Consequence modeling procedure

Toxic release and dispersion models are an important part of the consequence modeling procedure shown in Figure 4-1. The toxic release model represents the first three steps in the consequence modeling procedure. These steps are... 

The release mitigation procedure is part of the consequence modeling procedure shown in Figure 4-1. After selection of a release incident, a source model is used to determine either the release rate or the total quantity released. This is coupled to a dispersion model and subsequent models for fires or explosions. Finally, an effect model is used to estimate the impact of the release, which is a measure of the consequence. 

Generally, the results obtained through the numerical simulation showed good agreement with the experimental data leading to the conclusion that CFD techniques can be effectively used in consequence assessment procedures concerning toxic/flammable dispersion scenarios in real terrains, where box models have limited capabilities. 

Use an appropriate atmospheric dispersion model to assess the consequences or risk of each scenario. For screening purposes, atmospheric dispersion models which are less costly may be used to identify the most important scenarios examples are discussed in the following subsection. More expensive modeling procedures can be applied to the most important scenarios provided such procedures are more appropriate and accurate. Screening methods may also be useful in considering the validity of more complicated models. 

It is apparent from the above that only very few catchment areas in alpine regions have access to runoff data. Consequently, regionalization procedures need to be developed and applied for the purpose of estimating runoff characteristics [42]. In turn, however, the value of such estimates depends on the runoff data available for calibrating these models. This gives rise to the same dilemma mentioned above in connection with mnoff measurement networks In alpine regions with few runoff measurement stations it will be difficult to develop effective regionalization approaches. 

For the model of semiflexibie macromolecule accepted in Sect. 3.1, the attractive part of the second virial coefficient of the interactions of segments is given directly by Eqs. (2.16) and (2.21). Thus, the procedure for the determination of the most stable homogeneous phase of the solution of freely jointed semiflexibie macromolecules is absolutely identical with the corresponding procedure for the solution of disconnected rods (compare Eqs. (2.3) and (3.1)) consequently, this procedure leads to Eqs. (2.25) (see also Fig. 5). 

Those interested mostly in structure determination from powder diffraction see the texture problem differently. The presence of the preferred orientation makes a good pattern fitting difficult or even impossible and, consequently, a procedure is needed to correct for the texture effect in the Rietveld codes. For that it is not necessary to find the ODF, but to have a reliable model of the pole distribution whose parameters are refined together with the structure and other parameters. 

However, as parts of Process Models have been developed before or during the elaboration of the modeling procedure described in Subsect. 2.4.2, some difficulties can occur when Process Models is used for the formalization of C3 models. The modeling concepts of Process Models differ substantially from those of C3. For instance. Process Models does not provide modeling concepts equivalent to the synchronization bar in C3 in consequence, it must be paraphrased using the available concepts. Thus, describing the formal content of a generalized C3 model can be awkward or even impossible in some cases, even before a formalization of the informal content of a C3 model - such as textual annotations - is addressed. 

The necessary effort becomes largest when a quantitative risk assessment is to be performed. Besides identification techniques, quantitative consequence modelling methods and procedures to determine the event probability of the incident being considered must be applied. 

The mode of operation of Fixed Bed Reactors is strongly dependent upon many parameters, the main ones being flow regimes, geometry, feeding devices, reactant physical and chemical properties product and possibly solvent properties. These incertitudes affect reactor modelling and consequently design procedures. 

Safety historical data has been highlighted as part of the conceptual plant safety model. Figure 3-11 showed the detailed data groups of safety historical data component where safety historical data is divided into two parts plant specifications, which covers all specification changes due to design, operation, or any other process throughout the plant lifecycle and accident/incident data, which includes plant, events, process, equipment, cause, consequence, and procedures in-place. 

The next part of the procedure involves risk assessment. This includes a deterrnination of the accident probabiUty and the consequence of the accident and is done for each of the scenarios identified in the previous step. The probabiUty is deterrnined using a number of statistical models generally used to represent failures. The consequence is deterrnined using mostiy fundamentally based models, called source models, to describe how material is ejected from process equipment. These source models are coupled with a suitable dispersion model and/or an explosion model to estimate the area affected and predict the damage. The consequence is thus determined. 

This model of accident causation is described further in Figure 1.3. This represents the defenses against accidents as a series of shutters (engineered safety systems, safety procedures, emergency training, etc.) When the gaps in these shutters come into coincidence then the results of earlier hardware or human failures will not be recovered and the consequences will occur. Inap-... 

When performing human reliability assessment in CPQRA, a qualitative analysis to specify the various ways in which human error can occur in the situation of interest is necessary as the first stage of the procedure. A comprehensive and systematic method is essential for this. If, for example, an error with critical consequences for the system is not identified, then the analysis may produce a spurious impression that the level of risk is acceptably low. Errors with less serious consequences, but with greater likelihood of occurrence, may also not be considered if the modeling approach is inadequate. In the usual approach to human reliability assessment, there is little assistance for the analyst with regard to searching for potential errors. Often, only omissions of actions in proceduralized task steps are considered. 

The SRK model can also be used as part of a approach for the elimination of errors that have serious consequences proactive for the plant. Once specific errors have been identified, based on the SRK model, interventions such as improved procedures, training or equipment design can be implemented to reduce their likelihood of occurrence to acceptable levels. This strategy will be discussed in more detail in Chapter 4. 

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