External Explosion Research Articles

К ВОПРОСУ ОБ ОЦЕНКЕ ЖИВУЧЕСТИ СЕТЕЙ НАРУЖНОГО ПРОТИВОПОЖАРНОГО ВОДОПРОВОДА

The problem of quantitative assessment of survivability of networks of the fire-fighting water supply at the enterprises of petrochemical industry as internal (corrosion, pressure throws) and external (explosions of technological installations, earthquakes) can lead to damage of various sites of networks is considered. The definition of the concept of survivability of external fire water supply networks in comparison with similar formulations in relation to other objects is given. Quantitative indicators of survivability assessment are substantiated, examples are given.

Experimental Study on Explosion Pressure and Rock Breaking Characteristics under Liquid Carbon Dioxide Blasting

A liquid carbon dioxide blasting experiment was carried out under free field conditions, alongside a liquid carbon dioxide rock breaking experiment, to investigate explosion pressure variation and rock breaking characteristics under liquid carbon dioxide blasting. The experimental results show that the internal and external explosion pressures of the liquid carbon dioxide fracturing devices all rapidly increased at first, before attenuating vibrantly after blasting. When the explosion pressure was raised, the internal explosion pressure increased first exponentially and then linearly, while the external explosion pressure increased exponentially throughout. The duration time of the blasting effect stage was about 45 ms. Under the combined effect of jet impingement and a gas wedge of high‐pressure carbon dioxide, the rock is subjected to tensile failure. The impact failure and the “gas wedge effect” of high‐pressure carbon dioxide play a key role in the rock breaking of liquid carbon dioxide blasting technology.

Performance of Semi-Active Base Isolation Systems under External Explosion

Structures designed against earthquake loads based on using control systems may experience explosions during their lifetime. In this paper, the performance of a hybrid control system composed of a low-damping base isolation and a supplemental magneto-rheological (MR) damper under external explosion has been studied. Base isolation system has the ability of decreasing the maximum structural response under blast loadings by shifting the period of the structure. In addition, MR damper improves the base isolation system performance by controlling the base drift of the structure. Hence, in this paper, the capability of a hybrid base isolation system equipped with an MR damper at the base has been evaluated in reducing the maximum structural response and base drift under external blast loadings. To determine the voltage of the semi-active MR damper, the H2/Linear Quadratic Gaussian (LQG) and clipped-optimal control algorithms have been applied. For numerical simulations, a 10-storey shear frame subjected to blast loadings applied on different floors has been considered and the performance of the hybrid isolation system and MR damper has been studied. The results have proven the effectiveness of the hybrid control system in controlling the maximum response and base drift of the isolated structure against spherical external explosion. Furthermore, comparing the performance of the hybrid passive and semi-active base isolation systems indicates that the semi-active hybrid base isolation system is more effective in reducing the root-mean-square (RMS) value of the base drift. Similarly, it has been found that the semi-active hybrid base isolation system also performs better than the high-damping base isolation system.

Numerical simulations of vented hydrogen deflagration in a medium-scale enclosure

A validation study was performed to investigate the ability of Computational Fluid Dynamics (CFD) models to predict hydrogen deflagrations in vented enclosures. The validation exercise was aimed at assessing the suitability of CFD as a reliable tool for explosion safety assessments and involved comparing CFD predictions with measurements from an experiment carried out by FM Global in a 64 m3 enclosure. The enclosure included a large square vent located in the center of one of its walls. The enclosure was filled with a homogenous hydrogen-air mixture of 18% v/v composition before ignition at its center. In this paper, CFD model predictions of the transient pressure and the flame speed are compared against experimental measurements. Additionally, peak overpressure predictions are compared against empirical correlations and the NFPA 68 vent sizing standard. The study focuses on the prediction of the first overpressure peak that is generated by external explosion. The agreement between the models’ predictions and experimental results is found to be satisfactory, which suggests that CFD models have the potential to predict explosion phenomena with reasonable accuracy. However, more extensive model validation and sensitivity studies are required before CFD models can be used with confidence in explosion safety assessments.

