Operators at the Crandall Canyon mine experienced serious structural problems in the mine in March and entirely abandoned work in an area about 900 feet from where six miners remained trapped Saturday.
A memo obtained by The Salt Lake Tribune shows that mine owners were trying to work around "poor roof conditions" before halting mining of the northern tunnels in early March after a "large bump occurred . . . resulting in heavy damage" in those tunnels.
A bump or bounce occurs when the intense pressure on the coal pillars supporting the mine causes the pillars to burst, "sending coal and rock flying with explosive force," according to that National Institute for Occupational Safety and Health.
The memo indicates that mine operators knew the tremendous pressures of a mountain bearing down on the mine were creating problems with the roof, and they were searching for a way to safely keep the mine from falling in as they cut away the coal pillars supporting the structure.
"It's dangerous. Damn dangerous I would say," Robert Ferriter, now director of the mine safety program at the Colorado School of Mines and a 27-year veteran of the Mine Safety and Health Administration. "What is MSHA doing in all this? They're the ones who are supposed to catch this sort of thing."
The problems between the 133rd and 139th crosscuts, numbers given to passages cut across the entry tunnels, prompted operators to quit mining the northern tunnels of the Main West corridor. The operators also hired Agapito Associates Inc., a Colorado mining engineering firm, which wrote a memo for the company explaining steps that could be taken to allow the south tunnels to be retreat mined safely.
It is near crosscut 138 on the south side of the main corridor, where rescue workers believe the six miners were trapped, that the enormous pressures on the roof of the mine created a "bump" early Monday morning and caused a catastrophic cave-in.
The miners were working in a spot about 900 feet from where the dangerous roof conditions were noted in March, according to a detailed map of the mine. The damage from Monday's cave-in stretched hundreds of yards, with rubble blocking entries more than half a mile away and numerous additional bumps making rescue work unsafe.
Repeated calls to UtahAmerican Energy Inc., the mine operators, seeking information on the roof issues were not returned. Robert Murray, part owner of the mine, said he was not aware of any prior roof concerns. "It's the first time I've heard of this," Murray said of the March incident.
A message left at Agapito Associates last week was not returned.
Richard Stickler, assistant secretary of the U.S. Labor Department and head of MSHA, acknowledged the March incident, but said it occurred in an area hundreds of feet away.
But in a mine that stretches for miles, conditions in both areas would be "nearly identical," Ferriter said. "If you had problems up there on the north side, I would expect you would have the same problem on the south side."
The memo and mine map both indicate that, along the northern tunnels, there undoubtedly was retreat mining - a process in which support pillars are carved away by a mining machine, recovering the last remnants of the coal seam and causing the roof to collapse.
Murray had initially denied there had been retreat mining done, but MSHA officials said that technique was used in the mine.
On June 15, MSHA district manager Allyn Davis accepted a "roof control amendment," permitting retreat mining along the southern tunnel as well, documents show.
The retreat mining along the northern tunnels through the spring had progressed to crosscut 138 when unstable roof conditions prompted a decision not to cut down the next several supports.
When the pillars at the next two crosscuts were pulled in early March, "A large bump occurred at this point resulting in heavy damage to the entries located between (crosscuts) 133 and 139," the Agapito memo says.
To do damage to entries across six crosscuts, nearly 800 feet in the Crandall mine, the March bump would have to have been huge. It is unclear if it caused the roof to fall or the floors to buckle or heave. Such events are supposed to be reported to the MSHA, but MSHA's public data shows the last reported roof fall was in 1998.
An MSHA official began an inspection of the roof in the Crandall Canyon mine in late May, which was still under way, according to MSHA records. No violations had been reported. Stickler would not discuss the inspection.
But roof conditions prompted operators of Crandall Canyon to abandon the retreat mining on the north barrier.
"What that would tell me right up front is that's a bad section of the mine, and it's so bad they decided to not even try to mine it," said Bruce Dial, a former federal mine safety official.
To safely mine the south barrier, the Agapito consultants wrote, the width of the support pillars should be increased by more than a third, from 92 feet to 129 feet. Such an increase "helps to isolate bumps to the face and reduce the risk of larger bumps overrunning crews in outby locations," the memo says.
It is not clear from the mine map if the wider pillars were being used.
Mining was progressing along the south end of the main tunnel last week when it is believed a major bump caused the cave-in, trapping the miners working about 900 feet from where the March problems occurred.
"It was a bounce," Jameson Ward, one of four miners who escaped the mine, told The Tribune. "Bad things happen. Nothing can be done about it."
Ferriter isn't so sure. He said the retreat mining practice UtahAmerican was using in the mine is suspect in light of the amount of pressure created by 2,100 feet of mountain above the mine.
"The whole thing, to me, looks like you're taking a real risk because you have all this high stress there," said Ferriter.
Both areas to the north and south of the main tunnel had been "longwalled," meaning the coal had been extracted and the areas had caved in, leaving no support on either side of the main tunnel. Digging out the last supports for the main tunnels is extremely dangerous.
"I'm surprised that they would try to take that last section," Ferriter said. "I would've thought that would have triggered someone from MSHA to say, 'Wait a minute, let's take a look at this.' . . . I think this needs to be looked at in a lot more detail."
* KRISTEN MOULTON and GLEN WARCHOL contributed to this report.