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“BOW TIES and BARRIERS” David Slater - Cardiff University

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1 “BOW TIES and BARRIERS” David Slater - Cardiff University
Simple Structured Risk Assessment (Learning from experience – the importance of Near Miss and Incident Reporting/ Investigation) “BOW TIES and BARRIERS” David Slater - Cardiff University October 19th 2011 19/10/2011 Bow Ties and Incidents

2 Risk Assessment is a Simple, Natural Process
19/10/2011 Bow Ties and Incidents

3 How to Manage my Risk? save time save ££££ be safe
incomplete risk picture How to Manage my Risk? save time save ££££ be safe I like to do a good job I want to be safe I’ve done this often before I am judged on…. Is it different from usual? I want the business to succeed Does doing this feel right? Will my boss/shareholders support me if ..…? 19/10/2011 Bow Ties and Incidents

4 and if I get it wrong…… 19/10/2011 Bow Ties and Incidents

5 or…… $ 19/10/2011 Bow Ties and Incidents

6 and quite possibly…… 19/10/2011 Bow Ties and Incidents

7 What are the hazards - how bad could it be?
$ 19/10/2011 Bow Ties and Incidents

8 Failure thro’ Imperfection – “Human” Error?
In the Swiss Cheese model, individual weaknesses are modelled as holes in slices of Swiss cheese, such as this Emmental. They represent the imperfections in individual safeguards or defences, which in the real world rarely approach the ideal of being completely proof against failure. 19/10/2011 Bow Ties and Incidents

9 Bow Ties – an overview Bow ties evolved out of Reason’s “Swiss cheese” mould. They added a crucial insight There is a point between “Cause” and “Consequences” where you lose control. This is the “Knot”. Up to the “knot” any "barriers" are there to stop you losing control - they are a measure of the Vulnerability of the system. After the knot the outcome is often pure chance (slipping on ice, falling off a ladder!). Any barriers here are to avoid/reduce the consequences (seat belts, air bags!). Their effectiveness is then a measure of the Resilience of the system. The big advantage of the method is that it is an overview of the incident structure(and underlines (justifies?) the importance of recording near misses - the one's that don't get past the knot!) It gives especially non technical people a feel for where their performance or otherwise affects a particular barrier and the purpose of resilience barriers which are not necessarily redundant (BP gulf of Mexico). The advantages of adopting this way of analyzing accidents, is that you quickly find that the majority fit a reasonably small set of Bow tie templates. By recording incident and near miss data on to these templates you start to build up a real life indication of barrier effectiveness (Swiss Cheese permeability) or not? Finally you can use this recorded data to calculate a value of system integrity using LOPA. 19/10/2011 Bow Ties and Incidents

10 What prevents the hazards being realised?
cause cause Loss of control cause cause cause “barriers” or “safeguards” cause 19/10/2011 Bow Ties and Incidents

11 What mitigates the consequences?
$ consequence Loss of control consequence consequence consequence consequence “barriers” or “safeguards” 19/10/2011 Bow Ties and Incidents

12 A shared picture of how the hazard is managed
$ cause consequence cause Loss of control consequence cause consequence cause consequence cause consequence “barriers” or “safeguards” cause 19/10/2011 Bow Ties and Incidents

13 The “Bowtie” Methodology
Everything leading up to the accident Everything following the Accident Fault-tree Accident Causes Event-tree Damage 19/10/2011 Bow Ties and Incidents

14 After the Knot! (La Deluge?)
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15 FOR A “SIMPLE” MODEL THERE ARE SOME FUNDAMENTAL INSIGHTS FROM THE “BOW TIE” PARADIGM
The Knot is highly significant, it is the point where we lose control A logical (and useful )definition of “Vulnerability” then follows as - “The Propensity to loss of control” i.e. The Left Hand (LHS) And similarly “Resilience” is - “The Effectiveness and depth of Defences, once control is lost” i.e. The Right Hand Side (RHS) Aren’t these more rational and rigorous definitions ? 19/10/2011 Bow Ties and Incidents

16 MANAGEMENT IMPLICATIONS OF THE
“BOW TIE” PARADIGM LHS – Reduce VULNERABILITY (avoid the accident!) Design out branches, ideally ensure inherent safety, limits and boundaries ;Design in checks and balances. (ABS) “RISK” is then what you can’t control or guarantee to stop! RHS – (Its going to happen), ensure RESILIENCE! Barrier effectiveness/ performance checks, availability/ (maintainability), permeability, and degradation (complacency, relevance/ credibility/(short) Cuts) - Panic Button, Fail to Safety, ESD, Dump and Recover, Dead man’s handle, Response, Redundancy. (Airbags) If the consequences are really serious – Plan for Worst case survivability (or if in doubt, don’t do it!) 19/10/2011 Bow Ties and Incidents

