Fire

Fire, Andrew Zachary, 1959-, American geneticist, b. Palo Alto, Calif., Ph.D. Massachusetts Institute of Technology, 1983. After a long association with the Carnegie Institution of Washington (1986-2003), Fire became a professor at Stanford Univ. in 2003. Fire and Craig Mello received the 2006 Nobel Prize in physiology or medicine for their joint discovery of RNA interference, in which the activity of a specific gene is silenced by double-stranded RNA. In this catalytic process, double-stranded RNA sets in motion a biochemical mechanism that corrupts messenger RNA molecules carrying the same genetic code as that of the double-stranded RNA. RNA interference has providea new method for the study of gene function, and it has the potential to lead to the development of novel medical therapies.

fire, the phenomenon of combustion as seen in light, flame, and heat; it is one of the basic tools of human culture. In ancient Greece and later, fire was considered one of the four basic elements, a substance from which all things were composed. Its great importance to humans, the mystery of its powers, and its seeming capriciousness have made fire divine or sacred to many peoples. Fire as a god is a characteristic feature of Zoroastrianism, in which, as in many sun-worshiping religions, fire is considered the earthly representative or type of the sun. The belief that fire is sacred is widespread in mythology, and such beliefs have survived in some highly developed cultures. The connection between the Greek colony and the metropolis was the fire kindled in the colony from a brand brought from the mother city's fire. The most carefully preserved cult in Rome was that of Vesta, goddess of the hearth, and her virgins guarded the holy fire. One of the greatest Greek myths is the story of Prometheus, the fire bringer. The theft of fire is a common element in the myths of many other cultures. The ramifications of the human ideas about fire are tremendously complex, extending as they do into the concepts about light and the heavens.

fire, forest: see forestry.

Religious ceremony that involves walking across hot coals, red-hot stones, or burning wood. It has been practiced in many parts of the world, including ancient Greece, India, Japan, China, Tahiti, New Zealand, Bulgaria, and Spain. The most common form of fire walking involves striding across a layer of embers spread thinly over the bottom of a shallow trench. More rarely, devotees may walk through a blazing log fire. The reasons for fire walking include purification and as an ordeal to prove innocence. Devotees believe that only those who lack faith will be burned, and many fire walkers do escape without injury.

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Means of rapid egress from a building, primarily intended for use in case of fire. Building codes define an exit as an enclosed and protected path of escape in the event of a fire, leading from an exit access through a combination of corridors, stairways, and doors to an exit discharge at an exterior court or public way. The term fire escape usually refers to open iron or steel balconies with steep stairways on the outside of buildings; often a retrofit of older buildings, these are rare in new construction. Other means of escape are by balconies leading to adjacent buildings, or through chutes, often used in hospitals.

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Any of a genus (Solenopsis) of insects in the ant family, several species of which are common in southern North America. They are red or yellowish and can inflict a severe sting. The semipermanent nest consists of a loose mound with open craters for ventilation. The workers (see caste) are notorious for damaging planted grain and attacking poultry.

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Rapid burning of combustible material, producing heat and usually accompanied by flame. For eons, lightning was the only source of fire. The earliest controlled use of fire seems to date to circa 1,420,000 years ago, but not until circa 7000 BC did Neolithic humans acquire reliable firemaking techniques, including friction from hardwood drills and sparks struck from flint against pyrites. Fire was used initially for warmth, light, and cooking; later it was used in fire drives in hunting and warfare, and for clearing forests of underbrush to facilitate hunting. The first agriculturalists used fire to clear fields and produce ash for fertilizer; such “slash-and-burn” cultivation is still used widely today. Fire also came to be used for firing pottery and for smelting bronze (circa 3000 BC) and later iron (circa 1000 BC). Much of the modern history of technology and science can be characterized as a continual increase in the amount of energy available through fire and brought under human control.

