Electrical groupings are based on the characteristics of the materials involved. These include the following:1.Class I, Group A: Atmospheres containing acetylene.2.Class I, Group B: Atmospheres containing hydrogen, fuel and combustible process gases containing more than 30 percent hydrogen by volume, or gases or vapors of equivalent hazard such as butadiene, ethylene oxide, propylene oxide, and acrolein.3.Class I, Group C: Atmospheres such as ethyl ether, ethylene, or gases or vapors of equivalent hazard.4.Class I, Group D: Atmospheres such as acetone, ammonia, benzene, butane, cyclopropane, ethanol, gasoline, hexane, methanol, methane, natural gas, naphtha, propane, or gases or vapors of equivalent hazard.5.Class II, Group E: Atmospheres containing combustible metal dusts, including aluminum, magnesium and their commercial alloys, or other combustible dusts whose particle size, abrasiveness, and conductivity present similar hazards in the use of electrical equipment.6.Class II, Group F: Atmospheres containing combustible carbonaceous dusts, including carbon black, charcoal, coal, or coke dusts that have more that 8 percent entrapped volatiles or dusts that have been sensitized by other materials so that they present an explosion hazard.7.Class II, Group G: Atmospheres containing combustibles dusts not included in Group E or F, including flour, grain, wood, plastic, and chemicals.