Quantifying the vulnerabilities of ceramic tile roofing assemblies to ignition during a firebrand attack

An experimental campaign was conducted to investigate the vulnerabilities of ceramic tile roofing assemblies to ignition under a controlled firebrand attack using the NIST firebrand generator. The results of a parametric study on the ignition propensity of ceramic tile roofing assemblies under a firebrand attack using the firebrand generator installed inside the Fire Research Wind Tunnel Facility (FRWTF) at the Building Research Institute in Tsukuba, Japan is presented. Over the range of parameters considered, ceramic tile roofing assemblies were found to be vulnerable to ignition during a firebrand attack.     

On the development and characterization of a firebrand generator

A unique experimental apparatus has been constructed in order to generate a controlled and repeatable size and mass distribution of glowing firebrands. The present study reports on a series of experiments conducted in order to characterize the performance of this firebrand generator. Firebrand generator characterization experiments were performed at the Fire Research Wind Tunnel Facility (FRWTF) at the Building Research Institute (BRI) in Tsukuba, Japan. The firebrand generator was fed with three different initial firebrand geometries, two different sized cylinders and one size of disks. Cylinders were used to simulate firebrand fluxes from vegetation, such as trees, while disks were used to simulate a firebrand flux from burning structures. Samples of these geometries were constructed from wood dowels, fed into the firebrand generator, ignited, and the glowing firebrands generated were collected using an array of water filled pans. The pans were filled with water in order to quench combustion. The collected firebrands were subsequently dried and the size and mass distribution was measured. These experiments were performed over a range of wind tunnel speeds, with no wind speed present to 9 m/s, to determine the lofting distance of the firebrands generated. Finally, the size and mass distribution produced from the firebrand generator are compared to those produced from burning trees. Results of the study are presented and discussed.     

Experimental investigation of firebrands: Generation and ignition of fuel beds

A series of real scale fire experiments were performed to determine the size and mass distribution of firebrands generated from Douglas Fir (Pseudotsuga menziesii) trees. The results of the real scale fire experiments were used to determine firebrand sizes to perform reduced scale ignition studies of fuel beds in contact with burning firebrands. The firebrand ignition apparatus allowed for the ignition and deposition of both single and multiple firebrands onto the target fuel bed. The moisture content of the fuel beds used was varied and the fuels considered were pine needle beds, shredded paper beds, and shredded hardwood mulch. Firebrands were constructed by machining wood (Douglas Fir) into small cylinders of uniform geometry and the size of the cylinders was varied. The firebrand ignition apparatus was installed into the Fire Emulator/Detector Evaluator (FE/DE) to investigate the influence of an air flow on the ignition propensity of fuel beds. Results of this study are presented and compared to relevant studies in the literature.     

Experiments to provide the scientific-basis for laboratory standard test methods for firebrand exposure

Firebrand ignition of structures is a major factor in large outdoor fire spread. Standard laboratory test methods are required to evaluate and compare the performance of different building elements and/or vegetative fuels ability to resist firebrand ignition. It is important to determine full-scale assembly performance when exposed to firebrand showers since weak points in a given assembly can be investigated. Such studies will lead to determining the necessary configuration of building component mock-ups that can be used in standard laboratory test methods. The basis of this paper is to present a comparison of results from full-scale roofing assembly experiments, to mockups using the recently developed experimental capability at National Research Institute of Fire and Disaster (NRIFD). The results demonstrated that similar firebrand penetration behavior/trends were observed for mock-ups of full-scale roofing assemblies, as compared to experiments where full-scale roofing assemblies were used, all under similar wind speeds. The experimental findings presented in this paper represent an important step to develop reduced-scale test methods for firebrand exposure.     

Experimental investigation of firebrand accumulation zones in front of obstacles

It is well accepted that as structures are exposed to wind, stagnation planes are produced around structures. Past work by the authors demonstrated for the first-time that wind-driven firebrand showers may accumulate in these stagnation planes. While those experiments demonstrated this important phenomenon, due to the limited duration of firebrand showers of the original NIST Batch-Feed Firebrand Generator, it was not possible to perform a more systematic study. To this end, a series of detailed experiments were performed using the recently developed NIST Continuous-Feed Firebrand Generator capable of firebrand showers of unlimited duration. Full-scale walls of varying size were placed downstream of the device and the wind speed was varied in increments up to 10 m/s. The experiments were conducted in the Building Research Institute's Fire Research Wind Tunnel Facility (FRWTF). For a given wall size exposed to specific firebrand size/mass distribution, it was observed that wind speed influences not only the spatial location and extent of the accumulated firebrands in the stagnation plane in front of the wall, but also the nature of the smoldering combustion intensity of the accumulated firebrands. The experiments demonstrated that higher wind speeds (10 m/s) did not promote accumulation of firebrands in stagnation planes in front of walls. The data may be used to provide guidance to appropriate separation distances that combustibles should be placed near structures and is also of great use to develop and validate numerical models of firebrand accumulation.     

Investigation on the ability of glowing firebrands deposited within crevices to ignite common building materials

A series of experiments was conducted to determine the range of conditions that glowing firebrands may ignite common building materials. The surface temperature of glowing firebrands burning under different applied airflow was quantified using an infrared camera. As the applied airflow was increased, the surface temperature of glowing firebrands was observed to increase. A crevice was constructed using plywood and oriented strand board (OSB) and the angle was varied to investigate the influence that this parameter has on promoting ignition after contact with glowing firebrands. The number of firebrands deposited within the constructed crevices was varied. Single firebrands were unable to ignite the materials used in this study over a range of applied airflows. For the tightest fuel bed angle of 60°, the glowing firebrands deposited on the fuel bed always resulted in smoldering ignition. For plywood, contact with glowing firebrands produced smoldering ignition followed by a transition to flaming ignition. At the fuel bed angle of 90°, no definitive ignition behavior was observed for either material; different ignition criteria (either no ignition or smoldering ignition) were observed under identical experimental conditions. As the fuel bed angle was increased up to 135°, ignition never occurred for both test fuel beds. For a given airflow and fuel bed material, the ignition delay time was observed to increase as the fuel bed angle was increased. A large difference was observed in the ignition delay time for plywood and OSB at a fuel bed angle of 90°. Based on these ignition results, the critical angle for ignition exists between 90° and 135° at a given airflow. These results clearly demonstrate that firebrands are capable of igniting common building materials.     

Firebrands generated from a full-scale structure burning under well-controlled laboratory conditions

Firebrand production from a real-scale structure under well-controlled laboratory conditions was investigated. The structure was fabricated using wood studs and oriented strand board (OSB). The entire structure was placed inside the Building Research Institute's (BRI) Fire Research Wind Tunnel Facility (FRWTF) in Japan to apply a wind field of 6 m/s onto the structure. As the structure burned, firebrands were collected using an array of water pans. The size and mass distributions of firebrands collected in this study were compared with sparsely available firebrand generation data from actual full-scale structure burns, individual building component tests, and historical structure fire firebrand generation studies. In this experiment, more than 90% of firebrands were less than 1 g and 56% were less than 0.1 g. It was found that size and mass of firebrands collected in this study were similar to the literature studies, yet differences existed as well. Different experimental conditions, as well as varied firebrand collection strategies, were believed to be responsible for the differences in firebrand size and mass measured in the present work, and those in the literature. The present study has provided much needed data on firebrand generation from structures.     

Experimental investigation of wood decking assemblies exposed to firebrand showers

Wildland-Urban Interface (WUI) fires have become a problem of great concern across multiple continents. An important mechanism of structure ignition in WUI fires and urban fires is the production of firebrands. During WUI fires, decking assemblies have been observed to be an ignition vulnerability based on post-fire damage surveys conducted by NIST and elsewhere. The authors have conducted scoping experiments and demonstrated the dangers of the dynamic process of continual, wind-driven firebrand showers landing on decking assemblies for wind speeds of 6 m/s. In this study, eight full-scale experiments were conducted with wood decking assemblies under a wind speed of 8 m/s. The basis for these new investigations was twofold: observe possible vulnerabilities of wood decking assemblies to continuous, wind-driven firebrands at higher wind speed as firebrand accumulation patterns were expected to be influenced by wind speed, and examine if wall ignition occurred due to the burning decking assembly. To this end, sections of wood decking assemblies (1.2 m by 1.2 m) were constructed and attached to a reentrant corner assembly. The deck/reentrant corner assembly was then exposed to continuous, wind-driven firebrand bombardment generated by a full-scale Continuous Feed Firebrand Generator installed in the Fire Research Wind Tunnel Facility (FRWTF) at the Building Research Institute (BRI) in Japan. The mass of firebrands required for flaming ignitions under a wind speed of 8 m/s was considerably less compared with those under a wind speed of 6 m/s. This result is postulated to be due to higher firebrand surface temperatures as the wind speed was increased. For the decking assembly to wall ignition studies, the interface between the decking assembly and the wall appeared to be a weak point; this is not addressed in the current test methods.     

