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Table of Content

    28 April 2020, Volume 30 Issue 4
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    Safety engineering technology Public safety Technology and engineering of disaster prevention and mitigation Occupational health
    Safety engineering technology
    Influence of multi-component combustible gases on explosion characteristics and free radical emission spectrum of CH4
    LUO Zhenmin, WANG Zijin, SU Bin, LI Kui, SHI Jing
    2020, 30(4):  1-7.  doi:10.16265/j.cnki.issn1003-3033.2020.04.001
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    In order to investigate influence of multi-component combustible gases on explosion characteristics of CH4 in fire area of mines, a 20 L multifunctional spherical gas explosion device was used for experiments to collect explosion pressure parameters. Then, emission spectra of key free radicals OH* and CH2O* of CH4 explosion were obtained through a digital oscilloscope. Finally, influence of multi-component combustible gases on explosion characteristics of CH4 was analyzed from macro and micro aspects, and they were correlated and compared. The research shows that their influence indicates different characteristics due to different oxygen contents. An increase in multi-component combustible gas content under an oxygen-depleted state can inhibit explosion of CH4. But its inhibition effect gradually weakens as oxygen content increases until an oxygen-rich state is reached. Relative intensity of key radical emission spectra is basically consistent with corresponding changes of explosion pressure parameters. Although different radicals have the same change trend in participating in reaction process, they are affected by oxygen content to different degrees, and CH2O*, compared with OH*, is more susceptible to oxygen content during the process.
    Image detection method of combustible dust cloud
    ZHAO Xinran, ZHANG Qi, WANG Weidong, XU Zhiqing
    2020, 30(4):  8-13.  doi:10.16265/j.cnki.issn1003-3033.2020.04.002
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    In recent years, production accidents caused by dust explosion occur frequently, and on-line detection and early warning of dust cloud concentration in dust gathering places has become a key means to control dust explosion. However, installation and identification of dust concentration sensors were limited in large space where dust cloud gathers. In order to address this, combustible dust cloud recognition method based on deep learning was proposed. End-to-end detection and identification of explosive dust cloud were conducted by using CNN-based Faster R-CNN model. Then, a standard concentration image database was established to verify experimental results. The results show that Faster R-CNN model can effectively detect and identify explosive dust clouds, and it has high recognition accuracy.
    Overcharging safety characteristics of retired VRLA
    WU Jingyun, SHI Cheng, GUO Pengyu, YAO Lijuan, SUN Yiting, JIN Yang
    2020, 30(4):  14-20.  doi:10.16265/j.cnki.issn1003-3033.2020.04.003
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    In order to solve problems of battery temperature rise, gas generation and failure caused by overcharged VRLA, an experiment was conducted on a module composed of 8 VRLA cells in parallel with rated parameter of each cell at 12 V/160 Ah, and it was overcharged at constant current of 0.17 C (27 A). The results show that H2, SO2, and CO are generated in sequence 169, 189, and 209 s after overcharge while hydrocarbon gas is generated at 33 minutes. 17.6 V is the maximum charging voltage for retired VRLA batteries, and once it is reached, internal electrolytic water as well as other reactions will be intensified. According to thermal simulation temperature curve, internal and external temperature difference of the module can be 40 ℃ while temperature difference of each cell can also be significant after overcharge for a long time with a maximum gap of 30 ℃ . In addition, retired VRLA does not cause obvious deformation and combustion after overcharging. But abnormal status of batteries, like overcharging, can be warned by monitoring concentration variation of H2.
