Standard

ISA 84.91.03

Published

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Abstract

This document applies to a wide variety of industries within the process sector, for example, chemicals, oil and gas, pulp and paper, pharmaceuticals, food and beverage, and nonnuclear power generation. This document does not address codes, regulations and other requirements that apply only to the nuclear power industry. This document specifies requirements for achieving functional safety using instrumented protection layers as LI-PLs that are not intended to conform to the ANSI/ISA-61511-1-2018 requirements for safety instrumented systems (SISs). NOTE LI-PLs that are not intended to conform to the ANSI/ISA-61511-1-2018 requirements for SISs are referred to as basic process control system (BPCS) protection layers in ANSI/ISA-61511. Requirements for the management of alarm systems are provided in ANSI/ISA-18.2, Management of Alarm Systems for the Process Industries, and are excluded from this standard. Requirements for cybersecurity of LI-PLs are provided in the ISA-62443 series and are excluded from this standard. NOTE Additional guidance on cybersecurity implementation is provided in ISA-TR84.00.09, Part 1: Cybersecurity Related to the Safety Lifecycle. Requirements for identifying and classifying protection layers as LI-PLs and their risk reduction claims are provided in ANSI/ISA-61511-1-2018 Clauses 8 and 9 and are excluded from this standard. This document addresses instrumented protection layers that are identified and classified by the authority having jurisdiction as LI-PLs, where the protection layer does not have a risk reduction claim greater than 10 and the protection layer is not intended to conform to the ANSI/ISA-61511-1-2018 requirements for SIS. NOTE ANSI/ISA-61511-3-2018 provides additional information on classification methods. NOTE 1 The risk reduction claim for a LI-PL might not be obvious (e.g., when using a risk graph). Depending on the classification method, the LI-PL might have been considered in determining the demand rate on the SIS or in meeting the minimum risk tolerance criteria. NOTE 2 A safeguard has no impact on the performance needed from a protection layer or the judgement that minimum risk tolerance criteria have been achieved. NOTE 3 “The effectiveness of some safeguards cannot be quantified due to lack of data, uncertainty as to independence or effectiveness, or other factors” (Layer of Protection Analysis: Simplified Process Risk Assessment, CCPS, 2001). This document identifies activities and requirements for a LI-PL throughout its life from identification to decommissioning. Requirements for human-machine interfaces for process automation systems are provided in ANSI/ISA-101.01, Human Machine Interfaces for Process Automation Systems, and are excluded from this standard.

Document information

  • Standard from ISA_AC
  • Published:
  • Version: 0
  • Document type: IS