Minimum Explosible Concentration Research Articles

CFD Simulations of the Effect of Dust Diameter on the Dispersion in the 20 L Bomb

Prevention and mitigation measures for dust explosion are based on the knowledge of the thermokinetic parameters which characterise flammability such as Minimum Explosible Concentration, MEC, and explosion behaviour such as maximum explosion pressure, PMAX, and deflagration index, KSt. Measurements of these parameters are performed in spherical vessels (20 L sphere or 1 m 3 sphere). The main issues in performing such measurements are related to the dust dispersion and to the turbulence level reached inside the sphere. Also, the dispersion and then concentration of the dust/air mixture in the vessel significantly affects the flame propagation, if stratification and sedimentation occurs. In this work we use a previously validated CFD 3D model to simulate the dust dispersion inside the sphere at different dust diameters. Results show that on increasing the dust diameter the dust is mainly concentrated at the vessel walls and the dust paths are different from those of the fluid flow.

Experimental investigation of the complex deflagration phenomena of hybrid mixtures of activated carbon dust/hydrogen/air

This paper aims to develop quantitative insights based on measured deflagration parameters of hybrid mixtures of activated carbon (AC) dust and hydrogen (H2) gas in air. The generated experimental evidence is used to reject the claim of the null hypothesis (H0) that severity of deflagrations of H2/air mixtures always bound the severity of deflagrations of heterogenous combustible mixtures of AC dust/H2/air containing the same H2 concentrations as in the H2/air binaries. The core insights of this investigation show that the maximum deflagration pressure rise (ΔPMAX) and maximum rate of pressure rise ((dP/dt)MAX) of this hybrid mixture are greater than those corresponding to deflagrations of H2/air mixtures for all the dust and H2 concentrations being examined. The deflagration severity indices (KSt and ES) of the hybrid mixture containing 29 mol% H2 are found to be greater than those of the H2/air mixture containing 29 mol% H2. Also, the minimum explosible concentration (MEC) of the hybrid mixture is lower than that of the AC dust in air only. The insights gained should lead to better realization of the severity of a postulated safety-significant accident scenario associated with on-board cryoadsorption H2 storage systems for fuel-cell (FC) powered light-duty vehicles. The identified insights could also be relevant to other industrial processes where combustible dusts are generated in the vicinity of solvent vapors. Moreover, these insights should be useful for supporting quantitative risk assessment (QRA) of on-board H2 storage systems, designing improved safety measures for cryoadsorption H2 storage tanks, and guiding H2 safety standards and transportation regulations.

The development of an experimental method for the determination of the minimum explosible concentration of biomass powders

Biomass powders, in both raw and thermally treated (torrefied) form, are used in 100% biomass fired or in coal co-fired plants for power generation. They pose significant fire and explosion risks during storage, handling, processing and combustion, and therefore their explosibility characteristics need to be assessed for the design of safe systems and operations. Wood biomass powders are difficult to characterise for explosibility through standard methods because of their bulky and fibrous nature. This has resulted in the lack of reliable data on the explosibility of these materials. In this study we present a new methodology – with example measurements – for the determination of the minimum explosible concentrations (MECs) of raw and torrefied wood biomass powders, using a modified Hartmann tube. This equipment can also be used as a fast screening tool for the determination of other reactivity parameters, such as flame speeds and rates of pressure rise, through which the most reactive mixture can be identified for more detailed measurements in the larger ISO 1 m3 vessel. MEC measurements reported in this paper showed that both raw and torrefied pulverised wood biomass, were explosible at equivalence ratios as low as 0.2. This was one-third (1/3) the corresponding concentration for Kellingley coal (measured with the same method). Flame speeds 5–10 times higher than those of coal were measured for biomass. Flame speed differences will also have a direct effect on burner performance and flame stability for systems originally designed to burn coal and now firing biomass without modifications.

