Click for next page ( 328


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 327
10 IMPACT OF VENTILATION AND AIR CLEANING ON AS th ma Indoor exposures to pollutants associated with the incidence or symptoms of asthma are affected by many aspects of building design, maintenance, and operation. Building features modify the indoor sources of pollutants, the rates of pollutant entry from out- doors, and the rates of pollutant removal from indoors. Building ventilation and air cleaning are the two primary processes used intentionally within buildings to remove pollutants from the in- door air and maintain acceptable indoor environmental condi- tions. This chapter provides an overview of the relationship of building ventilation and particle air cleaning to exposures to in- door-generated pollutants that are associated with asthma. The findings from experimental assessments of the effects of air clean- ing on allergy and asthma symptoms are also summarized. Be- cause the association of asthma with pollutants from outdoor air is not a primary focus of this report, even though the exposures may occur primarily indoors, the dependence of these exposures on ventilation and air cleaning is not addressed in this chapter. THEORETICAL BACKGROUND This section provides a very brief overview of theoretical con- siderations that are necessary to understand the influence of building ventilation and air cleaning on indoor pollutant concen 327

OCR for page 327
328 CLEARING THE AIR "rations. Emphasis is placed on indoor particles because the in- door-generated pollutants most clearly associated with asthma are particles. Appendix A provides a more detailed technical dis- cussion of this topic along with the equations and parameter val- ues used for the theoretical predictions later in this chapter. From conservation of mass, the steady-state indoor air con- centration~ of a pollutant that is emitted indoors and absent from outdoor air equals the indoor pollutant generation rate divided by the sum of all pollutant removal rates. In the present context, the most important pollutant removal processes are (1) ventila- tion (i.e., the flow of indoor air containing pollutants to outdoors); (2) pollutant depositional losses on indoor surfaces; and (3) air cleaning (i.e., intentional removal of pollutants from indoor air by air filters and other types of air cleaners). The influence of changes in ventilation or air-cleaning rates on the indoor pollut- ant concentration depends on the magnitude of the other two pol- lutant removal processes. Many of the indoor-generated pollutants important for asthma are particles with diameters ranging from a fraction of a micrometer (1 ,um equals one-millionth of a meter) to approxi- mately 20 ,um. Table 10-1 provides information of the sizes (aero- dynamic diameters)2 of these particles. The available data are lim- ited and sometimes contradictory. Many of the bioaerosols associated with asthma, particularly dust mite allergens, whole pollens, cockroach allergen, and many fungal spores are large par- ticles greater than a few micrometers in diameter. There are con- tradictions among available data on the size of particles with cat allergen; however, a significant fraction of airborne cat allergen appears to be associated with particles smaller than a few mi- crometers. Environmental tobacco smoke is composed almost en- tirely of submicron-size particles (i.e., particles smaller than 1 rim). Droplet nuclei from coughs and sneezes, which often contain vi- rus, are included in Table 10-1 because viral infections are strongly iFor this discussion, we have assumed perfect mixing of the indoor air. See Appendix A for more information. 2Except that the sources of the data for pollens and fungal spores do not indi- cate whether the sizes are physical or aerodynamic diameters.

OCR for page 327
329 Cal In ~5 Cal . _ Cal o cn cn cn Cal . _ Cal o cn o . _ Q . _ cn . _ C] . _ CD ~5 o Q tr to - m U' C' Or ~7 o Q Or U' Cal Or .N CD .O Cal o Q O) Q a) _ ._~ ~ ~ ~t O) U'~ ~ _ ~ ~ ~ it - ~ o - ~ ~C/~ Us ~ ~ Us Cry oo - Q (D C,,) ~ TIC ~ .= ~- a' _ ~cn s ~ ~ ~ . =, ~o ~ o =7 ~CD s~ ~tc: ~ c, ti, O E '~ ' v E s W c, ~=' ~ ~ E ~, ~ v 5 E = e E s, E E _ o o ~D ~ V ae :~ V ae E ~ ~ ~ co ae . CO ~C~ ~1 ~1 1 U' _ ~ llJ U' _ =7 ~C~ o U' U' U' o o ~C ~ ~ E o ~`,, E ~ c ~ ._ Q ~O C ~O ~0 C] ~C~ C ~C~ 113 C]

OCR for page 327
330 linked to exacerbation of asthma, at least in children Johnston et al., 1995~. There is evidence that rates of building ventilation and occupant density modify the rates of respiratory illness experi- enced by building occupants (Fisk, 1999; Fisk and Rosenfeld, 1997), presumably by changing exposures to infectious droplet nuclei. Data on the size distribution of droplet nuclei are ex- tremely limited and the methods employed to obtain the data may have resulted in an undercounting of the larger particles. The available data indicate that most of these particles are submicron in size but most of the particle volume is associated with particles larger than 1 ,um. It is not clear whether the number concentration or volume concentration of infectious droplet nuclei is more rel- evant for disease transmission. The magnitude of two of the particle removal processes- deposition on surfaces and air cleaning can vary dramatically with particle size. Particles deposit on indoor surfaces when in- door air motion, gravitational settling, electrostatic forces, and other phenomena cause them to collide with indoor surfaces. For particles, larger than a few micrometers in diameter, depositional losses are dominated by rates of gravitational settling. A 20-,um particle falls a distance of 1 m in about 80 seconds so it remains suspended indoors for only a short period. The deposition losses of such large particles tend to overwhelm normal rates of particle removal by ventilation or air cleaning. In contrast, a 0.2-,um par- ticle falls a distance of 1 m in about five days. The rate of deposi- tional removal of 0.2-,um particle from the indoor air, which is controlled by the indoor air motion, indoor surface roughness, and other factors, is almost a factor of 100 lower than the rate of depositional removal of a 20-,um particle. Some gaseous pollutants such as nitrogen dioxide and ozone are also removed from indoor air at a significant rate by deposi- tion (often called sorption) on or reaction with indoor surfaces. Rates of depositional removal depend on the chemical nature of the pollutant, the intensity of indoor air motion, and other fac- tors. Gravitational settling is unimportant for gaseous pollutants. Particles deposited on indoor surfaces can be resuspended in indoor air when the surfaces are disturbed by human activities (e.g., walking, vacuuming) or by high air velocities (e.g., air exit- ing a fan). Theory (Hinds, 1982) and limited empirical data

