The venting of dust explosions in a dust collector

Pressures generated by dust explosions in a commercial dust collector have been measured. The dust clouds were formed while the collector was operating under normal working conditions, i.e. dusts were dislodged from the filter elements inside the collector by pulsed reversed air jets. The vented explosion pressures measured under these conditions provide a realistic guide to the explosion pressures that the filter may have to withstand in practice. These pressures are low (2 kPa) when the explosion is vented through a vent close to the ignition source. If, however, the vent is remote from the ignition source and flame turbulence is generated, the rate of combustion is increased and the explosion pressures are higher (14 kPa). The vented explosion pressures encountered when the flame becomes turbulent are reasonably well predicted by the K_st nomograph approach. Pressures generated by highly turbulent explosions in a silo-shaped container have also been compared to the K_st homograph predictions. In these experiments, the pressures were always much higher than predicted.     

化工厂储罐区事故分析与危险控制

对某化工厂三个罐区进行了危险源辨识;确定了重大危险源及其危险物质,进而运用重大事故模拟方法,计算了火灾、爆炸和中毒事故的死亡事故范围(半径);根据计算结果,提出了预防罐区火灾、爆炸和中毒事故的控制措施.     

Metallurgical failure analysis of a propane tank boiling liquid expanding vapor explosion (BLEVE)

A severe fire and explosion occurred at a propane storage yard in Truth or Consequences, N.M., when a truck ran into the pumping and plumbing system beneath a large propane tank. The storage tank emptied when the liquid-phase excess flow valve tore out of the tank. The ensuing fire engulfed several propane delivery trucks, causing one of them to explode. A series of elevated-temperature stress-rupture tears developed along the top of a 9800 L (2600 gal) truck-mounted tank as it was heated by the fire. Unstable fracture then occurred suddenly along the length of the tank and around both end caps, along the girth welds connecting the end caps to the center portion of the tank. The remaining contents of the tank were suddenly released, aerosolized, and combusted, creating a powerful boiling liquid expanding vapor explosion (BLEVE). Based on metallography of the tank pieces, the approximate tank temperature at the onset of the BLEVE was determined. Metallurgical analysis of the ruptured tank also permitted several hypotheses regarding BLEVE mechanisms to be evaluated. Suggestions are made for additional work that could provide improved predictive capabilities regarding BLEVEs and for methods to decrease the susceptibility of propane tanks to BLEVEs.     

Damage investigation on the explosive destruction of a tank at a chlorine liquefaction plant

This paper summarizes the investigation of a serious explosion, which shattered the chemical facility of a chlorine/alkaline plant in Northern Germany in 1981. A pressure tank made from HSB 50 S steel and used as storage of liquid residues from a chlorine liquefaction process violently ruptured and the explosion threw parts of the tank approximately 100 m through the air. The local county government ordered an investigation to determine the root cause of this incident.The main objective of the investigation was to determine whether a nitrogen overpressure or a chemical reaction of residuals inside the so-called ‘Taffy’ receiver caused the explosion. A fracture mechanics based analyses evaluated the conditions the material was exposed to during the damage. Metallographic and mechanical tests confirmed that the material specifications were within the values specified by the guidelines but corrosion had reduced the wall thickness considerably.Analytical calculations to determine the minimum required pressure for the rupture and to cause plastic deformation to the tank confirmed that the failure did not occur due to nitrogen overpressure and therefore, a chemical reaction must have occurred. A detailed chemical analysis confirmed that the explosive disintegration of methylnitrate, which is highly sensitive to heat and impact, and its halogenated derivatives likely caused the incident. Due to the design and operational mode of the plant, impurities could accumulate and form explosive compounds in the Taffy receivers without control.     

Diaphragm gauge for measuring explosive impulse

The measurement of shock and stress waves under the action of explosion and impact loading has long been a concern of scientists and engineers. A number of methods have been developed over the years for measuring the physical parameters that are involved in the material dynamics resulting from an explosion. This work describes the development, calibration and validation of a passive copper diaphragm gauge aimed at measuring the impulse acting on it, resulting from an explosion in air. It is found that the diaphragm deformation (central deflection) can be used to measure the impulse, given the calibration curve. Once the gauge is calibrated, it can be used to measure the impulse acting on it in other media (water, soil, etc.). Such gauges are useful in measuring explosion induced impulses acting on structures. This usefulness is the result of the gauge simplicity and reproducibility. It can be used as a passive gauge or, when instrumented with strain gauges, as a passive and active (electronic) gauge.     

