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Authorities scoured the 10-acre campus of a U.S. Energy Department lab in Albany, Oregon, for seven hours Tuesday before declaring a phoned-in bomb threat to be "unsubstantiated."

Employees at the National Energy Technology Laboratory's Albany Research Center, about 65 miles south of Portland, were being advised when to return to work, the agency said after a state police bomb squad packed up and left the campus about 3 p.m. (6 p.m. ET).

The National Energy Technology Laboratory's Albany Research Center in Albany, Oregon.

The lab received the threat by telephone about 8 a.m., said Cynthia Powell, the facility's director of research. She called it a "credible threat," and the campus was immediately evacuated.

"Somebody called and said, 'There is a bomb on your site,' and that was sufficient for us to take action," Powell told reporters. "Very certainly, we knew they were talking about our facility."

The NETL, which researches clean production and use of domestic energy resources, has 126 employees at the Albany campus, most of them contractors, the Energy Department said.