Charleston, W.Va. » Air samples did not show high levels of explosive gases just before an explosion in a West Virginia coal mine that killed 29 workers, and what caused the disaster remains unknown, the mine's owner said Monday.

Massey Energy Co. board member Stanley Suboleski said the samples were taken by foremen as part of a shift change exam at the Upper Big Branch mine, just "tens of minutes" before the blast. The examination also showed that air flow in the underground mine was fine.

"All the indicators are that at the start of the shift, everything was OK," said Suboleski, a mining engineer.

Suboleski, two other Massey board members and Chief Executive Don Blankenship held a news conference Monday to address several issues related to the explosion, the nation's worst coal mining disaster in 40 years.

The news conference was held a day after President Barack Obama, Vice President Joe Biden and Gov. Joe Manchin led a memorial for the fallen miners. Two other miners were injured in the blast.

Blankenship told reporters that the president "honored the grieving families with his presence."

"This has left us humbled and hurt, and searching for answers," Blankenship said, adding that the company was dedicated to finding out what happened.

Suboleski told reporters that the overall number of violations for this year and in 2009 was comparable to those at similar operations in the Appalachian coalfields. About 60 percent of Upper Big Branch's violations were deemed "nonserious or nonsubstantial" by inspectors, Suboleski said.

Massey board member Bobby Inman called allegations that the company put profits over safety a "big lie." He blamed such sentiment on plaintiffs' lawyers and leaders of the AFL-CIO and United Mine Workers union. The UMW said Monday that it would help investigate the blast.

"The big truth is, 52 people have been killed on Massey property since 2000," said Phil Smith, a UMW spokesman. "No other coal company has had even half that. The numbers are pretty clear."