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15 December 2022, Volume 41 Issue 12 Previous Issue    Next Issue

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Study on combustion characteristics of spray paint on thin metal surface Liu Guolei, Niu Junfen, Cui Yu, Ma Qiufeng 2022, 41 (12):  1619-1622.  Abstract ( 835 )   The combustion characteristics of spray paint on thin metal surfaces were studied by cone calorimeter. Four heat radiation intensities of 35, 50, 65 and 80 kW/m2 were selected, and parameters such as ignition time, heat release rate and CO release rate were obtained. It was found that the paint on the thin metal surface is a typical hot thin solid, and the reciprocal of the ignition time has a linear relationship with the thermal radiation intensity. The more the number of spray layers, the smaller the heat radiation intensity required for ignition, and the higher the fire hazard. The experimental results show that the critical heat flux intensity of 1-layer spraying, 2-layer spraying and 3-layer spraying is about 30.8, 10.0 and 5.0 kW/m2, respectively. The heat release rate showed a bimodal characteristic, the first peak and the second peak increased linearly with the thermal radiation intensity, and the peak increased with the increase of the number of sprayed layers. The CO release rate showed three peaks. With the increase of thermal radiation intensity, the fire performance index of each sample continued to decrease, the fire spread index continued to increase, and the fire risk increased. Related Articles | Metrics

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Photovoltaic DC series arc fault area identification Kong Lingzhe, He Baina, Bian Chenxi, Liu Yujia 2022, 41 (12):  1623-1628.  Abstract ( 803 )   The series arc in the photovoltaic DC system cannot be detected and cut off by the protection device, the arc continue to burn and generate high temperatures, which cause great harm to the safe operation of the photovoltaic system. Aiming at which, Cassie arc model is analyzed, the electrode spacing is introduced into the model, and the relationship between electrode spacing and arc stable combustion is analyzed. Then, the photovoltaic series arc simulation model is established, and the current data in different regions during steady combustion is obtained, feature vectors are determined by analyzing the arc fault characteristics, a probabilistic neural network model is built to identify the arc fault, and BP neural network model is established as comparison, the series arc category corresponds to the area to realize the identification of the series arc fault area. The results show that the improved Cassie arc model can be used to characterize the dynamic process and stable combustion state in different areas; under the same data, the recognition rate of the probabilistic neural network model is higher than the BP neural network, and the series arc fault area can be accurately located. Related Articles | Metrics

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Experimental study on explosion pressure of micron lignite dust Liu Tianqi, Tian Weiye, Jia Ruiheng, Sun Ruicheng 2022, 41 (12):  1629-1631.  Abstract ( 739 )   A near spherical coal dust explosion experimental device was used to test and analyze the change law of explosion pressure characteristics with micron lignite dust as the research object. The research shows that the maximum pressure of micron lignite dust explosion is 0.73 MPa, and the maximum pressure rise rate is 65.78 MPa/s. The explosion intensity can cause great harm to people near the explosion source. The mass fraction of volatile matter involved in the explosion reached 26.25%, indicating that volatile matter is the main component involved in the explosion of lignite dust. When the dust injection pressure is between 1.4 MPa and 2.6 MPa, the maximum explosion pressure and the maximum pressure rise rate first increase and then decrease. When the dust injection pressure is 1.8~2.2 MPa, the maximum explosion pressure is relatively large, indicating that the lignite dust diffuses most fully in the area near the ignition head under this condition. As the increase of the ignition delay time from 70 ms to 130 ms, the maximum explosion pressure and the maximum pressure rise rate both increase first and then decrease, and the optimal ignition delay time is about 100 ms, indicating that under this condition, lignite dust particles reach the best dispersion state, so that the explosion intensity can be maximized. Related Articles | Metrics

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Early fire source location in aircraft cargo hold based on crossover arrangement of sensors Xiong Xiao, Chen Da, Han Zhou, Zhang Wei, 2022, 41 (12):  1632-1636.  Abstract ( 734 )   This paper presents an early fire source location method for cargo hold fire location under low temperature and low pressure during high altitude flight. The method is based on the cross arrangement of sensors, the delay interval of smoke signal detected by sensors is used to calculate the displacement difference of smoke propagation, and the fire source location is traced. It can accurately locate the fire source in the early stage of fire, effectively reduce the amount of fire extinguishing agent, reduce the damage of fire extinguishing agent residue to the atmosphere environment, and promote the construction of green civil aviation. In order to verify the accuracy of the positioning algorithm, A330-300 rear lower cargo compartment model is 1∶1 established in PyroSim fire simulation software, and 20 fire source points are randomly selected. The average relative error of fire source location under low temperature and low pressure is 2.44%. The results show that this positioning method has high positioning accuracy and is suitable for fire source detection in aircraft cargo hold. Related Articles | Metrics

