EMPLOYEE WAS DRILLING HOLES IN ROCK WALL. AS HE WAS SHAKING THE STEEL TO LOOSEN THE LOWER COUPLING THE UPPER COUPLING SHOOK LOOSE AND FELL ABOUT 8 FT ONTO HIS HAR HAT. WE HAD HIM TAKEN TO THE HOSPITAL WHERE HE WAS EXAMINED AND RELEASED SEVERAL HOURS LATER. HE DOES STILL HAVE A HEADACHE SO TOTAL INJURY IS NOT YET KNOWN.