Simultaneous operations (SIMOPs) are situations where two or more operations or activities occur at the same time and place in a facility. They may interfere or clash with each other and may involve risks that are not identified when each activity is considered by itself. Thus, they can increase the risks of the activities or create new risks. A number of major process industry accidents have involved simultaneous operations.

In the wake of Hurricane Harvey, the Chemical Safety Board (CSB) issued a Safety Alert on precautions needed during restart of processes that were shut down. The CSB noted that startup requires a higher level of attention and care than normal processing because numerous activities occur simultaneously. This is one example of when simultaneous operations occur. Other examples include construction activities near active equipment and maintenance activities near process operations.

Usually, the situations involved in simultaneous operations are not considered during process hazards analysis (PHA) studies which focus attention on individual process operation. Moreover, PHA teams may not recognize the importance of examining how simultaneous operations may interfere with each other. Furthermore, it is difficult to do so within the constraints of a regular PHA study. Consequently, a SIMOP review should be performed prior to conducting simultaneous operations, for example, before restarting a process after shutdown. 

SIMOP reviews have been described in:

Simultaneous Operations (SIMOPS) Review: An important hazard analysis tool, Process Safety Progress, Volume 36, Issue 1, pages 62–66, March 2017.