In the framework of the evaluation of the three-dimensional, finite volume code ADREAHF, a computational simulation of the Thorney Island Dense Gas Trial No. 8 is performed. A one-equation turbulence closure scheme is adopted in this first approach. The results of the simulation are compared with the experimental data in the form of concentration-time histories. The model predictions are satisfactory, with a tendency of the model to underestimate the maximum gas concentration and the time of its occurrence. The differences between model predictions and experimental data can be reduced by taking into account concentration fluctuations, utilization of finer numerical grids and improvements of the turbulence modelling.