The LITFIRE code was modified and used to model lithium chemical reactions with steam-air mixtures in situations representative of accidental spills in fusion reactors. New water pool nodes were added to the primary and secondary cells representing the reactor and its building. An iterative energy balance routine was developed to determine the temperature of the cell gas; heat transfer to structures was modified to include the effect of water condensation and the cell gas emissivity calculation was changed to account for the presence of polar water vapor molecules. Calculations were performed describing a spill on the building floor as well as a spill within the plasma chamber. Humidity and steam injection were also represented. The results indicated that the primary effect of the steam was to raise the emissivity of the cell gas, and thus the gas temperature and pressure, while reducing somewhat the temperatures of both the lithium combustion zone above the pool and the lithium pool itself.