Road Tunnel Fire Research Articles

Experimental study on the effects of exhaust vent layout on plug-holing for ceiling central smoke extraction in road tunnel fires

In this study, a series of reduced-scale experiments are performed to study the phenomenon of plug-holing induced by ceiling central smoke extraction in road tunnel fires. By changing the side length of the vent perpendicular to the longitudinal direction of a tunnel (vent width), the heat release rate and the area of the ceiling extraction vent, the influencing factors for the occurrence of plug-holing are analysed. The experimental results show that increasing any of the three aforementioned factors can increase the smoke exhaust flow rate corresponding to the occurrence of plug-holing. The experimental results are then compared with the results obtained by previous research, and it is found that the previous research is no longer applicable with respect to the change in the vent width. On this basis, we propose a modified Froude number to predict the occurrence of plug-holing, considering the influence of vent width. The critical value corresponding to the plug-holing for the newly proposed Froude number is a constant having a value of 4.71 (Frc = 4.71), regardless of the variation in the abovementioned three influencing factors. The results can be used as a reference for the design of ceiling central smoke extraction in road tunnels.

A numerical method for studying the effect of calcium silicate lining on road tunnel fires

Road tunnel fires can jeopardize the life safety of occupants and the structural integrity of the tunnel. Such fires are usually characterized by the heat release rate (HRR) parameter. Most tunnel fire safety systems are designed based on this parameter. The tunnel structure (walls and ceilings) are usually protected with a passive protections such as magnesium oxide boards, cementitious sprays, polypropylene fiber mix or calcium silicate boards. Amongst these materials, calcium silicate boards are the most popular choice due to their easy installation and capability to protect the tunnel at very high temperatures for several hours. The HRR in a tunnel fire depends on various parameters such as type of vehicle involved in the fire, amount of fuel, location of fuel and ignition source, tunnel geometry, presence of fixed firefighting systems/ventilation, and several other factors. However, no evidence of structural linings (passive protection) affecting the heat release rate is found in the literature. To investigate the role of structural linings (calcium silicate) on the HRR, a numerical study using Fire Dynamic Simulator (FDS) is conducted for a road tunnel involving fire in a heavy goods vehicle. Two scenarios are investigated; one considering concrete tunnel linings without any passive protection while in the second scenario the tunnel is protected with calcium silicate linings. Comparison of the results from the two abovementioned scenarios reveal different patterns of HRR and tunnel temperatures and suggests that in large fires, structural linings such as calcium silicate lining can alter the overall HRR by enhancing the heat feedback and fuel burning rates inside the tunnel.

Analysis of Important Factors Having an Impact on Safety in Road Tunnels – Research Findings

Aim: This article presents relevant safety issues in road tunnels based on the results of a survey and evacuation experiments conducted on real scale in two existing road tunnels in Poland. Project and methods: An analysis of the relevant factors influencing the level of safety in road tunnels was carried out based on the results of experi - mental studies in two road tunnels in which the course of evacuation under fire conditions was observed. As part of the study, several evacuation trials were carried out at equal smoke levels, examining a different parameter each time: pre-movement time, speed of movement, the effect of smoke on the speed of movement, the effect of tunnel infrastructure on evacuation, among others. A survey carried out among 504 respondents, in turn, attempted to assess the awareness of hazards and safety procedures in road tunnels. The survey has four parts and questions covered the following issues: knowl - edge of tunnel infrastructure, behaviour in case of congestion, choice of evacuation route, behaviour during the evacuation, personal belongings during the evacuation, self-assessment of tunnel safety knowledge and the role of experience. An analysis was also carried out of the information available in Poland on safety guidelines for road tunnels, which can help tunnel users to improve their knowledge on tunnel safety. Results: The survey results indicate an insufficient level of knowledge regarding safety in road tunnels – only 16% of respondents answered more than 50% of the questions correctly. Ignorance of road tunnel infrastructure itself and the safety rules for the tunnel was also diagnosed. An analysis of the information available to the road users demonstrates that this information is difficult to access and that there is a lack of uniform guidelines to educate the public on the topic raised in the article. A significant impact of evacuation exercises carried out on an accurate scale was emphasised, providing valuable data on the evacuation process and increasing the level of safety in the engineering facilities analysed by raising the awareness of the partici - pants in the experiment. Conclusions: The research findings presented in this article allow for better understanding of the behaviour of the participants of accidents and fires in road tunnels. In addition, the need to raise the awareness of the road users on the dangerous situations that may occur in a tunnel and the appropriate response to them has been demonstrated. Keywords: safety, fire, smoke, evacuation, road tunnel Type of article: original science article