    Lateral collision dynamics of CSPRs paired approach under influence of wake vortex field
    LU Fei, TENG Jingjie, WU Jun, ZHANG Zhaoning, ZHANG Zonglu
    2020, 30(4):  21-27.  doi:10.16265/j.cnki.issn1003-3033.2020.04.004
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    In order to study lateral collision risk of CSPRS paired approach, firstly, considering traditional approach motion process, an interval model of paired approaching aircrafts was established to determine theoretical interval between them at any time. Secondly, characteristics of aircrafts' wake vortex field were analyzed to establish a strength calculation model and dissipation model for leading aircraft's wake flow. Rear aircraft's response mechanism after encountering wake flow was also studied, and a torque balance model of it in wake vortex field of leading aircraft was developed to determine safety spacing between them. Then, lateral positioning error of aircrafts was analyzed to obtain probability distribution of actual interval between paired aircrafts, and a risk calculation model was established, which was applied to analyze changes of lateral collision risk between leading and rear aircrafts during paired approach. The results show that lateral collision risk increases with the increase of initial interval and positive side wind, and then decreases with the increase of aileron's deflection angle. It rises to the maximum value when paired aircrafts reach the head of runway.
    Influence mechanism of alkaline solution on methane adsorption of coal
    ZHOU Yinbo, WANG Siqi, ZHAO Zhou, GUAN Pinpin, XU Jingxin, WU Jin'gang
    2020, 30(4):  28-32.  doi:10.16265/j.cnki.issn1003-3033.2020.04.005
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    In order to explore alkaline solution's enhancement on coal's chemical permeability, pore test and adsorption test were carried out to analyze influence of alkaline solution on chemical erosion effect of coal and its adsorption capacity of methane. With Qingdong coal mine from Anhui Province as research object, samples' pore and methane capacity characteristics before and after alkaline solution treatment were tested with low temperature liquid nitrogen adsorption method and isothermal adsorption method. Then, experiment results were quantitatively discussed using fractal theory and adsorption theory. The results show that alkaline solution can effectively change pore structure of coal and increase content of micropores at pore size less than 5 nm. Coal samples' adsorption capacity greatly improves with its maximum value increasing from 17.83 mL/g to 21.97 mL/g after alkali treatment.
    Characterization and assessment of safety situation for regional railway transportation
    YAN Xu, PENG Qiyuan, YIN Yong, LI Wenxin
    2020, 30(4):  33-40.  doi:10.16265/j.cnki.issn1003-3033.2020.04.006
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    In order to ensure safety of regional railway transportation and improve its comprehensive management level, safety situation of regional railway transportation was characterized through accident multi-attribute analysis, a characterization indicator system of situation assessment was established and corresponding quantitative methods were presented. Then, an improved TOPSIS-Cosine Similarity assessment model based on combined weights was constructed from levels of relative distance and relative trend, and parameters concerning accident grade and nature were preliminarily estimated. Finally, a real-life case study was carried out according to statistical accident data in a certain region of China from 2016 to 2018, and effectiveness of the model was verified by two sets of comparative tests. The results show that the proposed method can reasonably characterize safety situation of regional railway transportation, and evaluate its pros and cons as well as its fluctuation degree from relative distance and relative trend, thus providing a basis for its safety management decision-making.
    Experimental research on suppression of NH4H2PO4 on sucrose dust explosion
    QIN Xiaoling, LI Xiaoquan
    2020, 30(4):  41-46.  doi:10.16265/j.cnki.issn1003-3033.2020.04.007
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    In order to study suppression effects of NH4H2PO4 on sucrose dust explosion, the maximum explosion pressure pmax and maximum rate of pressure rise(dp/dt max) of NH4H2PO4-sucrose mixed dust were analyzed through experiment with a 20 L spherical explosion device. The results show that NH4H2PO4can reduce pmax and (dp/dt) max of sucrose dust and delay the time they take to reach peaks, thus weakening intensity of sucrose dust explosion. For sucrose dust whose mass concentration are 200, 350, 500 and 750 g/m3, they would be completely inert when mass fraction of NH4H2PO4 is 8%, 14%, 14% and 13% respectively. That of NH4H2PO4 at different particle sizes (48-74, 38-47, 25-37 μm) which makes 350 g/m3 sucrose dust completely inert is 14%, 13% and 11% respectively. Adding NH4H2PO4 can effectively reduce damage of sucrose dust explosion, and within a certain range of particle size, the smaller it is, the better suppression effect there will be.