17 LHS -Take away the causes, Reduce Vulnerability
Fault-tree Accident Causes Event-tree Damage 19/10/2011 Bow Ties and Incidents

18 LHS - can’t remove cause or- for all RHS pathways – Put up barriers
Fault-tree Accident Causes Event-tree Damage But how effective are the Barriers really? 19/10/2011 Bow Ties and Incidents

19 Barrier effectiveness
What are the “barriers”? How do I know what makes a barrier effective? How do I know when it won’t work? With multiple barriers could one failure go undetected? How might my actions impair the effectiveness of a barrier? How can I improve the effectiveness of barriers? 19/10/2011 Bow Ties and Incidents

20 Barriers are the same as in the Swiss Cheese model
Lines of defence Defects 19/10/2011 Bow Ties and Incidents

21 - and fail as in the Swiss Cheese model!
Lines of Defence 19/10/2011 Bow Ties and Incidents

22 This means we can still see a path thro’ - An Accident Sequence ……
Fault-tree Accident Causes Event-tree Damage 19/10/2011 Bow Ties and Incidents

23 Bow Ties and Barriers Used extensively now in Hazardous Industries
Accident Used extensively now in Hazardous Industries Equally useful in all Operational Phases Before – Design, During – “Tool Box Talks”, and After – Incident investigation This is a case where an offshore crane operator dropped a load of drill pipe in a lay down area which was supposed to be “off limits” and controlled by CCTV and “Safety Rules”!. 19/10/2011 Bow Ties and Incidents

24 BARRIERS– Defence in Depth or Leaky False Comforters?
Safeguard 1 Safeguard 3 Safeguard 5 Accident Safeguard 2 Loss of Control Safeguard 4 19/10/2011 Bow Ties and Incidents

25 19/10/2011 Bow Ties and Incidents

26 A Common Format Loss of Control Threat /Cause . This is consistent with the standard Bow tie analysis output, HAZOP output and Incident/ occupational databases (such as Story builder) and accident investigation (cause and effect) Templates. F1 – Cause/ Threat frequency – From a choice of sources (incident databases, Delphi sessions, Markow/Montecarlo distribution functions (from e.g. Goldsim, etc)) P1,P2, P3,- The Probabilities of Failure on Demand of the Protective Barriers P4, P5, P6 - The Probabilities of Failure on Demand of the Mitigation Barriers N1,N2, N3 – The consequences of the unmitigated and mitigated outcomes So What? – (Stage 4) From the sequence and Data above, the analyst has now the ability to print out and record a range of essential outputs (displayed in real time if he wishes). F2 – the Expected Frequency of the Loss of Control (Top event) – the VULNERABILITY to that threat. (F1xP1xP2xP3-- F3 – the Expected Frequency of the Consequences identified – the RESIDUAL RISK (F2 x P4xP5 xP6 ---- The system RESILIENCE is then F2 / F3 etc and PIG outputs are logF and logN Consequences Protection Barriers Mitigation Barriers . 19/10/2011 Bow Ties and Incidents

27 A Virus Attack How would this work for a Virus attacking our Computer System?. This is still consistent with the standard Bow tie analysis output, F1 – Cause/ Threat frequency – How likely is it my system will be attacked? Probably - Very likely = at least once per year and increasing? (from records?) P1,P2, P3,- The Probabilities of Failure on Demand of the Protective Barriers which are?-Standard Firewalls, Training/standards compliance, access restriction? P4, P5, P6 - The Probabilities of Failure on Demand of the Mitigation Barriers – Virus removal patch- unless its a new virus, isolation, quarantine, Hard Disk firewall For each of these we can use incident records, or intelligence estimates, plus the option of cloud sources, real time monitoring, Dependency analysis and/or a combination of all of the above.. Loss of Control Threat /Cause Protection Barriers Mitigation Barriers Consequences . 19/10/2011 Bow Ties and Incidents

28 Barriers can be Hard and Soft
And helpful visually 19/10/2011 Bow Ties and Incidents

29 PFD’s from Actual Incident Records
We can utilise actual incident databases – Company ones are best(such as TRACTION in BP) This Storybuilder database is available in the Netherlands 19/10/2011 Bow Ties and Incidents

