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15 May 2021, Volume 40 Issue 5 Previous Issue    Next Issue

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Thermal runaway characteristics of lithium ion batteries in low voltage environment CHEN Xian-tao, ZHANG Xu, LIU Yi, ZHAO Yi-fan 2021, 40 (5):  605-609.  Abstract ( 1875 )   In order to explore the thermal characteristics of lithium-ion batteries under different environmental pressures, thermal runaway experiments of 18650 cylindrical lithium- ion batteries with 100% SOC (state of charge) under different environmental pressures (30 kPa, 50 kPa, 70 kPa, 90 kPa) were carried out with dynamic pressure and temperature chamber and ISO-9705 flue gas analyzer. The results show that the thermal runaway caused by external heat source can be divided into three stages in either normal pressure or low pressure environment. With the decrease of the environmental pressure, the peak temperature, heat release rate and total heat release rate of the battery surface decrease, and the detonation response time point is prolonged; at 30 kPa, the explosion response time point is 515 s, which is 348 s longer than that under 90 kPa condition. The peak temperature of the thermal surface of the battery is 703 ℃ at 90 kPa, which is 1.299 times of that under 30 kPa.With the decrease of environmental pressure, the release of CO gas increases gradually, while that of CO2 and CxHy decreases gradually. It can be seen that the lithium-ion battery in normal pressure environment has higher thermal hazard. In low- pressure environment, it will have greater risk of toxic hazard. Related Articles | Metrics

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Influence of ventilation on gas diffusion law of lithium iron phosphate battery fire in energy storage container< WU Yong, LI Li-na, WANG Zhi-gang, LUO Jian-fei, SUN Xu-kun 2021, 40 (5):  610-612.  Abstract ( 1913 )   In recent years, with the accelerating commercialization process of energy storage power station, the safety and fire protection problems of energy storage power station have attracted much attention. Lithium iron phosphate battery thermal runaway characteristic gas as a detection and early warning method has been widely used in energy storage power station. The diffusion law of gas in energy storage container directly affects the accuracy of detection and early warning. However, the influence of ventilation on the thermal runaway characteristic gas diffusion law of LiFePO4 battery in energy storage container is not well understood. In order to explore the influence of ventilation on the characteristic gas diffusion of energy storage container, the types and components of characteristic gas in 109 Ah lithium iron phosphate battery under thermal runaway were studied by using lithium- ion battery thermal runaway experimental platform, and then the full-scale simulation of gas diffusion in energy storage power station was carried out by using numerical analysis technology. The characteristics were discussed by changing the ventilation rate, ventilation size and ventilation position. The diffusion law of characteristic gas and the change law of longitudinal characteristic gas are given, which provides a certain theoretical basis for real gas detection and early warning. Related Articles | Metrics

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Investigation on combustion characteristics of combustible liquids in high-plateau airport pressure environment LIU Quan-yi, ZHU Wen-tian, ZHU Bo, HU Lin 2021, 40 (5):  613-616.  Abstract ( 1696 )   Jet fuel and n-heptane were selected as fuels, a series of experiments were carried out with different oil pan diameters，and the typical characteristic parameters such as the burning rate, the heat release rate and the centerline temperatures of the fire plume were recorded and analysed. The results show that: The entire combustion process of jet fuel and n- heptane are roughly divided into three stages:the initial combustion stage, the stable combustion stage, and the attenuation extinguishment stage. The heat release rate of n- heptane is higher and the combustion time is shorter than that of jet fuel under the same conditions. There is a certain exponential relationship between the peak heat release rate and the oil pan diameter, which can be used to predict the maximum heat release rate of pool fire under the low pressure environment. A certain exponential relationship exists between the temperature rise in the center of the fire plume and the height and power of the fire source. The ideal fire plume model is modified and applied to Kangding high-plateau airport with a correction coefficient of 8.43. Related Articles | Metrics

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Explosion risk classification of wood fiber dust GUO Lu , WANG Sheng-hua, LIU Jia-wei, QIN Wen-jing, MOU Jie 2021, 40 (5):  617-620.  Abstract ( 2735 )   In this paper, the explosion characteristics and explosion risk classification of wood fiber dust from the dust collector of a wood processing factory were investigated. Combined with explosion characteristic parameters, the risk level of wood fiber dust is strong according to the American Explosion Index E Comprehensive Classification Method; the explosion grade is St1 (weak explosion) based on the German Hazard Classification Method. While according to the International Electrotechnical Commission (IEC) Classification Method, the wood fiber dust does not require special attention. In China, the wood dust is classified as a high risk level flammable dust. However, we need to design and modify the explosion-proof devices according to the dust explosion parameters from the actual production process. Related Articles | Metrics

