Within the next 48 hours a crew is expected to enter the Soudan Underground Laboratory for the first time since a fire broke out last Thursday at the mine that houses it. The facility, which is managed by the University of Minnesota, is home to a number of high-profile physics experiments, including the MINOS neutrino detector and the detector of the Cryogenic Dark Matter Search (CDMS) experiment. The lab lies more than 700 m below ground where the rocks above shield the experiments from unwanted cosmic rays and other disturbances.

© UnknownFirefighters tackling the blaze at the Soudan Mine, Friday
According to the Minnesota Department of Natural Resources (DNR), the fire was detected in the mine's main lift shaft around 9 p.m. local time on Thursday (17 March) when nobody was in the mine. By Friday the DNR had established that the fire was blazing inside the shaft between levels 23 and 25 - just two levels above the physics laboratory, which is located 60 m below on the mine's lowest level.

There were also fears that the lab could suffer flood damage after electrical systems automatically shut down, deactivating pumps that were designed to keep groundwater from entering the mine.

After fire-fighting efforts over the weekend, in which thousands of gallons of foam and water were sprayed into the mine, the Minnesota Interagency Fire Center reported on Sunday that the fire was 99% extinguished. Fire officials will only declare the blaze officially "out" once its source has been located and any smouldering ashes or embers have been extinguished.

A three-man team has already descended down the lift shaft to restart some of the pumps. By Sunday night they had reached the physics lab on level 27, where they encountered a large amount of foam, which seems to have prevented them from entering the lab. The laboratory's back-up systems, however, including infrared sensitive cameras, have so far indicated that the laboratory seems to have escaped the initial fire.

© Minnesota Incident Command Center/Daria KeaneSoudan Mine cage emerges from mine shaft covered in foam.
"We already know that there was no flooding and since we saw by video camera that - at least on Friday - there was no smoke on level 27," says Kurt Riesselmann, a spokesperson for the Fermilab National Laboratory, which manages the MINOS experiment, "our scientists expect that the experiments will look okay."

Riesselmann told physicsworld.com on Monday that if conditions are safe, a crew will enter the underground lab in the next two days. The main question now, he says, is whether the unexpected and long power outage damaged the experiments.

Alfons Weber, a physicist at the University of Oxford, who works on the MINOS experiment, is confident that the laboratory is robust enough to have escaped significant impacts. "There is lot of foam at the lowest level, but there seems to be no flooding," he says. "The lab is sealed from the rest of the mine by heavy iron doors and we don't expect damage."