At least 10 Hanford workers were exposed to radioactive waste Tuesday at the nuclear cleanup site’s tank farm in southeast Washington.

Workers were removing a connection line that’s used to transfer radioactive waste between tanks when the contamination was detected. A test found radioactive waste on the workers’ skin and clothing. The contractor, Washington River Protection Solutions, says the contamination was low.

Tom Carpenter, who heads the worker advocacy group, Hanford Challenge, disputed that characterization.

“There’s no such thing as a safe level of exposure,” he said. “There’s no such thing as an acceptable level of exposure.”

Carpenter said this was one of the largest contamination events over the past 15 years at Hanford, where plutonium was produced for nuclear weapons during World War II and the Cold War.

Washington River Protection Solutions said no other contamination has been found outside the area. It said in a statement it’s still gathering information about the event.