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{{Short description|Explosive}}
{{Refimprove|date=September 2008}}
{{More citations needed|date=November 2011}}
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{{Use dmy dates|date=February 2020}}
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'''ANFO''' (or '''AN/FO''', for '''ammonium nitrate/fuel oil''') is a widely used ] mixture. It consists of ] (NH<sub>4</sub>NO<sub>3</sub>) and, commonly, ] or ]; any ] source such as ], ] ], or even ] and ] can be used. ] is one of the most effective carbon sources in this sort of explosive. '''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 ]. It consists of 94% porous ]ed ] (NH<sub>4</sub>NO<sub>3</sub>) (AN), which acts as the oxidizing agent and absorbent for the fuel, and 6% number 2 ] (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></ref>


It is by far the most widely used explosive in ], ], metal ], and civil construction: it accounts for an estimated 80% of the {{convert|6000000000|lb}} of explosive used annually in North America.<ref></ref> It also sees service in ]s, where it is also known as a '''fertilizer bomb'''.<ref>{{cite news |author = Jo Thomas |title = Jury to Be Picked in 2d Oklahoma Bomb Trial |work = ] |date = 1997-09-29}}</ref> It has found wide use in ], ], metal ore ], 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 ], 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 ].<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== == Chemistry ==
ANFO under most conditions is considered a ]; it decomposes through ] rather than ] and with a high ]. It is a ] consisting of distinct fuel and ] phases and requires confinement for efficient detonation and ]. Its sensitivity is relatively low; it generally requires a ] (e.g., one or two sticks of ], as historically used, or in more recent times, ] or cast boosters of ] (TNT)/] or similar compositions) to ensure reliable detonation.


The basic chemistry of ANFO detonation is the reaction of ammonium nitrate (NH<sub>4</sub>NO<sub>3</sub>) with a long chain (hydro)carbon (C<sub>n</sub>H<sub>2n+2</sub>) to form ], ] and ]. In an ideal ]ally balanced reaction, ANFO is composed of approximately 94.3% AN and 5.7% FO by weight. The normal ratio recommended is 2 U.S. ]s of fuel oil per 50 ]s of ammonium nitrate (80 ml/kg). In practice, a slight excess of fuel oil is added, i.e., 2.5 to 3 quarts of fuel oil per 50 pounds of ammonium nitrate, as underdosing results in reduced performance while overdosing merely results in more post-blast fumes.<ref name="pothole" /> When detonation conditions are optimal, the aforementioned gases are the only products. In practical use, such conditions are impossible to attain, and blasts produce moderate amounts of toxic gases such as ] and ] (]). The chemistry of ANFO detonation is the reaction of ammonium nitrate with a long-chain ] (C<sub>n</sub>H<sub>2n+2</sub>) to form ], ], and ]. In an ideal ]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 aforementioned gases are the only products. In practical use, such conditions are impossible to attain, and blasts produce moderate amounts of toxic gases such as ] and ]s (]).


The fuel component of ANFO is typically diesel, but ], coal dust, racing fuel, or even ] have been used instead. Finely powdered ] 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>
==Industrial use==
Ammonium nitrate is widely used as a ] in the ]. In many countries its purchase and use is restricted to buyers who have obtained the proper license. This restriction is primarily because it is an attractive and simple component used in the production of fertilizer bombs.


