[Photon Guy]

First off, lets make it clear, are you talking about "gunpowder" (Black Powder) or modern smokeless powder, "gunpowder"?

despite what movies, tv, and most people think, modern (smokeless) gunpowder is NOT an explosive. DOT classes it as a flammable solid.

Black powder on the other hand IS an explosive. And it is NEVER properly stored in a safe of other sealed strong metal box. Doing so creates a bomb. Proper storage for quantities of black powder is always in something that will rupture and vent the pressure of an explosion easily. A wooden building/shed for example. Early venting of pressure prevents a larger explosion.

IF you were using a torch, or power saw to cut into a gun safe with smokeless powder inside, it is REMOTELY possible you could ignite the powder. IF so, it would burn very fast (deflagrate), but not explode.

Not sure about legal warnings and liability, best check your local laws, carefully. A safe full of smokeless powder is LESS dangerous than that can of gasoline you use to fill your lawnmower, physically. People believe different, but people believe a lot of stuff that isn't true. Just look at who we elect!

I think a "warning" sign like you described is less a matter of legal liability than a matter of warning an ignorant thief to look for a "safer" and easier target. Assuming, of course, they actually read it, and understand the language...

The warning signs I've seen warn against black powder. Here is an example.

http://www.libertysafe.com/accessory...-17-pg-49.html