©2013 Chevron U.S.A. Inc. All rights reserved.
Quantitative Risk Assessment in
Chevron
Use in Decision-Making Involving Major Risks
Rod Travis
Team Lead, HES Risk Management
Chevron Energy Technology Company
©2013 Chevron U.S.A. Inc. All rights reserved.
Presentation Outline
– Risk, quantitative risk assessment (QRA) and risk tolerance criteria
– Use of QRA in Land Use Planning around Major Hazard Facilities
– QRA Techniques
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©2013 Chevron U.S.A. Inc. All rights reserved.
Risk and Quantitative Risk Assessment Defined
– Risk A measure of human injury, environmental damage, or economic
loss in terms of both the incident likelihood and the magnitude of the
injury, damage, or loss… or the probability that a hazard will result in a
specified level of loss
– Risk is defined mathematically as:
Risk = [Consequences] x [Likelihood]
[Severity] x [Frequency]
– Quantitative risk assessment (QRA) The systematic development of
numerical estimates of the expected frequency and consequence of
potential accidents associated with a facility or operation based on
engineering evaluation and mathematical techniques.
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Risk Tolerance and Risk Tolerance Criteria
Risk Tolerance
– A “willingness by society as a whole to live with a risk so as to secure
certain benefits in the confidence that the risk is one that is worth taking
and that it is being properly controlled. However, it does not imply that …
everyone would agree without reservation to take this risk or have it
imposed on them.” [United Kingdom, Health and Safety Executive, 2001]
Risk tolerance criteria
– A predetermined measure of risk used to aid decisions about whether
further efforts to reduce the risk are warranted.
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Individual Risk
Individual Risk represents the likelihood that a
person will sustain a fatal injury by all of the
hazardous events to which he or she may be
exposed. Presented as a frequency number
(fatalities/year). Individual risk ensures that each
person is not exposed to an aggregation of different
risk exposures, the sum of which leads to an overall
high risk exposure for the individual.
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Specifies an upper limit amount of 10-4 fatalities/year for individual members of the public exposed to an industrial hazard
Example of
Individual
Risk Criteria
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Individual Risk Criteria Examples
Singapore
– The 5 x 10-5 per year Individual Risk Contour remains within the fenceline
– The 5 x 10-6 per year Individual Risk Contour extends into Industrial Developments only
– The 1 x 10-6 per year Individual Risk Contour extends into Commercial and Industrial Developments only
Source – Singapore Pollution Control Department Guidelines for Quantitative Risk Assessment, April 2007
Western Australia
– A risk level in residential zones of 1 x 10-6 per year or less is so small as to be acceptable to EPA
– A risk level in “sensitive” areas of 5 x 10-7 per year or less is so small as to be acceptable to EPA
– Risk level from Industrial facilities should not exceed 5 x 10-5 per year at the boundary
Source - Guidance for Risk Assessment and Management: Offsite individual risk from Hazardous Industrial Plant, No.2 WA EPA, July 2000
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Societal Risk
Societal Risk represents the number of people who may
be killed by large, single events and how often those
events might occur. Presented as F-N Curves (Plots
depicting the frequency “F” of exceeding “N” or more
fatalities) which set:
– Risk criteria for the public
– Risk criteria for employees
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Major
Hazard
Total Number of Exposed People
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Societal Risk Criteria Examples
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1.00E-09
1.00E-08
1.00E-07
1.00E-06
1.00E-05
1.00E-04
1.00E-03
1.00E-02
10 100 1000
F, C
um
mu
lati
ve F
req
uen
cy o
f N
or
mo
re F
ata
liti
es
N, Fatalities
UK Dutch Hong Kong Victoria NSW
Guidelines for Developing
Quantitative Safety Risk
Criteria, CCPS, 2009
©2013 Chevron U.S.A. Inc. All rights reserved.
