Experimental and numerical studies on fire suppression at underground substations: The impact of obstacles on water mist efficiency

Underground substations are characterized by complex internal structures and confined spaces. In case of fires, heat can easily accumulate to form a concealed fire, which significantly increases the difficulty of fire suppression. This study established a full-scale high-pressure water mist fire suppression experimental platform and combined with computational fluid dynamics (CFD) simulations to investigated the effects of obstacle height and blockage ratio on the effectiveness of water mist fire suppression. Key parameters such as the fire suppression process, mist flux distribution, suppression time, and gas concentrations were systematically analyzed.  The results show that obstacle height and blockage ratio influence the surrounding flow field in the burning area. The mist flux reaching to the burning zone can be significantly reduced, which affects the efficiency of water mist fire suppression. Obstacle height is negatively correlated with suppression time, whereas the blockage ratio is positively correlated with suppression time. The fire suppression mechanism of water mist is primarily based on the coupling effects of cooling and oxygen displacement. The oxygen concentration during successful fire suppression was found to range from 18.4% to 19.1%. However, water mist promotes the production of CO, with higher CO concentration peaks observed as suppression time increases. These findings provide valuable insights for optimizing the design of high-pressure water mist fire suppression systems in underground substations and offer theoretical and practical guidance for fire prevention and control in confined spaces.