Highlights of the Flame Acceleration in a Confined Nonuniform H2/O2/N2 Mixture

International audienceGaseous explosion models generally assume the gas mixture to be uniform. However, in a real explosion, the vapor cloud may not be homogeneous, and repartitioning of the reactivity inside the cloud can be subject to wide spatial variations. In this work, experimental tests were run to study the flame propagation and acceleration in nonuniform mixtures. Experiments were performed in a long vertical confined tube with a square cross section, composed of four equal sections. A gate valve separated the tube into two parts, and the composition of the gases was different on each side of the valve. The opening of the valve permitted the mixing of gases by molecular diffusion. For nonuniform mixtures, a mode of propagation identical to that seen in uniform mixtures was observed; however, a third phase of propagation was found, in which the flame velocity increased strongly. This increase occurred with higher hydrogen concentration in an upwardpropagating flame. A concentration gradient can appreciably modify the trajectory and acceleration of a flame. Here, however, the incidence of pressure effects remained modest, since the combustion was confined and the final pressure depended mainly on the quantity of reactants available

Propagation of Shock Waves in Two Rooms Communicating through an Opening

Confined explosions represent a serious safety hazard as significant damage to humans and structures is observed, unlike in free-field explosions. An experimental small-scale study investigated the blast wave in a single-story building. The blast waves were generated by the detonation of a gaseous charge. The building was divided into two rooms by a movable wall which could be positioned at three different locations. The presence of an opening in this movable wall means that two rooms were considered: a transmitter room (TR) and a receptor room (RR). The configuration without the movable wall was also studied. Pressure profiles recorded with pressure gauges at ground level and on the wall presented numerous reflections. The damage effects were severe since the maximum overpressure never fell below 0.2 bar. Although this study is limited to a small scale and gaseous detonation charge, the results can be applied to a large scale and for a TNT charge

Impact d'une onde de choc sur une structure cylindrique

Dans un contexte de sécurité industrielle, il est important de connaître les caractéristiques de l'onde de souffle consécutive à une explosion d'origine quelconque, lorsque cette explosion se produit à proximité d'un bâtiment, ceci dans le but de protéger les installations et le personnel. Pour cela, une approche expérimentale est envisagée. L'objectif du présent travail est de définir des modèles de chargements appliqués à une structure de forme cylindrique rencontrée dans l'industrie et susceptible de subir une explosion à proximité des murs mais pas à leur contact. Cet objectif est poursuivi de manière originale à travers la réalisation d'essais d'explosions de gaz menés en laboratoire. Un certain nombre de lois sont exprimées et validées par les expériences. Des simulations numériques sont réalisées en parallèle à l'aide du code Autodyn, et une bonne corrélation avec les résultats expérimentaux est obtenue

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

International audienceThe 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 industrials 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 overpressures effects arising from detonation and shows the advantage of using a barrier with a vertical front or rear face

The Fourth International Symposium on Hazards, Prevention, and Mitigation of Industrial Explosions

International audienc

Direct initiation of gaseous detonation: the Jungle

International audienc

Blast effects: physical properties of shock waves

This book compiles a variety of experimental data on blast waves. The book begins with an introductory chapter and proceeds to the topic of blast wave phenomenology, with a discussion Rankine-Hugoniot equations and the Friedlander equation, used to describe the pressure-time history of a blast wave. Additional topics include arrival time measurement, the initiation of detonation by exploding wires, a discussion of TNT equivalency, and small scale experiments. Gaseous and high explosive detonations are covered as well. The topics and experiments covered were chosen based on the comparison of used scale sizes, from small to large. Each characteristic parameter of blast waves is analyzed and expressed versus scaled distance in terms of energy and mass. Finally, the appendix compiles a number of polynomial laws that will prove indispensable for engineers and researchers

Blast Wave Characteristics and Equivalency

ISBN 978-5-94588-079-5The characteristics of blast waves generated by detonation of gas clouds are studies theoretically and validated by both small-scale and large-scale experiments with ethylene-air mixtures of different equivalence ratio. The mixtures were confined in hemispherical or spherical balloons made from thin polyethylene foils of 0.75 m³ and 15 m³ in volume. The detonation of gas mixtures was initiated by a solid explosive. The characteristics of the blast wave in terms of overpressure, impulse and duration of the positive phase obtained in this study were compared with those obtained in author's previous work and with the principal results available in the literature. This comparison made it possible to raise the significant problem of the definition of equivalent TNT according to the scale at which the tests are carried out and according to the characteristics parameters of the blast wave. The sensitivity of equivalent TNT with respect to the reduced distance was clearly shown

