Dust Explosion Research Articles

Estimating the maximum size of explosive iron sulfide particles

Introduction. There are estimates of the maximum size dcr of explosive particles of the two types of sulfide ores. The estimates are based on a qualitative approach to the dispersion analysis of combustible ore specimens (Soundararajan, Amyotte & Pegg, 1996): 49 μm < dcr, PO < 63 μm for pyrrhotite (PO) and 85 μm < dcr, PY < 145 μm for pyrite (PY). The task was to refine these estimates using the quantitative method of the mentioned analysis, taking into account the lower explosive limit (LEL) of flame propagation in terms of ore suspensions. Experimental data processing method. Continuous functions F of particle size distribution d were constructed for the two polydisperse specimens of pyrrhotite (LELPO,1 = 475 g/m3 and LELPO,2 = 1,375 g/m3) and two polydisperse specimens of pyrite (LELPY,1 = 375 g/m3 and LELPY,2 = 500 g/m3). The obtained functions FPO,1(d), FPO,2(d), FPY,1(d) and FPY,2(d) were converted using Rosin – Rammler distributions, filling the gaps between the discrete data of the grain-size analysis of the specimens. dcr rating. The procedure for estimating dcr (Poletaev, 2014) was employed to find the values of dcr, PO and dcr, PY using the following equations: FPO,1(dcr, PO)/FPO,2(dcr, PO) = LELPO,2/LELPO,1 and FPY,1(dcr, PY)/FPY,2(dcr, PY) = LELPY,2/LELPY,1. The solutions were presented in the visual graphic format.Discussion of the results. Due to the low values of explosion parameters of pyrrhotite and pyrite in a 20‑liter chamber (maximum explosion pressure Pmax ≤ 350 kPa, index Kst ≤ 2 MPa ∙ m/s), the validity of classifying ores as explosive dusts was discussed. Low explosion values have proven that sulfur is the main fuel in the air suspension. The explosiveness of ores is proven empirically (Selle & Zehr, 1954) by estimating the combustion temperature, which exceeds 1,000 °С.Conclusions. The values of dcr for sulfide ores have been refined: for pyrrhotite, dcr = 40 μm; for pyrite dcr = 107 μm. In the air suspensions of ores, only sulfur is burnt out, which substantially reduces the explosiveness of ores.

Computational assessment of biomass dust explosions in the 20L sphere

Determination of the explosion severity parameters of biomass is crucial for the safety management and dust explosion risk assessment of biomass-processing industries. These are commonly determined following experimental tests in the 20L sphere according to the international standards. Recently, CFD simulations have emerged as a reliable alternative to predict the explosion behavior with good accuracy and reduced labor and capital. In this work, numerical simulations of biomass dust explosions are conducted with the open-source CFD code OpenFOAM. The multi-phase (gas-solid) flow is treated in an Eulerian-Lagrangian framework, using a two-way coupling regime and considering the reactions of biomass conversion (moisture evaporation, devolatilization, and char oxidation), the combustion of volatile gases, and convective and radiative heat transfer. The model is validated with pressure-time and concentration-dependent experimental measurements of two biomass samples. Results suggest that the characteristics of the cold-flow (ı.e., turbulence levels, actual dust concentration, spatial distribution of the dust cloud, and turbophoresis effect) govern the course of the explosion process, and depend strongly on particle size, dust concentration, and ignition delay time effects. These findings may be relevant in the design of better dust explosion testing devices and to the reexamination of the guidelines for the operation of the experiment. Finally, a thorough discussion on the explosion pressures, degree of biomass conversion, flame temperature, flame propagation patterns, and the dust agglomeration effect is presented.

Influence of inlet duct turning on dust-collector explosion

A 12-L dust-explosion model was designed to conduct a corn-starch explosion experiment to investigate the influence of the turning structure of the inlet duct on the dust-explosion propagation process. The development in the dust explosion in the dust collector and the propagation process of the explosive flame in the inlet duct were examined. Additionally, the influence of the turning distance of the inlet duct on the dust-collector explosion was analyzed. By changing the distance from the turning position of the inlet duct to the dust collector, the distance had a negative correlation with the maximum explosion pressure of dust in the vessel and a positive correlation with the explosion duration. The pressure curve in the duct exhibited a bimodal structure, and the secondary explosion phenomenon was relatively pronounced in the middle of the turning inlet duct. Owing to the obstruction of the turning inlet duct, the decay rate of the explosion pressure decreased before turning and increased after turning. In addition, with an increase in the turning distance, the decay rate of the explosion pressure in the duct decreased, whereas the secondary explosion in the duct became more intense.

