Probabilistic explosion risk analysis for offshore topside process area. Part II: Development of gas cloud multivariate frequency distribution (MVFD)

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>Flammable gas cloud frequency distribution forms a key part of the CFD-based probabilistic explosion risk analysis (ERA). As part of this series work, a new type of gas cloud frequency distribution, namely, ignited gas cloud frequency distribution has been proposed in the previous study (Part I). On that basis, an advanced gas cloud frequency distribution is to be introduced continuously, which is the ultimate goal of this series work. The current study contributes to proposing a multivariate frequency distribution (MVFD), which can provide both gas cloud size and position to investigate explosion scenarios. As a matter of fact, the consequences of explosion accidents may vary greatly, depending on variables such as ignition position, gas cloud size, position and shape etc. So far, except for the gas cloud size that can be provided by the gas cloud frequency distribution, the remaining variables are more likely to be determined by engineering judgement and experience. Though this process follows standard guidelines or recommended practices, the determined variables can vary widely depending on engineers. In the present study, however, the gas cloud position is determined probabilistically as well. In order to input the gas cloud position into the proposed MVFD, the volumetric center of the equivalent gas cloud (ESC) is used to quantify the cloud position. To this end, the methodology introduced in Part I is consistently adopted in this paper, but the volumetric center is additionally monitored in the whole transient process of cloud propagation. Using the proposed distribution, the explosion scenarios can be investigated without the subjective engineering judgment of the gas cloud position, and therefore one can expect that the investigated explosion scenarios become more accurate than before. This paper provides a detailed procedure on how to obtain the proposed distribution and then presents case studies to demonstrate how the ERA results can change with the choice of the gas cloud position. Through the case studies, it is proven that the proposed MVFD is more reasonable for evaluating correct explosion design accidental loads.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new type of gas cloud frequency distribution is proposed to consider both the position and size of gas clouds in a probabilistic manner. </LI> <LI> The position of a gas cloud is defined as the volumetric center of a corresponding equivalent stoichiometric gas cloud. </LI> <LI> The entire footprints of gas cloud propagation are reflected into the proposed distribution. </LI> <LI> Investigated explosion scenarios are consistent with the results of dispersion simulations, and become more realistic than before. </LI> </UL> </P>