Explosion Venting Research Articles

Numerical Study on Protective Measures for a Skid-Mounted Hydrogen Refueling Station

Hydrogen refueling stations are one of the key infrastructure components for the hydrogen-fueled economy. Skid-mounted hydrogen refueling stations (SHRSs) can be more easily commercialized due to their smaller footprints and lower costs compared to stationary hydrogen refueling stations. The present work modeled hydrogen explosions in a skid-mounted hydrogen refueling station to predict the overpressures for hydrogen-air mixtures and investigate the protective effects for different explosion vent layouts and protective wall distances. The results show that the explosive vents with the same vent area have similar overpressure reduction effects. The layout of the explosion vent affects the flame shape. Explosion venting can effectively reduce the inside maximum overpressure by 61.8%. The protective walls can reduce the overpressures, but the protective walls should not be too close to the SHRS because high overpressures are generated inside the walls due to the confined shock waves. The protective wall with a distance of 6 m can effectively protect the surrounding people and avoid the secondary overpressure damage to the container.

Quasi-Static Pressure Characteristics of Explosion Venting Vessel Under Confined Explosion

Quasi-Static Pressure Characteristics of Explosion Venting Vessel Under Confined Explosion

Processing of experimental data describing internal deflagration explosions

This article is devoted to issues related to experimental studies of internal deflagration explosions or emergency explosions occurring inside buildings and premises. In internal emergency explosions, the main role in reducing the explosive pressure to a safe level is played by discharge openings blocked by safety structures (SS). As discharge openings, windows are often used, covered with glazed window blocks, or opened explosion venting structures (EVS). The article deals with processing experimental data obtained in the study of deflagration explosions occurring inside buildings and premises. The main features and difficulties that arise while analyzing experimental materials are described. The article considers the general methodology for processing experimental data to study deflagration explosions inside buildings and premises. Examples of processing materials from experiments performed in chambers equipped with a transparent edge allow high-speed filming of the explosive combustion process inside the chamber. The article presents a technique that allows, based on data processing on the overpressure in the explosion chamber, to obtain complete characteristics of the loads that occur in the experimental chamber during an internal deflagration explosion. The proposed technique makes it possible to abandon the transparent edge of the explosion chamber and obtain data on the explosion process based on the numerical processing of the excess pressure created in the explosion chamber. An example of processing a full-scale experiment to determine the effectiveness of a real explosion venting structure (EVS) is given.

A simple design method of dust explosion venting size at elevated static activation pressure

To develop the application of explosion venting technology in high-pressure vessels, a new model for the design of dust explosion venting size was presented, which took the physicochemical phenomenon deriving from the elevation of the static activation pressure into account. Firstly, for confined pressure rise, the wall quenching effect originating from the dust flame thickness was considered by adopting the three-zone model. Secondly, for the venting pressure rise, the energy loss due to the discharge of high-energy burnt mixture (quantified as the specific surface area loss of the flame) was taken into account and the induced turbulence factor was introduced. Thirdly, for the venting pressure drop, a dynamic pressure relief capability evaluation model which takes into account the flame morphology evolution (tear-shaped flame) and the proportion of discharged mixture (relative volume ratio) at elevated activation pressure was proposed. The predicted maximum reduced pressure and venting size were checked against the PMMA explosion experiments and a more great performance was obtained compared with standards.

Flame propagation characteristics of methane explosion under different venting conditions

Air mixed with methane commonly causes explosion accidents. Explosion vents can discharge the explosion pressure and release energy to reduce the explosion impact. Explosion vents are widely applied to gas transportation pipelines and other pressure equipment. To determine the influence of explosion vent areas and types on dynamic characteristics of methane flame propagation, in this study, an explosion pipe system was established to explore the effects of the 22.89-cm2 circular (1#), 15.20-cm2 circular (2#), 9.07-cm2 circular (3#), and 15.20-cm2 cross-shaped (4#) vents on flame propagation of methane explosion and to compare these effects with those of a closed pipe. The experimental results indicated that the explosion vent accelerated flame propagation velocity (v) and considerably reduced explosion pressure (P) and flame temperature (T) compared with the closed pipe results. v, T, and P reached maximum values at 10 vol% methane concentration. As the vent area increased, the v of the three circular vents increased. Flame propagation velocity in 1#, 2#, and 3# increased by 23.13 %, 21.57 %, and 4.55 % compared with that of the closed pipe (13.40 m/s), respectively. Compared with the closed pipe values of 0.973 MPa and 1678.13℃ for P and T, decreases of 10.30 %, 12.50 %, 38.00 %, and 1.82 %, 10.53 %, 11.22 % were observed in 1#, 2#, and 3#, respectively. Under equal explosion vent areas (15.20 cm2) but different vent types (2# circular and 4# cross), as the equivalent diameter of vents increased, P and T decreased by 12.50 %, 20.91 %, and 10.53 %, 10.01 %, and v increased by 21.57 % and 12.61 %.

Research on the effect of the vent area on the external deflagration process during the explosion vent

Explosion-vent area is an important parameter for pressure vessel explosion vent design, which is of great significance to the safe operation of pressure vessels. The phenomenon of external explosion occurs outside the vent when the pressure vessel vents. The impact of explosion vent area on the external explosion was researched by numerical simulation in this paper. The results show that the impact of the explosion vent area on the external explosion is relatively significant. The large vent area has a larger area of high pressure, higher pressure and higher fluid turbulence intensity outside the vessel, which leads to more powerful explosion intensity. The smaller vent area leads to weaker external explosion intensity, but leads to higher pressure values inside the vessel. Additionally, the pressure-relief process of vessel with smaller vent area tends to form a “jet fire” and the pressure-relief efficiency is low, in which process, the external flame’s shapes show a long strip. The pressure-relief form of vessel with larger vent area tends to “external explosion” and the process of pressure relief is quicker, in which process, the shape of the external flame showing a “spherical”. Gas from the vent, the under-expansion flow in high-pressure develops into sub-atmospheric in process of moving forward, which can be compressed by surrounding air to intensify the thermochemical reaction, thus prompting the occurrence of external explosions. The larger the venting area is, the quicker the dissipation of the high-pressure area appears. As a result of the external explosion, the Helmholtz oscillation appears inside vessels. Larger vent area leads to larger amplitude and higher frequency of Helmholtz oscillations, in which process, the duration of Helmholtz oscillations is longer.

Fire and explosion characteristics of vent gas from lithium-ion batteries after thermal runaway: A comparative study

The combustion and explosion of the vent gas from battery failure cause catastrophe for electrochemical energy storage systems. Fire extinguishing and explosion proof countermeasures therefore require rational dispose of the flammable and explosive vent gas emitted from battery thermal runaway. However, the fire and explosion nature of the multiphase vent gas remains unclear. This paper comparatively investigates the fire and explosion hazards of the vent gas emitted by different kinds of lithium-ion batteries after thermal runaway. Hazard data are collected for batteries with cathode LiNixCoyMnzO2 (x from 0.33 to 0.8) and LiFePO4, which are prevailingly used or to be used in energy storage scenarios. The composition and content of the vent gas were analyzed using a pressurized container and gas chromatography. A 1-liter explosion sphere was used to determine the explosion limits, explosion pressure, and maximum rise rate of explosion pressure for five cell chemistries at 298 K and 101 kPa absolute pressure. The laminar burning velocities of the five vent gases were measured by Bunsen burner. The minimum concentration of fire extinguishing agent was tested using a cup burner. The results show that the fire and explosion hazards posed by the vent gas from LiFePO4 battery are greater than those from Li(NixCoyMn1-x-y)O2 battery, which counters common sense and sets reminders for designing electric energy storage stations. We may need reconsider the choice of cell chemistries for electrical energy storage systems, and care more about the safety design against the fire and explosion disaster that may occur at system level. The explosion characteristics of the vent gases from five cell chemistries and the minimum fire extinguishing concentration can enlighten future risk assessments of electrochemical energy storage systems.

