A hazardous location is an area where the possibility of fire or explosion can exist due to the presence of flammable or combustible gases or vapors, combustible dusts, or ignitable fibers/flyings. Electric arcs, sparks, and/or heated surfaces can serve as a source of ignition in such environments.

Article 500 is the first of seven articles that address hazardous locations. It’s the basis for the other six. Articles 501, 502, and 503 provide the requirements for Class I, Class II, and Class III locations, respectively. The class designations are defined by 500.5. Article 504 provides the requirements for “intrinsically safe” equipment used in Class I, II, and III locations. Articles 510 through 517 cover specific occupancies, garages, aircraft hangers, motor fuel dispensing facilities, bulk storage plants, spray application, dipping and coating processes, and health care facilities [500.9].