View source for Astronomy:Fire

{{Short description|Rapid and hot oxidation of a material}}
{{pp-semi-protected|small=yes}}
{{multiple image
|align=right
|direction=vertical
|width=250
|image1=Large bonfire.jpg
|caption1=An outdoor wood fire
|image2=Feu-de-paille-couverture.ogg
|caption2=The ignition and extinguishing of a pile of wood shavings
|image3=
|caption3=A beach bonfire on Guy Fawkes Night
}}
'''Fire''' is the rapid oxidation of a material (the fuel) in the exothermic chemical process of [[Physics:Combustion|combustion]], releasing [[Physics:Heat|heat]], [[Physics:Light|light]], and various reaction [[Chemistry:Product|products]].<ref>{{Citation |title=Glossary of Wildland Fire Terminology |date=October 2007 |url=http://www.nwcg.gov/pms/pubs/glossary/pms205.pdf |journal= |pages=70 |access-date=2008-12-18 |archive-url=https://web.archive.org/web/20080821230940/http://www.nwcg.gov/pms/pubs/glossary/pms205.pdf |url-status=deviated |publisher=National Wildfire Coordinating Group |archive-date=2008-08-21}}</ref>{{efn|Slower oxidative processes like rusting or [[Biology:Digestion|digestion]] are not included by this definition.}}
At a certain point in the combustion reaction, called the ignition point, flames are produced. The ''flame'' is the visible portion of the fire. Flames consist primarily of carbon dioxide, water vapor, oxygen and nitrogen. If hot enough, the gases may become ionized to produce [[Physics:Plasma|plasma]].<ref>{{cite web | url = http://chemistry.about.com/od/chemistryfaqs/f/firechemistry.htm | title = What is the State of Matter of Fire or Flame? Is it a Liquid, Solid, or Gas? | publisher = About.com | access-date = 2009-01-21 | last = Helmenstine | first = Anne Marie | archive-date = 24 January 2009 | archive-url = https://web.archive.org/web/20090124152217/http://chemistry.about.com/od/chemistryfaqs/f/firechemistry.htm | url-status = dead }}</ref> Depending on the substances alight, and any impurities outside, the [[Color|color]] of the flame and the fire's [[Physics:Intensity (heat transfer)|intensity]] will be different.<ref>{{cite web | url = http://chemistry.about.com/od/chemistryfaqs/f/firechemistry.htm | title = What is the State of Matter of Fire or Flame? Is it a Liquid, Solid, or Gas? | publisher = About.com | access-date = 2009-01-21 | last = Helmenstine | first = Anne Marie | archive-date = 2009-01-24 | archive-url = https://web.archive.org/web/20090124152217/http://chemistry.about.com/od/chemistryfaqs/f/firechemistry.htm | url-status = live }}</ref>

Fire, in its most common form, has the potential to result in [[Physics:Conflagration|conflagration]], which can lead to physical damage, which can be permanent, through burning. Fire is a significant process that influences ecological systems worldwide. The positive effects of fire include stimulating growth and maintaining various ecological systems.
Its negative effects include hazard to life and property, atmospheric pollution, and water contamination.<ref>Lentile, ''et al.'', 319</ref> When fire removes protective vegetation, heavy rainfall can contribute to increased soil erosion by water.<ref>{{cite journal | last1 = Morris | first1 = S. E. | last2 = Moses | first2 = T. A. | year = 1987 | title = Forest Fire and the Natural Soil Erosion Regime in the Colorado Front Range | journal = Annals of the Association of American Geographers | volume = 77 | issue = 2| pages = 245–54 | doi=10.1111/j.1467-8306.1987.tb00156.x}}</ref> Additionally, the burning of vegetation releases [[Chemistry:Nitrogen|nitrogen]] into the atmosphere, unlike elements such as [[Chemistry:Potassium|potassium]] and [[Chemistry:Phosphorus|phosphorus]] which remain in the [[Chemistry:Wood ash|ash]] and are quickly recycled into the soil.<ref>{{Cite news |date=1990-08-14 |title=SCIENCE WATCH; Burning Plants Adding to Nitrogen |language=en-US |work=The New York Times |url=https://www.nytimes.com/1990/08/14/science/science-watch-burning-plants-adding-to-nitrogen.html |access-date=2023-11-02 |issn=0362-4331}}</ref><ref>{{Cite web |date=2019-11-12 |title=How Do Wildfires Affect Soil? - Applied Earth Sciences |url=https://aessoil.com/how-do-wildfires-affect-soil/ |access-date=2023-11-02 |language=en-US}}</ref> This loss of nitrogen caused by a fire produces a long-term reduction in the fertility of the soil, which can be recovered as atmospheric nitrogen is [[Biology:Nitrogen fixation|fixed]] and converted to [[Chemistry:Ammonia|ammonia]] by natural phenomena such as [[Astronomy:Lightning|lightning]] or by [[Biology:Legume|leguminous]] plants such as [[Biology:Clover|clover]], [[Biology:Pea|pea]]s, and [[Biology:Green bean|green bean]]s.

Fire is one of the four [[Unsolved:Fire (classical element)|classical elements]] and has been used by humans in rituals, in agriculture for clearing land, for cooking, generating heat and light, for signaling, propulsion purposes, [[Engineering:Smelting|smelting]], [[Engineering:Forging|forging]], [[Engineering:Incineration|incineration]] of waste, cremation, and as a weapon or mode of destruction.

