EMPLOYEE WAS RUNNING CONTROL TOWER WHEN BF-1 BECAME CLOGGED WITH ICE. EE TURNED OFF BF-1 THEN C8 LOCKED AND TAGGED BOTH. GOT A SLEDGE HAMMER STEPPED UP ON THE LOWER BEAM, REACHED UP AND LOST F OOTING. HIT SHINS ON BEAM ON THE WAY DOWN. EE LANDED ON HANDS AND FACE ON STOCK PILE BELOW.