HUNTINGTON, Utah - Rescuers searching for six coal miners trapped for 10 days were drilling yet another hole into the mine Thursday, this time aiming for a location where they had detected mysterious vibrations in the mountain.
Officials said Thursday that the latest of three holes previously drilled reached an intact chamber with potentially breathable air.
Video images were obscured by water running down that bore hole, but officials said they could see beyond it to an undamaged chamber in the rear of the mine. It yielded no sign the miners had been there.
The drill holes can be used to pump air and send food down the mine, but the rescue effort is taking place underground, where miners have advanced to only 826 feet in nine days. They still have 1,200 feet to go to reach the area where the men were working.
The digging was most recently set back Wednesday night, when a coal excavating machine was half buried in rubble by seismic shaking. Another so-called 'mountain bump' interrupted work briefly Thursday morning.
'The seismic activity underground has just been relentless. The mountain is still alive, the mountain is still moving and we cannot endanger the rescue workers as we drive toward these trapped miners,' Bob Murray, chief of Murray Energy Corp., the co-owner and operator of the Crandall Canyon Mine, said Thursday.
Murray has become more reticent to predict when the excavation would be complete. At the current rate, it figures to take several more days.
Murray said it would take at least two days for the latest drill to reach its target, in an area where a seismic listening device detected a 'noise' or vibration in 1.5-second increments and lasting for five minutes. Officials say it's impossible to know what caused the vibrations.
Officials said results of air quality samples taken from the intact chamber, accessed by the third deep borehole, showed oxygen levels of roughly 15 to 16 percent.
Normal oxygen levels are 21 percent, and readings in other parts of the mine taken since the Aug. 6 collapse have registered levels as low as 7 percent.
At 15 percent oxygen, a person would experience effects such as elevated heart and breathing rates, according to Richard Stickler, head of the federal Mine Health and Safety Administration.
Video images from the same shaft showed an undamaged section complete with a ventilation curtain that divides intake air from exhaust air. Behind the curtain, in theory, the men might have found refuge and breathable air when the mine collapsed 10 days ago.
The sounds detected Wednesday could be a rock breaking underground or even an animal above.
'We saw some indication of noise for a period of about five minutes that we had not seen before,' Stickler said.
Nothing had been detected or heard since the five-minute period Wednesday, Stickler said Thursday.