Filtern
Erscheinungsjahr
Dokumenttyp
- Beitrag zu einem Tagungsband (24)
- Zeitschriftenartikel (18)
- Vortrag (6)
- Beitrag zu einem Sammelband (3)
- Buchkapitel (1)
- Posterpräsentation (1)
- Forschungsbericht (1)
Schlagworte
- CFD (7)
- Fire (7)
- Computational fluid dynamics (5)
- Concrete (4)
- FDS (4)
- Tunnel (4)
- Brandszenarien (3)
- Computational Fluid Dynamics (3)
- Modellierung von Bränden (3)
- Rauchausbreitung (3)
Organisationseinheit der BAM
Paper des Monats
- ja (2)
Eingeladener Vortrag
- nein (6)
The amount of heat, which is released by fire loads during the combustion
process, depends on the material characteristics, the ventilation
conditions, the storage density and the distribution. To evaluate the
structural stability of buildings in case of fire, the fire load has to be
quantified. In Germany, the fire load is quantified by using the combustion
factor m, while internationally the combustion efficiency χ is
applied. Both factors assess the burning behavior of materials, but the
determination is carried out in different ways. Since the testing facility
was abolished fifteen years ago, it is not possible to determine the combustion
factor m anymore. So, it should be found out, if the combustion
efficiency χ is a convenient method to quantify the fire load under the
consideration of the German standards. As a part of the research, combustion
efficiencies χ were determined for eight materials in the cone
calorimeter and the single burning item test at different heat fluxes.
The values of the combustion efficiencies χ as well as the corresponding
combustion factors m were discussed and compared to the values of the
literature. The results show an influence of the testing facility on the
combustion efficiency. The values of the combustion efficiency determined
in the single burning item test were higher than the values from
the cone calorimeter.
Die Brandlastberechnung für Industriebauten erfolgt in Deutschland entsprechend der DIN 18230-1. Brandlasten bestehen in den meisten Fällen aus verschiedenen brennbaren Feststoffen und Flüssigkeiten, die in Abhängigkeit ihrer Lagerungsart, ihren stofflichen Eigenschaften und den Ventilationsbedingungen unterschiedliche Wärmeleistungen zur Folge haben. Als Eingangsgröße zur Brandlastberechnung berücksichtigt der sogenannte Abbrandfaktor m (m-Faktor) das individuelle Abbrandverhalten von Feststoffen und
Flüssigkeiten. Sein Wert ergibt sich aus dem Vergleich der zeitlichen Temperaturentwicklung beim Abbrand einer Probe mit der Referenzprobe. Bei der Referenzprobe handelt es sich um sägerauhes Fichtenholz, dem ein m-Faktor von m = 1,0 zugeordnet wurde. Die Bestimmung des m-Faktors erfolgte bis vor einigen Jahren entsprechend der DIN 18230-2 in dem m-Faktor-Ofen. Bis zu der Verschrottung des letzten in Deutschland existierenden m-Faktor-Ofens wurden mehr als 100 m-Faktoren von verschiedenen Stoffen ermittelt. Zurzeit ist es nicht möglich zur Brandlastermittlung m-Faktoren experimentell zu bestimmen.
Da infolge industrieller Entwicklungen zunehmend neue Stoffe auf den Markt kommen, deren Abbrandverhalten zu bestimmen.
Brandlasten stellen eine Gefahr für den Menschen sowie für das industrielle Gebäude dar, in dem sie gelagert sind. Das Brandverhalten der Brandlasten bestimmt dabei maßgeblich die Schwere der Gefahr. Brandschutzmaßnahmen dienen dazu, im Brandfall das Schadensausmaß zu minimieren. Um geeignete Brandschutzmaßnahmen ableiten zu können, ist es erforderlich, das Brandverhalten der Materialien zu bewerten. Eine international angewandte Möglichkeit zur Bewertung des Brandverhaltens von Feststoffen und Flüssigkeiten ist die Verbrennungseffizienz χ. Sie ist das Verhältnis der während einer Verbrennung effektiv freigesetzten Wärme (effektive Verbrennungswärme) zu der maximal möglichen Wärmemenge (Heizwert). Die Grundlage zur Bestimmung von Verbrennungseffizienzen stellen die Wärmefreisetzungsrate (HRR) und die Massenverlustrate (MLR) dar. Ein standardisiertes Bestimmungsverfahren existiert nicht. So liegt es in dem Ermessen des Anwenders, in welcher Prüfapparatur die Experimente durchgeführt werden und welcher Zeitbereich der HRR und der MLR zur Berechnung der Verbrennungseffizienz verwendet wird. Im Rahmen dieser Arbeit wurden Versuche im Cone Calorimeter und im Single Burning Item test anhand von hölzernen Materialien durchgeführt. Die Ergebnisse zeigen auf, dass sich in Abhängigkeit von der verwendeten Prüfapparatur und in Abhängigkeit des für die Berechnung betrachten Versuchszeitraumes verschiedene Werte der Verbrennungseffizienz ergeben. Auf Grundlage dieser Erkenntnisse wurde eine Methode entwickelt, mit der reproduzierbare Werte berechnet werden können. Dabei erfolgt die Berechnung lediglich für die Vollbrandphase. Diese Brandphase stellt die Hauptbrandphase dar und ist durch eine gleichmäßige Verbrennung mit wenigen Änderungen in der Branddynamik gekennzeichnet.
