Liquid fuel leakage on sloped porous media, such as loess, is a common hazard in oil storage, transportation, and the chemical industry in the loess-covered areas of China. On inclined terrain, the gravity effect changes the seepage and the heat and mass transfer of liquid fuel inside the porous medium, which accelerates fire spread and expands the thermal influence range. Most existing studies on liquid fuel fire spread over porous media adopt quartz sand as the research medium, while the pore structure, permeability, and adsorption characteristics of natural loess are obviously different from those of quartz sand; therefore, the existing conclusions cannot be directly applied to loess fire scenarios. In addition, the coupling mechanism between base inclination angle and ignition position on fire spread behavior has not been systematically clarified. It is therefore of practical significance to explore the fire spread rules of kerosene-infiltrated loess under different inclination conditions, which can provide theoretical support for fire prevention, risk assessment, and emergency disposal in loess areas.

In this work, a self-designed experimental platform with an adjustable inclination angle was adopted to carry out a series of fire spread experiments. Dry loess with a particle size range of 0.116–3.675 mm was paved evenly in the experimental tank to form a uniform porous medium bed. Kerosene was injected slowly into the loess bed in multiple small doses until the medium reached full saturation. Seven working conditions with equivalent inclination angles of −9°, −6°, −3°, 0°, 3°, 6°, and 9° were set by combining different base angles and ignition positions. Anhydrous ethanol was used as the ignition source in the designated ignition area to initiate combustion, and the total duration of fire spread was set to 20 min. A high-definition camera with a frame rate of 50 frames per second was arranged 100 cm away from the experimental platform to record the evolution of flame morphology and the spread process. Meanwhile, 12 K-type armored thermocouples with a probe diameter of 0.5 mm were arranged in a 6 × 2 array to synchronously measure the temperature distribution on the surface and inside the loess bed along the axial direction. All flame characteristics, spread velocity, and temperature data were collected and analyzed quantitatively.

The experimental results revealed that the coupling effect of inclination angle and ignition position exerted a prominent influence on flame structure and propagation. Under the same inclination angle, the flame height and propagation distance of lower-end ignition were greater than those of upper-end ignition. For the upward fire spread on positive inclination bases, the height of the yellow flame zone increased with the rise of inclination angle; for the downward fire spread on negative inclination bases, the height of the yellow flame zone gradually decreased as the inclination angle increased. The flame spread at a constant velocity under all working conditions, and the spread velocity rose monotonically with the increase of inclination angle. The velocity of upward spread was obviously higher than that of downward spread under the same absolute inclination value. When the flame front arrived at the measuring points, an obvious layered heat transfer feature was observed: the surface heating rate of loess was far higher than the internal heating rate. Compared with the horizontal base, the inclined base presented a lower steady combustion temperature, a shorter time to reach thermal stability, and a larger internal temperature gradient inside the loess bed.

The base inclination angle changes the fuel seepage path and the intensity of heat feedback through gravity, and further regulates flame morphology, spread velocity, and the internal temperature field of the loess bed. The layered heat transfer characteristics of the loess bed are determined by differences in heat transfer mechanisms between the surface and the internal porous structure. The results clarify the mechanisms by which inclination angle and ignition position influence fire spread in kerosene-wetted loess. These findings can provide guidance for the design of fire isolation zones, the development of emergency response plans, and the optimization of firefighting strategies in sloped loess terrains. They also lay a foundation for further study on the evolution of fire hazards associated with liquid fuel leakage on loess substrates.

The safety of rescue personnel is a critical factor in determining the success of rescue operations. The ability to accurately identify the motion states of rescue personnel is key to ensuring their safety. However, monitoring their motion states in real time is challenging because of the complex and dangerous environment they operate in. This study aims to develop a method for identifying the motion states of rescue personnel based on triaxial motion data to enhance the efficiency of personnel safety monitoring during rescue missions.

