EE WAS READING TO REFILL THE ANTIFREEZE TANK.HE OPENED THE DEPRESSURINZING VALVE & RELEASED THE AIR PRESSURE FROM THE TANK BUT NEGLECTED TO SHUTOFF THE VALVE WHICH ALLOWS THE TANK TO BE CHARGE D WITH AIR PRESSURE. AS HE UNSCREWED THE CAP, THE PRESSURE THAT HAD ENTERED THE TANK CAUSED THE CAP TO POP OFF. WHEN THE CAP POPPED OFF IT STRUCK EE IN THE LOWER LEFT LIP