Assessment Of Explosion Hazards Research Articles

Experimental and theoretical study on the inhibition effect of CO2/N2 blends on the ignition behavior of carbonaceous dust clouds

Gaseous inhibitors are used in many industries for the explosion prevention of combustible dusts, mitigating the potential hazard to humans, properties and environments. This work experimentally and theoretically studied the inerting effect of gaseous inhibitors on the ignition process of dust clouds in O2/N2/CO2 atmospheres, with an emphasis on the role of the CO2/N2 ratio. 10 different combustible carbonaceous dusts were selected, including grain dust, biomass dust and coal dust. Experimental results showed that the inhibition effect of CO2/N2 is closely related to the ignition mechanism of dust clouds. Specifically, a higher ratio of CO2/N2 yields a stronger inhibition effect on the ignition process of dust samples with relatively low volatile matter contents predominated by heterogeneous ignition. In addition, two novel steady-state ignition mechanism models were developed to interpret the experimental observations. Maxwell-Stefan equations were used to describe the diffusivity in the ternary O2/N2/CO2 gas mixtures. The analytical results were in good agreement with the experimental data of the minimum ignition temperature of dust cloud (MITC) in oxygen-lean atmospheres. The mechanism modelling can be used to estimate the critical ignition temperature of all carbonaceous dust clouds with a wide range of volatile matter content under different inert atmospheres, which will provide a reference for the explosion hazard assessment of dust posed by a hot surface in the process industries.

Hydrogen explosion mitigation in DEMO vacuum vessel pressure suppression system using passive recombiners

An important issue for the Fusion Reactors is the hydrogen explosion hazard assessment. For this reason, in the Work Package of Safety Analyses and Environment (WPSAE) of the EUROFusion consortium, a task was established to identify the potential for hydrogen production in DEMO vessel in accident situations and to investigate the possible solutions which can prevent the risk of hydrogen and dust explosion. The hydrogen in the Vacuum Vessel (VV) can lead to combustion progressing in deflagration and detonation. Besides, the tungsten dust could enhance the effects of H2 reaction as demonstrated by experiments, however, in this first set of accidents, only the H2 generated by the chemical reaction is accounted for.For these reasons, the solutions to avoid or limit the H2 production and/or to control safely the risk of H2 accumulation and explosion need to be screened starting from the solutions adopted in the fission technology, and later on, adapted and assessed in the Pressure Suppression System (PSS) foreseen in DEMO. One promising idea seems to install passive catalytic recombiners in the PSS.The aim of this paper is firstly to set a range of operating parameters for the PAR functioning and intervention suitable in DEMO PSS configuration. Secondly to verify if the present criteria and parameters work efficiently in mitigating the H2 accumulation a PSS in accidental conditions. To test the theoretical effectiveness of the PAR intervention, two reference accidents have been analyzed: an in-VV Loss Of Coolant Accident (LOCA) in the frame of the Design Basis Accident (DBA) and a Loss Of Flow Accident (LOFA) without active plasma shutdown in the context of the Beyond Design Basis Accidents (BDBA).The results seem promising if the performances of the PAR will be confirmed in sub atmospheric and saturated conditions.

Evaluation of explosion characteristics of 2-methylfuran/air mixture

Herein, the explosion characteristics such as the peak explosion pressure, maximum pressure rise rate and deflagration index of 2-methylfuran (MF)/air mixture have been investigated at high pressures and temperatures. Knowledge of these parameters can be used in the safety assessment of MF explosions. The explosion experiments were performed at the initial pressure of 1, 2, 3, and 4 bar, the initial temperature of 333, 363, 393, and 423 K and the equivalence ratio of 0.7–1.4 using a constant volume combustion bomb. The pressure data obtained from the experiment were carefully processed to examine MF peak explosion pressure, maximum pressure rise rate, explosion time as well as the deflagration index. Explosion characteristics of MF were sensitive to the initial pressure and temperature conditions and the mixture concentration. An increment in the initial pressure triggered a dramatic growth in the peak explosion pressure, maximum rate of pressure rise and the deflagration index. Alternatively, an increment in the initial temperature decreased the peak explosion pressure, maximum pressure rise rate and the deflagration index. By and large, MF explosion parameters obtained in this investigation can offer firsthand information on MF explosion hazard assessment at high pressures and temperatures.

