The rapid urbanization in China has led to many utility tunnels containing a variety of municipal pipelines including natural gas, heating, water and electrical power that are key infrastructure components in cities. The most dangerous hazard is the natural gas pipelines that can leak to form explosive gas clouds in the confined tunnels which brings huge explosion risks to the safe operation of the utility tunnels. The propagation characteristics of gas explosions in a complex, confined utility tunnel were studied experimentally as a function of various factors to support safety control and assessments of gas explosions in utility tunnels. The experiments studied the effects of methane concentration, pressure relief ports and auxiliary facilities such as the gas pipeline design, distribution boxes and fire boxes on the flame propagation and the overpressures. The results show that the maximum overpressure occurs for a methane concentration of 9.5%, vents in the tunnel significantly reduce the overpressures compared with closed utility tunnels, and the peak overpressure attenuation rate is 28.4%. Auxiliary facilities in the tunnel accelerate the flame propagation and lead to greater overpressures. This study provides guidance for improving disaster mitigation for natural gas utility tunnels in cities.

The characteristics of fires in continuous oil spills along various slopes were investigated experimentally to improve theoretical models for the prevention and control of oil spill fires. The spreading and burning rates of continuous oil spill fires along various slopes were observed for point source oil spills. The spill fire spreading was divided into three stages for various slopes based on whether the fire became stable or was shrinking. For the n-heptane spill fire on the glass surface, the relationship between gravity, friction and surface tension forces during the spreading characterizes the three stages as the "surface tension dominant" stage for slopes of 0°-3°, the "friction dominant"stage for slopes of 4°-5° and the "gravity dominant" stage for slopes greater than 5°.

Glowing contacts triggered by poor electrical contact are one of the most important ignition sources for fires. The glowing contacts with high temperature are commonly hidden in electric wires. The glowing contact involves complex coupling between the copper oxidation, heat transfer, and electric field. The relationships between the key parameters are investigated experimentally by measuring the growth rate of the oxide bridge length as well as the glowing contact resistance and temperature. The results show that the oxide bridge length and the glowing contact resistance increase with time. The maximum contact temperature increases with time up to 1 400-1 600℃. Increasing currents increase the oxide bridge growth rate and growth time. The increasing rate of the resistance first increases and then decreases with the current increase. The results further show that the glowing contact is due to interactions between the oxidation extent, the changes in the copper oxide resistivity with the current, and the increases in the specific heat with temperature.

Ten types of shape memory fabrics were fabricated using shape memory alloys to evaluate the thermal protective performance of these temperature-responsive smart fabric systems. Tests with these fabrics studied the effects of the shape memory alloy spacing, the shape memory fabric density and the aramid yarn type of the fabric on the thermal protective performance. The results demonstrate that the smart fabric systems significantly reduce the temperature rise, specifically prolonging the times for temperature rises of 12℃ and 24℃. The smart fabric systems provide the best thermal protection with 2 cm shape memory alloy spacings and shape memory fabrics woven using aramid 1414 with a fabric density of 20 wale/cm.

The resilience of the urban public transport systems was evaluated using a system function curve model to quantify the urban public transport system resilience. The model included the bus and taxi systems with the bus service rate and the taxi online rate used as the system function to evaluate the urban public transport system resilience. This method was then used to evaluate the resilience of the public transport system during the Zhengzhou storm and flooding in 2021. The results show that the Zhengzhou public transport system is moderately resilient and various recovery schemes could affect the recovery capacity and adaptability of the system. The model describes the system functions in stages from the initial disturbance to a new equilibrium state to calculate the urban public transport system resilience. This method is suitable for single disasters and multiple, coupled disasters and can provide guidance for improving the ability of urban public transport systems to deal with unknown disruptions.

