Ahead, probe of Utah mine cave-in

US investigators are likely to examine the growing – some say perilous – use of 'retreat mining.'

from the August 29, 2007 edition

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Seismic activity is not necessarily a predictor of a catastrophic event. For example, the magnitude 1.6 event on Aug. 16 that killed three rescuers and injured six others "would have been in the realm of the size of many thousands of events we've recorded without having any direct impact in the mine," says Walter Arabasz, director of the University of Utah Seismograph Stations. The reading on Aug. 6 was 3.9.

That's because most seismic events don't occur right where miners are working, unlike the one Aug. 16, which happened near the mine opening where rescuers were valiantly digging their way in.

"Seismic monitoring might be diagnostic of stress conditions in the mine, but it's only one piece of information available to a mining engineer," says Dr. Arabasz. For example, he says, information about mining activity at the time of the seismic event, including where coal extraction is taking place, would complement data from seismologists and possibly lead to better predictions about future stress points in the mines.

MSHA officials have indicated that so-called retreat mining, in which the barrier pillars are removed, was taking place at the Crandall Canyon Mine. The agency no doubt will look at the application and approval process that allowed the practice.

Those documents are ordinarily posted on MSHA's website, but they're not there now. Officials say the documents aren't publicly available at this time. Experts who've had access to these documents say Crandall Canyon Mine officers requested permission on June 3 to engage in retreat mining, and that MSHA granted it June 15.

"The circumstance in that mine that eventually became troublesome was a decision to remove elements of that barrier pillar," says Arabasz.

"The last mine [owner] left that barrier wall for a reason," McAteer says. "This remining really raises safety and health considerations that weren't there when the original mining was done." Secondary mining is increasing, he says, because "the good stuff is gone. So now they are trying to pick up the scraps."

Murray Energy Group bought Crandall Canyon Mine a year ago, according to MSHA documents. It also owns two other mines, officials say.

Other mines in the region may be prone to similar accidents "depending on how much coal they want to get out and how deep they are," says civil engineer Stephen Dmytriw, who worked for MSHA for 23 years and now teaches at the Colorado School of Mines in Golden.

"Those companies would submit a plan to MSHA – a ground control plan and a ventilation plan," Mr. Dmytriw says, and MSHA would approve the plan or not.

The investigation is likely to take months, at least. But many experts say the MSHA needs to act quickly to ensure that similar accidents do not occur at other mines operating in the region.

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