Fire Behavior of Upholstered Furniture and Mattresses

FIRE BEHAVIOR OF UPHOLSTERED FURNITURE AND MATTRESSES

by

John F. Krasny Fire Technology Consultant Kensington, MD 20895

William J. Parker Fire Technology Consultant Germantown, MD 20874

Vytenis Babrauskas Fire Science and Technology Inc. Issaquah, WA 98027

NOYES PUBLICATIONS Park Ridge, New Jersey, U.S.A. WILLIAM ANDREW PUBLISHING, LLC Norwich, New York, U.S.A.

Copyright © 2001 by Noyes Publications No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without permission in writing from the Publisher. Library of Congress Catalog Card Number: 00-104716 ISBN: 0-8155-1457-3 Printed in the United States Published in the United States of America by Noyes Publications / William Andrew Publishing, LLC 13 Eaton Avenue Norwich, NY 13815 1-800-932-7045 www.williamandrew.com www.knovel.com 10 9 8 7 6 5 4 3 2 1

NOTICE To the best of our knowledge the information in this publication is accurate; however the Publisher does not assume any responsibility or liability for the accuracy or completeness of, or consequences arising from, such information. This book is intended for informational purposes only. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the Publisher. Final determination of the suitability of any information or product for use contemplated by any user, and the manner of that use, is the sole responsibility of the user. We recommend that anyone intending to rely on any recommendation of materials or procedures mentioned in this publication should satisfy himself as to such suitability, and that he can meet all applicable safety and health standards.

Preface

This book is a collection of the up-to-date science and engineering knowledge in the field of furniture fire flammability. For continuity and perspective, citations to older work are still maintained, even in cases where newer research has brought forth improved methods or better knowledge. Thus, the advancement of the state of the art can be seen in these pages. In 1985, two of the present authors (Babrauskas and Krasny) published the first monograph devoted to upholstered furniture flammability. This was issued by National Bureau of Standards (now NIST, National Institute of Standards and Technology) as “Fire Behavior of Upholstered Furniture” (NBS Monograph 173). Many new concepts and experimental results have been published since that time. The most comprehensive recent research study in this area has been “Combustion Behavior of Upholstered Furniture” (CBUF) which was sponsored by the European Union. Two of the authors, Babrauskas and Parker, had the privilege of participating in CBUF. This project, as well as many others, resulted in major improvements in this field. Thus, it became opportune to revise the monograph. To be most useful to its intended user, this book was reorganized and structured more along the expected lines of enquiry from the user. This involved a major reexamination of the literature, especially coverage of new regulations and standard test methods. The review of regulations, however, is selective. Discussions are focused only on US, UK, and EU activities in this area. While numerous other countries have various regulations affecting

v

vi

Preface

aspect of furniture flammability, little if any technical work making reference to such regulations has ever been published in the English language. In this book, the term upholstered item will sometimes be used to include upholstered furniture as well as upholstered parts of bedding (solid core and innerspring mattresses and upholstered bed frames). In many cases, however, it is appropriate to consider that statements made about chairs or about upholstered furniture also apply to various other types of upholstered items. Bedding, such as blankets, sheets, pillows, etc., are treated separately. The book is arranged as follows: • Chapter 1 provides a brief overview of the structure and materials, fire safety design, fire statistics, and standards development. • Chapter 2 discusses some of the fundamentals of fire which affect the fire safety of upholstered furniture. These include smoldering and flaming ignition, flame spread, heat release, inter-item fire spread, room-fire interaction, flashover, smoke, and toxic gases. • Chapter 3 describes the pertinent test methods and regulations for smoldering and flaming ignition, flame spread, heat release rate (HRR), and smoke and toxic gas production for residential, public, and high risk occupancies. • Chapter 4 addresses smoldering and flaming ignition and includes the historical development and the details of the ignition tests. • Chapter 5 compares results obtained by different test methods, especially bench-scale and full-scale results, and furniture calorimeter and room results. • Chapter 6 covers fire safety design, considering the effects of upholstered item construction and materials, separately for smoldering (cigarette) and flaming ignition. Emphasis is on thermal behavior, flaming or smoldering; the relative rates of smoke and combustion products release, which are, in the first approximation, related to the HRR for flaming fires, are less extensively reviewed.

Preface

vii

• Chapter 7 briefly discusses room fire zone and field models as they pertain to furniture fires, furniture fire models, and correlation formulas, and a method for predicting the HRR of composites in the Cone calorimeter based on measurements of the individual components. • Chapter 8 discusses fire hazard analysis, and describes a method of predicting the available escape time based on the HRR of the burning furniture. • Chapter 9 offers brief conclusions about the current state of knowledge about furniture flammability. July, 2000 Issaquah, Washington

Vytenis Babrauskas

Contents

1 Introduction ............................................................................ 1 1.1.0 OVERVIEW.......................................................................... 1 1.2.0 ARRANGEMENT OF THIS BOOK .................................... 2 1.3.0 UPHOLSTERED FURNITURE STRUCTURE AND MATERIALS ........................................................................ 2 1.4.0 UPHOLSTERED FURNITURE AND MATTRESSES ....... 5 1.5.0 DESIGN AND FIRE SAFETY ............................................. 5 1.6.0 UPHOLSTERED ITEM FIRE STATISTICS ....................... 7 1.7.0 SUMMARY OF REGULATORY DEVELOPMENT ........ 10

2 Fundamentals ........................................................................ 18 2.1.0 PYROLYSIS AND COMBUSTION .................................. 18 2.2.0 SMOLDERING ................................................................... 21 2.2.1 Cellulosic Material ............................................... 21 2.2.2 Polyurethane Foam ............................................... 26 2.3.0 TRANSITION TO FLAMING ............................................ 27 2.4.0 FLAMING IGNITION ........................................................ 30

ix

x

Contents 2.5.0 FLAME SPREAD ............................................................... 34 2.6.0 HEAT RELEASE ................................................................ 39 2.6.1

Heat Release Rate ................................................. 39

2.6.2

Heat of Combustion .............................................. 42

2.6.3

Effect of The Ignition Source On The HRR Curve in Full-Scale Tests...................................... 51

2.7.0 PROPAGATING AND NON-PROPAGATING FIRES .... 52 2.8.0 INTER-ITEM SPREAD ...................................................... 56 2.9.0 INTERACTION WITH ENCLOSURE .............................. 62 2.10.0 FLASHOVER ...................................................................... 63 2.11.0 SMOKE AND TOXIC GASES ........................................... 66 2.11.1 General .................................................................. 66 2.11.2 Smoke ................................................................... 67 2.11.3 Toxic Gases .......................................................... 72

3

Test Methods, Standards and Regulations ......................... 83 3.1.0 CIGARETTE IGNITION .................................................... 83 3.1.1 Introduction ........................................................... 83 3.1.2 Upholstered Furniture ........................................... 87 3.1.3 Mattresses ............................................................. 96 3.1.4 Test Criteria For Cigarette Ignition Resistance .... 97 3.1.5 Critiques of Cigarette Ignition Standards ............. 99 3.2.0 FLAMING FIRE TESTS, STANDARDS, AND REGULATIONS ............................................................... 102 3.2.1 Introduction ......................................................... 102 3.2.2 Uses and Limitations of Flaming Fire Tests ....... 103 3.2.3 Description of Flaming Fire Tests ...................... 108 3.2.4 Development of Full-scale HRR Measurement Techniques .......................................................... 140 3.2.5 Flame Spread - Standard Tests ........................... 142 3.2.6 Transportation Seating Tests and Regulations ... 143 3.2.7 Miscellaneous Tests ............................................ 150

Contents

xi

3.3.0 SMOKE AND TOXIC GASES ......................................... 151 3.3.1 Smoke Tests ........................................................ 151 3.3.2 Toxicity Tests ..................................................... 156

4 Ignition Sources .................................................................. 163 4.1.0 MATCHES, SMALL GAS FLAMES, AND METHENAMINE PILLS .................................................. 168 4.2.0 WOOD CRIBS .................................................................. 171 4.3.0 NEWSPAPER SHEETS AND THEIR GAS BURNER REPLACEMENTS ............................................................ 175 4.4.0 WASTE PAPER BASKETS: REAL AND SIMULATED .. 178 4.5.0 RADIANT FLUX IGNITION SOURCES ........................ 179 4.6.0 OTHER IGNITION SOURCES AND LOCATIONS ....... 179 4.7.0 LARGE OPEN-FLAME OR RADIATION SOURCES ... 182

5 Effects of Test Apparatus and of Test Scale..................... 187 5.1.0 COMPARISON OF BENCH-SCALE RESULTS ............ 187 5.1.1 Comparison of Fabric and Fabric/Padding Composite Test Results ...................................... 188 5.2.0 COMPARISON OF BENCH AND FULL-SCALE RESULTS ......................................................................... 190 5.2.1 Flammability Results .......................................... 190 5.2.2 Comparison of Cone Calorimeter and Full-Scale Results ................................................................. 191 5.2.3 Comparison of Furniture Calorimeter and Room Results ................................................................. 200 5.2.4 Smoke Results .................................................... 204 5.2.5 Toxicity Test Results .......................................... 204

6 Upholstered Item Design Engineering .............................. 207 6.1.0 IGNITION RESISTANCE TO CIGARETTES ................ 207 6.1.1 Effect of Fabrics ................................................. 213 6.1.2 Effect of Padding Material ................................. 217

xii

Contents 6.1.3 Effect of Interliner (Barrier, Blocking) Materials .. 218 6.1.4 Effect of Welt Cords and Trim ........................... 218 6.1.5 Effect of Configuration ....................................... 219 6.1.6 Effect of Moisture ............................................... 219 6.1.7 Cigarette—Upholstered Item Interaction ........... 220 6.1.8 Low Ignition Propensity Cigarettes .................... 225 6.2.0 FLAMING FIRES ............................................................. 237 6.2.1 Ignitability........................................................... 237 6.2.2 Post-Ignition Behavior ........................................ 244 6.2.3 Flame Spread ...................................................... 299 6.3.0 SMOKE ............................................................................ 302 6.4.0 TOXIC PRODUCTS ......................................................... 307 6.5.0 FIRE INVESTIGATIONS ................................................ 316

7

Modeling .............................................................................. 320 7.1.0 INTRODUCTION TO MODELING ................................ 320 7.2.0 FURNITURE FIRE MODELS .......................................... 322 7.2.1 Physics-Based Models ........................................ 323 7.2.2 Combined Physics/Correlation Models .............. 328 7.2.3 Correlations-Based Models ................................ 331 7.3.0 A COMPONENT HRR MODEL FOR FURNITURE COMPOSITES .................................................................. 339 7.4.0 CFD ROOM FIRE MODELS ........................................... 342

8

Fire Hazard Analysis .......................................................... 346 8.1.0 SMOLDERING FIRES ..................................................... 346 8.2.0 FLAMING FIRES ............................................................. 347 8.2.1 Small Closed Rooms........................................... 347 8.2.2 Open (Ventilated) Rooms ................................... 348 8.3.0 THE ROLE OF HRR ......................................................... 351 8.4.0 THE ROLE OF OTHER FACTORS ................................. 352

Contents

xiii

8.5.0 RELATIONSHIP OF HRR AND AVAILABLE ESCAPE TIME ............................................................................ 354 8.6.0 HAZARD PREDICTIONS BASED ON MODELING ..... 354

9 Conclusions ......................................................................... 358 Exercises and Solutions ............................................................ 360 EXERCISES

............................................................................ 360

SOLUTIONS

............................................................................ 367

Abbreviations ............................................................................ 377 References .................................................................................. 379 Index .......................................................................................... 423

1 Introduction

This book is a comprehensive revision of a 1985 monograph[1] authored by Babrauskas and Krasny. The intervening years saw few advances in the basic science of furniture combustion, but much work was done in applied areas, both in empirical studies and in regulatory activities. Thus, this edition is organized differently from the preceding book, and is specifically intended to provide useful information to any individuals with a responsibility for the fire safety of furniture. Research from various parts of the world are encompassed in this book, but focus on regulation is mainly from the US perspective, with significant additional material on UK and EU activities, and more limited coverage of other parts of Europe. Other, briefer, overviews of the upholstered item fire situation in the UK and the US are found in Refs. 2–6. A comprehensive report on the results and analysis of an extensive European project on the post-ignition Combustion Behavior of Upholstered Furniture (CBUF)[7] references many important literature sources. This chapter contains an overview of the basics of upholstery structure and fire safety design. Following this, fire statistics are presented.

1

2

Fire Behavior of Upholstered Furniture and Mattresses

The chapter concludes with a brief history and status of US and EU regulations covering upholstered furniture and mattresses.

1.1.0

UPHOLSTERED FURNITURE STRUCTURE AND MATERIALS

Upholstered furniture has a complex structure, as shown in Fig. 1-1. One item can contain fifteen or more components. In the ignition process, whether it be from a cigarette (smoldering ignition) or small flame, the cover and interliner fabric, if any, and material immediately below them (one or several different padding materials) are important. As the fire progresses, other materials contribute, including the bulk of the padding as well as the frame, staples, and springs, which can affect the manner in which the burning item collapses. This in turn affects fire growth. Bedding (pillows, blankets, sheets, etc.), mattresses, and bed frames contain a different variety of materials and construction factors. A large variety of component materials are used in upholstered furniture and mattresses. Cover fabrics can be made from char-forming fibers, such as cellulosic, acrylic, wool, and silk fibers, or from thermoplastic fibers. Among the cellulosic fibers, cotton and rayon predominate but flax, hemp, jute, etc. are also used. Thermoplastic fibers include nylon, olefin (polypropylene or polyethylene), and polyester. Fabrics using blends of more than one fiber type have become very popular in the last decade. Fabrics often contain dyes and dye auxiliaries, print auxiliaries, and other finishes, e.g., stain and water repellents, and softeners. Raw cotton fabrics contain smolder promoting alkali metal ions, as do many of the fabric finishing agents. Many fabrics have latex back-coatings. Paddings today are predominantly polyurethane foams varying in density and additives. Polyurethane may be used as a thin layer combined with other paddings, or, more frequently, as the entire core. Cellulosic batting (mostly cotton but also containing hemp, jute, etc.), both untreated or flame retarded treated (FR), and cotton/man-made fiber blend batting are also used. Polyester batting is popular for special comfort and appearance effects.

Introduction

Figure 1-1. Upholstered furniture construction details.

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4

Fire Behavior of Upholstered Furniture and Mattresses

Interliners (also often called barrier materials, fire blockers, or blocking layers) are used between the cover fabric and padding to increase ignition resistance and improve burning behavior. For cigarette ignition resistance, thin layers of polyester batting are popular (paddings of 100% polyester batting are less widely used; they tend to have excessive loft and are mostly found in uses other than seats). Flame-resistant interliners are FR-treated cotton, aluminized materials, glass fabrics, layers of FR foams, aramid non-wovens, etc. In addition, furniture and mattresses often contain innersprings, frames (mostly wood or steel, but sometimes rigid polyurethane or highdensity polypropylene), springs, or straps to hold up cushions, bottom cover fabrics (usually nonwoven or cotton fabrics), nails, and staples.

1.2.0

UPHOLSTERED FURNITURE AND MATTRESSES

Many aspects of flammability are similar for upholstered furniture and mattresses. The similarities and differences pertinent to predicting the fire performance have been analyzed in Ref. 8. Upholstered items in residential or public occupancies, or air, maritime, and ground transportation are all subject to different functional requirements and regulations. Upholstered items include a large variety of constructions: three-ortwo seat sofas, chairs, mattresses, and some bedframes. The furniture geometry can have a large effect on progress of the fires. There are fully and partially upholstered types, recliners, and lightly upholstered office and stacking chairs. Chairs or sofas can have straight or curved sides, the seating area can be square or rounded (barrel chairs), there may or may not be upholstered armrests, etc. Loose or puckered cover fabrics have appeared in recent times, and their effect on flame and cigarette ignitability has not been established. There are also such features as open or padded seat sides, open spaces between seat and backrest, etc. Mattresses have predominantly flat, horizontal surfaces which are not as easily ignited from flame ignition sources as the vertical surfaces. Upholstered bed frames (divan bases) are more common in Europe than in the US. Both mattresses and upholstered furniture may have depressions at the welt cord and, due to tufting, these may affect cigarette ignition propensity.

Introduction

5

Cigarettes on mattresses may be covered inadvertently with sheets, blankets, and/or pillows. This increases the probability of smoldering ignition. These intermediary materials may also ignite more readily than mattresses from flames, and then expose the mattress to a much more severe fire than the original ignition source, e.g., a match. Fire development is also affected by the nature and materials of the bed frame. Consequently, it is more difficult to develop relevant ignition tests and standards for bedding than for upholstered furniture, which is not usually covered by extraneous items.

1.3.0

DESIGN AND FIRE SAFETY

While fire problems with upholstered furniture have been of concern for some decades, it has been mainly since the 1970s that quantitative data have been available for common materials used in upholstered items. These efforts have made it possible to treat the subject as a design or prediction problem. In a design problem, the designer is typically required to come up with materials and configurations suitable to meet a set objective, which may be resistance to ignition by cigarettes, resistance to small or large flames, or, smoke and toxic pyrolysis product release rates below some specified amount. Several means of solving such problems are: 1. Test items made from the same materials, in the same configuration, as the proposed line of furniture in a full scale facility, e.g., a room or furniture calorimeter; 2. Test large-scale mock-ups of the fabric, interliner, and padding; 3. Test bench-scale composites of the materials in item 1 and use the results in a full-scale model or correlation formula; 4. Test the fabrics and foams individually and use the results in a composite model or correlation formula to predict the results of tests of furniture composites in the Cone Calorimeter. However, the tests on the individual components require

6

Fire Behavior of Upholstered Furniture and Mattresses modified test procedures in the Cone Calorimeter which are not, at this writing, generally available in the testing laboratories; although the testing protocols are described in the CBUF report.[7]

In the last years, much progress has been made to eliminate the burden of full scale testing of every material/configuration combination a manufacturer may wish to produce, and to place greater reliance on strategy 3 and, possibly, strategy 4. At the end of this chapter, an overview is given of the CBUF project which is the latest of such efforts. Details of CBUF and other available literature on this subject are reviewed in Chs. 5, 6, and 8. Briefly, it is now possible, within certain limits, to estimate from benchscale tests of both mattresses and upholstered furniture fabric/padding composites whether the actual item will support a smoldering or a flaming ignition and whether the flaming ignition will lead to a fully involved fire. Such estimates can be used to decide whether certain regulatory pass/fail levels can be met. Progress has also been made in predicting the heat release rate (HRR) of propagating furniture and mattress fires.

1.4.0

UPHOLSTERED ITEM FIRE STATISTICS

During the 1991 to 1995 period, there was an average of 446,700 home fires, 3590 civilian deaths, 20,382 civilian injuries, and $4.5 billion property damage.[576]–[579] This is a decrease of almost 150,000 fires from the 1983–1987 period, and of a 19% decrease in civilian deaths. However, the number of deaths per 100,000 fires has not been decreasing. Furthermore, the number of civilian injuries and property damage increased during this period. Civilian deaths may be reduced by better medical treatment, and the increase in property damage can perhaps be explained by the 1991 Oakland, CA, firestorm. The table below shows the number of fires, deaths, injuries, and property damage due to upholstered item fires. As in earlier such compilations, these fires were by far the largest cause of fire deaths; ranked high in injuries and relatively low in property damage. While together they represented only about 10% of the fires, they caused about 35% of the deaths; this indicates that upholstered item fires are considerably more likely to cause death than other categories.

Introduction

7

Death, Injuries, and Damage Due to Fires in Which Upholstered Items Were The First Item to Ignite Number of Fires

Civilian Deaths

Civilian Injuries

Direct Property Damage, Million$

Upholstered Furniture 1985–1989

14,600

658

1810

237

1989–1993

16,000/3.4*

742/19

1967/9.4

239/5.5

1992–1996

13,900/3.2

653/18

1721/8.7

228/5.3

Mattresses and Bedding 1985–1989

39,000

774

3050

283/

1989–1993

31,200/6.7

627/16

3232/16

331/7.6

1992–1996

28,900/6.5

578/16

2997/15

320/7.4

*The number after the slash indicates the percent of the total fires, deaths, injuries, or property damage. Note: The next lower first item-to-ignite category was electrical insulation, 7.7% of fire deaths, followed by floor covering and cooking materials, 3.5% each.

Cigarettes or “discarded material,” presumably matches, account for 39% of the upholstered item fires and 52% of deaths dues to upholstered items. Incendiary fires were next in frequency. People falling asleep while smoking accounted for 13% of the fires. For mattresses and bedding, 56% of fires occurred on items with cotton fabrics, 24% in man-made fiber items, while the fabric was unclassified or classified “other known” in 20%. Children started 8700 (30%) fires, and smoking materials and matches or lighters, 5800 (20%). People falling asleep again were a major factor in these fires, with 1700 (6%) fires.

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Fire Behavior of Upholstered Furniture and Mattresses

The CPSC estimated that in 1996 there were 650 deaths due to upholstered furniture as first item to ignite, 1640 injuries and $250 million in direct damages and $3.7 billion in total societal cost.[580] There were 470 cigarette-initiated fire deaths (down from 1200 in 1981). Small open-flame ignitions accounted for an average of 90 deaths over the years 1990–1996, 440 injuries and $50 million damages. Two thirds of the deaths were children under five years of age. Children of that age also were the mostly responsible for these fires. An earlier analysis of US fire accident data by the National Fire Protection Association (NFPA) estimated that there were an average of 22,900 residential fires in which upholstered furniture was the first item to ignite, and 42,500 mattress and bedding fires during the years 1983 to 1987.[9] The upholstered furniture and mattress fires represented 11% of the residential fires, 40% of the deaths, 27% of the injuries, and 16% of the property damages. Upholstered item fires are the single largest cause of fire fatalities in the US; the next highest death figure is 7% for interior wall covering fires (as reported to be the first item to ignite but some walls might have been ignited by upholstered furniture). Another report reviews the available data in considerable detail.[10] It specifically discusses the increasing role of polyurethane foam in furniture fires, which may have increased the severity of furniture fires, even as their number is decreasing. In the US, 69% of all fires attended by the fire services are postflashover fires, with the majority of deaths occurring outside the room of fire origin.[11][12] This implies the need for studying both fire development in the room of origin and spread of hot smoke and toxic gases to the rest of the building. Computer fire simulation programs have been found very useful in this area. On the other hand, the majority of elderly fire victims in the UK die in the room of origin, as reported in Ref. 7. The conclusions of another NFPA investigation, this one specifically of US smoking-material initiated fires and using a variety of sources, were:[13] • In 1988, lighted tobacco products caused 230,500 fires, an estimated 1,660 deaths, 4,300 civilian injuries, and $440 million in damage. This represents about 27% of the total number of US civilian fire deaths, and is by far the leading

Introduction cause of fire deaths. However, smoking ranks only sixth among the causes of structural fires. Other major causes were heating equipment, matches and lighters, and electrical malfunction. • Upholstered furniture and mattresses and bedding were the first item to ignite in 24,000 smoking material initiated residential fires, and resulted in 1,250 deaths, 2,700 civilian injuries, and $200 million in property damage. Other major items ignited in smoking material residential fires were trash and clothing not on a person. Smoking-material initiated fires also were a major factor in nonresidential structure fires, with trash, discarded mattresses and bedding, and upholstered furniture leading the list of first ignited items. The mortality and morbidity in the latter fires were much lower than those in residential fires. • During the period of 1980 to 1988, the number of deaths per 100 smoking-related fires increased from 1.88 to 2.04 indicating an increase in the severity of such fires. This is in spite of the fact that there is a general reduction in fire deaths due to advances in the clinical treatment of burn injuries. Smoking-related fires were the second largest cause of civilian burn injuries. • More than 95% of the smoking-material caused fires were started by cigarettes. • Data for 1984 to 1988 shows that the risk of smoking material fire caused deaths increased with age. Death rate per million persons of all ages averaged 8.5 for men, and 4.2 for women. It was roughly twice that for the age

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Fire Behavior of Upholstered Furniture and Mattresses group 55 to 64, and three times that for those between 75 and 84. • Smoking-material fires of trash, grass, and brush were more frequent than those in residences, but caused fewer civilian deaths. However, such fires can destroy very large areas, and cause fire fighter injuries and deaths.

An ignition risk analysis for cigarette initiated upholstered furniture fires showed that the US incident rate from 1975 to 1982 was related to the annual cigarette consumption rate and the estimated average cigarette ignition resistance of the upholstered items in use.[14] The efficacy of upholstered furniture standards is illustrated by the California fire experience. In 1988, ten years after the cigarette and small flame ignition standards were first enforced, upholstered furniture fires had declined by 50%.[15] Part of this can be ascribed to the increased use of smoke detectors and lower percentage of smokers; on the other hand, the California population increased considerably during that period. California fire statistics for 1980 to 1984 show that upholstered items were the first to ignite in 35% of the hotel/motel and nursing home fires. Combined figures for the UK and the Netherlands showed similar trends.[16] Bedding and upholstered furniture accounted for approximately 10% of residential and 2% of public building fires. Smoking materials caused 32% of the residential fires (presumably mostly in upholstered items), electrical equipment 20%, and matches and lighters 10%. Figures for the UK alone show that upholstered furniture and bedding fires accounted for about 15% of the residential fires (total 63,000) but 50% of the deaths (total 710) and 30% of the injuries. About 30% of the deaths occurred in rooms other than that of the fire origin. Canada experiences about 4,000 upholstery fires a year, causing 100 deaths, 310 injuries, and a $28 million loss.[17]

1.5.0

SUMMARY OF REGULATORY DEVELOPMENT

This is a nontechnical overview of the voluntary and regulatory activities regarding upholstered item flammability. As the most significant recent development, the European Union (EU) (formerly called European Community, EC) completed the program leading to the CBUF report.[7] It was designed to provide a scientific base for potential regulations to control

Introduction

11

post-ignition fires of upholstered items. At the time of this writing, however, no regulatory activity has ensued. The technical details of tests and standards are given in Ch. 3. Recent reviews of US activities in this area can be found in Refs. 18–20. They cover the available tests, with emphasis on American Society for Testing and Materials (ASTM) standards. Damant has discussed the California standards, their effects, and changes made over the years on the basis of experience.[15][21] Because cigarette-initiated fires are much more frequent than flame ignition caused fires, particularly in residences, prevention of the former was assigned priority in the US in the 1970s. Voluntary standards for cigarette ignition exist in the US for residential and institutional upholstered furniture.[22][23] A Federal Standard applies to mattresses.[24] The upholstered furniture standards have almost identical ASTM and NFPA counterparts.[25]–[28] During 1994–1997, the US Consumer Products Safety Commission (CPSC) developed a small-flame ignition test in response to a petition from the National Association of the State Fire Marshals. Congressional action raised the spectre that meeting any new flammability requirements would require use of fire retardants and the latter might present toxic hazards. Despite decades of safe and effective use of fire retardants worldwide, CPSC was forced to pause the study and to commission a toxicity research project instead. The results are expected to become available towards the end of 2000. The draft CPSC test method itself is discussed in Ch. 3. California enforces its own regulations of cigarette and small flame resistance of fabrics and paddings, and of large flame resistance of institutional upholstered items.[29]–[31] Besides the long standing California Bureau of Home Furnishings and Thermal Insulation (BHFTI) Technical Bulletins TB 116 and TB 117 covering cigarette and small flame ignition requirements for residential furniture components,[29] standards were developed for institutional occupancies. TB 133 applies to furniture,[30] and TB 129 to mattresses.[31] They have been adopted as standards by ASTM.[32]–[33] TB 133 has also been adopted in a number of additional states and localities, and is being actively promoted for use all over the US. The International Association of Fire Fighters, an organization with about 200, 000 members, undertook a political effort to get TB 133 adopted in all 50 states.[34] Going to the individual states seemed indicated because of the anti-regulatory environment at the US Federal level, but presents difficulties because each legislature may use somewhat different wording, causing confusion for the furniture manufacturers. General adoption of TB 133 also was supported by

12

Fire Behavior of Upholstered Furniture and Mattresses

the American Furniture Manufacturers Association, BIFMA, and other industry organizations, and has made good progress. TB 133 applies to behavior after exposure to a substantial ignition source, about 18 kW, one of its (several) pass/fail requirements is that the HRR not exceed 80 kW. This requirement was based on a comprehensive series of full-scale room and furniture calorimeter tests on upholstered furniture conducted at the US National Institute for Standards and Technology (NIST) and BHFTI in which the original room temperature rise requirement was correlated with HRR.[35]–[36] At that peak in HRR, there is no possibility of flashover, and little possibility of the ignition of an adjoining or very close item. There are also prescribed pass/fail levels of smoke and CO. The NFPA Life Safety Code has provisions for upholstered furniture.[37] It requires cigarette resistance of components according to NFPA 260 for residential occupancies,[25] and of furniture mock-ups according to NFPA 261 for public occupancies.[26] For mattresses, the Federal Test is prescribed.[24] Exceptions are made for rooms with sprinklers installed. In addition, in the US, furniture in public occupancies is also frequently subject to state and local fire codes with widely differing requirements.[38] This variety of local codes can make compliance complicated for furniture manufacturers. With respect to flame ignitability, as well as behavior after ignition under flaming conditions, an important development of recent years is the use of HRR for characterization of materials, including upholstered items. The leading instrument for this is the Cone Calorimeter, which also permits measurement of smoke and toxic pyrolysis products.[39]–[41] A book covering the state-of-the-art use of HRR appeared in 1992,[42] and an annotated bibliography on the Cone Calorimeter publications through 1991 has been published.[43] One of the advantages of these measurements is that the results are in engineering units which can be used in computer programs for calculations of the fire hazard presented by various occupancies. The UK passed ignitability regulations in 1988 for all types of furniture and amended them in 1989.[44] An excellent guide to these regulations is Ref. 45, the testing is based on BS 5852.[46] A similar standard for mattresses is BS 6807.[47] Additional standards used for UK government procurement apply to various upholstered items.[48] In general, they are similar to those described in the UK Regulations but there are differences in specimen orientation, etc.

Introduction

13

Various provisions of the UK regulations had effective dates varying from only a few months after promulgation in 1988 to March 1993. Nevertheless, they were apparently accepted without major objections.[49] The development of combustion modified (CM) polyurethane, containing melamine or exfoliated graphite, made the regulation for polyurethane foam cushions technologically practicable for selected cover fabrics, without the use of interliners. However, the short lead times for enforcement (for some parts less than a year), the additional burden on the furniture industry of labeling and record keeping, the vagueness of the original regulations, and the more severe requirements for polyurethane foam than for latex foam were criticized by the British Furniture Industry Research Association. Brief histories of the circumstances leading to the British regulations and means to meet them are found in Refs. 50 and 51. Fire services all over the world are concerned about the rapidly developing fire in polyurethane foam containing furniture, compared to the older materials such as cellulosic battings and horse hair.[52] A survey of European fire brigades published in 1989 showed that 96% believed that fires became worse and produced more smoke and toxic gases than previously. Seventy seven percent ascribed this to the use of polyurethane foam, and 79% indicated that there was need for legislation to reduce the hazard. As discussed earlier, similar concerns were expressed by the US fire fighting community and led to its endorsement of California TB 133 for institutional furniture. Various aspects of the UK Regulations are discussed in Refs. 53 and 54. The regulations define occupancies according to the level of hazard presented by upholstered furniture and mattresses, and assign ignition sources used in BS 5852 (upholstered furniture) and BS 6807 (mattresses) accordingly. Resistance to ignition by cigarettes and a small gas flame simulating a match is required for all occupancies. Resistance to larger ignition sources is specified for High Risk Facilities, such as jails, prisons, detention centers, nursing care facilities, retirement homes, health care facilities, public auditoriums, condominiums, etc. The UK Regulations and related documents contain guidelines for the contents of homes, offices, work places, hospitals, residential care premises, places of entertainment, hotels, and boarding houses. A few years ago, a major effort was undertaken in Europe directed toward unification of flammability standards for the European Union (EU). Some of the preparatory activities were described in a series of papers presented at the Conference on Fire and Furnishing in Buildings and Transport, held in Luxembourg in November 1990[55] and subsequent

14

Fire Behavior of Upholstered Furniture and Mattresses

meetings. The Commission for European Standardization (CEN) formed Technical Committee TC 207 in 1989. Its activities as of 1992 were described by the Convener of its working group WG 6, Fire Test Methods, R. P. Marchant of the UK Furniture Industry Research Association (FIRA).[56] Meanwhile, the European Commission had announced a Draft Directive (subsequently withdrawn) relating to upholstered items, citing the following essential requirements: 1.

Ignitability—three levels of ignition resistance: cigarette resistance for all three levels; match equivalent flame resistance for residential furniture; resistance to an ignition source equivalent to a double sheet of newsprint for general public assembly occupancies; and resistance to five or six newsprint sheets for high risk areas such as locked wards of hospitals and prisons.

2.

Escape time in terms of smoke, toxicity, and heat released during the fire.

3.

Provisions to avoid adverse effects on the environment by FR treatments.

4.

Provisions for giving suitable information on the fire properties of furniture to the end user.

As a first step response, the present regulations, rules, and tests used by the EU members for residential, institutional, and transportation upholstered items were identified in 1990. The UK upholstered item fire regulations formed the basis for discussions in the organizations responding to CEN, ISO, and EU.[57]–[60] The ISO ignitability standard is patterned after BS 5862.[61] A study of the requirements and a proposal for further work was undertaken by the European Group of Official Laboratories for Fire-testing (EGOLF) and related to UK and ISO activities.[58] The Working Group evaluated ignition sources larger than cigarettes and matches, such as paper bags containing newspapers, gas flames, and wood cribs. Tests for mattresses based on the same concepts were proposed. Similarly, tests for post-ignition behavior, reaction-to-fire tests, using the full-scale NORDTEST 032 Furniture Calorimeter[62] and the Cone Calorimeter,[41] were considered. An ambitious inter-laboratory test evaluation, including six

Introduction

15

ignition sources (20 to 2500 kJ), six fabric/padding combinations, and 14 laboratories was planned in 1990. Use of full-scale room tests (ISO 9705)[63] to verify the results from the furniture calorimeter and methods of hazard assessment with use of computer codes were proposed. Measurement of heat release, smoke, and toxic product release rates on bench-scale (for example, with the Cone Calorimeter) would have to be related to full-scale experiments, and furniture geometry effects established. Fire spread to adjacent articles would have to be established by ignitability measurements at various levels of irradiance. Among the other items under discussion were the need to establish levels of protection needed for various occupancies, ranging from residential (for which the BS 5852[46] and ISO 8191[61] cigarette and match simulation flame ignitability tests seemed acceptable), to prisons and mental institutions, where escape is difficult or impossible and where arson is a distinct possibility. Individual governments would establish the levels of protection needed for various occupancies; interstate traffic of furniture would not be hampered by this because items would be labeled according to their behavior in various tests. The main research program, which actually materialized to increase the state of knowledge of fire testing upholstered items, was CBUF. The basic thinking leading up to the CBUF program is discussed in Refs. 7 and 64. The objective was the development of a new technology for assessment of the post-ignition burning behavior of upholstered furniture in support of the Second Essential Requirement included in the draft EU furniture directive. This requirement stated: “The atmosphere in the room in which the upholstered furniture or related article are on fire should despite the production of heat and smoke ... remain for a reasonable period of time after ignition such that it does not endanger the lives or physical well being of exposed persons. This will be achieved by controlling the rates of heat release, and of smoke and toxic gas production. This would allow time for the escape by alert and ablebodied persons.” The CBUF research program was authorized by the European Commission and part-funded by it. The rest of the funding came from industry, governments, and laboratories within the Member States of EU. The consortium conducting the research consisted of three organizations in

16

Fire Behavior of Upholstered Furniture and Mattresses

the UK, and one each in Belgium, Denmark, Finland, France, Germany, Italy, and Sweden. The technical coordinator was Björn Sundström of the Swedish National Testing and Research Institute in Borås. The major results of this research can be briefly summarized as follows:[65] 1. The HRR history of the full-scale furniture in the furniture calorimeter was identified as the principal measure of the hazard. From that, the height of the interface between the hot upper gas layer and the near ambient temperature lower layer, through which the room occupants would have to escape, could be calculated. The HRR combined with the yields of smoke and toxic gases could be used to predict the smoke obscuration and toxic gas concentrations in the room of fire origin and in the other rooms in the building. 2. A furniture fire model, a mattress fire model and a set of correlation formulas were developed to predict the HRR in the furniture calorimeter based on measurements on the furniture composites in the Cone Calorimeter. This would reduce the amount of full scale testing required. 3. A composite model was developed, as an option, to predict the HRR of furniture composites based on measurements on the individual components in the Cone Calorimeter. This would reduce the amount of bench scale testing required and make it practical to shift the responsibility for the testing from the furniture manufacturers to the material suppliers. 4. It was left to the regulator to specify the minimum time that must be allowed for escape from the room of fire origin and the minimum height of the hot gas interface during that period. In order to determine the acceptability of an upholstered furniture item, the actual escape time and minimum interface height can be predicted from its full scale HRR curve using existing room fire models.

Introduction

17

The full-scale fire test methods for the various furniture items varying in material assemblies and configuration were the ISO room/corner test[63] and the furniture calorimeter.[62] The fabrics and the foam were tested both as composites and as separate components in the Cone Calorimeter.[41] Detailed testing procedures for the room fire test and for the furniture and Cone Calorimeters were written based on an extensive investigation of the effects of the various test parameters. The ignition source for the full-scale tests was a gas burner with a nominal 30 kW HRR applied for 120 seconds, to assure ignition of most items. Commercial solid core and innerspring mattresses, innersprings, two and three seat sofas, and a large variety of upholstered chairs, as well as upholstered chairs varying systematically in fabric and padding and configuration were included. There were 71 room tests, 154 furniture calorimeter tests, and Cone Calorimeter tests of 1098 composites, along with 172 individual fabrics and foams tested. A number of preliminary experiments established the ignitability of the various items, and the effects of increased room size, variations in room ventilation, reproducibility and repeatability, and test procedure details. The report is an important source for information for the development of furniture fire models and furniture design engineering, as well as for the 1995 state of the art upholstered furniture fire experiments. The essential findings are summarized in the appropriate chapters of this book. Many countries currently have no encompassing upholstered item regulations but rely, to varying degrees, on local authorities and purchase specifications for the fire safety of upholstered items. Limited regulations apply to certain public occupancies in France, Germany, Italy, and Spain. The activities in the Nordic Countries, which proceed within the framework of EU, are described in Ref. 64. The regulation of transportation seating will also be unified throughout the EU. For aircraft, most countries comply with the US Federal Administration (FAA) standard[66] and the aircraft producers often have additional standards. For ships, compliance with the International Maritime Organization (IMO) rules is universally accepted. There appear to be few regulations for automobile upholstery except in the US,[67] however, this standard provides very little protection. On the other hand, bus upholstery is regulated in some countries, using paper or radiant ignition sources, or with the BS 5852 in the UK. Details are given in Ch. 3.

18

Fire Behavior of Upholstered Furniture and Mattresses

2 Fundamentals

This chapter briefly summarizes some of the fire science fundamentals that need to be considered in dealing with the fire behavior of upholstered furniture and provides references to research that has been carried out in these areas. The topics covered include pyrolysis, combustion, smoldering, transition to flaming, flaming ignition, flame spread, HRR, propagating and non-propagating fires, inter-item spread, interaction with the enclosure, flashover, smoke and toxic gases. For more detailed discussions of fire science fundamentals, the reader is referred to Drysdale’s book on Fire Dynamics[68] and the SFPE Handbook.[69] Because of the central role played by heat release rate, the book Heat Release in Fires[42] is also a useful reference. The report on the CBUF project deals with the application of many of these elements to a comprehensive research program on the fire behavior of upholstered furniture.[7]

2.1.0

PYROLYSIS AND COMBUSTION

Combustion of solid materials that exhibit charring can occur by smoldering, glowing, or flaming. They undergo thermal decomposition (pyrolysis) to produce volatiles and char at elevated temperatures. Here the term volatile refers to any substance that would be in the gaseous state at temperatures characteristic of a fire environment. The rate of production of volatiles, m· , (kg s-1) during the thermal decomposition of a solid element having a uniform absolute temperature, T (K) is usually expressed by the Arrhenius equation, 18

Fundamentals (Eq. 2-1)

19

m· = ( m-mf )n A exp(-E/RT)

where m is the remaining mass of the element at any time during the decomposition, mf is the final mass of its char, A is an effective frequency factor, E is an effective activation energy and R is the gas constant (8.3 × 10-3 kJ mole-1 K-1). The exponent, n, is the order of the reaction that is usually taken to be unity, which means that the rate of volatilization is directly proportional to the amount of mass left that can be volatilized. The constants A, E, and n have physical significance for gas phase reactions. In the case of the thermal decomposition of solids, they are only empirical constants which have been found to provide a good correlation of the mass loss rate with (1) the absolute temperature of the specimen and (2) the mass remaining to be lost before it reaches its final char state. To use Eq. 2-1 for computing the mass loss rate, one has to obtain the kinetic constants. These can be obtained by thermogravimetric analysis (TGA). Such an approach is usually reserved for research studies, since for product testing it is normally much easier to measure the mass loss rate directly (see Sec. 2.6.0). For cellulosic materials a rule of thumb is that a 10°C rise in temperature approximately doubles the rate of decomposition. If the volatiles form a combustible mixture with the surrounding air and come in contact with a flame, a spark, or a high temperature surface (in the neighborhood of 500°C) they will ignite to form a flame. Otherwise, the volatiles with boiling points above room temperature will condense into liquid droplets to form smoke. If the char structure is sufficiently porous and flaming does not occur, oxygen can diffuse into the pores and produce highly exothermic reactions with the char. If the rate of internal heat production is high enough and the heat losses are small enough, the temperature will be elevated sufficiently to sustain the reaction. In that case, a smoldering front will move through the material, eventually reducing it to ash. If the reaction rate eventually becomes high enough to produce a combustible mixture outside the surface and a surface temperature high enough to ignite it, there will be a transition to flaming. If there is a pilot such as a flame, spark, or high temperature surface nearby, the transition will occur earlier. If the porosity is too low to provide an oxygen supply sufficient to sustain the smoldering front and the rate of volatilization is too low to maintain a flame, oxidation of the charred surface can still occur. However, this requires a temperature around 600°C. The rate of heat loss from the surface is so high at this temperature that it can only be maintained by external radiant heat. At 600°C, the surface will appear to be red. The char

20

Fire Behavior of Upholstered Furniture and Mattresses

combustion will produce some CO which will undergo gas phase oxidation to CO2 in the neighborhood of the surface with the production of a faint blue glow. This process is referred to as glowing combustion. Sometimes glowing combustion is regarded as a form of smoldering. A combustible item, which is porous and allows air to permeate through it, can be subject to smoldering. Smoldering of an upholstered furniture item generally starts from a cigarette, or, less frequently, from sources such as heaters, etc. Flaming fires can be started with matches, lighters, or other, often much larger, flaming objects. The smoldering fire may turn into a flaming one later, or a flaming fire may convert to smoldering due to oxygen depletion or due to burning rates too small to support flaming. While the HRR of the smoldering fire is very small, its hazards can be significant. Even limited smoldering of upholstered items can cause casualties due to suffocation in the room of fire origin or even adjoining rooms in under-ventilated spaces. A given material may be capable of either smoldering, flaming, or both. Many materials used in upholstered furniture (for example, cellulosic and acrylic fabrics, polyurethane foam, and cellulosic batting) fall into the latter category. The rates of burning are very different, being on the order of 0.1 g s-1 for a smoldering chair and 100 g s-1 for a flaming one. The rate of glowing combustion is typically less than that of flaming but much greater than that of smoldering. The ignition scenarios are likewise different. Thermoplastic materials degrade at elevated temperature to produce lower molecular weight components which melt and evaporate. The liquid, which is not immediately converted to a vapor, can form pools or be absorbed temporarily by porous surfaces onto which they may fall. The rate of volatilization of the liquid pool is given by

(Eq. 2-2)

m ′′ =

′′ q net Lv

(kg m − 2s −1 )

where q·´´net is the net heat flux (kW m-2), which is the incident flux minus the heat losses, and Lv is the heat of vaporization (kJ kg-1). The mass loss rate from the solid surface can also be expressed by Eq. 2-2 if Lv is replaced by an effective heat of gasification hg which includes the heats of degradation and melting as well as the heat of vaporization. While Lv is a constant, hg can vary during the burning period when the liquid is not immediately converted to a vapor.

Fundamentals

21

Thermoplastic frames, padding, and fabrics initially consume energy during the decomposition and melting phase. After they form pool fires they typically have high HRRs because most of the heat feedback from the flames goes into the evaporation of the liquid pool. Radiation losses from the surface are small because the temperature of the boiling liquid is usually low compared to the surface temperature of charring solids. Also, the pool can spread to provide large burning areas. Melting foams can form large pool fires. Melting fabrics usually fall onto the padding to form puddles and evaporate from there to feed the flames. With many (but not all) upholstered items made from thermoplastic materials, a large pool tends to form on the floor under the object in burning. The HRR from this pool can be roughly similar to what is being released from the remaining components of the item.

2.2.0

SMOLDERING

This section is a brief review of the literature on smoldering of cellulosic materials and polyurethane foams. There is a considerable body of knowledge of the type of upholstered item constructions which ignite from cigarettes, as discussed in Ch. 6. A descriptive overview of the smoldering processes can be found in Ref. 70. Ohlemiller has provided the most recent and comprehensive review.[71] In the interest of safety, it is important to note that self-sustaining smoldering in cotton batting and polyurethane foams can occur well inside the slab, essentially undetectable from the surface, even if the fire has apparently been extinguished with, for example, water. When the smolder front reaches the outside of the slab, transition to flaming ignition is likely to occur. There is anecdotal evidence that smoldering mattresses have reignited after prolonged submersion in water. 2.2.1

Cellulosic Material

Smoldering ignition of upholstered items due to inadvertently dropped cigarettes is the major cause of residential fire deaths, as discussed in Ch. 1. Both the tobacco column and the paper covering a cigarette contain cellulose and are designed to smolder readily. Experience shows that smolder transfers easily from cigarettes to medium and heavy weight cellulosic and acrylic fabrics and from them to many commercial padding materials, especially cotton, cotton blend batting, and polyurethane foam.

22

Fire Behavior of Upholstered Furniture and Mattresses

Certain materials, such as medium to heavy weight thermoplastic fabrics and batting, wool fabrics, and halogen-containing materials (for example, vinyl-coated fabrics, vinyl-vinylidene back-coatings, or polyurethane with smolder resistant, SR, treatment) can interfere with this transfer. The literature on cigarette/upholstered substrate interaction is reviewed in Ref. 72. There is a plethora of analyses of cigarette (mostly tobacco column) smoldering behavior in air; however, it must be emphasized that cigarette behavior in air is not indicative of the behavior on a substrate. Figure 2-1 shows how the temperature/time relationship inside cigarettes and eventual ignition/non-ignition were influenced by the fabric on which the cigarette smoldered. A series of papers analyzes the smoldering behavior of cellulosic materials, for example, shredded paper insulation.[73]–[79]

Figure 2-1. Temperature versus time curves for cigarettes burning in air and on different fabrics.

The smoldering of cellulose is a two-step process. It is initiated by heating some local region up to its pyrolysis temperature. In the first step, char volatiles and gases are produced by thermal decomposition. The smoke observed during smoldering is due to the condensation of these volatiles. During the second step, the char is oxidized in a highly exothermic reaction (approximately 30 MJ kg-1) producing the heat required to

Fundamentals

23

bring the adjacent region up to its pyrolysis temperature. If the supply of oxygen is high enough and the heat losses are low enough, a smolder wave will propagate through the material, leaving only an ash deposit. If the oxygen supply is restricted, the first step is usually endothermic and the reaction rate is slow. If the supply of oxygen is adequate, oxidative pyrolysis occurs in the first step and the reaction will be mildly exothermic (less than 1.0 MJ kg-1). The products will still consist of char and volatiles. However, their rate of production will be faster and their detailed chemical composition will be different. Char will be formed in the first step whether the oxygen supply is adequate or restricted. However, the two chars are probably not identical in reactivity or in other properties. These chars are typically somewhat more resistant to oxidation than the initial fuel but ultimately can be completely consumed. The char oxidation wave can often be visually observed as a glow traveling over a previously charred area, e.g., paper or a log in the fireplace. In experiments involving shredded cellulose insulation on a heated plate, smoldering could be initiated at temperatures as low as 290°C.[76][77] Temperatures measured in free-burning tobacco columns ranged up to 900°C.[72][80]–[83] However, Salig found core temperatures in cigarettes at the beginning of smoldering on cotton print cloth/polyurethane foam and cotton duck/polyurethane foam composites of only about 600°C.[84] The heavier duck composite continued smoldering after the exposure to the cigarette was over, the print cloth composite self-extinguished as seen in Fig. 2-1. The smoldering rate increases with denser packing of the cellulose insulation, thicker insulation beds, increased oxygen supply, and favorable air current direction over the ranges tested.[76][77] However, the rate will decrease when the packing becomes so dense that the supply of oxygen becomes restricted. The role of smolder retardants like boric acid is to interfere with the oxidation process; it does not reduce temperatures in the smolder wave.[76][79] Much of the literature on burning cigarettes discusses the effects of tobacco type, packing density, cigarette paper porosity, etc., on the linear burning rate (the mass burning rate is less affected by these parameters); this is reviewed from the point of view of furniture item ignition in Ref. 72. As regulation of the ignition propensity of cigarettes appeared to become a possibility, a number of papers were published which touched on basic mechanisms of cigarette ignition of substrates but also covered items related to an appropriate test method; these are discussed in Sec. 6.1.7.

24

Fire Behavior of Upholstered Furniture and Mattresses

Two similar methods were chosen to investigate smoldering of fabrics. In both, cylindrical cartridge heaters were used to initiate smoldering because their heat flux could be controlled and they did not consume oxygen as cigarettes do.[573][574] In one, the heater tip was held on the top of the fabric specimens (five cotton ducks varying widely in weight and a 300 g m-2 cotton rayon, commercial upholstery fabrics) and an infrared imaging camera was placed underneath the fabric samples. No correction for emissivity was applied since the emissivity of cellulosic materials is >0.90, and that of char, 0.98. To study the effect of alkali metal ion concentrations, some duck samples were rinsed, and others treated in potassium acetate solutions. When the cartridge heater was placed on the fabric, a sharp rise in temperature and then a plateau was observed, followed by another steep rise to about 670°C when smoldering ignition occurred, followed by fairly stable temperatures. In the second method, the cartridge heater was placed flat on the fabrics which were supported by PU foam, and the ignition point was defined as the time when the specimen was visibly judged to have started glowing. The ignition times were shorter at higher heat fluxes, as expected, and there was a linear relationship between the heat flux and the inverse of the time to ignition. The ignition times increased with fabric weight and decreasing alkali metal and oxygen concentrations. Minimum heat fluxes for ignition were about 15 kW m-2, and a potassium ion level of about >1300 ppm was required to sustain smoldering after ignition took place. The authors found the ignition temperatures of the unwashed cotton ducks to be 384–424°C, for the washed ducks, up to 493°C. In a striped commercial upholstery fabric the ignition time varied for different colored stripes, from roughly 30 s to no ignition, because of differences in ion concentrations. This indicates that for appropriate testing of cigarette ignition resistance of fabrics, all major areas differing in color or construction should be tested separately. The results of this work were used to construct a model of fabric smoldering ignitions by cartridge heaters.[574] At about 400°C, the cellulose of the specimen is gradually converted to char, and ignition can be observed. The temperature then rapidly reaches a maximum as the char itself undergoes combustion. The mathematical model was developed from these observations based on the heat transfer mechanism involved, and agreed generally with the experimental results. The important parameters for fabric smoldering ignition are heating flux, heating area, fabric weight, and ion content; the latter may affect the reaction kinetics.

Fundamentals

25

Infrared imaging of the bottom surface of fabrics below a radiant heat source simulating smoldering cigarettes was used to measure dynamic surface temperature gradients.[575] The fabrics used were again the three heavy, dense, unfinished cotton duck fabrics and two commercial upholstery fabrics. They were tested without padding, so that the oxygen scavenging and heat sink effects normally encountered in upholstery were not present. The pyrolytic degradation and oxidation reactions are governed by the heat transfer from the ignition source and the kinetics of the oxidation in the initial stages of smoldering. The further growth of the smoldering zone depends on the oxygen supply and the heat losses, which, in turn, depend on fabric construction and permeability. In this experimental setup, two zones are clearly visible: red glow in a central charring zone and a discolored pyrolysis zone, with volatile gases emerging from the surface. All fabrics reached temperatures of 500°C, and the heavier fabrics generally maintained this temperature longer than the lighter ones. Smoldering was maintained above 450°C. Isothermal areas on the duck fabrics did not correlate to fabric weight or alkali metal ion contents. Based on peak temperatures and isothermal areas, washing to remove the smolder-promoting alkali metal ions did not affect smoldering propensity of the ducks. Measurements on the upholstery fabrics may have been affected by their loftier structures (which would affect the heat transfer through the fabric); their time/temperature curves are more irregular, and for the lighter fabric, the temperature after the peak descended more rapidly than for the other fabrics. The two upholstery fabrics also showed lower peak temperatures and smaller isothermal areas at 450°C after washing even though their original ion content was less than half of that of the ducks. This may indicate that there were also structural changes due to washing.

2.2.2

Polyurethane Foam

The smoldering of polyurethane foam is discussed in Refs. 84–88, and in the above-mentioned review.[72] Few polyurethane foams were found to smolder in contact with burning cigarettes unless a smoldering fabric cover was present.[84] Smolder temperatures are about 400°C and smolder front progress in those foams which smolder is about 0.1 mm s-1. About 5% of the mass of the combustion products consist of carbon monoxide (CO).

26

Fire Behavior of Upholstered Furniture and Mattresses

The smoldering process can be divided into two major competing phases: the formation of smoldering char and the formation of nonsmoldering tar.[75][85] The first phase of polyurethane foam pyrolysis, which involves 10–15% weight loss, is virtually the same in air as in an inert atmosphere. The product is colored but still has some of the resiliency of original foam. In the presence of air the initially degraded foam is cross-linked to form char with the release of water and heat. This black cellular char, which retains much of the foam structure, undergoes further oxidation in air and provides the heat required to drive the smolder wave. If the char oxidation is sufficiently fast then the rate of heat production may be adequate to replace the outside ignition source so that smoldering becomes self-sustaining. If not, smoldering may still proceed until it recedes so far from the external heat source (for example, smoldering fabric or cigarette) that its own heat generation can no longer overcome the heat losses; it will then extinguish. In the absence of air, or when the rate of char production is prohibitively slow, the degraded foam is converted to tar with the loss of the cellular structure essential for smolder. In the absence of air the tar is completely gasified leaving only a small residue (1–3%) at 500°C.[75][85] Several approaches to making SR (smolder resistant) foam have been suggested. One is the use of agents which would interfere with char formation during the degradation process. The second is promotion of tar formation by weakening the polyol chain and urethane links. This, however, may increase the probability for flaming combustion.[87] Others are inclusion of inert or hygroscopic materials in the foam; more recently, quite flame resistant foams are based on inclusion of melamine or certain forms of carbon, as discussed in Ch. 6. More specific modeling equations for the smoldering of polyurethane foam and reasonable experimental validation can be found in Ref. 87. The difficulties caused by the fact that smoldering is very incomplete combustion are discussed. Both conduction and radiation affect the smoldering rate in open structures, such as flexible polyurethane foams. Smolder intensity was found to be governed by oxygen supply, but smoldering can proceed at oxygen supply rates as low as 5% of the stoichiometric one. The threshold oxygen concentrations at which self-extinguishment, continued smoldering, or transition to flaming occur was established for three polyurethane foams.[88] This work was performed with an electrical heating coil rather than a cigarette ignition source. Such heating coils appear to give different results than cigarettes and seem to lead to faster transition to flaming than

Fundamentals

27

cigarette induced smoldering.[84] They obviously present a stationary ignition source, as compared to the moving smolder front of a cigarette.

2.3.0

TRANSITION TO FLAMING

Many, but by no means all, fires which start as smoldering fires eventually begin flaming. This transition is governed by a complex interaction of heat conduction, gas flows, and reaction chemistry and is not well understood.[75] For upholstered items, three main empirical observations can be made: 1. Oxygen availability and air currents play a major part in this transition. Typically, a smoldering furniture item may flame when a door is opened, assuring a new oxygen supply. Reports on shredded, tightly packed grass clippings are available;[80][81][89] they burst into flames most readily when the air movement exceeded 0.83 m s-1 (3 km hr -1). On the other hand, flaming may revert to smoldering if the oxygen in a room is depleted[90] or the mass loss rate in the form of gases and volatiles becomes too small to support flaming. However, the rate of mass loss may drop only slightly just after reversion to smoldering, while it always increases very significantly after a transition to flaming. The increase in the rate of mass loss rate during flaming is due to the flame heat transfer to the surface. When flaming stops, the oxygen which would have been consumed by the flame is now available to oxidize the high temperature char. Thus the high mass loss rate may continue for a while due to the char consumption contribution. In order to maintain the surface temperature high enough to sustain the char oxidation, it will generally require an external radiant flux which can include reinforcement from other parts of the burning item as discussed above. 2. When a transition to flaming occurs, HRR, smoke production, etc. were sometimes found to be essentially identical to a fire that would have been started at that instant by flaming means.[91] When this holds

28

Fire Behavior of Upholstered Furniture and Mattresses true, it can allow great simplification in practical analysis, since it states that the history of the fire does not have a “memory.” However, since changes in the chemical structure do occur during smoldering, there are undoubtedly conditions under which such simplification does not hold. 3. The transition to flaming cannot yet be predicted by knowing the materials of construction of the item.

The following studies are summarized in Table 2-1. The California Bureau of Home Furnishings (BHFTI) placed cigarettes on 15 commercial chairs.[92] Five chairs self-extinguished after prolonged periods; one smoldered until it was extinguished after 330 minutes; and nine eventually went into flaming. Because these were commercial furniture items varying greatly in shape as well as materials, little could be learned about construction factors which resulted in flaming except, perhaps, that the presence of thermoplastic fibers seemed to reduce the tendency for transition to flaming. Similar results regarding the transition to flaming were found in a few experiments with cigarette ignited chairs containing thermoplastic batting in the seats.[90] When polyester batting was the padding material, the probability of transition to flaming was decreased as compared to polyurethane and cotton batting. However, the rate of glowing (for those fabrics which did glow) seemed to be increased when polyester batting was substituted for polyurethane foam or cotton batting. The fastest transition from smoldering to flaming (22 minutes after placement of the cigarette) was in a chair in which a heavy cotton fabric covered the cotton batting; in chairs with lighter cellulosic fabrics and mostly polyurethane padding it was about one hour. A draft in the test room favored flaming. In tests performed in abandoned housing in the Indiana Dunes in the late 1970s, an assortment of commercially available new and secondhand furniture was ignited with a glowing heater element.[93][94] The average times of smoldering before flaming were 70 minutes for the chairs and sofas and 83 minutes for the mattress/box spring assembly in the original test series. Another test series was later conducted at NBS under somewhat different conditions on replicate chairs and resulted in flaming after an average of 44 minutes.[95] The chairs were covered with a cotton upholstery fabric, and padded with either cotton batting or polyurethane foam. None of the components were fire retarded. It is interesting to note that for this

Fundamentals

29

set of 12 identical chairs, the transition times varied from 29 to 63 minutes. This kind of variation emphasizes that all aspects of smoldering phenomena are highly statistically variable and that this variation must be considered before placing much reliance on mean values. In 1970, Southwest Research Institute reported cigarette ignition test results on innerspring mattresses using cellulosic ticking.[96] In some cases, where no smoldering ignition took place with one cigarette, two cigarettes were placed side by side; these results are thus pertinent for times from inception of smoldering to flaming but not for cigarette ignition resistance of the composites. These mattresses were tested without and with sheets or blankets containing various fibers; pillows were included in some test arrangements. A vinyl mattress cover underneath the sheet caused relatively slow transition to flaming. Six chairs with cover fabrics made from various fibers were also tested. A chair covered with polypropylene fabric flamed in 22 minutes (it may have been a rather thin fabric; medium or heavy weight thermoplastic fabrics generally have relatively good cigarette ignition resistance. However, this was one instance where two cigarettes side by side were used). Foam rubber (latex) seemed to transit into flaming relatively early. Table 2-1 shows that out of a total of 102 items subjected to smoldering ignition in laboratory tests, 32% burned up partially or completely without erupting in flaming; 64% did go to flaming, while the remainder were manually extinguished or were indeterminate. For the chairs which did not go to flaming, the time for the chair to be essentially consumed can be long; one study reported an experiment where smoldering persisted for over 6 hours. The mean smoldering-to-flaming transition observed in the laboratory tests was 88 min, the minimum 22 minutes, and the maximum 306 minutes. The conclusion can be drawn that transition times in the range 22 to 306 minutes are possible, but NOT that transitions outside of this range are impossible. The maximum and the minimum values found in a given sample of a population will depend not only on the traits of the population but on the sample size. Thus, if more than 102 fires of smoldering origin were examined, it is likely that values outside the given range would have been found. There are physical limits to this, however. Times in the range of seconds or days, for example, would be unlikely since smoldering is not established before some minutes have elapsed. Conversely, an item cannot transition to flaming if it has been smoldering long enough to be essentially consumed.

30

Fire Behavior of Upholstered Furniture and Mattresses

Table 2-1. Smoldering-To-Flaming Transition Times Reference Type of Item

Number of Items

Time to Flaming (min) Total Burned Went Other2 Avg. Range up or to went flaming out without flaming

[92]

Commercial chairs

15

5

9

1

142 60–306

[90]

NBS experimental chairs

6

3

3

0

48

[93][94]1

sofas and chairs

24

7

17

0

72

28–132

[93][94]1

mattresses and box springs

18

8

10

0

85

51–129

[95]1

chairs

22

10

12

0

44

29–63

[96]

solid foam and innerspring mattresses

11

0

8

3

140 97–233

[96]

chairs

Totals

22–65

6

0

6

0

97

22–152

102

33

65

4

88

22–30

1. Electric ignition source; the remaining test series used cigarette ignition 2. Manually extinguished, or status unclear

2.4.0

FLAMING IGNITION

Kanury provided a review of the ignition process of cellulosic materials[97] and a mathematical discussion of flaming ignition of solid fuels.[98] Also, Drysdale’s book on Fire Dynamics covers piloted ignition of solids.[68] A comprehensive treatment of piloted ignition is given by Janssens in his Ph.D. dissertation.[99] Flaming ignition occurs when (1) the flow of volatiles from a decomposing solid or a boiling liquid exceeds some critical value, depending on the material, its moisture content and orientation, the air flow conditions, ambient humidity and oxygen concentration and(2) the mixture of these volatiles with the surrounding air encounters a flame, a spark, or a high temperature surface (approximately 500°C or greater) which can serve as a pilot ignitor. The critical flow of volatiles required for flaming ignition is that which is needed to reach the lower flammability limit for the resultant fuel/air mixture.

Fundamentals

31

The ignition temperature is the lowest temperature at which piloted ignition of a material can occur. The minimum flux for ignition is the lowest incident flux for which this ignition temperature can be achieved. As the flux is increased above its minimum value, the time to ignition gets shorter, the depth of the thermal wave and the zone of pyrolysis at the time of ignition gets smaller. Therefore, the temperature in this zone must be increased in order to produce the required flow of volatiles to achieve ignition. Thus, the temperature at which ignition occurs is an increasing function of the incident flux. In order to avoid running tests at many different fluxes to find the smallest one for which the specimen will ignite, it can be determined graphically using a small number of different fluxes. Straight-line plots can usually be made by plotting the ignition flux on the x-axis versus some function of the ignition time (t -1, t -0.55, etc.) on the yaxis. The point at which the straight line intersects the x-axis is then defined as the critical flux for ignition. Further details are given in Ref. 99. Ignition by flame contact occurs if the incident flux is primarily due to the heat transfer from a flame contacting the surface. Radiant ignition occurs if the critical flux is primarily due to a radiation source not in contact with the surface. Radiant ignition is referred to as piloted or forced ignition if there is a flame, spark, or high temperature surface present. If there is no external pilot the surface needs to be heated to a sufficiently high temperature (for example, the generally accepted value is 400–500°C for cellulose) to act as its own pilot. In this case it is called auto-ignition or spontaneous ignition. The latter term is not preferred, since it may be confused with spontaneous combustion, below. Self-ignition or spontaneous combustion occurs under certain conditions of self-heating due to internal chemical reactions (bacteria can be involved). After long periods of time, the interior temperature can reach a sufficient level to produce the critical flow of volatiles required for ignition even when the ambient temperature is still relatively low. Some classic examples are oily rags and high piles of coal. A detailed discussion of spontaneous combustion is given in Ref. 100. Ignition by flame contact is always piloted. If the surface continues to flame after removal of the exposure flame, it is referred to as sustained ignition. If the flame on this surface is not maintained after removal of the ignition source, it is referred to as transient ignition. A uniform, large-area irradiance of about 20 kW m-2 suffices to ignite not only all common upholstered assemblies but even many fire retarded (FR) ones. While higher fluxes may be required to ignite over a small area, even these are normally achieved in typical fire scenarios. Yet,

32

Fire Behavior of Upholstered Furniture and Mattresses

in many practical cases, a small area ignition source may cause the material to be ignited locally but the fire will not spread; instead, it will die out once the source is removed. An extreme example of this is a welding torch. With many fabrics and foam compositions, sustained ignition by such torches is impossible in spite of their especially high fluxes; a hole is melted/burned through them but sustained ignition does not result. Sustained ignition is a necessary condition for flame spread. Ignition sources are discussed in Ch. 4. The most commonly used equation to predict the time to ignition is based on the solution of the classical heat conduction problem of an inert semi-infinite solid with constant properties exposed to a constant flux with no heat losses. The front surface temperature rise is given by Ref. 101

(Eq. 2-3)

T − To =

′′ t 2 q ext

π kρ C

where T is the surface temperature as a function of time, To is the ambient temperature, q·´´ext is the constant exposure flux, k is the thermal conductivity, ρ is the density of the solid, C is the specific heat of the solid, and t is time. The product kρ C is called thermal inertia. This equation can be inverted to yield the time to ignition as a function of the ignition temperature, the flux and the thermal inertia kρ C:

(Eq. 2-4)

(

ð kñ C Tig − To tig = ′′2 4qext

)

2

It must be recognized that in addition to the solid not being inert, both the thermal conductivity and the specific heat are increasing functions of the temperature for most materials. In the case of wood they are directly proportional to the absolute temperature. Also surface heat losses are too large to neglect at the pyrolysis temperature. Furthermore, Eq. 2-4 does not take into account the dependence of the ignition temperature on the flux. In spite of the shortcomings, it remains the classic analytical solution and has often been used for correlation of ignition time and flux data. However, improvements can be made with approximation methods as discussed by Janssens.[99] An analytical solution which takes linear heat losses from the surface into account does exist for the surface temperature. It is given by

Fundamentals

(Eq. 2-5)

T − To =

[

33

( )]

q ext ′′ 1− exp(ô ) erfc ô h

where

(Eq. 2-6)

τ=

h 2t kρC

Equation 2-5 reduces to Eq. 2-3 when the surface heat transfer coefficient h equals zero. The functions inside the brackets can each be replaced by a power series in order to provide for an approximate solution for the time to ignition. However, in order to account for the temperature variation in the thermal properties, the variation in ignition temperature with flux, and the heat of pyrolysis of the decomposing solid, it is necessary to use a computer model to predict the time to ignition. A computer model for piloted ignition of wood has been provided in Ref. 99. Another computer model has been constructed to calculate the HRR of wood.[102] The time to ignition is routinely obtained as a necessary by-product of this model. However, there is a scarcity of data on these properties at elevated temperatures to put into the models, particularly in the vicinity of the ignition temperature. Deterministic models for the HRR of upholstered furniture materials are not available at this time.

2.5.0

FLAME SPREAD

Typical upholstered item dimensions range from 0.5 to 2.0 m. Fires of this scale are large enough so that flame spread and heat release behaviors are predominantly by radiative, rather than convective, mechanisms. It can further be assumed that in most room fires, only natural convection and not forced convection flows need to be considered. Flame spread is usually distinguished as being one of two types: concurrent-flow (wind-aided) or opposed flow (against-the-wind). In natural convection situations, the wind is induced by the fire itself due to its buoyancy. Opposed-flow flame-spread can be along a horizontal surface or along a vertical surface in the lateral or downward direction. Horizontal and lateral flame-spreads are controlling factors in furniture fires; they have much lower rates than the upward or

34

Fire Behavior of Upholstered Furniture and Mattresses

wind aided spread. Wind-aided flame-spread is normally irrelevant to mattresses. On upholstered chairs, it will occur on vertical panels which are ignited at their bottom. The time for vertical flame-spread to occur is usually very fast and for furniture this component is sometimes approximated as being instantaneous. A theory was first presented by Rockett[103] for providing a calculational basis to determine opposed flow flame-spread when external radiation is the primary mechanism and convection is small enough that a simple treatment is adequate. The flame-spread process is assumed to be one-dimensional, i.e., spreading from a line source, not a point source. This theory has been applied, in a somewhat simplified way, to ASTM E 162, a test method for downward flame-spread on wall paneling materials.[104][105] It is sometimes used for other types of materials including upholstered items. An apparatus was constructed by Babrauskas and coworkers at NIST for making horizontal flame-spread measurements on fabric/padding composites in a thermal radiation field with the goal of obtaining data suitable for analysis with Rockett’s theory, but was used only for a few experiments.[106] However, the following observations were made: (1) at zero irradiance the spread rates ranged from 0 to 3.7 mm s-1 depending on the material combination; (2) at 2.5 kW m-2 irradiance the spread rates were typically about doubled, except for those cases which fell below 1.0 mm s-1 at zero flux. The flame-spread rate equations are usually based on the assumption that (1) there is a well defined preheating region which extends a distance beyond the area of the pyrolyzing surface along the direction of spread and (2) that the local heat flux from the flame to the surface in this region is constant. The flame-spread rate is given by

(Eq. 2-7)

v fs =

ä tig

where tig is time it takes to go from the surface temperature Ts ahead of the preheating region to the ignition temperature Tig. By substituting Eq. 2-4 into Eq. 2-7 Quintiere obtained the flame spread equation that was used in the development of the LIFT test method.[107][108]

(Eq. 2-8)

v fs (t ) =

( ) ð k ñ C (T − T ) 4ä q ′ft′

2

2

ig

s

Fundamentals

35

By letting (Eq. 2-9)

Φ=

( )

4 δ q ′ft′ π

2

Eq. 2-8 reduces to

(Eq. 2-10)

v fs (t ) =

(

Φ

k ρ C Tig − Ts

)

2

In principle, Eq. 2-10 could be applied for upward, lateral, downward and horizontal spread. The flame spread constant, Φ, would depend on the material, the scale of the problem, and the direction of flame spread. To a first approximation the ignition temperature, Tig, and the thermal inertia kρ C depend only on the material. However, k and C increase with the temperature which varies from the quasi-equilibrium temperature of surface ahead of the flame to the ignition temperature. Therefore, the effective thermal inertia should also depend to some extent on Ts. This has been ignored for practical reasons. The LIFT apparatus was designed to measure Φ, kρ C and Tig for use in the fire growth models to predict the lateral flame-spread using Eq. 2-10. A modified LIFT test has occasionally also been used in the horizontal orientation to obtainΦ for horizontal flamespread. The external flux plus the flux from the flame must be equal to or greater than the minimum flux for ignition in order to sustain the ignition and allow the flame to spread along the surface. Thus, the minimum flux for flame spread is given by (Eq. 2-11)

′′ = qigs ′′ − q ′ft′ q mfs

The minimum surface temperature for flame spread is the equilibrium temperature of the surface when it is exposed to this critical flux. Thus, Tmfs is defined by the following energy balance,

(Eq. 2-12)

(

) (

)

4 − T 4 + h T − T +  k ∂T  ′′ = εσ Tmfs q cfs o cfs o  ∂z  z =0

36

Fire Behavior of Upholstered Furniture and Mattresses

where z is the coordinate normal to the surface. The last term which is due to conduction losses to the interior can be considered to be small after long exposures. The total hemispherical emissivity, ε, for organic solids is usually close to unity. The Stefan-Boltzmann constant σ is 5.67 × 10-11 kW m-2 K-4. The convective heat transfer coefficient h will depend on the size and orientation of the surface. It can be determined experimentally from Eq. 2-12 by exposing an inert specimen of the same size and orientation to a known constant flux and measuring the surface temperature. Somewhat more empirical but closed-form expressions for mattress flame-spread were sought by Pagni et al.[109] They tested one half-size polyurethane foam mattress (0.89 m by 0.89 m) with a ticking and a cotton/ polyester sheet in two configurations intact, and with a 100-mm hole cut out of the ticking and sheet, surrounding the methenamine pill ignition point. For the specimens with the hole, they found three burning regimes: (1) for the first 30 s, flame-spread was traveling across the surface, up to the edge of the cut hole; (2) in the next 100 s, there was little horizontal flame-spread. Instead, the burning surface regressed downward until the bottom burned through; (3) in the final period, there was a steady, somewhat accelerating radial spread. However, this was not surface spread alone, but rather a progressively enlarging cylindrical consumed area. The interior of the cylindrical void was filled with a luminous turbulent flame. The uncutcover case was generally similar, but with less distinct regimes. (Similar observations also were made with specimens subjected to a linear ignition source on the apparatus described in Ref. 106.) Flame spread and mass loss rates, as well as flame base diameters for various times from ignition are listed in Table 2-2. An expression for flame height, measured above the specimen top, was obtained as:

(Eq. 2-13)

 m 2  = 0.36  5  D D 

h ft

14

where hfl is the height of the flame (m) and D is the flame base diameter (m). Other correlations have also been reported in the literature for similar, but not identical, polyurethane foam mattresses by Land[110] and Mizuno.[111] Land found a significant effect of foam moisture absorption on the flame spread. The higher moisture contents gave lower flame spread rates, smoke, and flame heights; the mass loss rates of samples conditioned to 92% RH were 50% or less than those conditioned to 35% RH. Other moisture effects are discussed in Ch. 6.

Fundamentals

37

Table 2-2. Flame Spread Rates, Flame Diameters, and Mass Loss Rates In Mattress Burns Time after Ignition (s)

Flame Spread Rate (mm/s)

Mass Loss Rate (g/s)

Flame Base Diameter (m)

0–30

1.82

≈0

3.84 × 10-3 t

0.028 e

0.024t

1.02 × 10-3 t + 0.061

30–130

0.51

130–220

-0.68 + 9.0 × 10-3 t

0.099 e 0.014t

220–360

1.69 - 1.58 × 10-3 t

0.099 e 0.014t -1.58 × 10-6 t2 + 3.38 × 10-3 t - 0.300

9.0 × 10-6 t2 - 1.36 × 103 t + 0.222

Mizuno[111] studied mattress foams, without ticking, in two sizes: 0.50 m by 0.50 m by 0.14 m thick, and 0.90 m by 0.90 m by 0.12 m thick. The foams were ignited in the center with a methenamine pill. The flame radius, r (m), was measured as: (Eq. 2-14) r = 2.3 × 10-3 t

0 < t < 30 s

r = 3.5 × l0-2 e0.026t for the smaller specimens 30 < t < 70 s r = 4.0 × 10-2 e0.021t for the larger specimens 30 < t < 130 s The mass loss rate (kg s-1) from t = 20 s to total surface involvement (t = 90 s for the smaller specimens) was evaluated as a function of the instantaneous radius: (Eq. 2-15)

m• = 0.0461 r 2.23

At the time of full surface involvement, 14% of the mass was lost. Some illustrations offlame spread over vertical polyurethane foam slabs are available.[112] In one configuration a single slab was ignited at the top with a point source. Melting, dripping, and cratering was seen. The basic burn pattern was V-shaped, with some additional burning at the top (Fig. 2-2). In the case of the corner-top ignition of two slabs in the same figure, the predominant flame pattern was straight down, due to radiation reinforcement from the second panel. The work of Mizuno[111] quantitatively illustrates the very difficult aspect of studies of furniture flame-spread. For reasons of tractability, theories of flame spread are invariably based on one of two simplifying

38

Fire Behavior of Upholstered Furniture and Mattresses

assumptions—the fuel is taken to be either thermally thick or thermally thin.[103][113] For the thick case, a negligible fraction of the mass is lost during flame spread; after initial flame involvement the burning surface regresses parallel to its original plane. For the thin case (for example, a burning card) the entire thickness is involved in the spreading flame. Actual measurements of the pyrolysis zone contours for a polyurethane foam (Fig. 2-3), however, show a behavior which does not conform to either of these limiting cases. For fabric/foam composites the reality is usually somewhat closer to the thermally thick case. It depends on the fabric which often burns by itself in the thermally thin case while the foam burns later in the thermally thick mode.

Figure 2-2. Downward burn pattern on a polyurethane foam slab for point ignition on a flat surface and on a corner configuration.

Figure 2-3. Pyrolysis zone contours for a horizontal polyurethane slab at different times.

Fundamentals

39

Intensive consideration was given by Friedman and others[114]–[115] in the 1970s and early 1980s to describing analytically a generalized fire growth process. In the conceptual model, the initial fire spread is considered as a growth in the fire area. This is reasonable for large surfaces, such as upholstered chairs, or for arrays of fuel items progressively becoming involved. In a process of this sort, it is often observed that the rate at which new material becomes involved in the fire is proportional to the amount already burning. That is (Eq. 2-16)

dAb /dt ~ Ab

This can be integrated to give the involved area, as an exponential function of time, as (Eq. 2-17)

Ab(t) = C1eC2t

where C1 and C2 are empirical constants. These constants were obtained for various individual items and collections of upholstered furniture and bedding.[116][117] The main application of such fire growth models, suggested by Friedman,[114] is for studying the time to such critical events as detection, alarm, and sprinklers. It is of importance in assessing fire hazard to determine the time from ignition to these critical events. The method works best when the objective is to determine fire growth from a non-zero start (for example, from detection) to a later event (for example, sprinkler activation). Exponential-growth schemes have not been found to be useful in assessing the hazard of furniture itself. This is because the constants needed for the exponential model could only be computed a posteriori— predictive methods were never found for them.

2.6.0

HEAT RELEASE

2.6.1

Heat Release Rate

Strictly speaking, the total heat release rate, (i.e. the HRR integrated over the area of the furniture item) in kW, should be used to express the HRR of a piece of furniture measured in the furniture calorimeter or in a room fire test and the HRR per unit area, in kW m-2, should be used to express the results of tests in the bench-scale HRR calorimeters such as the OSU,[118] Factory Mutual Research Corporation (FMRC),[119] and Cone Calorimeters.[41][120] However, it is common practice to refer to the results of both the bench-scale and the full-scale tests as simply “HRR,” even

40

Fire Behavior of Upholstered Furniture and Mattresses

though they have different units and cannot be compared directly. This causes no problem to those familiar with the field but could lead to some misunderstanding among those who are new to it. Nevertheless, the common practice is used in this book. It is essential, however, that the units are correct when expressing these results. The peak HRR per unit area is perhaps the most quoted parameter used to express the results of Cone Calorimeter tests in general, as described in Ch. 3. The 180 s average HRR per unit area refers to the average over the first 180 s after ignition. It is often used in expressing Cone Calorimeter results on furniture composites. These are 100 by 100 by 50 mm thick specimens containing the fabric, padding and interliner, if any. They are intended to represent small elements of the full-scale furniture. Averages over 60 s and 300 s intervals are also used. When the relationship between the 180 s average HRR (kW m-2) of the furniture composite in the Cone Calorimeter and the peak HRR (kW) of the burning furniture was investigated, it was found that the 180 s average HRR (kW m-2) provided a better correlation than the peak HRR (kW m-2) in the Cone Calorimeter.[121] This is because at the time of the peak full-scale HRR, not all portions of the upholstered item are at their peak burning rate. Some portions are not yet ignited, some are mid-way through burning, and others may already be burned out. Similarly, narrow peaks in the bench scale tests may not directly translate to the real-scale object, since no two portions of it are likely to undergo the same pyrolysis history at the same moment. The total heat released, in kJ or MJ, is obtained in the furniture calorimeter or room tests by adding up the products of the time between scans and the total HRR in each time interval over the duration of the test. This is also true of the total heat released (kJ m-2 or MJ m-2) in the bench-scale tests. Since the 1970s, HRR has come to be recognized as one of the most important fire properties of a material. The role of HRR in hazard prediction and optimization of its use is based on papers by Babrauskas and others.[7][122]–[126] A bibliography of HRR studies can be found in Ref. 43 and general and specific application discussions of it in Ref. 42. The usefulness of the HRR is exemplified by the following: • If the total HRR history in a room is combined with a detailed description of that room, the temperature of the hot upper layer and the elevation of its interface can be predicted as a function of time, as discussed in Ch. 1.[7] • If the smoke and toxic gas yields of the burning materials are also known, the smoke and toxic gas

Fundamentals

41

concentrations in the upper layer can be predicted from the HRR. • The rate at which smoke and toxic gases are transported to other parts of the building also depends on the total HRR and the smoke and gas yields of the burning materials. • The occurrence of flashover in the room depends on the HRR exceeding some critical level. • Flaming ignition of a material depends on exceeding some critical rate of pyrolysis which can be expressed in terms of a critical HRR. • The upward flame spread rate on a wall depends on the height of the flame which can be expressed as a function of the HRR. • Spread of flame from a burning chair to another chair some distance from it depends on the radiant flux at that distance which can be expressed in terms of the total HRR of the burning chair. Huggett has shown that the heat released during the combustion of polymers is directly proportional to the amount of oxygen consumed, to within about± 5%. The proportionality constant is 13.1 MJ per kg of oxygen consumed.[115] Note, by contrast, that the heat of combustion is given as the heat released in MJ per kg of fuel consumed and differs widely for different materials. Parker provided the basic formulas for the calculation of HRR from oxygen consumption measurements, opening a radical new approach to fire engineering.[127] A treatment which may be easier to use is presented in Ref. 128. These formulas provide the basis for the Cone Calorimeter, the furniture calorimeter, the room fire test and other applications of the oxygen consumption method. In the usual way of measuring the HRR by oxygen consumption, all of the combustion products along with the entrained air are collected by a canopy hood which is connected to an exhaust duct and fan. A small fraction of the exhaust gases are continuously drawn through a system of filters and gas analyzers to determine the concentrations of oxygen, carbon dioxide and carbon monoxide that are used along with volume flow in the duct as input to the formula for calculating the HRR. The technique is described in detail by Janssens and Parker.[128]

42

Fire Behavior of Upholstered Furniture and Mattresses

One important advantage of HRR measurements is that, unlike many other fire tests, the data are presented in engineering units which can be used for modeling, which is discussed in Ch. 7. The HRR of furniture items is affected by the material combination, the configuration of the item, its total mass and the ventilation conditions.[129] These can potentially be taken into account in a deterministic furniture fire model. Progress in this direction is discussed in Ch. 7. The first correlation formula was developed for residential furniture by Babrauskas and Krasny,[121][129] which takes the 180 s average HRR of the furniture composite in the Cone Calorimeter at an exposure flux of 25 kW m-2, the total mass of the furniture item and a style factor into account to predict its peak HRR in a full scale test in the furniture calorimeter. An improved correlation formula and more detailed furniture fire models for seating furniture and mattresses were developed on the CBUF program.[130] These are discussed in Ch. 7. 2.6.2

Heat of Combustion

The instantaneous effective heat of combustion is equal to the HRR divided by the mass loss rate and can vary considerably over the burning period for charring materials. During the flaming period the heat release is due to the volatile thermal decomposition products which typically have much lower heats of combustion than the virgin material. During the glowing combustion period which follows, it is due to the char which has a much higher heat of combustion than that of the virgin material. During a fire the water produced in the combustion process remains in the vapor phase. Thus, it is the net heat of combustion that is important in fires rather than the gross (upper) heat of combustion that is measured in an oxygen bomb calorimeter. The effective heat of combustion will, in general, tend to depend on burning conditions. In highly under-ventilated fires, the effective heat of combustion will be reduced. Its dependence on ventilation can be determined in a HRR calorimeter which can measure the HRR in reduced oxygen atmospheres. The average effective heats of combustion obtained in the CBUF room fire tests for a range of furniture in the European marketplace are shown in Table 2-3 while the average effective heat of combustion for specially designed chairs varying only in fabric and padding are shown in Table 2-4.[131] For the 13 commercial items which exhibited propagating fire behavior, the effective heat of combustion varied from 14 to 18 MJ kg-1. For the non-propagating ones it varied from 6 to 23 MJ kg-1. For

Fundamentals

43

the 14 fully upholstered items of marketplace furniture, the range was similar, from 15 to 20 MJ kg-1. With office chairs and mattresses the range was considerably greater. Table 2-5 shows the results obtained in the furniture calorimeter. The technical descriptions for these furniture items are given in Tables 2- 6 and 2-7. Table 2-3. CBUF Room Burn Results On Commercial Furniture Heat and Smoke Release Item

Peak HRR (kW)

Time to Peak HRR (s)

1:1a,b 1:2a 1:3a 1:4 1:5 1:6 1:7 1:8 1:9 1:10 1:11a 1:12 1:13 1:14 1:15 1:16 1:17 1:18 1:19 1:20 1:21a 1:22a 1:23 1:24 1:25 1:26 1:27a

1959 1714 2107 991 917 1696 664 1570 661 1027 1849 1181 662 614 1094 1035 933 44 1430 699 2122 1599 414 49 33 30 2363

152 608 232 424 480 337 656 168 1240 268 308 209 1313 1157 353 445 397 121 193 308 187 317 85 121 122 121 196

Total Heat Peak Heat of Smoke (mJ) Combustion Release (mJ/kg) Rate (m2/s)

Total Smoke (m2)

Smoke Yield (m2/kg)

Length of Test (s)

256.9 202.9 357.4 405.6 528.6 353.3 354.9 519.2 184.2 431.6 138.1 200.5 163.3 166.6 267.6 267.2 331.9 5.3 241.3 106.9 114.2 132.6 32.9 18.7 2.8 2.0 238.7

7334 2886 8119 1906 5032 2040 1466 3179 1532 3425 1058 1262 1460 1300 5459 5804 4554 146 3529 706 1966 10191 140 93 43 8 4690

429 235 463 74 147 95. 68 116 113 122 110 96 194 174 510 538 403 471 280 99 329 1528 104 119 286 83 339

215 616 270 1320 1800 713 1800 1276 1800 1296 311 1277 1800 1800 1217 1297 1173 1229 1205 1261 187 332 809 1161 1290 308 220

15.03 16.50 20.39 15.82 15.44 16.43 16.35 15.56 13.53 15.38 14.33 15.28 21.66 22.33 24.99 24.76 29.37 16.56 19.15 14.95 19.10 19.88 24.37 23.97 18.67 22.22 17.27

73 18 75 6 14 24 3 22 5 16 24 7 7 7 25 21 13 1 19 4 27 87 2 <1 <1 <1 50

a:Data prior to extinguishment with water (before 1800 s) b:Total heat release is adjusted by a factor 1.10 to account for the energy lost due to escaping smoke and gases from the hood.

