Experimental determination of flash points of flammable liquid aqueous solutions

International audienceThe flash point is considered as a determinant parameter to classify the flammable liquids, regarding the European CLP regulation, as well as the transport of dangerous goods regulation. In the case of some low concentrated flammable liquid aqueous solutions, the existence of a flash point is not very well defined, and their flammability is not precisely known. The experimental measurements of flash points are described in numerous national or international standards, which differ by their range of validity and by the specified experimental conditions. The flash point of ethanol, acetone, acetic acid and formic acid aqueous solutions was measured using Abel and Pensky-Martens in close cup methods, chosen regarding predicted values of flash point. Results obtained show that, for the most flammable products, such as acetone or ethanol, weakly concentrated aqueous solutions still remains flammable. In the case of acetic or formic acid aqueous solutions, a threshold concentration can be determined under which the solutions are considered as non flammable, regarding the European CLP regulation and the transport of dangerous goods regulation

Large scale characterisation of the concentration field of supercritical jets of hydrogen and methane

When an orifice or breach appears in the wall of a tank containing flammable gas under pressure. a jet is created which develops into an explosive cloud. Research has shown that the intensity of the explosion likely to take place in this cloud is then hiehly variable and depends on the cloud characteristics

Towards the improvement of UN N.5 test method for the characterization of substances which in contact with water emit flammable gases

International audienceThis paper deals with a sensitivity analysis of main parameters affecting the measurement of the gas flowrate emitted during testing substances for their potential to emit flammables gases in dangerous quantities where in contact with water, according to the UN N.5 test procedure. UN N.5 is described in the Manual of Tests and Criteria of United Nations (part of the Orange Book) (ONU Manual of Test and Criteria, 2008), serving both applications of international transport regulations as well as classifications of dangerous substances according to Globally the Harmonized System (GHS) and the derived regulation applying in the EU known as 'CLP' Regulation (Regulation (EC) No 1271/2008). The main reason that justifies the present research is that the measurement of emitted gases is highly critical in the final classification resulting from the interpretation of the test results. Moreover, that idea has been raised to adapt the UN N.5 test protocol for classifying, in the future, substances that by contact with water would emit dangerous quantities of toxic gases. Experiments have been carried out to cover the analysis of the influence of ambient temperature, overall volume of glassware, nature of aqueous media, mass sample and sample-to-liquid mass ratio, since such parameters are not fixed within any defined range in the UN N.5 test procedure. The influence of the flow rate measuring device was also considered. Results confirm that the above mentioned parameters may play a significant role to such an extent as to finally alter the final classification resulting from the testing. Guiding principles have also been derived from our measurements and observations towards an improved and more robust UN test protocol in the future

Conditions de formation d'une atmosphère explosive lors de la mise en oeuvre d'un liquide inflammable

National audienceWhen employing a flammable liquid, the conditions in which an explosive atmosphere (ATEX) can form depend to a great extent on the liquid itself (flash point, temperature); if the liquid is in an open space, they are also linked to the evaporation flow rate, which in turn depends on the air renewal conditions at the surface of the liquid. An evaporation model has been established from the results of a series of measurements carried out with volatile solvents, where the vaporization flow rate and the vapor concentration at the surface of the liquid were measured. Knowledge of these different features permits the implementation of the ATEX regulations in a precise and realistic way.Au cours de la mise en oeuvre d'un liquide inflammable, les conditions de formation d'une atmosphère explosive (ATEX) dépendent au moins des caractéristiques du liquide (point d'éclair, température ambiante) ; dans le cas où le liquide se trouve en milieu ouvert, les conditions de formation d'une ATEX sont également liées au débit d'évaporation du liquide, lui-même associé aux conditions de renouvellement de l'air à sa surface. Un modèle d'évaporation a été établi d'après les résultats d'une campagne de mesures effectuées sur des solvants volatils courants, au cours de laquelle le débit d'évaporation du liquide et la concentration en vapeur à proximité de sa surface ont été mesurés. La connaissance de ces différents éléments permet une application précise et réaliste de la réglementation ATEX

Correlation between self-ignition of a dust layer on a hot surface and in baskets in an oven

International audienceEvaluation of self-ignition hazard of bulk materials requires experimental determination of self-ignition temperatures as a function of volume. There are two standardised methods : determination of the self-ignition temperature of dust samples in oven and measurement of the self-ignition temperature of a dust layer deposited on a hot surface. Sometimes, the sample behaviour during these tests makes the second method difficult to apply. The self-ignition phenomena in these two tests rely on the same principles. Their results are interpreted with the help of theoretical relations. The correlation described in this paper can be considered acceptable to deduce self-ignition temperature of a dust layer, based on results of self-ignition of the same dust in heating ovens, if the Biot number (alpha) can be estimated. Uncertainty on the correlation is near 30 K. This uncertainty is on the same order of magnitude as the difference in the self-ignition temperature on a hot surface for thickness between 5 and 15 mm

