SIPI61508 Soft computing based qualitative method for determination of SILs István Ajtonyi 1 – László Ormos 2 1 University of Miskolc, Institute of Electric Engineering, Department of Automation 2 College of Nyíregyháza, Technical and Agricultural Faculty, Department of Electrotchnics and Automation

SIPI61508 “Functional safety is that part of the overall safety of a plant that depends on the correct functioning of its safety related systems.” (from IEC part 4.)

SIPI61508 Quantitative method for determining safety integrity level evaluation of hazard event rate without protection, definition of target risk frequency, and record of all details of the SIL, addition of external and non-SIS protection and evaluation of effect on risk frequency, proposition of an SIS risk reduction measure which reduces the hazard event rate and hence the risk frequency, conclusion of a practical risk reduction factor for the SIS consistent with being below the target risk frequency, conversion of the risk reduction factor to an SIL value for the SIS, draft the SRS with a reference to the calculation sheet and risk reduction model, finalization SIS detail SRS. The quantitative method is used to assist in development of the safety requirements specification (SRS) and the defining of the safety integrity level (SIL) by historical data. The steps of quantitative method are:

SIPI61508 Hazard and risk analysis: Operating Equipment Operating Equipment Control System Protection System recognizing and understanding the safety problem to be solved, separation of safety control from process control.

SIPI61508 Risk reduction and classification unprotected risk frequency, protected risk frequency, risk reduction factor, safety availability, probability of failure on demand, safety integrity level from the fallowing table: basic data estimated event frequency, chance of occurrence for an event, event likelihood. Safety integrity level Low demand mode of operation (average probability of failure to perform its design function on demand) 4  to  to  to  to 10 -2

SIPI61508 Qualititative method for determining safety integrity level In practice the process industries there are separate versions for three categories of hazard: harm to persons, harm to environment, loss of assets (production and equipment losses/repair costs). The qualitative method is a very attractive alternative for arriving at SILs because it avoids the need to place actual quantitative figures on the hazard demand rules, risk frequency and the consequences.

SIPI61508 Thom’s catastrophe theory - the conditional catastrophe

SIPI61508 Risk parameters charts based on IEC C Extent of damage C A slight injury, C B severe irreversible injury to one or more persons or death of person, C C death of several persons, C D catastrophic consequences, multiple deaths F frequency and exposure time F A seldom to relatively frequent, F B frequent to continuous events. P hazard avoidance/ mitigation P A possible under certain conditions, P B hardly possible. W occurrence probability W 1 very low, W 2 low W 3 relatively high. Starting point CACA CBCB C CDCD FAFA FBFB FAFA FBFB FAFA FBFB PAPA PBPB PAPA PBPB PAPA PBPB PAPA PBPB W1W1 W2W2 W3W3 a a a b no safety requirement a no special safety b a single E/E/PES is not 1,2,3,4 safety integrity Function for SIL determination by risk graph

SIPI61508 The safety layer matrix method for SIL determination Basic requirements for safety layers before the logic of the matrix diagram can be used: independent SIS and non-SIS risk reduction facilities, each risk reduction facility is to be an independent protection layer, each protection layer reduces the SIL by 1, only one SIS is used.

SIPI61508 Hazardous event severity matrix method for SIL determination SIL1 SIL2 low med. high Event likelihood SIL1 SIL2 SIL3 low med. high Event likelihood SIL1 SIL3 low med. high Event likelihood MinorSeriousExtensive Independent protection layer Severity Function for SIL determination by severity matrix

SIPI61508 Conclusion qualitative method requires professional experience, qualitative method does not require the collection of historical data, qualitative method can take into consideration information which might not be quantified, qualitative method carries out information from information.

SIPI61508 Thank you for your paying attention. Thank you for your paying attention.