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What is ammonium nitrate, which caused the massive explosion in Beirut?

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Beirut blast: What is ammonium nitrate, how and where is it used or misused, what hazards does it present, and what are the rules and regulations about its use in India?

The catastrophic explosion at Beirut port on Tuesday evening (August 4) that has so far killed at least 100 people and injured around 4,000, with an unknown number feared trapped under rubble was, according to the government of Lebanon, caused by over 2,700 tonnes of ammonium nitrate kept in storage for over six years.

A common chemical ingredient of agricultural fertilisers, the nitrogen rich compound is also the main component of the explosive composition known as ANFO — ammonium nitrate fuel oil.

What is this chemical, how and where is it used or misused, what hazards does it present, and what are the rules and regulations about its use in India?

Ammonium nitrate, the substance

In its pure form, ammonium nitrate (NH4NO3) is a white, crystalline chemical which is soluble in water. It is the main ingredient in the manufacture of commercial explosives used in mining and construction.

In India, The Ammonium Nitrate Rules, 2012, under The Explosives Act, 1884, define ammonium nitrate as the “compound with formula NH4NO3 including any mixture or compound having more than 45 per cent ammonium nitrate by weight including emulsions, suspensions, melts or gels but excluding emulsion or slurry explosives and non explosives emulsion matrix and fertilizers from which the ammonium nitrate cannot be separated”.

Ammonium nitrate as an explosive

Pure ammonium nitrate is not an explosive on its own. It is classified as an oxidiser (Grade 5.1) under the United Nations classification of dangerous goods. If mixed with ingredients like fuel or some other contaminants, or because of some other external factors, it can be very explosive.

However, for combinations to explode, triggers like detonators are required. Many Improvised Explosive Devices (IEDs) used by terrorists around the world have ANFO as the main explosive, triggered by primary explosives like RDX or TNT. In the majority of terror attacks in India, including those in Pulwama, Varanasi, Malegaon, Pune, Delhi, Hyderabad, and Mumbai, ammonium nitrate has been used along with initiator explosives like RDX.

Stored ammonium nitrate is a major fire hazard

Large quantities of stored ammonium nitrate are regarded as a major fire hazard, with multiple reported cases across the world. The explosion of large storage can happen primarily in two ways.

One is by some type detonation or initiation because the storage comes in contact with explosive mixture. Second, the blast can result due to a fire which starts in the ammonium nitrate store because of the heat generated due to the oxidation process at large scale. The second one seems to be the primary likely cause of the incident at Beirut port. There are several documented examples of deadly ammonium nitrate fire and explosion incidents in the past, some with large numbers of fatalities like in China in 2015 and in Texas in 1947.

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