CHAPTER 9 - Electrical Hazardous (Classified) Area Design and Safe Work Practices

Abstract

Hazardous (classified) locations are defined by two separate methods: division classification and zone classification. These classification methods are defined in the National Electrical Code (NEC) Articles 500 and 505. The division classification system uses three descriptors to define the presence of combustible or flammable materials. Class designation describes the type of materials that may be present, including gas, liquid-produced vapors, dusts, fibers, or flying. The Division designation defines the degree of probability that those materials will be present to form flammable or combustible fuel–air mixtures. Group designation is based on the physical characteristics of the flammable or combustible properties of the gases, liquid-produced vapors, or dusts. The NEC®), NFPA 70® establishes the requirements for electrical installations in areas that are classified as hazardous locations due to materials handled, processed, or stored. It does not classify any areas involved with the manufacture, handling, storage, transportation, or use of explosive materials. Explosive materials would consist of blasting powder, dynamite, and ammunition. Standards involving those materials can be found in NFPA 495, Explosive Materials Code. NEC Article 500.5 establishes the criteria for defining division classification for hazardous locations. Areas are classified by the class of the vapors, liquids, gases, combustible dusts, flyings, or fibers, which may be present, as well as the likelihood that a sufficient ignitable quantity or concentration of flammable or combustible materials will be present.