|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.
Ounce of Prevention . . .
is list of things you can do to prevent the invisible killer from
entering your home!
& install a
- Check all your duct work which is vented to the outside (chimneys, water
heaters, etc.) on an annual basis for any signs of blockage (bird nests, large
you have a fireplace or wood-burning stove, have the chimney cleaned annually.
your heating system inspected annually, (before the cold weather sets in) to
check for proper and safe operation of all parts.
your home is extremely airtight, you may want to contact your local utility
company for information regarding adequate ventilation, back-drafting
concerns, or to measure the carbon monoxide level in your home.
your vehicle's exhaust system for leaks. Most muffler shops will do this for
forget your water heater. Make sure that is properly vented and the ductwork
does not leak any exhaust gases into the room.
a Carbon Monoxide Detector. It's an
economical and accurate way to warn you if dangerous levels of carbon monoxide
are accumulating in your home or RV.
year, many people will needlessly die from Carbon Monoxide poisoning.
Passive CO Detectors
Passive CO Detector Badges
Each year, thousands of people die or are seriously injured from exposure to
carbon monoxide gas. Low levels of exposure can cause symptoms which mimic
the flu or other viruses. High levels of exposure can kill in minutes.
Fortunately, there is a simple and inexpensive method for detecting this
silent and invisible killer. The passive Carbon Monoxide Detector has
an easy-to-see, visual indicator which warns of the presence of CO gas.
The circle on the indicator will turn gray or black, depending on the concentration
of CO. It will return to normal when exposed to fresh air again.
The detector has a convenient adhesive strip on the back, and mounts almost anywhere. Shelf life in an
unopened pack is three years; once opened it should be replaced approximately every 60 days.
The detector is made of non-toxic materials, making it safe for use around children or pets.
It can detect as little as 100 ppm (parts per million) carbon monoxide gas. The detector will be inactivated
and damaged by the presence of halogens (iodine, chlorine, bromine), and
ammoniac or nitrous gases. Persons with cats may not be able to use the
detector due to the presence of ammonia in the air from the cat litter
box. Also, the detector is not an appropriate device for detecting CO gas in connection with diesel engines.
Active CO Detectors
In the early 1990s, a number of companies started selling low-cost electronic carbon monoxide detectors for consumer use.
These seemed to offered great promise, but their history has been something of a roller coaster ride.
In 1992, Underwriter's Laboratory issued its UL2034
Standard for low-cost residential CO detectors. A number of manufacturers,
including American Sensor, BRK Brands (First Alert), and Nighthawk Systems,
quickly introduced UL-approved CO detectors priced in the $50 range. A few
companies ran a massive campaign of "scare tactic" TV ads and quickly became
the leading supplier of residential CO detectors. The industry really took off
when the City of Chicago mandated the installation of CO detectors in
residences beginning October 1, 1994.
The worst false-alarm offenders were the market-leading
units that made use of the "biomimetic" (color-change) sensor technology. The
sensor module simply passed a light beam through the "biomimetic" spot, and
alarmed if the light was sufficiently attenuated (presumably because the spot
had turned dark in color). Not only did this mean that the units had a limited
sensor life and cross-sensitivity to gases and vapors other than CO), but the
detector was plagued by false alarms due to the fact that other things could
attenuate the light beam (smoke, contamination, even insects that crawled
inside the sensor module).
In response to the false-alarm crisis, Underwriter's
Laboratory revised its UL2034 Standard in June of 1995, but the false alarm
problems didn't get any better. Meantime, in late 1995 and early 1996, the gas
utility industry and the Consumer Product Safety Commission (CPSC) started
getting concerned about the very opposite problem: CO detectors that would not
go off when they should! While First Alert had obtained an exclusive license
on the biomimetic sensor technology for residential CO detectors, virtually
all other detectors sold prior to 1996 (including #2 and #3 market leaders
American Sensor and Nighthawk) made use of a metal-oxide-semiconductor (MOS)
sensor, which was the only other low-cost sensor technology available at the
time. CPSC tests revealed that some of the MOS-based units would fail to alarm
even at life-threatening CO concentrations of 1,000 PPM or more! Many of these
units were recalled.
In short, your choice in 1996 was between two sensor
technologies, one (biomimetic) plagued by false positives and the other (MOS)
plagued by false negatives.
Since then, the industry has gone through considerable
improvements. Pittway Corporation wound up divesting itself of First Alert,
which subsequently went public, then nearly bankrupt, and finally was acquired
by Sunbeam in 1998. American Sensor wound up going bankrupt, while the assets
of Nighthawk Systems were acquired by fire extinguisher giant Kidde Safety who
subsequently redesigned their CO detector products to use a more reliable
electrochemical sensor technology.
In 1998, Underwriters Laboratory finally revised its UL
2034 specification, but implementation was delayed until January 1, 2000. For
a CO detector to be UL-approved for residential use after that date, UL
requires that it must not indicate CO levels less than 30 parts per million
(PPM), nor alarm at levels below 100 PPM. This requirement was imposed by UL
at the request of gas utilities and firefighters to minimize the number of
unnecessary emergency calls from homeowners.
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