Editing ANFO

{{Short description|Explosive}}
{{More citations needed|date=November 2011}}
{{Use dmy dates|date=February 2020}}
[[File:Ammonium nitrate-fuel oil (ANFO) explosive.jpg|thumb|Ammonium nitrate prills used in ANFO at a [[potash|potash mine]].]]
[[File:Anfoa.jpg|thumb|{{convert|25|kg|abbr=on}} sacks containing ANFO]]

'''ANFO''' ({{IPAc-en|ˈ|æ|n|f|oʊ}} {{respell|AN|foh}})<ref>{{Cite web|url=https://www.britannica.com/technology/ANFO|title=ANFO {{!}} explosive|website=Encyclopedia Britannica|language=en|access-date=2019-05-04}}</ref> (or '''AN/FO''', for '''ammonium nitrate/fuel oil''') is a widely used bulk industrial [[high explosive]]. It consists of 94% porous [[prill]]ed [[ammonium nitrate]] (NH<sub>4</sub>NO<sub>3</sub>) (AN), which acts as the oxidizing agent and absorbent for the fuel, and 6% number 2 [[fuel oil]] (FO).<ref>{{cite book |last=Cook |first=Melvin A. |title=The Science of Industrial Explosives |publisher=IRECO Chemicals |year=1974 |page=1 |asin=B0000EGDJT}}</ref> The use of ANFO originated in the 1950s.<ref>[http://www.britannica.com/EBchecked/topic/198577/explosive/82378/Ammonium-nitrate-fuel-oil-mixtures Encyclopædia Britannica]</ref>

It has found wide use in [[coal mining]], [[quarrying]], metal ore [[mining]], and civil construction in applications where its low cost and ease of use may outweigh the benefits of other explosives, such as water resistance, oxygen balance, higher [[detonation velocity]], or performance in small-diameter columns. The [[mining industry]] accounts for an estimated 90% of the more than {{convert|5.5|e6lb|e3t|abbr=off|order=flip}} of explosives used annually in the United States.<ref>{{cite journal|author=Edward M. Green|date=June 2006|title=Explosives regulation in the USA|url=http://www.crowell.com/documents/DOCASSOCFKTYPE_ARTICLES_408.pdf|journal=Industrial Materials|issue=465|page=78|access-date=3 March 2013|archive-date=11 October 2022|archive-url=https://web.archive.org/web/20221011005714/https://www.crowell.com/documents/DOCASSOCFKTYPE_ARTICLES_408.pdf|url-status=dead}}<!--This isn't a peer-reviewed journal, but a trade journal; is {{cite journal}} correct?--></ref> ANFO is also widely used in [[Avalanche control|avalanche hazard mitigation]].<ref>{{cite book |last=Cook |first=Melvin A. |title=The Science of Industrial Explosives |publisher=IRECO Chemicals |year=1974 |page=2 |asin=B0000EGDJT}}</ref>

== Chemistry ==

The chemistry of ANFO detonation is the reaction of ammonium nitrate with a long-chain [[alkane]] (C<sub>n</sub>H<sub>2n+2</sub>) to form [[nitrogen]], [[carbon dioxide]], and [[steam]]. In an ideal [[stoichiometric]]ally balanced reaction, ANFO is composed of about 94.5% AN and 5.5% FO by weight. In practice, a slight excess of fuel oil is added, as underdosing results in reduced performance while overdosing merely results in more post-blast fumes.<ref name="pothole" /> When detonation conditions are optimal, the gases are the only products. In practical use, such conditions are impossible to attain, and blasts produce moderate amounts of toxic gases such as [[carbon monoxide]] and [[nitrogen oxide]]s ([[NOx|NO<sub>x</sub>]]).

The fuel component of ANFO is typically diesel, but [[kerosene]], coal dust, racing fuel, or even [[molasses]] have been used instead. Finely powdered [[aluminium]] in the mixture will sensitise it to detonate more readily.<ref>{{cite book |last=Singh |first=R. D. |title=Principles and Practices of Modern Coal Mining |year=2005 |publisher=New Age International |isbn=9788122409741 |page=532}}</ref>

=== Explosive properties ===
ANFO is highly insensitive, making it a [[tertiary explosive]] (or a "blasting agent"). Without a sensitizer, it cannot be detonated by a typical (such as No. 8) [[Detonator|blasting cap]]  with the small amount of primary explosives within. A larger quantity of secondary explosive, known as a primer or a [[explosive booster|booster]], must be used.<ref name=duPont>{{cite book |publisher=E. I. du Pont de Nemours & Company |title=Blasters' Handbook |edition=15th |year=1969 |pages=64–68 |asin=B000JM3SD0}}</ref> One or two sticks of [[dynamite]] were historically used; current practice is to use [[Tovex]] or [[cast booster]]s of [[pentolite]] (TNT/[[PETN]] or similar compositions).<ref>{{cite web |url=http://www.globalsecurity.org/military/systems/munitions/explosives-anfo.htm |title=Explosives – ANFO (Ammonium Nitrate – Fuel Oil) |publisher=GlobalSecurity.org |access-date=3 March 2013}}</ref>