Study on influence of breathing zone combined with underfloor makeup air supplement on smoke exhaust of road tunnel fire

In the era of rapid economic development, tunnel construction projects are increasing year by year in China, continuously expanding the urban network In the era of rapid economic development, tunnel construction projects are increasing year by year in China, continuously expanding the urban network radiation area, and accelerating the progress of the national modernization project. The subsequent tunnel traffic fire accidents are also increasing When a tunnel fire occurs, how to effectively supply makeup air to prevent the fire smoke from spreading to the evacuation passage of the When a tunnel fire occurs, how to effectively supply makeup air to prevent the fire smoke from spreading to the evacuation passage of the tunnel and exhaust the smoke as soon as possible has become a key concern in the field of tunnel disaster prevention. The layout of the smoke exhaust outlets under the mode of breathing zone combined with underfloor makeup air supplement was mainly used to study the problem of smoke exhaust in tunnel fires. The results show that under the same smoke exhaust flow rate, with the increase in the area of the results show that under the same smoke exhaust flow rate, with the increase in the area of the smoke outlet, the smoke exhaust efficiency of each exhaust outlet increases, and the total efficiency also increases. The width of the exhaust outlet has a significant effect on the smoke exhaust efficiency. However, the length of the exhaust vent has little effect on the efficiency of smoke exhaust. Under the mode of breathing zone combined with underfloor makeup air supplement, arranging smoke outlet with a size of 2 m×1.5 m every 10 m has a better smoke extraction effect, and the total smoke exhaust efficiency can reach 75.77%. Fire safety of road tunnels has always been the focus of social concern. The makeup air supplement and smoke exhaust mode proposed in this study is expected the makeup air supplement and smoke exhaust mode proposed in this study is expected to provide a theoretical basis for the design of tunnel smoke prevention and exhaust systems.

Influence of Light Wavelengths on Visibility in Smoke during a Tunnel Fire

The occurrence of fire in road tunnels poses high risks to the life and health of people. The resulting smoke, fire gases and high temperatures can be the cause of poisoning and burns. Additionally, dense smoke can significantly reduce visibility, which can result in difficulties during evacuation. This paper aims to investigate the effect of specific wavelengths of visible light on visibility in smoke conditions and to determine the wavelength of light (colour) that can improve visibility in smoke-filled environments. A rubber mixture with polyester and polyamide spacers was selected as a combustible material in order to obtain more realistic conditions with respect to smoke parameters. These plastics are commonly used, among others, in tires, elements of engine plating, upholstery or truck trailer covers. Then, in a test fire chamber laboratory, the colour of light (wavelength) was determined, obtaining the highest transmittance value, understood as the amount of radiation transmitted through the substance. It has been shown that devices emitting a light wave of a specific length can significantly improve visibility in smoke-filled environment.

Emergency preparedness for tunnel fires – A systems-oriented approach

Efficient emergency response is key to preventing major losses in tunnel fires. Our general concern in this paper is the degree to which tunnel systems are prepared and the means by which we can be prepared for a major fire in a single-tube road tunnel. Conformance to prescriptive regulations dominates existing practice in the area of emergency preparedness. Risk-based approaches exist but have little influence on emergency preparedness designs for tunnel systems. A successful emergency response to tunnel fires is dependent on many actors collaborating under serious time constraints. Safety becomes a matter of controlling critical processes necessary to keep the system in a safe state. Efficient decision-making in situations of major uncertainty is vital, to achieve safety goals. This essentially means that efficient emergency preparedness for road tunnels is a matter that needs attention in the early design phases and continuous improvements during the operational phase. To achieve high-performance emergency preparedness against tunnel fires, there is a need for radical changes to the design and operation of tunnels. In this paper, it is claimed that a system-theoretic approach is appropriate to deal with the tunnel system’s complexity and to drive the design of appropriate control structures for critical processes, from the design phase to the actual emergency. It is shown how system theoretic approaches will change the safety management practices for tunnels and how this will increase consistency between potential fire scenarios and associated control actions.