    Prediction of coal-gas outburst induced by rock-burst tendency based on AHP-TOPSIS
    CHEN Liuyu, LI Xijian, BI Juan, HUA Youjin, WEI Zeyun
    2020, 30(4):  47-52.  doi:10.16265/j.cnki.issn1003-3033.2020.04.008
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    In order to evaluate coal-gas outburst induced by rock burst more reasonably, grading criteria of coal-gas outburst indicators were studied from three aspects of in-situ stress conditions, coal seam gas, and physical and mechanical properties of coal by using index critical value and classification number method. Then, a grading evaluation model of outburst tendency was established based on AHP and TOPSIS. Finally, its rationality was verified through actual engineering cases. The study show that the prediction result of proposed model is medium risk, consistent with actual cases. In-situ stress is a major reason for occurrence of rock bursting with coal-gas, followed by gas factor and physical and mechanical properties of coal have the least impact. Specifically, coal structure, gas pressure, gas dynamic phenomenon, coal damage type and coal solidity coefficient have a greater impact on such outburst.
    Effective extraction radius of gas drilling in coal seam
    ZOU Shichao, XIN Song
    2020, 30(4):  53-59.  doi:10.16265/j.cnki.issn1003-3033.2020.04.009
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    In order to predict effective extraction radius of drilling hole in gas control of coal mine, taking No. 6 coal seam of Sijichun mine in Guizhou Province as an example, a gas seepage model of surrounding units of boreholes was established. Then, gas pressure distribution cloud chart along radial direction at different drilling time was obtained through Comsol numerical simulation. Finally, effective extraction radius was determined based on theoretical derivation and numerical simulation data while considering critical gas pressure (0.5 MPa), and verification was made with on-site test. The results show that relative error rate of theoretical and simulated effective extraction radius is less than 10%, verifying accuracy of both calculation results. Effective radius is linearly dependent on extraction time. Considering its complexity to measure effective radius on site, it can be obtained through theoretical and numerical simulation methods used in this paper, which provides a theoretical basis for underground gas control.
    Competitive adsorption difference during coal spontaneous combustion process in noble gas atmosphere
    LOU Hezhuang, JIA Tinggui
    2020, 30(4):  60-67.  doi:10.16265/j.cnki.issn1003-3033.2020.04.010
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    In order to explore spontaneous combustion characteristics in low temperature oxidation process of coal after absorption in CO2 and N2 atmospheres, with anthracite coal in No. 9 coal seam of Sihe No. 2 mine taken as research object, warming test and TG test of coal during low temperature oxidation were conducted to analyze gas product characteristics and weight loss characteristics of CO and CH4 during spontaneous combustion of coal. Then, a physical adsorption model of different gas molecules, such as O2, CO2 and N2, was established on the surface of coal macromolecules, and adsorption of O2 gas molecules was analyzed from a micro perspective using grand canonical Monte Carlo simulation (GCMC) method. Finally, difference in competitive adsorption between mixed gas molecules on surface of coal macromolecules were discussed. The research shows that spontaneous combustion characteristics of coal in low temperature oxidation process change after adsorption in CO2 and N2 atmospheres, with concentration of CO and CH4 gas products being reduced and rate of weight loss of coal spontaneous combustion decreasing, thus inhibiting low temperature oxidation capacity of coal. The mixed adsorption of coal macromolecules on gas molecules, like CO2 and N2, suppresses their adsorption of O2 molecules. And gas competitive adsorption on coal surface ranks as H2O>CO2>N2>O2>CH4>CO.
