Fault tree analysis diagrams are commonly used to illustrate events that might lead to a failure so the failure can be prevented. Fault tree analysis diagrams are commonly used in Six Sigma processes, particularly in the Analyze phase of the Six Sigma business improvements process.
You begin by defining the top event (or failure). Then you can use event and gate shapes to illustrate, top-down, the process that might lead to the failure. Once you complete the diagram, you can use it to identify ways to eliminate causes of the failure and to devise corrective measures for preventing such failures.