the state of process safety qra and the road to...
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MMI Engineeringwww.mmiengineering.com
The State of Process Safety QRA and The
Road to Meaningful and Actionable Decisions
PERF Workshop – Environmental QRA
June 28-29, 2017 Houston
Andrew StaszakMMI Engineering
Email: [email protected]
Tel: (1) 281-810-5011
Mob: (1) 979-575-1897
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Topics Covered:
▪ What is ‘Quantitative Risk Assessment’ in
Process Safety?
▪ Who and What are the/our Drivers?
▪ The Quantitative Risk Assessment Construct
▪ Metrics
▪ QRA in Application – Case Study
▪ Pitfalls / Hotbed Issues
Overview
QRA in Process Safety
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Risk in Definition
Quantitative Risk Assessment (QRA)
utilizes a systematic process to identify
potential impacts and consequences of
events, while considering their
likelihood of occurrence; with
cumulative consideration against a pre-
defined set of metrics.
Risk (according to Merriam-Webster)
▪ Possibility of loss or injury
▪ Someone or something that creates or suggests a hazard
▪ The chance of loss or the perils to the subject matter of an insurance contract
▪ Etc., etc., etc…
Pioneered in the nuclear industry in early 1960s.
O&G applications stated in early 1980s.
Driven by large scale incidents:
• Flixborough, UK 1974 (VCE – 28 fatalities)
• Bhopal, India 1984 (Toxic exposure – 4000
fatalities)
• Mexico City, Mexico 1984 (VCE/BLEVE – 650
fatalities)
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Globally
▪ Multiple regulatory bodies (UK HSE, New South Wales,
Singapore, Australia, ...)
▪ Long history with strict requirements and specific
methods
United States
▪ No single governing body or driver
▪ Sub-sets have limited but specific requirements (FERC –
LNG, PHMSA)
▪ Multiple regulatory bodies utilize the word and recognize
the practice of risk assessment but have little or no
specifics (OSHA PSM)
▪ Guidance comes from industry bodies – CCPS, API, etc.
Numerous sources with numerous focuses
▪ Corporate policies and requirements:
BP GP and Chevron RiskMan
The Drivers
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Who:
Us
• Corp
• Insurance
• People and Cultures
The Drivers Cont.
What:
Best Practices!?!?
• Ever changing and ever argued
• Depends on who you ask
• In many cases swayed by our own biases,
experiences, morals, …
Despite this, there exists a base general method for QRA which falls under generally
accepted and best practices. But, unless driven by an individual company, no two
QRAs will be identical.
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The Construct of a QRA
Risk = f (scenario, consequence, frequency)
Construct a quantitative assessment that allows ‘us’ to adequately
evaluate risk; such that safeguards, corrective actions, and/or
engineered modifications can be used for risk reduction.
This function can be EXTREMELY complex, with numerous different
measures and assumptions required to close the equation.
A QRA of a large scale Refinery could have 1000s of base scenarios,
100,000s of end point consequences, and 1,000,000s of historical data
points considered.
Easy Right?
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The Construct of QRA
Define
Objectives
Hazard
IdentificationHAZID
Frequency
Assessment
Consequence
Assessment
Risk
Formulation
Risk
EvaluationMitigations
Operations/Design Cont. –
Continuous Evaluation
Acceptable
Intolerable
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HazID (Qualitative / Semi-Quantitative):
▪ Conducted to determine what potential upset conditions may
need to be captured
• Natural disasters (tsunami, earthquake, etc.)
• Man-made external causes (airplane, rail, or truck crash)
• Outside of normal operating conditions (human error, runaway
reaction, etc.)
• SIMOPS
▪ Risk rank (qualitative risk matrix) scenario and include in QRA if
necessary (identified as credible ???)
▪ Can include intentional acts – security vulnerability assessment
Hazard Identification - Qual
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Process Breakdown:
▪ Scenario Development
• Examine P&IDs, PFDs, H&M Balance sheets, General
Arrangement
• Discretize: Breakdown process based on logical sections
(physical separation, isolation valves, process barriers)
• Determine suite of releases/hole sizes. A representation of
random failures (leaks, breaks, ruptures, manufacturing flaws,
etc..)
3 is usually considered acceptable – but may not be a good representation.
• It is possible to group similar sections; multiplies the risk
• Upset conditions (from HAZID). How will they be represented?
• What operational conditions will be evaluated?
Normal, temporary, batch, emergency, …
Hazard Identification - Quant
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Process Breakdown:
▪ Frequency Assessment
• Perform parts count and use appropriate failure frequency
database to determine leak frequency for defined process
sections (on/off-shore, cryogenic, custom)
How will frequencies be discretized (median, log average, upper/lower
biased)
Most release frequency is biased to less than 25mm hole sizes
Are there cases that results in no-consequence and can be filtered (<3mm)
• Perform LOPA style analysis to determine failure frequency for
upset scenarios
• Develop frequencies for “unknown/unique events”, requires
input from industry experts and “best” engineering judgment
• Determine if process is operating as designed?
Hazard Identification – Quant 2
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Modeling:
▪ Define outcomes for each scenario – end point consequences –
build event tree
• Careful! – how deep down the rabbit hole do you go?
