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Quantitative Risk Assessment in

Chevron

Use in Decision-Making Involving Major Risks

Rod Travis

Team Lead, HES Risk Management

Chevron Energy Technology Company


Presentation Outline

– Risk, quantitative risk assessment (QRA) and risk tolerance criteria

– Use of QRA in Land Use Planning around Major Hazard Facilities

– QRA Techniques

2


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.

3


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.

4


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


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

6


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

7

Major

Hazard

Total Number of Exposed People


Societal Risk Criteria Examples

8

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


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”

9


Consequence (Deterministic) Approach

10

-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


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

11

Offshore Hydrocarbon Releases

2001 – 2008, HSE RR672, 2008


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

12


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

13

Predominant Worldwide Practice is to Use a Risk-Based Approach for Land Use Planning


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

14


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


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

16


Event Frequency Determination

17

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


Vulnerability Determination

Flammables

Probability of Fatality =

a + b(Q4/3t)

Toxics

Probability of Fatality =

a + bLn(Cnt)

18


QRA Approach Determination of Risk Contours

19


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

20


Typical QRA Output

21

1.00E-03

1.00E-04

1.00E-05

1.00E-06

1.00E-07

1.00E-02


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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