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<br />If full shift exposures for miners are appropriate, the results should be compared to the peak ' <br />concentrations measured in the corresponding area(s) or location(s). If compliance with the ' <br />TLV®s is maintained at the same time that the gaseous contaminant levels in the return air course <br />are greater than the 50 percent action level, the district manager may increase the action level. <br />Sampling should provide sufficient data representative of normal operating conditions. Duration , <br />should be appropriate depending on the circumstances at the mine. Data logging instrumentation <br />will generally provide the most usable data for this analysis. MSHA should confirm through , <br />sampling that the increased action levels continue to provide protection to mine personnel. <br />Under §75.371(nn) the minimum ventilating air quantity for multiple units of equipment must be ' <br />stipulated in the ventilation plan. This air quantity should be the sum of the nameplate air <br />quantities of the units ofdiesel-powered equipment that are typically operated on the working <br />section. However, if other units ofdiesel-powered equipment are being operated in addition to ' <br />those that were used to calculate the air quantity stipulated in the ventilation plan, the minimum <br />air quantity provided in locations stipulated in paragraph(g) must be the sum of the nameplate air <br />quantities for all of the diesel-powered equipment, excluding exempted equipment, on the , <br />working section. This would result in a greater ventilating air quantity than the quantity stipulated <br />in the ventilation plan. <br /> , <br />MSHA inspectors, therefore, must measure the air quantity in the last open crosscut or other <br />appropriate locations specified in §75.325, to determine if that air quantity is equal to or greater <br />than the minimum air quantity stipulated in the ventilation plan. Inspectors must also identify the , <br />diesel-powered equipment on the working section and add up all of the equipment nameplate air <br />quantities, excluding exempted equipment, to determine if the measured air quantity in the last <br /> <br />open crosscut is equal to or greater than that summed minimum. , <br />Corrective Action in Response to Sampling Results above the Action Level under §70.1900(c~ <br />§70.1900(c) states that "Except as provided in §75.325(j) ofthis chapter, when sampling results <br />indicate a concentration of CO and/or NOZ exceeding an action level of 50 percent of the <br />threshold limit values(TLV®) adopted by the American Conference of Governmental Industrial ' <br />Hygienists, the mine operator shall immediately take appropriate action to reduce the <br />concentrations of CO and/or NO2 to below the applicable action level." <br />Actions that an operator may take to reduce the concentrations below the applicable action level <br />include the following: <br />1. identification of the contaminant source, such as a poorly maintained diesel engine, , <br />and removing it from service; <br />2. redistribution of the available ventilating air quantity; , <br />3. increasing the air quantity in the affected area; and ' <br />September 1997 (Release 2) ' <br /> <br />