Evaluation of Flame Stability for Development of Pulverized Coal Fired Burners by Using a Japanese Industrial Standard Method (JIS Z8818 ; Test Method for Minimum Explosible Concentration of Combustible Dusts)

Evaluation of Flame Stability for Development of Pulverized Coal Fired Burners by Using a Japanese Industrial Standard Method (JIS Z8818 ; Test Method for Minimum Explosible Concentration of Combustible Dusts)

Mg-Al합금 분진의 폭발특성에 미치는 마그네슘 성분의 영향

Mg-Al합금 분진의 마그네슘 성분 비율이 분진폭발특성에 미치는 영향을 알기 위하여 Siwek 20 L 구형 분진폭발시험장치를 사용하여 농도를 변화시키면서 실험적으로 조사하였다. 이를 위하여 체적평균입경이 <TEX>$151{\sim}160{\mu}m$</TEX>의 Mg-Al합금 분진을 사용하였다. 그 결과 Mg-Al합금에서의 Mg성분의 증가는 폭발하한농도의 감소와 최대폭발압력의 증가로 나타났다. 또한 Mg-Al합금의 최대폭발압력과 최대폭발압력상승속도는 주로 분진 농도에 의존하였다. 그러나 Mg-Al (40:60 wt%), Mg-Al (50:50 wt%) 및 Mg-Al (60:40 wt%)의 폭발지수(Kst)에 있어서, 마그네슘 성분의 증가에 따라서 폭발지수가 증가함을 알 수 있었다. Using the Siwek 20 L spherical explosion vessel, the explosion properties have been examined to understand the influence of magnesium content in Mg-Al alloy dusts with different concentration. For this purpose, the Mg-Al alloy dusts (volume mean diameter : <TEX>$151{\sim}160{\mu}m$</TEX>) with magnesium content ratio were used. As the results, the increase of Mg content in Mg-Al alloy causes an decreased minimum explosion concentration and an increased maximum explosion pressure. Also the maximum explosion pressure and maximum rate of pressure rise in Mg-Al alloy dusts mainly depended on the dust concentrations. However, for the explosion index (Kst) of Mg-Al (40:60 wt%), Mg-Al (50:50 wt%) and Mg-Al (60:40 wt%), it was founded to increase the Kst with increasing of magnesium content ratio.

Study on the influence of material thermal characteristics on dust explosion parameters of three long-chain monobasic alcohols

Sensitivity and severity parameters are critical for risk assessment and safety management of dust explosions. In this paper, to reveal the effects of material thermal characteristics on dust explosions parameters during monobasic alcohols dust explosions, three long chain monobasic alcohols, being solid at room temperature and similar in physical–chemical properties, were chosen to carry out experiments in different functional test apparatus according to the internationally accepted ASTM standards. As a result, it was found that the material thermal characteristics strongly affected these basic explosive parameters. On the one hand, for the sensitivity parameters, Minimum Ignition Temperature, Minimum Ignition Energy and Electrical Resistivity were the highest in the Eicosanol dust cloud, while Minimum Explosible Concentration in this cloud was the lowest. On the other hand, for severity parameters, Maximum Explosion Pressure in Eicosanol dust cloud always maintained the highest values as varying the dust concentrations. In contrast, Deflagration Index showed a complex trend.

Experimental determination of dust cloud deflagration parameters of selected hydrogen storage materials: Complex metal hydrides, chemical hydrides, and adsorbents

This paper discusses the results of an experimental program carried out to determine dust cloud deflagration parameters of selected solid-state hydrogen storage materials, including complex metal hydrides (sodium alanate and lithium borohydride/magnesium hydride mixture), chemical hydrides (alane and ammonia borane) and activated carbon (Maxsorb, AX-21). The measured parameters include maximum deflagration pressure rise, maximum rate of pressure rise, minimum ignition temperature, minimum ignition energy and minimum explosible concentration. The calculated explosion indexes include volume-normalized maximum rate of pressure rise (KSt), explosion severity (ES) and ignition sensitivity (IS). The deflagration parameters of Pittsburgh seam coal dust and Lycopodium spores (reference materials) are also measured. The results show that activated carbon is the safest hydrogen storage media among the examined materials. Ammonia borane is unsafe to use because of the high explosibility of its dust. The core insights of this contribution are useful for quantifying the risks associated with use of these materials for on-board systems in light-duty fuel cell-powered vehicles and for supporting the development of hydrogen safety codes and standards. These insights are also critical for designing adequate safety features such as explosion relief venting and isolation devices and for supplementing missing data in materials safety data sheets.