An efficient storage scheme for reduced chemical kinetics based on orthogonal polynomials

Simplified chemical kinetic schemes are a crucial prerequisite for the simulation of complex three-dimensional turbulent flows, and various methods for the generation of reduced mechanisms have been developed in the past. The method of intrinsic low-dimensional manifolds (ILDM), e.g., provides a mathematical tool for the automatic simplification of chemical kinetics, but one problem of this method is the fact that the information which comes out of the mechanism reduction procedure has to be stored for subsequent use in reacting-flow calculations. In most cases tabulation procedures are used which store the relevant data (such as reduced reaction rates) in terms of the reaction progress variables, followed by table look-up during the reacting-flow calculations. This can result in huge amounts of storage needed for the multi-dimensional tabulation. In order to overcome this problem a storage scheme is presented which is based on orthogonal polynomials. Instead of the use of small tabulation cells and local mesh refinement, the thermochemical state space is divided into a small number of coarse cells. Within these coarse cells polynomial approximations are used instead of frequently used multi-linear interpolation. This leads to a considerable decrease of needed storage. The hydrogen-oxygen system is considered as an example. Even for this small chemical system, a decrease of the needed storage requirement by a factor of 100 is obtained.     

CFD analysis of gas explosions vented through relief pipes

Vent devices for gas and dust explosions are often ducted to safe locations by means of relief pipes. However, the presence of the duct increases the severity of explosion if compared to simply vented vessels (i.e. compared to cases where no duct is present). Besides, the identification of the key phenomena controlling the violence of explosion has not yet been gained. Multidimensional models coupling, mass, momentum and energy conservation equations can be valuable tools for the analysis of such complex explosion phenomena. In this work, gas explosions vented through ducts have been modelled by a two-dimensional (2D) axi-symmetric computational fluid dynamic (CFD) model based on the unsteady Reynolds Averaged Navier Stokes (RANS) approach in which the laminar, flamelet and distributed combustion models have been implemented. Numerical test have been carried out by varying ignition position, duct diameter and length. Results have evidenced that the severity of ducted explosions is mainly driven by the vigorous secondary explosion occurring in the duct (burn-up) rather than by the duct flow resistance or acoustic enhancement. Moreover, it has been found out that the burn-up affects explosion severity due to the reduction of venting rate rather than to the burning rate enhancement through turbulization.     

Quantum chemical treatment of cyanogen azide and its univalent and divalent ionic forms

An explosive material, cyanogen azide (CN4) and its univalent and divalent anionic and cationic forms have been studied quantum chemically by using different theoretical approaches. In this study, the structures considered have been screened for their relative stabilities. Also, they have been investigated whether the charged forms play a role in the usual explosion process or any electrical charging during storage cause explosion. Various quantum chemical properties are obtained and discussed. It has been found that the univalent cation and anion and divalent cation formations do not cause much change in the molecular structure as compared to the neutral cyanogen azide molecule, whereas the divalent anionic form exhibits drastic changes in the geometry, resulting in bond cleavage to eliminate nitrogen molecule.     

Two-component radiation-gasdynamic model of a turbulent fireball

A two-dimensional computational model of the dynamics of a radiating turbulent fireball that can form in accident-induced explosion of a rocket at the launching position or in flight is presented. The model is based on the system of Navier-Stokes equations, two-component diffusion of explosion products (water vapor) in the ambient air, and a multigroup system of equations of thermal radiation transfer. The possibility of employing three models of turbulent mixing — the Prandtl model, the Penner-Haselman-Edwards model, and the Launder-Spalding model — is investigated. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 73, No. 1, pp. 31–38, January–February, 2000.     

亚稳态富硅烷-氮-氧混合气制备及其着火特性

采用氮气预稀释方法制备了亚稳态的富硅烷－氧－氮混合体系，对这种混合气的稳定性和着火特性进行了实验，表明氮气预稀释对抑制硅烷着火有明显效果，所制备的亚稳态混合物有较高的稳定性，但是释放时的阻流会引发爆炸，只有在总压力低于0.5MPa，氮气含量高于86％V／V时才能抑制爆炸的发生。     

Safety and security issues relating to low capacity storage of AN-based fertilizers

