wire (120/240 V)]
N
G
FIGURE 6.1.7 One Main Provided (Two Permitted). Grounding terminal block may not be required, depending on wiring system used.
6–24 SECTION 6 ■ Fire Prevention
Feeder Feeder
2-100A mains 200A panelboard
N G 125A device at distribution panelboard
125A panelboard
N
G
N
FIGURE 6.1.9 No Mains Required. Grounding terminal block may not be required, depending on wiring system used.
G
FIGURE 6.1.8 Two Mains Required. Grounding terminal block may not be required, depending on wiring system used.
supporting surface. Where located in corrosive atmospheres, equipment must be suitable for the conditions. Special requirements in Chapter 5 of the NEC govern installation of panelboards in hazardous (classified) locations. Overcurrent Protection. Conductors are provided with overcurrent protection to open the circuit, if the current is greater than the value that will cause the conductor’s temperature to exceed the temperature of its insulation. Equipment also needs overcurrent protection to minimize the effects of an electrical fault within the equipment, thereby reducing the amount of arcing and ejection of hot metal. No feature of an electrical installation deserves more careful attention and supervision. In general, overcurrent devices should be rated or set in accordance with the tables for conductor ampacity, as shown in Tables 6.1.1 through 6.1.8. They should be installed in each ungrounded conductor of each circuit and feeder, at the point where the conductor to be protected receives its supply. Fixture wires, cords, taps, motor circuits, remote-control circuits, and fire protective signaling circuits are covered in Articles 240, 430, 725, and 760 of the NEC.
Overcurrent Protective Devices The most commonly used overcurrent protective devices for feeders, circuits, and equipment are fuses and circuit breakers. (Overcurrent and undervoltage relays, and so on, are used on high-voltage, high-current systems.) Thermal motor running
G
N
FIGURE 6.1.10 One Service Circuit Breaker in Upper Section Serving as the Main for Lower Section Buses Supplying Branch Circuits
overload sensing devices are not considered to be overcurrent protection but are used in the same manner. Plug Fuses. There are two basic types of plug fuses: (1) the ordinary Edison-base type and (2) Type S. Either of these may incorporate time delay. An Edison-base fuseholder will take an Edison-base fuse of any size up to a maximum 30 A rating. Plug fuses of the Edison-base type are allowed only for replacements in existing installations where there is no evidence of tampering.
Time-Delay Plug Fuses. Whether of Type S or Edison-base design, time-delay fuses permit short-time current surges, such as motor starting currents, without interruption of the circuit. These momentary surges are harmless unless repeated a number of times at short intervals. This makes it possible to use Type S fuses in sizes small enough to give better protection than a nontime-delay type, which must be oversized to allow for such surges. In the case of a short circuit or a high-current fault, however, the time-delay type will operate and open the circuit as rapidly or even more rapidly than the non-time-delay type. Some representative plug fuses are shown in Figures 6.1.11, 6.1.12, and 6.1.13. The time-lag type of fuse shown in Figure 6.1.13 is acceptable but not required by the NEC. These fuses have been designed to minimize tampering or bridging. The NEC specifies that fuseholders for plug fuses of 30 A or less must not be used unless they are designed to accept a Type S fuse or to accept a Type S fuse through use of an adapter. Cartridge Fuses. Cartridge fuses are of both the time-delay and the non-time-delay types. They are also of the one-time and the renewable link types. When a one-time fuse opens, the en-
Electrical Systems and Appliances
6–25
U nd erwrite La bI nspected
BUS
r's
The Type S fuse is designed to minimize tampering or bridging. Adapters are available that fit the Edison-base fuseholders and that, once properly installed, cannot be removed without damaging the fuseholder. The adapters are designed to prevent the use of Edison-base fuses in the fuseholder and to prevent the use of a higher rated Type S fuse in an adapter designed for a lower rating. They also prevent the use of pennies and other common bypassing schemes.
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...
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S Fustat Fus
e
FIGURE 6.1.13 Type S Nonrenewable Fuse (Source: Cooper Bussman)
tire fuse must be replaced. But when a renewable link fuse opens, the fuse link can be replaced inside the same cartridge unless the cartridge has also been damaged. Renewable link fuses have two disadvantages: (1) the links can be doubled, tripled, and so on, thereby defeating their purpose and usefulness, and (2) the links, on replacement, can be left with loose connections. Several representative cartridge fuses are shown in Figures 6.1.14 and 6.1.15.
(a)
(b) BUSS Un sdkfii
ie
Un sdkfii
ie
W FU S E
(c)
FIGURE 6.1.14 Three Types of Cartridge Fuses: (a) Ordinary Dropout Link Renewable Fuse; (b) Super-Lag Renewable Fuse; (c) One-Time Fuse (Source: Cooper Bussman) FIGURE 6.1.11 Typical Edison-Base Nonrenewable, Single-Element Fuse (Source: Cooper Bussman)
FUSETRON
T L ELEMDEUA NT FUSE -
FIGURE 6.1.12 Edison-Base Nonrenewable, DualElement Fuse. (Source: Cooper Bussman)
FIGURE 6.1.15 A Fusetron Cartridge-Type Fuse (Source: Cooper Bussman)
6–26 SECTION 6 ■ Fire Prevention
Circuit Breakers. There are two basic types of breakers: (1) adjustable trip and (2) nonadjustable trip. The adjustable-trip type may be of either the air- or oil-immersed type. The setting of the trip point is adjustable between a minimum and a maximum range. This type is usually used only on large installations having qualified operators and maintenance personnel. They are designed to trip when the current reaches that of the setting. The nonadjustable-trip type comes in a molded case, making it extremely difficult or impossible to change its rating. A moldedcase breaker can be of the inverse-time thermal-magnetic type or of the magnetic-only inverse-time type. Inverse-time thermalmagnetic breakers consist of two elements: (1) an electromagnetic trip element that trips quickly on high fault current and (2) a bimetallic trip element that provides a time delay. Moldedcase circuit breakers are designed so that the current has to exceed the rating (as is also true with all types of fuses) before it will trip. Unless it is the thermally compensated type, high ambient temperatures can reduce the current required to trip the circuit breaker (or fuse). A representative nonadjustable circuit breaker is shown in Figure 6.1.16. Thermal Devices. These are not intended for protection against short circuits, but only for the protection of overload currents of a comparatively lower magnitude unless otherwise designed. An example is overload protection for a motor where short-circuit and ground-fault protection is provided by the branch-circuit fuses or circuit breakers and motor running overload protection is provided by the thermal relay. Another thermal device is the type used in recessed luminaires (lighting fixtures), which temporarily opens the circuit when the luminaire (fixture) exceeds a predetermined temperature. For detailed requirements for motors and other equipment, see Articles 410 and 430 of the NEC.
comparable impedance (Figure 6.1.17). Fuseholders for currentlimiting fuses are designed to make it difficult to install a noncurrent-limiting fuse.
Ground-Fault Circuit-Interrupters (GFCI) Circuit breakers and fuses open a circuit and stop the flow of electricity when the current flow exceeds their ratings. Lighting and receptacle circuits are usually rated 15 or 20 A. Under certain conditions, as little as 20 mA can kill a normal healthy adult; thus, the rating of lighting and receptacle circuits is high, relative to the amount of current that could kill a person. Ground-fault circuit-interrupters (GFCIs) are devices that sense when even a small amount of current passes to ground through any path other than the proper conductor. When this condition exists, the GFCI trips almost instantly, stopping all current flow in the circuit, including through a person who might be in contact with it. Simplicity of design is one reason for the reliability of the GFCI. Figure 6.1.18 shows a typical circuit arrangement of a GFCI for personnel protection. Figure 6.1.19 shows types of GFCI units and a GFCI tester.
Current-Limiting Overcurrent Protective Devices. These devices are provided in some installations where high current (more than 10,000 A) is available under short-circuit conditions. They are designed so that, when interrupting a specified current, they will consistently limit the short-circuit current in that circuit to a magnitude substantially less than that obtainable in the same circuit if the device were replaced with a solid conductor having
FIGURE 6.1.17 Class R Current-Limiting Fuses with Rejection Feature to Prohibit Installation of Non-CurrentLimiting Fuses (Source: Cooper Bussman)
Shunt trip coil Amplifier Circuit breaker Hot “incoming” line To load
Grounded “neutral” line
FIGURE 6.1.16 15-A, Single-Pole, 120-V Branch-Circuit Breaker (Source: Eaton’s Cutler-Hammer Business)
Sensing ring
FIGURE 6.1.18 Circuit Arrangement for a Typical GroundFault Circuit-Interrupter for Personnel Protection
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Electrical Systems and Appliances
6–27
Currently available GFCIs are set to operate when line-toground currents exceed 5 mA. Evaluation standards permit a differential of 4 to 6 mA. Even at trips of 5 mA, it should be clearly understood that the instantaneous current will be higher and any shock during the time the fault is being cleared will be uncomfortable. The key to the ground-fault circuit-interrupter is its time-current characteristic. Trip-out time is about 1/40 of a second (25 ms) when the fault reaches or exceeds 6 mA. There are two classes of GFCIs—Class A and Class B. The Class A GFCI trips at not more than 6 mA. The Class B GFCI trips when the current exceeds 20 mA and is for use only with swimming pool underwater lighting fixtures that were installed prior to local adoption of the 1965 edition of the NEC. The Class A GFCI is used where personnel protection against ground fault is required or desired. (a)
(b)
(c) FIGURE 6.1.19 (a) Portable Plug-in Type of GFCI; (b) Raintight GFCI with Open Neutral Protection for use on Line End of a Flexible Cord; (c) 15-A Duplex Receptacle with Integral GFCI that also Protects Downstream Loads (Source: Pass & Seymour/Legrand ®)
GFCIs at Construction Sites. All 125-V, single-phase, 15-, 20-, and 30-A receptacle outlets must have GFCI protection for personnel or an assured equipment grounding conductor program. Precautions must be taken to aid the efficient operation of GFCIs on construction sites. Most laboratory-tested 120-V appliances have 0.5 mA leakage or less under normal operating conditions. However, moisture and improper maintenance on portable handheld tools, which is common at construction sites, can create conditions under which GFCIs can be expected to trip. Flexible cords with standard attachment plug cap and connector, when dropped in water (e.g., puddles), can be expected to cause leakage currents of 100 to 300 mA or greater, far in excess of GFCI trip currents. Motors with dirty brushes, carbon tracking on commutators, or moisture in the windings contribute to leakage current. A commonsense approach to installing, using, and maintaining GFCI circuits goes a long way toward eliminating nuisance tripping at construction sites. (Actually, tripping under any of the conditions mentioned is not nuisance tripping, but merely a device performing its intended function.) Moisture is the major culprit in current leakage on wiring and equipment. Panelboards, receptacles, and cord caps and connectors intended for dry locations must not be subjected to wet conditions. GFCIs in Residential and Commercial Occupancies. The NEC requires ground-fault protection for personnel (i.e., a GFCI) on all 125-V, single-phase 15- and 20-A receptacles installed in the following locations in dwelling units: bathrooms, garages and accessory buildings that have a floor at or below grade level not intended as habitable rooms and limited to storage areas, work areas and areas of similar use, the outdoors, unfinished basements, crawl spaces that are at or below grade level, boathouses, receptacles that are installed to serve kitchen countertop surfaces, and receptacles that are located within 6 ft (1.8 m) of the outside edge of a wet-bar sink. A single or duplex receptacle does not need GFCI protection if (1) it is located within a dedicated space for an appliance that is not easily moved from one location to another and is cord-and plug-connected or (2) it is not readily accessible and supplied by a dedicated circuit for snow-melting or de-icing equipment. In other than dwelling units, receptacles that are installed must have GFCI protection for personnel in all bathrooms and rooftops.
6–28 SECTION 6 ■ Fire Prevention
All 125-V receptacles, whether of the parallel blade or twist locking type, that are located within 20 ft (6 m) of a swimming pool, fountain, or outdoor spa or hot tub are required to be GFCI protected. Where spas or hot tubs are installed indoors, receptacles that provide power to the spa or hot tub must be GFCI protected. Hydromassage bathtubs and their associated equipment are required to be GFCI protected, as well as any receptacles within 5 ft (1.5 m) of the tub. In addition, in all occupancy types, non-GFCI-protected receptacles that are replaced due to damage or other causes that were not previously required to be GFCI protected under previous NEC editions must be GFCI protected if the present NEC requires it.
Arc-Fault Circuit-Interrupters (AFCIs) Fixed wiring in homes accounted for 13,000 reported structure fires in 1998, with associated losses of 96 civilian deaths and 293 civilian injuries.1 As early as the mid- to late-1980s, when home wiring fires were averaging 17,000, with more than 150 deaths a year, the U.S. Consumer Product Safety Commission (CPSC) identified arc fault detection as a promising new technology. Since then, CPSC electrical engineers have tested arcfault circuit interrupters (AFCIs) and found these devices to be effective. An arc fault is an unintentional electrical discharge characterized by low and erratic current that is capable of igniting combustible materials. Although standard circuit breakers provide overload protection, short circuit protection, and (when specified) ground fault protection for personnel, they do not provide protection against potential fire hazards that can result from lowlevel arcing faults. An AFCI is a safety device that uses electronics to recognize the current and voltage characteristics of arcing faults and interrupts the circuit when the arcing fault occurs. The AFCI is expected to provide enhanced protection from fires resulting from these unsafe wiring conditions. AFCI technology was first used to protect the areas surrounding downed utility lines. Advances in electronic technology make arc fault protection available for use on 125-V, 15- or 20-A branch circuits. AFCIs are already recognized for their effectiveness in preventing fires. The current edition of the NEC requires AFCIs for bedroom circuits in new residential construction. Future editions of the NEC, updated every three years, could expand this coverage. Short Circuits and Arcing Faults. Short circuits, also known as faults, are usually high and rapid current flows. Conventional circuit protective devices quickly detect these short circuits. Arcing faults are characterized by low and erratic current flow. Due to these characteristics, arcing faults in damaged cords or cables can continue undetected by conventional circuit protective devices, thus creating hazardous situations such as ignition of nearby combustive materials. There are three types of arc faults: • A parallel arc fault is an arc resulting from direct contact of two conductors with opposite polarity (e.g., damaged extension cord).
• A ground arc fault is an arc between a single conductor and ground (e.g, improperly installed wall receptacle). • A series arc fault is an arc across the break in a single conductor (e.g., cable pierced by a nail). Arcing can occur and lead to fire in these and the following common situations: • Deterioration of the insulation due to aging • Extension cords caught in a doorjamb or crimped between a piece of furniture and a wall • Deterioration of the cord’s insulation by exposure to sunlight or a hot air duct • Frayed appliance extension cords • Appliances where the insulation of the internal wires are impaired • Appliance wire damaged by constant use, bending, and abuse • Wire stapled too tightly against a stud, severing or damaging insulation • Overheated cords or wires • Exposed stranded wiring on an old style plug caps, including frayed and loose wiring • Receptacles that have loose connections When unwanted arcing occurs, it generates high temperatures that can ignite nearby combustibles such as wood, paper, and carpets. The AFCI uses unique current sensing circuitry to discriminate between normal and unwanted arcing conditions. Once an unwanted arcing condition is detected, the control circuitry in the AFCI trips the internal contacts, thus de-energizing the circuit and reducing the potential for a fire to occur. An AFCI should not trip during normal arcing conditions, such as those that occur when a switch is opened or a plug is pulled from a receptacle. The AFCI circuit breaker provides protection for the branch circuit wiring as well as power cords, extension cords, and internal wiring of equipment. AFCIs can be installed in any single-pole 125-V, 15- or 20-A branch circuit and are currently available as built-in features to circuit breakers. In the near future, other types of devices with AFCI protection will be available. In homes equipped with conventional circuit breakers rather than fuses, an AFCI circuit breaker can be installed in the panel box in place of the breakers. Homes with fuses are limited to receptacle or portable-type AFCIs, which are expected to be available in the near future.
AFCI and GFCI Combination Devices The AFCI should not be confused with the ground fault circuit interrupter (GFCI). The GFCI is designed to protect people from severe or fatal electric shocks whereas the AFCI protects against fires caused by arcing faults. The GFCI also can protect against some electrical fires by detecting arcing and other faults to ground but cannot detect hazardous across-the-line arcing faults that can cause fires. Based on U.S. Consumer Products Safety Commission Reports, combination devices that include both AFCI and GFCI protection in one unit will become available soon.
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Electrical Systems and Appliances
6–29
Types of Wiring Methods and Materials The NEC recognizes a number of standard wiring methods, some of which are suitable for general use whereas others are suitable only for special purposes. In some localities, regulations restrict the use of some of the wiring methods recognized by the NEC. The most widely used wiring methods are rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit (IMC), electrical metallic tubing (EMT), metal-clad cable (MC), armored cable (AC; trade name: “BX”), nonmetallic sheathed cable (NM, NMC, NMS; trade name “Romex”), surface metal and nonmetallic raceways, wireways, busways, underfloor raceways, and cellular metal floor raceways (Figures 6.1.20 through 6.1.23.) In some areas of the country, flexible metal conduit (trade name: “Greenfield”) is used for complete wiring systems. None of these wiring methods should be used for either temporary or permanent work where they do not fully conform to NEC safety requirements.
FIGURE 6.1.22 Installation of a Typical Metal Raceway System Showing an All-Steel Baseboard and a Multi-Outlet System (Source: The Wiremold Co.)
Identification of Conductors, Terminals, Circuits, and Branch Circuits With few exceptions, all interior wiring systems have a grounded circuit conductor that is continuously identified throughout. The
FIGURE 6.1.20 Type UF Sheathed Cable. The insulated conductors are jacketed in parallel and the overall covering must be flame retardant, moisture resistant, fungus resistant, corrosion resistant, and suitable for direct burial in the earth.
FIGURE 6.1.23 Multioutlet Assembly Installed to Serve Countertop Appliances (Source: The Wiremold Co.)
FIGURE 6.1.21 Systems, Inc.)
Type AC Cable (Source: AFC Cable
identification for conductors of 6 AWG or smaller (except for Type MI cable) should consist of an outer white or natural gray colored insulation. Insulated conductors larger than 6 AWG should have similar identification or be identified by distinctive white markings at their terminations during installation. The grounded conductors of Type MI cable are also identified by distinctive markings at their terminations during installation.
6–30 SECTION 6 ■ Fire Prevention
In general, the terminals of electrical devices to which a grounded conductor is to be connected are identified by being made of metal substantially white in color, having a metallic plating substantially white in color, or having the word “white” located adjacent to the terminal. If the terminal is not visible, the conductor entrance hole may be colored white. In the case of screw-shell-type lampholders, the (white) terminal is the one that is connected to the screw shell. Where a terminal is provided for the connection of an equipment grounding conductor, it must be designated by a green-colored hexagonal-head screw or nut, or, if the terminal is not visible, the conductor entrance hole must be marked with the word “green,” or the letters “G” or “GR,” or the grounding symbol ( ).
Lighting and Appliance Branch Circuits A branch circuit is that portion of a wiring system extending between the final overcurrent device protecting the circuit and the outlets on the circuit. Branch circuits are further defined as (1) a small-appliance branch circuit supplying one or more outlets to which appliances are to be connected that has no permanently connected luminaires (lighting fixtures) other than those that are part of the appliance, (2) a general-purpose branch circuit supplying two or more outlets for lighting and appliances, and (3) an individual branch circuit supplying only one utilization equipment. The equipment grounding conductor of a circuit can be bare or insulated. Where it is insulated, it must be identified by a continuous green color or green with one or more yellow stripes. Conductors larger than 6 AWG that are insulated or covered must be identified by stripping the insulation from the exposed length, coloring the insulation green, or covering it with green tape or green adhesive labels. Ungrounded conductors of different voltages are permitted to be of any color other than green, white, or natural gray. In some special applications, for example, isolated (ungrounded) power systems used in hospital operating rooms, the circuits are identified as follows: isolated conductor No. 1—orange; isolated conductor No. 2—brown. Lampholders, where connected to branch circuits having a rating in excess of 20 A, must be of the heavy-duty type with a rating of not less than 660 W if of the admedium type, and not less than 750 W if of any other type. Receptacles, when connected to circuits having two or more receptacles or outlets, must not supply loads greater than the values given in Table 6.1.13. They must not be supplied by circuits of ratings greater than the values listed in Table 6.1.14. Where larger than 50 A, the receptacle rating is not permitted to be less than the branch circuit rating, except for motor loads. Individual branch circuits may supply any loads. Branch circuits having two or more outlets may supply only loads as follows. Branch circuits rated at 15 and 20 A are for lighting units or appliances. The rating of any one cord- and plug-connected appliance must not exceed 80 percent of the branch circuit ampere rating. The total rating of fixed appliances must not exceed
TABLE 6.1.13 to Receptacle
Maximum Cord- and Plug-Connected Load
Circuit Rating (A)
Receptacle Rating (A)
Maximum Load (A)
15 or 20 20 30
15 20 30
12 16 24
Source: NFPA 70-2002, National Electrical Code®.
TABLE 6.1.14 Circuits
Receptacle Ratings for Various Size
Circuit Rating (A)
Receptacle Rating (A)
15 20 30 40 50
Not over 15 15 or 20 30 40 or 50 50
Source: NFPA 70-2002, National Electrical Code®.
50 percent of the branch circuit ampere rating when lighting units or other appliances are also supplied. Branch circuits rated at 40 and 50 A are permitted to supply fixed lighting units with heavy-duty lampholders, infrared heating units, or other utilization equipment in other than dwelling units. Branch circuits rated larger than 50 A may supply only nonlighting loads. Receptacle outlets in dwelling occupancies, including guest rooms in hotels and motels, should be installed in every kitchen, family room, dining room, living room, parlor, library, den, sunroom, bedroom, recreation room, or similar room or area of dwelling units. Insofar as practical, the outlets should be spaced equal distances apart (Figure 6.1.24). Receptacles should be installed so that no point along the floor line is more than 6 ft. (1.8 m), measured horizontally, from an outlet so as to permit a lamp or appliance equipped with a 6 ft. (1.8 m) cord to be located anywhere along the wall, in the room. In guest rooms of hotels, motels, and similar occupancies, the NEC allows the receptacles outlets to be located conveniently for permanent furniture layout, with at least two receptacle outlets in a readily accessible location. The total number of receptacle outlets cannot be less than the minimum number that would comply with the provisions of Section 210.52(A) of the NEC. Where receptacles are installed behind the bed, the receptacle must be located so that the bed does not contact any attachment plug that may be installed, or it must be provided with a suitable guard. (See the NEC Handbook for a better understanding of this requirement.) Most appliances and portable lamps are provided with flexible cords at least 6 ft (1.8 m) in length. Countertop appliances for use in the kitchen are usually supplied with 2 ft (600 mm) cords. Therefore, the NEC requires receptacles to be installed so that no point along the wall is more than 2 ft (600 mm),
Electrical Systems and Appliances
1 ft (300 mm) 2 ft 6 in. 2 ft (750 mm) (600 mm)
Refrigerator
GFCI
GFCI
DW
Fixed panel
2 ft (600 mm)
Kitchen
12 ft (3.7 m)
12 ft (3.7 m)
GFCI
2 ft (600 mm)
GFCI
4 ft (1.2 m)
Sink
GFCI
1 ft (300 mm)
1 ft (300 mm)
Floor receptacle
2 ft (600 mm)
6 ft (1.8 m)
6 ft (1.8 m)
2 ft (600 mm)
6–31
2 ft (600 mm)
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CHAPTER 1
2 ft (600 mm) GFCI GFCI
6 ft (1.8 m)
FIGURE 6.1.24 NEC Requirements on the Placement of Receptacles in Dwelling Occupancies
measured horizontally, from a receptacle. All receptacles that serve countertop spaces are required to be GFCI protected (Figure 6.1.25). Receptacles installed on 15- and 20-A branch circuits must be of the grounding type and must be effectively grounded. This does not mean that all cord- and plug-connected equipment must be of the grounded type. (See the current NEC for specific details on grounding.)
Calculation of Loads The methods specified in the NEC provide a basis for calculating the expected branch circuit and feeder loads and for determining the number of branch circuits required. Where in normal operation the maximum load of a branch circuit will continue for 3 hr or more, such as store or office lighting, the loads specified must be increased by 25 percent. The minimum unit lighting loads in volt-amperes (VA) per square foot for various types of occupancies are given in Article 220 of the NEC. In determining the load, open porches and garages in connection with dwelling occupancies are not included. Unfinished and unused spaces in dwellings need not be included unless adaptable for future use. For other than general illumination lighting, general-use receptacles, appliances, and loads other than motor loads, the following minimum unit load should be included for each outlet:
2 ft (600 mm)
GFCI
4 ft (1.2 m)
GFCI
4 ft (1.2 m)
6 ft (1.8 m)
12 ft (3.7 m)
GFCI
2 ft (600 mm)
1 ft (300 mm)
4 ft (1.2 m)
FIGURE 6.1.25 NEC Requirements on the Placement of Receptacles at Countertops and Islands in Kitchens and Dining Areas of Dwelling Units
1. Outlets supplying specific appliances and other loads—ampere rating of appliance or load served 2. Outlets supplying heavy-duty lampholders—600 VA 3. Other outlets—180 VA (This does not apply to the smallappliance branch circuit.)
Feeder Loads Feeder conductors must have sufficient ampacity to supply the load served. The computed load of a feeder must not be less than the sum of all branch-circuit loads supplied by the feeder, subject to the demand factor provisions of the NEC. Tables of demand factors for general illumination, electric ranges and other cooking appliances, and for clothes dryers are found in the NEC. Table 6.1.15 lists the demand factors that may be applied to that portion of the total feeder load computed for general illumination. An optional method of calculating the load for a single dwelling unit served by a 120/240 V or 208/120 V-system, with feeder or service conductors rated 100 A or greater, is to use the percentage values provided in Table 6.1.16. Examples of branch circuit and feeder calculations for other buildings and occupancies are given in Annex D of the NEC.
6–32 SECTION 6 ■ Fire Prevention
TABLE 6.1.15
Lighting Load Feeder Demand Factors Portion of Lighting Load to which Demand Factor Applies (VA)
Demand Factor Percent
Dwelling Units
First 3000 or less at From 3001 to 120,000 at Remainder over 120,000 at
100 35 25
Hospitalsa
First 50,000 or less at Remainder over 50,000 at
40 20
Hotels and Motels— Including Apartment Houses without Provision for Cooking by Tenantsa
First 20,000 or less at From 20,001 to 100,000 at Remainder over 100,000 at
50 40 30
Warehouses (Storage)
First 12,500 or less at Remainder over 12,500 at
100 50
All Others
Total volt-amperes
100
Type of Occupancy
General Lighting Load: 1500 ft2 at 3 VA per ft2 4500 VA. Number of Branch Circuits Required General Lighting Load: 4500 120 37.5 A; 37.5 15 2.5 or three 15-A, 2-wire circuits; or two 20-A 2-wire circuits.
a
The demand factors of this table shall not apply to the computed load of feeders to areas in hospitals, hotels, and motels where the entire lighting is likely to be used at one time, as in operating rooms, ballrooms, or dining rooms. Source: NFPA 70-2002, National Electrical Code®.
TABLE 6.1.16 Dwelling Unit
per ft2. For receptacle outlets in other than dwelling units, each single or multiple receptacle on a single yoke or strap is considered at not less than 180 VA. An example from the NEC of how to calculate the load in a single-family dwelling is presented to illustrate the principles involved. For a dwelling that has a floor area of 1500 ft2 (457 m2) (exclusive of an unoccupied cellar, unfinished attic, and open porches), a 12-kW range, and 5-kW clothes dryer, the load may be computed as follows:
Optional Calculation for One-Family
Largest of the following five selections (1) 100 percent of the nameplate rating(s) of the air conditioning and cooling, including heat pump compressors. (2) 100 percent of the nameplate ratings of electrical thermal storage and other heating systems where the usual load is expected to be continuous at the full nameplate value. Systems qualifying under this selection must not be figured under any other selection in this table. (3) 65 percent of the nameplate rating(s) of the central electric space heating including integral supplemental heating in heat pumps. (4) 65 percent of the nameplate rating(s) of electric space heating if less than four separately controlled units. (5) 40 percent of the nameplate rating(s) of electric space heating of four or more separately controlled units. Plus: 100 percent of the first 10 kVA of all other load. 40 percent of the remainder of all other load. Source: NFPA 70-2002, National Electrical Code®.
These calculations are not applicable to receptacle outlets required by the NEC for dwelling units. The 20-A smallappliance branch circuits and laundry branch circuits in dwelling units are calculated at 1500 VA per circuit. Other receptacle outlets rated 20 A or less in dwelling units are considered part of the general lighting load, based on the area and calculated at 3 VA
Small-Appliance Circuit: Two 20-A, 2-wire circuits. Laundry Circuit: One 20-A, 2-wire circuit. Minimum Size Feeders Required Computed Load General Lighting 4500 VA Small-Appliance Load 3000 VA Laundry 1500 VA Total (without range and dryer) 9000 VA 3000 VA at 100 percent 3000 VA 9000 – 3000 6000 VA at 35 percent 2100 VA Net Computed (without range and dryer) 5100 VA Range Load 8000 VA Clothes Dryer 5000 VA Net Computed (with range and dryer) 18,100 VA For 120/240 V system feeders 18,100 240 75 A. Therefore, feeder size for total load may be selected on the basis of 75-A load. Net computed load exceeds 10 kVA, so service conductors must have a rating of 100 A.
Flexible Cords and Cables Flexible cords are made for various kinds of service, ranging from wiring for portable lamps to elevator cables. Article 400 of the NEC gives a description, the ampacities, and the intended use of the various flexible cords now available. The ampacity of flexible cords is limited by type and gauge of wire used. They must not be overloaded nor their size reduced where the gauge is intended for mechanical strength. Flexible cords are frequently subject to physical damage and rapid wear. Ground faults or short circuits may occur if the insulation is damaged and the resulting arc may ignite the insulation or nearby combustible material. Replacement of flexible cords as soon as they show damage or appreciable wear is of utmost importance. Under present labeling practices, only replacement nondetachable power supply cords; range and dryer power supply cords; and cord sets, such as extension cords, carry the label on the product itself. Formerly, the original cords and power supply cords were labeled, and some consumers may have thought a
CHAPTER 1
label on the cord of an electrical appliance signified the appliance itself was investigated for safety. Nondetachable cords on new appliances no longer carry a label, so the consumer cannot be misled into assuming that the appliance itself has been tested, which may not be the case. Flexible cords are not considered by the NEC as a wiring method. They are covered in Chapter 4 of the NEC, “Equipment for General Use.” Flexible cords, including extension cords, are not acceptable as a substitute for the fixed wiring of a structure, but they are acceptable for use in extending the length of a cord on a portable lamp or on cord- and plug-connected appliances. The appliance should be used in accordance with any instructions included with the listing or labeling and the flexible cord itself should be used in accordance with Article 400 of the NEC. Flexible cords are not limited solely to “temporary wiring.”
Switches Switches are required for the control of lights and appliances and as the disconnecting means for motors and their controllers. Switches may be of either the air-break or the oil-break type. In the oil-break type, the interrupting device is immersed in oil. A chief fire hazard in switches is the arcing produced when the switch is opened. This hazard is somewhat greater with oilbreak switches. If operated much beyond their rated capacity or if the condition of the oil is poor or its level is not properly maintained, the arc can vaporize the oil, rupture the case, and cause a fire. However, the amount of oil is comparatively small (except in high-voltage equipment) and these switches present no hazard if properly used and maintained.
ELECTRICAL HOUSEHOLD APPLIANCES Electric Heating Equipment Electric heating equipment is used widely and it is important that all such devices be tested and listed by qualified electrical testing laboratories. Some fixed spaceheating equipment covered in Article 424 of the NEC is acceptable for installation in direct contact with combustible material. Baseboard heaters, for example, has been tested and found to incorporate suitable safeguards against fire hazards that might result from contact with draperies, furniture, carpeting, bedding, and so on, although discoloration or scorching (but no glowing embers or flaming) is possible on adjacent materials. Other electric air heaters, however, may present fire hazards if they come in contact with combustible materials or if they are covered or blocked in any manner. Space heating systems must not be installed where exposed to severe physical damage unless adequately protected, nor in damp or wet locations unless approved for such locations. A heater installed in an air duct or plenum must be of a type suitable for that purpose. Article 424 of the NEC covers installation of heaters for ducts and plenums and such items as airflow reliability, problems of condensation, fan circuit interlock, limit controls, and location of disconnecting means. NFPA 90B, Standard for the Installation of Warm Air Heating and Air Conditioning Systems, also contains details on central systems.
