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Le Sirta, une nouvelle infrastructure pour renforcer les services dédiés à la recherche et à l'enseignement
No full textInternational audienc
CFD Simulation of an Unconfined Vapor Cloud Explosion through obstacles using OpenFoam
No full textInternational audienceIn this work, numerical simulations are carried out to characterize the impact of obstacles on flame propagation velocity to properly assess the consequences of Unconfined Vapor Cloud Explosions (UVCE).Within this scope, an UVCE within a congested environment is simulated using RANS modeling of the turbulence. Combustion phenomena are characterized through the progress variable transport equation. The simulation is done with the open source library OpenFoam. Numerical results are compared with data from the INERIS and GDF-SUEZ experimental campaign EXJET (hydrogen-air and methane-air explosions)
Assessing the influence of real releases on explosions : selected results from large-scale experiments
No full textInternational audienceThe research activities in the project Assessing the Influence of Real Releases on Explosions (AIRRE) included a unique series of large-scale explosion experiments with ignited high-momentum jet releases directed into congested geometries. The primary objective for the AIRRE project was to gain improved understanding of the effect realistic releases and turbulent flow conditions have on the consequences of accidental gas explosions in the petroleum industry, to develop methodology that can facilitate safe and optimal design of process facilities. This paper presents selected results from experiments involving ignition of a highly turbulent gas cloud, generated by a large-scale, pressurised release of natural gas. The paper gives an overview of the effect on maximum explosion overpressures of varying the ignition position relative to the release point of the jet and a congested region placed inside the flammable cloud, with either a high or medium level of congestion. For two of the tests involving a jet release and the medium congestion rig, the maximum overpressures significantly exceeded those obtained in a quiescent reference test. The paper presents detailed results for selected tests in the campaign. The effects on the relevant explosion phenomena from introducing initial turbulence, initial flow momentum and concentration gradients, as generated by the realistic release, are discussed
A new technique to produce well controlled electrical sparks. Application to MIE measurements
No full textInternational audienceFew laboratories in the world have kept the capability of measuring minimum ignition energies (MIE). When a flammable gas needs to be allocated an ATEX group other measurements may be performed like determining the minimum experimental safety gap (MESG). However, the relationship between MESG and MIE is statistical and certainly lacks accuracy and when more accurate information is required as for instance when investigating the influence of the initial conditions on the ignitability, direct MIE measurements are required. To be able to meet such request, the author’s team re-developed an expertise in this field be using up to date technologies. A brief review of the methods used in the past is first given highlighting the difficulties. Then a new technique is described with which the losses can be accurately estimated. The method was used for propane and hydrogen air
Understanding the role of thermal radiation in dust flame propagation
No full textInternational audienceThe role of thermal radiation in premixed flame propagation has been a matter of debate for decades. And it is not only a challenging scientific point, it has significant practical implications. For instance, a proposed explanation of the Buncefield explosion (HSL, 2009) was tiny particles were raised by the blast and promoted flame acceleration through enhanced heat exchanges by thermal radiation through the flame front. In dust explosion protection, the flame is implicitly supposed to propagate like a in a gaseous mixtures but if it happens that thermal radiation is dominant for some dusts, many aspects concerning the way to mitigate the explosions for those particular dusts would need to be revised. The present research team (Ben Moussa et al., 2013, 2017; Proust et al., 2017a, 2017b) and another one (Julien et al., 2015) have been working on this subject for some time. The scientific problem was settled and a significant experimental effort was done. It was shown that thermal radiation could accelerates flames possibly to a considerable extent but without any firm confirmation. In the present paper a numerical modelling of this problem is proposed to help understanding the physics of the flames seeded with particles and especially aluminum dust flames. The code uses the discrete element method and was developed from scratch over the last years. Some information to understand how the code work is provided into the paper and the results are compared to the experiments. From this comparison it can be concluded that thermal radiation is readily capable of strongly accelerating dust flames depending on the experimental conditions. Large scale experiments are now needed which however could be complicated to perform
Research Roadmap : Environmental Impact of Fires in the Built Environment. Final report.