Vor dem Hintergrund der Zurückziehung der DIN 18230 Teil 2 zur Bestimmung des m-Faktors von Materialien für die Brandlastbewertung im Industriebau müssen neue Wege gefunden werden, wie das Abbrandverhalten alternativ quantifiziert werden kann. Der Beitrag fasst die Entstehung und die Entwicklung der Bestimmungsweise von Abbrandfaktoren zusammen und gibt Ausblick auf eine neue Möglichkeit zur Bewertung von Brandlasten, die Verbrennungseffizienz.
Brandverhalten von Bauprodukten: Brauchen wir Regelungen für die Menge und Giftigkeit der Rauchgase?
(2008)
The time dependent thermal behavior is analyzed with FLUENT for the fluid as well as the solid region (concrete component) in case of a 100 MW n-heptane fire. To study the effect of parameters in mathematical-physical models several sensitivity studies were carried out to investigate the effect on the fluid flow as well as on the component. The influence of soot was additionally considered. FDS simulations as well as empirical calculations considering underlying assumptions are additionally used to examine the plausibility of results from the FLUENT simulations. This is an appropriate method if no experimental results are available. Recommendations are given for choosing parameters in mathematical-physical models e.g. radiation models. The results of the CFD investigations show that considering the influence of soot provides maximum temperatures which were 200 K lower than without soot.
Methodologies on fire risk analysis in road tunnels consider numerous factors affecting risks (risk indicators) and express the results by risk measures. But only few comprehensive studies on effects of risk indicators on risk measures are available. For this reason, this study quantifies the effects and highlights the most important risk indicators with the aim to Support further developments in risk analysis. Therefore, a system model of a road tunnel was developed to determine the risk measures.
The system model can be divided into three parts: the fire part connected to the fire model Fire Dynamics Simulator (FDS); the evacuation part connected to the evacuation model FDS+Evac; and the frequency part connected to a model to calculate the frequency of fires. This study shows that the parts of the system model (and their most important risk indicators) affect the risk measures in the following order: first, fire part (maximum heat release rate); second, evacuation part (maximum preevacuation time); and, third, frequency part (specific frequency of fire). The plausibility of These results is discussed with view to experiences from experimental studies and past fire incidents.
Conclusively, further research can focus on these most important risk indicators with the aim to optimise risk analysis.
In urban areas the demand for public transportation is constantly growing. Underground railway systems overcome the problem of limited space on the ground and are therefore one of the most powerful systems in urban public transportation. These facilities can be very complex and are used by a large amount of passengers. Therefore, it is important to maintain the safety for people and buildings. Especially in the case of fire or arson attack.
This paper focusses on a fire scenario in a complex subway station for different weather conditions. The purpose is to identify the influences of different weather conditions on the smoke spread and the ability of self-rescue in case of a burning luggage.
The evaluation of the fire simulations will focus on toxicity and visibility taking into account the FED concept.
A probabilistic approach for finite element analysis (FEA) for tunnel linings exposed to the nominal fire is presented. The probabilistic FEA accounted for the uncertainties distributions tied to the conductivity and specific heat as well as of the compressive strength, tensile strength, Young’s modulus, and ultimate strain in compression. To get an understanding on the influence of different probability density functions on the distribution of maximum displacements of the tunnel lining, a sensitivity analysis was performed. Four sets of FEAs were carried out with different probability distributions of the conductivity, the specific heat, and the compressive strength of the concrete, respectively. An experimental design based on a Latin Hypercube Sampling algorithm was performed to define the input parameters which describe each analysis case. A reliability analysis was executed considering a limit state function based on the temperature-dependent ultimate strain. The results show that, depending on the distribution adopted, the standard deviation of the maximum displacements can vary up to 47,4% of the minimum standard deviation. The large standard deviation is associated with the possibility of a greater displacement and, hence, to a structure more vulnerable to fire.
