EMPLOYEE WAS STANDING ON BOTTOM SHELF OF STORAGE RACK, SECURING THE BOARDS ON THE MIDDLE SHELF. THE SHELF SUPPORT BOARDS THE EE WAS STANDING ON WERE NOT SECURED TO FRAME AND PULLED AWAY FROM FRAME CAUSING THE EE TO FALL APPROX FOUR FT TO GROUND LEVEL. DURING THE FALL THE EE'S RIBS STRUCK A METAL GEAR, THUS CAUSING A FRACTURE TO RIGHT RIBS.