30 Lets work thro’ an Example
The Macondo Well Incident Outcomes: - Safety: 11 fatalities / 115 rescued / Rig sinks - Environment: Largest oil spill in US history - Multiple inquiries - Regulatory agency reorganizations - Many new technical and permitting requirements 19/10/2011 Bow Ties and Incidents

31 “Wrong” kind of cement in well casing. (Hard, Extant, Unrevealed)
Drill pipe NRV failed. (Hard, Design) Staff “misread” key pressure reading (Soft, Human, Procedures, Training) Rig crew did not recognise the (oil & gas) influx (Soft, Human, Training) At the surface – flow diverter failed to dump oil and gas overboard(Hard, Design, Management of Change) Oil and gas vented directly on to the rig (drilling floor)( Hard, Design) Fire Detection/Prevention system failed – “allowing flammable gas into the engine rooms” (Hard, Design) The “failsafe” blowout preventer (BOP Stack) failed. Fire prevented remote shutdown, but the BOP had flat batteries and a faulty solenoid anyway (Jackpot!) What Went Wrong? 19/10/2011 Bow Ties and Incidents

32 Lets take BP’s Barriers!
(The following is taken from the BP report on the Macondo Well incident and is used as an illustrative application, treating the information as a given and not necessarily accurate!) 19/10/2011 Bow Ties and Incidents

33 BP project had LHS Barriers, (to reduce their vulnerability, of Three kinds)
It was designed to ensure well containment and “shut-inability”!(Barriers 1&2) There was a range of instrumentation, procedures, training and designated management responsibilities to monitor, check and assure “normal” behaviour(Barriers 3&4) There was a dedicated “Blow out Preventer” function, cabin, full time operator, instrumentation and emergency valves to protect against “Loss of Control” (Barriers 5&6) But ---Design, construction, systems and procedures all failed --- it was (de facto?) very VULNERABLE? 19/10/2011 Bow Ties and Incidents

34 The project had RHS – (Resilience) Barriers again three kinds
Fire and Gas Detection, and Ignition prevention/suppression to avoid Fire, (Barrier 7 shown the wrong side of knot in BP’s diagram?) Emergency Procedures/drills to Isolate/ disperse potential casualties ( note it worked for support vessels) (Barrier ? unclaimed) Sub-sea wellhead BOP valves to seal in the well. Again all failed , so they were highly Vulnerable and as it turned out also had no effective defences(B8) = Zero Resilience? How can that be? What mouse was eating their CHEESE? 19/10/2011 Bow Ties and Incidents

35 Lets put some numbers in?
The knot (Top Event) in the Bow Tie should be the uncontrolled release of oil and gas, the fire and environmental effects are the consequences. F1 in this case is the expected frequency of occurrence of hitting a high pressure gas pocket. (If they had used the HAZOP input spreadsheet this would have been a cause of the deviation MORE PRESSURE) This is a function of specific geology, but generic data say from OREDA suggest it is to be expected at least once per hole? (say 10 per year conservatively) 19/10/2011 Bow Ties and Incidents

36 Probabilities of Failure on Demand – PFD’s
First Protective Barrier – Cemented casing – probability of failure on demand can be estimated from direct experience with this contractor in his track record and an estimate of the quality of the crew.(10 -1?) Second Protective Barrier – Non Return Valve – If we took this from engineering plant commissioning and operational data, some companies would have assessed the probability of its failure on demand as 50%!(0.5) Third Protective Barrier – Crew/operator training and procedures. Most people would look at the latest audit data for this region/ crew? Are they in compliance (also check the auditor –PFD – 10 -1?) We would also be able to interface to the BSI/Infogov online compliance and audit checking package – Proteus; which could return (via XML) an indication of the status of compliance with procedures and ISO Standards. Which status %, is a measure of (the inverse of) the probability of failure number we require. 19/10/2011 Bow Ties and Incidents

37 Real Time Status? Fourth (and final) Protective Barrier –The Blow out Preventer – This is such a crucial piece of equipment that, although we could take historical data for its failure probability, the more useful way would be to monitor the real time status of the equipment. If there is a control cabin with all the relevant feeds available, our NIMBi module could relay its status data in real time. In the Gulf of Mexico incident there were queries as to its availability due to flat batteries, this would have given a probability of failure on demand of 1? Once you’re past the BOP, you’re out of control (past the knot on the Bow Tie!). Hence the other four BP barriers come after, as mitigation, not protection. (The expected frequency of a blow out was then their expected state of vulnerability– from 1 in 10 to 1 in a 100 per year?) 19/10/2011 Bow Ties and Incidents

