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15 September 2024, Volume 43 Issue 9 Previous Issue    Next Issue

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Research progress on fire safety protection of electric vehicles in urban traffic tunnels Li Yanfeng, Du Tianmei, Liu Shuang, Dong Qiwei 2024, 43 (9):  1195-1203.  Abstract ( 2578 )   The increase in the number of urban electric vehicles brings new challenges to urban traffic tunnel fire safety belts. The paper first summarizes the scientific and key technical issues related to the study of electric vehicle fires in tunnels, and then presents research findings in areas such as the causes of electric vehicle fires and research methodologies, thermal characteristics of fire combustion, characteristics of fire combustion products, etc. It also examines the impact of the narrow and confined environment of tunnels on the development of electric vehicle fires and discusses fire rescue strategies for electric vehicle fires in urban traffic tunnels. According to current fire safety standards and tunnel fire design guidelines, the key points for improving the design of fire protection systems in traffic tunnels to address electric vehicle fires are discussed. Research indicates that fire incidents involving new energy vehicles are more complex compared to those involving conventional fuel-powered vehicles. This complexity is primarily manifested in unstable battery ignition sources, prolonged durations, peak heat release rates, peak temperatures, and the risk of electric vehicle electrification. Moreover, there remains a lack of systematic studies on the influence of confined tunnel spaces on battery combustion characteristics, the characteristics of plumes generated by electric vehicle fires, as well as the spread and control of toxic smoke. The findings of this study can provide valuable insights for the design of fire protection systems in urban traffic tunnels, ensuring safe operations, and formulating emergency response plans. Related Articles | Metrics

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Overview of the research progress of TOD building fire protection in underground rail transit An Weiguang, Lu Jiaming, Yuan Diping, Chen Jiaxiang 2024, 43 (9):  1204-1212.  Abstract ( 75 )   In order to understand the progress of fire research on underground rail transit TOD buildings and to provide research ideas and references, a typical underground rail transit TOD building is taken as the research object, and the current status of TOD fire research is sorted out from the three angles of TOD structural fire hazards, current research progress and specification interpretations, and the outlook of the research direction to explore the fire risks that are easily neglected and the possible fire protection problems, and the results of the analyses show that: The combination of the traditional structures of aboveground shopping malls, underground commerce, and underground rail transit in rail transit TODs will present a more complex structure, which makes the overall fire risk of TODs increase dramatically. The domestic fire code for TOD is too scattered, not taking into account the complexity of the TOD scene, there is an urgent need to establish TOD fire design system. Underground rail transit TOD-related research is carried out slowly, and there is a lack of fire research on the overall TOD interactions, interconnections, and smoke control and exhaust. Future researchers should first focus on solving the key technical problems of ventilation and smoke exhaust, monitoring and warning, personnel evacuation, and lack of special emergency equipment in TOD buildings. Therefore, it is important to carry out continuous research on TOD building fires, establish a proprietary fire protection system, and develop related technologies. Related Articles | Metrics

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A review of research on cable fire in power cabin of utility tunnels Xu Desheng , Li Yanfeng , Yang Quan 2024, 43 (9):  1213-1217.  Abstract ( 2535 )   The safe management of utility tunnel is crucial for re⁃ silient cities. Analyzing the causes of power cabin fires, fire char⁃ acteristics and the special measurements of fire safety, the key sci⁃ entific issues of cable fires in utility tunnels are summarized. From the three aspects of cable fires, such as combustion dynamic mechanism, risk assessment and fire detection and protection, the overall progress of the research on power cabin fires in utility tunnels are summarized. The results show that the current re⁃ search have been achieved in the basic theory and practical applica⁃ tion of power cabin fires. However, there is a lack of in-depth dis⁃ cussion on the impact of complex tunnel structural factors on fire development. The flame spread of cable fires in long ventilation compartments and effective fire prevention and automatic control are important issues for future research on utility tunnel fire pro⁃ tection systems. Related Articles | Metrics

