Rescue crews will drill a third hole into a collapsed Utah coal mine in an effort to locate six missing miners, a federal official says.
Richard Stickler, head of the Mine Safety and Health Administration, told a Sunday news conference in Huntington that poor lighting allowed the camera to only see 4.5 metres into the void.
Rescuers saw only things like a tool bag, chains and other equipment.
"We did not see any sign at all of any of the miners," Stickler said.
Rescuers would try again with a better lighting system that should give about 30 metres of visibility, he said, but didn't make it clear when that would happen.
The new hole would target an area that the miners would have gone if the air in the original location was bad, said Bob Murray, head of Murray Energy Corp., the mine's operator.
A new hole could take up to six days to drill, one official estimated.
Rescuers believe their most promising plan at reaching the men remains with the crews digging a path through the mine's rubble-filled passageway.
Crews have made it through about 180 metres of the 600 metres of collapsed tunnel. Stickler wouldn't estimate how long it might take to reach the miners.
The six miners became trapped in the Crandall Canyon mine when it collapsed early Monday.
On Saturday, crews drilled a second hole deep into the earth and lowered a camera into the cavern where they believed the men were trapped.
While no signs of life were found, images showed promising conditions that include an intact ceiling over almost a metre of rubble mixed with water. Mine officials remain optimistic that the trapped workers will be found alive.
After meeting with the miner's families, Bob Murray, chief of the mine and co-owner of Murray Energy Corp., maintained that the search remains a rescue mission. He urged patience as crews struggled to find alternatives ways of reaching the miners.
On Friday, an earlier hole was drilled into the mine and a microphone was dropped down to establish contact with the survivors but an air sample contained low levels of oxygen, suggesting crews drilled into the wrong underground chamber.
If the entombed miners are still alive, they may be sitting in darkness, their headlamps having burned out. They are wearing thin work clothes in the 14C cold, 580 metres below ground.
Authorities initially believed an earthquake was responsible for the collapse of the mine.
Scientists at the University of California, Berkeley, did their own analysis of Monday's seismic event and determined the seismic waves came from an underground collapse.
With files from the Associated Press