A comparative study on aluminum dust explosion suppression by powder inhibitors

ABSTRACT An aluminum dust explosion is a major safety hazard that cannot be ignored. It is of great practical significance to investigate explosion flame propagation characteristics and powder inhibition mechanisms of aluminum dust. Based on a self-designed dust explosion experimental system, explosion flame propagation characteristics such as flame shape, temperature and velocity were captured. The effect of aluminum particle size on the flame propagation was explored, and inhibition performances and mechanisms of NaHCO3, CaCO3 and Na2HPO4 on aluminum dust explosion were experimentally and theoretically revealed. The proportion of white bright areas decreased from 17.9% to 7.9%, 8.0% and 8.8% respectively, and the temperature and velocity decreased obviously with powder inhibitors. Especially, NaHCO3 can reduce the maximum flame temperature and maximum flame velocity to 1411°C and 14.27 m/s respectively, and its inhibition performance was optimal. CaCO3 had better performance than Na2HPO4 in suppressing the flame propagation velocity and in delaying the ignition time, and Na2HPO4 was more advantageous in suppressing the explosion flame temperature. It is explained by the mechanism that substances containing Na and P can play an important role in the suppression of gas-phase reactions. The Na cycle (NaO ↔ Na) is effective in scavenging free radicals.

Explosion inhibition of coal dust clouds under coal gasification atmosphere by talc powder

During coal gasification, the explosion intensity of coal dust was enhanced and more difficult to inhibit due to the presence of CO and H2. To mitigate the risk of dust explosion under a coal gasification atmosphere, the inhibition performance of talc powder (TP) on coal dust explosion was investigated by using a 20 L spherical explosive vessel. The results showed that the explosion intensity of dust clouds was attenuated with the inhibition of TP. As the particle size of TP decreased, the explosion pressure gradually was reduced and the explosion time was extended. The maximum explosion pressure of dust clouds decreased from 0.845 to 0.270 MPa after the addition of 8000 mesh TP, representing a reduction of 68 %. And the flame propagation velocity was consequently dropped from 1.22 to 0.17 m/s. Moreover, the explosion of higher rank coal dust was more easily inhibited by TP. XPS analysis demonstrated that the C–C and C–O–C in coal dust were effectively protected under the effect of TP. And the inhibition mechanism of TP on coal dust explosion was elaborated thoroughly in combination with the analysis of explosion products.

Fire extinguishing and explosion suppression characteristics of explosion suppression system with N2/APP after methane/coal dust explosion

The study aims to examine the suppression performance of an inhibitor after a methane/coal dust explosion. The design of an explosion suppression system included the carrier gas of nitrogen (N2) with an inhibitor of ammonium polyphosphate (APP). The study investigated fire extinguishing and explosion suppression of methane/coal dust by N2/APP in a vertical pipe. Flame propagation characteristics were measured by a high-speed camera, micro-thermocouple, and pressure sensor. The residues after the explosion were characterized chemically by X-ray photoelectron spectroscopy, and the thermal decomposition characteristics of coal dust and APP in the N2 atmosphere were analyzed by synchronous thermal analysis. Experimental results show that the explosion suppression system can effectively hinder the flame propagation of methane/coal dust explosion. The flame height, bottom velocity, and temperature were all weakened significantly. The optimum level of suppressant minimizes the explosion pressure and suppresses the flame significantly. In addition, the fire extinguishing and explosion suppression mechanisms of N2/APP were summarized. The suppression method used in this study blocks the explosion after it occurs rather than preventing it through premixed inerting.

Mechanism Analysis of Delayed Water Inrush from Karst Collapse Column during Roadway Excavation Based on Seepage Transition Theory: A Case Study in PanEr Coal Mine

Water inrush disaster is one of the major disasters affecting the production safety of coal mines following roof caving, fire, gas outburst, and dust explosion disasters. It is urgent to reveal the water inrush mechanism and take effective measures to prevent the disasters. More than 80% of water inrush accidents occur around geological structural zones such as faults and karst collapse columns (KCCs). The water inrush events from KCCs caused huge economic losses and heavy casualties, and the water inrush process often shows certain hysteresis characteristics. Taking the water inrush disaster from a KCC during roadway excavation in PanEr Coal Mine of Huainan Mining Area as the case study, the delayed inrush mechanism of KCC was analyzed from the aspects of floor failure, KCC activation, seepage transition, and water inrush development characteristics. The results show that the rock mechanical properties and the excavation depth are the main factors affecting the floor failure characteristics. The seepage transformation from pore flow to fracture flow and pipeline flow, with the change in internal composition structure, is the internal mechanism of the delayed water inrush from KCC. The research is of great significance for the prediction and prevention of water inrush disasters from KCCs.