44

Fire Behavior of Upholstered Furniture and Mattresses

Table 2-3. (Cont’d.) Smoke and Toxic Gases Item

Peak extinction coefficient of smoke in lower part of room (m-1)

HCN peak (ppm)

1:1a 1:2a 1:3a 1:4 1:5 1:6 1:7 1:8 1:9 1:10 1:11a 1:12 1:13 1:14 1:15 1:16 1:17 1:18 1:19 1:20 1:21a 1:22a 1:23 1:24 1:25 1:26 1:27a

1.77 0.90 1.31 a 0.38 0.08 — 0.04 0.12 0.85 0.07 1.07 0.06 0.14 0.44 0.94 0.48 0.30 0.02 0.09 0.10 1.26 1.15 0.08 0.06 <0.01 0.02 1.66

— 275 — 332 279 88 15 255 — — — — 31 39 — 38 — 38 — — 192 151 — — 6 — —

HCLb Hbr COc peak peak peak (ppm) (ppm) (ppm) — 342 — 269 239 293 40 241 — — — — 94 85 — 353 — 90 — — 14 845 — — 147 — —

— 31 — 17 33 10 16 24 — — — — 12 10 — 12 — <10 — — 11 361 — — 11 — —

— 3397 — 2080 2994 5052 557 4185 — — — — 494 398 — 1799 — 188 — — 2182 8823 — — 184 — —

NO Time of peak test (ppm) (s) 199 178 193 232 246 349 178 239 176 251 297 256 185 122 141 161 149 76 280 200 274 151 210 34 9 22 230

215 616 270 1320 1800 713 1800 1276 1800 1296 311 1277 1800 1800 1217 1297 1173 1229 1205 1261 187 332 809 1161 1290 308 220

a:Data prior to extinguishment with water (before 1800 s) b:HC1 peak concentrations not corrected for HC1 trapped in sampling-line (approx. 30%) c:Reported CO concentrations based on FTIR measurements

Fundamentals

45

Table 2-4. CBUF Room Burn Results On Chairs Designed To Study Effect of Fabric/Padding Variations Heat and Smoke Release Item

Peak HRR (kW)

2:1 2:2 2:3 2:4 2:5 2:6 2:7 2:8 2:9 2:10 2:11 2:12 2:13 2:14 2:15 2:16

832 850 1054 1176 867 872 868 1325 887 1007 768 880 34 712 43 33

Time Total to 50 kW Heat HRR (s) (MJ) 90 40 55 45 55 45 60 55 55 45 105 85 — 55 — —

120.4 113.4 214.6 202.5 172.3 117.4 171.4 296.7 172.1 203.8 114.8 132.1 1.0 209.1 3.3 14.5

Heat of Combustion (MJ/kg)

Smoke Yield (m2/kg)

Total Smoke (m2)

16.47 17.15 17.05 18.23 16.98 17.82 14.48 17.50 18.01 15.26 17.42 14.33 5.65 16.84 9.32 23.38

105 67 96 149 82 94 111 55 60 125 101 91 68 62 368 62

768 442 1217 1654 829 621 1316 936 578 1674 668 836 13 773 131 39

SRR - smoke release rate;

Peak Length SRR of Test (m2/s) (s) 5.27 2.93 7.38 11.0 4.14 3.64 6.95 6.80 4.16 10.7 4.09 5.92 0.08 2.48 1.48 0.18

1295 1245 1320 1285 1275 1245 1340 1250 1260 1245 1270 1245 1245 1845 1245 1845

HRR- heat release rate

Smoke and Toxic Gases Item

2:1 2:2 2:3 2:4 2:5 2:6 2:7 2:8 2:9 2:10 2:11 2:12 2:13 2:14 2:15 2:16

Peak extinction coefficient of smoke in upper part of room (m-1) 2.41 1.80 2.59 5.06 — 1.99 3.43 2.34 2.14 4.16 2.36 2.45 0.36 2.28 1.96 0.37

HCN peak (ppm)

HCL peak (ppm)

HBr peak (ppm)

33 — 61 599 36 — 68 — 30 202 — 111 — — 93 —

178 — 192 727 179 175 188 239 221 762 234 181 — — — —

— — — — — — — — — — — — — — — —

CO NOx SO2 Time of peak peak peak test (ppm) (ppm) (ppm) (s) 655 621 735 2322 589 587 601 972 1105 2119 757 962 174 846 874 199

— — — — — — — — — — — — — — — —

— — — 18 196 — — 80 — — — — 46 — 99 —

1295 1245 1320 1285 1275 1245 1340 1250 1260 1245 1270 1245 1245 1845 1245 1845

46

Fire Behavior of Upholstered Furniture and Mattresses

Table 2-5. CBUF Furniture Calorimeter Results on Commercial Furniture Heat and Smoke Release Item

Peak HRR (kW)

Total Heat Release (MJ)

1:1 1:2 1:3 1:4 1:5 1:6 1:7 1:8 1:9 1:10 1:11 1:12 1:13 1:14 1:15 1:16 1:17 1:18 1:19 1:20 1:21 1:22 1:23 1:24 1:25a 1:26a 1:27

2154 1346 2285 784 742 1158 596 1490 552 866 1259 652 829 486 946 778 853 39 1119 574 866 297 330 29 16 10 1796

704.4 520.4 658.4 368.4 463.3 412.8 314.2 497.6 143.6 449.0 374.6 171.9 156.4 150.3 261.5 245.2 303.7 13.4 224.4 104.4 157.5 162.0 34.2 17.1 — — 987

Heat of Combustion (MJ/kg)

13.4 15.0 14.7 14.5 15.0 16.5 15.5 15.4 12.6 15.9 15.1 15.8 22.2 21.9 26.0 24.8 28.5 19.2 18.6 14.8 21.6 13.0 24.4 19.0 — — 15.0

Peak Smoke Release Rate (m2/s)

Smoke Yield (m2/kg)

Total Length of Smoke Test (m2) (s)

33 14 28 4 12 8 3 17 4 15 6 7 10 6 25 19 13 1 22 4 13 61 2 <1 <1 <1 32

97.7 110.9 102.0 69.1 159.1 63.3 64.9 93.1 143.1 123.2 50.5 120.0 191.3 171.4 562.0 510.8 380.9 781.4 310.9 106.2 291.9 2744 106.8 151.2 — — 101.1

5120 3739 4572 1752 4926 1570 1315 2997 1666 3485 1244 1307 1347 1178 5658 5061 4063 546 3751 751 2131 34274 150 136 43 6 6584

1456 1700 1453 1560 1800 1472 1800 1488 1800 1800 1316 1240 1800 1800 1256 1212 1264 1800 1233 1300 1128 1800 936 1325 420 600 1800

a:Very limited burning in items 1:25 and 1:26 after the burner was removed. Almost no mass loss was recorded.

Fundamentals

47

Table 2-5. (Cont’d.) Toxic Gases b

Item

HCN Peak (gs-1)

HCI Peak (gs-1)

HBr Peak (gs-1)

CO Peakd (gs-1)

Totald CO (kg)

NO Peak (gs-1)

Length of Test (s)

1:1 1:2 1:3 1:4 1:5 1:6 1:7 1:8 1:9 1:10 1:11 1:12 1:13 1:14 1:15 1:16 1:17 1:18 1:19 1:20 1:21 1:22 1:23 1:24 1:25a 1:26a 1:27

— 0.31 — 0.14 0.18 0.02 0.02 0.02 — — — — 0.02 0.02 — 0.04 — 0.01 — — 0.12 0.08 — — — — —

— 0.28 — 0.30 0.26 0.10 0.07 0.23 — — — — 0.12 0.12 — 0.20 — 0.04 — — 0.04 0.70 — — — — —

— _c — _c _c _c _c _c — — — — _c _c — _c — _c — — _c 0.42 — — — — —

— 1.96 — 0.83 1.70 0.59 0.56 1.24 — — — — 0.46 0.33 — 1.13 — 0.10 — — 1.04 3.17 — — — — —

— 1.02 — 0.76 1.21 0.46 0.54 0.82 — — — — 0.20 0.20

0.82 0.33 0.60 0.24 0.21 0.32 0.17 0.51 0.15 0.28 0.33e 0.18 0.17 0.10 0.19 0.14 0.17 0.03 0.40 0.15 0.24 0.03 0.17 0.02 — — 0.57

1456 1700 1453 1560 1800 1472 1800 1488 1800 1800 1316 1240 1800 1800 1256 1212 1264 1800 1233 1300 1128 1800 936 1325 420 600 1800

0.38 — 0.12 — — 0.25 1.56 — — — — —

a:Very limited burning in items 1:25 and 1:26 after the burner was removed. Almost no mass loss was recorded. b:HCI production was not corrected for the HCI trapped in sampling line (≈ 30%). c:Measured HBr concentrations were lower than 10 ppm. d:CO production rate and total CO production are based on FTIR measurements. e:Real peak was higher. NOx analyzer out of range during peak burning period.

48

Fire Behavior of Upholstered Furniture and Mattresses

Table 2-6. Construction of CBUF Commercial Furniture Items Item 1:1

1:2

1:3 1:4 1:5

Design

Main Filling

Wrap

Cover

Use

Fully upholstered 3 seat sofa / loose seat and back cushions Fully upholstered 3 seat sofa / loose seat and back cushions As 1 but 2 seat sofa As 2 but single seat chair Fully upholstered chair/loose seat and back cushions

Polyester foam seat/ polyester interior back

Polyester fiber, seat cushion

Polyester ground cloth/polyacrylic pile

D

CMHR foam seat/ shredded foam interior cushion

None

FR treated cotton

D

as 1

as 1

as 1

D

as 2

as 2

as 2

D

CMHR foam seat/ FR polyester interior back

FR polyester fiber

D

HR foam

None

Polyacrylic pile fabric/FR back coated/cellulosic ground Leather

Polyether foam

100% FR cotton

D

as 1

Polyester fiber, back cushions as 1

as 1

D

CMHR foam

None

FR treated cotton

D

CMHR foam

FR Polyester fiber

D

HR foam

None

Polyacrylic pile fabric/FR back coated/cellulosic ground Leather

Polyether foam

Polyester fiber

Polyester

D

1:6

Fully upholstered chair/loose seat and back cushions 1:7 Fully upholstered chair/loose seat and back cushions 1:8 As 1 but single seat chair back 1:9 Fully upholstered chair, loose seat cushion, fixed back 1:10 Fully upholstered chair, loose seat cushion, fixed back 1:11

Fully upholstered chair, loose seat cushion, fixed back 1:12 Fully upholstered chair, loose seat cushion, fixed back

D

D

(Cont’d.)

Fundamentals

49

Table 2-6. (Cont’d.) Item

Design

Main Filling

Wrap

Cover

Use

1:13

Chair-metal frame, seat and back pads mounted on boards (reception/typist) as 13 as 13 as 14

CMHR foam

—

FR treated wool

C

CMHR foam polyether foam Polyether foam

— — —

C C C

HR foam

—

wool FR polyester vinyl coated cover FR polyester

C

to meet Cal. TB 133

wool tweed

C

1:14 1:15 1:16 1:17 1:18 1:19

1:20

1:21

1:22 1:23 1:24 1:25

1:26

1:27

executive swivel chair executive swivel chair Fully upholstered, fixed upholstery, high arm (reception) Fully upholstered, fixed upholstery, high arms solid foam mattress solid foam mattress spring interior mattress spring interior mattress solid foam mattress (prison) spring interior mattress/sprung edge divan set as 1 but sofa bed

HR foam

—

FR polyester

C

CMHR foam

FR polyester fiber, seat

wool

C

polyether foam

FR polyester fiber, quilted to cover —

cotton/ viscose

D/C

D/C

—

cotton/ viscose polyester

—

polyester

D

—

FR vinyl reinforced sheet 75% polyester, 25% viscose

HR

as 1

D

latex foam polyether foam CMHR foam impregnated foam

various fibrous natural layers

as 1

D = domestic, C = contract, HR = high risk

as 1

D

D

50

Fire Behavior of Upholstered Furniture and Mattresses

Table 2-7. Construction of CBUF Chairs Designed To Study Effect of Fabric/Padding Variations Item

Fabric

Filling

Interliner

2:1

FR cotton

HR urethane foam

—

2:2

FR cotton

polyether foam

—

2:3

polyester

HR urethane foam

—

2:4

polyacrylic pile FR backcoated cellulosic ground

HR urethane foam

—

2:5

wool

HR urethane foam

—

2:6

cotton

HR urethane foam

—

2:7

FR (inherent) polyester

HR urethane foam

—

2:8

leather

HR urethane foam

—

2:9

cotton

HR urethane foam

Kevlar™

2:10

polyacrylic pile - FR backcoated cellulosic ground

CMHR urethane foam

polyester wadding

2:11

FR cotton

CMHR urethane foam

—

2:12

FR cotton

CMHR urethane foam

polyester wadding

2:13

FR wool

full depth impregnated urethane foam

—

2:14

polyester

polyether foam

Unigard™

2:15

wool

HR urethane foam

Springs F187™

2:16

cotton

CMHR urethane foam

Unigard™

All chairs had beech wood frames, loose seat and back cushions and were fully upholstered to the floor.

In principle, the HRR of a material could be computed by multiplying the calculated mass loss rates in the pyrolysis and evaporation Eqs. 21 and 2-2 by its effective heat of combustion. In practice, this gives only a semi-quantitative estimate. The reason is that most multi-layered, composite materials show substantial variation of the effective heat of combustion throughout the burning process and the value is not simply a fixed constant. Andersson attempted such comparison for a number of mattresses and chairs.[132] In this case, there was good agreement between the curves. However, such good agreement cannot be depended upon in general.

Fundamentals 2.6.3

51

Effect of The Ignition Source On The HRR Curve in FullScale Tests

Several studies have shown that, for a propagating furniture fire, the size of the ignition source and its location on the furniture item affect the time at which the HRR curve ascends significantly above the time-axis, but not its shape after that point nor the peak value.[133]–[136] An example is shown in Fig. 2-4.[133] Similar effects were observed when a series of chairs were ignited at NIST with a gas burner located at the side arm and duplicate chairs were ignited at FRS with a T-head burner near the seat/back juncture.[134] Even though the HRR of the FRS burner was only about half of that used at NIST, the fire was much more rapidly developing at FRS during the early stage.

Figure 2-4. HRR versus time for identical chairs ignited at various points.

The constant peak HRR and the changing time to peak dependency on ignition source size and location is further confirmed in a study which found that for chairs constructed in a typical manner (the same cover fabric throughout but thin layers of foam on the side, cardboard in back, a wooden board in front, and common materials in the seat, back, and sides),[135] the peak HRR varied little whether ignition was in the seat, front, side or back but the times to peak varied by factors of 2 to 3.

52

Fire Behavior of Upholstered Furniture and Mattresses

It was found in the CBUF program that if the time was measured from the point at which the HRR of the chair reached 50 kW, the times to peak were similar regardless of the size and location of the ignition source.[136][137] The choice of 50 kW was based on that being a reasonable level at which the fire in the room would certainly be detected by the occupants even if their attention were directed elsewhere. The conclusion regarding the independence of the peak HRR on the ignition source should not be expected to hold for non-propagating upholstered items; however, the latter intrinsically represent a situation of lower fire hazard, thus, quantifying it may be unnecessary.

2.7.0

PROPAGATING AND NON-PROPAGATING FIRES

Furniture fires can be either propagating or non-propagating. Propagating fires are those in which flaming continues after ignition until most of the item has been consumed. Fires which only burn in the vicinity of the ignition source are called non-propagating fires. The fire may go out once the ignition source is removed. Similarly, fires which eventually consume all of the fabric but never involve the padding are also referred to as non-propagating. A few fires are difficult to classify since they burn very slowly, nearly die out but eventually increase in burning rate, reach a peak, and then proceed to burn until near completion. HRR studies on upholstered furniture up to 1985 focused almost solely on propagating fires. Partly, this was due to the composition of products in the marketplace: non-propagating items started becoming more common with the introduction of requirements by the State of California in the 1980s. The State of California first proposed TB 133 on a voluntary basis in the early 1980s, later making it mandatory for certain public occupancies.[30] Certain other jurisdictions have also followed suit. In its initial form, TB 133 required the measurement of temperature rise, smoke obscuration, and CO concentrations, but HRR was not included. A collaborative project between NIST and the BHFTI was formulated in 1988 to quantify and improve the TB 133 test method. This study, which entailed a series of experiments using TB 133, the proposed ASTM room, the furniture calorimeter, and the Cone Calorimeter, was completed in 1990.[35][36][138] As a result of this study, TB 133 was revised to measure the HRR and to use a gas burner instead of the original crumpled-paper ignition source. An equivalence was demonstrated between the existing

Fundamentals

53

temperature rise criterion and a HRR of 65 kW (with the HRR of the ignition source subtracted out). A slightly less conservative peak HRR of 80 kW was accepted as a suitable pass/fail criterion. It was also demonstrated that the room interaction was not significant below 600 kW and thus the test could be conducted in a furniture calorimeter. An analysis of the later CBUF data indicated that a room interaction effect can be found for fires with HRR as low as 500 kW, but that is still a long ways above the 80 kW limit specified by the revised TB 133.[139] In the NIST/BHF study, Cone Calorimeter measurements were made at an irradiance of 35 kW m-2. This was necessary since institutional furniture samples may not burn reliably at the lower 25 kW m-2 irradiance used in the earlier studies on residential furniture. The peak HRR values from the furniture calorimeter was compared with the 180 s average HRR values from the Cone Calorimeter in Fig. 2-5.[35] It is noted that the data is correlated with two straight lines: (1) the upper line which extends down to 100 kW m-2 corresponds to propagating fires and (2) the lower line which stops at 180 kW m-2 corresponds to non-propagating fires. Based on this small data set, the lower limit for propagating fires was seen as approximately 100 kW m-2 and the upper limit for non-propagating fires as 180 kW m-2 in the Cone Calorimeter. For intermediate values, delayed propagation can occur. Specimens where both a primed and an up-primed letter (for example, I and I´ ) are given in Fig. 2-5 exhibit such delayed propagation.[35] The initial peak (corresponding mostly to fabric burning) is denoted with the primed letter, while the delayed peak (corresponding mostly to padding burning) is shown as unprimed. Based on the larger data set on studied in that project, the CBUF recommendation was to use a lower limit for propagating fires as 65 kW m-2.[130] An independent analysis of the CBUF data suggests an alternate criterion. Using an irradiance of 50 kW m-2 in the Cone Calorimeter and a 300 s averaging period for the HRR* gives a lower limit value of 120 kW m-2 under such conditions.[139] This is demonstrated in Fig. 2-6 which compares the peak HRR in the ISO room with the 300 s average HRR in the Cone Calorimeter with exposure fluxes of 50 kW m-2. Again, this is a limited data set.

*

Note that for Cone Calorimeter results obtained for one irradiance or time period cannot be directly compared to those obtained at a different irradiance or time period.

54

Fire Behavior of Upholstered Furniture and Mattresses

Figure 2-5. Peak HRR in furniture calorimeter versus 180 s average HRR in Cone calorimeter at an exposure of 35 kW m-2.

Figure 2-6. Peak HRR in ISO room versus 300 s average HRR in Cone calorimeter at an exposure of 50 kW m-2.

Fundamentals

55

Predicting the value of HRR for fires in the non-propagating regime will generally not be necessary, since such furniture items show minimal hazard. Nonetheless, a predictive correlation can be seen in Fig.2-5 between the bench- (bs) and full-scale (fs) results: (Eq. 2-18)

′′ q fs = 0.75qbs

This relationship is not fully general, since in that study mass, frame type, and chair style variables were not independently studied, but were designed to be within narrow limits. However, total mass, frame type and style factor would not be expected to play a role in these limited fires. On the other hand, the scaling coefficient could be expected to increase with the size of the ignition source. From Eq. 2-18 it is seen that the TB 133 limit of 80 kW for the full-scale test item corresponds to a 180 s average HRR of 107 kW m-2 in the Cone Calorimeter. To avoid implying an unwarranted precision, this number can be rounded to 100 kW m-2. Even in non-propagating furniture fires, the rates of production of toxic gases and smoke increase with the mass loss rate. However, the relative distribution of toxic products, tends to be different from that for propagating fires, as discussed in Chs. 6 and 8. In general, chairs required to pass the 80 kW limit requirement can be built in two ways: (1) by limiting the amount of combustible upholstery material; or (2) by ensuring the HRR behavior of the upholstery system is low enough that a propagating fire cannot result. Chairs which pass by limiting only the amount of combustible mass are not typical upholstered chairs. These would normally be stacking, secretarial, etc., chairs where only a very small amount of padding is used on a rigid chair, often with a metal frame. The situation for furniture items with intermediate fire performance bears investigation. A research study was conducted at FRS using both the Cone and full-scale furniture calorimeters.[140][141] While the UK has furniture regulations and corresponding test methods,[44]–[47] the objective of the FRS studies has been to examine the feasibility of a heat releasebased alternative to this regulatory test. The specimens examined in this program were of an intermediate behavior: they typically do not qualify as non-propagating, but show either delayed propagation or the low end of propagating fires. This regime is especially difficult to predict, and is, of course, quite ignition source dependent.

56

Fire Behavior of Upholstered Furniture and Mattresses

The furniture calorimeter studies were initially conducted with a natural-convection driven exhaust system, but this has since been changed to a forced draft system similar to the ISO furniture calorimeter standard.[63] The studies at FRS used a T-head gas burner; the cover fabric was the standard FR polyester fabric specified in BS 5852[46] combined with various commercial standard and combustion-modified (CM) foams. Comparative Cone Calorimeter tests were conducted at a 35 kW m-2 irradiance. Peak values obtained in the Cone Calorimeter were compared to peak HRR values measured in the furniture calorimeter but the correlation was far from perfect.

2.8.0

INTER-ITEM SPREAD

Real fires rarely occur in rooms with only one combustible furniture item. More commonly, there are multiple items—some contiguous and some separate. There may also be combustible materials on walls, floors, and ceilings, but those are outside the scope of this monograph. Only the question of multiple furniture items are addressed here.[142] If a piece of furniture is not capable of producing a high enough HRR to induce flashover or even untenable conditions in the room, it may still be able to ignite neighboring furniture so that their combined HRR may be sufficient to do this. The spread of fire from one piece of furniture to another may be due to (1) normal flame spread if the items are in direct contact, (2) flame impingement if there is a small separation between them, or (3) radiant ignition if they are outside of the range of flame contact. A concept useful for analysis is the fuel package. Items such as theater seats or stacked chairs are presumed to burn as one discrete item. Thus, they would be tested in the room or the furniture calorimeter as a single item. The fabric and padding would also be tested as furniture composites in the bench-scale tests in the same way as they would be for single burning items. However, the correlation between bench-scale and full-scale HRR for such fuel packages has not been developed yet. Not surprisingly, single chairs which pass TB 133 can cause flashover conditions when several of them are included in a stack. Items which are not contiguous and are outside of the range of flame contact do not constitute a fuel package. Here, the governing factors are the ignitability of the second item and the incident radiant flux upon it. The irradiance imposed on the second item is governed by the HRR of the

Fundamentals

57

first, plus the spacing between the items. This radiation can be augmented to some extent by radiation from the hot upper layer. Due to radiation reinforcement from the first item, the newly ignited item can have a burning rate higher than if it were burning alone. Its radiation may become high enough to increase the burning rate of the first item. Fluid flow aspects also may be affected; eventually the two fires can merge. This problem has been studied for simple fuel arrays, in which case flames merge when the clear spacing is less than about 0.2 of the flame height.[143] Since flame heights tend to be about 1–5 times the item width for sizeable furniture items, some estimates of flame merging are possible. Empirical studies of the burning of two chairs, separated by 1 meter, with the first chair acting as a potential ignition source for the second have been conducted.[144] Before radiant augmentation or flame merging effects can take place, the second item must ignite. This is experimentally simple to determine, but a huge variety of tests would have to be run, (for example, the sort of program as conducted in reference)[144] but with the inclusion of modern HRR instrumentation. Heat fluxes from burning furniture items have been investigated in Refs. 35, 36, 131, and 145–146. Reference 142 illustrates a simplified approach, which measures the radiant flux from the first item and the ignitability of the second item separately. According to this procedure, the radiant fluxes generated by the first burning item are determined in full-scale, as a function of height and lateral distance. The ignitability is then measured only in a bench-scale test. Times to ignition versus incident flux are shown for some upholstered furniture composites in Fig. 2-7. The minimum fluxes required for ignition are determined from these plots and are listed on the graph. The actual times to ignition are of less importance than the critical fluxes. For upholstered furniture materials, these times are generally short compared to the duration of the peak fluxes from the first item. Representing the fluxes from the first item in a simple way is not trivial, however. Figs. 2-8 and 2-9 show the results for a wicker couch.[142] Note especially that the l/r2 representation of fluxes is not appropriate except for larger distances r. For upholstered furniture, peak fluxes are seen to occur typically at a height of about 0.5 m. A fair number of measurements have been collected for a height of 0.5 m and a lateral distance of 0.5 m.[129][147] Figure 2-10 shows a linear dependence of the radiant flux on the burning rate of the item at that location. For separation distances other than 0.5 m, additional relationships are needed. Typical plots of ignition distances versus peak burning rates are given in Fig. 2-11.[142] These data suggest that about 1.5 m is a limit beyond

58

Fire Behavior of Upholstered Furniture and Mattresses

which second item involvement will be unlikely prior to flashover. For vertical targets farther than 1 or 1.5 m, a power law relationship is reasonable. Mizuno and Kawagoe[117] have found that the radiant flux can be expressed by (Eq. 2-19)

′′ = 320 q rad

m r1.8

(kW m −2 ) for r > 1

where m• is the mass loss rate (kg s-1) and r is the radial distance (m).

Figure 2-7. Time to ignition versus irradiance curves for a range of upholstery composites.

Fundamentals

59

Figure 2-8. Peak irradiance versus distance from a wicker couch for different heights.

Figure 2-9. Irradiance versus time at a height of 0.41 m for different distances from a wicker couch.

60

Fire Behavior of Upholstered Furniture and Mattresses

Figure 2-10. Irradiance versus mass loss rate at a distance of 0.5 m from the chair and at a height of 0.5 m.

Figure 2-11. Ignition range versus peak mass loss rate of initial item for second items of varying ignitability.

Fundamentals

61

Ahonen, et al.,[146] found a similar formula for horizontal targets:

(Eq. 2-20)

′′ = q rad

460 m r2

Andersson also defined a function which expressed radiant heat flux as a function of the mass burning rate and the distance from the flame.[132] The peak radiant flux at a distance of 0.76 m was measured for a series of 10 chair burns as a function of their peak HRR.[35] The results, which are shown in Fig. 2-12, could be represented by (Eq. 2-21)

′′ = 0.011 q fs q rad

where q•fs is the total HRR in kW. This is consistent with the formula of Mizuno and Kawagoe.[117]

Figure 2-12. Peak heat flux versus peak HRR at 0.76 m from a series of chairs of identical construction but with different upholstery materials.

There is some uncertainty associated with the above formulas which are based on the peak HRR or the peak mass loss rates. The radiant fluxes are actually due to the fraction of the HRR that goes into thermal

62

Fire Behavior of Upholstered Furniture and Mattresses

radiation. This fraction can, in principle, vary with the smoke-producing tendency of the test item. In practice, the effect has not been studied to such fine detail as to bring out correlation components based on specimen smokiness.

2.9.0

INTERACTION WITH ENCLOSURE

There are two major ways in which the presence of the room can affect the burning rate of the furniture item. First, there is a radiation feedback from the hot walls, ceiling, and upper gas layer. Second, since the inflow of fresh air is restricted to open windows or doorways, underventilated conditions can develop when the HRR becomes high enough. There are also other effects. The inflow of air to the burning item will not be axially symmetric as in the case of open burning. Airflow direction and magnitude can affect the flame-spread rates. The adjacent wall surface can be heated up in a furniture fire and in turn re-radiate to the burning item, causing some increase in its burning rate. If the item is flush against, or nearly flush against, a wall, the flame will attach to the wall and become taller.[148] This effect can sometimes decrease the radiation to the item since the flame zone gets extended farther away from the burning surface. Also, the heat losses to the wall will reduce the flame temperature and thus its radiation to the furniture item. Parker et al. found no significant interaction between burning chairs and TB 133 or ASTM rooms below a peak HRR of about 600 kW.[35] For a peak HRR of 1200 kW in the furniture calorimeter the HRR in the room was about 50% higher. Twenty-seven items of commercially available furniture including fully upholstered chairs, sofas, office chairs, and mattresses were tested in the CBUF project in both the ISO room and in the furniture calorimeter.[131][149] A further analysis of this series of tests showed that (excluding the mattresses which were exceptionally sensitive to heat feedback from the room) the furniture items which had peak HRR less than 500 kW in the furniture calorimeter were not affected significantly by the room enclosure.[139] The percentage increase in the peak HRR measured in the room over that measured in the furniture calorimeter went up linearly above 500 kW. It was 40% for 1300 kW fires in the furniture calorimeter. Above that, the room enhancement was mitigated by underventilation. Only one study[150] has been published on the interactions between burning items of upholstered furniture and combustible room walls. It was

Fundamentals

63

done in conjunction with a reconstruction of a major fire. The data there are specific to the one fire in question and do not provide general guidance. Experiments were conducted on the effect of the position of a furniture item in the room.[117][151]–[153] The latter authors concluded that the mass burning rate of a chair is the same whether the chair is located in the center of the room or near a wall. However, more studies are needed since there are conflicting data.

2.10.0 FLASHOVER As a room fire grows, flaming hot gases and smoke form a layer near the ceiling. The interface between this layer and the cooler layer beneath it travels downward as the HRR increases. Eventually, this layer can reach down nearly to floor level. Flashover occurs when the flaming gas layer descends to the lower part of the room. In the 1960s flashover was identified as the time at which the radiation from the hot upper layer became sufficiently large to ignite all combustibles in the lower part of the room. When the first item is ignited by the radiation from the hot upper layer, the increase in the total HRR suddenly increases the temperature of the layer and thus its radiation, causing more items to ignite until everything in the room is involved within a very short period of time, creating a strong feedback effect. A quantitative definition of flashover has been proposed as the time at which the radiant heat flux to the center of the floor reaches 20 kW m-2. This is sufficient to ignite the common light combustible materials in a very short time. Thus, in the proposed ASTM room fire test, the occurrence of flashover is measured with a heat flux gauge. Since this flux requires an upper air temperature of about 600°C, this temperature has also been used as an indicator. The large increase in the HRR at the time of flashover in a furnished room often results, a short time later, in a transition from a fuel-limited fire to a ventilation-limited one. This leads to a large increase in the rate of CO production and to flaming combustion of unburned volatiles outside of the room. Therefore, the time to flashover is also sometimes related to the time that flames come out of the doorway. This is the definition used in the ISO room corner test.[61] In many practical cases, flames out the doorway occur near the time at which the flux on the floor reaches 20 kW m-2. The above concepts for defining flashover have been developed from extensive laboratory studies with fairly steadily burning combustibles.

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Fire Behavior of Upholstered Furniture and Mattresses

Furniture fires often show a very spiky peak HRR curve. Quantification of the flashover event for fires where the HRR may increase by hundreds of kilowatts in an interval of a few seconds and the subsequent decrease are quite difficult, and large uncertainties are to be expected. Large rates of production of smoke and toxic gases occur due to oxygen starvation when flashover is reached. The toxic gases and smoke escape from the room and travel through any available opening to other parts of the building where untenable conditions can be created. The smoke will reduce the visibility and thus limit the chance for the occupants to escape. Flashover is rarely survivable in the room of fire origin, and only when a heavy protective assembly and breathing apparatus is worn. The use of furniture conforming to TB 133 minimizes the probability of flashover. Finally, flashover must be differentiated from “backdraft;” when a window or door is opened or breaks open due to the heat in a room fire, the sudden availability of air in the underventilated room may cause a violent backdraft, an extreme hazard to any person in the vicinity. The possibility of a backdraft requires significant care by anyone approaching an underventilated room fire. The full-scale HRR required to produce flashover can be predicted. For this discussion, a room fire is understood to take place in a single compartment, with no forced ventilation and with a single window or doorway providing natural ventilation. The maximum airflow (kg/s) through the opening of height hv (m) and area Av (m) is:[154] (Eq. 2-22)

m a = 0.5 Av hv

At the stoichiometric limit the HRR that can be developed inside the room, q•st (kW), is given by:[155] (Eq. 2-23)

q st = 13100 YO 2 m a

where 13100 kJ kg-1 is the heat released per kg of oxygen consumed, and Y0 is the oxygen mass fraction of the incoming air which is 0.23. Thus, 2

(Eq. 2-24)

q st = 1500 Av hv

The relationship between the rate that the fuel mass is pyrolyzed and the available HRR given by

Fundamentals (Eq. 2-25)

65

q = ∆hc m

where ∆hc is the heat of combustion. If fuel is being released at m• > q•st /∆ hc , the excess pyrolysate cannot be burned within the room, but is available for burning outside. Flashover conditions can be predicted on the basis of the HRR in the room. Very roughly, about 50% of q•st must be supplied by the burning combustibles to cause flashover.[155] In a more precise estimate, wall loss details are taken into account.[156] A review and evaluation of these procedures has been published.[157] Flashover can be expected if the peak HRR exceeds a critical value which depends on the ventilation and Aw , which is the total area of the walls, ceiling, and floor. The area of the doorways and windows are not subtracted out for this calculation. Flashover is expected to occur if: (Eq. 2-26)

q ≥ 378 Av hv + 7.8 Aw

This equation assumes that the thermophysical properties of the room lining materials are similar to those of normal gypsum wallboard. It would not be applicable to, say, bare steel walls or walls covered with a ceramic fiber blanket. The ISO room is 2.4 m high, 2.4 m wide and 3.6 m deep.[63] It has a 2.0-m high open doorway which is 0.8 m wide. Eq. 2-26 predicts a required HRR of approximately 1.0 MW for flashover of the ISO room if it is lined with gypsum wallboard. Full-scale experiments indicate that flashover occurs in the ISO room at about 1.5 MW; thus the formula is conservative, but not highly precise. The proposed ASTM room has almost the same dimensions. Tables 2-3 and 2-5 give the peak HRR values in the ISO room and the furniture calorimeter for the CBUF series of 27 furniture items including mattresses.[131][149] It must be pointed out that Eq. 2-26 assumes the peak HRR is maintained for a relatively long time; this is not necessarily the case with upholstered items. Consequently, considerably higher peak HRR values than indicated in Eq. 2-26 may be required before flashover is caused. In other words, Eq. 2-26 may be quite conservative when applied to spiky furniture fires. This was observed in the NIST/BHF cooperative project.[35][36] Based on the reading of 20 kW m-2 on the floor, flashover did not occur below 1.7 MW, while Eq. 2-26 would indicate approximately 1.1 MW.

66

Fire Behavior of Upholstered Furniture and Mattresses

A better approach can be to put the complete HRR history of the item, as measured in the furniture calorimeter, into a room fire model such as CFAST,[158][159] and use it to predict the temperature rise in the upper layer and the radiant flux on the floor. However, even this is an approximation because it neglects radiation feedback onto the chair from the room which would actually increase the HRR in the room. Thus, the computer fire modeling method somewhat over-predicts the HRR required for flashover, while Eq. 2-26 will under-predict it.

2.11.0 SMOKE AND TOXIC GASES 2.11.1 General The following is a general discussion of the effects of smoke and toxicity. They are covered separately in more detail in the next two subsections. Test methods are discussed in Ch. 3, and test results in Ch. 6. The inhalation of toxic gases is the major cause of human incapacitation and fatalities due to fire. Smoke makes it difficult to escape due to the loss of visibility and, thus, prolongs the exposure to these gases. When the HRR is high, the elevated air temperature and the exposure to thermal radiation are contributing factors to the hazard in the room of fire origin. However, during smoldering or low intensity flaming fires these thermal effects are generally minimal. They are also small at locations remote from the fire; the smoke and toxic gases can travel large distances to other parts of the building but heat is lost along the way.[160][161] Individual tenability criteria have been established for CO and CO2 concentrations, O2 depletion, heat flux, and smoke obscuration and have been applied to the fire safety of mattresses, as discussed in Refs. 162, and 163. Because of their effect on evacuation times smoke and toxic gas generation has been a major area of investigation for aircraft seating applications. Earlier efforts to develop a “combined hazard index” are briefly discussed in Ch. 3. Aircraft cabin performance in fires has been assessed in terms of the available escape time determined during full-scale tests.[164] The escape time needs to be based on the predicted time for incapacitation which takes all of the tenability criteria into account in a rational way. This requires an aircraft cabin fire model, which can account for the fire spread from seat to seat, to predict the concentration of smoke and toxic gases as a function of time.

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67

Using a room fire model, the spatially averaged concentrations of smoke and toxic gases can be predicted in the upper layer for a room with a single burning item and no other combustible materials present. This requires input data on the full-scale mass loss rate and HRR, along with the room geometry, yields of smoke and the various toxic gases, and a pertinent set of tenability criteria.[160] Modeling and hazard analysis are discussed in Chs. 7 and 8 respectively. The full-scale mass and HRR can be measured in the furniture calorimeter if they are small enough to avoid large interaction effects with the room. Provided that the room fire is not ventilation-limited, the smoke and toxic gas concentrations can be calculated using yield values (kg per kg of mass loss of the burning material) as measured in the Cone or furniture calorimeters.[163][165][166] However, poor ventilation affects the production rates of smoke and toxic gases. For the purpose of assessing smoke and toxic gas hazards of upholstered furniture using room fire models, it is necessary to establish predictive relationships for yields of toxic gases (especially CO) and visible smoke. The progress being made for in these areas is discussed in subsequent sections. The connection between smoke and toxic gas effects and those of other fire characteristics, such as HRR, is discussed in Ch. 8. The general point needs to be made here that by limiting the HRR, one can also limit the rate of production of smoke and toxic gases in flaming fires. 2.11.2 Smoke Smoke is defined in ASTM E 176[167] as the airborne solid and liquid particulates and gases evolved when a material undergoes pyrolysis or combustion. This is a broad definition for engineering purposes. Normally, in engineering studies, when we discuss quantification of smoke, we do not intend to include CO, CO2, or other gaseous product species. Instead, the discussion is normally limited to solids and condensible aerosols. One way to determine the amount of smoke is to simply collect it on a filter which allows the gases to pass through. The mass of the trapped particulates is then measured. Another way to measure the quantity of smoke is by its light attenuation. In this case, the quantity is expressed as the total capture cross section (m2), or the specific extinction area, σm (m2 per kg of specimen mass loss). The capture cross section of a single smoke particles is equal to the area of an opaque plate which when placed normal to the direction of the light beam would produce the same amount of attenuation. Since the carrier is usually air which does not absorb

68

Fire Behavior of Upholstered Furniture and Mattresses

significantly at the wavelengths of visible light, it is only the extinction by the particulates that is being measured. More detailed presentations of the production and properties of smoke have been published.[168][169] The primary measured smoke property is theextinction coefficient, k. The intensity of a collimated light beam of length L in a smoke filled medium falls off with distance from the light source in accordance with Bouguer’s law, which can be stated as

(Eq. 2-27)

I = e −kL Io

where I is the radiant flux measured at the end of the light beam, Io is the intensity at the light source and k is the extinction coefficient. Hence, the extinction coefficient can be measured using the formula,

(Eq. 2-28)

k=

1  Io  ln  L  I 

and the units of k are (m-1). The extinction coefficient is comprised of two additive components, absorption and scattering, although they are only rarely measured individually. The smoke produced under non-flaming conditions (for example pyrolysis and smoldering) is generally lightcolored and attenuates largely by scattering. The smoke produced during flaming combustion is composed mostly of black carbon soot particles that have survived the flame and attenuate the light primarily by absorption. Since k is proportional to the density ρs of the collection of smoke particles in the beam, a particulate specific extinction area σp can be defined for a particular type of smoke:

(Eq. 2-29)

σp =

k ρs

This also has the units of (m2 kg-1); however, it is a property of the soot and is independent of the soot liberation rate of the specimen. In an early study, Seader and Einhorn[170] found values of σp = 7600 m2 kg-1 for smoke produced during flaming combustion of assorted wood and plastic specimens, and σp = 4400 m2 kg-1 for smoke produced during non-flaming

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69

pyrolysis. A more recent survey of the literature on this topic leads to the recommendation[169] for using a value of σp = 9000 to 10,000 m2 kg-1 for smoke generated from flaming fires. While the particulate extinction area of the smoke is nearly constant, the mass of smoke produced per unit of specimen mass loss varies between materials. The ratio of the mass of smoke produced to the mass lost by the material is called its soot particulate mass fraction or simply its soot yield and is given by

(Eq. 2-30)

Γi =

m s ρ s = m i ρ i

where m•s is the smoke production rate, m•i is the mass loss rate of material i and ρi is the density of all the particulate, volatile and gaseous decomposition products in the beam that are contributed by material i. It is useful to define a specific extinction area for material i (i.e., per mass of fuel liberated) as (Eq. 2-31)

σi =

k ρi

This is the normal “specific extinction area” that is reported in Cone Calorimeter and other fire test results. It refers to the area of smoke produced, per mass of specimen lost. We can relate it to the particulate specific extinction area by substituting Eqs. 2-29 and 2-30 into Eq. 2-31: (Eq. 2-32)

σ i = Γiσ p

When a direct measurement is desired, the soot yield Γi can be determined by collecting the soot during a Cone Calorimeter test and dividing the total mass of the soot by the total mass loss of the specimen. • If ρs, which is equal to m•s /V, and k, which is given by Eq. 2-28, are substituted into Eq. 2-31, then

(Eq. 2-33)

σi =

V I  ln  o  m i L  I 

70

Fire Behavior of Upholstered Furniture and Mattresses •

where V is the actual volume flow (m3 s-1) in the duct. Note that it must be computed at the temperature where the light beam is situated, not at room temperature, nor at some other duct measuring station, remote from the light beam. The smoke attenuation in the exhaust duct of the Cone Calorimeter is measured by a laser photometer developed by Babrauskas and Mulholland.[169] Room fire tests and furniture calorimeters have earlier used photometers of varying designs. Current designs of those, however, are normally a scaled-up version of the Cone Calorimeter photometer. The photometer continuously measures I across a light path distance L. The volume flow in the duct depends on the local temperature which is measured with a thermocouple located near the photometer. The mass loss rate is routinely measured with load cells in the Cone and furniture calorimeters. Mass loss rate measurements can also be made in room fire tests of furniture. Eq. 2-33 is then normally used to report an instantaneous value of smoke extinction area. Note that, as with the effective heat of combustion, caution needs to be exercised in deriving a test-average value for the specific extinction area. It is not equal to the average of a column of instantaneous values reported at each scan interval. Instead, it must be computed as: (total m2 smoke produced)/(total specimen mass lost) for the test. For determining the specific extinction area in a closed-box test, such as the NBS smoke density chamber, the equation to be used is:[171]

(Eq. 2-34)

σi =

I V ln o mi L  I f

   

where V is the volume of the chamber, mi is the specimen mass loss during the test, L is the length of the light beam, If is the intensity at the end of the test period and Io is the intensity at the beginning of the test. The quantity σi is an important fire property of a material. It is often used in room fire models to calculate the rate of smoke production which is given by (Eq. 2-35)

Si = σ i m i

(m 2s −1 )

in a room and by (Eq. 2-36)

Si′′ = σ i m i′′

(m 2s −1 )

in a bench-scale test. This assumes that only a single material is involved.

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71

When the burning consists of more than one material the contributions of each are additive. Thus, the total rate of smoke production is given by (Eq. 2-37)

S = m

∑yσ i

[m s ] 2 -1

i

i

where m• is the total mass loss rate, and yi is the mass fraction for the ith material. The total production of smoke up to time t is given by 1

(Eq. 2-38)

S = S dt

∫

(m 2 )

0

If this is uniformly distributed throughout a closed room of volume V, the transmission of light over a path of length L is given by

(Eq. 2-39)

I  − SL  = exp  Io  V 

Bench-scale measurements of smoke have earlier been made in the NBS smoke chamber[171] and, more recently, are done in the Cone Calorimeter.[120] Occasionally, studies in the ISO (Dual Chamber) Smoke Box[172] and other instruments[173]–[175] are reported. The Dual Chamber Smoke Box, like the NBS smoke chamber, is a closed-box test. For such test apparatuses, the specific extinction area σf (m2 kg-1 pyrolyzed) is determined from Eq. 2-34. Many authors describing the use of the NBS smoke chamber or the ISO Smoke Box[174]–[177] often emphasized testing specimens under both “smoldering” (i.e., pyrolyzing without the presence of an ignition source) and flaming conditions. Today, not much scientific work is being done with a “smoldering” mode of smoke testing. There are two main reasons for this: (1) No usable model has ever been published for predicting full-scale fire smoldering on the basis of bench-scale data. Thus, such test data, if collected, are lacking an application. (2) Smolder-prone products are usually regulated on a go/no-go basis, rather than quantitatively. Thus, all standards for smolderability of furniture items (see Ch. 3) require that the item be shown to be smolder-resistant, not just to smolder at a slow rate. Consequently, the need does not exist for quantifying the smoldering process, including the generation rate of smoke.

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Fire Behavior of Upholstered Furniture and Mattresses

Optical measurement of smoke is done mainly to be able to address the hazards associated with limited visibility on the escape path. Estimates of the visibility distance Lv (m), based on observations of exit signs, were given by Jin as (Eq. 2-40)

Lv =

8 k

for light-emitting signs and by (Eq. 2-41)

Lv =

3 k

for reflecting signs.[178] Note that the extinction coefficient used here is not simply the raw value measurement obtained in some standard test. Instead, it is to be computed from the smoke properties and from the properties of the actual room in question. From the definitions of σi and ρi it is seen that (Eq. 2-42)

k=

σfm V

where m is the total specimen mass lost into the room, V is the volume of the room in question and σf is the weighted average value of σi for all of the contributing materials. It is given by (Eq. 2-43)

σf =

∑yσ i

i

i

The effect of smoke obscuration on lethality is not direct; nonetheless it is real in that escape can be hindered or precluded where visibility is diminished. (The ability to see is affected both by smoke obscuration and by lachrymators, such as HCl). The conversion of specimen mass into soot mass, just as for toxic gas species, is dependent on ventilation and other effects. 2.11.3 Toxic Gases According to general reviews of toxicity data for hazard evaluation, about 80% of fire deaths result from inhalation, and nearly two thirds of deaths occur in rooms other than the room of fire origin.[11][12][161] Therefore, toxicity is a very important topic of fire science but one that must

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73

be kept in proper perspective. Especially to be avoided is an oversimplified reaction that “If toxicity is the major reason for fire deaths, then regulations must be passed to control product toxicity.” The reasons why this kind of conclusion is misleading are discussed below. The quantity of toxic gases produced in a fire depends very strongly on the processes of ignition, smoldering, flame spread, and HRR already discussed in this chapter as well as on the chemical composition of the burning materials. It is a complex subject and only some highlights can be summarized here. A handbook review has been presented by Purser.[179] It covers primarily U.K. research; U.S. work is reviewed in more detail below. Toxic Fire Hazard Analysis Principles. Various studies developed a systematic methodology for analyzing the toxic effects of fire. Here, a brief summary can be made to create the context for upholstered furniture hazard analysis. The toxic hazards from a fire to an exposed person are clearly related to the concentrations of the various gas species and to the person’s time of exposure. The length of time a person will be exposed to combustion products in a fire is, of course, in general unknown. Thus, typically toxicologists have taken 30 min as a nominal exposure time. To evaluate the total toxic gas effect, it is convenient to define the fractional exposure dose, FED. Time effects can be taken into account in its definition, but here, the simplest case will be considered, namely of fixed exposure time. Then,

(Eq. 2-44)

FED = ∑ i

Ci LC i

where Ci are the concentrations (g m-3) for the i gas species present, and LCi represent the toxic potency LC50 for each of the species. The toxic potency for gas i, in turn, is defined as the concentration at which there is a 50% probability for lethality, for a specified time of exposure. As mentioned, in fire toxicology this time is normally taken as 30 minutes. It is readily seen that the FED is a dimensionless number. Furthermore, a value of FED = 1 denotes a just-lethal condition; values < 1, denote decreasing danger of fire lethality, while values > 1 denote conditions even more toxic than the lethal one. From the above definition, one can easily note that the toxic hazard from fire can be increased by either increasing the gas concentration or decreasing the LC50 (note the inverse scale: higher numbers of LC50 denote lower hazard).

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Fire Behavior of Upholstered Furniture and Mattresses

The LC50 for a particular product might, to a first approximation, be taken to be a property of the material, although we shall see below that this is not necessarily true. The gas concentrations Ci however, are clearly not just a material property. Instead, they reflect both the propensity of the product to burn (lose mass, produce combustion products) and the geometry and flow conditions of the building in question. For conceptual simplicity, we can assume that the furniture item mass loss rate does not vary over time and is a constant m•. Then, if the room is closed, the concentration is:

(Eq. 2-45)

Ci =

f i m⋅ ∆t V

where fi is the yield of species i, that is, (g of species i produced) / (g specimen lost). The duration of the fire is ∆t, and the volume of the room is V. If the room is ventilated, then

(Eq. 2-46)

Ci =

f i m⋅ ⋅ V

•

where V is the air ventilation rate (m3 s-1). Since the building volumes and ventilation rates are not associated with any particular product, in terms of assessing the product itself, it is clear that its hazard will vary as:

(Eq. 2-47)

hazard ∝

m⋅ LC50

where the LC50 here is for the entire gas stream evolving from the specimen and is not subdivided into the component gases. Mass loss rates of products are only occasionally tabulated. There are two reasons for this: (1) to determine mass loss rate requires that numerical differentiation be made of load cell data. This often requires tedious smoothing in order to decrease the innate noisiness of such a signal. (2) sometimes there is a relationship between HRR and mass loss rate. For some upholstered items, in particular, the effective heats of combustion tend to vary only within a narrow range. Thus, HRR, which is necessary for the characterization of many other

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75

aspects of the fire, is sometimes taken as a surrogate for mass loss rate in hazard estimations. Thus, under some conditions it is possible to approximately take:

(Eq. 2-48)

hazard ∝

HRR LC50

The above relation shows that two of the primary factors in establishing the toxic fire hazard of an upholstered item are the HRR and the LC50. Given this relation, the essential question that a manufacturer of upholstered furniture might ask is: “What are my options—can I increase life safety more readily by decreasing the HRR of the product or by reducing its toxic effects (raising the LC50 value)?” A study was made of NIST data a few years ago to answer it. The findings[123][124] were striking. In the NIST database, the worst performing item of upholstered furniture showed a full-scale peak HRR value of 3120 kW. The best-performing item measured 25 to 31 kW, which we can round to 30 kW. Thus, for HRR the range of product performance for actual commercial products was seen to be slightly over 100:1. The NIST database of bench-scale test results for LC50, contained only a limited assortment of upholstered items, so the total database of all types of products, measured with the NIST radiant toxicity test (NIST/SWRI)[180] was examined. The range of LC50 values was from 13 to 56 g m-3. This is a range of 4:1. The conclusions were clear: Upholstered item toxic fire hazard can be reduced drastically by reducing its HRR, but the LC50 values vary only within a narrow range and offer much less room for improvement. The above discussion should also help to refute the common fallacy that since fire deaths are most typically attributed to inhalation of toxic gases, regulators should start controlling the “toxicity” (i.e., the toxic potency) of products. The numbers above indicate that the hazard can be reduced more by reducing the amount of gases being liberated than by striving to make them less noxious. A recent study[181] approached the same problem from a different point of view. A full-scale room was set up with several ventilation conditions. Upholstered chairs were burned and the effects were monitored with mice as the test animals. For a variety of chairs and mattresses tested, the gas concentrations necessary to cause incapacitation were between 17

76

Fire Behavior of Upholstered Furniture and Mattresses

and 27 g m-3. Similarly, lethality (LC50) was observed at between 21 and 37 g m-3. These are very narrow ranges and again confirm that differences between the hazard of furniture items are mainly due to the burning rate, not to LC50 variations. Testing For Toxic Potency. The above discussion should help to clarify that the primary toxic fire hazard associated with upholstered items (as with most other combustibles) is the HRR, not the per-gram toxicity (LC50). Thus, in principle, there should be little need to do further measurements of LC50 on these types of combustibles. For the sake of completeness, however, some of the testing and analysis principles will be reviewed below. The individual tests are described in Ch. 3. In the bio-assay approach to fire toxicity, a small amount of the test material is burned in a chamber in which laboratory animals are exposed. The toxic potency is expressed by the variableLC50. The LC50 is determined by analyzing the percentage of dead animals at various concentrations and finding the concentration at which exactly 50% of the animals would have died. The test time is normally fixed at 30 min. Some animals are critically injured during the exposure, but actually die some time subsequently from the effects. Thus, it is considered good laboratory practice to include any lethalities which occur during a 14-day post-exposure period. TheLC50 will also depend somewhat on the animal type selected, not only the species but also the strain and the weight of the animal. Primates are generally the closest in their response to humans, but these can only rarely be used for experiments. Most commonly, rats or mice are used. Mice are less desirable than rats in fire gas toxicity testing for two reasons: (1) it is very difficult to take blood gas samples from mice; (2) the response of the mouse to irritant gases such as HCl is quite dissimilar to the human’s (or the rat’s). Bio-assay testing has been widely done in the US and is even incorporated into regulatory fire tests in Japan. In Europe, however, current sentiments tend to preclude use of bio-assay techniques for any routine or regulatory purposes. Current work in the US in this area is also nearly non-existent, since NIST concluded this research area and finalized a proposed test method.[180][182][183] The major features of this test method have been adopted in the standard NFPA 269.[184] Other, earlier bio-assay test methods have been reviewed.[185] In the chemical analysis approach, the material is burned in a bench-scale test such as the Cone Calorimeter or in a full-scale fire test. The combustion gases normally flow through an exhaust hood (although closed-box experiments are also possible) and chemical measurements are done in the duct. For full-scale testing, usually the objective is to create a

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77

plausible fire scenario. For bench-scale testing, the exposure conditions (heat flux, ventilation) can often be widely varied and these can be selected to suit the study being done. Using the chemical analysis approach, a finite number of gases are measured in the combustion gas stream. The gases chosen must include ones which are either copious or especially toxic, or both. The yields of CO, CO2, and the depletion of O2 are routinely measured in most bench-scale and full-scale test methods. In the mid-1980s the use of FTIR (Fourier Transform InfraRed) spectrometry was first proposed[186] for quantifying species such as HCN, HCl, HBr, HF and SO2 for which convenient stand-alone analyzers are not available. This technique has now become quite popular in European laboratories for studying fire toxicity since use of animal-based testing there tends to be more controlled and restricted than in the US. Its use is still relatively uncommon in the US. The chemical analysis approach becomes practicable with the use of FTIR instrumentation, since most of the gases of interest can be quantified from the infrared spectrum, and this can be done automatically, without the need of batch sampling and analysis. Bench-scale testing for LC50 is only useful at all if it reflects the full-scale LC50. NIST studies on this subject[185][187][188] concluded that the predictivity is within a factor of three. Earlier toxicity studies have shown extreme variabilities (by an order of magnitude), so predictivity within a factor of three was considered a major improvement. This positive conclusion is tempered by the fact that the total range of product LC50 variations was only 4:1, as discussed above. Some newer research (on building products) also points to significant inability of bench-scale LC50 values to predict even trends of full-scale variations.[189] Thus, at the moment, one can say that bench-scale LC50 are being used with the hopes of predicting the full-scale situation, but this hope may be questionable or dubious. Presently, the LC50 is generally assumed to be predictive of the full-scale situation, but, in view of the findings of Ref. 189, this appears to be a suspect presumption. When chemical analysis testing is done, it is also possible to derive the yields of the various combustion gases. To use this data in computing the toxicity of full-scale fire, it is necessary to consider what happens to the yield as the scale and other problem conditions are changed. In general, very little changes, provided the full-scale burning is not ventilationlimited. The rates of production of the various toxic gases in a full-scale furniture fire, then, is found by multiplying their yields, determined from the bench-scale test, by the mass loss rate of the furniture item. When these production rate histories are combined with the HRR and the mass loss rate

78

Fire Behavior of Upholstered Furniture and Mattresses

histories in a room fire model, the concentrations of the toxic gases in the upper layer can be calculated as a function of time. Although there will also be some relatively small concentrations of these gases in the lower layer due to mixing, the zone modeling presently used for room fires does not calculate it. The Special Role Of CO. When fires do become oxygen-limited, the most noticeable effect is a large rise in the yield of CO which increases with the oxygen depletion.[190] Computations become tractable since it is empirically observed that the yield of CO under oxygen-limited conditions is nearly totally controlled by the ventilation conditions and is almost independent of the chemical nature of the material that is burning. Pitts has addressed this problem in order to provide predictions both for typical cases and for some anomalous ones.[191]–[193] For the oxygen reaching the fuel rich upper layer by entrainment into the fire plume, the rate of CO production can be related to the global equivalence ratio. This is the ratio of the fuel concentration to the fuel concentration necessary to consume all of the oxygen present. An instrument was recently invented to measure this ratio experimentally in room fires.[194] It has been used to examine one of the anomalous cases, where a large fraction of the total combustibles comprises wood (or other materials with oxygen atoms in the fuel structure) on the ceiling or in the upper gas layer. Such conditions lead to unusual CO production tendencies,[195] but this situation is not encountered with regards to furniture items. Numeric Evaluation Of Gas Mixtures. There are two main categories of toxic gases and vapors: those that are narcotic and those that are irritant. Narcotic (asphyxiant) gases cause incapacitation mainly by effects on the central nervous system, and to some extent the cardiovascular system.[196] Most narcotic gases produce their effects by causing brain tissue hypoxia. The two major narcotic gases occurring in fires are CO and HCN. CO is the most important and is always present in fires. HCN may also be present when nitrogen-containing materials such as acrylics, nylon, polyurethane foams, or wool are burned, and it has been detected at high concentrations in the blood of fire victims.[197] In addition, low concentrations of oxygen (less than 15%)[198] and very high concentrations of CO2, (greater than 5%) can have narcotic effects.[199] Irritant fire gases produce incapacitation during and after exposure in two distinct ways. During exposure the most important form of incapacitation is sensory irritation and detrimental effects to the eyes and upper respiratory tract, and often also the lungs. Although exposure may be painful and thus incapacitating, it is unlikely to be immediately lethal

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during exposure unless exceptionally large concentrations of irritants are present. However, the second effect of the irritants penetrating into the lungs is acute pulmonary irritant response, consisting of inflammation and edema, which can cause respiratory difficulties and may lead to death 6 to 24 hours after exposure. Also, because irritants may cause choking which, in turn, causes deeper breathing, they often increase the uptake of other toxicants. HCl which is released during the pyrolysis of PVC and isocyanates evolved from flexible polyurethanes are examples of irritant gases. The partially oxidized decomposition products of essentially all organic materials include some highly irritant products. However, when they pass through a flame they are destroyed to produce largely CO2 and water. The irritancy of the fire atmosphere depends upon how much irritant gas escapes the flame zone and thus on the efficiency of the combustion. In addition to its role of increasing the breathing rate and, thus, increasing the intake of CO and HCN, carbon dioxide in itself can have narcotic effects at concentrations above 5%. Its effects are not simply additive, however, as is the case for most other gases. The “N-gas Model,” developed at NIST by Levin and coworkers, has been presented at various stages of development.[182][183][200]–[203] It provides a means for combining the concentrations of various gases to predict when the atmosphere will become lethal. Based on experimental studies with rats, the following equation can be used to determine the combined effects:

[ ] (Eq. 2-49) FED = m CO + [CO 2 ]− b

[HCN] + 21 − [O 2 ] + [HCl] + [HBr] LC50 [HCN] 21 − LC50 [O 2 ] LC50 [HCl] LC50 [HBr]

The units for (O2) are present in the above equation, with the units for the remaining gases being ppm. The values of m and b are -18 and 122000 if the CO2 concentrations are 5% or less, and 23 and -38600 when the CO2 concentration is above 5%. The 30-min LC50 values for other gases are: HCN = 150 ppm, HCl = 3800 ppm, HBr = 3000 ppm. The LC50 for O2 depletion is 5.4% which in the equation is subtracted from the normal concentration of O2 in air, i.e., 21%. Other gases can be added to this equation, for instance NO2.[202] Modeling of Fire Toxicity. Even though toxic potency is not a variable with as much importance as would have been thought earlier, toxic effects do still need to be considered and evaluated properly in product hazard assessment. An example of integrating the various fire properties,

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Fire Behavior of Upholstered Furniture and Mattresses

including toxicity, into a computer model is shown in Ref. 204. Such models commonly use bench-scale test results which may or may not correctly present conditions during real-life fires. In some cases, they can be corrected for real-life fire conditions,[190] but other features remain yet unquantified. In general, it is clear that the heat release rate is the dominant variable describing all aspects of upholstered item fire hazard, including its toxicity. The recent CBUF research program focused significantly on modeling of the toxic fire effects, thus some of its conclusions are important to review. For closed room environments, the CBUF work[7] supported the earlier French findings.[181] In such rooms, the gases are normally quite well mixed and a fairly uniform concentration can be assumed to occur. The hazard then scales directly with the amount of specimen mass lost into the room. An LC50 determination is not necessary. The total mass pyrolyzed can be directly measured in full-scale fire tests on upholstered items. It can also be derived from HRR data or from HRR models, by using appropriate values of the effective heat of combustion. For a room of fire origin having window or door ventilation openings, numerous experiments and theoretical studies were done in the course of CBUF research in order to represent the situation comprehensively. Again, a need for specific measurement of LC50 was not found. The study identified, instead, the pivotal role of the formation of two gas layers in the room under ventilated conditions. It was found that conditions in the upper gas layer were lethal or untenable, both from toxicity and heat exposure considerations. Conversely, conditions in the lower layer were tenable in a layered environment and could allow escape. Thus, the problem reduced, first, to determining the height for the interface of the layers at which escape activities were possible. This was established at approximately 1.0~1.2 m above the floor. At such a height also mixing between the layers is not triggered by furniture objects themselves acting as “stirrers.” Thus, for the room of fire origin untenability was determined to occur at the time (if ever) that the interface layer drops to about 1.1 m off the floor. Next, a series of experiments and modeling runs with the computer model HAZARD I were used to relate the occurrence of this interface height to the HRR of the fire. It may not be intuitively obvious that such a connection exists, but the experiments and the model did indicate a very good connection, applicable to upholstered items only. (The study used HRR curves only from upholstered items, thus, it was not examined to what extent the conclusions would hold for other types of commodities). The

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results indicated that for a room with the size and ventilation of the ISO 9705 test room—about the size of a small bedroom—the critical layer height would be reached when the HRR first reaches 400 kW. This was true for both rapidly burning fires and for fires that were slow in their buildup. Thus, the HRR curve could be used directly to predict the untenability due to toxic gases within the room. Extensive gas measurements were made in the CBUF research in various experiments, but the conclusions did not support a need for such instrumentation in characterizing the furniture hazard. The above numeric conclusion only applies to rooms similar to the ISO 9705 room. For larger size rooms, the hazard is less, all else remaining equal. The CBUF work also examined larger rooms, but did not derive a quantitative room size vs hazard relationship. It must be pointed out that even with the extensive CBUF studies, not all possible conditions were examined. Specifically, not examined was the situation where the rooms are not closed and have ventilation flows, but the occupants are remote from the room of fire occurrence. In that case, there can be substantial mixing in gas travel down corridors, through stairs, etc. Such mixing is very difficult to quantify and existing models, such as HAZARD I, do not currently attempt to represent this phenomenon in a realistic way. Other issues connected with the fire toxicity of upholstered items are also not yet fully understood. For instance, no usable computer or mathematical models exist for predicting the evolution of toxic gases during smoldering. Consequently, the lethality of fires which only smolder is difficult to assess quantitatively. Equally difficult are fires which start as smoldering then become flaming. Normal fire hazard analysis proceeds from the concept that a flaming fire has the potential to be much more hazardous than a smoldering one. The reason has to do with the time scale of the HRR, mass loss, and toxic gas production. If a chair smolders, it will take several hours for it to be largely consumed. If the same chair burns in a flaming manner, however, it may typically be consumed over a 10 min period, with peak HRR taking place over an interval only 3~5 min. Even if the smoldering effluent contains a higher representation of toxic compounds, such toxicity difference will be small compared to the huge difference in evolution rates. Persons do, however, frequently die in smoldering-only fires. This usually occurs when the victim was sleeping and may have been exposed to fire gases for several hours. In flaming fires, by contrast, the exposed individuals often have only a very few minutes in which to make their

82

Fire Behavior of Upholstered Furniture and Mattresses

escape. From a risk reduction point of view, it is clear that both kinds of hazards must be controlled in order to make the best impact on fire losses. Purser reviewed some basic concepts regarding toxic hazards and available data and addressed the inordinate results obtained with PTFE.[160][205][206] He distinguished between various types of fires, all of which can occur in a single incident, and which affect the toxic products generated: • Non-flaming/smoldering fire: this can be started by a cigarette left on an upholstered item, or overheating due to electrical malfunction, heaters, etc. It may smolder for hours and its major hazard is incapacitating and killing sleeping persons in the room of origin, or even in other rooms. • Early or small flaming fires: the hazard here is to persons in the room or nearby rooms who are overcome by smoke and toxic gases before they are burned. In such fires, FR materials, which may prevent ignition and slow fire growth as compared to untreated materials, play an important role. However, a balance must be achieved between slower fire growth and frequently occurring higher toxicity of the pyrolysis products of FR materials. The reduction in the rate of production of toxic products, due to the impact of the fire retardant on the fire growth, can be far greater than the increase in their toxic potency in such small fires.[185] • Fully developed, large, post-flashover fires: the hazard in these fires extends to persons even in remote locations in a building. Even before flashover, smoke development in these fires tends to be high, and the types and proportions of toxic products generated may change. The efficacy of FR materials is generally low in such fires because of the high heat fluxes involved.

3 Test Methods, Standards and Regulations

Cigarettes remain the leading cause of upholstered fire ignitions. This chapter begins with an examination of cigarette ignition resistance tests. This discussion is followed by general flame and spread tests, standards, and regulations. Last, tests for smoke and toxic gases are presented. 3.1.0

CIGARETTE IGNITION

3.1.1

Introduction

Most knowledge about cigarette-upholstered substrate interactions has been acquired through bench-scale tests performed in the 1970s and early 1980s by the California Bureau of Home Furnishings and Thermal Insulation (BHFTI), several UK organizations, the US Consumer Products Safety Commission (CPSC), the US National Bureau of Standards (NBS), (later renamed National Institute of Standards and Technology, NIST), the US Upholstered Furniture Action Council (UFAC), Finnish workers, and others. An extensive description of the factors underlying the concern with cigarette ignition of upholstered furniture and the choices for a US standard test method can be found in Ref. 207. Another literature review of burning behavior of cigarettes in air and on upholstered substrates was undertaken in 1987.[72] It also reviewed most of the pertinent literature on commercial cigarette/upholstered furniture interaction. 83

84

Fire Behavior of Upholstered Furniture and Mattresses

After some voluntary and regulatory action to reduce cigarette initiated furniture item fires by regulating fabric/padding composites had been taken both in the UK and US in the 1980s, few additional publications were produced. However, research undertaken since then with experimental cigarettes with widely varying parameters established that cigarettes could be changed to be less ignition prone.[208] A test method for the ignition propensity of cigarettes was developed and is being considered in an ASTM committee; however, it has encountered strong opposition from the cigarette industry. A summary of these developments can be found in Ch. 6. The history and present status of regulations for upholstered furniture and mattresses in the EU and the US is discussed in Ch. 1. Table 1 lists the important upholstered item flammability tests. Results obtained with these tests on various substrates are discussed in Ch. 6. Types of Tests. Regulatory and voluntary cigarette ignition standards for upholstered furniture and mattresses either prescribe mock-up or component tests. In mock-up tests, cover fabrics, padding materials (also known as filling or stuffing), welt cord, and interior fabrics (there are two types: fabrics used to hold padding such as feathers or shredded polyurethane foam together, and fabrics which are used to improve burn behavior; the latter are commonly called interliners, blocking layers, or barrier materials) are arranged as in the planned line of furniture. The mock-up tests require more effort than the component tests, because they are generally performed for all of the combinations of cover fabric and back, side arm, and seat cushion padding materials, and (in some standards) welt cords and tufted areas, in the crevice and the flat areas. However, they provide the only means to evaluate the important effects of interaction between component materials and furniture configuration. In component tests, the individual upholstery components are subjected to separate tests, and assigned a pass-fail rating or a classification. Such tests are used to screen the individual materials and to restrict the use of those with low cigarette ignition resistance. Components are tested in combination with a standard material, e.g., fabrics are tested over a standard padding, and padding under a standard fabric. To be fully effective, such standards should prescribe standard materials with worstcase cigarette ignition resistance; however, this is not generally the case. Problems are also encountered with the reproducibility of the standard materials.

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Table 3-1. Important Furniture Item Flammability Tests Cigarette Flame ignition ignition

Test ISO 8191 (Nordtest 039)

X

X

BS 5852

X

X

ASTM E 1352 (Mock-ups)

X

ASTM E 1353 (Components)

X

NFPA 261 (Mock-ups)

X

NFPA 260 (Components)

X

California TB 116, 117

X

Upholstered Furniture Action Council

X

Business and Institutional Furniture Manufacturers Association (BIFMA)

X

Code of Federal Regulations 1 Part 1632

X

1

BS 6807

X

HRR

Smoke Toxicity

X

X

California TB 133

X

X

X

X

California 1 TB 129

X

X

X

X

California TB 1211

X

X

X

ASTM E 1537

X

X

X

1. Mattress test; 2. Surface flammability test; 3. Vandalized specimen

(Cont’d.)

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Fire Behavior of Upholstered Furniture and Mattresses

Table 3-1. (Cont’d.) Test

Cigarette ignition

Flame ignition

ASTM E 1 1590

X

ASTM E 2 162

X

ASTM D 2 3675

X

HRR

Smoke

Toxicity

X

X

ISO 5660

X

X

X

ASTM E 1474

X

X

X

ASTM E 1354

X

X

X

NFPA 264-A

X

X

X

ASTM F 1550 M3

X

ISO TR 5924

X

ASTM E 662

X

ASTM E 906

X

X

ISO TR 9122

X

ISO TR 6543

X

ASTM E 1678

X

1. Mattress test; 2. Surface flammability test; 3. Vandalized specimen

In addition, many tests are carried out on full-scale upholstered furniture, in furniture calorimeters, and in standard room calorimeters. In the US Mattress Cigarette Ignition Standard (enforced by the CPSC), both prototypes and production pieces are tested according to a sampling plan.[24]

Test Methods, Standards and Regulations

3.1.2

87

Upholstered Furniture

United States. The CPSC considered a regulatory cigarette ignition standard for upholstered furniture in the years 1976 to 1981.[209] This was in part a mock-up test; however, to avoid the need for testing the thousands of fabrics used by the furniture industry in mock-ups, it allowed a component test for fabrics, resulting in a fabric classification scheme. The reasons for the choice of test arrangements in this standard, based on numerous results including those of an inter-laboratory evaluation of the method, are described in an extensive back-up report.[207] The Business and Institutional Furniture Manufacturers Association (BIFMA) voluntarily adopted the original, proposed CPSC standard, adding provisions for small flame ignition resistance of fabrics and padding based on California TB 117.[23] The Upholstered Furniture Action Council (UFAC), an industry group created to represent industry views on flammability to government bodies, found the BIFMA/CPSC standards too onerous and prepared its own component standards.[22] In 1981, CPSC voted to accept, on a trial basis, these UFAC voluntary standards. This status prevails at the time of this writing. The NFPA adopted the UFAC cigarette ignition standards test for residential furniture and the CPSC/BIFMA standard for public occupancy.[25]–[26] ASTM also lists such standards, plus one for the smoldering resistance of cotton batting.[27][28][210] Two features of the BIFMA/CPSC procedure have been adopted for all United States cigarette ignition tests: the standard cigarette and the placement of a piece of sheeting over the cigarette after it is placed into its test position. The cigarette has no filter and is made from natural tobacco, 85 ± 2 mm long, with a tobacco packing density of 0.27 ± 0.02 g cm-3 and a total weight of 1.1 ± 0.1 g. These specifications were originally developed on the basis of the Pall Mall king-size cigarette. The ASTM version of the test also specifies that the smoldering rate of the cigarette should be 0.10 ± 0.01 mm s-1, with the cigarette burning downward in a draft-protected area. The sheeting is cotton or polyester/cotton percale, 115 ± 28 g m-2, 67–79 threads/cm, without chemical finish. The presence of this sheeting on top of the smoldering cigarette makes the test slightly more severe and more reproducible.[207][211]

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Fire Behavior of Upholstered Furniture and Mattresses

The BIFMA/CPSC mock-up and locations for placement of the cigarettes are shown in Fig. 3-1. All materials in the mock-up are identical to those in the proposed line of furniture. The mock-up consists of a horizontal cushion, 450 × 550 mm, and vertical back and side cushions, approximately 300 × 500 mm. In addition, the decking (the materials under removable seat cushions) and flat areas on top of the side arms and back are mocked up if they are large enough for cigarettes to rest on them. Three cigarettes each are placed into the two crevices formed by the seat and the back or side cushions, in the flat area of the seat cushion and the welt edge area in its front, and, if applicable, in flat mock-ups of the decking and back and sidearm tops. The cigarettes are then covered with the above-mentioned sheeting, 125 × 125 mm. If all the resulting char lengths, measured from the nearest point of the original cigarette location, are less than 75 mm, the furniture composite passes. Provisions are made for retesting if cigarettes go out before burning their whole length, or if only one cigarette per location produces a char length exceeding 75 mm.

Figure 3-1. BIFMA/CPSC mock-up for testing cigarette ignition resistance of upholstered furniture.

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89

A furniture manufacturer may use several thousand fabrics in one year, but relatively few padding material combinations. To eliminate the need for testing these padding material combinations with each fabric, the proposed CPSC test contains a fabric classification scheme. The minimock-up testing device used in fabric classification is shown in Fig. 3-2. The fabric is tested over glass fiberboard, 200 × 200 mm for the horizontal and 200 × 300 mm for the vertical piece. The glass fiberboard (an insulation material, Fed. Spec. HH-I-558B, Form A, Class 1, plain faced) is approximately 25 mm thick and has a density of 40 ± 8 kg m-3. A cigarette is placed into the crevice formed by the two fabric-covered boards, covered with a piece of sheeting, and allowed to burn completely. The fabric classification scheme shown in Fig. 3-3 is used. If the char length is less than 38 mm, the fabric is Class B; if 38–75 mm, Class C; if more than 75 mm, Class D. Class B fabrics can then be subjected to an additional test in which the vertical glass board is replaced with a plywood board covered with 50 mm thick cotton batting without FR treatment. If the char length is then less than 38 mm, the fabric is Class A.

Figure 3-2. Mini mock-up used for UFAC, TB 117, and BIFMA/CPSC cigarette ignition tests.

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Fire Behavior of Upholstered Furniture and Mattresses

Figure 3-3. Proposed CPSC fabric classification scheme.

The results of the fabric classification test are used as follows: if a composite of padding material and welt cord passes with a Class A fabric, this combination may be used with all Class A fabrics. Combinations which pass with the Standard Class B fabric (the above-mentioned sheeting used to cover the cigarettes) can be used with all fabrics classified to be Class A or B. Similarly, combinations which pass with the Standard Class C fabric (Fed. Spec. CCC-C-436D, cloth, ticking, twill, cotton, Type I, Class I, untreated, 305 ± 14 g m-2, without finish) can be used with all Class A, B, or C fabrics. However, all furniture which is to be covered with Class D fabric must be tested in mock-up form. It should be noted that alkali metal ion concentration in cellulosic fabrics, which greatly affects the smoldering propensity as discussed in detail in Ch. 6, is not specified for the Standard Class B and C fabrics. The UFAC voluntary program further reduces the testing effort by using component standards for the individual furniture components.[22] Manufacturers who sign up to conform with the UFAC standards labeling

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91

program are issued hang-tags to be attached to each piece. The original label stated that the furniture is made in accordance with the new, improved UFAC methods, designed to reduce the likelihood of furniture fires from cigarettes. However, upholstery fires are still possible. The label also recommends use of smoke detectors. The UFAC test methods use the above discussed cigarette, cigarette cover, and mini-mock-up test frame. The testing scheme for the individual components is outlined in Table 2, together with materials which usually pass the tests. This table also lists specifications for the UFAC standard polyurethane foam and two standard test fabrics. The alkali metal ion content of the fabrics is not specified which may contribute to the difficulties in obtaining consistent results with different rolls of standard fabric. Upholstery fabrics to be classified are placed over the UFAC standard foam in both the horizontal and vertical panel of the mini-mockup and a cigarette is placed into the crevice and covered with the sheeting. If the vertical char length in any of three replicate tests is equal to or exceeds 44 mm, the fabric is Class II. Class II fabrics must have a UFAC approved barrier material between cover fabric and padding material in the seat cushion; polyester batting is commonly used for this purpose. Class I fabrics can be used with any UFAC approved components. Similarly, the padding material to be tested is mounted in both parts of the mini-mock-up and covered with the UFAC standard ticking which is identical to the CPSC Class C standard fabric. This standard ticking is also used in testing any interior fabric layers, if present over the padding. The welt cord is tested with the more ignition-prone UFAC standard Class II fabric and UFAC standard foam in both panels. The same fabric is used to test barrier and decking materials (the latter are only tested in a horizontal panel). The UFAC test methods can be readily upgraded, to take advantage of newly developed materials with higher cigarette ignition resistance. A case in point was the upgrading of the welt cord standard by changing from the more cigarette ignition resistant standard ticking to the less ignition resistant Standard Class II velvet fabric. This change followed development of welt cords containing heat dissipating aluminum foil strips and eliminated the previously acceptable ignition-prone cellulosic welt cords.[212] A more recent addition is a Decorative Trim Test Method.

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Fire Behavior of Upholstered Furniture and Mattresses

Table 3-2. UFAC Component Test Method Components to be Tested Location of Materials

Cover fabric classification

Filling/ 1 Welt Cord Padding

Barrier/ Interliner

Interior Fabric

Decking

std. ticking

std. class II

std. foam

test material

std. ticking

—–

2

Horizontal panel Fabric

test fabric

std. ticking

Padding

std. foam

test filling

Fabric

test fabric

std. ticking

Padding

std. foam

test padding

std. foam

std. foam

std. foam

—–

44/1.75

38/1.5

38/1.5

51/2.0

38/1.5

38/1.5

TP

similar to filling material

std. class II std. class II std. foam

test barrier over std.

Vertical panel

Vertical char length (mm/in.)

std. class II std. class II

class I: most most PU, SR cotton TP, wool some TP, batting Materials which PE batting, PVC, class II: Med. cell./TP generally pass aluminized special PU batting, weight and cell (min. 70% heavy cell TP)

TP- thermoplastics (nylon, olefin, polyester) PU - polyurethane PE - polyester Standard Materials: Standard Class I fabric:

3

cell. - cellulosics (cotton, rayon, jute, linen, hemp) SR - smoldering resistant

100% cotton mattress ticking fabric, Fed. Spec. CCC-C-436-D, cloth, (14.5 oz/.yd2.) ticking, twill, cotton; Type I, laundered and tumble dried once.

Standard Class II fabric:

100% cotton velvet, 490 g/m2 ± 14 g/m2, undyed, containing no FR finishes or backcoating.

Sheeting used to cover cigarette:

cotton fabric, (124 ± 28 g/m2), white, no FR finish.

Standard foam:

polyester type PU foam, containing no organic fillers or FR’s. 24 ± 1.6 kg/m3, hand crushed before use.

1. placed into crevice, 2. tested as horizontal specimen only, 3. measured in any direction

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93

The State of California has standards requiring cigarette ignition resistance of resilient cellular material (i.e., foam) used in upholstered furniture, as well as certain levels of flame resistance of all components.[29][213] TB 116 is a voluntary standard requiring that furniture either be cigarette ignition resistant or be labeled that it is not; TB 117 requires conformance with flammability tests for fabrics and padding. The above described mini-mock-up configuration, standard cigarette, and cigarette cover sheeting are again used in this test. The foam is tested with a standard fabric (beige, 100% cotton velvet, 330 g m-2) without a backcoating. The test is carried out until obvious, sustained combustion occurs or until 5 minutes after the system appears to have self-extinguished; then the remains of the fabric and carbonaceous char are removed from the foam, and the remainder of the foam weighed. Foams pass if the specimens retain more than 80% of their original weight (this is a better criterion than char length since foam can smolder inward and sideways under non-smoldering fabrics which would not be measured by the char length). The background of this standard and its effects on material selection are discussed in Refs. 15, 21, and 214. United Kingdom. The UK promulgated regulations for cigarette and flame resistance of upholstered furniture and mattresses in the late 1980s.[44]–[47] The basic principles were laid down in BS 5852 which consists of two parts: Part 1 refers to ignition by smoker’s materials, which includes both cigarettes and wooden matches (simulated by a butane burner) and is intended for residential furniture; Part 2 (discussed in 3.2.3) covers flaming ignition sources, consisting of three butane flames and four wood cribs and is intended for institutional furniture.[46] Some parts of BS 5852 have been replaced (while the basic principles stand) by BS EN 1021,[564] which is the EU adaptation of ISO 8191.[61] Standard BS 5852 and its successors can be conducted on actual furniture pieces or as a mockup test with the materials arranged as in the actual line of furniture. The mockup, Fig. 3-4, consists of a seat cushion (450 × 300 × 75 mm) and a cushion simulating the back or side (450 × 300 × 75 mm for Part 1: cigarette and simulated match ignition; and 450 × 450 × 75 mm for Part 2: larger ignition sources). The cushions are placed into a hinged steel frame while both halves are horizontal. The cover fabric is then placed over the seat padding material, threaded under a bar at the crevice, and then placed over the vertical material. The fabric is clamped on the outside of the frame and the back brought into the upright position. This causes formation of an approximately 90 degree interface

94

Fire Behavior of Upholstered Furniture and Mattresses

between seat and back cushion (crevice), with the actual angle determined by the fabric tension due to the movement of the frame and the compressibility of the padding. The ignition source is placed into the crevice, at least 50 mm from the side edges.

Figure 3-4. Mock-up for BS 5852 test.

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95

Standard BS 5852 and its successors have certain features not found in some other standards: • If the upholstered furniture to be qualified has seams, they are to be reproduced in the mock-up. • However, trimmings, and welt cords (braids) are not included in the mock-up. This is in contrast to US practice where welt cords and tufted areas are included in all cigarette ignition testing, because they have been shown to affect the results.[207] • If the materials on the outside are different from those on the inside surfaces of a furnished items, they must be tested separately, in the same crevice configuration as the inside. • If the seat is not upholstered, a seat constructed with the materials in any upholstered back or side has to become part of the mock-up. If the sides and back are not upholstered, the seat must be tested with a back made from the same materials. • A cover fabric or interliner which has been treated with a fire resistant chemical has to be subjected to a water soaking: water hardness, 8–10; unspecified nonionic wetting agent, 40°C; ratio of water to specimen 20:1 by weight; 30 minutes; followed by a 2 minute rinse at the same water hardness. • Test can be performed with various crevice geometries, simulating those in the actual furniture line. • There are labeling requirements indicating under which of the varying stages of compliance requirements between 1988 and 1993 the furniture is covered. The test criteria are described in Sec. 3.1.4, below. It also specifies the cigarette smoldering rate, and the ignition procedure. The Crown Suppliers (formerly the PSA Suppliers, an organization responsible for government procurement) use different cigarette and flame ignition procedures.[48] The major differences are in the use of a horizontal specimen, and time specifications for observations of smoldering after the cigarette burns out. More details about these tests can be found under flaming tests, below.

