By James Nelson HUNTINGTON, Utah, Aug 18 (Reuters) - Rescuers punched through a fourth drill hole into a collapsed Utah coal mine but heard no signs of life from six miners trapped for almost two weeks, a U.S. mine safety official said on Saturday. Rescue crews spent four hours listening through a microphone dropped about 1,600 feet (488 meters) into the Crandall Canyon Mine for any sign from the six men, who haven't been heard from since the mine caved in on Aug. 6. "We did not detect any signals from miners underground," Richard Stickler, head of the U.S. Mine Safety and Health Administration, told a news conference. Efforts to dig a tunnel 2,000 feet (609 meters) through fallen rock and coal to reach the miners was suspended after three rescuers were killed and six injured by a cave-in on Thursday. Stickler said a fifth drill hole was planned once video taken from the fourth hole was viewed later on Saturday for signs of the miners. Officials said they have not given up hope of saving the trapped miners. "This continues to be a rescue effort," said Rob Moore, vice president of mine co-owner Murray Energy.
