Academic literature on the topic 'Backlayering'
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Journal articles on the topic "Backlayering"
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Leong, Jik Chang, C. L. Chang, Y. C. Chen, and L. W. Chen. "Smoke Propagation in an Inclined Semi-Circular Long Tunnel." Advanced Materials Research 446-449 (January 2012): 2143–48. http://dx.doi.org/10.4028/www.scientific.net/amr.446-449.2143.
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This work used FDS to simulate tunnel fires occur in a semi-circular longitudinally ventilated tunnel. By varying the parameters such as the tunnel gradient, the fire size, and the ventilation velocity, their influence on the backlayering effect and downstream propagation rate can be recognized. Under weak ventilation, the backlayering effect either advances or vanishes depending on the slope of the tunnel. Under stronger ventilation, the backlayering effect would break up. The temperature distributions may become less and less dependent on the tunnel gradient when the ventilation velocity is increased. Although the hot gases and smoke in uphill tunnels propagate faster than those in downhill tunnels, their difference reduces with ventilation velocity.
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Ho, Yu-Tsung, Nobuyoshi Kawabata, Miho Seike, Masato Hasegawa, Shen-Wen Chien, and Tzu-Sheng Shen. "Scale Model Experiments and Simulations to Investigate the Effect of Vehicular Blockage on Backlayering Length in Tunnel Fire." Buildings 12, no. 7 (July 13, 2022): 1006. http://dx.doi.org/10.3390/buildings12071006.
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This study used model experiments and numerical simulations to investigate the backlayering length of a vehicle-blocked tunnel fire. The experimental setup included two types of obstacles (low obstacles and high obstacles), as well as three configurations: no obstacles, one side with a car obstacle, and two sides with a car obstacle. If there were vehicles on one side of a lane, it would have little effect on the elongation of the backlayer length. When there were vehicles on both sides of a lane, the elongation of the backlayer length was greatly reduced. In addition, the effects of the vehicular blockage ratio and blockage configuration on the properties of the backlayering length were investigated. We created Pattern A, where fire is was in the center, and Pattern B, where fire was on the side of the tunnel. In Pattern A, almost all obstacles could be approximated using the formula. When the vehicle blockage ratio of a single lane was small, an approximation formula for Pattern B was applicable. However, if the distance between stationary vehicles on the upstream side of the fire source was small, the backlayering length could have been longer than in the case with no vehicular blockage.
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Hansen, Rickard. "The Throttle Effect – Blower Fan Versus Exhaust Fan." Mining Revue 28, no. 3 (September 1, 2022): 1–20. http://dx.doi.org/10.2478/minrv-2022-0016.
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Abstract One of the risks connected to fires underground is the throttle effect which may cause unforeseen smoke spread. This paper investigates the throttle effect for a blower fan and an exhaust fan case in a mine drift. The aim of the paper is to perform a parametric study on the throttle effect, varying influencing parameters such as the heat release rate and fan flow velocity. Data from fire experiments in a model-scale mine drift and results from CFD simulations were used during the study. It was found that the differences between the two fan cases were significant both in magnitude and occasionally in direction. For the base cases the throttle effect as well as the backlayering were more severe in the exhaust fan case. When increasing the heat release rate to 116 kW an increasing backlayering resulted, but the throttle effect was found to increase for the exhaust fan case and decrease for the blower fan case. The throttle effect decreased in the blower fan case as the gas density decrease levelled off, but the flow velocity increased even further, causing an increase in the downstream mass flow rate. This finding was confirmed by similar experimental results in model-scale mine drifts. The resulting mass flow rate induced by the fire plume changes was found to be higher than the externally imposed increase of the fan flow velocity. When increasing the distance between the fire and the exhaust fan, the backlayering increased and the throttle effect decreased.
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Haddad, Razieh Khaksari, Cristian Maluk, Eslam Reda, and Zambri Harun. "Critical Velocity and Backlayering Conditions in Rail Tunnel Fires: State-of-the-Art Review." Journal of Combustion 2019 (May 28, 2019): 1–20. http://dx.doi.org/10.1155/2019/3510245.
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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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Zhao, Hong Li, Zhi Sheng Xu, and Xue Peng Jiang. "Reduced-Scale Model Tests of Fires in Railway Tunnel and Structure Fire Safety." Advanced Materials Research 168-170 (December 2010): 2473–76. http://dx.doi.org/10.4028/www.scientific.net/amr.168-170.2473.