96

Fire Behavior of Upholstered Furniture and Mattresses

3.1.3

Mattresses

While the US lagged behind some other countries in regulations for upholstered furniture, its mattress standard has been in place since 1972.[24] Full-sized prototypes of planned, new production lines, as well as production mattresses sampled according to regulations which are part of the standard, are tested. One half of the mattress is covered with a sheet like the sheeting used to cover cigarettes in the upholstered furniture tests, and nine cigarettes are placed on smooth surfaces and near tufts and tape edges, and covered with another sheet. Nine other cigarettes are placed on the same features of the uncovered half of the mattress, and covered with the standard sheeting material. Char length exceeding 51 mm in any one location constitutes failure. California had earlier developed a similar standard, TB 106, which was preempted by the Federal standard. TB 26 is a question-and-answer explanation of record keeping requirements and testing procedure for both the Federal and State flammability standards.[215] Standard BS 6807 is for cigarette and flame ignition of mattresses, divans, and bed bases, with provisions for testing with secondary ignition sources such as pillows and bed covers.[47] It has been superseded in part by three successor standards, one covering mattresses and bed parts,[565] one mattresses, divans, and bed bases,[566] and one bedcovers and pillows.[567] As in the upholstered furniture standards, cigarette and small flame ignition on one hand, and larger flame ignition sources on the other (see Sec. 3.2.3), are covered in separate parts. In all three tests, specimens 450 × 350 mm in nominal thickness or full size mattresses are tested on platforms. Several points of ignition are specified to represent various surface characteristics of the item to be simulated in the test. The test criteria are described in 3.1.4. Standard BS 7177[566] is similar to BS EN 597[565] and BS 6807[47] except that there are provisions for various occupancies including those in which arson may be encountered. Thus, for residential furniture, again only cigarettes and match equivalent flame ignition sources are prescribed. For medium hazard occupancies (hotels, hostels, parts of old people homes, dormitories, etc.), wood crib ignition source 5 (see 4.2) is prescribed, and for high hazard occupancies (certain parts of medium hazard occupancies, hospitals, off-shore installations, etc.), crib 7. Finally, for very high hazard occupancies (prison cells, closed psychiatric wards, etc), additional tests specified by the user may be required.

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Standard BS 7175[567] applies the principles of the above standards to individual items or “known” composite arrangements of bedding (pillows, continental quilts and quilt covers, mattress cases and covers, sheets, pillowslips, blankets, bedspreads), configured as in real life situations. Specimens 450 × 450 × 25 mm (or actual thickness) are placed on a mineral wool fiber pad on an elevated platform. Cigarettes and flames are placed in a number of locations on individual items or composites, in some cases cigarettes are placed between bedding items, and their effects observed after dismantling after 60 minutes. In other tests, the flames are also applied from below, without the mineral wool pad present. Crown Suppliers standards also exist for several items of bedding including pillows, continental quilts, mattresses (including tufted and taped areas), and bedding assemblies.[48] An interesting feature is that bedding is loosened by pushing a block with a 200 × 400-mm cross section between the sheets before testing, to simulate a vacated bed. The EU has decided not to test mattresses in mock-up form because their features (tape, welt cords, tufts, quilting) are important for ignitability.[56] Either the actual mattress or a section cut from it is tested. Canada has a mattress cigarette ignition test, requiring a 300 × 300 mm piece of mattress fitted tightly into a box to minimize edge effects.[216] The specimen is put under 24.5 kPa pressure by means of an indentation tester. The cigarette is placed on a stitched area near the pressure point. The passing requirement is that the char length not exceed 50 mm, and that there must be no continued combustion ten minutes after the cigarette burned out. ISO is considering a mattress test in which the cigarette would be covered with a glass fiber or a cotton batting; these are more severe test conditions than obtained with an uncovered cigarette and are intended to simulate the conditions which exist when a blanket covers the cigarette.[61] 3.1.4

Test Criteria For Cigarette Ignition Resistance

Different criteria for cigarette ignition resistance of upholstered items are used in the various standards. UFAC, BIFMA, and the CPSC mattress and proposed upholstered furniture standards use char length criteria, based on the experience that if a certain char length is exceeded, continuous smoldering is likely to occur.[207] Failure is also recorded if obvious ignition occurs. TB 116 stipulates specifically measuring the char length in any direction, including that going into the padding.[213]

98

Fire Behavior of Upholstered Furniture and Mattresses

The British and ISO cigarette and match equivalent ignition standards rely on the observation of progressive smoldering or flaming.[46][61][564] Progressive smoldering is defined as “exothermic ignition, not accompanied by flaming, that is self-propagating, i.e., independent of the ignition source. It may or may not be accompanied by incandescence.” Flaming is defined as “undergoing combustion of the gaseous phase under emission of light.” It was found that these observations have to be continued for 60 minutes to get reliable results. More specifically, the criteria for ignition are:[564] (1)

It becomes unsafe to continue the test.

(2)

The specimen is essentially consumed by smoldering or flaming.

(3)

Smoldering or flame reaches the edges or the bottom of the specimen.

(4)

The char length exceeds 100 mm in any direction except upward.

Two of the successor standards have only minor variations from these criteria.[565][566] On the other hand, BS 7175[567] defines progressive smoldering as detectable amounts of glow, heat, or smoke after 60 minutes for cigarettes, 120 s for the match equivalent flame. Concealed smoldering is detected after dismantling the composites after 60 minutes. The California standards prescribe maximum acceptable mass loss as the criterion in addition to obvious ignition, as discussed earlier. A suggestion to use the second derivative of the mass loss versus time curve (the rate of change of the rate of mass loss) was made but this would require complex calculations or sophisticated instrumentation.[217] Using that method resulted in fabric rankings similar to the CPSC fabric classification test, which is based on char length. In another investigation, mini-mock-up mass loss of cotton fabrics over untreated and FR polyurethane foam gave very similar results to the UFAC classification test, and also to the subjective judgment of obvious ignition of the substrates.[218] Time to ignite the substrate is another quantitative measure, but requires removal of cigarettes after 1, 2, 3, ... minutes, until an ignition time is obtained.[219] Trying to establish ignition time by visual observation of the fabric under the cigarettes was found to be difficult because the cigarette and ash interfere with visible observation and the exact time at which sustained substrate combustion occurs is difficult to judge.

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Furthermore, many heavy, cellulosic fabrics which start smoldering only after a considerable time, smolder more vigorously after ignition than those who ignite quickly, making ignition time a poor indicator of hazard. It should be mentioned that continued smoldering has occasionally been observed to continue deeply into the PU foam below the crevice while the cover fabric exhibits only a short char length and may be considered a pass.[220] This causes doubt about the reliability of use of surface char length and obvious ignition to determine cigarette ignition resistance. The California TB 117 practice of measuring weight loss appears preferable. Furthermore, dismantling (which is now recommended as a safety feature in most standards) and judging the inside of the smoldering item should be required. 3.1.5

Critiques of Cigarette Ignition Standards

Many organizations have criticized the various cigarette ignition standards. Comprehensive reports particularly worth mentioning originated with the Canadian Department of Consumer and Corporate Affairs[17] and cover various aspects of cigarette ignition of upholstered substrates. Among them are a survey of the Canadian furniture industry, description and critique of test methods, results on a variety of substrates, and recommendations for a Canadian test. These and the experience of other organizations indicate possible improvements in the present standards and areas to be further investigated. Some of these are: Standard Test Materials and Component Tests. Interactions of furniture components in smoldering (and flaming) situations cannot be reliably predicted from component tests using standard materials. In addition, present standard materials are too loosely specified. As discussed earlier, fabrics vary widely in cigarette ignition resistance. Thus, it would be desirable that standard fabrics used in the UFAC, CPSC, UK, and California tests would have very low cigarette ignition resistance, to assure that padding, welt cord, etc., which pass with the standard fabric would not ignite with any of the cover fabrics used on upholstery items. Such is not the case, however. The standard fabrics were chosen to eliminate only some of the materials with low cigarette ignition resistance, but not to completely change the market by requiring highly cigarette resistant, and, possibly, unpopular or expensive materials. For example, with a worst case fabric (possibly a heavy, unfinished cellulosic fabric containing high concentrations of alkali metal ions) few presently used padding materials would pass the tests.

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Fire Behavior of Upholstered Furniture and Mattresses

Similarly, the standard foams which are used in the qualification of fabrics, welt cords, and interliners are by far not the least cigarette ignition resistant foams available, allowing the industry to use less than state of the art materials. In addition, standard cover fabrics and foams are hardly standard: there is considerable variation within and between fabric rolls, as well as differences between fabric and foam lots.[221] CPSC, BHFTI, and UFAC have worked on this problem, aided by industry committees.[222] It does not seem to be completely solved; part of the reason may be that while a standard fabric construction is specified, there are no finish and dye specifications. Specifically, it would be important to specify the alkali metal ion content of cellulose containing fabrics; these ions have been shown to be smolder promoters, as discussed in detail in Ch. 6. Similarly, chemical formulation of foams should be specified. Thus, a significant fraction of UFAC-labeled furniture items that were compliance-tested during the early stages of the program showed ignition from cigarettes.[223]–[225] When CPSC tested 78 upholstered furniture items both as furniture items and in mock-up form, several of the mock-ups covered with the light weight (approx. 4 oz yd-2, all cotton or polyester/cotton blend, alkali metal content not specified) Class B standard fabric did not ignite, but the chairs covered with fabrics classified as Class B ignited. This and similar experiences indicate that the standard Class B fabric is by far not a worst case fabric for its class, and should be replaced with a fabric with less cigarette ignition resistance. This difficulty did not seem to arise with the Class C standard fabric which is a heavier mattress ticking. In other than Class B cases, the mock-up and actual furniture items results agreed very well. Very good agreement was found between mock-up and full-scale chair results, using the same fabrics and padding.[223][226] Later, CPSC and UFAC tested 40 furniture items conforming to UFAC standards which were procured in late 1983.[225] Resistance to cigarette ignition was found to have been improved but some UFAClabeled items still ignited. Crevice Angles. The 90° crevice ignition tests are not applicable to all possible scenarios. An Australian study indicated that when cigarettes were dropped in an open crevice formed by compression of the seat cushion such as caused by sitting on it, and the pressure released, sustained smoldering occurred even if the fabric/padding material combination did

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101

not produce smoldering in the rectangular mock-up crevice.[227] Similar results were found in another study of three crevice angles.[228] Cover Fabric For Cigarettes. It is claimed that the use of a cover fabric over the cigarette on upholstered furniture is unrealistic. It makes the test slightly more severe; however, it also makes it more reproducible, perhaps because it reduces the effect of ambient air motion which is not strictly controlled in many laboratories.[207][211] It should be specified that the sheeting should fit tightly over the cigarette to be effective. The specifications calling for all-cotton or polyester/cotton blend sheeting should be changed to one or the other. Sheeting may compensate for the effect of aging and dirt accumulation which has been reported to decrease cigarette ignition resistance in one study.[229] However, in this study char length was measured after the cigarette was left on the substrate for only a limited time; this has been shown to be a dubious procedure because some heavy fabrics ignite only after considerable time (this reference is included here because of the rarity of studies on the effect of soiling in use). In another brief study, dirt was extracted in water and solvent baths from a discarded, very dirty furniture fabric. This was carefully applied a to fabric of known ignition propensity, conditioned, and tested for cigarette ignition resistance.[208] No effect of such soiling was observed. Failing Fabrics. Some standards eliminate medium to heavy cellulosic fabrics which are popular in the US market place; however, many of these fabrics would pass if some of the steps which increase cigarette ignition resistance are taken, such as use of effective interliners and/or removal of alkali metal ions. The Proposed CPSC Method For Upholstered Furniture. The U. S. residential upholstered furniture industry called the proposed CPSC upholstered furniture method cumbersome and material consuming, even with the fabric classification method. However, this also would apply to the US mattress standard and the UK furniture mock-up methods which are operative and have been reasonably well accepted even without a fabric classification system. The flaming part of the latter required a major switch to considerably more fire-resistant polyurethane foam padding. Also, BIFMA has adopted the standard for institutional furniture. The UFAC and California Component Test Methods. As mentioned before, the major objection to these methods is that they only test individual components and that the results are not necessarily predictive of the effect of the interaction of the components. However, these

102

Fire Behavior of Upholstered Furniture and Mattresses

standards are only designed to reduce the incidence of cigarette ignitions of furniture, not eliminate it completely. The UK Regulations. Some of the difficulties described above, especially regarding the crevice modeling and use of standard fabrics, also apply to the UK standards. In addition, the requirement that the padding material must be 75 mm thick, rather than actual thickness, requires splitting of the popular 100 mm foam, an extra operation. Actual thickness could be used with minor adjustments to the test procedure. While the backup literature for the test indicates that the present arrangement achieves reproducible tension of the fabrics, it appears that the actual fabric tension depends on the compressibility of the padding material and stretch of the fabric, which could also affect crevice geometry. Constant tension could be applied to the clamps which hold the fabric, rather than holding them in fixed positions. The UK Standard does not address the cigarette ignitability of welt cords and tufted areas which can significantly affect ignition by cigarettes.[207] It does address other conditions which most other standards ignore, as discussed above. Different results are obtained when the flames or smolder reach the sides where the padding is not covered with fabric than if the padding is covered by fabric, as in actual furniture.[230]

3.2.0

FLAMING FIRE TESTS, STANDARDS, AND REGULATIONS

3.2.1

Introduction

The present flame test methods arose from the desire to be able to regulate furniture in residences and public occupancies without using antiquated or irrelevant methods still prescribed in many fire safety codes.[38] Several others were developed to conduct research on the fire behavior of upholstered items. Some of the methods share certain similarities, but many different testing philosophies exist, especially since the relatively recent emphasis on HRR instead of flame spread rate as the most important fire hazard parameter. Thus, the available test methods differ substantially in the quantities being measured and in the performance aspects mandated in their criteria. Chapter 2 discussed these differences and examined the performance variables which are the most essential.

Test Methods, Standards and Regulations

3.2.2

103

Uses and Limitations of Flaming Fire Tests

The more important modern flammability tests should be considered with a few general points in mind. It is obvious that during the last decade or two, substantial progress has been made towards establishing an engineering basis for fire test development, to replace the older empirical methods. This topic has been examined at length.[231][232] Some of the main points are summarized as follows: • Only full-scale room fire tests can serve as primary references for the fire hazard performance of upholstered furniture and mattresses. However, a scenario must be chosen, involving the ignition source and its location on the item, ventilation, position of item in room, room size, wall and ceiling materials, presence of other items, etc. which may not be representative of all possible fire situations. • Consequently, a sound full-scale test requires that a well-justified fire scenario be established. For example, if post-ignition behavior is of interest and the HRR during flaming combustion is to be measured, then the ignition source must be strong enough to initiate flaming combustion. If ignitability is of interest, weaker ignition sources must be used; a range of ignition sources as in BS 5852[45] makes it possible to rank the ignitability of upholstered furniture and mattresses. • All bench-scale methods and those full-scale methods which do not use an actual test room (e.g., furniture calorimeters) need to be validated by full-scale room fire results. It should be noted, however, that for TB 133, which is used for regulatory purposes, the pass/ fail level for HRR 80 kW is low enough that room parameters are not important.[35][36] Smoke and toxic gas development are ventilation dependent at low ventilation levels, whether in a closed room with very low HRR, or in a room with an open doorway where the HRR is much higher than the 80 kW pass/fail level of the TB 133.

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Fire Behavior of Upholstered Furniture and Mattresses

• Bench-scale tests are preferred for most routine testing, due to lower cost and better reproducibility, but are acceptable only if validated by full-scale tests. Specimen preparation techniques may be just as important as the details of operating the actual test equipment when it comes to upholstered composites. Computer modeling is used to provide projections from bench scale to room tests (see Ch. 7). Much progress has lately been made in this direction. • Bench-scale tests should be designed so as to come as close as possible to measuring engineering fire properties of materials. • Tests which provide quantitative, numerical data are needed for further engineering fire analysis and product development while tests which simply rate a product on a pass/fail basis alone may serve the regulatory purposes quite adequately in some cases. • Some of the material fire properties that can be measured in bench scale tests include: – complete HRR curve at a specified flux – heat of combustion – minimum flux for ignition or time to ignition at a specified flux – ignition temperature – flame spread constant and the effective thermal inertia – critical flux for flame spread – smoke yield – toxic gas species yields As for any other engineering test, emphasis should be placed on well-controlled test conditions and on achieving repeatable and reproducible results. Tests such as the British BS 5852 and the full-scale mock-up version of California TB 133 which utilize mock-ups rather than end-use articles may not be able to represent the aspects of frame materials, shape, construction details, and mixed construction types in the test piece.

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Even though a burning furniture item is one of the more complex types of combustible article to be dealt with, progress has been made with respect to computer modeling of such items. Such efforts are likely to lead to the improved ability to design optimal test methods and are discussed in Ch. 7. Certain issues do not necessarily arise for general combustibles, but become important when trying to establish bench-scale tests for furniture (some of these have been mentioned before but are repeated for emphasis). These include: • While a proper bench-scale test can treat composites, in the sense of layers of foam, interliner, fabric, etc., it can, of course, represent neither the shape of the fullscale article nor the frame materials. That is the job of the furniture fire models and correlation formulas discussed in Ch. 2 and 7. The role of the bench scale test is simply to provide the input data on the properties of the furniture composites for the furniture fire models and correlation formulas. Work at NIST originally suggested some procedures for dealing with both of these issues,[121] albeit based on scant data; additional work on this problem has been done by CBUF[7] and others.[230] • Some furniture, especially stacking chairs, are only lightly upholstered in the seat and perhaps the back, and such chairs are often in long rows in public occupancies so that fire spread from chair to chair in rows must be considered. Also, when not in use, such chairs are often stacked about 20 high, in adjoining rows, representing fuel loads of the order of tons. The test for stacking chairs that is under development in ASTM only involves short stacks. The correlation between such tests and the large number of chairs that can be stacked together in practice has yet to be known. • Some furniture items exhibit the spread of fire in internal cavities. This behavior is difficult to treat in fire models or predictive methods.

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Fire Behavior of Upholstered Furniture and Mattresses

• With the exception of the Boston Fire Department Test and the initial research studies at NIST, most full-scale test methods apply the ignition source at the junction of the back and seat. Except for the cover fabric, entirely different materials are frequently used in the seat, back, and sides, and especially on the outside of furniture, where thin foam and batting layers, wood and cardboard, etc. are often used. Since furniture is often ignited on the outside by, e.g., electrical malfunctions or space heaters, it would be appropriate to routinely test, with the appropriate ignition source position, all surfaces which differ in material combination from those tested by the various methods below. BS 5862 prescribes testing such materials, mounted as if they were seat and back surfaces, with ignition at the junction. Several studies have addressed the question of ignition source location and intensity.[133]–[136] One paper described the application of a Bunsen burner to both the inside and outside of the furniture,[133] another one simulation of likely accidents, e.g., a space heater in front, and a dropped table lamp in the inside of chairs.[135] One study describes ignition studies at FRS and NIST in which a smaller ignition source was applied to the crevice and a larger one at the outside of chairs; shorter times to peak were observed for the crevice ignitions.[134] Similar experiments were conducted during the CBUF program.[136][137] In all cases the peak HRR was essentially independent of ignition source intensity and location, but ignitability and the time to peak HRR differed greatly. This could, in principle, affect escape times. However, if the time to escape is realistically measured from the time of detection (assumed to occur at, say, a HRR of 50 kW) rather than the time of ignition, the time to peak differences are not very dependent on ignition source variations.[136][137] Note that where arson or children’s fire-setting can be a problem, the underside of furniture is sometimes first involved. This location was not examined in any of the above studies, although some unpublished work was done in the course of the CBUF studies. The latter concluded that standardizing on an under-chair fire location was impractical, since some furniture items lay so close to the floor as to not permit the introduction of a usable ignition source into that location.

Test Methods, Standards and Regulations

• The effects of other items in a room and room configuration: None of the existing full-scale tests and only the Cone Calorimeter bench-scale test provide for external specimen heating which can, to a certain extent, simulate conditions when an item in a room is already burning and radiation from it and the walls and ceiling preheat other items. This could make a difference in borderline constructions. A case in point was provided by a study in which specially constructed furniture items were examined in the Cone and furniture calorimeters and a fully-furnished full-scale room fire test.[35][36] A chair with wool fabric, glass interliner, and California TB 117 type FR padding did burn in the room fire, but failed to burn in the furniture calorimeter, achieving essentially zero HRR readings. Data from the Cone Calorimeter, however, reflected the relative specimen performance as seen in the room fire and not as recorded in the furniture calorimeter. Similarly, CBUF data showed better correlation between Cone Calorimeter and room data than between Cone Calorimeter and furniture calorimeter data; however, there were also certain other variations between room and furniture calorimeter data.[7] • With respect to ignition sources for full-scale tests, it has been found that crumpled or shredded newspapers, which seemed realistic and had rather wide application, present serious problems of reproducibility.[138][233] While there are proponents of both wood cribs and gas burners, the gas burner is much easier to implement and avoids problems of irreproducibility that do occur with wood cribs, due to, e.g., variations in wood itself and in the manner in which the cribs collapse. The square-ring burner developed at NIST (and based on an earlier T-head design of FRS) is especially well suited to challenging a chair in the particularly vulnerable crevice position and was adopted for TB 133.[138] However, occasionally an item of furniture with polyester batting in the seat passed with the gas burner but failed with the original TB 133 source, a

107

108

Fire Behavior of Upholstered Furniture and Mattresses

metal cage containing crumpled newspaper. The heavy cage followed the fire into the melting batting and ignited it whereas the gas burner is held fixed in place.[234] 3.2.3

Description of Flaming Fire Tests

The following test descriptions are based on a critical review of advantages and limitations of the most commonly used test methods.[231] The tests include those (1) which only consider the ignitability of the test items, (2) tests which measure ignitability as well as HRR and sometimes smoke and CO release, and (3) flame spread tests. The tests can also be divided into bench scale and full-scale tests, as well as into mockup and component tests. Some test procedures are used for more than one mode. Details of the ignition sources will be discussed in Ch. 4. Bench-scale Flammability Tests THE (UK) FURNITURE AND FURNISHINGS (FIRE) (SAFETY) REGULATIONS Designation: The Furniture and Furnishings (Fire) (Safety) Regulations 1988, No 1324, Consumer Protection; and the Furnishings and (Fire) (Safety) (Amendment) Regulations 1989, No 2358, Consumer Protection Public, HMSO, London (1988, 1989).[44] This replaced the regulations of 1980, amended in 1983. Background: The initial draft of this regulation was prepared by the British Standards Institution (BSI). The final document was prepared by the Department of Trade and Industry, and is not a BSI publication. The method makes extensive use of the testing approach developed in BSI’s method BS 5852 and 6807,[46][47] many of which were incorporated into ISO 8191[61] and BS EN 1021[564] (upholstered furniture), and mattress and bedding standards BS EN 597,[565] BS 7177[566] and 7175.[567] The main added requirements are for measurement of specimen mass loss. The Regulations[44][45] were promulgated in 1988; they became effective for polyurethane foam in 1988, with other effectiveness dates for other materials and various furniture types between 1989 and 1993 (secondhand furniture).

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The UK Regulations and the BS 5852, referenced in them, cover both flame and cigarette ignition; the latter test procedures, including specimen size, frames, etc., have been discussed earlier in this chapter. Good overviews were provided by Christian,[53] by Paul,[54] and by a guide prepared by the Department of Trade and Industry.[45] Summaries of UK fire tests are given in Table 3-3 (The column “Failure Criteria Waived” refers to sections of BS 5852). In addition to seating goods, the Regulations also apply to beds, sofabeds, nursery and garden furniture and children’s beds. The Regulations also apply to mattress padding materials, to loose cushions and pillows, and to re-upholstery services. The Regulations do not apply to export furniture.

Table 3-3. UK Furniture and Furnishings Regulation Test Requirements A: Filling Materials—All Tested With Specified FR Polyester Fabric Filling

Standard Test

Ignition Source

Failure Criteria waived

Additional Criteria

Polyurethane foam

BS 5852/2

IS5

Mass loss < 60 g See note 1

IS2

4.1e, 4.1f, 4.2f 4.1e, 4.1f, 4.2f None 4.1e, 4.1f, 4.2f None

Polyurethane foam crumb Rubber latex Non-foam filling singly Composite fillings for other than mattresses, bed bases, cushions and pillows Composite fillings for mattresses and bed bases after removal of outer covering fabric

BS5852/2

IS2

BS 5852/2 BS 5852/2

IS2 IS2

BS 5852/2

BS 6807

IS2

None

None

None None None

Note 1. Original PU foam blocks to meet test for PU foam Note 2. Pillows and cushions with primary covers and “solid” or loose fillings and tested as composites. See Table C: Final Composite Assemblies (below).

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Fire Behavior of Upholstered Furniture and Mattresses

Table 3-3. (Cont’d.) B: Fabrics Filling

Standard Test

Ignition Test Source Modification

Failure Criteria Waived

Additional Criteria

Cover fabric

BS 5852/1

1

A, B, D

None

None

Loose covers

BS 5852/1

1

A, B, D

None

None

Stretch covers

BS 5852/2

5

C

Interliners

BS 5852/2

5

B, D, E

4.1e, 4.1f, Mass loss 4.2f < 60 g None

None

A: Except for fabrics containing more than 75% by weight of cotton, flax, viscose, modal, silk, or wool when used with an interliner. B: With non-FR PU foam, Type B hardness grade 130, 20–22 kg/m3. C: With PU foam, 24–26 kg/m3 conforming to BS 5852/2 Ignition Source 5, mass loss < 60 g. D: With water soak for FR treated fabrics. E: Covered with FR polyester fabric.

C: Final Composite Assemblies Final Composite Assembly

Standard Test

Ignition Source Failure Criteria Wavied

Additional Criteria

Upholstered furniture

BS 5852/1

Cigarette

None

Mattresses1

BS 68071

None

Pillows and Cushions2 with primary cover and non-loose fillings Pillows and Cushions2,3 with primary cover and loose fillings

BS 5852/2

Cigarette, and cigarette covered with noncombustible insulation 2

Water soak for FR treated fabrics None

BS 5852/2

2

4.1e, 4.1f, 4.2f 4.1e, 4.1f, 4.2f

None

None

1. Not part of Consumer Protection Act but applied by UK industry as a voluntary code of practice. This will be included in the relevant British Standard and used to define “fitness for purpose.” 2. Cushions are covered by the specified FR polyester fabrics. 3. For loose fillings, the test rig is lined with the specified FR polyester fabric.

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111

Several papers described the background for the UK regulations and their consequences from various points of view.[49][50][235] They originated from the concern by the British fire services about rapidly developing fires in polyurethane foam containing furniture, compared to older materials such as cellulosic battings and horsehair.[52] The development of combustion modified, high resiliency polyurethane (CMHR), containing melamine or exfoliated graphite made the rather stringent institutional regulations for polyurethane foam slabs or cushions technologically practicable for many constructions even without the use of interliners. Principle: The Regulations cover a component bench-scale test: fabrics are tested over standard paddings, while paddings are tested under a standard fabric. If seat, back, and arm constructions are not identical, then individual, separate tests are required. The successor standards require actual fabric/padding arrangements. Test Apparatus: The test rig is a medium-scale mock-up, representing a 2-cushion simulation on a steel frame, as described under cigarette ignition tests, and shown previously in Fig. 3-4. Details of mock-up preparation, etc. are the same for the flame ignition as the cigarette tests, which were described above, with exception of a larger back cushion for flame ignition testing. A. Regulations for Institutional Furniture Fabrics and Interliners: Specimens: Fabrics are mounted over a standard polyurethane foam, as described in BS 3379 (Type B, hardness grade 130, density of 20– 22 kg m-3). Fabrics which are visible must undergo a water wash, those which are on underside of cushions, etc., do not. Interliners are mounted between the standard fabric and the standard foam. Ignition Source: For cover fabric/standard foam assemblies, gas ignition Source 1 which simulates a match, is used; for cover fabric/ interliner/standard foam assemblies, Wood Crib 5. Ignition Source Location: At the seat/back juncture, at least 100 mm from an edge, but not necessarily at the center (allows for multiple testing).

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Criteria for Passing: The flame front must not reach the lower face, or either of the edges. If this is not met, a qualified interliner or a more effective FR padding must be used. Padding: Material Requirements: The test requires a back cushion 450 × 450 × 75 mm thick and a seat cushion 450 × 300 × 75 mm thick. The specimen is covered with a prescribed standard knit fabric, FR polyester, 220 g m-2. Ignition Source: The ignition source specifications are discussed in detail in Ch. 4. The lowest burner exposure is intended to represent the heat output of a burning wooden match (this requirement must be passed by all furniture, including residential furniture; the other ignition sources can be used for public occupancy furniture, the choice depending on occupancy risk). The following ignition sources are prescribed for institutional furniture padding:[46] • For polyurethane slabs: Wood Crib 5 • For latex foams, polyurethane crumbs, fiber and other padding (filling) components: Gas Burner 2 The following ignition sources are prescribed for institutional furniture: • Low risk: cigarette and Burner 1 • Medium risk: cigarette and Crib 5 • High risk: cigarette and Crib 7 Ignition Source Location: As for fabrics Criteria for Passing: • For polyurethane foam (slab or crumb) specimens: flaming for not more than 600 s after the ignition of the crib • For polyurethane slab foam specimens, also: specimen mass loss ≤ 60 g • For latex foam specimens and fiber filling specimens: flaming for not more than 120 s after removal of the burner

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B. Regulations for Both Residential and Institutional Furniture The previously discussed cigarette ignition and the simulated match test portions of BS 5852, Part 1 are prescribed.[46] Specimen Size: Back cushion is 300 × 450 × 75 mm, otherwise as in A. The padding and cover fabric are the same as in the actual furniture. Ignition Source: Cigarettes and Gas Burner 1. Ignition Source Location: Along the seat/back juncture, no less than 50 mm from either edge. Criteria for Passing: When the cover fabric is tested, the flame front must not reach the lower face, or either of the edges. If this is not met, a qualified interliner must be used. (The interliner test uses Crib 5 and prescribes both a standard cover fabric and a standard foam, as discussed above). For Both Parts A and B: Advantages: Easy tests to conduct, low cost; reasonable pass/fail test for ignitability. Limitations: Various padding materials are not held to the same requirement; specifically, latex foam is tested to much weaker requirements than polyurethane foam. For Sec. A only: it is a component test, rather than composite test. There is confusion with the Crown Suppliers standards discussed below:[48] material combinations which may pass in these tests may fail BS 5852 and vice versa, presumably because of differences in fabric tension, specimen configuration, etc. The UK Regulations affected the market by causing major material displacements. For example, ordinary foam in many composites was replaced by CMHR or interliners were required; for polyester batting, resin binding was replaced completely by thermal bonding; water soak for fabrics required different, permanent FR treatments. However, the UK industry has successfully handled these product dislocations, with modest-to-nil cost increases. Status: The Regulations came into force on 1 March 1989 as regards the flammability of padding materials, and other parts were phased in up to 1993.

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Similar Tests: Nordtest[236] is based on BS 5852. Notes: BS 7176[572] recognizes that there are no legal requirements for contact and office furniture but was offered to simplify compliance with statutory requirements. It includes the provisions for ignition sources for furniture for occupancies with varying hazard classification discussed in Sec. 3.1.4. It specifies a drycleaning procedure where applicable. It requires that each composite be tested every 2500 units, or once a month, and after any major change construction. It permits “Predictive Testing:” testing of the fabric with a “relevant standard filling,” one which can be safely assumed to have lower ignition resistance than the filling used in the proposed item. BS 6807, UK MATTRESS TEST Designation: British Standard Methods of Test for Assessment of the Ignitability of Mattresses, Divans, and Bed Bases with Primary and Secondary Ignition Sources.[47] Principle: This is either a bench-scale test of mock-ups, or a test for full size items, including mattress, divans and bed bases, with three options: 1. Testing with primary ignition sources—cigarettes and BS 5852 Burners 1, 2, and 3, and Cribs 6 and 7. 2. Testing with known bed covers. 3. Testing with ignition sources simulating unknown bed covers. This test has been upgraded and, in part, incorporated into the newer tests, BS EN 597 and BS 7177 for mattresses,[565][566] and BS 7175 for bedding.[567] Some parts are similar to the BS 5852 and DOE specifications. Test Apparatus: Specimens are tested on top of a 380 mm high, 450 × 450 mm platform formed by wires, spaced 50 mm apart in one and 100 mm apart in the other direction. Specimens overhang the platform on one side by 125 mm. Specimens: 450 × 350 mm, representative of the mattress to be evaluated in fabric tension, material arrangement, edge finishing, tufting, quilting, (for divans and bed bases, spring or board arrangements are included). Full size items.

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For secondary ignition source testing: nominal mattress width 1 m; actual thickness; mock-ups or full size items plus pillows and tucked in bed covers (Sec. 3 of BS 6807). Ignition Sources: Primary ignition sources: cigarettes and the flame ignition sources of BS 5852 applied to the overhang of the specimen; Secondary ignition sources: for actual pillows and bed covers, or simulated secondary ignition sources: cigarettes alone or covered by non-smoldering glass fiber insulating batting or, more severely, smoldering cotton wool (similar to US surgical cotton); or BS 5852 Burner 1; To simulate unknown bedclothes: cigarette, alone or covered by nonsmoldering or smoldering insulation, or BS 5852 Burner 1. Ignition Source Location: Cigarettes: on flat surface at least 50 mm from edge; Flames: either on top or on bottom of the overhang, at distances from the top of the burner of 5, 10, and 15 mm for the three gas flames, and of 20, 30, 60, and 100 mm from the top of the crib for Cribs 4 to 7. The same distances apply to bottom testing of divans and bed bases. For tests including bedclothes, the ignition source is placed at the junction of the pillow and folded back bed cover on top or below the overhanging bed cover. External Heating Source: None except secondary ignition sources discussed above. Measurements To Be Reported: Similar to BS 5852 Criteria for Passing: See Sec. 3.1.4. requirements for BS 7177 Advantages: Procedure covers more situations than most tests. NT FIRE 037, BEDDING COMPONENT: IGNITABILITY NT Fire 037[237] has quite different wording but is technically similar to BS 6807.[47] NT Fire 037 also applies to pillows and requires the recording of the cigarette smoldering rate in air. Criteria for Ignitability: Detectable amounts smoke, heat, or glowing after one hour; escalating combustion which makes test continuation unsafe; consummation of specimen by smoldering within an hour; smoldering to either side or through the full thickness.

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Criteria for Quilts, Blankets, Thin Mattresses: Flaming due to cigarette ignition; flaming for more than 150 s after flame removal; consumption of specimen in 150 s; escalating combustion; burning to either side of specimen. UK CROWN SUPPLIERS (DOE/PSA) TESTS The UK Department of the Environment/Property Services Agency (DOE/PSA), now called Crown Suppliers, developed specifications for furniture in government facilities.[48] These differ in many details from BS 5852; somewhat different test arrangements are specified and cigarettes and a series of flame ignition sources, including matches, gas burners, and wood cribs are used. Samples pass the tests if all flaming, smoldering, and smoking has ceased 2 minutes after the ignition source has stopped burning, and it is judged that no further combustion will take place. If two tested products give otherwise similar results, the one producing less smoke is to be chosen. For fullscale tests, ignition sources are placed on top of fully made up beds and on uncovered mattresses and in the corners formed by the seat, back, and side cushions of upholstered furniture. Gas burners are also applied to the front vertical surface, as well as the bottom, of seat cushions. Interliners are tested while mounted over a 300 × 300 × 75 mm foam block. Components can be screened first but must also be tested in assembled mock-up or product form. Another difference is the use of horizontal specimens for cigarette ignition, and vertical specimens (not the juncture of horizontal and vertical cushions) with the ignition source below the bottom edge of the cushion for flame ignition. There are several Crown Suppliers Specifications for mattresses. For example, DOE/TCS/FR 5 uses the actual mattresses, placed on a simulated bedstead. Bedding assemblies are also tested in various configurations in full-scale. As mentioned earlier, an original feature of the specifications is that bedding is loosened by pushing a block with a 200 × 400 mm cross section between the sheets before testing, to simulate a vacated bed. DOE/TCS/FTS 15 prescribes simulating vandalism by cutting of the fabric/padding specimens; mattresses are exposed to the No. 7 wood crib, and must burn less than 13 minutes and have weight loss of less than 8% over 45 minutes.

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Other Vandalism Tests: ASTM F 1550M addresses vandalism of upholstered items.[238] It involves Cone Calorimeter testing with the specimens slashed along the two diagonals. Similarly, Australia considered testing of slashed upholstered specimens.[174] CALIFORNIA TECHNICAL BULLETIN 117 Designation: Requirements, Test Procedure and Apparatus for Testing the Flame Retardance of Resilient Filling Materials Used in Upholstered Furniture (Technical Bulletin 117), Bureau of Home Furnishings, State of California, North Highlands, CA.[29][213] The cigarette ignition part of this standard has been discussed earlier. Principle: A series of bench-scale tests conducted on components, not on composites. Various methods are prescribed for foam and other padding materials such as shredded foam, cotton batting, etc. Note: Materials are tested before and after aging. After-flame and afterglow time include ablated material. A. Foams Test Apparatus: Test cabinet and ignition source according to Federal Test Method 5903.[239] Specimen: Foam specimen, 305 × 76 × 13 mm thick, held vertically restrained by a metal frame. Ignition Source: A modified Bunsen burner, applied for 12 s. Ignition Source Location: 19 mm below the bottom of the specimen. Measurements and Criteria for Passing: • Average char length for three specimens ≤ 152 mm, maximum char length ≤ 203 mm. • Average after-flame for three specimens ≤ 5 s, maximum after-flame ≤ 10 s. • Average afterglow for three specimens ≤ 15 s. B. Shredded Resilient Cellular Materials, (i.e., shredded foam) Specimen: A cushion, 320 × 320 mm, covered by a FR ticking fabric. Foam must pass requirements of A, above, or be treated after shredding.

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Ignition Source Location: 193 mm below the horizontal cushion. Measurements and Criteria: Weight loss not exceeding 5%. C. Expanded Polystyrene Beads Test Apparatus: Convection air circulating oven at 95°C. Specimen: Beads in a 193 × 193 × 76 mm wire mesh basket. Ignition Source: Methenamine reagent tablets No 1588, manufactured by Eli Lilly, placed on top of beads and ignited. Measurement and Criteria: Weight loss shall not exceed 5%. D. Non-Man-Made Fiber Filling Materials, e.g., Cotton, Hair, etc. And Batting Containing More Than 60% Non-Man-Made Fibers Specimens: 305 × 76 × 25 (or thickness as used), not aged, vertical, no holder. Measurements and Criteria for Passing: See A. E. Man-Made Fiber Filling Materials Specimen: 151 × 76 mm, thickness as in use, in a holder at 45°. Ignition Source and Location: Apparatus and burner of CFR 1610, a fabric ignitability test,[240] is used: 16 mm flame, applied from above near the lower specimen edge for 5 seconds. Measurements and Criteria for Passing: Flame spread time: average >10 s, minimum >7 seconds. Advantages: Easy to run, inexpensive tests, designed to remove the most hazardous materials from the market. Limitations: Small-flame ignition, component test only; the vertical test gives an undesirable advantage to materials which melt faster than they burn; test may be passed by PU foams containing only a small amount of FR agent. Foams may pass this test method but, with larger fire exposures, perform no better than untreated foams (see Ch. 6). Status: Mandatory use within State of California for all padding used in upholstered furniture (and mattress) trade. Regulation aimed at the residential occupancy; TB 133 is aimed at high-risk occupancies.

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F. Fabrics Fabrics are required to meet the Federal minimum standard for flammability of apparel fabrics, CS 191-53.[240] Advantages: No actual testing is required, since conventional fabrics suitable for use in upholstering furniture have not been found to fail this test (only sheer, ultra-lightweight fabrics or fuzzy fabrics generally have problems in passing this test). Disadvantages: Small flame ignition behavior of an upholstery system is dominated by the performance of its outer layer, the fabric. If controls are not established on the performance of fabrics, there is not much possibility of achieving significant improvements to the smallflame ignitability of actual upholstery systems. Note: In late 1999 BHFTI announced plans to make substantive revisions to TB 117. The new version is not expected to be available until 2001. The BUSINESS AND INSTITUTIONAL FURNITURE MANUFACTURERS ASSOCIATION (BIFMA) STANDARD Designation: The Business and Institutional Manufacturer’s Association First Generation Voluntary Upholstered Furniture Flammability Standard for Business and Institutional Markets, BIFMA, Grand Rapids, MI.[23] For flame ignition, this standard is quite similar to TB 117, above. Its cigarette ignition part has been discussed earlier. BIFMA will accept TB 133 results. CONE CALORIMETER Designations: ASTM E 1474* , Determining the HRR of Upholstered Furniture and Mattress Components or Composites Using a Bench Scale Oxygen Consumption Calorimeter.[39]

*

Note that the original edition of this standard specified a rudimentary specimen preparation technique which was found not to be adequate in the course of the CBUF study. The standard was subsequently revised to incorporate the CBUF preparation steps.

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NFPA 264A, Standard Method of Test for HRRs for Upholstered Furniture Components or Composites and Mattresses Using an Oxygen Consumption Calorimeter.[40] ISO 5660 Fire Tests Reaction to Fire Rate of Heat Release from Building Products (Cone Calorimeter Method).[41] Principle: These standard methods describe applications of the Cone Calorimeter to the measurement of the HRR and other fire properties of furniture composites. Test Apparatus: The Cone Calorimeter (Fig. 3-5) has a cone shaped heater which provides uniform and constant radiant fluxes to horizontal specimens; a spark is provided for pilot ignition; and the HRR is measured by oxygen consumption.

Figure 3-5. Schematic of Cone calorimeter.

Specimen: A furniture composite comprising cover fabric, interliner (if any), and padding. The overall size is 100 × 100 × 50 mm thick. Fabric (and interliner) also cover sides of specimen. The specimen is wrapped completely in aluminum foil except for the exposed upper

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surface. The aluminum foil forms a pan which retains the melted fabric and foam during the test. The foil wrapped specimen is set on the standard specimen holder for the Cone Calorimeter. The foam is actually cut to 102.5 × 102.5 by 50 mm but it is compressed to 100 × 100 × 50 mm by the fabric cover in order to provide some tension on the fabric at the very beginning of the test. The currently used specimen preparation procedure was developed during the CBUF program [Ref. 7, Appendix 6]. A special CBUF report[241] and a 1988 user’s guide for the Cone Calorimeter[242] provide basic instructions. Ignition Source: Electric spark. Ignition Source Location: 12 mm above center of specimen. External Heating: Uniform irradiance of 35 kW m-2; other irradiances can be chosen for special purposes. Measurements To Be Reported: • Curve of HRR versus time (kW m-2) • Time to ignition(s) • Effective heat of combustion (MJ kg-1) • Average HRR for 180 s (or other periods) after ignition (kW m-2) • Peak HRR (kW m-2) • Total heat release (kJ m-2) • Mass loss • Smoke yield (m2 kg-1) • Yields of CO, CO2, HCl, HBr, HCN, NOx, (kg/kg) (with optional equipment) Criteria for Passing: None. Note: The test was designed primarily for obtaining material fire properties, not for pass/fail determinations. Advantages: See discussion in Ch. 2; • Gives data on actual end-use composites which can be used directly • Unambiguous data in engineering units usable in modeling • No reliance on subjective observation

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• Is readily supplemented with instrumentation for gas analysis

additional

Limitations: Specimen requires careful preparation. This has been addressed in detail in the CBUF testing instructions.[7][241] The fabric to foam ratio is not identical to that for full-size chair cushions. However the contribution to the HRR from the material at the sides has minimal effect on the peak HRR values. Unlike heavy-object ignition sources, the heat source does not follow a melting specimen. The increase in heater-specimen distance due to melting may cause some anomalies; Vanspeybroeck et al. made quantitative measurements of this effect.[243] Status: Accepted by numerous organizations worldwide; used by CBUF in the furniture fire models. Notes: The cone shaped heater, similar but not identical to the one in ISO 5657[244] was especially designed to give even heat flux distribution across the specimen face. The CBUF studies confirmed the earlier NIST findings that no edge frame should to be used for testing of upholstered item composites in the Cone Calorimeter. More detailed discussions of the general issue of edge conditions can be found in Ref. 245. Issues of using Cone Calorimeter data for fire modeling are presented in Ch. 5. The Cone Calorimeter is one of the few furniture fire tests for which extensive round robin data are available[246] demonstrating good repeatability and reproducibility of the method. PORT AUTHORITY OF NEW YORK AND NEW JERSEY Designation: The Port Authority of New York and New Jersey, Specifications Governing the Flammability of Upholstered Materials and Plastic Furniture[247] The Port Authority of New York and New Jersey sets flammability standards for many public buildings in its area. Upholstery materials, including covering, lining, webbing, cushioning or padding, and selfsupporting (rigid) materials are tested by means of the vertical Bunsen burner test 5903.[239] Char length must not exceed 153 mm; After-

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flame must be less than 15 seconds for the specimen and 5 seconds for ablated drips. Padding materials thicker than 12 mm are tested by ASTM E 162, the radiant panel test.[104] Materials with flame propagation indices under 100 are permitted. Materials with higher indices may be covered with self-extinguishing materials, as determined by the 5903 test, if the cover/padding assembly has a flame propagation index of less than 100 in ASTM E 162. Full-Scale Fire Tests The advantage of full-scale tests is realism, and in a suitably instrumented apparatus collection of large amounts of information (e.g., ignitability, heat, smoke, and toxic product release, information on extinguishing characteristics). The disadvantage is, of course, cost, and that the behavior seen in any one test is only applicable to one fire scenario. It should also be again noted that with the exception of the Boston Fire Department procedure, the ignition source is placed at the seat/back junction, and other locations, which often may contain different materials, are not tested. BOSTON FIRE DEPARTMENT PROCEDURE BFD IX-10 Designation: Procedure for Approval of Upholstered Furniture: BFD IX-10. Boston Fire Department, Boston MA.[248] Principle: This is a full-scale room test. Test Apparatus: Burn room, no specific size, but at least 3.7 × 2.4 × 2.4 m high; thermocouple (unspecified gauge) over the center of the chair, 2.4 m above the floor. (This could make it exactly on the ceiling; it is presumed the actual procedure used involves placing it slightly below the ceiling.) Specimen: The actual full-scale test article, or optionally a 2-cushion (seat and back only) mock-up. In the latter case, the cushions are to be 460 × 460 × 100 mm thick. Ignition Source: Brown paper bag, 180 × 280 × 460 mm; weighing 48 g. The bag is filled with four crumpled double newspaper sheets, each sheet weighing 18.5 g. The total ignition source mass is 122 g. The source, by itself, burns for about 2 minutes.

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Ignition Source Location: On the seat, in contact with the chair back. The large face dimension of bag is placed against the seat. Measurements To Be Reported: • Time when flaming ceases • Maximum temperature reached • Whether flaming continues after bag is burned out Criteria for Passing: • Significant flaming must not continue after bag is burned out • Flaming drops of molten material must not occur • The specimen must not burn through to the underneath face, and at least 12.7 mm thickness must remain everywhere • Excessive smoke (based on visual observation) does not occur • Maximum time from ignition to flameout does not exceed 480 s • Better specimens flameout in about 180 s • Specimen mass loss does not exceed 10% Note 1: In addition to the performance requirements above, the individual components must also be accepted. For fabrics, various qualifying tests may be used. Padding materials are normally qualified underneath modacrylic fabric; acceptable ones have included certain low smoke neoprenes, FR polyurethanes, plain polyurethanes with FR interliners, FR treated cotton battings, or polyester fiber fill. The FR and the interliners must be selected from a list of pre-qualified products. Melamine-treated polyurethanes are specifically restricted from being used with PVC coverings, since the Boston Fire Department observed such combinations to be quite flammable. (This problem is addressed in Ch. 6.) In addition, the Boston Fire Department may require that ASTM tests E 162, radiant panel flame spread,[104] D 2683, limiting oxygen index, [249] or E 662, smoke chamber test[171] results be presented. Note 2: The Boston Fire Department now also accepts passing results from California TB 133 testing as a substitute for the BFD IX-10 test.

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Advantages: Realism, due to use of full-scale test article. By requiring tests of all components (albeit, tests which use different ignition source types and intensities) the method addresses the hazards due to material combinations other than those present at the back/seat juncture. Limitations: Only total mass lost and maximum temperature are measured. Crumpled newspaper ignition sources have difficulties in reproducibility. Visual estimates of smoke production are not well correlated to quantitative measures. The method, as described, would be difficult to reproduce in other laboratories. Status: Method was originally developed from a procedure used by E.I. duPont de Nemours & Co. to test furniture in the 1970s. Mandatory in the City of Boston, it is also used extensively by surrounding jurisdictions. The test procedure is not intended to be used for the evaluation of residential furniture. NORDTEST NT FIRE 032 Designation: Furniture Calorimeter - NT Fire 032: Burning Behavior - Full Scale Test.[62] If chemical gas analysis for toxicity is done, this follows the standard NT Fire 047: Combustible Products: Smoke Gas Concentrations, continuous FTIR Analysis,[250] NORDTEST, Espoo, Finland. Principle: This is a furniture calorimeter test, with the actual fullscale article being burned in an open environment. A schematic drawing of a furniture calorimeter is shown in Fig. 3-6. Background: This method and its relationship to other tests and reallife fires are discussed in Ref. 7. Test Apparatus: A furniture calorimeter; Fig. 3-6 is a schematic drawing. Specimen: Full-size, end-use article, or optionally a full-size steelframed sofa or chair mock-up.

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Figure 3-6. Schematic drawing of NORDTEST furniture calorimeter.

Ignition Source: BS 5872 Crib 7; this crib provides about 6 to 7 kW HRR and burns for about 350 s. Ignition Source Location: On seat cushion, at juncture of side arm and back cushion. Measurements to be Reported: • Mass burning rate vs time (kg/s) • Total HRR vs time (kW) • CO and CO2 production rates vs time (m3/s at standard temperature and pressure) • Mass flow in the exhaust duct vs time (kg/s)

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• Production rate of light obscuring smoke vs time (obm3/s), where “ob” is a smoke unit, defined as “obscura” = (10/L)log10(Io/I), and where L = path length (m) • Results of FTIR tests for toxicity evaluation • Description of the fire development (photographs) Criteria for Passing: None. Advantages: Realism, due to use of full-scale test article. Status: Specified by CBUF as the standard reference test for upholstered furniture.[7] Note, however, that in CBUF work the wood crib source has been replaced by a 30 kW burner. It is anticipated that a future edition of NT FIRE 032 will also incorporate this change. Note: The CBUF report gives a detailed procedure for the use of the furniture calorimeter. (Ref. 7; Appendices 5 and 7.) This includes description of the 30 kW gas burner ignition source and of smoke collection procedures based on existing standards, reproducibility and repeatability studies, etc. FIRE RESEARCH STATION FURNITURE CALORIMETER TEST A number of furniture flammability studies were done by FRS using a unique natural-convection furniture calorimeter. This apparatus did not have an exhaust fan to provide the draw, but used the stack effect in a vertical duct instead.[251] The unit eventually was concluded not to have adequate performance, so FRS replaced it with a unit based directly on NORDTEST NT FIRE 032. CALIFORNIA TECHNICAL BULLETIN 133 Designation: Flammability Test Procedure for Seating Furniture for Use in Public Occupancies, State of California, Department of Home Furnishings and Thermal Insulation, North Highlands, CA.[30] Similar Tests: ASTM E 1537, Test Method for Fire Testing of Real Scale Upholstered Furniture.[32] BIFMA and the Boston Fire Department allow substitution of this test for their own.

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Principle: This is a room fire test, using numerous single-point measurements in the room and/or heat release measurements in the hood for evaluation. Test Apparatus: California burn room (Fig. 3-7), 3.7 × 3.1 × 2.4 m high, with doorway 0.97 × 2.06 m high. In a revised edition, the proposed ASTM corner test room[252] which measures 3.6 × 2.4 × 2.4 m high, was also allowed as acceptable. (Results in the two rooms were comparable for a series of chairs.[35][36] Figure 3-8 shows the mock-up frame; actual furniture can also be used. Also introduced was an option permitting testing in an open furniture calorimeter. Specimen: Full-scale end-use specimen, or optionally a full-scale mock-up. The mock-up frame shown in Fig. 3-8 is 0.91 m long and the back can be tilted up to 45 degrees back from vertical. The specimen is placed in the corner of the room, within 254 mm of the walls. Ignition Source: 1. The currently-used square gas burner, based on the British Fire Research Station T-burner was designed to simulate the original crumpled newspaper source (Fig. 3-9), with a propane flow adjusted to produce 18 kW for 90 s. 2. The original paper ignition source (Fig. 3-10) can still be used for screening: five double sheets of loosely wadded newspaper (total = 90 g) contained in a box made of galvanized sheet steel and wire mesh, 250 × 250 × 250 mm. Three different variants of the box are provided, one for specimens that have a crevice at the seat/back juncture, one for specimens which do not, and a third one for specimens that, instead, have a gap in that area. This source provides about 18 kW during the first 80 s of the test. Ignition Source Location: Figure 3-9 shows the mock-up frame arrangement and ignition source placement. For specimens less than 1.0 m long, the ignition source is placed centrally at the seat/back juncture. For longer specimens, at seat/back juncture and 127 mm away from the left side arm.

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Figure 3-7. Layout of TB 133 test room.

Figure 3-8. Mock-up frame for TB 133.

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Figure 3-9. Square ring gas burner for TB 133 and CBUF.

Figure 3-10. Mock-up configuration and placement of TB 133 paper ignitor.

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Criteria for Passing: For room test using oxygen consumption calorimetry: • HRR of < 80 kW instead of temperature measurement • Total heat release of < 25 MJ in the first 600 s of the test • Less than 75% opacity at 125 mm above the floor • CO concentration of < 1000 ppm for 300 s For room tests without oxygen consumption calorimetry equipment: • Temperature rise less than 111°C at thermocouple 25 mm below the ceiling • Temperature rise less than 28°C at thermocouple 90 mm in front of the ignition source and 121 mm below the ceiling • Smoke obscuration and CO concentrations as above • Mass loss less than 1.35 kg by the end of the test For furniture calorimeter option: • Peak HRR less than 80 kW • Total heat release of less than 25 MJ in the first 600 s of the test Advantages: • Realism due to use of full-scale test article • Appropriate hazard components are addressed Note: This test is widely accepted as a regulatory standard in the US, as discussed below. Limitations: When the test is conducted in the room, there are criteria for smoke and CO concentrations which are obtained at locations and limits which are somewhat arbitrarily chosen. For example, CO is measured near the ceiling and is not relevant to the occupants that are located fully within the lower layer as they would be for a fire whose peak HRR is less than 80 kW according to the HRR criterion. The smoke obscuration in the lower layer where the meter is located is not vitally important if the HRR is less than 80 kW since the occupants are not being threatened by thermal radiation, high air temperatures or high toxic gas concentrations. These limitations are not present if the furniture calorimeter option is chosen.

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Specimen testing using the mock-up variant shows repeatability problems due to a tendency in this arrangement for the back cushion to topple over during burning. This type of behavior is rarely seen with real chairs. Note: Grand et al. reported observations during 700 California TB 133 tests in 1992 as follows:[253][254] • The ignition source provides about 18 kW during the first 80 s. This is included in the peak HRR if it occurs during that time; if not, it does not affect passing or not passing. Thus, if a chair has a peak HRR of 65 kW early in the test, it fails; if it produces this rate later, it passes (but also may present a somewhat lower hazard condition). • The test result can be very different if the ignition source were not on the inside of the chair but on the outside, as discussed earlier. • Comparing data taken in the room and in the exhaust duct: at the time of this writing, both methods were permissible but temperatures in the room and HRR in the duct did not necessarily correspond. (In the NIST/ BHFTI study, there was good correlation between these results.[35][36]) However, gas analyses in these two locations tended to parallel each other. After conducting about 700 tests, Grand concluded that values obtained in the duct had more validity, repeatability, and utility than those taken in the room. • In many cases, there are several peak HRR peaks, often indicating separate burning of the fabric, then the padding, and finally, the frame. • Smoke criterion: items which only smolder and thus produce only cool smoke which does not rise often fail only because of the smoke criterion measured at 4 feet. However, in view of the fact that many victims die in bed of smoke inhalation, and such low smoke interferes with escape attempts even if the person crawls, this seems a reasonable criterion.

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With respect to the last observation, it should be noted that the smoke criterion based on the optical transmission is only related to the ability to escape. How toxic that smoke is and how long a person could survive in it would have to be determined by gas analysis or by bioassay with animals. Smoldering fires are dangerous if they occur in a closed room and the concentration of toxic gases is allowed to build up and the concentration of oxygen to drop beyond survival limits. Status: It has been mandatory in California for certain public occupancy categories since September 1989. A method very similar to TB 133 has been proposed by the International Association of Fire Fighters for adoption by the individual States and other jurisdictions. Some have already done so, others are in the process. Going to the individual states seemed to be indicated because the of the unfriendly environment for regulations at the federal level in the 1980s and 1990s, but presents difficulties because each legislature has to be convinced to accept the same text. The TB 133 concept is also being promoted by the National Association of Fire Marshals, the American Furniture Manufacturers’ Association, the Business and Institutional Furniture Manufacturers’ Association, the Western Furniture Manufacturer’s Association, and others. TB 133 is intended to be applicable to high risk occupancies, defined as any building or facility which is to be occupied by 50 or more persons and are designated as high risk by the California State Fire Marshal. Such designation criteria shall be established by the State Fire Marshal within six months of enactment of the Act. Such facilities shall include especially, but are not limited to, jails, prisons, detention centers, nursing care facilities, retirement homes, health care facilities, public auditoriums, condominiums, hotels, and motels. TB 133 tests can be performed by about a dozen laboratories in the US. History of TB 133 Because of its growing importance, the process of the development of TB 133 seems of interest. The philosophy underlying it, its history, and its relationship to other furniture tests is described in Refs. 255

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and 256. Various efforts to correlate its results with bench scale test results are described in Ch. 5. California started to address high-risk occupancy fire protection by developing a mattress standard, TB 121.[257] Its Bureau of Home Furnishings started development of a standard for furniture in public occupancies in 1982. The first version was published in 1984 as a voluntary standard. The California Bureau of Home Furnishings and Thermal Insulation (renamed when the agency took on thermal insulation responsibilities) has shown highly commendable willingness to technically improve its standards in response to new findings. Since its inception in 1982, TB 133 pass/fail criteria have been changed several times in response to new information. Most important, a heat release requirement now optionally replaces temperature measurements. The gas burner was substituted for the newspaper ignition source, but the newspaper source can be used for screening. Prior to that, the temperature test criterion was changed to specify a rise in room temperature, rather than an absolute temperature, which is important because such burn rooms are not climate controlled. The CO criterion was changed to state that CO levels should not continuously exceed 1000 ppm for more than a minute, rather than at any time during the test. In addition to full-scale furniture, mock-ups of upholstery in an adjustable steel frame were permitted. The weight loss criterion was changed from a percentage* to an absolute value, 1.35 kg (3 lbs). One of the smoke opacity measurements was dropped; the room used in the proposed ASTM[252] and ISO 9705 room corner tests[63] are permitted; and furniture calorimeter test results were considered acceptable since they do not appear to differ from the room results at and below the HRR pass/fail level of 80 kW. Another item of interest is a statement by a representative of the Fire Retardant Chemicals Association that it should be technically feasible, with proper choice of fabric/CMHR foam combination, to extend the TB 133 requirements to residential furniture.[258] The economic impact of such measures was not addressed.

*

We may observe that many test results are expressed in percentage weight loss, but clearly the absolute mass loss better represents the hazard of a fire; weight of furniture is greatly influenced by the frame.

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A study examining test results with the method established the reasons for 49 failures of furniture items, in descending order of frequency: CO concentration and temperature rise above the chair; weight loss; smoke density at 4 feet; temperature rise at 4 feet; and smoke density at floor level.[253] Twenty-nine items failed only one criterion, eleven items failed two criteria, and fourteen items failed four or more criteria. STACKING CHAIRS BHFTI has proposed a method for testing stacking chairs, because there had been several incidents of fires in these items, either stacked or spread out.[259] In their proposed test, the burner described in the mattress test TB 129 is used in front of a stack of 3 to 7 chairs, with 5 being the recommended number for the test. The effects of number of chairs in the stack, of time of gas flow, of interliners, for both upholstered and thinly upholstered chairs were investigated. As expected, stacks of chairs passing TB 133 singly generally did not pass in stacks, but unexpectedly, chairs which singly failed TB 133 (HRR of 133 kW at 6 minutes) took up to one hour to proceed to full burn. It appears that further development is needed before this standard can be promulgated. When such chairs have thermoplastic frames, the mode in which they collapse determines much of the outcome of the test. Since the number of chairs that can be tested is much lower than the number of chairs stacked in actual use, only a modeling procedure using the HRR results of one or a few tests could be expected to predict actual hazard. Following a limited amount of further development (mostly conducting a round-robin), ASTM issued the test as ASTM E 1822 in 1999.[569] CALIFORNIA TECHNICAL BULLETIN 129 - MATTRESSES Designation: Flammability Test Procedure for Mattresses for Use in Public Buildings, State of California, Department of Home Furnishings and Thermal Insulation, North Highlands, CA.[31] Similar Tests: ASTM E 1590, Test Method for Fire Testing of Real Scale Mattresses.[33]

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Fire Behavior of Upholstered Furniture and Mattresses

Principle: This is a room fire test somewhat similar to TB 133, using four test criteria. There are three test options in this draft, two utilizing the TB 133 room, and the third a furniture calorimeter. Procedures for testing mattresses with and without bedding, and bedding over an inert mattress, are provided. Test Apparatus: The TB 133 room is used in Options 1 and 2, with the mattress placed on a weighing platform in a corner so the mattress is between 100 and 250 mm from the walls, parallel to the longer wall not containing the doorway. In Option 3, in a furniture calorimeter, the mattress is placed on a metal bed frame, 500 mm high. Ignition Source and Location: A gas burner with a 12 l min-1 flow of propane at 101.3 kPa, positioned horizontally 25 mm from the side panel of the mattress. The ignition source is applied for 180 s. Procedure: The following procedure is suggested for component tests, for the purpose of substituting materials other than those tested: 1. Conduct full-scale fire test on original mattress or bedding system. 2. If results indicate compliance with criteria, conduct bench scale tests (NFPA 264A, Cone Calorimeter)[40] on combinations of materials as in full-scale test 3. Conduct bench-scale tests on substitute component material. 4. Compare peak and total heat release of the two benchscale tests. If the results for the substitute materials are lower than those of the mattress, a mattress made from the substitute materials can be expected to be in compliance in the full scale test. Criteria for Passing: • Weight loss of less than 1.36 kg in the first 10 minutes of the test • Maximum HRR of less than 100 kW (test has a time limit of 1 h) • Total heat release of <25 MJ in the first 10 minutes of the test

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These criteria are only applicable when a single mattress is tested. Smoke and CO criteria are being developed at the time of this writing. Advantages: Realism due to use of full-scale test article, with and without bedding. Offers an alternative to TB 121, for high-risk occupancies, below. Limitations: Bedding can make a considerable difference in the fire outcome;[162] this is not considered. TB 129 passes thermoplastic materials when they melt, ablate or shrink in a flame. When actual bedding is used, the fire can be propagated by the bedding and the specimen is unlikely to pass due to melting or shrinking. Status: Test designed for public occupancies. Comments: Work leading to TB 129 started in late 1988, and the standard was published in 1992. In 1997, results on 126 mattresses submitted to the California Bureau of Home Furnishings and Thermal Insulations were published.[587] It appears that ample technology exists to pass this standard: 100 (79%) of the mattresses passed. Fortyone mattresses had a peak HRR of less than 20 kW and 52 of less than 50 kW; these typically self-extinquished after removal of the ignition source. Eight specimens had peak HRR values between 50 and 100 kW and were nonpropagating; of those, seven passed the TB 129 requirements. Ten mattresses had peak HRR values of 101–150 kW and did not pass, but the authors still consider this in the range of nonpropagating fires. Fifteen mattresses exceeded 150 kW; two of them reached flashover conditions before 10 minutes. CALIFORNIA TECHNICAL BULLETIN 121 - MATTRESSES Designation: Flammability Test Procedure for Mattresses in High Risk Occupancies, California Bureau of Home Furnishings, N. Highlands, CA[257] This was the first of the three California institutional furniture item tests, a full-scale room test for high-risk occupancies (e.g., penal institutions). Its background is discussed in Refs. 260 and 261. Test Apparatus and Specimen: The mattress without bedding is placed on a steel support in the corner of the TB 133 test room. Ignition Source and Location: The ignition source is placed underneath the center of the mattress. A T shaped burner (see TB 129) can

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Fire Behavior of Upholstered Furniture and Mattresses

be used. Originally, a metal waste paper basket filled with 21 g of loosely wadded newspaper was used. Criteria for Passing: • Mass loss during the first 600 s of the test must be less than 10% of the original mass. • Thermocouple reading at the ceiling must be less than 260°C. • Peak CO readings (measurement scheme not described) must be less than < 1000 ppm at any point in the room at any time during the test. Advantages: While this test method does not use bedding, the fire location directly under the center of the item is realistic. Specimens which otherwise may be hazardous are unlikely to pass due to melting/ retreating out of the range of this ignition source. Limitations: Bedding is not used. THE BUSINESS AND INSTITUTIONAL MANUFACTURER’S ASSOCIATION (BIFMA) STANDARD This standard is quite similar to California TB 133; it also specifies cigarette and small flame ignition tests, as described earlier.[23] UNDERWRITERS LABORATORIES TEST UL 1056 Designation: Standard for Fire Test of Upholstered Furniture (UL 1056), Underwriters Laboratories Inc., Northbrook, IL.[262] Principle: This is a furniture calorimeter test, with the actual fullscale article being burned in an open environment. Test Apparatus: Furniture Calorimeter. A fan-driven exhaust is specified. Specimen: Full-size item, up to 1.22 m long. Ignition Source: Wood crib, 340 g. Crib is of setback design, having a 75 × 75 × 254 mm long bottom portion and a 75 × 75 × 127 mm long top portion. This crib burns at about 15 kW, with a burn time of about 180–210 s.

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Ignition Source Location: At the center of the seat/back cushion juncture, 25 mm from the back cushion. Number of Replicates Required: Three Measurements to be Reported: •

curve of HRR vs time (kW)

•

peak HRR (kW)

•

curve of mass loss rate vs time

•

total heat released for the first 300 s (MJ)

Criteria for Passing: Total heat released for the first 300 s < 25 MJ (83 kW average, as compared to TB 133 criterion of 80 kW peak HRR). Advantages: Realism, due to use of full-scale test article. Limitations: No gas and smoke criteria Status: Used for testing at UL. Passing specimens are qualified to be Classified Upholstered Furniture With Regard to Resistance to Rapid Heat Release Only. The test is intended for items used in hotels, public occupancies, and similar applications. DRAFT CPSC FLAMING-IGNITION TEST During 1994–1997, CPSC staff conducted extensive studies on the small-flame ignitability of upholstered seating furniture.[580] Based on extensive laboratory testing, they concluded that (1) the California TB 117 test, which exposes only components and not composites, did not give results predictive of real-furniture performance, and (2) that the British BS 5852 approach, where a fair-sized composite is subjected to test, holds more promise of giving results that do correlate to real furniture performance. Starting from this point, they then developed a draft test method. The test is in three parts. The first part is based on a mockup of the seat/back area, similar in concept to the BS 5852 mockups. The other two parts are unique—one describes testing of the dust cover and the other of the skirt. In the development process, however, work on skirt testing was discontinued on the basis that accidental ignitions of this area are relatively rare. Before the Congressional mandated suspension of work, test development had progressed to the point that a four-laboratory round-robin was conducted on the test method. If regulatory activities are resumed by CPSC on

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Fire Behavior of Upholstered Furniture and Mattresses

this topic, it is not clear what further changes might be made to the draft procedures. 3.2.4

Development of Full-scale HRR Measurement Techniques

The importance of the HRR as a dominant variable was discussed in Ch. 2; here we will discuss the history of its measurement. It was not generally measured until the 1970s, when early attempts were made to evaluate the HRR in most full-scale fire tests. Once it became clear that HRR measurements were needed, a suitable measurement method had to be found. The HRR of furniture in a room was first determined by measuring its mass loss rate and multiplying it by an estimated heat of combustion. But furniture contains more than one material burning at the same time with different heats of combustion; there is no way to know the burning fraction of each. Furthermore, the only measurement of heats of combustion were done in oxygen bomb calorimeters which yield the gross rate of combustion and assume complete combustion of the material. However, it is the net heat of combustion of the volatiles produced in the thermal decomposition of the furniture that is important in the room fire. Mass loss rate measurements are also subject to error due to buoyancy effects. A somewhat better way to measure the HRR in a room fire is to measure the sensible enthalpy of the fire gas outflow. A technique of this kind was tried by Fitzgerald,[263][264] who built a test room with a blower air supply and a ceiling exhaust duct. Thermocouples located in the exhaust duct give the primary indication of heat output. However, since a large amount of heat is lost to the room walls and ceiling, additional thermocouples were installed in these surfaces. These were used to provide an empirical correction for wall losses. This correction, even after calibration with a test gas, could only be very approximate since the fraction of heat lost to different surfaces depends on soot radiation, plume combustion, and other variables differing for different fuels. The inability to achieve a universal calibration is the most serious limitation of any such thermocouple measurement scheme. Furthermore, the amount of heat released within this calorimeter was limited to 680 kW by the air supply rate of 0.22 kg s-1. The pioneering unit designed by Fitzgerald was thus limited to HRR values much smaller than necessary to characterize

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common upholstered furniture items, the more hazardous of which can reach to 2~3 MW. As discussed in detail in Ch. 2, Huggett showed that the heats of combustion of most organic materials were similar, and that their HRR could be measured by the oxygen consumption during the fire.[115] The first investigator to measure HRR in a room fire using oxygen consumption was Sensenig in 1976.[265][266] Most of the work was done with quarter scale rooms but one full-scale room was included in the series. An exhaust duct was installed above the doorway just outside the room to collect all of the combustion gases. From the product of the volume flow rate in the exhaust duct and the drop in oxygen concentration, the HRR could be calculated. After Sensenig’s pioneering work, Fitzgerald added an oxygen probe to the exhaust duct of his room calorimeter and obtained reasonable agreement with the HRR calculated from the thermocouple measurements. But the presence of an enclosed chamber itself can be a limitation to obtaining characteristic HRRs for upholstered furniture. Since HRRs can, in general, be influenced by wall heating and re-radiation effects, air vitiation effects, and effects due to unsymmetrical air inflow patterns, these factors must be quantified or, alternatively, free-burn measurements can be sought. These effects of selected room enclosures have been quantified in a few experiments in Ref. 267, and the effect of position in the room in Ref. 153. Results on upholstered furniture items obtained in the furniture calorimeter, two room sizes, and in the Cone Calorimeter are shown in Refs. 35 and 36, and discussed further in Ch. 5. In experiments at the University of Ghent as part of the CBUF project, it was found that the HRR measurements in the furniture calorimeter were not affected by two enclosure walls. The furniture calorimeter could be operated near the corner of a large test bay without ventilation restriction effects. Consequently, the CBUF test protocol for the furniture calorimeter specifies that the environment around the burning item shall be a draft free area, with no more than two enclosing walls, no closer than 2 m from the outer edge of the smoke collection hood (Ref. 7, Appendix 7:3.1). To overcome these limitations due to room enclosures, the first freestanding furniture calorimeter was built at NBS by Babrauskas and coworkers.[268][269] The furniture is burned on a weighing platform under a large hood. The heat release measuring system is identical to that of the

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Fire Behavior of Upholstered Furniture and Mattresses

room fire test. There is sufficient clear area around the furniture calorimeter to provide an unrestricted air inflow and not permit heated surfaces that would radiate back to the furniture. Similar devices were subsequently implemented at FRS in the UK;[251] at SP in Sweden[270] where it led to Nordtest NT Fire 032; at Underwriters Laboratory;[262] and elsewhere. Factory Mutual Research Corporation developed a much larger calorimeter designed to measure heat release of materials in warehouses,[271] but this has not been reported to be used for any furniture testing. Full-scale tests in the furniture calorimeters are relatively labor intensive and costly. Thus, methods have been developed for several types of upholstered furniture items which, in many cases, predict furniture calorimeter or room fire results from Cone Calorimeter measurements, as discussed in Ch. 2 and 5. Once a basic correlation is established for a product class, bench-scale data can subsequently be used, which are both less costly and more reproducible. Full-scale testing then remains desirable only for those classes of articles where such a predictive correlation has not been established. This full-scale testing would be done in the furniture calorimeter. 3.2.5

Flame Spread - Standard Tests

Flame spread measurements were traditionally considered the appropriate characterization of post-ignition burning behavior, e.g., automotive fabrics,[66] building materials,[104] and apparel.[240] Today, it has been recognized that this does not adequately characterize flammability hazards, and heat release measurement methods have come to the forefront. The physics of flame spread over upholstered furniture is not yet fully quantified. In one study, mock-up tests indicated that flame spread rate is related to HRR during the early stages of the upholstered chair fire.[272] Initial flame spread was evaluated visually on the seat surface; these observations correlated with time to breakage of trip threads above the chair, as well as the HRR results. After that, flames from the seat obscured flame spread observations on the vertical surfaces. Most commonly, US standards and regulations for some transportation seats[273][274] refer to the ASTM E 162 flame spread test.[104] The specimen is held at an angle from vertical in this test so that melting materials ablate. A variant of this is the ASTM D 3675 test[275] designed for retaining foam plastics in the holder by the use of wire mesh; a slightly different radiant panel is also prescribed. Composite fabric/padding assemblies can be accommodated in this apparatus; nonetheless, most tests

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and requirements have been for padding alone. As with other measurements, the available flame spread research suggests that an end-use composite must be evaluated and that little meaning can be attached to flame spread measurements on individual components, especially subsurface components. From a hazard prediction view, it is not at all clear that any flame spread test is needed for furniture flammability assessment, since this aspect of performance will be subsumed into the HRR characterization. If one were designing a flame spread test for upholstered furniture (for research or model development, for example), it should possess certain desirable traits. It should have a provision for retaining composite specimens and preventing them from curling on the side during test. It should use a horizontal face-up orientation to enable melting and dripping materials to be tested, and there should be a linear ignition source at one end. To enable analysis with available theory, the specimen should be subjected to a uniform radiant heating, with a flux of up to about 10 kW m-2. An apparatus incorporating these features was, in fact, developed at NIST, but it saw only limited use (see Ch. 2).[106] Attempts have occasionally been made to gather flame spread data on the Ohio State University (OSU) HRR apparatus[118] and on the ISO ignitability apparatus.[244] Circularly spreading rates based on a center point ignition have been observed by exposing composites to a radiant heat source and igniting them with a methenamine pill.[276] There was a linear relationship between the irradiance and the flame spread. Paul compared distances burned on fabrics in a vertical and an horizontal flame spread test.[233] The latter test is used in the US for transportation seats;[67] it produced only no flame spread or 10 inch burning length results in this case. There was at best a rough agreement between the tests. In other experiments, he measured burn length and burn time on various foams; as expected, these properties did not rank the foams in the same manner. 3.2.6

Transportation Seating Tests and Regulations

Rail Vehicles. For US commuter and intercity rail transportation, cushions and mattresses must pass ASTM D 3675[275] (Is ≤ 25) and E 662[171] (Ds 1.5 ≤ 100) tests.[277] Seat upholstery, mattress ticking and covers must pass the FAR 25.853[66] vertical (char length ≤ 6 inches, flame time ≤ 10 seconds) and ASTM E 662 with the above requirements.

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Fire Behavior of Upholstered Furniture and Mattresses

Peacock et al. wrote an extensive report on the status of passenger rail transportation flammability in the US.[278] In the US, the responsibility for passenger safety is divided among three Federal organizations, which issued regulations and guidelines (Federal Railroad Administration, US Urban Mass Transportation Administration, and Amtrak).[274][279] Work on a proposed ASTM Hazard Assessment Standard for rail transportation was described in Ref. 280. Peacock et al. provided a new, critical look at railroad fire safety. They found that several studies indicated that there is a nearly random ability of current tests to predict actual fire behavior. They compared approaches used in the US, France, and Germany. (The US and French standards were also compared in Ref. 281; they share little in common.) They suggested that rail safety take the same path as many other branches of fire safety: to use measurements of HRR instead of flame spread rate to support fire hazard and risk assessment methods. A number of earlier studies are cited here because they provide insight into the problems encountered with transportation fire safety. Some were undertaken in the early 1980s to establish the need for improvement of railroad fire safety regulations, and to determine the path which such regulations should follow. Rakaczky has reviewed rail car flammability studies prior to 1980.[282] Hathaway surveyed a number of topics in this area, including a listing of fire development scenarios,[283] a comparison of regulations for different classes of transportation vehicles,[284] and a background for proposed Department of Transportation regulations.[285] A review of subway car fires in six US subway systems was published by the American Iron and Steel Institute.[286] Following the San Francisco underground rail (BART) fire of 1979, the general fire safety of existing subway systems was examined.[287]–[289] A study of rail car and transit bus mock-ups demonstrated that seats which met the Urban Mass Transportation (UMTA) guidelines caused flashover in 6 to 7 minutes.[290] Another study using a different ignition source and an overland rail car compartment design showed an UMTA seat arrangement to perform well, but conventional polyurethane seats flashed over in 8 minutes.[291] The UK fire safety practices for rail transportation seating are described in Ref. 292. BS 6853[293] divides Passenger Rolling Stock into Category 1, e.g., underground and sleeping cars, and Category 2, day stock, somewhat less stringent requirements. Complete seats must pass BS 5852 crib 7 testing both on the top and underside; the flames must not

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propagate to the sides of the cushion and must extinguish within 13 minutes after ignition of the crib. Usual seat construction consists of a wool fabric, an interliner, and FR polyurethane foam; usually a metal or plywood sheet is placed on the underside of seats. Motor Vehicles. A general discussion of motor vehicle fire safety in the UK can be found in Ref. 294. A LOI index of 28 is considered appropriate for general purposes, and an index of 33 for special applications. BS 476, an ignition test, is also used. However, the major bus operating organizations have their own requirements. US Motor Vehicle Safety Standard No. 302[67] covers the flammability of interior materials used in passenger cars, multipurpose passenger vehicles, trucks, and buses. It was developed after a comprehensive study of flame spread of over 200 headliner and seating materials.[295] It covers essentially all nonmetal parts of the interior of such vehicles, including seat and back cushions. The surface material, i.e., the cover fabric, is tested by itself unless it is bonded, sewn, or otherwise attached to the padding material. Specimens, 356 × 102 mm, fabric face down, are held in horizontal U-shaped steel frames and a Bunsen burner flame applied to the uncovered specimen end for 12 s. Materials which have a burn rate of less than 1.7 mm/s (102 mm/minute) pass the test. This test is very easy to pass; interest in improving it for at least some vehicle categories has existed since the 1970s. Tests by Braun on transportation vehicle mock-ups[296] included a comparison between full-scale results and measurements of flame spread rate with the vertical Method 5903 and horizontal MVSS 302 tests. Neither of these Bunsen burner tests was found useful in predicting the full-scale hazard. After extensive testing of full size school bus seat mock-ups, a test protocol was suggested[297][298] (somewhat similar to that suggested by Nelson):[290] • Two full size seat assemblies, one placed behind the other, in a corner of the ASTM room, to determine across seat and seat to seat flame spread. • A gas burner ignition source, 100 to 300 kW, applied to the inside edge of the rear seat. • Measurement of mass loss, temperature at several points, heat flux near the floor, HRR and toxic gas yields.

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Fire Behavior of Upholstered Furniture and Mattresses

• Bench scale tests were not found to predict full-scale performance in this test series. A national industry standard prescribes testing three rows of seats with a 7 oz. paper bag containing newspaper sheets as the ignition source, on the seat surface and on the floor next to the seat.[299] Maximum time from ignition to flameout shall be 8 minutes, the flames shall not spread to adjoining seats, and weight loss shall not exceed 10% of the original weight of padding and fabric. ASTM is working on a school bus standard. Göransson and Lundqvist discussed the fire test methods used in Europe for trains and buses.[300] Ships. A summary of UK practices with regard to maritime fire safety is provided in Ref. 301. The IMO standards which are based on UK test methods are prescribed for furniture items. Use of the Cone Calorimeter is under consideration, especially for smoke and toxicity measurement. Internationally, furniture on shipboard is covered by the International Maritime Organization (IMO) Resolutions A.652 (16).[302] This is essentially BS 5852, Part 1, cigarette and small flame ignition resistance. Beds are covered by IMO Resolution A.688 (17), which follows Crown Suppliers[48] methods.[303] This means that cigarettes are covered by a piece of untreated cotton batting, and that a small flame is used for flaming ignition testing. Failure criteria for both the cigarette and flame tests are: detectable amounts of heat, smoke, or glowing after one hour in the cigarette test; destruction reaching to either side or throughout the thickness (except 25 mm or less) of the specimen; flaming or weight loss of 66% or more 50 s after removal of the ignition source. The US Coast Guard has a guide to structural fire protection aboard merchant vessels, dated April 1980, to be used for reviewing plans for vessels.[304] It limits shipboard space fuel load to 10 lbs ft-2 except for spaces containing fire resistant furnishings (this fire load is purported to be roughly equivalent to a fire of 60-minute duration. Of this, 2.5 lbs is assumed to be personal effects, and 7.5 lbs is allowed for combustible furniture, drapes, trim, interior finishes, etc. The fuel load requirement also applies to passenger vessels. In addition, free-standing chairs or sofas must have non-combustible (essentially metal) frames; cushions may be combustible. Fabrics used for furniture in stairways and corridors must pass both the small and largescale NFPA 701 standards, which prescribe vertical specimens and bottom ignition and eliminates many furniture cover fabrics.[305] On the other

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hand, foam and other plastic paddings are considered fire resistant when they pass the discontinued ASTM D 1692 standard; this is similar to the US motor vehicle standard, MVSS No. 302,[67] a horizontal flame spread test which almost all materials pass. (Note that ASTM D 1692 was withdrawn because its reporting “non-burning” or “self-extinguishing” results was considered misleading according to a consent agreement reached between industry and the Federal Trade Commission. The Coast Guard uses the test to define “easily ignited” materials.) A critical study of the US Navy specifications calling for testing of mattress cores with the ASTM E 162 radiant panel flame spread and the ASTM E 662 Smoke Density Chamber is reported in Ref. 306. The conclusions, based on tests with one quarter size mattresses were that the use of the ASTM E 622 should be maintained, but that ASTM E 906 OSU heat release measurement apparatus provided more indication of hazard than ASTM E 162. (Today the recommendations would probably be for the Cone Calorimeter test which provides heat, smoke, and toxic gas release rate measurements.) Aircraft. Improvement in aircraft cabin materials has historically been accomplished when the FAA, the regulator, suggested that it would institute new, severe requirements, which caused industry and NASA to cooperate in developing advanced materials. This has resulted in substantially improved performance. General reviews of aircraft fires, fire scenarios, material usage, etc. have been published in the 1970s and early 1980s by a number of organizations.[307]–[310] Detailed surveys of aircraft incidents involving fires prior to 1975 was compiled,[311] with a follow-up in 1990.[312] This was after the approximately 600,000 seats in the US air fleet had been equipped with interliners (blocking layers in FAA parlance). A thorough investigation of a 1988 accident in which a post-crash fire occurred and all but 14 of 104 passengers survived led to estimates that the fire blocking layers added 40 to 60 s escape time, resulting in 37 additional survivors. A brief history of US aircraft seat flammability test development is presented below. The earliest full-scale tests on aircraft cabin interiors, including seating, were conducted at the Federal Aviation Administration (FAA) facilities in Atlantic City.[164][313][314] Other early cabin tests were reported by the Airline Pilots Association in 1966[315][316] and by the Aerospace Industries Association in 1968.[317] A full-scale testing program was conducted at the NASA Johnson Space Center during 1974–1976 to compare the performance of existing cabin materials with

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Fire Behavior of Upholstered Furniture and Mattresses

new improved or experimental materials.[318]–[320] Full-scale aircraft fire tests were conducted at the Johnson Space Center in a test series which included improved polyurethane and polyimide foams and was used to validate the existing aircraft fire mathematical models.[321] Initially, aircraft seat fabrics were required by the FAA to be tested by Method 5903,[239] the vertical Bunsen burner test. A study was designed to establish whether fabric testing by small bench scale method is predictive of behavior of fabrics in aircraft seat assemblies.[322] The small BS 5852 butane flame No. 1, methenamine pills, and 18 g of newsprint were used as ignition sources. There was no correlation between the fabric test results and fabric/polyurethane padding assembly results, as could be expected. The earliest reduced-scale test developed specifically for aircraft materials, including seating, was the “T-3” test developed at NASA in the late 1960s.[323] Small specimens were exposed at openings on top of a small furnace fed by an oil burner.[324] The furnace fire rate was adjusted to produce specimen irradiance of 85 or 113 kW m-2. Criteria involved primarily measurement of specimen back face or internal temperatures. However, it was concluded that the flux levels are too high in the T-3 test to adequately distinguish behavior of seating materials. Later testing of aircraft seat assemblies in full-scale mock-ups has been centered around the cabin fire simulator (CFS) developed by Douglas Aircraft.[325] It consists of a test chamber containing a steel frame for a double-seat mock-up. Two each of seat cushions 460 mm × 500 mm × 80 mm thick and back cushions 430 mm × 610 mm × 50 mm thick are used. This assembly is heated by a large radiant panel located parallel to one side and 150 mm away. The panel imposes a maximum flux of 100 kW m-2 on the edge of the cushions next to it. Fluxes incident on the front face of the back cushion range from 48 kW m-2 to less than 3 kW/m2 at the far side. The peak on the seat cushion face is 53 kW m-2. Ignition is with a propane torch held to the side edge. Temperatures and other variables are measured, but the primary determination is of specimen mass loss. An ignitability test similar to the T-3 test is used in the present FAA Standard for airplane seating.[326] A 2-gallon/hour oil burner is fitted with a discharge cone and aimed on a two seat mock-up assembly (Fig. 3-11). Heat flux is up to 115 kW m-2. The mock-up comprises a 457 mm × 508 mm × 102 mm seat cushion and a 432 mm × 635 mm × 51 mm back cushion, placed on a steel frame. The assembly is exposed to the burner flame for 120 s. Assemblies fail if they lose more than 10% weight,

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if the flame spread reaches the side opposite the ignition flame, or if there is flaming drip. Brown and Johnson, studying a variety of aircraft materials, recommended this test on the basis of adequate agreement to full-scale results.[327] They also found good agreement of the full-scale with OSU calorimeter results. The HRR and the mass loss rate are related by the heat of combustion, as discussed in more detail in Ch. 2. The heat of combustion of foam padding is determined by its chemical properties; interliners reduce the pyrolysis mass loss rate. Consequently, Kourtides suggested that interliner efficacy be evaluated by measuring the heat of gasification (kJ/kg) of interliner/padding materials in a bench-scale apparatus (higher heats of gasification means the material is harder to pyrolyze).[324] Table 4 shows the heat of gasification measured in a modified ASTM E 662 chamber.[171] It was concluded that assemblies showing heats of gasification > 50 × 103 kJ kg-1 at 25 kW m-2 be satisfactory for aircraft use, based on a rough correlation to full scale performance. (Based on other studies, these values seem improbably high.) The FAA is also looking into the fire safety of seat components such as frames, armrests, and trays.[328] Since 1990, materials used in these components have to have low smoke development; the FAA is investigating the need for further regulations.

