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Q measured <br />- ____ <br />`4 projected -------------- TW`~ measured <br />Q requested <br />The projected TWA must be less than the associated TLV for each contaminant for the reduced <br />air quantity to be approved. <br />After calculating the projected TWA for the sampling data, the MSHA representative responsible <br />for the data review can determine the potential for exceeding the 50 percent action level for <br />sampling conducted as required under §70.1900. This can be calculated in the same manner as <br />the projected TWA and is a method that can be used in determining if an increase in the action <br />level requested by the mine operator is warranted: <br />_ Q me_as_u_re_a * PEAK <br />PEAK - ----- <br />projected n measured <br />`! rcqucstM <br />When a reduction in the minimum ventilating air quantity has been approved and the reduction has <br />been implemented, MSHA should confirm through sampling that the reduced air quantity is <br />adequate to maintain compliance with the applicable TLV®s. <br />Approval of Higher Action Levels under §75325(jl <br />The mine operator may request that the action level specified in §70.1900(c) be raised. The <br />increase in action level maybe requested either separately or at the same time that a request for <br />reduction in minimum ventilating air quantities is made. <br />It is the mine operator's responibility to provide MSHA with data, such as results of on-shift, <br />environmental, and personal sampling, to support any request for an increased action level. Such <br />data may include a continuous and complete record of carbon monoxide, nitrogen dioxide, and <br />the air quantities measured on the section where the sampling is conducted. Data should be <br />collected for all locations where the minimum air quantity is required to be maintained. Data <br />logging instrumentation generally provides the most usable results. Computer-based mine wide <br />monitoring systems may also provide valuable data. <br />Sampling in the area(s) or location(s) being evaluated, and/or personal sampling, should be <br />conducted to demonstrate that an increased action level would continue to ensure that miners are <br />not being overexposed to gaseous diesel exhaust contaminants. Gas sampling data submitted to <br />MSHA should include the peak concentrations for each location and time-weighted averages for <br />each occupation. <br />September 1997 (Release 2) <br />