An IAQ Overview

Increasing ventilation is a fundamental method to reduce concentrations of several substances of concern.

INDOOR air pollution has been present since man moved into enclosed shelters. The earliest dwellings, from caves to lean-tos, undoubtedly held some amount of pollutants, especially once fire was domesticated. In current times, indoor air quality became an issue when the 1973 oil embargo sparked a movement to improve energy efficiency by reducing airflow throughout structures. As structures became more airtight, an increasing level of gases, chemicals, and particulates merged with the ambient air. Heating, ventilating, and air-conditioning (HVAC) systems trapped and recirculated pollutants throughout structures.

The U.S. Environmental Protection Agency consistently ranks indoor air pollution as one of the top five risks to public health.1 The effect of air pollution upon occupants is a variety of maladies ranging in severity from chronic to acute. The term "Sick Building Syndrome" is used to describe the cluster of symptoms (headaches, nausea, and respiratory distress) that people develop when they are in the building but the symptoms lessen or disappear when they leave. A more serious condition known as Building Related Illness occurs when a specific environmental agent is cited as the cause of an identifiable infection or allergy.2

In the past two decades, the National Institute for Occupational Safety and Health experienced a 69 percent increase in requests to conduct air quality investigations. In the same manner as an industry was created to address the energy efficiency of structures, the identification and remediation of indoor air quality problems has been recognized as an industry.

The dramatic increase in asthma (now considered to be at epidemic levels) has been a primary reason for the IAQ investigation requests. The Centers for Disease Control and Prevention reports a 75 percent increase in asthma between 1980 and 1994 and a 160 percent increase for very young children.3 Age and socioeconomic factors are considerations; while people of all backgrounds develop asthma, the preponderance falls upon those who are young and poor. The National Academy of Sciences finds strong evidence that exposure to indoor air pollutants can cause development or a worsening of asthma. Although the development of the illness is not well understood, strong causal evidence indicates a combination of factors, including environmental exposure, is necessary.4

Homes and Indoor Air Pollution Sources
Gases and particles released by indoor pollution sources create the air quality problems encountered in homes. A lack of air exchange in modern housing is a primary reason these pollutants build to levels that affect health.

The modern home has foam sheathing, multiple windowpanes, storm doors, and airtight qualities; in contrast, older homes had much looser fittings, single panes of glass, screen doors, and air-transferring transoms over doors. Modern homes are unable to "breathe" because they get only a fraction of the air exchange of older homes. Older homes are cold and drafty, but the air quality is much healthier.

The cliché that the "solution to pollution is dilution" has great accuracy where air quality is concerned. Lower ceilings that increase pollutants by decreasing cubic air space also contribute to the problem, as do the higher temperatures and humidity of the home environment.5 An entire industry devoted to reducing utility bills has successfully done so with the unintended consequence of decreasing air quality in the home.

Combustion Sources
One of the most dangerous sources of pollution is combustion gases within the home. Regardless of the type of heating fuel utilized (gas, oil, or wood), particulates in the air result from combustion. Gas cooking stoves, furnaces, and water heaters have produced symptoms colloquially referred to as "housewife blues" resulting from low-level carbon monoxide (CO) emissions.

CO exposure symptoms are often improperly diagnosed because fatigue, nausea, and headache are similar to those of the common cold or flu. The latest year for which U.S. statistics are available lists more than 20,000 cases of CO poisoning.5 The condition of the fuel-burning appliance and the efficiency of the fuel burned largely determine the amount of pollutants emitted. Propane cook stoves have been installed with fittings for natural gas and vice versa; neither will allow the incorrect fuel to burn properly and are responsible for dangerously elevated CO levels.6 Detectors warning of CO concentrations are becoming as commonplace as smoke detectors and are credited for saving lives since their introduction.

Kerosene heaters that were ubiquitous a few years ago have fallen out of favor as the hazards associated with their use have become better known. Because they are unvented, all of the combustion byproducts become part of the ambient air and significantly increase CO concentrations, sometimes in excess of EPA air standards. Experts recommend limited use of unvented heaters, using them only with sufficient ventilation to provide a diluting effect. They also recommend a working CO detector.

