Thirteen people were exposed to radioactive material being transported from the Harborview Medical Center Research and Training building in Seattle.
The radioactive breach occurred at Terrace Street and Terry Avenue, just off the main Harborview Medical Center campus. Initial reports said the substance came from Harborview Hall.
There is no threat to the public, according to Seattle Fire.
Ten people were released from Harborview Friday morning, according to hospital officials. UW Medicine tweeted Friday that the "exposure occurred when a piece of equipment in our research building across from the hospital was being decommissioned."
"All patients are undergoing decon and are asymptomatic at this time," Seattle Fire tweeted. "Eight will be transported to Harborview. No threat to general public, breach contained."
The material the group was exposed to is believed to be Cesium-137. According to the Environmental Protection Agency, Cesium-137 is produced by nuclear fission for use in medical devices and gauges.
Cesium, according to the EPA, moves "easily through the air," "dissolves easily in water," and "binds strongly to soil and concrete" without traveling far below the surface.
Exposure to a large amount of Cesium-137 can cause burns, acute radiation sickness and death. However, exposure to such a large amount would have to come from the mishandling of a "strong industrial source of Cesium-137, a nuclear detonation or a major nuclear accident." Large amounts of Cesium-137 are not typically found under normal circumstances.