Mangled metal and crushed vehicles are all that remains at the blast site of the fertilizer company, Thursday, April 18, 2013 in West Texas. The cause was not immediately known but a fire official said it was an anhydrous ammonia explosion. AP PHOTO/THE FORT WORTH STAR-TELEGRAM, PAUL MOSELEY
Ammonium nitrate is an ammonia in crystalline form and nitric acid that is widely used in explosives and fertilizers.
Large-scale production of the substance started during World War II, when it was used for munitions. After the war, the substance became popular as fertilizer because of its ease of handling and relatively high nutrient content. It is also known as a flower inducer for fruit-bearing trees.
Ammonium nitrate is very potent and highly volatile and must be stored in controlled conditions. Stockpiles of the material can be a major fire risk, and when exposed with other chemicals, the substance can be highly explosive.
In April 1947, over 500 were killed in a chain of explosions that started when a fire on a ship at the Port Texas detonated around 2,300 tons of ammonium nitrate.
In April 1995, over 1,000 kilos of ammonium nitrate were used by Timothy McVeigh to detonate a truck bomb in front of a federal building in Oklahoma, killing over 160 people and injuring over 600 others.
In October 2002, ammonium nitrate was also used at the Bali bombing that was carried out by Jemaah Islamiyah, killing over 200 people.
The substance was also reportedly used in recent terrorist attacks such as the Delhi bombing in September 2011, which killed 11 people, as well as the blasts in Hyderabad in February, which claimed at least 17 lives and injured over a hundred others.
Concerns over the illegal use of ammonium nitrate for explosives have caused strict government regulation in the United States and many other countries, placing restrictions on the sale and transportation of the material.—Inquirer Research
Sources: Inquirer Archives; International Plant Nutrition Institute; Encyclopedia Brittanica; Homeland Security