In emergency evacuations where real-time access to comprehensive information on the incident environment and crowd conditions is limited and rescue resources are constrained, rescue strategy selection significantly influences evacuation efficiency. This work examine the following question: Under these constraints, should rescuers prioritize Nearest Response Rescue (NR), Maintain Rescue Mission (MM), or combined strategy to maximize overall efficiency? We developed a cellular automaton evacuation model that considers rescue and guidance behaviors and integrates diverse crowd movement patterns, rescue search, rescue target selection, and guidance strategies to investigate dynamic crowd interaction processes under coupled rescue and guidance behaviors. Additionally, we developed search floor field to represent rescue search under limited situational awareness and multi-objective target selection model based on distance and local density. Based on the proposed model, the efficiency differences of NR, MM, and combined strategies across key evacuation parameters are compared, with a focus on their applicability under insufficient rescue resources. Simulation results indicate that evacuation efficiency under different strategy combinations depends on crowd characteristics and contexts (e.g., crowd size, injured pedestrians or guides' initial distribution). Moreover, various strategies under varying parameters can achieve different optimal efficiencies, such as maximizing overall evacuation efficiency or minimizing time to rescue injured pedestrians.

Objective Liquid fuel leakage on sloped porous media, such as loess, is a common hazard in oil storage, transportation, and the chemical industry in the loess-covered areas of China. On inclined terrain, the gravity effect changes the seepage and the heat and mass transfer of liquid fuel inside the porous medium, which accelerates fire spread and expands the thermal influence range. Most existing studies on liquid fuel fire spread over porous media adopt quartz sand as the research medium, while the pore structure, permeability, and adsorption characteristics of natural loess are obviously different from those of quartz sand; therefore, the existing conclusions cannot be directly applied to loess fire scenarios. In addition, the coupling mechanism between base inclination angle and ignition position on fire spread behavior has not been systematically clarified. It is therefore of practical significance to explore the fire spread rules of kerosene-infiltrated loess under different inclination conditions, which can provide theoretical support for fire prevention, risk assessment, and emergency disposal in loess areas. Methods In this work, a self-designed experimental platform with an adjustable inclination angle was adopted to carry out a series of fire spread experiments. Dry loess with a particle size range of 0.116u20133.675 mm was paved evenly in the experimental tank to form a uniform porous medium bed. Kerosene was injected slowly into the loess bed in multiple small doses until the medium reached full saturation. Seven working conditions with equivalent inclination angles of u22129u00B0, u22126u00B0, u22123u00B0, 0u00B0, 3u00B0, 6u00B0, and 9u00B0 were set by combining different base angles and ignition positions. Anhydrous ethanol was used as the ignition source in the designated ignition area to initiate combustion, and the total duration of fire spread was set to 20 min. A high-definition camera with a frame rate of 50 frames per second was arranged 100 cm away from the experimental platform to record the evolution of flame morphology and the spread process. Meanwhile, 12 K-type armored thermocouples with a probe diameter of 0.5 mm were arranged in a 6 u00D7 2 array to synchronously measure the temperature distribution on the surface and inside the loess bed along the axial direction. All flame characteristics, spread velocity, and temperature data were collected and analyzed quantitatively. Results The experimental results revealed that the coupling effect of inclination angle and ignition position exerted a prominent influence on flame structure and propagation. Under the same inclination angle, the flame height and propagation distance of lower-end ignition were greater than those of upper-end ignition. For the upward fire spread on positive inclination bases, the height of the yellow flame zone increased with the rise of inclination angle; for the downward fire spread on negative inclination bases, the height of the yellow flame zone gradually decreased as the inclination angle increased. The flame spread at a constant velocity under all working conditions, and the spread velocity rose monotonically with the increase of inclination angle. The velocity of upward spread was obviously higher than that of downward spread under the same absolute inclination value. When the flame front arrived at the measuring points, an obvious layered heat transfer feature was observed: the surface heating rate of loess was far higher than the internal heating rate. Compared with the horizontal base, the inclined base presented a lower steady combustion temperature, a shorter time to reach thermal stability, and a larger internal temperature gradient inside the loess bed. Conclusions The base inclination angle changes the fuel seepage path and the intensity of heat feedback through gravity, and further regulates flame morphology, spread velocity, and the internal temperature field of the loess bed. The layered heat transfer characteristics of the loess bed are determined by differences in heat transfer mechanisms between the surface and the internal porous structure. The results clarify the mechanisms by which inclination angle and ignition position influence fire spread in kerosene-wetted loess. These findings can provide guidance for the design of fire isolation zones, the development of emergency response plans, and the optimization of firefighting strategies in sloped loess terrains. They also lay a foundation for further study on the evolution of fire hazards associated with liquid fuel leakage on loess substrates.