Consequence vs. Risk-Based Approach to Land Use
Planning
Consequence (Deterministic) approach uses only the consequence
variable in the risk equation. Theoretically this approach would
ensure no fatalities will occur as the result of facility operations, but
typically results in impractical and unenforceable requirements
– Examples “All airplanes must be designed to never crash” or “no toxic
release shall never pass a facility fence line”
Risk approach uses both the consequence and the likelihood
parameters of the risk equation, taking into account the significant
safeguards in place that lower the frequency of major
accidents/releases and align the risk with overall societal nor
– Example “Require an exclusion zone where the risk of fatality to any
individual exceeds the chance of 1 in 10,000 years”
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Consequence (Deterministic) Approach
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-400.0
-300.0
-200.0
-100.0
0.0
100.0
200.0
300.0
400.0
0.0 500.0 1000.0 1500.0 2000.0 2500.0 3000.0 3500.0 4000.0 4500.0
Momentum Jet CloudCONCENTRATION CONTOURS: OVERHEAD VIEW
Wellpad I Pipeline
CANARY by Quest Thu Aug 18 10:33:38 2011F stability
windspeed = 1.00 m/scasename=WPI1AA3L
1000 ppm Hydrogen Sulfide 100 ppm Hydrogen Sulfide
Cro
ssw
ind
Dis
tan
ce
(m
ete
rs)
Downwind Distance (meters)
-400.0
-300.0
-200.0
-100.0
0.0
100.0
200.0
300.0
400.0
0.0 500.0 1000.0 1500.0 2000.0 2500.0 3000.0 3500.0 4000.0 4500.0
Momentum Jet CloudCONCENTRATION CONTOURS: OVERHEAD VIEW
Wellpad I Pipeline
CANARY by Quest Thu Aug 18 10:34:15 2011F stability
windspeed = 1.00 m/scasename=WPI1AA0L
1000 ppm Hydrogen Sulfide 100 ppm Hydrogen Sulfide
Cro
ssw
ind
Dis
tan
ce
(m
ete
rs)
Downwind Distance (meters)
50mm Hole
Full Bore Rupture
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Likelihood of Different Consequences
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 50 100 150 200 250 300
% o
f H
ole
siz
e
Hole Size, mm
COMPRESSORS, CENTRIFUGAL COMPRESSORS, RECIPROCATING FILTERS
HEAT EXCHANGERS, HC IN SHELL HEAT EXCHANGERS, HC IN TUBE HEAT EXCHANGERS, PLATE
FIN FAN COOLERS INSTRUMENTS PIG LAUNCHERS/RECEIVERS
PRESSURE VESSEL PUMPS, CENTRIFUGAL PUMPS, RECIPROCATING
PIPES, VALVES & FLANGES =<3" PIPES, VALVES & FLANGES >3"
80% of releases from pressure vessels are less than 50mm equivalent diameter
95% of releases from all other equipment are less than 50mm equivalent diameter
88% of releases from piping are less than 50mm equivalent diameter
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Offshore Hydrocarbon Releases
2001 – 2008, HSE RR672, 2008
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Why Chevron Use a Risk-Based Approach
Many countries worldwide have recognized that a consequence
based approach results in land use requirements for industrial
developments that are not sustainable.
This is particularly true of densely populated regions such as UK &
Europe, Singapore, Hong Kong and the urban areas of Australia and
the risk based approach is therefore enshrined in law in these
countries
Chevron (in common with the majority of international energy
companies) has adopted a risk based approach as its default position
for the management of hazards associated with its operations
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Governments that Require (or Use) QRA and Set (or
Use) Risk Criteria
Australia
Brazil
Canada
China (Hong Kong)
Czech Republic
Demark
France
Hungary
Netherlands
Norway
Singapore
Switzerland
United Kingdom (UK)
US Department of
Energy/Nuclear Regulatory
Commission
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Predominant Worldwide Practice is to Use a Risk-Based Approach for Land Use Planning
©2013 Chevron U.S.A. Inc. All rights reserved.
