The equipment is simply contained in a heavy protective enclosure, usually made of die cast steel, occasionally plastic. If heat or sparks from faulty equipment within the enclosure ignite flammable gas present with it the resulting explosion is contained within the enclosure. In North America metal conduit must be used for field wiring. In Europe and elsewhere suitably rated cable is connected directly to the equipment using certified flame proof cable glands.
Advantage – simple to design the system, suitable for high power equipment
Disadvantage – equipment becomes extremely heavy & expensive; opening the enclosure while powered is not permitted