Fire

From Wikipedia, the free encyclopedia

Conflagration redirects here. For other uses of the term "Fire", see Fire (disambiguation). See Enjo for the 1958 film by Ken Ichikawa.

A forest fire

Fire is a rapid oxidation process that creates light, heat, and smoke, and varies in intensity. It is commonly used to describe either a fuel in a state of combustion (e.g., a campfire, or a lit fireplace or stove) or a violent, destructive and uncontrolled burning (e.g., in buildings or a wildfire). The discovery of making fire is considered one of the most important evolutions of humankind, for it allowed higher hominids to ward off wild animals, cook food, and provide warmth as well as a source of light in darkness.

1 Controlling fire
2 Fire and religion
3 Fire as a power source
4 Chemistry
- 4.1 Flame
- 4.2 Typical temperatures of fires and flames
5 Fire protection and prevention
6 See also
7 References
- 7.1 Citations
- 7.2 General references
8 External links

[edit] Controlling fire

The ability to control fire in order to provide heat and light was one of humankind's first great achievements. Fire making to generate heat and light made it possible for people to migrate to colder climates and enabled people to cook food — a key step in the fight against disease. Archaeology indicates that ancestors of modern humans such as Homo erectus might have controlled fire as early as 790,000 years ago. The Cradle of Humankind site has evidence for controlled fire from 1 to 1.8 million years ago.^[1] 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" that 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 fall. 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.

A blacksmith's fire, used primarily for forging iron.

The first technical application of the fire may have been the extracting and treating of metals. 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.

The use of fire in warfare has a long history. Hunter-gatherer groups around the world have been noted as using grass and forest fires to injure their enemies and destroy their ability to find food, so it can be assumed that fire has been used in warfare for as long as humans have had the knowledge to control it. Homer detailed the use of fire by Greek commandos who hid in a wooden horse to burn Troy during the Trojan war. Later the Byzantine fleet used Greek fire to attack ships and men. American and British warplanes destroyed the German city of Dresden on February 14, 1945 by creating a firestorm, in which a ring of fire surrounding the city was drawn inward by an updraft caused by a central cluster of fires. In the Vietnam War, the Americans dropped napalm from the air. More recently many villages were burned during the Rwandan Genocide. Aerial bombing of cities, including firebombing using incendiary bombs, was also used frequently during World War II. Molotov cocktails are cheap to construct and are common used as well.

[edit] Fire and religion

See also Fire worship.

Vulcan of ancient mythology, using fire for his forge

Fires and burning have often been used in religious rites and symbolism.

Fire is one of the four classical elements, as well as one of the five Chinese elements. In Hinduism fire is one of five sacred elements (space, air, fire, water, earth) of which all living creatures are comprised and is considered an eternal witness essential to sacred religious ceremonies.

Fire is a symbol of Ahura Mazda, the god of the Zoroastrian religion. A Zoroastrian place of worship is known as a Fire Temple. Fire is also an important part of Calcination, the fire operation in the art of alchemy.

In Roman mythology, Vulcan is the god of fire. The analogue in Greek mythology is Hephaestus. In Greek mythology, Prometheus is the Titan chiefly honored for stealing fire from the gods in the stalk of a fennel plant and giving it to mortals for their use. Orthodox Christians light candles in Churches for the spirit of the dead and for the well being of the living.

In Judaism fire also has great significance. Candles are lit to usher in holidays and to separate Sabbath from the rest of the week, as well as to remember the dead. Another important fire symbol is the Eternal Flame, which was a fire always kept burning in the First and Second Temples.

In Wicca, the element or spirits of fire are one of the four sacred elements of nature. Fire is associated usually with the southern side of a circle or altar arrangement. The other elements include water, air, and earth.

In Christianity, fire is a symbol of the Holy Ghost. It is also often used in descriptions of Hell. Additionally, a fire is used in the Roman Catholic Mass during the Easter Vigil. In the Middle Ages, the judgment of God was appealed to by the ordeal of fire. In Spain, bonfires as associated to the eve of Saint John the Evangelist, a Christianization of the summer solstice, especially in Alicante. In Valencia, Saint Joseph is celebrated by burning allegorical figures on the streets, a Christianization of the spring equinox.

Fire was also a purifier. Giovanni da Pian del Carpine narrates that when he visited the Mongol Batu Khan, he was made to pass between two fires^[2] to remove possible witchcraft or poisons.

Fire is sometimes associated with Halloween.

In the Rastafarian tradition fire has a significant role. At the Holy Ceremonies, known as Groundation and Nyahbinghi Theocracy, a very large fire is lit, and is symbolic in creating contact with the Almighty Jah Rastafari. In Rastafari Theology, fire is recognized as the main force in all things, or fire being a means to describe heat. For instance, when a human being dies or animal, they loose their heat, or as the Rastas insist, fire.

