Introduction to Consequence Modelling - DNV

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SOFTWARE

Introduction to Consequence Modelling

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Webinar February 2017

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Speakers

Kenny Shaba

Phast and Safeti Product Manager with extensive experience in

Technical Safety projects (especially QRA) for both onshore

and offshore assets

Mark Hunter

Chartered Engineer in DNV GL’s Advisory business

11 years’ experience of safety related studies in the oil & gas

sector

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Agenda

Why consequence modelling? E.g. societal and regulatory drivers

– What is consequence modelling etc?

Key hazards types to consider (fires, explosions and toxic hazards) and how to evaluate their impact potential

Operational and practical applications of consequence modelling

Challenges to robust and rigorous consequence modelling

Q&A

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Why Consequence Modelling?

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The Oil and Gas/Chemical/Process Industries

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The Oil and Gas/Chemical/Process Industries

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Reference: Geoff Chamberlain and Bassam Burgan (2016) The Explosion at the Caribbean Petroleum Corporation (CAPECO) storage facility at Bayamon, Puerto Rico. Proceedings of FABIG TM 86 “Lessons Learnt from Recent Accidents”.

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Controlling the hazards is key…

Robust and detailed evaluation of process hazards is key to developing an effective management

strategy. Why?

To control risks you have to manage processes to reduce them

To be able to manage risks you have to understand them.

To be able to understand risks you have to analyse the risks.

If you don’t do the analysis you might not fully understand the issues.

If you don’t fully understand, you might not be able to target your effort to reduce risks cost

effectively and it will be harder to justify your decisions.

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Control of Risks

Management

Understanding

Analysis

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IMPACTS and DRIVERS

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IMPACTS DRIVERS

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THE SAFETY PARADOX

Most successful companies – good at managing risk

+ exploiting opportunity

CM is a key element of risk management – “business

enabler”/ “adds value”

“People react to what they see”

Here comes the paradox – “Safety done well is

not visible”/”Safety done badly is highly

visible”

Safety is the status quo – This is what is expected

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THE COST OF GETTING IT WRONG

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$1860

MILLION

LOST REVENUE

FINES

INSURANCE PAYOUTS

ENVIRONMENTAL

REMEDIATION

ASSET DAMAGE

SHARE PRICE

COMPANY REPUTATION

LITIGATION

ECONOMIC COSTS

BUSINESS DISRUPTION

Reference: Marsh (2016). “The 100 Largest Losses 1974-2015 Large property damage losses in the hydrocarbon industry” 24th

Edition. Available Online.

PROPERTY LOSS

“If you think safety is expensive, try having an accident” – Trevor Kletz

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Key hazards types to consider (fires, explosions and toxic hazards) and how to evaluate their impact potential

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Key hazards types to consider

Flammable (Natural Gas etc.)

– Fires

– Jet, Pool, Flash, Fireball, BLEVE

– Explosions

– Confined VCE, Unconfined CVE

Toxic (e.g. H2S, Ammonia)

Cryogenic (e.g. LNG)

Asphyxiation (Inert Gas e.g. CO2 and N2)

Smoke

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Consequence Modelling - Stages

Stage 1: Physical Effects Modelling

– Key goal – understanding the physical

characteristics/make up of hazard in the

environment

Stage 2: Impact modelling

– Key goal – translation of hazard ranges

to Tangible impacts: life, property,

environment

– Less tangible impacts

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Evaluating Impact Potential

Various methods exist

Simple to Complex

«Hand calculations» to «Look up tables» to «Excel»

to «Software applications»

Key decision factors – validated models and

methodology, reflects latest science, transparent,

high quality trusted platform, widely accessible, user

friendly, long shelf life…

Recommend a fully integrated package (effects

modelling and impact analysis) with detailed

modelling logic e.g Phast

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Factors to consider for consequence modelling

Scenario/Case information

Environmental conditions

Choice of scientific tool/model

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Operational and practical applications of consequence modelling

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A few popular applications…

As part of a (Quantitative Risk Analysis) QRA study

Hazardous Area Classification

Facility Siting

Chimney Stack sizing

Fugitive emissions

Vent modelling

Equipment Separation Distances

Site Layout Optimization

Flare height determination

Emergency Response

Etc.

