A presentation by: Dr. Alexander Cohen

1. Task Analysis • A presentation by: • Dr. Alexander Cohen

2. In this presentation: Task analysis goals Failure modes of humans HAZOP of tasks Basic task analysis Quantitative analysis

3. Task analysis goals • The term ‘task analysis’ refers to the analysis of the human interface with the process. • Protecting the (human) operator. • Human errors reduction. • Inherently safe processes. • Human engineering aspects. • Standing operating procedures (SOP) and safety SOP (SSOP).

4. In many cases task analysis is only a by-product of the risk analysis due to the complexity of the analysis of human behavior.

5. Failure modes of humans

6. An operator in a plant Plant (perception) Detection Information processing Operation Plant (real)

7. Human errors – Human mistakes • Errors • Operator is skilled. • Incorrect/absent information. • Incorrect/absent interface. • Environmental conditions. Mistakes ? And sometimes, the operator just slip, hang on the first thing he can grab and - Unfortunately it is an emergency releasing valve, and the rest is history…

8. Basic modes of human errors • Omission of a task (the oops syndrome). • Commission of an extra action. • Changes in operator’s physical conditions. • Changes in operator’s mental conditions.

9. Psychological failure modes • Failure to consider special circumstances. • Shortcut invoked. • Stereotype takeover. • Need for information not prompted. • Misinterpretation. • Assumption.

10. Psychological failure modes (cont.) • Forget isolated acts. • Mistake among alternatives. • Place-losing error. • Other slip of memory. • Motor variability. • Topographic or spatial orientation inadequate.

11. Environmental aspects • Dust. • Noise. • Radiation. • Ventilation. • Visibility. • Heat/cold stress • Work at heights • Slippery floor. • Limited approach. • Hot/cold surfaces. • Rails. • Vibrations. • Repulsive odor.

12. Ineffectiveness • Response to gauge in auto-mode (100%). • Response to gauge in manual mode (10%). • Failure to confirm shutdown (15%). • Response to multiple alarms (15%). • Response to single alarms (2%). • Critical action under high stress (30%). • Critical action – SOP available (10%). • Procedure on a checklist (2%).

13. Task analysis methodology • This analysis could be carried out in many methods such as: • HAZOP of operating procedures. • Task analysis • Workplace study (occupational health & hygiene). • Ergonomic (human engineering) surveys. • Performance analysis.

14. Hazard & operability study • Carried out as a standard HAZOP with the application of the guidewords on tasks rather than process nodes. • (In many batch processes a HAZOP of the tasks gives better results than a HAZOP of the process diagrams) • .

15. Task HAZOP Changing a flat tyre

16. Changing tyreSOP - summary • Park the car in a safe place. • Jack up car. • Remove flat tyre and replace with spare. • Un-jack car.

17. Changing tyreSOP breakdown • Park in a safe place. • Identify flat tyre. Get wheel spanner and jack. • loose nuts. • Jack up car. • Unscrew nuts and remove flat tyre. • Fetch spare and fit in place. • Screw nuts. • Un-jack car. • Tight nuts. • Get your staff and … • drive safely …

18. JACK UP CAR

19. HAZOP exampleJack up car

20. HAZOP exampleJack up car

21. HAZOP: pros • Structural. • Thorough. • Technical solutions to human engineering problems.

22. HAZOP: cons • Time consuming. • Requires a specific HAZOP team*. • Many uncertainties in the design phase. • Many subjects fall into ‘other than’. *In many cases, the technical team doesn’t know how to assess human engineering aspects.

23. Basic tasks analysis (the WH-questions approach) • Task analysis keywords • WHAT • WHEN • WHERE • HOW • WHO • & • WHY

24. Questions What, When, How, Who, Where

25. Questions (cont.) What, When, How, Who, Where

26. n-Pentane fillingTGC system, simplified • … • Verify a low level in the tank. • Open V1, and the two connected valves V2,3. • Activate the pump. • Monitor filling and close pump when level reaches high level indication. • … vent LI n-pentane HL V1 filter V2,3 Manual pump

27. n-pentane n-Pentane fillingAsking questions

28. n-pentane n-Pentane fillingAsking questions (cont.)

29. n-pentane n-Pentane fillingCleaning the filter • … • NEVER open filter cop when pump is operating. • Insert a large metal bowl below the filter to collect possible spillage. • Unscrew the cap cautiously by hand. • If stuck DO NOT attempt to use any tools. • Wash the cop with small portions of pentane until well cleaned. • Re-screw the cop by hand. • Activate the pump for 5 seconds (V2,3 closed!) and see if cop leaks. • …

30. n-pentane n-Pentane fillingCleaning the filter (cont) • Unscrew the cop cautiously by hand. • If stuck DO NOT attempt to use any tools. What, When, How, Who, Where

31. Quantitative analysis of human activities • In fault trees. • In event trees.

32. Failure densities

33. Failure densities (cont.) *2nd order errors are errors composed by a sequence of ‘simple’ human errors.

34. n-pentane n-Pentane fillingEvent tree 0.95 Operator fills OK 0.95 Operator stops 0.9 0.00041 Alarm sounds 0.9 Overflow failure 0.01 Operator fails 0.1 0.0000045 Alarm fails 0.1 0.00005 Failure to detect HL 0.05 Overflow functions 0.99 0.0495

35. Task AnalysisWORKSHOP

36. Tasks • Task analysis or HAZOP of SOPs. • Uranium oxide / graphite – mixing. • Uranium oxide / graphite – pill making • Methylal filling • Isobutane inspection • Action items • Task analysis or HAZOP of SOPs. • Event tree for the task.

37. Tasks (alternative) • Do it yourself… • Choose a task that you are familiar with. • Write your own SOP (name it draft and keep it). • Analyze your task (choose a method as convenient). • Rewrite the SOP (if required, and name it final). • Compare the draft SOP with the final SOP.