|Carbon monoxide is an invisible,
odorless, colorless gas created when fossil fuels (such as gasoline)
burn incompletely. In a piston-powered aircraft, engine exhaust
contains high concentrations of CO, particularly at mixture settings
richer than peak EGT. The most common way for this CO to find its
way into the home is through the home heating system.
Normally, oxygen inhaled into your lungs
combines with the hemoglobin in the red cells of your blood to form
"oxyhemoglobin." The oxygen is then transported throughout your body
by your arteries and capillaries, where it disassociates from the
hemoglobin and oxygenates the cells of your tissues and organs
(including your brain). The deoxygenated hemoglobin then returns
through your veins to your lungs, where it is combines with more
oxygen and the cycle repeats.
(parts per million)
symptoms after 8 hours of exposure.
after 2 to 3 hours.
nausea after 1 to 2 hours.
and dizziness after 45 minutes; collapse after 2 hours.
after 1 hour.
Table 1. Effects of various CO
after 30 minutes.
concentrations at sea level.
(At altitude, the effects of CO
poisoning and altitude hypoxia
|0 - 10
(Smoking yields 3% to 10% COHb.)
|10 - 20
||Tension in forehead, dilation of blood vessels.
|20 - 30
||Headache and pulsating temples.
|30 - 40
||Severe headache, weariness, dizziness, vision problems,
nausea, vomiting, prostration.
|40 - 50
as above, plus increased breathing and pulse rates,
|50 - 60
as above, plus coma, convulsions, Cheyne-Stokes respiration.
|60 - 70
convulsions, weak respiration and pulse. Death is possible.
|70 - 80
||Slowing and stopping of breathing. Death within hours.
|80 - 90
in less than 1 hour.
Table 2. Effects of various COHb saturations.
|90 - 100
When carbon monoxide is inhaled, the CO
combines with your hemoglobin to form "carboxyhemoglobin" (COHb).
The COHb bond is over 200 times stronger than oxygen's bond with
your hemoglobin. Thus, the CO effectively puts your hemoglobin "out
of commission" and deprives your body of the oxygen it needs to
survive. The strong COHb bond explains why even very tiny
concentrations of carbon monoxide can poison you slowly over a
period of several hours, and why it may take a long, long time for
your body to eliminate CO buildups from your bloodstream.
How long? According to an authoritative
medical text (Rosen's Emergency Medicine, 3rd Ed., 1992),
COHb has a "half-life" of more than five hours for a patient
breathing fresh air. In other words, if you crash-land in a hay
field with COHb saturation of 40%, your COHb level can be expected
to drop to about 20% after five or six hours, to 10% after another
five or six hours, and so forth. If you're taken to the emergency
room and they put you on oxygen therapy, the half-life drops to 1.5
to 2.5 hours (depending on whether the docs put you on a ventilator
or just use a face mask). In extreme cases of CO poisoning, you may
be rushed to a large medical center and put into a hyperbaric
chamber with pure oxygen at three times normal atmospheric pressure,
which reduces the half-life to under a half-hour.
According to the FAA Civil Aeromedical
Institute, cigarette smoking will normally produce a COHb saturation
of 3% to 10%. Smokers are consequently far more vulnerable to CO
poisoning in flight, since they're already in a partially-poisoned
state when they first get into the aircraft. Because of COHb's long
half-life, smokers would do well to abstain from smoking for 8 to 12
hours prior to flight. (Unfortunately, the more common scenario is
that the last cigarette is stubbed out on the tarmac moments before
flight, and the next one is lighted seconds after the aircraft comes
to a stop at the destination.)
As the CO level in your blood increases, the
amount of oxygen transported to your body's cells decreases. It is
this oxygen deprivation that makes CO so deadly. Sensitive parts of
your body like your nervous system, brain, heart and lungs suffer
the most from this lack of oxygen. Symptoms of mild CO poisoning
include headache, fatigue, dizziness, vision problems (particularly
double vision), nausea, and increased pulse and respiration.
Unfortunately, these symptoms are often attributed to flu,
indigestion, or the common cold. At higher levels of COHb
saturation, you may suffer difficulty in breathing, loss of
consciousness, collapse, convulsions, coma, and even death.
Just how sick you'll get from CO exposure
varies greatly from person to person, depending on age, overall
health, the concentration of CO (measured in parts per million), and
the duration of exposure. High concentrations can cause
incapacitation within minutes, but low concentrations can still be
extremely dangerous if you're exposed for a period of hours. As CO
continues to be inhaled, the percentage of COHb gets higher and
higher, and you get sicker and sicker. Your eyes are particularly
vulnerable to the effects of CO poisoning, and permanent damage can
Whereas hypoxia tends to make you turn blue
(the medical term is "cyanotic"), CO poisoning has the opposite
effect — it makes you turn red. Carboxyhemoglobin is red in color,
just as oxyhemoglobin is. (That's why a
oximeter is unable to detect CO poisoning.) But, since CO does
not disassociate readily from hemoglobin the way O2 does, your
venous blood remains red rather than turning the normal bluish
color. This morbid little fact is useful mostly to coroners and
morticians, however, because by the time CO poisoning has progressed
far enough to turn you noticeably red, you're at least comatose if
The accompanying tables give you some idea of
how various levels of CO concentration in the air and COHb
saturation of the blood affect an average person. As you can see, a
CO concentration of one tenth of one percent (1,000 parts per
million) is enough to render you unconscious in an hour. OSHA has
established the maximum permissible CO level for continuous
8-hour-per-day exposure in the workplace at 35 parts per million.
Early Warning Signs
Your Home - Due
to its nature, carbon monoxide cannot be detected by
the human senses. But sometimes the gas will leave clues to its presence. These
are things to look for which might indicate (but not always) that you have
excessive concentrations of CO:
stuffy air that never seems to clear.
humidity that condensates on windows.
hot draft venting from the chimney into the home, or no draft at all in the
which accumulates around the outside of a fireplace, chimney, or furnace.
smell of exhaust fumes in the air.
In Your Body
physical symptoms of CO poisoning are often misdiagnosed as the flu or virus.
Some of the symptoms may include:
or blurred vision.
fatigue and drowsiness.
pulsed or fluttering of the heart, tightness of the chest.
fainting, unconsciousness, or dimmed vision.
absence of any of these symptoms once you leave your house.
- Confusion, anxiety, irritability, disorientation, loss of muscle
small children and persons with cardiovascular problems are more susceptible to
the ill effects of carbon monoxide. Even low concentrations of the gas can cause
problems for individuals in these categories. Since the physical symptoms of CO
poisoning are similar to the flu or virus, it is important to remember that if
you do experience some of these symptoms, you may indeed have the flu. But
if the conditions persist and nothing seems to help, or your entire family seems
to be experiencing the same illnesses, you should seek medical advice
immediately and mention your fear of carbon monoxide poisoning.