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Industrial accidents can be triggered by natural hazards (as earthquakes, floods, lightning, and extreme temperatures) which can result in fires, explosions, or release of hazardous substances. These high impact accidents are called NaTech (Natural Hazards Triggered Technological Accident). NaTech can determine huge damages and their rapid growth in the latter years is also associated with climate change evolution. In this context, refineries are among the facilities majorly affected by NaTech and the presence of large amounts of hazardous materials makes easier to envisage potentially catastrophic scenarios. Risk assessments should include NaTech scenarios, and this should come with the availability of robust and efficient screening tools for safety engineering applications. Due to the complexity of extreme natural events, no general or reference models are officially available, leaving to the analyst the duty to estimate aspects such as probability of occurrence of an extreme natural event. Extreme events weather databases are also often incomplete, reporting data on past natural events with insufficient information for risk assessment purposes. This is particularly true for extreme winds. This paper applies a modified version of a literature reference model, based on the analysis of the occurrence of extreme winds on a Lat-Long quadrant classification. A grid choice dependence is shown, highlighting the variation of extreme winds likelihood of extreme winds on 3 Italian refineries located close to the sea. By changing the reference area for extreme winds analysis, the screening analysis leads to different results. [ABSTRACT FROM AUTHOR]

The British Petroleum (BP) American Refinery accident, back in 2005, was one of the most severe explosions recorded in any industrial accident database. According to both the reconstruction and the interviews with the company, it was found that the causes of the accident where both technical, with the failure of a level controller, which was also badly designed for the isomerization unit, and human, with a very stressed and undersized personnel. In this work, a Quantitative Risk Assessment (QRA) based on the Recursive Operability Analysis (ROA), as hazards and accidental scenarios identification tool, was performed on the unit (BP isomerization unit) involved in the accident. The analysis was carried out exploiting many different techniques, to provide a proper assessment. The quantification of all node-deviation-variables (necessary to establish the real behaviour of the system) was performed by implementing the BP plant in CoCo simulator. Basic events were identified using a simplified Failure Mode and Effects Analysis (FMEA). Then, the magnitude of fire and explosion was estimated basing on the simulation results provided by the ALOHA software. Finally, a Fault Tree Analysis for the BP isomerization unit was performed, quantifying the probability of occurrence of all the most credible scenarios. Probabilities, magnitudes, and risk indexes (function of the distance with respect to the source point) were also estimated. From the analysis, the importance of redundant measurements of the most crucial variables, such as liquid level, and the impact of human errors was highlighted. [ABSTRACT FROM AUTHOR]

Accidental high-pressure flammable gas releases are among the most relevant hazards in the process safety, and consequences could be severe. In the recent decades, there have been numerous efforts to study high- pressure jets in open field (i.e., free jets). Easy-to-use mathematical models have been developed, to rapidly assess the main physical variables involved in safety evaluations. However, in a realistic scenario, the accidental leak may involve either the ground or a piece of equipment. As demonstrated by recent works, when a jet interacts with an obstacle, its behavior can significantly change. Therefore, the mathematical models extrapolated for the free jet scenario could be a source of incorrect predictions. Focusing on the scenario of an accidental high-pressure unignited flammable jet, this work shows how the presence of one or two obstacles, placed at a different distance from the source of the leak, can influence the lower flammability limit cloud extent of methane. Varying the height of the source term, the effect of the interaction among the jet, both the obstacles, and the ground was systematically studied through a Computational Fluid Dynamics analysis. [ABSTRACT FROM AUTHOR]