Dust explosion risk moderation for flocculent dusts

The research presented in this paper is focused on dust explosions of coarse and fine flocculent (or fibrous) samples of wood and polyethylene. Hybrid mixtures of fibrous polyethylene and admixed ethylene were also studied. Experimentation was conducted by following standardized test procedures and using standardized apparatus for determination of maximum explosion pressure, size-normalized maximum rate of pressure rise, minimum explosible concentration, minimum ignition energy, and minimum ignition temperature. A general trend was observed of enhanced explosion likelihood and consequence severity with a decrease in material diameter, as well as enhanced consequence severity with admixture of a flammable gas to the combustion atmosphere. The same phenomena are well-established for dusts composed of spherical particles; this highlights the importance of inherently safer design and the principle of moderation in avoiding the generation of fine sizes of flocculent dusts and hybrid mixtures of such materials with flammable gases.In addition to presenting experimental findings, the paper describes phenomenological modelling efforts for the flocculent polyethylene using four geometric equivalence models: radial equivalence, volumetric equivalence, surface area equivalence, and specific surface area equivalence. The surface area equivalence model was found to yield the best estimates of maximum rate of pressure rise for the flocculent polyethylene samples investigated experimentally.

When solids meet solids: A glimpse into dust mixture explosions

Mixing an inert solid or a less flammable compound with a combustible dust can be regarded as a direct application of the inherent safety principle of moderation. An experimental investigation was carried out to determine the evolution of the ignition sensitivity and the explosion severity of such various mixtures as a function of their compositions. It demonstrates that the introduction of small amounts of highly combustible powders (such as sulphur or nicotinic acid) to a less flammable dust (such as microcrystalline cellulose or carbon black) can strongly influence the ignition sensitivity as well as the explosion severity.It has notably been shown that the ignition sensitivity of solid/solid mixtures significantly rises up when only 10–5%wt. of highly flammable dust is introduced. Simple models can often be applied to estimate the minimum ignition energy, minimum ignition temperature and minimum explosive concentration of such mixtures. Concerning the dust explosivity, three cases have been studied: mixtures of combustibles dusts without reaction, dusts with reactions between the powders, combustible dusts with inert solid. If the evolution of the maximum explosion pressure can be estimated by using thermodynamic calculations, the maximum rate of pressure rise is more difficult to predict with simple models, and both combustion kinetics and hydrodynamics of the dust clouds should be taken into account. These results were also extended to flammable dust/solid inertant mixture. They clearly show that the concentration of solid inertant at which the ignition is not observed anymore could reach 95%wt. As a consequence, the common recommendation of solid inertant introduction up to 50–80%wt. to prevent dust explosion/ignition should be reconsidered.

A critical evaluation of combustible/explosible dust testing methods – Part 1

Tests were conducted by the Center for Agricultural Air Quality Engineering and Science (CAAQES) and by Safety Consulting Engineers Inc. (SCE) to determine if dust found in cotton gins (gin dust) would serve as fuel for dust explosions. In other words, is gin dust explosible? The laboratory tests used by CAAQES and SCE are very different. SCE used a totally enclosed 20 liter (L) chamber, flame from a 10,000 J (10 kJ) ignition source, reported that gin dust was a class ‘A’ explosible dust. CAAQES used a 28.3-L (1 ft3) chamber with diaphragm, a stationary coil as the igniter, video and pressure recordings of each test and concluded that gin dust was not explosible. SCE followed the protocols specified by ASTM E1226 and E1515. The only indicator used to determine whether a deflagration occurred during a test was pressure. If the pressure rise exceeded one bar gage (g) in a 20-L chamber test with a flame from a 10 kJ energy source as the igniter, it was assumed that a deflagration occurred in the chamber and the dust was classified as explosible (ASTM E1226-05, 2005). The CAAQES criterion for determining if a dust was explosible consisted of determining the minimum explosive concentration (MEC). If the MEC existed using the CAAQES test system, it was explosible! The criteria used with the CAAQES method for determining the MEC was to test concentrations starting at concentrations above the MEC and lowering the concentrations until at least one of the three tests at that concentration failed to result in a deflagration. The indicators of a deflagration were (1) bursting of a diaphragm, (2) flame front leaving the chamber and (3) characteristic pressure vs. time curve.It was concluded that the ASTM method of using only pressure as the indicator of a deflagration in a totally enclosed chamber would likely result of an “over-driven” test and an incorrect finding that gin dust was explosible. The result of CAAQES testing was that gin dust was not explosible.

