Smoke Propagation Research Articles

The influence of wind on smoke propagation to the lower layer in naturally ventilated tunnels

A tunnel fire is a dangerous accident, which may lead to serious injuries and deaths. This work studies the flow of combustion products during naturally ventilated tunnel fires, i.e., without a mechanical ventilation system. In such an event, two stratified layers with opposing velocity directions are formed. The safety of tunnel users is compromised if the smoke, initially flowing in the upper layer, contaminates the lower one, which has been found to happen abruptly at a distance xc from the fire. This is caused by the cooling of the jet leading to a large enough decrease in momentum for the smoke to be entrained by the lower layer. Natural ventilation may be an effective and inexpensive smoke control strategy if the fire-to-portal distance is shorter than xc. However, there is a lack of research to predict under which conditions this occurs and how xc is influenced by factors such as natural wind. An open-source Computational Fluid Dynamics (CFD) code, fireFoam, was used to conduct Large Eddy Simulations (LES) of naturally ventilated tunnel fires. The numerical model was validated by performing a simulation of a large-scale tunnel fire test. Additionally, 7 fire scenarios with varying wind velocities were simulated. The contamination distance xc was found to decrease for higher wind velocities. Furthermore, a simple semi-analytical model was employed to obtain quick estimates of xc, by calculating ceiling jet properties using balance equations and empirical correlations. Model coefficients were calculated using the CFD results.

Investigation of critical velocity in curved tunnel under the effects of different fire locations and turning radiuses

Toxic smoke is one of the main threats to people trapped in tunnel fires. Propagation characteristics of smoke flow differ between curved and straight tunnels, depending on the tunnel turning radius. In this study, experiments and numerical simulations were conducted to analyze the critical velocity of a curved tunnel under different fire scenarios, where different heat release rates, tunnel turning radiuses and fire locations were considered. Results showed that the critical velocity varied as the transverse fire location changed, reaching its minimum value when the fire was located at the transverse center of the tunnel, and increased gradually as the fire source approached the tunnel sidewall. For a given fire location, the critical velocity increased with the tunnel turning radius. It is speculated that a decrease in the tunnel turning radius may increase the resistance to smoke flow and has the advantage of preventing smoke propagation. A predicted correlation of the critical velocity considering the effects of different heat release rates, tunnel turning radiuses, and fire locations has been proposed. Predicted results of the improved correlation are consistent with results obtained from the numerical simulation. The outcomes of this study may provide a reference for tunnel ventilation system design.

Enhancement of smoke extraction in tunnels in the case of fire by using L-shape curtain near smoke extraction vents

One of the challenges in the case of fire in tunnels is how to limit the propagation of smoke efficiently. Solid curtains which are released from the tunnel ceiling at the time of fire can prevent the smoke from further spread in the tunnel. The main issue with the traditional straight shape curtains is that there is no guarantee for providing a complete safe environment as enough visibility, temperature, and smoke concentration for the people at the region where the smoke is trapped behind the curtain. This paper introduces an idea to make a modification of the straight curtain shape to be L-shape and to use it at a location close to the smoke extraction vent. Results showed that in the case of straight curtain, part of the smoke moves downward after hitting the curtain and then diffuses at low elevations. On the other hand, the L-shape curtain redirects the smoke stream moving downward about 90° before being captured by the smoke extraction vent. The L-shape curtain increased the visibility and provided lower temperatures and smoke concentration compared with the straight curtain shape. Moreover, L-shape curtain created better interaction with the vent resulting in higher smoke flow extraction rate.

Full-scale experimental study on fire under natural ventilation in the T-shaped and curved tunnel groups

To assess the fire risk during the construction of the pumped storage power station, full-scale fire experiments in the ventilation and safety tunnel were conducted to research temperature distribution and smoke diffusion under ventilation. The temperature profile and airflow velocity of air flow under different conditions were recorded and analyzed. The results show that the airflow velocity was mainly influenced by the large space like powerhouse and transformer chamber under natural ventilation. By analyzing smoke propagation characteristic parameters including the maximum ceiling temperature rise, smoke front arrival time and temperature variation with time, the fire-induced smoke hazard under different fire locations was assessed. The research results can provide reference data for smoke exhaust design and help developing the emergency evacuation plan for the large underground space building with similar structure.

