Abstract: The conventional performance test method of organic molded fire barrier in cable tunnel is difficult to reflect the heat insulation performance after aging, and it is impossible to judge the deterioration failure. Therefore, this paper proposes a quantitative method for the thermal insulation performance of the fire barrier after aging. Firstly, the fire barrier is subjected to hygrothermal aging treatment, and then the equivalent combustion test is carried out to obtain the high temperature tolerance time of the aged fire barrier. Combined with the statistical law of the action time of the fire extinguishing appliance, the failure cycle based on the thermal insulation performance of the fire barrier is obtained. Furthermore, the residual strength model and the mechanical properties test data of the fire barrier under different aging cycles are used to calculate the failure cycle of the fire barrier based on the mechanical properties. Finally, based on the comprehensive comparative analysis of the service life of thermal insulation performance and mechanical properties, the failure period of the fire barrier is determined. The results show that the failure periods based on the impact strength and bending strength of the fire barrier are about 45.19 years and 15.07 years, respectively. The life of the fire barrier in the 220 kV and 110 kV high voltage cable tunnels is determined by the thermal insulation performance of the barrier, and the failure periods are 10.1 years and 11.4 years, respectively. The service life of the fire barrier of 35 kV cable tunnel is 17.19 years considering the thermal insulation performance, so its life is determined by the mechanical properties of the barrier, and the failure period is about 15.07 years.

Key words: fire barrier, failure cycle assessment, damp heat aging, mechanical properties, thermal insulation performance