Explosion Intensity Research Articles

The flammability limits and explosion behaviours of hydrogen-enriched methane-air mixtures

The effects of hydrogen(H2) on the macroscopic explosion parameters and microscopic chemical kinetics of methane(CH4)-air mixtures were investigated. First, the effect of H2 on the flammable limit of CH4 was studied with a.standard test device. Second, the explosion characteristic parameters of CH4-H2-air mixtures were measured in a standard 20-L spherical chamber, including the maximum explosion pressure, maximum pressure rise rate and combustion time. Finally, based on the GRI mech 3.0 and USC mech 2.0 mechanisms, the effect of H2 on the chemical kinetics of CH4-air mixtures was studied. The results reveal that the flammable limit of CH4 is expanded and the explosion risk value is enhanced with the addition of H2, and more inert gas is required to inertize CH4. The explosion intensity of the CH4-air premixed gas rises after H2 addition in the fuel-lean state. The explosion intensity first increases and then decreases with increasing H2 addition under stoichiometric conditions. The addition of H2 under fuel-rich conditions reduces the explosion intensity of the premixed gas. Moreover, under the three CH4 conditions, the main elementary reactions affecting the sensitivity and production rate of the key free radicals (H, O and OH) are the same, and as the H2 addition amount increases from 0% to 2%, the sensitivity coefficient of the elementary reactions accordingly increases.

Shallow conduit dynamics fuel the unexpected paroxysms of Stromboli volcano during the summer 2019

Open conduit basaltic volcanoes can be potentially hazardous as the eruptive activity may turn suddenly from a steady state to highly explosive. Unexpected changes in explosion intensity are recurrent at Stromboli volcano, where major explosions and large-scale paroxysms sometimes break off the ordinary, Strombolian activity with little or no warning. Two powerful paroxysmal eruptions took place at Stromboli volcano during the summer 2019, causing widespread fires, consistent damages across the island, injuries and one fatality. Prediction of similar events is really challenging for the modern volcanology, though models propaedeutic to early-warning monitoring systems are not properly assessed yet in many volcanoes worldwide. Here, we present a multi-parametric study that combines petrological and geophysical data to investigate processes generating the two paroxysms. The time information derived by Li enrichments in plagioclase crystals correlates with tilt time series derived by seismometers installed on the island, highlighting the dominant role of shallow conduit processes in triggering the 2019 paroxysmal activity. Our dataset conceives a mechanism of gas slug formation and fast upward migration that finally triggered the eruptions in very limited times. The proposed model questions our capability to forecast such kind of paroxysms in times that are rapid enough to allow mitigation of the associated risk.

Principal component analysis of the effect of coal quality indexes on the maximum explosion pressure of coal dust

It is well-known that the calorific value and heat transfer speed of coal are closely related to the coal quality index, and affect the explosion intensity and the maximum explosion pressure of coal dust explosion. In this paper, the pressure for different coal quality indexes is studied experimentally, and the main parameters affecting the pressure are elucidated by the principal component analysis of multivariate statistical analysis.

Transient reaction process and mechanism of cornstarch/air and CH4/cornstarch/air in a closed container: Quantitative research based on experiments and simulations

Both dust/air explosion and flammable gas/dust/air explosion are common forms of energy release. Experiments and simulation models with a multi-step chemical reaction mechanism were used to study the intensity parameters and mechanism of the CH4/air explosion, cornstarch/air explosion and CH4/cornstarch/air explosion in a closed container. Results showed that the peak overpressure, maximum flame temperature, and average flame propagation speed of the stoichiometric CH4/air explosion reach 0.84 MPa, 2614 K and 3.5 m/s, respectively. The optimal concentration of cornstarch explosion is 750 g/m3, and its peak overpressure, maximum flame temperature and average flame propagation speed are 0.76 MPa, 2098 K and 1.77 m/s, respectively. For a three-components system, adding methane can significantly increase the explosive intensity and combustion performance of cornstarch. The explosive intensity parameters (peak overpressure, maximum flame temperature, average flame propagation speed) of a certain concentration of cornstarch first increase and then decrease with the increase of methane concentration. The maximum explosion intensity parameters of a three-components system with a certain concentration of lean-methane/air are higher than that of single-phase, but always lower than that of the stoichiometric methane/air. Moreover, the mutual coordination of dust and combustible gas in energy release and the mutual competition mechanism in oxygen consumption are described.