Abstract An extended floor field model, incorporating rescue behavior and pedestrians' movement decisions based on flood depths, is proposed to study pedestrian evacuation dynamics during subway flooding. Pedestrians' movement decisions are influenced by floodwater depth and can be classified into three stages: self-evacuation, following rescuers, or relocating to carriages to await rescue. The results indicated that evacuation efficiency increases with the number of rescuers, but this effect may plateau or even decline once a certain threshold is reached. When rescuers enter the subway from both sides, rescue effectiveness is more efficient than unilateral entry. However, increasing the number of rescuers can help close this gap. Moreover, the effectiveness of different rescue strategies depends on the flood depth. When the flood depth is below 0.5 m, increasing the number of rescuers proves more effective than reducing their arrival time. Otherwise, reducing the arrival time of rescuers becomes a more critical factor.

To better understand the resilience evolution dynamics of urban lifeline systems over extended operational periods, this study introduces a model inspired by the susceptible-infected-recovered (SIR) model, which is traditionally used to simulate population health transitions. By analyzing the mechanisms governing the performance state evolution of urban lifeline systems under disaster scenarios, integrating a disaster scenario model with resilience assessment methodologies, and comprehensively considering three key resilience components—resistance, recovery, and adaptability—we develop a system dynamics resilience‒reliability (SDR-R) model. A hypothetical case study is conducted to validate the model’s applicability. The results indicate that the interplay of resistance, recovery, and adaptability influences the dynamic evolution of system performance across three states: disability performance, survivability performance, and recovery performance. The model reveals a cyclical pattern in resilience enhancement, with adaptability emerging as a critical determinant. Moreover, the SDR-R model not only simulates urban lifeline performance state evolution under single disaster scenarios but also captures resilience evolution trends over long-term system operations. The case study findings reveal that resilience decreases as disaster severity intensifies, yet positive feedback from adaptability fosters resilience improvement over time. The process of resilience evolution can be divided into four distinct phases: initial impact, adaptive priming, adaptive enhancement, and threshold effect. Notably, resilience dynamics vary significantly across disaster levels. While systems exhibit high resilience under low-level disasters, resilience gradually stabilizes at a high level in medium- and high-level disaster scenarios. However, extreme disasters introduce greater fluctuations in resilience, underscoring the necessity for targeted resilience-enhancing strategies. The insights derived from this study offer methodological guidance for understanding urban lifeline resilience evolution and developing strategies to enhance system robustness.

In the actual installation of cables, inclined cable laying within covered cable trays is a relatively common method. To investigate the effects of different tilt angles on the combustion behavior of cables within covered cable trays, aluminum conductor polyethylene-insulated power cables were used as the test cables. The flame morphology, temperature distribution, and fire spread rate during the cable combustion process were analyzed for experimental scenarios for which the cable laying angles and the ignition positions changed. The results indicate that the inclination angle of the covered cable tray has a significant impact on flame propagation and temperature distribution. For the ignition located at the lowest part of the cable, the fire spread rate increases significantly with the tilt angle. In contrast, for the ignition located at the highest part of the cable, the fire spread rate initially decreases slightly and then increases, with a relatively smaller overall change in magnitude. Under both ignition positions, the flame spread rate significantly increases at 15–30°. Therefore, in actual cable installation processes, cables within covered troughs should avoid large-angle inclinations.