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Research status and future prospect of the development and spread law of spill fire in tunnel Ye Chenghao, Zhang Peihong 2024, 43 (9):  1218-1226.  Abstract ( 1416 )   In the tunnel environment, the combustion dynamics of spill fires, encompassing phenomena such as flame bifurcation fusion, oscillations, and tilting, coupled with the fluidic behavior of diffused fuel layers and heat transfer interactions with the tunnel's bottom wall and flame smoke, exhibit significant complexity and instability. These complexities heighten the risk of igniting neighboring combustible materials, posing significant threats to human life and property safety. The present study delves into a comparative analysis of the diffusion, combustion characteristics, flame height, oscillations, heat radiation models, heat transfer mechanisms, smoke dissemination, and ceiling temperature escalation models of oil spill fires in both open spaces and tunnel environments. Notably, it highlights the need for further research to refine our understanding of flame oscillations, heat radiation models, and other flame behavioral patterns. By elucidating the heat transfer mechanisms, unsteady combustion dynamics, and smoke dispersal dynamics of spill fires, this work provides vital theoretical and technological underpinnings for the prevention and emergency response strategies against tunnel flow fires. Related Articles | Metrics

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Study on smoke stratification stability in inclined tunnel fire Sun Chaopeng, Liu Fang, Weng Miaocheng 2024, 43 (9):  1227-1233.  Abstract ( 1559 )   The smoke stratification characteristics in the tunnel play an important role in analyzing the difficulty of evacuation and rescue and formulating effective emergency strategies. The smoke flow in inclined tunnels is affected by both buoyancy and stack effect, resulting in significant differences in the distribution and movement of smoke between inclined tunnels and horizontal tunnels. In inclined tunnels, the stability of smoke stratification is affected by many factors, and there are few related studies. In this paper, the numerical simulation method is used to study the smoke distribution characteristics and its influencing factors of inclined tunnel fires with openings at both ends with an inclination angle of 1%～15%. The research shows that the critical dimensionless temperature difference proposed by Newman to determine the stratification state of smoke is still applicable in inclined tunnel fires (the slope is within the range of 1%～15%). After the fire in the inclined tunnel, the smoke layer between the fire source and the low-end entrance can always maintain a stable smoke stratification. The smoke layer between the fire source and the high-end outlet increases with the chimney effect, and the area where the stable stratification is destroyed continues to expand and gradually expands to the entire downstream area. The fire source power and the height difference between the fire source and the high-end outlet can directly affect the stack effect in the tunnel and the smoke buoyancy, thus affecting the smoke stratification state. On this basis, a calculation model for predicting the smoke stratification characteristics of inclined tunnel fires is proposed, and the critical Froude number between zone 1 and zone 2 is determined to be 0.9. The research conclusions can provide useful reference for tunnel fire smoke exhaust and evacuation design. Related Articles | Metrics

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Research on the impact of shaft aspect ratio on natural smoke exhaust performance of tunnel shafts in high-altitude tunnels Gao Zihe, Cai Jiajun Fan, Chuangang, Zhong Wei 2024, 43 (9):  1234-1239.  Abstract ( 61 )   By using FDS numerical simulation software, the impact of the shaft aspect ratio on the smoke flow and the performance of shaft natural smoke exhaust under different ambient pressures is studied. The study considers the shaft aspect ratio and ambient pressures, and analyses parameters such as temperature and flow field distribution near the shaft, and the amount of each component in the smoke exhausted from the shaft. The study results showed that the increase of the shaft aspect ratio caused the smoke exhaust capacity to first decrease and then remain stable while keeping the shaft cross-sectional area constant. In the case of the shaft aspect ratio is too small, eddy will be generated at the shaft opening, which will reduce the smoke exhaust capacity. The increase in ambient pressure results in an increased stack effect and a slight increase in smoke exhaust capacity, while it can make plug-holing more likely to occur. Therefore, for the design of natural smoke exhaust systems in high-altitude tunnels, setting a proper shaft aspect ratio is convenient for exhausting more smoke and improves the smoke exhaust capacity. Related Articles | Metrics

