SEATTLE (AP) — UW Medicine employees might have to wait at least six more weeks to return to work at a building where a radioactive substance was spilled three weeks ago.

A device called an irradiator, containing the radioactive material cesium-137, was being moved to a disposal site when the substance spilled on May 2.

Radiation was detected on the loading dock of the building.

Thirteen people were exposed and 10 were admitted to Harborview’s emergency room and discharged the next day.

UW Medicine spokesperson Susan Gregg says the public is not in danger. She couldn’t give a firm date for how long the cleanup will take. About 200 researchers and staff are moving into other UW facilities and will remain there until the building reopens.