Figure 3-11. FAA seat cushion flammability test apparatus (only one seat shown).

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Fire Behavior of Upholstered Furniture and Mattresses

Table 3-4. Heats of Gasification For Aircraft Seat Composites Padding Foam

Interliner

Fabric

120 second average heat of gasification (kJ/kg × 103) at the following irradiances: 25W/m2

50kW/m2 75kW/m2

FR PU

none

none

4.8

NA

NA

FR PU

none

wool/nylon

19

8

NA

polyimide

none

wool/nylon

∞

∞

∞

FR PU

Vonar 3

wool/nylon

60

19

27

NFR PU

Vonar 3

wool/nylon

190

19

27

FR PU

fiberglass

wool/nylon

63

20

NA

FR PU

Norfab™*

wool/nylon

94

21

11

NFR PU

Norfab™*

wool/nylon

210

45

38

* 70% Kevlar, 25% Nomex, 5% Kynol, aluminized layer NA- not available

Because the US is the biggest market for international airlines, other countries generally follow US regulations. An analysis of these regulations from a UK point of view and some of the difficulties with their use are presented in Ref. 329. Besides the FAA test,[326] tests with ISO 5657, a conical radiant heater similar to that in the Cone Calorimeter, with the output increased until ignition occurs, and furniture calorimeter tests of three seat assemblies were conducted. Improved seat covers and padding were identified in this study. 3.2.7

Miscellaneous Tests

In Ch. 5 there are discussions of the development of various tests which were intended to predict BS 5852 or TB 133 results, especially by the polyurethane foam industry. These were modified LOI and Ohio State Calorimeter tests, and comparison with the results of TB 133 and BS 5852 are made. Horrocks et al. developed yet another method for evaluating foams.[330] They used the extinction oxygen index (EOI), obtained in an

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151

LOI apparatus by contacting foam specimens at the top for 10, 8, 6, 4, and 2 seconds with an ignition source and lowering the oxygen concentration till the specimens extinguishes. The EOI is then obtained by extrapolating to zero ignition time. They interpreted the results with respect to foam density and chemistry but, without comparable results with those of established methods, the methods seems to be only of academic interest at this point. 3.3.0

SMOKE AND TOXIC GASES

It is beyond the scope of this book to discuss smoke and toxicity tests methods in detail; unlike many of the furniture testing methods described above, they are used for a wide variety of materials, and are not specific for upholstered furniture. The fundamentals applying to these measurements have been discussed in Ch. 2. 3.3.1

Smoke Tests

The principles employed in testing smoke development have been discussed in Ch. 2. A description of various smoke measurement tests can be found in Refs. 174 and 175. Perhaps the most widely used test has been ASTM E 662, also called the NBS smoke box[171] (Fig. 3-12); many other methods, including BS 6401, are similar. The ASTM test method prescribes: • A closed chamber, 910 × 910 × 510 mm. • An electrically heated, radiant energy source mounted within a ceramic tube and producing an irradiance of 25 kW m-2 evenly distributed over the specimen. • A 65 × 65 mm, vertical specimen, up to 25 mm thick. • For tests in the non-flaming mode, only the radiant heater is used; for tests in the flaming mode, a six-tube gas burner applies a row of flamelets to the lower edge of the specimen, in addition to the radiant heating. • A photometric system with a vertical light path providing data for calculation of specific optical density.

152

Fire Behavior of Upholstered Furniture and Mattresses

Figure 3-12. NBS Smoke Chamber: general view and principle of operation.

ASTM E 662 has been criticized for several short comings:[173] • Air vitiation, because of the closed chamber, flaming combustion stops at 14% oxygen for thicker and composite specimens. • Smoke is re-circulated through heater and recombusted. • No mass loss measurement. • Use of only one irradiance for heating. • Vertical specimens make no allowance for melting. • Polychromatic light source cannot be treated with Beer-Lambert law used for data analysis. ISO has modified this method:[172] • Replacing the furnace by a cone heater similar to that used in the Cone Calorimeter providing 0–50 kW m-2 irradiance on the specimen surface.

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153

• Allowing either a vertical or an horizontal specimen configuration, thus providing a method to avoid the dripping and ablating of vertical, thermoplastic specimens. • Mounting the specimens on a load cell. • Increasing specimen size to 76 × 76 mm. • Test duration is specified to be 20 minutes or 5 minutes after maximum obscuration is reached. ISO also has developed the rarely-used “dual-chamber” ISO TR 5924 smoke box, with one chamber for smoke generation and the other a measuring chamber; they are connected at the top and bottom.[172][174] Paul compared the results of the ASTM D 2843 (popularly called the Rohm & Haas XP2 test), ASTM E 662 (smoldering and flaming) type tests, and ISO TR 5924 methods and found a fairly good correlation.[331] He made a number of recommendations for smoke test parameters including horizontal and vertical specimen orientation, mixing fan, but no ventilation, etc. A number of studies were conducted at FRS comparing the quality of smoke measurements obtained from several types of apparatuses.[332][333] The ISO TR 5924 apparatus was seen to have the most difficulties, especially due to preferential smoke loss of certain size ranges. The Cone Calorimeter was seen to have the least difficulties in providing valid smoke measurements. The NBS Smoke Chamber, the Rohm & Haas XP2 chamber, and the Arapahoe chamber (ASTM D 4100; the specimen is exposed to a small flame and the smoke is measured by collecting it on a filter and weighing it) were also found to be deficient.[334] Hirschler provided a critique of the various smoke measuring methods.[166] He divided test methods as follows: 1. Static bench scale smoke obscuration tests, e.g., ASTM 662, the NBS smoke box 2. Dynamic (flow-through) bench-scale smoke obscuration tests, e.g., the Cone Calorimeter 3. Traditional large scale smoke obscuration measurements in room fire tests 4. Full-scale tests measuring heat and smoke release rates in, e.g., the furniture calorimeter

154

Fire Behavior of Upholstered Furniture and Mattresses

The dynamic tests measure smoke in concert with other fire properties. Hirschler proceeds to list requirements for a bench scale test for smoke obscuration, which can be, in part, fulfilled by the Cone Calorimeter procedure: 1. Measure fire properties in such a way that they can be used for purposes beyond rankings or pass/fail criteria 2. Measure smoke obscuration along with other fire properties impacting hazard, primarily HRR 3. Use tests which have been correlated to full-scale tests 4. Compensate for complete specimen consumption, which generally occurs in bench-scale tests when irradiance is applied throughout the test, but infrequently in full-scale fires According to these criteria, most smoke measuring devices, including most older ones as well as the NBS smoke chamber (ASTM E 662) or other closed-box tests, appear to fall short. These devices are not designed to perform a quantitative fire hazard analysis. There are many reasons for this and most are unconnected with furniture, per se. The issues center around several points: 1. With respect to choices of test parameters: In the most widely used ASTM E 662 procedure, as in most other fire tests, only one experimental condition is used; the 25 kW m-2 irradiance used is rather low and leads to anomalies in some cases. Also, the specimen burning in a small closed box rapidly uses up the available oxygen. This often leads to actual self-extinguishment of the specimen during the course of exposure from lack of oxygen. Thus, the test seems to simulate the situations where a large furniture fire rapidly uses up the oxygen from a room, but other scenarios may be more frequent in real life. Moreover, testing in the NBS smoke chamber is done under two conditions: flaming mode (that is, a pilot flame is applied, but the specimen often subsequently extinguishes due to oxygen consumption or due to FR action), and non-flaming mode (no pilot used, although

Test Methods, Standards and Regulations

some specimens burst into flame spontaneously). It has sometimes been presumed that the non-flaming mode is indicative of the smoldering behavior of the specimen. This is only a rough approximation. Smoldering is non-flaming combustion (oxidation). The non-flaming ASTM E 662 exposure, however, is more appropriately termed an overheat condition. It simulates the mass loss and chemical degradation when a material is exposed to high temperatures. Also a genuine smoldering reaction (i.e., non-flaming oxidation) can be started by the overheat condition, but, again, this is not the typical result. Thus, for furniture (with cigarette ignition the most frequent cause of smoldering), the non-flaming, overheat condition can be considered less important. Sometimes, however, smoldering in furniture is initiated by heating equipment, for example; then, as in e.g., electric wire, an overheat condition seems to simulate the real life scenario. 2. The data presentation is such that one cannot do reasonable smoke hazard computations from the test results. One cannot take the NBS smoke chamber results, for instance, and use them to compute the smoke production rates (or total smoke extinction area, etc.) occurring under actual fire conditions. Thus, such tests serve largely only for rank-order comparisons, but even there anomalies are common. Conducting the tests under various conditions may alleviate the situation but may still present difficulties in using the results for hazard estimation. No bench-scale test method currently exists for measuring the smoke obscuration under smoldering conditions. This is due, partly, to the serious difficulty of creating reproducible smolder conditions. Partly, however, it is also due to a lack of demand. If one were to develop such a method one could conceivably use a smoke chamber without a heat source for test of self-sustaining smoldering furniture composites (e.g.,

155

156

Fire Behavior of Upholstered Furniture and Mattresses

those which ignite with cigarettes), and at various incident fluxes to simulate common ignition sources for furniture, such as space heaters, which often lead to prolonged smoldering before flaming. A fair bit of furniture data have also been collected with the OSU apparatus. While this is, suitably, a flow-through device, its smoke measurement system may be considered obsolete by present day standards. Again, the data presentation does not lend itself any more to quantitative hazard analysis than does the data from the NBS smoke chamber. However, for flaming fires, good correlation between various smoke box and full-scale measurements, albeit with notable exceptions, have been reported.[331] 3.3.2

Toxicity Tests

Chapter 2 discussed the fundamentals of pyrolysis product toxicity. This section addresses toxicity test concepts and test methods as applied to furniture composites. Originally, bioassay testing by exposure of animals to pyrolysis products under conditions simulating specific fire conditions was conducted almost exclusively, with the concurrent measurement of the concentrations of the major toxicants by chemical analysis. As extensive information about the toxic effects of the major toxicants (CO, CO2, HCN, HCl, HBr, HF and NOX, and O2 depletion) became available the use of animals in many test protocols was considered less important. The effect of heat in conjunction with toxicants has not yet been extensively explored. The toxicity of a material is generally expressed in terms of the concentration of its pyrolysis or combustion products in air at which half of the animals die (LC50 in g/m3, mg/l, or ppm) or become incapacitated in a bioassay toxicity test. The toxic potency is expressed as 1/LC50. In the case of the common toxic gases produced during burning in a wellventilated space the LC50’s have already been established. Thus, it is only necessary to measure their yields in kg per kg of total mass loss during a HRR test. The empirical N-gas model can be used to estimate the synergistic reaction of CO and the other major toxic gases (some additive and others antagonistic), as discussed in Ch. 2.[200]–[203] This analytical approach was reported to be a satisfactory predictor of bioassay results.[176][202]

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157

The toxic products that can be produced in a fire can be separated into four classes which ideally should be quantified by tests: Class 1. Super toxicants (hardly ever found) Class 2. Partially oxidized pyrolysis products (an almost unlimited variety of volatiles), which occur in smoldering and under-ventilated room fires Class 3. Toxic combustion products (primarily CO, CO2, HCN, HCl, HBr, HF and NOx; also O2 depletion) occurring in free-burning furniture fires or the pre-flashover period in rooms Class 4. High concentrations of CO which predominate in the hot, under-ventilated upper layer that characterizes a post flashover fire The super toxicants can only be found as a result of bioassay tests with animals, since they may be of a previously unknown nature. It is not practical to identify all of the partially oxidized pyrolysis products of Class 2 for each material. Even if that could be done, a major effort would be required to determine the toxic potency of each species. Thus the toxic potency for a material should also be determined for this class of toxic products through animal testing. The products occurring in Class 3 are limited in number, their toxic potency is already known, and their concentrations are easy to determine by gas analysis. Such analysis can be performed during a standard bench-scale HRR test, e.g., in the Cone Calorimeter. The yields of the individual gases can be determined from this type of test and be used in the N-gas and in the room fire models. After flashover, the toxic gases are dominated by a very high concentration of CO which is essentially independent of the material burned but depends on the upper layer temperature and the degree of under-ventilation, which are controlled by fire dynamics. Ongoing studies are directed toward the development of calculational methods for predicting these concentrations.[190]–[193] Almost all of the oxygen going into the upper layer will be consumed in the oxidation of any available carbon to CO. Bench-scale toxicity tests are not useful in determining the concentrations of toxic gases in the post-flashover room. These are the gases that kill people in remote parts of the building.

158

Fire Behavior of Upholstered Furniture and Mattresses

It becomes evident that several test protocols are needed to cover all stages of a fire. Originally, test methods prescribed testing under nonflaming conditions, e.g., by finding the approximate ignition temperature, and then exposing specimens at some temperature above and below it. However, such LC50’s are often reported without noting the temperature at which they were tested; this seems to discriminate against materials which decompose only at high temperatures. Later it was decided, since most asphyxiation casualties occur in rooms other than that of fire origin and most toxicants in such rooms are produced by post-flashover conditions, to test primarily in modes simulating that condition. Purser lists the following stepwise approach to application of toxicity tests:[179] 1. Decide the scenario of interest—smoldering, small flame ignition, or post-flashover conditions—and decide on the test procedure which most closely simulates it; 2. Run the test without animals using only chemical analysis to measure the concentrations of the above mentioned major toxicants; 3. Determine, from earlier comparisons of analytical and bioassay results, a just sub-lethal atmosphere for test animals (the major toxicant is CO but the synergistic reactions can be determined using the Ngas model discussed in Ch. 2). 4. Expose animals to this atmosphere, noting time of onset and duration of such effects as narcosis, irritancy, incapacitation, and deaths during the exposure period and for 14 days afterwards. This will indicate the presence of supertoxicants or not previously documented toxic effects among the pyrolysis gases from a product. 5. If supertoxicants or unusual toxic effects are indicated, try to identify the reason from the determination of the composition of the original product. Purser warns, however, not to project the results from benchscale tests to real life fire conditions, given the example of PTFE (TeflonR) which caused deaths at two to three orders of magnitude

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159

lower concentrations than almost all other products in the NBS test, indicated a somewhat higher than usual toxicity in the Pittsburgh test, and a lower than usual toxicity in the DIN test. Toxicity Test Methods. Purser described three small-scale toxicity test methods.[179] In the original NIST method, a furnace heats a quartz cup to 25°C below the ignition temperature to simulate smoldering, and to 25°C above it to simulate flaming of specimens.[187] Six rats are exposed (nose only) in restraining tubes in a 200 l transparent box for 30 minutes. This results in an initial period of increasing toxicant concentration followed by a period of relatively constant concentration. The concentration can be varied by placing different amounts of ground up specimen into the cup. This is a “static method” because there is no ventilation in the box. The atmosphere in the box is analyzed for the major toxicant gases. The major objections to this method are:[335] • The small size of the specimen holder limits the specimen size, which is critical for low-density materials. • There are no provisions for measuring weight loss continuously. • The concentrations of toxicants change during the test. • The effect of specimen orientation can not be assessed since the specimens are ground up. • Non-uniform structures, for example, fabric/padding composites, can not be properly accommodated. Most of these objections are overcome by analyzing the concentrations of toxic gases in the Cone Calorimeter which can also determine smoke and HRR at the same time. The conical radiant heater used in this test is also used in testing with animals. In the “dynamic” DIN 53436 method, fresh material is decomposed at a constant rate throughout the test.[336] It has been used with mice, rats, and primates. A strip of the test material is exposed in a silica tube under a constant airflow, and an annular furnace is moved along the outside of the tube at a constant rate. The products are diluted, and passed through the animal chamber for 30 minutes. Concentrations in the chamber are varied mainly by the airflow; the decomposition conditions thus remain constant during this test. The advantage of this method is that it can

160

Fire Behavior of Upholstered Furniture and Mattresses

simulate smoldering, flaming, as well as high temperature decomposition. Good correlation has been reported with full-scale smoldering conditions. One difficulty is that the flame in the tube travels ahead of the furnace to varying degrees, and thus does not provide even decomposition conditions. It is also impossible to view the burning specimen in the furnace. The method requires specifying the air flow rate and the furnace temperature. The results are sensitive to these choices, yet little realistic guidance exists here. The University of Pittsburgh method differs from the above in several ways.[337] An airflow is maintained over the sample. Thus, the mice in the test chamber are continuously exposed to fresh products. The sample temperature is raised in steps of 20°/minute, starting with indications of weight loss on the load cell, or tests can be conducted at constant temperatures. The animal breathing rate is recorded, to establish onset of narcosis or irritancy. Several animal exposure chambers are used; the concentration in them is varied by diluting the gases; this increases the amount of results produced per test. One advantage of this method is its versatility, and that it produces a variety of results, covering a variety of decomposition conditions, concentrations, etc., in one run. Specimens with a short time to flaming or smoke evolution can be considered more hazardous than those which decompose at higher temperatures. Objections to the method include the difficulty of characterizing an incapacitating or lethal dose, since, e.g., deaths at a certain temperature may occur due to the delayed effect of an earlier, lower dose, or that of the dose at the point of death. More recently, a method was developed during a period of several years of work at NIST and the Southwest Research Institute (SwRI).[183] It has been called the “radiant toxicity test” or “NIST/SwRI” method. It eliminates many problems with the design of previous combustion systems or with the toxicological assessment procedures. It prescribes both analytical and bioassay procedures. An ASTM standard covers its use in hazard analysis.[338] It is also used in the proposed ISO standard; the regulators in the individual countries are given a choice whether to require only the analytical testing or the extent to which animal testing will be required.[339] There is considerable discussion as to how to apply the results to hazard evaluation, which seems unresolved at the time of this writing. In the NIST/SwRI analytical tests, a horizontal quartz cylinder, (127 mm diameter, 320 mm long) contains the specimens. They are

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161

exposed to 50 kW m-2 with a cone radiant heater for 15 minutes, in presence of a spark ignitor. The pyrolysis products are collected in a 200 liter transparent chamber. The method is intended to approximate postflashover conditions, as being the most likely to cause fatalities. However, it does not duplicate the high temperatures and ventilation conditions that produce the large concentrations of CO in the upper gas layer of a postflashover fire in a room, as noted above. In the NIST/SwRI bioassay test, Fig. 3-13, rats are exposed head on in 6 restraining tubes protruding into the 200 l chamber for 30 minutes. Specimen size is selected, according to estimates based on results of the analytical tests, to be equivalent to 70 to 130% of estimated LC50. Animal deaths are recorded during the test and for a 14 day observation period afterwards. All the products are kept in the transparent chamber (except the aliquots used for analysis), but smoke particulates are filtered out.

Figure 3-13. NIST/SwRI radiant smoke toxicity apparatus.

162

Fire Behavior of Upholstered Furniture and Mattresses

The NIST/SwRI method uses gas analysis for the principal toxic products in order to minimize the use of animals and to estimate the LC50 to be used in the bioassay test. The next step is either a confirmation by animal testing that this estimate is correct (by assuring that there is no super toxicant for which no gas analysis was performed) or a complete animal-based determination of the actual LC50. In two extensive studies conducted for the new radiant toxicity test method the method adequately predicted toxicity in real-scale fires.[183][200] ISO has prepared extensive technical reports.[339][340] These documents contain reviews of the philosophies prevailing on the development of tests intended as a technical background for future international standards, and appraisals of the state of the art. There are six parts, covering the various aspects of toxicity testing: Part 1-General; Part 2-Bioassay Methodology; Part 3-Analytical Methods; Part 4-The Fire Model; Part 5Prediction of the Toxic Effects of Fire Effluents; Part 6-Guidance for Regulators. Hartzell has compared the methods considered by ISO with those used in the US.[177]

4 Ignition Sources

This chapter discusses the technical details of ignition sources which have caused upholstery fires or have been used in fire tests for upholstered items. Other aspects of ignition are discussed as follows: the fundamentals of smoldering and flame ignition are covered in Ch. 2; the section on flame ignition tests and standards in Ch. 3 include general descriptions of the ignition sources; Ch. 5 compares the results of various ignition tests; and a section of Ch. 6 discusses results of ignition tests of many different upholstery materials. Paul and Christian[233] and Murrell[341] published general papers on ignition sources. The first mentioned paper includes 1984 UK statistics for involvement of various ignition sources in fire incidents, and data on the duration, heat of combustion, heat flux and other parameters of a large number of ignition sources such as matches, lighters, electric light bulbs, arcs and sparks, various arrangements of folded and crumpled newspaper, torches, etc. It provides useful background for the three gas flame and four wood crib choices in BS 5852 and detailed comparisons of the characteristics and the effects on a variety of substrates of small butane and propane diffusion flames, methenamine pills, and matches. The characteristics of many such ignition sources are shown in Tables 4-1– 4-7.

163

164

Fire Behavior of Upholstered Furniture and Mattresses

Table 4-1. Characteristics of BS 5852 Ignition Sources Ignition Source Cigarette Gas Flame 1 Gas Flame 2 Gas Flame 3 Wood Crib 4 Wood Crib 5 Wood Crib 6 Wood Crib 7

Total heat release (kJ) 16 2 12 46 142 285 1040 2110

Flame height (mm) — 35–40 140–150 185–240 150–245 250–335 250–350 345–490

Heat Fuel supply Time to 90% flux rate mass loss (s) (kW m-2) — 30–40 20–40 20–40 15 18 23 25

— -1

45 ml min 160 ml min-1 350 ml min-1 6 g min-1 10 g min-1 15 g min-1 32 g min-1

Burn time (s)

—

1200

— — — 180 150 330 375

20 40 70 195 180 360 390

Table 4-2. Characteristics of Ignition Sources Used in Furniture Tests Type of Ignition Source

Cigarette 1.1 g (not puffed, laid on solid surface), bone dry conditioned to 50% R.H. Methenamine pill, 0.15 g Match, wooden (laid on solid surface) Wood cribs BS 5852 Part 2 No. 4 crib, 8.5 g No. 5 crib, 17 g No. 6 crib, 60 g No. 7 crib, 126 g Crumpled brown lunch bag, 6 g Crumpled wax paper, 4.5 g (tight) Crumpled wax paper, 4.5 g (loose) Folded double-sheet newspaper, 22 g, (bottom ignition) Crumpled double-sheet newspaper, 22 g, (top ignition) Crumpled double-sheet newspaper, 22 g, (bottom ignition) Polyethylene wastebasket, 285 g, filled with 12 milk cartons (390 g) Plastic trash bags, filled with cellulosic trash (1.2–14 kg)5 1

Typical Heat Output (W)

Burn Time1

5 5 45 80

1200 1200 90 20–30

1000 1900 2600 6400 1200 1800 5300 4000

190 200 190 350 80 25 20 100

7400

40

17000

20

50000

2002

120000 to 350000

2002

(s)

Peak Flame Peak Flame Width Heat Height Flux (mm) (mm) (kW/m2)

30

14

42 35 4 18–20 154 174 204 254

550

200

353

Time duration of significant flaming. 2Total burn time in excess of 1800 s. 3As measured on simulation burner. from 25 mm away. 5Results vary greatly with packing density.

4Measured

Ignition Sources

165

Table 4-3. Characteristics of Potential Furniture Ignition Sources Source of Ignition

Duration (s)

Total Heat Release (kJ)

Peak Heat Flux (kW/m2)

380 420 85 152 223 333 335 36 91 106 330 513 900 1200 330 360

1680 3500 175 340 680 1020 1600 840 1680 2520 9500 11000 44000 130000 2100 8400

14 15 7–10a 7–22a 7–21a 5–22a 6–23a 17–24a 7–14a 7–17a 20–39a 17–28a 10b 26b 7b 14b

Folded paper 5 sheets Folded paper 10 sheets Crumpled paper 1/2 sheet Crumpled paper 1 sheet Crumpled paper 2 sheets Crumpled paper 3 sheets Crumpled paper 4 sheets Shredded paper in wire basket, 50 g Shredded paper in wire basket, 100 g Shredded paper in wire basket, 150 g Small stuffed toy Scatter cushion Scatter cushion (vandalized) Bedding Wood sticks Wood sticks a

25 mm from edge of source

b

100 mm from edge of source

Table 4-4. Effect of Gas Burner Variations on Flame Characteristics Burner Type*

Tube diameter

Fuel

(mm) straight tube straight tube straight tube straight tube Rieber

Supply rate (W)

Peak Peak flame flame height width (mm) (mm)

Peak flux at various locations (kW/m2) P1 P2 P3 R1 R2 R3 R4

6.4

butane

315

49

9.1

34 35 42 341 38 25 29

6.4

propane

305

59

8.4

40 34 48 34 31 37 28

7.0

propane

305

42

9.0

33 30 41 35 42 26 19

7.4

propane

305

41

8.7

31 43 48 43 43 34 23

–

propane

305

45

9.9

30 35 47 32 29 45 32

* Burner tube is always horizontal in these measurements. P1: at top of flame exposure on a vertical surface, P2: at center of flame exposure on a vertical surface, P3: at base of flame exposure on a vertical surface, R 1: at tip of free flame in air, R2: at center of free flame in air, R3: at base of free flame in air at end of burner tube, R4: on horizontal surface at end of burner tube laying on the surface.

166

Fire Behavior of Upholstered Furniture and Mattresses

Table 4-5. Characteristics of Some Furniture Ignition Sources Ignition Source

Peak HRR (kW)

Duration (s)

THR (kJ)

Heat Flux (kW/m2)

Comments

CBUF gas burner

30

120

3600

Seat attack: main area 30–40; maximum at small spots 40–50; Back attack: main area 40–60; max. at flame attack 60–70

fixed position

NIST gas burner TB 1331 100g paper 100g paper2

20

80

1600

20-40

20 g paper2,3

about 5

BS 5852 standard wood crib 7 Match Flame4

about 10

<1

90-200 about (above 10% 1700 of peak HRR) about 90 about 325 1820

20–100 (average maximum 74) maximum approximately 603

fixed position laying on the sample laying on the sample

maximum approximately 203 central area under crib; approximately 80

laying on the sample laying on the sample

15

approximately 20

1

Furniture Flammability: an investigation of the California TB 133 Test. Part II: Characterization of the Ignition Source and a Comparable Gas Burner, Ohlemiller and Villa, NISTIR 4348 2 CBUF data 3 Burning of small Ignition Sources, Holmlund, C., VTT paper 569 4 Standard Flaming Ignition Sources for Upholstered Composites, Furniture and Bed Assembly Tests, Paul, K. T., Christian, S. D., Journal of Fire Sciences, Vol. 5 (May/June 1987)

Table 4-6. Characteristics of Burning Furnishings as Potential Furniture Ignition Sources Item

waste paper baskets curtains, velvet, cotton curtains, acrylic/cotton TV sets chair mock-ups sofa mock-ups arm chair Christmas trees, dry a

Total Mass (kg)

Total Heat (MJ)

Peak HRR

0.73–1.04 1.9 1.4 27–33 1.3 2.8 26 6.5–7.4

0.7–7.3 24 15–16 145–150 21–22 42 18 11–41

4–18 160–240 130–150 120–290 63–66 130 160 500–650

(kW)

Measured at approximately 2 m away from the burning object

Peak Thermal Radiation to center of floora (kW/m2) 0.1 1.3–3.4 0.9–1.2 0.3–2.6 0.4–0.5 0.9 1.2 3.4–14

Ignition Sources

167

Table 4-7. Characteristics of Some Flame and Electrical Ignition Sources Source of Ignition Match flames Cigarette lighter Small diffusion flame Large diffusion flame Small premixed flame Large premixed flame Blow lamp Electric spark Electric arc Electric arc Hot plate kW Electric radiator 60 W electric bulb 100 W electric bulb 275 W electric bulb a

At edge of source.

b

Duration (s)

Total Heat Release (kJ)

Peak Heat Flux (kW/m2)

2–35 30 30 30 30 30 30 – 1 5 30 30 30 30 30

6 24 8 15 50 – 40 <100 mJ 0.4 15 30 90 2 3 8

18–20 16–24 18–32 6–37 58 120 > 100a – – – – 20–25c – – 13a, 10b

25 mm from edge of source.

c

At the guard.

A somewhat different description of ignition sources used in the UK for testing various materials other than furniture, but which may have some pertinence to it, is given in Ref. 341. These are designed to simulate flames produced by a failing electrical component; a cigarette lighter; four sheets of newspaper; a plumber’s blow lamp (Bullfinch 1210 fishtail burner); a welding torch, i.e. a small area, high intensity source (Bullfinch 1240 or 1250 burners); and a small area, high intensity flame (Sievert 3537 or Bullfinch 1470 burners). Various parameters of these sources are described in detail in the cited reference. Tables 4-1 and 4-2 describe the BS 5852 and other relatively small ignition sources, including a variety of paper ignition sources. Table 4-4 shows the effect of variations in tube diameter and gas flow for the BS 5852 flame. Table 4-5 compares some ignition sources used in various tests (Ref. 7, Appendix 4). The values in the tables for varying ignition sources do not always agree, presumably because of differences in the manner in which they were measured. Table 4-6 shows the characteristics of typical furnishings which could be primary ignition sources for upholstered items; Table 4-7 shows the characteristics of other items which may act as primary ignition sources for furniture.

168

Fire Behavior of Upholstered Furniture and Mattresses

Various ignition sources cited in the literature ranged over four orders of magnitude, from HRR values of 5 W to 50 kW.[233][341]–[344] An examination of the data reveals a certain consistency: the peak heat fluxes for all the sources, excluding the methenamine pill, are approximately 15–42 kW m-2. What differs mainly when ignition source strength is increased is not the peak incident flux, but rather the area over which the flux is applied. In the case of the wastebasket, the area over which fluxes exceed 20 kW m-2 is about 60 × 700 mm; for a match this would be approximately 10 × 30 mm. To put the heat fluxes in the above tables into perspective, the following approximate values are given: sunlight provides about 1 kW m-2; the human tenability limit for radiation is about 2.5 kW m-2; typical room furnishings are easily ignited at 20 kW m-2; maximum heat fluxes in a room fire can be as high as 150 kW m-2 or higher.

4.1.0

MATCHES, SMALL GAS FLAMES, AND METHENAMINE PILLS

Among the small ignition sources suggested at one time or the other, the BS 5852 gas and crib ignition sources have become most prominent. Tables 4-1 and 4-2 show their characteristics.[227][230] BS 5852, Part 1, gas flame 1 is used by EC and ISO, and there are plans to further investigate others. Gas flame 1 was intended to simulate a match. Table 4-4 shows the effects of butane vs propane, tube diameter, and of the complex German “Rieber” burner on the flame characteristics.[345] It indicates that the Rieber burner gave results similar to the premixed and diffusion gas flame 1 of BS 5852.[233][345] Consequently, ISO did not accept the use of the much more complex, expensive Rieber burner, but permitted use of propane with the British burner. The 20 s period of exposure to the BS 5852 simulated match, gas flame 1, was considered too long, and this led to an investigation of UK wooden “Strike Anywhere” and “Safety” matches.[233] The authors state that the flame temperature of the gas flame is within the range of that of the matches. The matches burned between 30 and 36 s in air, but one may assume that they would not often be dropped immediately after striking. Matches, even from one manufacturer, were found to be too variable to be used in a standard test.[233] On a number of substrates, various types of matches burned an average of about 15 s, with a standard deviation of 6.4 s.

Ignition Sources

169

Matches were more likely to ignite the upholstery substrate when placed near, rather than in, the crevice.[346] However, the rate of flame spread was more rapid when ignition was in the crevice. The gas flame burner results were not affected by position. The match flame is quenched when it comes in contact with the surface. In general, there was good agreement between the ignition/no ignition results for matches and the BS 5852 gas flame 1 on a variety of fabric/foam composites while the methenamine pill gave somewhat different results (Tables 4-8 and 4-9).[233][347] The effect of the increase in severity of the three BS 5852 gas flames, as well as methenamine pill and cigarette results, is shown in Table 4-9.[347] It is interesting to note that only wool or FR fiber containing fabrics passed with any of the gas flames, and that TB 117 type FR polyurethane foam helped several fabrics pass with flames 2 and 3. An ISO study showed similar fabric behavior.[348] Since both TB 117 foams and untreated foams generally ignite easily in large fires, this indicates that small gas flame tests can only demonstrate small differences in ignition resistance which may be of dubious relevance from a practical point of view. A number of commercial fabric/padding combinations were exposed to the Italian UNI 9175 furniture ignition source (gas flow rate 45 ml/ min, flame height 40 mm, exposure times 20, 80, or 140 seconds) and BS 5852 gas flames 2 and 3 as well as to newspaper ignition sources.[349] However, since there were relatively few ignitions with the BS source, no comparative rankings between these ignition sources could be established.

Table 4-8. Ignitability of Composites With Three Small Ignition Sources Composite* Fabric Acrylic Pile/Cotton Acrylic Pile/Cotton Viscose Viscose Cotton Cotton Polypropylene Polypropylene

BS 5852 Part 1 Butane Flame

Match

Foam

Methenamine Pill

PU HR PU HR PU HR PU HR

F F F S P F F F

F F F P P F F F

F F S S F F F F

* Two cushions arranged as seat/back junction, PU = standard polyurethane foam, HR = high resilience polyurethane foam, P - no ignition, S - smoldering, F - sustained flaming.

170

Fire Behavior of Upholstered Furniture and Mattresses

Table 4-9. Ignitability of Composites With BS 5852 Ignition Sources And Methenamine Pills Fabric Structure

Fabric weight g/m2

Fabric burn time s

Mockup Test Results Methen- 40 g CigFoam2 Butane flame amine wood arette 1 2 3 pill crib

cotton chenille

355

13

NFR FR

F F -

-

F F

-

F F

56 Cot + vis/5pe/ 39 acr plush

400

26

NFR FR

F F -

F F

F F

-

P P

52 linen/ 48 cot panama

430

41

NFR FR

F F -

-

F F

-

F F

54 nyl/32 FR vis/ 14 pe plush

400

47

NFR FR

F - P P P

P P

P

P P

34 wool/52 vis/ 14 nylon panama

450

56

NFR FR

P F P P P

P P

-

P P

65 wool/ 35 FR vis twill

540

SE

NFR FR

P P P P P P

P P

P

P P

52 wool/27 cot/ 21 nylon twill

575

SE

NFR FR

P F P P P

P/F P

P

P P

wool reps

375

SE

NFR FR

P F P P P

P P

-

P P

PVA/ PVC twill

475

SE

NFR FR

P F F P P P

F P

P P

P P

87 cot/ 13 FR vis.

200

SE

NFR FR

P P F P P P

P P

-

F P

1. CS-191 test with forced ignition. 2. Polyurethane foam: untreated (NFR) 30 kg/m3; flame retardant (FR) 33 kg/m3, cot- cotton, acr - acrylic, pe - polyester, vis - viscose, F - fail, P - pass.

The methenamine pill (150 mg) ignition source (about 120 s burn time), which is used in US residential carpet testing was considered by some countries, especially Australia and the Nordic countries.[346]–[348][350][351] As mentioned above, it often but not always gives results similar to the BS 5852 flame l or to matches (Tables 4-8 and 4-9).[349][351]–[353] In some cases, the pill ignited substrates which were not ignited by the other ignition sources, particularly when placed on flat surfaces of mattresses where it sinks into the substrate. The pill appeared to be slightly less severe than a 40 g wood crib.[346]

Ignition Sources

171

In one study, bone dry and 65% r.h. conditioned mockups were exposed to cigarettes, methenamine pills, and matches.[346] Pill (burning time 90 to 120 s) and cigarette (burning time about 20 minutes) ignitions were not affected by the moisture content of the substrates, but matches ignited some dry substrates but not the corresponding conditioned ones. This indicates that the longer cigarette and pill burning times may make results less sensitive to moisture content, because the substrates have time to dry out. This should be verified with a variety of hygroscopic fabrics and padding materials. The use of the pill, or long exposures with the gas burner, may make it possible to use less stringent conditioning of the specimens, which would be an advantage. The methenamine pill can probably be placed reproducibly into the well-defined crevices of the British mockup, but crevice geometry, and especially width, varies widely in actual furniture (a visit to a furniture store will show an amazing number of gaping and wavy crevices). For use in a test applicable to actual furniture, as well as to mockups, a device to hold pills in gaping crevices would have to be developed. Such crevices may not present as much of a problem to the gas burner tube.

4.2.0

WOOD CRIBS

Tables 4-1 and 4-2 describe the four BS 5852 wood cribs, and Tables 2 and 5 compare them with other ignition sources which have been or are used in various tests.[233] The largest ignition source, wood crib 7, is intended to simulate the heat characteristics of four double sheets of a British newspaper. Cribs, rather than newspaper, were chosen because newspaper ignition sources are hard to standardize and exhibit poor reproducibility, as discussed below. On the other hand, gas burners are more reproducible than cribs. The construction of cribs 5 and 7 is shown in Fig. 4-1,[230][233] their heat flux distribution is shown in Fig. 4-2.[354] Crib 7 was found to give the most reproducible heat flux values. The crib preparation is complex. They are made from pine wood (pinus silvestris), approximately 500 kg m-3, heat of combustion 20.5 MJ kg-1 as measured in the oxygen bomb calorimeter, which measures gross heat of combustion of the solid material. The net heat of combustion of the volatiles released from the burning wood is considerably lower. The cribs are conditioned under warm, dry conditions for a week. The sticks are cut and sorted by mass, to assure the correct mass for the assembly. The

172

Fire Behavior of Upholstered Furniture and Mattresses

sticks are glued with a PVA-based or other suitable wood glue. A 40 × 40 mm piece of “PC grade surgical lint” (absorbent cotton) weighing 0.3 g is placed into the center of the crib and soaked with 1.4 ml of isopropanol to facilitate ignition.

Figure 4-1. BS 5852 wood cribs 5 and 7.

Ignition Sources

173

Figure 4-2. Heat flux distribution under BS 5852 crib 5 (upper figure) at 185 s and BS 5852 crib 7 (lower figure) at 155 s.

174

Fire Behavior of Upholstered Furniture and Mattresses

A study of crib 5 discusses some aspects of this ignition source.[355] If it collapses toward the back of the mockup, it concentrates the energy toward the furniture back; other collapse modes seem to have less severe consequences. The origin of the pinus silvestris could cause differences of as much as 15 s in ignition time. Variations in resin content from 0 to 4% and in calorific value from 18.32 to 20.69 MJ kg-1 were found.[355] Wood density variations also exist. Cone Calorimeter tests of six different pine materials resulted in a 25% variation in the peak HRR and the time to reach the peak, 17% in combustion time, and 20% variation in total heat emitted. Even greater variations were found with crumpled newspaper, because of (1) the difficulty of reproducing the degree of crumpling and (2) their uncontrolled movement during burning. Disagreement exists with regard to the proper weight and base area of the wood cribs. The larger the weight and the smaller the base area, the greater the probability of a charred fabric to break open and expose the padding material. This appears to be particularly common with wool and FR cotton chars. On the other hand, one can assume that fabrics which char and shrink are more likely to split open when the heated area is large, as in a furniture item than in small bench scale specimens. Lighter wood species (balsa and an Australian pine) and different dimensions of the cribs have been suggested.[356]–[358] An Australian study describes a procedure differing somewhat from the British Standard, including six wood crib ignition sources varying from 50 to 400 g and a standard test room, which can be used for mockups as well as actual furniture items.[358] A study compared NORDTEST and BS 5852 cribs, as well as other ignition sources.[359] The following ignition sources were compared: • NT Fire 007, 100 × 100 mm, 20 mm high, 40 g, 0.67 MJ. • One quarter of NT 007, 50 × 50 mm, 20 mm high, 17 g, 0.28 MJ. • BS 5852 crib 5, 40 × 40 mm, 65 mm high, 17 g, 0.28 MJ. • BS 5852 crib 7, 80 × 80 mm, 110 mm high, 126 g, 2.10 MJ. • A polyester fiber filled pillow, 50 × 130 mm, 20 g, about 0.42 MJ. Of these, the ignition behaviors of the quarter NT 007, the BS 5852 crib 5, the polyester fiber pillow and the burning bedclothes (quilt, blanket, pillow, and bed linen) were similar to each other.

Ignition Sources

175

The lower and wider NT cribs require fewer (though longer) sticks in two layers and are, thus, more easily assembled than the BS 5852 cribs. They also exert less pressure per unit area, more like bedclothes. The authors suggest a low, 15–20 g wood crib, ignited as in BS 5852 with alcohol drenched cotton wool (cotton batting). They found good reproducibility of test results with the polyester pillow and the conditioned BS 5852 crib 5. They also found that cigarette tests in which the cigarettes were covered with cotton wool rather than left uncovered were more reproducible.

4.3.0

NEWSPAPER SHEETS AND THEIR GAS BURNER REPLACEMENTS

Paul and Christian’s paper included a discussion of paper ignition sources.[233] Crumpled newspaper ignition sources were found to deliver peak heat fluxes from 10 kW m-2 for half a sheet to 22 to 23 kW m-2 for one to four sheets. When the papers were placed in a wire cage, the peaks were lower. Newspaper sheets, in various arrangements, were used in much of the original work on BS 5852 and in full scale room burns,[261][322][342][358] [360][361] as well as for TB 133. A number of possible arrangements, their heat outputs, and reproducibility have been discussed by Australian workers.[342] Obviously, their severity depended on their weight and arrangement and they could not be readily compared to the other ignition sources. Balled up pieces of newspaper, spread over the test article showed extreme variability.[360] The ignition source originally specified in California TB 133 for institutional upholstered furniture and mattresses consisted of five loosely wadded double sheets of newspaper, 90 ± 5 g, held in a steel wire cage and placed at the juncture of back and seat. As it became evident that TB 133 was going to be adopted in many jurisdictions and possibly nationwide, this newspaper source was thoroughly investigated by NIST with a view to a possible replacement by a more reproducible ignition source.[138] Heat flux was measured for this arrangement at several points on the back of the TB 133 mockup consisting of inert material; the peak heat fluxes in five replicate tests varied by a factor of 2. Consequently, a square gas burner, derived from the British Fire Research Station T Burner but with flames directed against both sides as well as the back and seat of the mockup for 80 s, was adopted. (See Ch. 3, Fig. 3-9.)

176

Fire Behavior of Upholstered Furniture and Mattresses

The results of both chair mockups and full-scale furniture made from a variety of materials ignited with both TB 133 ignition sources are shown in Table 4-10.[138] They were similar enough that the gas burner is now specified for TB 133 tests, with a slightly higher gas flow than used in these experiments, to produce about 18 kW m-2, the same as the accepted value for the original TB paper ignition source.

Table 4-10. Chair Burns: Comparison of TB 133 Results With Paper and Gas Burner Ignition Sources

Fabric/liner/foam

Ignition Source

180 s moving ave. peak HRR (mW)

Time to peak HRR (s)

Total heat released (mJ)

Weight loss (%)

Wool/ Calif. 117 A

CB133 Burner

1.15 1.11

310 310

459 448

85 89

Wool/fiberglass/Calif. 117 B

CB133 Burner

0.03 0.03

100 79

8 4

0 0

Nylon/Calif. 117 E

CB133 Burner

1.50 1.52

361 313

460 462

92 89

Nylon/fiberglass/Calif. 117 F

CB133 Burner

0.40 0.11

1870 100

400 18

81 4

Nylon/melamine C

CB133 Burner

1.15 1.16

848 831

499 446

87 91

Nylon/fiberglass/melamine D

CB133 Burner

0.09 0.04

129 154

30 39

2 3

PVC fabric/Calif. 117 G

CB133 Burner

0.72 0.16

1830 69

422 13

84 3

PVC fabric/melamine H

CB133 Burner

0.08 0.14

61 51

6 8

1 1

Polyolefin/Calif. 117 I

CB133 Burner

0.47 0.67

1690 4430

396 434

82 89

Polyolefin/Calif. 117 J

CB133 Burner

1.72 1.65

230 222

494 436

89 93

Ignition sources: CB 133 - newspaper; Burner - 17 kW propane burner; Calif. 177 - foams which pass CA TB 117 (modestly FR); melamine - melamine treated PU (highly FR); Note: CA TB 133 now specifies 18 kW propane burner.

Ignition Sources

177

CBUF used the TB 133 burner but increased its HRR to nominally 30 kW, applied at the crevice for 120 seconds. Its heat flux patterns to the back and seat are shown in Fig. 4-3 (Ref. 7, Appendix 4). This burner, which delivers at an average 30 to 40 kW m-2 to the seat and 40 to 60 kW m-2 to the back was adopted to assure ignition of most composites, for postignition studies.

Figure 4-3. Heat flux to the furniture specimen from the CBUF burner;(upper graph) back, (lower graph) seat.

178

Fire Behavior of Upholstered Furniture and Mattresses

A preliminary study cited in the CBUF report used the TB 133 burner as follows: 40 kW/120 s, 30 kW/120 and 180 s, and 20 kW/300 s (Ref. 7, Appendix 4). For two different chairs, the peak HRR, total heat release, rate of smoke production and total smoke, and effective heat of combustion had standard deviations varying between 2.4 and 10.3% of the mean values. 4.4.0

WASTE PAPER BASKETS: REAL AND SIMULATED

This section contains mostly historical information, as an “institutional memory” of the fire test development community and is presented here for those interested in the development of ignition sources. Most of the following ignition sources have only been used for experimental purposes. l. The Berkeley Wastebasket was first characterized in Ref. 145 and used for igniting a wide variety of furniture and building materials. The specifications are: (1) A 7-liter polyethylene wastebasket weighing 0.285 kg; (2) 12 paper/polyethylene milk cartons, 6 upright, 6 shredded with a total mass of 390 g and a total heat content of 19.7 MJ; and (3) an average HRR during flaming combustion of 50 kW for 200 s. The heat released during the later slow burning period is about 9.7 MJ.[142] The burning rate is somewhat operator-dependent as it is affected by packing and ignition procedures. Ignition variability with the wastebasket and other paper (and wood crib) ignition sources sometimes arises when they burn down one side instead of burning down uniformly. This tends to open up a gap between the basket and the test piece, thereby greatly reducing the heat flux. 2. The wastebasket simulation gas burner which was developed to simulate the characteristics of the Berkeley wastebasket, but was intended to be more reproducible. The burner is placed almost flush against the side of the test piece and does not move as the wastebasket does in collapsing (there must be some small gap between the burner and the item of furniture

Ignition Sources

179

to allow accurate mass loss measurements).[269] The peak heat flux is only 35 kW m-2, but the area covered by the 20 kW m-2 contour is substantial. 3. A wire mesh paper basket was proposed by Moulen and Grubits of Australia.[342] They used a cubical 0.25 × 0.25 × 0.25 m wire mesh basket filled with shredded paper. Because of varying packing densities, combustible loads of 50 to 150 g gave approximately 15-25 kW HRR, lasting for 30 to 90 s. 4. A circular galvanized metal wastebasket ignition source was developed by the California Bureau of Home Furnishings for use with the California TB 121 mattress test.[261]

4.5.0

RADIANT FLUX IGNITION SOURCES

The ISO 5657 Ignition Apparatus[244] uses a conical heater to impose a radiant flux on a bench-scale sample. The flux can be varied over the range of 10-50 kW m-2. A gas pilot igniter is used. The Cone Calorimeter is used for HRR as well as ignitability testing [362] and was discussed in detail in Ch. 3. A conical heater, similar to the one in the ISO apparatus, with a flux capability of up to 100 kW m-2 and an electric spark pilot ignitor are used. This reference includes discussions of the spectral distribution of the various ignition sources, the effect of airflows on ignition time, specimen size and orientation, edge effects, etc. The effect of various strength radiant ignition sources on a number fabric/padding composites is described in several papers[342][347] (see also Ch. 6).

4.6.0

OTHER IGNITION SOURCES AND LOCATIONS

Grand made the important point of the need to ignite not only in the seat but also at other locations on the furniture item.[253][254] He cited the examples of chairs which have interliners at the inner surfaces but not on the outer surfaces or below the seat. Ignitions by faulty electric cords, burning waste paper baskets, children playing with matches, etc., would likely be on the outside, however. This problem is addressed in the UK

180

Fire Behavior of Upholstered Furniture and Mattresses

Regulations but not in TB 133. The CPSC started working on this problem in 1995. In a study at NIST, chairs were exposed to five ignition sources, chosen because of their frequent mention in accident reports and their use in standard tests: cigarettes, the California TB 133 gas burner mentioned above, a radiant heater first pre-heating the chair and then tipped toward it, and a quartz-halogen light bulb.[135] Five fabric/padding composites were tested: cotton fabric over cotton batting wrapped polyurethane foams; a nylon/olefin/acrylic blend fabric over polyester batting wrapped over polyurethane foam; olefin fabric, acrylic pile with cotton/rayon backing, and expanded vinyl fabrics over urethane foam without wrapping. The experiments were conducted in the furniture calorimeter, with the ignition sources placed at the locations of the chair where they could be situated in real life fires, and led to the following conclusions: • Not all ignition sources ignited all chairs. • The ignition source affected the time from ignition to peak HRR but not the magnitude of the peak, within the scatter of the data; however, CO yields varied by a factor of 2, depending on ignition source. • The fastest time to the peak HRR occurred with the TB 133 gas burner, followed generally by the radiant space heater, the match, the lamp, and the cigarette. • The authors suggest that ignitability of upholstered furniture fires be assessed by three ignition sources: cigarettes, a small gas flame, and the TB 133 gas burner, and that time to peak HRR and peak HRR should be noted. To make these results more meaningful in terms of hazard, the hazard analysis package, HAZARD I, was used to predict the chances of survival for the occupants of a building, based on the furniture calorimeter results. For this exercise, a six room, one story ranch type home was chosen. Two occupants were considered able bodied, but a grandmother and an infant would require assistance in escaping. The results can be summarized as follows: • None of the chair fires were large enough to cause flashover unless they ignited other furnishings. • Incapacitation, if it would occur, would be due to heat and not CO concentrations; this depends, however,

Ignition Sources

181

very much on the house layout, open or closed doors, ventilation system, etc., and thus cannot be considered a general case. • No deaths were judged to occur if a working smoke detector were present; without one, there were differences according to the ignition source, with the gas burner the most severe, followed by the heater, the match, the lamp, and the cigarette. CBUF conducted furniture calorimeter experiments in which a propane burner, 115 × 115 mm, delivered 1.7 or 5.8 kW for 90 seconds, and 30 kW for 120 s (measured heat released by the burner was 153, 522, and 3600 kJ, respectively).[131] (See Ref. 7, Appendix 4.) Again, the shapes of the HRR versus time curves were very similar for all three ignition conditions but the peaks occurred at different times when measured from time of ignition. However, the times to peak measured from sustained ignition (defined as when 50 kW HRR first occurs) were essentially identical. CBUF assumes detectable fires to be of about 50 kW size, and that below this HRR the occupants of the room may not notice a fire if their attention is directed somewhere else.[137] Times from 50 kW to peak HRRs were practically identical, regardless of ignition source. With this assumption, the ignition source becomes unimportant for estimates of escape times. Similarly, three sets of chairs ignited with a 10 kW gas burner at the outside front, back, side, and inside seat produced similar peak HRR values, but again at different times from ignition.[133] A group of Finnish workers have studied the burning behavior of furnishing items which are often the first item to ignite and may serve as an ignition source for upholstered furniture: polyethylene waste paper baskets, cellulosic curtains, commercial chair and chair mockups built according to the BS 5852 with cellulosic fabric and polyurethane foam; television sets; and Christmas trees.[146] The room size was 3.6 × 2.4 × 2.4 m, with a 2.0 × 0.8 m door. The results are shown in Table 4-6. The items could be grouped according to peak HRR as follows: below 100 kW, waste paper baskets which could only ignite items very near or above them; HRRs of 100–200 kW, from TV sets (which burned for a long time), curtains, and chairs (the latter with much shorter burning times); and 500–600 kW, dry Christmas trees with such rapid heat evolution that escape would be difficult.

182

Fire Behavior of Upholstered Furniture and Mattresses

4.7.0

LARGE OPEN-FLAME OR RADIATION SOURCES

For discussion purposes here, a large open-flame source is one which is substantially larger than a match, a cigarette lighter, or even the TB 133 newspaper or gas ignition sources (approximately 18 kW). The small polyethylene wastebasket, of about 7 liters capacity, which has been discussed above, has been used for testing;[145] filled with milk cartons, it burns at an average of approximately 50 kW heat output for 200 s.[142] This HRR is much smaller than that of a fully-involved, full-sized upholstered item itself (several hundred kW). The results in Table 4-11 show that ignition with a small wastebasket, with peak fluxes of about 35 kW m-2, as discussed below, is easily achievable for almost any common upholstered item. This table also shows ignition times under 20 and 40 kW m-2 irradiance for the 12 furniture combinations. They range from 20 s to no ignition at the lower irradiance, and only from about 11 to 18 s for the higher irradiance. However, since this study was performed, more ignition resistant constructions have become more common, due to use of FR fabrics, effective interliners, and FR paddings such as CMHR foams and FR cotton batting. Nevertheless, a large part of the existing, and many of the newer, residential furniture items can be expected to ignite from large ignition sources and ignitability may not be an important variable for direct hazard assessment. As discussed earlier, the consequences of ignition in terms of HRR, time at which HRR increases rapidly and time of peak, flame spread, smoke, and toxic gas development differ greatly for various furniture composites. TB 133 has approached this problem for institutional furniture by stipulating that no institutional furniture should have a peak HRR of more than 80 kW, which would not cause ignition of other furniture except in very close proximity. Thus, the ignition and weak burning of such furniture would not only preclude flashover but also, in most cases, ignition of adjoining items. Smoke and toxic gases distributed throughout the structure may still be a problem, particularly if there is prolonged smoldering. CBUF found that the smallest flux which ignited upholstered composites was about 7 kW m-2 (Ref. 7, Appendix 3.2). Based on this, a chair burning with a HRR of 400 kW, a rather conservative value, combustible materials could ignite at distances up to 1.3 m.

Ignition Sources

183

Table 4-11. Comparison of Full-Scale Ignition Results Using a Wastepaper Basket and 20 and 40 kW/m2 Irradiance Sources Item

Type

Frame

Fabric

Padding

Total Waste- Time to Ignition(s) mass basket @ 20 @ 40 kW/m2 kg Ignition kW/m2

F02

tulip chair

molded thermoplastic

cotton

polyurethane foam

8.5

Yes

29

14

F16

traditional chair

wood

poly propylene

polyurethane foam

23.4

Yes

38

14.5

F08

side chair (Breuer)

chromed steel

nylon

polyurethane

9.4

Yes

did not ignite

41

F03

armchair

chromed steel

PVC

polyurethane foam

13.2

Yes

25

14

F04

armchair

oak (exposed)

PVC

polyurethane foam

27.8

Yes

18, 311

11, 9.3

F05

loveseat

oak (exposed)

PVC

polyurethane foam

45.9

Yes

29

11

F12

armchair

chrome steel

PVC

polyurethane foam

17.1

Yes

24

11.4

F13

sidechair

oak (exposed)

PVC

7.3

Yes

41

18.5

F15

armchair

oak (exposed)

PVC

polyurethane foam polyurethane foam

18.5

Yes

22

15.3

F17

molded pedestal chair

polyethlene

PVC

polyurethane foam

18.0

Yes

20,31

12.0, 17.3

F20

stacking chair

metal

PVC

polyurethane foam

7.7

Yes

32,32

12.4, 11.3

F18

prison chair

FR polyurethane

Nomex

neoprene foam

35.6

No

did not ignite

did not ignite

1. Denotes values for seat and back, respectively. NA - not available.

184

Fire Behavior of Upholstered Furniture and Mattresses

Figure 2-7 in Ch. 2 shows Cone Calorimeter irradiance-ignition time curves for commercial upholstery composites covering essentially the complete range of fire resistance, from the highly fire resistive wool fabric/ neoprene padding combination, to the readily ignitable polyolefin/nonFR PU combination.[362] The irradiance at which ignition occurred1 ranged from 5.6 to 14.5 kW m-2. The most ignition-resistant composite (wool/ neoprene) showed a minimum irradiance for ignition of 14.5 kW m-2. Exploratory tests were also run on this composite in a larger, experimental calorimeter on 250 × 250 mm specimens.[363] Despite the fact that both provide uniform, well-characterized irradiances and similar electric spark ignition, the tests in the latter required 65 kW m-2 for ignition. The explanation lies in detailed observations of the ignition event. In the first case, the wool intumesced, pyrolyzed, charred, eventually cracked in the char, and then ignited and burned primarily at the crack. In the second case, ignition was not achieved until the surface was raised enough in temperature to ignite uniformly. Minor differences in specimen size and tension and, consequently, amount of shrinkage and tendency to split open, edge conditions, convective flows, and pilot spark details can be enough to create the different ignition sequences. Similar effects of wool fabric splitting have been observed by others.[322][364] While no systematic study is yet available on apparatus effects for fabric/padding ignition, observations suggest that significant differences are likely to occur only for a few highly ignition-resistive materials, such as wool, and not for more common furniture materials, especially not thermoplastic fabrics. Times to ignition at 20 and 50 kW m-2 irradiance and threshold irradiances at which ignition occurred varied greatly, as shown in Table 12. [365] Table 13 shows the effect of irradiance level on ignition times and HRRs of ordinary and FR polyurethane foams.[366] Such results are very substrate dependent and are discussed in Ch. 6.

1

These measurements were made early during the development of the Cone Calorimeter. The CBUF value of 7 kW m-2 would apppear to be more reliable than 5.6 kW m-2 as an indicator of the minimum flux for ignition.

Table 4-12. Ignition Times and Critical Fluxes of Various Composites As A Function of Irradiance Fabric

Wt.

Mineral Fiber batting t20 t50 s s

crf

None

–

∞

∞

–

Cotton

14 9 31 9 34 8

7

3 1 3 9 5 6

Cotton 55/45 cotton /linen Rayon

t20 s

crf

t50 s

t20 s

crf

t50 s

t20 s

crf

11

5

30

16

5

23

12

11

7

28

11

8

25

11

10

9

41

12

11

46

10

11

1 1

50

11

13

54

11

1 6 2 8

51

10

17

57

10

80

11

22

10 3

9

1 9 1 1

∞

24

20

∞

32

40

11

11

44

11

34

9

7

35

8

∞

25

4

11

37

12

7

10

9

52

10

11

1 1

48

12

1 1 1 3

3 7 2 8 4 0 5 4

5 7 8 3

10

1 2 8

70

10 10

6 7 8 9

10

11 6

1 3 2 4

1 9 1 1

∞

25 11

6 9 4 0

12

43

2 1 1 1

32

8

6

4 0

17

45 8 38 3

20

∞

25

11

4 0

11

7

3 3

8

66 1

t50 s

1 0 7

43 8 77 3

32

PU foam

10

6

9

11

8

8

Latex foam

Wt. - weight, g/m2; t50 - time to ignition (s) at a radiant flux of 50 kW/m2; t20 - time to ignition (s) at a radiant flux of 20 kW/m2; crf - critical radiant flux for ignition (kW/m2)

185

PU; cotton scrim PVC; cotton scrim

12

Cotton batting

Ignition Sources

54/46 rayon/ wool wool

10

Wool waste, teased t50 t20 crf s s

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Fire Behavior of Upholstered Furniture and Mattresses

Table 4-13. Effect Of Irradiance Level On Ignition Time And Heat Release Rate Of Various Foams Fire Property

NFR PU foams

FR PU foams

21 kg/m3

25 kg/m3

25 kg/m3

28 kg/m3

5.5

5.2

39.2

15.0

433

466

438

467

278

272

276

230

3.3

3.3

4.1

4.1

1059

876

1029

844

443

470

456

428

1.3

NA

2.7

2.9

Irradiance = 25 kW kg/m2 Ignition time (s) Peak HRR

(kW/m2)

60 s avg. HRR (kW/m2) Irradiance = 50 kW/m2 Ignition time (s) Peak HRR

(kW/m2)

60 s avg. HRR (kW/m2) Irradiance = 75 kW/m2 Ignition time (s) 2

Peak HRR (kW/m )

1773

1810

14229

1862

60 s avg. HRR (kW/m2)

501

646

545

561

Note: All tests were conducted in the Cone Calorimeter. Horizontal orientation, 100 × 100 × 50 mm thick samples.

5 Effects of Test Apparatus and of Test Scale

In this chapter, results of various tests of the same composites will be compared. Some of these will be comparisons of results of various bench scale methods; others are comparisons of full-scale and bench-scale test results. This is of major interest because of the complicity and cost of fullscale tests. This chapter focuses on the quality of the correlations; review of the actual results, in terms of ignitability, heat release, etc. of the materials tested can be found in Ch. 6. The fundamental principles of correlation between HRR results obtained on the Cone and furniture calorimeters and in room tests are discussed in Ch. 2, and the appropriate modeling in Ch. 7. Experimental results along these lines are discussed below.

5.1.0

COMPARISON OF BENCH-SCALE RESULTS

Ohio State University Calorimeter (OSU) heat and smoke release plots are given for California TB 117, melamine modified, and hydrate alumina filled polyurethane foams.[367] The results, obtained at various heat fluxes, were compared with the downward flame spread rate in a Limited Oxygen Index (LOI) apparatus, at various oxygen concentrations. Correlation of OSU and LOI results was obtained only by choosing different

187

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Fire Behavior of Upholstered Furniture and Mattresses

constants for the LOI measurements for each foam type. Mass burn rate was found to be irrelevant for predicting HRR for foams differing in FR agents and fillers (e.g., the hygroscopic hydrated alumina fillers had big mass loss and low HRR). Temperature increase in the chamber of a horizontal LOI test setup correlated well with weight loss in BS 5852 crib 5 tests, for a variety of FR foams tested without fabric.[368] Cone Calorimeter and BS 5852 rankings were very similar in tests of composites of two foams, one ordinary and one containing melamine, and 18 fabrics.[369] Among the fabrics were commercial thermoplastic and commercial and experimental PVC fabrics. The authors also found the Cone Calorimeter an excellent predictor of full-scale fire performance. Twenty eight mock-ups (four fabrics, seven foams varying in density and FR additives) were tested in two calorimeters: the Cone Calorimeter at 17.5 and 25 kW m-2, and the Ohio State University (OSU) calorimeter at 17.5 kW m-2. [370] The correlation coefficient for the Cone and OSU peak HRR results was 0.75, for total heat release, 0.84, and for total heat release at 4 minutes, 0.93. Similar results have been obtained with other product types. The lower results obtained in the OSU calorimeter are due to heat losses. 5.1.1

Comparison of Fabric and Fabric/Padding Composite Test Results

Bench-scale fabric tests which measure vertical, 45°, or horizontal flame spread rates were found to be poor predictors for the behavior of thermoplastic fabrics which melt and ablate instead of burning rapidly and which generally pass such flame spread tests. However, in real upholstery, thermoplastics open up and expose the padding. Sometimes the melting material forms ridges which themselves act as secondary ignition sources. With some laboratory effort a fabric test probably could be developed which would take into account both resistance to ignition and resistance to cover fabric penetration by the flame after ignition. Also, putting tension or pressure on Cone Calorimeter specimens may indicate which fabrics open up because of melting or formation of brittle chars. A study carried out in New Zealand[357] compared the results of a variety of fabric tests (horizontal and vertical flame spread tests as well as a flammability index, a combination of HRR and spread of flame on fabrics), with those in the British 5852 mock-up, using PU foam as the

Effects of Test Apparatus and of Test Scale

189

padding. Ignition sources were wooden matches, 13.2 g newspaper, and the BS 5852, 8.5 g wood cribs. Another study, from Finland, compared the results of mock-up tests and tests on residential upholstery fabrics alone.[347] Twenty-five upholstered furniture cover fabrics were tested with small fabrics specimens held at 45° and ignited 25 mm from their bottom end with a tiny gas flame. (This is similar to the US apparel fabric test[240] except that a 60 s ignition time was used instead of 1 s). The time to burn 127 mm was reported. The results were compared to those of mini-mock-up tests in which six padding substrates (glass fiberboard, untreated and FR PU foam, cotton batting, and untreated and FR polyester batting) were exposed to the small BS 5852 No.1 gas flame. Some of the fabrics were also tested in the British mock-up arrangement over untreated and FR PU foams. For some fabrics (wool blends, cellulosic blends, etc.) the 45° test was somewhat predictive of mock-up behavior. The wool blends generally self-extinguished in the fabric test, and did not ignite in any of the minimock-ups, while fabrics which ignited and burned fairly rapidly in the 45° test also ignited in the mini-mock-ups. Three fabrics, with burn times of 40 to 56 s, ignited in some mini-mock-ups and not in others. However, the one 100% thermoplastic fabric in this series performed poorly in the minimock-up tests but very well in the fabric test. In a similar study, vertical and 45° fabric tests also did not predict ignition when the fabrics were used as mattress covers.[352] When ten of these fabric/foam composites were tested in the larger BS 5852 mock-up arrangement, the non-thermoplastic fabrics, which selfextinguished in the 45° test, passed the BS 5852 gas flame 1 test and performed quite well with a more intense flame as well as with the methenamine pill and the NORDTEST 40 g wood crib, especially over FR foam (Table 4-9).[347] Among the fabrics which burned in the 45° test, time to burn 127 mm was somewhat predictive of behavior in the UK mock-up. Again, the 45° fabric test seemed to approximately predict behavior of the non-thermoplastic fabrics. Tests by Braun et al. on transportation vehicle mock-ups[288][289][296] included a comparison between full-scale results and measurements with the vertical 5903 (vertical specimen, bottom edge ignition)[239] and horizontal MVSS 302 bench-scale ignition[67] tests. Neither of these Bunsen burner tests was found useful in predicting the full-scale hazard. A major project had the objective of demonstrating the practicality and effectiveness of HRR-based methods and hazard analysis techniques when applied to passenger rail car safety.[583] The results are discussed in

190

Fire Behavior of Upholstered Furniture and Mattresses

more detail in Sec. 6.2.2. Cone Calorimeter results were compared with those of the presently prescribed ASTM tests for a number of materials, and it was concluded that the Cone Calorimeter HRR data would better predict the real scale burning materials and assemblies in a more cost effective way than presently prescribed methods. In addition, HRR data can be used as an imput in fire modeling and hazard analysis. The FAA and the US Coast Guard have already accepted the use of HRR data to evaluate the performance of certain aircraft and marine vessel materials. The European Railway Research (ERRI) and the Commission for European Standardization (CEN) are developing a database using the Cone Calorimeter to provide small-scale test data on materials and assemblies, and the furniture calorimeter to provide real-scale assembly test data. In addition, less uncertainty is claimed for the Cone Calorimeter data. Similarly, results for aircraft seating type fabrics tested by Method 5903 as required by the Federal Aviation Administration,[66] did not relate to the behavior of fabrics in aircraft seat composites.[346] The small BS 5852 gas flame l, methenamine pills, and 18 g of newsprint were used as ignition sources in the seat tests. Only three fabrics, FR nylon, FR polyester, and FR wool, passed the vertical fabric test. The FR wool passed the mock-up test (with PU foam as the padding) with all three ignition sources; as could be expected, FR nylon and polyester failed when exposed in the same manner. On the other hand, an untreated wool fabric which failed the vertical fabric test passed in the seat test with the butane flame but not the other ignition sources. All other fabrics (nylon, polyester, polypropylene, acrylic, cotton, and acrylic/cotton) failed both the fabric and mock-up tests.

5.2.0

COMPARISON OF BENCH AND FULL-SCALE RESULTS

5.2.1

Flammability Results

An early analysis by Paul of the relationship between bench and full- scale ignition, flame spread, and smoke tests covered the 1985 state of the art.[230] Since that time, considerably more progress has been made, as discussed below. Because the TB 133 procedure requires a special test room and extensive instrumentation, several attempts have been made to develop screening tests providing results which correlate with TB 133 results. Some

Effects of Test Apparatus and of Test Scale

191

of these studies have been discussed in Ch. 2 from a somewhat different point of view. Several papers report attempts by members of The Society of the Plastics Industry, Inc. (SPI) to predict TB 133 results by means of benchscale tests. Results from the OSU heat release apparatus and the TB 133 were compared.[371] Thirty-nine fabrics were tested with one melamine treated foam. At a very low heat flux of 10 kW m-2, 11 of 12 specimens which clearly failed TB 133 had a weight loss of between 42 and 92% in the OSU test; 22 of 23 samples which clearly passed TB 133 lost between 8 and 35%; and the results were inconclusive for four samples which marginally passed TB 133 and lost between 8 and 80%. In another paper, a self-propagating flux parameter in the radiant panel test ASTM 906 was suggested as a predictor of TB 133 results; however, this was not adopted because the parameter was considered too subjective.[372] Also suggested as a TB 133 results predictor was the cumulative heat release over 3 minutes in the OSU calorimeter.[373] Correlation of TB 133 room temperature results with results by an instrument using the LOI principle was somewhat erratic.[374] The horizontal fabric/foam specimens were placed on a load platform inside a watercooled heating duct. An oxygen concentration of 45% was found to give the best differentiation between specimens differing in FR characteristics. In a comparison of results of BS 5852, crib 7, TB 133, and the Boston Fire Department Test, composites covered with thermoplastic fabrics failed all three tests; char forming fabrics fared better.[375] All tests agreed on mass loss and flame out time pass/fail criteria, but smoke results were not consistent. 5.2.2

Comparison of Cone Calorimeter and Full-Scale Results

In the following, comparisons of Cone Calorimeter and various full-scale and large-scale results will be discussed. In some cases, the Cone Calorimeter results were predictive of the other tests, in others they were not. Considering the infinite number of fabric/padding combinations, furniture configuration and frame materials, this should not be too surprising. In a joint study by NIST and BHFTI, ten pairs of chairs were tested in the BHFTI and ASTM rooms, and the results were compared with Cone and furniture calorimeter tests.[35][36][126] The use of the results to predict propagating and non-propagating fires has been discussed in Ch. 2. In addition, the following was concluded:

192

Fire Behavior of Upholstered Furniture and Mattresses • Similar results were obtained in the TB 133 room and the somewhat smaller ASTM room. • Below 600 kW the HRR of the chairs in the two rooms were the same as those measured in the furniture calorimeter. • The correlation of the peak HRR in the furniture calorimeter and the 180 s average HRR in the Cone Calorimeter is shown in Fig. 2-5. As discussed earlier, a linear correlation was obtained until the 180 s average HRR in the Cone Calorimeter reaches about 110 kW m-2. Up to this range, the chair fires were nonpropagating; from 110 to 180 kW m-2 they were borderline between propagating and non-propagating. Above 180 kW m-2 the correlation is also linear but with a much steeper slope, and the fires were selfpropagating. Similar correlations were obtained with the room fire test results, but the second slope was about 50% higher, (Fig. 5-1; note that ordinate scale is in MW rather than kW), due to the radiation reinforcement from the walls, ceiling, and the hot upper gas layer. • A peak HRR of 65 kW in either of the rooms or in the furniture calorimeter was equivalent to one of the original TB 133 pass/fail criteria of 111°C (200°F) heat rise 25 mm below the ceiling above the chair in the TB 133 room; this corresponds to a 180 s average HRR of 87 kW m-2 in the Cone Calorimeter. This would, of course, have to be confirmed by further experiments and may only apply to the particular style and size of the chairs in these experiments. In the mean time, once a particular chair with a specified style and frame has been tested in the furniture calorimeter and found to have a 180 s average HRR indicating non-propagating fires, the effect of changing fabric, interliner, and padding could conceivably be evaluated in the Cone Calorimeter.

Effects of Test Apparatus and of Test Scale

193

• A heat flux of 20 kW m-2 on the floor of a room is sometimes taken as an indication of flashover. Figure 5-2 shows the peak heat flux on the floor versus the peak HRR. The plot suggests that a peak HRR of 1.8 MW was required for flashover with these chairs. This is consistent with the observed sharp rise in the peak concentration of CO at that peak HRR (Fig. 5-3). (The lack of data points in the TB 133 room for the chairs with the high HRRs was due to the fact that these fires were extinguished before the peak HRR was reached.) • Finally, the peak radiant heat flux 0.76 m from the chairs correlated well with the peak HRR, as shown in Fig. 2-12.

Figure 5-1. Peak HRR in ASTM room versus 180 second average HRR in Cone Calorimeter.

194

Fire Behavior of Upholstered Furniture and Mattresses

Figure 5-2. Peak heat flux on floor versus peak HRR.

Figure 5-3. Peak CO concentration versus peak HRR in the ASTM room.

Effects of Test Apparatus and of Test Scale

195

An opportunity to validate these results occurred when some years later, CBUF also compared room and Cone and furniture calorimeter HRR results.[131][149] In addition to the CBUF statistical predictions (Ch. 7), Krasny and Parker examined the CBUF data for simple correlations but included the data from an earlier joint NIST/BHFTI study.[139] The ignition conditions differed in the two studies: CBUF used the TB 133 gas burner, but increased its gas flow from 18 to 30 kW and the duration from 80 to 120 s; NIST/BHFTI used the original approximately 18 kW newspaper ignition source. Based on this study, which included a much larger number and variety of typical European commercial as well as some systematically varied chairs, and some sofas and mattresses they concluded that: • The best simple correlation between the CBUF fullscale results and Cone Calorimeter results was obtained at a Cone 300 s average HRR with 50 kW m-2 incident flux. By contrast, the NIST/BHFTI study earlier had compared the Cone 180 s average HRR at 35 kW m-2 with the full-scale peak HRR.[35][36] Such conclusions cannot be generalized about truly best test conditions, however, since an extensive variety of test conditions was not tried. • As indicated in Ch. 2, below a Cone Calorimeter HRR of about 110 kW m-2, (50 kW m-2 irradiance, 300 s averaging period) the corresponding full-scale chair fires did not propagate; above 130 kW m-2, the chair fires propagated. The transition zone of 110–130 kW m-2 was thus much narrower than that found in the NIST/BHFTI work, which was 105–180 kW m-2.[35][36] • The CBUF data show that above a peak HRR of 450 kW, the room peak HRR values were higher than those in the furniture calorimeter; the corresponding value was 600 kW in the BHFTI/NIST work. The increased HRR in the room can be readily explained by reradiation from the hot walls and ceiling and from the hot smoke layer. The interaction would be greater in rooms even smaller than the 9 m2 ISO room, or with walls of lower thermal conductivity than the lightweight concrete used in the ISO room. Figure 5-4 shows the relationship for the BHFTI/NIST and the CBUF chairs, which included various frame types and

196

Fire Behavior of Upholstered Furniture and Mattresses fully upholstered, executive, and secretarial chairs, with the later having only metal frames and plastic shell, lightly upholstered supporting structures. • Thermoplastic fabrics and leather, which shrink and expose the padding to the ignition source, had relatively high room peak heat release values, as indicated by the uppermost line in Fig. 5-4.

Figure 5-4. Peak HRR in the ISO and ASTM rooms versus that in the furniture calorimeter for CBUF and NIST/BHF chairs.

The relatively similar results obtained in the CBUF and NIST/ BHFTI studies lead to the following conclusions: • Fabric/padding combinations which have a peak HRR of less than 80 kW in the furniture calorimeter using the BHFTI/NIST ignition source (or slightly more under the CBUF conditions) can be assumed to correspond to chairs which pass TB 133, and are nonpropagating. • Furniture calorimeter peak HRR values of less than about 400 kW would not produce higher HRR in most rooms. Besides the above work, CBUF developed three models for prediction of full-scale from Cone Calorimeter results on the fabric and foam separately, as discussed in Ch. 7.

Effects of Test Apparatus and of Test Scale

197

The mattress HRR behavior was investigated during another joint NIST/BHFTI investigation.[8][260] Results from the Cone Calorimeter tests conducted at an irradiance of 35 kW m-2 were compared against the fullscale test results for mattresses (Fig. 5-5). A simple correlation for the propagating-fire regime of mattresses without bedding was not observed in these tests. One reason may be the relatively small number of propagating fires that were studied. Other BHFTI tests were conducted with box springs or with bedding and could not be compared to the bench-scale results. The results show that propagating full-scale mattress fires did not occur until a Cone Calorimeter value of around 140–150 kW m-2 HRR (180 s average) was reached. The difference in this range and the ranges found in other studies on upholstered chairs may be due to the differences in specimen geometry.

Figure 5-5. Full-scale peak HRR of mattresses in TB 133 room versus their 180 s average HRR in the Cone Calorimeter.

198

Fire Behavior of Upholstered Furniture and Mattresses

Ames and Rogers used the original natural convection (12 m chimney) FRS furniture calorimeter and the NORDTEST NT 032 furniture calorimeter (fan exhaust) as well as the Cone Calorimeter to test a number of composites typical of the UK market.[140] They ranged from polypropylene fabric over ordinary polyurethane to contract furniture utilizing such materials as wool/FR viscose, interliners, and FR foam. The tested articles included mock-ups, armchairs, and settees. The peak HRR in the Cone Calorimeter at 35 kW m-2 irradiance ranged from 220 to 665 kW m-2 and from 280 to 855 kW m-2 at 50 kW m-2. In the furniture calorimeter, they varied from 34 to 920 kW for mock-up armchairs and from 572 to 2260 kW for real armchairs (including frames, etc.). The corresponding range of times to peak were from 100 s to 24 min, and from 160 s to 26 min, respectively. Except for one specimen, the peak HRR in duplicate Cone Calorimeter tests at 35 kW m-2 irradiance varied by only 1 to 12%. The times to peak, however, varied more. The correlation between Cone Calorimeter and the furniture calorimeter results (peak HRR) of a number of composites was examined. A rank order correlation coefficient of 0.96 was obtained. Note that these results apply to mock-ups; use of different frames may change such results. In a later, large experimental series at FRS, the NORDTEST (NT 032) furniture calorimeter procedure was used on a variety of bedding and upholstered furniture composites which exhibited a wide variety of ignitability characteristics (igniting with BS 5852 flames 1 to 7).[126][140] Very little correlation was seen between the bench-scale and the large-scale results in this test series. Hurd et al. analyzed some three-seat settees and armchairs in a furniture calorimeter, the TB 133 room, and in a semi-quantitative roomcorridor test.[376] Data for the composites were obtained from the Cone Calorimeter at 10, 17.5, and 30 kW m-2 irradiance. Various composites were not tested under all of these test conditions, which makes general comparisons somewhat difficult. It was noted that some match-ignitable composites did not ignite at the lower level Cone irradiance; this may be because matches can deliver more than 20 kW m-2, or because of differences in flame and irradiance/spark ignitability. Different irradiances produced different rankings of some of the composites, perhaps again for some of the above reasons and the possibility of fabrics opening up and exposing the padding at higher irradiances. With some exceptions, the authors considered the Cone Calorimeter peak HRR predictive of the full-scale results, and the 180 s average Cone results at 35 kW m-2 related very well to the visual observations of the

Effects of Test Apparatus and of Test Scale

199

fires. However, the Cone Calorimeter results for non-propagating tests, or time to peak heat release were not considered related to full-scale results. A large cooperative study of the relationship between Cone Calorimeter and TB 133 results was undertaken by the Association of Contract Textiles, the Decorative Fabric Association, and the California Bureau of Home Furnishings.[377] It has not been fully evaluated but tentative findings were: • The TB 133 mock-ups (with the gas ignition source removed after 80 s) generally produced a single HRR peak, while the Cone Calorimeter (at 35 kW m-2 irradiance, with the spark ignitor active during the test period) produced two distinctive peaks. Often the second peak occurred after a period of low heat release. • The large data base 80 TB 133 and 300 Cone Calorimeter tests on mock-ups of 27 typical fabrics, two interliners (aramid and coated glass), and two foams (TB 117 and melamine types) did not produce a simple relationship between Cone Calorimeter and TB 133 results. (The performance of one of the interliners was found to be erratic, and this may have led to part of the difficulties). Another comparison of Cone Calorimeter results with TB 133 mock-ups exposed in a furniture calorimeter instead of a room also gave inconclusive results.[378][379] In the latter cooperative study between NIST and DuPont, the authors investigated a number of detailed full-scale phenomena which could affect bench-scale predictability. Among them are: seat cushion width; fire tunnels at the juncture of seat, side and back cushion; char formers which protect the foam especially in the presence of barriers while thermoplastic fabrics break open; position of the ignition source, etc. As far as correlations go, the authors investigated a number of possibilities (including correlation functions of, e.g., full-scale peak HRR, and Cone peak HRR, peak time, ignition time, heat of combustion, etc). More simply, they found a fair predictability of the first full-scale peak, on the basis of the 60 s average Cone Calorimeter HRR (at 35 kW m-2) irradiance. In general, predictability was easier for charring fabrics than for thermoplastic ones. Other full-scale features were harder to predict, and the authors recommended that further work was needed.

200

Fire Behavior of Upholstered Furniture and Mattresses

5.2.3

Comparison of Furniture Calorimeter and Room Results

Besides the studies discussed above, there are several older studies designed to yield comparisons between furniture calorimeter free-burn rates and rates in room fires, including post-flashover fires. One such study was for chairs,[155] and one for beds.[267] In the latter study the furnishings included, in addition to a bed (mattress, box spring, and bedding), a plywood headboard and night table. The room tests were done in a 2.4 m × 3.7 m × 2.4 m high room with a 0.76 m wide by 2.03 m high doorway. Thus, a minimum expected flashover level (Eq. 26, Ch. 2) would be 1130 kW. The free burning rate was determined with a furniture calorimeter and is shown in Fig. 5-6. Two peaks are seen: an initial one corresponding to a rapid burning of the bed linens, at 480–720 kW; and a second one corresponding to mattress involvement, at 1090–1210 kW.

Figure 5-6. Comparison of furniture calorimeter and room fire HRR values for bed, bedding, and night table.

Effects of Test Apparatus and of Test Scale

201

The room fire data, also shown in Fig. 5-6, are somewhat difficult to interpret since the test room was not fully noncombustible, but had a paper lining on gypsum wallboard. This paper lining, when ignited, burns rapidly and can contribute a relatively high rate of heat release spike, generally very shortly after ignition. The spikes at 2000–2040 kW are attributed to wallboard paper flaming (the time sequence was sensitive to very minor test differences). Ignoring the peaks due to paper burning, the initial bedding peak is at 440 kW, i.e., not showing any radiative augmentation. The second peak is at 1430 kW, compared to 1090–1210 kW in the open burns, suggesting a 15–30% augmentation. Finally, there is a third peak seen in one of the room burns, not seen in the replicate or in the open burns. This is believed to be due to an earlier dying-down in the second peak for that test. Thus, the heat output seen in the third peak is divided in other room burns between increased duration of the second peak and increased heat liberated during the final, smoldering period. Another test series including furniture calorimeter and room tests was for an upholstered armchair and a love seat.[157] The room size was 3.94 × 2.26 × 2.31 m high. The armchair (F21) was tested with a single ventilation opening, while the love seat (F31) was tested with three ventilation configurations. In each case the openings were so sized as to produce flashover, but not ventilation-limiting. Peak heat release values ranged from 0.42 to 0.68 of the maximum stoichiometric limit for burning within the room. The results are shown in Fig. 5-7 and 5-8. To within the scatter of the data (about ± 15%), there does not appear to be a significant burning rate enhancement in the room fires in this case, compared to freeburn furniture calorimeter measurements (the time shift is due to differences in ignition). The CBUF study provides opportunity for comparison of room and furniture calorimeter results (Tables 2-3 and 2-4).[131][149] Discussions of this comparison and the augmentation effect of the room enclosure on HRR can be found in Ref. 139. The ranges of HRRs at which this augmentation seems to occur in the CBUF and other studies is discussed in detail in Ch. 2 and in Sec. 5.2.2. CBUF also compared the results for different room and door [131] The smaller ISO room produced somewhat higher mass loss rates sizes. than an eight times larger room. In the ISO room, ventilation is restricted for fires larger than about 1000 kW. Reducing the door size to 1/4, 1/8, and 1/16 resulted in peak heat release reduction of about 25% for each step for one chair, and by about 60% from fully open to 1/8 door opening for three faster burning chairs.

202

Fire Behavior of Upholstered Furniture and Mattresses

Figure 5-7. Comparison of furniture calorimeter and room fire HRR values for an upholstered chair.

Effects of Test Apparatus and of Test Scale

Figure 5-8. Comparison of furniture calorimeter and room fire HRR for a loveseat.