Explosion mechanism of aluminum powder mixed with low-concentration hydrogen

This paper examines dust explosion characteristics and mechanisms for aluminum powder (Alp) in four different low-concentration hydrogen environments (0%, 1%, 2%, and 4 vol%). The aluminum powder's combustion characteristics were determined and the minimum ignition temperature and minimum ignition energy were found to be 690 °C and 45 mJ, respectively. A 20-L apparatus was used to evaluate how the explosive characteristics varied under different hydrogen concentrations. The explosion pressure generated by 4 vol% H2 was ca. 8.3% stronger than an explosion in the air, and the explosion pressure rise rate showed an increase of 48%. In addition, the time to maximum rate of pressure rise was shortened in the mixed Alp/hydrogen experiment. The experimental residues were observed, and from this it was inferred that the explosion mechanism changed when a low concentration of H2 was present.

Иерархическая структура аэрологических рисков в угольных шахтах

Introduction. As the actual data show, the safety of coalmines is the most vulnerable in the event of explosions of methane and coal dust, often accompanied by a complex manifestation and implementation of several hazardous factors, such as gas, dust, exogenous fires, leading to catastrophic consequences. To assess, predict, manage and reduce the consequences of the complex implementation of dangerous aerological factors in the occurrence of accidents in coalmines, a methodology has been developed for assessing and managing aerological risks in coalmines, based on the hierarchical structure of aerological risk. Objective. Assessment, forecasting, management and reduction of rank III aerological risks for extraction areas and development workings of highly gas-rich coalmines. Methodology. To assess, predict, control and reduce the consequences of the complex implementation of hazardous production factors in the occurrence of accidents associated with explosions of gas and dust in coal mines, a methodology has been developed for assessing and managing aerological risks in coal mines, based on a systematic approach in accordance with the hierarchical structure of aerological safety. The aerological safety of mines can be quantified in terms of aerological risks: the lower the risks, the higher the safety. All aerological risks were divided into three ranks according to their importance in the production activities of the mine, corresponding to the hierarchical structure of the aerological safety of the mine. Aerological risks of the I rank are understood as aerological risks covering the entire mine, aerological risks of the II rank cover layers, wings, deposits; aerological risks of III rank cover separate mining or development sites. Comparison of mines by aerological risks should be made according to aerological risks of the same rank. When performing research, an analysis of literary domestic and foreign sources was used; generally accepted methods, including methods of mathematical statistics and probability theory; a method of expert assessments to obtain the values of the hazard and vulnerability coefficients of ventilation methods for excavation areas and development workings. Results and discussion. A methodology has been developed for constructing a hierarchical structure of aerological risks in coal mines. A block diagram of aerological risks of III rank has been compiled, including the main hazards in the excavation areas and development workings and the main types of vulnerability of the ventilation schemes of the excavation areas and the methods of ventilation of dead-end workings. Calculations have shown that when developing the most dangerous mine seams, the lowest values of aerological risk of III rank for excavation areas are characterized by combined ventilation schemes in the absence of a diagonal connection in the scheme; the presence of an unstable diagonal connection in the ventilation scheme of the excavation area increases the aerological risk by 2.7 times. For development workings carried out along seams prone to rock bumps, spontaneous combustion, sudden outbursts of coal and gas, with a specific dust emission of more than 1200 g/t, only ventilation methods with a high degree of gas mixing activity in the bottomhole zone can be applicable. Conclusions. The developed hierarchical structure of aerological risks makes it possible to rank risks by levels and compare risks of the same rank. The application of the developed risk assessment methodology makes it possible to predict and reduce aerological risks in the design and operation of coal mines.

