Fault Tree Creation
Fault Tree Analysis (FTA) provides a means to logically and graphically display the paths to failure for a system or component. One way to manage a complex system is to start with a reliability block diagram (RBD). Then create a fault tree for each block in the RBD.
Whether a single block or a top level fault for a system the basic process to create a fault tree follows a basic pattern.
1. Define the system. This includes the scope of the analysis including defining what is considered a failure. This becomes important when a system may have an element fail or a single function fail and the reminder of the system still operates.
2. Define top level faults. Whether for a system or single block define the starting point for the analysis by detailing the failure of interest for the analysis.
3. Identify causes for top level fault. What events could cause the top level fault to occur. Use the logic gate symbols to organize which causes can cause the failure alone (or), or require multiple events to occur before the failure occurs (and).
4. Identify next level of events. Each event leading to the top level failure may also have precipitating events.
5. Identify root causes. For each event above continue to identify precipitating events or causes to identify the root or basic cause of the sequence of events leading to failure.
6. Add probabilities to events. When possible add the actual or relative probability of occurrence of each event.
7. Analysis the fault tree. Look for the most likely events that lead to failure, for single events the initiate multiple paths to failure, or patterns related to stresses, use, or operating conditions. Identify means to resolve or mitigate paths to failure.
8. Document the FTA. Beyond the fault tree graphic include salient notes from the discussion and action items.
FTA is a convent means to logically think though the many ways a failure may occur. It provides insights that may lead to product improvements or process controls.