What Is Ammonium Nitrate?

A massive explosion that rocked Lebanon's capital city of Beirut Tuesday evening is being blamed on nearly 3,000 tons of ammonium nitrate that had been confiscated six years earlier and was stored in a warehouse in Beirut's port. As search and recovery continue, with at least 100 reported dead and more than 4,000 injured, what exactly is ammonium nitrate and why is it so dangerous?

According to CNN, ammonium nitrate is a compound of ammonia and nitrogen. The highly volatile material, which looks like a crystal-white solid, is typically used in agricultural fertilizers, though it is also used in bombs. The compound is deemed stable as a "pure" solid, though because it can become prone to detonation when mixed with any contaminants, there are stringent government guidelines for how to treat and store it properly. According to the EPA, ammonium nitrate should not be stored with any fuel, organic materials, chlorides or metals. It is also recommended it be stored in a place with fire-resistant walls, noncombustible flooring, and controlled temperatures, as ammonium nitrate can melt and release combustible toxic gases when exposed to heat.

Speaking with the BBC, Andrea Sella, professor of chemistry at University College London, explained that a major issue with ammonium nitrate is the fact that "over time it will absorb little bits of moisture and it eventually turns into an enormous rock." This makes the compound more dangerous, as it means if there is a shock, it will spread much more quickly. Philip Ingram, meanwhile, said that the longer ammonium nitrate is left, the more likely it will get contaminated, which can produce a reaction. Ingram explained that "it generates its own heat and, once it's started, it continues to generate it and that will build up over time." Ingram said that this could potentially lead "to the high-order explosion" that was witnessed in Beirut.

Although relatively safe, ammonium nitrate has been linked to several disasters before the explosion in Beirut. In 1921, roughly 4,500 tons of ammonium nitrate caused an explosion at a plant in Oppau, Germany, that killed more than 500 people. In 1947, a ship loaded with ammonium nitrate caught fire while docked in Texas City. That fire led to an explosion that damaged more than 1,000 buildings and killed nearly 400 people. More recently, the 1995 Oklahoma City Bombing, which left 169 people dead, was caused by just two tons of ammonium nitrate.

In response to the blast in Beirut and its likely cause, Lebanese President Michel Aoun has promised an investigation into the incident, stating that those responsible would be held accountable and face "severe punishment." Prime Minister Hassan Diab has also promised an investigation, stating that he will "impose maximum punishment."