Health Effects of Exposure to Carbon Monoxide, CO
World Health Organization
Environmental Health Criteria
Carbon Monoxide, 1999
Effects of Exposure to Carbon Monoxide
Decreased oxygen uptake and the resultant decreased work capacity under maximal exercise
conditions have clearly been shown to occur in healthy young adults starting at 5.0%
carboxy-haemoglobin(COHb, (the level of CO in the bloodstream)), and several studies have
observed small decreases in work capacity at carboxy-haemoglobin levels as low as 2.3–4.3%.
These effects may have health implications for the general population in terms of potential
curtailment of certain physically demanding occupational or recreational activities under
circumstances of sufficiently high carbon monoxide exposure.
At higher carboxy-hemoglobin saturations of 10–30%, neurological symptoms of carbon
monoxide poisoning can occur, such as headache, dizziness, Summary and Conclusions
19weakness, nausea, confusion, disorientation and visual disturbances. Exertional dyspnoea,
increases in pulse and respiratory rates and dizziness are observed with continuous exposure,
producing carboxy-haemoglobin levels from 30% to 50%. When carboxy-haemoglobin levels
are higher than 50%, coma, convulsions and cardiopulmonary arrest may occur.
World Health Organization Guidelines
The following guideline values (ppm values rounded) and periods of time-weighted average
exposures have been determined in such a way that the carboxy-haemoglobin level of 2.5%
is not exceeded, even when a normal subject engages in light or moderate exercise:
100 mg/m 3 (87 ppm) for 15 min
60 mg/m 3 (52 ppm) for 30 min
30 mg/m 3 (26 ppm) for 1 h*
10 mg/m 3 (9 ppm) for 8 h
*Exposure of normal subjects to levels of Carbon Monoxide at 26 ppm for the duration of more
than one hour (as during a typical hockey game or practice), exceed carboxy-haemoglobin levels
of 2.5%
Environmental Protection Agency
Health and Environmental Impacts of CO: Carbon Monoxide
Low levels can cause shortness of breath, mild nausea, and mild headaches, and may have longer
term effects on your health. Since many of these symptoms are similar to those of the flu, food
poisoning, or other illnesses, you may not think that carbon monoxide poisoning could be the
cause. At moderate levels, you or your family can get severe headaches, become dizzy, mentally
confused, nauseated, or faint. At high levels, CO can cause lost of consciousness or death.
Fetuses, children, elderly people and people with heart disease can be especially susceptible.
Cardiovascular Effects: The health threat from lower levels of CO is most serious for those
who suffer from heart disease, like angina, clogged arteries, or congestive heart failure. For a
person with heart disease, a single exposure to CO at low levels may cause chest pain and reduce
that person's ability to exercise; repeated exposures may contribute to other cardiovascular
effects.
Central Nervous System Effects: Even healthy people can be affected by high levels of CO.
People who breathe high levels of CO can develop vision problems, reduced ability to work or
learn, reduced manual dexterity, and difficulty performing complex tasks. At extremely high
levels, CO is poisonous and can cause death.
Occupational Safety and Health Administration
US Department of Labor
Besides tightness across the chest, initial symptoms of CO poisoning may include headache,
fatigue, dizziness, drowsiness, or nausea. Sudden chest pain may occur in people with angina.
During prolonged or high exposures, symptoms may worsen and include vomiting, confusion,
and collapse in addition to loss of consciousness and muscle weakness. Symptoms vary widely
from person to person. CO poisoning may occur sooner in those most susceptible: young
children, elderly people, people with lung or heart disease, people at high altitudes, or those who
already have elevated CO blood levels, such as smokers. Also, CO poisoning poses a special risk
to fetuses.
Journal of Occupational Environmental Medicine
The brain, heart, and exercising skeletal muscles tend to be the most sensitive targets for CO.
Clinical reports and controlled experimentation have shown that a particular group of
symptoms are associated with specific concentrations of Carboxy-haemoglobin (COHb).
At low concentrations of COHb: vision is altered and the arteries dilate. Nausea, headaches, and
disorientation occur at higher concentrations. Certain psychomotor abilities (hand eye
coordination e.g.) were affected at COHb levels of 5%. In tests of cognitive abilities, subjects
showed an increasing number of errors and completion time as COHb levels increased, the effect
becoming apparent at 5% COHb. These results indicate that even before clinical symptoms are
reported (around 20% COHb), cognitive skills can be affected. Very high concentrations can be
life threatening.
Uptake of CO during exercise has been shown to be three to four times greater than at rest.
The exposure-absorption studies of Lévesque et al and Spengler et al found a linear relation
between percentage saturation of COHb in hockey players and exposure time and concentrations
of CO. Lévesque et al have shown that for each 10 parts per million (ppm) of CO in an arena, an
adult male hockey player, during a 1.5 hour game of hockey, will have a COHb increase of
1.0%. Spengler et al found that an average environmental concentration of 22.5 ppm CO is
sufficient to raise the average COHb concentration in hockey players from 1.1% to 3.2% (above
acceptable WHO guidelines). This concentration has been exceeded by most arenas tested in
various studies.
At the time of skating, the respiratory rate can be 10 times higher than at rest. Therefore, upon
exposure to a similar concentration of CO, the rate of COHb in the blood will increase much
more rapidly in the hockey player, for example, than in the arena employee. This is
particularly true for children who have a higher metabolic rate than adults.
Several studies have suggested that high risk people (children, elderly people, people with
cardiovascular inefficiencies, or pregnant women) were more susceptible to increased
concentrations of COHb while participating in or observing activities in enclosed rinks
As well as the acute adverse health effects of CO poisoning, research has suggested that long
term exposure to CO can increase the risk of cardiovascular heart disease (CHD). For people
who have CHD, exposure to increased concentrations of COHb can lead to myocardial ischemia,
abnormal cardiac rhythms or arrhythmias, or in severe cases, myocardial infarction. Along with
the adverse effects placed on the cardio-respiratory system, low level exposure to CO has been
associated with impaired neuropsychological function. Attention span, memory, cognitive
planning, and information processing have been shown to be jeopardized. In cases of CO
poisoning, neuropathological hippocampal changes and diffuse cortical atrophy have been found
with magnetic resonance imaging.
Symptoms associated with the absorption of COHb
COHb concentration
0.0%±2.5%
Effects
No apparent symptoms
2.5%±5.0%
Altered vision, Arterial dilation, Reduced
attention span particularly while driving an
automobile
5.0%±10%
Altered brightness sensitivity, Unusual
increase in strained breathlessness,
Distortion of fine manual dexterity
20%±30%
Headaches
Start of nausea
Coordination problems
30%±40%
Severe headaches
Dizziness
Nausea and vomiting
Judgment alteration
40%±50%
Aggravation of the same symptoms
Confusion
50%±60%
Loss of consciousness
Convulsions
>60%
Coma
Respiratory arrest, Death
Prepared by Clara J. Owen, Intern for Representative Rick Hansen