BARTON, Md. (AP) _ Crews were removing about 3,000 tons of rock each hour.
But as the excavation continued into the night Wednesday, rescuers still hadn't located two men who had been trapped for more than 30 hours under a pile of rubble in an open pit coal mine here in western Maryland.
The miners' chances of survival were diminishing with each passing hour, said Bob Cornett, acting district manager for the federal Mine Safety and Health Administration. Crews had removed more than half of the debris that buried the miners by Wednesday night.
``We're working it hard,'' Cornett said.
The miners were trapped Tuesday morning when the bottom of a high wall collapsed, burying them and the equipment they were operating, Cornett said.
The collapse created a layer of rocks that ranges from 45 feet to 100 feet deep, but rescuers believe the collapse pushed the men and their equipment toward the shallower end.
``There are some very large rocks on that side that you can see gaps, spaces, vacuums or holes that potentially, if the machinery was pushed that way, there could be air pockets,'' Cornett said.
The miners were working at the bottom of the pit at the Tri-Star Job No. 3 mine when the collapse occurred. One miner was operating a tracked backhoe and the other was using a loader. Both pieces of equipment have enclosed cabs and CB radios, although the men have not communicated with anyone since the collapse.
Cornett said he did not believe the machines were equipped with emergency breathing apparatus. The so-called ``self-contained self-rescuers'' provide one hour of oxygen.
The rescue effort suffered a setback late Wednesday afternoon when a large amount of the boulder-strewn material workers were removing slid back into a cleared area. ``That probably set us back a half hour to an hour,'' he said.
The cause of the collapse was not known, but Cornett said that rain tends to cause more high wall failures at this time of year.
``When you have rain like we've been having here, and freezing and thawing, it may have had an impact,'' he said.
The site is in a rugged area of mountains called Georges Creek and is near the Eastern Continental Divide. The region is dotted with abandoned mines and fading former company towns.
The mine has had no fatal injuries since at least 1995 and was not cited for violations in its most recent inspection, which began March 5, according to MSHA. The mine employed 51 people at the end of 2006 and produced nearly 653,000 tons of coal last year.
The company operates at least two other surface mines in Maryland, according to Ron Wyatt, a family liaison for MSHA.
Owner George R. Beener was at the site, according to a woman who answered the phone at a mine office. She said the company had no comment and declined to identify herself.
Tri-Star Mining Inc. had 15 to 20 people working on the rescue. Joining them were a crew of eight from MSHA, local firefighters and search-and-rescue teams from Baltimore and Montgomery County.
``We will continue this as a rescue operation until we know it's not,'' Cornett said.