Response of a Thin Flat Scored Metallic Disc Under Pressure Impulse

This paper presents the large deformation, and failure response of a thin flat scored metallic disc (FSMD) subjected to a pressure impulse as experienced in a break-away disc or an explosion vent. The response of this thin FSMD is numerically simulated for a loading rate and validated with an experiment, where a good agreement is found on plastic strains, burst pressure, and deformation pattern. The loading rate and several geometric parameters of FSMD significantly influence its response. Therefore, the influence of loading rate ( P& ), score depth and width-todisc thickness ratio (t 1 /t and b/t), diameter-to-disc thickness ratio (D/t), score length-to-disc radius ratio (l/R), score pattern, and score geometry on the deformation and failure response of the thin FSMD is thoroughly investigated. The studies demonstrate that 1) the failure initiation point shifts from disc centre to between 1/5th and 1/3rd radius for loading rates ≤ 25 MPa/s; 2) the responses such as burst pressure, burst time, central deflection, and equivalent strain are i) sensitive to the loading rates up to 100 MPa/s, ii) sensitive to score’s depth, only up to 0.6t and insensitive to score’s width, iii) significantly unaffected for the number of scores N > 8, iv) stabilised for l/R > 0.5 and D/t > 250, v) almost the same for semi-circular, rectangular and triangular score geometries, and vi) very minimal for the number of scores N = 3; and 3) the failure do not initiate and propagate along all scores for N > 4 in the disc.

Study on the Influence of Vent Shape and Blockage Ratio on the Premixed Gas Explosion in the Chamber with a Small Aspect Ratio.

Given the current situation of deflagration caused by gas leakage for domestic use and the study of the single shape of the vent, the differential change law of vent parameters on the small aspect ratio of the chamber explosion flame evolution and explosion overpressure and other effects were experimentally investigated. Based on the theory of geometric similarity, the experimental platform of a small length–diameter ratio explosion chamber was designed and built, and the premixed gas explosion experiment was carried out by changing the shape (square and rectangle) and blockage ratio (0.1, 0.3, 0.5, 0.7, and 0.9). The explosion flame structure, flame front position, flame propagation speed, explosion pressure waveform, overpressure peak value, and so on were tested and analyzed. The results showed that the blockage ratio had the most significant effect on flame propagation and explosion flame evolution. With the increase of blockage ratio, the stretching degree of the flame became more and more obvious, the flame front became sharper and sharper, and the sharp flame changed from the lower part to the upper part. The position of the flame front increased rapidly, and the steepness and peak value of explosion overpressure became larger. The oscillation of the flame propagation velocity was more violent after the turn, and the speed of propagation to the outside of the chamber gradually accelerated. In the same blockage ratio, there was a difference in the time point at which the flame propagation velocity turned under the rectangular and square shape of the vent. In blockage ratios of 0.1, 0.3, 0.5, and 0.9, the peak overpressure reduction under the shape of the blast square relative to the rectangle was 41.3, 47.9, 1.03, and 27.6%. This indicated that the explosion relief effect of the square was better than that of a rectangle. The research results can provide a reference and basis for the reasonable deployment of explosion venting and explosion decompression work.

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.

Effect of different vent covers on the overpressure and flame propagation characteristics of hydrocarbon fuel-air mixture venting explosion

A series of hydrocarbon-air fuel venting explosion experiments were carried out in a 20-L small-scale vent tank, and the effect of four different vent covers with an inherent rupture pressure of 10 kPa on the overpressures and flame propagation characteristics was studied. The results of the experiments showed that all the internal and external overpressure-time profiles have five typical overpressure peaks, induced by burst of the vent cover (△p1), inertia effect (△pneg), burned gas releasing (△p2), external explosion (△p3) and Helmholtz oscillation (△phel), respectively. The dynamic process of the flame was basically tally with the rule of ‘smooth and hemispherical flame-twisted and stretched flame-mushroom cloud-like/ellipsoidal flame-extinguishing flame’, but some differences were still existed due to the specific damage mode of each vent cover. When the vent opening was sealed by different vent covers, the values of internal and external overpressure peaks, maximum rate of overpressure rises, flame front location along different directions, and flame front speed along different directions showed various trends. Specifically, the enhancement effect of the metal cover plate and PE vent cover was significantly weaker than that of the paper vent cover and Al vent cover for the overpressure and vertical flame parameters, while, the enhancement effect of the metal cover plate was found to be greater than the other three for the horizontal flame parameters. Consequently, PE cover had the optimum performance for the explosion venting under the same inherent rupture pressures. These results improve our understanding on gas explosion dynamics in a semi-confined space with a vent cover, and provides the overpressure and flame characteristics of gas venting explosion under different vent boundary conditions from the qualitative and quantitative view.

