Tunnel Fire Research Articles

Effect of different configurations of multi-blockages on the fire characteristics in tunnel fires with longitudinal ventilation

A tunnel vehicle fire is usually accompanied by traffic jams and less attention has been paid to the effect of multi-blockage on the fire characteristics in longitudinal ventilated tunnel fires. Thus, this study has revealed this point based on a full-scale model tunnel(100 m in length, 12 m in width, and 6 m in height) by Fire Dynamic Simulator(FDS) considering the different configurations of blockages, namely transverse and longitudinal. Results show there exist significant differences between two typical configurations of blockages and the distances between blockages have great effects on the fire characteristics in the cases with transversely arranged blockages. Moreover, the empirical models for maximum temperature rise and longitudinal temperature decay are developed and predict the numerical results well.

Experimental evaluation and real-time forecast of smoke propagation in tunnels under intervention of sub-critical longitudinal ventilation

Sub-critical longitudinal ventilation can restrict the back-layering length in the upstream region and maintain suitable smoke stratification in the downstream region of a tunnel fire. In this study, experiments using a 1/15 scale, 80-m long, 1.2-m wide, and 0.5-m high model tunnel were conducted to investigate the effects of sub-critical longitudinal ventilation velocity and heat release rate (HRR) on the key parameters describing smoke propagation. The smoke front temperature near the fire source decreased significantly as the longitudinal ventilation velocity increased. The longitudinal ventilation velocity and HRR were incorporated into a regression model describing the smoke front velocity, which was applied to the evaluated fire scenarios using an ensemble Kalman filter to account for intervention of sub-critical longitudinal ventilation. The smoke front temperatures at discrete locations were assimilated to estimate the heat exchange correction coefficient and air entrainment ratio of smoke front in real-time and dynamically correct the forecasted smoke front temperature and velocity accordingly. When sub-critical longitudinal ventilation intervened, the smoke front parameters could be forecasted with a maximum lead time of 60 s and an average error within 5%. Therefore, the proposed forecasting method can inform the selection of disposal measures in early tunnel fire emergencies.

Prediction of back-layering length in subway tunnel with on-fire train running

The exploitation and utilization of urban underground space effectively contribute to the sustainable development of society. Tunnel fire safety is necessary to ensure normal operation. Motion train fire is more serious and complex than stationary fire in tunnels due to the influence of unsteady piston wind. This study investigates the smoke back-layering characteristics of a burning subway train during emergency braking. A three-dimensional unsteady numerical model adopting the dynamic mesh technique is built to investigate the smoke diffusion characteristics of motion train fire. Experimental tests are conducted based on a 60 m-long scaled-down experimental setup to verify the accuracy of the numerical model. On this basis, the dynamic characteristics of smoke back-layering length as the longitudinal wind pressure is less than the critical value are studied, considering the influence of heat release rate (HRR), train speed, and train deceleration. The results indicate that the maximum back-layering length follows the logarithmic law with the variation of longitudinal wind pressure. An empirical model is proposed to predict the maximum back-layering length at various longitudinal wind pressure, and it is helpful to the optimization design of ventilation systems for tunnel motion fire.

An experimental study on the evolution of flame length and tilt angle under the joint effect of tunnel curved ceiling restriction and longitudinal ventilation

The model about flame length and fuel mass loss rate in this paper was developed based on the flame morphology with different longitudinal ventilation speeds when the flame was confined by the tunnel curved ceiling restriction. Secondly, after analyzing the experimental data, it was found that the air entrainment velocity was proportional to the 0.22nd power of longitudinal ventilation speed. Thirdly, the product of flame length and air entrainment velocity was proportional to the fuel mass loss rate, and the above models could better describe the characteristic evolution behaviors of flame length. Furthermore, the relation between fuel mass loss rate and longitudinal ventilation speed was established. Finally, this paper broadened the applicability of other scholars' flame tilt angle models, and found that the flame tilt angle is smaller when the flame is attached to the wall at the same wind speed. It is obvious that the above results supplement the classical tunnel-fire theory, which can be further applied to prevention and control of tunnel fire, and ultimately ensure building safety.

