What is IEC 61511?

What is IEC 61511? IEC 61511  is the functional safety standard for the process industry

IEC 61511:2016+A1:2017 was published as Edition 2 in 2016/2017. Edition 3 is already under consideration.

One of the objectives of IEC 61508 is to provide a framework for the development of industry sector international standards regarding functional safety. This ensures consistency with the approach and underlying principles laid down in IEC 61508 whilst allowing a more streamlined set of requirements to be tailored to a specific industry. Hence, IEC 61511 is the international functional safety standard for the process industry.

IEC 61511 is entitled ‘Functional Safety – Safety instrumented systems for the process industry sector’ and is published in three parts:

  • Part 1 (normative): Framework, definitions, system (hardware and software) requirements
  • Part 2 (informative): Guidance on how to apply Part 1
  • Part 3 (informative): Guidance on how to determine SIL requirements


The CASS Scheme Association has published several templates for the assessment of functional safety according to IEC 61511 (examples are CASS-511-FSM and CASS-511-FSA). These are free to use and available via our downloads page.

The standard is written specifically for those who deal with process application ‘Safety Instrumented Functions’ (SIFs), e.g., SIL determination analysts, SIF specifiers, system suppliers, engineering procurement contract (EPC) companies, installers, operators and maintainers. In terms of the Safety Instrumented System (SIS) design, IEC 61511 requires the component devices to be pre-compliant with IEC 61508 or be selected on a ‘prior use’ basis, and focuses on the system lifecycle activities needed to meet and maintain the functional safety requirements.

The 61508 Association includes many members who are specifically involved in the process industry and we are active in producing a range of guidance for those working in this sector. Our members reflect the entire equipment supply chain, consultants and process plant end-users, and we have particularly good relationships with regulators in the process industry. Our guidance often deals with the practical challenges that are not covered in standards such as how to deal with legacy systems, how process and machine safety come together, combining control and safety systems, etc.

Please see downloads for more information.

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