SPOKANE, Wash. (AP) — A cleanup contractor says the release of radiation that triggered an alarm at a former plutonium production site in Washington state was so low that it did not pose a threat to human health.

Contractor CH2M Hill said radiation was detected Thursday at low levels outside a building being demolished at the Hanford Nuclear Reservation.

About 350 workers were ordered to take cover after the alarm sounded at the shuttered Plutonium Finishing Plant. The order was lifted less than four hours later.

The Energy Department says no one was injured and workers in protective suits applied an adhesive product to the contamination to prevent the contamination from spreading.

Many workers were back on the job after the mishap.

Workers at Hanford are cleaning up nuclear waste left from decades of producing nuclear weapons.