Naoma, West Virginia (CNN)  -- Crews planned to pump nitrogen into a West Virginia coal mine as the search resumed early Friday for four miners who may be trapped after a deadly explosion earlier in the week.





Kevin Stricklin of the U.S. Mine Safety and Health Administration (MSHA) said crews would neutralize potentially explosive air in the Upper Big Branch coal mine with nitrogen, allowing rescuers to go back in and remain there even if an explosive mixture builds again in the air.





The hope, though slim, is that the four missing miners were able to survive by entering one of the chambers, which were stocked with enough food, water and air to keep 15 miners alive for four days.





"We committed to the families that we wanted to get into the chambers within 96 hours and we're trying to everything in our power to do that without taking a chance on the rescue teams, and I think this is the way to do it," Stricklin said.





Officials said the rescue teams will make "a mad dash" to one of the mine's two airtight rescue chambers.





"The rescue teams have taken four breathing apparatuses with them," Stricklin said. "In the best case scenario, we would find four survivors. Once they get in there, we'll put oxygen masks on the survivors and bring them out."





At least 25 miners died in Monday afternoon's explosion in West Virginia, while four others remain missing and two were injured.





Rescuers -- 32 of them working in four teams -- got within 500 feet of one of the rescue chambers before having to turn back Thursday, said J. Christopher Adkins, chief operating officer of Massey Energy, the mine's owner.





They were pulled back after it was determined that noxious gas levels were high enough to cause another blast. The readings showed potentially explosive levels of methane and hydrogen and high levels of carbon monoxide.





Stricklin said air samples were tested at regular intervals Thursday night and that rising barometric pressure in the wake of a cold front that moved through the region had helped reduce the chances of another blast.





Rescuers had been using high-pressure fans to pull the toxic air through 1,100-foot holes to the surface Thursday.





One of the four unaccounted-for miners and 18 of the dead were working in an area where longwall cutting was taking place. The technique uses a large grinder to extract the coal. It creates large amounts of coal dust and methane, both of which are explosive.





The other three missing miners are believed to be about 2,000 feet away in a new development area of the mine.





Authorities have acknowledged it is unlikely the four missing men are alive, but they refuse to give up hope.





Officials hope to determine whether either rescue chamber has deployed by lowering a camera through the second hole.





"If they're deployed, more than likely someone's in them," said West Virginia Gov. Joe Manchin said. "That means we have a chance of that miracle."





But he added: "If they're not deployed, we know that our chances are diminished tremendously."





In an interview with CNN, Manchin noted that the mine was outfitted with gas sensors to alert mine personnel when levels become danger.





"In gaseous mines, you want to monitor and you want to have good ventilation," he said. "If that has worked before, whenever the levels got out of control they pulled them out and stopped, why did it not happen this time?"





The cause of the explosion is unknown, and state and federal officials have pledged a full investigation.





The White House announced Thursday that President Obama will meet next week with Secretary of Labor Hilda Solis and an MSHA official to hear their initial assessment of the cause of the blast and their recommendations on steps the federal government should take to improve safety.





CNN's Rachel Streitfeld and Samira J. Simone contributed to this report.
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