Several spill fire experiments were carried out in a reduced-scale sealed tunnel, considering different discharge rates, sealing ratios, and initial sealing time. The burning characteristics of tunnel spill fires were analyzed. The results show that in the scenario of continuous fuel leakage, tunnel spill fires will eventually fall into three different burning behaviors as the sealing ratio increases: quasi-steady combustion, unsteady combustion diffusion, and self-extinction. The fundamental reason that the sealing ratio influences the burning characteristics of tunnel spill fires is that it alters the ventilation factor at the tunnel opening, thereby affecting the maximum burning rate of the liquid fuel. This leads to variations in the relative magnitudes of the discharge rate and evaporation rate, resulting in different diffusion regimes of the tunnel spill fire. Moreover, when the tunnel exits are sealed at the quasi-steady combustion stage, the three regimes of tunnel spill fires observed are similar to those observed when the exits are sealed at the initial moment. The transition mechanisms of various diffusion regimes were analyzed, and a correlation model between the critical sealing ratio and the discharge rate was established. Additionally, the temperature distribution law of the smoke below the tunnel ceiling under various sealing ratios was studied. The maximum smoke temperature rise exhibits two distinct regions of variation as the sealing ratio increases. When the sealing ratio is small, the maximum smoke temperature rise remains relatively steady with the increase of the sealing ratio. However, as the sealing ratio increases, the tunnel spill fire transitions to the ventilation-controlled, resulting in a reduced burning rate and a rapid decrease in the maximum smoke temperature. Empirical models characterizing the maximum temperature rise were developed for different sealing situations. This study could provide an essential reference for conducting emergency rescue operations during tunnel spill fires.

The presence of drunk crowds complicates the evacuation process compared to sober crowds. We construct a Floor-Field Cellular Automata (FFCA) model considering the role of drunken pedestrian perturbations to investigate the impact of drunken gait on pedestrian dynamics. A random floor field is constructed to simulate the drunken gait of pedestrians, considering the role of surrounding pedestrians and the random movement behaviour of "drunken walk". A drunkenness factor is proposed to modulate the randomness of drunken gait, and a velocity model is formulated to account for the intermittent speed fluctuations observed in drunken pedestrians. In addition, a probabilistic model incorporating the coupled effects of drunkenness level and movement speed is proposed to address the pedestrian conflict. The FFCA model can reproduce some real features of the drunken evacuation process to some extent. For example, (1) Drunken pedestrian staggers while moving. (2) Blockage occurs at the gathering place of drunk pedestrians. (3) Drunken crowds are pushed to move by the flow of the crowd. The results show that drunken gait disrupts the orderly movement of pedestrians, whereas the presence of sober pedestrians can foster the formation of adaptive orderly behaviors, maintaining a orderly movement structure. When drunken pedestrians are located at the rear of the crowd flow, evacuation efficiency is higher in the early stage but the overall efficiency of the entire evacuation process is the lowest. Conversely, when distributed in the front and middle, although the gait of drunken people hinders in the early stage evacuation, sober pedestrians in the rear can act as guides and improve the overall evacuation efficiency.

When liquid fuel spills on a sloping ground and an ignition source is nearby, it could lead to a continuous spill fire. To investigate the diffusion and burning characteristics of continuous liquid fuel spillage on sloped ground, a series of experiments were conducted, considering different discharge rates (60∼140 ml/min) and ground slopes (2o, 4o, 6o, 8o). Characteristic parameters were measured, including fuel diffusion rate, diffusion shape, flame temperature, and burning rate. A new theoretical model for the diffusion velocity was established and the diffusion shape characteristics of the liquid fuel were revealed for the first time. Results indicate that under non-ignited conditions, the diffusion velocity of the liquid fuel gradually decreases, eventually converging toward an asymptotic velocity. Under ignited conditions, the burning process of the spill fire could be categorized into three distinct stages. Moreover, the mass burning rate per unit area of spill fires is obviously lower than that of pool fires. This is because the fuel thickness in spill fires is so thin that the radiant heat flux emitted by the flame to the fuel cannot be fully absorbed by the fuel. This work could provide a critical reference for predicting the diffusion process of a spill fire.

