4. Bow tie quantification

4.1 Principle of quantification

Quantifying a bowtie, the aim of which is to estimate the probabilities of occurrence of hazardous phenomena, requires first assessing those of the dreaded event. This is followed by assigning failure probabilities to the mitigation/protection barriers listed in the event tree, in order to deduce the probabilities of the hazardous phenomena.

Quantifying a bowtie involves three main steps (figure 16 ):

• 1. evaluation of the frequency of occurrence of the feared event, either "directly" by referring to...