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A simplified model that calculates the deflagration pressure–time curves of a hydrogen explosion was proposed. The deflagration parameters (pressure peak, duration, deflagration index, and impulse) of hydrogen–air mixtures with different hydrogen concentrations were experimentally investigated. The results show that the pressure curves calculated by the model are consistent with experimental data pertaining to a methane and hydrogen explosion. By comparison, the pressure peak and deflagration index are found to be influenced by the aspect ratio and surface area of vessels. The impulse and explosion times at fuel-lean hydrogen concentrations are greater than those at fuel-rich concentrations. When the hydrogen concentration is between 34 vol.% and 18 vol.%, the greatest explosion damage effect is formed by both the overpressure and the impulse, which should be considered for hydrogen explosion safety design in industrial production. [ABSTRACT FROM AUTHOR]

Earth-covered magazine has some characteristics that are safer than the above-ground magazine and are more economical than underground magazine. To investigate the pressure distribution and the structural failure under the internal explosion, the scaled tests of the earth-covered magazine were conducted under a 0.5 kg TNT explosive charge. The overpressure in the 0°, 90°, and 180° directions outside the structure and the debris distribution were obtained. The numerical simulations were constructed in LS-DYNA software to analyze the test results. The results show that the external overpressure has a directional characteristic that the maximum and minimum overpressure appear in 0° and 180° directions, respectively. In the double logarithmic coordinate system, the overpressure peaks in three directions are linearly related to the scaled distance. Most of the fragments in the 0° direction hit the ground within the front range of ±60°, and the further fragments (40 m or more) were confined to a limited sector within the front range of ±30°. The internal explosion numerical simulation shows that the concrete cracks first appeared at the roof and the ground, and then the damage occurred at the intersection of the walls, and then the damage occurred at each surface. The maximum debris velocity of the side and rear walls is lower than that of the front wall due to the limitation of the soil. The motion equations of the debris combined with numerical simulation can be adopted to predict the projection distance of fragments. [ABSTRACT FROM AUTHOR]

Gas explosion accidents under shock wave stimulation cause more severe hazards than electric spark ignition. To explore the initiation mechanism and explosion characteristics of methane induced by shock waves. A series of experimental investigations of methane-air mixtures initiated by hexogen (RDX) was performed based on a self-developed closed pipeline. The effects of incident shock wave intensity and methane concentration on the characteristics of methane explosion were studied. The results indicate that methane participating in the reaction can significantly increase the positive pressure duration compared with RDX explosion. With the increase of incident shock Mach number (Ma), methane deflagration pressure increases and counteracts the attenuation of RDX detonation pressure. When the ignition distance is 0 cm, the overpressure inside the pipeline is directly proportional to the methane concentration from 5 vol% to 13 vol%. When the concentration approaches the upper explosion limit, the flame velocity exceeds the theoretical detonation velocity, resulting in the unstable detonation of methane in the pipeline. • The methane combustion mechanism initiated by RDX was investigated in a closed pipeline. • The effect of the shock wave intensity on the explosion characteristics was analyzed. • Significant influence of methane concentration on overpressure peak and flame velocity was obtained. [ABSTRACT FROM AUTHOR]

According to the scaling law of cratering explosions in a monolayer medium and the theory of similarity, this research derived a scaling law for cratering explosions in multi-layered media. Except for the influence of scaled depth of burial, for cratering explosions in multi-layered media, the wave impedance of the layered media will affect the distribution of the total energy, which ultimately affects the crater. At present, there are two main methods used to investigate cratering or underground explosions: centrifuge model tests and equivalent material model tests. Based on the use of a mini-spherical explosive charge and a pouring type of equivalent material, we carried out modeling experimental design and implementation of explosion cratering in multi-layered media. Specifically, a center-initiating explosive charge with the 1 gTNT equivalent yield was used to simulate the explosive source with 10 kg TNT equivalent yield on an equivalent material of low strength but high density to simulate high-strength geotechnical materials such as concrete and rock. There were 12 groups of blasting model tests, which were carried out to investigate the influence of wave impedance matching and the scaled depth of burial on the cratering effects in multi-layered media. A high-speed movie camera was used to capture the photographs of ejecting and bulging movement, and molten paraffin wax was poured into the explosion craters to obtain a mold of the crater. Generally, the basic law of explosion cratering in multi-layered media was obtained. The cone radius of the crater at the interface exhibited either expanding or necking phenomena. After analysis of the experimental data, the ejecting and bulging, and the crater geometries, as affected by the ratio of wave impedance and the scaled depth of burial, were assessed. [ABSTRACT FROM AUTHOR]