An extended floor field cellular automata (FFCA) model considering the stampede accidents on inclined staircases is proposed to study shoving behavior and pedestrian dynamics. In this model, two stampede evolution pathways are investigated: Pedestrians falling after losing balance, and falling directly due to being crowded. The results show that this model could reproduce some real characteristics of real irrational evacuation process, such as: (1) the mutual crowding and shoving among pedestrians; (2) the unbalance phenomenon on inclined staircases; (3) the pedestrian domino effect, which is consistent with the findings of most stampede accident investigations to some extent. The proposed model considers the impact of fallen pedestrians on the movement of ordinary pedestrians, which shows a reduction in the overall evacuation efficiency. Moreover, the steeper the slope, the greater the risk and severity of injuries during the crowded evacuation in this scenario. Additionally, pedestrian falling shows a certain lag related to the state of unbalance. Unbalanced pedestrians tend to appear from the rear to the front successively, and falls often occur some time later the onset of unbalance, frequently progressing from front to rear. This pattern reflects the “domino effect” among pedestrians. Lastly, unbalanced pedestrians constitute a significant portion of the total injured pedestrians. Considering the delay in falls after unbalance, this emphasizes the importance of early emergency response and intervention during crowded evacuations. It is expected to provide some theoretical support for safety management.

A series of tunnel spill fire tests were carried out, considering different tunnel slopes and discharge rates. Characteristic parameters, including diffusion distance, diffusion area, mass burning rate per unit area, and smoke temperature, were measured, and the influence of the tunnel slope on the characteristic of these parameters was analyzed. The results show that the combustion process of the tunnel spill fire could be separated into four distinct stages: the combustion diffusion stage, the combustion shrinking stage, the quasi-steady combustion stage, and the extinction stage. The occurrence of the shrinking stage could be attributed to the increase in the fuel’s mass burning rate per unit area. Moreover, the transition between combustion stages primarily depends on the relative magnitude of the fuel’s mass burning rate and discharge rate. A correlation model was developed to characterize the diffusion area and diffusion distance of the liquid fuel. During the quasi-steady combustion stage, the average diffusion width significantly decreases with increasing tunnel slope. Therefore, the maximum temperature decreases as the slope increases. Furthermore, the mass burning rate per unit area increases as discharge rate increases. This is primarily due to the flame hitting the ceiling, increasing the radiant heat flux to the liquid fuel. Additionally, the maximum temperature rise decreases as the slope increases. However, when beyond a specific slope threshold, additional increases in slope have a minor effect on the maximum temperature rise. This could be attributed to the variation of fuel's diffusion width with the tunnel slope. Finally, a dimensionless model was developed to characterize the decay of smoke temperature below the tunnel ceiling. This study could serve as a critical reference for assessing disaster risks and executing emergency rescue operations in the case of tunnel spill fire incidents.

A series of fire tests were conducted in a bifurcated tunnel model with branch tunnel ventilation. Three fire locations were considered. The characteristics of smoke movement and temperature profile under various fire source location scenarios were analyzed. The results indicate that when the fire source is not at the intersection, the ventilation airflow in the branch tunnel is diverted at the intersection before it is imposed on the fire source, which results in the actual velocity of ventilation air imposed on the fire source being less than the velocity of ventilation air in the branch tunnel. A new parameter, named the diversion coefficient, was introduced for convenient analysis. By substituting the diversion coefficient values into a classic maximum temperature rise prediction model for the single-line tunnel fires, good prediction results were observed. Moreover, a new dimensionless smoke temperature decay model was developed. The applicability of the model was validated using full-scale fire test data from previous research. The dimensionless temperature decay law of smoke was analyzed based on the newly established model. Results show that when the fire is positioned at the intersection, the decay coefficient of the smoke downstream of the fire decreases linearly as the ventilation rate increases, while decay coefficient of the smoke upstream of the fire decreases slowly at first and then increases with the increase of ventilation rate. When the fire source is not at the intersection, the branch tunnel ventilation conditions could be classified into three categories: sub-critical, critical, and super-critical velocity. Changes in the ventilation velocity within the branch tunnel have little influence on temperature decay process of smoke in the main tunnel under critical and sub-critical velocity conditions. However, under super-critical velocity conditions, the smoke temperature decreases rapidly after reaching the intersection. Furthermore, predictive models for the critical velocity of the branch tunnel under various fire locations were established based on theoretical analysis and experimental data. Within a specific range of heat release rate, the critical velocity is proportional to the cube root of the heat release rate. Compared to when the fire is located at the intersection, the critical velocity is reduced significantly when the fire is not in the intersection.

