Fire

Related Topics:
Fire :: Firestorm :: Fireworks :: Firestarter :: Fire_Dragon :: Firefight :: Fireblade :: Fire_Down_Below :: Fire_Ecology :: Fire_in_the_Sky

Fire is a phenomenon of combustion manifested in intense heat and light in the form of a glow or flames. The word fire when used with an indefinite article is commonly used to describe either a fuel in a state of combustion (such as a campfire or a fire in a fireplace or kitchen stove) or an instance of violent, destructive and uncontrolled burning (such as a wildfire and fires in buildings and vehicles.

Creation of fire

Fire is not a state of matter: rather, it is an exothermic chemical reaction accompanied by intense heat released during a rapid oxidation of combustible material. Fire may be visible as the brilliant glow and flames and may produce smoke.

Fires start when a flammable or combustible material with adequate supply of oxygen or other 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 when 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 continuous supply of oxygen and fuel. Fires may become uncontrolled and cause great damage to and destruction of human life, animals, plants and property.

Fire is extinguished when any of the elements of so-called fire triangle—heat, oxygen or fuel—is removed. The unburnable solid remains of fire are called ash.

Flames can conduct electricity, as a small portion of any fire is ionized. This has been demonstrated in the laboratory and also in large wildfires that occur in the vicinity of power lines. This ability to conduct electricity is due to its partially plasmatic nature.

Controlling fire

Controlling fire for the purposes of providing heat and light was one of mankind's first great achievements. The ability of fire making to generate heat and light made possible migration to colder climates and enabled people to cook food — a decisive step in the endless fight against disease. Smoke signals were an early use of fire for communication, and fire soon enabled advancements in metallurgy such as smelting and forging. Archaeology indicates that ancestors of modern humans such as Homo erectus seem to have been using controlled fire as early as some 790,000 years ago. The Cradle of Humankind site has evidence for controlled fire 1 million years ago.

By the time of the Neolithic Revolution, during the introduction of grain based agriculture, people the world over 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. Such 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. The modern applications of fire are numerous. In its broadest sense, fire is used by nearly every human being on earth in a controlled setting every day. Owners of internal combustion vehicles use fire every time they drive. Thermal power stations provide electricity for a large percentage of humanity. However, fire is also used more directly; many nomadic peoples still use fire for cooking. It is also used for smoking, and as a weapon.

In fact, the use of fire for warfare has a long history up to the present day. Homer detailed its use by Greek commandoes 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. In the Vietnam War, the Americans dropped a modern version, 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 frequently used during World War II. Molotov cocktails are cheap to construct and are in common use as well.

Typical temperatures of fires and flames

Oxyacetylene Flame (3000 C or above)(5432 F)
Oxyhydrogen Flame (2000 C or above)(3632 F)
Bunsen Burner Flame (Max. Setting) (1300 - 1600 C)(2372 - 2912 F)
Candle Flame (1400 C)(2552 F)
Blowtorch (1300 C)(2372 F)
Log fire (1000 C ~)(1832 F)
Heather Fire (500 1000 C~)(932 1832 F)
Paper — (approximately 235 C)(455 F)

Fire and religion

See also fire worship. Fires and burning have often been used in religious rites and symbolism. One reason may be that the smoke of the fire disperses upwards, into what may be considered into the heavens, considered by many religions to be the home of their supernatural deities.

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 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 church 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.

In Judaism fire also has great significance. Candles are lit to usher in holidays and to separate Shabbat 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 kept in the First and Second Temples and will always be kept burning.

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.

Fire is sometimes associated with Halloween.

Fire as a power source

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 it is nearly 80%"Share of Total Primary Energy Supply", 2002; International Energy Agency. Mexico is typical with thermal energy providing 76% of all energy "Mexico Grid Summary", 2000; Global Energy Network Institute; thermal energy defined as oil, gas and coal.

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"Energy in Africa - Chapter 3", United States Department of Energy information administration. 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"How Can Burning Wood Help Reduce Global Warming", The Guardian : 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-neutralThe Straight Dope: What exactly is fire?. Adams, C. (2002). Retrieved December 19, 2004.. It is also claimed that this power station will be more efficient than coal: accelerants can be used to spread fire faster or have it burn hotter.

The fire in a power station is used to heat water, creating steam that drives turbines. The turbines are linked to an electrical generator.

Uncontrolled fire

The self-sustaining nature of fire makes it extremely dangerous if uncontrolled. Fire can consume structures and trees and can severely injure or kill living beings through burns or smoke inhalation. Structure fires can be started by cooking accidents, electrical faults, fuel leaks, the misuse of lighters and/or matches, and accidents involving candles and cigarettes. Fire can propagate rapidly to other structures, especially where proper building standards are not met.

Outside of urban settings, wildfires can consume large areas of forest and brush and often damage nearby settlements.

Fire protection and prevention

The destructive capacity of fire has led governments around the world to adopt fire 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 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.
Shock Risk (formerly known as 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 U.S., 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.

Science of fire

A flame is an exothermic, self-sustaining, oxidizing chemical reaction producing energy and glowing gas, of which a very small portion is plasma. It consists of reacting gases 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. Spiral flames in microgravity, National Aeronautics and Space Administration, 2000.

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.

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. 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. CFM-1 experiment results, National Aeronautics and Space Administration, April 2005. Experiments by NASA in microgravity reveal that diffusion flames in microgravity allow more soot to be completely oxidised 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. LSP-1 experiment results, National Aeronautics and Space Administration, April 2005. Premixed flames in microgravity burn at a much slower rate and more efficiently than even a candle on Earth, and last much longer. SOFBAL-2 experiment results, National Aeronautics and Space Administration, April 2005. These discoveries have potential applications in applied science and industry, especially concerning fuel efficiency.

Fire ecology is the study of the interaction of living things with fire.

References

Citations

General references

Dave Reay, (2005). Climate Change Begins at Home. Palgrave Macmillan. ISBN 1403945780

External links

What exactly is fire? (from The Straight Dope)
Early human fire mastery revealed BBC article on archeological discoveries
Flames in microgravity
Spiral flames in microgravity
moebuildingcontrol.co.uk - UK Guidance on fire safety codes and fire engineering
Smokey Bear- Prevent Wildfires