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himself beyond the last permanent or temporary roof support that <br />• has previously been set. If. tests are necessary beyond the last <br />permanent or temporary support, then probes shall be used. All <br />tests will be performed with MESA approved methane detectors. <br />E. Methane Control in Outby Areas <br />1. "The methane content in any return aircourse other than an aircourse <br />returning the split of air from a working section (as provided in <br />Sections 75.309 and 75.310 30 CFR 75) shall not exceed 2.0 volume <br />per centum. The methane content in the air in active workings shall <br />be less than 1.0 volume per centum. If at any time the air in any <br />active working contains 1.0 volume per centum or more of methane, <br />changes or adjustments shall be made at once in the ventilation in <br />the mine so that the a'. shall contain less than 1.0 volume per <br />centum of methane." <br />• 2. Present plans are based on developing two to five entry headings for <br />the purpose of exploration and development. No mining is now planned <br />whereby a worked section of the mine is to be abandoned and isolated <br />from the active workings of the prospecting or exploration entries. <br />Since no pillaring is anticipated, there is no request for permis- <br />Sion to ventilate these areas. <br />3. If explosion-proof seals or bulkheads are required, the seals shall <br />be constructed in the following manner: <br />(a) Solid 8" x 8" x 16" concrete blocks are to be used with an <br />average compressive strength of 1800 psi, using ASTM C-140-70 <br />standards. <br />(b) Recesses (hitches) at a depth of 16 inches are to be cut in the <br />ribs and floor for the installation of the 8" x 8" x 16" con- <br />• . Crete blocks in order to prevent possible movement. No recess <br />-7- <br />