How reliable is your SIL verification actually?

Keywords: IEC 61508, IEC 61511, Failure rate data, Certification, FMEDA, Verification

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Abstract:

Nowadays most process plants are being built according the IEC standards for functional safety. The IEC 61511 standard describes various methods to determine the required risk reduction of Safety Instrumented Functions (SIF's) based upon the actual risk associated with a certain hazard scenario and the tolerable risk criteria. The required risk reduction of a SIF has to be confirmed by a Safety Integrity Level (SIL) verification calculation. How reliable is this calculation actually ?

The objective of this paper is to give the reader a better understanding of the possible pitfalls in the SIL verification calculation. The paper will first discuss the reliability requirements of the IEC standards on Functional Safety, which leaves space for different implementations. Secondly, it will discuss the reliability of the failure rate data as supplied by the instrument vendors or third parties, which are sometimes too good to be true. Thirdly, the paper will discuss the reliability of the Failure Modes, Effects and Diagnostic Analysis (FMEDA) for components, which are located in the harsh environment of a process plant. Fourthly, the paper will discuss what the required reliability of the SIL verification should be and how to obtain that. Finally the concluding remarks are presented. © 2010 Inside Publishing. All Rights Reserved.

Volume: 2010   Issue: 1
EUR 6.88
(Pages: 10, Words: 4586)

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