Predicting the structural response of a compartment fire using full-field heat transfer measurements

Inverse heat transfer analysis (IHT) was used to measure the full-field heat fluxes on a small scale (0.9 m×0.9 m×0.9 m) stainless steel SS304 compartment exposed to a 100 kW diffusion flame. The measured heat fluxes were then used in a thermo-mechanical finite element model in Abaqus to predict the response of an aluminum 6061-T6 compartment to the same exposure. Coupled measurements of deflection and temperature using Thermographic Digital Image Correlation (TDIC) were obtained of an aluminum compartment tested until collapse. Two convective heat transfer coefficients, h =35 W/m²-K and h =10 W/m²-K were examined for the thermal model using the experimentally measured heat fluxes. Predictions of the thermal and structural response of the same compartment were generated by coupling Fire Dynamics Simulator (FDS) and Abaqus using the two values for h, h =35 W/m²-K and h from convection correlations. Predictions of deflection and temperature using heat fluxes from IHT and FDS with h=35 W/m²-K agreed with experimental measurements along the back wall. The temperature predictions from the IHT-Abaqus model were independent of h, whereas the temperature predictions from the FDS-Abaqus model were dependent on h.     

Description of small and large-scale cross laminated timber fire tests

A large-scale fire test was conducted on a compartment constructed from cross laminated timber (CLT). The internal faces of the compartment were lined with non-combustible board, with the exception of one wall and the ceiling where the CLT was exposed directly to the fire inside the compartment. Extinction of the fire occurred without intervention. During the fire test, measurements were made of incident radiant heat flux, gas phase temperature, and in-depth temperature in the CLT. In addition, gas flow velocities and gas phase temperatures at the opening were measured, as well as incident heat fluxes at the facade due to flames and the plume leaving the opening. The fuel load was chosen to be sufficient to attain flashover, to achieve steady-state burning conditions of the exposed CLT, but to minimize the probability of uncertain behaviors induced by the specific characteristics of the CLT. Ventilation conditions were chosen to approximate maximum temperatures within a compartment. Wood cribs were used as fuel and, following decay of the cribs, self-extinction of the exposed CLT rapidly occurred. In parallel with the large-scale test, a small scale study focusing on CLT self-extinction was conducted. This study was used to establish: the range of incident heat fluxes for which self-extinction of the CLT can occur; the duration of exposure after which steady-state burning occurred; and the duration of exposure at which debonding of the CLT could occur. The large-scale test is described, and the results from both the small and large-scale tests are compared. It is found that self-extinction occurred in the large-scale compartment within the range of critical heat fluxes obtained from the small scale tests.     

Smoke production,radiation heat transfer and fire growth in a liquid-fuelled compartment fire

A detailed investigation is described of the interaction between fire development, smoke production and radiative exchange in a half-scale ASTM compartment in which the source is a heptane pool fire. Measurements of heat flux, fuel mass loss rate, ventilation flow rates, temperature and soot volume fraction are reported for the compartment for varying door widths. Data from the compartment are compared with open pool fire measurements using the same equipment. The confined geometry is shown to exert a strong influence on pool fire development and suggests that considerable caution is needed in employing open pool fire data as boundary conditions for CFD simulation. Numerical simulations based on the direct calculation of radiative exchange between the liquid fuel surface, the smoke-laden environment and bounding walls do reproduce the behaviour observed when combustion, soot production and radiation are modelled in detail and finely resolved spatially.     

Experimental and computational studies of compartment fire behavior training scenarios

Because of the substantial risk to fire fighter safety in fighting compartment fires, the New South Wales Fire Brigade (NSWFB) in Australia has implemented Compartment Fire Behavior Training (CFBT). The CFBT scheme equips fire fighters with the knowledge and experience required to effectively, efficiently and safely deal with this type of fire, via the use of a demonstration cell (in this case a shipping container) within which the fire fighter can experience, observe and deal with real flashover situations. A crib fire is used as the fuel source with the addition of several particle boards lining the closed end of the demonstration cell. In the current study, the CFBT demonstration cell has been studied both experimentally and computationally while the cell undergoes a variety of different conditions including fuel load and ventilation changes. This data will provide useful additional information in further assisting NSWFB fire fighters in their understanding of fire growth and smoke movement and by allowing them to extrapolate their experiences of handling other possible fires they may face in compartments.     

