FTA is a graphical technique used
to determine the various combinations of hardware (and software) failures and
human errors, which can result in an undesirable outcome. The specified
undesirable outcome is referred to as a ‘top event’, where
the deductive analysis about the general conclusions and their causes is often
described as a ‘top down’
approach. A Fault Tree Analysis begins with a construction of a fault tree,
relating the sequences of events leading to the top event. This may be
illustrated by considering the probabilities of events and by constructing a
tree with AND and OR logicgates.
the steps involved in a fault tree analysis are:
Define the Top Event
Know the system
Construct the tree
Validate the tree
Evaluate the tree
Consider alternatives and recommend actions
tree analysis can also include human error contribution to the
overallsystem,ifthe probabilities for human error are described in the same
term as component and hardware failures.
Thus the main purpose of fault tree analysis is to evaluate
the probability of the top event using analytical and statistical methods. By
providing useful information concerning the likelihood of a failure and its
means, efforts can be made to improve system safety and reliability. It also
evaluates the effectiveness and the need for redundancy. Hence, the resulting
benefits of fault tree analysis to project management are reduction of analysis
time and precision in identifying and correcting deficiencies
Fault tree diagrams are logic block diagrams that display the
state of a system in terms of the states of its components.
of Fault Tree Diagram.
Fault tree analysis and failure modes and effects
Design for reliability
Design for safety Benefits of fault tree diagram:
Used to identify possible system reliability or
safety problems at design time,
Used to assess system reliability or safety during
Helps to improve understanding of the system,
Can identify root cause of equipment failures.