Wood is widely used in building materials, furniture and handicrafts due to its excellent thermal insulation properties, mechanical strength and ornamental value. However, wood is a combustible material that undergoes pyrolysis, ignition, charring and cracking. Most current studies on the burning characteristics of wood have used relatively homogeneous artificial boards or logs without defects. However, in practical applications, wood structures vary among different species, the wood surface grain is not uniform, and there are many structural defects in the logs, such as knots. These factors cause the wood burning characteristics to differ significantly from that of a homogeneous board. This study experimentally investigated the burning of small logs made of white pine, radiata pine and Chinese fir. The burning behaviors were compared with different external radiative fluxes with measurements of the burning phenomenon, heat release rate, and ignition characteristics. The results show that the wood species, the grains and the defects (knots) all affect the wood burning characteristics. Increasing the external heat flux reduces the ignition time and increases the peak heat release rate. In the range of operating conditions in this paper, the difference of the log ignition time at the external radiative heat flux of 15 kW/m² in the repeated tests is about 35%, which is higher than that of the homogeneous artificial wood. This trend indicates the effect of structural heterogeneity on the combustion characteristics of logs, but this difference decreases with the increase of the external radiative heat flux. For the same tree species, the combustion characteristics of sparse and dense grain samples are different. The highest ignition time difference is more than 500 s, and the charring rate is higher in the direction parallel to the grain than in the direction perpendicular to the grain. The Chinese fir contains a large number of knots, which can reduce the ignition time and increase the peak heat release rate at the low external radiative heat flux.

The use of emulsified diesel fuel in internal combustion engines reduces fuel consumption and engine emissions. The water content is a key factor affecting the combustion efficiency of emulsified diesel fuels. The combustion and boiling characteristics of emulsified diesel fuel pool fires were studied here using a 150 mm diameter stainless steel tray to find ways to reduce casualties and property losses. The water contents of the emulsified diesel fuels were 0%, 5%, 10%, 15% and 20%. The combustion characteristics of the emulsified diesel fuel pool fires were divided into the initial growth stage, boiling combustion stage, pulsation stage, stable combustion stage and extinguishing stage based on the variations of the burning rate and the flame height. The combustion characteristics during the first three stages were affected by the water content while the combustion characteristics during the final two stages were similar to those of pure diesel fuel fires. Increasing the water content caused the durations of the boiling combustion stage and the pulsation stage to first become longer, then become stable and then become longer again while the duration of the stable combustion stage first decreased, then became stable and then decreased again with increasing water content. Boiling combustion occurs during emulsified diesel fuel pool fires which wakes the flame heights decrease. This study will help risk assessments of emulsified diesel fuel fires.

New energy vehicles are mainly powered by high energy density batteries that can experience thermal safety issues that have received extensive attention from researchers. The battery thermal management system is designed to prevent thermal runaway in the batteries. This paper presents a coupled heat transfer and battery heat generation study using porous medium composite phase change materials (CPCM) for battery thermal management. The study uses numerical models and experiments with particle image velocimetry (PIV) to research the heat generation in lithium-ion batteries in the porous composite phase change unit and the heat transfer in the composite phase change materials. The results show that the porous media accelerate melting of the phase change materials (PCM), composite phase change materials can slow the battery temperature increase and the current intensity can significantly impact the melting process, energy storage and energy storage efficiency of the thermal management system. Thus, the composite phase change material improves the heat dissipation in the battery which slows the temperature increase. Dual-battery models should have a space between the batteries to improve the heat dissipation for the thermal management system.

Droplet transmission and aerosol transmission are both possible transmission pathways for many respiratory infections (e.g., COVID-19) and human movements may affect these viral particle transmission pathways. Realistic 3-D human models were used here in a computational fluid dynamics (CFD) study to analyze the effect of human movements on the transmission of virus particles exhaled by a patient. The changes in the airflow, pressure and particle diffusion were compared with experimental data to verify the accuracy of the computations. The results show that when a person passes by a sitting patient in a poorly ventilated room, the wake velocities can reach 1.6~2.0 m/s. The airflow velocity can reach 0.53 m/s at 0.10 m from the moving person, 0.22 m/s at 0.25 m away, and 0.13 m/s at 0.55 m away. The airflow fluctuations can last more than 10 s. Double peak airflow velocities are found near the moving person. The pressure difference of 0.49 Pa caused by the moving person moves the air and the viral particles into the wake of the moving person and slows the nearby droplet deposition. More than 50% of the viral particles are deposited on the moving person's body or spread further. Thus, this study recommends less cross-area movement in epidemic areas and that all people should wear masks and use personalized ventilation equipment.