▪ Determine level of “models” to be used…
▪ Perform consequence analysis to determine extent of impact to
targets of interest
• Toxic lethality
• Blast loadings
• Thermal impacts
• Building damage
• Kinetic impacts
• Dispersion
▪ Exceedance or continual damage model
Consequence Assessment
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Consequence Assessment 2
Events and Probabilities:
▪ Apply modifying probabilities
• Weather (direction and speed, seasonal, yearly,
average, …)
• Lethality
• Exposure duration (time discretization)
• Ignition, and so on
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Example event tree
Consequence Assessment 3
Two-Phase Release Event Tree
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▪ Risk is a relative metric, it means
nothing on its own.
▪ Define risk criteria metrics
Risk Matrix (qualitative)
Individual Risk (IRPA)
Societal Risk (F-N curve)
Fatal Accident Rate (FAR)
Risk Indices
Injury Rate
Potential Loss of Life (PLL)
Cost Analysis…
▪ If possible the criteria should be
selected before the project begins.
▪ Risk is typically defined uniformly for
all hazards and across all business
types.
▪ Define how it will be evaluated and
implemented.
▪ Can the criteria be reached and
maintained?
Risk Criteria
The universal choice
1x10-4
But why?
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Individual Risk:
▪ Typically a single value that is defined as: consequence at a
given rate
• Fatalities/year
• Injuries/year
• $ lost/year
• Environmental impact/year
▪ There are multiple indices in which individual risk can be
measured by:
• LSIR (location specific)
• IRPA (per annum)
• PLL (Potential Loss of Life)
• Average IR
• Maximum IR
Risk Criteria 2
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Societal Risk:
Risk Criteria 3
Societal Risk Criteria
1.00E-09
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1.00E-03
1.00E-02
1 10 100 1000
N (Number of Fatalities)
F (
the F
req
uen
cy o
f N
or m
ore F
ata
liti
es)
Intolerable
NegligibleALARP
Intolerable
Negligible
Can and is evaluated for on and off-site.
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Alternate Risk Result Applications:
Risk Criteria 4
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Risk Interpretation and Mitigation Strategies:
▪ If risk criteria is exceeded, then you must determine what/how to
mitigate:
• Threat (change process, alter scenario, application of
consequence, etc.)
• Target (adjust occupancy, strengthen buildings or equipment,
add shielding, etc.)
• Determine level and priority of required mitigations, may include
quantification for ALARP.
▪ Sensitivity calculations – Do you understand what is driving
the risk.
• Should assumptions, frequency, or consequence be further
investigated?
▪ Is the project / activity / operation still feasible?
▪ What will be the revalidation interval, or what changes (MOC) will
trigger a reval?
Risk Evaluation
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Case Study: Asset Protection
▪ Data generated during a QRA can be utilized in risk based design of
asset protection systems.
• Guidance documents provide – prescriptive steps, but significant
cost and operational constraints can be reduced in performance
(risk) based design.
• Quantitative risk analysis allows us to do this.
▪ Using QRA a performance of the system can be evaluated against a
desired criteria.
▪ In this case, setting the survivability of equipment to a return
period (/year selection) and constrained by evacuation time.
▪ The analysis can determine what level of passive fire protection is
required for various elements of the system.
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Case Study: Asset Protection 2
Peak Heat Flux
Background Heat Flux
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Case Study: Personnel Safety
▪ Individual Risk (IR) is a critical metric in QRA evaluation.
• Allows the identification of risk to specific people and locations on a
site.
• Allows identification of where or what events may be contributing to
risk.
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Case Study: Personnel Safety 2
Sensitivity Case
LSIR Category (/yr)
Jet Fire Pool Fire Explosion
/ FF JF + EXP
/ FF Total
BC 4.57E-05 0.00E-00 6.12E-05 3.24E-06 1.10E-04
S-1 5.99E-05 0.00E-00 1.18E-04 4.90E-06 1.83E-04
S-2 5.99E-05 0.00E-00 7.87E-05 4.22E-06 1.43E-04
S-3 4.57E-05 0.00E-00 4.08E-05 2.89E-08 8.94E-05
S-4 5.86E-05 0.00E-00 1.18E-04 4.48E-06 1.82E-04
Percent Change from Base Case
S-1 31% 0% 93% 51% 66%
S-2 31% 0% 29% 30% 30%
S-3 0% 0% -33% -99% -19%
S-4 28% 0% 93% 38% 65%
▪ If risk is identified as unacceptable/ALARP:
• Investigate data to identify best course of mitigation….i.e. “Best Bag
for the Buck”
• Sensitives can confirm reduction to an appropriate level.
Inclusion of
increased detection
capabilities,
improved isolation,
and control room
protection.
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Issues that arise…
▪ Which frequency database to use
• Onshore vs. offshore
• Is the data relevant?
• Do incidents need to be filtered or revised?
• What if the frequency does not exist or is limited?
▪ Which modifiers to use
• Assume weather parameters are dependent or treat independently
• Process modifiers (as per API 581)
• Ignition probability (many different models)
• Does the frequency database adequately represent the
equipment/process?
• Is the process operating as designed?
• Should we utilize facility specific data (existing sites) or known
company data?
Pitfalls & Hotbed Issues
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Issues that arise…
▪ The calculated risk is based on a snap-shot in time
• How do we account for continued changes during design?
• How do we account for changes/additions to a process or facility?
• What if the location or layout of the facility changes?
• Risk during turn-around?
▪ Risk criteria can vary both intercompany and across countries/
governing bodies, how do we handle this?
▪ In an effort to make risk “As low as reasonably practicable” where do
we stop?
• Analyzing the risk away
• Safety vs Cost
• Perceived Risk…viewed from the public
▪ Mitigations can reduce risk but they can also displace them to
somewhere / something else.
Pitfalls & Hotbed Issues 2