Abstract: Employee #1 was preparing to fill the water tank after bleeding off the air pressure. When Employee #1 released the cam locks, residual pressure caused the cap to fly off, hitting the underside of the elevated bed, striking Employee #1, causing a laceration along the hair line and causing a mild concussion. The company used long bed dump trucks to carry limestone sludge, which, after dumping, left considerable residue on the trucks that obscured truck lights and would blow and settle on other vehicles as the trucks drove down the road. For this reason, the trucks were equipped with water tanks, pressurized by air from the trucks' braking systems. A regulator set the pressure on the water tank to 30 psi. Before removing the cap to refill the tank with water, it is necessary to bleed off the air pressure to keep the cap from flying off.