Explosion Hazards Research Articles

Chemical reaction process and dynamic characteristics of urea pyrolysis products in inhibiting gas explosion

During the coal mining process, gas explosions pose significant hazards, causing casualties and property losses. In order to develop new types of inhibitors for gas explosions, this paper explores the reaction mechanisms of urea pyrolysis products NH3 and HNCO inhibiting gas explosions based on density functional theory (DFT), transition state theory, and grand canonical ensemble Monte Carlo method (GCMC). It analyzes the reaction processes and kinetic characteristics of urea pyrolysis products with key radicals and gas molecules involved in explosions from a microscopic dynamic perspective. The results show that urea pyrolysis products exhibit good inhibition effects on active radicals involved in explosion reactions·NH3 and HNCO show stronger van der Waals forces in electrostatic attraction towards O2 and *H, respectively, and faster rate advantages in reaction rate constants. The lower Gibbs free energy barrier indicates higher reaction activity of pyrolysis products, thereby diluting the concentration of key radicals involved in explosion reactions and effectively inhibiting explosion key elementary reactions (R32, R38, R53, R57, R156, and R170). This study provides new insights into the microscopic inhibition mechanism of urea pyrolysis products on gas explosions, offering a new approach for designing more targeted modified inhibitors, which helps reduce the hazards of gas explosions during coal mining and provides scientific support and technical guidance for safe coal mining production.

Advancing respirable coal mine dust source apportionment: a preliminary laboratory exploration of optical microscopy as a novel monitoring tool

Exposure to respirable coal mine dust (RCMD) can cause chronic and debilitating lung diseases. Real-time monitoring capabilities are sought which can enable a better understanding of dust components and sources. In many underground mines, RCMD includes three primary components which can be loosely associated with three major dust sources: coal dust from the coal seam itself, silicates from the surrounding rock strata, and carbonates from the inert ‘rock dust’ products that are applied to mitigate explosion hazards. A monitor which can reliably partition RCMD between these three components could thus allow source apportionment. And tracking silicates, specifically, could be valuable since the most serious health risks are typically associated with this component-particularly if abundant in crystalline silica. Envisioning a monitoring concept based on field microscopy, and following up on prior research using polarized light, the aim of the current study was to build and test a model to classify respirable-sized particles as either coal, silicates, or carbonates. For model development, composite dust samples were generated in the laboratory by successively depositing dust from high-purity materials onto a sticky transparent substrate, and imaging after each deposition event such that the identity of each particle was known a priori. Model testing followed a similar approach, except that real geologic materials were used as the source for each dust component. Results showed that the model had an overall accuracy of 86.5%\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$86.5\\%$$\\end{document}, indicating that a field-microscopy based monitor could support RCMD source apportionment and silicates tracking in some coal mines.

Quantitative classification of equipment protection level in concept of zone classification with downtime of protective measures

Handling flammable materials has a risk that can create explosive atmosphere. Such locations are classified as hazardous area, depending on the frequency and volume of explosive atmospheres. General electrical equipment is prohibited in the hazardous area and explosion protected equipment is used. These are the spatial isolation of ignition sources within the fire triangle, but even time isolation can prevent explosion hazards as well. It is proposed a method to classify zones from the calculation of downtime of protective measures based on failure rates and repair times of protective measures related to ventilation in explosive gas atmospheres with the Functional Safety under the time isolation concept. On the other hand, according to International Electrotechnical Commission (IEC) System for Certification to Standards Relating to Equipment for Use in Explosive Atmospheres, explosion protected equipment was also classified as an Equipment Protection Level, "EPL". The EPL should be selected according to the risk of the hazardous area. However, in IEC60079–14:2013, users can choose any EPL according to their risk assessment. In this paper, we clarify the quantitative risk difference of EPLs with expansion the idea of classifying hazardous area from the downtime of protective measures and introduce a means to quantitatively classify the EPL of equipment in an explosive gas atmosphere.

Research on explosion hazard and prevention of ultrafine aluminium powder based on orthogonal matrix analysis

This study investigated the coupled effects of multiple factors, namely dust mass concentration, dust particle size, and oxygen volume concentration, on the explosion intensity of ultrafine aluminium powder (UAP); the study determined the weight of each factor by using an orthogonal experimental design. Explosion intensity was evaluated using the maximum explosion pressure (MEP) and MEP rise rate (MEPR) of UAP. Explosion tests were performed using a 20 L standard spherical explosive device. A weight matrix for the explosion intensity was calculated. The results revealed that the MEP and MEPR increased most with the oxygen volume concentration. They also increased with the dust mass concentration to a lesser extent. The dust particle size had the smallest effect; the MEP and MEPR initially increased and then decreased as the particle size increased. The weights for oxygen volume concentration, dust mass concentration, and dust particle size were 69.191%, 18.761%, and 13.038%, respectively. The optimal factor combination for minimizing intensity was a dust mass concentration of 500 g/m3, an oxygen volume concentration of 9 vol%, and a dust particle size of 0.172 µm. On the basis of these findings, the study proposes industrial explosion-proofing countermeasures to increase the safety of production in aluminium-related enterprises.

Evaluating the moderating role of management inspection between safety hazards in hospital working conditions: A study of hospitals in Islamabad

The study identifies the relationship between safety hazards and hospitals working conditions. The management inspection role supported by the management in hospitals is identified to bring safety measures precautions and effectiveness for the healthcare staff and make the hospital working conditions better. The hospital management inspection role helps to accomplish occupational safety and better working conditions. The objective of this study is to identify the relationship of management inspection role in tackling with the safety hazards to find out working conditions in Al-Shifa International hospital and Pakistan Institute of Medical Sciences hospital. The study used various statistical tests like Pearson’s correlation and KMOs Bartlet’s test to evaluate the predictors of safety barriers, working conditions and management inspection role. Data was gathered using research questionnaire and the response rate was 73%. Among the 500 respondents, 75% were males while 25%were females. The age range was 40 or above years with a mean of 2.5. The reliability analysis for the constructs is in the acceptable range. The management lacking in providing the safety information rated as 0.61 correlation matrix. The medical doctors’ responded noise as the most detrimental factor resulted with 0.70 communality and lack of health facility comes as 0.61. The structure matrix shows biological hazards rated as 0.66 and physical explosion hazards rated as 0.70 which is analyzed through KMO Bartlet’s test. The safety hazards existence in the hospitals calls upon the attention on conducting research on inspection, detection and reporting of the hazards.

A baseline approach for probabilistic blast risk analysis of building cladding under external explosions

The state of the practice in blast-resistant applications against explosions is to design the structural components for a prescribed combination of explosive mass and location, namely the design basis threat. In this context, the blast source is represented by specific scenarios, mostly associated with expert judgement, rating systems or code provisions. While offering a useful basis for practical applications, the level of detail can be significantly enhanced within a probabilistic framework for risk assessment. In research practice, plenty simplified probabilistic approaches have been proposed on external explosions in order to perform risk assessment. A rigorous methodology for such an assessment is presented herein, using tools and techniques derived from seismic risk-assessment applications. Specifically, the mean annual frequency of different explosive mass hazards is represented via a recurrence law, while the potential locations are modelled as a 2D spatial distribution, accounting for the various layers of defense that exist around the structure, i.e., perimeter protection, landscape, public or private spaces, etc. The methodology is finally substantiated with the case study of a typical building subjected to potential blast loadings from external aggressors.

Thermal stability analysis of nitrile additives in LiFSI for lithium-ion batteries: An accelerating rate calorimetry study

Although lithium-ion batteries (LIBs) are extensively used as secondary storage energy devices, they also pose a significant fire and explosion hazard. Subsequently, thermal stability studies for LiPF6- and LiFSI-type electrolytes have been conducted extensively. However, the thermal characteristics of these electrolytes with thermally stable additives in a full cell assembly have yet to be explored. This study presents a comprehensive accelerating rate calorimetry (ARC) study. First, 1.2-Ah cells were prepared using a control commercial LiPF6 electrolyte and LiFSI with a specific succinonitrile additive and ethyl-methyl carbonate as a thermally stable electrolyte additive. The kinetic parameters involved in heat generation and their effects on the thermal properties of the ARC module were analyzed from the heat-wait-seek (HWS), self-heating (SH), and thermal runaway (TR) stages. The results indicate that the addition of a succinonitrile additive to the LiFSI electrolyte lowers the decomposition temperatures of the solid electrolyte interface (SEI) owing to polymerization with Li at the anode, while simultaneously increasing the activation energy of reaction temperatures at SEI between the separator and the electrolyte. The maximum thermal-runaway temperature decreased from 417 °C (ΔH = 5.26 kJ) (LiPF6) to 285 °C (ΔH = 2.068 kJ) (LiFSI + succinonitrile). This study provides key insights to the thermal characteristics of LiPF6 and LiFSI during the self-heating and thermal runaway stages and indicates a practical method for achieving thermally stable LIBs.

LPG gas leakage detection using ESP32

This research paper presents the development of an LPG gas detection system utilizing the capabilities of the ESP32 microcontroller and email notification functionalities. Liquefied Petroleum Gas (LPG), a widely used fuel source, poses a significant threat due to potential fire and explosion hazards in case of leaks. This project addresses this concern by proposing a cost-effective and user-friendly solution for early leak detection. The system employs an MQ-series sensor specifically designed for LPG detection. The sensor's output voltage changes in response to LPG concentration in the surrounding air. This data is acquired by the ESP32 microcontroller and processed to trigger email notifications when gas levels exceed a pre-defined threshold indicative of a potential leak. This allows for remote monitoring and prompt intervention, potentially mitigating safety risks associated with LPG usage in homes and industries. The paper further discusses the system's functionality, development process, and potential applications, along with suggestions for future improvements. Keywords— LPG gas detection, ESP32, MQ-series sensor, email notification, leak detection, safety system, Internet of Things (IoT), microcontroller, sensor data acquisition

Investigation of gas explosion hazards and characteristics during overcharged behavior of nickel-cobalt-manganese (523) lithium-ion battery

Compared with hard-shell lithium batteries, the obvious thermal runaway (TR) characteristic of nickel‑cobalt‑manganese pouch cell (NPC) is that it cannot release a large amount of gas in time. Therefore, the fire risk during the TR process of NPC is centralized by gas explosion hazard. The overcharged TR process of nickel‑cobalt‑manganese (523) NPC (NCM523) was explored in this work. The jetting flame phenomenon still occurs during the TR process of NCM523 in the absence of air, indicating that it is primarily attributed to self-reaction and exhibits spontaneous properties. Moreover, the air environment can increase the intensity of jetting and gas explosion hazards. The gases produced during the TR process of NCM523 in the air and nitrogen are mainly CO, H2, N2, CO2, CH4, C2H6, C2H4, and C3H6. The volume percentages of combustible gases in the air and nitrogen are 64.87 % and 46.24 %, respectively. The lower explosion limit (volume ratio) of gases in the air environment is between 10 % and 11.25 %, while the upper is between 39.37 % and 40 %. The maximum flammable intensity of gases generated from the TR process of NCM523 is 25 %. As revealed by CHEMKIN simulations, H∙, O∙, and OH∙ are the most important key radicals that catalyze the entire chain reaction and gas explosion during the TR process of NCM523. The interaction and mutual promotion of reactions R1, R2, and R3 are crucial for the generation of free radicals. Therefore, the combustion and explosion risk during the TR process of NCM523 can be reduced by increasing inert gases and suppressing the free radical reaction chemically during gas phase combustion.

Triboelectric Charging Properties of the Functional Groups of Common Pharmaceutical Materials Using Density Functional Theory Calculations.

Triboelectrification is a ubiquitous and poorly understood phenomenon in powder processing, particularly for pharmaceutical powders. Charged particles can adhere to vessel walls, causing sheeting; they can also cause agglomeration, threatening the stability of powder formulations, and in extreme cases electrostatic discharges, which present a serious fire and explosion hazard. Triboelectrification is highly sensitive to environmental and material conditions, which makes it very difficult to compare experimental results from different publications. In this work, density functional theory (DFT) is used to investigate the charge transfer characteristics of several functional groups of paracetamol in order to better understand the mechanisms of charging at the nanoscale and the influence of the environmental and material properties on charge transfer. This is achieved by studying the structure and electronic properties at the molecule-substrate interface. Using this molecule-substrate approach, the charging contributions of individual functional groups are explored by examining the Hirschfeld charges, the charge density difference between the molecule and substrate, the density of states, and the location of the frontier orbitals (HOMO and LUMO) of a paracetamol molecule. Charge density difference calculations indicate a significant transfer of charge from the molecule to the surface. Observable regions of electron density enrichment and depletion are evident around the electron-donating and -withdrawing groups, respectively. The density of states for the paracetamol molecule evolves as it approaches the surface, and the band gap disappears upon contact with the substrate. Hirshfeld charge analysis reveals asymmetry in the charge redistribution around the molecule, highlighting the varying charging tendencies of different atoms.