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Glow accompanying the brushlike discharges of atmospheric electricity that usually appears as a tip of light on the extremities of such pointed objects as church towers or the masts of ships during stormy weather. It is commonly accompanied by a crackling or fizzing noise. It is commonly observed on the periphery of propellers and along the wing tips, windshield, and nose of aircraft flying in dry snow, in ice crystals, or near thunderstorms. St. Elmo is an Italian corruption of St. Erasmus, patron saint of Mediterranean sailors, who traditionally regarded St. Elmo's fire as a sign of his guardianship over them.

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Any of several flammable mixtures used in ancient and medieval warfare, particularly a petroleum-based mixture invented by the Byzantine Greeks in the 7th century. Flammable materials such as pitch and sulfur had been used in war since ancient times, but true Greek fire was especially deadly. Thrown in pots or discharged from tubes, it apparently caught fire spontaneously, and water could not put it out. Greek fire launched from tubes mounted on ship prows wrought havoc on the Arab fleet attacking Constantinople in 673. Its effectiveness was a prime reason for the long survival of the Byzantine Empire. The recipe was so secret that its precise composition remains unknown.

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Elongated sandspit, off the southern shore of Long Island, New York state, U.S. The island measures 32 mi (51 km) long and 0.5 mi (1 km) at its widest, and its name refers to fires that were built there as signals to ships during the War of 1812; a lighthouse was built at its western tip in 1858. Now a popular summer resort, it is connected to Long Island by two bridges and by ferry. Fire Island (now Robert Moses) State Park was opened in 1908, and a 19,000-acre (7,700-hectare) section of the island was dedicated as a national seashore in 1964.

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Fire is the heat and light energy released during a chemical reaction, in particular a combustion reaction. Depending on the substances alight, and any impurities outside, the color of the flame and the fire's intensity might vary. Fire in its most common form can result in conflagration, and has the potential to cause physical damage through burning.Fire can be red, orange, yellow, blue, and even green.

Chemistry

Chemical reaction

Fires start when a flammable and/or a combustible material with an adequate supply of oxygen or another oxidizer is subjected to enough heat and is able to sustain a chain reaction. This is commonly called the fire tetrahedron. No fire can exist without all of these elements being in place.

Once ignited, a chain reaction must take place whereby fires can sustain their own heat by the further release of heat energy in the process of combustion and may propagate, provided there is a continuous supply of an oxidizer and fuel.

Fire can be extinguished by removing any one of the elements of the fire tetrahedron. Fire extinguishing by the application of water acts by removing heat from the fuel faster than combustion generates it. Application of carbon dioxide is intended primarily to starve the fire of oxygen. A forest fire may be fought by starting smaller fires in advance of the main blaze, to deprive it of fuel. Other gaseous fire suppression agents, such as halon or HFC-227, interfere with the chemical reaction itself.

Flame

A flame is an exothermic, self-sustaining, oxidizing chemical reaction producing energy and glowing hot matter, 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 depends on the chemical composition of the burning elements and intermediate reaction products.

In many cases, such as the burning of organic matter, for example wood, or the incomplete combustion of gas, incandescent solid particles called soot produce the familiar red-orange glow of 'fire'. This light has a continuous spectrum. Complete combustion of gas has a dim blue color due to the emission of single-wavelength radiation from various electron transitions in the excited molecules formed in the flame. Usually oxygen is involved, but hydrogen burning in chlorine also produces a flame, producing hydrogen chloride (HCl). Other possible combinations producing flames, amongst many more, are fluorine and hydrogen, and hydrazine and nitrogen tetroxide.

The glow of a flame is 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 on 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, the fire is white, the hottest color possible for organic material in general, or yellow. Above the yellow region, the color changes to orange, which is 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 National Aeronautics and Space Administration (NASA) of the United States has recently found that gravity plays a role. Modifying the gravity causes different flame types. 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, 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 it 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. Experiments by NASA 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 behave differently in microgravity when compared to normal gravity conditions. These discoveries have potential applications in applied science and industry, especially concerning fuel efficiency.

In combustion engines, various steps are taken to eliminate a flame. The method depends mainly on whether the fuel is oil, wood, or a high-energy fuel such as jet fuel.

