SILniveauer

SILniveauer, or Safety Integrity Levels, are a measure used in functional safety to quantify the reliability of safety-related systems and the risk reduction they provide for a safety function. They are defined by IEC 61508 and used in related standards such as IEC 61511 for process industries. The levels indicate the likelihood that a safety function will perform correctly when required.

There are four SILs: SIL 1, SIL 2, SIL 3 and SIL 4. Each higher level represents a greater degree of risk reduction and requires more stringent design, verification, and maintenance. The assignment of a SIL to a safety function is determined through a risk assessment that considers the hazard, exposure, and severity, and defines target metrics such as the probability of failure on demand (PFD) or the probability of a dangerous failure per hour (PFHD) appropriate to the mode of operation.

To achieve a given SIL, organizations implement lifecycle processes including rigorous design, verification, and validation; use of proven architectures with redundancy and diagnostics; diversity to reduce common-cause failures; protection against safe failure modes; and robust software engineering. Regular proof testing and diagnostics coverage are typically required.

SIL is used across industries, notably oil and gas, chemical processing, power generation, and automation. It is complementary to other safety standards such as ISO 13849-1's Performance Levels in machinery contexts. Understanding the required SIL helps guide system design, supplier selection, and maintenance regimes, ensuring that safety functions meet the intended level of risk reduction.