Analytical Techniques
Analytical Techniques : The main technique for analysis of the mechanisms, or failure logic, leading to hazardous events is the use of Logic Diagrams. They can be classified as "top down" or "bottom up" depending upon whether they trace outcomes back to causes or follow causes through to possible outcomes. They provide a powerful method of displaying qualitative information, but also provide a model for quantification. The main techniques, although there are other variations, are Fault Tree Analysis, Event Tree Analysis, and Cause-Consequence Analysis. Fault Tree Analysis works back from an undesired event, known as the Top Event, to the sub-events which are immediate precursors of the top event, then to the precursors of those sub-events and so on. Combinations of events are illustrated by Gates, which, when the logical combination of the input conditions is satisfied, produce a specified output which is propagated. A fault tree models system states but can only show sequences of events with difficulty. There is a considerable amount of terminology specific to fault trees for which the reader should refer to a specialised text. Event Tree Analysis follows a cause through to the possible outcomes, branching at each point where there is more than one possible result from the precursor event, until the final outcomes of interest are reached. The outcomes are conditional on the occurrence of the precursor events and so event sequences and time dependence can be readily displayed. Cause-Consequence Analysis also follows through cause to events, but allows for the use of gates to show logical combinations of events or stages while retaining the ability to show sequences and therefore time delays. Although potentially very useful where these factors are important it is necessarily more complicated than fault tree and event tree analysis and is not used widely
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