Corner Fire Research Articles

An integrated section model to enable simulating composite slabs in fire simply as modelling a flat slab

Modelling slabs is vitally necessary when simulating building structures in fire. The composite action between slabs and beams and tensile membrane action after fire induced deflections significantly reshape the load redistribution mechanisms and failure patterns. Modelling slabs particularly composite slabs of ribbed sections as a common choice of modern steel structures is a challenging task. Currently, those existing modelling approaches, such as beam & shell model and strip models, require elements for ribbed and flat parts separately, which produces much complexity and ideally it can be solved using a suitable section model to appropriately represent the behaviour. This paper begins with formulating the theoretical base of state determination in the integrated composite section, which enables correct deformation distribution to ribbed and flat subsections. While being compatible to typical modelling infrastructure for slabs, the integrated section model has demonstrated excellent capability in comparison to the strip models and fire tests. Even using a coarse mesh scheme (e.g. 8 × 6 elements), the prediction error of mid-span deflection remains low (around 10%). The appealing benefit is further shown in modelling Cardington Corner fire test, which significantly reduces the efforts of determining geometric details, the number of nodes & elements, and the computation time cost.

Flame height and axial plume temperature profile of bounded fires in aircraft cargo compartment with low-pressure

A series of n-heptane buoyancy bounded fire tests (center fires, wall fires, corner fires) are conducted in a full-scale simulated aircraft cargo compartment at 70 kPa, 80 kPa, 90 kPa, 100 kPa to measure the flame heights and axial plume temperatures. Based on the Heskestad's model, the flame heights at different horizontal positions are normalized by introducing the respective mirror coefficients β of wall fires and corner fires, a prediction formula for flame heights with pressure correction coefficients Kp is established. The influence of air entrainment on flame height is further revealed by analyzing the experimental data through Quintiere and Grove's model. In addition, by comparing with the McCaffrey's model after the introduction of the mirror coefficient β, it is found that the axial temperature values of wall fires and corner fires are lower than the predicted values because the model ignores the heat radiation feeding back into the plume from the heated sidewalls, and the longitudinal dimension of the corner fire plumes is stretched resulting in an extended intermittent region. The prediction equations for the axial temperature distribution of bounded fires in low-pressure are proposed by introducing pressure correction coefficients.

Experimental study on burn through properties of PVC membrane room under fire

The thermal properties of PVC fabric membrane itself make it insufficient in fire resistance, and the overall stability of the membrane structure will be seriously threatened after a fire. In this paper, a small-size membrane burn-through test platform was designed and built, and the intermediate fire and corner fire tests were conducted to obtain smoke filling and membrane surface temperature law of change. Results showed that the softening and melting temperature of the membrane is about 164 °C, and the critical temperature of the membrane is about 257 °C. At the same time, the comparative analysis of the experiment and simulation results verified that the feasibility of Fire Dynamics Simulation to study the membrane structure fire.

Modelling concrete slabs subjected to fires using nonlinear layered shell elements and concrete damage-plasticity material

Floor slabs are crucial in the global load bearing mechanism during fire by providing critical alternate load-paths including tensile membrane action. It is desirable, but expensive and difficult, to predict their behaviour accurately with minimal calibration of model parameters. Two new developments are added to OpenSEES for this purpose. First, a thermo-mechanical nonlinear shell element extended for modelling large deflection of slabs in fire along with a multi-layered section to account for temperature-dependent material behaviour including plasticity and thermal expansion. The shell model is ported to include fire induced thermal action definitions induced by real fire exposure, which is critical in accurate simulation of deflections and stress states. Second, a plane-stress formulation of the concrete damage-plasticity material at elevated temperature is introduced to effectively model concrete response and damage in fire. These state-of-the-art developments provide a new, powerful, and open-source tool for researchers and engineers to investigate structural-fire problems at different scales with satisfying accuracy. The code is verifiedusing benchmark solutions and validated by modelling flat reinforced concrete slabs tested at ambient temperature and in fire,followed by simulating the large-scale Cardington Corner fire test. The results of these exercises agree well with analytical and experimental data and show that the new developments are well conceived and implemented.

