if its the old style ones they have a tablet of sodium azide(same shit as solid booster rockets on the space shuttle) about the size of an aspirin. the newer style use pellets that look like candy sprinkles.
dynamite type explosion????? I don't think so. confined space explosion yes. they can kill someone if you launch a projectile with it. as much fun as the stupidity in the videos looks like I would pass on making anything out of one.