Due to the height differences during the power transmission, the upward-bending installation of cables is a common method. An experimental study was conducted to investigate the effect of the bending angle and number of cables on the flame spread behavior of upward-bending cables. Different bending angles (30°, 60°, and 90°) and a range of number of cables (1–5) were included in this work. The characteristic parameters, e.g., temperature on the cable surface, flame spread rate, flame feature, etc., were measured and analyzed. Results show that the flame spread rate of upward-bending cables gradually increases, as the number of cables increases. And the total flame length and flame-base length are positively related to the number of cables. Meanwhile, as the bending angle of upward-bending cables increases, the peak temperature on the cable surface increases, and the flame spread time decreases. The peak temperature on the cable surface is approximately 910 °C in the condition of five cables at 90° bending, which is 1.6 times as much as that in the condition of five cables at 0° bending. The faster flame spread rate increases in both the bending and inclined sections of upward-bending cables, with increasing bending angle. This is mainly because the larger the bending angle, the more intense the thermal convection and radiation on unburned cables, and the easier it is for the melt drippings to flow along the cable surface. Finally, within the current experimental range, a simplified heat transfer model of upward-bending cable was established.

A series of spill fire tests were carried out in a reduced-scale tunnel (6 m x 0.6 m x 0.45 m), considering different discharge rates (60-140 ml/min), ventilation rates (0 similar to 1.26 m/s), and tunnel slopes (3 %, 5 %, 7 %). Some crucial characteristic parameters during the quasi-steady combustion stage of tunnel spill fires were analyzed, including the diffusion shape of the liquid fuel, mass burning rate per unit area, flame morphology and plume temperature, and the critical ventilation velocity. The results show that as the tunnel slope increases, the diffusion shape of the liquid fuel transitions from circular to an ellipse shape and then to rectangular or linear shape. Moreover, the mass burning rate per unit area decreases with increasing ventilation rates at low ventilation (V < 0.5 m/s), while it remains almost constant at high ventilation rates (V >= 0.5 m/s). This could be attributed to variations in flame tilt behavior under different ventilation conditions. Predictive models for the flame tilt angle and the vertical temperature distribution of tunnel spill fires under the effect of ventilation were further established and verified. Furthermore, the critical ventilation velocity of tunnel spill fires remains essentially unchanged as the discharge rate (or fire source power) increases. This phenomenon was explained by analyzing the resistance of the spill fire plume and the buoyancy generated by the smoke temperature. This work could serve as a critical reference for assessing disaster risks and executing emergency rescue operations during tunnel spill fires.