The process industry is a sector characterized by the sale of 50 % of its products in the form of powder and in which 80 % of the goods generated are made through a production system that involves the use of a powder. This sector massively employs solid materials and, using operations such as material transport, crushing, screening, sanding, trimming, feeding tanks and bins, storage of granular materials and many other activities, is very often characterized by the collateral emission of dusts. A similar scenario makes the risk of a dust explosion one of the major concerns of the process industry. In this context, to ensure the safety of people and infrastructures, it is crucial to obtain the parameters that characterize the explosiveness of the dust. Actually, these parameters are all determined experimentally, involving large economic costs, technical difficulties, and long dead times. This work focused on the estimation of one of these parameters, the Minimum Ignition Energy (MIE), which is considered to be one of the most important to assess the probability of having a dust explosion. Therefore, starting from the experimental test within a 1.2 L Hartmann tube, two new versions of a mathematical model capable of predicting the MIE for an organic powder were proposed. The models characterize the powder analysed through its particle size distribution and a few chemical-physical characteristics obtained from literature. Six organic powders were selected to validate the model (aspirin, cork, corn starch, sugar d50=135 μm, sugar d50=34 μm and wheat flour), with the intention of comparing the theoretical data obtained with literature experimental ones. [ABSTRACT FROM AUTHOR]

Understanding how dust can ignite and explode in an industrial contest is an important and complex task, and much of the work around this is mainly performed via experimental measurements, in accordance to specific standards. However, those same properties are straightforwardly closely related to the nature of the experimental tests. Among these, the Minimum Ignition Energy (MIE) of a dust cloud, that is usually measured in a MIKE 3 apparatus, can be affected by several factors, as: delay time of the electric spark with respect to the dust-air dispersion formation inside the apparatus, dust concentration, humidity content, dust granulometry, etc. The delay time is one of the worst parameters to adjust, because the fluid-dynamics of the dust-air mixture inside the tube is not easily predictable. Within this work, a study on the characteristic times of all the relevant phenomena occurring within a MIKE 3 apparatus was done by means of slow-motion videos of the tests. Particularly, three different characteristic times were compared referring to a given sample of niacin dust: dust lifting and settling times, effective spark delay time (that is, the time at which the spark is visible) and combustion time (that is, the time at which the flame is visible). According to the results, the effective delay time is almost always quite different with respect to the theoretical one, influencing the effective concentration of dust between the electrodes and, finally, the possibility to have a flame ignition or not within the apparatus. This means that the value of the MIE parameter can be profoundly influenced by the effective delay. [ABSTRACT FROM AUTHOR]

A common accident in the industrial process industry is the puncturing of storage tanks or rupture of process pipelines containing gases. In these scenarios, the gas will escape the piece of equipment producing a single- phase gas jet. If the fluid is flammable, an ignition source is most probably encountered during the accidental scenario and a jet-fire can follow the leak. Free jets of hazardous gases and free jet-fires have been extensively analyzed in the past literature to assess their shape and extension for safety purposes. Similar analyses have been conducted to observe the effect on shape/extension of neutral jets if obstacles were present. Also, the effect of the ground proximity to the jet source has been studied. In general, the presence of obstacles and the proximity to the ground lead to enlarged hazardous areas, mainly because of the Coandă effect. In this work, flammable jets igniting and forming a jet-fire were considered. The effect of the ground proximity was analyzed, to observe the extension of the flame. Two opposed phenomena were supposed to act on the fire, differently from non-ignited jets: the Coandă effect having an attractive nature towards the ground and the buoyancy effect on the opposite direction. The relevant methane jet-fires case study was considered carrying out computational fluid dynamics (CFD) simulations using the Fire Dynamics Simulator software. The study considered both the jet source height from the ground and the gas relief flowrate effects. CFD results were summarized basing on simple dimensionless parameters to determine the eventual variation of jet-fire extension for preliminary safety analyses. [ABSTRACT FROM AUTHOR]

In the summer of 2007, in Fossano, Italy, one of the most catastrophic and famous dust explosions in Italy, caused by flour dust, occurred in Molino Cordero, a historic cereal milling and flour storage plant. The explosion happened during the pneumatic unloading operation of a tank truck, previously accidentally overfilled. Five people lost their lives, and the building was partially destroyed by the powerful explosion. The forensic reconstruction and investigation of this accident were carried out years after the explosion. This paper has presented an assessment of the main potential ignition sources that can be expected in a flour mill, taking into account the typical equipment that is normally installed in this process. The target is to provide the employer and the users of flour mill plants with basic information that can be helpful in carrying out the specific explosion risk assessment, necessary for every single process. Possible improvements, which could be implemented to reduce the risk of explosion to a tolerable level, will be highlighted. [ABSTRACT FROM AUTHOR]