Fireball and flame venting comparisons: Test data, CFD simulations, and industry standard prediction

Baker Engineering and Risk Consultants, Inc. (BakerRisk®) has performed vented deflagration testing of congested enclosures over a range of configurations, congestion levels, and fuels. This paper provides a comparison of the measured flame jetting distances to predictions made applying standard methods commonly used to calculate the associated hazard zone. These methods include the National Fire Protection Association Standard on Explosion Protection by Deflagration Venting (NFPA 68 (National Fire Protection Association, 2018, )), the British Standard's Gas Explosion Venting Protective Systems (EN 14994 (British Standard EN 14994, 2007)), and a computational fluid dynamics (CFD) analysis.Nine test series were carried out using BakerRisk's Deflagration Load Generator (DLG) test rig. The DLG is a rectangular steel enclosure measuring 48-feet wide × 24-feet deep × 12-feet tall, yielding a total volume of 13,800 ft3 (391 m3), and is enclosed by three solid steel walls, a roof, and floor. The rig vents through one of the long walls (i.e., 48-foot × 12-foot). The venting face was sealed with a 6-mil (0.15 mm) thick plastic vapor barrier for these tests to allow for the formation of the desired fuel air-mixture throughout the rig. Both slightly hyper-stoichiometric propane and lean hydrogen mixtures have been tested in the DLG. Congestion was provided by an array of vertical cylinders. A range of congestion levels and fill fractions were tested. DLG testing was performed with and without vent panels present.Flame jetting distances from the venting face of the DLG were measured using high-speed video. Flame jetting distances were predicted using the Fireball Dimensions calculation from NFPA 68 and the Flame Effects calculation from EN 14994. Blind (i.e., pre-test) simulations were also performed using the FLACS CFD code (Gexcon, 2014). The flame jetting distance in the CFD simulation was determined as the horizontal distance from the DLG vent to the location where the gas temperature dropped below a specified value; the predicted distance for the fuel concentration to drop below half the lower flammability limit (LFL) was also evaluated to assess jetting distance.

Investigating the explosion hazard of hydrogen produced by activated aluminum in a modified Hartmann tube

Metallic powders exposed to water are sources of hydrogen gas that may result in an explosion hazard in the process industries. In this paper, hydrogen production and flame propagation in a modified Hartmann tube were investigated using activated aluminum powder as fuel. A self-sustained reaction of activated aluminum with water was observed at cool water and room temperatures for all treatments. One gram of Al mixed with 5 wt% NaOH or CaO resulted in a rapid rate of hydrogen production and an almost 100% yield of hydrogen generation within 30 min. The flame structures and propagation velocity (FPV) of released hydrogen at different ignition delay times were determined using electric spark ignition. Flame structures of hydrogen were mainly dependent on hydrogen concentration and ignition delay time, likely due to different mechanisms of hydrogen generation and flame propagation. As expected, FPVs of hydrogen in the Hartmann tube increased with ignition delay time. However, the FPV of upward flame propagation was much larger than that of downward flame propagation due to the effect of spreading acceleration at the explosion vent. Once ignited, the FPV of upward flame propagation reached 31.3–162.5 m/s, a value far larger than the 7.5–30 m/s for downward flame propagation. Hydrogen explosion caused by the accumulation of wet metal dust can be far more dangerous than an ordinary hydrogen explosion.

An analysis of gas-induced explosions in vented enclosures in lithium-ion batteries