Experimental study of CH4/O2/CO2 mixtures flammability

International audienceThe oxy-combustion process uses CH4/O2/CO2/H2O mixtures at various concentrations, according to the different operation phases. To analyze the risks associated to this process, the safety characteristics of these explosive mixtures have to be taken into account. A literature review showed that some safety features of methane in oxygen or in air were not available. Thus, the flammability ternary diagram of CH4/O2/CO2 mixtures was determined at room temperature and 1 bar pressure. Furthermore, the influence of oxygen content on the explosion severity (Pmax; dP/dt) was investigated. The ternary mixtures were prepared directly in a 20 L spherical test vessel. The concentrations of reactants were adjusted using the relationship between the partial pressure and the molar fraction of gas. The ignition source used was an alumel fusing wire. The flammability limits of methane in oxygen were extrapolated at 5 and 68% vol., by using the established CH4/O2/CO2 mixtures ternary diagram. It also confirmed that when the carbon dioxide concentration increases, the flammability range decreases: no ignition was observed when carbon dioxide content exceeded 73%. A significant influence of the oxygen concentration on the explosion severity has been highlighted for CH4/O2/CO2 mixtures containing respectively 10, 25, 45 and 65% vol. of carbon dioxide. The maximal explosion overpressure and the maximum pressure rise were both measured near the stoechiometry. Maximum values of Pmax and dP/dt measured for a 10% vol. carbon dioxide concentration were 11.2 bar rel. and 5904 bar/s respectively, while they were 3.6 bar rel. and 72 bar/s respectively in the case of a 65% vol. carbon dioxide content in the mixture

Explosion de poussières dans les lieux de travail : recensement et analyse

National audienceUse of combustible dusts or powders may lead to the formation of explosive atmospheres (ATEX) under specific conditions. One hundred and ninety dust explosions, which occurred between 1903 and January 2010, were recorded on the French (BARPI) "ARIA" database. This study was based on industrial sectors, in which explosions have been recorded, including the wood, metal, agricultural foodstuff, chemical and pharmaceutical industries as well as bulk storage of cereals. Data sought in this research were: 1) equipment most often involved in the explosions, 2) factors that led to dust dispersion in air and, 3) ignition source. The study also highlights the human and/or material impact of these explosions. It is clear from this work that assessment and prevention of risks associated with ATEX remains a major challenge for improving workplace safetyLa mise en oeuvre de poudres ou de produits pulvérulents combustibles peut entraîner, dans certaines conditions, la formation d'atmosphères explosives (ATEX). Cent quatre-vingt-dix explosions de poussières, survenues sur la période de 1903 à janvier 2010, ont été répertoriées dans la base de données ARIA du BARPI. Cette étude a porté sur les secteurs d'activité pour lesquels des explosions ont été recensées. Il s'agit des secteurs du bois, des métaux, de l'agroalimentaire, de la chimie et de la pharmacie ainsi que du stockage en vrac de céréales. Les éléments recherchés concernent les équipements le plus souvent impliqués et les éléments qui ont conduit à la mise en suspension des poussières, ainsi que la source d'inflammation. Ils mettent en évidence les conséquences humaines et/ou matérielles de ces explosions. Il ressort de cette étude que l'évaluation et la prévention des risques associés aux ATEX constitue encore aujourd'hui un fort enjeu pour l'amélioration de la sécurité au travail

Explosions. Protection : lieux de travail et environnement

Une explosion se définit comme la transformation rapide d'un système s'accompagnant d'une libération brutale d'énergie et se traduisant par une expansion de gaz. Différents phénomènes dangereux qualifiés d'explosions physique ou chimique, suivant la nature de la transformation du système, sont susceptibles de se produire dans les industries mettant en oeuvre des produits pulvérulents : l'éclatement d'une enceinte pressurisée, comme un réservoir de compresseur ; la décomposition de substances instables, telles que les ammonitrates ; la combustion d'une atmosphère explosive (ATEX), constituée d'une suspension d'un solide pulvérulent combustible dans l'air, comme le sucre, la sciure de bois, certains produits pharmaceutiques..

Implementation of Directive 1999/92/EC : some concerns for the definition of ATEX zones

Directive 1999/92/EC is to be implemented within a year. It requires the determination of hazardous zones where an explosive atmosphere (ATEX) may occur. This zoning is expected to be accurate. So is to be the evaluation of effects associated with an ignition of the so defined ATEX zones. Hence, Physical phenomena which are involved in the formation of ATEX must be taken into account and quantified : leak and vaporization of a flammable liquid, leak of a flammable gas, dispersion of a layer of combustible dust. It is not recommended to oversize a zone, nor to design a zone having such a small volume that the effects of an ignition would be negligible

Application de la réglementation ATEX au laboratoire

La réglementation ATEX a pour objectif l'amélioration de la santé et de la sécurité des travailleurs exposés au risque d'atmosphères explosives (en abrégé, ATEX). Or, il est fréquent que les activités pratiquées dans un laboratoire requièrent l'utilisation de produits inflammables, à l'état de gaz ou de liquides plus ou moins volatils. La formation d'ATEX est donc a priori possible et la directive ATEX doit, par conséquent, être appliquée, même si sa mise en pratique tient évidemment compte du fait que, contrairement à une installation industrielle de production, les quantités de produits inflammables mises en oeuvre au laboratoire sont nécessairement limitées. Ce document rappelle les exigences de la réglementation ATEX, il présente des situations qui ont conduit à des incidents ou accidents et propose des mesures de prévention qui doivent être prises, en application de cette réglementation, et qui permettent d'exercer les activités de laboratoire dans des conditions de sécurité suffisante vis-à-vis du risque d'explosion