Combustion By-products

General Information:

Combustion byproducts are produced whenever carbon-based fuels such as gas, oil, kerosene, wood, or charcoal are burned and are also produced by tobacco smoking. The major pollutants released during combustion are carbon monoxide, nitrogen dioxide, sulfur dioxide and particulates. Carbon monoxide is an odorless, colorless, tasteless, and nonirritating gas that can be deadly.

Combustion byproducts enter buildings and homes directly from the use of unvented kerosene and gas space heaters, gas fireplaces, gas stoves, indoor use of charcoal or gas grills. They also can enter and accumulate as a result of poorly ventilated appliances, and from cars idling in attached garages. Combustion gases and particles can get into buildings and homes from chimneys and flues that are improperly installed or maintained and cracked furnace heat exchangers. Pollutants from fireplaces, woodstoves, even furnaces with no dedicated outdoor air supply can be “back drafted” from the chimney into the living space, particularly in weatherized homes. Unvented kerosene heaters may also generate acid aerosols.

Health Effects of Exposure to Combustion By-products

Carbon monoxide (CO) interferes with the delivery of oxygen throughout the body. An estimated 1,500 people die each year because of carbon monoxide poisoning and thousands of others end up in hospital emergency rooms. At high concentrations it can cause unconsciousness and death within minutes. Lower concentrations can cause a range of symptoms from headaches, dizziness, weakness, nausea, confusion, and disorientation, to fatigue in healthy people and episodes of increased chest pain in people with chronic heart disease. The symptoms of carbon monoxide poisoning are sometimes confused with the flu or food poisoning. Fetuses, infants, elderly people, and people with anemia or with a history of heart or respiratory disease can be especially sensitive to carbon monoxide exposures.

Nitrogen dioxide (NO2) is a colorless, odorless gas that irritates the mucous membranes in the eye, nose, and throat and causes shortness of breath after exposure to high concentrations. There is evidence that high concentrations or continued exposure to low levels of nitrogen dioxide increase the risk of respiratory infection; there is also evidence from animal studies that repeated exposures to elevated nitrogen dioxide levels may lead, or contribute, to the development of lung disease such as emphysema. People at particular risk from exposure to nitrogen dioxide include children and individuals with asthma and other respiratory diseases.

Particles, released when fuels are incompletely burned, can lodge in the lungs and irritate or damage lung tissue. A number of pollutants, including radon and benzo(a)pyrene, both of which can cause cancer, attach to small particles that are inhaled and then carried deep into the lung.

Water vapor also results from unvented or improperly vented combustion appliances. This can lead to excessive humidity levels inside and encourage the growth of mold on building materials.

Testing for Carbon Monoxide

Carbon monoxide sensors/alarms are now widely available at retail outlets. Make sure to purchase a high-quality unit and follow the manufacturer’s instructions for installation and placement.


  • Make sure all combustion appliances are performing as intended and are in proper working order. Have boilers, furnaces, ductwork, oil or gas-fired water heaters, flues, and chimneys, inspected annually and promptly repair cracks or damaged parts.
  • Take special precautions when operating fuel-burning unvented space heaters (kerosene or gas). A persistent, yellow-tipped flame is generally an indicator of maladjustment and increased pollutant emissions. While a fuel-burning unvented space heater is in use, open a door from the room where the heater is located to the rest of the house and open a window slightly.
  • When operating exhaust fans or using a clothes dryer, make sure woodstove and furnace chimneys do not backdraft, allowing combustion gases into the home.
  • Install and use exhaust fans over gas cooking stoves and ranges and keep the burners properly adjusted.
  • Ask your gas company to adjust the burner so that the flame tip is blue. If you purchase a new gas stove or range, consider buying one with pilotless ignition because it does not have a pilot light that burns continuously.
  • Never use a gas stove to heat your home. Always make certain the flue in your gas fireplace is open when the fireplace is in use.
  • If you suspect or know that combustion gases have entered the building, open doors and windows, turn off combustion appliances, and leave the building.
  • If symptoms of CO poisoning are evident or you suspect CO poisoning, evacuate first. Call the Maine Poison Center at 1-800-442-6305 (TTY 1-877-299-4447) or your physician.

Maine Resources for Combustion By-products


The Maine Poison Center can provide information about CO. Call 1-800-442-6305 (TTY 1-877-299-4447).

Web Links

EPA Publications:

U.S. Consumer Product Safety Commission. “The Senseless Killer”. 1993. GPO Publication No. 1993-0-356-764.

Maine Links: