Flame Heights and Heat Transfer in Façade System Ventilation Cavities

The design of buildings using multilayer constructions poses a challenge for fire safety and needs to be understood. Narrow air gaps and cavities are common in many constructions, e.g. ventilated façade systems. In these construction systems flames can enter the cavities and fire can spread on the interior surfaces of the cavities. An experimental program was performed to investigate the influence of the cavity width on the flame heights, the fire driven upward flow and the incident heat fluxes to the inner surfaces of the cavity. The experimental setup consisted of two parallel facing non-combustible plates (0.8 × 1.8 m) and a propane gas burner placed at one of the inner surfaces. The cavity width between the plates ranged from 0.02 m to 0.1 m and the burner heat release rate was varied from 16.5 kW to 40.4 kW per m of the burner length. At least three repeated tests were performed for each scenario. In addition, tests with a single plate were performed. The flame heights did not significantly change for Q′/W < 300 kW/m² (where Q′ is the heat release rate per unit length of the burner and W is the cavity width). For higher Q′/W ratios flame extensions up to 2.2 times were observed. When the distance between the plates was reduced or the heat release rate was increased, the incident heat fluxes to the inner surface increased along the entire height of the test setup. The results can be used for analysing methodologies for predicting heat transfer and fire spread in narrow air cavities.     

Smoke Movement in a Sloping Subway Tunnel Under Longitudinal Ventilation with Blockage

Critical velocity and smoke back-layering length are two of the determining parameters to the fire risk assessment of subway tunnel. These two parameters of a sloping subway tunnel with train blockage were investigated both experimentally and numerically in this paper. To address the influences of slope, the slopes of 0, 3, 6, 9, 12, 15% in downhill subway tunnel were studied and the height (H) of the tunnel was replaced by the inclined tunnel height (\( H/\cos \theta \)). The train model with a dimension of 2 m (length) × 0.3 m (width) × 0.38 m (height) was also chosen in simulations and experiments for the tunnel blockage. Thenceforward, 30 reduced-scale experimental and 150 numerical scenarios were analyzed to predict the critical velocity and smoke back-layering length in various sloping subway tunnels. Six different heat release rates including 5.58, 11.17, 16.67, 22.35, 27.94, and 33.52 kW were considered in the experiments and five different heat release rates including 2.79, 5.58, 8.38, 11.17 and 16.67 kW were considered in the simulations. Based on the comparison in the horizontal tunnel, numerical results were quite consistent with the experiments. The results showed that train blockage influenced the smoke back-layering length, and the critical velocity increases with the tunnel slope. Finally, empirical models were developed to predict the critical velocity and smoke back-layering length in a sloping subway tunnel with train blockage.     

野外组合式软体油罐罐体材料燃烧特性研究

为了研究野外组合式软体油罐在不同辐射强度下的燃烧特性,通过锥形量热仪对软体油罐样本进行燃烧实验,选用25,35,50 kW/m2三种典型的热辐射强度进行研究,得到点燃时间、热释放速率、比消光面积、烟气生成速率、火焰形态等参数的变化规律.结果发现:热辐射强度为50 kW/m2时,点燃时间分别为25,35 kW/m2时的3...     

低气压环境下飞机货舱轰燃规律的实验研究

为研究低气压环境下飞机货舱火灾发展至轰燃的内在规律,利用1/4体积标准飞机货舱在海拔4 260 m、气压60 kPa的环境下开展了一系列火灾轰燃实验。选择航空煤油作为主燃料,以单壁瓦楞纸箱被引燃作为轰燃发生的判据,研究低气压环境下不同火源尺寸对轰燃的影响。通过对飞机货舱内热烟气层平均温度、地板所受辐射热通量、燃料热释放速率和烟气体积分数的测量和分析,探讨低气压环境下轰燃发生的临界条件和表现形式。结果表明,火源尺寸的增大提高了轰燃发生的可能性和轰燃的剧烈程度,在达到引发轰燃所需的临界火源尺寸后,继续增大火源尺寸会使轰燃发生的时间提前;60 kPa压力环境下飞机货舱轰燃所需的临界条件为：上部热烟气层平均温度达到553.5 ℃,地板所受辐射热通量达到19.85 kW/m2。     

Experimental study of natural roof ventilation in full-scale enclosure fire tests in a small compartment

An analysis of full-scale fire test experimental data is presented for a small compartment (3×3.6×2.3 m). A square steady fire source is placed in the center of the compartment. There is an open door and a horizontal opening in the roof, so that natural ventilation is established for the well-ventilated fire. A parameter study is performed, covering a range of total fire heat release rates (330, 440 and 550 kW), fire source areas (0.3×0.3 m and 0.6×0.6 m) and roof ventilation opening areas (1.45×1 m, 0.75×1 m and 0.5×1 m). The impact of the different parameters is examined on the smoke layer depth and the temperature variations in vertical direction in the compartment. Both mean temperatures and temperature fluctuations are reported. The total fire heat release rate value has the strongest influence on the hot smoke layer average temperature rise, while the influence of the fire source area and the roof opening is smaller. The hot smoke layer depth, determined from the measured temperature profiles, is primarily influenced by the fire source area, while the total fire heat release rate and the roof opening only have a small impact. Correlations are given for the hot smoke layer average temperature rise, the buoyancy reference velocity and the total smoke mass flow rate out of the compartment, as a function of the different parameters mentioned. Based on the experimental findings, it is discussed that different manual calculation methods, widely used for natural ventilation design of compartments in the case of fire, under-predict the hot layer thickness and total smoke mass flow rate, while the hot layer average temperature is over-estimated.     

Occupant Tenability in Single Family Homes: Part II: Impact of Door Control,Vertical Ventilation and Water Application

This paper describes experimental investigations of fire service ventilation and suppression practices in full-scale residential structures, including a one-story, 112 m², 3 bedroom, 1 bathroom house with 8 total rooms and a two-story 297 m², 4 bedroom, 2.5 bathroom house with 12 total rooms. The two-story house featured a modern open floor plan, two-story great room and open foyer. Seventeen experiments were conducted varying fire location, ventilation locations, the size of ventilation openings and suppression techniques. The experimental series was designed to examine the impact of several different tactics on tenability: door control, vertical ventilation size, and exterior suppression. The results of these experiments examine potential occupant and firefighter tenability and provide knowledge the fire service can use to examine their vertical ventilation and exterior suppression standard operating procedures and training content. It was observed that door control performed better at controlling the thermal exposure to occupants than did fully opening the door. Additionally, the impact of increased vertical ventilation area was minimal, and only slightly reduced the thermal exposure to occupants in a few non-fire rooms. In the two-story structure, the non-fire rooms on the second floor consistently had larger thermal fractional effective rate (FER) values (approximately 2.5× the thermal risk to oocupants) than did the non-fire rooms on the first floor. Water application was also shown to reduce the thermal risk to occupants 60 s after water application 1/3rd the original values on second floor rooms of the two-storry structure and by at least 1/5th of the original values on the first floor rooms of both structures. Data also showed that the impact of front door ventilation on the toxic gases exposure was minimal, as the toxic gases FER actually increased after front door ventilation for several experiments. However, after vertical ventilation there was a 30% reduction in the toxic gases exposure rate in two of the one-story structure experiments.     

Experimental and Numerical Study of Window Glass Breakage with Varying Shaded Widths under Thermal Loading

To investigate the effect of shaded width on the breaking behavior of window glass, a series of experiments was carried out on float glass with dimension of 600 mm × 600 mm × 6 mm in an enclosed compartment under radiant heat. The shaded width of glass pane ranged from 10 mm to 50 mm with an interval of 10 mm. Experimental results showed that crack patterns of the glass pane were influenced little by the shaded width, while the average value of the first breaking time of the glass pane decreased firstly and then increased with an increase in the shaded width. The average time to the first crack with the shaded width of 20 mm was shortest in experiments and the corresponding time was 572.5 s. In addition, the finite element method was also used to simulate the process of crack initiation and single crack propagation. Temperatures measured by thermocouples in experiments were employed as thermal loads for the problem of glass breakage. The first breaking time obtained by the program was in good agreement with experimental data.     

Radiant Ignition of Polyurethane Foam: The Effect of Sample Size

Although smouldering ignition of upholstery items remains a leading cause of residential fire deaths, relatively little research is conducted on the topic. An experimental investigation of the effect of sample size on the ignition and spread of smouldering and flaming in polyurethane foam under natural flow conditions is reported here. Polyurethane foam samples are used because this is a common material in modern, residential environments and one for which there exists significant quantities of previous experimental data in the literature. Samples of different square cross-section size and a fixed height of 150 mm are insulated on all sides except the top which is exposed to a radiant heat flux and is open to the air. Samples with side lengths of 50 mm, 100 mm, and 140 mm are studied. Ignition and spread dynamics are diagnosed using thirteen thermocouples located along the vertical centre line. The onset of smouldering ignition (13  $\hbox{kW}\, \hbox{m}^{-2}$ , 8  $\hbox{kW}\, \hbox{m}^{-2}$ and $7\,\hbox{kW}\, \hbox{m}^{-2}$ for 50 mm, 100 mm and 140 mm sample sizes respectively) is observed at significantly lower heat fluxes that flaming (45  $\hbox{kW}\,\hbox{m}^{-2}$ , 32  $\hbox{kW}\,\hbox{m}^{-2}$ and $30\,\hbox{kW}\,\hbox{m}^{-2}$ respectively). Critical heat fluxes for smouldering and flaming ignition increase with decreasing sample size, with smouldering ignition being significantly more sensitive to sample size than flaming ignition under the size range studied. Smouldering spread rates are measured in the range from 3  $\hbox{mm}\, \hbox{min}^{-1}$ to $25\,\hbox{mm}\, \hbox{min}^{-1}$ and found to be a strong function of the heat flux and depth of the smoulder front. The effect of sample size on smouldering has been theoretically proposed before but this is the first time that this effect has been demonstrated experimentally for ignition. The fact that large samples result in the lowest critical heat flux could have implications for testing procedures and translation of results from small-scale testing to real-scale in the built environment.     

室内烟气运动影响因素模拟研究

运用FDS模拟室内火灾烟气的运动规律,分析烟气层稳定性,以及门的尺寸、火源位置和火源面积对烟气温度及高度的影响。结果表明,具有稳定热释放速率的火源,燃烧一段时间后烟气层高度不会随时间发生变化;烟气层高度随门的高度和宽度增加而升高;火源处于房间中心时,烟气层高度随着门宽度增加迅速升高,与门高度的关系较小;随着火源面积增加,烟气层高度下降,温度升高。     

Occupant Tenability in Single Family Homes: Part I—Impact of Structure Type,Fire Location and Interior Doors Prior to Fire Department Arrival

This paper describes an experimental investigation of the impact of structure geometry, fire location, and closed interior doors on occupant tenability in typical single family house geometries using common fuels from twenty-first century fires. Two houses were constructed inside a large fire facility; a one-story, 112 m², 3-bedroom, 1-bathroom house with 8 total rooms, and a two-story 297 m², 4-bedroom, 2.5-bathroom house with 12 total rooms. Seventeen experiments were conducted with varying fire locations. In all scenarios, two bedrooms had doors remaining open while the door remained closed in a third bedroom immediately adjacent to the open door bedrooms. Temperature and gas measurement at the approximate location of a crawling or crouching trapped occupant (0.9 m from the floor) were utilized with the ISO 13571 fractional effective dose (FED) methodology to characterize occupant tenability up to the point of firefighter intervention. The FED values for the fire room were higher for heat exposure than for toxic gases, while target rooms reached highest FED due to CO/CO₂ exposure. The closed interior door decreased FED significantly, with the worst case scenario resulting in a 2% probability of receiving an incapacitating dose compared to the worst case scenario for an open bedroom of 93% probability of receiving an incapacitating dose. In fact, in 7 of the 17 experiments, the closed interior door resulted in a less than 0.1% chance of an occupant receiving an incapacitating dose prior to firefighter ‘intervention.’     

Numerical Simulation of Fire Exposed Façades Using LEPIR II Testing Facility

The fire behavior of external wall insulation system on façades is assessed during LEPIR II testing. This facility involves a 600 kg wood crib fire in a 30 m³ lower compartment of a two levels high concrete structure. External flames develop in front of the façade from the fire compartment through windows with dimensions 1?×?1.5 m (W?×?H). In order to predict the fire exposure of a façade during the test, CFD simulations were carried out with the computational fluid dynamics code Fire Dynamics Simulator (FDS) for two full-scale experiments. The main objective of this study was to evaluate the ability of FDS to reproduce quantitative results in terms of gas temperatures and heat fluxes close to the tested façade. This is an important step before the fire performances of any insulation system can be predicted by numerical tools. A good repeatability was observed in terms of measured gas temperatures for experiments. Maximum heat release rate of the fire, close to 5 MW, was achieved after 5 min of test. When experimental results were compared with numerical calculations, good agreement was found for every quantity. The most critical zone on the facade is located above the fire room and is directly impacted by external flame outgoing from the fire compartment. Temperatures up to 500°C were observed in this zone. For the thermocouples located up to the second level opening, these probes were not located directly in the flames, but rather in the hot gases above the fire plume. The maximum temperature achieved was thus close to 400°C. The proposed model gives correct thermal loads and flames shape near the façade during calibration tests and can be used for further evaluation of combustible material on façade.     

An experimental study on backdraught: The dependence on temperature

This paper presents the results of a series of reduced scale experiments to investigate the temperature conditions leading to backdraught in a fire compartment (0.8 m×0.4 m×0.4 m), using solid polypropylene pellets as the fuel. The factors of primary interest are the pre-burn time, before the fire becomes oxygen limited, the duration of door closure, and the temperature distribution in the compartment. It is shown that the temperature inside the compartment is crucial for the occurrence of backdraught. Above 350 °C, backdraught by auto-ignition is possible. If a pilot spark is present, backdraught may occur at temperatures down to 300 °C. It is shown that backdraught conditions can be achieved in the early stages of a fire as long as a suitable temperature is reached, at considerably lower temperatures than those generated during flashover. Further investigation on gas concentration is essential to understand the chemistry of backdraught combustion.     

Experimental Study of the Fire Behaviour on Flat Roof Constructions with Multiple Photovoltaic (PV) Panels

Fire experiments were conducted on four mock-up roof constructions with an array of six photovoltaic (PV) panels to study the fire dynamics and flame spread behaviour, so as to better characterise the fire risks of such a system. As it is customary to retrofit PV panels to existing warehouse roofs, where expanded polystyrene (EPS) and polyvinylchloride-based roofing membrane B_ROOF(t2) is a typical roofing, the experiments were carried out on such installations, but with a mitigation solution on top; 30 mm mineral wool or 40 mm polyisocyanurate (PIR). All mock-ups were 6.0 m long, whereas the width was 2.4 m (Experiments 1 and 2) and 4.8 m (Experiments 3 and 4), respectively. A wood crib was placed under the PV panels and it ignited the roofing membrane after 7 min to 8 min, which in all four experiments resulted in fire spread under all the six PV panels covering an area of 5.1 m?×?2.0 m. However, no self-sustained fire was observed beyond the area below the PV array. Within the first hour, the maximum temperatures were measured to respectively 175 °C and 243 °C underneath the two mitigation solutions of PIR insulation and mineral wool, which is more than 100 °C below the piloted ignition temperature for the EPS insulation. However, the EPS was ignited in both experiments with the PIR insulation due to thermal degradation of the protective material after approximately 1 h. These experiments confirm that a small initial fire underneath a PV installation can transform into a hazardous scenario due to the changed fire dynamics associated with adding the PV panels to the existing roof.     

污水源热泵制热模型及外在参数影响

分别建立了污水源热泵四大部件(蒸发器、压缩机、冷凝器、膨胀阀)模型,并进行耦合。采用MATLAB软件进行编程模拟,分别计算了污垢热阻、污水流量、污水进口温度变化对热泵冬季制热性能的影响。结果显示:当污垢热阻在0~1(m2·K)/kW范围内变化,系统制热量由353kW降低到301kW,降低了14.8%;当污水入口温度由8℃升高到20℃时,系统制热量由320kW升高到423kW,升高了32.1%;当污水流量由10kg/s升到20kg/s时,系统制热量由339kW增加到364kW等。过程中热泵COP在3.6~4.8范围内变化,说明污水源热泵具有较好的热性能。     

Model scale railcar fire tests

A series of tests has been performed in a model of a typical passenger train compartment (railcar). The tests were carried out on a scale of 1–10. The main purpose of the tests was to investigate if it is possible to calculate the heat release rate for a flashed over train compartment with simple mathematical expressions derived for ordinary compartment fires. The combustion that takes place outside the windows was considered in the study. The parameters that were varied include: the ventilation, the fuel load and the type of interior surface material. In all tests, one door was open and the number of windows varied from all windows closed, to all windows opened. The ignition took place in the corner of the model compartment opposite the door opening.     

不同车门开闭状态下地铁车厢火灾特性研究

考虑地铁车窗受高温破碎的因素,利用FDS研究不同车门开闭状态下车厢火灾发展,对比热释放速率、温度、车窗破碎时间等.结果显示:车门开启数量对车厢火灾热释放速率的影响较大,最大热释放速率可达14.4 MW.在400℃和600℃的破碎温度下,当车门开启数量大于3扇和4扇时,车厢火灾最大热释放速率下降.火灾发展初期,车门开启数...     

