The search for four missing miners in Montcoal, West Virginia, came to a halt Tuesday when poisonous methane leaks made it too risky for the rescue attempt to continue. On Wednesday, rescuers began drilling into the mine to ventillate dangerous methane gases, but by some estimates it will take at least 96 hours for the deadly gases to clear. A Massey Energy Co. executive said the explosion that collapsed the mine was “very violent,” so the men had little chance for survival. Twenty-five were killed in Monday’s blast, and two others were critically wounded. Investigators haven’t determined the exact cause of the explosion, but the Upper Big Branch mine has faced hundreds of citations involving methane ventilation in the past decade. The coal executive said higher demand for coal recently hadn't caused shortcuts in mine safety, and that its safety record was good by industry standards. Rescuers had hoped the trapped men would have been able to make their way to an airtight chamber with food and enough oxygen for four days, but when they reached one of the shelters, they found it empty. Rescuers were unable to reach the second shelter.