The discharge characteristics of a typical CO2 fire extinguisher system under consideration for the US space station have been analyzed using the FLOW-NET computer program. The discharge time, mass, and ultimate pressurization are determined by calculating the transient until a resting state is achieved. Accuracy of the numerical solution procedure is demonstrated using different nodalizations and by comparing calculated results for an ideal gas against analytic results. Because the length of the supply tank can be several orders of magnitude smaller than the length of the transfer line, transient calculations may require a very small time step and considerable computer time. A procedure is described to modify the geometric model, which reduces required computer time by an order of magnitude without loss of accuracy. Sensitivity of the results to the equation of state model is discussed. Condensate formation in the supply tank during discharge is shown to be a direct consequence of CO2 vapor properties and energy conversion.