Abstract:

To address the safety technical issue in local application fire suppression systems for Class B pool fires, where the gas discharge impulse plays a dual role of both highly effective flame knockdown and inducing splashing, a systematic gas discharge impulse prediction model was developed and experimental studies were conducted. Firstly, an array-based dynamic pressure measurement device was designed and fabricated to accurately quantify the spatial distribution and transient evolution of the gas discharge impulse field beneath the nozzle. Based on experimental data, a predictive model was established, incorporating both discharge pressure and duration. Secondly, a comprehensive fire suppression effectiveness model was constructed, which comprised two sequential phases: flame knockdown and extinguishment. A flame lift force calculation model based on plume theory was established, and the critical extinguishment criterion was defined as the gas discharge impulse exceeding the flame lift force. Finally, a surface tension criterion for central splash and a geometric morphology criterion for edge overflow were proposed innovatively to quantify the upper impulse threshold for safe discharge. The results demonstrate that the developed models and device can accurately predict both the critical impulse required for successful extinguishment and the upper safety limit for splashing. The extinguishment was observed to occur during the peak impulse release and early decay stages, which is consistent with the theoretical criterion prediction. The predicted splash behavior also agrees well the experimental observations, thereby validating the effectiveness of the dual-criterion approach.

Key words: local application, fire systems, gas discharge impulse, pool fire, flame lift force, critical splashing