203

204

Fire Behavior of Upholstered Furniture and Mattresses

5.2.4

Smoke Results

The fundamentals of smoke and toxic products generation are discussed in Ch. 2, and results for individual materials and composites can be found in Ch. 6. Paul found a good correlation between results on upholstery composites obtained by four bench-scale smoke tests and full-scale data.[331] Difficulties arise when composites are completely burned in the benchscale tests but not in the full-scale tests (because of, e.g., effective interliner or FR treatment of foams), in which case bench-scale tests can produce overestimates. In a smaller test series conducted in Finland, however, a correlation was not found between Cone Calorimeter smoke results and the peak smoke densities in room and furniture calorimeter results on full-scale furniture.[380] It should be noted that irradiance levels in the Cone Calorimeter strongly affected the results; considerably more smoke was found with 25 kW m-2 irradiance in the Cone Calorimeter which caused only smoldering in certain substrates than in flaming. Smoke production per mass burned was found to be higher in the Cone Calorimeter than in the furniture calorimeter. A specific model for predicting smoke results was developed in the CBUF study; this is presented in Ch. 7. Also, in the CBUF ventilationvariation experiments, some smoke observations were made. The smoke peak rate dropped to about 1/4 to 2 when the door opening size was reduced to 1/8th of original, depending on the materials involved.[131] Further, reduction to 1/16th resulted in no further reduction in the peak smoke release rate but increased the time to reach the peak. 5.2.5

Toxicity Test Results

Earlier work on comparison of bench-scale and full-scale toxicity results was reviewed in 1987.[188] Newer comparisons involving upholstered furniture are discussed in Ref. 161. A cotton upholstery fabric with an ordinary polyurethane foam and with a TB 117 FR foam were used in the NBS Toxicity Protocol bench-scale test and in two fire room tests: (1) a single cushion burning by itself in a single compartment, and (2) four cushion chair mock-ups in a three compartment test.[188] The ignition sources were cigarettes and a gas flame. The following was concluded:

Effects of Test Apparatus and of Test Scale

205

• Within a factor of two, the bench and full-scale tests yielded similar LC50 results; a factor of three is considered acceptable. • There were major differences in the post-exposure time of animal deaths. • The CO2/CO ratios for the bench and full-scale tests were similar, but differences in HCN production indicate different decomposition mechanisms. • The N-gas model for CO, CO2, HCN, and reduced O2 accounted for deaths within-exposure plus twentyfour hours during the full-scale tests and the fact that there were no within-exposure plus twenty-four hours deaths during the bench-scale tests. During another study of composites containing non-FR and FR polyurethane foams, they were tested in the Cone Calorimeter, by the NBS cup furnace method, in the NIST furniture calorimeter, and in room/ corridor tests.[181] In general, the large-scale tests confirmed the smallscale toxicity results, in terms of not finding extremely or unusually high toxicity. The NBS cup furnace and the Cone Calorimeter produced lower CO values than the furniture calorimeter. There was no agreement between the furniture calorimeter and the room/corridor tests. However, CO2 and HCl, HBr, and HCN yields, wherever they were significant, showed agreement in these tests. The authors concluded that the answer to the question of bench-scale ability to predict full-scale results was mixed for the five products tested. Purser compared toxic gas yields obtained with a heavy cotton fabric over ordinary and FR polyurethane foams in the NBS cup furnace and the Cone Calorimeter and full-scale results of furniture calorimeter and room/corridor tests.[206] He obtained results during flaming and smoldering (both before and after flaming) decompositions, and calculated the estimated times to incapacitation from the two types of foam. The results provide a complex, not wholly consistent picture: • There was considerable spread between the bench scale results for CO, HCN, and CO2. • The furniture calorimeter test produced more CO than the room test for both foams, but the picture was reversed for HCN and CO2 for the untreated foam and inconsistent for the FR foam.

206

Fire Behavior of Upholstered Furniture and Mattresses • Toxic product yields were increased when smoldering preceded flaming. • The FR foam appeared to be more toxic to the test animals.

The author concluded that small-scale tests can be used to predict full-scale fire performance during early stages of flaming and that more data are needed. In another study, there were differences between Cone Calorimeter and full-scale CO peak concentration rankings.[376] Cone Calorimeter CO/CO2 ratios did not differ greatly from those observed in the room chair burns, while those in the furniture calorimeter were much higher. The effect of reduction of open door size in the ISO room to 1/8th normal width was material dependent, as expected.[131] CO concentration increased from close to 0 to over 1%, and HCN from about 30 to over 300 ppm for a chair covered with FR cotton over HR polyurethane foam.

6 Upholstered Item Design Engineering

The designer concerned with the flammability of upholstered items may need performance information to varying degrees of specificity. In the simplest case, generic information on the relative performance of various proposed component materials and their interaction may be sufficient. In the first several sections below, such information is presented in consolidated form. At the next level of detail, standard tests may need to be run on the component materials or their components under consideration. The more important available tests for this purpose have been described in Ch. 3. At the most detailed level, a state-of-the-art engineering analysis using modeling may need to be made. The pertinent techniques available for this are reviewed in Ch. 7.

6.1.0

IGNITION RESISTANCE TO CIGARETTES

The heats of combustion and other thermal properties of fiber materials from which upholstery fabrics are made are shown in Table 6-1. [379] It shows which fibers are thermoplastic, i.e., melt, and which are char formers. Otherwise, these properties seem to relate only in a few cases to the burning behavior in composite form. The relatively low cigarette ignition resistance of polypropylene (olefin) could be related to its 207

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Fire Behavior of Upholstered Furniture and Mattresses

low density (affecting its effectiveness as a heat sink) and melting point (exposing the padding). Similarly, polypropylene and nylon have relatively high heats of combustion which may contribute to their high HRRs found in many test series. Table 6-1. Thermal Properties of Polymers Fiber

Polypropylene Nylon Acrylic Modacrylic Polyester Wool Cotton Rayon Kevlar

Density g/cm3

Pyrolysis temp. °C

Ignition temp.a °C

LOI %

Heat of combustion MJ/kg

Melting temp. °C

0.96 1.14 1.17 1.35 1.34 1.31 1.35 1.50 1.44

320 to 400 300 to 400 250 to 500 140 to 170 285 to 305 130 to 300 285 to 300 177 to 230 475 to 495

350 to 495 390 to 510 465 to 500 s.e.b 390 to 508 570 to 600 250 to 260 420 to 570 s.e.b

18 to 19 20 to 21 18 to 19 27 to 31 20 to 22 24 to 25 17 to 19 17 to 19 28 to 32

46.5 33.1 31.8 ... 23.9 20.5 17.0 17.0 ...

160 to 177 216 to 260 does not does not 252 to 292 does not does not does not does not

a: by ASTM D 1929

b: self-extinguishing

During the 1970s and early 1980s, especially in the US, the emphasis was on the cigarette ignition resistance of various upholstery material composites. A 1981 bibliography of papers on cigarette and flame ignition of upholstered furniture contains 149 references.[2] Later, interest in flame ignition resistance and post-ignition behavior became more prevalent. While an attempt has been made in the following pages to separate the effects of various upholstery components, e.g., fabrics, padding, welt cord, etc. on cigarette ignition resistance, many papers on flame resistance and fire growth did not make these distinctions, and emphasis was more on fabric/padding composites which pass certain standards, for example, California TB 116 and 133, BS 5852, UFAC, or BIFMA. Table 6-2 summarizes the smoldering and flame ignition resistance of upholstery materials. The materials in the table are listed from top to bottom in the approximate order of decreasing resistance to cigarette ignition (Part A) and in order of decreasing resistance to small flames (Part B). There is considerable overlap between materials listed near each other, depending on such additional factors as furniture item configuration, fabric finish and back coating, and efficacy of any SR or FR agents.

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Table 6-2. Upholstered Item Components Listed in Approximate Order of Decreasing Ignition Resistance Cover Fabric1

Padding

Interliner

Welt Cord

Construction Parameters

A: Cigarette Ignition Resistance 1. wool, PVC 1. 2. heavy TP 2. 3. cellulose/TP blends (depend- 3. ing on TP%) 4. 4. light TP 5. 5. light cellulosics 6. 6. heavy cellulosics 7.

special foams2 SR cellulosic batting PE batting SR PU untreated PU mixed fiber batting cellulosic batting

1. aluminized 1. aluminized fabrics PVC 2. neoprene 2. TP sheets 3. SR cellulosics 3. vinyl coated 4. cellulosics glass fabrics 4. novoloid felt 5. TP fabrics 6. cellulosic fibers

1. flat areas 2. flat areas near welt cord 3. tufts 4. crevices

B: Small Flame Ignition Resistance and Fire Growth 1. FR wool 2. wool, PVC coated cellulosics3 3. cellulosics3 4. TP

1. special foams2 2. FR cellulosic batting 3. cellulosic batting 4. FR PU 5. PU 6. PE batting 7. latex foam

1. aluminized gas, impermeable fabrics 2. neoprene sheets3 3. novoloid fabrics3 4. aramid fabrics3 5. vinyl coated glass fabrics3 6. FR cellulosic fabrics3 7. cellulosic fabrics3 8. TP fabrics

not investigated

1. flat areas 2. vertical areas 3. corner areas

SR - smolder resistance; FR - flame resistant; PU - polyurethane foam; PVC - polyvinyl chloride; TP - thermoplastic 1 - Data on acrylic fabrics are scarce, but it seems to smother 2 - Neoprene; combustion modified, high resiliency PU foam 3 - heavier materials generally have higher ignition resistance and lower flame spread rate Note: There is much overlap between the categories, and much depends on FR finish efficacy, back coating, etc.

Comparison of Parts A and B of Table 6-2 shows that materials do not rank in the same order for cigarette and flame ignition resistance. Furthermore, while a furniture item combining materials from the upper to medium range of the listings can be considered essentially cigarette

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ignition resistant, even a composite of the materials ranking at the top in flame resistance may ignite if the flames are large enough and applied long enough. However, Part B may still be helpful in choosing material composites with a low probability of ignition from matches, for example, but not necessarily from higher energy ignition sources. Some of the difference in the relative resistance to cigarettes and flames can be explained in terms of char forming and thermoplastic materials. Char formation can be initiated by low energy, for example, that of a burning cigarette, in cellulosic and acrylic but not most wool materials. If the cellulosic fabrics contain enough alkali metal ions, the char will propagate. However, in flame exposures, such chars can protect the padding from the flames, at least until they split due to fabric tension or are consumed. Generally, heavy cellulosic fabrics are better for flame resistance, but lighter fabrics for cigarette ignition resistance (in part, because they contain fewer smolder promoting alkali metal ions). The flame resistance of wool fabrics also increases with weight. Acrylic fabrics are susceptible to both cigarette and flame ignition, but an effect of weight and finish has not been established. On the other hand, the heat from a cigarette melts thermoplastic fabrics in the area of contact and smoldering does not generally spread to the padding, unless the fabric is relatively lightweight. However, upon flame exposure, the thermoplastic fabrics melt and shrink, rapidly exposing the padding. The molten area can form a burning bead which often constitutes a secondary ignition source with more available heat than the original one, e.g., a match. One often can observe two flame fronts: one, the foam burning, and a burning molten, thermoplastic bead in front of it.[272] Among other sources, a paper by Pakkala et al. compares the results of ignitability tests for fabric/foam composites, using cigarettes and BS 5852 gas flames 1, 2, and 3.[381] Polyurethane foam composites covered with FR polyester fabric passed when exposed to cigarettes, but not with the flame ignition sources. On the other hand, a FR cotton fabric failed the cigarette test with three ordinary polyurethane foams, but passed with gas flame 1. In most other cases, cigarette and flame 1 results were the same. The results discussed below are based on experiments with minimock-ups (UFAC and California TB 117), large scale mock-ups (e.g., BS 5852, TB 133, BIFMA, the US mattress test FF4-72), or full-scale furniture. A substantial part of the work on cigarette ignition resistance was performed by the governmental organizations, including the California Bureau of Home Furnishing (BHFTI), by the National Bureau of Standards

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(NBS), now the National Institute of Standards and Technology (NIST), the US Consumer Products Safety Commission (CPSC), by the UK Fire Research Station (FRS) and other UK organizations, by the Technical Research Center of Finland (VTT), by the US Furniture Industry (UFAC), and, in the last few years, by the cigarette industry. The details are given in following sections; below is a brief summary. To prevent ignition by cigarettes, it is not necessary to use only the materials listed on top of each column in part A of Table 6-2. For example, a composite of a medium weight thermoplastic fabric with ordinary polyurethane foam or a composite of light to medium weight cellulosic fabric with a layer of polyester batting over the same foam generally do not ignite. Increasing the weight of cellulosic fabrics decreases their cigarette ignition resistance,[212][217]–[220][223][224][226][228] primarily due to the presence of alkali metal ions found in unscoured as well as in most dyed and finished cellulosic fabrics. Most heavier commercial cellulosic fabrics simply tend to have a higher alkali metal ion content per unit area (in g m-2, not percent or ppm). Cellulosic fabrics with low alkali metal ion content (e.g., after a low hardness water rinse) over polyurethane foam are unlikely to ignite, regardless of weight.[382]–[384] The position of other fibers in the Table 6-2 are not based on as many reports, but it appears that many wool and medium to heavy PVCcoated (vinyl) fabrics can be used with smolder resistant (SR) or ordinary polyurethane foam or mixed batting. For PVC coated fabrics, nylon base fabric has been found to have less cigarette ignition resistance than SR cellulosic fabric. Acrylic fabrics tend to smolder. Upholstery composites which are, for all practical purposes, cigarette ignition resistant in a crevice configuration, can be chosen on the basis of a few trials in a qualified laboratory. The number of such trials can be reduced by using the information from the table. Sheets and blankets can increase the probability of mattress ignition when they are placed on top of a cigarette, but, with the possible exception of some blankets, they generally do not ignite from cigarettes dropped on top of them.[352] Tables 4-8, 4-9, and 6-3 are examples of data on which the following discussion will be based. Table 6-3 summarizes several studies by the California Bureau of Home Furnishings. [385]–[389] In one, conducted in the late 1970s, over eighty upholstery fabrics popular in California at that time were tested over ten padding materials each, in the mini-mock-up configuration.[385]

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Fire Behavior of Upholstered Furniture and Mattresses

Table 6-3. Cigarette Ignition Resistance of Typical Fabric/Padding Composites Percent of Fabrics Igniting 100% cellulosics cellulosic/ thermoplastic blends A: Mini Mock-up Results Batting: 100% cotton Untreated FR 70/30 cotton/polyester 100% polyester Non-resinated Resinated Foam: Polyurethane Untreated FR 1 FR 2 High Resiliency Neoprene Neoprene interliner over cotton batting Glass Fiberboard B.Results on 171 furniture items (various filling materials

100% thermoplastics

100 76 79

82 43 32

9 0 0

33 19

7 4

0 0

41 86 38 83 93

25 54 25 57 39

0 0 0 0 0

19 14 100 54 B: Full-Scale Furniture fabric weight > 70% cellulose: 82 <270 g/m2: 67 fabric wieght < 70% cellulose: 6 >270 g/m2: 95

0 0 6

Specifications Batting: 100% cotton, untreated FR cotton, 12–15% boric acid 70/30 cotton/polyester, bonded 100% polyester, resinated with 28% acrylic resin 100% polyester, non-resinated, with polyester scrim

Density Foam: kg/m3 38 38 37 8

Untreated PU FR PU 1 (antimony trioxide and PVC) FR PU 2 (brominated biphenyl) High resiliency PU (brominated organophosphate) Neoprene (4% antimony trioxide, 16% alumina trihydrate)

8

Neoprene Interliner: 5 mm thick with cotton scrim backing, 950 g/m2

Density kg/m3 20 37 32 42 56

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Other studies covered commercial furniture items sampled in California to check compliance with the California TB 116 (requiring labeling) and the TB 117 standards.[387]–[389] The percentage of furniture items which passed regulations increased from 57 to 90% during the period covered. However, a 1993 survey of upholstered furniture fabrics indicated an increasing use of cotton fabrics in the US, many of which ignite from cigarettes.[390] Another study introduced the concept of smoldering procliv[228] Four experimental cigarettes varying somewhat in circumference ity. and tobacco density were exposed on flat surfaces, in a rectangular and a 20° crevice, of mock-ups made from thirty-three different commercial furniture fabrics over polyurethane foam and untreated cotton batting. The fabrics were characterized by weight, density, air permeability, and sodium and potassium ion content. The smoldering proclivity of the cellulosic yarns was defined as the time individual yarns smoldered after exposure to cigarettes or an electrical heater. On the polyurethane mock-ups, this smoldering proclivity (which was found to be related to alkali metal ion concentration in the fabrics) was found to have the largest effect on cigarette ignition propensity of mock-ups, followed by fabric weight and density. Cigarette caloric output (measured in air, not on a substrate) was found to be the fourth most important variable. An ignitability index for fabric/padding composites, an estimate of the probability of a substrate to ignite, was developed by means of mockup tests.[383] The sensitivity of frequency of cigarette ignition to shifts in the market fabric distribution was investigated. Similar estimates based on variations in polyurethane foam formulations are discussed in Ref. 391. 6.1.1

Effect of Fabrics

Fiber Content and Weight. The highest cigarette ignition resistance is obtained with wool and many PVC-coated fabrics;[346][347][352] the resistance increases with fabric weight and thickness of coating. PVCcoating on FR or ordinary cotton provides better cigarette ignition resistance then coatings on nylon. The role of cellulosic fabric weight and alkali metal content has been discussed earlier. Increasing the mass of thermoplastics (nylon, polyester, and polyolefin in fabrics and thermoplastic fibers, usually polyester, in batting) increases the cigarette ignition resistance, because a large portion of the heat from the cigarette is consumed in melting the thermoplastic fibers. The data shown in Table 6-3 imply that fabrics with 20 to 50% thermoplastic

214

Fire Behavior of Upholstered Furniture and Mattresses

content rarely ignite from cigarettes. Later surveys, by BHFTI, first of 450, then of 700, and finally of 1200 commercial furniture items confirmed the previous findings.[387]–[389] Cellulose fiber content and weight of cover fabrics: over 90% of the fabrics containing 30% or less cellulosic fibers resisted cigarette ignition, while the percentages of cigarette ignition resistant fabrics were about 70% for 30–79% cellulosic content fabrics, but only about 25% in the 80–100% cellulosic content range. Among 100% cellulosic fabrics weighing 300 g m-2, 43% ignited from cigarettes; among fabrics over 440 g m-2, 86% ignited. Adding thermoplastic to cellulosic fibers improved ignition resistance, and higher percentages of thermoplastic fibers were needed for heavier fabrics. However, no systematic study of such blends to optimize cigarette ignition resistance has been undertaken. Possible variables in such a study would be: location of the thermoplastic fibers, for example, by placing them in the filling in weaves where mostly the filling appears on the surface; more exact determination of the amounts needed in intimate yarn blends to obtain cigarette ignition resistance; type of thermoplastic-nylon, olefin, or polypropylene; alkali metal ion content of blended fabrics, etc. Fabric Construction. No systematic studies of the effect of fabric parameters, such as weave, yarn size and density, pile vs non-pile, etc., have been carried out. In non-fabric substrates, for example, grass clippings and foam, denser packing has increased the smolder tendency.[88][392] This indicates that not only weight but a certain minimum packing density is required for smoldering. This packing density is obviously present in conventional furniture fabrics and cotton batting. Of 500 commercial (not only upholstery) fabrics, 145 ignited when exposed to an experimental cigarette.[393] Important factors for ignition were reported to be cellulose content, sodium and potassium content in ppm, weight (related to actual potassium and sodium content), but not air permeability. Combined sodium and potassium concentrations of 500 to 6000 ppm were encountered. However, even some of the fabrics with low sodium and potassium content ignited; they may have contained other smolder promoting alkali metal ions, for example, calcium ions. Examination of another set of commercial fabrics indicated that lowering the air permeability increases cigarette ignition resistance.[221]

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215

Other experiments showed the same but the lower air permeability was achieved by applying back coatings, which introduces extraneous factors.[394] Increasing the air permeability by making slits in the fabric increased smoldering rate but not smoldering temperature and char areas. Finishes, Back Coatings, and Contamination. The effect of flame retardants on cigarette ignition resistance has not been fully explored. Many flame-retardant systems for cellulosic fibers rely on char formation as a barrier to flame propagation, and can exacerbate the smolder tendency of cellulosic fabrics.[385] Treatment of cellulosic fabrics and cotton batting with certain nonpermanent materials, for example, borax and boric acid, can increase both flame and smolder resistance.[211][386][395]–[401] Borax is a flame retardant which, however, somewhat increases smolder tendency. Boric acid is added to the borax to counteract the smoldering tendency. Higher concentrations of boric acid/borax are needed for smolder than for flame resistance. Such treatments can affect the color and feel of fabrics but have been successfully applied to cotton batting, for general use but especially for high risk occupancies, for example, prison mattresses. Proprietary spray products claimed to make possible cigarette and flame ignition resistance of upholstered items by retrofit in the home are occasionally promoted; tests with three such sprays indicated that this is indeed possible but that the amount of spray necessary is very large, and the fabrics appeared discolored and harsh to the hand.[402] Spraying by hand evenly and lack of permanency of such applications also present problems. Water and stain repellent finishes were found to have little effect on cigarette ignition propensity.[382] Cleaning of fabrics first treated with a borax based smolder resistant formula with perchloroethylene reduced cigarette ignition resistance (some perchloroethylene cleaning formulations contain suspended water), but other cleaning media had only minor effects.[403] Even very heavy, raw cotton fabrics which ignited very readily did not ignite after a rinse in low hardness water.[404] Most commercial back coatings did not affect the cigarette ignition resistance.[224][385][386][405][406] A vinyl vinylidene latex back coating and certain FR compounds improved furniture fabric cigarette ignition resistance.[406]–[408] Back coatings which improve smolder and ignition resistance are now commercially available. To examine the results of soiling furniture fabrics, specimens were cut from exposed and hidden areas of 66 used upholstered furniture fabrics obtained from reupholstering shops in Georgia.[584] As in a similar study with specimens obtained in Virginia,[585] soiling did not increase the smoldering potential. Sodium, potassium, chloride, and sulfate levels were higher in the soiled areas of those fabrics which ignited.

216

Fire Behavior of Upholstered Furniture and Mattresses

The paramount importance for the smoldering of cellulosic fabrics is the presence of alkali metal ions as has been mentioned earlier. Such smolder promoting ions are found in natural cotton (unfinished fabrics are often used in upholstered items, and natural cotton fibers are used in cotton batting) or as residues of dye assistants, softeners, or detergents in finished fabrics.[228][382]–[384] The contribution of dyes to fabric smoldering is discussed in Ref. 409. The cigarette industry performed several studies of the effect of alkali metal ions, in which potassium acetate was applied at varying concentrations.[228][382]–[384][410] In some of these studies, the fabrics were intended for use as standard fabrics for a test method for the measurement of cigarette ignition propensity. However, the alkali metal ion concentration vs ignition resistance curve is generally very steep, so that very tight, possibly not attainable control over the concentration and evenness of the treatment would be required to obtain reproducible standard fabrics. Attempts to find a fabric treatment which would not produce such a steep curve were, thus far, unsuccessful.[411] Smolder and combustion of cellulosic fabrics was investigated by DSC/TG/MS, TRP/GC, and IR thermographic systems, in inert and oxygen-containing atmospheres.[586] A cellulosic, patterned fabric containing four differently colored yarns showed more smoldering along some yarns than others. The various yarns were analyzed by the above methods, and their similar behavior was explained by competitive action of alkali metal and pigment compounds. Similarly, when unwashed, water washed, and bleached cotton duck were investigated, bleaching and UV exposure were found to lower the decomposition temperatures and to affect smoldering behavior. A model of smoldering for cellulosic fabrics was developed. Fabric Tension: Interaction of Fabric and Padding. No systematic study of the effect of fabric tension on cigarette ignition resistance is available, but a few observations can be reported. When tension is low, as in old furniture or certain styles, the fabric may make little or no contact with the padding and cigarette ignition may be determined entirely by the fabric. With higher tension, intimate contact between the fabric and padding is achieved and padding can act either as a heat sink (for example, SR cotton batting) or it can smolder along with the fabric. Polyester batting can absorb heat during melting, but untreated cotton batting propagates smolder started by the fabric on its own. (Note that some polyurethane foams exhibit considerable melting and shrinking from the heat source; others, depending on their chemistry, exhibit more smoldering behavior.)

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Bedding. Bedding materials have various effects on cigarette ignition resistance. Cigarettes may ignite some blankets, primarily cellulosic and acrylic blankets but not wool and thermoplastic bedding. They are unlikely to ignite sheets,[352] but sheets in close contact with the mattress can help to ignite it, especially pure cotton sheets. The probability of ignition is increased if additional layers of sheets and blankets are placed on top of the cigarette, rather than between the cigarette and the mattress. Accordingly, most cigarette ignition tests require placing one layer of sheeting on top of the cigarette, but this is not the worst case, since additional sheet or blanket layers would increase ignition propensity. Some European tests prescribe placement of inert fiber batting or cotton wool (cotton batting) on top of the cigarettes.[47] 6.1.2

Effect of Padding Material

Polyurethane Foam. The effect of padding material on cigarette ignition resistance is illustrated in Tables 6-2 and 6-3. Smolder resistant neoprene and the CMHR polyurethane foams rank high. Earlier FR treatment for polyurethane did little or nothing to improve smolder resistance but, mainly in response to the BS 5852 and California TB 117 requirements, FR treatments which impart both smolder and flame resistance to foams were developed. Several studies describe improvement in smoldering resistance of fabric/polyurethane mock-ups due to use of proprietary smolder and flame retardants.[412]–[417] HR foam had higher cigarette ignition resistance than ordinary foam.[418] Modest SR effects can be overwhelmed by the presence of a strong smoldering (or burning medium), such as heavy weight cellulosic cover fabrics or bedclothes which provide substantial amounts of heat. The UFAC and California tests for padding are based on a medium weight standard fabric; heavier, smoldering fabrics still can cause ignition of the padding materials which pass this test. A report on an inter-laboratory evaluation to establish reproducibility of results obtained with a standard foam claims that there was no difference due to location of specimens along the length and from top to bottom of a foam bun (the several feet thick foam production units from which foam padding is cut).[222] An effect of breathability of the foam was found, and it was suggested that foam samples be flexed before testing; this increases breathability and would simulate conditions in actual use. Batting. Polyester batting can be considered more cigarette ignition resistant than ordinary polyurethane, and untreated cellulosic batting less so (Table 6-2). Most cellulosic batting contains primarily

218

Fire Behavior of Upholstered Furniture and Mattresses

cotton but other fibers are also used, for example, hemp, jute, etc., particularly in mattresses. Untreated cellulosic batting smolders badly.[382][396][397][399]–[401] Treatment with boric acid crystals is the most common SR treatment for cotton batting; concentrations required are roughly 8 to 12%. The boric acid is not applied as a water solution, since an expensive drying would be required. It is important that the boric acid particles adhere to the batting and not segregate during use. For this, a light oil application is often used. As mentioned earlier, an admixture of thermoplastic fibers to cotton fibers, often found in reprocessed mill wastes, increases cigarette ignition resistance; the higher thermoplastic fiber content blends pass UFAC batting requirements. 6.1.3

Effect of Interliner (Barrier, Blocking) Materials

The UFAC program[22] requires that all fabrics be tested, and those which are more ignition prone (Class II) must be used with a barrier material between the fabric and padding in the seat surface. The most common barrier material passing UFAC is polyester batting which is also often used as padding to achieve certain appearance and comfort effects. However, many fabrics, especially heavy cellulosics, cause cigarette ignition even with UFAC approved polyester barriers.[223][225] Other interliners which are primarily used to increase flame resistance are neoprene and CMHR polyurethane sheets, glass fabrics, Nomex and Kevlar non-wovens, and aluminized fabrics; they generally are effective in also increasing cigarette ignition resistance; this is discussed in more detail below. A Norwegian study[418] found no effect on cigarette ignitability of various stitch-bonded polyester, nylon, and polyurethane interliners. Presumably these interliners were being specified solely for comfort or appearance purposes. 6.1.4

Effect of Welt Cords and Trim

Welt cords caused chairs to fail in cigarette tests; at times only the area around the welt cord smoldered.[207] In a full-scale test, only a small charred area around the welt cord was visible but there was considerable smoke, indicating smoldering inside the padding.[419] Welt cords consisting of aluminum foil twisted with strands of cellulosic materials have been shown to have better cigarette ignitionresistance than untreated and FR treated cellulosic welt cords.[224] Accordingly, UFAC upgraded its welt cord standard to eliminate the latter.[22] Some thermoplastic and PVC welt cords also conform to the upgraded welt cord standard.

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Furniture trimmings (welt cords and fringes) were tested by themselves, on PU slab, and on fabric/padding composites.[588] Ignition sources were cigarettes (with the test specimen on an inert surface) and the BS 5852 match equivalent butane flame. In most cases, rayon materials failed and thermoplastic materials passed. However, when pinned to vertical fabric/padding assemblies, some thermoplastic materials burned sufficiently to ignite the cover fabric substrates (based on the afterflame time specifications of BS 5852, Part 1). Both non-FR and FR polyester “cut ruches” (fringes), ignited an acrylic pile with cotton backing, as well as, surprisingly, a Nomex fabric over a ceramic fiber batting. Apparently, the ruche burned because it adhered to the fabric and could not ablate. 6.1.5

Effect of Configuration

For any composite of fabric and padding material, cigarette ignition resistance is better in flat areas than in crevices.[17][207][212][223][224] Several factors may contribute: re-radiation of heat from two rather than one surface in the crevice; a chimney effect of air in the channel below the cigarette;[84][208] and in the case of cellulosic fabrics, increase in the mass of cellulosic fibers and alkali ions due to multiple layers at the seams.[17] For this reason, when the mock-ups are used without such multiple layer seams (as prescribed in most tests), the ignition resistance for cellulosic fabrics tends to be overestimated, and the contrary is true for thermoplastics. Most tests require testing in a 90° crevice. Smaller angle crevices, which could be formed by the cigarettes falling between the seat and back or sides of the furniture, have been reported to have lower ignition resistance.[228][358] Tufted areas also may have lower cigarette ignition resistance than flat areas and are usually tested separately, as are areas near the welt edge outside the crevices.[17][207] If cigarettes rest inside the tufted indentation, ignition has been observed to be more frequent than in flat areas; however, if the burn cone tends to stick out into the air, and the rest of the cigarettes rests on the flat area, the likelihood of ignition should not be enhanced.[17] 6.1.6

Effect of Moisture

Tobacco, cigarette paper, and cellulosic substrates and wool fabrics all are quite hygroscopic, while thermoplastic and acrylic fibers, and polyurethane are considerably less so or not at all. Whether this has a major effect on cigarette ignitability has not been clearly established; since the cigarette burns for about 20 minutes, one could speculate that it may dry out

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Fire Behavior of Upholstered Furniture and Mattresses

the substrate if it has been dropped soon after ignition and this may affect the outcome of ignition/non-ignition tests on some borderline substrates. Temperatures of around 20°C and relative humidity of 50 to 65% are specified in most test procedures, usually fairly tightly for conditioning but within fairly wide limits in the burn room because of the difficulty of maintaining the conditions in areas where large exhaust hoods are operating. Cigarette ignition frequencies were not found to be different in bone dry and 65% RH, environments.[346] In experiments at the California Bureau of Home Furnishings, about 2/3 of tests at below 40% RH resulted ≥ 5 g mock-up weight loss, but only 1/10 caused weight loss of ≥ 5 g at more than 40% RH.[420] The heat flux, measured with the cigarettes on a copper sheet, was higher at low than at higher humidity.[83] Others found no effect of drying of cigarettes on burn temperature or heat flux.[421][422] 6.1.7

Cigarette—Upholstered Item Interaction

This section discusses the burning characteristics of cigarettes in air, how they are changed when in contact with substrates, and attempts to produce cigarettes with low ignition propensity by changing some of their parameters. The cigarette industry has published extensively in the first area. An Act by the US Congress initiated research on developing low ignition propensity cigarettes and another such Act initiated research on development of a test method to measure the ignition propensity of cigarettes.[423][424] A review of pertinent literature was undertaken under the first Act.[72] The following is a summary of the findings in that review. Until fairly recently, most US cigarette packings* had rather similar characteristics such as packing density, circumference, and presence of filter, while they differed in cigarette paper parameters, and tobacco blend and flavoring.[80][81][207][425]–[427] Typical European, Australian, British, Canadian, and Japanese cigarettes fell within the same ranges of the first mentioned parameters while their tobacco blend variations were not determined.[428]–[430] However, since 1987, several cigarette packings outside the earlier ranges have been introduced. Some of these have relatively low ignition propensity. Similarly, a certain popular Hungarian cigarette brand was found to frequently self-extinguish on relatively heavy, cotton duck fabrics.[430] The authors state that despite the large percentage * A cigarette packing is defined as a commercial cigarette, described by its name, circumference, length, whether menthol or non-menthol, filter or non-filter, and hard or soft pack.

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of the market held by this brand, Hungary has a high rate of cigarette-caused fire casualties. It is not clear whether these are due to upholstered item fires or other causes, such as trash and wildland fires. Burning temperatures for 16 US cigarettes positioned on a copper plate did not correlate with their heat flux, under dry as well as under typical laboratory conditions.[83] A large study was conducted on 128 US cigarette packings of the physical parameters such as length, circumference, weight, etc., as well as their burning rates and temperatures in air in 1982.[426] The cigarette chosen for all US upholstered furniture and mattress tests is a non-filter cigarette (Pall Mall) which was popular at the time the tests were developed, and fell in the upper range of burning temperature.[207] Its heat flux seems to be intermediate.[83] In spite of the increasing popularity of filter cigarettes, this cigarette has been continued for test use. It was observed that the increased glow and burning rate at the very end of the butt of non-filter cigarettes presents a more severe condition than prevails with filter cigarettes.[207] Increased ignition propensity of nonfilter cigarettes was also observed on forest ground substrates.[431] However, in mock-up testing of many 120 fabric/padding composites, results obtained during full length burning of the standard and a filter cigarette were almost identical [432] indicating, perhaps, that the number of borderline composites which would ignite from non-filter cigarettes but not from filter cigarettes is small. The reason may be that many upholstery substrates ignite in as little as 2 minutes, long before the end of the cigarette is reached at about 20 minutes.[219] A 1956 study of cigarette temperatures found the following:[427] Temperature On Surface At Centerline

No Drag on Cigarette

Drag on Cigarette

In Air

Insulated

Insulated

288oC 566oC

510oC 620oC

427oC 732oC

This shows the increase in temperature due to confining the cigarette by insulating matter, as by use of a sheet to cover the cigarette in most testing methods, and in real life situations, as cigarettes covered by bedclothes, for example, or, to a lesser degree, in a crevice. It is also important to note that the burn behavior of cigarettes on substrates is quite different from that in air. Cigarette core temperature versus burning time plots are given in Fig. 2-1 (for cigarettes burning in air and on two substrates) and in Fig. 6-1 (temperature versus time at four

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Fire Behavior of Upholstered Furniture and Mattresses

Figure 6-1. Time/temperature relationships measured in four locations inside cigarette core.

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places, denoted 1C to 4C, along the length of a cigarette).[72][84] The cigarette burned in air exhibited a very narrow peak. The time/temperature relationship of cigarettes placed into the crevice of cotton fabric/polyurethane mock-ups and covered with sheeting depended on the weight of cotton fabrics, with the heavier cotton fabric producing prolonged preheating before the peak was reached. The temperature versus time curves measured at three points of the fabric surface and inside a foam are shown in Fig. 6-2.[72][84] For covered cigarettes they were somewhat broader but showed the same peaks as uncovered cigarettes. Also, visual observation shows that cigarettes in air burn with a short burn cone, but the smolder at the cigarette/fabric interface often moves ahead of the tobacco column burn cone if the fabric substrate smolders at all. Burning temperatures measured with thermocouples placed near the cigarette-substrate interface or at various distances from it varied according to substrates: they were lower on inert glass fiberboard crevices than when fabrics were placed over the fiberboard. In the latter mock-ups, they differed with fabric construction.[211] The cigarette linear burning rate was 1.3 mm/s for the glass fiberboard mock-up and between 1.4 and 2.1 mm/s for the four fabric mock-ups. The temperatures and burning rates ranked the fabrics in the same order. A similar dependence of burning temperatures on fabric and foam parameters was demonstrated in other studies. However, because neither fabrics nor foams were systematically varied, the results cannot be used to predict temperatures as a function of the physical parameters of the substrates. A number of cigarette ignition studies in related areas are relevant here. Two experimental studies indicate that it is very unlikely that cigarettes will ignite apparel fabrics worn by a person,[427][433] presumably because they are usually not thick enough (apparel packed in a hamper, for example, may be prone to cigarette ignition, however). Smoldering ignition requires a certain minimum depths of the substrate, as discussed earlier. However, wildlife material, including compacted conifer needles, grass if densely packed in form of clippings, and punk wood can start to smolder and then proceed to flaming after contact with burning cigarettes.[89][392][431][434] Conditions which increase the probability of such ignition are:[78][79][88][434] dense packing of material; a thick layer of material; high ambient temperature and low humidity; and modest winds, especially in the direction of the burn cone travel on the cigarette.

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Fire Behavior of Upholstered Furniture and Mattresses

Figure 6-2. Time/temperature relationships at fabric surface and 20 mm inside vertical and horizontal polyurethane padding.

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Especially in winds of the right direction and velocity, these substrates also seem to burst into flames rather rapidly, without lengthy smoldering periods. Optimum conditions for ignitions were winds of 4.8– 6.4 km/hr velocity, in the direction of the burn cone travel of the cigarette. Other wind velocities and directions could lower ignition propensity as compared to quiescent conditions. 6.1.8

Low Ignition Propensity Cigarettes

Some advocates for fire safety were of the opinion that certain US and European cigarette packings had a lower propensity to ignite and that it may be possible to, by voluntary industrial action or by regulation, to produce all cigarettes to those specifications. At first this evidence was anecdotal but it was later confirmed by several studies.[17][420][435][436] Even the earliest such assumptions led to interest by US Federal and state legislators in the 1930s, and bills were proposed which would require cigarettes to conform to yet to be developed ignitability standards. For several decades, these proposed bills required self-extinguishment of the cigarettes burning in air without puffing within a certain number of minutes. After it became clear that this requirement would not be sufficient because some such self-extinguishing cigarettes can still ignite substrates,[219] later versions of those bills did not include this requirement. The cigarette industry claimed that self-extinguishing cigarettes would increase CO and toxic product delivery.[82] However, this delivery in present-day cigarettes is primarily controlled by filters and ventilation, i.e., perforations in the cigarette paper and filter which cause the smoke to be diluted by air during the drag on the cigarette.[437] After many previous attempts to pass such legislation, the Cigarette Safety Act became law in 1984.[423] It set up a mechanism to study the feasibility of producing cigarettes with a minimum propensity to ignite upholstered items without major impact on smoke toxicity (as defined by tar, nicotine, and CO content) and economics. A number of NIST reports and journal articles resulted from this work.[208][438]–[444] They covered many aspects: the ignition propensity of experimental cigarettes covering a wide range of construction variables; the thermophysics and the modeling of cigarette ignition of substrates; and the impact on accident incidence, economics, and health of use of low ignition propensity cigarettes. Another congressional act[424] instructed CPSC and NIST to develop a test method for cigarette ignition propensity which could be used for voluntary or regulatory compliance. The reports submitted to the US

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Congress under that act cover a variety of subjects:[445] test method development; further modeling of the ignition process; the groundwork for a study of the factors involved in real-life cigarette ignition accidents; a plan for comprehensive toxicity testing of the experimental cigarettes (which could be applied to all cigarettes); and a study of the societal cost of cigarette caused fires. The resulting studies are summarized below. Literature Review The previously mentioned review of the literature on the general burning characteristics of cigarettes, the factors which may affect their propensity to ignite furniture, and steps taken to reduce this propensity produced little information pertinent to the given task. However, ample information on the burning behavior of cigarettes in air was found.[72] It lists over 100 patents, the oldest one dated 1882, which purportedly reduce the ignition propensity of cigarettes. However, most such patents cover modifications of the cigarette paper, and do not take into consideration that this may increase the tar, nicotine, and CO contents of the smoke. Many of the patents were based on the mistaken belief that cigarettes which selfextinguish when burning in air without puffing could not ignite substrates. The results of laboratory investigations mandated by the two acts of the US Congress resulted in the following conclusions. Commercial Cigarettes Screening tests for the ignition propensity of commercial cigarettes generally identified some with lower ignition propensity, in the NIST and other investigations. NIST conducted two investigations, one of six, the other of twenty commercial US packings, by placing them on substrates with varying cigarette ignition resistance. The first study, in 1981, found that some packings showed slightly lower ignition propensity.[219] However, on a practical level, the differences were so small that they probably would not significantly affect the numbers of upholstered items ignited (only borderline composites) if all cigarettes were constructed like the lower ignition propensity commercial ones available at the time of the study. The second study, concluded in 1993 on the 20 commercial cigarette packings, was conducted after NIST developed two test methods for measuring ignition propensity.[445] Selected for this study were 14 cigarette

Upholstered Item Design Engineering packings with large shares of the market, and six packings with characteristics leading to low ignition propensity (primarily low circumference, low packing density, and low porosity paper) which together comprised only about 1% of the market. Five of these six packings were found to indeed have lower ignition propensity and similar tar/ nicotine/CO ratings as the best sellers. The others differed little in their characteristics and ignition propensity. Similarly, a study by the BHFTI in which weight loss of the substrate as well as char length was measured established differences between packings.[420][436] Twelve commercial cigarette packings could be divided into three ignition propensity groups. A Canadian study also identified several commercial cigarettes with lower ignition propensity on a borderline substrate.[17] On the other hand, a report from the cigarette industry showed no difference between a number of commercial US and cigarettes from abroad.[428]–[430] However, in the first of these studies, all cigarettes ignited all substrates, indicating that the substrate ignition resistance was not in the range to show differences. Feasibility of Low Ignition Propensity Cigarettes The study also found that it is technically feasible and may be commercially feasible to produce cigarettes with very low ignition propensity.[438]–[444] This was based on experimental work in which 41 experimental cigarettes varying widely in tobacco type and packing density, cigarette circumference, and paper porosity and smolder promoter content were varied over wide ranges. Statistical interpretation of the results showed that the cigarettes with the lowest ignition propensity were those with a combination of low packing density, small circumference, and low paper porosity and low citrate (a commonly used smolder promoting additive) content. Taking the variables individually, packing density, paper porosity, and cigarette circumference produced statistically significant decreases in ignition propensity, but citrate content and tobacco type had no significant effect. The five commercial cigarette packings with low cigarette ignition propensity all had a

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Fire Behavior of Upholstered Furniture and Mattresses very low circumference, but were not necessarily exceptional in packing density and paper porosity.[445] These results were obtained in experiments in which cigarettes were exposed on a series of mock-up substrates varying in cigarette ignition resistance.[439] Two laboratories, at the Center for Fire Research at NIST and the BHFTI, using the same substrate materials were in good agreement. The results were further confirmed by experiments on full-scale furniture. Other reports on the agreement between mock-up and full-scale chair results were discussed in Ch. 5. Eight of the experimental cigarettes were tested again after having been stored in freezers for several years on the same substrates.[446] The cigarettes were chosen to evenly span the ranges of ignition propensity in the earlier testing, and, as nearly as possible, cover the range of the design factors which define the cigarette packings. A significant increase in ignitions was found for one of the substrates, and one of the eight cigarettes. However, the general ranking of the cigarettes appeared to be the same. A new set of these cigarettes was then produced and used in the test method development work. Their ignition propensity rankings were essentially as expected from the previous work. Some of the lowest ignition propensity experimental cigarettes had per puff tar, nicotine, and CO yields within the ranges of yields from the best selling commercial cigarettes.[439][440][442][444] The manufacture of low ignition propensity cigarettes may require some changes in cigarette design and production practice. Cost benefit studies indicated that such practices would result in only minor overall economic effects on the industry, but would produce savings of lives and property.[439] Some progress was made in investigating the heat flux and temperature relationship on the cigarette/substrate interface.[439][445] A computer model of a multi-layer substrate subjected to a stationary heat source was developed; the work has not been extended to a moving source, such as a cigarette burn cone. A comparison of the characteristics of smokers which had not experienced fires with others who apparently were

Upholstered Item Design Engineering involved in cigarette initiated fires as well as of the cigarettes they smoked was undertaken.[447] It identified filter presence and length, paper porosity, and pack types as distinguishing factors between the two groups, pointing more to socio-economic than cigarette construction effects. Also, since the low ignition propensity cigarettes represent a very small portion of the present market, they probably were not significantly represented in this limited study. Cigarette Ignition Propensity Test To evaluate the ignition propensity of cigarettes, it is necessary to find a series of substrates with step-wise increasing cigarette ignition resistance. This can be done by choosing well-defined commercial fabrics by trial and error.[17][219][439][445] Another approach is to apply increasing concentrations of smolder promoting alkali metal ions to clean fabrics. The problem with this approach is that small increases in ion concentration cause large decreases in ignition resistance, and it is difficult to reproducibly apply exact amounts of such ions to fabrics. The US Congress mandated that the CPSC and NIST develop a standard test method for cigarette ignition propensity for voluntary or regulatory use.[445] Two test methods were developed and supplementary studies performed of the practicability of such a standard and development of a mathematical model of the cigarette ignition of upholstered items. In addition, reports on cigarette ignition initiated fire incident statistics, on the societal cost of cigarette fires, and on a plan to test the toxicity of low ignition propensity cigarettes were submitted. Two approaches to providing standardized substrates with graduated cigarette ignition resistance were chosen (see Ref. 445, Sec. 2). The first one, called the Mock-up Ignition Test Method, employs a series of three commercial cotton ducks, varying in weight and construction, which do not contain any finishes but contain potassium maleate found in the raw cotton fibers. These fabrics have been produced to strict specifications for a long time, and their reproducibility over time, and between and within bolt, was demonstrated. Testing is in the flat configuration,

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Fire Behavior of Upholstered Furniture and Mattresses with a commercial polyurethane under the fabric. The practicability of using this foam as a standard material was also investigated in some depth. The experimental cigarettes produced for an earlier investigation[439] were again used in part of this work; it was shown that there was no effect of aging in freezers during the interval of several years in these studies.[446] Several additional cigarettes were produced later for this work to the same specifications as the earlier ones. This method is under consideration as an ASTM standard. Cigarette industry laboratories published numerous papers investigating this proposed standard, especially whether the standard duck fabrics are representative of the wide variety commercial upholstery fabrics; these are discussed in detail below. A second method, the Cigarette Extinction Method, consists of placing the cigarettes on multiple layers of standardized cellulose chemical filter paper. The ignition propensity of the cigarettes correlated with the number of filter paper layers required to cause cigarette self-extinguishment. With only three steps, 3, 10, and 15 layers, the method, while simple, did not seem to differentiate between cigarettes as well as the first one; it may do so with smaller steps in the number of layers. Interlaboratory tests of the two methods, with nine laboratories participating, were completed in early 1993, and indicated that the test methods are repeatable and reproducible within acceptable limits for fire tests. The cigarette industry contributed suggestions to control certain parameters in ignition propensity testing. A report indicating the need to control the airflow in the test box led to adoption of an appropriate test box.[448] Similarly, the need to standardize the time and position of the cigarettes between igniting the cigarette and placing it on the substrate was pointed out.[449] It was found that while these factors had no significant effect on the ranking of cigarettes in the ignition tests, they improved its reproducibility; consequently, they were standardized in the test procedure. One could assume that airflow in any direction would have a cooling effect, and alleviate air vitiation at the

Upholstered Item Design Engineering interface of the cigarette burn cone and substrate. It can be observed to enhance the glow of cigarette fire cones, especially when the flow is directed straight at them. If the smolder on the substrate is well established, it, too, can be enhanced by air flow; if not, the cooling effect of the air can extinguish it. These competing phenomena were addressed by a series of papers covering the effect of oxygen concentration and air velocity in the test chamber.[384][450][451] The substrates were commercial fabrics previously used in cigarette testing to which various concentrations of smolder promoting ions were applied. It was found that airflow reversed the rankings of two experimental cigarettes. One cigarette resembled a typical commercial cigarette, the other combined two of the parameters found to be important for low cigarette ignition propensity, lower packing density and lower paper air permeability, but both cigarettes had the same circumference. The airflow was always in the direction of the burn cone travel, the condition previously mentioned as being most likely to cause ignition of wildlife material[392] but not likely to prevail under more turbulent conditions. Similar reversals of the rankings of those two cigarettes were observed when the oxygen concentration in the test chamber was varied from 13 to 26%.[384][450] The paper claims that oxygen concentration changes present various conditions of air velocity. However, the direction of air movement and its cooling effect must also be considered. Spears et al.[452] stipulated that cigarette ignition propensity is dominated either by the mass burn rate (instantaneous heat flux) or linear burn rate (rate of movement of the fire cone), measured not on the substrate but in air. Which of these two parameters prevails depends on the fabric characteristics: dense, heavy fabrics are good heat sinks and rank cigarette ignition propensity according to their extinguishability, viz. mass burn rate. Moderate to lightweight fabrics with higher air permeability rank cigarettes according to fabric smolder areas, viz. linear burn rate. Ignition resistance of a number of commercial fabrics was evaluated with experimental cigarettes varying in

231

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Fire Behavior of Upholstered Furniture and Mattresses ignition propensity as evaluated by the above discussed test using cotton duck fabrics; the behavior of the duck fabrics was found to be not typical of the commercial fabrics. They contained more smolder promoting alkali metal ions, and were relatively heavy and dense; this is believed to account for the inconsistency in ranking of the experimental cigarettes on the duck and other fabrics.

All commercial cigarettes with low ignition propensity investigated in Ref. 445 had low circumference. However, experimental cigarettes differing in circumference were found not to differ in cigarette ignition propensity.[453] In this study, experimental cigarettes varying in circumference from 21 to 27 mm caused no ignition on mock-ups similar to those used in the NIST work. Trials on fabrics treated with various concentrations of alkali metals showed inconsistent results. Differences were found when measurements were carried out on fabric/foam composite while air was forced through the foam from below. In experiments to determine temperatures by color changes on liquid crystal impregnated papers placed 1/4 inch below the cigarette burning in air, the time to reach color changes in the temperature indicator method tended to decrease with circumference. The question arose whether the rankings of cigarette ignition propensity on the heavy, dense, unfinished cotton ducks were applicable to the wide variety of commercial upholstery fabrics. As discussed below, cigarette industry laboratories, under the auspices of the “Cigarette Ignition Propensity Joint Venture” and others, have devoted considerable effort to answering this question. The conclusions of the various papers depend in part on the manner in which the fabrics were grouped for statistical analysis of the results. Fifty commercial, cellulosic fabrics were tested with six commercial cigarettes which had been identified by NIST as having relatively low ignition propensity (all of which had small circumferences, i.e., “slim” cigarettes), and five commercial, normal circumference cigarettes which had been found to have higher ignition propensity by NIST.[589] The authors essentially followed the NIST procedure using the commercial fabrics, except that they omitted the polyethylene film used with one of the duck standard fabrics by NIST. Statistical analysis of the results found no difference in the ignition propensity of the cigarettes classified by NIST to have low and high ignition propensity when tested on the commercial fabrics, which differed widely from the NIST standard fabrics in weight and construction. However, another statistical analysis of the data and a large amount of experimental

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work on upholstered furniture and mattress type substrates found the NIST classification to be generally valid, as discussed below. Five hundred commercial fabrics (not all upholstery fabrics) were tested in several cigarette industry laboratories with a high ignition propensity cigarette.[393] As discussed in Sec. 6.1.1, only 145 fabrics ignited; their ignition behavior was explained as due to several fabric characteristics. Four experimental cigarettes used in earlier work, two slim ones found to have low ignition propensity, and two normal ones with higher ignition propensity, were exposed on many of these fabrics and the three standard duck fabrics in two industry laboratories.[590] About half of the fabrics either ignited with all four cigarettes or showed no ignitions. Based on their statistical analysis, the authors concluded that, on about half the commercial upholstery fabrics, the cigarettes were ranked like on the NIST duck fabrics, and on the other half, the rankings were reversed. The normal circumference cigarettes showed an increasing trend of ignitions with increasing fabric weight, and the slim cigarettes a decreasing trend with increasing fabric weight; the crossover point was at about 340–375 g m-2. The physical and chemical characteristics of the NIST fabrics were similar only to those of a fraction of the commercial fabrics. Combined sodium and potassium ion levels of at least 1500 ppm resulted in almost 100% ignitions with cellulosic fabrics. Potassium was found to be more effective than sodium as a burn promoter, but this effect varied somewhat for the four cigarettes. Calcium and magnesium were found to be burn inhibitors. As in an earlier study,[452] ignition propensity was related to mass and linear burn rate measured in air. The slim cigarettes had a high linear and a low mass burn rate, the normal ones a low linear and a high mass burn rate. Heat flux measured with a specially constructed flow calorimeter showed the slim cigarettes to produce 6.1–6.8 W, and the normal cigarettes 7.4–9.8 W. The lighter fabrics generally ignited with the slim cigarettes while the heavier fabrics generally ignited with the normal cigarettes. Hirschler analyzed these results and concluded that the classification of the cigarettes on only thirteen of the commercial fabrics differed from that obtained on the standard duck fabrics.[591] He also compared results of various other attempts to classify cigarette ignition propensity and generally found the NIST method to be valid. Two communications took issue with Hirschler’s conclusions and one basically agreed with them. Rhyne[592] related the physical characteristics of the fabrics to their ignitability by the high ignition propensity cigarette which was in the original screening of the fabrics: 90% of the

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fabrics containing > 1600 ppm of sodium plus potassium ions ignited, only 9% with lower such ion levels. Similarly, 60% of the heavyweight fabrics ignited, but only 21% of the lighter ones. The author then used an entirely different analysis method from that of Hirschler by grouping the fabrics based on their alkali metal ion content and weight (and included the many fabrics which did not ignite in the initial screening). He concluded that the standard duck fabrics cigarette rankings disagreed with those obtained for the individual fabric groups and suggests that standard fabrics representing each group be found. Norman took issue with some statements by Hirschler.[594] Again, he found that the results obtained on the duck fabrics do not correlate with cigarette ignition propensity rankings obtained on differently constructed commercial fabrics. On the other hand, Eberhardt et al., again using the same data, found the NIST method to be of the same validity as most fire tests.[595] By eliminating from consideration fabric which did not produce cigarette rankings because they either showed all or zero ignitions, they based their analysis on seventy-nine fabrics. Sixty-one of these fabrics, primarily duck-like ones, ranked the cigarettes in the same order as the standard duck fabrics, while six to ten would be predicted to show persistent ranking reversals if additional tests were performed. Paul undertook a major investigation to establish whether conformance to the cigarette ignition propensity tests developed by NIST[445] would result in similar reduction of cigarette initiated fires as the UK and other European standards which require upholstered items be cigarette resistant (e.g., BS 5852).[593] He compared ten commercial low-circumference (slim) cigarettes, which had been found to have relatively low ignition propensity in the NIST work, with cigarettes with normal circumference, six with filters and six without. The slim cigarettes had tobacco packing densities of 7.1 to 11.3 mg mm-1, the normal cigarettes 11.6 to 13.7 mg mm-1. All but one normal cigarette had similar in air burn rates, the slim cigarettes were generally longer than the normal ones and had longer burn times. In the Mock-up Smoldering Propensity Test using the least demanding substrate (a cotton duck, polyethylene film, and PU foam), essentially all slim cigarettes failed to ignite the substrates, while the normal circumference cigarettes caused ignitions. In the NIST Smoldering Propensity Test, essentially all cigarettes burned to completion (Class 2), regardless of the number of filter paper layers used as a substrate. There was no difference between filter and filterless cigarettes.

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Fifteen fabric/padding substrates which were expected to smolder and fail BS 5852 were used to further explore the differences between the slim and normal cigarettes in the BS 5852 arrangement. The lowest number of ignitions were obtained with the slim cigarettes, followed by the filter cigarettes, with filterless cigarettes causing the highest number of ignitions. The same general differences between slim, normal (filter) and filterless cigatrettes were observed when the cigarettes were centered on five mattress type substrates. However, when the cigarettes were placed near welt cords, or covered with a non-smoldering pad, there were no differences between the three groups. The cigarette ranking patterns established earlier were again observed in additional tests carried out with mattress specimens cut from a variety of commercial substrates as well as from inert material pads, covered by various blankets and a quilt. More ignition occurred with the cigarettes covered by bedding than on top of bedding. Behavior of the substrates followed the expected pattern: substrates with latex padding ignited more readily than those with PU. The 100% cotton materials smoldered more readily than viscose/ polypropylene or other materials containing thermoplastics. Among the three cigarette configuration modes in the mattress test, flat configurations had the fewest ignition, locations near the weltcord were intermediate, and covered cigarettes worst. Smoldering was more likely to occur with cigarettes covered by bedding than on top of bedding. Table 6-4 shows the general trends discussed above based on ten replicate tests. Statistical analysis showed a significant difference between cigarette packings classified by NIST as low and normal propensity. A few inordinate results were obtained but were not considered to be important for real life situations. The author emphasizes that the fabric/padding combinations used in this work would not be legal in the U.K. since they do not conform to the BS 5852 Standard which precludes fabrics which ignite from cigarettes. However, in other jurisdictions, fire safety would be clearly promoted by prescribing the cigarettes identified as having low ignition propensity in the NIST test. This is particularly so because even if standards like BS 5852 were introduced today in those jurisdictions, the half-life of US furniture is estimated to be fifteen years, so cigaretteinitiated fires would continue for a long time, while cigarettes have a shelf life of a few months. Consequently, use of only low ignition propensity cigarettes would, in a short time period, result in a substantial reduction of upholstered item fires.

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Table 6-4. Percentage Ignitions for Low and Normal Ignition Propensity Cigarettes Cover Fabric

Smoldering Ignitions, Percent

-2

Fiber gm Configuration Cigarette type

Crevice

Mattress (flat)

Slim Filter Filterless Slim Filter Filterless

PU Padding Cotton 325 0 Cotton 325* 100 Cotton 185 0 Visc/PP 233 0 Latex Padding Cotton 385 86 Cotton 185 100 Visc/PP 233 100

100 100 66 0

100 100 83 0

0 0 50 0

0 0 67 0

0 0 100 50

100 100 100

100 100 100

88 100 100 100 0 0

100 100 0

* Includes a cotton batting between the fabric and the foam

In an interlaboratory test of the NIST Mockup Test Method, the coefficient of variation for repeatability was found to be 0.06 and for reproducibilty, 0.10.[581] There was an excellent correlation (correlation coefficient 0.95) between the repeatability in each laboratory and the reproducibilty established by the various laboratories. Another interlaboratory evaluation was conducted to compare the reproducibility and repeatability of results on flat surfaces and in crevices.[596] Seven laboratories tested two experimental cigarettes on two relatively lightweight (245 and 340 g m-2) commercial upholstery fabrics. The cigarette with a 21 mm circumference caused considerably fewer ignitions than the 25 mm cigarette in the flat configuration. Operator-tooperator variability was statistically significant in three of the seven laboratories and not significant in the four others in the crevice tests, but little training had been provided to the operators. Laboratory-to-laboratory variability was not statistically significant for the crevice tests, and for the flat configuration with one fabric but was significant for the other fabric. Transition from smoldering to flaming is discussed in some detail in Ch. 2.[570] Times of between twenty-two minutes and several hours have been reported in the literature. No clear-cut relationship between time of

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placement of a smoldering ignition source and flaming and type of fabric/ padding assembly could be established for those assemblies which started to smolder. As expected, increased ventilation seemed to decrease this time.

6.2.0

FLAMING FIRES

In the following, ignitability is discussed first, and then postignition behavior, primarily heat, smoke, and toxic gas release, as they relate to material performance. When post-ignition behavior rather than ignition resistance is of interest, the test methods usually prescribe larger igniting flames, for example, the cribs of BS 5852 and the California TB 129 and 133 gas burners; often incident radiation is applied to the specimens, alone or along with a flaming pilot ignition source, to simulate conditions during a developed fire. Results sought are generally total heat release or HRR, heat of combustion, mass loss, flame spread, and smoke and toxic gas release. The relative ranking of materials for resistance to small flame ignition is not necessarily identical to resistance to fire growth in a well developed fire, primarily because larger ignition sources or well developed fires overwhelm flame resistance properties, and because the padding plays a larger role in post-ignition behavior than the fabric. 6.2.1

Ignitability

Ignition By Flame Contact. The ranking of materials in Table 6-2 can be used as a rough guide to small flame ignitability of upholstered item components. But unlike in the case of cigarette ignition, relatively few studies exist in which either fabric or padding were varied systematically. Rather, the emphasis was on identifying material composites which would pass certain requirements. Requirement severity is chosen according to estimated risk in various occupancies, for example, the graduated ignition sources of BS 5852.[46] On the other hand, California TB 133[30] and TB 129[31] employ single ignition sources for all public occupancies, and the pass/fail criteria are not presently adjusted according to occupancy risk, but could be. In general, resistance to small flames of upholstered items depends more on the fabric than the padding. However, self-extinguishment after small flame ignition of fabrics is more likely with the padding materials at the top of Table 6-2 than with those lower down.

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Fabrics. Heavier char forming fabrics generally have better small flame ignition resistance than lighter fabrics, and smooth fabrics perform better than pile fabrics. Unlike behavior toward cigarettes, composites with thermoplastic fabrics have low flame ignition resistance because they tend to open up in contact with flames and expose the padding. Back coating thermoplastic fabrics may help. Among thermoplastic fabrics, olefin covered composites have been shown in several studies to ignite more readily than nylon composites. Similarly, vinyl coated fabrics have better flame resistance if the coating is applied to cellulosic rather than thermoplastic base fabrics. Wool has natural resistance to flames which can be further enhanced by FR treatment. Natural leather tends to shrink and disintegrate. Generally, only fabrics containing wool or FR cellulosics, or nonthermoplastic fabrics coated with vinyl, resist BS 5852 gas flame 1 (match simulation) ignition when used with ordinary polyurethane foam. Untreated cellulosics, acrylics, and thermoplastic fabrics fail. FR wool and FR cellulosics often pass even larger ignition sources. The studies leading to these conclusions are summarized below. Several studies have been performed in which upholstered items were subjected to a number of ignition sources (see also Ch. 4).[322] [346][347] Table 4-9 shows that cellulose containing fabrics except a cotton blend with 13% FR viscose ignited both with the BS 5852 gas flame 1 and the methenamine pill; all wool containing fabrics passed with this and generally with gas flames 2 and 3. With borderline fabrics, FR polyurethane foam performed better than untreated foam. Paul et al. published extensively on ignitability.[50][51][230][233][454][455] Again only fabrics containing wool or FR cellulosic fibers, as well as heavily PVC coated fabrics, or, in one case, a fairly heavy nylon fabric, had satisfactory resistance to the BS 5852 gas flame 1 and matches. Fortunately, such fabrics, except the FR cellulosics, also tended to have good cigarette ignition resistance. Untreated cellulosic fabrics, acrylic fabrics, acrylic/cotton blends, and thermoplastic fabrics (nylon, polyester, polypropylene, untreated or FR treated) performed poorly. As a rough estimate, at least 40–60% wool or FR viscose fiber, may be necessary to pass the BS 5852 gas flame 1 test. FR treatment of wool, polyester, and cellulose fabrics tended to improve ignition resistance to the smaller ignition sources but the effect is not as apparent with larger ignition sources.

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More specifically, Table 6-5 shows the behavior of a number of these fabric/padding composites when exposed to various UK ignition sources.[51] Paul classified the fabrics as “flammable, non-protective” (acrylic, polypropylene), “non-flammable*, non-protective” (nylon, polyester, FR polyester) “flammable, protective” (cotton/viscose, wool/cotton), and “low flammable, protective” (wool, cotton, modacrylic, and a back-coated acrylic fabric) when combined with various paddings. The results were improved by the use of an interliner and/or HR foams or FR cotton batting. There can be range of performances within each type, and the pass/fail result will depend on factors such as weight and weave of fabric, surface finish, etc. The designation of any thermoplastic fabric as “non-flammable” is a proposal of questionable merit. Small crevice mock-ups of a series of fabric/padding composites were subjected to several ignition sources, as well as Cone Calorimeter tests at 10 and 15 kW m-2 irradiance.[364] Composites which reached HRRs of 50 kW m-2 in less than 60 s generally ignited with the pill and a BS 5852 gas flame 1; all of these were covered with a medium weight polyolefin fabric with ordinary polyurethane, cotton batting, or neoprene padding; a cotton velvet/ordinary polyurethane composite also was in this group. Conversely, specimens which took longer than 60 seconds to reach 50 kW m-2 in the Cone Calorimeter generally only ignited with the stronger ignition sources, if at all. The specimens covered with polyolefin ranked poorest, followed by cotton velvet, heavy cotton fabric and, best, wool. The neoprene padding did not ignite (though the polyolefin fabric burned on it), the cotton batting was next in ignition resistance, and the polyurethane foam was worst. Among bedding materials, use of wool comforters and wool ticking greatly improved the small flame ignition resistance of mattresses.[456] Padding. As seen in Table 6-2, latex foam has the lowest small flame ignition resistance. Among polyurethane foams, the order is, lowest, ordinary foam; foam with traditional phosphorus or halogen based FR treatment (foam passing California TB 117 requirements); and, most resistant, high-resiliency, combustion modified (CMHR) foam. Cotton batting ranks close to the better CMHR foams.[8] The differences between foams were masked when a highly small flame resistant, FR wool fabric was used. *

The designation of any thermoplastic fabric as “non-flammable” is a proposal of questionable merit.

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Fire Behavior of Upholstered Furniture and Mattresses

Table 6-5. Fabric/Padding Composites Passing or Failing UK Regulations Fabric Type

Fillings not meeting 1988 regulations S HR Cotton Latex PU PU wool +SPU

Polyester

Fillings meeting 1988 regulations HR CM CM FR PU PU PU poly+int +int. ester

Flammable/non-protective Acrylic Polypropylene

N N

A A

N N

N N

A A

A A

F F

F F

F F

A A

N N

N N

A A

A AB

F F

C C

F F

A A A

N N

N N

A A A

AB AB AB

B B B

B B B

F F F

A A A A A

A A N A

N N N A

A A A A A

AB AB AB AB AB

B B B B B

CB CB CB CB CB

B B B B B

Flammable/protective Cotton/viscose Wool/ Cotton

N A

Non-flammable/non-protective Nylon Polyester FR Polyester

A A A

Low-flammable/protective Wool FR Cotton Modacrylic PVC Backcoated Acrylic

A A A A

N - Not meeting any regulations. A - Resists cigarette ignition (1980 regulations). B - Acceptable contract use post-1976 (No. 5 crib and cigarette). C - Meets 1988 regulations for fabric and filling for domestic upholstery. F - Meets 1988 regulations for fillings only for domestic upholstery. SPU Standard PU foam. CMPU - combustion-modified PU foam. Polyester - Polyester fiber mat. HRPU - high-resilience PU foam. Latex - Rubber latex foam. int. - interliner.

It was reported that ignition resistance increased with polyurethane foam density and with increasing isocyanate/polyol ratio.[457] Above a density of 50 kg/m3, the effect of this ratio disappeared. Similar effects of foam density on ignitability by irradiance have been reported, but in other cases, there appeared to have no consistent effect on ignition times under various irradiance levels.[366] Bench-scale results normalized for foam density are reported in Ref. 372, as discussed under Fire Growth, below.

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With the advent of polyurethane foam, numerous natural fiber materials are used less today, such as horsehair, wool batting, and cellulosic materials like kapok, hemp, jute, and other similar products. Wool padding has been found to be generally more ignition resistant than any of the other materials.[365] Ignition By Thermal Radiation. Both the critical heat flux for ignition and the time to ignite under a given irradiance have been used to determine ignitability of fabric/padding composites. This is relevant to the scenario in which an upholstered item is exposed to the radiant heat from other burning items or from the heated walls, ceiling, or upper hot gas layer. When the critical heat flux is the measure of ignitability, a pilot flame or electrical spark is usually present. The effect of the pilot flame on OSU heat release results was found to be negligible.[367] Figure 2-7 shows that the minimum heat flux for ignition in the Cone Calorimeter varied from 5.6 to 14.5 kW m-2 for a series of fabrics spanning a wide range of commercial upholstery assemblies.[362] It was highest for a wool/neoprene composite, followed closely by polyolefin/FR polyurethane; polyolefin/ordinary polyurethane was next, and cotton/ ordinary polyurethane and cotton/TB 117 polyurethane ignited at the lowest irradiance. It is important to observe that the times for ignition varied very little, even over a wide range of materials, although the time was a bit shorter for the polyolefin/ordinary polyurethane composite than for others. A similar search for the minimum heat flux for ignition was undertaken as part of the CBUF study,[7] although only a small portion of the total specimen collection was thus examined. For nine different composites examined, the minimum flux ranged from 6.5 to 21 kW m-2. The lowest value was for an FR cotton/HR polyurethane foam composite, while the highest value was for an FR wool/full-depth impregnated polyurethane foam composite. The times to ignition at two irradiance levels have been obtained by Moulen and Grubits (Table 4-12).[365] They investigated eight fabrics (cellulosics, wool, PVC and polyurethane coated, cotton base), over five paddings, ranging from inert mineral fibers, wool waste, cotton batting, and polyurethane and latex foam. The fabric had again more effect on the results than the padding. The fabric weight and weave (i.e., tight or fuzzy) are likely to be important variables in ignition behavior. As expected, lighter or fuzzier fabrics generally ignited in less time than compact or smooth ones. Use of wool in the fabric and increasing the weight of cellulosic fabrics increased the time to ignition. Polyurethane fabric coating was superior to the PVC coating.

242

Fire Behavior of Upholstered Furniture and Mattresses

Among the paddings, the wool batting was best, followed generally by the cotton batting, polyurethane foam, and latex. The effects of the padding were found to depend more on padding density than combustibility. Vanspeybroeck et al. published several important studies of foam flammability. BS 5852 and the Cone Calorimeter tests were performed on a polyester, a polypropylene, and a FR cotton fabric combined with three HR foams containing phosphorus-halogen type additives (TB 117 types), and two melamine CMHR foams.[243][368][458][459] With some of these fabrics, the TB 117 HR foam passed the BS 5852 gas flame 2 test, the CMHR foam containing 15% melamine the crib 5, and the CMHR foam with 40% melamine, the California TB 133 test. A Cone Calorimeter investigation of composites formed from 14 fabrics combined with lightweight Kevlar interliners and TB 117 and melamine foam is described in Ref. 460. Use of melamine foam increased the ignition time by an average of 20%, that of the interliner by about 10%. Wool, 100% nylon and polyester and a modacrylic/cotton blend covered composite had relatively long ignition times. In an investigation of a variety of upholstered furniture composites, including polypropylene, PVC, acrylic, and cotton fabrics and TB 117, HR, and CMHR foams, the BS 5852 crib 5 was found to be less severe than a radiant exposure of 25 kW m-2.[459] A notable finding was the poor performance of the PVC fabric (possibly with a nylon fabric base which could open up in contact with heat) while the performance of the polypropylene, acrylic, and cotton fabrics (from worst to best) was better. The TB 133 foam performed well with the polypropylene but not the PVC fabric. The peculiarities of the PVC fabric/melamine foam composite (previously observed by the Boston Fire Department) was further investigated by Villa et al.[461] She measured the ignitability of several fabric/ padding composites in the Cone Calorimeter at three irradiance levels. The ignition times for the fabrics combined with ordinary foam ranked, from shortest to longest, bare foam, polyolefin, PVC coated on nylon backing, and nylon fabric. For the melamine foam, the fabric ranking was somewhat different: PVC coated, polyolefin, nylon, and bare foam. There was little effect on these rankings of radiant flux levels. A 100 mm thick polyester batting was only used with the melamine foam; it increased ignition time, total heat release, and CO yield but reduced the 180 second average HRR. The authors concluded that the foam response was nearly proportional to the applied irradiance, but the fabric response was fairly insensitive to it. This paper also reported the appearance changes of the irradiated specimens. The PVC formed a liquid on the surface; then the composite

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specimen bulged up, bubbled, and ignited. The polyolefin fabric melted immediately, the nylon fabric after a period of several seconds. Melamine foam formed bubbles, and retracted from the heating source, while the polyurethane foam ignited very rapidly. An polyester batting interliner resulted in large amounts of soot. The polyurethane foam volatilized completely, while about a 20% residue remained of the melamine foams. The nylon fabric produced a black residue, the PVC a rust brown one. Five lounge chairs containing ordinary polyurethane foam covered with a cotton fabric and cotton batting; nylon/olefin/acrylic back-coated fabric and polyester batting; back-coated olefin; acrylic facing on rayoncotton fabric; and expanded vinyl were subjected to a number of ignition sources.[135] A TB 133 gas burner ignited all chairs; a 1.5 kW radiant heater directed at the front of the chairs caused only slight pyrolysis in 30 minutes but when it was then tipped forward, the pyrolysis gases ignited in presence of an electric spark; a focused quartz/halogen reading lamp used as the heater caused only ignition of the acrylic fabric covered chair; the BS 5852 flame No. 1 did not ignite the cotton covered and the expanded vinyl covered chairs; and the cigarette ignited only the cotton covered chair. Composites of an ordinary commercial and a melamine foam, and 18 fabrics were tested in the Cone Calorimeter and by BS 5852.[369] Among the fabrics were commercial thermoplastic and vinyl as well as experimental vinyl fabrics. As mentioned earlier, the Cone Calorimeter results agreed with those from BS 5852 tests. Some of the experimental fabrics passed with BS 5852 crib 7, with both types of foam. The commercial fabrics failed with the BS 5852 crib 4 on the commercial foam and with crib 7 on the melamine foam. Some studies have also been reported on the ignitability of bare foam. The utility of such results is questionable, however, since (1) foam is never used in furniture uncovered; and (2) there does not exist any means whereby bare-foam ignitability could be correlated to some performance aspect of the actual composite. Ignitability studies with the Cone Calorimeter and in the BS 5852 test on bare polyurethane foams with various FR treatments and on fabric/ foam composites are discussed in Refs. 243 and 458. In testing the bare foams, an irradiance level of 20–25 kW m-2 was found to provide the best differentiation between foams. The ignition resistance was, in the first instance, increased by higher foam density, and was higher for HR and MDI based molded foams than ordinary foams of the same density. Melamine treatment improved the time to ignition and other characteristics.

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Fire Behavior of Upholstered Furniture and Mattresses

The bare TB 117 type foam ignited in 135 s, i.e., half the ignition time of the FR cotton/TB 117 foam composite, and the other two bare foams had similar ignition times. The longest ignition times were obtained with the FR cotton fabric; the polyester fabric ignition time was half of that with the cotton fabric with the TB 117 foam, and 1/10th or less with the other two foams. With the polypropylene fabric, all times were relatively short. The post-ignition behavior of these composites will be discussed in a later section. The differences between the foams was explained by melting which absorbs energy and increases the distance from the radiant source. Ignition time increased when the thickness was increased from 25 to 50 mm for the more FR foam types. 6.2.2

Post-Ignition Behavior

Post-ignition behavior of fabric/padding composites is most frequently characterized by the (1) peak (maximum) HRR of full scale furniture, (2) the average HRR over a certain time period, often 180 s, for a small section of the furniture in bench scale tests, or (3) the total heat release. Other measures are mass loss rate and total mass lost, irradiance at a distance from a burning item, flame spread, and smoke and toxic gas release (discussed in separate sections). The Cone Calorimeter procedure under a specified irradiance, usually 35 kW m-2, and piloted ignition, is the most frequently used bench-scale test. The Ohio State University (OSU) bench-scale calorimeter has also been used for upholstered furniture materials. Other procedures are large mock-up tests, e.g., California TB 133 and BS 5852, or full-scale tests in furniture calorimeters (unlimited air supply) or rooms of various sizes and doorway arrangements. On basis of experience with over 700 TB 133 tests of all types of furniture, Grand provided a list of parameters which affect post-ignition behavior (Table 6-6).[253] These include style (ranging from chairs with only thin upholstered pads in the seat to fully upholstered sofas); fabric fiber content and weight; interliner type; padding type; frame material; combustible weight of upholstery and frame. For each of these factors he provided classifications: thirteen for styles; nine for fabric type plus three for fabric weight; seven for padding and interliner; and three for frame material. Such factors were, according to his study, relevant to creating fire models for upholstered furniture.

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Table 6-6. Upholstered Furniture Parameters Which Affect Flammability

FABRICS

A C L N O P V W X

Acrylic Cellulosics (cotton, rayon, linen) Leather Nylon Olefin (e.g., polypropylene) Polyester Vinyl Wool Other fabric (≥ 1%) or unknown blend

FABRIC WEIGHT

L

Light (up to 8 oz/54 in. width, or 5.33 oz/yd2, or 0.18 kg/m2) Medium (range of 8–16 oz/54 in.width, or 5.33–10.67 oz/yd2, or 0.18–0.36 kg/m2) Heavy (greater than 16 oz/54 in. width, or 10.67 oz/ yd2, or 0.36 kg/m2)

M H FIRE BLOCKER

T

F I

O PADDING AND FOAM

C H M P

Y

CMHR foam HR foam Melamine Padding (fill) between cover/interliner and foam (e.g., polyester) “Code Red” foam Technical Bulletin 117 (California) foam, or equivalent Foam not specified

M W P

Metal Wool Plastic

R T

FRAME

Treatment of fabric for fire retardancy, whether top coating, backing, spray or soak, including FR treatment of fibers during processing Foam treatment, e.g., protective layer for fire retardancy Interliner or barrier layer with flame resistance qualities (G = glass, A = Aramid such as Kevlar, I = interliner not otherwise described) Other barrier or treatment

(Cont’d.)

246

Fire Behavior of Upholstered Furniture and Mattresses

Table 6-6. (Cont’d.) COMPONENT WEIGHTS

C F

STYLE

S SB S/B S//B A /A SBA U ST STS MO SF OTHER

Cushion (or “combustible,” compared to frame) weight, lbs Frame weights, lbs seat only (or with non-upholstered back and arms) seat and back with no gap seat and back separated (<2 in.) seat and back widely separated (≥2 in.) upholstered arms (also plastic; but not wood) arm(s) separated from seat (also “open loop” or “pad” arms) seat, back, and arms attached (no gaps), generally office type “fully” upholstered chair (i.e., same as SBA, but not office type) stacking chair - plastic stacking chair with upholstered seat mock-up (generally, MSOB, designated seat and back together) sofa (generally assumed to be 2-cushion, SF3 would be 3-cushion) other than upholstered chair (e.g., all-wood furniture, table, etc.)

In many studies reported below, ignition was at the juncture of seat and back. Again, it is emphasized that some of the results would have been very different had it been at the juncture of seat and side or on the outside of the upholstered items. There, the material composites often differ since there is little need for resilient padding: for example, inside sides often contain less foam or cotton batting rather than the foam used in most backs, outsides very little or no padding. Such arrangements may have entirely different ignition characteristics than the seat/back crevice; as far as heat release properties are concerned, it has been shown that maximum HRR is not greatly affected by ignition size and location but time to maximum is.[133]–[136] A simple provision in, e.g., TB 133, stating that any area of a furniture item which differs in construction and/or materials from the seat/ back crevice would have to be tested separately would take care of this situation. BS 5852, on the other hand, addresses this problem. Effects of Individual Components. Studies on the fire properties various materials, along with strategies for their improvement, are

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reviewed in this section. In recent years, regulatory requirements have created a beneficial fire safety effect on the marketplace, specifically on the availability of more suitable materials. The UK Regulations have resulted in the development of moderately improved polyurethane foams, without an accompanying cost rise. The California TB 133 test and FAA requirements have resulted in a great deal of progress being made in the development of effective interliners. As a result, numerous American manufacturers have learned much about materials selection in order to optimize fire performance. CBUF discusses the performance of individual materials in Ref. 462. The effect of individual materials on HRR curves of composites can often be seen. Typical heat release/time curves are shown in the next few figures, showing the multiple peaks due to fabric and foam involvement (an additional peak may occur when frames get involved), and the effects of various experimental conditions. Figure 6-3 shows the effect of irradiance in the Cone Calorimeter on a heavy olefin fabric/CMHR polyurethane composite. The separate peaks for fabric and foam decreased in sharpness as well as height as the irradiance decreased. The curves for a number of composites are shown in Fig. 6-4; the polyolefin fabric composites showed much higher HRR values than the comparable cotton composites, and the differences between ordinary and TB 117 type foams were small, with the heavy cotton/ neoprene or cotton batting composites having the lowest HRR values. Another study confirmed the above findings on fabrics, as well as the lower HRR values for cotton batting compared to TB 117 type foam.[269] In many reports on composite testing, however, the effects of individual components cannot be distinguished because materials were not systematically varied. The following sections have to be read with this in mind; they present generalizations only and may not apply to any specific composite. Fabrics. Fabric selection plays an important role in the fire safety of furniture. While the same types of fabrics are generally available the world over, their usage tends to be nationally-specific. For instance, currently in some countries leather coverings are highly popular (about 25% of the marketplace) while in others their role is minimal. Similarly, there is a wide range in the national liking for heavy cotton fabrics. Even amongst the thermoplastics there is a variation in national preferences. Thus, the fire picture is intrinsically affected by existing national preferences. Note, however, that these change over time, as these are fashion items.

248

Fire Behavior of Upholstered Furniture and Mattresses

Figure 6-3. Effect of irradiance level on Cone calorimeter measurements of the HRR of heavy olefin fabric/CMHR foam composite.

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Figure 6-4. Cone calorimeter measurements of HRR for various fabric/padding composites at an irradiance of 25 kW m-2.

Upon exposure to flame ignition sources, thermoplastic fabrics melt, shrink away from the flame or form pools, and thus expose the padding. The burning molten polymer pools intensify the flames. Ignition resistance is lowered, and the HRR may be relatively high. Olefin has a lower melting point and a higher heat of combustion than the other thermoplastics (nylon, and polyester), and generally produces higher HRR values. CBUF recommends against the use of olefin (polypropylene) fabric.[462] On the other hand, charring fabrics protect the padding until they break open due to brittle char formation, heat shrinkage, and/or tension due to the upholstering process. Since upholstering is mostly a manual process, this tension can vary somewhat between otherwise similar chairs. Many leathers have high heat shrinkage and form very brittle chars.[131] Wool fabrics also form brittle chars, and exhibit some heat shrinkage; test results

250

Fire Behavior of Upholstered Furniture and Mattresses

for replicates or for small-scale–large-scale comparisons appear to be sensitive to fabric tension and are often quite different. Cotton and other cellulosic fabrics appear to have less brittle chars. The position of acrylics is not clear; they tend to shrink and to leave a char; however, when ignited they generally result in high heat release, smoke, and toxic gases release rates. In blends of thermoplastics and char formers, the latter hold the melting component in place but the fabrics also shrink when heated. Thus, the important aspects of the combustion behavior of charforming fabrics are: (1) to produce an initial peak heat release; (2) until the char breaks, reduce radiation and prevent penetration of the flames to the padding. Fabric weight undoubtedly plays a role in char formation. The role of various types of back coating is not clear; back coating formulations with FR components are available.[462][463] An additional complicating factor is that polyurethane foams shrink away from the heat source;[458][459] burning fabrics which lose their integrity will fall on the foam, propagating the flaming while those whose chars remain will have a lesser effect on the foam. How protective a charring fabric is thus depends on a number of factors which are essentially uncontrolled in manufacture and in experimental specimen preparation (tension is controlled in the BS 5852 and in current Cone Calorimeter test procedures). In one study the weight of the cover fabrics was varied systematically.[370] For the woven fabrics, a trend toward increased peak heat release for heavier weights was detected but for knitted fabrics, no such trend existed. McCormack et al. discussed the results of several hundred chair burns according to TB 133.[387]–[389] They found that PVC (vinyl) coated and polypropylene fabrics produced relatively high HRR values but that these could be reduced by proper choice of interliners. In an effort to reduce the number of TB 133 tests, the flammability of a large number of styles used by a manufacturer of institutional furniture were tested, as a means to predict TB 133 performance from fabric, padding, and configuration parameters.[464] Fabrics were ranked from best to worst: wool and vinyl fabrics; modacrylic/nylon; 100% polyester and polyolefin; nylon/wool; nylon/polyester; and acrylic/olefin (this ranking is similar to numerous other studies, as discussed below). In a similar study where three different interliners were used, a modacrylic/nylon fabric again was best, followed by polyester, polyester/ cotton which is similar to cotton, and two weights of polypropylene fabric.[378]

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Cone Calorimeter results for a number of fabric/interliner/foam composites are described in Refs. 379 and 460. Fourteen common upholstery fabrics were used, including 100% wool, polyester, and nylon fabrics, and various blends containing these fibers and cotton, modacrylic, rayon, and olefin. The following trends were observed: • Wool and modacrylic composites had the lowest HRR, nylon and polyester composites the highest. In this test series, blending of nylon with wool tended to result in HRR values closer to nylon. • Use of melamine foam reduced the peak heat release by about 16% as compared with TB 117 foam (but when an interliner was used, this reduction did not occur in these tests), reduced HRR averaged over the first 180 s by only 12%, and had no effect on the total heat release. Without an interliner, the melamine foam smoke level was 12% higher, but with an interliner, 36% lower than that of the TB 117 foam. • A Kevlar interliner (68 g m-2)+ laminated to the cover fabric reduced the peak HRR by 16%, the HRR averaged over the first 180 s by 73%, total heat by 69%, and smoke obscuration rate by 20%. • Wool, FR polyester, and modacrylic cotton blend/ interliner composites had the lowest peak HRR values per unit weight. Andersson provided HRR vs time curves for a variety of upholstered items.[132] The ignition source was a trough with 0.1 L heptane, providing about 20 kW for 2½ –3 minutes, located at the left front of sofas which were covered with an acrylic fabric, combined with either ordinary or TB 117 polyurethane foam. In this case, the TB 117 foam caused some delay in the start of rapid fire development, and lower peaks. For these materials, the HRR calculated from mass loss and that measured by oxygen consumption agreed rather well. The smoke obscuration peak occurred slightly after the HRR peak. For a 60 m3 room, CO levels would have reached dangerous levels in about 3 minutes, CO2 levels in about 4½, and NOx levels in about 5 minutes.

