TABLE OF CONTENTS Page No.

17. RESIDENTIAL BUILDING CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 17.1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 17.2. BUILDING CHARACTERISTICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 17.2.1. Key Volumes of Residence Studies . . . . . . . . . . . . . . . . . . . . . . . 2 17.2.2. Volumes and Surface Areas of Rooms . . . . . . . . . . . . . . . . . . . . . 4 17.2.3. Mechanical System Configurations . . . . . . . . . . . . . . . . . . . . . . . 6 17.2.4. Type of Foundation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 17.3. TRANSPORT RATES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 17.3.1. Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 17.3.2. Air Exchange Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 17.3.3. Infiltration Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 17.3.4. Deposition and Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 17.3.5. Interzonal Airflows . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 17.3.6. Water Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 17.3.7. House Dust and Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 17.4. SOURCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 17.4.1. Source Descriptions for Airborne Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 17.4.2. Source Descriptions for Waterborne Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 17.4.3. Soil and House Dust Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 17.5. ADVANCED CONCEPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 17.5.1. Uniform Mixing Assumption . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 17.5.2. Reversible Sinks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 17.6 RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 17.7. REFERENCES FOR CHAPTER 17 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Air In Water In Soil In Out Concentration, C Exposure, E for Occupant( s)

Decay Removal Resuspension Source Reversible Sinks Volume III  Activity Factors Chapter 17  Residential Building Characteristics Exposure Factors Handbook Page August 1997 17 1 Figure 17 1. Elements of Residential Exposure 17. RESIDENTIAL BUILDING CHARACTERISTICS 17.1. INTRODUCTION Unlike previous chapters in this handbook which a wide range of indoor materials. In addition, the activity of focus on human behavior or characteristics that affect human receptors greatly affects their exposure as they move exposure, this chapter focuses on residence characteristics. from room to room, entering and leaving the exposure Assessment of exposure in residential settings requires scene. information on the availability of the chemical( s) of concern Inhalation exposure assessments in residential and at the point of exposure, characteristics of the structure and other indoor settings are modeled by considering the microenvironment that affect exposure, and human presence building as an assemblage of one or more well mixed within the residence. The purpose of this chapter is to zones. A zone is defined as one room, a group of provide data that are available on residence characteristics interconnected rooms, or an entire building. This that affect exposure in an indoor environment. Source macroscopic level, well mixed perspective forms the basis receptor relationships in residential exposure scenarios can for interpretation of measurement data as well as simulation be complex due to interactions among sources, and of hypothetical scenarios. Exposure assessment models on transport/ transformation processes that result from a macroscopic level incorporate important physical factors chemical specific and building specific factors. Figure 17 and processes. These well mixed, macroscopic models 1 illustrates the complex factors that must be considered have been used to perform indoor air quality simulations when conducting exposure assessments in a residential ( Axley, 1989), as well as indoor air exposure assessments setting. In addition to sources within the building, ( McKone, 1989; Ryan, 1991). Nazzaroff and Cass ( 1986) chemicals of concern may enter the indoor environment and Wilkes et al. ( 1992) have used code intensive computer from outdoor air, soil, gas, water supply, tracked in soil, and programs featuring finite difference or finite element industrial work clothes worn by the residents. Indoor numerical techniques to model mass balance. A simplified concentrations are affected by loss mechanisms, also approach using desk top spreadsheet programs has been illustrated in Figure 17 1, involving chemical reactions, used by Jennings et al. ( 1985). deposition to and re emission from surfaces, and transport out of the building. Particle bound chemicals can enter indoor air through resuspension. Indoor air concentrations of gas phase organic chemicals are affected by the presence of reversible sinks formed by Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 2 August 1997 In order to model mass balance of indoor waterborne sources, and soil/ house dust sources. Section contaminants, the indoor air volume is represented as a 17.5 summarizes advanced concepts. network of interconnected zones. Because conditions in a given zone are determined by interactions with other connecting zones, the multizone model is stated as a system of simultaneous equations. The mathematical framework for modeling indoor air has been reviewed by Sinden ( 1978) and Sandberg ( 1984). Indoor air quality models typically are not software products that can be purchased as " off the shelf" items. Most existing software models are research tools that have been developed for specific purposes and are being continuously refined by researchers. Leading examples of indoor air models implemented as software products are as follows:

° CONTAM  developed at the National Institute of Standards and Technology ( NIST) with support from U. S. EPA and the U. S. Department of Energy ( DOE) ( Axley, 1988; Grot, 1991; Walton, 1993);

° EXPOSURE  developed at the Indoor Air Branch of U. S. EPA Air and Energy Engineering Research Laboratory ( EPA/ AEERL) ( Sparks, 1988, 1991);

° MCCEM  the Multi Chamber Consumer Exposure Model developed for U. S EPA Office of Pollution Prevention and Toxics ( EPA/ OPPT) ( GEOMET, 1989; Koontz and Nagda, 1991); and ° THERdbASE  the Total Human Exposure Relational Data Base and Advanced Simulation Environment software developed by researchers at the Harry Reid Center for Environmental Studies at University Nevada, Las Vegas ( UNLV) ( Pandian et al., 1993).

Section 17.2 of this chapter summarizes existing data on building characteristics ( volumes, surface areas, mechanical systems, and types of foundations). Section 17.3 summarizes transport phenomena that affect chemical transport ( airflow, chemical specific deposition and filtration, and effects of water supply and soil tracking). Section 17.4 provides information on various types of indoor sources associated with airborne exposure, 17.2. BUILDING CHARACTERISTICS 17.2.1. Key Volumes of Residence Studies Versar ( 1990)  Database on Perfluorocarbon Tracer ( PFT) Ventilation Measurements  A database of time averaged air exchange and interzonal airflow measurements in more than 4,000 residences has been compiled by Versar ( 1990) to allow researchers to access these data ( see Section 17.3.2). These data were collected between 1982 and 1987. The residences that appear in this database are not a random sample of U. S. homes; however, they do represent a compilation of homes visited in about 100 different field studies, some of which involved random sampling. In each study, the house volumes were directly measured or estimated. The collective homes visited in these field projects are not geographically balanced; a large fraction of these homes are located in southern California. Statistical weighting techniques were applied in developing estimates of nationwide distributions ( see Section 17.3.2) to compensate for the geographic imbalance. U. S. DOE ( 1995)  Housing Characteristics 1993, Residential Energy Consumption Survey ( RECS)  Measurement surveys have not been conducted to directly characterize the range and distribution of volumes for a random sample of U. S. residences. Related data, however, are regularly collected through the U. S. DOE's RECS ( U. S. DOE, 1995). In addition to collecting information on energy use, this triennial survey collects data on housing characteristics including direct measurements of total and heated floor space for buildings visited by survey specialists. For the most recent survey ( 1993), a multistage probability sample of over 7,000 residences was surveyed, representing 96 million residences nationwide. The survey response rate was 81.2 percent. Volumes were estimated from the RECS measurements by multiplying the heated floor space area by an assumed ceiling height of 8 feet, recognizing that this assumed height may not apply universally to all homes. Results for residential volume distributions from the RECS ( Thompson, 1995) are presented in Table 17 1. Estimated parameters of residential volume distributions ( in cubic meters) from the PFT database ( Versar, 1990) are also summarized in Table 17 1, for comparison to the RECS data. The arithmetic means from the two sources are identical ( 369 cubic meters). The medians ( 50th percentiles) are very similar: 310 cubic meters for the RECS data, and 321 cubic meters for the PFT database. Volume III  Activity Factors Chapter 17  Residential Building Characteristics Exposure Factors Handbook Page August 1997 17 3 Figure 17 2. Cumulative Frequency Distributions for Residential Volumes from the PFT Data Base and the U. S. DOE's RECs. Cumulative frequency distributions from the two sources predominant housing type single family detached homes ( Figure 17 2) also are quite similar, especially between the also has the largest average volume ( Table 17 2). 50th and 75th percentiles. Multifamily units and mobile homes have volumes Table 17 1. Summary of Residential Volume Distributions in Cubic Metersa Parameter RECS PFT Database ( 2) Data ( 1)

Arithmetic Mean 369 369 Standard Deviation 258 209 10th Percentile 147 167 25th Percentile 209 225 50th Percentile 310 321 75th Percentile 476 473 90th Percentile 672 575 In cubic meters a Sources: ( 1) Thompson, 1995; ( 2) Versar, 1990 The RECS also provides relationships between average residential floor areas and factors such as housing type, ownership, household size and structure age. The averaging about half that of single family detached homes, with single family attached homes about halfway between these extremes. Within each category of housing type, owner occupied residences average about 50 percent greater volume than rental units. The relationship of residential volume to household size ( Table 17 3) is of particular interest for purposes of exposure assessment. For example, one person households would not include children, and the data in the table indicate that multi person households occupy residences averaging about 50 percent greater volume than residences occupied by one person households. Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 4 August 1997 Table 17 2. Average Estimated Volumes of U. S. Residences, by Housing Type and Ownership Ownership Owner Occupied Rental All Units Housing Type ( m ) of Total ( m ) of Total ( m ) of Total Volume Percent Volume Percent Volume Percent a 3 a 3 a 3 Single Family 471 53.1 323 8.5 451 61.7 ( Detached)

Single Family 406 4.6 291 2.9 362 7.5 ( Attached)

Multifamily 362 1.6 216 6.7 243 8.3 ( 2 4 units)

Multifamily 241 1.7 183 15.2 190 16.8 ( 5+ Units)

Mobile Home 221 4.6 170 1.2 210 5.8 All Types 441 65.4 233 34.6 369 100.0 Volumes calculated from floor areas assuming a ceiling height of 8 feet. a Source: Adapted from U. S. DOE, 1995.

Table 17 3. Residential Volumes in Relation to Household Size and Year of Construction Volumea ( m ) Percent of Total 3 Household Size 1 Person 269 24.3 2 Persons 386 32.8 3 Persons 387 17.2 4 Persons 431 15.1 5 Persons 433 7.0 from the mean of 369 m given in Table 17 1. Murray's 6 or More Persons 408 3.6 All Sizes 369 100.0 Year of Construction 1939 or before 385 21.1 1940 to 1949 338 7.1 1950 to 1959 365 13.5 1960 to 1969 358 15.5 1970 to 1979 350 18.7 1980 to 1984 344 8.8 1985 to 1987 387 5.7 1988 to 1990 419 4.9 1991 to 1993 438 4.7 All Years 369 100.0 Volumes calculated from floor areas assuming a ceiling height a of 8 feet. Source: U. S. DOE, 1995.

Data on year of construction indicate a slight decrease in residential volumes between 1950 and 1984, followed by an increasing trend over the next decade. A ceiling height of 8 feet was assumed in estimating the average volumes, whereas there may have been some timerelated trends in ceiling height. Murray ( 1996)  Analysis of RECS and PFT Databases. Using a database from the 1993 RECS and an assumed ceiling height of 8 feet, Murray ( 1996) estimated a mean residential volume of 382 m using RECS estimates 3 of heated floor space. This estimate is slightly different 3 ( 1996) sensitivity analysis indicated that when a fixed ceiling height of 8 feet was replaced with a randomly varying height with a mean of 8 feet, there was little effect on the standard deviation of the estimated distribution. From a separate analysis of the PFT database, based on 1,751 individual household measure ments, Murray ( 1996) estimated an average volume of 369 m , the same as 3 previously given in Table 17 1. In performing this analysis, the author carefully reviewed the PFT database in an effort to use each residence only once, for those residences thought to have multiple PFT measurements.