Review of the Explosibility of Nontraditional Dusts

This paper explores the explosion characteristics of three nontraditional dusts: nanomaterials, flocculent materials, and hybrid mixtures. Nanomaterials have a high likelihood of explosion with minimum ignition energies potentially less than 1 mJ. These low ignition energies may therefore allow nanomaterials to ignite due to electrostatic sparks, collision, or mechanical friction. The severity of nanomaterial explosions is affected by agglomeration and coagulation of the particles. Flocculent materials with a high length-to-diameter ratio exhibit explosion behavior patterns similar to those for spherical dusts. The length of flocculent particles plays a role in explosion likelihood which is not yet fully understood. High voltage discharge during the electrostatic flocking process is a common flocculent ignition hazard. Hybrid mixtures of a combustible dust and a flammable gas/vapor display a higher explosion severity and a lower minimum explosible concentration than that of the dust alone. Violent hybrid explosions may occur even if the dust and the gas/vapor are below their respective lean limit concentrations.

An Extensive Discussion on Experimental Test of Dust Minimum Explosible Concentration

An extensive investigation on experimental test of dust minimum explosible concentration (MEC) was carried out by using the Siwek 20 L vessel. Systematic data were reported on the MEC of various dusts and the influences of ignition energy, dust calorific value, moisture content and particle size were taken into account. It is found that the overly low or high ignition energy will result in unrealistic MEC results. To reliably measure MEC, the experimental tests should be preformed under the condition that the test result is independent of ignition energy. For the Siwek 20 L vessel, the 4-6 kJ is the most appropriate energy ranges to determine the MEC of various dusts. The more incombustible component contained in lower calorific value dust acts as a thermal sink in the ignition and heating process of dust cloud, and therefore, the higher MEC can be found in the MEC measurement of lower calorific value dust. Moreover, due to the notable dust agglomeration, to validly measure MEC, the moisture content of test dust should not exceed 10 wt %. When the moisture content is lower than 10wt %, the MEC smoothly increases with the rise of moisture content. With the decrease of particle size, the measured MEC becomes lower, and the MEC has an approximate linear relation with particle size. The results reported in this work provide the experimental basis and data guidance for the prevention and evaluation of dust explosion risk.

Research on Characteristic Parameters of Coal-dust Explosion

The parameters of explosive characteristics of the coal-dust are assessed systematically with the test device of minimum ignition temperature of dust clouds and 20L sphere explosion test units. The minimum ignition temperature of dust is a main safety index when handling combustible dusts in industrial production, and while hazard evaluation, the maximum explosion pressure and the explosion index are key parameters. Five kinds of coal-dust with different particle diameters were tested in order to determine the temperature sensitivity and the ferocity under the given conditions, which can be used as the criteria to classify dust explosion hazards. The experiment results indicate that the minimum ignition temperature of coal-dust cloud reduces with the decrease of particle diameter under temperature of (293±5) K and powder spraying pressure of 0.08MPa, and when the particle size reduces to (25-48) μm, the minimum ignition temperature is between (793-803)K; Besides that, the results can also show that minimum explosive concentration of coal-dust cloud is between 20 gam-3 and 30 gam-3under temperature of (293±5) K, powder spraying pressure of 2MPa and ignition energy of 10kJ, the maximum explosion pressure is 0.45MPa and the maximum explosion index is 11.14 MPaamas-1, which classifies coal-dust explosion hazards to Level I. The conclusions drawn from the experimental results are of great significance to the safe application of these combustible substances.