The "first law" of environmental health is that if a substance is bad for critters, it is bad for people. This is proving to be especially true in the case of indoor pesticide use, which is strongly linked with childhood leukemia.7

Exposure during pregnancy and immediately after birth creates the highest risk; the risk is markedly increased from one year before birth to three years after birth. Frequency of exposure also increases the risk. While the elevated risk was noted with indoor applications, neither outdoor exposure nor herbicide use was associated with risk. The risk associated with indoor pesticide use was sufficient to suggest that timing and location of exposure were significant.

These findings are based on the Northern California Childhood Leukemia Study, which was conducted with subjects exposed to pesticides applied by professional pest control services. The authors cited a compelling need for further evaluation of the relationship between pesticides and illness, including the pesticides applied by homeowners that were not explored in their study.

A primary indoor air pollutant that has received attention is tobacco. Research continues to prove that secondhand smoke is extremely harmful, particularly for children. There are 4,700 particulates identified in tobacco smoke; carbon monoxide levels in smokers' homes are increased.

Tight construction of new homes has offset the reduction of the number of persons smoking. Tobacco smoke is cited by the American Lung Association as being responsible for the dramatic rise in childhood asthma, along with bronchitis, pneumonia, and a host of respiratory and other medical problems. Tobacco smoke also was associated with Sudden Infant Death Syndrome by an Environmental Protection Agency study. EPA and child advocacy groups have campaigns in place to reduce the number of exposed children from the currently estimated 9-12 million.8

Building materials and furnishings are a primary source of harmful gases and chemicals. Formaldehyde is a preservative and adhesive and is a component of furnishings and building materials. The products can release formaldehyde from the moment of introduction into a home and can continue to "off-gas" as they age and deteriorate.

Particleboard is especially noxious because a formaldehyde-based adhesive holds it together. New carpet and the padding installed under it can contribute to increased formaldehyde levels for up to two years.2 Other sources of formaldehyde are wood products such as cabinets, interior plywood, and laminated furniture. Floor finishes cured with an acid-based process are the worst non-wood source. Higher temperatures and humidity increase the release rate of the chemical. Formaldehyde is a strong irritant that in lower doses causes respiratory problems and mucous membrane irritation. Higher concentrations can cause serious damage to internal organs and the central nervous system, along with asthma attacks.

Individual sensitivity can vary greatly, causing serious distress for some people while hardly bothering other people in the same environment. Government action caused the problems associated with one formaldehyde emitter to lessen: The Consumer Product Safety Commission banned urea formaldehyde foam in 1982, and manufactured housing materials must meet limits set by the Department of Housing and Urban Development.1

Radon Gas
Radon is a naturally occurring radioactive element found in decaying earth and in granite rock. When found beneath homes, it can become a problem with elevated indoor levels. Radon is classified as a definite Class A carcinogen; death rates from it are difficult to determine precisely because of a lack of large-scale epidemiological studies, particularly of residences.

There are numerous difficulties associated with residential studies: People are mobile; radon levels lower with ventilation and rise as foundation cracks occur; precise levels over a period are difficult to maintain. Genetics, lifestyle (particularly tobacco use, which may combine synergistically with radon), and previous exposure to other substances are additional complicating factors when trying to determine residential exposure risk. A solid body of data documenting occupational exposure in the mining industry has caused researchers to declare the lethality of radon. Meta-analysis of existing studies has further solidified the certainty of danger. Scientists from the EPA and the National Cancer Institute estimate there are 15,000 deaths annually from radon, or about 10 percent of all lung cancer deaths.9 It is the number two cause of lung cancer in the United States.

Volatile Organic Compounds
Literally hundreds of household products are detected in measurements of indoor air. Cleaning products, paints and varnishes, hair spray, fragrances, and office equipment emit compounds that at times adversely affect health. Chlorination byproducts from public water supplies are suspected carcinogens and a cause for concern. Risk assessments for chlorine are based largely upon ingestion of cold water, but public health officials have concluded that bathing and showering are at least as great an exposure route and that overall risk is underestimated.

Organohalogen compounds that are used as flame retardants in consumer products are another concern because they can accumulate in human tissue and constitute a health threat.1 New compounds are formed by the mixing of these and may synergistically create new problems; little is known out of a lack of study.

