New in Version 11.2

Integrated Parts Libraries

The IsoLib NPRD and IAEA Parts Libraries have now been integrated into FaultTree+. These libraries may now be accessed directly by selecting the ‘Parts Library’ tab at the top right of the main window. There are two libraries available – the IAEA library (IAEA-TECDOC-508) and the NPRD library (NPRD-95). Both these libraries contain failure rate data for mechanical components and may be used to populate the generic models and generic failure rate parameters in a FaultTree+ project. The parts database may be quickly searched by part category or by text filters and selected parts may be transferred to a FaultTree+ project using drag and drop.

Extension of Phase Models

The fault and event tree phase models have been extended to allow users to enter absolute unavailability and failure rate values for each phase. Previously users were forced to use adjustment factors. To use absolute values with the ‘Fixed-Phase’ and ‘Rate-Phased’ models set the appropriate flag in the ‘Phases’ tab of the ‘Project Options’ dialog. In addition, users may now automatically set the project lifetime to the sum of phase durations by selecting the appropriate flag in the ‘Phases’ tab of the ‘Project Options’ dialog.

New in Version 11.1

Special Sensitivity Analysis

This new facility may be accessed from the ‘Analysis’ pull-down menu. It allows users to determine the sensitivity of results to changes to the parameters of individual events and generic models. Users may choose the target gate, consequence or risk category.

The required input parameter is then chosen (e.g. failure rate) and a range of factors by which the parameter should be varied. FaultTree+ will then re-calculate the results for the target gate, consequence or risk category and construct a matrix of how the results change for each change in the specified input parameter. This new facility provides an efficient and flexible method of determining the sensitivity of a system parameter to input data.

New IEC 61508 Method for Analyzing Dormant Failure Model Combinations

In previous versions of FaultTree+ users could choose to select the ‘Use Max Risk Dormant Model’ option in the ‘Sets Generation’ tab of the ‘Project Options’ Dialog. If this option was selected the following expression was used to determine the unavailability of events associated with the ‘Dormant’ model:

If this option was not selected, FaultTree+ would calculate an average unavailability given by:

The expression above represents an average unavailability, or probability of failure on demand for a dormant failure.

The maximum risk model represents a pessimistic viewpoint that any potential demands will be placed on dormant equipment just before inspection (or testing) of the equipment.

If the maximum risk model is not selected in previous versions, then the average dormant value defined above would be applied to all dormant failure events even if these events occurred in combination with other dormant events in the same cut set. That is, the average method would multiply the average unavailability of one dormant event with the average unavailability of the other dormant event to obtain the overall unavailability due to dormant failures in the cut set.

In this new version an additional average dormant method has been added that complies with the IEC 61508 Standard (section 6). This new method takes the average unavailability after multiplying the two dormant event probabilities together.

Gate and Event Report Page Field Extended to Memo

The length of the gate and event page reference fields in reports has now been extended to ‘memo’.

Combinatorial Cut Set Calculation Method

A new combinatorial cut set calculation method has been added to FaultTree+. The new method may be selected as an alternative to the existing default method that employs a ‘bottom-up’ Boolean algebra method to evaluate the minimal cut sets for fault trees.

The new combinatorial method is likely to produce cut sets more efficiently than the default method when analyzing complex fault trees where basic event probabilities are relatively small compared to the cut-off values set in the ‘Sets Generation’ tab of the ‘Project Options’ Dialog.

The new method is also likely to be significantly more efficient than the default method when handling fault trees containing complex NOT logic arrangements at high or intermediate levels of the fault tree structure. The new combinatorial method may only be used with the ‘Post Process Success States’ option set on for fault trees (i.e. where success states are removed from the remaining cut sets once invalid sets have been removed).

Cut sets are generated to a maximum of 6th order. The method may not be applied to event trees. The new combinatorial method may be selected in the ‘Custom Options’ Dialog.

Double Bars Shown in Printed Reports

Double bars underneath transfer gate symbols are used to indicate that the gate is repeated on the same page. Previously these double bars were only shown in the screen fault tree diagrams and not in printed reports. They are now shown in both.

Automatic Fault Tree Diagram Compression

Fault tree diagrams may now be compressed automatically to allow more information to be displayed on each printed portrait page. This new facility may be accessed from the ‘Shift’ pull-down menu option.