Hi

Black powder is extremely safe if stored and handled correctly.
It will not ignite unless there is a source of a spark or from, grit, flame, or static.
It cannot be detonated by pressure at all. Black powder only burns on it's surface area and does not change molecularly like a high explosive when a detonation wave is passed through it.
Store it in sealed container, take care not to introduce static, (nylon y fronts, etc!) or pouring between plastic containers from great heights and don't use near the fire or when smokin' a fag an it'll be as safe as houses!

Hope that helps

regards Steve, (ex army felix)