17.2.2. Volumes and Surface Areas of Rooms Room Volumes  Volumes of individual rooms are dependent on the building size and configuration, but summary data are not readily available. The exposure assessor is advised to define specific rooms, or assemblies of rooms, that best fit the scenario of interest. Most models for predicting indoor air concentrations specify airflows in Volume III  Activity Factors Chapter 17  Residential Building Characteristics Exposure Factors Handbook Page August 1997 17 5 Table 17 4. Dimensional Quantities for Residential Rooms Nominal Dimensions Length ( m) Width ( m) Height ( m) Volume ( m ) 3 Wall Area ( m ) 2 Floor Area ( m ) 2 Total Area ( m ) 2 Eight Foot Ceiling 12' x15' 4.6 3.7 2.4 41 40 17 74 12' x12' 3.7 3.7 2.4 33 36 13 62 10' x12' 3.0 3.7 2.4 27 33 11 55 9' x12' 2.7 3.7 2.4 24 31 10 51 6' x12' 1.8 3.7 2.4 16 27 7 40 4' x12' 1.2 3.7 2.4 11 24 4 32 Twelve Foot Ceiling 12' x15' 4.6 3.7 3.7 61 60 17 94 12' x12' 3.7 3.7 3.7 49 54 13 80 10' x12' 3.0 3.7 3.7 41 49 11 71 9' x12' 2.7 3.7 3.7 37 47 10 67 6' x12' 1.8 3.7 3.7 24 40 7 54 4' x12' 1.2 3.7 3.7 16 36 4 44 cubic meters per hour and, correspondingly, express surface area to volume, or loading ratio. Table 17 4 volumes in cubic meters. A measurement in cubic feet can provides the basis for calculating loading ratios for typicalbe converted to cubic meters by multiplying the value in sized rooms. Constant features in the examples are: a room cubic feet by 0.0283 m / ft . For example, a bedroom that is width of 12 feet and a ceiling height of 8 feet ( typical for 3 3 9 feet wide by 12 feet long by 8 feet high has a volume of residential buildings), or a ceiling height 12 feet ( typical for 864 cubic feet or 24.5 cubic meters. Similarly, a living commercial buildings). The loading ratios for the 8 foot room with dimensions of 12 feet wide by 20 feet long by 8 ceiling height range from 0.98 m m to 2.18 m m for wall feet high has a volume of 1920 cubic feet or 54.3 cubic area and from 0.36 m m to 0.44 m m for floor area. In meters, and a bathroom with dimensions of 5 feet by 12 feet comparison, ASTM Standard E 1333 ( ASTM, 1990), for by 8 feet has a volume of 480 cubic feet or 13.6 cubic large chamber testing of formaldehyde levels from wood meters. products, specifies the following loading ratios: ( 1) 0.95 Murray ( 1996) analyzed the distribution of selected m m for testing plywood ( assumes plywood or paneling on residential zones ( i. e., a series of connected rooms) using all four walls of a typical size room); and ( 2) 0.43 m m for the PFT database. The author analyzed the " kitchen zone" testing particleboard ( assumes that particleboard decking or and the " bedroom zone" for houses in the Los Angeles area underlayment would be used as a substrate for the entire that were labeled in this manner by field researchers, and floor of a structure). " basement," " first floor," and " second floor" zones for houses outside of Los Angeles for which the researchers labeled individual floors as zones. The kitchen zone contained the kitchen in addition to any of the following associated spaces: utility room, dining room, living room and family room. The bedroom zone contained all the bedrooms plus any bathrooms and hallways associated with the bedrooms. The following summary statistics ( mean ± standard deviation) were reported by Murray ( 1996) for the volumes of the zones described above: 199 ± 115 m for 3 the kitchen zone, 128 ± 67 m for the bedroom zone, 205 ± 3 64 m for the basement, 233 ± 72 m for the first floor, and 3 3 233 ± 111 m for the second floor. 3 Surface Areas  The surface areas of floors are Table 17 5 also are not scaled to any particular residential commonly considered in relation to the room or house volume. In some cases, it may be preferable for the volume, and their relative loadings are expressed as a exposure assessor to use professional judgment in 2  3 2  3 2  3 2  3 2  3 2  3 Products and Materials  Table 17 5 presents examples of assumed amounts of selected products and materials used in constructing or finishing residential surfaces ( Tucker, 1991). Products used for floor surfaces include adhesive, varnish and wood stain; and materials used for walls include paneling, painted gypsum board, and wallpaper. Particleboard and chipboard are commonly used for interior furnishings such as shelves or cabinets, but could also be used for decking or underlayment. It should be noted that numbers presented in Table 17 5 for surface area are based on typical values for residences, and they are presented as examples. In contrast to the concept of loading ratios presented above ( as a surface area), the numbers in Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 6 August 1997 combination with the loading ratios given above. For mixing. Without a blower, these heaters still have the example, if the exposure scenario involves residential ability to induce mixing through convective heat transfer. carpeting, either as an indoor source or as an indoor sink, If the heater is a source of combustion pollutants, as with then the ASTM loading ratio of 0.43 m m for floor unvented gas or kerosene space heaters, then the 2  3 materials could be multiplied by an assumed residential combination of convective heat transfer and thermal volume and assumed fractional coverage of carpeting to buoyancy of combustion products will result in fairly rapid derive an estimate of the surface area. More specifically, a dispersal of such pollutants. The pollutants will disperse residence with a volume of 300 m , a loading ratio of 0.43 throughout the floor where the heater is located and to floors 3 m m and coverage of 80% would have 103 m of above the heater, but will not disperse to floors below. 2  3 2 carpeting. The estimates discussed here relate to Central forced air HAC systems are common in macroscopic surfaces; the true surface area for carpeting, many residences. Such systems, through a network of for example, would be considerably larger because of the supply/ return ducts and registers, can achieve fairly nature of its fibrous material. complete mixing within 20 to 30 minutes ( Koontz et al.,

Table 17 5. Examples of Products and Materials Associated with Floor and Wall Surfaces in Residences Material Sources Surface Covered Assumed Amount of a Silicone caulk 0.2 m2 Floor adhesive 10.0 m2 Floor wax 50.0 m2 Wood stain 10.0 m2 Polyurethane wood finish 10.0 m2 Floor varnish or lacquer 50.0 m2 Plywood paneling 100.0 m2 Chipboard 100.0 m2 Gypsum board 100.0 m2 Wallpaper 100.0 m2 Based on typical values for a residence. a Source: Adapted from Tucker, 1991.

Furnishings  Information on the relative abundance of specific types of indoor furnishings, such as draperies or upholstered furniture, was not readily available. The exposure assessor is advised to rely on common sense and professional judgment. For example, the number of beds in a residence is usually related to household size, and information has been provided ( Table 17 3) on average house volume in relation to household size.

17.2.3. Mechanical System Configurations Mechanical systems for air movement in residences can affect the migration and mixing of pollutants released indoors and the rate of pollutant removal. Three types of mechanical systems are: ( 1) systems associated with heating and air conditioning ( HAC); ( 2) systems whose primary function is providing localized exhaust; and ( 3) systems intended to increase the overall air exchange rate of the residence. Portable space heaters intended to serve a single room, or a series of adjacent rooms, may or may not be equipped with blowers that promote air movement and 1988). The air handler for such systems is commonly equipped with a filter ( see Figure 17 3) that can remove particle phase contaminants. Further removal of particles, via deposition on various room surfaces ( see Section 17.3.2), is accomplished through increased air movement when the air handler is operating. Figure 17 3 also distinguishes forced air HAC systems by the return layout in relation to supply registers. The return layout shown in the upper portion of the figure is the type most commonly found in residential settings. On any floor of the residence, it is typical to find one or more supply registers to individual rooms, with one or two centralized return registers. With this layout, supply/ return imbalances can often occur in individual rooms, particularly if the interior doors to rooms are closed. In comparison, the supply/ return layout shown in the lower portion of the figure by design tends to achieve a balance in individual rooms or zones. Airflow imbalances can also be caused by inadvertent duct leakage to unconditioned spaces such as attics, basements, and crawl spaces. Such imbalances usually depressurize the house, thereby increasing the likelihood of contaminant entry via soil gas transport or through spillage of combustion products from vented fossilfuel appliances such as fireplaces and gas/ oil furnaces. Mechanical devices such as kitchen fans, bathroom fans, and clothes dryers are intended primarily to provide localized removal of unwanted heat, moisture, or odors. Operation of these devices tends to increase the air exchange rate between the indoors and outdoors. Because Volume III  Activity Factors Chapter 17  Residential Building Characteristics Exposure Factors Handbook Page August 1997 17 7 Figure 17 3. Configuration for Residential Forced air Systems local exhaust devices are designed to be near certain indoor basements provide some resistance, but still have numerous sources, their effective removal rate for locally generated pathways for soil gas entry. By comparison, homes with pollutants is greater than would be expected from the crawl spaces open to the outside have significant dilution effect of increased air exchange. Operation of these opportunities for dilution of soil gases prior to transport into devices also tends to depressurize the house, because the house. replacement air usually is not provided to balance the exhausted air. An alternative approach to pollutant removal is one which relies on an increase in air exchange to dilute pollutants generated indoors. This approach can be accomplished using heat recovery ventilators ( HRVs) or energy recovery ventilators ( ERVs). Both types of ventilators are designed to provide balanced supply and exhaust airflows and are intended to recover most of the energy that normally is lost when additional outdoor air is introduced. Although ventilators can provide for more rapid dilution of internally generated pollutants, they also increase the rate at which outdoor pollutants are brought into the house. A distinguishing feature of the two types is that ERVs provide for recovery of latent heat ( moisture) in addition to sensible heat. Moreover, ERVs typically recover latent heat using a moisture transfer device such as a desiccant wheel. It has been observed in some studies that the transfer of moisture between outbound and inbound air streams can result in some re entrainment of indoor pollutants that otherwise would have been exhausted from the house ( Andersson et al., 1993). Inadvertent air communication between the supply and exhaust air streams can have a similar effect. Studies quantifying the effect of mechanical devices on air exchange using tracer gas measurements are uncommon and typically provide only anecdotal data. The common approach is for the expected increment in the air exchange rate to be estimated from the rated airflow capacity of the device( s). For example, if a device with a rated capacity of 100 cubic feet per minute ( cfm), or 170 cubic meters per hour, is operated continuously in a house with a volume of 400 cubic meters, then the expected increment in the air exchange rate of the house would be 170 m h / 400 m , or approximately 0.4 air changes per 3  1 3 hour.

17.2.4. Type of Foundation The type of foundation of a residence is of interest in residential exposure assessment. It provides some indication of the number of stories and house configuration, and provides an indication of the relative potential for soilgas transport. For example, such transport can occur readily in homes with enclosed crawl spaces. Homes with Lucas et al. ( 1992)  National Residential Radon Survey  The National Resdental Radon Survey, sponsored by the U. S. EPA, was conducted by Lucas et al. ( 1992) in about 5,700 households nationwide. In addition to radon measurements, information on a number of housing characteristics was collected, including whether each house had a basement. The estimated percentage ( 45.2 percent) of homes in the U. S. having basements ( Table 17 6) from this survey is the same as found by the RECS ( Table 17 7). Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 8 August 1997 Table 17 6. Percent of Residences with Basement, by Census Region and EPA Region Census Region Region with Basements EPA Percent of Residences Northeast 1 93.4 Northeast 2 55.9 Northeast 3 67.9 South 4 19.3 Midwest 5 73.5 South 6 4.1 Midwest 7 75.3 West 8 68.5 West 9 10.3 West 10 11.5 All Regions 45.2 Source: Lucas et al., 1992.

The National Residential Radon Survey provides data for more refined geographical areas, with a breakdown by the 10 EPA Regions. The New England region ( i. e., EPA Region 1), which includes Connecticut, Maine, Massachusetts, New Hampshire, Rhode Island, and Vermont, had the highest prevalence of basements ( 93 percent). The lowest prevalence ( 4 percent) was for the South Central region ( i. e., EPA Region 6), which includes Arkansas, Louisiana, New Mexico, Oklahoma, and Texas. Table 17 8 presents the States associated with each Census Region and EPA Region. U. S. DOE ( 1995)  Housing Characteristics 1993  Residential Energy Consumption Survey ( RECS)  The most recent RECS ( described in Section 17.2.1) was administered in 1993 to over 7,000 households ( U. S. DOE, 1995). The type of information requested by the survey questionnaire included the type of foundation for the residence ( i. e., basement, enclosed crawl space, crawl space open to outside or concrete slab). This information was not obtained for multifamily structures with five or more dwelling units or for mobile homes. Table 17 7 presents estimates from the survey of the percentage of residences with each foundation type, by census region, and for the entire U. S. The percentages can add to more than 100 percent because some residences have more than one type of foundation; for example, most split level structures have a partial basement combined with some crawlspace that typically is enclosed. The data in Table 17 7 indicate that close to half ( 45 percent) of residences nationwide have a basement, and that fewer than 10 percent have a crawl space that is open to outside. It also shows that a large fraction of homes have concrete slabs ( 31 percent). There are also variations by census region. For example, nearly 80 percent of the residences in the Northeast and Midwest regions have basements. In the South and West regions, the predominant foundation types are concrete slabs and enclosed crawl spaces. Table 17 8 illustrates the four Census Regions.

17.3. TRANSPORT RATES 17.3.1. Background Major air transport pathways for airborne substances in residences include the following:

° Air exchange  Air leakage through windows, doorways, intakes and exhausts, and " adventitious openings" ( i. e., cracks and seams) that combine to form the leakage configuration of the building envelope plus natural and mechanical ventilation;

° Interzonal airflows  Transport through doorways, ductwork, and service chaseways that interconnect rooms or zones within a building; and ° Local circulation  Convective and advective air circulation and mixing within a room or within a zone.

