Rescuers drilled through to a pocket in the coal mine where six miners have been trapped, but heard no sound through a microphone that was lowered into the collapsed mine.
The mine's co-owner remained hopeful that the six men were still alive despite the silence.
"I wouldn't look at it as good or bad news. The work is not done," said Bob Murray, chairman of Murray Energy Corp.
Mining officials were able to take an air reading from the pocket and said the air quality was good, with 20.5 percent oxygen, some carbon monoxide and no methane.
"That means if they're alive, they're going to stay alive in that atmosphere," Murray said during a news conference early Friday.
The air sample was drawn more than 1,800 feet through a steel tube, which remained in the narrow hole to keep the slender lifeline open in case the miners heard a tone from the microphone and tried to respond.
The sample, however, did not pick up carbon dioxide, the gas that is exhaled from the lungs when people breathe. Still, mine officials warned that the lack of carbon dioxide did not necessarily mean that the miners were dead.
"What you got was a quick sample from a crude instrument, so you don't get all the constituents reported," said Christopher Van Bever, an attorney for Murray Energy.
The drill bit finally broke through around 10 p.m. MDT on Thursday. Two hours later, Murray and officials from the Mine Safety and Health Administration said that there was no immediate response after the drill reached the pocket.
Drilling continued on a wider hole, which could accommodate a powerful camera to provide a view inside the pocket, deliver food and water, and hopefully give a more definitive answer about the miners' fate.
Work also continued in the mine itself, where workers were slowly burrowing through the debris to try to reach the site where the miners were when the walls caved in early Monday.
"It's incredibly labor-intensive," said Rob Moore, vice president of Murray Energy.
If the trapped miners are alive, they may be sitting in inky darkness, their headlamps having burned out. Wearing thin work clothes in the 58-degree cold, they could be chilled to the bone if water is seeping into their chamber 150 stories below ground.
Murray said they are doing "everything humanly possible" to rescue them.
Murray has repeatedly insisted that an earthquake triggered the cave-in, but evidence to the contrary is mounting.
A team of geologists from the University of California at Berkeley said the seismological data from the mine collapse does not match what they would expect to see in a natural earthquake.
"What we found is that this seismic event was is in fact very different from what we typically see in earthquakes and it seems to suggest that there was a closure of an underground cavity," said Doug Dreger, the chief author of the study from Berkeley Seismological Laboratory.
In other words, the seismic data was the result of the mine itself collapsing, not a triggering earthquake. No one from Murray Energy Corp., which owns the mine, was immediately available to comment on the study.
The cause of the collapse could be important in determining who is responsible and whether safety measures were adequate.
In a briefing with reporters, Murray would only talk about the ongoing rescue efforts.
Murray held two golf-ball-sized chunks of shiny black coal. He said tons of such coal sits between rescuers and miners.
"We'll go through this very fast to get to the men because it's loose and it's fine and it's small like this," he said.
He said he has been worried about ventilation in the mine, but now that he has seen the area of the collapse.
"I can tell you that I'm more optimistic than I ever was, that there's ventilation back there to keep those men alive," Murray said.
He said crews still were removing the rubble blocking the mine, but that it could still take a week or more. Two drills have made significant progress boring through the hundreds of feet of rock and sandstone. Murray thinks a 2 1/2-inch hole and another measuring 8 1/2inches will be completed within a day or two.
Until then, residents of this mining town have scheduled daily gatherings of mutual support.
About 200 people gathered at the rodeo grounds in Huntington, near the mine, for a candlelight vigil Wednesday night. They sat on rickety wooden benches under a white banner with the word "hope" in large letters.
Melody Sinclair's husband is a miner - not one of those trapped — but the mine collapse has clearly affected her.
"Every day that your husband goes to work anywhere — any tragedy or accident can happen anywhere. But when they go underground, there's no communication. That's what makes it really hard," she said.
From NPR reports and The Associated Press
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