38 Display it in Real Time? Wouldn't that have been very useful?
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39 Expected Mitigation Effectiveness?
Now let’s deal with the barriers which were designed to mitigate the consequences of an uncontrolled release of oil and gas. (It is planned to include access to a consequence modelling package (perhaps based on PHAST or similar), to give quantitative estimates of impacts- probably in categories) We can then assess the RESILIENCE of the system. 19/10/2011 Bow Ties and Incidents

40 Barrier PFD’s First Mitigation Barrier – Flow Diverter – This was no longer used as a diverter and so is a missing barrier – (P = 1) Second Mitigation Barrier – Fire and Gas Detection system/Alarms – Again seems not to have been adequate for the scale of incident? (P = 1?) Third Mitigation Barrier – Fire /Explosion suppression – inadequate for scale of release? (P = 1) Fourth Barrier – Evacuation survival procedures – Support Vessel Response was prompt, as required, but in total not effective in containing consequences (P=1?) Hence the residual risk was still 1 in 10 to 1 in 100 – not the kind of (lack of) resilience that the operators could have ignored, had they been aware. 19/10/2011 Bow Ties and Incidents

41 So What is the Relevance to the BP Incident?
The company needs to look again at the effect of “influencing factors” affecting human performance in that environment. Economic and (lack of?) Regulatory pressures need also to be identified and their mode of influence recognised. It was almost certainly not the result of the sudden, simultaneous and statistically improbable failure of 8 completely independent Barriers!(extant fail and unrevealed) But we do need to recognise their inherent complexity as more than simple “Reason-able?”“cheese” Barriers! We need to use “state of the art” tools to manage “state of the art” projects’ and move on from nice pictures and analogies. We need to learn from incidents – yes, but we would prefer to predict and avoid them ---if all else fails---? 19/10/2011 Bow Ties and Incidents

42 Monitoring Barriers Knowledge of the status of Barriers is key:
Formal focused in-depth reviews – excellent, but infrequent - TTS (e.g. Statoil) − 5 yearly - Audits − 3 yearly - Planned Inspections − 1 year Lessons learned from Incident investigations − excellent AND high frequency - BSCAT approach − every incident / near miss means some barriers failed / degraded - For many facilities this is 100+ events / year - Only current answer - collect statistics and root causes Can we afford to wait? Barrier Status – a to f 19/10/2011 Bow Ties and Incidents

43 Top-Ten Missed Opportunities from Accident Investigation (Kletz, 2003)
Accident investigations often find only a single cause Accident investigations are often superficial Accident investigations list human error as a cause Accident reports look for people to blame Accident reports list causes that are difficult to remove We change procedures rather than designs We may go too far! We do not let others learn from our experience We read or receive only overviews We forget the lessons learned, and allow the accident to happen again 19/10/2011 Bow Ties and Incidents

44 Societal THE ESSO LONGFORD EXPLOSION
Market forces Societal THE ESSO LONGFORD EXPLOSION Govt failure to provide alternative supply Govt/ regulatory system Inadeq regulatory system Corporate Poor change mgt Esso cost cutting Exxon control failure Organisational Absence of engineers Focus on LTIs Poor engineer-ing design Failure to ID interconnection hazard Poor auditing Failure to HAZOP GP1 Maintenance backlog Poor super-vision Failure of incident reporting system Operating in alarm mode Poor maintenance priorities Inadequate procedures & training Poor shift handover Plant inter-connections Warm oil restart Incorrect operation of manual bypass valve Loss of supply Cond-ensate overflow Warm oil pump trip Embrittle-ment of heat exchanger 2 wk site closure Expl-osion Physical accident sequence 19/10/2011 Bow Ties and Incidents

45 So What? We need to accept reality and the lessons of recent history.
Modern Infrastructure Systems have become (“stiff”); too complicated for simplistic risk management approaches! Complex Systems can have “Normal Accidents” (Perrow). Management requires a more "Holistic” overview of how incidents occur (Hopkins). We need to adopt a much more thoughtful and structured approach to Risk Management and Incident Investigation And we need to ensure we have a system for recording, analysing and monitoring/ warning us of our actual incident and near miss records to really “learn the lessons!” “Bow Ties” is a “Cheese" development which fits the bill! We can now focus on designing in “Adequate RESILIENCE”!- rather than “Acceptable Risk”! If it can --, It will ! – 19/10/2011 Bow Ties and Incidents

46 Risk Management really is a matter of life or Death!
19/10/2011 Bow Ties and Incidents


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