Field Testing of Fence Type Blast Wall for Blast Load Mitigation

To protect structures from external explosions, solid protective barriers have been demonstrated by experimental and numerical studies to be able to effectively mitigate blast loads on structures behind them. However, to protect against blast loads, barriers normally need to be designed to have high structural resistance and ductility. This often requires bulky and heavy protective barriers which are not only highly costly but also often not appropriate for application in downtown areas as they are not friendly to city planning or appearance. Fence type blast wall consisting of structural columns was recently proposed and its effectiveness in mitigating blast loads was investigated through numerical simulations. It was found that the wave–fence interaction and interference of waves significantly reduced the wave energy when the blast wave passed through the fence blast wall. To further investigate the effectiveness and applicability of fence type blast wall as a highly potential technology for structural protection in an urban area, field tests have been conducted and results are reported in this paper. Columns with circular and triangular cross-sections were adopted to build fence blast walls. In addition, a masonry wall was also constructed as solid barrier for comparison. Hemispherical TNT explosive weighing 1.0 kg with different stand-off distances was detonated on the ground to generate the blast load. Blast overpressures in free air, behind the fence blast wall and behind the masonry wall were recorded by pressure sensors. The effectiveness of the fence blast wall in reducing blast wave and protecting structures was demonstrated by the test data.

ASSESSMENT OF EMPIRICAL FORMULAS FOR ESTIMATING RESIDUAL AXIAL CAPACITY OF BLAST DAMAGED RC COLUMNS

Columns are the most important load bearing structural elements in buildings. Under the effect of external explosions near the building, columns in the ground and first floors may have severe damage that can cause progressive collapse of the whole building frames. Residual axial load bearing capacity of the reinforced concrete column after the effect of lateral blast loading could be a practical criterion to damage assessment of the column. This is essential to determine whether the column has to be replaced or repaired for future use. In this paper, residual axial capacity of the square RC columns under the effect of initial axial force and lateral blast loading is investigated. Explicit finite element package LS-DYNA is used for analysis of the considered models and determining their residual capacity. There are some empirical formulas for estimating of the residual axial capacity of the blast damaged RC columns including Bao and Li (2010), Wu et al (2010) and Arlery et al (2013). Here, FEM results are compared to the estimations of these formulas. Different levels of initial axial force in the columns and different scale distances of blast loading are considered. Keywords: blast loading, reinforced concrete column, residual axial capacity, LS-DYNA.

Integrated Blast Resistance Model of Nuclear Power Plant Auxiliary Facilities

Standards, guidelines, manuals, and researches refer mainly to the required protection of a nuclear power plant (NPP) containment structure (where the reactor's vessel is located) against different internal and external extreme events. However, there is no consideration regarding the man-made extreme event of external explosion resulting from air bomb or cruise missile. A novel integrated blast resistance model (IBRM) of NPP's reinforced concrete (RC) auxiliary facilities due to an external above ground explosion based on two components is suggested. The first is structural dynamic response analysis to the positive phase of an external explosion based on the single degree-of-freedom (SDOF) method combined with spalling and breaching empirical correlations. The second is in-structure shock analysis, resulting from direct-induced ground shock and air-induced ground shock. As a case study, the resistance of Westinghouse commercial NPP AP1000 control room, including a representative equipment, to an external above ground blast loading of Scud B-100 missile at various standoff distances ranging from 250 m (far range) till contact, was analyzed. The structure's damage level is based on its front wall supports' angle of rotation and the ductility ratio (dynamic versus elastic midspan displacement ratio). Due to the lack of specific structural damage demands and equipment's dynamic capacities, common protective structures standards and manuals are used while requiring that no spalling or breaching shall occur in the control room while it remains in the elastic regime. The engineering systems and equipments' spectral motions should be less than their capacity. The integrated blast resistance model (IBRM) of the structure and its equipment may be used in wider researches concerning other NPP's auxiliary facilities and systems based upon their specifications.

