Performance of a light timber‐framed compartment in natural fire subjected to lateral load

A common approach for designing buildings for lateral stability during and post‐fire in New Zealand is to ensure that a fire‐rated structure does not collapse when subjected to a nominal horizontal force. For external walls of residential buildings, which are required to resist a lateral load of 0.5 kPa, it is hypothesised that the adjacent unrated construction could provide sufficient support. A natural fire experiment has been conducted to evaluate the fire performance of a laterally loaded light timber‐framed compartment, with external dimensions of 4.33 m × 3.35 m and a stud height of 2.4 m constructed with a timber truss roof and plasterboard ceiling. During the experiment, the ceiling collapsed at 12 to 13 minutes, and the bottom chord of the roof truss failed in tension after 28 minutes which resulted in the fire‐rated wall losing its lateral stability at 28 minutes. The fire severity experienced in the compartment has been estimated to correspond to an equivalent time of 33‐minute exposure to a standard furnace time‐temperature. It is concluded that there is no need to provide nominal (additional) moment‐resisting fixity at the base of the fire‐rated wall when exposed to the standard fire for no more than 30 minutes.     

Experimental study of fire growth and ejected plume in a cross‐ventilation compartment under wind condition

In this study, a set of reduced‐scale experiments were conducted to study the influence of external wind on the fire growth and ejected plume in a compartment with two openings. The approaching wind velocity was set as 1.5 and 3.0 m/s, respectively. The temperatures in the fire compartment were also measured by thermocouple matrixes. The images of the projected flames from the opening and the fuel mass loss rate were recorded by digital video and electronic balance, respectively. It is observed that the wind with velocity of 1.5 m/s can reduce the combustion severity by decreasing the ventilation in the fire room and enhance the duration time of combustion. On the contrary, the wind with velocity of 3 m/s can promote the combustion severity by increasing the ventilation in the fire room and reduce the duration time of combustion. The theoretical analysis shows how the external wind that coupled with the thermal buoyance influence the ventilation of the compartment, and a critical velocity or a dimensional number are suggested to predict the ventilation of the fire room, which is believed to influence the compartment fire behavior greatly.     

Experimental study of tenability during a full‐scale motorcoach tire fire

Full‐scale fire experiments were conducted at the National Institute of Standards and Technology (NIST) to investigate tire fire interactions with the passenger compartment of a motorcoach. A single full‐scale experiment with a partially furnished interior was conducted to investigate tire fire growth within the passenger compartment and the onset of untenable conditions. A tire fire was initiated using a burner designed to imitate the frictional heating of hub and wheel metal caused by failed axle bearings, locked brakes, or dragged blown tires. Measurements of interior and exterior temperatures, interior heat flux, heat release rate, toxic gases, and visibility were performed. Standard and infrared videos and still photographs were also recorded. The results of this single experiment showed that after fire penetration into the passenger compartment, the tenability limits were reached within 8 minutes near the fire and within 11 minutes throughout the passenger compartment.     

Experimental and numerical simulation studies on diesel pool fire

Experimental studies are performed under different ventilation conditions to investigate the effect of ventilation on compartment fires. A compartment of size 4 m × 4 m × 4 m having a door of size 2 m × 1 m is used for experiments. The experiments are conducted with full door open and half door open conditions. Diesel, used as a fuel source, is placed in a pan of 40 cm diameter and 15 cm height, which is kept in the center of the compartment. During experiments a constant 12 cm height of the fuel is maintained above the pan bottom. The maximum heat release rate is found to be 100 kW and 115 kW in full door open and half door open experiments respectively. It is observed that the size of door opening affected the heat release rate, burning rate and thermal environment inside the compartment after the growth period of 800 s. The numerical simulation is also performed for full door open experiment using CFD code, Fire Dynamics Simulator (FDS, version 6.0.1) developed by NIST. Simulation is accomplished with the refinement of mesh size near the fire source; results from FDS closely match with the experimental results. Copyright © 2016 John Wiley & Sons, Ltd.     