Auto-extinction of engineered timber: Application to compartment fires with exposed timber surfaces

A series of compartment fire tests with multiple exposed timber surfaces have been undertaken to explore the effect of exposed timber on the fire dynamics and the potential for auto-extinction. A test with exposed wall and ceiling achieved auto-extinction after approximately 21 min. Firepoint theory is applied using temperature data at the charline, is shown to predict a mass loss rate dropping below the critical value at 20–21 min, and thus is successful in predicting auto-extinction. Additional uncertainties caused by delamination are explored, and recommendations for the use of auto-extinction in design are given.     

机械排烟与水喷淋对仓室火灾控制效果的实验研究

研究了大空间建筑中仓室消防措施的有效性，按照规范设计的工况设计了全尺寸实验，研究了机械排烟和水喷淋对烟气层温度及高度的控制效果，并将结果与消防措施实效的情况下相比较，说明按照规范设计的消防措施能够有效的控制火灾，在规范设计基础上增大风机排烟量和水喷淋压力，取得了更加良好的效果，达到了灭火的目的。     

The simulation of fire sprinklers thermal response in presence of water droplets

When a fire occurs, the sprinkler closest to the location of the fire typically activates first and releases water droplets into the rising plume of hot gases. Part of these droplets is entrained by the plume and may impact on adjacent sprinklers providing evaporative cooling and thus delaying their activation. The model of the thermal response of sprinklers in these conditions suggests the introduction of the concept of equivalent cylindrical links: a solid metallic cylinder is said to be equivalent to a given fire sprinkler link if it reaches the activation temperature of the sprinkler at the same time, both in dry conditions and in presence of water droplets carried by the hot gas flow. Tests are conducted on both fire sprinklers and equivalent cylindrical links to validate this theoretical approach. The results compare favorably both in dry and wet conditions for the range of parameters considered in this study. Therefore, this approach enables the transient quantification of the sprinkler thermal response in an actual fire scenario such as a large-scale fire test.     

Time-dependent smoke yield and mass loss of pool fires in a reduced-scale mechanically ventilated compartment

Technical and pure grades of the combustibles heptane and dodecane were used in a series of small-scale fire tests conducted in a 1 m³ compartment that was mechanically ventilated at 5 and 8 air changes per hour (ACH). Combustible mass loss rates, soot mass concentrations, soot size distributions, several gas species concentrations, and compartment temperatures were measured during the fire. Results for the two pure-grade hydrocarbons were compared with results obtained for their respective technical grades. Technical-grade dodecane produced the highest soot emissions; pure n-heptane produced the lowest. Soot size distributions of all four combustibles attained a steady profile whose modal diameter was about 200 nm. Underventilated fires showed higher carbon monoxide yields than soot yields. Both compartment ventilation rates produced similar results, although the fire self-extinguished earlier for 5 ACH.     

Using suppression and detection devices to steer CFD fire forecast simulations

Firefighters would greatly benefit from a technology based on predictive fire simulations, able to assist their decision making process. For those simulations to be useful, they need a certain degree of precision and resolution that can only be provided by CFD type fire models. But CFD simulations typically take large periods of time to complete, and their results would thus not be available in time to be of use during an emergency. Due to the high complexity of fire spread dynamics that arises from the interaction between solid and gas phase and the corresponding physical-chemical processes (e.g. pyrolysis), the spread of the fire cannot be predicted from first principles in real-time using contemporary computers, and has to be given as parameters to the model. Data can be incorporated into the model to characterise the fire, but only a limited range of measurements are recorded in current buildings. While it might be possible that buildings of the future incorporate a higher density of sensors than contemporary buildings, it is likely that emergency response systems will have access only to conventional data such as smoke detectors and sprinkler activation time for the foreseeable future. In this study the use of conventional detection and suppression devices for the estimation of fire characteristics by means of an inverse modelling framework is explored. Additionally to the growth rate of the fire, the location of the fire origin is successfully estimated. Inverse CFD modelling and tangent linearisation is used to assimilate the data. The nature of the incoming data is consistent with current detection and suppression devices, in such that only a time of activation is recorded and fed into the model. It is shown that the growth rate of the fire and the location of its origin can be correctly and efficiently estimated using sprinkler and smoke detector activation time only. It is further shown that the estimated spread rate is not sensitive to fire origin location.     

