A motorman was removing a threaded two-inch to one-inch swedge from a two-inch ball valve and nipple. The swedge threads were tight, so heat was applied to the ball valve with a torch. The swedge was broken loose and turning freely. As the motorman put the pipe wrench down on the workbench, the worker assisting him closed the ball valve. This caused a sudden gush of hot water and steam, striking the motorman on the forearm.