To meet the NEC criteria for the explosion-proof rating, an enclosure must be able to contain any explosion originating within its housing and prevent sparks from within its housing from igniting vapors, gases, dust, or fibers in the air surrounding it.
Explosion-proof, when referring to electrical enclosures, does not mean that it is able to withstand an exterior explosion. Instead, it is the enclosures ability to prevent an internal spark or explosion from causing a much larger blast.
Explosion-proof equipment must also meet the temperature specific requirements of the application in which it is to be installed. The operating temperature of the motor (and its enclosure) or other component cannot be greater than the lowest ignition/combustion temperature of the gases or dust in the atmosphere where the component is to be installed.
All explosion-proof equipment is labeled on their nameplate with the classification level in which they have been tested and approved for installation.