A supply boat crewman was struck on the head by a flexible hose during pressure venting after transfer of bulk drilling chemicals. Transfer of bulk drilling chemicals used compressed air at a low pressure. On transfer completion, instructions were given to close all valves, purge and depressurize the transfer lines and disconnect the bulk transfer hose. The 4″ diameter flexible vent hose was lowered over the starboard side of the vessel into the sea to prevent dust clouds during venting. To keep the hose submerged an old valve and ballast chain had been secured to its outboard end. A length of rope was tied between the outboard hose end and the vessel rail to allow for hose recovery, leaving about a 4m (13.2 feet) arc of movement between secured points.