1,720,985 research outputs found
Development of Speditive Explosibility Test (SET): a statistical reliable method for combustible dust explosibility investigation
Full text linkThe present work of thesis investigate the explosibility sensitivity and behavior of combustible solid materials, in the form of dusts. The first phase of the work has focused on the ignition sensitivity of combustible dusts, both in form of clouds than deposed as layers. Standard test methods has been used to assess ignition parameter of the samples, i.e. UNI EN 50821: 1999. MITC and MITL were measured for pure combustible dusts and for mixtures of different dusts. In particular mixtures of combustible and inert dusts were analyzed. The experimental results underlined the increase of the ignition temperature (both in clouds than in layers) as the weight content of inert material increase. Extinguishing powders with chemical heat depletion effect had demonstrated to be more effective in increasing the ignition temperature with respect to inert acting with physical inertia mechanism. MITC of two combustible dusts mixture have been analyzed and results have shown the poor accuracy of the standard procedure in defining the ignition temperature, particularly when there is little difference between ignition temperatures of the pure materials. The author has attempted to reduce this lack of accuracy, inadequate when a high level of details is required (like for scientific purposes) in ignition measurements through different statistical analysis of experimental data. This study has generated a statistical approach to the investigation of dust ignition temperature with the definition of the SIT (Statistical Ignition Temperature) and the definition of a Probability Escalation Interval (PEI); within PEI ignition probability of dusts vary between 0 and 1 with respect to temperature. The results obtained show that standard methods adopted worldwide could fail in determine the MITC of dusts and bring a new, more accurate methodology as a contribution on the definition of ignition concept of dusts. The statistical study could also apply to ignition criteria of the explosibility test proposed here, in order to give to SET procedures and results a more reliable statistical value. The Speditive Explosibility Test has the form of a screening procedures for defining explosibility of dust samples, with the aim of avoiding time and cost-consuming standard procedures. The test consist in different procedures derived from standards (mainly UNI EN 50821 and UNI EN 13821) which ignition conditions are modified to be "as worst as possible", in order to avoid marginally explosive dusts to be classified as non explosible. Tests were performed on different dusts samples (by chemical composition, nature, PSD) and results were validated through explosion test in the 20 L Siwek-sphere. The test classification shows, for the majority of the samples collected, good agreement with literature standard explosibility tests. The SET could be assumed as standard test for the explosibility determination of a dust. A second experimental campaign was performed on non-traditional dusts coming from textile industries. All samples PSD was analyzed and 15 over 100 total were submitted to the SET with the aim to obtain more data on explosive behavior of those type of dust
Metal waste dusts from mechanical workings - explosibility parameters investigation
Full text linkThe reactivity of metal scraps or fine particles, typical residual wastes of mechanical workings, is significantly high to cause violent deflagration when particles disperse in the air in the form of clouds. However, literature information is scarce regarding the explosive risks of mixtures of pure metals, oxides and other impurities (like waste dust) whereas the form the bulk of materials in abatement systems and bag filters in the metal industry. Mechanical working could produce a different type of dust, depending on the process, the source material, and the operating conditions, main differences are in the particle size distribution, oxide content and morphology of samples. The present study investigates several samples of metal/oxide dust mixtures. The results of this work help to recognize the most hazardous dust in term of ignition sensibility when dispersing in clouds. The dust from sanding and welding processes fall into this group, while dust from laser-cutting does not ignite with standard ignition sources (like an electric arc or a hot wire). The work also aimed to establish a correlation between sample properties and explosibility parameters, like KST and Pmax. The results indicate a direct proportionality between these values and the particle size distribution of samples (in particular with the d-tenth percentile of the mass distribution) and with the metal oxide content. Additional research is needed to assess the influence of other variables (morphology, chemical composition) and the actual hazards related to different mechanical workings to prevent and mitigate explosive events
Dust explosion risk in metal workings
No full textSeveral episodes of metal dust explosions have been reported to have affected industries throughout the world, some of which have caused huge losses (Li et al., 2016). These dusts are typically wastes or by-products derived from machinery within metal manufacturing plants, which are collected in abatement systems (suction units, bag filters). A recent work by Marmo et al. (2017) has demonstrated the deflagration hazards of these dusts and how they are influenced by the particle size (mainly d10), chemical composition and metal oxide content.
The dust samples studied in this work were collected from the following mechanical workings of metals.
