OPERATOR HAD JUST CHANGED GRADES OF CLAY FROM S-TANKS CAUSING A DRY GAP IN THE SCREEN FEED LINES. WHEN CLAY DID GET TO SCREENS, THE SUDDEN RUSH CAUSED THE CLAY TO RUN OVER SCREENS THUS CAUSING A SLURRY SPILL. AS OPERATOR RUSHED UP STEPS TO STOP SPILLAGE SHE MADE AN AWKWARD STEP CAUSING HER LEFT FOOT TO SLIP OFF OF NEXT STEP CAUSING ALL HER WEIGHT TO SHIFT TO THE LEFT FOOT-FRACTURE.