From Wikipedia:
Ammonium nitrate is a white crystalline solid consisting of ions of ammonium and nitrate. It is predominantly used in agriculture as a high-nitrogen fertilizer and is readily available.
Its other major use is as a component of explosive mixtures used in mining, quarrying, and civil construction.
It is the major constituent of ANFO, (ammonium nitrate and fuel oil), a popular industrial explosive, and Ammonal (ammonium nitrate and aluminum powder) commonly used in mining. (Similar formulations have been used in improvised explosive devices. See: Oklahoma City)
While ammonium nitrate, by itself, is stable at ambient temperature and pressure under many conditions, it may detonate from a strong external initiation charge.
Accidental ammonium nitrate explosions have killed thousands of people since the early 20th century. It ranks number 6 in the table below:
Largest accidental explosions/detonations by approximate magnitude
1. Texas City, TX April 1947 Ammonium Nitrate 3 kt of TNT
2. Halifax, NS December 1917 High Explosives 2.9 kt of TNT
3. Staffordshire, UK November 1944 Military Munitions 2 kt of TNT
4. Port Chicago, CA July 1944 Military Munitions 1.9 kt of TNT
5. Ludwigshafen, DEU September 1921 Ammonium Sulfate 1.5 kt of TNT
6. Beirut, LEB August 2020 Ammonium Nitrate 1.25 kt of TNT
