Class = form of the hazard that is present. Group = actual charactertics of the substance that is hazardous. Class I (Gas or Vapor) Group; A = Acetylene; B = Hydrogen and Manufactured Gas; C = Ethyl-Ether, Ethylene, and Cyclopropane; D = Gasoline,Hexane, Naphtha, Benzine, Butane, Propane; Alcohol,Lacquer Solvent Vapors and Natural Gas Class II (Dusts) Group E = Metal Dusts (Special Seals); F = Carbon Black, Coal, or Coke Dust; G = Flour, Starch or Grain Dust