Comparative energy analysis from fire resistance tests on combustible versus noncombustible slabs

Standard fire resistance tests have been used in the design of structural building elements for more than a century. Originally developed to provide comparative measures of the level of fire safety of noncombustible products and elements, the recent resurgence in engineered timber construction raises important questions regarding the suitability of standard fire resistance tests for combustible structural elements. Three standard fire resistance floor tests (5.9 m × 3.9 m in plan), one on a concrete slab and two on cross-laminated timber (CLT) slabs, were undertaken to explore some of the relevant issues. The fuel consumption rate within the furnace was recorded during these tests, and the energy supplied from this was determined. An external fuel supply (from natural gas supplied to the furnace) equating to approximately 3 MW was recorded throughout the concrete test, whereas this was about 1.25 MW throughout the CLT tests. The total heat release rate was calculated using carbon dioxide generation calorimetry; this yielded values of approximately 1.75 MW during the CLT tests (ie, an additional energy contribution of approximately 0.5 MW from the timber). This demonstrates that considerably more energy input (by about 1.25 MW) was needed to heat the system when the test sample was noncombustible. A further series of six large-scale compartment fire experiments (6 m × 4 m × 2.52 m) was undertaken to further explore comparative performance of combustible versus noncombustible construction when the external fuel load is kept constant and is governed by more realistic compartment fire dynamics. For a fuel-controlled case, the peak temperatures in the compartment with an unprotected CLT ceiling were approximately 200°C higher than in the compartments with a concrete ceiling, whereas for a ventilation-controlled case, the compartment with a CLT slab ceiling displayed a burning duration that increased by approximately 15 minutes. Potential implications for standard fire resistance testing of combustible specimens are discussed.     

Flame extension and the near field under the ceiling for travelling fires inside large compartments

Structures need to be designed to maintain their stability in the event of a fire. The travelling fire methodology (TFM) defines the thermal boundary condition for structural design of large compartments of fires that do not flashover, considering near field and far field regions. TFM assumes a near field temperature of 1200°C, where the flame is impinging on the ceiling without any extension and gives the temperature of the hot gases in the far field from Alpert correlations. This paper revisits the near field assumptions of the TFM and, for the first time, includes horizontal flame extension under the ceiling, which affects the heating exposure of the structural members thus their load-bearing capacity. It also formulates the thermal boundary condition in terms of heat flux rather than in terms of temperature as it is used in TFM, which allows for a more formal treatment of heat transfer. The Hasemi, Wakamatsu, and Lattimer models of heat flux from flame are investigated for the near field. The methodology is applied to an open-plan generic office compartment with a floor area of 960 m² and 3.60 m high with concrete and with protected and unprotected steel structural members. The near field length with flame extension (fTFM) is found to be between 1.5 and 6.5 times longer than without flame extension. The duration of the exposure to peak heat flux depends on the flame length, which is 53 min for fTFM compared with 17 min for TFM, in the case of a slow 5% floor area fire. The peak heat flux is from 112 to 236 kW/m² for the majority of fire sizes using the Wakamatsu model and from 80 to 120 kW/m² for the Hasemi and Lattimer models, compared with 215 to 228 kW/m² for TFM. The results show that for all cases, TFM results in higher structural temperatures compared with different fTFM models (600°C for concrete rebar and 800°C for protected steel beam), except for the Wakamatsu model that for small fires, leads to approximately 20% higher temperatures than TFM. These findings mitigate the uncertainty around the TFM near field model and confirm that it is conservative for calculation of the thermal load on structures. This study contributes to the creation of design tools for better structural fire engineering.     

Performance evaluation of bromofluoropropene in extinguishing liquid fuel spray fires

Liquid fuel spray fires emit high radiation heat fluxes, posing great threat to humans. The study of suitable agents and techniques for extinguishing this particular type of fire is of great importance. In this study, degradable 2‐bromo‐3,3,3‐trifluoropropene (BTP), a new clean fire extinguishing agent, was tested for its effectiveness in extinguishing three types of liquid fuel spray fires, namely diesel, gasoline, and ethanol. Bench‐scale experiments were conducted in a 6 × 5 × 3 m compartment with natural ventilation. The liquid fuels sprayed at varying pressures were ignited by a small open flame and then extinguished by a portable BTP extinguisher. Results showed that BTP of less than 60.0 g could extinguish all liquid fuel spray fires of 0.20 to 1.0 MPa in less than 2.0 s. The results also showed that when compared with fire sparked by gasoline and diesel, it is significantly easier to put out ethanol spray fires because of its high flame temperature and low flame power. Based on well‐established fire suppression theories and experimental results, the detailed mechanism of how BTP functions as an extinguishing agent in the suppression of liquid fuel spray fires will be discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

Development of water content sensor composed of small copper electrodes for use during fire resistance tests of concrete and cement mortar elements

