Smoke Control Strategy Research Articles

Advancements in smoke control strategies for metro tunnel cross-passage: A theoretical and numerical study on critical velocity and driving force

Cross-passage is a commonly encountered structure within metro tunnels, providing a swift route for evacuating personnel from the accident tunnel to the safe tunnel opposite. Ventilation in the cross-passage of metro tunnels is established through the collaborative operation of ventilation systems on both sides of the tunnel. Concurrently, smoke movement within the metro tunnel is impacted by factors such as train blockage and the accumulation of heat within the train carriages. The former correlations need further refinement to predict the critical velocity and driving force required to prevent smoke from spreading into a metro tunnel cross-passage. One-dimensional theoretical analysis and full-scale cold smoke experiments were performed to investigate the relationship between the air supply parameters of tunnel fans on both sides and the ventilation velocity in the cross-passage. A calculation model of fan type selection in the opposite side safe tunnel for smoke control in the tunnel cross-passage is proposed. The influence of train location, fire heat release rate, and main tunnel ventilation velocity on critical velocity in the cross-passage was quantified by numerical simulations. The results show that the critical velocity in the cross-passage under unobstructed conditions surpasses that under blocked conditions. Meanwhile, the critical velocity exhibits relative stability under both unobstructed and blocked conditions. On the basis of the dimensionless analysis, a piecewise function was proposed to predict the critical velocity in tunnel cross-passage. The outcomes of this study provide valuable guidance for the implementation of fire prevention and smoke control measures in tunnels with similar structures.

Influence of the water spray particle diameter and flow rate on the smoke flow and the back-layering in tunnels with longitudinal ventilation

When there is a fire in a tunnel, the heat released by the combustion is difficult to dissipate and the temperature inside the tunnel would rise rapidly. Longitudinal ventilation (LV) has been commonly adopted as the smoke control strategy in tunnel fires, which is essential to safeguard the tunnel structure and the trapped people. Besides the smoke control method by LV, the water mist system (WMS) can provide a powerful cooling effect for the high-temperature smoke in the tunnel. This article aims to investigate the impact of WMS on the smoke back-layering (BL) length with LV and the mutual effect process between the smoke spread and the WMS. The findings show that the BL length is restricted more effectively by the combined action of water mist and LV. Upon activation of the WMS, the water mist’s effect inhibits the smoke’s ability to spread upstream and causes the smoke layer to settle down, which disturbs the stability of the smoke layer. An unstable layer of smoke is more likely to be blown downstream by longitudinal ventilation. All water mist particle diameters show a significant reduction in smoke back-layering with an increased flow rate. The BL length would gradually reduce as the particle diameter is decreased. The tendency of flow rate and particle diameter on the BL length shows similar effects to the critical velocity ( Vcr). The Vcr is reduced with the rising flow rate and increased with expanding particle diameter.

Performance-Based Fire-Protection Design of Public Amenities with Restrained Personnel Activities

In this paper, performance-based fire-protection design is used for the fire-safety design of public amenities with restrained personnel activities. In these places, tourists’ activities are constrained in a limited space such as cockpit moving along the track. Since it is another typical scenario of fire-protection problem that cannot fully comply with the current mandatory codes and regulations, simulation analysis is used in order to ensure that such fire scenario could achieve performance objectives as expected. Firstly, corresponding fire-protection performance objectives, strategies and simplified evaluation criteria are brought forward in this paper. Then, through simulating the smoke flow in the fire using the computational fluid dynamics software FDS, the effectiveness of the smoke control strategy is verified. Meanwhile, the escaping environments of these fire scenes are analyzed. Further, the personnel evacuation simulation software (Pathfinder) is resorted to simulate the personnel emergency evacuation. The efficiency and the total time that consumed are obtained. Finally, by analyzing the similarities and differences of evacuation under different fire scenes, the fire and smoke spread in the riding area can be effectively controlled, and a safe evacuation environment can be provided for the evacuation of tourists.

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.

Study on Tunnel Fire Smoke Control and Transverse Passageway Interval under Traffic Congestion

When there are traffic jams in the tunnel, if the critical velocity is used for longitudinal smoke exhaust, it will pose a threat to the vehicles and people congested downstream. Using FDS + EVAC for numerical simulation, this paper has studied the fire smoke control strategies and transverse passageway intervals. The results show that: (1) When there is congestion at the downstream of the fire source, excessive longitudinal smoke exhaust will reduce the available safe evacuation time (ASET) in the downstream area of the fire source, and the longitudinal velocity should be controlled within 1 m/s. (2) When the transverse passageway for vehicles cannot be used for evacuation, the time necessary for safe evacuation increases by 43%. In order to ensure the safe evacuation, the transverse passageway intervals should be no more than 400m, and the transverse passageway for vehicles should have the function of pedestrian evacuation.