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Fire Behavior of Upholstered Furniture and Mattresses

Using the Cone and the OSU calorimeters and testing fabrics of roughly similar weight, a wool/nylon fabric performed best and a cotton was next. This was followed by a nylon and a polypropylene fabric which were similar in performance.[370] Eleven parameters were measured during the tests; no consistent, major difference was found between the untreated, California TB 117 treated, and two melamine modified, HR and CMHR foams in this work. The authors state that further improvements in fire performance should be attained by use of interliners rather than trying to improve foams; this, however, may not be viable where arson is a possibility. Results of comparison testing of composites of five fabrics with a CMHR (melamine treated) polyurethane foam by the TB 133, BS 5862 (crib 7) and the Boston Fire Department Tests are shown in Table 6-7.[375] Fabric/foam mock-ups covered with a nylon or a standard vinyl fabric failed all three tests. Those covered with wool/nylon, modacrylic/nylon, and a FR vinyl passed; they formed chars which protected the foam. All tests passed or failed the same materials according to the weight loss and flame out time criteria. However, for smoke obscuration, the results were not as consistent, indicating that the tests do not necessarily pass or fail the same composites. Note that smoke obscuration and carbon monoxide concentration are not part of the pass/fail criteria in BS 5852 test. The values are provided for comparison only. While the Boston Fire Department test includes smoke in the pass/fail criteria, it does not include carbon monoxide. It should also be noted the actual concentrations of CO and smoke will depend on the flow rate of the exhaust system which is different for each of the three test methods. NIST furniture calorimeter studies showed the quantitative effects of fabric material on the HRR (Table 6-8).[95][269] The largest data set (Group 3) comes from a mock-up test series. The rank order, best to worst, with FR polyurethane padding, is heavy cotton, no fabric, light cotton, heavy olefin, light olefin. This is almost exactly the inverse of the order by cigarette ignitability, with the exception of thermoplastic fabrics, where heavier weight was preferable in both cases. In yet another study, in room fire tests with crib 7 as the ignition source, a wool/cotton/nylon fabric resulted in lower HRR than a FR cotton velvet and a FR polyester velvet.[381] FR treatment of wool and cotton reduced flame growth, though it increased smoke development.[346][465]

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Table 6-7. Results of TB 133, Boston Fire Department, and BS 5852 Tests

Criteria Wool/nylon 55/45

Nylon

Fabrics Modacrylic/ nylon 75/25

FB™ Vinyl

Std. vinyl

Results of California Technical Bulletin 133 Test Weight loss (%)

6.8

35

8.5

4.8

80

Smoke obs. 4 ft.

52

82

44

55

100

Smoke obs. floor

26

60

17

40

CO maximum ppm

800

400

1186

2300

2100

CO (s over 1000 ppm)

0

0

25

50

80

Max. temp. at ceiling (°F)

227

205

171

220

365

Flame-out time (min/s)

3/40

20/0

3/20

2/30

14*

5.3

50

Results of Boston Fire Department BFD IX-10 - Chair Burn Test Weight loss (%)

1.5

11.0

Penetration

none

yes

none

none

yes

Max. temp (°F)

136

145

179

200

220

5.7

Smoke obs. at 4 ft (%)

19 light

39 mod. 52 mod.

52 mod. 100 heavy

Flame-out time (min/s)

2/20

18/0

6/15

3/20

9†

CO max. (ppm)

151

102

400

463

512

Results of British Standard BS 5852 (Crib 7) Flame-out time (min/s)

6/15

20/0

6/40

10/45

15‡

Weight loss(%)

10.7

44

9.9

20

43

Smoke obs. at 4 ft. (%)

37

50

48

50

100

CO max. (ppm)

131

185

172

249

371

Padding: melamine FR treated HR PU, 48 kg/m3 obs. = obscuration; mod. = moderate; underlined entries indicate failure * Test aborted at 14 minutes.

† Test aborted at 9 minutes. ‡ Test aborted at 15 minutes.

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Fire Behavior of Upholstered Furniture and Mattresses

Table 6-8. Effect of Fabric Type on Heat Release Rate Item

Full-Scale Peak HRR (kW)

Fabric

Weight (g/m2)

Padding

F24

700

cotton

750

FR PU foam

F21

1970

polyolefin

560

FR PU foam

F22

370

cotton

750

cotton batting

F23

700

polyolefin

560

cotton batting

28

760

none

17

530

cotton

650

FR PU foam

21

900

cotton

110

FR PU foam

14

1020

polyolefin

650

FR PU foam

7, 19

1340

polyolefin

360

FR PU foam

Group 1

Group 2

Group 3 FR PU foam

Padding. The effect of padding material on HRR is generally more important than that of fabrics. The approximate ranking from best to worst, with some overlap, would be: • neoprene • rubberized hair • wool batting or felt • FR cotton batting • untreated cotton batting • batting containing cotton and mixed fibers • melt-bonded polyester batting • resin bonded polyester batting • latex Neoprene and cotton batting, and to a slightly lesser degree, polyurethane foams, tend to smolder after the flames are extinguished, and extreme care must be exercised when disposing of them to prevent re-ignition.

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Polyurethane foam can show a significant range of performance, depending on the efficacy of formulation or treatment. The best-ever fire performance seen by the authors was close to that of neoprene, but this product* (now not on the market) also had density and cost similar to neoprene. Run-of-the-mill polyurethane foam without special retardants is ranked near latex, close to the bottom. Increasing foam density for non-FR foams tends to worsen the HRR behavior. For FR foams, this is entirely dependent on the FR nature. In general the order of polyurethane foams, best to worst is: • US CMHR foams† • UK CMHR foams, i.e., highly retardant treated (melamine or exfoliated graphite) and foams filled with large amounts of hydrates • cold cure foams • FR formulations such as foams passing TB 117 • ordinary polyurethane foams In the CBUF work, with a 30 kW ignition source, the HRR difference between polyether (ordinary polyurethane) and HR foam was found to be insignificant.[462] Examples of papers leading to this ranking are discussed below. HRR values for a number of padding materials, before and after leaching, are shown in Table 6-9.[8] In this study, a Cone Calorimeter HRR of 100 kW m-2, averaged over 180 s, was considered to be the lowest HRR which could cause self-propagating fires. This was exceeded by ordinary, California TB 117, and two proprietary CMHR polyurethane foams and polyester batting. The performance of polyester batting relative to some of these foams is, however, not clearly established: unsupported, it shrinks away from the Cone heater and melts, increasing the distance to the heat source (see, however, discussion of sample preparation to obviate the distance effect in Ch. 3).

* A hydrophilic type formulation. † CMHR foams were introduced in the US about 1980 and were highly retardant filled and highly expensive. These were not commercially popular and the term CMHR now has been taken over by UK practice. The current CMHR foams are normally of UK-spec, unless noted otherwise.

256

Fire Behavior of Upholstered Furniture and Mattresses

Table 6-9. Heat Release Rates of Various Paddings, Before and After Leaching Core Material

180 s Average HRR (kW/m2) As Received Leached

Normal PU Normal PU PU/FR cotton batting California 117 PU CMHR (type A) PU FR cotton batting CMHR (type B) PU CMHR (type C) PU CMHR (type D) PU Neoprene foam Polyester batting FR cotton batting (used) FR cotton batting (new)

170 194 144 162 164 51 31 34 126 32 141 60 57

179 196 142 165 186 110 33 29 172 30 139 86 113

Polyurethane foam is, by far, the most widely used padding today. It has moderate cigarette ignition resistance, but poor small flame resistance which can be slightly improved by the low efficacy, TB 117 type treatment. However, the rapid fire growth of such foams in even moderately hot fires has led to suggestions that it be removed from the market. This was considered an overkill by Damant.[466] He reviewed the development of polyurethane foam. The heat of combustion of polyurethane is 24 MJ kg-1, as compared to wood, 17 MJ kg-1; its cellular structure further accounts for the rapid burning. He mentioned the following mechanisms for improving the flame resistance: • Increasing the thermal stability to increase the heat of gasification. • Decreasing the combustion efficiency which, however, increases the amount of smoke and CO. • Promotion of charring. • Addition of flame-retarding elements such as chlorine, bromine, or phosphorous which provide resistance to small ignition sources.

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• Diluting fire gases by releasing inert gases; e.g., hydrated alumina (up to 50% of the total weight of the material) releases substantial amounts of water vapor above 195°C. Its use is limited by its poor functional properties, due to the large amounts of additives needed. • Development of high resiliency foams which melt away from ignition sources. • Following UK strategy, using melamine or (less commonly) exfoliated graphite additives. Most of the mentioned additives are included in the foam formula, but others are applied as after-treatments to the foam surface. The latter obviously cannot be used where vandalism can be expected. Paul described various FR foam types and gave typical formulations.[50] Melamine treated and exfoliated graphite containing foams both met the BS 5852 requirements (cigarette and crib 5) but by different mechanisms: the former by melting, the latter by charring. Composites of melting and char forming materials can burn readily because melting foam can wick into char forming fabrics, instead of evading the ignition source. Formulations for conventional and HR foams which conform to the different requirements of TB 117, TB 133, and BS 5852, crib 5, are listed in Ref. 467. Conventional polyol foam can be used with low level melamine add-on to pass TB 117, slightly more melamine in HR foam to pass BS 5852, crib 5, and (depending on the cover fabric) 32 kg m-3 density foams with 40–90 parts by weight of melamine to pass TB 133. The roles of various polyols used in foam manufacture are described, and the physical properties of such foams are presented in several tables. In a study of the effects of the BS 5852 ignition sources on foams, it was found that foams that formed solid chars were more likely to cause self-propagating fires than those which shrank and formed voids or air bubbles.[468] Table 6-10 summarizes some full scale, peak mass loss rate and HRR results for chairs and love seats varying widely in fabric, padding, and configuration (note the large variation in peak HRR).[95][269] Figure 6-5 shows the reduction in the HRR measured in the furniture calorimeter when the padding is changed from FR polyurethane to cotton batting and when the fabric is changed from polyolefin to cotton.

258

Fire Behavior of Upholstered Furniture and Mattresses

Table 6-10. Peak Mass Loss and Heat Release Rates of Typical Chairs Item

Mass (kg)

C12

17.9

Comb. Style (kg) 17.9

TEC

Frame

Padding

Fabric

Peak MLR (g/s)

Peak HRR (kW)

wood

cotton

nylon

19

290

F22

31.9

TEC

wood

FR cotton

cotton

25

370

F23

31.2

TEC

wood

FR cotton

olefin

42

700

F27

29.0

TEC

wood

mixed

cotton

58

920

F28

29.2

TEC

wood

mixed

cotton

42

730

C02

13.1

12.2

TEC

wood

cotton, PU

olefin

13

800

C03

13.6

12.7

TEC

wood

cotton, PU

cotton

18

460

C01

12.6

11.7

TEC

wood

cotton, PU

cotton

18

260

C04

12.2

11.3

TEC

wood

PU

nylon

76

1350

n.a.

180

80

1990

C16

19.1

F25

27.8

18.2

TEC

wood

PU

nylon3

TEC

wood

PU

olefin

T66

23.0

TEC

wood

PU, PE

cotton

28

640

F21

28.3

TEC

wood

FR PU

olefin

83

1970

F24

28.3

TEC

wood

FR PU

cotton

46

700

3

C13

19.1

18.2

TEC

wood

PU

nylon

15

230

C14

21.8

20.9

TEC

wood

PU

olefin3

13

220

3

C15

21.8

TEC

wood

PU

olefin

13

210

T49

15.7

20.9

EC

wood

PU

cotton

14

210

F26

19.2

Thin EC

wood

FR PU

olefin

61

810

F33

39.2

TL

wood

mixed

cotton

75

940

F31

40.0

TL

wood

FR PU

olefin

130

2890

F32

51.5

TS

wood

FR PU

olefin

145

3120

T57

54.6

L

wood

PU, cotton

PVC

62

1100

756

11.2

OC

wood

latex

PVC

3

80

C09/T64

16.6

16.2

FBC

part wood

PU PE

none

20

460

C07/T48

11.4

11.2

MEC

PS foam

PU

none

38

960

C10

12.1

8.6

PC

RPU foam

PU

none

15

2401

C11

14.3

14.3

FBC

PU

nylon

n.a.

18102

F29

14.0

TEC

PP foam

PU

olefin

72

1950

F30

35.2

TEC

RPU

PU

olefin

41

1060

(Cont’d.)

Upholstered Item Design Engineering

259

Table 6-10. (Cont’d.) Item

Mass (kg)

Comb. Style (kg)

Frame

Padding

Fabric

Peak MLR (g/s)

Peak HRR (kW)

C08

16.3

15.4

PSC

MPeth

PU

PVC

112

8302

C05

7.3

7.3

BBC

PS beads

PVC

22

3701

C06

20.4

20.4

FFBC

PU

acrylic

151

24802

T50

16.5

WRC

metal

cotton

PVC

n.a.

<10

T53

15.5

1.9

WRC

metal

PU

PVC

13

270

T54

27.3

5.8

MFL

metal

PU

PVC

20

370

T75/F20

7.5

2.6

SC

metal

PU

PVC

7

160

(×4) 1 - estimated from mass loss records and assumed heat of combustion; 2 - estimated from doorway gas concentrations; 3 - neoprene interliner; TEC - traditional easy chair; EC - easy chair; TL traditional love seat; TS - traditional sofa; L - love seat; OC - office chair; FBC - foam block chair; MEC - modern easy chair; PC - pedestal chair; PSC - pedestal swivel chair; BBC - bean bag chair; FFBC - frameless foam back chair; WRC - waiting room chair; MFL - metal frame love seat; SC - four stacking chairs; RPU - rigid PU; MPeth - molded polyurethane; PS - polystyrene; MLR mass release rate; HRR - heat release rate

Figure 6-5. Comparison of the effects of FR polyurethane foam and cotton batting and of polyolefin and cotton fabrics on the HRR of furniture items in the furniture calorimeter.

260

Fire Behavior of Upholstered Furniture and Mattresses

The Cone Calorimeter has been suggested for simplified, approximate materials screening of foams.[231] It was found from analysis of NIST Cone Calorimeter data that numerical cut-off values of HRR could be established representing each type, which are essentially independent of the fabric used (but the results are not applicable to the testing of bare foams, without fabric covering). These are, approximately: Type of foam

HRR (kW m-2) (180 s average after ignition)

ordinary, TB 117 polyurethane

> 280

melamine polyurethane

< 280

US CMHR polyurethane

< 160

hydrate filled polyurethane

< 85

neoprene

< 45

This work was done on materials available in the mid-1980s. A similar classification was not attempted during the more recent CBUF work, so it is not clear if present day materials still would lend themselves to such screening. It must also be kept in mind that all Cone Calorimeter testing prior to the availability of the CBUF test protocol was done using the old test procedure and may not give results comparable to testing under the latest version of ASTM E 1474. The Cone Calorimeter was found to be a useful tool to evaluate the efficacy of FR agents in experimental foams.[469] The results, obtained at 35 kW m-2 irradiance, correlated well with melamine content, and reproducibility was good. Peak HRR values were reduced proportionally to additive concentration, while average heats of combustion were only slightly affected, indicating a greatly reduced rate of burning. Many other papers report the behavior of melamine filled CMHR foams in combination with a large variety of fabrics and interliners.[461][469]–[471] Again, melamine foams combined with carefully selected fabrics, wool or FR cotton (but not thermoplastics, untreated cellulosics, or acrylics), for example, seem to provide a satisfactory combination of flame retardance, physical properties, and price. Söderbom et al. exposed two types of chair, one FR type (acrylic/ cotton with FR back coating over polyester wrapped CMHR foam) and one ordinary (the same fabric without the back coating over polyester wrapped

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261

polyether foam) to the TB 133 burner.[136] Ignition conditions were 20 kW for 300 s, 30 kW for 120 or 180 s, and 40 kW for 120 s. At an average, the FR chair produced twice the peak HRR, almost three times the total heat release. This indicates that the much heavier CMHR foam was readily ignited by any of these exposure modes, and was not protected by the FR back coating. The peak rate of smoke release was about 20% higher for the FR chair, and its total smoke was twice that of the non-FR chair. The results did not seem to be affected by the ignition mode. The effect of variations in density of polyurethane foams from 27 to 85 kg m-3 was studied on a series of thermally compressed foams.[472] The heat release characteristics were measured with the OSU calorimeter under several irradiances. The peak HRR increased with density for melamine, polyester, and polyether foams, and major differences between melting and charring systems were found. While melamine treated foams generally perform well, an exception was found by the Boston Fire Department and others: the poor initial behavior of the composite of some vinyl fabrics and melamine foam.[473] This is also discussed in detail in Refs. 461, 470, and 471. This composite, and others in which nylon and polyolefin fabrics were placed over ordinary and melamine foam as well as polyester batting, with and without interliners, were tested in a Cone Calorimeter at three heat flux levels.[461] The HRR of the vinyl/melamine foam composite was only found to be higher than that of other materials during the first 15 to 20 s but not at the peak. This composite also produced more CO and smoke than the other vinyl composites, which, in turn, produced more smoke than the other fabric/foam composites. This paper provides highly detailed data, including average HRR over 15 and 120 s intervals, peak HRR, total heat, mass loss, heat of combustion, and pyrolysis product generation. The Society of the Plastics Industry, Inc. (SPI) sponsored a program directed toward finding a procedure for ranking all types of polyurethane foam. Heat and smoke release plots, obtained in the OSU Calorimeter, were given for TB 117, melamine, and hydrated alumina filled foams.[367] The relationships between these results, obtained at various heat fluxes, were compared with the downward flame spread rates in an LOI apparatus, at various oxygen concentrations. A very low irradiance of 17.5 kW m-2 was suggested for use in various SPI projects; however, no irradiance level was found to be truly appropriate for differentiation between all types of foam.

262

Fire Behavior of Upholstered Furniture and Mattresses

Similarly, an instrument using the limiting oxygen principle (called the Oxygen Index Calorimeter-OIC) was tried for differentiation of foam performance.[374] An oxygen concentration of 45% was found to give the best differentiation between specimens. However, the correlation with TB 133 room temperature results was erratic. The Cone Calorimeter ignition behavior of polyurethane foams without fabric covers has been discussed earlier.[243][458][459] A large variety of foams were tested by means of a horizontal oxygen index apparatus and by BS 5852 crib ignition sources.[243] Weight loss in BS 5852 decreased with a decrease in foam density. CMHR foams gave better results than diphenyl methane-4,4-diisocyanate (MDI) foams at comparable filler levels. Even high filler levels in ordinary slabstock did not permit passing BS 5852. The effectiveness of a large number of foam filler types are discussed in this paper. A comparison of results in the TB 133 test and three bench-scale tests was performed during the development of flexible, moldable foam.[474] The advantages of the MDI foam systems relative to toluene-2,4-diisocyanate (TDI) are reported to be less release of gas in manufacture, higher reactivity, faster cure, and shortened de-mold times, etc., as well as higher flame resistance. The higher boiling point of MDI, 353 vs 252°C for TDI, explains the higher flame resistance of the former. Processing of MDI is described briefly. Melamine content did not have an effect on burn rate, but decreased the HRR and effective heat of combustion at several irradiance levels, in HR and in MDI-molded foams.[243] The effective heat of combustion was similar for MDI molded and ordinary HR foams. Total heat release was about 20 MJ m-2 for TB 117 and HR foams, and about 15 MJ m-2 for CMHR foam. A paper from Italy describes processing and physical and fire properties of molded furniture foams.[475] In the Italian test, which uses the BS 5852 mock-up but a 140 second exposure to a 40 mm propane flame, TDI or TDI/MDI formulations performed better than MDI, while BS 5852 was easier to meet with MDI foam. The differences were attributed to different melting characteristics of these foams. MDI based foams had lower smoke emission. Total heat release and effective heat of combustion of fabric/foam Cone Calorimeter mock-ups corresponded to the values for the individual materials.[458] The effective heat of combustion of a 470 g m-2 polypropylene fabric was 43 MJ kg-1, that of a 300 g m-2 polyester fabric, 14 MJ kg-1, and

Upholstered Item Design Engineering

263

that of a similar weight FR cotton fabric, about 11 MJ kg-1. On the other hand, the effective heats of combustion of HR foam was 27 MJ kg-1 and of CMHR (the latter passing BS 5852, crib 5 test and TB 133) melamine filled foam, 16 MJ kg-1. Covering the TB 133 foam with the above fabrics delayed ignition and reduced the peak HRR, except for the polypropylene fabric. Sundström[476] found effective heats of combustion of 20 MJ kg-1 for polyurethane cushions on a steel frame. Similar values were found by other investigators.[147] Older, highly filled with hydrophilic and other materials, FR treated polyurethane foams (with poor physical properties) behaved similarly to neoprene, with one major exception: the neoprene foam cores supported smoldering combustion and often burned up completely, albeit slowly. A smoldering neoprene article is often impossible to extinguish, except by cutting it up into small pieces and total submersion under water. The highly FR treated polyurethane specimens, by contrast, did not tend to smolder; lacking a strong external source, the fire tended to go out.[261] Batting. Cotton batting is a cheap and relatively flame (but without SR treatment, definitely not cigarette) ignition resistant material, and it tends to smolder rather than burn. Treatment with boric acid/borax combinations can further greatly increase its fire performance. Several papers comparing cotton batting with other padding are discussed elsewhere in this chapter; it appears to rank similarly to the better CMHR polyurethanes in post-ignition fires. Mixed fiber batting generally contains primarily cotton but also various amounts of other fibers, primarily polyester. It has been found to release heat substantially more rapidly than comparable all-cotton batting in full-scale tests, but its smoldering tendency was reduced.[477] Melt-bonded (but not latex bonded) all-polyester batting is used frequently in a layer between cover fabric and polyurethane foam in seats and in sides of upholstered furniture. In mattress tests, one such product showed low HRR comparable to those of all-cotton.[477] In other mattress tests, melt-bonded polyester batting combined with selected tickings passed TB 121, TB 133, and BS 5852, cribs 5 and 7, tests.[478] However, even meltbonded polyester batting can increase HRR if it wicks into fabrics or other padding. Interliners. Interliners (barrier materials, blockers, blocking layers) are often used in upholstered furniture to pass TB 133, BS 5852 crib, and similar larger ignition source tests. They are not appropriate for use in furniture intended for prisons, hospital alcoholic and psychiatric wards,

264

Fire Behavior of Upholstered Furniture and Mattresses

buses, subway cars, and other situations where vandalism or malicious fire setting can be expected. In other applications, however, interliners can offer increased design options for achieving good fire performance. Interliners have been studied as a means of reducing the cigarette and flame ignitability (as discussed above), and the fire growth. Systematic engineering data are not available; however, enough studies have now been reported to enable some generalizations to be made. Interliners, like other upholstery materials, have to be chosen with an expected ignition source in mind. For example, polyester batting generally reduces cigarette but not flame ignitability. Many interliners provide added resistance to fabric ignition and flame spread from a small flaming source, and some are effective against larger ignition sources, e.g., the TB 133 gas burner which has also been used in EC research work. The ignition resistance of composites involving, say, a readily flammable fabric over a slow burning padding would gain little benefit from an interliner but after a flaming ignition, a properly chosen interliner can again be highly useful in reducing the HRR values of the padding. However, their effectiveness with respect to smoke and toxic gas generation rate cannot be readily predicted. If they slow down fires moderately, they may increase CO and smoke; but if they prevent the fire or slow it down to a very low rate, they may also reduce the release rate of these products. The development of interliners was spurred by the requirements of TB 133 and the aircraft safety regulations.[324][479] The former paper provides data on the performance of various interliners used in institutional furniture (albeit not well characterized), indicating that they have to be chosen with care so as to provide low peak HRR as well as smoke and CO development. Interliner Characterization. For flaming behavior improvement, Kourtides et al.[324] have classified the possible retardant mechanisms of interliners (many are similar to those discussed under padding, above): • Transpiration cooling: this occurs if the interliner contains substances which gasify rapidly but are nonflammable. Typically hydrated alumina, which releases water vapor, can be used as a filler for foams. • Re-radiation: this effect is noted for materials of low thermal conductivity and good high temperature stability.

Upholstered Item Design Engineering

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• Thermal insulation: this mechanism is effective if the barrier is thermally stable, of low conductivity and density, and, if cellular, of closed-cell form. Effectiveness increases with thickness. • Reflection: typically, aluminum foil or aluminized fabrics are useful materials for this, but this is much more effective if the reflective surface is on the outside than when it is in contact with other surfaces on both sides. • Local heat dissipation: a material of relatively high density and thermal conductivity can limit small-scale ignitability by dissipating heat over a wide area. Cigarette ignitability can also be improved. Aluminum is a suitable material for this. • Barrier to pyrolysates: a dense, nonporous substance is required for this. Additional benefits can be derived from limiting oxygen access to the pyrolysis region and from thermal cracking of the retained pyrolysates. Commonly proposed interliners can be grouped into several categories: 1. Interliners which improve flaming properties if they do not split due to tension, but which may sacrifice cigarette ignition resistance, e.g., FR cotton fabrics.[144][464][479] The behavior appears to be typical of cellulosic fabrics; increasing interliner weight may improve the HRR behavior but worsen cigarette ignitability. Its effect on flame ignitability is presumed to be small. 2. Interliners which improve both flame and cigarette ignition resistance behavior, e.g., certain neoprene foam barriers (e.g., Vonar®) and other CM foams. These are seen to offer an improved behavior in all three aspects (cigarette ignitability, flame ignitability, HRR). Performance improved with barrier thickness (density is usually constant).[324] A neoprene foam interliner was considered to be

266

Fire Behavior of Upholstered Furniture and Mattresses completely satisfactory even for the fire environment in aircraft; however, its weight precludes its use in that application. The neoprene foam interliner derives a significant fraction of its effectiveness from the action of the filler, aluminum trihydrate, in releasing water as a cooling mechanism. 3. Fiberglass cloth.[378][461][464] Quite widely used but unless coated, this is porous and not practical in larger thicknesses because of its brittleness. Its mechanical strength under heating can be usefully exploited in single or multi-layer constructions. Fiberglass cores with FR cotton wrappings or with PVC coatings are used widely. 4. Novoloid and Kynol. These were seen to be effective in some full-scale chair tests[480] where they reduced the peak HRR from 600 kW to 150 kW. 5. Aramid non-woven interliners are also used widely but sometimes they seem not thick enough for satisfactory performance.[378][460] 6. Interliners of uncertain benefit: Layers of TB 117 foams have been tested occasionally as barrier materials.[351] Considerably more effective FR formulation is usually needed.

Test Results Using Interliners. Many papers describe the effects of interliners intermingled with other construction effects, and are described elsewhere. A number of papers describing primarily results with interliners are reviewed below. As stated before, the relative performance of interliners can vary with cover fabric and padding characteristics, as well as intensity of the ignition source. This is illustrated in Table 6-11 A and B which show Cone and furniture calorimeter results for eight fabrics, each paired with three interliners, over TB 117 and a medium level melamine (IFR) foam.[378] In this case, the 60 and the 180 second average HRR generally ranked a coated glass fiber interliner best, followed by a non-woven aramid fabric and a coated glass fabric (fabric weights were 120, 68, and 265 g m-2).

Upholstered Item Design Engineering

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Table 6-11. Heat Release Rates of Various Fabric/Interliner/Padding Composites A: Time-Averaged Cone Calorimeter Test Results (Average. ± Average Deviation) Set Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Materials

PE/A/Cal 117 "/B/" "/C/" Nylon/A/Cal 117 "/B" "/C/" MA-N/A/Cal 117 "/B/" "/C/" PE-Cot/A/Cal 117 "/B/" "/C/" Cot/A/Cal 117 "/B/" "/C/" Lt PP/A/Cal 117 "/B/" "/C/" Lt PP/A/FR foam "/B/" "/C/" Hvy PP/A/Cal 117 "/BB/" "/C/" Hvy PP/A/FR foam "/BB/" "/C/"

60 Second Average HRR (kW/m2) 128 ± 0.9 139 ± 5.3 96 ± 6.7 211 ± 6.2 263 ± 4.4 204 ± 1.8 86 ± 15.5 82 ± 9.4 53 ± 6.3 201 ± 4.2 173 ± 7.0 113 ± 2.7 175 ± 7.0 178 ± 8.7 113 ± 9.1 234 ± 2.2 137 ± 5.1 133 ± 0.9 225 ± 7.3 130 ± 5.1 127 ± 9.8 256 ± 4.7 169 ± 4.7 133 ± 16.2 226 ± 9.5 145 ± 4.9 131 ± 8.2

180 Second Average HRR (kW/m2) 82 ± 16.1 154 ± 5.0 32 ± 2.0 132 ± 8.0 203 ± 9.7 71 ± 0.4 39.5 ± 10.5 44 ± 7.5 18 ± 2.7 114 ± 1.1 100 ± 2.0 38 ± 1.1 100 ± 2.0 143 ± 3.0 51 ± 5.7 162 ± 6.3 147 ± 9.0 45 ± 0.7 139 ± 5.3 129 ± 6.3 49 ± 8.3 189 ± 9.2 89 ± 15 48 ± 5.0 144 ± 3.0 94 ± 9.2 51 ± 4.3

Fabrics: PE - polyester; MA - modacrylic; cot - cotton; PP - polypropylene. Interliners: A - aramid non-woven; B - knitted glass/charring fiber blend; C - same as B, but with a PVC coating.

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Fire Behavior of Upholstered Furniture and Mattresses

Table 6-11. (Cont’d.) B: Peak Heat Release Rates In Full-Scale Mock-up Burns Set Number

Peak HRR during burner exposure (kW/m2) at time (s)1

Peak HRR after burner exposure (kW/m2) at time (s)1

PE/A/Cal 117 "/B/"

60 (128 s) 84 (138 s)

83 (938 s) 20 (640 s)

3

"/C/"

100 (128 s)

12 (750 s)

4

Nylon/A/Cal 117

ca.100

ca. 300

1 2

Materials

5

"/B/"

141 (138 s)

476 (1098 s)

6

"/C/"

135 (139 s) 147 (138 s)

32 (900 s) <20 (860 s)

7

MA-N/A/Cal 117

ca. 35

None

8

"/B/"

35 (128 s)

None

9

"/C/"

35 (138 s)

None

10

PE-Cot/A/Cal 117

ca. 60

ca. 40

11

"/B/"

177 (108 s)

326 (1808 s)

12

"/C/"

117 (118 s)

22 (370 s)

13

Cot/A/Cal 117

66 (138 s)

106 (958 s)

14

"/B/"

90 (128 s)

32 (1138 s)

15

"/C/"

70 (125 s)

<10 (640 s)

16

Lt PP/A/Cal 117

109 (199 s) 151 (148 s)

378 (670 s) 242 (478 s)

17

"/B/"

130 (138 s)

188 (668 s)

18

"/C/"

150 (128 s)

744 (648 s)

19

Lt PP/A/FR foam

235 (118 s)

272 (538 s)

20

"/B/"

96 (138 s)

229 (598 s)

21

"/C/"

136 (128 s)

326 (1048 s)

22

Hvy PP/A/Cal 117

175 (128 s)

290 (598 s)

23

"/BB/"

82 (138 s)

57 (1438 s)

24

"/C/"

128 (138 s)

473 (1038 s)

25

Hvy PP/A/FR foam

112 (108 s) 165 (138 s)

419 (828 s) 108 (1169 s)

26

"/BB/"

98 (138 s) 92 (120 s)

35 (1088 s) 23 (4900 s)

27

"/C/"

144 (138 s)

72 (1318 s)

1 - Time began 60 seconds before ignition of the burner to provide a baseline. Thus, the 80 second exposure ended at 140 seconds. 2 - The peak in number 13 was possibly enhanced by failure of the seat cushion zipper.

Upholstered Item Design Engineering

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An interliner which breaks open or which does not have sound bonding at the edges and seams (because of use of sewing threads with low heat resistance) can readily let the padding become involved at an early stage and lose its protective value. The tendency to break open can be examined only in full-scale tests because the fabric tensions may differ between actual furniture and mock-ups. Interliners seemed to reduce flame spread, but differences between flame spread behavior due to various interliner materials were found to be minor in two early studies.[144][465] In another study, 10 or 40 g wood cribs were ignited on large mock-ups of ordinary polyurethane covered with a 60/40 wool/viscose fabric.[481] Three interliners, a FR polyurethane, a modified neoprene, and a Novoloid felt, greatly extended times to certain temperature and pyrolysis product levels in the room, with only minor differences between these interliners. Interliners with open weaves may help with cigarette ignition resistance but permit pyrolysis gases from the padding to enter the burning process.[254] Molten thermoplastic fabrics can penetrate porous interliners resulting in flames below the interliners.[378] Thermoplastic interliners were found ineffective in Cone Calorimeter tests.[461] The use of a 68 g m-2 aramid non-woven fabric extended ignition time in the Cone Calorimeter by about 10%, reduced the peak HRR by about 15%, the 180 s average HRR by about 70%, and the smoke obscuration rate by about 20%.[379][460] In the CBUF study with a 30 kW ignition source, this type interliner did not perform as well as glass fiber-based interliners.[131] One paper describes the OSU calorimeter results obtained with composites of nylon, polypropylene, and cotton fabrics over TB 117 and TB 133 (melamine treated) polyurethane, with and without various interliners.[481] The author emphasized that generalizations about such composites should not be made, but each system needs to be tested. Interliners generally improved the performance of composites containing TB 117 but not TB 133 foams. But for thermoplastic fabrics used with a glass cloth interliner, the HRR at low irradiance was the same for both foams. This is explained by the collection on the glass cloth of the molten fabric material which then burned; type of foam did not affect the results. In a heavy cotton fabric/interliner/melamine foam composite, the flames almost extinguished but then re-ignition occurred, presumably because of depletion of the melamine. Cotton and polyester batting interliners acted like wicks for thermoplastic outer fabrics, and increased heat release. A Finnish study ranked interliners, from worst to best: FR polyurethane, pre-oxidized carbon fabric, and FR cotton fabrics; FR treated wool felt; glass fabric.[381] Plots of heat and smoke release rate and CO

270

Fire Behavior of Upholstered Furniture and Mattresses

concentration for these interliners in a composite with a FR polyester fabric and polyurethane foam are given in the paper. Obviously, the weight of the interliner, and the flammability of the cover fabric would affect such rankings. Interliners were found necessary with larger ignition sources even for certain FR cover fabrics. Welt Cord and Sewing Thread. The materials used in the construction of the welt cord can have an impact on the flaming fire behavior. It is imperative that heat resistant, for example, aramid or glass sewing thread, be used in all cases where the cover fabrics or interliners are expected to protect the padding. Ordinary and FR cotton thread char and thermoplastic threads soften and melt, causing them to lose strength and to open up the seams. Frame Materials. Frame material obviously has no effect on the ignitability or the early stages of the fire. It can have a substantial effect on the peak HRR, both by heat release from the frame or by the manner in which it collapses. In a series of chair burns where frame material was varied, with all other construction features kept constant it was found that the analysis is simplified if the HRR values are normalized by the specimen mass.[129] On that basis, it is seen that the rigid polyurethane foam frame chair shows a per-unit-mass burning rate about half that of the wood frame unit, while the polypropylene frame chair burning rate is about double. Tentatively, the following explanation is offered, although it is understood that this is on the basis of these very limited tests. The wood frames fail when the frame connections give way. These connections are normally not designed to be fire resistive and fail early in the fire. When the frame starts falling apart, large quantities of fresh padding material are rapidly exposed to the fire. On the other hand, the polyurethane foam frame is a rigid, charring, monolithic assembly. It does eventually burn through and fail, but the process takes longer. The polypropylene frame, by contrast, is a thermoplastic unit, melting and collapsing early in the fire. In the particular case, the polypropylene frame was very lightweight, so that while the perunit-mass burning rate was much greater, the actual burning rate of the chair was very similar to that of the heavier wood frame chair. The behavior of furniture frames at elevated temperatures was studied in detail.[482] The strengths, deflections, and failure times of plastic and wooden beams, joints, and bends at elevated temperatures were measured. A computer code was written to calculate the stresses and strains inside the wood, the changes in strength, and the failure time of loaded wooden beams and bends exposed to high temperatures. It was again noted

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271

that the areas where fasteners held furniture together often failed early during fires, especially those in thermoplastic frames. Furniture Configuration. Factors for adjusting for furniture style or configuration when estimating full-scale behavior from Cone Calorimeter HRR values are discussed in Ch. 2 and 7. Also, as stated earlier, Grand mentioned several style factors as shown in Table 6-6.[253] Observations suggest that flame spread over curved and convoluted surfaces can be slower initially but may be appreciably accelerated when larger, radiationdriven flames come to dominate. Peak HRR per unit mass was found to increase when simulated furniture geometry was changed from a single cushion to two, three, and four sides of a cube, with ignition in the enclosed space.[272] When cushion thickness was varied, it was found that the peak HRR was not quite proportional to specimen mass, but was somewhat higher, per unit mass, for thinner cushions. A review of the results of hundreds of TB 133 chair tests at BHFTI found that narrow furniture had higher HRRs than wider furniture; fully upholstered arm higher heat release than open arm chairs and chairs with gaps between back and seat; and plastic structural parts often caused pool fires and high HRR.[479] Similarly, armchairs with upholstered arms produced considerably higher HRR than armless mock-ups containing the same fabric/padding composites.[140] An open space between the seat and the back or sides was found to provide more ventilation and also permits flames to reach the back or sides.[253][479] On the other hand, it provides a less severe fire enclosure, as does absence of arms. Some items, such as stacking chairs, contain too little fuel to exceed the pass-fail criteria in California TB 133, but can still cause a conflagration when many chairs are stacked for storage, or if they are placed closely together. CBUF explored the effect of the thickness of CMHR foam covered with FR polyester fabric, and of cotton covered ordinary polyurethane foam, on the HRR/time relationship.[483] The time of significant HRR increased with thickness but there was no consistent effect on peak values. For the polyester covered CMHR, the time intervals between HRR peaks due to fabric and foam became shorter as foam thickness decreased; at 30 mm thickness, there was only one relatively high peak. The results were used for thickness scaling in the models. To investigate the style factor effect, CBUF tested 14 chairs, 2 sofas, and 2 mattresses, with HR polyurethane foam covered by FR cotton or FR polyester fabric, in the furniture calorimeter.[131][149] They found that

272

Fire Behavior of Upholstered Furniture and Mattresses

use of armrests almost doubled the peak HRR and the peak occurred about two minutes earlier. Similarly, the peak HRR of a fully upholstered armchair, with the cushion supported by webbing, was 800 kW as compared to about half that much for the same materials with the cushions resting on wooden panels. Other important effects were those of size of furniture and of the internal cavity, as well as the mass, for example, fully upholstered chairs vs lightly upholstered metal office chairs. In this study, differences in wooden frame style, tufting, and minor differences in back height had little effect on the results. Seemingly minor construction factors can make a difference. Mock-ups made up from loose cushions as in the TB 133 test were found to form fire tunnels at the juncture of the side, back, and seat cushions; results were different when the back cushion was on top of the seat cushion, rather than on the decking.[378] Chair skirts (reinforced fabrics extending below the seat cushions) were found to burn easily and with considerable flames.[464] Problems were also identified with polyester batting, especially when it was tufted or channelized by seams. There is some evidence to suggest that the currently-fashionable style of fabrics being covered loosely over padding is deleterious to good fire performance. The data on the effects of button tufting are scant and no conclusions can be drawn on this time. Differences in room size had no effect on heat release unless the fires exceeded 600 kW, as discussed earlier.[139] Similarly, Japanese workers found that mass burning rates for an upholstered chair were similar when the chairs were located in the center, along a wall, or in a corner.[153] Fuel Load and Specimen Mass. Very rough estimates of fire hazard potential are sometimes based on fuel mass alone. Figure 6-6 shows chair and mattress data from Refs. 147, 477, and 480. It is seen that any correlation between peak HRR and fuel mass is sometimes poor. Total fuel content can be used as one measure for estimating duration of a fire; however, the active hazard to occupants is related to how big the fire gets, at what rate it grows, as well as how long it lasts. If all the other factors are accounted for, a limited proportionality of peak HRR to total combustible specimen mass is seen when fabric, padding, frame type, and style of design were all fixed and only size and total mass were varied.[129] A similar relationship could also be seen in the case of data from mock-ups.[95]

Upholstered Item Design Engineering

273

Figure 6-6. Comparison of fuel load and peak HRR for various upholstered items.

After flashover, the rate of burning is generally governed by the available ventilation, but in large, well-ventilated rooms, it can be controlled by the fuel surface area.[614] The primary objective of this thesis was to illustrate the use of fire load data including the exposed area of the items comprising the load. At first, simple wooden objects were investigated, and the HRR was found to be a function of the surface exposed to the fire, while the duration of the fire was related to the thickness of the object. Time/HRR graphs are shown for a variety of furnishings, including a bed and an upholstered chair. A survey methodology for room fire loads was established and prediction of HRR was developed. Moisture Content. Moisture content can affect test results in some cases and this must be considered when using test results in engineering design. Many synthetic polymer materials are not hydroscopic. The amount of moisture held by such a specimen will normally not exceed the amount present in the air and the effects of the moisture on flame spread or heat release can be ignored. Cellulosic materials (cotton, rayon, wood products, etc.) and wool can, however, absorb large amounts of moisture.

274

Fire Behavior of Upholstered Furniture and Mattresses

Benisek exposed bone dry and 65% RH conditioned mock-ups to cigarettes, methenamine pills, and matches. [322] Pill (burning time 90 to 120 s) and cigarette (burning time about 20 min) ignitions were not affected by the moisture content of the substrates, but matches ignited some dry cellulosic fabric substrates but not the corresponding conditioned ones. This may indicate that longer burning time may make results less sensitive to conditioning, because the substrate may have time to dry out. Most fire tests prescribe conditioning temperatures of around 20–24°C and relative humidity (RH) of 50–65%. This may be very different from actual use conditions. Data are available on the moisture sorption properties of wood,[267][484][485] their effect on flame spread,[486] and on HRR.[487] It was found that, for fiber-board, changing specimen conditioning RH from 0 to 100% changed the moisture content from l% to 25% and the flame spread rate was cut roughly in half. This was attributed to the increase in thermal inertia by about 2½ times. A more theoretical study[488] considered also the effect of the vaporization of water as a heat loss term in the flame spread equation. For the HRR of solid wood, Chamberlain[487] concluded that each 10% rise in RH decreased the HRR by about 4%. He also tabulated data on the effect on increasing ignition time and time to peak HRR. Land also found a substantial effect of moisture on flame spread rates, flame heights, and smoke development for mattresses.[110] The mass loss rate was reduced to half for an RH of 92%, compared to 35% RH. Hägglund[151] conducted tests on chairs at 20 and 60% RH. For thermoplastic fabrics and polyurethane foams, no effect was seen. In the case of cellulosic fabrics and padding, however, an effect was observed. The process of fire development took substantially longer at the higher RH; the peak mass loss rates were not affected, however. The disagreement between these findings and those of Land may be attributed to the specific RH levels used: Land’s upper value of 92% was much higher than Hägglund’s 60%. This is plausible since cellulose sorption curves are roughly linear in the range of 20–80% RH, but increase steeply past about 80% RH. Combined Effects. Upholstered furniture. Starting in the early 1980s, upholstered items were increasingly tested in full-scale (room or furniture calorimeter) as well as bench-scale tests. In many of these investigations, the objective was to find fabric/padding composites which would conform to certain regulations and the components were not varied systematically. Palmer et al. surveyed the fire behavior of a wide variety of typical U.K. furniture items.[489] Chapter 5 describes studies in which results of two or more tests were compared.

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275

As alluded to earlier, actual chairs, unlike the experimental chairs and mock-ups considered here, usually incorporate a variety of padding materials in one chair; the back and especially the sides are differently padded than the seat, and while the seat usually rests on a variety of padded, strong supports, the backs and sides are again less heavily constructed and their outsides and insides contain different materials. There are some indications that such a mixed construction type shows peak HRR values close to that of the worst performing element.[135] CBUF provided a list of furniture items showing limited burning, under the ignition conditions explored in that study, a 30 kW gas burner application for 120 s (Table 6-12).[137] The items of Series 1 (designated by “1:” in the first column) represent typical European commercial constructions; those in the other series, items varying primarily in fabric/foam selection. All items were tested in the furniture calorimeter and many also in room fire tests. In the top part of the table (furniture calorimeter HRR under 100 kW) most cover fabrics were either wool or FR cotton, and most padding HR or CMHR polyurethane. One mattress covered with 100% polyester over CMHR foam is in this group, as well as a divan bed with a 75/25 polyester/cotton over various natural fiber materials. The lower part lists items with peak HRR values of 150~360 kW. Most fabrics were FR cotton, and foams HR polyurethane. Finding a mattress with ordinary polyurethane and a polyester cover in this group is surprising. One could assume that the fact that the burner does not have holes on the bottom and is suspended 25 mm above the flat surface may have some effect on this result. Figure 4-3 shows the heat flux distribution caused by the burner on seat and back seat surfaces. However, the table indicates that there are numerous possibilities to produce relatively safe furniture items. CBUF also recommends use of non-melting frames, and against use of polypropylene (olefin) fabrics, as did Palmer.[489] Tables 2-3 and 2-4 shows the HRR obtained in the CBUF room for the commercial furniture of Series 1 and the furniture with systematically varied materials of Series 2. Furniture and Cone Calorimeter tests provided similar rankings. In general, it can be seen that simple rank-ordering of performance by material type may not be productive: a predictive model is needed if one wants to predict the full-scale performance without running full-scale tests. Nevertheless, the poor performance of the acrylic pile fabrics and FR polyester as well as leather covered chairs is in sharp contrast to the wool covered items. The acrylic covered items also generally produced some of the highest smoke, CO, HCN, and HCl peaks. For flaming fires (with the large ignition source used by CBUF) there seems to

276

Fire Behavior of Upholstered Furniture and Mattresses

Table 6-12. Composites Showing Limited Burning in CBUF Full-scale Tests Item

Type

Peak HRR (kW)

Padding

1:26

10

1:25

divan bed mattress

Various fibrous materials Impregnated foam

5:7

chair

22

1:24 3:18

mattress mattress

29 40

2:13

chair

49

1:18

39

2:16 2:15

office chair chair chair

58 71

Full depth impregnated urethane foam To meet Cal. TB 133* CMHR foam HR urethane foam

4:4 4:5

2 seat sofa chair

82 98

CMHR foam CMHR foam

3:16

chair

167

HR urethane foam

2:5 3:13

chair chair

201 226

HR urethane foam HR urethane foam

3:4

chair

251

HR urethane foam

3:6

chair

262

HR urethane foam

3:17

mattress

263

HR urethane foam

3:8

chair

310

HR urethane foam

3:9

chair

313

HR urethane foam

1:23 3:3

mattress chair

330 361

Polyether foam HR urethane foam

16

To meet Cal. TB 133* CMHR foam HR urethane foam

Interliner

Fabric

75% polyester 25% viscose FR vinyl reinforced sheet Glass fiber 100% cotton FR treated 100% polyester 100% cotton FR treated 100% wool Fr treated 100% wool tweed Glass fiber 100% cotton Proprietary 100% wool FR product 100% wool FR vinyl coated cover 100% FR polyester 100% wool 100% FR polyester 100% cotton FR treated 100% cotton FR treated 100% cotton FR treated 100% cotton FR treated 100% cotton FR treated 100% polyester 100% cotton FR treated

* This chair is designed to meet Californian Standard TB 133.

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277

have been no beneficial effect of FR treatment of wool. Among mattresses, innerspring constructions had much lower HRR than solid foam constructions. Peak HRR, smoke, and toxic gas data obtained during the CBUF program[7] on five upholstered chairs, with the room ventilation conditions varied, were analyzed at FRS.[597] Two chairs designed for public occupancy (contract chairs), one with 100% wool fabric, the other with FR vinyl fabric over CMHR PU, generally performed considerably better than three chairs designed for residential use, FR cotton over HR PU, FR polyester over HR PU, and acrylic pile with a FR cotton base fabric, polyester batting interliner, and CMHR PU. Peak HRR, smoke, and concentrations of nine gases and minimum oxygen levels, each for 12.5 and 100% door openings, are tabulated. The domestic chairs showed much higher peak HRR values than the contract chairs with the door open. With the door opening reduced to 12.5%, the peak HRR’s were reduced by 45 to 78% for the residential chairs while the contract chairs hardly burned. For the burning chairs, the time to peak HRR was not significantly affected. The previously discussed joint study by the California Bureau of Home Furnishing and NIST, comparing results on ten fabric/foam composites obtained in the TB 133 and ASTM rooms, and the furniture and Cone Calorimeters has been discussed in Chs. 2 and 5.[35][36] The lowest HRR values in the Cone Calorimeter, the ASTM room, and the furniture calorimeter were obtained with three composites all containing a fiberglass interliner and TB 117 foam: one covered with wool, another with nylon, and still another with polyolefin fabric. Two borderline composites produced low results in the room during one test but somewhat higher results during duplicate testing: nylon/fiberglass interliner/TB 117 foam, and PVC/TB 117 foam. Considerably higher results were obtained, in order of ascending HRR, for: wool/TB 117 foam, nylon/melamine foam, polyolefin/TB 117 foam, and nylon/TB 117 foam (no interliner). An important test series compared results for full scale settees, with additional furniture in the room, with those of chairs in a furniture calorimeter, in a TB 133 room, in a room corridor test, and in the Cone Calorimeter at various irradiance levels.[376] Eight fabrics were tested in composites with three foam types, as well as non-foam paddings; interliners were used in some cases. Several furniture geometries were explored. In summary, the average combustion efficiency of the furniture items tested is given as about 62%. The effect of fabric/padding interaction is illustrated by comparing peak heat, smoke, and CO release rates of the fabrics over inert padding and those of fabric over foam. Ranking differences were

278

Fire Behavior of Upholstered Furniture and Mattresses

observed in the different tests. The authors recommended that melting fabrics be used with melting foams, and char forming fabrics with char forming foams; and that penetration of chair backs by the flames which enhances fire development be avoided by proper construction. The effect of fabric and padding materials on the time at which HRR starts to increase and on time of peak HRR was investigated.[615] The ignition source was a gas burner, 35 kW, held to the chair for 1 minute. For a cotton fabric/latex padding chair, the HRR increased almost immediately and reached a peak of about 1700 kW. The comparitive, approximate results for peak HRR for the other chairs were: FR cotton/FR PU, 700 kW at 400s; cotton/CMFR PU 1000 kW at 450s; FR cotton/HR PU; 1100 kW at 900s; FR cotton/CMHR PU 1000 kW at 1200s. Ames and Rogers tested sixteen composites in duplicate in mockup and real chairs in furniture calorimeters and the same composites in the Cone Calorimeter.[140] The following was found: • There was little relationship between the ignitability of the material composites and their peak HRR. • The relationship between Cone Calorimeter and full scale peak HRR was fair. • In many replicate tests, furniture calorimeter peak HRR and times to peak HRR varied greatly; they were generally somewhat more reproducible in the Cone Calorimeter tests. • Real armchairs produced considerably higher peak HRR than the mock-up chairs. • Very roughly, the composites ranked as follows, based on a combination of full scale and Cone Calorimeter results, from lowest to highest HRR: (A) For composites containing interliners –

Wool-FR viscose/Ferex® interliner/HR polyurethane.

–

Cotton-viscose/cotton batting interliner polyurethane.

–

Wool-FR viscose/FR cotton interliner/HR polyurethane.

Upholstered Item Design Engineering –

Modacrylic/FR cotton interliner/HR polyurethane.

–

Wool-FR viscose/HR polyurethane composite.

279

(B) For composites containing polyester batting padding, without polyurethane –

PVC/polyurethane and FR PVC/FR cotton interliner/HR polyurethane.

–

Viscose velour/polyurethane (most of these rankings cannot be readily explained).

–

Nylon-FR viscose/HR polyurethane composite (which had excellent BS 5862 ignition resistance).

–

Viscose and cotton/viscose/polyester batting/HR polyurethane; and worst, acrylic velour/HR polyurethane.

Eighteen chairs containing standard, high resilience, and melamine modified polyurethane foams, covered with various fabrics and varying in geometry were burned in the RAPRA room/corridor arrangement.[51] The following was found: • Chair design, cover fabric, and foam type all affected the ignitability and burning behavior. • Used chairs appeared to behave similar to new chairs. • Proper selection of fabric/foam composites (in this case, a FR cotton fabric with a CM foam) passed the cigarette and crib 7 flame ignition tests, while none of the other composites reached this level. • Proper selection of furniture parameters increased the times to the start of rapid burning from 3 to about 21 min, and somewhat decreased smoke density and release rate, as well as the HRR by about 30%. Such delays in fire development together with smoke detectors can greatly reduce the fire hazard.

280

Fire Behavior of Upholstered Furniture and Mattresses

In a previously discussed study that generally agreed with findings by other authors, ten cover fabrics were tested over a TB 117 and a melamine foam, with and without a thin aramid interliner.[378] The melamine foam extended ignition time by 20%; it reduced peak HRR by about 16%, extended the total burn time but had little effect on the 180 s average HRR. It increased the smoke levels by about 12% without the interliner, and decreased it by 36% with the interliner. With the exception of the smoke results, the effects of the melamine were made negligible by the interliner. The lowest HRR was found with wool, FR polyester, and modacrylic fabrics; the HRR of blend fabrics was close to that of the more flammable fiber fabrics; non-FR polyester generated the most heat per weight; and lighter fabrics caused higher peak HRR than heavier fabrics. Peak and total heat release, heat flux, temperature, and smoke, CO and CO2 concentrations in room fire tests at the Technical Research Center of Finland for a number of fabric/interliner/padding composites are given in Ref. 381. The highest HRR, 550 kW, was obtained with a polyester/cotton fabric, and polyurethane foam interliner and padding. Composites containing FR polyurethane interliner and padding generally resulted in negligible HRRs; however, they produced relatively high smoke release rates. In an investigation of effects of various ignition conditions, an FR treated chair (CMHR foam, polyester cushion wrap, and acrylic/cotton fabric with FR back coating produced about half the HRR, total HR, and total smoke than a similar chair with ordinary polyurethane foam and untreated acrylic/viscose fabric.[131] Leather over HR urethane foam performed poorly while CMHR foam seemed to reduce the peak HRR and the time at which it occurred. Numerous fabrics over TB 117 and several more FR, proprietary foam composites were tested in the TB 117 mini-mock-up configuration, with foam cubes as the ignition source.[490][491] Differences in ignitability, burn time, weight and volume loss was found for the various foams. Thermoplastic fabrics produced worse results than the highly FR foams by themselves; in this case, a nylon fabric was better than polyester, with a polypropylene fabric worst. The Society of the Plastics Industry, Inc. (SPI) Flexible Foam Combustibility Committee explored the possibility of defining combustion modified CM) as applied to polyurethane foam.[372][373][492] Foams varying from TB 117 foam to melamine modified, HR polyurethane combined with polyolefin, nylon, cotton, and wool/nylon fabrics were tested in the OSU Calorimeter in four laboratories. The peak HRR, total heat at each minute up to 6, self propagating flux range (the irradiance level at which at least

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281

80% of the specimen surface was consumed), and the slope E, (the ratio of the peak HRR and the time to reach it) were measured. It appeared that the foams could be categorized by three of the measured parameters: self propagating flux range, peak HRR, and heat release at 180 s under 17.5 kW m-2 irradiance. There were considerable inter-laboratory variations in the results. The wool/nylon fabric again performed best, especially with the CMHR and melamine foams. In fully developed fires, the polyolefin and nylon fabrics performed similarly but with a small ignition source, the nylon performed better. The cotton fabric was similar to these two thermoplastics at low heat flux but at high heat flux formed a char which provided some protection to the foam. The heavier foam and the HR foam performed slightly better than the lighter one, and the various CMHR foams performed similarly. Ames et al. used the FRS furniture calorimeter on mock-ups and on chairs.[126][140] The fabrics were cotton/rayon, PVC, acrylic, and polypropylene, and there were several types of foams. The fabrics ranked, from best to worst, cotton, acrylic, PVC, and polypropylene; the foams, TB 133, CMHR, HR, and TB 117 type. Even chairs made from CMHR (UK type) reached peak rates of heat release of over 1 MW. The authors state that ignition is affected by fabric and foam to about the same extent while postignition behavior is mainly affected by the fabric; this is not in accordance with other studies. The correlation using the mass factor as described in Ref. 121 was rather poor in this study, and both the mass and area adjustment factors were larger than those found previously. A small test series of six chairs differing somewhat in geometry was also conducted in the furniture calorimeter, using BS 5852 crib 7 as ignition source.[493] It showed remarkably superior behavior of a chair combining cotton print fabric over polyester batting-CM foam in the seat and polyester batting in the back. The actual ignition occurred after about 20+ min, and heat, smoke, and CO releases were low. However, a somewhat differently constructed chair covered with polypropylene/polyester tapestry fabric and the same padding arrangement exhibited much faster burning and higher releases. Sundström[494][495] performed full-scale furniture calorimeter burns of upholstered furniture items combining nine fabrics (acrylic, cotton, wool and wool blends, and PVA/PVC) and polyurethane foams of varying fire retardancy, as well as latex. Two items included neoprene interliners. Peak HRR varied from 30 to 1200 kW (the ranges in replicate tests went as high as 560 kW), total heat released from 45 to 630 MJ. The lowest values were

282

Fire Behavior of Upholstered Furniture and Mattresses

obtained with a wool blend, a 10 mm neoprene interliner, and HR polyurethane foam; the highest HRR with ordinary, low density polyurethane covered with acrylic velour and cotton. Smoke and CO data were also presented. In some of the older studies, only peak heat release values and, in some cases, also total heat release values, were obtained. In Sweden and Finland, upholstered chairs[132][146][151][152] and beds[270] were so tested. At the Science University of Tokyo, a series of upholstered chairs were burned.[117] Finally, in the United States a series of chair tests was conducted.[496] In other, earlier full-scale work, only semi-quantitative observations were reported[497][498] which tended, however, to corroborate bench-scale findings of relatively fire safe performance. In one of the furniture calorimeter tests, a steel framework was used and the combustibles consisted solely of normal size cushions.[272] Five arrangements were used: a single seat cushion; seat and back; seat, back and one arm; seat, back and two arms (chair mock-up); and six cushions simulating a love seat (two seat, two back, both arms) (Fig. 6-7). Fabrics were cotton and olefin, each of two weights, padding ordinary and California TB 117 polyurethane, and neoprene. The ignition source was a l50 g methenamine pill, except for the heavy cotton fabric, which required a paper ignition source. The results are shown in Table 6-13. The following was found: • Fabrics: The heavy cotton fabric mock-up had the lowest heat release and peak HRR; the light cotton fabric and the heavy polyolefin fabrics were similar; the light olefin fabric mock-up developed more heat, much faster, than the others. Similar rankings were obtained for flame spread rate and smoke and gas production. • Foams: neoprene was superior on all counts; combined with it, the heavy cotton fabric flames selfextinguished but the composite continued smoldering. In these tests with a small ignition source, the TB 117 FR foam delayed the fire growth and reduced the HRR but produced more smoke, as compared to ordinary foam. • Configuration and mass: going from one horizontal cushion to a chair configuration, (4 cushions) the peak heat release, smoke, and gas release, and flame spread rate increased roughly with fuel mass.

Left hand arm and cushion supports not shown.

Dimensions in millimeters.

Location of ignition source unless otherwise specified.

THREE CUSHIONS

FOUR CUSHIONS

TWO CUSHIONS

SIX CUSHIONS

283

Figure 6-7. Cushion mockup and frame arrangement.

SINGLE CUSHION

Upholstered Item Design Engineering

FRAME

284

Fire Behavior of Upholstered Furniture and Mattresses

Table 6-13. Predicted and Actual Peak Heat Release Rates of Various Chair Mock-ups

Test

Foam

Fabric

Com- Number Bench Actual Full bustible of scale scale peak mass cushions HRR HRR (kg) (kW/m2) (kW)

1 2

NFR PU NFR PU

lt. olefin lt. olefin

11

NFR PU

lt. olefin

3.11

3

259

1120

850

12, 27 NFR PU

lt. olefin

4.14

4

259

1460

1130

1.00 2.00

1 2

259 259

320 540

Predicted Full scale peak HRR (kW) 270 540

25

NFR PU

lt. olefin

4.06

4

259

1370

1100

13b

NFR PU

lt. olefin

2.60

4

259

1050

710

20

NFR PU hv. cotton

5.32

4

113

430

630

3

FR PU

lt. olefin

1.17

1

265

260

330

4

FR PU

lt. olefin

2.38

2

265

410

660

5, 8

FR PU

lt. olefin

3.53

3

265

790

980

9b

FR PU

lt. olefin

2.26

3

265

660

630

7, 19c

FR PU

lt. olefin

4.77

4

265

1340

1330

26c

FR PU

lt. olefin

4.74

4

265

1460

320

c

FR PU

lt. olefin

4.72

4

265

1160

1310

166

FR PU

lt. olefin

4.70

4

265

1430

1310

24

23b

FR PU

lt. olefin

2.98

4

265

930

830

6

FR PU

lt. olefin

7.02

6

265

1360

1950

14

FR PU

hv. olefin

5.84

4

304

1020

1860

21

FR PU

lt. cotton

3.62

4

137

900

520

17

FR PU

hv. cotton

5.84

4

132

530

810

15

NP

lt. olefin

20.08

4

64

120

a

10,

18

NP

lt. olefin

21.34

4

64

110

a

22

NP

hv. cotton

9.92

4

49

~0

a

29

NFR PU

none

2.52

4

1210

d

28

FR PU

none

3.02

4b

760

d

a - Prediction method not suitable for high mass, low rate of heat release constructions. b - Half thickness cushions. c - Ignition source variations. d - Prediction method not intended for bare foams.

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• Thinner cushions, as expected, burned faster. • The mock up HRRs predicted on basis of the Cone Calorimeter results and mass factors gave similar rankings as the actual results. • The flame spread along the horizontal cushion was estimated from videos taken during the fires (ignition was at the mock-up crevice), as shown in Fig. 6-8. The results are shown in Fig. 6-9. Time to 100 kW HRR correlated with a simple measure of flame spread, (burn through time for trip threads 400 mm above the seat), as well as the visual estimate of flame spread on the seat cushions. As part of a major study of the effect of flame retardants, two fullsize chair mock-ups, one containing ordinary polyurethane foam and the other fire retarded with an organic chlorinated phosphate, an organic brominated retardant, and 35% alumina trihydrate, both covered with nylon, were tested in the NIST furniture calorimeter.[157][187] The nylon/ foam composites were also tested in the Cone Calorimeter, and by the NBS Toxicity Test Method.

Figure 6-8. Fire of mock-up of four cushions.

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Fire Behavior of Upholstered Furniture and Mattresses

Figure 6-9. Flame spread over horizontal cushion in four cushion mock-up.

In the NIST furniture calorimeter, the ignition source was a 50 kW gas burner, 180 × 150 mm face dimensions, applied for 200 s to the side of the test item. The results of replicate tests of the ordinary foam showed good agreement. In this series, the FR specimen results showed negligible HRR and mass loss, but similar smoke obscuration as the non-FR chairs. When tested in the Cone Calorimeter, at two irradiance levels, the FR materials took longer to ignite, and lost a smaller fraction of their mass. Their peak HRR and heat of combustion were 35 to 40% lower, the smoke yield unchanged, and CO and HCN yields doubled, while the CO2 yield was greatly reduced. Without the fabric, approximately the same results were obtained. Because the FR mock-up hardly burned in the furniture calorimeter, these results cannot be compared to the Cone Calorimeter results. The ignitability of chairs made with an ordinary polyurethane foam, two interliners, and five commercial cover fabrics with a variety of ignition sources has been discussed in Ch. 4 and earlier in this chapter.[135] The most hazardous conditions were judged to be caused by the chair with acrylic fibers on the fabric surface, followed closely by the one with the nylon/olefin/acrylic blend combined with polyester batting. The cotton fabric/cotton batting composite and the olefin fabric were next, and the expanded vinyl fabric represented the lowest hazard in this series.

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Chairs containing ordinary TB 117, melamine, and US type CMHR (alumina hydrate filled) foams, covered with heavy polypropylene, cotton, and vinyl on cotton scrim fabrics, some also a coated glass fabric interliner, were tested in a room.[454] Again, ease of flame ignition was governed by the fabric, with the polypropylene covered chair more easily ignited and producing a higher peak HRR than the cotton chair (however, the raw cotton Haitian fabric is very prone to cigarette ignition). The vinyl chair was intermediate in this respect. Also, as expected, the melamine and CM foams produced lower HRR peaks, as did the interliner. None of the chairs produced a peak HRR exceeding 600 kW. This paper provides time/HRR plots for the chairs. In this case, the correlation between Cone Calorimeter and room test results was mixed. Mattresses and Bedding. Some results on mattresses have been discussed above; this section mostly summarizes a few other studies on mattresses and the effects of bed clothes, i.e., blankets, linens, pillow, mattress pads, etc. In general, materials behaved similarly in mattresses as in upholstered furniture but the horizontal orientation must be considered. The differences are discussed in Ch. 2, and, in more detail, in Ref. 8. Based on California TB 129 (test for public occupancies) results on 126 full scale mattresses, the effects of fabric, padding, interliners (barriers), in innerspring and other mattresses are discussed.[582] One hundred (79%) of the mattresses passed; information on their overall pass/fail performance can be found in 3.2.3, as comments to the description of the TB 129 test. About 50% of the mattresses had vinyl ticking, and 89% of these passed. Cotton ticking was used in 19%, and 63% of those passed, albeit the majority with the help of interliners. In non-innerspring mattresses, all those with CMHR PU passed, some with interliners. On the other end of the scale, all mattresses with CA 117 PU without interliner failed, while those with a interliner passed. Prison mattresses with vinyl covers and “densified” polyester batting passed, as did regular mattresses containing FR cotton batting. The materials performed generally similarly in innerspring mattresses. Fifteen mattresses exceeded 150 kW, two of them reached flashover conditions before 10 minutes. These mattresses contained nonFR PU and a low density TB 117 foam, respectively. Paul[455] discussed the performance of mattresses with laminated layers of polyester foam impregnated with a resin bonded hydrated alumina system. When fully vandalized, they burned for a longer time, compared to polyether foam, but the weight loss was only about 4–10%.

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Fire Behavior of Upholstered Furniture and Mattresses

Another set of mattress data was taken at the Centre Scientifique et Technique du Bâtiment (CSTB).[499][500] Kapok mattresses had the lowest heat release and mass loss rates, followed by FR polyurethane and ordinary polyurethane foams. Of special interest to the institutional and corrections community has been the issue of permanence of fire retardants in mattresses.[8] A significant fraction of current-day correctional mattresses use boric acid treated cotton batting as the core material. Cone Calorimeter tests were performed on as-received and leached specimens of typical institutional and prison mattresses. Leaching made no difference in HRR of ordinary, TB 117, and some other FR polyurethane and neoprene foams as well as polyester batting while it affected the boric acid treated batting samples and, surprisingly, an FR polyurethane foam sample. Two unused boric acid treated cotton batting mattresses roughly doubled in HRR when leached, to about 110 kW m-2. Such loss of boric acid also would reduce cigarette ignition resistance. Ranked by the average HRR on leached specimens, going from lowest to highest, were neoprene, some types of polyurethane foam, used FR cotton batting, new FR cotton batting, polyester batting, and other types polyurethane foam. Since bedclothes comprise the outer exposed layers, it is their properties, rather than those of the mattress, which determine the flaming behavior; bed frames may also need to be considered. Bed clothes are not customarily made in fire retarded grades, although the US Veterans Administration has used them at times. Wool and modacrylic blankets have been shown to be hard to ignite and have low flame spread, as compared to other blanket materials.[352][455][489][501] Thermoplastic blankets in the flat configuration probably have no advantage in ignition resistance over other fibers. Cellulosic blankets, especially when napped, are easily ignited and burn readily. A tightly made-up bed, as for military inspection, will spread flame much more slowly than an unmade or loosely draped bed. For realistic fire testing it is important to disturb and/or pull back the covers to permit easy flame spread; this has been recognized in the UK Crown Suppliers specifications.[48] Pillows can have a major effect on bed fires. The NBS mattress test series[162] was conducted using shredded polyurethane foam pillows. These were chosen as being both commercial and fast-burning. Figure 6-10 shows HRR results for standard size pillows, covered with polyester/cotton pillowcases and ignited at one end.[502] Much better behavior was obtained from pillows filled with down, feathers, or polyester padding or when

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covered with pillow covers of FR fabrics, in this case, coated fiberglass than with polyurethane or latex pillows with flammable covers. Since the pillow fire can serve as a major driving force for flame spread over the rest of the bedding, its behavior should be considered.

Figure 6-10. HRR’s of various pillows.

In hospital beds, decubitus (bedsore) pads are sometimes necessary. A test series has been reported.[503][504] With three sheets over the pads and with a TB 117 foam mattress under them, and ignition at the top of the bed, fire growth was lowest for the CMHR pad; intermediate for polyester fleece; and worst, for TB 117 pads. The mattresses, when ignited with a simulated waste paper basket at the side, became the primary fuel, but the pads caused the fires to rank in the above order.

290

Fire Behavior of Upholstered Furniture and Mattresses

Paul carried out a full-scale study of mattress/blanket assemblies.[455] Lower maximum room temperature and CO results were obtained with wool than acrylic blankets, and with innerspring (interior spring) than with polyurethane mattresses. FR polyurethane seemed beneficial, and while latex caused a slightly higher room temperature rise, it took a much longer time to reach this temperature. An important study on mattresses has been undertaken by the BHFTI.[260][505] The ignition source in most test series was the T-head, 17 kW, propane gas burner, placed for 180 s at 50 mm below the front lower edge and 25 mm from the side. Some mattresses were tested uncovered, some with several bed clothes combinations, and some also with box springs. The tests on 40 typical US residential and institutional mattresses indicated that the fully developed fire results were, in the first instance, affected by the mattress core materials, while the difference between conventional cover fabrics was of lesser importance unless they were highly flame resistant. In some cases, highly flame resistant cover fabrics or interliners successfully protected otherwise highly flammable cores. The importance of mattress construction, in this case innersprings covered by various foams vs solid core foam mattresses is illustrated by the following:[260] in innerspring mattresses covered with cotton ticking, neoprene performed far better than melamine foam, TB 117 foam, and ordinary polyurethane foam. The use of TB 117 as well as melamine foams did not constitute an improvement in these tests. By contrast, in solid core mattresses, melamine foam performed considerably better than TB 117 foam, while the ordinary foam mattress caused room flashover. However, the presence of box springs often did not increase the peak HRR; cotton batting covered box springs performed better than polyurethane covered ones. Visual observation indicated that flame spread was slower on the mattress/box spring combinations than when mattresses were tested alone, presumably because the box springs reduced airflow to the underside of the mattresses. Boric acid treated cotton batting used as a layer around other, more flammable materials or especially as the major core material produced remarkably good results. However, it tended to continue to smolder upon removal of the ignition source. A higher boric acid concentration is needed to prevent smoldering than for flame retardance only. Two other interliners proved to be effective in improving fire performance. The paper lists fifteen mattresses which produced less than 80 kW results (11 under 30 kW); among the materials represented in these are vinyl

Upholstered Item Design Engineering

291

cover fabrics, vinyl/glass interliners, and, either as solid cores or sometimes only as layers combined with other, more flammable layers, boric acid treated cotton batting, neoprene, and solid melamine treated polyurethane foam. However, because some combinations of components can cause antagonistic reactions, testing of prototypes seems important. Nine mattresses produced 600 kW or less peak HRR (to be used in low risk, sprinklered facilities), and probably would not lead to flashover by themselves but could ignite adjoining items. Six mattresses or mattress/ innerspring and bedding combinations were considered to be leading to flashover conditions. Bedclothes consisting of mattress pad, two 50/50 polyester/cotton sheets, a polyester fiber pillow, and two acrylic blankets tested on an inert mattress produced a heat release of more than 300 kW. In match ignition testing of six identical, cotton batting/innerspring mattresses but varying in other bedding components maximum ceiling temperatures varied by a factor of four, maximum CO concentrations by a factor of seven, and weight losses at 10 minutes after ignition from 0.4 to 4.3 kg. The lowest values were generally observed when only one single 50/50 cotton polyester sheet was used, and the highest with two such sheets, a polyester resin treated batting mattress pad covered with 50/50 cotton/polyester fabric, a polyester fiber pillow covered by cotton ticking, and two acrylic blankets. Further bedclothes tests were conducted with the T-shaped gas burner. With this more severe ignition source, the test specimens which included mattresses alone and with bed clothing, including a two sheet, pillow, and one blanket combination, produced 17 to 94 kW HRRs, ceiling temperatures of 88 to 300 oC, and at 4 feet, 141 to 273 oC. CO ranges were 255 to 1680 ppm, and the weight loss after 10 minutes, 2.4 to 5.2 lbs. Nine commercial FR mattresses, including such components as aluminized interliners, woven and vinyl covers, FR cotton batting, and FR polyurethane foams all exceeded the maximum specified room temperature of 93°C. Some of the mattresses passed some, but not necessarily all, of the other TB 129 requirements (see Ch. 3). The HRR results of early room fires with mattresses, top, bottom, and draw sheet, bedspread, and pillow, and non-combustible bed frames are discussed in Ref. 477. The worst HRR behavior occurred with PVC covers combined with latex or polyurethane padding. Dense polyurethane foams behaved worse than a foam which weighed only 18 kg m-3. This, however, is not necessarily a manifestation of a density effect, per se, since chemical foam composition has to be changed to produce foams of substantially different densities. Small amounts of fire retardant are again

292

Fire Behavior of Upholstered Furniture and Mattresses

seen to have little benefit. Very low HRR was achieved by CMHR formulations incorporating large amounts of fillers and fire retardants. Some aspects of this combined effectiveness have been studied in detail;[506] full-scale tests also qualitatively verify the bench-scale findings.[507] Studies like this again proved that a much more effective treatment than that of TB 117 type foams is needed to significantly reduce HRR, as opposed to simply improving Bunsen burner ignitability behavior. However, such foams often tend to be heavy and their physical characteristics tend to be poor. Because of the effect of bedding, for mattresses the effect of normally used cover fabric (ticking) is much less important for the HRR behavior than it is for upholstered chairs. Rapid exposing of the padding by a thermoplastic ticking is also less important in the case of mattresses.[162][352][477][499][500] In one example, the peak HRR was doubled and the time to its occurrence reduced when a cotton sheet and quilt were placed on a mattress, as compared to the bare mattress. In a UK study, three specimens each of various mattress assembly types containing four types of blankets and counterpanes (comforters), mattresses covered with water-proofed polyurethane/nylon fabrics, with either an alumina hydrate containing barrier foam glued to a polyurethane core or polyurethane foam covered with FR cotton knit fabric (Central Contract type mattresses), were tested on standard hospital bed bases or on an open wire mesh support.[455] Besides the mattress and bed base, each assembly contained three polyurethane pillows in FR cotton cases, 100% spun polyester pillowcases and sheets, and blanket and counterpane. The BS 5852 crib 7 was used in all tests. The barrier foam/FR cotton, modacrylic, or polyester blanket assemblies produced relatively low HRR, but the ordinary polyurethane mattresses and the barrier foam mattress covered with untreated cotton produced significant amounts of smoke and CO. Transportation Seating. Under the general category of transportation vehicle seats, buses, subways, inter-urban rail cars, and aircraft will be considered. The problems associated with buses and rail cars are very similar and so is materials usage. Passenger car and truck seating has not been restricted in the United States except by the horizontal flame spread test FMVSS 302 test,[67] which is very easy to pass. Aircraft seat design involves similar concerns but additional fire safety (with emphasis on smoke development) is desired while weight has to be minimized. Thus the actual materials used in aircraft seating differ substantially from those on ground vehicles; test procedures and criteria are also different.

Upholstered Item Design Engineering

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Ground Transportation. A number of programs involving fullscale fire tests or full-scale mock-ups of buses and rail cars and full-scale seat tests have been reported: a full-scale rail car mock-up;[508] urban buses[296] and subway cars;[288][289] sectional mock-ups of rail car and bus configurations;[290] and subway car seats.[509] The results ranked materials generally as expected from work with other upholstered items. Peacock and Braun tested inter-urban rail car interiors, including pairs of seats alone in the furniture calorimeter, and bench-scale specimens of seat construction.[291] The peak HRR of ordinary polyurethane foam (without fabric cover) was about 20 times that of neoprene or of a CMHR, hydrate filled foam in full-scale, and eleven times in the Cone Calorimeter. A number of fully-furnished railcar section mock-up tests were also conducted in this program. Their results cannot be directly correlated to data on seating since other variables were not kept constant. However, polyurethane foam padded armrests acted as a significant fire growth mechanism, compared to slower burning ones. A paper at a conference on UK transport fire safety made the point that for short distance rail seats, comfort can be sacrificed for FR characteristics, but in long distance seats, softer but less FR cushions are used.[292] BS 5852 crib 7 is used to test seats, mostly full thickness polyurethane foam; foam sheets over springs are also used. Solid arms on seats seem to restrict airflow and improve fire performance.[510] When the British rail wool fabrics split during the fire and expose the padding, much larger fires resulted.[381] The effect of interliners or barriers on flame ignition and fire growth has been discussed earlier, including a warning that they should not to relied upon in those transportation modes where vandalism is a problem. Specific tests have been run on bus seats.[511] In these full-scale mock-up tests a neoprene interliner was highly effective in reducing burning rates and smoke on a vinyl fabric/polyurethane foam assembly, giving a performance very similar to vinyl fabric/neoprene foam composite. When the seats were slashed, however, the improvement was only slight. Studies of land transportation vehicle seating are reviewed in Ref. 294. As could be expected, these studies generally pointed out the problems arising from replacing wood and metal with plastic materials. A particularly serious US school bus fire lead to renewed attention to their fire hazards.[297] Interior materials for this use are required to pass the horizontal flame spread test FMVSS No. 302[67] and it was assumed that the cover material in this incident passed this requirement. Typical school bus seat assemblies were submitted to a variety of bench- and full-scale

294

Fire Behavior of Upholstered Furniture and Mattresses

tests, for ignitability, flame spread, HRR, and smoke and toxic gas yields. A seat containing re-bounded polyurethane foam covered by vinyl coated polyester knit fabric (a typical US construction at that time) had a very high HRR and caused the fire to spread to other seats. It produced higher results than the same seat with a Kevlar®/Kynol® interliner, and a cover fabric certified by the Urban Metropolitan Transit Administration (UMTA) over four foams: melamine treated, CMHR, FR re-bonded polyurethane, and neoprene. Tenability was determined using Hazard I. The above mentioned vinyl/re-bounded polyurethane foam seats were the only ones which represented a temperature as well as toxicological threat to bus occupants. UMTA type vinyl fabric and melamine foam or FR re-bounded polyurethane foam also produced untenable conditions, due to temperature rise only. A test protocol was developed and is described in Ch. 3, and smoke development is discussed later. It has been demonstrated that rail car and transit bus interior mockups which met the voluntary UMTA guidelines caused flashover in 6 to 7 minutes.[290] In another test series discussed earlier, however, using a different ignition source and compartment design, a FR polyurethane conforming to the UMTA guidelines performed well, while ordinary polyurethane led to flashover.[291] In engine compartment fires of automobiles, firewall temperatures of over 400°C were observed.[512] Ignition of adjacent materials can be prevented by use of FR materials, but smoke development cannot be adequately suppressed. Good design practices, and use of materials which either do not ignite or include both flame retardants and smoke retardants and which the author claims were not yet available for this market, are recommended. As part of a study of the flammability of automotive parts, a front seat assembly was ignited with a 7 kW gas heater on one side of the seat back.[598] Flames spread over the full height of the seat back and across its width in 1½ minutes, and the flames broke through to the front of the seat after 2½ minutes. The peak HRR, about 550 kW, was reached at about 200 s. As frequently observed in fires involving PU cushions, there was burning of ablated material under the seat. Railroad Cars. Peacock and Braun tested inter-urban rail car interiors, including pairs of seats alone in the furniture calorimeter, and bench-scale specimens of seat construction.[291] The peak HRR of ordinary polyurethane foam (without fabric cover) was about 20 times that of neoprene or of a CMHR hydrate filled foam in full scale, and 11 times in

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the Cone Calorimeter. A number of fully-furnished railcar section mockup tests were also conducted in this program. Their results cannot be directly correlated to data on seating since other variables were not kept constant. However, polyurethane foam padded armrests acted as a significant fire growth mechanism, compared to slower burning ones. It has been demonstrated that rail cars and transit bus interior mockups, which met voluntary UMTA guidelines, caused flashover in 6 to 7 minutes.[290] In another test series discussed earlier, however, using a different ignition source and compartment design, a FR polyerethane conforming to the UMTA guidelines performed well, while ordinary polyurethane led to flashover.[291] For several decades, the U.S. flammability and smoke emission requirements for passenger seats, and sleeping and dining car upholstered items have been: Cushion and mattresses ASTM D 3675: Is < 25 ASTM E 662: Ds(1.5) < 100, Ds(4.0) < 175 Seat and mattresses frames ASTM E 162: Is < 35 ASTM 662: Ds(1.5) < 100, Ds(4.0) < 200 Seat upholstery, mattress ticking and covers FAR 25.853 (vertical) flame time <10 s, burn length < 152 mm ASTM E 622: Ds (4.0) coated < 250, Ds (4.0) uncoated <100 These criteria had been established before the current generation of fire test methods was developed. Thus, during the late 1900s, the Federal Railroad Administration sponsored a major program of fire safety of passenger trains at NIST.[599]-[601] Its objective was to demonstrate the practicability and effectiveness of HRR-based test methods and hazard analysis techniques when applied to passenger car safety. Peacock and Braun wrote a comprehensive report on this program.[601] Summaries of the findings and analysis thereof are given in Refs. 599 and 600. The latter reference presents examples of fire hazard calculations using CFAST. Calculated upper and lower layer heights and temperatures, and heat flux and chances for escape are given for a fire on two rail car seats, with and without a trash bag present.The history of the project is summarized and future plans are discussed in Ref. 602. The comprehensive report includes

296

Fire Behavior of Upholstered Furniture and Mattresses

discussions of recent train fires, previous train fire safety studies, of the presently enforced U.S. safety requirements for rail transit and motor vehicles, aircraft, and passenger vessels, and a comparison of exposure conditions in unwanted fires and in the new generation test methods.[601] In US passenger rail cars, wool/nylon fabrics or PVC cover fabrics, muslin interliners, and PU cushions, along with FR cotton fabrics covering the seat bottoms, are typically used in coach seats, and bedding includes wool blankets, foam pillows, and cotton sheets.[602] Cone Calorimeter results for some individual materials used in upholstered items were presented, as well as for a number of typical assemblies. Incident heat flux was 50 kW m-2; this compares to maximum radiant energy of 11 to 40 kW m-2 in the ASTM E 162, D 3675, E 662, and E 648 tests which are in use for the same materials. The lowest results, 65 kW m-2 peak heat release and SEA of 40 m2 kg-1, were obtained with a graphite filled foam. This is important since the seat foam is one of the largest combustible materials in a rail car; however, this best-performing material does not meet the presently used ASTM D 3675 requirements. The differences were explained by the smaller grid size used in the Cone Calorimeter which limited the specimen movement toward the radiant source of the material due intumescence, while in the ASTM D 3675 the larger size resulted in more expansion and consequently more rapid flaming along the sample. Three items—a foot rest cover, arm rest cover, and chloroprene seat support diaphram—had low flame spread index but had high HRR values. Many seat cushion assemblies were tested; at this high incident flux, ignition times varied only from 7 to 12 s, peak HRR values 250 to 420 kW m-2, and times to peak of 10 to 35 s. The UK standard, BS 6853, has two categories, a more severe one for trains which operate underground, sleeping cars, and unmanned trains, and one for all other vehicles.[603] Germany uses a systems approach to prevent or delay danger to passengers, crew and rescue personnel due to fire. A higher level of protection is required for trains operating in tunnels; these are considered generally at least as stringent than the U.S. requirements.[604] The International Union of Railways (UIC) Code has requirements similar to the French ones which rely mostly on material controls, using complex classification indices based on several tests.[605] Maritime Furniture Items. A US Coast Guard report[513] suggested that a proposed International Maritime Organization (IMO) test

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would have minimum impact on the materials now used in US manufactured seating materials used by the maritime industries. This was based on testing of six commonly used material composites by a modified UFAC cigarette test, and a butane flame ignition source similar to Source 1 of BS 5852. Acceptance of the IMO test procedure was recommended. The text of the preliminary IMO draft recommendation on fire test procedures for upholstered furniture is included in that report. Recently, the U. S. Coast Guard has been seeking Cone Calorimeter criteria to qualify materials, including furniture, which are currently tested in the ISO 9705 and the IMO surface flammability test. Some testing was already conducted at Southwest Research Institute in support of this activity.[616] In the UK, maritime upholstered items have to pass BS 5852 gas flame 1; many wool and PVC covered items pass.[301] Air Transportation. In the 1960s, aircraft seats generally had either latex or polyurethane foam padding and an assortment of fabrics, including nylon, modacrylic, nylon/wool/rayon, and a PVC/wool fabric. By about 1970 the latex foams were dropped in favor of polyurethane and a 90% wool/10% nylon upholstery fabric became dominant. This offered some improvement over earlier composites; nonetheless it still was evident that seats were a major potential contributor to cabin fires. Thus, a development program, organized in the late 1960s at NASA-Ames by J. A. Parker and D. Kourtides for improved aircraft materials entailed a significant amount of work on seating, much of it done by contract at the major airframe manufacturers. Early research work was reported at a conference in 1976,[514] followed by a second conference in 1978.[515] A 1978 study of ignitability by radiant heat showed wool containing fabrics to be superior to other fabrics in use at that time.[516] The early development program work on aircraft seats was completed in 1983 with the publication of a final report, summarizing tests during the latter part of the project and issuing final recommendations.[517][518] The recommended composite retains the wool/nylon cover fabric and uses ordinary polyurethane foam (which is lighter than FR foam) with an aluminized Kevlar® interliner. The behavior of certain aircraft cover fabrics used in the 1970s in mock-up tests with modest ignition sources has been discussed in Ch. 5.[346] Only FR wool passed, while the FR nylon, FR polyester, olefin, acrylic, acrylic/cotton, and cotton fabrics failed.

