The use of explosion-proof housings is based on recognition of the fact that in many types of electrical equipment the amount of energy transferred to a combustible mixture during normal operation of the equipment or during probable and nonpreventable faults cannot in any way be reduced below that required for ignition. One way in which such equipment can be used safely in a hazardous location is to provide an enclosure so constructed that, if ignition does occur around the equipment, the flame cannot propagate outside the enclosure and spread to the surrounding atmosphere. For the enclosure to perform this function it must contain the internal explosion without damage and cool any gases which escape so that they cannot ignite a flammable mixture surrounding the enclosure.
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