occurs normally in Earth's atmosphere in concentrations of about 0.036%
(360 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.
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,
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.
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.