HUNTINGTON, Utah (CNN) -- Rescuers trying to find six miners will begin boring a sixth hole down into Utah's Crandall Canyon mine Friday, and the search will stop if no signs of life are found, the coal mine's co-owner said.
Bob Murray, CEO of Murray Energy Corp., says he is hurt by criticism he did not do enough to find the miners.
"This is the last hole," Bob Murray, CEO of Murray Energy, said Wednesday evening. "If we don't find anybody alive in that hole, there's nowhere else that anyone ... would know where to drill."
Murray said work on the sixth hole, which will go down into the area where the miners were known to be working when the mine collapsed August 6, should be completed by Saturday.
However, he expressed little optimism that the effort would be successful, saying it was "totally unlikely" any signs of the miners will be found.
Murray also said that he has already filed paperwork with federal regulators to permanently close and seal the Utah mine.
"I will never come back to that evil mountain," he said.
Earlier Wednesday, a fifth hole drilled down into the mine found just six inches of open space left between the roof and rubble in an 8-foot-high tunnel, said Jack Kuzar, a district manager with the federal Mine Safety and Health Administration.
Kuzar said the fifth hole would be tested for oxygen, and a camera may be lowered down the shaft, although the small amount of space may limit its usefulness.
Cameras lowered into previous holes drilled into the mountain turned up no signs of the miners, and tests showed that oxygen levels in parts of the mine were too low to sustain human life. Watch how the safety record at Murray's mines stacks up »
An effort to send rescuers through the collapsed mine tunnel to attempt an underground rescue was suspended last week, after a new cave-in killed three rescuers and injured six others.
A panel of experts brought in to examine the mine after the second collapse determined that it was too unstable to resume the underground rescue.
Both the mine owners and federal officials also ruled out trying to find the miners by lowering rescuers in a capsule through a hole drilled down into the mine, saying the dangerous maneuver wasn't justified absent any signs of life.
The news was a blow to the family members of the missing miners, who have been holding out hope for a miracle and criticized Murray for not at least trying the rescue capsule. Signs reading "Bring them home" and "Bob Murray keep your promise" were posted overnight at the rescuers' command post.
Kuzar said he met with the miners' families Wednesday, "and they're holding up very well."
"They're very strong people," he said.
Earlier Wednesday, in an interview with CNN, Murray said plans were under way to establish a memorial for the missing miners at the site after the mine is closed.
"We're already discussing how we might go about to honor the trapped miners and make this a site for perpetuity," he said.
Friends and family have identified the six missing miners as Luis Hernandez, Manuel Sanchez, Kerry Allred, Carlos Payan, Brandon Phillips and Don Erickson. E-mail to a friend