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15 June 2022, Volume 41 Issue 6 Previous Issue    Next Issue

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Effect of the combined placement of aerogel felts on the thermal runaway characteristics of lithium-ion batteries LIU Quan-yi, ZHU Qian, ZHU Wen-tian, YI Xiao-ying 2022, 41 (6):  727-731.  Abstract ( 1474 )   Abstract: In order to slow down the heat transfer between lithium-ion battery goods, this paper studies the effectiveness of aerogel felt placed in different positions of lithium-ion battery packaging on thermal runaway heat barrier by self-built lithium-ion battery explosion experimental platform. Combined with the analysis of the test results, the peak temperature, thermal runaway propagation time and velocity, gas concentration, mass loss and packaging damage were selected as the evaluation parameters of lithium battery packaging performance, and the simplified N-GAS toxicity quantitative evaluation model was introduced. Through the evaluation of lithium-ion battery packaging parts in different aerogel felt combinations, it can be seen that from the protection effect on the safety of the battery pack and the integrity of the outer packaging, there is the best effect of the thermal runaway propagation barrier in the combination of the top and the middle, and it is not recommended to use the three-sided full packaging in the actual transportation of lithium-ion batteries. Related Articles | Metrics

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Study on the key element reaction of urea inhibition of methane explosion ZHANG Qing-li, LI Xiao-bin, ZHANG Rui-jie, SUN Jing-wen 2022, 41 (6):  732-734.  Abstract ( 1385 )   Abstract: In order to explore the mechanisms of urea inhibition on methane explosion, we use Gaussian 09 software with density functional theory (DFT)' B3LYP6-31G** calculation method, to study the key element reactions of urea inhibition on methane explosion, to look for the transition states，to optimize the structures of reactions,transition states and products, to find out the reaction paths of the thermal decomposition of urea and the mechanisms of NH3·and HNCO· inhibition of methane explosion. It is concluded that the reaction barrier thermal decomposition of urea is 48.73 kcal/mol, the reaction could occur easily; the NH3· and HNCO· could consume the O2 and OH· radicals obviously，which bring good effects to the inhibition of methane explosion. The results could bring some support for the methane inhibition mechanism study. Related Articles | Metrics

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Experimental study on ignition sensitivity of rice husk dust XIONG Jing-wen, YE Ya-ming, JIANG Dai, LEI Cheng-wen, 2022, 41 (6):  735-738.  Abstract ( 1471 )   Abstract: In order to study the ignition sensitivity of rice husk dust, the particle size and morphology of the rice husk dust were analyzed by laser particle size analyzer and SEM. The spontaneous combustion temperature, minimum ignition temperature were measured by Godbert-Greenwald furnace, solid spontaneous ignition point device and minimum ignition temperature of dust layer test device. The results indicated that the larger particle size of rice husk powder, the more concentrated the particle size distribution. The minimum ignition temperature of rice husk dust cloud decreases gradually with the decrease of dust particle size. The spontaneous combustion point of rice husk dust（D50=52.9 μm）was 225.1 ℃ under standard test mode. The minimum ignition temperature of rice husk dust layer decreases with the increase of mould height in the specific particle range when the particle size is the same. The minimum ignition temperature reaches the lowest as the mould height was 20 mm, and was no longer increasing with the increase of mould height. The test results can provide data and theoretical support for industrial process safety. Related Articles | Metrics

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Leakage monitoring method of hybrid load branch of the self-using power system in substation CHEN Hao, CUI Yun-guang, MA Zhao-xing, YAO Kai 2022, 41 (6):  739-743.  Abstract ( 1324 )   Abstract: The real-time leakage monitoring method and implementation of hybrid load branch are studied. Firstly, a differential compensation method of inherent residual current is proposed through branch load state identification. Using differential compensation, a composite criterion composed of steady-state residual current criterion and residual current increment criterion of hybrid load branch is proposed, which improves the identification sensitivity of branch leakage under different load states. Through the field practice of Jiangsu power grid, it is verified that the proposed method can adapt to the load state change of hybrid load branch, effectively identify leakage faults, and improve the maintenance level of hybrid load branch in self-using power system. Related Articles | Metrics

