MIL-STD-810G METHOD 511.5
Explosive Atmosphere testing is performed to:
A. Test the ability of equipment to operate in an atmosphere of explosives in fuel, without causing ignition, or.
B. To prove that an explosive reaction or fire that occurs inside packaged and contained equipment does not perpetuate out of the test system.
This method applies to all equipment intended for use in the vicinity of atmospheric fuel associated with aircraft fuels, vehicles and marine fuels at or above sea level. The second procedure specifically refers to the atmosphere in a space where flammable liquids or vapors are present, continuously or intermittently (e.g., in fuel tanks or inside fuel systems).