Joe Manchin said . Monday : Used to pump nitrogen in West Virginia coal mine to flush out toxic gas . Rescuers hold onto hope of finding four miners trapped in blast . Cause of Monday 's explosion unknown ; state and federal authorities plan full investigation .
Monday : Used to pump nitrogen in West Virginia coal mine to flush out toxic gas . Rescuers hold onto hope of finding four miners trapped in blast . Cause of Monday 's explosion unknown ; state and federal authorities plan full investigation .