Unit category
Selection for type of
explosive atmosphere
Avoidance sources
of ignition
Degree of
security
Use in
zone
1 G
Gas / gas-mixture or
steam / gas-mixture or
fog
Even
in rare malfunctions
very high
0
2 G
Gas / gas-mixture or
steam / gas-mixture or
fog
Even with the usu-
al malfunctions
high
1
3 G
Gas / gas-mixture or
steam / gas-mixture or
fog
In normal operation
normal
2
1 D
Dust / gas-mixture
Even
in rare malfunctions
very high
20
2 D
Dust / gas-mixture
Even with the usu-
al malfunctions
high
21
3 D
Dust / gas-mixture
In normal operation
normal
22
Table 13:
AHU categories
Classification according to surface temperature for devices of group II G:
Temperature class
Max. surface temperature (°C)
T1
450
T2
300
T3
200
T4
135
T5
100
T6
85
Table 14:
Temperature classes of AHU category 2 G
For devices of group II D, the maximum surface temperature is specified.
The maximum allowable surface temperature must always be lower than
the ignition temperature of the explosive atmosphere.
