Characterizing Heat Release Rates Using an Inverse Fire Modeling Technique

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.     

Effects of nanoclay and fire retardants on fire retardancy of a polymer blend of EVA and LDPE

The effects of nanoclay (organoclay) and fire retardants (aluminium tri-hydroxide and magnesium hydroxide) on the fire retardancy of a polymer blend of ethylene-vinyl acetate (EVA) and low-density polyethylene (LDPE) were assessed using thermogravimetric analysis (TGA) and the cone calorimeter. TGA measurements were conducted in nitrogen and air atmospheres at different heating rates (1–20 °C/min), whilst in the cone calorimeter square samples were tested under various external heat fluxes (15–60 kW/m²). The TGA results indicate that the nanoclay (NC) alone has little effect on the degradation of the polymer blend, whereas aluminium tri-hydroxide (ATH) and magnesium hydroxide (MH), used as fire retardants (FRs), generally decrease the onset degradation temperature and also reduce the peak mass loss rate. However, it was found in the cone calorimeter that, though having negligible effect on ignition, the nanoclay reduces the heat release rate (HRR), and increases smoke and CO yields. In comparison, FRs (ATH or MH) were found to delay ignition owing to loss of water at lower temperatures, reduce the HRR, and have similar smoke and CO yields compared to the polymer blend. The reduced HRRs for both the nanoclay and FRs can be attributed to the formation of a surface layer (a nano layer for nanoclay and a ceramic-like layer of Al₂O₃/MgO for FRs), which acts as mass and heat barriers to the unpyrolysed material underneath. The global effect of the surface layer for the polymer blend nanocomposite was examined using a previously developed numerical model, and a methodology for predicting the mass loss rate was subsequently developed and validated.     

The Use of Fractional Factorial Design for Atrium Fires Prediction

In order to mitigate the excessive computational cost of atrium fire simulations, a novel methodology based on the use of the Fractional Factorial Design technique to obtain an experimental validated tool, in the form of a surface response model, capable to predict fire induced conditions is proposed. This methodology is supported by results from a Design of Experiments benchmark, which consists of a set of FDS simulations in the present work. Specifically, a \(2^{6-2}_{IV}\) approach has been considered and applied to a 20 m cubic atrium. Thus, six factors have been considered, namely the fire Heat Release Rate (HRR) and location, the exhaust flow rate, the exhaust location and activation time, and the inlet vents area. Furthermore, the smoke temperature at the roof and 15 m high and the smoke layer height have been considered the variables of interest. Subsequently, a multiple linear regression analysis has been performed to predict and compare the steady and non-steady temperature profiles and the smoke layer drop with six novel full-scale atrium fire tests, and also with specific adjusted FDS models. In addition, this methodology has been extended successfully to predict the non-steady behaviour of the fire tests. At the steady state, the HRR and the exhaust flow rate have been found to be the most relevant factors. The results obtained with the proposed methodology show a good fit both with the fire tests and with the adjusted FDS models, with discrepancies mostly below 14%. For non-steady conditions, a time analysis of the influence of the six factors has been carried out. Again, remarkable good agreement with the time-dependent experimental results is achieved, with average discrepancies below 12%, being the larger differences found in the prediction of local effects, such as the smoke ceiling jet, for high HRR or when the make-up air influence is significant. The results turn this methodology into a powerful and useful tool for fire safety designs.     

Investigation of the effect of tunnel ventilation on crib fires through small-scale experiments

This paper adopts a series of 1:20 scale tunnel experiments based on a series of large-scale tunnel experiments to study the influence of forced ventilation on fires. The small-scale tunnel has dimensions of 0.365 m (W)×0.26 m (H)×11.9 m (L). Cribs using a wood-based material provide the fuel source and forced ventilation velocities from 0.23 to 1.90 m/s are used. From the study of the measured heat release rate (HRR) and mass loss rate data it is found that the forced air velocity affects the fire spread rate and burning efficiency and further affects peak HRR values at different air velocities. A simple model to describe these influences is proposed. This model is used to reproduce the enhancement of peak HRR for cribs with different porosity factors noted by Ingason [1] and to assess the effects of using different length of cribs on peak HRR. The results from these analyses suggest that different porosity fuels result different involvement of burning surface area and result different changes in peak HRR. However, no significant difference to the enhancement on fire size is found when the burning surface area is similar. It is also found that the trend in the enhancement on fire size by using sufficiently long crib and available ventilation conditions matches the predictions of Carvel and Beard [2] for two-lane tunnel heavy goods vehicle fires.     

