Fire is the rapid oxidation Redox describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. This can be either a simple redox process, such as the oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), or a complex process such as the oxidation of sugar(C6H12O6) in the of a material in the chemical process of combustion Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame. Fuels of interest often include organic compounds in the gas, liquid or, releasing heat In physics and thermodynamics, heat is the process of energy transfer from one body or system to another due to thermal contact, which in turn is defined as an energy transfer to a body in any other way than due to work performed on the body, light Light is electromagnetic radiation of a wavelength that is visible to the human eye . In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not, and various reaction products A product is a substance that forms as a result of a biological- or chemical reaction. While the end product of some chemical reactions may be the result of a relatively rapid reaction, nanoseconds to seconds, chemical equilibria in complex systems may require years or even centuries to be established. For example, equilibria in groundwater.[1] Slower oxidative processes like rusting Rust is a general term for a series of iron oxides. Colloquially, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture. Yet, there are also other forms of rust, such as the result of the reaction of iron and chlorine in an environment deprived of oxygen, such as rebar used in or digestion In mammals, food enters the mouth, being chewed by teeth, with chemical processing beginning with chemicals in the saliva from the salivary glands. Then it travels down the esophagus into the stomach, where hydrochloric acid kills most contaminating microorganisms and begins mechanical break down of some food , and chemical alteration of some. The are not included by this definition.

The flame A flame is the visible (light-emitting) gaseous part of a fire. It is caused by a highly exothermic reaction (for example, combustion, a self-sustaining oxidation reaction) taking place in a thin zone. If a fire is hot enough to ionize the gaseous components, it can become a plasma is the visible portion of the fire and consists of glowing hot gases. If hot enough, the gases may become ionized to produce plasma In physics and chemistry, plasma is a gas in which a certain portion of the particles are ionized. The presence of a non-negligible number of charge carriers makes the plasma electrically conductive so that it responds strongly to electromagnetic fields. Plasma, therefore, has properties quite unlike those of solids, liquids, or gases and is.[2] Depending on the substances alight, and any impurities outside, the color Color or colour is the visual perceptual property corresponding in humans to the categories called red, green, blue and others. Color derives from the spectrum of light (distribution of light energy versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical specifications of of the flame and the fire's intensity The factor π is a result of the fact that intensity is defined to exclude the effect of reduced view factor at large values θ; note that the solid angle corresponding to a hemisphere is equal to 2π steradians might vary.

Fire in its most common form can result in conflagration Conflagration is an uncontrolled burning that threatens human life, health, property or ecology. A conflagration can be accidentally or intentionally created . Arson can be accomplished for the purpose of sabotage, diversion, and also can be the consequence of pyromania. During conflagration the property is destroyed by fire. Sometimes the, which has the potential to cause physical damage through burning Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame. Fuels of interest often include organic compounds in the gas, liquid or. Fire is an important process that affects ecological systems across the globe. The positive effects of fire include stimulating growth and maintaining various ecological systems. Fire has been used by humans for cooking, generating heat, signaling, and propulsion purposes. The negative effects of fire include decreased water purity, increased soil erosion, an increase in atmospheric pollutants and an increased hazard to human life.[3]

Contents

Physical properties

Chemistry

Main article: Combustion Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame. Fuels of interest often include organic compounds in the gas, liquid or The fire tetrahedron In geometry, a tetrahedron is a polyhedron composed of four triangular faces, three of which meet at each vertex. A regular tetrahedron is one in which the four triangles are regular, or "equilateral", and is one of the Platonic solids. The tetrahedron is the only convex polyhedron that has four faces

Fires start when a flammable and/or a combustible material, in combination with a sufficient quantity of an oxidizer In the above equation, the iron has an oxidation number of 0 before and 3+ after the reaction. For oxygen (O) the oxidation number began as 0 and decreased to 2−. These changes can be viewed as two "half-reactions" that occur concurrently: such as oxygen gas or another oxygen-rich compound (though non-oxygen oxidizers exist that can replace oxygen), is exposed to a source of heat In physics and thermodynamics, heat is the process of energy transfer from one body or system to another due to thermal contact, which in turn is defined as an energy transfer to a body in any other way than due to work performed on the body or ambient temperature above the flash point Flash point of a volatile liquid is the lowest temperature at which it can vaporize to form an ignitable mixture in air. Measuring a liquid's flashpoint requires an ignition source. This is not to be confused with the autoignition temperature, which requires no ignition source. At the flash point, the vapour may cease to burn when the source of for the fuel/oxidizer mix, and is able to sustain a rate of rapid oxidation that produces a chain reaction A chain reaction is a sequence of reactions where a reactive product or by-product causes additional reactions to take place. In a chain reaction, positive feedback leads to a self-amplifying chain of events. This is commonly called the fire tetrahedron The fire triangle or combustion triangle is a simple model for understanding the ingredients necessary for most fires. It has been replaced in the fire fighting and protection industry partially by the fire tetrahedron. Fire cannot exist without all of these elements in place and in the right proportions. For example, a flammable liquid will start burning only if the fuel and oxygen are in the right proportions. Some fuel-oxygen mixes may require a catalyst Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations. Catalysts that speed the reaction are called positive, a substance that is not directly involved in any chemical reaction during combustion, but which enables the reactants to combust more readily.

