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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Entries tagged with: SIS
- by Dr. Steve Gandy, CFSP
- Tuesday, April 08, 2025
- Functional Safety
What is Prior Use Justification & How To Achieve it?
- by Dr. Steve Gandy, CFSP
- Thursday, February 22, 2018
- Functional Safety
What Managers Need To Know About Functional Safety
If you’re a manager in the process industries then you should be familiar with the concept of Functional Safety and the need to have well defined processes and procedures in place. If not, then how else will you be able to ensure that your Safety Instrumented System and plant…
- by Dr. Steve Gandy, CFSP
- Thursday, June 22, 2017
- Functional Safety
Why Run-to-Fail Is Not A Good Maintenance Strategy For SIS
One of the fundamentals of the Probability of Failure on Demand (PFDavg) calculations in SIL verification analysis, is the concept of a constant failure-rate during useful life of the equipment. Probabilistic calculations assume that the failure rate of the devices used in a Safety Instrumented System (SIS)…
- by Dr. Steve Gandy, CFSP
- Tuesday, March 30, 2021
- Functional Safety
Why Sharing Components Between SIS & BPCS Is Not A Good Idea
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)…