Simultaneous operations (SIMOPs) occur within process facilities when two or more activities occur at the same time and place. They may involve risks that are not identified when each activity is considered by itself. A SIMOP review identifies possible interactions between activities that may adversely impact people, property, or the environment. SIMOP reviews are an important adjunct to the performance of process hazard analyses such as hazard and operability studies. A number of major process industry accidents have involved SIMOPs. Several examples are described. A procedure for conducting a SIMOP review and an example are provided. The development of a plan to address the performance of SIMOPs using the results of SIMOP reviews is discussed and plan contents are identified. (C) 2016 American Institute of Chemical Engineers Process