The validity of the top-hat model for predicting the flammable mass produced by a continuous, turbulent, buoyant fuel-gas release is examined by comparing top-hat model predictions with those of a numerical Gaussian jet model that fully accounts for significant jet density variations and realistic radial profiles of jet properties. The numerical calculations confirm the top-hat model for jet flammable mass calculations. The Gaussian model also provides numerical predictions of the axial distance (z(LFL) ) at which the lower flammability limit fuel concentration is reached. A rational correlation of the z(LFL) predictions is developed using a dimensionless parameter scheme suggested by the top-hat model.