I am sorry, but Static Electricity cannot ignite black powder. It was demonstrated here when someone posted a film clip showing an experiment, where you could actually see the static electricity charge pas through a small pile of black powder. There is not enough heat generated by static electricity to ignite the powder. In fact, according to that source, the electricity uses the graffite coating to go around the powder itself and not through it.
If you store the powder in its original cans, and keep it in a cool, dry place9 like a closet in an air conditioned home, it will last indefinitely .
You can put the cans in some of the inexpensive ammo cans sold in surplus stores, and that will give added protection from flame in a fire, but they will eventually go off if enough heat is applied. The same can be said for the more expensive " safe " being sold. You can make a wooden or metal box, lined on the inside with styrofoam, or even dry-wall, to insulate the powder and delay an explosion until the fire can be knocked down. Insulation is Insulation. YOu can ask the fire department what the fire rating is for various thicknesses of drywall, or some of the suppliers know that. Your library should have access to the local fire and building codes, or the national BOCA code, and you can look it up yourself. If you use an old Coleman style metal cooler, and line the inside with insulation, it would make a very fine storage safe, and let you put a lock on it for security, too.