Experimental study on the cooling effect of fine water mist on the thermal runaway in a single lithium ion battery

Lithium ion battery (LIB) has been widely utilized, owing to the various advantages. However, extreme thermal hazard, namely the thermal runaway (TR), can be triggered under abusive conditions, leading to the fire or even explosion hazard. Unfortunately, efficient mitigation strategy is still lack, especially for the confined spaces. In this work, the fine water mist (FWM) is introduced into the air flow, and the cooling effect has been comprehensively study. Results show that the cooling capacity can be significantly improved with FWM droplets addition. The maximum improvement reaches 29.5 %, and the local evaporation of droplets will dominate the cooling process when the FWM flow rate exceeds 0.6 mLs−1. With the increase of air speed, the cooling capacity also increases, but the retention time of droplets in the high temperature region has been significantly shortened, leading to the decreased cooling efficiency. Inhomogeneous cooling process has been revealed, and the cooling power is found to decrease with the decreasing temperature. Moreover, the FWM cooling presents basic characteristics of convection heat transfer. The average cooling coefficient shows close relationship with the droplet content. The FWM can be used to efficiently mitigate the TR hazard, which is promising for practical utilization.

Study of Leakage and Explosion Hazard Characteristics of a Compressed Natural Gas at a Gas Station

Study of Leakage and Explosion Hazard Characteristics of a Compressed Natural Gas at a Gas Station

AUTOMATION OF PETROLEUM STORAGE TANK LEAKAGE THROUGH PRODUCT TRANSFER CONTROL USING PROGRAMMABLE LOGIC CONTROLLER

Industrial storage tanks have always been a critical part of the petrochemical industry due to their capacity to either act as a buffer to other plant processes or simply to store enormous amounts of fluids for a long period of time in a controlled environment. These petroleum storage tanks are supposedly constructed to follow specific sets of instructions guided by the American Petroleum Industry from the type of material used up to the welding procedure. But due to inefficient construction, unmaintained and uninspected problems, welding defects, and environmental concerns among others, a leak in a storage tank can occur and will be a major problem as this can cause fire, explosion, and environmental hazards. Additionally, due to tensions between Ukraine and the Russian government and the succeeding Russian ban on oil imports, the cost of 1 barrel of oil rises at an alarming since 2020. With that in mind, an automation procedure is proposed by the researchers, to save as much of this oil from leaking and being unusable and to reduce the causes of further accidents. This paper not only seeks to use an existing tank layout, with currently installed level indicator transmitters, motor-operated control valves, and other equipment, but also to introduce flammable gas detectors that could detect the leaked petroleum on the ground and would initiate the automation procedure. The automation setup was realized by flowcharts, PLC, and ladder logic simulation using Picosoft software. Automation procedures are analyzed wherein the tanks are being filled, the trucks are being loaded, a leaking tank has its contents pumped to another tank, and a leaking tank has its contents pumped to the truck loading station. Results show that a minimum number of 8.89 barrels of oil saved could breakeven the cost of an estimated amount of $80-90 dollars per barrel of oil can be saved by the proposed automation.

Improvement of the methodology for predicting gas-dynamic phenomena on the basis of modern sound-capturing equipment

