Control of Radon in Houses: Recommendations of the National Council on Radiation Protection and Measurements (Ncrp Report ; No. 103)

NCRP REPORT No. 103

CONTROL OF RADON IN HOUSES Recommendations of the NATIONAL COUNCIL O N RADIATION PROTECTION AND MEASUREMENTS

Issued September 1,1989 National Council on Radiation Protection and Measurements 7910 WOODMONT AVENUE / Bethesda, M D 20814

LEGAL NOTICE This report was prepared by the National Council on Radiation Protection and Measurements (NCRP). The Council strives to provide accurate, complete and useful information in its reports. However, neither the NCRP, the members of NCRP, other persons contributing to or assisting in the preparation of this report, nor any person acting on the behalf of any of these parties (a) makes any warranty or representation, express or implied, with respect to the accuracy, completeness or usefulness of the information contained in this report, or that the use of any information, method or process disclosed in this report may not infringe on privately owned rights; or (b) assumes any liability with respect to the use of, or fordamages resulting from the use of any information, method or process dsclosed in this report, under the Civil Rights Act of 1964, Section 701 et seq. as amended 42 U.S.C. Section 2000e et seq. (Title VZZ) or any other statutory or common law theog governing liability.

Library of Congre6a Cataloging-in-PublicationData National Council on Radiation Protection and Measurements. Control of radon in houses : recommendations of the National Council on Radiation Protection and Measurements. cm.-(NCRP report ; no. 103) p. "Issued September 1,1989." Includes bibliographical references. ISBN 0-929600-07-X : $15.00 (est.) 1. Radon-Environmental aspects. 2. RadonSafety measures. 3. Dwellings-Environmental engineering. I. Title. II. Series. [DNLM: 1. Environmental Pollution-prevention & control. 2. Housing. 3. Radon-analysis. WN 300 N2765cJ TD886.5R33N38 1989 693'.&dc20 DNLM/DL.C for Library of Congress

Copyright O National Council on Radiation Protection and Measurements 1989 All rights reserved. W publication is protected by copyright. NOpart of this publication may be reproduced in any form or by any means, including photocopying, or utilized by any information storage and retrieval system without written permission from the copyright owner, except for brief quotation in critical articlea or reviews.

Preface

The exposure of the general population and the occupational exposure of various types of miners to radon and its decay products are recognized as significant contributors to the incidence of lung cancer in the United States and in other countries. In NCRP Report No. 77, Exposures From the Uranium Series With Emphasis On R a h n and Its Daughters, the radiation exposure to the U.S. population from the Uranium Series, including radon and its decay products, was estimated. In NCRP Report No. 78, Evaluation of Occupational and Environmental Exposures to Radon and Radon Daughters In The United States, an estimate of the biological effects to the U.S. population from exposure to radon and radon decay products was made based on exposure information and the incidence of lung cancer in miners. In NCRP Report No. 97, Measurement of Radon and Radon Daughters In Air, a detailed appraisal of the equipment available to make measurements of radon and radon decay products in air was presented. This report, drafied by NCRP Scientific Committee 82 on Control of Radon in Houses, evaluates the techniques available to reduce radon and radon decay product concentrations. It is intended that this report would be useful to home owners, to individuals involved in marketing services to reduce radon and radon decay products in houses, and to the scientific community interested in control techniques for radon and radon decay products. Sections 1 and 2 of the report provide background information on the public health significance of indoor radon and on the sources and behavior of this radionuclide and its airborne decay products inside houses. The reader desiring information primarily on the control of radon may prefer to shift to Section 3 immediately after reading the Introduction. Included in Section 6 of the report are tables comparing the removal effectiveness and estimated costs ofvarious control techniques, and a glossary of terms used in the report is provided. The International System of Units (SI) is used in the report, followed by conventional units in parentheses, in accordance with the procedures set forth in NCRP Report No. 82, SI Units In Radiation Protection And Measurements.

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PREFACE

Serving on Scientific Committee 82 during the preparation of the report were:

Dade W. Moeller, Chairman Harvard School of Public Health Boston, Massachusetts Members Charles T. Hess University of Maine Orono, Maine

Arthur G. Scott Mississauga, Ontario Canada

Edward F. Maher Occupational and Environmental Health Laboratory Brooks Air Force Base, Texas Consultants

John H. Harley Richard J. Guimond Hoboken, New Jersey Omce of Radiation Programs U.S. Environmental Protection Agency Washington, District of Columbia NCRP Secretariat-William

M. Beckner

The Council wishes to express its gratitude to the members of the Committee for the time and effort devoted to the preparation of this report. Bethesda, Maryland July 10,1989

Warren K. Sinclair President,NCRP

Contents Preface

.

............................................................. iii

1 Introduction .............................. .- .................. 2 Sources and Behavior of Radon ........................... 2.1 Origins of Radon-222 ...................................... 2.1.1 Radioactive Equilibrium Considerations ......... 2.1.2 Radon Emanation-Influencing Factors .......... 2.2 Radon Concentrations in Outdoor Air ................... 2.3 Sources of Radon Inside Houses .......................... 2.3.1 Soil Gas .............................................. 2.3.2 Construction Materials ............................. 2.3.3 Water Supplies ...................................... 2.3.4 Natural Gas ......................................... 2.3.5 Summary ............................................ 2.4 Radon Behavior Inside Houses ........................... 2.4.1 Ambient Aerosol Characteristics .................. 2.4.2 Effect of Ventilation and Air Infiltration ......... 2.4.3 Radon Air Concentrations .......................... 2.4.4 Decay Product Disequilibrium ..................... 2.4.5 Decay Product Air Concentrations ................ 3 General Approaches for Control ........................... 3.1 Passive Techniques ........................................ 3.1.1 Source Removal ..................................... 3.1.2 Closing Entry Routes ............................... 3.2 Active Techniques .......................................... 3.2.1 Soil Ventilation ...................................... 3.2.2 Structure Ventilation ............................... 3.2.3 Air Treatment .......................................

.

.

1 3 3 3 5 7 7 7 10 12 14 14 15 15 17 17 18 19 21

22 22 23 23 24 25 26 4. Source Dependent Control Techniques ................... 27 4.1 Soil Gas ..................................................... 27 4.1.1 Sealing as a Mitigating Measure .................. 27 4.1.1.1 Routes of Soil Gas Entry .................. 27 4.1.1.2 Sealing Materials .......................... 29 ............... 31 4.1.1.3 Sealing Methods . ............... 32 4.1.1.4 Epoxy Sealants . . ............... 32 4.1.1.5 Performance .....

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CONTENTS 4.1.2 Ventilation ........................................... 4.1.2.1 Soil Ventilation ............................. 4.1.2.1.1 Subsoil Collection Systems ..... 4.1.2.1.2 Subfloor Exhaust ................ 4.1.2.1.3 Weeping Tile Exhaust .......... 4.1.2.2 Wall Cavity Exhaust ....................... 4.1.2.3 Crawl Space Ventilation ................... 4.1.2.4 Removal Efficiencies for Source

Dependent Control Techniques ...........

.

4.2 Water Supplies ............................................. 4.2.1 Activated Carbon Filters ........................... 4.2.2 Aeration Systems ................................... 4.3 Construction Materials .................................... 4.3.1 Material Substitution ............................... 4.3.2 Changes in Building Design .......................

5 Source Independent Control Techniques ................ 5.1 Introduction ................................................ 5.2 Increased Ventilation ...................................... 5.2.1 Forced Air Supply ................................... 5.2.2 Forced Air Exhaust .................................. 5.3 Increased Air Circulation ................................. 5.4 Air-Cleaning Devices ...................................... 5.4.1 Electrostatic Precipitation ......................... 5.4.2 High Efficiency Filtration .......................... 5.4.3 Unipolar Space Charging .......................... 5.5 Application of Combined Approaches .................... 5.6 Summary of Experimental Data .......................... 6 Selection of Control Techniques ...........................

.

6.1 Source-Dependent Control Techniques ................... 6.2 Source-Independent Control Techniques .................

7. Commentary and Recommendations

..................... Glossary ............................................................ References ......................................................... The NCRP .......................................................... NCRP Publications .............................................. Index ................................................................

1. Introduction Naturally-occurring short-lived decay products of radon gas (222Rn), i.e., 218Po(RaA), 214Pb(RaB), 214Bi(RaC), and 214Po(RaC') in indoor air, are the dominant source of ionizing radiation exposure to the U.S. public (NCRP, 1987a). By recent estimates (NCRP, 1987a),the average annual dose equivalent to the lung bronchial epithelium of the U.S. population is 24 mSv (2.4 rem). There are estimates that these exposures may be causing some 5,000 to 10,000 lung cancer deaths per year in the United States (NCRP, 1984a; NASINRC, 1988). High radon concentrations in the home environment typically result from radon gaining access to houses from the underlying soil or from groundwater supplies. To some degree, reduced air infiltration rates resulting from energy conservation may also have led to higher radon concentrations. Recognition of the importance of the accompanying exposures, however, has been primarily due to a growing awareness on the part of public health officials of the significance of indoor air pollution and the development of more sensitive and practical radon monitoring instruments. Nero et al. (1986) estimated that annual exposures in approximately one million of the eighty million homes in the U.S. exceed 7 x joule-hours per cubic meter or 2 working level months (WLM)'. This estimate was based on an analysis of the published data using both a lognormal and a nonparametric method to aggregate the various data sets (Figure 1.1). Assuming that the decay products are a t 50 percent equilibrium, such an exposure would correspond to an annual average indoor radon concentration in these one million homes in excess of 300 Bq per cubic meter (8 pCi per liter). This annual exposure of 7 x joule-hours per cubic meter (2 WLM) is equal to the exposure proposed by the National Council on Radiation Protection and Measurements for remedial action (NCRP, 1984a). The corresponding remedial action level recommended by the U.S. Environmental Protection Agency is about 150 Bq per cubic meter (4 pCi per liter) which would yield an integrated annual exposure of about 3.5 x joule-hours per cubic meter (1WLM) (EPA, 'For definitions of specific terms used in this report, the reader is referred to the Glossary, page 62.

NCRP "ACTION LEVEL"

\- 8

lalRn CONCENTRATION (pCl11)

Fig. 1.1 Frequency distribution of "2Rn concentrations from direct aggregation of 552 individual data points from 19 sets of measurements in houses throughout the U.S. (Adapted from ~ e r eto al., 1986).

1986a; GAO, 1986). As may be noted, there is a factor of two difference in the action level currently recommended by these two organizations. This difference is not significant in light of the many uncertainties involved in assessing the health effects of airborne radon. In view of the potential health hazard presented by indoor radon, a considerble amount of effort has been devoted to the development of mitigation techniques and strategies that might limit or control exposures to this source of radiation exposure. Techniques and procedures applicable to existing buildings have been developed and attention has also been directed to control measures that can be incorporated into new construction. The purpose of this report is to describe and evaluate various methods that can be used to control elevated concentrations of radon. The report includes a review of the strategies available for the control of radon and its decay products inside residences and presents information on the relative effectiveness and costs of specific control techniques.

2. Sources and Behavior of Radon 2.1 Origins of Radon-222 There are three radioisotopes of the element radon: radon-219, radon-220 and radon-222. Radon-222 (222Rn) and its short-lived decay products, 218Po(RaA), 214Pb(RaB), 214Bi(RaC), and 2 1 4 P(RaC'), ~ are intermediate decay products of the naturally occurring, primordial decay series of (Figure 2.1). The parent radionuclide, =U, is a relatively stable redionuclide with a half-life of 4.5 x lo9 years, about the same order of magnitude as the age of the earth. Uranium238, a trace constituent of the earth's crustal materials, occurs in concentrations that vary with geographic location, depending on the predominant geologic formations. Sedimentary rock, e.g., shale, sandstone, and carbonates, are the most common in the U.S. and cover about 85 percent of the inhabited lands, while igneous rock covers the remaining areas (Oakley, 1972). Typical concentrations of U for these rock and soil types range from 7 to 60 Bq per kilogram (0.2 to 1.6 pCi per gram) (NCRP, 1987b).The other radioisotopes of radon, 219Rnand 220Rn,are produced through the decay of the actinium and thorium series. Because these two isotopes rarely, if ever, contribute quantities of radioactive material to the atmosphere that are significant compared to that from 222Rn,they are not discussed in this report. 2.1.1 Radioactive Equilibrium Considerations From a global perspective, the 23BUseries members are in secular equilibrium. However, physical or chemical geologic processes with rates comparable to, or greater than, the decay rates of series radionuclides will result in varying degrees of local disequilibrium between series members. Local disequilibrium can also be caused by human actions such as the mining of uranium, thorium and phosphate ores, which purposely or inadvertently segregate series members. Whether through natural forces or human actions, the redistribution of series radionuclides has the potential for increasing human radiation expo-

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2. SOURCES AND BEHAVIOR OF RADON

.

wne (RIA)

~0.214 (R.C~ 1 . 6 l~o 4 $

3.05 nYI 6.0 MaV

# 7.7 MeV

B2l4 (hC) 19.7 min 0.4 3.3 MeV

Pan4 (R.8)' 26.8 mtn 0.7. 1.0 MeV

-

'

W210 0 5.0 d 1.2MeV

#

'

1386 5.3YeV

/ Pb210 (MI)

a 4 . 1 MeV

Pbm(ma) Sloble

Fig.2.1 Principal decay scheme of the uranium series.

sure. For example, the use of uranium tailings as backfill around housing foundations brings radionuclides into closer proximity to people. The most important source of radiation exposure from the -U decay series begins with 226Ra,which decays to 222Rnand initiates the short-lived radon decay products. Since 222Rnis an inert gas, it is capable of escaping from the mineral soil into the air spaces within the soil or other materials by molecular diffusion. Radon-222 can also escape from the soil by virtue of the recoil energy it obtains upon the radioactive decay of radium-226. Because the recoiling radon atoms have a range of 20 to 70 nanometers in mineral soils (Tanner, 19801,only those n2Rn atoms formed near the surface of the solid are able to enter the soil air space. "Emanating power" is defined a s the fraction of radon formed in the mineral solid that escapes from the solid. Most soils have a n emanating power of less than 0.2. That value would probably be higher if the effects of moisture were taken into account because the presence of water in the pores increases the probability that the recoil energy is dissipated in the pore and that the recoil particle is not injected into the interior of a second soil particle. A few soil types (notably clays) can have a n emanating power value as high as 0.6. Smaller soil grain sizes have higher emanating power values. Radon gas migration from the soil air spaces results from simple diffusion, by movement with the soil air, or by transportation with water in the soil. Radon concentrations in the soil air space in normal soils reportedly range from 7 to 220 kBq per cubic meter (0.2 to 6 fCi

2.1 ORIGINS OF RADON

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5

per liter) (Israelsson, 1980; Kraner, et al., 1964; Scott, 1979). Because of the large concentration gradient between the soil air space and the atmosphere, radon soil gas migrates towards the ground surface via the air channel capillaries in the soil. Diffusion through soils is a relatively slow process because of the tortuous path the gas must travel in order to reach the ground surface. The distance that radon can travel in soil is limited in part by its 3.82 day half-life; upon decay, the gaseous radon atom becomes a polonium atom. Since radon progeny are metal atoms, they are retained in the diffusing medium. For this reason, radon formed a t soil depths greater than a few meters is unlikely to reach the soil surface. The instantaneous rate of radon activity per unit area that crosses the soillair boundary surface is referred to as the emanation rate, expressed in units of radioactivity (Bq or pCi) per square meter per second.

2.1.2

Radon Emanation-Influencing Factors

The radon emanation rate from the soil surface is modified by physical and meteorological factors unrelated to the soil radionuclide concentration. The more important physical factors include the soil porosity (ratio of interstitial air volume to bulk soil volume), soil moisture, soil grain size, and the condition of the soil surface, e.g., snow cover and standing water (NCRP, 1984a; NCRP, 1984b; Stranden et al., 1984; Tanner, 1980; LTNSCEAR, 1977). Studies of the effect of soil moisture on the radon emanation rate show that the optimum moisture content, for the release of radon, ranges from 20 to 30 percent (Kraner et al., 1964; Stranden et al., 1984). In general, the optimal moisture content for radon emanation tends to be lower for low porosity soils. Below the optimal moisture content, the effective pore volume is reduced, but pores remain open for diffusion to occur in the gaseous phase. The reduced effective pore volume gives rise to a higher linear rate of movement of the diffusing radon. Above the optimum values of moisture content, pores tend to become saturated so that there are fewer open pores for gaseous transport and more of the diffusion must take place through water. The viscosity of water for radon gas is about 100 times that of air so that the diffusion velocities of gases in water are about a factor of 100 slower than in air. The effect of physical factors, mostly related to soil permeability, has been shown to modify the emanation rate by less than two orders of magnitude over a range of extreme conditions. Meteorological factors also influence the emanation rate, although there is some disagreement as to their relative importance (Scott and Findlay, 1985). Among those reported are changes in barometric

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2. SOURCES AND BEHAVIOR OF RADON

pressure, soil temperature, surface wind speeds, and rainfall (Steinhausler, 1975; UNSCEAR, 1977). Numerous investigators have reported rapid increases in the radon emanation rate with sudden and transient decreases in barometric pressure. A sudden drop in barometric pressure reduces the pressure head on the interstitial soil air and facilitates the movement of radon to the surface. Under these conditions, the emanation rate can be ten times or more greater than that predicted by simple diffusion, (UNSCEAR, 1977). Such episodes are brief, however, since the barometric pressure differences between the soil air and atmosphere eventually equilibrate or the soil radon production rate will not sustain the flux increase. Conversely, a sudden increase in barometric pressure will reduce the emanation rate, although the effect is less dramatic, perhaps due in part to the resistance offered by the soil to downward soil air movement, as well a s the persistence of diffusion towards the surface. The influence of other meteorological variables is less understood and the available literature is limited. There is conflicting information concerning the influence of soil temperature. Stranden et al. (1984) reported a three to four fold increase in the radon emanation rate from soils as their temperature increased from 5" to 50" C, and explained that this was due to decreased adsorption of radon on the solid material. Their results are consistent with observed decreases in flux when the soil is frozen (Kraner et al., 1964). Auxier (1973) reported that the radon emanation rate from concrete is relatively unchanged between 23" and 49" C; however, this observation may not be applicable to soils. Most of the experimental data indicate that the radon emanation rate increases with surface wind speed. High wind speeds are believed to cause turbulent convection patterns near the ground and small local pressure gradients that "pump" radon out of the ground (Israelsson, 1980).Kraner et al. (1964) observed a depletion of radon concentrations in soil down to depths of about 1 meter during periods of high surface winds. Rainfall and other forms ofprecipitation can modify the emanation rate by changing the soil moisture content. Light rains tend to have little effect, whereas heavy, soaking rains that saturate the lower soil depths as well as the surface, can cause a substantial decrease in the emanation rate for several days (UNSCEAR, 1977). In consideration of all the known and possible variables that may have an influence on the radon emanation rate, it is not surprising that the emanation rate is difficult to interpret and highly variable, even in nearby locations. Measurements over dry land have been reported to vary by a factor of over 250, ranging from 0.2 to 53 mBq

2.3 SOURCES O F RADON INSIDE RESIDENCES

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(5 to 1400 fCi) per square meter per second, with an average value of approximately 0.016 Bq (0.43 pCi) per square meter per second (Wilkening et al., 1972).

