The RFI was published in the Federal Register on August 8, with a 60-day comment period closing on October 7. MSHA extended the comment period to December 6, to allow additional time for interested parties to review National Institute for Occupational Safety and Health (NIOSH) studies that bear on certain issues raised in the RFI. In response to a subsequent request to further extend the comment period, MSHA is extending the comment period to June 2, 2014, to allow time for NIOSH to finalize the relevant studies and for interested parties to review them.