Fires in road tunnels constitute complex scenarios with interactions between the fire, tunnel users and safety measures. More and more methodologies for risk analysis quantify the consequences of these scenarios with complex models. Examples for complex models are the computational fluid dynamics model Fire Dynamics Simulator (FDS) and the microscopic evacuation model FDS+Evac. However, the high computational effort of complex models often limits the number of scenarios in practice. To balance this drawback, the scenarios are often simplified. Accordingly, there is a challenge to consider complex scenarios in risk analysis.
To face this challenge, we improved the metamodel used in the methodology for risk analysis presented on ISTSS 2016. In general, a metamodel quickly interpolates the consequences of few scenarios simulated with the complex models to a large number of arbitrary scenarios used in risk analysis. Now, our metamodel consists of the projection array-based design, the moving least squares method, and the prediction interval to quantify the metamodel uncertainty. Additionally, we adapted the projection array-based design in two ways: the focus of the sequential refinement on regions with high metamodel uncertainties; and the combination of two experimental designs for FDS and FDS+Evac.
To scrutinise the metamodel, we analysed the effects of three sequential refinement steps on the metamodel itself and on the results of risk analysis. We observed convergence in both after the second step (ten scenarios in FDS, 192 scenarios in FDS+Evac). In comparison to ISTSS 2016, we then ran 20 scenarios in FDS and 800 scenarios in FDS+Evac. Thus, we reduced the number of scenarios remarkably with the improved metamodel. In conclusion, we can now efficiently integrate complex scenarios in risk analysis. We further emphasise that the metamodel is broadly applicable on various experimental or modelling issues in fire safety engineering.
Vehicle fires in tunnels can have catastrophic consequences for the road users, the property and traffic inffastructure. To support an evacuation planning, this study simulates the fire smoke toxicity and the smoke layer of a vehicle fire in a full-size test tunnel. The three dimensional prediction of the fire smoke toxicity in the test tunnel is realized by implementing the Fractional Effective Dose and the Fractional Summation concept in a CFD environment. The developed model facilitates to calculate fire scenarios for various types of tunnels and to quantify the hazard e.g. during an evacuation scenario.
Brände in Wohnungen entwickeln sich heutzutage sehr schnell, weil der Anteil an brennbaren Materialien in Einrichtungsgegenständen und elektrischen Geräte in den letzten Jahren signifikant zugenommen hat. Insbesondere Brände in Kinderzimmern können sehr gefährlich sein, was mehrere Brände in Deutschland in den letzten Jahren belegen. Um die Brand- und Rauchentwicklung bei einem solchen Brand zu untersuchen, wurde ein Testraum wie ein typisches Kinderzimmer möbliert und mit 36 Thermoelementen sowie einem Druckmessgerät ausgestattet. Zusätzlich wurden Rauchmelder installiert. Der Brand wurde mittels eines Teelichts initiiert, das für ca. eine Sekunde mit einer Matratze in Kontakt gebracht wurde. Der Feuerüberschlag fand nach nur vier Minuten statt. Sowohl die Brandlast als auch die Brand- und Rauchentwicklung wurden untersucht. Vorschriften zur Brandsicherheit von Einrichtungsgegenständen, elektrischen Geräten und Spielzeugen wurden diskutiert. Ergänzend wurde der Temperaturanstieg im Brandraum unter Anwendung des Verfahrens von McCaffrey vorhergesagt.-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Fires in homes develop very fast nowadays, because the amount of
combustible materials in furniture and electrical devices has increased
significantly in recent years. Especially fires in children's
rooms can be very hazardous as several recent fires in Germany
showed. To investigate the fire and smoke development in such a fire
the test room was furnished like a typical childrens room and
equipped with 36 thermocouples and a pressure measurement device.
Also smoke detectors were installed. The fire was ignited by a small
candle which was in contact with a mattress only for one second.
Flashover occurred only after 4 minutes. The fire load and the fire and
smoke development were investigated. The fire safety regulations for
the furnishings, electrical devices and toys were discussed. Additionally
the temperature rise in the compartment was predicted according
to the method of McCaffrey.