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Electrical Systems and Appliances
6–33
Electric Ranges, Wall-Mounted Ovens, and Counter-Mounted Cooking Units Each of these devices needs a means for disconnection from all ungrounded conductors of the supply circuit. A separable connector or a plug and receptacle may serve as the disconnecting means for free-standing household ranges. A plug and receptacle connection at the rear base of the range, if accessible from the front by removal of a drawer, is considered satisfactory. Grounding requirements for ranges are covered in Article 250 of the NEC. In new installations, the grounded conductor (neutral) is not allowed as a means of grounding the frame of an electric range or counter-mounted cooking unit. Therefore, the flexible power cord must contain four conductors, and a four-blade plug. Where there is an existing branch circuit containing only three conductors supplying a three-wire receptacle, the grounded conductor (neutral) is allowed to be used for grounding the frame of the appliance. The NEC gives the methods for calculating feeder loads for household electric ranges and other cooking appliances.
Refrigerators Fire problems with refrigerators can include deterioration in service of the fractional horsepower motors used and the possibility of overheating. Refrigerant coils and motors are susceptible to accumulations of lint and oily deposits, so cleanliness is a primary consideration in fire prevention. New devices have sealed motors not requiring oiling or maintenance, but overheating can result from improper use or inefficient cooling of the refrigerant due to coil dirt or damage. Ordinary household or commercial refrigerators must not be used to store flammable liquids. [Refrigerators listed for use in Class I hazardous (classified) locations and for flammable materials storage in laboratories, in accordance with Chapter 10 of NFPA 99 and NFPA 45, Standard on Fire Protection for Laboratories Using Chemicals, are available.] Exposed noncurrent-carrying metal parts of refrigerators and freezers that are likely to become energized need to be grounded under provisions of the NEC.
Room Air-Conditioning Units Room air-conditioning units have the same fire hazards as other motor-operated appliances. The exposed noncurrent-carrying metal parts must be grounded as required by Article 250 of the NEC.
Incandescent Lamps Because incandescent lamps produce considerable heat, they inherently possess a fire hazard and can ignite combustible material in contact with them. Under normal conditions, with the lamp in an approved lampholder and the fixture properly guarded, the heating hazard is negligible, but ignition of combustible material may result if lamps are surrounded by or laid on such combustible material. Table 6.1.17 presents information on surface and base temperatures of standard lamps in open sockets. The temperature measurements are all taken at an ambient temperature of 77°F (25°C). In most instances where lamps are incorporated in various kinds of lighting equipment, the ambient temperature at which the lamps operate is higher;
TABLE 6.1.17 General Service Lamps for 115-, 120-, and 125-V Circuits (Will Operate in Any Position, but Lumen Maintenance Is Best for 40 to 1500 W when Burned Vertically Base-Up)a
Watts 10 15 25 40 40 50 60
6–34
75 100 100f 100 100f 150 150 150 150 200 200
Bulb and Other Description
Base
Filament
Rated Average Life (hr)
Maximum Overall Length [in. (mm)]
Average Light Center Length [in. (mm)]
3½ (89) 3½ (89) 37/8 (98) 4¼ (108) 35/16 (59) 47/16 (113) 47/16 (113) 47/16 (113) 47/16 (113) 47/16 (113) 5¼ (133) 515/16 (151) 5½ (140) 5½ (140) 63/16 (157) 615/16 (176) 65/16 (160) 615/16 (176)
2½ (63) 23/8 (60) 2½ (63) 215/16 (75) 15/8 (41) 31/8 (79) 31/8 (79) 31/8 (79) 31/8 (79) 31/8 (79) 37/8 (98) 47/16 (113) 4 (102) 4 (102) 45/8 (117) 5¼ (133) 45/8 (117) 5¼ (133)
S-14 inside frosted or clear A-15 inside frosted A-19 inside frosted A-19 inside frosted and white S-11 clear
Med.
C-9
1500
Med.
C-9
2500
Med.
C-9
2500
Med.
C-9
1500
Intermed.
A-19 inside frosted A-19 inside frosted and whitee A-19 inside frosted and whitee A-19 inside frosted and whitee A-19 inside frosted and white A-21 inside frosted A-23 inside frosted or clear A-21 inside frosted A-21 white
Med.
CC-2V or C-7A CC-6
350 500 1000
Med.
CC-6
1000
Med.
CC-6
750
Med.
CC-8
750
Med.
CC-8
1000
Med.
CC-6
750
Med.
C-9
Med.
CC-8
750
Med.
CC-8
750
A-23 inside frosted or clear or white PS-25 clear or inside frosted A-23 inside frosted or white or clear PS-25 clear or inside frosted
Med.
CC-6
750
Med.
C-9
750
Med.
CC-8
750
Med.
CC-6
750
1000
Rated Initial Lumen (s per Wattc )
Lamp Lumen Depreciationd (percent)
80
8.0
89.0
—
126
8.4
83.0
110 (43) 260 (127) 570 (299) —
108 (42) 221 (105) 390 (199) —
230
9.2
79.0
455
11.4
87.5
477
11.9
—
680
13.6
—
255 (124) 275 (135) 300 (149) —
200 (93) 205 (96) 208 (98) —
860
14.3
93.0
1,180
15.7
92.0
1,740
17.4
90.5
1,680
16.8
—
194 (90) —
1,640
16.9
90.0
—
260 (143) —
1,480
14.8
—
2960
—
—
2,880
19.2
89.0
2930
—
—
2,790
18.6
89.0
2925
280 (138) 290 (143) 345 (174) —
210 (99) 210 (99) 225 (107) —
2,780
18.5
89.0
2,660
21.2
87.5
4,000
20.0
89.5
3,800
19.0
—
Approximate Initial Filament Temp. (K)
Max. Bare Bulb Temp. [°F (°C)]
2420
106 (41) —
106
— 2550 2650 2800 — 2790 2840 2905 — 2880
2910 2980 —
Base Temp.b [°F (°C)]
Approximate Initial Lumen (s)
TABLE 6.1.17
Watts 200 300 300 300 300 500 500
6–35
750 750 1000 1000 1500 a
Continued
Bulb and Other Description PS-30 clear or inside frosted PS-25 clear or inside frosted PS-30 clear or inside frosted PS-30 clear or inside frosted PS-35 clear or inside frosted PS-35 clear or inside frosted PS-40 clear or inside frosted PS-52 clear or inside frosted PS-52 clear or inside frosted PS-52 clear or inside frosted PS-52 clear or inside frosted PS-52 clear or inside frosted
Rated Average Life (hr)
Maximum Overall Length [in. (mm)]
Average Light Center Length [in. (mm)]
81/16 (205) 615/16 (110) 81/16 (205) 85/8 (219) 93/8 (238) 93/8 (238) 9¾ (248) 131/16 (332) 131/16 (332) 131/16 (332) 131/16 (332) 131/16 (332)
6 (152) 51/16 (132) 6 (152) 7 (178) 7 (178) 7 (178) 7 (178) 9½ (241) 9½ (241) 9½ (241) 9½ (241) 9½ (241)
Base
Filament
Med.
C-9
750
Med.
CC-8
750
Med.
C-9
750
Mog.
CC-8
1000
Mog.
C-9
1000
Mog.
CC-8
1000
Mog.
C-9
1000
Mog.
C-7A
1000
Mog.
CC-8 or 2CC-8 C-7A
1000
CC-8 or 2CC-8 C-7A
1000
Mog. Mog. Mog.
1000
1000
Lamp burning base up in ambient temperature of 77°F (25°C). At junction of base and bulb. c For 120-V lamps. d Percent initial light output at 70 percent of rated life. e Lumen and lumen per watt values of white lamps are generally lower than for inside frosted. f Used mainly in Canada. b
Base Temp.b [°F (°C)]
Approximate Initial Lumen (s)
Rated Initial Lumen (s per Wattc )
305 (152) 401 (205) 275 (135) —
210 (99) 234
3,700
18.5
85.0
6,360
21.2
87.5
175 (79) —
6,100
20.3
82.5
5,960
19.8
—
215 (102) 175 (79) 215 (102) —
5,860
19.6
86.0
10,600
21.2
89.0
10,140
20.3
—
2990
330 (166) 415 (213) 390 (199) —
15,660
20.9
—
3090
—
—
17,000
22.6
89.0
2995
480 (249) —
235 (113) —
21,800
21.8
—
23,600
23.6
89.0
510 (265)
265 (129)
34,000
22.6
78.0
Approximate Initial Filament Temp. (K)
Max. Bare Bulb Temp. [°F (°C)]
2925 3015 3000 — 2980 3050 2945
3110 3095
Lamp Lumen Depreciationd (percent)
6–36 SECTION 6 ■ Fire Prevention
thus, the surface temperatures of the bulbs are also higher. The bulb temperatures may be further increased if the lamp is in other than a vertical, base-up position. Figure 6.1.26 shows surface temperatures of 100-W A-19 and 500-W PS-35 lamps in various positions but, again, these temperatures were measured in an ambient temperature of 77°F (25°C); so where enclosed in fixtures, the temperatures will be higher. The older style conventional Christmas tree lamps of U.S. manufacture have approximate average bulb surface temperatures at the hottest spot of approximately 260°F (127°C) for the blue and green colors, and somewhat lower for the white, red, and yellow colors.* In clothes closets, an open, partially enclosed, pendant, or lampholder with incandescent lamp in a luminaire (fixture) is not permitted to be installed. In locations where there are flammable vapors or gases, combustible dusts, or readily ignitable fibers or flyings, lamps in fixtures specially approved for the location must be used. Luminaires (lighting fixtures) approved for Class I, Division 1 locations must be marked to indicate the maximum wattage of the lamps for which they are approved, and they must be protected against physical damage by a suitable guard or located beyond the area of potential damage. Fixed luminaires (lighting fixtures) in Class I, Division 2 locations must be protected from physical damage by a suitable guard or located out of the area of potential damage. Where there is the potential for sparks or hot metal falling from the lamps and igniting localized concentrations of flammable vapors or gases, suitable enclosures or other means must be provided. Where lamp size might be increased so that, under normal operating conditions, the surface temperature of the luminaire (fixture) could exceed 80 percent of the ignition temperature (°C) of the gas or vapor involved, the fixture must be of a type that has been tested for the marked temperature operating range.
Electric Discharge (Fluorescent) Lamps The operating temperature of a fluorescent tube is lower than that of the glass envelope of the incandescent lamp, but high voltage is often used to start the lamp. This requires the use of transformers, reactors, capacitors, and switches. The heat produced by this equipment must be taken into account, and the equipment properly safeguarded. Bulb temperatures on the surface of fluorescent lamps average between 100 and 110°F (38 and 43°C) over most of their length, since this is a requirement for efficient light production. There is a small area of higher bulb temperature directly above the cathode at each end of a fluorescent lamp that ranges from 120 to 250°F (49 to 121°C), depending on the type involved. Where fluorescent lamps having an open circuit voltage of more than 300 V are installed in dwelling occupancies, they must have no exposed live parts when lamps are in place and when being inserted or removed.
*The data in Table 6.1.16 was extracted from the IES Handbook, 5th ed., of the Illuminating Engineering Society, and is used here with the permission of the Society. The reader is asked to keep in mind the above comments in the text regarding use of data in Table 6.1.17 and Figure 6.1.26.
588 (309) 291 (144)
446 (230) 477 (247)
460 (238) 194 (90)
214 (101)
293 (145) 131 (55)
280 (138)
151 (66)
271 (133) 172 (78)
(a)
228 (109)
495 (251)
126 (52)
208 (98)
162 (72)
113 (45) 113 (45)
109 (43)
129 (54) 124 (51)
239 (115)
160 (71) 540 (282) 298 (148)
191 (88) 300 (149)
241 (116)
291 (144) 117 (47)
127 (52) 120 (49)
138 (59) 181 (83)
198 (92) 460 (238)
536 (280)
151 (66) 167 (75) 174 (79) 414 (212)
217 (103)
239 (115)
(b) 203 (95)
FIGURE 6.1.26 Surface Temperatures of Lamps in Various Positions: (a) 100-W, A-19 Lamp; (b) 500-W, PS-35 Lamp
Extreme care is required in mounting fluorescent lamp luminaires (fixtures) containing a ballast on combustible, lowdensity, cellulose fiberboard. In this case, low-density refers to combustible low-density, cellulose fiberboard tiles or sheets that have a density of 20 lb/ft3 (320 kg/m3) or less, and are formed of bonded plant material. It does not include solid or laminated wood or fiberboard that has a density in excess of 20 lb/ft3 (320 kg/m3). Luminaires (fixtures) containing ballasts should not be mounted in contact with low-density, cellulose fiberboard, unless specifically listed by a qualified electrical testing laboratory for mounting in that manner. If not so listed, they should be spaced not less than 1½ in. (38 mm) from the surface of the combustible material. A principal hazard is ignition of the fiberboard, which under some conditions can ignite at relatively low temperatures. Integral thermal ballast protection is now provided for fluorescent luminaires (fixtures) installed indoors to protect against ballast overheating as a result of failure of capacitors, lamps, ballast winding shorts, and so on.
Electric (High-Intensity) Discharge Lamps The operating temperature of a high-intensity discharge lamp, such as a mercury vapor lamp, is usually much higher than the operating temperature of either Edison-base incandescent or fluorescent lamps, exceeding 550°F (288°C) in some sizes. Extreme care is therefore necessary where such lamps are encountered to prevent their contacting combustible material. Although such lamps were at one time used primarily for street lighting and other outdoor lighting applications, their higher lighting efficiency and new designs providing good color correction and lower wattages have resulted in increased use indoors. Such lamps usually require ballasts (transformers), sometimes capacitors, and are designed to fit into Edison-base lampholders. There are, however, self-ballasted lamps that can be substituted directly for incandescent lamps. High-intensity discharge lamps
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Electrical Systems and Appliances
6–37
should be used only in luminaires (fixtures) listed by a qualified electrical testing laboratory for their use, as indicated on the luminaire (fixture).
Portable Handlamps Metal-shell, paper-lined lampholders are not designed to be used as portable handlamps. A fire hazard may result from a defective or worn cord or from the breaking of a lamp. A personnel hazard may result from personal contact with bare spots on the cord or by contact with a live metal lamp socket. Portable handlamps must have a handle of molded composition or other insulating material and a substantial guard attached to the lampholder or handle. Metallic guards must be grounded by means of an equipment grounding conductor that runs with the circuit conductors within the power-supply cord. Portable handlamps are not required to be grounded where supplied through an isolating transformer with an ungrounded secondary of not over 50 V. Portable handlamps used in hazardous (classified) locations must be suitable for the purpose (Figure 6.1.27).
Home Entertainment Equipment Outdoor antennas and lead-in conductors must be of corrosionresistant material and securely supported (Figure 6.1.28). They must not be attached to poles or similar structures carrying electric light or power wires or trolley wires, nor should they cross over or be near electric light or power circuits (to avoid accidental contact). Where antennas or lead-in conductors are in proximity of outdoor electric light or power circuits operating at less than 250 V, they must have at least 2 ft (600 mm) of clearance, and at 250 V or more, 10 ft (3.0 m) clearance. Lead-in conductors also must be kept at least 6 ft (1.8 m) from any conductor
(b) FIGURE 6.1.27 (b) Portable Hand Lamp with Grounded Metal Guard and Reflector and Swivel-Type Hook (Source: Daniel Woodhead Co.)
(a) FIGURE 6.1.27 (a) Explosionproof Hand Lamp for Use in Class I Locations (Source: Appleton Electric LLC, EGS Electrical Group)
FIGURE 6.1.28 Dangerous Arrangement of a Lightly Supported Television Antenna in Proximity of Power Lines
6–38 SECTION 6 ■ Fire Prevention
forming a part of a lightning protection system. The metal sheath of the coaxial cable used for cable television systems must be grounded in accordance with Article 820 of the NEC, to avoid electric shock and fire hazards. The sheath must be electrically bonded to the electrical system power ground. Where a separate ground rod is installed for the cable television ground, it must be bonded to the electrical system grounding electrode system or to the electrical service equipment. Masts and metal structures supporting antennas must be well grounded, and each conductor of a lead-in from an outdoor antenna must be protected by an approved antenna discharge unit. Metal masts on buildings are required by NFPA 780 to be bonded to the nearest lightning conductor (where available). This is normally done with standard lightning conductors. Radio interference eliminators and noise suppressors connected to power supply leads and devices, intended to permit an electric supply circuit to be used in lieu of an antenna, should be listed for the purpose by a qualified electrical testing laboratory. Operating television sets, even solid-state sets, can develop considerable heat, so most cabinets housing such equipment are provided with ventilation openings at the rear and bottom. It is important not to install television receivers so that the desired ventilation is cut off or significantly reduced (e.g., by recessing the set in a wall, bookcase, etc.), unless the receiver is designed for such use.
Stoddard solvent or perchloroethylene) and are normally labeled “Do Not Dry Clean.”
INDUSTRIAL AND COMMERCIAL EQUIPMENT Furnaces
These appliances are required to have a means for disconnecting all ungrounded conductors from the supply circuit. A separable cord connector or an attachment plug and receptacle may serve as the disconnecting means. Electric clothes washers and dryers and similar appliances are usually installed within reach of a person who can make contact with a grounded surface or object. Consequently, the exposed, noncurrent-carrying metal parts of these machines must be grounded to remove the danger of electric shock. Accumulations of lint in dryers and in lint traps also present a potential fire hazard if not periodically cleaned.
Industrial furnaces generally employ transformers, which may be either the dry type, askarel-insulated type, oil-insulated type, or insulated with a less flammable fluid (e.g., dimethyl silicone). Although new transformers are no longer made with askarel (a material containing polychlorinated biphenyl, or PCB), many such transformers are still in use. The NEC requires oil-insulated transformers of a total rating exceeding 75 kVA to be located in a fireresistant vault. Electric furnace transformers that have a total rating not exceeding 75 kVA are permitted to be installed without a vault in a building or room of fire-resistant construction, provided suitable arrangements are made to prevent a fire involving the transformer oil from spreading to other combustible material. Oil-filled circuit breakers that control arc furnaces are subject to unusually severe duty and, unless frequently inspected and properly maintained, may fail with disastrous results. Circuit breakers on circuits operated at more than 600 V and which are used to control oil-filled transformers must be located outside the transformer vaults. Vents on high-voltage circuit breakers must be piped outdoors. Electric arc furnace circuits, due to the nature of the operation, are also subject to high surge voltages that can cause failure of the arc circuit breakers used. In these cases, shunt capacitors are installed in the circuit to prevent these high-voltage surges. Inductive and dielectric heat-generating equipment employing high-frequency alternating currents is used in many heat-treating processes. To eliminate both the personnel hazards and fire hazards of such equipment, construction and installation should comply with the special requirements of the NEC. Other hazards of electric furnaces are similar to those of furnaces employing other means of heating.
Flatirons
Motors
These appliances intended for use in residences are required by the NEC to be equipped with approved means to limit the temperature. Even with the widespread use of automatic irons, some hazard still remains because satisfactory ironing of many fabrics requires a degree of heat sufficient to cause ignition if the iron is left in contact with some combustible materials for a considerable period of time.
Ignition of motor insulation or nearby combustible material can be caused by sparks or arcs when the motor winding short circuits or grounds or when brushes operate improperly. Bearings may overheat because of improper lubrication and sometimes excessive bearing wear allows the rotor to rub on the stator. The individual drives of machines of many different types sometimes make it necessary to install motors in locations and under conditions that are injurious to motor insulation. Dust that can conduct electricity may be deposited on the insulation, or deposits of textile fibers, and so on, may prevent the normal dissipation of heat. Motors should be cleaned and lubricated regularly. All motor installations should comply with the requirements of the NEC, which includes special rules for motors in hazardous (classified) locations.
Clothes Washers and Dryers
Electrically Heated Pads and Bedding The user must be warned by means of a marking on the appliance and by instructions packed with it against the common possible abuses that would increase the fire or shock hazard. Because many fabrics readily absorb moisture, listed pads (unless of the waterproof type) are provided with moistureresistant envelopes. This envelope should be examined frequently for signs of deterioration. Blankets are normally designed so that they may be laundered; some cannot be dry cleaned (as with
Machine Tools The electrical equipment of a modern machine tool or plastics processing machine may vary from a simple single-motor drill
CHAPTER 1
press or extruder to a large complicated multimotor automatic machine involving highly complex control systems and equipment. This latter type is generally custom designed and factory wired. Machine tools incorporate many devices and safeguards to provide safety to life, safety from fire, reduction of machine lost time due to replacement of parts, safety to the machine itself, and safety to the work in process. NFPA 79 covers the specific electrical equipment, apparatus, and wiring furnished as a part of an industrial machine, starting at the electrical supply connection, provided that it is 600 V or less. The NEC contains requirements for general application, particularly for protection of several motors on one branch circuit. Electrical equipment is subject to damage by oil, metal chips, coolants, and moving parts. The fixed wiring to the machines specified in the NEC should generally be conductors in conduit, tubing, or Type MI cable. Exceptions are connections to continuously moving parts, which can be extra-flexible, multiconductor cable. For flexible connections where small or infrequent movement is involved, as at motor terminals, flexible metal conduit, liquid-tight flexible metal conduit, or liquid-tight flexible nonmetallic conduit is permitted.
Motor Control Center Rooms Automation of production machinery has greatly increased the use of motors and their related control circuits, resulting in grouping the motor control equipment in relatively large, compartmented metal enclosures. These are specially designed, factory-built equipment, commonly referred to as “motor control centers.” They are usually located in large rooms, sometimes referred to as “motor control center rooms.” Electrical failures or fires in motor control centers can result in the destruction of the equipment in many compartments of the control center due to rapid temperature rise. A serious fire hazard can be created if multiconductor circuits are installed stacked one above the other in cable trays. Heat from arcing or a fire in the control center can raise the temperature in the control center room to a point where normally slowburning cables become readily combustible. A fire in such cables can shut down a process or an entire plant for weeks or months. The NEC covers the use and construction of cable trays, and should be strictly followed where this type of support is used. The number of motor control centers in one room should be limited or arranged so that exposure of a large number of circuits or equipment to any one fire is avoided. Motor control center rooms should be of noncombustible construction, with a roof or ceiling not readily weakened by a major electrical disturbance or fire. In addition to normal ventilation, the room should be provided with emergency ventilation for removal of heat and smoke in event of a severe fire. Suggested fire protection for motor control center rooms may consist of preaction sprinkler systems or fixed water spray protection to cover exposed cables, fire detectors to initiate an alarm at a central point in the event of abnormally high temperatures or smoke conditions, total flooding carbon dioxide or other gaseous agent system, portable Class C fire extinguishers located at each entrance to the control room, and small hose connections with suitable hose and adjustable spray nozzles readily available near the control room.
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Electrical Systems and Appliances
6–39
Switchboards Ideally, switchboards are installed in clean, dry locations. They should be under competent supervision and accessible only to qualified persons. Switchboards operating at voltages over 600 V must be provided with protection to avoid damage from condensation leaks and breaks in piping. Piping for fire suppression is allowed within the electrical room for the protection of the electrical installation. Where it is necessary to install a switchboard in a wet location or outside a building, the enclosure must be weatherproof. Ample space must be provided for maintenance operations, as stipulated in the NEC. Insulated conductors grouped within switchboards, as well as the instrument and control wiring, should have a listed flameretardant outer covering. Circuit breakers and switches must have ample ratings for the maximum loads and sufficient interrupting capacity for the maximum short-circuit currents. Contacts of switches and circuit breakers should be kept in good condition and the oil in oil circuit breakers renewed periodically and kept at the proper level.
Capacitors Capacitors may be insulated with a combustible or a nonflammable liquid. Capacitors containing more than 3 gal (11 L) of flammable liquid must be enclosed in vaults or outdoor fenced enclosures. These safeguards prevent persons from coming into accidental contact or bringing conducting materials into accidental contact with exposed energized parts, terminals, or buses. Capacitors must have a means of draining the stored energy, such as through a suitable resistance. The residual voltage of a capacitor must be able to be reduced to 50 V, nominal, or less, within 1 min after the capacitor is disconnected from the source of supply. The discharge circuit must be either permanently connected to the terminals of the capacitor or capacitor bank, or provided with automatic means of connecting it to the terminals of the capacitor bank on removal of voltage from the line. Manual means of switching or connecting the discharge circuit cannot be used. If no means were provided for draining off the charge stored in a capacitor after it is disconnected from the line, a severe shock might be received by a person servicing the equipment, or the equipment might be damaged by a short circuit.
Resistors and Reactors Except when installed in connection with switchboards or control panels whose locations are suitably guarded from physical damage and accidental contact with live parts, resistors should always be completely enclosed in properly ventilated metal boxes. A resistor is always a source of heat and, when mounted on a combustible wall, a thermal barrier should be required if the space between the resistors or reactors and any combustible material is less than 12 in (305 mm). Large reactors are commonly connected in series, with the main leads of large generators or the supply conductors from high-capacity network systems assisting in limiting the current delivered under short-circuit conditions. Small reactors are used with lightning arresters to offer a high impedance to the passage of a high-frequency lightning discharge and aid in directing the
6–40 SECTION 6 ■ Fire Prevention
discharge to ground. Another type of reactor, having an iron core and closely resembling a transformer, is used as a remotecontrol dimmer for stage lighting in some of the older installations. Reactors are sources of heat and therefore should be mounted in the same manner as resistors.
Motion Picture Projection Rooms The provisions of NEC Article 540 apply to motion picture projection rooms, motion picture projectors, and associated equipment of the professional and nonprofessional types using incandescent, carbon arc, xenon, or other light sources that develops hazardous gases, dust, or radiation. (For further information, see NFPA 40, Standard for the Storage and Handling of Cellulose Nitrate Film.) All professional projectors should be operated by qualified personnel. A professional projector is a type that uses 35- or 70mm film that has a minimum width of 13/8 in. (35 mm) and has on each edge 5.4 perforations per in., or that uses carbon arc, xenon, or other light source equipment that develops hazardous gases, dust, or radiation. Motor generator sets, transformers, rectifiers, rheostats, and similar equipment for the supply or control of current to projection or spotlight equipment must be located in a separate room, if cellulose nitrate film is used. When placed in the projection room, cellulose nitrate film must be located or guarded so that arcs or sparks cannot come in contact with film. The commutator end or ends of motor generator sets must comply with one of the conditions in NEC Section 540-11. Switches, overcurrent devices, or other equipment not normally required or used for projectors, sound reproduction, flood or other special effect lamps, or other equipment cannot be installed in projection rooms. There are exceptions: (1) In projection rooms approved for use only with cellulose acetate (safety) film, the installation of appurtenant electrical equipment used in conjunction with the operation of the projection equipment and the control of lights, curtains, and audio equipment, and so on, is permitted. In such projection rooms, a sign reading “Safety Film Only Permitted in This Room” must be posted on the outside of each projection room door and within the projection room itself in a conspicuous location. (2) Remote-control switches for the control of auditorium lights or switches for the control of motors operating curtains and masking of the motion picture screen are permitted to be installed in projection rooms. Approved projectors of the nonprofessional or miniature type, when employing cellulose acetate (safety) film, may be operated without a projection room. Special rules are also given in the NEC to cover electrical installations in motion picture studios, factories, laboratories, stages, or areas of buildings in which work is done on cellulose nitrate film. Provisions include wiring on stages, sets, dressing rooms, viewing, cutting, and patching tables, and film storage vaults.
Cranes and Hoists Wiring methods and installation of electrical equipment for cranes and hoists are covered in Article 610 of the NEC. Where bare contact conductors are objectionable because of the pres-
ence of easily ignitable material, current may be conducted to a crane or hoist via a multiple cable on a cable reel or suitable takeup device. Where a crane operates over combustible material, the resistors must either be placed in (1) a well-ventilated cabinet of noncombustible material that will not emit flames or molten metal, or (2) a cage or cab constructed of noncombustible material that encloses the sides of the cage or cab from the floor to a point at least 6 in. (152 mm) above the top of the resistors. Collectors must be designed to reduce sparking between them and the contact conductors to a minimum. When operated in rooms where easily ignitable fibers or materials producing combustible flyings are handled, manufactured, used, or stored, the installation must comply with the special requirements of Section 503.13 of the NEC. All exposed metal parts of cranes, monorail hoists, hoists, and accessories (including pendant controls) should be metallically joined together into a continuous electrical conductor so the entire crane or hoist will be grounded.
Elevators, Dumbwaiters, Escalators, Moving Walks, Wheelchair Lifts, and Stairway Chair Lifts Installation of electrical equipment and wiring used in connection with elevators, dumbwaiters, escalators, moving walks, wheelchair lifts, and stairway chair lifts are covered in Article 620 of the NEC. For further information, see Safety Code for Elevators and Escalators, ASME/ANSI A17.1-1996, and Elevator and Escalator Electrical Equipment Certification Standard, ASME/ANSI A17.5-1996 (CSA B44.1-1996). All live parts of electrical apparatus in the hoistways, at landings, in or on cars of elevators and dumbwaiters, in the wellways or the landings of escalators or moving walks, or in the runways and machinery spaces of wheelchair lifts and stairway chair lifts must be enclosed to protect against accidental contact. [See NEC Section 110.27 for guarding of live parts (600 V, nominal, or less)]. The conductors to the hoistway door interlocks from the hoistway riser must be flame retardant and suitable for a temperature of not less than 392°F (200°C). Conductors must be Type SF or equivalent. Other wiring in raceways must have flame-retardant insulation. Bonding of elevator rails (car and/or counterweight) to a lightning protection system grounding down conductor(s) is permitted. However, the lightning protection system grounding down conductor(s) cannot be located within the hoistway. Elevator rails or other hoistway equipment cannot be used as the grounding down conductor for lightning protection systems. (See NEC Section 250.106 for bonding requirements. For further information, see NFPA 780.) Traveling cables must be suspended at the car and hoistways’ ends, or counterweight end where applicable, so as to reduce the strain on the individual copper conductors to a minimum and must be supported by one of the following means: (1) by its steel supporting member(s), (2) by looping the cables around supports for unsupported lengths less than 100 ft (30 m), and (3) by suspending from the supports by a means that auto-
CHAPTER 1
matically tightens around the cable when tension is increased for unsupported lengths up to 200 ft (60 m). Unsupported length for the hoistway suspension means is that length of cable as measured from the point of suspension in the hoistway to the bottom of the loop, with the elevator car located at the bottom landing. Unsupported length for the car suspension means is that length of cable as measured from the point of suspension on the car to the bottom of the loop, with the elevator car located at the top landing. Traveling cables used as flexible connections between the elevator or dumbwaiter car or counterweight and the raceway must be of the types listed in NEC, Table 400.4 or other approved types. To reduce the danger of electric shock, the following equipment must be effectively grounded in accordance with the grounding requirements of the NEC: (1) metal raceways, Type MC cable, Type MI, or Type AC cable attached to elevator cars, (2) the frames of all motors, elevator machines, and controllers, (3) the metal enclosures for all electric devices in or on the car or hoistway, and (4) the frames of nonelectric elevators if accessible to persons and if any electric conductors are attached to the car. Each 125-V, single-phase, 15- and 20-A receptacle installed in pits, elevator car tops, and in escalator and moving walk wellways must be of the ground-fault circuit-interrupter type, and all 125-V, single-phase, 15- and 20-A receptacles installed in machine rooms and machinery spaces must have ground-fault circuit-interrupter protection for personnel. A single receptacle supplying a permanently installed sump pump does not require ground-fault circuit-interrupter protection. This protection does not include a GFCI circuit breaker located in a distribution panel; the intent is to allow personnel to reset the GFCI receptacle without climbing around in the dark. Receptacles installed in the machine room are allowed to be protected by either a GFCI receptacle or a GFCI circuit breaker.
Heating Cable Recognized testing laboratories have listed a number of heating cables for use within buildings. These cables are of the resistance type, primarily designed to be used around water pipes to prevent freezing and facilitate the flow of viscous liquids. The cable is secured to the pipe with straps or wrapped around the pipe with the pitch recommended by the manufacturer. Electric heating cables are required to have a grounded metal outer covering. The pipe and heating cable are usually encased in thermal insulation. Some units incorporate a thermostat that automatically turns on the heating cable when the temperature drops below a predetermined value. The pipe heating cables are intended to be connected to a permanent supply wiring system. Unless specifically indicated otherwise by marking on the heating cables or in the installation instructions, the heating cables are intended for use only on metallic pipes. Ground-fault protection of equipment must be provided for each branch circuit supplying electric heating equipment; this is not GFCI protection. For industrial establishments where only qualified persons will service the installation and the continued circuit operation is necessary for safe operation of the equipment or process, ground fault protection is not required, but an alarm indication of a ground fault is required.