All these unit operations involve the generation of by-products or scraps that may be classified as dust, with different size distributions and chemical compositions, which of course depend on the nature of the processed goods. Among these, it is known that the aluminum industry is affected by a significant hazard, due to the high reactivity of aluminum dust. However, ferrous dust is also reactive and widespread. Light alloys, such as Magnesium alloys, are becoming frequent, especially in the automotive and aerospace industries. Therefore, new hazards are now coming to light.
This work presents a study of 43 metal dust samples, collected at various process plants, and discusses how the unit operation that generated the dust samples may influence their ignition sensitivity and explosion violence. The paper includes size distribution and chemical characterization data, and SEM observations of the samples, as well as the results of KST and Pmax measurements.
Of all the studied dusts, 59% were found to be explosible, according to the standard test (ISO 80079-20-2), while 100% of the samples collected at some of the dust abatement systems were explosible. Process dusts, such those collected at metal recovery plants from exhaust catalysts or foundry wastes, were found to be less hazardous. The findings of the work could contribute toward identifying the most hazardous operations and suggesting adequate explosion moderation measures for the metal manufacturing industry
Minimum Ignition Temperature of layer and cloud dust mixtures
No full textThe prevention of dust explosions is still a challenge for the process industry. Ignition, in particular, is a phenomenon that is still not completely understood. As a consequence, safety conditions pertaining to ignition suppression are rarely identified to an adequate level. It is well known that, in general, the ignition attitude of a dust depends on several factors, such as the nature of the chemical, the particle size, moisture content, etc., but there is still a lack of knowledge on the effect of the single variables. This paper aims has the aim of providing data on the minimum ignition temperatures of dust mixtures obtained from a mixing of a combustible dust (flour, lactose, sucrose, sulphur) and an inert dust (limestone, extinguishing powders) as well as from the mixing of two different combustible dusts. Various mixtures with different weight ratios have been tested in a Godbert Greenwald (GG) furnace and on a hot plate in order to measure the effect of mixture composition on the minimum ignition temperature (MITL) of the layer and on the minimum ignition temperature (MITC) of the cloud. In order to further verify the effects of inert dust particle size, inerts sieved to different size ranges have been tested separately. Generally, both MITL and MITC increase as the inert content is increased. MITC is poorly affected by inert particle size when limestone is used. The MITL of pure flour is higher than the MITL of mixtures containing up to 40% of 32-75 micrometers of limestone. This was probably due to the behaviour of pure flour during the test, which demonstrated strong tendency to produce char, cracks in the layer and detachment from the hot plate
Influence of Operating Conditions on Pre-wetted Powder Explosion
No full textPre-wetting of powders or wet granulation are commonly used in industrial processes and the presence of a flammable liquid compound can affect the ignition sensitivity and explosion severity of such admixtures. This study shows that for risk assessment, it is not possible to consider this type of admixture to be equivalent to a hybrid gas/solid mixture of the same composition. Indeed, if the introduction of a solvent tends to increase the explosion risk, pre-wetting also significantly modifies the particle size distribution of the admixture, which counterbalances the positive contribution of the flammable liquid. Dispersing the dust requires then a greater dispersion pressure to reach the same surface area between solid fuel and oxidizer. In the case of the determination of the minimum ignition temperature, such changes lead to a modification of the optimal operating conditions. It should also be noted that the fuel equivalence ratio is a good indicator for assessing the chemical contribution of such admixtures
Small magnitude explosion of Aluminium powder in an abatement plant: A Telling Case
No full textOn the 16th June 2000, an aluminum dust deflagration occurred in a small factory in the north-west of Italy. The explosion took place in an aluminum dust collecting and abatement unit that served a surface polishing plant. The collecting unit was made up of several ducts that conveyed dust into a manifold, which was connected to a cyclone and a bag filter. The cost of the deflagration cost was six injured workers, and relevant damage to the plant machinery, the process building and to other surroundings buildings. Although aluminum dust explosions are well known and have been well documented in the literature, this case study can be considered interesting because of its complex dynamics,which started with a first weak explosion that then evolved into a more severe chain of explosions.This article has drawn upon the official documents written during the investigation and the technical reports prepared by a number of expert witnesses. The data collected during the investigation have made it possible to determine the causes and dynamics of the accident and to calculate the strength of the explosion, on the basis of the distribution of the damage and the launching distance of the fragments. The magnitude of the damage seems to indicate that the amount of dust that took part in the explosion corresponds to the dust that settled on the bag filter
A parametric fire risk assessment method supporting performance based approaches application to health-care facilities in northern italy
