According to the Lebanese government, the source of the explosion was 2,750 tons of ammonium nitrate, an explosive chemical often used as fertilizer and sometimes in bombs, which had been stored in the port warehouse after being confiscated from an abandoned Russian-owned ship in 2014. In the following years, court records show, senior customs officials had tried and failed to win court permission to remove the dangerous stockpile by donating it to the Lebanese Army or selling it to the privately owned Lebanese Explosives Company.
Such a stockpile, if ignited, could easily cause the kind of blast and devastation seen in Beirut.
Lebanon’s National News Agency reported that the fire first ignited fireworks, and some videos showed flashes that could indicate fireworks and would not have been caused by ammonium nitrate.
Another news channel, LBCI, reported that welding work being conducted on the warehouse started the fire.
Whatever caused it, the fire apparently spread to the ammonium nitrate.
The dark and reddish color of the debris and smoke cloud that towered above the blast suggests two things: that ammonium nitrate was present and that it was not military grade, according to Dr. Rachel Lance, an explosives expert. Explosions with extremely dark smoke plumes indicate that not all of the explosive material burned up, meaning it was not a military explosive, and ammonium nitrate burns reddish, she wrote in an email.