What is ammonium nitrate?

Lebanese Prime Minister Hassan Diab said that an estimated 2,750 tons of ammonium nitrate had been stored at a warehouse in Beirut for six years. Lebanese Interior Minister Mohammad Fahmi said that the explosive chemicals may have caused the explosion. 

Ammonium nitrate has a number of different uses, but the two most common are as an agricultural fertilizer and as an explosive.

Ammonium nitrate does not burn. However, it will support and increase the rate of combustion in the presence of flammable or combustible materials even in the absence of oxygen.

Prime Minister Diab said in the statement it was "unacceptable" that so much explosive material was stored in a warehouse "without taking preventive measures while endangering the safety of citizens."