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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