Carbon Monoxide (CO)

Carbon monoxide (CO) is an odorless, colorless gas formed when carbon in fuels does not burn completely. Hundreds of Americans die every year from carbon monoxide poisoning caused by improperly used or malfunctioning fuel-burning appliances. Fetuses, young children, and the elderly are particularly susceptible to carbon monoxide poisoning.

Carbon monoxide is a “combustion pollutant”—a gas (or particle) that comes from burning carbon-based materials. Combustion pollutants are most often released into the home by vented or unvented appliances and vehicles running in an attached garage. Carbon monoxide is produced when there is a lack of oxygen or enough heat to burn fuels completely. The smoldering burn of incense or cigarettes also produces carbon monoxide.

Indoor Sources of Carbon Monoxide

The main indoor cause of carbon monoxide poisoning are combustion appliances (those which burn fuels for warmth, cooking, or decorative purposes), such as furnaces, space heaters, gas ranges, gas water heaters, and fireplaces. The most serious effects of carbon monoxide in the home occur in the winter when homes are closed up more tightly. If combustion appliances are used properly and are well maintained, the amount of carbon monoxide produced is not usually hazardous to human health. However, if appliances are used incorrectly or vented improperly, the levels of carbon monoxide indoors can become dangerous.

Vented appliances are designed to be used with a pipe, chimney, duct, or other device that sends the pollutants outside the home. If a vent is blocked, leaking, or improperly installed, the appliance can release a large amount of combustion pollutants, including carbon monoxide, directly into the home. Unvented appliances do not have a pipe, chimney, or other duct to carry the pollutants outside the home, and therefore disperse carbon monoxide and other pollutants throughout the home.

Other sources of indoor carbon monoxide include: cars in attached garages, especially when the engine is being warmed up; gas stoves (with a flame that burns yellow); furnaces with cracked heat exchangers or leaking chimneys that leak gases into the ventilation system; house fires; and non-electric space heaters used indoors without enough fresh air. Outdoor sources of carbon monoxide include vehicle exhaust, industrial processes, and fuel combustion in incinerators and boilers.

Reducing Exposure to Carbon Monoxide

Properly selecting, installing, inspecting, and maintaining appliances in the home can reduce the risk of exposure to dangerous levels of carbon monoxide. Good ventilation in the home is also critical to preventing hazardous levels of carbon monoxide. Because carbon monoxide is impossible to see or smell, a carbon monoxide detector or alarm is the only way to determine one’s exposure.

Sources and Additional Information:

American Lung Association – Carbon Monoxide, February 2000 –

American Lung Association – Carbon Monoxide Fact Sheet, May 2004-

American National Standards Institute (ANSI), American Society of Heating, Refrigeration, and Air-Conditioning Engineers (ASHRAE), Ventilation for Acceptable Indoor Air Quality, Standard 62-2001, ISSN 1041-2336

Canada Department of National Health and Welfare – Exposure Guidelines for Residential Indoor Air Quality, Ottawa. April 1987.

Consumer Product Safety Commission – Carbon Monoxide Detectors Can Save Lives, Document #5010 –

Consumer Product Safety Commission – Carbon Monoxide Questions and Answers, Document #466 –

Consumer Product Safety Commission – Non-Fire Carbon Monoxide Deaths and Injuries Associated with the Use of Consumer Products, Annual Estimates, October 2000 –

Consumer Product Safety Commission, U.S. Environmental Protection Agency, and American Lung Association – What You Should Know About Combustion Appliances and Indoor Air Pollution, Document #452 –

Drs. Thom, Penn, Ischiropoulos, and Xu, University of Pennsylvania Medical Center – New Mechanism To Explain Carbon Monoxide Poisoning Identified, September 27, 1997 –

US Centers for Disease Control and Prevention – Carbon Monoxide Fact Sheet –

US Environmental Protection Agency – Sources of Indoor Air Pollution, Carbon Monoxide, February 2003 –

World Health Organization, Report on a WHO meeting, August 21-24, 1984, Indoor Air Quality Research. EURO Reports and Studies 103, Regional Office for Europe, Copenhagen, Denmark, 1986