Im Rahmen der schutzzielorientierten Brandschutzbemessung müssen, neben dem Nachweis der Wirksamkeit von Schutzmaßnahmen, Nachweise zur Einhaltung von in Abhängigkeit des Sicherheitsniveaus festgelegter Grenzwerte für die zulässige Wärmestrahlung, die Temperatur der oberen und unteren Rauchschicht, die toxische Konzentration von Rauchgasen und die Mindestsichtweite zum Schutz von Personen im Bauwerk erbracht werden.
Fire smoke contains a variety of highly toxic substances and can lead to unconsciousness within a few minutes and to death for critical concentrations. Currently the engineer’s methods of fire safety include various procedures to calculate the fire propagation and smoke spread in buildings.
However, up to now the evaluation and calculation of smoke concerning its optical properties and toxic potential on the basis of a detailed combustion is still a field of research. Since smoke composition is highly variable and not fully characterised it has to be examined whether and how the Chemical composition and the optical properties of smoke are correlating. A method has been developed that establishes the relation between the smoke components and smoke toxicity.
Anwendung und Vergleich von Verfahren zur Berechnung der äquivalenten Branddauer im Industriebau
(2013)
Die äquivalente Branddauer tä wird zur Bestimmung der Feuerwiderstandsdauer erftp von Bauteilen in Industriebauten verwendet. Die Berechnung erfolgt bislang auf der Grundlage des normativenAnsatzes nach DIN 18230 (Verfahren I) und gilt im Zusammenhang mit der Muster-Industriebaurichtlinie (M IndBauRL). Im Rahmen von brandschutztechnischen Nachweisen für Industriebauten ist es ebenfalls möglich, die äquivalente Branddauer unter Anwendung numerischer Methoden zu berechnen (Verfahren II). Die Anwendung solcher Ingenieurmethoden des Brandschutzes ermöglichen die Berücksichtigung komplexer Gebäudegeometrien und Ventialtionsbedingungen sowie lokaler Brandwirkungen auf Bauteile infolge inhomogener Brandlastverteilungen.
Am Beispiel einer Industriehalle werden die Verfahren I und II angewendet und die Ergebnisse gegenübergestellt.
This paper presents a probabilistic methodology based on the thermo-mechanical finite elements analysis to investigate the impact of the variability of the thermal properties of the concrete in the fire safety of structures. This is meant to evaluate if characteristic values or safety factors for the conductivity and specific heat are required during the semi-probabilistic structural fire safety assessment. To illustrate the use of the proposed methodology, this work includes a case-study with a tunnel lining which considers the uncertainties related to the thermal and mechanical properties of the concrete, the soil load, and the temperatures described by the standard temperature-time curve. Two failure criteria are considered: one was the maximum temperature of 300 °C at the reinforcement and the other based on the temperature-dependent strength as provided in the Eurocode EN 1992-1-2. Several finite element analyses are performed. The design of experiments is executed by a Correlation Latin Hypercube Sampling. The calculated probability of failure has different values depending on the adopted failure criteria. A sensitivity analysis using the Spearman's rank correlation coefficient was carried out and demonstrates that the uncertainty related to the specific heat has the greatest impact on the results.
Nach DIN 18230-1 erfolgt in Deutschland die Brandlastberechnungen unter Anwendung
des Abbrandfaktors m. Der Abbrandfaktor m ist ein dimensionsloser Beiwert mit dem die
Brandlast aus einem Stoff oder Stoffgemisch bewertet wird. Neben dem Brandverhalten
des Stoffes berücksichtigt er das Temperatur-Zeit-Verhalten im Bauteil. Die einzige
Prüfapparatur, mit der Abbrandfaktoren bestimmt wurden, ist jedoch nicht mehr existent.
Ein Wiederaufbau der abgeschafften Prüfapparatur wurde wegen apparateabhängigen
Messunsicherheiten und auch aus wirtschaftlichen Gründen als nicht sinnvoll angesehen.
Die Erarbeitung eines äquivalenten Verfahrens zum Abbrandfaktor m unter Verwendung
der Verbrennungseffektivität und unter Berücksichtigung der Bauteilerwärmung war daher
Gegenstand dieses Forschungsvorhabens. Ziel war es für Brandlastberechnungen
nach DIN 18230-1 die Verbrennungseffektivität anzuwenden. Die Verbrennungseffektivität
beschreibet jedoch nur den verringerten Energieumsatz von Stoffen im Brandraum.
Es wurde daher ein Verfahren erarbeitet, dass ergänzend zur Brandlastberechnung unter
Anwendung der Verbrennungseffektivität das Temperatur-Zeit-Verhalten in einem
brandbelastenden Bauteil berücksichtigt.
