1 Scope

1.1 These requirements cover explosion-proof, dust-ignition-proof and dust-tight portable and fixed electric heaters for installation and use in hazardous (classified) locations, Class I, Divisions 1 and 2, Groups A, B, C, and D; Class II, Division 1, Groups E, F, and G; Class II, Division 2, Groups F and G; and Class III, Divisions 1 and 2, in accordance with the National Electrical Code, NFPA 70.

1.2 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.

1.3 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 55.4.

1.4 These requirements cover electric air heaters, electric hot-water or steam radiators, and electric hot plates rated 600 volts or less.

1.5 These requirements also cover paint heaters, rated 600 volts or less, for use at pressures not exceeding 100 psig (690 kPa). Paint heaters operating at more than 100 psig may be investigated in accordance with these requirements and any additional requirements judged to be necessary.

1.6 These requirements do not cover medical equipment.

1.7 These requirements cover heaters for use only under the following atmospheric conditions:

a)    A minimum ambient temperature of minus 50°C (minus 58°F);

b)    An oxygen concentration not greater than 21 percent by volume; and

c)    A nominal barometric pressure of one atmosphere.