Coal Tattoo blogRead more stories on the mine disasterView a PDF of the mine layout and its location in the stateMONTCOAL, W.Va. -- Rescuers were hoping late Wednesday night that toxic gas levels inside a Massey Energy mine in Raleigh County would soon drop, so crews could safely resume the search for four missing miners in what is already the worst U.S. mining disaster in more than a quarter-century.Rescue leaders and government officials said hope was fading, but that crews would continue drilling ventilation holes into the Upper Big Branch Mine to try to make it safe for specially trained and equipped mine rescue teams."We just can't take any chances," said Kevin Stricklin, coal administrator for the U.S. Mine Safety and Health Administration, an agency that lost rescue workers during similar efforts in 1976 at the Scotia Mine in Kentucky and in 2007 at Crandall Canyon in Utah.Crews have drilled one ventilation hole into the mine and another was about halfway there, as workers rushed to try to rid the mine of dangerous gases so specially trained teams could resume searching for the miners.Rescue crews had previously said they planned a third and fourth ventilation hole, and Stricklin announced that Massey plans to drill an additional ventilation hole and lower cameras near the location of a rescue chamber to see if the miners can be located.Stricklin said air monitoring for an initial borehole at first showed "extremely high" levels of carbon monoxide and hydrogen, very low levels of oxygen, and methane concentrations that were just below the explosive range. "We're dealing with numbers that are way beyond what we would normally see in a mine," Stricklin said."The numbers don't surprise me," he said. "We're hoping that someone had the ability to get to that chamber. That would be the only way anyone could survive. There's always hope, but it's miniscule."Later, Stricklin said readings at the top of the first hole have dropped to a point where it would be safe to proceed. But officials want to be sure that levels have also dropped inside the mine before sending in the six-person rescue teams.During an afternoon briefing, Gov. Joe Manchin repeated his earlier assertions that he, the rescue crews and the families were maintaining a "sliver of hope" that the four missing miners made it to one of two airtight chambers that rescue crews have not yet been able to check."The odds are not in our favor, because of the horrendous blast we had," Manchin said during a briefing early in the day.Twenty-five miners died in the Monday explosion, which officials believe was fueled by methane and perhaps made much worse by coal dust. Two miners remain hospitalized following the worst U.S. coal-mining disaster in a quarter-century. Their conditions have not been released, but Manchin said one of them was in intensive care. As the rescue effort dragged on through its second full day, hope for a miracle was waning, officials said.Three of the missing miners are believed to be in one location and the fourth in another location, somewhere near one of two rescue chambers located near the working face of the mine. Rescuers already checked a third rescue chamber, but did not find any survivors there.Stricklin said once rescue teams can get into the mine, it might take them about two hours to get into the areas where the miners are believed to be."They may not be in the exact location we think they are, so we may have to fan out a little bit," Sticklin said. "You have to play it by ear ... you have to shoot from the hip."Early Tuesday morning, rescue teams had reached 500 to 600 feet from the area where the miners may be before bad air readings forced them out of the mine.New miner tracking systems installed following a string of mine disasters in 2006 were of little help to the rescuers. Like most mines nationwide, Upper Big Branch has not yet complied with the new federal requirements. And West Virginia's state rules do not require operators to track miners' specific locations once they enter active sections of the mine.Even as the rescue effort continued, plans for investigations were moving forward.Labor Secretary Hilda Solis said her agency's team would be headed by Norman Page, a 25-year MSHA employee who is currently district manager in Pikeville, Ky."Twenty-five hardworking men died unnecessarily in a mine Monday," Solis said. "The very best way we can honor them is to do our job. MSHA's investigation team is committed to finding out what happened, and we will take action."MSHA has also said it will conduct an "internal review," its typical practice after disasters of appointing agency officials from another district to examine how well MSHA policed the Upper Big Branch Mine.Manchin has said West Virginia would hold a public hearing as part of its investigation, as it did following the Sago disaster. The governor has not announced plans for that hearing or the investigation.Rep. Nick J. Rahall, D-W.Va., has said that Congress will hold hearings on the disaster as well.Reach Andrew Clevenger at firstname.lastname@example.org or 348-1723. Reach Ken Ward Jr. at email@example.com or 304-348-1702. Reach Gary Harki at firstname.lastname@example.org or 304-348-5163.