The effects of automatic sprinklers on compartment fires has been investigated in this report. The interaction of a sprinkler spray with a buoyant hot upper layer has also been examined. A model was developed to predict the rate of smoke production and hence the depth of a smoke layer that may be produced, for an uncontrolled growing fire. Flow out of vents was included in this model. The model compared well to the predictions of 'Firecalc'. An method for the prediction of detector actuation has been used that is valid for growing fires, avoiding the quasi-steady assumption used in 'Firecalc' and 'FPEtool'. This method also includes the transport lag time of the fire signature from the source to the detector. The interaction of a sprinkler spray with a fire induced hot upper layer is a very complex problem. The combining effects of drag induced on the upper layer and evaporative cooling by the sprinkler spray may cause the layer to fall to a lower level. The model developed to predict the rate of smoke production, hence smoke layer depth, is only valid for uncontrolled fires. Time constraints prevented the effects of sprinklers on compartment fires to be incorporated into this model, although the theory of the effects is included with this report.