Montcoal, W.Va. ? Crews prepared early Friday to pump nitrogen into a coal mine where an explosion killed 25 in a bid to flush dangerous gases out and allow anxious rescuers to reach up to four survivors.

Safety officials conceded that any hope of finding workers alive in rescue chambers more than three days after the seismic blast was quickly fading, but said search teams were carrying four extra oxygen masks into the mine on the chance the men had made it.

“We committed to the families we were going to get into the chambers within 96 hours and we’re doing everything in our power to do that,” said Kevin Stricklin, a coal administrator from the federal Mine Safety and Health Administration.

Air holes drilled into the Upper Big Branch mine have ventilated lethal carbon monoxide and highly explosive hydrogen and methane but not enough to make the atmosphere safe, so nitrogen tankers were to start pumping.

“We’re just moving as quickly as we can,” Gov. Joe Manchin said. “We want to bring the loved ones back.”

The teams expected to be able to go back in early today. Stricklin estimated it should take the teams an hour and a half to reach the search area.

Once methane levels inside the mine have dissipated, the nitrogen will be sucked back out so the air inside the mine will return to normal, Stricklin said.

On Thursday, searchers came within 500 feet of a rescue chamber where possible survivors may have taken refuge, but were told to abandon their mission because the explosive mix of gases had become too dangerous.

Besides finding possible survivors, teams will eventually be recovering the 18 known dead. Seven bodies have been recovered and two miners survived with injuries in the worst coal mine disaster in more than two decades.

Teams spent more than four hours in the morning working their way by rail car and on foot through the mine. When told to abandon their mission, they were angry, but their safety was paramount, said Chris Adkins, chief operating officer for mine owner Massey Energy Co.

Rescue teams were headed first to an airtight chamber that has at least four days worth of food, water and oxygen.

During the morning foray, rescue crews did not get far enough to see the bodies of the dead or if anyone had made it to the chamber. They knew where the bodies would be because rescuers made it that far before gases forced them out of the mine after the explosion Monday.

Massey’s chief executive officer, Don Blankenship, continued to defend his company’s record and disputed accusations from miners that he puts coal profits ahead of safety.

“To some extent the fact that there were more survivors than those that are lost suggests that the mine was in pretty good shape relative to what mines would have been in the past and hopefully by today’s standards,” he told The Associated Press on Thursday. There were 61 miners in Upper Big Branch when it exploded.