Vented deflagrations are one of the most challenging phenomenon to be replicated numerically in order to predict its resulting pressure time history. As a matter of fact a number of different phenomena can contribute to modify the burning velocity of a gas mixture undergoing a deflagration, especially when the flame velocity is considerably lower than the speed of sound. In these conditions acceleration generated by both the flow field induced by the expanding flame and from discontinuities, as the vent opening and the venting of the combustion products, affect the burning velocity and the burning behaviour of the flame. In particular the phenomena affecting the pressure time history of a deflagration after the flame front reaches the vent area, such as flame acoustic interaction and local pressure peaks, seem to be closely related to a change in the burning behaviour induced by the venting process. Flame acoustic interaction and local pressure peaks arise as a consequence of the change in the burning behaviour of the flame. This paper analyses the video recording of the flame front produced during the TP experimental campaign, performed by UNIPI in the project HySEA, to analyse qualitatively the contribution of the generated flow field in a vented deflagration in its pressure-time history.