Fast facts: Ammonium nitrate

WASHINGTON, D.C., United States (AFP) — Ammonium nitrate, which Lebanese authorities have said was the cause of the Beirut blast, is an odorless crystalline substance commonly used as a fertilizer that has been the cause of numerous industrial explosions over the decades.

These include notably at a Texas fertilizer plant in 2013 that killed 15 and was ruled deliberate, and another at a chemical plant in Toulouse, France in 2001 that killed 31 people but was accidental.

When combined with fuel oils, ammonium nitrate creates a potent explosive widely used by the construction industry, but also by insurgent groups like the Taliban for improvised explosives.

It was also a component in the bomb behind the 1995 Oklahoma City attack.

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.

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 blown up, killing dozens of people and causing unprecedented damage to the Lebanese capital.

However, under normal storage conditions and without very high heat, it is difficult to ignite ammonium nitrate, Jimmie Oxley, a chemistry professor at the University of Rhode Island, told AFP.

“If you look at the video of the Beirut explosion, you saw the black smoke, you saw the red smoke, that was an incomplete reaction,” she said.