>>10199712 lb

Theory and reality work a little differently from each other. I assure you, if you have a few bags of ammonium nitrate sitting around and manage to set them on fire, they will eventually explode. If you let the bags sit in the sun through enough heating and cooling cycles, they will explode when a bird shits on them.

The reason comes from the growth of the powder into crystalline grains. When those crystals are stressed is when the explosion begins as molecules break down. Nitrogen and ammonia are being forced to accept oxygen atoms - none of which want anything to do with each other, sparing a discussion of molecular physics.

They will all readily decompose into free gasses when the molecule is strained.