Enough oxygen was found to keep the men alive if they had survived the collapse.
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.
But later there were concerns that the drill might have missed its target and punched into a neighbouring chamber.
The hole was made with a steel drill bit that went down more than 500 metres into the ground.
Authorities had warned that over that distance a small drill could drift from its target.
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"
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 debris to reach the workers.
Rob Moore, vice president of Murray Energy, said: "It's incredibly labour-intensive."
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 men's families were praying for their survival. Some gathered in a catholic church in predominantly Mormon Huntington.
Jose Luis Bainz, whose son is among the missing, told Al Jazeera: "He just started working at the mine a short time ago. We're all trying to remain strong but it's difficult waiting with no word from them."
In an unrelated incident on Friday, three miners were killed in a coal mine in Indiana after a device, known as a "sinking bucket", by which they were being lowered into the mine, fell over 150 metres.