https://www.scientificamerican.com/article/how-could-the-beirut-explosion-happen-experts-explain/

An enormous explosion in Beirut’s seaport area this week ruined nearby buildings and caused damage and shattered windows across the city, killing scores of people and wounding thousands more. As videos of the disaster spread on social media, people around the world immediately began speculating about the cause.

Lebanese government sources eventually said it was 2,750 metric tons of ammonium nitrate, a chemical routinely used as agricultural fertilizer and, when mixed with fuel oil, as a mining explosive. The stockpile had been sitting in a warehouse since 2014, when the ship that carried it into port was abandoned. This incident is not the first time ammonium nitrate has caused devastation. In 2013, for instance, a stockpile a tenth the size of the one in Beirut blew up a West Chemical and Fertilizer Company facility in Texas.