Wall Fire Research Articles

Review on the Fire Safety of Exterior Wall Claddings in High-rise Buildings in China

In recent years, several major fires occurred in high-rise buildings involving rapid fire spread upon the exterior walls and facades, and caused severe damage and loss. The extensive use of combustible insulation materials without proper fire protections and barriers were believed to contribute to the uncontrollable fire spread in the high-rise buildings. This paper reviews the current code and standard environment regulating the fire safety of exterior wall claddings in China. Three high-rise building fire cases involving rapid exterior wall fire spread are also discussed by analyzing the fire causes, propagation mechanisms and problems. The recent research progress and regulation development on the fire protection of exterior wall claddings are also presented. It was suggested that limiting the combustibility of insulation materials used in the exterior wall cladding associated with building heights, as well as proper fire protections and barriers would provide acceptable fire safety performance of exterior wall claddings in high-rise buildings.© 2013 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of the Asia-Oceania Association for Fire Science and Technology.

Using cone calorimeter data for the prediction of upward flame spread rate

In a cone calorimeter, the specimen receives uniformly distributed irradiance from the cone heater. Producing a heating environment simulating the heating intensity in real fires, this apparatus consequently is capable of providing information of materials relevant to their fire performance. Several previous upward flame spread models utilized the data as input with an assumption of uniformly distributed heat fluxes. Satisfactory flame spread rates were predicted. However, the heat flux in the heating region in upward flame spread is not uniform. This study introduces an alternative protocol of the cone calorimeter and a sample holder by which the following differences were made, including specimen turned 42° before ignition, lower ignition source before ignition, heater removed after ignition, and specimen moved back to vertical orientation after ignition. The heating environment is more consistent to real wall fire conditions. In addition, the prediction of flame spread rate using the alternative test protocol is closer to the measured flame spread rate than standard test methods.

Experimental investigation on influence of different transverse fire locations on maximum smoke temperature under the tunnel ceiling

In former studies, fires were always assumed to occur at the longitudinal centerline of tunnels. In fact, fires will occur at any locations in tunnels, with different distances to the sidewall. A set of model scale experiments were carried out, to investigate the influence of different transverse fire locations on maximum smoke temperature under the tunnel ceiling. Results show that the restriction effect of the sidewalls of tunnels cause the maximum smoke temperature rise under the ceiling to increase compared with the unconfined space, even fires occurs at the longitudinal centerline. The maximum smoke temperature rises above the fire keep almost unchanged with the fire moving closer to the sidewall at the beginning and then increase significantly after the distance between the fire and the sidewall decreases to a certain value. For small pools of wall fire, the “mirror” effect is reasonable, and for large pools, will bring a relatively large error without considering the influence of the equivalent diameter of a wall fire, resulting in underestimating the mass flow rate of fire plume and then overestimating the smoke temperature. Under all fires, the maximum smoke temperature rise under the ceiling decreases exponentially as the longitudinal distance from fire increases. Correlations for related parameters are proposed.

Under-Ventilated Wall Fire Behaviour during the Post- Flashover Period

This work is aimed the evolution of the behaviour of a strongly contained wall fire in an enclosure during the postflashover period. It has characterised the fire intensity decay up to extinction of a wall fire by lack of oxygen and the effects of a sudden door opening on the formation of an air gravity wave capable to bring the backdraft phenomenon. To better understand these two sequential fire scenarios, the study was divided into two complementary parts performed in the same laboratory scale experimental setup. The first part consists to stabilise a steady wall fire at the rear of the compartment and to follow its evolution when a door closes the aperture leaving only a thin slot opened to limit the air entering. It has been observed the formation of a ghosting flame moving through the compartment before dying at the aperture. By supposing the continuation of the fuel solid pyrolysis after flame extinction due to the radiation of the hot environment, fuel vapours continue to fill the compartment. The second part will study the effects of a reopening of the door. It has been observed and characterised the formation and the propagation of a gravity wave through the enclosure. This is representative of the development of the first stage of the backdraft. Tests are performed to measure the aerodynamic properties of the flow behaviour.

