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The first of two reports by the agency released Wednesday outlined the "bump" that led to the entrapment of the initial six workers at the mine in Huntington, near Salt Lake City.
"Monday, August 6, 2007, at approximately 2.52am, a major coal bump/bounce occurred on the Main West pillar section trapping six miners. All four entries were rendered impassable approximately 2000 feet outby the section," MSHA said.
Borehole air samples showed results of an "irrespirable atmosphere" and camera images reflected debris and coal in mine entries.
The agency suggested the following best practices for mines to avoid similar situations in the future:
Ensure that the roof control plan is adequate for ground conditions and mining practices;
Ensure that miners are trained on the provisions of the approved roof control plan;
Be alert for changing and adverse conditions on the section;
Know and follow the approved pillaring procedures in the roof control plan; and
Conduct a thorough examination of the roof, face and ribs immediately before any work is performed and thereafter as conditions warrant.
The six workers brought the number of coal-mining related deaths to 24 in 2007.
Also on Wednesday, MSHA released a fatalgram regarding the three rescuers whose lives were lost while volunteering their efforts to rescue/recover the six Crandall workers.
The agency said: "Rescue/recovery efforts had started approximately 2000 feet outby the section and had advanced about 870ft in the No. 1 entry. The accident occurred while rescue crews were installing roof supports in an area where coal debris had been removed."
While it did not outline any best practices for operations from the incident, it did classify both the first and second group of deaths as Fall of Face, Rib, Side or Highwall.
In both reports, MSHA also requested that any individual who can offer an additional remedy that can prevent future similar occurrences contact them through the agency website, citing the fatality numbers and year.
A final report on the entire Crandall Canyon accident is pending.
