An analysis of tunnel fire characteristics under the effects of vehicular blockage and tunnel inclination

To address the effect of metro train blockage on the critical ventilation velocity in a long tunnel, a series of scenarios were conducted numerically through this study, including different fire sizes (5-10 MW), metro train lengths (80-120 m), and blockage ratios (φ, 0.50, and 0.57). It is known from the numerical results that the metro train length shows a limited effect on the critical ventilation velocity, which is because the longitudinal ventilation has become stable before reaching the fire source to prevent smoke back-layering, and increasing the metro train length only increases the distance of stabilizing the longitudinal ventilation. The blockage ratio shows an obvious influence on the critical ventilation velocity, which is because the presence of the metro train can obviously reduce the flow cross-sectional area of the tunnel. An empirical model is developed as well, while it is known that the critical ventilation velocity increases with the one-third power of dimensionless heat release rate and (1-φ). The research outcomes of this study provide a technical guide for the design of the metro tunnel and the relevant emergency management of fire rescue under fire conditions. K E Y W O R D S blockage ratio, critical velocity, FDS, metro train, subway tunnel 1 | INTRODUCTION An increasing number of metro systems have been designed and constructed recently to release the urgent issues of accelerated urbanization and growing population in metropolises. The companied fire risk is always an important and hot research topic from both the academia and industries. Consequence and impact of the relevant fire accidents are very high, which can be proved by the large number of fire casualties and very bad influence in the past few decades, such as the Daegu metro fire in South Korea, the Viamala tunnel fire in Switzerland, and the Burnley tunnel fire in Austria. [1][2][3][4] To benefit with the fire safety of those metro systems, smoke movement is an inevitable aspect during the design as it is the most fatal factor of a tunnel fire. 5-7 Therefore, how to control the smoke movement effectively to provide a safe zone for the occupants and firefighters during the evacuation and rescuing processes, respectively, becomes an important question that needs to be answered urgently.It is indicated that the metro train fails to reach the next station and stops between the two stations in about 50% of fires. 8,9 When a fire occurs in the metro tunnel, the relevant ventilation facilities in the adjacent stations will be started, where longitudinal ventilation is triggered, which not only can prevent the smoke from spreading to the upstream and also offer a safe zone without smoke for both occupants and firefighters. If the designed longitudinal ventilation velocity is smaller than the critical value, the smoke released from the fire can break through the barrier raised by the longitudinal ventilation and then threaten the people upstream.Many studies have been undertaken in identifying the appropriate longitudinal ventilation v...

Section: Numerical Methodologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Critical ventilation velocity under the blockage of different metro train in a long metro tunnel

Zhang

Shi

et al. 2020

“…1 Owing to the long-narrow structure, the fire accident in tunnels could cause vast casualties and huge property loss as a result of hot smoke. 3 Therefore, the control of the smoke flow during a tunnel fire is often an important part of emergency planning. 3 Therefore, the control of the smoke flow during a tunnel fire is often an important part of emergency planning.…”

Section: Introductionmentioning

confidence: 99%

“…2 Heavy traffic, which can lead to the obstruction of tunnels, makes it even more difficult to counter possible tunnel fire hazards. 3 Therefore, the control of the smoke flow during a tunnel fire is often an important part of emergency planning. [4][5][6][7] Since the commonly used smoke control method in tunnels is the longitudinal ventilation, understanding the smoke behaviors under various longitudinal ventilation scenarios is of great importance.…”

Section: Introductionmentioning

confidence: 99%

“…13 This is because a blockage in the upstream of the fire source can alter the smoke movement and, consequently, the ventilation requirements of the tunnel. 3 Lee et al 18 25 The code has been widely used in the fire research field, and its validity has been extensively verified. 26,27 To reduce the amount of mesh cells and improve the resolution of the flow field, the Froude modeling strategy has been adopted by Although the passengers are slowly moving to the exit in reality, the piston wind generated by the passenger flow has insignificant effect on the flow field inside the tunnel so the passenger blockage between the exit and the fire source was set to be stationary during the whole simulation process.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effects of passenger blockage on smoke flow properties in longitudinally ventilated tunnel fires

Wang

2019

This paper investigates the effects of passenger blockage on smoke flow properties in longitudinally ventilated tunnel fires. A series of numerical simulations were conducted in a 1/5 small-scale tunnel with the different heat release rates (50-100 kW), longitudinal ventilation velocities (0.5-1 m/s), passenger blockage lengths (2-6 m), and ratios (0.17-0.267). The typical smoke flow properties in different tunnel fire scenarios are analyzed, and the results show that under the same heat release rate and longitudinal ventilation velocity, the smoke back-layering length, maximum smoke temperature, and downstream smoke layer height decrease with increasing passenger blockage length or ratio. The Li correlations can well predict the smoke backlayering length and maximum smoke temperature in tunnel fire scenarios without the passenger blockage. When the passenger blockage exists, the modified local ventilation velocity that takes the blockage length and ratio into account has been proposed to correct the Li correlations. The smoke back-layering length and maximum smoke temperature with the different blockage lengths and ratios can be predicted by the modified correlations, which are shown to well reproduce the simulation results. K E Y W O R D S passenger blockage, smoke flow, tunnel fire

Large eddy simulation for improving smoke extraction efficiency by inverted V‐shaped baffle in the urban tunnel

Deng

Sun

et al. 2021

Summary In order to reduce the undesirable effect of boundary layer separation and plug‐holing in a naturally ventilated tunnel with shaft for smoke extraction, a new design of baffle has been proposed in this paper. Large eddy simulation (LES) was performed with fire dynamics simulator (FDS), the influence of the angle formed by the boards (θ) and the distance between the baffle top and the shaft bottom (d) has been investigated. The simulation results show that the smoke extraction efficiency is not simply a monotonic function of the distance d or the angle θ, the influence of d and θ has been discussed, and the mechanism has been investigated. With proper configuration of the inverted V‐shaped baffle, the negative effect of plug‐holing can be eliminated, and the boundary layer separation can also be alleviated; the maximal smoke extraction efficiency is 2.04 times of that in the traditional shaft.