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Fire Behavior of Upholstered Furniture and Mattresses

Grand and Valys[519] reported on a series of full-scale mock-up tests of aircraft seats in the Southwest Research Institute (SwRI) calorimeter. The test rig comprised a seat and a back cushion placed on a metal frame. The specimen was heated with radiant panels placed parallel to the seat and to the back, giving fluxes in the range of 31–99 kW m-2; ignition was with a gas pilot. In seven tests with wool containing cover fabrics, the best results were obtained with a wool/Kermel® fabric and polyimide foam. More recently, Ames wrote a review of the state of the art on airplane seating.[520] He exposed one side of three seat mock-ups and real seats to a 1 m2, 70 kW gas panel. (This heat level was recorded in aircraft cabin fire experiments; the US standard ignition source delivers 100 kW.[66] FR wool cover fabric was used throughout. Relatively low peak HRR values were observed with standard aircraft grade HR foam, combined with an aramid, a coated glass or a FR viscose interliner; however, the interliners increased the total smoke development to varying degrees. A system using a Ferex® barrier foam over a base polyurethane foam gave the best heat release and smoke results. The real seat produced a very high peak HRR and total smoke. Reproducibility in three tests of standard aircraft grade HR polyurethane foam without interliner was poor. When airplane seats are intended to be flotation devices, and are to be of low density (down to 12.5 kg m-3), closed cell polyethylene foams are used, covered with wool/nylon or wool fabrics; FR polyester, nylon, or vinyl fabrics were used earlier.[521] The chemical and physical properties of a proprietary, melamine modified, molded foam for use in aircraft seats are described in Ref. 522. A balance between melamine content sufficient to pass the FAA test[66] and mechanical properties, especially tear resistance, was achieved. An entirely new aircraft seat design was developed by the NASA Ames Research Center.[523] It consists of a FR fabric, interliner, and spring assembly inside a heat sealed air bag. Among the advantages claimed are lighter weight than foam, durability, simple fabrication, and reduced cost. Other Items. Most experimental work has been done on regular furniture and mattresses and those upholstered items which either have a traditional wood frame or a plastic frame of similar shape and function. But there are also other kinds, for example, beanbag chairs, foam block chairbeds, stacking chairs, single-piece molded items, etc. These types of furniture are more difficult to evaluate since bench-scale flame spread and HRR testing procedures for conventional frame upholstered chairs have not

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been correlated with results on such items. However, some full-scale test data are available.[91] These included a polystyrene beanbag chair, a molded polyurethane foam block chair, a foam block chair-lounger, and molded polyurethane and polyethylene pedestal chairs. They ranged in HRR from 370 kW for the bean bag chair, to 2480 kW for the large chair-lounger. Use of bench-scale procedures for the evaluation of this type of furniture will be difficult, due to the possible geometric complexities, both in the basic design and as caused by melting and collapsing during the fire. A peak HRR of 300 kW was reported for an auditorium (folddown) seat with a steel frame, wood back and seat structural panels (8.0 kg), polyurethane foam padding (1.23 kg), and PVC fabric (2.2 kg), with a total mass of 22 kg and a combustible mass of 11.4 kg.[150] In a general review of Finnish work on furniture, Pakkala discussed fires of polypropylene seats as used in sports arenas.[524] The seats were arranged in rows or stacks and ignited with a wood crib. Fire spread was mostly due to dripped polypropylene “pool” fires. The fire of a stack of seats reached maximum HRR in 10 minutes, of a row, in about 30 minutes. A stack of six seats or a row of eight seats could cause flashover in a small room. In the U.S., ASTM has developed a standard[617] for HRR testing of stacking chairs, based on work conducted at BHFTI and Omega Point Laboratories. 6.2.3

Flame Spread

As discussed in Ch. 3, flame spread was commonly used to characterize fire growth until HRR was found to be more appropriate. Below we discuss a few flame spread results on upholstered furniture mock-ups. It must be emphasized that measuring flame spread on upholstered items is difficult, because of simultaneous burning on seat, sides, and backs, through the cushions into the frame, and to the outside of furniture. Optimally, measuring flame spread in such situations would require recording of the temperature rise in a number of thermocouples placed strategically throughout the furniture items. Obviously, measuring the heat release characteristics is considerably easier and more meaningful. In a previously discussed study, flame spread measurements across the seat were taken using full-sized cushions to form seat, sides, and back, mounted in a steel frame.[272] Small flame ignition sources were used in the crevice to ignite composites of olefin and cellulosic fabrics, each in light

300

Fire Behavior of Upholstered Furniture and Mattresses

and heavy weights, and ordinary and TB 117 type polyurethane, and neoprene foam padding. Typical flame spread is illustrated in Fig. 6-8; it shows the grid used to estimate flame spread on the horizontal cushion and the cotton trip thread suspended over the mock-up. The horizontal flame spread results, measured by counting the squares marked on the seat burning at certain times from ignition, are shown in Fig. 6-9. These visual estimates on the horizontal cushion of chair mockups and other flame spread estimates (the time at which the other cushions got fully involved, the times at which the trip threads above the mock-ups were burned through, and the time at which the HRR reached 100 kW) all ranked the materials as follows, from best to worst: • Heavy cotton fabric covered assemblies • FR polyurethane without fabric • Light cotton fabric covered assemblies • Polyolefin fabric covered assemblies • Ordinary polyurethane foam without fabric Again, we emphasize that these rankings were very similar to those obtained by measuring time to 100 kW HRR, and the times at which the trip threads burned through. This is encouraging because the visual estimates are tedious, and do not represent flame spread to the sides and back, while the HRR and trip thread time results represent the total mock-up burning. This study thus indicates that flame spread over furniture does not have to be measured directly. Visual observations of the horizontal (seat) cushions indicated major differences between the olefin and the cellulosic fabrics. The cellulosics charred ahead of the flaming area. In a somewhat periodic progression of flaming, the olefin fabrics melted and peeled back from the fire, and thus formed melt beads which burned ahead of the foam fire front, causing more foam ignition. Since the ignition source was towards the back of the seat area, the chair back became rapidly exposed to a high fire plume. Time of ignition and flame spread on this surface, bathed with flame, was difficult to identify. The burning side (arm) cushions was generally in the form of un-piloted ignition, in distinct steps on one arm and very soon thereafter over the whole surface on the other arm, rather than a flame progression. Neoprene foam padding generally did not burn once its fabric had burned away, although it continued smoldering in crevices. The FR polyurethane mock-ups showed two flame fronts most distinctly: a faster moving one associated with the fabric burning, and one behind it for the foam itself.

Upholstered Item Design Engineering

301

Mock-up geometry affected the flame results, just as it affects the HRR.Increasing the number of cushions from one (single seat) to two (seat and back) to three (one arm) to four (two arms) increased the overall flame involvement rate, so that for the last case, full seat involvement of the first ignited cushion was about 40% faster than in the first. Expanding the mockup to six cushions, to simulate a love seat, brought about a substantial spread rate decrease of the first ignited cushion, so that times were more similar to the three-cushion case. This can be understood as a reduction in the radiative feedback of the more open geometry during the early burning stages. The second seat cushion showed the sudden peeling over substantial areas of the olefin fabric generally observed on vertical surfaces, with subsequent flaming ignition simultaneously over the whole surface. On the other hand, varying cushion thickness from 50 mm to 100 mm had no effect on flame spread rates, although it did somewhat affect the HRR. Paul compared horizontal and vertical flame spread rates in half scale mock-up chairs over a variety of fabric/padding composites.[230] In most cases, the vertical test produced flame spread rates of 10 mm s-1 over FR polyester foam and cotton padding (except for seats covered by a proprietary FR viscose or a wool fabric). Horizontal flame spread in these cases was also relatively low. There was no difference in horizontal flame spread when foam thickness was reduced from 100 to 75 mm, but it was cut in half when the foam the thickness was 25 mm. Burn length and burn time on various foams did not rank the foams in the same manner. In the previously discussed test arrangement in which horizontal specimens were exposed to irradiance and pilot ignited, several observations could be made:[106] (1) at zero irradiance, spread rates ranged from zero to 3.7 mm s-1; (2) at 2.5 kW m-2 irradiance, spread rates were typically about doubled, except for those cases which fell below 1.0 mm s-1 at zero flux; (3) polyurethane foam without fabric showed high flame spread rates, exceeded only by a light olefin fabric/polyurethane composite; and (4) general ranking followed similar trends to the results from mock-up tests. In two other studies, time to full involvement of chairs varied by only about five minutes for a large variety of fabrics. Exceptions were PVC and polyurethane coated FR cotton and FR wool/viscose fabrics which burned slowly.[144][464] Horizontal furniture composites were ignited on one end with kerosene and the flame travel was timed.[525] Initial tests with no padding showed approximately the inverse dependence of flame spread rate on specimen mass-per-unit-area predicted from theory.[107] The variations for fabrics over polyurethane foam were surprisingly small, covering a range

302

Fire Behavior of Upholstered Furniture and Mattresses

of 0.7 to 1.1 mm s-1, with cotton fabrics on the lower end, and acetate fabrics tending towards the higher end. Cellulosic fabrics tested over cotton batting showed flame-spread rates about one-half those over polyurethane foams. Increasing specimen width by a factor of three increased the flame spread rate by about 30%. Increasing specimen thickness six-fold resulted in a barely noticeable further flame spread increase.

6.3.0

SMOKE

Below, a review of studies pertinent towards the design of smokereduced upholstered items is given. Due to the considerations discussed in Ch. 3, however, it should be realized that the guidance is largely only qualitative. In general, due to the significant mass differences, smoke results tend to be dominated largely by the padding and eventually by the frame, and not by the cover fabric. Very roughly, the following rankings were observed, from best to worst (these rankings are based mostly on behavior in fires, not in smoke chamber tests): Fabrics wool; FR cotton; aramid cellulosics thermoplastics vinyl Paddings wool batting FR cotton batting cotton and other cellulosic batting CMHR polyurethane TB 117 rated or ordinary polyurethane latex These rankings are similar but not identical to those for fire growth. The studies on which these approximations are based are described in more detail below. Again, it should be remembered that these rankings are very dependent on the ignition conditions, the ventilation conditions during the fire, whether the frame collapses, as well as the materials involved.

Upholstered Item Design Engineering

303

Tomann compared the smoke production of six composites in the Cone and the furniture calorimeter.[380] The composites included three fabrics commonly used in Finland, FR cotton, FR polyester, and wool/nylon. Ordinary polyurethane foam (25 kg m-3) and CMHR foam (35 kg m-3) were used with each fabric. Polyester batting was used in all chairs. Average smoke production rates at 25, 35, and 50 kW m-2 irradiance in the Cone Calorimeter were lowest for the wool/nylon fabric, intermediate for the FR cotton fabric, and highest for the FR polyester fabric. In the Cone Calorimeter, the CMHR foam produced more total smoke, at a lower rate, than the ordinary foam. There was no consistent effect of irradiance on ordinary vs CMHR foam. The furniture calorimeter tests produced much less smoke per unit mass; the FR cotton composite produced the lowest smoke values. The CMHR sofas released more smoke than the ordinary polyurethane sofas, and generally produced higher average specific extinction area values. The highest average specific extinction areas values were produced by the FR polyester/CMHR composites. Using the Hazard I zone fire model to estimate the escape time from 3 room, the escape time for the FR polyester covered sofas was a 75 m calculated to be two to three minutes, and for the FR cotton/CMHR foam sofa thirteen minutes. Smoke and toxic gas results obtained in room tests during the CBUF project on Series 1 market furniture are shown in Table 2-3 B.[131] (The construction variables are shown in Table 2-6 and 2-7.) Two three-seat sofas and solid polyurethane and latex foam mattresses produced the highest peak extinction coefficients, while the lowest ones were produced by an innerspring mattress, an innerspring mattress wrapped with layers of natural fibers, and an impregnated foam prison mattress covered with FR vinyl fabric. Wool and FR cotton fabric with CMHR foam produced relatively low results. Among interliners, there seemed to be little difference between aluminized, glass, and FR cotton fabrics; they all delayed smoke release.[144][481] Woolley et al. reported smoke release from mock-ups consisting of assemblies of four normal size cushions in room fires.[465] Wool and FR cotton/polyurethane composites showed similar low smoke production values, thermoplastic fabrics increased the smoke production by 50 to 200%, while a PVC covering increased it about six-fold. Substituting latex foam increased the rate by roughly an order of magnitude.

304

Fire Behavior of Upholstered Furniture and Mattresses

Typical upholstered furniture and mattress data obtained in full scale and bench scale tests are shown in Table 6-14.[95][129] Smoke production generally was again affected more by the padding materials than by the cover fabric, unlike ignitability and flame spread. Among the fabrics, wool resulted in relatively little smoke release, at a low rate. Next in order were cellulosic fabrics, thermoplastic fabrics, and, worst, PVC cover fabrics. Modacrylic fabrics produced high values, while aramid fabrics produced low ones, and acrylic/cellulosic blends seemed to be worse than allcellulosic fabrics.[144] Table 6-14. Bench and Full-Scale Peak Smoke Values Obtained With Various Chair Mock-ups Item

Padding

Fabric

Full scale peak σm [m2/kg]

Bench Scale Peak σm [m2/kg]

σm at peak HRR [m2/kg]

Average σm [m2/kg]

Upholstered Furniture F25 F21, F26 F31, F32 F24 F23 F22

NFR PU FR PU

LO LO

236 258

880 770

420 535

562 578

FR PU FR C FR C

HC LO HC

99 152 84

295 443 222

43 393 NA

82 121 15

12, 17

NFR PU

LO

422

1050

602

624

7, 19

FR PU

LO

520

NA

600

706

14

FR PU

HO

403

1360

690

610

20

NFR PU

HC

137

516

111

102

21

FR PU

LC

243

530

530

359

17

FR PU

HC

167

487

57

118

15

NP

LO

783

877

733

393

29

NFR PU

none

137

382

367

275

28

FR PU

none

296

590

455

510

Mock-up Series

σm NP LO HO LC

-

Specific extinction area Neoprene Light olefin Heavy olefin Light cotton

NFR PU FR PU FR C HC

-

Non fire retarded polyurethane foam Fire retarded polyurethane foam Fire retarded cotton batting Heavy cotton

Upholstered Item Design Engineering

305

Ranking the paddings, again latex foam constituted the worst case, with 20% of the specimen mass becoming smoke particulates. Polyurethane foams typically yielded 10–15% smoke, although some specimens yielded values as low as 2–5%. Neoprene smoke production also depended on the foam formulation, while polyester and mixed fibers battings showed low values, similar to cotton battings. Cotton batting mattresses illustrated, that with a low smoke producing padding, the composition of the cover fabric can be important: a mattress with a PVC cover had a 5% mass loss; another one, at 0.5%, had a cotton fabric ticking. In other padding series the order from best to worst padding was: wool, cotton and other vegetable fiber battings, and polyurethane foams.[95][190][480] FR polyurethane foam generally released more smoke than ordinary polyurethane, but at a somewhat lower rate. HR polyurethane released smoke at a yet lower rate. In bedding fires, such fabrics as acrylic and wool/viscose blankets, and cotton sheets or quilts over ordinary and FR polyurethane foam, accelerated the rate, but not the total smoke release; the FR foam produced twice as much smoke as the ordinary foam; bedding made little difference on a FR foam mattress until the mattress was opened.[480] Two chairs, as expected, produced twice the amount of smoke than one. The mechanism of smoke development during burning of flexible polyurethane is described in several papers.[526]–[528] Scission of the polyurethane bond at 250°C produces volatile isocyanate and relatively nonvolatile polyol. At higher temperatures, the polyol produces alkenes, alkynes, aldehydes, ketones, etc., and finally black smoke. The isocyanate produces CO and nitrogen containing yellow smoke which, upon further heating degrades to black smoke and hydrogen cyanide. Stone et al. exposed non-modified and CM foams in the NBS Smoke Chamber under flaming and non-flaming conditions.[490][491][529][530] Questions were raised about the validity of comparisons of results for melting and charring foams, and the effect of density on the results. Comparisons were made of smoke evolution as a function of time, flaming and non-flaming under different levels of radiation, and of non-treated and various treated polyether and polyester polyurethane foams. It was concluded that: Under Non-flaming Conditions: • Smoke generation was generally slower and the total smoke was less than during flaming.

306

Fire Behavior of Upholstered Furniture and Mattresses • Smoke generation always increased during smoldering, while in the flaming mode it varied according to burning behavior; e.g., it increased steeply when fires became oxygen starved. • Differences between foam types were relatively small. Under Flaming Conditions: • There is more difference between melting and charring materials, but otherwise differences between foam types are generally small. • Smoke generation was slower and lower for polyester than polyether foam. • Combustion modifying agents generally caused higher smoke levels, with large differences for different types of FR additives. • Effects due to choice of polyol were relatively minor. General Findings: • Measuring smoke only under flaming or non-flaming conditions, or at only one radiant level, does not characterize smoke behavior (but note the discussion above). • No generalizations with respect to smoke generation can be made for polyurethane foam as a class.

Smoke and toxic gas levels were compared for two reclining chairs, one with vinyl fabric, the other with cotton fabric, over polyurethane foam in the fire room and other rooms in a two-story house.[369] The vinyl fabric delayed onset of a serious fire for about 2½ minutes; visibility was zero after about three minutes but none of the gas concentrations measured seemed lethal. The cotton fabric caused earlier ignition but less smoke. The Cone Calorimeter was found to be a useful tool to evaluate the effect of FR agents in experimental foams.[469] Increasing melamine content reduced times to peak smoke and CO release rate. As presented in Ch. 5 and in Ch. 7, Cone Calorimeter smoke results can be used to predict large-scale results quantitatively.

Upholstered Item Design Engineering

307

Paul and King discussed ignitability, temperature rise, and smoke and toxic gas release of chairs made with several types of FR foam, using various fabrics.[50] More smoke and CO were developed with an HR than an ordinary foam, but CMHR foam performed somewhat better. The smoke results of typical and experimental school bus seat assemblies in the NIST furniture calorimeter are discussed in Ref. 297. Two 50 kW burners, one a box burner on the outside of a two seat assembly, and one a line burner in the crevice of one seat, gave similar material rankings but different individual results. However, the repeatability of the results was very poor. There was no consistent relationship of material composite and smoke development except, perhaps, that a low smoke neoprene material produced less smoke than melamine treated or CMHR foam. However, this advantage was not found in the Cone Calorimeter tests, where a FR re-bonded polyurethane foam gave the lowest results and a Kevlar® interliner increased smoke development. The problem of predicting smoke levels in full-scale tests from bench-scale results is particularly evident in this paper. Smoke Suppression. The results of smoke suppressant screening are described in Refs. 526–531. Examples of multi-component foam systems designed for reduction of smoke and toxic gases were classified as follows:[531] Char formers: pyromellitic, trimellitic, and maleic acids. Char stabilizers: ascorbic and tartaric acids. Combustion modifiers: oxalic and trimellitic acids. Suppressants reduce the amount and rate of release of smoke and may make it more buoyant. The latter was more apparent in full-scale than in bench-scale experiments, such as the ASTM E 662 radiant panel and Cone Calorimeter). Different fabrics can enhance or reduce the effect of smoke suppressants.

6.4.0

TOXIC PRODUCTS

Toxic hazard in fires depends on ignitability, fire growth rate, toxic product yield, and the toxic potency of the products. The toxic potency for various upholstered furniture composites varies only over a modest range in pre-flashover fires, and over an even smaller range in postflashover fires. Thus, smoke hazard from upholstered items is governed

308

Fire Behavior of Upholstered Furniture and Mattresses

predominantly by the mass loss rate of the item, which is correlated to the HRR. Of course, the ventilation of the room is equally important, but that is an independent variable and is not a property of the furniture item. These issues have been discussed in Ch. 2 and 3. Brief descriptions of toxicity results have been discussed in some of the papers mentioned earlier in this chapter. The significance of analytical and bioassay toxicity tests has been discussed in Ch. 2 and 3. In brief, for flaming fires the HRR results can be generally predicitive of toxicity hazard. For non-flaming fires, toxicity measurements may have predictive value but the choice of test conditions in the older methods have been criticized.[180][185][532] The newer NIST/ SwRI method is intended to simulate post-flashover conditions. Given the above caveats, we discuss below papers which include substantial toxicity test results for upholstery materials. Among fabrics, neither nylon nor polyester fabrics were found to significantly differ in toxicity from many other polymeric materials, according to literature reviews on their toxic effects.[533][534] Within this toxicity range, nylon appeared less toxic than cotton or rayon, while blending of wool with nylon (such blends are predominant in aircraft seat covers) increased the measured toxicity. The two reports contain detailed data on the pyrolysis products and toxic effects of fabrics made from these materials. Paul provided data on temperature dependency of nitrogenous species from typical polyurethane foams:[535] °C

Nitrogenous Species

200–400

isocyanates, nitrogenous hydrocarbons

400–600

ammonia, nitrogenous hydrocarbons

>600

hydrogen cyanide, organo-nitriles

>800

nitrogen oxides

Obviously, in any one fire, there will be a whole range of temperatures. For each type of fire, the proportions of the products depend on the temperature. Small-scale tests can predict full-scale yields only if the appropriate decomposition conditions are used. If smoldering precedes flaming combustion, rate of fire growth and toxic product yields are increased.[536]

Upholstered Item Design Engineering

309

NBS workers compared ordinary and TB 117 polyurethane foam in two room tests: single cushions in a single compartment, and four cushion chair mock-ups in a three-compartment test.[185] The heat release results have been discussed earlier. Ignition sources were cigarettes for smoldering fires and a gas flame. The following was concluded: • Within a factor of two, the small and large-scale tests yielded similar LC50 results. • There were differences in the time of animal deaths between the FR and the untreated foams. • A two-step heating sequence, whereby the foam first charred and subsequently flamed, led to increased HCN production, and it was larger for FR than for ordinary polyurethane foam. • The CO2/CO ratios for the small and full-scale tests were similar, but differences in HCN production indicate differences in the decomposition mechanism. • The N-gas model for four gases, CO, CO2, HCN, and reduced O2, accounted for deaths within-exposure plus 24 hours during the large scale tests and the lack of within-exposure and 24 hours deaths during the bench-scale tests. In an earlier study of mattresses, CO release data were related to toxic levels in rooms of various sizes.[190] Toxic product yields were again found to be increased when smoldering preceded flaming. As in many other studies, FR foams produced higher toxic product yields* than standard foams during smoldering and in full-scale, well ventilated fires. Smoldering polyurethane produced primarily isocyanates and CO; in well ventilated, developing fires, CO, HCN, and NOx was found; while in fully developed (post-flashover) fires, CO and HCN predominated. The author concluded that small scale tests can be used to predict full scale fire performance but that more data are needed.

* It is often found that FR treatments increase the yield of toxic species (g of toxic substance, per gram of specimen mass lost). However, this is often overshadowed by the positive effect of the more effective FR treatments in reducing the rate of the burning or the total amount burned.[187] Thus, the net consequence is often favorable.

310

Fire Behavior of Upholstered Furniture and Mattresses

Purser analyzed a wealth of toxicity data for an ordinary and a FR foam, using a heavy, natural cotton fabric cover.[160][206] Table 6-15 shows toxic gas yields in obtained in the NBS cup furnace, Cone, and furniture calorimeters, and a room/corridor test. Table 6-16 lists the estimated times to incapacitation (calculated by the fraction of an incapacitating dose of the major intoxicating gases each minute during the fire, and integrating the dose until the fraction is one; it is assumed that death occurs at twice the incapacitating dose) from the two types of foam. Again, toxic product yields were increased when smoldering preceded flaming. And again, the FR foam produced higher toxic product yields than ordinary foams during smoldering and in full-scale, well ventilated fires but burned more slowly; this has to be weighed against its higher resistance to small flame ignition. There may be a safety gain from using FR or CM foams but the rate of hazard development for these products depends on the fire scenario. Finnish workers tested a number of cotton, viscose, polyester, modacrylic, wool, and PVA/PVC coated fabrics, some with various FR or waterproofing finishes, and polyester batting, neoprene, and a number of polyurethane paddings by DIN 53436.[537] The results of analysis of the combustion products and mortality rate at two temperatures are shown in Table 6-16 (decomposition temperature A: 700°C, B: 500°C). The paper also lists the concentration of 30 gases for wool, modacrylic and polyester fabrics and polyester fiber-fill. More death occurred when the decomposition was at 700 than at 500°C. The blood carboxyhemoglobin (COHb, primary cause of death due to CO) levels were compared to CO concentrations; in some cases the correspondence was clear, but with FR polyester the COHb was surprisingly high and with FR cotton and FR viscose, unexpectedly low. Other attempts to explain mortality in terms of concentrations of various compounds met with mixed success. Hundred percent mortality was observed at 500°C with modacrylic, FR cotton, and FR polyester batting and at 700°C, also with wool and FR cotton and viscose. Levin et al. analyzed (using the NBS cup furnace method) the toxicity of a polyurethane foam and polyester fabric, separately and together.[538] In the non-flaming mode, both materials contributed in an additive manner to the concentrations of the combustion products. However, under flaming conditions, the generation of HCN and CO was greater than that predicted from the maximum amount produced by the separate materials.

Upholstered Item Design Engineering

311

Table 6-15. Comparison of Results of Toxicity Tests of Ordinary and FR Polyurethane Foam Experiment

Temp (°C)

CO kg/kg

HCN kg/kg × 10-3

CO2 kg/kg

CO2/CO v/v

CO/HCN v/v

1.58 2.34 2.00 3.10

43 115 25 54

15

0.073 1.71 13.00 1.0

1 27 34 4.2

71

1.09 2.74

3.60 3.18

19 32

117 25

5.24

1.53 1.13 1.90 2.16

20 15 13 27

10

0.035 0.74 8.00 0.7

1 12 15 2

123

1.90 2.53

9 18

20 27

STANDARD FOAM Flaming decomposition: NBS Cup 450 Cone Calorimeter Furniture Calorimeter Room/Corridor 680

0.023 0.013 0.05 0.037

1.7 0.62 0.59

86 67

Non-flaming (NS) or smoldering (S) decomposition: NBS Cup 400 Cone Calorimeter Furniture Calorimeter Room/Corridor 61

0.046 0.040 0.24 0.15

0.35 1.43 0

179

Flaming decomposition following smoldering: NBS Cup (ramp to 800°C) Furniture Calorimeter Room/Corridor 673

11 0.12 0.062 FR FOAM

Flaming decomposition: NBS Cup 425 Cone Calorimeter Furniture Calorimeter Room/Corridor 500

0.045 0.045 0.09 0.054

1.75 1.57

55 34

Non-flaming (NF) or smoldering (S) decomposition: NBS Cup 375 Cone Calorimeter Furniture Calorimeter Room/Corridor 40

0.035 0.039 0.35 0.17

0.2 0.46 0

Flaming decomposition following smoldering: NBS Cup (HCN only) Furniture Calorimeter Room/Corridor 640

0.13 0.088

14 7.00 3.64

312

Table 6-16. Toxic Gas Concentrations and Mortality Results for Various Fabrics and Paddings Flame +/-

CO ppm

A: Results at 500°C (18 mg/1) Fabrics Modacrylic + 4200 Wool --+ 2500 Co FR 6800 Flamentin Vi FR 6400 Sandoflam Co FR Proban 5400 Co/Vi FR 4700 Pyrovatex CP Cotton FR 5700 Pyrovatex CP PVA-PVC + 4000 Polyester FR + 1600 Cotton + 2500 Cotton + 1900 Fluorochem. Tr.

CO2 %-

O2 %

HCN ppm

HCI ppm

1.1 0.7 1.1

21 19.5 20

1010 610 290

1590

0.7

20

<5

1.4 1.0

19 20

50 40

1.1

20

1.6 1.9 1.2 1.1

19 19 20 20

Mortality% 30 min + 14 days Test 1 Test 2 Comb

COHb% at end of exposure Alive Dead

100 100 100

100 100

100 100 100

41 (12) 32 (24) 56 (6)

100

100

100

30 (12)

15 15

67 50

100 50

83 50

30

20

67

17

38

<5 <5 <5 15

630

17 0 0 0

0 17 17 -

8 8 8 0

255

<5 <5

13 (2)

44 (10) 28 (3) 74 (10)

20 (7) 22 (12) 41 (22) 28 (12)

64 (1)

(Cont’d.)

+ = presence of flame; - = absence of flame; Co - cotton; Vi - viscose; PES - polyester; comb = combined data of two tests except with cotton, cotton FR Pyrovatex CP, and wool which combined the data from three tests. The tables have been arranged in the order of descending animal mortality. Total number of rats was 12 except wool, cotton, and Pyrovatex CP FR cotton where it was 24 and for E-33 FR which was 10. The number of rats from which blood samples could be taken are shown in parentheses. The deviation of the combined data was in average 32% in mortality and the deviation of the mean was 15% in CO, 14% in CO2, 1% in O2, 13% in HCN and 11% in HCL

Fire Behavior of Upholstered Furniture and Mattresses

Material

Table 6-16. (Cont’d.)

Material

Flame +/-

CO2 %-

O2 %

HCN ppm

HCI ppm

-

2800

0.5

20

110

390

100

100

100

+ + + +

3400 1600 1600 1400 1600

1.4 1.6 1.4 2.0 1.5

19.5 19 19.5 18.5 19.5

35 70 30 55 40

760

83 100 20 0 0

67 17 0 0

75 58 20 0 0

35 10

Mortality% 30 min + 14 days Test 1 Test 2 Comb

COHb% at end of exposure Alive Dead

14 (12) 18 (10) 44 (5) 18 (10) 9 (6) 1 (4)

21(1) 23(7)

(Cont’d.)

+ = presence of flame; - = absence of flame; Co - cotton; Vi - viscose; PES - polyester; comb = combined data of two tests except with cotton, cotton FR Pyrovatex CP, and wool which combined the data from three tests.

Upholstered Item Design Engineering

Fillings PES FR fiber fill Neoprene Foam HR-50 foam E-33 FR foam E-35 PF foam E-35 foam

CO ppm

313

314

Table 6-16. (Cont’d.) Material

CO ppm

CO2 %-

O2 %

HCN ppm

HCI ppm

Mortality% 30 min + 14 days Test 1

COHb% at end of exposure Alive Dead

+ -

600 6600 4000 2400 3100 3100 1700 3200 1800 1000 600

0.15 0.85 0.7 0.85 0.8 0.6 0.9 0.35 0.3 0.2 0.15

19.5

1370

20 20 20 20 20 20.5 20.5 20.5 21

860 300 45

100 100 42 42 33 25 25 8 0 0 0

18 (12) 77 (12) 75 (5) 40 (12) 25 (8) 1 (4) 18 (9) 42 (3) 38 (12) 51 (12) 26 (12) 42 (6) 5 (12)

+ + + + -

2600 2600 1300 2000 1500 1000

0.45 0.3 0.3 0.55 0.55 0.6

20.5 20 20.5 20.1 20 20

100 92 42 40 17 0

74 (12) 54 (9) 75 (3) 47 (12) 9 (10) 52 (12) 26 (12)

B: Results at 700°C (18 mg/1) Fabrics Modacrylic Co FR Flamentin Co/Vi FR Pyrovatex CP Cotton Cotton FR Proban Cotton FR Pyrovatex CP Cotton Fluorochem. Tr. Vi FR Sandoflam PVA-PVC Polyester FR Wool

50 35 10

<5 2070

220

Fillings PES FR fiber fill E-35 foam E-35 PF foam E-33 FR foam HR-50 foam Neoprene Foam

250 35 40 25 30

450

1200

+ = presence of flame; - = absence of flame; Co - cotton; Vi - viscose; PES - polyester; comb = combined data of two tests except with cotton, cotton FR Pyrovatex CP, and wool which combined the data from three tests.

Fire Behavior of Upholstered Furniture and Mattresses

Flame +/-

Upholstered Item Design Engineering

315

Detailed results of the cup furnace and of full size chair furniture calorimeter and room toxicity tests of composites of a cotton fabric and ordinary and FR foam, again separately and in composites, are reported.[188][200] In this case, the FR foam produced lower CO concentrations in the non-flaming mode but in the flaming mode, this was reversed (Cone Calorimeter peak HRR values were similar). In an attempt to develop their combined hazard index, FAA toxicity and smoke tests were performed in a full-scale aircraft cabin by the FAA to examine seating material variables.[164] Four paddings were tested, in each case with a wool/nylon fabric and with the incapacity time estimated by gas analysis in the cabin. The incapacitation times were estimated as follows: • 166 s for FR polyurethane foam. • 209 s for the aluminized high-temperature fabric interliner (Norfab®) recommended for aircraft seats by Kourtides[324] over FR PU foam (note that in addition to lower weight, Kourtides found a better fire performance for this barrier installed over ordinary, as opposed to FR polyurethane. • Very similar incapacitation times (226 and 233 seconds) for Vonar® interliner over FR PU foam (somewhat heavy for aircraft use) and for noncombustible refractory batting. Smoke visibility was evaluated separately, and it appeared that in all three cases, visibility limits would be exceeded before the toxicity limits were reached. CBUF obtained a large number of toxic gas concentration results in their furniture calorimeter and room tests (Tables 2-3 B, 2-4 B).[131][149] Not surprisingly, CO peaks were quite dependent on specimen mass. Among the materials, wool generally produced the lowest toxic gas concentrations. The solid foam mattress produced the highest CO peak, while an impregnated foam prison mattress with a vinyl cover and a TB 133 foam chair covered with wool produced the lowest CO peaks. Also low were office chairs covered with wool fabric. During previously discussed room tests of chairs ignited by ciga[90] rettes, gas measurements were made and mice exposed to the fumes, with several sets of mice being exposed to various dilutions of the collected pyrolysis products (University of Pittsburgh Method).[539] Chairs

316

Fire Behavior of Upholstered Furniture and Mattresses

containing polyurethane were found to create more severe toxic effects than those containing polyester or cotton padding. Similar but relatively small differences were found in bench-scale tests, also using the University of Pittsburgh procedure. Results for the cigarette ignition test of a chair covered with a heavy, raw cotton fabric (Haitian cotton) covering polyester cushions which only smoldered are shown in Fig. 6-11 and those for an identical chair but with cotton batting padding which went into flaming at 22 minutes in Fig. 6-12. The authors emphasized that for all chair burns intense sensory irritation occurred during smoldering, prior to flaming; this would have been intolerable for humans and would impede escape efforts.

6.5.0

FIRE INVESTIGATIONS

NFPA 921, Guide for Fire and Explosion Investigations, does not address the differences in fire patterns due to smoldering or flaming ignition of furniture.[606] This matter was addressed by igniting with cigarettes or small flames, ten used upholstered furniture pieces, varying in fabric and geometry, but all containing PU padding. Initially, cigarettes caused charring of the fabric without consuming it and the substrate was charred and only partially consumed. The color change of the fabric did not indicate the extent of the smoldering wave below; in one case, the PU foam was charred below a cover fabric which showed no discoloration. Eventually, the horizontal smolder spread rate was faster than the vertical one. The authors found that remains of cigarettes sank straight through the cushion until transition to flaming occurred, in 60 to 120 minutes. This generally occurred when the smolder reached an outside surface of the cushion and resulted in rapid consumption of the charred material, so that the remainder of the cigarette and the patterns caused by smoldering were lost. In fires ignited with a flaming source, the fabric and the material below it were consumed. For the PU cushions, the horizontal flame spread rate was faster than the vertical one. If the fire self-extinquished due to lack of ventilation, flaming fire patterns were found near ignition point and smoldering patterns at the perimeter of the fire area. In the backs and side arms, the flame spread upwards more rapidly than horizontally across the surface and into the padding. Once the fire reached the other side of the cushions, they were consumed rapidly. Burnthrough did not always occur near the point of ignition.

Upholstered Item Design Engineering

317

Figure 6-11. Toxicity data obtained in cigarette ignition test of chair which only smoldered.

318

Fire Behavior of Upholstered Furniture and Mattresses

Figure 6-12. Toxicity data obtained in cigarette ignition test of flaming chair.

Upholstered Item Design Engineering

319

Assuming that the upholstered furniture is the first item to ignite, and based on experiments where there were only crevice ignitions, the authors offer the following points for determining the cause and origin of a fire: • If the fire was extinguished early, cigarette ignition will be restricted to the first exposed furniture parts, while flaming ignition can have proceeded to other parts; both cause and origin can be determined. • Extinction during fire growth leaves signs of transition from smoldering to flaming, i.e., breakthrough and spread from the point of origin, and cause can perhaps be determined while origin should still be obvious. • Extinction during the full involvement makes it impossible to determine the cause while the origin may still be determined in some cases.

7 Modeling

Upholstered furniture burning behavior is an important aspect of fire hazards in buildings. The HRR from burning upholstered furniture can cause flashover in a few minutes in a typical room. The smoke and toxic gases from such fires, even from fires that only smolder, can spread long distances and fill large volumes. As discussed earlier, this has been recognized by the European Commission, which proposed a draft directive on the fire safety of upholstered furniture. The second essential requirement of the directive states that burning furniture must not, within a certain time allowing for escape, give rise to conditions dangerous to a person in the same room. Although the draft Directive has not resulted in any regulations at this time, it led to the comprehensive CBUF research program[7] being performed. The CBUF work was the first opportunity since the mid-1980s (NIST and University of Dayton) to substantially advance fire modeling in the upholstered furniture area.

7.1.0

INTRODUCTION TO MODELING

For a hazard assessment of upholstered furniture it is necessary to know the conditions developed in a room fire resulting from the burning of the furniture. These conditions include the upper layer gas temperature, 320

Modeling

321

thermal radiation fluxes, smoke obscuration, toxic gas concentrations and the height of the interface between the upper and lower gas layers in the room. While these can be determined directly from running a room fire test, it is not practical to do so on a routine basis. Furthermore, the results of tests in one room do not directly apply to other rooms. The fire models which have been developed for upholstered furniture and mattresses are reviewed in this chapter. First, however, it is necessary to clarify the role and task of fire models. Most commonly today, when a user refers to a fire model, he has in mind a room fire zone model, the most popular of these is currently CFAST,[159] which is part of NIST’s HAZARD suite.[540] A model of this type starts with a known full-scale fire as input, then proceeds to calculate room temperatures, gas flows, species concentrations, etc. This type of model is very useful for predicting room or building hazard conditions, once the full-scale furniture item’s HRR is known. Thus, this type of model, while of importance to the individual concerned with furniture fire safety, is not in any way specific to furniture, but is part of the general fire safety engineer’s tool kit. Consequently, the details of such general-purpose room fire zone models are not discussed here. However, the CFD (computational fluid dynamics) room fire models, also referred to as field models, are briefly discussed in Sec. 7.3 at the end of this chapter. These room fire models do not rely on freestanding furniture fire models for input when they are dealing with furnished rooms. The flame-spread over the surface of the furniture and the resulting HRR can be calculated directly by the CFD room fire model as part of the fire growth in the room. For the reader wishing to pursue information on general-purpose room fire zone models, there is an excellent review of fire modeling by Janssens.[541] Another helpful review concentrating on the practical aspects of a number of models is that of Friedman.[542] A more specific discussion on furniture modeling was provided by Parker and Sundström.[543] In this chapter, we discuss other types of fire models pertinent to upholstered furniture. A furniture fire model predicts furniture calorimeter fire performance on the basis of bench-scale data on the upholstered composite, typically obtained in the Cone Calorimeter. More recently, however, the CBUF program has resulted in a drastically new innovation. The first component furniture model has been offered.[544][545][607] This type of model takes Cone Calorimeter data on individual components (the fabric and the padding) and predicts the composite’s behavior, i.e., predicts the Cone Calorimeter results which would have been obtained had the

322

Fire Behavior of Upholstered Furniture and Mattresses

entire composite been tested as a composite. In the future it may be possible to base the furniture fire model directly on component data and thus permit the fabric and the foam to be scaled differently. The fabric in the furniture composite, tested in the Cone Calorimeter, has the same thickness that it does in the full-scale furniture item while the full-scale thickness of the foam is usually much larger. Finally, one can envision a model which undertakes the prediction of room fire behavior on the basis of furniture calorimeter results. This type of prediction is discussed in Ch. 5. There could also, in principle, be a model which translates the fire performance of a furniture item in one type of room (size, ventilation, etc.) to the performance in another type of room. Both the last two situations have not resulted in what might be considered models, but some designer guidance has successfully been presented and is discussed in this chapter. The furniture designer likes to know what options are available concerning testing vs modeling. While the full-scale fire performance of the furniture in a particular room is the main concern, tests can be conducted in a standard room, run in a furniture calorimeter, performed on a furniture composite in the Cone Calorimeter or possibly even on the individual foams and fabrics in the Cone Calorimeter using special testing protocols. Models are being developed to take the test results at any given level and predict the results that would have been obtained if the tests had been performed at the next higher level.

7.2.0

FURNITURE FIRE MODELS

Modeling the fire on an upholstered furniture item is extremely complicated. Real furniture shows such traits as delamination, curling, burn-through (and burning on two sides), fall-off, pool burning of molten material, fire “tunneling” underneath the surfaces, frame collapse, etc. Fire physics and thermo-structural behavior research are not advanced enough to be able to represent any of these phenomena. The best that can be done is to track heat fluxes and flame spread, and from those to compute the HRR. Thus, it can immediately be seen that the state of the art in furniture modeling is exceedingly primitive. The approaches which have been taken towards tackling this problem can roughly be divided into three types:

Modeling

323

• Physics-based. This type of model proceeds by tracking the known phenomena by direct computation, and ignoring all of the phenomena which are not yet quantified (as explained above). • Combined physics/correlation approach. In this type of scheme, some basic physics phenomena are established and tracked. To eliminate systematic divergence from actual data, however, functions are introduced into the solution which are based on data correlations. Two such models were developed under the CBUF aegis. • Correlations-based. This approach identifies controlling variables and uses them in a statistical correlation approach. This type of model is the simplest to develop and to use, but should not be used to extrapolate to configurations greatly different from any that were available in the original data set used for correlation. (This caveat also applies to the proceeding approach.) 7.2.1

Physics-Based Models

In this section, we examine two physics-based models: Dietenberger’s FFM,[546][547] and the CBUF Model III. An early, limitedfunctionality physics-based model was also presented in the 1970s by Bard et al.[548] Dietenberger’s FFM. The furniture fire model (FFM)[546][547] developed by Dietenberger has been the most ambitious physics-based model for predicting the results of tests in the furniture calorimeter from the results of bench-scale tests on furniture composites. The needed benchscale data for HRR and soot production come from the Cone Calorimeter. It also requires bench-scale data on ignition and flame spread from the LIFT apparatus.[108] It considers two burning rate processes: a spreading pool fire on the horizontal seat and vertical flame spread on the rear and side cushions. The fire grows from the initially ignited area on the seat. The total HRR is calculated from the area of involvement, the net heat flux to the surface and an effective heat of gasification determined from the Cone Calorimeter. From the HRR a flame height and flame area are calculated. The rate of soot production is used in the calculation of the thermal radiation

324

Fire Behavior of Upholstered Furniture and Mattresses

from the flame. The thermal radiation fluxes on the un-ignited areas of the cushions are used to calculate surface temperature. The surface temperature at the boundary of the flame determines whether flame spread will occur and if so how fast. When the flame reaches a vertical surface it will spread upward in accordance with vertical flame spread theory. The thermal radiation fluxes on the burning area will define new total heat and soot release rates for the next step. Two important features of this model are the scaling of the HRR data and the assumption of a thermally thin layer at the surface of the furniture composite in the analysis of the ignition and flame spread data from the LIFT. In a fire environment a material is exposed to a time varying incident heat flux. The incident heat flux in the Cone Calorimeter is constant during the entire test. The HRR of a material at any given time depends not only on the incident flux but also on the total amount of heat that has been released up to that time. By plotting the HRR as a function of the total heat released, instead of the time, for several irradiances and using a HRR scaling factor, it is possible to approximately collapse the HRR data from the Cone Calorimeter into a single curve. This curve can be used in the furniture fire model to calculate the HRR for any combination of the instantaneous incident flux and the total amount of heat released in the local area where the calculations are made. FFM was combined with an early version of the room fire model FAST to produce FAST/FFM.[546] This combined model calculates the burning rate of the furniture which is then used as input to the calculation of the conditions in the room. This includes the instantaneous external radiation heat flux which contributes to the net heat flux into the furniture and increases its burning rate. During the examination of the Dietenberger model in the CBUF program (Ref. 7; Appendix A9) along with its computer code and its documentation, the following conclusions were drawn: “(1) the model incorporates some significantly advanced aspects of fire physics but it only covers the period of fire growth that can be described as simple flame spread over flat surfaces; this excludes the bulk of the burning period of most real chairs; (2) the computer program is not in such condition that it could be utilized by furniture industry staff nor fire safety engineers engaged in design work and (3) the computer code dates from the mid 1980s and no reasonable amount of effort in revising it would likely make it suitable for the intended users.”

Modeling

325

The CBUF Model for Mattresses. During the course of CBUF work, a physics-based model was developed for predicting the HRR of burning mattresses. In the CBUF nomenclature[130] this was their Model III. The CBUF mattress model involves some sophisticated mathematics and is based on novel extensions to the thermal fire spread theory. This physicsbased approach follows in broad outline a thermal fire spread theory originally developed for vertical wall surfaces, but with a number of extensions and adaptations to convert it into a furniture fire model. It should be able to predict the time history of HRR, not just the peak HRR value. The model starts with the concepts for concurrent flame spread as discussed in Sec. 2.5. Although the fire spread configuration over the top of a mattress corresponds to what is called opposed-flow flame spread, approximations are made in the physical model in such a way that the mathematical model resembles as much as possible the referenced models for upward flame spread. This was done to employ the existing numerical procedures without requiring excessive effort for the development. The burning area is assumed to be a circle with the fire spreading radially outwards (Fig. 7-1). The flame is approximated as a cylinder to permit the calculation of the preheating of the surface to its ignition temperature. In order to calculate the propagation of fire along the surface we need to know the heat flux at every position as a function of time. Outside of the assumed cylindrical flame, the heat flux (r,t) to the surface decreases with increasing radial distance. The flux distribution depends on the size and shape of the flame. However, for calculations the flux is approximated as a constant between the position of the flame front rp and a radial distance rf which is termed the exposure range. For r < rf the heat flux to the surface is assumed constant. This simplification of the actual flux distribution resembles that used in thermal models for upward flame spread. The exposure range depends on the HRR and on the size and shape of the cylindrical flame. It is expressed in the form: (Eq. 7-1)

rf = kf q• n

where kf and n are constants. The height of the flame cylinder is taken as: (Eq. 7-2)

zf = -1.022rp + 0.235 q• 2/5

The heat flux to the surface outside of the flame cylinder is assumed to be purely radiative. The radiation from the flame is calculated as: (Eq. 7-3)

q• ´´f = Φεf σTf4

326

Fire Behavior of Upholstered Furniture and Mattresses

where Φ is the view factor and Tf the flame temperature, which is taken to be 900°C. The view factor is a function of rp , zf and the position r. The view factor is calculated from Ref. 549. By fitting the above equations for different values of HRR per unit area, values are obtained for kf and n. The flame spread velocity is computed similarly as in Refs. 106–111, except that special provisions are made for the finite size of the mattress. The characteristic time constant for the flame spread model is taken from Cone Calorimeter ignition data.

Figure 7-1. Schematic of the flame spread process on the mattress in CBUF Model III.

The total HRR is the sum of the HRR of the ignition source (gas burner) and the HRR of the burning mattress, (Eq. 7-4)

q fs (t ) = q b (t ) + q f (t )

The heat release rate from the burning area is obtained by integration, assuming that for each point the HRR per unit area is obtained from the Cone Calorimeter tests. To take care of the disparity in thicknesses between the actual mattress and the Cone sample, thickness scaling of the

Modeling

327

HRR curve is performed. The integration over the surface is represented by a convolution integral,

(Eq. 7-5)

t

dAp (τ )

0

dτ

q fs (t ) = Apo q′′(t ) + ∫ q "(tτ )

dτ

The ensuing model has the following “free” parameters: • The initial “burning” area Apo. • The exponent n and coefficient function kf in the heating range expression. • The irradiance at which the HRR per unit area is measured in the Cone Calorimeter. • The irradiance at which the effective time to ignition τig is measured in the Cone Calorimeter. • The “effective” width 2R and length 2L of the mattress. The appropriate values of these parameters were found by a few rounds of trial and error. The value of the initial effective burning surface used is 0.2 × 0.2 m2. This value corresponds to the surface of the propane burner. The parameter n in the heating range equation was fixed to a constant 0.62. The parameter kf was found to vary approximately as (Eq. 7-6)

kf = 30.7 • (Q/Ap)-0.88

The effective ignition times were taken from Cone Calorimeter tests at an irradiance level of 25 kW m-2. The dimensions R and L of the mattress are chosen to be the physical width and length. When necessary, the thickness of the foam was taken into account by a thickness scaling procedure.[130] Example results are shown in Fig. 7-2. The limitations of the CBUF Model III are mainly in the fact that innerspring constructions are not specifically modeled. Thus, model agreement for those types of mattresses should not be expected to be good, once the top layer has burned through and there is flaming in the cavity. In principle, the ideas of Model III could be extended to cover other types of upholstered items; however, this has not been explored so far.

328

Fire Behavior of Upholstered Furniture and Mattresses

Figure 7-2. Measured and calculated HRR’s for a 100 mm latex foam mattress with a cotton/ viscose cover.

7.2.2

Combined Physics/Correlation Models

During the course of the CBUF work, a model for upholstered furniture was developed which is based on physics, but with an empirical component derived from data correlations. This was termed “Model II,” the Convolution Model,[130] and is applicable to upholstered chairs and sofas. It is based on an extension of ideas originally developed for representing flame spread over wall and ceiling surfaces.[550][551] The basic idea is simple: portions of the wall/ceiling surface contribute no HRR until they are ignited. After ignition, each piece contributes the same time-history to the room as it did during its Cone Calorimeter test. The total contribution is the integral over all the burning area. With this approach, it is essential to have a method for predicting the burning area, as a function of time. Here, the techniques developed for wall/ ceiling linings are not directly useful and a technique specific to the chair case had to be evolved. It is assumed that the heat release rate q•fs measured in the furniture calorimeter can be predicted as the convolution integral of the burning area • → rate A, and the heat release rate q•´´ (r , t) from the area that is burning: t

(Eq. 7-7)

H q fs (t ) = q ′′(r ; t − τ )A (τ )dτ

∫ o

Modeling

329

The heat release rate from the burning area A is dependent on the → irradiance history of the elementary area dA( r ) of surface, which is caused by the radiative heat transfer between the surfaces and flame. We do not → • know either q•´´ (r , t) or A exactly. To simplify the calculation, it is assumed that the heat release from the surfaces is to be the same as in the Cone Calorimeter tests with an irradiance of 35 kW m-2. The effects of falling burning pieces, collapsing and pool burning in the Furniture Calorimeter are not individually represented. Indirectly, however, they are partly represented through the use of a “de-convoluted” area. To a certain extent, the surface area covered by flames can be determined visually. However, this does not include important phenomena such as burn-through, burning on both sides, falling-burning pieces, collapsing, and pool burning. All of these contribute to making the actual area impossible to measure. Thus, the concept of an effective area (or deconvoluted area) is used. That is, it is necessary to find an area equal to such a value that when it is convoluted with the Cone Calorimeter HRR curve (taken at 35 kW m-2 irradiance), the resulting prediction of the full- scale HRR curve is exactly the experimentally measured value. Mathematically such a process is known as de-convolution. The effective areas obtained by de-convolution vary for different chair styles because the irradiance between different parts of the chair and the flame is dependent on the geometry of the chair. Thus, effective areas have to be found for each chair style separately. It is possible to create an effective area function for each of these styles, but within CBUF work an area function was developed only for certain styles (Styles 1, 3, 5, 13, and 14; see the discussion on styles below). In the de-convolution process, it was found that the peak magnitude of the effective areas varied for different chairs of the same style, but the form of the function was quite similar. Thus, the following scaling was adopted for the burning areas: (Eq. 7-8)

A(t ) = Amax a (θ ),

θ=

t t max

where Amax and tmax are the peak value of the burning area and the time to reach the peak. It was found that the non-dimensional area functions a(θ) for different chairs of Style 1 look similar. A mean of six typical scaled areas was chosen as the basis function am(q). This function is given in Table 7-1.

330

Fire Behavior of Upholstered Furniture and Mattresses

Table 7-1. Dimensionless Area Function Used In CBUF Model II Time

Dimensionless time θ

Dimensionless Area am (t)

0

0.00

0.00199

30

0.12

0.04867

60

0.24

0.15481

90

0.36

0.29059

120

0.48

0.38431

150

0.60

0.41067

180

0.72

0.44631

210

0.84

0.68213

240

0.96

0.97168

270

1.08

0.94622

300

1.20

0.74378

320

1.28

0.57367

340

1.36

0.44603

370

1.48

0.44219

400

1.60

0.55134

430

1.72

0.50275

´´ and on The peak values Amax were found to be dependent on q•180 msoft. Also, tmax was found to be relatively constant; consequently, a fixed value of 250 s was chosen for it. Finally, the HRR is calculated by using following equations: t

Eq. (7-9)

q fs (t ) = Amax q ′′(t − τ ) a m (τ / t max ) dτ

∫ o

Eq. (7-10)

0 .35 ′′ )−0.76 · m soft Amax = 150 .2 (q180

where q•´´(t) is the Cone Calorimeter HRR and q•´´180 is its average value for the period of 180 s post-ignition [kW m-2], tested at an irradiance of 35 kW m-2, tmax = 250 s, and msoft is the total mass of soft upholstery material [kg]. An example of the agreement achieved is shown in Fig. 7-3.

Modeling

331

Figure 7-3. The prediction of CBUF model II for an example chair (the predicted curve is the lighter and smoother one).

7.2.3

Correlations-Based Models

NIST Correlations For Chairs and Sofas. The availability of a completely deterministic and user-friendly model for the burning behavior of all types of upholstered furniture would represent the optimum situation. However, such a model does not exist at present. When some feature of the burning rate history, such as the peak HRR or the time to a critical HRR, is all that is needed, then there is another alternative. The parameter of interest in the full-scale burning rate curve can be empirically correlated against one or more parameters of a bench-scale test of the furniture composite. This requires the analysis of many results from full-scale and bench-scale tests, covering a wide range of furniture types. Such a correlation can give reasonable predictions for furniture which is similar to those upon which the correlation was based. The choice of bench-scale parameters with which to correlate is determined by trial-and-error. However, this choice must be governed by a basic understanding of fire physics. Even where more comprehensive models are available, correlation formulas can still be useful for determining certain desired answers, without the need for much mathematical computation. No correlationsbased approaches, however, can be feasible for large extrapolations. Modest extrapolations can be treated, but items of styles or construction types not encompassed in the original correlation work cannot be expected to be successfully predicted.

332

Fire Behavior of Upholstered Furniture and Mattresses

The first correlation for upholstered chairs and sofas was provided by Babrauskas and Krasny in 1985.[121] It focused on residential furniture having relatively high HRR values. The predicted peak HRR in the furniture calorimeter is given by: Eq. (7-11)

q•peak = 0.63 q•´´180 [mass factor][frame factor][style factor]

where q•peak is the full-scale peak HRR (kW) and q•´´180 is the 180 s average HRR (kW m-2) obtained in the Cone Calorimeter with an exposure flux of 25 kW m-2. The mass factor is the total mass (kg) of the combustibles in the specimen, and the other factors are given as:

frame factor =

style factor

=

{

{

1.66 for noncombustible frames 0.18 for charring plastic frames 0.30 for wood frames 0.58 for melting, thermoplastic frames

1.0 for plain, primarily rectilinear construction 1.5 for convoluted shapes

1.0 – 1.5 for intermediate shapes.

Other authors, using different furniture and full-scale conditions, found agreement with this concept in principle, but additional testing is clearly needed.[35][36][122] Chapter 5 provides more data on this bench scale/ full-scale correlation. Even though flame spread plays an important role in this problem, it is not included in this correlation. Good results were nevertheless achieved since there tends to be a high degree of correlation between flamespread rate and HRR, depending on the materials involved.[107][121] The correlation between flame spread and HRR follows since the flame spread rate depends on the incident flux and the thermal radiation flux from the burning item is directly proportional to the total HRR. For full-scale tests,

Modeling

333

the peak heat release rate (kW) depends not only on the materials but also on how much of the material is burning at the peak. This, in turn, additionally depends on item mass, configuration, frame or innerspring contribution, etc. The NIST/BHFTI research program on the TB 133 for seating furniture, which was discussed in Ch. 5, provided an opportunity to study in detail the opposite end of the spectrum: institutional-use chairs which show very good fire properties.[35][36] This test series included ten chairs of identical construction; differing only in their upholstery materials. When the peak HRR in the furniture calorimeter was plotted against the 180 s average HRR in the Cone, the data could be represented by two lines, one for the propagating chairs and another for the non-propagating chairs. The ones that propagated fire could be adequately represented by the equation, (Eq. 7-12)

q• peak = 4.7 q•´´180

as can be seen in Fig. 2-5 by redrawing the line slightly to pass through the origin.[35][36] In this case the bench-scale data were taken at 35 kW m-2 instead of 25 kW m-2. If the average HRR in the Cone Calorimeter is proportional to the exposure flux, then Eq. 7-11 could be generalized to other exposure fluxes by multiplying by the ratio of the new flux to 25 kW m-2. Thus,

(Eq. 7-13)

q peak = 15.8

′′ q180 [mass factor][frame factor][style factor] flux

where flux is the exposure flux in the Cone Calorimeter. The chairs in the NIST/BHFTI study weighed approximately 35 kg, had wood frames and were of plain construction. When this data and the 35 kW m-2 exposure are put into the above general equation, the predicted full-scale HRR was in agreement with the measured one represented by Eq. 7-12. Another NIST study intended to produce a correlation-based model was undertaken by Ohlemiller and Shields.[378] They tested a series of 27 material combinations in a 4-cushion mock-up using the furniture calorimeter at NIST. In their work, only the fabric, the interliner, and the foam were varied. CBUF Correlations For Chairs and Sofas. The original NIST correlation by Babrauskas and Krasny was based on furniture types and

334

Fire Behavior of Upholstered Furniture and Mattresses

construction practices prevalent about 1980.[121] It did not include FRtreated fabrics, interliners, newer types of CMHR foams, etc. Thus, the correlation-type approach was re-examined during the CBUF program, using a much larger data set. CBUF Model I was developed in greatest detail for upholstered chairs. Sub-models were also developed for mattresses and for office-type upholstered chairs which have a hard-plastic shell. Submodels for the latter two categories were only carried through to a preliminary level of detail. We refer to the comprehensive CBUF report [130] for information about Model I application to these product categories. Furniture modeling according to Model I proceeds in two steps: 1. Determine if the fire is propagating or non-propagating 2. Find HRR peaks and other variables according to correlations, if the fire is determined to be propagating. For non-propagating fires, no specific hazard parameters need to be determined. This is because such fires, intrinsically, are of the lowest hazard, producing less than about 100 kW peak HRR values. (However, in small, closed rooms they may cause a hazard due to smoke and toxic gases.) The earlier NIST studies had suggested that a propagation/nopropagation criterion could be set as a Cone Calorimeter value of q•´´180 = 75 kW m-2, measured at a flux of 35 kW m-2. This issue was re-examined during CBUF research. Using the performance of the various items actually tested, a criterion value of q•´´180 = 65 kW m-2 was determined. It is reasonably consistent with the earlier-used limit value of 75 kW m-2. Note, however, that the amount of highly improved furniture (for example, with state-of-the-art interliners) tested in the CBUF program was not large, and that the limit value adopted is highly provisional. For actual details of how the CBUF correlations were achieved, we refer to the original study.[130][552] Here, we point out just a few of the salient issues. In the original NIST correlations, the mass of the specimen was represented by the total mass. In the CBUF work, the mass factor adopted uses the combustible mass of the soft parts. Specifically, it excludes frame mass and mass of any other rigid, combustible components. The reason for separating out the soft parts only is that this improves predictability. The primary burning of the frame parts normally does not take place until some time after the peak HRR of the fire has already been passed. Thus, this frame burning should best be excluded from estimations of how much mass will be contributing to the peak HRR value. The following is based on the discussions in Ref. 552. The earlier correlations did not evaluate the Cone Calorimeter time to ignition as one

Modeling

335

of the variables affecting fire growth. Yet, time to ignition is often seen to be an important variable in predicting fire development rates. Specifically, it is the combination q•´´/tig, which is often necessary to predict flame development that includes a flame spread component. A non-linear regression indicated that t.-0.7 ig was helpful in accounting for some of the variance. Furthermore, a better correlation was found with the use of an additive term onto the ignition time. Furniture style was always known to be an important variable affecting fire development but earlier data available were not adequate to derive quantitative characterization. The CBUF furniture selection process included a wide variety of commercially important furniture styles, enabling the style effect to be quantified. Table 7-2 shows the furniture styles adopted for use in Model I. Table 7-2. Furniture Styles Used in the CBUF Program Code

Style Factor A

Style Factor B

Type of Furniture

1

1.0

1.0

Armchair, fully upholstered, average amount of padding

2

1.0

0.8

Sofa, 2-seat

3

0.8

0.8

Sofa, 3-seat

4

0.9

0.9

Armchair, fully upholstered, highly padded

5

1.2

0.8

Armchair, small amount of padding

6

1.0

2.5

Wingback chair

7

—

—

Office Swivel chair, plastic arms (unpadded), plastic rear back shell

8

—

—

High back office swivel chair, plastic arms (unpadded), plastic rear back shell

9

—

—

Mattress, without innersprings

10

—

—

Mattress, with innersprings

11

—

—

Mattress and box spring (divan base) set

12

0.6

0.75

Sofa-bed (convertible)

13

1.0

0.8

Armchair, fully upholstered, metal frame

14

1.0

0.75

Armless chair, seat and back cushions only

15

1.0

1.0

Two-seater, armless, seat and back cushions only

336

Fire Behavior of Upholstered Furniture and Mattresses

Two different style factors are listed in the table, style factor A and style factor B. In the context of Model I, style factors are used for two purposes: for predictions of peak HRR values and for predictions of time to peak. Style factor A is pertinent to calculations of peak HRR, while style factor B pertains to calculations of time to peak. With the above considerations in mind, the correlation for q•fs, the peak HRR (kW), was obtained as follows: if ´´ > 70 and x1 > 40) or (style = [3, 4] and x1 > 70) (x1 > 115) or (q•35-tot then q•fs = x2 Else, if x1 < 56 then q•fs = 14.4 x1 Else, (Eq. 7-14)

q•fs = 600 + 3.77 x1

where (Eq. 7-15)

0.7 -0.7 x1 = (msoft)1.25 (style fac. A)(q•´´35-pk + q•´´ 35-300) (15 + tig-35)

and the subscript 35 denotes that the Cone Calorimeter HRR tests run at a 35 kW m-2 irradiance. The msoft is the mass of the soft combustible parts of the item (kg); it includes fabric, foam, interliner, dust cover, etc., but does not include the frame nor any rigid support pieces. And,

(Eq. 7-16)

(

x2 = 880 + 500 msoft

)

0.7

 Ä hc,eff   ′′ −tot   q 35

(style fac. A)

1.4

Modeling

337

Here, ∆hc,eff is the test-average effective heat of combustion in the Cone Calorimeter (MJ kg-1), and q•´´35-tot is the total heat released (MJ m-2)at a flux of 35 kW m-2. Another correlation within the context of Model I was developed for predicting the total heat release: qtotal = 0.9msoft•∆hc,eff + 2.1(mcomb, total - msoft)1.5

(Eq. 7-17)

Here, the value of the effective heat of combustion comes from Cone Calorimeter tests of the composite (soft parts) and the masses are simply those measured for the full-scale article. For the full-scale article, mcomb,total denotes the entire combustible mass, i.e., all except metal frame parts or other non-combustible pieces. The next aspect which was predicted with CBUF Model I is the time to peak. This time is defined to occur when the peak value of HRR is recorded. Generally, all other hazard variables are also at or near their peak values when the HRR peak occurs. For this analysis, the starting time (t = 0) was taken to be at the time of sustained burning, defined as when the level of 50 kW is first reached. The prediction is: (Eq. 7-18)

tpk = 30 +4900(style fac. B)(msoft)0.3(q•´´pk#2)-0.5(tpk#1 + 200)0.2

where tpk style fac. B

= time to peak, from start of sustained burning [s] = style factor B

msoft

= mass of upholstery (soft components only) of full-scale item [kg]

q•´´pk#2

= second peak of Cone Calorimeter HRR curve [kW m-2]

q•´´trough tpk#1

= trough of Cone Calorimeter HRR curve [kW m-2] = time to first peak of Cone HRR curve, from start of test [s]

The time to untenability in the ISO room is taken as starting at the time that the full scale HRR exceeds 50 kW and ends when it reaches 400 kW. The lower HRR corresponds to the time at which the fire is expected to be detected and the upper value corresponds to the HRR when the bottom of the hot upper layer drops to 1.1 m above the floor making it extremely

338

Fire Behavior of Upholstered Furniture and Mattresses

difficult to escape. The untenability time predicted during CBUF was obtained with the following correlation: (Eq. 7-19) -0.8(q•´´ )-0.5(t 0.15 tUT = 1.5 × 105 (style fac. B)(msoft)-0.6(q•´´ trough) pk#2 pk#1 – 10)

where q•´´trough is the minimum HRR between the two peaks, q•´´pk#2 is the second peak HRR and t´´pk 1 is the time to the first peak all measured in the Cone Calorimeter at an exposure flux of 35 kW m-2. CBUF Model I does not specifically predict the shape of the HRR curve, beyond providing the peak HRR, the time to peak and the total heat release. Using this information, however, it is readily possible to produce predictions of triangular-shaped HRR curves for upholstered furniture. This has been shown to be a suitable strategy in an earlier study.[268] To apply the triangular technique to the CBUF Model I, we note that the total area under the triangle must be the total heat release. The height of the triangle is the peak HRR, thus, the triangle base width is:

(Eq. 7-20)

Ä t base = 2

qtotal q fs − pk

The HRR is assumed = 0 for times t < (tpk - ∆tbase /2). After that, the HRR curve rises linearly to the peak value, then descends down to 0 at t = (tpk + ∆tbase /2). Correlations For Mattresses. Correlations-based predictions for mattresses have been somewhat scant. A study examining room fire relationship to Cone Calorimeter results[8] was done several years ago cooperatively with NIST and the BHFTI. The behavior in that study was found to be: • Mattresses with a bench-scale HRR (180 s average value) of ≤100 kW m-2 led to room fires of less than 100 kW. • Mattresses with a bench-scale HRR (180 s average value) of ≥ 100 kW m-2 generally led to room fires on the order of 1 to 2 MW. • The transition between those extremes was very abrupt.

Modeling

339

The test room in question was the room of the California BHFTI laboratories, which is only slightly larger than the ISO 9705 room. The cut-off value in this study was conservatively selected at 100 kW m-2 to allow for some performance degradation due to degradation when exposed to moisture (some fire retardants can be leached out, an area of concern for prison mattresses, which are often treated with water-soluble fire retardants). The very sharp transition between low-hazard burning and flashover, as seen in the BHFTI/NIST study, is an inherent characteristic of mattress fires, and is distinctly different from upholstered chair behavior. CBUF work similarly documented mattresses showing a moderate HRR in the furniture calorimeter, but leading to room flashover when burned in the ISO 9705 room.

7.3.0

A COMPONENT HRR MODEL FOR FURNITURE COMPOSITES

Until recently, it had not been considered feasible to compute the HRR behavior of a composite, when given information solely about the HRR of the individual layers (components) forming that composite. The utility of such a model would be to reduce the burden of testing. If a manufacturer is using n fabrics and m foams, then possibly up to (n × m) test runs have to be made to cover all the combinations. If a component model were available, the test burden could be reduced to a much smaller number (n + m) of tests. Another significant advantage of this model is that it could make it possible to shift the responsibility for the small-scale testing from the furniture manufacturers to the material suppliers. This would avoid the duplicate testing of the same composite by every manufacturer that uses it. Furthermore, the HRR data obtained on the individual components could be used by the material producer for product development, advertising and for establishing empirical relationships between the HRR and the other material properties. This could provide a basis for reducing the amount of testing even further. In the course of the CBUF project, the first model was developed which has this capability. The model, inevitably, is somewhat complex and not quite as straightforward as the above description would imply. The data which turned out to be needed was not simply standard Cone Calorimeter HRR curves for the individual components; a modified experimental strategy needed to be adopted.

340

Fire Behavior of Upholstered Furniture and Mattresses

The model has been described in detail in Refs. 544 and 545. Here, a very brief overview is given. It is a two-component model applicable to a melting foam covered by either a melting or a charring fabric. It does not apply to fillings of the charring type like cotton batting. It can include interliners but only if they are tested together with the fabric with which they will be used. The testing strategy comprises three steps: 1. The fabric cover is tested over a standard foam according to the standard test protocol for furniture composites in the Cone Calorimeter. 2. The fabric cover is tested in a special holder by itself with methane passing through it to simulate the volatiles from the foam. 3. The foam is tested alone with a methane flame above it. This flame establishes the flame heat transfer conditions required by the model. The data from the three test runs are combined in a mathematical model. The HRR contribution of the foam is defined as being equal to its “sensitivity,” multiplied by the heat flux passed on to it by the fabric. The sensitivity of the foam is equal to its heat of combustion divided by its effective heat of gasification and is measured in the bare foam tests. The heat flux passed on by the fabric is determined by measuring the HRR contribution of a standard foam of known sensitivity when it is covered by the fabric. The HRR of the composite is then equal to the HRR of the fabric, burning by itself, plus the contribution by the foam. The charring fabrics absorb most of the flux from the Cone and reradiate to the foam at a temperature which is controlled by the external flux and the flux from the flame. The melting fabrics fall onto the foam and burn as a pool fire there. They consume part of the incoming flux due to their heat of vaporization during their burning period. The HRR curve calculated for the cotton fabric over the HR polyurethane foam is compared with measurements taken at two different laboratories in Fig. 7-4.[545] The differences between the calculated and the measured curves are no greater than the differences between the measured curves. While there are some distinctive shape differences, the first peaks and the minimum between the peaks of all three curves are similar. The second peak of the calculated curve is in between the two peaks of the measured curves. The same is true of the 180 and 300 s average HRR values

Modeling

341

which are needed for the CBUF Model I correlation formulas. The abrupt drop at the end of the calculated curve is due to an automatic correction built into the computer program to insure that the predicted total heat contribution of the foam is the same as the measured value when it is tested alone. This model was also reduced to a set of simple correlation formulas for predicting the peak HRR, the 180 and 300 s average HRR, and the trough HRR of the composite based on the component tests. The prediction for the 300 s average is shown in Fig. 7-5.[544]

Figure 7-4.Comparison of predicted and measured HRR curves for a cotton fabric over HR foam. (FMPA is the Forschungs-und Materialsprüfungsanstalt, Baden-Wurtemberg; LNE is the Laboratoire National d’ Essais, France.)

Figure 7-5. Comparison of predicted and measured 300 s average HRR for seven different fabrics over three different foams.

342

Fire Behavior of Upholstered Furniture and Mattresses

7.4.0

CFD ROOM FIRE MODELS

In the CFD (Computational Fluid Dynamics) model for a room fire, the air space in the room is divided up into many (perhaps millions) of small control volumes of uniform temperture, density, pressure and chemical composition. The initial conditions, along with the boundary conditions over all of the solid and liquid surfaces in the room are specified. This includes the surfaces on any upholstered furniture that might be present in the room. These boundary conditions will vary over the surfaces in accordance with the properties of the liquid or solid medium at each location. In general, they can vary with time as the properties change due to temperature rise and thermal decomposition. The heat and mass flow between adjacent control volumes are governed by the laws of diffusion and the conservation laws for mass, energy, momentum, and species. When the incoming flows of fuel and oxygen form a combustible mixture at the existing temperature in a control volume, a quantity of heat equal to the mass of the fuel consumed times its heat of combustion will be released. The reactants will be replaced by combustion products. Soot may be generated or consumed. The control volumes in which combustion takes place will define the location of the flame. Flame-spread occurs when combustion begins in adjacent control volumes. In the case of a pool fire, the boundary conditions at the surface of the fuel consist of (1) a constant surface temperature equal to its boiling point and (2) a mass flow equal to the net flux at the surface divided by the heat gasification of the fuel. In the case of solid surfaces, particularly those of char forming materials, the situation is much more complex. For some materials there are models which can calculate the surface temperature and mass flow histories for a time-dependant flux at the surface. Such models could typically increase the demands on the computer by orders of magnitude. Their use must wait for much more powerful computers. However, there are special cases like thermally thin solids where it may be straightforward to calculate the surface temperature and mass loss rate. In other cases, appropriate assumptions and approximations might be made to simplify the problem. The usefulness of these techniques would have to be verified experimentally. When the mass flow of fuel from the surface of a char forming material becomes too low to support a flame, oxygen will diffuse into the control volumes adjacent to the surface and react with the char. Since the

Modeling

343

combustion occurs at the surface for this char oxidation reaction, the heat transfer is very efficient. The temperature of the surface will generally increase sufficiently to take on a red glow. Both the flame and the glowing surfaces are well described by the CFD fir model, if the grid size is small enough. Unfortunately the division of a large room into 1.0 mm cubes is beyond capabilities of the present day computers. However, the available memory size continues to increase with every passing year. Meanwhile compromises in grid size could lead to acceptable approximations in some cases. Increases in grid size in noncritical directions or using larger grid sizes in non-critical locations might be partial solutions. The Fire Dynamics Simulator (FDS) is a CFD model developed at NIST. It is described in the Fire Dynamics Simulator - Technical Reference Guide[608] which illustrates the principles of CFD fire modeling, provides the basic equations, and demonstrates the application of FDS to fire suppression by sprinklers. The computation used in a CFD model can be treated as Direct Numerical Simulation (DNS) or as a Large Eddy Simulation (LES). The discussion in the previous paragraphs was based on DNS, where the heat release rate and the flame-spread are calculated directly by the room fire model. DNS requires a grid small enough to define the location of the flame. At the present time it also has to be limited to small spaces because of computer memory limitations. LES computes the large scale eddies directly, but the HRR and smoke input must be specified. This computation is ideal for simulating the flow of smoke through a large multi-room enclosure. A relatively large grid size is adequate for that purpose. In order to calculate fire growth in a room with LES, auxiliary models for HRR and flame spread must be incorporated. Fire environments in a prototype multi-room apartment in a multistory building were studied by Luo and Beck[609] at the Centre for Environmental Safety and Risk Engineering (CESARE) at the Victoria University of Technology in Melbourne. Two well-instrumented fire tests were conducted using standard polyurethane mattresses for the fuel. One was designed to go to flashover. The other was designed to avoid it. The flamespread velocity, mass release rate, gas temperature, radiation heat flux, and gas concentrations were measured. A CFD fire model, called CESARECFD, was used to simulate these polyurethane slab fires. The model was described by three-dimensional transport equations for mass, momentum and enthalpy. The turbulence flow was based on the k-,model. A soot

344

Fire Behavior of Upholstered Furniture and Mattresses

formation model and a flame-spread model were incorporated into the CFD model. The flame spread velocity and the mass release rate of the polyurethane mattresses were predicted in this study. It was found that the CFD model provided reasonable predictions of the magnitude and trends for the experiments both in the flashover and the non-flashover fire cases. Luo et al.[610] compared the predictions from CESARE-CFD model and the two-zone model, CFAST (version 2.0), against a comprehensive set of data obtained from one flashover fire experiment at CESARE. The experimental results were obtained from a full-scale prototype apartment building under flashover conditions. Three polyurethane mattresses were used as fuel. The mass release rate, gas temperature, radiation heat flux and gas compositions (O2, CO2 and CO) were measured. A simple flame-spread model was incorporated into the CESARE-CFD model to predict the mass release rate and HRR during the fire instead of providing it as an input that is required for most zone models. It was found that CESARE-CFD provided reasonable predictions of the magnitude and the trends for the temperatures in the burn room and the species concentrations, but over-predicted the temperatures in the adjacent room. From a life safety perspective, the CFD model conservatively predicted the concentrations of CO and CO2. The temperatures predicted by CFAST agreed well with the measurements in most areas. However, CFAST under-predicted the temperature in the lower layer of the room of fire origin and the concentration of CO in most areas. The PhD thesis, “Prediction of Fire Growth on Furniture Using CFD” by R. Pehrson[611] provides a good background on this topic. He has developed a fire growth calculation method that couples a CFD model with bench scale Cone Calorimeter test data for predicting the rate of flame spread on compartment contents such as furniture. The commercial CFD code TASCflow has been applied to solve the time averaged conservation equations using and algebraic multi-grid solver with mass weighted skewed upstream differencing for advection. The closure models include k - , for turbulence, eddy breakup for combustion following a single step irreversible reaction with an Arrhenius rate constant, finite difference radiation transfer, and conjugate heat transfer. Radiation properties are determined from concentrations of soot, CO2, and H2O using the narrow band model of Grosshandler[612] and exponential wide band curve fit model of Modak.[613] The growth in pyrolyzing area is predicted by treating flame spread as a series of piloted ignitions based on coupled gas-fluid boundary conditions. The mass loss rate from a given surface element

Modeling

345

follows the bench scale test data for input to the combustion prediction. The fire growth model has been tested against foam-fabric mattresses and chairs burned in the furniture calorimeter. In general, agreement between model and experiment for peak HRR, time to peak HRR, and total energy lost is within ±20%. Used as a proxy for the flame-spread velocity, the slope of the HRR curve predicted by the model agreed with experiment within + 20% for all but one case.

8 Fire Hazard Analysis

This chapter reviews the upholstered furniture fire problem with respect to fire hazard analysis. A large part of this material has been discussed before, albeit from different points of view; specifically, HRR and smoke and toxic gases are treated in the appropriate sections of Ch. 2. The reader is also referred to the hazard analysis chapter in the CBUF final report.[137] The fundamental hazard to life that a person can encounter during the course of a furniture fire is the exposure to a lethal or incapacitating atmosphere. This may consist of one or more of the following four elements: (1) high concentrations of toxic gases, (2) high levels of thermal radiation, (3) high temperature air and (4) smoke obscuration which can interfere with the ability to escape. The relative importance of these hazard elements varies according to the type of fire: well ventilated, propagating fire; under-ventilated propagating fire; non-propagating fire; and smoldering fire.

8.1.0

SMOLDERING FIRES

Smoldering fires can and do kill people, yet have been subjected to only limited study. Efforts to prevent smoldering ignitions have been 346

Fire Hazard Analysis

347

notable, both in the design of furniture and, potentially, in the design of cigarettes. Yet our ability to quantify or predict the details of smoldering fires is very limited. The state of the art has been reviewed recently by Ohlemiller,[71] but notably he cites no predictive models. An earlier review by Quintiere et al.[553] discussed CO production levels from a number of experimental fires in closed rooms. They observed that in two tests (only two were analyzed in detail) the smoldering mass loss rate continuously increased during the test and could be expressed as (Eq. 8-1)

m• = ct

where c varies from 5 × 10-5 to 10-4 g s-2. They also found that for those tests the yield of CO was about 0.1 kg/kg, and the effective heat of combustion was 11 MJ kg-1 for cotton batting and 15 MJ kg-1 for polyurethane foam. No model can be built on the basis of two data points, however, and more extensive analyses have not been forthcoming.

8.2.0

FLAMING FIRES

A fire in a room with ventilation will tend to stratify: a hot gas layer forms at the top, with cool, near-ambient conditions prevailing at the bottom. A thermal discontinuity, or interface, defines the boundary between the two layers. For our purposes, ventilation means an open window, a breaking-out window, or an open door. Forced-air ventilation is normally supplied at a slow enough flow rate that its effects can be ignored on most, except slow-growing, long fires. By contrast, if a room is nearly sealed, the momentum of the fire gases is often sufficient to mix the gases in the room fairly well; under some conditions, however, a stratified fire can also occur in a closed room. 8.2.1

Small Closed Rooms

A flaming fire in a small closed room presents some of the same issues as a smoldering fire in a small room. Oxygen becomes depleted, CO and other toxicant levels rise, and untenability can ensue. Since the room is closed, the combustion products, instead of exiting through openings, mix with the fresh air. Such fires usually show a fairly well mixed atmosphere, with no sharp demarcation between different layers. Similar to smoldering fires, this type of situation has also not been the subject of much

348

Fire Behavior of Upholstered Furniture and Mattresses

modeling efforts. As discussed in Ch. 2, a recent experimental study was conducted on this geometry using mice to monitor toxicity conditions.[181] The results were essentially independent of the composition of the furniture being burned. For the specimens tested, the gas concentrations necessary to cause incapacitation were between 17 and 27 g m-3, while lethality (LC50) was observed at between 21 and 37 g m-3. These values were computed simply as the grams of specimen mass lost, divided by the volume of the closed room. Thus, for a small bedroom of 20 m3, only around 0.6 kg of specimen needs to be burned before lethality can be expected to occur. 8.2.2

Open (Ventilated) Rooms

In many fires, the room of fire origin is ventilated, allowing combustion products to exit and new air to enter the space. This ventilation can happen in many ways: a window is open; a window breaks out during fire; a door is open; a door burns through during fire, etc. The distinguishing feature of such a fire is that, under most conditions, a two-layer pattern is established: hot, combustion-product laden gases are in the upper portion, while low-temperature, relatively clean atmosphere is in the lower portion. In such a well-ventilated room fire, hazard elements (1), (3), and (4) which were mentioned at the beginning of this chapter are mostly limited to the upper gas layer in the room. The hot, smoky and noxious gases can mix somewhat with fresh air at the interface and pollute the environment of the lower layer, but it is not likely that they will cause lethality in a short time or prevent a person, who remains completely within the lower layer, from escaping. However, when the temperature of the upper layer, ceiling and upper walls becomes sufficiently high, debilitating thermal radiation will be found throughout the room. This will occur before flashover is reached. In addition, the occupant will be exposed to direct thermal radiation from the burning item. One can expect to be safe in the lower layer for a certain length of time, but not indefinitely, if the fire keeps growing. By contrast, if the individual is directly exposed to the upper layer even for a modest time, incapacitation can be expected before escape can be completed. Thus, the basic hazard criterion can be expressed simply: Is the occupant’s head above or below the bottom of the hot gas layer? The above assumptions, proven out by measurements, formed the basis for the recommendations made by CBUF.[137] The times needed to reach incapacitation due to heat flux, smoke, narcotic gases (for example, CO and HCN), and irritant gases (HCl and

Fire Hazard Analysis

349

partially oxidized volatiles) at different heights in the room were measured in a number of the CBUF tests.[137] The times at which the thermal interface reached these heights were also determined for the tests. It was found that the criteria for incapacitation due to the irritant gases and the tenability limit for the visual obscuration were exceeded just as the interface descended to that level or at a time very soon thereafter. In every case, they occurred earlier than the limits for the thermal radiation and the narcotic gases. This was because of the dense mixture of partially burned volatiles in the ventilation starved upper layer. This confirmed that thermal interface height can be considered the height of demarcation between the survivable zone and the un-survivable zone. The interface between the upper and lower layers moves downward as the HRR in the room increases. For upholstered items, it was found that relationship exists between the interface height and the HRR in the ISO room,[63] based on full-scale furniture fire tests.[35][36] This relationship could also be calculated with the room fire model CFAST as seen in Fig. 8-1, using the measured HRR data in the room as input.[137] Since the interface height is quite tedious to measure experimentally in a room (and cannot be determined at all in a furniture calorimeter), it is fortunate that the CBUF findings demonstrate that a functional connection exists between the interface height and the HRR.

Figure 8-1. Measured interface heights compared to those calculated as a function of the HRR in the room.

350

Fire Behavior of Upholstered Furniture and Mattresses

To summarize the implications of the above findings, it was shown that for a ventilated room the exact nature of the toxic products and their toxic potency become unimportant to measure or to predict. If one wishes to define an escape strategy to protect against toxic products, a minimum time allowed for the interface to descend to a critical interface height could be specified. If 1.1 m were chosen to be the minimum acceptable interface height, the time at which the HRR reaches 400 kW would constitute the available escape time. The occupant would have to bend down and run or crawl out of the room within that time period. Thus, the time to reach 400 kW (if at all) becomes a primary measure of hazard to the occupant within the fire room. CBUF work did not explore much of the implications to persons located outside the fire room. General fire modeling results, however, normally indicate that for locations somewhat remote from the fire source, the peak HRR and the total heat release are two of the primary governing hazard variables. For larger fires, the HRR is eventually affected by the nature of the room enclosure (dimensions of the room and its openings, along with the thermophysical properties of the walls and ceiling). Thus, it is not practical to measure HRR in a standard room fire test and try to deduce how it would be modified if the furniture item were burning in a completely different room. A better approach is to measure the HRR in the furniture calorimeter which provides a free-burning condition. A relationship for the modification of the heat release history as a function of the characteristics of the room then needs to be established. Fortunately, there is a HRR threshold (which depends on the particular room) below which there is no significant effect of the enclosure. In the ISO room this was found to be about 500 kW, which is above the critical HRR at which people could no longer escape.[35][36][139] Thus, by the time that the room interaction is strong enough to impact the burning rate of the furniture, it has already exceeded the tolerance of the occupants. While the threshold HRR for the room interaction effect will depend on the particular room, the critical HRR for escape, which also depends on the room, will normally be below it. Therefore, the HRR history determined in the furniture calorimeter can be safely used in the hazard analysis to determine the available escape time from rooms. Another issue to consider is that if the occupants are required to stay in the room of fire origin for an extended period of time waiting to be

Fire Hazard Analysis

351

rescued, as they would in facilities for incapacitated persons, the thermal radiation flux in the lower layer must not exceed the tenability limit of about 2.5 kW m-2.[137] (Some additional studies have determined the time to incipient second-degree burn condition.)[554][555] The heat flux of 2.5 kW m-2 corresponds to a black-body radiation from a temperature of 185°C. From the temperature-rise versus peak-HRR relationship found in the NIST/BHFTI study, this corresponds to a peak HRR of 120 kW, assuming that the ambient temperature prior to the fire is 20°C.[35][36] Note that the furniture that passes the California TB 133 test must have a peak HRR < 80 kW, and therefore, easily meets the extended-stay thermal radiation criterion. If the occupants are able bodied and alert, a critical interface height and a minimum time to reach it can be specified by the regulator. In that case the maximum permissible HRR may be considerably higher than 120 kW. Another much less stringent requirement that could be made on the basis of fire hazard analysis would be that the peak HRR never get above some fraction of what is required for flashover.* That would provide little or no protection for the fire room occupants but would limit the large rates of smoke and toxic gas production that would threaten other people in adjacent or even remote regions in the building after flashover.