Mittels Propan-Brennern mit einer Brennerleistung 750 kW wurden in einer U-Bahn-Station Heißgasversuche durchgeführt und die zeitlichen und örtlichen Verteilungen der physikalischen Größen (Stoffkonzentration, Temperatur und Rauchgasdichte) erfasst. Laborversuche sowie die Feldversuche sind Validierungsgrundlage für ANSYS CFX und FDS und die später im Rechenmodell der U-Bahn-Station zur Untersuchung der Grundströmung und Rauchausbreitung verwendeten mathematisch-physikalischen Modelle. Der Aufsatz stellt das Projekt ORPHEUS vor und diskutiert die ersten Ergebnisse.
Based on forensic evidence, a smouldering fire was observed to have occurred at a murder scene. Identification of a reasonable timeline – specifically the fire dynamics of the ignition and fire growth that occurred coincident with the death that took place – became an important focus of the criminal investigation that followed. The fire service was called when a neighbour saw a grey smoke escaping through the ventilation system of the bathrooms on the roof of the house. One flat door with elevated temperatures was found. The fire fighter who entered the flat first reported later that the flat was completely filled with smoke and all windows were closed. When the fire fighter opened the balcony door, he saw flames on the sofa that he extinguished. Then he found a body on the floor. The autopsy showed later that the victim was dead before the fire started. The police suspected that the murderer probably had deliberately set the fire to destroy evidence. One suspect had been witnessed to be in the flat approximately 2 h before the fire was detected by the neighbour. The aim of this project was to investigate how the fire most likely started and developed.
Safety measures like tunnel emergency Ventilation Systems cause high financial costs. Hence, safety measures have to be chosen with the focus on the expected reduction of the consequences like fatalities or damage on structures and in conjunction with the investments. Since 2004, the European directive EU 2004/54/EC proposes therefore the application of risk assessments. Because the EU directive provides only few legal requirements on risk assessments, the methodologies developed on this basis have large differences. After one decade of intensive research, the comparative study now highlights common aspects and differences of several methodologies.
Approaches towards a generic methodology for storage of hazardous energy carriers and waste products
(2013)
Energy carriers – either conventional or 'new' ones – have to be provided in large amounts to meet the requirements of permanent availability and reliable supply of electricity. Depending on their state of aggregation, energy carriers are either stored in large masses (if solid or liquid) or at elevated pressures (if gaseous). Both impose the hazard of large-scale fire, in the latter case additionally the danger of explosion or unintended release. Very similar hazards occur for wastes. Solid wastes are present in large masses and only a small part is recycled. Most of the solid wastes are used in energy conversion. The main gaseous waste is CO2. During capturing also the hazard of unintended release exists. In this article, existing approaches for safe storage and fire prevention are discussed and a generic methodology is outlined. This methodology consists of the following steps:
gaining knowledge about the behaviour of the material stored (reactivity, thermal stability, etc.),
assessing the environmental conditions for the storage site (neighbourhood, safety distances, etc.),
assessment of prospective consequences of an incident and
development of individual loss prevention conceptions.
All steps require both experimental testing and theoretical considerations about accident scenarios as integral parts of the methodology.
In Europa kommen ca. 80 % der Brandtoten bei Wohnungsbränden ums Leben. Dabei sind Brände in Wohn- und Schlafzimmern besonders gefährlich. Einige Objekte, wie Polstermöbel und Fernseher, stellen im Brandfall eine besonders große Gefahr dar, da sie sich schon durch kleine Zündquellen, wie ein Feuerzeug oder eine Kerze, leicht entzünden lassen, eine hohe Wärmefreisetzungsrate haben und viel Rauch produzieren. Ein einzelnes Sofa kann in einem Raum einen Flashover erzeugen. Besonders im Kinderzimmer tritt oft eine Häufung an besonders gefährlichen Objekten wie Polstermöbeln, Matratzen und elektrischen Geräten auf. Da Kinder sich im Brandfall oft falsch verhalten sie verstecken sich an schwer zugänglichen Orten wie unter dem Bett oder im Schrank anstatt den Raum zu verlassen sind sie besonders gefährdet.
The Fractional Effective Dose model was used to predict the fire smoke toxicity numerically. In this context fire tests were carried out for three different building materials: polyurethane, flame retardant polyurethane and polyvinyl chloride. The fire tests were performed for flaming and smoldering combustion. The aim of the fire tests was to determine the light extinction, the smoke density and the combustion products at varying oxygen concentrations, different temperatures and different irradiance levels. The fire tests were performed in the German DIN-tube and also in the Cone Calorimeter. Stoichiometric coefficients at varying oxygen concentrations and temperatures were determined from measurements. With these stoichiometric coefficients reaction equations were defined and implemented in the Computational Fluid Dynamics (CFD) program, ANSYS CFX. The implemented reaction equations were used to account for different ventilation and temperature conditions in the simulation. The fire and smoke propagation was calculated numerically with CFD in the room corner test geometry. Equations to account for toxicity and light extinction were also implemented and were used to analyse the toxicity and the optical properties of fire smoke with CFD.
