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National Fire Protection Association

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0015-2684

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    Guldborgsund Arson House Fire Experiment and Numerical Investigation

    Bjarne Paulsen HustedKarlis LivkissAna Sauca
    247-274页
    查看更多>>摘要：Abstract This paper describes the Guldborgsund arson house fire experiment performed in Denmark and the subsequent numerical investigation. Gas temperatures were measured with four thermocouple trees, and smoke detector activation times were recorded in all rooms. A two-step approach was used to perform the numerical modelling for reproduction of the fire scene. The measured temperatures in the room of fire origin were used as an input for back calculating the Heat Release Rate (HRR) with the two-zone model Argos. As a next step, this HRR was used in the Fire Dynamic Simulator (FDS) to predict the temperatures and the smoke detectors’ activation times in other rooms. The FDS model was partly build using output files from the laser scanning. A sensitivity analysis is presented, where the effect of nine input parameters was investigated, including HRR, the material properties, the height of the fuel bed, the fire area, level of geometrical detail of the first item ignited etc. This study showed that the measured soot deposition heights on the walls differed from the heights of measured sharp temperature gradients used to indicate the hot smoke layer. The numerical simulations resulted in less than 50% error for most of the temperature measurement points during the fuel-controlled stage of the fire and results were the most sensitive to the input HRR. Material properties in FDS had a significant influence on the computed upper-layer gas temperatures at late stages of the fire.
      原文链接:
    • NETL
    • NSTL
    • Springer Nature

    Characterization and Evaluation of Fire Response Performance in Shanghai Based on Fire Department Statistics

    Qize HePengfei DingYun Yang
    275-293页
    查看更多>>摘要：Abstract The efficiency of the emergency response plays a crucial role in both fire suppression and personnel rescue operations, where the travel time and speed are determined. However, there is limited research on the factors that influence travel time and speed, especially in the quantitative influences of time, space, and incident classification factors. In this work, the distribution of all incidents in Shanghai, 2022 are presented. The correlation of temporal factors such as time, date, and month, spatial factors such as distance to the city center, economic scale, population, and incident classification is studied and discussed. The results reveal that as the urgency of incidents increases, the travel time and speed tend to decrease and increase respectively. In the early morning, despite favorable traffic conditions, actual travel time significantly increases due to firefighter fatigue, resulting in a notable decrease in travel speed. During the lockdown period in March, April, and May for Covid-19 pandemic, there is a significant decrease in travel time and an increase in travel speed. Regarding spatial factors, there is a distinct regional distribution of actual travel time strongly correlated with area size, distance to the city center, and average travel distance. Notably, the relative speed difference between firefighting vehicles and regular vehicles increases as the incident type changes from fire to emergency rescues and social assistance. This speed difference is primarily influenced by the economic and population scale of the coverage area. As the severity level increases from Level 0 (lowest) to Level 5 (highest), travel time significantly decreases, while travel speed and relative speed difference markedly increase. The work will contribute to the theoretical foundation for fire station planning.
      原文链接:
    • NETL
    • NSTL
    • Springer Nature

    A Mixed Convection Model for Estimating the Critical Velocity to Prevent Smoke Backlayering in Tunnels

    Michael BeyerConrad StaceyGünter Brenn
    295-342页
    查看更多>>摘要：Abstract A novel mathematical model for the critical ventilation velocity to prevent smoke backlayering in tunnels is presented, addressing limitations of prior approaches. The basis of the model is a rigorous characterisation of the physical processes by the characteristic quantities. Empirical parameters within the new model are determined, to align with results from both full-size and small-scale tunnel experiments. Data from numerical simulations (CFD, Computational Fluid Dynamics), validated by known test data, are then used to estimate the effects of tunnel slope and other parameters on the critical velocity. The model is seen to approximate the critical velocity well, following all trends identified by test data and CFD parameter studies. The empirically calibrated equation permits prediction of the critical velocity beyond the narrow range of tunnel geometries where known results already give an answer. The resulting equation has practical application for tunnel design.
      原文链接:
    • NETL
    • NSTL
    • Springer Nature

    Experimental Dimension and Boundary Analysis of Upward Flame Spread Over U-Shaped Facade in Energy-Saving Building Fires

    Yanqiu ChenYifan NieJiwei ZhangYi Zhao...
    343-361页
    查看更多>>摘要：Abstract Insulation layer is usually used in building facade for energy-saving design, and it also endangers the human safety in buildings due to its combustibility. U-shaped facade is a commonly used structure form in high-rise buildings for energy-saving design since it could improve both the light and ventilation conditions indoors. Through a series of experiments, this paper investigated the flame spread over insulation in u-shaped building facade fires under effect of structural dimensions (back wall length W, side wall length L, height H) and boundary conditions based on the flame spread rate, temperature and heat flow. It was found that the flame spread rate Vf, the temperature rise ΔT and the heat flow q over u-shaped facade were all positively correlated with the side wall length L and structural height H, while they were negatively correlated with the back wall length W. On the other hand, the lateral air entrainment restriction and flame interaction were both significantly increased the temperature and heat flow, strengthened the thermal feedback, accelerated the flame spread. However, the bottom air entrainment restriction slowed down the flame spread. Further, a modified structure factor was introduced to comprehensively analyze the influence of L, W and H on flame spread behavior over u-shaped structures, and the theoretical equations of Vf*, ΔT*max and q′*max were established. This study provides theoretical basis and technical guidance for the fire prevention design of building facade covered with insulation.
      原文链接:
    • NETL
    • NSTL
    • Springer Nature