8.3.0

THE ROLE OF HRR

The HRR is the single most important variable describing fire hazard. The establishment of the role of HRR in hazard prediction and the optimization of its use is based on papers by Babrauskas and others.[8][122]– [126] One important advantage of HRR measurements is that, unlike many other fire tests, they provide data in engineering units which can be used in modeling. Once the HRR and the mass loss rate histories and the smoke and toxic gas yields are put into a room fire model, not only the interface height discussed above, but also the thermal radiation levels throughout the room, and the gas temperature, toxic gas concentrations and smoke obscuration in the upper layer can be determined. Fire spread to another furniture item depends on the distance between them and the thermal radiation from the burning chair which can be linked, at least approximately, to the HRR.[35][142] * Around 1 MW is commonly taken as a value that will not lead to flashover in the ISO 9705 standard test room, which is understood to simulate a typical bedroom with an open door.

352

Fire Behavior of Upholstered Furniture and Mattresses

The HRR required to produce flashover can be calculated based on the geometry of the room and the thermophysical properties of the linings. This can be done directly using a fire model such as CFAST.[159] For more approximate computations, simple formulas are available.[157] Such formulas require a steady-state HRR, which rarely happens with upholstered items. For more realistic HRR curve shapes, the issue has recently been reexamined.[556]

8.4.0

THE ROLE OF OTHER FACTORS

Having discussed the dominant role of the HRR in the fire hazard assessment, one can reflect on other hazard components, some of which are included in present day fire modeling: • Heat is lost as the distance away from the fire increases, but smoke and toxic combustion gases generally are not. The exception is HCl; it is readily lost on the building walls and contents along the way (and, incidentally, in human tissue, for example, breathing passages and lungs).[557][558] • The primary role of smoke is to impede the escape of individuals from the toxic and hot environment. It is very difficult, however, to equate obstruction of visibility with direct bodily damage that occurs from toxic gases and elevated temperature environments (see also Ch. 2). The work of Jin et al. provides some guidance here.[178] • Toxic gases can be narcotic, primarily CO and HCN, or irritant, such as HCl. Irritants (as well as CO2) increase the breathing rate and intensity, and thus increase the effects of the narcotics. The irritants are mostly incompletely oxidized pyrolysis products. • The hazard due to smoke and toxic gases depends on the mass loss rate, the dilution with fresh incoming air, and the yields of smoke and toxic gases, along with their toxic potencies.

Fire Hazard Analysis • The yields of smoke and toxic gases can depend on ventilation and other combustion factors. For fires with poor oxygen supply, CO generation tends to the dominant toxicity effect. • Toxic potency differences among commercial materials, as measured by bench-scale LC50 tests, have been found to be relatively small, compared to other effects such as those of mass loss rate, smoldering vs flaming, ventilation, etc. They do not justify a need for LC50 testing of all organic materials, as used to be required by regulators in New York State;[559] in November 1998, this regulation was repealed in NY State. • Real-scale LC50 data from high intensity room fires are even more tightly clustered.[179][180][185][200] The reason is that real-scale fires generate CO yields which can be much higher than those obtained in bench scale tests where the specimen is burned in a more adequately ventilated environment. Therefore the toxicity is dominated by CO. Furthermore, these CO levels are essentially independent of the product burned because most of the CO production in high intensity room fires is due to incomplete combustion of the carbon contained in the product burned.[190][191] The CO production rate increases rapidly as a room fire becomes O2 starved shortly before flashover, but further downstream, the CO levels may drop, if additional air is entrained. • The victim may be challenged by a combination of heat and oxygen deprivation; such combined effects on humans have not been studied in sufficient detail. • Smoldering fires present a challenge to modeling. The connection between mass loss and HRR is not as clear, because the combustion efficiency and the heat of reaction under smoldering conditions have not been well characterized. Also, no model exists for predicting the mass loss rates under smoldering conditions.

353

354

Fire Behavior of Upholstered Furniture and Mattresses

8.5.0

RELATIONSHIP OF HRR AND AVAILABLE ESCAPE TIME

The available escape time, as a measure of the hazard to life, can be estimated from tests of a single furniture item, even though the fire may eventually spread to other items in the room. By the time that the first item reaches a high enough HRR to ignite the second item (unless they are very close to each other, for example, curtains behind a sofa), the available escape time will have already been exceeded in most cases. The time from ignition to the time at which the HRR of the furniture item reaches the critical value, corresponding to the tenability limits of the room occupants, will depend on the location and size of the ignition source. However, if the available escape time is measured from the time of discovery of the fire (assumed by CBUF to occur at 50 kW) rather than from the time of ignition, the location and size of the ignition source is not critical. [137] As indicated earlier, the effect of ignition source size is also supported by Cleary, et. al.[135] and Söderbom et. al.[136] These observers found that although the starting part of the HRR curve was dependent on the size of the ignition source, the main part of the HRR curve was essentially independent of it. In the CBUF studies the fire is assumed to be large enough to be discovered by the room occupants when the HRR reaches 50 kW even if they are concerned with other activities at that time. Flame spread along a row of seating is governed by exactly the same physical relationships that govern the spread along a single specimen. If the 180 s average heat release value is < 65 kW m-2,[130] flame propagation will not occur. Similarly, spread from row-to-row is also governed by the HRR of the burning item, which along with the spacing between the items, determines the irradiance of the second item. The critical flux for ignition of most upholstered furniture items is quite similar.[142] (Items covered with wool and certain PVC coated fabrics may be exceptions.) Thus, to restrict the row-to-row spread, it is again only necessary to limit the peak HRR generated by the first item. Inter-item spread is discussed in Sec. 2.8.

8.6.0

HAZARD PREDICTIONS BASED ON MODELING

Several papers discussing tenability limits derived by models, especially Hazard I, have been discussed earlier, for upholstered item fires: Braun et al. in school bus fires;[297][298] Andersson,[132] Cleary et al.[135] and

Fire Hazard Analysis

355

Purser[206] in upholstered item fires. The National Fire Protection Research Foundation conducted a risk assessment project; the first case studied was upholstered furniture burning in one-and-two family dwellings.[560][561] For this study, an expert panel determined which of the large number of test data on various furniture constructions and arrangement to choose; they also chose other parameters including room size and floor plans, in a Delphi type of exercise. The results obtained with Hazard I appeared in reasonable agreement with the national estimates for fire losses, including demography, age distribution, housing type, time of day, smoke detector presence, and ignition source estimates. The method could aid in risk assessment of upholstered furniture with known ignitability, flame spread, burning rate, combustible mass, and smoke and toxic product evolution. Among the early papers using computer modeling for evaluation of furniture fires was one by Bukowski.[562] The Fire (Toxic) Hazard Assessment computer model was used to evaluate the potential for hazard reduction by the modification of the combustion properties of chairs, love seats, and sofas in a residential occupancy consisting of bedroom, hall, and living room. The potential benefits of these modifications were compared with the effects of variations in room size and construction to determine if they would be realized across a range of housing sizes and types. Upper and lower layer temperatures, interface layer height, optical density and fractional lethal dose in the upper layer were calculated for each 10 s of the fire duration. The results demonstrate that the greatest benefit is obtained by the reduction of the mass loss (burning) rate of the item regardless of room size, even if the means to reduce the burning rate results in an increase of smoke yield and toxic potency of the material. The author warns that the results are meant to serve as directions for further work, and should not be used without experimental verification. Quintiere examined the hazards due to furniture fires and their relationship to criteria prescribed by the California TB 133 standard.[563] Theoretical analyses are given to quantify the hazards due to the ignition of an adjoining item, flashover, CO toxicity, and reduced visibility due to smoke, and typical parametric values are given for several materials. Examples of calculated relationships between HRR and radiant flux are shown in Fig. 8-2 and of HRR values leading to flashover as functions of room dimensions in Fig. 8-3.

356

Figure 8-2. Radiant heat flux required to cause piloted ignition in terms of HRR.

Fire Behavior of Upholstered Furniture and Mattresses

PILOTED IGNITION AT 1.5 FT. FROM CHAIR

Fire Hazard Analysis 357

Figure 8-3. HRR at the onset of flashover for a typical room.

358

Fire Behavior of Upholstered Furniture and Mattresses

9 Conclusions

In the US, upholstered furniture and mattresses have been associated with a higher fraction of residential fire deaths than any other single cause. Thus, it is not surprising that this particular category of combustible has also been studied and modeled in greater detail than any other manufactured commodity. The large number of individual components, the way in which they are arranged into composites, and the great variability in furniture geometry make this study challenging indeed. Nevertheless, progress has been made in predicting the course, especially the HRR, of upholstered item fires from the knowledge of the bench-scale fire properties of individual components, or of composites. There are areas of notable strength, yet many areas of weakness remain. During the last decade, most of the advances in this area have been in the regulatory arena, not in the area of fundamental science or engineering studies. The most notable exception has been the CBUF research program, which substantially advanced an engineering understanding of certain aspects of upholstered item fires. For characterizing cigarette ignitability there is as yet no encompassing theory available, but progress has been made in modeling the process. Testing procedures vary greatly in fine details, but are all conceptually similar and yield generally similar results. Most commercial categories of fabric and paddings have been tested and generic performance guidelines are available. Cigarette construction parameters which would reduce ignition propensity have been defined. 358

Conclusions

359

There is little scientific information for quantifying the processes that lead from smoldering to flaming of furniture. No model is available for predicting or characterizing the small-flame ignition of upholstered items. Flame spread over upholstered furniture has not been investigated in depth. Considering the many possible geometrical arrangements, this may be very difficult. The effects of frame material and geometric style effects have been examined only over a small range of variations. Multiple-item burning has yet to be examined beyond prediction of the ignition of the second item. The California TB 133 standard, which in its current version encompasses standard HRR measuring technology for furniture, has had a major impact in recent years on the furniture marketplace. The 80 kW peak HRR value required for passing the test is quite stringent, thus, a whole new generation of furniture components, primarily interliners, became available which allowed new benchmarks in fire safety to be reached. The CBUF program developed procedures to use room-scale, furniture calorimeter-scale, and Cone Calorimeter-scale HRR measurements interchangeably, with modeling used to translate the results from one scale to another. For the first time, a yet-smaller scale is incorporated. The CBUF strategy allows the Cone Calorimeter results for certain upholstered composites to be predicted from measurements on the individual components. Verification with a larger variety of components and composites is needed. To the user, one of the most important facts is unchanged from what was stated in the first edition of this book: cigarette ignition resistance and flame ignition resistance of upholstered items do not necessarily go hand in hand. Thus, furniture cannot be considered to have good or bad fire properties unless we either restrict our interest to smoldering or flaming fires alone, or else the pertinent conclusion has been separately assessed for both types of fires. We must also emphasize that good resistance to flame ignition in a regulatory test with small or modest ignition sources does not necessarily imply a low rate of fire development when items are exposed to some ignition sources encountered in real life. This point has often been missed by regulators. Therefore, it is important to point out that most of the ignitability tests in regulatory use prescribe rather modest ignition sources. However, the California TB 133 Test and the larger ignition sources of the U.K. furniture tests come closer to the case, where, say, a newspaper has been ignited on top of a sofa.

Exercises and Solutions

EXERCISES Chapter 1 1.

Why is study of upholstered item fire important?

2.

Name some of the components of upholstered chairs and sofas, and of mattresses.

Chapter 2 1.

When a heat flux of 50 kW m-2 is impinging onto an upholstered sofa, its ignition time is 20 s. Estimate the ignition time if the heat flux is only 25 kW m-2.

2.

A full-scale heat release rate test was run on an upholstered chair and the HRR was reported to be 575 kW m-2. Do you believe or disbelieve this value? Why?

3.

A bench-scale HRR test was run on a sample from an upholstered chair. The 180 average HRR at an exposure of 35 kW m-2 was determined to be 225 kW m-2. If a full-scale California TB 133 test is run on this chair, is it likely to pass? 360

Exercises and Solutions 4.

A mass loss rate of 0.133 kg s-1 was measured for a burning sofa. At a distance of 1.5 m away, what will be the heat flux expected on a potential ignition target which is oriented vertically?

5.

A bedroom 2.4 m wide 3.6 m deep and 2.4 m high has a door 0.8 m wide and 2.0 m high. The door is only 1/4-open, that is, open to 1/4 of the full opening width. What HRR will it take to cause flashover in this bedroom?

6.

A mattress is tested in a bench-scale calorimeter and its smoke production is measured. An extinction area of 200 m2 kg-1 is reported. Suppose now the size of the test specimen is quadrupled. What will be the specific extinction area?

7.

A hotel banquet room is 10 × 20 × 4 m high. The exit door is at far end of the 20-m length and it has a red, nonilluminated Exit sign. The doors are closed to the room and there is negligible air movement through the ventilation system. A stack of upholstered chairs is burning and it has been determined that the extinction area for the chairs 200 m2 kg-1. How much chair mass can be lost before the Exit sign will cease to be visible to an occupant at the far end of the room from it?

8.

A room fire test was conducted on a chair in a nearlyclosed room. The concentrations of gases were measured and it was found that CO2 = 4.4%, CO = 2500 ppm, HCN = 30 ppm, and O2 = 14.7%. The meters for HCl and HBr did not move off the zero mark. Viewing the 30-minute test through the viewing window, the technician noticed that there is a rat running around in the room; this was not surprising, as the laboratory had problems with rodents. If the rat is unable to find its way out, is it likely to be alive at the end of the test?

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Fire Behavior of Upholstered Furniture and Mattresses

Chapter 3 1.

Compare component and mockup tests; give an example for each.

2.

Which type of test, component or mockup, gives more reliable results, and why?

3.

Give an example of a country and of a state where regulatory cigarette ignition standards are in force?

4.

Name some criteria for fire test methods for upholstered furniture items.

5.

How can ignitability be expressed?

6.

What are some of the special considerations in the fire testing of stacking chairs?

7.

What was the main finding of various studies with respect to the effects of various ignition sources and their point of application to the upholstered furniture items? How can the results be used in estimating escape time?

8.

What situation in a real-life fire does the external radiant heating in a bench scale test represent? In which test is this considered?

9.

The use of the California Technical Bulletin 133 furniture calorimeter standard for high-risk occupancies has been advocated by such organizations as the National Association of Fire Marshals and the American Furniture Manufacturers Association. What are its main features and what is being measured?

10.

What are the main differences between the static ASTM 662 (NBS smoke chamber), which measures the specific optical density, and the dynamic smoke measurements (e.g., Cone Calorimeter, Room Calorimeter)?

11.

Are there meaningful differences in in vivo toxicity measurement results for different organic materials?

Exercises and Solutions 12.

Under what conditions is hazard due to toxic pyrolysis products most important?

Chapter 4 1.

Which European Standard prescribes different size ignition sources for various occupancies?

2.

At what heat flux do typical upholstered furniture items ignite?

3.

What are some disadvantages of using wood cribs and newspaper as ignition sources?

4.

For a full determination of the fire hazard, where should the ignition sources be applied to an upholstered chair or sofa?

5.

What is the lowest incident heat flux required to ignite a typical upholstered furniture item? Based on this finding, what is the upper limit for the peak HRR of an upholstered chair that would insure that it would not cause radiant ignition of another chair separated by a distance of 0.76 meters?

Chapter 5 1.

What are the main fabric types and how do they affect flammability?

2.

Were similar HRRs obtained when identical upholstered chairs were tested in the ISO room and in the furniture calorimeter?

3.

Roughly at what ranges of HRR measured in the Cone Calorimeter for a furniture composite would you expect a full-scale furniture fire to be (a) propagating and (b) nonpropagating?

4.

What heat flux, measured on the floor of a room, is a good indication that flashover has occurred? Why?

363

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Fire Behavior of Upholstered Furniture and Mattresses 5.

What are some of the fire test parameters determined in the Cone Calorimeter that can be referred to in the test criteria?

Chapter 6 1.

Given the cover fabrics and padding of the upholstered furniture items in a hotel room, you are to estimate the flammability hazard. What three methods are available to you?

2.

Which components and spatial arrangements have been shown to affect the ignitability by cigarettes and small flames?

3.

Which fabrics and paddings have both relatively high cigarette and small flame ignition resistance?

4.

Generally, how do thermoplastic fabrics and paddings behave when exposed to (a) burning cigarettes; (b) small flames? (c) How is this behavior affected by flame retardant treatments?

5.

Discuss the same for cellulosic fabrics.

6.

Discuss the same for PU foam.

7.

What role does bedding (sheets, blankets, etc.) play in mattress ignition by (a) cigarettes? (b) small flames?

8.

Can the post-ignition behavior of upholstered furniture items be predicted from small flame ignition behavior? Explain your answer.

9.

What is the role of interliners and where are they often used?

Exercises and Solutions 10.

Some materials, e.g., wool and certain flame retardant PVC fabrics, and neoprene do not ignite easily and do not burn readily in post-ignition fires. What other hazards do they represent?

Chapter 7 1.

A mattress is burning with cylindrical-shaped flame at the middle. The radius of flame cylinder is measured to be 0.4 m and the flame height is measured to be 1.1 m. What is the HRR of the mattress?

2.

A wingback chair uses a rigid polyurethane frame. The 180-s average Cone Calorimeter HRR, measured at 25 kW m-2, is 172 kW m-2, and the combustible mass of the chair is 25 kg. Find the expected peak HRR for the full-scale item.

3.

Estimate the peak HRR and the total heat release of a twoseat sofa using the CBUF Model I. The following data were obtained for the specimen: Total combustible mass = 45.8 kg; mass of soft parts = 13.3 kg; peak Cone Calorimeter HRR = 368 kW m-2; 300-s average heat release rate = 116 kW m-2; total heat release = 35 MJ m-2; effective heat of combustion = 19 MJ kg-1; and ignition time = 28 s.

4.

For the same sofa as described in Problem 3, find (a) the time to peak HRR, and (b) the time to untenability in the ISO-size room. The additional needed information from the Cone Calorimeter data is: q·´´pk#2 = 349 kW m-2; q·´´ trough = 266 kW m-2; and tpk#1 = 49 s.

5.

Suppose that at some time in the future, the supplier of the fabric and the supplier of the foam are both required to measure the 180 second average heat release rates of their products in the Cone Calorimeter at an exposure of 35 kW/m2 using the testing strategy referred to in Sec. 7.3. The furniture manufacturer would simply combine these data in a general correlation formula, described in reference 544, to predict the 180 second average heat release rate of the composite (fabric + foam) that would be

365

366

Fire Behavior of Upholstered Furniture and Mattresses obtained in a standard Cone Calorimeter test. This formula would be: Where is the predicted 180-second average heat release rate of the furniture composite? Is the 180-second average heat release rate of a standard reference foam? Are the 180-second average heat release rates measured individually for the foam and the fabric that will be used on the upholstered furniture item, and is the measured 180-second average heat release rate of a composite consisting of the fabric and the standard reference foam. A chair of plain rectilinear construction has a rigid polyurethane frame and a combustible mass of 30 kg. The values of the heat release rates provided by the suppliers was 200 and 300 kW/m2 respectively for the fabric and foam to be used in the chair and 400 kW/m2 for the composite consisting of the fabric over a the standard reference foam. The heat release rate of the standard reference foam by itself is 250 kW/m2. What would be the predicted peak heat release rate of the chair if it were tested in the furniture calorimeter?

Chapter 8 1.

An upholstered chair has been burned in the furniture calorimeter and it was found that 12 kg of mass was lost during the test. In the case of an actual fire in a closed room involving only this piece of furniture, how large would the room have to be for lethality not to be expected to occur for a trapped victim? How large would the room have to be if even incapacitation is to be avoided?

2.

A man was sitting in his easy chair reading a book when he nodded off to sleep and the cigarette he was smoking dropped into a crevice. He soon woke up and decided to lie down on his cot to take a nap, forgetting all about the

Exercises and Solutions cigarette. After nearly an hour he woke up when his face began to feel hot. Then he realized that a flaming fire was rapidly building up on his chair. He knew that he had to get out of there as soon as he could or he would be grilled by the radiant heat that seemed to be coming down from the whole ceiling. Yet if he were to stand up so that his face penetrated the hot toxic mixture of fire gases and air in the upper part of the room, he would be an immediate casualty. He would never get out of even this very small room, alive. He would have to stay bent over and run or crawl out. What is the height of this relatively cool and toxic gas free layer, in the lower part of the room, through which he must make his escape? Assume that the dimensions of this room and its open doorway are identical to those of the ISO fire test room. Also assume that the chair was in compliance with a local fire code which required that it could not have a peak HRR in excess of 250 kW.

SOLUTIONS Chapter 1 1.

Upholstered furniture item fires represent only about 10 percent of all fires but perhaps as much as 40 percent of the fire deaths.

2.

Cover fabrics; padding; interliners; welt cord; frames; spring supports; springs; and innersprings.

Chapter 2 1.

Using Eq. (2.4), it can be taken that ignition time is proportional to 1/q·´´ext2. Thus, the ignition time is estimated to be (50/25)2 = 80 s.

367

368

Fire Behavior of Upholstered Furniture and Mattresses 2.

The proper units for measuring whole furniture items are kW, not kW m-2. The latter quantity is used only for measuring bench-scale samples. The reason is because the exposed surface area is precisely known for bench-scale samples, but is not possible to easily or accurately measure for a full-scale item.

3.

No, since any upholstered item showing a 180 s average HRR > 180 kW m-2 when exposed to 35 kW m-2 in the Cone Calorimeter will be self propagating in the TB133 room fire test and will have a peak HRR >> 80 kW. Therefore, it would fail the TB133 test.

4.

Using Eq. (2.19), the solution is found as 20.5 kW m-2. This is more than the minimum ignition flux of most upholstered furniture composites, so if the target is another sofa, it is likely to get ignited.

5.

The surfaces of the walls and the ceiling add up to 37.4 m2. The opening width is 0.2 m and the height is 2.0 m. Thus, Eq. (2.26) gives 506 kW as the flashover level.

6.

The extinction area will remain 200 m2 kg-1. While a specimen which is 4 times as large will be estimated to have a mass loss rate of 4 times that for the smaller one, the mass is normalized out in the definition of the specific extinction area; thus increasing the specimen size will not change its value.

7.

If it is required that Sv = 20 m, then the maximum value of the extinction coefficient is k = 0.15 m-1 according to Eq. (2.41) for reflecting signs. The extinction area for the chairs is given as &f = 200 m2 kg-1. The volume of the room is 800 m3. Using Eq. (2.42), the permissible value of m = 0.15x800/200 = 0.60 kg. This is a very small mass and is likely to be less than the combustible mass of a single banquet chair.

8.

Noting that oxygen values are to be inserted in percent while the remaining values are in ppm, Eq. (2.49) is evaluated as:

Exercises and Solutions Since FED > 1, the rat problem in the building is likely to be reduced. It is also concluded that the technician was prudent in not being in the room while running the test. Chapter 3 1.

In component tests, (e.g., the UFAC standards) a single component, such as cover fabric, padding, or welt cord, is tested in an assembly with a standard material, e.g., fabric with a standard foam padding, and foam padding with a standard fabric. In mockup tests (e.g., BS 5862, mockups tested in the California TB 133), the fabric, padding,, and interliner that will be used in the full scale furniture item are tested together in the same arrangement as in a planned line of furniture. The components are held together in a standard frame. However, the frames, webbing, etc. are not reproduced in the present mockup tests, and the angle between the seat cushion and back is normally 90 degrees in these tests, unlike in many furniture pieces.

2.

The mockup tests produce more reliable results than the component tests. The effect of the interaction of such furniture components as cover fabric and padding is only considered in the mockup tests. The standard fabrics used in component tests are usually not worst case materials, and may permit some quite flammable padding to pass. Similarly, standard foams may permit the passing of flammable fabrics, etc.

3.

The state of California and the U.K.

4.

Some of the fire test criteria that might be used for the acceptance of upholstered furniture items include: the absence of smoldering ignition; and the individual requirements that the char length or area, peak heat release rate, peak upper air temperature in the burn room, total mass loss, smoke and combustion product yields, and toxic effects on animals must not exceed their assigned critical values.

369

370

Fire Behavior of Upholstered Furniture and Mattresses 5.

Critical flux for ignition; ignition time; ignition temperature.

6.

A single stacking chair rarely presents a significant fire load. However, if many chairs are stacked vertically or arranged in rows such that the fire can spread from chair to chair along a row and to adjacent rows, they present large fire loads and the opportunity for rapid flame spread and high HRRs.

7.

The maximum HRR was not affected by these variables provided that they were in a range such that a sustained ignition was guaranteed, but the time from ignition to the maximum HRR varied greatly. The escape time should be expressed as the time from the probable detection of the fire (In the CBUF program this detection time was assumed to be the time at which the HRR reached 50 kW.) to the time at which the peak HRR occurred.

8.

The external radiant flux in a bench scale HRR test represents the radiant exposure of the furniture item due to the hot upper layer of combustion products, the hot walls and ceiling and the other burning items in the room. This situation is considered in the Cone Calorimeter, where the incident radiant flux can be varied up to 100 kWm-2.

9.

The TB 133 is a room fire test for upholstered furniture. An actual furniture item or large standard mockup is placed in a rear corner away from the doorway. A square gas burner is placed at the seat/back juncture. The gas flow is adjusted to provide a heat release rate of 18 kW for 90 seconds. Oxygen calorimetry is used to determine the HRR and the total HR. The smoke opacity and the CO concentration are also measured in the room.

10.

In the ASTM 662 test, the obscuration due to the smoke from a smoldering or flaming fire is measured in a closed chamber. The measurements are affected by smoke deposition on the walls of the chamber. Since the mass loss rate is not measured, the quantity of smoke per kg of specimen mass loss cannot be determined. In the dynamic methods, the smoke flows continuously through the system. This is

Exercises and Solutions often done in conjunction with measurements of other hazard factors, e.g., HRR, toxic gas concentrations, etc. 11.

Within the very wide confidence limits for in vivo experiments, there is little difference between the materials usually used in furniture, and, in fact, between most organic materials.

12.

In cigarette initiated upholstered item fires in a closed room, where smoldering can last for extended periods, and under post-flashover conditions. In both cases, casualties often occur in rooms other than the fire room, because in most cases the toxic gases will travel throughout the dwelling.

Chapter 4 1.

The U.K. Furniture Fire Safety Regulations.

2.

The critical heat flux for the ignition of typical furniture items falls in the range between 7 and 20 kWm-2.

3.

Wood crib assembly is labor intensive, and the manner in which the cribs collapse cannot be predicted but can affect the outcome. The properties of the wood can vary along the length of a single stick. The intensity of a newspaper ignition source will depend on the packing. Both the newspaper and crib ignition sources depend on the relative humidity. Neither source has been found to be sufficiently reproducible.

4.

Because different materials are used in various parts of furniture items, e.g., inside and outside, seat, back, and arms, etc., ignition sources should ideally be applied to each location containing a specific cover fabric/padding combination, and to each geometric configuration, e.g., flat areas, crevices, junctions of seat, side, and back, underside, etc.

5.

CBUF found that 7 kWm-2 was the smallest radiant flux which would ignite furniture composites formed from the common foams and fabrics being used in Europe.

371

372

Fire Behavior of Upholstered Furniture and Mattresses According to Eq. (2.21) in Ch. 2 of this book, a peak HRR of 636 kW is required to produce a radiant flux of 7.0 kWm-2 at a separation distance of 0.76 m. Therefore, a suitable upper limit for the full scale peak HRR of the chair, based on no ignitions at a separation distance of 0.76 m, would be 600 kW.

Chapter 5 1.

Many char forming fabrics (e.g., cotton, rayon, linen, jute, and wool) tend to smolder when exposed to cigarettes; exposed to small flames they can protect padding for brief periods till the char breaks open and exposes the padding, or the fabric ignites. Thermoplastic fabrics (nylon, polyester, olefin, polyethylene, polypropylene) melt, absorbing heat from cigarettes and thus reducing probability of ignition. Exposed to small flames, they melt and shrink away from the ignition source, exposing the padding.

2.

Similar peak HRR’s were found in both tests when the peak HRR was 500 kW or below. Above that range the HRR’s in the ISO room were greater due to significant levels of thermal radiation from the hot upper gas layer.

3.

The furniture fire was found to be propagating if the 300 second average HRR measured in the Cone Calorimeter at an incident flux of 35 kW-2 was greater than 180 kWm-2. It was found to be non-propagating if the 300 second average was less than110 kWm-2. For 300 second averages between 110 and 180 kWm-2, it could be either propagating or non-propagating.

4.

A heat flux of 20 kW m-2 on the floor of a room can be taken as an indication of flashover. Essentially all light combustible materials in the room will have been ignited by the time that the radiant flux has reached that level. Thus the heat release rate will be increasing rapidly, leading to ventilation limiting conditions which cause flames to emerge from the doorway.

Exercises and Solutions 5.

Peak HRR (kWm -2 ),180 s or 300 s average HRR (kWm -2 ), total heat released (kJm-2 ); time to ignition (s), critical flux for ignition (kWm-2 ), smoke yield (m2 kg-1) and toxic gas yields (kg kg-1).

Chapter 6 1.

a) Generic information about the relative propensity to ignite from cigarettes or small flames of various cover fabric/padding combinations. b) Performing standard, component, mockup, or full-scale tests of the material combinations or upholstered items. c) Modeling of the fire, provided appropriate input data are available or can be measured.

2.

Cover fabric; padding; welt cords, tufting (cigarette ignition only); interliners; flat areas or junctions of flat and vertical cushions.

3.

Fabrics: wool, some PVC coated fabrics; paddings: neoprene, some highly flame retardant treated PU foams, flame and smolder resistant treated cotton batting (smolder resistance requires higher concentrations).

4.

a) Thermoplastic fabrics weighing 10-12 oz/yd generally resist cigarette ignition, and thermoplastic (mostly polyester) batting used between the fabric and padding generally increases cigarette ignition resistance. b) They do not easily ignite from small flames but shrink and melt, exposing the padding. c) In fires, they melt, form pools or ablate, and burn.

5.

a,b) Cellulosic fabrics generally have low cigarette ignition resistance, especially heavier weights. This is not improved by the common flame-retardant treatments because they rely on increasing the charring (smoldering) tendency of the fabrics. Cotton batting can be treated for cigarette and flame resistance (Note: cigarette ignition resistance requires higher concentrations).

373

374

Fire Behavior of Upholstered Furniture and Mattresses c) Cellulosic fabrics burn readily while cotton batting, especially when flame retarded, does not burn readily. 6.

a) The cigarette ignition resistance of PU foam depends on the cover fabric—it will smolder along with a strongly smoldering fabric but not with a barely smoldering fabric. It can be improved by flame retardant treatments. b, c) Untreated PU burns readily when exposed to small flames. Commercial flame retardant treatments for PU vary from almost no effect to high flame resistance.

7.

a) Bedding will generally not ignite from cigarettes unless the cigarette is covered by it. b) bedding will generally ignite from small flames, and can expose the mattress to a large additional fire load.

8.

No. After ignition the flame-retardant properties may be overwhelmed. Also, the effect of padding and frames, (including the manner in which they collapse) etc., becomes more important.

9.

Interliners protect the padding from smoldering or flaming fabrics. They are occasionally used in upholstered furniture items, airplane seats, etc.

10.

Through smoldering and generation of smoke and toxic gases.

Chapter 7 1.

Using Eq. (7-2), the values of rp and zf are known, and it is required to find q·. Then,  z f + 1.0 2 2 r p  q =    0 .2 3 5 

5/2

 1.1 + 1.0 2 2 × 0 .4  =  0 .2 3 5 

5/2

= 104 kW

Exercises and Solutions 2.

Since the chair uses a plastic frame, only the NIST correlation is applicable. Wingback chairs represent a highly convoluted design, thus, style factor = 1.5. Using Eq. (7.11), the full-scale peak HRR is = 0.63 × 172 × 25 × 0.18 × 1.5 = 731 kW.

3.

First, the value of x1 is determined. Using Eq. (7.15), x1 = (13.3)1.25(1.0)(368 + 116)0.7(15 + 28)-0.7 = 138.3 This value is > 115, thus q·fs = x2 where x2 = 880 + 500(13.3)0.7(1.0)(19/35)1.4 = 2180 kW This sofa was actually tested in the CBUF program and the measured HRR was 1991 kW. The total heat release is determined as: qtotal = 0.9 × 13.3 × 19 + 2.1(45.8 – 13.3)1.5 = 617 MJ. The measured HR was 658 MJ.

4.

The time to peak HRR is given by: tpk = 30 + 4900(0.8)(13.3)0.3(349)-0.5(266)-0.5(49 + 200)0.2 = 114 s. The actual time which was measured was 168 s. The untenability time is computed as: tUT = 1.5 × 105(0.8)(13.3)-0.6(266)-0.8(349)-0.5(49 – 10)0.15 = 27 s. The actual untenability time measured in the room calorimeter was 40 s.

5.

Using the given formula, the predicted 180 second average heat release rate of the composite in the Cone Calorimeter is 403 kW/m2. Since the chair would have a plastic frame, the NIST correlation should be used. The style factor is 1.0. Because polyurethane is a charring plastic, the frame factor is 0.18. The flux used in the Cone Calorimeter tests

375

376

Fire Behavior of Upholstered Furniture and Mattresses was 35 kW/m2. The mass factor is 30. Equation (7.13) yields a predicted value of 980 kW.

Chapter 8 1.

According to Sec. 8.2.1, the ranges of the fire gas concentrations necessary to cause incapacitation and lethality (LC50) are 17 to 27 g m-3 and 21 to 37 g m-3, respectively. They are based on closed room experiments which determine the specimen mass loss required to produce incapacitation and lethality when animals are exposed to the wellmixed atmosphere. These determinations were made for a large range of upholstery materials. The concentrations were calculated by dividing the specimen mass loss by the volume of the room. Given the anticipated combustible mass loss in grams, it can be divided by the lethal concentration to obtain the maximum volume at which lethality would be expected to occur. Thus the volume of the room must be greater than12000/21 = 571 m3. Assuming a normal ceiling height of 2.4 m, the area will be 238 m2. This is quite a large room of 15.4 × 15.4 m. The area is closer to the entire floor area of an average house than it is to one room. To also avoid incapacitation, the volume must be greater than 706 m3. This could represent a room of 17.2 × 17. 2 m.

2.

Figure 8.1 shows the measured height of the interface in the ISO room as a function of the HRR. In the linear region this can be represented by the formula: h = 1.5 m – 10-3 HRR m (kW)-1. For 250 kW the height of the region available for escape is 1.25 m. (approximately 4 ft). For room and doorway dimensions different than those of the ISO room, the interface height can be calculated with a room fire model like FAST.

Abbreviations

ASTM

American Society for Testing and Materials

BHF

California Bureau of Home Furnishings

BHFTI

California Bureau of Home Furnishings and Thermal Insulation (formerly BHF)

BIFMA

Business and Institutional Furniture Manufacturers Association, International

BRI

Building Research Institute (Japan)

CBUF

Combustion Behavior of Upholstered Furniture

CEN

Commission for European Standardization

CMHR

Combustion Modified High Resiliency PU Foam

Conf

Conference

DBI

Danish Fire Technology Institute

EC

European Community

EGOLF

European Group of Official Laboratories

EU

European Union

FC

Furniture Calorimeter

FIRA

UK Furniture Industry Research Association

FMC

FMC Corporation Ltd. (UK)

FMPA

Forschungs-und Materialprufüngsanstalt BadenWürttemberg (Germany) 377

378

Fire Behavior of Upholstered Furniture and Mattresses

FR

Fire-Retardant

FRI

Fire Research Institute (Japan)

FRS

Fire Research Station (UK)

HR

High Resiliency PU Foam

HRR

Heat Release Rate

IMO

International Maritime Organization

INT

International

ISO

International Organization for Standardization

LIFT

Lateral Ignition and Flame Spread Test

LNE

Laboratoire National d’ Essais (France)

NBS

(U.S.) National Bureau of Standards

NBSIR

NBS Internal Report

NFPA

National Fire Protection Association

NFR

Not Fire Retarded

NIST

National Institute of Standards and Technology (formerly NBS)

NISTIR

NIST Internal Report

NP

Neoprene

NTIS

National Technical Information Service (U.S.)

PU

Polyurethane

RAPRA

Rubber and Plastics Research Association

SFPE

Society of Fire Protection Engineers

SP

Swedish National Testing and Research Institute; also Special Publication

SR

Smolder Resistant

TB

California Bureau of Home Furnishings Technical Bulletin

TN

Technical Note

UFAC

Upholstered Furniture Action Council

UJNR

U.S./Japan Government Cooperative Program on Natural Resources

VTT

Technical Research Center of Finland

References

1. Babrauskas, V., and Krasny, J. F., Fire Behavior of Upholstered Furniture, NBS Monograph 173, NBS, Gaithersburg, MD (1985) 2. Damant, G. H., A Bibliography of Published Information on Furniture Flammability, J. Consumer Product Flammability, Part I, 5:245–248 (1978); Part II, 7:127–129 (1980); Part III (coauthor: Wortman, P. S.), 8:235–238 (1981) 3. References to Literature on the Fire Hazards of Furniture and Furnishings, Library Bibliography No. 182, FRS, Borehamwood, Herts, (1979); supplement (1982) 4. Fires in Furniture, (Building Research Establishment Digest No. 285), FRS, Borehamwood, Herts (1984) 5. Smith, A. G., Improving the Fire Behavior of Furniture, British Plastic Federation Conference Flame Retardants 90, London (1990) 6. Babrauskas, V., and Krasny, J. F., Upholstered Furniture and Mattresses, Chapter 2–12, Fire Protection Handbook, 17th ed., NFPA, Quincy, MA (1991) 7. Fire Safety of Upholstered Furniture - The Full Report of the European Commission Research Programme CBUF (B. Sundström, ed.), Interscience Communications Ltd., London (1995) 8. Babrauskas, V., Bench-Scale Predictions of Mattress and Upholstered Chair Fires—Similarities and Differences, ASTM SP 1233, ASTM, Philadelphia, PA (1994); also NISTIR 5152, NIST, Gaithersburg, MD (1993)

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23. The Business and Institutional Furniture Manufacturer’s Association (BIFMA) First Generation Voluntary Upholstered Furniture Flammability Standard for Business and Institutional Markets, BIFMA, Grand Rapids, MI (1980) 24. Code of Federal Regulations, Part 1632, Standard for the Flammability of Mattresses (and Mattress Pads), FF pp. 4–72 (1983) 25. NFPA 260, Methods of Tests and Classification System for Cigarette Ignition Resistance of Components of Upholstered Furniture, NFPA, Quincy, MA 26. NFPA 261, Method of Test for Determining Resistance of Mock-up Upholstered Furniture Material Assemblies to Ignition by Smoldering Cigarettes, NFPA, Quincy, MA 27. ASTM E-1352, Test Method for Cigarette Ignition Resistance of Mock-Up Furniture Assemblies, ASTM, Philadelphia, PA 28. ASTM E-1353, Test Methods for Cigarette Ignition Resistance of Components of Upholstered Furniture, ASTM, Philadelphia, PA 29. Flammability Information Package, BHFTI, North Highlands, CA 30. TB 133, Flammability Test Procedure for Seating Furniture in for Use in Public Occupancies, BHFTI, North Highlands, CA (1991) 31. TB 129, Flammability Test Procedure for Mattresses for Use in Public Buildings, BHFTI, North Highlands, CA (1993) 32. ASTM E 1537, Standard Fire Test Method for Fire Testing Real Scale Furniture Items, ASTM, Philadelphia, PA 33. ASTM E 1590, Test Method for Fire Testing of Real Scale Mattresses, ASTM, Philadelphia, PA 34. Zoeller, L. P., Who’s Minding the Regulatory Store? Public-Private Sector Cooperation in Winning Acceptance of TB 133, Fire and Materials, 1st Intl. Conference, pp. 73–79, Interscience Communications Ltd., London (1992) 35. Parker, W. J., Tu, K-M., Nurbakhsh, S., and Damant, G. H., Furniture Flammability: An Investigation of the California Technical Bulletin 133 Test - Part III: Full Scale Chair Burns, NISTIR 4375, NIST, Gaithersburg, MD (1990) 36. Parker, W. J., Tu, K. -M., Nurbakhsh, S., and Damant, G., Chair Burns in the TB 1933 Room, the ASTM Room, the Furniture Calorimeter and the Cone Calorimeter, Fire Safety Science, 3rd Intl. Symposium, pp. 699–708, Interscience Communications Ltd., London (1994) 37. NFPA 101, Life Safety Code, NFPA, Quincy, MA 38. Dull, R. P., Office Furnishings Requirements: Today and Tomorrow, Fire and Materials, 1st Intl. Conference, pp. 81-88, Interscience Communications Ltd., London (1992)

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39. ASTM E 1474, Test Method for Determining the Heat Release Rate of Upholstered and Mattress Components or Composites Using a Bench Scale Oxygen Calorimeter, ASTM, Philadelphia, PA 40. NFPA 264A, Standard Method of Test of Heat Release Rates of Upholstered Furniture Components or Composites and Mattresses Using an Oxygen Consumption Calorimeter, NFPA, Quincy, MA 41. ISO 5660, Fire Tests–Reaction to Fire–Rate of Heat Release from Building Products (Cone Method), ISO, Geneva 42. Heat Release in Fires, (V. Babrauskas and S. J. Grayson, eds.), Elsevier Applied Science, London and New York (1992) 43. Babrauskas, V., Cone Calorimeter Annotated Bibliography, 1982–1991, TN 1296, NIST, Gaithersburg, MD (1992) 44. Consumer Protection: The Furnishings and (Fire) (Safety) Regulations 1988, No. 1324, and The Furniture and Furnishings (Fire) (Safety) (Amendment) Regulations 1989, No. 2358, HMSO, London 45. A Guide to the Furniture and Furnishings (Fire) (Safety) Regulations, Department of Trade and Industry, Central Office of Information, HMSO, London 46. BS 5852, Part 1, Methods of Test for the Ignitability by Smokers Materials of Upholstered Composites for Seating; Part 2, Methods of Test for the Ignitability of Upholstered Composites for Seating by Flaming Sources, British Standards Institution, London, 47. BS 6807, Assessment of the Ignitability of Mattresses, Divans, and Bed Bases with Primary and Secondary Ignition Sources, British Standards Institution, London 48. Standards of the Crown Suppliers (previously PSA), London: FR 3, Fire Barrier Standards for Upholstery (Seating and Bedding). FR 4, Composite Upholstery Ignition Standard (Seating and Bedding) DOE/TCS/FTS5, Methods of Test for Assessing the Ignitability of Mattresses and Bedcovers by Smouldering and Flaming Ignition Sources (1982). DOE/PSA/FR 5, Flammability of Beds and Bedding (1978). FR10, Ignition Source Standard. DOE/TCS/TCS 15, Method of Test for Assessing the Ignitability of a Vandalized Mattress by Flaming Ignition Source, DOE/TCS, London 49. Marchant, R. P., Working with the New UK Regulations, Papers of the 1st European Conference on Furniture Flammability (1988) 50. Paul, K. T., and King, D. A., The Burning Behavior of Domestic Upholstered Chairs Containing Different Types of Polyurethane Foams, Fire Safety J., 16:389–410 (1990) 51. Paul, K. T., Fire and Polyurethane Foam: Furniture Testing and Specification, Rev. Prog. Coloration, 20:53–68 (1990) 52. Survey of European Fire Service Views on Fire Hazard in Domestic Furniture, Greater Manchester Fire Service (1989)

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552. Babrauskas, V., Baroudi, D., Myllymäki, J., and Kokkala, M., The Cone Calorimeter Used for Predictions of the Full-scale Burning Behaviour of Upholstered Furniture, Proc. Fourth Intl. Fire and Materials Conf., pp. 203–217, Interscience Communications Ltd., London (1995) 553. Quintiere, J. G., Birky, M., Macdonald, F., and Smith, G., An Analysis of Smoldering Fires in Closed Compartments and their Hazard Due to Carbon Monoxide, Fire and Materials, 6:99–110 (1982) 554. Stoll, A. M., and Chianta, M. A., Heat Transfer through Fabrics as Related to Thermal Injuries, Transactions, New York Academy of Sciences, 33:649–670 (1971) 555. Derksen, W. L., Monahan, T. L., and DeLhery, The Temperature Associated with Radiant Energy Skin Burns, in Temperature, - Its Measurement and Control in Science and Industry, 13(3):171–175, Reinhold Publ. Co., New York (1961) 556. Peacock, R. D., Reneke, P. A., Bukowski, R. W., and Babrauskas, V., Defining Flashover for Fire Hazard Calculations, Fire Safety J., 32:331–345 (1999) 557. Galloway, F. M., Hirschler, M. M., and Smith, G. F., Generation of Hydrogen Chloride Under Forced Conditions of Minimal Decay for Modelling Purposes, 13th International Conference on Fire Safety, pp. 81– 103, Millbrae, CA (1988) 558. Galloway, F. M., Hirschler, M. M., and Smith, G. F., Surface Parameters from Small Scale Experiments Used Measuring for HCl Transport and Decay in Fire Atmospheres, Fire and Materials, 15:181–189 (1991) 559. New York State Statute L. 1982, c.552, Building Materials and Finishes Data File, Secretary of State, Albany, NY 560. Clarke, F. B., III, and Steele, S., How Do Burning Products Affect Life Safety? Fire J., 84:48–52, 54, 55 (1990) 561. Stiefel, S. W., Bukowski, R. W., Hall, J. R., Jr., and Clarke, F. B., Fire Risk Assessment Method, NISTIR 90-4243, NIST, Gaithersburg, MD (1990) 562. Bukowski, R. W., Evaluation of Furniture-Fire Hazard Using a HazardAssessment Computer Model, Fire and Materials, 5:159–166 (1985) 563. Quintiere, J. G., Furniture Flammability: An Investigation of the California Technical Bulletin 133 Test. Part 1: Measuring the Hazards of Furniture Fires NISTIR 4360, NIST, Gaithersburg, MD (1990) 564. BS EN 1021, Furniture - Assessment of the Ignitability of Upholstered Furniture, Part 1: Ignition Source: Smouldering Cigarette; Part 2: Ignition Source: Match Flame Equivalent, British Standards Institution, London 565. BS EN 597, Assessment of the Ignitability of Mattresses and Upholstered Bed Bases, Part 1: Ignition Sources: Smoldering Cigarette; Part 2: Ignition Source: Match Flame Equivalent, British Standards Institution, London

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566. BS 7177, Specification of Resistance to Ignition of Mattresses, Divans and Bed Bases, British Standards Institution, London 567. BS 7175, British Standard Method for the Ignitability of Bedcovers and Pillows by Smoldering and Flaming Ignitions Sources, British Standards Institute, London. 568. Wanna, J. T., Rouse, C. A., Chen, P. L., Henderson, G. E., and Greear, L. C., Smoldering Potential and Characterization of Used Upholstery Fabrics, J. of Fire Sciences, 14:379–392 (1996) 569. Standard Test Method for Fire Testing of Stacked Chairs (ASTM E 1822), ASTM, West Conshohocken, PA (1999) 570. Babrauskas, V., and Krasny, J. F., Upholstered Furniture Transition from Smoldering to Flaming, J. Foresnic Sciences, 1029–1031 (Nov. 1997) 571. Tu, K. M., and Aaronson, A., The Lower Level of Detection in the ASTM Burn Room, Proc. Intl. Conference on Fire Safety, 20:22–32 (1995) 572. BS 7176, Resistance to Ignition of Upholstered Furniture for Non-Domestic Seatings by Testing Composites, British Standards Institution, London 573. Chen, P., Kellog, D. S., Waymack, B. E., and McRae, D. D., A Model of Fabric Smoldering Ignition by Cartridge Heaters, J. of Fire Sciences, 16:75–89 (1998) 574. Kellog, D. S., Waymack, B. E., McRae, D. D., Chen, P., and Dwyer, R. W., Initiation of Smoldering Combustion in Cellulosic Fabrics, J. of Fire Sciences, 16:90–104 (1998) 575. Gandhi, S., and Spivak, S. M., A Study of Smoldering Conditions in Upholstery Fabric Using Thermal Imaging, Textile Research J., 68:687–696 (1998) 576. Steward, L. J., The U.S. Home Product Report, 1989–1993, Forms and Types of Materials First Ignited in Fires, NFPA, Quincy, MA 02269-9101 577. Rohr, K. D., The U.S. Home Product Report, 1991–1995, Forms and Types of Materials First Ignited in Fires, NFPA, Quincy, MA 02269-9101 (1998) 578. Rohr, K. D., The U.S. Home Product Report, 1992–1996, Forms and Types of Materials First Ignited in Fires, NFPA, Quincy, MA 02269-9101 (1999) 579. Rohr, K. D., An Update on What’s Burning in Homes, Fire and Materials, Proc. 5th Intl. Conference, pp. 43–52 (1998) 580. Directorate for Epidemiology and Health Sciences, CPAS, Small Open Flame Ignitions of Upholstered Furniture, Final Report, CPSC, Bethesda, MD (1997) 581. Hirschler, M. M., Repeatability and Reproducibility of Fire Tests for Cigarette Ignition of Upholstered Furniture Composites, Fire and Materials, 22:25– 37 (1998)

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582. Nurbakhsh, S., and McCormack, J., A Review of the Technical Bulletin 129, Full Scale Test Method for the Flammability of Mattresses for Public Occupancies, J. of Fire Sciences, 16:105–124 (1998) 583. Peacock, R. D., and Braun, E., Fire Safety of Passenger Trains, Phase I: Material Evaluation (Cone Calorimeter), NISTIR 6132, NIST, Gaithersburg, MD (1999) 584. Wanna, J. T., Rouse, C. A., Chen, P. L., Henderson, G. E., and Greear, L. C., Smoldering Potential and Characterization of Used Upholstery Fabrics, J. of Fire Sciences, 14:379–392 (1996) 585. Wanna, J. T., Polo, A., and Schettine, D., Smoldering Potential of Used Upholstery Fabrics: Unsoiled vs. Soiled, J. of Fire Sciences, 14:144–158 (1996) 586. Dyakonov, A. J., Grider, D. A., and Ihrig, A. M., Smolder of Cellulosic Fabrics IV, Participation of Dye and Bleach Residues, J. of Fire Sciences, 17:438–458 (1999) 587. Nurbakhsh, S., and McCormack, J., A Review of the Technical Bulletin 129, Full Scale Test Method for the Flammability of Mattresses for Public Occupancies, J. of Fire Sciences, 16:105–124 (1998) 588. D’Silva, A. P., and Sorensen, N., The Flammability Aspects of Decorative Trimmings: Part 1 - Flammability of Trimmings used in Upholstered Furniture, J. of Fire Sciences, 14:26–49 (1996) 589. Greear, L., Hudson, W. Z., Jupe, R., Pinion, D. O., and Wanna, J. T., Ignition Responses of Fifty Upholstery Fabrics to Commercial Cigarettes, J. of Fire Sciences, 14:413–425 (1996) 590. Lewis, L. S., Morton, M. J., Norman, V., Ihrig, A. M, and Rhyne, A. L., The Effects of Upholstery Fabric Properties on Fabric Ignitabilities by Smoldering Cigarettes, J. of Fire Sciences, 13:445–471 (1995) 591. Hirschler, M. M., Comparison of the Propensity of Cigarettes to Ignite Upholstered Furniture Fabrics and Cotton Ducks (500 Fabric Study), Fire and Materials, 21:123–141 (1997) 592. Rhyne, A. L., Comparison of the Propensity of Cigarettes to Ignite Upholstered Furniture Fabrics and Cotton Ducks (500 Fabric Study): A Second Opinion, Fire and Materials, 22:175–178 (1998) 593. Paul, K. T., Assessment of Cigarettes of Reduced Ignition Power and Their Role to Reduce Fire Risks of Upholstered Seating, Mattresses, and Bed Assemblies, J. of Fire Sciences, 18:28–73 (2000) 594. Norman, V., Comments on “Comparison of the Propensity of Cigarettes to Ignite Upholstered Furniture Fabrics and Cotton Ducks (500 Fabric Study)” by M. M. Hirschler, Letter to the Editor, Fire and Materials, 22:129–130 (1998) 595. Eberhardt, K. R., Levenson, M. S., and Gann, R. G., Fabrics for Testing the Ignition Propensity of Cigarettes, Fire and Materials, 21:259–264 (1997)

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596. Wanna, J. T., and Chen, P. L., Results of a Preliminary Study of Ignitions in Flat vs. Crevice Configurations, J. of Fire Sciences, 16:15–24 (1998) 597. Goodall, C. A., Colwell, R. J., Shaw, K., and Vollam, S., The Effect of Ventilation on the Fire Behavior of Upholstered Furniture, Interflam ’96, Interscience Communications, Ltd, London (1996) 598. Ohlemiller, T. J., and Shields, J. R., Burning Behavior of Selected Automotive Parts from a Minivan, NISTIR 6143, NIST, Gaithersburg, MD (1998) 599. Peacock, R. D., Reneke, P. A., Jones, W. W., Bukowski, R. W., and Babrauskas, V., Concepts for Fire Protection of Passenger Rail Transportation Vehicles: Past, Present, and Future, Fire and Materials, 19:71–87 (1995) 600. Peacock, R. D., Bukowski, R. W., and Markos, S. H., Evaluation of Passenger Train Car Materials in the Cone Calorimeter, Fire and Materials, 23:53–62 (1999) 601. Peacock, R. D., and Braun, E., Fire Safety of Passenger Trains: Phase I: Material Evaluation (Cone Calorimeter), NISTIR 6132, NIST, Gaithersburg, MD (1999) 602. Bukowski, R. W., and Markos, S. H., Fire Safety of Trains: Hazard Assessment, Fire Risk and Hazard Assessment, Research Application Symposium, Research and Practice:Bridging the Gap, pp.7–37, National Fire Protection Research Foundation, San Francisco (1998) 603. BS6853, Standard Code of Practice for Fire Precautions in Design and Construction of Railway Passenger Rolling Stock, British Standards Institution, London 604. DIN 5510, Preventive Railway Fire Protection in Railway Vehicles, Deutsche Industrial Norm, Berlin 605. UIC Code 564-2, Regulations Relating to the Fire Protection and FireFighting Measures in Passenger-Carrying Railway Vehicles or Assimilated Vehicles Used on International Services, International Union of Railroad Standards 606. Ogle, R. A., and Schumacher, J. L., Fire Patterns on Upholstered Furniture: Smoldering vs. Flaming Combustion, Fire Technology, 34:247–265 (1998) 607. Parker, W. J., A Procedure for Predicting the Heat Release Rate of Furniture Composites from Measurements on their Components, Fire Safety Science: Proc. of the Fifth Intl. Symposium, (Yuji Hasemi, ed.) International Association for Fire Safety Science, pp. 129–140 (1997) 608. McGrattan, K., Baum, H. R., Rehm, R. G., Hamins, A., and Forney, G. P., Fire Dynamics Simulator, Technical Reference Guide, NISTIR 6467, NIST (January 2000)

422

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609. Luo, M., and Beck, V., A Study of Non-Flashover and Flashover Fires in a Full Scale Multi-room Building, Fire Safety Journal, 26:191–219 (1966) 610. Luo, M., He, Y., and Beck, V., Application of Field Model and Two-zone Model to Flashover Fires in a Full-scale Multi-room Single Level Building, Fire Safety Journal, 29:1–25 (1997) 611. Pehrson, R., Prediction of Fire Growth on Furniture Using CFD, Ph.D. Thesis, Worcester Polytechnic Institute (1999) 612. Grosshandler, W. L., RADCAL: A Narrow Band Model for Radiation Calculations in a Combustion Environment, Technical Note 1402, NIST, (1993) 613. Modak, A. T., Radiation from Products of Combustion, Fire Research 1:339–361 (1979) 614. Yii, H. W., Effect of Surface Area and Thickness on Fire Loads, Fire Engineering Report 00/13, School of Engineering, University of Canterbury, Christchurch, N.Z. (2000) 615. Creif, H., Hurd, R., and King, D., Europur Studies on the Burn Behavior of Upholstered Furniture, Cellular Polymers, 14 (1995) 616 Janssens, M. L., Garabedian, A., and Gray, W., Establishment of International Standards Organization (ISO) 5660 Acceptance Criteria for Fire Restricting Materials Used on High Speed Craft, Final Report to U. S. Coast Guard, Southwest Research Institute, San Antonio, TX, available from NTIS, CGD-22-98 (1998) 617. Standard Test Method for Fire Testing of Stacked Chairs (ASTM E 1822), ASTM, West Conshohocken, PA (1999)

Index

Accident statistics 7–10, 163, 355 Aircraft 147–150, 297, 298 Air flow, wind 31, 34, 160, 223, 225, 230, 231 Air permeability 213–215, 231 Alkali metal ions 24, 25, 90, 91, 99–101, 210–216, 219, 229, 232–235 Area factor 281 Arson 15, 96, 104, 116, 117, 252, 257, 264, 293 ASTM (American Society for Testing and Materials) Life Safety Code 12 Room corner test. See also Corner tests 63, 128, 134, 145 D 1692 147 D 2843 153 D 3675 142, 143, 295, 296 D 4100 153 E 162 34, 48, 123, 124, 142, 147, 295, 296 E 176 67 E 622 147, 295 E 648 296 E 662 143, 147, 295 E 1352 11, 87 E 1353 11, 87 E 1357 11 E 1474 119–122 E 1590 11

E 1678 159, 160 E 1822 135 F 1550M 117 Auto-ignition 31, 32

Barrier materials. See Interliners Batting blended 212, 218, 278, 279, 305 cellulosic. See also Cotton batting cotton 21, 26–29, 87, 89, 92, 97, 117, 118, 124, 146, 175, 180, 182, 185, 189, 212–218, 236, 239–243, 247, 248, 254–259, 263, 286–290, 291, 301, 302, 305, 316, 340, 347 miscellaneous 13, 263, 305 polyester 2, 28, 48–50, 91, 107, 113, 124, 174, 175, 180, 189, 212, 216–219, 240, 243, 245, 255, 256, 260–264, 272, 277, 279, 280, 286–289, 291, 292, 305, 310, 316 Bedding 2, 5, 7–10, 30, 39, 49, 96, 97, 101, 108–110, 114–116, 136–138, 165, 174, 175, 197, 198, 200, 201, 211, 217, 221, 235, 239, 287–292, 296, 305 Business and Industrial Furniture Manufacturers Association (BIFMA) 12, 85, 87, 97, 101, 119, 127, 138, 222, 224

423

424

Fire Behavior of Upholstered Furniture and Mattresses

BIFMA/CPSC toxicity test 87–89, 97 Blankets. See Bedding Borax, boric acid 24, 215, 218, 263, 288, 290, 291 Boston Fire Department Test 106, 123, 124, 127, 252, 253, 191, 261 Box springs 29, 197, 290 BS (British Standards) 14, 98, 102 BS 5852 12, 93–95, 108–114, 160, 167, 219, 234, 235, 257 BS 6401 151 BS 6807 12, 96, 108–110, 114, 115 BS 6853 296, 310 BS 7175 96–98, 108 BS 7176 114 BS 7177 96, 98, 108 BS EN 597 96, 98, 108 BS EN 1021 92, 93, 108 Burn injury 351 Burning rate 20, 24, 40, 52, 57, 61–63, 76, 126, 178, 200, 201, 221, 223, 260, 270, 272, 273, 323, 324, 331, 350, 355

California Technical Bulletins 11, 98, 101, 117–119 TB 116 10, 11, 93, 96, 97 TB 117 10, 11, 93, 96, 213, 300 TB 129 11, 135–137 TB 133 11, 127–135, 354, 359 Canadian upholstered furniture investigation 97, 99 CBUF 1, 2, 7–10, 14, 19–22, 45–64, 80, 81, 104–107, 119, 121–123, 127, 130, 141, 166, 177, 178, 181, 182, 195, 196, 201, 204, 241, 247, 249, 255, 260, 269, 271, 275–277, 303, 315, 320–341, 346, 349, 350, 354, 358, 359 Cellulosic material thermal behavior 19, 21, 22, 24, 30 Char, char forming, charring. See also pyrolyis, smoldering 16–19, 21–28, 42, 93, 174, 184, 188, 191, 199, 210, 215, 238, 249, 250, 256, 257, 270, 278, 281, 300, 305

Char length 88–99, 101, 117, 118, 227 Cigarette. See also Smoldering burn rate 24, 231, 233 burn temperature 23, 25, 221–224 characteristics 24, 220, 227–237 heat flux, heat release 164, 220, 221 ignition 5–11, 21, 22, 24, 26–28, 30, 83, 220–222 ignition propensity 4, 5, 10, 25, 29, 169, 171, 175, 180, 181, 204, 207– 220, 225–237, 243, 263, 265, 269, 274, 279, 288, 297, 309, 315–319, 358 low ignition propensity cigarettes 225–229 ignition propensity tests 229–237 ignition resistance 207–219, 229, 239 effect of configuration 219 fabrics 213–217 interliners 218 moisture 219 padding 217, 218 welt cords 218 ignition standards and tests 10–15, 24, 83–102, 109, 110–116, 229–237 interaction with upholstered item 208, 220–225, 282, 316 low ignition propensity cigarettes 225–237 packing (definition) 220 safety legislation 225–229 Combustion modified, high resiliency (CMHR) foam. See FR foam Combustion. See also Pyrolysis 18–21, 25, 26, 31, 32, 41, 55, 63, 68, 74, 76, 77, 79, 93, 97, 98, 103, 115, 116, 152, 155–157, 174, 216, 250, 256, 263, 277, 306–308, 342–345 efficiency 277 heat of 42–50, 65, 70, 74, 80, 104, 121, 140, 141, 149, 163, 171, 178, 208, 249, 256, 260–263, 286, 337, 340, 347 products. See Smoke, Tenability, Toxicity Commission for European Standardization (CEN) 14, 28, 190

Index

Cone Calorimeter. See also Heat release, Heat release rate 6, 12, 14, 41 test method 12, 16, 17, 40, 41, 69, 70, 107, 117–122, 140–142, 146, 152–154, 179, 196–199, 204–206, 230, 241–243, 247–251, 255, 260–262 Configuration, style. See also Construction, Crevice furniture 2–5, 42, 55, 84, 95, 191, 192, 208, 211, 216, 219, 244, 246, 250, 257–259, 271, 272, 282, 288, 323, 331–339, 335 room configuration 67, 74, 335, 352, 359, 371 test configuration 113, 116, 130, 153, 229, 235, 236, 280, 282 Construction, geometry. See also Configuration furniture 2–5, 15, 28, 48–50, 61, 104, 107, 111, 114, 145, 197, 209, 246, 270, 272, 275–279, 281, 284, 290, 293, 294, 301, 303, 316, 327, 329, 331–335, 358 fabric 21, 25, 100, 182, 214, 223, 232, 244, 333 Corner tests. See also ASTM, ISO 136, 137, 141, 209, 272 CPSC (Consumer Products Safety Administration) 8, 11, 83, 86–91, 97–102, 139, 180, 211, 225 Crevice as point of ignition 88–95, 107, 128, 177, 209, 211, 221 configuration, geometry 99–102, 169, 171, 213, 219, 223 test results 106, 219, 223, 236, 239, 246, 285, 299, 300, 307, 319 Crown Suppliers (DOE/PSA) (U.K.) Tests 95, 97, 113, 116, 130, 146, 288

Decorative trim test 91 Decubitus pad tests 289 Detection, detectable 18, 21, 39, 52, 98, 116, 129, 146, 337, 370

425

Emissivity 24, 31 Escape time. See also Incapacitation, Tenability, Visibility 64, 66, 72, 80, 82, 106, 132, 133, 147, 181, 295, 303, 316, 318, 338, 346, 348–350, 352, 354 Evaporation 21, 50 Extinction, extinguishability 21, 145, 154, 263, 269, 319 extinction area (smoke tests) 67–71, 155 extinction coefficient (smoke tests) 43– 45, 68, 72, 303, 304 self-extinction 28, 123, 137, 147, 154, 189, 208, 282, 316 self-extinction (from smoldering) 208, 282, 316

Fabrics acetate 302 acrylic 20, 21, 48, 50, 78, 166, 169, 180, 190, 209–211, 217, 219, 238–243, 250, 251, 253, 259, 260, 275, 277, 279–282, 286, 290, 291, 297, 304, 305 aluminized 4, 91, 92, 150, 209, 218, 265, 291, 297, 303, 315 blends 36, 48, 49, 87, 100, 101, 110, 166, 169, 170, 180, 185, 189, 190, 198, 235, 238–240, 242, 250–254, 260, 263, 269, 276–281, 286, 288, 291, 292, 297, 304, 305, 328 cellulosic. See also Fabric, cotton 2, 20, 28, 48, 50, 90, 92, 99, 101, 111, 164, 181, 209–219, 232, 233, 238, 241, 245, 250, 260, 265, 273, 274, 288, 299, 300, 302, 304 cotton 2, 4, 7, 23–25, 28, 29, 48–50, 60, 87, 90, 93, 98, 100, 101, 160, 168, 169, 180, 183, 185, 188, 190, 204–210, 213, 216, 217, 220, 223, 229, 232–236, 239–244, 247, 250, 252, 254, 257–260, 263–271, 275–279, 281–284, 286, 287, 290–292, 296, 297, 300–310, 312– 314, 316, 340, 341

426

Fire Behavior of Upholstered Furniture and Mattresses

ferex 298 Kevlar™ 50, 140, 208, 218, 242, 245, 251, 294, 297, 307 modacrylic 124, 239, 240, 242, 250–252, 265–267, 278, 279, 288, 292, 297, 303, 304, 310, 312, 314 Nomex™ 150, 183, 218, 219 nylon. See also Thermoplastics 78, 92, 150, 170, 176, 180, 183, 190, 208, 211, 213, 214, 218, 238–243, 245, 249–253, 258, 261, 267–269, 277, 279–281, 285, 286, 292, 296–298, 303, 308, 315 olefin (polypropylene). See also Thermoplastics 176, 180, 184, 207, 213, 214, 238–254, 257–261, 275, 277, 280–284, 286, 297, 299, 300, 301, 304 polyester. See also Thermoplastics 36, 48–50, 56, 92, 109, 110, 170, 190, 208, 210, 213, 219, 238, 239, 242, 244, 245, 249–252, 262, 267, 269–271, 275–277, 280, 281, 290, 294, 297, 298, 301, 308, 310, 312, 314 PVC, vinyl 30, 49, 79, 92, 124, 170, 176, 180, 183, 185, 188, 209, 211–213, 238, 240–245, 250, 252, 253, 258–261, 266, 267, 276, 277, 279, 281, 286, 287, 290–299, 301–305, 310, 312, 314, 315, 354 rayon 16, 24, 185, 210, 243, 251, 281, 297, 308, 328 standard fabrics. See Standard materials thermoplastic. See also nylon, olefin, polyester viscose. See also rayon, cellulosics 49, 110, 169, 198, 235, 238–240, 269, 276–280, 298, 301, 305, 310, 312–314 wool 22, 49, 50, 78, 92, 97, 107, 110, 145, 150, 169–176, 184, 185, 189, 190, 198, 208–213, 217, 219, 238–242, 245, 249–254, 260, 269, 273, 275–282, 288, 290, 293, 296–298, 301–305, 308, 310, 312–315, 354

effect of air permeability 213–215, 231 backcoating 22, 93, 208, 209, 215, 238, 250, 260, 261, 280 drycleaning 114, 215 finishes. See also alkali metal ions 208, 211, 215, 229, 232, 239, 310 laundering, soiling 92, 100, 215 tension 94, 102, 113, 114, 121, 184, 202, 210, 216, 249, 250, 255 thermal properties 208 fabric flammability tests 117, 119, 148, 170 vertical 117, 122, 123, 145, 148, 189, 190 MVSS 302 145, 147, 189, 292, 293 CFR Part 1610, formerly CS 191-53 119, 170 Federal Aviation Administration (FAA) 17, 18, 149, 150, 190, 247, 298, 315 Fire Research Station (U.K.) (FRS) 51, 55, 56, 106, 107, 128, 141, 142, 153, 175, 198, 211, 277, 281 Flame spread 34–39, 56, 62, 92, 104, 118, 124, 142–149, 169, 175, 187, 198, 204, 209, 261, 264, 269–273, 282, 285–289, 316, 319, 321–328, 332, 335, 342–345 Flashover 63–66, 82, 137, 144, 157, 158, 180, 182, 193, 200, 201, 273, 287, 290, 291, 294, 295, 299, 303, 308, 320, 330, 343, 344, 348, 351–355, 357 Foam. See Polyurethane, Latex, Neoprene Frames (upholstered furniture) 2, 4, 17, 21, 49, 50, 55, 89, 94, 104, 105, 111, 117, 122, 125, 129, 132–136, 149, 183, 192, 195–198, 244–247, 258, 270–272, 275, 295, 298, 299, 302, 324, 332–337, 359 Frame factor 332, 333 Fuel load 105, 146, 272, 273, 282 Furniture construction (geometry, configuration, style) geometry 15, 18, 102, 106, 171, 197, 271, 279, 281, 301, 316, 329, 358

Index

Furniture calorimeter 12–17, 39–46, 52–56, 62, 65–67, 70, 86, 103, 107, 125–127, 131, 134, 141, 142, 150, 153, 180, 181, 187, 190–192, 195, 196, 198–206, 244, 252, 257, 259, 266, 271, 274–278, 281, 282, 285, 286, 293, 294, 303, 307, 310, 311, 315, 321–323, 329, 332, 333, 339, 345, 349, 350, 359

Glow. See also Char, Combustion, Smolder 18, 20, 23–25, 28, 42, 98, 115, 117, 146, 221, 231, 343

Hazard analysis 348–357 factors 352–354 hazard predictions 354–357 role of HRR 351, 352, 354 Heat flux. See also Cone Calorimeter Heat of gasification 20, 149, 150, 270, 340, 342 Heat release, heat release rate (HRR). See also Cone Calorimeter background, fundamentals 6, 12, 18, 28, 34, 39–42, 50, 55, 56, 61, 64–66, 75–81, 140–143 effect of moisture 274 heat release/time curves 16, 51, 104, 181, 200, 202, 203, 247–249, 259, 271, 345 heat release rate of ignition sources 166, 168, 174, 176–182 heat release models 16, 33, 320–345 time to peak 43, 51, 52, 104, 106, 176, 180–182, 198, 199, 204, 274, 277, 278, 294, 296, 299, 306, 336–338, 345 relationship to flame spread 142–144, 299, 300, 345 flashover 63, 64, 193 ignitability 239, 278 mass loss rate 74, 75 room temperature 12, 192 smoke production 66, 67, 70, 71, 304 tenability 350, 351, 354 toxicity 75–77, 80, 156–159, 194, 308

427

role in hazard analysis 14–16, 189, 190, 346–357 High resiliency (HR) foam. See FR Polyurethane Humidity. See Moisture

Ignitability 12, 14, 15, 17, 57, 60, 183–186, 239 Ignition. See also Cigarette critical heat flux (irradiance) for 23, 31–33, 57, 58, 104, 261, 354 flaming 8, 11, 41, 30–34, 209, 237–244, 316, 319 flaming ignition tests 102–151, 188–190, 281 piloted 31–33, 120, 154, 179, 184, 237, 241, 244, 298, 300, 301, 344, 356 location (point) of 106, 111–132, 136–139, 146, 180, 246, 299, 354 relationship to HRR 278 role in modeling 324–328, 344 smoldering (cigarette) 21–27, 29, 30, 71, 83–102, 155, 213, 217, 316, 319, 346 sources 5, 12–17, 27, 29, 36, 51, 52, 55, 103, 106, 107, 109–128, 132, 136–138, 143, 145, 146, 148, 163–186, 188, 243, 280 temperature 22, 24, 25, 31–33, 104, 158, 159, 325 test methods 83–102 time to 24, 31–33, 39, 57, 58, 104, 106, 121, 124, 146, 180, 183, 185, 241, 243, 327, 334, 335, 340 Incapacitation. See also Escape, Tenable, Visibility 66, 75, 78, 82, 156, 160, 180, 205, 310, 315, 346, 348, 349, 351 Innersprings 4, 17, 277, 290, 335 Inter-item fire spread. See also Stacking chairs 12, 15, 41, 56–62, 66, 105, 107, 135, 145, 146, 182, 289–302, 351, 354, 355, 359 Interaction with enclosure. See also Room fires 53, 62, 63, 67, 141, 201, 271, 343, 350 Interface (gas layers) 16, 40, 63, 80, 321, 347–351, 355

428

Fire Behavior of Upholstered Furniture and Mattresses

relationship to HRR 349 Interliners 6, 7, 13, 33, 41, 71, 80–92, 98, 105, 107–109, 127, 139, 146, 151, 166, 168, 170, 173, 174, 178–182, 185, 186, 192–194, 197, 198, 200, 204, 209, 212, 218, 239, 240–244, 247, 250–252, 259–270, 276–282, 290–298, 303, 307, 315, 333, 334, 336, 340, 359 characterization 264–266 ISO 160, 162, 168, 169 ISO 5657 143, 150, 179 ISO 5660 120–122 ISO 5924 152, 153 ISO 8191 85, 93, 98, 108 ISO 9705 77, 134, 196, 201, 206, 297, 337, 339, 349, 350

Labeling 13, 15, 90, 91, 93, 95, 100, 213 Latex 13, 30, 49, 109, 112, 113, 185, 199, 209, 235, 236, 289–291, 297, 302, 303, 305, 328 LC 50. See Toxicity Leaching, effect of on padding 255, 256, 288, 339 Leather 50, 196, 238, 245, 247, 249, 275, 280 LIFT 35, 323, 324 LOI 145, 150, 151, 187, 188, 191, 208, 261, 262

Mattresses 7–13, 20, 21, 25, 31, 32, 40, 47, 52–54, 61–65, 75, 85, 86, 96, 97, 108–110, 114–120, 134–137, 143, 147, 170, 197, 200, 211, 215, 217, 218, 235, 236, 239, 274–277, 287–292, 295, 303–305, 309, 315, 325–328, 334, 335, 338, 339, 343–345 prison mattresses 49, 215 Mass factor 281, 285, 332–334 Mass loss 46, 70, 81, 84, 98, 108–112, 121, 124, 131, 134, 138, 145, 148, 155, 160, 179, 188, 191, 237, 251, 261, 286, 305

Mass loss rate 19, 20, 27, 36, 37, 42, 50, 55, 58, 60, 61, 67, 69–71, 74, 75, 77, 81, 139, 140, 149, 156, 201, 244, 257–259, 274, 288, 308, 342, 344, 347, 351, 352, 355 Modeling 320–345 aircraft fire model 148 CFAST model 66, 195, 321, 324, 344, 349, 352 CFD model 321, 342–345 CESARE CFD mattress model 343, 344 fire growth model 35, 39 furniture fire models 5, 16, 17, 25, 26, 105, 244, 321–330 CBUF mattress model 324–328 convolution model 328–331 composite model 16, 196, 321, 322, 339 -341 correlation models 42, 105, 323, 331–339 CBUF chair and sofa model 333–338 NIST correlation model 331–333 Dietenberger model 323, 324 HAZARD model 80, 81, 180, 303, 321, 354 ISO fire modeling 162 literature review listings 321 piloted ignition model 33 room fire models 6, 7, 70, 78, 157, 321, 322, 343, 344, room zone model 321 smoldering fire models (includes cigarettes) 216, 225, 226, 228, 229 time to ignite model 33 toxicity model-N-gas model 79, 80, 156–158, 205, 309, 347

Moisture 31, 37, 171, 219–221, 223, 271, 273, 274, 339 Molded furniture 262 Motor vehicles 145–147, 292–294

Index

Neoprene 138, 183, 184, 209, 212, 217, 218, 239, 241, 247, 254–256, 259, 260, 263, 265, 266, 269, 281, 282, 288, 290–294, 300, 304, 305, 307, 310, 313, 314 National Fire Protection Association (NFPA) NFPA 260 11, 87 NFPA 261 11, 87 NFPA 264 120–122 NFPA 269 76 NFPA 701 144 Novoloid. See also Fabrics, Kevlar™, Nomex™ 209, 266, 269 Nordtest 14, 85, 114, 115, 125–127, 140–142, 174, 188, 189, 198

OSU Calorimeter (Ohio State University) 39, 149, 188, 191, 252, 261, 269, 280 Oxygen concentration, supply 19, 23–25, 27, 31, 42, 64, 78, 133, 141, 151, 152, 191, 231 Oxygen consumption 25, 41, 64, 78, 119, 120, 131, 141, 154, 157 Oxygen depletion 20, 78, 251, 261, 265, 277, 342, 347, 353

Padding. See also Batting, cotton, Latex, Neoprene, Polyurethane Pillows. See Bedding Polyurethane crumbed. See Polyurethane shredded formulation 256 FR general 112, 114, 145, 169, 184, 205, 238, 241, 252, 259, 269, 280, 285, 288, 290–294, 300, 305, 311, 315 CM, HR, CMHR 13, 18, 49, 50, 56, 111, 113, 134, 182, 217, 218, 239–248, 252, 255, 256, 260–265, 271, 275–282, 287, 289, 292–294, 298, 302–305, 307, 310, 313, 314, 334, 340–344

429

exfoliated graphite treated 13, 40, 111, 255, 257 hydrate alumina filled 187, 188, 212, 257, 261, 275, 285, 287, 292 general, untreated 4, 8, 13, 16, 20–23, 26–29, 36–38, 78, 79, 91, 92, 98, 101, 108-114, 124, 144, 145, 148, 169, 170, 180, 184, 187, 198, 204, 205, 209–213, 216–219, 223, 224, 230, 238–243, 247, 250–263, 269–271, 274, 275, 278–282, 286–311 heat of combustion 347 melamine treated 13, 40, 111, 124, 176, 187, 188, 191, 199, 242, 243, 251253, 255, 257, 260–263, 266, 269, 277, 279–281, 287, 290, 291, 294, 298, 306, 307 heat of combustion 347 shredded 48, 84, 111, 112, 117, 288 toxicity 308–311, 315, 316 Pool fires 20, 21, 249, 263, 271, 299, 322, 323, 329, 340, 342 Porosity 19, 24, 265 Port Authority of NY and NJ 122, 123 Post-ignition fire behavior 11–15, 103, 244–299, 328 Propagating/non-propagating fires 6, 32, 52–55, 98, 137, 191, 192, 196, 197, 199, 255, 257, 333, 334, 346 self propagating flux 191, 280, 281 PTFE. See Teflon PVC, vinyl 30, 49, 79, 92, 124, 170, 176, 180, 183, 185, 188, 209, 211–213, 238, 240–245, 250, 252, 253, 258–261, 266, 267, 276, 277, 279, 281, 286, 287, 290–299, 301–305, 310, 312, 314, 315, 354 Pyrolysis. See also Combustion, Smolder 18–21, 22–26, 31, 33, 38, 40, 41, 50, 67, 68, 79, 157, 208, 243, 265, 269, 352

Quilts. See Bedding

430

Fire Behavior of Upholstered Furniture and Mattresses

Rail vehicles 143–145, 294 Regulations 4, 10–17, 24, 31, 55, 71, 73, 84, 85, 93, 96, 102, 108, 113, 118, 133, 142–144, 149, 150, 180, 213, 225, 240, 247, 264, 274, 320, 353 Risk 82, 112, 144, 355 low, high risk facilities 14, 15, 49, 96, 112, 118, 133, 134, 137, 215, 237, 291 Room fire tests 5, 8, 10, 12, 15–17, 20, 27, 28, 34, 39–45, 52–56, 62–72, 75, 78, 80–82, 103, 104, 107, 168, 180, 181, 191, 220, 244, 251, 252, 259, 262, 269, 273, 275, 277, 279, 280, 287, 290, 291, 303, 306, 309–311, 315, 320, 322, 324, 328, 334, 337–339, 342–344, 347, 348, 354, 357 comparison of room test with other test results 191–206 fire models 342–346 open room fires 348–351 small, closed room fires 347, 348 test methods 125–161, 174

Safety 17, 21, 66, 75, 98, 99, 115, 116, 144, 189, 225, 235, 247, 263, 264, 275, 282, 292, 309, 310, 320, 324, 344, 362 Sewing thread 269, 270 Sheets. See Bedding Ships 146, 147, 296, 297 Smoke (often includes CO, CO2, HCN, HCl, other toxic products) definition 67 detectors 10, 91, 181, 279, 293, 355 general 67–72, 82, 103, 160, 182, 195, 256, 321, 334, 343, 346, 348, 351– 355 suppression 307 tests 62, 67–72, 85, 86, 98, 108, 115, 116, 121, 124, 125, 127, 131–137, 141, 146, 147, 151–156, 161, 294, 295 test results 35, 149, 178, 187, 190, 191, 204, 218, 250–253, 261, 262, 264, 269, 274–282, 286, 292–294, 302–307, 315

Smolder, smoldering. See also Char, Cigarettes, Pyrolysis general 21–27, 66, 68, 71, 81, 97, 98, 102, 133, 155, 157, 159, 204–206, 216, 231, 235, 236, 306–311, 316, 359 burning rate 20 effect of air currents 23, 27, 225, 231 fabric 22, 25, 99, 210, 211, 215, 216 fabric/padding composite 169, 211, 216–218, 254, 263, 282, 290, 300, 309, 316, 317 smolder promoters. See also Alkali metal ions 22, 24–26, 90, 100, 210, 213, 215, 217 smolder retardants (SR) 22, 24, 26, 210, 215 substrate density and depths 23, 214, 223 hazard 20, 81, 82, 93, 320, 346, 347, 353, heat of combustion 347 mass loss rate 347 model 25, 26, 81, 216, 353 resistance 10, 11, 87, 92, 208, 215, 217 temperature 22–26, 215, 223 transition to flaming 27–30, 81, 319 Spontaneous ignition 31, 32 Stacking chairs 105, 135, 259, 271, 299, 354 Standard cigarette 87, 91, 93, 221 duck fabrics 229–234 fabrics 56, 84, 87, 90–92, 96, 99, 100, 102, 111, 112, 216, 217 filter paper 229, 230 polyurethane foam 56, 84, 87–92, 100, 111, 114, 169, 217, 230, 239, 340 Style factor 43, 55, 271, 332, 333, 335–338 Style. See Configuration

Teflon - PTFE 82, 158 Tenability, untenable. See also Escape time, Incapacitation, Toxicity, Visibility 56, 64, 66, 67, 80, 81, 168, 294, 316, 337, 338, 347, 349, 351, 354

Index

Test methods. See also Cone Calorimeter, Standards 83–162 comparison of results obtained in various tests 187–206 criteria 97 critiques 99, 113, 154–156, 159 crown suppliers (DOE/PSA) 95, 97, 113, 116, 132, 288 miscellaneous items 150, 151 smoke 151–156 toxicity (see also smoke) 156–162 Thermal decomposition. See also Pyrolysis 12, 19, 42, 140, 311, 342, 365 Thermal inertia 32, 35, 104, 274 Thermal radiation 19, 28, 34, 66, 131, 241, 322 -324, 332, 346, 348, 349, 351 Thermoplastics shrinkage, melting 269, 278 Toxicity (includes combustion products, decomposition products). See also Escape time, Interface, Tenability 5, 8, 11–16, 26, 40–47, 55, 60, 72–82, 85, 86, 103, 104, 125–127, 131, 133, 145–147, 151–162, 182, 214–226, 229, 237, 244, 250, 264, 277, 285, 294, 303, 304, 307–321, 334, 346–355, 362, 370 super toxicants 157, 158, 162 Transportation air 17, 66, 147–150, 190, 264, 292, 296–298 maritime 17, 146, 147, 296, 297 motor vehicle 17, 144–146, 264, 292–295, 307, 354 rail 17, 143, 144, 292–296 Tufts 7, 64, 70–72, 76, 85, 152, 188, 253

University of Pittsburgh toxicity test 160, 315 Upholstered Furniture Action Council (UFAC) 11, 83, 87, 89–92, 97–101, 208, 210, 211, 217, 218, 297 Underwriters Laboratories (UL) 138, 139, 132

431

Urban Metropolitan Transit Administration (UMTA) 158, 294, 295 U.S. Coast Guard 136, 147, 190, 296, 297 U.S. Navy 147

Vandalism. See arson Ventilation 46–50, 54–62, 77, 81, 102, 111, 114–116, 128, 140, 141, 150, 164, 187–191, 209, 218, 237–239, 241, 246, 253 Vinyl. See PVC Visibility. See also Incapacitation, Tenable 64, 66, 72, 315, 316, 352, 355 Welt Cord 7, 64, 67–76, 143, 144, 151, 162, 186