Strictly speaking in terms of concepts, ESD and SIS are not entirely equivalent

Thread Content

Generally, people consider ESD to be the same as SIS; they are equated. In fact, this understanding is problematic. In terms of timing, ESD was introduced in the 1980s, primarily for emergency shutdown. The SIS concept was introduced around the year 2000. SIS is a system of SIF; SIF determines the required probability of hazardous failures through analysis and the allocation of safety functions. For SIL1, the PFD is less than 0.1, while ESD does not have such requirements. For example, in the case of pump cavitation, to protect the pump, it is possible to activate an emergency interlock to stop the pump when the liquid level is low. Previously, it was possible to implement ESD measures or not, but now whether to incorporate SIS depends on the results of such analysis. In other words, SIS standardizes ESD; it’s not done arbitrarily, but there are procedures and standards to follow. It’s roughly like a plate of scrambled eggs; SIS standardizes the quality of such scrambled eggs by assigning them stars. Of course, there are other aspects of standardization as well. Furthermore, ESD is a concept that arises from the perspective of process production status, whereas SIS is a system concept, and their conceptual meanings are also different.