Landslides are common geological disasters that frequently occur in mountainous areas. Landslides can threaten the safety of people around hidden danger points; thus, timely, accurate monitoring and early warning systems are needed for landslides. This study analyzed the acoustic emission signal and displacement monitoring parameters for existing acoustic emission monitoring systems and early warning models of the deformation before a landslide. A landslide early warning model was then developed based on acoustic emission monitoring using wavelet transforms and an improved tangential angle model. The reliability was verified against laboratory simulation data from Loughborough University, UK. Monitoring equipment was then installed at a key point in the very large landslide prone area in Liannan County, Guangdong Province, China. The acoustic emission monitoring parameters and the displacement parameters were then compared with the measured deformation of the slope. The results show that the acoustic emission monitoring parameters are more sensitive and more accurate than the displacement parameters.

Human thermo-physiological responses to cold environments need to be accurately known to assess human thermal safety and thermal comfort in cold environments. Existing studies have mainly concentrated on people at low exercise intensity, with little consideration of exercising people. Human subject experiments were conducted in a climate chamber to study the thermo-physiological responses and the factors influencing the responses of people exercising in cold environments. The thermo-physiological parameters, including the skin temperature, core temperature and thermal sensation, were measured from six young men for various ambient temperatures of 5, 0, -5 and -10℃ and two clothing with 2.57 and 1.34 clo. The results show that the mean skin temperature and the local skin temperature are linearly related to the ambient temperature with the slope decreasing with additional thermal clothing insulation. The rate of change of the core temperature is linearly related to the body's heat accumulation rate with the slope increasing with additional thermal insulation. Thermal sensation is affected by the ambient temperature and clothing at low and medium exercise intensities, but is not significantly affected at high intensities. The thermal sensation of the exercising people shows no correlation with physiological temperature. The results lead to suggestions to the choice of clothing for exercising people in cold environments. This research provides reference for assessing the thermal safety, thermal comfort, exercise capability and clothing needs for exercising people.

Flooding can cause extensive damage. Accurate flood damage assessments are needed to formulate effective prevention and mitigation measures. A flood damage assessment index was established based on such factors from the Chinese Flood Damage Assessment Standard (SL579-2012) as the death toll, affected population, crop damage area, direct economic loss, house damage, and economic losses of water conservancy facilities. The grey relational analysis and entropy weight methods were used to develop a damage assessment method that assessed and classified rainstorm and flood damage in China using annual flood data from 2014 to 2018. The assessment results and actual evaluations were combined to develop ways to mitigate and prevent rainstorm and flood damage. The results show that national rainstorm disasters with high entropy weight-grey relational degrees have been concentrated in the southeast and northwest regions and that flood prevention and control should focus on urban and desert flood control. The national rainstorm disaster entropy weight-grey relational degree was highest in 2016 which saw many serious floods.

Environmentally friendly intumescent flame retardant thermoplastic polyurethane (TPU) composites were prepared using ammonium polyphosphate (APP), melamine cyanurate (MCA) and boric acid as additives. The combustion, smoke suppression and thermal stability of the composites were characterized by a cone calorimeter and smoke density tests. The results show that this flame retardant greatly reduces the peak heat release rate by up to 80% and the total heat release and generates a compact char layer which effectively prevents volatile releases. The limit oxygen index (LOI) results show that this flame retardant increases the LOI. The TPU composites with the mass fraction of 15% APP, 2.5% MCA and 2.5% boric acid have the highest UL-94 level and LOI (32%). In addition, a thermal gravimetric analysis shows that the TPU composites have better thermal stability. APP, MCA and boric acid additives enhance the smoke suppression and flame retardant effects in the intumescent flame retardant TPU composites.

