Transcript No Slide Title

Risk Estimation
Two distinct categories of Risies
• Voluntary Risks
• e.g. driving or riding in an automobile, and
working in an industrial facility.
• Involuntary Risks
• e.g. exposure to lighting, disease, typhoons
and persons in residential or recreational
areas near the industrial facilities.
Examples of risks associated with activities
Voluntary
Activity
Smoking (20
cigarettes/day)
Motor cycling
Car racing
Car driving
Rock climbing
Football
Involuntary
Risk fatalities
(death) per
person per yr
(x106)
5000
2000
1200
170
40
20
Activity
Influenza
Leukemia
Run over by road
vehicle (UK)
Run over by road
vehicle (USA)
Floods (USA)
Storms (USA)
Lightning (USA)
Falling aircraft
(USA)
Falling aircraft
(UK)
Risk fatalities
(death) per
person per yr
(x106)
200
80
60
50
2.2
0.8
0.1
0.1
0.02
Individual Risk
• Individual risk is defined formally (by Institution of
Chemical Engineering, UK) as the frequency at which
an individual may be expected to sustain a given
level of harm from the realization of specified
hazards. It is usually taken to be the risk of death,
and usually expressed as a risk per year.
• The term ‘individual’ may be a member of a certain
group of workers on a facility, or a member of the
public, or anything as defined by the QRA.
Location Specific Individual Risk
IRx ,y ,i  pifi
• IRx,y,i is the individual risk at location (x,y) due to event i,
• pi is the probability of fatality due to incident i at location
(x,y). This is normally determined by FTA
• fi is the frequency of incident outcome case i, (per year). This
value can be determined using Probit Analysis
When there are more than one release events, the
cumulative risk at location (x,y) is given by equation
n
IRx ,y   IRx ,y ,i
i 1
Average Individual Risk /
Individual Risk Per Annum
• The average individual risk is the average of all individual
risk estimates over a defined or exposed population. This is
useful for example in estimating the average risk of workers
in reference with existing population. Average individual risk
over exposed population is given by CCPS (1989) as
IRAV 
IRx y Px y

x y
,
,
,
Px y

x y
,
,
Here, IRAV is the average individual risk in the exposed population
(probability of fatality per year) and P x, y is the number of people at
location x, y
Example: LSIR for Ship Explosion at a
Proposed Port
1 x 10-5
1 x 10-6
Societal Risk
• Societal risk measures the risk to a group of people.
It is an estimation of risk in term of both the
potential size and likelihood of incidents with
multiple consequences.
• The risk can be represented by Frequency-Number
(F-N) Curve.
Determination of Societal Risk
• To calculate the number of fatalities resulting from each
incident outcome case, the following equation is used:
Ni  Px ,y pf ,i
x ,y
Here, Ni is number of fatalities resulting from Incident
Outcome case i, pf,i is the probability of fatality and Px,y is the
number of population.
• The cumulative frequency is then calculated using the
following equation:
FN  Fi
i
Here, FN is the frequency of all incident outcome cases affecting N or more
people, per year and Fi= is the frequency of incident outcome case i per
year.
Frequency (F) on or more Fatalities (per year)
Example: The corresponding Societal
Risk
1x10-3
Intolerable
Region
1x10-4
1x10-5
ALARP
Region
1x10-6
1x10-7
Broadly Acceptable
Region
1
10
100
Fatalities (N)
1000
10000
Risk Tolerability
and
ALARP Concept
In life, there is always some risks…
• There is no such thing as zero risk
• All activities involve some risks
• The issue is at level should we tolerate
these risks…
Tolerable Risk
• Risk cannot be eliminated entirely.
• Every chemical process has a certain amount of risk
associated with it.
• At some point in the design stage someone needs to
decide if the risks are “tolerable".
• Each country has it owns tolerability criteria.
• One tolerability criteria in the UK is "as low as
reasonable practicable" (ALARP) concept formalized
in 1974 by United Kingdom Health and Safety at Work
Act.
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ALARP Criteria
INTOLERABLE LEVEL
(Risk cannot be justified
on any ground)
THE ALARP REGION
(Risk is undertaken if benefited
is desired)
TOLERABLE only if risk reduction
is impracticable or if its cost is
grossly disproportionate to the
improvement gained
TOLERABLE if cost of reduction
would exceed the improvement
gained
BROADLY
ACCEPTABLE
REGION
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Tolerability Criteria in Malaysia
• LSIR is used as a measure of individual risk
– This means that the risk is not influenced by
population
• The Upper limits for LSIR are as follows
– For residential receptors : 1 X 10-6 fatality per
year
– For industrial receptors : 1 X 10-5 fatality per year
– For workers on site: Voluntary risk (1 X 10-3
fatality per year). This is considered maximum in
UK for offshore industry.
Tolerability Criteria (UK)
• This framework is represented as a three-tier system as
shown in figure. It consists of several elements :
(1) Upper-bound on individual (and possibly, societal) risk
levels, beyond which risks unacceptable. In UK, the
guideline and criteria are spelled out in R2P2 (reducing
Risk Protecting People) document. (refer to www.
hse.gov.uk)
(2) Lower-bound on individual (and possibly, societal) risk
levels, below which risks are deemed not to warrant
regulatory concern.
(3) intermediate region between (1) and (2) above, where
further individual and societal risk reductions are required
to achieve a level deemed "as low as reasonably
practicable (ALARP)".
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Tolerability Criteria (UK)
Dotted line –
general public
Solid line - workers
Tolerability criteria (Netherland)
1. Risk to public cannot be
more than 1X 10-6 fpy
2. Fatality cannot be more
than 10 at risk 1X 10-5 fpy
3. Slope -2
General public only
Tolerability Criteria (Australia)
Tolerability Criteria (Canada)
Major industrial accident council of Canada (MIACC)
recommends the above Individual risks level