Effect of longitudinal slope on the smoke propagation and ceiling temperature characterization in sloping tunnel fires under natural ventilation

In order to reduce risk and increase resilience of transportation tunnels, the early-phase detection and protection of fire are of great significance for the safety assessment of tunnel. In this work, numerical simulations are conducted to characterize the thermal plume propagation and ceiling temperature profile in a tunnel with longitudinal slope increasing from 0% to 15%. For the sloping tunnel, as there exists elevation difference between the tunnel ends, the longitudinal air flow will be induced from the lower end. Under such circumstances, the stack effect occurs and it becomes the primary driving force for the smoke movement in tunnel. Results show that the thermal plume behaviors in the sloping tunnel, including the thermal flow field and the temperature profile, show apparently different from those in the horizontal one. The induced air flow rate that directly related to the strength of stack effect is quantified, and on this basis, the predictive correlation of the temperature profile under the ceiling is proposed by considering the influence of the stack effect for different tunnel slopes. Besides, the accuracy and applicability of the obtained correlation are further verified by comparing to a total of four series of previous experimental data with a wider range of tunnel slopes, dimensions, and heat release rates.

Modeling wind and air temperature effect on propagation of smoke and toxic gases during fire on metro bridge

Modeling wind and air temperature effect on propagation of smoke and toxic gases during fire on metro bridge

Numerical Simulation Study of Effect of Tunnel Slope on Smoke Propagation

Tunnel slope is an important factor affecting smoke spreading for a stopped subway train on fire. In this paper, a multi-scale method where one-dimensional (1D) network is coupled with three-dimensional (3D) field simulation is used to calculate smoke and temperature distributions for a fire occurred in the middle part of the subway train in tunnel. The tunnel slopes of 0‰, 12‰, 21‰ and 30‰ are considered. By comparing the temperature distribution in a condition with natural ventilation and with 2 m/s longitudinal ventilation, we comprehensively analyzed temperature, smoke spread characteristics. Results show that tunnel slope has a great influence on temperature and smoke profile when slope is higher than 12‰. The temperature at 1.8m would exceed the safe limit of 60°C at 60 s after fire ignition. The larger the slope, the higher temperature would be in the train carriage. For a train fire scenario with natural ventilation, within initial 120 s period the train compartment could keep a safe evacuation condition. This research would provide reference for making right evacuation plan of subway tunnel fire.

Influence of draft curtain height on smoke exhaust effect in a large area metro depot

The metro depot area has the characteristics of large area and high storey and the smoke diffusion under fire conditions in these areas are more complicated. It is important to investigated smoke exhaust effect which is closely related to the safety of firefighters. FDS (Fire Dynamics Simulator) numerical simulation method was adopted to investigate the influence of draft curtain height on the performance of smoke exhaust fan which were installed on the inside wall of the metro depot area. The curtain heigh was set as 0.5m,1.0m,1.5m,2.0m,2.5m,3.0m respectively. The propagation of fire smoke, the concentration of CO2 at the exhaust outlet and the exhaust efficiency was analyzed. For the smoke vents set on the side wall, the height of the draft curtain would have greatly influence on the smoke exhaust efficiency. As the height of the draft curtain increases, the spread distance of smoke in the horizontal direction becomes short.it is beneficial to improve the exhaust efficiency of the fan on side wall. The research results could provide references for the fire protection design of the subway depot area.

Experimental investigation of the thermal back-layering length in a branched tunnel fire under longitudinal ventilation

The smoke propagation in branched tunnel is more complicated because of the special bifurcation structure that has not been clarified, despite the fact that the scenario exists in practice. In this paper, the thermal smoke movement behavior in branched tunnel fire were experimentally investigated under the combined effect of bifurcation angle and ventilation velocity. The theoretical analysis was conducted to develop the smoke back-layering length equation based on the applied force of smoke propagation upstream of the fire source, and the smoke back-layering length under various longitudinal ventilation velocities was quantified. The results indicate that the smoke back-layering length decreases with the increasing of longitudinal ventilation velocity for a given heat release rate. The stronger heat release rate results in the longer smoke backflow distance under same ventilation velocity. The smoke back-layering length varied with bifurcation angle due to the bifurcation structure weakens the inertial force of longitudinal ventilation, but the affected degree varies with bifurcation angle. The experimental smoke back-layering length can be well correlated using the deduced logarithmic function. The empirical model taking the bifurcation angle into consideration is proposed to predict the smoke back-layering length in branched tunnel fire. Finally, the correlation for critical ventilation velocity of branched tunnel fire under varied bifurcation angles was also proposed based on the boundary condition of none smoke back-layering.