Study on smoke control under mechanical exhaust strategy in a cross-type interchange subway station

In order to analyze the effect of the smoke exhaust system, a series of experiments were conducted in a 1:20 scale model of a cross-type interchange subway station. Fire dynamics simulator code was used to evaluate different mechanical smoke control strategies conducted in a full-scale interchange subway station. The numerical results were compared with experimental data. Results show that the experimental data of the air temperature distribution in the station platform were in good agreement with the simulation results and the research indicated that the different smoke control system had different influence on smoke confinement induced by the fire occurred in the 3rd basement, which was the platform of the No.10 line in Beijing. In the same smoke control strategy, the velocity of airflow at stairs with a full-seal screen platform door system in the transfer station is higher than that of platform the half-height screen platform door system.

An integrated approach for the analysis and modeling of road tunnel ventilation. Part I: Continuous measurement of the longitudinal airflow profile

The knowledge of the flow field inside road tunnels under normal operation, let alone fire conditions, is only approximate and partial. The reason is that while the full three-dimensional, unsteady problem is out of reach of numerical methods, on the other hand accurate measurement of the airflow in road and railway tunnels constitutes an extremely demanding task. The present work, structured as a twofold study, takes up the challenge and proposes an original integrated experimental and numerical approach for the analysis and modeling of flow inside a road tunnel and its ventilation systems, aiming at defining a methodology for the creation of “digital twins” of the system itself, on which advanced ventilation and smoke control strategies can be tested and fine-tuned. In this first part, an innovative experimental facility for the continuous acquisition of the longitudinal velocity profile along the whole length of a road tunnel has been designed and built. The facility consists of a survey rake with five bidirectional vane anemometers, which is mounted on a small electric vehicle that can travel through the tunnel at constant speed. This paper reports the design procedure of the measurement facility, with particular focus on the conception and realization of the vehicle carrying the survey rake. Results of the first experimental campaign carried out under the 11611 meters long Mont Blanc road tunnel are presented to corroborate the validity of the approach adopted and the accuracy of the measurement chain.

Thermo-Fluid Dynamics Analysis of Fire Smoke Dispersion and Control Strategy in Buildings

Smoke is the main threat of death in fires. For this reason, it becomes extremely important to understand the dispersion of this pollutant and to verify the influence of different control systems on its spread through buildings, in order to avoid or minimize its effects on living beings. Thus, this work aims to perform thermo-fluid dynamic study of smoke dispersion in a closed environment. All numerical analysis was performed using the Fire Dynamics Simulator (FDS) software. Different simulations were carried out to evaluate the influence of the exhaust system (natural or mechanical), the heat release rate (HRR), ventilation and the smoke curtain in the pollutant dispersion. Results of the smoke layer interface height, temperature profile, average exhaust volumetric flow rate, pressure and velocity distribution are presented and discussed. The results indicate that an increase in the natural exhaust area increases the smoke layer interface height, only for the well-ventilated compartment (open windows); an increase in the HRR accelerates the downward vertical displacement of the smoke layer and that the 3 m smoke curtain is efficient in exhausting smoke, only in the case of poorly ventilated compartments (i.e., with closed windows).

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.

Experimental and numerical study on the smoke movement and smoke control strategy in a hub station fire

Smoke movement is more complex in a station fire hub than in a common situation, and it is also difficult to deal with. In this paper, full-scale experiments were conducted to investigate the ceiling temperature, smoke-layer thickness and the temperature distribution within the station. The effect of smoke exhaust system and the velocity at staircase on smoke flow were investigated when the fire source located near the staircase, using a series of FDS numerical simulation. From the full-scale experiment and simulation results, several conclusions were made: (1) The full-scale experiment results showed that the sprinkler system was capable of confining the temperature rise if it is activated; (2) Meanwhile, it also proved that the propagation of smoke could be effectively controlled when the mechanical smoke exhaust system is switched on; (3) Based on the simulation results, smoke spread rapidly in the platform floor at the early stage and then it entered into the staircase when the smoke exhaust system was absent; (4) Even though the exhaust and supply system opened, smoke could still propagate through the staircase if there’s no downward airflow at the entrance; (5) When the downward airflow existed, smoke still cannot be effectively discharged without the smoke exhaust system.

