The Lebanese have learned this the hard way. Ammonium nitrate, which caused the double explosion in the port of Beirut on Tuesday, has been the cause of rare but devastating disasters in the past. As such, it has been the subject of increased surveillance in recent years.
Over 20 million tonnes of ammonium nitrate are produced per year, the equivalent of 20 times the amount (2,700 tonnes) that exploded in Beirut every day. Storages of several hundred and even thousands of tonnes are therefore common across the world, and a single farmer can use several tonnes per year, according to experts.
Fertilizers and explosives
According to the specialist firm IHS, a little more than about three quarters are intended for agriculture - rich in nitrogen, the product promotes plant growth - and the rest for explosives, especially in the mining and public works sector, with a higher concentration and therefore more dangerous.
The product is found naturally on the surface of the globe, especially in Chile. But since the invention of industrial synthetic processes at the start of the 20th century, it has been produced almost exclusively in factories, by reacting nitric acid and ammonia.
Appalling balance sheets without security measures
If they remain rare - a few dozen for a century - accidents involving ammonium nitrate have appalling results. One of the first, at the BASF plant in Oppau, Germany, killed 561 in 1921. In 1947, in Texas City, the explosion of two docked ships carrying 3,500 tons killed 581 people.
Production sites, warehouses and transport have all suffered accidents, according to a memo from the European Commission on the subject. "Even small storages of ammonium nitrates, sometimes barely 10 tonnes according to certain laws, can entail a high risk for populations if security measures are not fully in place", notes the EU.
The manufacturers stress them that the risk is minimal when the safety instructions are respected, and that a high temperature - of a little less than 200 degrees - is necessary to burn it.
Explosive mixtures
"Insensitive to shock and friction, ammonium nitrate is a poor explosive unless it is mixed with fuels such as hydrocarbons, or if it is melted and confined during, for example, a violent fire", summarizes the Chemical Society of France.
“It cannot burn or explode spontaneously,” adds a spokesperson for Yara, one of the main world producers, with the Russian Eurochem, the American CF Industries or the Chilean Enaex. According to the FAO, Russia is by far the world's largest producer, ahead of Egypt in particular.
More and more strict regulations
“There is constant pressure around the world to regulate the use and trade of ammonium nitrate due to its misuse for terrorist purposes or the risk of accidental detonation. Several countries have banned its sale as fertilizer, such as Afghanistan, China, Colombia, the Philippines and Turkey, ”according to IHS.
In Europe, storage is governed by the Seveso 3 directive, which was reinforced following the accident at the AZF factory in Toulouse, France in 2001. The measures are increasingly strict depending on the quantity stored , but "there are no maximum limits" to the quantities stored, according to Lukasz Pasterski, spokesperson for the sector organization Fertilizers Europe.
"Concentrated ammonium nitrate storage falls under Seveso low threshold status from 350 tonnes of ammonium nitrate and high threshold Seveso status from 2,500 tonnes", explained to AFP the French ministry of Ecology, which lists 16 high Seveso warehouses. Small and separate islands, distancing from heat sources, smoke detectors and regular cleaning and monitoring are thus imposed, according to the ministry.
Limit of 2,500 tonnes in the United States
In the United States, for example, it is forbidden to store more than 2,500 tons in a building not equipped with automatic extinguishers.
China took action after the severe accident in Tianjin in 2015, where ammonium nitrate was also involved. And Beijing has ordered a safety inspection at its ports, docks, chemical industry sites and warehouses of hazardous materials, the state press said.
Often used in terrorist attacks
A trivial and inexpensive product, ammonium nitrate has often been used in attacks and is proving to be a headache for counterterrorism authorities. Two tons of the product combined with gasoline in a car bomb was enough for American extremist Timothy McVeigh to devastate an entire neighborhood of Oklahoma City in 1995, killing 168 people.
A procedure copied in 2011 in Oslo by the Norwegian Anders Behring Breivik, who had obtained the product from an agricultural dealer.
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