The maximum admissible concentration is the concentration of a gas, vapor or dust which a human can inhale for eight hours daily, i.e. year-round constant exposure, without harmful effect. This is identical to the threshold limit value (TLV), which is the admissible concentration of a harmful substance (gas, vapor or dust) in the ambient air of a workplace. The TLV is usually stated in mg/m³.
At elevated concentrations, vapors and gases which have neither toxic nor narcotic properties may displace oxygen in the atmosphere. Air normally has an oxygen content of 20.95 vol.%; a drop in oxygen content to < 13 - 15% disrupts human bodily functions, causing headaches, reduced visual acuity, fatigue, ringing in the ears and loss of coordination.
When transporting fruit and vegetables, accidents may occur due to the build-up of CO2.
Carbon dioxide concentrations of just 2 - 6 vol.% in inhaled air are harmful to humans, causing labored breathing. Duration of exposure is significant in determining the degree of harm: breathing air with a CO2 content of 3.5 vol.% for half to one hour will endanger human life.
8 - 10 vol.% carbon dioxide in the inhaled air cause shortness of breath, unconsciousness and, after 6 - 10 minutes' inhalation, death. A concentration of 20 vol.% in the inhaled air is immediately fatal.
Excessive concentrations of carbon dioxide are life-threatening to humans in two ways:
- by asphyxiation (by displacement of atmospheric oxygen)
- to a minor extent by intoxication (due to carbon dioxide's intrinsic irritant action on certain parts of the brain)