Fires and burning have often been used in religious sacrifices, as the smoke of the fire disperses into the heavens. Fire is one of the four classical elements, as well as one of the five Chinese elements.
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 Nowadays, large scale energy is usually not produced by fires of burning wood, but has been replaced by hydrocarbon oil and coal, and in some cases nuclear energy or renewable energy sources.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.
The Fire Tetrahedron
There are four elements that maintain the combustion process, and the absence of any one of them will prevent a fire. The removal of these elements is the job of firefighters.
- The reducing agent (fuel) may be removed from the site of a fire to curb its spread. In forestry, controlled burns are used to keep the available fuel supply low, so that intense fires do not occur. Sometimes you can stop the flow of a liquid or gas fuel. In the case of a burning pipeline, sometimes the flow of fuel can simply be turned off.
- An oxidizer (usually oxygen) is needed to react with the fuel. Sand, foam, or gases which do not support combustion (such as carbon dioxide) may be used to stop the flow of oxygen to a fire (smother the flames). In particularly violent fires, such as those of the Kuwaiti oil wells during the Gulf War, explosions may be used instead.
- Heat is what allows liquid fuels to be vaporized, and solid fuels to undergo pyrolysis. Solids and liquids do not burn directly, they must first be converted into a gas through pyrolysis or vaporization. Removal of enough heat prevents fuels from burning. Water is uniquely effective at removing heat due to its high specific heat capacity.
- The chemical chain reaction is what perpetuates combustion; compounds such as halon extinguishing agents cause the chain reaction to be broken. The precise mechanism is not known, but it is thought that the halogen radicals end the reactions that support combustion.
FIRE can also refer to the Foundation for Individual Rights in Education a civil liberties organization.