Experimental investigation of dust MEC measurement

The minimum explosible concentration (MEC) is a crucial parameter in dust explosion evaluation and prevention. The standardized method currently used to determine the MEC relies on the measurement of explosion pressure Pm and the test results are strongly affected by dust dispersion behaviors. To investigate this effect, systematical experiments were performed for coal dust explosion in the Siwek 20-liter sphere. It is found that the measured values of Pm are apparently dependent on the ignition delay time tig because of the time-dependence of dust dispersion behaviors. For the dust with a given mass concentration and size distribution, there always exists an optimal ignition delay time tig,opt at which the Pm will reach its maximum value, Pmax, and a slight deviation of tig from the tig,opt may cause the measured Pm to be obviously lower than the Pmax. To reliably determine the MEC, the tig,opt should be adopted in the test, rather than the fixed tig of 60ms as prescribed by IEC, otherwise, the resultant MEC may be overestimated. Based on the analysis of flame propagation in dust cloud, an alternative method by using combustion duration time tcom is proposed to determine the MEC. Analysis for experimental data shows that the values of MEC determined by using tcom are basically consistent with those obtained by using Pm at the tig,opt, but less affected by the tig, since the sensitivity of the tcom to the tig is much less than that of the Pm.

Ignition sensitivity of gas–vapor/dust hybrid mixtures

The explosion sensitivity of various gas or vapor/dust mixtures has been studied thanks to specifically modified apparatuses based on a 20L sphere and a Hartmann tube. Experiments have shown that concentration of gas/vapors as low as 1% vol. causes a significant decrease of the minimum ignition energy and induces changes in the rate-limiting step of the combustion reaction, from boundary diffusion to homogeneous gas phase reaction. They also confirm that a hybrid mixture explosion is possible even when both dust and vapor concentrations are respectively lower than their minimum explosion concentration and lower explosivity limit. Comparisons have been done between our experimental data and classical models such as those developed by Bartknecht or Le Chatelier. It appears that these laws are not always conservative from a safety point of view. The influences of the diameter, of the adiabatic flame temperatures and of the critical ignition kernel, directly related to the quenching distance, have also been highlighted. This work demonstrates the peculiar behavior of gas or vapor/dust explosions and proposes simple models in order to estimate their ignition sensitivity.

The mass loading monitor—fundamental principles and proof of concept

The operating principle, and proof-of-concept data, for a physical device (the mass loading monitor) to alert plant operators when airborne dust approaches the minimum explosive concentration (MEC) level are presented. The MEC, stated as g m−3, is dependent upon the material and environmental factors. Values as low as 30 g m−3 must be evaluated. The measurement strategy, a temporal integration of the piston face pressure as the air-plus-dust charge is impulsively expelled from a cylinder compared with the same integral for an air-only sample, is shown to yield the mass loading (xx g m−3) of the airborne dust. This measurement strategy is demonstrated using a dedicated test apparatus. This demonstration establishes the proof of concept.

Imperial sugar refinery combustible dust explosion investigation

AbstractOn February 7, 2008, at about 7:15 p.m., a series of sugar dust explosions at the Imperial Sugar manufacturing facility in Port Wentworth, GA, resulted in 14 worker fatalities. Thirty‐six workers were treated for serious burns and injuries—some caused permanent, life‐altering conditions. The explosions and subsequent fires destroyed the sugar packing buildings, palletizer room, and silos, and severely damaged the bulk train car loading area and parts of the sugar refining process areas.The Imperial Sugar manufacturing facility housed a refinery that converts raw cane sugar into granulated sugar. A system of screw and belt conveyors and bucket elevators transported granulated sugar from the refinery to three 105‐foot tall sugar storage silos. Granulated sugar was then transported through conveyors and bucket elevators to specialty sugar processing areas and granulated sugar packaging machines. Sugar products were packaged in a four‐story building surrounding the silos that contained packaging machines for the sugar products. Granulated sugar was also bulk shipped in railcars and tanker trucks in the bulk sugar loading area.The U.S. Chemical Safety and Hazard Investigation Board (CSB) determined that the first dust explosion occurred in the enclosed steel belt conveyor located below the sugar silos. Steel cover panels installed on the belt conveyor less than a year before the explosion allowed explosive concentrations of sugar dust to accumulate inside the enclosure. An unknown source ignited the sugar dust, causing a violent explosion. The explosion lofted sugar dust that had accumulated on the floors and elevated horizontal surfaces, propagating more dust explosions through the buildings. Secondary dust explosions occurred throughout the packing buildings, parts of the refinery, and the bulk sugar loading buildings. The pressure waves from the explosions heaved thick concrete floors and collapsed brick walls, blocking stairwell and other exit routes. The resulting fires destroyed the packing buildings, silos, palletizer building and heavily damaged parts of the refinery and bulk sugar loading area.The CSB investigation identified the following incident causes: Sugar and cornstarch conveying equipment was not designed or maintained to minimize the release of sugar and sugar dust into the work area. Inadequate housekeeping practices resulted in significant accumulations of combustible granulated and powdered sugar and combustible sugar dust on the floors and elevated surfaces throughout the packing buildings. Airborne combustible sugar dust accumulated above the minimum explosible concentration inside the newly enclosed steel belt assembly under silos 1 and 2. An overheated bearing in the steel belt conveyor most likely ignited a primary dust explosion. The primary dust explosion inside the enclosed steel conveyor belt under silos 1 and 2 triggered massive secondary dust explosions and fires throughout the packing buildings. Accumulated sugar dust and spilled sugar fueled the secondary explosions and fires. All 14 fatalities were the result of these secondary events. This article presents the CSB investigation and discusses important management practices to prevent similar combustible dust explosions. Published 2011 American Institute of Chemical Engineers Process Saf Prog, 2011

