A full scale fire model for an enclosed environment needs a quantitative description of the fire source itself. This is because of the time dependent power output of a flame arising from oxygen depletion. The objective of this research was to develop a quantitative understanding of the behavior of simulated gas flames and liquid pool fires of low initial momentum (buoyancy controlled) in a two-dimensional, axi-symmetric situation. Specifically, we predicted velocity, temperature and species concentration fields as a function of axial and radial coordinates. Knowing these fields, we can estimate the quantity of feed back energy which in turn determines the mass burning rate of a liquid pool. This enables us to determine the power output of the fire source in question, as a function of the chamber environment.