GB/T 21109.3-2026 Functional safety of safety instrumented systems in the process industry sector—Part 3:Guidance for the determination of the required safety integrity levels

Scope

This document provides the following relevant information:
—— The basic concept of risk and the relationship between risk and safety integrity (see A.4);
—— Determining tolerable risk (see Appendix K);
—— Different methods of determining the safety integrity level (SIL) of safety instrumented functions (SIFs) (see Appendices B to K);
—— The impact of multiple safety systems on calculating the expected risk reduction capability (see Appendix J).
This document:
a) Applies to the use of one or more SIFs to achieve functional safety for the protection of personnel, public facilities, or the environment;
b) Also applies to non-safety applications, such as asset protection;
c) Describes typical hazard and risk assessment methods that may be used when defining safety function requirements and the SIL of each SIF;
d) Describes the techniques and measures that can be used to determine the required SIL;
e) Provides a framework for establishing the SIL, but does not specify the SIL required for specific applications;
f) Does not provide examples of determining the requirements of other risk reduction methods.
Note 1: This document only provides specific examples of implementing the requirements of GB/T 21109 in certain situations. Users are required to select methods and techniques suitable for their own circumstances.
Appendices B to K describe various quantitative and qualitative methods and are simplified to illustrate their basic principles. These appendices are intended to explain the general principles of these methods but do not provide authoritative explanations.
Note 2: If you intend to use the methods given in these appendices, you need to consult the original materials referenced in the corresponding appendices.
Note 3: The SIL determination methods contained in this document may not be suitable for all applications. In particular, for high-demand

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