Explosion Characteristics of Aluminum Nanopowders

In 2005, an investigation conducted on three nanoscale attrition millers in Taiwan revealed that all three had undergone metal nanopowder explosions in the past. This research was aimed at determining the relationships between the particle diameter of an aluminum nanopowder and its maximum explosion pressure (Pmax), maximum rate of pressure rise ((dP/dt)max), minimum explosion concentration (MEC), and minimum ignition energy (MIE) by 20 liter apparatus and 1.2-L Hartmann apparatus. The results revealed that 35-nm aluminum powder has a Pmax of 7.3 bar and deflagaration index (KSt) of 349 bar•m/s, in 100-nm aluminum powder, Pmax of 12.5 bar and KSt of 296 bar•m/s and 40-μm aluminum powder, Pmax of 5.9 bar and KSt of 77 bar•m/s. The value of (dP/dt)max for the 35-nm aluminum powder is 4.5 times that for the 40-μm aluminum powder. The 35-nm, 100-nm, and 40-μm powders have MEC values of 40, 50, and 35 g/m3, respectively. The 35-nm and 100-nm powders both have MIEs less than 1 mJ, while the 40-μm powder has an MIE of 59.7 mJ.

Hazard assessment of complex hydrides as hydrogen storage materials

Hydrogen storage materials containing NaAlH4, LiNH2, Mg(NH2)2, LiH and LiBH4 were subjected to standardized safety tests in order to assess the potential hazards caused by the environmental exposure of these materials. All the materials were judged ‘flammable’, ‘pyrophoric’ and ‘water-reactive’, resulted in being classified as the United Nations Packing Group I, the most stringent category of container regulations in transporting these materials. A small spark energy (1.4 mJ) can trigger an intense dust cloud explosion of the Mg(NH2)2 + LiH system of which the minimum explosive concentration was determined to be 90 mg dm−3. Although this value is lower than those of the hydrogen storage alloys, the minimum explosive concentration of complex hydrides can be comparable to the alloys if expressed in terms of the amount of stored hydrogen in the material. Also examined was the eruption test, a non-standard test, in which the sample powder was pushed out of a container into the atmosphere by pressurized H2. Despite the pyrophoricity, we observed only one explosion of the Ti-doped NaAlH4 in dozens of trials using all the materials. A comparison with other materials points to the inevitability of more cautious measures than metal hydrides when handling these complex hydrides.

Explosions of vapour/dust hybrid mixtures: A particular class

The aim of this work is to demonstrate the particular aspects of the explosion of hybrid mixtures with respect to either vapour or dust explosions. This work is focused on pharmaceutical products from excipients to active drug substances and their associated solvents. Experiments with an explosion sphere has been used to determined the influence of dusts and vapours concentrations on the severity of explosions (maximum pressure P max and maximum rate of pressure rise (d P/d t) max). Results clearly show that the explosion behaviour of such hybrid mixtures reveals significant differences with respect to either vapour or dust explosions; especially a promotion effect on the combustion kinetics and on the rate of pressure rise for poor mixtures. The influences of the introduction of small amount of vapour on the minimum explosible dust concentration (MEC) and of dust addition on the lower explosion limit (LEL) are noteworthy.