The Obama administration's push to reduce black lung disease by limiting coal dust in mines is taking effect.
Initial requirements of the U.S. Department of Labor's coal dust rule become effective Friday. It was proposed in 2010.
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New requirements include increased dust sampling in mines and citations when coal operators don't take immediate action for high levels.
In February 2016, better monitoring equipment will be required. In August 2016, the allowable concentration of coal dust will drop.
Ohio-based Murray Energy and the National Mining Association sued separately over the rule.
The National Institute for Occupational Safety and Health says black lung has killed more than 76,000 miners since 1968.
It is an irreversible and potentially deadly disease caused by coal dust exposure, where particles accumulate in the lungs.