The distribution of airflows across the building envelope that contribute to air exchange and the interzonal airflows along interior flowpaths is determined by the interior pressure distribution. The forces causing the airflows are temperature differences, the actions of wind, and mechanical ventilation systems. Basic concepts have been reviewed by ASHRAE ( 1993). Indoor outdoor and room to room temperature differences create density differences that help determine basic patterns of air motion. During the heating season, warmer indoor air tends to rise to exit the building at upper levels by stack action. Exiting air is replaced at lower levels by an influx of colder outdoor air. During the cooling season, this pattern is reversed: stack forces during the cooling season are generally not as strong as in the heating season because the indoor outdoor temperature differences are not pronounced. In examining a data base of air leakage measurements, Sherman and Dickerhoff ( 1996) observed that houses built prior to 1980 showed a clear increase in leakage with increasing age and were leakier, on average, Volume III  Activity Factors Chapter 17  Residential Building Characteristics Exposure Factors Handbook Page August 1997 17 9 Table 17 7. Percent of Residences with Certain Foundation Types by Census Region Census Region Percent of Residencesa With With With Crawlspace With Basement Enclosed Crawlspace Open to Outside Concrete Slab Northeast 78.0 12.6 2.8 15.8 Midwest 78.1 19.5 5.6 14.7 South 18.6 31.8 11.0 44.6 West 19.4 36.7 8.1 43.5 All Regions 45.2 26.0 7.5 31.3 Percentage may add to more than 100 percent because more than one foundation type may apply to a given residence. a Source: U. S. DOE, 1995.

Table 17 8. States Associated with EPA Regions and Census Regions US EPA Regions Region 1 Region 4 Region 6 Region 9 Connecticut Alabama Arkansas Arizona Maine Florida Louisiana California Massachusetts Georgia New Mexico Hawaii New Hampshire Kentucky Oklahoma Nevada Rhode Island Mississippi Texas Vermont North Carolina Region 10 Region 2 Tennessee Iowa Idaho New Jersey Kansas Oregon New York Region 5 Missouri Washington Region 3 Indiana Delaware Michigan Region 8 District of Columbia Minnesota Colorado Maryland Ohio Montana Pennsylvania Wisconsin North Dakota Virginia South Dakota West Virginia Utah South Carolina Region 7 Alaska Illinois Nebraska Wyoming US Bureau of Census Regions Northeast Region Midwest Region South Region West Region Connecticut Illinois Alabama Alaska Maine Indiana Arkansas Arizona Massachusetts Iowa Delaware California New Hampshire Kansas District of Columbia Colorado New Jersey Michigan Florida Hawaii New York Minnesota Georgia Idaho Pennsylvania Missouri Kentucky Montana Rhode island Nebraska Louisiana Nevada Vermont North Dakota Maryland New Mexico Ohio Mississippi Oregon South Dakota North Carolina Utah Wisconsin Oklahoma Washington South Carolina Wyoming Tennessee Texas Virginia West Virginia Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 10 August 1997 than newer houses. They further observed that the post years, there has been a diversity of protocols and study 1980 houses did not show any trend in leakiness with age. objectives. Since the early 1980s, however, an inexpensive The position of the neutral pressure level ( i. e., the perfluorocarbon tracer ( PFT) technique has been used to point where indoor outdoor pressures are equal) depends on measure time averaged air exchange and interzonal airflows the leakage configuration of the building envelope. The in thousands of occupied residences using essentially stack effect arising from indoor outdoor temperature similar protocols ( Dietz et al., 1986). The PFT technique differences is also influenced by the partitioning of the utilizes miniature permeation tubes as tracer emitters and building interior. When there is free communication passive samplers to collect the tracers. The passive between floors or stories, the building behaves as a single samplers are returned to the laboratory for analysis by gas volume affected by a generally rising current during the chromatography. These measurement results have been heating season and a generally falling current during the compiled to allow various researchers to access the data cooling season. When vertical communication is restricted, ( Versar, 1990). each level essentially becomes an independent zone. As the wind flows past a building, regions of positive and negative pressure ( relative to indoors) are created within the building; positive pressures induce an influx of air, whereas negative pressures induce an outflow. Wind effects and stack effects combine to determine a net inflow or outflow. The final element of indoor transport involves the actions of mechanical ventilation systems that circulate indoor air through the use of fans. Mechanical ventilation systems may be connected to heating/ cooling systems that, depending on the type of building, recirculate thermally treated indoor air or a mixture of fresh air and recirculated air. Mechanical systems also may be solely dedicated to exhausting air from a designated area, as with some kitchen range hoods and bath exhausts, or to recirculating air in designated areas as with a room fan. Local air circulation also is influenced by the movement of people and the operation of local heat sources.

17.3.2. Air Exchange Rates standard deviation of 2.01. Air exchange is the balanced flow into and out of a building, and is composed of three processes: ( 1) infiltration  air leakage through random cracks, interstices, and other unintentional openings in the building envelope; ( 2) natural ventilation  airflows through open windows, doors, and other designed openings in the building envelope; and ( 3) forced or mechanical ventilation  controlled air movement driven by fans. For nearly all indoor exposure scenarios, air exchange is treated as the principal means of diluting indoor concentrations. The air exchange rate is generally expressed in terms of air changes per hour ( ACH, with units of h ), the ratio of the airflow  1 ( m h ) to the volume ( m ). 3  1 3 No measurement surveys have been conducted to directly evaluate the range and distribution of residential air exchange rates. Although a significant number of air exchange measurements have been carried out over the Nazaroff et al. ( 1988)  Prior to the Koontz and Rector ( 1995) study, Nazaroff et al. ( 1988) aggregated the data from two studies conducted earlier using tracer gas decay. At the time these studies were conducted, they were the largest U. S. studies to include air exchange measurements. The first ( Grot and Clark, 1981) was conducted in 255 dwellings occupied by low income families in 14 different cities. The geometric mean ± standard deviation for the air exchange measurements in these homes, with a median house age of 45 years, was 0.90 ± 2.13 ACH. The second study ( Grimsrud et al., 1983) involved 312 newer residences, with a median age of less than 10 years. Based on measurements taken during the heating season, the geometric mean ± standard deviation for these homes was 0.53 ± 1.71 ACH. Based on an aggregation of the two distributions with proportional weighting by the respective number of houses studied, Nazaroff et al. ( 1988) developed an overall distribution with a geometric mean of 0.68 ACH and a geometric Versar ( 1990)  Database of PFT Ventilation Measurements  The residences included in the PFT database do not constitute a random sample across the United States. They represent a compilation of homes visited in the course of about 100 separate field research projects by various organizations, some of which involved random sampling and some of which involved judgmental or fortuitous sampling. The larger projects in the PFT database are summarized in Table 17 9, in terms of the number of measurements ( samples), states where, and months when, samples were taken, and summary statistics for their respective distributions of measured air exchange rates. For selected projects ( LBL, RTI, SOCAL), multiple measurements were taken for the same house, usually during different seasons. A large majority of the Volume III  Activity Factors Chapter 17  Residential Building Characteristics Exposure Factors Handbook Page August 1997 17 11 Table 17 9. Summary of Major Projects Providing Air Exchange Measurements in the PFT Database Project Code State Month( s) Measurements Exchange Rate SD a Number of Mean Air Percentiles b 10th 25th 50th 75th 90th ADM CA 5 7 29 0.70 0.52 0.29 0.36 0.48 0.81 1.75 BSG CA 1,8 12 40 0.53 0.30 0.21 0.30 0.40 0.70 0.90 GSS AZ 1 3,8 9 25 0.39 0.21 0.16 0.23 0.33 0.49 0.77 FLEMING NY 1 6,8 12 56 0.24 0.28 0.05 0.12 0.22 0.29 0.37 GEOMET1 FL 1,6 8,10 12 18 0.31 0.16 0.15 0.18 0.25 0.48 0.60 GEOMET2 MD 1 6 23 0.59 0.34 0.12 0.29 0.65 0.83 0.92 GEOMET3 TX 1 3 42 0.87 0.59 0.33 0.51 0.71 1.09 1.58 LAMBERT1 ID 2 3,10 11 36 0.25 0.13 0.10 0.17 0.23 0.33 0.49 LAMBERT2 MT 1 3,11 51 0.23 0.15 0.10 0.14 0.19 0.26 0.38 LAMBERT3 OR 1 3,10 12 83 0.46 0.40 0.19 0.26 0.38 0.56 0.80 LAMBERT4 WA 1 3,10 12 114 0.30 0.15 0.14 0.20 0.30 0.39 0.50 LBL1 OR 1 4,10 12 126 0.56 0.37 0.28 0.35 0.45 0.60 1.02 LBL2 WA 1 4,10 12 71 0.36 0.19 0.18 0.25 0.32 0.42 0.52 LBL3 ID 1 5,11 12 23 1.03 0.47 0.37 0.73 0.99 1.34 1.76 LBL4 WA 1 4,11 12 29 0.39 0.27 0.14 0.18 0.36 0.47 0.63 LBL5 WA 2 4 21 0.36 0.21 0.13 0.19 0.30 0.47 0.62 LBL6 ID 3 4 19 0.28 0.14 0.11 0.17 0.26 0.38 0.55 NAHB MN 1 5,9 12 28 0.22 0.11 0.11 0.16 0.20 0.24 0.38 NYSDH NY 1 2,4,12 74 0.59 0.37 0.28 0.37 0.50 0.68 1.07 PEI MD 3 4 140 0.59 0.45 0.15 0.26 0.49 0.83 1.20 PIERCE CT 1 3 25 0.80 1.14 0.20 0.22 0.38 0.77 2.35 RTI1 CA 2 45 0.90 0.73 0.38 0.48 0.78 1.08 1.52 RTI2 CA 7 41 2.77 2.12 0.79 1.18 2.31 3.59 5.89 RTI3 NY 1 4 397 0.55 0.37 0.26 0.33 0.44 0.63 0.94 SOCAL1 CA 3 551 0.81 0.66 0.29 0.44 0.66 0.94 1.43 SOCAL2 CA 7 408 1.51 1.48 0.35 0.59 1.08 1.90 3.11 SOCAL3 CA 1 330 0.76 1.76 0.26 0.37 0.48 0.75 1.11 UMINN MN 1 4 35 0.36 0.32 0.17 0.20 0.28 0.40 0.56 UWISC WI 2 5 57 0.82 0.76 0.22 0.33 0.55 1.04 1.87 1 = January, 2 = February, etc. a Standard deviation b Source: Adapted from Versar, 1990.

