EMPLOYEE WAS USING A WARM WATER HOSE TO WASH AROUND A FROST CHUNK OF CONCENTRATE AT THE DISCHARGE END OF THE APRON FEEDER. SHE WAS STANDING ON THE SECOND STEP OF A 3 STEP STAIRWAY WHEN SHE LOS T HER BALANCE AND FELL ONTO THE WALKWAY. SHE WAS TAKEN TO THE HOSPITAL & DIAGNOSED FX RIBS.