Experimental studies on the smoke extraction performance by different types of ventilation shafts in extra-long road tunnel fires

Ventilation shafts are widely applied in extra-long road tunnels. Experiments were conducted in a 1/20 scale model tunnel to investigate the smoke extraction performance with a ventilation shaft. Four types of shafts were compared under the normal ventilation mode and the smoke extraction mode. The influence of shaft types, the operation frequency of the jet fan and board locations were investigated. Results indicate that the smoke extraction capacity of the mechanical ventilation shaft (MTS) is almost the same as the operation frequency increases, but the smoke extraction efficiency declines as the operation frequency increases. Besides, it can be found that the smoke extraction capacity and the smoke extraction efficiency of the mechanical board-coupled shaft (MBCS) decrease as the operation frequency increases. Moreover, it was found that the smoke extraction performance of the MBCS is highly affected by the distance between the board and the shaft. And the optimal board location for the MBCS changes with the operation frequency. Furthermore, the coupling-effect of the momentum induced by the mechanical ventilation and the buoyancy induced by the hot smoke in the ventilation shaft during a fire was explored. And the dimensionless smoke extraction Froude number (Frs), was developed for characterizing the buoyancy-momentum transition during the smoke extraction process with the mechanical ventilation shaft. These studies may contribute positive significance in the smoke control and extraction design with extra-long road tunnels.

Some Tips on Numerical Modeling of Airflow and Fires in Road Tunnels

The efficiency of tunnels systems is often evaluated using numerical simulations. This concerns both to normal and emergency mode of tunnel systems operation. Therefore the safety level of tunnel users may depend on the quality of numerical models being built. The most often studied areas cover the researches on natural and forced airflows in the normal mode and on fire development and smoke spreading in the emergency mode as well as modeling of fan operation. Thus, many software packages implementing Computational Fluid Dynamics (CFD) are applied here. Despite the available software is recognized as reliable, the problem arises because the built numerical models should be validated at least partially with experimental data. There is a shortage of experimental data from real tunnels due to high costs and many organizational or formal difficulties. Some researchers use data from scaled experiments, but this leads to problems connected with scaling. The paper presents the application of two widely used software packages—Fire Dynamics Simulator (FDS) and ANSYS Fluent to reproduce some scenarios of the operation of a tunnel ventilation system for normal and emergency mode. Most of results were compared with data obtained by own full scale measurements or data available in literature. Some practical issues concerning the application of FDS and ANSYS Fluent were discussed as well.

Theoretical and numerical study on mass flow rates of smoke exhausted from short vertical shafts in naturally ventilated urban road tunnel fires

The study focuses on the mass flow rate of the buoyancy-driven gases exhausted from the shaft in naturally ventilated urban road tunnel fires. Theoretical analyses and numerical simulations are performed. The model to predict the mass flow rate of the incoming smoke exhausted by the nearest shaft is developed by considering that the smoke is exhausted along the four sides of the shaft separately. Based on the heat balance between the incoming smoke exhausted and the total gas flow exhausted, the model to estimate the total mass flow rate exhausted from the shaft (both smoke and entrained air) is also established. Meanwhile, a series of numerical simulation in a naturally ventilated tunnel considering the heat release rate (HRR), the shaft height, shaft length and width, shaft location was carried out. The simulation results show that the shaft height has a limited contribution to the mass flow rate of the incoming smoke exhausted while a larger shaft cross-sectional area shows a favorable performance in exhausting the smoke. Further, the air entrainment into the shaft increases with both the shaft height and shaft cross-sectional area. Comparisons of the mass flow rates of the incoming smoke and the total mass flow rates exhausted between simple calculations and simulations are made, showing that the simple models perform well. Further, it is found that there exist two regimes for the total mass flow rate corresponding to different smoke modes in the shaft (complete plug-holing, plug-holing and without plug-holing), which is caused by the different driven forces in the shaft. The outcomes of this work could provide some guidance for the design of vertical shaft and smoke control in naturally ventilated tunnel in urban area.

道路トンネル火災時の模擬高齢者によるバス降車実験

道路トンネル火災時の模擬高齢者によるバス降車実験

CFD Modelling of High-Pressure Water Mist System in Road Tunnels

Fire safety is an inherent part during the road tunnel design. As road tunnels pose an important part of road public infrastructure, their endangering by fire may cause significant life, material or traffic costs. Hence are the fire safety systems in road tunnels under constant development and CFD tunnel fire models are used increasingly as an advanced tool during this process. This paper deals with modelling high-pressure water mist system which is still considered as a latter-day firefighting method in road tunnels. Scenarios created in Fire Dynamics Simulator vary in water mist system operating pressure and nozzle lay-out by constant longitudinal velocity 2 m/s in case of 15 MW small truck fire. The analysis of how these variable inputs effect the simulation results is the main aim of the paper focusing on heat flux and air temperature as main water mist fire suppression parameters. Besides, smoke layer height is monitored as essential parameter in solving the problem of evacuation and fire brigade intervention by road tunnel fires. Obtained data cover expected results in sufficient measure and provide foundation of CFD tunnel fire modelling application and further research in this field.

