AbstractA theory is developed for calculating the heat transferred from a buoyant layer of fire gases and smoke, to a sprinkler spray. The theory involves calculating the heat transfer to a single water drop as it describes its trajectory, and uses experimentally derived information on the nature and structure of such sprays to calculate heat transfer to the whole spray. Because such experimental information is sparse for sprinklers, a very simple model of the ballistic properties of a sprinkler spray is adopted. Calculations using the teory suggest that the practive of installing sprinklers in the smoke reservoirs of shopping malls would, in some cases at least, reduce the effectiveness of natural venting of smoke by reducing the buoyancy of the hot smoky gases.