Explosion Severity Research Articles

The effect of particle size polydispersity on the explosibility characteristics of aluminum dust

This paper reports experimental results elucidating the effect of particle size polydispersity (σD) on the explosion severity of aluminum dust. Five mixtures with a median diameter (D50) of 15μm and σD values of 0.95, 1.17, 1.48, 1.87, and 2.51, were systematically prepared by mixing original aluminum samples having narrow size distributions. The explosion severity of each sample was determined in a 36L dust explosion vessel by measuring the maximum pressure (Pmax), the maximum rate of pressure rise ((dP/dt)max), and the deflagration index (KSt). Interestingly, we found that values of Pmax and KSt revealed an increase in explosion severity as σD increases, where the latter presented a more dramatic effect due to the contribution of fine particles on the combustion kinetics. The effect of dust concentration on the explosion propagation was analyzed comparing the time span to reach (dP/dt)max, (τ), during a dust explosion. τ was obtained from the experimental pressure traces of the original samples and their mixtures. The values of Pmax and KSt were plotted as a function of the median diameter (D50) and the volume- (D4,3) and surface- (D3,2) weighted mean diameter. We observed that D3,2 provided a better description of the average sample size and D50 is inadequately related to the real hazard potential of aluminum dust. Therefore, we suggest that the explosion hazard characterization of these types of materials should be reported in terms of D3,2 and σD.

Approach determining maximum rate of pressure rise for dust explosion

The risk assessment requires the knowledge of dust explosion hazard data. Maximum rate of pressure rise is an important parameter of explosion severity characteristics. Its accuracy depends on the experimental conditions and the approach determining maximum rate of pressure rise. Previous method determining maximum rate of pressure rise is to draw a tangent on pressure time history profile and the tangent is approximated maximum rate of pressure rise, which has a poor repeatability and great error. This paper presents a new method used to calculate the rate of pressure rise for dust explosion which is called Recursive Fitting Method (RFM). Compared with previous methods, this new method (RFM) has better repeatability and higher accuracy.

Effects of Obstacle Separation Distance on Gas Explosions: The Influence of Obstacle Blockage Ratio

Obstacle separation distance (pitch) has received little systematic study in the literature. Either too large or small spacing between obstacles would lead to lesser explosion severity. Therefore, an optimum value of the pitch that would produce the highest flame acceleration and hence overpressure is needed. It was the aim of this work to investigate the influence of obstacle blockage ratio on the obstacle spacing in gas explosions. The explosion tests were performed using methane-air (10% by vol.), in an elongated vented cylindrical vessel 162mm internal diameter with an overall length-to-diameter, L/D of 27.7. Double 20-40% blockage ratio, BR orifice plates were used as obstacles. The spacing between the obstacles was systematically varied from 0.5 m to 2.75 m. The 40% BR produced the highest explosion severity in terms of overpressure and flame speeds when compared to 30% and 20% BR. However, the worst case obstacle spacing was found to be shorter with increase in obstacle blockage. In general, similar profiles of overpressures and flame speeds were obtained for all the obstacle blockages. This trend was equally observed in the cold flow turbulence intensity profile generated behind a grid plate by other researchers. In planning the layout of new installations, the worst case separation distance needs to be avoided but incorporated when assessing the risk to existing set-ups. The results clearly demonstrated that high congestion in a given layout does not necessarily imply higher explosion severity as traditionally assumed. Less congested but optimally separated obstructions can lead to higher overpressures.

CORRELATION OF EXPLOSION PARAMETERS AND EXPLOSION-TYPE EVENTS FOR PREVENTING ENVIRONMENTAL POLLUTION

The naturally or industrially occurring flammable mixtures containing combustible gases or/and dusts represent a potential risk of explosion with major consequences on the environment and human personnel. Methane and coal dust are among the best known components able of leading to the formation of such mixtures either in coal mining activities or in different industries using coal dust as fuel. In order to assess the risk of explosion and the explosion evolution in such composite mixtures, the knowledge of the characteristic explosion parameters under standardized conditions is necessary. In this paper the maximum explosion pressure pmax, maximum rate of pressure rise (dp/dt)max and explosion severity factor for methane-air mixtures, air - coal dust mixture and hybrid air-methane-coal dust mixture were determined in a standard 20 dm3 spherical explosion vessel.