Evaluation of Explosion Characteristics of Waste Dust Generated from the Cement, Non-ferrous Metal Ingot, and Alloy Manufacturing Industries

This study evaluated the explosive hazardous properties and the likelihood of dust explosion in four types of waste dust collected from industrial sites. Waste dust samples were collected from the cement manufacturing industry, aluminum, and aluminum alloy ingot manufacturing industry, and copper alloy and non-ferrous product manufacturing industry. We evaluated whether the dust waste contained explosive substances using a standard method. Additionally, the factors that may affect the dust explosion, the presence of combustible substances, average particle size, particle size distribution, particle shape, moisture content, and calorific value were also evaluated. It was confirmed that the likelihood of dust explosion of dust waste generated in the aluminum and aluminum alloy manufacturing industry is higher than that of dust waste generated in other industries.

In situ analysis of suppression mechanism of DMMP water mist in coal dust explosions using pyrolysis time-of-flight mass spectrometry

Suppression mechanism of dimethyl methylphosphonate (DMMP) water mist on coal dust explosions is extremely difficult to understand, but it is of great significance for the development of high-efficiency suppressants. In this study, a novel in-situ pyrolysis time-of-flight mass spectrometry (in-situ Py-TOF-MS) is used to detect the evolution of volatile matter from coal/DMMP composite pyrolysis, which is produced during the explosion. During the coal primary pyrolysis, PO(OH)(OCH3)2, P(OH)(CH3)(OCH3)2, CH3OPO2 are the major suppression species. At 300-600℃, CH3PO2, PO(OH)2(CH3), PO(H)(CH3)(OCH3), and small P-containing compounds play a key role in flame suppression. DMMP can inhibit the generation of shorter-chain products, interrupt the transfer of H atoms to react with the phenoxy group to form dihydroxy aromatics. Thereby, the volatiles concentration significantly decreases, resulting in coal dust being less prone to ignition. The key suppression reactions of P-containing species at different temperature ranges are revealed, which guides the development of high-efficiency suppressants.

Experimental and CFD Simulation Techniques for Coal Dust Explosibility: A Review

Experimental and CFD Simulation Techniques for Coal Dust Explosibility: A Review

Flame Propagation Characteristics of Hybrid Explosion of Ethylene and Polyethylene Mixture under Pressure Accumulation

In order to study the flame propagation characteristics of a ethylene/polyethylene hybrid explosion under pressure accumulation, a visual pressure-bearing gas/power hybrid-explosion experimental platform was built. The flame propagation characteristics of polyethylene and ethylene/polyethylene hybrid explosions in the closed vessel were analyzed. The results show that the flame brightness, flame front continuity and average flame propagation velocity of polyethylene dust explosion in the closed vessel increased first and then decreased when the polyethylene dust concentration increased. The curve of the flame propagation velocity with time had obvious pulsation characteristics. Adding 1% and 3% ethylene to different concentrations of polyethylene dust significantly improved its explosion flame brightness, flame front continuity and average flame propagation velocity. Moreover, it also improved the fluctuation amplitude of the explosion flame propagation velocity with time curve. The explosion flame of the polyethylene dust and ethylene/polyethylene hybrid mixture included four zones during the propagation process, which were denoted as the unburned zone, preheated zone, premixed flame zone and dust flame zone. The addition of ethylene to polyethylene dust can significantly increase its thickness of premixed flame zone and preheated zone, and the thickness increased when the ethylene concentration increased.

Suppression mechanisms of ammonium polyphosphate on methane/coal dust explosion: Based on flame characteristics, thermal pyrolysis and explosion residues

To explore the suppression mechanisms of ammonium polyphosphate (APP) on methane/coal dust explosion flame, the experiment tests of methane/coal dust explosion flame propagation under different mass fraction of APP were conducted in a vertical pipe. Using Simultaneous Thermal Analysis and Py-GC/MS to analyze the effects of APP on the thermal decomposition process and thermal pyrolysis products of coal dust. The chemical characterization of explosion residues was carried out by confocal Raman and Fourier transform infrared spectroscopy (FTIR). Based on the apparent suppression ways of APP such as absorption of heat, reduction concentration of combustibles and adsorbent of free radicals, APP also limited the thermal decomposition process of coal dust and leaded to the reduction or even disappearance of some organic matters at coal dust pyrolysis. Noticeably, the investigation of explosion residues found that the carbonization effect of APP pyrolysis products and the activity reduction of functional groups (–CH3/–CH2 and –OH) which contribute to ignition of coal dust, these coupling effects made it difficult for coal dust to ignite, and thus the methane/coal dust compound explosion were suppressed significantly.