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Characteristics and heat transfer analysis of n-heptane spill fire on sand base ZHANG Kang, ZHANG Xiao-cui, LI Hai-hang, QU Fang 2022, 41 (6):  744-748.  Abstract ( 1390 )   Abstract: The spread experiment of unignited n-heptane and the combustion experiment of ignited n-heptane were carried out on the sand substrate to study the influence of sand particle size on the spread and combustion characteristics of n-heptane. The spreading distance, flame front and burning rate were analyzed, and the influence of heat transfer process on the characteristics of flowing fire was explored. The results show that because the adsorption capacity of sand decreases with the increase of sand particle size, the spreading distance and speed of unignited n-heptane in the spreading stage increase with the increase of sand particle size, and are smaller than those of no-sand working conditions. With the increase of sand particle size, during the stable combustion flame front of ignited n-heptane first increases and then decreases, and the stable combustion rate first decreases and then increases. The heat transfer analysis shows that when the sand particle size increases from 0.25 mm to 4 mm, the reduction of heat conduction feedback is the main reason for the reduction of the combustion rate; and when the sand particle size is further increased to 8 mm, the heat radiation feedback increases, leading to an increase in the burning rate. Finally, it is concluded that the adsorption capacity of sand is the main factor that affects the spreading stage, the thermal feedback is the main factor that affects the stable combustion stage, and the 0.25 mm fine sand is more suitable for blocking and extinguishing the flowing fire. Related Articles | Metrics

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Difficulty in fire fighting of flammable liquidwith low boiling point and the fireextinguishing technical countermeasures BAO Zhi-ming, CHEN Yang, ZHANG Xian-zhong, HU Cheng 2022, 41 (6):  749-752.  Abstract ( 1420 )   Abstract: The existing research has proved that due to the high volatility and high vapor pressure of low boiling point flammable liquids, it is difficult to extinguish the fire thoroughly. The main reasons for the difficulty of extinguishing fire are the poor sealing effect of foam layer, water film and gel film, and the fact that the oil sparging ability of fire extinguishing foam is not strong enough. This paper introduces the more mature technical means such as Heptafluoropropane foam technology, compressed air foam extinguishing technology and high performance foam extinguishing agent. It is pointed out that the future application of the fixed foam system in the storage tank, the development of the general foam extinguishing agent and the application technology on the fire field should be thoroughly explored so as to comprehensively solve the fire fighting problem of the low boiling point flammable liquid. Related Articles | Metrics

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Experimental study on the influence of cumulated dimensions on the combustion characteristics of straw DU Wei, CHENG Hai-tao, ZOU Biao, LI Cong 2022, 41 (6):  753-757.  Abstract ( 1327 )   Abstract: Straw is a typical common combustible that may cause wildfires. The combustion process of naturally cumulated is necessary to be studied. In this paper, the combustion experiments of cylindrical straw were carried out. The diameters were 60 cm and 90 cm, and the thicknesses were from 2.94 cm to 12.23 cm. The combustion process of straw under different conditions were compared, and the parameters of combustion characteristics such as the mass loss rate and flame temperature were analyzed. The results show that the straw combustion process can be divided into four stages, including initial central stage, merged annular stage, separated annular stage, and decay stage. The mass loss rate has an excellent linear relationship with the thickness of straw. And a larger diameter would cause a larger mass loss rate as well. The flame temperature presents a trend of “increase rapidly-decrease slowly” via time. The flame axis temperature decreases gradually with the elevated height, which is close to 800 ℃ near the straw surface and lower than 200 ℃ at the height of 0.9 m. The conclusions benefit to deepen the understanding of the development and spread process and characteristics of straw fire. Related Articles | Metrics

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Locating of multi-point leakage in pipeline based on ICEEMD sample entropy YANG Jian, WU Yu-jia, XU Ning, LI Min 2022, 41 (6):  757-762.  Abstract ( 1316 )   Abstract: In order to reduce the multi-point leakage positioning error of urban pipeline, a method of locating multi-point leakage in pipeline based on improved complete ensemble empirical mode decomposition (ICEEMD) sample entropy was proposed. Firstly, the ICEEMD algorithm was suggested, to denoise and decompose the multi-point leakage sound signal into real leakage signal component and redundant component; sample entropy analysis was used to remove redundant components, and obtain effective signal. Secondly, observed signal was separated by blind source separation and maximum likelihood estimation, which obtains independent effective leakage signal.Then, the cross-correlation time delay method was used to calculate the time difference between the two signals reaching the upstream and downstream sensors. Finally, the precise location of a single leakage point was calculated. The results show that the method has better signal decomposition effect and can greatly improve the accuracy of multi-point leak location of pipelines. Related Articles | Metrics