    Study on kinetics features of coal spontaneous combustion influenced by polyurethane
    GUO Pengwei, TANG Yibo, WANG Hua'e, HU Shihua, ZHOU Jinqiang
    2020, 30(4):  68-73.  doi:10.16265/j.cnki.issn1003-3033.2020.04.011
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    In order to explore dangerous impacts of polyurethane on coal spontaneous combustion, kinetic characteristics before and after introduction of polyurethane were studied through experiment and analyzed by using thermal analysis. Then, kinetic parameters were calculated with Flynn-Wall-Ozawa (FWO) and Starink models. Finally, mechanism function was determined by Bagchi method. The results show that with existence of polyurethane, reaction is accelerated and weight loss rate increases greatly in the initial stage (168-300 ℃). However, the latter becomes relatively mild in subsequent stage of high temperature (465-714 ℃) with value of activation energy being increased by about 6 kJ/mol compared with that before addition of polyurethane. And when reaction stops, final residual mass is approximately zero, and reaction is more complete than that of coal pyrolysis alone. Anthracite coal conforms to the randomly nucleating and nucleus growth model while mixture of coal and polyurethane is more inclined to first-order chemical reaction mechanism.
    Public safety
    Cellular automation model of pedestrian evacuation considering obstacle crossing behaviors
    SONG Yinghua, TU Wenhao, HUO Feizhou, LYU Wei , FANG Danhui
    2020, 30(4):  74-79.  doi:10.16265/j.cnki.issn1003-3033.2020.04.012
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    In order to study influence of obstacle crossing behaviors on pedestrian evacuation, a cellular automation model of evacuation considering such behaviors is established. Concept of risk degree was introduced in the model and used to define surmountable obstacles and unsurmountable obstacles. And through two different neighborhoods, crossing obstacles was realized. Then, a scenario of evacuation after earthquake was created to simulate evacuation process with different initial pedestrian density and proportion of pedestrians crossing obstacles, and influence of initial density, obstacle crossing behaviors and pedestrian ratio on evacuation process was analyzed. The results show that obstacle crossing behaviors make simulation process more consistent with pedestrian's movement mode in reality and eliminate some obstructions caused for them to detour obstacles. Increasing initial pedestrian density has less effect on scenes of crossing obstacles than on detouring obstacles. When they are faced with surmountable obstacles, the higher the proportion of pedestrians crossing obstacles is, the shorter time evacuation takes.
    Research on flight conflict prediction method for non-cooperative large unmanned aerial vehicles
    GAO Yang, WU Wentao, JIA Xiaoshan, XU Minghe
    2020, 30(4):  80-85.  doi:10.16265/j.cnki.issn1003-3033.2020.04.013
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    In order to reduce risk of collision between non-cooperative large UAVs, firstly, in light of analysis on their operation mode, predication mechanism and procedure of flight conflict based on UAVs operation and management platform were proposed. Secondly, a conflict prediction model building on UAVs flight state data was proposed, which predicted conflicts in both horizontal and vertical directions and determined whether there would be a conflict. And then warning threshold was analyzed to prevent too late reception of alarm information by UAVs ground station. Finally, real-time flight status data of 3 UAVs were used to analyze and verify the model. The results show that the proposed mechanism and program can realize prediction and early warning between non-cooperative large UAVs, and the prediction model can accurately determine whether there is a flight conflict as well as calculate when it will happen.
    Simulation of personal evacuation in smoke scenario
    LI Changhua, HE Haitong, LI Zhijie, ZHANG Jie
    2020, 30(4):  86-92.  doi:10.16265/j.cnki.issn1003-3033.2020.04.014
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    In order to address the problem that people are greatly affected by real-time dynamic changes of smoke diffusion during evacuation, an improved cellular automaton model is developed to simulate personnel evacuation in smoke scenario. Firstly, change rules for evacuees' sight radius were proposed based on a dynamic parameter model to describe influence of smoke environment changes on their behaviors, and meanwhile movement rules of regional herd behaviors were established. Then, numerical simulation research on evacuation process in scenarios of single and double exits were conducted by using the model. Finally, impacts of visual field changes, herd behaviors and width of exits on evacuation in smoke scene were analyzed. The results show that herd behaviors have uncertainty on evacuation in some cases, and presence of guides can greatly improve evacuation efficiency. Changes of visual field have an impact on evacuation time, which is greater when number of evacuees is smaller. Increasing exit width can improve evacuation efficiency, but improvement is not obvious when the width reaches certain degree.
