After three days of around-the-clock work, crews have almost completely extinguished a fire that had been burning since Thursday in the Soudan Mine between the surface and the University of Minnesota research laboratories, located 2,341 feet underground.

While University researchers who operate laboratories in the mine worth up to $100 million are relieved to know the fire is no longer visible, they are anxiously awaiting their chance to go underground and examine the extent of damage.

On Sunday night the Minnesota Department of Natural Resources announced that a three-man team was able to travel down the mineshaft to view the extent of the damage. The crew was the first to enter the mine since an initial exploration team that descended shortly after the fire was detected.

Officials are waiting to declare the fire completely extinguished until the source of the flames is found and any remaining embers are put out.

No one was in the mine when the fire set off alarms Thursday night, but University researchers were alerted by sensors located in the 27th underground level of the mine where the labs are located.

âÄúIt was one of those middle-of-the-night phone calls you hate to get,âÄù said Alec Habig, associate director of the lab. âÄúNo one is happy, but things are very well organized.âÄù

In coordination with the DNR, research teams worked quickly to stabilize what they could remotely before power in the mine was manually shut down to prevent further problems.

âÄúThings didnâÄôt snowball like they could have because people were quick,âÄù Habig said. âÄúBut itâÄôs never good to turn things on and off. In a way this equipment is like light bulbs âÄî it takes a lot of energy to shut it down and fire it back up.âÄù

Crews had reduced the fire to a smolder Saturday by placing a cover over the entrance to the mine to starve the fire of oxygen.

Occasionally, firefighters removed the cover to douse the shaft with more than 500 gallons of fire-retardant foam.

The cause of the fire is still unknown, but timbers lining the shaft of the mine had been feeding the flames. âÄúProperty damage inside the mine is anticipated to be extensive,âÄù a DNR news release stated.

For researchers, the fire hasnâÄôt been the biggest concern because it has been contained two levels above the labs. The lack of power, however, has them worried.

Turning off the power meant stopping sump pumps from removing groundwater from the mine.

Before the fire, the groundwater level was 244,500 gallons short of reaching the entrance to the lab, but pumps had been removing 35,000 gallons per day. If officials cannot put out the fire and get the pumps running again, water would reach the door of the lab in about a week, damaging expensive equipment and possibly interfering with projects.

âÄúWe donâÄôt have a lot of time, but they think they have a shot at getting the water out,âÄù DNR spokesman Carson Berglund said Saturday.

On Sunday crews were able to start up two of the three pumping stations slowing the seeping water.

âÄúBefore we couldnâÄôt pump at all the concern was that in days we would see water,âÄù Soudan Lab Director Marvin Marshak said. âÄúNow the time scale we have to work on is lengthened.âÄù

And while water damage was a concern for all of the groups who use the labs on the 27th floor, the power outage could cause additional setbacks to the UniversityâÄôs Cryogenic Dark Matter Search, which relies on detectors that must be maintained at very low temperatures in order to work. A lack of power means those temperatures will naturally rise.

CDMS project manager Dan Bauer said Saturday that if his crew were able to get back into the lab soon, itâÄôs possible the temperature could be brought back down without the need to restart the process.

It isnâÄôt clear yet how immediate that access will be. When crews traveled down the shaft Sunday they reported a wall of foam between the elevator and the door to the lab.

Marshak said that tomorrowâÄôs goal would likely be to restore the final sump pump.

Carbon monoxide levels in the mine have been dropping since the shaft was covered. Lower levels of carbon monoxide, the byproduct of combustion, means less burning is occurring in the mine.

SundayâÄôs exploration team wasnâÄôt given the go ahead until carbon monoxide levels were declared safe.

âÄúFriday morning was probably the low point in terms of worrying that we may never get back down there again,âÄù Bauer said. âÄúThe news in the past day and a half has been very encouraging.âÄù

In addition to serving as a research area, the mine is at the core of the Soudan Underground Mine State Park. The mine is one of only two underground mines in the country that gives public tours, according to the DNR. About 37,000 people tour the mine each year.

âÄúWhen you think about it, this is like the first forest fire of the season,âÄù Marshak said. âÄúIt has been very impressive to watch [the DNR] in action.âÄù