IEC-61508 Implementing a Compliance Program

1. IEC-61508 Implementing a Compliance Program • Motivation • Education • Implementation

2. Overview

3. Overview

4. Overview

5. Motivation • Do you or your company believe in the infallibility of Engineered systems?

6. Motivation • Roche Ireland does not have this delusion • 25 + years operational experience • Including some close calls • Reality has motivated out safety culture.

7. Education Much of the rest of this presentation has been generated from training presentations given in Roche Ireland to • Management • Process Engineering • Instrument / Electrical Engineering

8. Education Need to educate yourself : • Guidelines for Safe Automation of Chemical Processes {CCPS/AIChE} • ISA S84 • Functional Safety, {Smith & Simpson} • IBC conferences • Various WWW resources (exida/ sis-tech etc)

9. IEC-61508, SOP 973 • Functional safety of electrical / electronic & programmable electronic safety-related systems. • Critical Protective equipment - Safety Instrumented Systems

10. ... hazards due to incorrect function ... heat Protection against ... ... radiation ...electrical shock Safety IEC-61508, SOP 973 • Safety requires protection from hazards of different causes (movement, heat, radiation, el. shock, etc.) • “Functional Safety” means protection from hazards due toincorrect functioning.

11. IEC-61508 Will Effect: • Process Engineers: • Instrument/Electrical Designers: • Mechanical Engineering • Commissioning:- Extra Effort • Documentation :- Extra Effort

12. IEC-61508 is legally vague • Not legislation • Meets ‘Reasonably practicable’ duty • Health, safety & welfare at Work act, 1989 • Have to put in place a compliance program.

13. Risk (deaths/year) Intolerable region 1 x 10-4 ALARP 1 x 10-6 Negligible risk Figure 65-1

14. RISK Reduction - ALARP • As low as reasonably practicable. • IEC 61508 based on ALARP concept. • ALARP concerns region of risk. • Risk is an emotive and irrational thing. • Commonly accepted values are:upper limit 1 x 10-4 deaths per yearlower limit 1 x 10-6 deaths per year

15. Safety life cycle - milestone approach • ISA S84 life cycle depicted in Fig 65-3. • ISA S84 focuses on Box 9 of IEC 61508.

16. Passive systems layer Active systems layer Fail-safe design One way valves Controlsystems layer ESD Duality Alarm handling Intrinsic safety Back-up Diagnostics F&G Bursting discs Alarms, trips & interlocks Pressure relief valves Figure 64-1

17. Start Figure 65-3 1 Conceptual process design 2 Perform process HAZAN & risk assessment 3 Apply Category 0 protection systems to prevent hazards & reduce risk No 4 Are any Category 1 protection systems required? 5 Define target safety integrity levels (SIL) 6 Develop safety requirements specification (SRS) 7 Conceptual design of active protection systems & verify against SRS 8 Detailed design of protection system 11 Establish operating & 9 & 10 Installation, commissioning maintenance procedures and pre-start-up acceptance testing 12 Pre-start-up safety review 13 Protection system start-up, maintenance & periodic testing yes 14 Modify protection system? 15 Decommission system End

18. Process Engineering • First Stage of realisation of high-integrity safety instrumented systems • Modified PHA • Feeds into SRS • Based on good process data & good process judgement.

19. Process Chemistry • Carius Tube test for decomposition • Pressure Dewar Calorimetry • Understanding of Exotherms • Knowledge of onset temperatures • {Chilworth}

20. Process Engineering • Good process judgement. • Hazop • Margins of safety

21. Hazard identification, Interlock Identification • Reactant being transferred in from Reactor 1 without agitation could accumulate & react in a sudden, violent manner. • Reactor 2 Inlet valve 205 should OPEN only if agitator ON

22. Hazard identification, Interlock Identification • Simplified Technique. • MIL Std 882

23. Consequences • Consequence of this is overpressure, loss of batch, over-temperature, possible destruction of vessel. • 1 week downtime to recover. • Fatality or Serious injury unlikely. • Critical • (C2)

24. Occupancy factor • Building is continually occupied • (F2)

25. Manual Avoidance factor • There is quite a good chance of an operator observing that something is going wrong & intervening successfully. • (P1)

26. Unmitigated demand rate. • Likely to occur once every 5 years. • Occasional • The process is DCS automated. • DCS is not a SIS – no SIL rating. • DCS control reduces frequency of Unmitigated Demand. • (W2)

27. Least risk W3 W2 W1 C1 x0? P1 1 F1 x0? P2 1 1 C2 x0? P1 2 1 1 F2 Start P2 2 3 1 F1 2 3 3 C3 F2 3 3 4 C4 4 3 x2? Most risk EN 954 Approach

29. Roche Consequences

30. Roche ‘unmitigated’ demand rate.

31. Instrument / Electrical Design • Second Stage of realisation of high-integrity safety instrumented systems • Modified Instrument design • Modified Instrument Commissioning • Feeds into SRS