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A simple prediction model for the flight distance of fragments in storage tank explosions ZHU Ming-hui, WU Chen-jie 2022, 41 (6):  763-766.  Abstract ( 1293 )   Abstract: In order to determine the flight distance of fragments in the explosion accident by liquefied petroleum gas storage tank, the prediction model for the flight distance of fragments in explosion was built based on dynamic principle and theoretical analysis.The numerical simulation and verification analysis were also carried out according to the data from some LPG explosion accident cases. The results show that the predicted values of the model are consistent with the accident data and the previous results of Monte-Carlo numerical simulation, and the model has good applicability to explosion accidents of spherical tank and cylindrical tank. The model can quickly and conveniently predict the damage range of the fragments in explosion.The prediction results can provide technical support for emergency departments to make rescue decisions, and it can also provide theoretical basis for the planning, construction and risk control of petrochemical parks. Related Articles | Metrics

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Parameters and experimental research of high expansion foam generator for large ships WANG Yue-yong, LE Zhi-bin, QIU Bo, ZENG Zhong-hua, 2022, 41 (6):  767-771.  Abstract ( 1325 )   Abstract: High-expansion foam generator is a kind of fire-fighting equipment used by large ships and plays an important role in fighting LNG and oil fires. The foaming ratio is an important indicator of the equipment, and parameters such as wind pressure and wind speed have a greater impact on it, and design and experimental research are needed. Changing the number of layers, angles and spacing between layers of the air duct, and using numerical simulation analysis, the distribution of wind speed at different working conditions of the foamed mesh is obtained. According to the mesh size parameter, the foaming ratio is tested and researched. The results show that with the increase of the number of air duct layers and the matching of angles and spacings, the uniformity of wind speed can be effectively improved. The increase in mesh size can effectively increase the wind pressure, but it will cause the expansion ratio to decrease. Related Articles | Metrics

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Experimental study on fire resistance of connections in prefabricated modular steel structures HUANG Yi-liang, PENG Lei, XUE Gang, SHI Jian-feng 2022, 41 (6):  772-776.  Abstract ( 1358 )   Abstract: This paper focuses on steel connections using “rotating angle connecting module” in prefabricated modular structures. Fire resistance tests were carried out to study the fire performance of the steel connections with two different fire protection methods. The deformation curves, failure modes and fire resistance of the connections were studied. The National Standard GB/T 9978.1-2008 was applied to carry out the tests. Test results show: 1) for specimen A of which the columns were protected with 3-layers of high-performance gypsum boards (15+20+20) mm and the beams were protected with 2-layers of high-performance gypsum boards (20+20)mm, the fire resistance rating was more than 193 min. The gypsum boards remained a relatively good integrity, but a few gypsum boards in the middle of specimen fell off. The temperature at the steel column corners were higher due to the 2-diretional heat transfer. The temperature of connection was lower than that of steel columns and beams, due to the fact that the connection has thicker steel than columns and beams. The temperature of beams were higher than that of columns because beams had larger section factor. From the axil displacement of columns it could be sawn that the specimen stayed in its thermal expansion stage and the criteria of fire resistance rating were not met yet. 2) for specimen B of which the columns and beams were protected with 2-layers of fiber-reinforced calcium silicate boards and 60 mm-thick rock wool（120 kg/m3）, the specimen was elongated as the steel temperature raised up, and the gaps between gypsum boards expanded, but the boards remained integrity; the specimen started to reveal compression deformation at 131 min, and the test was stopped to prevent any damage to the furnace. It was shown that specimen B has similar temperature profiles as specimen A, but there was divergence among the temperature profiles because deformed steel stud at high temperature caused large gaps between gypsum board, and hot gases might reach the specimen through gaps and result in deferent temperature profiles at different spots. From the axil displacement of columns it could be sawn that the column stopped thermal expansion and stared to crush. Therefore, the specimen started to buckle, and it reached its failure stage and would fail soon. After the test, local buckling was observed on the column. Based on the results, specimen B was very closed to its failure at the end of the test. 3) the temperature curves showed a plateau at about 100 ℃ for both specimens, and this is because the moisture in the specimens evaporated and absorbed a large amount of heat. 4) for specimen B, the gypsum boards remained integrity, but the gaps between gypsum boards expanded a lot due to the deformation of steel studs at high temperature. Therefore, the stability of steel studs at high temperature is very important if they are used for supporting gypsum boards. 5) Test results show that the connection protected with 3-layers of high-performance gypsum boards (with thickness of (15+20+20) mm) has a fire-resistance rating of 3.00 h, while the connection protected with 2-layers of fiber-reinforced calcium silicate boards and 60 mm-thick rock wool has a fire-resistance rating of 2.00 h. Related Articles | Metrics

