Using computational fluid dynamics as a tool for hydrogen safety studies

Quantitative Risk Assessments (QRA) of hydrogen applications presents new challenges due to a large difference in properties of hydrogen and natural gas, namely in reactivity, flammability limits, buoyancy and transport properties. However. it is not realistic to perform an extensive risk assessment for ail hydrogen applications similar to that carried out for petrochemical installations. On the other hand, simplified tools and techniques based on codes and standards likely have a limited applicability, as these are not able to represent actual geometry and physics of the explosion. Computational Fluid Dynamics (CFD) tools have the potential to model the relevant physics, but without proper user guidelines based on extensive validation work, very mixed prediction capability can be expected. In this article, a review of the recent validation effort for the CFD tool FLACS-HYDROGEN is described with focus on explosion simulations (a review of the dispersion validation has also been presented recently). A range of different experiments is simulated. Some of the simulations are performed as blind predictions. Recently, we have presented a 3-step approach for performing such analyses. It includes a typical "worst-case" calculation where the entire geometry is filled with a stoichiometric gas cloud (this is unrealistic in most cases, especially for hydrogen), a more realistic analysis involving several dispersion calculations to obtain likely gas clouds, and a probabilistic study to evaluate the likelihood of unacceptable events. The current article summarizes this approach and also presents an example of the use of FLACS under this framework for a relevant problem for hydrogen safety. (C) 2008 Elsevier Ltd. All rights reserved.