The air sample also indicated that there was no methane gas in the chamber, but no carbon dioxide, the gas exhaled when people breathe, was picked up.

"The work is not done. They're going to stay alive in that atmosphere," Murray said.

Second hole

The air sample was taken from the cavity through a steel tube, with a microphone attached to pick up any signs of life.

"The work is not done. They're going to stay alive
in that atmosphere"


Bob Murray,
co-owner of the Crandall Canyon mine
Meanwhile, drilling continued on a second, wider hole, which could accommodate a powerful camera to provide a view inside the pocket, deliver food and water, and give a more definite answer about the miners' fate.

Richard Stickler, head of the mine safety and health administration, said there was a chance the smaller hole could collapse, so rescuers were leaving the steel pipe in place.

The second hole was about 305m deep just before sunrise on Friday, Stickler said, leaving more than 244m to go. He said that drilling could be finished by Friday night.

Work was also under way in the mine itself, where rescuers were slowly burrowing through the debris to reach the workers.

Rob Moore, vice president of Murray Energy, said: "It's incredibly labour-intensive."

Earthquake blamed

Murray has insisted that an earthquake triggered the mine's collapse but geologists have disputed that, saying that shaking recorded by their instruments was caused by the cave-in.

The mining company has withheld the names of the six miners but the Associated Press has confirmed five identities: Carlos Payan, Don Erickson, Kerry Allred, Manuel Sanchez and Brandon Phillips.

The men's families were praying for their survival.

Arch Allred, cousin of miner Kerry Allred, said: "There are all types of conditions that could be in there for these folks ... some little cavity, some little corner.''

The Crandall Canyon mine is on a high desert plateau about 225 km south of Salt Lake City, in what is known as Utah's "castle country" because of the towering rock spires that dot the landscape.