Study on the critical velocity in a sloping tunnel fire under longitudinal ventilation

Weng, Miaocheng; Lu, Xin-Ling; Liu, Fang; Du, Cheng-xian

doi:10.1016/j.applthermaleng.2015.10.059

Cited by 128 publications

(49 citation statements)

References 15 publications

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“…The velocity at the wall is calculated as the average value of the velocity in the first cell that touches the wall and zero velocity on the wall cell. The heat release from the fire source is defined as full power at the beginning of the simulation, because data available from the experiment are only for fully developed fires [24]. Thermal radiation initial conditions are defined with radiation intensity based on the initial temperature of objects (ambient temperature) and the energy absorption in the air, mostly formed by nitrogen.…”

Section: Initial and Boundary Conditionsmentioning

confidence: 99%

Novel Approach in Tunnel Safety Assessment

Vidmar¹

2020

Accident Analysis and Prevention

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The definition of a deterministic approach to risk analysis stems from the need to understand the conditions that are developed in the event of an accident with a fire in a road tunnel. From the point of view of the tunnel manager and rescuers, these data are important during planning the operation of the tunnel and in coordinating the rescue. The methods of tunnel control in crisis situations are most often based on the experience of operators and crisis plans, which are also made by experience or using simple calculation tools. In recent years, due to many tragic accidents in European tunnels, there has been a lot of talk and work in the field of risk assessment and the possibilities of risk reduction. The methodology of safety analyses and the determination of the level of risk arise predominantly from the nuclear and chemical industry, where it has been in use for more than 50 years. The paper presents the methodology for integrating methods of rapid processing of risk assessment with time-consuming CFD methods for analysing the consequences of fire in the tunnel safety assessment process. The main observed variables are the density and the temperature of the carbon black, which are analysed during the fire step in a minute. Human behaviour is considered in the evacuation model, which is necessary for the assessment of fatalities during the progress of the fire. The use of the methodology is presented by assessing the national tolerable risk for transport in tunnels and compared to the EU reference criteria.After the entering in force of EU directive 2004/54/EC [3] on minimum safety requirements for tunnels, the risk assessment methods have been proposed by PIARC [4] with the QRAM model [5]. Other tools and methodologies for risk assessment in road tunnels were developed-the Dutch RWQRA model and the Austrian RVS 09.03.11-TuRisMo methodology. The fire consequence calculations, as a main part of risk evaluation, are done with a simple one-dimensional flow model or at most with zone models, where in every step volume is divided into a hot and cold layer. These models cannot cover a specific flow dynamic, smoke stratification, influence of different ventilation systems, vorticity, and crossflow. Effects like back layering are modelled directly in one-dimensional models, but its reliability is scenario dependent and is not reliable, or in other scenarios overestimated [6]. Following this idea, we believe that a methodology of fire safety valuation, which improves existing methodologies and is based on a deterministic approach, is necessary, as the approach to integrate CFD consequence results in a probabilistic QRA method [7].The presented analysis includes the fire modelling based on CFD results [8,9] for different standard fire scenarios and includes basic human behaviour, e.g. resistance on height temperature and gas concentration, evacuation velocity, reaction times and other features. These consequences are further multiplied with the probability (likelihood) of the same events, and the result is the indivi...

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Section: Initial and Boundary Conditionsmentioning

confidence: 99%

Novel Approach in Tunnel Safety Assessment

Vidmar¹

2020

Accident Analysis and Prevention

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“…In order to study the backlayering length and the critical velocity of smoke in the metro tunnel with different sectional coefficients, longitudinal ventilation velocities, HRRs, and tunnel slopes, the method of dimensionless analysis and the FDS simulation were used by Weng et al [52]. In the experiment, 45 small-scale models were carried out to provide verification of CFD simulations.…”