The object of the study is the sound accompaniment of the processes of stress redistribution in the bottom part of the coal seam, which precede the release of rock, coal, and gas. Among the hazards of underground coal mining, gas-dynamic phenomena (GDP) are the most complex in nature and the most dangerous in terms of consequences of high dynamic power and the release of a large amount of mechanical energy in the form of fractures and gas in a short period of time. This leads to accidents due to sudden gassing and blockages of workings with coal and rock, as well as explosions of methane and coal dust, destruction of the workings' support, damage to machinery and mechanisms, equipment, and devices. The greatest hazard among GDPs is posed by sudden releases of coal and gas, rock and gas, gas releases with destruction of host rocks and with destruction of the ground of the workings, as well as gas breakthroughs from tectonic fault zones. Therefore, the accuracy of predicting possible gas-dynamic phenomena significantly affects the level of safety of miners. The acoustic emission (AE) method is used to predict the gas-dynamic activity of a rock massif. The analysis of acoustic emission studies based on archival data in coal seams subject to gas-dynamic activity has made it possible to substantiate the possibility of improving the accuracy of the forecast of emission hazard, which has a social and economic effect. On the basis of exploratory research and production tests, the software for automated calculations of the GDP forecast was improved and an improved Methodology for forecasting gas-dynamic phenomena based on modern sound-capturing equipment was developed. A scientific justification for the reference interval of AE observations in the conditions of a particular longwall was developed. The developed software and the forecasting methodology were tested in the conditions of the Tsentralna mine of the Toretskugol State Enterprise (Toretsk, Donetsk region, Ukraine). The practical significance of the work is that a method for predicting explosion hazard has been developed, taking into account the modern capabilities of equipment and methods of input data processing, which allows to increase the productivity of mining and tunneling operations in coal seams without reducing the safety of miners.

Sustainable process design for heat exchanger network considering inherent safety and process economics

AbstractProcess lifecycle has several stages, including process design covered in multiple stages. Process economics is a vital factor in finalizing the process design. Besides economics, inherent safety is an important concept contributing to sustainable process design generation. The inherent safety concept has been applied via equipment characteristics for individual equipment. Since a method considering inherent safety with equipment aspects and process economics has not been available, therefore, a new method has been proposed, namely sustainable process design for heat exchanger network (SPDHEN), to integrate inherent safety, equipment aspects, and process economics. SPDHEN uses indexing to identify the critical heat exchanger, which is then examined via hazard analysis for an explosion. For unacceptable hazards, inherent safety principles are engaged to generate design alternatives for which process economics is examined too. The final design would be inherently safer with the best profit margin. The proposed method has been studied for the ammonia synthesis loop. It is concluded that the explosion hazard has been reduced to a tolerable level by using inherent guide words with a marginal compromise on quantity of ammonia produced, that is, 0.32%. This method is straightforward and can be useful for process engineers to generate sustainable process designs for heat exchanger networks considering safety and process economics simultaneously.

Model for estimating the maximum water content that would maintain the flammability of an aqueous−organic mixture

Adding water to liquid fuels can make them nonflammable; substantial amounts of water are required to do so for highly volatile fuels. A limited amount of water being required to eliminate the flammability of low-volatility fuels would enable adjustments to be made to fire and explosion (F&E) hazard assessments for such fuels and the requirements for preventing F&E hazards of various regulations. This study developed a novel generic model for determining two critical parameters used to assess F&E hazards and that can be leveraged to eliminate these hazards: (1) the maximum water composition in the liquid phase for which the aqueous solution remains flammable and (2) the maximum flash point (FP). The model was verified using experimental data on nine low-volatility aqueous−organic mixtures and published data on eight high-volatility aqueous−organic mixtures. The model made acceptable predictions for ignitable chemicals with an FP range of −19 to 145 °C. Both the simulations and measurements revealed that only a small amount of water is required to render low-volatility fuels nonflammable, whereas substantial amounts of water are required for highly volatile fuels. The proposed model and present results can be employed to reduce the cost of F&E protection.

Explosion characteristics of hydrogen-nitrous oxide mixtures with carbon dioxide addition

In this work, the explosion of hydrogen/nitrous oxide/carbon dioxide mixtures with various equivalence ratios (0.6–1.0), initial pressures (40–100 kPa), and carbon dioxide fractions (20%–40 %) at ambient temperature (298 K) was conducted inside a normative 15.625-L cubic container. The maximum explosion pressure and pressure rise speed were obtained and analyzed. The results show that carbon dioxide plays a crucial role in weakening H2/N2O explosion intensity, flame instabilities, as well as the tendency of deflagration to detonation. In addition, the addition of carbon dioxide has affected the two competitive effects between adiabatic temperature and molecular number. The variations of maximum explosion pressure and pressure rise speed with equivalence ratios depend on the carbon dioxide fraction. Only a linear dependence was found between maximum pressure rise speed and original pressure. These results would be useful in developing explosion-proof devices in the event of potential fire and explosion hazards.

