HUNTINGTON, Utah - As frustration mounts over the slow pace of the digging to free six trapped miners, more questions arose Tuesday about whether risky mining methods may have left parts of the coal mine dangerously unstable.
Some mining companies consider the "retreat mining'' methods used at Utah's Crandall Canyon so dangerous, they will leave behind coal rather than risk the safety of their workers.
Video images taken early Tuesday showed miners working to clear a heavily damaged mine shaft. They were only a third of the way to the presumed location of the trapped miners -- eight days after a thunderous collapse blew out the walls of mine shafts.
A top mining executive estimated the digging would take up to another week.
"It's not fast enough for me,'' said Bob Murray, chief of Murray Energy Corp., co-owner and operator of the Crandall Canyon mine. "It's very painful.''
Much of the rescuers' time is spent shoring up walls and ceilings before a 65-tonne machine can safely resume clawing away at the rubble-filled mine shaft.
"We're doing the very best we can as fast as we can,'' said Richard Stickler, head of the federal Mine Safety and Health Administration. "You couldn't get another person into that working area.''
Around the clock, shifts of 80 miners are digging and helping to remove the rubble.
A mining worker who says he was the last to see the six men before the collapse said the slow progress is understandable because of concern for rescuers' safety.
"They do have a good point ... we don't want to lose 15 more going after six,'' said Jameson Ward, 24, who lives two doors down from trapped miner Brandon Phillips. Ward helped Phillips get his job.
"But there has to be a way to go faster. It's just too slow,'' he told The Associated Press.
Above ground, crews drilling another camera hole were about halfway to breaking into a rear section of the mine where they believed the men may have taken refuge in an air pocket. Murray said it could take another day for the drilling to break through.
A second 20-centimetre drill hole is being used to pump fresh air into the mine. Officials are taking air samples from a smaller hole at 6.3 centimetres.
The mine may have been made more dangerous by what Murray acknowledged was decades of digging using retreat mining, a common though sometimes dangerous method in which miners yank out a mine's pillars, grabbing the last of the coal.
Murray said the retreat mining took place before he took over the mine a year ago. He said no retreat mining was taking place at the time of the collapse, which he insists was triggered by an earthquake. Government seismologists say the mine's collapse registered as an earthquake.
"There's no connection between retreat mining and the natural disaster that occurred here,'' Murray said Tuesday. "I've said that from the beginning, and that's the way it will eventually come out.''
Mine-safety experts say that two sections of the Crandall Canyon Mine that collapsed in March may have been an early warning sign. They questioned whether the company -- and the government agency that oversees its work -- should have closed the mine then.
Instead, operators moved to another section and continued chipping away at the coal.
