Logical tree models

Logical models aim at analysing the canses of accidents in terms of logical relations between events and conditions in the affected system. The models are based on the systems concept, which means that a production system is understood in terms of its components and the relationship between these. They are typically applied in theoretical analyses to estimate the risk of accidents (risk analyses) but may also be employed in diagrams to display the results of an accident investigation. 

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. 

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Fig. 18 Example of a logic tree model (Adopted from Kramer (1996))...

A logic model that graphically portrays the combinations of failures that can lead to a particular main failure (TOP event) or accident of interest. Given appropriate data, fault tree models can be quantitatively solved for an array of system performance characteristics (mean time between failures, probability of failure on demand, etc.)... 

Linking event tree and fault tree models to generate sequences of failure events using Hnntean logic and... 

In many instances, data are intended to be associated with a natural structural representation. A typical hierarchical structure is that of a classic organization. A more general representation than a hierarchy, or tree, is known as a network. It is often possible to represent a logical data model with a hierarchical data structure. In a hierarchical model, we have a number of nodes that are connected by links. All links are directed to point from child to parent, and the basic operation in a hierarchy is that of searching a tree to find items of value. When a query is posed with a hierarchical database, all branches of the hierarchy are searched and those nodes that meet the conditions posed in the query are noted and then returned to the DBMS system user in the form of a report. 

Figure 4. Different models used in the logic tree method.

Frank, S., Bommer, J. J., Bungum, H., Cotton, F., Abrahamson, N. A. (2005). Composite Ground-Motion Models and Logic Trees Methodology, Sensitivities, and Uncertainties. Bulletin of the Seismological Society of America, 95(5), 1575-1593. doi 10.1785/0120040229... 

Faidt tree models These logical cause-effect models trace the failures of the safety system functions considered in the event-trees back to basic events hke, for instance, the failures of system components. As result, they provide values for the unavailabiUties of the individual functions. 

Fault-tree models are used to determine the unavail-ahflities of the safety system functions to be considered in the event-trees. They are logical cause-effect models which trace the failure of a system function like, for instance, a technical safety system back to basic events like the failures of technical components. Finally, the fault-tree model provides a value for the unavailability of a system function which is derived from the unavailahilities of the components. 

The analysis necessitates a number of calculation methods. These range from the logical event and fault tree models used in the event sequence analysis, to the models of phenomena which could occur within the containment following a core... 

In addition, the review of programmable controller Implementation of process control logic by means of fault tree models revealed situations wherein the assignment of a number of control functions to the same programmable controller led to some loss of system redundancy. These were corrected by re- allocatlon of the control functions to different PCs. 

Fault Tree Atwfysis, FTA, for representing the logical combinations of various tystem states which lead to a partiailar outcome an undesired event known as the top event A fiuilt tree model can only relate tystem states with difficulty and often stops at the release of material when modelling an incident scenario. 

The system fault trees models developed for the power PSA could, with appropriate changes (i.e. components and trains in maintenance), be used for SLP PSA. The logic of systems basically remains the same, but the conditional availabihty of components or systems may be significantly different. 

In general, a logic tree consists a classical statistical tool for dealing with this type of assessment problems, in which based of the overall knowledge available, the engineer sets up a number of alternative models and associates to each choice a weight factor representative of his subjective (based on judgment or experience) belief on the validity of the choice. In this manner ... 

On the basis of an industrial-engineering system s view, taxonomies have been developed that focus on the control of the production system from a management point of view (Johnson 1975, Adams 1976). These models are especially relevant to studies of the control of initial-phase deviation that falls under the purview of management responsibility. The Management Oversight and Risk Tree (MORT) was developed in logical tree format and provides a systematic approach for use in detailed investigations conducted by safety experts (Johnson 1975). 

A series of monographs and correlation tables exist for the interpretation of vibrational spectra [52-55]. However, the relationship of frequency characteristics and structural features is rather complicated and the number of known correlations between IR spectra and structures is very large. In many cases, it is almost impossible to analyze a molecular structure without the aid of computational techniques. Existing approaches are mainly based on the interpretation of vibrational spectra by mathematical models, rule sets, and decision trees or fuzzy logic approaches. 

Fault Tree Analysis Faiilt tree analysis permits the hazardous incident (called the top event) frequency to be estimated from a logic model of the failure mechanisms of a system. The top event is traced downward to more basic failures using logic gates to determine its causes and hkelihood. The model is based on the combinations of fail-... 

A logic model that graphically portrays the range of outcomes from the combinations of events and circumstances in an accident sequence. For example, a flammable vapor release may result in a fire, an explosion, or in no consequence depending on meteorological conditions, the degree of confinement, the presence of ignition sources, etc. These trees are often shown with the probability of each outcome at each branch of the pathway... 

The use of component logic models to build system fault logic has been discussed by several authors for chemical and electrical systems (Powers and Thompkins, 1974 Fussell, 197.S and Powers and Lapp, 1976). In addition, generic sabotage fault trees have been used for some time in the analysis of security concerns for nuclear power plants (NUREG /CR-0809, NUREG/CR. 121,... 

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