Explosion characteristics of micron- and nano-size magnesium powders

Explosion characteristics of micron- and nano-size magnesium powders were determined using CSIR-CBRI 20-L Sphere, Hartmann apparatus and Godbert-Greenwald furnace to study influence of particle size reduction to nano-range on these. The explosion parameters investigated are: maximum explosion pressure (Pmax), maximum rate of pressure-rise (dP/dt)max, dust explosibility index (KSt), minimum explosible concentration (MEC), minimum ignition energy (MIE), minimum ignition temperature (MIT), limiting oxygen concentration (LOC) and effect of reduced oxygen level on explosion severity. Magnesium particle sizes are: 125, 74, 38, 22, 10 and 1 μm; and 400, 200, 150, 100, 50 and 30 nm. Experimental results indicate significant increase in explosion severity (Pmax: 7–14 bar, KSt: 98–510 bar·m/s) as particle size decreases from 125 to 1 μm, it is maximum for 400 nm (Pmax: 14.6 bar, KSt: 528 bar·m/s) and decreases with further decrease of particle size to nano-range 200–30 nm (Pmax: 12.4–9.4 bar, KSt: 460–262 bar·m/s) as it is affected by agglomeration of nano-particles. MEC decreases from 160 to 30 g/m3 on decreasing particle size from 125 to 1 μm, its value is 30 g/m3 for 400 and 200 nm and 20 g/m3 for further decrease in nano-range (150–30 nm). MIE reduces from 120 to 2 mJ on decreasing the particle size from 125 to 1 μm, its value is 1 mJ for 400, 200, 150 nm size and <1 mJ for 50 and 30 nm. Minimum ignition temperature is 600 °C for 125 μm magnesium, it varies between 570 and 450 °C for sizes 38–1 μm and 400–350 °C for size range 400–30 nm. Magnesium powders in nano-range (30–200 nm) explode less violently than micron-range powder. However, likelihood of explosion increases significantly for nano-range magnesium. LOC is 5% for magnesium size range 125–38 μm, 4% for 22–1 μm, 3% for 400 nm, 4% for 200, 150 and 100 nm, and 5% for 50 and 30 nm. Reduction in oxygen levels to 9% results in decrease in Pmax and KSt by a factor of 2–3 and 4–5, respectively, for micron as well as nano-sizes. The experimental data presented will be useful for industries producing or handling similar size range micron- and nano-magnesium in order to evaluate explosibility of their magnesium powders and propose/design adequate safety measures.

Methods for more accurate determination of explosion severity parameters

Accurate determination of explosion severity parameters (pmax, (dp/dt)max, and KSt) is essential for dust explosion assessment, identification of mitigation strategy, and design of mitigation measure of proper capacity. The explosion severity parameters are determined according to standard methodology however variety of dust handled and operation circumstances may create practical challenge on the optimal test method and subsequent data interpretation. Two methods are presented: a statistical method, which considers all test results in determination of explosion severity parameters and a method that corrects the results for differences of turbulence intensity. The statistical method also calculates experimental error (uncertainty) that characterises the experimental spread, allows comparison to other dust samples and may define quality determination threshold. The correction method allows to reduce discrepancies between results from 1 m3 vessel and 20-l sphere caused by difference in the turbulence intensity level. Additionally new experimental test method for difficult to inject samples together with its analysis is described. Such method is a versatile tool for explosion interpretation in test cases where different dispersion nozzle is used (various turbulence level in the test chamber) because of either specific test requirements or being “difficult dust sample”.

Consequence modelling of dust explosion

Dust explosion is a serious hazard in process industries where combustible dust is handled. Dust explosion commonly occurs in a confined space such as a silo, a vessel or a warehouse. Based on industrial accidents involving dust explosion, it may cause fatality, injury and property damage. Therefore, a practical approach for integrated risk management of dust explosion hazards is required. This research focuses on the development of a spreadsheet tool for predicting the severity of dust explosion. The consequence modelling is required to enable the assessment of risk associated with dust explosion. Various published models were studied for initial work of consequence modelling. Parameters considered were the dust deflagration index (Kst), the maximum explosion pressure (Pmax), the maximum rate of pressure rise (dP/dt)max and the laminar burning velocity (Slbv). Reliable value for these dust explosion parameters has been tabulated based on closed vessel laboratory tests. A case study of dust explosion involving maize starch in closed vessel was used to test and validate the developed consequence modelling tool. The modelling result was discussed by comparing the predicted value against experimental value. The spreadsheet tool that was developed in this work can be used for the purpose of risk management of a facility associated with dust explosion hazards. It can be used to assist the application to combustion suppressant agent and design of explosion venting to prevent and mitigate the consequence of dust explosion. Keywords Consequence modelling, dust explosion, risk assessment Language: en

The acceleration of flames in tube explosions with two obstacles as a function of the obstacle separation distance