The critical condition of ghosting flame state in the enclosed tunnel

The purpose of this study is to clarify the unity of the critical conditions of ghosting flame in enclosed tunnel, and to establish a general criterion suitable for the determination of ghosting flame state in vitiated tunnel fire. The ghosting flame in vitiated tunnel fire going through three processes: detachment, oscillation, and ghosting, which are different from traditional compartment ghosting flame. The critical oxygen concentration and critical oxygen consumption rate of ghosting flame are linearly related to the fire source height and heat release rate, respectively. Meanwhile, the criteria to determine the critical conditions proposed in this paper agrees well with the data in previous work. Furthermore, a model that characterizes the critical conditions was established considering the formation process of ghosting flame in vitiated tunnel fire. This work promotes the fundamental understanding of ghosting flame phenomenon in confined tunnel fire and benefits the development of fire protection engineering practice in the future.

Study of critical velocity and back-layering length with fire sources both inside and outside a tunnel

The smoke back-layering length and the critical ventilation velocity in double fire scenarios where the fire sources were both inside and outside the tunnel were studied by small-scale tests and theoretical analysis. Results showed that the smoke back-layering length increased with an increase of the fire separating distance when the dimensionless fire separating distance was less than 3, and the values were larger than the results of a single internal fire at each fire separating distance. The dimensionless critical ventilation velocity segmentally increased with the increase of the dimensionless fire separating distance when the dimensionless fire separating distance was less than 10, and then remained constant. Moreover, the constant value was found to be close to that in the case of a single tunnel fire. In addition, an empirical model of dimensionless critical ventilation velocity was established for the double tunnel fire scenario both inside and outside a tunnel.

Numerical analysis of the performance of a PID-controlled air curtain for fire-induced smoke confinement in a tunnel configuration

In order to effectively meet the requirements of smoke confinement in different fire scenarios, this paper proposes an adaptive intelligent smoke control method combining PID (Proportional Integral Derivative) system with a traditional air curtain. By taking a tunnel fire configuration as an example, the feasibility of PID-controlled air curtains is explored and the calculation method of PID control parameters is clarified. The stability and reliability of the PID-controlled air curtain in realizing the smoke control effect in different complex fire scenarios are studied. The method of determining optimal PID coefficients is first proposed. Then, the robustness of the PID-controlled air curtain has been assessed by discussing the sensitivity of these parameters with different fire scenarios. The results show that the PID-controlled air curtains can effectively meet the requirements of smoke control in different complex fire scenarios. The impact of different fire scenarios on the PID-controlled air curtain system lies in the pre-control period, such as the system features of delay time, response time, overshoot, etc.

Research on Intelligent Monitoring of Fire Safety and Fire Rescue Plan for Tunnel Operation under Quasi-Unattended Background

Tunnel structures account for la large proportion of the structures in mountain highway transportation systems. Most tunnels are located in remote areas in which the geological conditions are complex and harsh and in which the layout of the management facilities along the way is complex. Thus, the management and maintenance costs of various facilities are expensive, the cost of fire safety operations and management is high, and disaster prevention and rescue have a difficult time meeting the objective requirements. Therefore, it is urgent to carry out research on quasi-unmanned operations and intelligent remote monitoring. This study firstly proposes a fire safety intelligent monitoring framework for quasi-unattended tunnels. By making full use of various intelligent sensor monitoring data in the tunnel, the tunnel operation status can be grasped in real time. Then, a fire safety evaluation model can be established through the analytic hierarchy process (AHP), and, based on the monitoring data, the AHP model parameters can be evaluated to realize the real-time evaluation and management of tunnel fire safety. Finally, on the basis of the fire safety intelligent monitoring system and the fire safety evaluation system, an adaptive fire rescue plan formulation scheme is proposed for the quasi-unattended tunnels so as to provide guaranteed support for the rapid automatic response of tunnel fire protection and to provide technical data support for the design and realization of intelligent and efficient tunnel management

Experimental investigation on fire damage to staggered segmental lining of shield tunnel

