Simulation of the flow induced by positive pressure ventilation fan under wind driven conditions

Abstract

Positive Pressure Ventilation (PPV) is a tactical forced ventilation technique used by many fire departments to remove smoke, heat and contaminants from a burning building. PPV usage as a post fire strategy is generally proven and widely accepted as an effective ventilation tool. However, its success as a pre-attack strategy in controlling the spread of fire and smoke is only ensured when it is used correctly and with caution. The efficiency of PPV depends mainly upon net air flow rate through the fire structure. The amount of fresh air blown into the building during a PPV attack is affected by various factors such as fan capacity, distance between the fan and inlet door, inlet dimensions, exhaust opening area, wind and fire conditions etc. Computational Fluid Dynamics (CFD) is a useful and costeffective tool in improving our understanding on various factors affecting the effectiveness of PPV and could be used to improve both the fire fighter and fire victim’s safety. In the present investigation, the SMARTFIRE CFD fire field model is validated using two full-scale experiments characterising a PPV fan. This work is extended by investigating the relationship between the exhaust/inlet area ratio and the net air flow rate into the room geometry under wind and no wind conditions. Finally, results from the simulations of a complex multi-storey structure involving wind driven fire and PPV fan are also presented. Suggestions have been made on the choice of vent locations for better fan performance