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Experimental study on spreading performance of fire foam on liquid fuel Chen Yang, Bao Zhiming, Zhang Xianzhong, Zhao Tingting 2022, 41 (12):  1637-1639.  Abstract ( 768 )   For the fire-fighting of liquid fires, the fire-fighting process often has the phenomenon of long fire-fighting time and repeated fire. The fundamental reason lies in the lack of in-depth study of foam on liquid fuel fire extinguishing process. The spread of foam on liquid surface is probably the most important factor to suppress the fire on liquid surface. It is of great significance to study the spread and coverage of foam extinguishing agent in the process of extinguishing fuel surface. In this paper, 3%AFFF, 3%AFFF/AR and 3%FP were selected to study the spreading performance of foam in rectangular channel.The results show that the spreading speed of 3% AFFF and 3% AFFF/AR is faster than that of 3% FP because the shear stress on the fuel surface is small. Because 3% AFFF and 3% AFFF/AR can form water film on the surface of solvent oil, their spreading speed is similar to that on the surface of water. 3% FP cannot form water film on the surface of solvent oil, which is slower to spread than that on the surface of water. Related Articles | Metrics

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Research on monitoring signal drift and burr suppression of intelligent fire warning system Sun Lei, Ma Yong, Guo Dongliang, Liu Jianjun 2022, 41 (12):  1640-1643.  Abstract ( 763 )   The safety accident of prefabricated cabin type lithium iron phosphate battery power station will cause serious economic losses and social impact. It is very necessary to develop an intelligent fire warning system for timely intervention and rapid response. In this paper, a fire intelligent warning system based on characteristic gas (H2, CO) concentration and BMS temperature signal is developed. However, there are some abnormal problems such as burr and drift in monitoring signal of gas detector, which maybe led to false alarm of the system. The effects of these abnormal problems are eliminated by means of time delay and comparison of monitoring data from multiple detectors, which verified the effectiveness and reliability of the accurate intervention of the fire warning system by the analysis of practical application cases. Related Articles | Metrics

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Research on mass loss of double fire sources in a sealed ship engine room Wang Zhe, Liu Jiahao, Li Dongxia, Chai Xincheng 2022, 41 (12):  1644-1648.  Abstract ( 744 )   The fire experiments were carried out in a 3 m (length) × 3 m (width) × 3.5 m (height) confined cabin with square double oil pools with side lengths of 10, 15, 20 cm, respectively, at different spacings to investigate the variation law of combustion rate. The results show that the double oil pool fire in the confined compartment can be divided into three typical combustion stages: initial, stable and extinguished, and the dimensionless spacing S/L of different oil pools shows a parabolic relationship with the combustion rate and the threshold value of S/L at the peak of mass loss rate is between 0.70 and 0.85, which is obviously different from the development of double fires in open space and tunnel semi-enclosed space. On this basis, a prediction model for the dimensionless heat release rate in a confined compartment with a modified spacing S is given. Related Articles | Metrics

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Study on the burning and explosion risks of sludge thermal drying process Ouyang Gang, Liang Jun, Jiang Huyijia, Wang Xinhua, 2022, 41 (12):  1649-1653.  Abstract ( 833 )   In order to prevent the safety accident occurrence in the thermal drying process of municipal sludge, the burning and explosion properties of sludge in the state of accumulation and dispersion were analyzed by using relevant instruments. And combined with the technique and equipment of the sludge heat drying workshop, the safety risks in the thermal drying process of the sludge are researched systematically. The results showed that no self-heating occurs when sludge was stored at 140 ℃ for 24 hours, but when the temperature increased to 170 ℃ sludge releases heat, and spontaneous combustion occurs between 200 ℃and 220 ℃. Which means that when the internal temperature of the layer drying process system is greater than 170 ℃, the possibility of sludge exotherm and spontaneous combustion is high, while the safety risk of storing dry sludge at room temperature is low. When the sludge dust and air form a mixture dust, explosion will occur, and the explosion pressure will increase as the sludge particle size becomes smaller, which indicates that there is a danger of sludge dust explosion inside the sludge dust collector. When the sludge is dried, ammonia gas, hydrogen sulfide and methane will be produced, so that there is a danger of gas combustion or explosion in the closed drying system. These results can provide safe technical support for the design of intrinsically safe sludge drying equipment and the development of sludge drying technology. At the same time, it has guiding significance and reference value for the safety of municipal sludge drying. Related Articles | Metrics