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Experimental study on combustion performance of FEP communication cable BAO Guang-hong, HU Lin-ming 2021, 40 (5):  621-624.  Abstract ( 1758 )   Full scale experimental study on combustion characteristics of FEP communication cable was carried out by using FIPEC test device. The flame spread of communication cable was studied by testing the parameters of heat release rate, smoke production rate, combustion growth rate index and flame spread distance in the combustion process. Meanwhile, the factors influencing the flame spread of communication cable were analyzed. It is found that the power of ignition source has little effect on flame spread of FEP communication cable; The arrangement of cables and thermal boundary conditions are important factors affecting flame spread of FEP communication cables. Under the same fire power, the flame spread speed of cable spacing arrangement is faster than that of contact arrangement, and the fire risk is greater; The flame spread speed and fire risk of the steel ladder with non-combustible back plate ar much faster than those without back plate; The combustion performance of FEP communication cable can reach B1 level of GB 31247- 2014 Classification of Combustion Performance of Cables and Optical Cables. Related Articles | Metrics

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Study on smoke spread characteristics of super-long highway tunnel under piston wind LI Guo-dong 2021, 40 (5):  624-628.  Abstract ( 1709 )   The piston wind would be produced when the vehicle is driving in the tunnel, the effective use of piston air could reduce the cost and energy consumption of mechanical smoke extraction system. In this paper, the theoretical analysis was carried out first, and then the smoke spread characteristics of the highway tunnel under piston wind were investigated by using the computational fluid dynamics software. Numerical simulation was carried out to explore the influence of different piston wind speeds on smoke layer movement, temperature field and velocity field distribution under different heat release rate (10,30, 50 MW) in the tunnel. The results showed that the recent and long- term piston wind speed attenuation model have the same variation rules of smoke layer movement, temperature field and flow velocity field under different heat release rates. With the heat release rate became larger, the time for smoke to return to the tunnel entrance was shorter, and the time for the flow velocity field to change was later. Related Articles | Metrics

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Study on the longitudinal ceiling temperature distribution characteristics of tunnel transverse offset fire source HU Jia-wei, MAO Jun, XI Yan-hong, LIU Bin 2021, 40 (5):  629-634.  Abstract ( 1689 )   To study the influence of tunnel transverse fire source location on the ceiling temperature distribution along longitudinal process, the method of combining numerical simulation with full-size model experiment is adopted to analyze the ceiling temperature rise generated by the combustion of the three ignition sources at various lateral offset positions and central line ignition sources. The results show that for a variety of transverse offset fire sources, the longitudinal temperature rise attenuation of the fire source can still be described in exponential form, and the closer to the side wall of the tunnel, the faster the temperature rise attenuation is. The coupling effect of the offset distance and longitudinal distance between the ignition source and the transverse center can be described by a relatively independent experienced formula. The larger the power of the ignition source, the smaller the range of the influence of different offset ignition sources on the longitudinal attenuation of temperature rise. Related Articles | Metrics

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Fire resistance analysis of linked column frame based on hybrid simulation CAI Xin-jiang, CHEN Zhe-ying, MAO Xiao-yong, TIAN Shi-zhu, 2021, 40 (5):  634-638.  Abstract ( 1724 )   This paper adopts the hybrid simulation method, taking the three- story plane linked column frame as the research object, aiming at the fire condition of the bottom middle column, carries out the fire resistance performance of the whole frame with solid elements, the whole frame with multi-scale elements, the whole frame with multi- scale hybrid simulation elements and traditional single column, then compares with the fire resistance limit, axial deformation, axial force and lateral deformation. The results show that the traditional fire column lacks the restraint effect and the fire resistance limit is smaller, the deformation rate of the axial deformation is faster in the later stage, and the larger lateral deformation occurs earlier, the result is conservative. The multi- scale hybrid simulation results are more consistent with the overall structure, the efficiency is improved under the premise of ensuring the accuracy. The conclusions verifies the feasibility of the hybrid simulation method for the fire resistance analysis of the whole structure, and provides a new method for the fire resistance analysis of the structure. Related Articles | Metrics

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Comparison of smoke exhaust effect between ceiling and lateral mechanical smoke exhaust in tunnel ZHONG Wei, SUN Chao-peng, MA Wen-hui, GAO Zi-he, ZHAO Jun 2021, 40 (5):  639-643.  Abstract ( 1798 )   In order to compare the smoke exhaust effect of ceiling mechanical smoke exhaust and lateral mechanical smoke exhaust in tunnel fire, the temperature distribution, velocity vector field distribution, smoke output, heat output, and smoke exhaust efficiency of the two smoke exhaust methods in tunnel fire were numerically simulated. The results show that the velocity vector field distribution and the smoke inhalation method of the two smoke exhaust methods are quite different. The ceiling mechanical exhaust has higher smoke exhaust volume and exhaust heat, and the exhaust effect is better; The lateral mechanical smoke exhaust is more likely to occur plug-holing and cause the fresh air drawn directly into the smoke exhaust system, and its smoke exhaust efficiency is always less than that of the ceiling mechanical smoke exhaust. Related Articles | Metrics