2.2

Radon Concentrations in Outdoor Air

Outdoor radon concentrations 1to 10 meters above the ground are quite variable for the reasons discussed above. In addition, the degree of vertical mixing in the atmosphere, local surface winds, and turbulence can cause wide variations in outdoor concentrations of radon, even over land with a constant emanation rate. The seasonal and diurnal variations in radon concentrations depend primarily on atmospheric conditions and are less dependent on variations in the emanation rate. The radon concentration in U.S. continental air, measured by several investigators, has been reported to range from 0.7 to 35 Bq per cubic meter (0.02 to 1pCi per liter) with an average of about 7 Bq per meter (0.2 pCi per liter) (NCRP, 1987b). Radon concentrations in the air over the ocean are approximately one percent of those over land, while the average for coastal region air tends to lie somewhere between these two values, depending on the prevailing coastal wind direction, i.e., on-shore or off-shore. Diurnal variations in radon air concentration tend to follow a sinusoidal pattern with a maximum during the early morning and a minimum during the afternoon. This response pattern is consistent with the typical diurnal profiles of atmospheric stability, in that inversions are more apt to occur during the early morning, whereas atmospheric mixing increases during the day due to solar heating of the earth's surface. Atmospheric stability is generally considered to have the greatest influence on radon concentrations in the air over continental land masses. Wind direction, although important over coastal regions, has only a minor effect on radon concentrations over large land masses with relatively constant emanation rates.

2.3 Sources of Radon Inside Residences

2.3.1

Soil Gas

The major source of radon in most houses is the soil directly under the building. Radon emanation into an enclosed volume, where the free mixing of indoor and outdoor air is restricted, will result in

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2. SOURCES AND BEHAVIOR OF RADON

elevated steady-state concentrations compared with those outdoors. Radon from the underlying soil can enter a home through several pathways: diffusion and transport through microscopic cracks and imperfections in the foundation; transport through open or unsealed service connections in the basement floor, e.g., floor drains, loosefitting pipes, etc.; and by diffusion through intact foundations. Attenuation of the emanation rate caused by impeding the diffusion of soil gas is often expressed in terms of the "relaxation" or "diffusion" length, which is defined as the material thickness required to reduce the emanation rate to 37 percent of its initial value. For poured concrete, the relaxation length varies from 4 to 30 cm, with typical values being nearer to 10 to 15cm (Nero and Nazaroff, 1984). Since the typical relaxation length for concrete is comparable to or less than the thickness of most basement floors and walls, the attenuation of the soil emanation rate by such structures is substantial. One pathway of radon soil gas into homes appears to be transport through cracks in the foundation and floors (Landman, 1982). The median entry rate of radon from soil for U.S. single family houses is approximately 14 Bq per cubic meter (0.4 pCi per liter) per hour. Based on emanation rate measurements from concrete (Ingersoll, 1983), soil gas contributions via diffusion through a n intact foundation would account for a median of only 2.5 Bq per cubic meter (0.07 pCi per liter) per hour, far below that normally observed in houses. Nevertheless, the potential contribution based on typical emanation rates from soil corresponds well with a 25 Bq per cubic meter (0.7 pCi per liter) per hour entry rate. However, understructures of houses, e.g., concrete floors, should be expected to impede substantially the ingress of radon by diffusion. A recent review of the sources of indoor radon (Nero and Nazaroff, 1984) suggests that although simple diffusion might reasonably explain the observed emanation rates from exposed soil, and possibly the smaller emanation rates observed from concrete, diffusion cannot account for the total radon entry rates in most houses. Therefore, other mechanisms, not yet fully characterized, must be responsible for the efficiency with which soil gas containing radon enters homes. A primary mechanism is the bulk flow of soil gas that is driven by small pressure differences between the lower sections of the house interior and the outdoors. These pressure differences can arise from two environmental factors. First, the difference in temperature between indoors and outdoors can create a small pressure gradient across the building shell. The pressure gradient, which extends from the understructure and points in the direction of higher temperature, i.e., heated interiors, produces local air currents that direct colder (outdoor) air into a

2.3 SOURCES OF RADON INSLDE RESIDENCES

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building and enhance the loss of heated air to the outdoors. This socalled "stack effect" establishes a convection pattern in the house that causes a n exchange between the indoor and outdoor air, and the outdoor air is taken partially from the building understructure. The second factor of importance is surface wind speed, which causes a slight depressurization of the house interior and establishes a pressure gradient across the building shell. The pressure gradients caused by temperature differences and wind are roughly comparable in size, averaging on the order of a few pascals (equivalent to a few hundredths of a millimeter of mercury), with higher values in severe climates. These small pressure differences account for air infiltration through the building shell and are the dominant means of home air infiltration during the heating season. These same pressure differences can, in principle, be responsible for the movement of radon soil gas into a building. For example, soil gas contains enough radon so that only one-tenth percent of the infiltrating air would have to be drawn from the understructure (Nero and Nazaroff, 1984) in order to account for the observed entry rate into houses. A relatively simple and useful method for relating the infiltration rates of homes to temperature differences and outside wind speed has been proposed by Grimsrud et al. (1982). Nero and Nazaroff (1984) have begun to characterize the potential for pressure differences to cause indoor entry of radon via the soil through loose-fitting seams and cracks in the house understructure. A study by Nazaroff et al. (1987a) of the radon entry into a singlefamily house with a basement, in which measurements of the entry rate versus the ventilation rate were made over a period of months, showed that entry rates could be adequately described by a twocomponent model: the first and less important component was independent of ventilation rate (corresponding to entry via simple diffusion); whereas the second, more decisive component was proportional to ventilation rate (corresponding to entry by pressure driven flow). Moreover, these authors concluded that the observed pressure differences and soil parameters in the house were in good agreement with the soil gas flow rate that was implied by the measured indoor concentrations and ventilation rates. A more detailed theoretical analysis (DSMA, 1983) has been helpful in formulating a fundamental model of the pressure and air current gradients in the soil surrounding houses with basements. Experiments by Nazaroff et al. (1985), involving two houses with basements, have shown good agreement between the measured and predicted understructure depressurization. These experiments included measurements of understructure soil gas movement using tracer gas methods. Pressure differences across the slab foundation can also be expected to

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2. SOURCES AND BEHAVIOR OF RADON

draw soil gas into a home through defects (cracks) in or a t the junction between the walls and slab floor, as well as through other openings in the basement walls and floor; however, experimental verification in such structures has not been attempted. To some extent, a crawl space beneath a house will isolate the building interior from pressure-driven radon entry from the soil. Limited measurements of the transport efficiency of radon &om understructure crawl spaces suggest that a substantial portion of the radon from bare soil can still enter a house, even if the crawl space is ventilated (Nazaroff and Doyle, 1985). This is not totally unexpected, since the "stack effect" will still tend to draw radon contaminated air from the crawl space into the house. Furthermore, for structures where the crawl space vents are sealed, e.g., for energy conservation, it is conceivable that the crawl space will still provide a sufficient connection between the house interior and the soil such that simple diffusion may also contribute to radon entry. Soil beneath a dwelling is generally considered to be the primary source of indoor radon, but several other sources and pathways have been suggested as contributors to indoor concentrations in certain situations. Two of these, construction materials and water supplies, are discussed in the sections that follow.

2.3.2

Construction Materials

Several organizations and investigators have reported that some construction materials in the U.S. contain unusually high concentrations of radium or uranium (EPA, 1975; Guimond et al., 1978; Ingersoll, 1983; Moeller et al., 1980; UNSCEAR, 1977). Such materials are mostly concrete, cement block, gypsum board, and masonry. Several tons of masonry and concrete are used in the construction of a typical house. These materials acquire their radioactive constituents from the rock aggregate or sand. Masonry and concrete materials have been reported to have 226Raconcentrations of 7 to 100 Bq per kilogram (0.2 to 3 pCi per gram); an average concentration of 35 Bq per kilogram (1 pCi per gram) has been commonly reported (UNSCEAR, 1977). This is comparable to the average concentration reported in soil. Concretes made from aggregates of granite, pumice, and shale have among the highest reported radon emanation rates. Wood has a particularly low 226Raconcentration and is a negligible source of indoor radon. Bruno (1983) has estimated that the total radon contribution (activity per unit time) to a typical house from masonry materials would be in the range of 0.01 to 0.1 Bq (0.3 to 3 pCi) per second.

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2.3 SOURCES OF RADON INSIDE RESLDENCES

11

TABLE2.1-Estimates of 2d6Raconcentratwns in building materials" concentration

Material

Bq per kilogram 1 16-61 42-96 78

pCi per gram

Wood 0.03 Concrete 0.43-1.65 Brick 1.1-2.6 Tile 2.1 Wall board 0.11-0.27 Natural gypsum PI0 Phosphogypsurn 27 0.73 Insulating material Glass woolb 13-40 0.35-1.1 "Adaptedfrom UNSCEAR (1982) page 184. T h e impervious (glassy) nature of these products retards the release of radon.

The use in building and construction materials of industrial solid wastes that contain technologically enhanced concentrations of 226Ra is a contributing source to high radon concentrations indoors. In some countries, especially in Europe, the use of such building materials may be a major source of indoor radon. Published data on 226Ra concentrations in a variety of building materials are shown in Table 2.1. Waste gypsum or phosphogypsum is a by-product of the phosphate fertilizer industry. In processing the raw calcium phosphate rock to produce phosphates, the 226Rais included in the calcium sulfate waste (phosphogypsurn). The specific distribution of the 226Radepends on the process. The 22BRacontent of phosphogypsum has been reported to range from 0.5 to 1 kBq per kilogram (13 to 27 pCi per gram), considerably greater than most other building materials (Wrixon, 1981). Phosphogypsum has been used extensively in parts of Europe and Japan in the manufacture of partition blocks, wallboard, and cements. To date, there have been no known instances of phosphogypsum use in U.S. building materials. Phosphate slag, another by-product of phosphate fertilizer production, has been used in concrete and is estimated to be present in the building materials of tens of thousands of U.S.houses. The use and disposal of phosphate mining by-products are now under stricter control in the U.S. and elsewhere. In the U.S., phosphate industry wastes are now classified as hazardous and are regulated under the Resource Conservation and Recovery Act (RCRA) of 1976 (RPC, 1980). The emanation rates of radon from building materials depend upon many of the same variables that influence diffusion through soil, e.g., moisture content and porosity of the material. In addition, meteorological factors such as changes in barometric pressure and tem-

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2. SOURCES AND BEHAVIOR OF RADON

perature have been shown to modify the emanation rate of building materials (Jonassen, 1975; Stranden et al., 1984). The emanating rates of most concretes, brick, and gypsum board are relatively low. The application of sealants, i.e., paints or decorative coverings on wall board, reduces the radon emanation rate. In most U.S. houses where elevated radon levels have been observed, the contribution from building materials has been minor compared with that from soil and water-borne sources.

2.3.3.

Water Supplies

Radon is moderately solublein water a t standard temperature and pressure (0.5 liter 222Rnper kilogram of water; 2.7 x 1016 Bq per liter of water). However, the solubility decreases with increasing temperature. Most surface waters have 222Rnconcentrations less than 2 Bq (50 pCi) per liter, and rarely do concentrations exceed 75 exists Bq (2 nCi) per liter (Nazaroff et al., 1987b); significant only in bottom sediments. Groundwater aquifers containing radiumrich rock can support water concentrations of n2Rn greater than 2 kBq (50 nCi) per liter even though the concentration of dissolved 226Racan be one thousand times less (Colle and McNall Jr., 1980). Groundwater itself, on the other hand, has concentrations of 222Rn that range from 0.020 to 44 kBq (0.5 to 1,200 nCi) per liter. The geometric mean value (in Bq per liter) for 222Rnin groundwater for supplies in selected states has been reported as follows: Rhode Island (901, Maine (40), New Hampshire (35), Virginia (13),and Pennsylvania (14) (Hess et al., 1985). Private wells in Maine have been reported to have an average radon concentration greater than 0.37 kBq (10 nCi) per liter, and range as high as 44 kBq (1.2 pCi) per liter. Concentrations in some private wells in Pennsylvania have ranged up to 7.5 kBq (0.2 pCi) per liter. Most houses in the United States (approximately 60 percent) are served by water supplies that come from surface sources which have relatively low radon concentrations (EPA, 1987). Houses served by water supplies from other sources, such as private wells, may contain extremely elevated concentrations of radon. In addition, since most of the water &om private wells is used soon after removal from the ground, radioactive decay of the radon is negligible. Radon in water supplies can be released into the air within a home during water use (Prichard and Gesell, 1981). The rate a t which radon is released from the water depends on the degree to which it is aerated and heated. The total amount of radon released depends on the total amount of water used and the concentration of radon within it.

2.3 SOURCES OF RADON INSIDE RESIDENCES

1

13

TABLE 2.2-Potable water m e mtes for v c u i o ~ household ~s activities and the estimated percentage of mdon released Houshold activity

Drinking and cooking Dish washing Garbage disposal Laundering Bathing Water closet (toilet) Showering Average Estimate

Water usage (gallons per day per person) Bond et al. Partridge et al. (1973) (1979)

1-2 1-4 0-4 3-9 10-25 24 55

8-10 20-30 30-40 4-6 20-30 100

Percentage of radon released horn water into indoor air

0-100 98 60-98 31-60 31-60 27 98 70

Rates of water usage in typical houses range from 0.3 to 1m3 (70

to 250 gallons) per day, depending on the number of individuals in the household. Rates of use per person in a home range from 0.09 to 0.3 m3 (25 to 70 gallons) per day (Bond et al., 1973; Partridge et al., 1979). A summary of rates of water use for different purposes for typical household activities and estimates of the accompanying fractional release rates of radon into the air are given in Table 2.2. Field data show direct correlations between indoor airborne radon concentrations, the accompanying ventilation rates within a house and the timing of the use of showers and dish and clothes washers. Because of the nature of the releases of radon for different water usage, roomto-room radon concentrations within a home can show considerable variation. On a nationwide basis, Cothern et al. (1986) have estimated that the population-weighted-average radon concentration in drinking water is between 2 and 10 Bq (50 and 300 pCi) per liter. The estimated airborne radon concentrations in houses using these waters, assuming a transfer coefficient of 1 x (Hess et al., 19851, would be in the range of 0.2 to 1 Bq per cubic meter (5 to 30 fCi per liter). On this basis [and assuming a mean radon concentration in U.S. homes of 37 Bq per cubic meter (1pCi per liter)], it can be estimated that, of the total average concentration of radon currently in the air in houses in the U.S., about 0.5 to 3 percent originates from domestic water supplies. This is in general agreement with data published by Nazaroff et al. (198713) who have estimated that, for houses served by public groundwater supplies, a n average of 2 percent of the mean indoor radon concentration is contributed through this source. In general, the health risks due to consumption of waters containing elevated concentrations of radon are insignificant. The dose to the stomach due to the ingestion of radon-rich water, for example, has been estimated to be less than 10 percent of that to the lungs

14

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2. SOURCES AND BEHAVIOR OF RADON

from breathing the accompanying airborne radon and its decay products (Cross et al., 1985). In the case of exposures to radon from any source and, most particularly in the case of exposures originating through the release of radon from water supplies used within a house, it is important to make a distinction between average indoor air concentrations and average daily personal exposures. As an example of the importance of this distinction, it might be noted that if a person taking a shower were exposed to an airborne radon concentration two to three orders of magnitude higher than the household average for a period of only 10 minutes, this might result in an exposure equivalent to from one to five times that received indoors during the remainder of the day. An additional consideration, in this case, however, is whether the elevated exposure in the shower would result in an increased dose in proportion to the increased exposure (due to the potential difference in the state of equilibrium of the radon decay products). 2.3.4 Natural

Gas

In certain cases natural gas may be a contributor to indoor concentrations of radon. This is particularly true if the source of natural gas is located near or in geological formations with high radium concentrations. Radon can diffuse from the rock and soil surrounding a natural gas well and infiltrate the gas. Entry into a house occurs when the gas is used for cooking and unventilated space heating. The radon concentration in natural gas as it reaches the consumer, however, can be quite different from well-head concentrations. Decay during storage and transmission substantially reduces the delivered radon concentration. Measurements in gas distribution systems for eight major U.S. cities revealed 222Rnconcentrations ranging from 0.037to 3.7 kBq per cubic meter (1to 100pCi per liter) (EPA, 1973). Information on indoor 222Rnconcentrations resulting from natural gas service is limited, but the concentrations are likely to be negligible due to the small volume of natural gas used on a daily basis for cooking and space heating (Barton et al., 1973;EPA, 1973;Gesell, 1974). Although safety regulations generally require venting of appliances that burn natural gas to prevent the buildup of hazardous concentrations of carbon monoxide, venting of gas stoves is not required. 2.3.5 Summary Table 2.3 summarizes data on release rates for various sources of radon in a house based on a review of the published literature (Bruno,

15

2.4 RADON BEHAVIOR INSIDE HOUSES 1 TABLE2.3-Approximate contributions from sources of mdon in housep Estimated contribution (activity per second)

Sam

Soil gas transportb &6 Bq Release from potable water 0-2 Bq Soil gas diffusion" 0.14.2 Bq 0.01-1 Bq Diffusion from building materials "From Bruno (1983). bMay be a f a h r of 10 to 100 times higher in certain regions.

