The level of protection for personal protective equipment (PPE) in firefighting is important for Swedish shipowners; they want to be sure that the equipment they provide is sufficiently safe for the types of fires that can occur onboard. Shipowners also want to be updated on risks related to the carriage of alternative fuel vehicles (AFVs). Safety products and equipment used onboard ships with a European flag must be certified in accordance with the Marine Equipment Directive (MED) and follow the regulations in the International Convention for the Safety of Life at Sea (SOLAS). For fire suits, this means that they must be certified according to one of three standards listed in MED. Two of these standards cover suits used in special cases, with very intense radiant heat, and should only be worn for short periods. The third standard, EN 469, is the same standard that is referred to the PPE Regulation 2016/42, making EN 469-approved fire suits used among European firefighters ashore. However, EN 469 contains two different performance levels where the lower level is not suitable for protection against risks encountered when fighting fires in enclosures. Based on a user study and a risk assessment for AFVs, a set of suggested changes to MED and SOLAS were prepared, together with a set of recommendations for operators that were found important but not subject for regulations. A ready-to-use quick guide, containing the most important results, has been developed for operators.
The project BREND investigated risk with alternative fuel vehicles inside ro-ro spaces. BREND 2.0 is a continuation and has in particular investigated two of the major risks identified in BREND, namely the risk of toxic gases from electric vehicle fires and the risk of a pressure vessel explosion for fire exposed biogas or hydrogen vehicle tanks. Simulations of electric vehicle fires inside a ro-ro space based on real input fire data has been performed. Field experiments that investigate the conditions that can lead to pressure vessel explosion were made with fire exposed biogas and hydrogen tanks. Recommendations are given about how ro-ro space fires in alternative fuel vehicles, or indeed any vehicle fire, can be managed.
Dust explosion is a constant threat to industries which deal with combustible powders e.g. woodworking, metal processing, food and feed, pharmaceuticals and additive industries. Physics-based, well-verified and well-validated models and numerically efficient codes are important tools for designing dust explosion protection systems where the current standards are not applicable. This work aims at (i) presenting a physics-based dust explosion model based on an open source code OpenFOAM, (ii) comparing the computed pressure traces with the measured ones for a vented corn starch dust explosion in a 11.5 m3 vessel, and (iii) highlighting the future work.
Dust explosion is a constant threat to industries which deal with combustible powders such as pellets producers, food industry, metal industry and so on. The present work aims atdeveloping a numerical tool by (i) implementing a premixed turbulent combustion model into an open-source CFD software OpenFOAM, (ii) verifying the implementation using analytical solutions,and (iii) validating the approach in unsteady 3D RANS simulations of cornflour dust explosions investigated experimentally using the Leeds fan-stirred bomb [1-3]. A detailed description of thiswork is reported in a recent publication [4].
Dust explosion has been a constant threat to the physical working environment of the Swedish process industries which deal with combustible powders. Examples of such industries are pellets, paper, metal processing, food and feed, pharmaceuticals, and additive industries. This project aims at (i) development of physics-based and well-validated models which address the important combustion phenomena in dust explosions, (ii) development of a well-verified and an efficient numerical tool based on an open-source toolbox OpenFOAM for predicting consequences of dust explosions and (iii) simulation of large-scale dust explosions in the process industries. The project result improves the understanding of dust explosions, and it provides the process industries with a numerical tool for designing safer process plant regarding dust explosions.The model and code development were carried out in a step-by-step fashion. First, the so-called Flame Speed Closure (FSC) model for premixed turbulent combustion, was implemented into OpenFOAM. The implementation was verified against analytical solutions for 1-dimensional planar and 3-dimensional spherical turbulent flames. Second, the developed code including the model, i.e., FSCDustFoam, was validated against experimental data on corn starch dust explosion in a fan-stirred explosion vessel under well-controlled laboratory conditions. Third, the FSC model was extended by adapting the well-known experimental observations of the self-similarity of the flame acceleration to address large-scale industrial dust explosions. An excellent agreement between measurements of vented corn starch dust explosions in an 11.5 m3 vessel and the simulations using the extended the FSC model was obtained.In spite of the successful development of FSCDustFoam, challenges remain. Specifically, the current version of FSCDustFoam cannot address the effect of different shapes of vent openings on dust explosions. Nevertheless, FSCDustFoam is a promising tool to be applied and further developed to resolve the challenging reality regarding dust explosions in the Swedish process industries.
