Increasingly Double-Skin Façade (DSF) structure has been applied in new buildings since 1970s, as it potentially offers many environmental benefits, such as solar control, noise abatement, thermal flue and day lighting control. One of the functions that the structure can perform is to provide natural ventilation. Many such façade structures therefore have no horizontal separation within the cavity. While this design accelerates the airflow within the shaft, it also raises a concern of smoke propaganda between storeys in a fire event. Furthermore, the time of smoke fill up the building compartment can be associated with the safety escape time of occupants. This study investigates the process of smoke filling in rooms connected by the DSF system. A computational fluid dynamics (CFD) model was developed to simulate the progressive dispersion of smoke in its early development. The model was validated by a full size fire test data and a salt-water experiment. The model is then used to test a number of DSF designs commonly seen in industry. Running the models under various scenarios will allow the escape time, the key fire safety parameter, to be examined with a number of key design parameters. This will then improve DSF design with better fire safety features.