Towards understanding the effect of cedar roof covering application on firebrand production in large outdoor fires.

Due to the increased concern for the environment, sustainable construction materials are getting increased attention. Wood is considered a renewable, sustainable construction material. The problem with wood is that it is a fire-prone material. With an increasing number of wildland-urban interface (WUI) fires recently, it is important to consider that wood buildings are in danger to be ignited as well as may produce new sources of ignition due to firebrand production. Experiments were performed to investigate cedar roof covering effects of firebrand production from roof assemblies. Two wind speeds, 6 m/s and 8 m/s were selected for this experiment for a comparison with literature. The wood materials used were untreated cedar shingles, untreated cedar shakes, fire retardant cedar shingles and fire retardant cedar shakes. The roof assembly with fire retardant cedar shakes applied produced little or no firebrands under both wind speeds tested. Roof coverings fitted with cedar siding produced more variety of firebrands compared to only base sheathing materials. The mass and the projected area of firebrands were found to have a linear relationship. The firebrand coefficient was used for comparison. With attendant increase in wind speed, the firebrand coefficient increased in this study.

Role of Firebrand Combustion in Large Outdoor Fire Spread.

Large outdoor fires are an increasing danger to the built environment. Wildfires that spread into communities, labeled as Wildland-Urban Interface (WUI) fires, are an example of large outdoor fires. Other examples of large outdoor fires are urban fires including those that may occur after earthquakes as well as in informal settlements. When vegetation and structures burn in large outdoor fires, pieces of burning material, known as firebrands, are generated, become lofted, and may be carried by the wind. This results in showers of wind-driven firebrands that may land ahead of the fire front, igniting vegetation and structures, and spreading the fire very fast. Post-fire disaster studies indicate that firebrand showers are a significant factor in the fire spread of multiple large outdoor fires. The present paper provides a comprehensive literature summary on the role of firebrand mechanisms on large outdoor fire spread. Experiments, models, and simulations related to firebrand generation, lofting, burning, transport, deposition, and ignition of materials are reviewed. Japan, a country that has been greatly influenced by ignition induced by firebrands that have resulted in severe large outdoor fires, is also highlighted here as most of this knowledge remains not available in the English language literature. The paper closes with a summary of the key research needs on this globally important problem.

Garnering understanding into complex firebrand generation processes from large outdoor fires using simplistic laboratory-scale experimental methodologies.

A simple laboratory-scale experimental method was developed to study firebrand generation processes. As part of these experiments, Japanese wind facilities were used to elucidate the effect of wind speed on firebrand generation from structural materials. It was found that very simple experimental methodologies developed as part of this study for mock-ups of full-scale roofing assemblies yielded important understanding into firebrand generation processes for both real-scale structure combustion processes as well as available firebrand information from urban and wildland-urban interface (WUI) fires.

Investigating Effect of Wind Speeds on Structural Firebrand Generation in Laboratory Scale Experiments.

Firebrands generated from structures are known to be a source of rapid flame spread within communities in large outdoor fires, such as wildland-urban (WUI) fires, and urban fires. It is important to better understand firebrand generation mechanism to prevent structure ignitions by firebrands. Though the wind plays an important role during the large outdoor fires, little known is the influence of wind speeds on firebrand production. To this end, a series of experiments were performed using mock-ups of full-scale wall assemblies exposed to wind. The objective of this study was to examine if experiments with mock-ups of full-scale wall assemblies may provide insight into firebrand generation from structures. Specifically, generated firebrands were collected and compared with those collected from full-scale components and a full-scale structure. The relationship between projected area and mass of firebrands were compared with previous experimental data. It was found that the projected area of firebrands was proportional to the firebrand mass in this study, which is the same as those from experimental studies performed for full-scale components and a full-scale structure. The slope of the relationship of the projected area and the mass of firebrands was the same under the same wind speed and was affected by the applied wind speed within this experimental range.

Initial Study on Thatched Roofing Assembly Ignition Vulnerabilities to Firebrand Showers.

Structures fitted with thatched roofing assemblies are prone to ignition during the course of large outdoor fires. Experiments with thatched roofing assemblies were performed by using a reduced-scale continuous-feed firebrand generator in a wind facility to investigate fundamental ignition mechanisms. The wind speed was varied from 3 m/s to 6 m/s to observe the ignition and flame spread of thatched roofing assemblies. It was observed that firebrands penetrated into the thatched roofing assembly, sometimes unseen from the outside, resulting in ignition and ultimately rapid flame penetration. Information obtained in this study would be useful to evaluate and develop effective counter measures to protect historical structures with thatched roofing assemblies, especially for historical buildings, such as The United Nations Educational, Scientific and Cultural Organization (UNESCO)'s world heritage sites in Japan.

Influence of Board Spacing on Mitigating Wood Decking Assembly Ignition.