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Experimental study on characteristic parametersof typical combustibles fire in aircraft cargo Wang Haibin, Wang Maohua, Qu Chen, Zhen Yongjun 2022, 41 (12):  1654-1658.  Abstract ( 758 )   Photoelectric smoke fire detector is the mainstream used in the civil aircraft cargo, is the key to guarantee the safe operation of the aircraft. The detector is based on the smoke particles of light scattering signal for alarm, but because of suspended particles in the air (water vapor or dust, etc.) also has scattering effect, will trigger the fire detector alarm occurs. False alarms caused by such defects in principle occur from time to time. Taking the cargo plane typical combustion corrugated sheets, ju wood and the cotton rope as examples, blue light scattering power (representation for the surface area of concentration), infrared light scattering power (characterization for volume concentration) and particulate matter sauter mean diameter of fire characteristic parameters were analyzed, to optimize the fire characteristic parameters for the development of composite detectors. The results showed that: under atmospheric pressure, blue and infrared light have a good response to the change of particle concentration, and the sault average particle size can distinguish fire smoke particles from non-fire smoke particles, which can reduce the false alarm rate effectively. Related Articles | Metrics

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Simulation of evacuation of outpatient halls and optimization of window layout Luo Lin, Hong Hailang, Xiong Xingwen, Fu Zhijian, 2022, 41 (12):  1659-1664.  Abstract ( 810 )   To ensure the safety of the evacuation of the outpatient hall, the evacuation simulation and the optimization of the layout of the service windows were carried out. In this paper, several typical window layouts and the number and composition of patients in different outpatient halls are explored through field observations; modifying the fine discrete cellular automaton model by setting different moving and competing abilities based on the field survey data, an evacuation dynamic model for outpatient hall is proposed to simulate evacuation under different window layouts, and further set the special window. The main results include: A layout of windows on both sides is optimal, and the evacuation time is the shortest in this situation; The opposite layout has the highest evacuation fluency; The window layout has a greater impact on the patients with weaker moving ability; Setting priority windows can ensure the priority evacuation of people with disabilities, and setting priority windows on both sides near the exit is the most efficient for evacuation. This study provides support for the design of the service window layout in the outpatient hall and for the crowd evacuation management. Related Articles | Metrics

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Study on the performance-based fire design of a homestay inn Chen Jing, Xiao Zenan, Zheng Chanchan, Ma Zichao 2022, 41 (12):  1665-1668.  Abstract ( 792 )   Most rural buildings have smaller fire separation distance and lower fire-resistant levels. Now more and more rural residence is changed to a place of business, such as homestay inn. When the function is changed, the fire risk will increase because of evacuation difficulty and higher fire load. This paper applies performance-based fire design method to rural buildings. Performance-based fire design of a typical rural homestay inn was carried out. Uses theoretical calculation and numerical simulation methods, the safety of evacuation, fire spread and structure were analyzed. The strategy of adding automatic fire alarm device, setting self closing door, installing insulated fire window, adding noncombustible ceiling etc. were suggested. The strategy can decrease fire risk, increase fire safety, and provide a guide for the application of performance-based fire design in rural buildings. Related Articles | Metrics