Numerical Simulation of Impact Loads of Main Fan Blades in Gas Explosion

The shock wave generated by a severe gas explosion accident can damage the main fan, and the toxic and harmful gases in the well cannot be discharged in time, leading to the expansion of disaster accidents. Therefore, it is meaningful to study impact loads of main fan blades in gas explosion. In this paper, a full-scale three-dimensional numerical simulation model has been established based on No. 2 Yangchangwan Coal Mine in China. The propagation of shock wave in shaft and air tunnel and the dynamic process of main fan blade subjected to shock load when gas explosion of different volume occurs in heading face have been simulated. The overpressure on the blade at different times, the overpressure distribution on the blade, and the relationship between the overpressure and the explosion intensity have been obtained. The results showed that the time when the explosion shock wave reached, each blade of the wind turbine was basically the same, and the time when each blade reached, the maximum overpressure was basically the same. With the increase of gas explosion volume, occurrence time of overpressure and maximum overpressure time on the fan blade were shortened, and the time interval between them was also shortened. There is a little difference in the overpressure of each blade. Fan blade directly above the hub was subject to the highest overpressure, and fan blade directly below the hub was subject to the lowest overpressure. The overpressure of the maximum overpressure blade was 5.44% to 6.77% higher than that of the minimum overpressure blade. The distribution of overpressure on each fan blade was uneven, and the overpressures on blade edges were the lowest. The overpressure on the fan blades showed a corrugated distribution along the radial direction. There was 12.06% to 15.40% difference between the maximum and minimum overpressure section on the fan blade.

Effect of multi-oxidants on mechanical response and reactive characteristics of PTFE/Al reactive material under dynamic impact

PTFE/Al/Fe2O3, PTFE/Al/MnO2 and PTFE/Al/MoO3 reactive materials specimens were fabricated by referring to the traditional thermite and adding PTFE as matrix. Split Hopkinson pressure bar system tests were carried out to investigate the effect of multi-oxidants on mechanical response and reactive characteristics of PTFE/Al reactive material under dynamic impact. The results show that three oxidants have significant influence on the mechanical behavior and reactive characteristics of the reactive materials. PTFE/Al/Fe2O3 had the highest strength while PTFE/Al/MoO3 exhibited the lowest strength. The reaction time and reaction thresholds of PTFE/Al/Fe2O3, PTFE/Al/MnO2 and PTFE/Al/MoO3 were measured to be 2.5 ms, 2.9 ms, 1.9 ms and 6250 s−1, 5600 s−1, 6500 s−1, respectively. The addition of MnO2 could dramatically improve the explosion intensity, prolong the reaction time and reduce reaction threshold of PTFE/Al reactive material. All the results indicate that MnO2 has great potential for serving as an additive into PTFE/Al system to improve the energy release rate.

Primary headache associated with sexual activity: A case series of 13 patients

Primary headache associated with sexual activity is an infrequent kind of headache mostly seen in the male gender and initiates during the third decade. Although the pathophysiology is still unknown, it is a benign type of headache and must be reminded of the differential diagnosis of the secondary headache. Thirteen patients were diagnosed and assessed by their clinical and demographic data. The mean age was 37.07 ± 7.67. Headache was usually localized at the bilateral occipital area or diffuse, starting with a severe ache and sudden explosive intensity in association with pre orgasm in eight patients and orgasm in five patients with a mean VAS score of 7.8 ± 1.2. The mean duration was 21.53 ± 15.32 min. Five patients had a history of migraine, three had arterial hypertension, and two were diagnosed as primary thunderclap headache with sudden beginning and high-intensity ache. Herein, we present our cases to highlight the importance of differential diagnosis. Patients may have difficulty explaining the problem; therefore, their sexual activity could be limited. Apart from pharmacological prevention, counseling plays an essential role in managing.

Experimental investigation on the effects of thermal treatment on the physical and mechanical properties of shale

Shale is affected by high temperature and loads in deep mining, shale gas extraction, underground disposal of nuclear waste, and other shale projects. This paper aims to investigate the effects of thermal treatment on the physical and mechanical properties of shale. The uniaxial compression test and acoustic emission (AE) monitoring were conducted on shale specimens with different bedding plane inclinations (0°, 30°, 45°, 60°, and 90°) after thermal treatment of different temperatures. The results show that the P-wave velocity decreases with the increase in bedding plane inclination at each thermal treatment temperature showing anisotropy. A thermal explosion occurs when the specimen reaches the macroscopic thermal damage threshold temperature, and the threshold temperature and intensity of the thermal explosion are linked to the bedding plane inclination. The peak stress of specimens with the bedding plane inclinations of 0°, 45°, and 90° increases with the rise in thermal treatment temperature. After thermal treatment, the relationship curve between the cumulative AE counts of specimens with different bedding plane inclinations and time presents a step-jump trend. The thermal treatment has no significant effect on the failure modes of specimens with bedding plane inclinations of 30°, 60°, and 90°, while specimens with bedding plane inclinations of 0° and 45° begin to splitting failure with a rise in the thermal treatment temperature. The rockburst failure occurs in the shale specimens, and the main phenomena are spalling, particle ejection, and block collapse. The thermal treatment has a significant influence on the rockburst intensity of specimens with different bedding plane inclinations.