== Etymology ==
The word "fire" originated {{Etymology|ang|Fyr|Fire, a fire}}, which can be traced back to the Germanic root {{Lang|gem-x-proto|*fūr-}}, which itself comes from the [[Social:Proto-Indo-European language|Proto-Indo-European]] {{Lang|Pie|*perjos}} from the root {{Lang|pie|*paewr-}} 'Fire'. The current spelling of "fire" has been in use since as early as 1200, but it was not until around 1600 that it completely replaced the [[Social:Middle English|Middle English]] term "fier" (which is still preserved in the word "fiery").<ref>{{Cite web |title=Fire |url=https://www.etymonline.com/word/fire |access-date=2023-03-24 |website=Online Etymology Dictionary |language=en}}</ref>

== History ==

=== Fossil record ===
The fossil record of fire first appears with the establishment of a land-based flora in the [[Earth:Middle Ordovician|Middle Ordovician]] period, {{ma|470}},<ref name="Wellman2000">{{cite journal |last1=Wellman |first1=C. H. |last2=Gray |first2=J. |year=2000 |title=The microfossil record of early land plants |journal=Philos Trans R Soc Lond B Biol Sci |volume=355 |issue=1398 |pages=717–31; discussion 731–2 |doi=10.1098/rstb.2000.0612 |pmc=1692785 |pmid=10905606}}</ref> permitting the accumulation of [[Chemistry:Oxygen|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 [[Biology:Wildfire|wildfire]].<ref name="Jones1991">{{cite journal |last1=Jones |first1=Timothy P. |last2=Chaloner |first2=William G. |year=1991 |title=Fossil charcoal, its recognition and palaeoatmospheric significance |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=97 |issue=1–2 |pages=39–50 |bibcode=1991PPP....97...39J |doi=10.1016/0031-0182(91)90180-Y}}</ref> Wildfire is first recorded in the Late Silurian fossil record, {{Ma|420}}, by fossils of [[Chemistry:Charcoal|charcoal]]ified plants.<ref name="DoiGMissing">{{cite journal |last1=Glasspool |first1=I.J. |last2=Edwards |first2=D. |last3=Axe |first3=L. |year=2004 |title=Charcoal in the Silurian as evidence for the earliest wildfire |journal=Geology |volume=32 |issue=5 |pages=381–383 |bibcode=2004Geo....32..381G |doi=10.1130/G20363.1}}</ref><ref name="Scott2006">{{cite journal |last1=Scott |first1=AC |last2=Glasspool |first2=IJ |year=2006 |title=The diversification of Paleozoic fire systems and fluctuations in atmospheric oxygen concentration |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=103 |issue=29 |pages=10861–5 |bibcode=2006PNAS..10310861S |doi=10.1073/pnas.0604090103 |pmc=1544139 |pmid=16832054 |doi-access=free}}</ref> Apart from a controversial gap in the Late Devonian, charcoal is present ever since.<ref name="Scott2006" /> The level of atmospheric oxygen is closely related to the prevalence of charcoal: clearly oxygen is the key factor in the abundance of wildfire.<ref name="Bowman2009">{{cite journal |last1=Bowman |first1=D. M. J. S. |last2=Balch |first2=J. K. |last3=Artaxo |first3=P. |last4=Bond |first4=W. J. |last5=Carlson |first5=J. M. |last6=Cochrane |first6=M. A. |last7=d'Antonio |first7=C. M. |last8=Defries |first8=R. S. |last9=Doyle |first9=J. C. |last10=Harrison |first10=S. P. |last11=Johnston |first11=F. H. |last12=Keeley |first12=J. E. |last13=Krawchuk |first13=M. A. |last14=Kull |first14=C. A. |last15=Marston |first15=J. B. |year=2009 |title=Fire in the Earth system |journal=Science |volume=324 |issue=5926 |pages=481–4 |bibcode=2009Sci...324..481B |doi=10.1126/science.1163886 |pmid=19390038 |s2cid=22389421 |last16=Moritz |first16=M. A. |last17=Prentice |first17=I. C. |last18=Roos |first18=C. I. |last19=Scott |first19=A. C. |last20=Swetnam |first20=T. W. |last21=Van Der Werf |first21=G. R. |last22=Pyne |first22=S. J.|url=https://resolver.caltech.edu/CaltechAUTHORS:20090707-150808418 }}</ref> Fire also became more abundant when grasses radiated and became the dominant component of many ecosystems, around {{Ma|6|7}};<ref name="Retallack1997">{{cite journal |last1=Retallack |first1=Gregory J. |date=1997 |title=Neogene expansion of the North American prairie |journal=PALAIOS |volume=12 |issue=4 |pages=380–90 |bibcode=1997Palai..12..380R |doi=10.2307/3515337 |jstor=3515337}}</ref> this kindling provided tinder which allowed for the more rapid spread of fire.<ref name="Bowman2009" /> These widespread fires may have initiated a [[Positive feedback|positive feedback]] process, whereby they produced a warmer, drier climate more conducive to fire.<ref name="Bowman2009" />