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The high-temperature toxic gas released by long railway tunnel fires not only causes great harm to persons, but also damages the structure of the tunnel which will reduce the overall stability of tunnel. In order to diminish the damage to tunnel structure produced by a tunnel fire, on the basis of the first extra-long underwater railway tunnel in China, some reduced-scale tests were carried out to study the distribution of smoke temperature along the tunnel ceiling, the smoke velocity and the backlayering distance with the fire size of 63KW. The longitudinal ventilation velocity and the tunnel gradient varied in these tests. The smoke temperature below the tunnel ceiling in different times and under different longitudinal ventilation velocity, the smoke velocity under the ceiling, and the backlayering distance in the presence of different ventilation velocity are acquired from the tests. The conclusions have the guiding meaning to the disaster prevention design and construction of structure fire safety in tunnel fires, and all the experimental data presented in this paper are applicable for the verification of numerical models.
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Ko, Yoon J., and George V. Hadjisophocleous. "Study of smoke backlayering during suppression in tunnels." Fire Safety Journal 58 (May 2013): 240–47. http://dx.doi.org/10.1016/j.firesaf.2013.03.001.
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FUJITA, Katsushi, Tomoya MINEHIRO, Nobuyoshi KAWABATA, and Futoshi TANAKA. "Temperature Characteristics of Backlayering Thermal Fumes in a Tunnel Fire." Journal of Fluid Science and Technology 7, no. 3 (2012): 275–89. http://dx.doi.org/10.1299/jfst.7.275.
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Ilias, Nicolae, Omar Lanchava, Giorgi Nozadze, and David Tsanava. "Study of propagation of harmful factors of fire in short road tunnels with different inclinations." MATEC Web of Conferences 342 (2021): 03023. http://dx.doi.org/10.1051/matecconf/202134203023.
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The paper considers the spread of combustion products caused by fires with different heat release rates: 5, 10, 15, 20, 30, 50 MW in up to 400 m long tunnels. The slope of the tunnels on numerical models is - 0, 1, 3, 5, 7, 9%. The cross-sectional area of the tunnel is 42.5m2. The paper describes the dynamic variability of damaging factors caused by the “chimney effect” such as carbon monoxide and temperature. Modeling was done with FDS software by using the finite volume method. The time of process modeling is 180 s. The minimum cell size of the finite volume is 0.25x 0.25 x 0.25m. The hearth of fire is in the central part of the tunnel. The obtained results are given in the plane of the central longitudinal section of the tunnel. The boundary condition is given as an increment of the dynamic pressure caused by the height difference between the portals in normal conditions. The dependence of fire-induced backlayering distance on the fire heat release rate and the increment of the dynamic pressure caused by tunnel inclination are studied. The theoretical results and those obtained by modeling of the backlayering distance and velocity are analyzed and compared. The locations of high-risk factors for each damaging factor along the tunnel are identified. Their quasi-stationary nature is described and the intervals of transient processes typical to each factor are determined in the course of modeling. It is advisable to use the obtained results to respond to emergencies caused by fire in relevant tunnels.
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Weng, Miao-cheng, Xin-ling Lu, Fang Liu, Xiang-peng Shi, and Long-xing Yu. "Prediction of backlayering length and critical velocity in metro tunnel fires." Tunnelling and Underground Space Technology 47 (March 2015): 64–72. http://dx.doi.org/10.1016/j.tust.2014.12.010.
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ISHIKAWA, Masao, Nobuyoshi KAWABATA, Takuji ISHIKAWA, and Yuko KUNIKANE. "K-1034 Backlayering Velocity of the Thermal Plume Induced by Tunnel Fires." Proceedings of the JSME annual meeting II.01.1 (2001): 9–10. http://dx.doi.org/10.1299/jsmemecjo.ii.01.1.0_9.
Full textDissertations / Theses on the topic "Backlayering"
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Boehm, Mélanie. "Études expérimentale et numérique de l’influence d’un jet plan pariétal sur une nappe de retour." Thesis, Lyon 1, 2011. http://www.theses.fr/2011LYO10128/document.
