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Indoor Air Pollution

Indoor air can become polluted if contaminants accumulate inside buildings. Common contaminant groups include dusts (particulates), vapors and gasses, as well as biological agents. Some indoor contaminants occur naturally, but most are generated by materials or activities in or around the building. Certain indoor air pollutants, such as asbestos, formaldehyde, carbon monoxide, and lead, cause great health risks to individuals. Indoor air pollution can occur in any type of building, including homes, offices, and schools.

Incomplete or inadequately controlled combustion is a major cause of indoor air pollution world-wide. Sources of polluting combustion include fireplaces, wood stoves, kerosene heaters, natural gas stoves, furnaces, and water heaters. When these sources are worn, improperly adjusted, or inadequately vented, they burn inefficiently and produce increased levels of smoke, deadly carbon monoxide gas, and other substances. Different materials burn with different characteristics, but as a general rule, a hot blue flame indicates an adequate mix of fuel and air, while a persistent yellow-tipped flame is associated with increased pollutant emissions and need for adjustment. Routine inspection and maintenance by a qualified technician helps maximize appliance efficiency, reduce unwanted byproducts of combustion, and identify dangerous conditions that should be corrected by venting to the outdoors.

Two other products of combustion, second-hand tobacco smoke and diesel exhaust, are also frequent indoor pollutants. Second-hand tobacco smoke is associated with increased number and severity of asthma attacks in children. Diesel exhaust, which is also associated with increases in respiratory disorders, can enter buildings when vehicles idle near windows and air intakes. The problem is particularly severe when the building ventilation system air intake is located near a busy loading dock or an electrical power generator that runs on diesel fuel. Where this condition exists, building owners may request that drivers turn off their engines while making deliveries, the loading area can be relocated, or the building air intake duct can be extended or routed away from the source of contamination.

Paint, cleaning products, and other household chemicals can also produce unacceptable levels of indoor air pollution. Components of these substances are released during normal use and also if containers leak or are not closed tightly in storage. Because containers can deteriorate, leak, and contribute to indoor pollution over time, limit stored supplies to that which will be used in a reasonable amount of time. Properly dispose of aging containers and excess or unused products.

Certain building materials also contribute to indoor air pollution under some circumstances. Common construction materials that are associated with indoor pollution include asbestos insulation, formaldehyde resin pressed wood products, lead paint, and certain volatile organic compounds, such as those associated with some carpets.

Naturally occurring radon gas, molds that grow on wet or damp building materials, and dust mites can pose health hazards if they are allowed to increase indoors. Radon gas is gradually formed below ground in some types of geological formations and rises up through soil. The gas enters buildings through cracks in the foundation or basement and accumulates in areas with poor air circulation. Adding fans to increase air exchange usually prevents this radioactive gas from building up in occupied spaces. Mold spores and other parts can trigger asthma and allergies if they become airborne. Active mold growth is best controlled by keeping building surfaces dry. This is particularly challenging in hot, humid environments where moisture in air condenses on cool building surfaces. Mold management typically involves construction, maintenance, insulation, and ventilation combined. Dust mites are also associated with asthma and allergy symptoms. Structures (body parts) of these very small organisms can become airborne and constitute another component of indoor air pollution in dusty environments.

Regardless of the pollutant or its source, modern energy-efficient building practices have inadvertently increased the problem by increasing the extent to which the building is sealed from the outdoor environment. With less air leaks in and out of the building, more heated or cooled air is retained, but so are the indoor air pollutants. Building owners and occupants find that the best way to minimize air pollution in these buildings is by reducing the amount of polluting sources (for example by purchasing furnishings that give off lower levels of volatile organic compounds), taking steps to keep ventilation systems operating effectively or improve venting when necessary, and improving routine maintenance and venting of equipment and appliances that can contribute air contaminants.

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