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WE MAKE IDEAS WORK Quantitative Risk Assessments for Industrial Developments
Tebodin
Peter van Gorp
January 2016

Content
Principles of Quantitative Risk Assessment (QRA) (4 Slides)
QRA Methodology .(10 Slides)
Risk Criteria ...(7 Slides)
QRA Case Study ......(10 Slides)
Peter van Gorp page 2

severity of consequence likelihood
QRA Terms & Definitions
A measure of human injury, environmental damage or economic loss in terms of both the incident likelihood and the
magnitude of the loss or injury
Hazard / Hazardous Event a chemical or physical condition with potential to cause harm to people, asset / property,
or the environment
Consequence harm (i.e. physical injury, health damage. asset or environmental damage) resulting from a
hazardous event

Quantitative Risk Assessment (QRA)
a systematic process, using mathematical methods, to estimate the consequences and likelihood of
hazardous events and evaluate quantitatively the effects in terms of numerical values of risk to people, asset,
or environment.
a key tool applied in risk based safety management
can provide a basis for emergency preparedness and land use planning

Risk Indicators commonly used to express the risk level
Individual Risk risk to an individual located in the vicinity of a hazard which takes into account his/her occupancy
or work pattern within the vicinity of the prescribed hazard (expressed in terms of risk of fatality per year)
Location Specific Individual Risk risk to an individual at a specific geographic location in the vicinity of a hazard
who is exposed continuously to the hazard. Commonly used in land use planning criteria for fatality or injury
(expressed in terms of risk per year)
Societal Risk risk to a group of people located in the vicinity of a hazard. It is commonly expressed in terms of the
frequency of multiple fatalities per year.

As Low as Reasonably Practicable (ALARP) Principle
residual risk (risk after mitigation)
shall be as low as reasonably
practicable
ALARP Triangle
ALARP or
TOLERABLE REGION
UNACCEPTABLE REGION
ACCEPTABLE
REGION
In
cre
asin
g R
isk
Risk reduction
measures are essential
& required regardless
of costs
A level of risk that is tolerable
and cannot be reduced further
without expenditure of costs
that are disproportionate to
the benefit gained or where
the solution is impractical to
implement
Ideal Level of Risks - Risks are
negligible or so low that can be
managed by routine
procedures and additional
measures are not needed

Quantitative Risk Assessment Methodology
Hazard Identification
Frequency Analysis
Risk Estimation
Consequence Analysis
Risk Evaluation
Acceptable or ALARP
Input to Risk Management
Risk Reduction Measures
Project Scope Definition
No
Yes

QRA Methodology Hazard Identification
Process of identifying existing or possible hazards / hazardous events
Commonly informal desktop review of the layout, process flow, and Piping & Instrumentation Diagrams (P&IDs) to
identify potential sources of incidents and different modes of release of hazardous materials based on professional
judgement
Can be based on formal process such as facilitated group brainstorming session or as part of the safety
assessment (e.g. HAZOP workshop)
Can also be based on historical records from company audits, surveys, investigation reports of past occurrences

QRA Methodology Consequence Analysis
Estimation of the effects or magnitude of the hazards
involves the application of mathematical, analytical and computer models for calculation of the physical effects (e.g.
fire, explosion or toxic dispersion) resulting from a release of hazardous substances
translating the physical effects in terms of degree of injuries and extent of damage to exposed population, assets /
property, and environment (e.g. minor, severe, catastrophic) by comparing with impact criteria (can be company
developed or Internationally recognised criteria)

