CENTRALIA — An ammonia leak Monday night caused one Centralia plant to evacuate its employees.

ConAgra on West Calumet estimates that 40 employees were evacuated when an ammonia alarm sounded late Monday night.

Centralia firefighters responded to the scene and shut a valve in a mall building where the ammonia is stored.

Employees were not allowed to return for the two-and-a-half hours firemen were on the scene.

An outside contractor was called to repair the problem.