According to IEC standards, which parameters must be verified in SIF calculations?

• A. PFDavg, SFF
• B. PFDavg, SFF, False Trip Rate
• C. System availability, PFDavg
• D. Lifecycle cost, PFDavg, SFF, False Trip Rate

Answer: (A)

The most accurate choice reflects the essential parameters of the Safety Instrumented Function (SIF) calculations as outlined in IEC standards. In the context of SIFs, the Probability of Failure on Demand (PFDavg) and the Safety Function Failure (SFF) are key metrics used to assess and measure the effectiveness and reliability of safety instrumented systems.

PFDavg provides an average probability that the safety function will fail to operate when called upon in a demand situation, while SFF indicates the reliability of the safety function in terms of its operational performance. These two parameters are crucial for determining whether a safety system meets the necessary performance and safety integrity level (SIL) for the specific application in question.

The other choices include additional parameters that may be relevant in specific contexts or analyses but are not required in the fundamental SIF calculations as specified by the IEC standards. For instance, the False Trip Rate and lifecycle costs pertain to broader risk management and economic considerations, rather than directly to the core SIF calculations as dictated by the standard. Thus, the focus on PFDavg and SFF as the primary verification parameters aligns with the standards set forth in functional safety regulations.