DENVER Mustard gas vapors were detected seeping from a chemical weapons depot in southern Colorado on Tuesday, but no one was sickened or injured, the U.S. Army said in a statement.
Workers at the Army Chemical Depot in Pueblo, Colorado, detected the vapors during a routine monitoring operation.
As a result, workers installed an air-filtering system on the earth-covered igloo where the gas is stored to supplement a similar containment system already in-place, the military said.
Crews will return to the site on Wednesday to trace the source of the leak, the Army said. The Pueblo Army depot is one of five U.S. facilities charged with storing and destroying chemical weapons.
Mustard gas was used repeatedly during World War One, and was later prohibited under the Geneva Protocol in 1925.
Exposure is usually not fatal and less than 5 percent of those exposed to the agent during World War One died, according to the U.S. Centers for Disease Control and Prevention.
(Reporting by Keith Coffman: Editing by Alex Dobuzinskis and Cynthia Johnston)