Mine Safety and Health Administration spokesperson Amy Louviere told media outlets on the weekend the accident occurred between midnight and 1.00am local time at the Darby No. 1 mine during its maintenance shift. Darby is owned by Kentucky Darby LLC.

Kentucky Governor Ernie Fletcher said preliminary tests showed methane may have escaped from the mine’s sealed portion.

The five deceased miners, who were located by rescue teams, included Amon Brock, 51, Roy Middleton, 35, Jimmy Lee, 33, George William Petra, 49, and Paris Thomas Jr, 53.

The sole survivor, Paul Ledford, walked out of the mine on his own and was taken to a hospital for treatment but has since been released, according to a report by Associated Press.

Federal investigators said Ledford was closer to the mine’s exit than his co-workers and was able to meet rescue teams walking into the operation about 15 feet from the portal opening.

The surviving miner’s family added that he suffered blistering and burns to his hands and chest in the explosion.

Associated Press reported that preliminary autopsy reports released Sunday afternoon showed three of the five deceased workers were likely to have survived the blast but that their cause of death was carbon monoxide poisoning.

It is not known whether the five dead miners activated their self-contained self-rescuers after the blast, but Ledford has said his rescuer only worked for about five minutes, causing him to pass out from the exposure several times.

While some news groups have spotlighted Darby’s level of MSHA violations since its current operator took over in 2001, 264 altogether, the agency’s mine safety and health administrator Ray McKinney told local paper the Lexington Herald-Leader the mine had no previous deaths since that point and that it did not have a high level of safety violations.

For a mine of its size, McKinney said, “I think that would be normal, maybe a little fewer.”

The National Mining Association (NMA) said it expected the incident would spur Congress to enact the bipartisan mine safety legislation this year, which embodies the safety principles supported by the coal mining community.

Details of what caused the early morning explosion at Darby Mine No. 1 are still being investigated.

Darby employs 34 people with an annual production of 220,000 tons. Kentucky has 608 mining operations, according to the state’s Mine Safety and Licensing office, 296 of which are underground.