Fire and Explosion Risk Assessment: Application to the Fine Chemicals Industry

The "so-called" Seveso III directive (Directive 2012/18/EU) impose to plant managers to perform a detailed risk assessment and to adopt adequate protection measures in the case their facility is included among those considered subjected to Major Accident, i.e., if the amount of hazardous substances stocked and handled within it is superior to defined threshold limits. Fire risk evaluation needs to consider each plant's complexity and the different regulations and codes it is subjected to. Meanwhile, a thorough approach is required, which does not base itself uniquely on qualitative methods (such as checklists) or semi-quantitative (such as fire load-based approach) but should consider these latter as starting processes to develop a more comprehensive evaluation. Besides this, accident scenarios associated with chemical plants may differ significantly, according to the substances handled, the activities and processes implemented: Typically, they could range from small to medium scale in terms of consequences, depending on the impact on human operators and structures. Several "risk screening" methods exist, differing from their fields of applications and limitations, as detailed by Danzi et al. (2018). The SWandHI methodology was developed by Khan et al. (2001). It is a fast tool that allows to identify the most hazardous units in chemical process plants, underline the criticalities associated with different substances, processes, and operations, evaluate the effectiveness of the protection measures in place, compare the risk level attributed to different chemical processes, define the adequate additional measures to reduce the risk to an acceptable level. In this work, the SWandHI method (with the modifications proposed in Danzi et al. 2018) is adopted as a preliminary risk screening approach in the production departments of a fine chemicals production plant in Northern Italy, which is identified as a relevant case study due to the heterogeneity of substances and chemical processes available. This study aims to verify the applicability and effectiveness of SWandHI when adopted in the evaluation of fire risk of "medium-size" plants, or "just below" Seveso III thresholds facilities (which could be considered as a majority in Italy), and to identify the prevention and protection measures most suitable to be implemented in this context to mitigate the fire and explosion scenario. The risk assessment conducted in this work will contribute, with further applications, to: (a) the tuning and calibration of the SWandHI method to "medium" scale chemical industrial realities; (b) the definition of a standard procedure of fire and explosion risk screening through SWandHI; (c) the implementation of the validated method into the Italian fire risk regulations

A numerical micro-mechanical study of the influence of fiber–matrix interphase failure on carbon/epoxy material properties

A finite element micromechanical study of unidirectional carbon–epoxy system is performed in order to investigate the role of fiber–matrix debonding in the degradation of mechanical properties and in the onset of failure for this class of composite materials. The presence of interphase flaws, that can be induced during the manufacturing processes, into micro-scale FE models is obtained by means of an original damage injection technique developed by the authors. The fibers are considered as transversally isotropic solids and the matrix is modeled as an isotropic, elasto-plastic, material with damage. The effect of fiber–matrix debonding is analyzed by means of a quasi 3-D unitary cell with a single fiber, with periodic boundary conditions, for different loading cases. Subsequently, multi-fiber representative volume elements are investigated with the same boundary and loading conditions. Finally, the effect of a 3-D debonding propagation is studied via single fiber model with an increased fiber-wise depth

CFD simulation of multiple dust explosion occurred in a flour mill

Dust explosions pose a serious hazard to both personnel and equipment in industries that handles combustible powders. Although prevention and mitigation technology of dust explosions has progressed greatly, continual accidents in the process industries demonstrate the need for improved knowledge in this area (Mercan, 2016; Russo et al., 2017). On July 16, 2007, a primary explosion followed by secondary explosions happened in the Cordero mill (Italy) and 5 persons died (Marmo et al., 2012). The accident occurred at the end of the loading operation of a tanker, when a surplus of flour was overcharged. This extra amount was then pneumatically conveyed to a silo placed in the flour-warehouses, by connecting the tanker to the pneumatic transport line through one of the tanker hoses. The flour was loaded at a low flow rate, and hence a low concentration of flour in the duct occurred. The source of ignition of the dust cloud was attributed to an electrostatic arc that took place in the pneumatic transport duct (Marmo et al., 2012). The technical enquire found signs of the explosion in the duct: internal pressure provoked evident deformation of the duct. As widely discussed in the literature (Fiorentini and Marmo 2019; Marmo et al., 2013), Computational Fluid Dynamics can be a valid aid to forensic engineering because it allows to discern the incidental sequence that is more adherent to the evidence. The aim of this work is to reproduce the conditions present in the mill at the time of the accident using the CFD-code DESC, which is being developed for simulating dust explosions in complex geometries. The results obtained from the simulations were compared to the damage observed after the accident in order to identify the more credible scenario. Simulations with different levels of flour in the silo, concentration of dust in the air mixture and position of ignition were performed. Analysis of results revealed the effect of different parameters on the severity of dust explosion, not only limited to the case study investigated, in order to adopt the appropriate prevention and protection measures

Investigation of the fluid dynamic of the modified Hartmann tube equipment by high-speed video processing

