If a powder flask is sufficiently mistreated to 'go off' then its more like a blow torch out of the end rather than a grenade.

A guy down my range decided it would be a great idea to loosen up his caked powder in his flask by stabbing a screwdriver down the spout - this eventually managed to ignite the powder and the blow-torch effect then happened and burned off the front of his clothes. Think he only lost one layer of skin so was very lucky indeed !