Definition of a shortcut methodology for assessing flood-related Na-Tech risk

Abstract. In this paper a qualitative methodology for the initial assessment of flood-related Na-Tech risk was developed as a screening tool to identify which situations require a much more expensive quantitative risk analysis (QRA). Through the definition of some suitable key hazard indicators (KHIs), the proposed methodology allows the identification of the Na-Tech risk level associated with a given situation; the analytical hierarchy process (AHP) was used as a multi-criteria decision tool for the evaluation of such qualitative KHIs. The developed methodology was validated through two case studies by comparing the predicted risk levels with the results of much more detailed QRAs previously presented in literature and then applied to the real flood happened at Spolana a.s., Neratovice, Czech Republic in August 2002.</p

Influence of Ground on Jet Fire Extension

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

Predictive models for the estimation of the minimum ignition energy of polydisperse organic dusts

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

Study of the Interaction Between a High-Pressure Jet and Horizontal Tanks using CFD

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

Modelling of indoor air pollutants dispersion: New tools

Ventilation systems are used for create a thermally comfortable environment and good indoor air quality. It is therefore essential to have adequate tools for predicting the performance of these systems. Among the various approachs, the computational fluid dynamics could be a useful tool for the design of the ventilation system. When dealing with pollutants dispersion problems, a steady state averaged simulation can be misleading because it is not able to properly predict and model peak concentrations, which can be relevant even if temporary. An interesting approach is the use of LES (Large Eddy Simulations) simulations to obtain a better description of concentrations oscillations. In this framework, the aim of this work is the validation of simulation carried out using the FDS (Fire Dynamic Simulator) software with an actual case study, already studied with a mock-up. Secondly, two new configurations of the ventilation system are proposed, in order to stress the capacity of the software to describe complex and different features, classical of HVAC (Heating, Ventilation and Air Conditioning) systems. Interesting conclusions about efficiency are drawn from the comparison, highlighting the potentiality of the software

High-pressure methane jet: Analysis of the jet-obstacle interaction

The study of unplanned high-pressure gas releases is of paramount importance in the industrial safety framework because of the possible large consequences, both in case of flammable and toxic substances leakage. In addition, if an obstacle is involved in the release, it is known that the main effect on the jet behavior is the enhancement of the risk area. Pointing out the importance to consider the obstacle presence, among the various available numerical approaches, the sole reliable tool able to correctly model the scenario of a jet interacting with an obstacle seems to be the Computational Fluid Dynamics (CFD). This work lies in the context outlined through the examination of a realistic unignited high-pressure methane jet interacting with a realistic obstacle placed along its axis via CFD simulations: a stationary 65-bara unignited methane jet outflowing from a one-inch diameter hole and a medium size horizontal cylindrical tank are the building blocks of the realistic scenario. The aim is to deeply investigate how the distance between obstacle and jet orifice modifies the jet behavior. In particular, the final purposes are: i) to establish when the obstacle most influences the jet cloud extent and, ii) to assess when the obstacle influence expires. Moreover, a sensitivity analysis on the obstacle shape and size is conducted for comparison purposes