The investigation into an explosion in the harbor of Lebanon's port city of Beirut is focusing on how 2,750 tons of ammonium nitrate, a highly explosive chemical used in fertilizers, came to be stored at the facility for six years, and why nothing was done about it.
The explosion Tuesday blasted a crater into the port and hit the city like a freight train, killing more than 100 people and injuring thousands. Buildings were damaged for miles around the city. Some other recent deadly explosions involving ammonium nitrate:
Aug. 12, 2015: A massive warehouse explosion rocked the port city of Tianjin, China, killing 173 people and injuring nearly 800. Investigators found the warehouse held illegal stores of ammonium nitrate, which caught fire and caused a series of blasts.
April 17, 2013: A fire intentionally set at the West Fertilizer Co. facility in West, Texas, caused ammonium nitrate to ignite, triggering a massive explosion that killed 15 people, injured at least 236 and left part of the small town in ruins. The fire ignited in a seed room and quickly engulfed an area where ammonium nitrate was stored in wooden containers.
April 22, 2004: An explosion in the North Korean town of Ryongchon, near the border with China, killed 161 people and injured 1,300. It was believed to have been sparked by a train laden with oil and chemicals hitting power lines. North Korea blamed the explosion on "electrical contact caused by carelessness during the shunting of wagons loaded with ammonium nitrate fertilizer."
Oct. 12, 2002: A series of nightclub bombings on the Indonesian island of Bali killed 202 people, mostly Western tourists. According to investigators, the primary ingredient of the main bomb that tore through the popular Kuta nightclub district was ammonium nitrate.
Sept. 21, 2001: A chemical plant explosion in Toulouse, France, killed 31 and injured some 2,000. A 2006 report by judicial investigators blamed the blast on negligence that allowed ammonium nitrate to come into contact with other chemicals in the AZF plant, a subsidiary of oil giant Total.
April 19, 1995: The deliberate explosion of a 2,200-kilogram fertilizer-and-fuel-oil bomb in a rented Ryder truck parked outside the Alfred P. Murrah Federal Building in Oklahoma City killed 168 people and injured more than 500. Ammonium nitrate was found to be the main ingredient. Hatred of the federal government motivated former Army soldier Timothy McVeigh and his co-conspirator, Terry Nichols, to commit what many experts still refer to as the deadliest act of domestic terrorism on U.S. soil.