In fault tree analysis, a tree-like diagram is used to identify a single event and determine what led up to it. Consisting of a variety of symbols, a fault tree can be used as a troubleshooting tool or to decide how an event such as an explosion or forklift accident happened. The symbols include gates and rectangles as well as triangles, circles, and diamonds. End results are represented at the top of the fault analysis tree, and the other elements aid in deductive reasoning until a root cause is presented at the bottom. Fault tree analysis was first created in the 1960s and has often been used in manufacturing, power plants, and weapons systems design.
The top rectangle of a fault tree is usually referred to as a "top gate." An event that was the end result of a failure, or which represents a problem that needs to be solved, is typically represented here. Other gate symbols can identify whether every event mentioned needs to happen prior to the end result. They can also show if one or another, or a combination of factors, can lead to an event.
Fault tree analysis generally uses circles to show root causes and events that cannot be broken down. Circles are usually at the bottom of the tree diagram. Diamonds are often used when further analysis is prohibited by too little information; personnel or hardware can be represented here. In the diagram, ovals are generally used to express certain situations that can occur only under particular circumstances. Triangles often help make connections between different branches of the tree.
These basic symbols are used in fault tree analysis, while other sets of symbols are sometimes used as well. The concept can help evaluate the safety or reliability of a system while it is being designed, during normal operation, or when there is a problem. Such analysis also helps to understand how systems work, determine where testing is needed, or to pinpoint the cause of an accident or equipment malfunction.
A negative event typically needs to be predictable for a fault tree analysis tool to be effective. This also requires anticipation of the key factors that led up to a problem. Analysts, therefore, need to be skilled in the area that they are assessing, regardless of the tool they use. Fault tree analysis software can help organize information graphically, report on issues, and manage the various data that are analyzed.