Thermal runaway is a major concern for lithium-ion batteries in electric vehicles. A manufacturing fault or unusual operating conditions may lead to this event. Starting from a single battery cell, more cells may be triggered into thermal runaway, and the battery pack may be destroyed. To prevent this from happening, safety solutions need to be evaluated. Physical testing is an effective, yet costly, method to assessing battery safety performance. As such, the potential of a numerical tool, which can cut costs and reduce product development times, is investigated in terms of capturing a battery module’s tolerance to a single cell failure. A 3D-FE model of a battery module was built, using a commercial software, to study thermal runaway propagation. The model assumes that when the cell jelly roll reaches a critical value, thermal runaway occurs. This approach was considered to study the module’s tolerance to a single cell failure, which was in reasonable agreement with what had been observed in full-scale experiments. In addition, quantitative sensitivity study on the i) model input parameters, ii) model space, and iii) time resolutions on the computed start time instant and time duration of thermal runaway were performed. The critical temperature was found to have the greatest influence on thermal runaway propagation. The specific heat capacity of jelly roll was found to significantly impact the thermal runaway time duration. The multi-physics model for battery thermal propagation is promising and worth to be applied with care for designing safer batteries in combination with physical testing.
A vented corn starch dust explosion in an 11.5 m3 vessel is studied using both experimental and numerical methods. The reduced explosion overpressure in the vessel is recorded using two pressure sensors mounted on the wall inside of the vessel. Unsteady three-dimensional Reynolds-Averaged Navier-Stokes simulations of the experiment are performed using the Flame Speed Closure (FSC) model of the influence of turbulence on premixed combustion. The model was thoroughly validated in previous studies and was earlier implemented into OpenFOAM CFD software. The self-acceleration of a large-scale flame kernel is associated with the influence of combustion-induced pressure perturbations on the flow of unburned reactants ahead of the kernel. Accordingly, the FSC model is extended by adapting the well-known experimental observations of the self-similarity of the kernel acceleration. Influence of different turbulence models on the simulated results is also explored. Thanks to the extension of the FSC model, the measured time-dependence of the pressure is well predicted when the k-omega-SST turbulence model is used. © 2021 The Authors
A vented corn starch dust explosion in an 11.5 m3 vessel is studied by comparing experiments, simulations and thestandards. The reduced explosion overpressure inside the vessel is recorded using two pressure sensors installed on theinner wall of the vessel. 3D Unsteady Reynolds-Averaged Navier-Stokes simulations of the experiment are performedusing the Flame Speed Closure (FSC) model and its extended version. The FSC model predicts the influence of turbulenceon premixed combustion, and the extended version allows for self-acceleration of a large-scale flame kernel, which isassociated with the combustion-induced thermal expansion effect. Such an extension is highly relevant to large-scaleindustrial application. The explosion overpressure-time trace computed using the extended FSC model agrees reasonablywell with the experimental data. Furthermore, the effect of vent size and ignition location on the explosion overpressureis studied by comparing the simulation results and the standards. The developed numerical tool and model is especiallyuseful for scenarios, which are not addressed in the standards, and it deserves further study in simulations of other largescalesdust or gaseous explosions together with comparison with experiments.
The design of explosion mitigation strategies e.g. vent design is mainly based on dust explosioncharacteristics such as the maximum explosion pressure XÇïÓ and the deflagration index n! of dustcloud, which are defined in various standards.The wood dust explosion characteristics can be directly obtained by performing standard tests, and testresults are also available in the literature. However, the parameters for one type of dust may varysubstantially in the literature. For example, the n! value for one wood dust is 11.4 times higher thananother wood dust in Gestis-Dust-Ex database. The reason for such large variation in explosionparameters is due to factors such as material properties, particle size distribution, particle shape, moisturecontent, turbulence level during tests and so on.The objectives of this paper are (i) to carry out dust explosion tests for XÇïÓ and n! for two wood dustswith well-described material parameters such as particle size distribution and moisture content accordingto European standards, (ii) to perform statistical analysis of wood dust explosion characteristics includingXÇïÓ and n! in the literature, (iii) to identify the effects of dust material parameters such as particle sizeand moisture contents on XÇïÓ and n! and (iv) to highlight the variation in XÇïÓ and n! and theimportance of obtaining knowledge about these properties of an individual dust, e.g. via dust explosiontests.
