SPOKANE, Wash. (AP) — Radiation warning alarms sounded Thursday at a former plutonium production plant in Washington state, prompting a take-cover order that sent about 350 workers seeking cover indoors during the demolition of a plant that for decades had helped make nuclear weapons.

The order was lifted less than four hours later after low levels of radiation were detected at the Hanford Nuclear Reservation, the site of a massive cleanup.

The Energy Department said no injuries were reported, and workers had applied an adhesive product to the contamination to prevent it from spreading from locations on sidewalks and near a vehicle access gate at the Plutonium Finishing Plant, which dates to the late 1940s.

“The contamination detected has been at very low levels, levels not harmful to human health,” CH2M Hill, the private contractor demolishing the plant, said in a statement.

Workers were continuing to monitor the air for any further contamination, the company said.

The Plutonium Finishing Plant is one of the most polluted facilities at the sprawling Hanford site, which is half the size of Rhode Island.

“Air monitoring alarms during demolition are not unexpected,” the Energy Department said in a news release, noting the alarms are used to ensure demolition of the plant proceeds safely.

The incident followed the collapse last month of a tunnel at a separate Hanford facility that contained nuclear waste, prompting another evacuation. The Energy Department has said no injuries or contamination was reported as a result of the collapse. Continue reading.