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Control of Industrial Major Accident Hazards (CIMAH) Report Page 5
Ranhill SAJ Sdn. Bhd. Revision 01
Part D: Information on the Potential Major Accident Date Aug 2019

Risk calculation is given in the following formula:

Risk = Likelihood of Occurrence x Consequence of Occurence

Thus, in the qualitative risk assessment (QIRA), a Likert scale is used to assign the
rating for “likelihood of occurrence of an event” and “Consequence of an event if it
happens”. This is normally described in a 5x5 table or matrix.

A sample of qualitative risk assessment matrix is presented as follows.

Severity (S)

Likelihood (L) 1 2 3 4 5

5 5 10 15 20 25
4 4 8 12 16 20
3 3 6 9 12 15

2 2 4 6 8 10
1 1 2 3 4 5

High
Medium
Low

Source: DOSH.
As of quantitative risk assessment (QnRA), the “likelihood of an occurrence” is
quantitatively calculated based on event tree analysis, fault tree analysis or other
formal safety assessment. These studies look into the failure rate of equipment,
machinery and system based on the historical data published by professional and
government organisation, supplier or manufacturer of such equipment / machinery /
system or insurance companies. Some companies do maintain the historical data of
the system used in the plant via the computerized maintenance management system
(CMMS) or maintenance database.

In terms of consequence analysis, typically for process incidents / events that related
to CIMAH reporting are:
i. Fire;
ii. Explosion; or
iii. Toxic Release.