Summary of workshop for fire structure interaction and urban and wildland-urban interface (WUI) Fires–operation Tomodachi–fire research

A workshop, known as “Operation Tomodachi—Fire Research” was held in Tokyo, Japan from July 1 to July 4, 2012. Tomodachi means friendship in Japanese. This workshop, under the direction of Dr. Samuel L. Manzello of EL-NIST and Dr. Tokiyoshi Yamada of the University of Tokyo, was conducted in partnership with the Japan Association of Fire Science and Engineering (JAFSE). The objective was to: (1) develop scientific knowledge and translate it to building codes and standards that will be of use to both countries to reduce the devastation caused by unwanted fires, (2) provide a forum for next generation researchers to present their work in order to develop new research collaborations, (3) and allow USA participants a chance to visit excellent large-scale research facilities available in Japan that are of use to the research topics of this workshop. This is a formal continuation of the kickoff meeting held at NIST's Engineering Laboratory (EL-NIST) in June 2011. USA presentations were delivered from: NIST, Purdue University, University of Texas-Austin, Michigan State University, University of Michigan, Insurance Institute for Business and Home Safety (IBHS), Worcester Polytechnic Institute (WPI), University of California-Berkeley, California Polytechnic University (CALPOLY), Underwriters Laboratories (UL), and the University of Delaware (organizations are listed based on the order of oral presentation). Japanese presentations were delivered from: The University of Tokyo, Building Research Institute (BRI), Takenaka Corporation, Center for Better Living, Shimizu Corporation, Tokyo University of Science (TUS), National Institute for Land and Infrastructure Management (NILIM), Kyoto University, National Research Institute of Fire and Disaster (NRIFD), Yamagata University, and Kobe University (organizations are listed based on the order of oral presentation). All of the presentations are documented in a recent NIST Special Publication (NIST SP 1137). The present paper provides a detailed summary for the need of this workshop as well as the findings obtained from the event. It is desired that this activity will motivate the next generation of researchers to explore and develop research collaborations related to emerging areas of fire safety science. The authors are hopeful that new and exciting activities specific to other countries may come out of this type of event.     

Determination of smoldering time and thermal characteristics of firebrands under laboratory conditions

The laboratory experiment was conducted to simulate the transfer of smouldering particles produced in forest wildfires by a heated gas flow. The pine bark pieces with the linear dimensions L=(15; 20; 30) mm and a thickness of h=(4−5) mm were selected as model particles. The rate and temperature of the incident flow varied in the range of 1–3 m/s and 80–85 °C, respectively. The temperature of the samples was recorded using a thermal imager. To determine the minimum smouldering temperature of pine bark, the thermal analysis was conducted. The minimum smouldering temperature of pine bark was found to be 190 °C. This temperature will cause thermal decomposition of bark only at the first stage (oxidation of resinous components). In the study the smouldering time, the temperature and the weight of samples were obtained and analyzed under various experimental conditions. The data analysis shows that the increase in the particle size leads to the decrease in their mass loss, and the rate change of the incident flow does not practically influence the mass change. For particles with the linear dimensions of 10 mm and 20 mm, the mass varies from 6% to 25%. The maximum mass loss is observed for the flows with a rate of 1 and 2 m/s. The results have shown that the increase in the particle size leads to the increase in the smouldering time. The position of the particle plays an important role, the effect of which increases with increasing the particle size. The calculations showed that the smouldering time of bark samples is long enough for the particles to serve as new sources of spot fires. The particles were found to be transported to a distance of 218 m from the fire line which can certainly influence the propagation of the fire front.     

Development of rapidly deployable instrumentation packages for data acquisition in wildland–urban interface (WUI) fires

In an effort to quantify structure ignition mechanisms during wildland–urban interface (WUI) fires, rapidly deployable instrumentation packages were developed. For a structure under a WUI fire attack, the packages are designed to: (1) provide temporally resolved images of structure ignition mechanisms and (2) provide quantitative data on total heat flux, wind speed, wind direction, ambient temperature, and relative humidity near a structure. The unique design of the packages allowed for wireless transmission of all data signals collected to a hardened location. Prior to attempting to use these instrumentation packages in real WUI fires, a proof-of-concept test was conducted under a prescribed fire. In these tests, a shed was used as a surrogate for a typical structure that would be found in the WUI. The proof-of-concept test was successful and has demonstrated that relatively inexpensive instrumentation can be used to image structure ignition in the path of an approaching crown fire and that directional flame thermometers (DFT) were acceptable instrumentation to measure total heat flux in place of cumbersome water cooled total heat flux gages.     

