In LOPA, safety instrumented systems (SIS) relate to what type of reliability?

In Layer of Protection Analysis (LOPA), safety instrumented systems (SIS) are crucial components related to the reliability of systems intended to prevent or mitigate hazardous occurrences. SIS are specifically designed to provide an additional layer of protection in the event of a process safety incident and ensure that dangerous conditions are detected and addressed effectively.

The reliability of SIS must meet stringent requirements to ensure that they function correctly during safety-critical scenarios. This reliability is measured through various metrics, including probability of failure on demand (PFD), which reflects the likelihood that the SIS will fail to operate as intended when needed. By focusing on preventing hazardous occurrences, SIS play a vital role in reducing risk and protecting personnel, the environment, and assets.

In contrast, systems designed to enhance productivity, backup systems for failures, or communication systems during emergencies do not capture the primary function of SIS within the framework of LOPA, which is centered around risk reduction and safety. Therefore, the focus on the reliability of systems to prevent or mitigate hazards underscores the central purpose of SIS within the context of LOPA.