There is no applicable existing standard for the determination of safety characteristics for hybrid mixtures. While developing a new standard in a joint research project in Germany first results from parameter studies led to a standard procedure that can be adopted by laboratories that are already testing dusts in the so called 20L-sphere with as little additional effort as necessary. In fact, one of the main objectives of this research project was to keep modifications and adjustments from the generally accepted dust testing procedures as easy and minimal as possible so as to limit potential deviations from one laboratory to another. In this first round robin test on hybrid mixtures ever, with methane as gas component and a specific corn starch as dust sample, the practicality of the whole procedure, the scattering of the results and the deviation between the testing apparatuses is investigated. This paper summarizes the experimental procedure adopted and objectives of the first round-robin phase involving three of the four original German companies, plus volunteering laboratories from Australia, Belgium, Czech Republic, France, Poland and P.R. China. The results will have an impact on the new standard and may lead to robust data for later simulation purposes.

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Many industrial processes handle, use, or produce metallic particles small enough to explode in air, thus posing severe explosion hazards. Finishing operations, for example, create very fine particles and have been involved in a growing number of accidents in recent years. New emerging processes, such as 3D printing, are being rapidly developed and directly use micrometric particles to create complete objects by welding layers of material together. Finely divided metals also enter into the composition of plastics, rubber, fibers, paints, coatings, inks, pesticides, detergents, and even drugs; additionally, they are used as catalysts for major industrial chemical reactions, and are even being explored as possible clean alternatives to fossil fuels. Metal dusts are of special concern due to their peculiar combustion properties, including their higher heat of combustion and pyrophoric nature,. As a result, metal dusts explosions are often much more devastating than explosions involving organic materials. Additionally, due to their high reactivity, many fine and most ultra-fine metal powders can burn in carbon dioxide, water vapor and even nitrogen. Whereas preventive measures may reduce explosion risks efficiently, they rarely are sufficient to eliminate explosions completely, especially when dealing with highly reactive metallic particles. Therefore explosion protection measures usually also need to be considered. The high energetic content of metal dusts poses new challenges to conventional explosion protection systems in terms of robustness and response time. This paper reviews the special hazards of metal dusts and presents the state-of-the-art in terms of explosion protection.

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The Chemical-Engineering model describes how the synergetic combination of chemical and engineering factors determines gas, particulate, and hybrid explosion behavior. Explosion behavior is expressed as explosion sensitivity (e.g. probability of explosion), explosion severity (e.g. adverse effects of explosion), and explosion types (deflagration or detonation). Chemical factors are ranked using NFPA methodology. Engineering includes whether explosion occurs in open or enclosed spaces, equipment shape/size, and initial T, p, and flow conditions. The model is semi-quantitative; its virtues are its unique integration of chemical and engineering factors in determining explosion risk, its didactic qualities, provision of insight, and practical utility to engineers who are not experts in combustion science.

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In facilities handling combustible dusts, the isolation of propagating deflagrations requires great attention due to the potential catastrophic consequences of secondary dust explosions. While the ability of dust explosions to propagate is widely recognized, some misconceptions still exist. One of the common myths is that a dust explosion cannot propagate through small diameter pipes and that explosion isolation may not be required in that case. This article first presents a simplified theory of flame propagation in pipes. Dust explosion experiments performed in industrial-scale pipes smaller or equal to 4 in (or 100 mm) in diameter are then reviewed. The findings of the experiments are interpreted in the light of the simplified theory. Our study reveals that dust explosion propagation has been consistently observed in pipes with a diameter as small as 1 in. While the likelihood of flame propagation seems to decrease with pipe diameter and other “chemical” and “engineering” factors, it remains a realistic scenario and therefore should be addressed in the design and operation of powder handling systems.

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Metal dust deflagrations have become increasingly common in recent years. They are also more devastating than deflagrations involving organic materials, owing to metals' higher heat of combustion, rate of pressure rise, explosion pressure and flame temperature. Aluminum finishing operations offer a particularly significant hazard from the very small and reactive aluminum particles generated, and thus require high attention to details of operation and explosion safety management. This paper presents available statistics on metal dust explosions and studies the specific explosion hazards of aluminum finishing operations. The analysis of seven case studies shows that the proper design, monitoring and maintenance of dust collection systems are particularly important. Furthermore, the isolation of deflagrations occurring in dust collection systems, as well as good housekeeping practices in buildings, are critical safeguards to avoid the occurrence of catastrophic secondary explosions.

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Dust explosibility is traditionally described by two parameters, namely the maximum explosion pressure, P_max, and the deflagration index, K_St, usually determined through testing in a closed, pressure-resistant spherical vessel, either 20 L or 1 m³ in volume. These parameters constitute key variables in the design of explosion protection systems, such as venting, suppression or isolation systems. The potential for overdriving dust combustion with pyrotechnical igniters in the 20-l sphere has been recognized, discussed and analyzed for many years, notably in the determination of the minimum explosible and limiting oxygen concentrations, which has led to specific guidelines regarding the ignition source strength in ASTM standards. The current paper presents new experimental evidence that the energy provided by pyrotechnical igniters may, in some instances, physically alter the dust being tested in the 20-l sphere. K_St values can be several times greater in the small vessel compared to those measured in the 1-m³ chamber. Further visual evidence is provided to show that high energy ignition can produce a turbulent flame region, possibly consisting of a hybrid mixture of flammable gas (or vapor) and dust, which can propagate faster than the corresponding pure dust. The experiments suggest that K_St values measured in the 20-l sphere may no longer be representative of a dust deflagration in a real process environment. We recommend additional tests in a 1-m³ chamber when a dust exhibits a low flash point, or when it's K_St is above 300 bar m/s in the 20-l sphere.

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Fires and explosions are a major cause of property damage and injuries around the world. The rapid injection of sodium bicarbonate solid particles is one of the techniques used to suppress or prevent the propagation of explosions in industrial facilities. The current study investigates the effect of sodium bicarbonate on the laminar and turbulent burning velocities of hybrid fuel mixtures which combine gas phase and solid phase fuels using a steady state Bunsen burner style apparatus. The hybrid flame in this work has a methane-air gas phase equivalence ratio of one and iron dust concentrations ranging from 25 g/m3 to 100 g/m3. Sodium bicarbonate concentrations added to the hybrid flame range from 25-75 g/m3. Turbulent intensities range from 0.65 m/s to 0.72 m/s. When the sodium bicarbonate enters the flame zone it acts as both a heat sink and a source of carbon dioxide and water. At the higher concentrations of sodium bicarbonate both reduction in the burning velocity and extinguishment of the hybrid flame is seen over a range of turbulent intensities.@en

The complexity of domino scenarios represented a considerable obstacle to the quantitative assessment of risk posed by escalation events. In the present chapter, the state of the art concerning quantitative approaches proposed for the assessment of risk caused by domino accidents is summarized. A procedure for the quantitative risk assessment of domino accidents, suitable for the calculation of individual and societal risk indexes, is outlined. Alternative approaches proposed for the quantitative assessment of domino effects, based on Bayesian techniques and Monte Carlo simulations, are also described.

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