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 Fire protection is the study and practice of mitigating the unwanted effects of fires. It involves the study of the behaviour, compartmentalisation, suppression and investigation of fire and its related emergencies, as well as the research and development, production, testing and application of mitigating systems. In structures, be they land-based, by removing any one of the elements of the fire tetrahedron. Consider a natural gas flame, such as from a stovetop burner. The fire can be extinguished by any of the following:

In contrast, fire is intensified by increasing the overall rate of combustion. Methods to do this include balancing the input of fuel and oxidizer to stoichiometric Stoichiometry is a branch of chemistry that deals with the quantitative relationships that exist among the reactants and products in chemical reactions. In a balanced chemical reaction, the relations among quantities of reactants and products typically form a ratio of whole numbers. For example, in a reaction that forms ammonia (NH3), exactly one proportions, increasing fuel and oxidizer input in this balanced mix, increasing the ambient temperature so the fire's own heat is better able to sustain combustion, or providing a catalyst; a non-reactant medium in which the fuel and oxidizer can more readily react.

Flame

Main article: Flame A flame is the visible (light-emitting) gaseous part of a fire. It is caused by a highly exothermic reaction (for example, combustion, a self-sustaining oxidation reaction) taking place in a thin zone. If a fire is hot enough to ionize the gaseous components, it can become a plasma A candle A candle is a solid block of fuel and an embedded wick, which is lit to provide light, and sometimes heat.[citation needed]'s flame A flame is the visible (light-emitting) gaseous part of a fire. It is caused by a highly exothermic reaction (for example, combustion, a self-sustaining oxidation reaction) taking place in a thin zone. If a fire is hot enough to ionize the gaseous components, it can become a plasma

A flame is a mixture of reacting gases and solids emitting visible and infrared Infrared light is electromagnetic radiation with a wavelength between 0.7 and 300 micrometres, which equates to a frequency range between approximately 1 and 430 THz light, the frequency spectrum The frequency spectrum of a time-domain signal is a representation of that signal in the frequency domain. The frequency spectrum can be generated via a Fourier transform of the signal, and the resulting values are usually presented as amplitude and phase, both plotted versus frequency of which depends on the chemical composition of the burning material and intermediate reaction products. In many cases, such as the burning of organic matter Organic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds. The definition of organic matter varies upon the subject it is being used for, for example wood, or the incomplete combustion Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame. Fuels of interest often include organic compounds in the gas, liquid or of gas, incandescent Incandescence is the emission of light from a hot body due to its temperature. The term derives from the verb incandesce, to glow white solid particles called soot Soot is a general term that refers to impure carbon particles resulting from the incomplete combustion of a hydrocarbon. It is more properly restricted to the product of the gas-phase combustion process but is commonly extended to include the residual pyrolyzed fuel particles such as cenospheres, charred wood, petroleum coke, etc. that may become 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 Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of 1.00794 u (1.007825 u for Hydrogen-1), hydrogen is the lightest and most abundant chemical element, constituting roughly 75 % of the Universe's elemental mass. Stars in the main sequence are mainly composed of hydrogen in its burning in chlorine Chlorine (pronounced /ˈklɔriːn/ KLOR-een, from the Greek word 'χλωρóς' (khlôros, meaning 'pale green'), is the chemical element with atomic number 17 and symbol Cl. It is a halogen, found in the periodic table in group 17 (formerly VII, VIIa, or VIIb). As the chloride ion, which is part of common salt and other compounds, it is abundant also produces a flame, producing hydrogen chloride The compound hydrogen chloride has the formula H (HCl). Other possible combinations producing flames, amongst many, are fluorine Fluorine is the chemical element with atomic number 9, represented by the symbol F. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F2 molecule. F2 (fluorine) is a supremely reactive, poisonous, pale, yellowish brown gas. Elemental fluorine is the most chemically reactive and electronegative of all the and hydrogen Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of 1.00794 u (1.007825 u for Hydrogen-1), hydrogen is the lightest and most abundant chemical element, constituting roughly 75 % of the Universe's elemental mass. Stars in the main sequence are mainly composed of hydrogen in its, and hydrazine Hydrazine is an inorganic chemical compound with the formula N2H4. It is a colourless liquid with an ammonia-like odor and is derived from the same industrial chemistry processes that manufacture ammonia. However, hydrazine has physical properties that are closer to those of water and nitrogen tetroxide Dinitrogen tetroxide is the chemical compound N2O4. It forms an equilibrium mixture with nitrogen dioxide; some call this mixture dinitrogen tetroxide, some call it nitrogen dioxide. Dinitrogen tetroxide is a powerful oxidizer, highly toxic and corrosive. N2O4 is hypergolic with various forms of hydrazine, i.e., they burn on contact without a.