( 0-150

pCi )

( 0-60 pGi) ( 3-6 pCi)

(0.3-30 pCi )

1983). These values are only approximate, since they differ depending on geographical region, housing construction type, and water concentration and usage rates. The relative contribution from each of these sources to the total radon in the air in a house will depend on the relative release rate for each source. 2.4 Radon Behavior Inside Houses

Once inside a house, radon freely mixes with the room air and decays to initiate its short-lived decay series. This series, shown in the dashed box of Figure 2.1, consists of heavy metal atoms of polonium, lead, and bismuth, each radioactive, and possessing a short half-life, i.e., less than 30 minutes. Radioactive decay of 214Poto 210Pb effectively completes the short-lived decay series since the half-life of 'lOPb, the next series member, is 22 years. Airborne decay series members (radon decay products) rapidly collide with and attach to aerosol particles within the house airspace. The combined effective size of the decay series members and their aerosol particle ranges from 0.05 micrometer to a few micrometers in diameter. Depending on the size distribution and concentration of the aerosol particles (number of particles per unit volume) present in the room air, up to 20 percent of the progeny can exist in the unattached state. Since the unattached radon progeny are positively charged, they often attract other small polarized molecules in the air, such a s water vapor and trace gases (Busigin et ad., 1980; Frey et al., 1981; Raabe, 1969). These decay product ion cluster complexes remain very small, highly diffusive species that have very different deposition efficiencies in the lung as compared to radon decay products that are in the attached state. 2.4.1 Ambient Aerosol Chamteristics

The influence of aerosol particle size distribution and concentration on their interactions with radondecay products involves two

16

1

2. SOURCES AND BEHAVIOR OF RADON

factors: (1)the fraction of decay products attached to aerosol particles, and (2) the dependence of the decay product attachment rate on the surface area of the aerosol particles (NCRP, 1984a).The fraction of unattached decay products has been found to be highly dependent on the aerosol concentration (Jacobi, 1972; Raabe, 1969)with higher unattached fractions being associated with lower aerosol concentrations. The reason for this is that, with lower aerosol number concentrations, there are fewer particles available for the decay products to randomly collide with or diffuse towards. Polonium-218 has a radioactive mean life of 4.5 minutes. According to the kinetic theory of attachment, the mean attachment time for 218Poto particles in the 0.2 p,m size range a t an aerosol concentration of lo6 particles per cubic centimeter is 0.12 minute. For an aerosol concentration of lo4 particles per cubic centimeter, the attachment mean time is 12 minutes, considerably longer than its mean life. The first example typifies conditions in a dusty mine atmosphere where high aerosol concentrations (greater than lo6) per cubic centimeter result in mean attachment times that are fractions of a second, virtually assuring that nearly all the 218Pois attached to particles. In contrast, the typical aerosol concentration in houses is about lo4per cubic centimeter. A similar analysis can be performed for 214Pband 214Bi;but, due to their longer mean decay lives (i.e., 38.6 and 28.4 minutes, respectively), extremely low aerosol number concentrations would be necessary to cause a significant fraction of either to be unattached. One mitigating effect of a low aerosol number concentration is the enhancement of plateout or surface deposition (Jonassen, 1984; Shreve and Cleveland, 1972).In an environment where the aerosol concentration is less than lo4 per cubic centimeter, a greater number of highly mobile unattached decay products will exist, each undergoing Brownian movement for a longer period of time before becoming attached to an aerosol particle. The longer time spent unattached increases the probability that airborne progeny will impinge upon and plate out on room. surfaces by molecular diffusion. The shiR of radon decay products from the air to room surfaces will result, in t u n , in a decrease in the airbone potential alpha energy concentration (PAEC)or working level. The radiobiological consequence of the attachment state of inhaled decay products is that highly diffusible unattached decay product atoms preferentially deposit in the nasal-pharyngeal region and upper regions of the tracheobronchial tree of the lungs. The upper regions of the tracheobronchial tree are the primary s i t . of lung cancer associated with radon decay product exposure (NCRP, 1984a). As a result, the unattached decay products are believed to have the potential of causing a greater localized lung dose (absorbed energy per

2.4 RADON BEHAVIOR INSIDE HOUSES

1

17

unit mass of tissue), and therefore, are assumed to have a higher associated risk per unit amount of radioactive material inhaled. In contrast, the decay products attached to aerosol particles are deposited mainly in the~pulmonaryregion (see paragraph 159, UNSCEAR 1977). 2.4.2

Effect of Ventilation and Air Znfiltration

Residential dwellings are not airtight, and even though windows and doors are closed, outside air enters through openings in the structure. The rate of air infiltration is governed by meteorological factors such as outdoor wind speed, temperature and pressure differences between the inside and outside, as well as the porosity of the dwelling and the frequency and duration of opening of windows and doors. The rate of outside air infiltration has a substantial influence on indoor radon and radon decay product concentrations. The relationship between infiltration rates and radionuclide concentrations has been evaluated and modeled by several investigators (Haque et al., 1965; Jacobi, 1972; Porstendorfer et al., 1978), on the basis that the radon supply rate was constant. The assumption that radon supply rate is constant is reasonably accurate for building material sources, but it is not true for soil gas or groundwater sources. In a dwelling with total volume V, room air that escapes to the outdoors a t a rate Q (volume per unit time), must be replaced by an equal volume of outside air during the same time period. If it is assumed that the volume is well-mixed so that radionuclide concentrations are homogeneous, then the airborne activity removed per unit vol-

Q - C o d , where Cin and C,t are ume and time is expressed as -(Ci,

v

Q the indoor and outdoor radionuclide concentrations, respectively. -

v

is the removal rate constant for ventilation, where Q is the volume removed per unit time and V is the volume under consideration, or more commonly known as the room air ventilation rate, I,, in units of reciprocal time. If the outdoor radionuclide concentration (Cmr)is much smaller than indoors (Cb), as it frequently is, then C, is negligible and the airborne activity removal rate then becomes ZvCin. 2.4.3

Radon Air Concentmtions

Since radon is a chemically inert gas, radioactive decay and ventilation (infiltration of air from outdoors) are the only mechanisms

18

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2. SOURCES AND BEHAVIOR OF RADON

which act to reduce indoor radon concentrations. Molecular collisions of radon atoms with room surfaces establish almost instantaneous equilibrium with little or no adsorption involved. To a first approximation, the following is useful in expressing the relationship for radon that exists inside a well-mixed volume, V. It can be expressed as follows:

where: C, = radon activity concentration in air, Bq per liter

Q,

= radon exhalation rate into V, Bq per second V = well-mixed volume, liters A, = decay constant for radon, 2.1 x per second I, = ventilation rate, per second

2.4.4 Decay Product Disequilibrium

Because of radon's 3.8 day half life, steady-state radon concentrations are established by the radon emanation rate into the volume and the outside air exchange rate. Polonium-218 (RaA), with a half life of 3.11 minutes, is only slightly influenced by typical ventilation rates and usually remains near radioactive equilibrium with radon. The half lives of 214Pb(RaB) and 214Bi(RaC) (27 min. and 20 min., respectively) are about the same as typical house ventilation rates; as a result, substantial disequilibrium between these radon progeny and their respective parent radionuclides can be caused by ventilation. Radioactive disequilibrium between radon and its progeny is also affected by the presence of removal processes other than ventilation. Such processes include surface deposition driven by the internal convective airflows, the influence of electrostatic forces, and gravitational settling of the decay products. The removal rates for these processes add to the effects of radioactive decay and cause further disequilibrium between the radionuclide and its parent. The final steady-state decay product concentrations are therefore determined by the relative magnitude of all removal rates and radioactive decay rates. Some of these removal rates are highly dependent on other room conditions such as the room aerosol concentrations and size distribution, convective turbulence, and any resuspension processes (Porstendorfer et al., 1978;Raabe, 1969;Rudnick et al., 1982a, 1982b, 1982~).

2.4 RADON BEHAVIOR INSIDE HOUSES

1

19

2.4.5 Decay Product Air Concentrations Short-lived radon progeny air concentrations, within a well-mixed dilution volume, V,may be mathematically modeled by a linear, first order differential equation which accounts for all known sources and sinks (Jacobi, 1972; Pol-stendorfer et al., 1978). The removal rate constant for ventilation or air infiltration, I,, is assumed to be the same for each radionuclide. The plateout rate constant, PN, denotes the removal rate of the N"hairborne progeny by deposition onto room surfaces by Brownian diffusion, enhanced by turbulent convection. For a room aerosol, the plateout rate constant, PN, is an average deposition rate constant that can be estimated from knowledge of the aerosol size distribution and the individual plateout rate constants for the various particle sizes in the aerosol distribution (Knutson et al., 1983). The deposition or plateout rate in a size class depends largely on the molecular diffusion coefficient for the class. Because unattached progeny atoms have diffusion coefficients roughly five hundred times greater than the smallest attached progeny, most of the plateout observed under tranquil mixing conditions can be attributed to the unattached atoms. Under more turbulent conditions, some plateout contribution may come from those attached to condensation nuclei. Gravitational settling has not been included as a removal mechanism since i t should be negligible for aerosols with a size distribution normally found indoors, i.e., count median diameters of 0.05 to 0.1 pm with few particles greater than one pm in diameter (Knutson et al., 1983). Steady-state expressions for the progeny airborne concentrations can be approximated by the following: (where the subscripts 0 to 3 denote the appropriate decay constants for 222Rn,218P~, '14Pb, and 214Bi,respectively)

The term shown to the left of the product series in equation (2.2) represents the steady-state radon air concentration which is inversely proportional to the air infiltration rate since I, >> A, (I, typically ranges from 0.5 to 2 per hour). By inspection of equation (2.2), it is apparent that the air infiltration and plateout rates have distinct influences on the steady-state progeny air concentrations. The equilibrium activity ratios can differ considerably from one another depending on the magnitude of I,, P N , and other progeny removal constants (if present), relative to the decay constant AN.Since it is rare for steady state conditions to exist, and for radon concentrations

20

1

2. SOURCES AND BEHAVIOR OF RADON

to be constant, these equations are, a t best, a guide to modeling longterm averages. The assumption that indoor airborne radon and radon decay product concentrations can be accurately modelled assuming that all indoor sources are well-mixed is not appropriate, especially for sources of radon such as water supplies. In this case, the microenvironment within the house, particularly the rate of air mixing between the shower, bathroom, kitchen and remainder of the home, is an important factor with regard to the exposures that occur to the people living in the house. For most situations inside buildings the assumption is made that the airborne radon decay products are a t 50 percent equilibrium with the parent radon. Information on methods of monitoring radon and radon decay products in house is contained in NCRP Report No. 97 Measurement of Radon and Radon Daughters in Air (NCRP, 1988).

3. General Approaches for Control As noted in Section 2, the primary source of airborne radon in most houses is the underlying soil. One technique for minimizing the concentrations of radon gas and its decay products within a house is to impede the entry of radon from this source. This can be accomplished by removing the source of radon, diverting the radon before it enters the structure, andlor placing a barrier between the source and the living space. Although such techniques are applicable to houses undergoing construction, they are not always applicable or feasible in existing houses. In those cases, or in instances where the source cannot be identified, the alternative approaches are to employ some method of air treatment or to increase the rate of intake of outside air. Increased ventilation provides effective control (the radon concentration is inversely proportional to the air infiltration rate); however, it is generally accompanied by other problems, such as an increase in heating and cooling costs and increased radon infiltration if exhaust ventilation is used. As would be expected, a variety of techniques have been developed to control radon in residences, depending on the radon source and the building construction style (see Section 7). Because the control techniques that can be applied are influenced by a large number of factors, there can be no one best system to recommend in every situation. For purposes of this report, these methods have been loosely grouped under the headings of Passive or Active Techniques. The basic principles of each of these techniques will be discussed in this section. Detailed information on the variety of methods that can be used in the application of each of these techniques will be provided in Sections 4 and 5. In the final analysis, however, the basis on which any remedial action should be evaluated is its effectiveness in reducing the dose to the bronchial tissues of the lungs. As will be noted later in this report, certain methods that have proven effective in reducing the concentrations of airborne radon decay products do not provide equivalent reductions in estimates of the accompanying doses to the lungs. In fact, certain methods may actually increase the dose to the lungs of people breathing the treated air.

22

1

3. GENERAL APPROACHES FOR CONTROL

3.1 Passive Techniques A passive technique is one that, after it has been implemented or incorporated into a building, requires no further action or maintenance. Such methods are generally preferred by the public since they can be unobtrusively incorporated into the building fabric, will not affect the saleability of the property, and do not require maintenance and its associated costs. Unfortunately, in existing houses, some problems cannot be handled by passive measures, nor are the costs and disruption involved always acceptable. Examples of passive methods are source removal and closure of entry routes.

3.1.1 Source Removal Source removal is the prime example of a passive technique. If the source of elevated radon concentrations is highly active radium bearing material-such as uranium mine waste rock, uranium mill tailings, or uranium refinery wastes, experience has shown that the removal of most of this material adjacent to a building foundation effectively and permanently reduces the indoor radon concentrations. Material removal is often surprisingly expensive, since much of the excavation may have to be done by hand, as limited clearances around buildings often prevent the use of machinery. Even when mechanical equipment can be used, excavation adjacent to buildings is difficult. Radioactive material used as backfill may be mixed with local, excavated material containing rubble, boulders or broken rock. Below ground services may either require protection or need to be relocated. Additions to buildings may not have proper foundations, and below ground structures may become unsafe when material around them is excavated and the ground support is removed. Inexperienced contractor personnel may damage the structure with equipment. Finally, when all radioactive material is removed, extensive landscaping is required to restore the area to its original appearance. If the source material was used in a nonload bearing manner as fill around walls or beneath floors, removal, although expensive, is possible. However, in some cases, the structure will have been built on pre-existing source material which is supporting the building weight. This cannot be removed short of lifting the building superstructure and replacing the entire foundation andlor basement. In these cases, source removal has to be replaced by soil gas exclusion methods, such as closing entry routes.

3.2 ACTIVETECHNIQUES

1

23

3.1.2 Closing Entry Routes The subgrade portion of the basement or foundation of a building is not airtight for conventional building styles. As a result, there are many openings through which soil gas containing radon can flow freely from the soil into the building interior. The ease of soil gas movement can be significantly reduced by closing these openings. In order of importance, such openings include exterior drains brought into the building to connect to sumps or soakaways, voids left in the floor slab to assist in the installation of plumbing fixtures or service entries, junctions between walls and floors, and the air spaces in hollow concrete block walls. Other openings are produced as a side effect of architectural features in houses, such as sunken living rooms and sunken baths. In some cases, cracks through the building materials, caused by shrinkage or settling, can be significant portals for the entry of soil gas. The equivalent leakage area of all these openings in standard house basements having floor areas of 120 to 200 square meters (1,300 to 2,150 square feet) can be up to several hundred square centimeters, i.e., up to 0.01 percent or more of the total basement floor area. Most of the resistance to soil gas movement is that of the soil itself, so a major reduction in the area of subgrade openings is needed to significantly reduce the soil gas flow rate. Experience suggests that the total effective area of such openings within the building must be reduced to less than 10 square centimeters (i.e., a factor of 10 or more) to produce a major reduction in average indoor radon concentrations. In modem communities with a relatively uniform style of construction, it has been possible to identify a number of routes that are common to the building techniques used, and to develop standard methods for closing some of those routes. In older communities, variations in building styles, techniques and materials may be too great to permit the development of standard control methods. Such variations may also result in the presence of so many different entry routes that sealing becomes too expensive or impractical. An example of this situation is homes in older rural communities whose foundations include suspended floors with bare earth beneath, or cellars with walls of fieldstone or random rubble, and floors of bare earth, exposed rock or flagstone. In these cases, control can best be accomplished through application of an active mitigation technique.

3.2 Active Techniques An active technique is one in which radon or its decay products are diluted or intercepted. Ventilation is an example of dilution; air

24

1

3. GENERAL APPROACHES FOR CONTROL

treatment (filtration and/or space charging) is an example of interception. Ventilation, filtration, and some forms of diversion require a pressure differential which is usually provided by a fan. The techniques for the active control of radon and its decay products may be classified as soil ventilation, structure ventilation and air treatment.

3.2.1 Soil Ventilation Where the soil connections are either so many, so large, or so well concealed that sealing them is impractical or uneconomical (DSMA, 1979a; Haubrich and Leung, 1980; Leung, 1980), the radon entry rate into a building can only be reduced by decreasing the radon concentration in soil gas near the building, diverting the soil gas from the building or reducing the pressure differential between the building and the soil. All three effects can be achieved simultaneously by use of a soil ventilation system, which withdraws soil gas from around and beneath the building and exhausts it to the atmosphere. Practical approaches can vary from a withdrawal system utilizing the granular fill beneath a floor slab to one involving an elaborate perforated pipe network, installed beneath and around the building. The average natural pressure difference between the soil and building is only a few pascals, and even a small fan is able to produce much higher pressure differentials in the pipe network. All of these approaches are designed to cause local reversal of the pressure differences so that air flows from the building through the adjacent soil air spaces to the collection system, effectively preventing the entry of soil gas into the building. This flow of comparatively radon-free air into the soil from the building, and also from the atmosphere, dilutes the radon concentrations in the soil adjacent to the building, and diverts the locally produced radon to the collection system instead of permitting it to enter the building. This system has been successfully applied in a number of locations in Canada, Sweden and the United States, to buildings with all forms of subsurface construction. The wind and thermal forces that make the building pressure lower than that in the soil can also be used to produce passively the pressure differentials in the pipe network by means of a stack. However, as these differentials between the soil and the pipe network are only minutely larger than those between the soil and the building, a large pipe network is needed for the passively vented system to compete effectively. An extreme example of this is a cross-vented crawlspace, where the passive pressure Werence between the upwind

3.2 ACTNETECHNIQUES

1

25

and downwind sides of a house creates ventilation flow rates large enough to maintain radon concentrations in the space a t a low level.

3.2.2. Structure Ventilation In general, radon concentrations in the outdoor air are relatively low. Therefore, one of the methods that can be used for reducing the airborne concentrations of this gas and its decay products inside houses is ventilation. Application of this technique, however, is not without problems, including the following: (a) The natural ventilation rate in houses averages 25 to 50 liters per second (50 to 100 cubic feet per minute). To reduce the concentration by a factor of three would require an air supply of 75 to 150 liters per second (150 to 300 cubic feet per minute). The additional air would require up to seven kilowatts of heating in cold weather areas, and up to three kilowatts of cooling in hot weather areas. These requirements can readily represent a large fraction of the total energy consumption within a house and the added costs can amount to hundreds of dollars per year. These costs and available equipment suitable for house use limit the maximum additional ventilation rate to less than 100 liters per second (200 cubic feet per minute). (b) In practice, the beneficial effects of adding ventilation are hard to predict. If a supply fan is used, the additional air forced in tends to lower the building neutral plane (the plane above which the air flows out of the building, and below which the air flows in) and thus reduces the natural ventilation rate. As a result, the rate of ventilation does not increase by as much as the fan air supply (Desrochers and Robertson, 1985). (c) The increase in pressure within the building decreases the inflow of soil gas. The effect of this reduction in radon supply rate on the concentrations within the building can be much larger than the change in ventilation rate. Similarly, an exhaust fan increases the building-soil pressure differential, and can increase the radon infiltration rate (supply) enough to more than compensate for the increased ventilation rate. Changes in the radon supply rate can lead to changes in radon concentrations much larger than those caused by ventilation rate changes. Unfortunately, the size of the change is hard to predict since it depends on the total leakage area, which varies from building to building. (d) The noise resulting from the addition of fans, or changes in the speed of existing fans, may be unacceptable.

26

1

3. GENERAL APPROACHES FOR CONTROL

(e) In cold weather areas, changing the existing ventilation systems can change the temperature distribution in the soil adjacent to a building and induce freezelthaw cycling that can be highly damaging. In the above ground parts of the building, air leakage can cause condensation damage. (0 The addition of a supply andlor exhaust system in buildings with established and satisfactory air movement patterns can disrupt the existing air flows. (g) Satisfactory and effective ventilation systems are remarkably difficult to achieve even when competent and qualified design assistance is available. Careful and informed inspection and maintenance are a necessity.

