Developments in SIL determination

Safety integrity level (SIL) determination has become increasingly required as part of the design and operation of safety instrumented systems (SIS). Yet many engineers and managers in industry have only a limited knowledge of assessment methods. The methods themselves are evolving as experience is gained and pooled across the functional safety community. Consequently, the generally favoured approach to SIL determination held when IEC 61508 was published around five years ago has already altered. Various methods have been developed and applied with differing degrees of success. The dominant methods that have emerged and considered here are risk graphs, LOPA and fault tree analysis.