Experimental investigation of fire temperature distribution and ceiling temperature prediction in closed utility tunnel

Urban utility tunnel is a relatively independent underground closed space. This paper conducted experiments in a utility tunnel with a length of 20 m, inner diameter of 1.5 m and outer diameter of 1.8 m to explore the temperature distribution in the case of closed utility tunnel fire. The formula of Li's is used to calculate the maximum temperature rise of ceiling, and it is found that it is not applicable to closed utility tunnel, mainly because the formula does not consider the temperature of smoke in closed space. Therefore, it is modified, and the calculated result of the modified formula is in good agreement with the actual value. The following conclusions are drawn:(1) The temperature in the roof of the utility tunnel directly above the fire source is the highest; In the longitudinal direction, the temperature drop is very rapid with the increase of the distance from the fire source. In the vertical direction, the temperature in the utility tunnel appeared obvious stratification phenomenon. (2) The maximum temperature of closed utility tunnel ceiling can be predicted by increasing characteristic temperature of smoke based on Li's formula. This paper does not consider the impact of flame on the ceiling.