3.2.3 Air Treatment Air treatment is one of the more attractive methods for reducing exposures to airborne radon decay products in existing houses. The reasons for the appeal of this approach are: (a)the control technology is immediately available; (b) the overall cost is generally lower than that for other alternatives; and (c) air treatment does not require a priori knowledge concerning the location(s)of the radon entry points into the structure. In recent years, however, problems in the maintenance of air treatment systems and the need to monitor their performance continuously to know when to replace filters, etc., have been recognized. In addition, such methods of air treatment may increase the fraction of unattached radon decay products in the treated air. This, in turn, could increase the biological damage to the lungs. For this reason, care should be taken to assure that the air treatment method being applied is one that not only reduces the concentration of airborne radon decay products but also reduces the accompanying dose to the lungs of people breathing the treated air. Radon is an inert gas, making it difficult andlor expensive to remove by air treatment. As a result, most air treatment methods are designed to remove the airborne radon decay products. Treatment devices that have been tested for removal of the decay products include: (a) high efficiency filters, (b) electrostatic precipitators, (c) ceiling fans, which provide enhanced convection; (d) ion generation systems (which provide unipolar space charging); and (e) combinations of these approaches. Current data on the application of each of these methods for the removal of radon decay products will be covered in later sections of this report.

4. Source Dependent Control Techniques 4.1 Soil Gas The fundamental mitigation methods used for the control of radon arising from soil gas can be grouped into four categories. The first is source removal. The second involves increasing the resistance of the building fabric to soil gas entry, generally referred to as sealing. The third relies on reduction of the pressure gradient between the building and soil, generally referred to as soil ventilation. The fourth depends on increasing the removal rate of radon from the building by increasing the structure ventilation rate. Another method of control, which as yet is not practical, would be to select homesites for new construction that have low levels of soil gas. The complexities and costs of mitigation are due almost entirely to the difficulties of applying these simple principles to existing buildings. Tasks that could have been performed a t low cost during construction can approach a major fraction of the building's cost when they have to be introduced or implemented in a completed building.

4.1.1. Sealing as a Mitigating Measure 4.1.1.1 Routes of Soil Gas Entry. The observation that solid concrete was essentially impermeable to soil gas containing radon led naturally to the development ofmethods to seal the openings through which soil gas entered a structure. It was soon found that the subgrade structure of most buildings is not air tight and the actions taken during construction of a building produces many openings through which soil gas containing radon can flow freely from the soil into a building (see Section 3.1.2). These include implacement of drains and basement sumps (see Figure 4.1). The basement floor is often poured late in the construction of a building's foundation, while the building supports, and supports and piping for the furnace, oil tank, and stairs are resting on the subfloor fill. As a result, the concrete beneath or around these areas often has

28

1

4. SOURCE DEPENDENT CONTROL TECHNIQUES

Fig. 4.1 Routes of soil gas entry via drainage system.

openings in it. If the building supports are hollow steel or concrete block columns, they can provide major soil gas entry routes via the column center. In buildings with poured concrete basements, the major joint connecting to the soil is the basement wall/floorjoint (Figure 4.2). The concrete floor is poured after the walls have been erected, and it touches the walls when the concrete is wet. As it cures, the floor

Fig. 4 2 Routes of soil gas entry through a concrete floor slab.

4.1 SOILGAS

1

29

shrinks away from the walls, leaving a small gap around the entire perimeter of the basement. The fraction of this crack that connects to the soil, and hence its importance as a route of soil gas entry, depends very much on the circumstances during the pour and subsequent curing conditions for the concrete. The gap can be much less than a millimeter, or a s large as three millimeters, and the total effective open area can be several hundred square centimeters. Sometimes a compressed fiber board "expansion joint" is placed between the wall and floor before pouring the floor. This creates a n even larger porous connection to the soil. To minimize shrinkage stresses, concrete that covers large areas is poured in sections. New sections are butted against the old sections, and can shrink away as far as one millimeter on setting. The openings pass completely through the slab, but may not reach the soil if a plastic sheet is laid beneath the slab for moisture control. This treatment, commonly in use today, can be a n effective barrier to soil gas. Poured concrete floor slabs and basement walls sometimes crack as the result of stress during curing, or by unbalanced forces created by settling. In general, these cracks are small, and they are minor routesof entry if the floor slab was poured over a plastic sheet. Curing cracks are produced by shrinkage tension forces in the slab, and they tend to radiate from floor openings, drains, or service entries, where there are also openings in the subfloor plastic sheeting (Figure 4.2). The presence of this kind of crack makes it difficult to seal the opening, since the crack provides a bypass around the sealant. Ifthe foundation walls are of hollow concrete block, there are many potential openings (Figure 4.3). Soil gas can enter the concrete block walls through porous mortar, through openings in the mortar joints, and through cracks or openings in the wall created by soil movement. Once within the walls, the gas moves through the interconnecting block cavities and can pass into a building through openings in interior mortar joints, cracks, or open block cavities a t the top of the walls. As concrete block walls are literally a collection of inaccessible holes held together by cement, it is futile to hope that all these openings can be sealed effectively at a reasonable cost (DSMA, 1979a). Sealing is not a valid mitigation measure for concrete block foundations. 4.1.1.2 Sealing Materials. The ground on which a building stands is not stable. In cold weather areas the freezelthaw cycle changes the volume of the upper soil layers over time, and in warm weather areas with clay soils, a similar shrinkagelswelling takes place in response to seasonal rainfall variations. Although foundations are generally

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4. SOURCE DEPENDENT CONTROL TECHNIQUES

Fig. 4.3 Routes of soil gas entry through wnerete block walls.

placed a t a depth to minimize movement, a significant amount of relative movement can still take place and cracks are not uncommon. Water often leaks in a t a crack causing localized moisture in the concrete. Laboratory experiments have been reported (DSMA,1979b) in which ten potential sealants were tested for their ability to form a n airtight seal to both dry and damp concrete, to maintain their seal in the presence of water, and to withstand movement of the substrate. Satisfactory materials included two catalyzing rubber-based seal-

4.1 SOILGAS

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31

ants that used a primer coat to prepare the surface, and one solvent hardening primer-less rubberlasphalt sealant. One rubber sealant was intended for use in channels; the other two sealants were intended to form water tight membranes over surfaces. In areas where limited movement takes place, and large openings such as service entries need to be filled, an asphaltlsolvent mix (roofing cement) was found to seal to concrete with minimum surface preparation (DSMA, 1981a). The other materials examined were not flexible enough to work satisfactorily. Epoxy materials are good sealants, but they are rigid and so strong that new cracks will often form adjacent to old epoxy filled joints as a result of stresses from soil movement. Flexible sealants allow the building to move, while maintaining their seal, and do not produce new stresses that might cause new cracks. 4.1.1.3 Sealing Methods. Joints can be closed either by opening them with a power chisel wide enough to allow a channel type sealant to be inserted, or by cleaning the concrete surface on either side of the joint for better adhesion, and then placing a membrane type sealant over the joint (DSMA, 1981b). The walllfloor joint is the most difficult to seal, since the sealant must form a good bond to both the horizontal floor and the vertical wall. Experience has shown that a satisfactory solution for all joints and cracks is to use a formed-in-place membrane sealant of sufficient viscosity and film strength that it can be applied to vertical wall surfaces as well as to the floor. Preparation for use ofthis type sealant involves removal of the surface layer of concrete on either side of the joint with a powered chipping gun, vacuum removal of the dust, application of a primer followed by application of a catalyzing urethane rubber sealant over the joint. Elaborate preparation is needed because the concrete surface is covered by a coating of laitance (a thin layer of cement with poor adhesion), and this is often covered with paint. It is virtually impossible to obtain a permanent bond between this type surface and a sealant. All paint and loose material must be removed to expose a fresh concrete surface before a reliable bond and effective closure of the opening can be obtained. To ensure bonding, most sealants require the fresh surface to be treated with a primer. A satisfactory primer is fluid with a high solvent fraction that penetrates the concrete pores and forms a thin skin of material on the surface that is firmly bonded to the concrete. The sealant adheres to this primer (DSMA, 1981b). Sewer and water connections are normally brought into a building through a formed opening in the concrete floor slab. The material (paper, fiber insulation) that was packed around the pipe to keep the

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4. SOURCE DEPENDENT CONTROL 'IXCHNIQUES

concrete away is usually left in place, but provides very little resistance to soil gas movement. This route can be closed by removing the packing material, and pouring a sealant into the annular opening between the pipe and the concrete. Similar openings exist beneath the toilets on concrete floor slabs, but are concealed by the foot of the bowl. The toilet can be lifted to expose the opening and a sealant poured into the opening. The drains of baths on concrete floor slabs are usually placed in a large formed opening that is concealed. Access to the area can usually be gained by cutting through an adjacent wall to fill the opening with a liquid sealant. A high solvent asphaltic material has proven satisfactory, since the solvent tends to penetrate the concrete over time and thus helps the asphalt form a good bond despite the presence of dirt and laitance. In many areas the peripheral groundwater that gains access to the weeping tile is drained to an internal sump or a basement floor drain. This results in a direct entry route for soil gas, which can enter the perforated weeping tiles and move into the building via the drain connections. In other areas floor drains are not connected to the sanitary sewer, but to an untrapped soakaway, which collects soil gas as effectively as the drain tiles. Such entries can be closed by replacing the drain or sump with one that incorporates a water trap and by connecting a priming line to a regularly used fixture ( e g . , laundry tub or toilet) to maintain the water seal. A lower cost alternative is to close the drain or sump with a plastic water-trap adaptor, and either to rely on drainage water to maintain the seal or to routinely pour water into the trap. However, the junction between the drain pipe and the edge of the sump crock or the floor is often not airtight, and sealing is required a t those locations.

Epoxy Sealants. All cracks and joints in a poured concrete basement can be sealed if the entire basement surface is coated with a multilayer seamless epoxy coating material. Since epoxy coatings will not adhere properly to laitance and old paint, the entire basement surface has to be ground to expose fresh concrete, and then a t least two coats of epoxy applied to ensure a continuous film. The massive disruption, the toxic vapors released during application, and the high cost make this method impractical for most situations. It is only in the unique case where the concrete contains relatively high concentrations of radium, and is itself a major radon source, that such treatment is recommended.

4.1.1.4

4.1.1.5

Performance. The performance of sealants in a retrofit sit-

4.1

SOIL GAS

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33

uation is difficult to evaluate, since in many cases additional remedial action is terminated once the radon concentrations are reduced to a n acceptable level. In general, experience a t mitigation sites is that closing just the major openings, such as drains, produces reduction factors of two to three in about half of the houses. The other half requires sealing of additional routes to achieve comparable reductions. In cases where all the soil connections are accessible and can be effectively sealed, i.e., reducing the total open area of all the connections to the soil to less than one square centimeter, radon concentrations can be reduced to the contributions estimated to arise from the building materials alone, which generally are low and of little concern. In more usual retrofit situations, a five-fold reduction is achievable with closure of the larger obvious entry routes. However, if cracks later develop in or around the sealant, or if new cracks develop in other areas of the basement, control may be significantly degraded.

4.1.2

Ventilation

Ventilation can be applied as a control technique to the soil beneath a building, to the building itself, andlor to the crawl space between the building and the soil.

Soil Ventilation As suggested previously (Section 3.2.1), the best way to reduce radon entry rates into a building is to decrease the flow of soil gas by increasing the pressure differential between the building and soil, or by reducing or reversing the pressure-driven flow of radon from beneath the building. One way to accomplish this is to install a perforated pipe network beneath and around the building, with the network being maintained a t a pressure lower than the pressure within the building either by a small fan or by a passively vented stack. The local reversal of the pressure differential causes air to flow out from the building to the collection system through the soil, thus effectively preventing the entry of soil gas into the house through the soil connections. The air drawn into the soil from both the building and from the atmosphere also dilutes the radon concentrations in the soil adjacent to the building (Vivyurka, 1979). This system has been successfully applied in a number of buildings in Canada, Sweden, and the United States. These include buildings with concrete block foundations as well as those with poured concrete foundations. The average natural pressure difference between the soil and a building is only a few pascal, and even a small axial fan produces 4.1.2.1

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4. SOURCE DEPENDENT CONTROL TECHNIQUES

pressure differentials of 25 to 50 pascal in a pipe network. A passively vented stack extending into the low pressure zone over a roof produces a negative pressure of a few pascals, comparable to that existing between a building and the soil, since it is produced by the same wind and thermal forces. As the collection system must compete with the building for soil gas, a passive system will always need a much larger and hence more costly collection system than would a powered exhaust. For this reason, passive systems are rarely as cost-effective a s powered systems. Although soil ventilation is generally effective, it is not a panacea. The use of low permeability fill, local variations in soil permeability, or large building-to-soil connections can prevent reversal of the soil to building pressure gradient over the entire foundation, particularly in retrofit situations. I t is difficult to predict the size of the fan required; a 50 liters per second (100 cubic foot per minute) axial fan is often satisfactory, but more permeable soils or many openings can require larger centrifugal fans to achieve the needed pressure drop. The noise of the fan can be a nuisance. In those areas where winter temperatures fall below freezing for considerable periods of time, the cold air drawn from the atmosphere may cause the frost line to penetrate deeper around foundations and this may cause structural damage. The soil gas discharged by the system is saturated with moisture, which can freeze in the exhaust portions of the system and may block the exhaust, or damage the fan. To prevent this, fans for use in colder areas should be mounted on the end of long vertical risers (DSMA, 1979~).Condensation or freezing takes place in the riser, thus protecting the fan. In addition, care should be taken to assure that the fan does not discharge into occupied areas. 4.1.2.1.1 Subsoil Collection Systems. To be effective, a subsoil collection system must produce slightly sub-atmospheric pressures in the soil adjacent to each wall and the floor of a building. An approach is to install perforated pipe beneath the basement floor or slab and in excavated trenches surrounding the building. If such piping is then coupled to an exhaust system (either a fan or a passively vented stack) to provide the pressure differential necessary to prevent the radon from the soil entering the building, proper protection can be assured. Installation of such equipment, however, is expensive and causes considerable disruption. If a n exhaust fan is used, the extent of the collection system can be reduced, since a fan can generate much higher pressure differentials than a passive stack. In many cases, the collection network can be dispensed with entirely, and the existing structure utilized to

4.1 SOIL GAS

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35

control the airflow. Two common systems used in low cost mitigation work are discussed below. 4.1.2.1.2 Subfloor Exhaust. If a building has a concrete floor slab, subfloor exhaust ventilation can be used. This approach consists of a pipe inserted through the floor into the soil. The opening around the pipe is sealed, the pipe is extended outside the building, and a small exhaust fan is placed a t the elevated end of the pipe. The fan draws the soil gas to the cavity in the soil through the layer of coarse material present under most floor slabs and, in turn, draws air from the building atmosphere through every crack and opening in the floor slab and through the wall-floor joint, thus preventing soil gas and radon from moving from the soil into the building through these openings. This can be a very effective approach if the basement walls are poured concrete. In such a case, the entry routes will be restricted to cracks through the floor and wall-floor joint. If the walls are concrete block, the system may be less effective because it may not reduce the flow of soil gas into the building through the block walls. The radius over which the exhaust system will be effective is difficult to predict, as it depends on the permeability of the subfloor fill, and the size distribution of openings. Usually, however, it will extend to four to five meters with a fan that develops a 50 to 100 pascal pressure differential. Small houses may require only a central exhaust location for satisfactory performance, but larger houses generally require two locations so that no portion of the floor is farther than four to five meters from the point of exhaust. To reduce costs, both exhaust pipes may be connected so they can be served by a single fan. 4.1.2.1.3 Weeping Tile Exhaust. Peripheral ground water drain (weeping tile) pipe can be used as a collection system if combined with an exhaust fan. Following this approach, air is drawn from the atmosphere through the soil adjacent to the walls, and a smaller amount is also drawn from the basement through wall cracks and the walVfloor joint. This not only reduces the radon concentration in the soil adjacent to the walls, but also decreases or prevents the flow of soil gas into the building through wall openings. As a result, this will reduce radon entry rates into buildings with concrete block walls, provided that the floors do not have too many openings. There are two different practical methods to exhaust the weeping tile. Weeping tiles are often drained into a sump inside the building. In this case, soil gas and radon that enter by this route and that may enter through wall and floor openings can be removed by placing an airtight cover over the sump and exhausting the soil gas to the

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4. SOURCE DEPENDENT CONTROL TECHNIQUES

exterior using a fan. This provides a double benefit, for not only is the suction transmitted to the weeping tile via the drain pipe, but any openings between the edge of the sump and the floor slab (which would normally be a route for radon entry) allow the fan to draw soil gas from beneath the floor slab. This widespread pressure reduction is usually effective in reversing the soil gas flow over most of the basement area. For houses with sumps, it is probably one of the most cost-effective measures available. In a building where the weeping tile drains into the interior floor drain rather than into a sump, it is rarely convenient to place an exhaust cover over the drain. An alternative is to dig down outside the building to the weeping tile and attach an exhaust pipe via a ''T" piece. The weeping tile connection to the floor drain then must be closed by a water trap to prevent the exhaust fan from simply drawing air from within the building. Similarly, on sloping sites the weeping tile may not enter the house; it may discharge to a lower level on the site. In this case, both ends of the drain must be closed with water traps, and a riser and exhaust fan connected to the pipe a t some point between the traps. Not all weeping tile installations are satisfactory as soil gas collection systems. For example, the tile may not surround the house. In some areas window wells are drained to the weeping tile either through coarse fill provided near the footing, or by a n open ended pipe connected to the weeping tile. Both of these provide a low resistance path for air to enter the tile. This can be partially compensated for by increasing the size of the exhaust fan, but generally drains will have to be excavated and the open end partially closed or trapped so that the flow of soil gas is reduced but water can still enter. 4.1.2.2 Wall Cavity Exhaust. The major radon entry routes in buildings with hollow concrete block foundation walls are the walls themselves and the walllfloor joint. If there is no weeping tile system, both of these flow paths can be controlled by using the wall cavities as the collection system, exhausted either by a small fan inserted into each wall or by a header system tapped into each wall. Suction is needed a t each wall because the blocks a t the comers are often filled with concrete for reinforcement, and therefore there is no connection between walls. If the pressure in the block cavities is significantly lower than in the building, then air will flow into the wall a t all connections-including the walvfloor joint. Exhausting the walls is appropriate only if the leakage areas to the house can be controlled such that there is no danger of back drafting combustion appliances. In this case, blowing air into the walls is a n alternative. The goal then is to displace soil gas from the walls with fresh outside air, so

