Ahead, probe of Utah mine cave-in

As the three-week search for six men missing in a Utah coal mine enters a last-ditch-effort phase, the federal investigation into what caused the catastrophic cave-in is likely to begin soon and to include a close look at mining practices in this seismically volatile region.

Like the investigation by the Mine Safety and Health Administration (MSHA) after the 2006 Sago mine accident in West Virginia, this probe at the Crandall Canyon Mine will determine if anything could have prevented the cave-in and could lay the groundwork for industry improvements that reduce the likelihood of similar tragedies in the future.

The investigation will be crucial for the nine other coal mines operating in the same vicinity as the Crandall mine. At 1,500 to 2,000 feet below the surface, they are the deepest coal mines in the United States. All are susceptible to "bumps," the mining-induced seismic activity that apparently caused the Aug. 6 cave-in.

Assessing the risks from such susceptibility becomes increasingly critical as more US mines are subject to two or three rounds of mining. In such operations, coal pillars left during the initial mining period – which support the weight of the mountain above – are being removed as miners finish their extraction work, allowing the mine cavity to refill. Such was the case at Crandall Canyon, officials say.

"MSHA has to look at these practices and say, 'if we're going to do this, we have to up the ante in terms of safety recommendations, and say there are certain limitations [on the extent of this kind of mining],' " says J. Davitt McAteer, former head of MSHA and now vice president at Wheeling Jesuit University in West Virginia.

Over the weekend, rescue workers drilled a sixth bore hole at the mine to try to gain some information about the missing men, but it yielded no definitive results. Owner Bob Murray and government officials agreed to try one more location "that may provide conclusive evidence of the fate of the six trapped miners," said MSHA assistant secretary Richard Stickler, in a statement late on Aug. 26. That work, impeded Monday by bad weather, was set to resume Tuesday.

Utah's richest seam of coal swings in the shape of a canted "L" from Colorado westward, under the Wasatch Plateau and dropping down south into Emery County – where Crandall Canyon Mine is located.

This area has been mined for the past 30 years, and that activity has caused the mountainous region to routinely "bump," or readjust, to redistribute the mountains' massive vertical weight above the cavities created by long-wall mining. In long-wall mining, the process used in most Utah mines, machines called continuous miners run forward along a tunnel, chewing up the coal along the face of the tunnel and spitting it into a mine car waiting behind.

Mining engineers help mine owners map out the tunnels and decide which pillars of coal need to be left behind and how many man-made pillars, or jacks, need to be installed to support the weight of the mountain.

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