=== Human control of fire ===

==== Early human control ====
{{Main|Biology:Control of fire by early humans}}
[[File:Des8.jpg|thumb|left|Bushman starting a fire in Namibia]]
The ability to control fire was a dramatic change in the habits of early humans.<ref>{{cite journal |last1=Gowlett |first1=J. A. J. |title=The discovery of fire by humans: a long and convoluted process |journal=[[Organization:Philosophical Transactions of the Royal Society B|Philosophical Transactions of the Royal Society B: Biological Sciences]] |date=2016 |volume=371 |issue=1696 |pages=20150164 |doi=10.1098/rstb.2015.0164 |pmid=27216521 |pmc=4874402 |doi-access=free}}</ref> Making fire to generate heat and light made it possible for people to cook food, simultaneously increasing the variety and availability of nutrients and reducing disease by killing pathogenic microorganisms in the food.<ref>{{Cite journal |last1=Gowlett |first1=J. A. J. |last2=Wrangham |first2=R. W. |date=2013 |title=Earliest fire in Africa: towards the convergence of archaeological evidence and the cooking hypothesis |journal=Azania: Archaeological Research in Africa |volume=48 |issue=1 |pages=5–30 |doi=10.1080/0067270X.2012.756754 |s2cid=163033909}}</ref> The heat produced would also help people stay warm in cold weather, enabling them to live in cooler climates. Fire also kept nocturnal predators at bay. Evidence of occasional cooked food is found from {{Ma|1.0}}.<ref>{{cite journal |last1=Kaplan |first1=Matt |year=2012 |title=Million-year-old ash hints at origins of cooking |url=https://www.nature.com/news/million-year-old-ash-hints-at-origins-of-cooking-1.10372 |url-status=live |journal=Nature |doi=10.1038/nature.2012.10372 |s2cid=177595396 |archive-url=https://web.archive.org/web/20191001174313/http://www.nature.com/news/million-year-old-ash-hints-at-origins-of-cooking-1.10372 |archive-date=1 October 2019 |access-date=25 August 2020}}</ref> Although this evidence shows that fire may have been used in a controlled fashion about 1 million years ago,<ref>{{cite web |last1=O'Carroll |first1=Eoin |date=5 April 2012 |title=Were Early Humans Cooking Their Food a Million Years Ago? |url=https://abcnews.go.com/Technology/early-humans-cooking-food-million-years-ago/story?id=16080804#.T4IyWe1rFDI |url-status=live |archive-url=https://web.archive.org/web/20200204145413/https://abcnews.go.com/Technology/early-humans-cooking-food-million-years-ago/story?id=16080804#.T4IyWe1rFDI |archive-date=4 February 2020 |access-date=10 January 2020 |work=ABC News |quote=Early humans harnessed fire as early as a million years ago, much earlier than previously thought, suggests evidence unearthed in a cave in South Africa.}}</ref><ref>{{cite journal |last1=Francesco Berna |display-authors=0 |date=May 15, 2012 |title=Microstratigraphic evidence of in situ fire in the Acheulean strata of Wonderwerk Cave, Northern Cape province, South Africa |journal=PNAS |volume=109 |issue=20 |pages=E1215–E1220 |doi=10.1073/pnas.1117620109 |pmc=3356665 |pmid=22474385 |doi-access=free}}</ref> other sources put the date of regular use at 400,000 years ago.<ref name="Bowman2009b">{{cite journal |last1=Bowman |first1=D. M. J. S. |last2=Balch |first2=J. K. |last3=Artaxo |first3=P. |last4=Bond |first4=W. J. |last5=Carlson |first5=J. M. |last6=Cochrane |first6=M. A. |last7=d'Antonio |first7=C. M. |last8=Defries |first8=R. S. |last9=Doyle |first9=J. C. |last10=Harrison |first10=S. P. |last11=Johnston |first11=F. H. |last12=Keeley |first12=J. E. |last13=Krawchuk |first13=M. A. |last14=Kull |first14=C. A. |last15=Marston |first15=J. B. |display-authors=1 |year=2009 |title=Fire in the Earth system |journal=Science |volume=324 |issue=5926 |pages=481–84 |bibcode=2009Sci...324..481B |doi=10.1126/science.1163886 |pmid=19390038 |s2cid=22389421 |last16=Moritz |first16=M. A. |last17=Prentice |first17=I. C. |last18=Roos |first18=C. I. |last19=Scott |first19=A. C. |last20=Swetnam |first20=T. W. |last21=Van Der Werf |first21=G. R. |last22=Pyne |first22=S. J.|url=https://resolver.caltech.edu/CaltechAUTHORS:20090707-150808418 }}</ref> Evidence becomes widespread around 50 to 100 thousand years ago, suggesting regular use from this time; interestingly, resistance to [[Earth:Air pollution|air pollution]] started to evolve in human populations at a similar point in time.<ref name="Bowman2009b" /> The use of fire became progressively more sophisticated, as it was used to create charcoal and to control wildlife from tens of thousands of years ago.<ref name="Bowman2009b" />

Fire has also been used for centuries as a method of torture and execution, as evidenced by death by burning as well as torture devices such as the iron boot, which could be filled with water, [[Chemistry:Oil|oil]], or even [[Chemistry:Lead|lead]] and then heated over an open fire to the agony of the wearer.
[[File:Potjiekos over a fire.gif|thumb|Here, food is cooked in a cauldron above fire in {{wipe|South Africa}}.]]
By the [[History:Neolithic Revolution|Neolithic Revolution]], during the introduction of grain-based agriculture, people all over the world used fire as a tool in [[Earth:Landscape|landscape]] management. These fires were typically [[Biology:Controlled burn|controlled burn]]s or "cool fires", as opposed to uncontrolled "hot fires", which damage the soil. Hot fires destroy plants and animals, and endanger communities.<ref>{{cite book |last=Pyne |first=Stephen J. |title=Advances in Historical Ecology |date=1998 |publisher=University of Columbia Press |isbn=0-231-10632-7 |editor-last=Balée |editor-first=William |series=Historical Ecology Series |pages=78–84 |chapter=Forged in Fire: History, Land and Anthropogenic Fire |chapter-url=https://books.google.com/books?id=A5cUpbvNcH4C&dq=Neolithic+revolution+spread+of+fire&pg=PA76}}</ref> 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 autumn. They clear undergrowth, burning up [[Biology:Biomass|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. Another human use for fire in regards to landscape management is its use to clear land for agriculture. Slash-and-burn agriculture is still common across much of tropical Africa, Asia and South America. For small farmers, controlled fires are a convenient way to clear overgrown areas and release nutrients from standing vegetation back into the soil.<ref name="blogs.ei.columbia.edu">{{cite web |last=Krajick |first=Kevin |date=16 November 2011 |title=Farmers, Flames and Climate: Are We Entering an Age of 'Mega-Fires'? – State of the Planet |url=http://blogs.ei.columbia.edu/2011/11/16/farmers-flames-and-climate-are-we-entering-an-age-of-mega-fires/ |url-status=live |archive-url=https://web.archive.org/web/20120526005052/http://blogs.ei.columbia.edu/2011/11/16/farmers-flames-and-climate-are-we-entering-an-age-of-mega-fires/ |archive-date=2012-05-26 |access-date=2012-05-23 |publisher=Columbia Climate School}}</ref> However, this useful strategy is also problematic. Growing population, fragmentation of forests and warming climate are making the earth's surface more prone to ever-larger escaped fires. These harm ecosystems and human infrastructure, cause health problems, and send up spirals of carbon and soot that may encourage even more warming of the atmosphere – and thus feed back into more fires. Globally today, as much as 5 million square kilometres – an area more than half the size of the United States – burns in a given year.<ref name="blogs.ei.columbia.edu" />

