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

Foreword

This document complies with the provisions of GB/T 1.1-2020 "Standardization Work Guidelines Part 1: Structure and Drafting Rules of Standardization Documents".

Drafting.

This document is Part 3 of GB/T 21109 "Functional Safety of Safety Instrumented Systems in Process Industries". GB/T 21109 has been...

The following sections were published.

---Part 1: Framework, Definitions, System, Hardware, and Application Programming Requirements;

---Part 2: Application Guidelines for GB/T 21109.1-2022;

---Part 3: Guidelines for determining required security integrity levels.

This document replaces GB/T 21109.3-2007 "Functional safety of safety instrumented systems in process industries - Part 3: Determining requirements".

The "Guidelines on Security Integrity Levels" differs from GB/T 21109.3-2007 in that, aside from structural adjustments and editorial changes, the main technical changes are as follows.

as follows.

---Added explanations of the appendix to this document and the application of specific methods (see Chapter 3);

---Appendix A has been modified. The original Chapter 3 has been reorganized into Appendix A of this document, and a section on "Dangerous Events and Dangerous Situations" has been added.

Description of "situation and injury incident" (see Appendix A, Chapter 3, 2007 edition);

---The legend regarding the relationship between GB/T 21109, DINV19250, and VDI/VDE2180 has been removed (see the 2007 edition).

Figure E.2).

This document adopts IEC 61511-3:2017 "Functional safety - Safety instrumented systems in process industries - Part 3: Determining requirements" the guidelines for security integrity levels.

The following editorial changes have been made to this document.

---To harmonize with existing standards, the standard name has been changed to "Functional safety of safety instrumented systems in the process industry - Part 3: Safety".

Guidelines for defining required security integrity levels.

Please note that some content in this document may involve patents. The issuing organization of this document assumes no responsibility for identifying patents.

This document was proposed by the China Machinery Industry Federation.

This document is under the jurisdiction of the National Technical Committee on Standardization of Industrial Process Measurement, Control and Automation (SAC/TC124).

Introduction

In process industries, Safety Instrumented Systems (SIS) used to perform Safety Instrumented Functions (SIFs) have been in use for many years. To ensure the instruments are effective...

For safety instrument functions, the most important thing is that the instrument must meet certain minimum standards and performance levels.

GB/T 21109 describes the application of safety instrumented systems in the process industry. It involves performing a process hazard and risk assessment to derive...

Specifications for safety instrumented systems. The contributions of other safety systems are considered only when relevant to the performance requirements of the safety instrumented system.

The instrumentation system includes all devices and subsystems, from sensors to final components, necessary to perform safety instrumented functions.

GB/T 21109 includes the following parts.

---Part 1: Framework, Definitions, System, Hardware, and Application Programming Requirements. The aim is to define the specifications, design, and requirements for Safety Instrumented Systems (SIS).

Design, installation, operation, and maintenance requirements to ensure that the system enables the process to reach or remain in a safe state.

---Part 2: Application Guidelines for GB/T 21109.1-2022.The purpose is to provide guidance on safety devices as defined in GB/T 21109.1.

Guidelines for the specification, design, installation, operation, and maintenance of instrumented safety systems and related safety instrumented systems.

---Part 3: Guidelines for Determining Required Safety Integrity Levels. The aim is to determine the safety integrity level of safety instrumented functions.

Various different methods.

GB/T 21109 includes two concepts that form the basis of the application. security lifecycle and security integrity level.

GB/T 21109 addresses safety instrumented systems based on the use of electrical (E)/electronic (E)/programmable electronic (PE) technologies. In logic solution...

When the calculator uses other technologies, the basic principles of GB/T 21109 must be applied to ensure that functional safety requirements are met. GB/T 21109 it also covers sensors and final components of safety instrumented systems, regardless of the technology used. GB/T 21109 is within the framework of GB/T 20438.

It is designed specifically for process applications within the framework.

GB/T 21109 provides a method for achieving minimum standards in SIS safety lifecycle activities. This method enables reasonable consistency.

The use of technical strategies.

In most cases, inherent safety process design can achieve good safety. When necessary, one or more protection systems can be combined.

To mitigate identified residual risks, a comprehensive approach is needed. Protection systems can rely on various technologies (chemical, mechanical, hydraulic, pneumatic, electrical, and electromechanical).

(Including programmable electronic components). Any security strategy needs to be determined for each individual SIS, taking into account other protection systems.