Molds and Biologic Pollutants
In addition to the chemical and gaseous substances, biological constituents of indoor air also pose a health risk. Homes are fertile hosts for a variety of organisms shed from humans, pets, or pests. Humidity is the determining factor in the growth of fungi and dust mites, and numerous household appliances are support systems.

Humidifiers, dehumidifiers, air conditioners, and evaporative coolers popular in arid climates all contribute the moisture necessary for biological growth. EPA estimates up to half of all structures in the United States have the conditions necessary to promote the growth and accumulation of biological pollutants.

A mold that has received much attention recently is Stachybotrys. It contains toxic mycotoxins that appear to be particularly virulent to the rapidly growing lungs of young children. An unusually high percentage of pulmonary hemorrhage in pediatric cases was connected to exposure to Stachybotrys.10 Health officials are trying to increase awareness of this potentially lethal pollutant and encourage correction of conditions that promote the growth of it and other molds.

Dust mite allergy may be the most common health problem associated with indoor air quality. The symptoms produced by the allergies range from mild to life threatening and have been associated with respiratory illnesses, particularly asthma in children. As much as 10 percent of the U.S. population is allergic to dust mites.10

Monitoring household dust as a source of pollutants has shown that it is not the benign bane of housework but a serious collector of toxicants. A technique called wipe sampling reveals dust is composed of residue from cooking, cleaning, and smoking and may contain heavy metals, pesticides, and pollen brought from outdoors.

Lead dust is a greater hazard to children than paint chips because chips are large enough to be excreted while the dust is absorbed.1 Dust sampling was the initial indicator of lead in the home environment and was a catalyst in the process that ultimately removed lead from gasoline.11 Some of the compounds found in dust are known or suspected carcinogens. Studies by the National Exposure Research Laboratory in Research Triangle Park, N.C., found pesticide concentrations in carpet dust 10-100 times that of the yard soil. Exposure lasts considerably longer indoors; DDT banned in 1972 was the highest concentration of any substance in a carpet studied in 1990.1 Dust in carpets is a particular concern for young children who spend a greater amount of time at floor level.

Indoor Air Quality and Children
Children are not little adults. The scientific community's relatively recent acknowledgement that the bulk of toxicity research has been on adult subjects has led to a new emphasis on children's environmental health issues. During the past four years, research and disease prevention centers devoted to children have proliferated at medical and public health universities.12

A landmark study conducted by the National Academy of Sciences in 1993 that identified pesticides in the diets of infants and children served as a catalyst for this increased interest. There is now a body of knowledge about developmental disabilities, autism, and asthma linked to environmental exposures, and it is indisputable that neurological and developmental disabilities are linked to exposure. Because exposure can occur through skin or inhalation, children are often at the greatest risk for exposure because of the concentration of pollutants near floor level. Additionally, young children mouth toys and other objects in their environment. The bioavailability of toxins once ingested has not been researched sufficiently, and there is concern organic compounds are accumulating in human tissue with effects yet unknown. Children have a special susceptibility to damage during their early development when their organs are still maturing.1

Remediation Methods
The average person spends 90 percent of his time indoors, with 65 percent of it in his home. Indoor air pollution can cause or contribute to numerous maladies. Recognizing this fact, the National Environmental Health Association resolved to advocate for regulations, research, and resources to enhance the ability of local public health agencies to address indoor air quality. NEHA urged the development of asthma prevention and control programs and tracking of asthma morbidity and mortality rates, particularly among minority populations.

The eliminating of involuntary exposure to tobacco smoke and radon through education and legislation is another goal. Promoting best practices such as preventive maintenance, control of allergens, and integrated pest management is the essence of the association's resolution.3

Constructing new homes using a variety of materials and strategies will minimize exposure to hazards. Ventilation systems for radon gas, heating equipment that has no combustion gas byproducts, and alternative materials for cabinets and furniture are some methods employed to reduce the potential for harm. However, given that most people do not live in custom-built houses, there are other strategies to prevent adverse effects:

  • Service gas-fired heating appliances annually to ensure proper combustion.
  • Qualified service personnel should vacuum ductwork.
  • Use gas stoves only with an operating exhaust fan and avoid ventless heating systems.
  • Carbon monoxide detectors are the best protection against poisoning and should be installed in every home with gas-fired appliances.1

Radon is of sufficient concern that the EPA recommends that anyone living below the third floor of a dwelling have it tested for radon, either professionally or by using a store-bought kit. Levels are prone to fluctuation, so a long term process is recommended, usually 90 days. When radon levels are sufficient to cause concern, the strategies are to seal the floor from the crawl space, to depressurize that space with vents and fans, and to provide better ventilation for the living area. In Scandinavian countries where decaying granite creates a radon problem, increasing ventilation in living areas has been a successful remediation technique.