Propagation of a confined explosion to an external cloud

Since the pioneering work of Harrison and Eyre (1986), the existence of secondary or external explosion outside explosion vents is recognized and rather systematic. This explosion can be much more powerful (Proust, 2004, 2010) than the internal explosion particularly when the mixture is very reactive. But today, the understanding of the formation of the external cloud and its subsequent combustion remains largely outstanding. Very rapid burning was noticed and significant UVCE pressure effects. In some circumstances, a preexisting flammable cloud encompasses the vented vessel, like in Buncefield for instance. This paper presents experimental work and CFD simulations (OpenFoam) which investigate the aerodynamics of the flow and the flame propagation. The experimental device is composed of a 4 m3 chamber linked to an unconfined 54 m3 volume via a square vent. These two volumes are filled with a stiochiometric propane air mixture and ignited by a pyrotechnical match in the 4 m3 chamber. When the vent area is small enough, the vortex bubble formed by the gas ejection is disrupted and a jet is formed entraining a significant portion of the outside atmosphere. The explosion overpressure outside can be 10 time larger as compared to the fully unconfined case (no chamber).

The effect of ignition location on explosion venting of hydrogen–air mixtures

The effect of ignition location and vent burst pressure on the internal pressure-time history and external flame propagation was investigated for vented explosions of hydrogen–air mixtures in a small cylindrical vessel. A high-speed camera was used to record videos of the external flame while pressure transducers were used to record pressure-time histories. It was found that central ignition always leads to the maximum internal peak overpressure, and front ignition resulted in the lowest value of internal peak overpressure. The internal peak overpressures are increased corresponding to the increase in the vent burst pressure in the cases of central and rear ignition. Because of the effect of acoustic oscillations, the phenomenon of oscillations is observed in the internal pressure profile for the case of front ignition. The pressure oscillations for the cases of rear and central ignition are triggered by external explosions. The behavior of flames outside the chamber is significantly associated with the internal pressure of the chamber so that the velocity of the jet flame is closely related to the internal overpressure peak.

Recent developments to evaluate global explosion loading on complex systems

During the engineering phase, a “Design Explosion loads Specification” is often developed by the safety discipline in order to provide the necessary explosion response inputs to other engineering disciplines for each individual item part of a safety critical system. This includes the specific targets, the associated performance criteria and the corresponding design explosion loads. This is an efficient way to manage explosion in design for each individual item composing a safety critical system but when combination of items need to be addressed, for instance global loading on complex items (e.g. modules, critical pipework or packages), this approach may result in an overly conservative design if the maximum explosion loads on each item are summed simultaneously. Indeed each component may experience variability in loading time due to the propagation of blast wave during the explosion event. In the opposite, only considering explosion loads on each individual item successively may be not safe enough. An alternative methodology based on Computational Fluid Dynamics (CFD) FLACS® software simulations is presented in the article in order to get more adequate global blast loads for design verification, in particular taking into account potential shielding effects, group effects of elements. It focuses on the development of dedicated blast load cases for the design in order to address both internal and external explosion events related to complex items such as whole onshore units or offshore modules on floating facilities. This method will be favorably implemented on generic typical systems in order to develop blast loads cases combination rule sets on future projects. This will contribute to enhance blast design approaches and promote opportunities for further optimization.

Effect of ignition location on external explosion in hydrogen–air explosion venting

The external explosion in a stainless cylindrical explosion vessel with the hydrogen–air mixture is investigated as the function of the vent burst pressure. The internal and external pressure curves measured by four piezoelectric pressure transducers with three ignition locations are used to analyze the effect of ignition location on the whole explosion venting. It was shown that central ignition always generates the highest internal peak pressure; but the highest external peak pressure always appears on the pressure curve with the rear ignition. The external explosion is demonstrated by the jet flame photographs captured by the high speed camera. As the vent burst pressure increases, it is a general trend that the internal and external peak pressures are increasing accordingly; but just for the rear ignition, it seems that the external peak pressure is less affected by the vent burst pressure. And not only that, the external explosion site remains the same roughly with the change of the vent burst pressure for whatever ignition location.

The flexible perforated screens are a protection of buildings against external explosions

This work studies the parameters of the blast wave passing through a screen placed in its path. It determines the degree of pressure reduction behind the barrier depending on its permeability, the relative size of the obstacles, the length of the positive phase of the wave, the degree of removal of waves from the source. It also determines the size of the zone of decompression. Experiments are made with models of buildings that are located behind a barrier in the course of wave motion. These experiments gave grounds to conclude that such obstacles can serve as an effective explosion protection. It is proposed to use a flexible sheet as elements subject to blast load. It is shown that a sheet of soft steel, with a thickness of 1 mm and a length of 6000 mm can take a maximum load of 100 kPa. The strengthening of the sheet by increasing its effective thickness in proportion to extends its capabilities.

