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Accident Near Misses and Precursor Analysis Case Study: Fire in a CSTR System Presented by: Mohammed AlShammasi Ashwin Ariyapadi Kevin Anglin November 19, 2012
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Course project presentation Quantitative Risk Assessment Course at Texas A&M University Fall 2012
Transcript of Accident near misses and precursor analysis2
Accident Near Misses and Precursor AnalysisCase Study: Fire in a CSTR System
Presented by:
Mohammed AlShammasi Ashwin Ariyapadi Kevin AnglinNovember 19, 2012
November 19, 2012
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Accident Near Misses and Precursor Analysis
Overview
•Introduction•Identification of Precursors •Modeling and Analysis•Risk Management •Recommendations
November 19, 2012
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Accident Near Misses and Precursor Analysis
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
Introduction
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Accident Near Misses and Precursor Analysis
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
Introduction
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Accident Near Misses and Precursor Analysis
Case Study
•Applying QRA conceptsbased on precursor analysis to fire (top event) in a CSTR system
Introduction
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Accident Near Misses and Precursor Analysis
Case Study, continued
•Hazard barriers:▫Coolant system▫Temperature controller▫Rupture disc▫Fire alarm ▫Manual shutdown▫Firefighting emergency
Introduction
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Identification of Precursors
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Accident Near Misses and Precursor Analysis
Identification of Precursors
•Methods to identify precursor events:▫Regular surveys ▫Interviews with safety engineers▫Direct observation▫Voluntary reporting▫Alarm databases▫Automated detection systems
Identification of Precursors
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Accident Near Misses and Precursor Analysis
Initiating Events
• Four main initiating events were identified:
Identification of Precursors
Initiating events Frequency, yr-1
Coolant failure 2.50
Inlet valve malfunction 1.74
External fire 0.82
Agitator failure 4.16
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Accident Near Misses and Precursor Analysis
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 0.040 0.960 Rupture disk failure 0.120 0.880 Alarm Fails 0.250 0.750 No manual shutdown (alarm works) 0.120 0.880 No manual shutdown (alarm fails) 0.240 0.760 Quick emergency response failure (Alarm works) 0.316 0.684 Quick emergency response failure (Alarm fails) 0.544 0.456
Identification of Precursors
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Accident Near Misses and Precursor Analysis
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 behavior4. Common failure causes5. Unconsidered process upsets6. Operational errors due to inadequate
training or attitudes
Identification of Precursors
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Modeling and Analysis
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Accident Near Misses and Precursor Analysis
Fault Tree AnalysisCSTR catches
on fire
Coolant failure
Inlet valve malfunction
External fire
Agitator failure
Tempcontroller
failure
Rupture disk
failure
Alarm failure
Manual shutdown
failure
Tempcontroller
failure
Rupture disk
failure
Alarm failure
Manual shutdown
failure
Tempcontroller
failure
Rupture disk
failure
Alarm failure
Manual shutdown
failure
Tempcontroller
failure
Rupture disk
failure
Alarm failure
Manual shutdown
failure
Modeling and Analysis
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Accident Near Misses and Precursor Analysis
•Probability of coolant failure P(C=True)=
•Probability of fireP(=True) =
•The posterior probability of fire may be recalculated based on observing an initiating event.
𝑃 ( 𝐸|𝐶 )=𝑃 ( 𝐸 ) 𝑃 (𝐶∨𝐸)
𝑃 ( 𝐸 ) 𝑃 (𝐶∨𝐸)+𝑃 (𝐸)𝑃 (𝐶|𝐸 )
Modeling and Analysis
Bayesian Approach for Updating
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Accident Near Misses and Precursor Analysis
Bayesian Approach for Updating
Modeling and Analysis
•Based on observing a coolant failure, probability of fire significantly increases
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Accident Near Misses and Precursor Analysis
Consequences
•Consequences were identified based on Estimated Monetary Value (EMVs)
Consequence 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
Major plant damage with fatalities 7.00 7.00
Modeling and Analysis
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Accident Near Misses and Precursor Analysis
Consequences •Contributors to uncertainty in
consequences:1. Incomplete knowledge of number of
fatalities/injuries2. Flammability behavior assumptions3. Ignition source model4. Explosion model and efficiency assumptions5. Changes in market dynamics for acceptable
risk magnitude 6. Neglecting environmental costs of fire
Modeling and Analysis
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Accident Near Misses and Precursor Analysis
Event Tree
Alarm
Fails
Fails
Fails Works
I S
Temp controller S
Rupture disk S
Works
Works
Works
Manual shutdown
Fails
F
S
No damage
No damage
No damage
No damage
Minor plant damage
Major plant damage
No damage
Major plant damage
Injuries/fatalities
Manual shutdown
F
SQuick
emergency response
Quick emergency response
Works
Works
SWorks
SWorks
Frequency of I
0.960
0.040
0.880
0.120
0.750
0.250
0.880
0.760
0.120
0.240
0.684
0.456
0.544
Fails
Fails
0.316
Outcome ScenarioConsequence
S1
S2
S3
S4
S5
S6
S7
S8
S9
Modeling and Analysis
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Accident Near Misses and Precursor Analysis
Scenario Frequency
•The frequency of each scenario was calculated for each initiating event as:
= scenario frequency
= initiating event frequency
= basic event probability with
Modeling and Analysis
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Accident Near Misses and Precursor Analysis
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
Modeling and Analysis
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Risk Management
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Accident Near Misses and Precursor Analysis
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.
