Trying to understand (SIS) Safety Instrumented Systems?

As automation process engineers, we know about safety instrumented systems in process industry, but safety systems are in multiple industries and applications with their own safety standards and their own Safety Integrity Levels (SIL). 

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IEC 61508 standards started in the mid 80’s and the seven parts were published between 1998 and 2000.   Edition 2.0 of the standard was launched in 2010. 

 This standard covers all safety-related systems electrotechnical in nature (electromechanical systems, solid-state electronic systems and computer-based systems).  IEC 61508 is generic and can be applied to all kinds of industries (no military applications, nor aerospace).  IEC 61508 is like an “umbrella” that covers different industries and applications, and their objective was that different industry sectors wrote their own industry standard in accordance with the concepts presented in the standard. 

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The title of the IEC61508 standard is: “Functional safety of electrical/electronic/programmable electronic safety-related system”.

Nowadays, IEC 61508 is commonly used to certify devices for a given SIL level.  Certification involves the assessment of specific design details as well as the assessment of the safety management of the product manufacturer and the competence of the people involved in the design and product manufacturing. 

The standard concerns those failures that could affect the safety of persons and/or the environment, but also may be applied to business loss and asset protection cases.  It focuses attention on the risk-based safety-related system design, putting attention on the details that are vital to any safe system design.  The design must demonstrate that it meets particular performance measurements and one of these measurements is based on the process equipment probability of failure.

There are many things that could go wrong when designing and manufacturing a product including how a safety system is implemented/integrated and also how you use it.

 Generic standard for multiple sectors:

  –  IEC 61508 is aimed to Manufacturer and suppliers of devices.

For industry process sector:

  –  IEC 61511 is oriented to SIS designers, Integrators and users.

The standards are “good engineering practice” to achieve Functional Safety for Safety Systems.  To ensure this, it is necessary to consider every phase from the initial concept through the development of the safety requirements, design, construction and installation, to maintenance and modifications; this is the “safety life-cycle”. It facilitates the building and implementation of safety systems to define safety performance levels and lessens the risk of an accident.

The topic of Safety Systems is very important and I will focus my next blog more on the explanation of the IEC 61511.

Schneider Electric has a completed Process Safety offer, which included: HSBY Safety Quantum PLC’s, and Safety expertise and project execution experience.

Do you have some experience with Safety Systems?