In the preamble to MSHA’s final rule titled Lowering Miners’ Exposure to Respirable Coal Mine Dust, Including Continuous Personal Dust Monitors (CPDMs) published in 2014, MSHA committed to conducting a retrospective study of the rule to assess whether it achieves MSHA’s goals of reducing and maintaining respirable coal mine dust levels to protect miners from black lung, a disabling occupational lung disease.  Specifically, MSHA committed  to evaluate data collected using the CPDMs to determine whether:  1) the 1.5 mg/m3 respirable dust standard should be lowered to protect miners’ health; 2) the frequency of CPDM sampling should be increased; 3) engineering controls and work practices used by mine operators achieve and maintain the required respirable coal mine dust levels; and 4) samples taken on shifts longer than 8 hours should be converted to an 8-hour equivalent concentration to protect miners who work longer shifts.  MSHA is requesting public comment on the Agency’s retrospective review of this rule.