[edit] Fire as a power source

A coal-fired power station in the People's Republic of China.

Fire has supplied much of the energy which has helped humans since ancient times. Wood was a prehistoric fuel. The use of fossil fuels such as petroleum, natural gas and coal in power plants supplies the vast majority of the world's electricity today. The International Energy Agency states that nearly 80% of the world's power comes from these sources.^[3] The fire in a power station is used to heat water, creating steam that drives turbines. The turbines then spin an electric generator to produce power.

The burning of wood is often the first association to the word "fire". It is common in a developing country for wood to be the primary energy source as well. For instance, in Africa, 65% of the energy used comes from the burning of biomass.^[4] What is less obvious is that wood burning power stations are less environmentally destructive than the fired oil power station in two major respects. E.ON UK is soon to build a 44 megawatt wood fired power station in the United Kingdom for these reasons, as reported in the Guardian newspaper in October 2005:^[5] first, wood is a renewable resource, especially if trees are grown in a modern, sustainable way. Second, the carbon dioxide emissions are negligible because no more carbon dioxide can be produced by burning than would be produced by the natural rotting of wood. Thus, over a 100-year timescale, the effect is carbon-neutral.^[6]

[edit] Chemistry

A car on fire.

Broadly speaking there are two types of fire, flaming and smouldering fires. The former is the rapid oxidation of a fuel (combustion) with associated flame, heat, and light. The flame itself is a thin region of gas where intense chemical reactions are taking place. The reacting gas in this area is often hot enough to glow visibly, although some flames can be nearly invisible. Typical flames are just incandescent gas, and are plasmas, because they are hot enough to be sufficiently ionized.

The latter, a smouldering fire, is a flameless form of combustion, deriving its heat from oxidations occurring on the surface of a solid fuel. Two common examples are glowing coals and cigarettes. Smoulder propagates in a creeping fashion over solid fuels or inside porous fuels, and its temperature and heat released are low in comparison. The difference between flaming and smouldering combustion is that the former occurs on the surface of the solid rather than in the gas phase.

Fires start when both a flammable and/or a combustible material with an adequate supply of oxygen or another oxidizer is subjected to enough heat. The common fire-causing sources of heat include a spark, another fire (such as an explosion, a fire in the oven or fireplace, or a lit match, lighter or cigarette) and sources of intense thermal radiation (such as sunlight, a flue, an incandescent light bulb or a radiant heater). Mechanical and electrical machinery may cause fire if combustible materials used on or located near the equipment are exposed to intense heat from Joule heating, friction or exhaust gas. Fires can sustain themselves by the further release of heat energy in the process of combustion and may propagate, provided there is a continuous supply of oxygen and fuel. Fires may become uncontrolled and cause great damage to and destruction of human life, animals, plants and property. Fires can also occur through instantaneous combustion. This highly disputed phenomenon is currently under research. It is known that this does occur in a vacuum^{[citation needed]} but is disputed as to whether or not it occurs in nature. This act of combustion leads to an exothermic reaction, which in turn is able to be used as a power source. By harnessing this heat from the combustion of coal, wood, petroleum, and oils; we are able to produce power for things such as automotives, power cells, and power plants.

Fire is extinguished when any of the elements of the so-called fire tetrahedron—heat, oxygen, fuel or the self-sustaining chemical reaction — are removed. The unburnable solid remains of a combustible material left after a fire are called ash.

Fire can be considered to be a low temperature partial plasma. Plasma; an ionized gas, usually considered to be a distinct state of matter

[edit] Flame

For more detailed information on the color of flames, see flame.

A flame is an exothermic, self-sustaining, oxidizing chemical reaction producing energy and glowing hot flame, of which a very small portion is plasma. It consists of reacting gases and solids emitting visible and infrared light, the frequency spectrum of which is dependent on the chemical composition of the burning elements and intermediate reaction products.