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Study on the effectiveness of single-sided and double-sided mechanical smoke exhaust in the upper lane of a double-layer Wang Enshi , Wang Zhan, Tang Zhi 2024, 43 (9):  1240-1246.  Abstract ( 25 )   To investigate the impact of single-sided and double-sided mechanical smoke exhaust on fire smoke control and spread at the upper lane in a double-deck tunnel, FDS was used to conduct a comparative study on the smoke control effectiveness in a typical double-deck tunnel under different exhaust control modes.Based on illustrating the rationality of the model, the smoke spreading distance, gas mass flow rate and temperature distribution at the smoke exhaust vent were comparatively analyzed under different smoke exhaust fan opening modes. The study showed that the gas mass flow rate distribution at the smoke exhaust outlet shows different patterns when the exhaust fan is activated on the single-side or double-side. When the smoke exhaust fans on both sides of the tunnel are turned on, the smoke spread range is the smallest, which is 47.8%~88.1% of the exhaust fan on the downstream side of the tunnel are opened under the same smoke exhaust volume. And the average temperature at each smoke exhaust outlet is lower, which comprehensively reflects that turning on the smoke exhaust fans on both sides of the tunnel has a better smoke control effect. In addition, the variation of the tunnel smoke spread range with the fire source position under the single-side and double-side smoke exhaust modes was also discussed. Related Articles | Metrics

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Study on the effect of tilted air baffle below the sidewall exhaust vent to improve the lateral smoke exhaust performance Zhang Shaogang, Li Shangyang, Liu Jiahao , Wang Jinhui, Cong Beihua 2024, 43 (9):  1247-1252.  Abstract ( 30 )   To study the lateral smoke exhaust performance with the air baffle, the characteristics of temperature field and flow velocity vector field near the lateral exhaust vent, as well as the smoke exhaust efficiency, were explored under the air baffle with different tilt angles. The results show that the air baffle below the lateral exhaust vent can effectively inhibit the inflow of cold air and improve the performance of lateral smoke extraction. After the air baffle is set below the sidewall vent, the streamline of the hot smoke near the vent increases significantly, and the cold air streamline becomes sparse, and the high-temperature smoke area in the lateral vent increases with the tilt angle of the baffle. When the exhaust vent aspect ratio is 1：2, the lateral smoke exhaust efficiency is increased with the larger title angle of air baffle within 0≤θ≤45°, and then remains basically unchanged with the larger title angle of air baffle, achieving the best lateral smoke exhaust performance within 45°≤θ≤60°. When the vent aspect ratio is 2：1, the lateral smoke exhaust efficiency is increased with the larger title angle of air baffle within 0≤θ≤30°, and it shows decrease trend with the larger title angle of air baffle within 30°≤θ≤60°, achieving the best smoke exhaust performance at 30°. Finally, a prediction model of lateral exhaust efficiency under air baffles with different tilting angles is obtained through data fitting, which can provide a corresponding technical guidance for the design of tunnel lateral smoke exhaust system. Related Articles | Metrics

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Experimental study on critical ventilation speed in asymmetric herringbone tunnel fire Guo Zhicheng, Li Junmei, Ouyang Li, Li Yanfeng 2024, 43 (9):  1253-1258.  Abstract ( 22 )   Herringbone tunnels are often found in mountain tunnels and new-built urban traffic tunnels. The smoke flow is complicated in case of fire and controlling the smoke effectively with longitudinal ventilation is relatively difficult. By setting up a 1：20 herringbone tunnel model test rig, the critical ventilation speed under different slope composition and different fire power in asymmetric herringbone tunnel was studied. The results show that when the longitudinal ventilation flows from the small slope side to the large slop side, the critical ventilation speed is greater than that in the normal tunnel with the same tunnel cross-section and same fire power. The critical ventilation speed increases with the increase of the slope difference on both sides of the variable slope point. When longitudinal ventilation flow from large slope side, the critical ventilation speed is less than that in the normal tunnel, and the critical ventilation speed decreases with the increase of the slope difference. For the engineering application, the slope correction of the critical ventilation speed model of the normal tunnel is carried out based on the experimental results, and the correction coefficient of the critical ventilation speed is obtained. Related Articles | Metrics

