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Control of Industrial Major Accident Hazards (CIMAH) Report Page 50
Ranhill SAJ Sdn. Bhd. Revision 01
Part D: Information on the Potential Major Accident Date Aug 2019

D.6.2 Individual or Societal Risk

A quantitative risk assessment (QRA) has been conducted that provides the location
specific individual risk (LSIR) iso-risk contours or frequency-fatalities (F-N) curves.
Individual risk is the annual risk of death to which specific individuals are exposed.

D.6.2.1 Generation of Risk Numbers

To generate the quantitative risk number for the major accident scenario, the
probabilistic risk analysis such as Vulnerability Model is adopted and the formula is
given as follows.

F = F × P × P
F
wd
T
f

In which,
F T is the risk of exposure to a fatal concentration in an area
F f is the failure frequency
P wd is the probability of the specified wind direction and atmospheric stability
P F is the probability of fatality at that distance (as a value between 0 and 1)

For the purpose of this study, the basic equation is modified so that the wind
direction probabilities are removed where wind does not affect the final outcome.
This calculation is performed for failure scenario at the specified distances from the
source of release.

D.6.2.1.1 Failure Frequency

Event-tree analysis (EVA) is performed for obtaining the failure frequency (F f) of a
major accident. EVA allows modelling of a sequence of events, and works for
domino effects.