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Analysis on the fire spread law of brick-wood structured ancient buildings under different flow velocity YUAN Chun-yan, LANG Yu-jia, WANG Kun, LIU Xing, WANG Yao-lin 2021, 40 (5):  643-648.  Abstract ( 1738 )   Fire spread characteristics, heat release rate, temperature change etc. have been studied to explore the the changing rules of the fire spread characteristics under different flow velocities in the brick-wood structured ancient buildings. Taking Sanyuan Town God's Temple, a typical brick- wood structure system in China, as an example, with the help of BIM, fire scenarios have been developed to do the fire simulation analysis. The results show that the flame spread fluctuates periodically. within certain areas, the higher the flow velocity, the shorter time for the heat release rate to reach the peak, the shorter time interval between the primary peak and the second peak, and the shorter time to reach the flashover. The buoyancy of hot smoke will cause the flame to spread upward to the roof, where the temperature is the highest, and the structure there will be endangered more easily. Related Articles | Metrics

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Study on overflow fire behavior of parallel double windows on facade wall out of building based on FDS QING wei-jian, HUANG bin 2021, 40 (5):  649-654.  Abstract ( 1733 )   The former theory of single window overflow fire is not suitable for multi window, and there are obvious differences between them. In order to explore the phenomenon and mechanism of multi window overflow fire, two building models were established based on FDS, and two parallel windows were set up on the facade wall. The influence of fire source power (HRR) and window spacing (D) on the behavior of overflow fire in parallel double windows, indoor air flow rate, height of overflow flame (Hef) and superstructure facades were studied. The results showed that in the ventilation control fire, the air mass flow rate coefficient k decreases with the increase of D, and finally tends to be stable. In the fuel control fire, the larger the HRR, the greater the k. Under the same HRR, with the increase of D, k increases at the beginning and then decreases, and then tends to be stable. Under the same D, the bigger the HRR, the higher the Hef. Under the same HRR, with the decrease of D, Hef decreases at the beginning and then increases. That is, there is a critical transition distance D*, and the larger the HRR, the greater the D*. H ˉef /ζ1 = cQ* 2/5 ex is only applicable to single window or relatively independent window with little influence among multiple windows. In the range of D≤1 m, the heat receiving area of facade increases with the increase of D. Related Articles | Metrics

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Analysis of failure mechanism and influencing parameters of prefabricated steel bracket connection under high temperature LIU Bing, MAO Xiao-yong, 2021, 40 (5):  654-660.  Abstract ( 1714 )   In order to study the failure process, failure mode, and failure mechanism of the prefabricated steel bracket connection at high temperature, and the influence of different loads, eccentricity, rib thickness, stud diameter, and angle steel thickness on the temperature distribution, fire resistance, and displacement curve of the connection, the finite element model of prefabricated steel bracket connection is established through ABAQUS, and the accuracy of the model is verified by the test results. The results show that the average critical temperature of the side plate yield is 516.54 ℃ . The average critical temperature range of rib yield is 583.38~691.42 ℃. The average critical temperature range of rib failure is 610.85~728.96 ℃ . There are three final failure modes of connections under high temperature: 1) local buckling of the rib; 2) local bulge of the rib; 3) yield of the stud. The fire resistance of connections increases with the increase of rib thickness, the decrease of the load, and the increase of equal- leg angle steel thickness. The change of the eccentricity will change the failure mode of the ribs at high temperature.The increase in diameter of the stud will cause the temperature of the stud to increase, which harms improving the fire resistance of the connection. Related Articles | Metrics

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Studies on the smoke exhaust efficiency of the vertical shaft in naturally ventilated tunnel fires GUO Qing-hua, ZHU He-hua, YAN Zhi-guo 2021, 40 (5):  661-664.  Abstract ( 1742 )   The paper focuses on the smoke exhaust efficiency of the vertical shafts in naturally ventilated tunnel fires by using numerical simulation. The impact of the heat release rate (HRR), shaft height, length and width and shaft location on the tunnel ceiling are taken into consideration. The results are compared higher. The smoke exhaust efficiency becomes greater with the increase of the shaft length and width. Besides, it is found that when the shaft is located on the centerline of the tunnel ceiling, more smoke will be exhausted in comparison with that the shaft is located on the tunnel side, and the smoke can be controlled well. Furthermore, the proposed model can predict the smoke exhaust efficiency of the shaft in the naturally ventilated tunnel fires. Related Articles | Metrics

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Study on outdoor platform evacuation of mega-city complex MA Zi-chao, LI Xiao-ran , XIAO Ze-nan, CHEN Jing, YAN Chao 2021, 40 (5):  665-667.  Abstract ( 1767 )   In order to improve the personal evacuation safety of super large city complex, based on the architectural characteristics of urban complex with outdoor platform, this paper discusses the way of using outdoor platform for evacuation. FDS software and Pathfinder software are used to simulate the smoke flow and evacuation of the selected fire scenario in the building, the results show that using outdoor platform for evacuation, the evacuation time of the whole building is 2 234 s, which is far lower than the risk arrival time, the evacuation effect is better and the safety of personnel can be guaranteed. Related Articles | Metrics