==== Later human control ====
{{multiple image
| align             = right
| total_width       = 400
| image1            = The Great Fire of London, with Ludgate and Old St. Paul's.JPG
| alt1              =
| image2            = Royal Air Force Bomber Command, 1942-1945. CL3400.jpg
| alt2              = The Lyceum in 1861
| footer            = The Great Fire of London (1666) and [[Place:Hamburg|Hamburg]] after four fire-bombing raids in July 1943, which killed an estimated 50,000 people<ref>"[http://news.bbc.co.uk/2/shared/spl/hi/pop_ups/03/europe_german_destruction/html/4.stm In Pictures: German destruction] {{Webarchive|url=https://web.archive.org/web/20191213141457/http://news.bbc.co.uk/2/shared/spl/hi/pop_ups/03/europe_german_destruction/html/4.stm |date=2019-12-13 }}". BBC News.</ref>
}}
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 [[Chemistry:Power station|power station]]s provide [[Physics:Electricity|electricity]] for a large percentage of humanity by igniting fuels such as [[Earth:Coal|coal]], [[Chemistry:Oil|oil]] or [[Chemistry:Natural gas|natural gas]], then using the resultant heat to boil water into [[Physics:Steam|steam]], which then drives [[Physics:Turbine|turbine]]s.

==== Use of fire in war ====
The use of fire in [[Social:Conventional warfare|warfare]] has a long [[Social:Military history|history]]. Fire was the basis of all [[Engineering:Early thermal weapons|early thermal weapons]]. The [[Place:Byzantine Empire|Byzantine]] fleet used [[Engineering:Greek fire|Greek fire]] to attack ships and men.

The invention of [[Chemistry:Gunpowder|gunpowder]] in China led to the [[Engineering:Fire lance|fire lance]], a flame-thrower weapon dating to around 1000 CE which was a precursor to [[Engineering:History of the firearm|projectile weapons driven by burning gunpowder]].

The earliest modern [[Physics:Flamethrower|flamethrower]]s were used by infantry in the [[Social:World War I|First World War]], first used by German troops against entrenched French troops near Verdun in February 1915.<ref>{{Cite web |title=Flamethrower in action |url=https://nzhistory.govt.nz/media/photo/flamethrower-action |access-date=2023-11-02 |website=nzhistory.govt.nz |language=en}}</ref> They were later successfully mounted on armoured vehicles in the Second World War.

Hand-thrown incendiary bombs improvised from glass bottles, later known as Molotov cocktails, were deployed during the Spanish Civil War in the 1930s. Also during that war, incendiary bombs were deployed against Guernica by Fascist Italian and Nazi German air forces that had been created specifically to support Franco's Nationalists.

Incendiary bombs were dropped by Axis and Allies during the Second World War, notably on Coventry, Tokyo, Rotterdam, London, Hamburg and Dresden; in the latter two cases [[Earth:Firestorm|firestorm]]s 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.<ref name="BarashWebel2008">{{cite book |author1=David P. Barash |url=https://books.google.com/books?id=eeze4_wGViMC |title=Peace and Conflict Studies |author2=Charles P. Webel |date=10 July 2008 |publisher=SAGE |isbn=978-1-4129-6120-2 |pages=365 |access-date=2 September 2022}}</ref> 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. The incendiary fluid [[Engineering:Napalm|napalm]] was used in July 1944, towards the end of the [[Social:World War II|Second World War]], although its use did not gain public attention until the Vietnam War.<ref>{{Cite journal |last=Guillaume |first=Marine |date=2016-12-01 |title=Napalm in US Bombing Doctrine and Practice, 1942-1975 |url=https://apjjf.org/-Marine-Guillaume/4983/article.pdf |journal=The Asia-Pacific Journal |volume=14 |issue=23}}</ref>

==== Fire manipulation ====
Controlling a fire to optimize its size, shape, and intensity is generally called ''fire management'', and the more advanced forms of it, as traditionally (and sometimes still) practiced by skilled cooks, [[Engineering:Blacksmith|blacksmith]]s, [[Engineering:Ironmaster|ironmaster]]s, and others, are highly [[Philosophy:Skill|skill]]ed activities. They include knowledge of which fuel to burn; how to arrange the fuel; how to stoke the fire both in early phases and in maintenance phases; how to modulate the heat, flame, and smoke as suited to the desired application; how best to bank a fire to be revived later; how to choose, design, or modify stoves, fireplaces, bakery ovens, industrial [[Engineering:Industrial furnace|furnace]]s; and so on. Detailed expositions of fire management are available in various books about blacksmithing, about skilled camping or military scouting, and about [[Finance:Home economics|domestic arts]].

