ISA TP-973013

The new ANSI/ISA S84.01 standard requires that companies assign a target safety integrity level (SIL) for all safety instrumented systems (SIS) applications. The assignment of the target SIL is a decision requiring the extension of the process hazards analysis (PHA) process to include the balance of risk likelihood and severity with risk tolerance. This paper examines the three most common techniques currently utilized by many process industries: the risk matrix, the IEC 61508 methodology, and a strict policy choice.