Abstract: At approximately 10:30 a.m. on May 6, 2008, Employee #1 and coworkers #1 and #2 were working on Rig Number 10 drilling at Well Number 7099F-2. They set a Hydril blow out preventer (BOP), Model Number 10-9, weighing approximately 4,500 pounds, on the well's conductor pipe located underneath the rig floor. They used the rig's main hoist and slings that went through an opening in the rig floor to set the equipment. Employee #1 and coworker #2 were connecting piping to the BOP and momentarily left the work area. Coworker #1 came down from the rig floor and disconnected the lifting slings from the BOP. They had failed to secure the BOP to the conductor pipe after it was set with 6 locking bolts. Employee #1 returned to finish installing pipe, and coworker #2 started raising the slings through the rig floor with the hoist. As the slings were being raised, one of them became entangled on one of the BOP's lifting eyes causing the BOP to rise off the conductor pipe and fall. Employee # 1 was struck by the BOP on his lower left leg. Employee #1 was hospitalized, and his left leg was amputated below the knee.