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Research on water damage of ancient wooden structure after spraying with high pressure water mist fire extinguishing system YU Ping-wei, WANG Yi-xin, GUO Qing-bo, YANG Wan-qing, QIAO Yi-qiang, SHI Xiao-long 2021, 40 (5):  668-672.  Abstract ( 1781 )   High pressure water mist fire extinguishing system will cause water stain damage on the wooden components, in order to understand the water- stain loss, this paper studied the rates of water content, drying rates in shade and rotten state of 10 kinds of wood. Through setting up an experiment platform and conducting simulation experiments, the change of water content in the experimental wood bricks after spraying high pressure water mist was tested under different atmospheric humidity and temperatures, the trend of water content, drying rates in shade and rotten state of the experimental wood bricks after spraying were analyzed. The experimental results showed that the measured values of the water content in the experimental wood bricks after spraying high pressure water mist were within 35%, after drying 2 h，the values dropped to 20%, and the values decreased below the equilibrium water content of Henan province after drying 5 h in shade, the experimental wood bricks didn’t decay after 45-days. Through the introduction of the fire protection design project of Jidu Temple, highpressure water- mist fire extinguishing systems technical advantages in the fire- fighting renovation of ancient buildings are illustrated, which provides reference for the design of fire extinguishing system in ancient buildings. Related Articles | Metrics

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Numerical simulation of maximum temperature of urban V-shaped slope tunnel fire JIANG Xue-peng, , , YU Si-wei, , JIN Jun, 2021, 40 (5):  672-678.  Abstract ( 1703 )   By using the FDS numerical simulation method, the smoke movement characteristics of the V- shaped slope tunnel and the temperature distribution on the longitudinal centerline of the tunnel during a fire are studied, and an empirical prediction model for the maximum temperature rise parameters of the roof at different fire positions is proposed. The results show that when the fire source is 120 m away from the right of the slope change point, the peak temperature point of the longitudinal centerline of the tunnel shifts to the downstream direction, the shift distance increases with the increase of the slope, and the maximum temperature of the tunnel roof decreases with the increase of the slope. By deriving the prediction model of the maximum temperature rise parameter when the distance between the nondimensional fire source position and the variable slope point is different, it is concluded that the dimensionless maximum temperature rise parameter increases with the increase of the dimensionless fire source position, and is proportional to the 0.8th power of the dimensionless heat release rate, and has a nonlinear and non-monotonic relationship with the slope of the tunnel. Related Articles | Metrics

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Study on prediction accuracy of radiant models of gasoline pool fire LIU Hong-sheng, GUO Song, LIU Xiao-yong, ZHOU Yun, WANG Zi 2021, 40 (5):  679-683.  Abstract ( 1748 )   In this paper, the variation of the prediction accuracy of the semi-empirical model of pool fire radiation with the diameter of gasoline pool fire was analyzed. The error between the calculated radiant heat flux of each combination model and the experimental has been analyzed by MATLAB value. The optimal combination model was screened out. The result verified that the prediction accuracy of classical solid flame model can be improved by using the new formula of radiative fraction ηrad presented here，and the combination of classical solid flame model and the formula of the radiative fraction presented here is optimal to predict the radiant heat flux of gasoline pool fire. When the diameter of the pool fire ranges from 0.3 to 22.3 m, the normalized mean square error between the predicted value and the experimental value is less than 0.05, the updated combination model can provide more accurate prediction than other semi- empirical models, such as Mudan model and Shokri-Beyler model. Related Articles | Metrics

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Multi paradigm modeling of emergency evacuation based on Anylogic GUO Hao-xiang, HU Yu-ling, 2021, 40 (5):  683-687.  Abstract ( 1825 )   In order to solve the problems of current emergency evacuation simulation model lacking operability, reusability and extensibility, this paper combines the multi-paradigm modeling theory with the emergency evacuation system, and proposes a multi paradigm modeling method for emergency evacuation based on the Anylogic platform. Based on the meta-model idea of the multi-paradigm modeling, the whole multi-paradigm evacuation model is composed of the evacuation individual meta-model, evacuation environment meta-model, and emergency discrete event meta-model. The Agent technology, differential equation and discrete events are used respectively to model the three main parts. Case analysis of the evacuation of people in the building with fire as the emergency situation is carried out.The experimental results prove the feasibility of the multi-paradigm modeling method. Related Articles | Metrics

