The food industry improves the level of hygiene by controlling the airborne contamination. The use of localised air delivery systems allows low particle counts to be achieved. In classical uni-directional air flows , air is blown downward through a filter giving rise to a free jet. This kind of flow is known to be sensitive to external as well as internal disturbances stemmed from the filter, which are amplified through the flow development. The present study aims at analysing the characteristics of this air flow near the outlet and further downstream, in the light of air flow stability and of the impact on the transfer of contamination. Experimental approach has shown the topology of the streamlines, the local unsteadiness and the level of turbulence of the flow. The consequences on the dispersion of contamination have been highlighted and discussed.