Assessment of safety distance between components of nuclear plant and study of the vulnerabiliy of the damage caused by an explosion

This paper deals with the assessment of external explosion, resulting from accidental release of jet fuel from the large commercial airliner in the nuclear power plant (NPP). The study used three widely prediction methods such as Trinitrotoluene (TNT), multi energy (TNO) and Baker-strehow (BST) to determine the unconfined vapour cloud explosion (UVCE) overpressure within the distances of 100-1400 m from the first impact location. The containment building was taken as the reference position. The fatalities of persons and damage of structures was estimated using probit methodology. Analysis of the results shows that both reactor building and control-room will be highly damaged with risk consequences and probability, depending on the assumed position of the crash. The structures at the radial distance of 600 m may suffer major structural damage with probability ranging from 25 to 100%. The minor structural damage was observed throughout the bounds of the plant complex. The people working within 250 m radius may get affected with different fatality ranging from 28 to 100%. The findings of this study is valuable to evaluate the safety improvement needed on the NPP site and on the risk and consequences associated with the hydrocarbon fuel release/fires due to external hazards.

A New Design of Energy Absorbing Bolt

Rock movement caused by external explosion loading can damage the nearby tunnel or cavern.To avoid damage, energy absorbing bolts with high load-displacement and large energy absorptioncapacities are required. The deformation and friction of the bolt absorb energy during the rock movementand preventing the structure from damage. To maximize the energy absorption capacity in the limitedspace inside the borehole, we developed a new bolt that utilizes the friction and plastic deformation ofthe sleeve. To develop the new bolt, FE simulation in Abaqus was used to improve designs beforefabrication. Two prototypes of the new design was fabricated and tested by static pull test. The resultsshowed the bolts yielded in the desired way. The experimental results prove the new bolt is capable ofabsorbing large amount of energy and accommodating large displacement.

Experimental Study on Duct-Vented Explosion of Hydrogen–Air Mixtures in a Wide Range of Equivalence Ratio

A relief duct is often used for indoor vented enclosures to discharge unburnt and burnt gas mixtures to outdoors, but its use can significantly affect pressure relief and flame behavior. In the current paper, duct-vented explosions of hydrogen–air mixtures with equivalence ratios ranging from 0.8 to 4.0 were experimentally investigated in a small cylindrical vessel with a 50-cm-long relief duct. Different from “coherent deflagration” as previously reported, the maximum pressure rise rate in the duct is always larger than that in the vessel. Three pressure peaks can be identified on the external pressure profile, which result from the burst of the vent cover, the burn-up in the duct, and the external explosion, respectively. Whether the second or the third pressure peak is the dominant one depends on the hydrogen equivalence ratio. Compared with simple vented explosions, the use of a relief duct decreases the pressure relief efficiency and the external flame size for all equivalence ratios tested.

외부 폭발에 의한 축소형 방폭문 변형 및 터널 내부 폭풍파 전파 거동의 수치해석

In this paper, we present the results of the numerical analysis employing CONWEP, LS-DYNA FSI(Fluid Structure Interaction), AUTODYN FSI, LS-DYNA ALE(Arbitrary Lagrange Eulerian) and combination of CONWEP and LS-DYNA ALE for blast door fracture and wave propagation through the tunnel by the external explosion. We compared the numerical analysis results with the subscale test data and selected combination of CONWEP and LS-DYNA ALE method as adequate data generation method for the FRM(Fast Running Model) software development. It is expected to save much time and costs by using the numerical simulation data for the various test conditions.

Explosion venting of rich hydrogen-air mixtures in a small cylindrical vessel with two symmetrical vents

The safety issues related to explosion venting of hydrogen-air mixtures are significant and deserve more detailed investigations. Vented hydrogen-air explosion has been studied extensively in vessels with a single vent. However, little attention has been paid to the cases with more than one vent. In this paper, experiments about explosion venting of rich hydrogen-air mixtures were conducted in a small cylindrical vessel with two symmetrical vents to investigate the effect of vent area and distribution on the pressure buildup and flame behavior. Experimental results show that venting accelerates the flame front towards the vent but has nearly no effect on the opposite side. The maximum internal overpressure decreases while the maximum external flame length increases with the increase of the vent area. Two pressure peaks can be identified outside the vessel, which correspond to the external explosion and the following gas jet, respectively. Compared with the case of single vent, the use of two vents with same total vent area leads to nearly unchanged maximum internal and external overpressure but much smaller external flame length.