4.1 SOILGAS

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37

that leakage into the house consists only of air with low radon concentration. This effectively prevents back drafting, but the walls tend to be colder than before. A problem with this approach is that the leakage area of the walls is large, and predominantly on the building side of the wall. Some work will be needed to reduce the size of the openings. This could be as little as gluing sheets of foam insulation to the inside face of the wall, but this approach requires access to the walls which is often difficult. If the block cavities at the top of the wall are left open, as is the case in some areas, these openings will have to be closed by filling them with mortar or an expanding foam. A high standard of closure is needed, for the walls will be filled with soil gas that is high in radon, which may be forced out into the house from the upwind walls when the wind blows. Although a wall cavity exhaust system can be effective, it is generally more cost-effective to install a subslab ventilation system with several exhaust points near each wall. 4.1.23 Cmwl Space Ventilation. Structures with crawl spaces oRen have high radon concentrations within such spaces due to a combination of large areas of exposed soil and low ventilation rates. Unfortunately, natural circulation airflows distribute crawl space air to the rest of the building (Nazaroff and Doyle, 1985). Furthermore, mitigative work is difficult due to poor access and limited space. Where winters are not severe, the crawl space is often unheated, and is essentially outside the building. In those cases, significant reductions in radon concentrations can be accomplished by improving the crawl space ventilation and reducing the air exchange with the building by sealing the openings between the crawl space and the living area. Additional insulation to reduce heat loss through the floor may be needed because improved ventilation will lower the temperature of the crawl space to a value close to the exterior temperature. Heated crawl spaces that are essentially part of a building interior present the greatest problems for mitigation by ventilation. There are two ventilation strategies that can be applied. The first strategy is direct introduction of fresh outside air. This not only dilutes the radon concentration in the crawl space, but it also slightly pressurizes the crawl space and reduces the emanation rate of radon from the soil. In cold climates, floors, sewices and heating ducts may have to be insulated. If this is not feasible due to limited access, the air may have to be heated. The high costs of a heater unit and of energy to power it makes this an unattractive approach. The second strategy is to exhaust air from the crawl space,creating a small negative pressure so that the normal flow of air is from the

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4. SOURCE DEPENDENT CONTROL TECHNIQUES

building to the crawl space. As the house air is already heated, there will be no drop in the crawl space temperature, and insulation will not be needed. The radon concentrations in the air within the crawl space will tend to increase, so the effectiveness of this method will depend on the fan being large enough to ensure that air flow is from the building into the crawl space. The entry of soil gas from exposed soil in unpaved crawl spaces can also be reduced by placing a perforated collection pipe network over the soil and covering it with an air barrier. The barriers can be concrete, plastic sheet, or even a sprayed and formed-in-place membrane material. The barrier does not have to be completely airtight, as long as the openings are small enough to allow a small fan to produce the required exhaust rate. The advantages of this approach, over ventilation of the space itself, are that the amount of air withdrawn from the building is small, and the impact on energy costs is negligible. The disadvantage is that access to the crawl space is needed to install the barrier. 4.1.2.4 Removal Efficiencies for Source Dependent Control Techniques. If the collection and exhaust system is large enough to reverse the house-to-soil pressure gradient over the entire foundation surface, the systems described above can be very effective. Experience with houses in Pennsylvania with concrete block walls shows that sub-floor ventilation or wall ventilation can reduce radon concentrations in basements from original values of about 60 kBq per cubic meter (1.5 nCi per liter) down to 70 to 100 Bq per cubic meter (2 to 3 pCi per liter), an overall reduction by a factor between 600 and 850. Installation of weeping tile ventilation systems produced reductions in radon concentrations from about 8 kBq per cubic meter (200 pCi per liter) down to 70 to 140 Bq per cubic meter (2 to 4 pCi per liter).

4.2

Water Supplies

Two basic methods, carbon adsorption and aeration, can be used

to remove radon from house water supplies (Lowry and Brandon, 1981; Reid, et al.,1985). In applying these techniques, however, one must realize that they provide control of only this one source, i.e., groundwater. If there are other major sources of radon, which is often the case, the control provided by these techniques may not be adequate.

4.3 CONSTRUCTION MATEFUALS

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4.2.1 Activated Carbon Filters

Activated carbon filters are designed to adsorb and retain radon from water flowing through them. Modern installations include a prefilter to clear accumulated foreign matter from the incoming water. Such filters eliminate the necessity for backflushing. Home units that remove 80 to 90 percent of the radon from water are available commercially for about $450; units that remove 90 to 99 percent are commercially available for about $900. One of the advantages of this approach is that it is essentially passive. However, the radon that is removed from the water is retained on the charcoal, and its decay can produce radiation fields as high as 2.58 x coulombs per kilogram (1mr) per hour a t 1meter from the container, and shielding of 20 grams per square centimeter may be needed to reduce fields to acceptable levels. This would increase the total cost to about $2,000-comparable to the cost of an aeration system which has no radiation build up problem (see below). 4.2.2 Aeration Systems

Systems that remove radon from water through aeration are also available. These systems may consist of packed columns with countercurrent air flow or they may spray the water inside a large container which then circulates air through the spray and vents the released radon to the atmosphere (Hinckley, 1977,1982). The cost of a system that will provide a removal efficiency of 90 to 99 percent is about $2,000.

4.3 Construction Materials

Since all materials derived from the earth's crust contain uranium and radium, building materials such as concrete, masonry, wall board, plaster, and mineral wool insulation, have trace amounts of radionuclides that can be sources of radon. A typical single-story brick or stone North American house'contains 30 to 60 tons of concrete or concrete block, 15 tons of brick or masonry facing, 7.5 tons of wall board and plaster, and more than a ton of mineral insulation. In modern housing, bricks and masonry are not a significant radon source because they are now used only as facing materials. As a result, they are outside the house shell and are separated from the interior by the house-air barrier. The radon they release does not enter the house.

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4. SOURCE DEPENDENT CONTROL TECHNIQUES

As pointed out in Section 4.1.1 the release rate of radon from building materials can be reduced by applying a surface sealant or barrier. The difficulties are not those of finding an effective barrier. It is in applying the sealant in an effective manner. For example, ordinary vinyl floor tiles that are set in an adhesive floor covering (not self-sticking) will greatly reduce the radon escape rate from a concrete slab floor. In contrast, an unglued sheet of vinyl covering may be less effective, even though it is a superior barrier material, since radon can enter the small air gap between the floor and the sheet, and escape to the house a t the edges of the sheet. A barrier raises the radon concentration behind it, so the diffusion rate through any openings, or along routes that bypass the barrier will be increased. Large reductions in radon releases require barriers that have few openings, adhere to the surface without air gaps, and extend to the edge of the material or beyond. In retrofit situations, the most convenient way of ensuring this has been to apply a low permeability membrane, usually a n epoxy, to the surface. Rubber based membranes have also been used.

4.3.1 Material Substitution

As indicated above, the radon concentrations in houses resulting from building materials of "normal" radium concentrations are low. In general, contributions from these sources result in indoor radon concentrations less than 40 Bq per cubic meter (1 pCi per liter), which is about 10 percent of the concentration that would produce exposure rates approaching the NCRP recommended remedial action joule-hours per cubic meter (2 WLM) in a year level of 7 x (NCRP, 198413). As previously indicated, an average airborne radon concentration of 300 Bq per cubic meter (8 pCi per liter) would produce over the period of one year, assuming that the radon decay products were in 50 percent equilibrium, an integrated exposure of 7 x joule-hours per cubic meter (2 WLM). The 40 Bq per cubic meter (1pCi per liter) concentration represents the baseline of exposure in buildings. Since this level of exposure cannot be avoided (in the U.S.),the main concern is that it should not be increased through the use of building materials with radium concentrations significantly above average. In some cases, identification of such materials is relatively easy. For example, phosphogypsum is a by-produd of phosphate fertilizer production, and has been used in Europe to make wallboard. It has also been added to cement. Much of the radium in the phosphate ore is transferred to gypsum, so i t can have radium concentrations up to

4.3 CONSTRUCTIONMATERIALS

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1.4Bq per kilogram (38pCi per gram) implying house radon concentrations of up to 100 Bq per cubic meter (3 pCi per liter) due to the wallboard alone. In North America there are large deposits of natural gypsum and the phosphogypsum plants are remote from the wallboard, factories, so there is little incentive to use phosphogypsurn. Furthermore, since the enhanced radioactive nature of phosphogypsum is well. known, it i s even less likely that by-product gypsum would be accepted a s marketable in the United States. In contrast, the situation is much more difficult in the case of concrete. There are thousands of concrete batching plants that generally obtain their aggregates from locally excavated gravels or crushed rocks, and their radionuclide content is typically not known by plant operators. Nonetheless, i t is unlikely that there are large areas of the U.S. using aggregates with high radium concentrations. However, the existence of a few such locations cannot be ruled out. 4.3.2

Changes in Building Design

Radon exposures from building materials could, if necessary, be reduced by decreasing the mass of mineral-containing building materials used in a house. Perhaps the simplest approach would be to use concrete slabs, preserved wood foundations, or prefabricated housing which, including the floor, is entirely made of wood and steel. In the US.,prefabricated housing is largely single story (mobile homes), but two-story housing is possible. However, because the largest radon source in U.S. housing is not, a t present, the building materials, but the ground on which the house stands, reducing the radon contribution from these materials need not be a consideration in the selection of such materials.

5. Source Independent Control Techniques 5.1 Introduction Whenever a specific and isolated radon entry point can be identified, the most appropriate remedial action is to divert or impede radon entry a t that point before it enters the air space of the dwelling. The remedial control techniques discussed in Section 4 are directly applicable to these situations. Although such techniques are preferred to those which attempt to remove radon or its decay products after entry into a house, they may not be economically feasible in existing houses where the radon entry pathways are multiple or cannot be identified. In such situations, the alternative approaches are: (1) to increase the outside air infiltration rate into the house, or (2) to employ some method of air treatment. Remedial methods of these types are generally classified as source independent because their application or effectiveness does not require a priori knowledge of the locations and sources of radon within a house. In some cases, adequate control may require a combination of source independent and source dependent remedial control techniques. Described in the remaining portions of this section are those techniques that have been found to be useful in the control of radon or radon decay products without dependence on knowledge of their source.

5.2 Increased Ventilation 5.2.1 Forced Air Supply The ventilation in a building can be increased conveniently by a small fan blowing untempered outside air into the building. The amount of air that can be delivered by this means is limited by the capacity of the heating/cooling system to accept inflow without upsetting temperature control. A separate fan is not always required in a building if it has a forced air system. When a separate fan system is

5.3 INCREASED AIR CIRCULATION

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not used, the circulating fan is arranged to run a t low speed continually, going to full speed when the thermostat calls for heating or cooling, and an air supply duct is connected to the return air duct close to the fan. The volume of air drawn in can be regulated by an orifice, or by a two-position electrically-controlled damper. In modern, tight houses and buildings, quite small airflows can provide significant reductions in radon concentration due to the effect of pressurization in reducingradon inflows. In older houses, however, the needed air flows are likely to be more than the temperature control systems can tolerate. A tempered supply is needed for such structures. It can be provided either by supplementary heating or cooling or an air-to-air heat exchange. If the required reduction in radon concentrations is large, then air-to-air heat exchangers may not be satisfactory, since they operate with nominally balanced supply and exhaust flows and do not provide pressurization. As a result, the pressure in a house is unchanged by their operation, and both the natural ventilation rate and soil gas flows are unchanged. Consequently, the radon concentration in a house is reduced only by the increase in the ventilation rate. In order for heat exchangers to be effective, houses must be relatively airtight and have low natural ventilation rates. If the natural ventilation rate is high, the size of the unit required for a significant reduction may prove uneconomical or impracticable. Most older houses are not airtight; hence heat exchangers have limited use as a mitigative measure for existing houses and are likely to be less costeffective than a simple fan. 5.2.2 Forced Air Exhaust

The ventilation rate can be increased by a small fan exhausting air from a house. As the discharged air must ultimately come from outside the building, the limit on the amount of air that can be exhausted is the capacity of the heatinglcooling system to maintain temperature control. As decreased pressure in the house tends to increase the radon inflow, exhaust is useful as a mitigative method only where spaces can be closed off so that the airflow is almost entirely into that space, e.g., inaccessible crawl spaces.

5.3

Increased Air Circulation

Reduction of radon decay product concentrations in houses through increased air circulation or enhanced convection has been reported

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5. SOURCE INDEPENDENT CONTROL TECHNIQUES 5.1-PAEC reductions by enhanced convection TABLE

Investigator

Air circulation Rate (per hour).

Condensation Nuclei (per cubic centimeter)

PAEC Reduction

Wrenn et al., 196gb 20-60 200-2,000 90-958 Holub et al., 1979 20 <100,000 41% AbuJarad and Not Reported Not Reported 28% Fremlin, 1982c,d Rudnick et al., 1982a 80-150 6,000-100,000 40-75% Rudnick et al., 1982b Rudnick et al.. 1982cc." " Air movement rate (cubic meters per hour) divided by the room volume (cubic meter). Measurements conducted in an unventilated mine shaft. ' Measurements conducted in experimental chamber. Cigarette smoke used as condensation nuclei source. "Relative humidity 20% to 60%; outside air infiltration rate 0.2 to 0.8 air exchanges per hour.

in several studies (Holub et al., 1979; Rudnick et al., 1982a). Similar observations have been made in mines (Wrenn et al., 1969). In these investigations, the increased air circulation was achieved by an air mover or fan forcing recirculation without added make-up air or an increased outside air infiltration rate. The reported potential-alphaenergy concentration (PAEC) reductions that were achieved varied from 40 to 95 percent (see Table 5.1) depending on the volume rate of air recirculated in relation to the total volume of the room, condensation nuclei concentration, and relative humidity of the air. The reductions in radon decay product concentrations with enhanced convection have been attributed to the increased surface deposition (plateout) of the unattached decay products and, to a lesser extent, the plateout of small particles to which the decay products were attached. Because the diffusion coefficients for unattached decay products are 500 times larger than for typical airborne particles, plateout of the unattached activity is far more efficient and is believed to be more responsible for the observed PAEC reductions. For this reason, it is expected that high condensation nuclei concentrations (greater than lo4 per cubic centimeter) or high humidities, which tend to reduce the fraction of unattached decay products or increase the effective diameter of the unattached activity, will inhibit the plateout removal of the airborne activity. Holub et al. (1979) demonstrated that fan induced plateout of radon decay products becomes negligible a t relative humidities greater than 80 percent. Despite the large variations in condensation nuclei concentrations and relative humidities which might be expected in houses, enhanced convection appears to be a relatively inexpensive control option which is capable of modest progeny concentration reductions, i.e., less than

5.4 AIR-CLEANINGDEVICES

1

45

about 60 percent. Many houses already have ceiling fans andlor central ventilation systems installed for heating and cooling purposes, and their operation is already reducing the airborne PAEC in those houses. One of the most attractive features of enhanced convection is that the PAEC reductions appear to be achieved with little or no change in the fraction of the total PAEC that is unattached. This, perhaps, is because enhanced convection does not appreciably remove or affect the larger particles (greater than 0.05 micrometers diameter) in the room air. Consequently, enhanced convection does not significantly reduce the total aerosol surface area available for decay product attachment. Thus, PAEC reductions from enhanced convection and air circulation are essentially equivalent to mean bronchial dose reductions because the mean bronchial dose per unit of inhaled activity is unchanged.

5.4

Air-Cleaning Devices

Nearly all the early experience gained in removing radon or radon decay products from air was obtained through studies in the mining industry (Lindsay et al., 1978). Although the principles and devices available to remove radon decay products are similar, whether intended for the mine or home, differences in the environmental conditions, volume of air to be treated, and cost considerations render much of the mine experience inapplicable to houses. The published literature contains only a handfbl of reports of investigations in which air treatment methods have been applied in houses. At first glance, the most logical approach to reduce indoor exposures to radon decay products would seem to be removal of the parent radionuclide, radon-222. Several techniques for removing radon gas from mines have been reported (Goodwin, 1973); however, because radon is an inert gas, the chemical and physical methods available (Stein, 1972)have, for some time, appeared to be quite complex and expensive. For these reasons, the removal of radon by means other than ventilation has not been put into practice. In fact, the costs associated with radon removal technology in mines using adsorption onto activated charcoal or oil-silica gel (Reiter, 19671, have been thought to place these techniques beyond the reach of most homeowners. This, however, is a developing field and laboratory tests have recently been reported (Rudnick and Abrams, 1989) of a charcoal adsorption system that may have application in the home. This system consists of two units, one used to absorb the radon while the

46

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5. SOURCE INDEPENDENT CONTROL TECHNIQUES

second unit is being recharged. A novel approach in the system is the use of untreated outdoor air to regenerate the charcoal. There are several types of air cleaning methods that have been tested for the removal of radon decay products under conditions which could be considered representative of those in private houses. These methods include electrostatic precipitation, high efficiency filtration, and unipolar space charging. The first method is already in use in some U.S.and Canadian houses with forced air heating systems to remove allergy-causing spores and dust and particulates, including those from tobacco smoking.