OCR for page 327
IMPACT OF VENTILATION AND AIR CLEANING ON ASTHMA 331 (Thatcher and Layton, 1995) indicate that resuspension occurs predominantly for particles larger than approximately 2 ,um. Based on our current knowledge of the behavior of particles, ex- posures to some of the larger particles associated with asthma may be substantially influenced by the localized resuspension of particles that results from occupant activities. BUILDING VENTILATION Background In this document, the term "ventilation" refers to the flow of outside air indoors, which is always accompanied by an equal flow of indoor air outdoors. Ventilation removes and dilutes in- door airborne pollutants, brings outdoor air pollutants into build- ings, and often removes or supplies heat and water vapor. Venti- lation is also needed to maintain oxygen concentrations inside buildings, although the quantity of ventilation needed to supply oxygen is very small relative to other ventilation requirements. Increasing the rate of ventilation generally leads to overall improvements in indoor air quality; however, the indoor concen- trations of some pollutants from outdoors, such as outdoor par- ticles and ozone, can increase with the ventilation rate. Indoor humidity can increase or decrease with ventilation rate. When it is cold and dry outdoors, increased ventilation usually reduces the indoor humidity. While increased ventilation rates are usually considered ben- eficial for health and for improving perceived air quality (e.g., odors), ventilation air must often be heated (and sometimes hu- midified) or cooled and dehumidified. Consequently, the ventila- tion rates selected for buildings must strike a balance between the benefits of energy savings with reduced ventilation and the known or suspected benefits to health with increased ventilation. Several metrics are used to specify the rates of building venti- lation. Generally, these metrics are flow rates of outside air nor- malized by the number of occupants, floor area, or indoor vol- ume. Corresponding units of ventilation rates include the following: liters per second per person (L so per person); liters

OCR for page 327
332 CLEARING THE AIR per second per square meter of floor area (L so per square meter); and air changes per hour (h-~. Municipalities typically adopt one of the several building de- sign codes used in the United States. These codes, or state energy codes, include building design provisions intended to maintain ventilation rates above a minimum rate that varies with the build- ing type. The American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) publishes a minimum venti- lation standard that is the basis for the ventilation specifications in many codes. The current version of the ASHRAE standard is Standard 62-1999 Ventilation for Acceptable Indoor Air Quality (ASHRAE, 1999~. Standard 62-1999 lists 0.35 ho as a minimum ventilation rate in residences,3 10 L so per person (20 cubic feet per minute [cfm] per person) as a minimum ventilation rate in offices, and 8 L so per person (15 cfm per person) as a minimum ventilation rate in schools. Due to a paucity of scientific data on the relationship of building ventilation rates with the health and well-being of occupants (Seppanen et al., 1999), the minimum ventilation rates in the ASHRAE standard are based substantially on professional judgment and on studies performed in laborato- ries with conditions quite different from those encountered in real buildings. Building design codes and ASHRAE's minimum ventilation standard do not ensure that all buildings maintain the specified minimum ventilation rates. In most states and municipalities, there are no legal requirements to actually maintain ventilation rates at or above the levels in building design codes. Additionally, building ventilation rates are difficult to measure accurately, in- frequently measured, and as discussed later, poorly controlled. Ventilation systems, although intended to remove indoor pol- Jutants, can also become sources of pollutants. Portions of venti- ration systems, particularly components that become wet, can be- come colonized by microorganisms and produce bioaerosols that 3Standard 62-1999 states that the 0.35 h-i of ventilation is normally satisfied by infiltration and natural ventilation but includes no technical specifications for the building to ensure that this ventilation rate is met continuously or on average. Standard 62-1999 also specifies installed mechanical exhaust capacities of 50 L s-i (100 cfm) per kitchen and 25 L s-i (50 cfm) per bathroom.

OCR for page 327
IMPACT OF VENTILATION AND AIR CLEANING ON ASTHMA 333 are transported by the airflow to the occupied space. In addition, particles, fibers, and odorous and potentially irritating volatile organic compounds (VOCs) may be emitted from synthetic mate- rials, including fibrous insulation materials, from residual oils used in component production, from deposited dusts, and from microorganisms. Ventilation also affects the indoor humidity which in turn influences the growth or survival of microorgan- isms within buildings. Heating, ventilating, and air conditioning (HVAC) is the more general process of thermally conditioning and ventilating build- ings. In commercial buildings, these functions are usually inte- grated. The HVAC process employed in commercial buildings is reviewed here because HVAC features may influence exposure to pollutants that are known or thought to be associated with asthma. Methods and Rates of Ventilation in U.S. Single-Family Residences Diamond (1999) has summarized many of the basic physical characteristics of the U.S. residential building stock. In 1997, de- tached single-family units and row houses constituted 73/O of the U.S. housing stock, 6% of the housing stock was mobile homes, and the remainder was apartments. The average heated floor space in all U.S. housing stock was 181 m2 (1,950 square feet) and air conditioning was installed in 70/O of these dwellings. The av- erage conditioned floor area of mobile homes was 87 m2 (940 square feet) and 70/O of mobile homes had air conditioners. Four- teen percent of all housing units used humidifiers, and nine per- cent had dehumidifiers. When windows are closed, the ventilation of single-family residences in the United States is almost exclusively an uncon- trolled process. In air infiltration (or infiltration and exfiltration), air leaks through unintentional cracks and holes in the building envelope. The infiltration rate is driven by small pressure differ- ences across the building envelope that are typically less than a few pascals in magnitude. These pressure differences arise due to the differences between the indoor and outdoor air temperatures, resulting in different indoor and outdoor air densities, and also as

