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 the 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 it with computational fluid dynamics (CFD) simulations to investigate the effects of the 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 the obstacle height and blockage ratio influence the surrounding flow field in the burning area. The mist flux reaching the burning zone can be significantly reduced, which affects the efficiency of water mist fire suppression. The obstacle height is negatively correlated with the suppression time, whereas the blockage ratio is positively correlated with the suppression time. The fire suppression mechanism of water mist is based primarily on the coupling effects of cooling and oxygen displacement. The oxygen concentration during successful fire suppression ranged from 18.4% to 19.1%. However, water mist promotes the production of CO, with higher CO concentration peaks observed as the 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.