Risk Estimation

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Risk Estimation
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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.

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Examples of risks associated with activities
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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.

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Location Specific Individual Risk

• 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
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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

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
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Example LSIR for Ship Explosion at a Proposed
Port
1 x 10-5
1 x 10-6
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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.

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Determination of Societal Risk

• To calculate the number of fatalities resulting
  from each incident outcome case, the following
  equation is used

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

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.
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Example The corresponding Societal Risk
1x10-3
Frequency (F) on or more Fatalities (per year)
Intolerable Region
1x10-4
1x10-5
ALARP Region
1x10-6
Broadly Acceptable Region
1x10-7
1
10
100
1000
10000
Fatalities (N)
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Risk Tolerability and ALARP Concept
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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

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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
THE ALARP REGION (Risk is undertaken if
benefited is desired)
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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.

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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
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Tolerability criteria (Netherland)

• Risk to public cannot be more than 1X 10-6 fpy
• Fatality cannot be more than 10 at risk 1X 10-5
  fpy
• Slope -2

General public only
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Tolerability Criteria (Australia)
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Tolerability Criteria (Canada)
Major industrial accident council of Canada
(MIACC) recommends the above Individual risks
level