32. Hazardreductionfactor HRF Safety integrity level SIL Demand mode of operation Continuous mode PFD (fractional) Availability A (fractional) Failure rate  (failures per hr) 1 10-1 to 10-2 0.9 to 0.99 10-5 to 10-6 >101 2 >102 10-2 to 10-3 0.99 to 0.999 10-6 to 10-7 3 >103 10-3 to 10-4 10-7 to 10-8 0.999 to 0.9999 4 >104 10-4 to 10-5 10-8 to 10-9 0.9999 to 0.99999 Table 65-1

33. Equipment implications • SIL value is measure of quality of protection system, end to end. • System has to be designed, specified, built and maintained to that standard. • Proof testing at regular intervals • Conformance assessment for safety systems

34. PFD Calculation • Simplified Equation • ISA-TR84.00.02-2002 Part 2 • Equation B.34 – Rare event approximation • “Adequate” for SIL 1 or 2, where the plant is well controlled, well maintained, understood process, conservative engineering with good mechanical integrity

35. PFD Calc. Motion Sensor • MTBF = Mean (Average) time between failures • Information provided by vendor. • MTBF = 86 Years

36. PFD Calc. Motion Sensor Failures can be • fail to danger (Falsely shows agitator moving)or • fail to safe (Falsely shows agitator stopped) • Aim of good design is to maximise fail to safe, minimise fail to danger. The failure mode split is the percentage in the fail to danger category. • Failure mode split = .1 (SA estimate)

37. PFD Calc. Motion Sensor • Proof test interval = 1 year (8760 hours) • Time between re-tests of the interlock. • Need to be genuine tests

38. PFD Calc. Motion Sensor • 86 years * 8760 hours/year = 753,000 (MTBF in hours) •  = 1/ MTBF = 1.30 E-6 failures per hour • FMS =.1 • Proof test = 1 year (8760 hours) • PFD(SS) = 1.30 E-6 * .1 * 1 * (8760/2) • PFD(SS)=.0006

39. PFD Calc. Barrier 6 • MTBF = 4 Years • Failure mode split = .4 • Proof test interval = 1 year (8760 hours)  = 1/ MTBF = 2.87 E-5 failures per hourPFD(B6) = 2.87 E-5 * .4 * 1 * (8760/2) • PFD(B6)=.0500

40. PFD Calc. Relay 5 • MTBF = 100 Years • Failure mode split = .01 • Proof test interval = 1 year (8760 hours)  = 1/ MTBF = 1.14 E-6 failures per hourPFD(R5) = 1.14 E-6 * .01 * 1 * (8760/2) • PFD(R5)=.00005

41. PFD Calc. Main Barrier • MTBF = 10 Years • Failure mode split = .9 • Proof test interval = 1 day (24 hours)  = 1/ MTBF = 1.14 E-5 failures per hourPFD(MB) = 1.14 E-5 * .9 * 1 * (24/2) • PFD(MB)=.001242

42. PFD Calc. Solenoid • MTBF = 10 Years • Failure mode split = .4 • Proof test interval = 1 day (24 hours)  = 1/ MTBF = 1.14 E-5 failures per hourPFD(SOL) = 1.14 E-5 * .4 * 1 * (24/2) • PFD(SOL)=.00006

43. PFD Calc. Valve & Actuator • MTBF = 10 Years • Failure mode split = .2 • Proof test interval = 1 day (24 hours)  = 1/ MTBF = 1.14 E-5 failures per hourPFD(VA) = 1.14 E-5 * .2 * 1 * (24/2) • PFD(VA)=.00003

44. PFD Calc. Overall • PFD(VA)=.00003 • PFD(SOL)=.00006 • PFD(MB)=.00124 • PFD(R5)=.00005 • PFD(B6)=.0500 • PFD(SS)=.0006 • PFD = .052 => SIL 1

45. PFD Mapping ∑ PFD = 10% SIL 1 Limit Overall Valve Barrier ∑ PFD = 1% SIL 2 Limit Relay Logic Barrier Instrument

46. PFD Calc. Issues • Elements in series: USYS Ui 62-16Elements in parallel: USYS  Ui -17 • Common cause failure: SYS = IND + . MAX -18 • Voting systems: UKOON n.Uk -19 • For more complex systems – Fault Tree Analysis using ISA-TR84.00.02-2002 Part 3. • “Probabilistic Risk Assesment” – Henley, E J

47. Design issues • Roche have decided that valve & actuator may be shared for SIL 1 only. • SIS & BPCS share barrier, solenoid, actuator & Valve. This is not recommended • Solenoid has local SMO, which might be OK for normal operation, but not for SIS.

48. Design issues

49. Design issues • ##### ####-# type barrier not recommended (TTL Logic switching – independent energy source) • No clear indication on loop sheet or in field of safety critical nature of instruments

50. Design issues • Design of periodic re-test method is the instrument designers responsibility. • This would help facilitate periodic testing • Loop sheet to indicate safety critical nature of instruments