Assessment of the Use of Fire Dynamics Simulator in Performance-Based Design

This paper discusses a procedure for the use of fire modelling in the performance-based design environment to quantify design fires for commercial buildings. This procedure includes building surveys, medium-and full-scale experiments and computer modelling. In this study, a survey of commercial premises was conducted to determine fire loads and types of combustibles present in these buildings. Statistical data from the literature were analysed to determine the frequency of fires, ignition sources, and locations relevant to these premises. Based on the results of the survey and the statistical analyses a number of fuel packages were designed that represent fire loads and combustible materials in commercial buildings. The fuel packages were used to perform medium- and full-scale, post-flashover fire tests to collect data on heat release rates, compartment temperatures and production and concentration of toxic gases. Based on the experimental results, input data files for the computational model, Fire Dynamics Simulator (FDS), were developed to simulate the burning characteristics of the fuel packages observed in the experiments. Comparative analysis between FDS model predictions and experimental data of HRR, carbon monoxide (CO), and carbon dioxide (CO₂), indicated that FDS model was able to predict the HRR, temperature profile in the burn room, and the total production of CO and CO₂ for medium- and large-scale experiments as well as real size stores.     

The application of a genetic algorithm to estimate material properties for fire modeling from bench-scale fire test data

A methodology based on an automated optimization technique that uses a genetic algorithm (GA) is developed to estimate the material properties needed for CFD-based fire growth modeling from bench-scale fire test data. The proposed methodology involves simulating a bench-scale fire test with a theoretical model, and using a GA to locate a set of model parameters (material properties) that provide optimal agreement between the model predictions and the experimental data. Specifically, a GA based on the processes of natural selection and mutation is developed and integrated with the NIST FDS v4.0 pyrolysis model for thick solid fuels. The combined GA/pyrolysis model is used with cone calorimeter data for surface temperature and mass loss rate histories to estimate the material properties of two charring materials (redwood and red oak) and one thermoplastic material (polypropylene). This is done by finding the parameter sets that provide near-optimal agreement between the model predictions and experimental data, given the constraints imposed by the underlying physical model and the accuracy with which the boundary and initial conditions can be specified. The methodology is demonstrated here with the FDS pyrolysis model and cone calorimeter data, but it is general and can be used with several existing fire tests and almost any pyrolysis model. Although the proposed methodology is intended for use in CFD-based prediction of large-scale fire development, such calculations are not performed here and are recommended for future work.     

Examination of WFDS in Modeling Spreading Fires in a Furniture Calorimeter

Validation of physics-based models of fire behavior requires comparing systematically and objectively simulated results and experimental observations in different scenarios, conditions and scales. Heat Release Rate (HRR) is a key parameter for understanding combustion processes in vegetation fires and a main output data of physics-based models. This paper addresses the validation of the Wildland-urban interface Fire Dynamics Simulator (WFDS) through the comparison of predicted and measured values of HRR from spreading fires in a furniture calorimeter. Experimental fuel beds were made up of Pinus pinaster needles and three different fuel loadings (i.e. 0.6, 0.9 and 1.2 kg/m²) were tested under no-slope and up-slope conditions (20°). An Arrhenius type model for solid-phase degradation including char oxidation was implemented in WFDS. To ensure the same experimental and numerical conditions, sensitivity analyses were carried out in order to determine the grid resolution to capture the flow dynamics within the hood of the experimental device and to assess the grid resolution’s influence on the outputs of the model. The comparison of experimental and predicted HRR values showed that WFDS calculates accurately the mean HRR values during the steady-state of fire propagation. It also reproduces correctly the duration of the flaming combustion phase, which is directly tied to the fire rate of spread.     

Experimental investigation on transverse ceiling flame length and temperature distribution of sidewall confined tunnel fire

This paper presents an experimental investigation on the transverse ceiling flame length and the temperature distribution of a sidewall confined tunnel fire. The experiments were conducted in a 1/6th scale model tunnel with the fire source placed against the sidewall, 0 m, 0.17 m and 0.35 m above the floor, respectively. Experiments of fire against a wall without a ceiling, 0.35 m above the floor in a large space, were also conducted as a control group. Results shows that for small heat release rate (HRR), the flame is lower than the ceiling and extends along the sidewall. With the increase of HRR and elevation of burner height, the flame gradually impinges on the ceiling and spreads out radially along it. The flame impingement condition and the flame shapes of the wall fire with and without ceiling are presented. From the viewpoint of the physical meaning of flame impinging on the ceiling, the horizontal flame length should be a function of the unburned part of the fuel at the impinging point. Based on the proportional relation between the flame volume and HRR, the effective HRR (Q_ef) at the ceiling is determined and the effective dimensionless HRR, Q^*_ef is defined to correlate the horizontal ceiling flame length. Additionally, predictive correlations of transverse ceiling temperature distribution are proposed for the continuous flame region, the intermittent flame region and the buoyant plume region under the ceiling, respectively.     

