Carbon monoxide (CO) is a colorless, odorless, and tasteless gas. It may
temporarily accumulate at harmful levels, especially in calm weather during
winter and early spring, when fuel combustion reaches a peak and carbon monoxide
is chemically most stable due to the low temperatures.
Sources of carbon monoxide include:
Automobile emissions. (High levels are possible near large parking lots,
traffic jams, or crowded city streets, where large numbers of slow-moving
Volcanoes, thunderstorms and forest fires.
Vegetation during various growth stages.
The chemical transformation of methane, a gas emitted from decaying plants
in swamps and marshlands.
Carbon monoxide from natural sources usually dissipates quickly over a large
area, posing no threat to human health.
Carbon monoxide enters the blood stream by combining with hemoglobin, the
substance that carries oxygen to the cells. This combination occurs 200 times
more readily with carbon monoxide than with oxygen, reducing the amount of
oxygen distributed throughout the body by the blood stream. Carbon monoxide
adversely impacts health in many ways:
It affects the central nervous system at relatively low concentrations.
It weakens heart contractions, lowering the volume of blood distributed to
various parts of the body.
It significantly reduces a healthy person's ability to perform manual
tasks, such as working, jogging and walking.
It causes healthy people to feel tired and drowsy from short-term exposure
to concentrations greater than 30 parts per million (ppm).
It causes shortness of breath and chest pain in people with heart disease
at exposures as low as 10 ppm.
It induces irritability, headaches, rapid breathing, blurred vision, lack
of coordination, nausea, dizziness, confusion and impaired judgement in
healthy people at levels greater than 35 ppm.
Even three or four hours after exposure, half the excess carbon monoxide may
remain in the blood stream.
People especially susceptible to CO include:
Children (and the human fetus).
Those with respiratory or heart illnesses. (The 4.2 million people in the
U.S. suffering from angina pectoris - a disease characterized by brief
spasmodic attacks of chest pain due to insufficient oxygen levels in the
heart muscles - are especially susceptible.)
Those with anemia.
Those exposed for long periods of time, such as traffic officers and
people sitting in parked/idling cars over sustained periods.
Cigarette smokers. (Smoking while driving in heavy traffic may result in
increased exposure - from cigarette smoke and engine exhaust. Tests of
automobile drivers show exposure to high levels of carbon monoxide can
impair a driver's judgment and ability to respond rapidly in traffic. It can
also impair vision and produce headaches.)
At concentrations commonly monitored in the ambient air, carbon monoxide does
not appear to adversely affect plants, wildlife, or materials.
Carbon monoxide is a common indoor air contaminant. Concentrations of 1 to 2
ppm are common in homes with normal gas-fired furnaces; malfunctioning furnaces
can lead to indoor concentrations of up to 120 ppm.