measurements are from the SOCAL project that was such a way that the resultant number of cases would conducted in Southern California. The means of the represent each state in proportion to its share of occupied respective studies generally range from 0.2 to 1.0 ACH, housing units, as determined from the 1990 U. S. Census of with the exception of two California projects RTI2 and Population and Housing. SOCAL2. Both projects involved measurements in Summary statistics from the Koontz and Rector Southern California during a time of year ( July) when ( 1995) analysis are shown in Table 17 10, for the country windows would likely be opened by many occupants. as a whole and by census regions. Based on the statistics Koontz and Rector ( 1995)  Estimation of Distributions for Residential Air Exchange Rates  In analyzing the composite data from various projects ( 2,971 measurements), Koontz and Rector ( 1995) assigned weights to the results from each state to compensate for the geographic imbalance in locations where PFT measurements were taken. The results were weighted in for all regions combined, the authors suggested that a 10th percentile value of 0.18 ACH would be appropriate as a conservative estimator for air exchange in residential settings, and that the 50th percentile value of 0.45 ACH would be appropriate as a typical air exchange rate. In applying conservative or typical values of air exchange rates, it is important to realize the limitations of the Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 12 August 1997 Table 17 10. Summary Statistics for Air Exchange Rates ( air changes per hour ACH), by Region West Region North Central Region Northeast Region South Region All Regions Arithmetic Mean 0.66 0.57 0.71 0.61 0.63 Arithmetic Standard Deviation 0.87 0.63 0.60 0.51 0.65 Geometric Mean 0.47 0.39 0.54 0.46 0.46 Geometric Standard Deviation 2.11 2.36 2.14 2.28 2.25 10th Percentile 0.20 0.16 0.23 0.16 0.18 50th Percentile 0.43 0.35 0.49 0.49 0.45 90th Percentile 1.25 1.49 1.33 1.21 1.26 Maximum 23.32 4.52 5.49 3.44 23.32 Source: Koontz and Rector, 1995. underlying data base. Although the estimates are based on and February were defined as winter, March, April and May thousands of measurements, the residences represented in were defined as spring, and so on. The results of Murray the database are not a random sample of the United States and Burmaster ( 1995) are summarized in Table 17 11. housing stock. The sample population is not balanced in Neglecting the summer results in the colder regions which terms of geography or time of year. Statistical techniques have only a few observations, the results indicate that the were applied to compensate for some of these imbalances. highest air exchange rates occur in the warmest climate In addition, PFT measurements of air exchange rates region during the summer. As noted earlier ( Section assume uniform mixing of the tracer within the building. 17.3.2), many of the measurements in the warmer climate This is not always so easily achieved. Furthermore, the region were from field studies conducted in Southern degree of mixing can vary from day to day and house to California during a time of year ( July) when windows would house because of the nature of the factors controlling mixing tend to be open in that area. Data for this region in ( e. g., convective air monitoring driven by weather, and type particular should be used with caution since other areas and operation of the heating system). The relative within this region tend to have very hot summers and placement of the PFT source and the sampler can also cause residences use air conditioners, resulting in lower air variability and uncertainty. It should be noted that sampling exchange rates. The lowest rates generally occur in the is typically done in a single location in a house which may colder regions during the fall ( Table 17 11). not represent the average from that house. In addition, very high and very low values of air exchange rates based on PFT measurements have greater uncertainties than those in A variety of mathematical models exist for prediction the middle of the distribution. Despite such limitations, the of air infiltration rates in individual buildings. A number of estimates in Table 17 10 are believed to represent the best these models have been reviewed, for example, by available information on the distribution of air exchange Liddament and Allen ( 1983), and by Persily and Linteris rates across United States residences throughout the year. ( 1984). Basic principles are concisely summarized in the Murray and Burmaster ( 1995)  Residential Air Exchange Rates in the United States: Empirical and Estimated Parametric Distributions by Season and Climatic Region  Murray and Burmaster ( 1995) analyzed the PFT database using 2,844 measurements ( essentially the same cases as analyzed by Koontz and Rector ( 1995), but without the compensating weights). These authors summarized distributions for subsets of the data defined by climate region and season. The coldest region was defined as having 7,000 or more heating degree days, the colder region as 5,500 6,999 degree days, the warmer region as 2,500 5,499 degree days, and the warmest region as fewer than 2,500 degree days. The months of December, January 17.3.3. Infiltration Models ASHRAE Handbook of Fundamentals ( ASHRAE, 1993). These models have a similar theoretical basis; all address indoor outdoor pressure differences that are maintained by the actions of wind and stack ( temperature difference) effects. The models generally incorporate a network of airflows where nodes representing regions of different pressure are interconnected by leakage paths. Individual models differ in details such as the number of nodes they A ' a % b * T i & T o * % cU n A ' L 0.006 ) T % 0.03 C U1.5 Volume III  Activity Factors Chapter 17  Residential Building Characteristics Exposure Factors Handbook Page August 1997 17 13 Table 17 11. Distributions of Residential Air Exchange Rates by Climate Region and Season a Climate Region Season Sample Size Arithmetic Mean Standard Deviation Percentiles 10th 25th 50th 75th 90th Coldest Winter Spring Summer Fall 161 254 5 47 0.36 0.44 0.82 0.25 0.28 0.31 0.69 0.12 0.11 0.18 0.27 0.10 0.18 0.24 0.41 0.15 0.27 0.36 0.57 0.22 0.48 0.53 1.08 0.34 0.71 0.80 2.01 0.42 Colder Winter Spring Summer Fall 428 43 2 23 0.57 0.52 1.31 0.35 0.43 0.91  0.18 0.21 0.13  0.15 0.30 0.21  0.22 0.42 0.24  0.33 0.69 0.39  0.41 1.18 0.83  0.59 Warmer Winter Spring Summer Fall 96 165 34 37 0.47 0.59 0.68 0.51 0.40 0.43 0.50 0.25 0.19 0.18 0.27 0.30 0.26 0.28 0.36 0.30 0.39 0.48 0.51 0.44 0.58 0.82 0.83 0.60 0.78 1.11 1.30 0.82 Warmest Winter Spring Summer Fall 454 589 488 18 0.63 0.77 1.57 0.72 0.52 0.62 1.56 1.43 0.24 0.28 0.33 0.22 0.34 0.42 0.58 0.25 0.48 0.63 1.10 0.42 0.78 0.92 1.98 0.46 1.13 1.42 3.28 0.74 In air changes per hour a Source: Murray and Burmaster, 1995.

( Eqn. 17 1)

where: A = air infiltration rate ( h )  1 T = indoor temperature ( E C) i T = outdoor temperature ( E C) o U = windspeed ( ms )  1 n is an exponent with a value typically between 1 and 2 a, b and c are parameters to be estimated ( Eqn. 17 2)

where: A = average air changes per hour or infiltration rate, h 1 L = generalized house leakiness factor ( 1 < L < 5) C = terrain sheltering factor ( 1 < C < 10) ) T = indoor outdoor temperature difference ( C E ) U = windspeed ( ms )  1 can treat or the specifics of leakage paths ( e. g., individual estimates for making such predictions. components such as cracks around doors or windows versus A reasonable compromise between the theoretical a combination of components such as an entire section of a and empirical approaches has been developed in the model building). Such models are not easily applied by exposure specified by Dietz et al. ( 1986). The model, drawn from assessors, however, because the required inputs ( e. g., correlation analysis of environmental measurements and air inferred leakage areas, crack lengths) for the model are not infiltration data, is formulated as follows: easy to gather. Another approach for estimating air infiltration rates is developing empirical models. Such models generally rely on collection of infiltration measurements in a specific building under a variety of weather conditions. The relationship between the infiltration rate and weather conditions can then be estimated through regression analysis, and is usually stated in the following form:

Relatively good predictive accuracy usually can be conditions where the indoor temperature is 20 E C ( 68 E F), obtained for individual buildings through this approach. the outdoor temperature is 0 E C ( 32 E F) and the windspeed However, exposure assessors often do not have the is 5 ms , the predicted infiltration rate for that house would information resources required to develop parameter be 3 ( 0.006 x 20 + 0.03/ 5 x 51.5), or 0.56 air changes per The value of L is greater as house leakiness increases and the value of C is greater as terrain sheltering ( reflects shielding of nearby wind barrier) increases. Although the above model has not been extensively validated, it has intuitive appeal and it is possible for the user to develop reasonable estimates for L and C with limited guidance. Historical data from various U. S. airports are available for estimation of the temperature and windspeed parameters. As an example application, consider a house that has central values of 3 and 5 for L and C, respectively. Under  1 Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 14 August 1997 Figure 17 4. Idealized Patterns of Particle Deposition Indoors Source: Adapted from Nazaroff and Cass, 1989. hour. This prediction applies under the condition that air exchange. Theoretical considerations specific to indoor exterior doors and windows are closed, and does not include environments have been summarized in comprehensive the contributions, if any, from mechanical systems ( see reviews by Nazaroff and Cass ( 1989) and Nazaroff et al. Section 17.2.3). Occupant behavior, such as opening ( 1993). windows, can, of course, overwhelm the idealized effects of For airborne particles, deposition rates depend on temperature and wind speed. aerosol properties ( size, shape, density) as well as room 17.3.4. Deposition and Filtration Deposition refers to the removal of airborne gravitational settling; the motions of smaller particles are substances to available surfaces that occurs as a result of subject to convection and diffusion. Consequently, larger gravitational settling and diffusion, as well as particles tend to accumulate more rapidly on floors and upelectrophoresis and thermophoresis. Filtration is driven by facing surfaces while smaller particles may accumulate on similar processes, but is confined to material through which surfaces facing in any direction. Figure 17 4 illustrates the air passes. Filtration is usually a matter of design, whereas general trend for particle deposition across the size range of deposition is a matter of fact. general concern for inhalation exposure (< 10 F m). The <IP_ADDRESS>. Deposition The deposition of particulate matter and reactive gas knowledge gaps relating to near surface air motions and phase pollutants to indoor surfaces is often stated in terms other sources of inhomogeneity ( Nazaroff et al., 1993).

of a characteristic deposition velocity ( m h ) allied to the  1 surface to volume ratio ( m m ) of the building or room 2  3 interior, forming a first order loss rate ( h ) similar to that of  1 factors ( thermal gradients, turbulence, surface geometry). The motions of larger particles are dominated by current thought is that theoretical calculations of deposition rates are likely to provide unsatisfactory results due to Wallace ( 1996)  Indoor Particles: A Review  In a major review of indoor particles, Wallace ( 1996) cited overall particle deposition rates for respirable ( PM ), 2.5 Volume III  Activity Factors Chapter 17  Residential Building Characteristics Exposure Factors Handbook Page August 1997 17 15 inhalable ( PM ), and coarse ( difference between PM and 10 10 PM ) size fractions determined from EPA's PTEAM study. Residential structures consist of a number of rooms 2.5 These values, listed in Table 17 12, were derived from that may be connected horizontally, vertically, or both measurements conducted in nearly 200 residences. horizontally and vertically. Before considering residential Table 17 12. Deposition Rates for Indoor Particles Size Fraction Deposition Rate PM 0.39 h 2.5 PM 0.65 h 10 Coarse 1.0 h  1  1  1 Source: Adapted from Wallace, 1996.

Thatcher and Layton ( 1995)  Deposition, Resuspension, and Penetration of Particles Within a Residence  Thatcher and Layton ( 1995) evaluated removal rates for indoor particles in four size ranges ( 1 5, 5 10, 10 25, and > 25 F m) in a study of one house occupied by a family of four. These values are listed in Table 17 13. In a subsequent evaluation of data collected in 100 Dutch residences, Layton and Thatcher ( 1995) estimated settling velocities of 2.7 m h for lead bearing particles captured in  1 total suspended particulate matter ( TSP) samples.

Table 17 13. Particle Deposition During Normal Activities Particle Size Range Particle Removal Rate ( h )  1 1 5 0.5 5 10 1.4 10 25 2.4 > 25 4.1 Source: Adapted from Thatcher and Layton, 1995.

<IP_ADDRESS>. Filtration A variety of air cleaning techniques have been applied to residential settings. Basic principles related to residential scale air cleaning technologies have been summarized in conjunction with reporting early test results ( Offerman et al., 1984). General engineering principles are summarized in ASHRAE ( 1988). In addition to fibrous filters integrated into central heating and air conditioning systems, extended surface filters and High Efficiency Particle Arrest ( HEPA) filters as well as electrostatic systems are available to increase removal efficiency. Freestanding air cleaners ( portable and/ or console) are also being used. Product by product test results reported by Hanley et al. ( 1994); Shaughnessy et al. ( 1994); and Offerman et al. ( 1984) exhibit considerable variability across systems, ranging from ineffectual (< 1% efficiency) to nearly complete removal. 17.3.5. Interzonal Airflows structures as a detailed network of rooms, it is convenient to divide them into one or more zones. At a minimum, each floor is typically defined as a separate zone. For indoor air exposure assessments, further divisions are sometimes made within a floor, depending on ( 1) locations of specific contaminant sources and ( 2) the presumed degree of air communication among areas with and without sources. Defining the airflow balance for a multiple zone exposure scenario rapidly increases the information requirements as rooms or zones are added. As shown in Figure 17 5, a single zone system ( considering the entire building as a single well mixed volume) requires only two airflows to define air exchange. Further, because air exchange is balanced flow ( air does not " pile up" in the building, nor is a vacuum formed), only one number ( the air exchange rate) is needed. With two zones, six airflows are needed to accommodate interzonal airflows plus air exchange; with three zones, twelve airflows are required. In some cases, the complexity can be reduced using judicious ( if not convenient) assumptions. Interzonal airflows connecting nonadjacent rooms can be set to zero, for example, if flow pathways do not exist. Symmetry also can be applied to the system by assuming that each flow pair is balanced.