The glow of a flame is complex. Black-body radiation In physics, a black body is an idealized object that absorbs all electromagnetic radiation falling on it. Blackbodies absorb and incandescently re-emit radiation in a characteristic, continuous spectrum. Because no light is reflected or transmitted, the object appears black when it is cold. However, a black body emits a temperature-dependent is emitted from soot, gas, and fuel particles, though the soot particles are too small to behave like perfect blackbodies. There is also photon In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force. The effects of this force are easily observable at both the microscopic and macroscopic level, because the photon emission by de-excited atoms The atom is a basic unit of matter that consists of a dense, central nucleus surrounded by a cloud of negatively charged electrons. The atomic nucleus contains a mix of positively charged protons and electrically neutral neutrons . The electrons of an atom are bound to the nucleus by the electromagnetic force. Likewise, a group of atoms can remain and molecules A molecule is defined as an electrically neutral group of at least two atoms in a definite arrangement held together by very strong chemical bonds. Molecules are distinguished from polyatomic ions in this strict sense. In organic chemistry and biochemistry, the term molecule is used less strictly and also is applied to charged organic molecules in the gases. Much of the radiation is emitted in the visible and infrared Infrared light is electromagnetic radiation with a wavelength between 0.7 and 300 micrometres, which equates to a frequency range between approximately 1 and 430 THz bands. The color depends on temperature for the black-body radiation, and on chemical makeup for the emission spectra The emission spectrum of a chemical element or chemical compound is the relative intensity of each frequency of electromagnetic radiation emitted by the element's atoms or the compound's molecules when they are returned to a ground state. 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 The National Aeronautics and Space Administration is an agency of the United States government, responsible for the nation's civilian space program. NASA was established by the National Aeronautics and Space Act on July 29, 1958, replacing its predecessor, the National Advisory Committee for Aeronautics (NACA). The agency became operational on (NASA) of the United States ^ b. English is the de facto language of American government and the sole language spoken at home by 80% of Americans age five and older. Spanish is the second most commonly spoken language has recently found that gravity Gravitation, or gravity, is one of the four fundamental interactions of nature , in which objects with mass attract one another. In everyday life, gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped. Gravitation causes dispersed matter to coalesce, thus accounting for also plays a role in flame formation. Modifying the gravity causes different flame types.[4] The common distribution of a flame under normal gravity conditions depends on convection Convection is the movement of molecules within fluids . It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids, as soot tends to rise to the top of a general flame, as in a candle in normal gravity conditions, making it yellow. In micro gravity 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 may go out if not moved steadily, as the CO2 from combustion does not disperse as readily in micro gravity, and tends to smother the flame). There are several possible explanations for this difference, of which the most likely is that the temperature is sufficiently evenly distributed that soot is not formed and complete combustion occurs.[5] Experiments by NASA reveal that diffusion flames in micro gravity 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 micro gravity when compared to normal gravity conditions.[6] 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.

Heat

Main article: Heat

Fires give off heat, or the process of energy transfer from one body or system due to thermal contact.

Typical temperatures of fires and flames

Temperatures of flames by appearance

A Fire at 1/4000th of a second

The temperature of flames with carbon particles emitting light can be assessed by their color:[10]

Fossil record

Main article: Fossil record of fire

The fossil record of fire first appears with the establishment of a land-based flora in the Middle Ordovician period, 470 million years ago,[11] permitting the accumulation of oxygen in the atmosphere as never before, as the new hordes of land plants pumped it out 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, 420 million years ago, by fossils of charcoalified plants.[12] Apart from a controversial gap in the Late Devonian, charcoal is present ever since.[12] The level of atmospheric oxygen is closely related to the prevalence of charcoal: clearly oxygen is the key factor in the abundance of wildfire.[13] Fire also became more abundant when grasses radiated and became the dominant component of many ecosystems, around 6 to 7 million years ago;[14] this kindling provided tinder which allowed for the more rapid spread of fire.[13] These widespread fires may have initiated a positive feedback process, whereby they produced a warmer, drier climate more conducive to fire.[13]

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