MSHA announced on May 22 it would not approve any requests to construct alternative seals. Coal mine operators were also required to immediately examine the structural integrity of all existing underground alternative seals as well as revise their ventilation plans to assess the mine atmosphere behind these seals.

This reassessment is to include mine methane liberation history, seam history (spontaneous combustion potential or seam liberation potential), mine ventilation experience and a proposed sampling regime.

MSHA said the sampling regime should include a description of how sealed atmospheres would be sampled, such as in-mine sampling, through boreholes from either the mine surface or by other means.

“As with all other ventilation plan provisions, the proposed sampling and any necessary remediation will be evaluated on a mine-by-mine basis,” MSHA said.

“Based on the size and orientation of the sealed area, seam and mine history, experience with the mine and similar mines, as well as the quantitative in-mine sample results, further sampling, which may include surface boreholes, may be needed.”

MSHA said in addition, the plan should propose remedial actions to be taken if the atmosphere in a sealed area is found to be in the explosive range. Atmospheres found to be near the explosive range when considering barometric pressure changes and other factors, such as temperature and accumulations of water, could also require remedial action.

Remedial actions could include inert gas injection or the use of water to inert the area if the mine dip and other conditions are conducive to this type of action. In some cases, resealing, grout injection or other remedial measures may be necessary to provide protective isolation of the sealed area.

MSHA’s temporary moratorium on construction of alternative seals will remain in effect until further in-mine evaluations are completed. MSHA said if an in-mine evaluation conducted by the agency showed the seal was performing adequately, “the use of the alternative method or material may resume on a mine-by-mine basis”

The moratorium and reassessment of existing seals follow the two recent and deadly mine explosions at the Sago Mine in January 2006 and the Darby No. 2 Mine in May 2006, where investigations show that there were problems with the use of alternative methods and materials to create seals.

“After reviewing this information and the use of these alternative methods and materials allowed in mine ventilation plans, MSHA is concerned because the failures of these seals are not preventing hazards which they were intended to prevent in underground bituminous coal mines,” MSHA said.