A METAL SHARD CAME OFF A DRAG CHAIN LINK AS THE CONNECTING PIN WAS BEING REMOVED & STRUCK THE EE IN THE UPPER LEFT LEG. THE MECHANIC WAS ASSISTING ANOTHER MECHANIC WHO WAS USING A SLEDGE HAMMER, DRIFT PINS & HOLDERS. AS THE PIN WAS BEING STRUCK WITH THE HAMMER, THE HAMMER STRUCK THE CONNECTING LINK CAUSING THE FRAGMENT TO STRIKE EE.