On July 26, 2006, Employee #1 performed a pneumatic leak test on a 6-in. diameter, Schedule 40, jacketed, steel pipe, after coworkers welded sections of it. Employee #1 then secured a test tree on the end of the pipe with an adjustable wrench, then pressurized the pipe, and checked it for leaks for ten minutes. After the pipe passed the leak test, Employee #1 tried to bleed pressure from the pipe.