Facade flame height ejected from an opening of fire compartment under external wind

This paper presents an experimental study and analysis on the facade flame height ejected from an opening of fire compartment under external wind. Experiments are carried out in a reduced-scale model consisting of a cubic fire compartment with a vertical facade wall. An opening is designed at the center of one sidewall of the fire compartment at the facade side and subjected to external wind (normal to the opening) provided by a wind tunnel. The facade flame heights are measured by a CCD camera for five different openings at various fuel supply heat release rates and wind speeds. It is found that the facade flame height decreases with increasing external wind speed. A scaling analysis is performed to interpret this behavior based on the change of air entrainment into the flame from both the facing-facade and parallel-facade directions caused by the external wind flow. A global model incorporating the external wind speed, the two characteristic length scales of the opening as well as the dimensionless excess heat release rate is developed for describing the facade flame height of various conditions. The proposed model correlates the experimental data well.     

Wind effects on smoke motion and temperature of ventilation-controlled fire in a two-vent compartment

High-rise building fire is often influenced by the ambient wind. Study concerning fire behavior in the compartment of high-rise buildings in wind environment is needed for exploring some effective methods used for evaluation of compartment fire smoke movement and control. In this paper, smoke flowing direction and temperature of ventilation-controlled fire in a two-vent compartment are studied when ambient wind blows to the vent at higher altitude. It is found that there is a critical wind speed, above which the direction of smoke movement is dominated by wind rather than by buoyancy. It is also found that ambient wind has a complex influence on smoke temperature in the compartment. When wind speed exceeds another critical value, only one steady state appears in the smoke temperature rising curve. Otherwise three steady states appear. Heat transfer through the compartment walls has great influence on the second critical wind speed.     

Heat transfer model for unprotected steel members in a standard compartment fire with participating medium

A heat transfer model accounting for the radiative properties of combustion products in a compartment standard fire is presented. The model used is based on a conceptual scheme of a grey gas mixture exchanging radiative energy with a black enclosure. The proposed model, with a radiation heat transfer that accounts for the effect of combustion products on the rate of heat transfer from the fire to the structural elements, is simple to use and the predictions of the temperature response of unprotected I-columns heated from all sides are superior to those predicted by the classical method using the Stefan-Boltzmann radiation equation with constant emissivity.     

Full-scale evaluations on heat resistance of glass panes incorporated with water film or sprinkler in a room fire

In this study, a full-scale room (573 cm×420 cm×330 cm) fire test was developed to investigate the performance and the variations of the absorption of convection heat and the resistance of radiation by using either the water film or the closed-pendent-type sprinkler onto the non-heat-resistant fireproof glass panes. The results showed that in the initial stage of the fire, the water film could completely restrain the surface temperature of the glass, and when the fire induced the flashover and further proceeded to the intense burning, the surface temperature of the glass could still be controlled around 100 °C. Although the flow rate of the sprinkler system was 3 times of the water film system, the effective heat resistance was only a third to a half that of the water film system only. Thus, for situations where the available amount of water flow is limited, by using a layer of uniform down-flowing water film with appropriate thickness and velocity, reducing the temperature of the glass surface could be achieved effectively. The usage of the water film onto the glass pane to assure the fire insulation and fire integrity of the glass pane has been proven workable, through a series test using small-scale [Wu CW, Lin TH, Lei MY, Chung TH, Huang CH, Chiang WT. Fire test on a non-heat-resistant fireproof glass with down-flowing water film. Proceedings of the eighth international symposium on fire safety science, 2005. p. 327–39], full-scale [Wu CW, Lin TH. Fire resistance tests of a glass pane with down-flowing water film. Technical Report, Safety Technology Co., Ltd., Taiwan, ROC, 2005; based on ISO 834-1] and real-scale (this study) fire.     

建筑火灾调查工作存在的问题及对策

我国社会经济快速发展的今天,城市化进程进一步加快,城市中的建筑也越来越密集,高层建筑不断增加,人们生活水平提高,生活环境也变得更加复杂,给城市的防火安全带来了一些隐患,再加上大部分人安全意识的缺乏,在平时的生活与工作中不注重合理摆放、安置危险物品,很容易造成重大火灾事故的发生。建筑火灾威胁着人们的生命财产安全,影响着整个社会的和谐和稳定,必须要做好建筑火灾的调查工作,从以往发生过的火灾事故中分析火灾发生的原因,总结经验,吸取教训,为后续的建筑火灾事故预防和处理提供一些有用的参考和借鉴。文章就此展开了探讨,希望可以有效提升整个社会的防火安全意识,减少火灾事故的发生。     

