Electrical hazardous area classification is often a confusing item for plant personnel. They are more familiar with pressures, temperatures and the like. But basic understanding of the different terminologies should be understood. An article mentions the following:
"Installing electrical and automation panels in hazardous areas requires use of one of three protection methods: explosion-proofing (EXD), purge and pressurization (EXP) or intrinsic safety (IS).
EXD contains the pressure of the explosion, and then cools it through a critical flame path to a level that will not ignite the surrounding environment.
EXP protects the environment by segregating hazardous material from the ignition source before equipment is powered. First, explosive mixtures are purged from the enclosure; then a positive pressure is maintained inside the enclosure to insure hazardous gasses do not propagate back in during operation.
IS protection limits the energy entering the hazardous area to a level incapable of igniting the easiest ignitable concentrations of gas/air mixtures under fault conditions".
Read more of the article in this link.
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