In recent years, harsh environmental conditions (lightning, wind and rain) have posed significant threats to the safe operation of long oil and gas pipelines, especially in oil and gas pipelines in other countries. The operation and emergency responses for oil and gas pipelines abroad have faced various problems such as insufficient pipeline risk accident data and difficult cross-border coordination during harsh environmental conditions. Current pipeline accident early warning models rely too much on field data or accident-related data. Thus, this paper presents a station accident risk evolution early warning method based on a knowledge graph that uses a small amount of accident report data from natural gas pipeline stations for harsh environmental conditions. The method uses a bidirectional long short-term memory-conditional random field algorithm (Bi-LSTM-CRF) to extract the causal relationships from station accident reports, with a Neo4j graph database then used to establish the knowledge graph for accident risk evolution in natural gas pipeline stations abroad experiencing harsh environmental conditions. The results show that this knowledge graph based station accident risk early warning method not only provides earlier warnings of station accidents than traditional station accident early warning methods for long pipelines, but also predicts the accident path with recommended accident responses. The results show that this early warning method can effectively help safety management personnel in natural gas pipeline stations abroad provide better risk control and accident prevention.

Combustion experiments were conducted with cylindrical straw bales with various diameters and thicknesses. The flame spread and flame structure were analyzed with a model developed to predict the mass loss rate (ṁ) and flame temperature. The flame structure progresses from a hollow conical flame to a separated annular flame and then a broken annular flame. The mass loss rate first increases and then slowly decreases. The peak mass loss rate is linearly related to the initial straw mass, which implies that a larger initial mass increases the heat accumulation during the straw combustion. The flame temperature distribution along the vertical axis has the same trend as the mass loss rate with the dimensionless flame temperature decreasing slowly with increasing (z-z₀)ṁ^-2/5 for small values of this parameter and then decreasing more quickly at larger values of (z-z₀)ṁ^-2/5. (z-z₀ is the relative flame height.) The conclusions deepen the understanding of straw fire development and spread characteristics.

High-voltage transmission wires, a key part of electrical transmission systems, can cause serious fires. There have been few studies of the effect of electrode shapes on gap breakdown around the transmission wires. This study analyzed the effect of electrode shapes on gap breakdown with ignition conditions in terms of the breakdown voltage, breakdown polarity and breakdown arc characteristics. The tests used a high voltage power frequency discharge system (type 30 kV·A/50 kV), propane injection as a simulated fire source and combinations of rod or plate electrodes. For gaps less than 8.0 cm with flames present, the breakdown waveform had a discharge induction stage, a gap breakdown point, an arc conduction stage and a breakdown vanishing point. The average breakdown voltages and the average breakdown field strengths of the various electrode combinations were measured by setting various gap sizes. The rod-rod electrode had the slowest increase of the breakdown voltage with increasing gap size while the rod (negative)-plate (positive) electrode had the fastest increase. The air gap breakdown had polarity characteristics due to the flame flow field and buoyancy. The different electrode shapes affected the probability of forming conductive channels with positive and negative periods. When the breakdown was during a positive period, the combination of negative rod and positive plate electrodes had the highest breakdown probability, while when the breakdown was during a negative period, the combination of positive rod and negative plate electrodes had the highest breakdown probability. The results show that the evolution of the breakdown arc can be divided into the conduction stage, the combustion stage and the extinction stage. A flame significantly increases the arc volume and the upward drift. The flame flow field and the buoyancy both change the electrode discharge position. This research is important for forest fire prevention and safe operation of high voltage power grids in mountainous regions.

The locations of urban emergency shelters are important for improving the evacuation efficiency and safety of the local population. This paper considered various factors such as the road network accessibility, shelter construction costs, and carrying population capacity on the emergency shelter utilization with the shelter locations determined based on the minimization facility model and the maximization coverage model with capacity constraints in a geographic information system (GIS) location-allocation model. The model was used to divide up the central area of Kunming as an example for empirical analyses. The results give an optimal number of 9 emergency shelters in the study area based on the minimum construction cost and the highest utilization rate of the emergency shelters. The results also show that the government needs to expand the capacity of Zhuantang Park and open both Wuhua Square and Victory Square as emergency shelters to create the best evacuation service for this study area. The total evacuation responsibility area can then be divided into 8 regions. These results provide support for emergency decision-making and rescue programs during urban emergencies.