Investigators looking into the Sago Mine disaster have turned to lightning experts to help explain whether a lightning bolt could have reached 260 feet underground and ignited a pocket of methane, setting off the explosion that left 12 miners dead.

So far, they've been unable to find any obvious conduit, such as a bore hole or a set of rails, that would have guided lightning into the sealed section of the mine in which the blast is thought to have originated.

This has prompted some of them to question why International Coal Group, which operates the Sago Mine, announced on March 14 that lightning sparked the explosion. The company resumed mining operations at Sago the following day.

Company officials said they based their "initial findings" of a lightning ignition on the near-simultaneous occurrence of a major lightning strike, a measurable seismic event and the setting off of a carbon monoxide alarm in the mine.

Investigators say there were at least three strong lightning strikes within a mile or two of Sago Mine No. 1 on the morning of Jan. 2, but how they might have penetrated to the underground mine remains a puzzle.

"That's what we're trying to find out from people who are familiar with lightning strikes," said Joe Pavlovich, a retired federal mine agency district manager in Kentucky who is assisting the state investigation.

"What actually happens? Does it penetrate? Does it follow the path of least resistance? Could there be a charge that comes through some rock strata and energizes a roof bolt?"

This week, ICG Vice President Charles Snavely reiterated that "we have not yet determined the precise path by which the energy from the lightning passed into the sealed area."

But that's no small point, according to some experts.

"In general, there must be some conducting path for lightning to travel to the mine void," said Dr. Vladimir A. Rakov, a University of Florida-based expert on lightning propagation.

While early evidence suggests lightning is a likely cause for the Sago explosion "at least a partial conducting path should exist to substantiate this scenario," he said. "I think it is too early to speculate on the exact cause of this explosion."

Two of the team of outside experts hired by ICG to conduct its in-house investigation are Jack Tisdale, a former Mine Safety and Health Administration official and Tom Novak, a Virginia Tech professor and co-author of two widely circulated papers on lightning propagation and its connection to methane explosions in mines.

Neither man would comment on how the ICG team reached its preliminary conclusions. Dr. Novak said that, after submitting his preliminary findings to the company, he received a telephone call from one of its attorneys instructing him not to discuss his findings publicly.

Martin Uman, Dr. Rakov's colleague at the University of Florida and another expert on lightning, said that while a metal conductor would make it more likely that lightning could penetrate deep into the earth, it would not be necessary.

"There's no obvious conduit, but there's metal all over the place," Dr. Uman said, noting the presence of steel rails and heavy equipment in mines. "There are also some other situations where there were no metal pipes going into other mines and they blew up anyway when there was lightning. It's certainly easier when there's a metal pipe, but it doesn't mean there has to be a metal pipe."

Both Dr. Rakov and Dr. Uman have been privately retained as outside experts. Dr. Uman is working on behalf of a lawyer with a possible civil claim in connection with the blast. Dr. Rakov did not indicate who has retained him.

Jurgen Brune, branch chief for disaster prevention and response at the Pittsburgh Research Lab for the National Institute for Occupational Safety and Health, said "there could be all kinds of potential conductors that could track a lightning charge into the mine" such as rails, gas lines or buried telephone lines.

But without determining what that is, "they're going to have to take that to court, because I'm pretty sure someone is going to contest that."

Dr. Uman, though, said the confluence of events strongly suggests a connection between the lightning and the blast.

"That would be one hell of a coincidence if it wasn't the lightning," he said.

Both the federal Mine Safety and Health Administration and the state of West Virginia have investigators looking into the Sago disaster, but MSHA spokesman Dirk Fillpot said Thursday they would not comment on their findings until the investigation is completed.

J. Davitt McAteer, who supervises West Virginia's investigators, signalled some skepticism about the ICG determination that lightning was the source of the blast.

"You've got tests to be conducted on the [mine] roof. You've got tests to be conducted on the seals. You've got tests to be conducted on other elements that you're dealing with. I think it's premature to come to a conclusion about the cause," he said.

Mr. McAteer, a former top MSHA official, said he was awaiting a copy of the data on which ICG based its preliminary findings.

"We're ready to take a look at their report and any science that backs it up," he said.

But while ICG widely distributed its early findings, it later told other agencies that it has no document to deliver, saying the company is still investigating the cause of the explosion.