Improvement of heat and smoke confinement using air curtains in informal shopping malls

The present study numerically analyzes, from an evacuation perspective, the heat and smoke propagation in case of a fire incident in typical informal shopping malls with air curtains employed at critical locations and compared the same with no air curtains in place. Three different designs of shopping malls, having the commonly observed geometric and architectural features and multiple origins of fire with clothing as fuel, are examined. The effect of the distribution and arrangement of clothing fuel inside the stores on the propagation of heat and smoke is evaluated. Encouraging results are obtained in terms of the effectiveness of the air curtains in mitigating the spread of heat and smoke and in increasing the safe evacuation time. About 37% of the fire-generated heat could be confined within the fire-source store by discharging the air curtain jet at a velocity of 10 m/s. Implementation of a two-stage air curtain barrier, at the fire-origin and the staircase, might confine up to 68% of the heat towards the staircase. Since the practically observed fuel density within these stores inevitably shows flashover to occur, the effect of an alternate and more standardized clothing arrangement on the fire safety is also analyzed. The findings of the present study could provide a comprehensive insight into the role and effectiveness of air curtains in confining the heat/smoke and hence assisting safe evacuation in case of fire incidents in informal shopping malls.

Effect of ceiling extraction on the smoke spreading characteristics and temperature profiles in a tunnel with one closed end

A series of fire tests in a 1/15 scaled-model tunnel with one closed end have been conducted. Analysis was carried out to explore temperature distribution and smoke propagation under the influence of ceiling extraction system. Five different heat release rates, three dimensions of exhaust outlet, and numerous extraction rates were considered. Experimental results led to some interesting findings about the relationships between smoke extraction rate, fuel mass burning rate, and ceiling temperature. Two distinctive ceiling temperature regions were identified according to their different responses to smoke extraction rate, i.e., ceiling temperature decay between the fire and outlet was almost independent of smoke extraction rate while temperature upstream of the outlet decreased sharply with the increase of smoke extraction rate. Analysis was also conducted about smoke back-layering length, revealing its strong dependence on heat release rate and induced air velocity. Based on the experimental results and dimensional analysis, three empirical formulas were proposed to capture ceiling temperature decay and smoke back-layering length for tunnels with one closed end utilizing ceiling smoke extraction.

Evaluation of fire smoke control in underground space

The main goal of the fire management strategy is to avoid people interaction with fire hazards, therefore several studies are carried out for optimal escape route planning as well as smoke management and mechanical ventilation design. Underground spaces are a special case of study due to their technical characteristics that create different fire spread conditions compared to conventional buildings. In this paper, a comparative study on the fire smoke propagation is carried out taking into account the use and performance of smoke mitigation techniques. The Underground Hazardous Waste Management Repository of Lavrion Technological and Cultural Park in Greece, is selected as a case study to achieve the paper objectives. A Computer Fluid Dynamic software is used to simulate various fire scenarios based on the specific characteristics of the underground space. Parameters that have significant impact on evacuation procedure and human health such as visibility and carbon monoxide concentration are monitored. Finally, the results are presented and an evaluation method is proposed based on evacuation simulation results, in order to predict the impact of the smoke control design on the conditions inside the underground space. The results reveal that the ventilation shaft (passive system) offers an effective smoke control without any other combined control system and that the installation of smoke curtains, which are activated on time, offers significant improvement on smoke spread control extending the available egress time (ASET) in case of fire.

Effects of unsafe workplace practices on the fire safety performance of ready-made garments (RMG) buildings

A coupled CFD modelling for fire growth and evacuation modelling is conducted to evaluate the fire safety performance of a multistoried ready-made garments (RMG) building. The geometric and architectural features, occupant density, and other features of the factory are selected to represent those of a standard RMG building in Bangladesh. The smoke propagation and evacuation scenarios are selected to resemble some of the typical and often overlooked unsafe practices, such as open fire-doors, obstacle in the egress routes, and reduced exit numbers, observed in the RMG sector in Bangladesh. The effects of these practices are examined separately and in different combinations to obtain a comprehensive understanding of their effect on the occupant safety. It is observed that when there is no compartmentation in place near the stairway (resembling open fire doors), different areas of the building become untenable very quickly. If all the unsafe practices are considered at the same time (open fire door, obstructed egress route, and reduced number of exits), about 6% (334 out of a total of 5381) of the occupants fail to evacuate safely. This happens due to the reduction in visibility in smoke below the threshold that permits safe escape, considering the physiological and psychological effects of smoke on the way-finding ability and escape behavior of the occupants. The critical issue of the possible effects of these unsafe or non-standard practices in the garment factories on the safety of the workers has not been addressed in a systematic manner before. Therefore, the findings of this study can be useful in assessing the potential consequences of a fire-hazard due to the unsafe workplace practices even in the standard RMG buildings complying with relevant building codes.