Dust explosion is a constant threat to industries which deal with combustible powders such as pellets producers, food industry, metal industry and so on. The current standards regarding dust explosion venting protecting system are based on empirical correlations and neglecting complex geometry, which may lead to failure in estimating explosion overpressure and therefore risk for fatalities at workplaces. Therefore, there is an urgent need for a reliable tool for vent protection design in the process plants. The objectives of this presentation are (i) to implement a model that focuses on turbulent burning of a dust-air cloud in an open source platform OpenFOAM, (ii) to verify the implementations against analytical solutions for 1-D planar and 3-D spherical premixed turbulent flames and (iii) to validate the model against Leeds cornflour dust explosion vessel experiments.
Dust explosion is a constant threat to industries which deal with combustible powders such as woodworking, metal processing, food and feed, pharmaceuticals and additive industries. The current standards regarding dust explosion venting protecting systems, such as EN 14491 (2012) and NFPA 68 (2018), are based on empirical correlations and neglect effects due to complex geometry. Such a simplification may lead to failure in estimating explosion overpressure, thus, increasing risk for injuries and even fatalities at workplaces. Therefore, there is a strong need for a numerical tool for designing explosion protecting systems. This work aims at contributing to the development of such a tool by (i) implementing a premixed turbulent combustion model into OpenFOAM, (ii) verifying the implementation using benchmark analytical solutions, and (iii) validating the numerical platform against experimental data on cornflour dust explosion in a fan-stirred explosion vessel, obtained by Bradley et al. (1989a) under well-controlled laboratory conditions. For this purpose, the so-called Flame Speed Closure model of the influence of turbulence on premixed combustion is adapted and implemented into OpenFOAM. The implementation of the model is verified using exact and approximate analytical solutions for statistically one-dimensional planar and spherical turbulent flames, respectively. The developed numerical platform is applied to unsteady three-dimensional Reynolds Averaged Navier-Stokes simulations of the aforementioned experiments. The results show that the major trends, i.e. (i) a linear increase in an apparent turbulent flame speed St,b with an increase in the root mean square (rms) turbulent velocity u' and (ii) and an increase in St,b with an increase in the mean flame radius, are qualitatively predicted. Furthermore, the measured and computed dependencies of St,b(u') agree quantitatively under conditions of weak and moderate turbulence. © 2020
Dammexplosioner är ett konstant hot mot de svenska industrier som hanterar material eller utför processer som skapar brännbart damm, såsom pelletstillverkare, livsmedelsindustri, metallindustri m.m. Det aktuella projektet syftar till att (i) utveckla välvaliderade numeriska modeller som kan ta hänsyn till de viktigaste förbränningsfenomenen, (ii) utveckla ett numeriskt verktyg baserat på en öppen källkod, och (iii) beräkna verkliga dammexplosionsscenarier i samråd med representanter för berörda industrier. Projektresultatet kan fylla kunskapsluckorna när det gäller förståelse för dammexplosioner, att uppskatta konsekvenser av dammexplosioner, ge rekommendationer för bättre konstruktion av byggnader och relevanta säkerhetssystem, och därmed ge personalen en säkrare arbetsmiljö. Under det första året, har den öppna källkodsplattformen OpenFOAM installerats och testats. Den så kallade FSC (Flame Speed Closure) modellen för förblandade turbulenta flammor implementerades i OpenFOAM. Implementeringen av FSC-modellen har verifierats mot analytiska lösningar för 1-D plana och 3-D sfäriska förblandade turbulenta flammor. Verifikation av implementationen visar att modellen implementerades korrekt. För närvarande är den numeriska modellen under validering mot småskaliga experimentella resultat för 3-D sfäriska flamma i Leeds förbränningskärl. De första beräkningarna visar att modellen och koden predikterar trenden. Det vill säga, flamhastigheter ökar när turbulenta hastighetsfluktuationer ökar. Beräkningar visar också att modellen och koden även kvantitativt predikterar flamhastigheter om rimliga modelleringsparametrar används. I nästa steg, kommer modellen och koden utvecklas ytterligare för att ta hänsyn till värmeförluster och strålning. Därefter kommer beräkningsresultaten att jämföras med experimentella resultat från de storskaliga tryckavlastningsförsöken, med olika geometrier, utförda vid Rembe® Research and Technology Center.