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Study on smoke dispersion pattern of dual-fire source fire in highway tunnel under longitudinal ventilation Xu Chenggang, Qiu Jinwei, Lv Yifei, Miao Baocheng 2022, 41 (12):  1669-1673.  Abstract ( 718 )   Experimental and numerical simulations were used to study the variation of critical wind velocity of a dual-fire source fire in a tunnel. The effect of fire power and fire source spacing on the critical wind speed was studied. The results show that: as the spacing between the two fire sources increases, the required critical wind speed of smoke gradually decreases, and when the spacing between the two fire sources reaches the limiting distance, the required critical wind speed of smoke no longer changes; when the power of the fire source on the inlet side is determined, the required critical wind speed increases when the power of the fire source on the outlet side increases within the limiting distance, which means that the fire source on the outlet side has a facilitating effect on the smoke back-flow on the inlet side; within the limiting distance, the critical wind speed decreases quadratically to a stable value with the increase of spacing; the larger the total power of the two fire sources, the more obvious the reduction of the critical wind speed with the increase of the spacing. And the prediction formula of the critical wind speed was obtained. Related Articles | Metrics

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Discussion on enhanced smoke prevention of enlarged vestibule on the first floor of building Li Zhijun, Liao Shujiang, Wang Xing 2022, 41 (12):  1674-1678.  Abstract ( 1365 )   More and more architectural designs set the fire vestibule together with the lobby on the first floor to form an enlarged vestibule. The increase of floorage，personnel gathering and presence of combustibles puts forward higher requirements for smoke prevention safety of the enlarged vestibule on the first floor. This paper analyzes the structural characteristics and smoke prevention requirements of the enlarged vestibule on the first floor, and puts forward the way of enhanced smoke prevention. Related Articles | Metrics

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Establishment of fire spread model for village buildings based on UAV Lu Ting, Zheng Feiyang, Gao Xuewen 2022, 41 (12):  1679-1682.  Abstract ( 741 )   The lack of building information and drawings is the primary problem facing the fire prevention and control of village buildings. Aiming at the problems of heavy workload, high cost and inaccurate data obtained from traditional on-site surveying and mapping, based on the detailed modeling data of typical single buildings obtained from on-site investigation, this paper uses UAV tilt photography technology to obtain the geographic information data of village buildings, and establishes the analysis model of fire spread of village buildings. The simplified analysis method is further used to determine the fire spread and fire spread loss of different buildings in the building complex. Finally, this paper takes a village in Yunnan Province as the research object, establishes the fire spread model of the village and analyzes the risk of fire spread. The results show that this method can effectively obtain the modeling data of the village building fire spread model, and provide data support for the subsequent fire spread risk analysis. Related Articles | Metrics

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Research on fire detection experiment and numerical simulation of cable trench in substation Liu Guoqiang, Hao Yanan, Li Guihai, Li Guochun 2022, 41 (12):  1683-1687.  Abstract ( 776 )   In order to explore the influence of the sensitivity of the fire detector on the fire response of the cable trench and to verify the accuracy of the fire monitoring system, four types of fires: point temperature detectors, point smoke detectors, cable temperature detectors and suction smoke detectors were applied. A full-scale cable fire test was carried out in the standard substation cable trench fire compartment to test the fire alarm sequence of fire detectors with different sensitivities. Finally, according to the actual size of the cable trench, the FDS was used to build a numerical simulation model to simulate two different fire scenarios of open flame and smoldering, and the temperature field, toxic gas mass concentration and fire alarm sequence of fire detectors with different sensitivities are analyzed. The experimental results show that the average fire response time of cable temperature detectors, suction smoke detectors and point smoke detectors in substation cable trench fire detection are 41.2, 111.4 and 331.8 s respectively. The sensitivity of the detector has a great influence on the detection result, and its fire alarm response time is about 50% delayed compared with the cable-type linear temperature detector. Related Articles | Metrics

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Simulation analysis of leakage explosion of LPG tank car in locally blocked space Wang Yue, Xiao Ze, Ren Changxing, lv Dong 2022, 41 (12):  1688-1691.  Abstract ( 732 )   Taking loading and unloading station of LPG tank truck in an industrial park as an example, a physical model is established, and CFD method is used to simulate the leakage and explosion scenarios of LPG tank truck with different leakage rates in open space and partially blocked space. The results show that the close trees resist most of the initial kinetic energy of LPG leakage, and the LPG leakage stays within the range of 20 m. Over 20 m, the leakage is mainly affected by the dominant wind direction. Under the influence of trees, LPG spreads radially. The leakage area is large, but the LPG volume fraction is low. In an explosion scenario, explosion overpressure can be affected by many factors such as accelerated flame propagation, spatial blocking probability and volume fraction of LPG. For 25 mm leak aperture, explosion overpressure is basically the same in the case with or without trees, mainly because LPG does not leak into the tree area. For 200 mm leak aperture, the short-range explosion overpressure is affected by the volume fraction of LPG, the intermediate stage by the spatial blocking probability, and the final stage by the volume fraction of LPG. The maximum explosion overpressure is 5 739 Pa, which occurs 80 m away from the ignition point. Related Articles | Metrics

