Was cutting out an old come-along hook, which was inside a metal frame. He cut the hook from the frame using a 5/32"" diam. chamfered rod. Sparks from the cutting process fell onto a rag.The sparks caused the rag to smolder, he put it out by using his four pound hammer. Throwing the rag into the dumpster outside. Later noticed the dumpster on fire. Fire was 45 min in length.