Applies to electric equipment and wiring in locations classified according to the properties of any flammable gases, liquids or vapors, or combustible fibers or dusts, that may be present, and to how likely a flammable or combustible concentration or amount is. Each room, section or area is classified on its own, into the Class I, II and III, Division 1 and 2 designations defined in 1926.449, and all other subpart K rules apply unless modified here. Equipment, wiring methods and installations in these locations must be intrinsically safe, approved for the hazardous location, or safe for the hazardous location. Intrinsically safe equipment and wiring are allowed in any classified location covered by their listing or labeling. Equipment approved for the location must be approved both for the class and for the ignition or combustion properties of the particular gas, vapor, dust or fiber present, and may not be used unless marked with class, group and operating temperature or range based on a 40 degree C ambient, the temperature marking not exceeding the ignition temperature of the substance present. Marking exceptions: non-heat-producing items such as junction boxes, conduit and fittings, and heat-producing items whose maximum temperature is 100 degrees C (212 degrees F) or less, are exempt from temperature marking; fixed lighting fixtures marked only for Class I, Division 2 need no group; fixed general-purpose Class I equipment other than fixtures that is acceptable for Class I, Division 2 need not show class, group, division or temperature; and the same applies to fixed dust-tight equipment other than fixtures acceptable for Class III and for Class II, Division 2. Equipment that is safe for the location must be of a type and design that the employer demonstrates will protect against the combustibility and flammability hazards present; the NEC (NFPA 70) guidelines are one way, though not the only way, to show this. All conduits must be threaded and made wrench-tight, and where a tight threaded joint is impractical a bonding jumper is used.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.