Federal investigators swarmed the coal mine where an explosion left 12 workers dead, supervising the drilling of ventilation holes Friday to allow safe inspections of the tunnel where the miners huddled in their final hours.

The work to rid Sago Mine of enough potential explosives and noxious gases may take several days, said Ben Hatfield, chief executive of the International Coal Group, the mine's owner.

"The foremost concern throughout this process has been that 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 has appointed an eight-person team to investigate Monday's blast, which killed one miner immediately and left a dozen more trapped more than two miles inside the mine. Only one was alive when they were found 41 hours later behind a plastic curtain erected to block deadly carbon monoxide.

In addition to investigating possible causes, including lightning that may have ignited naturally occurring methane or coal dust, MSHA said the probe will also look into the mistaken communication from rescue teams that had anxious relatives believing for three hours that 12 of the trapped miners had survived.

A transcript of a radio conversation between emergency services workers released Friday shows that even emergency crews were confused soon after 11:45 p.m. Tuesday, when the mine rescue command received word that the 12 had survived.

"You might as well just stand still right where you're at, Gary," said a rescue worker identified as Matt. "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 the other worker asked how many to prepare for, Matt replied: "Twelve, and they're bringing them out." When asked if all 12 were alive, he said, "Uh, as far as I know."

The lone survivor, 26-year-old Randal McCloy Jr., was blinking his eyes and showing other hopeful signs Friday at the Pittsburgh hospital where he was moved a day earlier to receive intense hyperbaric oxygen treatments. But doctors cautioned that McCloy was still critically ill from extensive carbon monoxide poisoning and remained in a medically induced coma.

Doctors said they believed McCloy's movements were reflexive, but his family said they have sensed a reaction from him.

"I know he knows when I'm there because when I'm there, he gets excited," his wife, Anna McCloy, said Friday on ABC's "Good Morning America."

McCloy's father, Randal McCloy Sr., told The Associated Press that he believes — though he has no evidence — that his son survived because his older colleagues dragged him to their makeshift hiding place and shared the last of their oxygen with him because he was the youngest, and had two small children at home.

"Those men were like brothers. They took care of each other," he said.

Of the 12 miners who died, at least a handful managed to scrawl a last testament to their families, according to loved ones. The exact number of messages was not known.

In wobbly printing, written in ink on the back of an insurance application, 51-year-old miner Martin Toler Jr. said goodbye. For now.

"See them on the other side," the note said. "It wasn't bad. I just went to sleep. I love you."

His brother, Tom, a miner himself for 30 years, was so shocked by the simple, eloquent farewell that he didn't think to ask just where his brother had stashed the piece of paper. In his pocket? In his lunch box?

"It just shook me up when they gave it to me," he said.

And as he read the boxed letters fashioned with a shaky pen, he said, "I took it to mean that it was written in the final stages. I'd call it more or less scribbling."

Peggy Cohen went to a makeshift morgue in an elementary school to identify the body of her 59-year-old father, Fred Ware Jr. There was no note for her, but the medical examiner assured her that some men had written farewells with the same assurances:

"The notes said they weren't suffering, they were just going to sleep," she was told.

Autopsies were to be completed Friday, and the first funerals were to be held Sunday.

ICG's Hatfield said the Sago Mine would remain closed during the investigation, and the company was trying to find temporary jobs elsewhere for the site's 145 employees.

"In the interim, certainly this week, they are being paid and we're meeting with the employees over the weekend to draw up longer-term plans," Hatfield told The Associated Press in an interview a few miles from the mine. "We're going to do our very level best to take care of our people."

As for when the mine would reopen, he couldn't say. "That's a function of how quickly we can complete the investigation, and we can't rush it because the answers are too important."

The federal mine agency said cited the Sago mine for 208 violations in 2005, a number an agency official said was higher than normal for a mine of its size. The violations included 18 orders shutting parts of the mine until alleged violations were corrected. None was deemed serious enough to close the entire operation.