A US classification for an area in which explosive gas/air mixtures are, or may be expected to be, present in quantities such as to require special precautions for the construction and use of electrical apparatus.
Division 1 (hazardous). Where concentrations of flammable gases or vapors exist a) continuously or periodically during normal operations; b) frequently during repair or maintenance or because of leakage; or c) due to equipment breakdown or faulty operation which could cause simultaneous failure of electrical equipment. (See the US “National Electrical Code, Paragraph 500 4(a)” for detailed definition.)
Division 2 (normally nonhazardous). Locations in which the atmosphere is normally nonhazardous and may become hazardous only through the failure of the ventilating system, opening of pipe lines, or other unusual situations. (See the US “National Electrical Code, Paragraph 500 4(b)” for detailed definition.)
Nonhazardous. Areas not classified as Division 1 or Division 2 are considered nonhazardous. NOTE: It is safe to have open flames or other continuous sources of ignition in nonhazardous areas [S12.4].