If it's just raw ammonium nitrate like they are claiming... then how does the gas pressure get high enough to cause that big of an explosion?
On a ship it's because it is in the cargo hold. Ammonium Nitrate doesn't just "blow up" from fire.
IMO - Looked like ordinance cooking off to me. I would say this is what happens when you store rockets you got from Iran next to a huge pile of ammonium nitrate. Be advised. Not a good idea.
