Due to its high density, escaping carbon dioxide can displace the air, especially near the ground, and therefore reach concentrations that can lead to breathing difficulties and subsequently to unconsciousness and even death by suffocation. This already occurs with a proportion of 7 - 10 % in the air.

For this reason, a so-called MAK value has also been defined for CO2 in accordance with TRgA900 (Technical Rules for Hazardous Substances), according to which it has been categorised as Category IV (MAK value: 5,000 ppm [0.5 % in the atmosphere]).

This means that the CO2 content of the air at the workplace may rise to 10,000 ppm (1 % in the atmosphere) a maximum of three times during a shift, each time for one hour.

At 1 % CO2 in the air we breathe, breathing is accelerated; up to 3 %, breathing becomes deeper and headaches occur with prolonged exposure. At 3 - 5 %, the respiratory centre is clearly irritated and the breathing rate increases to four times the normal value. This effect can also be utilised therapeutically.


Short-term value

Frequency per shift
Height Duration
I Locally irritating substances 2 - MAK 5 min, instantaneous value 8
II Resorptively active substances
Onset of action < 2 h
IIa: half-life < 2 h
2 - MAK 30 min, mean value 4
  IIb: half-life 2 h - shift length 5 - MAK 30 min, mean value 2
III Resorptively active substances
Onset of action > 2 h
Half-life > shift length
(highly cumulative)
10 - MAK 30 min, mean value 1
IV very low effect potential
MAK > 500 ml/m3
2 - MAK 60 min, instantaneous value 3
V Odour-intensive substances 2 - MAK 10 min, instantaneous value 4