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Cette thèse porte sur l'influence d'un jet plan pariétal sur une nappe de retour (backlayering). Cette étude peut être divisée en deux parties : une étude expérimentale et une étude numérique. Les expériences ont permis d'identifier le comportement de la nappe de retour en présence du jet. L'étude numérique débute par une validation du modèle numérique à partir des résultats de l'étude expérimentale. Une étude paramétrique est réalisée afin de déterminer l'influence du jet sur les caractéristiques et la stratification de la nappe de retour. La présence du jet plan pariétal induit une diminution de la longueur de la nappe de retour et une variation de l'épaisseur de la nappe de retour du fait de l'introduction du jet :pour une vitesse débitante fixée, l'augmentation du rapport entre la vitesse d'éjection, du jet et la vitesse débitante induit une augmentation de l'épaisseur de la nappe de retour ; pour un rapport entre la vitesse d'éjection du jet et la vitesse débitante constant, l'augmentation de la vitesse débitante conduit à un affinement de la nappe de retour. La stratification de la nappe de retour est conservée en présence du jet plan pariétalThe aim of this study is to determine the influence of a wall attached plane jet on the backlayering. This study is composed of two parts. The experimental part consists in identifying the behaviour of the backlayering in presence of the jet. The numerical part started with a validation of the numerical model using experimental study results. Then, a parametric study enables to determine the influence of the jet on the backlayering. The presence of the parietal plan jet induces a decrease of the backlayering length. Two main conclusions are achieved for the backlayering thickness change due to the jet : for a constant air flow velocity, the increase of the ratio between jet velocity and air flow velocity induces an increase of the backlayering thickness ; for a constant ratio between jet velocity and air flow velocity, the increase of the air flow velocity leads to an increase of the backlayering thickness. Finally, the backlayering stratification is maintained on the presence of the jet
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Oucherfi, Myriam. "Contribution à l'étude de la ventilation transversale lors d'un incendie en tunnel routier." Phd thesis, Université Claude Bernard - Lyon I, 2009. http://tel.archives-ouvertes.fr/tel-00652385.
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L'objectif de cette thèse est de présenter des critères simples pour l'évaluation des performances d'une ventilation transversale. On définit l'efficacité et le rendement, calculés à partir du flux de déficit de densité créé par l'incendie. Après une étude préliminaire permettant de caler les modèles numériques, l'influence de différents paramètres sur ces valeurs a été évaluée. Dans un premier temps, l'étude a porté sur une seule trappe et a montré que le courant d'air dans le tunnel est le paramètre le plus important. A l'inverse, la forme de la trappe pour une surface donnée n'a que très peu d'importance, sauf dans des cas limites (fente sur toute la largeur du tunnel). L'étude d'un canton à huit trappes confirme l'importance du contrôle du courant d'air. Lorsqu'on diminue le nombre de trappes en conservant la même surface totale d'aspiration, cette sensibilité tend à disparaître, mais l'efficacité diminue. Enfin, l'étude de l'influence de l'encombrement montre une légère amélioration de l'efficacité, due à l'obstruction d'une partie de la section par des camions, qui bloquent les fumées au droit des trappes.
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Oucherfi, Myriam. "Contribution à l'étude de la ventilation transversale lors d'un incendie en tunnel routier." Phd thesis, Lyon 1, 2009. http://n2t.net/ark:/47881/m6cc0z3v.
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L’objectif de cette thèse est de présenter des critères simples pour l’évaluation des performances d’une ventilation transversale. On définit l’efficacité et le rendement, calculés à partir du flux de déficit de densité créé par l’incendie. Après une étude préliminaire permettant de caler les modèles numériques, l’influence de différents paramètres sur ces valeurs a été évaluée. Dans un premier temps, l’étude a porté sur une seule trappe et a montré que le courant d’air dans le tunnel est le paramètre le plus important. A l’inverse, la forme de la trappe pour une surface donnée n’a que très peu d’importance, sauf dans des cas limites (fente sur toute la largeur du tunnel). L’étude d’un canton à huit trappes confirme l’importance du contrôle du courant d’air. Lorsqu’on diminue le nombre de trappes en conservant la même surface totale d’aspiration, cette sensibilité tend à disparaître, mais l’efficacité diminue. Enfin, l’étude de l’influence de l’encombrement montre une légère amélioration de l’efficacité, due à l’obstruction d’une partie de la section par des camions, qui bloquent les fumées au droit des trappesThe aim of this study is to present simple criteria to evaluate the performances of a transverse ventilation system. Efficiency and yield have been defined, based on the flux of density deficit createdby the fire. After a preliminary study of numerical models, the influence of different parameters on those criteria has been investigated. First, the study focused on the simplified case of a single damper. We showed that the air flow speed in the tunnel is the more important parameter. On the contrary, the shape of the damper has little influence on the efficency, except in unusual cases (slit on the whole width of the tunnel). Then, the study of a longer portion of the tunnel confirmed the prominence of the limitation of air flow speed. Comparison with a case with fewer dampers but the same total extraction section showed that this sensibility to air flow speed tends to disappear for larger dampers, but that the efficiency is lowered. Finally the study of the influence of heavy-goods-vehicules obstructing the tunnel reports better results, due to the fact that big objects tend to confine smokes
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Zhuang, Ren-Xin, and 莊仁馨. "Critical Velocity and Smoke Backlayering Discussion in Small Scale Tunnel Fire." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/m34ftg.