Explosion characteristics assessment of premixed biogas/air mixture in a 20-L spherical vessel

The understanding of biogas explosion characteristics is needed to describe the severity of the explosion. Biogas is a flammable gas and will explode when ignited. This study reports the experimental results on biogas explosion characteristics in a standard 20-L spherical vessel under quiescent conditions using electric spark (10 J) as an ignition source. Computational Fluid Dynamic (CFD) code FLame ACcelaration Simulator (FLACs) was used to simulate the biogas explosion based on the experimental case study. The dependence of explosion characteristics such as explosion pressure (P max), rate of pressure rise (dP/dt), and deflagration index (KG), on biogas concentration and carbon dioxide, CO2 composition is demonstrated. The data allow for the evaluation of the potential severity of biogas explosion, which in turn helps engineers design the explosion mitigation and prevention device related to this gas. The experimental data reported from this study concluded that P max = 8–8.50 bar, the dP/dt = 100–400 bar/ms and the K G = 32.7–121 bar m/ms were recorded at equivalence ratio, (ER) = 1.2 with CO2 composition in the biogas = 30% vol/vol. It was found that the severity of the biogas explosion increased proportionally with the biogas concentration. On the contrary, the explosive intensity was weakened by increasing the CO2 concentration due to the physical effects of CO2 and thermal instability. This study also recorded that the biogas explosion was categorized under hazard level = St-3 indicating a catastrophic explosion. These data are important for preventing and mitigating the biogas explosion.

Influencing factors of the chain effect of spherical gas cloud explosion

Flammable gases and liquids are widely used in industry and have serious leakage hazards. When a leaking gas cloud accidentally encounters an ignition source, it results in vapor cloud explosion accidents and multiple explosions. Pressure and flow field monitoring of a primary exploding spherical gas cloud and the secondary explosion of the gas cloud were conducted using the pressure acquisition system and schlieren system, and the impact of different influencing factors on exploding were analyzed. It was found that the larger the size of the primary exploding gas cloud, the smaller the distance between the primary exploding gas cloud and the secondary explosion gas cloud, and the larger the explosion intensity of the two gas clouds. Ignition on both sides of the primary exploding gas cloud was more likely to cause a blasting effect than was central ignition. The change in sparking ignition energy had no obvious effect on explosion propagation. When multiple gas clouds were exploding, the position of the primary exploding gas cloud had a considerable influence on the chain effect of exploding. If the primary exploding gas cloud was located in the middle of multiple gas clouds, interaction occurred between the primary exploding spherical gas cloud and the secondary explosion gas cloud because the angle formed by the secondary explosion gas cloud decreased, and the explosive intensity of the exploding gas cloud was higher. When the primary exploding gas cloud was on the side, the smaller the angle, the closer the lateral gas cloud was to the flame development path of the explosive gas cloud, which increased the likelihood of a blast and increased explosion intensity.

Experimental study on dust explosion vented through a bent duct

AbstractIn this study, a self‐designed small cylindrical vessel was used to perform a dust explosion venting experiment through a bent duct. Based on this experiment, the influence of the bend distance and the static activation overpressure of the venting film on the explosion overpressure and the flame propagation was investigated. The results showed that both the maximum venting overpressure and pressure rise rate within the vessel increased with the decrease in the bend distance and increase in the static activation overpressure. In contrast, the duration of the combustion within the vessel exhibited the opposite trend. A typical “three‐peak” overpressure structure formed by the film rupture shock wave, secondary explosion in the duct, and continuous combustion within the vessel was observed in the duct. The third peak overpressure was dominant throughout the process. The intensity of the secondary explosion in the duct was positively correlated with the bend distance and static activation overpressure. Shorter bend distances led to greater peak‐overpressure drops after passing the bend. However, the attenuation of the secondary explosion intensity along the duct with static activation overpressure is not obvious.