==== Productive use for energy ====
[[File:ChineseCoalPower.jpg|thumb|A coal-fired power station in China]]
Burning fuel converts chemical energy into heat energy; [[Biology:Wood|wood]] has been used as fuel since [[History:Prehistory|prehistory]].<ref>{{Cite book |title=Alternative fuels and the environment |date=1995 |publisher=Lewis |isbn=978-0-87371-978-0 |editor-last=Sterrett |editor-first=Frances S. |location=Boca Raton}}</ref> The [[Organization:International Energy Agency|International Energy Agency]] states that nearly 80% of the world's power has consistently come from fossil fuels such as [[Chemistry:Petroleum|petroleum]], [[Chemistry:Natural gas|natural gas]], and [[Earth:Coal|coal]] in the past decades.<ref>(October 2022), "[https://www.iea.org/reports/world-energy-outlook-2022 World Energy Outlook 2022]", IEA.</ref> The fire in a [[Chemistry:Power station|power station]] is used to heat water, creating steam that drives [[Physics:Turbine|turbine]]s. The turbines then spin an [[Engineering:Electric generator|electric generator]] to produce electricity.<ref>{{Cite web |title=How electricity is generated |url=https://www.eia.gov/energyexplained/electricity/how-electricity-is-generated.php |access-date=2023-11-02 |website=U.S. Energy Information Administration }}</ref> Fire is also used to provide [[Physics:Work|mechanical work]] directly by [[Physics:Thermal expansion|thermal expansion]], in both [[Engineering:External combustion engine|external]] and [[Earth:Internal combustion engine|internal combustion engine]]s.

The [[Physics:Burn|unburnable]] solid remains of a combustible material left after a fire is called ''clinker'' if its [[Physics:Melting point|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.

== Physical properties ==

=== Chemistry ===
{{Main|Physics:Combustion}}

[[File:Combustion reaction of methane.jpg|thumb|The balanced chemical equation for the combustion of methane, a hydrocarbon]]
Fire is a chemical process in which a fuel and an [[Chemistry:Oxidizing agent|oxidizing agent]] react, yielding [[Chemistry:Carbon dioxide|carbon dioxide]] and [[Chemistry:Water|water]].<ref name="newscientist">{{cite web|title=What is fire?|url=https://www.newscientist.com/question/what-is-fire/|work=New Scientist|access-date=November 5, 2022}}</ref> This process, known as a combustion reaction, does not proceed directly and involves [[Chemistry:Reaction intermediate|intermediates]].<ref name="newscientist" /> Although the oxidizing agent is typically [[Chemistry:Oxygen|oxygen]], other compounds are able to fulfill the role. For instance, [[Chemistry:Chlorine trifluoride|chlorine trifluoride]] is able to ignite sand.<ref>{{cite news|last=Lowe|first=Derek|date=February 26, 2008|title=Sand Won't Save You This Time|url=https://www.science.org/content/blog-post/sand-won-t-save-you-time|work=Science|access-date=November 5, 2022}}</ref>

Fires start when a flammable or a combustible material, in combination with a sufficient quantity of an oxidizer such as oxygen gas or another oxygen-rich compound (though non-oxygen oxidizers exist), is exposed to a source of heat or ambient [[Physics:Temperature|temperature]] above the [[Physics:Flash point|flash point]] for the fuel/oxidizer mix, and is able to sustain a rate of rapid oxidation that produces a [[Philosophy:Chain reaction|chain reaction]]. This is commonly called 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 [[Chemistry:Catalyst|catalyst]], a substance that is not consumed, when added, 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.

If the oxidizer is oxygen from the surrounding air, the presence of a force of [[Physics:Gravity|gravity]], or of some similar force caused by acceleration, is necessary to produce [[Astronomy:Convection|convection]], which removes combustion products and brings a supply of oxygen to the fire. Without gravity, a fire rapidly surrounds itself with its own combustion products and non-oxidizing gases from the air, which exclude oxygen and extinguish the fire. Because of this, the risk of fire in a [[Engineering:Spacecraft|spacecraft]] is small when it is [[Astronomy:Orbital maneuver|coasting]] in inertial flight.<ref>{{cite web|url=https://www.youtube.com/watch?v=fuFftT6ZR4k| archive-url=https://ghostarchive.org/varchive/youtube/20211211/fuFftT6ZR4k| archive-date=2021-12-11 | url-status=live|title=Ask Astronaut Greg Chamitoff: Light a Match!|last=NASA Johnson|date=29 August 2008|access-date=30 December 2016|via=YouTube}}{{cbignore}}</ref><ref>{{cite web|url=http://io9.com/5779127/how-does-fire-behave-in-zero-gravity|title=How does fire behave in zero gravity?|first=Esther|last=Inglis-Arkell|date=8 March 2011 |access-date=30 December 2016|archive-date=13 November 2015|archive-url=https://web.archive.org/web/20151113161252/http://io9.com/5779127/how-does-fire-behave-in-zero-gravity|url-status=live}}</ref> This does not apply if oxygen is supplied to the fire by some process other than thermal convection.
[[File:Fire tetrahedron.svg|thumb|The fire [[Tetrahedron|tetrahedron]]]]
Fire can be [[Engineering:Fire protection|extinguished]] by removing any one of the elements of the fire tetrahedron. Consider a natural gas flame, such as from a stove-top burner. The fire can be extinguished by any of the following:
* turning off the gas supply, which removes the fuel source;
* covering the flame completely, which smothers the flame as the combustion both uses the available oxidizer (the oxygen in the air) and displaces it from the area around the flame with CO<sub>2</sub>;
* [[Engineering:Fire extinguisher#Halons, Halon-replacement clean agents and carbon dioxide|application of an inert gas]] such as [[Chemistry:Carbon dioxide|carbon dioxide]], smothering the flame by displacing the available oxidizer;
* application of water, which removes heat from the fire faster than the fire can produce it (similarly, blowing hard on a flame will displace the heat of the currently burning gas from its fuel source, to the same end); or
* application of a retardant chemical such as [[Chemistry:Halomethane#Fire extinguishing|Halon]] ([[Engineering:Fire extinguisher#Halons, Halon-replacement clean agents and carbon dioxide|largely banned]] in some countries {{asof|2023|lc=y}}) to the flame, which retards the chemical reaction itself until the rate of combustion is too slow to maintain the chain reaction.