Study of propagation of harmful factors of fire in short road tunnels with different inclinations

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.

Final smoke spread simulations for Tunnel traffic & operation simulator

Road and highwaz tunnels have become an essential part and an important element of the road network. In terms of general transportation and transit of goods they have also transnational significance. Tunnels located on the trans-European road network with a length of more than 500 m must also comply with the requirements of European Directive 2004/54/EC. That directive imposes an obligation on investors and management organizations to pay particular attention to the fire safety of tunnels. This paper describes final smoke spread simulations of road tunnel fires which were created as outputs of the project entitled “Models of formation and spread of fire to increase safety of road tunnels”.

On the Use of Solid Curtains Near Smoke Extraction Vents to Control Smoke Spread Resulting From Fire in Road Tunnels

AbstractThe effectiveness of the smoke control strategy plays an important role in increasing safety levels when fire accidents occur in road tunnels. This paper introduces clarifications about how the efficiency of smoke extraction control using solid curtains can be increased by placing smoke extraction vents close to the solid curtains. The effect of adding a solid curtain with different heights and at various positions relative to a smoke extraction vent was studied in this paper. A 14.3% increase in the vent flowrate occurs at the time corresponding to the fire peak heat release rate when the distance between the solid curtain and the vent is equivalent to 90% of the tunnel height and when the solid curtain height is equal to 16% of the tunnel height. High temperature and low visibility conditions occur near the solid curtain at the smoke-trapped area when the smoke curtain height exceeds 40% of the tunnel height. Using a solid curtain positioned far away from the vent with a distance equals to 90% of the tunnel height and with a height in the range from 16% to 30% of the tunnel height achieves the best results in terms of suppression of smoke spread and attaining acceptable visibility and temperature levels at the region where the smoke is trapped by the solid curtain.

The effect of technical installations on evacuation performance in urban road tunnel fires

Tunnels are separated from the ground by structural linings, and are enclosed and unfamiliar for occupants. In tunnel fires, occupants are faced with a dangerous environment and they need to evacuate. Conveying and obtaining information about the evacuation is the key issue for evacuees. Since tunnels typically have low lighting and little connection outside the tunnel, technical installations are the only approach to deliver information to occupants in order to guide their fast and safe evacuation. This is particularly an issue for urban road tunnels with large occupants’ flow in a large underground space. The present study explores the effect and role of technical installations (alarms, information signs, and lighting) on people’s evacuation performance in urban tunnel fires, through field experiments, questionnaires and interviews. Theory of affordance (sensory affordance, cognitive affordance and functional affordance) is taken into consideration and provides an integral evaluation for technical installations. Technical installations are useful in helping occupants notice the emergency, finding exits and guiding path, and information signs are regarded as the most powerful among those three. Besides, this experiment points out some side effect from alarms and ambiguity of signs which will result in serious consequence potentially. This study leads to guidance on improvement of technical installations on evacuation planning and procedures on urban road tunnels.

Tunnel Ventilation Analysis Using a Probabilistic Approach: Case Study, Fire in Road Tunnels with Longitudinal Ventilation

Tunnels are nowadays key elements in transport networks worldwide. To achieve a safe and efficient operation, a proper integration and design of Mechanical, Electrical and Intelligent Transportation Systems is required. Among these systems, tunnel ventilation is one of the most critical ones from the Fire Life Safety perspective, being smoke control to maintain safe conditions during self-evacuation and rescue operations one of its main objectives. Traditionally tunnel ventilation systems are sized following a deterministic approach. Designers, based on requirements and design criteria from Standards and Recommendations, focus on a limited number of fire scenarios and design parameters to reach a solution considered acceptable from a fire safety perspective. This paper proposes the use of a probabilistic approach to assess, in terms of probability of failure, the capacity of a tunnel ventilation system for fire scenarios. The model applied in the proposed process uses a 1D steady state model based on pressure losses, where critical design variables are considered random (unlike with the deterministic approach) to calculate a failure probability associated to an installed ventilation thrust. A case study example is used to analyse results using both, the traditional deterministic approach and the proposed probabilistic one. Results obtained with the deterministic approach show how, under the same design requirements, tunnels with similar characteristics allow different safety margins for the capacity of the ventilation system. These results are confirmed numerically using the probabilistic approach by evaluating failure probabilities. To avoid this, the paper proposes the use of the probabilistic approach to allow a definition of an equivalent uniform safety margin (to achieve a certain probability of failure) which would be of significant help for designers, administrations and tunnel operators. It is not the aim of the study to define the limit for the probability of failure or to characterise the design variables, but to present a useful tool with which important conclusions about the design criteria can be obtained.

