THE LINEMAN WALKED INTO THE PROP ARC OF THE OPERATING RT ENGINE AND WAS FATALLY INJURED AFTER DISCONNECTING A GROUND POWER UNIT (GPU) CABLE FROM THE RT ENGINE NACELLE. THE LINEMAN INITIALLY APPROACHED THE NACELLE FROM THE REAR, BUT WALKED FORWARD INTO THE PROP ARC AFTER DISCONNECT. THE FBO'S REPORTED NORMAL PROCEDURE FOR GPU DISCONNECT OPS ON THIS ACFT DIRECTED PERSONNEL TO APPROACH AND DEPART THE NACELLE AREA FROM THE REAR. THE PLT REPORTED THAT THE LINEMAN HAD PERFORMED GPU DISCONNECT PROCEDURES ON THIS ACFT WITHOUT ANY PROBLEM ON SEVERAL PREVIOUS OCCASIONS. TOXICOLOGICAL ANALYSIS WAS PERFORMED ON BLOOD AND URINE SAMPLES FROM THE LINEMAN: A LEVEL OF GREATER THAN 50 NG/ML CARBOXY THC WAS REPORTED TO EXIST IN THE URINE SAMPLE. THE REPORT NOTED THAT LEVELS OF GREATER THAN 50 NG/ML CARBOXY THC ARE 'TYPICALLY ASSOCIATED WITH VERY RECENT USE' (OF MARIJUANA). ADDITIONALLY, COCAINE AND MARIJUANA METABOLITES WERE DETECTED IN THE LINEMAN'S BLOOD SAMPLE.