Advantages and Disadvantages of Fault Trees

The main disadvantage of using fault trees is that for any reasonably complicated process the fault tree will be enormous. Fault trees involving thousands of gates and intermediate events are not unusual. Fault trees of this size require a considerable amount of time, measured in years, to complete. 

Furthermore, the developer of a fault tree can never be certain that all the failure modes have been considered. More complete fault trees are usually developed by more experienced engineers. 

Fault trees also assume that failures are hard, that a particular item of hardware does not fail partially. A leaking valve is a good example of a partial failure. Also, the approach assumes that a failure of one component does not stress the other components, resulting in a change in the component failure probabilities. 

Fault trees developed by different individuals are usually different in structure. The different trees generally predict different failure probabilities. This inexact nature of fault trees is a considerable problem. 

If the fault tree is used to compute a failure probability for the top event, then failure probabilities are needed for all the events in the fault tree. These probabilities are not usually known or are not known accurately. 

---

Define the four commonly used symbols to perform fault tree analysis. What are the main advantages and disadvantages of fault tree... 

---