Predicting the Fire Dynamics of Exposed Timber Surfaces in Compartments Using a Two-Zone Model

There is an increasing desire to use more engineered timber products in buildings, due to the perceived aesthetics of timber and desire for more sustainable architecture. However, there are concerns about fire performance of these products especially in taller buildings. This has led to renewed research to understand the behaviour of timber surfaces in compartments exposed to fire. This paper describes a two-zone calculation model for determining the fire environment within a compartment constructed from timber products where varying amounts of timber are exposed on the walls and ceiling. A set of eight full-scale compartment experiments previously reported in the literature are used to assess the capability of the model. The fire load energy density in the experiments ranged from 92 MJ/m² to 366 MJ/m² comprising either wood cribs or bedroom furniture with the largest compartment having dimensions 4.5?×?3.5?×?2.5 m high with an opening 1.069 m wide?×?2.0 m high. The experiments were ventilation-controlled. It is shown that the model can be used to provide conservative predictions of the fire temperatures for compartments with timber exposed on the walls and/or ceiling as part of an engineering analysis. There are several limitations that are discussed including the need to consider the debonding of layers in the case of cross-laminated timber. It is recommended that further benchmarking of the model be done for different ventilation conditions and with engineered timber products where debonding does not occur. This will test the model under a wider range of conditions than examined in this paper.     

热辐射强度对棉花燃烧特性的影响

利用锥形量热仪对两组质量为10、20g的棉花进行了热辐射点燃实验,热辐射强度分别选取35、30、25、20、15、10、5、4、3、2kW/m²,对其热释放速率曲线、总热释放量曲线、燃烧残留物形貌和残余质量进行了对比分析。研究结果表明：棉花明火燃烧时总是同时存在阴燃,明火燃烧的热释放速率峰值高于同条件下阴燃的热释放速率的最大值,随其规模程度的增大而增大。阴燃的热释放速率曲线没有峰值,热释放持续的时间较长。尺寸100mm×100mm×24mm、质量10g棉花样品的临界点燃热辐射强度为2~3kW/m²;尺寸100mm×100mm×24mm、质量20g棉花样品的临界点燃热辐射强度为4~5kW/m²。随着堆积密度、相对湿度增加,临界点燃热辐射强度提高。     

Transmission Through and Breakage of Multi-Pane Glazing Due to Radiant Exposure

A series of small and large-scale tests were performed to measure the radiant transmission of energy and the window breakage characteristics of seven different multi-plane glazing samples. The samples tested included both double and triple-pane glazing specimens with a laminate interlayer between panes for additional strength. These test series were designed to provide the information necessary to assess the hazard from radiant energy to building occupants and contents due to a large fire in close proximity to a structure with a large amount of exterior windows. For incident heat fluxes 30 kW/m² or lower, the triple-pane glazing samples had a total transmittance less than 10% of the incident heat flux, back-side surface temperatures did not exceed 100°C, and the back-side heat flux did not exceed 4 kW/m². For double-pane laminates, the total transmittance was less than 25% of the incident heat flux, the back-side temperature did not exceed 220°C, and the back-side heat flux did not exceed 5 kW/m². For incident heat fluxes greater than 30 kW/m², the glazing samples degraded very quickly, generally buckling and losing integrity. The time for the first pane to crack decreased with increasing incident flux level. A number of tests included a water deluge system, which served to maintain sample integrity for extended exposures. In these cases, the total transmittance was less than 6% of the incident heat flux, back-side surface temperatures did not exceed 45°C, and the back-side heat flux did not exceed 1 kW/m².     

密闭机舱双火源燃烧质量损失研究

在3 m×3 m×3.5 m的缩尺度船舶密闭机舱中,设置边长分别为10,15,20 cm的正方形双油池,试验研究双油池不同间距下的燃烧速率变化规律。结果表明：密闭舱室内的双油池火可分为初始、稳定、熄灭三个典型燃烧阶段,不同面积油池的无量纲间距S/L与燃烧速率之间呈现抛物线关系且质量损失率达到峰值时S/L的阈值在0.70～0.85,这与开放空间以及隧道半封闭空间下的双火源发展有很明显的区别。在此基础上,给出了密闭舱室内修正间距S的无量纲热释放速率预测模型。