What is ammonium nitrate? What does chemistry say about Beirut's huge explosion?

The Lebanese capital, Beirut, was rocked Tuesday evening by an explosion that left at least 78 people dead and thousands injured. The country's Prime Minister Hassan Diab said the explosion was caused by 2,700 tons of ammonium nitrate stored near the city's shipping port.

Video showing a fire burning near before the explosion:

Ammonium nitrate has the chemical formula NH4NO3, produced in the form of small porous granules, and it is one of the most widely used fertilizers in the world.

It is also a key component of many blasting materials used in mining, as it is mixed with liquid fuel and detonated with an explosive charge.

It takes a lot of mistakes for the industrial ammonium nitrate disaster to happen, and unfortunately, it seems that this is what happened in the case of Beirut. 

What could cause the explosion?

Ammonium nitrate does not burn by itself. It is a source of oxygen that can accelerate the combustion of other materials.

For combustion to occur, oxygen must be present. Granules of ammonium nitrate provide a more concentrated source of oxygen than the air around us. This is why they are so effective in making mining explosives, as they are mixed with oil and other fuels.

Ammonium nitrate can strongly decompose on its own at sufficiently high temperatures. This process produces gases that include nitrogen oxides and water vapor. The rapid release of these gases causes an explosion.

The decomposition of ammonium nitrate can begin if an explosion occurs at its storage site or if there is a severe fire near it, which is what happened in the 2015 Tianjin explosion, which killed 173 people because of storing flammable chemicals with ammonium nitrate in a chemical plant in eastern China.

Although we are not sure what caused the explosion in Beirut, the footage of the accident indicates that it may have occurred due to a fire that was visible in a part of the city’s port before the explosion.

It is relatively difficult for a fire to release an explosion of ammonium nitrate. The fire must be kept in the same area as the ammonium nitrate granules.

Besides, ammonium nitrate granules are not a fire fuel themselves, so they must be tainted or canned with other flammable materials.

The health of the population is in danger!

In Beirut, 2,700 tons of ammonium nitrate were reported to have been stored in the port warehouse for six years without proper safety controls.

This contributed almost inevitably to the tragic circumstances that led to a general industrial fire causing such a devastating explosion.

The explosion of ammonium nitrate produces huge quantities of nitrogen oxides. Nitrogen dioxide with formula NO2 is red in color and smelly. Pictures from Beirut reveal the distinct red color of the gas cloud from the explosion. Nitrogen oxides are common in polluted urban air and can irritate the respiratory system. High levels are especially worrisome for people with respiratory illnesses.

The fumes resulting from the explosion in Beirut will pose a health hazard to the population until it dissipates naturally, and this may take several days depending on the local weather.
An important reminder

In Australia, large quantities of ammonium nitrate are produced and imported, most of which are used in mining operations. It is made by mixing ammonia gas and liquid nitric acid, which in turn is made of ammonia.

Ammonium nitrate is classified as a hazardous substance and all aspects of its use are tightly regulated. For decades, Australia has produced, stored, and used ammonium nitrate without incident.

The explosion in Beirut shows us how important these controls are.