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Experimental study on smoke spread characteristics and temperature distribution in tunnel fire during construction 邱明轩, 于伟, 徐琳, 赵英浩 2024, 43 (9):  1259-1265.  Abstract ( 23 )   In order to study the smoke spread characteristics and smoke temperature distribution in construction tunnel fire under different longitudinal fire source locations and heat release rates, a reduced-scale construction tunnel model was established by using the model⁃scale experiment method. The longitudinal and vertical smoke temperature distribution under the tunnel ceiling was measured. The results show that under the condition of natural smoke exhaust, the smoke can not be discharged in time inside the construction tunnel, and then hit the wall to form a rebound smoke flow, which continuously settled to about 0.1 m above the tunnel floor. The longitudinal fire source location has great influence on the smoke spread speed and the longitudinal temperature attenuation rate. As the fire source moves to the left closed end, on the right side of the fire source, the smoke spread speed increases and the longitudinal temperature attenuation rate decreases. For the left side of the fire source, the smoke spread speed decreases and the longitudinal temperature attenuation rate increases. The dimensionless vertical smoke temperature rise accords with the self-similarity law, showing a composite function distribution. Considering the influence of longitudinal fire source location and heat release rate, the variation of the smoke spread velocity is summarized, and the experimental correlations are established to predict the vertical smoke temperature distributions under the tunnel ceiling. Related Articles | Metrics

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Study on smoke maximum back-layering length in a ventilated inclined tunnel fire Wu Shuangliang 2024, 43 (9):  1266-1271.  Abstract ( 30 )   In order to study the feasibility of fire smoke control in inclined tunnel by using environmental wind induced by stack effect, a systematic study on smoke flow distribution in inclined tunnel under the effect of environmental wind was carried out. The influence of stack effect caused by tunnel slope on smoke flow distribution in inclined tunnel is revealed, and the asymmetric flow effect of smoke in inclined tunnel under natural ventilation is analyzed. Result shows that as the elevation difference increases,the mass flow rate of smoke and air flowing in the positive direction increases from 50% to a value close to 100%, while that flowing in the negative direction decreases from 50% to a value close to 0%. By using elevation difference as the characteristic parameter, the empirical formula of mass flow rate of outflowing smoke and entraining air is presented. In addition, the prediction formula of maximum smoke back-layering length is proposed. Related Articles | Metrics

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Analysis of differences and feasibility of critical velocity models for tunnel fires Sun Feng , Li Jiangdong, Wang XiaofeiWu Ke 2024, 43 (9):  1272-1277.  Abstract ( 2057 )   Critical velocity is an important indicator of the smoke control design for longitudinal ventilation tunnel fires. Currently, two calculation methods, i.e., the critical Froude model (recommended by the World Road Association, PIARC) and the piecewise function model (recommended by National Fire Protection Association, NFPA) are widely adopted in practice. Nevertheless, the calculation result of the two models shows a significant difference, causing confusion and disagreement regarding tunnel fire safety design. This work analyzes the differences between the PIARC equation and the NFPA equation under various heat release rates, tunnel widths, and tunnel heights, respectively and the reasons are discussed in detail. Then, the smoke control performances and feasibilities of these two models are compared with a set of numerical simulations, full-scale and reduced-scale test data. Results show that the PIARC equation fails to describe the correlation between critical velocity and heat release rate due to the fixed Frc value and unrealistic uniform mixing assumption. The PIARC equation will underestimate the critical velocity and the error increases with the tunnel aspect ratio. The NFPA formula comprehensively considers the impact of the relationship between the fire plume and the tunnel structure on critical velocity. Therefore, the prediction shows a better smoke control performance and agrees well with physical test data. Moreover, realistic factors, e.g., blockage, altitude, fire source rising, and lateral locations will also affect the value of critical velocity and should be considered in future work. Related Articles | Metrics