Modeling of fire suppression by fuel cooling

Fire suppression with water spray was investigated, focusing on cases where fuel cooling is the dominant suppression mechanism, with the aim to add a specific suppression model addressing this mechanism in Fire Dynamics Simulator (FDS), which already involves a suppression model addressing effects related to flame cooling. A series of experiments was selected, involving round pools of either 25 or 35 cm diameter and using both diesel and fuel oil, in a well-ventilated room. The fire suppression system is designed with four nozzles delivering a total flow rate of 25 l/min and injecting droplets with mean Sauter diameter 112 μm. Among the 74 tests conducted in various conditions, 12 cases with early spray activation were especially considered, as suppression was observed to require a longer time to cool the fuel surface below the ignition temperature. This was quantified with fuel surface temperature measurements and flame video recordings in particular. A model was introduced simulating the reduction of the pyrolysis rate during the water spray application, in relation to the decrease of the fuel local temperature. The numerical implementation uses the free-burn step of the fire to identify the relationship between pyrolysis rate and fuel surface temperature, assuming that the same relationship is kept during the fire suppression step. As expected, numerical simulations reproduced a sharp HRR decrease following the spray activation in all tests and the suppression was predicted in all cases where it was observed experimentally. One specific case involving a water flow rate reduced such that it is too weak to allow complete suppression was successfully simulated. Indeed, the simulation showed a reduced HRR but a fire not yet suppressed. However, most of the tests showed an under-estimated duration before fire suppression (discrepancy up to 26 s for a spray activation lasting 73 s), which demonstrates the need for model improvement. In particular the simulation of the surface temperature should require a dedicated attention. Finally, when spray activation occurred in hotter environments, probably requiring a combination of fuel cooling and flame cooling effects, fire suppression was predicted but with an over-estimated duration. These results show the need for further modeling efforts to combine in a satisfactory manner the flame cooling model of FDS and the present suggested model for fuel cooling.     

An Experimental Study of Smoke Movement in Multi-Storey Buildings

This paper presents the results of an experimental study of smoke movement in a 10-storey building. Eight full-scale experiments including four real fuel fires and four propane fires were conducted in the National Research Council Canada (NRCC)’s 10-storey experimental tower to generate smoke movement data that can be used for the validation of computer models. The heat release rate (HRR) of fire cannot be measured in this tower, so to estimate the HRR of fuel-package fires in this study, an approach using propane as a fuel was developed to reproduce the temperature distribution of various fuel-package tests.     

A simulation model for fire growth on materials subject to a room-corner test

A mathematical model has been developed to simulate fire growth on wall and ceiling materials when subject to a room-corner fire test exposure. The model predicts the area of burning, the upper layer gas temperature, and the rate of energy release as a function of time. Material fire property data are developed from apparatuses described in ASTM E 1321 and E 1354. The results compare favorably to experimental data generated in Sweden for 13 materials tested. Furthermore, the model shows the sensitivity to ‘flashover’ for thin materials relative to small variations in their property data.     

考虑暴露表面积情况的火灾载荷的确定方法

主要研究可燃物表面积和厚度对估测释热速率的影响。在火灾载荷研究中包括可燃物暴露表面的研究，能更好的估算轰燃发生后可燃物燃烧的速率和时间。研究表明释热速率是表面积的一个函数，而燃烧时间是可燃物厚度的一个函数。轰燃后着火房间内可燃物的燃烧行为与暴露表面有关。     

Variation of heat release rate with forced longitudinal ventilation for vehicle fires in tunnels

Many tunnels are equipped with longitudinal ventilation systems to control smoke in the event of a fire. However, the influence of such ventilation on fire development and fire spread has rarely been considered. This paper presents the results of a study using a Bayesian methodology to estimate the effect of forced longitudinal ventilation on heat release rate (HRR) for fires in tunnels. The behaviour of car and heavy goods vehicle (HGV) fires with a range of forced ventilation velocities is investigated. Results are presented and the implications are discussed. It has been found that forced ventilation has a great enhancing effect on the HRR of HGV fires, but has little effect on the HRR of car fires.     

隧道内火灾大小和火灾蔓延模拟研究

隧道内火灾的热释放速率对火灾蔓延和烟气生成起着关键作用。影响热释放速率的关键参数包括：燃烧物特性、隧道形状、通风条件以及车辆流量。综述了几年来热释放速率对这些参数的依赖性所做的研究成果。设计了贝页斯概率模型来模拟火灾热释放速率受隧道形状以及纵向通风的影响，设计了定性模型来模拟火灾在类似海底隧道内从一个物体蔓延到另一个物体的情况，通风条件同样是纵向通风，并给出了此次研究的初步成果。     

Determination of the heat release rate inside operational road tunnels by comparison with CFD calculations

