Toxicity http://en.wikipedia.org/wiki/Carbon_dioxide#Chemical_and_physical_properties

See also: Carbon dioxide poisoning
Main symptoms of Carbon dioxide toxicity, by increasing volume percent in air.[2][41].

Carbon dioxide content in fresh air (averaged between sea-level and 10 hPa level, i.e. about 30 km altitude) varies between 0.036% (360 ppm) and 0.039% (390 ppm), depending on the location[42].

Prolonged exposure to moderate concentrations can cause acidosis and adverse effects on calcium phosphorus metabolism resulting in increased calcium deposits in soft tissue. Carbon dioxide is toxic to the heart and causes diminished contractile force.[41]

Toxicity and its effects increase with the concentration of CO2, here given in volume percent of CO2 in the air:

* 1%, as can occur in a crowded auditorium with poor ventilation, can cause drowsiness with prolonged exposure.[2]
* At 2% it is mildly narcotic and causes increased blood pressure and pulse rate, and causes reduced hearing.[41]
* At about 5% it causes stimulation of the respiratory centre, dizziness, confusion and difficulty in breathing accompanied by headache and shortness of breath.[41]. In addition at this concentration panic attacs may occur.[43][44]
* At about 8% it causes headache, sweating, dim vision, tremor and loss of consciousness after exposure for between five and ten minutes.[41]