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IEC 61511 Edition 2 Update

Lesson 1

Process sector safety instrumented system standard IEC 61511 has been revised and updated in several areas, and as of the end of 2017, the old standard is now fully replaced.

What is the IEC 61511 safety life-cycle all about?

​The safety life-cycle was first defined in basic safety standard IEC 61508; a basic safety standard for use of electrical, electronic and programmable electronic equipment in safety applications. It was designed to account for the unpredictability of dangerous failure and specifically the recognition that failure can creep into systems from multiple sources and stages in system life, including hardware and software elements.


The IEC 61511 standard was published a few years later, based upon the same principles as IEC 61508. IEC 61511 applies specifically to system applications of Safety Instrumented Systems (SIS) in the process industry sector.


SIS life-cycle origins were influenced by many different organizations, including UK regulator HSE - the Health and Safety Executive. Research published in the book "Out of Control" concluded that accidents involving automated system failure were dominated by inadequate specification.


Out of control - HSE control system accident causes. Picture/video by eFunctionalSafety online learning for functional safety.

Although this was just one study, it did involve researching multiple accidents. It can be noted from the research conclusions that the hazard owner (often referred to as the duty holder) is responsible for setting requirements, as well as operating, maintaining and modifying an SIS after it has been placed in service.


So, even if a duty holder contracts-out the design and installation of an SIS, this particular study suggests that around 80% of the primary causes of system failure are introduced before or after the design and installation stage.


The safety life-cycle is, therefore, intended to counteract the possibility of systematic failure being introduced into a system at any point in its specification, design and engineering, testing, operation, maintenance or modification.

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