Some Companies/Industries Using QRA for Risk
Decision-Making (Not Exhaustive)
Oil Industry
– BP
– Chevron
– Conoco/Phillips
– ExxonMobil
– Norske Hydro
– Shell
– Statoil
– Total
Pharmaceutical Industry
– Merck
– Eli Lilly and Company
Chemical Industry
– Eastman Chemical Company
– Albemarle
– Air Products and Chemicals, Inc.
– Rohm and Haas Company, retired
– Solutia, Celanese
– Dow Chemical
– Lyondell Basell Industries
– DuPont
– Croda, Inc.
– Intel
Aerospace/Defense/Nuclear
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Hazard Identification
(IHAZID process)
Scenario
Development
Frequency
Analysis
Consequence
Analysis
Risk
Assessment
Risk Tolerance
Criteria
Are risks reduced
to a level that
is as low as is
reasonable?
Document Plan to
Implement agreed risk
reduction measures
Yes
No
Investigate
Further Risk
Reduction
Measures
QRA Process
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PFDs / P&IDs
Historical data
Ignition models
Release modeling
Dispersion modeling
Explosion models
Fire models
Event Trees which
take consideration of: • Weather conditions
• Population distributions
• Plant layout
• Fatality models
• Protective equipment
• Emergency response
FN Curve (Societal Risk)
Individual Risk Contours
Good Practice
Codes & Standards
IHAZID
PHA
Walkthrough
PFDs
Process descriptions
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How Do We Quantify Risk?
Primary means of quantification is through event trees
– These take an initiating event (e.g. ¼-inch release from compressor
suction scrubber) and develop it into all possible outcomes – unignited,
early ignition leading to jet fire, delayed ignition in open leading to flash
fire, delayed ignition in congested / confined region leading to explosion.
Supported by fault trees, FMEA, part counts, reliability analysis and
ignition modeling to quantify frequency and branch probabilities
Supported by dispersion analysis, fire analysis, explosion analysis
and vulnerability assessments to quantify consequence
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Event Frequency Determination
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Loss of
Containment
Event / year
Probability of
Hole Size
Ignition? Delayed Ignition? Explosion? Outcome
Small Yes Yes Yes Explosion
No Flash Fire
No Jet Fire
No Toxic Exposure
Medium Yes Yes Yes Explosion
No Flash Fire
No Jet Fire
No Toxic Exposure
Large Yes Yes Yes Explosion
No Flash Fire
No Jet Fire
No Toxic Exposure
Massive Yes Yes Yes Explosion
No Flash Fire
No Jet Fire
No Toxic Exposure
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Vulnerability Determination
Flammables
Probability of Fatality =
a + b(Q4/3t)
Toxics
Probability of Fatality =
a + bLn(Cnt)
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QRA Approach Determination of Risk Contours
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Risk Measures
Risk Contours
– Probability of fatality per year to an individual located on the spot 24 hours per day/365 days per year
– Graphical representation of the potential impact zone of hazards
– Used primarily for public exposure since people living in close proximity to a facility can be continuously exposed
FN Curve
– Measure of the risk of incidents which can cause multiple fatalities
– Typically used to gauge the acceptability of having large congregations of people exposed to hazards (for example, in schools, hospitals, etc. or during turnarounds or in occupied buildings on site)
Individual Risk per Annum (IRPA)
– Likelihood of fatality per year for an individual based on their exposure to that risk. Used primarily for workers who are only exposed to the risk when at work
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Typical QRA Output
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1.00E-03
1.00E-04
1.00E-05
1.00E-06
1.00E-07
1.00E-02
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Further Reading
Guidelines for Developing Quantitative Safety Risk Criteria, CCPS,
2009
Guidelines for Chemical Process Quantitative Risk Analysis, CCPS,
2000
Reducing Risks, Protecting People, Health and Safety Executive,
2001
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Q & A
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