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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).
A broad range of inorganic nanoparticles (NPs) and their dissolved ions possess a possible toxicological risk for human health and the environment. Reliable and robust measurements of dissolution effects may be influenced by the sample matrix, which challenges the analytical method of choice. In this study, CuO NPs were investigated in several dissolution experiments. Two analytical techniques (dynamic light scattering (DLS) and inductively-coupled plasma mass spectrometry (ICP-MS)) were used to characterize NPs (size distribution curves) time-dependently in different complex matrices (e.g., artificial lung lining fluids and cell culture media). The advantages and challenges of each analytical approach are evaluated and discussed. Additionally, a direct-injection single particle (DI sp)ICP-MS technique for assessing the size distribution curve of the dissolved particles was developed and evaluated. The DI technique provides a sensitive response even at low concentrations without any dilution of the complex sample matrix. These experiments were further enhanced with an automated data evaluation procedure to objectively distinguish between ionic and NP events.
With this approach, a fast and reproducible determination of inorganic NPs and ionic backgrounds can be achieved. This study can serve as guidance when choosing the optimal analytical method for NP characterization and for the determination of the origin of an adverse effect in NP toxicity.
The standard cone calorimeter according to ASTM E 1354 and ISO 5660 enables reaction-to-fire tests to be performed in ambient atmospheric conditions. A controlled-atmosphere chamber modifies the standard apparatus in a way that allows tests to be performed in nonambient conditions as well. The enclosed chamber is placed underneath the standard exhaust hood and does not have a closed connection to the hood. With this open arrangement, the exhaust gases are diluted by excess air drawn in from the laboratory surroundings. Heat-induced changes in the consequential dilution ratio affect the calculation of fire quantities and, when neglected, lead to deviations of up to 30% in heat release rate. The paper introduces a test protocol and equations to calculate the heat release rate taking dilution effects into account. A mathematical correction is shown that compensates for the dilution effects while avoiding extensive mechanical changes in the equipment.
Um den Anforderungen der Bauordnung an den Brandschutz für Gebäude gerecht zu werden, sind bauliche Anlagen so zu errichten und zu betreiben, dass der Entstehung eines Brandes und der Ausbreitung von Feuer und Rauch vorgebeugt, die Rettung von Menschen und Tieren sowie wirksame Löscharbeiten ermöglicht werden.
Hierbei besteht, einer steigenden Komplexität sowie einem differenzierten Nutzungskonzept öffentlicher Gebäude geschuldet, häufig die Notwendigkeit von normativen Vorgaben abzuweichen und dennoch ein gleichwertiges Sicherheitsniveau nachzuweisen.
Es werden Personensimulationsmodelle eingesetzt, die einerseits das Vorhandensein eines Schutzzielniveaus durch die Abbildungen von Personenbewegungen nachweisen können und andererseits durch Parametervariation eine szenarienabhängige Betrachtung ermöglichen.
Der vorliegende Beitrag vergleicht die Ergebnisse einer kleinskaligen Evakuierungsübung mit drei mikroskopischen Personensimulationsmodellen und geht der Frage nach der Aussagekraft dieser Bewertungsmethode nach. Es zeigt sich, dass die alleinige Betrachtung absoluter Entleerungszeiten keine zuverlässige Beurteilungsgrundlage für das komplexe Schutzziel Personensicherheit darstellt.
Gegenstand des Aufsatzes ist die experimentelle Untersuchung der Auswirkungen verschiedener Zündquellen sowie der Systembeschaffenheit auf das Brandverhalten EPS-basierter Wärmedämm-Verbundsysteme (WDVS). Dazu wurden Brände ausgewertet, die mit EPS-basierten WDVS in Verbindung stehen. Ergebnis dieser Auswertung war, dass nicht wie bisher angenommen der Brand in dem Gebäude (z. B. der Wohnungsbrand), sondern vielmehr der Brand außerhalb des Gebäudes, insbesondere der des Abfallbehälters, das häufigste und kritischste Brandszenario für EPS-basierte WDVS darstellt. Daraufhin wurden an der BAM Bundesanstalt für Materialforschung und -prüfung Brandversuche in der Single Burning Item-Prüfeinrichtung (SBI) an nicht intakten EPS-basierten WDVS-Ausschnitten durchgeführt. Mit zunehmender Beschädigungsgröße und -tiefe stieg die vom System freigesetzte Wärmefreisetzungsrate an. Zusätzlich werden Brandversuche eines Sockelbrandszenarios mit einer abfallbehälteräquivalenten Brandlast vorgestellt. Aus den Brandversuchen werden Empfehlungen zur Verbesserung der Systemsicherheit abgeleitet.-------------------------------------------------------------------------------------------------------------------------------------------------
The influence of different ignition sources and conditions of the systems on the fire behaviour of external thermal insulating systems (ETICS) have been investigated experimentally. As a basis of the investigations real cases with EPS based ETICS have been analysed. The analysis showed that the fire in front of the building is the most common and critical fire scenario for these systems. These fires are often caused by waste containers. This result contradicts the former common assumption that the fire inside the building is the most critical fire scenario for ETICS. Intermediate scale experiments in the Single Burning Item (SBI) test apparatus have been performed at BAM with ETICS specimens. The render of the systems was partially damaged. The measured heat release rate of the specimens increased significantly with size and depths of the damages. Additionally results of large scale experiments with a waste container equivalent ignition source are presented and recommendations to enhance fire safety of these systems are given.
A controlled-atmosphere cone calorimeter that is built by modifying the Standard apparatus with the addition of a controlled-atmosphere chamber offers a time- and cost-saving approach for reaction-to-fire testing in vitiation- and ventilation-controlled atmospheres. Due to the design of the added enclosure no mechanical changes on cone calorimeter’s Standard ductwork are required. This offers some advantages but also important limitations. The design has an open connection between the outlet of the added enclosure and the cone calorimeter’s exhaust hood. Therefore, sufficient ambient air from the laboratory surroundings is drawn into the System to introduce effects which have the potential to affect test results significantly.
A procedure which is is suitable to consider physical effects of the ambient air on the calculation of the heat release rate is presented as well as initial results of an application towards toxic potency assessment. Signs for Chemical effects of the ambient air such as post reactions are shown but subject of an ongoing work.
Computer simulation tools were used to evaluate pedestrian movement. This study compares the reliability of three simulation tools and the calculation method by Predtetschenski und Milinski with a controlled evacuation exercise of a lecturer room. The comparison shows that each simulation tool used underestimate the total evacuation time and that an indicator for a low level of fitness does not necessarily lead to a long evacuation time. Results revealed that calibration of simulation tools is required to model heterogeneous population properly. Therefore, further experiments with a realistic, heterogeneous composition of participants have to be made.
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.
Validation of non-destructive testing methods is necessary to create a common basis where different systems can be compared and their applications and limitations be identified. This can be achieved through comparing the measurements taken by several systems used for a common diagnostic purpose under practical but controlled testing conditions. Well-designed small and large laboratory or field specimens promise such conditions.
The special concrete specimen (LCS) at BAM was constructed for validation purposes, in particular, to be used for evaluating the performance of echo methods. The thickness of the specimen is varying and it contains carefully designed built-in faults, such as voids, honeycombs and tendon ducts with various degrees of grouting defects. Since the geometry and condition of the defects are known, it can be used to compare the performance of radar, ultrasonic, impact-echo. The research was conducted within the Research group FOR384, sponsored by the German Research Society DFG.