These requirements cover explosion-proof and dust-ignition-proof electrical equipment for installation and use in hazardous (classified) locations@ Class I@ Division 1@ Groups A@ B@ C@ and D@ and Class II@ Division 1@ Groups E@ F@ and G@ in accordance with the National Electrical Code@ NFPA 70. These requirements also cover explosion-proof electrical equipment for installation and use in Class I@ Zone 1@ Groups IIA@ IIB@ and IIC hazardous (classified) locations and dust-ignition-proof equipment for use in Zone 20@ 21@ and 22 locations. These requirements also cover explosion-proof electrical equipment that has been investigated for use in one or more specific gas or vapor atmospheres with or without additional Class I Groups. See 60.6. These requirements do not cover equipment for use in hazardous (classified) locations specifically covered in a separate standard. These requirements do not cover electrostatic devices@ circuits or systems; refrigeration system controllers or the internal construction of electrical instruments such as meters. These requirements cover equipment for use under the following atmospheric conditions: a) A minimum ambient temperature of minus 50??(minus 58??; b) An oxygen concentration not greater than 21 percent by volume; and c) A nominal barometric pressure of one atmosphere. Equipment covered by this standard shall also comply with the applicable requirements for similar equipment for use in ordinary unclassified locations.