Carbon Monoxide

Carbonic Oxide, Flue Gas, CO Carbon Oxide
Chemical reference number (CAS): 630-08-0

Carbon monoxide (CO) is an odorless, colorless gas. It’s formed during incomplete burning of fuels, such as gasoline, kerosene, natural gas, oil, coal, or wood. Carbon monoxide is also found in cigarette smoke and vehicle exhaust. In homes, carbon monoxide can quickly build up from a poorly vented or malfunctioning heater, furnace, range or any fuel-powered appliance, or from a car left idling in a garage.

Carbon monoxide is the most common cause of fatal poisonings. Wisconsin State Law now requires carbon monoxide (CO) detectors in all residences in Wisconsin.

Take Action

Take immediate action if your CO detector sounds or if you have headaches, fatigue, dizziness, shortness of breath, nausea, and/or confusion.

Get fresh air immediately. Call your local fire department and move everyone outdoors into fresh air.

Do not re-enter the building until it has been inspected and declared safe.

Exposure Information


People can be exposed to dangerous levels of CO when charcoal, gas, oil, or wood are burned in poorly ventilated areas. Breathing automobile exhaust in a closed area can also result in CO poisoning.

Gas-fueled furnaces and water heaters can produce dangerous CO levels if they are malfunctioning. Common situations for CO poisoning include using gasoline powered generators indoors, idling automobiles in enclosed garages, using propane heaters indoors, and allowing children to ride inside enclosed truck beds. Smoke from tobacco products and wood fires also contains carbon monoxide.

About 50% of all CO poisonings occur in the home. Other common settings include cars, cabins, and tents. About 40% of CO poisonings are automobile-related and 10% occur at worksites. Work exposure is more likely where fuel-powered engines are used in enclosed areas.

How can I avoid exposure?
  • Review this carbon monoxide prevention fact sheet.
  • Have your furnace, gas stove, and fireplace checked annually by a qualified professional. Have the professional check for proper ventilation and function.
  • All homes must be equipped with carbon monoxide detectors. Carbon monoxide detectors function similarly to smoke detectors and are available at most hardware stores.
  • Make sure the exhaust system on your automobile is in good working condition.
  • Do not ride inside campers or trailers that are being towed by another vehicle.
  • Never run an engine in an enclosed space, such as a garage. This includes cars, snowmobiles, generators, and lawn mowers. Review this fact sheet on using generators safely, P-01561 (PDF, 521 KB).
  • Never use a gas oven to heat a home.
  • Never use a charcoal grill indoors.

Health Effects

Everyone's Reaction is Different

A person's reaction to chemicals depends on several things, including individual health, heredity, previous exposure to chemicals including medicines, and personal habits such as smoking or drinking. It’s also important to consider the length of exposure to the chemical, the amount of chemical exposure, and whether the chemical was inhaled, touched, or eaten.

Exposure to low levels of this odorless gas can produce a throbbing headache, dizziness, fatigue, mental confusion, and shortness of breath. Higher exposures result in severe headache, weakness, dizziness, nausea, irregular heartbeat, and unconsciousness. Occasionally, these symptoms can be mistaken for symptoms of the flu.

Exposure to very high levels of carbon monoxide can cause seizures, coma, respiratory failure, and death. Exposure during pregnancy is associated with birth defects and fetal death. In addition to the toxic effects of CO, this gas is very flammable and high concentrations may be explosive.


Carbon monoxide is removed from the body over a period of hours. Although CO levels can be measured in exhaled breath, urine, blood and other tissues, no reliable method exists to determine the level of your exposure.

Last Revised: March 12, 2018

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