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 [[Chemistry:Stoichiometry|stoichiometric]] 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 ===

[[File:Candle-light-animated.gif|thumb|upright|left|A candle's flame]]
A flame is a mixture of reacting gases and solids emitting visible, [[Physics:Infrared|infrared]], and sometimes [[Physics:Ultraviolet|ultraviolet]] light, the [[Physics:Frequency spectrum|frequency spectrum]] of which depends on the [[Chemistry:Chemical composition|chemical composition]] of the burning material and intermediate reaction products. In many cases, such as the burning of [[Chemistry:Organic matter|organic matter]], for example wood, or the incomplete [[Physics:Combustion|combustion]] of gas, incandescent solid particles called [[Earth:Soot|soot]] produce the familiar red-orange glow of "fire". This light has a [[Physics:Continuous spectrum|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 [[Chemistry:Hydrogen|hydrogen]] burning in [[Chemistry:Chlorine|chlorine]] also produces a flame, producing [[Chemistry:Hydrogen chloride|hydrogen chloride]] (HCl). Other possible combinations producing flames, amongst many, are [[Chemistry:Fluorine|fluorine]] and [[Chemistry:Hydrogen|hydrogen]], and [[Chemistry:Hydrazine|hydrazine]] and nitrogen tetroxide. Hydrogen and hydrazine/UDMH flames are similarly pale blue, while burning [[Chemistry:Boron|boron]] and its compounds, evaluated in mid-20th century as a high energy fuel for [[Engineering:Jet engine|jet]] and [[Engineering:Rocket engine|rocket engine]]s, emits intense green flame, leading to its informal nickname of "Green Dragon".

[[File:Northwest Crown Fire Experiment.png|thumb|A controlled burn in the Northwest Territories, showing variations in the flame color due to temperature. The hottest parts near the ground appear yellowish-white, while the cooler upper parts appear red.]]
The glow of a flame is complex. [[Astronomy:Black-body radiation|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 [[Physics:Photon|photon]] emission by de-excited [[Physics:Atom|atom]]s and [[Physics:Molecule|molecule]]s 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.

[[File:Space Fire.jpg|thumb|Fire is affected by gravity. Left: Flame on Earth; Right: Flame on the [[Astronomy:International Space Station|ISS]]]]
The common distribution of a flame under normal gravity conditions depends on [[Astronomy:Convection|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 [[Physics:Weightlessness|micro gravity or zero gravity]],<ref>[https://science.nasa.gov/headlines/y2000/ast12may_1.htm Spiral flames in microgravity] {{webarchive|url=https://web.archive.org/web/20100319113411/http://science.nasa.gov/headlines/y2000/ast12may_1.htm |date=2010-03-19 }}, [[Organization:National Aeronautics and Space Administration|National Aeronautics and Space Administration]], 2000.</ref> such as an environment in [[Astronomy:Outer space|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 CO<sub>2</sub> 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.<ref>[http://microgravity.grc.nasa.gov/combustion/cfm/usml-1_results.htm CFM-1 experiment results] {{webarchive|url=https://web.archive.org/web/20070912095009/http://microgravity.grc.nasa.gov/combustion/cfm/usml-1_results.htm |date=2007-09-12 }}, National Aeronautics and Space Administration, April 2005.</ref> Experiments by [[Organization:National Aeronautics and Space Administration|NASA]] reveal that [[Engineering:Diffusion flame|diffusion flame]]s 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.<ref>[http://microgravity.grc.nasa.gov/combustion/lsp/lsp1_results.htm LSP-1 experiment results] {{webarchive|url=https://web.archive.org/web/20070312020123/http://microgravity.grc.nasa.gov/combustion/lsp/lsp1_results.htm |date=2007-03-12 }}, National Aeronautics and Space Administration, April 2005.</ref> These discoveries have potential applications in [[Applied science|applied science]] and industry, especially concerning [[Physics:Fuel efficiency|fuel efficiency]].

