HUNTINGTON, Utah &

A tiny microphone lowered deep into the earth early today picked up no evidence that six coal miners are alive four days after they were caught in a cave-in.




However, crews drilling a hole for the microphone and other gear might have missed the chamber where the miners are believed to be trapped, and an air sample indicated the miners had enough oxygen to breathe if they survived the collapse, officials said around midday.




Using a steel drill bit to bore a 21/2-inch wide hole more than 1,800 feet into the mountain site of Monday's cave-in, rescuers reached their targeted spot late Thursday.




But the drill might have drifted into a neighboring sealed chamber.




"The advantage of the 21/2-inch hole is that it's fast. The disadvantage is that it's not as accurate," said Richard Stickler, head of the Mine Safety and Health Administration.




The drill bit finally broke through at 9:47 p.m. MDT on Thursday, more than two days after drilling began. Two hours later, Murray and officials from the Mine Safety and Health Administration said there was no immediate response after the drill reached the pocket.




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 hopefully give a more definitive answer about the miners' fate.




Stickler said there was a chance the smaller hole could collapse, so rescuers were leaving the steel pipe and microphone where they were and did not plan on sending down a camera until drilling the nearly 9-inch hole reached the chamber.




The second hole was about 1,000 feet deep just before sunrise today, Stickler said, leaving more than 800 feet to go. Stickler said that drilling could be finished by tonight.




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




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




Relatives shouldn't be discouraged by the lack of carbon dioxide, a lawyer for the company said.




"What you got was a quick sample from a crude instrument, so you don't get all the constituents reported," said attorney Christopher Van Bever.




If the miners are alive, they might be sitting in inky darkness, their headlamps likely 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, other miners say. Murray said each miner would typically have had a half-gallon of water.




At the time of the collapse, the six miners were working in an area with an 8-foot ceiling. Corridors in the mine are typically about 14 feet wide.




The mining company has withheld the names of the six miners. 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, one relative said.




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