Ammonium nitrate

Disasters

Ammonium nitrate decomposes into gases including oxygen when heated (non-explosive reaction); however, ammonium nitrate can be induced to decompose explosively by detonation. Large stockpiles of the material can be a major fire risk due to their supporting oxidation, and may also detonate, as happened in the Texas City disaster of 1947, which led to major changes in the regulations for storage and handling.

Related Topics:
Gas - Oxygen - Oxidation - Texas City disaster - 1947

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There are two major classes of incidents resulting in explosions:

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• In the first case, the explosion happens by the mechanism of shock to detonation transition. The initiation happens by an explosive charge going off in the mass, by the detonation of a shell thrown into the mass, or by detonation of an explosive mixture in contact with the mass. The examples are Kriewald, Morgan, Oppau, Tessenderloo, and Traskwood.
• In the second case, the explosion results from a fire that spreads into the ammonium nitrate itself (Texas City, Brest, Oakdale), or to a mixture of an ammonium nitrate with a combustible material during the fire (Repauno, Cherokee). The fire must be confined at least to a degree for successful transition from a fire to an explosion (a phenomenon known as "transition from a decomposition or deflagration", or DDT). Pure, compact AN is stable and very difficult to initiate. However, there are numerous cases when even impure AN didn't explode in a fire.

Ammonium nitrate decomposes in temperatures above 200 °C. Pure AN is stable and will stop decomposing once the heat source is removed, but in presence of catalysts (combustible materials, acids, metal ions, chlorides...) the reaction can become self-sustaining (known as self-sustaining decomposition, SSD). This is well-known phenomenon with some types of NPK fertilizers, and is responsible for loss of several cargo ships.

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Historically significant accidental explosions

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• In 1918, a fire broke out in the amatol loading plant in Morgan, New Jersey. Over 30,000,000 pounds (13,500 tons) of explosives were present on site, of that up to 9,000,000 lb (4,000 tons) of ammonium nitrate were involved in the explosion. The rest of the ammonium nitrate, stored in other sites within the area, was exposed to the shock and fire, but did not detonate.
• On September 21, 1921 a heavy explosion of 9,000,000 pounds (4,500 tons) of a mixture of ammonium nitrate and ammonium sulfate detonated during attempts to break up the caked pile with blasting charges (an operation apparently performed several times before), with 535-561 casualties (according to other sources, 450 or over 1000), occurred in the city of Oppau (on the grounds of BASF near Ludwigshafen in Germany). Over 700 homes were destroyed, the plant disappeared entirely and was replaced with a crater 50 ft deep and 250 ft in diameter, and the shock was felt 150 miles away. This was the largest man-made disaster in German history. http://de.wikipedia.org/wiki/Explosion_des_Oppauer_Stickstoffwerkes
• In 1924, in Nixon, New Jersey, ammonium nitrate was being recovered from amatol in order to be used as a fertilizer, when a fire broke out.
• In 1925, April 4 and May 3, two carloads, each containing 220 barrels of ammonium nitrate, were dispatched from Muscle Shoals, Alabama and caught fire in transportation. The barrels were stored in a warehouse with varying humidity for 6 years, so it is believed that they were ignited by friction of their nitrate-impregnated manilla paper lining. Other shipments were reportedly more successful.
• In 1941, an explosion of 300,000 pounds (136 tons) killed 100 people in Tessenderloo, Belgium.
• In 1944, an explosion occurred at a bomb-making plant in Milan, Tennessee, killing four.
• The Texas City Disaster on April 16, 1947, when 17,000,000 pounds (7,700 tons) of ammonium nitrate caught fire and then exploded on board of the SS Grandcamp, heavily damaging the port and killing 581 people, injuring over 5,000 more, and igniting the SS High Flyer, which exploded later, adding to the death toll. This is the best-known ammonium-nitrate related disaster.
• In September 21, 2001, at 10:15 am in the AZF (Azote de France) fertilizer factory in Toulouse, France. The explosion occurred in a warehouse where the off-specification granular AN was stored flat, separated by partitions. About 200-300 tons is said to be involved in the explosion, resulting in 31 people dead and 2,442 injured, 34 of them seriously. The blast wave shattered windows in 1.5-3 kilometer distance and the resulting crater was 10 meters deep and 50 meters wide. The exact cause remains unknown. The material damage was estimated at 2.3 billion Euros. http://www.uneptie.org/pc/apell/disasters/toulouse/home.html
• The Ryongchon disaster in April 22, 2004, in North Korea is suspected to have a shipment of ammonium nitrate involved, together with other explosives.

(Incidents not involving explosion, resulting only in self-sustaining decomposition or a fire, are not listed here.)

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