Reading an event tree
How an event tree is laid out, the two notation profiles, text and probabilities on branches, the summary strip, and what the Node Inspector and Focus branch show on an event tree.
How it is laid out
- The initiating event is on the left, and each step along a path is one column further right.
- An outcome is drawn one column after the node it follows, so the outcomes of shorter sequences sit further left.
- At every split, success is above failure. Order only decides between branches of the same kind.
- The branches of a split stay together beside the node they leave, and are never mixed in with another node's branches.
Nodes cannot be dragged. Change the result with Order, orientation, density and spacing. All four orientations are available under Diagram → Orientation; top to bottom puts the initiating event at the top, with success to the left of failure.
Notation profiles
| Profile | How it draws | Settings it controls |
|---|---|---|
| Custom (default) | A coloured symbol for each node type, and arrowed connectors coloured by branch. | None. |
| IEC 62502:2010 | Plain rectangles, and plain orthogonal lines without arrowheads. | Connector routing is fixed to orthogonal. Border width is limited to 1–4 px. |
Choose the profile under Diagram → Notation → Profile. Switching changes nothing about the sequences or their values.
Text and probabilities on branches
A Branch Label column, bound to Relationship label, writes its text on each branch, such as Detected or Not detected. Branch probabilities are not drawn on the diagram: hover a branch to see its probability in the tooltip. To show the number on the branch itself, include it in the Branch Label text, such as Detected (0.98).
Summary strip
Turn on Labels → Summary strip → Show summary. An event tree counts its outcomes, meaning success outcomes, failure outcomes and consequences, by Status. For the example it shows 5 outcomes: 2 Severe, 1 Acceptable, 1 Major and 1 Moderate.
To colour outcomes by severity, add conditional formatting rules on Status under Appearance → Conditional formatting, such as When Status, Is Equal to, Value Severe, Colour Node fill. Turn on Labels → Legend → Show legend so readers can decode the colours.
Node Inspector
The Analysis section shows the initiating event's Frequency and each node's Status. The probability of the branch into a node belongs to the branch, so it is shown when you hover the branch, not in the Inspector.
An event tree has no Relationships section, except on an outcome at the end of several sequences. That shows Used in with the number of branches arriving at it, and the nodes they come from.
Focus branch
Focus branch keeps the selected node, everything after it, and its path back to the initiating event. Focused on IGN-A in the example, it keeps Loss of containment, Gas detected?, Contained, no ignition, Fire suppressed? and both of its outcomes, and fades the path through IGN-B.