Abstract
Gas explosions, particularly those involving methane–air mixtures, present considerable hazards in confined spaces, such as coal mines. Comprehending the explosion characteristics and their ...correlations with initial gas concentrations is vital for devising effective safety measures. This study examines the influence of initial gas concentration on explosion temperature, overpressure, and flame evolution in methane–air premixed gas explosions, utilizing a custom-built 20-L spherical explosion experimental apparatus. The explosion temperatures display an oscillatory pattern, reaching maximum values at 6.5%, 9.5%, and 12% initial gas concentrations, with corresponding temperatures of 995 K, 932 K, and 1153 K. The maximum overpressure exhibits an initial rise and fall trend, modeled by an exponential function. Notably, in proximity to the 9.5% concentration, the pressure wave fosters the reverse propagation of the flame wave, leading to a secondary temperature increase. Flame sensors were employed to investigate the presence, absence, and duration of flames, demonstrating that elevated initial gas concentrations resulted in more prolonged flame durations and increased harm. At an initial gas concentration of 9.5%, a persistent flame is generated instantaneously during the explosion. Furthermore, the study analyzes the interplay between temperature and overpressure, underscoring the significance of mitigating high-temperature burns near tunnel walls and enclosed spaces. These findings advance the understanding of gas explosion dynamics and hold substantial implications for safety measures in coal mines.
•Analyzed the cause of secondary explosion accident in Hushan Gold mine in China.•Clarified the direct and indirect causes of the accident.•Calculated and verified the direct cause of the secondary ...explosion accident.•Put forward the suggestions for preventing secondary explosion accidents in mines.
Explosion accidents often occur during mining, especially sudden secondary explosions, which pose a serious threat to the life and property safety of employees. Based on the development process and consequences of typical secondary explosion accidents in Hushan Gold Mine, Qixia City, Shandong Province, China, this paper uses accident analysis model and cone measurement calculation method to determine the direct cause of secondary explosion accidents. The main conclusions are as follows: The HFACS-CM model is used to analyze the causes of secondary explosion from five aspects: external environment, organizational influence, unsafe leadership, the prerequisite conditions of unsafe behavior and unsafe behavior. It is found that the CO ignition explosion in the mining process is the direct cause of secondary explosion. Then, combined with the experimental data of the cone measuring instrument, the field CO amount was calculated, and the MCO ≥ 101.4 m3 was obtained, indicating that the CO production did reach the condition of explosion range, and the analysis results of the model were verified. Through HFACS-CM model analysis and calculation verification, the key causes of secondary explosion accidents in such mines are found and lessons are learned, which provides an effective reference for the effective prevention of deflagration accidents in the field of mine safety.
Gas explosion accidents are a leading cause of casualties in underground coal mines. This study investigates the variation patterns of explosion temperature and pressure under different initial gas ...concentration conditions using a 20 L explosion characteristic test system and high-precision sensors. Accurate post-explosion gas analyses were conducted using a GC9560 gas chromatograph. Our research aligns with global research, finding that initial gas concentrations within the range of 5.8%–13.3% generate maximum explosion pressures between 0.3 and 0.9 MPa, posing a significant overpressure hazard to humans. Comprehensive fitting analyses of various post-explosion gases reveal that at an initial gas concentration of 10.6%, the produced H2 can reach its lower explosion limit, indicating a risk of secondary explosions. Furthermore, post-explosion CO levels can peak at 9.87%, potentially causing poisoning or death, while elevated CO2 levels and diminished O2 concentrations could lead to asphyxiation. A unique observation at a 9.5% concentration was a secondary temperature rise, with the relationship between temperature delay, heating time, and initial gas concentration presenting a U-shaped pattern that mirrors theoretical expectations. This study advances the field by addressing research gaps in post-explosion gas analysis and emphasizing the necessity of precise monitoring and control of gas concentrations, thereby offering novel insights and substantial theoretical and practical contributions to the prevention of gas explosion incidents in underground coal mines.
Passive explosion-isolation facilities in underground coal mines, such as explosion-proof water troughs and bags, face challenges aligned with current trends in intelligent and unmanned technologies, ...due to restricted applicability and structural features. Grounded in the propagation laws and disaster mechanisms of gas explosions, the device in this paper enables accurate identification of explosion flames and pressure information. Utilizing a high-speed processor for rapid logical processing enables judgments within 1 ms. Graded activation of the operating mechanism is enabled by the device. The tunnel flame-proof device’s flame-extinguishing agent has a continuous action time of 6075 ms. Experiments on the active flame-proof effect of a 100 m3 gas explosion were conducted using a cross-sectional 7.2 m2 large-tunnel test system. With a dosage of 5.6 kg/m2, the powder flame-extinguishing agent completely extinguished the explosion flame within a 20 m range behind the explosion isolator. Numerical calculations unveiled the gas-phase chemical suppression mechanism of the powder flame-extinguishing agent NH4H2PO4 in suppressing methane explosions. Building upon these findings, application technology for active flame-proofing was developed, offering technical support for intelligent prevention and control of gas explosions in underground coal mines.
Dust dispersibility, the tendency of dust to form clouds that remain airborne, can be an important safety parameter in preventing dust explosion. One measure to moderate dust explosion hazards is ...adding solid inertants to combustible dust. In addition to being a solid inertant, noncombustible silica is sometimes used as an anti-caking agent or fluidization enhancement additive in powder systems, affecting particle interactions in dust clouds. In this study, six types of combustible dust were admixed with micro- and nano-sized silica to study the effect on dispersibility and ignition hazard in a Godbert-Greenwald (G-G) furnace. Both micro- and nano-silica increased dispersion for some dust types, by changing contact geometry between combustible particles, and thereby decreasing inter-particle forces. Only for polyethylene did addition of 1% micro-silica cause increased dispersibility resulting in enhanced ignition hazard, with minimum ignition temperature (MIT) slightly decreasing 10 °C. No reduced MIT values were found with 1% nano-silica.
