It is said that the explosion may have been caused by 2,750 tonnes of ammonium nitrate. Ammonium nitrate is a chemical substance that can be used for fertilizer. It can also be used to make explosives. The government took the ammonium nitrate from a ship in the port of Damascus, the MV Rhosus. The MV Rhosus had been abandoned in the port, after the Lebanese government said it was no longer fit to travel by sea. The ammonium nitrate was then stored in the port, for at least six years. This may have been without the proper precautions. There are various regulations how ammonium nitrate should be stored, and handled. In its pure form, ammonium nitrate does not burn; but it increases fires a great deal. It should therefore not be stored near flammable substances, and it should not be heated in a closed space. It is also very sensitive to temperature.