ARES Corporation is skilled at developing event trees and fault trees; providing a systematic method for investigating accident and/or failure scenarios involving complex systems. These trees evaluate the pathways leading to failure of a system and the associated risk(s).
The event tree development process determines the boundaries of the particular analysis by defining the initiating event and the possible outcomes for each sequence of events. The event tree analysis defines possible scenarios including success, and partial and/or complete system/subsystem failure. Fault trees are often used to quantify system events that are part of event tree sequences.
An event tree is a graphical representation of the logic model that identifies and quantifies the possible outcomes following an initiating event. Beginning with an initiating event; the event tree details a sequence of pivotal events that lead to specific end states (e.g. OK, Partial Failure or Failure). As each new top event is considered, a new node on the tree is added with a split of probabilities taking either branch.
Fault trees graphically represent the interaction of failures and other events within a system. Basic events at the bottom of the fault trees are linked via logic symbols (know as gates) to one or more top events. These top events represent identified hazards or system failure modes for which predicted reliability or availability data is required.

An “AND” gate indicates that all of the events below the gate must occur for failure of the preceding event, and an “OR” gate indicates that at least one of the top events below the gate must occur for failure of the preceding event. Other gates often used in fault trees include “Exclusive AND/OR” gates, “N of M” gates, “Transfer” gates and “Inhibit” gates. The probability of the top event is calculated using Boolean algebra.
ARES has applied event tree and fault tree analysis for DOE, DoD, NASA, nuclear utilities, aerospace companies, and national laboratories.
This analysis method is used to quantitatively determine the probability of a system failure and/or safety hazard.
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