People don't respect ammonium nitrate,because it so rarely explodes. But it's very unpredictable. One day, for no apparent reason, it can suddenly go off.
There are, of course a lot of things that will make it worse. Contact with paper, organic liquids, and the like makes it more dangerous. And it can nitrify paper and cardboard making it extremely flammable. Restricting air to burning ammonium nitrate is a huge mistake, because it can shift the reaction mechanism over to a much more endothermic reaction. This is what happened at Texas City; a ship with a load of ammonium nitrate had a fire in the hold. The fire department did what is normally a good practice; they sealed the hatches and pumped steam into the hold. That is likely what caused the explosion.