The purpose of this study is to develop a sensor for measuring the water content in concrete and cement mortar elements usable in fire tests. Annealed copper wires were used as electrodes of the water content sensor. Each electrode is 20 mm in length and 0.8 mm in diameter. The separation distance between the electrodes is 2 mm. By measuring the electric resistance, water content can be monitored continuously. Mortar bar specimens were used to calibrate the sensor by measuring electric resistance as a function of water content at a constant temperature of 26°C. The temperature dependence of the electrical resistance was approximated by a functional relationship developed by Ichinose for a similar type of sensor. As a result, a calibration formula was derived for electrical resistances in the range of 1.51 to 2330 kΩ, temperatures in the range of 10 to 175°C, and volumetric water content in the range of 0.084 to 0.201 m³/m³. To verify the applicability, the sensors were embedded in a wall specimen heated by ISO 834 fire for 30 minutes. As a result, it was possible to measure the water contents continuously.     

Performance of a non‐load‐bearing steel stud gypsum board wall assembly: Experiments and modelling

A gypsum wall assembly was exposed to an intense real‐scale compartment fire. For the wall assembly, temperatures were measured at the exposed face, within the stud cavity, and at the unexposed face during the fire exposure. Total heat flux gauges were used to measure the temporal variation of the energy incident on the walls, and cameras, both visual and infrared, were used to image the unexposed face of the wall assembly during the fire exposure. The behaviour of the wall assembly under the fire load is discussed as are current model results for a simulation of the fire test. Copyright © 2006 John Wiley & Sons, Ltd.     

Effects of static pressure,pressurization, and depressurization on n‐heptane pool fires in an airplane cargo compartment

The cargo compartment of an airplane in flight is a complex environment with dynamic pressure (pressurization and depressurization), nonconservative oxygen, and unidirectional ventilation. In this study, n‐heptane pool fires were performed under static pressure, pressurization, and depressurization in a full‐scale airplane cargo compartment. The static pressure included 30 and 90 kPa, the pressurization was from 30 to 90 kPa at rates of 6, 12, 19, and 25 kPa/min, while the depressurization was from 90 to 30 kPa at rates of 6, 12, 17, and 20 kPa/min. The effects of pressure, oxygen concentration, and ventilation on pool fire characteristics including fuel mass loss rate (MLR), flame centerline temperature, and flame shape under each condition were concluded. The results show that the predominant factor of MLR was different in three conditions. The flame is divided into four regimes, in which the fuel vapor regime is used to emphasize the influence of fuel vapor on flame temperature above the fuel surface. The concept of average flame shape is put forward to reflect the flame occurrence probability. And its bottom, which named average flame root, presents the negative correlation with compartment pressure.     

Experimental determination of the effective thermal conductivity of Vacuum Insulation Panels at fire temperatures

In this study, the effective thermal conductivity of a commercial Vacuum Insulation Panel (VIP) at temperatures up to 900 °C is experimentally determined. An experimental setup, based on the Heat Flow Meter Apparatus (HFMA) method, is designed and realized. Two commercially available VIPs (each 20 mm thick) are joined together to form a specimen, which is subjected to fire conditions from one side, while the other side is at ambient conditions. The temperatures on both sides of the specimen and the heat flux on the unexposed side are recorded. The experimental data are coupled with a numerical model, which takes into account the one dimensional steady state heat transfer through the thickness of the specimen and the detailed heat transfer mechanisms for the effective thermal conductivity of the VIP. Gas, solid and radiation conduction mechanisms are considered and their parameters are defined through an optimization technique. The defined optimized values are found to lie between the respective values reported in the literature. The contribution of each heat transfer mechanism to the overall effective thermal conductivity is also discussed. The paper provides a generalized methodology for the estimation of the effective thermal conductivity of VIPs from ambient to fire temperatures. Copyright © 2016 John Wiley & Sons, Ltd.     

Experimental investigation on smoke spread characteristics and smoke layer height in tunnels

A series of experiments were carried out in a model‐scale tunnel with dimension of 6.0 m × 1.0 m × 0.7 m to investigate the smoke spread behaviors and the typical smoke layer height. Alcohol was employed as fuel, and the heat release rate was set to be 9.5, 18.4, 30.1, and 63.5 kW, respectively. The temperature profile in the tunnel was measured, and the buoyant flow stratification conditions were visualized by a laser sheet. The experiment results show that the N percentage rule would greatly influence by subjective factors. As the N (10, 20, 30) value increases, the smoke layer height also increases. The results calculated by the buoyancy frequency method were more accurate. Fan's prediction method (Fan WC, Wang QG, Jiang FH. Concise Guide of Fire Science. He Fei: University of Science and Technology of China Press; 1995.161 p.) does not accurately evaluate the smoke layer thickness in tunnel fire. An enhanced empirical formula for predicting the smoke layer thickness in the one‐dimensional horizontal spread stage was proposed. It is shown that the empirical formula could well predict the smoke layer thickness by comparing with the experimental data of previous studies.     