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碩士長榮大學
職業安全與衛生學系碩士班
107
The number of long road tunnels has increased in recent years, and the hazardous level has increased accordingly. In order to ensure the safe evacuation of personnel, tunnel ventilation and smoke exhaust design is particularly important, but due to the special nature of tunnels, especially long tunnels, the ventilation and smoke exhaust design is unable to be verified on full scale, therefore the situations simulated on computers are often of reduced scale. However, the difference between the simulated reduction factor and empirical formulas often affects the accuracy and authenticity. This study collected and summarized domestic and international research on the critical wind speed and the smoke backlayer within tunnels, and compared the simulations with field experiments. The difference between the two could be used to propose revision parameters for future full-scale simulations, so that accuracy is improved when they are applied to the verification of field projects, further improving tunnel protection research. This research used FDS software to simulate different model-scale tunnel fires, which were 1:20, 1:10, 1:5 respectively, and set different wind speeds and detection points. The data was analyzed to find critical wind speeds at the various scales. The model-scale parameters were also brought into the empirical formulas of Thomas, NFPA 502, and Oka & Atkinson, and compared with the simulation data. It was found that the empirical formula of Oka & Atkinson et al. was closest to the FDS simulation results. At the same time, the field fire experiment was carried out. The 1:20 tunnel was used as the benchmark to observe its critical wind speed, and then compared with the FDS simulation. It was found that the field fire experiment data showed that the actual critical wind speed was greater than the FDS simulation data. It is determined the reason may be from the radiant heat feedback problem caused by the length of the tunnel as well as the wind speed in the special 1-D environment. However, the current available parameters in FDS do not allow for this factor to be accounted for, resulting in a lower heat release rate during simulations, and therefore prohibits the accurate representation of the field data.
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Oucherfi, Myriam. "Contribution à l’étude de la ventilation transversale lors d’un incendie en tunnel routier." Thesis, 2009. http://www.theses.fr/2009LYO10037/document.
Full textAbstract:
L’objectif de cette thèse est de présenter des critères simples pour l’évaluation des performances d’une ventilation transversale. On définit l’efficacité et le rendement, calculés à partir du flux de déficit de densité créé par l’incendie. Après une étude préliminaire permettant de caler les modèles numériques, l’influence de différents paramètres sur ces valeurs a été évaluée. Dans un premier temps, l’étude a porté sur une seule trappe et a montré que le courant d’air dans le tunnel est le paramètre le plus important. A l’inverse, la forme de la trappe pour une surface donnée n’a que très peu d’importance, sauf dans des cas limites (fente sur toute la largeur du tunnel). L’étude d’un canton à huit trappes confirme l’importance du contrôle du courant d’air. Lorsqu’on diminue le nombre de trappes en conservant la même surface totale d’aspiration, cette sensibilité tend à disparaître, mais l’efficacité diminue. Enfin, l’étude de l’influence de l’encombrement montre une légère amélioration de l’efficacité, due à l’obstruction d’une partie de la section par des camions, qui bloquent les fumées au droit des trappesThe aim of this study is to present simple criteria to evaluate the performances of a transverse ventilation system. Efficiency and yield have been defined, based on the flux of density deficit createdby the fire. After a preliminary study of numerical models, the influence of different parameters on those criteria has been investigated. First, the study focused on the simplified case of a single damper. We showed that the air flow speed in the tunnel is the more important parameter. On the contrary, the shape of the damper has little influence on the efficency, except in unusual cases (slit on the whole width of the tunnel). Then, the study of a longer portion of the tunnel confirmed the prominence of the limitation of air flow speed. Comparison with a case with fewer dampers but the same total extraction section showed that this sensibility to air flow speed tends to disappear for larger dampers, but that the efficiency is lowered. Finally the study of the influence of heavy-goods-vehicules obstructing the tunnel reports better results, due to the fact that big objects tend to confine smokes
Book chapters on the topic "Backlayering"
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Ho, Yu Tsung, Nobuyoshi Kawabata, Miho Seike, Masato Hasegawa, Shen-Wen Chien, and Tzu-Sheng Shen. "Influence of Stationary Vehicles to Thermal Fume Backlayering Length in Tunnel Fire." In The Proceedings of 11th Asia-Oceania Symposium on Fire Science and Technology, 1009–29. Singapore: Springer Singapore, 2019. http://dx.doi.org/10.1007/978-981-32-9139-3_73.