To implement this method, GB/T 21109 requires.

---Perform a hazard and risk assessment to determine overall safety requirements;

---Assign safety requirements to the safety instrumented system;

---Works within a framework that applies to all instrumentation measures for achieving functional safety;

---Details how certain activities (such as safety management) can be used, which are applicable to all approaches to achieving functional safety;

---Includes all SIS security lifecycle phases from initial concept, design, implementation, operation and maintenance until decommissioning;

--- Enables existing or new national standards specifically for process industries to be harmonized with GB/T 21109.

GB/T 21109 aims to achieve a high degree of consistency in the process industry (such as basic principles, terminology, and information). This will bring safety and it has both economic and social benefits.

Regarding authority, process safety design, process safety management, or other [mechanisms] have been established at the management level (such as national, provincial, or autonomous region levels).

Under specified circumstances, these requirements should take precedence over those defined in GB/T 21109.

GB/T 21109.3 provides guidance on determining the SIL (Safety Integrity Level) requirements in hazard and risk assessments. This document aims to provide guidance on various hazards.

A broad overview of risk assessment methods is provided. However, the information provided is not detailed enough to implement these methods.

First, we need to review the concept and determination requirements of SIL given in GB/T 21109.1-2022.GB/T 21109.3...

The informative appendix describes the following.

Appendix A provides information common to each hazard and risk assessment method shown in this document.

Appendix B provides an overview of semi-quantitative methods for determining the required SIL.

Appendix C provides an overview of the security layer matrix method used to determine the required SIL.

Appendix D provides an overview of the method for determining the required SIL using a semi-quantitative risk map approach.

Appendix E provides an overview of the method for determining the required SIL using the qualitative risk mapping approach.

Appendix F provides an overview of the method for selecting the required SIL using the Layer of Protection Analysis (LOPA) method.

Appendix G provides a protection layer analysis using a risk matrix.

Appendix H provides an overview of the qualitative methods used for risk assessment and SIL allocation.

Appendix I provides an overview of the basic steps involved in designing and correcting risk maps.

Appendix J provides an overview of the impact of multiple security systems on the SIL required for a given requirement.

Appendix K provides an overview of the tolerable risk and ALARP concepts.

Figure 1 illustrates the overall framework of GB/T 21109.1, GB/T 21109.2, and GB/T 21109.3, and points out that GB/T 21109...

The role it plays in achieving functional safety in SIS.

Figure 1 Overall framework of GB/T 21109 standard

Functional safety of safety instrumented systems in the process industry Part 3: Determining the Required Security Integrity Level guide

1 Scope

This document provides the following relevant information.

---Basic concepts of risk and the relationship between risk and safety integrity (see A.4);

---Determination of tolerable risk (see Appendix K);

---Different methods for determining the Safety Integrity Level (SIL) of a Safety Instrumented Function (SIF) (see Appendices B through K);

---The impact of multiple security systems when calculating the expected risk reduction capability (see Appendix J).

This document.

a) Applicable to the use of one or more SIFs to achieve functional safety in order to protect people, public facilities, or the environment;

b) It is also applicable to non-security applications, such as asset protection;

c) Describes typical hazard and risk assessment methods that may be used when defining safety functional requirements and the SIL for each SIF;

d) Describes the techniques and measures that can be used to determine the required SIL;

e) Provides a framework for establishing SIL, but does not specify SIL requirements for specific applications;

f) No examples were provided to identify the requirements for other risk reduction methods.

Note 1.The appendix to this document only provides specific examples of implementing the requirements of GB/T 21109 under specific circumstances. Users need to select the methods and procedures suitable for their own situations.

technology.

Appendices B through K describe various quantitative and qualitative methods, simplified to illustrate their basic principles. These appendices are for...

This explains the general principles of these methods but does not provide authoritative explanations.

Note 2.If you intend to use the methods given in these appendices, you should consult the original materials cited in the corresponding appendices.

Note 3.The SIL determination method contained in this document may not be applicable to all applications. In particular, for high-demand or continuous operation modes, specific methods may be required.

The technology or unspecified additional factors.

Note 4.When using the methods described in this document, if their potential limitations are exceeded and factors such as common causes, failure margins, and the overall application are not properly considered, they may lead to problems.

Factors such as a lack of prior experience in the methods used, and the independence of the protective layer, may lead to non-conservative results. See Appendix J.

Figure 2 provides an overview of typical protective layers and risk reduction measures.