This is the story of how the cumulative effects of several seemingly innocent changes to a catalyst system resulted in a near miss process safety incident. Several aspects will be discussed including cumulative effects of multiple changes to the system, identification of potential scenarios in safety reviews, and design of controls and alarms. Results from the root cause analysis and the lessons learned will be explained. (C) 2011 American Institute of Chemical Engineers Process Saf Prog 30: 393-395, 2011