The response of an enclosure having a ceiling safety-vent to a fire of solid propellant located on the floor is investigated numerically. The full Navier-Stokes equations are solved along with the species continuity equations. A recent method is used to compute chemical equilibria and the coupling between chemistry and thermodynamics is treated according to a new strategy. The particular boundaries, which are the combustion zone of the propellant and the outflow section, require an original treatment by solving a set of ’full’ or ’half’ Riemann problems taking into account the transport of chemical species. The SOLA-ICE algorithm is successfully developed for the reactive-diffusive case dealing with particular boundaries. A fire of a standard hot homogeneous propellant in a rectangular cavity initially filled with air is simulated for two opening conditions of the safety-vent. They predict the increase in the rates of energy release and CO2/H2O production in the reaction zone caused by afterburning processes involving the air of the enclosure. The course of the compartment fire is described in terms of time evolution of the average gas temperature and pressure, and oxygen depletion for both opening configurations.