PICKED UP SLEDGE HAMMER TO HIT SIDEOF SAND TANK TO LOAD OUT A TRUCK. THE WEATHER WAS VERY COLD AND THE SAND HA DFROZEN. AS THE EMPLOYEE HIT THE SIDE OF THE TANK HE FELT A PULL BETWEEN HIS S HOULDERS ON THE LEFT SIDE. HE AHD PULLED THE MUSCLE JUST UNDER THE LEFT SHOULDER. HE WAS TRANSORTED TO THE DR WHO PLACED EMPLOYEE ON LITE DUTY.