Combustion Pollutants

What combustion pollutants are
Where combustion pollutants are found
Health problems caused by combustion pollutants
Decreasing exposure to combustion pollutants

What Combustion Pollutants Are 

Combustion pollutants often come from appliances that burn fuels such as gasoline, natural gas, liquefied petroleum (LP), kerosene, oil; coal, charcoal, and wood. Examples of appliances are space heaters, boilers, stoves and ovens, furnaces, fireplaces, water heaters, and clothes dryers. These appliances are usually safe. However, under certain conditions, these appliances can produce combustion pollutants that can damage your health, or even kill you. Tobacco smoke and fireplaces are also major sources of combustion pollutants. The most common combustion pollutants are carbon monoxide, nitrogen oxides, sulfur dioxide, particulates, and polycyclic aromatic hydrocarbons (PAHs), which are organic particles and gases.

Carbon monoxide is a colorless, odorless gas produced by incomplete combustion of fuels. Nitrogen oxide, nitrogen dioxide, and sulfur dioxide are also gases formed during combustion. Unvented kerosene heaters may also generate acid aerosols. PAHs have been found stuck to tiny soot particles found in car exhaust. One study showed that a home's level of PAHs also rise when residents fry, sauté or broil food; and when they burn candles. The pollutants, which aren't found in the food itself, are produced by fuel use and, during frying, by the burning of hot cooking oil.¹

Where Combustion Pollutants are Found

• In outdoor air. Outdoor air that contains high levels of combustion pollutants can contaminate indoor air. Nearby wood stoves and fireplaces, motor vehicle traffic, outdoor barbecues, and gasoline-powered lawn and garden equipment pollute the outdoor air that flows into your house.

• In house dust and soil. Particles and PAHs stick to house dust and soil that is tracked into the house. These pollutants can be inhaled when house dust is stirred up; some can also be absorbed through the skin or swallowed through hand-to-mouth contact. This is most likely to happen with young children, who are often on the floor.

• In environmental tobacco smoke.

• From some hobby activities such as welding, woodburning and soldering.

• From the burning of candles and incense.

• In emissions from vented or unvented combustion appliances. Vented appliances are appliances designed to be used with a duct, chimney, pipe, or other device that carry the combustion pollutants outside the home. Unvented appliances do not vent to the outside, so they release combustion pollutants directly into the home. These appliances include space heaters, gas ranges and ovens, furnaces, gas water heaters, gas clothes dryers, wood or coal-burning stoves, and fireplaces. As a group, these are called "combustion appliances."

• From wood stoves. In one study researchers found that those who used woodburning stoves for heating were more likely to have respiratory illnesses than households who used other sources of heating.² Another study reported that infants exposed to woodsmoke were more likely to have asthma symptoms.³

• In chimneys and flues that are improperly installed or maintained and cracked furnace heat exchangers.

• Fireplaces and wood stoves with no dedicated outdoor ventilation; the air supply can be "back-drafted" from the chimney into the living space, particularly in weatherized homes.

Another problem with combustion is that it always produces water vapor. Though water vapor itself is not a pollutant, it can result in high humidity and wet surfaces that encourage the growth of biological pollutants such as dust mites, molds, and bacteria.

Health Problems Associated With Combustion Pollutants

There are many factors that determine if one might get sick due to exposure to combustion pollutants. These include:

• The concentration and amount of combustion pollutants in the air.

• Personal characteristics such as age, gender, weight, general health status. People with allergies, asthma, or chronic respiratory or heart problems are particularly susceptible to health effects from combustion pollutants. It is important to note, though, that these health effects can have many other causes as well.

• To what type of combustion pollutants is a person exposed? Are there also other chemical exposures? For example, polycyclic aromatic hydrocarbons (PAHs) are a particular concern since they may cause lung, stomach, bladder, or skin cancer.

• How long is one exposed to combustion pollutants? The longer the exposure, the more at risk one is.

Health effects from exposure to combustion pollutants vary from very mild to lethal. Typical health effects are:

• Headaches

• Dizziness

• Confusion

• Sleepiness

• Nausea/vomiting

• Fatigue

• Irritated eyes

• Fast heart rate (tachycardia)

• Breathing difficulties

• Respiratory problems  such as coughing and wheezing

Decreasing Exposure to Combustion Pollutants

• Only buy combustion appliances that have been tested and certified to meet current safety standards. Examples of certifying organizations include Underwriters Laboratories (UL), CSA International in addition to several other laboratories in North America, Europe and Asia. Look for the Blue Star and Blue Flame labels, whlich conform to applicable US and Canadian standards for safety and performance.

• Read and follow all of the instructions that accompany any fuel-burning device.

• Choose "sealed combustion" or "direct vent" gas appliances, with their exhaust vents and air supplies completely sealed from the indoors, to keep combustion pollutants from entering the home. You may want to consider using other alternatives such as new, high-efficiency electric appliances or solar heating systems.

• Use pilotless (electronic) ignition on gas appliances. These appliances are usually more energy efficient and eliminate the continuous low-level pollutants from pilot lights.

• Install and use an exhaust fan vented to outdoors over gas stoves. Remove and clean the metal mesh filters on your range hoods with detergent when they begin to look grimy (most can be put in the dishwasher). "Ductless" range hoods are not effective because they exhaust into the house rather than outside; add a duct or replace the hood with one vented to the outside (ducted).