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Electrical Systems and Appliances
6–41
Electrical heating cables for outdoor ice- and snow-melting systems are covered in the NEC Article 426.
ELECTRICAL EQUIPMENT FOR OUTDOOR USE Electric equipment that is installed outside of buildings must be weatherproof in design, that is, constructed such that exposure to the weather will not interfere with its successful operation; otherwise it must be enclosed in weatherproof cabinets, enclosures designed to prevent moisture or water from entering and accumulating within them. If mounted on a wall or other supporting surface, there should be at least ¼ in. (6 mm) air space between the box or cabinet and the supporting surface.
Description of Devices Electric equipment suitable for outdoor use is tested by recognized electrical testing laboratories. The tests encompass the following: (1) suitability of the materials used and the protective coatings for exposure to sunlight, rain, and snow, (2) effects of heat and cold, and (3) provisions for grounding. The term raintight, as used in the NEC, is applied to equipment that, on exposure to a beating rain, will not let water enter. The term weatherproof, as used in the NEC, is applied to equipment that, on exposure to the weather, will still operate successfully. Rainproof, raintight, or watertight equipment can fulfill the requirements for weatherproof equipment where varying weather conditions other than wetness, for example, snow, ice, dust, or temperature extremes, are not a factor.
Electric Signs and Outline Lighting Electric signs and outline lighting, whether fixed, mobile, or portable, are required to be listed. Except for portable indoor signs, signs and outline lighting equipment are usually constructed of metal or other noncombustible material. The spacing between wood or other combustible materials and an incandescent or high-intensity discharge (HID) lamp or lampholder must not be less than 2 in. (50 mm). Enclosures for outside use must be weatherproof. Signs and outline lighting systems must be constructed and installed so that adjacent combustible materials are not subjected to temperature in excess of 194°F (90°C). All steel parts of enclosures must be galvanized or otherwise protected from corrosion. Signs, troughs, tube terminal boxes, and other metal frames must be grounded in the manner specified in the NEC. Each electric sign (other than cord-connected) and each outline lighting installation must be controlled by an external operable switch or circuit breaker (handle on outside of switch enclosure), which will open all ungrounded conductors. The switch or breaker must be within sight of the sign or outline lighting installation unless it is capable of being locked in the open position. Portable outdoor electric signs must be equipped with factory-installed GFCI protection. The GFCI must be an integral part of the attachment plug or located in the power supply cord within 12 in. (300 mm) of the attachment plug.
6–42 SECTION 6 ■ Fire Prevention
Electric Fences Wire fences with electrical connections to produce a shock when animals come in contact with them are widely used on farms. To avoid hazard to persons and to livestock, the current and the time interval during which the current is on and off must be limited to values which will not cause fatalities or injuries to persons or animals, while still causing an unpleasant sensation of shock. Fatalities and fires can result from homemade equipment supplied from ordinary lighting circuits. The open circuit voltage need not be limited if the current is properly limited. UL Research Bulletins No. 14 and UL 69, “Standard for Safety Electric-Fence Controllers,” give detailed information on these installations. The output characteristics of some controllers are such that combustible material may be readily ignited when a grounded object occupies a position respective to the energized fence to produce an electric arc. To protect against fire from such a cause, users should determine whether the controller has been designed and tested with respect to this hazard. Electric fence controllers listed in accordance with the requirements of UL 69 have been so tested.
Marinas and Boatyards Wiring in marinas and boatyards presents special outdoor electric equipment problems, which are covered in Article 555 of the NEC. Electric service equipment for floating docks or marinas must be located adjacent to, but not on or in, the floating structure. Metal raceways and metal boxes must not be depended on for grounding; a continuous insulated copper conductor, not smaller than 12 AWG, must be provided as an equipment grounding conductor from outlet boxes and receptacles to the service ground. Electrical equipment and wiring located at gasoline dispensing stations must follow the requirements in Article 514 of the NEC and NFPA 30A, Code for Motor Fuel Dispensing Facilities and Repair Garages. Wiring over and under navigable water should be subject to approval by the authority having jurisdiction.
LOCATIONS EXPOSED TO MOISTURE AND NONCOMBUSTIBLE DUSTS Special electric equipment is required for use where moisture and noncombustible dusts might be present. For years, the NEC referred to such equipment as vaportight, but this term was dropped from the NEC because of confusion in the field between equipment so designated and explosionproof equipment. Many users assumed that vaportight equipment was safe to use in atmospheres containing flammable gases or vapors (Class I locations), combustible dusts (Class II locations), or easily ignitable fibers or flyings (Class III locations). To avoid this type of misunderstanding, the term enclosed and gasketed was developed for this type of equipment. Some inspection authorities permit enclosed and gasketed luminaires (lighting fixtures) in Class I, Division 2; Class II, Division 2; and in Class III, Divisions 1 and 2 locations when marked to show the operating temperature and maximum wattage of permissible lamps. The NEC requires luminaires (lighting fixtures) to be marked for use in wet and damp locations when so used.
SIGNALING AND COMMUNICATIONS SYSTEMS Communications systems, including telephone, telegraph, fire and burglar alarms, and watchman and sprinkler supervisory systems, usually operate with low voltages and currents and, if kept free from accidental contacts with higher voltage systems, they present no unusual hazards. There are, however, NEC requirements for the wiring of these systems if the wiring is in a duct, plenum, or other space for environmental air, because of the hazard of spreading products of combustion from one location to another. There are also NEC requirements for separation from other systems, such as lighting and power circuits, to minimize imposing higher voltages and current on the communication equipment and conductors. Where fire-rated walls, floors, or ceilings are penetrated, the integrity of the construction assembly must be maintained by proper sealing around cables to prevent the spread of fire or smoke. Fire alarm systems are classified as nonpower-limited or power-limited. Nonpower-limited cables (NPLFAs) must be identified and listed as NPLFP, where installed in spaces used for environmental air; NPLFR, where used as a vertical riser from floor to floor or in shafts; and NFPLF, where used for general purpose in other than risers, ducts, plenums, or environmental air-handling spaces. Power-limited systems (PLFAs) must be identified and listed with the following markings: FPLP, FPLR, and FPL; these are similar to those of nonpower-limited cables. Signaling systems and communications systems must be installed in accordance with Articles 725, 760, and 800 of the NEC, and NFPA 72®, National Fire Alarm Code®, which covers the proper electrical wiring and equipment for fire alarm services. NFPA 72 has cross references to the NEC. Telephone communications circuits may be used for completing the fireprotective circuits between the protected premises and fire alarm headquarters.
EMERGENCY SYSTEMS Requirements for the installation, operation, and maintenance of emergency system circuits and equipment are given in Article 700 of the NEC. The systems are intended to supply light and power when the normal supply fails. They are generally installed in places of assembly where artificial lighting is required, such as auditoriums, theaters, sports arenas, and so on, occupied by large numbers of persons (Figures 6.1.29 and 6.1.30). In Figure 6.1.29, the heavy lines represent walls required by typical local building codes to be of fire-rated construction. The light lines represent walls not required by typical local building codes to be of fire-rated construction. Legally required standby systems installed to serve loads such as heating and refrigeration systems, communications systems, ventilation and smoke removal systems, sewerage disposal, lighting systems, and industrial processes, that, when stopped during any interruption of the normal electrical supply, could create hazards or hamper rescue or fire-fighting operations, are covered in Article 701 of the NEC. NFPA 110, Standard for Emergency and Standby Power Systems, covers the performance requirements for such systems.
CHAPTER 1
NFPA 101®, Life Safety Code®, specifies where emergency lighting is considered essential for life safety. NFPA 99 gives minimum factors governing the design, operation, and maintenance of those portions of health care facility electrical systems where any degree of interruption would jeopardize the effective and safe care of hospitalized patients. The provisions in NFPA 99 do not supersede the recommendations in NFPA 101 or the NEC, which both limit the type of alternative source of electrical power allowable for use to ensure electric power continuity in health care facilities. NFPA 99 recognizes the progressively greater dependence being placed on electrical apparatus for the
Storage
Place of assembly
Place of assembly
Reception area
Food preparation area Exit corridor Serving corridors
Wash room
Storage Place of assembly
Place of assembly
Wash room
Office area
FIGURE 6.1.29 Walls in Places of Assembly Requiring (heavy lines) and Not Requiring (light lines) Fire-Rated Construction by Typical Local Building Codes
AC feed from normal utility Inlet air opening
DC feed to battery & engine start control
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Electrical Systems and Appliances
6–43
preservation of life of hospitalized patients and is a guide in the selection of the electrical services for emergency supply to all lighting and power equipment considered essential, and for their design and maintenance in health care facilities. The sources of electric current that can be used for emergency lighting equipment are (1) storage batteries of suitable capacity, (2) a generator driven by some form of prime mover, and (3) a second electric service separated electrically and physically from the regular service to minimize the possibility of simultaneous interruption of both services. NFPA 99 stipulates that the alternative source of power for health care facilities be primemover-driven generators or, where the normal source is an onsite generator, an external utility service may be the alternative source. Means must be provided for automatically energizing emergency lights upon failure of the regular lighting system supply. For hospitals, the transition time from the instant of failure of the normal power source to an emergency generator source must not exceed 10 s. Audible and visual signal devices are provided, where practical, to (1) warn of impairment of the emergency source, (2) indicate that the battery or generator is carrying load, (3) indicate when a battery charger is functioning properly, and (4) indicate a ground fault on large 480Y/277-volt systems. No appliances or lamps, other than those required for emergency use, are to be supplied by the emergency lighting circuits. A good emergency lighting system is designed so that the failure of any individual lighting element, such as the burning out of a light bulb, cannot leave any space in total darkness. The emergency lighting circuit wiring is independent of all other wiring and equipment and must not enter the same raceway, cable, box, or cabinet with other wiring except at transfer
Silencer
To load Emergency feed
Wall thimble Automatic transfer switch Supports
Flexible conduit
Drain
Flexible coupling Outlet air opening Battery charger
Engine generator control
Flexible fuel lines Day tank
Normal utility feed
Flexible fuel lines
Generator mounted circuit breaker
Return line
Vibration isolators Batteries
FIGURE 6.1.30 Power Systems
Main fuel fuel gauge
AC jacket water heater
Main fuel tank
Suction line
Typical Installation of a Diesel-Powered Standby Generator Such as Might be Used for Emergency Light and
6–44 SECTION 6 ■ Fire Prevention
switches and at exit lighting fixtures supplied from both the normal and the emergency sources. A transfer switch that supplies emergency power is not allowed to also supply normal loads. Loads other than emergency loads must be supplied from a different transfer switch. It is good practice to test the complete system upon installation and periodically thereafter to ensure it is maintained in proper operating condition. A written record should be kept of such tests and maintenance.
SPECIAL OCCUPANCY ELECTRICAL PROBLEMS Hazardous (classified) locations and other special problems require individual attention for which the NEC has specific recommendations.
Hazardous (Classified) Locations— General The NEC recognizes an additional method of classification of hazardous locations. This method uses zones that are consistent with the rules of the International Electrotechnical Commission (IEC). The method is described in Article 505 of the NEC. Electric power for lighting, motors, controls, and instrumentation, along with their associated wiring, is necessary or desirable in many hazardous locations. Due to the presence of flammable liquids, gases, vapors, combustible dusts, or readily ignitable fibers or flyings in these areas, special electrical equipment and wiring methods are necessary to prevent ignition and to minimize the occurrence of fire and explosion. A flammable liquid, as it pertains to Article 500 of the NEC, is defined as follows: “A liquid having a flash point below 100°F (37.8°C) and having a vapor pressure not exceeding 40 psia at 100°F (37.8°C) shall be known as a Class I liquid.” Explosionproof apparatus is defined in the NEC as follows: “Apparatus enclosed in a case that is capable of withstanding an explosion of a specified gas or vapor that may occur within it and of preventing the ignition of a specified gas or vapor surrounding the enclosure by sparks, flashes or explosion of the gas or vapor within, and that operates at such an external temperature that a surrounding flammable atmosphere will not be ignited thereby.” In Article 500 of the NEC, hazardous (classified) locations are divided into three classes depending on the kind of hazardous material involved; each class is further divided into two divisions according to the likelihood of the potential hazard existing. For the purposes of testing for approval and area classification, various air mixtures (not oxygen enriched) have been grouped on the basis of their characteristics. The groups are given in Tables 6.1.18 through 6.1.21 [statistics from Section 500.3 of the NEC and tables from NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas]. For Group A, B, C, and D materials with flash points of 100°F (38°C) and higher, see NFPA 497. For a more complete table of Group G dusts and information on Group E dusts, see Table 6.1.18 and NFPA 497.
TABLE 6.1.18 Group Classification and Autoignition Temperature (AIT) of Selected Flammable Gases and Vapors of Liquids Having Flash Points below 100°F (37.8°C) AIT Material
Group
°F
°C
Acetaldehyde Acetone Acetonitrile Acetylene Acrolein (inhibited)b Acrylonitrile Allyl alcohol Allyl chloride Ammonia n-Amyl acetate sec-Amyl acetate Benzene 1,3-Butadieneb Butane 1-Butanol 2-Butanol n-Butyl acetate iso-Butyl acetate sec-Butyl acetate Butylamine Butylene Butyl mercaptan n-Butyraldehyde Carbon disulfided Carbon monoxide Chlorobenzene Chloroprene Crotonaldehyde Cyclohexane Cyclohexene Cyclopropane 1,1-Dichloroethane 1,2-Dichloroethylene 1,3-Dichloropropene Dicyclopentadiene Diethyl ether Diethylamine Di-isobutylene Di-isopropylamine Dimethylamine 1,4-Dioxane Di-n-propylamine Epichlorohydrin Ethane Ethanol Ethyl acetate Ethyl acrylate (inhibited) Ethylamine Ethyl benzene Ethyl chloride Ethylene Ethylenediamine Ethylene dichloride Ethylenimine
Ca Da D Aa B (C)a Da Ca D DaPc D D Da B (D)a Da Da Da Da Da D D D C Ca —a Ca D D Ca D D Da D D D C Ca Ca Da C C C C Ca Da Da Da Da Da D D Ca Da Da Ca
347 869 975 581 455 898 713 905 928 680 — 1040 788 550 650 761 790 790 — 594 725 — 425 194 1128 1099 — 450 473 471 938 820 860 — 937 320 594 736 600 752 356 570 772 882 685 800 702 725 810 966 842 725 775 608
175 465 524 305 235 481 378 485 498 360 — 560 420 288 343 405 421 421 — 312 385 — 218 90 609 593 — 232 245 244 503 438 460 — 503 160 312 391 316 400 180 299 411 472 363 427 372 385 432 519 450 385 413 320
CHAPTER 1
TABLE 6.1.18
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Electrical Systems and Appliances
6–45
Continued AIT
AIT
Material
Group
°F
°C
Material
Group
°F
°C
Ethylene oxideb Ethyl formate Ethyl mercaptan n-Ethyl morpholine Formaldehyde (gas) Gasoline Heptane Heptene Hexane 2-Hexanone Hexenes Hydrogen Hydrogen cyanide Hydrogen selenide Hydrogen sulfide Isoamyl acetate Isoamyl alcohol Isobutyl acrylate Isobutyraldehyde Isoprene Isopropyl acetate Isopropylamine Isopropyl ether Isopropyl glycidyl ether Liquefied petroleum gas Manufactured gas (containing more than 30% H2 by volume) Mesityl oxide Methane Methanol Methyl acetate Methylacetylene Methylacetylenepropadiene (stabilized) Methyl acrylate Methylamine Methylcyclohexane Methyl ether Methyl ethyl ketone Methyl eormal Methyl eormate
B (C)a D Ca C B Da Da D Da D D Ba Ca C Ca D D D C Da D D Da C D Ba
804 851 572 — 795 536–880 399 500 437 795 473 752 1000 — 500 680 662 800 385 743 860 756 830 — 761–842 —
429 455 300 — 429 280–471 204 260 225 424 245 400 538 — 260 360 350 427 196 395 460 402 443 — 405–450 —
Da Da Da D Ca C
652 999 725 850 — —
344 537 385 454 — —
Da D C D Da Da C Da C C D D Da D Da Da D D Da Da Da C D Da D B (C)a Ca Ba Da Da Ca Da Ca D D Ca
840 994 — 792 780 892 382 550 778 785 401 — 403 446 470 572 846 527 842 775 750 405 842 851 1035 840 419 347 900 914 610 896 — — 488 480
440 534 — 422 416 478 194 288 414 418 205 — 206 230 243 300 452 275 450 413 399 207 450 455 557 449 215 175 482 490 321 480 — — 253 249
D D D Ca Da Ca D
875 806 482 662 759 460 840
468 430 250 350 404 238 449
Methyl isobutyl ketone Methyl isocyanate Methyl mercaptan Methyl methacrylate 2-Methyl-1-propanol 2-Methyl-2-propanol Monomethyl hydrazine Naphtha (petroleum)e Nitroethane Nitromethane Nonane Nonene Octane Octene Pentane 1-Pentanol 2-Pentanone 1-Pentene Propane 1-Propanol 2-Propanol Propionaldehyde n-Propyl acetate Propylene Propylene dichloride Propylene oxideb n-Propyl ether Propyl nitrate Pyridine Styrene Tetrahydrofuran Toluene Triethylamine Tripropylamine Turpentine Unsymmetrical dimethyl hydrazine (UDMH) Valeraldehyde Vinyl acetate Vinyl chloride Vinylidene chloride Xylenes
C Da Da D Da
432 756 882 1058 867–984
222 402 472 570 464–529
a
Material has been classified by test. If equipment is isolated by sealing all conduit (trade size) ½ in. or larger, in accordance with Section 501.5(A) of the NEC, equipment for the group classification shown in parentheses is permitted. c For classification of areas involving Ammonia, see “Safety Code for Mechanical Refrigeration,” ANSI/ASHRAE 15, and “Safety Requirements for the Storage and Handling of Anhydrous Ammonia,” ANSI/CGA G2.1. d Certain chemicals may have characteristics that require safeguards beyond those required for any of the above groups. Carbon disulfide is one of these chemicals because of its low autoignition temperature and the small joint clearance to arrest its flame propagation. e Petroleum naphtha is a saturated hydrocarbon mixture whose boiling range is 68° to 274°F (20° to 135°C). It is also known as benzine, ligroin, petroleum ether, and naphtha. Sources: NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas. Autoignition temperatures listed above are the lowest value for each material as listed in NFPA’s Fire Protection Guide to Hazardous Materials, which was originally NFPA 325, Guide to Fire Hazard Properties of Flammable Liquids, Gases, and Volatile Solids, or as reported in an article by Hilado, C. J., and Clark, S. W., Chemical Engineering, Sept. 4, 1972. NFPA 325 has been officially withdrawn from the National Fire Codes®, the information is still available in NFPA’s Fire Protection Guide to Hazardous Materials. b
6–46 SECTION 6 ■ Fire Prevention
TABLE 6.1.19 Selected Nonconductive Dusts Classified as Group G—Ignition Sensitivity Equal to or Greater than 0.2; Explosion Severity Equal to or Greater than 0.5
Agricultural Dusts Alfalfa meal Cellulose Cinnamon Cocoa, natural, 19% fat Corn Corncob grit Corn dextrine Cornstarch, commercial Cork Cottonseed meal Garlic, dehydrated Malt barley Milk, skimmed Potato starch, dextrinated Rice Rice bran Rice hull Safflower meal Soy flour Soy protein Sucrose Sugar, powdered Wheat Wheat flour Wheat starch Wheat straw Woodbark, ground Wood flour Yeast, torula Chemicals Acetoacetanilide Adipic acid Anthranilic acid Azelaic acid 2,2-Azo-bis-butyronitrile Benzoic acid Benzotriazole Bisphenol-A Chloroacetoacetanilide Diallyl phthalate Dihydroacetic acid Dimethyl isophthalate Dimethyl terephthalate 3,5-Dinitrobenzoic acid Diphenyl Ethyl hydroxyethyl cellulose Fumaric acid Hexamethylene tetramine Hydroxyethyl cellulose Isotoic anhydride Paraphenylene diamine
Minimum Cloud or Layer Ignition Temperaturea
Minimum Cloud or Layer Ignition Temperaturea
°F
°C
°F
392 500 446 464 482 464 698 626 410 392 680 482 392 824 428 914 428 410 374 500 662 698 428 680 716 428 482 500 500
200 260 230 240 250 240 370 330 210 200 360 250 200 440 220 490 220 210 190 260 350 370 220 360 380 220 250 260 260
824 1022 1076 1130 662 824 824 1058 1184 896 806 1076 1058 860 1166 734 968 770 770 1292 1148
NL
NL NL
Cl Cl
NL
M M M M
M M M M NL M M NL M NL M S NL NL M
440 550 580 610 350 440 440 570 640 480 430 580 570 460 630 390 520 410 410 700 620
Chemicals (continued) Paratertiary butyl benzoic acid Pentaerythritol Phthalic anhydride Salicylanilide Sorbic acid Stearic acid, aluminum salt Stearic acid, zinc salt Sulfur Terephthalic acid Drugs Aspirin Gulasonic acid, diacetone Mannitol l-Sorbose Vitamin B1, mononitrate Vitamin C (ascorbic acid) Dyes, Pigments, Intermediates Green base harmon dye Red dye intermediate Violet 200 dye Pesticides Crag No. 974 Dieldrin (20%) Dithane Ferban Manganese vancide Sevin Thermoplastic Resins and Molding Compounds Acetal resins Acetal, linear (polyformaldehyde) Acrylic resins Acrylamide polymer Acrylonitrile polymer Acrylonitrile-vinyl chloridevinylidene chloride copolymer (70–20–10) Methyl methacrylate polymer Methyl methacrylate-ethyl acrylate copolymer Methyl methacrylate-ethyl acrylatestyrene copolymer Methyl methacrylate-styrenebutadiene-acrylonitrile copolymer Methacrylic acid polymer Cellulosic resins Cellulose acetate Cellulose triacetate Cellulose acetate butyrate
°C
1040 752 1202 1130 860 572 950 428 1256
M M M M
1220 788 860 698 680 536
M NL M M NL
M NL
560 400 650 610 460 300 510 220 680 660 420 460 370 360 280 175 175 175
347 347 347 590 1022 356 302 248 284
Cl NL
310 550 180 150 120 140
824
NL
440 240 460 210
464 860 410
824 896
NL NL
440 480
824
NL
440
896
NL
480
290
554 644 806 698
NL NL
340 430 370
CHAPTER 1
TABLE 6.1.19
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Electrical Systems and Appliances
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Continued
Thermoplastic Resins and Molding Compounds (continued) Nylon (polyamide) resins Nylon polymer (polyhexamethylene adipamide) Polycarbonate resins Polycarbonate Polyethylene resins Polyethylene, high-pressure process Polyethylene, low-pressure process Polyethylene wax Polymethylene resins Carboxypolymethylene Polypropylene resins Polypropylene (no antioxidant) Rayon resins Rayon (viscose) flock Styrene resins Polystyrene molding cmpd. Polystyrene latex Styrene-acrylonitrile (70-30) Styrene-butadiene latex (>75% styrene; alum coagulated) Vinyl resins Polyvinyl acetate Polyvinyl acetate/alcohol Vinyl chloride-acrylonitrile copolymer
Minimum Cloud or Layer Ignition Temperaturea
Minimum Cloud or Layer Ignition Temperaturea
°F
°F
°C
806
1310
430
NL
716
710 380
788
NL
420
752
NL
400
968
NL
520
788
NL
420
482
250
1040 932 932 824
NL
1022 824 878
NL
NL NL
560 500 500 440
550 440 470
Vinyl toluene-acrylonitrile butadiene copolymer Allyl resins Allyl alcohol derivative (CR-39) Amino resins Urea formaldehyde molding compound Urea formaldehyde-phenol formaldehyde molding compound (wood flour filler) Epoxy resins Epoxy Epoxy-bisphenol A Phenolic resins Phenol formaldehyde Phenol formaldehyde molding compound (wood flour filler) Polyester resins Polyethylene terephthalate Styrene modified polyesterglass fiber mixture Polyurethane resins Polyurethane foam, no fire retardant Special Resins and Molding Compounds Ethylene oxide polymer Ethylene-maleic anhydride copolymer Petroleum resin (blown asphalt) Rubber, crude, hard Rubber, synthetic, hard (33% S)
°C
936
NL
530
932
NL
500
860
NL
460
464
240
1004 950
NL NL
540 510
1076 932
NL NL
580 500
932 680
NL
500 360
824
440
662 1004
NL NL
350 540
932 662 608
NL NL
500 350 320
a Normally, the minimum ignition temperature of a layer of a specific dust is lower than the minimum ignition temperature of a cloud of that dust. Since this is not universally true, the lower of the two minimum ignition temperatures is listed. If no symbol appears between the two temperature columns, then the layer ignition temperature is shown. Notes: Cl: cloud ignition temperature is shown; NL: no layer ignition temperature is available and the cloud ignition temperature is shown; M: dust layer melts before it ignites, and the cloud ignition temperature is shown; S: dust layer sublimes before it ignites, and the cloud ignition temperature is shown.
Group G includes combustible dusts, such as wood, flour, grain, corn starch, cocoa, food, chemical, and plastics dusts. Coal, coke, and carbonaceous dusts are classified in Group F. Group E includes metal dusts and other dusts of similarly hazardous characteristics. Determining the proper group classification for flammable gases and vapors involves a determination of explosion pressures and maximum safe clearance between parts of a clamped joint under several conditions and comparison of the values obtained with those obtained for materials that have already been evaluated. Listed equipment is marked to show the class, group, and operating temperature, or temperature range, referenced to a
248°F (120°C) ambient. The temperature range, if provided, is indicated by identification numbers, as shown in Table 6.1.22. The identification numbers are marked on equipment nameplates. The ignition temperature of a liquid, solid, or gaseous substance is the minimum temperature required to initiate or cause self-sustained combustion, independent of the heating or heated element. The flash point and the ignition temperature are not the same, and the flash point is always lower than the ignition temperature. Since there is no consistent relationship among explosion properties, explosion pressure, maximum experimental safe gap, minimum ignition energy, and ignition temperature, testing requirements for groups and classes are independent of each other.
6–48 SECTION 6 ■ Fire Prevention
TABLE 6.1.20 Selected Carbonaceous Dusts Classified as Group E—Ignition Sensitivity Equal to or Greater than 0.2; Explosion Severity Equal to or Greater than 0.5
TABLE 6.1.21 Selected Carbonaceous Dusts Classified as Group F—Ignition Sensitivity Equal to or Greater than 0.2; Explosion Severity Equal to or Greater than 0.5
Minimum Cloud or Layer Ignition Temperatureb Materiala
°F
Aluminum, atomized collector fines Aluminum, A422 flake Aluminum-cobalt alloy (60-40) Aluminum-copper alloy (50-50) Aluminum-lithium alloy (15% Li) Aluminum-magnesium alloy (downmetal) Aluminum-nickel alloy (58-42) Aluminum-silicon alloy (12% Si) Boron, commercial-amorphous (85% B) Calcium silicide Chromium, (975) electrolytic, milled Ferromanganese, medium carbon Ferrisilicon (885, 9% Fe) Ferrotitanium (19% Ti, 74.1% Fe, 0.06% C) Iron 98% H2 reduced Iron 99% carbonyl Magnesium, Grade B, milled Manganese Tantalum Thorium, 1.2% O2 Tin, 96%, atomized (2% Pb) Titanium, 99% Titanium hydride (95% Ti, 3.8% H2) Vanadium, 86.4% Zirconium hydride (93.6% Zr, 2.1% H2)
1022 608 1058 1526 752 806 1004 1238 752
CI
CI
NL
Minimum Cloud or Layer Ignition Temperaturea
°C
Material
°F
550 320 570 830 400 430
Asphalt, (blown petroleum resin) Charcoal Coal, Kentucky bituminous Coal, Pittsburgh experimental Coal, Wyoming Gilsonite Lignite, California Pitch, coal tar Pitch, petroleum Shale, oil
950 356 356 338 — 932 356 1310 1166 —
540 670 400
°C CI
NL NL
510 180 180 170 — 500 180 710 630 —
a
1004 752 554 1472 698 554 590 806 464 572 518 806 626 896 914 518
CI
CI CI CI
540 400 290 800 370 290 310 430 240 300 270 430 330 480 490 270
a Certain metal dusts may have characteristics that require safeguards beyond those required for atmospheres containing the dusts of aluminum, magnesium, and their commercial alloys. For example, zirconium, thorium, and uranium dusts have extremely low ignition temperatures (as low as 68° F [20° C]) and minimum ignition energies lower than any material classified in any of the Class I or Class II groups. b Normally, the minimum ignition temperature of a layer of a specific dust is lower than the minimum ignition temperature of a cloud of that dust. Since this is not universally true, the lower of the two minimum ignition temperatures is listed. If no symbol appears between the two temperature columns, then the lower ignition temperature is shown. “CI” means the cloud ignition temperature is shown. “NL” means that no layer ignition temperature is available and the cloud ignition temperature is shown. Source: NFPA 497, Recommended Practices for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas.
The operating temperature markings specified in Table 6.1.22 are not to exceed the ignition temperature of the specific gas or vapor to be encountered. For information regarding ignition temperatures of gases and vapors, see Table 6.1.18, NFPA 497, and NFPA’s Fire Protection Guide to Hazardous Materials.
Normally, the minimum ignition temperature of a layer of a specific dust is lower than the minimum ignition temperature of a cloud of that dust. Since this is not universally true, the lower of the two minimum ignition temperatures is listed. If no symbol appears between the two temperature columns, then the layer ignition temperature is shown. “CI” means the cloud ignition temperature is shown. “NL” means that no layer ignition temperature is available and the cloud ignition temperature is shown. Source: NFPA 497, Recommended Practices for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas.
TABLE 6.1.22
Temperature Identification Numbers
Maximum Temperature °F
°C
Identification Number
842 572 536 500 446 419 392 356 329 320 275 248 212 185
450 300 280 260 230 215 200 180 165 160 135 120 100 85
T1 T2 T2A T2B T2C T2D T3 T3A T3B T3C T4 T4A T5 T6
Classes on Divisions of Hazardous Locations Complete definitions of the several classes and divisions of hazardous (classified) locations and the methods of wiring and types of electrical equipment to be used in each are covered in detail in the NEC. Rules applying specifically to commercial
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6–49
garages, aircraft hangars, gasoline dispensing facilities and service stations, bulk storage plants, finishing processes, and areas in health care facilities containing flammable anesthetics are also covered in the NEC. Class I, Division 1. This includes locations in which (1) ignitable concentrations of flammable gases or vapors can exist under normal operating conditions, (2) ignitable concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or leakage, or (3) breakdown or faulty operation of equipment or processes might release ignitable concentrations of gases or vapors, and might also cause simultaneous failure of electrical equipment in such a way as to directly cause the electrical equipment to become a source of ignition. Motors and other rotating electrical machinery, luminaires (lighting fixtures), most switches, circuit breakers, and similar electrical equipment in these locations must be of the explosionproof type or purged type approved for Class I locations of the proper group (see NFPA 496, Standard for Purged and Pressurized Enclosures for Electrical Equipment) (Figures 6.1.31, 6.1.32, and 6.1.33). Approved intrinsically safe equipment and circuits may also be used. These are usually limited to low-energy control, signal, and instrumentation systems. Class I, Division 2. This includes locations (1) in which volatile flammable liquids or flammable gases are handled, processed, or used, but in which the liquids, vapors, or gases will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such containers or systems, or in case of abnormal operation of equipment; (2) in which ignitable concentrations of gases or vapors are normally prevented by positive mechanical ventilation, and which might become hazardous through failure or abnormal operation of the ventilating equipment; or (3) that are adjacent to Class I, Division 1 locations, and to which ignitable concentrations of gases or vapors might occasionally be communicated unless such communication is prevented by
Hot gas is cooled in passing through threads
FIGURE 6.1.32 Typical Luminaire for Use in Class I, Group C and D Locations (Source: Appleton Electric LLC, EGS Electrical Group)
Only cooled gas (not ignition capable) can get out
Hot flaming gas
Threaded joint opening
FIGURE 6.1.31 Principle of “Explosionproof” Equipment, Indicating Containment of Hot Gases Within the Enclosure
FIGURE 6.1.33 Explosionproof Panelboard (Source: Appleton Electric LLC, EGS Electrical Group)
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adequate positive-pressure ventilation from a source of clean air, and effective safeguards against ventilation failure are provided. In general, ordinary types of motors that do not have brushes, switching mechanisms, and so on, may be installed in these locations, but motors that do have sliding contacts, switches, and so on must have the switches in explosionproof or other type enclosure approved for Class I, Division 2 locations. Lamps that operate at temperatures above the ignition temperature of the gas or vapor involved must have approved explosionproof or purged enclosures. Units located where falling sparks or hot metal from broken lamps might ignite localized concentrations of flammable gases below the Division 2 location must also have suitable enclosures. Switches, circuit breakers, controllers, and other devices that create arcs or sparks and that are intended to interrupt ignition-capable energy in normal operation must either be explosionproof, have their contacts in hermetically sealed chambers, or have contacts immersed in oil. Enclosures for electrical equipment that does not interrupt ignition-capable energy or otherwise represent an ignition source under normal conditions may be of the general-purpose type. Portable lamps must be of the type satisfactory for use in a Class I, Division 1 location. Class II, Division 1. This includes locations (1) in which combustible dust is in the air under normal operating conditions in sufficient quantities to produce explosive or ignitable mixtures; (2) where mechanical failure or abnormal operation of machinery or equipment might cause such explosive or ignitable mixtures to be produced, and might also provide a source of ignition through simultaneous failure of electric equipment, operation of protective devices, or from other causes; or (3) in which combustible dusts of an electrically conductive nature may be present in hazardous quantities. Motors must be of an enclosed type approved as dust-ignitionproof for the proper Class II locations. Luminaires (lighting fixtures), switches, circuit breakers, controllers, and fuses that are intended to interrupt current in normal operation must be provided with dust-ignitionproof enclosures approved for the proper Class II locations. Maximum surface temperatures on equipment in Class II locations under actual operating conditions must not exceed the ignition temperature of the dust. See Tables 6.1.19 through 6.1.21 for information regarding ignition temperatures of dusts. For additional information, see NFPA 497. Class II, Division 2. This includes locations (1) in which combustible dust is not normally in the air in quantities sufficient to produce explosive or ignitable mixtures, and dust accumulations are normally insufficient to interfere with normal operation of electrical equipment or other apparatus, but combustible dust may be in suspension in the air as a result of infrequent malfunctioning of handling or processing equipment; and (2) where combustible dust accumulations on, in, or in the vicinity of the electrical equipment may be sufficient to interfere with the safe dissipation of heat from the electrical equipment or may be ignitable by abnormal operation or failure of electrical equipment. In general, totally enclosed motors are suitable. Under certain conditions, standard, open-type motors without sliding contacts, switches, and so on may be used in many of these locations.
Fixed lamps and lampholders must have enclosures designed to minimize the deposit of dust and prevent the escape of sparks, burning material, or hot metal. Switches, circuit breakers, controllers, and fuses should be provided with dust-tight enclosures. Division 1 temperature limits also apply to Division 2 locations. Class III, Division 1. This includes locations in which easily ignitable fibers or materials producing combustible flyings are handled, manufactured, or used. In general, motors in these locations must be of the enclosed type except that, where only moderate accumulations of lint are present and cleaning and maintenance are satisfactory, self-cleaning, squirrel-cage, textile motors or standard, open-type motors without sliding contacts, switches, and so on may be installed. Lamps and lampholders, switches, circuit breakers, controllers, and fuses must be dusttight. Maximum surface temperatures under actual operating conditions must not exceed 329°F (165°C) for equipment that is not subject to overloading, and 248°F (120°C) for equipment, such as motors, power transformers, and so on, that may be overloaded. Class III, Division 2. This includes locations in which easily ignitable fibers are stored or handled other than in process of manufacture. Motors must be of the enclosed type. Lamps, lampholders, switches, circuit breakers, controllers, and fuses must have enclosures similar to those specified for Class III, Division 1 locations. Division 1 temperature limits apply to Division 2 locations.
Equipment for Use in Hazardous Locations Equipment for use in Class I, Division 1 hazardous (classified) locations, as defined in the NEC, is sometimes referred to as “explosionproof ” equipment. The two basic design criteria for explosionproof apparatus for Class I locations are that it (1) withstand internal explosions of flammable gas or vapor-air mixtures and (2) prevent propagation of the internal explosion to the surrounding flammable atmosphere. In other words, it is recognized that surrounding flammable gas or vapor-air mixtures will enter the enclosure of this equipment and the possibility exists of their ignition within the enclosure. To prevent the propagation of flame to the outside surrounding atmosphere, which may likewise contain flammable vapor-air mixtures, the enclosures of this equipment must (1) arrest flame at joints or other openings to the outside, (2) be of sufficient strength to resist (without rupture or serious distortion) the internal pressure, and (3) ensure that the external surface temperature of the enclosure is not high enough to ignite the surrounding gas or vapor. The various gas or vapor-air mixtures vary considerably with respect to (1) the propagation of flames through joints of such assemblies, (2) the pressure developed within the enclosure following ignition, and (3) the ignition temperature of the gas or vapor-air mixture. Thus, equipment should be tested and listed for use, and the various groups listed in Table 6.1.18 should be addressed, as necessary. Equipment for use in Class I hazardous (classified) locations must also be designed to operate under full load and, in the
CHAPTER 1
case of equipment such as motors likely to be overloaded, must operate under overload conditions without developing surface temperatures above the ignition temperature of the flammable gas or vapor with which it is intended to be used. As an alternative to “explosionproof” motors, controllers, luminaires (lighting fixtures), switches, or equipment approved for use in Class I locations, it is permissible to use either of the following two designs: 1. Pressurizing System: The protected enclosure must be constantly maintained at a positive pressure of at least 0.1 in. water (25 Pa) above the surrounding atmosphere during operation of the protected equipment and if a positive pressure is not maintained in a protected enclosure, a suitable device such as an indicator, alarm, cutoff, or interlock switch must warn the user to take action or must automatically deenergize power from ignition-capable equipment. The type of device should be dependent on the type of pressurization used. An alarm must be provided to indicate failure of the protective gas supply to maintain the required pressure. If Type X pressurized equipment is provided with a protective gas supply, an alarm is not required. Electric motors require at least 10 volumes of air while maintaining a positive internal pressure of at least 0.1 in. water (25 Pa), in order to accomplish proper purging of the voids between windings. 2. Protective Gas System: The protective gas must be essentially free of contaminants or foreign matter and can contain no more than trace amounts of flammable vapor or gas. Protective gas supplies must be carefully designed to minimize chances for contamination. Air of normal instrument quality, nitrogen, or other nonflammable gas is acceptable as protective gas. Piping for the protective gas must be protected against mechanical damage. If compressed air is used, the compressor intake must be located in an unclassified location. If the compressor intake line passes through a classified location, it must be constructed of noncombustible material, designed to prevent leakage of flammable gases, vapors, or dusts into the protective gas, and protected against mechanical damage and corrosion. In addition, the electrical power for the protective gas supply (blower, compressor, etc.) must be supplied either from a separate power source or from the protected enclosure power supply before any service disconnects to the protected enclosure. When “double pressurization” is used (e.g., a Division I enclosed area pressurized to a Division 2 classification that contains ignition-capable equipment also protected by pressurization), the protective gas supplies must be independent. When either of these designs are used, no external surface of the motors, generators, or other rotating electrical machinery can have an operating temperature (°C) that exceeds 80 percent of the ignition temperature (°C) of the gas or vapor involved, as determined by ASTM E659, “Autoignition Temperature of Liquid Chemicals.” Appropriate devices (heat sensors) must also be provided to detect any increase in temperature of the equipment beyond its design limits and then to automatically de-energize the equipment. The detectors and control equipment used are to
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6–51
be suitable for the atmosphere involved without positive pressure; in other words, they must be explosionproof or intrinsically safe if the location is Class I, Division 1. NFPA 496 provides information for the design of purged enclosures for the purpose of eliminating or reducing within the enclosure a Class I hazardous (classified) location (gases or vapors in air in quantities sufficient to produce explosive or ignitable mixtures). Protective measures include supplying an enclosure with clean air or an inert gas at sufficient flow and positive pressure to achieve and maintain an acceptable safe level of the atmosphere. Another alternative is the use of intrinsically safe systems, which are assemblies of interconnected intrinsically safe apparatus, associated apparatus, and interconnecting cables whose parts that are located in hazardous (classified) locations are intrinsically safe circuits. An intrinsically safe circuit is a circuit in which any spark or thermal effect is incapable of releasing sufficient electrical energy under normal or abnormal conditions to cause ignition of a specific hazardous atmospheric mixture in air under prescribed test conditions. In many cases, the amount of “explosionproof,” purged, or intrinsically safe equipment required can be reduced through the exercise of ingenuity in the layout of electrical installations by locating much of the equipment in nonhazardous areas. The extent of the hazardous areas is normally defined by the codes and standards relating to the storage and handling of the specific flammable liquids, gases, or solids. Equipment for use in Class II and Class III hazardous (classified) locations presents a somewhat different problem, because the equipment is designed to be dust-ignitionproof for Class II, Division 1 and for some Class II, Division 2 locations, and to be dusttight or totally enclosed with telescoping covers for some Class II, Division 2 locations and for Class III locations. It is thus not intended to resist internal explosions of a dust-air mixtures. Such equipment is tested in specific dust-air mixtures to determine that the enclosures are dust-ignitionproof for Class II locations and that overheating does not occur when the device is blanketed with dust or lint and flyings.
Garages, Commercial (Repair and Storage) The requirements of Article 511 of the NEC apply to locations used for the servicing and repair of passenger automobiles, buses, tractors, trucks, and so on in which flammable liquids or flammable gases are used. NFPA 30A, NFPA 88A, Standard for Parking Structures, and NFPA 88B, Standard for Repair Garages, should also be consulted in connection with further classifications of, and the fire protection recommendations applying to, garages. The specific hazardous (classified) areas in these garages are defined in the NEC.
Aircraft Hangars Where aircraft containing gasoline, jet fuels, or other flammable liquids are stored or serviced, the specific (classified) hazardous areas are as defined in Article 513 of the NEC. Reference should
6–52 SECTION 6 ■ Fire Prevention
also be made to NFPA 409, Standard on Aircraft Hangars, for guidance on the construction and protection of these structures.
Motor Fuel Dispensing Facilities This occupancy group includes locations where gasoline or other volatile flammable liquids or liquefied petroleum gases are transferred to the fuel tanks or auxiliary fuel tanks of self-propelled vehicles. Reference should be made to NFPA 30, Flammable and Combustible Liquids Code, and NFPA 30A as well as Article 514 of the NEC for information on the hazardous (classified) areas and other guidance on fire safety in service stations.
Bulk Storage Plants (Flammable Liquid) Where gasoline or other volatile flammable liquids are stored in tanks having an aggregate capacity of one carload or more and from which such products are distributed, the hazardous (classified) areas are defined in NFPA 30 and Article 515 of the NEC. NFPA 30 also contains many requirements for the safe construction and utilization of bulk storage plants.
Spray Application, Dipping, and Coating Processes The NEC hazardous (classified) locations requirements apply to areas where paints, lacquers, or other flammable finishes are regularly or frequently applied by spraying or dipping, or by other means and where volatile flammable solvents or thinners are used, or where readily ignitable deposits or residues from such paints, lacquers, or finishes may occur. Further information regarding safeguards for finishing processes are contained in NFPA 33, Standard for Spray Application Using Flammable or Combustible Materials, and NFPA 34, Standard for Dipping and Coating Processes Using Flammable or Combustible Liquids. NFPA 33 also governs chopper-gun and hand-layup production of glass fiber reinforced plastics. Hazardous (classified) areas with respect to flammable vapors are defined in Article 516 of the NEC.
Chemical Plants
to a level 5 ft (1.52 m) above the floor. The remaining volume up to the structural ceiling is considered to be above a hazardous (classified) area. Any room or location in which flammable anesthetics or volatile flammable disinfecting agents are stored shall be considered to be a Class I, Division 1 location from floor to ceiling. For further information on the subject of flammable anesthetics, reference should be made to Chapter 3 of NFPA 99.
Places of Assembly, Theaters, Areas of Motion Picture and Television Studios, Performance Areas, and Similar Locations In places of assembly, theaters, areas of motion picture and television studios, performance areas, and similar locations where numbers of people congregate, it is important that the electric equipment be properly designed and installed. The general rules of the NEC, as well as its special requirements for these occupancies, should be followed in installing the equipment. NFPA 101 should be consulted for further information on use of emergency lighting.
SUMMARY Electricity can result in fire if an arc occurs or if elictrical equipment overheats, potentially causing injury or death through shock and burns. The risk of fire from electrical systems and appliances is incurred by improper installation, lack of maintenance, improper use, and carelessness, such as failure to turn off a device when no longer needed. The manufacture, use, and maintenance of electrical installations are governed in the United States by the National Electrical Code and other NFPA standards. These standards cover a wide variety of systems, locations, equipment, and procedures, ranging from building wiring, design, and protection to signaling and communications systems. Adherence to the requirements of these standards ensures that electrical systems and appliances are designed, installed, and maintained properly, thus reducing the risk of fire.
In chemical plants where flammable liquids or gases are processed or handled, NFPA 497 provides information on the extent of the hazardous (classified) location.
BIBLIOGRAPHY Reference Cited
Anesthetizing Locations The use of flammable anesthetics in health care facilities has been greatly reduced; however, there may be some older facilities that still use them. Special rules apply in hospital operating rooms and other locations where flammable anesthetics are or may be administered to patients. Article 517 of the NEC defines the anesthetizing location as follows: “Any area of a facility that has been designated to be used for the administration of any flammable or nonflammable inhalation anesthetic agent in the course of examination or treatment, including the use of such agents for relative analgesia.” In a flammable anesthetizing location, the entire area is considered to be a Class I, Division 1 location extending upward
1. Kimberly D. Rohr, “The U.S. Home Product Report (Appliances and Equipment Involved in Fires),” NFPA Fire and Analysis Division, Quincy, MA, Jan. 2002.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on the safeguards for electrical systems and appliances discussed in this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) Fire Protection Guide to Hazardous Materials NFPA 12, Standard on Carbon Dioxide Extinguishing Systems NFPA 20, Standard for the Installation of Stationary Pumps for Fire Protection NFPA 30, Flammable and Combustible Liquids Code
CHAPTER 1
NFPA 30A, Code for Motor Fuel Dispensing Facilities and Repair Garages NFPA 33, Standard for Spray Application Using Flammable or Combustible Materials NFPA 34, Standard for Dipping and Coating Processes Using Flammable or Combustible Liquids NFPA 70, National Electrical Code® NFPA 70B, Recommended Practice for Electrical Equipment Maintenance NFPA 70E, Standard for Electrical Safety Requirements for Employee Workplaces NFPA 72®, National Fire Alarm Code NFPA 75, Standard for the Protection of Electronic Computer/Data Processing Equipment NFPA 77, Recommended Practice on Static Electricity NFPA 79, Electrical Standard for Industrial Machinery NFPA 88A, Standard for Parking Structures NFPA 88B, Standard for Repair Garages NFPA 90B, Standard for the Installation of Warm Air Heating and Air Conditioning Systems NFPA 99, Standard for Health Care Facilities NFPA 101®, Life Safety Code® NFPA 110, Standard for Emergency and Standby Power Systems NFPA 409, Standard on Aircraft Hangars NFPA 496, Standard for Purged and Pressurized Enclosures for Electrical Equipment NFPA 497 Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas NFPA 501, Standard on Manufactured Housing NFPA 501A, Standard for Fire Safety Criteria for Manufactured Home Installations, Sites, and Communities NFPA 513, Standard for Motor Freight Terminals NFPA 780, Standard for the Installation of Lightning Protection Systems NFPA 1192, Standard on Recreational Vehicles NFPA 1194, Standard for Recreational Vehicle Parks and Campgrounds
Additional Readings Anderson, R. N., “Which Came First . . . The Arcing or the Fire. A Review of Auger Analysis of Electrical Arc Residues,” Fire and Arson Investigator, Vol. 46, No. 3, 1996, pp. 38–40. An Illustrated Guide to Electrical Safety, U.S. Department of Commerce, Occupational, Safety and Health Administration, Washington, DC, 1983. Barnes, M. A., and Matheson, A. F., “Technical Evaluation of Fire Related Characteristics of Vinyl Based and Non Halogenated Cable Materials,” EVC Compounds Ltd., Helsby, UK, Hydro Polymers Ltd., Aycliffe, UK. Beck, P. E., “1996 NEC: An Engineers Guide,” Consulting-Specifying Engineer, Vol. 18, No. 4, 1995, pp. 46–48. Beland, B., “Apparent Electrical Fires,” Fire and Arson Investigator, Vol. 47, No. 2, 1996, pp. 19–21. Bernstein, T., “Investigation of Alleged Appliance Electrocutions and Fires Caused by Internally Generated Voltages,” IEEE Transactions on Industry Applications, Vol. 25, No. 4, 1989, pp. 664–668. Braun, E., Shields, J. R., and Harris, R. H., “Flammability Characteristics of Electrical Cables Using the Cone Calorimeter,” NISTIR 88-4003, Center for Fire Research, Gaithersburg, MD, Jan. 1989. Brugner, F., and Schiff, N., “New Cord Technology Designed to Detect Fire-Causing Conditions,” Fire Findings, Vol. 7, No. 1, 1999, pp. 1–2. Castro N. S., “Test Procedure Development for Residential Dishwashers,” Appliance Engineer, Vol. 56, No. 8, 1999, pp. 70–76. Chubb, M., “Promoting Performance through Pro-Active Fire Prevention Regulation,” Proceedings of the 2nd International Symposium on Human Behavior in Fires: Understanding Human Behavior for
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Better Fire Safety Design, Boston, MA, International Science Communications Ltd., London, UK, 2001, pp. 419–430. Comeau, E., “When Fire Affects Communications,” NFPA Journal, Vol. 94, No. 4, 2000, p. 67. Comeau, E., and Puchovsky, M., “Burning up New Orleans,” Fire Prevention, No. 300, June 1997, pp. 25–27. Coombes, C., “Increasing Influence of Water Supplies on Appliance Design,” Fire, Vol. 93, No. 1140, 2000, pp. 31–32. Corbett, G. P., “So You Have to Inspect . . . A Restaurant,” Fire Engineering, Vol. 153, No. 4, 2000, p. 48. DeHaan, J. D., Kirk’s Fire Investigation, 4th ed., Brady Fire Science Series, Prentice Hall, Inc., NJ, 1997, p. 510. “Electrical Fire Threatens the Tate,” Fire Prevention, No. 303, Oct. 1997, pp. 34–35. Earley, M. W., Caloggero J. M., and Sheehan, J. V. (Eds.), National Electrical Code Handbook, 8th ed., National Fire Protection Association, Quincy, MA, 1999. Electrical Appliance and Utilization Equipment Directory, Underwriters Laboratories Inc., Northbrook, IL. Electrical Construction on Materials Directory, Underwriters Laboratories Inc., Northbrook, IL. “Electricity in Emergencies,” Industrial Fire World, Vol. 2, No. 4, 1987, pp. 24–27. Fanney, A. H., and Dougherty, B. P., “Thermal Performance of Residential Electric Water Heaters Subjected to Various Off-Peak Schedules,” Department of Energy, Washington, DC, Solar Engineering, Vol. 2, 1992, pp. 1221–1230; International Solar Energy Conference, April 5–9, 1992, Maui, HI, American Society of Mechanical Engineers, New York, 1992. Farrell, D., “Appliances on Fire,” Women’s Day, Vol. 59, No. 15, 1996, pp. 59–63. Farrell, G. W., “Designing for Safety,” Electrical Consultant, Cary, IL, Consulting-Specifying Engineer, Vol. 19, No. 5, 1996, pp. 47–48, 50. Finnerman, J. M., “Coffeemaker Fires. Special Report,” Fire Findings, Vol. 1, No. 4, 1996, pp. 7–9. Freund, A., “Fire-Testing Cast-Coil Transformers,” EC&M, NY, 1986. Gibbons, J. A. M., and Stevens, G. C., “Limiting the Corrosion Hazard from Electrical Cables Involved in Fires,” Fire Safety Journal, Vol. 15, No. 2, 1989, pp. 183–190. Goto, K., et al., “Flame Retardance and Flammability Test of Insulating Components of Electrical Apparatus,” Proceedings of the Symposium on Electrical Insulating Materials, Institute of Electrical Engineers of Japan, 1986, pp. 293–296. Gratton, G. H. K., “Standardisation and Rationalisation,” Fire Engineers Journal, Vol. 57, No. 191, 1997, pp. 25–29. Gregory, G., “AFCIs Target Residential Electrical Fires,” NFPA Journal, Vol. 91, No. 2, 2000, pp. 69–71. Handbook of Electrical Hazards and Accidents, Geddes, L. A. (Ed.), CRC Press, Inc., Boca Raton, FL, 1995. Hazardous Location Equipment Directory, Underwriters Laboratories Inc., Northbrook, IL. Hilado, C. J., Flammability of Electrical and Electronic Materials, Technomic Publishing Co., Lancaster, PA, 1985. Hoover, J., et al, “Full-Scale Fire Research on Concealed Space Communication Cables,” Proceedings of INTERFLAM ’96, 7th International INTERFLAM Conference, Interscience Communications Ltd., London, UK, 1996, pp. 295–304. Howitt, D. G., “Chemical Composition of Copper Arc Beads: A Red Herring for the Hire Investigator,” Fire and Arson Investigator, Vol. 48, No. 3, 1998, pp. 34–39. Isner, M. S., “Telephone Exchange Fire, Los Angeles, CA, March 15, 1994,” Fire Investigation Report, National Fire Protection Association, Quincy, MA, 1994. Jackson, A. L., “Electrical Aspects of I,” Fire Engineering, Vol. 151, No. 1, 1998, pp. 49–51. Jerome, I., “Serious Electrical Fires, January–December 1999,” Fire Prevention, No. 340, Jan. 2001, pp. 41–43. Johnson, I., “What Happens in a Direct Strike?” Fire Prevention, No. 315, Dec. 1998, p. 25.
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Kassabian, A., “Electrical Baseboard Heaters,” Fire Investigation Report, Office of the Fire Marshall, Canada, Mar. 31, 1993. Kaufman, S., “1990 National Electrical Code—Its Impact on the Communications Industry,” 38th International Wire and Cable Symposium, U.S. Army Communications Electronics Command (CECOM), 1989, pp. 301–305. Lazar, I., “System and Equipment Grounding for Industrial Plants,” Consulting-Specifying Engineer, Vol. 3, No. 3, 1988, pp. 86–89. “Leaving a Hot Iron on Fabric: What Do You Suppose Happens Next?” Fire Findings, Vol. 6, No. 4, 1998, p. 4. Lee, D. A., Trotta, A. M., and King, W. H., Jr., “New Technology for Preventing Residential Electrical Fires: Arc-Fault Circuit Interrupters (AFCIs),” Fire Technology, Vol. 36, No. 3, 2000, pp. 145–152. Liu, S. T., Kelly, G. E., and Terlizzi, C. P., “Performance Testing of a Family of Type I Combination Appliances,” NISTIR 5626, Department of Energy, Washington, DC, Apr. 1995. Magison, E. C., Electrical Instruments in Hazardous Locations, 3rd ed., Instrument Society of America, Pittsburgh, PA, 1978. Martin, B., “Appliance Stowage: How to Win the ‘Space Race,’” Fire, Vol. 89, No. 1095, 1996, pp. 39–40. McGuinnes, W. J., Mechanical and Electrical Equipment for Buildings, 7th ed., Wiley, New York, 1986. Meier, A. K., and Hill, J. E., “Energy Test Procedures for Appliances,” Energy and Buildings, Vol. 26, 1997, pp. 23–33. Menke, K., “Improving Apparatus Electrical Systems,” Fire Engineering, Vol. 149, No. 2, 1996, pp. 43–46. Miller, W., “Thorough Investigation Yields Results,” Fire and Arson Investigator, Vol. 46, No. 3, 1996, pp. 18–19. Monahan, B., “Maintaining Appliances in a Freezing Climate,” Fire International, No. 160, 1997/1998, pp. 17–18. Montagna, F. C., “Chasing Down Electrical Fires,” Fire Engineering, Vol. 152, No. 7, 1999, pp. 83–86. National Electrical Safety Code, Institute of Electrical and Electronics Engineers, New York, 1989. Norman, J., “Using Specialized Appliances, Applicators and Distributors,” Firehouse, Vol. 23, No. 11, 1998, p. 18. Northrup, S. D., “Evaluation of Less Flammable Transformer Liquids,” Proceedings of the 5th BEAMA International Electrical Insulation Conference, Cavanagh Associates, Leatherhead, UK, 1986, pp. 101–106. Orbeck, T., “Development of Guides for Fire Hazards Assessments for Electrical Insulating Materials and Systems,” Conference Record of the 1986 IEEE International Symposium on Electrical Insulation, IEEE, 1986, pp. 265–269. Palko, E., “1990 National Electrical Code: What the Changes Mean to Plant Engineers,” Plant Engineering, Vol. 44, No. 7, 1990, p. 79. Rakosnik, R. J., “Back-Wiring Poses Fire Hazard,” Fire Engineering, Vol. 148, No. 3, 1995, pp. 84–87. Schram, P. J., and Earley, M. W., Electrical Installations in Hazardous Locations, National Fire Protection Association, Quincy, MA, 1988.
Scoones, K., “Fires with Electrical Causes 1990,” Fire Prevention, No. 245, Dec. 1991, p. 18. Scoones, K., “Serious Fires Due to Electrical Causes during 1992,” Fire Prevention, No. 264, Nov. 1993, pp. 14–16. Small, K., “Trade-Offs between Automatic Sprinklers and Manual Fire Suppression Facilities,” Fire Engineers Journal, Vol. 60, No. 204, 2000, pp. 30–34. Smith, L. E., and McCoskrie, D., “What Causes Wiring Fires in Residences?,” Fire Journal, Vol. 84, No. 1, 1990, p. 18. Snell, J. E., “Measuring Hazards of Products of Combustion from Electrical Systems,” Fire Journal, Vol. 81, No. 5, 1987, pp. 108–109. Stallcup, J., Stallcup’s Electrical Design Book, Grayboy Publishing, Fort Worth, TX. “Stop Electrical Fires Short!” Record, Vol. 76, No. 4, 1999, pp. 3–7. Sundin, D. W., and Northrup, S. D., “Relationship between Liquid Flammability Tests and Transformer Fire Situations,” Conference Record—Industrial and Commercial Power Systems Technical Conference 1987, IEEE, 1987, pp. 117–121. Swingler, S. G., Stevens, G. C., and Gibbons, J. A. M., “Small-Scale Assessment of Flame Propagation and Heat Release Rate of Electric Cable Materials,” Proceedings of the 5th International Conference on Dielectric Materials, Measurements and Applications, IEEE Conference Publication No. 289, IEEE, London, UK, 1988, pp. 45–50. Teague, P. E., “1992 NEC Addresses Current Concerns,” NFPA Journal, Vol. 86, No. 5, 1992, pp. 50–52, 54–55. “Total Turnabout in the Concept of Appliance Design,” Fire International, No. 19, July 1999, p. 41. UL 94, “Standard for Safety Test for Flammability of Plastic Materials for Parts in Devices and Appliances,” UL 94, Underwriters Laboratories Inc., Northbrook, IL, 1991. UL 1410, “Standard for Safety Television Receivers and High-Voltage Video Products,” Underwriters Laboratories Inc., Northbrook, IL, 1986. “Understanding Electricity and Electrical Dangers,” Fire Engineering, Vol. 149, No. 4, 1996, pp. 57–92. Vyse, A., “Serious Electrical Fires, January–December 1997,” Fire Prevention, No. 320, May 1999, p. 44–45. Vyse, A., “Serious Electrical Fires, January–December 1998,” Fire Prevention, No. 323, May 2000, p. 55–57. Whittington, B. W., “Electrical Installations in Industrial Locations,” Industrial Fire Hazards Handbook, 3rd ed., A. E. Cote (Ed.), National Fire Protection Association, Quincy, MA, 1990, pp. 1103–1126. Yereance, R. A., Electrical Fire Analysis, Charles C. Thomas, Springfield, IL, 1987. “Your Home Wiring: Is It Safe?” Consumer Reports, Vol. 66, No. 8, 2001, p. 38–41.
CHAPTER 2
SECTION 6
Control of Electrostatic Ignition Sources
Revised by
Don R. Scarbrough Thomas H. Pratt
S
tatic electricity as a source of ignition is a hazard common to a wide variety of industries and processes. This chapter explains the nature of static electricity and the means and methods of eliminating or minimizing it as an ignition source. Information on the hazards of static electricity in specific circumstances and processes can be found in the following chapters: Section 2, Chapter 8, “Explosions”; Section 6, Chapter 21, “Storage of Flammable and Combustible Liquids”; Section 8, Chapter 7, “Gases”; Section 8, Chapter 15, “Dusts”; Section 6, Chapter 1, “Electrical Systems and Appliances”; Section 8, Chapter 14, “Explosion Prevention and Protection”; and Section 6, Chapter 16, “Spray Finishing and Powder Coating.” Additional information can be found in NFPA 77, Recommended Practice on Static Electricity, and in the bibliography at the end of this chapter.
tive “static” more meaningful. Electricity can move freely through some substances, such as metals, that are called “conductors,” but can flow with difficulty or not at all through or over the surface of a class of substances called “nonconductors,” “insulators,” or “dielectrics.” This latter group includes gases, glass, amber, resin, sulfur, paraffin, most synthetic plastics, and most petroleum oils (hydrocarbons). The development of an electrical charge in itself might not be a potential fire or explosion hazard. There must also be a discharge or sudden recombination of separated positive and negative charges. For static electricity to be a source of ignition, four conditions must be fulfilled: 1. There must be an effective means of separating charge. 2. There must be a means of accumulating the separated charges and maintaining a suitable difference of electrical potential between them. 3. There must be a discharge (release of charge) of adequate energy. 4. The discharge must occur in an ignitable mixture.
STATIC ELECTRICITY DEFINED The term static electricity as used in this chapter refers to the electrification of materials through the physical processes described later and the effects of the positive and negative charges so formed, particularly where their release constitutes a fire or explosion hazard. Other electrical terms used in this chapter are defined at the end of the chapter. When an electric charge is present on or in a nonconductive body and it is trapped or prevented from escaping, it is termed static electricity. Electricity on a conducting body that is in contact only with nonconductors or is otherwise isolated from the earth is also prevented from escaping and is therefore nonmobile or “static.” In either case, the body on which this electricity is evident is said to be “charged.” Around 1890, electricity was described as a “subtle agent, without weight or form, that appears to be diffused through all nature, existing in all substances, which gives no indication of its presence in the latent state, but is capable of producing sudden and destructive effects in its active state.” With the discovery of the electron, this definition now seems prophetic and the adjecDon R. Scarbrough is the former safety staff consultant for the Nordson Corporation, Westlake, Ohio, and is now a consultant. He serves on NFPA’s Technical Committee on Finishing Processes and Technical Committee on Static Electricity. Thomas H. Pratt is a consulting scientist with Burgoyne Incorporated, Marietta, Georgia, and is a member of NFPA’s Technical Committee on Static Electricity.
Static electricity can be produced as the result of motions that involve the separation or pulling apart of contacting surfaces, usually of dissimilar substances, either liquid or solid, one or both of which is usually a poor conductor of electricity. Charges separated by this mechanism are usually referred to as being the result of “frictional” or “triboelectric” charging. Examples of such motion that are commonly found in industry are • Motions of all sorts that involve friction between contacting surfaces, usually of dissimilar liquids or solids • Steam, air, or gas flowing from any opening in a pipe or hose, when the steam is wet or the air or gas stream contains particulate matter • Separation of a stream of liquid from a hose, faucet, or pouring spout • Pulverized materials passing through chutes or pneumatic conveyors • Nonconductive power or conveyor belts when in motion • Moving vehicles Accumulation of separated charges typically takes place on the surface of a nonconductive solid, within the body of a nonconductive liquid, or on a dispersed fog or mist. There will always be an electric field where such charges accumulate and these electric fields can have a profound effect on surrounding materials, particularly ungrounded conductors.