Section: = { { { { {mentioning

confidence: 99%

“…Moreover, the prediction models for the critical velocity on different slopes were compared with the prediction models proposed by Atkinson and Wu [2], Ko et al [48], and Chow et al [4]. It was shown that the results of the proposed model by Weng [52] were between Atkinson and Wu and Chow because of different aspect ration. A set of full-scale experiments was conducted by Yu et al [53] to study thermal and smoke control strategies using transverse ventilation system in a sloping urban traffic link tunnel.…”

Section: = { { { { {mentioning

confidence: 99%

Critical Velocity and Backlayering Conditions in Rail Tunnel Fires: State-of-the-Art Review

Haddad

Maluk

Reda

et al. 2019

Journal of Combustion

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The use of interurban and urban trains has become the preferred choice for millions of daily commuters around the world. Despite the huge public investment for train technology and mayor rail infrastructure (e.g., tunnels), train safety is still a subject of concern. The work described herein reviews the state of the art on research related to critical velocity and backlayering conditions in tunnel fires. The review on backlayering conditions includes the effect of blockages, inclination, and the location of the fire source. The review herein focuses on experimental and theoretical research, although it excludes research studies using numerical modeling. Many studies have used scaled tunnel structures for experimental testing; nevertheless, there are various scaling challenges associated with these studies. For example, very little work has been done on flame length, fire source location, and the effect of more than one blockage, and how results on scaled experiments represent the behaviour at real-scale. The review sheds light on the current hazards associated with fires in rail tunnels.

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“…Atkinson et al (1996) obtained a model experiment to determine the slope correction factor for the Wu and Bakar critical velocity model when the gradient changes from 0% to 10% . Weng et al studied the effect of different wind velocity on the return length of flue gas and the influence of slope on the critical velocity in a slope tunnel fire through model experiments and numerical simulations. Qingmin Men and Chuanjin Liu (2018) used fire dynamics simulator (FDS) to study the effect of slope and aspect ratio on the smoke temperature of tunnel fires and put forward the prediction model of maximum smoke temperature rise in tunnel roofs of different slopes and aspect ratios…”

Section: Introductionmentioning

confidence: 99%

A numerical study on critical ventilation velocity in slope tunnel fire under vehicle blockage

Liang

Pang²,

Gao

2020

Civil Engineering Design

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The particularity of highway tunnel location and the limitation of space result in the closure of its environment, which makes evacuation, rescue, and firefighting activities more difficult. In this study, a fire dynamics simulator was used for numerical simulation to study the effect of jamming on the critical velocity of slope tunnel fire. This experiment carried out two sets of working conditions simulations: (1) In the straight tunnel, the heat release rate and the blockage ratio are considered and numerically simulated. (2) Under the heat release rate of 20 MW fire source, the blockage ratio and the gradient of the tunnel are considered and numerically simulated. The vehicle blockage is set to distribute in two rows and two columns upstream of the fire source, accounting for 6.6%-22.0% of the cross-section of the tunnel. The slopes were selected in nine cases of 0%, ±1%, ±2%, ±3%, and ±4%. The six heat release rates were 5 MW, 10 MW, 15 MW, 20 MW, 25 MW, and 30 MW, respectively. The fire occurred on the tunnel centerline. The results show that in flat tunnels, the variation trend of critical velocity with heat release rate is basically the same, and it increases with the increase of heat release rate. However, when the heat release rate is the same, the larger the vehicle blockage ratio is, the smaller the critical velocity is. It can be seen from the second experimental case that the influence of the tunnel slope on the critical velocity is different. In the downhill tunnel, the critical velocity increases with the increase of slope. In the uphill tunnel, the critical velocity decreases with the increase of slope. K E Y W O R D Scritical ventilation velocity, heat release rate, slope tunnel, vehicle blockage

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Study on the critical velocity in a sloping tunnel fire under longitudinal ventilation

Cited by 128 publications

References 15 publications

Novel Approach in Tunnel Safety Assessment

Novel Approach in Tunnel Safety Assessment

Critical Velocity and Backlayering Conditions in Rail Tunnel Fires: State-of-the-Art Review

A numerical study on critical ventilation velocity in slope tunnel fire under vehicle blockage

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