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Hydrogen being commonly encountered in chemical plants, frequently the ex-
plosion group IIC is requested for maximum safety.
6.3.3 Unit categories
Moreover, the areas of use (zones) and the conditions of use (explosion
groups) are subdivided into categories for the electrical operating means:
6.3.4 Temperature classes
The maximum surface temperature for electrical components of explosion pro-
tection group I is 150 °C (danger due to coal dust deposits) or 450 °C (if there
is no danger of coal dust deposit).
In line with the maximum surface temperature for all ignition protection types,
the electrical components are subdivided into temperature classes, as far as
electrical components of explosion protection group II are concerned. Here the
temperatures refer to a surrounding temperature of 40 °C for operation and
testing of the electrical components. The lowest ignition temperature of the
existing explosive atmosphere must be higher than the maximum surface tem-
perature.
Unit
Explosion
categories
group
M1
I
M2
I
1G
II
2G
II
3G
II
1D
II
2D
II
3D
II
Temperature classes
T1
T2
T3
T4
T5
T6
Area of use
Fire-damp protection
Fire-damp protection
Zone 0 Explosive environment by gas, fumes or mist
Zone 1 Explosive environment by gas, fumes or mist
Zone 2 Explosive environment by gas, fumes or mist
Zone 20 Explosive environment by dust
Zone 21 Explosive environment by dust
Zone 22 Explosive environment by dust
Maximum surface
temperature
450 °C
300 °C
200 °C
135 °C
100 °C
85°C
Ignition temperature
of the combustible materials
> 450 °C
> 300 °C to 450 °C
> 200 °C to 300 °C
> 135 °C to 200 °C
>100 °C to 135 °C
> 85 °C to 100 °C
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