Full textConference papers on the topic "Backlayering"
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Azevedo, J. L. T., J. M. C. Pereira, and J. C. F. Pereira. "NUMERICAL SIMULATION OF UNSTEADY BACKLAYERING IN TUNNEL FIRES." In Annals of the Assembly for International Heat Transfer Conference 13. Begell House Inc., 2006. http://dx.doi.org/10.1615/ihtc13.p26.170.
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Blanco, Eduardo, Javier Cueto, Joaqui´n Ferna´ndez, and Rau´l Barrio. "Numerical Simulation of the Backlayer Critical Velocity in the Memorial Tunnel Test (MTFVTP)." In ASME 2008 Fluids Engineering Division Summer Meeting collocated with the Heat Transfer, Energy Sustainability, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/fedsm2008-55256.
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Road tunnels constitute key elements in the traffic net, especially for the long distance road transportation but also in the large urban areas. Although security preventions have permitted a relatively low index of accidents in tunnels, the analysis of the accidents in road tunnels during the last years shows an increment in both the number of cases and their gravity. In the case of fires, the control of the smoke propagation becomes crucial because the major risk for people is smoke inhalation rather than the direct exposure to the fire itself. Besides, a quick control of the fire requires that the access and evacuation routes are maintained without smoke. However, research in this field has been limited by the difficulties inherent in the problem, and so there are few experimental data available. This paper pursues the study of the control of the smoke propagation in tunnel roads with a longitudinal air stream. The methodology is based on the numerical simulation of the time evolution of the air and smoke flows induced after the onset of localized fires of different magnitude. Specifically, 10, 20, 50 and 100 MW fires were simulated. A general purpose computational fluid dynamics software is used for this investigation, due to its ability to model multi-species three-dimensional unsteady flows. The general purpose of the paper is the refinement and contrast of a numerical procedure for the simulation of fire tunnels with natural and longitudinal ventilation, as the particular case with the most complex and restrictive conditions, and the use of such procedure to study the backlayering phenomenon. The obtained results were compared with the natural and longitudinal ventilation tests of the Memorial Tunnel test as well as with previous studies.
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Vittori, Felipe, Luis Rojas-Solo´rzano, Armando J. Blanco, and Rafael Urbina. "Numerical Study of Smoke Propagation in a Simulated Fire in a Wagon Within a Subway Tunnel." In ASME 2008 Fluids Engineering Division Summer Meeting collocated with the Heat Transfer, Energy Sustainability, and 3rd Energy Nanotechnology Conferences. ASMEDC, 2008. http://dx.doi.org/10.1115/fedsm2008-55281.
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This work deals with the numerical (CFD) analysis of the smoke propagation during fires within closed environments. It is evaluated the capacity of the emergency ventilation system in controlling the smoke propagation and minimizing the deadly impact of an eventual fire in a wagon within the Metro de Caracas subway tunnel on the passengers safety. For the study, it was chosen the tunnel section between Teatros and Nuevo Circo subway stations, which consists of two parallel independent twin tunnels, connected through a transverse passage. The tunnels are provided by a longitudinal ventilation system, integrated by a set of reversible fans located at both ends of the tunnels. Three stages were considered in the study: (a) Model set up; (b) Mesh sensitivity analysis; (c) Validation of the physical-numerical parameters to be used in the numerical model; and (d) Simulation of fire scenarios in Metro de Caracas subway stations. Stages (b)–(c), aimed to testing and calibrating the CFD tool (ANSYS-CFX10™), focused on reproducing experimental data from Vauquelin and Me´gret [1], who studied the smoke propagation in a fire within a 1:20 scale road tunnel. Stage (d) critical scenarios were established via a preliminary discussion with safety experts from Metro de Caracas, in order to reduce the computer memory and the number of simulations to be performed. The analyses assessed the reliability of escape routes and alternative paths for the evacuation of passengers. Additionally, the smoke front movement was particularly computed, as a function of time, in order to determine the possible presence of the “backlayering” phenomenon [5]. Results demonstrate the strengths and weaknesses of the current ventilation system in the event of a fire in the subway tunnel, and suggest new strategies to address this potentially lethal event to minimize the risks for passengers.