    Water Sprays Cooling of a Hot Metallic Plate

    Z. AcemV. DréanG. ParentA. Collin...
    363-379页
    查看更多>>摘要：Abstract In the present work, spray cooling experiments of a hot steel plate were carried out with three different nozzles in order to provide accurate experimental data for the modellers. Special attention was paid to for both the measurement of the surface temperatures and the characterization of the sprays. Firstly, the surface temperatures were measured using K-type thermocouple wires welded directly to the surface of the plate in a separate contact. This technique provides an accurate measurement of the surface temperature during the cooling. Secondly, the spray characteristics of each nozzle were also thoroughly investigated. It was found that the droplet size and velocity distributions of each nozzle followed a log-normal law. The corresponding Sauter mean diameter (SMD) and mean velocity ranged from 170 to 230 µm and from 5.6 m s−1 to 22.4 m s−1, respectively. Spray cooling was started after heating the plate between 500°C and 600°C using a radiant panel. Cooling rates were very high and the time to reach ambient temperature varied from 4 s to 1 min depending on the nozzle used. Heat Flux (q˙′′\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\dot{q}}^{{\prime}{\prime}}$$\end{document}) and Heat Transfer Coefficient (HTC) were calculated from the temperature data. It was found that high levels of critical heat flux (CHF), around 9 MW m−2, were achieved for two of the three nozzles studied, including the one with the lowest flow rate of only 1.6 L min−1. Finally, the results obtained in this study could be used to validate numerical codes such as FDS and FireFOAM, which are commonly used in fire safety engineering.
      原文链接:
    • NETL
    • NSTL
    • Springer Nature

    Research on the Behavior on Axial Tensile Welded Hollow Spherical Joints Exposed to Elevated Temperature

    Xiaobin QiuBingsheng HuangZhen ZhangHaoyu Song...
    381-410页
    查看更多>>摘要：Abstract Welded hollow spherical joints (WHSJs) are commonly used joints in grid structures, and their mechanical behavior under fire will directly affect the service life and safety behavior of grid structures. Therefore, the WHSJs were heated to the specified high temperature, and the tensile experiments were performed on non-stiffened WHSJs exposed to elevated temperatures. The failure modes, axial load–displacement curves, and mechanical behavior of the non-stiffened WHSJs exposed to elevated temperature were obtained. The experiment indicates that the failure mode of the axial tensile non-stiffened WHSJs is a pull-out failure. With the increase of heating temperature, the mechanical behavior of non-stiffened WHSJs gradually declines. The ductility of the non-stiffened WHSJs gradually increases with the heating temperature. Compared with the existing studies, the load-bearing capacity reduction trend of WHSJ exposed to elevated temperature is basically similar, and the stiffener has basically no function to improve the behavior of tensile WHSJs exposed to elevated temperature. The reliability of the numerical simulation was proved by comparison with experiments. According to the finite element analysis, the design method for the mechanical behavior of the non-stiffened WHSJs subjected to axial tension exposed to elevated temperature was proposed.
      原文链接:
    • NETL
    • NSTL
    • Springer Nature

    The Smoke Flow Deflection Angles in Immersed Tunnel Fires with Multi-Point Concentrated Smoke Exhaust Mode: Representation Model and Influencing Mechanisms

    Daiqiang ZhuPai XuYixian LiuRongjun Xing...
    411-448页
    查看更多>>摘要：Abstract The smoke flows from the tunnel to the exhaust vent, and then to the exhaust duct under the multi-point concentrated smoke exhaust mode of immersed tunnel fires. This will cause resistance and energy loss by forming smoke flow deflection angles, which is the angle between the direction of smoke flow velocity and the longitudinal direction. In this study, the correlations between the smoke flow deflection angles and mechanical characteristics are revealed. Specifically, the smoke exhaust processes are divided into "from the tunnel to the exhaust vent" and "from the exhaust vent to the exhaust duct". Based on the dimensionless analysis, the presentation model with influencing factors of smoke flow deflection angles is established. Through numerical simulation, the influencing mechanisms of longitudinal ventilation velocity, exhaust volume flow rate, and distance of multi-point exhaust vents on the smoke flow are analyzed in a three-lane immersed tunnel under 50 MW. The quantitative relationships between the smoke flow deflection angle and factors are obtained. The correlations between the smoke flow deflection angles and component forces are established. The results show that smoke flow deflection angles are affected by the transverse and longitudinal forces. Additionally, the influence of longitudinal ventilation velocity and exhaust volume flow rate is related to the distance of the exhaust vent group from the fire source. Furthermore, the increase in the smoke flow deflection angle is not determined by the distance of the exhaust vent group from the fire source, but rather by the distance of the multi-point exhaust vents.
      原文链接:
    • NETL
    • NSTL
    • Springer Nature

