This work was focused on the characterization of flash fire scenarios resulting from the accidental release of liquefied natural gas (LNG) by keeping into account vapour stratification and temperature gradient, which deeply modify the combustion phenomena for the standard homogeneous cloud. An open-source computational fluid dynamic (CFD) tool was used to this aim, provided premixed and diffusive/convective modification for the combustion model.

The effects of the source model for the evaporation and the representative boundary conditions (wind velocity, heat flux from the substrate, relative humidity of the atmosphere, liquid pool diameter) were investigated. The heat flux from the substrate was found the most impacting parameter since it considerably helps vertical spreading, thus reducing the stand-off distances. The comparison with standardized procedures for the consequence assessment of flash fire highlights that the latter approach provides non-conservative results under certain circumstances. Hence, the adoption of the presented procedure is suggested.

Considering the nature of the investigated scenario, the effects of thermal and mass stratifications on combustion efficiency were analysed too. As a result, the safety distances calculated by CFD for stratified mixtures were found almost double than the corresponding values estimated for homogeneous cloud and by integral models, commonly adopted in risk analyses.

这项工作的重点是通过考虑蒸汽分层和温度梯度，来表征由液化天然气 (LNG) 意外释放引起的闪火场景，这深深地改变了标准均质云的燃烧现象。开源计算流体动力学 (CFD) 工具用于实现此目的，为燃烧模型提供预混和扩散/对流修改。

研究了蒸发源模型和代表性边界条件（风速、来自基底的热通量、大气的相对湿度、液池直径）的影响。来自基板的热通量被认为是最具影响力的参数，因为它极大地帮助了垂直传播，从而减少了隔离距离。与闪火后果评估的标准化程序的比较突出表明，后一种方法在某些情况下提供了非保守的结果。因此，建议采用所提出的程序。

考虑到所研究场景的性质，还分析了热分层和质量分层对燃烧效率的影响。结果，发现通过 CFD 计算的分层混合物的安全距离几乎是均匀云和积分模型估计的相应值的两倍，这些值通常用于风险分析。