OCR for page 327
334 CLEARING THE AIR a consequence of wind. Unintentional air leakage in the ductwork of forced-air heating and air-conditioning systems located in at- tics and craw! spaces, also causes large increases in air infiltra- tion. Even if the ducts do not leak, forced-air systems can pressur- ize or Repressurize specific rooms relative to the outdoor pressure, forcing air leakage through the building envelope. U.S. homes often have intermittently-operated exhaust fans in bathrooms and kitchens. When operated, these fans draw out- door air into the building. Window and door opening by occu- pants, predominantly during mild weather, also has a large influ- ence on residential ventilation rates. A very small portion of single-family dwellings in the United States have mechanical ventilation systems (i.e., fans operating continuously or intermittently to provide ventilation). Mechani- cal ventilation is most common in the State of Washington be- cause the state energy code now requires mechanical ventilation. The technologies used to mechanically ventilate residences are described in Roberson et al. (1998~. Ventilation rates in residences vary considerably over time. The lowest ventilation rates occur during mild weather with win- dows and doors closed. When weather is more severe, windows remain closed but ventilation rates are higher due to increased indoor-to-outdoor temperature differences and increased use of forced-air heating and air conditioning. The highest ventilation rates generally occur when windows or doors are open. Present data on ventilation rates in U.S. single-family resi- dences are limited and possibly not representative of the building stock. One source of information is measurements of the airtight- ness of building envelopes with windows and doors closed. Ven- tilation rates are predicted with semiempirical models, using mea- sured values of building airtightness4 combined with climate data and indicators of a building's shielding from wind, as mode] in 4Airtightness is used here as a general term understandable to a broad audi- ence. The actual measured parameter is the effective leakage area (ELA) at a ref- erence pressure, usually 25 or 50 Pa across the building envelope. The ELA is the area of an orifice that would leak air at the same rate as all the leakage paths in the building envelope. The ELA is usually normalized with building floor area and height to produce a normalized leakage.

OCR for page 327
IMPACT OF VENTILATION AND AIR CLEANING ON ASTHMA 335 puts. When annual average ventilation rates are desired, the pre- dictions may also include terms to account for natural ventilation via windows; however, the current knowledge of window use and effects on ventilation is cursory. The second source of infor- mation on residential ventilation rates is measurements made us- ing a tracer-gas procedure. Although considered more accurate than predictions based on airtightness, the measured data are more sparse than airtightness data. Therefore, we presently have only crude estimates of residential ventilation rates. Based on airtightness and climate data for about 12,000 houses, Sherman and Matson (1997) estimate that the arithmetic average effective ventilation rate of houses in the United States is 1.1 hot. This average reflects ventilation rates when windows are closed and also the higher ventilation rates that occur with open windows during mild weather. Airtightness normalized by house size is highly variable (Sherman and Dickerhoff, 1994), with a standard deviation that is approximately 50% of the mean. The mean of the airtightness data from individual states varies among states by more than a factor of three. In the available data, there is no trend in airtightness with severity of climate. The available data indicated that houses constructed after 1980 are more air- tight (by ~50%) than older houses (Sherman and Dickerhoff, 1994~; however, there was no trend evident in airtightness with age for houses constructed after 1980. A set of 2,844 measurements of residential ventilation rates in U.S. houses was analyzed by Murry and Burmaster (1995~. The measured data from 66 research projects are not from a represen- tative sample of residences; however, this analysis is probably the best available information on the distribution of ventilation rates in U.S. houses. When considering all climate zones and seasons, the arithmetic and geometric mean ventilation rates were 0.76 ho and 0.53 hot, with a geometric standard deviation of 2.3. There are large variations in ventilation rates with season and climate zone. The winter and summer arithmetic means, for all climate zones, are 0.55 and 1.50 hot. Approximately one-third of the measure- ments in the winter season are less than the 0.35 hot, the rate in the current ASHRAE ventilation standard. In the coldest climate zone, approximately 55% of the measured ventilation rates, from all seasons, are less than 0.35 hot.

OCR for page 327
336 CLEARING THE AIR Methods, Patterns, and Rates of Ventilation in U.S. Multifamily Apartment Buildings In 1997, 21% of U.S. housing units were apartments. The aver- age conditioned floor area of apartments was 85 m2 (920 square feet) and air conditioning was installed in 65% of apartments (Dia- mond, 1999~. Published information on the methods and rates of ventilation in multifamily apartment buildings are extremely sparse. Based on the limited information available,5 older low- rise (i.e., less than Three stories) apartment buildings usually have no mechanical supply of ventilation air. Much like single- family dwellings, these buildings are ventilated primarily by un- controlled infiltration and natural ventilation windows that can be opened. Intermittently operated bathroom and kitchen exhaust fans cause temporary increases in ventilation rates. Leakage in the ductwork of forced-air heating and air-conditioning systems and pressurization or Repressurization of individual rooms can drive infiltration and exfiltration in apartments, just as it does in single-family houses. Newer low-rise apartment buildings are ventilated similarly to older low-rise buildings; however, a larger portion of these buildings have continuous mechanical exhaust ventilation from the bathrooms and/or kitchens of each apart- ment. Older apartment buildings with more than approximately three stories typically have no mechanical air supply or some mechanical supply to the interior hallways. The air supply sys- tem, when present, is frequently not functional (Shapiro-Baruch, 1993~. Apartments within these buildings sometimes have a sys- tem for continuous exhaust ventilation from bathrooms and kitch- ens, although it is not always operational. Some portion of these older high-rise buildings have a vertical ventilation shaft that functions much like a chimney and passively draws air from the apartments. In new apartment buildings with more than three stories, 5The information in this section is based primarily on case studies, on two gen- eral guidance documents (Diamond et al., 1999; Liddament, 1996) and on discus- sions with Dr. Rick Diamond of Lawrence Berkeley National Laboratory. who conducts research on energy use and ventilation in apartment buildings.