Display omitted
•No particle breakage occurs in a G-G furnace•Actual particle size in dispersed dust clouds is larger than the primary particle size•Both micro- and nano-silica can increase dispersibility for some dust types•Addition of 1% micro-silica causes 10 °C decreases in MIT of polyethylene by increasing dispersion•No reduced MIT values are found by adding 1% nano-silica even with better dispersion
The fire and explosion risks of metal powders admixed with solid inertants have been extensively investigated for many years. However, it remains unclear why such solid mixtures have high potential ...fire and explosion risk even when mixed with high percentages of non-combustible solids. This paper investigates how to interpret these risks, from a microscopic perspective, with thermal and kinetic parameters including initial ignition temperature, mass unit exothermic energy, activation energy and risk index of spontaneous combustion. The results show that the initial ignition temperature based on TG (Thermogravimetry) analysis is related to ignition sensitivity, and increased with percentage of admixed solid inertant. The unit mass exothermic energy based on DSC (Differential scanning calorimetry) analysis is related to flame spread velocity. Activation energy and the risk index of spontaneous combustion can be used to explain the reactivity and spontaneous combustion hazard, respectively, of metal powders. We conclude that thermal and kinetic parameters may provide another way to describe the fire and explosion risk of combustible powders, especially for nano metal powders due to the laboratory safety in the normative tests for explosion parameter determination.
•Combining with the TG and DSC curves can be used as a basis for determining whether the mixed dust is flammable.•The initial ignition temperature based on TG analysis is related to ignition sensitivity.•The unit mass exothermic power based on DSC analysis is related to flame spread velocity.•The activation energy characterized the reactivity of nano mixed dust.•The risk index of spontaneous combustion indicated that nano Ti powder has a potential risk of spontaneous combustion.
Inspired by shell surface structure, the surface textures were extracted by curve fitting method and the corresponding bionic wavy textures filled with SnAgCu-WS2 composite solid lubricants were ...prepared on the surface of TC4. The coupling effect of bionic wavy textures and SnAgCu-WS2 and the effect of variable reciprocating friction frequency on the tribological properties of TC4 were explored. The results show that bionic textures improve the precipitation efficiency of SnAgCu-WS2, and the sliding effect of WS2 promotes the spreading and repairing of composite solid lubricants in the wear track, thus improving the formation quality of the lubricating film and its adaptability to the change of reciprocating frequency.
Display omitted
•Bionic textures with lubricants were used to improve tribological performance of TC4.•Bionic wavy textures improve the precipitation efficiency of SnAgCu-WS2.•Sliding effect of WS2 promotes spreading and repairing of lubricants in wear track.•Coupling effects improve adaptability to the change of reciprocating frequency.•The average friction coefficient of TWs-SACW02 is reduced to 0.219 at 20 N and 1 Hz.
Cadmium (Cd) is a type of toxic substance, which widely exists in nature. However, the effect of Cd exposure on the toxicity of swine lungs and its underlying mechanism involved have not yet been ...reported. In our study, we divided swine into two groups, including a control group (C group) and Cd-exposed group. Swine in the C group were fed a basic diet, whereas swine in the Cd group were fed a 20 mg Cd/kg diet. Immunofluorescence, qRT-PCR, western blot analysis, and H&E staining were performed to detect necroptosis-related indicators. Our results found that after Cd exposure, Th1/Th2 imbalance occurred, miR-181-5p was down-regulated, TNF-α expression was increased, and the NF-κB/NLRP3 and JAK/STAT pathways and RIPK1/RIPK3/MLKL axis were activated. Furthermore, histopathological examination showed necrosis in swine lung after Cd exposure. Together, the above-mentioned results indicate that subacute Cd exposure is closely linked with necroptosis in swine lung. Our study provided evidence that Cd may act through miR-181-5p/TNF-α to induce necroptosis in swine lung. The findings of this study supplement the toxicological study of Cd and provide a reference for comparative medicine.
The poor tribological performance of TC4 alloy limits its wide application in engineering field. Inspired by the layered structure of shell, the bionic composite coating of TC4-SnAgCu (TSAC) on TC4 ...was designed. The coatings with three different lubricant concentration ratios of TC4-5wt.%SnAgCu (TSAC-5), TC4-10wt.%SnAgCu (TSAC-10) and TC4-15wt.%SnAgCu (TSAC-15) were prepared using laser additive manufacturing (LAM) technology, respectively. Tribological tests were, respectively, carried out at the loads of 10 N, 15 N, 20 N and 25 N. The results show that compared with TC4, TC4 with bionic coating has better tribological behaviors and reducing ability of friction-induced vibration and noise. Furthermore, at 20 N and room temperature, the complete lubrication film is more easily formed on the worn surface of TSAC-10. Hence, TSAC-10 obtains the minimum friction coefficient and average equivalent noise pressure, which are, respectively, reduced by 21.28 % and 18.76 % compared to those of TC4.
Inspired by the surface texture of bivalve shell, bionic wavy grooves were designed and prepared on the bionic coating of TC4 using laser marking technology. A response surface method was used to ...optimize the parameters of bionic texture structure for improving the tribological behavior. The influence of coupling mechanisms of bionic coating and texture on the tribological performance of TC4 alloy was investigated. The results show that the bionic wavy grooves reduce the fluctuation of loading force. The coupling of bionic texture and coating breaks the continuity of coating interface, and the peeling wear debris is easily captured by the bionic wavy grooves. The repairing effect of solid lubricant is increased, so the complete lubrication film can be formed more easily on the worn surface during the sliding process.
