The explosion at the AZF factory in Toulouse in 2001, that of a fertilizer factory in Texas in 2013, the Oklahoma City bombing of 2005, that in a nightclub in Bali in 2002 or again the bomb used in 2011 in Oslo by the far-right Norwegian terrorist Anders Behring Breivik. In all of these dramas, ammonium nitrate played a key role. It is again this chemical compound that the Lebanese authorities suspect to be at the origin of the violent explosions, which shook Beirut on Tuesday, August 4.

About 2,750 tons of ammonium nitrate were in fact stored near the port of the country's capital, where the blasts took place, said Hassane Diab, the Lebanese Prime Minister.

Ammonium nitrate and heat don't mix

This white powder very soluble in water "is an ordinary fertilizer that farmers use a lot", explains Erick Dufourc, scientific deputy director of the CNRS chemistry institute, contacted by France 24. It is not, a priori , the very definition of the dangerous product at the origin of so many accidental or deliberate explosions. 

The problem arises when ammonium nitrate is exposed to high heat. “At around 300 degrees Celsius, it becomes very unstable and explodes, releasing a shock wave with a very strong blast effect and a release of gas into the atmosphere”, underlines Erick Dufourc. A description, which corresponds to the impressive images of the double explosion in Beirut. “We first see the flames of a fire, then the explosion and the blast effect”, confirms the CNRS researcher. The latter also notes the presence of red and brown fumes which are “the signature of nitrogen dioxide, one of the gases released by an explosion due to ammonium nitrate”.

The disaster in Beirut is also in many ways reminiscent of the deadliest explosion in American history, in Texas City, in 1947. At the time, a cigarette butt carelessly thrown around of a port warehouse where 2,300 tons of ammonium nitrate were stored caused an explosion, which killed 581 people and whose shock wave was felt over more than 16 km. 

Used by the military, minors or terrorists

This ability to cause strong explosions very early on attracted the attention of the military. Nitrate bombs were widely used during both world wars. Ammonium nitrate is also popular with the mining and oil industry, which find it much more stable than nitroglycerin and much more potent than TNT. “Much of the mining industry would not exist today without ammonium nitrate,” explained to the Los Angeles Times in 1995 George Griffith, a consultant specializing in the use of explosives for industrial use.

These “qualities” are highly valued by terrorist groups. From Oklahoma City to Bali, via Turkey (Istanbul bombings of November 2003) and Northern Ireland, this white powder is wreaking havoc in the hands of bombers. In France, the AZF group, responsible for several attacks against the railway network from 2003, and the Corsican separatists of the FLNC had made it the favorite compound of their homemade bombs. It must be said that with "five kilos of well placed ammonium nitrate, you can blow up an entire building", explained the newspaper Liberation in 2004. Another advantage is that this fertilizer "is easy to find and inexpensive, and it is even quite easy to make it yourself ”, recognizes Erick Dufourc.

Risk of acid rain

For the moment, nothing suggests a terrorist trail in the case of the double explosion in Beirut. But the fact that around 2,750 tonnes of ammonium nitrate are in a warehouse is surprising. “That's the whole problem. It is recommended to keep it in well ventilated places and not to store it in too large a quantity in the same place ”, notes the French researcher. The investigation by the Lebanese authorities will probably have to determine the conditions under which this fertilizer was stored.

Meanwhile, the consequences of an ammonium nitrate explosion are not limited to the direct effects of the blast. Two of the gases that are released - ammonia and nitrogen dioxide - can turn into little health time bombs. “If they come into contact with water in the clouds, they will fall back in the form of acid rain, which is very irritating and can cause respiratory problems”, specifies the deputy director of the CNRS Institute of Chemistry. 

In this regard, the explosion in the port of Beirut is not just a problem for the capital of Lebanon. “It all depends on the wind and when the next rains will take place,” notes Erick Dufourc. Neighboring countries - such as Syria or Israel - could very well be affected by the disaster.

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