THE INJURY OCCURRED WHEN THE EMPLOYEE & JACKLEG DRILL HE WAS HOLDING FELL APPROX. 6' FROM THE DECK OF A MOBILE WORK PLATFORM BEING USED TO INSTALL GROUND SUPPORT. THE EE & HIS ASST. HAD JUST REPOSITIONED & ENTERED THE WORK PLATFORM WHEN THE EE INADVERTENTLY STEPPED BACK THROUGH THE DECKS ACCESS AREA, FALLING TO THE FOOTWALL W/THE JACKLEG DRILL LANDING ON HIS UPPER BODY.