Solar activity as a possible cause of large forest fires--a case study: analysis of the Portuguese forest fires

Fires of large dimension destroy forests, harvests and housing objects. Apart from that combustion products and burned surfaces become large ecological problems. Very often fires emerge simultaneously on different locations of a region so a question could be asked if they always have been a consequence of negligence, pyromania, high temperatures or maybe there has been some other cause. This paper is an attempt of establishing the possible connection between forest fires that numerous satellites registered and activities happening on the Sun immediately before fires ignite. Fires emerged on relatively large areas from Portugal and Spain on August 2005, as well as on other regions of Europe. The cases that have been analyzed show that, in every concrete situation, an emission of strong electromagnetic and thermal corpuscular energy from highly energetic regions that were in geo-effective position had preceded the fires. Such emissions have, usually, very high energy and high speeds of particles and come from coronary holes that also have been either in the very structure or in the immediate closeness of the geo-effective position. It should also be noted that the solar wind directed towards the Earth becomes weaker with deeper penetration towards the topographic surface. However, the results presented in this paper suggest that, there is a strong causality relationship between solar activity and the ignition of these forest fires taking place in South-western Europe.     

Experimental validation of a numerical model for the transport of firebrands

The paper deals with the experimental validation of a numerical model for the transport and combustion of cylindrical and disk-shaped firebrands. The model solves the conservation equations of brand mass, kinetic and angular momentum, and volume. Validation consists in predicting the mass and spatial distributions of glowing firebrands that were produced from the experimental generator developed by Manzello and coworkers [S.L. Manzello, J.R. Shields, T.G. Cleary, A. Maranghides, W.E. Mell, J.C. Yang, Y. Hayashi, D. Nii, T. Kurita, On the development and characterization of a firebrand generator, Fire Saf. J. 43 (2008) 258–268]. Ten thousand firebrands per run are released with initial conditions that are randomly generated according to probability distribution functions deduced from experimental mass and spatial distributions under no-wind conditions. Whatever the wind conditions considered, numerical results are found to be in good agreement with experimental data.     

h形支挡结构的试验研究

h形支挡结构较常规抗滑桩不仅在抗弯刚度上具有明显优势,还能严格地控制桩顶位移。目前针对h形支挡结构支护的相关研究较少,为此进行了模型试验研究,分析前后桩排距B及前桩桩长L3这两个主要参数对h形支挡结构的桩顶位移、桩身弯矩、土压力及破坏模式的影响。研究表明,一定范围内增大前后桩排距B或前桩桩长L3都能减少桩顶水平位移;桩身弯矩最大值位于连系梁与后排桩连接处附近,且随前后桩排距B增大而增大,随前桩桩长L3增大而减小;开挖完成后后排桩桩后土压力接近于朗肯主动土压力;后排桩桩前土压力接近于静止土压力;前排桩桩后土压力在前后桩排距B较大时接近于朗肯主动土压力,而在排距B较小时接近于静止土压力;前排桩桩前土压力由静止土压力向朗肯被动土压力发展,分布为三角形加倒三角形组合分布模式。在前后桩排距B及前桩桩长L3影响下,h形支挡结构支护存在“V”字和“W”字两种破坏模式。研究结果可以为工程设计提供参考,同时为理论分析模型建立提供依据。     

Stochastic modeling of firebrand shower scenarios

Firebrand shower and its subsequent spot fires are responsible for more than half of the ignitions reported during wildfires, in particular at wildland urban interface (WUI) areas. The firebrand transport is a highly stochastic and nonlinear problem which directly influences the spotting distribution. Hence, a coupled stochastic model of firebrand showers, that is thoroughly and systematically validated against large scale wind tunnel experiments of lofting and downwind transport of model firebrands, is presented. It is shown that the developed model predicts the first and second order statistics of the flight accurately in relation to the experimental data. The sensitivity of the model to the initial conditions of the flight as well as the velocity field characteristics are examined.     

在受限和通风防火分区内对燃烧速率特性的试验研究

在核安全研究框架内对在受限和通风防火分区内油池火燃烧速率进行了试验研究。在实体火灾试验基础上，此研究为在受限和通风火灾场景下的燃烧速率机理提供了新的信息。描述了在自由条件和空气受限条件下所进行的试验，对试验装置、仪器以及火源进行了详细叙述。在相同场景（0．4m^2TPH油池火）下，对自由条件和空气受限条件的试验情况下的燃烧速率进行了对比。在空气受限情况下，燃烧速率与时间的变化曲线显示出三个不同阶段：自由条件和受限燃烧速率相同；不稳定阶段，空气受限条件下燃烧速率高于自由条件下的燃烧速率;稳定阶段。从图像分析看，不稳定阶段显示，动荡和间歇火焰大大提高了燃烧速率。介绍了通风速率和油池面积对此现象的影响。试验结果为理解有限区域内燃烧速率提供了新的试验信息。     

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。     

钢管混凝土结构地震模拟试验研究

对钢管混凝土 5层框架结构进行了地震模拟试验 .通过振动台试验及理论分析 ,对钢管混凝土结构的动力特性、多种地震波输入下的结构加速反应和位移反应进行了对比 ,综合评定了钢管混凝土结构的抗震性能 ,为结构设计提供了参考数据