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During a dust dispersion, the particle size distribution (PSD) depends on several factors such as the turbulence, the initial particle size and shape as well as the dust concentration. As a consequence, when determining safety parameters using standard procedures, its potential evolution should be considered. Different powders were chosen: glucose, starch, ascorbic acid, glass beads and cellulose. A Godbert-Greenwald furnace was used to disperse the powders and determine their minimum ignition temperature (MIT) according to ISO/IEC 80079-20-2:2016 standard. The PSD of each powder was determined in-situ at different locations using a laser diffraction sensor. Some powders showed clear signs of breakage, as for glucose whose mean diameter decreases from 166 to 76 µm during its dispersion. On the contrary, many samples tended to agglomerate, e.g. starch and cellulose. For instance, the d90 of starch can even be quadrupled under certain conditions. Agglomeration occurs especially for fine dusts due to strong inter-particles forces (e.g. starch) or for elongated fibres due to entanglement phenomenon (e.g. cellulose). During a powder dispersion in the Godbert-Greenwald furnace, the PSD evolves not only as a function of time but also along with its location. The impact of the glass elbow on PSD variation has notably been highlighted by placing the G-G furnace horizontally. For powders showing strong tendency to agglomeration or breakage, the influence of the dispersion pressure has also been studied. The role of such PSD modification on the MIT has been measured and, depending on the dispersion procedure, temperature differences of more than 50°C have been observed. The agglomerate strength was assessed using three models (from Rumpf, Weiler and Kendall works) and compare to the deagglomeration stress exerted on the powders. In the case of cohesive powders, fibres or brittle dusts, attention should be paid to the PSD evolution during MIT determination.

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.

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.

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 climate-neutral 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).

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.

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.

According to European “Offshore” Directive (2013/30/EU) by the next July, 19th safety cases (Relazioni Grandi Rischi - RGR, Major Accidents Report) should be submitted to the Authorities Having Jurisdiction (AHJ) in order to maintain the license to operate. By the preparation of RGRs the Owner should identify all the hazards connected with the installation, assess all the major risks, identify the acceptable/tolerable risks according to a defined ALARP criterion for human life and environment. Taking inspiration from real applications in Italy, this paper intends to highlight: the importance of a coherent assessment framework based on rule sets to manage all the information gathered during the various stages (also to facilitate the assessment conducted by the AHJ and the selected independent third-party inspector); the advantage coming from the use of a collector cloud-based IT system to manage data during assessment and to update them in the future leveraging the MOC process (also enforced as a specific requirement of the directive) across several installations and assets with a barrier-based management system.

Safety barrier-based management systems are widely adopted because of the advantages coming from the barrier approach. Different methods are available to implement it and the Bow-tie is one of the most recognized methodology. The Bow-tie method allows the risk analyst to have, in a single shot, the complex picture about the relations linking threats, preventive barriers, top events, mitigative barriers, consequences, and escalation factors. From this perspective, without a proper reference, there are significant possibilities to misuse the method and create confusion about the right role of each component of a Bow-tie diagram. This work intends to support the approach of the guidelines developed by the Center for Chemical Process Safety (CCPS) of the American Institute of Chemical Engineers (AIChE), to drive the analyst in the proper usage of the method, avoiding to misinterpret key elements like the human errors or the barrier failures, and helping in a congruent definition of the elements, thus resulting in a high-quality risk analysis and in a sound barriers management.

The 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.

Fire and explosion risk evaluation in the industrial context is a fundamental tool for work owners and safety manager to individuate critical scenario and issues related to fire and explosion in industrial facilities and sites. The primary objective of the risk evaluation is the definition of possible accident scenarios, their likelihood and consequences concerning damages to people and facilities, as to define an adequate fire strategy and preventive-protection measures. In this work, three real accidents were tested with three real fire and explosion risk evaluation methods, among the most adopted worldwide: F&EI “Fire and Explosion Index, by DOW Chemical Company; The Mond Index, by Imperial Chemical Industries; Safety Weighted Hazard Index (SW&HI), by Khan, Husain, Abbasi (2001). All these methodologies could be classified among semi-quantitative index methods, and their outputs are quantitative values (indexes) which indicate to analysts the most hazardous units or processes and help to define priorities on protection system implementation. A new index, incorporating the incomes of the three methods adopted is proposed in this paper. A sensitivity analysis was also performed, as to investigate whether operating conditions or peculiar characteristics of substances involved in processes has the more significant influence on the risk evaluation, according to the method adopted. This work has also posed the basis to develop a novel method, derived mainly from the SW&HI methodology: this will apply to a wide range of industrial facilities and incorporate relevant features of previous methodologies attempting to eliminate critical points and issues of former methods.