Experimental study of corner wall fires with one or two combustible walls

The corner fire characteristics with two inert walls are compared against those with one or two combustible corner walls through a set of standard Single Burning Item (SBI) tests. The study examines how the corner fire behavior is affected by flame spread over one or two walls. In the case of flame spread over one corner wall, the inert side is a Calcium Silicate (CS) panel. As for the combustible wall, two different materials have been tested, namely, plywood and Medium-Density Fiberboard (MDF) panels. The results indicate that the simultaneous burning of two panels in the corner geometry increases the Heat Release Rate (HRR) contribution of each panel by 45–50%. This is because the burning of one corner wall increases the temperatures on the adjacent wall significantly, occasionally by more than 200 °C, and increases the heat fluxes on both corner walls at the same time, sometimes by nearly 20%. The results of HRR, Smoke Production Rate (SPR), flame heights, pyrolysis front propagation, panel temperatures, and total heat fluxes at several characteristic locations are presented.

Effect of sidewall on the flame extension characteristics beneath a ceiling induced by carriage fire in a channel

Laboratory tests were firstly conducted in a reduced scale channel to investigate the conditions for flame ejections when the carriage was at the centre of the channel. The ejected flames were recorded by two cameras and the temperature inside the enclosure and on the ceiling were measured. The lower critical heat release rate (HRR) which would result in intermittent flame ejection and upper critical HRR which would lead to continuous external flame were analysed with regards to their variations with the ventilation factor. Correlations for the longitudinal and transverse flame extension lengths and flame extension area beneath the ceiling were proposed. Subsequently further experimental investigations were conducted to study the effect of sidewall constraint on flame extension by changing the position of the carriage along the transverse direction to vary the distance between the sidewall and the carriage opening, which was also systematically varied. With the decrease of the sidewall-to-opening distance, the longitudinal flame extension length was found to increase whereas the transverse flame extension length decreased. The changes are most significant when sidewall-to-opening distance was relatively small. These trends are different from those observed in previous wall-attached fires or corner fires in channels, where the flame extension length beneath the ceiling firstly increased with the decrease of sidewall-source distance, and then decreased slightly when the fire source was attached to the wall. New correlations were proposed to account for the effect of sidewall-to-opening distance for longitudinal and transverse flame extension lengths under the ceiling. They captured well the measurements for all the present cases and some published cases not used in their derivation, demonstrating the potential for fire safety engineering applications.

Experimental investigation of human tenability and sprinkler protection in hospital room fires

SummaryThe effectiveness of sprinklers in protecting hospital patients in the room of fire origin was investigated by 14 experiments with a residential‐grade sprinkler system, and by two free‐burns. The fire load was UL 1626 corner fire. Tenability conditions were evaluated for the UL 1626 corner fire using gas temperature and species concentration measurements, and by calculating the fractional effective dose (FED) and fractional irritant concentration (FIC) with the comprehensive model of Purser and a more simplified method of ISO 13571. In the sprinklered tests, the average FED at 15 minutes was 0.8 ± 1 with 95% confidence, when using the Purser's method, and 0.2 ± 0.2 with ISO 13571. The difference was mainly caused by the assumption in the Purser's method that all NOx gases behave like NO2. Ignoring the NO contributions decreased the Purser's FED values very close to those of ISO 13571. In nonsprinklered tests, the FED and FIC values indicated definite incapacitation and possibly death 3 minutes after ignition. The sprinklers effectively increase the possibility of surviving, but the toxic effects may still be dangerous. In hospital and health care environments, many of the exposed persons may have lower‐than‐average tolerance.

Experimental Study on Burning Characteristics of the Large-Scale Transformer Oil Pool Fire with Different Extinguishing Methods