Getting it right for projects in early design phase: Advanced techniques to ensure accurate explosion assessments

A large vapour cloud explosion followed by a fire is one of the most dangerous and high‐consequence events that can occur at petrochemical facilities. As the size and complexity of facilities increase, designs must consider the potential adverse effects associated with vapour cloud explosions in large congested areas. Designing topside structures to withstand a maximum credible event by avoiding unacceptable escalation of events and damage to safety critical equipment is an essential part of the path toward safer designs. One main factor inhibiting inherently safer designs is the lack of detailed geometry information in the early design phase. When congestion due to small components is not integrated into the explosion pressure analysis model, the design blast loads will be severely underestimated. This article will compare detailed computer‐aided design (CAD) models obtained for both early design phase and as‐built final detailed design, and demonstrate the gross under prediction of accidental explosion loads of the early phase models, as compared to as‐built. In fact, the explosion overpressures can differ by an order of magnitude underlining the need for guidance on the necessary levels of congestion required to obtain reliable blast loads.Gexcon has evaluated traditional congestion parameters such as volume blockage ratio, surface area to volume ratio and packing density as indicators of predicted overpressure as they are commonly used for explosion siting studies. On their own, these parameters have not proven reliable indicators of predicted overpressure and have shown no direct correlation to predicted overpressure across varying geometries. The lack of a direct relationship makes assessing the amount of required congestion to be added to early design phase models challenging. This study will focus on evaluating alternative ways of quantifying congestion, such as non‐dimensional congestion parameters, row spacing, and special obstruction density gradients, to evaluate combustion and eddy/turbulence decay downstream of obstructed areas. With these alternative parameters, we have further refined our anticipated congestion method for petrochemical facilities for accurate predictions of explosion consequences with early design phase models (concept or front‐end engineering design (FEED), phase). This methodology will define what levels of anticipated congestion are necessary to supplement CAD models in early design phase to ensure accurate assessment of explosion hazards and include recommendations for required congestion level for supplementing early phase designs. © 2018 American Institute of Chemical Engineers Process Saf Prog 38: e11995, 2019

Quick assessment of explosion hazard in small premises

Quick assessment of explosion hazard in small premises

Self-similar propagation of expanding spherical flames in large scale gas explosions

This paper presents the experimentally observed onset of self-acceleration and self-similarity of flame propagation during a large-scale gas explosion. Specifically, the critical Peclet number (flame radius relative to flame thickness) at which self-acceleration begins, Pec=r/δ, the experimental acceleration exponent, α, and the fractal excess, d, are evaluated from the results of field experiments of hydrogen/air, methane/air, and propane/air explosions at various concentrations. Experimental results show that Pec for the onset of self-acceleration correlates with Markstein number, Ma, of the mixture that measures the intensity of diffusional–thermal instability. This result demonstrates that the onset of self-acceleration depends on the intensity of hydrodynamic instability as well as that of diffusional–thermal instability. The value of power law exponent of flame radius, α, calculated from r∼tα, increased in Pe, and then it reached a limiting value when (Pe−Pec)/Pec≫1, from which the fractal dimension is calculated. The results suggest that a self-acceleration (α>1) and a self-similarity (α=constant) regimes exist for an expanding spherical flame. The experimental three-dimensional fractal dimension for real flames is found in the range of D3≈2.2–2.35 in the present study. It is confirmed that the fractal dimension is affected by the intensity of instabilities. The present results are expected to help improve the accuracy of the risk assessment of explosion hazards.

Toward Risk Assessment of Explosion Hazard: Experimental Determination of Flame Fractal Dimension

Quantitative risk analysis is a method to evaluate risk and to identify areas for risk reduction. The final goal of our study is to propose an effective method for risk assessment of explosion hazard. To achieve the goal, a phenomenon that influences the consequences of explosion is first identified: self-turbulization and resulting acceleration of expanding flame during explosion. The fractal dimension is then identified as the key parameter that characterizes the phenomenon. Since the previous method to determine fractal dimension relies on large-scale explosion experiment, it has not been easy to determine fractal dimension. This paper demonstrates the possibility of determining fractal dimension by analyzing flame images of small-scale experiment, which might significantly reduce the cost of risk assessment of explosion hazard.

Dust explosion hazard assessment

The majority of powders that are used in the processing industries are combustible (also referred to as flammable, explosible). An explosion will occur if the concentration of the combustible dust that is suspended in air is sufficient to propagate flame when ignited by a sufficiently energetic ignition source. A systematic approach to identifying dust cloud explosion safety against their consequences generally involves: -Identification of locations where combustible dust cloud atmospheres could be present -Understanding of the explosion characteristics of the dust(s) -Identification of potential ignition sources that could be present under normal and abnormal conditions -Proper process and facility design to eliminate and/or minimize the occurrence of dust explosions and protect people and facilities against their consequences -Adequate maintenance of facilities to prevent ignition sources and minimize dust release This presentation will discuss the conditions that are required for dust cloud explosions to occur and presents a well-tried approach to identify, assess, and eliminate/control dust explosion hazards in facilities.

Explosion characteristics of coal gas under various initial temperatures and pressures

Explosion limits data are essential for a quantitative risk assessment of explosion hazard associated with the use of coal gas. The present work is to investigate the influence of various initial temperatures and pressures on explosion characteristics of coal gas/air mixture. The explosion limits and the minimum ignition energy of coal gas/air mixture are obtained experimentally at various temperatures ranging from 20 to 80°C and pressures ranging from 0.1 to 0.2 MPa. An empirical equation is established from the experimental results for the effects of initial temperatures and pressures on explosion limits. By adding diluent (nitrogen) into coal gas/air mixtures, the dilution effects on the explosion limits have been explored as well, and a critical flammable concentration of coal gas is determined to be at 7.4–9.0% by volume. By means of a high-speed digital video camera, the flame front development is recorded and analyzed. The tests are carried out with lean, stoichiometric and rich mixtures of coal gas in air under the conditions of initial pressure and nitrogen addition. Furthermore, the influence of the initial pressure and the concentration on the explosion pressure is measured and compared against theoretical results, where a good agreement is observed.