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Study on fire risk evaluation of underground utility tunnel based on structural equation WANG Xiang, ZHOU Shi-yu, GUO Yi-bin, DUAN Yong-hui 2021, 40 (5):  688-691.  Abstract ( 1709 )   In order to understand the fire risk of utility tunnel, this paper explores the weight and mechanism of each risk factor, so as to enhance the fire risk control ability of underground utility tunnel. Firstly, based on the literatures related to building fire risk identification over the years, an index system was established by exploratory factor analysis method. Secondly, data samples were collected through questionnaires. Finally, the structural equation model is used to calculate the weight of each fire risk factor, and the potential influencing factors are deeply analyzed. The empirical results show that the fire prevention ability, personnel prevention and control ability, fire supervision ability and fire control system ability of the building have a positive effect on the fire risk control of the the tunnel. The results show that the correct selection of decorative materials and equipment the tunnel gallery is the key to fire prevention, and it is an important measure to perfect the supervision system and improve the safety quality of relevant personnel. Related Articles | Metrics

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Analysis of the situation and management strategy of metro fire control in China DU Yu-long, MA Jun-hai 2021, 40 (5):  692-695.  Abstract ( 1836 )   Based on the investigation of the situation of metro the time, region, object and result elements of the protection system is analyzed .To achieve the goal of fire protection, the existing problems are analyzed and sorted out.Starting from the improvement of social governance capacity, the paper puts forward solutions and suggestions at the national, local and individual levels, and points out the research direction and task requirements in points of model, quantitatively analysis and effectiveness evaluation. Related Articles | Metrics

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Inhibition effect of water mist with single and double nozzles on n-heptane pool fire WANG Jing-dong, HE Yuan-hua, TAO Bo 2021, 40 (5):  696-700.  Abstract ( 1705 )   In order to study the effectiveness and mechanism of single and double nozzle water mist in suppressing n- heptane pool fire，the droplet size of water mist with single and double nozzles and the suppression of a 20 cm n-heptane pool fire were studied in a simulated cargo compartment of a half volume aircraft. The results show that the cooperation of the double nozzles will lead to the collision between the droplets and secondary breakup, which is helpful to improve the atomization effect. Based on the measurement and calculation of fuel surface temperature, the average temperature of flame zone state and oxygen concentration in cabin, the dominant mechanism of water mist suppression with single and double nozzles is analyzed. The results show that the average time of single nozzle water mist fire extinguishing is 283.14 s, and the water consumption is about 3.54 L. The fuel surface cooling is the main mechanism of fire suppression. The average time of double nozzles water mist fire extinguishing is 212.22 s, and the water consumption is about 5.31 L. Flame cooling is the main mechanism of fire suppression. Related Articles | Metrics

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Research and development trend of sprinkler system in warehouse YANG Bing-jie 2021, 40 (5):  700-703.  Abstract ( 1780 )   Through the comparison and analysis of data and literature, this paper summarizes the fire situation of warehouses in China in recent years, and puts forward that the protection of warehouse fire at the initial stage should be strengthened. Based on the study of the latest standards and research literature at home and abroad, this paper compares the differences between domestic and foreign standards on the location of automatic sprinkler system in logistics warehouse, analyzes the research trends and development trend of automatic sprinkler system in domestic and foreign research institutions in recent years, and prospects and summarizes the new technology of automatic sprinkler system applied in logistics warehouse. It is proposed that the application technology research of automatic sprinkler system should be strengthened in new logistics warehouse, special protection object and wet system alternative technology. Related Articles | Metrics

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Study on large scale ultra-high voltage converter fire and foam water mist combined extinguishing system CHEN Guang, LUO Jian-fei, JING Wei, ZHANG Jian-cheng 2021, 40 (5):  704-708.  Abstract ( 1654 )   In order to study the combustion and extinguishing characteristics of the large- scale ultra- high voltage converter (UHV converter)pool fire, the UHA converter fire model was built, an experimental platform for fire extinguishing was designed. By pool fire and foam-water mist combined fire extinguishing experiment, the fire plume temperature around the UHV converter was analyzed. We found that the combustion behavior of tested pool fire is similar to the actual UHV converter fire. The wall attachment phenomenon and air entrainment effect were obvious, and the highest temperature is located in the valve side. The wall temperature of the converter increased rapidly, the yield strength of the steel was reduced, and the structure was deformed. But the internal transformer oil and firewall heated up slowly. Foam water mist combined system can extinguish the large- scale UHV converter fire quickly, and the cooling effect and oxygen dilution effect were obvious. Related Articles | Metrics

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Study on the solution to installation of water mist system in a domestic subway YANG Yan-long, HE Hong, HU Nai-lin, SONG Rui 2021, 40 (5):  709-712.  Abstract ( 1777 )   This article compares the automatic fire extinguishing systems in the industry and proposes the advantages of using water mist fire extinguishing systems in urban rail transit vehicles. Through an example of installing a water mist fire extinguishing system in a domestic subway, the scheme of the water mist fire extinguishing system, system composition and configuration scheme of the water mist device are introduced. According to the requirements of local standards, through the analysis of environmental parameters during fire fighting, it was verified that the installed water mist fire extinguishing system met the design requirements and achieved the purpose of fire suppression and control. Related Articles | Metrics