Fine chemical compounds and so-called "specialties" are generally synthesized through batch or semicontinuous processes. This is largely because such syntheses often involve complex and highly exothermic reactions, to be performed in semi-batch reactors for safety and/or selectivity reasons. An effective way to reduce costs and improve the reproducibility of such batch processes is to transform them into their continuous counterparts to reduce volumes and investment costs, while increasing the inherent safety of the process thanks to fewer hold-ups. The “shift to continuous” allows to reduce both the overall process times, with a general decrease in operating costs, and the content of solvents used as thermal flywheels, thanks to the greater efficiency of the heat exchange systems. All these aspects are defined as process intensification. In this work, the intensification of the production process of N-(4-nitro, 2-phenoxyphenyl) methanesulfonamide (NIM) by nitration in glacial acetic acid of N-(2-phenoxyphenyl) methanesulfonamide (FAM) will be proposed. Starting from the original semi-batch recipe two different continuous configurations will be proposed: a series of tubular reactors and a series of continuous reactors with complete mixing, in both cases with intermediate injections. The solvent content (glacial acetic acid) has been drastically reduced (from 82.5% to 50% by weight) to increase the levels of environmental sustainability of the synthesis. The high exothermicity of the process and the extremely rapid reaction kinetics were two fundamental aspects which had to be considered in the transition to the continuous process of the new formulation with reduced solvent content. For this reason, an ad hoc procedure was developed which allows the semi-batch recipe to be transformed into a corresponding one conducted in a tubular reactor with continuous lateral injections; this reactor was then discretized in the two reactor configurations mentioned above. The results obtained have shown how it is possible to obtain the desired product with practically unitary conversions using: a) a series of 4 isoperibolic tubular reactors, each with 4 discrete lateral feeds; b) a series of 5 mixed reactors with discrete side feeds. In both cases, the correct distribution of both the flow rate fed between the reactors in series and the temperatures of the cooling fluid (defined on the basis of the procedure developed for the passage of the process from discontinuous to continuous) was decisive for obtaining the desired performance. The series of tubular reactors was found to be optimal from the point of view of thermal control of the process, confirming that a series of tubular reactors is to be preferred in terms of safety compared to its counterpart with mixed reactors. [ABSTRACT FROM AUTHOR]

In this work, the possibility to shift from a batch to a continuous production of 16-hexadecanolide, one of the main components of the white musk essence, was theoretically studied. The selected synthesis was an upgraded version of that proposed by Story in 1968, who obtained macrocyclic compounds from the decomposition of ketone peroxides (in this case the involved peroxide was tricyclohexylidene triperoxide). But such reaction presents some huge criticalities: 1) high exothermicity and, 2) production of carbon dioxide, which are known to both modify the kinetics of the desired reaction and lead to a pressure increase inside the reactor whether the gases are not vented. For such reasons, to implement any safe continuous production of this chemical compound, two main points must be addressed: 1) determination of the system runaway boundaries and 2) identification of the optimal operating conditions to make sustainable the production of 16- hexadecanolide (that is, the theoretical design of a tubular reactor capable of continuously discharging the produced incoercible gases). For what concerns the first point, a sensitivity analysis was carried out to determine the safe operating range of the most important operating variables (that is, coolant temperature and reactant inlet temperature) possibly taking into account the effect of radial dispersion; for the second point, as carbon dioxide is produced over the decomposition and needs to be continuously vented to avoid reactor pressurization, a Teflon tube, highly permeable with respect to carbon dioxide, was proposed and its theoretical performances was investigated trying to maximize 16-hexadecanolide productivity also maintaining safe operating conditions. Results showed the theoretical possibility of developing a continuous production process capable of being also commercially sustainable. [ABSTRACT FROM AUTHOR]

