Post-flashover Compartment Fire Research Articles

Defining the fire decay and the cooling phase of post-flashover compartment fires

The current research study discusses and characterises the fire decay and cooling phase of post-flashover compartment fires, as they are often mixed up despite their important heat transfer differences. The two phases are defined according to the fire heat release rate time-history. The fire decay represents the phase in which the fire heat release rate decreases from the ventilation- or fuel-limited steady-state value of the fully-developed phase to fire extinguishment. This phase is highly influenced by the fuel characteristics, ranging from fast decays for hydrocarbon and liquid fuels to slow decays for charring cellulosic fuels (wood). Once the fuel is consumed, the compartment volume enters the cooling phase, where the cooling in the gas-phase and solid-phase happens with significantly different modes and characteristic times. The thermal boundary conditions at the structural elements are then defined according to physical characteristics and dynamics within the compartment. The research study also underlines how the existing performance-based methodologies lack explicit definitions of the decay and cooling phases and the corresponding thermal boundary conditions for the design of fire-safe structural elements under realistic fire conditions.

Experimental study and modeling of radiation from compartment fires to adjacent buildings

This paper presents twelve full-scale experiments conducted on radiation from compartment fires to a target wall. The impact of different window sizes, separation distances between the fire building and a target wall, and different fuels on radiation heat fluxes on target wall is investigated. The contribution of external flame to radiation heat flux on target wall was studied. The emissivity of external flame is analyzed which shows that the experimental value is larger than that suggested by previous studies. The experimental data have been compared with theoretical results. The discrepancy between experimental and theoretical data has been explained. The limitations and recommendations of some equations have been discussed. Furthermore, a modeling of radiation heat flux on target wall from post-flashover compartment fire is proposed. This work is expected to be used as the basis to develop modeling of fire spread between buildings, modeling of post-earthquake fire spread and modeling of urban/wildland interface fire spread.

Experimental justification on thermal empirical equations for post-flashover compartment fires

Many useful correlation equations derived for estimating the heat release rate for a postflashover room fire were applied in performance-based design. A postflashover room fire is very hazardous as demonstrated by several big accidents in the past few years. The authorities are starting to challenge the use of such equations as fire engineering design tools. Additional justification of the results with experiments in fire hazard assessment is now required. Two correlation equations on heat release rates with gas temperature for postflashover fire are commonly used. One was reported by Babrauskas and Williamson and the other by McCaffrey et al., denoted as BW and MQH equations, respectively. Both equations were justified in this article by reported experimental data. Two sets of reported experimental results on postflashover room fires with transient heat release rates measured by oxygen consumption calorimetry were used. One set was reported by Chow et al. on studying flashover in a compartment fire with gasoline pool fires up to 2.8 MW. The other set was the experimental data on cable fires in a long cavity reported by Hietaniemi et al. Direct comparison indicated that heat release rates estimated using the BW equation are lower than measured values of both sets of the experiments. This point should be watched while applying the BW equation in fire hazard assessment. Better agreement was observed in the equation by MQH. A possible reason is that the empirical constants in the MQH equation were deduced by fitting with experimental data.

Thermal Empirical Equations for Post-Flashover Compartment Fires

Thermal Empirical Equations for Post-Flashover Compartment Fires

Thermal Empirical Equations for Post-Flashover Compartment Fires

Many useful correlation equations derived for estimating the heat release rate are believed to be adequate in fire engineering application. However, heat release rates in deriving those equations were mainly based on estimating mass loss rate of fuel. Flashover in a compartment fire had been studied experimentally on gasoline pool fires with results on heat release rate reported earlier. Transient heat release rates were measured by oxygen consumption calorimetry. The gas temperature curves at different locations in the room were measured instantaneously. Correlation equations on heat release rates with gas temperature reported in the literature will be reviewed and justified with the experimental results. It was observed that heat release rate estimated were lower than the experimental measurement.

