Fire
Fire is the rapid oxidation of a fuel in the exothermic chemical process of combustion, releasing heat, light, and various reaction products.
Flames, the most visible portion of the fire, are produced in the combustion reaction when the fuel reaches its ignition point temperature. Flames from hydrocarbon fuels consist primarily of carbon dioxide, water vapor, oxygen, and nitrogen. If hot enough, the gases may become ionized to produce plasma. The color and intensity of the flame depend on the type of fuel and composition of the surrounding gases.
Fire, in its most common form, has the potential to result in conflagration, which can lead to permanent physical damage. Fire directly impacts land-based ecological systems worldwide. The positive effects of fire include stimulating plant growth and maintaining ecological balance. Its negative effects include hazards to life and property, atmospheric pollution, and water contamination. When fire removes protective vegetation, heavy rainfall can cause soil erosion. 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. 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. Various technologies and strategies have been devised to prevent, manage, mitigate, and extinguish fires, with professional firefighters playing a leading role. For example, most home fires start from unattended cooking, although cigarettes are a major cause. Smoke detectors and sprinkler systems greatly reduce harm from home fires.
Etymology
The word fire comes from Old English fȳr and has cognates in many Germanic languages and other Indo-European languages. The Proto-Germanic nominative form is reconstructed as fōr, descending from Proto-Indo-European péh2wr. An alternative spelling existed in Middle English: fier; still preserved in fiery.The word ignite is derived from the classical Latin ignis meaning fire. The Greek term for fire, pyr, is used in words such as pyroclastic or pyrotechnic.
History
Fossil record
The fossil record of fire first appears with the establishment of a land-based flora in the Middle Ordovician period,. These land plants contributed large amounts of oxygen to the atmosphere when they released it as a waste product. When this concentration rose above 13%, it permitted the possibility of wildfire. Wildfire is first recorded in the Late Silurian fossil record,, by fossils of charred plants. Apart from a controversial gap in the Late Devonian, charcoal is present ever since. The level of atmospheric oxygen is closely correlated with the amount of charcoal in the fossil record, clearly pointing to oxygen as the key factor in the prevalence of wildfire. Fire also became more abundant when grasses became the dominant component of many ecosystems, around, providing excellent tinder for more rapid spread of fire. This widespread emergence of wildfire may have initiated a positive feedback process, whereby they produced a warmer, drier climate more conducive to fire. Fire made it possible for humans to live at colder places and dark caves. It also protected humans against dangerous animals. It caused nutritional changes, it enabled us to eat with more variation.Human control
The period of history characterized by the influence of human-caused fire activity on Earth has been dubbed the pyrocene. This epoch includes the burning of fossil fuels, especially for technological uses.Early human control
The ability to control fire was a dramatic change in the habits of early humans. Making fire to generate heat and light made it possible for people to cook food, simultaneously increasing the variety and availability of nutrients and reducing disease by killing pathogenic microorganisms in the food. The heat produced would also help people stay warm in cold weather, enabling them to live in cooler climates. Fire also kept nocturnal predators at bay. Evidence of occasional cooked food is found from, suggesting it was used in a controlled fashion. Other sources put the date of regular use at 400,000 years ago. Evidence becomes widespread around 50 to 100 thousand years ago, suggesting regular use from this time; resistance to air pollution started to evolve in human populations at a similar point in time. The use of fire became progressively more sophisticated, as it was used to create charcoal and to control wildlife from tens of thousands of years ago.
File:Potjiekos over a fire.gif|thumb|Food being cooked in a cauldron above fire in South Africa.
By the Neolithic Revolution, during the introduction of grain-based agriculture, people all over the world used fire as a tool in landscape management. These fires were typically controlled burns or "cool fires", as opposed to uncontrolled "hot fires", which damage the soil. Hot fires destroy plants and animals, and endanger communities. This is especially a problem in the forests of today where traditional burning is prevented in order to encourage the growth of timber crops. Cool fires are generally conducted in the spring and autumn. They clear undergrowth, burning up biomass that could trigger a hot fire should it get too dense. They provide a greater variety of environments, which encourages game and plant diversity. For humans, they make dense, impassable forests traversable.