==== Typical adiabatic temperatures ====
{{Main|Physics:Adiabatic flame temperature}}

The adiabatic flame temperature of a given fuel and oxidizer pair is that at which the gases achieve stable combustion.
* [[Chemistry:Oxygen|Oxy]]–[[Chemistry:Dicyanoacetylene|dicyanoacetylene]] {{convert|4990|C|F|sigfig=2}}
* [[Chemistry:Oxygen|Oxy]]–[[Chemistry:Acetylene|acetylene]] {{convert|3480|C|F|sigfig=2}}
* [[Physics:Oxyhydrogen|Oxyhydrogen]] {{convert|2800|C|F|sigfig=2}}
* Air–[[Chemistry:Acetylene|acetylene]] {{convert|2534|C|F|sigfig=2}}
* [[Engineering:Blowtorch|Blowtorch]] (air–[[Engineering:MAPP gas|MAPP gas]]) {{convert|2200|°C|°F|abbr=on|sigfig=2}}
* [[Organization:Bunsen burner|Bunsen burner]] (air–[[Chemistry:Natural gas|natural gas]]) {{convert|1300|to|1600|C|F|sigfig=2}}<ref>{{Cite web|url=http://www.derose.net/steve/resources/engtables/flametemp.html|title=Flame temperatures|website=www.derose.net|access-date=2007-07-09|archive-date=2014-04-17|archive-url=https://web.archive.org/web/20140417022946/http://www.derose.net/steve/resources/engtables/flametemp.html|url-status=live}}</ref>
* Candle (air–[[Chemistry:Paraffin wax|paraffin]]) {{convert|1000|°C|°F|abbr=on|sigfig=2}}.

== Fire science ==
Fire science is a branch of physical science which includes fire behavior, dynamics, and [[Physics:Combustion|combustion]]. Applications of fire science include [[Engineering:Fire protection|fire protection]], fire investigation, and [[Biology:Wildfire|wildfire]] management.

== Fire ecology ==
{{Main|Earth:Fire ecology}}

Every natural ecosystem on land has its own [[Earth:Fire regime|fire regime]], and the organisms in those ecosystems are adapted to or dependent upon that fire regime. Fire creates a mosaic of different [[Earth:Habitat|habitat]] patches, each at a different stage of [[Earth:Ecological succession|succession]].<ref>Begon, M., J.L. Harper and C.R. Townsend. 1996. ''Ecology: individuals, populations, and communities'', Third Edition. Blackwell Science Ltd., Cambridge, Massachusetts, US</ref> Different species of plants, animals, and microbes specialize in exploiting a particular stage, and by creating these different types of patches, fire allows a greater number of species to exist within a landscape.

== Prevention and protection systems ==
[[File:Fire inside an abandoned convent in Massueville, Quebec, Canada.jpg|thumb|An abandoned convent on fire in Quebec]]Wildfire prevention programs around the world may employ techniques such as ''wildland fire use'' and ''prescribed or [[Biology:Controlled burn|controlled burn]]s''.<ref name="operations1">''Federal Fire and Aviation Operations Action Plan'', 4.</ref><ref>{{cite journal |date=January 1998 |title=UK: The Role of Fire in the Ecology of Heathland in Southern Britain |url=http://www.fire.uni-freiburg.de/iffn/country/gb/gb_1.htm |url-status=live |journal=International Forest Fire News |volume=18 |pages=80–81 |archive-url=https://web.archive.org/web/20110716212702/http://www.fire.uni-freiburg.de/iffn/country/gb/gb_1.htm |archive-date=2011-07-16 |access-date=2011-09-03}}</ref> ''Wildland fire use'' refers to any fire of natural causes that is monitored but allowed to burn. ''Controlled burns'' are fires ignited by government agencies under less dangerous weather conditions.<ref>{{cite web |title=Prescribed Fires |url=http://www.smokeybear.com/prescribed-fires.asp |url-status=dead |archive-url=https://web.archive.org/web/20081020171425/http://www.smokeybear.com/prescribed-fires.asp |archive-date=2008-10-20 |access-date=2008-11-21 |publisher=SmokeyBear.com}}</ref>

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 [[Engineering:Fire hydrant|fire hydrant]]s or they might use A and B class foam depending on what is feeding the fire.

Fire prevention is intended to reduce sources of ignition. Fire prevention also includes education to teach people how to avoid causing fires.<ref>[http://www.firecomm.gov.mb.ca/safety_education_nero_and_ashcan.html#6 Fire & Life Safety Education], Manitoba Office of the Fire Commissioner {{webarchive|url=https://web.archive.org/web/20081206013312/http://www.firecomm.gov.mb.ca/safety_education_nero_and_ashcan.html#6|date=December 6, 2008}}</ref> 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 [[Social:Arson|arson]] and is a crime in most jurisdictions.<ref>{{cite book |last1=Ward |first1=Michael |url=https://books.google.com/books?id=yXt5AW6bJiUC&q=purposely+starting+fire+arson+crime+most+jurisdictions&pg=PA349 |title=Fire Officer: Principles and Practice |date=March 2005 |publisher=Jones & Bartlett Learning |isbn=9780763722470 |access-date=March 16, 2019 |archive-url=https://web.archive.org/web/20220216083747/https://books.google.com/books?id=yXt5AW6bJiUC&q=purposely+starting+fire+arson+crime+most+jurisdictions&pg=PA349 |archive-date=February 16, 2022 |url-status=live}}</ref>

Model [[Engineering:Building code|building code]]s require [[Engineering:Passive fire protection|passive fire protection]] and active fire protection systems to minimize damage resulting from a fire. The most common form of active fire protection is [[Engineering:Fire sprinkler|fire sprinkler]]s. To maximize passive fire protection of buildings, building materials and furnishings in most developed countries are tested for [[Engineering:Fire-resistance rating|fire-resistance]], combustibility and flammability. Upholstery, carpeting and plastics used in vehicles and vessels are also tested.