Lithium-ion batteries (LIBs) have found wide usage and tremendous technological advancements in recent years, due to their numerous advantages, but the safe utilization of LIBs has been a major concern, which research, industry, and government agencies seek to address. During a LIB failure, a fire or explosion hazard may occur, depending on the failure mechanism, and safety vents can be designed to mitigate the explosion induced by gases released from LIBs in an enclosure. In the present study, explosion hazards of LIBs are analyzed, and a numerical model for gas explosion venting is developed and validated using experiments on hydrogen and methane explosions. Furthermore, the explosion characteristics of various hazardous gas mixtures emitted from LIBs at various equivalence ratios predicted by the model are compared to the NFPA 68 standards. The lithium‑cobalt oxide (LCO), lithium‑iron phosphate (LFP), lithium‑nickel‑cobalt‑aluminum oxide (NCA) and lithium‑nickel‑manganese‑cobalt oxide (NMC) batteries are used to determine the impact of battery chemistry, vent size, as well as the state of charge (SoC) of the batteries on the explosion characteristics. The impact of the equivalence ratio of the vented gas is also investigated as well as that of accounting for CO2 among the vented gas on the predicted peak pressure. In addition, the sensitivity of the explosion severity to variability in vented gas composition is also scrutinized.

Large-scale experimental and simulation study on gas explosion venting load characteristics of urban shallow buried pipe trenches

In this study, a series of explosion venting tests on a large-scale test system (30 m length) and numerical simulations were conducted to evaluate the venting behavior and venting load of a gas explosion in an urban shallow buried pipe trench according to the methane concentration, location and the existence of the vents. The time history characteristics of the gas explosion overpressure, load distribution law, and explosion venting mechanism of vents in the trench were considered. The results showed that the overpressure–time history curve of the gas explosion in the trench with top vents has a single peak. The explosion overpressure initially increased and then decreased with increasing methane concentration, and the maximum overpressure was observed at a methane concentration of 9.5 vol%. The change rate in the overpressure–time history curve decreased upstream of each vent and increased downstream. In addition, the peak overpressure suddenly dropped upstream and jumped downstream of each vent. Adding vents to the top of the pipe trench significantly reduced the upstream overpressure and overall impulse, and the overpressure attenuated to a greater degree.

The flow field behaviours of under-expansion jet flame in premixed hydrogen/air explosion venting

The short chemical reaction time and high heat release of hydrogen fuel make a fine propulsion performance. Hydrogen is recognized as an excellent new resource. However, the inherent hazard of combustion and explosion should not be ignored. In this paper, the formation of the under-expansion jet flame (UEJF) of premixed hydrogen/air in explosion venting was simulated by ANSYS Fluent, and the wave system structures of the UEJF were systematically analyzed. The changes of pressure, Mach number, and main gas mass fraction distribution in the formation of the UEJF structures were described. The results indicated that the pressure difference at the outlet of explosion venting tube induced the intersection of expansion wave and reflected wave, and the formation of an obvious negative pressure area in the flow field. Meanwhile, alternating changes of the pressure in the jet center area propagated forward with the flame, resulting in the generation of UEJF. The fluxion of airflow at the outlet of explosion venting tube can be regarded as Prandtl-Meyer flow. The expansion angle was a positive correlation to the Mach number and the pressure ratio of the internal and external of the explosion venting tube. The distribution of H2O, O2, and –OH on the Mach disk revealed that the residual hydrogen reacted with O2 to produce secondary or multiple explosions. Therefore, the attention and research on the hazard of the under-expansion jet field should be strengthened.

Coupling effect of side explosion vent and wire mesh on suppressing methane explosion in a closed duct

The coupling effect of the side explosion vent and wire mesh on suppressing methane explosion has been investigated in this study, aiming to prevent huge losses caused by a methane explosion in industrial organic waste gas treatment. It constructed a closed simulation duct with a length of 3000 mm and an internal dimension of 120 mm × 120 mm containing a side explosion vent at different positions, in which flame behaviours and overpressure characteristics accompanying methane explosion were analyzed to get conclusions. The results indicate that side explosion vents located in the same duct section have a similar explosive flame development trend, and the suppression effect is better as closer to the ignition source. Besides, it is necessary to avoid the redevelopment of flame and the backfire downstream of a side explosion vent. In addition, the overpressure released through side explosion vents is significantly suppressed. However, the wave-absorbing and heat-absorbing properties of the wire mesh installed in the duct are only effective for some configurations with low flame speeds. Moreover, the side explosion vent closed to the ignition source effectively suppresses undeveloped flame. In this case, it leads to a complete application of the porous media quenching performance. To sum up, the coupling suppression effect of the side explosion vent and wire mesh on flame is complementary. However, there is an opposite conclusion for the experimental configurations where side explosion vents are downstream of the duct; a high-speed turbulent flame is difficult to be suppressed by the wire mesh and side explosion vent in a flame acceleration mechanism.

