RENEE MONTAGNE, host:
It turns out that the mine cave-in in Utah last week was the second collapse at the Crandall Canyon mine this year. Another cave-in happened last spring in a section near where the six miners are now trapped.
According to a memo from a consultant, the earlier cave-in caused such heavy damage that the company had to abandon that section of the mine, which raises questions about why miners were still working in the vicinity.
NPR's Frank Langfitt reports.
FRANK LANGFITT: In mining lingo they call it a bump, but it's more like a cross between an explosion and an earthquake. Robert Ferriter spent 17 years studying ground stability at the Federal Mine Safety and Health Administration. He says when there's a bump, the floor buckles and coal shoots out from the pillars that hold up the ceiling.
Mr. ROBERT FERRITER (Director, Mine Safety and Health Program, Colorado School of Mines): If you are close enough to it, you know, you could be thrown up and then hit the roof. You could be inundated when the pillar failed, with all kinds of dust and coal flying around all over the place.
LANGFITT: Utah's Crandall Canyon mine suffered a similar bump in March. Although the mine owner denies it, by most accounts, the miners had been removing pillars of coal. That's a common method called retreat mining, but according to a consultant's memo, the area collapsed because the remaining coal pillars couldn't handle the pressure. Ferriter had read the memo.
Mr. FERRITER: Well, the first reaction, of course, is, you know, they have high stress levels in that mine. And, of course, once you have high stress levels, you need to be prepared to handle those. You know, you want to make sure that your pillars are big enough to handle that stress, that your floor is not being overloaded, your roof is not being overloaded.
LANGFITT: After the bump in March, the company, Murray Energy Corp, moved to another part of the mine, about 900 feet away. But Ferriter says working that section appeared risky as well. Swaths of pillars had been removed nearby, and entire stretches of roof had caved in.
Mr. Ferriter: I would not feel comfortable doing that myself. You are mining in a high stressed area, so that would give you things like crushing pillars and floor heave, and eventually you could cave the whole thing.
LANGFITT: Ferriter isn't the only mining engineer who wonders about the company's decision to work that area.
Professor LARRY GRAYSON (Energy and Mineral Engineering, Penn State University): I was surprised.
LANGFITT: That's Larry Grayson. He's a mining engineering professor at Penn State. He did retreat mining, that's removing coal pillars, back in the 1980s.
Prof. GRAYSON: In my days, it was our rule at that point in time, we would not do retreat mining between two caved areas.
LANGFITT: But Grayson was hesitant to second-guess the mine owner. He said firms today can use sophisticated computer models to figure out just how much stress pillars can take. The consultant on the Utah mine, a respected firm called Agipito, recommended using bigger pillars in the new area to support the roof. And according to maps, the company was doing that. Robert Murray co-owns the mine. At a news conference yesterday, he dismissed questions about his decisions.
Mr. ROBERT MURRAY (Co-owner, Murray Energy Corp): Our mining plan was recommended by Agipito, was approved by the Federal Mine Safety and Health Administration. This was a completely safe mining plan, and I'm not going to respond to that anymore because it doesn't apply. Any other questions?
LANGFITT: After the news conference, the Federal Mine Safety Agency appeared to back Murray. Bob Friend is the agency's deputy assistant secretary. He said he read the mining plant.
Mr. ROBERT FRIEND (Deputy Assistant Secretary, Federal Mine Safety Agency): There's nothing that's just glaring out at me as being inappropriate.
LANGFITT: But as the agency reviews its handling of the Utah mine, Friend said it will take another look.
Frank Langfitt, NPR News, Washington. Transcript provided by NPR, Copyright NPR.
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