what are the characteristics of ammonium nitrate?

► What is ammonium nitrate?

Coming as a powder or white granules, odorless and soluble in water, ammonium nitrate (chemical formula NH4NO3) is a salt of nitric acid (HNO3) and ammonia (NH3). It is a raw material used as a basis for the chemical industry. The term covers two main families of products: “industrial ammonium nitrate”, an intermediate for the manufacture of nitrate-fuel explosive used in mines and quarries, and “agricultural fertilizers”. These can be simple and are then called “ammonitrates”, containing up to 80% ammonium nitrate. They can also be composed, then containing a very variable amount of ammonium nitrate (from 3% to more than 80%), phosphorus and potassium, and are delivered to farmers in bags marked with the acronym NPK.

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Ammonium nitrate is not explosive if it is handled or stored in a ventilated shelter, away from any heating. ” In other words, it is not a fuel, but an oxidizer, a product allowing the combustion of another substance already ignited., explains André Picot, chemist at the CNRS. However, nitrate-fuel (94% ammonium nitrate, 6% gasoline, diesel or kerozene), can constitute a homemade bomb, the power of which is of the same order as the famous TNT (trinitrotoluene) of the film. The Wage of Fear (1952) », Continues the researcher.

► How dangerous is it?

On contact with a heat source (fire, electric spark, lightning), it decomposes at 210 ° C releasing very toxic gases (nitrogen monoxide) for humans, and can explode from 290 ° C. But for it to explode, you need a significant amount.

Detonation is only possible with contamination by an incompatible substance or an intense source of heat. Storage must therefore follow strict rules to isolate ammonium nitrate from flammable liquids (gasoline, oils, etc.), corrosive liquids, flammable solids or even substances which give off significant heat, among others that are prohibited.

During the accident at the AZF factory in Toulouse in 2001, which left 31 dead and many post-traumatic injuries (hearing loss, psychological disorders), the explosion took place from a stock of 300 tons, stored in a hangar, however open. The explosion was heard for up to 80 kilometers around. The exact cause of the AZF explosion has never been precisely identified, although a majority of chemists and detonics experts have assumed the hypothesis of an accidental mixture between ammonium nitrate and a chlorinated compound. .

► How is it managed in France?

In France, fertilizers containing ammonium nitrate are regulated by the rural code. Their placing on the market and their use are only authorized if they meet the European “CE fertilizer” standard or the French standard NFU, or if they have been approved or authorized. provisional sale or import from the Ministry of Agriculture. As regards ammonitrates with a high dosage of ammonium nitrate, they must pass a detonability test.

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Agricultural fertilizer storage sites and factories are classified as Seveso “high threshold” because they present major risks in terms of the escape of toxic products or explosions. France has approximately 1,200 Seveso classified sites, of which nearly 650 are classified as high risk throughout the country.

In 2000, nearly 13 tonnes of fertilizers were marketed in France, including 3.7 million tonnes of ammonitrates and 1.5 million tonnes of compound fertilizers based on ammonium nitrate. They are packaged in a 50 kg bag, in a large bag or in bulk.

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