As part of recent building code change discussions, it has been suggested that by increasing the spacing of boards, it may be possible to mitigate ignition of wood decking assemblies from wind-driven firebrand showers. An experimental series was undertaken to vary the board spacing from 0 mm (no gaps), 5 mm, and 10 mm, to determine if it was possible to observe reduced ignition propensity of full-scale wood decking assemblies fitted to a reentrant corner wall assembly. In these experiments, three common wood types were used and firebrand showers were directed at the wall/decking assemblies using wind speeds of 8 m/s generated using a realistic-scale wind tunnel. Based on the results of these experiments, it was observed that board spacing significantly influenced ignition propensity of these assemblies. Ignition events were observed for all board spacing considered and in particular, more ignition points were observed for a board spacing of 10 mm.

Summary of Workshop Large Outdoor Fires and the Built Environment.

Large outdoor fires present a risk to the built environment. Wildfires that spread into communities, referred to as Wildland-Urban Interface (WUI) fires, have destroyed communities throughout the world, and are an emerging problem in fire safety science. Other examples are large urban fires including those that have occurred after earthquakes. Research into large outdoor fires, and how to potentially mitigate the loss of structures in such fires, lags other areas of fire safety science research. At the same time, common characteristics between fire spread in WUI fires and urban fires have not been fully exploited. In this paper, an overview of the large outdoor fire risk to the built environment from each region is presented. Critical research needs for this problem in the context offire safety science are provided. The present paper seeks to develop the foundation for an international research needs roadmap to reduce the risk of large outdoor fires to the built environment.

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.

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.

Firebrand Production from Building Components Fitted with Siding Treatments.

Firebrand production from real-scale building components under well-controlled laboratory conditions was investigated. Re-entrant corner assemblies were ignited and during the combustion process, firebrands were collected to determine the size/mass distribution generated from such real-scale building components under varying wind speed. In prior work, a unique ignition methodology was developed to generate firebrands from re-entrant corner assemblies constructed of wood studs and oriented strand board (OSB). In this study, this ignition methodology was applied to re-entrant corners constructed from wood studs/OSB but fitted with actual siding treatments (tar paper and cedar siding) to determine the influence of siding treatments on firebrand generation from wall assemblies. Firebrands were collected with pans filled with water, and then the size and mass of firebrands were measured after drying. The size and mass distributions of firebrands collected in this study were compared with the data from prior component tests as well as the limited studies available in the literature on this topic. Some firebrands were found to be lighter for a given projected area than others, likely produced from cedar siding or tar paper. The effects of applied siding treatments on firebrand production are discussed in detail.

A dimensional analysis on firebrand penetration through a mesh screen.

A dimensional analysis on firebrand penetration through a mesh screen was carried out to correlate the experimental data previously reported in the literature. Three dimensionless variables, one dimensionless time and two dimensionless lengths, were obtained. The resulting dimensionless parameters correlated the data well and may provide a useful framework to assess firebrand penetration through mesh screens, a significant problem associated with the ignition of interior contents of built structures in wildland-urban interface fires.

The Influence of COVID-19 Stay at Home Measures on Fire Statistics Sampled from New York City, London, San Francisco, and Tokyo.

The COVID-19 pandemic kept people at home, in either a voluntary or non-voluntary capacity, in many countries. These suggested countermeasures were prominent in the so-called initial waves of the pandemic, especially from March 2020 to May 2020. As people stayed home, in many cases restaurants were closed. As a result, people spent more time in their kitchen, not only to cook meals but also as a personal hobby. It is well known that cooking fires are a main cause of fires in residential homes. In this study, the change in the number of cooking fires in residential homes as well as the number of residential fires during these COVID-19 countermeasure periods were examined in four cities: New York City (USA), San Francisco (USA), Tokyo (Japan), and London (UK). The time period examined was from January to June in 2020 in order to grasp overall effects of stay-at-home measures on fire incidents. The number of cooking fires and residential fires increased in Tokyo and San Francisco, while the number of cooking fires in New York City (no data was obtained for cooking fires in London.) and the number of residential fires in New York City and London remained similar to previous years.

Effect of three lockdowns in London: Case study for residential fires.

Objectives: The effect of lockdown periods on the number of residential fires was investigated based on three factors: the weekly change in the number of residential fires, the time of the day of residential fires, and the notional cost associated with residential fires. Study design: observational study. Methods: Analysis from Open Data Source. A new index was introduced and the weekly change during the lockdown periods was investigated to accommodate the seasonal differences in the number of residential fires. Results: From the index change, the number of residential fires increased at the beginning of each lockdown period. The timing of residential fires shifted during the day. Conclusions: These changes were associated with meal preparation or mealtimes. Adjustment to lockdowns as the global pandemic dragged on, such as changes to mealtimes, and getting used to lockdown life, are believed to be responsible for these changes.

Firebrands Generated in Shurijo Castle Fire on October 30th, 2019.