Fire-smoke control strategies in road tunnels: The effectiveness of solid barriers

This paper discusses the effect of introducing solid barriers at the ceiling of a tunnel on slowing down propagation of smoke resulted from a fire using numerical simulations. Significant reduction of smoke spread and great enhancement of visibility conditions in the tunnel were achieved using solid barriers with specific design arrangements including the dimensions and number of solid barriers used. Using solid barriers with a height of 1 m and with a 5 m distance between two successive solid barriers resulted in the reduction of the total smoke spread distance by 66.5 % compared to the case without using solid barriers for a 30 MW fire. Results referred to that smoke layer thickness increases and also the temperature increases at specific regions close to the fire location when using solid barriers but with various degrees depending on number and geometry of the solid barriers. Findings of this paper confirm the advantages of using solid barriers and open the way for future research towards developing more knowledge on smoke barriers performance.

Numerical Simulation of Converter Station Fire: A Study focus on the Fire Hazard of Valve Tower

The fire hazard of a valve tower in converter station fires were investigated by using the Fire Dynamics Simulator (FDS). The 2 m2, 5 m2 and 10 m2 transformer oil pool fires with the calculated heat release rate (HRR) of 2.02, 6.23 and 13.78 MW were considered in the simulations, and the smoke propagation process, smoke temperature and visibility were mainly concerned. The results showed that the whole valve tower was immersed in the fire smoke at about 600 s in 2 m2 fire condition, and the maximum temperature rise inside the valve hall was about 20ºC. In the 5 m2 fire condition, the smoke layer height descended to the bottom of the valve tower at about 300 s, and the visibility around the valve modules was lower than 5 m at about 450 s. The maximum smoke temperature inside the valve hall was over 60ºC, and the temperature of smoke around the valve modules ranged from 43 to 52ºC. In the 10 m2 fire condition, the valve tower was immersed in the fire smoke at about 210 s, and the visibility around the valve modules was lower than 5 m at about 300 s. The smoke temperature beneath the ceiling of the valve hall was over 100ºC, and the temperature at the height of valve towers ranged from 65 to 80ºC. It was observed that the larger the fire size was, the higher the fire hazard of the valve tower would be found. In the 5 m2 and 10 m2 pool fire conditions, the thermal damage to the valve tower was non-negligible. The normal operation of the electrical components in the valve tower might be affected, and the failure of electrical components might be occurred.

Simulation Study on the Influence of Fire Partition on Curtain Wall Temperature in Super High-Rise Buildings in China

The poor fire resistance characteristic of super high-rise curtain wall makes the curtain wall design one of the main approaches to improve its capacity for prevention and control over fire and smoke spread. The propagation of smoke leads to the increase in the temperature of the curtain wall on the upper and lower floors of the fire floor and consequently leads to glass fracture and other serious consequences. Current codes have control over fire resistance performance and size of fire partition materials but do not include requirements on the position of curtain walls on floors. By changing the position of fire partition in curtain walls, the paper carries out three comparative simulation experiments on two forms of fire partition: spandrel and fire prevention cornice. Besides, PyroSim is used to calculate the comparative simulation of fire and smoke spread and obtain the data on temperature variation nephogram and monitoring points in the center line of glass curtain walls during different fire scenarios, so as to discuss the influence of different positions of spandrels and fire canopy on fire hazard and smoke. This study finds out the following: fire canopy can better prevent the longitudinal spread of fire smoke than spandrels. The fire canopy above spandrels can reduce the flue-gas temperature. The higher the spandrels above floors, the faster the temperature of the central lines of glass curtain walls above fire floors reduced. However, the higher the spandrels above floors, the more uneven the distributions of high-temperature regions and low-temperature regions, thus leading to the increase in horizontal temperature differences of glass panels. This research conclusion can be taken as a reference for fire protection design of super high-rise glass curtain wall.

