Two miners have died following a ground collapse at Patriot Coal's Brody Mine No. 1 on Monday.
Brody coal mine is part of the Wells Mining complex near Wharton, in West Virginia's Boone County.
According to the Mine Safety and Health Administration (MSHA), the coalfield has many problems and violated safety standards 54 times between October 2012 and October 2013, causing it to be designated a 'pattern violator'; a term for the industry's worst offenders.
MSHA administrator Kevin Stricklin said the designation it is the strongest tool the agency has and subjects the mine to greater scrutiny from regulators.
Stricklin said that, according to the preliminary report, it appears that a rock outburst from the wall of the mine blocked up the entries with coal and debris.
"That's what caused the two fatalities," Stricklin said.
Patriot Coal said the incident occured when workers were involved in a risky process called retreat mining, which involves mining coal and leaving pillars behind to support the mine roof.
Patriot Coal operations executive vice-president Mike Day said the company is cooperating with state and federal regulators to investigate the incident.
According to mine safety data, seven US miners were killed while retreat mining between 2003 and 2007, and between 2008 and 2012 the number fell to zero; however, this has increased to 20 deaths in 2013 and five so far this year.
The mine safety data also reports that the state of West Virginia has the highest rate of coal mining fatalities, having recorded 124 since 2003, representing 39% of the total coal mining deaths in the US.