Motivated by both the Toulouse explosion, and a series of recent unexpected handling and storage accidents in well-developed countries, the safety issues associated with the storage of fertilizer grades of ammonium nitrate (AN) are considered with a focus on low storage capacity premises. Such facilities are numerous and, in large agricultural countries, include thousands of end-users and hundreds of small distributors. The strong oxidative (sometimes explosive) properties of products containing significant amounts of AN have led to a long history of major accidents including mass explosions in large storage units and pre 1950s, to mass explosions in ships. A major breakthrough in safety was achieved in the 1950s, with the promotion - amongst other improvements - of better anti-caking agents. Although modern AN fertilizers complying with current standards are not considered as explosive material per se, the latent risk of accidental detonation under specific conditions remains a real issue, and from a scientific point of view, cannot be completely ruled out-as dramatically demonstrated by the Toulouse disaster in France. The new insight provided here is derived from: (1) a literature review on hazardous properties of AN and AN-based fertilizers; (2) a review of accidents focusing more particularly on the reporting of recent new cases involving relatively small quantities of previously 'thought safe' products; (3) an examination of both the relevant regulatory framework and the level of hazard control achieved; (4) appropriate discussions of the economical, technical and organizational factors that could lead to some underestimation of the risk compared to large scale storage facilities. In terms of research requirements, the complex potential scenario 'mass explosion following a fire' requires further attention, as does the role and properties of molten ammonium nitrate, which could be the precursor for such an event to occur. Beyond research needs, reinforced legislative control by the authorities and further promotion of safe storage practices must be encouraged by the industry for end-users particularly. Such users have inherently the highest potential for undesirable situations, due both to the nature of their activities and also a possible lack of awareness of the real danger.     

Investigations of the formation of explosive mixtures in dryers for coatings

In the following we will discuss a specific problem of explosion protection in dryers for coatings. It is mainly encountered in chamber dryers as these pose specific problems as regards occupational safety and health. During the drying process of most coatings, solvent vapours are released most of which can form explosive mixtures when a specific concentration, the lower explosion limit, is reached. The European Standard EN1539:2000 requires explosion venting areas for most of these dryers without adequate explosion protection measures such as appropriate limitation of the solvent input being taken into account. Different aspects of the model underlying the calculations are evaluated, and it will be shown that this model is still reliable in most applications. The investigations consisted of three parts. At first there have been made investigations of the operating conditions in different enterprises aimed to get information about specific parameters, problems and failures. Laboratory experiments have been made to investigate in detail the major influencing parameters. Attempts to set up a simple but basic physical model for the experimental data have also been made. Evaporation and diffusion have been examined. The numerical models have been kept as simple as possible to be a potential tool for designers/manufacturers and users.     

Generation and characterization of nano aluminium powder obtained through wire explosion process

In the present study, nano aluminium particles were produced by wire explosion process (WEP) in nitrogen, argon and helium atmospheres. Thus produced nano particles were characterized through certain physico-chemical diagnostic studies using wide angle X-ray diffraction (WAXD) and by energy dispersive analysis by X-rays (EDAX). The size and shape of the powder were analysed by using transmission electron microscopic (TEM) studies. The particle size distribution studies were performed by adopting log-normal probability distribution. The relationship between size of the particle generated in the explosion process and the type of inert gas/pressure was analysed. The mechanisms of nano particle formation, the factors which can aid the process of formation of nano particle in the wire explosion process were analysed. It is realized that energy deposited to the conductor and duration of current flow have major impact on particles produced by this process.     

SiH4、N2二元混合气在低O2态下的潜在危险性

通常硅烷与氧很难共存,人们也决不会贸然在硅烷气体中作掺氧试验。一次偶然的机会,我们做配制SiH4与N2二元混合气的实验,事后发现所用N2中含氧量为4．2％(体积分数)。由此我们知道这种处于亚稳状态的硅烷混合气其潜在的危险非常之大。     

Understanding nanoparticle formation by a wire explosion process through experimental and modelling studies

A wire explosion process (WEP) has been used to produce nano aluminium powder in nitrogen, argon and helium atmospheres. The impact of energy deposited into the exploding conductor on the size and shape of the particles was analysed using TEM analysis, which forms the first part of the study. It is observed that the higher the energy deposited, the smaller the particles formed. In the second part, modelling studies were carried out by solving the general dynamic equation through the nodal approach, and the particle size distributions were predicted. It is realized that, at the point of high saturation ratio and nucleation rate, the size of the critical nucleus formed is low. The particle size distribution predicted by the model correlates well with the experimental results. Time-series analysis of particle formation indicates that particles of lower dimensions form and, in the process of coagulation, larger particles are formed. It is realized that the plasma formed during the explosion plays a major role in the particle formation, and the modelling studies confirm that particle formation is not an instantaneous process but requires a certain time period to form stable sizes and shapes.     

