NEC designations that define the specific type of gas, vapor, or dust present in a hazardous environment
Class I Groups
Group A: Acetylene
Group B: Hydrogen or gases of equivalent hazard
Group C: Ethylene, cyclopropane, and similar gases
Group D: Propane, gasoline, butane, alcohol, natural gas, acetone, benzene, and similar vapors
Class II Groups
Group E: Combustible metal dusts such as aluminum and magnesium
Group F: Carbonaceous dusts such as coal, carbon black, and coke with volatile content above 8%
Group G: Organic dusts such as grain, flour, starch, cocoa, wood, plastics, and chemicals
