Ammonium nitrate has the chemical formula NH₄NO₃. Produced as small porous pellets, or “prills”, it’s one of the world’s most widely used fertilisers.

Ammonium nitrate can be mixed with other substances to make a bomb. It was used in Irish Republican Army bombings in London in the 1990s, the 1995 explosion that blew up a federal building in ...

Ammonium nitrate is a colorless, crystalline salt used in some explosives, as a fertilizer, and in rocket fuel. However, the chemical was not a danger to the public, Hite said at the scene.