Numerical study on the smoke control using point extraction strategy in a large cross-section tunnel in fire

The Point Extraction System (PES) is effective for smoke control and popular for long and large cross-section shield TBM (Tunnel Boring Machine) tunnels. To clearly comprehend the fire characteristics on the cross-section and correctly apply the smoke control strategy, a series of 3D numerical Computation Fluid Dynamics (CFD) simulations are conducted. Smoke temperature, minimum visibility and carbon monoxide (CO) concentration are analyzed to evaluate the efficiency and effect of the PES on the evacuation environment according to the standard safety criteria. Three fire scenarios i.e. 5 MW, 20 MW, and 50 MW are employed in the simulations. Fire characteristics and smoke control in different transverse fire locations, dimensions of smoke exhaust openings and smoke exhaust rate are simulated, respectively. The results indicate that transverse fire location slightly affects the evacuation environment due to the nature of large cross section. With the same area, the slender exhaust opening perpendicular to the longitudinal direction of the tunnel can control the smoke better than the short one, especially in the areas far away from the fire source. The smoke extraction efficiency of PES is determined by the smoke exhaust rate. Higher smoke exhaust rate improves the smoke control efficiency to a large extent.

Experimental Research on the Smoke Control System in a Complex Road Tunnel Fire

Abstract Twelve full scale experiments are carried out to research the effectiveness of smoke control system designs in a complex road tunnel in the event of a fire. The segment of the tunnel used for the experimental program is equipped with mechanical exhaust ducts and mechanical air supply ducts along the tunnel. In the experiment program, two sizes of fires are included, having heat release rates of 1.5 and 3.8 MW. A variety of smoke control strategies are included in the program in order to compare smoke movement behavior and the relative effectiveness of the smoke control strategies. The experiments demonstrated that the spread of the smoke can be contained effectively within two zones with an adjusted transverse smoke control system.

Experimental study on thermal and smoke control using transverse ventilation in a sloping urban traffic link tunnel fire

A set of full-scale experiments was conducted to study thermal and smoke control strategies using transverse ventilation system in a sloping urban traffic link tunnel (UTLT). Results showed that it is not the case that the slower the smoke spread longitudinally, the better the smoke being controlled. For transverse ventilation, within the smoke extraction compartment, the faster the smoke spread to the exhaust vents the faster the smoke being extracted from the tunnel. More importantly, the operation of the exhaust and supply vents for transverse ventilation in real time should take the effect of tunnel slope into consideration. For tunnel with a slope going uphill from upstream to downstream, supplying air from the downstream is recommended while supplying air from the upstream or directly to the fire located smoke compartment should be avoided. Additionally, for a given total smoke exhaust volume flow rate, increasing the number of exhaust vents is an effective way of controlling the smoke layer interface height. For the kind of tunnel as studied at hand, open the exhaust vents in the fire located compartment and its downstream smoke compartment is recommended.

Numerical evaluation on the smoke control strategies and parameters for the road tunnel with converging junctions

Different smoke control strategies for the road tunnel with converging intersections are evaluated by the numerical method, and the optimum control strategy and longitudinal velocities are obtained. The results shown that when the fire occurs at the upstream to the intersection, longitudinal smoke control with the critical velocity can only prevent the backflow of the smoke at the main tunnel. The smoke can spread in the downstream ramp tunnel due to the stack effect, and this would be dangerous for the cars and the persons. The best smoke control strategy under this condition is that the longitudinal smoke control is implemented both in the main tunnel and the ramp tunnel, then the small longitudinal velocity in the ramp tunnel can prevent the smoke flowing in, this will be safe and economic.

A numerical study on the feasibility and efficiency of point smoke extraction strategies in large cross-section shield tunnel fires using CFD modeling

The strategy of smoke control is of high importance for the design process of tunnels, especially for long and large cross-section tunnels. The South Hongmei Rd. Tunnel (SHT) located in Shanghai, China, is a 3.39 km long shield TBM (tunnel boring machine) tunnel with an external diameter of 14.5 m. The point smoke extraction system was proposed initially as the main ventilation strategy during a tunnel fire. To investigate the fire characteristics in the tunnel and develop appropriate smoke control strategies, a series of numerical 3D Computation Fluid Dynamics (CFD) simulations were conducted. Three fire scenarios, namely 5 MW, 20 MW and 50 MW, were modeled to evaluate the point extraction system. The gas temperatures, the stratification of the smoke, air temperature, minimum visibility etc., during the smoke spreading of a fire were analyzed. Based on the results of the simulation, the smoke extraction strategies according to fire scale and fire location were proposed for fire extinguishing. It was found that the three-point extraction opening strategy can control the smoke better than two-point extraction opening strategy under various fire scales, especially under serious fire scenario. From the results, damper openings ranged at closer intervals were found more efficient in two-point extraction system. Besides, placing the damper openings in the longitudinal direction can improve the efficiency of smoke extraction. It also results in reduction of the quantity of prefabricated members of duct slab and the process of assembly will be simplified during the construction.