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Study on the selection of exhaust volume enrichment coefficient of ceiling exhaust system under the influence of air leakage Fan Xinyang, Tang Fei, Huang Yajun, Hu Longhua 2024, 43 (9):  1278-1285.  Abstract ( 1271 )   In order to study the exhaust volume enrichment coefficient of ceiling exhaust system under the influence of air leakage, a solution model of air pressure and air volume of ceiling exhaust system was established, and the accuracy of the model was verified by comparing with the full-scale test data. Based on the model, we analyzed the air pressure and air volume distribution under different design heat release rates, tunnel lengths, exhaust vent spacing and exhaust vent areas, and studied the exhaust volume enrichment coefficients under each parameter. The results show that: with the increase of heat release rate, the designed exhaust volume increases gradually, but there is no obvious correlation between the exhaust volume richness coefficient and the heat release rate. For the case of using high-tight exhaust vent, when the length of the tunnel is less than 10 km, the exhaust volume enrichment coefficient to meet the exhaust demand is below 10%. In the case of ordinary exhaust vent, the exhaust volume enrichment coefficient is almost always over 20% for both extra-long tunnels and super-long tunnels, and even over 100% when the length of the tunnel exceeds 9 km. With the expansion of the exhaust vent spacing, the exhaust volume enrichment coefficient and the designed exhaust volume show a consistent decreasing trend. With the increase of the exhaust vent area, the designed exhaust volume gradually increased, and the exhaust volume enrichment coefficient also has a similar trend, especially the common exhaust vent is more obvious. Therefore, in order to meet the demand for smoke exhaust, improving the quality of exhaust vent, expanding the spacing of exhaust vent and reducing the exhaust vent area can play a role in reducing the effect of exhaust volume enrichment coefficient. Related Articles | Metrics

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Study on the roof fire characteristics of running train in a tunnel Fan Xinyang, Tang Fei, Huang Yajun, Hu Longhua 2024, 43 (9):  1286-1291.  Abstract ( 34 )   In order to study the fire development characteristics of high-speed running train roof fires in subway tunnel, a series of moving fire experiments were conducted on a constructed downscaled tunnel train model, setting up different train running speeds and heat release rates, and full-scale numerical simulations were combined to reveal the evolution law of the fire characteristics of high-speed train roof fires in a tunnel（20～150 km/h）. The experimental results show that the maximum temperature on the train roof shows a trend of increasing and then decreasing with the increase of train running speed, in which the maximum temperature change reaches 205 °C; Moreover, with the increase of train running speed, the vertical flame height gradually decreases, and the horizontal flame length shows a trend of increasing and then decreasing, and the critical running speed increases with increasing heat release rate, which is verified by numerical simulation. Combined with the scaled-down experimental study, a segmented prediction model of the flame length of the roof fire of the running train in the tunnel was proposed. Related Articles | Metrics

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Fire source location and heat release rate inversion in tunnel fires based on deep learning Jiang Li, He Tingquan, Guo Xin, Yang Dong1 2024, 43 (9):  1292-1297.  Abstract ( 51 )   The fire source location and heat release rate （HRR） are crucial information guiding emergency firefighting and rescue perations during tunnel fires. However, in practice, the information that can be obtained about the fire is limited. It is difficult to get the fire source key parameters directly. Therefore, we researched the deep learning-based method for inversing thefire source location and HRR in tunnel fires. Firstly, a tunnel fire dataset under different boundary conditions is established based on numerical simulations validated by experimental data. Based on convolutional neural network （CNN） and long short-term memory network （LSTM）, the mapping relationship between fixed temperature sensor data and fire source location and HRR was established. The inversion effectiveness of the model for fire source parameters was evaluated. And the effect of time series length and sensor spacing on the inversion effectiveness were evaluated. The results demonstrate that the model has good inversion performance for both HRR and fire source location. When the time series length was 20 s and the sensor spacing was 30 m, the R2 values of the model inversion for HRR and fire location are 0.97 and 0.99, respectively. Related Articles | Metrics

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Numerical calculation of temperature distribution of lining based on standard fire curve and heat release rate Liu Qiulin1, 3, Zhang Chao2, Xu Zhisheng3, Tao Haowen1 2024, 43 (9):  1298-1302.  Abstract ( 28 )   In order to find out the temperature distribution characteristics of the lining under fire, a one-dimensional numerical calculation method of heat transfer lining temperature was established based on the mathematical model of tunnel fire-lining radiative convective heat transfer. The HC standard fire curve and the fire condition of 30 MW fire heat release rate were calculated and analyzed. The results show that the maximum temperature of the standard fire curve is generally greater than that required by the current Chinese code. Using fire temperature as the boundary condition for the lining wall will significantly increase the temperature wad on the lining. The maximum temperature of the lining is 778 °C and 351 °C under the 2 hour HC fire curve and the 30 MW fire condition, respectively. The influence range and high temperature value of the lining inside the standard fire curve condition are significantly greater than those of the 30 MW fire condition. Related Articles | Metrics

