Consequences Modelling Results

The consequence analyses that are passed to the impact calculations give the shapes and sizes of the different effect zones. For some impacts the results may be independent of weather conditions. For other impact there is a separate result for each weather condition. For example, the effect zone shape of BLEVE/fireball is a circle and is weather independent. Therefore, the effect zone is centred at the release point. This section presents the consequence modelling results for the hydrogen study objects by using PHAST Professional 6.4 (DNV). The procedure employed in the consequence computations is summarized in Section 4.5. The study considered three weather conditions that are available in PHAST model and recommended by the TNO [159] i.e. weather category of 1.5/F, 1.5/D, and 5.0/D. These weather categories represent wind speed and Pasquill stability, respectively.

This section presents a variety of results for accident outcomes of the hydrogen release (loss of containment, LOC) from the study objects described in chapter 3. These include results of dispersion and fire and explosion models. Dispersion models are presented as various graphs of dispersed hydrogen vapour cloud concentrations. Meanwhile, fire and explosion models are presented as thermal radiation flux and shock wave overpressure impacts, respectively. These models rely on the general principle that severity of the outcome is a function of distance from the source of release, called effect distance (z). The assessment of the effects on humans is presented in the risk calculation section (5.5).

The effect distances from the fire and explosion models are presented for different fatality levels (e.g. 1%, 10%, or 100%). These fatality levels are set based on the probit equation for thermal impact given in Eq. 4-11 (fire models), and Table 4-14 for overpressure impacts (explosion models). The maximum effect distance (z) of the outcomes is calculated as the sum of the downwind radius (a) and downwind distance (i.e. distance of the circle centre from the release centre, x) or z= a+x. The downwind distance (x) is equal to downwind radius (a) multiplied with the offset ratio (d), or x=a*d. The effect zone centred at the release point (d=0), the x is equal to zero. Therefore the maximum effect distance is equal to its downwind radius, z=a.

Due to a problem which may arise in distinguishing many curves in one graph, most of the consequence graphs show curves for two study objects only. They include GH2 storage at production plant (object 1) and LH2 storage at the CHP plant (object 5). All consequence calculation results, however, are presented in the associated tables.

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