Environmental Tobacco Smoke


Combustion Gases

Combustion Gases

In general combustion or burning is a chemical reaction in which a fuel combines with oxygen. When there is insufficient oxygen, burns incompletely and produces by-products of combustion. Incomplete combustion by-products of carbon-based material often have a color (red nitrogen dioxide) or an odor (aldehydes).
Toxic and other harmful products;

  • Carbon monoxide
  • Polynuclear aromatic hydrocarbons (PAHs)
  • Formaldehydes
  • Sulfur dioxide
  • Nitrogen dioxides
  • Particulates

There are a lot of combustion appliances including space heaters, gas ranges and ovens, furnaces, gas water heaters, gas clothes dryers, wood or coal-burning stoves, and fireplaces. The common fuels burned in these appliances are natural or LP gas, fuel oil, kerosene, wood, or coal.

Figure 1 Fractional distillation of crude oil

Therefore, the types and amounts of pollutants produced depend upon the type of appliance, how well the appliance is installed, maintained, and vented, and the kind of fuel it uses.

An Introduction to Indoor Air Quality (IAQ)

Combustion by-products are coming from un-vented kerosene and gas space heaters, woodstoves, fireplaces, and gas stoves. Un-vented kerosene heaters may also generate acid aerosols. Combustion gases and particles also come from chimneys and flues that are improperly installed or maintained and cracked furnace heat exchangers. Pollutants from fireplaces and woodstoves with no dedicated outdoor air supply can be "back-drafted" from the chimney into the living space, particularly in weatherized homes.

Wood-Burning Appliances

There are a large variety of wood-burning stoves. Typically, they are classified as two basic types: conventional and airtight. Conventional stoves have low combustion efficiencies, commonly in the range of 25-50 %. Combustion efficiencies in airtight exceed 50 %.

The major impact of wood appliance operation on indoor air quality is a source of particulate matters. Associated with increased particulate matter levels in homes heated with wood is an increase in carcinogenic polynuclear aromatic hydrocarbons (PAHs). For example, lowest and highest PAHs indoor concentrations from a series of measurements for a variety of wood heater types, as well as outdoor concentrations are as follows.

Figure 2 Indoor PAH concentrations (high and low 12-hr concentrations) associated with wood heater use compared to ambient level

Emission rates of pollutants are also dependent on the type of wood and the appliance used to burn it. Knight et al. measured the concentration of CO, NO and NO2 during the operation of different types of airtight and non-airtight woodstoves. Their results are shown in Table 1.

Un-vented Kerosene and Gas Space Heaters

Kerosene heaters are sold over ten million units in the United States by 1985. Kerosene heaters are of three basic designs: convective, radiant and two-stage.

Convective heaters employ a cylindrical wick and operate at relatively high combustion temperatures. Radiant heaters have a cylindrical wick whose flames extend up into a perforated metal baffle, which grows red hot, releasing infrared or radiant heat. Radiant heaters operate at a low temperature than convective ones. The two-stage heater is similar in design to the radiant type except that there is a second chamber above the radiant element. This second chamber is intended to further combust CO and unburned hydrocarbons.

The magnitude of emissions depends on heater type, heater operation parameters, and the type of fuel. The air contamination potential for both un-vented gas and kerosene space heaters is CO, CO2, NO, NO2, RSPs, SO2, and formaldehydes.

Laboratory results by Leaderer et al. are also illustrated in Figure 3.

Figure 3 Steady-state concentrations of contaminants associated with kerosene heater operation

Gas Cooking Stoves and Ovens

Gas cooking stoves and ovens are potential sources of CO, CO2, NO and NO2. They may also release aldehydes, a variety of organic gases, and RSPs. A number of experimental studies have been conducted to measure emission rates of pollutants from gas stoves and ovens. For example, their results by Hollowell et at. (1976) are shown in Table 3.

Flue Gas Spillage/Backdrafting

Under normal operating conditions, vented gas-fired forced-air furnaces and gas-fired water heaters should not result in measurable effects on indoor air quality. However, as a result of a variety of operating and climatic circumstances, substantial spillage of flue gases can occur with gas furnace, gas water heaters and wood-burning appliances. Under the extreme circumstances, such flue gas spillage and backdrafting can cause carbon monoxide poisoning.

Fig. 4 Backdrafting due to depressurization

Combustion gases in your home,
Godish, T. Indoor Air Pollution Control. Lewis Publishers, Chelsia, Michigan (1989). p.21-28.
Hines A. et al. Indoor Air Quality and Control . PTR Prentice Hall, Englewood Cliffs, New Jersey,(1993). p.74-85.

