Measurements of Smoke Characteristics in HVAC Ducts

Research paper published in the journal Fire Technology in 2001The characteristics of smoke traveling in an HVAC duct have been observed along with the response of selected duct smoke detectors. The simulated HVAC system consists of a 9 m long duct, 0.45 m in diameter. An exhaust fan is placed at one end of the duct and is capable of inducing airflow rates that range from 0 to 1.5 m 3 /s. The flow is controlled by means of a manual damper. On the upstream end of the duct there is a square exhaust hood approximately 2.2 m at the bottom and 0.3 m at the top. The bottom of the hood is approximately 2.5 m above the floor a shroud extends down to approximately 1.5 m above the floor. The test section, placed immediately downstream of the hood, is 3.5 m long duct with a square cross section of 0.4 m on a side. The instrumentation includes oxygen, carbon monoxide and carbon dioxide gas analyzers and a load cell to determine the energy release rate of the fires tested. The smoke within the duct is characterized by means of a laser light sheet and CCD camera, two white light source and photocell ensembles, a Pitot tube and an array of eight thermocouples placed on the vertical plane of symmetry. A smoke detector was placed at the downstream end of the test section. Two types of detectors were tested, ionization and photoelectric, with a single sampling probe geometry. The fires tested cover a wide range of fuels (propane, heptane, toluene, toluene/heptane mixture, shredded paper, polyurethane foam, wood cribs) with the peak energy release rates up to 800 kW. The smoke detector performance, temperature, flow field, smoke particle size and particle distributions are dependent on the fire characteristics and airflow through the duct. The different measurements could be scaled by means of the fire size and airflow rate but left a strong dependency on the fuel and burning characteristics (i.e. smoldering, flaming). The optical density and mass optical density are analyzed as metrics for characterizing smoke and smoke detector response. Detailed comparisons between the different metrics used are presented throughout this work. Clear evidence of stratification and aging of the smoke along the duct are also presented. The limitations of the present configuration and the need for a larger scale study are also discussed

A Priori Modelling of Fire Test One

Chapter 10 in the book: The Dalmarnock Fire Tests: Experiments and Modelling, Edited by G. Rein, C. Abecassis Empis and R. Carvel, Published by the School of Engineering and Electronics, University of Edinburgh, 2007. ISBN 978-0-9557497-0-4An international round-robin study of fire modelling was conducted prior to the Dalmarnock Fire Tests in order to assess the state-of-the-art of fire modelling in real scenarios. The philosophy behind the Dalmarnock Fire Tests was to provide instrumentation density suitable for comparison to field models and designed the scenario for maximum test reproducibility. Each participating team independently simulated a priori the test using a common detailed description of the compartment geometry, fuel packages, ignition source and ventilation conditions. The aim of the exercise was to forecast the test results as accurately as possible, and not to provide an engineering analysis with adequate conservative assumptions or safety factors. The modelling results and experimental measurements are compared among themselves, allowing for conclusions on the robustness, reliability and accuracy of current modelling practices. The results indicate large scatter and considerable disparity among predicted fires and also differing from the experimental data. The Dalmarnock Fire Test One was benchmarked against a second test to establish the potential experimental variability. The scatter of the simulations is much larger than the experimental error and the experimental variability. The study emphasises on the inherent difficulty of predicting fire dynamics and demonstrates that the main source of scatter is originated in the many degrees of freedom and the uncertainty in the input parameters. The conclusions from the study are made public to encourage debate and exchange of views on the topic of fire modelling

Round-robin study of a priori modelling predictions of the Dalmarnock Fire Test One

Peer-reviewed journal paper published in 2009 about the international modelling exercise conducted in 2006.An international study of fire modelling was conducted prior to the Dalmarnock Fire Test One in order to assess the state-of-the-art of fire simulations using a round-robin approach. This test forms part of the Dalmarnock Fire Tests, a series of experiments conducted in 2006 in a high-rise building. The philosophy behind the tests was to provide measurements in a realistic fire scenario involving multiple fuel packages and non-trivial fire growth, and with an instrumentation density suitable for comparison with computational fluid dynamics models. Each of the seven round-robin teams independently simulated the test scenario a priori using a common detailed description of the compartment geometry, fuel packages, ignition source and ventilation conditions. The aim of the exercise was to forecast the fire development as accurately as possible and compare the results. The aim was not to provide an engineering analysis with conservative assumptions or safety factors. Comparison of the modelling results shows a large scatter and considerable disparity among the predictions, and between predictions and experimental measurements. The scatter of the simulations is much larger than the error and variability expected in the experiments. The study emphasises on the inherent difficulty of modelling fire dynamics in complex fire scenarios like Dalmarnock, and shows that the accuracy to predict fire growth (i.e. evolution of the heat released rate) is, in general, poor

Flammability of solid materials: An experimental calorimetric approach

Flammability properties of solid materials are necessary to be a known parameter for many purposes: among them, forensic investigations of fire and explosion events, fire risk or hazard analysis, design and development of combustion-based systems. However, despite the large quantity of data in the literature, the flammability properties of many materials still appear not to be available or show a degree of uncertainty associated with them, which makes their value limited. The present work is aimed at proposing a calorimetric-based approach to determine some flammability and thermophysical properties of solids, with specific regard to time-to-ignition as a function of the imposed heat flux. Plastic materials have been here chosen as test cases, even though this approach has a general applicability. The two mentioned parameters have been analyzed to provide a quantitative estimation of the critical heat flux (minimum heat flux resulting in ignition). A cone calorimeter has been employed to conduct the experiments: the facility complies with standard ASTM E 1354; the related uncertainty and validity range has been evaluated through an appropriate error analysis. Finally, thermal inertia has been thereby calculated for the considered materials through a simple thermodynamic model, which is based upon critical heat flux and energy conservation. Copyright \uc2\ua9 2011 by ASME

Coronal Heating as Determined by the Solar Flare Frequency Distribution Obtained by Aggregating Case Studies

Flare frequency distributions represent a key approach to addressing one of the largest problems in solar and stellar physics: determining the mechanism that counter-intuitively heats coronae to temperatures that are orders of magnitude hotter than the corresponding photospheres. It is widely accepted that the magnetic field is responsible for the heating, but there are two competing mechanisms that could explain it: nanoflares or Alfv\'en waves. To date, neither can be directly observed. Nanoflares are, by definition, extremely small, but their aggregate energy release could represent a substantial heating mechanism, presuming they are sufficiently abundant. One way to test this presumption is via the flare frequency distribution, which describes how often flares of various energies occur. If the slope of the power law fitting the flare frequency distribution is above a critical threshold, $\alpha=2$ as established in prior literature, then there should be a sufficient abundance of nanoflares to explain coronal heating. We performed $>$600 case studies of solar flares, made possible by an unprecedented number of data analysts via three semesters of an undergraduate physics laboratory course. This allowed us to include two crucial, but nontrivial, analysis methods: pre-flare baseline subtraction and computation of the flare energy, which requires determining flare start and stop times. We aggregated the results of these analyses into a statistical study to determine that $\alpha = 1.63 \pm 0.03$. This is below the critical threshold, suggesting that Alfv\'en waves are an important driver of coronal heating.Comment: 1,002 authors, 14 pages, 4 figures, 3 tables, published by The Astrophysical Journal on 2023-05-09, volume 948, page 7