Experimental review of the homogeneous temperature assumption in post-flashover compartment fires

Traditional methods for quantifying and modelling compartment fires for structural engineering analysis assume spatially homogeneous temperature conditions. The accuracy and range of validity of this assumption is examined here using the previously conducted fire tests of Cardington (1999) and Dalmarnock (2006). Statistical analyses of the test measurements provide insights into the temperature field in the compartments. The temperature distributions are statistically examined in terms of dispersion from the spatial compartment average. The results clearly show that uniform temperature conditions are not present and variation from the compartment average exists. Peak local temperatures range from 23% to 75% higher than the compartment average, with a mean peak increase of 38%. Local minimum temperatures range from 29% to 99% below the spatial average, with a mean local minimum temperature of 49%. The experimental data are then applied to typical structural elements as a case study to examine the potential impact of the gas temperature dispersion above the compartment average on the element heating. Compared to calculations using the compartment average, this analysis results in increased element temperature rises of up to 25% and reductions of the time to attain a pre-defined critical temperature of up to 31% for the 80th percentile temperature increase. The results show that the homogeneous temperature assumption does not hold well in post-flashover compartment fires. Instead, a rational statistical approach to fire behaviour could be used in fire safety and structural engineering applications.

Quantitative comparison of FDS and parametric fire curves with post-flashover compartment fire test data

This paper presents a comparison of two parametric fire modelling techniques (Eurocode 1, and the BFD curve method) and one field model (fire dynamics simulator) against large-scale post-flashover test data. Using a method of the product moment correlation coefficient, it is shown that the BFD curve predictions are most closely representative of reality. For the computational test data, two grid resolutions are adopted in the FDS field model, the finer of which having comparable results in terms of regression analysis to the BFD method. Both the field model and the BFD curve method were found to give better predictions compared to the Eurocode method over the duration of the test. However, a direct comparison of the maximum gas temperatures shows the field model to be poorer in its predictive capability than the parametric methods, under-predicting the maximum gas temperatures. In addition, a more in-depth analysis of the FDS predictions indicates that by considering simply average compartment temperatures the more inaccurate spatially specific temperature predictions were disguised. This study provides useful quantitative data on the three techniques presented and discusses more general issues concerning fire modelling.

Simulating the effects of fuel type and geometry on post-flashover fire temperatures

This paper discusses the effect of fuel type and geometry on predicted compartment temperatures derived from computer modelling of post-flashover compartment fires. Many previous studies have investigated post-flashover fires with either wood crib or liquid pool fuels, but very few analytical or experimental studies have considered realistic wood-based fuels with different ratios of surface area to volume, combined with plastic-based fuels. A simple single zone fire model was used to calculate the temperatures in post-flashover compartment fires. The program includes a catalogue of furniture items, each with fuel mass loss rate evaluated on the basis of a constant regression rate on all exposed surfaces. The program also includes a pool-burning model and considers wood fuels and thermoplastic fuels burning together inside a compartment. Use of the model shows that the total fuels load alone is not sufficient to characterise a post-flashover fire. The fire temperature is highly dependent on the fuel type and geometry. For given ventilation and total fuel load, the resulting temperature depends greatly on the average thickness of the wood fuels and the presence of thermoplastic fuels. The ratio of the available fuel surface area to the ventilation opening is particularly important. Several fire scenarios involving different fuel types and characteristics are simulated and compared with Eurocode parametric fires.

Species Transport from Post-Flashover Fires

A study was performed to determine the use of an equivalence ratio to predict gas levels (CO, CO2, O2, and unburned hydrocarbons) transported to locations remote from a post-flashover compartment fire. A series of tests were conducted in a reduced-scale facility to measure the evolution of post-flashover compartment fire gases flowing down a hallway. Test variables included air entrainment into gases in the hallway, stoichiometry of the compartment fire gases entering the hallway, mass flow rate of compartment fire gases, and the presence of a vitiated smoke layer accumulated in the hallway. In cases with no layer accumulated in the hallway, species yields in the hallway were found to correlate with a control volume equivalence ratio. The control volume equivalence ratio is the ratio of the mass loss rate of fuel inside the compartment to the air flow into the compartment plus the air entrained into compartment fire gases flowing along the hallway. Layers that accumulate in the hallway were determined to limit oxidation, which in some cases resulted in CO yields transported to remote locations being 20% higher than those inside the compartment. Based on the experimental data, a methodology was developed for predicting species levels transported to remote locations.