OCR for page 327
IMPACT OF VENTILATION AND AIR CLEANING ON ASTHMA 337 exhaust ventilation is usually drawn continuously from the kitchen and bathrooms of each apartment. The exhaust fans may serve groups of apartments or individual apartments. Outside air enters either from unintentional leaks and vents at windows or via ventilation systems that supply air continuously to each apart- ment. When a mechanical air supply is present, often this air is supplied to a single room of each apartment from a duct system in the building's interior hallway. The airflow in heated multistory apartment buildings with- out mechanical ventilation often occurs in an upward direction from lower-level to upper-level apartments (e.g., Diamond et al., 1986; Modera et al., 1986~. Coo] outdoor air leaks into the lower apartments; flows upward, picking up moisture and pollutants; and exfiltrates through the walls and ceilings of upper-level apart- ments. Due to this airflow pattern, the lower-level apartments tend to have more fresh air supply, lower humidity, and more cold drafts. Humidity and pollutant levels are often increased in upper-level apartments because a portion of the air entering these apartments comes from lower levels of the building. As moist air exfiltrates out of the upper-level apartments, water vapor may condense within cold walls and ceilings. Possibly, the higher pol- lutant levels and humidity in upper-level apartments could con- tribute to asthma symptoms. This same upward-flow phenomenon occurs to a variable de- gree in all heated multistory buildings. When the building is air conditioned (i.e., cooled), the airflow direction can reverse; how- ever, the downward airflow in air-conditioned buildings will be less pronounced because the indoor-to-outdoor temperature dif- ferences are typically much smaller during air conditioning than during heating of buildings. By reducing the openings between floors, the vertical airflow between floors can be reduced. Me- chanical ventilation can also reduce or overwhelm the upward buoyancy-driven airflow. In addition to the buoyancy-driven upward airflow in apart- ments, other unintentional flows of air between adjacent apart- ments are reported commonly from case studies. These flows oc- cur through unintentional openings in walls and floors, and may be driven by mechanical ventilation systems, buoyancy, and wind.

OCR for page 327
IMPACT OF VENTILATION AND AIR CLEANING ON ASTHMA 383 to save energy, some modern air conditioners will stop the recir- culation and cooling of indoor air and instead provide ventilation (i.e., supply outdoor air to the building) when the outdoor air is relatively coo! and suitable for cooling the house. Summary and Discussion of Limitations of Assessment Many of the indoor pollutants associated with asthma are air- borne particles; thus, particle air cleaning has been considered a potentially beneficial technology for the prevention of asthma or asthma symptoms. Technologies for particle air cleaning are well developed. Air filters with a moderate to high efficiency for par- ticles larger than approximately 2 ,um are used routinely in the heating and air-conditioning systems of buildings. The magnitude of the reduction in indoor-generated particle concentrations accomplished with particle air cleaning depends on the air cleaner's particle removal rate relative to the particle removal rate by all other processes including ventilation and par- ticle deposition on surfaces. The rate of particle removal by an air cleaner varies with particle size and is proportional to the flow rate of air through the air cleaner multiplied by the air cleaner's size-dependent particle removal efficiency. The two primary air cleaning options for reducing indoor particle concentrations are to replace the existing filters in heating and air-conditioning sys- tems with higher-efficiency filters and to operate supplemental air cleaners with integral fans in the occupied space. In field studies, enhanced air cleaning has been associated with reductions in airborne particle concentrations that range from negligible to more than 90/0. For the airborne particles asso- ciated with asthma, the published data are very limited. Simple mode] predictions indicate that substantial reductions in indoor concentrations of 10-,um particles can be obtained only when the rate of airflow through the air cleaner per unit of indoor air vol- ume is large, for example, 10 room volumes per hour or more. The predicted effectiveness of air cleaning diminishes rapidly with increases in particle size above 10 ,um because gravitational settling rates increase with particle size. Thus, air cleaning does not appear to be an attractive option for reducing exposures to dust mite allergen, which predominantly involves particles larger

OCR for page 327
384 CLEARING THE AIR than 10 ,um. However, based on predictions it is feasible to reduce concentrations of particles smaller than 2 ,um, such as ETS par i] ticles, droplet nuclei, and smaller particles with cat allergen, by 70/O or more using air cleaners with a moderate to high efficiency rating and a flow rate of several indoor air volumes per hour. Both the available experimental data and mode] predictions ndicate that HEPA filters, which are more expensive and often require larger and noisier fans, are not likely to be superior to lower-efficiency filters in reducing concentrations of many of the bioaerosols associated with asthma. Even for submicron-size ETS particles, available data indicate that HEPA filters are not neces- sarily the preferred option. Thus, the very common recommenda- tion that HEPA filtration, in contrast to lower-efficiency air clean- ing, be used by allergic and asthmatic individuals when they choose to employ air cleaning, is not supported by either experi- ments or theoretical predictions. Unfortunately, the limited per- formance data available for many non-HEPA residential air clean- ers make it difficult to provide alternate recommendations. The influence of air cleaner use on asthma and allergy out- comes has been evaluated in numerous experimental studies; however, most of these studies have important limitations. Over- all, the data suggest that air cleaners are helpful in some situa- tions in reducing allergy or asthma symptoms, particularly sea- sonal symptoms, but it is clear that air cleaning, as applied in the studies, is not consistently and highly effective in reducing symp- toms. The available data provide no information regarding the effects of air cleaning on the development of asthma or the devel- opment of sensitization to allergens. Conclusion Regarding Air Cleaning and Asthma There is limited or suggestive evidence that particle air clean- ing is associated with a reduction in the exacerbation of asthma symptoms. There is insufficient evidence to determine whether or not the use of particle air cleaners is associated with decreased asthma development. Theoretical and limited empirical data sug- gest that air cleaners are most likely to be effective in reducing the indoor concentrations of particles smaller than approximately 2 ,um. Much of the airborne allergen appears to be within larger

OCR for page 327
IMPACT OF VENTILATION AND AIR CLEANING ON ASTHMA 385 particles. Relevant particles smaller than 2 ,um include environ- mental tobacco smoke particles, significant portions of airborne cat, grass, and birch allergen, and virus-containing droplet nuclei from coughs and sneezes. Research Needs Related to Air Cleaning and Asthma The results of existing experimental studies are inadequate to draw firm conclusions regarding the benefits of air cleaning for asthmatic and allergic individuals. Many of the existing studies have important limitations, such as small study size, lack of blind- ing, a small or undefined rate of air cleaning, placebo air cleaners that may significantly remove the larger particles associated with asthma, and no exposure assessment or inadequate assessment. Additional research to assess the benefits of air cleaning is clearly warranted, but future studies must overcome as many of these limitations as possible. Because air cleaning is most promising for reducing indoor concentrations of particles smaller than a couple of micrometers, future research should emphasize these agents. Sensitization to allergens a critical step in the development of allergic asthma often occurs early in life. No information is available to indicate whether air cleaning of spaces occupied early in life can reduce the rate of allergic sensitization. Research is needed to address this issue. As described in Appendix A, particles larger than a few mi- crometers have a complex and inadequately understood behav- ior in the indoor environment, including rapid rates of gravita- tional settling, resuspension from surfaces, and possibly incomplete mixing with the indoor air. Consequently, the influ- ence of air cleaning systems on exposures to particles in this size range is not well understood and the associated benefits from air- cleaning cannot be predicted with a high degree of confidence. A combination of aerosol science and air-cleaning research is needed to fill this gap in our knowledge. The limited data on the size distribution of many of the bioaerosols and allergens associated with asthma limit our un- derstanding of the benefits of air cleaning. Additional data are needed particularly for pet allergens and pollens. As stated earlier, HEPA filter units have been widely recom

