(Mandan, ND) — A chemical leak at a Marathon refinery in Mandan is under control after leading to an evacuation. The Department of Environmental Quality says the leak of gaseous hydrofluoric acid began yesterday morning. The chemical is dangerous to humans and employees were ordered to leave the refinery when the leak was found. The released acid was sealed by Marathon safety teams using water cannons to transform the gas into a liquid. Workers returned to the site mid-morning and there were no injuries. The cause of the leak is under investigation.