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Influence of inclined smoke deflector on mechanical smoke exhaust effect of tunnel JI Jing-wei, LI Fu-qing, LU Wen, CAI Wei-ming, 2022, 41 (6):  777-781.  Abstract ( 1367 )   Abstract: The wind speed at the exhaust outlet increases with the increase of negative pressure difference, increasing the negative pressure of the smoke exhaust outlet is prone to suction through effect. At the same time, due to the horizontal inertial force when the smoke diffuses longitudinally along the ceiling, it often flows to the rear before entering the smoke exhaust outlet, which makes the smoke control effect worse. To solve the above problems, an inclined smoke inflector (ISD) is designed under the smoke outlet to optimize the flow field at the smoke outlet, increase the negative pressure difference at the smoke outlet, resist the horizontal inertia force of the smoke below the smoke outlet, inhibit the penetration effect and improve the smoke exhaust efficiency. FDS simulation is used to verify the influence of inclined smoke deflector on smoke exhaust effect. The results show that ISD device can significantly improve the smoke exhaust capacity of smoke exhaust outlet. When the vertical height of inclined smoke deflector is 600 mm, compared with ordinary smoke exhaust outlet, the heat flow to downstream is reduced by 99.8%, and the negative pressure under smoke exhaust outlet is increased by 3 times. Moreover, it has obvious effect on inhibiting the phenomenon of suction penetration, and the smoke exhaust effect is improved. Related Articles | Metrics

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Study on smoke control technology by using cross passage in extra-long submarine tunnel YOU Wen-jiao, ZHONG Sheng-jun 2022, 41 (6):  782-785.  Abstract ( 1365 )   Abstract: In order to solve the smoke exhaust problem of extra-long subsea tunnel in fire, a ventilation scheme using service tunnel and cross passage to assist air supply is proposed. In this paper, fire dynamics simulation software (FDS) is used to establish the tunnel fire ventilation model. The technical parameters of the ventilation system are determined by studying the control effect of the air volume in service tunnel and the number of cross passage openings on the fire smoke. As a result, in the fire scenario, when the longitudinal ventilation wind speed in the accident tunnel is 2 m/s, three cross passages in upstream of the fire source are opened, and 1.3 m/s longitudinal ventilation wind speed is applied at both ends of the service tunnel, the smoke can be controlled on one side of the fire source without affecting the safety evacuation of personnel. The research shows that it is feasible in theory to control the spread of fire smoke in extra-long subsea tunnel by using cross-passage assisted ventilation scheme. Related Articles | Metrics

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Research on flexural performance of reinforced concrete beams strengthened by steel plate after high temperature DUAN Wen-feng, LI Dan, BIAN Bo, CAI Bin 2022, 41 (6):  786-791.  Abstract ( 1273 )   Abstract: In order to study the change law of the flexural performance of concrete beams strengthened by steel bonding after high temperature, a comparative test study was carried out on one unreinforced beam at room temperature, one reinforced beam at room temperature, two unreinforced beams after high temperature and two beams strengthened after high temperature. The distribution law of the cross-section temperature field and the variation law of the bending performance of the specimen were obtained. The research results show that the temperature field of the beam section is unevenly distributed with high outside and low inside. After heating for 60 min and 90 min, the flexural bearing capacity of the test beam is reduced by 7.1% and 10.9%, respectively, compared with that of the normal temperature beam. The reinforced beams were increased by 13.3% and 10.5% respectively. With reference to the calculation formula for the bearing capacity of beams strengthened at room temperature, combined with the simulation results of the temperature field, a theoretical calculation method for the flexural bearing capacity of the bonded steel beams after high temperature is proposed. The calculation results have small errors and meet the actual engineering accuracy requirements. Related Articles | Metrics

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Discussion on influence of longitudinal wind speed on fire extinguishing effect of water mist system in tunnel ZHANG Ao-yu, DENG Min, 2022, 41 (6):  792-796.  Abstract ( 1408 )   Abstract: In order to research smoke movement under water mist firefighting system and longitudinal ventilation, consequently, ensure best ventilation strategy under water mist firefighting system. A serious of numerical simulation model was conducted with fire dynamics simulator, and the change of temperature, carbon monoxide concentration and radiant heat flux under different longitudinal wind speeds were obtained. The results show that: under the fire scale of 30 MW, the smoke layer begins to gradually drop in the spray area 15 m upwind from the fire source, and the smoke layer drops below 2 m; when the fire is extinguished in 300 s, within 150 m upwind, the smoke layer all dropped below 2 m. Therefore, 5 minutes after the fire broke out, the evacuation distance of personnel should be greater than 150 m. Comparing the changes of radiant heat flux before and after the application of water mist under the same ventilation wind speed (1 m/s), it can be concluded that after the water mist fire extinguishing system is turned on for 25 s, the heat radiation intensity at 5 m downstream of the fire source decreases from 6 kW/m2 to 0. It is recommended to keep the ventilation wind speed of 1 m/s in the tunnel as much as possible when turning on the water mist fire extinguishing system. Related Articles | Metrics

