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A general concept of a hybrid modelling of fire dynamics in the compartments is presented. The hybrid fire model combines the advantages of both zone and field models. The assumptions applying to physical model of fire and its mat...
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A general concept of a hybrid modelling of fire dynamics in the compartments is presented. The hybrid fire model combines the advantages of both zone and field models. The assumptions applying to physical model of fire and its mathematical description are given. Some problems related to application and development as well as verification and validation of the model are discussed.
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The National Institute of Standards and Technology (NIST) conducted an extensive investigation of the collapse of the three tall World Trade Center (WTC) buildings. A central part of this investigation was the reconstruction and u...
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The National Institute of Standards and Technology (NIST) conducted an extensive investigation of the collapse of the three tall World Trade Center (WTC) buildings. A central part of this investigation was the reconstruction and understanding of the initiation and spread of the fires. This paper describes the reconstruction of the fires, the thermal environment they created within the buildings, and the raising of the temperatures of the structural components. NIST analyzed thousands of documents, interviews, photographs, and videos to obtain information on the layout of the floors and the progress of the fires. Experiments provided information on the factors likely to have determined the fire growth. Simulations using the Fire Dynamics Simulator gave good agreement with the fire spread as observed at the windows. Imposition of the probable thermal environment on the structural steel produced maps of the probable temperature profile of the steel as the fires progressed. For WTC 1 and WTC 2, even in the vicinity of the fires, it was unlikely that the columns and floor trusses with intact insulation heated to temperatures where significant loss of strength occurred. This was in part due to the short time between aircraft impact and building collapse. There were regions of the towers in which the loss of structural strength of floors and columns, whose insulation had been damaged by aircraft impact, was likely. For WTC 7, even though the insulation was intact, the long periods of heating resulted in floor components whose temperatures exceeded 600℃, but columns did not exceed 300℃.
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The degree of accuracy in model predictions of rate of spread in wildland fires is dependent on the model's applicability to a given situation, the validity of the model's relationships, and the reliability of the model input data...
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The degree of accuracy in model predictions of rate of spread in wildland fires is dependent on the model's applicability to a given situation, the validity of the model's relationships, and the reliability of the model input data. On the basis of a compilation of 49 fire spread model evaluation datasets involving 1278 observations in seven different fuel type groups, the limits on the predictability of current operational models are examined. Only 3% of the predictions (i.e. 35 out of 1278) were considered to be exact predictions according to the criteria used in this study. Mean percent error varied between 20 and 310% and was homogeneous across fuel type groups. Slightly more than half of the evaluation datasets had mean errors between 51 and 75%. Under-prediction bias was prevalent in 75% of the 49 datasets analysed. A case is made for suggesting that a ±35% error interval (i.e. approximately one standard deviation) would constitute a reasonable standard for model performance in predicting a wildland fire's forward or heading rate of spread. We also found that empirical-based fire behaviour models developed from a solid foundation of field observations and well accepted functional forms adequately predicted rates of fire spread far outside of the bounds of the original dataset used in their development.
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In 2005, a line-of-duty death of an instructor at a firefighter training facility spawned research into both firefighter training and improving firefighter protective gear. Since the incident, there has been additional research in...
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In 2005, a line-of-duty death of an instructor at a firefighter training facility spawned research into both firefighter training and improving firefighter protective gear. Since the incident, there has been additional research into the material properties, firefighter facepiece performance, and the classification of firefighter exposures. This has been in parallel to significant improvements in the ability to model fires and predict, rather than prescribe, fire growth. As this recent body of work was not available at the time of incident investigation, the incident was revisited using the current version of Fire Dynamics Simulator. The full day of training evolutions was modeled in Fire Dynamics Simulator using recent data on wood pyrolysis (the fuel) and facepiece reaction to heat. Fire Dynamics Simulator results were evaluated against the testing done following the incident. Facepiece research was used to develop hole formation criteria that could be evaluated from Fire Dynamics Simulator predictions of facepiece exposure. This was used to compare the performance of facepieces contemporary with the incident to today’s facepieces. In addition, exposure predictions were evaluated in the context of exposure hazard categories developed for firefighter protective gear.
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A novel hybrid fire model combining the traditional field and zone modeling approaches to simulate the fire smoke propagation in a multi-storey building is presented in this paper. In the hybrid model, the field model is used to m...
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A novel hybrid fire model combining the traditional field and zone modeling approaches to simulate the fire smoke propagation in a multi-storey building is presented in this paper. In the hybrid model, the field model is used to model the fire smoke movement in rooms with complex fire-induced airflow where the two-layer zone assumption of the zone model is not valid, e.g. in the room of fire origin. The zone model is used to model the fire smoke propagation in the rooms/corridors where the hot smoke layer is well stratified and the smoke movement can be reasonably simulated based on the two-zone concept. The fundamentals of the hybrid fire model are presented and discussed in this paper. The interface treatment between the field model and the zone model is presented in detail. In addition, some examples highlighting the application of the new hybrid model to simulate the smoke propagation in a multi-storey building are also presented. The hybrid model provides a more accurate prediction of fire smoke propagation and consumes less computational resources in comparison to the full zone and full field models, respectively.