5.4.1 Electrostatic Precipitation Reports of working level reductions by the use of electrostatic precipitators (electronic air cleaners) and the conditions under which these reductions were achieved are scarce, even though there have been some attempts to apply this method in uranium mines (Swindle, 1971 and Cooper, 1973). Cooper (1973) found that, following electrostatic precipitator (ESP) air treatment, the unattached fraction of the remaining airborne radon decay products could be increased to 0.5 from a typical mine value of 0.03 or less. Miles et al. (19801, reported that use of a n ESP inside a n unventilated room caused Potential Alpha Energy Concentration (PAEC) reductions by factors of between 6 and 19 a t an air treatment rate of 9.1 per hour. The larger reductions were associated with low (less than 4000 per cubic centimeter) condensation nuclei concentrations and consequently enhanced plateout of unattached decay products. These investigators also noted that the higher PAEC reductions were accompanied by unattached working level fractions greater than 0.5. Data on measurements df the effectiveness of electronic air cleaners in reducing airborne radon decay product concentrations have been published by Hinds et al. (1983), Maher (1985), and Rajala et al. (1986). All three investigations were conducted in a ventilated laboratory room under controlled environmental conditions using a free-standing, home-sized electrostatic precipitator. The first two authors reported PAEC reductions of up to 63 and 75 percent a t air treatment rates of 4.3 and 5.0 per hour, respectively, and outside air infiltration rates of 0.2 to 0.5 per hour. Approximately one-half of the PAEC reduction could be attributed to turbulent plateout on walls in the room and inside the fan blower units. Both investigators found that the fraction of unattached airborne radon decay products significantly increased (30 to 60 percent) after air treatment. The reason for this is that such cleaning processes remove the dust par-

5.4

AIR-CLEANING DEVICES

I

47

ticles from the air while, a t the same time, the radon gas remains. Under these circumstances, the radon decay products, subsequently formed in such an atmosphere through the continuing decay of the radon gas, have fewer dust particles to which to attach. As a result, a higher percentage of the newly formed decay products will exist in the unattached state. Using several dosimetric lung models, Maher (1985) estimated the mean brochial dose before and after treatment of indoor air with an electrostatic precipitator. His results suggest that, depending on the lung model used, the increased probability of bronchial deposition from a higher unattached fraction in the remaining airborne activity of the treated air could offset any bronchial dose reduction accomplished through reductions in the airborne PAEC. Rajala et al. (1986) observed similar decreases in the airborne activity and equilibrium factor and an increase in the unattached fraction for electrostatic precipitation while monitoring the aerosol concentration. These authors also noted that the ESP, itself, was a source of condensation nuclei when used in relatively clean air, presumably due to the production of ozone. The first reported measurements on the radon decay product removal efficiencies of ESPs in actual houses were performed by Lloyd and Mercer (1980) in a vacant apartment in Butte, Montana. Their measurements showed ESP working level reductions of 35 to 52 percent a t various locations inside an apartment a t an air treatment rate of 3.2 room volumes per hour. They suggested that the observed variations in the removal efficiencies were attributable to insufficient mixing of air inside the apartment and to diurnal fluctuations in the radon concentrations. No measurements were performed for the unattached h c t i o n or condensation nuclei concentrations. Scott (19831, conducted field measurements in which he investigated the effectiveness of ESPs installed in the central air conditioning systems of several houses built over Florida phosphate lands with elevated radium content. The ESPs were installed in the ventilation systems of the houses and operated continuously, with and without the high voltage stage. His observations showed that continuous operation of the air mover could reduce the PAEC by a factor of three to four with the high voltage on and by a factor of two with the high voltage off. In the latter case, the PAEC reduction was attributed to turbulent plateout of radon decay products inside the duding system and removal by a low efficiency pre-filter that was incorporated into the system. 5.4.2

High Efiiency Filtration

Radon decay product removal by high efficiency filtration of air in mines and rooms has been found to be one of the more effective

48

1

5. SOURCE INDEPENDENT CONTROL TECHNIQUES

methods for reducing the PAEC (Frame, 1969; Jonassen and McLaughlin, 1982; Maher et al., 1985; and Rudnick et al., 1982b). Reductions in PAECs as high as 97 percent were reported by Frame (1969), although no data were provided regarding the unattached fractions in the treated air. Rudnick et al. (1982b) measured PAEC reductions in a laboratory chamber of up to 90 percent for a n air filtration rate of five chamber volumes per hour and a n outside air infiltration rate of 0.5 chamber volume per hour. The effective air treatment rate (based on PAEC reduction) was considerably greater than five per hour. This was due to a n increase in the natural decay product plateout rate which resulted from the extremely high unattached fraction (greater than 80 percent). Other investigators (Jonassen and McLaughlin, 1982; Jonassen, 1984; and Maher, 1985) evaluated the effectiveness of air filtration in terms of the reduction in mean bronchial dose from airborne radon decay products, using various state-of-the-art dosimetric lung models (Harley and Pasternack, 1982; Jacobi and Eisfeld, 1980; James et al., 1980). The conclusions obtained in these investigations were similar and depended on the dosimetric lung model used to assess the exposure, on the assumed biological differences, and on the initial condensation nuclei concentrations. The dosimetric models of Harley and Pasternack (1982) and James et al. (1980) tended to predict no change or a slight increase in the bronchial lung dose with air filtration even though substantial decreases in the PAEC were obtained. At a n outside air infiltration rate of 0.2 per hour and low condensation nuclei concentrations (less than 3 x lo4 per cubic centimeter), the model calculations suggested that the bronchial lung dose could be increased by as much as a factor of two at an air filtration rate of 4.3 per hour (Maher et al., 1987). In contrast, the Jacobi-Eisfeld lung model predicted that air filtration would always result in a net reduction in bronchial lung dose. This difference is related to the assumption by Jacobi that unattached decay products are rapidly absorbed into the blood stream, thereby resulting in fewer of the unattached atoms decaying in the bronchial airways (James, 1984). At present it is unclear what health benefit, ifany, could be obtained from indoor air filtration or the use of ESPs since both may be ineffective in reducing the dose equivalent to bronchial tissues even though effective in reducing the PAEC.

5.4.3

Unipolar Space Charging

Space charging as a possible method of reducing indoor concentrations of radon decay products was first considered by Moeller et al.

5.4 AIR-CLEANING DEVICES

1

49

(1980). The technique involves the use of an air ion generator, which produces a continuous point source of unipolar charged air ions. The theory regarding the space charge removal of airborne particles was first developed by Whitby et al. (1965), and was later applied to radon decay product removal by Maher et al. (1985). The removal process can be described as follows: (1) radon decay products, as well as aerosol particles to which some of the decay products attach, are charged by diffusion of the air ions produced by the point generator; (2) the air ions also produce a nonuniform space charge in the room that results in an electric field gradient extending radially outward from the generator to the room surfaces; (3) because of the electric field, the charged decay products and particles migrate along the gradient and plate out onto room surfaces. The application of space charging for the removal of radon decay products in a vacant apartment was reported by Lloyd (1981). He employed one or more negative ion generators and positive collection plates in various configurations. His results, although confounded by varying radon concentrations, demonstrated working level reductions that ranged from 30 to 60 percent. However, measurements were not made of the unattached activity or condensation nuclei. A later study by Bigu (1983), concerning the effectiveness of a negative space charge and air circulating fan in reducing decay product concentrations, was conducted in a small (2.73 cubic meters) unventilated radon box. His data indicated PAEC reductions of greater than 70 percent when the ion generator was operated alone, and over 85 percent when the ion generator was operated simultaneously with a mixing fan. Data regarding the unattached fractions were not provided, although the aerosol concentration was approximately lo3 per cubic centimeter, and the size distribution primarily consisted of particles in the submicrometer size range. His results were insufficient to suggest any practical benefit or use for this type of air treatment. The most recent evaluation of unipolar space charging for control of radon decay product exposures was reported by Maher et al. (1987). These investigators applied both negative and positive space charging inside a large room that was ventilated a t a controlled rate ranging from 0.2 to 0.8 air exchanges per hour. Results from this study determined working level reductions of 67 and 85 percent for a negative and positive space charge, respectively. The unattached fraction of the airborne PAEC remaining after treatment was large (0.45 to 0.60) a t the low air infiltration rates and only slightly decreased (0.20 to 0.35) a t the higher air infiltration rates as compared to conditions without treatment (0.03 to 0.10). This is attributable to less particle removal a t the higher exchange rates, which is believed

50

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5. SOURCE INDEPENDENT CONTROL TECHNIQUES

to be related to shorter particle charging times, greater particle entry rates and a decrease in ion concentration by ventilation losses. Despite less particle removal a t the higher infiltration rate, the PAEC reductions were not significantly different with the positive space charge. The fraction of unattached PAEC following the application of a positive space charge was consistently less than with a negative space charge even though the PAEC reduction was much greater. The study data also indicated that the greater PAEC reduction with positive ions was due almost entirely to greater removal of 214Pb (RaB). This suggests that a large fraction of the 214Pbexists in a positively charged state following the decay of its parent, 218Po(RaA). In terms of the bronchial dose reductions predicted from dosimetric models, only the positive space charge was determined to result in a net benefit when the measurement data were applied in dosimetric modeling.

5.5 Application of Combined Approaches The application of combinations of various methods of air treatment for radon decay product removal has received little attention and, consequently, few data are available. The earliest mention of the combined application of two treatment methods is by Miles et al. (1980), who combined the effect of an electrostatic precipitator with that from a mixing fan within a n unventilated room. The investigators found that decay product removals by the mixing fan were enhanced through reductions in aerosol concentrations brought about by the electrostatic precipitator. This resulted in an increase in the fraction of decay products in an unattached state. The maximum PAEC reduction obtained using this form of air treatment was about 95 percent. The authors did not report the unattached fraction after air treatment; however, the condensation nuclei concentration was estimated to be between 150 and 3,800 per cubic centimeter. Jonassen (1984) combined the effect of filtration with a static electric field from a charged (less than 15 kilovolt) plate and determined that the removal efficiency of radon decay products by the charged disc was much greater when the air was simultaneously filtered. He suggested that this observation was due to the higher electrical mobilities of charged and unattached species, which represented a greater portion of the airborne activity following filtration a t a rate of three room volumes per hour. Jonassen also noted that the effect of the electric field on 214Pb(RaB) and 214Bi(RaC) was about

5.6 SUMMARY OF EXPERIMENTAL DATA

1

51

the same as for 21.ePo(RaA),although he cautioned that these results were preliminary. The remaining studies of combined air treatment involved the simultaneous use of a unipolar space charging and enhanced convection from a mixing fan. Bigu (1983) noted that the combined effect of a negative ion generator and mixing fan on the removal of radon decay products was substantially greater than that of either device operated alone. He further observed that the PAEC reductions were nearly independent of the relative humidity of the air (45 to 95 percent) inside the test chamber. The PAEC reductions reported for the combined air treatment approach were approximately 85 percent. Maher (1985) and Maher et al. (1987), evaluated the combined effect on the removal of airborne radon decay products of a negative or positive space charge and a ceiling fan in a series of experiments inside a ventilated room. The effectiveness of these combined air treatments was assessed in terms of mean bronchial dose reductions as well a s PAEC reductions. The study determined that the PAEC reductions were much greater when the ceiling fan was operated simultaneously with the generation of the space charge. This was true for both a positive and negative space charge. In addition, these investigators found that the combination of a space charge and ceiling fan did not increase the unattached fraction of the remaining airborne radon decay products as much as when the space charge was used alone. The combination of the space charge and ceiling fan yielded PAEC reductions approaching 85 percent for negative and 95 percent for positive space charges, respectively. The mean bronchial dose reductions that corresponded to these PAEC reductions were calculated to range from 55 to 91 percent for a positive space charge and ceiling fan, depending on the room air infiltration rate and lung model used. Independent support for these observations has been provided by Jonassen and Jensen (1984) and Keskinen et al. (1987). Lower dose reductions to bronchial tissue were determined for the combination of negative space charge and ceiling fan.

5.6 Summary of Experimental Data A summary of the data on the effectiveness of various radon decay product removal techniques, applied alone and in combination, is presented in Figures 5.1 through 5.3. Figure 5.1 presents data on the effectiveness of various air treatment methods for the removal of specific radon decay products and PAEC as a function of the

52

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5. SOURCE INDEPENDENT CONTROL TECHNIQUES

Fig. 5.1 Effectiveness of various air treatment methoda on the removal of specific radon decay products and PAEC as a function of the room ventilation rate: Q, ceiling fan; 0,electrostatic precipitator, (ESP);a,high-efficiency filter, (HEPA);A, negativeion generator; A, positive-ion generator; 0, negative-ion generator and ceiling fan; . positive-ion , generator and ceiling fan (Maher et al., 1987).

ventilation rate (expressed in terms of room air exchanges per hour). Figure 5.2 presents data on the fractions of the remaining radon decay products that are in the unattached state, again as a function of various air exchange rates. These data were based on measurements using a diffusion battery. Figure 5.3 presents data on the calculated fractions of the bronchial dose remaining as a function of the air exchange rate after application of various air treatment techniques. The calculation of the bronchial dose remaining was performed using the lung models developed by Harley and Pasternack (1982), Jacobi and Eisfeld (1980), and James et al. (1980). The preferred remedial control method is to prevent or impede the entry of radon into the house; this approach is most readily applied in the construction of new houses or when the source of radon entry is localized. Retrofitting such technology into some existing homes can be difficult and expensive. Under these conditions, removal of the radon decay products through the application of air treatment methods, either separately or as part of an overall remedial control program, may be the most economical means available. If air-cleaning devices are to be applied in the control of radon

5.6 SUMMARY OF EXPERIMENTAL DATA l%O

2 14

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ROOM VENTILATION RATE

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53

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)I-' I

Fig. 6.2 Fractions of the remaining radon decay products in the unattached state after application of various air treatment methods. Data are given as a function of three room ventilation rates: 8,ceiling fan; 0, electrostatic precipitator, (ESP); a, high-efficiency filter, (HEPA); A, negative-ion generator; A, positive-ion generator; 0, negative-ion generator and ceiling fan; H, pitive-ion generator and ceiling fan (Maher, 1985).

decay products, they should be designed and selected on the basis of bronchial dose reduction, not simply PAEC reduction. This requires that the air cleaning method not significantly increase the unattached airborne fraction of the remaining PAEC. PAEC reductions alone are not a good index of bronchial dose reduction. Inattention to this aspect can lead to the application of air treatment methods that reduce the working level without providing comparable reductions in the dose to bronchial tissue.

54

1

5. SOURCE LNDEPENDENT CONTROL TECHNIQUES HARLEY-PASTERNACK

JACOBI-NSFELD

AIR EXCHANGE RATE

JAMES-BIRCHALL

f?m

Fig. 5.3 Relative bronchial dose remaining after the application of various air treatment methods as a function of air exchange rate. Calculation of the bronchial dose was performed using the lung models developed by Harley and Pasternack (1982), Jacobi and Eisfeld (1980), and James et al. (1980): (3, ceiling fan; 0, electrostatic precipitator, (ESP); a, high-efficiency filter, (HEPA); A, negative-ion generator; A, positive-ion generator; 0, negative-ion generator and ceiling fan; positive-ion generator and ceiling fan (Maher, 1985).

.,

6. Selection of Control Techniques As discussed earlier, the fundamental control strategies available to the homeowner for reducing exposures to radon and its decay products can be summarized as follows: (1) eliminating the source of radon; (2) diverting or blocking the entry of radon into the living space; (3) modifying the operation of a n existing ventilation system to enhance the removal of the radon decay products; (4) installing air treatment equipment; and (5) increasing the outside air infiltration rate into a house. While the first two approaches are generally preferable, they can be expensive and they require knowledge of the source of the radon. They are also largely limited to houses newly planned or undergoing construction. At the same time, however, these methods can provide far more effective and efficient control than any other technique. Although the third method listed would appear, upon first impression, to be a good approach, it has several drawbacks. One is that it is applicable only to houses having some form of existing air circulating system. Second.is that it is not always easy to modify an existing system to incorporate newer (or upgraded) features such as high efficiency filters or an electrostatic precipitator. As previously mentioned, care must be taken to assure that the treatment method selected results in a reduction in the radiation dose to the lungs of the people breathing the treated air. The last two methods are applicable to most types of existing houses and they have the added advantage that their application does not require knowledge of the source of radon. It is important to note, however, that the effectiveness of air treatment equipment in reducing airborne concentrations of radon decay products may range from perhaps 50 percent (providing a factor of two reduction) to perhaps 90 percent (providing a factor of ten reduction), depending on parameters such as the volume of air being treated, the relative humidity, the air exchange rate, the concentration of dust in the air, and other conditions. As previously explained, reductions in the dose equivalents to the radiosensitive bronchial tissues may be much less. Increasing the outside air infiltration rate into a house will provide essentially identical reductions in the concentration of airborne radon

56

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6. SELECTION OF CONTROL TECHNIQUES

decay products and the associated dose equivalent to the bronchial tissues as that obtainable with air treatment methods. Since, as previously pointed out, the control techniques that can be applied are influenced by many factors, there is no one best system to recommend for every situation.

6.1 Source-DependentControl Techniques

As indicated in Section 4, the three primary control techniques for application where the source of the radon is known are blocking or diverting the radon from the soil beneath the house, removal of radon from the water to be used in the house, and the proper selection of building materials. The first and last of these control techniques are primarily applicable to new houses. Techniques for the control of radon in domestic water supplies can be applied in new or existing housing. Summarized in Table 6.1 are generalized data on the costs of applying each of these control techniques, and the anticipated reductions to be provided in the airborne PAEC and in the dose equivalents to the bronchial t i s ~ e sFor . ~ purposes of the table, the percent reductions in the dose equivalents to the bronchial tissues are assumed to be the same as the reductions in the PAEC since application of these control techniques would not be expected to change the fraction of the airborne unattached radon decay products. In interpreting the data in Table 6.1, care should be taken to recognize that the removal effectiveness quoted for each control technique may not be applicable in all situations. For houses with multiple sources of radon, the reduction efficiences may be well below those listed in the table.

6.2 Source-IndependentControl Techniques

As indicated in Section 5, there are four primary methods for removing radon decay products from the air inside the home. These techniques are increased ventilation, increased air circulation, particle removal and combinations of these approaches. Application of these techniques requires no knowledge of the source of radon. However, as previously mentioned, since several of these techniques (such as high-efficiency filtration and electrostatic precipitation) appear, %me of the data in Table 6.1 are based on EPA (1988).

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on the basis of laboratory data, to be ineffective in reducing the dose equivalent to the bronchial tissues (in fact, they may exacerbate the situation), the homeowner may want to evaluate these systems in more detail before incorporating them into the home. I n addition, it is important for the homeowner to realize that, when the concentrations of airborne radon and its decay products within a house are unusually high, there may be no choice but to apply a source dependent control technique, or to use a combination of approaches. Outlined in Table 6.2 is a summary of the specific source independent control techniques evaluated, including data on the costs of applying each technique (EPA, 198613,1988;Moeller and Fujimoto, 19841,and the reductions anticipated in terms of the PAEC and the dose equivalents to the bronchial tissues (Maher et al., 1987). Consideration was given to the incorporation of an air-to-air heat exchanger into an existing ventilation system to provide increased air exchange with the outdoors. Estimates of the cost of this approach were not included because of the general response from heating, ventilation, and air conditioning specialists that use of such exchangers would not be cost effective. Dose equivalent reductions presented in Table 6.2 were calculated using the model of Harley and Pasternack (1982).

TABLE6.2-Cost and effectiueness of source independent control techniques Costs Technique

Installation

Effectivenessb Annual operation PAEC reduction Dose reduction'

Increased air circulation --$100 50%-65% 50%-65% Home with existing air circulating system $10,000-$15,000 $100 50%45% 50%-65% Home in which air circulating system must be installed $600 $50 50%-65% 50%-65% Use of overhead ceiling fans to provide increased circulationd Increased air exchange with the outdoors Addition to home with existing air circulating system Addition to home without existing air circulating system Air cleaning devices (particle removers) e $300 70%-80% $3,000-$5,000 High efficiency filter system e $5,000 $100 60%-65% Electrostatic precipitators (electronic air cleaners) central system $1,400 $100 60%-65% e Individual room unitsd $400 $50 60%-70% e Negative ion generatorsd $400 $50 70%-80% 10%-70% Positive ion generatorsd Combined approaches 60%-80% 4570-70% $1,200 $300 Negative ion generator plus fand Positive ion generator plus fand $1,200 $300 70%-90% 60%-85% "Based on 1987 dollars. bReductionswill vary depending on the volume of the air being treated, the room air exchange rate, the relative humidity concentration in the air, and other factors. 'Mean bronchial dose. dAssumea three units on the first floor; one unit in the basement. "Data indicate that application of these techniques, particularly in homes with low air exchange rates (less than 0.5 per hour), could actually result in an increase in estimates of the dose.

