MAINTENANCE PERSONNEL WERE USING OXY-FUEL BURNING EQUIPMENT NEAR A CONDENSATE WATER TANK FOR A STEAM GENERATOR, WHICH WAS SHUT DOWN & COLD. A COVER PLATE ON THE CONDENSATE TANK (NOT A PRESSURE VESSEL) BLEW OFF DUE TO SOME SUDDEN RELEASE OF PRESSURE. IT IS BELEIVED A SMALL QUANTITY OF HYDROGEN GAS MAY HAVE ACCUMULATED IN THE TANK & WAS IGNITED BY A SPARK FROM THE TORCH. NO INJURIES.