Fire is a significant hazard to the safe operation of tunnels, causing extensive damage and deterioration to the lining. This research proposed a prototype test of a shield tunnel staggered segmental lining under stratum loads subjected to fire. The fire followed the ISO834 standard curve; the maximum temperature reached 1144.9 °C and lasted 195 min. The temperature evolution law of the lining is positively correlated with the distance from the fire source and negatively correlated with the depth of the lining. The fire surface of the lining undergoes severe cracking and peeling, accompanied by water seepage and water vapour escaping during the fire. The concrete spalled severely on the fire surface of the lining, the maximum depth and area reached 65 mm and 3.05 m2, respectively, and the reinforcement near the fire source was exposed after the fire. The mechanical behaviour of the entire lining was damaged by fire, and that in the fire area was more significant than that in the non-fire area, and the damage degree of the joint was more significant than the segment. Every mechanical parameter of the lining changes significantly during the firing process and only partially recovers during the cooling, with significant residual values. The ultimate bearing capacity of the lining after being damaged by fire was about two times the preset stratum load. And the failure characteristic of the lining damaged by fire was the plastic failure of the joints in the fire area. Specifically, in the fire area, there were numerous wide cracks, some joints were crushed, and some inner reinforcement yielded, while in the non-fire area, there were only a few micro-cracks on the segment and a few cracks on the joints. The research conclusions can also provide a reference for the post-disaster assessment of tunnel fire.

Studying the Synergetic Effect of Point-Extraction and Longitudinal Ventilation on the Maximum Smoke Temperature and Back-Layering Length in Tunnel Fires

This study investigates the impact of combining longitudinal and point-extraction ventilated systems on temperature distribution and back-layering length in tunnel fires. Numerical simulations are conducted using a fire dynamic simulator (FDS), and reduced-scale tunnel fire experiments with a scale of 1/10 are introduced to provide supplementary data. Results indicate that the longitudinal velocity is more critical than other factors in reducing the highest temperature and casualties. Lowering the temperature below the tunnel ceiling is not caused by increasing the ceiling extraction velocity. Additionally, the study reveals that the fire source-ceiling distance and their relative positions play a crucial role in temperature distribution and plug-holing phenomenon in the tunnel. By using the Taguchi method, it is determined that a fire at a height of 0.125 m has a maximum ceiling temperature of 1.8, 1.3, and 1.1 times when the fire source happens on the floor with longitudinal velocities of 0.133, 0.265, and 0.53 m/s, respectively. The extraction point has diverse effects provided that the longitudinal ventilation velocity is set by critical velocity. The study’s objective is to provide tunnel engineering managers with a correlation to predict the highest temperature, which is a vital parameter for emergency evacuation. In conclusion, this study highlights the importance of considering longitudinal and point-extraction ventilated systems and their relative speeds in reducing the severity of tunnel fires.

A fast wavelength detection method based on OTDR and 1-DDCNN in series overlapping spectra

To improve the rapidity and reliability of the subway tunnel fire monitoring system and realize the monitoring of small fire sources, the method of regional subsection demodulation is used to group several adjacent nearly identical ultra-weak fiber Bragg gratings (UWFBGs) sensors into a group, and the 1-D dilated convolutional neural network (1-DDCNN) is used to demodulate the same group of highly overlapping sensing signals. The well-trained 1-DDCNN model can achieve extremely low signal demodulation error. The experiment shows that the UWFBG demodulation scheme proposed in this paper improves the detection accuracy of the subway tunnel fire monitoring system and shortens the detection time. The root-mean-square error (RMSE) of four highly overlapping peak wavelengths of sensing signals is less than 1.5 pm, and the average demodulation time is less than 30 ms.

Experimental field study on smoke characteristics and CO concentration of high-altitude tunnel fires induced using gasoline and diesel

High-altitude environments exhibit reduced atmospheric pressure, low oxygen density, and low air temperature conditions, which considerably affect tunnel fire characteristics. In this study, small-scale tunnel fire field experiments were performed at high altitudes to investigate the heat release rate (HRR), smoke temperature, and CO concentration of gasoline and diesel pool fires. The results revealed that with the increase in altitude, the HRR declined but the combustion duration increased. Furthermore, the maximum ceiling temperature decreased with the increase in altitude. The longitudinal ceiling temperature declined slowly in the high-altitude tunnel. By contrast, the smoke temperature spread rapidly among the cross-section in the high-altitude tunnel. The ceiling CO concentration behaviors for gasoline and diesel pool fires were categorized into four and three stages, respectively. Furthermore, the steady ceiling CO concentration and the maximum ceiling CO concentration decreased slightly with the increase in the altitude for gasoline pool fires, whereas the differences were greater for diesel pool fires. However, the steady ceiling CO concentration per unit mass burning rate increased linearly with the altitude for both fuels. The results revealed that the steady CO concentration at the height of 110 mm in the cross-section was nearly identical for various altitudes in the case of gasoline pool fires. However, for diesel pool fires, the CO concentration was higher at higher altitudes.