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The information presented in this report shows that there is a variety of methods available for the control of radon inside houses. All systems can be effective when properly installed, but the best performance is achieved by active soil ventilation techniques. For new houses being planned or under construction, the installation of barriers between the soil and the house can be very effective. Properly done, this approach will solve the problem for the duration of the use of the house. Consideration could also be given to the selection of the land on which the house is going to be constructed, so a s to avoid radon prone areas to the extent practicable. Unfortunately, methods for testing homesites so as to avoid future radon problems do not currently exist. For existing houses, application of increased ventilation and air cleaning techniques can be useful. As may be noted from Table 6.2, the costs and the effectiveness of the available techniques cover a wide range. Although one might be inclined to select the method that is most effective on the basis of estimated dose reduction as shown in Tables 6.1 and 6.2, there are a number of other factors that should be considered. One of the most important of these is the degree of treatment (removal) required. Whereas a positive ion generator appears to be very effective in terms of the reduction in the airborne PAEC, it provides only an estimated 65 percent or less reduction in the dose equivalent to the bronchial tissues. If greater reductions are needed, the homeowner may want to consider a fan-positive ion generator combination a t a higher overall cost, or to apply one of the source dependent control techniques. Other factors that the homeowner may want to consider include the comfort of the method applied (for example, increased ventilation or air circulation can be annoying to many people) as well a s the potential side benefits or risks associated with some of the methods described in this report. Whereas the source dependent control techniques are specifically directed to the problem of radon and its decay products, the air cleaning techniques may have additional benefits through the removal of other hazardous airborne contaminants, such as dust or cigarette smoke, within the home. The homeowner may

7. COMMENTARY AND RECOMMENDATIONS

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take these benefits into account when making a decision on how to control the problem of radon and its decay products. In contrast to this, some investigators have reported various biological and behavioral effects due to exposures to air ions (Pfanenstiel, 1983). These have been both of a beneficial and a detrimental nature. Although these effects have not been confirmed, the homeowner may want to consider them in choosing a method to control airborne radon decay products. On the basis of this review of the various air treatment methods available to the homeowner for reducing the potential radiation dose to the lungs from radon decay products, there appear to be three acceptable methods: (1) increased ventilation with outside air; (2) enhanced convection or air circulation; and (3) the combination of unipolar space charging and enhanced convection. Air cleaning methods which employ particle removal for the reduction of radon decay product concentrations, i.e., filtration and electrostatic precipitation, while effective in reducing the PAEC, can significantly alter the radiological properties of the room air and the bronchial dose per unit of inhaled activity. Therefore, PAEC reductions alone are not a good index of bronchial dose reductions. As a result, their suitability for home use is doubtful, and they cannot be recommended in light of present information. In conclusion, a variety of techniques is available for low cost mitigation of excess radon and its progeny in existing houses. The costs and difficulties associated with them are largely those of obtaining access to parts of the building structure that are concealed by subsequent work, and the numerous slight variations in construction methods that cause the physical layout of similar systems to differ from house to house. All systems are effective in reducing radon and/ or radon-decay-product concentrations in indoor air when properly installed, but the best performance-to-cost ratio is achieved by active soil ventilation systems.

Glossary absorbed dose: The quantity of energy from ionizing radiation that is absorbed per unit mass is the absorbed dose. The special S.I. unit of absorbed dose is the gray (Gy). One gray of absorbed dose is numerically equal to one joule per kilogram. activity: The mean number of decays per unit time of a radioactive nuclide. The special S.I. unit of activity is the becquerel. One bequerel is equal to one reciprocal second. aerodynamic diameter: The diameter of a unit density particle that has the same settling velocity as the particle described. alpha particle: The nucleus of a helium atom which is ejected from some radionuclides during radioactive decay. background radiation: Radiation arising from natural sources; background radiation due to cosmic rays and natural radioactivity, including radon and its decay products, is always present in the human body and the earth. becquerel (Bq): A special unit of radioactivity in S.I. units. It is numerically equal to one per second. 1Bq = 27 pCi. bronchial epithelium: The surface lining of the conducting airways of the lung. The thickness decreased with bronchial generation from about 80 pm in the trachea to 15 pm in the finest airways. curie (Ci): A special unit of activity in conventional units. I t is numerically equal to 3.7 x 101° per second, or 3.7 x 10'O Bq. decay product: A nuclide that is formed as a result of radioactive decay. decay chain or decay series: A sequence of radioactive decays. An initial nucleus decays into a product nucleus, or progeny, that differs from the parent nucleus by whatever particles were emitted during the decay. If further decays take place, the subsequent nuclei are also usually called decay products or progeny. diffusion: Movement by Brownian or random motion. dose equivalent: A quantity that expresses, for the purposes of radiation protection, the assumed biological effectiveness of absorbed dose on a common scale for all kinds of ionizing radiation. The S.I. unit of dose equivalent is the sievert (Sv). One sievert equals one joule per kilogram. emanating power: Under steady-state conditions, the fraction of radon atoms formed in a solid which escape from the solid.

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emanation rate: In this report, the release rate of a gas (radon) from a surface in units such as Bq per square meter per second. equilibrium, radioactive secular: The condition in which the activities of a parent and progeny in a radioactive decay chain are essentially equal. g r a y (Gy): The S.I. unit of absorbed dose. One Gy of absorbed dose is equal to 1joule per kilogram. One Gy equals 100 rad. half-life, radioactive: Time required for a radioactive substance to lose 50 percent of its activity by decay. joule-hours p e r cubic meter: The S.I. unit for expressing exposure to airborne radon decay products. 1Working Level Month (WLM) = 170 WL hour = 3.5 x joule-hours per cubic meter. pascal (Pa):The S.I. unit for pressure. 1 Pa = 1 newton per meter squares. potential alpha energy concentration (PAEC): This is the energy that would eventually be released in a specified volume of undisturbed air by the short-lived decay products of radon through the emission of alpha particles. PAEC is expressed in units of Working Level (WL) or J per cubic meter. rad: The special unit of radiation absorbed dose in conventional units. One rad equals the absorption of 0.01 joule per kilogram (100 ergs per gram) of absorbing material. 1rad = 0.01 Gy. radon: In this report refers to the radioactive inert gas, 222Rn. r a d o n decay products: In this report, the short-lived radionuclides formed as a result of decay of n2Rn. They consist of 218Po(RaA), ~ Their respective half 214Pb(RaB), 214Bi(RaC) and 2 1 4 P(RaC'). lives are 3.05 minutes, 26.8 minutes, 19.7 minutes, and 164 microseconds. Their effective combined half life is approximately 30 minutes. rem: The conventional unit of radiation dose equivalent. One rem equals 0.01 Sv. sievert (Sv): The S.I. unit of radiation dose equivalent. One Sv equals 100 rem. space charging: A distribution of an excess of electrons or ions over a three-dimensional region, in contrast to the distribution of an electric charge over the surface of a conductor. unattached fraction: That fraction of the radon decay products, usually 218Po(RaA), which has not yet attached to particles. working level (WL):Any combination of short-lived radon decay products in one liter of air that will result in the ultimate emission of 1.3 x lo5 MeV of potential alpha particle energy. working level month (WLM): The cumulative exposure equivalent to exposure to one working level (WL) for a working month (170 hours).

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The NCRP The National Council on Radiation Protection and Measurements is a nonprofit corporation chartered by Congress in 1964 to: 1. Collect, analyze, develop, and disseminate in the public interest information and recommendations about (a) protection against radiation and (b) radiation measurements, quantities, and units, particularly those concerned with radiation protection; 2. Provide a means by which organizations concerned with the scientific and related aspects of radiation protection and of radiation quantities, units, and measurements may cooperate for effective utilization of their combined resources, and to stimulate the work of such organizations; 3. Develop basic concepts about radiation quantities, units, and measurements, about the application of these concepts, and about radiation protection; 4. Cooperate with the International Commission on Radiological Protection, the International Commission on Radiation Units and Measurements, and other national and international organizations, governmental and private, concerned with radiation quantities, units, and measurements and with radiation protection. The Council is the successor to the unincorporated association of scientists known as the National Committee on Radiation Protection and Measurements and was formed to carry on the work begun by the Committee. The Council is made up of the members and the participants who serve on the over sixty scientific committees of the Council. The scientific committees, composed of experts having detailed knowledge and competence in the particulararea of the committee's interest draft proposed recommendations. These are then submitted to the full membership of the Council for careful review and approval before being published. The following comprise the current officers and membership of the Council: Officers President Vice President Secretary and Treasurer Assistant Secretary Assistant Treasurer

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THENCRP

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Members

SEYMOUR ABRAHAMSQN S. JAMES A D E ~ I N PETER R. ALMOND EDWARD L. ALPEN LYNNR. ANSPAUGH JOHN A. AUXIER WILLIAM J. BAIR MICHAEL A. BENDER BRUCEB. BOECKER JOHN D. BOICE,JR. ROBERTL. BRENT ANTONEL. BROOKS MELVINW. CARTER RANDALL S. CASWELL JAMES E. CLEAVER FREDT. CROSS STANLEY B. CURTIS GERALD D. DODD W. DURBIN PATRICIA CHARLFS M. EISENHAUER THOMASS. ELY JACOB I. FABRIKANT R. J . MICHAEL FRY THOMAS F. GESELL ETHELS. GILBERT ROBERT A. GOEPP JOEL E. GRAY ARTHUR W. GUY ERICJ. HALL NAOMIH. HARLEY R. HENDEE WILLIAM DONALD G. JACOBS A. EVEJAMES. JR. BERNDKAHN KENNETH R. KASE CHARLES E. LAND R. LEOPOLD GEORGE

I t r D. ~ LLOYD HARRYR. MAXON CHARLES W. MAYS RCGER0.MCCLELLAN JAMES E. MCLAUGHLIN BARBARAJ. MCNEL THOMAS F. MEANEY CHARLES B. MEINHOLD MORTIMER L.MENDELSOHN FREDA. M ~ E R WILLIAM A. MILLS DADEW. MOELLER A. ALANMOGHLSSI MARYELLENO'CONNOR ANDREW K. POZNANSKI NORMAN C. RUMUSSEN CHESTERR RICHMOND MARVIN ROSENSTEIN LAWRENCE N. ROTHENBERG LEONABDA. SAGAN KEITHJ. SCHIAGER ROBERT A. SCHLENKER W~LLIAM J . SCHULL ROYE. SHORE WARREN K. SINCLAIR PALL S ~ V I C RICHARD A. TELL WILLIAM L. TEMPLETON THOMASS. TENFORDE Joop W. THIESSEN JOHN E. TILL ROBERTL. ULWCH ARTHUR C. UPPON GEORGE L. VOEW GEORGE M. WILKENING 0.ZISKIN MARVIN

Honorary Members

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Currently, the following subgroups are actively engaged in formulating recommendations: SC 1:

SC 3: SC 16: SC 40: SC 46:

SC 52: SC 57:

SC 59: SC 63:

SC 64:

SC 65: SC 66: SC 67: SC 68: SC 69:

Basic Radiation Protection Criteria SC 1-1 Probability of Causation for Genetic and Developmental Effects SC 1-2 The Assessment of Risk Estimates for ~ a d i a t i o nProtection Purposes Medical X-Ray, Electron Beam and Gamma-Ray Protection for Energies Up to 50 MeV-Equipment Performance and Use X-Ray Protection in Dental Offices Biological Aspects of Radiation Protection Criteria SC 40-1 Atomic Bomb Survivor Dosimetry Operational Radiation Safety SC 46-2 Uranium Mining and Milling-Radiation Safety Programs SC 46-3 ALARA for Occupationally Exposed Individuals in Clinical Radiology SC 46-4 Calibration of Survey Instrumentation SC 46-6 Maintaining Radiation Protection &cords SC 46-6 Radiation Protection for Medical and Allied Health Personnel SC 46-7 Emergency Planning SC 46-8 Radiation Protection Design Guidelines for Particle Accelerator Facilities SC 46-9 ALARA a t Nuclear Plants SC 46-10 Assessment of Occupational Doses from Internal Emitters Conceptual Basis of Calculations of Dose Distributions Internal Emitter Standards SC 57-2 Respiratory Tract Model SC 57-6 Bone Problems SC 57-8 Leukemia Risk SC 57-9 Lung Cancer b s k SC 57-10 Liver Cancer Risk SC 57-12 Strontium SC 57-14 Placental Transfer SC 57-15 Uranium Human Population Exposure Experience Radiation Exposure Control in a Nuclear Emergency SC 63-1 Public Knowledge about Radiation SC 63-2 Criteria for Radiation Instruments for the Public Environmental Radioactivity and Waste Management SC 6 4 6 Screening Models SC 64-7 Contaminated Soil a s a Source of Radiation Exposure SC 64-8 Ocean Disposal of Radioactive Waste SC 64-9 Effects of Radiation on Aquatic Organisms SC 64-10 Xenon SC 64-11 Disposal of Low Level Waste Quality Assurance and Accuracy in Radiation Protection Measurements Biological Effects and Exposure Criteria for Ultrasound Biological Effects of Magnetic Fields Microprocessors in Dosimetry Efficacy Studies

THENCRP SC 70: SC 71: SC 74: SC 76: SC 77: SC 78: SC 79: SC 80: SC 81: SC 83:

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Quality Assurance and Measurement in Diagnostic Radiology Radiation Exposure and Potentially Related Injury Radiation Received in the Decontamination of Nuclear Facilities Effects of Radiation on the Embryo-Fetus Guidance on Occupational and Public Exposure Ftesulting from Diagnostic Nuclear Medicine Procedures Practical Guidance on the Evaluation of Human Exposures to Radiofrequency Radiation Extremely Low-Frequency Electric and Magnetic Fields Radiation Biology of the Skin (Beta-Ray Dosimetry) SC 80-1 Hot Particles on the Skin Assessment of Exposures from Therapy

Research Needs

Study Group on Comparative Risk %k Force on Occupational Exposure Levels

In recognition of its responsibility to facilitate and stimulate cooperation among organizations concerned with the scientific and related aspects of radiation protection and measurement, the Council has created a category of NCRP Collaborating Organizations. Organizations or groups of organizations that are national or international in scope and are concerned with scientific problems involving radiation quantities, units, measurements, and effects, or radiation protection may be admitted to collaborating status by the Council. The present Collaborating Organizations with which the NCRP maintains liaison are as follows: American Academy of Dermatology American Association of Phvsicists in Medicine American College of ~ e d i c aPhysics i American College of Nuclear Physicians American College of Radiology American Dental Association American Industrial Hygiene Association American Institute of Ultrasound in Medicine American Insurance Association American Medical Association American Nuclear Society American Occupational Medical Association American Pediatric Medical Association American Public Health Association American Radium Society American Roentgen Ray Society American Society of Radiologic Technologists American Society for Therapeutic Radiology and Oncology Association of University Radiologists Bioelectromagnetics Society College of American Pathologists Conference of Radiation Control Program Directors Electric Power Research Institute

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Federal Communications Commission Federal Emergency Management Agency Genetics Society of America Health Physics Society Institute of Nuclear Power Operations National Electrical Manufacturers Association National Institute of Standards and Technology Nuclear Management and Resources Council Radiation Research Society Radiological Society of North America Society of Nuclear Medicine United States Air Force United States Army United States Department of Energy United States Department of Houaing and Urban Development United States Department of Labor United States Environmental Protection Agency United States Navy United States Nuclear Regulatory Commission United States Public Health Service

The NCRP has found its relationships with these organizations to be extremely valuable to continued progress in its program. Another aspect of the cooperative efforts of the NCRP relates to the special liaison relationships established with various governmental organizations that have an interest in radiation protection and measurements. This liaison relationship provides: (1) an opportunity for participating organizations to designate an individual to provide liaison between the organization and the NCRP; (2) that the individual designated will receive copies of draft NCRP reports (at the time that these are submitted to the members of the Council) with an invitation to comment, but not vote; and (3)that new NCRP efforts might be discussed with liaison individuals as appropriate, so that they might have an opportunity to make suggestions on new studies and related matters. The following organizations participate in the special liaison program: Australian Radiation Laboratory Cornmisarist a I'Energie Atomique (France) Commission of the European Communities Defense Nuclear Agency Federal Emergency Management Agency Japan Radiation Council National Institute of Standards and Technology National Radiological Protection Board (United Kingdom) National Research Council (Canada) Office of Science and Technology Policy Office of Technology Assessment United States Air Force

THE NCKP

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77

United States Army United States Coast Guard United States Department of Energy United States Department of Health and Human Services United States Department of Labor United States Department of Transportation United States Environmental Protection Agency United States Navy United States Nuclear Regulatory Commission

The NCRP values highly the participation of these organizations in the liaison program. The Council's activities are made possible by the voluntary contribution of time and effort by its members and participants and the generous support of the following organizations: Alfred P. Sloan Foundation Alliance of American Insurers American Academy of Dental Radiology American Academy of Dermatology American Association of Physiciets in Medicine American College of Medical Physics American College of Nuclear Physicians American College of Radiology American College of Radiology Foundation American Dental Association American Hospital Radiology Adrninietrators American Industrial Hygiene Association American Insurance Association American Medical Association American Nuclear Society American Occupational Medical Association American ~ & ~ a t h i College c of Radiology American Pediatric Medical Association American Public Health Association American Radium Society American Roentgen Ray Society American Society of Radiologic Technologists American Society for Therapeutic Radiology and Oncology American Veterinary Medical Association American Veterinary Radiology Society Asmiation of University Radiologists Battelle Memorial Institute Center for Devices and Radiological Health College of American Pathologists Commonwealth of Pennsylvania Defense Nuclear Agency Edison Electric Institute Edward Mallinckrodt, Jr. Foundation Electric Power Research Institute Federal Emergency Management Agency

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Florida Institute of Phosphate Research Genetics Society of America Health Physics Society Institute of Nuclear Power Operations James Picker Foundation h u n s b e r y Foundation National Aeronautics and Space Administration National Association of Photographic Manufacturers National Cancer Institute National Electrical Manufacturers Association National Institute of Standards and Technology Nuclear Management and Resources Council Radiation ~ e & a r c hSociety Radiological Society of North America Society of Nuclear Medicine United States Department of Energy United States Department of Labor United States Environmental Protection Agency United States Navy United States Nuclear Regulatory Commission

To all of these organizations the Council expresses its profound appreciation for their support. Initial funds for publication of NCRP reports were provided by a grant from the James Picker Foundation and for this the Council wishes to express its deep appreciation. The NCRP seeks to promulgate information and recommendations based on leading scientific judgment on matters of radiation protection and measurement and to foster cooperation among organizations concerned with these matters. These efforts are intended to serve the public interest and the Council welcomes comments and suggestions on its reports or activities from those interested in its work.

NCRP Publications NCRP publications are distributed by the NCRP Publications' office. Information on prices and how to order may be obtained by directing an inquiry to: NCRP Publications 7910 Woodmont Ave., Suite 800 Bethesda, Md 20814 The currently available publications are listed below.

