ISA TR84.00.02

Abstract

ISA-TR84.00.02-2015 is informative and does not contain any mandatory clauses. ISA-TR84.00.02 is intended for use by those with a thorough understanding of ISA-84.00.01-2004 Part 1. This document assumes that a SIS is required. It does not provide guidance on the hazard and risk assessment used to identify the need for a SIS. The user is referred to ISA-84.00.01-2004 Part 3, and CCPS&#8217;s <em>Hazard Evaluation Procedures and Layers of Protection Analysis</em>:<em>Simplified Risk Assessment</em> for guidance on assigning the SIL. <br>Prior to proceeding with use of ISA-TR84.00.02-2015, the hazards and risk assessment and the allocation of safety functions to protection layers should be completed and the following information provided: <br>At least one SIF is required <br>The functional requirements of the SIF <br>The integrity requirements of the SIF <br>ISA-TR84.00.02-2015 provides guidance on different issues that impact SIL verification: <br>Assessing random and systematic failures, classifying failure modes, and estimating the failure rates for individual devices of an SIF; <br>Assessing the impact of diagnostic and mechanical integrity choices on the performance of the SIF and its devices; <br>Assessing and estimating the potential for common cause and common mode failures; and Verifying that the SIF achieves a specified SIL and spurious trip rate. <br>ISA-TR84.00.02 provides guidance on techniques for evaluating the following: <br>Average probability of failure on demand for low demand mode Spurious trip rate <br>There are four topics that are being held until the next revision of ISA-TR84.00.02. Until then, the reader should refer to ISO 12489 for appropriate methodologies. </span><ul> <li> <br>Modeling of continuous and high demand mode systems</li> <li> <br>Understanding proof test effectiveness and how this is addressed by design and mechanical integrity practices</li> <li> <br>Understanding how to model common cause and systematic contribution to the failure of subsystems and systems and to the occurrence of the hazardous event</li> <li> <br>Expanding the discussion of common cause and systematic error to address these issues across the entire lifecycle</li></ul><br>