In many cases such as burning organic matter like wood or incomplete combustion of gas, incandescent solid particles, soot produces the familiar red-orange 'fire' color light. This light has a continuous spectrum. Complete combustion of gas has a dim blue color due to the emission of single wavelength radiations from various electron transitions in the excited molecules formed in the flame. Usually oxygen is involved, but hydrogen burning in chlorine produces a flame as well, producing the toxic acid hydrogen chloride (HCl). Other possible combinations producing flames, amongst many more, are fluorine and hydrogen, or hydrazine and nitrogen tetroxide. Recent discoveries by the National Aeronautics and Space Administration (NASA) of the United States also has found that gravity plays a role. Modifying the gravity causes different flame types.^[7]

The glow of a flame is somewhat complex. Black-body radiation is emitted from soot, gas, and fuel particles, though the soot particles are too small to behave like perfect blackbodies. There is also photon emission by de-excited atoms and molecules in the gases. Much of the radiation is emitted in the visible and infrared bands. The color depends on temperature for the black-body radiation, and chemical makeup for the emission spectra. The dominant color in a flame changes with temperature. The photo of the forest fire is an excellent example of this variation. Near the ground, where most burning is occurring, it is white, the hottest color possible for organic material in general, or yellow. Above the yellow region, the color changes to orange, which is somewhat cooler, then red, which is cooler still. Above the red region, combustion no longer occurs, and the uncombusted carbon particles are visible as black smoke. To eliminate a flame in combustion vehicles there are different steps that are taken. This depends largely on whether the fuel is oil, wood, or high energy (such as fuel for jet engines).

The common distribution of a flame under normal gravity conditions depends on convection, as soot tends to rise to the top of a general flame, such as in a candle in normal gravity conditions, making it yellow. In microgravity or zero gravity, such as an environment in outer space, convection no longer occurs, and the flame becomes spherical, with a tendency to become more blue and more efficient (although they will go out if not moved steadily as the CO₂ from combustion does not disperse in microgravity, and tends to smother the flame). There are several possible explanations for this difference, of which the most likely is that the temperature is evenly distributed enough that soot is not formed and complete combustion occurs.^[8] Experiments by NASA in microgravity reveal that diffusion flames in microgravity allow more soot to be completely oxidized after they are produced than diffusion flames on Earth, because of a series of mechanisms that behaved differently in microgravity when compared to normal gravity conditions.^[9] These discoveries have potential applications in applied science and industry, especially concerning fuel efficiency.

[edit] Typical temperatures of fires and flames

Oxyhydrogen Flame (2000 °C or above)(3645 °F)
Bunsen Burner Flame (min. to max. setting) (1300 to 1600 °C)(2372 to 2912 °F)
Blowtorch Flame (1800 °C)(2370 °F)
Candle Flame (760 °C)(1400 °F)
Smouldering cigarette:
- Temperature without drawing: Side of the lit portion; 400 °C (or 750 °F);Middle of the lit portion: 585 °C (or 1110 °F)
- Temperature during drawing: Middle of the lit portion: 700 °C (or 1290 °F)

[edit] Fire protection and prevention

Flammable gas warning

Main article: Fire protection

codes and life safety codes and offer fire fighting services to extinguish or contain uncontrolled fires. Trained firefighters use fire trucks, water supply resources such as water mains and fire hydrants, and an array of other equipment to combat the spread of fires.

To ensure fire safety of buildings, all building products, materials and furnishings in the United States must be tested for fire resistance, combustibility and flammability before they can be used in construction. The same applies to upholstery, carpeting and plastics used in vehicles and vessels. Buildings, especially schools and tall buildings, often conduct fire drills to inform and prepare citizens on how to react to a building fire.

Purposely starting destructive fires constitutes arson and is a criminal offense in most jurisdictions.

There are many different classification systems used for uncontrolled fires; in Europe and Australasia six groups are used:

Class A: Fires that involve flammable solids such as wood, cloth, rubber, paper, and some types of plastics.
Class B: Fires that involve flammable liquids or liquifiable solids such as petrol/gasoline, oil, paint, some waxes & plastics, but not cooking fats or oils.
Class C: Fires that involve flammable gases, such as natural gas, hydrogen, propane, butane.
Class D: Fires that involve combustible metals, such as sodium, magnesium, and potassium.
Class E: Fires that involve any of the materials found in Class A and B fires, but with the introduction of an electrical appliances, wiring, or other electrically energized objects in the vicinity of the fire, with a resultant electrical shock risk if a conductive agent is used to control the fire.
Class F: Fires involving cooking fats and oils. The high temperature of the oils when on fire far exceeds that of other flammable liquids making normal extinguishing agents ineffective.

In the United States fires are generally classified into five groups: A, B, C, D, and K

Class A: Fires that involve wood, cloth, rubber, paper, and some types of plastics.
Class B: Fires that involve gasoline, oil, paint, natural and propane gases, and flammable liquids, gases, and greases.
Class C: Fires that involve any of the materials found in Class A and B fires, but with the introduction of electrical appliances, wiring, or other electrically energized objects in the vicinity of the fire.
Class D: Fires that involve combustible metals, such as sodium, magnesium, and potassium.
Class K: Fires that involve cooking oils. Although, by definition, Class K is a subclass of Class B, the special characteristics of these types of fires are considered important enough to recognize.