EE WAS CARRYING A 5"" X 7"" X 10' WOODEN TIMBER WITH OTHER WORKMEN. THEY WERE INSTALLING ROOF SUPPORT IN A RETURN ENTRY. THE TIMBER SLIPPED FROM THE EE'S HANDS & STRUCK HIM ON THE TOP OF HIS THI GH. THERE WAS NOT ANY DAMAGE TO ANY EQUIPMENT OR IMPAIRMENT TO THE OPERATION. EE DID NOT HAVE A FIRM GRIP ON THE TIMBER. NO OTHER FACTORS WERE INVOLVED.