Indoor Air Quality

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Indoor air quality

An assessment of air quality in buildings and homes based on physical and chemical monitoring of contaminants, physiological measurements, and/or psychosocial perceptions. Factors contributing to the quality of indoor air include lighting, ergonomics, thermal comfort, tobacco smoke , noise, ventilation, and psychosocial or work-organizational factors such as employee stress and satisfaction. "Sick building syndrome" (SBS) and "building-related illness" (BRI) are responses to indoor air pollution commonly described by office workers. Most symptoms are nonspecific; they progressively worsen during the week, occur more frequently in the afternoon, and disappear on the weekend.

Poor indoor air quality (IAQ) in industrial settings such as factories, coal mines, and foundries has long been recognized as a health risk to workers and has been regulated by the U.S. Occupational Safety and Health Administration (OSHA). The contaminant levels in industrial settings can be hundreds or thousands of times higher than the levels found in homes and offices. Nonetheless, indoor air quality in homes and offices has become an environmental priority in many countries, and federal IAQ legislation has been introduced in the U.S. Congress for the past several years. However, none has yet passed, and currently the U.S. Environmental Protection Agency (EPA) has no enforcement authority in this area.

Importance of IAQ

The prominence of IAQ issues has risen in part due to well-publicized incidents involving outbreaks of Legionnaires' disease, Pontiac fever, sick building syndrome , multiple chemical sensitivity , and asbestos mitigation in public buildings such as schools. Legionnaire's disease, for example, caused twenty-nine deaths in 1976 in a Philadelphia hotel due to infestation of the building's air conditioning system by a bacterium called Legionella pneumophila. This microbe affects the gastrointestinal tract, kidneys, and central nervous system. It also causes the non-fatal Pontiac fever.

IAQ is important to the general public for several reasons. First, individuals typically spend the vast majority of their time—80–90%—indoors. Second, an emphasis on energy conservation measures, such as reducing air exchange rates in ventilation systems and using more energy efficient but synthetic materials, has increased levels of air contaminants in offices and homes. New "tight" buildings have few cracks and openings so minimal fresh air enters such buildings. Low ventilation and exchange rates can increase indoor levels of carbon monoxide , nitrogen oxides , ozone , volatile organic compounds, bioaerosols , and pesticides and maintain high levels of second-hand tobacco smoke generated inside the building. Thus, many contaminants are found indoors at levels that greatly exceed outdoor levels. Third, an increasing number of synthetic chemicals—found in building materials, furnishing, cleaning and hygiene products—are used indoors. Fourth, studies show that exposure to indoor contaminants such as radon , asbestos, and tobacco smoke pose significant health risks. Fifth, poor IAQ is thought to adversely affect children's development and lower productivity in the adult population. Demands for indoor air quality investigations of "sick" and problem buildings have increased rapidly in recent years, and a large fraction of buildings are known or suspected to have IAQ problems.

Indoor contaminants

Indoor air contains many contaminants at varying but generally low concentration levels. Common contaminants include radon and radon progeny from the entry of soil gas and groundwater and from concrete and other mineral-based building materials; tobacco smoke from cigarette and pipe smoking; formaldehyde from polyurethane foam insulation and building materials; volatile organic compounds (VOCs) emitted from binders and resins in carpets, furniture, or building materials, as well as VOCs used in dry cleaning processes and as propellants and constituents of personal use and cleaning products, like hair sprays and polishes; pesticides and insecticides; carbon monoxide, nitrogen oxides, and other combustion productions from gas stoves, appliances, and vehicles; asbestos from high temperature insulation; and biological contaminants including viruses, bacteria, molds, pollen, dust mites, and indoor and outdoor biota. Many or most of these contaminants are present at low levels in all indoor environments.

The quality of indoor air can change rapidly in time and from room to room. There are many diverse sources that emit various physical and chemical forms of contaminants. Some releases are slow and continuous, such as outgassing associated with building and furniture materials, while others are nearly instantaneous, like the use of cleaners and aerosols. Many building surfaces demonstrate significant interactions with contaminants in the form of sorption-desorption processes. Building-specific variation in air exchange rates, mixing, filtration , building and furniture surfaces, and other factors alter dispersion mechanisms and contaminant lifetimes. Most buildings employ filters that can remove particles and aerosols. Filtration systems do not effectively remove very small particles and have no effect on gases, vapors, and odors. Ventilation and air exchange units designed into the heating and cooling systems of buildings are designed to diminish levels of these contaminants by dilution. In most buildings, however, ventilation systems are turned off at night after working hours, leading to an increase in contaminants through the night. Though operation and maintenance issues are estimated to cause the bulk of indoor air quality problems, deficiencies in the design of the heating, ventilating and air conditioning (HVAC) system can cause problems as well. For example, locating a building's fresh air intake near a truck loading dock will bring diesel fumes and other noxious contaminants into the building.

Health impacts

Exposures to indoor contaminants can cause a variety of health problems. Depending on the pollutant and exposure, health problems related to indoor air quality may include non-malignant respiratory effects, including mucous membrane irritation, allergic reactions, and asthma ; cardiovascular effects; infectious diseases such as Legionnaires' disease; immunologic diseases such as hypersensitivity pneumonitis; skin irritations; malignancies; neuropsychiatric effects; and other non-specific systemic effects such as lethargy, headache, and nausea. In addition indoor air contaminants such as radon, formaldehyde, asbestos, and other chemicals are suspected or known carcinogens. There is also growing concern over the possible effects of low level exposures on suppressing reproductive and growth capabilities and impacting the immune, endocrine, and nervous systems.

Solving IAQ problems

Acute indoor air quality problems can be greatly eliminated by identifying, evaluating, and controlling the sources of contaminants. IAQ control strategies include the use of higher ventilation and air exchange rates, the use of lower emission and more benign constituents in building and consumer products (including product use restriction regulations), air cleaning and filtering, and improved building practices in new construction. Radon may be reduced by inexpensive subslab ventilation systems. New buildings could implement a day of "bake-out," which heats the building to temperatures over 90°F (32°C) to drive out volatile organic compounds. Filters to remove ozone, organic compounds, and sulfur gases may be used to condition incoming and recirculated air. Copy machines and other emission sources should have special ventilation systems. Building designers, operators, contractors, maintenance personnel, and occupants are recognizing that healthy buildings result from combined and continued efforts to control emission sources, provide adequate ventilation and air cleaning, and good maintenance of building systems. Efforts toward this direction will greatly enhance indoor air quality.

[Stuart Batterman ]

RESOURCES

BOOKS

Godish, T. Indoor Air Pollution Control. Chelsea, MI: Lewis, 1989. Kay, J. G., et al. Indoor Air Pollution: Radon, Bioaerosols and VOCs. Chelsea, MI: Lewis, 1991.

Samet, J. M., and J. D. Spengler. Indoor Air Pollution: A Health Perspective. Baltimore: Johns Hopkins University Press, 1991.