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Development of elevator evacuation warning and supporting system in high-rise buildings WANG Zi-you, LIU Sheng-peng, ZHANG Zhen-wei 2021, 40 (5):  713-716.  Abstract ( 1663 )   In high- rise building fire, changeable fire environment poses a serious threat to the operation of the elevator. Aimed to this problem, based on the technical requirements, the elevator evacuation warning and supporting system is proposed. The components and control logic of the system are introduced. The functional prototype is manufactured whose efficiency is shown by demonstration projects. Related Articles | Metrics

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Design and characteristic analysis of a load-sensing and automatic speed-regulating hydraulic decelerator ZANG Ke-jiang, CHEN Mu-feng, XIE Huang-sheng, JIN Lu, GUO Hao-zhi, YE Ting, LIU Xiao-chuan, ZHONG Xin-kui 2021, 40 (5):  717-721.  Abstract ( 1813 )   In order to solve the problem of the large range of falling speed of escape decelerator, on the basis of the fixed orifice hydraulic resistance escape control device, a load- sensing automatic speed- regulating hydraulic decelerator is proposed. In this paper, the working principle of the load-sensing automatic speed-regulating hydraulic decelerator is described, the structure and dynamic parameters of load-sensing hydraulic decelerator are established. The key factors that affect the descent of the load- sensing automatic speed- regulating hydraulic decelerator are analyzed, the relationship between the descent speed, the diameter of the throttle and the weight of the human body are deduced, the operating characteristics of the load-sensing automatic speed- regulating hydraulic decelerator were analyzed by an example. The load-sensing hydraulic decelerator is able to control speed automatically by sensing body weight, the decreasing speed within a narrow range of change, and improve the stability of escape speed, therefore, the load-sensing automatic speedregulating hydraulic decelerator can work in close to 1.5 m/s, which is implemented in the security of national standard drop speed within the range of 0.16~1.5 m/s, and enhancing the working efficiency of the escape velocity and decelerator. This research lays a theoretical foundation for the development of highend hydraulic decelerator. Related Articles | Metrics

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Design and application of video monitoring system for complete vehicle fire experiment XU Long-fei, ZHANG De-sheng, ZHAO Xiao-yang, LU Zhi-bao, XIAO Ling-yun 2021, 40 (5):  722-725.  Abstract ( 1695 )   In the process of investigating the cause of vehicle fire, the most important step is determining the fire location and ignition point based on the fire spreading trace analysis. The premise of accurate identification of fire trace features is to be familiar with the characteristics and spread process of fire.This paper collects the propagation path and key time nodes of the fire and smoke in the process of vehicle fire spreading through the omni-directional time synchronization video monitor system developed by ourselves. It analyzes and studies the characteristics of vehicle fire spread traces, and provides effective technical support for identifying the fire location and ignition point. Related Articles | Metrics

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Application of genetic algorithm to optimize BP neural network in multi-parameter fire detection ZHENG Hao-tian, ZHU Jun-qi, JIA Rong-tian 2021, 40 (5):  725-729.  Abstract ( 1753 )   This article proposes a multi- parameter data fusion method based on genetic algorithm to optimize BP neural network to realize fire detection, which can significantly improve the accuracy of fire detection. In view of the low stability of the random weight and threshold of BP neural network, it is proposed to use genetic algorithm to optimize the BP neural network to optimize the initial weight and threshold of the neural network to improve the generalization performance of the model, and use the model to compare the standard data fusion of temperature, smoke concentration and CO concentration in open flame and smoldering fire realize fire detection. The simulation results show that, compared with the pure BP neural network, the BP neural network fire detection algorithm optimized by the genetic algorithm can realize fire detection more quickly and accurately, the accuracy of fire detection is significantly improved, and the accuracy of fire recognition is increased to 98.84%. Related Articles | Metrics

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Effect of carbon materials on the flame retardant and smoke suppression performance of waterborne intumescent coatings FU Shi-jian, LONG Hai-yang 2021, 40 (5):  730-734.  Abstract ( 1733 )   This study uses expanded graphite (EG), carbon nanotubes (CNTs), fullerene (C60), and graphene (Gr) as fillers to study their performance as the flame retardancy, thermal stability, smoke suppression and water resistance in water-based intumescent coatings. The effect of carbon materials on the fire and smoke suppression performance in water-based intumescent coatings was studied. The carbon layer was characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), X- ray diffraction (XRD) and particle size distribution. The test results show that carbon materials can effectively improve the fireproof performance of water-based intumescent coatings. When heated for 300 s, the temperature of the back of the board coated with the fireproof coating is 50% lower than that of the steel plate without fireproof coating, and the fireproof coating with carbon materials have better heat insulation; SP-Gr has the largest expansion coefficient of the carbon layer, which is about twice that of no carbon material coating, and the coating with Gr added under high temperature heating has the largest carbon residual weight; the fire retardant coating with carbon material has a better smoke resistance effect. The density is reduced by more than 30%; the coating with Gr has the best water resistance. In this study, adding graphene to water-based fireproof coatings has the best performance. Related Articles | Metrics

