DENVER — The problem-plagued effort to rescue six miners trapped in a Utah coal mine suffered its most grave setback Thursday night, when a seismic shudder sent rock tumbling onto rescue workers, killing three and injuring six, authorities said.
The mountain "bump" occurred about 6:30 p.m., as the group of more than 100 rescue workers continued to carefully tunnel through the collapsed Crandall Canyon Mine. Since Aug. 6, when a predawn cave-in buried the miners, regular seismic tremors have slowed the dig to a virtual crawl.
There has been no indication of whether the trapped miners are alive, and officials emphasized that the rescuers were digging slowly to minimize risk. The tremors have been so bad that a dozen rescuers asked to be reassigned last week.
"All rescue workers have been evacuated from the mine," said Dirk Fillpot, a spokesman for the federal Mine Safety and Health Administration.
Officials said that the injured included two members of the Mine Safety and Health Administration, which is overseeing the effort to rescue the trapped miners.
Jeff Manley, chief executive of Castleview Hospital in nearby Price, told reporters six rescuers were brought there. One died, one was released, one was airlifted to another hospital and three were being treated, he said.
At a medical center in Provo, one rescuer died and one was in critical condition. The third death was confirmed by Rich Kulczewski, spokesman for the U.S. Department of Labor, but more details were not immediately available.
Price Mayor Joe Piccolo said: "It's a devastating blow to what was already a tragic situation. It's a very stressful part of the way of life that's been known here for years."
Seismologists registered a 3.9 tremor when the mine collapsed Aug. 6. Scientists say they believe that reading was caused by the cave-in. Robert E. Murray, whose company owns the mine, has insisted the reverse: that a quake triggered the disaster.
The mine has a history of trouble. In March, inspectors warned that the roof in a different portion of the complex was unstable. Miners had to shift to another section. Miners had been performing "retreat mining," a potentially risky technique in which pillars of coal are left to hold up the walls, then pulled down as miners flee.
Murray has said that his employees were not performing retreat mining during the collapse.
Initially, officials hoped to bore holes to the area where they believed the miners were trapped and drop in provisions. But the holes, which took several days to drill, opened to areas with no breathable air. No sound was heard from the miners.
Meanwhile, rescuers kept digging, but were working so slowly that authorities estimated it would take them two more weeks to get to the area where the miners had been working.
On Thursday, when the mine collapsed again, rescuers were pinning their hopes on a fourth hole burrowing toward an area where they had heard an unexplained sound. They hoped the miners might be in that area.
Officials have insisted the miners could still be alive.
Bob Ferriter, a professor at the Colorado School of Mines, said that federal mining officials would have to decide whether it was too risky to try to save the miners or whether to further delay the rescue to put in additional safeguards.
"You don't even know if these guys are alive," Ferriter said in an interview. "How many more lives are we going to take to find these people? Someone's going to have a very sleepless night" trying to make that decision.