Mechanisms of vapor cloud explosion and its chain reaction induced by an explosion venting flame

This experimental study focused on vapor cloud explosion and its chain reaction induced by an explosion venting flame. Two vapor clouds were installed in front of the explosion venting container along the horizontal direction. Explosion flame evolution process was recorded by a high-speed camera and a schlieren system. Pressure sensors at different locations were used to acquire the pressure data. The temperature data were collected by a high-speed infrared thermal imager and three thermocouples. The changes in flame propagation characteristics, flame temperature, and pressure distribution were determined, and the mechanisms of the vapor cloud explosion and its chain reaction induced by the venting flame were deeply analyzed. Results indicate that the venting flame could induce vapor cloud explosion and set off a chain reaction, leading to the high explosion intensity. As for the ignition condition, the venting flame directly came in contact with the vapor cloud and provided the required energy for the ignition. The pressure first increased and then decreased as the distance from the venting port increased, and the highest pressure appeared in the central region of the vapor cloud. The temperature distribution also presented a similar phenomenon.

Experimental study of the venting characteristics of dust explosion through a vent duct

To further understand the dynamic mechanism of dust explosion through a vent duct, we designed a small-scale cylindrical vessel connected with a vent duct and performed a dust explosion venting experiment under different opening pressures using corn starch as the explosive medium in this study. The results show that weakening effect of duct on venting is positively correlated with the opening pressure. The explosion pressure in the duct presents a three-peak-structure with time, successively caused by the membrane breaking shock wave, the secondary explosion in the tube, and the continuous combustion, and decreases gradually with the propagation distance. Meanwhile, the three pressure peaks are positively correlated with the opening pressure, while the time interval between them goes to contrary. The increase of opening pressure leads to the increase of secondary explosion intensity and reverse flow in the vessel, further accelerates the reaction rate in the vessel, and then shortens the duration of combustion in the vessel until the phenomenon of flame reignition in the vessel disappears.

Coupling effects of venting and inerting on explosions in interconnected vessels

The coupling effects of venting and CO2inerting on stoichiometric methane-air mixture explosions were investigated in an isolated vessel and interconnected vessels. The results indicate that venting mitigates the explosion intensity, especially for small vessels. For vessels connected by pipes, a venting design following EN 14994 (2007) and NFPA 68 (2013) could not meet the venting requirements. For an isolated big vessel and interconnected vessels, increasing the CO2 volume fraction (Φ) from 0 to 15.0 vol% decreased the maximum explosion overpressure (Pmax) and maximum rate of overpressure rise ((dP/dt)max) and delayed tmax. For closed interconnected vessels, Pmax varied approximately linearly with Φ. For both isolated vessel and interconnected vessels, the coupling effects of venting and CO2 inerting on methane-air explosion were more efficient than those of individual mitigative method (that is, venting alone or CO2 inerting alone).

Experimental study of the molten tin column impacting on the cooling water pool

This paper presents the interaction between molten tin column and cooling water using the high-speed camera and the transient pressure measurement system. The effects of the molten tin column temperature, dropping height, diameter of molten tin column, and surrounding gas environment on the interaction of molten tin column with the water are examined. The results show that three modes of no explosion, product-outside explosion and product-inside explosion are observed. With the increase in the tin column temperature, no explosion is first shifted to product-outside explosion and then product-inside explosion with the maximum overpressure. The dropping height of the molten tin column promotes the intensity of the product-inside explosion. As the molten tin column diameter increases, the intensity of steam explosion first increases and then decreases. N2 atmosphere induces the stronger steam explosion than air.

Explosion suppression of porous materials in a pipe-connected spherical vessel

To study the suppression of different porous materials on the explosion of combustible gas, some experiments were implemented. The porous materials were categorized into three kinds, including six subcategories, and the explosion suppression characteristics of the thin iron hoop, one-layer porous materials, two-layer composite porous materials, and three-layer composite porous materials were studied and analyzed. The results show that a rarefaction wave appears in the spherical vessel during the rapid development stage of combustion explosion. Further, the thin iron hoop could enhance the gas explosion intensity. And the explosion intensity suppression effect of the porous materials is obvious, the best effects of one-layer, two-layer and three-layer porous materials are from Fe–Ni 10 mm/40 PPI, Fe–Ni 10 mm/90 PPI + Al2O3 10 mm/30 PPI, and Al2O3 10 mm/50 PPI + Fe–Ni 10 mm/40 PPI + SiC 20 mm/20 PPI, respectively. According to the surface morphology of the porous materials, the anti-sintering ability of the three categories of porous materials follows the order of Al2O3 > SiC > Fe–Ni. Besides, the thickness and pore size of the combined porous material was changed, which has a great influence on the explosion pressure and the explosion intensity.