ANFO is technically a [[high explosive]] in that it decomposes through [[detonation]] rather than [[deflagration]] at a velocity higher than the speed of sound in the material, but the low sensitivity means that it is not generally regulated as such. ANFO has a moderate [[velocity of detonation|velocity]] compared to other industrial explosives, measuring 3,200&nbsp;m/s in {{convert|5|in|mm| abbr=on|order=flip}} diameter, unconfined, at ambient temperature.<ref name=duPont/> It is described as a ''non-ideal high explosive'', as its explosive velocity is far from the thermodynamic ideal due to its porosity and the phase separation of its two components.<ref name=improve>{{cite journal |last1=Fabin |first1=M |last2=Jarosz |first2=T |title=Improving ANFO: Effect of Additives and Ammonium Nitrate Morphology on Detonation Parameters. |journal=Materials |date=1 October 2021 |volume=14 |issue=19 |doi=10.3390/ma14195745 |doi-access=free |pmid=34640139|pmc=8510347 }}</ref>

== Industrial use ==
[[File:Charging with anfo.jpg|thumb|Charging a hole with ANFO for rock blasting]]

In the mining industry, the term ANFO specifically describes a mixture of solid ammonium nitrate prills and diesel fuel. Other explosives based on the ANFO chemistry exist; the most commonly used are [[emulsion]]s. They differ from ANFO in the physical form the reactants take. The most notable properties of emulsions are water resistance and higher bulk density.

While the density of pure crystalline ammonium nitrate is 1700&nbsp;kg/m<sup>3</sup>, individual prills of explosive-grade AN measure approximately 1300&nbsp;kg/m<sup>3</sup>. Their lower density is due to the presence of a small spherical air pocket within each prill: this is the primary difference between AN sold for blasting and that sold for agricultural use. These voids are necessary to sensitize ANFO: they create so-called "hot spots".{{efn|It was found by the IRA, in response to using low-[[brisance]] AN fertilizers, that "hot spots" can be created by blending powdered sugar into the ANFO mixture, effectively sensitizing the mixture to mining-standard [[prilled]] ammonium nitrate effectiveness in which the interaction of the detonation front with a spherical void concentrates energy. Blasting-grade AN prills are typically between 0.9 and 3.0&nbsp;mm in diameter.}} Finely powdered aluminium can be added to ANFO to increase both sensitivity and energy;<ref name=improve/> in commercial usages however, this has fallen out of favor due to cost.

ANFO has a [[bulk density]] of about 840&nbsp;kg/m<sup>3</sup>. In surface mining applications, it is typically loaded into boreholes by dedicated trucks that mix the AN and FO components immediately before the product is dispensed. In underground mining applications, ANFO is typically blow-loaded.

AN is highly [[hygroscopic]], readily absorbing water from air. In humid environments, absorbed water interferes with its explosive function.{{citation needed|date=September 2013}} AN is fully water-soluble; as such, it cannot be loaded into boreholes that contain standing water. When used in wet mining conditions, considerable effort must be taken to remove standing water and install a liner in the borehole; it is generally more productive to instead use a water-resistant explosive such as emulsion.

== Regulation ==

In most jurisdictions, ammonium nitrate doesn't need to be classified as an explosive for transport purposes; it is merely an [[oxidizer]]. Mines typically prepare ANFO on-site using the same [[diesel fuel]] that powers their vehicles. While many fuels can theoretically be used, the low volatility and cost of diesel make it ideal.

ANFO under most conditions is [[detonator]]-insensitive, so it is legally classified as a [[blasting agent]] (tertiary explosive)<ref>{{cite book |last=Cook |first=Melvin A. |title=The Science of Industrial Explosives |publisher=IRECO Chemicals |year=1974 |page=16 |asin=B0000EGDJT}}</ref> and not a [[high explosive]].<ref>{{cite web |url=http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_id=9755&p_table=STANDARDS |title=Explosives and blasting agents |publisher=Occupation Safety & Health Administration |access-date= 3 March 2013}}</ref>

Ammonium nitrate is widely used as a [[fertilizer]] in the [[agricultural industry]]. It is also found in [[ice pack#Instant ice packs|instant cold packs]]. In many countries, its purchase and use are restricted to buyers who have obtained the proper license.