=== Explosive properties ===
In the mining industry, the term ANFO specifically describes a mixture of solid ammonium nitrate ]s and heating oil. In this form, it has a ] of approximately 840&nbsp;kg/m<sup>3</sup>. The density of individual prills is about 1300&nbsp;kg/m<sup>3</sup>, while the density of pure crystalline ammonium nitrate is 1700&nbsp;kg/m<sup>3</sup>. AN prills used for explosive applications are physically different from fertilizer prills; the former contain approximately 20% air. These versions of ANFO which use prills are generally called explosives grade, low density, or industrial grade ammonium nitrate. These voids are necessary to sensitize ANFO: they create so-called "hot spots".<ref>It was found by the IRA, in response to using low ] 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 mm in diameter.</ref> Finely powdered ] can be added to ANFO to increase both sensitivity and energy; however, this has fallen out of favor due to cost. Other additions include ], chemical gassing agents, or glass air bubbles to create these voids.<ref>Mine Health & Safety Management, Michael Karmis</ref>
ANFO is highly insensitive, making it a ] (or a "blasting agent"). Without a sensitizer, it cannot be detonated by a typical (such as No. 8) ] with the small amount of primary explosives within. A larger quantity of secondary explosive, known as a primer or a ], 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 ] were historically used; current practice is to use ] or ]s of ] (TNT/] 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 ] in that it decomposes through ] rather than ] 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 ] 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>
AN is highly ], readily absorbing water from air. It is dangerous when stored in humid environments, as any absorbed water interferes with its explosive function. AN is also water soluble. When used in wet mining conditions, considerable effort must be taken to dewater ]s.


== Industrial use ==
Other explosives based on the ANFO chemistry exist; the most commonly used are ]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.
]


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 ]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.
The popularity of ANFO is largely attributable to its low cost and high stability. In most jurisdictions, ammonium nitrate need not be classified as an explosive for transport purposes; it is merely an ]. Many mines prepare ANFO on-site using the same ] that powers their vehicles, although heating oil, which is nearly identical, may cost less than diesel fuel due to lower ]. Many fuels can theoretically be used; the low volatility and cost of fuel oil makes it ideal.


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-] AN fertilizers, that "hot spots" can be created by blending powdered sugar into the ANFO mixture, effectively sensitizing the mixture to mining-standard ] 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.
==Disasters==
Unmixed ammonium nitrate can decompose explosively and has been responsible for industrial disasters, such as the ] in ] in 1947 and the ] in ] in 2004.


ANFO has a ] 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.
==Terrorist use==
ANFO has been used in terrorist bombings. First used in 1970 by student protesters at the ], 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}}</ref><ref>Mike Davis, ''Buda's Wagon: A Brief History of the Car Bomb'' (Verso: New York, 2007): 53.</ref> the ANFO ] was soon adopted by the ], such as in the ]. It has also seen use by groups such as the ] (FARC), ], and ]'s terrorists when they first tried to destroy the ]. A more sophisticated variant of ANFO (ammonium nitrate with nitromethane as the fuel called ANNM) was used in the 1995 ]. Improvised bombs made with agricultural-grade AN are less sensitive and less efficient than the explosive-grade variety.


AN is highly ], 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.
In November 2009, a ban on ], ammonium nitrate and ] fertilizers was imposed in the former ] - comprising the ], ], ], ] and ] districts of the ] (NWFP) of ], by the NWFP government, following reports that those chemicals were used by militants to make explosives.


== Regulation ==
In April 2010, police in Greece confiscated 180 kilograms 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.


In most jurisdictions, ammonium nitrate doesn't need to be classified as an explosive for transport purposes; it is merely an ]. Mines typically prepare ANFO on-site using the same ] that powers their vehicles. While many fuels can theoretically be used, the low volatility and cost of diesel make it ideal.
In January 2010, President ] of ] also issued a decree banning the use, production, storage, purchase or sale of ammonium nitrate, after an investigation showed that militants in the ] had used the substance in bomb attacks.<ref> "Afghanistan bans chemical used to make bombs - Afghanistan bans fertilizer chemical commonly used to make bombs; protesters denounce killings".</ref><ref> "Afghanistan bans chemical used to make bombs".</ref><ref> "Bomb Material Cache Uncovered in Afghanistan".</ref>


