FTA

A fault-tree analysis is a deductive process to analyse complex systems. The structured approach used in an FTA process leads to a detailed model of the system under investigation during the course of the analysis.  
For each previously defined undesirable event (hazard) a tree structure in a descending order is developed until ultimately all potential causes that may lead to the occurrence of the hazard have been identified.

An FTA is a model-based analysis methodology. Modelling occurs via icons which symbolize logical operators. Links between tree branches are frequently depicted as logical ANDs or logical ORs. A calculation is typically computer-aided using appropriate analysis tools and based on Boolean algebra.

A failure-tree analysis may be applied as a qualitative and quantitative process. Both variants can reveal weak areas in a system by means of a cut set analysis, among other things. This provides the basis for determining events or event combinations which in the case of their combined occurrence may lead to the manifestation of a hazard or violation of the safety objective.
In addition to those of a qualitative analysis, a quantitative failure-tree analysis can provide further results. Results such as the occurrence probability of fault combinations or the occurrence probability of the undesirable event may be determined which can then be used to demonstrate certain requirements. Furthermore, individual events can be investigated based on importance analyses and assessed in terms of their relevance regarding the occurrence of the hazard.