Electrical equipment intended for use in potentially explosive atmospheres must comply with the main certification standards: IEC, CENELEC and NEC.
IEC (International Electronic Commission) standards are accepted in almost all countries. They are identical to the European CENELEC standards.
The NEC (National Electrical Code) is the standard in the United States. Its 1996 edition, art. 505, uses the IEC designations for gas groups, equipment temperature classes and zone definitions.