No full textInternational audienc
Valorisation d’herbes de bords de routes par méthanisation
No full textInternational audienceLa valorisation par compostage ou méthanisation de l’herbe fauchée en bordure de route se développe en France et peu d’informations sur les contaminants des herbes (métaux lourds et composés organiques) sont disponibles. Au cours du projet CARMEN, réalisé en 2016-2017, des herbes de bords de routes ont été échantillonnées à différents endroits dans l’Ouest de la France, au cours de plusieurs périodes de fauche (printemps et automne), afin d’évaluer l’influence du trafic et de la saison. D’autres opérations (non détaillées ici) ont été conduites dans le cadre du projet : des tests de méthanisation en pilote et une étude coûts-bénéfices du fauchage avec exportation vers la méthanisation
A framework for coupled hydro-mechanical continuous modelling of gap-graded granular soils subjected to suffusion
No full textInternational audienceIn order to study the impact of internal erosion at the scale of an engineering structure, a hydro-mechanical continuous modelling approach considering suffusion is needed. It requires a relevant mechanical model for granular soils considering the-dependency (fines content) and a hydraulic model for suffusion to control the changes in the fines content. To this purpose, the mechanical models for granular soil, the unified modelling approaches for-dependency of granular soils and the hydraulic modelling of suffusion are first reviewed. Then, a hydro-mechanical model considering both suffusion and mechanical loading is developed by combining the three components. For each component of the model, alternative choices are provided. Simulations of laboratory tests as well as an example of a dike-on-foundation problem demonstrated the reliability and applicability of this coupled numerical approach for internal erosion problems
Evaluation des méthodes de mesure de 5 substances de la directive (UE) 2019/130
No full textDes objectifs européens de protection des travailleurs vis à vis des risques liés à des expositions à des agents chimiques sont fixés via des directives européennes notamment sous la forme de valeurs limites d’exposition professionnelle (VLEP).Dans la mesure où pour l’établissement de VLEP européennes, la Commission européenne s’appuie sur des recommandations émises par des comités d’experts scientifiques européens (le SCOEL1 ou le RAC2), une réévaluation des effets sanitaires des substances concernées n’est pas effectuée par l’Anses lorsque des directives européennes fixant des VLEP sont publiées.Par contre, étant donné qu’aucune évaluation approfondie des méthodes de mesure disponibles au regard des VLEP européennes n’est réalisée par le SCOEL ou le RAC, l’Anses est saisie pour réaliser ces évaluations afin que le ministère français chargé du travail puisse disposer de l’ensemble des éléments nécessaires pour fixer la nature contraignante ou indicative de la valeur limite dans le droit national.La directive (UE) 2019/130 du Parlement et du Conseil du 16 janvier 2019, modifiant la directive 2004/37/CE, établit une liste de valeurs limites contraignantes d'exposition professionnelle pour 6 nouveaux agents cancérigènes ou mutagènes.Parmi ces 6 agents, le trichloroéthylène a fait l’objet d’une expertise antérieure par l’Anses pour élaborer des VLEP et recommander des méthodes de mesure associées à ces recommandations de VLEP (Anses, 2017a). Aussi, une réévaluation des méthodes de mesure de ce composé n’a pas été réalisée dans le cadre de la présente expertise, puisque déjà disponible.Dans le cadre du protocole d’accord relatif aux valeurs limites d'exposition professionnelle et valeurs limites biologiques (VLEP et VLB) établi entre le ministère du travail et l’Anses, la direction générale du travail (DGT) a mandaté l’Anses pour conduire l’expertise métrologique uniquement sur les substances suivantes :- 4,4′-méthylènedianiline (VLEP-8h de 0,08 mg.m-3)- épichlorhydrine (VLEP-8h de 1,9 mg.m-3)- dibromure d'éthylène (VLEP-8h de 0,1 ppm soit 0,8 mg.m-3)- dichlorure d'éthylène(VLEP-8h de 2 ppm soit 8,2 mg.m-3)- émissions d'échappement de moteurs diesel (VLEP-8h de 0,05 mg.m-3 mesurée en carbone élémentaire
Sustainable risk management strategy selection using a fuzzy multi-criteria decision approach
No full textInternational audienceWhile several studies focused on the evaluation of risk management strategies to select the sustainable ones using multi-criteria analysis, most of these studies did not necessarily dealt with the integration of uncertainties. In a context where uncertainties are inherent to natural hazards management decision-making process, the challenge is to systematically take uncertainties into account throughout the assessment process in order to avoid biased decisions. This paper attempts to tackle this challenge by suggesting a methodological approach based on the application of fuzzy multi-criteria decision-making methods. Uncertainties are addressed in two main ways. First, fuzzy AHP is used to estimate the importance of each of the evaluation criteria. Then, fuzzy weighted arithmetic mean method or fuzzy PROMETHEE are used to prioritize the strategies regarding the set of criteria, considering a compensatory or non-compensatory reasoning in order to derive final ranking. This approach is tested in a case study proposing sensitivity analysis in order to study the impact of the compensation phenomenon and the integration of uncertainty in the choice of a sustainable risk management strategy. This hybrid fuzzy multi-criteria decision approach provides a structured framework for identifying the most sustainable strategy under uncertainty