Panic is a common emotion when pedestrians are in danger during the actual evacuation, which can affect pedestrians a lot and may lead to fatalities as people are crushed or trampled. However, the systematic studies and quantitative analysis of evacuation panic, such as panic behaviors, panic evolution, and the stress responses of pedestrians with different personality traits to panic emotion are still rare. Here, combined with the theories of OCEAN (openness, conscientiousness, extroversion, agreeableness, neuroticism) model and SIS (susceptible, infected, susceptible) model, an extended cellular automata model is established by the floor field method in order to investigate the dynamics of panic emotion in the crowd and dynamics of pedestrians affected by emotion. In the model, pedestrians are divided into stable pedestrians and sensitive pedestrians according to their different personality traits in response to emotion, and their emotional state can be normal or panic. Besides, emotion contagion, emotion decay, and the influence of emotion on pedestrian movement decision-making are also considered. The simulation results show that evacuation efficiency will be reduced, for panic pedestrians may act maladaptive behaviors, thereby making the crowd more chaotic. The results further suggest that improving pedestrian psychological ability and raising the standard of management can effectively increase evacuation efficiency. And it is necessary to reduce the panic level of group as soon as possible at the beginning of evacuation. We hope this research could provide a new method to analyze crowd evacuation in panic situations.

An extended floor field cellular automata model considering crowding and trampling damage mechanism under the internal crushing is proposed to study pedestrian dynamics with crowded pushing and shoving behavior under irrational conditions. In this model, two damage modes of pedestrian evacuation: mechanical asphyxiation due to crushing and fall due to crowding, are investigated by constructing injury gradients and fall probabilities. The results show that the model could reproduce some real features of irrational evacuation to some extent, such as (1) the mutual pushing and crowding of pedestrians; (2) the trampling and crushing damage phenomena that often occur in real trampling accidents; and (3) the accident location is located near the exit, which is consistent with the findings of most trampling accident investigations. In addition, the crowding resultant force acting on someonce within the crowd displays that the magnitude of crowding force gradually decreasing with the distance away from the exit, and the peak crowding force appears at the arch crowd in the region near the exit, which is very easy to cause pedestrian crushing damage. When the initial number of pedestrians is small, almost no crushing damage occurs, and the damage mechanism in the scene is mainly crowded fall; with the increase of the initial number of pedestrians, the number of pedestrians damaged by crushing will increase exponentially and become the main factor of pedestrian casualties. Crowding and trampling damage occurs obviously near the exits, but as the initial number of pedestrians increases, the number of crushing damage grows rapidly away from the exits and gradually exceeds that of relatively near the exits. Therefore, the safety management near the exit should be strengthened to ensure the personal safety of pedestrians in front of the exit.

为避免或减小狭长空间内高压电缆发生火灾的可能性,建立实验模型,研究狭长空间内 220 kV大截面电缆燃烧行为及火蔓延规律,分析电缆火灾下狭长空间顶棚温度分布特征,结合电缆燃烧过程,设置5 种不同排烟风速,探究排烟风速对其排烟效率的影响.研究结果表明:大截面电缆阻燃外护套受火后会形成高温熔融物,滴落在底板上的高温熔融物燃烧形成的火焰不断撞击电缆底部,在电缆底部形成的拓展火焰持续加热,引燃电缆外护套的未燃段,进而导致电缆外护套底部火焰在热对流和辐射的作用下稳定蔓延;狭长空间顶棚温度峰值及熔滴火焰前锋位置随着电缆阻燃外护套的持续燃烧不断推移;大截面电缆火焰蔓延速度呈现先增大、后稳定、再减小趋势;电缆燃烧过程中会产生大量有毒烟气,采用侧向排烟模式能够有效降低狭长空间内烟气浓度.研究结果可为狭长空间内敷设电缆的消防排烟设计提供参考.

This work experimentally and theoretically investigated the heat transfer feature and burning -decontamination rate of porous media environment soaked (contaminated) by leaked combustible liquid. A series of fire tests were performed employing typical combustible liquid and porous media materials. The burning rate, temperature distribution, and flame appearance, etc., were measured and identified. Results show that the variation of burning-decontamination rate of porous media bed soaked by com-bustible liquid can be divided into two characteristic stages, and as liquid level drops, burning rate in-creases rapidly and then decreases gradually. In rapid growth stage, flame thermal feedback directly could affect the burning features of top-layer combustible liquid, while in the attenuation stage, the isolation of dry porous media layer to the direct effect of flame thermal feedback and the increasing surface heat loss collectively make the burning rate attenuate. This stage-variation characteristic represents the variation of the dominant mode of heat transfer. Based on the theoretical analysis of heat transfer process in different burning stages and the empirical fitting of flame height, an explicit prediction model for burning rate is established, and the model prediction results are in reasonableagreement with most of the experimen-tal measurements within an acceptable error range. This work provides basic data and some references for burning-decontamination technology of porous media environment (e.g., soil, sand) contaminated by combustible liquid and corresponding fire safety issues.(c) 2022 Elsevier Ltd. All rights reserved.

