scope:

ISA-TR84.00.02-2022 is informative and does not contain any mandatory clauses. ISA-TR84.00.02-2022 is intended for use by those with a thorough understanding of ANSI/ISA-61511-1:2018. The user is referred to ANSI/ISA-61511-3:2017 and to the Center for Chemical Process Safety books, Guidelines for Hazard Evaluation Procedures and Guidelines for Initiating Events and Independent Protection Layers in Layer of Protection Analysis, for guidance on assigning the SIL.

Prior to proceeding with use of ISA-TR84.00.02-2022, the hazards and risk analysis and the allocation of safety functions to protection layers should be completed and the following information provided:

• The functional requirements of the safety instrumented function (SIF)

• The integrity requirements of the SIF

• The spurious trip rate constraints on the SIF

ISA-TR84.00.02-2022 provides guidance on the following:

• Assessing random and systematic failures, classifying failure modes, and estimating the failure rates for individual devices of a SIF;

• Assessing the impact of diagnostic and automation asset integrity (AAI) choices on the performance of the SIF and its devices;

• Assessing and estimating the potential for common cause and common mode failures; and

• Verifying that the SIF achieves a specified safety integrity level (SIL) and spurious trip rate.

ISA-TR84.00.02-2022 provides guidance on techniques for evaluating the following:

• Average probability of failure on demand (PFD) and probability of failure per hour (PFH)

• Spurious trip rate