    Fire Response Analysis of Prefabricated Combined Reinforced Concrete Beams Based on Finite Element Model Correction

    Caiwei LiuShuqi SunXuhong HuangJijun Miao...
    449-481页
    查看更多>>摘要：Abstract To obtain an accurate finite element model (FEM) for response analysis of prefabricated combined reinforced concrete beam (PCRCB) under fire exposure, a stepwise FEM correction method is proposed based on the improved response surface method. Four T-shaped PCRCBs were designed and cast to verify the accuracy and practicality of the proposed method. Firstly, based on the static and dynamic tests before fire exposure, the FEM was corrected using the proposed correction strategy. The proposed method is initially validated by comparing the modal responses. Subsequently, a fire test was carried out. The test phenomena, temperature field, mid-span deflection and dynamic response under fire were analyzed. Finally, considering the development of crack, the static and dynamic responses under fire exposure were further simulated based on the modified FEM. The results indicate that the established FEM can accurately simulate the structural response. The spanwise deflection and fundamental frequency exhibited nonlinear variations with fire exposure time, which were strongly influenced by the load ratio. The proposed model correction method establishes the basis for the detail response analysis of PCRCB during fire exposure.
      原文链接:
    • NETL
    • NSTL
    • Springer Nature

    An Image Restoration Method for Improving Matching Robustness of Indoor Smoke Scene

    Bowen LiangYourui TaoYao SongXinze Li...
    483-511页
    查看更多>>摘要：Abstract Smoggy interference caused by indoor fires makes machine vision technology challenging to apply in the fire rescue field. Smoke and condensed water vapor aerosol from suppression activities limit visibility, making image matching difficult. To overcome this problem, an image restoration method for indoor smoke scenes is proposed. First, the dark channel prior algorithm for indoor smoke scenes is improved, and the atmospheric light estimation method is optimized by combining the density peak clustering algorithm and position constraint. A model update approach is also advanced to achieve real-time dehazing of image sequences. Afterward, the effect of photometric changes caused by the image restoration on matching is analyzed. The feature matching is performed using the pyramid Lucas–Kanade (LK) optical flow method, while the random sampling consistency algorithm is used to eliminate outliers. Finally, an indoor smoke dataset is created to evaluate the algorithm, and a comprehensive analysis of the algorithm's limitations is conducted to provide a thorough understanding of the algorithm's potential shortcomings. The evaluations confirm that the proposed method can effectively improve the robustness and accuracy of indoor smoke scene image matching. The percentage increase in robustness is close to 100%, and the accuracy has increased by 10%. Overall, this approach holds practical value for the fire rescue field, and it may encounter limitations in handling scenarios with dense smoke, dark smog, and dynamic flames. Further improvements and optimizations are required to address these challenges.
      原文链接:
    • NETL
    • NSTL
    • Springer Nature

    Study of the Interactions Between a Water Spray and a Moving Layer of Hot Smoke

    Louis HardyAnthony CollinMathieu SuzanneGiacomo Erez...
    513-540页
    查看更多>>摘要：Abstract This study compares the effects on a smoke layer of water sprays injected downward, upward or according to an inclined counter-flow configuration. The impact is analyzed considering stratification, mixing and cooling effects upstream (fire side) and downstream (opening side) the position of the spray. The experiments were conducted in a 1/5th scale model reproducing a room connected to a corridor. The injection of the poly-dispersed spray was carried out in the corridor where a layer of smoke was flowing in the upper part. Thanks to the experimental configuration, there is no direct impact of the spray on the fire source and the production of smoke, but only on the hot flow of smoke. The effect of the spray was evaluated for the different directions of injection and two water feeding pressures. The measurements have shown that effective cooling of the upper layer is observed downstream of the spray. The efficiency of the cooling is dependent on the injection angle. A more or less significant heating of the lower layer is measured upstream for all the injection angles. The injection angle has an influence on the smoke mixing and cooling, an upward spray injection—either vertical or inclined—being more impactful. The strongest interaction is observed for an inclined counter-flow injection, similar to the configuration of firefighters cooling a smoke layer while moving forward in a corridor toward a fire source. Moreover, two water injection pressures were investigated: 4 and 8 bars. Increasing this pressure reduces the droplet diameter and increases the water flow rate. In the present experimental configuration, modifying the water injection pressure showed an effect, yet limited because the droplet size distribution was not strongly impacted. All experimental data are available in an open-access database for further uses.
      原文链接:
    • NETL
    • NSTL
    • Springer Nature