Volatile organic compounds (VOCs) can be reduced if not eliminated by restricting the use of scents, hair sprays, and household rug and oven cleaners. There are less-toxic counterparts for numerous consumer products that emit VOCs, and substitution is a standard recommendation from indoor air quality and environmental health specialists.1

The most effective way to keep formaldehyde levels low is to select products with minimal formaldehyde content, especially when building and remodeling homes. Sealants and varnishes can reduce the amount of formaldehyde that escapes from home construction materials and fixtures. Using mechanical equipment to control temperature and humidity will help reduce levels by slowing the release of the gas.1 Increasing ventilation is a fundamental method to reduce concentrations.

The molds and mildew that contribute to the misery of allergy sufferers and may cause more serious ailments can be controlled by reducing moisture levels. 2 Ventilation in the kitchen and bathroom and the venting of clothes dryers to the outside reduce moisture. Any leaks in the exterior of the house or in the plumbing within should be repaired immediately, and drip pans from HVAC systems should be cleaned regularly. Furniture, draperies, and carpets that have become wet should be discarded because the combination of mold spores and moisture make it impossible to eliminate mold and mildew from these items.1

Biological agents, pesticides, and heavy metals that have accumulated in carpeting can be reduced by vacuuming, although the usual household cleaning strategies and appliances may not appreciably reduce levels. Indoor air quality can be achieved using High Efficiency Particulate Accumulator (HEPA) filters on vacuums and ductwork, providing the air handler is of sufficient strength to draw air through. Hot water extraction methods of carpet cleaning will remove deeply imbedded pollutants, and the use of damp dusting and floor-cleaning methods will prevent others from becoming airborne. Low-tech items such as interior doormats will prevent particles from entering the house.13

Responsibility for indoor air quality lies primarily with the occupants of a dwelling. Federal laws such as the Clean Air Act affect outdoor air quality. The strategies provided in this overview are the current recommended mitigation methods; the sources provided in the bibliography offer additional information. Government agencies such as the Environmental Protection Agency and the Consumer Product Safety Commission, along with private organizations such as The Health House Institute, also will provide useful information.

Whether or not inhabitants are affected by symptoms of poor indoor air quality, they are well advised to keep the air in their dwellings as clean as possible because cumulative effect studies are still scarce. Prevention is always the recommended public health approach.

1. A Healthy Home Environment? Manuel, John, Environmental Health Perspectives 00916765, July 1999, Vol. 107, Issue 7.
2. Baltimore Resource Journal, Vol. 9, No. 2, Summer 1995, Baltimore, Maryland.
3. 2000 resolutions Adopted By The National Environmental Health Association, Journal of Environmental Health, Dec. 2000, Volume 63, Issue 5.
4. Applied Occupational and Environmental Hygiene Volume 16(2): 102, 2001.
6. Patton, Molly. A Study of CO levels in Rural Alaska, Indian Health Service Fellowship Project, 2001.
7. Critical Windows of Exposure to Household Pesticides and Risk of Childhood Leukemia. Environmental Health Perspectives, Volume 110, Number 9, September 2002.
10. Indoor Air Pollution--An Introduction for Health Professionals. U.S. Environmental Protection Agency publication.
11. Dust: A Metric for Use in Residential and Building Exposure Assessment and Source Characterization. Environmental Health Perspectives, Volume 110, Number 10, October 2002.
12. Environmental Health Perspectives and Children's Environmental Health. Environmental Health Perspectives, Volume 110, Number 10, October 2002.
13. Indoor Air, Research Triangle Institute, December 1997.

This article originally appeared in the October 2004 issue of Occupational Health & Safety.

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