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Fire radiative energy density (FRED, Jm(-2)) integrated from fire radiative power density (FRPD, Wm(-2)) observations of landscape-level fires can present an undersampling problem when collected from fixed-wing aircraft. In the pr...
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Fire radiative energy density (FRED, Jm(-2)) integrated from fire radiative power density (FRPD, Wm(-2)) observations of landscape-level fires can present an undersampling problem when collected from fixed-wing aircraft. In the present study, the aircraft made multiple passes over the fire at similar to 3min intervals, thus failing to observe most of the FRPD emitted as the flame front spread. We integrated the sparse FRPD time series to obtain pixel-level FRED estimates, and subsequently applied ordinary kriging (OK) and Gaussian conditional simulation (GCS) to interpolate across data voids caused by the undersampling. We compared FRED interpolated via OK and GCS with FRED estimated independently from ground measurements of biomass consumed from five prescribed burns at Eglin Air Force Base, Florida, USA. In four of five burns considered where undersampling prevailed, OK and GCS effectively interpolated FRED estimates across the data voids, improving the spatial distribution of FRED across the burning event and its overall mean. In a fifth burn, the burning characteristics were such that undersampling did not present a problem needing to be fixed. We also determined where burning and FRPD sampling characteristics merited applying OK and CGS only to the highest FRED estimates to interpolate more accurate FRED maps.
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The influence of meteorological conditions on wildfire behaviour and propagation has been recognised through the development of a variety of fire weather indices, which combine information on air temperature, atmospheric moisture ...
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The influence of meteorological conditions on wildfire behaviour and propagation has been recognised through the development of a variety of fire weather indices, which combine information on air temperature, atmospheric moisture and wind, amongst other factors. These indices have been employed in several different contexts ranging from fire behaviour prediction and understanding wildfire potential to identifying conditions conducive to blow-up fires. This paper considers four such indices in the absence of free moisture (i.e. zero rainfall, no dew, etc.) and demonstrates that to a very good approximation, and up to rescaling, all four fire weather indices are equivalent.
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Assumptions made and results obtained when applying three fire modeling approaches to study three accidental fires that occurred in single-family dwellings are presented in this article. The modeling approaches used are: a simplif...
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Assumptions made and results obtained when applying three fire modeling approaches to study three accidental fires that occurred in single-family dwellings are presented in this article. The modeling approaches used are: a simplified analytical model of fire growth, a zone model (CFAST), and a field model (FDS). The fires predicted are: a house fire of suspected initial location but of unknown ignition source, a small-apartment fire initiated by the ignition of a sofa, which extinguished due to oxygen depletion, and a one-story house fire started by a malfunctioning gas heater. The input to each model has been kept as independent as possible from the other models while consistent with the forensic evidence. The predictions from the models of the fires' characteristics are analyzed in the context of the forensic evidence for each accidental fire to compare the models' predictive capabilities. It is found that in spite of the differences in the sophistication of these three modeling approaches, the results are in relatively good agreement, particularly in the early stages of the fire. Simpler models can be used as a first step towards less approximate modeling or to confirm the order of magnitude of the results from more complex models. The results of this study can be used to reach conclusions about the complexity of the model required to describe a particular fire scenario.
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A ubiquitous source of uncertainty in fire modeling is specifying the proper heat release rate (HRR) for the fuel packages of interest. An inverse HRR calculation method is presented to determine an inverse HRR solution that satis...
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A ubiquitous source of uncertainty in fire modeling is specifying the proper heat release rate (HRR) for the fuel packages of interest. An inverse HRR calculation method is presented to determine an inverse HRR solution that satisfies measured temperature data. The methodology uses a predictor-corrected method and the Consolidated Model of Fire and Smoke Transport (CFAST) zone model to calculate hot gas layer (HGL) temperatures in single compartment configurations. The inverse method runs at super-real-time speeds while calculating an inverse HRR solution that reasonably matches the original HRR curve. Examples of the inverse method are demonstrated by using a multiple step HRR case, complex HRR curves, experimental temperature data with a constant HRR, and a case with an experimentally measured HRR. In principle, the methodology can be applied using any reasonably accurate fire model to invert for the HRR.
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Information from full-scale fire tests are gathered and systemised. The knowledge from these tests is used as input to three different models, ranging from a simple spreadsheet model to advanced computational fluid dynamics (CFD) ...
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Information from full-scale fire tests are gathered and systemised. The knowledge from these tests is used as input to three different models, ranging from a simple spreadsheet model to advanced computational fluid dynamics (CFD) modelling, for calculating the temperature in the smoke layer. The deviation between the fire tests and the computed results is described and an evaluation of how this may influence the use of the models is discussed from the point of view of risk analysis. For experiments with small fires, i.e., one to five cars, one bus or one truck without cargo, the calculated temperature time curves from all models comply well with the measurements from the full-scale fire tests. For the larger fires, more deviation was found. The computational results were, however, on the same "order of severity" as the test fires, and thereby useful for hazard calculations. In contradiction to the general belief, the simplest models gave, in the same way as the CFD codes, results close to the values of severity recorded in the test fires with respect to HRR and smoke layer temperatures. The simple models may therefore be a good tool in risk analysis for not too complex tunnel structures.
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