COMBUSTION PRODUCTS HEALTH EFFECTS BASIC INFORMATION


What Are the Health Effects of Combustion Products?

The major categories of products resulting from combustion can be listed as carbon monoxide (CO), nitrogen oxides (NOx), particulate material, and polynuclear aromatic hydrocarbons (PAH). Carbon monoxide (CO) is an odorless, tasteless and colorless gas.

Nitrogen oxides (NOx) includes nitrogen compounds NO, NO2, N2O, OONO, ON(O)O, N2O4 and N2O5. All are irritant gases, which can impact on human health.

Particulates represents a broad class of chemical and physical particles, including liquid droplets. Combustion conditions can affect the number, particle size and chemical speciation of the particles.

Polynuclear aromatic hydrocarbons (PAH) concentrations are usually low indoors. PAH concerns stem from their potential to act synergistically, antagonistically or in an additive fashion with each other and other contaminants. The chemical composition and concentrations of these compounds vary with combustion conditions.

Sources
Combustion products are released under conditions where incomplete combustion can occur, including: wood, gas and coal stoves, heaters and cooking surfaces; unvented kerosene heaters or appliances; unvented grilles; portable generators; fireplaces under downdraft conditions; and environmental tobacco smoke. Vehicle exhaust is a primary source, particularly from underground or attached garages, as well as from the outdoor air.

Health Effects
The impact on human health varies with the category of combustion product; so they are treated separately below. Carbon monoxide (CO) has about 250 times the affinity for hemoglobin than oxygen has. When carboxyhemoglobin (COHb) is formed, it reduces the hemoglobin available to carry oxygen to body tissues.

CO, therefore, acts as an asphyxiating agent. Common symptoms are dizziness, dull headache, nausea, ringing in the ears and pounding of the heart. Should CO inhalation induce unconsciousness, damage to the central nervous system, the brain and the circulatory system may occur.

Acute exposure can be fatal. Young children and persons with asthma, anemia, heart and hypermetabolic diseases are more susceptible. The extent to which nitrogen oxides (NOx) affect human health is unclear. The most information is available about nitrogen dioxide (NO2).

NO2 symptoms are irritation to eyes, nose and throat, respiratory infections and some lung impairment. Altered lung function and acute respiratory symptoms and illness have been observed in controlled human exposure studies and in epidemiological studies of homes using gas stoves.

Studies in the United States and Britain have found that children exposed to elevated levels of NO2 have twice the incidence of respiratory illness as children not exposed. Combustion particulates can affect lung function. The smaller respirable particles (less than 2.5 micron μm in size) present a greater risk as they are taken deeper into the lungs.

Particles may serve as carriers of contaminants, such as PAH, or as mechanical irritants that interact with chemical contaminants. The health effects of polynuclear aromatic hydrocarbons (PAH) are very difficult to determine or predict. PAH’s propensity to act in concert with other contaminants complicates any effort to attribute singular cause and effect. It is known that some PAHs are carcinogens while others exhibit co-carcinogenic potential. 

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