The standard IEC 62443: Security for industrial automation and control systems (IACS) proposes the assignment of security levels 1-4 to IACS zone provisions.

The temptation is to see these as comparable to the four Safety Integrity Levels of IEC 61508, but this would be a mistake; there is no equivalence. This paper will explore the relationship between SL and SIL and show how they may be related through an appropriate risk calibration for a given enterprise.

Harvey T. Dearden BSc CEng FIET FIMechE FInstMC FIChemE

Harvey T. Dearden is Engineering Director of HTS Engineering Group and a Director of SISSuite Ltd. and Time Domain Solutions Ltd. He is actively involved with the Institute of Measurement & Control and specialities include: Implementation of IEC61508/61511 (SIL), DSEAR/ATEX; Development/troubleshooting of control systems/strategies; Development of engineering management policy/procedures; Auditing of fiscal measurement systems and Training on control/measurement/protection systems. He previously held senior engineering positions at Great Lakes Chemical, Associated Octel Company, Costain Oil and Gas & Process Ltd.

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