WHILE PREPARING TO CONNECT HOSE TO ROCK DUST TANK OUTLET, THE 4"" COVER CAP THAT WAS RESTRAINED BY A CHAIN WAS REMOVED. THE TANK STILL HAD PRESSURE IN IT AND THE CAP BLEW OFF WHEN THE CLAMPS WE RE REMOVED. THE RESTRAINED CAP FLEW AROUND AND HIT A GLANCING BLOW TO NOSE, CHEEK LT, AND UPPER LIP CAUSING SWELLING BRUISES AND ABRASIONS. THE CONTENTS OF THE TANK (ROCK DUST) BLEW INTO EYES