In this study, the MPU6050 sensor, an integrated triaxial accelerometer and gyroscope, was utilized to collect the motion data from the leg and waist of rescue personnel. This sensor was selected based on its low power consumption, automatic sleep mode, and power management features, making it suitable for long-duration rescue tasks. Before data collection, the sensors were calibrated using zero-bias calibration to reduce errors and ensure data reliability. These sensors were strategically placed on the waist the and leg of the rescue personnel to capture their overall body dynamics and detailed movements. This study analyzed the acceleration data under four different motion states: standing still, working in a small area, walking, and running. The data were analyzed using time-domain feature analysis, focusing on the standard deviation of acceleration to quantify the fluctuation and stability of the motion states. This study proposed a classification mechanism based on the sum of the standard deviations of waist and leg accelerations to distinguish between different motion states.

The experimental results demonstrated that the proposed method effectively distinguished between different motion states. In the standing-still state, the total acceleration was close to zero, indicating no movement. In the state of working in a small area, the acceleration was greater than zero but remained within a small range with stable fluctuations. In the walking state, there was a significant difference between the waist and leg total accelerations, with the latter showing larger fluctuations and clear peaks and valleys. In the running state, both waist and leg total accelerations showed larger fluctuations, with the latter having a greater amplitude. The method showed high accuracy and stability in real-time monitoring of rescue personnel's motion states, effectively identifying the changes in motion states within a 2-min test period. The standard deviation analysis revealed a clear hierarchical distribution, indicating significant differences in acceleration fluctuations between different motion states. The sum of the standard deviations of waist and leg accelerations provided a reliable basis for distinguishing between the four motion states.

This study has provided a reliable method for monitoring the motion states of rescue personnel, which can substantially improve the safety and efficiency of rescue operations. The method's ability to accurately and stably identify different motion states in real time makes it a valuable tool for ensuring the safety of rescue personnel in complex and dangerous environments. The findings of this study contribute to the development of more effective monitoring systems for rescue operations, potentially reducing the risk of accidents and enhancing the overall success rate of rescue missions.

Due to the height differences during the power transmission process, the bending installation of cables is a common method. The stress in the bending section of cables is usually relatively concentrated and more susceptible to damage, leading to a greater fire hazard. According to the different bending forms, the bending cables can be divided into upward-bending cables and downward-bending cables.

An experimental study was conducted to investigate the effect of the bending angle and number of cables on the flame spread behavior of downward-bending cables.

Results show that: (1) the peak temperature on the cable surface of downward-bending cables gradually increases, as the number of cables increases. The temperature peak of 5 downward-bending with 60°bending angle was about 782.3℃, which was 1.8 times higher than that of a single cable at the same angle. This is mainly due to the fact that combustion of multiple cables laid side by side produces more combustible pyrolysis gases, while the flame has a stronger preheating effect on the cables. (2) As the bending angle increases the flame spread time of downward-bending cables is shortened and the average flame spread rate increases. Under the ignition condition of five 90°downward-bending cables, the average flame spread rate of the cables was 5.4 cm/min, which was 1.9 times of that of five 0° downward-bending cables; under the ignition condition of five 90°downward-bending cables, the temperature peak reached 868.3℃, which was about 1.4 times of that of that of five 0°downward-bending cables. This is mainly due to the larger bending angle, which was mainly due to the difference in the role of the flow of melt drippings on the cable under different bending angles, when the flame spread in the inclined section of the cables, the flow of high-temperature melt drippings was an important driving force to ignite the cables in the unburned section. As the bending angle increased, the force of gravity increased in the direction of the cables, and the drippings were more likely to flow downwards under the combined effect of the gravitational component force, surface tension, friction of the melt drippings. The melt drippings had a more significant effect on the preheating of the unburnt section of the cables, which in turn shortens the ignition time of the cable and increased the average flame spread rate. In addition, as the bending angle increased, the "flame attached" effect was more significant, which increased the thermal convection and thermal radiation in the unburned section of the cables.

The peak temperature on the cable surface of downward-bending cables are positively related to the number of cables and the bending angle. The average flame spread rate increases as the number of cables and the bending angle increase. Regressivity analyses between flame temperature and the number of cables were carried out to analyze the flow mechanism of melt drippings in inclined sections of cables in this work, these correlations are well described by physically based models for all the experimental results.

A spill fire can cause considerable property damage and casualties. Although research on spill fires in open spaces is abundant domestically and internationally, research on spill fires in confined spaces is limited.

