A worker died on Wednesday after collapsing in the early afternoon at the Hanford nuclear reservation.
The death of Teresa Weathers, 49, appeared to be from natural causes, say officials.
The worker was at the Plutonium Finishing Plant in central Hanford, where work is underway to tear down the building.
Co-workers and emergency responders reacted quickly, but the worker could not be saved, said Ty Blackford, president of Hanford contractor CH2M Hill Plateau Remediation Co., in a message to employees.
CH2M is in charge of demolition and other work at the Plutonium Finishing Plant.
Grief counseling is available to workers, Blackford said.
The name of the worker was not released Wednesday.
It was the second death of a worker in recent days, after an industrial hygiene program supervisor died in a car accident on the portion of Hanford closed to the public on Oct. 10.
The 580-square-mile site near Richland was used to produce nearly two-thirds of the plutonium for the nation’s nuclear weapons program from World War II through the Cold War.
Environmental cleanup of radioactive and other hazardous chemical contamination now is underway.