Abstract: Abstract: In order to study the effect of blocking on the fire extinguishing efficiency of liquid nitrogen in utility tunnel, this paper carried out an experimental study on the effect of blocking state on the fire extinguishing efficiency of liquid nitrogen. The research shows that the oxygen barrier suffocation of liquid nitrogen plays a dominant role, and the existence of blockage accelerates the suffocation process, thereby improving the liquid nitrogen fire extinguishing efficiency of the utility tunnel. The effect of lower blocking on nitrogen injection fire extinguishing is stronger than that of upper blocking, and the fire extinguishing efficiency is increased by 50.7% and 30.4% respectively compared with no blocking. The closer the fire blocking is to the fire source, the greater the blocking rate, and the more significant the promotion effect of liquid nitrogen oxygen isolation and asphyxiation. When the fire blocking is far away from the fire source, the fire extinguishing efficiency is 35.2% lower than that when the distance is short; the fire extinguishing efficiency with a blocking rate of 75% is up to 44.4% higher than that of 25%. Therefore, selecting reasonable blocking measures and optimizing sealing methods can maximize the effect of liquid nitrogen fire extinguishing.

Key words: Key words: long and narrow space, utility tunnel, fire blocking, liquid nitrogen fire extinguishing, fire extinguishing efficiency