Beirut explosion: What is ammonium nitrate?

Lebanese officials say that thousands of tons of ammonium nitrate stored in a warehouse at the port in Beirut caused the powerful explosion that devastated the city on Tuesday, killing more than 130 people, injuring at least 4,000 and displacing 300,000 from their homes.

Ammonium nitrate is used in fertilizer and in the mining industry as an explosive to blast rock and move mounds of earth. It has some military applications as well.

It has been the cause of previous industrial accidents, and an ingredient in acts of terrorism as well. It was used by white supremacists to blow up the Alfred P. Murrah Federal Building in Oklahoma City, Oklahoma in 1995.

What happened in Beirut?

A: Videos posted online from the Beirut waterfront on Aug. 4 showed an epic disaster unfold with terrifying speed. White smoke billowing from a fire burning out of control in a warehouse near towering grain silos gave way to a massive explosion of reddish-black smoke. A spherical cloud of water vapor formed as the shock wave raced outward, wrapping around the silos, and disappearing into downtown Beirut. Videos taken closer to the explosion showed how a wall of compressed air shattered everything in its path as it moved closer, eventually sending the cameras themselves flying.

What caused such a big explosion?

A: According to the Lebanese government, about 2,750 tons of ammonium nitrate fertilizer was stored in a warehouse on the Beirut waterfront and caught fire, later exploding. The fertilizer arrived in the city more than six years ago aboard a Russian-owned cargo ship that made an unscheduled stop in the city. Lebanese port officials said they made several requests to the courts to have the stockpile removed, but got no response.

How could fertilizer possibly explode?

A: Ammonium nitrate, by itself, is relatively harmless. But if added to a fuel source, and subjected to intense stresses like heat and pressure, it can explode. Although we do not know exactly what happened yet in Beirut, the sheer size of the collected ammonium nitrate offers some clues. If subjected to fire in such bulk quantities, and in a semi-contained environment like a warehouse, the potential for detonation is strong.

Has this happened before?

A: Yes. In 1947, an explosion in Texas City, Texas, killed at least 581 people and wounded 3,500 after two cargo ships carrying ammonium nitrate caught fire. In 2013, a fertilizer plant in West, Texas, caught fire and exploded, killing 15 people. In 2015, disaster struck in Tianjin, China, when a fertilizer explosion killed 165 people at a busy seaport.

Many Americans were introduced to the dangers of ammonium nitrate from the destruction in Oklahoma City, carried out by white supremacists in 1995. Two tons of the fertilizer were mixed with diesel fuel to create a bomb placed inside a rental truck that detonated in front of the building.

How powerful was the explosion in Beirut?

A: It was one of the largest non-nuclear explosions in recent history, according to Brian Castner, lead weapons investigator for Amnesty International’s Crisis Response Team. “It’s the biggest explosion in an urban area in decades,” he said. “The human impact of it is the important thing, and it affected people a dozen kilometers away.”

While it is difficult to precisely calibrate the force of the Beirut explosion, the US military offers a formula that allows bomb technicians a quick way to calculate the power of a blast with just paper and pencil, by converting the weight of a known quantity of explosives to that of TNT.

There were 2,750 tons of the fertilizer in the Beirut warehouse, roughly equivalent to 1,155 tons of TNT, which would produce a large enough blast wave to destroy most buildings within around 800 feet, and would shatter glass far beyond a range of 1.25 miles.

How does that compare to an airdropped bomb?

A: It is many times larger than the most powerful conventional airdropped bomb in the U.S. arsenal, which was used in combat for the first time in 2017. That bomb, the GBU-43 Massive Ordnance Air Blast, has a net explosive weight of 18,700 pounds or roughly 9.35 tons of TNT, according to data from the U.S. Army Defense Ammunition Center. But the Beirut explosion was far smaller than the 15,000-ton TNT equivalent of the smallest nuclear weapon ever used in war, which was dropped on Hiroshima 75 years ago this Thursday.

Could it happen elsewhere?

A: That partly depends on the enforcement of safety regulations, which can vary by country. In the United States, the Espionage Act of 1917 gave the Coast Guard strict regulatory oversight of all port facilities — specifically to prevent large explosions such as the one in Beirut. While intended to foil attempted sabotage, the regulations tightly control movements and storage of hazardous materials like ammonium nitrate for reasons of general public safety.