17.3.6. Water Uses Among indoor water uses, showering, bathing and handwashing of dishes or clothes provide the primary opportunities for dermal exposure. Virtually all indoor water uses will result in some volatilization of chemicals, leading to inhalation exposure. The exposure potential for a given situation will depend on the source of water, the types and extents of water uses, and the extent of volatilization of specific chemicals. According to the results of the 1987 Annual Housing Survey ( U. S. Bureau of the Census, 1992), 84.7 percent of all U. S. housing units receive water from a public system or private company ( as opposed to a well). Across the four major regions defined by the U. S. Census Bureau Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 16 August 1997 Figure 17 5. Air Flows for Multiple zone Systems ( Northeast, South, Midwest, and West), the percentage a 20 month period. The household selection process for varies from 82.5 in the Midwest region to 93.2 in the West this study was not random; it involved volunteers from region ( the Northeast and South regions both are very close water companies and engineering organizations, most of to the national percentage). which were located in large metropolitan areas. Nazaroff et The primary types of water use indoors can be al. ( 1988) also assembled the results of several smaller classified as showering/ bathing, toilet use, clothes washing, surveys, typically involving between 5 and 50 households dishwashing, and faucet use ( e. g., for drinking, cooking, each. general cleaning, or washing hands). Substantial A common feature of the various studies cited above information on water use has been collected in California is that the results were all reported in gallons per capita per households by the Metropolitan Water District of Southern day ( gcd), or in units that could be easily converted to gcd. California ( MWD, 1991) and by the East Bay Municipal Most studies also provided estimates by type of use Utility District ( EBMUD, 1992). An earlier study by the shower/ bath, toilet, laundry, dishwashing, and other ( e. g., U. S. Department of Housing and Urban Development ( U. S. faucets). A summary of the various study results is DHUD, 1984) monitored water use in 200 households over Volume III  Activity Factors Chapter 17  Residential Building Characteristics Exposure Factors Handbook Page August 1997 17 17 provided in Table 17 14. There is generally about a threefold variation across studies for total Table 17 14. In house Water Use Rates ( gcd), by Study and Type of Use Study All Uses or Bath Toilet Laundry Dishwashing Other Total, Shower MWD 93 26 30 20 5 12 1 EBMUD 67 20 28 9 4 6 2 U. S. DHUD 40 15 10 13 2  3 Nazaroff et al., 1988 52 6 17 11 18  Study 1 Study 2  Rural 46 11 18 14 3   Urban 43 10 18 11 4  Study 3 42 9 20 7 4 2 Study 4 45 9 15 11 4 6 Study 5 70 21 32 7 7 3 Study 6 59 20 24 8 4 3 Study 7 40 10 9 11 5 5 Study 8 52 86 20 40 4 6 20 30 8 10

Mean Across Studies 59 17 18 13 6 5 5 Median Across Studies 53 15 18 11 4 5 5 Metropolitan Water District of Southern California, 1991. 1 East Bay Municipal Utility District, 1992. 2 U. S. Department of Housing and Urban Development, 1984. 3 Results of eight separate studies. 4 The average value from each range reported in Study No. 8 was used to calculate the median across studies. The mean and median for the 5 " Total, all Uses" column were obtained by summing across the means and medians for individual types of water use.

in house water use as well as each type of use. Central The following sections provide a summary of the values for total use, were obtained by taking the mean and water use characteristics for the primary types of water uses median across the studies for each type of water use and indoors. To the extent found in the literature, each water then summing these means/ medians across uses. These use is described in terms of the frequency of use; flowrate central values are shown at the bottom of the table. The during the use; quantity of water used during each means and medians were summed across types of uses to occurrence of the water use; and quantity used by an obtain the mean for all uses combined because only a subset average person. Table 17 15 summarizes the studies of of the studies reported values for other uses. U. S. DHUD and the Power Authorities by locations and number of households.

Table 17 15. Summary of Selected HUD and Power Authority Water Use Studies Number of Households Location Reference U. S. DHUD Studies Study 1 37 Los Angeles, CA a, b Study 2 7 Sacramento, CA a, c Study 3 40 Walnut Creek, CA a, c Study 4 7 Washington, DC a Study 5 21 Sacramento, CA a Study 6 19 Los Angeles, CA a Power Authority Studies Study 1 32 Seattle, WA a Study 2 23 Denver, CO a Study 3 15 Aurora, CO a Study 4 10 Fairfax, VA a TOTAL 211 Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 18 August 1997 Sources: U. S. Department of Housing and Urban Development, 1984. a Metropolitan Water District of Southern California, 1991. b East Bay Municipal Utility District, 1992. c Caution should be exercised when using the data collected in these studies and shown here. The participants in these studies are not a representative sample of the general population. The participants consisted of volunteers, mostly from large metropolitan areas. Showering and Bathing Water Use Characteristics  1984, the newer ( post 1984) conserving toilets that are The HUD study ( U. S. DHUD, 1984) monitored 162 designed to use approximately 1.6 gallons per flush were households for shower duration. The individuals were also not tested. subdivided by people who only shower or only bath. The The frequency of use for toilets in households was results are given in Table 17 16. The flowrates of various examined in several studies ( U. S. DHUD, 1984; Ligman, types of shower heads were also evaluated in the study et al., 1974; Siegrist, 1976). The observed mean ( Table 17 17). frequencies in these studies are given in Table 17 19. Toilet Water Use Characteristics  The HUD study ( U. S. DHUD, 1984) reported water volume per flush for various types of toilets and monitored 162 households for shower duration. The results of this study are shown in Table 17 18. Since the HUD study was conducted prior to Tables 17 20 through 17 24 present indoor water use frequencies for dishwashers and clothes washers.

Table 17 16. Showering and Bathing Water Use Characteristics Characteristic Mean Duration Mean Frequency Individuals who Shower only 10.4 minutes/ shower 0.74 showers/ day/ person Individuals who Bath only NA 0.41 baths/ day/ person Individuals who Shower and Bath NA NA Source: Adapted from U. S. DHUD, 1984.

Table 17 17. Showering Characteristics for Various Types of Shower Heads Shower Head Type Mean Flow Rate ( gpm)

Non Conserving (> 3 gpm) 3.4 Low Flow ( # 3 gpm) 1.9 Restrictor ( # 3 gpm) 2.1 Zinplas 1.8 a Turbojector 1.3 a Types of low flow water fixtures. a Source: Adapted from U. S. DHUD, 1984.

Table 17 18. Toilet Water Use Characteristics Average Water Use ( gallons/ flush) Toilet Type Non Conserving 5.5 Bottles 5.0 Bags 4.8 Dams 4.5 Low flush 3.5 Source: Adapted from U. S. DHUD, 1984. Volume III  Activity Factors Chapter 17  Residential Building Characteristics Exposure Factors Handbook Page August 1997 17 19 Table 17 19. Toilet Frequency Use Characteristics Study ( flushes/ person/ day) Flush Frequency U. S. DHUD, 1984 4.2 flushes/ household/ day a Ligman, et al., 1974 Rural, M F 3.6 flushes/ person/ day Ligman, et al., 1974 Rural, Sat Sun 3.8 flushes/ person/ day Ligman, et al., 1974 Urban, M F 3.6 flushes/ person/ day Ligman, et al., 1974 Urban, Sat Sun 3.1 flushes/ person/ day Siegrist, 1976 2.3 flushes/ person/ day Unweighted Mean 3.43 flushes/ person/ day The HUD value may in fact be flushes/ household/ day a Table 17 20. Dishwasher Frequency Use Characteristics Study Use Frequency U. S. DHUD, 1984 0.47 loads/ person/ day Ligman, et al., 1974 Rural 1.3 loads/ day Siegrist, 1976 0.39 loads/ person/ day Unweighted Mean 0.92 loads/ day Table 17 21. Dishwasher Water Use Characteristics Brand ( gallons/ regular ( minutes) Average Water Use Cycle Duration cycle) 140 E F 120 E F Maytag 11.5 75  Frigidaire 12 75 75 General Electric 10.5 80 95 Sears 10 75 95 Whirlpool 9.5 60 110 White/ Westinghouse 12 75 75 Waste King 11.5 65 85 Kitchen Aid 9.5 80 80 Magic Chef 11.5 70

Unweighted Mean 10.9 72.8 87.9 Source: Adapted from Consumer Reports, 1987.

Table 17 22. Clothes Washer Frequency Use Characteristics Study Use Frequency U. S. DHUD, 1984 0.3 loads/ person/ day Ligman, et al., 1974 Rural 0.34 loads/ person/ day Ligman, et al., 1974 Urban 0.27 loads/ person/ day Siegrist, 1976 0.31 loads/ day Table 17 23. Clothes Washer Water Use Characteristics Brand ( gallons/ regular cycle) ( minutes) Average Water Use Cycle Duration Maytag 41 32 Frigidaire 48 40 General Electric 51 48 Hotpoint 51 48 Sears 49 40 Whirlpool 53 44 White/ Westinghouse 54 47 Kelvinator 46 52 Norge 55 49 Source: Adapted from Consumer Reports, 1982.

Table 17 24. Range of Water Uses for Clothes Washers Type of Clothes Washer Range of Water Use Conventional 27 59 gallons/ load Low Water 16 19 gallons/ load All Clothes Washers 16 59 gallons/ load Source: Adapted from Consumer Reports, 1982.

17.3.7. House Dust and Soil House dust is a complex mixture of biologicallyderived material ( animal dander, fungal spores, etc.), particulate matter deposited from the indoor aerosol, and soil particles brought in by foot traffic. House dust may Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 20 August 1997 contain VOCs ( see, for example, Wolkoff and Wilkins, 1994; Hirvonen et al., 1995), pesticides from imported soil particles as well as from direct applications indoors ( see, for example, Roberts et al., 1991), and trace metals derived from outdoor sources ( see, for example, Layton and Thatcher, 1995). The indoor abundance of house dust depends on the interplay of deposition from the airborne state, resuspension due to various activities, direct accumulation, and infiltration. In the absence of indoor sources, indoor concentrations of particulate matter are significantly lower than outdoor levels. For some time, this observation supported the idea that a significant fraction of the outdoor aerosol is filtered out by the building envelope. More recent data, however, have shown that deposition ( incompletely addressed in earlier studies) accounts for the indoor outdoor contrast, and outdoor particles smaller than 10 F m aerodynamic diameter penetrate the building Particle Deposition Particle Resuspension envelope as completely as nonreactive gases ( Wallace, 1996). Roberts et al. ( 1991)  Development and Field Testing of a High Volume Sampler for Pesticides and Toxics in Dust  Dust loadings, reported by Roberts et al. ( 1991) were also measured in conjunction with the Non Occupational Pesticide Exposure Study ( NOPES). In this study house dust was sampled from a representative grid using a specially constructed high volume surface sampler ( HVS2). The surface sampler collection efficiency was verified in conformance with ASTM F608 ( ASTM, 1989). The data summarized in Table 17 25 were collected from carpeted areas in volunteer households in Florida encountered during the course of NOPES. Seven of the nine sites were single family detached homes, and two were mobile homes. The authors noted that the two houses exhibiting the highest dust loadings were only those homes where a vacuum cleaner was not used for housekeeping.

Table 17 25. Total Dust Loading for Carpeted Areas Household Total Dust Load Fine Dust (< 150 F m) ( g m ) Load ( g m )  2  2 1 10.8 6.6 2 4.2 3.0 3 0.3 0.1 4 2.2; 0.8 1.2; 0.3 5 1.4; 4.3 1.0; 1.1 6 0.8 0.3 7 6.6 4.7 8 33.7 23.3 9 812.7 168.9 Source: Adapted from Roberts et al., 1991.

Thatcher and Layton ( 1995)  Deposition, Resuspension and Penetration of Particles Within a Residence  Relatively few studies have been conducted at the level of detail needed to clarify the dynamics of indoor aerosols. One intensive study of a California residence ( Thatcher and Layton, 1995), however, provides instructive results. Using a model based analysis for data collected under controlled circumstances, the investigators verified penetration of the outdoor aerosol and estimated rates for particle deposition and resuspension ( Table 17 26). The investigators stressed that normal household activities are a significant source of airborne particles larger than 5 F m. During the study, they observed that just walking into and out of a room could momentarily double the concentration. The airborne abundance of submicrometer particles, on the other hand, was unaffected by either cleaning or walking.

Table 17 26. Particle Deposition and Resuspension During Normal Activities Particle Size Range Rate Rate ( F m) ( h ) ( h )  1  1 0.3 0.5 ( not measured) 9.9 x 10 0.6 1 ( not measured) 4.4 x 10 1 5 0.5 1.8 x 10 5 10 1.4 8.3 x 10 10 25 2.4 3.8 x 10 > 25 4.1 3.4 x 10  7  7  5  5  4  5 Source: Adapted from Thatcher and Layton, 1995.