OCR for page 327
386 CLEARING THE AIR mended for allergy and asthma patients who desire to use air cleaners. Air cleaner manufacturers have responded by aggres- sively marketing air cleaners with HEPA filters and offering few other products. However, experimental data and theoretical pre- dictions indicate that air cleaners with a lower efficiency rating are likely to be equally effective in reducing the concentrations of most, and perhaps all, of the indoor-generated particles associ- ated with allergies and asthma. These lower-efficiency air clean- ers could have a lower product cost, less powerful or noisy fans, higher rates of airflow and particle removal, and reduced energy consumption. The scientific and medical community should de- velop revised recommendations regarding the selection of air cleaners by allergic and asthmatic individuals, and air cleaner manufacturers should respond by providing new air-cleaning products. REFERENCES Aberg N. Sundell J. Eriksson B. Hesselmar B. Aberg B. 1996. Prevalence of allergic diseases in schoolchildren in relation to family history, upper respiratory infections, and residential characteristics. Allergy 51~4~:232-237. American Lung Association. 1997. Residential air cleaning devices: types, effectiveness, and health impact. American Lung Association, Washington, DC. American Thoracic Society. 1997. American Thoracic Society Workshop, Achieving Healthy Indoor Air. American Journal of Respiratory and Critical Care Medicine 156(Suppl 3~:534-564. Antonicelli L, Bilo MB, Pucci S. Schou C, Bonifazi F. 1991. Efficacy of an air cleaning device equipped with a high efficiency particulate air filter in house dust mite allergy. Allergy 46~8~:594-600. ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers). 1992. ASHRAE Standard 52.1-1992-Gravimetric and Dust-Spot Procedures for Testing Air-Cleaning Devices Used in General Ventilation for Removing Particulate Matter. Atlanta, GA: American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc. ASHRAE. 1996. 1996 ASHRAE Handbook: HVAC Systems and Equipment. Atlanta, Georgia: American Society of Heating, Refrigerating, and Air- Conditioning Engineers, Inc. ASHRAE. 1999. ASHRAE Standard 62-1999. Ventilation for Acceptable Indoor Air Quality. Atlanta, GA: American Society of Heating, Refrigerating, and Air- Conditioning Engineers, Inc.

OCR for page 327
IMPACT OF VENTI~TION AND AIR CLEANING ON ASTHMA 387 Bascom R. Fitzgerald TK, Kesavanathan J. Swift DL. 1996. A portable air cleaner partially reduces the upper respiratory response to sidestream tobacco smoke. Applied Occupational and Environmental Hygiene 11~6~:553-559. Batterman SA, Burge H. 1995. HVAC systems as emission sources affecting indoor air quality a critical review. International Journal of HVAC and Research 1~1~:61-80. Bencko V, Maelichercik J. Melichercikova V, Wirth Z. 1993. Microbial growth in spray humidifiers of health facilities. Indoor Air 3~1~:20-25. Berglund B. Johansson I, Lindvall T. 1982. The influence of ventilation on indoor/ outdoor air contaminants in an office building. Environment International 8:395-399. Bowler SD, Mitchell CA, Miles J. 1985. House dust control and asthma: A placebo- controlled trial of cleaning air filtration. Annals of Allergy 55~3~:498-500. Burroughs HE. 1997. Filtration: an investment in IAQ. Heating, Piping, and Air Conditioning (August):55-65. Cohen MB. 1927. The prophylaxis and treatment of hay fever and asthma in rooms made pollen and dust free by means of mechanical filters. Journal of Laboratory and Clinical Medicine 13:59-63. Criep LH, Green MA. 1936. Air cleaning as an aid in the treatment of hay fever and bronchial asthma. Journal of Allergy 7:120-133. Custovic A, Simpson A, Pahdi H. Green RM, Chapman M, Woodcock A. 1998. Distribution, aerodynamic characteristics, and removal of the major cat allergen Fel d 1 in British homes. Thorax 53~1~:33-38. de Blay F. Chapman MD, Platts-Mills TAP. 1991. Airborne cat allergen (Fel D 1~: Environmental control with the cat in-situ. American Review of Respiratory Disease 143~6~:1334-1339. de Blay F. Sanchez J. Hedelin G. Perez-Infante A, Verot A, Chapman M, Pauli G. 1997a. Dust and airborne exposure to allergens derived from cockroach (Blattella germanica) in low-cost public housing in Strasbourg (France). Journal of Allergy and Clinical Immunology 99~1 Pt 1~:107-112. de Blay F. Colas F. Richard MC, Ott M, Verot A. 1997b. Air cleaners and airborne allergens. Journal of Investigational Allergology and Clinical Immunology 7~5~:335-337. Diamond RC. 1999. An Overview of the U.S. Building Stock. In: Indoor Air Quality Handbook. Spengler JD, Samet JM, McCarthy JF, Eds. McGraw Hill, ~n-press. Diamond RC, Modera MP, Feustel HE. 1986. Ventilation and occupant behavior in two apartment buildings. In: Proceedings of the 7th Air Infiltration and Ventilation Centre Conference. Coventry, Great Britain: Air Infiltration and Ventilation Centre, pp. 6.1-6.18. Diamond RC, Feustel HE, Matson NE. 1999. Energy Efficient Ventilation for Apartment Buildings. U.S. Department of Energy, Rebuild America technical guide series. July. Dietz RN, Cote EA. 1982. Air infiltration measurements in a home using a convenient perfluorocarbon tracer technique. Environment International 8~1- 6~:419-433.

