STANDING ON DECK BUILT AROUND DRILL TO SECURE A CABLE OVERHEAD. DECK BUILT OF WOOD AND WAS SLICK DUE TO WATER. DECK BOARD MOVE AS IT WAS NOT PROPERLY SECURED OR BECAME UNSECURED. EE FELL APPRO X 2' TO THE GROUND, STRIKING UPPER TORSO ON THE DRILL (CONTROL PANEL GUARD PLATE).