Mass loading of floor surfaces ( Table 17 27) was measured in the study of Thatcher and Layton ( 1995) by thoroughly cleaning the house and sampling accumulated dust, after one week of normal habitation. Methodology, validated under ASTM F608 ( ASTM, 1989), showed fine dust recovery efficiencies of 50 percent with new carpet and 72 percent for linoleum. Tracked areas showed consistently higher accumulations than untracked areas, confirming the importance of tracked in material. Differences between tracked areas upstairs and downstairs show that tracked in material is not readily transported upstairs. The consistency of untracked carpeted areas throughout the house, suggests that, in the absence of tracking, particle transport processes are similar on both floors. Volume III  Activity Factors Chapter 17  Residential Building Characteristics Exposure Factors Handbook Page August 1997 17 21 Table 17 27. Dust Mass Loading After One Week Without Vacuum Cleaning Location in Test House Dust Loading ( g m )  2 Tracked area of downstairs carpet 2.20 Untracked area of downstairs carpet 0.58 Tracked area of linoleum 0.08 Untracked area of linoleum 0.06 Tracked area of upstairs carpet 1.08 Untracked area of upstairs carpet 0.60 Front doormat 43.34 Source: Adapted from Thatcher and Layton, 1995.

17.4. SOURCES Product and chemical specific mechanisms for indoor sources can be described using simple emission factors to represent instantaneous releases, as well as constant releases over defined time periods; more complex formulations may be required for time varying sources. Guidance documents for characterizing indoor sources within the context of the exposure assessment process are limited ( see, for example, Jennings et al., 1987; Wolkoff, 1995). Fairly extensive guidance exists in the technical literature, however, provided that the exposure assessor has the means to define ( or estimate) key mechanisms and chemical specific parameters. Basic concepts are summarized below for the broad source categories that relate to airborne contaminants, waterborne contaminants, and for soil/ house dust indoor sources.

17.4.1. Source Descriptions for Airborne Contaminants Table 17 28 summarizes simplified indoor source descriptions for airborne chemicals for direct discharge sources ( e. g., combustion, pressurized propellant products), as well as emanation sources ( e. g., evaporation from " wet" films, diffusion from porous media), and transport related sources ( e. g., infiltration of outdoor air contaminants, soil gas entry). Direct discharge sources can be approximated using simple formulas that relate pollutant mass released to characteristic process rates. Combustion sources, for example, may be stated in terms of an emission factor, fuel content ( or heating value), and fuel consumption ( or carrier delivery) rate. Emission factors for combustion products of general concern ( e. g., CO, NO ) have been measured for a x number of combustion appliances using room sized chambers ( see, for example, Relwani et al., 1986). Other direct discharge sources would include volatiles released from water use and from pressurized consumer products. Resuspension of house dust ( see Section 17.3.7) would take on a similar form by combining an activity specific rate constant with an applicable dust mass.

Table 17 28. Simplified Source Descriptions for Airborne Contaminants Description Components Dimensions Direct Discharge Combustion E H M g h Volume Q C _ , g h Discharge Q = volume delivery rate m h Mass M w , g h Discharge M = mass delivery rate g h f f f E = emission factor g J f H = fuel content J mol f M = fuel consumption rate mol h f p p p C = concentration in carrier g m p , = transfer efficiency g g p e p w = weight fraction g g e , = transfer efficiency g g  1  1  1  1  1 3  1  3  1  1  1  1  1 Diffusion Limited ( D * ) ( C  C ) A g h Exponential f s i i  1 D = diffusivity m h f * = boundary layer thickness m  1 C = vapor pressure of surface g m s C = room concentration g m i A = area m i A E e g h i o  k t A = area m i E = initial unit emission rate g h m o k = emission decay factor h t = time h  1 2  1  3  3 2  1 2  1  2  1 Transport Infiltration Q C g h Interzonal Q = air flow from zone j m h Soil Gas C = air concentration in zone j g m ji j ji j  1 3  1  3 Diffusion limited sources ( e. g., carpet backing, furniture, flooring, dried paint) represent probably the greatest challenge in source characterization for indoor air quality. Vapor phase organics dominate this group, offering great complexity because ( 1) there is a fairly long list of chemicals that could be of concern, ( 2) ubiquitous consumer products, building materials, coatings, and furnishings contain varying amounts of different chemicals, ( 3) source dynamics may include nonlinear mechanisms, and ( 4) for many of the chemicals, emitting as well as nonemitting materials evident in realistic settings may promote reversible and irreversible sink effects. Very detailed descriptions for diffusion limited sources can be constructed to link specific properties of the chemical, the source material, and the receiving environment to calculate expected behavior ( see, for example, Schwope et al., 1992; Cussler, 1984). Validation to actual circumstances, however, suffers practical shortfalls because many parameters simply cannot be measured directly. The exponential formulation listed in Table 17 28 was derived based on a series of papers generated during M ' m 4 o E o e & k s t dt ' E o k s E c E o ' e & kstc or M c M ' 1 & e & kst Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 22 August 1997 ( Eqn. 17 4) the development of chamber testing methodology by EPA ( Dunn, 1987; Dunn and Tichenor, 1988; Dunn and Chen, 1993). This framework represents an empirical alternative Residential water supplies may convey chemicals to that works best when the results of chamber tests are which occupants can be exposed through ingestion, dermal available. Estimates for the initial emission rate ( E ) and contact, or inhalation. These chemicals may appear in the o decay factor ( k ) can be developed for hypothetical sources form of contaminants ( e. g., trichloroethylene) as well as s from information on pollutant mass available for release naturally occurring byproducts of water system history ( e. g., ( M) and supporting assumptions. chloroform, radon). Among indoor water uses, showering, Assuming that a critical time period ( t ) coincides bathing and handwashing of dishes or clothes provide the c with reduction of the emission rate to a critical level ( E ) or primary opportunities for dermal exposure. The escape of c with the release of a critical fraction of the total mass ( M ), volatile chemicals to the gas phase associates water use c the decay factor can be estimated by solving either of these with inhalation exposure. The exposure potential for a given relationships: situation will depend on the source of water, the types and ( Eqn. 17 3)

The critical time period can be derived from productspecific considerations ( e. g., equating drying time for a paint to 90 percent emissions reduction). Given such an estimate for k , the initial emission rate can be estimated by s integrating the emission formula to infinite time under the assumption that all chemical mass is released: The basis for the exponential source algorithm has also been extended to the description of more complex diffusion limited sources. With these sources, diffusive or evaporative transport at the interface may be much more rapid than diffusive transport from within the source material, so that the abundance at the source/ air interface becomes depleted, limiting the transfer rate to the air. Such effects can prevail with skin formation in " wet" sources like stains and paints ( see, for example, Chang and Guo, 1992). Similar emission profiles have been observed with the emanation of formaldehyde from particleboard with " rapid" decline as formaldehyde evaporates from surface sites of the particleboard over the first few weeks. It is then followed by a much slower decline over ensuing years as formaldehyde diffuses from within the matrix to reach the surface ( see, for example, Zinn et al., 1990). Transport based sources bring contaminated air from other areas into the airspace of concern. Examples include infiltration of outdoor contaminants, and soil gas entry. Soil gas entry is a particularly complex phenomenon, and is frequently treated as a separate modeling issue ( Little et al., 1992; Sextro, 1994). Room to room migration of indoor contaminants would also fall under this category, but this concept is best considered using the multiple zone model. 17.4.2. Source Descriptions for Waterborne Contaminants extents of water uses, and the extent of volatilization of specific chemicals. Primary types of residential water use ( summarized in Section 17.3) include showering/ bathing, toilet use, clothes washing, dishwashing, and faucet use ( e. g., for drinking, cooking, general cleaning, or washing hands). Upper bounding estimates of chemical release rates from water use can be formulated as simple emission factors by combining the concentration in the feed water ( g m ) with the flow rate for the water use ( m h ), and  3 3  1 assuming that the chemical escapes to the gas phase. For some chemicals, however, not all of the chemical escapes in realistic situations due to diffusion limited transport and solubility factors. For inhalation exposure estimates, this may not pose a problem because the bounding estimate would overestimate emissions by no more than approximately a factor of two. For multiple exposure pathways, the chemical mass remaining in the water may be of importance. Refined estimates of volatile emissions are usually considered under two resistance theory to accommodate mass transport aspects of the water air system ( see, for example, Little, 1992; Andelman, 1990; McKone, 1987). Release rates are formulated as: S ' K m F W C w & C a H 1 K D Li D Lr 1/ 2 ' 1 K Lr ' 1 K Gr & 1 H D Gr D Gi 2/ 3 D Li D Lr 1/ 2 S d ' M d R d A f Volume III  Activity Factors Chapter 17  Residential Building Characteristics Exposure Factors Handbook Page August 1997 17 23 ( Eqn. 17 5)

where: S = chemical release rate ( g h )  1 K = dimensionless mass transfer coefficient m F = water flow rate ( m h ) w 3  1 C = concentration in feed water ( g m ) w  3 C = concentration in air ( g m ) a  3 H = dimensionless Henry's Law constant ( Eqn. 17 6)

where: D = liquid diffusivity ( m s ) L 2  1 D = gas diffusivity ( m s ) G 2  1 K = liquid phase mass transfer coefficient L K = gas phase mass transfer coefficient G H = dimensionless Henry's Law constant Because the emission rate is dependent on the air indicates that, for an instantaneous release from a point concentration, recursive techniques are required. The mass source in a room, fairly complete mixing is achieved within transfer coefficient is a function of water use characteristics 10 minutes when convective flow is induced by solar ( e. g., water droplet size spectrum, fall distance, water film) radiation. However, up to 100 minutes may be required for and chemical properties ( diffusion in gas and liquid phases). complete mixing under quiescent ( nearly isothermal) Estimates of practical value are based on empirical tests to conditions. While these experiments were conducted at incorporate system characteristics into a single parameter extremely low air exchange rates (< 0.1 ACH), based on the ( see, for example, Giardino et al., 1990). Once results, attention is focused on mixing within a room. characteristics of one chemical water use system are known The situation changes if a human invokes a point ( reference chemical, subscript r), the mass transfer source for a longer period and remains in the immediate coefficient for another chemical ( index chemical, subscript vicinity of that source. Personal exposure in the near i) delivered by the same system can be estimated using vicinity of a source can be much higher than the well mixed formulations identified in the review by Little ( 1992): assumption would suggest. A series of experiments 17.4.3. Soil and House Dust Sources The rate process descriptions compiled for soil and exceeded those several meters away by a factor that varied house dust in Section 17.3 provide inputs for estimating inversely with the ventilation intensity in the room. At indoor emission rates ( S , g h ) in terms of dust mass typical room ventilation rates, the ratio of source proximate d  1 loading ( M , g m ) combined with resuspension rates ( R , to slightly removed concentration was on the order of 2: 1. d d  2 h ) and floor area ( A , m ):  1 2 f ( Eqn. 17 7) Because house dust is a complex mixture, transfer of particle bound constituents to the gas phase may be of concern for some exposure assessments. For emission estimates, one would then need to consider particle mass residing in each reservoir ( dust deposit, airborne).

17.5. ADVANCED CONCEPTS 17.5.1. Uniform Mixing Assumption Many exposure measurements are predicated on the assumption of uniform mixing within a room or zone of a house. Mage and Ott ( 1994) offers an extensive review of the history of use and misuse of the concept. Experimental work by Baughman et al. ( 1994) and Drescher et al. ( 1995)