OCR for page 327
388 CLEARING THE AIR DOE-EIA. 1994. Commercial Building Characteristics 1992. Report DOE/EIA- 0246~92), (U.S. Department of Energy, Energy Information Administration), Washington DC: U.S. Government Printing Office. DOE-EIA. 1995. Commercial Buildings Energy Consumption and Expenditures 1992. Report DOE/EIA-0318~92), (U.S. Department of Energy, Energy Information Administration), Washington DC: U.S. Government Printing Office. Dots SW, Persily AK. 1994. Measurements of Outdoor Air Distribution in an Office Building. Report NISTIR 5320. Gaithersburg, MD: National Institute of Standards and Technology. Emenius G. Egmar A, Wickman M. 1998. Mechanical ventilation protects one- story single dwelling houses against increased air humidity, domestic mite allergens and indoor pollutants in a cold climate region. Clinical and Experimental Allergy 28~11~:1389-1396. Emmerich S. Persily A. 1998. Energy impacts of infiltration and ventilation in U.S. office buildings using multi-zone airflow simulation. Proceedings of IAQ & Energy 98. Atlanta, GA: American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc., pp. 191-203. Fisk WJ. 1999. Estimates of potential nationwide productivity and health benefits from better indoor environments: an update. Lawrence Berkeley National Laboratory Report, LBNL-42123, To be published as a chapter in Indoor Air Quality Handbook. Spengler J. Samet JM, McCarthy IF, Eds. McGraw Hill, in press. Fisk WJ, Faulkner D. 1992. Air exchange effectiveness in office buildings: measurement techniques and results. In: Proceedings of the 1992 International Symposium on Room Air Convection and Ventilation Effectiveness, July 22- 24, Tokyo, pp. 213-223, ASHRAE, Atlanta. Fisk WJ, Rosenfeld AH. 1997. Estimates of improved productivity and health from better indoor environments. Indoor Air 7~3~:158-172. Fletcher AM, Pickering CAC, Custovic A, Simpsom J. Kennaugh J. Woodcock A. 1996. Reduction in humidity as a method of controlling mites and mite allergens: the use of mechanical ventilation in British domestic dwellings. Clinical and Experimental Allergy 26~9~:1051-1056. Friedlaender S. Friedlaender AS. 1954. Effectiveness of portable electrostatic precipitator in elimination of environmental allergens and control of asthma symptoms. Annals of Allergy 12:419-428. Gerone PI, Couch RB, Keefer GV, Douglas RG, Derrenbacher ED, Knight V. 1966. Assessment of experimental and natural viral aerosols. Biological Reviews 30~3~:576-588. Hanley IT, Ensor DS, Smith DD, Sparks LE. 1994. Fractional aerosol filtration efficiency of in-duct ventilation air cleaners. Indoor Air 4~3~:169-178. Harving H. Korsgaard J. Dahl R. 1994. House-dust mite exposure reduction in specially-designed, mechanically ventilated "healthy" homes. Allergy 49~9~:713-718. Hinds WC. 1982. Aerosol Technology. New York: John Wiley & Sons.

OCR for page 327
IMPACT OF VENT TON AND AIR CLEANING ON ASTHMA 389 Hodgson AT, Rudd AF, Beat D, Chandra S. 1999. Volatile organic compound concentrations and emission rates in new manufactured and site built houses. LBNL-43519, Lawrence Berkeley National Laboratory Report, Berkeley, California. (in draft). Holmquist L, Vesterberg O. 1999. Quantification of birch and grass pollen allergens in indoor air. Indoor Air 9~2~:85-91. Johnston SL, Pattemore PK, Sanderson G. Smith S. Lampe F. Josephs L, Symington P. O'Toole S. Myint SH, Tyrrell DA, Holgate ST. 1995. Community study of role of viral infections in exacerbations of asthma in 9-11 year old children. British Medical Journal 310~6989~:1225-1229. Kooistra JB, Pasch R. Reed CE. 1978. The effects of air cleaners on hay fever symptoms in air-conditioned homes. Journal of Allergy and Clinical Immunology 61~5~:315-319. Lagus Applied Technologies. 1995. Air Change Rates in Non-Residential Buildings in California. Report P400-91-034BCN, Prepared for the California Energy Commission by Lagus Applied Technology, Inc., San Diego, CA. Liddament MW. 1996. A Guide to Energy Efficient Ventilation. Document AIC- TN-VENTGUIDE-1996. Coventry, Great Britain: Air Infiltration and Ventilation Centre, International Energy Agency. Luczynska CM, Li Y. Chapman MD, Platts-Mills T. 1990. Airborne concentrations and particle size distribution of allergen derived from domestic cats (Felis domesticus). Measurement using cascade impactor, liquid impinger, and two- site monoclonal antibody assay for Fel d 1. American Review of Respiratory Disease 141~2~:361-367. Martiny H. Moritz M, Ruden H. 1994. Occurrence of microorganisms in different filter media of heating, ventilation and air conditioning (HVAC) systems. In: Proceedings of IAQ '94 Engineering Indoor Environments, Atlanta, GA: ASHRAE. pp. 131-137. McIntyre DA. 1992. The control of house dust mites by ventilation: a pilot study. In: Proceedings of the 13th AIVC Conference Ventilation for Energy Efficiency and Optimum Indoor Air Quality. Air Infiltration and Ventilation Centre, Coventry, Great Britain. pp. 497-507. Mendell MJ. 1993. Non-specific symptoms in office workers: a review and summary of the epidemiologic literature. Indoor Air 3~4~:227-236. Menzies R. Tamblyn R. Farant JP, Hanley J. Nunes F. Tamblyn R. 1993. The effect of varying levels of outdoor-air supply on the symptoms of sick building syndrome. New England Journal of Medicine 328~12~:821-827. Miller SL. 1996. Characterization and Control of Exposure to Indoor Air Pollutants Generated by Occupants. Ph.D. Dissertation, Civil and Environmental Engineering, University of California, Berkeley. Miller-Leiden S. Lobascio C, Nazaroff WW, Macher JM. 1996. Effectiveness of in- room air filtration and dilution ventilation for tuberculosis infection control. Journal of the Air and Waste Management Association 46:869-882. Mitchell EA, Elliott RB. 1980. Controlled trial of an electrostatic precipitator in childhood asthma. Lancet 2~8194~:559-561.