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Charge can appear on the surface of a conductive object when that object is simply brought into the electric field of another object that bears a static electric charge. This is known as induction and results fundamentally from manipulation (through repulsion and attraction) of the inherently balanced charges within an uncharged conductive object to produce separate regions on its surface that bear balanced, but opposite charges. An initially uncharged surface can become charged through “contact” with another object or surface that is charged. For example, a pail placed to collect a falling stream of liquid or pulverized material poured from a faucet or other container (the stream therefore being charged by “separation”) will become charged by contact with the charged stream of material. Yet another mechanism for placing charge upon a surface involves bombardment of the surface with charged molecules (ions) of air, which themselves have been charged by a corona from a high-voltage electrode. This mechanism is usually intentional, for example, impressing a charge on the drum of a photocopy machine. Other processes through which charge is imparted to an object or fluid involve exposure to an electron beam or flow of a liquid around a high-voltage electrode. These techniques are commonly referred to as “charge injection.” The separation of static electric charges cannot be prevented absolutely, because the intrinsic origins of static electricity are present at every interface. The object of most electrostatic corrective measures is to provide a means whereby charges separated by whatever cause can recombine harmlessly before sparking potentials are attained. If hazardous conditions cannot be avoided in certain operations, means must be taken to ensure that there are no ignitable mixtures at points where static electric sparks might occur.
If one of the bodies is itself a nonconductor, the flow of electrons across its surface is inhibited and the charge tends to remain at the points where electron transfer originally occurred. A highly charged insulating surface can be discharged with the appearance of a spark by bringing an “earthed” conductor close to it, but only a limited area will be so discharged. Sparks so produced seldom release enough energy to cause ignition. Thus, nonconductors, the bodies most directly involved in charge separation, are usually not directly responsible for fires and explosions. (There are exceptions, which are discussed later in this chapter.) However, such charges can in some cases be the agency for building up or accumulating a charge on a conductive body, which can release all of its stored energy in an incendive (ignition-capable) spark. On a conductive body the charge is free to move. Because like charges repel each other, the charges will distribute themselves evenly over the surface. If the body is of irregular shape, charge will concentrate in areas having a small radius of curvature: the smaller the radius, the higher the concentration of charge and the higher the electric field in the area having the small radius of curvature. For a point, if the voltage is high enough, the electric field (voltage gradient) will exceed the breakdown strength of air (about 3,000,000 V/m), and the air will become ionized and a corona or brush discharge will result. Like charges repel each other and unlike charges attract, because of forces resident in the electrical fields that surround them. These forces have a strong influence on nearby objects. If the neighboring object is a conductor, it will experience a separation of charges by induction. Its repelled charge is free to give or receive electrons as the case may be; if another conductor is brought near, the transfer might occur through the agency of a spark, very often an energetic spark. When the inducing charge is moved away from the insulated conductor, there follows a reversed sequence of events and sparks can result. Thus, in many situations, induced charges are far more dangerous than the initially separated ones on which they are dependent.
CHARGE SEPARATION When two bodies composed of dissimilar materials are in close physical contact, there is likely to be a transfer of free electrons between them, one giving up electrons to the other, and an attractive force is established. When the bodies are separated, work must be done in opposition to these attractive forces. The expended energy reappears as an increase in electrical tension or voltage between the two surfaces. If the bodies are insulated from their surroundings, both are said to be “charged”; the one having the excess of electrons is said to have a negative charge, whereas the other is said to have an equal positive charge. If a conductive path is available between them, the charges thus separated will reunite immediately. If no such path is available, as is the case with insulators, the charges will remain and an electric field will result. In many cases, one of the objects has a deliberate or inherently conductive path to the earth, and its charge is immediately lost to the earth, which is considered to have an infinite capacity to absorb or give up electrons. The other (insulated) object now retains its charge and would hold this charge indefinitely, except for the fact that it must somehow be supported and no supporting insulator (even air) is a perfect nonconductor.
Storage Two conductive bodies separated by an insulator constitute a capacitor (sometimes called a condenser), and where a potential difference is applied between these bodies, charge can be stored. One body receives a positive and the other an equal negative charge. In many instances involving accumulation of static electricity, one of the bodies is the earth, the insulating medium is the air, and the insulated body is some object to or from which a charge (electrons) has been transferred by one of the mechanisms previously described. When a conducting path is made available between two conductive bodies, the energy stored on them is released, that is, the capacitor is “discharged,” possibly producing a spark. The energy so stored and released is related to the charge, Q, the capacitance of the conductive body, C, and the voltage, V, in accordance with the following: Energy C ½CV2 C ½QV C ½Q2/C (V C Q/C) where energy is in joules; capacitance, C, is in farads; charge, Q, is in coulombs; and voltage, V, is in volts.
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Control of Electrostatic Ignition Sources
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Discharge Energy
Ignitable Mixtures
The ability of a discharge to produce ignition of a flammable mixture is governed largely by the energy transferred to the mixture, which will be some fraction of the total stored energy available because some energy is expended in heating the electrodes. Experiments at atmospheric pressure with plane electrodes have shown that the spark breakdown voltage has a minimum value at a critical short gap distance—about 350 V for the shortest measurable gap (about 0.01 mm). Increased gap distance requires proportionately higher voltages. At close spacing, the electrodes can be so close to the ignitable mixture that they adsorb enough heat to preclude ignition of the mixture. Progressing from lowest to highest intensity, discharges through air can occur as corona, brush, spark, or propagating brush discharge. Corona discharge is generally thought of as not energetic enough to ignite gases and vapors. Brush discharges range from corona levels to higher energies that are capable of igniting gases and vapors but not capable of igniting common dusts. Spark discharges and propagating brush discharges are capable of igniting gases, vapors, and dusts. At most favorable electrode spacing, tests have shown that optimum mixtures of saturated hydrocarbon vapors and gases in air require about 0.25 mJ of discharge energy to produce ignition. This level of discharge energy is typical of flammable vapors; however, there are many exceptions. The capacitance necessary to store this level of energy depends on the amount of charge (or voltage) on the capacitor. This leads to the question of how small a capacitor can be and still hold enough charge to ignite the typical hydrocarbon vapor. Experience has shown that a beverage can is big enough. In the same vein, uncomfortable discharges from the human body (usually at the fingertips) are likewise energetic enough.
Elimination of ignitable mixtures in the areas where sparks of static electricity can occur is the surest method of preventing static electricity-caused fires. The subject of ignitable mixtures is beyond the scope of this chapter but is discussed in other NFPA literature, for example, NFPA 30, Flammable and Combustible Liquids Code; NFPA 77; NFPA 497, Recommended Practice for the Classification of Flammiable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas; and NFPA 921, Guide for Fire and Explosion Investigations.
Manifestation of Static Electricity Static electricity will be manifest only where highly insulated bodies or surfaces are found. If a body is “charged” with static electricity, there will always be an equal and opposite charge produced. If a hazard is suspected, the situation should be analyzed to determine the location of both charges and to see what conductive paths are available to both of them. Since no object can be entirely insulated from the earth, there will always be a path for charges to dissipate (discharge). Problems arise where the rate of charge accumulation exceeds the rate of dissipation. If the resistance to ground is less than 1,000,000 ) (1 M)), there are no practical systems that will accumulate charge fast enough to lead to problems of ignition with ordinary gases, vapors, or dusts. In many cases, resistance to ground will be much greater. Tests of such highresistance paths should be made with an applied potential of 500 V or more, in order that any minor interruption (e.g., paint or grease film or air gap) will be broken down and a correct reading of the resistance obtained. Resistance as high as 1000 M) might provide an adequate leakage path in many cases; however, when charges are generated rapidly (e.g., pneumatic transport) a resistance as low as 1 M) might be required.
DISSIPATION OF STATIC ELECTRICITY A static charge that already exists can be removed or allowed to dissipate itself. One obvious way to accomplish this is to reduce the resistance between where the charge resides and ground. Another way is to neutralize the charge by adding an equal charge of opposite polarity.
Humidification A static charge cannot persist except on a body insulated from its surroundings. Most commonly encountered materials that are not usually thought of as conductors, such as fabrics, paper, wood, concrete or masonry foundations, and so on, have a certain amount of moisture on their surface in equilibrium with that in the surrounding atmosphere. This moisture content varies, depending on the weather, and it controls to a large measure the surface conductivity of the material and, thus, its ability to allow the escape of static electricity. In an analogous manner, under some conditions water vapor will condense on the surface of some nominally insulating materials, notably glass and porcelain, to render the surface conductive enough to allow static charges to dissipate. The surface conductivity of the materials under discussion (wood, paper, etc.) is controlled by the water content of the air. Under conditions of high humidity, the materials in question will reach equilibrium conditions containing enough moisture to make the surface conductive enough to prevent accumulations of static electricity. The generating mechanism might still be present, but the rate of charge dissipation exceeds the rate of charge generation and the charge leaks away so fast that no observable accumulation results. At the opposite extreme, that is, with low humidity, these same materials might dry out, become good insulators, and manifestations of static electricity become noticeable. There is no definite boundary line between these two conditions. Where static electricity has introduced operational problems, such as the adhesion or repulsion of sheets of paper, layers of cloth, fibers, and the like, humidifying the atmosphere has proved to be a solution. It is usually stated that a relative humidity of about 50 percent or higher at normal room temperature will avoid such difficulties. Unfortunately, it is not practical to humidify all occupancies in which static electricity might be a hazard. Some operations
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must be conducted in an atmosphere having a low humidity to avoid deleterious effects on the materials handled. High humidity can also cause intolerable comfort conditions in operations where the dry bulb temperature is high. On the other hand, a high humidity might advantageously affect the handling properties of some materials, thus providing an additional advantage. In some cases, localized humidification produced by directing a steam jet onto critical areas can provide satisfactory results without the need for increasing the humidity in the whole room. However, it must be remembered that steam that contains droplets of water can itself generate static electricity. This situation can sometimes be overcome by using a low-velocity jet of humidified air. Humidification is not a cure for all static electricity problems. In particular, it must be remembered that the conductivity of the air is not appreciably increased by the presence of water in the form of a gas. If static electricity accumulates on some surface that is heated above normal atmospheric temperature (e.g., cloth passing over heated rollers), increasing the relative humidity in the surrounding air might do no good whatsoever. Another situation where the control of atmospheric humidity appears to accomplish little is in controlling the charge of static electricity that appears as a space charge in the body of oils. In order to dissipate, such a charge must move through the body of the liquid; therefore, altering the surface conductivity of the oil does little, if anything, to help in the dissipation process. Therefore, increasing the relative humidity of the atmosphere to 50 percent or higher at ordinary room temperatures might eliminate static electricity problems where the surfaces on which the charge accumulates can reach equilibrium with the atmosphere, such as paper or wood. For heated surfaces and for electrostatic charges in oils and other liquid and solid insulating materials, high humidity will not provide a means for draining off charges and some other solution must be sought.
Bonding and Grounding Where natural conditions, including humidity, do not ensure a conductive path to prevent accumulation of static electricity, artificial conducting paths (bonding, grounding) might be necessary. Bonding is the process of connecting two or more conductive objects together by means of a conductor. Grounding (earthing) is the process of connecting one or more conductive objects to the earth and is a specific form of bonding. A conductive object can also be grounded by bonding it to another conductive object that is already connected to the ground. Some objects are inherently bonded or inherently grounded by their contact with the earth. Examples are underground piping or large storage tanks resting on the ground. Bonding eliminates the potential difference between conductive objects. Grounding eliminates potential differences between objects and the earth. When grounding and bonding wires are used to dissipate static electric charges, the currents are quite small and even the smallest of wires are usually adequate to carry the current. The currents encountered in the bond connections used in the protection against accumulations of static electricity are on the order of microamperes (one millionth of an ampere). However, the wires used for bonding and grounding must be able to with-
stand the rigors of the workplace. The acceptable resistance in a ground connection depends on the type of hazard for which it is intended to give protection. To prevent the accumulation of static electricity, the resistance need not be less than 1 M) and in most cases may be even higher. To protect electrical power circuits, the resistance must be low enough to ensure operation of the fuse or circuit breaker under fault conditions. Any ground that is adequate for power circuits or lightning protection is more than adequate for protection against static electricity. A bond or ground is composed of suitable conductive materials having adequate mechanical strength, corrosion resistance, and flexibility for the service intended. Since the bond or ground does not need to have low resistance, nearly any conductor size will be satisfactory from an electrical standpoint. Solid conductors are satisfactory for fixed connections. Flexible conductors are used for bonds that are to be connected and disconnected frequently. Conductors can be insulated, although this is not necessary, or uninsulated. Some prefer uninsulated conductors so that defects can be easily spotted by visual inspection. If insulated for mechanical protection, the concealed conductor should be checked for continuity at regular intervals, depending on the inspector’s experience. Connections can be made with pressuretype ground clamps, brazing, or welding. Battery clamps, or magnetic or other special clamps, ensure good metal-to-metal contact. A special situation requiring substantial conductors might arise if there is a possibility that a ground wire might be called upon to carry current from power circuits or lightning protection systems.
Ionization Were it not for cosmic radiation, air would be nonconductive in its normal state. But, under certain circumstances, air can become sufficiently conductive to bleed off electrostatic charges. For instance, cosmic radiation creates ion pairs in the air. An electric field from an accumulated charge will attract its opposite counterpart ion and repel its like counterpart ion such that the accumulated charge will slowly dissipate. This process is usually too slow to be of much commercial value, but similar mechanisms can be employed. Static Comb. A static electric charge on a conducting body is free to flow and, on a spherical body in space, it will distribute itself uniformly over the surface. If the body is not spherical, self-repulsion will cause the charges to concentrate on the surfaces having the least radius of curvature. If the body is surrounded by air (or other gas) and the radius of curvature is reduced to almost zero, as with a sharp needle point, the charge concentration on the point can produce ionization of the air, rendering the air “conductive.” As a result, whereas a surface of large diameter can receive and hold a high voltage, the same surface equipped with a sharp needle point can reach only a small voltage before the leakage rate through the self-ionized air equals the rate of generation. A static comb is a metal bar equipped with a series of such needle points. A variation uses a metal wire surrounded with metallic tinsel. If a grounded static comb is brought close to an insulated charged body (or a charged insulating surface), ion-
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ization of the air at the points will provide enough conductivity to make the charge speedily leak away or be “neutralized.” This principle is frequently employed to remove the charge from fabrics, power belts, paper, and plastic webs. Electrical Neutralization. The electrical neutralizer is a linepowered high-voltage device that is an effective means for removing electrostatic charges from materials, such as cotton, wool, silk, or paper in process, manufacturing, or printing. It produces a conducting ionized atmosphere in the vicinity of the charged surfaces, enabling the charges to leak away to an adjacent grounded conducting body. Electrical neutralizers should not be used where flammable vapors, gases, or dust might be present, unless approved specifically for such locations. Radioactive Neutralizer. Another method for dissipating static electricity involves ionization of the air by radioactive material. Such installations require no redesign of existing equipment, but engineering problems are involved, such as elimination of health hazards, dust accumulations, determination of radiation required, and proper positioning in relation to the stock, machine parts, and personnel. These considerations are best worked out in consultation with radiation specialists.
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Control of Electrostatic Ignition Sources
FLAMMABLE LIQUIDS Static electric charge can be generated when liquids having a low conductivity move in contact with other materials. This occurs commonly in operations in which liquid flows through pipes and in which liquid is mixed, poured, pumped, filtered, or agitated. Under certain conditions, particularly with liquid hydrocarbons, with high-velocity flow and with filtration through nonconducting, resin-bonded media, static electricity can accumulate on the body of the liquid. If the accumulation is sufficient, a static electric spark can occur even though all conductive equipment is properly grounded. If the spark occurs in the presence of an ignitable vapor–air mixture, ignition is likely. Therefore, steps must be taken to prevent the simultaneous occurrence of these three conditions: low conductivity, energetic manipulation, and ignitable mixture. Before a container is filled, contact should be made between the filling nozzle and the container and the contact should be maintained throughout the filling operation. With this procedure, any difference in potential between the container and nozzle will be dissipated before the filling operation is started and differences in potential between the nozzle and container are prevented from forming during the filling operation. See Figure 6.2.1 for methods of bonding containers and nozzles during container filling.
Open Flame. Ionization of the air can also be obtained by an open flame. This method is frequently used in the printing industry to remove static from paper sheets as they come off the press, thus avoiding the mechanical problems involving one sheet of paper adhering to another, but obviously avoiding ignition.
Hose should be conducting
Nozzle in contact with container (no other bonding necessary)
CONTROL OF IGNITABLE MIXTURES Despite efforts to prevent accumulation of static electric charges, which should be the primary aim of good design, there are many operations involving the handling of nonconductive materials or nonconductive equipment that do not lend themselves to this built-in solution. In these cases it becomes necessary to provide other measures to supplement or supplant static electricity dissipation. For example, where a normally ignitable mixture is contained within a small enclosure, such as a processing tank, an inert gas can be used to render the vapor space safe from ignition. When operations are normally conducted in an atmosphere above the upper flammable limit, it might be practical to apply the inert gas only during the periods when the mixture passes through its flammable range. Mechanical ventilation can be used in many instances to dilute an ignitable mixture to a point below its normal flammable range, that is, below the lower flammable limit. Also, by directing the air movement, it might even be practical to prevent the flammable liquids or dusts from approaching an operation where an otherwise uncontrollable electrostatic hazard exists. To be considered reliable, mechanical ventilation should be interlocked with the equipment it protects to ensure proper operation. Where a static electricity-accumulating piece of equipment is unnecessarily located in a hazardous area, it should be relocated to a safe location.
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Insulating support 106 ohms or more
Conducting support less than 106 ohms
Bond wire necessary except where containers are inherently bonded together or arrangement is such that fill stem is always in metallic contact with receiving container during transfer
Metal strips fastened to floor
FIGURE 6.2.1 Recommended Methods of Bonding Flammable Liquid Containers during Container Filling
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The relative static electricity-accumulating tendencies of a number of petroleum products have been measured in laboratory tests.1,2 In general, aliphatic solvents and lower boiling point hydrocarbons exhibited lower charging tendencies than did higher boiling products. However, the charging tendency of any given product was found to vary widely from one sample to the next. The conductivity of a liquid is a measure of its ability to hold a charge. The lower the conductivity, the greater the ability of the liquid to hold a charge. If the conductivity of a hydrocarbon liquid is greater than 50 pS/m (picoseimens per meter), any charges that are generated will dissipate without accumulating to a hazardous potential as long as all of the associated conductive equipment is properly grounded.
Free Charges on Surface of Liquid If an electrically charged liquid is poured, pumped, or otherwise transferred into a tank or container, the unit charges of similar sign (i.e., = or >) within the liquid will be repelled from each other toward the outer surfaces of the liquid, including not only the surfaces in contact with the container walls but also the top surface adjacent to the air space, It is this latter charge, often called the “surface charge,” that is of most concern in many situations. In most cases, the container is made of metal and is conductive. Two situations can occur, somewhat different with respect to protective measures, depending on whether the container is in contact with the earth or is insulated from it. Examples of these two situations are (1) an ordinary storage tank resting on earth or concrete or other slightly conducting foundation, and (2) a metal can resting on a plastic surface. In the first situation, the metal vessel is connected to ground. The charges that reach the surfaces in contact with the vessel will reunite with charges of opposite sign that have been attracted there. During this process, the tank and its contents, considered as a unit, are electrically neutral; that is, the total charge in the liquid and on its surface is exactly equal and opposite to the charge on the interior of the tank shell. This charge on the tank shell is “bound” there, but gradually disappears as it reunites with the charge migrating through the liquid. The time required for this to occur is called “relaxation time.” The relaxation time depends primarily on the conductivity of the liquid. It might be a fraction of a second or several minutes. During this process, the tank shell is at ground potential. Externally, as already mentioned, the container is electrically neutral. But internally, there could be differences of potential between the container wall and the fluid, lasting until charges on the fluid have gradually leaked off and reunited with the unlike charges on the tank walls. If the potential difference between any part of the liquid surface and the metal tank shell should become high enough to cause ionization of the air, electrical breakdown can occur and a spark might jump to the shell. A spark across the liquid surface is an ignition hazard where flammable vapor–air mixtures are present. No bonding or grounding of the tank or container can remove this internal surface charge. In the second situation, where the can is highly insulated from the earth, the charge on the liquid attracts an equal and op-
posite charge to the inside of the container. This leaves a “free” charge on the outside of the can, of the same sign as that in the liquid and of the same magnitude. This charge can escape from the can to the ground in the form of a spark. In filling a gasoline can resting on a plastic bedliner of a pickup truck, it is this source of sparking that is suspected of creating an ignition potential in some situations; in this case, the spark jumps from the edge of the fill opening to the fill pipe, which is at ground potential. This hazard can be easily controlled by removing the can from the vehicle and placing it on the ground, where any accumulated charge can leak to the earth. The foregoing discusses the distribution of charges delivered into a container with a flowing stream. Further generation or separation can occur inside the container in several ways to produce a space or surface charge: (1) flow with splashing or spraying of the incoming stream, (2) disturbance of “water bottoms” by the incoming stream, (3) bubbling of air or gas through a liquid, (4) jet or propeller blending within the tank, or (5) the settling out of a water layer from a hydrocarbon. These charges on the surface of a body of liquid cannot be prevented by bonding or grounding, but can be rendered harmless by inerting, that is, displacing part of the oxygen with a suitable inert gas, or by increasing the concentration of flammable gas in the vapor space to a point above the upper flammable limit. In some cases additives can be used to increase the conductivity of the liquid such that the charge will rapidly relax and prevent a hazardous condition from developing. It must be recognized that mists and foams of flammable and combustible liquids can be ignited by static electric sparks in much the same way as dusts can be ignited. Ignition is possible even though the liquid in the mist is below its flash point.
GASES Gases not contaminated with solid or liquid particles will not generate any electrification in their flow. When flowing gas is contaminated with dust, metallic oxides, scale particles, or with liquid particles or spray, however, electrification is possible. A stream of such particle-containing gas directed against a conductive body will charge the latter unless it is grounded or bonded. Compressed air or steam containing particles of condensed water vapor often manifests strong static electric charges when escaping. Carbon dioxide, discharged as a liquid from orifices under high pressure (where it immediately changes to a gas and “snow”), can result in electrostatic accumulations on the discharge device and the receiving container. This condition is not unlike the effect from contaminated compressed air or from steam flow where the contact effects at the orifice play a part in the accumulation of static electricity. High-pressure carbon dioxide should not be discharged into flammable atmospheres because it presents a high risk of ignition due to static electric spark. Hydrogen-air and acetylene-air mixtures can be ignited by a spark energy of as little as 0.017 mJ. In the pure state, no static electric charges are generated by the flow of hydrogen. However, as gaseous hydrogen is commercially handled in industry, such as flowing through pipelines, discharging through valves at
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filling racks into pressure containers, or flowing out of containers through nozzles, the hydrogen will often be found to contain particles of oxide carried off from the inside of the pipes or containers. In this contaminated state, hydrogen can accumulate a static electric charge.
DUSTS AND FIBERS Charge Generation in Dust As previously pointed out, the flow of a stream of gas containing small particles can result in a separation of electrons and the accumulation of a static electric charge on any insulated conductive body with which it comes in contact. Also, dust displaced from a surface on which it rests can develop a considerable charge. The ultimate charge depends on the inherent properties of the substance, size of particle, amount of surface contact, surface conductivity, gaseous breakdown, external field, and resistance to leakage in a system. Greater charges develop from smooth rather than from rough surfaces, probably because of greater initial surface contact. Electrification develops during the first phase of separation. Charge separation seldom occurs if both materials are good electrical conductors, but it is likely to occur with a conductor and a nonconductor or two nonconductors. When like materials are separated, as in dispersing quartz dust from a quartz surface, positive and negative charges are developed in the dispersed dust in about equal amounts to give a net zero charge. With materials differing in composition, a charge of one polarity might predominate in the dust. Each of the materials becomes equally charged but with opposite polarity. Charge generation in moving dust normally cannot be prevented. The method of dispersion of the dust, the amount of energy expended in dispersal, the degree of turbulence, and the composition of the atmosphere usually affect the magnitude and distribution of the charges in the dust. Not only can dust participate in the generation of static electricity, it can also be the material ignited by a discharge spark. A suspension of finely divided combustible particles in air has much the same properties as a flammable gas–air mixture, except for a generally higher ignition energy. (With some metallic dust, ignition energy is comparable to gas–air mixtures.) It can burn to produce explosive effects. Dusts have a lower flammable limit, usually referred to as the “minimum explosible concentration,” but no strictly definable upper limit.
Ignition of Dust by Static Electric Discharge Clouds and layers of many combustible dusts (with or without a volatile constituent) have been ignited experimentally by static electric discharge. With dust clouds, it has been shown that a minimum ignitable dust concentration exists below which ignition cannot take place regardless of the energy of the spark. At the minimum ignitable dust concentration, a relatively high energy is required for ignition. At higher dust concentrations, less energy is required for ignition.
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A layer of combustible dust can be ignited by static electric discharge and will burn with a bright flash, glow, or, for some metallic dusts, with flame. Apparently, there is little correlation in the minimum energy required for ignition of dust layers and clouds. Layers of some metallic dusts, such as aluminum, magnesium, titanium, and zirconium, require less energy for ignition than carbonaceous materials. Primary explosives, for example, mercury fulminate, are readily initiated by static electric discharge. Steps necessary to prevent accidents caused by static electricity in explosives manufacturing operations and storage areas vary considerably with the ignition sensitivity of the material being handled. In all instances in which static electricity was authentically established as the cause of ignition of a dust, the spark occurred between an insulated conductor and ground. It has not been verified experimentally that a dust cloud can be ignited by discharge within itself, that is, in a manner analogous to lightning.
STATIC DETECTORS The following devices have an application in the measurement and determination of static electricity within the limitations of each device as described.
Electroscopes The leaf electroscope is a simple but sensitive device that indicates the presence or absence of electric charge by the repulsion of its leaves when the device is charged. Only units intended as portable dosimeters for ionizing radiation and one or two classroom demonstration models are available.
Neon Lamps A small neon lamp or fluorescent tube will light up feebly when one terminal is grounded (or held in the hand) and the other makes contact with any sizeable conductor that carries a charge potential of 70 V or more. Like the electroscope, it gives but little quantitative information; however, when it passes current, it might give a rough idea of the rate at which charges are being produced in certain operations. Adjustable series-parallel groupings of such lamps and small capacitors can be arranged to give a semblance of quantitative information.
Electrostatic Voltmeters These meters operate by electrostatic attraction between movable and stationary metal vanes. A small current is required to deflect the needle, but no current is passed to maintain the deflection because one set of vanes (usually the stationary one) is very highly insulated. Small portable, accurately calibrated instruments are available in several ranges from 100 to 10,000 V. This type of meter can be used for quantitative electrostatic analysis.
Electrometers Electrometers are frequently used for laboratory and field investigations of static electricity. These instruments employ special
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input stages designed for high input resistance and low grid current and can be used in several ways. With a small antenna mounted on the grid terminal, they are very suited for detecting transient electrostatic charge effects; in the presence of a constant field, the charge induced on the grid will leak off and the meter pointer will return to zero. However, as the rate of leakage is not high, the electrometer finds considerable use for “on-the-spot” checks. Often electrometers are equipped with high-resistance terminal shunts to convert them to current meters in the nanoampere range. They can thus be used in many applications to indicate the rate of charge development. A simple adaptation converts the instrument into a megohm meter, as explained in the manufacturer’s instruction manual. Electrometers can be rather expensive and require a user of some sophistication.
Field Mills A field mill is a device that overcomes the serious limitations of the electrometer in that it provides a continuous indication of charge by providing its own transients in the form of continuous grid modulation. It can therefore “look” at a distant charge and determine its sign and potential. The electrical field extending from the charge is “chopped” by a motor-driven variable condenser or window. The resulting pulsations are transformed, amplified, and rectified to give a dc meter deflection proportional to the strength of the field. A similar instrument of suitable design can be immersed in a liquid, as in a pipeline, to measure charge density. Since a field mill senses an electric field, it likewise senses the presence of an accumulated charge. Thus, field mills are handy devices for qualitatively determining the presence of an accumulated charge; with some modest experience, they can even be quantitative.
DEFINITION OF TERMS Some terms used in this chapter are defined as follows. Brush discharge: A form of corona discharge in which brighter “fingers” or “streamers” can be seen. Brush discharges are capable of igniting flammable gases and vapors, but not dusts. Capacitance: The ability to store an electric charge. Electrons received by an electrically neutral body of conductive material, such as a person, a car, or an aircraft, raise the voltage at a rate determined by the surface area and shape of the body. The voltage is determined by the surface characteristics (capacitance) of the body and the number of electrons on this surface. The larger the body, the more electrons are needed to raise the voltage a specific amount; hence, the higher the capacitance of the body. Capacitance is measured in “farads” or millionths of a farad (i.e., microfarads). Millionths of one millionth of a farad are called picofarads. Charge: Measured in coulombs or fractions thereof, the quantity of separated electrons on the body (negative charge) or the quantity of separated electrons not on the body (positive charge). Electrons cannot be destroyed, short of an encounter with antimatter (a positron); so when an electron is removed from one body, it must go to another body. Thus there are always equal and opposite charges produced. Since it would be awkward to
say there are 6,240,000,000,000,000,000 electrons on a body, the body is said to have a charge of one coulomb. A coulomb is simply a name for this specific quantity of electrons. In electrostatics an even more practical unit is a microcoulomb, representing a charge of 6.24 ? 1012 electrons. Corona: A type of air discharge that can occur between flat electrodes or as a single-point discharge at an electrode that has a very small radius or a point. The discharge has a faint blue glow and can make a hissing sound. Corona discharge is usually not capable of causing ignition of ordinary gases and vapors; however, acetylene, carbon disulfide, and hydrogen are among the exceptions. Current: A measure of the flow of electricity. Just as water flow is measured in terms of the amount of water that passes a certain point in a specific period of time (liters per min), so too is the flow of electrons past a certain point measured by time. The flow of electrons is called current. Current is measured in terms of electrons per second, coulombs per second, or amperes. When dealing with static electricity, current is commonly limited to the microampere range. Energy: The ability to do work. Energy is measured in joules or fractions thereof. A spark is energy being expended. The measure of energy takes several forms. Often it is physical energy, which is measured in joules. If it is heat energy, it is measured in calories (cal), and if it is electrical energy it is measured in watt-seconds or in joules. A joule is the energy expended in one second by an electric current of one ampere in a resistance of one ohm (approximately 0.738 foot-pound). Static electric discharge energy is usually measured in thousandths of a joule (millijoules or mJ). A static spark must contain a minimum amount of energy to ignite flammable or combustible materials. Incendive: Capable of causing ignition. A discharge that has enough energy to ignite an ignitible mixture is said to be incendive. Thus an incendive spark can ignite an ignitible mixture and cause a fire or explosion. A nonincendive discharge does not possess the energy required to cause ignition even if it occurs within an ignitible mixture. Incendivity: The ability of a discharge to ignite an ignitible mixture. The energy level required for incendivity varies as described in the text. Potential: Stored energy is able to do work. In electricity, this ability is expressed in terms of the potential of doing work. Potential in electricity is measured in terms of volts, kilovolts, or millivolts. Potential, or voltage, is measured from a base point. This point can be any voltage but is usually “ground,” which is theoretically zero voltage. When one point with a potential of x volts to ground is compared with another point with a potential of y volts to ground, then it is said that a potential difference of x–y volts exists between the two. Then, when a point with a potential of 2500 (= ) volts to ground is compared with a point with a potential of 1500 (>) volts to ground, the potential difference is 4000 volts. Propagating brush discharge: An energetic discharge from an insulative surface on which an intense charge has been stored. To store adequate charge, the insulator must be thin (less than
CHAPTER 2
6 mm) and be backed by a conductive surface that is either grounded or at opposite polarity. The discharge is branched, occurs over an area of several square centimeters, and produces a loud popping sound. Resistance: Electrical current encounters difficulty in passing through an electrical circuit or conductor. This difficulty can be measured and is called resistance. Resistance can be measured in terms of voltage drop over a part of the circuit but is usually measured in terms of ohms or megohms. The resistance of a circuit in ohms is equal to the ratio of voltage in volts to current in amperes. Spark: An energetic discharge, usually accompanied by a popping sound, that occurs when air or gas between two charged conductors becomes highly ionized, enough to break down conducting current through a distinct, luminous channel.