    Study on direct causes of electrical fire accidents in buildings based on "2-4" model
    SUN Shimei, GENG Xiaoshuai, FU Gui
    2020, 30(4):  93-99.  doi:10.16265/j.cnki.issn1003-3033.2020.04.015
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    In order to identify direct causes of electrical fire accidents in buildings, 40 typical fire accidents were analyzed by using "2-4" model, and classification and statistical analysis were conducted on unsafe acts and unsafe conditions of direct causes. Then, unsafe actions were analyzed from on six aspects, including fire source, fire development, safety management and personnel allocation, self-rescue, rescue and fire extinguishing. And frequency of unsafe acts, human violation, frequency of actors and unsafe conditions, proportion of all kinds of unsafe conditions and other data were obtained. The results show that there are 412 items of unsafe acts, which fall into 35 categories, and among them, acts of improper fire extinguishing measures, illegal storage and use of flammable, explosive and combustible goods and lack of fire safety training are in top 3 in terms of frequency. There are 127 items of unsafe conditions from 3 categories, among which polystyrene foam and other flammable and combustible materials and short circuit in electrical circuit have higher frequency.
    Clustering and deduction of typical dangerous scenarios between passenger vehicles and two-wheelers at crossroads
    ZHOU Hua, ZHANG Qiaoyu, MU Yaoyao, TAN Zhengping, SUN Qing, ZHANG Daowen
    2020, 30(4):  100-107.  doi:10.16265/j.cnki.issn1003-3033.2020.04.016
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    In order to provide an effective scenario deduction and construction scheme for research and development of intelligent vehicles, statistical analysis was conducted on data of accident scenarios between passenger vehicles and two-wheelers at crossroads from National Automobile Accident In-depth Investigation System (NAIS) database, and two types of basic scenarios with high proportion were obtained. Then, seven scenario correlation variables were selected for cluster analysis on static characteristics of these two types of scenarios. Finally, a kinematics deduction model was established, and furthermore, considering actual threshold of dynamic parameters of five types of typical dangerous scenarios, speed-distance danger models of them were constructed. The results show that through methods of statistical classification, cluster analysis and kinematic model superposition deduction, five kinds of typical hazard scenes of passenger cars and two-wheeled vehicles at intersections can be obtained in conformity with traffic situation in China, and moreover five sets of dangerous scenarios are obtained.
    Scenario analysis of stampede accidents in scenic spots
    LI Hua, LI Linqian, YI Peng
    2020, 30(4):  108-113.  doi:10.16265/j.cnki.issn1003-3033.2020.04.017
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    In order to improve emergency management and control ability of huge crowds in scenic spots, a combination of scenario analysis and dynamic Bayesian network was used to study evolution process of stampede accidents. Situation state, disaster-causing body, disaster-bearing body and driving factors were selected as key elements to explore law and path of accident scenario evolution. Then, the dynamic Bayesian network was used to construct a scenario network of huge crowd stampede incidents, and development trend of the scene was deduced by using situation state probability. The results show that scenarios with high risk of accidents are population fall, crowd stalemate, population flow increase and crowd gathering in turn. And the major reasons for them are interventions of corresponding driving factors such as inadequate preparation for prevention, inadequate security management of scenic spots, imperfect human flow monitoring equipment and crowd diversion facilities.
    Characteristic analysis of subway escalator accidents based on disordered multinomial Logistic regression
    WANG Zhiru, GAO Linyuan, WANG Min
    2020, 30(4):  114-120.  doi:10.16265/j.cnki.issn1003-3033.2020.04.018
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    In order to explore major reasons for subway escalator accidents, with data of such accidents in Beijing subway as an example, disordered multinomial Logistic regression method was used to study characteristics of accidents and to prevent their occurrence by controlling related influencing factors. Then, by analyzing accident forms, types and attributes of explanatory and response variables in 894 subway escalator accidents, a disordered multinomial Logistic regression model was constructed to identify significant correlation factors and calculate their contribution level to accidents. The results show that developing different key control strategies concerning environmental factors, passenger characteristics, passenger behaviors and paths for different types of accidents can effectively reduce occurrence of subway escalator accidents. At the same time, this method can be applied in research of accident predication as well as solve problems of correlation analysis of disordered multivariant variables and quantitative analysis of their contribution.