• The effects of vent area and ignition on the internal and external pressure were investigated during venting. • The formation mechanisms of external pressure peaks were analyzed. • The relationship between external overpressure and distance was proposed. • External flame development was visualized during vented explosion. • The relationship between internal pressure peak and external pressure peak was investigated. Explosion venting can cause not only internal damage but can cause external damage to buildings. Since little attention is paid to the damage caused by both explosions simultaneously, vented explosion tests were performed in a 4.5 m3 square chamber, to investigate the internal and external pressure characteristics and their correlation. The results show that ignition location has little effect on venting pressure (P 1), but significantly affects the Helmholtz oscillations and high-frequency oscillation pressure (P 4). Central and front ignitions lead to the maximum P 4 and longest Helmholtz oscillation, respectively; during venting, two pressure peaks (defined as P e1 and P e2) were recorded due to the shock wave and combustion wave, respectively. P e1 has an inverse proportional relationship with distance. P e2 is proportional to P 1. When the vent area exceeds 0.16 m2, P e2 under rear ignition plays a more dominant role than that of other ignition points, however, the vent area is equal to 0.16 m2, P e2 with central ignition becomes dominant. The external pressure peaks corresponding to the external flame development were captured. The longest length of the jet flame was observed at central ignition and rear ignition forms the largest external combustion area. [ABSTRACT FROM AUTHOR]

• Large-scale methane vented explosion was conducted. • Explosion pressure oscillations were analysed in terms of oscillation frequency. • Internal flame development was analysed via changes in flame colour and profile. • Initial turbulence effects on pressure and flame development were discussed. The testing of vented explosion of methane-air mixtures was conducted in a custom-designed 4.5-m3 steel chamber. Methane concentrations in the mixed gas varied between 7 and 13 vol% and the static hysteresis time was set as 0, 1, and 5 min to characterize strong, medium and weak turbulence levels. The effects of concentration and initial turbulence on pressure characteristics and flame development were investigated. It is found that the quasi-static pressure in the chamber during vented explosion can be divided into three stages: pressure release, Helmholtz oscillation, and acoustic oscillation. The Helmholtz oscillation at a frequency of about 20–40 Hz is produced after the peak pressure P 1 caused by the pressure release at all concentrations; however, the acoustic oscillation at a frequency of about 300 Hz only occurs after Helmholtz oscillation when the concentration is near the optimum. In the early stage of internal flame development, the cellular structure is generated due to hydrodynamic instability and diffusive-thermal instability, and the flame front is distorted owing to the instability caused by venting. Initial turbulence distorts the flame front, significantly increases the peak pressure, and stimulates the generation of acoustic oscillation at the upper and lower limits of concentration. Under the influence of initial high turbulence, the internal flame propagation distance has a power function relationship with time, and the turbulence acceleration factor and distance also show a power function relationship. [ABSTRACT FROM AUTHOR]

Knowledge of vented flame propagation is of significance in the design of protective work against the effects of a gas explosion. Since there is little attention paid to the damage caused by the vented flame, the propagation characteristics of a vented flame in an external space were studied. Vented explosion experiments were conducted in a custom-designed chamber under three concentrations of ethylene/air mixtures and numerical simulation was also used. The propagation of a vented flame in an external space mainly depends on the combustion with unburnt gas and four typical flame profiles due to the effect of Darrieus–Landau flame instability and diffusional-thermal instability are observed. At different stages of propagation, characteristics such as velocity, stretch rate, and distance are all different. The reach of the vented flame can be expressed as an exponential relationship with time and the acceleration exponent is 0.65, which indicates that the vented flame is essentially undergoing spherical decelerating propagation under unconfined deflagration conditions. The numerical simulation applied is in good agreement with the experiments, which provides a basis for the analysis of the external flow field. Vented explosion experiments were conducted in a custom-designed chamber under three concentrations of ethylene/air mixtures. The propagation characteristics of the vented flame such as flame profile, velocity, stretch rate and duration were presented and analysed. Numerical simulation was also used to further study the flow characteristics of the vented flame. Image 1 • Four typical flame profiles are observed and analyszed. • Trends in theSpecific regularities about propagation characteristics at different stages are presented. • The reachdistance of a vented flame followedwas expressed as an exponential relationship with time. • The duration and reachdistance of a vented flame are compared at two equivalence ratios. [ABSTRACT FROM AUTHOR]

Abstract: A structural model experiment was carried out on a buried scaled-down reinforced-concrete arch structure subjected to underground close-in explosions. The aim of the experiment is to provide believable results of dynamic responses of large-span structures, including the dynamic loads, deflections, strains and failure modes. To achieve this objective, blast experiments were carried out under 0.6 kg, 3 kg, 6 kg and 17.4 kg TNT charges, respectively. Distribution laws of the applied dynamic loads, deflections, strains, accelerations and the failure modes of the arch were revealed. Different from the quasi-uniform distribution style subjected to far-field explosions, the dynamic loads applied on the buried arch subjected to close-in explosions have tense local effects and render a triangle-like distribution style. According to the tested deformations and strains, it can be concluded that subjected to close-in explosions, the buried arch deforms at a dominant flexural mode, companying with compression mode. Spalling, tensile cracks and shear failures of the concrete and yielding of the steel bars are the main failure modes of the blast-loaded arch. The arch will collapse after four or five plastic hinge lines formed. The experimental data are helpful for engineers and well support further theoretical analysis. [Copyright &y& Elsevier]