Study on the key parameters of vehicle fires for the growth stage in road tunnels

AbstractAs the golden period for evacuation and rescue in road tunnel fires, the fire growth stage is indispensable for security. The key parameters of this stage must be clearly defined, including the maximum heat release rate (HRR), growth time, and growth coefficient. Based on the squared model, the correlations between the key parameters are investigated according to the existing fire tests of vehicle‐related materials and actual vehicles or mock‐ups. The maximum HRR and the growth coefficient of different types of vehicles are obtained. The results show that the maximum HRR is linearly related to the growth coefficient in the fire tests of vehicle‐related materials. And it is logarithmically related in the fire tests of actual vehicles or mock‐ups. The growth coefficient and growth time represent the possibility of a disaster. The larger the growth coefficient is or the shorter the growth time is, the greater the possibility is. The maximum HRR in a fire is 2 ~ 10 MW for a car, 10 ~ 50 MW for a bus, and 50 ~ 200 MW for a heavy goods vehicle. The growth coefficient in a fire is 0.003 ~ 0.013 kW/s2 for a car, 0.05 ~ 0.15 kW/s2 for a bus, and 0.2 ~ 0.3 kW/s2 for a heavy goods vehicle. The corresponding fire growth types are slow and medium, fast, fast, and ultra‐fast, respectively. This study is beneficial for the establishment of the fire growth model and the setting of emergency response time.

Numerical modeling on mechanical smoke extraction efficiency of multiple lateral smoke extraction vents system in an immersed tunnel

In the case of immersed tunnel fires, lateral smoke extraction is a method employed to control the smoke movement with vents set in tunnel sidewalls due to limited space in height. This paper has investigated the smoke extraction efficiency of multiple lateral vents system using large eddy simulations (LES) in a fire dynamics simulator (FDS). The analysis is done on the impact of the lateral vent aspect ratio AR (n), lateral extraction velocity (v), and vent spacing distance (d) at various heat release rates HRRs (Q) on smoke extraction efficiency (E). The results show that the vent spacing distance (d) has a negligible impact on the smoke extraction efficiency. The smoke mass flow rate and smoke layer thickness in the tunnel changed significantly because of lateral extraction vents. The smoke extraction efficiency increases with dimensionless HRR Q* and vent aspect ratio n at constant lateral extraction velocity v, but decreases drastically with increasing dimensionless lateral extraction velocity v* due to an increase in fresh air drawn into the lateral vents. The smoke extraction efficiency reached to 100% at 1 m/s extraction velocity for vents of 3.25 aspect ratio. Finally, a correlation for smoke extraction efficiency in one-dimensional smoke spread stage was established based on dimensional analysis, which can provide a reference guide for designing a ventilation system in tunnels with lateral vents.

Research on ceiling gas temperature rise and floor heat flux driven by strong fire plume in a sealing tunnel

Sealing is one of the important means to extinguish fire in tunnel. It is necessary to investigate the strong fire plume in tunnel under sealed conditions. In this paper, the fire experiments were carried out in a 1:10 tunnel platform, and the influence of different sealing forms, heat release rates of fire source and heights of fire source on the ceiling gas temperature rise and floor heat flux driven by strong fire plume were analyzed. As expected the tests show that the ceiling gas temperature rise under sealing effect will be lower than that without sealing. The larger the total sealing ratio, the greater the temperature rise and floor heat flux. When the total sealing ratio is the same, the higher the proportion of the upper part sealing structure, the larger the ceiling gas temperature rise and the floor heat flux, meanwhile, these two parameters are also positively correlated with the height of fire source. In the region close to the fire source, the longitudinal temperature rise along the ceiling attenuates rapidly, but the decays trend becomes slower as the distance away from the fire source increases. In this paper, the sealing opening coefficient is introduced, and the prediction models of the longitudinal temperature rise decay along the tunnel ceiling and the floor heat flux under sealing effect are proposed respectively.

Simulation research on the temperature distribution and smoke control in tunnel fires under a water curtain system

This study determined the optimum number of water spray particles and the angle of the inner angle of the nozzle, simulated and studied the suppression effect of the water curtain system on roadway belt fires and toxic and harmful gases, and analysed the barrier effect of heat and smoke under the water curtain system using the flow field. The results show that the number of water curtain rows has a suppressive effect on the temperature and that increasing the number of rows has a better barrier effect on the hot smoke downstream of the roadway. From the velocity and temperature fields, it is clear that there is significant upward movement between the water mists of the water curtain system, which is caused by the water mists colliding with each other on the roadway floor. These jets are entrained into the water mists and merge to form an area of upward movement that acts as a 'barrier’ to prevent the fumes from spreading downstream of the water curtain. When the water curtain system is activated, it increases the concentration of component gases in the downstream space of the roadway and rapidly restores visibility to meet the requirements for safe evacuation.

