Abstract: At approximately 2:15 p.m. on March 21, 1990, Employee # 1 and a coworker were approximately 70 ft above floor level in an H-2 vacuum, fitting a 180 degree elbow onto two 6 in. stainless steel tubes. The stainless steel elbow was resting on an approximately 2 in. wide saddle support that was about 10 3/4 in. away from the wall of the heater. Employee # 1 climbed down about 15 ft to a two-board scaffold level to adjust the nylon choker on the tubes to raise the left one about 3/4 in. When the left tube moved, the right tube, which was close to the bottom of the elbow, rubbed against it and caused the elbow to fall. It struck Employee #1 on the head and he and the elbow fell about 60 feet to the floor of the heater. Employee #1 was killed. The two-board scaffold level was equipped with a top guardrail approximately 37 in. above the planking, but no midrail.