Experimentally validated 3-D simulation of shock waves generated by dense explosives in confined complex geometries

Accidental blast wave generation and propagation in the surroundings poses severe threats for people and property. The prediction of overpressure maxima and its change with time at specified distances can lead to useful conclusions in quantitative risk analysis applications. In this paper, the use of a computational fluid dynamics (CFD) code CFX-5.6 on dense explosive detonation events is described. The work deals with the three-dimensional simulation of overpressure wave propagation generated by the detonation of a dense explosive within a small-scale branched tunnel. It also aids at validating the code against published experimental data as well as to study the way that the resulting shock wave propagates in a confined space configuration. Predicted overpressure histories were plotted and compared versus experimental measurements showing a reasonably good agreement. Overpressure maxima and corresponding times were found close to the measured ones confirming that CFDs may constitute a useful tool in explosion hazard assessment procedures. Moreover, it was found that blast wave propagates preserving supersonic speed along the tunnel accompanied by high overpressure levels, and indicating that space confinement favors the formation and maintenance of a shock rather than a weak pressure wave.

Experimental study of flammability limits of natural gas–air mixture

Flammability limits data are essential for a quantitative risk assessment of explosion hazard associated with the use of combustible gas. The present work is to obtain the fundamental flammability data for prevention of the hazards in the practical applications. Experiments have been conducted in a constant volume combustion bomb, and the fuel considered here is natural gas (NG). The pressure histories in the combustion bomb are recorded and a criterion of 7% pressure rise has been used to judge a flammable mixture. The effects of ethane on NG–air flammability limits have been investigated. By adding diluent (carbon dioxide, nitrogen or their mixture) into NG–air mixture, the dilution effects on the flammability limits have been explored as well, and the results are plotted as functions of diluent ratio.

Phreatic explosion hazard assessment by numerical simulation

Phreatic explosions (or eruptions) represent very common and dangerous phenomena occurring in active volcanic and geothermal regions. In spite of this, the understanding of their dynamics and the assessment of their hazards are still scarcely known and quantified. In the present work we try to simulate the dynamics of a phreatic explosion by using a transient, two-dimensional, three-phase flow model. Simulations predict the effects of an explosion of a mixture of compressed gases and ground particles into the atmosphere. The governing transport equations of mass, momentum, and energy are solved by a finite difference multifield scheme for both solids and gas phases. We performed several simulations, assuming different initial conditions and system parameters. The model allows analysis of the timewise and spatial distribution of the groundhugging surge generated by the explosion and estimation of its potential hazards in terms of dynamic pressure, ash-in-air concentration, and temperature.

Methods for vapour cloud explosion blast modelling

The potential explosion hazard of fuels is quantified by methods in which the explosive potential of a flammable fuel-air mixture is expressed as an equivalent explosive charge whose blast characteristics are known. In this paper, the two most current methods are described and demon- strated in a simple case study. TNT-equivalency methods have been widely used for this purpose for a long time now. Generally speaking, TNT- equivalency methods state a proportional relationship between the quantity of fuel available and the weight of a TNT charge expressing the cloud's explosive potential. However, fundamental and practical objections are met if the TNT-equivalency concept is used for vapour cloud explosion hazard assessment. To some extent, these difficulties are remedied in an alternative approach, the multi-energy method. In the multi-energy method, a flammable fuel-air mixture is considered to be explosive only if it is in a partially confined, congested or obstructed area in the cloud. The explosive potential of the fuel-air mixture in the various partially confined, congested or obstructed regions can be expressed as a corresponding number of equivalent fuel-air charges. The multi-energy concept is shown to be a flexible concept which makes it possible to incorporate current experimental data and advanced computational methods into the procedure of vapour cloud explosion hazard analysis.

The assessment of explosion hazards from electrical equipment on aircraft in the light of elementary probability theory

The paper discusses the influence of statistical considerations on the design of tests intended to lead to an assessment of the explosion risks arising from the normal operation of electrical equipment on aircraft The statistical approach implies that a finite amount of testing cannot establish a nil risk, the amount of testing depends upon the degree of assurance required. It is shown that an apparently ‘reasonable’ degree of assurance leads to an unmanageable amount of test effort if the tests are made under fully simulated service conditions.Test effort can be reduced by orders of magnitude if it is possible to assess separately each of several factors that are simultaneously necessary for an explosion Testing can be further reduced when it is possible to speed up the operation of the unit for test purposes. The proposition that test effort may be reduced by using ‘enhanced’ test conditions is considered. In this Connection, dependence on extrapolation procedures is particularly criticized.It is noted that standardization of enclosures for equipment would much reduce test effort. The advantage in relieving the test situation, of dependence on sealed enclosures that need only mechanical testing is emphasized.