An experimental investigation on char pattern and depth at postflashover compartments using medium‐density fibreboard (MDF)

To determine the fire origins for postflashover compartments, the char pattern and depth are investigated. A set of experiments was carried out using large‐scale compartments made of medium‐density fibreboard. A liquefied petroleum gas burner was used as the ignition source to mimic the fire origin. The burner was set at different locations in different experiments. It is found that time to flashover, intermittent flame of gas burner and ventilation condition have effects on the char patterns. The ‘ventilation patterns’ are likely to confuse the fire investigators; therefore, it needs to be identified from the ‘flame patterns’. In general, the ventilation patterns at the floor would initiate directly from the compartment opening. CFD simulations is used to reflect the ventilation conditions during fires thus assisting the identification of ventilation patterns. For those cases with less distinguishable char patterns, the profiles of total leftover material thickness and char depth were used to determine the fire origin. The char layer and total thickness in the flame regions were found to be respectively deeper and thinner than the rest parts of the compartment. The ventilation condition also affects the char depth profile; therefore, it cannot be ignored from analysis. At the end, a strategy of fire origin determination is proposed. Copyright © 2014 John Wiley & Sons, Ltd.     

Experimental study on heat release rate measurement in tunnel fires

Knowledge about the heat release rate (HRR) is essential for studying tunnel fires. The standard method in ISO 9705 is widely applied to calculate the HRR of combustion by measuring the consumption of oxygen in a fire. However, the studies of HRR measurement in full‐scale tunnel fires are rare because of the complication and costs of large experiments. This paper presents a system based on the principle of oxygen consumption calorimetry for the measurement of HRR and total heat release (THR) of full‐scale fires in tunnels. A total of 22 fire experiments are performed in a large‐scale ventilated testing metro tunnel with dimension of 100.0 m × 5.5 m × 5.5 m to validate the reliability and effectiveness of this system. Firstly, four oil spray fire tests are conducted with nozzle flow of 106 L/h at (1 ± 0.1) MW HRR to calibrate the instrumentation. Then, 18 full‐scale fire tests using square diesel pools at five sizes (0.5, 1.0, 2.5, and 5.0 m²) and wood cribs as fire sources are carried out for the measurement of HRR and THR. Results provided by the comparison between the measured HRR and THR values of the fire tests and the theoretically calculated ones show that our system works effectively in the HRR measurement of full‐scale fires in tunnels.     

Temperature of post‐flashover compartment fires—Calculations and validation

This paper describes and validates by comparisons with tests a one‐zone model for computing temperature of fully developed compartment fires. Like other similar models, the model is based on an analysis of the energy and mass balance assuming combustion being limited by the availability of oxygen, ie, a ventilation‐controlled compartment fire. However, the mathematical solution techniques in this model have been altered. To this end, a maximum fire temperature has been defined depending on combustion efficiency and opening heights only. This temperature together with well‐defined fire compartment parameters was then used as a fictitious thermal boundary condition of the surrounding structure. The temperature of that structure could then be calculated with various numerical and analytical methods as a matter of choice, and the fire temperature could be identified as a weighted average between the maximum fire temperature and the calculated surface temperature of the surrounding structure as a function of time. It is demonstrated that the model can be used to predict fire temperatures in compartments with boundaries of semi‐infinitely thick structures as well as with boundaries of insulated and noninsulated steel sheets where the entire heat capacity of the surrounding structure is assumed to be concentrated to the steel core. With these assumptions, fire temperatures could be calculated with spreadsheet calculation methods. For more advanced problems, a general finite element solid temperature calculation code was used to calculate the temperature in the boundary structure. With this code, it is possible to analyze surrounding structures of various kinds, for example, structures comprising several materials with properties varying with temperature as well as voids. The validation experiments were accurately defined and surveyed. In all the tests, a propane diffusion burner was used as the only fire source. Temperatures were measured with thermocouples and plate thermometers at several positions.     