Cleavage failure of transformer storage tank under dynamic rates of loading: Influence of base plate and weldment microstructure and toughness

A high capacity transformer storage tank that was in service for more than a decade ruptured due to an explosion and a visual examination showed that the fracture facets were essentially brittle in nature with little evidence of plastic deformation. Fracture occurred mainly along weld seam; however, there were sharp cracks even in the base plate. Present study is a focused effort to find reasons for this brittle behavior of normally ductile steel. This entailed an in-depth metallographic examination of samples, selectively cut out from the tank walls and fractured weldments, supplemented by characterization of hardness, tensile, ductility and toughness properties. Results indicate that base plate and weld metal meet the required specifications for static design but not for the dynamic loading experienced under this failure mode (i.e. cleavage). Under dynamic loading conditions, the weld metal is the weakest link in terms of toughness and resistance to crack propagation. The need for adopting modern strong, tough, weldable steels to the construction of these tanks are pointed out.     

Modelling and performance evaluation of explosive storage policies in internet fulfilment warehouses

Internet Fulfilment Warehouses (IFWs) are designed to exclusively process online retail orders. An observational study reveals that IFW operating and design attributes are significantly different from traditional warehouses in their storage and fulfilment policies. Specifically, we identify six IFW differentiators: explosive storage, very large number of beehive storage locations, bins with commingled SKUs, immediate fulfilment, short picking routes with single unit picks and high transactions with total digital control. Explosive storage of incoming bulk allows for faster fulfilment of customer orders often within a few hours. A new IFW control model is developed. This describes the associated receiving and fulfilment flows. Two decision algorithms for generating (i) a stocking list and (ii) an order picking list are presented. A simulation model was built to evaluate the fulfilment performance of the explosive policy. Experimental runs on a problem with 400 SKUs, 3240 bins and 22,000 customer orders over nine days are reported. Results show that increasing levels of explosion reduce the linear fulfilment time by as much as 16%, confirming the IFW storage policy is advantageous. The results also show that fulfilment time behaviour is convex as a function of the maximum number of stops allowed by the picking algorithm parameter.     

Venting of gas explosion through relief ducts: interaction between internal and external explosions

Relief ducts fitted to venting openings is a widespread configuration in the industrial practice. The presence of a duct has been reported to severely increase the violence of the vented explosion posing a problem for the proper design of the venting device. Several studies have reported the leading importance – in the whole complex explosion phenomenology – of a secondary explosion in the duct. Modern approaches in the study of simply vented explosions (without ducts) have focused on the study of the interaction between internal and external explosion as a key issue in the mechanisms of pressure generation. The issue is even more relevant when a duct is fitted to the vent due the confined nature of the external explosion. In this work the interaction between internal and external events is experimentally investigated for gas explosions vented through a relief duct. The work has aimed at studying mechanisms underlying the pressure rise of this venting configuration. The study has put the emphasis on the mutual nature of the interaction. A larger scale than laboratory has been investigated allowing drawing results with a greater degree of generality with respect to data so far presented in literature.     

LPG explosion damage of a reinforced concrete building: A case study in Sanliurfa,Turkey

Around the morning EET of 17 June 2011, at Karakopru town of Sanliurfa in Turkey, a LPG explosion at a petrol station took place and as a result of this explosion 1 person was died and 21 people were seriously wounded. The in situ investigation revealed that the explosion was originated by the ignition of an explosive atmosphere that had formed at the basement space of the building due to the LPG leakage. Although it is considered the risk of LPG release to be low, the potential consequences of such a leak is devastating. In the present study, the interesting damages of RC members and their mechanisms in the building exposed to the explosion were explained in conjunction with photos and drawings. Damages observed were so interesting that, they were far beyond the imagination of anyone. It is considered that the presented damages and their mechanisms will give a new insight to the people interested in explosion damages.     

A non-ideal model for predicting the effect of dissolved salt on the flash point of solvent mixtures

Flash point is one of the major quantities used to characterize the fire and explosion hazard of liquids. Herein, a liquid with dissolved salt is presented in a salt-distillation process for separating close-boiling or azeotropic systems. The addition of salts to a liquid may reduce fire and explosion hazard. In this study, we have modified a previously proposed model for predicting the flash point of miscible mixtures to extend its application to solvent/salt mixtures. This modified model was verified by comparison with the experimental data for organic solvent/salt and aqueous-organic solvent/salt mixtures to confirm its efficacy in terms of prediction of the flash points of these mixtures. The experimental results confirm marked increases in liquid flash point increment with addition of inorganic salts relative to supplementation with equivalent quantities of water. Based on this evidence, it appears reasonable to suggest potential application for the model in assessment of the fire and explosion hazard for solvent/salt mixtures and, further, that addition of inorganic salts may prove useful for hazard reduction in flammable liquids.