The separation distance (or pitch) between two successive obstacles or rows of obstacles is an important parameter in the acceleration of flame propagation and increase in explosion severity. Whilst this is generally recognised, it has received little specific attention by investigators. In this work a vented cylindrical vessel 162 mm in diameter 4.5 m long was used to study the effect of separation distance of two low blockage (30%) obstacles. The set up was demonstrated to produce overpressure through the fast flame speeds generated (i.e. in a similar mechanism to vapour cloud explosions). A worst case separation distance was found to be 1.75 m which produced close to 3 bar overpressure and a flame speed of about 500 m/s. These values were of the order of twice the overpressure and flame speed with a double obstacle separated 2.75 m (83 characteristic obstacle length scales) apart. The profile of effects with separation distance was shown to agree with the cold flow turbulence profile determined in cold flows by other researchers. However, the present results showed that the maximum effect in explosions is experienced further downstream than the position of maximum turbulence determined in the cold flow studies. It is suggested that this may be due to the convection of the turbulence profile by the propagating flame. The present results would suggest that in many previous studies of repeated obstacles the separation distance investigated might not have included the worst case set up, and therefore existing explosion protection guidelines may not be derived from worst case scenarios.

Modelling of the effect of size on flocculent dust explosions

The effect of size on the severity of explosions involving flocculent materials has been simulated by means of a model previously developed for spherical particles and here extended to the cylindrical geometry of flock. The model consists of the identification of the regime (internal and external heating, pyrolysis/devolatilization reaction, and volatiles combustion) controlling the explosion by the evaluation of dimensionless numbers (Bi, Da, Th and Pc) and then of the estimation of the deflagration index as a function of flocculent size. The model has been validated by means of explosion data of polyamide 6.6 (nylon) at varying diameter and length. The comparison between model and experimental data show a fairly good agreement.

Atypical Flash Burns following Low Voltage Electrical Explosion: The Importance of Forensic Engineering

Background:Accidental electrocutions during working activities account for a considerable amount of morbidity and mortality. Case Report: In this case, the findings were suggestive of a high voltage electrocution but the opinion of the electrical engineer helped the forensic pathologists to ascertain the real mechanism.A labourer was cleaning an abandoned porcelain factory, wearing incomplete protective attires, had a sudden explosion when he attempted to remove an iron pole with a shovel. He was thrown off and lost consciousness. There were dark brown superficial burns on facing and exposed sides. Areas covered by the helmet, hair and beard were spared. There were burn-free radially arranged elongated areas of the skin around eyes and nose. Eye brows were partially singed and eye lashes were completely burnt. Inner aspects of both forearms (right more than left) were burnt leaving a horizontal upper margin at the elbow. The right sleeve of the shirt was melted along the fold with blister formation on the skin. Superficial light brown burns were on dorsum of both feet sparing the areas covered by the straps of slippers. There were no charring, joule burns or multiple circumscribed and cavitated lesions. Though it was severe explosion involving more energy, the electrical engineer confirmed that it was a low voltage electrical explosion. Conclusion:Severe flash burns including partial loss of eye brows, complete loss of eye lashes and melting of clothes suggested high voltage electrocution. The electrical expert confirmed a low voltage electrocution and the severity of the explosion could have been due to three phase supply and the close proximity to the transformer.

Explosibility of micron- and nano-size titanium powders

Explosibility of micron- and nano-titanium was determined and compared according to explosion severity and likelihood using standard dust explosion equipment. ASTM methods were followed using a Siwek 20-L explosion chamber, MIKE 3 apparatus and BAM oven. The explosibility parameters investigated for both size ranges of titanium include explosion severity (maximum explosion pressure (Pmax) and size-normalized maximum rate of pressure rise (KSt)) and explosion likelihood (minimum explosible concentration (MEC), minimum ignition energy (MIE) and minimum ignition temperature (MIT)). Titanium particle sizes were −100 mesh (<150 μm), −325 mesh (<45 μm), ≤20 μm, 150 nm, 60–80 nm, and 40–60 nm. The results show a significant increase in explosion severity as the particle size decreases from −100 mesh with an apparent plateau being reached at −325 mesh and ≤20 μm. Micron-size explosion severity could not be compared with that for nano-titanium due to pre-ignition of the nano-powder in the 20-L chamber. The likelihood of an explosion increases significantly as the particle size decreases into the nano range. Nano-titanium is very sensitive and can self-ignite under the appropriate conditions. The explosive properties of the nano-titanium can be suppressed by adding nano-titanium dioxide to the dust mixture. Safety precautions and procedures for the nano-titanium are also discussed.

