(CNN) -- Firefighters Thursday continued to battle a wind-driven brush fire that has consumed about 170 square miles at the Idaho National Laboratory's desert site, authorities said.
The fire at the facility, which is about 40 miles west of Idaho Falls, has been burning since Tuesday afternoon, and the cause is still unknown.
Crews continue to monitor hot spots, which reside mostly on the fire's north side. Laboratory officials said as of 9 p.m. Wednesday, the fire was 60 percent contained.
About 80 percent of the 109,000 acres belongs to the U.S. Department of Energy. The facility is an applied engineering national laboratory supporting the Energy Department's missions in nuclear and energy research, science and national defense.
Some employees have been relocated due to the fire threat.