Carbon Monoxide

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.

Health Impacts

When carbon monoxide enters the bloodstream, it reduces the amount of oxygen received by the body’s organs and tissues. Unborn babies, children, the elderly, and people with respiratory problems or heart disease are especially sensitive to carbon monoxide. Even at low levels, carbon monoxide causes serious health problems, and the longer the exposure, the more damage that occurs.

Low levels of carbon monoxide can cause flu-like symptoms, headaches, dizziness, and make it difficult to think clearly. Often a family may not realize that their illnesses are related to chronic exposure to carbon monoxide in the home.

At higher levels of exposure, carbon monoxide is related to visual impairment, reduced work capacity, poor learning ability, and difficulty in performing complex tasks. At very high levels, carbon monoxide can also kill. Each year, more than 200 Americans die accidentally from carbon monoxide poisoning in the home, unrelated to fires and engine exhaust (other sources of carbon monoxide poisoning). Seventy-six percent (76%) of these deaths are from carbon monoxide released from heating systems. Another 8% are from gas water heaters. Many victims of carbon monoxide poisoning die in their sleep. An additional 10,200 people visit the emergency room due to accidental carbon monoxide poisoning from consumer products.

Fatal exposures to carbon monoxide are highest among men and older adults because men are historically more likely to work with fuel-burning appliances and tools and seniors are more likely to assume that fatigue, headaches, nausea, dizziness, or confusion are symptoms of the flu. These are also signs of CO poisoning.


Common indoor sources of carbon monoxide are:

  • Cars in attached garages, especially when the engine is being warmed up.
  • Combustion appliances, such as gas stoves (with a flame that burns yellow), house fires, non-electric space heaters used indoors without enough fresh air, and furnaces with cracked heat exchangers or leaking chimneys that leak gases into the ventilation system.

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.

Common outdoor sources of carbon monoxide are fumes from vehicle exhaust, fuel combustion in incinerators and boilers, and various industrial processes.


Since carbon monoxide is impossible to see or smell, carbon monoxide detectors and alarms can be another key part of protecting against carbon monoxide poisoning.

The Consumer Product Safety Commission (CPSC) recommends placing carbon monoxide detectors on each level of the home and near all sleeping areas. Although the presence of a carbon monoxide detector can help identify problems, they should not be used in place of preventive efforts, nor should their silence be interpreted as unquestionable proof of the absence of carbon monoxide hazards.

The U.S. Environmental Protection Agency (EPA) states that the technology of carbon monoxide detectors is still in development and that they are not generally considered as reliable when compared to current smoke detectors. In fact, in some laboratory tests, very high levels of carbon monoxide were not detected by properly installed units. Concerns have also been raised that these alarms do not sound until the level of carbon monoxide reaches very high levels.

Despite these potential reservations, these detectors can be useful tools in assessing hazards in the home, but they should not replace preventative measures against carbon monoxide poisoning.

Reducing Exposure

Tenants, landlords, and homeowners can reduce the likelihood of hazardous carbon monoxide exposures by taking steps such as these:

  • Choose and use heating appliances wisely. Properly install, maintain, ventilate and check regularly all fuel-fired heating systems, water heaters, appliances, fireplaces, wood and coal stoves, and space heaters.
  • Always ensure proper ventilation in any room where a fuel-burning appliance of any sort is in use.
  • Do not use any gas appliance (such as a stove or range) for home heating purposes.
  • Do not burn any other type of fuel inside the home except firewood in an appropriately maintained and ventilated fireplace. This also means that grilling with charcoal briquettes indoors should be avoided.
  • Leave garage doors open while the car is running and limit the amount of time a running car is in the garage. (It is also important to note that carbon monoxide can build up inside the car itself while operating if there are leaks in the exhaust system.)

Even with precautionary measures, a situation involving high levels of carbon monoxide in the home may occur. Whether discovered by an individual experiencing symptoms or an active alarm, there are certain procedures to take if high levels of carbon monoxide are present.

  • Immediately remove anyone who is experiencing symptoms from the environment and seek medical attention.
  • Open windows and doors to ventilate the space, turn off any potential source of the carbon monoxide, and notify the landlord and/or fuel supplier.
  • Arrange for the proper inspection of all fuel-fired systems, appliances, and fireplaces and further arrange for any necessary repairs.

Carbon Monoxide Resources

American Lung Association (sitio en Español)

Carbon Monoxide Fact Sheet
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

Carbon Monoxide Headquarters – Operated by Dr. David Penney, Professor of Occupational and Environmental Health in the School of Medicine at Wayne State University, this site contains links to background information, research articles, data, and other resources focused solely on carbon monoxide.

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

U.S. Centers for Disease Control and Prevention, Carbon Monoxide Poisoning Program – This area provides a collection of documents and resources on carbon monoxide, including a fact sheet on the gas (English) (Español).

U.S. Consumer Product Safety Commission
Carbon Monoxide Questions and Answers, Document #466
Carbon Monoxide Detectors Can Save Lives, Document #5010
Non-Fire Carbon Monoxide Deaths and Injuries Associated with the Use of Consumer Products, Annual Estimates, October 2000.

U.S. Environmental Protection Agency
Indoor Air Quality — The carbon monoxide section of the EPA’s Indoor Air Quality Division contains information pertaining to sources, health effects, remediation options, and more.
Protect Your Family and Yourself from Carbon Monoxide Poisoning

Some Spanish-language carbon monoxide materials:
El medio ambiente y su salud: Monóxido de carbono en exteriores
El medio ambiente y su salud: Monóxido de carbono en interiores

General IAQ Hotline (IAQINFO): 1-800-438-4318
Sponsored by EPA, this hotline provides general information on indoor air quality and related pollutants.

Su Familia (Your Family) Helpline
The National Alliance for Hispanic Health sponsors this toll-free helpline (1-866-SU FAMILIA or 1-866-783-2645) to offer Hispanic consumers free, reliable, and confidential health information in Spanish and English and help navigate callers through the healthcare system.  |  En español: La National Alliance for Hispanic Health (Alianza Nacional para la Salud de los Hispanos) patrocina esta línea de ayuda gratuita (1-866-SU FAMILIA o 1-866-783-2645) para ofrecer a los consumidores hispanos información de salud gratuita, confiable y confidencial en español e inglés y ayudar a las personas que llaman sistema de cuidado de la salud.


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