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