The RoboCupRescue Simulation project aims at simulating large-scale disasters in order to explore coordination strategies for real-life rescue missions. This can only be achieved if the simulation itself is as close to reality as possible. In this paper, we present a new fire simulator based on a realistic physical model of heat development and heat transport in urban fires. It allows to simulate three different ways of heat transport (radiation, convection, direct transport) and the influence of wind. The protective effects of spraying water on non-burning buildings is also simulated, thus allowing for more strategic and precautionary behavior of rescue agents. Our experiments showed the simulator to create realistic fire propagations both with and without influence of fire brigade agents.