8. Frequently asked questions

In what order should mitigation barriers appear in the event tree?

Safety barriers generally operate in chronological order. This chronological order is dictated by the barrier's response time, i.e. the time between when it is called upon and when it fulfills its safety function.

In practice, therefore, the barrier with the lowest response time appears first in the tree. The other barriers then appear in ascending order of response time.

Is there any software available to exploit event trees?

There are a number of commercial software packages on the market today that enable :

• to build the tree structure,

• calculate the frequency of the various ERS or consequences at the output of the shaft.

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