    A proposed model and application for pedestrian evacuation time calculation in road tunnels
    CHENG Yanying, XIE Wei, ZHANG Yuchun, PENG Qi, LIU Jiewei, CHEN Ke
    2020, 30(4):  121-126.  doi:10.16265/j.cnki.issn1003-3033.2020.04.019
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    In order to accurately calculate pedestrians' evacuation time and provide a theoretical basis for reasonable design of evacuation routes in tunnels, an innovative empirical model was proposed to calculate evacuation time in road tunnels, which considered influence of parameters like distance, movement speed, tunnel width, occupant flow and traffic volume. In this model, critical conditions of exit clogging, its start time and duration were all taken into consideration. Then, with a real underwater tunnel as an example, influence of occupant density and their movement speed on evacuation time and exit clogging was analyzed after different horizontal or vertical escape routes were set, and rules of equivalent setting space of horizontal and vertical routes were proposed. The results show that pedestrians' evacuation time is affected by their walking speed to different degrees in the event of different (horizontal/vertical) routes,but it is closely related with occupant density. And evacuation capacity of horizontal routes is significantly greater than that of vertical ones under the same condition.
    Influence of designs of landings at egress doors on children's evacuation behaviors
    YAO Yishu, LU Wei
    2020, 30(4):  127-134.  doi:10.16265/j.cnki.issn1003-3033.2020.04.020
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    In order to explore design rationality of landings at egress door of kindergartens and to fill in the blank of children's evacuation behavior data in this part, evacuation drills on landings at egress doors in two fulltime six-classroom kindergartens were conducted and evacuation behavioral data at landings of 4 different designs were obtained. Then, their walking speed, evacuation time and flow rate were analyzed and compared. The results show that walking speed of children aged 4-6 on non-smooth steps is between 0.52-0.98 m/s. Design difference of landings has obvious influence on children's evacuation behavior and evacuation effect, and double-sided landings can increase flow rate by 1.8 times.
    Influence of walking height on motion features of evacuees
    ZHANG Yi, MA Jian, LUO Qian, LIN Peng
    2020, 30(4):  135-140.  doi:10.16265/j.cnki.issn1003-3033.2020.04.021
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    In order to quantify influence of walking height on motion features of evacuees, VR technology was adopted to construct evacuation scenarios of different heights. Then, experiment data were collected with laser radar, and fear of height was classified by using acrophobia questionnaire (AQ) and K-means clustering algorithm. Finally, influence of different levels of acrophobia and gender on evacuees' speed, stride and step frequency were investigated at controlled height. The results show that evacuation speed, stride and step frequency of pedestrians decrease along with the increase of height, which is more obvious as it is between 0 m and 50 m. When at the same height, those whose acrophobia is more severe will have lower speed, smaller stride, faster step frequency and are more sensitive to height changes. It is also found that female's walking speed and stride decrease more observably than those of males while the latter's walking speed and stride are larger than females at the same height.