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Mesh optimization method for fire numericalsimulation based on LES Xin Hailin, Wei Zheng, Yang Peizhong 2022, 41 (12):  1692-1697.  Abstract ( 769 )   Mesh division is an important part of fire numerical simulation, which has a great influence on the accuracy of simulation results and simulation time. Aiming at mesh division in fire numerical simulation, a mesh optimization method based on Large Eddy Simulation (LES) is proposed. According to the principle of decomposing motion signals in LES, a calculation method of filter scale is proposed, and the grid sizes of different areas in the fire field are optimized and adjusted according to filter scale and grid ratio coefficient. The optimization method is applied to a high-rise building fire simulation, and FDS software is used to carry out numerical simulations on the pre-optimization mesh, post-optimization mesh and fine mesh respectively. Temperature, oxygen and carbon dioxide volume fractions of different mesh division are compared. The results show that: after mesh optimization, the mean value of the correlation coefficient with the fine grid simulation results is 0.987, which ensures the simulation accuracy. At the same time, the simulation running time is reduced to 16% of the fine grid, which effectively improves the computational efficiency of fire simulation. Related Articles | Metrics

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Experimental evaluation study on key characteristics of fire intumescent seals Yang Liang, Zhuang Shuang, Zhao Jing 2022, 41 (12):  1698-1701.  Abstract ( 715 )   This paper makes a full comparative analysis of the development process of fire intumescent seals standardization. On this basis, it focuses on the main technical indicators and test methods of the current standards. Taking the expansion ration and smoke density as the breakthrough point, it discusses the suitability of technical indicators and the reliability of test methods, and puts forward the optimization and improvement scheme. The repeatability and representativeness of the test results are significantly improved by the new expansion ratio test scheme and SDR classification evaluation system under different working conditions, and the experimental verification is carried out. Related Articles | Metrics

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Application of FDS in VR scene design Niu Kun, Song Wenqi, Tao Pengyu 2022, 41 (12):  1702-1704.  Abstract ( 748 )   In order to complete the optimization of its built-in fire scenario, FDS is used to analyze the temperature, visibility and smoke diffusion process, and the calculation results are output in the form of data, pictures and videos. Then, referring to the numerical simulation results, the VR scene is constructed and optimized to make the fire development process more scientific and realistic, and further enhance the user's sense of experience and immersion. At the same time, FDS numerical calculation can solve the problem of lack of real data in large scene fire, and provide technical support and data support for the optimization and upgrading of system. Related Articles | Metrics

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Study on dynamic characteristics of powercoupling device of electric ARFF vehicle Zou Ruiming, Xiong Shenghua, 2022, 41 (12):  1705-1708.  Abstract ( 705 )   A new type of electric ARFF vehicle developed in China is taken as the research object. The dynamic response of the power coupling transmission device under heavy load and high speed condition is analyzed by dynamic simulation. The dynamic model is established by considering the nonlinear characteristics of the gear transmission in detail, such as time-varying stiffness and backlash. The gear shaft is considered as a flexible shaft based on Timoshenko beam theory. The bearing force is calculated by Lamina model according to the geometric characteristics of the bearing type. The results show that the 44th order caused by gear meshing contributes most to the overall level vibration of the power coupling device, and there is an obvious resonance peak near 2 568 r/min in reverse condition. Through the analysis of operational deflection shape, it can be seen that the resonance is related to the flexible vibration mode of the output shaft. Increasing the section size of the output shaft can effectively improve its bending stiffness and change the vibration frequency, so as to avoid possible resonance in the range of working speed and improve the linearity of the system order. Related Articles | Metrics

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A video analysis system for detecting potential fire hazard Lu Kuo 2022, 41 (12):  1709-1712.  Abstract ( 748 )   Aiming at common fire, this paper introduces a kind of video analysis method, and presents a design of a fire safety risk video analysis system. This paper describes the monitoring methods of fire service centre control room and fire-fighting facilities independently, and introduces the smart video analysis ability of this system through the detection effect pictures. The given system can support accurate abnormal event analysis and rapid alarm triggering, and can save the labor cost of video surveillance system and improve its automatic level, and is of obvious practical significance to ensure the safety of people's lives and property. Related Articles | Metrics