conducted by GEOMET ( 1989) for the U. S. EPA involved controlled point source releases of carbon monoxide tracer ( CO), each for 30 minutes. " Breathing zone" measurements located within 0.4 m of the release point were ten times higher than for other locations in the room during early stages of mixing and transport. Similar investigations conducted by Furtaw et al. ( 1995) involved a series of experiments in a controlledenvironment room sized chamber. Furtaw et al. ( 1995) studied spatial concentration gradients around a continuous point source simulated by sulfur hexafluoride ( SF ) tracer 6 with a human moving about the room. Average breathingzone concentrations when the subject was near the source 17.5.2. Reversible Sinks For some chemicals, the actions of reversible sinks are of concern. For an initially " clean" condition in the sink material, sorption effects can greatly deplete indoor concentrations. However, once enough of the chemical has Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 24 August 1997 been adsorbed, the diffusion gradient will reverse, allowing ( i. e., holding constant the pollutant generation rate and the chemical to escape. For persistent indoor sources, such effect of indoor sinks), lower values for either the indoor effects can serve to reduce indoor levels initially but once volume or the air exchange rate will result in higher indoorthe system equilibrates, the net effect on the average air concentrations. Thus, values near the lower end of the concentration of the reversible sink is negligible. Over distribution ( e. g., 10th percentile) for either parameter are suitably short time frames, this can also affect integrated appropriate in developing conservative estimates of exposure. For indoor sources whose emission profile exposure. declines with time ( or ends abruptly), reversible sinks can For the volume of a residence, both key studies ( U. S. serve to extend the emissions period as the chemical DOE ( 1995) and Versar ( 1990) PFT database) have the desorbs long after direct emissions are finished. Reversible same mean value  369 m ( see Table 17 1). This mean sink effects have been observed for a number of chemicals value is recommended as a central estimate residential in the presence of carpeting, wall coverings, and other volume. Intuitively, the 10th percentile of the distribution materials commonly found in residential environments. from either study  147 m for RECS survey or 167 m for Interactive sinks ( and models of the processes) are the PFT database  is too conservative a value, as both of a special importance; while sink effects can greatly these values are lower than the mean volume for multifamily reduce indoor air concentrations, re emission at lower rates dwelling units ( see Table 17 2). Instead, the 25th over longer time periods could greatly extend the exposure percentile  209 m for RECS survey or 225 m for PFT period of concern. For completely reversible sinks, the database, averaging 217 m across the two key studies  is extended time could bring the cumulative exposure to levels recommended ( Table 17 1). approaching the sink free case. Recent publications ( Axley For the residential air exchange rate, the median et al., 1993; Tichenor et al., 1991) show that first principles value of 0.45 air changes per hour ( ACH) from the PFT provide useful guidance in postulating models and setting database ( see Table 17 9) is recommended as a typical assumptions for reversible/ irreversible sink models. value ( Koontz and Rector, 1995). This median value is Sorption/ desorption can be described in terms of Langmuir very close to the geometric mean of the measurements in the ( monolayer) as well as Brunauer Emmet Teller ( BET, PFT database analyzed by Koontz and Rector ( 1995). The multilayer) adsorption. arithmetic mean is not preferred because it is influenced 17.6 RECOMMENDATIONS Table 17 29 presents a summary of volume of for the PFT database  0.18 ACH  is recommended residence surveys and Table 17 30 presents a summary of ( Table 17 10). air exchange rates surveys. Table 17 31 presents the There are some uncertainties in, or limitations on, the recommended values. Tables 17 32 and 17 33 provide the distribution for volumes and air exchange rates that are confidence in recommendations for house volume and air presented in this chapter. For example, the RECS used to exchange rates, respectively. Key studies or analyses infer volume distributions used a nationwide probability described in this chapter were used in selecting sample, but measured floor area rather than total volume. recommended values for residential volume. The air By comparison, field studies contributing to the PFT data exchange rate data presented in the studies are extremely base measured house volumes directly, but the aggregate limited. Therefore, studies have not been classified as key sampling frame for these studies is not statistically or relevant studies. However, recommendations have been representative of the national housing stock. provided for air exchange rates and the confidence Although the PFT methodology is relatively simple recommendation has been assigned a " low" overall rating. to implement, it is subject to errors and uncertainties. The Therefore, these values should be used with caution. Both general performance of the sampling and analytical aspects central and conservative values are provided. These two of the system are quite good. That is, laboratory analysis parameters  volume and air exchange rate  can be used will measure the correct time weighted average tracer by exposure assessors in modeling indoor air concentration to within a few percent ( Dietz et al., 1986). concentrations as one of the inputs to exposure estimation. Nonetheless, significant errors can arise when conditions in Other inputs to the modeling effort include rates of indoor the measurement scene greatly deviate from idealizations pollutant generation and losses to ( and, in some cases, re calling for constant, well mixed conditions. Principal emissions from) indoor sinks. Other things being equal concerns focus on the effects of naturally varying air 3 3 3 3 3 3 fairly heavily by extreme values at the upper tail of the distribution. For a conservative value, the 10th percentile Volume III  Activity Factors Chapter 17  Residential Building Characteristics Exposure Factors Handbook Page August 1997 17 25 exchange and the effects of temperature in the permeation ASHRAE. ( 1993) ASHRAE Handbook: Fundamentals. source. American Society of Heating, Refrigerating, and Air Sherman ( 1989) carried out an error analysis of the Conditioning Engineers. Atlanta, GA. PFT methodology using mathematical models combined ASTM. ( 1989) Standard laboratory test method for with typical weather data to calculate how an ideal sampling evaluation of carpet embedded dirt removal system would perform in a time varying environment. He effectiveness of household vacuum cleaners. found that for simple single story ( ranch) and two story plus Designation: F 608 89. American Society for Testing basement ( colonial) layouts, seasonal measurements would and Materials, Philadelphia, PA. underpredict seasonal average air exchange by 20 to 30 ASTM. ( 1990) Test method for determining percent. Underprediction can occur because the PFT formaldehyde levels from wood products under methodology is measuring the effective ventilation ( the defined conditions using a large chamber. Standard E product of ventilation efficiency and air exchange), and the 1333 90. American Society for Testing and temporal efficiency will generally be less than unity over Materials: Philadelphia. averaging periods of this length. Sherman ( 1989) also Axley, J. W. ( 1988) Progress toward a general analytical noted, however, that while the bias could have an impact on method for predicting indoor air pollution in determining air exchange ( absent knowledge of ventilation buildings: indoor air quality modeling phase III efficiency) for calculating energy loads, the effective air report. NBSIR 88 3814. National Bureau of exchange term is directly relevant to determining average Standards, Gaithersberg, MD. indoor concentrations resulting from constant sources. Axley, J. W. ( 1989) Multi zone dispersal analysis by Leaderer et al. ( 1985) conducted a series of element assembly. Building and Environment. experiments in a room sized environmental chamber to 24( 2): 113 130. evaluate the practical impacts of varying air exchange and Axley, J. W.; Lorenzetti, D. ( 1993) Sorption transport the temperature response of the permeation sources. The models for indoor air quality analysis. In: Nagda, N. L. negative bias anticipated in the measured ( effective) versus Ed., Modeling of Indoor Air Quality and Exposure. actual air exchange as conditions varied diurnally between ASTM STP 1205. Philadelphia, PA: American 0.4 and 1.5. ACH was evident but minor ( 3 to 6 percent), Society for Testing and Materials, pp. 105 127. most likely due to the mechanical mixing in the chamber Baughman, A. V.; Gadgil, A. J.; Nazaroff, W. W. ( 1994) and the relatively short integration time ( 72 h). Similarly, Mixing of a point source pollutant by natural cycling temperature diurnally over an 8 E C range ( holding convection flow within a room. Indoor Air. 4: 114 air exchange steady at 0.6 ACH) would cause 122. concentrations changes of about 20 percent as emissions Chang, J. C. S.; Guo, Z. ( 1992) Characterization of organic fluctuated. The investigators found, however, that using a emissions from a wood finishing product  wood time weighted average temperature to define the emission stain. Indoor Air. 2( 3): 146 53. rate reduced the temperature bias to essentially zero. Consumer Reports. ( 1982) Washing machines. Consumer 17.7. REFERENCES FOR CHAPTER 17 Andelman, J. B. ( 1990) Total exposure to volatile organic Cussler, E. L. ( 1984) Diffusion. Cambridge University compounds in potable water. In: Ram, N, et al., eds. Press, New York, NY. Significance and Treatment of Volatile Organic Dietz, R. N.; Goodrich, R. W.; Cote, E. A.; Wieser, R. F. Compounds in Water Supplies. pp 485 504, Lewis ( 1986) Detailed description and performance of a Publishers, Chelsea, MI. passive perfluorocarbon tracer system for building Andersson, B., K. Andersson, J. Sundell, and P. A. ventilation and air exchange measurements. H. R. Zingmark. ( 1993) Mass transfer of contaminants in Trechsel and P. L. Lagus, Eds. In: Measured Air rotary enthalpy heat exchangers. Indoor Air. 3: 143 Leakage of Buildings. ASTM STP 904. 148. Philadelphia, PA: American Society for Testing and ASHRAE. ( 1988) ASHRAE Handbook: Equipment. Materials, pp. 203 264. American Society of Heating, Refrigerating, and Air Conditioning Engineers. Atlanta, GA. Reports Magazine. 47( 10). Consumer Reports. ( 1987) Dishwashers. Consumer Reports Magazine. 52( 6). Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 26 August 1997 Drescher, A. C.; Lobascio, C.; Gadgil, A. J.; Nazaroff, Grot, R. A. ( 1991) User manual NBS/ AVIS W. W. ( 1995) Mixing of a Point Source Indoor CONTAM88. NISTIR 4585, Gaithersberg, MD: Pollutant by Forced Convection. Indoor Air. 5: 204 214. National Institute of Standards and Technology. Dunn, J. E. ( 1987) Models and statistical methods for Grot, R. A.; Clark, R. E. ( 1981) Air leakage characteristics gaseous emission testing of finite sources in well and weatherization techniques for low income mixed chambers. Atmospheric Environment. housing. In: Proceedings of the American Society of ( 21) 2: 425 430. Heating, Refrigerating and Air Conditioning Dunn, J. E.; Chen, T. ( 1993) Critical evaluation of the Engineers Conference. Thermal Performance of diffusion hypothesis in the theory of porous media Exterior Envelopes of Buildings. ASHRAE SP28, volatile organic compounds ( VOC) sources and sinks. Atlanta, GA, pp. 178 194. In: Nagda, N. L. Ed., Modeling of Indoor Air Quality Hanley, J. T.; Ensor, D. S.; Smith, D. D.; Sparks, L. E. and Exposure. ASTM STP 1205. Philadelphia, PA.: ( 1994) Fractional aerosol filtration efficiency of in American Society for Testing and Materials, pp. 64 duct ventilation air cleaners. Indoor Air. 4( 3): 179 80. 188. Dunn, J. E.; Tichenor, B. A. ( 1988) Compensating for sink Hirvonen, A.; Pasanen, P.; Tarhanen, J.; Ruuskanen, J. effects in emissions test chambers by mathematical ( 1995) Thermal desorption of organic compounds modeling. Atmospheric Environ., 22( 5) 885 894. associated with settled household dust. Indoor Air. EBMUD. ( 1992) Urban water management plan. East 5: 255 264. Bay Municipal Utility Water District, in written Jennings, P. D.; Carpenter, C. E.; Krishnan, M. S. ( 1985) communication to J. B. Andelman, July 1992. Methods for assessing exposure to chemical Furtaw, E. J.; Pandian, M. D.; Nelson, D. R; Behar, J. V. substances volume 12: methods for estimating the ( 1995) Modeling indoor air concentrations near concentration of chemical substances in indoor air. emission sources in perfectly mixed rooms. EPA 560/ 5 85 016, U. S. Environmental Protection Engineering Solutions to Indoor Air Quality Agency, Office of Pesticides and Toxic Substances, Problems. Presented at Sixth Conference of the Washington, DC. International Society for Environmental Epidemiology Jennings, P. D.; Hammerstrom, K. A.; Adkins, L. C.; and Fourth Conference of the International Society for Chambers, T.; Dixon, D. A. 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( 1990) Real time measurements of distributions for residential air Exchange rates, EPA trichloroethylene in domestic bathrooms using Contract No. 68 D9 0166, Work Assignment No. 3 contaminated water. Proceedings of the 5th 19, U. S. Environmental Protection Agency, Office of International Conference on Indoor Air Quality and Pollution Prevention and Toxics, Washington, DC. Climate, Toronto, 2: 707 712. Koontz, M. D.; Rector, H. E.; Fortmann, R. C.; Nagda, N. L. Grimsrud, D. T.; Sherman, M. H.; Sondereggen, R. C. ( 1988) Preliminary experiments in a research house to ( 1983) Calculating infiltration: implications for a investigate contaminant migration in indoor air. EPA construction quality standard. In: Proceedings of the 560/ 5 88 004. U. S. Environmental Protection American Society of Heating, Refrigerating and Air Agency, Office of Pesticides and Toxic Substances, Conditioning Engineers Conference. Thermal Washington, DC. Performance of Exterior Envelopes of Buildings II. Layton, D. W.; Thatcher, T. L. ( 1995) Movement of ASHRAE SP38, Atlanta, GA, pp. 422 449. outdoor particles to the indoor environment: An analysis of the Arnhem Lead Study. Paper No. 95 Volume III  Activity Factors Chapter 17  Residential Building Characteristics Exposure Factors Handbook Page August 1997 17 27 MP4.02. Annual Meeting of the Air and Waste Nazaroff, W. W.; Cass, G. R. ( 1986) Mathematical Management Association, San Antonio, TX. modeling of chemically reactive pollutants in indoor Leaderer, B. P.; Schaap, L.; Dietz, R. N. ( 1985) air. Environ. Sci. and Technol. 20: 924 934. Evaluation of perfluorocarbon tracer technique for Nazaroff, W. W.; Cass, G. R. ( 1989) Mass transport determining infiltration rates in residences. Environ. aspects of pollutant removal at indoor surfaces. Sci. and Technol. 19( 12): 1225 1232. Environment International, 15: 567 584. Liddament, M.; Allen, C. ( 1983) Validation and Nazaroff, W. W.; Doyle, S. M.; Nero, A. V.; Sextro, R. G. comparison of mathematical models of air infiltration. ( 1988). Radon entry via potable water. In: Nazaroff, Technical Note AIC 11. Air Infiltration Centre, Great W. W. and Nero, A. V., Eds., Radon and Its Decay Britain. Products in Indoor Air. John Wiley and Sons, NY. Ligman, K.; Hutzler, N.; Boyle, W. C. ( 1974) Household pp. 131 157. wastewater characterization. J. Environ. Eng. Nazaroff, W. W.; Gadgil, A. J.; Weschler, C. J. ( 1993) 100: 201 213. Critique of the use of deposition velocity in modeling Little, J. C. ( 1992) Applying the two resistance theory to indoor air quality. In: Nagda, N. L. Ed., Modeling of contaminant volatilization in showers. Environ. Sci. Indoor Air Quality and Exposure, ASTM STP 1205, and Technol. 26( 7): 1341 1349. American Society for Testing and Materials. Little, J. C.; Daisey, J. M.; Nazaroff, W. W. ( 1992) Philadelphia, PA, pp. 148 165. Transport of subsurface contaminants into buildings  Offerman, F. J.; Sextro, R. G.; Fisk, W.; Nazaroff, W. W.; an exposure Pathway for Volatile Organics. Environ. Nero, A. V.; Revzan, K. L.; Yater, J. ( 1984) Control of Sci. and Technol. ( 26) 11: 2058 2066. respirable particles and radon progeny with portable Lucas, R. M.; Grillo, R. B.; Perez Michael, A.; Kemp, S. air cleaners. Report No. LBL 16659, Lawrence ( 1992) National residential radon survey statistical Berkley Laboratory, Berkley, CA. analysis  volume 2: summary of the questionnaire Pandian, M. H.; Behar, J. V.; Thomas, J. ( 1993) Use of a data. RTI/ 5158/ 49 2F. Research Triangle Institute, relational database to predict human population Research Triangle Park, NC. exposures for different time periods. Proceedings of Mage, D. T.; Ott, W. R. ( 1994) The correction for Indoor Air ` 93, Helsinki 3: 283 288. nonuniform mixing in indoor environments. ASTM Persily, A. K.; Linteris, G. T. ( 1984) A comparison of Symposium on Methods for Characterizing Indoor measured and predicted infiltration rates. ASHRAE Sources and Sinks, Washington, DC. Transactions 89( 2): 183 199. McKone, T. E. ( 1987) Human exposure to volatile Relwani, S. M.; Moschandreas, D. J.; Billick, I. H. ( 1986) organic compounds in household tap water: The Effects of operational factors on pollutant emission inhalation pathway. Environ. Sci. and Technol. rates from residential gas appliances. J. Air Poll. 21( 12): 1194 1201. Control Assoc. 36: 1233 1237. McKone, T. E. ( 1989) Household exposure models. Roberts, J. W.; Budd, W. T.; Ruby, M. G.; Bond, A. E.; Toxicol. Letters. 49: 321 339. Lewis, R. G.; Wiener, R. W.; Camann, D. E. ( 1991) MWD. ( 1991) Urban water use characteristics in the Development and field testing of a high volume metropolitan water district of southern california. sampler for pesticides and toxics in dust. J. Exposure Draft Report. Metropolitan Water District of Anal. and Environ. Epidemiol. ( 1) 2: 143 155 Southern California, August 1991. Ryan, P. B. ( 1991) An overview of human exposure Murray, D. M. ( 1996) residential house and zone volumes modeling. J. Exposure Anal. and Environ. Epidemiol. in the United States: Empirical and Estimated ( 1) 4: 453 474. Parametric Distributions. Submitted to Risk Analysis Sandberg, M. ( 1984) The Multi chamber theory in 1996. reconsidered from the viewpoint of air quality studies. Murray, D. M.; Burmaster, D. E. ( 1995) Residential air Building and Environment ( 19) 4: 221 233. exchange rates in the United States: Empirical and Sextro, R. G. ( 1994) Radon and the natural environment. Estimated Parametric Distribution by Season and IN: Nagda, N. L. Ed., Radon  Prevalence, Climatic Region. Submitted to Risk Analysis in 1995. Measurements, Health Risks and Control, ASTM MNL 15, American Society for Testing and Materials, Philadelphia, PA, pp. 9 32. Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 28 August 1997 Shaughnessy, R. J.; Levetin, E.; Blocker, J.; Sublette, K. L. Housing and Urban Development, Office of Policy ( 1994) Effectiveness of portable air cleaners: sensory Development and Research. testing results. Indoor Air 4( 3): 179 188. U. S. DOE. ( 1995) Housing characteristics 1993, Sherman, M. H. ( 1989) Analysis of errors associated with Residential Energy Consumption Survey ( RECS) passive ventilation measurement techniques. Building Report No. DOE/ EIA 0314 ( 93), Washington, DC: and Environment 24( 2): 131 139. U. S. Department of Energy, Energy Information Sherman, M.; Dickerhoff, D. ( 1996) Air tightness of Administration. U. S. dwellings. In: The Role of Ventilation 15th AIVC Conference Proceedings. Buxton, Great Britain, September 27 30, 1994. Siegrist, R. ( 1976) Characteristics of rural household wastewater. J. Environ. Eng. 1: 533 548. Sinden, F. W. ( 1978) Multi chamber theory of infiltration. Building and Environment. 13: 21 28. Sparks, L. E. ( 1988) Indoor air quality model version 1.0. Report No. EPA 600/ 8 88 097a.. Research Triangle Park, NC. U. S. Environmental Protection Agency. Sparks, L. E. ( 1991) Exposure  Version 2., U. S. Environmental Protection Agency, Office of Research and Development, Research Triangle Park, NC. Swope, A. D.; Goydan, R.; Reid, R. C. ( 1992) Methods for assessing exposure to chemical substances Volume 11: Methodology for Estimating the Migration of Additives and Impurities from Polymeric Substances. EPA 560/ 5 85 015, U. S. Environmental Protection Agency, Office of Pollution Prevention, Pesticides, and Toxic Substances, Washington, DC. Thatcher, T. L.; Layton, D. W. ( 1995) Deposition, resuspension, and penetration of particles within a residence. Atmos. Environ. 29( 13): 1487 1497. Thompson, W. ( 1995) U. S. Department of Energy ( U. S. DOE) and Energy Information Administration. Personal communication on distribution of heated floor space area from the 1993 RECS. Tichenor, B. 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Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 30 August 1997 Table 17 29. Volume of Residence Surveys Study Number of Residences Survey Type Areas Surveyed Comments Key Studies U. S. DOE, 1995 ( RECS) Over 7,000 Direct measurement of floor area;