Hartmann tube equipment is used in the dust explosion experimental test to screen the flammability of powdered materials (according to ISO 80079-20) and to determine the Minimum ignition energy of dust (UNI EN 13824:2004). For the test, the nominal concentration, as the ratio between the dust sample mass and the chamber test volume (1.2 liters), is considered, assuming a uniform concentration distribution. Even though adopted as standard procedure, this approach does not consider the dust cloud's non-stationary conditions inside the tube: The effect of turbulence decrease and dust sedimentation during the test duration will affect the dust concentration locally and globally within the test enclosure. Moreover, it is well known that the turbulence intensity influences Minimum Ignition Energy. This work derives from previous investigation on describing the dust cloud behavior within dust explosibility laboratory apparatuses. High-speed video recordings have recently been adopted to support the dust cloud dynamic analysis and visualize the cloud dispersion within a standard test setup, as the 20 L sphere and the modified Hartmann tube. This work intends to use different high-speed videos of dust dispersions in the modified Hartmann tube, with different injection pressure and sample mass, to focus on the behavior of the cloud at the typical delay time of the MIE measurement, i.e., 60-180 ms. Each video is processed frame by frame to reveal information on the cloud dynamics, otherwise hidden. The dust dynamic is accounted for calculating the variation in time of the brightness of pixels. This way, it is possible to obtain a set of data that incorporate the effects of the dust cloud distribution and the velocity of the particles clusters. The experimental data processing will help to focus on the time-scale and the length scale of the turbulence. The next study will focus on evaluating the time and space scale of the dust cloud and identifying the effect of ignition time delay on the MIE measurement to provide indications to operate at the most conservative conditions (higher concentration) and to avoid issues and under/overestimates due to agglomeration, sedimentation or segregation of dust particles

Biomass from winery waste: Evaluation of dust explosion hazards

Food and drink supply chains have significant environmental impacts due to their use of resources, emissions, and waste production. An efficient method to reduce this impact is the valorisation of biomass waste through energy recovery by using it as a source of heat. The European energy system faces several fundamental challenges being currently the largest emitter of greenhouse gases due to its large dependence on fossil fuels (mostly natural gas). Therefore, the energy sector's decarbonization will play a central role in achieving a climateneutral economy in Europe. Identifying the suitable material for biofuel is basically focused on the amount of energy that the material stores, availability, and logistic considerations. Sawdust and wood chips have been extensively used as biofuel in recent years, but other promising raw and waste materials could be adopted (with the positive effect of reducing the impact on forestry soil and the food chain). Novel materials bring consequently novel challenges, also regarding their safe use. As an example, a relevant waste flow is produced from wine manufacturing. A solid with high moisture content is obtained from grapes pressing, and it could be reused to produce distillates. The obtained exhausted pomace could be considered among the materials potentially involved in energy recovery. It is also carrying dust explosion hazard, as solid residues could be present in the form of coarse and fine powders. In this work, grape pomace is examined: its explosion safety-related properties are evaluated to define the severity of events in which this material could be ignited. Minimum Ignition Energy (MIE), explosion pressure peak (Pmax), deflagration severity index (KSt), autoignition temperature (MIT), and Volatile Point (VP) are measured according to standard procedures. This material's thermal susceptibility and ignition sensitivity are studied and compared with biomasses from different sources (ligneo-cellulosic and herbaceous)

Energy recovery from vinery waste: Dust explosion issues

The concern about global warming issues and their consequences is more relevant than ever, and the H2020 objectives promoted by the EU are oriented towards generating climate actions and sustainable development. The energy sector constitutes a difficult challenge as it plays a key role in the global warming impact. Its decarbonization is a crucial factor, and significant efforts are needed to find efficient alternatives to fossil fuels in heating/electricity generation. The biomass energy industry could have a contribution to make in the shift to renewable sources; the quest for a suitable material is basically focused on the energy amount that it stores, its availability, logistical considerations, and safety issues. This work deals with the characterization of a wine-waste dust sample, in terms of its chemical composition, fire behavior, and explosion violence. This material could be efficiently used in energy generation (via direct burning as pellets), but scarce information is present in terms of the fire and explosion hazards when it is pulverized. In the following, the material is analyzed through different techniques in order to clearly understand its ignition sensitivity and fire effects; accelerating aging treatment is also used to simulate the sample storage life and determine the ways in which this affects its flammability and likelihood of explosion

Issues of “Standard” explosion tests for non-spherical dusts

Measurements of the flammability and explosion parameters for non-spherical dusts are performed according to standard procedures in standard explosion equipment developed and tested for spherical dusts. Studies have shown that the standard procedures and equipment applied to spherical particles suffer from many issues: control of the turbulence level, non-uniform dust dispersion, and particle fragmentation due to the injection system. The applicability of the standard procedures and equipment to non-spherical particles is still an open issue. In this work, we have investigated, via CFD simulations, the distribution of turbulence and dust concentration in the standard 20 l spherical vessel for non-spherical particles. Results have shown that a higher turbulence level and a higher amount of dust actually fed into the vessel are reached with respect to spherical particles