Main window of the FTAnalyzer

Fault Trees are one of the most widely used methods in system reliability and failure probability analysis. A fault tree is a graphical representation of a logical structure representing undesired events ("failures") and their causes. You create the logical structure by using gates and represent undesired events by using basic events. Reliability parameters are assigned to the basic events. Widely used in system reliability studies, fault tree analysis offers the ability to focus on an event of importance, such as a highly critical safety issue, and work to minimize its occurrence or consequence. The probability of the top-level event can then be determined by using mathematical techniques. The resulting fault tree diagram is a graphical representation of the chain of events in your system or process, built using events and logical gate configurations.

FTA Basic Event data

Two types of analysis can be conducted using Fault Trees:
o Qualitative Analysis: performed by means of Minimal Cut Sets (MCS) building
o Quantitative Analysis: calculating the Absolute probabilities, i.e. the probabilities of system failures

Example of FTA Unavailability and MCS Analysis report

After Unavailablity calculation and MCS analysis, Importance and Sensitivity Analysis may be performed. Importance analysis results help to select those fault tree events, which contribute most to the system's unavailability. Sensitivity analysis helps to choose those events, where a relatively small change will lead to a relatively large system unavailability changes. Calculated values are Fussell-Vesely importance (FV Imp), Risk Decrease Factor (RDF), Fractional Contribution (FC), Risk Increase Factor (RIF) and Sensitivity Value for each Basic or Undeveloped Event.

Example of FTA Importance and Sensitivity Analysis report

Fault Tree Analysis is acknowledged as a key tool for increasing safety. It is unique and indispensable in analyzing risks and determining various combinations of hardware, software, and human error failures that result in a specified risk or system failure. Fault tree analysis is useful both in designing new products/services and in dealing with identified problems in existing products/services. In the quality planning process, the analysis can be used to optimize process features and goals and to design for critical factors and human error. As part of process improvement, it can be used to help identify root causes of trouble and to design remedies and countermeasures.