Typical temperatures of fires and flames

• Oxyhydrogen flame: 9000 or above (3645 °F)
• Bunsen burner flame: 1300 to 1600 °C (2372 to 2912 °F)
• Blowtorch flame: 1,300 °C (2372 °F)
• Candle flame: 1000 °C (1832 °F)
• Smoldering cigarette:
• Temperature without drawing: side of the lit portion; 400 °C (750 °F); middle of the lit portion: 585 °C (1110 °F)
• Temperature during drawing: middle of the lit portion: 700 °C (1290 °F)
• Always hotter in the middle.

Temperatures of flames by appearance

The temperature of flames with carbon particles emitting light can be assessed by their color:

• Red
• Just visible: 525 °C (977 °F)
• Dull: 700 °C (1290 °F)
• Cherry, dull: 800 °C (1470 °F)
• Cherry, full: 900 °C (1650 °F)
• Cherry, clear: 1000 °C (1830 °F)
• Orange
• Deep: 1100 °C (2010 °F)
• Clear: 1200 °C (2190 °F)
• White
• Whitish: 1300 °C (2370 °F)
• Bright: 1400 °C (2550 °F)
• Dazzling: 1500 °C (2730 °F)

Controlling fire

The ability to control fire was a major change in the habits of early humans. Making fire to generate heat and light made it possible for people to cook food, increasing the variety and availability of nutrients. Fire also kept nocturnal predators at bay. Archaeology indicates that ancestors or relatives of modern humans 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.

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.

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. In the First World War, the first modern flamethrowers were used by infantry, and were successfully mounted on armoured vehicles in the Second World War. In the latter war, incendiary bombs were used by Axis and Allies alike, notably on Rotterdam, London, Hamburg and, notoriously, at 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 caused by a central cluster of fires. The United States Army Air Force also extensively used incendiaries against Japanese targets in the latter months of the war, devastating entire cities constructed primarily of wood and paper houses. In the Second World War, the use of napalm and molotov cocktails was popularized, though the former did not gain public attention until the Vietnam War. More recently many villages were burned during the Rwandan Genocide.

Fire fuel

Setting fuel aflame releases usable energy. Wood was a prehistoric fuel, and is still viable today. 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. 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 unburnable solid remains of a combustible material left after a fire is called clinker if its melting point is below the flame temperature, so that it fuses and then solidifies as it cools, and ash if its melting point is above the flame temperature. Incomplete combustion of a carbonaceous fuel can result in the production of soot.

Fire protection and prevention

Fire fighting services are provided in most developed areas to extinguish or contain uncontrolled fires. Trained firefighters use Fire apparatus, water supply resources such as water mains and fire hydrants or they might use A and B class foam depending on what is feeding the fire. An array of other equipment to combat the spread of fires.

Fire prevention is intended to reduce sources of ignition, and is partially focused on programs to educate people from starting fires. 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.

Model building codes require passive fire protection and active fire protection systems to minimize damage resulting from a fire. The most common form of active fire protection is fire sprinklers. To maximize passive fire protection of buildings, building materials and furnishings in most developed countries are tested for fire-resistance, combustibility and flammability. Upholstery, carpeting and plastics used in vehicles and vessels are also tested.

Practical uses

Fire is or has been used:

• For light, heat (for cooking, survival and comfort), and protection
• As a weapon of warfare, especially during ancient and medieval times.
• For fire-stick farming
• For cremation
• For welding
• For celebration (such as, birthday candles)
• For back-burning in fighting fires
• For controlled burn-offs for preventing wildfires
• For burn-offs to clear land for agriculture
• For recreational use as a campfire.

See also

References

External links

• How Fire Works at HowStuffWorks
• What exactly is fire? (from The Straight Dope)
• On Fire, an Adobe Flash-based science tutorial from the NOVA (TV series)
• Early human fire mastery revealed BBC article on archaeological discoveries
• Flames in microgravity
• Spiral flames in microgravity
• moebuildingcontrol.co.uk - UK Guidance on fire safety codes and fire engineering
• Smokey Bear- Prevent Wildfires
• Fun Uses with Fire with a Rubens' Tube