Influence of the geometry of protective barriers on the propagation of shock waves

The protection of industrial facilities, classified as hazardous, against accidental or intentional explosions represents a major challenge for the prevention of personal injury and property damage, which also involves social and economic issues. We consider here the use of physical barriers against the effects of these explosions, which include the pressure wave, the projection of fragments and the thermal flash. This approach can be recommended for the control of major industrial risks, but no specific instructions are available for its implementation. The influence of a protective barrier against a detonation-type explosion is studied in small-scale experiments. The effects of overpressure are examined over the entire path of the shock wave across the barrier and in the downstream zone to be protected. Two series of barrier structures are studied. The first series (A) of experiments investigates two types of barrier geometry with dimensions based on NATO recommendations. These recommendations stipulate that the barrier should be 2 m higher than the charge height, the thickness at the crest should be more than 0.5 m, while its length should be equal to twice the protected structure length and the bank slope should be equivalent to the angle of repose of the soil. The second series (B) of experiments investigates the influence of geometrical parameters of the barrier (thickness at the crest and inclination angles of the front and rear faces) on its protective effects. This project leads to an advance in our understanding of the physical phenomena involved in the propagation of blast waves resulting from an external explosion, in the area around a protective physical barrier. The study focuses on the dimensioning of protective barriers against overpressure effects arising from detonation and shows the advantage of using a barrier with a vertical front or rear face.

Нагрузки, разрушающие строительные конструкции в результате аварийных взрывов

To determine the bearing capacity limits of main structures of buildings and constructions with explosive productions it was analyzed data on destruction and damage rate of various constructive elements of buildings and constructions which took place as due to emergency explosions inside production premises so due to external explosion; it were also used results of tests of structures under the action of explosive loads. The analysis of past accidents shows that one of the most vulnerable spots of brickwork created during construction of buildings are sections at seams which cohesion is often insufficient to provide shearing resistance, breaking strength or resistance to the main tensile stresses. Advantages of large-panel industrial buildings before brick buildings, in regards to their explosion stability, are proved. Recommendations on designing of collapsible reinforced concrete structural frames of buildings with explosive productions are given. Data on bearing capacity of structures of industrial buildings obtained on the basis of materials on emergency explosions, analysis of results of researches stated in literary sources and also data on loadings causing destruction of constructions and structures of various degree and character are presented. Classification of building structures according to their damage rate is given. Data on explosive loads which cause destruction of different types of the main building structures that can be used for creation of the explosion protection system of buildings (using construction methods) with explosive productions are given. Behavior of structures in case of emergency explosions, tests and calculations of structures is defined; permissible loads on the bearing and filler structures with the purpose to obtain the initial data for recommendations on design of buildings for explosive productions is determined.

A computational platform for gas explosion venting

Explosions occurring in enclosures can be found in many technological applications such as internal combustion engines and typical chambers contacting combustibles. However, it is also possible to reach these events in facilities and buildings because of the leakage of a flammable gas, with usually devastating consequences. In this respect, vents are designed to relief the explosion-associated overpressures by allowing part of the fuel mixture gas to evacuate as the flame propagates. In the present work, a computational model is developed to analyse such vented explosion scenarios. The model solves the corresponding governing equations in a single-zone approximation, including the external explosion produced once the vented mixture is ignited by the expanding flame, to calculate the attained overpressures in relation to the domain geometry and burning conditions. A parametric study is performed varying the container dimensions and shapes, given by cuboids and cylinders with central and rear ignition locations, as well as the concentrations of a hydrogen-air fuel mixture. Moreover, different flame velocity expressions are employed to account for a variety of effects influencing the flame dynamics. A mitigating effect of the vent on the enclosure explosion intensity is demonstrated, thereby relating the different conditions to the attained burning regime, essential for the establishment of safety considerations in these partially confined enclosures.