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shall be made in the roof. <br />(c) The concrete blocks will be laid in mortar in a transverse <br />pattern. In the bottom row or Row B1, the concrete blocks <br />_; <br />_ are set parallel to the ribs, while in the next row, or Row <br />_ ~2, the long faces of the blocks are perpendicular to the <br />ribs. This same alternating placement is repeated. Vertical <br />mortar joints shall be offset. The materials of construction <br />shall be packed tightly against the roof and ribs, the full <br />length of the bulkhead. <br />(d) An interlaced pilaster shall be constructed in the center of <br />the bulkhead when the bulkhead exceeds a width of 16 feet or <br />a height of 10 feet, exclusive of recesses. <br />(e) A sealant coating, acceptable by MSHA and listed in Part K of <br />this plan, shall be applied to the accessible face and perimeter <br />of the seal to effectively limit the gas-air exchange through the <br />bulkhead. The sealant will be equivalent to a 0.25 inch coating <br />of wood fiber and mortar. <br />(f) A surveillance tube shall be installed in the bulkheads whereby <br />a seal area can be readily sampled for gas. The surveillance <br />tube shall be 0.25 in. copper tubing; a 0.5 inch I.D., Schedule <br />40 pipe~or equivalent and shall be sealed at the accessible <br />outlet with a valve. (Tube and fittings shall withstand a mini- <br />mum pressure of 75 psig). <br />(g) Where necessary, pipe(s) for water drainage shall be incorporated <br />,. <br />and located at the lowest elevation of the bulkhead. The pipes <br />are to be corrosion resistant and equal in strength to Schedule <br />~~ 40 steel pipe. Multiple pipes will be used where high volumes <br />of water are encountered. <br />-8- <br />