QRA Methodology Consequence Analysis Damage Criteria Thermal Radiation
page 10
Thermal radiation
Damage
Assets People
1.6 kW/m2 - Causes no discomfort for long exposure
4.0 - 5.0 kW/m2 - Sufficient to cause pain to personnel if unable to reach cover within 20 seconds; however blistering of the skin (second-degree burns) is likely; (0% lethality)
9.5 kW/m2 - Pain threshold reached after 8 seconds; second-degree burns after 20 seconds
12.5 15 kW/m2 Building made of cellulosic materials may suffer damage after prolonged exposure. 1% lethality in 1 min; first-degree burns
23.0 kW/m2 Buildings that are made of cellulosic materials or not fire-resistant will suffer damage after short exposures. Fire-resistant structures and metal may suffer damage after prolonged exposure.
-
25 kW/m2 - 100% lethality in 1 min; significant injury in 10 seconds
35-37.5 kW/m2 Fire resistant structures suffer damage after short duration. Buildings of cellulosic materials ignite spontaneously. Metal fatigue after a short to medium exposure.
100% lethality in 1 min; 1% lethality in 10 seconds

QRA Methodology Consequence Analysis Damage Criteria Overpressure
page 11
Overpressure Assets People
0.15 - 0.30 PSIG
(0.01 - 0.02 bar) Glass Damage to about 10 % of panes Slight Injury from flying glass
0.5 1.0 PSIG
(0.03 0.07 bar) Glass Damage Injury from flying glass
1.0 - 2.4 PSIG
(0.07 0.17 bar)
Repairable damage to buildings and damage to
facades of dwellings
1% Eardrum rupture
1% Serious wounds from flying objects
2.5 - 5 PSIG
(0.17- 0.35 bar)
Heavy damage to buildings and to process
equipment
1% death from lung damage
> 50% eardrum rupture
> 50% serious wounds from flying objects

QRA Methodology Consequence Analysis Thermal Radiation Contour
page 12
4 kw/m2 JET FIRE ELLIPSE
EVENT: Jet fire SHAPE: Considering prevailing wind direction and speed EFFECT ZONE: Effects in all directions regardless of wind direction
12.5 kw/m2 JET FIRE ELLIPSE
35 kw/m2 JET FIRE ELLIPSE
4 kw/m2 EFFECT ZONE
12.5 kw/m2 EFFECT ZONE
35 kw/m2 EFFECT ZONE

QRA Methodology Consequence Analysis Overpressure Contour
page 13
0.02068 bar VCE RADIUS
EVENT: Vapour Cloud Explosion SHAPE: Considering prevailing wind direction and speed EFFECT ZONE: Effects in all directions regardless of wind direction
0.02068 bar EFFECT ZONE

QRA Methodology Frequency Analysis
Estimation of the likelihood or probability of an incident commonly based on historical data on
incident frequencies or Event Tree Analysis
Historical Incident Frequencies calculation of total failure frequencies of all components of a defined system
such as flanges, valves and equipment based on the release frequencies database (such as International Oil &
Gas Producers (IOGP) Process Release Frequencies; Publication Series on Dangerous Substances (PGS 3)
Guidelines for Quantitative Risk Assessment).

QRA Methodology Frequency Analysis
Event Tree Analysis a logical model that
portrays the combination of failures of events
in an incident sequence
begins with initiating event where
consequences of this event create a path in
which a series of successes or failures will
occur where the overall probability of
occurrence for that path can be calculated
Event Tree Model
Initial Scenario
Pool Fire 2.42 10-10
Flash Fire 0
Explosion 1.62 10-9
Jet Fire 9.67 10-10
Loss of Containment
Flammable Gas Flash Fire 0
Outflow Frequency : 1.24 10-8
Explosion 6.47 10-10
No effect 3.10 10-9
0.5 m3
0.87
1.0
0.25
0.15
0.6
Total Inventory
5.0 m3
1.0
0.13
0.0
0.13
0.0
0.87
Relevant Release Direct Ignition Delayed Ignition Event

QRA Methodology Risk Estimation & Assessment
Risk calculation is done using mathematical models or modelling software to combine the consequence
analysis and frequency analysis
The risk results are presented in the form of risk contours for Individual Risk or Location Specific Individual Risk and
F-N curves for Societal Risk.
Risk evaluation is carried out by comparing the calculated risks with respect to risk criteria (local or
International)
page 16

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