Abstract:

To evaluate the fire suppression performance of liquid nitrogen in a long-narrow confined space with a high blockage ratio and to reveal the key influence mechanism of the blockage effect, liquid nitrogen fire suppression experiments were conducted in a scaled-down urban underground logistics tunnel. The effects of blockage effect on fire suppression time and diffusion behavior of liquid nitrogen were investigated by varying the nitrogen injection distance and obstruction distance. The results show that when nitrogen is injected between two obstacles, a reduction in obstruction distance facilitates the formation of a more enclosed space, which significantly enhances the oxygen isolation and asphyxiation effect. When nitrogen is injected 1 m away from the fire source, reducing the obstruction distance from 6.3 m to 2.3 m shortens the fire suppression time by 23.1%. Conversely, when nitrogen is injected on the leeward side of an obstacle, the diffusion path is hindered, leading to a "blocking-detouring-rejoining" phenomenon that reduces fire suppression efficiency. In this configuration, with an injection distance of 3 m from the fire source, increasing the obstruction distance from 4.3 m to 6.3 m results in a 25% reduction in suppression time. It is concluded that the obstruction distance and nitrogen injection location are core parameters affecting the efficiency of liquid nitrogen fire suppression.

Key words: blockage effect, underground logistics tunnels, liquid nitrogen fire suppression, fire suppression efficiency, long-narrow confined space