A concept of capillary active, dynamic insulation integrated with heating, cooling and ventilation, air conditioning system

When a historic facade needs to be preserved or when the seismic considerations favor use of a concrete wall system and fire considerations limit exterior thermal insulation, one needs to use interior thermal insulation systems. Interior thermal insulation systems are less effective than the exterior systems and will not reduce the effect of thermal bridges. Yet they may be successfully used and, in many instances, are recommended as a complement to the exterior insulation. This paper presents one of these cases. It is focused on the most successful applications of capillary active, dynamic interior thermal insulation. This happens when such insulation is integrated with heating, cooling and ventilation, air conditioning (HVAC) system. Starting with a pioneering work of the Technical University in Dresden in development of capillary active interior insulations, we propose a next generation, namely, a bio-fiber thermal insulation. When completing the review, this paper proposes a concept of a joint research project to be undertaken by partners from the US (where improvement of indoor climate in exposed coastal areas is needed), China (indoor climate in non-air conditioned concrete buildings is an issue), and Germany (where the bio-fiber technology has been developed).

Safety and Efficacy of Pulmonary Vein Antral Isolation in Patients With Obstructive Sleep Apnea

Background— Obstructive sleep apnea (OSA) may be associated with pulmonary vein antrum isolation (PVAI) failure. The aim of the present study was to investigate if treatment with continuous positive airway pressure (CPAP) improved PVAI success rates. Methods and Results— From January 2004 to December 2007, 3000 consecutive patients underwent PVAI. Patients were screened for OSA and CPAP use. Six hundred forty (21.3%) patients had OSA. Patients with OSA had more procedural failures ( P =0.024) and hematomas ( P <0.001). Eight percent of the non-OSA paroxysmal atrial fibrillation patients had nonpulmonary vein antrum triggers (non-PV triggers) and posterior wall firing versus 20% of the OSA group ( P <0.001). Nineteen percent of the non-OSA nonparoxysmal atrial fibrillation population had non-PV triggers versus 31% in the OSA group ( P =0.001). At the end of the follow-up period (32±14 months), 79% of the non-CPAP and 68% of the CPAP group were free of atrial fibrillation ( P =0.003). Not using CPAP in addition to having non-PV triggers strongly predicted procedural failure (hazard ratio, 8.81; P <0.001). Conclusions— OSA was an independent predictor for PVAI failure. Treatment with CPAP improved PVAI success rates. Patients not treated with CPAP in addition to having higher prevalence of non-PV triggers were 8 times more likely to fail the procedure.

Performance of Different Temperature Sensors in Standard Fire Resistance Test Furnaces

Defining a methodology for measuring temperature in fire resistance furnaces is a challenge. This paper presents and discusses the performance of six different types of temperature sensors in wall and floor fire resistance furnaces namely: the ASTM E119 shielded thermocouples, ISO 834 plate thermometers, directional flame thermometers, bare-bead thermocouples, Inconel grounded and ungrounded sheathed thermocouples. The Inconel grounded and ungrounded sheathed thermocouples provided comparable results to those of the bear-bead thermocouples and are most suitable when a fast response time is desirable. Because of the fast response time and good durability, grounded and ungrounded junction thermocouples are well-suited for use in controlling the temperature in fire resistance standard test furnaces. The predicted and measured incident heat flux in furnaces controlled by either the bare-bead or grounded and ungrounded sheathed thermocouples are in good agreement.

Experimental study on melting and flowing behavior of thermoplastics combustion based on a new setup with a T-shape trough

