Zhenkun Wu

Micron‐sized dry water particles assembled from gaseous silica and deionized water were prepared by physical dispersion method, and the effects of two chemical components on the microstructure and fire extinguishing efficiency of dry water materials were analyzed. Three different filling pressures were selected to study their effect on dry water extinguishing efficiency of wood crib fire. The effect of dry water on fire extinguishing efficiency of wood crib was studied by building wood crib of different sizes. The results show that the larger filling pressure inhibits the fire more obviously, but the dry water structure is easy to be damaged. Dry water can adhere to the inside of the wood crib structure and exert its role of cooling and isolating oxygen to inhibit its smoldering under a certain release pressure. With the increase of the size of wood crib, the suppression efficiency of dry water materials on wood crib fire gradually decreases with increasing extinguishing time. The fire extinguishing efficiency of dry water with sodium acetate is improved, but its structure is not stable. By comparing and analyzing the critical combustion rate and oxygen concentration of wood crib, it was found that continuous cooling to reduce the combustion rate and smoldering is the dominant mechanism of dry water on wood crib fire.

This paper has analyzed the longitudinal ventilation on the effect of the efficiency of the smoke evolution mechanism in a metro tunnel of multi‐window carriage fires. These were simulated by Large Eddy Simulation (LES) with Fire Dynamics Simulator (FDS). In the past, analyses of smoke temperature under the tunnel ceiling and smoke overflow characteristics have been conducted. However, longitudinal ventilation has a different impact on temperature than natural ventilation, especially in a subway tunnel with a multi‐door carriage fire. Consequently, several simulations were run in a subway tunnel (360‐m long, 6.0‐m wide, and 4.8‐m high). The longitudinal ventilation velocity is set by 0–10 m/s with the heat release rate of 1–10 MW. The results show that there is a linear relationship between the maximum temperature and the longitudinal ventilation velocity. An empirical model considering various longitudinal ventilation velocities was developed to predict the maximum smoke temperature underneath the subway tunnel ceiling. The effects of the longitudinal ventilation velocity, the heat release rate, and the distance of the fire source on the characteristics of longitudinal temperature distribution were analyzed. What's more, smoke overflow characteristics under different longitudinal ventilation velocities have been described. The findings and results can also provide a reference for the fire risk assessment of a metro tunnel of multi‐window carriage fires.