In this study, a 100 m2 steel tank was used to simulate transformer oil fires, with an aim of investigating the burning characteristics of a large-scale pool fire. To recover a real thermal state of transformer oil in operation, a heating system was employed to raise the initial fuel temperature. In total, three fire-extinguishing tests were performed using two delivery methods, i.e., a hand-held fire water branch (FWB) and fire water monitor (FWM) to understand their performance in fighting large-scale pool fires. The extinguishing activities using the FWB method were conducted by four trained firefighters, and the FWM was operated by a trained firefighter. Also, a sequence of bench-scale tests was conducted to investigate the impact of initial fuel temperature on the mass burning rate of transformer oil pool fires. This part is a supplement to the large-scale tests. The results demonstrated that the temperatures adjacent to the tank border were reduced as the vertical height increased. The growth rate of the flame height was enhanced in the development stage when the initial fuel temperature was pre-heated to a higher value. Meanwhile, it was found that the burning rate of transformer oil pool fire occurred a slight increase with the initial fuel temperature was grown according to the bench-scale data, while the impact of initial temperature was limited within the tested temperature range. In addition, it was shown that the FWB and FWM were both effective for fighting a large-scale transformer oil pool fire. However, their efficiency was influenced significantly by the concentration of the extinguishing agents and the application density of delivery. In contrast, the FWM might be a good choice when considering the safety of firefighters, because its delivery range is greater and extinguishing time is shorter as compared to the FWB. Here, it shall be noted that the FWM has also its flipsides. Sometimes, the application of a single FWM is not well to extinguish the corner fire or other fire types, in such cases, the FWM strategy should be to use two or more fire trucks in order to cover the whole accident pool.

Study of the importance of non-uniform mass density in numerical simulations of fire spread over MDF panels in a corner configuration

The distribution of mass density through the thickness of Medium Density Fiberboard (MDF) panels is known to be non-uniform. A few studies have previously investigated the influence of this non-uniform through-thickness density distribution on the thermal behavior of MDF panels in small-scale tests. This study assesses the significance of this material property on flame spread simulations in a medium-scale set-up, namely that of Single Burning Item (SBI) corner fire tests. Simulations are performed using FireFOAM 2.2.x, considering both uniform and non-uniform MDF material density profiles, using model-effective material properties determined from bench-scale pyrolysis tests conducted in a Fire Propagation Apparatus (FPA). The heat transfer from the gas phase is modeled by means of empirical expressions with adjusted parameters. The simulations are assessed against the results of several SBI experiments with MDF panels and a test with Calcium Silicate (CS) panels. When the non-uniform nature of the through-thickness density is taken into account, the fire growth prediction in terms of the total Heat Release Rate (HRR) is considerably different (20% higher peak HRR), mainly due to the characteristic high peak mass loss rate at the initiation of pyrolysis of MDF material, resulting from the higher mass density near the surface of the panels. Furthermore, total heat fluxes on the panels, lateral flame spread, surface pyrolysis and through-thickness char formation visibly depend on the non-uniform distribution of mass density, particularly in regions further away from the corner where the influence of thermal attack from the burner is less dominant. A new diagnostic is proposed for determining the pyrolysis front location and spread on the surface of the charring panels.

Safety Performance of Exterior Wall Insulation Material Based on Large Security Concept

In order to evaluate the fire spread characteristics of building insulation materials under corner fire, an experiment is carried out with small-scale fire spread test system. The change rule of the parameters such as the average height of the flame, the average temperature of the flame and the shape of the flame are analyzed. The variations of the fire spread characteristic parameters of the building insulation materials are investigated. The results show that the average temperature of Expanded Polystyrene (EPS) board, with different thickness, decrease - rise - decrease - increase. During the combustion process, the fire of 4cm thick plate spreads faster.

Experimental study of corner fires—Part I: Inert panel tests

Corner fires are known to spread more intensely in comparison with single wall fires. In view of the challenges associated with prediction of such fire behavior, the fire growth in a corner configuration of Medium Density Fiberboard (MDF) panels is investigated to provide a set of experimental data, performing Single Burning Item (SBI) tests. First, though, test results with inert calcium silicate panels are discussed for three values of HRR (10, 30 and 55 kW), allowing to address the main physics involved. The experimental data for 30 kW, the default SBI HRR, is used for detailed discussion of the observations. The SBI testing methodology, materials, and set-up are described. The results of total Heat Release Rates (HRR) and Smoke Production Rates (SPR), as well as the panel temperatures and total heat fluxes at several characteristic locations are analyzed. Moreover, the puffing frequency of the corner fire is characterized thanks to Video Fire Analysis (VFA) of the experimental footage. Additionally, flame heights are discussed, including the concept of mirroring. A new correlation for mean flame height is introduced, using the hypotenuse of the triangle as characteristic length for entrainment of air into the fire plume, and expressing that the flame height increases proportional to the square root of the fire heat release rate. The 30 kW propane burner of the standard SBI test is shown to feature a mean flame height of nearly 0.9 m and a puffing frequency of 2 ± 0.3 Hz, and an average total heat flux exceeding 44 kW/m2 near the burner early on in the test. The completeness of the dataset is expected to be useful for testing and development of CFD codes for corner fire scenarios.