Full-scale experimental and theoretical study of an air leakage model and the applicable limit length for ceiling centralized smoke exhaust systems in tunnel fires

Based on the Jiangxinzhou Yangtze River Tunnel, this study investigated the air leakage of a ceiling-centralized smoke exhaust system through full-scale tests and theoretical analysis. The theoretical analysis established a functional relationship between the pressure of the exhaust vent and air leakage volume. The air leakage coefficient of the exhaust vent was defined. The exhaust vent air leakage coefficient, exhaust flue area, hydraulic diameter, resistance coefficient along the exhaust flue, and exhaust vent spacing were integrated to establish the exhaust flue air leakage coefficient. Through full-scale tests, the exhaust flue pressure and air volume distribution were analyzed under different opening schemes of the exhaust vent. A section-by-section calculation method was established for the applicable limit length and air leakage of the ceiling centralized smoke exhaust system. This study further established a simple calculation method for the applicable limit length of a ceiling centralized smoke exhaust system through theoretical analysis, which made the calculation simple and easy to perform and enabled the results to be calculated with a certain degree of accuracy.

Effect of Flow Rate on Smoke Control System for Railway Tunnel Fire

Tunnel is a semi-closed structure with a high risk of fire becuse of difficulty of smoke exhaust and restricted evacuation route in fire. No specific guidelines on smoke control systems have been developed for railway tunnels. Therefore, in the railway tunnel design, an average airflow velocity of 2.5 m/s inside a tunnel for the entry and exit of workers has been used as a reference. In this study, a fire simulation conducted to examine whether the average flow velocity can sufficiently apply on smoke control system in railway tunnel design. An 870-m-long railway tunnel with a single track and double track was modeled, and fire scenarios for light rail cars were simulated. It was found that the reference flow velocity showed sufficient smoke control performance, even at a maximum fire source of 60 MW. However, evacuees might be exposed to smoke due to the backlayer formed immediately. Furthermore, the smoke control performance for the reference velocity does not reflect the influence of the tunnel length. It is necessary to conduct a study on standard for appropriate smoke control performance to reduce fire risk in a railway tunnel fire.

A dimensionless model and ant colony optimization fusion temperature prediction in tunnel fires

Prior studies have noted the importance of ceiling temperature distribution prediction of tunnel fires. To overcome the limitations of precise modeling difficulties for model-driven methods and biased toward the convergence for the data-driven methods due to loss of physical interpretations, a hybrid model-driven and data-driven fusion algorithm is established to predict ceiling temperature distribution in tunnel fires based on dimensional analysis method and ant colony optimization algorithm. Thus, full-scale tunnel fire experiments with different ventilation speeds are conducted to support the algorithm. In contrast to the experimental data as well as the known theoretical model, data-driven back propagation neural network algorithm and hybrid ant colony optimization and back propagation neural network algorithm, the effectiveness and ability of the algorithm are verified, which can be used for the tunnel fire prediction.

Design and Implementation of a Quantitative Risk Assessment Model for UK Road Tunnels

One of the critical transportation infrastructures is road tunnels and fire safety is one of the important aspects of their operation. Interaction between the fire, tunnel users, traffic, and fire safety measures influences fires in road tunnels. Therefore, a complex model is required to analyse the risk and quantify the consequences. In this paper, a novel quantitative risk analysis model developed for UK road tunnels is presented consisting of a quantitative consequence analysis model and a quantitative frequency frequency analysis model. The proposed quantitative consequence analysis model is provided through three sub-models; queue model, distribution model, and egress model. The frequency analysis is via an event tree that takes into account the tunnel fire rate in UK road tunnels. After a brief description of this model, the proposed method is illustrated through a case study of an urban road tunnel. The effect of different emergency ventilation systems on societal risk and sensitivity of the model to pre-movement time, accident frequencies involving Heavy Good Vehicles (HGVs), tenability threshold temperature, and different burning vehicles were studied in this case study.