4. How do you define the initiating event?

In risk assessments, the event tree method is commonly used in the detailed analysis phase to identify the various possible consequences associated with a feared event.

There are five main stages in an event tree analysis:

• define the initiating event (starting point of the tree) ;

• identify and characterize the safety barriers put in place to deal with them ;

• build tree structure ;

• describe event sequences to determine the nature of events identified at tree output;

• quantify the tree, i.e. evaluate the frequencies of occurrence of the tree's output events.