Indoor Air Quality --- Carbon monoxide (CO)
Carbon monoxide (CO) is a colorless, odorless, poisonous gas. Deaths
are usually caused by carbon monoxide poisoning from combustion in
poorly ventilated enclosures. The symptoms of carbon monoxide poisoning
are: headache, nausea, shortness of breath, dizziness and confusion. The
severity of symptoms depends on the concentration of gas. High
concentrations quickly cause death. Low level exposure produces flu-like
symptoms and is usually not recognized.
Carbon monoxide gas is produced when fossil fuel burns incompletely
because of insufficient oxygen. During incomplete combustion, the carbon
and oxygen combine to form carbon dioxide, water, heat, and carbon
monoxide. In properly installed and maintained appliances, the fuel
burns cleanly and produces only small amounts of carbon monoxide.
Anything that interferes with the burning process or results in a
shortage of oxygen can increase carbon monoxide production. Wood, coal,
and charcoal fires always produce carbon monoxide, as do gasoline
Exposures in parts per million (PPM)
|30 PPM Permissible
||Averaged over 8 hours
||Maximum for acute exposure
|800 PPM Lethal
||< 2 hour exposure
Sources: Combustion - furnaces, boilers, space-heaters, stove tops,
hot water heaters ( gas), clothes dryers (gas), wood stoves, fireplaces,
BBQ's, tobacco smoking, combustion engines, candles, incense, kerosene
lanterns, propane appliances. Official recommendation: concentration
levels should be below 30 PPM average exposure.
Our recommendation: safe concentration levels are 0 (zero),
the hazard increases dramatically above 30 PPM. Average occupational
exposures above 10PPM (sustained through the work day) are unacceptable
if your goal is normal function and good health long term. Smokers
provide their own personal supply of carbon monoxide and will often have
exposure levels above safe limits when their personal CO exposure is
added to exposure in ambient air.
- Stain indicator tubes are useful for screening industrial
- electronic devices for continuous monitoring
- electrochemical devices - accuracy +/- 5%
When Carbon Monoxide is inhaled, the CO combines with the hemoglobin
to form carboxyhemoglobin
(COHb). CO displaces oxygen attached to
the carrier molecule, hemoglobin. The COHb bond is over 200 times
stronger than oxygen's bond with hemoglobin. The strong COHb bond makes
it difficult for the body to eliminate CO
from the blood.
Carbon Monoxide can poison slowly over a period of several hours,
even in low concentrations. Sensitive organs such as the brain, heart,
and lungs suffer the most from a lack of oxygen. Unfortunately, the
symptoms of CO poisoning are easily mistaken for other common illnesses
and low level CO poisonings are often misdiagnosed. Symptoms such as
headaches, dizziness and fatigue are common to a number of illnesses
such as the flu or the common cold. These symptoms can occur with a COHb
blood saturation levels of 10-30%.
At 30-50% COHb symptoms are nausea, severe headaches, dizziness, and
increased pulse and respiration. COHb levels over 50% cause progressive
symptoms proceeding to loss of consciousness, collapse, convulsions,
coma, and finally death.
How much is dangerous? High concentrations of carbon monoxide kill in
less than five minutes. At low concentrations it will require a longer
period of time to affect the body. Exceeding the EPA concentration in
air of 9 ppm for more than 8 hours will have adverse health affects. The
U.S. Occupational Health and Safety limit for healthy workers is 50 ppm
in inhaled air.
Carbon monoxide detectors, which are designed to protect against high
concentration of carbon monoxide are required to sound an alarm when
concentrations are greater than 100 ppm. Continued exposure to carbon
monoxide can cause permanent brain, nerve, or heart damage. Some people
require years to recover while others might never fully recover. The
time of exposure, the concentration of CO, the activity level of the
person breathing the CO, and the person's age, sex, and general health
all affect the danger level. Exposure to CO at a concentration of 400
ppm will cause headaches in 1 to 2 hours; in 3 to 5 hours the same
concentration can lead to unconsciousness and death. Physical exertion,
with an accompanying increase in respiration rate, shortens the time to
critical levels by 2 or 3 fold. Respiratory capacity decreases and the
risk of heart attack increases at levels well below 50 ppm.
Low Level CO poisoning should be suspected when
- Entire family or work group is sick at the same time.
- Flu-like symptoms decrease while away from the house or workplace.
- Illness is present when gas appliances are in use.
- Excess moisture on the interior of windows.
Urgent treatment- CO poisoning
Move immediately into fresh air; administer oxygen if available. go
to hospital for treatment. In severe cases, patients are treated in a
hyperbaric chamber which forces carbon monoxide from the body.
half-life of carboxyhemoglobin in fresh air is approximately 4 hours -
complete flushing takes 12 to 24 hours. Oxygen and hyperbaric chambers,
can reduce CO damage, speed recovery, and reduce brain damage.
Loss of consciousness suggests high levels of carbon monoxide
poisoning. Death is imminent unless the victim is rescued and treated in
a well equipped emergency room.
Even patients who recover have symptoms for several weeks. They will
suffer from headache, fatigue, loss of memory, difficulty in thinking
clearly, irrational behavior and irritability. Recover can be slow and
frustrating. Some individuals suffer permanent brain and organ damage.
Victims may be highly sensitive to CO for the rest of their lives.
A breath test can determine carbon monoxide levels. Medical
laboratories can measure carboxyhemoglobin levels in the blood.
Carboxyhemoglogin levels in the blood drop after the victim is removed
from the carbon monoxide source Because the effects of carbon monoxide
poisoning may last for months, normal carboxyhemoglobin levels in the
blood 24 or more hours after exposure are not relevant.
Protection from the dangers of carbon monoxide poisoning
Do not use combustible fuel devices in closed spaces.
Purchase and use carbon monoxide detector(s).
Checkheating appliances by a qualified heating contractor.
Replace open heating units - space heaters, wood stoves and
fireplaces with direct-vent, sealed combustion units.
Auto Emissions of CO
cities, about two-thirds of the carbon monoxide
emissions come from transportation sources, with the largest
contribution coming from highway motor vehicles. In urban areas, the
motor vehicle contribution to carbon monoxide pollution can exceed 90
percent. In 1992, carbon monoxide levels exceeded the Federal air
quality standard in 20 U.S. cities, home to more than 14 million people.
Carbon monoxide results from incomplete combustion of fuel and is
emitted directly from vehicle tailpipes. Incomplete combustion is most
likely to occur at low air-to-fuel ratios in the engine. These
conditions are common during vehicle starting when air supply is
restricted ("choked"), when cars are not tuned properly, and at
altitudes where "thin" air reduces the amount of oxygen available for
combustion (except in cars that are designed or adjusted to compensate
By 1975, most new cars were equipped with catalytic converters that
convert carbon monoxide to carbon dioxide.
In the 1980's,
automakers improved CO conversion with computers and oxygen sensors that
increased the efficiency of
catalytic converters. Carbon monoxide
emissions from automobiles increase in cold weather because cars need
more fuel to start at cold temperatures, and because some emission
control devices (such as oxygen sensors and catalytic converters)
operate less efficiently when they are cold.