Carbon Monoxide and Nitrogen Dioxide

Alex Manning, Clean Air Advice
June 2006

Carbon Monoxide and Nitrogen Dioxide are colorless odorless gases that can lead to poor indoor air quality and a wide range of health effects. The main sources of these gases indoors are combustion processes. Kerosene and gas space heaters; chimneys and furnaces; gas water heaters, stoves and fireplaces; gasoline powered equipment; car exhaust from attached garages; and Environmental Tobacco Smoke are all common sources.

There are a number of health risks associated with Carbon Monoxide exposure. At low concentrations symptoms may include fatigue and chest pain. Higher concentrations may induce effects such as impaired vision and coordination, headaches, dizziness, confusion and nausea. Symptoms can be commonly mistaken for the flu, but will greatly improve after leaving the problematic area. Very high concentrations of Carbon Monoxide pose a serious problem and can lead to death by restricting the body's ability to intake and distribute oxygen properly.

Nitrogen Dioxide can cause irritation to the mucus membranes of the eyes, nose and throat. At low concentrations of exposure, symptoms may be increased sensitivity in asthmatics; impaired lung functions; and increased risk of respiratory infections, especially in children. Consistent exposure to high levels may result in the development of acute or chronic bronchitis. Exposure to extremely high concentrations, such as a building fire, can cause pulmonary edema and lung injury.

There are no set standards for indoor air quality pertaining to levels of either Carbon Monoxide or Nitrogen Dioxide. Average indoor levels of Carbon Monoxide range from 0.5 to 5 parts per million (ppm) in homes without gas stoves to under 15ppm in homes with properly adjusted gas stoves to over 30ppm in homes with poorly adjusted gas stoves. The U.S. National Ambient Air Quality Standards for outdoor air have been set at 9ppm over an 8-hour period.

Average indoor levels of Nitrogen Dioxide are around half the average outdoor concentration in homes without gas stoves and other combustion appliances. Homes with combustion appliances may have concentration levels that exceed average outdoor levels. The U.S. National Ambient Air Quality Standards have set the average 24-hour limit for outdoor air as 0.053ppm for Nitrogen Dioxide.

There are several ways in which you can improve the indoor air quality of your home and protect yourself and your family from the dangers of Carbon Monoxide and Nitrogen Dioxide. The first and most important step is to install a Carbon Monoxide detector in your home, preferably near sleeping areas. This will warn you if concentrations reach dangerous levels. Other ways to help keep concentrations of Carbon Monoxide and Nitrogen Dioxide to a minimum include keeping combustion appliances properly adjusted; using only vented space heaters; making sure stoves have exhaust fans that vent directly outdoors; opening flues when using the fireplace; having a trained professional annually inspect and repair furnaces, flues and chimneys; and never leaving your car running in the garage.

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