An Alliance Resource Partners coal mine in Hopkins County, Ky., had 19 instances of falling debris in the year before the roof buckled Wednesday in an accident that killed two workers, according to Mine Safety and Health Administration data.

Thirteen of the incidents of “roof falls” at the Dotiki mine resulted in injuries, the MSHA records show. Federal regulators cited the mine 11 times this year for violations pertaining to roof support.

“Roof falls are the No. 1 killer of coal miners,” said Tony Oppegard, a mine safety advocate and former regulator who practices law in Kentucky. “When you have a lot of roof violations, it is very troubling.”

Eb Davis, general counsel for Tulsa, Okla.-based Alliance, said of the 11 roof citations, none was deemed “significant and substantial” by U.S. regulators.

“Significant and substantial” describes violations that have “a reasonable likelihood” of resulting in an injury “of a reasonably serious nature,” according to MSHA’s website. An MSHA spokeswoman declined to comment about specific violations.