IEC EN 61511-3 Functional Safety - Safety Instrumented Systems for the Process Industry Sector - Part 3: Guide to Determining the Required Safety Integrity Levels

The standard “IEC EN 61511-3 Functional safety - Safety instrumented systems for the process industry sector - Part 3: Guide to the determination of required safety integrity levels” developed by the International Electrotechnical Commission (IEC) provides information on:

• Basic concepts of risk and its relationship to security integrity
• Determining tolerable risk
• A number of different methods for determining the level of security integrity for security instrumented functions
• The impact of multiple security systems on calculations that determine the ability to achieve the desired risk reduction.

This standard specifically:

• Functional safety is applicable when one or more safety integrity levels are used to ensure the protection of personnel, the general public or the environment.
• It can be applied in non-security applications such as asset protection.
• It shows the safety functional requirements of each safety integrity level and typical hazard and risk assessment methods that can be performed to define the safety integrity level.
• Demonstrates techniques and measures used to determine the required level of security integrity
• It provides a framework for establishing the level of security integrity but does not specify the level of security integrity required for specific applications.
• It does not provide examples to identify requirements for other risk reduction methods.

The examples given in the annexes to this standard are intended only as case-specific examples for applying the requirements of IEC EN 61511 in a particular situation and the user should ensure that the methods and techniques chosen are appropriate for their own situation.

Appendix B - Inter-Appendixes illustrate the quantitative and qualitative approaches and are simplified to illustrate the basic principles. These appendixes are included to illustrate the general principles of a range of methods but do not provide a definitive explanation.

Those considering applying the methods outlined in these appendices may refer to the source material referenced in each appendices.

The safety integrity level determination methods included in IEC EN 61511-3 may not be suitable for all applications. In particular, for high demand or continuous operation mode, specific techniques or additional factors not shown may be required.

The methods shown here may lead to non-conservative results when used beyond their fundamental limits and when factors such as common cause, fault tolerance, holistic considerations of the application, lack of experience with the method used, independence of protection layers, etc. are not properly taken into account.

An overview of typical layers of protection and risk mitigation tools is provided as provided in the standard.

Annexes to the IEC EN 61511-2 standard include:

• Annex A (informative): Risk and security integrity - General guidance
• Appendix B (informative): Semi-quantitative method - Event tree analysis
• Appendix C (informative): Security layer matrix method
• Appendix D (informative): A semi-qualitative method: calibrated risk plot
• Appendix E (informative): A qualitative method: risk graph
• Annex F (informative): Protection layer analysis
• Annex G (informative): Protection layer analysis using risk matrix
• Annex H (informative): A qualitative approach to risk estimation and safety integrity level assignment
• Annex I (informative): Designing and calibrating a risk chart
• Annex J (informative): Multiple security systems
• Annex K (informative): Concepts of risk as low as reasonably practicable and tolerable

Among the numerous testing, measurement, analysis and evaluation studies that our organization has provided for businesses in various sectors, it also provides testing services defined in the standard “IEC EN 61511-3 Functional safety - Safety instrumented systems for the process industry sector - Part 3: Guide to determining the required safety integrity levels” with its trained and expert staff and advanced technological equipment.