ASSESSING THE SIMILARITIES OF 3D SIMULATION MODEL OUTCOMES

Abstract. The recent advancement of simulation modeling to represent phenomena in three spatial dimensions (3D) requires the development of techniques that will allow comparison of the modeling outputs in multiple dimensions. However, many existing techniques for map comparison in two spatial dimensions (2D) have been developed from non-spatial method such Cohen’s Kappa. These techniques are not yet fully extended to deal with 3D map data or simulation outcomes. Therefore, the main objective of this study is to investigate the use of the 3D Accuracy and 3D Cohen’s Kappa coefficients to compare simulation model outputs in 3D. An existing agent-based model (ABM) of forest-fire smoke propagation was used to generate multiple scenarios for the purpose of comparing 3D simulation outputs. The results for 3D Accuracy and 3D Cohen’s Kappa produces meaningful values when comparing several scenarios with different 3D ABM outputs. This study emphasizes the need for the development of more advanced simulation output comparison techniques that operate in 3D and potentially over time (4D).

Full-scale experimental investigation on smoke spreading and thermal characteristic in a transversely ventilated urban traffic link tunnel

Transverse ventilation system is an effective method to control the smoke propagation in tunnel fires. In the current research, 14 full-scale burning tests were conducted in an urban traffic link tunnel in Chongqing, China. Temperature and velocity profiles, as well as the smoke stratification characteristics affected by the transverse ventilation were successively explored. Results underlined that 1) Fire location and air supply system have limited influence on the induced air velocity while the induced air velocity slightly decreased as heat release rate increased. When more smoke outlets were activated, the induced air velocity increased; 2) Ceiling temperature was very sensitive to the fire location, smoke extraction, and air supply system. A distinct temperature decrease was observed when (a) the fire moved closer to the outlet; (b) more outlets were activated; (c) supply vents near the fire were opened; 3) Thermal stratification could be well predicted by the temperature quotient proposed by Newman. Considering the transverse ventilation, the relationship between temperature ratio ΔTcf/ΔTavg and Froude number Fr accounting for the transverse ventilation was modified based on the present measurements.

A SYSTEM OF TRANSFORMABLE CROSSPIECES TO BLOCK HARMFUL COMBUSTION PRODUCT PROPAGATION IN TUNNELS

Controlling the events and processes caused by fires is one of the key issues of all projects dedicated to the fire safety of tunnels. These processes are characterized by the dynamics of the propagation of high temperature, smoke and toxic combustion products around the seat of fire and in tunnels. With longitudinal ventilation, two main parameters are to be considered: the critical velocity and the backlayering length. An important impact on both parameters is exerted by the proposed system of flexible crosspieces, which, by increasing the aerodynamic resistance of a tunnel, makes it possible to reduce the speed of propagation of harmful factors of fire through the tunnel. Moreover, with certain limitations, the given crosspieces can be used to divide the tunnel into small sections what, among other things, will hinder the propagation of fire for a certain time. Thorough theoretical and experimental study of the mentioned transformable crosspieces, as well as the development of their various structures and operating principles is necessary to ensure the safety of traffic tunnels. The present article proposes a novel technology of light transformable crosspieces, which can be used in both, the existing road tunnels and the ones planned to design.

Expanding the FDS Simulation Capabilities to Fire Tunnel Scenarios Through a Novel Multi-scale Model

Computational Fluid Dynamics (CFD) is widely used to simulate tunnels and partially substitute on-site tests. As technology advances, new application opportunities appear; some examples are the optimal operation of ventilation and emergency systems, risk assessment of tunnels and training of the operators. Even when the computational capacity of computers has grown, CFD is still constrained by the large amount of computational resources needed in long tunnels. This introduces a need for methods able to reduce the amount of time required for simulations. To face this need, a novel 1D–3D multiscale model is presented in this paper. The model incorporates the code Whitesmoke into FDS (Fire Dynamics Simulator) through a direct coupling. Whitesmoke manages the fluid dynamics, temperature and concentration of species in the 1D portion, while FDS calculates these fields in the portion where fire occurs. Using this multiscale model, the computation time for long tunnels is reduced, proportionally to the 1D length in the domain. Also, additional simulation capabilities particularly useful for tunnel analysis are obtained. Some new characteristics are pressure boundary conditions can be easily imposed at the tunnel portals or at the ventilation shafts; the characteristic curves of the fans/jet-fans can be included, also considering the degradation effects due to smoke propagation; the piston effect can be properly considered. Our research verifies most of its capabilities, also clarifying its limitations and the criteria used to set the domain for the analysis. As a final step, the model is tested in a tunnel with a cross section of 4.8 m and 600 m of length with a 2 MW fire, comparing its performance with a full 3D FDS simulation. The difference in temperature and velocity is minimal for most of the domain, making It a good way to optimize resource usage in large simulations. Furthermore, the multiscale manages to reduce the computational time of more than a 50%.