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Research on video smoke detection and tracking technology based on convolutional neural network Lu Jian 2022, 41 (12):  1713-1715.  Abstract ( 740 )   Fire detection and early warning technology is an important technical guarantee to effectively reduce fire loss, assist fire fighting and protect people's life and property safety, and smoke detection is one of the more effective means. At present, most smoke detection and alarm devices are mainly set in indoor space, and only have detection and alarm functions. At the same time, the false alarm rate is relatively high, and real-time video information cannot be transmitted synchronously, and detection cannot be carried out for outdoor space areas. Based on the above situation, this paper mainly studies the real-time detection of smoke based on video monitoring system. In the experiment, the network (CNN) architecture was improved, and the res-EfficientNet residual module was added in the EfficientNet, which was used for more accurate detection and recognition of smoke. The spatiotemporal regularized correlation filter (STRCF) was used to achieve the accurate location of smoke. In order to improve the detection accuracy, the polarization transmission characteristics of smoke, such as smoke diffusion and translucency, are also considered. In order to better detect the smoke in the video, the energy of spatial frequency is taken as the one-dimensional constraint term of the filter, and the experiment is carried out on the benchmark data set. The experimental results show that the accuracy is improved by 3%. Related Articles | Metrics

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Discussion on innovation and development of emergency rescue system of Hainan Free Trade Port Sun Peng, Xue Ni 2022, 41 (12):  1716-1719.  Abstract ( 706 )   Hainan Free Trade Port is facing the challenges of multiple disasters and accidents brought about by natural disasters, urbanization development and industrial upgrading, so risk prevention has always been regarded as the bottom line project. In order to better coordinate development and safety, Hainan pays much attention to the construction of emergency rescue capabilities. Based on the new risks of disasters and accidents and new challenges in emergency rescue work faced by Hainan Free Trade Port, this paper draws on innovative practices of emergency rescue systems at home and abroad, and proposes a new pattern of emergency rescue system for Hainan Free Trade Port. It provides ideas and references for the construction of a comprehensive emergency rescue system with Chinese characteristics. Related Articles | Metrics

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Consideration and countermeasures of subway emergency communication guarantee under extreme conditions Liang Yunjie, Han Lin 2022, 41 (12):  1720-1723.  Abstract ( 784 )   In view of the shortcomings of the current emergency communication guarantee for fire rescue teams under extreme conditions such as public network paralysis and power interruption caused by major disasters and accidents in the subway, this paper puts forward countermeasures and suggestions for the emergency communication guarantee of the subway. At this stage, the hybrid networking of wired + wireless ad hoc network base stations is used, the standard specifications will be revised and improved in the future, the tunnel wireless signal coverage platform and special section telephone systems will be built in the tunnel by using the mode of "optical fiber repeater + antenna", the solutions are formulated, the extreme conditions such as "open circuit, power failure and network disconnection" are simulated, and the field tests and the whole process was organized in subway stations in different cities for many times. The feasibility of the solution is verified by the full element exercise. Related Articles | Metrics

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Rescue measures for vehicle accidents in ice and snow weather Zhou Jichen 2022, 41 (12):  1724-1726.  Abstract ( 743 )   In view of the emergency, paroxysm, uncertainty and wide social impact of vehicle traffic accidents on ice and snow roads, based on the analysis of the current situation of vehicle accident rescue on ice and snow roads and the analysis of rescue difficulties, this paper puts forward vehicle accident rescue countermeasures, in order to provide technical reference for vehicle accident rescue under low temperature conditions. Related Articles | Metrics

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Forest fire risk assessment based on ensemble feature selection Zhou Wentao, Zhang Hao, Chen Weijie, Zhou You 2022, 41 (12):  1727-1731.  Abstract ( 716 )   This paper proposes a forest fire risk assessment method based on ensemble feature selection. Considering the diversity and independence of algorithms, 15 kinds of feature select algorithms are selected to form the heterogeneous selectors based on their difference. By using the feature select algorithms, a feature subset set is obtained. And then a forest fire risk assessment model is constructed based on BP neural network by using each feature subset. The important factors of forest fires are selected based on the accuracy of neural network to construct the optimal forest fire risk assessment model. The results show that the accuracy of the algorithm proposed is 85.96%. The proposed model has good generalization ability and can assess forest fire risk effectively. Related Articles | Metrics

