The scare was serious enough to rattle the region: local broadcaster WRDW/WAGT reported that emergency dispatch described an 'unfiltered ground-level radiological release' tied to the fire.

A Federal Aviation Administration temporary flight restriction — which the New York Post reported cited a 'US Govt Nuclear Incident' — covered a 15-nautical-mile radius around the facility up to 10,000 feet, per Interesting Engineering.

Yet officials confirmed no radiological contamination was reported outside the affected facility.

According to the Department of Energy, one employee was taken to a hospital with minor injuries. Employees in the laboratory's Area A sheltered in place behind barricades for roughly 30 minutes, and other workers not involved in the response were also sheltered as a precaution.

Site entrances were barricaded to incoming traffic, and rail, river and air traffic in the vicinity were restricted, though Highway 125 remained open.

The Site Area Emergency declaration is the second-highest of three emergency categories at the site and indicates 'something more serious has occurred,' according to the site's community preparedness information cited by Newsday.

Edwin Lyman, director of nuclear power safety at the Union of Concerned Scientists, told Newsday it is reassuring that no off-site contamination was found, but warned that any fire involving radioactive material requires extreme precautions because of the potential for dispersal and public exposure.

Built in the early 1950s to produce plutonium-239 and tritium for nuclear weapons, the complex still produces tritium, handles spent nuclear fuel, and stores uranium and plutonium.

CNN also notes the site is central to a push to rebuild US warhead production, with NNSA recently green-lighting full-scale construction of a roughly $23.5 billion plutonium pit facility, per Exchange Monitor.

By 9:18 p.m. the site reported no operational emergencies or scheduled delays, all protective actions were lifted and entrance traffic resumed, with oncoming shift workers reporting as usual and other employees told to return Thursday, officials said.

The cause of the fire has not been disclosed, and officials said additional information would be released as it becomes available. Residents had been advised to monitor local radio and television for any instructions from state officials.