What Is Ammonium Nitrate?

A chemical compound comprising ammonium and nitrate ions, ammonium nitrate is widely used across the globe as a high-nitrogen fertilizer. Another common use of ammonium nitrate is in developing explosive mixtures, which is used for quarrying, mining and civil construction purposes. While its role as a potent fertilizer is unquestionable, it has nonetheless emerged as a controversial chemical compound over the years. That’s largely because several thousands of people have died due to accidental explosions caused by ammonium nitrate.

How ammonium nitrate is made?

Originally, ammonium nitrate was mined from a rare natural mineral called Gwihabaite. However, in modern times, almost all of ammonium nitrate is produced in factories. It is created by combining ammonia with nitric acid. Depending on the grade, the final product is 95% to 99.9% ammonium nitrate. It is usually sold in the form of prills or granules.

What makes ammonium nitrate so explosive?

In normal circumstances, ammonium nitrate is completely safe as it does not burn on its own. However, when mixed with fuel or with other explosive material or if put into a burning fire, ammonium nitrate can significantly increase the combustion rate. This is what gives ammonium nitrate its explosive properties.

As is evident from the chemical formula NH4NO3, ammonium nitrate contains significant amount of oxygen. This oxygen is available in concentrated form, which makes it more potent than the oxygen present in the air. That’s why ammonium nitrate is often a component of explosives used inside mines where natural oxygen supply may be limited.

Use of ammonium nitrate for terror activities

As ammonium nitrate is easily available as a fertilizer, it has often been misused by terrorists.

1. Sterling Hall bombing, 1970 – This building, located inside the University of Wisconsin–Madison campus, was bombed using around 910 kg of explosive material comprising fuel oil and ammonium nitrate. One person was killed and three people were injured.
2. Oklahoma City bombing, 1995 – The Alfred P. Murrah Federal Building was targeted in this attack by American terrorists Timothy McVeigh and Terry Nichols. The explosive comprised 2,300 kg of ammonium nitrate, 540 kg of liquid nitromethane and 160 kg of Tovex. At least 168 people lost their lives and around 700 were injured.
3. Delhi bombing, 2011 – The blast occurred in Delhi High court, killing fifteen people and injuring at least 79. It was an improvised explosive device created by combining ammonium nitrate with Pentaerythritol tetranitrate (PETN).

Industrial accidents involving ammonium nitrate

Over the years, ammonium nitrate has led to various industrial accidents.

1. Oppau explosion, 1921 – Nearly 4,500 tons of ammonium nitrate and ammonium sulfate exploded in this accident in Germany. The explosion killed around 500 people and injured more than 2000 people.
2. Texas City disaster, 1947 – A ship carrying around 2,300 tons of ammonium nitrate exploded due to on-board fire. At least 581 people were killed in the accident.
3. Tianjin explosions, 2015 – Around 800 tons of ammonium nitrate exploded when it came in contact with fire. Around 173 people lost their lives and 800 were injured.
4. Beirut explosions, 2020 – This was one of the most massive, involving around 2750 tons of ammonium nitrate. At least 220 deaths and 7000 injuries have been reported.

It’s apparent that ammonium nitrate needs to be stored properly. It will not burn on its own, but contact with external fuel and heat sources can prove disastrous.