Thisstandard specifies the particular requirements for construction@ test and marking for electrical apparatus of Group II intended for use in Class I@ Zone 0 as defined in the National Electrical Code@ ANSI/NFPA 70. This electrical apparatus@ within the operational parameters specified by the manufacturer@ ensures a very high level of protection that includes rare faults related to the apparatus or two faults occurring independently of each other. NOTE 1 A malfunction may result from a failure of the component parts of the electrical apparatus or from anticipated externally applied influences. Two independent malfunctions which may occur more frequently and which@ separately@ would not create an ignition hazard but which@ in combination@ could create a potential ignition hazard@ should be regarded as occurring together to form a rare fault. This electrical apparatus is intended for use in Class I@ Zone 0 hazardous areas@ in which explosive gas atmospheres caused by mixtures of air and gases@ vapours or mists under normal atmospheric conditions are present continuously@ for long periods or frequently. This standard also applies to apparatus mounted across the boundary between Class I@ Zone 0 and Class I@ Zone 1. EXAMPLE: In the wall of a storage vessel. This standard also applies to apparatus installed outside Class I@ Zone 0@ but electrically connected to apparatus inside Class I@ Zone 0 (associated apparatus). This standard supplements the general requirements in ANSI/ISA-60079-0 NOTE 2 In designing apparatus for operation in explosive gas atmospheres under conditions other than the atmospheric conditions given in IEC 60079-0@ this standard may be used as a guide. However@ additional testing is recommended related specifically to the intended conditions of use. This is particularly important when the types of protection ??Flameproof enclosure' (ANSI/ISA-60079-1) and ??Intrinsic safety' (ANSI/ISA- 60079-11) are applied. NOTE 3 The classification of hazardous areas in zones is defined in the National Electrical Code. NOTE 4 There may be other non-electrical sources of ignition (for example ultrasonic@ optical or ionizing radiation) that are not addressed by this standard; these should also be taken into consideration (see@ for example@ EN 1127-1).