Abstract: The enclosure integrity of total flooding gaseous fire suppression protected areas deteriorates annually, leading to attenuation of fire suppressant agent hold time, which significantly reduces the long-term reliability of fire suppression system performance. Therefore, it is essential to provide mass compensation for the original design dosage of fire suppressant agents. Building upon previous research, this paper analyzes the leakage patterns, hold time, and mass loss of perfluorohexanone within protected areas under quantified enclosure integrity conditions by establishing more uniformly distributed air leakage areas and developing simplified yet reliable simulation models. The results are compared with the ISO hold time prediction model. The findings demonstrate that the evolution of the "fire suppressant leakage-air mixing" pattern at leakage points across different levels causes non-monotonic evolution of the descending interface, whereas the ISO model's simplified assumptions ("top air intake/bottom leakage" and "single leakage morphology") result in monotonic evolution predictions of the descending interface. Under identical fire suppression concentration and protection height parameters, the ISO model significantly overestimates the hold time. Current standards such as ISO neither provide calculation methods for fire suppressant mass compensation nor address the potential misjudgment of hold time in their prediction models. For high-value protected facilities, the methodology proposed in this study enables simulation of complex leakage morphologies and precise quantification of fire suppressant mass compensation required to meet hold time specifications, thereby establishing a design basis for fire suppressant dosage in long-service-life protected areas.

Key words: total flooding extinguishing, enclosure integrity, perfluorohexanone, descending interface, fire extinguishing agent leakage, mass compensation