Electrical equipment is defined and certified as explosion-proof when it is enclosed in a case, which is capable of withstanding within it the explosion of a hydrocarbon gas/air mixture, or other specified flammable gas mixture. It must also prevent the ignition of such mixture outside the case either by spark or flame from the internal explosion or as a result of the temperature rise of the case following the internal explosion. The equipment must operate at such an external temperature that a surrounding flammable atmosphere will not be ignited.