Accident near misses and precursor analysis2
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Course project presentation Quantitative Risk Assessment Course at Texas A&M University Fall 2012
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Accident near misses and precursor analysis2
- 1. Accident Near Misses and Precursor Analysis Case Study: Fire in a CSTR System Presented by: Mohammed AlShammasi Ashwin Ariyapadi Kevin Anglin November 19, 2012
- 2. 2 November 19, 2012 Overview • • • • • Introduction Identification of Precursors Modeling and Analysis Risk Management Recommendations Accident Near Misses and Precursor Analysis
- 3. 3 Introduction November 19, 2012 Definitions • Near Miss- a severe precursor that is directly connected to a potential accident in the accident chain • Accident Precursor- an event that could escalate to an accident A precursor is a more general term while a near miss can consist of more than one precursor Accident Near Misses and Precursor Analysis
- 4. 4 Introduction November 19, 2012 Precursor Analysis v. Accident Analysis • Precursor events at the base of the pyramid. • High consequence accidents at the top of the pyramid • Precursor events ▫ ▫ ▫ ▫ simpler to analyze easier to prevent smaller in scale less costly to resolve Accident Near Misses and Precursor Analysis
- 5. 5 Introduction November 19, 2012 Case Study • Applying QRA concepts based on precursor analysis to fire (top event) in a CSTR system Accident Near Misses and Precursor Analysis
- 6. 6 Introduction November 19, 2012 Case Study, continued • Hazard barriers: ▫ ▫ ▫ ▫ ▫ ▫ Coolant system Temperature controller Rupture disc Fire alarm Manual shutdown Firefighting emergency Accident Near Misses and Precursor Analysis
- 8. 8 Identification of Precursors November 19, 2012 Identification of Precursors • Methods to identify precursor events: ▫ ▫ ▫ ▫ ▫ ▫ Regular surveys Interviews with safety engineers Direct observation Voluntary reporting Alarm databases Automated detection systems Accident Near Misses and Precursor Analysis
- 9. 9 Identification of Precursors November 19, 2012 Initiating Events • Four main initiating events were identified: Initiating events Frequency, yr-1 Coolant failure 2.50 Inlet valve malfunction 1.74 External fire 0.82 Agitator failure 4.16 Accident Near Misses and Precursor Analysis
- 10. 10 Identification of Precursors November 19, 2012 Basic Failure Events • An initiating event can be followed by a number of basic failure events: Basic Event Probability of failure Probability of success Temperature controller failure Rupture disk failure Alarm Fails 0.040 0.120 0.250 0.960 0.880 0.750 No manual shutdown (alarm works) No manual shutdown (alarm fails) 0.120 0.240 0.880 0.760 Quick emergency response failure (Alarm works) Quick emergency response failure (Alarm fails) 0.316 0.544 0.684 0.456 Accident Near Misses and Precursor Analysis
- 11. 11 Identification of Precursors November 19, 2012 Basic Failure Events • Contributors to uncertainty in frequencies: 1. Incomplete list of initiation events 2. Incomplete knowledge of hazard scenarios 3. Assumptions about material properties and technical behavior 4. Common failure causes 5. Unconsidered process upsets 6. Operational errors due to inadequate training or attitudes Accident Near Misses and Precursor Analysis
- 13. 13 Modeling and Analysis November 19, 2012 Fault Tree Analysis CSTR catches on fire Coolant failure Temp controller failure Rupture disk failure Inlet valve malfunction Alarm failure Temp controller failure External fire Agitator failure Manual shutdown failure Rupture disk failure Temp controller failure Alarm failure Manual shutdown failure Temp controller failure Rupture disk failure Accident Near Misses and Precursor Analysis Alarm failure Manual shutdown failure Rupture disk failure Alarm failure Manual shutdown failure
