3. Build the event tree

As with the fault tree, in hazard studies, the downstream part of the dreaded event is generally represented by a tree structure in which the mitigation barriers are symbolically represented (by a vertical bar that runs counter to the accident sequence). As a result, the tree structure does not correspond strictly speaking to an event tree, since it does not show the different possible consequences depending on whether or not the mitigation barriers are fulfilling their safety function. An example of a simplified representation is shown in the figure "Simplified event tree for the dreaded event: Chlorine leak during wagon unloading".