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Hydraulic calculation method and application ofsprinkler system in mechanical garage YIN Gui-Xu1, MO Hui2, YANG Dan2 2022, 41 (6):  797-801.  Abstract ( 1386 )   Abstract: A hydraulic calculation method for sprinkler system in mechanical stereo garage, which is the main node pressure balance method, is proposed in view of the fact that the common drawing software can only calculate the hydraulic network of plane network, but not the three-dimensional network. According to the principle of pressure balance of main nodes, the method combines manual and software for hydraulic calculation, which is simple and easy to operate. The calculation results are verified by manual actuarial calculation of pressure balance at each node. The results show that this method can be used for accurate hydraulic calculation of sprinkler system in mechanical stereo garage. At the same time, the influence of main pipe and riser pipe arrangement on flow rate of automatic sprinkler system in mechanical garage is studied by this method, which provides reference for sprinkler system design. Related Articles | Metrics

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Experimental study on fire-extinguishing efficiency of water mist fire-extinguishing system in small car garage fire PENG Jin-zhi 2022, 41 (6):  802-806.  Abstract ( 1417 )   Abstract: Aiming at the fire protection of small car garages, a full-scale car garage fire experiment platform of 5.95 m×7.6 m×3.6 m was established. The water distribution performance of a single nozzle of high-pressure water mist fire-extinguishing system under different system working pressures （6, 8 ,10 MPa） was studied experimentally. Therefore, the design parameters and the arrangement position of the nozzles of the water mist fire-extinguishing system in the small car garage were analyzed and determined. Besides that，the determined water mist fire extinguishing system was used to carry out the fire-extinguishing test of the fire in the back seat of the car in the garage. The results showed that the high-pressure water mist fire-extinguishing system can suppress the development of the car fire in the small garage effectively, and can protect the enclosure structure of the garage and the adjacent car well. In this paper, it is determined that the high-pressure water mist fire-extinguishing system of the small car garage adopts a closed system, the working pressure of the system is 10 MPa, the design spray intensity is not less than 2.0 L/（min·m2）, the flow coefficient is K=3.0 and other design parameters as well as the arrangement position of the nozzle, which can make the fire extinguishing system achieve better fire extinguishing and fire control effect. Related Articles | Metrics

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Image fire detection algorithms based on object detection convolutional neural networks ZHANG Miao, LI Pu, YANG Yi, SONG Wen-hua 2022, 41 (6):  807-811.  Abstract ( 1401 )   Abstract: The existing image fire detection algorithms have the problems of weak generalization ability, high false alarm rate, and low practicality. Based on four advanced object detection convolutional neural networks (e.g. Faster-RCNN, R-FCN, SSD and YOLO v3), new image fire detection algorithms were developed. The comparison of the proposed and current algorithms reveals that the algorithms based on object detection CNNs have significant advantages. Especially, the average precision of the algorithm based on YOLO v3 reaches to 84.5%, and the detection velocity is 28 frame/s. Besides, the YOLO v3 also has stronger robustness of detection performance, and is suitable for developing fire detection system. Related Articles | Metrics

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Construction of knowledge graph for emergency disposal of gas transmission and distribution emergencies LI Si-jie, WANG Ya-hui, ZHANG Zi-hao, 2022, 41 (6):  812-817.  Abstract ( 1396 )   Abstract: Based on the knowledge graph technology, the knowledge of gas emergencies and their emergency disposal information was extracted and represented, and the construction method of knowledge graph for gas emergency disposal was put forward, so as to provide technical support for complete emergency disposal management in the later stage. In order to solve the problem of few samples of gas emergency cases, this paper adopts Web crawler technology to crawl online gas emergency cases. Taking the crawling gas emergency case and the gas emergency case provided by a gas company as the research object, the top-down hierarchical model of gas emergency disposal is established. The BiLSTM-CRF model and topology network diagram are used to extract entities in the case, and the effectiveness of entity extraction is verified by experiments. The relationship between entities is defined and classified by semi supervised collaborative training method. The neo4j graph database is used to visualize the knowledge graph of gas emergencies and emergency disposal methods. Through the verification and analysis of three practical cases, it is proved that the above method has good effect. Related Articles | Metrics

