The flame itself occurs within a region of gas where intense exothermic reactions are taking place. Flaming fires involve the chemical oxidation of a fuel with associated flame, heat, and light. Depending upon the specific chemical and physical change taking place within the fuel, the flame may or may not emit light in the visible spectrum. For example, burning alcohol or burning hydrogen is usually invisible to the naked eye although the heat given off is tremendous. An exothermic reaction is a chemical reaction whereby heat and energy are released as a substance changes to a more stable chemical form . As chemical reactions occur within the fuel being burned, light and heat are released
The method depends mainly on whether the fuel is oil, wood, or a high-energy fuel such as jet fuel. In combustion engines, various steps are taken to eliminate a flame
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
Modifying the gravity causes different flame types. 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. The National Aeronautics and Space Administration of the United States has recently found that gravity plays a role. 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. 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 . 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. These discoveries have potential applications in applied science and industry, especially concerning fuel efficiency
Archaeology indicates that ancestors or relatives of modern humans might have controlled fire as early as 790,000 years ago. Making fire to generate heat and light made it possible for people to cook food, increasing the variety and availability of nutrients. The ability to control fire was a major change in the habits of early humans. The Cradle of Humankind site has evidence for controlled fire from 1 to 1. Fire also kept nocturnal predators at bay. 8 million years ago
The temperature of flames with carbon particles emitting light can be assessed by their color:
The color of a fire may also be affected by chemical elements in the flame, such as barium giving a green flame color. In such cases the unoxidized hot carbon particles emit radiation in the light spectrum, resulting in a yellow/red flame, such that of a common house fireplace. The color of the flame is dependent upon the energy level of the photons emitted. In some cases there is a partial fuel oxidation due to oxygen lack in the central part of the flame, where combustion reactions take place. Lower energy levels produce colors toward the red end of the light spectrum while higher energy levels produce colors toward the blue end of the spectrum. The flame color depends also on the unoxidized carbon particles. The visible flame has little mass, and it is comprised of luminous gases which emit energy as part of the oxidation process. The hottest flames are white in appearance
The dominant color in a flame changes with temperature. The photo of the forest fire is an excellent example of this variation. Above the yellow region, the color changes to orange, which is cooler, then red, which is cooler still. Near the ground, where most burning is occurring, the fire is white, the hottest color possible for organic material in general, or yellow. Black-body radiation is emitted from soot, gas, and fuel particles, though the soot particles are too small to behave like perfect blackbodies. The glow of a flame is complex. 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. Above the red region, combustion no longer occurs, and the uncombusted carbon particles are visible as black smoke. There is also photon emission by de-excited atoms and molecules in the gases
Depending on the substances alight, and any impurities within, the color of the flame and the fire’s intensity might vary. Fire is the heat and light energy released during a chemical reaction, in particular a combustion reaction. Fire in its most common form can be highly destructive in its very nature, and has the potential to kill and harm through burning
Usually oxygen is involved, but hydrogen burning in chlorine also produces a flame, producing hydrogen chloride . This light has a continuous spectrum. 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’. Other possible combinations producing flames, amongst many more, are fluorine and hydrogen, and hydrazine and nitrogen tetroxide. 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
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. A flame is an exothermic, self-sustaining, oxidizing chemical reaction producing energy and glowing hot matter, of which a very small portion is plasma
Fire extinguishing by the application of water acts by removing heat from the fuel faster than combustion generates it. A forest fire may be fought by starting smaller fires in advance of the main blaze, to deprive it of fuel. Fire can be extinguished by removing any one of the elements of the fire tetrahedron. Other gaseous fire suppression agents, such as halon or HFC-227, interfere with the chemical reaction itself. Application of carbon dioxide is intended primarily to starve the fire of oxygen