Apoplectic newscasters love to make a fuss over what they consider to be a large and dangerous stash of ammo when reporting the "news." More often than not, the giant stash doesn't even qualify as a small supply for a day at the range for many of us. But with that said, does a really large stash of ammo pose a real risk? According to SAAMI... not so much.
https://www.youtube.com/watch?v=-8cshlhdliE
The video shows that sporting ammunition *outside* a firearm:
1) Is unlikely to ignite under extreme conditions of impact.
2) Will not propagate in a chain reaction from one cartridge or shell to another.
3) Does not mass explode.
4) May be controlled by fire fighters using water and wearing standard structural fire fighter protective clothing and self-contained breathing apparatus.