SO2‐catalyzed steam explosion: The effects of different severity on digestibility, accessibility, and crystallinity of lignocellulosic biomass

Lignocellulosic biomass is the most promising feedstock for biofuels production. To enhance the efficiency of enzymatic hydrolysis, lignocellulosics needs to be pretreated to lower their recalcitrance. SO(2) -catalyzed steam explosion is an efficient and relatively cost-efficient pretreatment method for softwood. This work investigates the effects of steam explosion severity on the digestibility, accessibility, and crystallinity of Loblolly pine. Higher severity was found to increase the accessibility of the feedstock while also promoting nonselective degradation of carbohydrates. The adsorption behavior of Celluclast® enzymes on steam-exploded Loblolly pine (SELP) can be described by a Langmuir isotherm. Cellulose crystallinity was found to first increase and then decrease with increasing pretreatment severity. A linear relationship between initial hydrolysis rates and crystallinity index (CrI) of pretreated Loblolly pine was found; moreover, a strong correlation between X-ray diffraction intensities and initial rates was confirmed. The findings demonstrate the significance of CrI in enzymatic hydrolysis of pretreated lignocellulosic biomass.

Experimental study on gas explosion and venting process in interconnected vessels

A pilot scale interconnected vessels experiment system was established, and the closed and vented gas explosion characteristics in the system were studied, using 10% methane–air mixture. Regularity of pressure variation in vessels and flame propagation in linked pipes was analyzed. Furthermore, the effects of transmission style, ignition position, pipe length, and initial pressure on explosion severity were discussed. For the closed explosion: explosion in interconnected vessels presents strongly destructive power to secondary vessel, especially transmission from the big vessel to the small one; the worst ignition position is shifting from ignition in the interconnected pipe to the walls of the two vessels; as far as ignition in big vessel is concerned, the peak pressure in secondary vessel increases with the pipe length much faster than that for ignition in small vessel; the peak pressures in two vessels are approximate linear functions of initial pressure. For the vented explosion: the transmission style and interconnected pipe length have significant impacts on the effect of venting on the protection; in order to obtain the better venting effect, the use of a divergent interconnected pipe from the big vessel to the small one in industry is advised and it is necessary to reduce the interconnected pipe length as far as possible or install flame arrester in the interconnected pipe.

Limiting oxygen concentration for coal dusts for explosion hazard analysis and safety

Investigation of explosion characteristics of coal dust was undertaken as a part of regular research program at CSIR-CBRI, Roorkee, India, for designing explosion safety measures for coal dust handling installations. This paper presents results of detailed experimental work on determination of Limiting Oxygen Concentration (LOC) and influence of reduced oxygen levels on explosion severity data for two types of coals with varying volatile matter as 27.18% (coal A) and 19.69% (coal B) from Jharia coalfield of India determined at ambient conditions with 20-L Spherical Vessel established at CSIR-CBRI. The effects of coal particle size and moisture content were evaluated. Data presented will be used for hazard analysis, designing explosion preventive measures, and explosion severity reduction by involving the use of inert gases for installations handling pulverized coal with similar nature. The importance of ignition source energy in determining LOC data is highlighted. The data collected lead to an extension of the current data for coal dusts as found in the literature. Limiting oxygen concentrations were found as 7% for coal A and 8% for coal B for the size representative to that used in pulverized coal boilers and moisture content ∼4%.

The Minimum Ignition Energy of Coal Dust in an Oxygen Enriched Atmosphere

In oxy/fuel combustion of coal, the pulverised coal is burned with oxygen at concentrations greater than the currently allowed value of 21 %. This may well provide advantages in carbon sequestration against other technologies such as pre- and post-combustion capture. However the risk of dust explosions increases significantly with increasing oxygen concentration and temperature. In this study the influence of enriched oxygen concentrations is researched on the dust explosion characteristics of Indonesian (Sebuku) coal dust and of Pittsburgh coal n°8. First the ignition sensitivity characteristics (minimum ignition energy and minimum ignition temperatures) and explosion severity characteristics (maximum explosion pressure, Pmax, and maximum rate of pressure rise, Kst ) are determined in air. Thereafter the minimum ignition energy is determined of both coals in an oxygen enriched CO2 atmosphere. The minimum ignition energy in air of the Sebuku coal was equal to 55 mJ, while the minimum ignition energy of the Pittsburgh coal was higher than 1000 mJ. The ignition sensitivity in a 30 vol% O2 in CO2 mixture was in good agreement to the ignition sensitivity in air. In a 50 vol% O2 in CO2 mixture the ignition energy decreased significantly to a value of 1.4 mJ for the Sebuku coal and 4.7 mJ for the Pittsburgh coal n°8.