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Study on hot pressing process and flame retardancy of magnesium inorganic particleboard WANG Jun-zhe, NIU Geng-wu, LU Jun-hui, WANG Xin 2022, 41 (6):  818-822.  Abstract ( 1273 )   Abstract: In order to study the influence of experimental parameters on the properties of magnesium based inorganic particleboard in the production process and the influence of various parameters on the flame retardant properties of the board, the single factor experiment method was used to study the influence of different densities on the physical and mechanical properties and combustion properties of the board. And the orthogonal experimental study was set on the 4 factors of concentration of acrylic glue, enhance agent, inorganic adhesive glue content, moisture content of the slab which affect the performance of the plate, and the only sheet made of MDI adhesive was set as control group, the contrast analysis of different inorganic particle boards' heat total release, heat release rate, smoke production, smoke production rate, was conducted. When the density of board is 0.95 g/cm3, the concentration of water-based adhesive is 7.5%, the dosage of reinforcing agent is 2.5%, the amount of inorganic adhesive is 50%, and the water content of paving is 23%, the performance of board is the best, with all performances meet the requirements of non-combustible P2 particleboard in the national standard GB/T 39032-2020, Non-combustible Particleboard. Related Articles | Metrics

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Applicability of standard test method for self-heating goods to azo-dye powder WANG Gao-jun, WU Hao, NIE Wen-lei, 2022, 41 (6):  823-826.  Abstract ( 1351 )   Abstract: In the process of maritime transportation, self-heating substances are one of the most common causes of maritime accidents. The standard test method N.4, United Nations “Recommendations on the transport of dangerous goods” manual of tests and criteria, is used to identify whether the goods belong to self-heating substances. The standard test method N.4 is developed based on the "heat basket" model and studies based on the self-heating characteristics of carbon substances.The applicability of standard test method N.4 to azo-dye powder lacks relevant verification data. By exploring the self heating characteristics of azo-dyes, it is found that the "heat basket" model is suitable to describe the self-heating process of azo-dyes. The activation energy of self-heating reaction of azo-dyes is 129.6 J / mol and the standard test method N.4 is not fully suitable to judge azo-dyes, which may lead to the misjudgment of "false positive". It is suggested that the relevant standard test methods or management regulations should give more detailed management to the chemical goods whose self-heating characteristics have been fully studied, so as to reduce the waste of resources and economic losses. Related Articles | Metrics

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Characteristics and main influential factors of igniting typical forest vegetation materials by faults of simulated broken and fallen segments of high voltage transmission lines ZHOU Kai, ZHANG Rui-zhe, ZHAO Yao-peng, YOU Fei, 2022, 41 (6):  827-831.  Abstract ( 1371 )   Abstract: In order to explore the characteristics and typical influential factors of fierce wildfires developed from ignition of typical forest vegetation materials via accidental faults inducing discharge breakdown processes of simulated broken and fallen segments of high voltage transmission lines(steel bar electrodes), a platform of such case was self designed to perform simulation experiments. Corresponding discharge and ignition experiments of simulated broken and fallen power lines were carried out on eucalyptus leaves, tuber fern chips, cedar pine needles and poplar chips under different gaps. Results show that the discharge inducing ignition stages can be summarized as "two phases and two points" (discharge induction period, gap breakdown point, arc induction period and fault removal point) when there is a proper gap between the simulated broken and fallen lines and the vegetation surfaces. There is no fault removal point in case of direct contacts. The possibility of ignition of the above four vegetation materials by the discharges is as follows: cedar pine needles>eucalyptus leaves≈poplar chips>tuber fernchips. With increasing water contents, eucalyptus leaves can still be ignited and the breakdown voltages required for discharge inducing ignition gradually decrease. For different forest ground vegetation types, under proper gaps and moisture contents, once they are ignited by the discharges between simulated broken and fallen lines and the vegetation materials, ignition and sustained flames will be produced, the formations of streamer channels will be promoted and the discharges and burning processes will be further aggravated until a wildfire is possibly triggered. Related Articles | Metrics