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Example - Flammable Gas

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Unit-12

Unit-15Unit-21

Unit-25Unit-10

Control Room

Warehouse

Utilities

Unit-30

½ LFL

LFL

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Example - Explosions – 100mbar

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10-3 per year

10-4 per year

10-5 per year

10-6 per year

10-7 per year

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Example - Risk - QRA

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10-3 per year

10-4 per year

10-5 per year

10-6 per year

10-7 per year

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Many challenges exist. Some key ones are as follows:

Inadequate problem definition and understanding

Analytical tools (Selection, Application, Analyst Expertise and Limits)

Poorly defined background assumptions

Lack of Quality Control/Assurance

Results Interpretation

Personnel Competency

Silo’ed delivery. CM should be a team effort

Reproducible (documentation problem)

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Underlying Assumptions INFLUENCE Results

Goes by various names:

– Assumptions Register

– Study Basis

– Calculation Basis

Any result should always be considered in

tandem with the assumptions made

A number of things are key:

– Sensitivity Analysis, Social consent,

Conservatism

Finally – CM is always about numbers – need to

remember the context is largely about keeping

people safe

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Background Assumptions: Approach to Modelling Two-phase releases

Modelling single phase releases is

straightforward

Two-phase is more involved

Rationalising to a single phase can be

dangerous

Need to model 2-phase as realistic as possible

Phast has an excellent way of approaching

this…

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Background Assumptions: Explosion modelling

Science in this area has improved significantly in

recent years

Congestion/confinement are needed for explosions

with appreciable overpressure

Older models e.g. TNT do not account for

congested/confined area

Nevertheless – still used. Possible reasons?

– Simple?

– Lack of awareness?

Historical focus has been on the overpressure. Now

overpressure and pulse duration

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Background Assumptions: Vulnerability Modelling

All about converting hazard ranges into human/asset

impact

Based on historical evidence, experience and

experimental science (some animal studies)

Relatively straightforward for fires and explosions

Toxics is based on animal data and extrapolated to

human beings – hence somewhat uncertain and thus

subject to change

E.g. RIVM recently updated their probits for certain

chemicals. The UK HSE also update toxicity data for

use in risk assessments from time to time.

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Background Assumptions: Mixtures

Various boiling points

Vapour phase will be richer in the more volatile

components; Liquid phase will be richer in the

heavier components

Average compositions will not reflect the

characteristics of the real situation

– for e.g a pool fire from heavy hydrocarbons has

different characteristics from one with lighter

material (sootier flame, more smoke)

– Lighter gases will disperse differently

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Top tips for conducting Consequence Modelling

Clear problem definition

Clearly outlined and agreed assumptions and study basis

upfront

Selection of a robust consequence analysis tool

Sensitivity Analysis to key assumptions is key – need to

understand the associated uncertainty/influence on the

results

Robust documentation convering all aspects

Do not work in isolation – CM is a team effort that needs

input from various disciplines

Perform Quality Assurance checks

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Summary and Conclusions

We have explored Consequence Modelling from a

broad perspective…

Identified some applications and challenges…

And concluded with some top tips for conducting

consequence modelling

Key conclusions:

– Consequence modelling is a key pillar of risk

management

– Done right it can help achieve many RM objectives

– Need to be aware of the pitfalls to leverage it

successfully

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Useful References

“Reducing Risks, Protecting People" Health and Safety Executive (2001).

TNO Yellow Book – CPR14E Methods for the Calculation of Physical Effects

Chemical Process Safety: Fundamentals with Applications (2nd Edition), Daniel A. Crowl and Joseph F. Louvar,

2002 Edition, Publishers : Prentice Hall, Inc. Englewood Cliffs, New Jersey.

Lees – Loss Prevention in the Process Industries

CCPS Publications (Various) E.g. Guidelines for consequence analysis of chemical releases (1999)

Kletz, T. What Went Wrong? Case Histories of Process Plant Disasters (1998) Gulf (and others)

Trade industry Publications: OGP, Oil and Gas UK, CIA, API etc.

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Notes

For further information about today’s webinar or Phast, please

contact us:

[email protected]

For more information about Phast, please see:

https://www.dnvgl.com/phast

For future events, please see:

https://www.dnvgl.com/software-events

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mailto:[email protected]

https://www.dnvgl.com/phast

https://www.dnvgl.com/software-events

Introduction to Consequence Modelling - DNV

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