• Buy appliances that are the correct size for the area you want to heat. Using the wrong size heater may produce more pollutants in your home and is not an efficient use of energy. Talk to your dealer to determine the type and size of appliance you will need. You may wish to write to the appliance manufacturer or association for more information on the appliance.

• Choose vented appliances whenever possible.

• Before considering using an unvented space heater, check with your local and state building codes and fire ordinances. These types of unvented heaters are not allowed to be used in some communities, dwellings, or certain rooms in the house.

• Choose appliances, such as gas dryers, that vent their fumes to the outside. Have them properly installed and maintain according to the manufacturer's instructions.

• Never disconnect vents on combustion appliances, even if it seems like a way to get extra heat in the winter

• Never sleep in any room with an unvented gas or kerosene space heater.

• Keep tobacco smoke (ETS) out of your home and away from open doors or windows. Environmental tobacco smoke can increase the chance of lung cancer in nonsmokers. Children, pregnant women, or persons with lung or heart disease are especially sensitive to smoke.

• Clean the house frequently to remove house dust particles, especially if there are children or pets running in and out of the house. Vacuum rugs and furniture with a vacuum cleaner that has a very efficient air filter and damp mop the floors.

• Have people use doormats and leave their shoes by the door to help keep indoor particle levels down.

• Never idle the car in a garage?even if the garage door to the outside is open. Exhaust vapors can build up very quickly in the garage and living area of your home.

• Seal off the house from the garage to prevent car exhaust as well as other toxic emissions from leaking into the house. Hire a contractor to spray the dense expanding-foam product Icynene into stud cavities in the wall shared by the house and garage.

• Keep cars well tuned to reduce the amount of PAHs coming out of your car's tailpipe. A badly tuned car burns fuel inefficiently, and that creates higher amounts of PAHs.¹

• Have a trained professional inspect your fuel-burning appliances, including oil and gas furnaces, gas water heaters, gas ranges and ovens, gas dryers, gas or kerosene space heaters, fireplaces, and wood stoves, at the beginning of every heating season. The central heating system (furnaces, flues, and chimneys) should also be inspected, cleaned, and tuned-up annually.

• Install combustion appliances away from the home's living area (such as living room and bedrooms).

• Make sure any space heater you use is a new one. Heaters made after 1982 have a pilot light safety system called an oxygen depletion sensor (ODS). This system shuts off the heater when there is not enough fresh air and the heater is beginning to produce large amounts of carbon monoxide. Look for the label that tells you that the appliance has this safety system. Older heaters will not have this protection system.

• NEVER use a gas oven to heat your home even for a short time, and do not ever use a charcoal grill or hibachi indoors even in a fireplace or garage. This also applies to tents and camping trailers.

• Do not use any gasoline-powered engines (mowers, weed trimmers, snow blowers, chain saws, small engines or generators) in enclosed spaces.

• Supply adequate outdoor make-up air for combustion so there will not be backdrafting into the indoor environment.

• Inspect and clean flues and chimneys regularly to make sure they are in good condition and not blocked.

• Appliances designated as supplemental or "decorative" heaters (including most unvented gas fireplaces) are not designed for continuous use. To avoid excessive exposure to pollutants, never use these appliances for more than four hours at a time. When operating unvented combustion appliances, safe practices must be carefully followed. Besides observing fire safety rules, make sure the burner is properly adjusted and there is good ventilation?never use in a closed room, keep doors open throughout the house, and open a window for fresh air.

• Use proper fuel in kerosene space heaters. Only use water-clear ASTM 1-K kerosene for kerosene heaters, otherwise you could have even more pollutants get in your home. Never use gasoline in a kerosene heater because it can cause a fire or an explosion. Using even small amounts of gasoline could cause a fire.

• Open flues when fireplaces are in use.

• If you choose to use a wood stove, make sure they are the right size that that they are certified to meet US Environmental Protection Agency emission standards. Make certain that doors on all wood stoves fit tightly.

• Use only seasoned hardwoods (elm, maple, oak) instead of softwoods (cedar, fir, pine) in fireplaces or stoves. Hardwoods are better because they burn hotter and form less creosote, an oily, black tar that sticks to chimneys and stovepipes. Do not use green or wet woods as the primary wood because they make more creosote and smoke. Never burn painted scrap wood or wood treated with preservatives, because they could release highly toxic pollutants, such as arsenic or lead. Plastics, charcoal, and colored paper such as comics, also produce pollutants. Never burn anything that the stove or fireplace manufacturer does not recommend.

• Use an air cleaner to help in removing particulates from the air.

• Upgrade your furnace filter to pleated or extended surface filters, which have a medium- or high-efficiency rating. Change this filter at least every month or two during periods of use. As a minimum, air filters with a dust spot efficiency of 30 percent are recommended.

• If your household has young children or someone with allergies or lung disease, consider using a high-efficiency air cleaner in your forced-air heating system or add a stand-alone unit. Some stand-alone air cleaners (HEPA or electrostatic types) can remove particles in a single room; some also can help remove gases. Small desktop air cleaners generally are not effective.

1. Watson T. "Pollution can sneak indoors, scientist warn..." USA Today. September 2, 1999.

2. Dockery DW, et al. An association between air pollution and mortality in six U.S. cities. N Eng J Med. 1993;329(24):1753-59.

3. Koenig JQ, et al. Pulmonary lung function in children associated with fine particulate matter. Env Res. 1993;63(1):26-38.