An employee was standing on the side of stacked pipe to remove a chock, manually position the pipe, and hook a 16-foot metal cable sling around the north end of a pipe weighing approximately 2,500 lbs. After the employee removed the chock on the north end of the pipe, the pipe began to roll on the piling boards, causing it to fall off the rack and crush the employee's right leg. The employee was hospitalized, and their right leg was amputated below the knee.