When I saw the heading I figured this was going to be about metal cans. Anyway I tried the pop a dent out on a metal can, it was empty, with compressed air through the spout, it's the old style with the big screw on center cap and the little spout with a small screw on cap. Anyway I get the wise idea to remove the small cap, stuff a rag around the air nozzle in the small spout and let her rip. part of the dent popped and then BOOM, the big center cap let go of threads and I was darn lucky it did hit me in the face. My wife just stood back laughed. It must have been doing about 100 mph when it blew off. It's kinda funny now but it was stupid thing to do.