Event tree analysis influencing factors

Event Tree Analysis. Event tree analysis is a forward-looking method that takes an initiating event, identifies post-initiating event influencing factors, and combines the information into a logic tree in which the occurrence of each influencing factor is either true or false. ... 

A risk model often comprises a formal logical representation of the system. Fault- and event tree analysis is often building blocks in such a representation. Barriers, safety functions and/or layers of protection are typically represented by basic events. Probabilities are assigned to the outcome of the basic events, i.e., success or failure. A wide range of factors and conditions will influence the outcome of the basic events, and these need to be taken into account when assigning the basic event probabili-... 

In analyzes of risk of adverse events event tree or fault tree may be used for the case of the railway system. In (Albrechtsen Hokstad 2003) this kind of analysis has been extended to include the risk influencing factors. The issue has been shown on the example of a single-track line, for which the peak event is the collision of two trains coming from the opposite directions. An analysis of the factors affecting the risk shows the relationships and sequences of cause and effect going beyond a simple event tree analysis. In the studies case it... 

The growth of a defect into what becomes a fault or a faulty component really depends on many factors, which is predominantly the type of corrosion that is progressing. In the fault-tree analysis context, the fault event of a component is defined as a state transition from the normal state to a faulty state of that component. These state transitions are irreversible, which means that a faulty state does not return to the intended state even if the influences that caused the fault event in the first place disappear. 

There are many different models that can be used to apply common causes, but the most common (and the one preferred by EC 61508) is the Beta factor (j8) model. This model applies a /J factor between 0 and 1 representing the fraction of the failure of all affected inputs resulting from the common cause. For instance, a fl value of 0.1 implies that 10% of failures where aU inputs fail were in fact the result of a common cause. There are some specialised resources for appropriate CCF values that can be apphed, but fundamentally a sensitivity analysis should be performed to determine how much an effect the CCF has on the top event probability. A large influence would indicate the need for further analysis [see NASA Fault Tree Handbook paragraph 7.2]. 

ABSTRACT In Human Reliability Analysis (HRA) the assessment of dependence between human failure events refers to evaluating the influence of the failure on one task on the performance of the subsequent task. In Probabilistic Safety Assessments (PSAs), human action dependencies are commonly evaluated with the THERP method, often extended with Decision Tree (DT) models, to reduce the expert judgment element. This paper compares different DT models used in the HRA practice. The comparison addresses the factors entering the models and the underlying relationships. The comparison shows that, depending on the features of the task under analysis, the results may vary substantially if different DTs are used. Also, often there is limited guidance for the analyst in the assessment of the DT factors this prejudices the repeatability of the assessments because different analysts may very well decide for different assessments. 

Software Fault Tree ( Soft Trees ) The soft tree technique is used to determine what software event, failure, or combination of each will result in a real or hypothetically loss event (a top event). This top-down analytical approach, which assumes a problem and then evaluates affecting conditions backward to determine causal factors, also takes into consideration any influencing environmental factors. It is concerned primarily with the analysis of any hardware-software interfaces that deal directly with the operation of mechanical components. 

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