The SIL concept

SIL stands for ‘Safety Integrity Level’. The concept is described in the international standards: IEC 61508 /61511. It is ‘a risk based approach’, leading to the need for risk reduction with the aid of Safety Instrumented Systems (SIS). The SIL represents the necessary risk reduction. The risk analysis is called SIL Classification. SIL Classification is normally performed in combination with a HAZOP.

The SIL includes requirements for the Safety Systems (e.g. Probability of Failure on Demand- PFD). The standards require a transparent demonstration that the SIL requirements are fulfilled. This is called "SIL Verification".

Although not formally required by law, in practice the SIL concept needs to be used. Unless the company has an alternative, equivalent approach. But that is usually not available.

For more than10 years, SSC is the specialist in The Netherlands with respect to both SIL  Classification and  SIL Verification.
For assistance with SIL implementation in your company: please contact us.

Risk Reduction  Factors and failure probabilities for a certain SIL.

Safety integrity level (SIL) PFD (for low demand rates) Risk Reduction Factor (RRF)
4 10-5 < PFD 10-4; 10.000 < RRF < 100.000
3 10-4 < PFD 10-3 1000 < RRF < 10.000
2 10-3 < PFD 10-2 100 < RRF < 1000
1 10-2 < PFD 10-1 10 < RRF < 100
Only 44% of Major Hazards companies apply SIL !

Column November 2010
Only 44% of Major Hazards companies apply SIL !

The Dutch Labor Inspectorate performed an inspection of 58 Major Hazards companies . This was a follow up of the BP Texas City disaster. Recently, a report with the inspection results have been p...

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