Use of zone models on simulating compartmental fires with forced ventilation

Performance of three fire zone models BR12, CCFM.VENTS and CFAST in simulating forced ventilation fires with low heat release and high ventilation rates were studied experimentally. A fire chamber of length 4.0 m, width 3.0 m height 2.8 m with adjustable ventilation rates was used. Burning tests were carried out with wood cribs and methanol to study the preflashover stage of a compartmental fire and the effect of ventilation. The mass loss rate of fuel, temperature distribution of the compartment and the air intake rate were measured. The heat release rates of the fuel were calculated from the measured mass loss rate. The smoke temperature was used as the validation parameter. A scoring system is proposed to compare the results predicted by the three models. An empirical expression for calculating the smoke temperature is assessed. Lastly, the Computational Fluid Dynamics technique is also used for comparing the simulated fire environment.     

Thermal effect on surrounding combustibles in minivan passenger car fires

In the fire safety design of parking lots and buildings, estimating the possibility of fire spreading to surrounding combustibles, such as neighboring buildings and cars, is essential. The ignition possibility to surrounding combustibles can be predicted from the heat flux from a burning car to the combustibles. In this study, we conducted 2 full‐scale car fire experiments using minivan passenger cars and measured the heat fluxes to their surroundings. The cars were ignited at the rear bumper with 80 g of alcohol gel fuel. The windows were closed. Heat flux gauges were placed around the car to measure the heat flux in various directions. Cedar boards were placed next to the gauges, and burn damage to the boards was observed. When the windows shattered in succession, combustion in the passenger compartment became larger. At a distance of 50 cm from the burning car, the heat flux was greater than 40 kW/m², and most of the cedar boards were completely burned. At a distance of 1 m, the heat flux was 10 to 20 kW/m², and some of the cedar boards were burned. We devised a method for modeling the shape and temperature of flames in the burning cars. Furthermore, we propose a method for calculating heat fluxes in the lateral direction of the burning minivan passenger car, and we compared the calculated and measured heat fluxes as a means of verifying the proposed method. The shape of flame in the burning car was approximated as a rectangular prism to calculate the heat flux. The calculation results were in good agreement with the experimental results. The proposed method is expected to be useful for fire safety engineering.     

Evaluation of standard and real fire exposures on thermal response of rail car floor assembly

This work developed a computational methodology to evaluate and compare standard fire exposures such as those outlined in ASTM E119 with real fire exposures and determine the difference in the temperature rise of a rail car floor assembly. The real fire exposures simulated in this work were identified in a review of incidents and consisted of a constantly-fed diesel fuel spill, a localized trash fire, and a gasoline spill simulated from a collision of the railcar with an automobile. These realistic fire exposures were applied to a variety of exemplar rail cars representative of single-level and bi-level passenger cars. These floor assembly models exposed to realistic fires were simulated in Fire Dynamics Simulator (FDS). The thermal exposure at the underside of railcar provided by FDS was coupled with a thermal model in ABAQUS, which provided the evolution of temperature in different components of the floor assembly. The standard scenarios were simulated for 2 hours instead of the typical 30 minutes to identify the appropriate exposure duration in ASTM E119, which can better represent a real fire scenario. The average and maximum temperatures predicted at the unexposed surface for both scenarios were compared with the threshold values given in NFPA 130.     

Development of a numerical approach based on coupled CFD/FEM analysis for virtual fire resistance tests—Part A: Thermal analysis of the gas phase combustion and different test specimens

In the present two‐parted study, a numerical approach is shown to consider fire resistance tests in virtual space, including the combustion, thermal analysis of the test specimen, and the deformation process. This part is dealing with the combustion process and thermal analysis of different building materials tested in a fire resistance furnace. Instead of using coupled computational fluid dynamics (CFD)/finite element method simulation for the combustion and thermal heat conduction in the solid, which is commonly used in literature, the present approach considers these transport phenomena in one CFD simulation. This method enables a two‐way coupling between the gas phase and the solid material, where chemical reactions and the release of volatile components into the gas phase can occur (eg, release of water vapour from gypsum). To validate the numerical model, a fire resistance test of a steel door, which is a multilayer construction, and a wall made of gypsum blocks were experimentally and numerically investigated. Due to the chemical reactions inside the gypsum, water vapour is released to the gas phase reducing the flue gas temperature about 80 K. This effect was taken into account using a two‐way coupling in the CFD model, which predicted temperatures in close accordance to the measurement.