SUMMARY Ignition caused by static electricity is a potential fire hazard in many operations and processes. Static electricity is produced by motions involving the separation or pulling apart of contacting, usually dissimilar, surfaces, one or both of which is usually a poor conductor of electricity. Whenever possible, ignitable mixtures should be removed from areas where sparks of static electricity can occur. Another way to reduce the hazard is to dissipate the static electricity through a variety of means, including humidification (50 percent or higher at normal room temperature), artificial conducting paths (bonding or grounding), or ionization of the air. In cases where dissipation is not possible, measures must be taken to reduce the flammability of ignitable mixtures, for example, by inert gas or mechanical ventilation. Certain operations are especially hazardous with regard to static electricity and require precautionary measures. Such operations include flammable liquid flowing through pipes or being mixed, poured, pumped, filtered, or agitated and gaseous hydrogen flowing through pipelines or discharging through valves at filling racks into pressure containers or flowing out of containers through nozzles. Dust presents a particular hazard as it can both generate static electricity and be ignited by it. Several devices can be used to detect and measure the presence of static electricity, including electroscopes, neon lamps, electrostatic voltmeters, electrometers, and field mills.
BIBLIOGRAPHY References Cited 1. Klinkenberg, A., and van der Minne, J. L. (Eds.), Electrostatics in the Petroleum Industry, Elsevier, Amsterdam, 1958. 2. Walmsley, H. L., “The Avoidance of Electrostatic Hazards in the Petroleum Industry,” Journal of Electrostatics (special issue), Vol. 27, No. 1–2, 1992.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on electrostatic ignition sources discussed in this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.)
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Control of Electrostatic Ignition Sources
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NFPA 30, Flammable and Combustible Liquids Code NFPA 33, Standard for Spray Application Using Flammable or Combustible Materials NFPA 45, Standard on Fire Protection for Laboratories Using Chemicals NFPA 61, Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Product Facilities NFPA 65, Standard for the Processing and Finishing of Aluminum NFPA 70, National Electrical Code® NFPA 77, Recommended Practice on Static Electricity NFPA 385, Standard for Tank Vehicles for Flammable and Combustible Liquids NFPA 407, Standard for Aircraft Fuel Servicing NFPA 480, Standard for the Storage, Handling, and Processing of Magnesium Solids and Powders NFPA 481, Standard for the Production, Processing, Handling, and Storage of Titanium NFPA 482, Standard for the Production, Processing, Handling, and Storage of Zirconium NFPA 651, Standard for the Machining and Finishing of Aluminum and the Production and Handling of Aluminum Powders NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids NFPA 655, Standard for Prevention of Sulfur Fires and Explosions NFPA 664, Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities NFPA 850, Recommended Practice for Fire Protection for Electric Generating Plants and High Voltage Direct current Converter Stations NFPA 1124, Code for the Manufacture, Transportation, and Storage of Fireworks and Pyrotechnic Articles NFPA 1125, Code for the Manufacture of Model Rocket and High Power Rocket Motors
Additional Readings American Petroleum Institute, RP2003, Recommended Practice for Protection against Ignitions Arising out of Static, Lightning, and Stray Currents, Washington, DC, 1998. Atherton, J. G., and Pratt, T. H., “Electrostatic Ignitions in Everyday Chemical Operations: Three Case Histories,” Process Safety Progress, Vol. 18, No. 4, 1999, pp. 241–246. Berkey, B. D., Pratt, T. H., and Williams, G. M., “Review of Literature Related to Human Spark Scenarios,” Plant/Operations Progress, Vol. 7, No. 1, 1988, pp. 32–36. Britton, L. G., Avoiding Static Ignition Hazards in Chemical Operations, Center for Chemical Process Safety of the American Institute of Chemical Engineers, New York, 1999. ISBN 0-8169-0800-1. Britton, L. G., “Static Hazards Using Flexible Intermediate Bulk Containers for Powder Handling,” Process Safety Progress, Vol. 12, No. 4, 1993, pp. 240–250. Britton, L. G., “Systems for Electrostatic Evaluation in Industrial Silos,” Plant/Operation Progress, Vol. 7, No. 1, 1988, pp. 45–50. Britton, L. G., “Using Material Data in Static Hazard Assessment,” Plant/Operations Progress (Plant Safety Progress), Vol. 11, No. 2, 1992, pp. 56–70. Britton, L. G., and Smith, J. A., “Static Hazards of Drum Filling, Parts 1 & 2,” Plant/Operations Technology, Vol. 7, No. 1, 1988, p. 53. Bustin, W. M., and Dudek, W. G., Electrostatic Hazards in the Petroleum Industry, Research Studies Press, Ltd., UK, 1983. Cross, J. A., Electrostatics: Principles, Problems, and Applications, Adam Hilger, Bristol, UK, 1987. ISBN 0-85274-589-3. Crow, R. M., “Static Electricity: A Review of Literature,” DREO-TN91-28, Defense Research Establishment Ottawa, Ontario, Canada, Nov. 1991. Dahn, C. J., Kashani, A., and Reyes, B., “Static Electricity Hazards of Flexible Intermediate Bulk Containers,” Process Safety Progress, Vol. 13, No. 3, 1994, pp. 123–127. Davis, K., “Electrostatic Discharges—Stopping the Sparks Flying,” Fire Prevention, No. 228, Apr. 1990, pp. 21–24.
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Expert Commission for Safety in the Swiss Chemical Industry, “Static Electricity: Rules for Plant Safety,” Plant Operations Progress, Vol. 7, No. 1, 1988, pp. 1–22. “Fire and Explosion Due to Electrostatic Charges in the Plastics Industry,” Bulletin No. 6, Society of the Plastics Industry, NY. Fowler, S., and Morrison, W., “Shock Corridor,” 9-1-1 Magazine, Vol. 14, No. 4, 2001, pp. 50–51. Generation and Control of Static Electricity, National Paint and Coatings Association, Washington, DC, 1988. Glor, M., Electrostatic Hazards in Powder Handling, Research Studies Press/Wiley, Letchworth, UK. Gomez, A., and Chen, G., “Charge-Induced Secondary Atomization in Diffusion Flames of Electrostatic Sprays,” Combustion and Flame, Vol. 96, No. 1–3, 1994, pp. 47–59. Handbook of Electrical Hazards and Accidents, L. A. Geddes (Ed.), CRC Press, Inc., Boca Raton, FL, 1995. Hansheng, L., “Experimental Investigation of Electrostatic Fire Accidents After Aircraft Landing and Preventive Measures,” Journal of Aircraft, Vol. 26, No. 5, 1989, pp. 405–419. Horstmann, T., Leuckel, W., Mass, U., and Mauer, B., “Influence of Turbulent Flow Conditions on the Ignition of Flammable Gas/Air Mixtures,” Process Safety Progress, Vol. 20, No. 3, 2001, pp. 215–224. Howells, P., “Electrostatic Hazards of Foam Blanketing Operations,” Industrial Fire Safety, Vol. 2, No. 4, 1993, pp. 18, 21–24. “Ignition Tests of Gasoline by Spark of Metal,” Japan Association for Fire Science and Engineering, Vol. 47, No. 4, 1997, pp. 31–35. “Instantaneous Fire Detection/Suppression System for Jaguar Paint Spray Electrostatic Plant,” Product Finishing, Vol. 40, No. 7, 1987, pp. 14–15. Jones, T. B., and King, J. L., Powder Handling and Electrostatics: Understanding and Preventing Hazards, Lewis Publishers, MI, 1991. Kinney, P. D., et al., “Use of Electrostatic Classification Method to Size 0.1 mum SRM Particles. A Feasibility Study,” Journal of Research of the National Institute of Standards and Technology, Vol. 96, No. 2, 1991, pp. 147–176. Lampert, B., “Protecting 9-1-1 Systems against an Invisible Threat,” APCO Bulletin, Vol. 61, No. 1, 1996, pp. 83–85. Louver, J. F., Mauren, B., and Biocourt, G. W., “Tame Static Electricity,” Chemical Engineering Progress, Vol. 90, No. 11, 1994, pp. 75–79.
Luo, H., “Experimental Investigation of Electrostatic Fire Accidents After Aircraft Landing and Preventive Measures,” Journal of Aircraft, Vol. 26, No. 5, 1989, pp. 405–409. Mancini, R. A., “The Use (and Misuse) of Bonding for Control of Static Ignition Hazards,” Proceedings of the 21st Annual Loss Prevention Symposium, AICHE, August 1987. Moore, A. D., Electrostatics and Its Applications, Wiley-Interscience, New York, 1973. ISBN 0-471-61450-5. Nifuku, M., and Enomoto, H., “Evaluation of the Explosibility of Malt Grain Dust Based on Static Electrification during Pneumatic Transportation,” Proceedings of the 3rd International Symposium on Hazards, Prevention, and Mitigation of Industrial Explosions, Tsukuba, Japan, October 23–27, 2000, pp. 166–171. Nifuku, M., and Katch, H., “Incendiary Characteristics of Electrostatic Discharge for Dust and Gas Explosions,” Proceedings of the 3rd International Symposium on Hazards, Prevention, and Mitigation of Industrial Explosions, Tsukuba, Japan, October 23–27, 2000, pp. 240–245. Owens, J. E., “Spark Ignition Hazards Caused by Charge Induction,” Plant/Operations Progress, Vol. 7, No. 1, 1988, pp. 37–39. Pratt, T. H., “Electrostatic Ignitions in Enriched Oxygen Atmosphere: A Case History,” Process Safety Progress, Vol. 12, No. 4, 1993, pp. 203–205. Pratt, T. H., Electrostatic Ignitions of Fire and Explosions, Center for Chemical Process Safety of the American Institute of Chemical Engineers, New York. ISBN 0-8169-9948-1. Pratt, T. H., “Static Electricity in Pneumatic Transport Systems: Three Case Histories,” Process Safety Progress, Vol. 13, No. 3, 1994, pp. 109–113. Rosenthal, L. A., “Static Electricity and Plastic Drums,” Plant Operations/Progress, Vol. 7, No. 1, 1988, pp. 51–52. Schram, P. J., and Earley, M. W., Electrical Installations in Hazardous Locations, National Fire Protection Association, Quincy, MA, 1997. Schram, P. J., and Earley, M. W., Electrical Installations in Hazardous Locations, 2nd edition, National Fire Protection Association, Quincy, MA, 1997. Tremblay, K. J., “Static Electricity Ignites Propane: Ohio,” NFPA Journal, Vol. 91, No. 4, 1997, p. 4. “Understanding Electricity and Electrical Dangers,” Fire Engineering, Vol. 149, No. 4, 1996, pp. 57–92.
CHAPTER 3
SECTION 6
Lightning Protection Systems Revised by
John M. Caloggero
I
n the period from 1994 to 1998, lightning caused an estimated 35,000 fires per year reported to U.S. municipal fire departments, with associated annual losses of 12 civilian fire deaths and $223 million in direct property damage. From 1993 to 1997, lightning was also cited as the direct cause of 68 deaths per year.1 Unlike many other causes of death and injury that one can run away from, lightning strikes before the warning thunder. The principles of protection and personal safety are well known and are spelled out in NFPA 780, Standard for the Installation of Lightning Protection Systems. It must be remembered, nevertheless, that lightning involves many uncertainties and that, although a given pattern of lightning behavior might be probable, there is no guarantee that a lightning discharge will not deviate from that pattern.
FACTORS IN THE NEED FOR LIGHTNING PROTECTION
Since 1894, the recording of thunderstorms has been defined as the local calendar day during which thunder was heard. A day with thunderstorms is recorded as such, regardless of the number occurring on that day. The occurrence of lightning without thunder is not recorded as a thunderstorm. For statistical data on the frequency of thunderstorms in Canada, see Figure 6.3.2, and for the world, see Figure 6.3.3.
Earth Resistivity Figure 6.3.4 illustrates the estimated average resistivity of the earth, measured at various locations in the United States, in ohm-meters. Resistivity is measured in ohm-centimeters and is defined as the resistance of a cube of material measured in centimeters. In Figure 6.3.4, however, it is measured in ohm-meters. The highest resistivity is located in the northeastern segment of the country, with 2000 ohm-meters measured in Long Island, New York, northern New Hampshire, and Vermont. Structures in these areas are susceptible to more frequent lightning strikes.
Value and Nature of Building and Contents
Frequency and Severity of Thunderstorms The frequency of thunderstorms varies throughout the world. The severity of thunderstorms, as distinguished from their frequency of occurrence, is much greater in some locations than in others. Hence, the need for protection varies geographically, although not necessarily in direct proportion to thunderstorm frequency. A few severe thunderstorms a season can, in fact, make the need for protection greater than a relatively large number of storms of lesser intensity. See Figure 6.3.1 for statistical data on the yearly number of flashes to ground per km2 due to thunderstorms in the United States. Note that the highest flash density is encountered in south-central Florida. The data show the average number of lightning flashes per year for the United States. Eleven years of lightning data (1989 to 1999) were collected to make the flash density map in Figure 6.3.1. Measured lightning flash density has been corrected for NLDL detection efficiency.
Buildings and structures that are essential to life safety, such as hospitals, fire stations, police stations, and military and civil defense facilities, should have a lightning protection system installed if they are located in areas where lightning commonly occurs. Some buildings have an uninsurable historical or cultural value. The type of building construction also influences the degree of protection to be considered. Some buildings require no supplemental lightning protection due to their construction. The real or intangible value of the building’s contents must also be considered, and, in some cases, attention must be given to the nature of the contents and its susceptibility to damage by induced lightning currents, for example, storage of explosives. Appendix H of NFPA 780 contains a risk assessment guide that provides guidelines for assessing the need for lightning protection. Not part of the requirements of NFPA 780, the appendix is included there for informational purposes only.
Personnel Hazards John M. Caloggero is principal electrical specialist at NFPA and NFPA staff liaison to NFPA’s Technical Committee on Lightning Protection.
The lightning hazard to personnel in buildings or structures is a major concern. Because a stroke of lightning may lead to
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6–66 SECTION 6 ■ Fire Prevention
1989–1994 Avg. Vermont Lightning Fl. Density (fl./km 2/yr.)
>2
>1
>1 >1
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>2
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Lightning data provided by the U.S. National Lightning Detection Network (Measured lightning flash density corrected for NLDN detection efficiency)
FIGURE 6.3.1 Statistics for Continental United States Showing the Average U.S. Lightning Flash Density in Flashes/km2/Year (Source: Global Atmospherics, Inc.)
considerable discomfort, if not injury or death, lightning protection may be necessary to eliminate possible personnel hazards in buildings of any type (other than those constructed of structural steel framing).
Relative Exposure Lightning will nearly always strike the highest point in its area of impact. In closely built-up towns and cities, this means the hazard is not as great to one-story buildings or individuals outside as it is in open country. In rural areas, however, a one-story barn is likely to be the tallest object in its area. In hilly or mountainous areas, a building located on high ground is usually subject to greater hazard than one in a valley or in an otherwise sheltered area.
Indirect Losses In addition to direct losses (e.g., damage to buildings or their contents by lightning, fire resulting from lightning, death of livestock, etc.), there could be indirect losses. Interruption of business, computer, or farming operations, especially at certain times of the year, can involve losses quite distinct from and in addition to those arising from direct property damage. In some cases, whole communities depend on the integrity of a single structure for a measure of safety and comfort, for example, the brick chimney of a water pumping plant. A stroke of lightning to the unprotected chimney of a plant of that sort might have serious consequences, resulting in lack of sanitary drinking water, irrigating water, water for fire protection, or some similar effect.
CHAPTER 3
1 5 10 0 1 5
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FIGURE 6.3.2 Canadian Statistics Showing Annual Average of Days with Thunderstorms in the Period 1957 to 1972 (Source: Meteorological Division, Department of Transportation, Canada)
NATURE OF LIGHTNING The planet and its atmosphere can be viewed as a large spherical capacitor, with the earth at about 300,000 V negative, with respect to the upper ionosphere. This potential difference powers a flow of electricity from the earth to the atmosphere. The rate of current flow, calculated at approximately 1400 to
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Lightning Protection Systems
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1800 A, is spread out over the earth’s entire surface. Therefore, this amounts to about 0.00009 A per sq mi (0.000035 A/km2). Under clear, normal conditions, the electrostatic field intensity at the earth’s surface is 150 to 200 V per meter (V/m) of elevation. As a thunderstorm approaches, the potential difference rises to 10,000 to 30,000 V/m of elevation. Air currents pick up moisture as they pass over large bodies of water, such as lakes, rivers, and oceans. This air mass is heated when it passes over warmer land masses, causing it to rise. As the moist air mass passes through the 14,000-ft (4,200-m) elevation, the moisture condenses and forms ice crystals. The ice crystals in an active cloud become positively charged, whereas the water droplets usually have negative charges. Due to these conditions, a thundercloud normally develops a positive charge at the upper level and negative charge at the lower level. An electric field now exists within the cloud as well as above and below it. This negative charge in the lower level of the cloud induces a positive charge in grounded objects below it. Sharp pointed objects, such as flagpoles, steeples, corners of buildings, and trees, develop concentrated fields at these locations, resulting in a pointdischarge current of a few amperes that moves upward in the electric field. As the voltage between the earth and the cloud increases, the lightning discharge to earth starts at the cloud, progressing in incremental steps with a faintly luminous discharge, called a leader stroke in lengths of about 65 ft (20 m). The current in these leaders is estimated at about 200 A. When the faint lightning leader reaches an upward leader, an intense flash can be seen traveling upward to the cloud. This is called the return stroke and is a direct short circuit between the negative portion of the cloud and the electrostatically induced positive charge of the earth.
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1
FIGURE 6.3.3 Annual Frequency of Thunderstorm Days as Compiled by the World Meteorological Organization, 1956 (Source: World Meteorological Organization)
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FIGURE 6.3.4
Estimated Average Earth Resistivity in Continental United States
The development of a stepped leader is diagrammed in Figure 6.3.5. When sufficient charge has built up on a cloud, a “pilot streamer” will develop in a generally downward direction. This streamer ionizes a path in the air. The current associated with it is small, on the order of only a few amperes. The streamer initially extends on the order of 150 ft (45.7 m) below the cloud. After a pause of about 50 microseconds, the streamer will proceed for a second step, again generally downward but usually in a somewhat different direction from the initial step. Subsequent steps occur at intervals of about 50 microseconds. The path of each step is essentially straight, but each new step generally takes a different direction. The change in direction at each junction results in the zigzag path characteristic of lightning. Branches can (and often do) occur but, for simplification, these are not shown in Figure 6.3.5. As the leader progresses downward, it creates a highly conductive ionized path in the air. Thus, the tip of the leader essentially remains at cloud potential, and the voltage gradient between the tip and the earth increases as the tip progresses downward. At some critical point (point 6 in Figure 6.3.5), the voltage gradient becomes high enough to break down the remaining air gap, and the initial stroke to ground is completed. The point from which the final breakdown occurs is called the point of discrimination; the distance over which this breakdown occurs is defined as the striking distance. As many as 40 component strokes have been observed in a single flash. Speeds range from 100 mi/s (161 km/s) for the first pilot leader stroke to 20,000 mi/s (32,190 km/s) for the main
1 1
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FIGURE 6.3.5
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stroke. Currents average about 24,000 A but range up to 270,000 A in extreme cases, lasting for a few millionths of a second, but lesser currents are present for a longer period. Potentials have been estimated as high as 15 million volts. Because of the high voltage and rapid changes in current flow, induced charges are important. Thus, NFPA 780 requires the interconnection of metallic masses as a part of any lightning protection system. Lightning causes fire when sufficient heat is produced to ignite combustible materials in its vicinity. Substantial damage, however, can be produced without resulting in fire. Dry wood
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CHAPTER 3
beams in houses struck by lightning can be severely splintered and windows can be blown outward. Such damage primarily results from pressure generated by the expanding lightning channel. Because some effects of lightning can be indirect, it is not necessary for lightning to strike a building to cause damage. Lightning striking an overhead wire can be conducted over the wire to a building. Therefore, lightning arresters (surge arresters) should be provided to minimize such damage. Although there are several types of surge arresters, all permit the free flow of lightning charges to ground, while preventing the flow of ordinary electric current over the same path. The surge arrester should be backed up with a transient voltage surge suppressor on branch circuits that serve computers and electronic appliances.
TRADITIONAL THEORY OF LIGHTNING PROTECTION The theory of lightning protection is simple—to provide means by which a lightning discharge can enter or leave the earth without damaging the protected property. There is no evidence that any form of protection can prevent the occurrence of a lightning discharge. A lightning protection system has two functions: (1) to intercept a lightning discharge before it can strike the object protected, and (2) to discharge the lightning current harmlessly to earth.
Conventional Concept The zone protected by a grounded rod or mast is conventionally taken as the space enclosed by a cone that has its apex at the top of the mast. Similarly, the zone protected by a grounded horizontal overhead wire is conventionally taken as a triangular prism, with the upper edge along the wire. In either case, the degree of protection is generally assumed to be a function of the shielding angle, that is, the angle between an element of the cone and a vertical line through the apex, or between the side of the prism and the vertical plane through the horizontal wire. This is sometimes expressed as the ratio of the horizontal distance protected to the height of the mast or wire. Figure 6.3.6 illustrates this concept and tabulates some generally accepted zones of protection. NFPA 780 states that, for
O
A
B
C
C′ D
Zone AOA′ BOB′ COC′
D/H 2/1 1/1 0.58/1
FIGURE 6.3.6
∝ 63° 45° 30°
Geometric Concept of Lightning Protection The geometry of lightning protection is illustrated in Figure 6.3.7, which shows a hypothetical cross section of an area protected by two vertical masts (or horizontal overhead wires). Consider first a downward leader descending to the right of Mast A. Final breakdown will occur when the leader tip approaches within a specified distance, X (the striking distance), of any grounded object or surface. If the point of discrimination, P (the point at which final breakdown will occur), is equidistant
P2 Protected zone Mast B
B′
A′
D Authority NFPA NFPA British code British code
Recommended for Ordinary cases Important cases Ordinary structures Danger structures
Conventional Concept of Protected Zones
P1
Mast A
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X H
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G R
= = = =
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Point of discrimination Striking distance Horizontal distances for protected height B Minimum elevation completely protected
2X 2X D = H — – 1 – B — –1 H B
∝
H
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structures not greater than 50 ft (15 m) in height, a horizontal distance equal to the height of the rod or mast has been found to be substantially immune to direct strokes. This horizontal distance extends to twice the height of the rod or mast if the structure does not exceed 25 ft (7.6 m) in height. The British Standard Code of Practice, “The Protection of Structures Against Lightning,”2 states that a shielding angle of 45 degrees provides an acceptable level of protection for ordinary structures, but for structures with explosives or highly flammable contents, the shielding angle should not exceed 30 degrees. Both codes indicated that complete protection cannot be guaranteed in any case. It is assumed, however, that the criteria presented reduce the probability of lightning strikes to a practical minimum. Although these criteria provide essentially complete protection in most cases, theoretical consideration indicates that even the 30-degree shielding angle is not always adequate.
P 1 ,P 2 X R,D G
∝ = Shielding angle
Lightning Protection Systems
(H ≤ X )
2X 2X R = (H – G) — – 1 – (B – G) — –1 (H – G ) (B – G )
S2 2 G=H–X+ X – — 2
( )
For H >X, D = X –B
FIGURE 6.3.7
(S ≤ 2 X )
2X — –1 B
Geometric Concept of Lightning Protection
6–70 SECTION 6 ■ Fire Prevention
protection system should be designed to protect against minimum anticipated striking distances. The peak stroke current is usually at least 10,000 A. This corresponds to a striking distance of slightly over 100 ft (30.5 m). It is, therefore, believed that a protective system based on this minimum striking distance will essentially provide complete protection. This is considered to be a reasonable design basis.
Design Curves Using the derived equations and an assumed striking distance, the protection provided by a single mast (or horizontal overhead wire) can be readily calculated. Similarly, the configuration of masts or overhead wires required to protect a given structure can be investigated. However, the calculations are tedious, and it is not convenient to determine directly by simple algebra the mast or overhead wire height required to protect a structure of given dimensions. Hence, curves showing the relationship between protected zones and various mast or horizontal overhead wire configurations are useful. Such curves can be readily constructed graphically (Figures 6.3.8 and 6.3.9). In Figure 6.3.8, the solid curves are the geometric concept, with a striking distance of 100 ft (30.5 m). The dashed lines are the conventional concept, with a shielding angle of 45 degrees. H equals the height of the mast or horizontal wire. In Figure 6.3.9, the striking distance is 100 ft (30.5 m). H equals the height of the horizontal wire, S is the spacing between masts or wires, and B is the height protected above ground.
1. Striking distance 2. Height of mast or overhead wire above ground 3. Distance between two or more masts or overhead wires
Horizontal distance, D (m) 6.1 12.2 18.3
100
Striking Distance The striking distance is related to the potential of the lightning stroke, which is directly related to the charge on the cloud. Since the peak stroke current is also related to the charge on the cloud, it can be shown that the striking distance is directly related to the peak stroke current. For a given mast or ground wire height, the protected distance increases with increasing striking distance. Thus, an adequately designed lightning protection system provides maximum protection against what could be the most damaging strokes. Since minimum protection exists for a minimum striking distance (and minimum stroke current), the lightning
30.6
H = 100 ft or 30.5 m (conventional concept) 24.4
80
Height protected, B (ft)
Figure 6.3.7 shows why the protected zone between two masts is greater than the total of the zones of the two masts considered individually. Previous NFPA lightning protection codes recognized this qualitatively but not quantitatively. The figure also shows why the shielding angle required on transmission lines decreases as tower (and overhead ground wire) height increases.
24.4
H = 100 ft or 30.5 m (geometric concept) 60
18.3 80 ft (24.4 m)
60 ft 40 (18.3 m)
12.2
40 ft (12.2 m) 20
0
30 ft (9.1 m) 20 ft (6.1 m) 10 ft (3 m)
6.1
20
40 60 Horizontal distance, D (ft)
80
FIGURE 6.3.8 Zone Protected by a Single Mast, Horizontal Wire, or Air Terminal
100
Height protected, B (m)
from the tip of the mast and the ground, either the mast or the ground can be struck. If P is close to the mast, it will intercept the stroke; if P is farther from the mast, the ground will be struck. If any structure to the right of the mast extends above ground to within a distance less than X of point P, the structure will be struck. It can be seen that the zone protected by a single mast or by an outside mast of a multimast system, in a direction away from the other masts, is bounded by the arc of a circle of radius X, passing through the tip of the mast and tangent to the ground. Geometrically, it can be shown that the protected distance D, at an elevation B above ground, is given by the expression shown, where H is the height of the mast above ground and X is the striking distance. Similarly, for a leader extending downward between the two masts, the protected zone is bounded by the arc of a circle of radius X passing through the tips of the two masts. If the masts are close enough together, the space between them is completely protected for an elevation above ground, which is a function of mast height H and spacing S. In this case, the protected distance R at elevation B and the minimum elevation G, which is completely in the protected zone, are given by the two expressions shown. These equations hold only if H is less than or equal to X and S is less than or equal to 2X. Furthermore, G must be positive. If G is negative, complete protection does not exist between the two masts, and the equation for D holds. The geometric concept shows that the protected zone is not a cone or prism but is bounded by surfaces generated by concave arcs. This fact is not generally appreciated, although it is at least partially recognized in transmission line shielding. Furthermore, the protected distance is seen to be a function of
CHAPTER 3
Horizontal distance, R (m) 6.1
12.2
18.3
24.4
30.5
S = 100 ft (30.5 m) 120 ft (36.6 m)
20
6.1 140 ft (42.7 m) 160 ft (48.8 m)
40
12.2
180 ft (54.7 m) 190 ft (57.9 m)
60
18.3
24.4
80 200 ft (61 m) 100 0
20
40 60 Horizontal distance, R (ft)
80
Height of mast – height protected, H – B (m)
Height of mast – height protected, H – B (ft)
0
30.5 100
FIGURE 6.3.9 Zone Protected by Two Masts, Two Horizontal Wires, or Two Air Terminals
PROPERTY PROTECTION Components Air Terminals. According to current United States practice, as indicated in NFPA 780, conditions required for protection of ordinary buildings are met by placing metal air terminals on the uppermost parts of the building or its projections, with conductors connecting the air terminals with each other and to the ground. By this means, a relatively small amount of metal, properly proportioned and distributed, affords a satisfactory degree of protection and can be installed in a way that interferes only minimally with the contour and appearance of the building. In the current British Standard Code of Practice,2 the use of pointed air terminals (vertical finials) is not considered essential, except where dictated by practical considerations. One theory states that a protective system based on a minimum striking distance of 100 ft (30.5 m) for structures containing flammable liquids and gases will provide 99.9 percent protection, and a minimum striking distance of 150 ft (45.7 m) will provide 99.5 percent protection for ordinary structures that are generally capable of withstanding minor direct strokes.3–5 This theory supports the use of 10-in. (254-mm) minimum height air terminals above the object to be protected at 20-ft (6.1-m) maximum intervals. A convenient geometric equation ƒ Y C R 2 > (R > h)2 where Y C radius of horizontal protected zone R C striking distance h C height of air terminal
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Lightning Protection Systems
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illustrates that a striking distance of 100 ft (30.5 m) will provide a 12.9-ft (3.9-m) radius of horizontal protected zone or 25.8-ft (7.9-m) horizontal protected zone between air terminals, and a striking distance of 150 ft (45.7 m) will provide a 15.8-ft (4.8-m) radius of horizontal protected zone or 31.6-ft (9.6-m) horizontal protected zone between air terminals. The subject of sharply pointed versus blunt air terminals is under study by the NFPA Lightning Protection Committee. According to Moore et al.,6 pointed air terminals have a built-in defense against lightning strikes. The strength of the electric field around the tip of an air terminal is limited by a phenomenon called “point discharge.” When the electric field reaches a certain strength but before lightning strikes, the stepped leader current flows from the air through the air terminal to the ground. The effect is called point discharge because the point is letting the surrounding air lose charge or discharge electricity. A pointed air terminal will presumably discharge sooner than a blunt one. Accordingly, Moore et al.6 concluded that a blunt air terminal is more likely to intercept a lightning strike and complete a circuit. Conductors. NFPA 780 specifies the use of copper or aluminum metals for lightning conductors. When copper and aluminum are used together, special precautions must be taken against electrolytic corrosion. Conductors are coursed along ridges of sloping roofs, around the edges of flat roofs, and vertically from these and from the air terminals to ground. Vertical runs are designated as “down conductors,” and there are never fewer than two on any kind of structure, except for flagpoles, masts, spires, and similar structures. The down conductors are normally placed at diagonally opposite corners of square or rectangular structures, but other factors, such as direct coursing, security against displacement, location of metallic elements in the structure, location of water pipes, and favorable ground conditions, need to be considered in determining optimum placement. For detailed instructions about the installation of conductors, their form and size, and about the installation of air terminals, refer to the latest edition of NFPA 780. The down conductors to ground must be substantial and must provide a reasonably direct path. The blocking effect (choke) of electrical induction must be avoided. For example, a lightning conductor that is installed within a piece of iron pipe for mechanical protection must be bonded to the pipe at both ends to reduce the choke effect on the conductor, which increases the impedance of the conductor.7 Grounding. Ground connections are essential if a lightning protection system is to be effective; every effort should be made to provide ample contact with the earth (Figure 6.3.10). Resistance of the protective system to ground is not critical. However, resistance and surge impedance must be low enough to prevent side flashes between the down conductor and other grounded objects. The resistance also must be low enough to prevent excessive voltage gradients in the soil surrounding the ground electrode. Excessive voltage gradients can be dangerous or fatal to people or animals that might be standing or walking in the
6–72 SECTION 6 ■ Fire Prevention
1 2 Typical air terminal for metal or masonry flat roof
Bonding conductor to purlin
2
1
3
Bonding column to ground 60 avg. 3
FIGURE 6.3.10 Grounding and Bonding of Lightning Down Conductors. Water pipe grounds (if pipes are metallic) can be made at 1, 2, or 3.
vicinity when a lightning stroke occurs. If the down conductor is remote from other grounded objects and people or animals are not likely to be near the ground electrode during a lightning storm, a relatively high ground resistance can be tolerated. Otherwise, an extensive wire network will need to be laid on the surface. NFPA 780 does not specify any maximum recommended ground resistance. The British Standard Code of Practice2 recommends a maximum resistance of 10 ) for a lightning protection system that will normally include two or more ground electrodes. Also 10 ) is generally considered a reasonably good ground resistance for transmission towers. In this case, a high ground resistance might result in flashover to the line conductors, even though the overhead ground wire intercepts the direct lightning stroke. The U.S. Department of Agriculture recommends a ground resistance not greater than 50 ) as acceptable for protection of farm structures. The ground resistance of a ground electrode is directly proportional to soil resistivity. Soil resistivity varies over wide limits, as shown in Figure 6.3.4; nevertheless, 10,000 )/cm is a reasonable order of magnitude average for many areas. Figure 6.3.11, which is based on derived equations,8 has been prepared
to show the variation in resistance to earth of vertical rods or pipes as a function of length in 10,000 )/cm soil. For other soil resistivities, the resistance to ground can be obtained by multiplying the indicated resistance by the known soil resistivity divided by 10,000. Vertical rods driven into the ground are commonly used as grounding electrodes. In addition, where buried metallic water pipes are nearby, it is required to connect the lightning protection ground system to the piping system. If bedrock is on or near the surface, it would be impossible to make a ground connection in the ordinary sense of the term because most kinds of rock are insulating or at least of high resistivity and, in order to obtain effective grounding, other and more elaborate means are necessary. An effective method to achieve grounding is to use an extensive wire network (grid) laid on the surface of the rock surrounding the building, to which the down conductors are connected. Another method is to install a ground ring interconnecting the down conductors, with metal straps run outward in a radial formation on the surface of the rock from each of the down conductors. One ground ring should be installed at the bottom of the foundation to which the down conductors or structural steelwork are connected, with a second ring conductor provided by blasting a circular trench around the
CHAPTER 3
Rod length (m) 0.6
1.5
3
6.1
15.2
30.5
61
100 O.D. of rod 1.000 in. (25.4 mm)
Resistance to earth (Ω)
50
2.375 in. (60.3 mm) 3.500 in. (88.9 mm) 4.500 in. (114.3 mm) 6.625 in. (168.3 mm)
20
10
5
2 2
5
10
20 Rod length (ft)
50
100
200
FIGURE 6.3.11 Resistance of Vertical Ground Rods in 10,000 L/cm Soil
periphery and placing in it a strip conductor. The blasted area should be thoroughly compacted with backfill, and the two ground ring conductors should be electrically interconnected. Using one of these methods would make the distribution of the electrical potential around the protected building substantially the same as if it were resting on conducting soil; the resulting protective effect would be equal. For sandy soil or any dirt covering the foundation, a concrete-encased electrode (commonly called a Ufer ground, after the inventer Herb Ufer) should be installed for new construction. This electrode consists of steel reinforcing bars or rods tied together in the footing of the foundation that is in direct contact with the earth. In general, the extent of the grounding arrangements will depend on the character of the soil, ranging from simple extension of the conductor into the ground where the soil is deep and of high conductivity, to an elaborate buried network where the soil is very dry or of very poor conductivity. Where a network is required, it should be buried if there is soil enough to permit it, as doing so adds to its effectiveness. Its extent will be determined largely by the judgment of the person planning the installation, following the minimum requirements of NFPA 780, and keeping in mind that, as a rule, the more extensive the underground metal available, the more effective the protection.
