The Agrium Redwater Nitrogen Operations Ammonia 2 plant underwent a phased project to upgrade and modernize its automatic safety shutdown system. Agrium incorporated the use of safety integrity levels in the functional design and detailed design of the safety shutdown system to ensure that all required protections were implemented in a safe and cost-effective manner. This article discusses the methodology used to determine the scope of the system, the methodology used to define the functional design, the implementation strategy chosen and the key lessons learned from the execution of this project. (C) 2009 American Institute of Chemical Engineers Process Saf Prog 28: 282292, 2009