exida explains Blog

In several of our technical papers over the years, we have noticed that failure rates for the manufacturer, model number are different at different sites, even when the processes were quite similar.  When I have mentioned this to end users and manufacturers, often the response is “Yes, I have…

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It’s very interesting to me to find that people are still using excel to do PFD calculations.  Whereas this is probably okay for simple single element architectures (i.e. single sensor, single logic solver and single final element), it becomes extremely complicated when dealing with redundant architectures.  Moreover, for performing…

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It’s hard to believe that the IEC61511 standard has been in existence since 2003, and most companies operating in the process, chemical, and refining industries (or any other hazardous process manufacturer) have adopted its practices.  It’s also significant that any plants that were built back then with a…

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I did my homework, purchased certified devices, and specified physical redundancy. I expected an uneventful SIL Verification but the assessor is telling me that I have functions failing Architectural Constraints in the sensor and final element groups. How can that be? 

Low demand mode Safety Instrumented Function (SIF)…

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When the latest edition of IEC61511 was published in 2016, one of the key changes was the emphasis on competency and some further guidance on what this means.  The relevant clauses in the IEC61511:2016 are 5.2.2.1 to 5.2.2.3 under Clause 5.2.2: Organization and Resources.  I am often asked what…

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This is an intriguing question.  One that I often ask my classes when I’m teaching our FSE100 Functional Safety course. Very often, they do not know or do not fully understand what this means and why it is important.

The IEC61511 standard requires that any failures that occur within the…

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I’ve been following some discussions from one of the online forums regarding competency and it’s clear from the correspondence that the issue of competency is still very subjective.  It made me think about “what is competency?” To me it’s a blend of knowledge and experience and just how well…

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This is a question I have often been asked in the past.  Most people I have spoken with don’t have a good appreciation of what this means and the purpose.  From the IEC61511 perspective, designers of Safety Instrumented Systems (SIS) are required to justify the selection…

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The new release of IEC61511:2016 has caused some confusion when it comes to the Functional Safety Assessments (FSAs). Which ones are mandatory?

The confusion comes from the wording in the standard and the clarifications in the notes. The relevant clause in the standard 5.2.6.1.4 states:

A FSA team…

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Site audits have shown many differences in how things are done from site to site. This impacts many variables in a safety instrumented system!

A key metric for process industry designs is called average Probability of Failure on Demand (PFDavg).  After several studies of many field failure and proof…

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It’s interesting to note that with the release of the 2016 edition of IEC61511, there’s more emphasis being placed on the need for better functional safety management.  Having taught many courses on Functional Safety over the past few years, I find that most of the…

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This is a topic which comes up time and again, especially when reviewing legacy systems.  Although IEC61511 doesn’t preclude the use of shared devices, it does however provide guidance under Clause 11 of what the constraints are.  Even though the Safety Instrumented System (SIS) and Basic Process Control System (BPCS)…

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