The objective of this work is to quantitatively study the burning characteristics of thermoplastics. A new experimental setup with a T-shape trough is designed. Based on this setup, the loop mechanism between the wall fire and pool fires induced by the melting and dripping of thermoplastic can be well simulated and studied. Additionally, the flowing characteristics of pool fires can also be quantitatively analyzed. Experiments are conducted for PP and PE sheets with different thicknesses. The maximum distances of the induced flowing pool flame in the T-shape trough are recorded and analyzed. The typical fire parameters, such as heat release rates (HRRs), CO concentrations are also monitored. The results show that the softening and clinging of the thermoplastic sheets plays a considerable role for their vertical wall burning. It is illustrated that the clinging of burning thermoplastic sheet may be mainly related with the softening temperatures and the ignition temperatures of the thermoplastics, as well as their viscosity coefficients. Through comparing the maximum distances of flowing flame of induced pool fires in the T-shape trough for thermoplastic sheets with different thicknesses, it is indicated that the pool fires induced by PE materials are easier to flow away than that of PP materials. Therefore, PE materials may be more dangerous for their faster pool fire spread on the floor. These experimental results preliminarily illustrate that this new experimental setup is helpful for quantitatively studying the special burning feature of thermoplastics although further modifications is needed for this setup in the future.

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.

Fire dynamics simulations of buoyant diffusion flames stabilized on a slot burner

In recent years fire dynamics simulator (FDS) [1,2], a CFD model for buoyancy-driven flames developed at the National Institute of Standards and Technology (NIST), has been used in simulations of numerous fire scenarios and buoyancy-driven flows. FDS is based on a set of equations describing the behavior of thermally driven buoyant flows proposed by Rehm and Baum [3]. Validation of the various submodels in FDS has been performed using small-scale round plumes [4], small and large round pool fires [4–7], rectangular pool fires [8,9], and vertical wall fires [8]. Based on the confidence gained in these validation studies and also by a rapidly growing practical applications base, FDS has been applied to practical considerations of room airflows [10], fire and smoke behavior in large building fires including the World Trade Center fires [11], compartment fires [12,13], oil pool fire in a containment test facility [14], and tunnel fires [15]. To the best of our knowledge, FDS has not been used to simulate linear buoyant fire sources like line fires and slot burner flames. Fires above twodimensional fuel sources are important in some practical fires scenarios such as forest fires and wall fires. For round plumes and flames, 3D simulations were found to be necessary for capturing the mixing behavior, which was grossly underpredicted by the 2D simulations [4]. Given the two-dimensional source geometry, whether two-dimensional mixing considerations are adequate is an interesting question.

Incident heat flux measurements in floor and wall furnaces of different sizes

This paper presents the results of incident heat flux experiments in standard (full-scale) and non-standard (intermediate-scale) wall and floor fire resistance furnaces. These experiments were conducted to investigate the effects of full-scale furnace depth (wall and floor furnaces), furnace size (full- and intermediate-scale furnaces) and intermediate-scale furnace orientation (vertical and horizontal positions) on the incident heat flux in fire resistance test furnaces. Copyright © 2005 Crown in the right of Canada. Published by John Wiley & Sons, Ltd.

On The Numerical Modeling Of Buoyancy-dominated Turbulent Fires By Using Large Eddy Simulation

This study concerns the modeling of three characteristic buoyancy-dominated turbulent diffusion flames such as pool-like, vertical and interaction between pool-like and vertical wall fires. Controlling mechanisms of three dimensional flow, combustion, soot production and radiation are coupled with a Large Eddy Simulation (LES). An EddyBreak-Up concept which accounts for the interaction between combustion and turbulence, is implemented in LES. The numerical models have been validated using experimental data from three turbulent diffusion flames. The predicted mean temperature, velocity and total heat feedback from the high temperature gases in the flame to the wall surface follow closely to the experimental data. Moreover, it is found that LES successfully predicted the important features of highly oscillating buoyancy-controlled pool-like fire (recirculation zone, narrowing and broadening of the flame). While, the standard Smagorinsky sub-grid scale model should be improved to predict the variation of the fluctuating velocity and temperature for the vertical wall fires.