Measurements of Combustion Gases

As mentioned above, combustion pollutants are generated in according to the type of combustion appliances, operation parameters and the type of fuel. Sampling and analytical methods of them depend on a substance interested because these pollutants are composed of different chemicals. Therefore, we summarize measurements of exposure to a chemical based on the major pollutants related to adverse health effects.

Concentration of combustion gases in home
Ideally, carbon monoxide level indoors should be the same as outdoors. Average levels in homes without gas stoves vary from 0.5 to 5 parts per million (ppm). Levels near properly adjusted gas stoves are often 5 to 15 ppm and those near poorly adjusted stoves may be 30 ppm or higher. Traynor et al.(1985) reported that CO concentration ranged from 0.4 to 2.8 ppm in nonairtight stoves.

Carbon dioxide ambient level is 340 ppm to 370 ppm and carbon dioxide level in homes should be the same as outdoors. In indoor air, the primary source of carbon dioxide is human expelled air that builds up in airtight buildings, confined air spaces, overcrowded spaces and high activity area. Other sources are by-product of combustion by gas cooking appliances, space heaters, and wood-burning appliances.

Nitrogen dioxide Average level in homes without combustion appliances is about half that of outdoors. In homes with gas stoves, kerosene heaters, or un-vented gas space heaters, indoor levels often exceed outdoor levels. For example, Traynor et al.(1984) reported that nitrogen dioxide levels in three kerosene-heated homes ranged from 25 to 117 ppb and Leaderer et al.(1984) reported that NO2 levels averaged 19.6 ppb in those homes with one heater and 37 ppb in those with two.

Sulfur dioxide levels indoors may be exceed outdoor levels. Cooper and Alberti (1984) monitored 14 homes with kerosene heaters in suburban Richmond, Virginia and sulfur dioxide levels averaged 0.4 ppm with a range of 0 to 1.0 ppm.

Measurements of combustion pollutants in home
The measurements protocol depends on largely on the objectives. Personal and area sampling are available for CO, NO2 and SO2. Personal samplers can work in either the passive or active mode.
Direct reading instruments or colorimetric detectors are used as a tool of area monitoring. Both methods provide instantaneous data, and the direct reading instruments provide on-going data. Direct reading instruments incur a high initial cost, and colorimetric detectors involve a low cost per sample. The choice of method should be based on desired number of samples and accessibility of equipment.
A brief note of concentrations and measurements of combustion gases is shown in table 4.

Hess-Kosa, K. Indoor Air Quality - Sampling and Methodology-. CRC Press, Boca Raton, NewYork,(2002). p.187-188. Godish, Thad. Indoor Air Pollution Control. Lewis Publishers, Chelsia, Michigan (1989). p.21-28.
Hines A. et al. Indoor Air Quality and Control . PTR Prentice Hall, Englewood Cliffs, New Jersey,(1993). p.85-90.

Strategy for Control of Combustion Pollutants

A strategy for control the combustion pollutants is (1) limitation of source contaminants that prevent combustion contaminants occurring or releasing, (2) dilution of contaminants that prevent contaminants exceeding the exposure criteria for human health, (3) and maintenance of combustion appliances for a good conditions. (4) Additionally, residential carbon monoxide gas detectors may use to reduce deaths from carbon monoxide poisoning

Source control
Appliance selection: Choose vented appliances whenever possible and choose combustion appliances that have been tested and certified to meet current safety standards.

Proper Installation: You should have your appliances professionally installed. Professionals should follow the installation directions and applicable building codes. Improperly installed appliances can release dangerous pollutants in your home and may create a fire hazard. Be sure that the installer checks for backdrafting on all vented appliances. A qualified installer knows how to do this.

To reduce combustion pollutants, a good supply of fresh outdoor air is needed. Normally, air comes through cracks around doors and windows. This air helps reduce the level of pollutants indoors. This supply of fresh air is also important to help carry pollutants up the chimney, stovepipe, or flue to the outside.

Keep doors open to the rest of the house from the room where you are using an unvented gas space heater or kerosene heater, and crack open a window.

Use a hood fan, if you are using a range. They reduce the level of pollutants you breath, if they exhaust to the outside. Make sure that enough air is coming into the house when you use an exhaust fan. If needed, slightly open a door or window, especially if other appliances are in use

Make sure that your vented appliance has the vent connected and that nothing is blocking it. Make sure there are no holes or cracks in the vent

Inspection and Maintenance
Combustion appliance regularly inspected and maintained to reduce your exposure to pollutants. Appliances that are not working properly can release harmful and even fatal amounts of pollutants, especially carbon monoxide.

What you should know about combustion appliances and indoor air pollution