ALLOCATION OF SAFETY FUNCTIONS TO PROTECTION LAYERS
The standards recognise that safety functions can be required to operate in quite different ways. In particular they recognise that many such functions are only called upon at a low frequency / have a low demand rate.
IEC 61511 offers the following as tools for SIL Determination:
- Semi-quantitative method
- Safety layer matrix method, described as a semi-qualitative method
- Calibrated risk graph, described in the standard as a semi-qualitative method, but by some practitioners as a semi-quantitative method
- Risk graph, described as a qualitative method
- Layer of protection analysis (LOPA)
Risk graphs and LOPA studies are popular methods for determining SIL requirements, particularly in the process industry and oil and gas sector.
WHAT WE DO
Using experience TUV Certified Engineers to facilitate and scribe Risk graphs and LOPA studies, either as part of the design of the process plant or part of a modification to an installed system. We ensure we utilise the cause consequence pairs from the HAZOP giving that linked life cycle approach.
The output from the SIL Determination study would be a required risk reduction per Safety Instrumented Function (SIF).
A TYPICAL SIL DETERMINATION STUDY WILL BE CONDUCTED BY:
- focus on a specific hazardous event
- identify initiating causes and frequencies
- identify protective measures
- assess the level of risk and the contribution to risk reduction required (if any) from a SIF to meet the required risk target(s)
- evaluate whether the risk is reduced to ALARP
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