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Experimental study on fire spread rate characteristics of forest surface fuels in South China FENG Jun-wei 2022, 41 (6):  832-835.  Abstract ( 1281 )   Abstract: South China is rich in vegetation and the human activities are frequent. Once the forest fires occur, the consequences are serious. In order to explore the influence law of forest surface fuel kinds and fuel bed characteristics on fire spread rate in South China and provide reference data for forest fire fighting, the paper quantitatively analyzed the fire spread rate characteristics of forest surface fuels through field sampling and indoor fuel bed fire spread rate measurement experiments. The experimental results showed that the spread rate of Eucalyptus robusta Smith leaf bed was the largest among the five fuel beds. Combined with its planting in this region, it had a high fire risk. The influence law of Eucalyptus robusta Smith leaf bed characteristics on the fire spread rate was obtained. It was found that in the stage when the moisture content began to increase, the spread rate decreased slightly. When the moisture content exceeded 14%, the spread rate decreased rapidly, and then the spread rate decreased slightly again when the moisture content reached 18%; The spread rate was a power function of thickness, and the increase of thickness would contribute to the increase of the spread rate; The bulk density and width had little effect on the fire spread rate. Related Articles | Metrics

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Study on the burning characteristics of organic matter in leaves and bark of common broad-leaved tree species in Changbai Mountains ZHOU Yong, ZHANG Lin, YU Chun-bo, SUN Jing-hua 2022, 41 (6):  836-840.  Abstract ( 1300 )   Abstract:Taking the leaves and bark of seven common broad-leaved combustibles in Changbai Mountain as examples, and measured the ignition point, the starting temperature of the carbonization stage, the calorific value, and the ash content were measured by thermogravimetry, and the thermal stability of the tree species was evaluated by TOPSIS analysis method. According to experimental results, we parameterized the mathematical model of the combustion process of organic matter in leaves and bark to study the mass loss and heat release of organic matter in leaves and bark. The thermal stability ranking of seven broad-leaved tree species was obtained. The thermal stability of Populus davidiana Dode, Populus ussuriensis Kom., Fraxinus mandshurica Rupr., Tilia amurensis Rupr., Juglans mandshurica Maxim., Phellodendron amurense Rupr. and Quercus mongolica Fisch. ex Ledeb. are weakened in turn. In the process of organic matter combustion of seven common broad-leaved tree species in Changbai Mountain, the heat released by leaf combustion is more sustainable and the bark combustion intensity is higher. The two prediction models effectively explain the thermal stability of common broad-leaved tree species in Changbai Mountain. During the transformation of low-quality and low-efficiency forest and fire prevention forest belt in Changbai Mountain area, tree species with strong thermal stability can be selected for forest regeneration, which provides a reference for formulating forest fire prevention and disaster reduction countermeasures and strategic decisions of relevant departments in Changbai Mountain area. Related Articles | Metrics

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Research on forest fire emergency road network planning of Liangshui National Nature Reserve based on GIS technology YUAN Ming-ju, LU Zhao-lin, ZHOU Yuan, SUN Shu-fa 2022, 41 (6):  841-846.  Abstract ( 1322 )   Abstract: Analyze the forest fire emergency road network of Liangshui National Nature Reserve and optimize the route selection to meet the road network density requirements of 2025 in the national forest fire prevention plan (2016-2025). K-means clustering algorithm is used to select road nodes. Considering terrain and other environmental factors, ArcGIS multi factor superposition analysis is used to select the overall line. The line is verified to be feasible through field investigation. Establish an evaluation system for emergency roads in forest areas. Finally, the forest road density will be increased to 3.22 m/hm2, which is in line with the national expectation of forest road density in 2025. Regional area mean in regional segmentation index (S`)and regional area variance (D) decreased by 45.7% and 94.7% respectively, which provides a reference for the establishment of emergency road network in Liangshui protection area. Related Articles | Metrics

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Risk analysis and countermeasure research in vehicle accident rescue SHEN Rui, QIN Li-peng, CHEN Hai-tao 2022, 41 (6):  847-850.  Abstract ( 1499 )   Abstract: There are many risks in the process of vehicle accident rescue, which shows a great threat to firefighters. In order to carry out the rescue more scientifically, it is necessary to analyze the dangerous factors in the rescue of vehicle accidents and discuss the corresponding countermeasures in a targeted manner. In this paper, the vehicle accident risk evaluation index system is established from four aspects：personnel quality, equipment, on-site situation and fire rescue management. The fuzzy comprehensive evaluation is applied to make quantitative analysis of non-quantitative events, which realizes the quantitative evaluation of risks in vehicle accident rescue. On this basis, countermeasures such as attaching importance to on-site safety assessment, strict safety operation procedures, and strengthening professional skill training are proposed. Related Articles | Metrics

