Editing Fire (section)

=== Chemistry ===
{{Main|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 [[oxidizing agent]] react, yielding [[carbon dioxide]] and [[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|archive-date=February 2, 2023|archive-url=https://web.archive.org/web/20230202012338/https://www.newscientist.com/question/what-is-fire/|url-status=live}}</ref> This process, known as a [[combustion reaction]], does not proceed directly and involves [[Reaction intermediate|intermediates]].<ref name="newscientist" /> Although the oxidizing agent is typically [[oxygen]], other compounds are able to fulfill the role. For instance, [[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|archive-date=February 19, 2023|archive-url=https://web.archive.org/web/20230219062224/https://www.science.org/content/blog-post/sand-won-t-save-you-time|url-status=live}}</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, such as chlorine),<ref name=Stauffer_NicDaéid_2017/> is exposed to a source of heat or ambient [[temperature]] above the [[flash point]] for the [[fuel]]/oxidizer mix, and is able to sustain a rate of rapid oxidation that produces a [[chain reaction]]. This is commonly called the [[Fire triangle|fire tetrahedron]].<ref>{{cite journal | title=New Techniques and a New Approach to the Effective Extinguishing of Fully Developed Fires in Enclosed Spaces | first1=Norbert | last1=Tuśnio | first2=Paweł | last2=Wolny | journal=Internal Security | volume=8 | issue=1 | year=2016 | doi=10.5604/20805268.1231596 }}</ref> 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.<ref name=Stauffer_NicDaéid_2017>{{cite book | contribution=Chemistry of Fire | first1=E. | last1=Stauffer | last2=NicDaéid | first2=N. | year=2017 | title=Forensic Engineering | pages=137–143 | editor-first=Max M. | editor-last=Houck | series=Advanced Forensic Science Series | publisher=Elsevier, Inc. | isbn=978-0-12-802718-9 | chapter-url=https://books.google.com/books?id=EIPDDgAAQBAJ&pg=PA137 }}</ref> Some fuel-oxygen mixes may require a [[catalyst]], a substance that is not consumed, when added, in any [[chemical]] reaction during combustion, but which enables the reactants to combust more readily.<ref>{{cite journal | title=Catalytic combustion (review) | first=D. L. | last=Trimm | journal=Applied Catalysis | volume=7 | issue=3 | date=September 15, 1983 | pages=249–282 | doi=10.1016/0166-9834(83)80027-X }}</ref>

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.<ref>{{cite journal | title=Fundamentals of Fire Behavior | first=H. T. | last=Gisborne | journal=Fire Management Today | pages=15–23 | volume=64 | issue=1 | date=Winter 2004 | publisher=U.S. Department of Agriculture, Forest Service | url=https://books.google.com/books?id=IhxqmIV7ybUC&pg=PP15 }}</ref> If the oxidizer is oxygen from the surrounding air, the presence of a force of [[gravity]],<ref>{{cite journal | title=An investigation into the effects of gravity level on rate of heat release and time to ignition | first=D. | last=Bryant | journal=Fire and Materials | volume=19 | issue=3 | date=May 1995 | pages=119–126 | doi=10.1002/fam.810190304 }}</ref> or of some similar force caused by acceleration, is necessary to produce [[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 [[wikt:extinguish|extinguish]] the fire. Because of this, the risk of fire in a [[spacecraft]] is small when it is [[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|work=io9 |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]]]]
Fire can be [[fire protection|extinguished]] by removing any one of the elements of the fire tetrahedron.<ref name=Stauffer_NicDaéid_2017/> 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>;
* [[Fire extinguisher#Halons, Halon-replacement clean agents and carbon dioxide|application of an inert gas]] such as [[carbon dioxide]], smothering the flame by displacing the available oxidizer;<ref>{{cite journal | title=Comparative study of single inert gas in confined space inhibiting open flame coal combustion | first1=Baiwei | last1=Lei | first2=Binbin | last2=He | first3=Bowen | last3=Xiao | first4=Peiying | last4=Du | first5=Bing | last5=Wu | journal=Fuel | volume=265 | date=April 1, 2020 | doi=10.1016/j.fuel.2019.116976 }}</ref>
* application of water, which removes heat from the fire faster than the fire can produce it<ref>{{cite journal | title=Fire suppression by water sprays | first1=G. | last1=Grant | first2=J. | last2=Brenton | first3=D. | last3=Drysdale | journal=Progress in Energy and Combustion Science | volume=26 | issue=2 | date=April 2000 | pages=79–130 | doi=10.1016/S0360-1285(99)00012-X }}</ref> (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 [[halomethane#Fire extinguishing|Halon]] ([[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.<ref>{{cite journal | title=Thermal characteristics of fire extinguishing agents in compartment fire suppression | first1=Tae-Sun | last1=Kim | first2=Tae-Hee | last2=Park | first3=Jeong-Hwa | last3=Park | first4=Ji-Hyun | last4=Yang | first5=Dong-Hun | last5=Han | first6=Byeong-Chae | last6=Lee | first7=Jin-Suk | last7=Kwon | journal=Science Progress | date=August 2024 | volume=107 | issue=3 | doi=10.1177/003685042412634 | pmid=39096047 }}</ref>

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 [[stoichiometry|stoichiometric]] proportions,<ref name=Stauffer_NicDaéid_2017/> 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.