Protection of Structures (Traditional Systems) Underwriters Laboratories Inc. “Master Label Service” for Lightning Protection Systems. Underwiters Laboratories Inc. (UL) has had a “Master Label Service” for lightning protection systems since 1923. It provides for both factory inspection and labeling of lightning protection materials (components), as well as field inspections of a substantial number of installa-
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tions for which Master Labels have been issued. The service covers the installation of labeled lightning protection materials (components) on all types of structures, with the exception of those used for the production, handling, or storage of ammunition, explosives, flammable liquids or gases, and explosive ingredients. Protection of electrical transmission lines and equipment is not within the scope of the “Master Label Service.” Structural Steel Buildings. Buildings constructed of structural steel framing can be protected by the installation of air terminals at the high parts of the building, connecting such air terminals to the metal framing, and grounding the framing at the bottom end. This assumes that the structural steel framework is inherently electrically continuous or is made electrically continuous by bonding. Grounding is required from approximately every other steel column around the perimeter and is arranged so that grounds average not more than 100 ft (30.5 m) apart, except as noted in the following. Air terminals are not required if the steel columns extend at least 10 in. (254 mm) above the object to be protected. Air terminals are not required on metal roofs where the metal is not less than 3/16 in. (4.8 mm) thick. Additional grounding is not required if the steel column extends 10 ft (3.05 m) or more into the earth or is connected to a concrete-encased electrode. Reinforced Concrete Structures. Reinforced concrete buildings in which the reinforcing rods are electrically bonded together and grounded are similar to structural steel buildings in regard to lightning protection. In usual building practice, as successive reinforcing bars are fitted, they are made to overlap lengthwise with bars already installed and are then tied together with metal binding wire. With thousands of such connections in a completed framework, the electrical resistance is fully acceptable for the purpose of lightning protection. However, if the reinforcing rods are electrically discontinuous, the building should be treated the same as a building of nonconducting materials. Lightning strokes to reinforced concrete buildings where there are insulating gaps between reinforcing rods can cause cracks at places where beams and floor slabs are connected to their supports. Prestressed concrete buildings are a particular problem. If the wires in precast units are not interconnected (as they frequently are not), individual units are isolated and when a lightning charge is induced, serious damage can result. Metal-Roofed and Metal-Clad Buildings. Metal roofing and siding must not be substituted for the main conductors and air terminals of a lightning protection system, unless constructed of 3/16-in. (4.8-mm) minimum sheet metal that has been made electrically continuous by bonding or an approved interlocking contact. This is because there is a likelihood that lightning will puncture thinner sheet metals and ignite wood framing. Tanks Containing Flammable and Combustible Liquids and Gases. Tanks containing flammable and combustible liquids or flammable gases stored at atmospheric pressures have been ignited by lightning. Fires can be started by direct hits, which ignite vapors escaping from metal floating roof tanks. Roofs of
6–74 SECTION 6 ■ Fire Prevention
H
Floating roof tanks with hangers located within the vapor space can be protected by bonding the roof to the shoes of the seal at 10-ft (3.05-m) intervals around the circumference of the tank and by providing insulated joints or installing jumper bonds around each pinned joint of the hanger mechanism. Floating roof tanks without vapor spaces do not appear to need lightning protective measures. Aboveground storage tanks or containers of flammable liquids or liquefied petroleum gas under pressure are considered to be safe from lightning-caused explosions since the vapor–air mixture is “too rich” to burn and the vapor is contained within the tank. Tall Structures. Spires, masts, and flagpoles of materials other than metal and other slender structures require one air terminal extending 10 in. (254 mm) or more above the uppermost point, a down conductor, and a ground terminal in compliance with NFPA 780. Church steeples will require one air terminal with a two-way path to ground at the extremities and additional air terminals on the lower-level portion that is outside of the steeple’s zone of protection. In Great Britain, brick chimneys, church spires, and so on are protected by two down conductors connected at the top to an existing metal cap or to a circular conductor with no air terminals (Figure 6.3.13). Note the absence of air terminals on the lower-level portion; protection is provided by an elevated conductor above the ridge. Metal smokestacks need no protection against lightning other than that provided by their construction if they are grounded. Trees, Other Specialized Structures, and Facilities. Trees are sometimes provided with lightning protection if they are es-
10 Radiu 0f s (str ikin t (30m gd ista ) nce )
Mast
Rad ius 100 (stri ft (3 king 0m dist ) anc e) 100 ft (30 m)
wooden tanks can ignite from a direct strike. A lightning stroke in the vicinity can, by induction, produce sparks that might ignite such vapors. If there are openings in the roof, either intentional or unintentional, externally ignited vapors might carry flame inside the tank, resulting in an explosion or fire if it contains a flammable or combustible vapor–air mixture. Aboveground tanks storing flammable or combustible liquids or flammable gases at atmospheric pressures are considered to be reasonably well protected against lightning if constructed entirely of steel, and if (1) all joints between steel plates are riveted, bolted, or welded; (2) all pipes entering the tanks are metallically connected to the tank at point of entrance; (3) all vapor openings are closed or are provided with flame arresters (for Class I liquids as defined by NFPA 30, Flammable and Combustible Liquids Code); (4) the tank and roof are constructed of 3/16-in. (4.8-mm) minimum thick sheet metal so holes will not be burned through by lightning strokes; and (5) the roof is continuously welded, bolted, or riveted and caulked to the shell to provide a vapor-tight seam and electrical continuity. Where additional protection is desired, the internal supporting members of the roof can be bonded to the roof at 10-ft (3.05-m) intervals or an overhead ground-wire system or mast protection can be installed in accordance with NFPA 780 (Figure 6.3.12). Steel tanks in direct contact with the ground or aboveground steel tanks connected to extensive properly grounded metallic piping systems are considered to be inherently grounded. Steel tanks with wood or other nonmetallic roofs are not considered self-protecting, even if the roofs are essentially vapor-tight or sheathed with thin metal. Such tanks should be protected by an overhead catenary ground-wire system or mast protection (see Figure 6.3.12).
Overhead ground wires
(a) Single Mast Zone of protection defined by dashed lines
FIGURE 6.3.12
H
(b) Overhead Ground Wires Zone of protection defined by ground wire(s) and dashed lines
Zone of Protection for Mast Height H
100 ft (30 m)
Ground surface
R 100 adius ft (3 0m )
Supporting mast H
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Lightning Protection Systems
Surge Arresters and Suppressors on Electrical Apparatus and Circuits Bonding to electrical installation and bell frame
FIGURE 6.3.13 Installation of a Lightning Protection System in a Church Steeple According to British Standard Code of Practice2 Requirements
pecially valuable, are of historical significance, overhang buildings, or provide a shelter for livestock. Guidance on the installation of lightning protection is given in the appendices of NFPA 780, such as for (1) parked aircraft; (2) livestock in fields; and (3) picnic grounds, playgrounds, ballparks, and other open places (Figure 6.3.14). Grounding Metal Masses (Bonding). Extensive masses of metal that form part of a building or its appurtenances, such as metal ventilators and television or radio antennas, must be bonded to the lightning protection system. Nevertheless, the grounding of metal windowsills could be a hazard to human life in the event of a direct lightning strike. Details are given in NFPA 780, under “Metal Bodies,” “Potential Equalization,” and “Bonding of Metal Bodies,” which determine the need for bonding and require loop conductors around a structure at various levels to be bonded to all down conductors. This provides an equipotential ground grid that causes the different metal components in the structure to be at the same voltage, thereby minimizing the shock and arcing hazard and also decreasing the amount of current that could affect computers and other electronic equipment.
Maintenance Proper maintenance of lightning protection systems is essential. Particular attention should be given to air terminals and connections in the vicinity of water gutters and ground rod connections, as rods might be broken or corroded at ground level or just below, where the damage is not apparent. Materials (components) might be missing because of storm damage or stolen because of their value.
The installation of surge arresters on power and communications lines where they enter structures and at power utility plants is covered in Article 280 of NFPA 70, National Electrical Code®. More information on the protection of electrical apparatus and circuits against damage due to lightning can be found in the Additional Readings section of the Bibliography, under Surge Arresters. The use of secondary service arresters on electric services is required for buildings equipped with a UL MasterLabeled Lightning Protection System. Such arresters can be installed at the yard pole, at the outside electric service entrance, or at the interior service entrance equipment, depending on local regulations. Home lightning protectors are available that are designed for installation at the dwelling weatherhead or indoors at the service entrance equipment. These protectors (arresters) drain lightning surge-induced charges harmlessly to ground and then open to restore electrical service to normal. Before a secondary service arrester is installed, it should be determined that the neutral wire is grounded. The surge arrester should be coupled with a transient voltage surge suppressor on branch circuits that serve computers and electronic appliances. These devices are constructed as portable (plug-in) or permanently wired units. In the United States, except on the Pacific Coast where lightning storms are infrequent, most electric utilities install lightning arresters on the primaries of important transformers on systems of 44,000 V or less.
10 6 5 9 3 2 1
12
4 8 7
11
13 14
FIGURE 6.3.14 Lightning Protection System on a Typical Large Barn. The numbers indicate the following features: (1) ground-attached wire fence; (2) extended protection to any addition; (3), (4), and (5) bonding conductors to litter, metal door, and hay tracks; (6) air terminal on cupolas, ventilators, and so on; (7) ground connection (there should be at least two grounds); (8) tie-in of metal stanchions; (9) power lines to building need lightning arresters; (10) at least one air terminal should be on each domed silo (at least two on each flat roof or unroofed silo); (11) special ground for silo, if required; (12) connections to vents; (13) connections to water pipes; and (14) desirability of protecting adjacent buildings.
6–76 SECTION 6 ■ Fire Prevention
PROTECTION OF PERSONS The risk of direct lightning strike is greatest among persons whose occupations keep them outdoors. Prevention of injuries due to lightning or lightning-induced fire involves a combination of protection of the structure from fire due to lightning and the usual steps to protect occupants of a building from injury due to fire.
Guide for Personal Safety During Thunderstorms Persons should not go out of doors or remain outside during thunderstorms, unless it is necessary. They should seek shelter inside buildings, vehicles, or other structures or locations that offer protection from lightning, such as the following places: • Dwellings or other buildings that are protected against lightning • Underground shelters, such as subways, tunnels, and caves • Large metal or metal-framed buildings • Large unprotected buildings • Enclosed automobiles, buses, and other vehicles with metal tops and bodies • Enclosed trains and streetcars • Enclosed metal boats or ships • Boats that are protected against lightning • City streets that are shielded by nearby buildings If possible, they should avoid the following places that offer little or no protection from lightning: • Small unprotected buildings, structures, barns, sheds, and so on • Tents and temporary shelters (not lightning protected) • Automobiles (nonmetal top or open tops) • Recreational vehicles (nonmetal or open) They should also avoid use of or contact with electrical appliances, telephones, and plumbing fixtures. Certain locations are extremely hazardous during thunderstorms and should be avoided if at all possible. Approaching thunderstorms should be anticipated and the following locations avoided when storms are in the immediate vicinity: • • • •
Open fields, athletic fields, hilltops, and golf courses Parking lots and tennis courts Swimming pools, lakes, and seashores Areas near wire fences, clotheslines, overhead wires, and railroad tracks • Areas under isolated trees In the preceding locations, it is especially hazardous to be riding in or on any of the following during lightning storms: • Open tractors and other farm machinery operated in open fields • Golf carts, scooters, bicycles, and motorcycles • Open boats (without masts) and hovercraft • Automobiles (nonmetal top or open)
It might not always be possible to choose an outdoor location that offers good protection from lightning. Persons should follow these rules when there is a choice in selecting locations: • Seek low-lying areas; avoid hilltops and other high places. • Seek dense woods; avoid isolated trees. • Seek buildings, tents, and shelters in low areas; avoid unprotected buildings and shelters in high areas. • If you are isolated in an exposed area, believe a lightning strike is imminent, and cannot reach shelter, crouch as low as possible, with your feet close together to minimize the area of the body in contact with the ground. Do not lie flat on the ground or place your hands on the ground.
SUMMARY Lightning or lightning-caused fire results in dozens of deaths a year. The need for lightning protection depends in part on geography, because the frequency and severity of thunderstorms vary throughout the world. The degree of lightning protection installed should take into account the nature of the building. For instance, certain types of buildings that are essential to life safety, such as hospitals, police and fire stations, and military installations, or historically important buildings should have lightning protection systems installed if they are in vulnerable areas. However, some buildings do not require supplemental protection because of their construction. Although no lightning protection system can prevent the occurrence of a lightning discharge, protection is achieved by intercepting the current, which is then discharged harmlessly into the earth. A lightning protection system usually consists of a grounded metal mast or multimast system, overhead wires, or air terminals. The type of lightning protection system needed is determined by the physical characteristics of the building and the properties of its contents. For personal protection against lightning, certain areas such as golf courses, swimming pools, areas near railroad tracks, and areas under isolated trees should be avoided during thunderstorms. Vulnerable vehicles such as open cars, tractors, or boats and electrical appliances and plumbing fixtures should also be avoided. People who find themselves out of doors should seek shelter in a lightning-protected building or, if this is not possible, seek low areas or dense woods. An individual who is isolated in an exposed area should crouch down with feet close together and with hands off the ground.
BIBLIOGRAPHY References Cited 1. National Safety Council, Injury Facts, Ithaca, IL, 1996–2000. 2. “The Protection of Structures against Lightning,” British Standard Code of Practice, BS 6651, British Standards Institute, Milton Keynes, 1985. 3. Offerman, P. F., “Lightning Protection of Structures,” IEEE Conference Record of 1969 4th Annual Meeting of the IEEE Industry and General Applications Group, 69 C5-IGA, 1969.
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4. Lee, R. H., “Protection Zone for Buildings against Lightning Strokes Using Transmission Line Protection Practice,” IEEE Transactions on Industry Applications, Vol. 1A-14, No. 6, 1978. 5. Davis, N. H., “The Rolling Sphere Interception Concept,” Proceedings of the 19th International Conference on Lightning Protection, Graz, Austria, Vol. 1, April 25–29, 1988. 6. Moore, Brook, and Krider, “A Study of Lightning Protection Systems,” Atmospheric Science Program of the Office of Naval Research (under Contract No. 00014-78M-0090). 7. Kaufmann, R. H., “Some Fundamentals of Equipment—Grounding Circuit Design,” AIEE Transactions, Vol. 54, No. 244, 1954. 8. Sunde, E. D., Earth Conduction Effects in Transmission Systems, D. Van Nostrand Co., Inc., 1949, pp. 75–80.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on lightning protection systems discussed in this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 30, Flammable and Combustible Liquids Code NFPA 70, National Electrical Code® NFPA 302, Fire Protection Standard for Pleasure and Commercial Motor Craft NFPA 780, Standard for the Installation of Lightning Protection Systems
ANSI Standards, Surge Arresters ANSI/IEEE C62.1-1989, Gapped Silicon-Carbide Surge Arresters for Alternating-Current Power Circuits. ANSI/IEEE C62.11-1993, Standard for Metal-Oxide Surge Arrestor for AC Power Circuits. ANSI/IEEE C62.31-1987, Specifications for Gas Tube Surge-Protective Devices, Test. ANSI/IEEE C62.32-81, Standard Test Specifications for Low-Voltage Air Gap Surge-Protective Devices (Excluding Valve and Expulsion Devices) (R 1994).
Additional Readings Adams, R., “When Lightning Strikes,” Firehouse, Vol. 16, No. 7, 1991, p. 18. Becker, J., “Addressing Power Protection for Facilities,” APCO Bulletin, Vol. 62, No. 8, 1996, pp. 93–95. Bird, T., “Protecting Your Equipment against Lightning,” APCO Bulletin, Vol. 64, No. 11, 1998, pp. 46–47. Brown, T. C., and Gurr, D. E., “Zapped,” JEMS, Vol. 23, No. 12, 1998, pp. 66–72. Burrell, M., “Explosion Rocks Somerset’s Procedures,” Fire, Vol. 91, No. 1121, 1998, p. 9. Cramer, J. A., Lyons, W. A., Nelson, T. E., Turner, T. R., and Williams, E. R., “Enhanced Positive Cloud-to-Ground Lightning in Thunderstorms Ingesting Smoke from Fires,” Science, Vol. 282, No. 5386, 1998, pp. 77–80. Custer, G., and Thorsen, J., “Stand-Replacement Burn in the Ocala National Forest: A Success,” Fire Management Notes, Vol. 56, No. 2, 1996, pp. 7–12. Electrical Construction Materials Directory, published annually in May with November supplements, Underwriters Laboratories Inc., Northbrook, IL. Esselstyn, S., “Big Fire, Small Town,” APCO Bulletin, Vol. 64, No. 1, 1998, pp. 82–85. Factory Mutual Research Corp., “Lightning Arresters and Grounds,” Loss Prevention Data Sheets, 5-11/14-19, FMRC, Norwood, MA. Frary, M., “Ute Creek Fire—Lessons Learned,” Wildfire, Vol. 7, No. 3, 1999, pp. 28–33.
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Frydenlund, M. G., “Understanding Lightning Protection,” Plant Engineering, Vol. 44, No. 9, 1990, pp. 62–66. Frydenlund, M. M., “Protecting Industrial Plants against Lightning’s Dangers,” Consulting/Specifying Engineer, Vol. 8, No. 3, 1990, pp. 60–62, 64, 66, 68. Golde, R. H., Lightning Protection, Academic Press, New York, 1977. Golde, R. H., “Protection of Structures against Lightning,” Proceedings, Institution of Electrical Engineers, Vol. 115, No. 10, 1968. Graham, G. L., Holle, R. L., and Lopez, R. E., “Lightning Detection and Data Use in the United States,” Fire Management Notes, Vol. 57, No. 2, 1997, pp. 4–9. Gupta, R. S., “Fires Due to Electrical Hazards,” Fire Engineers Journal, Vol. 56, No. 183, 1996, pp. 40–42. Hart, C. W., and Edgar, W. M., Lightning and Lightning Protection, Interference Control Technologies, Gainesville, VA, 1988. Hayasaka, H., and Shinohara, M., “Forest Fires in Boreal Forest: FROSTFIRE in Alaska Taiga,” Proceedings of the 4th AsiaOceania Symposium on Fire Science and Technology, Tokyo, Japan, May 24–26, 2000, pp. 191–201. Hedlund, C. F., “Lightning Protection for Buildings,” IEEE Transactions on Industry and General Applications, Vol. IGA-3, No. 1, 1967. IEEE Standard 142-1982 (ANSI/IEEE), Chapter 3, “Static and Lightning Protection Grounding.” Jackson, A. L., and Vallas, P. S., “Struck by Lightning: An Investigation,” Fire Engineering, Vol. 149, No. 3, 1996, pp. 61–62, 64–65. Johnson, I., “What Happens in a Direct Strike,” Fire Prevention, No. 315, Dec. 1998, p. 25. Journal of the Franklin Institute, Vol. 283, No. 6, 1967 (special issue on lightning research). Layton, J. E., “Why GFCIs Fail,” Occupational Health & Safety, Vol. 69, No. 11, 2000, pp. 72–74. “Lightning Detection Service Can Monitor Strikes within 1,500-Foot Radius,” Fire Findings, Vol. 5, No. 3, 1997, pp. 14–15. “The Lightning Flash,” published bi-monthly by Lightning Technologies, Inc., Pittsfield, MA. “Lightning Protection System, General with Regard to Installation,” German Standard DIN 57185, Part 1/VDE 0185, English Translation, 1983. Marinoff, E., “Fire Causes by Lightning, Sandwich South Township, September 7, 1990,” Fire Investigation Report, Office of the Fire Marshall, Canada, June 22, 1993. Martin, G., “High Rise Fire Pattaya Thailand Investigation,” Proceedings of the inFIRE (international network for Fire Information and Reference Exchange) Conference, Fire Information for the 21st Century, Melbourne, Australia, May 4–8, 1998, pp. 14/1–24. Milzman, D. P., Moskowitz, L., and Hardel, M., “Lightning Strikes at a Mass Gathering,” Southern Medical Journal, Vol. 92, No. 7, 1999, pp. 708–710. Mohr, F., and Both, B., “Confinement—A Suppression Response for the Future?” Fire Management Notes, Vol. 56, No. 2, 1996, pp. 17–22. Moreno, J. M., and Vazquez, A., “Patterns of Lightning-, P-Caused Fires in Peninsular Spain,” International Journal of Wildland Fire, Vol. 8, No. 2, 1998, pp. 103–105. Plumer, J. A., “We Need Better Lightning Protection,” Fire Journal, Vol. 81, No. 1, 1987, p. 41. Proceedings of the International Conference on Lightning Protection, published bi-annually by different publishers, 20th ed. by Swiss Electromechanical Assn., Interlocken, Switzerland. Queen, P. L., “Thunder and Lightning,” American Fire Journal, Vol. 45, No. 10, 1993, p. 7. “Refining Safety Procedures,” Fire Findings, No. 305, Dec. 1997, pp. 14–15. Rielage, R. R., “Molehill out of a Mountain,” Fire Chief, Vol. 41, No. 3, 1997, p. 50. Rosenthal, J., “Concern over Claims for Lightning Conductors,” Fire Prevention, No. 248, Apr. 1992, p. 10.
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Schram, P. J., and Earley, M. W., Electrical Installations in Hazardous Locations, 2nd ed., National Fire Protection Association, Quincy, MA, 1997. Sielaff, P., “Tracking Thunderbolts: Technology at Work,” Fire Management Notes, Vol. 57, No. 2, 1997, pp. 11–13. Smith, D. P., “AATCO Pipeline Tank Fire: Responding to the Volcanic Inferno,” Proceedings of the 1997 National Oil Spill Conference, Improving Environmental Protection Progress, Challenges, Responsibilities, Fort Lauderdale, FL, April 7–10, 1997, pp. 926–927. Stewart, C. E., “When Lightning Strikes,” Emergency Medical Services, Vol. 29, No. 3, 2000, pp. 57–67. “Take the Shock out of Electrical Storms—Disruption Threat: Electrical Storms,” Contingency Planning & Management, Vol. 4, No. 7, 1999, p. 38. Taylor, M., “One Strike and You’re Out,” Fire Prevention, No. 315, Dec. 1998, pp. 22–25.
Towne, H. M., Lightning—Its Behavior and What to Do about It, United Lightning Protection Association, Inc., Webster, NY, 1956. Uman, M. A., All About Lightning, Dover Publication, Inc., Mineola, NY, 1986. Uman, M. A., Lightning, Dover Publication, Inc., Mineola, NY, 1983. Underwriters Laboratories Inc., UL 96, Standard for Safety Lightning Protection Components, 4th ed., Northbrook, IL, 1995. Underwriters Laboratories Inc., UL 96A, Standard for Safety Installation Requirements for Lightning Protection Systems, 10th ed., Northbrook, IL, 1995. Viemeister, P. E., The Lightning Book, MIT Press, Cambridge, MA, 1975.
CHAPTER 4
SECTION 6
Emergency and Standby Power Supplies Revised by
George W. Flach
T
he Northeast blackout of 1965 and the recent electrical power shortage in California associated with electric utility deregulation dramatically demonstrate the need for a source of electric power independent of public electric utilities. The Northridge, California, earthquake of January 1994 is another example of the need for localized electric power in an emergency. Power interruptions occur due to natural or manmade causes. Natural causes include storms, floods, earthquakes, and the like; man-made causes are many, such as vehicles striking transformers or utility poles, equipment failure from one or more causes, and human operational error. More generally, the electric utility industry’s capacity margins have steadily declined in recent years, leaving less room to compensate for unexpected loads and events. Summer capacity margins shrank from one-fourth of capacity in the early 1980s to one-tenth in the late 1990s. Winter capacity margins shrank from one-third of capacity in the early 1980s to one-fourth in the late 1990s.1 The chapter provides information on the components that, alone or in combination, form emergency and standby power systems.
POWER SUPPLY SYSTEM CODE AND STANDARD NFPA 70, National Electrical Code® NFPA 70, National Electrical Code® (NFPA 70 or NEC), recognizes two types of private power supply systems: (1) emergency and (2) standby. The latter is further subdivided into (a) legally required standby systems and (b) optional standby systems. Requirements for the proper installation of any of these systems are found in Articles 700, 701, and 702 of the NEC. Emergency power systems are systems supplying power for illumination; elevators, critical heating, ventilation, and air conditioning (HVAC); fire pumps and alarms; public address systems; and other loads essential to the safety of life and property
George W. Flach is president of Flach Consultants in New Orleans, Louisiana. He is a member of the NFPA Technical Committee on the National Electrical Code—Panel 15 and a member of NFPA 20, Standard for the Installation of Stationary Pumps for Fire Protection.
when public utility power is unavailable and where required by local, state, or federal codes (Figure 6.4.1). Legally required standby systems are provided as an alternate source to the normal power source (e.g., a public utility), where an electric power interruption to a continuous industrial process could endanger lives or hamper rescue or fire fighting operations. These systems are also installed for heating, refrigeration, and ventilation systems, or to serve other electrical loads that are specified by municipal, state, federal, or other codes or by any governmental agency having jurisdiction. Optional standby systems are intended to protect private business or property where life safety does not depend on the performance of the system. Some examples of loads that are connected to these systems are heating and cooling equipment, data processing, and communications systems. Optional standby systems, selected by the owner, are also used on farms and in residences to supply loads during a power failure. The loads to be served by the emergency or standby power system can be classified as critical and noncritical. Critical loads are loads that must be served within a relatively short time period after the power is needed in order to preserve life or property. Noncritical loads are all other loads that are permitted to be connected to the system. In hospitals, alternate power source wiring and equipment are termed an essential electrical system. One or more on-site generators must be used to supply this system. The essential electrical system comprises an emergency system and an equipment system. The emergency system is further divided into (1) the life safety branch and (2) the critical branch.
NFPA 110, Standard for Emergency and Standby Power Systems Several terms overlap each other, for example, alternate power systems, standby power systems, legally required standby systems, alternate power sources, and so on. NFPA 110, Standard for Emergency and Standby Power Systems, places all such systems into categories defined in terms of type, class, and level, rather than using such aforementioned terms. Type defines the maximum allowable time that the load is without acceptable electrical power. Class defines the minimum allowable time that the alternate source has the capability of providing its rated load without being refueled. Level defines the equipment performance stringency requirements.
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AC feed from normal utility Inlet air opening
DC feed to battery and engine start control
Silencer
To emergency load
Emergency feed Wall thimble Automatic transfer switch Supports
Flexible conduit
Drain
Flexible coupling Outlet air opening Battery charger
Engine generator control Day tank
Normal utility feed
Flexible fuel lines
Generatormounted circuit breaker
Main tank fuel gauge
Return line
Vibration isolators Batteries
AC jacket water heater
Main fuel tank
Suction line
FIGURE 6.4.1 Typical Generator Installation Used to Supply Emergency Power (Source: Caterpillar)
ENERGY SOURCES NFPA 70 recognizes five electric sources for emergency power supplies: (1) storage batteries, (2) generator set(s), (3) uninterruptible power supplies, (4) a separate service, and (5) unit equipment. Item 4 is not recognized as an acceptable emergency power source for those occupancies covered by NFPA 101®, Life Safety Code®. To cope with emergencies, a plaque or directory is required at each electric power source. Each sign must indicate where all other sources are located. Energy sources for emergency and standby power supplies are generally one of the following: liquid petroleum products, liquefied petroleum gas, natural or synthetic combustible gas, or batteries. Other sources, for example, steam, rotating mass (flywheel), and compressed noncombustible gas, have limitations that restrict their use for these purposes. On-site storage of the energy source to supply power for the duration of the need for emergency and standby power is an important consideration, especially in areas subject to severe environmental disturbances, such as storms, earthquakes, flooding, and so on. Section 6, Chapter 10, “Stationary Combustion Engines and Fuel Cells,” provides details on safeguards for onsite fuels.
Batteries Batteries, in general, are the most dependable energy source for emergency and standby power and are primarily used for emergency lighting, either as a central battery system or as a self-
contained lighting assembly defined as “unit equipment” in NFPA 70. They are also used with uninterruptible power supplies (UPS), a system that automatically provides power, without delay or transients, during a period when the normal power source is incapable of performing acceptably. A single battery or a group of batteries is limited in the amount of usable energy it is capable of delivering before becoming discharged; hence, backup to the battery source is often supplied in the form of other on-site emergency or standby power supplies. Batteries used for this service must have sufficient capacity to supply the total emergency load for at least 1½ hr. During this time the voltage cannot drop below 87.5 percent of normal. They are usually either lead-acid or nickel-cadmium type. The lead-acid battery is less costly and requires less space for the same capacity; but the nickel-cadmium type has a longer life, more rugged construction, and requires less maintenance. Sealed batteries, that is, those not requiring periodic replacement of water, are favored for use with self-contained lighting assemblies. After use, batteries must be recharged to have power available again when needed. A self-contained lighting assembly normally is provided with an automatic recharger and a sensing relay for determining normal power supply loss to the normal illuminating means. Consideration should be given to having the battery recharger connected to the emergency or standby power source (when such a source is installed) upon loss of normal power where evacuation of the installation is not expected during a normal power outage or where a large number of people could be stranded in a high-rise building for a duration longer than the
CHAPTER 4
expected usual discharge time of the battery without recharging. Central battery systems and UPS systems are normally provided with more complex battery rechargers, such as dual-rate, regulated, and so on, to maximize battery life and minimize gassing. Proper location of batteries with adequate ventilation and liquid electrolyte containment are important environmental considerations. The gaseous products of electrolysis (hydrogen and oxygen) can be a fire hazard.