Reducing the unwanted deflagration enhancement of C3HF7 on fuel-lean hydrogen-air mixture by diluting CO2: An experimental and numerical research

To prevent the explosion hazards of hydrogen energy, in this work, the deflagration behaviors of H2-air mixtures at equivalence ratios from 0.6 to 1.4 under the effects of C3HF7 and CO2 are experimentally investigated. Deflagration pressure and time indexes at ambient pressure and temperature are obtained. The characteristic parameters of chemical kinetics are analyzed according to a detailed mechanism. The results suggest that C3HF7 has dual effects of pressure enhancement and suppression with the rising volume ratio in fuel-lean H2-air mixtures. It is the F-involved reactions that govern the exothermic process, facilitate the comprehensive conversion of crucial free radicals, and augment the exothermicity of the principal reaction, leading to the elevation in peak pressure. Dilution of CO2 would decrease the heat release rate of the F-involved reactions and reduce the explosion enhancement effect of C3HF7. The results of this work are beneficial to the formulation of mitigation measures for hydrogen explosions.

Explosion incidents associated with comprehensive studies on methyl ethyl ketone peroxide under thermal decomposition: A review

AbstractThis review gathered and discussed the available results on the thermal hazards, thermal kinetics, decomposition mechanism, autocatalytic behavior, thermal explosion, deflagration ability, and incompatibility hazards associated with the thermal decomposition of methyl ethyl ketone peroxide (MEKPO). The present review constructed a diagram showing all activation energy Ea and log A values for the thermal decomposition of MEKPO. Some disagreement exists in the values of Ea and log A (unit: s−1 M1−n) derived from differential scanning calorimetry; thus, more extensive studies must be conducted to resolve disputes. Nearly no literature exists on the thermal explosion and deflagration ability of MEKPO, and the reactions of MEKPO with incompatible contaminants remain unclear. Concerning the complex decomposition mechanism of MEKPO, experimental determination and identifications of intermediates have not been obtained. Available technology must be improved to enable the collection of accurate data on thermal hazards, thermal kinetics, decomposition mechanisms, explosion and deflagration phenomena, autocatalytic behavior, and incompatibility. This review has integrated an up‐to‐date summary of the most recent approaches and offers perspectives regarding future research. These current findings can serve as a reference for completing subsequent experimental investigations, theoretical studies, and designs of inherently safer measures for producing or handling MEKPO.

Effect of vent area on vented ammonia-hydrogen-air deflagrations in a 1-m-long duct

Although ammonia-hydrogen blended fuel has become a research hotspot, it is essential to recognize that adding hydrogen to ammonia increases the potential explosion hazard before considering the development of ammonia-hydrogen fuel. In this study, the effect of vent area on vented deflagrations of ammonia-hydrogen-air mixtures is investigated in a 1-m-long horizontal rectangular duct with a right end opening at an initial temperature of 293 K and an initial pressure of 101 kPa. A dimensionless vent coefficient Kv is used to define the vent area in this work to clarify the evolution of flame structures and overpressure inside and outside the duct. For a specific Kv, the amplitude of the maximum internal explosion overpressure (Pmax) monitored at the left end of the duct (LE) has a greater difference compared with other pressure monitoring points. The maximum amplitude of Pmax is always reached at the LE for Kv ≤ 3.2, while the difference in the maximum amplitude of Pmax between different monitoring points decreased significantly for Kv > 3.2. With the increasing of Kv from 2.2 to 20.1, Pmax obtained at the right end of the duct (RE) and the center of the duct increases monotonously, but Pmax monitored at the LE shows a non-monotonic increasing trend. A spike structure of penetrating flame bubbles resulting from negative pressure balance is only observed inside the duct for Kv ≤ 5.6. Two types of oscillations (Helmholtz and Acoustic oscillations) can be distinguished in some tests, and only acoustic oscillations of overpressure can be clearly found in tests with Kv > 7.8. With the increasing of Kv from 2.2 to 20.1, the shape of the external fireball will change significantly. As Kv increases from 2.2 to 5.6, the external fireball shapes are always mushroom-shaped. However, the shapes of the fireball become elongated for Kv > 7.8, and even the external fireball presents a jet shape for Kv = 20.1. With the increasing of Kv from 2.2 to 20.1, The maximum external overpressure increases first, thereafter decreases, and finally increases.