Before tackling the complex problem of the gas circulation in a ventilated room in case of fire, we have tested the ability of a field modelling code (TRIO-VF) to simulate the air circulation in the cell before fire breaks out. Tracer gas experiments have been performed and have allowed us to make comparisons between numerical simulations and experiments. Globally, the numerical simulations are in good agreement with the-experiments and give us a good understanding of the air circulation in the ventilated room. Moreover, this comprehension has been confirmed by using DTS, a code based on the distribution of residence times.