Safety integrity level analysis for processes: Issues and methodologies

The performance based ANSI/ISA S84.01 and IEC 61508 standard provide overal l risk based safety life cycle models for industrial processes. Among other guidance, they provide the basic methodology and guidelines for the identi fication of safety instrumented systems necessary for a process to meet the established target risk levels. In order to arrive at risk based solutions , many practical issues need to be addressed Such issues include identifica tion of target risk levels, identification of hazardous events associated w ith the process tinder consideration, establishing the existing risk associ ated with the process, and selection of appropriate non-instrumented and in strumented safety systems to meet the target risk. This paper outlines the basic methodology, and discusses some of the related issues mentioned above . Further, it provides a few methodologies to establish the requirements of the safety instrumented systems and their safety integrity levels.