Beirut Tragedy: How Does Ammonium Nitrate Cause Explosion?

On Tuesday, the whole World was shocked by the news of catastrophic powerful explosion at Lebanon's main port. The port is located in Beirut city, the capital city of Lebanon - which means a place where its population is the highest.

Until 5.00 pm on 8th of August 2020, there were at least 135 people dead, and is expected to keep increasing due to the large area damaged from the explosion shockwave. 

According to the latest news, the main explosion was said to be linked to about 2,750 tonnes of ammonium nitrate equivalent to 1.1 kTonnes of TNT that had been confiscated by the government from an abandoned ship MV Rhosus and was stored in the port without any proper safety measure for six years. Despite inefficient transmission of the shock waves into the ground, the explosion was detected as a seismic event of magnitude 3.3 by the United States Geological Survey. By the following day, 5th August, the fire was largely extinguished with the help of rescue helicopters.

So How Does Ammonium Nitrate Cause Explosion?

Ammonium nitrate is a chemical compound with a form of white crystalline solid consisting of ions of ammonium and nitrate. It is predominantly used in agriculture as a high-nitrogen fertilizer and as a component of explosive mixtures used in mining, quarrying, and civil construction. Accidental ammonium nitrate explosions have killed hundreds of people since the early 20th century.

Solid ammonium nitrate decomposes on heating. At temperatures below around 300 °C, the decomposition mainly produces nitrous oxide and water, while at higher temperatures nitrogen, combustional oxygen and water are produced.

Both decomposition reactions are exothermic and have gaseous products. Under certain conditions, this can lead to chain of reactions, with the decomposition process becoming explosive. The brown color in the explosion cloud is because of the nitrogen dioxide, a secondary reaction product.

The explosion in Beirut resulted from a fire that was spreading into the ammonium nitrate itself. To avoid possible explosion, the fire should have been confined at least to a degree for successful transition from a fire to an explosion: a phenomenon known as "deflagration to detonation transition".