The Use of Wood Pellets in the Production of High Quality Biocarbon Materials.

Biomass is one of the most important sources of renewable energy. One of the most widely used biomass biofuels is wood pellets. It is an economical, homogeneous and easy-to-use raw material. Biomass is used to generate low-emission energy utilizing the pyrolysis process. Pyrolysis allows for higher energy efficiency with the use of commonly available substrates. This thesis presents the results of research on the possibility of using the pyrolysis process to produce high-energy biocarbons from wood pellets. Data on basic energy parameters and explosivity of biocarbon dust were compiled as criteria for the attractiveness of the solution in terms of energy utility. The research used pellets made of oak, coniferous, and mixed sawdust, which were subjected to a pyrolysis process with varying temperature and time parameters. Carbon, ash, nitrogen, hydrogen, volatile substances, heavy metals, durability and calorific value of the tested materials were carried out. The highest increase in calorific value was determined to be 63% for biocarbons obtained at 500 ℃ and a time of 15 min, compared with the control sample. The highest calorific value among all analyzed materials was obtained from coniferous pellet biocarbon at 31.49 MJ kg−1. Parameters such as maximum explosion pressure, Pmax, maximum pressure increase over time, (dp/dt)max, and explosion rates, Kst max, were also analyzed. It was noted that biomass pyrolysis, which was previously pelletized, improved the energy parameters of the fuel and did not increase the risk class of dust explosion. The lowest and highest recorded values of Kst max for the analyzed materials were 76.53 and 94.75 bar s−1, respectively. The study concluded that the process used for processing solid biofuels did not affect the increase in the danger of dust explosion. The results presented in this article form the basis for further research to obtain detailed knowledge of the safety principles of production, storage, transport and use of these new fuels.

Suitability of electrostatic ignition to determine the explosive characteristics of different types of dust in the 5-L explosion vessel

To reveal the effect of electrostatic ignition on the measurement of different types of dust explosion characteristics. In this study, the explosion characteristics of corn starch, aluminum powder, and hexogen (RDX) were studied in the 5-L explosion vessel using electrostatic and pyrotechnical igniter respectively. The energy release characteristics of these two ignition methods were studied using the schlieren technique. The results showed that the explosion pressures of the three dust clouds measured by electrostatic and pyrotechnical igniter under the same conditions were basically the same. The rate of explosion pressure rise for corn starch and aluminum powder measured by electrostatic ignition was less than that measured by the pyrotechnical igniter. Whereas the opposite was true for RDX. Different ignition methods affect the rate of explosion pressure rise by influencing the time it takes for the flame to propagate from the center of the explosion vessel to its walls.

Iron dust explosion characteristics with small amount of nano-sized Fe2O3 and Fe3O4 particles

Iron powder, as one of the most abundant metal fuels that can be used as recyclable carriers of clean energy, is a promising alternative to fossil fuels in a future low-carbon economy. It may pose a potential explosion hazard during the process of processing, storage, transport, and reduction/oxidation (redox). The explosion characteristics of iron dust in air were undertaken via a 20 L spherical explosion chamber with an emphasis on minimum explosion concentration (MEC) of iron dust. The alternative method of combustion duration time (tc) was used to determine MEC and compared with the standardized over pressure method. Two kinds of nano-sized iron oxides (Fe2O3 and Fe3O4) were used as inertants to determine the inhibition effect of different oxidation products. The iron dust explosion products with various shapes and sizes were found to be able to grow up 4–6 times of the iron dust for the first time. Adding small amount of Fe2O3 or Fe3O4 could reduce the explosion severity and sensitivity of iron dust. The MEC data determined by both methods were comparable. The addition of 5 % oxide has obvious inhibition effect under 1500 g/m3 concentration. With the increase of oxide concentration to 10 %, the inerting effect increases, and the MEC of iron dust increases more than 3 times. The increase of dust concentration will weaken the inerting effect. When the concentration increases from 500 g/m3 to 3000 g/m3, the weakening effect of 10 % Fe2O3 on the explosion pressure decreases from 38.45 % to 2.24 %, and 10 % Fe3O4 decreases from 46.21 % to 10.63 %. Unlike coal, biomass or aluminum dusts, the iron dust explosion was found to have a unique secondary acceleration of pressure rise rate for the first time. These results provide a fundamental basis to mitigate the iron dust explosion via solid inerting method without adding extra elements.