From Safe Nanomanufacturing to Nanosafe-by-Design processes

Industrial needs in terms of multifunctional components are increasing. Many sectors are concerned, from the integrated direct nanoparticles production to the emerging combinations which include the metal matrix composites (MMC), ductile ceramics and ceramic matrix composites, polymer matrix composites (PMC) for bulk application and advanced surface coatings in the fields of automotive, aerospace, energy production and building applications. Moreover, domains with a planetary impact such as environmental issues, as well as aspects for instance health (toxicity) and hazard assessment (ignition and explosion severity) were also taken into account. Nanotechnologies play an important role in promoting innovation in design and realization of multifunctional products for the future, either by improving usual products or creating new functions and/or new products. Nevertheless, this huge evolution in terms of materials could only be promoted by increasing the social acceptance and by acting on the different main technological and economic challenges and developing safe oriented processes. Nowadays, a huge number of developments of nanoparticles are potentially industrial up-scalable. However, some doubts exist about the handling's safety of the current technologies. For these reasons, the main purpose was to develop a self-monitored automation in the production line coupling different techniques in order to simplify processes such as in-situ growth nanoparticles into a nanostructured matrix, over different substrates and/or the nanopowders synthesis, functionalization, dry or wet safe recovery system, granulation, consolidation in single-step, by monitoring at real time the processing parameters such as powder stoichiometry. With the aim of assuring the traceability of the product during the whole life, starting from the conception and including the R&D, the distribution and the use were also considered. The optimization in terms of processing, recovery and conditioning, permits to increase its versatility, thus leading to the increase of the added value to the production. This review put in evidence -by different examples- the progress achieved since the beginning of Nanosafe integrated initiative developed by CEA and its partners as well as promoting, firstly the safety at work place, and then extending to an integrated and controlled in-situ production by of Nanosafe-by-Design controlled processes.

Experiment-based investigations on the effect of ignition energy on dust explosion behaviors

Explosion behaviors of typical light metal and carbonaceous dusts induced by different ignition energies were investigated based on systematic experiments in a Siwek 20 L vessel. Comparative analysis reveals that the explosion mechanism of carbonaceous dust is the volatile combustion, whereas the mechanism for light metal dust mainly features the surface heterogeneous oxidation. Influences of ignition energy on severity and flammability limit are much more significant for carbonaceous dust than light metal, especially for the powder with less volatile. An innovative approach was introduced to derive flame thickness from the pressure–time trace. The relation between explosion induction time and combustion duration of ignitor was also analyzed. Results show inappropriate ignition energy will cause under-/over-driving in the thermodynamic/kinetic characteristic measurements. In this way, a dimensionless parameter pressure ratio was introduced to evaluate the under-driving, while two methods by using flame thickness and induction time respectively, were proposed to evaluate over-driving. To improve the accuracy of dust explosion tests, authors advocate that explosion severity determination should be conducted at the critical ignition energy. Moreover, a comparison between the European and Chinese flammability limit determination procedures was also conducted, indicating that EN 14034-3 is suitable for light metal but not for carbonaceous, while GB/T 16425 appears to be slightly conservative for both carbonaceous and light metal dusts.

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.

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.

Comparison of Escherichia coli KO11 and Saccharomyces cerevisiae ATCC 96581 in fermenting Pinus patula hydrolysate pretreated at different steam explosion severity

Bioconversion of wood residues to biofuels such as ethanol is one of the feasible initiatives towards production of renewable energy. This work compares the effectiveness of Escherichia coli KO11 and Saccharomyces cerevisiae ATCC 96581 in fermenting Pinus patula (pine) hydrolysate pretreated by acid-catalyzed steam explosion. The results show no significant difference in terms of the ethanol yield when E. coli KO11 and S. cerevisiae ATCC 96581 were used. The maximum ethanol concentration obtained in test tubes fermentation were 18.30 and 19.41 g/l for E. coliKO11 and S. cerevisiae ATCC 96581, respectively, from samples pretreated at 225°C/5 min. The ethanol yields obtained using bioreactors for samples pretreated at 225°C, 0.5% SO2, and 5 min, were 21.30 and 19.63 g/l for E. coli and S. cerevisiae, respectively. Overall, ethanol yields were higher in bioreactors than in test tubes for both strains. In comparison, S. cerevisiae consumed the substrate faster than E. coli, thus making S. cerevisiae the most preferred strain in fermentation of hydrolysates from steam pretreated P. patula. Key words: Pinus patula, steam explosion pretreatment, enzymatic hydrolysis, fermentation, Escherichia coli, Saccharomyces cerevisiae.