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A CFD study is reported which attempts to shed light on the problem of estimating air entrainment into buoyant balcony "spill plumes". This topic has been of some controversy for several years but is of substantial practical importance to the design of smoke control systems in atria and other multi-level complexes. The study described here concerns numerical simulation of the reduced scale physical model from which much of the semi-empirical formulae have been derived. Excellent agreement between measured and predicted mass fluxes is demonstrated in the regions of lower heights of plume rise, but the two apparently diverge at greater heights of rise. Two possible explanations involve the apparently unrealistic assumption of a horizontal smoke layer surface and the validity of the turbulence modeling of this flow. The study does support recent dimensional analyses which suggest only a small degree of air entrainment into the turning region of the smoke flow from the horizontal to the vertical.