Abstract: Employee #1, a crane operator, and a coworker were adding a 15 ft section of latticework boom to an 18 ton truck crane. Cotter keys and one locking pin had been removed from the bottom section of the boom. Employee #1 walked under the boom, which was 4 ft from ground level, and, using a sledge hammer, knocked out the other locking pin. The top boom locking pins were still in place and acted as a hinge. The boom section fell, striking Employee #1 across the neck and back. Emergency services responded within 5 to 6 minutes and transported Employee #1 to the hospital, where he was pronounced dead.