In the present study, the microalga Scenedesmus obliquus CCAP 276/38 has been applied in the treatment of a real wastewater (RWW) derived from an anaerobic digestion process of corn silage and livestock wastewater. The liquid phase of the digestate showed a low viscosity value and a high content of ammonia up to 3 g/L. In a preliminary phase, the experimental tests were carried out in Erlenmeyer flasks in order to identify the optimal RWW concentration and, in particular, its influence on biomass growth and productivity. The tests were carried out at 20°C at an artificial dark/light cycles of 12 hours. Three different concentrations were tested: 1, 2 and 3% of RWW in water, in the presence of sodium bicarbonate (NaHCO3, 50 mM) as inorganic carbon source. The obtained results showed that S. obliquus was able to grow in all the tested RWW concentrations even if a higher growth rate and biomass production were observed in the cultures containing 1% RWW. In order to test the influence of N/P ratio on microalgal growth, two different salts, KNO3 (0,2 g/L) and K2HPO4 (0,02 g/L), were added to the medium containing 1% RWW (N/P = 84.4), to correct the N/P value. The biomass growth rate increased in the medium with the lower N/P value (N/P = 27.9). The microalgal production process was scaled-up in a stirred tank photobioreactor (working volume 5 L), in the same temperature and illumination conditions using a medium with the composition optimized in flask tests. The culture was carried out for 124 hours, fed-batch addition of RWW (1%) was done during the fermentation in order to replace the carbon source. The results (growth rate, biomass dry weight and productivity) were compared with those obtained in presence of a synthetic medium with sodium bicarbonate 50 mM as carbon source. The work clearly demonstrated the capability of S. obliquus CCAP 276/38 to grow in alkaline wastewater and the possibility to employ this species in the treatment of effluents containing high ammonia concentration.

Cheese whey results as by product of cheese or casein production in large amounts. Depending on the ceesemaking process, the amount can rise to more than 6 times, on a weight basis, the cheese produced. Cheese whey has considerable nutritional value and a strong organic and saline content, such to pose serious disposal problems. The Chemical Oxygen Demand (COD) can be as high as 100 kg m-3, a value so high to make impossible the direct disposal in superficial water and to make critical any biological treatment withoutprevious dilution. Many cheese whey components have significant value in the light of their direct use (proteins, lactose), or as a feedstock to obtain building blocks or chemicals (lactose fermentation to ethanol, lactic acid ecc.). In this paper a conceptual process for the valorisation of whey through the recovery of added value components is presented. The process includes lipids recovery via thermocalcic precipitation, protein recovery via ultrafiltration and lactose valorisation through biological processes to obtain polyhydroxyalcanoates (PHA) and/or Lactic Acid (LA). In this work many of the unit operation of the process were developed and optimized at a lab scale. Ultrafiltration with 10 kDa membranes allowed to obtain a stream having protein concentration of more than 80 g/l, permeate fermentation led to obtain a biomass concentration of more than 1,5 g/l with a PHA content ranging between 50-60%. A first attempt of a mass flow balance of the entire process can be drawn.

Fire 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 m2). 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. In general, the level of risk is identified as shown in Table 1.

Photovoltaic (PV) plants have known a steep increase in number and installed power in the last decade all over the world. Together with this growth, also associated risks grew significantly. Among these fire risk has caught the attention of both Authorities, plant managers and any other stakeholders (such has owners of the property) due to the high number of fire involving solar plants. In 2012 around 600 fires involving solar plants occurred in Italy, with this figure in constant growth. In this paper fire risk assessment of PV installations is presented through several steps since the problem has gained a significant importance.

This paper contains the forensic reconstruction of a powerful explosion that occurred in a flour mill in Italy in 2007. The mill produced wheat flour and was organised over 4 floors inside a very old building. The explosion occurred just after a tanker had been loaded with flour which was to be delivered to customers. Since the truck was loaded with a slight excess of flour, a small amount was sent back to one of the silos, via pneumatic transport, through a rubber hose connected to a steel pipe. The explosion destroyed the building and killed 5 workers. Through an analysis of the collected evidence, the testimony of the witnesses and an examination of the debris, the causes and dynamics of the explosion are here described. It was recognised that the explosion was ignited because of an electrostatic arc that occurred in the pneumatic transport duct. Signs of the explosion in the duct were evident because of the deformation that was provoked by internal overpressure. The triggering discharge occurred at the joint between the hose and the pipe. The pipe deformations were coherent with calculations of an internal pressure increase according to EN 14491. The explosion propagated to a flour silo and then to the whole building through the elevator case, and resulted in many secondary explosions. The explosion dynamics are here described and the lesson that have been learned are also proposed.

The Authors of this paper were technical consultants of the Public Prosecutor in the trial for the accident occurred at the ThyssenKrupp(TK) plant in Turin on Dec. 6, 2007. The accident has been recorded as one of the most serious and impressive work accidents happened in Italy in the last years. It caused seven fatalities. On the early morning of December the 6th a modest fire started in the entry section of a pickling and annealing line in the TK plant in Turin. The eight workers that were then on duty started fighting the fire by using portable fire extinguishers and a fire hydrant, and got close to the fire. A violent jet fire, originated by the rupture of a hydraulic circuit, occurred. The flames instantaneously hit the eight workers while they were still trying to control the initial fire. Seven workers suffered very serious burst, one died instantaneously while the other six during the following month. One of them, that had been partially shielded by a fork lift, suffered only minor bursts and survived. The Authors conducted the investigation and followed the whole trial on charge by the Public Prosecutor Office. This paper summarizes the accident dynamics, the causes and the consequences and the forensic methods adopted by the Authors during their investigation. This paper is based on the technical documents provided by the Authors to the Public Prosecutor and presents the Authors’ perspective. Full content can be found in the official documents used in the trial.

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