Fault, cause and event trees

Operating safety (as explained in the articles Operating safety: methods for controlling risks and Dependability: approaches to risk management ) in the service of risk management, describes the mechanisms that lead to incidents and accidents. This discipline naturally includes methods designed to represent the logic of combinations of facts or conditions that have led, are leading or could lead to incidents or accidents.

It's hardly surprising, then, that tree representations are among the most common tools used in dependability analysis. In this article, we present the three most common methods: the fault tree, the cause tree and the event tree.

What these three methods have in common is that they produce tree-like representations of the logic of a system (or part of it). This superficial similarity is misleading: these three methods meet distinctly different needs, and the trees produced do not contain the same information. This resemblance in form and, naturally, in name has motivated us to present them together, to help the reader distinguish between them.

So these three methods should not be taken as variants of the same method, or as three ways of carrying out the same reasoning, but as three different methods.