"Obviously, I don't want to speculate, but either something went wrong from a natural/unnatural manner that was not foreseeable by us or human beings or somebody made a mistake or something," Blankenship said. "We don't know.
"It's not due to us not being focused on safety, not having a strong safety culture, not putting safety first. Some of the implications have been that we don't focus on safety or we put dollars in front of safety and nothing could be further from the truth."
Still, state and federal regulators confirmed Thursday they planned to investigate reports from several Upper Big Branch widows that miners at the operation were sent home on April 2, the Friday before the explosion, because of "bad air" in the mine.
"We were not made aware of any evacuation on April 2 and will investigate this report," said Jama Jarrett, spokeswoman for the state Office of Miners' Health, Safety and Training.
Amy Louviere, spokeswoman for the U.S. Mine Safety and Health Administration, said MSHA was also not notified of any ventilation issues at the mine that day or any evacuation. MSHA did not have an inspector at the mine that day, she said.
"The team will follow up on every one of these complaints," Louviere said.
Louviere also said Thursday that air quality tests of the Upper Big Branch Mine turned up the presence of ethylene and acetylene, both gases that could indicate a fire is burning somewhere underground.
"So, until they figure out exactly what the source of these gases is, the teams will not be allowed to go underground," Louviere said.
Jarrett said it could keep investigators out of the mine for another month or so.
Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.