Abstract: EMPLOYEE #1, WHILE LOADING A SEMI-TANKER TRAILER THROUGH THE REAR BOTTOM LOADING VALVE, FAILED TO OPEN THE TOP CENTER LID TO RELIEVE THE BUILD UP OF AIR PRESSURE. HE BEGAN OPENING THE LID AFTER LOADING WAS COMPLETED BY REMOVING FOUR HOLD-DOWN NUTS AND DOGS. AFTER THE ACCIDENT, THREE DOGS AND NUTS WERE FOUND LOOSE, WITH ONE OF THE NUTS BLOWN OUT OF THE DOCK AREA INTO A PARKING LOT. IT DID NOT APPEAR THAT THE FOURTH DOG AND NUT HAD BEEN TOUCHED. AFTER REMOVAL OF THE THREE NUTS, THE LID BLEW OUT, STRIKING EMPLOYEE #1 IN THE JAW AREA AND KNOCKING HIM TO THE FLOOR. (HE WAS KILLED.) THERE WAS A SMALL PIECE OF PLASTIC MATERIAL FITTED INTO THE LID TOP WHICH HAD SEVEN SMALL HOLES IN IT, NOT SUFFICIENT TO RELIEVE THE HIGH PRESSURE. IT IS NOT KNOWN WHO PLACED THE PLASTIC PIECE IN THE LID'S VENT FITTING OR WHO PLACED IT THERE.