system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does fertilizer explode?
gpt
Most fertilizers contain ammonium nitrate.

Ammonium nitrate is an oxidizer that reacts with other combustible materials.

Normally it's fairly safe to have around at normal temperatures.  But when it's heated up to higher temperatures, or exposed to a hot fire, a run-away chain reaction can occur with ammonium nitrate to cause a violent explosion.

It's often used for improvised explosive devices, and for accelerating the reaction of other explosives, such as in some forms of dynamite.