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Visualization analysis of nano flame retardant technology based on CiteSpace ZHANG Ding-ran, YANG Xiao-xi, LU Yu-xin, WANG Hui-ya 2021, 40 (5):  734-737.  Abstract ( 1746 )   In order to visually analyze the knowledge base, research hotspot, research frontier and development trend of domestic nano flame retardant technology，1 156 domestic literatures on nano flame retardant technology collected in CNKI database from 2000 to 2019 were selected as research samples. The knowledge map was studied with bibliometrics and CiteSpace software. The key words co-occurrence network map and the distribution table of emergent words were drawn, and the possible new research directions in this field were explored. The experimental results show that: After the research of nano flame retardant technology in China has gone through three development frontier stages of "early frontier", "medium frontier" and "latest frontier", the field of nano flame retardant will continue to lead the future with clean and efficient flame retardant new technology. Related Articles | Metrics

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Study on foam extinguishing agent for vehicle ethanol gasoline fire BAO Zhi-ming, ZHAO Ting-ting, ZHANG Xian-zhong, CHEN Yang, JING Li-shuai 2021, 40 (5):  738-741.  Abstract ( 1712 )   With the wide use of ethanol gasoline, in order to effectively deal with this particular liquid fire, a new type of highly efficient non PFOS foam extinguishing agent has been developed through the study of key components screening and blending. The product has passed the national standard GB 15308- 2006 foam extinguishing agent detection, the highest level of fire extinguishing performance has been achieved, and the fire extinguishing performance of the product is better than that of other domestic products through comparative tests. Further study is made on the key parameter of extinguishing supply intensity. Related Articles | Metrics

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Optimization and study of three-phase foam foaming agent for polymer gel ZUO Xi-xi, WANG Bin, ZHU Xi-ying, LI Ya-dong, ZUO Sheng, MA Xiang-mei, 2021, 40 (5):  741-743.  Abstract ( 1819 )   In order to improve the performance of fire- fighting three-phase foam, five agents, including polymer gelling agent, surfactant, and foam stabilizer, are mainly used to optimize the compounding of three-phase foam foaming agent by orthogonal experiment. The self-designed air compressor and foaming gun were used to determine the foaming multiple and stabilization time of the compound system. Orthogonal experiment design includes 5 factors and 4 levels. The results show that through comprehensive analysis of the foaming multiple and stabilization time of the compound system, when the mass ratio of AES, 6501, K12, PAM, FM- 550 is 6 ∶ 6 ∶ 9 ∶ 0.3 ∶ 2, the foam performance is the best, and the polymer gelling agent, surfactant and foam stabilizer have good synergistic effect. The three- phase foam performance of the polymer gel foaming agent is compared with the three- phase foam foaming agent for mines purchased on the market. The polymer gel foaming agent is compared with the three- phase mine foaming agent purchased on the market, and the results show that: the foaming ratio of the three- phase foam formed by the foam blowing agent has increased by 52% , and the stabilization time has increased by 117%. Related Articles | Metrics

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Simulation study on gas flow law of aerosol fire extinguishing agent GE Meng-zhu, ZHOU Yang 2021, 40 (5):  744-746.  Abstract ( 1731 )   Based on the optimized S-type aerosol fire extinguishing agent formula, the fire extinguishing performance of S-type aerosol fire extinguishing agent in smoke chamber was tested, the similar curve model was obtained through FDS software simulation. A similar curve model was obtained by simulating the extinguishing time of aerosol fire extinguishing agent at different space locations. The maximum temperature of simulated aerosol fire extinguishing agent is between 500 ℃ and 600 ℃, which is consistent with the experimental data measured by infrared imager. Related Articles | Metrics

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Research on sustainable development of social rescue force construction in the new era ZHU Jun-yu, HOU Ya-xin, XIAO Lei, WANG Hui-fei, YANG Ming 2021, 40 (5):  747-750.  Abstract ( 1811 )   In view of the basic characteristics and development stages of China's social rescue forces, the challenges faced by China's social rescue forces are analyzed from the aspects of top- level design mechanism, social security system, team management system, professional construction, culture and spirit. Some suggestions to promote the sustainable development of social rescue forces in China are put forward. In the future, the development of social rescue forces should start a new model of sustainable development in the aspects of government policy support, scientific regulation and social security, and form a benign ecosystem. Related Articles | Metrics

