Abstract: Employee #1, age 20, was working at a vertical drilling mud standpipe alongside the southeast derrick leg. Approximately 55 in. above the drill rig floor, a nipple had been welded near the end of a 4 in. diameter standpipe. A high pressure collar had been screwed onto the threads at the opposite end of the nipple. A second nipple had been screwed into the other end of the high pressure collar. An Oteco 5,000 psi gate valve had been threaded onto the opposite end of this second nipple and another high pressure nipple had been screwed in opposite the gate valve. On the other end of this high pressure nipple had been threaded a high pressure T-joint. A high pressure bull plug had been screwed into the opening at the top of the T, and an employee stated that an open-ended pipe had been screwed into the other end of the T. The first part of this piping configuration, up to the Oteco gate valve, was under 3,250 psig of pressure. A representative of an in-line pressure instrumentation and information company came to the drill rig floor and told Employee #1 that he was going to change the location of the drilling mud pump pressure sensor and that he wanted to move it to where the blank bull plug was located in the high pressure T. The open-ended pipe was removed from the end of the high pressure T. A 36 in. pipe wrench with a cheater pipe was used to remove the bull plug from the top opening in the high pressure T, and it was placed on the end opening. A different bull plug with the new sensor was then screwed into the top opening. The service company representative proceeded to tighten the connection by pulling on the end of the wrench while Employee #1 pushed on it. The configuration of high pressure collar, nipples, gate valve, high pressure T, and bull plug, was blown off of the threads of the high pressure nipple that was directly welded to the drilling mud standpipe. The drill parts struck Employee #1 in the left upper arm. He was killed.