Following the Three Mile Island accident in 1979, the nuclear industry began to utilise probabilistic risk assessment to assess its own safety. And in 1981, the US Nuclear Regulatory Commission (NRC) issued the Fault Tree Handbook, NUREG-0492. Although originally intended for nuclear power applications, the Fault Tree Handbook has been extensively used in all fields where this powerful systems analysis methodology has been applied.
UReason provides Fault Trees that let you specify pathways within a system that can lead to foreseeable, undesirable, events. Using standard logic symbols, these pathways interconnect causal event listeners and conditions:
Fault Trees are normally created for known undesirable events associated with high risk/loss, and can generally be used to find
- Interrelationships between failure events - the way(s) in which a system can fail
- System failure probabilities
- System weaknesses.
Fault Trees can be specified either for specific equipment event relationships, or generically - eg across a range of process equipment and associated classes.
UReason Fault Tree analysis can be used in different ways:
- read upwards, they provide users with a prediction of what might happen
- read downwards (and verified against other events), they provide users with root-cause diagnoses of what has happened.
Numerical probabilities of occurrence can be entered and propagated through the model to evaluate the probabilities of foreseeable events.