Full text linkFire risk assessment has always been a challenging issue. Furthermore, performance based approaches to fire engineering showed that risk based decisions and fire scenarios are a fundamental element of the fire safety strategy assurance. In particular, a correct assessment of the risk allows all the involved stakeholders to identify a specific strategy among a pool of possibilities. Risk assessment is the perfect tool to identify comparable fire protection strategies and to measure fire risk reduction associated to the single specific prevention and protection measures composing each different fire strategies. This approach implies the need to abandon a classic, not even conservative approach, that in many cases linked the total fire load to the fire risk level, despite specific dynamics, layouts, prevention measures and risk management issues during time. During the years, a number of different methodologies have been developed: for specific cases, for industrial or civil buildings, to adopt a method enforced by the local law and regulations acts, etc. Methods have been based on matrices, indexes, check-lists, etc. Present paper illustrates a method developed by the authors taking into account several international recognized methods; even coming back to methodologies developed in early seventies. The Method is named "FLAME" (Fire risk Assessment Method for Enterprises), it goes back to the fire safety fundamentals against a generalized approach to fire safety engineering based on complex and time-consuming methods like CFD that deals only with the ‘consequences' aspect of the fire risk (that is indeed characterized also by frequency estimation) using as reference scheme the "Fire Safety Concept Tree" explained in detail in the NFPA 550 Standard. In order to identify the most appropriate fire safety strategy it is important to identify the associated fire risk that the strategy is intended to mitigate to a certain level. Alternative solutions can be evaluated considering the risk reduction operated by different strategies and by different elements composing the fire strategies themselves and also costs with a modern ALARP approach. A clear advantage is the possibility to get an overview of the whole fire risk as the cumulative risk assessed by the model and not solely related with the consequences evaluation of a limited number of fire scenarios (usually the most obvious ones). Risk level assessment leads to the identification of the fire scenario (or a pool of) that governs and limits the specific situation, declined for both humans and structures (assets) considering that the two vulnerabilities could be linked to different fire risk scenarios. The method has been tested against different buildings occupancies. In the present case results of the FLAME method application to hospitals and health-care facilities are reported. A fire compartment-based risk estimation has been conducted on an overall of about 300 compartments (overall size of about 60000 m 2 ). Coherence has been found among risk estimation by FLAME parametric code and prescriptions of the Italian fire code. There is good agreement when assessing the RSET with the method proposed in FLAME, dealing with the occupants' behaviour and the actual characteristics of occupants in clinics or hospitals and difficulties due to poor mobility or incapacity to understand emergency cues
Fire risk assessment of photovoltaic plants. A case study moving from two large fires: From accident investigation and forensic engineering to fire risk assessment for reconstruction and permitting purposes
No full textA speditive explosibility test for dusts
No full textCombustible dusts explosion risk depends on a huge number of dust characteristics which allows the analyst to assess its behavior at different conditions. To characterize dust behavior a huge number of parameters can be measured according to several technical standards. In general, each standard describes how to measure a single parameter, which characterize a specific dust behavior. Nowadays there's no standard conceived to simply determine if the dust can cause an explosion. As available standard tests are often costly in terms of time and money for both laboratory analysts and customers, moreover the latter are sometimes in the condition to submit to expensive tests dust samples that could not explode. The aim of this paper is to describe a simplified and straightforward test that can assess whether a dust is explosible or not. The test is called Speditive Esplosibility Test (SET). It is composed of 4 different tests, each of them representing a different ignition mechanism derived from standards procedures. These are: -High voltage continuous arc ignition and glowing wire ignition in Hartman 1.2l tube (based on UNI EN 13821:2004); -Dust cloud ignition in G-G furnace and dust layer ignition on hot plate (based on UNI EN 50281:1999). In this context the 4 experimental procedures were slightly modified respect to standards procedures: the test conditions have to be "as worst as possible" in terms of energy transferred to the sample. This approach assure that also dusts that have relative weak tendency to ignite is considered and classified. The test classifies dusts in 3 categories: explosible at ambient temperature (in case of ignition in Hartmann tube tests), explosible at high temperature (in case of ignition in GG or hot plate tests), not explosible (in case of no ignition). Fundamentally, the test procedure is configured as a statistical investigation in which a defined number of tests is made. Screening test has been performed for several types of dusts and results compared with kst tests in 20l Siwek Sphere for some of the samples. Results sees to confirm the hypothesis of the Screening Test and its reliability to assess explosibility of combustible dust
- …
