Functional safety plays a key role in protecting modern industrial facilities from catastrophic events. A major component of functional safety is the Safety Instrumented System (SIS), which implements Safety Instrumented Functions (SIFs) to bring a process to a safe state when deviations occur. Safety Integrity Level (SIL) is a measure of the reliability of these SIFs.

SIL Selection (LOPA)

Before designing an interlock, we must determine the required safety performance (SIL 1, SIL 2, or SIL 3). This is typically done through a Layer of Protection Analysis (LOPA), a semi-quantitative method that assesses the risk of a scenario and determines what risk reduction is required from the safety instrumented loop after taking credit for other protection layers (like safety valves or operator response).

SIL Verification

Once the design is established, we perform SIL Verification to ensure the physical loop (sensor, logic solver, final element) meets the target reliability. Verification involves calculating the Probability of Failure on Demand (PFDavg) and checking architectural constraints (hardware fault tolerance) according to IEC 61508 / IEC 61511 standards. High-quality calculation models ensure that safety systems operate precisely when needed, preventing major accidents.