ON THE NUMERICAL MODELING OF BUOYANCY-DOMINATED TURBULENT DIFFUSION FLAMES BY USING LARGE-EDDY SIMULATION AND k–ϵ TURBULENCE MODEL

This work concerns the modeling of buoyancy-dominated turbulent diffusion flames. In these flames, ambient air is entrained just above the burning surface into the reactive zone at large mass flow rates. To describe the buoyancy-induced flow, both large-eddy simulation (LES) and the k–ϵ turbulence model are used. The two models, including direct effects of buoyancy, have been validated using experimental data from three (pool-like, vertical, and interaction between pool-like and vertical wall fires) turbulent diffusion flames. It is found that LES successfully predicted the variation of both the mean and fluctuating velocity/temperature. Important features of highly oscillating buoyancy-induced flows (recirculation zone, narrowing and broadening of the flame) have been correctly reproduced by LES, whereas the standard Smagorinsky model should be improved to model turbulent mixing near the vertical burning wall. It is found that interaction between pool-like and vertical wall fires induces an entraining ambient air at larger mass flow rates compared to a pool-like fire or a single vertical burning wall.

Simultaneous optimization of linear firing shrinkage and water absorption of triaxial ceramic bodies using experiments design

In the development and manufacture stages of floor and wall ceramic tiles, firing shrinkage and water absorption are basically determined by the combination of raw materials and frequently used as quality control parameters. This configures the ideal scenario to apply the techniques of experiments design, often used in various other areas, to model those properties of such ceramics bodies. In the present study, 10 formulations of three different raw materials, namely a clay mixture, potash feldspar and quartz (triaxial compositions) were selected and used in the experiments design. Those formulations were processed under conditions similar to those used in the ceramics industry: powder preparation (wet grinding, drying, granulation and humidification), green body preparation (pressing and drying), firing (at 1170 °C) and characterization. With the experimental results, regression models were calculated, relating linear firing shrinkage and water absorption with composition. After statistical analysis and verification experiments, the significance and validity of the models were confirmed. The regression models can then be used to select the best combination of those three raw materials to produce a ceramic body with specified properties.

Aerodynamic Characterization Of A Compartment Fire As A Function Of Its Behavior

An experimental setup is realized to study the behavior of a confined fire when the fire source is placed in combustion products trapped by a soffit, or located at the lower part of the rear wall of an enclosure. As a function of the source position, the flame, the heat release rate and the ventilation factor are drastically modified. In the first configuration, different flame behaviors are identified corresponding to jet flames, horizontal flames on the whole room surface at the level of the soffit, or extinction. In the second one, the wall fire interacts with the burnt gases close to the ceiling. The outwards hot smoke layer at the aperture always occupies one third of the open height. Based on the analysis of Babrauskas et al [1], a two zones hydrostatic model is developed, and a relation between the input air mass flow rate entering the room, the ventilation factor Fv and the heat release rate Q is obtained : mair = f(F 2 / 3Q1/ 3 ). For a fixed heat release rate, mair only depends on the ventilation factor but stays independent of the flame structure in the room. This relation corroborates the experimental data and the theoretical analysis to results available in the literature and can be used to model for the structure of such flames.

Flame height correlation and upward flame spread modelling

AbstractPrevious work has demonstrated that flame height is one of the two most important parameters determining the rate of vertical flame spread on a wall. Flame spread models rely on empirical flame height correlations of the form Xf=KQ̇′n, but there have been no carefully controlled experiments designed to establish the validity of such correlations and there are no data for values of Q̇′< c.25 kW/m. Two new sets of data are presented here, one based on experiments with 6 mm thick PMMA slabs (heights 25–250 mm, width 50–150 mm) as the fire source, measuring Q̇′ and Xf simultaneously. This set relates to the early stages of a wall fire when Q̇′< 30 kW/m. The other set of data was obtained with a vertical gas‐fired panel which consisted of an array of 14 independent burners arranged to allow the aspect ratio of the burning surface to be varied. The data confirm that the flame height correlates with Q̇′, but reveal (inter alia) that there are two regions, for values of Q̇′ greater than and less than c. 20 kW/m.An existing upward flame spread model was modified to allow these two correlations to be incorporated to predict the development of a small fire on a vertical surface for these two regions, which would provide more realistic modelling information. Copyright © 2002 John Wiley & Sons, Ltd.

