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Performance of the natural smoke venting systems (known as static smoke exhaust systems) in a large cargo hall in Hong Kong will be evaluated by Computational Fluid Dynamics. Elevation of the smoke layer interface is demonstrated to be kept above an agreed height. Numerical simulations on the smoke exhaust were carried out with a 5 MW fire at two levels. The simulation tool selected was the Fire Dynamics Simulator (FDS) developed at the Building and Fire Research Laboratory, National Institute of Standards and Technology in USA. Wind action is another factor affecting the efficiency of the natural smoke venting systems. Effect of wind is simulated by imposing incident air flow with speeds varying up to 20 ms-1. Adverse effects might be resulted when strong wind is blowing towards a tall vertical surface adjacent to the large cargo hall. Smoke might be pushed downwards under some conditions leading to negative wind pressure coefficients on the leeward side. Performance of an adjacent wall next to the hall was also studied.