Predicting the outcome of a leak from a container with liquefied gas is a nontrivial but important task in the field of atmospheric dispersion modelling. This event includes rapid and violent processes, including partially flashing of the liquid, which result in a high-speed two-phase jet. Due to insertion of external heat, caused by turbulence and pressure gradients, the jet transits into a purely gaseous plume consisting of the released substance mixed with entraining air. The gas will undergo an adiabatic expansion which causes a sudden drop in temperature. The resulting mix of released substance and air at a low temperature may end up with a density substantially higher than that of the surroundings, which then renders the gas to be a dense gas. A model for the jet that aims to serve as a compatible source term for further Lagrangian dispersion modelling is presented in this report.