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Research on occupational injury factors of firefighters and countermeasures DONG Kai, ZHU Guo-qing, SONG Chun-jing, CHEN Wen-jia 2022, 41 (6):  851-855.  Abstract ( 1364 )   Abstract: In order to reduce the occupational injuries of firefighters and promote the overall improvement of the combat effectiveness of the fire brigade，the factors affecting the occupational injury of firefighters were comprehensively evaluated by means of questionnaire survey and factor analysis, the key factors of occupational injury of firefighters were discussed, and the prevention and control measures of occupational injury of firefighters were proposed. Research shows that training factor, rest factor, pre-employment physical activity factor, and injury prevention education factor are the four main factors that affect firefighters' injuries, and their cumulative variance contribution rate is 78.906%. Overall training plans to reduce training injuries and prevent over-fatigue; strengthen the physical foundation, improve business skills and psychological quality, and build a solid foundation for actual combat; improve injury treatment plans, strengthen injury prevention education, and promote the concept of precision medicine and other countermeasures are put forward. Related Articles | Metrics

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Characteristics and countermeasures of fire and explosion accidents in chemical enterprises LV Yan-jie 2022, 41 (6):  856-859.  Abstract ( 1378 )   Abstract: Based on the research and analysis of fire and explosion accident disposal cases in chemical enterprises, this paper summarized the characteristics of fire and explosion accidents in chemical enterprises, put forward the main existing problems from the aspects of personnel, equipment, on-site communication and joint operation, and discussed the improvement countermeasures and suggestions combined with the practical experience of daily fire fighting and rescue work, including improving operational safety control measures, on-site communication guarantee, and the joint logistics linkage mechanism, strengthening the construction of professional chemical fire fighting and rescue teams, and the fire fighting battle evaluation summary and discussion, so as to benefit the team construction and development, give better play to the role of the main force and national team, focus on the needs of "full disaster and major emergency" tasks, and improve the team's ability to escort economic development. Related Articles | Metrics

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Experimental research on arc ignition ability of low-voltage circuit with poor contact WANG Wei-feng, LIU Qiang, ZHANG Fang-zhi, JI Xiao-han, 2022, 41 (6):  860-863.  Abstract ( 1289 )   Abstract: In view of the frequent fire caused by low-voltage arcs and unclear ignition mechanism, simulate the poor contact fault with the multiple electrical fire causes and prevention device, and study the influence of system power and power factor and carbon electrode diameter on the ignition ability of low-voltage poor contact arcs. The results show that when the system power is no more than 320 W, the paper filter only turns yellow and being carbonized. When the system power is more than 370 W, the paper filter starts to be ignited, and the ignition probability increases with the increase of the system power, and when the power is no less than 480 W, the paper filter can be ignited; the power of the arc decreases with the decrease of the power factor under the experimental conditions; the influence of the diameter on the ignition ability of the arc mainly depends on the size of the anode spot, when the anode spot is larger than the diameter of the carbon electrode, the paper filter can be ignited; on the contrary, the paper filter can hardly be ignited. The research results provide certain basic parameters and theoretical basis for the fire prevention of low-voltage electricity use and the prevention of electrical faults. Related Articles | Metrics

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Study on characteristics of overloaded wires igniting surrounding combustibles CHEN Yi-lin, LIANG Dong, GAO Dian-ce, 2022, 41 (6):  864-868.  Abstract ( 1305 )   Abstract: In order to study the ignition characteristics of overloaded BV wires to surrounding combustibles, the wires with cross-sectional area of 2.5 and 4 mm2 were selected to conduct experiments with overcurrent of 90~180 A and 90~300 A at an interval of 30 A. The temperature change of the wires was measured and the image of arcing and bead splashing were captured. The ignition capacity with the spacing between the wires and cotton cloth of 0.5, 1, 2 cm respectively was studied. The results show that the overload process of wires can be divided into three processes: heating up, arcing and cooling down. In the process of arcing, the arc is generated at the wire gap and gradually grows to both sides until being extinguished, resulting in liquefaction and gasification of wire copper core, molten bead splashing and fluid flame. High temperature arc and bead splashing have the ability to ignite surrounding combustibles. Related Articles | Metrics

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Investigation of a blade battery fire caused by impingement and damp HUANG Wen-xiao 2022, 41 (6):  869-872.  Abstract ( 2542 )   Abstract: This paper analyzed the accident investigation process of a blade battery damaged by impingement and then caught fire due to moisture. The location of the fire was determined through video analysis, on-site investigation. The fire cause was identified by the theoretical knowledge of electrical faults, thermal runaway of lithium-ion batteries, remote monitoring data, personnel description and other evidence. The field experiment was used to analyze the formation of the impact hole on the lower guard plate and the hole on the cover plate. Combined with the knowledge of electrical theory, problems of the blade battery were analyzed, and some suggestions were put forward to improve its quality. Related Articles | Metrics