Effect of CaCl2, Al(OH)3 and NH4H2PO4 on the explosion sensitivity of pulverized coal

ABSTRACT In this paper, the effects of 30 wt%, 50 wt% aluminum hydroxide, calcium chloride and ammonium dihydrogen phosphate three explosion inhibitors on the two sensitivity parameters of the minimum explosion concentration and the minimum ignition energy of pulverized coal were investigated. It was found that for the same explosion inhibitor, the higher the content of explosion inhibitor, the higher the increase of MEC and MIE of pulverized coal-explosion inhibitor. At the same time, dust reduction measures should be taken in time when the coal dust concentration will be close to 70 g/m3. It was found that for the same explosion inhibitor, the higher the content of explosion inhibitor, the higher the increase of MEC and MIE of pulverized coal-explosion inhibitor. In the meantime, dust reduction measures should be taken in time when the coal dust concentration will be close to 70 g/m3. Furthermore, 150 g/m3 was the critical concentration of the ignition energy of pulverized coal. In order to prevent the occurrence of coal dust explosion accidents, it was necessary to resolutely prevent the concentration of pulverized coal from approaching this value on site. In addition, when the pulverized coal-explosion inhibitor concentration was 100 g/m3-250 g/m3, whether it was 30 wt% NH4H2PO4 or 50 wt% NH4H2PO4, the ignition energy required for mixing with pulverized coal was greatly increased. Overall, in the concentration range of 30–50 wt%, 50 wt% NH4H2PO4 was more advantageous in the suppression of coal dust explosion.

Explosibility of nuclear graphite measured in a 1 m3 chamber

Introduction. Nuclear graphite poses a threat due to the formation of the graphite dust – air mixture (GDAM) during the dismantling of decommissioned nuclear reactors. However, there is no clear answer to the question on the GDAM explosibility. A review of international studies suggests that GDAM is either inexplosive or its explosibility is weak (Phylaktou H.N. et al., 2015). In this paper, the authors advance arguments for the explosion safety of GDAM.Selected research result. The authors considered a well-known result of a study on the combustion of GDAM with an average particle size of 5 μm, the concentration of about 450 g/m3 in a 1.138 m3 chamber, and an ignitionsource made by Fr. Sobbe GmbH («Sobbe 10 kJ»). The maximum overpressure ΔPmax was 0.47 bar in the chamber, and it fitted the case of an explosive air suspension, according to EN 14034-3 (1 bar = 100 kPa).Interpretation of the research result. Pressure oscillograms were compared for the following two cases: the case of the maximum manifestation of the GDAM explosion hazard (ΔPmax = 0.47 bar; dP/dt|max = 3.8 bar/s) and the case of combustion of an ignition source in the absence of air suspension (ΔPmax = 0.027 bar; dP/dt|max = 2.7 bar/s). The comparison shows that the first 20 ms of a pressure change inside the chamber is mainly due to the combustion of the ignition source: the characteristic values ΔP = 0.03 bar and (dP/dt) ≈ 3.8 bar/s are close to the «Sobbe 10kJ» combustion index in the absence of GDAM. A further increase in ΔP is accompanied by the constant or sharply decreasing value of (dP/dt), which means a monotonous decrease in the flame velocity and proves the incombustibility of GDAM.Conclusions. Due to the smallness of ΔPmax, GDAM can be considered nonexplosive under normal atmospheric conditions. Dependency diagrams, relating the pressure of combustion products and its growth to time offer important information about the combustion of the air suspension in explosion chambers under the condition of a low dust explosion hazard.

Experimental investigation of the pressure characteristics in the dust explosion venting

Effects of nondimensional vent area (Kv: 4.17– 58.63) and static activation pressure (Pstat: 0.6 bar ~2.5 bar) on venting pressure are investigated. For internal pressure, the increase of Kv would significantly enhance the frequency of pressure oscillation and the elevation in Pstat would enhance the effect of induced turbulence. The equilibrium relief range with different particle sizes was clarified, and the dynamic mechanism was revealed. An empirical prediction model and an optimal design range of relief efficiency were proposed. For external pressure, the external explosion was verified by two pressure waves captured in the BOS images. The enhancement of Pstat and Kv would promote the development of external explosion within a certain range. The attenuation of external pressure with distance relies on the product of explosion source intensity and size, and the trend of recession index with variable venting conditions resembles the external explosion pressure.