Inserting and Managing Disjoint Event Groups
Disjoint events are a group of two or more events that are mutually exclusive. The occurrence of one event in the group means that none of the other events in the group can occur. Disjoint events can be used to model multi-state components and/or multiple failure modes.
When cut set calculations run, any cut set with two or more events from the same disjoint event group has a probability of 0 and is not shown in the cut set list. Exact calculations also take disjoint event groups into account during computations.
You can create and manage disjoint event groups when a tree is active.
1. From an FTA pane, do one of the following to open the Disjoint Event Groups window:
◦ Select > .
◦ Right-click in the diagram and select Disjoint Events.
The
Disjoint Events window provides for inserting, modifying, and deleting disjoint event groups. For more information, see
Disjoint Event Groups Window.
2. To insert a disjoint event group, do the following:
a. Click New Group. The Group Name window opens.
b. Enter the name for the disjoint event group and click OK. The group is inserted and added to the Group list in the Disjoint Event Groups window.
Once you have created one or more disjoint event groups, all options in the window are made available.
c. Select the events to add to the disjoint event group by moving them to the Events in group list. If a disjoint group does not have two or more events in it, it is ignored when FTA calculations are run.
You can select multiple events and move them to and from the All events list and Events in group lists at the same time. To select contiguous events, click the first event and then drag the mouse until all of the desired events are selected. To select noncontiguous events, press and hold down Ctrl while clicking the desired events.
3. To modify or delete disjoint event groups, use the appropriate options.
4. When finished, click OK to close this window.