ANFO under most conditions is ]-insensitive, so it is legally classified as a ] (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 ].<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>
In July 2011, an ]-enriched ANALFO explosive was used in the ].<ref>http://www.theglobeandmail.com/news/world/europe/gunman-kills-85-oslo-explosion-by-oklahoma-city-type-bomb-police/article2107535/.</ref>
==ANNM==
ANNM or ammonium nitrate and nitromethane is one of the most powerful improvised types of AN-based explosives. The ] of ANNM varies depending on the mix but does not exceed 1 (annmal = RE 1-1.1). ANNM usually contains a 60:40 (kinepak) mix of AN and NM (60% ammonium nitrate, 40% nitromethane by mass), though this results in a wet slurry. Sometimes more AN is added to reduce liquidity and make it easier to store and handle, as well as providing an oxygen-balanced mix. ANNM is also more sensitive to shock than standard ANFO and is therefore easier to detonate. When ANNM ]s, the primary byproducts produced are H<sub>2</sub>O, CO<sub>2</sub> and N<sub>2</sub>, but NO<sub>x</sub> and other toxic gases are inevitably formed because of impurities. The balanced equation is as follows:


Ammonium nitrate is widely used as a ] in the ]. It is also found in ]. In many countries, its purchase and use are restricted to buyers who have obtained the proper license.
3NH<sub>4</sub>NO<sub>3</sub> + 2CH<sub>3</sub>NO<sub>2</sub> -> 4N<sub>2</sub> + 2CO<sub>2</sub> + 9H<sub>2</sub>O


== Disasters ==
However, depending on the detonation impetus (for example a #6 versus a #10 ]), the products of the detonation can be decidedly un].
{{Main|List of ammonium nitrate disasters}}


Unmixed ammonium nitrate can decompose explosively, and has been responsible for several industrial disasters, including the following:
==References==
{{reflist|2}}


* 1921 ] in Germany
==External links==
* 1947 ] in ]
*
* 1995 ]
*
* 2004 ] in ]
{{Use dmy dates|date=July 2011}}
* 2011 ] in ]
* 2013 ] in ]
* 2015 ]
* 2020 ]


Environmental hazards include ] 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>
{{DEFAULTSORT:Anfo}}
]
]


== Paramilitary use ==
]

]
ANFO was used in 1970 when protests by students became violent at the ], 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= |lccn=2007274127 |isbn=978-1844671328 |url-access=registration |url=https://archive.org/details/budaswagonbriefh00davi }}.</ref> resulting in the ].
]

]
ANFO used to be widely used by the FLNC (]), 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 ] was adopted by the ] in 1972 and, by 1973, ] 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 ] (UVF) also made use of ANFO bombs, often mixing in ] as a booster, in the ] 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 ] and ]. In 1992, ] perpetrated the ] in ], using two ANFO truck bombs.
]

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

]
The ] 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 ] (NWFP) of ] imposed a ban on ], ammonium nitrate, and ] fertilizers in the ], ], ], ] and ] districts (the former ]) 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 ] of ] also issued a decree banning the use, production, storage, purchase, or sale of ammonium nitrate, after an investigation showed militants in the ] 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 ].<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 ] 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 ] group ] 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 ==
{{notes}}
{{reflist}}

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

*

{{Authority control}}

]

Latest revision as of 02:20, 21 January 2025

Explosive
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Ammonium nitrate prills used in ANFO at a potash mine.
25 kg (55 lb) sacks containing ANFO

ANFO (/ˈænfoʊ/ AN-foh) (or AN/FO, for ammonium nitrate/fuel oil) is a widely used bulk industrial high explosive. It consists of 94% porous prilled ammonium nitrate (NH4NO3) (AN), which acts as the oxidizing agent and absorbent for the fuel, and 6% number 2 fuel oil (FO). The use of ANFO originated in the 1950s.

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 2.5 thousand tonnes (5.5 million pounds) of explosives used annually in the United States. ANFO is also widely used in avalanche hazard mitigation.

Chemistry

The chemistry of ANFO detonation is the reaction of ammonium nitrate with a long-chain alkane (CnH2n+2) to form nitrogen, carbon dioxide, and water. In an ideal stoichiometrically 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. When detonation conditions are optimal, the aforementioned 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 oxides (NOx).

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.

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) blasting cap with the small amount of primary explosives within. A larger quantity of secondary explosive, known as a primer or a booster, must be used. One or two sticks of dynamite were historically used; current practice is to use Tovex or cast boosters of pentolite (TNT/PETN or similar compositions).