- 14. 14 Modeling and Analysis November 19, 2012 Bayesian Approach for Updating • Accident Near Misses and Precursor Analysis
- 15. 15 Modeling and Analysis November 19, 2012 Bayesian Approach for Updating • Accident Near Misses and Precursor Analysis
- 16. 16 Modeling and Analysis November 19, 2012 Consequences • Consequences were identified based on Estimated Monetary Value (EMVs) Low monetary value, $ MM High monetary value, $ MM Expected monetary value, $ MM No damage 0.00 0.00 0.00 Minor plant damage 0.40 1.00 0.70 Major plant damage without injuries 2.00 3.00 2.50 Major plant damage with injuries 1.00 2.00 1.50 Consequence Major plant damage with fatalities 7.00 Accident Near Misses and Precursor Analysis 7.00
- 17. 17 Modeling and Analysis November 19, 2012 Consequences • Contributors to uncertainty in consequences: 1. Incomplete knowledge of number of fatalities/injuries 2. Flammability behavior assumptions 3. Ignition source model 4. Explosion model and efficiency assumptions 5. Changes in market dynamics for acceptable risk magnitude 6. Neglecting environmental costs of fire Accident Near Misses and Precursor Analysis
- 18. 18 Modeling and Analysis November 19, 2012 Event Tree Outcome I Works S Consequence Scenario No damage S1 No damage S2 S No damage S3 S No damage S4 S Minor plant damage S5 Major plant damage S6 S No damage S7 S Major plant damage S8 F Injuries/fatalities S9 Fails Frequency of I Temp controller 0.960 Fails 0.040 Works Rupture disk S 0.880 Works 0.750 Fails Works Manual shutdown 0.880 Works 0.120 Alarm 0.120 0.684 Works Fails 0.316 Fails 0.250 Quick emergency response Manual shutdown F 0.760 Works 0.240 Quick emergency response 0.456 Works Fails 0.544 Accident Near Misses and Precursor Analysis
- 19. 19 Modeling and Analysis November 19, 2012 Scenario Frequency • The frequency of each scenario was calculated for each initiating event as: Accident Near Misses and Precursor Analysis
- 20. 20 Modeling and Analysis November 19, 2012 Scenario Frequency • Take Scenario 5 for the coolant failure – coolant fails, temperature controller fails, rupture disc fails, alarm works, manual shutdown fails, and emergency response is quick: F(S) = (2.5 1/yr)(0.04)(0.12)(0.75)(0.12)(0.684) F(S) = 0.000739 1/yr Accident Near Misses and Precursor Analysis
- 22. 22 Risk Management November 19, 2012 Risk Evaluation • The risk for each scenario was evaluated by multiplying scenario frequency by associated consequence. • This type of risk evaluation is based on expected monetary values. Accident Near Misses and Precursor Analysis
- 23. 23 Risk Management November 19, 2012 Total Risk • The total risk was estimated by summing the risks for each initiating event over all scenarios Accident Near Misses and Precursor Analysis
- 24. 24 Risk Management November 19, 2012 Scenario Importance • The importance percentage of each scenario was evaluated as follows: • The importance % is a measure of scenario contribution to the total risk Accident Near Misses and Precursor Analysis
- 25. 25 Risk Management November 19, 2012 Total Fire Risk • The total risk of fire was calculated by summing the risks of all initiating events: Accident Near Misses and Precursor Analysis