Numerical assessment of conventional regulation effectiveness for smoke removal from a two level underground station

The effectiveness of an underground smoke control system mainly depends on fire safety engineering that is provided, and which is generally established using smoke spread field and temperature distribution predictions. In the present study, smoke spread and temperature predictions are carried out for a typical two level underground station, under conventional smoke control regulation. The aim is to examine the effectiveness of the conventional regulation and, to look for better smoke control strategies which ensure safe evacuation operations. To this end, an in-depth investigation is carried out on selected ventilation strategies. The calculations are made using FDS code. Results highlight the ineffectiveness of the conventional regulation for some zones of the station and showed irrefutable positive impact of blowing with a moderate flow rate, and the implementation in the vicinity of the stairways of smoke barriers, when smoke control strategy through tunnels is performed. Keywords: underground station; conventional regulation; ventilation strategies; smoke temperature; smoke barriers

Study on Smoke Control Strategy in a High-rise Building Fire

During the high-rise building fire, it is crucial to win the time for occupant evacuation. One of the possible methods is to utilize HVAC operations to control/slow down smoke propagation on the fire floor. It is also possible to supply fresh air to the path of the evacuation so that occupants will not breathe into the poison gases. HVAC operations can control heat change and smoke conditions and change the fluid flow directionally so that it is possible to optimize the HVAC operations to make the building safer during fire. In this paper, the effects of HVAC operations, air supply system and mechanical smoke exhaust system will be studied. A smoke propagation model using the Large Eddy Simulation will be developed to study the smoke propagation under different HVAC operations. Simulation results show the temperatures at the fire room exit for different supply air quantities. Results also show that smoke propagation method is affected by the building construction, air supply and smoke exhaust system. The smoke control strategy is investigated.

Study on Smoke Control of Wuhan CBD Urban Traffic Link Tunnel

Abstract An Urban Traffic Link Tunnel (UTLT) is a novel type of underground transportation system consisting of a main tunnel in a loop shape and several linked tunnels. It has a higher level of fire risk compared to other common road tunnels. In this study, numerical and experimental study has been conducted to investigate the smoke control of Wuhan Central Business District (CBD) UTLT. The transient distributions of the smoke spread have been analyzed, and the optimal smoke control strategy for the Wuhan CBD UTLT has been put forward.

Simulation research on natural smoke ventilation and external airflow in large space: Case study of the improvement project of Taoyuan International Airport, terminal 1

The paper analyzed the influence of external airflow on natural smoke ventilation in large space by means of computational fluid dynamics (CFD) and engineering calculation. The purpose of the paper is Terminal 1 of Taiwan Taoyuan International Airport after renovation. In the renovation project, the separate departure and arrival halls will be connected to create a large atrium; natural smoke ventilation will be adopted as the smoke control strategy for the new space. As external airflow may directly impact natural smoke ventilation, the study means to investigate the extent to which external airflow influences natural smoke ventilation by analyzing scales of fire and presence of external airflow. Conclusions of the study are as follows: 1) when directly affected by headwind, entrances and exits on the first floor pose danger to the safety of certain parts of the floor; 2) when directly affected by headwind, natural smoke ventilation becomes weaker than when unaffected; 3) in the case study, natural smoke ventilation proves effective under the premise that the scale of fire is less than 2000 kW. Key words: Airport terminal, natural smoke ventilation, external airflow, evacuation safety, FDS.

Numerical Study on Effects of Induced Velocity on Central Extraction System in Large Tunnel Fire

Abstract The effects of different induced velocities on the central extraction system for a tunnel are investigated for a 100MW fire scenario. Computer modeling is used for the investigation with a numerical simulation method. The selection of five different induced velocities is evaluated and compared. The smoke control strategy in this study is downstream dampers in the vicinity of fire site opened with number of three and the upstream jet fans supplying airflow as the induced velocity. Distributions of smoke propagation, temperature and visibility in variation of induced velocities are analyzed. The results show that larger induced velocity is needed to restrict smoke to the region between the fire site and the damper openings for safe evacuation. Additionally, the gradients of upstream temperature decreases as the induced velocity increases. The results also suggest that the impacts of the induced velocity on the upstream visibility have a correlation with the back layering.