Hazardous areas and locations are classified by group, class, and division. These classifications are determined by the atmospheric mixtures of various gases, vapors, dust, and other materials present. The intensity of the explosion that can occur depends on concentrations, temperatures, and many other factors that are listed in NFPA codes.

Hazardous locations must be well understood by anyone designing, installing, working on, or inspecting electrical equipment and wiring in such areas. Such locations carry a threat of flammable or combustible gases, vapors, or dusts being present some or all of the time.

Information in this section will assist in classifying areas or locations with respect to hazardous conditions, whether from atmospheric concentrations of hazardous gases, vapors, and deposits, or from accumulations of readily ignitable materials.

This section covers the requirements for electrical equipment and wiring in locations that are classified according to the properties of the flammable vapors, liquids, or gases or combustible dusts that may be present and the likelihood that a flammable or combustible concentration is present. The hazardous (classified) locations are assigned the following designations:

1. Class I Division 1

2. Class I Division 2

3. Class II Division 1

4. Class II Division 2.

5. Class I, Zone 0, Zone 1, Zone 2

Class III fibers and flyings are not covered in this section. The following contain more in-depth design and engineering requirements:

1. National Electrical Code, NFPA 70, Chapter 5, Article 500

2. 29 CFR 1910 Subpart S, Electrical 1910.307

3. NFPA 497M, "Classification of Gases, Vapors, and Dusts for Electrical Equipment in Hazardous Classified Locations"

4. NFPA Handbook, "Electrical Installations in Hazardous Locations, " by P. J. Schram and M. W. Earley

5. NFPA 70E, Chapter 5, "Hazardous (Classified) Locations"

6. Manufacturers' product recommendations and suggestions for hazardous areas (e.g., the Crouse-Hinds Code Digest)

7. NFPA 325, "Fire Hazard Properties of Flammable Liquids, Gases, and Volatile Solids"

8. Underwriters Laboratory, "Hazardous Location Equipment Directory," containing listings and classifications currently in effect

9. ANSI/UL 913, "Intrinsically Safe Apparatus"

10. NFPA 496, "Purged and Pressurized Enclosure for Electrical Equipment in Hazardous Locations."