EMPLOYEE WAS ATTEMPTING TO LIGHT THE PROPANE HEATERS, WHEN A RELIEF VALVE POPPED AND WAS RELEASING PROPANE. HE STARTED TO LEAVE THE AREA WHEN THE PILOT LIGHT CAME ON AND IGNITED THE PROPANE. THIS CAUSED A SUDDEN FLASH OF FIRE, SINGEING THE EMPLOYEE'S HAIR AND FACE, CAUSING 1ST AND SOME 2ND DEGREE BURNS ON HIS FACE.