Evaluation of Models of Fully Developed Post-flashover Compartment Fires

Closed-form models of fully developed enclosure fires are evaluated by comparing model predictions to temperature and burning rate data from experiments. The experimental data selected represent a wide spectrum of ventilation conditions, including fuel-controlled and ventilation-controlled burning. Most methods are found to underpredict either compartment fire temperatures or duration of burning under some conditions. Based on the comparisons, a recommendation is made as to which method should be used in a design or analysis context to model post-flashover fires in compartments that are nearly cubic in shape.

A tool to design steel elements submitted to compartment fires—OZone V2. Part 1: pre- and post-flashover compartment fire model

The computer code OZone V2 has been developed to help engineers in designing structural elements submitted to compartment fires. The code is based on several recent developments, in compartment fire modelling on one hand and on the effect of localised fires on structures on the other hand. It includes a single compartment fire model that combines a two-zone model and a one-zone model. In this paper, the description of this compartment fire model is given. The main model is first presented. It consists of the usual zone model equations fully coupled with the partition model equations. The partitions are modelled by the finite element method. The switch from the two-zone to the one-zone model is then explained. The vertical, horizontal and forced vent sub-models are presented, followed by the fire source and the combustion models. A comparison between this code and another compartment fire model NAT is made. The OZone calculations are then compared to full scale fire tests. Considerations as to how this model is used for the design of steel elements will be presented in a companion paper (Fire Saf. J., this issue).

Carbon Monoxide Levels in Structure Fires: Effects of Wood in the Upper Layer of a Post-Flashover Compartment Fire.

This experimental study was performed to determine the effects of wood pyrolyzing in a high-temperature, vitiated compartment upper layer on the environment inside the compartment and an adjacent hallway. This was done by comparing species concentrations and temperature measurements from tests with and without wood in the compartment upper layer. Experiments were performed with a window-type opening and a door-type opening between the compartment and the hallway. In these tests, the wood in the compartment upper layer caused CO concentrations inside the compartment to increase, on average, to 10.1% dry, which is approximately 3 times higher than levels measured without wood in the upper layer. Down the hallway 3.6 m from the compartment with wood in the upper layer, CO concentrations were measured to be as high as 2.5% dry. The use of the global equivalence ratio concept to predict species formation in a compartment was explored for situations where wood or other fuels pyrolyze in a vitiated upper layer at a high temperature.

Light Timber-Framed Walls Exposed to Compartment Fires

The objective of this project was to determine the equivalent time of exposure (to the ISO-834 standard fire), for a number of light timber-framed wall assemblies exposed to a range of time temperature curves characteristic of compartment fires.This analysis considered only the thermal behavior of the walls. Load bearing performance will be the subject of the next phase of the study.The overall method was as follows.(1) The data from four full-scale ISO-834 wall tests were used to calibrate a finite element model of the wall assembly developed using the TASEF program. Subsequently the model was validated using test on walls with different layouts.(2) A set of characteristic time-temperature curves for compartment fires was developed using the computer program COMPF-2, a post-flashover compartment fire model.(3) The finite element models of the walls developed in Step 1 were subjected to the time temperature curves developed in Step 2.(4) The temperatures within the wall assembly found in Step 3 were compa...

A closed-form approximation for post-flashover compartment fire temperatures

A method is developed, suitable for design purposes, which allows approximate post-flashover fire temperatures to be calculated without the use of computer codes. This method may be used for thermoplastic pool fires, wood crib fires, and other fires of known fuel release rate. Both ventilation-limited and fuel rate-limited fires are treated. Results typically agree to within 3% of exact computer code solutions.

Temperature Calculation of Insulated Steel Columns Exposed to Natural Fire

A method suitable for design purposes has been developed which allows the approximate post-flashover compartment fire temperature to be plotted versus time in one curve, the general natural fire curve; time is then modified or scaled to take into consideration ventilation conditions and wall properties. In the analysis the common assumptions of constant and ventilation controlled combustion, uniform temperature, and wall losses proportional to the thermal inertia are made. The general natural fire curve is given an analytical expression, which is then used to calculate temperature in fire exposed insulated columns by a simple integration procedure. The results are plotted in handy diagrams, and temperatures obtained in columns exposed to natural fires and standard fires according to ISO 834 are compared.