Abstract: Employee #1 and a coworker were hooking into existing plumbing in a building. The coworker was unsweating a cap in the existing building. Employee #1 was approximately 6 ft away on the other side of a cement block wall, in the new addition, installing pipe hangers. An 8 in. diameter sleeve was in place in the wall for the pipe to pass through. The coworker doing the unsoldering said he had heated the cap at the valve. Solder was running out of the joint when a loud bang was heard and the end cap went flying. The cap went through the sleeve, striking Employee #1 on the left side of his face while he was lowering himself from the ceiling in the bucket of a portable lift.