The search for six Utah miners is continuing with the drilling of a third hole toward the back of a mine where officials hoped the men sought an air pocket.
Crews already have drilled two holes and fitted a camera down one of them, but they have yet to find coal miners, eight days after the mine partly collapsed.
The camera's images revealed a tool bag for hammers, wrenches and chisels hanging from a post, 3.4 miles from the entrance and more than 1,800 feet underground.
The collapse of the mine's midsection was thought to have pushed ventilated air into a pocket at the rear of the mine, where the miners may have fled when their escape routes were cut off by rubble, said Richard Stickler, chief of the federal Mine Safety and Health Administration.
The collapse blew out the walls of mine shafts but left reinforced ceilings mostly intact. About five feet of headroom remained in the deeper mine shafts.
The third drill was set to drop 1,300 feet deeper into the mine and near its back wall. The rig required more roads to be built to reach the location on a steep mountainside.
A microphone lowered down the first hole picked up no sound, and air samples sucked up the hole revealed just over 7 per cent oxygen - not enough to sustain life. The hole is now being used to pump 2,000 cubic feet of fresh air a minute into the mine.
Mining rescues after eight or more days are not unheard of. In May 2006, two miners were rescued after being trapped for 14 days following a collapse at an Australian mine.
AP