Many of the clean agents currently used in total flooding fire suppression applications have vapor densities greater than ambient air. The denser agent-air mixture creates hydrostatic pressure differences causing flow of the mixture out of the enclosure as well as flow of ambient air in through leakage paths inherent in building construction. Hold time refers to the amount of time it takes for the concentration of the agent-air mixture to drop below a specified concentration at a designated height within the protected enclosure. In this study an experimental test enclosure was used to evaluate an analytical model of agent-air mixture leakage and to investigate the effects of different leakage areas on agent hold times. The analytical model, known as the descending interface model, demonstrated favorable agreement with experimental measurements for heights greater than one-half the height of the enclosure for the agent used in this investigation.