Physics experiments in a major US underground laboratory remain suspended today as crews work to restart pumps shut down following a fire. The fire at the Soudan Mine in Minnesota broke out on the evening of March 17 in timbers in an elevator shaft serving the Soudan Underground Laboratory, which hosts several high energy physics experiments and is operated by the University of Minnesota and based in a state park. The cause is unknown.

Physicist Marvin Marshak, who directs the lab, says as of March 20 there was no sign of fire, smoke or carbon monoxide on the site, and teams are working today to restart pumps at the deepest level of the mine, about 710 metres underground, where the lab is based. There has been no damage to the laboratory but considerable foam remains, from foam and water being sent into the elevator shaft to put the fire out, says Carson Bergland of the Minnesota Interagency Fire Center, which tackled the fire together with The Minnesota Department of Natural Resources (DNR). The DNR described the fire on March 20 as “99% out.”

Marshak says the largest experiment whose operations have been seriously affected by the fire is the Cryogenic Dark Matter Search (CDMS), which looks for signals of dark matter passing through crystals of germanium. CDMS relies on a cryogenic cooling system that has been shut down and will take some time to start up again. Eight scientific staff that work at the lab have been unable to go to work since the fire, and will not be going back until it is confirmed to be out and the site has been inspected and pumps and ventilation are back on, Marshak says. Marshak says despite being underground, the Soudan Underground Laboratory is not especially hazardous. “Any lab could experience a fire. These things happen. What is really important is state park staff and university staff have dealt with it in a professional manner and minimized the damage.”

Image: CMDS cryostat / CDMS collaboration