Experimental study of corner fires—Part II: Flame spread over MDF panels

Having explained the characteristics of a corner fire in the configuration of Single Burning Item (SBI) test in Part I [1], the results of three flame spread experiments conducted with Medium Density Fiberboard (MDF) panels are discussed. The fire growth, in terms of flame heights and spread, is examined from two different angles visually and through Video Fire Analysis (VFA) with a flame detection algorithm. Total Heat Release Rates (HRR) and Smoke Production Rates (SPR), as well as total heat fluxes at several characteristic locations, are presented. Moreover, temperature evolutions are discussed for multiple locations and through the thickness of the panels. Also the backside temperatures, important as boundary condition for numerical simulations, are reported. The corner fire tests with MDF panels yield an average peak HRR of 151 kW and an average total heat flux exceeding 60 kW/m2 close to the burner, with average flame heights surpassing 1.5 m in about 60 s.

LES and Multi-Step Chemical Reaction in Compartment Fires

Numerical studies on two large-scale compartment buoyant fires were performed utilizing a fully coupled Large Eddy Simulation (LES) and strained laminar flamelet combustion model, extended from single-step to multistep chemical reaction. Two Subgrid-Scaled (SGS) turbulent models, Smagorinsky and WALE, were examined for center and corner fires. Compared with the experimental and existing numerical data, the WALE model with a multistep chemical reaction gave the best prediction for the upper hot layer and doorway gas temperatures. Specie concentrations including oxygen, carbon dioxide, and carbon monoxide were also found to compare well against the experimental measurements when the WALE model with a multistep chemical reaction was adopted.

Cone calorimeter and room corner fire testing of balsa wood core/phenolic composite skin sandwich panels

Polymer composite sandwich core panels are of interest for lightweight construction and portable shelter use. In this article, material selection and construction design were considered for an application which required a high level of fire safety performance. Phenolic + fiberglass skin composites with balsa wood core sandwich panels were constructed and first screened for fire performance with the cone calorimeter (ASTM E1354) at different heat fluxes. From these data, fire testing in the room corner test (ISO 9705) was conducted. The results indicated that these composites could only pass the room corner test if an aluminum skin was used to provide some additional fire protection to the underlying composite. Furthermore, it was found that cone calorimeter testing at very high heat flux (100 kW/m2) was not always indicative of fire performance in the room corner test. How the aluminum skin was mechanically attached to the panel as well as underlying composite construction played an important role in the full-scale fire test results.

Tree Island Response to Fire and Flooding in the Short-Hydroperiod Marl Prairie Grasslands of the Florida Everglades, USA

Within the marl prairie grasslands of the Florida Everglades, USA, the combined effects of fire and flooding usually lead to very significant changes in tree island structure and composition. Depending on fire severity and post-fire hydroperiod, these effects vary spatially and temporally throughout the landscape, creating a patchy post-fire mosaic of tree islands with different successional states. Through the use of the Normalized Difference Vegetation Index (NDVI) and three predictor variables (marsh water table elevation at the time of fire, post-fire hydroperiod, and tree island size), along with logistic regression analysis, we examined the probability of tree island burning and recovering following the Mustang Corner Fire (May to June 2008) in Everglades National Park. Our data show that hydrologic conditions during and after fire, which are under varying degrees of management control, can lead to tree island contraction or loss. More specifically, the elevation of the marsh water table at the time of the fire appears to be the most important parameter determining the severity of fire in marl prairie tree islands. Furthermore, in the post-fire recovery phase, both tree island size and hydroperiod during the first year after the fire played important roles in determining the probability of tree island recovery, contraction, or loss.

A two‐step method for predicting time to flashover in room corner test fires using cone calorimeter data

ABSTRACTA method to predict time to flashover in ISO 9705 room corner fire tests based on cone calorimeter data is proposed in this paper. The method involves classification of materials and estimation of time to flashover as two steps in sequence. In the first step, the investigated material is classified into discriminating material groups. In the second step, the time to flashover is calculated with a derived formula for the corresponding material group, which contains material density, time to ignition and heat release rate collected from small‐scale experiments. Compared with two existing models, the proposed method has improved the prediction precisions in both the time to flashover and classification of material categories for a wide range of materials. Copyright © 2012 John Wiley & Sons, Ltd.