Temperature control is probably the most important factor that influences a chemical reaction yield, in particular when working with strongly exothermic reactions. The oxidation of 2-octanol to 2-octanone is a well-known two phase (liquid-liquid) oxidation reaction, and it suffers of yield loss due to side reactions that lead to further oxidation to a mixture of carboxylic acids. As the reaction is exothermic, controlling the reactor temperature is extremely important for a safe operation. A temperature control naturally induces fluctuations within the system, which can impact the kinetics of the desired reaction. The aim of this work is to investigate the impact of the Proportional-Integral temperature controller parameters on the conversion to 2-octanone. The reaction is carried out in a semi-batch reactor, dosing 2-octanol on a solution of nitric acid. The production of nitrosonium ion is promoted by adding sodium nitrite to the nitric acid. The reaction is carried out with high stirring speed, in order to work under full chemical control regime, avoiding the effect of material diffusion between the two phases. Several simulations were done referring to an Easymax™ 402 Workstation (Mettler Toledo) under an isothermal temperature control mode. Target temperatures were chosen in the -15 - 15 °C range. The proportional parameter was tested in the range of 5-15, and the integral parameter was kept in the range of 60-600 s. Results showed that runaway boundaries are significatively affected by the values of the temperature controller parameters, highlighting how it is fundamental a calorimetric investigation of the process in view of a safe process optimization. [ABSTRACT FROM AUTHOR]

Worksite activities are time-limited events associated with continuous releases of airborne pollutants, such as carbon monoxide, particulate matter, and NOx, and they impact potentially vast areas. The side-effects on the environment can be severe, and they are subject of literature studies, with the final aim of proposing solutions that may improve the management of air emissions. No general assessment method or approach is yet available to estimate their effects on the environment and workers' health. In this work, a general procedure that can be potentially applied to every type of worksite is proposed (i.e., construction sites, upgrading of chemical plants, road sites, etc..). The approach involves a detailed assessment of emissions and their expected pollutant concentrations. A dedicated mathematical model has been defined to assess pollutant emissions over time, consistent with all the different phases of foreseen activities. Emissions are defined on base of the GANTT descriptions of the activities and air pollutant dispersion is simulated with a dedicated model. Finally, the obtained results are evaluated against air quality thresholds as defined by laws and conditioning the human health risks for workers and citizens potentially exposed to pollutants. [ABSTRACT FROM AUTHOR]

Industrial safety has been a topic of growing interest during the last decades, mainly because of the increased awareness and knowledge about safety issues. In this framework, the detailed reconstruction of the dynamics of an explosion (1 killed and 8 injured) occurred, on the 26th of June 1971, at Noury Italy (a plant dedicated to the production of chemicals for hardening plastics) is worth of interest and it could be used to improve actual safety guidelines related to the storage of peroxides. The accident happened before whatever Seveso Directive release. Therefore, root-causes reconstruction and related risk assessment were carried out making a comparison between a hypothetical plant layout at that time and a modern plant layout implemented with minimum safety systems, such as acoustic alarms and adequate bypass lines. The accident reconstruction was carried out by doing a deep literature research, mainly based on newspaper clippings of the time, to both remodel the accident at best and draw the most likely layout of the plant. The latter is of fundamental importance to carry out a risk assessment procedure by applying the Recursive Operability Analysis (ROA), which allows for a direct generation of the fault trees that can provide an easy estimation of the probability of occurrence of all unwanted events. This method was applied to the Noury Italy case study to show the criticalities of the storage equipment also underlining the possible improvements which could be implemented also in the '70s, therefore preventing the fatal explosion. [ABSTRACT FROM AUTHOR]

