Docu-No.: 1090020601-EN Rev. 1.2.1 Page 15
Assembly and Function 2
Field of application 2.1
2.1.3 Zones and device categories (dust)
2.1.4 Dust deposits and glow temperature
Zone Description Use of KCM
Zone 20 An area in which a dangerous, explo-
sive atmosphere in the form of a cloud
of flammable dust suspended in the air
is either constantly present, or frequent-
ly or for long periods at a time.
Not allowed
Zone 21 An area in which a dangerous, explo-
sive atmosphere in the form of a cloud
of flammable dust suspended in the air
may form at times under normal operat-
ing conditions.
Not allowed
Zone 22 An area in which a dangerous, explo-
sive atmosphere in the form of a cloud
of flammable dust suspended in the air
may form at times under normal operat-
ing conditions.
Allowed
▲ Observe the requirements of the standard IEC/EN 60079-14
Chapter 5.6.3.1 with regard to reduced glow temperature at dust
deposits.
In case of dust deposits of up to 5 mm:
• Glow temperature of the material at a thickness of the layer of dust
5 mm: ≥ max. Surface temperature (Tmax) + 75 K.
T
max
= T
5 mm
- 75 °C
In case of dust deposits greater than 5 mm to max. 50mm:
• The difference to be observed between the glow temperature of the
material and the surface temperature (T
max
) depends on how thick
the dust layer is. The context is shown in Fig. 1 of the standard EN
60079-14 Chapter 5.3.3.2.1
• Avoid Dust deposits > 5mm (see 8 cleaning).
Dust deposits ≥ 50 mm avoid or complete covered:
• not allowed
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