Numerical simulation of the spread of smoke in an atrium under fire scenario

The Fire Dynamics Simulator code is used to investigate the smoke movement in an atrium under fire scenario. At first, by comparing with experimental data of the atrium fire under low and high heat release rates, reasonable model constants of C s and Pr t and appropriate grid system are determined for simulating smoke movement in the atrium, the simulation results are in good agreement with those experimental data. Then, the performance of different smoke exhaust methods in the atrium is studied. Smoke filling processes are investigated under different natural and enhanced smoke exhaust methods. Simulated results show that natural smoke exhaust method is preferred when the smoke exhaust vents are located at the ceiling of the atrium. On the other hand, when the smoke exhaust vents are located on the walls of the atrium, the higher positions of the smoke exhaust vents are preferred. In addition, the influence of the fire source locations on the smoke spreading process is presented in this paper, three kinds of fire source locations are studied, they are central fire, side wall fire and corner fire. Results indicate that the descending process of the smoke layer is the slowest when the fire source is at the corner of the atrium.

Behaviour of Double Glazing in Corner Fires

The results of fifteen experiments in which a double glazing assembly was exposed to enclosure fires of increasing severity are presented. The glazing assembly was exposed to the typical two zone or one zone fire enclosure environment with consistency and repeatability within each set of three experiments conducted at each severity level, evident from the enclosure gas temperature profiles. The results presented include; enclosure local gas temperatures, local exposed glass surface temperatures, local shaded glass temperatures, total incident fluxes, convective and radiative fluxes, incident flux distributions at time of first cracking and inner and outer pane behaviours. A simple lumped model approach is developed to predict the response of the glazing to thermal insult. Total loss of glazing integrity is related graphically to the time of first crack.

Evaluation of Intumescent Coatings for Shipboard Fire Protection

In response to several claims from Manufacturers that intumescent coatings could be used in place of fire insulation and provide equal protection to shipboard structures during a fire, U.S. Navy conducted an extensive investigation of several fire protective coatings for use aboard ship. These fire protective coatings included water and solvent based coatings, insulative coatings, and foams. The objective of this program was to identify passive fire protection (PFP) coatings for shipboard interior applications capable of meeting U.S. Navy (USN) fire resistance requirements (DRAFT MIL-PRF-XX 381) of 30 min rating with backside average temperature rise less than 139 C using UL-1709 fire curve (post flashover fire). This evaluation consisted of small scale fire, adhesion, and impact tests; intermediate scale room corner fire tests, and full scale fire tests conducted aboard ex-USS SHADWELL. The test results with steel substrate show that all candidate coatings failed to meet minimum U.S. Navy fire resistance criteria when used as stand-alone coatings. Furthermore, many coatings demonstrated poor adhesion, and fell off from the substrate during the fire test. These data have led the Navy to conclude that intumescent coatings tested in this study are not sufficient to protect shipboard spaces during a fire and are not equivalent when used alone as direct replacement for batt or blanket type fibrous fire insulation (mineral wool, StructoGard) installed aboard U.S. Navy ships. However, U.S. Navy smallscale fire tests have also demonstrated that some of the intumescent coatings, when applied over substrates such as Glass Reinforced Plastic (GRP), did reduce flame spread and smoke generation.

Corner Fire Growth in a Room With a Combustible Lining

The flammability of interior finish materials for many applications is regulated using the ISO 9705 large-scale room corner fire test. To aid designers in developing new materials, a fire growth model has been developed to predict material performance in the ISO 9705 test using small-scale test data from ASTM E1354 cone calorimeter. The fire growth model includes a flame spread model linked with a two zone compartment fire model, CFAST Version 3.1.2. At a user selected time interval, the flame spread model uses the gas temperature from CFAST to predict the heat release rate of the fire at that time interval, and then provides CFAST with a new heat release rate to predict conditions during the next time step. The flame spread model is an improved version of the flat wall flame spread model previously developed for the U.S. Navy. The model is capable of predicting flame spread in a variety of configurations including a flat wall, a corner with a ceiling, flat wall with a ceiling, unconfined ceiling, and parallel walls. The fire growth model was used to predict the heat release rate and smoke production rate measured in eight ISO 9705 room corner fire tests on composite materials used in marine applications.