Abstract: At approximately 2:00 p.m. on November 27, 2007, Employee #1, a mechanic at a truck repair shop, was conducting preventive maintenance work on a HIAB crane (Model Number D2006, Serial Number 8220216) with an articulating knuckle boom mounted behind the cab of a flatbed truck. Employee #1 was not trained and certified to work on this type of crane. Employee #1 had raised the boom approximately two feet then unscrewed the valves that control the hydraulic boom. Employee #1 then climbed onto the truck behind the boom to continue working on another valve. By unseating the face plate on the valve the safety relief valve built up so much pressure that it blew causing the boom to fall and pin Employee #1 underneath the boom. Employee # 1 sustained trauma to the chest. Employee #1 was pulled out and transported to a local hospital where he died.