Bei der Erstellung von brandschutztechnischen Nachweisen für Industriebauten werden häufig Ingenieurmethoden des Brandschutzes genutzt. Dazu zählen die Modellierung und Berechnung von Brandszenarien mittels numerischer Strömungsmechanik (computational fluid dynamics, CFD). In dieser Arbeit wurde ein auf numerischer Strömungs- und Strukturmechanik basierendes Verfahren zur brandschutztechnischen Bemessung von Bauteilen am Beispiel einer Industriehalle angewendet. Instationäre Temperaturverläufe aus der Heißgasschicht dienten dabei als Eingangswerte für die Bauteilberechnung. Aus den Ergebnissen wurde die äquivalente Branddauer berechnet, mit der die rechnerisch erforderlichen Feuerwiderstandsdauern der Bauteile bestimmt werden konnte.
In the frame of the European harmonization, new European technical standards (Eurocodes) have been developed in recent years. Classical methods, like tables and simplified analytical procedures, as well as general engineering techniques are allowed by the Eurocodes for the fire protection design. The modeling and calculation of fire scenarios with CFD (Computational Fluid Dynamics) numerical methods is one of the general engineering methods. It is nowadays still difficult to check and evaluate the CFD results for their use as technical documents for fire safety design.
Analytical engineering techniques, zone models and CFD-models have been used and compared in the present work for the prediction of the fire development in a building.
To solve the conservation equation for the CFD-model, the CFD-program FDS, with the mixture fraction model, and the CFD-program FLUENT, with the one step reaction model as well as with the volumetric source term model, have been used.
The combustion of polyurethane is modeled in FDS by specifying the heat release rate and the stoichiometry. For the combustion in volumetric source term model, the heat release rate and the smoke release were specified with respect to the stoichiometry. The input parameter for the one step reaction model is the pyrolysis mass flow.
In the one step reaction model, the transport equations for polyurethane, H₂O, N₂, O₂, CO₂, CO and C (soot) are solved and the heat of combustion is determined from the standard formation enthalpy of all the components. In volumetric source term model, the transport equation is solved for air and smoke. FDS solves the transport equation for the mixture fraction.
To model the fire development, and where no literature data was available, the required material characteristics like specific heat capacity, absorption coefficient and heat of combustion were measured.
In all the investigated CFD-models the heat- and species transport equation has been solved and the absorption coefficient of soot has been considered.
Furthermore, the fire development has also been investigated using zone models with the programs CFAST and MRFC.
Results from analytical engineering techniques (plume calculations), which were design criteria in the past, have been used as plausibility checks for the present work. The calculation results from the investigations were compared to measurements in the same building performed by the National Institute for Standards and Technology (NIST).
Probabilistic thermo-Mechanical analysis of a concrete tunnel lining subject to fire The probability distributions of the parameters related to the thermal analysis was considered in order to study the variability of the results and to carry out a reliability analysis. This assessment considered as random variables the thermo-mechanical properties of the concrete, the maximum heat release rate (HRR), the duration of the period of maximum HRR, the convective coefficient, the emissivity at the surface exposed to the fire, the air velocity within the tunnel, and the initial fire radius. The temperature-time curve was described by a correlation. An experimental design based on a Latin Hypercube Sampling algorithm was performed to define the input parameters to each analysis case. The definition of a limit state function based on the punctual strain status has permitted to carry out a reliability analysis.
CFD modeling approach of smoke toxicity and opacity for flaming and non-flaming combustion processes
(2016)
Current engineer’s methods of fire safety design include various approaches to calculate the fire Propagation and smoke spread in buildings by means of computational fluid dynamics (CFD). Because of the increased computational capacity, CFD is commonly used for prediction of time-dependent safety parameters such as critical temperature, smoke layer height, rescue times, distributions of chemical products, and smoke toxicity and visibility. The analysis of smoke components with CFD is particularly complex, because the composition of the fire gases and also the smoke quantities depends on material properties and also on ambient and burning conditions. Oxygen concentrations and the temperature distribution in the compartment affect smoke production and smoke gas toxicity qualitatively and quantitatively. For safety designs,
it can be necessary to take these influences into account. Current smoke models in CFD often use a constant smoke yield that does not vary with different fire conditions. If smoke gas toxicity is considered, a simple approach with the focus on carbon monoxide is often used. On the basis of a large set of experimental data, a numerical smoke model has been developed. The developed numerical smoke model includes optical properties, production, and toxic potential of smoke under different conditions. For the setup of the numerical model, experimental data were used for calculation of chemical components and evaluation of smoke toxicity under different combustion conditions. Therefore, averaged reaction equations were developed from experimental measurements and implemented in ANSYS CFX 14.0.
