The agency said that the screening period was between February 1, 2019 and January 31, 2020. It was the sixth consecutive screening that resulted in no notices for POV - a designation given to operations with a demonstrated recurring pattern of significant and substantial (S&S) violations.

MSHA conducts the checks at least one each year. The last review prior to this was between September 1, 2018 and August 31, 2019.

The POV rule has been a part of the federal regulator's powers since January 2013, when it sought to strengthen safety at the most dangerous mines in the country. Its ability to enforce it originated with the Federal Mine Safety and Health Act of 1977, or the Mine Act, which outlined its intent for those operations with chronic violation records.

"Safety and health is what we care about most at the Mine Safety and Health Administration; it's what miners care about, it's what miners' families care about and we can see it's what mine operators care about," MSHA assistant secretary David Zatezalo said.

"We'll issue pattern of violations notices when we need to, but it's a good feeling to look at the screenings and see no mines meeting the criteria."

MSHA has two online tools to assist US mines with its compliance, the POV tool and the S&S rate calculator. The first shows operators how they rate against the screening criteria; the latter enables them to monitor their S&S violations.

The agency noted that, between 2011 and 2019, the rate of significant and substantial violations fell from 32% to 20%.