Safety Integrity Levels in Design

Abstract

The hazards identified with a new or modified chemical or petroleum refining process can be mitigated in numerous ways. If a system cannot be designed so that it is inherently safe, then other safeguards such as instrumented systems, mechanical controls or operating procedures need to be implemented. If an instrumented system is to used to mitigate the hazard then some consideration must be given towards the integrity of this system based upon the risk presented by the hazard. Based upon recent ISA standards, the integrity level of this instrumented system must be specified so that the corresponding probability of failure on demand can be achieved. This paper discusses the overall process of mitigating hazards including the role of safety integrity levels for instrumented systems.