Heute verfügbare Technik ermöglicht es, die Wärmetransportmechanismen im Brand, an der Bauteiloberfläche und im Bauteil mittels CFD zu koppeln. Die Kopplung von Fluid und Struktur wurde am Beispiel eines 100-MW-Tunnelbrands mit CFD (Computational Fluid Dynamics) untersucht. Die instationären Berechnungen wurden mit dem CFD-Programm ANSYS Fluent durchgeführt. Der infolge eines Lkw-Unfalls verursachte n-Heptan-(C7H16)-Brand wurde mit dem Eddy-Dissipation-Verbrennungsmodell modelliert.
Das Fluid- und Solid-Gebiet wurden durch ein ‚Interface‘ gekoppelt. Die instationäre Wärmeleitung des Bauteils mit einer Höhe von 0,4 m wurde mit der dreidimensionalen Fourier´schen Wärmeleitungsgleichung modelliert und das instationäre thermische Verhalten des quarzhaltigen Betonbauteils analysiert. Temperaturabhängige Stoffkennwerte wurden berücksichtigt.
This paper presents a probabilistic methodology based on the thermo-mechanical finite elements analysis to investigate the impact of the variability of the thermal properties of the concrete in the fire safety of structures. This is meant to evaluate if characteristic values or safety factors for the conductivity and specific heat are
required during the semi-probabilistic structural fire safety assessment. To illustrate the use of the proposed methodology, this work includes a case-study with a tunnel lining which considers the uncertainties related to the thermal and mechanical properties of the concrete, the soil load, and the temperatures described by the
standard temperature-time curve. Two failure criteria are considered: one was the maximum temperature of 300 °C at the reinforcement and the other based on the temperature-dependent strength as provided in the Eurocode EN 1992-1-2. Several finite element analyses are performed. The design of experiments is executed by a Correlation Latin Hypercube Sampling. The calculated probability of failure has different values depending on the adopted failure criteria. A sensitivity analysis using the Spearman's rank correlation coefficient was carried out and demonstrates that the uncertainty related to the specific heat has the greatest impact on the results.
In this paper, the influence of a fixed water mist firefighting system on a high-speed non-premixed horizontal methane jet fire is investigated with focus on its effect on temperatures and heat load of the jet fire and on ist surroundings. Six tests are performed in which gas is released out of an orifice with a diameter of 1 mm and a release pressure of up to 186 bar. In addition to temperature and radiation measurements, the release pressure, gas mass flow rate and exhaust gas concentrations are detected to determine the heat release. Video and IRanalysis are used to evaluate the interactions between jet fire and water mist. The experiments show, that water mist reduces the temperatures inside the jet fire flow field and its radiative heat flux. It can lower the Risk of ignition of adjacent surfaces and materials, as temperatures fall below autoignition temperatures of common materials like plastics. Although water mist does not extinguish the fire, it has an impact on the energy release by reducing combustion efficiency due to heat exchange with the water mist and oxygen displacement.
This paper analyses the suitability of the Sensible Enthalpy Rise Approach for measuring the heat release rate of electric-vehicle-scale lithium-ion batteries. An apparatus is designed that meets the conditions of an electric-vehicle-scale lithium-ion battery fire by using cement board as wall material. Modifications of the Sensible Enthalpy Rise Methodology are presented due to the high emissivity and inhomogeneous temperature distribution of the apparatus wall material: a power 4 approach for the heat flow from the walls to the ambient air and an alternative determination methodology for the wall temperature. A one factor at a time parameter study is performed with Computational Fluid Dynamics simulations, investigating a new calibration method based on a fit approach compared to common methods, the wall temperature determination, the approach for the ambient heat flow, the calibration power and the volume flow at the outlet. The simulations show, that suitable estimations of the heat release rate are obtained by using the modifications for wall temperature determination and the power 4 approach for the ambient heat flow. The three calibration methods provide suitable constants, if the calibration power in the same order of magnitude as the mean of the heat release rate profile of the test object.
