Workers began drilling three ventilation holes into the mine. But International Coal Group chief executive Ben Hatfield said it could be days before the first investigators go in.

"There are so many things we don't know about what went wrong," Hatfield said. "We don't want to put any more people at risk until we know answers."

The Mine Safety and Health Administration appointed an eight-person team to investigate Monday's blast that killed one miner immediately and left 12 others trapped more than two miles inside. Only one miner was alive when they were found nearly 42 hours later, huddled together behind a plastic curtain erected to keep out deadly carbon monoxide.

Investigators said they are looking into all possibilities, including suspicions that lightning ignited naturally occurring methane gas or coal dust. Even before the blast, those were areas of concern at the mine, which had been cited for violations in 2005 regarding the ventilation plan to control dust and explosive gases.

The accident took place after the mine had been closed for the holiday weekend; the explosion was believed to have originated in an unused section of the mine.

Mine safety experts said gas can build up in a mine after just one day of idled operations, especially in the winter, when the barometric pressure drops. Also, the metal casings of abandoned natural gas wells above a mine can conduct an electrical current into the ground.

"If this is in fact a strike of lightning onto a well, gas or oil, that sits above an abandoned section of the workings, that well should have had a substantial barrier to avoid this," said David McAteer, who oversaw MSHA during the Clinton administration. "We've had lightning strikes cause accidents in mines, and they're very disconcerting because they do just what this did. They go down and blow the seals out."

A federal report in 2001 documented at least seven instances in the 1990s alone of methane or coal dust being ignited by lightning, three of those in one mine in Alabama.

"I've heard those theories, but we have no concrete evidence one way or another," said Bob Friend, MSHA's acting deputy assistant secretary of labor for mine safety. "Nothing has been dismissed."

Friend said when the mine is safe to enter, the team will examine every aspect of it, including its physical structures and all equipment. They will be looking for the direction of the explosive forces. They will take dust samples. They will seize any equipment that might have contributed to the blast and, if necessary, test it in a lab.

The investigation will also involve interviews with dozens of people, including the approximately 13 minors who escaped, workers on previous shifts, and managers, Friend said.

The sole survivor's recollections could prove crucial. But 26-year-old Randal McCloy Jr., was believed to have brain damage from oxygen deprivation and remained in a medically induced coma Friday at the Pittsburgh hospital where he was moved a day earlier to receive intensive oxygen treatments.

Dr. Richard Shannon suggested rescuers reached McCloy just in time, because it appeared that in his last hour or so in the mine, he lost the ability to sneeze and cough, and his lungs began to fill with coal dust and the low-lying gases as he lay on his side.

In hopes of jogging McCloy back to consciousness, his family planned to play the music of his favorite country artist, Hank Williams Jr.

The probe will also look at the miscommunication from rescuers inside the mine that led anxious relatives to believe for three hours that their loved ones had miraculously survived. That period of confusion was reflected in 911 tapes, in which emergency workers were heard discussing the false report.

In what officials said appeared to be chatter between two ambulances, one emergency worker said: "You might as well just stand still right where you're at, Gary. They did find them, and they're all OK, I guess, so, I think we might be transporting them. I'm not exactly sure, but we're stuck right here."

When asked how many to prepare for, the other said: "Twelve, and they're bringing them out."

In other developments, autopsies were completed and the bodies of the miners were returned to the families. State law prohibits the public release of autopsy results. Asked about speculation among the families that the 11 trapped miners died from carbon monoxide, state Health Department spokesman John Law said only: "I don't think it will be a great surprise."

The first funerals for the fallen miners were being scheduled, with at least three services planned for Sunday.

The Sago Baptist Church, which was a gathering place for families during the vigil for the trapped miners, has become a shrine, with flowers filling the tiny altar.

They included a vase with 13 red roses, one for each of the miner's families, and a basket of peach-colored roses and daisies from a mining shift in Alberta, Canada. To the right of the altar was a large spray of snapdragons, carnations and chrysanthemums from a woman in Galt, Calif.

"I want you to know that there are thousands, probably millions of people who mourn with you and pray for you," said an accompanying letter from Jennifer Coumbs. "People you have never met are at this time asking the Lord to be with you to strengthen you and hold you in His hands."