Beirut explosion: Why is ammonium nitrate dangerous 

Ammonium nitrate in its pure form is not dangerous.

By   |  Published: 6th Aug 2020  5:09 pm

The huge explosion that rocked the Lebanese capital on Tuesday is thought to have been caused by ammonium nitrate. Ammonium nitrate is an odorless crystalline substance commonly used as a fertilizer and has caused numerous industrial explosions over the decades.  When combined with fuel oils, ammonium nitrate creates a potent explosive widely used in the construction industry, but also by insurgent groups such as the Taliban for improvised explosives.

Ammonium nitrate in its pure form is not dangerous. It is, however, heat sensitive. At 32.2 degrees Celsius (89.96 degrees Fahrenheit), ammonium nitrate changes its atomic structure, which in turn changes its chemical properties.

When large quantities of ammonium nitrate are stored in one place, heat is generated. If the amount is sufficiently vast, it can cause the chemical to ignite. Once a temperature of 170 C is reached, ammonium nitrate starts breaking down, emitting nitrous oxide, better known as laughing gas. Any sudden ignition causes ammonium nitrate to decompose directly into water, nitrogen and oxygen, which explains the enormous explosive power of the salt.

Lebanese Prime Minister Hassan Diab said 2,750 metric tons of ammonium nitrate that had been stored for years in a Beirut portside warehouse had exploded, killing dozens of people and causing widespread damage to the capital.

In agriculture, ammonium nitrate fertilizer is applied in granule form and quickly dissolves under moisture, allowing nitrogen — which is key to plant growth — to be released into the soil.

Deadly disasters

Ammonium nitrate is made all over the world and is relatively cheap to buy. It is a highly explosive chemical, many countries strictly regulate its use. Over the past 100 years, there have been several disasters involving the chemical .

-Explosion at a Texas fertilizer plant in 2013 killed 15.  North Korean railway blast that left 161 dead in 2004 also had ammonium nitrate behind the explosion. 

-Two tonnes of it were used to create the bomb in the 1995 Oklahoma City attack that destroyed a federal building, leaving 168 people dead.

-Ammonium nitrate was among the chemicals stored in a warehouse in China’s northern city of Tianjin that ignited in 2015, triggering a blast that killed at least 165 people and caused over $1 billion in damages. An investigation found improper storage of the chemicals was to blame.

 Safe and regulated usage

Many countries in the European Union require that calcium carbonate to be added to ammonium nitrate to create calcium ammonium nitrate, which is safer.

In the United States, regulations were tightened significantly after the Oklahoma City attack. Under the Chemical Facility Anti-Terrorism Standards, for example, facilities that store more than 2,000 pounds (900 kilograms) of ammonium nitrate are subject to inspections.

Despite its dangers, Oxley said legitimate uses of ammonium nitrate in agriculture and construction have made it indispensable.

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