A sub-sea engineer was fatally injured while working on a semi-submersible rig. The deceased was standing inside the H4 Connector cavity of the Blowout Preventer (BOP) inspecting the ring gasket seating area. The BOP (approximately 110 tons) was suspended by two 70-ton bridge cranes (forward and aft). The mechanical brakes of the forward bridge crane failed. This allowed the BOP to swing free from the forward side of the drill rig toward the aft. The subsea engineer was pinned between the BOP and the test stump.