What is a Fault Tree Diagram (FTD)?
Fault tree diagrams (or negative analytical trees) are logic block diagrams that display the state of a system (top event) in terms of the states of its components (basic events). Like reliability block diagrams (RBDs), fault tree diagrams are also a graphical design technique, and as such provide an alternative to methodology to RBDs. An FTD is built top-down and in term of events rather than blocks. It uses a graphic “model” of the pathways within a system that can lead to a foreseeable, undesirable loss event (or a failure). The pathways interconnect contributory events and conditions, using standard logic symbols (AND, OR etc). The basic constructs in a fault tree diagram are gates and events, where the events have an identical meaning as a block in an RBD and the gates are the conditions.
