EE WAS WORKING ON #12 ATLAS DRILL. WORKING SURFACE OF DRILL WAS ELEVATED APPROX 40"" OFF GROUND. HE CLIMBED UP THE EQUIPMENT TO RETRIEVE A BATTERY CHARGER USING AN 8"" BLOCK OF WOOD AS A STEP LA DDER. AS HE STEPPED DOWN, THE WOOD BLOCK TURNED & EE FELL BACKWARDS & TURNED IN THE AIR LANDING ON HIS LEFT HAND & RIGHT WRIST.