OCR for page 327
390 CLEARING THE AIR Modera MP, Brunsell IT, Diamond RC. 1986. Improving diagnostics and energy analysis for multi-family buildings: a case study. In: Proceedings, Thermal Performance of the Exterior Envelopes of Buildings III, SP 49. Atlanta, GA: ASHRAE. pp. 689-706. Morey PR.1988. Microorganisms in buildings and HVAC systems: a summary of 21 environmental studies. In: Proceedings of IAQ'88 Engineering Solutions to Indoor Air Problems. Atlanta, GA: ASHRAE. pp. 10-24. Morey PR. 1994. Suggested guidance on prevention of microbial contamination for the next revision of ASHRAE Standard 62, In: Proceedings of IAQ'94- Engineering Indoor Environments. Atlanta, GA: ASHRAE, pp. 139-148. Morey PR, Williams CM. 1991. Is porous insulation inside an HVAC system compatible with a healthy building? In: Proceedings of IAQ'91 Healthy Buildings. Atlanta, GA: ASHRAE, pp. 128-135. Murry DM, Burmaster DE. 1995. Residential air exchange rates in the United States: empirical and estimated parametric distributions by seasonal and climatic region. Risk Analysis 15~4~:459-465. Nagda N. Koontz M, Lumby D, Albrecht R. Rizzuto J. 1990. Impact of increased ventilation rates on office building air quality. Proceedings of Indoor Air 90(4):281-286. Nazaroff WW, Gadgil AG, Weschler CJ. 1993. Critique of the Use of Deposition Velocity in Modeling Indoor Air Quality. ASMM Standard Technical Publication 1205. Philadelphia, PA: American Society for Testing and Materials, pp. 81-104. Nelson HS, Hirsch SR, Ohman JL, Platts-Mills TAE, Reed CE, Solomon WR. 1988. Recommendations for the use of residential air-cleaning devices in the treatment of allergic respiratory diseases. Journal of Allergy and Clinical Immunology 82~4~:661-669. Nelson T. Rappaport BZ, Walker WH.1933. The effect of air filtration in hay fever and pollen asthma: further studies. Journal of the American Medical Association 100:1385. Offermann FJ, Hollowell CD, Nazaroff WW, Roseme GD, Rizzuto JR. 1982. Low infiltration housing in Rochester New York: a study of air exchange rates and indoor air quality. Environment International 8:435-445. Offermann FJ, Loiselle SA, Sextro RG. 1991. Performance comparisons of six different air cleaners installed in a residential forced air ventilation system. Proceedings of IAQ'91. Atlanta, GA: ASHRAE. pp. 342-350 Orme M. 1998. Energy impact of ventilation. Technical Note 49. Coventry, Great Britain: International Energy Agency Air Infiltration and Ventilation Centre. Ozkaynak H. Xue J. Spengler J. Wallace L, Pellizzari E, Jenkins P. 1996. Personal exposure to airborne particles and metals: results from the Particle TEAM Study in Riverside, California. Journal of Exposure Analysis and Environmental Epidemiology 6~1~:57-78. Pasanen PO, Pasanen AL, Kalliokoski P. 1995. Hygienic aspects of processing oil residues in ventilation ducts. Indoor Air 5~1~:62-68.

OCR for page 327
IMPACT OF VENTILATION AND AIR CLEANING ON ASTHMA 391 Pehkonen E, Rantio-Lehtimaki A. 1994. Variations in airborne pollen antigenic particles caused by meteorologic factors. Allergy 49~6~:472-477. Pejtersen J. 1996. Sensory pollution and microbial contamination of ventilation filters. Indoor Air 6~4~:239-248. Persily AK. 1999. Myths about building envelopes. ASHRAE Journal 41~3~:39-47. Persily AK, Grot RA. 1985. Ventilation measurements in large office buildings. ASHRAE Transactions 91~2A):488-502. Persily A, Norford L. 1987. Simultaneous measurements of infiltration and intake in an office building. ASHRAE Transactions 93~2~:42-56. Platts-Mills TA, Heymann PW, Longbottom JL, Wilkins SR. 1986. Airborne allergen associated with asthma: particle sizes carrying dust mite and rat allergens measured with a cascade impactor. Journal of Allergy and Clinical Immunology 77~6~:850-857. Rantio-Lehtimaki A, Viander M, Koivikko A. 1994. Airborne birch pollen antigens in different particle sizes. Clinical and Experimental Allergy 24~1~:23-28. Rappaport BZ, Nelson T. Walker WH. 1932. Effect of air filtration in hay fever and pollen asthma. Journal of the American Medical Association 98:1861. Reisman RE, Mauriello PM, Davis GB, Georgitis JW, DeMasi JM. 1990. A double blind study of the effectiveness of a high-efficiency particulate air (HEPA) filter in the treatment of patients with potential allergic rhinitis and asthma. Journal of Allergy and Clinical Immunology 85~6~:1050-1057. Roberson JA, Brown RE, Koomey JG, Greenberg SE. 1998. Recommended Ventilation Strategies for Energy Efficient Homes. LBNL-40398, Lawrence Berkeley National Laboratory, Berkeley, CA. Schappi GF, Suphioglu C, Taylor PE, Knox RB. 1997. Concentrations of the major birch tree allergen Bet v 1 in pollen and respirable fine particles in the atmosphere. Journal of Allergy and Clinical Immunology 100~5~:656-661. Scherr MS, Peck LW. 1977. The effects of high efficiency air filtration system on nighttime asthma attacks. West Virginia Medical Journal 73~7~:144-148. Seppanen O. 1998. Ventilation strategies for good indoor air quality and energy efficiency. In: Proceedings of IAQ and Energy 98 Using ASHRAE Standards 62 and 90.1. Atlanta, GA: ASHRAE, pp. 257-276. Seppanen O. Fisk WJ, Mendell MJ. 1999. Association of ventilation rates and CO2- concentrations with health and other responses in commercial and institutional buildings. Indoor Air 9~4~:226-252. Shapiro-Baruch I. 1993. Evaluation of Ventilation in Multifamily Dwellings. Report 93-5. Albany, NY: New York State Energy Research and Development Authority. Shaughnessy RJ, Turk B. Casey M, Harrison J. Levetin E. 1997. Use of energy recovery ventilators to provide ventilation in schools and the impact on indoor contaminants. Proceedings of Health Buildings'97 1:161-166. Shaughnessy RJ, Levetin E, Rogers C. 1998. The effects of UV-C on biological contamination of AHUs in a commercial office building: Preliminary Results. In: Proceedings of IAQ and Energy 98 Using ASHRAE Standards 62 and 90.1. Atlanta, GA: ASHRAE, pp. 229-236.