Proceedings of the Annual Meeting No. 1 2 3 4

5 6

7

Title Perceptions ofRisk, Proceedings of the Fifteenth Annual Meeting, Held onMarch 14-15,1979 (Including Taylor Lecture No. 3) (1980) Quantitative Risk in Standards Setting, Proceedings of the Sixteenth Annual Meeting, Held on April 2-3, 1980 (Including Taylor Lecture No. 4) (1981) Critical Issues in Setting Radiation Dose Limits, Proceedings of the Seventeenth Annual Meeting, Held on April 8-9,1981 (Including Taylor Lecture No. 5) (1982) Radiation Protection and New Medical Diagnostic Procedures, Proceedings of the Eighteenth Annual Meeting, Held on April 6-7,1982 (Including Taylor Lecture No. 6) (1983) Environmental Radioactivity, Proceedings of the Nineteenth Annual Meeting, Held on April 6-7, 1983 (Including Taylor Lecture No. 7) (1984) Some Issues Important in Developing Basic Radiation Protection Recommendations, Proceedings of the Twentieth Annual Meeting, Held on April 4-5, 1984 (Including Taylor Lecture No. 8) (1985) Radioactive Waste, Proceedings of the Twenty-First Annual Meeting, Held on April 3-4, 1985 (Including Taylor Lecture No. 9) (1986)

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NCRP PUBLICATIONS

Nonionizing Electromagnetic Radiation and Ultrasound, Proceedings of the Twenty-Second Annual Meeting, Held on April 2-3,1986 (Including Taylor Lecture No. 10) (1988) New Dosimetry at Hiroshima and Nagasaki and Its Implications for Risk Estimates, Proceedings of the Twenty-Third Annual Meeting, Held on April 8-9, 1987 (Including Taylor Lecture No. 11)(1988). Radon, Proceedings of the twenty-fourth Annual Meeting held on March 30-31,1988 (Including Taylor Lecture No. 12) (1989).

Symposium Proceedings The Control of Exposure of the Public to Ionizing Radiation in the Event of Acciclent or Attack, Proceedings of a Symposium held April 27-29,1981 (1982)

Lauriston S. Taylor Lectures No.

1

Title and Author

The Squares of the Natural Numbers i n Radiation Protection by Herbert M. Parker (1977) Why be Quantitative About Radiation Risk Estimates? by Sir Edward Pochin (1978) Radiation Protection--Concepts and Tmde Offsby Hymer L. Friedell (1979) [Available also in Pemeptwns of Risk, see abovel From "Quantity of Radiation" and "Dose" to "Exposure" and "Absorbed Dose''-An Historical Review by Harold 0.Wyckoff (1980) [Available also in Quantitative Risks in Standards Setting, see abovel How Well Can We Assess Genetic Risk? Not Very by James F . Crow (1981) [Available also in Critical Issues in Setting Radiation Dose Limits, see abovel Ethics, Trade-offs and Medical Radiation by Eugene L. Saenger (1982) [Available also in Radiation Protection and New Medical Diagnostic Approaches, see abovel The Human Environment-Past, Present and Future by Merril Eisenbud (1983) [Available also in Environmental Radioactivity, see abovel

NCRP PUBLICATIONS

8

9 10

11

12

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Limitation and Assessment in Radiation Protection by Harald H. Rossi (1984) [Available also in Some Issues Important i n Developing Basic Radiation Protection Recommendations, see above] Truth (and Beauty) in Radiation Measurement by John H. Harley (1985) [Available also in Radioactive Waste, see abovel Nonionizing Radiation Bioeffects: Cellular Properties and Interactions by Herman P. Schwan (1986) [Available also in Nonionizing Electromagnetic Radiations and Ultrasound see abovel How to be Quantitative about Radiation Risk Estimates by Seymour Jablon (1987) [Available also in New Dosimetry at Hiroshima and Nagasaki and itsImplications for Risk Estimates, see above] How Safe is Safe Enough? by Bo Lindell(1988) [available also in Radon, see abovel NCRP Commentaries

Commentary Title No. 1 Krypton45 i n the Atmosphere-With Specific Reference to the Public Health Significance of the Proposed Controlled Release at Three Mile Island (1980) 2 Preliminary Evaluation of Criteria for the Disposal of Transuranic Contaminated Waste (1982) 3 Screening Techniques for Determining Compliance with Environmental Standards (1986), Rev (1989) 4 Guidelines for the Release of Waste Water from Nuclear Facilities with Special Reference to the Public Health Significance of the Proposed Release of Treated Waste Waters at Three Mile Island (1987)

NCRP Reports No. 8

22

23

Title Control and Removal of Radioactive Contamination in Laboratories (1951) Maximum Permissible Body Burdens and Maximum Permissible Concentrations of Radionuclides in Air and in Water for Occupational Exposure (1959) [Includes Addendum 1issued in August 19631 Measurement of Neutron Flux and Spectra for Physical and Biological Applications (1960)

NCRP PUBLICATIONS

Measurement o f Absorbed Dose ofNeutrons and Mixtures of Neutrons and Gamma Rays (1961) Stopping Powers for Use with Cavity Chambers (1961) Safe Handling of Radioactive Materials (1964) Radiation Protection in Educational Institutions (1966) Dental X-Ray Protection (1970) Radiation Protection in Veterinary Medicine (1970) Precautions in the Management of Patients Who Have Received Thempeutic Amounts of Radionuclides (1970) Protection Against Neutron Radiation (1971) Protection Against Radiation f b m Bmchytherapy Sources (1972) Specification of Gamma-Ray Bmchytherapy Sources (1974) Radiological Factors Affecting Decision-Making in a Nuclear Attack (1974) Krypton-85 in the Atmosphere-Accumulation, B iological Significance, and Control Technology (1975) Alpha-Emitting Particles in Lungs (1975) Tritium Measurement Techniques (1976) Radiation Protection for Medical and Allied Health Personel (1976) Structural Shielding Design and Evaluation for Medical Use of X Rays and Gamma Rays of Energies Up to 10 MeV (1976) Environmental Radiation Measurements (1976) Radiation Protection Design Guidelines for 0.1-100 MeV Particle Accelerator Facilities (1977) Cesium-137 From the Environment to Man: Metabolism and Dose (1977) Review of NCRP Radiation Dose Limit for Embryo and Fetus in Occupationally Exposed Women (1977) Medical Radiation Exposure of Pregnant and Potentially Pregnant Women (1977) Protection of the Thyroid Gland in the Event of Releases of Radioiodine (1977) Instrumentation and Monitoring Methods for Radiation Protection (1978) A Handbook of Radioactivity Measurements Procedures, 2nd ed. (1985) Operational Radiation Safety Program (1978) Physical, Chemical, and Biological Properties of Radiocerium Relevant to Radiation Protection Guidelines (1978)

NCRP PUBLICATIONS

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Radiation Safety Training Criteria for Industrial Radiography (1978) Tritium in the Environment (1979) Tritium and Other Radionuclide Labeled Organic Compounds Incorporated in Genetic Material (1979) Influence of Dose and Its Distribution in Time on DoseResponse Relationships for Low-LET Radiations (1980) Management of Persons Accidentally Contaminated with Radionuclides (1980) Mammography (1980) Radiofreqency Electromagnetic Fields-Properties, Quantities and Units, Biophysical Interaction, and Measurements (1981) Radiation Protection in Pediatric Radiology (1981) Dosimetry of X-Ray and Gamma-Ray Beams for Radiation Therapy i n the Energy Range 10 keV to 50 MeV (1981) Nuclear Medicine-Factors Influencing the Choice and Use ofRadionuclides in Diagnosis and Therapy (1982) Operational Radiation Safety-Training (1983) Radiation Protection and Measurement for Low Voltage Neutron Generators (1983) Protection in Nuclear Medicine and Ultrasound Diagnostic Procedures in Children (1983) Biological Effects of Ultrasound: Mechanisms and Clinical Implications (1983) Iodine-129: Evaluation of Releases from Nuclear Power Generation (1983) Radiological Assessment: Predicting the Transport, Bioaccumulation, and Uptake by Man ofRadionuclides Released to the Environment (1984) Exposures from the Uranium Series with Emphasis on Radon and its Daughters (1984) Evaluation of Occupational and Environmental Exposures to Radon and Radon Daughters in the United States (1984) Neutron Contamination from Medical Electron Accelerators (1984) Induction of Thyroid Cancer by Ionizing Radiation (1985) Carbon-14 in the Environment (1985) SI Units in Radiation Protection and Measuremenis (1985) The Experimental Basis for Absorbed-Dose Calculations in Medical Use of Radionucldes (1985) General Concepts for the Dosimetry of Internally Deposited Radionuclides (1985)

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NCRP PUBLICATIONS

Mammography-A User's Guide (1986) Biological Effects and Exposure Criteria for Radiofrequency Electromagnetic Fields (1986) Use of Bioassay Procedures for Assessment of Internal Radionuclide Deposition (1987) Radiation Alarms and Access-Control Systems (1987) GeneticEffects o f ~ n t e r n a l l ~ ~ e ~ o s~zat de di o n u c 1 i .(1987) s Neptunium: Radiatwn Protection Guidelines (1987) Recommendations on Limits for Exposu& to Ionizing Radiatwn (1987) Public Radiation Exposure from Nuclear Power Generation in the United States (1987) Ionizing Radiation Exposure of the Population of the United States (1987) Exposure of the Population in the United States and Canada from Natural Background Radiation (1987) Radiation Exposure of the U.S. Population from Consumer Products and Miscellaneous Sources (1987) Comparative Carcinogenicity of Ionizing Radiation and Chemicals (1989) Measurement ofRadon and Radon Daughters in Air (1988) Guidance on Radiatwn Received in Space Activities (1989) Quality Assurance for Diagnostic Imaging Equipment (1988) Exposure of the U.S. ~ o ~ u l a t ifrom o n ~ i a ~ n o s tMedical ic Radiatwn (1989) Exposure of the U.S. Population From Occupational Radiation (1989) Medical X-Ray, Electron Beam and Gamma-Ray Protection for Energies Up to 50 MeV (Equipment Design, Performance and Use) (1989) Control ofRadon in Houses (1989) Binders for NCRP Reports are available. Two sizes make it possible to collect into small binders the "old series" of reports (NCRP Reports Nos. 8-30) and into large binders the more recent publications (NCW Reports Nos. 32-103). Each binder will accommodate from five to seven reports. The binders cany the identification "NCRP Reports" and come with label holders which permit the user to attach labels showing the reports contained in each binder. The following bound sets of NCRP Reports are also available: Volume I. NCRP Reports Nos. 8,22 Volume 11. NCRP Reports Nos. 23,25,27, 30

NCRP PUBLICATIONS

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Volume 111. NCRP Reports Nos. 32, 35,36, 37 Volume IV. NCRP Reports Nos. 38,40,41 Volume V. NCRP Reports Nos. 42,44,46 Volume VI. NCRP Reports Nos. 47,48,49,50,51 Volume VII. NCRP Reports Nos. 52,53,54,55,57 Volume VIII. NCRP Reports No. 58 Volume IX. NCRP Reports Nos. 59,60,61,62,63 Volume X. NCRP Reports Nos. 64,65,66,67 Volume XI. NCRP Reports Nos. 68,69,70,71,72 Volume XII. NCRP Reports Nos. 73,74,75,76 Volume XIII. NCRP Reports Nos. 77,78,79,80 Volume XIV. NCRP Reports Nos. 81,82,83,84,85 Volume XV. NCRP Reports Nos. 86,87,88,89 Volume XVI. NCRP Reports Nos. 90,91,92,93 Volume XVII. NCRP Reports Nos. 94,95,96,97 (Titles of the individual reports contained in each volume are given above). The following NCRP Reports are now superseded and/or out of print: No. 1

Title X-Ray Protection (1931). [Superseded by NCRP Report No. 31 Radium Protection (1934). [Superseded by NCRP Report No. 41 X-Ray Protection (1936). [Superseded by NCRP Report No. 61 Radium Protection (1938). [Superseded by NCRP Report No. 131 Safe Handling of Radioactive Luminous Compounds (1941). [Out of Print] MedicalX-Ray Protection Up to TwoMillion Volts (1949). [Superseded by NCRP Report No. 181 Safe Handling of Radimctive Isotopes (1949). [Superseded by NCRP Report No. 301 Recommendations for Waste Disposal of Phosphorus32 and Iodine-131 for Medical Users (1951). [Out of Print] Radiological Monitoring Methods and Instruments (1952). [Superseded by NCRP Report No. 571 Maximum Permissible Amounts of Radioisotopes in the H u m Body and Maximum Permissible Concentmtions in Air and Water (1953). [Superseded by NCRP Report No. 221

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Recommendations for the Disposal of Carbon-14 Wastes (1953). [Superseded by NCRP Report No. 811 Protection Against Radiations from Radium, Cobalt-60 and Cesium-137 (1954). [Superseded by NCRP Report No. 241 Protection Against Betatron-Synchrotron Radiations Up to 100 Million Electron Volts (1954). [Superseded by NCRP Report No. 53.1 Safe Handling of Cadavers Containing Radioactive Isotopes (1953). [Superseded by NCRP Report No. 211 Radioactive Waster Disposal in the Ocean (1954). [Out of Printl Permissible Dose from External Sources of Ionizing Radiation (1954) including Maximum Permissible Exposure to Man, Addendum to National Bureau of Standards Handbook 59 (1958). [Superseded by NCRP Report No. 391 X-Ray Protection (1955). [Superseded by NCRP Report No. 261 Regulation of Radiation Exposure by Legislative Means (1955). [Out of Printl Protection Against Neutron Radiation U p to 30 Million Electron Volts (1957). [Superseded by NCRP Report No. 381 Safe Handling ofBodies Containing Radioactive Isotopes (1958). [Superseded by NCRP Report No. 371 Protection Against Radiations from Sealed Gamma Sources (1960). [Superseded by NCRP Report Nos. 33, 34, and 401 Medical X-Ray Protection Up to Three Million Volts (1961). [Superseded by NCRP Report Nos. 33,34,35, and 361 A Manual of Radioactivity Pmcedures (1961). [Superseded by NCRP Report No. 581 Exposure to R a d i a t i o n i n a n Emergency (1962). [Superseded by NCRP Report No. 421 Shielding for High Energy Electron Accelerator Installations (1964). [Superseded by NCRP Report No. 511 Medical X-Ray and Gamma-Ray Protection for Energies up to 10 MeV-Equipment Design and Use (1968). [Superseded by NCRP Report No. 1021 Medical X-Ray and Gamma-Ray Protection for Energies Up to 10 MeV-Structural Shielding Design and Evaluation (1970). [Superseded by NCRP Report No. 491

NCRP PUBLICATIONS

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Basic Radiation Protection Criteria (1971). [Superseded by NCRP Report No. 911 Review of the Current State of Radiation Protection Philosophy (1975). [Superseded by NCRP Report No. 911 Natural Background Radziztwn in the United States (1975). [Superseded by NCRP Report No. 941 Radiation Exposure from Consumer Products and Miscellal~eouSources (1977). [Superseded by NCRP Report No. 951 A Handbook on Radioactivity Measurement Procedures. [Superseded by NCRP Report No. 58 2nd ed.]

Other Documents The following documents of the NCRP were published outside of the NCRP Reports and Commentaries series: "Blood Counts, Statement of the National Committee on Radiation Protection," Radiology 63,428 (1954) "Statements on Maximum Permissible Dose from Television Receivers and Maximum Permissible Dose to the Skin of the Whole Body," Am. J. Roentgenol., Radium Ther. and Nucl. Med. 84,152 (1960) and Radiology 75, 102 (1960) Dose Effect Modifying Factors In Radiation Protection, Report of Subcommittee M-4 (Relative Biological Effectiveness) of the National Council on Radiation Protection and Measurements, Report BNL 50073 (T-471) (1967) Brookhaven National Laboratory (National Technical Information Service, Springfield, Virginia). X-Ray Protection Standards for Home Television Receivers, Interim Statement of the National Council on Radiation Protection and Measurements (National Council on Radiation Protection and Measurements, Washington, 1968) Specification of Units of Natural Uranium and Natural Thorium (National Council on Radiation Protection and Measurements, Washington, 1973) NCRP Statement on Dose Limit for Neutrons (National Council on Radiation Protection and Measurements, Washington, 1980) Control of Air Emissions of Radionuclides (National Council on Radiation Protection and Measurements, Bethesda, Maryland, 1984) Copies of the statements published in journals may be consulted in libraries. A limited number of copies of the remaining documents listed above are available for distribution by NCRP Publications.

Index Activated carbon filters 39 Active techniques 23 air treatment 26 soil ventilation 24 structure ventilation 25 Aeration systems 39 Aerosol characteristics 15 Air cleaning devices 45 electrostatic precipitation 46 high efficiency filtration 47 unipolar space charging 48 Air infiltration 17 Air treatment 26,55,60 Attached fraction 15 Barometric pressure 6 Behavior of radon inside houses 15 Bronchial (lung) dose 16,52,53,54 Building materials 39 Ceiling fans 26,51, 52 Concrete in buildings 27 Construction materials 10 Control techniques 21 active techniques 23 general approaches 21 passive techniques 22 selection of technique 55 source-dependent techniques 27 source-independent techniques 42 Crawl space ventilation 37 Decay products air concentrations 19 deposition (plateout) 44 disequilibrium 18 Diurnal variations 7 Emanating power 4 Emanation rate 5 Entry routes 23 Epoxy sealants 31,32 Electrostatic precipitators 26,46,52,61 Fans 42,60 Flexible sealants 3 1

Glossary of terms 62 High efficiency filters 26,47,52, 61 Increased air circulation 43 Ion generators 26,48,60 Lung (bronchial) dose 16,52,53,54 Natural gas 14 Origins of radon 3 Passive techniques 22 closing entry routes 23 source removal 22 Phosphate slag 11 Phosphogypsum 11 Potential alpha energy concentration (PAEC) 16 Pressure differences 8,24,33 Pressure gradients 9 Radioactive disequilibrium 18 Radioactive equilibrium 3 Radon radon-222 3 air concentrations 17, 18 behavior inside houses 15 concentrations in houses 1,2 concentrations in outdoor air 7 deaay product deposition 44 decay products 18, 19,44 emanation 5 gas migration 4 sources inside residences 7 Recommendations on control techniques 60 References 65 Sealing as s mitigating measure materials 29 methods 31 Selection of control techniques 55 source-dependent techniques 56 source-independent techniques 56

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INDEX

Soil gas 4,7.27 Soil ventilation 24,33,55,60 Source-dependent control techniques 27 changes in building design 41 construction materials 39 coat and effectiveness 57 removal efficiencies 38 sealing a s a mitigating measure 27 ventilation 33 water supplies 38 Source-independent control techniques 42 air-cleaning devices 45 combined approaches 50 cost and effectiveness 59 experimental data 51 increased ventilation 42 increased air circulation 43 air-cleaning devices 45 Source removal 22.55 Sources of radon 3,7 construction materials 10 natural gas 14 soil gas 7 water supplies 12 Structure ventilation 25.55,60

Subfloor exhaust 35 Subsoil collection system 34 Unattached fraction 15 Unipolar space charging 26,48,51,52, 60 Uranium decay series 3,4 Ventilation 17 crawl space 37 forced air exhaust 43 forced air supply 42 soil 33 subfloor exhaust subsoil collection 34 wall cavity exhaust 36 weeping tile exhaust 35 Wall cavity exhaust 36 Waste gypsum 11 Water supplies 38 Water radon removal systems 38 activated carbon filters 39 aeration systems 39 Water supplies 12.38 Water use rates 13 Weeping tile 35