ITEM TOOLKIT

Chapter 8 Fault Tree 179
Furthermore, BDD-based algorithms are generally more efficient than other quantification methods. Depending on the
model, these algorithms can identify millions or even billions of cut-sets within seconds. The BDD algorithms embedded in
ITEM products identify all cut-sets for a given model, and then filter out the significant cut-sets based on probability and/or
order.
BDD algorithms do not allow for truncation of probabilistically insignificant elements in the logic. Conventional methods
allow models to be solved by considering only the high-probability cut-sets. Studies have shown however that the numerical
results produced by conventional methods must be treated with care, due to the truncations and approximations involved in
their calculations.
Using the Fault Tree Module
The Fault Tree Analysis application uses a Fault Tree workspace area where all project, system, and Fault Tree data and
graphics are entered. This area is the foundation on which you build your projects. The workspace area consists of menus,
toolbars, and project and system windows.
The Fault Tree workspace area features a Multiple Document Interface (MDI), which allows you to:
• Choose which windows to display, and move and resize all open windows.
• Open and create multiple Fault Tree projects at the same time in order to compare analysis results.
• Drag and drop gate and event components between projects. This feature allows you to quickly create a new
project by reusing components from other projects.
3. Creating a Fault Tree Project
To demonstrate ToolKit’s Fault Tree features, we’ll create an example Fault Tree project based on the following.
Consider two switches in series as shown bellow. The points A and B are points on the wire. Wire failures would be ignored
A
B
Creating a Fault tree system consists of:
• Constructing the system
• Adding Gates
• Adding Events and editing their Failure models
• Performing analysis