This standard specifies the construction and testing of intrinsically safe apparatus@ intended for use in potentially explosive atmospheres and for associated apparatus@ which is intended for connection to intrinsically safe circuits which enter such atmospheres. It also contains details of the test apparatus previously published as IEC 60079-3. This standard supplements ANSI/ISA-12.00.01 (IEC 60079-0 Mod):1999@ the requirements of which apply to intrinsically safe apparatus and to associated apparatus except as indicated in the following list. If associated apparatus is protected by a type of protection listed in ANSI/ISA-12.00.01 (IEC 60079-0 Mod) then the requirements of that method of protection together with the relevant parts of ANSI/ISA-12.00.01 (IEC 60079-0 Mod) also apply to the associated apparatus. The list of exclusions which follows is directly applicable to associated apparatus intended for use in situations where there is no potentially explosive atmosphere and in other circumstances should be used in combination with the requirements of the other methods of protection. This standard is applicable to electrical apparatus in which the electrical circuits themselves are incapable of causing an explosion in the surrounding explosive atmospheres. This standard is also applicable to electrical apparatus or parts of electrical apparatus located outside the potentially explosive atmosphere or protected by another type of protection listed in ANSI/ISA-12.00.01 (IEC 60079-0 Mod)@ where the intrinsic safety of the electrical circuits in the potentially explosive atmosphere may depend upon the design and construction of such electrical apparatus or parts of such electrical apparatus. The electrical circuits exposed to the potentially explosive atmosphere are evaluated for use in such an atmosphere by applying this standard.