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Thermogravimetric study of 5 tree species at different heating rates Zhang Jinqi, Li Xiangchen, Li Xianyu, Zhou Mei 2022, 41 (12):  1732-1736.  Abstract ( 722 )   To explore the pyrolysis characteristics of five typical tree species at different heating rates, the twigs of Betula platyphylla, Betula davurica, Larix gmelinii, Quercus mongolica and Populus simonii were taken as the main research objects. Based on OFW thermogravimetric analysis, the heating range was from 30 ℃ to 600 ℃ with oxygen as carrier gas in air atmosphere. Firstly, the temperature was raised to 100 ℃ and kept for 5 min. The gas flow rate was 20 mL/min, then the temperature was raised at 40, 60, 80 ℃/min respectively. TG-DTG curve was used to analyze the pyrolysis process of the sample, and OFW method was used to analyze the kinetics of the rapid pyrolysis stage of the sample. The results show that the effect of heating rate on the pyrolysis process is mainly concentrated in the weight loss stage. As the heating rate increases, the pyrolysis characteristic temperature increases and the weight loss rate of the sample increases. At this stage, when the heating rate was 60 ℃/min, the pyrolysis degree of five typical tree species was Larix gmelinii＞Quercus mongolica＞Populus davidiana＞Betula platyphylla＞Betula platyphylla. The activation energy of the five tree species analyzed by OFW method changed with the conversion rate. The activation energy calculation results were reliable and the model was better. The activation energy range of Populus davidiana was 659.788～712.664 kJ/mol, and the adjusted R2 range was 0.962 6～0.999 7. The activation energy decreased first and then increased with the increase of conversion rate, and good exothermic reaction was still maintained in the latter part of the reaction process. Related Articles | Metrics

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UAV forest fire fighting technology in "forest block" environment facing plateau Wang Min, He Cheng, Song Xifeng, Lv Zhenyi 2022, 41 (12):  1737-1740.  Abstract ( 988 )   Using unmanned scientific and technological equipment to extinguishment forest fire can greatly improve efficiency and effectively avoid sacrifice, which is an important development direction. This paper puts forward the concept of "forest block" in the special environment of plateau, and tries to explore the method of forest fire fighting of UAV in the environment of plateau "forest block" through the experimental research and practical application of small UAV as firefighting equipment and technology, and sums up the water injection equivalent required to extinguish a cliff fire. The actual combat verification of Motuo "3.7" forest fire shows that small electric UAV is very safe and efficient in extinguishing "cliff fire" in plateau forest, which is worth studying and promoting. Related Articles | Metrics

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Comparison and analysis of kinetic models of pyrolysis of forest humus Chi Hongying, Xin Ying, Zhu Menglong, Ji Wenyue 2022, 41 (12):  1741-1744.  Abstract ( 719 )   Forest fire is a natural disaster that damages forest resources seriously, and once started, it spreads rapidly in the forest and is not easy to be extinguished. Therefore, it is of great practical importance to study and analyze the pyrolysis characteristics of combustible materials in the forest. In this paper, we analyzed the pyrolysis process of humus using TG-DTG curves in an artificial broad-leaved red pine forest in Mao'er Mountain. The experimental data were analyzed using Coats-Redfern(CR) method, Doyle method, Flynn-Wall-Ozawa(F-W-O) method, and four typical equations of distributed activation energy model (DAEM) for kinetic modeling, and the reaction activation energy, reaction level and frequency factor were calculated respectively. The experimental results showed that the pyrolysis of humus was mainly divided into four stages: dehydration stage, transition stage, major weight loss stage and carbonization stage. The kinetic parameters of the major weight loss stages were calculated, and the results showed that the Doyle method and the DAEM model were more suitable for the kinetic analysis of the pyrolysis of humic substances than the other two equations. Among them, the DAEM model is suitable for analyzing the trend of activation energy of samples, and the Doyle method is suitable for finding the activation energy at different weight loss rates. Related Articles | Metrics