- 26. 26 Risk Management November 19, 2012 Results Coolant failure Scenario Inlet valve malfunction External fire Agitator failure # frequency, yr-1 Risk, $/yr IM, % frequency, yr-1 Risk, $/yr IM, % frequency, yr-1 Risk, $/yr IM, % frequency, yr-1 Risk, $/yr IM, % S1 2.50 0 0.00% 1.74 0 0.00% 0.82 0 0.00% 4.16 0 0.00% S2 2.40E+00 0 0.00% 1.67E+00 0 0.00% 7.87E-01 0 0.00% 3.99E+00 0 0.00% S3 8.80E-02 0 0.00% 6.12E-02 0 0.00% 2.89E-02 0 0.00% 1.46E-01 0 0.00% S4 7.92E-03 0 0.00% 5.51E-03 0 0.00% 2.60E-03 0 0.00% 1.32E-02 0 0.00% S5 7.39E-04 517 10.15% 5.14E-04 360 10.15% 2.42E-04 170 10.15% 1.23E-03 860 10.15% S6 3.41E-04 853 16.74% 2.38E-04 594 16.74% 1.12E-04 280 16.74% 5.68E-04 1,420 16.74% S7 2.28E-03 0 0.00% 1.59E-03 0 0.00% 7.48E-04 0 0.00% 3.79E-03 0 0.00% S8 3.28E-04 985 19.32% 2.29E-04 686 19.32% 1.08E-04 323 19.32% 5.46E-04 1,639 19.32% S9 3.92E-04 2,742 53.79% 2.73E-04 1,908 53.79% 1.28E-04 899 53.79% 6.52E-04 4,562 53.79% Total 5.000 5,097 3.480 3,548 1.640 1,672 8.320 8,481 Accident Near Misses and Precursor Analysis
- 27. 27 Risk Management November 19, 2012 Risk Profile 1.2 Cumulative Probability 1 0.8 Coolant failure 0.6 Inlet valve malfunction External fire 0.4 Agitator failure 0.2 0 0 500 1000 1500 2000 2500 Risk ($/yr) Accident Near Misses and Precursor Analysis 3000
- 29. 29 Recommendations November 19, 2012 Risk Control • An example of risk control is installation of automatic sprinkler system as an emergency response system in case of fire Cost of installation, $/yr Associated costs, $/yr No sprinkler system 0 Sprinkler system 1 14,000 0.99 2,100 Sprinkler system 2 10,000 0.82 5,400 Sprinkler system 3 7,000 0.72 8,700 Accident Near Misses and Precursor Analysis
- 30. 30 Recommendations November 19, 2012 Risk Control Continued • The expected value of control was calculated assuming a useful life period of 10 years for each system Accident Near Misses and Precursor Analysis
- 31. 31 Recommendations November 19, 2012 EMVs for Control • The EMVs for various control systems were as follows: Expected monetary values of control, $/yr No sprinkler system Sprinkler system 1 Sprinkler system 2 Sprinkler system 3 Accident Near Misses and Precursor Analysis
- 32. 32 Recommendations November 19, 2012 Identification • • • • • • Other potential initiating events Other weak points/critical basic events Examining of mechanical integrity of CSTR Considering common failure modes Performing HAZOP Implementing reliability testing on hazard barriers (TC, alarm, …) Accident Near Misses and Precursor Analysis
- 33. 33 Recommendations November 19, 2012 Analysis & Modeling • Using Bayesian Network software • Using probability distribution functions instead of single-point probabilities • Analyzing effects of fire or other initiating events on other equipment in the facility • Developing empirical probability functions based on test data • Creating a risk-level matrix Accident Near Misses and Precursor Analysis
- 34. 34 Recommendations November 19, 2012 Risk Management • Adding redundancy in hazard barriers for ▫ temperature controller ▫ overpressure alarm system • Using risk distribution functions • Using utility function to account for risk attitudes • Accounting for societal risk • Developing frequent maintenance and testing procedure • Adapting an inherently safer reactor design Accident Near Misses and Precursor Analysis
- 35. 35 Recommendations November 19, 2012 Inherently Safer Design • The current cooling jacket has a failure frequency of 2.5 times per year • A jacket with a failure rate of only 2 times per year is safer: Accident Near Misses and Precursor Analysis
- 36. 36 November 19, 2012 Conclusion • A brief risk assessment of a CSTR system based on precursor analysis was presented using fire as top event. • Four initiating events were identified followed by a number of possible basic failures. • A number of recommendations were provided for precursor identification, analysis and modeling, and risk management. Accident Near Misses and Precursor Analysis
- 37. Thank you for your attention Questions?
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