OCR for page 327
392 CLEARING THE AIR Sherman MH, Dickerhoff D. 1994. Air-tightness of U.S. dwellings. Proceedings of the 15th AIVC Conference The Role of Ventilation. Coventry, Great Britain.: Air Infiltration and Ventilation Centre, pp. 226-234. Sherman MH, Matson N. 1997. Residential ventilation and energy characteristics. ASHRAE Transactions 103~1~:717-730. Spieksma FT, Kramps JA, van der Linden AC, Nikkels BH, Plomp A, Koerten HK, Dijkman JH. 1990. Evidence of grass-pollen allergenic activity in the smaller micronic atmospheric aerosol fraction. Clinical and Experimental Allergy 20~3~:273-280. Spieksma FT, Kramps JA, Plomp A, Koerten HK. 1991. Grass pollen allergen carried by the smaller micronic aerosol fraction. Grana 30:98-101. Stymne H. Eliasson A. 1991. A new passive tracer gas technique for ventilation measurements. Proceedings of the 12th AIVC Conference: Air Movement and Ventilation Control Within Buildings 3:1-18. Teijonsalo J. Jaakkola JJK, Sepannen O. 1996. The Helsinki Office Environment Study: air change in mechanically ventilated buildings. Indoor Air 6~2~:111- 117. Thatcher TL, Layton DW. 1995. Deposition, resuspension, and penetration of particles within a residence. Atmospheric Environment 29~13~:1487-1497. Trasoff A, Blumstein G. 1936. The value of air-conditioned room in the treatment of seasonal and perennial asthma. Journal of Laboratory and Clinical Medicine 22:147-150. Tsubata R. Sakaguchi M, Yoshizawa S. 1996. Particle size of indoor airborne mite allergens (Der p 1 and Derf 1~. Proceedings of Indoor Air '96 3:155-160. Turk BH, Brown JT, Geisling-Sobotka K, Froelich DA, Grimsrud DT, Harrison J. Koonce JF, Prill RJ, Revzan KL. 1987a. Indoor Air Quality and Ventilation Measurements in 38 Pacific Northwest Commercial Buildings, Volume 1: Measurement Results and Interpretation, LBL-22315 i/:, Lawrence Berkeley National Laboratory, Berkeley, CA. Turk BH, Grimsrud DT, Harrison J. Prill RJ. 1987b. A Comparison of Indoor Air Quality in Conventional and Model Conservation Standard New Homes in the Pacific Northwest: Final Report. LBNL-23429, Lawrence Berkeley National Laboratory, Berkeley, CA. Turk BH, Grimsrud DT, Brown JT, Geisling-Sobotka KL, Harrison J. Prill RJ. 1989. Commercial building ventilation rates and particle concentrations. ASHRAE Transactions 95~1~:422-433. Turk B. Powell G. Casey M, Fisher E, Ligman B. Marquez A, Harrison J. Hopper R. Brennan T. Shaughnessy R. 1997. Impact of ventilation modifications on indoor air quality characteristics at an elementary school. Proceedings of Healthy Buildings '971:155-160. U.S. Department of Commerce. 1997. Statistical Abstract of the United States 1997, Washington, DC. U.S. EPA. 1999. Ozone Generators That Are Sold as Air Cleaners. URL: http:// www.epa.gov/iaq/pubs/ozonegen.html. Accessed September 6,1999.

OCR for page 327
IMPACT OF VENTILATION AND AIR CLEANING ON ASTHMA 393 van der Heide S. Kauffman HE, Dubois AEJ, de Monchy JGR. 1997. Allergen reduction measures in houses of allergic asthmatic patients: effect of air- cleaners and allergen-impermeable mattress covers. European Respiratory Journal 10~6~:1217-1223. Vaughan WT, Cooley LE. 1933. Air conditioning as a means of cleaning pollen and other particulate matter and of relieving pollinosis. Journal of Allergy 5:37-44. Verall B. Muir DC, Wilson WM, Milner R. Johnston M, Dolovich J. 1988. Laminar flow air cleaner bed attachment: a controlled trial. Annals of Allergy 61~2~:117- 122. Villaveces JW, Rosengren H. Evans J. 1977. Use of laminar flow portable filter in asthmatic children. Annals of Allergy 38~6~:400-404. Viner AS, Lawless PA, Ensor DS, Sparks LE. 1989. Ozone emissions from electronic air cleaners. Paper 89-84.1, presented at the 82nd Annual Meeting of the Air and Waste Management Association, Anaheim, CA. Warburton CJ, Niven RM, Pickering CAC, Fletcher AM, Hepworth J. Francis HC. 1994. Domiciliary air filtration units, symptoms and lung function in atopic asthmatics. Respiratory Medicine 88~10~:771-776. Warner JA, Marchant JL, Warner JO. 1993. Double-blind trial of ionizers in children with asthma sensitive to the house dust mite. Thorax 48~4~:330-333. Wickman M, Emenius G. Egmar AC, Axelsson G. Pershagen G. 1994. Reduced mite allergen levels in dwellings with mechanical exhaust and supply ventilation. Clinical and Experimental Allergy 24~2~:109-114. Wood RA, Johnson EF, Van Natta ML, Chen PH, Eggleston PA. 1998. A placebo- controlled trial of a HEPA air cleaner in the treatment of cat allergy. American Journal of Respiratory and Critical Care Medicine 158~1~:115-120. Zwemer RJ, Karibo J. 1973. Use of a laminar flow device as adjunct to standard environmental control measures in symptomatic asthmatic children. Annals of Allergy 31~6~:284-290.