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Research on fire resistance of 5 conifer species in Beijing area Cao Meng, Bi Yanning, Yang Shaobin, Bai Ye, 2022, 41 (12):  1745-1748.  Abstract ( 717 )   Winter and spring season is the peak period of forest fire in Beijing. In order to select appropriate tree species to build biological fire prevention forest, prevent forest fire spreading, reduce the loss of forest fire, fire resistance of five common conifer in Beijing was studied. The moisture content, bark thickness, ratio of leaf surface area to volume, leaf burning point, leaf calorific value and leaf coarse ash content of the barks and leaves of different coniferous trees were measured. Factor analysis was used to comprehensively evaluate and sort the fire resistance of the tree species. Through the analysis of 7 fire resistance univariate factors of different tree species, the comprehensive order of fire resistance of 5 tree species is: Juniperus Formosana Hayata＞Pinus Bungeana Zucc＞Pinus TabuliformisCarr＞Juniperus Chinensis Linnaeus＞Platycladus Orientalis(L.) Franco. Related Articles | Metrics

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Practice and thinking on strengthening the investigation of fire accident liability under the new situation Wu Zhenkun 2022, 41 (12):  1749-1752.  Abstract ( 865 )   The importance of fire accident liability investigation was analyzed. Considering the problems of strengthening the investigation of fire accident liability under the new situation, the main methods of constructing the fire accident liability investigation system by Liaoning Fire and Rescue Brigade were introduced in points of system formulation, procedure prescription and talent team construction. Combining with the exploration and practice during the liability investigation of some major fire accident, the key steps of fire accident liability investigation were summarized. The study can provide reference for fire and rescue departments to strengthen the fire accident liability investigation. Related Articles | Metrics

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Study on identification interference of pyrolysis products of polyurethane foam on flammable liquids Xu Jie, Jin Jing, Wang Haochen 2022, 41 (12):  1753-1757.  Abstract ( 711 )   In this paper, the pyrolysis characteristics of polyurethane foams with different densities and their influence on gasoline identification were analyzed by simultaneous thermal analysis（STA）and gas chromatography-mass spectrometry（GC-MS）.Experiments result indicated that there are two main weight loss processes during the thermal decomposition of polyurethane foams. In the first stage, the initial pyrolysis temperature of 80 kg/m3 polyurethane foam is slightly lower and the mass loss rate is slightly larger. The target characteristic components of aromatic hydrocarbons, polycyclic aromatic hydrocarbons and Indane gasoline can be detected in the combustion residue of polyurethane foam, but the number of characteristic components detected in the combustion residue of 40 kg/m3 polyurethane foam is obviously higher, so the 40 kg/m3 The research results provide some data support for the identification of flammable liquids.density polyurethane foam has stronger interference than 80 kg/m3 in gasoline identification. Related Articles | Metrics

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Effect of characteristic temperature on gasoline detection in arson investigation Shen Yutong, Liu Ling 2022, 41 (12):  1758-1762.  Abstract ( 737 )   In order to analyze the influence of characteristic temperature on gasoline detection in arson fire, this paper uses the gas chromatography and MS combined technology to study the gasoline combustion residue, selects the characteristic temperature points through the thermal analysis technology, and conducts GC-MS analysis on the changes of sample components at different characteristic temperatures. The results show that the increase of temperature can change the physical and chemical properties of gasoline, accelerate the loss of gasoline components, affect the detection effect of gasoline combustion products. The study can provide more accurate identification opinions for practical work. Related Articles | Metrics

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Investigation of 10 kV overhead conductor single-phase contact tree grounding fault fire Zhang Yang, Zhang Liang, Li Gengchen 2022, 41 (12):  1763-1766.  Abstract ( 737 )   Fires caused by overhead line faults have occurred frequently in recent years. Because it involves the power supply principle of the power system, high technical requirements are placed for fire investigator. This paper introduces the investigation process of a 10 kV overhead line ground fault fire. When the fire scene was severely damaged and the fire location was identified as ambiguity in the preliminary investigation, the investigators comprehensively analyzed the cause of the fire through video analysis, investigation and inquiry, on-site inspection and other methods, combined with power data analysis, ground fault principles and models, restore the process of fire spread and development, and provide reference for fire investigation and identification of 10 kV overhead line ground fault. Related Articles | Metrics