IEC
IEC 60079-1
Explosive Atmospheres — Equipment Protection by Flameproof Enclosures 'd'
The standard behind the Ex d concept, where an internal explosion is permitted but the enclosure contains it and cools the escaping gas below the ignition temperature of the surrounding atmosphere. Almost everything that matters to an inspector follows from that mechanism: the flame path gap and length, the number of threads engaged on a cover or a gland, the condition of the joint faces, and why painting, corroding, shimming or drilling a flameproof enclosure destroys its certification. It also sets the bolt grade and the window retention requirements that site repairs most often get wrong.
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