CFD-Aided Tenability Assessment of Railway Tunnel Train Fire Scenarios

Abstract

Five fire scenarios have been simulated with the CFD model Fire Dynamics Simulator (FDS) to analyse the performance-based fire safety design of a 2935 m-long railway tunnel. The influence of tunnel longitudinal ventilation fan activation time, fire size and the type of burning materials on tunnel tenability was investigated based on variations of two primary scenarios: Scenario #1 assumed a 15 MW fire at the front end of a train, and Scenario #2 assumed a 15 MW fire at the rear of a train. In both scenarios the burning material was assumed to be predominantly polyurethane, and tunnel fans were assumed to activate 901 seconds after fire initiation. Scenario #3 was a variation of Scenario #1 with the dominant burning material changed to wood; Scenario #4 was a variation of Scenario #2 which assumed that fans activated 180 seconds after fire initiation; and Scenario #5 was a 6 MW fire, which was scaled down from the 15 MW fire of Scenario #1.For all of the scenarios, a reversible bi-directional ventilation strategy was implemented, and the worst wind condition was considered. The burning materials (polyurethane and wood) were assumed to generate a soot rate of 10% and 1% per unit weight of fuel respectively. Maximum tenable time (known as Available Safe Egress Time, ASET hereafter) was computed based on a visibility limit of 10 m at a height of 2.1 m.CFD virtual realisation results showed that the fire heat release rate, type of dominant burning material and the activation time of Smoke Management Systems (SMS) fans all influence tenability times within the tunnel. It is suggested that all these factors must be considered in the performance-based fire safety design and the accident management of a tunnel.