EMPLOYEE WAS CLIMBING ONTO A BULLDOZER WHICH WAS PARKED BY THE RAW COAL STOCKPILE. HE STEPPED ON THE DOZER PUSH ARM STEP. HIS FOOT SLIPPED OFF & HE FELL, STRIKING HIS SIDE ON THE PUSH ARM. HE DID NOT ASSURE SOLID FOOTING WHILE CLIMBING ONTO THE DOZER. NO OTHER FACTORS WERE INVOLVED.