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2. Section and face ventilation systems are shown in drawings appended <br />to this plan. <br />• 3. Coal shall not be permitted to accumulate at the outby end of the <br />face equipment to the extent that ventilation of the working face is <br />restricted. <br />G. Permanent Stoppings <br />1. "All ventilating devices such as stoppings, overcasts, and undercasts, <br />shall be substantial and incombustible construction installed in a <br />workmanlike manner and maintained in a condition to serve the purpose <br />for which they were intended, and any stopping leaking air excessively <br />shall be repaired immediately." <br />2. "Permanent stoppings shall be erected between the intake and return <br />aircourse and shall be erected to and including the third connecting <br />crosscut outby the faces of the entries. IJhenever the third connecting <br />• crosscut is broken through, work shall be started on building the stop- <br />ping as soon as possible and shall be completed by the end of two ~aork- <br />ing shifts after the shift in which the crosscut was broken through." <br />3. Metal stoppings supported with approved fire retardant treated wood <br />may be used in short lived entries such as panels, rooms, or butts as <br />belt or intake escapeway separation stoppings, separating these entries <br />from intake entries. Timbers laid longitudinally "skin to skin," and <br />packed with rock dust, may be used in heavy or squeezing areas if the <br />timbers are .treated with an approved fire retardant, listed in Part K. <br />4. The materials and methods used in the construction of stoppings are <br />as follows: <br />a. Permanent stoppings are to be comprised of S" X 8"'X 16" or larger <br />concrete blocks. The construction method shall consist of laying <br />the blocks dry in a running bond. The stopping face will be coated <br />redi-mix mortar or an,MSHA approved fire retardant sealant listed <br />-10- <br />