Fault tree analysis necessary cause

Fault Tree Analysis employs an analytical tree to display the results of an analysis (Suokas and Rouhiainen, 1993). It starts with the top event (injury or damage). The analysis proceeds backwards in order to identify all events and conditions that have caused the injury or damage. Logical relations (necessary and/or sufficient conditions) are estabhshed. Fault-tree analysis is not an accident model per se and gives limited support in the identification of causal factors. 

CONSTRUCTING THE FAULT TREE. Fault tree construction begins at the top event and proceeds, level by level, until all fault events have been traced to their basic contributing events or basic events. The analysis starts with a review of system requirements, function, design, environment, and other factors to determine the conditions, events, and failures that could contribute to an occurrence of the undesired top event. The top event is then defined in terms of sub-top events, i.e., events that describe the specific "whens and wheres" of the hazard in the top event. Next, the analysts examine the sub-top events and determine the immediate, necessary, and sufficient causes that result in each of these events. Normally, these are not basic causes, but are intermediate faults that require further development. For each intermediate fault, the causes are determined and shown on the fault tree with the appropriate logic gate. The analysts follow this process until all intermediate faults have... 

Fault Tree. When direct data allowing to calculate the probability of a failure mode are not available or this failure form is complex, it is proposed the elaboration of a fault tree. It is a method of multidisciplinar analysis that begins with the selection of a failure mode or event that is tried to avoid. The event is developed into its immediate causes, and the sequence of events continues until basic causes are identified. The fault tree is constructed showing the logical event relationships that are necessary to result in the top event. The fault tree reaches terminal events whose probability must be calculated or estimated. These events can be basic events, which do not require to be explained by means of other previous events, or events which are not developed because it is not considered necessary or for lack of information. 

Once the hazard scenarios have been identified, you will need to understand how those hazards came about. If the hazard analysis is not sufficient to understand the underlying causes of the hazard scenario, then further analysis will be necessary. A fault tree is particularly useful because it gives a good sequence of events that lead... 

Adopting a Safety-II perspective does not mean that everything must be done differently or that currently used methods and techniques must be replaced wholesale. The practical consequence is rather a recommendation to look at what is being done in a different way. It is still necessary to investigate things that go wrong, and it is still necessary to consider possible risks. But even a root cause analysis can be done with another mindset, and even a fault tree can be used to think about variability rather than probability. 

FTA emphasizes the lower-level fault occurrences that directly or indirectly contribute to a major fault or undesired event. The technique is one of "reverse thinking" where the analyst begins with the final undesirable event that is to be avoided and identifies the immediate causes of that event [11]. By developing the lower-level failure mechanisms necessary to produce higher level occurrences, a total overview of the system is achieved. Once completed, the fault tree allows an engineer to fully evaluate a system safety or reliabihty by altering the various lower-level attributes of the tree. Through this type of analysis, a number of variables may be visualized in a cost-effective manner. 

Using result by HAZOP system, the fault propagation scenario is created. The information of propagation is stored to the data base in the system. The analysis result shows the cause of propagation and identifies the hazards by the database. From this data base, it can remove the necessary information to create scenario tree. The proposed system creates the scenario tree of fault propagation automatically. This scenario tree system is developed to calculate automatically the accident frequency quantitatively. The model of the fault propagation scenario is created from many results of HAZOP system. It is shown in Figure 3. EiO is... 

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