Uninterruptible Power Supplies and Other Stored Energy Power Supplies A true UPS system providing continuous and transient-free single-phase or polyphase ac power is used to supply such critical load applications as sensitive electronic and computer equipment for data processing, life support, communications, and control equipment. Such a system, upon loss of normal power, continues to supply power without waveform distortion and the load is totally unaware of normal power loss. There are applications where such purity is not required and either waveform distortion (transient or phase displacement of waveform) or a brief lapse of power to the load, or both, is acceptable. Economic considerations will bear upon the type of stored energy power supply used. Batteries, combined with rectifiers and solid-state inverters (converters of dc power to ac power), provide power to the majority of UPS systems in use. Such systems are known as static UPS systems. This system rectifies the incoming ac power to dc power, then inverts the dc power back to ac power for delivery to the load. A battery is permanently connected between the rectifier and inverter (on the dc bus) and takes over as the power source immediately upon loss of the incoming ac power. On return of the incoming ac power, the load is supplied by the incoming ac power and the batteries are recharged. The inverter serves to determine the characteristics of the ac power to the load, so that any voltage or frequency variations or transients on the incoming power are absent from the load. The rectifier is continuously sized to the capacity of the load, plus that required for battery recharging, while the inverter is continuously sized to the capacity of the load. Other UPS systems are variations of a rotating generator driven by various drivers (engines, ac and dc motors), with or without a flywheel. A stored energy power supply system similar to the UPS system, but economically more attractive, is one in which the normal ac power is fed through to the load with a static transfer switch transferring the load to an inverter supplied by a battery upon loss of the normal ac power. The inverter receives a continuous synchronizing signal from the normal ac power, so that, upon loss of this power, the inverter is still approximately in phase with the power just lost. This, coupled with a transfer time of a few milliseconds, permits the load to be without power for only a brief period and without serious transients occurring upon application of inverter power. Note, however, that the inverter need only be sized intermittently for the load power and that the rectifier be sized only to accommodate the recharging power of the battery.
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Emergency and Standby Power Supplies
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ENGINE-DRIVEN GENERATOR POWER SYSTEMS An engine-driven generator power system usually consists of a prime mover, a governor, a generator coupled thereto (either direct or geared), transfer equipment, and distribution and protective equipment (Figure 6.4.2). Such a system is supplied for either standby or emergency service and is most common where such power is required for a considerable period of time.
Prime Mover The prime mover can be a reciprocating engine fueled by gasoline, diesel fuel, or natural or synthetic gas. Gas turbines are also used, particularly for larger power outputs. Gasoline and natural and synthetic gas engines are less costly than diesel engines but have disadvantages that are considerable. For example, the gasoline engine and its fuel storage are more susceptible to fire and explosion. Also, the natural gas engine usually obtains its energy supply from an off-site gas utility, a supply that might not be available at the same time of unavailability of the normal power supply (for this reason, an on-site fuel supply might be required by the authority having jurisdiction). Gas turbines are much smaller than reciprocating engines of the same output and operate at much higher speeds. They require no cooling-water connection and burn natural gas, kerosene, diesel fuel, or fuel oil. They are, however, quite inefficient and are slow in coming up to full speed (more than 10 s). The prime mover and its associated auxiliary equipment are required by the NEC to have the following characteristics for emergency service: 1. The prime mover must start automatically and come up to full speed and power capability within 10 s of demand. 2. A minimum on-site fuel supply permitting full enginegenerator output for 2 hr must be available. 3. When water-cooled engines are used (generally above 50 kW), the municipal water supply cannot be used for cooling (i.e., municipal water supply input, waste to drain output). 4. When a battery is used for engine starting, the battery must have an automatic charging means independent of the prime mover. 5. When the prime mover requires more than 10 s to come up to full speed and power capability, an auxiliary power supply can supply the required power (within 10 s) to the load, provided it can continue to do so until the load is assumed by the prime mover. A prime mover driving a legally required standby power system must meet conditions 2, 3, and 4 above, and condition 1 within 60 s.
Governor A governor maintains an approximately constant speed of the prime mover throughout the full power output range by varying
6–82 SECTION 6 ■ Fire Prevention
Normal power source
Alternate source generator
Main OCD
Nonemergency loads Transformer Generator Overcurrent device with switching mechanism—OCD
EPSS Load 1
EPSS Load 2
EPSS Load 3 Emergency power supply system
Automatic transfer switch
Automatic or manual transfer device
FIGURE 6.4.2
Typical Rotating Emergency Power Supply System (EPSS)
the fuel input to the prime mover. Governors can be mechanical, electrical, hydraulic, or a combination thereof.
might not be possible to have selective tripping of overcurrent devices in the current loop.
Generator
Transfer Equipment
Generators convert the mechanical shaft output of the prime mover into the electrical power for use by the loads connected thereto. The performance of the generator and its voltage regulator under varying load conditions must be considered in determining its suitability. The output voltage of a generator drops suddenly when a load is applied and rises suddenly when a load is removed. At present, generators larger than a few kilowatts in size have automatic voltage regulators that quickly bring the voltage back to the specified value. The initial voltage drop is important because if the drop is excessive, even for a few cycles, electromagnetic components, for example, relays and motor starters, might drop out and might or might not, depending on circuitry, reclose when the voltage is restored, or they might cycle open and close repeatedly, causing equipment damage. Voltage rise (overshoot) upon load removal can cause damage to equipment remaining connected. The initial voltage drop is not usually of concern when the loads being connected are within the ratings of the generator. However, it is customary to exceed the rated current of the generator by two to three times during motor starting only. The initial voltage dip during these current overloads is, therefore, one of the limiting factors in sizing the generator. The performance of the generator when subjected to a short-circuit or heavy overload condition is also a matter of consideration. Under this condition, the generator current output decays with time, a characteristic inherent in the generator, so that, in a relatively short time, the current lessens to a magnitude of only several times its rating. If the decay rate is too rapid, it
Electromechanical automatic transfer switches are normally used to transfer selected loads to the engine generator power supply when the normal source fails. The transfer switch senses normal power, usually all phases, and upon loss of normal power automatically signals the prime mover to start. A brief time delay is generally built into the transfer switch logic to delay the signal so that a momentary normal power interruption or flicker does not activate the prime mover. The transfer switch also senses the voltage and frequency of the generator output and, when these reach acceptable levels, either immediately thereafter or after a time delay (for selective load pickup), the switch transfers the load to the engine generator output. Upon restoration of the normal power supply to acceptable levels, the transfer switch might transfer the load automatically (usually after a time delay to allow for permanent normal power restoration) back to the normal source, or manual transfer of the load might be required, the choice having been originally made by the characteristics of the load. Transfer switches, in general, immediately retransfer the load back to the normal source (if available and at an acceptable level) should the emergency source fail. Maintenance of a transfer switch might require deactivation of loads connected to the switch while the maintenance is being performed. Some loads are so critical that such deactivation is unacceptable. In such cases, the transfer switch is furnished with an isolation bypass switch, making it possible for the load to be served by the normal or emergency source while the automatic transfer switch is being serviced.
CHAPTER 4
■
Emergency and Standby Power Supplies
6–83
Distribution and Protective Equipment
Motor-Starting Methods
Distribution of the available auxiliary power (emergency or standby) concerns itself with the loads served, the order of priority, and the total loading of the engine generator set. Protection concerns itself primarily with equipment protection and with continued availability of power to unfaulted loads upon a system electrical fault. Engine generator set loading prioritizes the need for power and the magnitude of the various loads. Critical loads must be served first, followed by noncritical motor loads. A motor load produces large power and kVA load upon first starting, which influences momentary voltage and frequency output of the generator, causing a decrease in each. Step loading of the engine generator set is accomplished by using multiple transfer switches, timed to operate in sequence in the order of priority. Other more complex arrangements with programmable controllers or computers are sometimes used. Permissible loading of the engine generator set during periods of loss of normal power is governed by codes and standards. Generally, during such periods, it is permissible to use available power not being used for critical loads to power noncritical loads and to resort to load-shedding techniques to pick up the critical loads when needed. Protection, although generally in accordance with established procedures for the normal power supply, must take into account the usual situation of limited power availability of the engine generator set versus the larger power availability of the normal source. As indicated earlier, generators, under shortcircuit or heavy overload conditions, have collapsing outputs such that the sustained total current output of the generator drops to a magnitude comparable to its full-load value. Rapid clearing of the fault is essential (prior to the drop in current to its sustained value); otherwise the protective device will not see the short-circuit condition. Rapid fault clearing is also important to enable the generator to reestablish itself (voltage restoration) and continue to serve the loads still connected to it.
Motor-starting methods for large motors are another significant consideration. Two matters of concern are (1) the power required from the prime mover and (2) the kVA required from the generator. Selection of the proper type of reduced voltage starting is equally important. Open-transition reduced voltage starting is not a recommended method, nor is primary resistance reduced voltage starting. Autotransformer starting and closed-transition wye-delta starting are generally preferred to other methods.
SUMMARY Electrical power interruptions can occur from natural causes, such as storms, floods, and earthquakes, or from man-made causes, such as human operational errors or accidents to, or failure of, equipment. Such power interruptions as well as the rising threat of electrical power shortages and associated blackouts or brownouts point to the need for an independent source of power. This chapter examined the components of emergency standby power systems, including batteries, uninterruptible power supplies and other stored energy power supplies, and engine-driven generator power systems—the latter consisting of a prime mover, a governor, a generator, transfer equipment, and distribution and protective equipment. The chapter also discussed two other considerations—that is, peak shaving, whereby some loads from the normal power source are transferred to the auxiliary power source during periods of maximum loading of the former, and motor-starting methods.
BIBLIOGRAPHY Reference Cited 1. U.S. Bureau of the Census, Statistical Abstract of the United States: 2000, Table 963, Washington, DC, 2000.
References
MISCELLANEOUS CONSIDERATIONS Peak Shaving Multiple-engine generator sets are sometimes used to supply emergency and standby power. Such sets are usually operated in parallel, with load-shedding provisions incorporated should one of the sets fail. Because of the sizable monetary investment in an emergency or standby power system, some installations use the engine generator set in conjunction with the normal power supply for peak-shaving purposes. Peak shaving is the transfer of some loads from the normal power source to the auxiliary power source during periods of maximum loading of the normal power source. The economic benefit of peak shaving is a result of the utility rate structure. If a user can keep the ratio of maximum (or peak) power usage to average power usage low, then the utility charge is lessened. By transferring selected loads to the engine generator set during periods of peak power usage, the aforementioned ratio is lowered.
Battery Service Manual, 11th ed., Battery Council International, Chicago, IL, 1995. “IEEE Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications,” ANSI/IEEE 446-1987, Institute of Electrical and Electronics Engineers, Inc., Piscataway, NJ. “Kohler Engineer’s Guidebook to Power Systems,” Consulting Engineer, Vol. 64, No. 2, Part 2 of 2, 1985.
NFPA Codes, Standards, and Recommended Practices Reference to the following NFPA codes, standards, and recommended practices will provide further information on emergency and standby power supplies discussed in this chapter. (See the latest version of The NFPA Catalog for availability of current editions of the following documents.) NFPA 37, Standard for the Installation and Use of Stationary Combustion Engines and Gas Turbines NFPA 70, National Electrical Code® NFPA 99, Standard for Health Care Facilities NFPA 101®, Life Safety Code® NFPA 110, Standard for Emergency and Standby Power Systems
CHAPTER 5
SECTION 6
Heating Systems and Appliances Revised by
Peter J. Gore Willse
H
eat-producing appliances and associated equipment are among the most prevalent causes of fire because they operate at temperatures above the ignition temperature of many common materials. In addition, combustion-type appliances can sometimes involve the hazards of an accumulated combustible mixture, the discharge of unburned fuel, and possible exposure of fuel to ignition sources. Additional information about heating systems and appliances can be found in: Section 2, Chapter 3, “Chemistry and Physics of Fire”; Section 6, Chapter 1, “Electrical Systems and Appliances”; Section 6, Chapter 6, “Boiler Furnaces”; Section 6, Chapter 8, “Industrial and Commercial Heat Utilization Equipment”; Section 6, Chapter 21, “Storage of Flammable and Combustible Liquids”; Section 6, Chapter 22, “Storage of Gases”; Section 8, Chapter 7, “Gases”; and Section 12, Chapter 15, “AirConditioning and Ventilating Systems.”
FUELS AND METHODS OF FIRING Combustion can be defined as a chemical reaction between a fuel and oxygen with evolution of heat and light. In a fuel-burning, heat-producing device, this reaction needs to be continuous so a balance will be established between the rate at which oxygen, or air, and fuel are supplied and the rate at which heat and the products of combustion are removed. Complete combustion (also known as stoichiometric combustion) takes place when all of the fuel is oxidized by the air supplied to it. Air left over after complete oxidation is called excess air. If only enough air is supplied for complete combustion, perfect combustion can theoretically result under suitable conditions. Because perfect combustion this is impractical in most heat-producing appliances, the appliances operate with some excess air. Air for combustion is supplied in two ways: (1) primary air is introduced through or with the fuel, and (2) secondary air is supplied to the combustion zone. In some cases, all of the air supplied is primary air, whereas in others only part is primary air and the balance is secondary air. Incomplete combustion in a fuel-burning device can produce hazardous carbon monoxide. This condition indicates poor Peter J. Gore Willse, P.E., is a research consultant at GE Global Asset Protection Services, Hartford, Connecticut. He chairs the Technical Committee on Liquid Fuel Burning Equipment and is a member of the Technical Committees on Boiler Combustion System Hazards and Ovens and Furnaces.
efficiency, since the fuel is not completely oxidized, and the total heating value of the fuel is not obtained. Incomplete combustion usually results from inadequate air supply, insufficient mixing of air and gases, or a temperature too low to produce or sustain combustion. For additional information on carbon monoxide, see Section 8, Chapter 2, “Combustion Products and Their Effect on Life Safety.” Also see Section 9, Chapter 9, “Carbon Monoxide Detection in Residential Occupancies.”
Solid Fuel—Coal Coal is one of the principal solid fuels used in heat-producing appliances. There are a number of types of coal, each having widely different characteristics. In many cases, there is no distinct line of demarcation between them, and the qualities of one type can overlap those of another. Pulverized coal systems, however, require the use of coals having characteristics within the specific range of the coal-handling and coal-burning equipment. The seven principal types of coal used in heat-producing appliances are Anthracite. Anthracite is a clean, dense, hard coal. It burns with a minimum of smoke and has a minimum dust hazard during handling. Semianthracite. Semianthracite coal has a higher volatile content than anthracite but not as hard. Bituminous. This type includes many types of coal with different properties, depending on where they are mined. It gives off considerable smoke and soot if improperly fired. Bituminous coal can be subject to spontaneous heating under some storage conditions and has a dust hazard during handling. Semibituminous. This dusty soft coal tends to break up. It can be subject to spontaneous heating under some storage conditions. It normally produces less smoke than bituminous coal. Subbituminous. Subbituminous coal is subject to spontaneous heating under some storage conditions. It burns with very little smoke or soot. Lignite. This coal has a woody structure and normally a high moisture content. It is subject to spontaneous heating under some storage conditions. It burns with little smoke or soot.
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Coke. Coke is a product of the destructive distillation of coal. The type of coke produced is determined by the coal used and the temperatures and time of distillation. Petroleum coke is produced from the destructive distillation of oil.
Combustion of Coal When coal is burned in a firebox, oxygen in the air passing through the grate (primary air) unites with the carbon in the lower portion of the fuel bed, called the oxidation zone, to form carbon dioxide. Some of this carbon dioxide is then reduced to carbon monoxide in the upper part of the fuel bed, called the reduction zone. Gases liberated from the fuel bed are carbon monoxide, carbon dioxide, nitrogen, and some oxygen. Oxygen from the air admitted over the fuel bed (secondary air) combines with some of the carbon monoxide to form carbon dioxide. When fresh coal is applied to the fire, moisture is driven off as steam and the hydrocarbon gases are distilled, combined with oxygen, and burned above the grate in what is called the distillation zone.
Methods of Firing Coal Coal is fired either manually or automatically by stokers or pulverized coal burners. Hand Firing. There are many acceptable hand-firing methods. With highly volatile coals, the objective is to leave a suitable bed of glowing fuel to ignite the gases as they are driven off from the fresh coal charge; otherwise the gas might accumulate and explode. Draft regulation is the only automatic feature of a hand-fired furnace. Draft can be controlled by a room thermostat, steam pressure, or water temperature. But, as with any hand-fired solid fuel, the fire is continuous, and overtemperature conditions are difficult to control unless the fire is continually attended. Mechanical Stokers. These are classified according to their coal burning capacities and range from those that handle 10 lb (4.5 kg) per hr to those handling over 1200 lb (540 kg) per hr. A stoker feeds fuel to the combustion chamber and usually supplies air for combustion under automatic control. There are four basic types of stokers: (1) underfed, (2) overfed, (3) traveling and chain grate, and (4) spreader, with fired grate or continuous ash discharge. Underfed stokers move the coal by screw conveyor or rams (Figure 6.5.1). Overfed stokers feed the coal pneumatically or by rotors. Spreader stokers feed coal by rotors or paddles and discharge onto stationary or traveling grates. Stokers feed from hoppers or directly from bins. They are equipped with fueling controls that either change the firing rate or stop the fuel altogether. Some stokers are equipped with a control that will stop the feeding of fuel if the fire goes out. Pulverized Coal Systems. These are of two general types: (1) the direct-fired, or unit, system, and (2) the storage, or bin, system. In the direct-fired system, raw coal is fed directly to a pulverizer where it is pulverized, mixed with air, and blown to
FIGURE 6.5.1
One Type of Underfed Coal Stoker
the burners. In the storage system, coal is delivered to a raw fuel bin and then passed to a pulverizer where it is reduced to a powder and dried for storage in a pulverized fuel bin before delivery to the furnace.
Solid Fuels—Miscellaneous Miscellaneous solid fuels include wood, logs, scrap lumber, and wood waste from lumber and paper mills (sawdust, shavings, bark); hogged fuel (sawmill refuse run through a disintegrator or “hog” to form uniform chips or shreds); charcoal; briquets; peat; bagasse; sugar cane; and a host of other combustibles such as tanbark, wet bark, straw, city refuse, paper, and so on. The methods of firing these fuels vary considerably with the type of device and the nature of the particular fuel. Since the mid-1970s, the most prevalent form of solid fuel usage has been in residential cordwood stoves, furnaces, and fireplaces. Concerns about price and availability of conventional residential energy sources sparked a surge in installation and use of such devices. Although the “crisis” attitude toward conventional energy has eased, solid fuel appliances remain a popular alternative source of supplemental heating. The rise in installation of wood-burning appliances was accompanied by a dramatic increase in heating-related home fires, especially in the early 1980s. The severity of this problem has also decreased since then, due to decreased usage of installed appliances and better installation, use, and maintenance practices. The hazards associated with wood-burning devices are discussed in detail in a later section of this chapter. An evolution from the wood burning stove was the introduction of pellet fuel–burning appliances in the mid- to late 1980s. Processed solid fuels of various types have long been used in commercial and industrial operations. Pellet fuel–burning appliances are relatively small-capacity residential appliances. Pellet fuel is produced by milling wood waste to fine particles, then extruding under high pressure to form pellets about ¼ in. (6 mm) in diameter by ½ in. to 1 in. (12 to 25 mm) long. The fuel is placed in the hopper of a pellet-fuel–burning appliance, from where it is metered to a burn pot, depending on heat demand. Pellet fuel–burning appliances thus bring a degree of automatic operation to residential solid fuel usage. Combustion of wood takes place in three stages. Unless the wood has been purposely kiln-dried before use, the first stage is the driving-off of moisture. The second stage is destructive distillation such as that which occurs in a charcoal kiln, where the
CHAPTER 5
heat drives off combustible gases from the wood and leaves charcoal. The third stage involves burning of the gases in the air above the wood and burning of the charcoal combined with oxygen, forming an intensely hot and luminous bed of coals. The heat from both burning gases and charcoal distills more volatiles from the wood and increases the temperature and rate of combustion. The acceleration of combustion is limited only by the rate at which air can be brought into contact with the burning wood.
Liquid Fuel—Fuel Oils This section discusses fuel oil used in heat-producing appliances and equipment. Fuel oil, like other petroleum products, is composed of varying compounds of hydrocarbons. Even the same grade of fuel oil will vary as to its chemical composition, depending on such factors as the type of crude oil used and the refining process employed. Types of Fuel Oil. Fuel oils obtained from present-day refining processes are known as “cracked” oils and practically all petroleum products on the market today are obtained by the cracking process. No. 1 and No. 2 fuel oils, as well as those fuels commonly known as kerosene, range oil, furnace oil, star oil, and diesel oil, are broadly classed as distillate and No. 4, No. 5, and No. 6 oils (as well as Bunker C) as residuals. Oil burners are constructed (and subsequently tested and listed by testing laboratories) for a specific grade or grades of fuel oil. For example, burners listed by Underwriters Laboratories Inc. (UL) have the grade or grades of fuel oil that can be used in each inscribed on the UL listing mark applied to the unit (Figures 6.5.2 and 6.5.3). It is important that only the proper grade or grades of oil be used in each burner for safety as well as efficiency. Note the grade of oil satisfactory for use in the device appears at the bottom of the markers. Specifications for fuel oil are outlined by the ASTM in ASTM D396, Standard Specification for Fuel Oils,1 and in Canadian Government Specification 3-GP-282 (Table 6.5.1).
Methods of Firing Fuel Oil Two methods, vaporization and atomization, are used to prepare fuel oil for combustion. Air for combustion is supplied by natural or mechanical draft. Ignition is by an electric ignition system, a gas pilot, an oil pilot, or manual means. Operation can be continuous, modulating with high-low flame, or intermittent. Although most burners operate from automatic temperature- or pressuresensing controls, some simpler types are operated manually. Oil burners are classified in several different ways: by application, by type of vaporizer or atomizer, by firing rates, and so on. They are divided into two major groups: (1) residential and (2) commercial-industrial. Vaporizing burners and atomizing burners having capacities of not more than about 6.5 gal/hr (25 L/hr) are considered residential types and are intended to be used with fuel oils not heavier than No. 2. The major portion of residential-type burners produced is the pressure atomizing type, commonly referred to as the gun type.
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Heating Systems and Appliances
6–87
Vaporizing Burners. These burners include the sleeve type, the pot type, and the vertical rotary wall flame type. Sleeve-type burners (Figure 6.5.4) are used in residential heating and cooking stoves. Perforated metal cylindrical sleeves are placed in the grooves so that the space between the inner two sleeves and the outer two sleeves becomes a combustion chamber. The space between the second and third sleeves is for the purpose of furnishing combustion air. Covers with annular openings are usually placed on top of the sleeves. Sleeve burners may or may not employ wicks in the annular spaces in the base, depending on the make and type of burner. Natural draft pot burners (Figure 6.5.5) have applications similar to sleeve-type burners, while forceddraft pot burners can be used in central heating furnaces. In a vaporizing pot-type burner, the oil is introduced into the bottom of the burner and is continually vaporized by the heat of the fire. The holes on the side permit primary and secondary air to enter the burner where they mix with the oil vapors for proper combustion. The primary air is mixed with oil vapors before combustion takes place, and the secondary air is supplied to complete the combustion process. At full fire, the velocity of the vapors and the amount of air required result in the flame burning only at the top of the burner. Vertical rotary wall flame vaporizing burners are used in residential boilers and furnaces for central heating. Although the gun-type burner is now the most common, many of the burners listed above are still in service. Atomizing. These burners include high- and low-pressure types, horizontal rotary cup types, and air and steam atomizing types, the latter used primarily for commercial and industrial applications. High-pressure, gun-type burners consist of a motor, oil pump (with integral or separate pressure-regulating and shutoff valve), strainer, fan, ignition transformer, nozzle, and electrode assembly (Figure 6.5.6). The motor-driven pump draws oil from the supply tank and delivers it to the nozzle at pressures of from 100 to 300 psi (690 to 2700 kPa). The nozzle atomizes the oil into fine particles and swirls it into the combustion chamber as a cone-shaped spray where it mixes with air and is ignited. These burners are generally designed to burn No. 2 oil, although some of the larger sizes are made for No. 4 oil. The industrial version of the high-pressure burner, known as the mechanical atomizing burner, is a high-capacity burner for use with large boilers and industrial furnaces. Figure 6.5.7 shows a typical piping arrangement for one or more burners supplied by separate pump sets. The low-pressure gun burner is similar to, but differs from, the high-pressure gun burner in two ways. First, the burner includes an air pump to supply compressed air for atomization, and second, the oil and air are delivered to the nozzle at pressures of 15 psi (100 kPa) or less. The size ranges, ignition, and fuel used are as described for the high-pressure gun burner. The horizontal rotary-cup oil burner atomizes the oil by spinning it in a thin film from a horizontal rotating cup and injecting high-velocity primary air into the oil film through an annular nozzle that surrounds the rim of the cup. Secondary air for combustion is supplied from a separate fan that forces air through the burner wind box. The introduction of secondary air by means of natural draft is not recommended. These burners are used for firing boilers and furnaces and can be used singly or as
TABLE 6.5.1
Detailed Requirements for Fuel Oils a,b
Flash Point [°F (°C)] Grade of Fuel Oil
Min
Water and Pour Sediment Point (Percent [°F by (°C)] Volume) Max c
Distillation Carbon Temperature Residue [°F (°C)] Ash on 10 10 Percent, (Percent 90 by Percent Bottoms Percent (Percent) Weight) Point Point
Saybolt Viscosity (s) Universal at 100°F (38°C)
Max
Max
Max
Max
Min
Max
Min
Max
—
550 (288)
—
—
6–88
No. 1: A distillate oil 100 or intended for vaporizing legal pot-type burners and other (38) burners requiring this grade of fuel
0
trace
0.15
—
420 (215)
No. 2: A distillate oil for 100 or general-purpose domestic legal heating for use in burners (38) not requiring No. 1 fuel oil
20c (–7)
0.05
0.35
—
—
No. 4: Preheating not usually required for handling or burning
130 or legal (55)
30 (–1)
0.50
—
0.10
—
—
—
45
No. 5 (Heavy): Preheating may be required for burning and, in cold climates, may be required for handling
130 or legal (55)
—
1.00
—
0.10
—
—
—
No. 5 (Light): Preheating may be required for burning and, in cold climates, may be required for handling
130 or legal (55)
—
1.00
—
0.10
—
—
No. 6: Preheating required for burning and handling
150 (65)
—
2.00g
—
—
—
—
Furol at 122°F (50°C)
Kinematic Viscosity (centistokes) At 100°F (38°C)
At 122°F (50°C)
Min Max Min
Max
Min Max
Gravity Copper Sulfur Strip (deg. API) Corrosion (Percent) Min
Max
Max
—
—
1.4
2.2
—
—
35
No. 3
0.5 or legal
—
—
2.0c
3.6
—
—
30
—
0.5 c,eor legal
125
—
—
(5.8) (26.4)
—
—
—
—
150
300
—
—
(32)
—
—
—
—
—
350
750
—
—
—
(900)
(9000)
—
—
540c 640 (32.6)d (37.93) (282) (338)
(65)
(23) (40) (75) (162) (42) (81)
45
300
—
—
(92) (638)
f
f
f
f
a It is the intent of these classifications that failure to meet any requirement of a given grade does not automatically place an oil in the next lower grade unless, in fact, in meets all requirements of the lower grade. b This table reprinted from ASTM D396.1 See complete specification ASTM D396. c Lower or higher pour points may be specified whenver required by conditions of storage or use. When pour point less than 0°F (–18°C) is specified, the minimum viscosity must be 1.8cSt (32.0 s, Saybolt Universal) and the minimum 90 percent point must be waived. d Viscosity values in parentheses are for information only and not necessarily limiting. e Outside U.S., the sulfur limit for No. 2 must be 1.0 percent. f The 10 percent distillation temperature point may be specified at 225°C maximum for use in other-than-atomizing burners. g The amount of water by distillation plus the sediment by extraction must not exceed 2.00 percent. The amount of sediment by extraction must not exceed 0.50 percent. A deduction in quantity shall be made for all water and sediment in excess of 1.0 percent.
CHAPTER 5
UL ®
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Heating Systems and Appliances
Holes to permit air entry
®
LISTED
OIL BURNER NO. W- 230418 FOR USE WITH PRINTED IN U S A
6–89
Oil supply line
GROUP 1 OR 2 PRIMARY SAFETY CONTROLS OIL NOT HEAVIER THAN NO. 2
FIGURE 6.5.2 Listing Mark Used on an Oil Burner Listed by Underwriters Laboratories Inc.
LISTED
OIL-FIRED BOILER ASSEMBLY
FIGURE 6.5.5
Vaporizing Pot-Type Burner
FOR USE WITH INTEGRAL
PRIMARY SAFETY OIL NOT HEAVIER THAN NO.
Oil pump and pressure regulating valve
N-87430-A
Fan Motor
Air adjustment
FIGURE 6.5.3 Listing Mark Used on an Oil-Fired Boiler Assembly Listed by Underwriters Laboratories Inc.
Air tube Deflector vanes Ignition transformer Nozzle
One of the combustion chambers
Solid cover with annular openings
Electrode assembly
FIGURE 6.5.6
Adjustable pedestal
High-Pressure Atomizing Oil Burner
Space for furnishing combustion air Base
Air
Air
FIGURE 6.5.4 Sleeve-Type Burner That Consists Essentially of a Flat, Cast-Iron or Pressed Steel Base Having Two or More Interconnecting Grooves
multiple units on a single appliance. No. 2 fuel can be used with some of the smaller sizes, but Nos. 4, 5, and 6 are generally used with the larger sizes (Figure 6.5.8). In the steam atomizing burner, atomization is accomplished by the impact and expansion of steam. Oil and steam flow in separate channels through the burner gun to the nozzle where the steam and oil mix before being discharged through an orifice into the combustion space. This type of burner is used mainly on large boilers generating steam at 100 psi (690 kPa) and higher and having capacities above 12,000,000 Btu per hr (3.5 MW) input. Air-atomizing burners are designed to use compressed air at either high or low pressure for atomization. The high-pressure
burner is nearly identical with the steam atomizing burner in design and application. Some burners operate well with either medium. The low-pressure air atomizing burner uses comparatively large volumes of air at low pressure of 5 psi (35 kPa) or less. Air from the blower passes through the burner body and is discharged through annular slots between the body and the nozzle tip, where it meets the film of oil at an angle as it issues from the tip. The impact of the air stream upon the oil film produces a fine mist that is projected into the combustion space. These burners can be fired with either light or heavy oil and are most often used to fire industrial heating and processing furnaces (Figure 6.5.9). Combination oil and gas burners, which combine the features of certain oil burners with provisions for burning gas, have been developed. These permit the operator to choose either fuel as circumstances dictate.
Fuel Oil Storage Details on the installation of fuel oil tanks and related piping are described in NFPA 31, Standard for the Installation of
6–90 SECTION 6 ■ Fire Prevention
By-pass valve Diaphragm relief valve Pressure gauge
Supply and return lines for any number of branch circuits
High pressure supply line
Fuel tip
Pressure gauge Main inlet shutoff valve for branch circuit
Shutoff valves Duplicate pumps with integral pressure relief valves
Low pressure return line
f
Cup Bearing Air nozzle
Primary air damper
Bearing
Fan
FIGURE 6.5.8 Gauge well
Shutoff valves Duplex oil filter Check valve Suction line Shutoff valve Tank suction heater (Not required for light oil)
Hole for pilot tip Manhole Vent
Fill pipe
Horizontal Rotary-Cup Oil Burner
Ground level
Oil storage tank
Movable oil tube Combustion air inlet
Oil valve
Atomizing vanes
Tile
Clean-out plug
Traps
Atomizing head assembly
FIGURE 6.5.7 Typical Piping Arrangement for Burners Supplied by Separate Pump Sets
Burner Oil inlet
Oil-Burning Equipment. NFPA 31 directly covers the installation of underground tanks, tanks inside buildings, and outside aboveground tanks that do not exceed 660 gal (2500 L). Larger outside aboveground tanks are covered by Chapter 2 of NFPA 30, Flammable and Combustible Liquids Code. The installation requirements of NFPA 31 differ somewhat from those in NFPA 30, which is more general in nature and covers liquids with a wider range of flash points and which are used in a variety of locations and occupancies. Corrosion of Tanks. Internal corrosion of fuel oil tanks caused by electrolytic action of water on steel can be a major problem. Corrosion and subsequent leakage are actually more of an environmental problem than a fire hazard. Fire can occur, however, when a burner is located in a pit in the basement of a building and oil from a leaking tank flows into the pit. Two generally accepted procedures are recommended to minimize corrosion. The first is to slope the tank toward one end and connect the burner supply line to the bottom of the tank at that end. In this way, water does not accumulate in the tank. The small quantity of water, which originates from condensation within the tank, is small enough to not affect operation of the bu
