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Fire is the rapid oxidation of a material (the fuel) in the exothermic chemical process of combustion, releasing heat, light, and various reaction products.[1][a] Flames, the most visible portion of the fire, are produced in the combustion reaction when the fuel reaches its ignition point. Flames consist primarily of carbon dioxide, water vapor, oxygen and nitrogen. If hot enough, the gases may become ionized to produce plasma.[2] The color and intensity of the flame depend on the type of fuel and composition of the air.[3]
Fire, in its most common form, has the potential to result in conflagration, which can lead to permanent physical damage. It impacts ecological systems worldwide. Fire's positive effects of include stimulating plant growth and maintaining ecological balance. Its negative effects include hazard to life and property, atmospheric pollution, and water contamination.[4] When fire removes protective vegetation, heavy rainfall can cause soil erosion.[5] Additionally, the burning of vegetation releases nitrogen into the atmosphere, unlike other plant nutrients such as potassium and phosphorus which remain in the ash and are quickly recycled into the soil.[6][7] This loss of nitrogen produces a long-term reduction in the fertility of the soil, though it can be recovered by nitrogen-fixing plants such as clover, peas, and beans, by decomposition of animal waste and corpses, and by natural phenomena such as lightning.
Fire is one of the four classical elements and has been used by humans in rituals, in agriculture for clearing land, for cooking, generating heat and light, for signaling, propulsion purposes, smelting, forging, incineration of waste, cremation, and as a weapon or mode of destruction.
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