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Influence of mainline slope on ceiling temperature distribution in mainline tunnel of bifurcated tunnel Liu Xi, Wang Bin Li Cheng, Huang Youbo, Dong Bingyan 2024, 43 (9):  1303-1308.  Abstract ( 21 )   In order to study the influence of mainline slope on fire smoke spread in mainline tunnel of bifurcated tunnel, the numerical simulation method was used to analyze the temperature distribution in tunnel under different mainline slope and fire source power of the mainline before the bifurcation. A maximum temperature rise prediction model of tunnel ceiling and a longitudinal temperature rise attenuation prediction model of downstream mainline tunnel were proposed considering mainline slope and fire source power. The results show that under the given heat release rate, the maximum temperature rise in the tunnel decreases with the increase of the mainline slope. The larger the slope of the main tunnel, the more obvious the inclination of the plume flow downstream of the main tunnel, and the maximum temperature under the ceiling shifted downstream. The thickness of the smoke layer in the downstream of the main tunnel decreases with the increase of the tunnel slope, and the longitudinal temperature rise in the downstream of the main tunnel also decreases. Related Articles | Metrics

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Study on equivalent longitudinal velocity and temperature field in the single slope V-shaped tunnel fire Wu Dongyang , Zhu Yu , Yin Yaolong, Xu Zhisheng 2024, 43 (9):  1309-1315.  Abstract ( 25 )   When the fire occurs near the slope change point of the underwater tunnel, the tunnel structure can be simplified into a single slope V-shaped tunnel. The smoke movement of the single slope V-shaped tunnel is affected by the stack effect. In this study, FDS numerical simulation research method is used to study the equivalent longitudinal velocity and tunnel temperature field in the single slope V-shaped tunnel fire under natural ventilation and establish a prediction model. The results show that the equivalent longitudinal wind speed generated by fire is related to the tunnel slope height and heat release rate, and its value is proportional to the 1/3 power of the heat release rate and the dimensionless slope height. The maximum temperature rise of smoke under the roof of a single slope V-shaped tunnel decreases linearly with the increase of slope. The temperature distribution of smoke downstream of the entire fire shows an exponential decay, and the steeper the slope, the more obvious the temperature decay of longitudinal smoke around the fire source, and the steeper the decay curve. Related Articles | Metrics

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The influence of water spray on fire suppression performance and ceiling temperature of tunnel shelter fire Yang Tao, Yu Zhihua, Wang Zhan, Li Qinwen, Tang Zhi 2024, 43 (9):  1316-1321.  Abstract ( 35 )   As an effective firefighting facility, water spray system is widely used in tunnels. Based on a 1:8 reduced scale double-layer tunnel platform (36 m long and a clear height of 0.58 m for each single-layer tunnel), this study carried out experiments in the lower deck space of the model and explored the effects of water spray system working pressure, opening time, spray section and number of opening sections on the fire control effect. Findings reveal a dual effect of water mist interaction with flames, with both enhancing flame intensity and inhibiting combustion, the latter being more pronounced with higher water spray pressures. When the water spray pressure exceeds 0.30 MPa, fire suppression becomes the dominant factor. The extinguishing time of fire source decreases with the increase of water spray sections. The earlier the water spray system is started, the more quickly and effectively the fire temperature can be controlled at alower level, while delayed activation leads to high-temperature vaporization, hindering combustion and attenuating fire progression. Importantly, the water spray sections have a significant influence on the temperature distribution in tunnel. Related Articles | Metrics

