An ammonia leak occurred in a refrigeration unit equipped with a turbocharger. A subcontractor performing maintenance would have removed non-insulated tubing with a solid plug. The ammonia would up intoxicating the worker as well as two plant employees. The leak was stopped by closing a valve, and a water curtain system dispersed the ammonia cloud. Damage was limited and no environmental consequences were observed. The procedures and instructions intended for subcontractor personnel were duly modified.