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Appendix D2 Event Tree Analysis

D 2.1 Frequency Analysis

Frequency analysis involves the estimation of the probability of occurrence of each

of the outcome events highlighted in the hazard identification exercise. Frequency
analysis involves the following steps:

• Quantification of the frequency of initiating events (such as leak or rupture of

the Chlorine drum) based on historical data; and
• Quantification of the frequency of various hazardous outcomes through Event

Tree Analysis, which is used to describe and depict chronologically various

outcomes from an initiating event, depending upon the nature and type of the
release.

D.3.2 Failure Rate

In this study, maximum forty-eight (48) units of Chlorine cylinders on-site KT1 and
twelve (12) units of Chlorine drums on-site KT2 to be considered as a conservative

estimation. The failure rates for each chlorine drum and cylinder are divided into two

(2) types of release; catastrophic failure and leaks as shown in Table D.3.2 below.
The failure rate is taken from HSE UK Failure Rate and Event Data.

Types of Release Failure Rate (per year)

-6
Catastrophic failure 2 x 10
-6
50mm diameter hole leak 5 x 10
-5
10mm diameter hole leak 1 x 10
Source: HSE UK
Table D.3.2: Chlorine Drum and Cylinder Failure Rate

1 | P age