Due to the severity of their consequences, accidental high-pressure flammable gas releases are relevant hazards in the process safety. In the recent decades, several are the efforts spent on the study of high-pressure jets in open field (i.e., free jets). In particular, easy-to-use mathematical models have been developed. These, by hand calculations, allow to quickly assess various physical variables that are of paramount importance in safety evaluations.
However, it is easily as possible that, in a realistic accidental scenario, the unwanted leak may involve either the ground or an equipment placed in its vicinity. As demonstrated by recent works, when a jet interacts with an obstacle, its behavior can significantly change. Hence, in the safety assessment of this situation, the mathematical models derived for the free jet scenario can lead to incorrect predictions. Focusing on the scenario of an accidental high-pressure unignited flammable jet, this work shows how the proximity to the ground can influence the lower flammability limit cloud extent of different substances. Varying the height above the ground of the source term, the effect of the ground was systematically studied through a Computational Fluid Dynamics analysis considering high-pressure unignited methane, propane and hydrogen jets. The main achievement is the demonstration that releases of compounds with similar or larger molecular weight than that of air are similarly affected by the ground while, releases of compounds lighter than air interact with the ground in a sensibly different way.