As has been pointed out, barriers are selected based on
scenarios, which are developed from so-called bowties.Combining
a fault tree and an event tree at their top events and
turning this on its side, results in a figure that resembles a
‘bow tie’. Scenarios then are formulated by describing escalation
paths through this bow tie, starting at initial events on
the fault tree side (‘threats’) and ending at unwanted ones on
the event tree side of the figure (‘consequences’). The use of
bow ties for this purpose has become quite common in the
last fewyears and, consequently, the development of scenario
based auditing techniques has become opportune.