    Optimization of AEB trigger width based on pedestrian crossing scenario
    HE Xia, ZHANG Daowen, CHE Yaoyue, LIU Qi, DONG Xiaofei, DONG Honglei
    2020, 30(4):  141-146.  doi:10.16265/j.cnki.issn1003-3033.2020.04.022
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    In order to study influence of trigger width on pedestrian crossing scenario results in AEB control strategy, road and vehicle models were built by using automatic driving simulation software PreScan. Then, AEB longitudinal control algorithm was designed in Matlab model’s control platform Simulink to simulate pedestrians crossing scenarios. And trigger width was continuously adjusted to observe whether collision was avoided. The results show that when car speed is 30-50 km/h, the system's trigger width is at 1.75 m, which can help avoid collision effectively. When speed is 50-80 km/h, it needs to increase along with the increase of pedestrian speed. The wider it is, the more information car receives, and the more possible AEB malfunction will be. Therefore, the maximum trigger width is set to be 3.5 m. When car speed reaches between 60-80 km/h, it is necessary to optimize alue and full braking advance time simultaneously so as to avoid collision.
    Determination method of smoke layer height in road tunnel fire
    YANG Xiaolong, ZHANG Yuchun, GAO Yunji, JIN Kaiyan, LI Zhisheng, LI Tao
    2020, 30(4):  147-153.  doi:10.16265/j.cnki.issn1003-3033.2020.04.023
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    Buoyancy frequency method, N percentage method, integral ratio method, are three common methods to determine smoke layer height in tunnel fire, the calculations of three methods are often biased from visual observations.In order to study and explain deviations of calculation results from visual observations, which were found in three common determination methods of smoke layer height in tunnel fire, a long tunnel model was established based on FDS, and six types of fire source power were set. Then, vertical visibility distribution was used to verify deviation between existing determination method and visual results before visibility mutation method was proposed. The results show that the deviation calculated fromabove four methods ranks as visibility mutation method (1.63%) < buoyancy frequency method (4.88%) <N percentage method (N=30, 7.88%) < integral ratio method (8.50%), among which results of integral ratio and buoyancy frequency method are higher than visual ones. It is also found that visibility value in vertical direction of tunnel remains constant and then decreases abruptly as the height increases, and the greater fire power is, the faster it declines, and the lower visibility value there is.
    Safety improvement effect of guiding visual reference system in long urban tunnels
    LUO Haoshun, XU Liangjie, DU Zhigang, ZENG Huan
    2020, 30(4):  154-159.  doi:10.16265/j.cnki.issn1003-3033.2020.04.024
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    In order to ensure traffic safety in long urban tunnels and to improve traffic efficiency, visual environment characteristics of these tunnels with multiple off-ramps were analyzed, and a stereoscopic guiding visual reference system was constructed based on visual illusion mechanism and color psychology principles. Then, an experiment of drivers' psychophysics perception was carried out by using E-prime software to study the system's effect on improving traffic safety in long urban tunnels and its optimized design. The results show that drivers are most comfortable with blue and green information while yellow has a strong warning effect but causes no sharp stimulus, which enhances driving attention. The reference system effectively shortens drivers' visual recognition time of guiding information and increases recognition distance. In addition, rhythm designs are moderately inclined to the entrance and the exit in order to induce drivers to have reasonable slope illusion. When it is 75° inclined, drivers can achieve best speed control on tunnel slopes.
    Technology and engineering of disaster prevention and mitigation
    Influence of particle size on overtopping dam break of tailings dam
    WU Ligong, XIAO Lixing, LIU Xiaofeng, YAO Chi, JIANG Qinghui, ZHOU Chuangbing
    2020, 30(4):  160-165.  doi:10.16265/j.cnki.issn1003-3033.2020.04.025
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    In order to explore overtopping break reactions of dam constructed by tailings of different particle sizes, with tailings of Yancang tailings pond in Yongping Copper Mine used as dam material, physical dam-break test was carried out with medium sand, fine sand and silt. Then, numerical simulation was conducted for verification by using FLOW3D software. The results show that when middle sand is used, dam collapse is mainly represented by surface scouring and displacement failure while being represented majorly by downward erosive when silt is used, and is both of them in the case of fine sand. The physical test and numerical simulation achieve good consistency in terms of dam break flow and time, etc., which indicates reliability of the method combining both test and numerical calculation in simulating tailings dam break.
