A fire in a single room at the lab caused an unfiltered ground-level radiological release, but surveys found no detectable contamination and no indication it spread beyond the site boundary.
One employee was hospitalized with minor injuries, while workers in Area A sheltered in place for about 30 minutes and incoming traffic by road, rail, river and air was temporarily restricted.
The 310-square-mile Department of Energy site near Aiken stores and processes nuclear materials and radioactive waste, making emergency drills for radiological releases a routine part of operations.