== Disasters ==
{{Main|List of ammonium nitrate disasters}}

Unmixed ammonium nitrate can decompose explosively, and has been responsible for several industrial disasters, including the following:

* 1921 [[Oppau explosion]] in Germany
* 1947 [[Texas City disaster]] in [[Texas City, Texas]]
* 2004 [[Ryongchon disaster]] in [[North Korea]]
* 2011 [[Norway attacks]] in [[Oslo, Norway]]
* 2013 [[West Fertilizer Company explosion]] in [[West, Texas]]
* 2015 [[2015 Tianjin explosions|Tianjin explosions]]
* 2020 [[2020 Beirut explosion|Beirut explosion]]

Environmental hazards include [[eutrophication]] in confined waters and nitrate/gas oil contamination of ground or surface water.<ref>P. Cosgrove. Ammogex Material Safety Data Sheet, Document No: HS-MSDS-03, Irish Industrial Explosives Ltd</ref>

== Paramilitary use ==

ANFO was used in 1970 when protests by students became violent at the [[University of Wisconsin–Madison]], who learned how to make and use ANFO from a Wisconsin Conservation Department booklet entitled ''Pothole Blasting for Wildlife'',<ref name="pothole">{{cite book |author=Mathiak, Harold A. |title=Pothole Blasting for Wildlife |page=11 |publisher=Wisconsin Conservation Department, Madison, Wisconsin 53701 |year=1965}}<!--Not in LOC catalog--></ref><ref>{{cite book |author=Mike Davis |title=Buda's Wagon: A Brief History of the Car Bomb |publisher=Verso |location=New York |year=2007 |page=[https://archive.org/details/budaswagonbriefh00davi/page/53 53] |lccn=2007274127 |isbn=978-1844671328 |url-access=registration |url=https://archive.org/details/budaswagonbriefh00davi }}.</ref> resulting in the [[Sterling Hall bombing]].

ANFO used to be widely used by the FLNC ([[National Liberation Front of Corsica]]), along with f15 explosive. Five containers of {{convert|500|kg|lb|abbr=off}} each were used to blow up the Tax Office building in Bastia on 28 February 1987.{{citation needed|date=December 2020}}

The ANFO [[car bomb]] was adopted by the [[Provisional IRA]] in 1972 and, by 1973, [[the Troubles]] were consuming {{convert|47,000|lb|kg|order=flip|abbr=off}} of ammonium nitrate for the majority of bombs.<ref>{{cite news |author=Henry Stanhope |title=The will to blow the lid off Ulster still remains strong |newspaper=The Times |location=London <!--url: Archive starts in 2000--> |date=8 November 1974}}</ref> The [[Ulster Volunteer Force]] (UVF) also made use of ANFO bombs, often mixing in [[gelignite]] as a booster, in the [[Dublin and Monaghan bombings]] of May 1974 which killed 34 people & injured almost 300, ANFO car bombs were used in Dublin.<ref>{{Cite web|url=https://balaclavastreet.wordpress.com/tag/bombs/|title=Bombs}}</ref> It has also seen use by groups such as the [[Revolutionary Armed Forces of Colombia]] and [[ETA (separatist group)|ETA]]. In 1992, [[Shining Path]] perpetrated the [[Tarata bombing]] in [[Lima, Peru]], using two ANFO truck bombs.

A more sophisticated variant of ANFO (ammonium nitrate with [[nitromethane]] as the fuel, called ANNM) was used in the 1995 [[Oklahoma City bombing]].

The [[Shijiazhuang bombings]] rocked the city of Shijiazhuang, China, on 16 March 2001. A total of 108 people were killed, and 38 others injured when, within a short time, several ANFO bombs exploded near four apartment buildings.<ref>{{cite news |author=<!--Staff writer(s); no by-line.--> |date=3 April 2001 |title=石家庄九名制贩爆炸物的嫌犯被刑事拘留 |trans-title=Shijiazhuang nine suspects of the sale of explosives were detained in criminal detention |url=http://news.sina.com.cn/c/222078.html&usg=ALkJrhgOJfTK3ZhEpPY9V8vwNL_TK_SjRA |language=zh |location=Beijing |access-date=12 August 2017 }}{{Dead link|date=September 2018 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

In November 2009, the government of the [[Khyber Pakhtunkhwa|North West Frontier Province]] (NWFP) of [[Pakistan]] imposed a ban on [[ammonium sulfate]], ammonium nitrate, and [[calcium ammonium nitrate]] fertilizers in the [[Upper Dir]], [[Lower Dir]], [[Swat, Pakistan|Swat]], [[Chitral]] and [[Malakand District|Malakand]] districts (the former [[Malakand Division]]) following reports that those chemicals were used by militants to make explosives.{{citation needed|date=December 2020}}