Usually, during a fire inside a tunnel, the average heat release rate (HRR) is estimated according to the type of vehicle. Frequently, the overall HRR is considered, however it is also necessary to know its time evolution to design real time systems, particularly ventilation, which respond to fire events or signals as fast as possible. Nowadays, there is not a well established and generally accepted procedure to know the power liberated at each instant of time inside an operational tunnel. That procedure could help in taking the correct actions to adapt the tunnel ventilation in order to diminish the effects of the fire and the smoke. This work shows a method to calculate the heat release rate using sensors that can be installed inside an operational road tunnel. Besides, the location of the fire could also be calculated accurately and quickly. To achieve the previous purposes, a stationary database that depends on HRR, its location, and the ventilation speed is calculated with CFD programs; the data are compared with temperatures measured by the sensors located inside the tunnel. The program used to generate the database is the simplified model UPMTUNNEL. The predictions of the model are compared with the results of calculations carried out using the general purpose code FLUENT, and with measurements done in a tunnel with a real fire, produced with a fuel tray.     

Design fire curves for tunnels

Various ways exist to represent a design fire curve for tunnels. These can include different fire growth rates or combinations of fire growth rates with constant levels of heat release rate (HRR) coupled to a decay period. This means that the curve has to be represented with different mathematical expressions for different time periods. A more convenient way is to describe the design fire curve with a single mathematical expression. Such a curve has been presented by the author (H. Ingason, Fire development in large tunnel fires, 8th International Symposium on Fire Safety Science, Beijing, China, 18–23 September 2005, pp. 1497–1508), but it does not include a constant HRR period. This paper presents a new, single exponential, design fire curve with a constant maximum HRR. A presentation of available design curves is given as well.     

Temperature and velocity distributions from numerical simulations of ceiling jets under unconfined,inclined ceilings

Numerical simulations of ceiling jets under unconfined, inclined ceilings were conducted with the open-source code FireFOAM. A range of ceiling inclinations, 0–30° was considered with a 14 kW convective heat release rate (HRR) heptane fire used as the plume source, and the ceiling mid-point clearance from the top of the 0.228 m diameter burner kept fixed at 0.89 m. The predicted temperature and velocity in the developing ceiling jets were compared against the experimental data and empirical correlations. Temperature and velocity predictions on the elevated side of the ceiling are in general agreement with experimental data. Flow reversal in the lower side of the ceiling was predicted with good confidence, and comparison with experimental data was found to be reasonable. Following existing convention in the literature, the predicted results were non-dimensionalized using the convective HRR, ceiling height and radial distance from the ceiling mid-point. Comparison of the non-dimensional data on the elevated ceiling side showed better agreement for temperature against the correlation, whereas predicted velocity data showed a wider spread around the correlation values.     

Evaluating the flammability of wood-based panels and gypsum particleboard using a cone calorimeter

This study examined the combustion characteristics of wood-based panels and gypsum particle board (GPB) made from wood particles using a cone calorimeter according to the ISO 5660-1 specifications. The combustion characteristics of the wood-based panels and GPB were measured in terms of the time to ignition (TTI), heat release rate (HRR), smoke production rate (SPR) and CO yield under a fire condition. The results demonstrated variations in the burning characteristics between the wood-based panels and a significant influence of the surface materials and construction elements on the HRR and SPR. The HRR, SPR and the CO yield of GPB were significantly lower than those of the wood-based panels.     

Estimating the Flashover Probability of Residential Fires Using Monte Carlo Simulations of the MQH Correlation

An important indicator of fire hazard in residential fires is the occurrence of flashover in the room of fire origin. Since the variability of residential fire scenarios is large, many different cases must be considered to evaluate the hazard of a given flammable product. Efficiently predicting the occurrence of flashover of a naturally ventilated compartment is possible using the correlation of McCaffrey, Quintiere, and Harkleroad (MQH). The large variability in United States (U.S.) living room fire scenarios is characterized from available data and propagated through the MQH correlation using Monte Carlo (MC) simulation. For the parameters, for which no relevant data was found, uniform probability distributions were assumed. The scenarios sampled in the MC simulations generally fell within the range of scenarios for which the MQH correlation has been validated. Flashover probabilities were estimated for fires up to 5 MW in heat release rate (HRR) and up to 8 min in duration. It was found that fires with HRRs less than 400 kW have a flashover probability of less than 0.01% regardless of their duration. Typical furniture fires were used as example cases, and it was predicted that a three seat upholstered sofa with a peak HRR of 2.15 MW has a 90% chance of flashing over a randomly chosen U.S. living room. The results of a global sensitivity analysis indicates that the fire location parameter and the vent opening width are the most important parameters affecting the prediction of the occurrence of flashover in U.S. living rooms. The methodology presented is generalizable, and the results can be readily improved by the collection of more data and the use of higher fidelity fire models.