Siemens 6DR50 Series Operating Instructions Manual page 291

Zone 20
Zone 20 is an area in which a potentially explosive atmosphere in the form of a cloud of
combustible dust in air is present continuously, over a long period, or frequently.
Zone 21
Zone 21 is an area in which a potentially explosive atmosphere in the form of a cloud of
combustible dust in air can be occasionally produced during normal operation.
Zone 22
Zone 22 is an area in which a potentially explosive gaseous atmosphere in the form of a
cloud of combustible dust in air never develops or develops only for a short while during
normal operation.
SIPART PS2 with and without HART
Operating Instructions, 09/2014, A5E00074631-12
Glossary
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