Performance-based standards: safety instrumented functions and safety integrity levels

This paper discusses two international performance-based standards, ANSI/ISA S84.01 and IEC d61508 and the requirements they place upon companies that rely on electrical, electronic and programmable electronic systems to perform safety functions. Performance-based regulations are also discussed and common safety elements between the standards and regulations are identified. Several risk analysis techniques that can be used to comply with the aforementioned requirements are discussed and a simple example is used to illustrate the use, advantages and disadvantages of the techniques. The evaluation of safety integrity level (SIL) of the Safety Instrumented System (SIS) in terms of the probability to fail to function is outside the scope of this paper.