Based on methane from renewable resources, LNG is an alternative fuel for heavy and long-distance traffic in land transport. Contrary to its positive properties, the fuel contains risks from an explosion and extremely low temperatures for personal and infrastructure safety. CFD-models are suitable for doing risk analyses for arbitrary scenarios. For examining how to model for risk research the dispersion of LNG-vapor, this paper contains a model variant study, with an evaluation by experiments.
This paper describes the use of the CFD-code ANSYS Fluent for simulating experiments of the ‘LNG Safety Program Phase II‘. The content of the well-documented experiments was the research of the vaporization rate of LNG on land and the dispersion of LNG-vapor in the air. Based on the comparison to two experiments, overall 12 CFD-model variants with varying thermal and turbulence parameters were examined how they affect the transient LNG-vapor dispersion in air.
The definition of turbulence-boundary-condition at the domain borders had the biggest impact on modeling, followed by the turbulence model. The most accurate model variant had been applied for observing the spreading behavior of LNG-vapor in the air after evaporation on land and analyzing the influence of the LNG-composition to the dispersion. The results show that the mixture of LNG-vapor and the air in the free field is cooler than the ambient air and spreads like a heavy gas on the ground.
From a fire safety point of view, the burning behavior of lithium-ion batteries is of high interest. The heat release rate (HRR) is the most important fire parameter to analyze the fire hazards of burning objects, so that an accurate determination of it is crucial. In this paper, two different measurement techniques, the Oxygen Consumption Calorimetry (OCC) and the Sensible Enthalpy Rise Approach (SERA) are simultaneously performed in the same calorimeter to measure the HRR of two different types of lithium-ion batteries. HRR values as well as total energies determined by SERA are higher than measured with OCC: The total energy released is about 10–12 times (SERA) and 6–9.5 times (OCC) the electrical stored energy for both battery types, whereas the timescales of the release differ strongly between the types, resulting in maximum HRRs of 3.4 MW (SERA) and 1.5 MW (OCC)
for one module of type A and 0.8 MW (SERA) and 0.6 (OCC) of type B respectively. Furthermore, a sensitive dependency of the HRR measurement with SERA on the position of the wall temperature measurement is observed.
Lithium-ion batteries are a key technology to achieve the goals of limiting climate change due to the important role as traction technology for Electric Vehicles and in stationary energy storage systems. Over(dis) charge, mechanical damage due to accidents or thermal abuse such as fires can initiate an accelerated self-heating process of the batteries, called thermal runaway. A thermal runaway can propagate from cell to cell within a larger assembly of cells such as modules or battery packs and can cause rapid heat and toxic gas emissions. The resulting battery fire can spread to adjacent facilities, e.g. other cars in underground car parks or to a whole building in case of a large stationary energy storage.
For proof of fire protection requirements or to design suitable fire protection systems, Computational Fluid Dynamic (CFD) simulations are getting more and more important. The aim of CFD fire simulations is to predict the global hazards of a fire to its surroundings, that is mainly characterized by the release of heat and smoke and its spread in the fire environment. There are many numerical investigations of lithium-ion batteries in the literature. One class of models is used to simulate the charge and discharge process of lithium-ion batteries and to predict the temperature or voltage evolution inside the battery. On the other hand, there are models describing batteries under abuse conditions to predict the consequences of a thermal runaway event to the local environment, like the temperatures inside a battery or at the battery surface. Henriksen et al. use a generic battery gas mixture to simulate an explosion of vented gases from a Lithium Iron Phosphate battery and compare experimental results for the explosion pressure and the position of the flame front to the outcomes of a simulation with Xifoam. Larsson et al. used a combination of CFD simulations with FDS and thermal model with COMSOL to predict the temperature development of neighboring cells in a thermal runaway propagation. Truchot et al. use a design Heat Release Rate (HRR) curve for a battery based on experimental measurements to build up an overall HRR curve for a truck loaded with 100 lithium-ion batteries. This summed up HRR and corresponding smoke production curve is then used as an input for a simulation of a truck fire in a tunnel with Fire Dynamics Simulator (FDS). The pre-definition of the HRR curve is a frequently used method in fire engineering. It has the disadvantage, that the heat release cannot be influenced by physical processes, such as changed ventilation conditions or extinguishing measures. In this paper, a model is presented that determines the release of heat and gases based on the thermal runaway mechanisms of the battery, which can be used in CFD fire simulations with focus on prediction of fire hazards to nearby environment.