IEC 61025

Fault tree analysis is mainly used in safety analyses. In contrast to FMEA, which can only deal with independent single faults, the strength of fault tree analysis lies in its ability to simulate complex failure scenarios or specific system behavior. Most of the time, these are scenarios that require multiple single failures, or even a specific sequence of failures.

While there are standards regarding fault tree theory, the method itself tends to be self-explanatory. At the top is the final event that is too undesirable, and at the bottom are the basic events that one cannot or does not want to separate further. In between are other events, as well as the logic.

For the basic events usually failure rates from a MTBF analysis and/or FMEA are used.
1. main difficulties of this method are the correct specific formulation of the top event,
2. in the correct mapping of the logic; this is less a mathematical problem, but rather lies in having fully understood the system behavior. In the FMEA method, exactly this problem is much less pronounced.
3. in the "economy" of the fault tree. Fault trees distributed over several pages are confusing.