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 Carbon
dioxide (CO2)
Carbon dioxide occurs
normally in Earth's atmosphere in concentrations of about 0.036% (350
parts per million). Because humans breathe out carbon dioxide as a basic
byproduct of metabolism, levels can increase if there is poor or no ventilation
to the outside air.
When
the CO2 level in the air increases:
- At
600 parts per million (ppm), people
notice the air is "stuffy."
- At
1000 ppm and up, some people may
begin to feel the classic symptoms of carbon dioxide poisoning: shortness
of breath, difficulty in breathing, rapid pulse rate, headaches, hearing
loss, hyperventilation, sweating, and fatigue.
- 5000
ppm (0.5%). Prolonged exposure to levels above 5000 ppm is
regarded as potentially dangerous to human health, especially if accompanied
by reduced oxygen levels.
- 15,000
ppm (1.5%). At this level, people can suffer symptoms within
an hour or two.
- At
30,000 ppm and up, people can suffer
serious symptoms, including nausea, dizziness, mental depression, shaking,
visual disturbances and vomiting. If exposure persists, people may pass
out, and if levels continue to increase, they may die.
Carbon dioxide (CO2)
should not be confused with carbon monoxide (CO). Carbon monoxide, a common
product of combustion, is lethal at comparatively low levels: CO concentrations
above 400 ppm are life-threatening and above 1600 ppm, will cause human
death within an hour.
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