5. Quantify the event tree

5.1 General case

The aim of quantifying an event tree is to determine the frequency of occurrence of the various HRAs at the output of the tree. To do this, it is necessary to evaluate :

• frequency of occurrence of the initiating event ;

• the probability of failure of the safety barriers put in place to reduce the intensity of the consequences (ERS) in the event of the initiating event.

For a safety barrier, the probability of failure under load corresponds to the probability that it will not be able to perform its function at the time it is loaded.

For each barrier, you need to associate :

• the PFD...