New approach to estimate temperatures in pre-flashover fires: Lumped heat case

This paper presents a model for estimating temperatures in pre-flashover fires where the fire enclosure boundaries are assumed to have lumped heat capacity. That is, thermal inertia is concentrated to one layer with uniform temperature and insulating materials are considered purely by their heat transfer resistance. The model yields a good understanding of the heat balance in a fire enclosure and was used to predict temperatures in insulated and non-insulated steel-bounded enclosures. Comparisons were made with full scale experiments and with other predictive methods, including CFD modeling with FDS and the so called MQH relationship. Input parameter values to the model were then taken from well-known literature and the heat release rates were provided from the experiments. The fire temperature predictions of the model matched very well with experimental data. So did the FDS predictions while the original MQH relationship gave unrealistic results for the problems studied. Major benefits of using the model in comparison with CFD modeling are its readiness and simplicity as well as the negligible computation times needed. An Excel application of the presented pre-flashover fire model is available on request from the author.     

住宅建筑自动喷水灭火技术发展及应用

概述了住宅建筑中自动喷水灭火系统发展历程、趋势和新技术，介绍了采用住宅喷头的自动喷水灭火系统应用状况，分析了住宅自动喷水灭火系统在保护人员生命财产安全的实际应用中具有的特点，提出在我国建筑防火规范的进一步修订中应加以采用。     

Spatial homogenization algorithm for bridging disparities in scale between the fire and solid domains

The analysis of structures exposed to non-uniform heating from localized fires is a challenging task due to the spatially varying boundary conditions and the differences in scale between the fire simulation and solid heat transfer model. This paper presents a spatial homogenization algorithm for capturing non-uniform boundary conditions from a high-resolution fire simulation in a low-resolution finite element heat transfer model of a structure. The homogenization algorithm uses numerical integration by the trapezoid rule to calculate the equivalent thermal flux vector in the finite element heat transfer model for a spatially varying surface flux. The proposed method is compared to other approximating techniques, including averaging, sampling, and least squares methods, for a 2D heat transfer problem. The results demonstrate that the proposed homogenization algorithm converges rapidly due to the energy-equivalent representation of the thermal boundary condition. The homogenization algorithm is then implemented in a 3D heat transfer model that uses macro-level plate elements. For an application involving a horizontal plate exposed to a localized fire, the model is shown to converge to the results obtained by a solid finite element model. The homogenization algorithm combined with the plate heat transfer element proves to be an accurate and highly efficient means for analyzing structures with spatially varying thermal boundary conditions calculated by computational fluid dynamics.     

Heat transfer in concrete-filled carbon and stainless steel tubes exposed to fire

Nowadays, performance-based design methods are increasingly used for fire resistance assessment of structures. To implement these methods, it is paramount to determine the temperature development within a structural member exposed to fire as accurately and efficiently as possible. Numerical models are developed in this paper to simulate the temperature development in concrete-filled carbon and stainless steel tubes. It was found that the influence of the moisture content in concrete and the thermal contact conductance at the steel–concrete interface is significant. New models for thermal conductivity of concrete and thermal contact conductance at the interface are proposed in this paper. Comparisons of temperature development are made between numerical simulations and extensive experimental results. Improved agreement with test results is achieved when the proposed models are used in the heat transfer analysis.     

Three-sided heating of I-beams in composite construction exposed to fire

A new and simplified model to analyse the thermal response of steel I-beams in composite construction exposed to the standard fire is presented. The model includes a convection and radiation heat transfer module, a resistance-capacitance formulation for heat conduction in the steel beam and a correlation for estimating heat conduction from the upper flange to the concrete slab. The radiation component accounts for the emission and absorption of radiation by the main combustion products of the standard fire. Heat transfer to the concrete is estimated using computer modelling of a number of case studies. The two dimensional I-beam section is represented by three lumped masses concentrated at nodes located at the centres of the lower flange, web and upper flange and connected by conduction paths. Comparison between measured and computed temperature profiles shows good correlation for most of the case studies investigated.     

A computer model for estimating the response of sprinkler links to compartment fires with draft curtains and fusible link-actuated ceiling vents

A computer program, LAVENT, is now available which computes the heating of fusible links due to the presence of a ceiling jet imbedded in an upper layer. An important new feature in this program is that the two-dimensional structure of the ceiling jet is taken into account such that the location of the link beneath the ceiling plays a role in the response of the link. The links can be used to activate ceiling vents such that the effect of venting the upper layer on the ceiling jet may be studied. Additional applications would include the study of upper layer containment through the use of a combination of draft curtains and ceiling vents. The geometry modeled by the program is that of a large compartment enclosed by a combination of walls and draft curtains.