New digital technology now makes it feasible to integrate process control and safety instrumented functions within a common automation infrastructure. While this can provide productivity and asset management benefits, if not done correctly, it can also compromise the safety and security of an industrial operation. Cyber security and sabotage vulnerability further accentuate the need for securing the Safety Instrumented System (SIS).
Certainly, a “common platform” approach, using similar hardware and software dedicated for control and safety functions, respectively, can provide the potential for cost savings. However, it is widely acknowledged that utilizing separate, independent, and diverse hardware/software for safety and control is the optimal way to protect against potentially catastrophic common cause and systematic design and application errors.
Different vendors offer varied degrees of integration and solutions. The question is how to provide an integrated control and safety solution with advanced functionality and productivity, without compromising safety and security. So where do users draw the line?
A TÜV certification of the hardware/software systems to IEC 61508 specifications carries significant advantages, but should this be the only criterion? How does a TÜV certificate extend to the plants overall assignment of risk reduction credits for all independent layers of protection (IPL)? Control system embedded safety logic solvers may actually increase the SIL requirements of the SIF if no credit is allowed for the DCS as an IPL.
This paper discusses engineering best practices in integrating control and safety in a secure manner, while maintaining independent layers of protection. Potential benefits and side effects of the different approaches are highlighted within the paper.