Updated

The chief executive of Massey Energy Co. is changing his tack on what caused the coal mine explosion that killed 29 miners in West Virginia, blaming the tragedy on natural gas rather than methane.

Massey investigators have discovered the Upper Big Branch mine was inundated at the time of the April explosion with natural gas, which the company now blames for causing the nation's deadliest coal mine explosion since 1970, Don Blankenship said at an investor conference Wednesday in New York.

"When you have natural gas, you have other gases included, like ethane or propane, that are a little bit more explosive," Blankenship said. "The big factor about it being natural gas instead of coal bed methane gas is, it illustrates that it's something unusual."

Massey had previously said it believed a crack in the mine floor let loose a dangerous amount of methane gas — a position the company bolstered with air samples taken in the hours after the blast. The federal Mine Safety and Health Administration had dismissed that theory.

If the explosion were caused by natural gas, it would bolster Massey's contention that safeguards required by law were overwhelmed. The company also has tried to blame MSHA for changes that Massey contends weakened the mine's ventilation system.

"It didn't come out of the normal mining process, and it's not something you would normally be guarding against," Blankenship said.

MSHA did not directly address Massey's latest version of events.

"MSHA continues to conduct its investigation, and we feel confident that we'll arrive at the cause of the explosion by the time the investigation has been completed," the agency said in a statement.

Blankenship also addressed the explosion's impact on the company. Richmond, Va.-based Massey has reported mounting losses since the blast and is now widely considered a takeover target for rivals such as Alpha Natural Resources and steel industry giant ArcelorMittal SA.

Massey's board of directors will consider mergers and acquisitions as well as management's regular five-year plan, Blankenship said.

"There will be a separate and distinct focus on M&A and M&A activities and possibilities," he said. "And I don't know exactly where that will go, and of course, I can't speak to the rumors and so forth."