3. Build the event tree

3.1 Construction principle

A tree is built using inductive reasoning which, for each of the safety barriers put in place to reduce the intensity of the consequences, allows two cases to be studied:

• The barrier fulfils its safety function.

• The barrier does not fulfil its safety function.

In other words, for each of the mitigation barriers implemented, the following two questions must be answered:

• What happens when the barrier "works"?

• What happens when the barrier "doesn't work"?

An example of an event tree is shown in the figure "Structure of an event...