Sounds like a happy ending, but... hmmm... fireworks?
Personally, I’d have guessed ammo.
Why? Ammunition doesn't explode when subjected to fire. Individual cartridges will "cook-off" but do not affect adjacent cartridges. In a huge fire, each of the cartridges will individually detonate, much akin to popping pop corn. There is no mass detonation when ammunition is burned.
All munitions are tested in fire by the Department of Transportation and assigned a "Hazard Classification" to assure bad things do not happen during transportation over public roads.