Estimating water density for tunnel fixed firefighting system and ventilation requirements to control fires in road tunnels

A potentially dangerous fire event that can occur in road tunnels is a gasoline tanker fire, where flammable liquid fuel spills on the tunnel roadbed and catches fire. In the USA typically, the water density required for fixed firefighting systems is based on NFPA 13 and the minimum ventilation is based on smoke back layering. This work calculates the required water density based on the tunnel geometry and compares the back layering ventilation to the ventilation needed to remove saturated air. The presented methodology presents an analytical approach to calculate the water density and ventilation required to control a gasoline pool fire, which is a function of the size of the gasoline pool, without considering the growth restriction due to fuel depth and limited oxygen.The tunnel geometry parameters presented in the examples are limited to specific cross slopes and road slopes, as well as resultant fire sizes of 50 MW, 100 MW, and 150 MW. This work considers standard sprinkler heads to calculate the required density in conjunction with the ventilation required to maintain evaporative cooling. The calculations are performed with a water only system and with modifications that could be expected from the use of foam additive.

Smoke flow in full-scale urban road tunnel fires with large cross-sectional vertical shafts

In this study, a series of full-scale fire tests are performed in a tunnel with large cross-sectional vertical shafts. The heat release rates and fire locations are considered, and the general smoke development, smoke flow pattern in the shaft, smoke temperature distribution, and smoke front velocity are analysed. It is found that complete plug-holing occurs in the tunnel with large cross-sectional vertical shafts. The smoke flows into the shaft from the bottom sides and spreads out along the shaft sidewalls. The smoke cannot fill the shaft cross-section, even at the shaft outlet. In the early and full-development stages of a fire, a well-stratified smoke layer exists, whereas in the decay stage and after burning out, the visibility significantly reduces. The smoke can be controlled within 80–125 m on each side of the fire source, and it takes approximately 10 min for the visibility to self-recover naturally for common car fires after burning out. The results of the full-scale experiment indicate that the shaft has acceptable performance in smoke control for the test scenario investigated. According to an analysis of the tunnel environment during a common car fire, as well as the evacuation movement, it can be concluded that the occupants can escape safely. The experimental results are used to verify the smoke control performance of the vertical shaft and provide guidance for the design of naturally ventilated tunnels with vertical shafts.

A simple model for predicting the smoke spread length during a fire in a shallow urban road tunnel with roof openings under natural ventilation

When a fire occurs in a road tunnel with roof openings, smoke generated by the fire is exhausted through the roof openings in the ceiling by natural buoyancy of the hot smoke, and as a result, the smoke spread length in the tunnel is limited. In this study, we conduct fire experiments using a 1:10 scale model tunnel with roof openings of a 10% opening ratio, and propose a simple model for predicting the smoke spread length in the tunnel based on the results of the experiments. A constant smoke spread length is both observed in the fire experiments and predicted by the simple model. Sensitivity analysis on the effects of the parameters used in the simple model on smoke spread length clarifies the dominant parameters. Furthermore, we clarify that the smoke spread length is decided by a balance between inertia and buoyancy in the hot smoke flow and the inertia of fresh cold air flow induced by the fire.

Experimental approach to suppress smoke diffusion in sloped road tunnels

In case of a fire in an urban road tunnel with a longitudinal ventilation system, for public safety, it is necessary to ensure that evacuation is initiated at a very early stage. The smoke from the fire can cause breathing difficulties and critically affect evacuees; thus, the smoke should be controlled by means of the ventilation equipment to suppress its diffusion. This paper focuses on the smoke behavior in sloped road tunnels and the airflow velocity required to ensure a safe evacuation environment.