SIL verification is a method to show that the Safety Instrumented System (SIS) meets the requirements of the particular SIL level. SSC has extensive expertise in conducting SIL verification studies.
Four criteria are verified:
SIL verification criterion 1. The SIS should be functional. That means: upon functioning of the SIS, the hazardous scenario will be avoided.
SIL verification criterion 2. The SIS should be independent of the control system. It often means that there should be separate measurements, apart from the present control measurements and alarm connections.
SIL verification criterion 3. Safety components must meet the architectural requirements of the appropriate SIL. The IEC standards indicate when a single or redundant component should be applied. That depends on the complexity of the components and/or experience with it.
SIL verification criterion 4. Safety systems (SIS) must have a sufficiently low probability of failure on demand. For instance, the probability of failure on demand (PFD) for a SIL2 system should be below 10-2.
The PFDâ€™s are calculated with the advanced SSC software SILK. This software uses Markov models and is developed by SSC in collaboration with the Technical University of Eindhoven. Failure rate data are derived from generic sources (e.g. Oreda and Sintef), specific failure rate data (e.g. determined by TÃœV or EXIDA) or SSC estimated based on available information and experience.
Read more about SIL Verification.
A SIS build up from a sensor, Logic Solver (PLC) and a Final Element (often a valve).
Column November 2010
Only 44% of Major Hazards companies apply SIL !
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