Heat and mass flow between cold and warm environments due to the pressure difference between both sides. This exchange causes a loss of energy and human comfort in the buildings. The indoor air quality (IAQ) also reduces because of the passage of dust, odour, insects and bacteria along with the fluid across a doorway. To minimise this heat and mass flux and to maintain IAQ, an air curtain is often used as an artificial separation barrier in public and industrial buildings. Its performance is determined by the sealing effectiveness, defined as the fraction of the exchange flow prevented by the air curtain compared to the open doorway. The controlling parameter for the air curtain is the deflection modulus (Dm), which is the ratio of the momentum flux of the air curtain and the transverse forces acting on it due to the stack effect. Although air curtains are used to facilitate the human and the vehicle passage through doorways, the effect of the traffic on the stability and the effectiveness of an air curtain has not yet been studied. In the present study, we conduct laboratory experiments to examine the effect of a person passing through the curtain. The experiments were conducted using fresh water and salt solutions, with dimensions such that they were dynamically similar to the real-scale air curtains installations in the doorways of a building. We find that the effectiveness is decreased by the passage of a person and that the effect increases with the increasing walking speed. We visualised the jet and the wake using dyes of different colours to determine how the air curtain is deflected by the passage of a person.