Functional safety in industrial explosion protection

The article presents the methodology for quantitative risk assessment, which was mainly directed towards the assessment of explosion risks at workplaces. The methodology is based on the principles of functional safety to be able to determine quantitatively the level of risk for typical manufacturing processes

Statistical method for the determination of the ignition energy of dust cloud-experimental validation

International audiencePowdery materials such as metallic or polymer powders play a considerable role in many industrial processes. Their use requires the introduction of preventive safeguard to control the plants safety. The mitigation of an explosion hazard, according to the ATEX 137 Directive (1999/92/EU), requires, among other things, the assessment of the dust ignition sensitivity. PRISME laboratory (University of Orléans) has developed an experimental set-up and methodology, using the Langlie test, for the quick determination of the explosion sensitivity of dusts. This method requires only 20 shots and ignition sensitivity is evaluated through the E50 (energy with an ignition probability of 0.5). A Hartmann tube, with a volume of 1.3 l, was designed and built. Many results on the energy ignition thresholds of partially oxidised previous termaluminiumnext term were obtained using this experimental device (Baudry, 2007) and compared to literature. E50 evolution is the same as previous MIE but their respective values are different and previous MIE is lower than E50 however the link between E50 and previous MIE has not been elucidated. In this paper, the Langlie method is explained in detail for the determination of the parameters (mean value E50 and standard deviation σ) of the associated statistic law. The ignition probability versus applied energy is firstly measured for Lycopodium in order to validate the method. A comparison between the normal and the lognormal law was achieved and the best fit was obtained with the lognormal law. In a second part, the Langlie test was performed on different dusts such as previous aluminium, cornstarch, lycopodium, coal, and PA12 in order to determine E50 and σ for each dust. The energies E05 and E10 corresponding respectively to an ignition probability of 0.05 and 0.1 are determined with the lognormal law and compared to previous MIE find in literature. E05 and E10 values of ignition energy were found to be very close and were in good agreement with previous MIE in the literature

Full scale test for explosion water barriers in small cross-section galleries

Underground coal mines explosions generally arise from the inflammation of a methane/air mixture. This explosion can also generate a subsequent coal dust explosion. Traditionally such explosions have being fought eliminating one or several of the factors needed by the explosion to take place. Although several preventive measures are taken to prevent explosions, other measures should be considered to reduce the effects or even to extinguish the flame front. Unlike other protection methods that remove one or two of the explosion triangle elements, namely; the ignition source, the oxidizing agent and the fuel, explosion barriers removes all of them: reduces the quantity of coal in suspension, cools the flame front and the steam generated by vaporization removes the oxygen present in the flame. Passive water barriers are autonomous protection systems against explosions that reduce to a satisfactory safety level the effects of methane and/or flammable dust explosions. The barriers are activated by the pressure wave provoked in the explosion destroying the barrier troughs and producing a uniform dispersion of the extinguishing agent throughout the gallery section in quantity enough to extinguish the explosion flame. Full scale tests have been carried out in Polish Barbara experimental mine at GIG Central Mining Institute in order to determine the requirements and the optimal installation conditions of these devices for small sections galleries which are very frequent in the Spanish coal mines. Full scale tests results have been analyzed to understand the explosion timing and development, in order to assess on the use of water barriers in the typical small crosssection Spanish galleries. Several arrangements of water barriers have been designed and tested to verify the effectiveness of the explosion suppression in each case. The results obtained demonstrate the efficiency of the water barriers in stopping the flame front even with smaller amounts of water than those established by the European standard. According to the tests realized, water barriers activation times are between 0.52 s and 0.78 s and the flame propagation speed are between 75 m/s and 80 m/s. The maximum pressures (Pmax) obtained in the full scale tests have varied between 0.2 bar and 1.8 bar. Passive barriers protect effectively against the spread of the flame but cannot be used as a safeguard of the gallery between the ignition source and the first row of water troughs or bags, or even after them, as the pressure could remain high after them even if the flame front has been extinguished

Simplified modelling of explosion propagation by dust lifting in coal mines

Dispersion of accumulated layers of combustible dust by turbulent flow or shock waves ahead of the propagating flame may sustain explosion propagation in coal mine galleries and other industrial facilities. The mechanisms involved in transforming dust layers into dust suspensions are rather complex, and detailed numerical modelling of this process is therefore practically impossible, at least on industrial scales. In the computational fluid dynamics code DESC (Dust Explosion Simulation Code), a simplified empirical relation describes the dust-lifting phenomenon. The relation originates from experimental work in a laboratory-scale shock tube, and a small wind tunnel, at Warsaw University of Technology. The present paper describes the modelling of dust lifting in the current version of DESC, and illustrates the performance of the code by simulating some large-scale dust explosion experiments conducted in a 100-m surface gallery at the Experimental Mine Barbara in Katowice, Poland. Although there are significant uncertainties associated with this type of calculations, the results suggest that a simplified approach to dust lifting may become a useful tool for risk assessments in the future.publishedVersio

Magnetic switching of nanoscale antidot lattices

We investigate the rich magnetic switching properties of nanoscale antidot lattices in the 200 nm regime. In-plane magnetized Fe, Co, and Permalloy (Py) as well as out-of-plane magnetized GdFe antidot films are prepared by a modified nanosphere lithography allowing for non-close packed voids in a magnetic film. We present a magnetometry protocol based on magneto-optical Kerr microscopy elucidating the switching modes using first-order reversal curves. The combination of various magnetometry and magnetic microscopy techniques as well as micromagnetic simulations delivers a thorough understanding of the switching modes. While part of the investigations has been published before, we summarize these results and add significant new insights in the magnetism of exchange-coupled antidot lattices.Web of Science775073

Properties of magnetic vortices at elevated temperatures

Thermal properties of steady-state magnetic vortices in soft materials are numerically evaluated using the recently proposed Landau-Lifshitz-Bloch approach. Circular samples with permalloy-like parameters are simulated. Relevant properties of the vortex core, as its radius, the magnetization drop in its center, and the radius of this magnetization drop are extracted. The dependence of the vortex core radius on temperature agrees well with the theoretical predictions, if only temperature-dependent parameters are taken into account. A new effect is found, which we call magnetization squeezing, resulting from the thermodynamic nature of the Landau-Lifshitz-Bloch approach. Our results show, however, that this squeezing in vortices is a rather weak effect in permalloy

Palność olejów i smarów

Oleje i smary, jako substancje organiczne, w określonych warunkach reagują z tlenem atmosferycznym, stwarzając zagrożenie pożarem, a nawet wybuchem. Zjawiska takie są rzadkie, ale należy przestrzegać pewnych elementarnych reguł bezpieczeństwa. Artykuł przedstawia: ogólne pojęcia palności i wybuchowości par cieczy wraz z opisem parametrów je charakteryzujących; miejsce olejów w klasyfikacji pożarów (klasa F); opisy zaistniałych pożarów.Oils and lubricants, being organic substances react with oxygen giving fire or even explosion in the determined circumstances. Paper presents: general notions of flammability and explosibility of liquid’s vapors with their characterizing parameters; place of oils and fats in the fire classification (F class); description of fire events involving oil and fats