In April 2010, police in Greece confiscated 180&nbsp;kg of ANFO and other related material stashed in a hideaway in the Athens suburb of Kareas. The material was believed to be linked to attacks previously carried out by the "Revolutionary Struggle" terrorist group.{{citation needed|date=December 2020}}

In January 2010, President [[Hamid Karzai]] of [[Afghanistan]] also issued a decree banning the use, production, storage, purchase, or sale of ammonium nitrate, after an investigation showed militants in the [[Taliban insurgency]] had used the substance in bomb attacks.<ref>{{cite news|url=http://www.timesunion.com/ASPStories/story.asp?StoryID=720948 |newspaper=Times Union |location=Albany, N.Y. |title=Afghanistan bans chemical used to make bombs; protesters denounce killings |url-status=dead |archive-url=https://web.archive.org/web/20100607130249/http://www.timesunion.com/AspStories/story.asp?storyID=720948 |archive-date=7 June 2010 }}<!--There are several different stories on archive.org matching this URL but none of them have anything close to this title--></ref><ref>{{cite news |url=https://www.theguardian.com/world/feedarticle/8910984 |agency=AP Foreign |date=22 January 2010 |newspaper=The Guardian | title=Afghanistan bans chemical used to make bombs |access-date=3 March 2013}}</ref><ref>{{cite news |author=Dexter Filkins |url=https://www.nytimes.com/2009/11/11/world/asia/11afghan.html |title=Bomb Material Cache Uncovered in Afghanistan |newspaper=The New York Times |date=11 November 2009 |access-date=3 March 2013}}</ref>

On 22 July 2011, an aluminium powder-enriched ANNM explosive, with total size of 950&nbsp;kg (150&nbsp;kg of aluminium powder), increasing demolition power by 10–30% over plain ANFO, was used in the [[2011 Norway attacks|Oslo bombing]].<ref name=nrk950kg>{{cite news |author=Stina Åshildsdatter Grolid |author2=Unni Eikeseth |url=http://www.nrk.no/nyheter/1.7726208 | title=Slik virket trykkbølgen etter bomben |language=no |trans-title=Such seemed the shock wave after the bomb |date=25 July 2011| publisher = NRK| access-date=28 July 2011 }}</ref><ref>{{cite news | url=https://www.bloomberg.com/news/2011-07-27/norway-police-spreads-breivik-terror-probe-europe-wide-after-twin-attacks.html | work=Bloomberg | first1=Marianne | last1=Stigset | first2=Josiane | last2=Kremer | first3=Stephen | last3=Treloar | title=Police in Norway Extend Terror Probe Across Europe After Breivik Attacks | date=27 July 2011}}</ref>

On 13 April 2016, two suspected [[Irish Republican Army|IRA]] members were stopped in Dublin with 67&nbsp;kg of ANFO.<ref>{{cite news |author=Daniel Hickey |title=Two men appear in court charged with possession of 150&nbsp;kg of homemade explosives |newspaper=Irish Independent |location=Dublin|url=http://www.independent.ie/irish-news/courts/two-men-appear-in-court-charged-with-possession-of-150kg-of-homemade-explosives-34631186.html|access-date=16 April 2016 |date=13 April 2016}}</ref>

On 6 March 2018, 8 members of the extreme right [[neo-Nazi]] group [[Combat 18]] were arrested in Athens, Greece, accused of multiple attacks on immigrants and activists. They had 50&nbsp;kg of ANFO in their possession.<ref>{{Cite web|url=http://news247.gr/eidiseis/koinonia/o-tsamp-ths-combat-18-kai-o-lukos-ths-xryshs-ayghs-epivevaiwnoyn-th-logikh-twn-sygkoinwnountwn-doxeiwn.5111561.html|title = Ο 'Τσαμπ' της 'Combat 18' και ο 'Λύκος' της Χρυσής Αυγής επιβεβαιώνουν τη λογική των 'συγκοινωνούντων δοχείων'}}</ref>

== References ==
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== External links ==
{{Commons category}}

* [https://purl.fdlp.gov/GPO/gpo37048 Securing Ammonium Nitrate: Using Lessons Learned in Afghanistan to Protect the Homeland from IEDs: Hearing before the Subcommittee on Cybersecurity, Infrastructure Protection, and Security Technologies of the Committee on Homeland Security, House of Representatives, One Hundred Twelfth Congress, Second Session, 12 July 2012]

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[[Category:Binary explosives]]