CCPS Safety Beacon – Safety Instrumented Systems

Every month the Center for Chemical Process Safety publishes out a ‘Safety Beacon’ poster that addresses some chemical process safety issue. This month the Safety Beacon deals with Safety Instrumented Systems (SIS); automated systems that are put into place to protect chemical processes from ‘upset’ conditions that can lead to an unsafe release of hazardous chemicals. Typically these systems are physically separated from ‘normal’ control system so that damage or an attack to that system would not affect the SIS. They are also provided with automatic backup power so that they continue to operate in the event of a power failure. These system consist of three separate parts. A sensor system is employed to detect the abnormal condition. A logic controller compares the output of the sensor to programmed set of pre-defined upset conditions. Finally a control device is employed to counteract or correct the process upset. SIS as Security Systems High-risk chemical facilities that already employ SIS technologies should take a hard look at those systems to see if they have some applicability to the facility’s site security plan. Systems that would limit the amount of a toxic release COI that would reach the fence line could be listed as a security system under RBPS #4 {Metric 4.5: “process controls or systems that rapidly render the critical asset nonhazardous even if a breach of containment were to occur” (pg 58, RBPS Guidance document)}. Fire suppression systems that would prevent or limit a flammable release COI from forming a detonatable cloud upon release should also be reportable under these circumstances. Similarly, facilities should also look to designing similar stand alone Security Instrumented Systems to perform a dedicated security function. The example that DHS uses in Metric 4.5 is ‘a rapid chemical neutralization system”, but any system that mitigates the effects of a release would serve the same purpose.