Propagation d'une onde de choc en présence d'une barrière de protection

Les travaux de thèse présentés dans ce mémoire s inscrivent dans le cadre du projet ANR BARPPRO. Ce programme de recherche vise à étudier l influence d une barrière de protection face à une explosion en régime de détonation. L objectif est d établir des méthodes de calcul rapides de classement des zones d effets pour aider les industriels au dimensionnement des barrières de protection. L une à partir d abaques, valable pour des configurations en géométrie 2D, sur des plages spécifiées de paramètres importants retenus, avec une précision de +/- 5%. L autre à partir d une méthode d estimation rapide basée notamment sur les chemins déployés, valable en géométrie 2D et en géométrie 3D, mais dont la précision estimée est de +/- 30%. Afin d y parvenir, l étude s appuie sur trois volets : expérimental, simulation numérique et analytique. La partie expérimentale étudie plusieurs géométries de barrière de protection à petites échelles pour la détonation d une charge gazeuse (propane-oxygène à la stoechiométrie). Les configurations expérimentées servent à la validation de l outil de simulation numérique constitué du solveur HERA et de la plateforme de calcul TERA 100. Des abaques d aide au dimensionnement ont pu être réalisés à partir de résultats fournis par l outil de simulation (3125 configurations de barrière de protection, TNT). L étude des différents phénomènes physiques présents a également permis de mettre en place une méthode d estimation rapide basée sur des relations géométriques, analytiques et empiriques. L analyse de ces résultats a permis d établir quelques recommandations dans le dimensionnement d une barrière de protection. Les abaques et le programme d estimation rapide permettent à un ingénieur de dimensionner rapidement une barrière de protection en fonction de la configuration du terrain et de la position de la zone à protéger en aval du merlon.This thesis is a part of the ANR BARPPRO project. This research program studies this influence of the protection barrier during an explosion detonation. The goal of this project is to establish fast-computation methods of area classification effects to help the industrial to design the protection barrier on the SEVESO sites. One from abacus, for configurations in 2D geometry on specified parameters used, with an accuracy of +/- 5%. The other from a fast-running method based on broken lines for configurations in 2D and 3D geometries, but the accuracy is +/- 30%. This study includes three approaches: experimental, numerical simulation and analytical approaches. The experimental part studies several geometries of the protection barrier for a gaseous explosion (stoichiometric propane-oxygen mixture) at small scales. The experimental configurations used to validate the numerical simulation tool constituted of the HERA software and the TERA 100 supercomputer. The overpressure charts were able to generate from the numerical results (3125 configurations of the barrier for a TNT charge). The analysis of these results allows to establish different recommendations in the design of the protection barrier. The study of the different physical phenomena present has also helped to set up a fast-running method based on the geometrical, empirical and analytical relations. All these tools will enable an engineer to analyze and estimate the evolution of overpressure around the barrier as a function of the site s dimensions.ORLEANS-SCD-Bib. electronique (452349901) / SudocSudocFranceF

Impact de fortes explosions sur les bâtiments représentatifs d une installation industrielle

Le travail de thèse présenté dans ce mémoire s inscrit dans le cadre des études relatives à la vulnérabilité des structures face à la détonation de substances explosives. L objectif est de proposer des outils afin de prédire les chargements appliqués aux structures. Cet objectif est poursuivi à travers la réalisation d essais menés en laboratoire. Ces essais simulent une forte explosion d un mélange stœchiométrique propane-oxygène ayant lieu au sol ou en altitude. L étude consiste donc en premier lieu à recueillir des données expérimentales sur les effets de pression d ondes de choc rencontrant des obstacles. Deux types d obstacles rencontrés fréquemment sur un site industriel sont étudiés : un obstacle de forme parallélépipédique et un obstacle de forme cylindrique, tous deux de dimensions connues. Enfin, un point important de la problématique de la thèse est la détermination d une équivalence énergétique entre le TNT et le gaz utilisé dans les expériences, afin de permettre au final de modéliser par le biais d explosion de gaz à petite échelle des explosions de TNT à échelle réelle.ORLEANS-BU Sciences (452342104) / SudocBOURGES-ENS Ingénieurs (180332301) / SudocSudocFranceF