Oyeboten is correct snakeguy, ammunition stored in a safe is perfectly fine even in a fire.
I've been to fires where all of a sudden there's gunfire. It sounds like an evening with the Hatfields and the McCoys but it's pretty safe. In fact, even loose ammo is fairly harmless as when it goes off in the heat of a house fir for example, it's the brass that gets shot around the room and not the lead.
But as Oyeboten correctly points out, NEVER, EVER store Black Powder in a safe. As you probably already know, Black Powder is an "A" explosive and does not need to be contained to be "explosive", but if you store it in a safe you're just asking for a huge explosion during a house fire. Whatever's left of the safe would likely be found in Fairbanks or Nome.
If you have a fairly watertight shed in the yard, or even a garage, store it there and not in the house in your gun safe.
Bud
ps
Apologies Phil, you certainly didn't need me to verify your point but I thought another voice on top of your excellent reply might be helpful due to the huge importance of the subject matter.
Fun subject, and good stuff to review now and then!
And, your further mentions regarding 'BP' are important, too -
Being: It is already a potential 'BOMB' just sitting in it's Keg or large enough Can, and if the Keg or Can is in a larger heavier Container, like a Safe or Fire Safe, it would merely cause the Safe to be just more resulting shrapnel, with the debris of the secondary container being added to the ejecta of the explosion.
Small 1 Lb Cans ( like most of us have ) are not a problem or issue, or are not thought to be enough of an issue or potential problem to be needing special storage conditions, but, once one gets 5 Lbs or more in a single container, then it is time to consider a special storage situation, and, one which is not in or too close to, the House or Garage.
As far as I gather, Smokeless does not tend to Go-off-like-a-Bomb, if ignited in bulk, as Black Powder ( when in enough 'bulk' ) can or will.
Smokeless will tend to make a really good 'Whoosh' instead of detonating.