Another human use for fire in regards to landscape management is its use to clear land for agriculture. Slash-and-burn agriculture is still common across much of tropical Africa, Asia and South America. For small farmers, controlled fires are a convenient way to clear overgrown areas and release nutrients from standing vegetation back into the soil. However, this useful strategy is also problematic. Growing population, fragmentation of forests and warming climate are making the earth's surface more prone to ever-larger escaped fires. These harm ecosystems and human infrastructure, cause health problems, and send up spirals of carbon and soot that may encourage even more warming of the atmosphere – and thus feed back into more fires. Globally today, as much as 5 million square kilometres – an area more than half the size of the United States – burns in a given year.
Later human control
Throughout much of history, cultures attempted to explain nature and the properties of matter by proposing a set of four classical elements, of which fire formed one of the components. As scientific understanding developed following the Middle Ages, this philosophy was replaced by a set of chemical elements and their interactions. Instead, the classical elements found an equivalency in the states of matter: solid, liquid, gas, and plasma.During the 17th century, a study of combustion was made by Jan Baptist van Helmont who discovered that burning charcoal released a gas sylvestris, or wild spirit. This was subsequently incorporated into Phlogiston theory by Johann Joachim Becher in 1667 and more formally by Georg Ernst Stahl in 1697; a concept that would strongly influence alchemical thinking for nearly two centuries. It was Antoine Lavoisier who demonstrated that combustion did not involve the release of a substance, but rather something was being taken up. In 1777, Lavoisier proposed a new theory of combustion based on the reaction of a material with a component of air, which he termed oxygène. By 1791, Lavoisier's chemistry concepts had been widely adopted by young scientists, and Phlogiston theory was rejected.
File:Burning stove fire.jpg|thumb|Firewood combusting into ash and coal in a wood-burning stove, 2025
Fire has been used for centuries as a method of torture and execution, as evidenced by death by burning as well as torture devices such as the iron boot, which could be heated over an open fire to the agony of the wearer.
There are numerous modern applications of fire. In its broadest sense, fire is used by nearly every human being on Earth in a controlled setting every day. Users of internal combustion vehicles employ fire every time they drive. Thermal power stations provide electricity for a large percentage of humanity by igniting fuels such as coal, oil or natural gas, then using the resultant heat to boil water into steam, which then drives turbines.
Use in war
The use of fire in warfare has a long history. Fire was the basis of all early thermal weapons, including incendiary devices, heated projectiles, and the use of smoke. This class of weapons was particularly evident during naval battles and siege warfare. The Byzantine fleet used Greek fire to attack ships and men.The invention of gunpowder in China led to the fire lance, a flame-thrower weapon dating to around 1000 CE which was a precursor to projectile weapons driven by burning gunpowder. The earliest modern flamethrowers were used by infantry in the First World War, first used by German troops against entrenched French troops near Verdun in February 1915. They were later successfully mounted on armoured vehicles in the Second World War.
Hand-thrown incendiary bombs improvised from glass bottles, later known as Molotov cocktails, were deployed during the Spanish Civil War in the 1930s. During that war, incendiary bombs were deployed against Guernica by Fascist Italian and Nazi German air forces that had been created specifically to support Franco's Nationalists.
Incendiary bombs were dropped by Axis and Allies during the Second World War, notably on Coventry, Tokyo, Rotterdam, London, Hamburg and Dresden. In the latter two cases, firestorms were deliberately caused in which a ring of fire surrounding each city was drawn inward by an updraft created by a central cluster of fires. The United States Army Air Force extensively used incendiaries against Japanese targets in the latter months of the war, devastating entire cities constructed primarily of wood and paper houses. The incendiary fluid napalm was used in July 1944, towards the end of the Second World War, although its use did not gain public attention until the Vietnam War.