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 compared to other industrial explosives, measuring 3,200 m/s in 130 mm (5 in) diameter, unconfined, at ambient temperature. 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.

Industrial use

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 emulsions. 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 kg/m, individual prills of explosive-grade AN measure approximately 1300 kg/m. 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". Finely powdered aluminium can be added to ANFO to increase both sensitivity and energy; in commercial usages however, this has fallen out of favor due to cost.

ANFO has a bulk density of about 840 kg/m. 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. 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) and not a high explosive.

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

Disasters

Main article: List of ammonium nitrate disasters

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

Environmental hazards include eutrophication in confined waters and nitrate/gas oil contamination of ground or surface water.

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, 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 500 kilograms (1,100 pounds) each were used to blow up the Tax Office building in Bastia on 28 February 1987.

The ANFO car bomb was adopted by the Provisional IRA in 1972 and, by 1973, the Troubles were consuming 21,000 kilograms (47,000 pounds) of ammonium nitrate for the majority of bombs. 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. It has also seen use by groups such as the Revolutionary Armed Forces of Colombia and 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.

In November 2009, the government of the 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, Chitral and Malakand districts (the former Malakand Division) following reports that those chemicals were used by militants to make explosives.

In April 2010, police in Greece confiscated 180 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.

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.

On 22 July 2011, an aluminium powder-enriched ANNM explosive, with total size of 950 kg (150 kg of aluminium powder), increasing demolition power by 10–30% over plain ANFO, was used in the Oslo bombing.

On 13 April 2016, two suspected IRA members were stopped in Dublin with 67 kg of ANFO.

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 kg of ANFO in their possession.

References

  1. 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 mm in diameter.
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  3. Encyclopædia Britannica
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  6. ^ Mathiak, Harold A. (1965). Pothole Blasting for Wildlife. Wisconsin Conservation Department, Madison, Wisconsin 53701. p. 11.
  7. Singh, R. D. (2005). Principles and Practices of Modern Coal Mining. New Age International. p. 532. ISBN 9788122409741.
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  10. ^ Fabin, M; Jarosz, T (1 October 2021). "Improving ANFO: Effect of Additives and Ammonium Nitrate Morphology on Detonation Parameters". Materials. 14 (19). doi:10.3390/ma14195745. PMC 8510347. PMID 34640139.
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  15. Henry Stanhope (8 November 1974). "The will to blow the lid off Ulster still remains strong". The Times. London.
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  17. "石家庄九名制贩爆炸物的嫌犯被刑事拘留" [Shijiazhuang nine suspects of the sale of explosives were detained in criminal detention] (in Chinese). Beijing. 3 April 2001. Retrieved 12 August 2017.
  18. "Afghanistan bans chemical used to make bombs; protesters denounce killings". Times Union. Albany, N.Y. Archived from the original on 7 June 2010.
  19. "Afghanistan bans chemical used to make bombs". The Guardian. AP Foreign. 22 January 2010. Retrieved 3 March 2013.
  20. Dexter Filkins (11 November 2009). "Bomb Material Cache Uncovered in Afghanistan". The New York Times. Retrieved 3 March 2013.
  21. Stina Åshildsdatter Grolid; Unni Eikeseth (25 July 2011). "Slik virket trykkbølgen etter bomben" [Such seemed the shock wave after the bomb] (in Norwegian). NRK. Retrieved 28 July 2011.
  22. Stigset, Marianne; Kremer, Josiane; Treloar, Stephen (27 July 2011). "Police in Norway Extend Terror Probe Across Europe After Breivik Attacks". Bloomberg.
  23. Daniel Hickey (13 April 2016). "Two men appear in court charged with possession of 150 kg of homemade explosives". Irish Independent. Dublin. Retrieved 16 April 2016.
  24. "Ο 'Τσαμπ' της 'Combat 18' και ο 'Λύκος' της Χρυσής Αυγής επιβεβαιώνουν τη λογική των 'συγκοινωνούντων δοχείων'".

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