estimation of volume Nationwide ( random sample) Volumes were estimated assuming 8 ft.

ceiling height. Provides relationships between average residential volumes and facilities such as housing type, ownership,

household size, and structure age.

Versar, 1990 ( PFT database) Over 2,000 Direct measurement and estimated Nationwide ( not random sample); a large fraction located in CA Sample was not geographically balanced;

statistical weighting was applied to develop nationwide distributions Murray, 1996 7,041 ( RECS)

1,751 ( PFT) Direct measurements and estimated RECS Nationwide ( random sample); PFT  Nationwide ( not random sample); a large fraction located in CA Duplicate measurement were eliminated;

tested the effects of using 8 ft. assumption on ceiling height to calculate volume; data from both databases were analyzed.

Table 17 30. Air Exchange Rates Surveys Study Number of Residences/ Measurements Survey Type Areas Surveyed Comments Versar, 1990 ( PFT database) Over 2,000 residences Measurements using PFT technique Nationwide ( not random sample); a large fraction located in CA Multiple measurements on the same home were included.

Koontz & Rector, 1995 ( PFT database) 2,971 measurements Measurements using PFT technique Nationwide ( not random sample); a large fraction located in CA Multiple measurements on the same home were included. Compensated for geographic imbalances. Data are presented by region of the country and season.

Murray and Burmaster, 1995 ( PFT database) 2,844 measurements Measurements using PFT technique Nationwide ( not random sample); a large fraction located in CA Multiple measurements on the same home were included. Did not compensate for geographical imbalances. Data are presented by climate region and season.

Nazaroff et al., 1988 255 ( Grot and Clark, 1981) Direct measurement 255, low income families in 14 cities Sample size was small and not representative of the U. S.

312 ( Grimsrud, 1983) Direct measurement 321, newer residences, median age < 10 years Sample size was small and not representative of the U. S. Volume III  Activity Factors Chapter 17  Residential Building Characteristics Exposure Factors Handbook Page August 1997 17 31 Table 17 31. Recommendations  Residential Parameters Volume of Residence 369 m ( central estimate) 217 m ( mean) Air Exchange Rate 0.45 ACH ( median) 0.18 ACH ( 10th percentile) 3 a c 3 b d a Same mean value presented in two studies ( Table 17 1)  recommended to be used as the central estimate. b Mean of two 25th percentile values ( Table 17 1)  recommended to be used as the mean value. c Recommended to be used as a typical value ( Table 17 10). d Recommended to be used as a conservative value ( Table 17 10).

Table 17 32. Confidence in House Volume Recommendations Considerations Rationale Rating Study Elements ° Level of peer review All key studies are from peer reviewed literature. High ° Accessibility Papers are widely available from peer review journals. High ° Reproducibility Direct measurements were made. High ° Focus on factor of The focus of the studies was on estimating house volume High interest as well as other factors.

° Data pertinent to U. S. Residences in the U. S. was the focus of the key studies. High ° Primary data All the studies were based on primary data. High ° Currency Measurements in the PFT database were taken between Medium 1982 1987. The RECS survey was conducted in 1993.

° Adequacy of data Not applicable collection period ° Validity of approach For the RECS survey, volumes were estimated assuming Medium an 8 ft. ceiling height. The effect of this assumption has been tested by Murray ( 1996) and found to be insignificant.

° Study size The sample sizes used in the key studies were fairly large, Medium although only 1 study ( RECS) was representative of the whole U. S. Not all samples were selected at random; however, RECS samples were selected at random.

° Representativeness of the RECS sample is representative of the U. S. Medium population ° Characterization of Distributions are presented by housing type and regions; Medium variability although some of the sample sizes for the subcategories were small.

° Lack of bias in study design Selection of residences was random for RECS. Medium ( high rating is desirable)

° Measurement error Some measurement error may exist since surface areas Medium were estimated using the assumption of 8 ft. ceiling height.

Other Elements ° Number of studies There are 3 key studies; however there are only 2 data Low sets.

° Agreement between researchers There is good agreement among researchers. High Overall Rating Results were consistent; 1 study ( RECS) was Medium representative of residences in the whole U. S.; volumes were estimated rather than measured in some cases. Volume III  Activity Factors Chapter 17  Residential Building Characteristics Page Exposure Factors Handbook 17 32 August 1997 Table 17 33. Confidence in Air Exchange Rate Recommendations Considerations Rationale Rating Study Elements ° Level of peer review The studies appear in peer reviewed literature. Although High there are 3 studies, they are all based on the same database ( PFT database).

° Accessibility Papers are widely available from government reports and High peer review journals.

° Reproducibility Precision across repeat analyses has been documented to Medium be acceptable.

° Focus on factor of The focus of the studies was on estimating air exchange High interest rates as well as other factors.

° Data pertinent to U. S. Residences in the U. S. was the focus of the PFT database. High ° Primary data All the studies were based on primary data. High ° Currency Measurements in the PFT database were taken between Medium 1982 1987.

° Adequacy of data Only short term data were collected; some residences were Medium collection period measured during different seasons; however, long term air exchange rates are not well characterized.

° Validity of approach Although the PFT technology is an EPA standard method Low ( Method IP 4A), it has some major limitations ( e. g., uniform mixing assumption).

° Study size The sample sizes used in the key studies were fairly large, Medium although not representative of the whole U. S. Not all samples were selected at random.

° Representativeness of the Sample is not representative of the U. S.. Low population ° Characterization of Distributions are presented by U. S. regions, seasons, and Low variability climatic regions; although some of the sample sizes for the subcategories were small and not representative of U. S. The utility is limited..

° Lack of bias in study design Bias may result since the selection of residences was not Low ( high rating is desirable) random.

° Measurement error Some measurement error may exist. Medium Other Elements ° Number of studies There are 3 key studies; however there are only 1 data set. Medium However, the database contains results of 20 projects of varying scope.

° Agreement between researchers Not applicable Overall Rating Sample was not representative of residences in the whole Low U. S., but covered the range of occurrence. PFT methodology has limitations. Uniform mixing assumption may not be adequate. Results will vary depending on placement of samples and on whether windows and doors are closed or opened.