= risk associated with a scenario = consequence of a scenario
Risk Management
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Accident Near Misses and Precursor Analysis
Total Risk
•The total risk was estimated by summing the risks for each initiating event over all scenarios
= average risk associated with an initiating event
Risk Management
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Accident Near Misses and Precursor Analysis
Scenario Importance
•The importance percentage of each scenario was evaluated as follows:
•The importance % is a measure of scenario contribution to the total risk
= risk associated with an initiating event
Risk Management
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Accident Near Misses and Precursor Analysis
Total Fire Risk
•The total risk of fire was calculated by summing the risks of all initiating events:
Risk Management
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Accident Near Misses and Precursor Analysis
Results Scenario Coolant failure 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, $/yr IM, %
S1 2.50 0 0.00% 1.74 0 0.00% 0.82 0 0.00% 4.16 0 0.00%
S2 2.40E+00 0 0.00% 1.67E+00 0 0.00% 7.87E-01 0 0.00% 3.99E+00 0 0.00%
S3 8.80E-02 0 0.00% 6.12E-02 0 0.00% 2.89E-02 0 0.00% 1.46E-01 0 0.00%
S4 7.92E-03 0 0.00% 5.51E-03 0 0.00% 2.60E-03 0 0.00% 1.32E-02 0 0.00%
S5 7.39E-04 517 10.15% 5.14E-04 360 10.15% 2.42E-04 170 10.15% 1.23E-03 860 10.15%
S6 3.41E-04 853 16.74% 2.38E-04 594 16.74% 1.12E-04 280 16.74% 5.68E-04 1,420 16.74%
S7 2.28E-03 0 0.00% 1.59E-03 0 0.00% 7.48E-04 0 0.00% 3.79E-03 0 0.00%
S8 3.28E-04 985 19.32% 2.29E-04 686 19.32% 1.08E-04 323 19.32% 5.46E-04 1,639 19.32%
S9 3.92E-04 2,742 53.79% 2.73E-04 1,908 53.79% 1.28E-04 899 53.79% 6.52E-04 4,562 53.79%
Total 5.000 5,097 3.480 3,548 1.640 1,672 8.320 8,481
Risk Management
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Accident Near Misses and Precursor Analysis
Risk Profile
0 500 1000 1500 2000 2500 30000
0.2
0.4
0.6
0.8
1
1.2
Coolant failureInlet valve malfunctionExternal fireAgitator failure
Risk ($/yr)
Cum
ula
tive P
robabil
ity
Risk Management
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Recommendations
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Accident Near Misses and Precursor Analysis
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
Recommendations
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Accident Near Misses and Precursor Analysis
Risk Control Continued
•The expected value of control was calculated assuming a useful life period of 10 years for each system
𝐸𝑀𝑉 (𝐶𝑖 )=𝐸𝑥𝑝𝑒𝑐𝑡𝑒𝑑 𝑏𝑒𝑛𝑒𝑓𝑖𝑡𝑜𝑓 𝑐𝑜𝑛𝑡𝑟𝑜𝑙−𝐶𝑜𝑠𝑡 𝑜𝑓 𝑖𝑛𝑠𝑡𝑎𝑙𝑙𝑎𝑡𝑖𝑜𝑛=𝑅 (𝐶𝑖 )× ¿
For example, for sprinkler system 1:
Recommendations
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Accident Near Misses and Precursor Analysis
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
Recommendations
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Accident Near Misses and Precursor Analysis
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, …)
Recommendations
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Accident Near Misses and Precursor Analysis
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
Recommendations
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Accident Near Misses and Precursor Analysis
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
Recommendations
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Accident Near Misses and Precursor Analysis
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:
𝑅𝑖𝑚𝑝𝑟𝑜𝑣𝑒𝑑=𝑅𝑜𝑙𝑑 𝐹 𝑖𝑚𝑝𝑟𝑜𝑣𝑒𝑑
𝐹 𝑜𝑙𝑑
=($5,097 / yr )(2.01/ yr )
2.51 / yr=$4,077.6 / yr
Recommendations
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Accident Near Misses and Precursor Analysis
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.
Thank you for your attention
Questions?
