Abstract: Employee #1 was a derrickman on an oil rig derrick. When an elevator bale retaining bolt on the traveling block came loose because of the vibration of the derrick, the driller told Employee #1 to climb to the block and tighten the bolt. Employee #1 secured the climbing belt to himself and then tied the end of the air hoist line to the belt rings on the front side of the belt. The hoistline was a 1/2 in. cable with an approximately 6 ft long section of chain attached to the end of it. The chain was secured to the belt ring by first running the chain through and tying a knot in it and then by securing the slack end to the taut side by means of a Clevis grab hook. No form of safety latch was used. The driller hoisted Employee #1 to the block. As he began to work, the Clevis grab hook on the chain came loose and worked its way past the knot and out of the ring of the climbing belt. Employee #1 fell approximately 38 ft to the floor of the oil rig and was killed.