SITKA -- A seafood processing plant in Sitka is back in operation after a brief shutdown because of an anhydrous ammonia leak.

The leak forced the evacuation of 150 people from the Silver Bay Seafoods processing plant on Thursday. Anhydrous ammonia is used in the plant's refrigeration system.

The Alaska Department of Environmental Conservation says the plant was deemed safe and operations resumed early this morning.

The cause of the leak may have been a pressure relief valve that malfunctioned. The system at the plant included redundant relief valves that allowed operations at the plant to resume.

When the leak occurred, 15 people were taken to a local clinic to be assessed for exposure to the gas.