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September 2015
Volume 67    Issue 9

Engineering practices for a safe, inert atmosphere in sealed areas of coal mines

Mining Engineering, 2015, Vol. 67, No. 9, pp. 53-60
Zipf, Jr., R.K.


ABSTRACT:

The 2008 Mine Safety and Health Administration Final Rule on Sealing of Abandoned Areas of Coal Mines focuses on seal design to resist explosion pressure. By designing sealed areas to become inert and remain permanently inert, it may be possible to use more economical 345-kPa (50-psi) seals under the new rule, if the required monitoring is met. Most sealed areas pass through the explosive range for methane in air within a few weeks after seal construction and then remain inert permanently, but data about the proportion of sealed-area atmospheres that are permanently inert and safe are lacking.

  Certain practices that were in use prior to the new regulation may have contributed to the formation of explosive atmospheres within sealed areas. Sealing low-methane-inflow mines at shallow depth may have created explosive atmospheres in sealed areas that persisted for months or more. Complex seal lines involving many seals could have led to some parts of the seal line ingassing to form an explosive mixture and other parts of the line outgassing to increase the methane gas load on the ventilation system.

  Recommended engineering practices to create and maintain permanently inert atmospheres within sealed areas are: (1) better overall mine layouts, (2) better mining practices near future seals and (3) better ventilation system design. Planning the mine layout is required years in
advance of sealing to minimize the number of seals required and to simplify the ventilation system considerations. Several practices to consider following near a future seal construction site are to (1) minimize the number of entries into panels, (2) increase the cross-cut spacing, (3) decrease the entry width and (4) increase ground support. When designing the ventilation system, minimize the pressure differential across seals and increase the resistance across seals and seal lines to decrease air exchange with sealed areas.


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