A model is developed to simulate the interaction of a sprinkler and a two-layer fire environment under arbitrary conditions of sprinkler elevation, upper- and lower-layer thickness, and temperature. The sprinkler is characterized by a water flow rate and four measurable device parameters. The model simulates the effects of the sprinkler spray as it entrains, drives downward, humidifies, and cools gases in the upper and lower layers. It predicts the flow rates. of mass, enthalpy, products of combustion and evaporated water to each of the two layers as a result of sprinkler operation. Results of example calculations are presented.