The hole started plugging up, making it impossible for technicians to get a separate robotic camera 1,856 feet down into the Crandall Canyon Mine to look for signs of the men, said Rich Kulczewski, a spokesman for the Mine Safety and Health Administration. It was not known whether the six men, not heard from since the Aug. 6 collapse, survived.
The video camera found 2.5 feet of clear space and 7 feet of rubble and mud, officials said Thursday. Another hole drilled earlier also was being tried, but the mud and rubble conditions were similar, Kulczewski said.
"That was a disappointment. There's no doubt about it," he said at a news conference in Huntington.
The robotic camera is 8 inches wide and can go down holes only a fraction wider, but if it could descend one of them, it could maneuver as far as 1,000 feet into the mine.
After the crews broke through the seventh hole about 4:15 a.m. Thursday, they rapped on the drill steel to try to signal the miners, but there was no response.
A decision was made to lower the robotic camera Thursday evening into a hole drilled Aug. 18 - despite an earlier determination that there was a high risk of losing the camera in the effort, Kulczewski said. There was no estimate of how long that would take.
"We haven't given up, but we're running out of possibilities," Kulczewski said.
Meanwhile, the U.S. Labor Department said an independent review will be conducted of the MSHA's handling of the mine disaster. Separately, the MSHA announced its own investigation, led by the man who was in charge of the review of the Sago mine tragedy in West Virginia, where 12 people died in January 2006.
Richard Gates, an MSHA district manager in Alabama, has been with the agency for 19 years.
"MSHA's investigation will fully examine all available evidence to find the cause of the ground failure at Crandall Canyon mine and any violations of safety and health standards," agency chief Richard Stickler said in a statement.
The six miners have been trapped more than 1,500 feet below ground since the collapse. Three rescuers trying to tunnel to the men died during another collapse Aug. 16.
The MSHA investigation at Crandall Canyon would involve people with no ties to the agency's Western district, which oversees safety at the mine, 120 miles south of Salt Lake City, Stickler said.
Hours after Stickler's announcement, Labor Secretary Elaine Chao said an independent team of mine-safety experts will review MSHA's handling of the Utah accident.
The review will look at the MSHA's actions before the collapse and during the rescue operations. The agency is an arm of the Labor Department. Their tasks will include studying mine plans and inspection records, as well as interviews with MSHA employees.
The United Mine Workers of America is critical of the Labor Department's announcement. "A truly independent investigation would be done by people who are from outside the agency with no ties to MSHA or its employees," President Cecil Roberts said in a statement.