The necessity of a new jet modelling approach in safety studies has been extensively discussed by the scientific society. The current work discusses the differences between flammable gas clouds formed by axisymmetric jets (modelling used in safety studies) and high aspect ratio jets (modelling that best represents most of the leak scenarios in industry). The RANS CFD modelling approach is used. A gas leak placed in a geometry representing an offshore platform is considered. The work is also focused on the efficiency of the computational tool in reproducing the jets. The centreline velocity decay and other indicators of how the jets behave are compared with experimental data. The results indicate the need of great computational effort in order to represent the short distance behaviour of high aspect ratio jets. Besides, it had been preliminarily observed that the total volume of their clouds is less than or equal to the volume of the clouds originated by axisymmetric jets.