Abstract: Employee #1, the derrick man on a drilling rig that was being rigged down, went up the ladder after the cathead line had become entangled as the stabbing board was being lowered. He was observed pulling on the catline and then had a coworker cut the tag line that went to the fall protection line. He was observed pulling on this tag line, and then climbed to a higher elevation, apparently free climbing because the climb assist was stuck. Shortly thereafter, the counterweight to the climb assist was heard coming down the line very fast and then hit the end of the line. Employee #1 lost his grip and fell 50 ft to the oil rig floor. He was killed. The climb assist apparently was entangled with the tag line for the fall protection. When Employee #1 climbed to a higher level, he created slack in the climb assist so that when it came free, it accelerated very rapidly. This caused a shock overload to its pulley, which apparently jerked Employee #1 off the ladder. Employee #1's failure to use the fall protection equipment also contributed to the accident.