Fault tree analysis

In contrast to FMEA, fault tree analysis (FTA) is used for quantitative analysis and to consider multiple failures. This allows the corresponding metrics to be calculated and evaluated (consideration of single failures, multiple failures) in order to reach a quantified analysis result.

Fault tree analysis is described in DIN 25424 (Fault tree analysis, Part 1: Method and graphical symbols, Part 2: Manual calculation procedures for the evaluation of a fault tree).

In contrast to FMEA, fault tree analysis does not use individual system components as the starting point, but rather the potentially disrupted overall system. Fault tree analysis builds on what is known as the negative logic. This means that the fault tree describes a failure function that expresses a failure with the state logic-1, and a functional system exists for logic-0.

The notation of FTA diagrams distinguishes between:
- Rectangles: Events
- Boolean gates, especially AND and OR gates
- Circles: Basic events are events that should not be further investigated (comet impact in harvesting machine)
Rhombuses: These events are still being analyzed

FTA is among the “top-down” analysis forms in risk management. In a first step, the overall system is thus described precisely in detail. Based on this, an analysis is conducted of which primary disruptions can cause or contribute to a disruption of the overall system. The starting point here is initially a single undesired event, which is at the top of the fault tree, called the top event. The top event generally results from a risk analysis or scenario analysis.

Glossary Technical terms at a glance