Shifting from discontinuous to continuous (BtoC) processes is one of the most studied topics in the current chemical engineering research mainly because it implies a huge impact on safety due to the strong reduction of the reactor size (which leads to intrinsically safe processes). The aim of this work is to carry out a high viscosity, high monomer content (70% w/w) emulsion tetrapolymerization reaction in a series of Continuously Stirred Tank Reactors (CSTRs). Emulsion polymerizations are usually carried out in semi-batch (SB) reactors, by dosing a mix of micelles swollen with unreacted monomer (which can be called "premix") on a water-based buffered solution. The reaction is highly exothermic thus a good temperature control can be maintained in an industrial reactor using long dosing times. The proposed BtoC procedure is quite simple, and it is based on the total accomplishment of three main constraints: 1) process productivity must be increased with respect to the SB recipe; 2) reactors workup must be reduced; 3) no loss of product during the start-up phase of the continuous system (this constraint also includes avoiding runaway reactions triggering). The approach suggests to: 1) divide the SB recipe in two main phases; 2) start-up the series of CSTRs following the first part of the SB recipe; 3) go to continuous by activating a pump to transfer the content of the first reactor in the second one; 4) fill the second reactor of the series following the second part of the SB recipe; 5) go to continuous by unloading the content of the second reactor in the final workup reactor. Such an approach was tested with a recipe of industrial interest, based on butyl acrylate. The experimental setup was carried out with a battery of 2 CSTRs, 5 pumps, and a tank for the final product. Multiple samples were collected overtime and analyzed, tracking free monomer content and particle size. From this study, we found that the process started up using the proposed BtoC procedure reached a steady state which was not acceptable from a product quality point of view. Anyway, the continuous process could be carried out for a limited amount of time (this means that it was possible to run a semi-continuous process) by optimizing dosing times and reactors volume. Under such conditions, it was possible to run a semi-continuous synthesis without loss of product due to the start-up phase, in smaller and easier to control reactors than the semi-batch ones. [ABSTRACT FROM AUTHOR]

For several years, dust explosions have been one of the major causes of industrial accidents, spanning from metalworking to pharmaceuticals sectors. In accordance with the latest Chemical Safety Board (CSB) investigations, three out of four dust explosions in the United States involved metallic dusts (iron, titanium, zirconium and aluminum). Many chemical processes involve metal powders for their exceptional mechanical, optical and catalytic properties, such as the production of plastics, rubber, paints, coatings, inks, pesticides, detergents and even drugs. The severity of a dust explosion can be defined using experimental parameters such as the maximum explosion pressure (Pmax), the maximum rate of pressure rise ((dP/dt)max) and the deflagration index (K5t), which are employed to predict the consequences of a dust explosion for a given scenario. Among these parameters, the deflagration index plays a fundamental role, as it is used for the design of deflagration nozzles aimed to protect industrial equipment and silos from internal dust explosions. The purpose of this work is to develop a mathematical model able to predict the K5t value of metal powders as a function of chemical-physical data and the particle size distribution (D50 was used as global information). The model structure is based on the writing and resolution of the material and energy balance equations on the single dust particle, also estimating the contribution of oxygen diffusion which, in the case of metal powders, greatly depends on both tortuosity and porosity. The results well agreed with experimental data, providing the basis for the development of more detailed models. [ABSTRACT FROM AUTHOR]

With the introduction of new regulations and sustainable technologies, revamping and upgrading already existing chemical plants is nowadays an important element in the framework of process engineering. Such important modifications must come along in parallel improvement of process safety. In this sense, risk assessment is a tool that should be versatile and easy to update by definition. However, even the most common methods currently used for accidental scenarios identification and risk assessment estimation (such as HazOp) may prove to be very time-consuming when discussing about safety from process modifications. The availability of a reliable and easy-to-update tool for safety engineering is crucial for process industries. In this work, we compare a risk analysis on a chemical plant subject of modifications performed with two different tools: HazOp and FTA vs Recursive Operability Analysis (ROA) and FTA. Both techniques have been applied to a tank dedicated to dust mixing that was subject of process modifications. Both methods come to the same conclusions, highlighting new failures and process criticalities, associated with the introduction of flow alarms and interlocks in case of excessive depressurizing. It is shown that the Recursive Operability Analysis, with its cause-consequence structure tied with process variable interactions, is much more effective in a risk assessment update. [ABSTRACT FROM AUTHOR]