Gas explosion venting of 20-litre vessel with and without various length of vent ducts

When gas explosion occurs in closed vessel, venting devices can reduce the pressure inside the protected equipment, and vent ducts can be used to direct burnt and unburnt mixtures. In this paper, some ductless and duct vented explosion measurements were performed in a standard 20-liter explosion chamber with 2.8 to 6.3 vol.% propane-air mixture at atmospheric pressure (1 barg) and ambient temperature (298 K). Experimental investigations were performed with different lengths of vent duct (0 meter, 0.15 meter, 1 meter). During the measurements, effects of vent ducts to the venting process had been studied. Aluminium foils were used as rupture disks with 30 mm diameter circular venting area. During each measurement, static activation overpressure of aluminium foil, maximum explosion overpressure of propane-air mixture, the gas deflagration index in case of the vented vessel, and the pressure drop along the 1 meter length duct were determined.

A relict oasis of living deep-sea mussels Bathymodiolus and microbial-mediated seep carbonates at newly-discovered active cold seeps in the Gulf of C\xe1diz, NE Atlantic Ocean

Extensive beds of the deep-sea mussel Bathymodiolus mauritanicus (currently also known as Gigantidas mauritanicus) linked to active cold seeps related to fissure-like activity on Al Gacel mud volcano, Gulf of Cádiz, were filmed and sampled for the first time during the oceanographic expedition SUBVENT-2 aboard R/V Sarmiento de Gamboa. Al Gacel mud volcano is one of up to 80 fluid venting submarine structures (mud volcanoes and mud volcano/diapir complexes) identified in the Gulf of Cádiz as result of explosive venting of hydrocarbon-enriched fluids sourced from deep seated reservoirs. This mud volcano is a cone-shaped edifice, 107 m high, 944 m in diameter constituted by mud breccias and, partially covered by pavements of seep carbonates. Extensive beds of this deep-sea mussel were detected at the northern flank at 810–815 m water depth associated with bacterial mats around intermittent buoyant vertical bubble methane plumes. High methane concentrations were measured in the water column above living mussel beds. Other chemosymbiotic species (Siboglinum sp., Solemya elarraichensis, Isorropodon sp., Thyasira vulcolutre and Lucinoma asapheus) were also found in different parts of Al Gacel mud volcano. Al Gacel mud volcano may currently represent one of the most active mud volcanoes in the Gulf of Cádiz, delivering significant amounts of thermogenic hydrocarbon fluids which contribute to foster the extensive chemosynthesis-based communities detected. This finding is of paramount importance for linking extremophile bivalve populations along the North Atlantic, including cold seeps of the Gulf of México, hydrothermal vents of the Mid-Atlantic Ridge and now, detailed documented at the Gulf of Cádiz.

Experimental and numerical study on explosion characteristics and hazards of methane-air mixtures in a chamber

ABSTRACT The high-frequency failure of hoses inside residential kitchens is easy to cause natural gas explosion accidents. A small-scale gas explosion experiment platform like a kitchen was constructed in this work. Three sets of explosion experiments for methane-air mixtures with 7.7%, 9.5%, and 11.2% were performed, respectively, and the explosion venting characteristics were analyzed. The influence of vent area ratio, vent opening pressure, and mass per unit area of pressure relief panels on the explosion hazards (i.e., explosion overpressure, flame temperature, dynamic pressure, explosion wind velocity, and combustion rate) were investigated using CFD simulations. Meanwhile, the accuracy of numerical model was validated against experimental data. The results show that the maximum peak overpressure at 9.5% could reach up to 5.55 kPa, whereas that was 2.34 kPa at 7.7% and 5.09 kPa at 11.2%. The numerical model with thermal radiation effect could reproduce the experimental results effectively. The vent area ratio and vent opening pressure have great influence on the external damage distances, whereas there is little effect of mass per unit area. The secondary injuries caused by flame temperature, dynamic pressure, explosion wind velocity, and combustion rate outside the buildings except explosion overpressure should be also paid special attention in a gas explosion accident.