A fire started in Shurijo Seiden, or the main hall of Shurijo Castle, Naha-city, Okinawa, Japan on the morning of October 30th, 2019. The fire resulted in loss of 8 structures and many important Okinawan cultural assets. The original Shurijo Castle was destroyed many years ago and a replica was constructed and rebuilt to be as close as possible to the original building. The replica was fabricated mainly from wood (Chamaecyparis taiwanensis). Firebrands were reported during the fire. In this study, firebrands from Shurijo Castle was collected and analyzed. The data was compared with those from other investigation as well as experimental data.

Ignition Vulnerabilities of Combustibles around Houses to Firebrand Showers: Further Comparison of Experiments.

Wildland fires and wildland urban-interface (WUI) fires have become a significant problem in recent years. The mechanisms of home ignition in WUI fires are direct flame contact, thermal radiation, and firebrand attack. Out of these three fire spread factors, firebrands are considered to be a main driving force for rapid fire spread as firebrands can fly far from the fire front and ignite structures. The limited experimental data on firebrand showers limits the ability to design the next generation of communities to resist WUI fires to these types of exposures. The objective of this paper is to summarize, compare, and reconsider the results from previous experiments, to provide new data and insights to prevent home losses from firebrands in WUI fires. Comparison of different combustible materials around homes revealed that wood decking assemblies may be ignited within similar time to mulch under certain conditions.

Toward understanding ignition vulnerabilities to firebrand showers using reduced-scale experiments.

Over the past few years, the large outdoor fire problem has been a growing concern throughout the world. It is recommended to clear the combustibles around homes and within communities to avoid potential loss of properties, as firebrand shower ignition is a dangerous threat. One of the common combustibles around homes is mulching materials. A reduced-scale experimental protocol was developed to study ignition of mulching materials by firebrands and resulting impact to adjunct wall assemblies. Reduced-scale experimental results were compared with full-scale experimental results. Specifically, two trends were of interest in the comparisons. First, the ranking of the ease of ignition for various mulch types from exposure to firebrand showers. Second, if a given mulch type ignited from exposure to firebrand showers, was the resulting mulch bed fire able to ignite the adjacent wall assembly. The reduced-scale experimental results captured some of these trends observed from full-scale experiments but not completely. The findings still suggest that the reduced-scale experiments may give insights into how easily different mulch beds may be ignited by firebrands, as compared to much more costly and time-consuming full-scale experiments. While it is interesting to conduct full-scale experiments, this is very expensive and not always practical, so the authors are devising far cheaper reduced-scale experiments to provide more in-depth scientific understanding of firebrand shower ignition of construction components.

Investigating Coupled Effect of Radiative Heat Flux and Firebrand Showers on Ignition of Fuel Beds.

Fire spread occurs via radiation, flame contact, and firebrands. While firebrand showers are known to be a cause of spot fires which ignite fuels far from the main fire front, in the case of short distance spot fires, radiation from the main fire may play a role for firebrand induced ignition processes. Many past investigations have focused on singular effects on fire spread, and little is known about coupled effects. The coupled effect of radiative heat flux and firebrand showers on ignition processes of fuel beds is studied by using a newly developed experimental protocol. The newly developed protocol includes the addition of a radiant panel to the existing experimental setup of a firebrand generator coupled to a wind facility. Experiments were performed under an applied wind field, as the wind is a key parameter in large outdoor fire spread processes. Results show that radiant heat flux plays an important role for ignition by firebrands under 6 m/s while little effect was observed under 8 m/s.

Experimental study on vulnerabilities of Japanese-style tile roof assemblies to firebrand exposures.

Roof assemblies are known to be vulnerable to firebrands in urban and wildland-urban interface fires. In the 2016 urban fire in Japan (Itoigawa-City Fire), at least 10 structures were ignited by firebrand showers and three of these structures were ignited by firebrand penetration under tile roof assemblies. In this study, the vulnerabilities of Japanese-style roof tile assemblies to firebrand exposures were investigated by using a continuous-feed firebrand generator with applied nominal wind speeds of 6 m/s and 9 m/s. It was observed that Japanese-style roof tile assemblies were more vulnerable than concrete flat, concrete profile, and terracotta flat roof tiles for applied wind speeds of 6 m/s. When the experiments were performed with debris placed underneath the roof tiles, penetrated firebrands ignited debris. Flaming ignition was observed under 9 m/s where flame was observed to protrude from the tiles in an effort to reach necessary oxygen for combustion.

On the Importance of Firebrand Processes in Large Outdoor Fires.

Firebrands are produced from combustion of both vegetative and structural fuels in large outdoor fires. It is well known that firebrand generation, transport, and ignition mechanisms result in rapid and potentially devastating fire spread processes in large outdoor fires. In this article, the basic mechanisms of firebrand generation, transport, and ignition are discussed with an emphasis on how fundamental combustion knowledge may play an important role in this complex problem.