The “Sheep Fire,” which is south of Highway 33 and north of Highway 20, was sparked by a lightning strike around 6:30 p.m. Monday, KBOI-TV reported.

By Tuesday the fire had grown to about 85,000 acres and traveled near the Idaho National Laboratory, the state’s nuclear research facility in Idaho Falls, KIVI-TV reported.

“Non-essential employees” were evacuated on Tuesday from several INL site facilities including, Central Facilities Area, Advanced Test Reactor, Naval Reactors Facility, EBR-1, Integrated Waste Treatment Unit, RWMC, AMWTP, and INTEC, according to INL.

Firefighters from INL and the Bureau of Land Management were on the scene to combat the fire, according to the Bureau of Land Management Idaho Fire.

The Naval Reactors Facility, meanwhile, has curtailed operations for its day and swing-shift employees, KIVI-TV reported. Gate 1, INL’s main entrance, is closed to non-emergency traffic, the report said.

Other INL facilities are preparing for the loss of commercial power as they switch to on-site backups, the East Idaho News reported.