The outlines reduce allowed dust levels from 2 to 1.5 milligrams per cubic meter of air. For ventilation air in working areas, as well as miners already diagnosed with pneumoconiosis (black lung), the standard reduces allowable levels from 1 to .05 milligrams per cubic meter of air.

In the time since the initial phase was effective on August 1, 2014, MSHA said it and operators have collected a combined 122,000 respirable dust samples, 99% of which have met compliance levels.

Additionally, last month, the agency said 99% of the samples it collected between April 1 and June 30 of this year also were in compliance with the standards. It cited the use of continuous personal dust monitors (CPDMs) for the ability to analyze more than 20,000 underground operator samples in real time.

“Black lung has claimed tens of thousands of lives,” said Joseph Main, MSHA assistant secretary of labor for mine safety and health. “The positive sampling results are due to the extraordinary efforts of MSHA and the industry working to clean up the air that miners breathe and successfully implement the respirable dust rule.”

According to data from the National Institute for Occupational Safety and Health (NIOSH), black lung has caused or contributed to more than 76,000 coal miner deaths since 1968.