WHILE TRYING TO CLEAN RIGHT SIDE MIRROR OF HAUL TRUCK #3, EMPLOYEE SLIPPED AND FELL ABOUT 57 IN. TO THE GROUND. THE RIGHT SIDE STEP HAD BEEN REMOVED FOR REPAIR AND INSTEAD OF USING A LADDER TO GET TO THE MIRROR, EMPLOYEE TRIED TO WALK ACROSS THE HAUL TRUCK'S FRONT BUMPER AND A SET OF CHOCK BLOCKS. EE STEPPED ON A CHOCK BLOCK, WHICH MOVED, AND EE FELL.