Ammonium nitrate: common fertiliser favoured by extremist groups for its explosive properties
Ammonium nitrate, which Lebanese authorities say was involved in the deadly blast in Beirut on Tuesday, is a fertiliser that has been favoured by extremist groups such as Al Qaeda and the Taliban because of its explosive properties.
An odourless, crystalline substance, ammonium nitrate must be stored with great care, experts say.
It has caused numerous industrial explosions over the decades.
Lebanese Prime Minister Hassan Diab said 2,750 tonnes of ammonium nitrate had been stored for years in the Beirut port-side warehouse that blew up on Tuesday.
Chemical weapons expert Hamish de Bretton-Gordon said it was not normal for such a large amount of the fertiliser to be stored in one place.
“Ammonium nitrate ... because of its volatility and its explosiveness, that is why terrorists and other people have used it and, of course, it’s very easy to get hold of,” he told The National.
“The storage of it is very, very tightly controlled because it is so volatile.”
Normally, strict rules would dictate where substances such as ammonium nitrate would be kept, he said.
“Because it is so volatile, you must store it somewhere where there is no possibility that it could be ignited by flame or any other explosion,” Mr de Bretton-Gordon said.
Ammonium nitrate caused a blast at a Texas fertiliser plant in 2013 that killed 15 people and was ruled deliberate, as well as an accidental explosion at a chemical plant in Toulouse, France, that killed 31 people in 2001.
Another worry was the potential spread of toxic gases emitted by the explosion, Mr de Bretton-Gordon said.
“Ammonium and nitrogen oxide, which is also produced by this explosion – they’re both very non-persistent, so they would disperse very, very quickly.”
He said it would be a concern at the time, but would be a concern only if the fires are still burning, meaning ammonium and nitrogen oxide are still being given off.
This presents a downwind hazard. “Hopefully everyone in the downwind hazard [zone] has been cleared out of the area as they certainly shouldn’t be breathing in these toxic fumes without wearing PPE [personal protective equipment].”
In agriculture, ammonium nitrate fertiliser is applied in granular form and quickly dissolves when wet, allowing nitrogen to be released into the soil.
When combined with fuel oils, ammonium nitrate creates a potent explosive widely used in the construction industry.
Under normal storage conditions and without very high heat, it is difficult to ignite ammonium nitrate, Jimmie Oxley, a chemistry professor at the University of Rhode Island, told Agence France-Presse.
“If you look at the video [of the Beirut explosion], you saw the black smoke, you saw the red smoke – that was an incomplete reaction,” she said.
“I am assuming that there was a small explosion that instigated the reaction of the ammonium nitrate – whether that small explosion was an accident or something on purpose I haven’t heard yet.”
As an oxidiser, ammonium nitrate intensifies combustion and allows other substances to ignite more readily, but is not itself particularly combustible.