A fire is an oxidation process of combustible gases ejected from a fuel subjected to heat or other energy source. Fire is one of the four classical elements, as well as one of the five chinese elements. Controlling fire was one of humankind's first great achievements and made possible migration to colder climes which otherwise would have remained out of reach for colonization.
The burning of wood is often the first association to the word fire, and trees have since ancient times supplied much of the energy needed by humans. In the past, metal smelting and charcoal production consumed large quantities of wood for their production. Nowadays, large scale energy is usually not produced by fires of burning wood, but has been replaced by hydrocarbon oil and coal, and in some cases nuclear energy or renewable energy sources. Wood burning remains a heat source in third world countries and where other sources of energy are unavailable.
There are four components that maintain the combustion process, namely fuel, oxygen, heat, and the ability to continue the chemical reaction. Fire fighters tackle fire by cutting off the supply to one or more of these components. For example, water is poured on a fire to reduce the heat (latent heat for water evaperation); controlled burning to exhaust the fuel sources; explosion to drive out air to suffocate a fire (e.g. in Kuwait's oil field fire after the gulf war); and halon is a chemical suppressant of the chemical reactions.