실내공간에서 화재 발생위치에 따른 연기거동에 대한 실험연구

In order to investigate the smoke movement in three dimensional room fires, the center fire, wall fire and corner fire plume in different sized fires were studied experimentally by rectangular pool fire using methanol as a fuel. As the fire size became larger for the center fires placed at the center of the floor, the air flow rate entrained through the opening, average hot layer temperature, flame angle deflected backwards and mean flame height was observed to increase. On the other hand, as the fire size became smaller, the neutral plane height in the door and time reached steady-state was observed to decrease. The average hot layer temperature, mean flame height and doorway neutral plane height obtained from comer fire were higher than those produced by wall fires and center fires. The simple model for describing the effect of walls on the mean flame height was presented. It was shown that the model provides a good description of the present measurements, when used with the assumption by Hansell(1993), that the increase of the average flame height is equal to the ratio of the open to the total perimeters of the trays. Also the two models for predicting the effects of walls on the mean flame height were presented. These models overestimated the measured values of the mean flame height above fuel trays close to a wall and in a corner by approximately 19-26%, respectively.

Wall fire behavior in an under-ventilated room

An experimental setup has been designed and built to study, at a laboratory scale, the behavior of a wall fire in a semi-confined compartment both in naturally ventilated and vitiated (combustion products) atmospheres. A diffusion flame is stabilized along a vertical porous flat burner located at the rear of an enclosure. The combustion is supplied by injection of propane through the vertical burner surface. Air enters into the compartment by natural convection through a door, topped by a soffit, opposite the burner. After reaching a thermal steady state, the temperature field in the compartment is characterized. Then, the door is closed leaving only a horizontal free slot (0.06 m height) between the top of the door and the bottom of the soffit. The flame behavior completely changes, the intensity of the spontaneous flame emission decreases drastically and a weakly blue vertical flame leaves the burner surface and moves, at low velocity, through the chamber, up to the open slot. Visualizations of the flame and measurements of the temperature and main stable chemical species fields are performed in order to characterize the behavior of a flame referred as a ghosting flame. This flame displacement mode has been already observed in full-scale fires by Audouin (Fifth International Symposium on Fire Safety Science, 1997, Melbourne, p. 1261–1272). After the initial “flame propagation”, combustion can be stabilized at the room aperture that participates to the development of the fire outside the compartment. This work contributes to a better understanding of this phenomenon in order to prevent such a fire.

Large-eddy-simulation of buoyancy-driven fire propagation behind a pyrolysis zone along a vertical wall

Large-eddy-simulation (LES) is performed to investigate the transport characteristics and structure of large-scale, turbulent fires on vertical surfaces under natural convection conditions. The combustion process in buoyancy-driven wall fire plumes is assumed to be diffusion controlled, permitting a mixture-fraction-based modeling approach. The three-dimensional, time-dependent Navier–Stokes equations and mixture fraction are solved with sufficient temporal and spatial resolution. The large-scale eddies are simulated directly and subgrid-scale motion is represented by Smagorinsky model. The computed, time-averaged flame height, velocity and temperature profiles are compared with experimental data, and a relatively good agreement is attained. For a given heat release, the air entrainment rate over a vertical wall fire decreases to 1/4 one of a pool fire plume. The predicted entrainment rate closely follows an adjusted entrainment rate correlation from a pool fire plume. It is observed that the flame height behind a pyrolysis region over a vertical wall is more important than that for turbulent jet fire, and also a function of the heat release raised to the nth power with n=2/5.

Simple Estimation Model on Ceiling Temperature and Velocity of Fire Induced Flow under Ceiling.

A new simple estimation model was described on excess temperature and velocity of ceiling jet under the flat, horizontal and sloped ceiling of an unconfined room from a t²-fire. This simple model was composed of ceiling height (H), distance along ceiling from the impinging point (r), and heat release rate (Q) which was given as a t²-fire. This model was verified by the experimental data which were conducted using at² model fire with ceiling heights of 2m, 2.1m, 4m, 8m, 15m and 20m. Flat and sloped ceiling with smooth surface was also used as a model ceiling, and those experimental data were used to verify the model. This model can deal with the cases of a corner fire and a wall fire for its early stages, and also verified by the data of corner and wall fires. The model for excess temperature and velocity with suitable RTI gave the estimation on the operation time of heat detector and sprinkler.