A helicopter arrived at a rig and was met two roustabouts to unload cargo. The pilot decided not to shut the helicopter down in order to make a quick turn-around. After the passengers exited the helicopter and claimed their personal belongings, the roustabouts began unloading the cargo bay. Unknown to them, the co-pilot was on the opposite side of the aircraft, pushing the cargo toward them. The two men looked up just in time to see a wheel-mounted casing cutter roll out of the cargo bay. One man was able to jump free, but the second man was injured when the heavy tool fell on his foot.