Overcome the challenges of implementing safety instrumented systems for reactive processes

Abstract Safety instrumented systems (SISs) are generally used against process safety hazards with the potential to severely injure, or even kill, personnel or members of the public. Reactive processes are a common application for SISs due to the potential for significant energy release during the reaction, which tends to cause catastrophic rupture of the vessel. While some applications can address the reactive hazard by closing emergency block valves, others may require blowdowns, kill agents, and other complex response actions. The more that needs to be done to address the reaction, the more complicated the SIS, resulting in the need for more experienced process engineering involvement to get the design right. The protection layers allocated to manage the risk of reactive applications typically focus on the prevention of runaway reactions by ensuring that the temperature or pressure never reach an unsafe state. This seems straightforward, but reactive processes can respond to loss of control in ways that are more difficult to predict, so the specification of trip point, response time, and sensor architecture requires more analysis than typical SIS. This paper discusses some of the unique challenges posed by reactive applications and provides examples to illustrate how to overcome these challenges.