CREW WAS MINING IN FACE OF LONG ROOM WHEN RELIEF HOLES, LOCATED AT ENTRANCE TO LONG ROOM & ANOTHER ABOUT 150'INTO L.R. STARTED BLOWING A LITTLE.AFTER CUTTING ANOTHER CAR OF MUCK, THE HOLES STA RTED BLOWING HARDER. THE ROOF BOLTER WAS MOVED INTO PLACE & BEGAN DRILLING ANOTHER RELIEF HOLE.FOREMAN WAS CALLED TO MONITOR AIR. OXYGEN METER ALARMED, INDICATING OXYGEN WAS BELOW 19.5%.