Where fire prevention and fire protection have failed to prevent damage, fire insurance can mitigate the financial impact.<ref>{{Cite book |last1=Baars |first1=Hans |url=https://books.google.com/books?id=l6ePCgAAQBAJ&q=fire+insurance+can+mitigate+the+financial+impact+of+fire&pg=PA33 |title=Foundations of Information Security Based on ISO27001 and ISO27002 |last2=Smulders |first2=Andre |last3=Hintzbergen |first3=Kees |last4=Hintzbergen |first4=Jule |date=2015-04-15 |publisher=Van Haren |isbn=9789401805414 |edition=3rd revised |language=en |access-date=2020-10-25 |archive-url=https://web.archive.org/web/20210411062229/https://books.google.com/books?id=l6ePCgAAQBAJ&q=fire+insurance+can+mitigate+the+financial+impact+of+fire&pg=PA33 |archive-date=2021-04-11 |url-status=live}}</ref>

== See also ==
{{div col|colwidth=22em}}
* Aodh (given name)
* Bonfire
* ''[[Chemistry:The Chemical History of a Candle|The Chemical History of a Candle]]''
* Colored fire
* [[Biology:Control of fire by early humans|Control of fire by early humans]]
* [[Physics:Deflagration|Deflagration]]
* [[Unsolved:Fire (classical element)|Fire (classical element)]]
* Fire investigation
* Fire lookout
* Fire lookout tower
* Fire making
* Fire pit
* Fire safety
* Fire triangle
* [[Physics:Fire whirl|Fire whirl]]
* Fire worship
* [[Chemistry:Flame test|Flame test]]
* [[Engineering:Life Safety Code|Life Safety Code]]
* List of fires
* [[Physics:List of light sources|List of light sources]]
* [[Physics:Phlogiston theory|Phlogiston theory]]
* Piano burning
* [[Religion:Prometheus|Prometheus]], the Greek mythological figure who gave mankind fire
* [[Unsolved:Pyrokinesis|Pyrokinesis]]
* [[Chemistry:Pyrolysis|Pyrolysis]]
* [[Medicine:Pyromania|Pyromania]]
* Self-immolation
{{div col end}}

== References ==
=== Notes ===
{{notelist}}

=== Citations ===
{{Reflist}}

=== Sources ===
* Haung, Kai (2009). [http://ecommons.txstate.edu/arp/287/ Population and Building Factors That Impact Residential Fire Rates in Large U.S. Cities. Applied Research Project]. Texas State University.
* {{Cite journal|title=Community Involvement in and Management of Forest Fires in South East Asia |url=http://www.asiaforests.org/doc/resources/fire/pffsea/Report_Community.pdf |year=2002 |publisher=Project FireFight South East Asia |last=Karki |first=Sameer |access-date=2009-02-13 |url-status=dead |archive-url=https://web.archive.org/web/20090225154641/http://www.asiaforests.org/doc/resources/fire/pffsea/Report_Community.pdf |archive-date=February 25, 2009 }}
* Kosman, Admiel (January 13, 2011). [http://www.haaretz.com/weekend/magazine/sacred-fire-1.329892 "Sacred fire"]. ''[[Social:Haaretz|Haaretz]]''.
* {{cite journal |author1=Lentile, Leigh B. |author2=Holden, Zachary A. |author3=Smith, Alistair M. S. |author4=Falkowski, Michael J. |author5=Hudak, Andrew T. |author6=Morgan, Penelope |author7=Lewis, Sarah A. |author8=Gessler, Paul E. |author9=Benson, Nate C |title=Remote sensing techniques to assess active fire characteristics and post-fire effects |url=http://www.treesearch.fs.fed.us/pubs/24613 |year=2006 |journal=International Journal of Wildland Fire |issue=15 |volume=3 |pages=319–345 |doi=10.1071/WF05097 |s2cid=724358 |access-date=2010-02-04 |archive-date=2014-08-12 |archive-url=https://web.archive.org/web/20140812022744/http://www.treesearch.fs.fed.us/pubs/24613 |url-status=dead }}
==Further reading==
* Pyne, Stephen J. ''Fire : a brief history'' (University of Washington Press, 2001).
** Pyne, Stephen J. ''''World fire : the culture of fire on earth'' (1995) [https://archive.org/details/worldfireculture0000pyne online]
** Pyne, Stephen J. ''Tending fire : coping with America's wildland fires'' (2004) [https://archive.org/details/tendingfirecopin0000pyne_x6q9 online]
** Pyne, Stephen J. ''Awful splendour : a fire history of Canada'' (2007) [https://archive.org/details/awfulsplendourfi0000pyne online]
** Pyne, Stephen J. ''Burning bush : a fire history of Australia'' (1991) [https://archive.org/details/burningbushfireh0000pyne online]
** Pyne, Stephen J. ''Between Two Fires: A Fire History of Contemporary America'' (2015)
** Pyne, Stephen J. ''California: A Fire Survey'' (2016)
* Safford, Hugh D., et al. "Fire ecology of the North American Mediterranean-climate zone." in ''Fire ecology and management: Past, present, and future of US forested ecosystems'' (2021): 337-392. re California and its neighbors [https://www.fs.usda.gov/research/treesearch/download/63841.pdf online]

== External links ==
{{Commons}}
* [http://www.howstuffworks.com/Fire.htm How Fire Works] at HowStuffWorks
* [http://www.straightdope.com/columns/021122.html What exactly is fire?] from The Straight Dope
* [https://www.pbs.org/wgbh/nova/fire/onfire.html On Fire], an [[Software:Adobe Flash|Adobe Flash]]–based science tutorial from the [[Physics:Nova (American TV program)|''NOVA'' (TV series)]]
* [http://discovermagazine.com/2011/oct/20-things-you-didnt-know-about-fire "20 Things You Didn't Know About... Fire"] from ''Discover'' magazine

{{Natural disasters}}

[[Category:Terrestrial plasmas]]

{{Sourceattribution|Fire}}