Here are two articles on mine bumps and why retreat mining and pillar removal is so dangerous. Pillar removal is when you're so coal-hungry that you'll go in and remove the support pillars, because, goddammit, you don't want to leave an ounce of coal behind:
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NPR.org, August 14, 2007 · The cave-in at a mine in Utah last week was the second such collapse there this year. Another cave-in occurred in the spring in the same general area where six miners are now trapped.
According to a consultant's memo, the earlier incident was so severe that the company had to abandon that part of the mine.
In mining lingo, it is called a "bump," but it is more like an explosion as the floor buckles and coal shoots out from the pillars that hold up the ceiling.
"If you're close enough to it, you could be thrown up and hit the roof," said Robert Ferriter, who runs the mine safety program at the Colorado School of Mines. "You could be inundated when the pillar failed, with all kind of coal and dust flying around all over the place."
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.
It is a technique commonly known as retreat mining. According to a consultant's memo, the March collapse at Crandall was caused by coal pillars that could not handle the pressure.
"The first reaction is 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," Ferriter said. "You want to make sure your pillars can handle that stress, that your floor is not being overloaded, you're roof is not being overloaded."
After the March bump, the company — Murray Energy Corp. — moved to another part of the mine, about nine hundred feet away. But Ferriter said working that section appeared risky as well.
Numerous pillars had been removed nearby and entire stretches of roof had caved in.
"I would not feel comfortable doing that myself. You're 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," he said.
MORE:
http://www.npr.org/templates/story/story.php?storyId=12769181A bump is a sudden release of the roof, wall or even floor rock into an open area of the mine. Bumps are different from roof falls. A roof fall is just what it sounds like: pieces of roof rock come apart and fall. A bump occurs because of pressure pushing down onto the mine roof or wall, as opposed to the roof or wall simply falling down.
Bumps can be huge. The one at Crandall Canyon measured 3.9 on the Richter scale, mimicking a small earthquake.
Very deep mines in the hard sandstone areas of Utah are especially prone to bumps. The hard rock roof and floor of mines adds to the pressure that can cause bumps.
At least 80 percent of bumps have been found to occur while operators are performing retreat mining or pulling pillars, according to another Bureau of Mines study published in 1991.
Various studies have found bumps can be especially hard to prevent. But, the studies show, they are not natural occurrences and can be reduced or avoided with proper mine planning.
“Inadequate mine planning or incorrect design can increase the occurrence of bumps in underground coal mines,” says the 1991 bureau study.snip/
In a Thursday interview, MSHA coal administrator Kevin Stricklin said the Crandall Canyon Mine had longwall mined in two long sections on either side of the mine’s main underground entry tunnels. After this mining, the roof of those sections would have caved in, as longwall mining does not leave support pillars behind.
When Murray Energy took over the operation last year, the company proposed plans to go in and remove coal from the pillars left in the mine’s main entry tunnels, MSHA officials said.
“They were trying to pick up all the coal they could,” Stricklin said.MSHA began a special roof control inspection on May 22, as part of its review of the company’s pillar removal proposal, Stricklin said.
MSHA found some problems with the proposal, but Stricklin could not immediately explain what they were. But, he said, the problems were corrected and the plan was approved.
Stricklin agreed that pulling pillars under the conditions in Crandall Canyon would be tricky. But, he said, MSHA would not have allowed it if the plan wasn’t safe.
“We should have evaluated it and taken it into account,” he said. “I’m sure that will be part of our investigation.”
Federal studies have found that pulling pillars, especially in the bump-prone mines of Utah, is always particularly dangerous.
snip/
A 1993 Bureau of Mines report concluded, “Retreat or pillar recovery mining redistributes the overburden weight onto the adjacent coal pillars in a room-and-pillar section.
“The additional stress and the resultant energy stored in the remaining pillars can become so great that pillars may bump or violently fail,” that report found.
snip/
One miner described a 1981 bump at a mine near Welch. “There came this giant bump and filled the place up with coal just like pouring water in a glass.”
Another miner described a bump at Bishop in 1979. “It sounded like the Earth had ended. The world had ended.”
http://www.wvgazette.com/section/News/2007081121?pt=0***************************************************************
Bumps have always been called "mine bumps," not "seismic bumps." It sounds to me like Murphy and his minions are attempting to make this bump appear to be caused by natural events, not by the mining itself. While I know that this was a rescue effort and the men who were involved in the accident tonight are to be commended, I also know that they wouldn't have had to be there, had not Bob Murphy been such a money-hungry tyrant. Had he not been trying to pull coal from support pillars, then there would have been no mine collapse and no miners to rescue.
I thought it wasn't possible to loathe this man any more than I already did. Today I found differently.
:grr: :grr: :grr:
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