Dammexplosioner är ett konstant hot mot de svenska industrier som hanterar material eller utför processer som skapar brännbart damm, såsom pelletstillverkare, livsmedelsindustri, metallindustri m.m. Det aktuella projektet syftar till att (i) utveckla välvaliderade numeriska modeller som kan ta hänsyn till de viktigaste förbränningsfenomenen, (ii) utveckla ett numeriskt verktyg baserat på en öppen källkod, och (iii) beräkna verkliga dammexplosionsscenarier i samråd med representanter för berörda industrier. Projektresultatet kan fylla kunskapsluckorna när det gäller förståelse för dammexplosioner, att uppskatta konsekvenser av dammexplosioner, ge rekommendationer för bättre konstruktion av byggnader och relevanta säkerhetssystem, och därmed ge personalen en säkrare arbetsmiljö. I slutet av det första och i början av det andra projektåret, har den utvecklade numeriska plattformen, som innehåller dammexplosionsmodellen validerats med de experimentella data för dammexplosioner i majsstärkelse i Leeds förbränningskärl under välkontrollerade experimentella förhållanden. Därefter har ett samarbete etablerats med Rembe Research and Technology Center i Tyskland för att applicera den utvecklade numeriska plattformen för att simulera en storskalig industriell dammexplosion. Parallellt med samarbetet med Rembe, har ett samarbete etablerats med Gexcon för att utföra en gemensam studie om dammexplosioner med det utvecklade verktyget i projektet och den kommersiella koden FLACS-DustEx.
Thermal propagation is one of the major challenges when batteries will be used in dwellings in large scale. It means the exothermic reactions in the cell are out of control and can lead to a fast release of flammable and toxic gases. In a system involving a large number of cells, thermal runaway can rapidly propagate from one battery cell to the whole system, which means substantial fire and explosion risks, an event that is important to mitigate and prevent. Multi-physics simulations together with full-scale testing is a cost-effective method for designing safer batteries. This project aims at simulating thermal runaway initiation and propagation using a multi-physics commercial software GT-Suite.
A battery thermal runaway model containing 12 prismatic cells based on 3-D Finite Element approach was built using GT-Suite. The computed thermal runaway time instants versus thermal runaway cell number were compared with full-scale experimental data with reasonable agreement. Quantitative sensitivity study on the model input parameters and model space and time resolutions on the computed start time instant and time duration of thermal runaway were performed. The thermal runaway model was then extended with an electric equivalent sub-model to simulate the short circuit. With the electrical model acting as the input to the thermal model, the most interesting output of the simulation is the change in temperature of the cells, dependent on the current in the cells, with respect to time. The current is determined by the value of the external resistance through which the short takes place and the voltage level of the battery pack. The obtained results from the above short circuit simulations can only be used as a starting point and not as absolute values for neither triggering the thermal model nor for accurately simulating a battery under an electrical load. Furthermore, GT-Suite was applied to simulate the gas dispersion inside a room. A comparative study of the dispersion of toxic gases during thermal runaway, utilising an arbitrary release of HCN to represent the battery gases, in a small compartment with natural ventilation was investigated and the results compared the same situation simulated in FDS. The pipe based modelling supported by GT-Suite has limited applicability and overestimated the concentrations close to the ceiling whereas the lateral concentrations where underestimated.
The multi-physics model for battery thermal runaway process is promising and worth to be applied with care for designing safer batteries in combination with full-scale testing.
The open source CFD code FireFOAM has been verified and validated against analytical solution and real fire tests. The verification showed that FireFOAM solves the three modes of heat transfer appropriately. The validation against real fire tests yielded reasonable results. FireFOAM has not been validated for a large set of real fires, which is the case for FDS. Therefore, it is the responsibility of the user to perform the validation, before using the code. One of the advantages of FireFOAM compared to the Fire Dynamic Simulator is that FireFOAM can use unstructured grid. FireFOAM is parallelised and scales reasonable well, but is in general considerably slower in computation speed than the Fire Dynamic Simulator. Further, the software is poorly documented and has a steep learning curve. At present it is more a tool for researchers than for fire consultants.
Fire in alternative fuel vehicles in ro-ro spaces (BREND)
A literature study has been carried out that compiles the body of research regarding hazards related to fire in alternative fuel vehicles (AFV) in ro-ro spaces. Alternative fuels include liquefied gas (e.g. LNG), compressed gas (e.g. CNG) and batteries. Hazards related to a conventional vehicle on fire are heat, smoke and toxic gases. Another hazard is projectiles related to small explosions of e.g. tyres or airbags. AFVs also include hazards of large explosion, jet flames, more apparent re-ignition, etc.
The study also includes land based fire fighting tactics related to AFV fires. If the fuel storage on an AFV is affected, land-based firefighters often use a defensive tactic, which means securing the area around the vehicle and preventing fire propagation from a distance. This tactic has been evaluated in the context of a ro-ro space and the results are compiled in a test report (Vylund et al 2019). The project has resulted in guidelines on how to handle AFV fires in roro spaces (see appendix 1).