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Current situation of earthquake disaster fire and rescue team development in China WANG Ping, HU Cheng, YAO Xin-qiang 2021, 40 (5):  750-753.  Abstract ( 1832 )   In this paper, we first analyze the current earthquake emergency rescue system in China, then summarize the state of earthquake disaster firefighting team, analyze the weak points, and finally put forward corresponding countermeasure suggestions for establishing a high-quality professional earthquake disaster fire and rescue team. Related Articles | Metrics

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Discussion on the key points of emergency plan revision from the perspective of "Trinity" YANG Zhen, KONG Sheng-li, JIA Yin, DENG Shi-xing 2021, 40 (5):  754-758.  Abstract ( 1715 )   This article analyzes the main problems existing in the preparation of the emergency plan, especially: the imperfect legal construction, the obvious assimilation of the contents, and the lack of cohesion between the plans. From the three perspectives of the legal system, the emergency plan system, and the technical standard system, this article provides the key points and suggestions for improving the compliance, rationality and operability of the emergency plan. The research results can provide references for various enterprises and institutions in the preparation of various plans. Related Articles | Metrics

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research on influencing factors of civil aircraft fire accidents in flight DU Hong-bing, WU Feng-ting, HU Hui, ZHANG Shi-bo 2021, 40 (5):  759-762.  Abstract ( 1728 )   In order to systematically analyze the influencing factors of civil aircraft fire accidents and effectively prevent the occurrence of similar accidents，the local control structure of aircraft fire accidents is constructed by using STAMP model based on the aircraft fire accident in flight. Eleven influencing factors of civil aircraft were extracted from fire occurrence and extinguishment. By means of DEMATEL- ISM method, the causality attribute and centrality ranking of the influencing factors were determined, and the multi- level hierarchical structure model of civil aircraft fire accident influencing factors is established. The hierarchical structure of the accident influencing factors was divided into four levels. The results showed that lack of pyrotechnic disposal ability, human error, information interaction obstruction, passive restraint failure and mechanical equipment failure are the key factors of the accident through the centrality ranking of factors, and cognitive defects and insufficient safety education and training are the root influencing factors of civil aircraft fire accidents through the analysis of multi-layer hierarchical structure model. Related Articles | Metrics

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Progress in identification, research and analysis of gasoline combustion-supporting agent WANG Xin, ZHANG Guan-nan, ZHU Jun, WAN Yi-fu, JIANG Hong, LIU Zhan-fang 2021, 40 (5):  763-768.  Abstract ( 1678 )   Gasoline is a commonly used combustion-supporting agent in arson. The instrumental analysis technology and the latest practice standards for the identification and research of gasoline-type combustion-supporting agents at home and abroad are reviewed, and the promotion of chemometric methods to the research and analysis of combustion- supporting agents is emphasized. It also forecasts the development direction of research and judgment analysis, such as identification, classification, and retrospective analysis of gasoline- type Combustion- Supporting agent. Related Articles | Metrics

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Fire cause analysis of fairs based on MCFM WANG Hui-ying, WU Qi-ming, WANG Zhao-qiang 2021, 40 (5):  768-771.  Abstract ( 1707 )   In order to reduce the large fair fire risk, explore its fire cause factors, the interpretation structure model is used to analyze the inner link and hierarchical relationship among various factors. Combining cross impact analysis method and Markov chains forecasting model, a quantitative analysis model is built to get the steady- state probability matrix of the fire cause factors. The results show that the Markov probability is more accurate, the model can clarify the key screening and controlling points of large fair fire cause. Related Articles | Metrics

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Investigation and rectification analysis of a high-rise building cable well fire HAO Guang-yu 2021, 40 (5):  772-774.  Abstract ( 1815 )   Based on a high-rise building cable well fire, the fire investigation progress is introduced. The investigation of more than 100 cable in the well is focused. The direct cause of the fire is decided. By extended survey, the fire cause is analyzed. The study can warn the communication industry to actively rectify and eliminate hidden fire danger, and achieve the goal of fire extended survey. Related Articles | Metrics

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Analysis and verification of the causes of the burning of truck air conditioner radiator WU Bing-bing, DENG Fan-lin, ZENG Zhi-wei, WANG Jun-zhao, 2021, 40 (5):  775-777.  Abstract ( 1726 )   This report analyzed the cause of the fan motor burnout through macroscopic, microscopic, and metallographic test methods to find out the root cause. The simulation verification was used to analyze the cause of burnout and replicate the burnout process. The results showed that the root cause of the primary short circuited of the copper wire was the existence of cracks on the surface of the copper wire. When the motor was running at high speed, the fatigue propagation of the crack caused the wire cross- sectional area to decrease. Excessive instantaneous current during startup caused high temperature fusing of the copper wire. After the copper wires fused, the fuse end was stuck between the rotor and the stator of the motor after stopping. When restarting, the motor could not rotate due to the low starting torque and was overloaded and eventually burned. Related Articles | Metrics