Effect of a Tilted Obstacle on the Flame Propagation of Gas Explosion in Case of Low Initial Pressure

ABSTRACT Obstacles are unavoidable in coalmine laneways and combustible gas pipeline. However, the obstacles may enhance the intensity of explosion, or change the propagation characteristic. The present paper deals with the flame propagation characteristic of explosion in the tube with a tilted obstacle (45 ~ 135°) under the condition of low initial pressure (0.2 ~ 0.35 kPa). Two models (a so-called modified model and a mathematical model) are adopted in order to describe the regularity of flame velocity for the first (i.e. after explosion at an edge of the tube) and third (i.e. before the flame reaches the end of the tube) stages, whereas some irregular phenomena are investigated during the second stage (i.e. in which the flame reaches the titled obstacle, and goes beyond it) of the whole process, i.e. explosion and flame propagation along the tube. A theoretical fitting model is built in order to describe the critical moments of the accident, i.e. explosion and propagation. It is shown that the initial pressure and obstacle, considered as governing factors, have specific influences on flameless zone and flame velocity. This research can provide a new basic study of the effects of obstacles on combustible gas explosion and a reference for actual explosion protection designs.

On the time coupling analysis of explosion pressure and intermediate generation for multiple flammable gases

In this paper, the key product (CH2O) from the explosive chain reaction of methane is selected as the research object, and a method for analysing the coupling mechanism between the explosion pressure and intermediate products is proposed; this method provides a theoretical basis for the construction of an explosion control system with chemical effects. A 20-L spherical closed explosion experimental system and spectral measurement system are used to investigate the pressure and flame emission spectra characteristics of the intermediate products during the mixed explosion process of five typical gases (CH4, C2H6, C2H4, CO, and H2). The time difference (ΔT) between the peak explosion pressure (Pmax) and the peak CH2O spectral intensity is proposed to analyse the coupling relationship between them. On the one hand, the results show that ΔT reflects the effect of the improvement in CH2O generation on explosion intensity; the smaller the ΔT value is, the greater the improvement is. On the other hand, ΔT reflects the main source of CH2O; when the sample concentration is smaller, CH2O is mainly formed during the explosive chain reaction. When the sample concentration is larger, CH2O mainly originates from the bond polymerization of alkylene compounds. The effects of the system conditions (sample concentration, sample composition and methane concentration) on the ΔT and CH2O formation rates are combined, and the correlation between Pmax and ΔT can reflect the coupling mechanism between the explosion pressure and intermediate products. When the oxygen is enriched, ΔT is negatively correlated with Pmax using the power function model, with R2 > 0.95.

Empirical analysis of a steam explosion in a slag yard based on a field investigation and 3D explosion damage simulation

Many types of explosions often occur in industrial settings, and research is being conducted to identify the causes and establish preventive measures. The aim of this study is to investigate slag yards, where metal residues are cooled in the steel industry, often causing steam explosions. The cause of accidents and explosion simulation analyses were used to investigate the sources of steam explosions in a slag yard. The explosion intensity of 4kg of TNT was measured for the purpose of predicting the intensity of a steam explosion. This was compared with a simulation of explosion damage that occurred in 2017. These results could not be produced from small-scale experiments, and they indicate that damage resulting from actual explosions poses a potential risk to pipes that cannot be directly observed. We conclude that this damage can lead to a domino accident, and this study provides results for estimating the possibility of future damage.

Inhibitory effects of three chemical dust suppressants on nitrocellulose dust cloud explosion

AbstractThree types of self‐prepared chemical dust suppressants (CDSs) were investigated for their inhibitory effects on nitrocellulose (NC) cloud dust explosion. The results revealed that NC is extremely sensitive to electric sparks and has a high explosion intensity. CaCl2‐CDS effectively increased the particle size to control fly dust substantially inhibiting dust cloud explosions. However, both Na2SO4‐CDS and MgCl2‐CDS exhibited poor abilities and even promoted explosion. Therefore, neither Na2SO4‐CDS nor MgCl2‐CDS is recommended as a CDS for NC. Inappropriately using CDSs may engender severe explosions. Furthermore, a mechanism underlying NC dust cloud combustion and explosion was proposed. NC has three stages of heat release: autoxidation, thermal decomposition, and combustion. Thermal decomposition, combustion, and explosion were triggered depending on the energy provided from autoxidation. CaCl2‐CDS inhibited only combustion. This study reveals the mechanism underlying NC dust cloud explosions and provides useful information for the development of more optimized CDSs.