To investigate the combustion spread law and temperature field distribution characteristics of spill fires in confined spaces, a 1:10 reduced-size confined space model was constructed. Seven types of spill fire tests with different mass leakage rates and 12 types of oil pool fire tests with varying sizes were carried out. The analysis focused on the fire source diameter, mass combustion rate, and temperature field distribution characteristics in the confined space. The dimensions of the confined space model were 9 m long, 0.6 m wide, and 0.45 m high. The walls were covered with 2 cm-thick asbestos panels. A fireproof glass with a length of 1 m and a width of 0.45 m was placed horizontally in the center of the model as a spilling burning platform for leaking fuel. The platform was 4 cm away from the bottom of the model. To simulate fuel leakage, a stainless-steel pipe with a diameter of 1 cm was used as a leakage pipe, extending vertically from the ceiling down to the flowing platform. In addition, an electronic balance with an accuracy of 0.1 g was placed under the fuel barrel to measure the fuel leakage rate in real time.

The spill fires in the confined space undergo three stages in accordance with the changes in the fire source diameter over time. These stages are combustion diffusion, stabilization, and extinction. The transition between stages is mainly determined by the relative sizes of the fuel mass leakage rate and mass combustion rate. Equilibrium between the mass combustion rate and mass leakage rate leads to complete fuel combustion before reaching the flame front, the fire source diameter stops increasing, and the combustion enters the stabilization stage. The mass combustion rate of ethanol fuel in a confined space demonstrates a linear correlation with the fire source area because the change in mass combustion rate per unit area exerts less influence on the fuel mass combustion rate than the change in fire source area. During the combustion stabilization, the temperature field distributions of the spill and oil pool fires are similar. The temperature at the root of the fire source gradually decreases as the power of the fire source increases, while the temperature at the top rises continuously. Moreover, the temperature of the ceiling in the confined space increases with the power of the fire source and decreases longitudinally. Finally, a prediction model of ceiling maximum smoke temperature rise during the steady combustion stage of spill and oil pool fires is established.

The findings can provide theoretical support for the detection design of spill fires in confined spaces.

Previous studies on propagation-type combustion have yielded fruitful results. However, relatively few studies have investigated the characteristics of fire spread behavior of nonvolatile high flash point liquid fuel in porous media.

A series of combustion tests were performed on typical high flash point liquid fuels (kerosene, 0# diesel) infiltrating quartz sand beds of various particle sizes. The average particle sizes of quartz sand under the designed experimental conditions were 0.428, 0.715, 1.200, 2.180, 3.675, and 4.500 mm. The fire spread was recorded using a high-definition video camera at 25 frames per second, with the camera positioned 100 cm away from the experimental tank. The mass loss rate was measured using an electronic balance with a 0.1 g accuracy, and the fire spread rate was determined from the flame front position data using MATLAB. A series of K-type armored thermocouples with a diameter of 0.5 mm were arranged on the side wall of the experimental tank to measure the temperature distribution in the quartz sand bed.

The experimental results reveal that the heat transfer rate of a fine-grained sand bed (d=0.428 mm) is faster than that of a coarse-grained sand bed (d=2.180 mm) at the same depth. This difference can be attributed to the effect of capillary action on the mass transfer efficiency of the sand layer, which in turn affects the heat transfer rate during the combustion reaction process. Furthermore, a preheating zone of a certain length exists near the flame front, which is primarily dominated by heat conduction and has minimal effect on convection and radiation heat transfer. In the process of fire spreading on the quartz sand bed with liquid fuel, the mass loss rate increases over time. However, the growth rate of mass loss rate varies under different particle size conditions. In the quasi-stable combustion stage, the growth rate of mass loss rate initially decreases and then increases with increasing particle size. As the particle size increases, the average fire spreading rate of kerosene and 0# diesel on the surface of the quartz sand bed first decreases and then increases. Because of the relatively high flash point and viscosity of 0# diesel, its average fire spreading rate on the surface of the quartz sand bed is lower than that of kerosene.

This study analyzes the characteristics of fire spread on the surface of a typical porous sand bed infiltrated with high flash point liquid fuel and reveals the mechanism of the effect of particle size on the characteristics of fire spread to a certain extent. The research results provide references for the security protection and decontamination treatment of the fire spread problem when liquid fuel leaks into porous media.