The rapid thermal oxidation (combustion) of a fuel source resulting in heat and light emission. There are various types of fire, classified by the type of fuel and associated hazards. In the US, the National Fire Protection Association (NFPA) classifies fires and hazards by types of fuel or combustible in order to facilitate the control and extinguishing of fires: Class A are ordinary combustibles such as wood, cloth, paper, rubber, and certain plastics; Class B are flammable or combustible liquids, flammable gases, greases, and similar materials; Class C is energized electrical equipment; Class D are combustible metals, such as magnesium, titanium, zirconium, sodium, and potassium.

http://www.nfpa.org/ Official website of the National Fire Protection Association in the US.