    Occupational health
    Effects of cooling garments on firefighters' thermal responses under high temperature
    TIAN Shuicheng, ZHOU Runkang, YANG Jie
    2020, 30(4):  166-171.  doi:10.16265/j.cnki.issn1003-3033.2020.04.026
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    In order to reduce firefighters' heat stress and improve fire rescue efficiency, effects of cooling garments on thermoregulation of firefighters were investigated. Three categories of garments were set under high temperature (35 ℃), including basic clothing (short sleeves and shorts), protective clothing (basic clothing and protective clothing), andcooling garmments (basic clothing, protective clothing and cooling garmments), and typical thermal responses of participants during exercise and rest phases were measured for these cases respectively. The results show that protective clothing, compared to basic one, leads to a significant increase in skin temperature, core temperature, heart rate and sweating rate, and a decline in sweat evaporation rate. Cooling garmments can effectively attenuate above-mentioned increases, and also further reduce sweat evaporation rate. Their cooling effects decrease over time and almost disappear after 40 minutes of work, or they may even increase thermal and physiological burden of firefighters
    Risk assessment on unsafe behavior of coal miner based on Monte Carlo method
    XU Surui
    2020, 30(4):  172-178.  doi:10.16265/j.cnki.issn1003-3033.2020.04.027
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    In order to prevent coal mine roof, gas explosion, coal and gas outburst and water damage accidents, the unsafe acts of 100 coal mine accidents were analyzed by 2-4 Model, then the risk assessment model of coal miners' unsafe behavior based on Monte Carlo method was established. The risk value of accident behavior and the influence degree of unsafe acts on behavioral risks in each type of accident are studied, and accident prevention measures based on individual behavior level are proposed. The results shows that the risk of gas explosion accidents is the biggest, followed by coal and gas outburst, water damage, and roof accidents. In addition, three kinds of unsafe acts have a great impact on the risk of coal mine accident behavior, including "not effective water exploration", "violation of regulations in construction and production" and "giving instructions against rules and regulations".
    Influence and work mechanism of framing strategies on effectiveness of safety slogans
    LIAO Bin, FENG Haiqin, WEI Xin, DUAN Qionghua
    2020, 30(4):  179-185.  doi:10.16265/j.cnki.issn1003-3033.2020.04.028
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    In order to improve effectiveness of safety slogans, firstly, safety slogans were divided into three types, safety meaning, safety strategy and safety knowledge type while framing strategies were classified into analogy and mental simulation frame. Then, experiment was designed, and eye movement and subjective evaluation data were recorded during viewing of slogans. Finally, analysis of variance (ANOVA) and intermediary effect analysis were carried out. The results show that framing strategies affect effectiveness of safety slogans. Safety meaning slogans should adopt mental simulation frame while analogy frame is more suitable for safety strategy and safety knowledge slogans. Number of fixations (NF) plays a major intermediary role in relation between framing strategies and acceptance of three types of slogans, and for comprehension of safety strategy slogans, NF and fixation duration (FD) play an intermediary role together.
    Value of statistical life in rail traffic safety based on mixed Logit model
    LIU Wen'ge, YANG Jing
    2020, 30(4):  186-191.  doi:10.16265/j.cnki.issn1003-3033.2020.04.029
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    In order to provide basic indicators for economic evaluation of rail traffic safety projects, estimation studies on VOSL in rail traffic safety were carried out. Firstly, VOSL calculation model was constructed based on ML model with normal distribution and lognormal distribution. Secondly, route-choice questionnaires were designed with hypothetical scenario of "Dalian to Shenyang route choice", and then survey was conducted and data were obtained. Finally, the model was calibrated by Monte Carlo simulation and comparatively analyzed before VOSL and its distribution function were gained. The results show that ML-2 model with lognormal distribution has high accuracy, whose goodness of fit is 0.213 5 and hit ratio 82.49%. VOSL based on ML-2 model obeys lognormal distribution with parameters (0.615 5,0.514 82), who has a mathematical expectation of 6.169 million RMB and reaches the maximum probability at 4.1 million RMB.
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