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Evaluation of fire service accessibility of extra-long road tunnels from a regional perspective Zhou Tian, Jiang Hong, Liu Dingli , Liu Weijun 2024, 43 (9):  1322-1327.  Abstract ( 32 )   Fire rescue in special highway tunnels has always been a challenge in the fields of public safety and highway transportation. Due to the characteristics of "long line type and double hole separation" of extra long highway tunnels, the accessibility of fire rescue varies greatly in different sections and driving directions, making it difficult to accurately evaluate using existing methods. Therefore, this article collects fire rescue demand points equidistant from different driving directions of lanes in a special highway tunnel, and then calculates the average travel time of fire rescue demand points to measure the accessibility of fire rescue. A time weighted evaluation model for the overall average accessibility of fire rescue in regional extra long highway tunnels has been established. To verify the effectiveness of the model, taking the extra long highway tunnel in Guizhou Province as an example, a total of 960 fire rescue demand points were collected, and the real-time rescue travel time was simulated through the network map application programming interface. 337 estimation scenarios were set up throughout the entire week (7 consecutive days), and a total of 323 520 valid evaluation samples were obtained. The overall average accessibility of fire rescue in Guizhou Province's extra long highway tunnels is calculated to be 0.242, with an average travel time of 2 560.68 seconds and an average travel distance of 32 870.18 meters. The result level is "poor", indicating that the accessibility of fire rescue in this area's extra long highway tunnels is low. From the perspectives of safety and economy, dedicated fire brigades can be established for extra long highway tunnels, and fire rescue points can be set up at toll stations or service areas along highways. The evaluation model proposed in this article can provide key methods and data support for enhancing the fire rescue capabilities of extra long tunnels from a regional perspective. Related Articles | Metrics

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Research on optimizing liquid nitrogen fire extinguishing efficiency in urban underground logistics systems through enhanced Ning Zhaoyu , Yuan Diping, Zhang Guowei, Xu Dunbin 2024, 43 (9):  1328-1334.  Abstract ( 41 )   Fire suppression systems commonly used in narrow and confined spaces have limitations when applied in urban underground logistics systems, making them difficult to implement directly. To investigate the improvement in liquid nitrogen extinguishing efficiency under the influence of enhanced longitudinal ventilation in urban underground logistics systems, this study analyzes the changes in oxygen volume fraction and ceiling temperature under different working conditions by varying wind speed and nitrogen injection position. The results indicate that nitrogen injection can effectively extinguish fires in underground logistics tunnels, and enhanced longitudinal ventilation significantly improves the extinguishing efficiency of liquid nitrogen. When the nitrogen injection distance is 50 m, the extinguishing efficiency under a wind speed condition of 2 m/s is increased by 41.86% compared to a wind speed condition of 0 m/s. Additionally, at a fixed nitrogen injection distance, enhanced longitudinal ventilation significantly advances the time when the temperature and oxygen volume fraction near the fire source begin to decline. Moreover, as the nitrogen injection distance increases, the time for the temperature and oxygen volume fraction near the fire source to decline is delayed; however, enhanced longitudinal ventilation can mitigate the lag in cooling and asphyxiation effects caused by the increased injection distance. These findings provide important theoretical support for fire suppression research in urban underground logistics systems. Related Articles | Metrics

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Experimental study on smoke control mode of longitudinal ventilation in existing subway station Duanmu Xiangling, Yang Zeyu, Zhang Wenbin, Wei Xiaoli 2024, 43 (9):  1335-1340.  Abstract ( 25 )   By the experiment on the existing railway station in Beijing, the smoke spread law and downdraft velocity under different smoke control conditions are analyzed. At the same time, the numerical simulation model corresponding to the actual size is established by FDS, and the working condition of smoke control mode change is added. Based on the available safe egress time judgment of the visibility, the smoke exhaust capacity in platform is studied. The results show that: for different smoke control modes, the smoke spreading law is not consistent. For the existing station, opening all fans and only opening No.1 fan will cause negative pressure at the staircase, that is, the smoke from the fire on the platform will not spread to the station hall; the analysis of the downdraft airflow velocity of the staircase section shows that the opening of all fans meets the requirements of the standard downdraft airflow velocity of the staircase of 1.5 m/s, while only opening No.1 fan, one side of the platform cannot meet the requirements of the standard; on the basis of the analysis of the smoke spreading law and the section wind speed, it is known that No.1 fan plays a main role in the station safety; combined with the test data of the staircase section wind speed and the simulated data of the available safe egress time judgment of the visibility, it is known that opening all fans greatly improves the safety of the station hall compared with only opening No.1 fan, but has little effect on the smoke exhaust capacity of the station. Related Articles | Metrics