Ten contractors hospitalized after an ammonia vapor release at a Bay City plant Friday have been treated and released. Officials say a valve over-pressurized during testing, briefly exposing workers before sealing itself. Those affected were taken to local hospitals for observation as a precaution. Others were treated on-site. Röhm, the plant’s owner, confirmed all individuals are now safe. Emergency crews responded quickly, and officials say safety systems worked as designed. With no public threat, work at the plant resumed that evening as startup preparations continue.