为提高消防救援人员安全保障能力,提升救援工作效率,综合运用新一代信息技术,将数字孪生技术应用到消防救援技术中.首先,分析消防救援人员在灭火救援过程中所面临的危险;然后,提出数字孪生消防救援技术的概念内涵,并分析数字孪生消防救援技术的特点,进而提出数字孪生消防救援技术的5层系统架构,以及适合救援过程的系统架构聚合和拓展方法;最后,明确数字孪生消防救援关键技术,主要包括高精度低时延移动定位技术、多层次多视图数字线程技术以及多维度救援数据驱动建模技术等.结果表明:数字孪生消防救援技术能够提高消防救援人员的安全保障能力和救援工作的效率.通过实时数据交互和信息融合,数字孪生消防救援技术全面集成孪生数据,为救援行动提供更精确的决策支持.数字孪生消防救援技术的5层系统架构及关键技术有效连接物理实体与虚拟实体,实现数字孪生体的聚合和拓展,可以为数字孪生消防救援的应用提供有力支撑.

A series of model-scaled tunnel fire tests were performed to investigate the temperature attenuation characteristics of thermal smoke. The internal temperature profiles of single-line tunnel and T-shaped tunnel were measured and compared. Results indicate that within the current measurement range, for the fire scenario with same fire power, the maximum smoke temperature of T-shaped bifurcated tunnel is slightly lower than that of the single-line tunnel under natural ventilation, which can be attributed to the reduction of smoke accumulation and the increase of air entrainment induced by bifurcation region. The longitudinal temperature decay of fire smoke in entire spread region shows an obvious region-variation feature. The temperature attenuation rate in the region near fire source is larger significantly than that of one-dimensional spreading region. Compared with the representation in the form of single exponential correlation, the double-exponential correlation can better characterize the temperature decay process in entire spreading region of fire smoke. While, if the single-exponential representation is adopted, the correlation formula is piecewise. Based on the analysis and physical observations of the longitudinal decay rate of smoke temperature in different spreading regions, a modified double-exponential correlation for longitudinal temperature attenuation is obtained. By comparing with the model-scaled measurement results in current work and the full-scaled experimental data of previous scholars, the proposed correlation is reasonably verified to be within an acceptable error range. This work is anticipated to serve as a resource for firefighters to evaluate the temperature profile and decay characteristics of fire smoke in tunnel-like space.

To assist the Department of Emergency Management in understanding the overall risk characteristics and situation of an urban agglomeration for a reasonable risk prevention and control strategy, this study developed a comprehensive multi-hazard risk assessment model for an urban agglomeration with multiple factors. The proposed model includes disaster probability and disaster loss sub-models. The model evaluated four types of disaster risk in urban agglomerations: natural disasters, accidental disasters, public health incidents, and social security incidents. In addition, a variety of factors were integrated into the model, including the socioeconomic foundation of urban agglomerations, the oligopoly effect of core cities, historical disaster losses, the effect of disaster chains, the ability of disaster prevention and mitigation, and intercity coordinated rescue capabilities. Finally, the risk assessment model was applied to the Beijing-Tianjin-Hebei urban agglomeration. The assessment results were compared to the distribution of the new coronavirus pneumonia epidemic in the target urban agglomeration. The results showed that after analyzing the risk characteristics and evaluating the risk levels, the model not only showed the comprehensive risk levels and distribution of urban agglomerations but also revealed the high-risk areas and the key points of risk prevention and control. More importantly, the results obtained through the model can facilitate the strategic planning of disaster prevention and mitigation for urban agglomerations.