EMPLOYEE WAS OPERATING DRILL, HYDRAULIC HOSE TO COMPRESSOR CAME LOOSE FROM FITTING SPRAYING HYDRAULIC FLUID ON DRILL. THE HOSE CONTACTED THE COOLER FAN, GENERATING SPARKS WHICH CAUSED THE HYD FLUID TO BURN. FLAMES CAME INSIDE CAB AND BURNED DRILLER'S LEFT FOREARM AS HE WAS EXITING DRILL CAB.