Master fault tree

The tree can then be converted into a master fault tree for use as a troubleshooting guide (Fig. 10-14). 

The feeling of having mastered the sources of risks so that the safety of industrial systems could be effectively managed was rather abruptly shattered by the disaster at the Three Mile Island (TMI) nuclear power plant on 28 March 1979. Before this happened, the consensus had been that the use of established methods such as HAZOP, FMEA, Fault Trees and Event Trees would be sufficient to ensure the safety of nuclear installations. The nuclear power plant at TMI had itself been through a PRA and... 

Qualitative reliability analysis are used to identify possible ways in which a system can fail. The calculation can result in all combinations of components and human failures that lead to safety (protection) system failure, which prevents the safety system to shut-down the reactor upon request. For this analysis a top-down logic model, known as a Master Logic Diagram (MLD), similar to a fault-tree, could advantageously be used with a top event of a safety system failure upon request. The results of this analysis can be used to prove the fulfillment of the important single failure design criteria. 

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