Many process automation systems (DCS and PLC alike) incorporate Safety Instrumented Systems (SIS) as an integral part of the system. These systems are Safety Integrity Level (SIL)-certified, exactly like older, separate systems. In order to illustrate the undiminished safety integrity of these fully integrated automation systems, they are described as "integrated, but separate."
Proponents of these systems say that they not only maintain undiminished safety integrity, but they also enhance operation by addressing additional sources of risk and providing a comprehensive platform for process safety management, including safety engineering tools, operation management tools alarm management and maintenance.
The challenge for the user is to assess how these Integrated Safety Systems can still act as a completely independent layer of protection.