A Review of Pathways for Building Fire Spread in the Wildland Urban Interface Part II: Response of Components and Systems and Mitigation Strategies in the United States

Structure loss in wildland fires has significantly increased over the past few decades, affected by increased development in rural areas, changing fuel management policies, and climate change, all of which are projected to increase in the future. This paper is Part II of a two-part review, which presents a summary of fundamental and applied research on pathways to fire spread in the wildland urban interface. Part I discussed the fundamentals of wildland fire spread via radiative heat transfer, direct flame contact, and firebrand exposure. Here in Part II, we cover the response of building components and systems, as well as mitigation strategies used to prevent fire spread into and within communities in the United States. Post-fire investigations, full-scale structural testing, individual component testing, and combined systems or assembly testing have been used to identify building component and system vulnerabilities such as roofs, vents, siding, decks, fences, and mulch. Using results from these tests and investigations at different scales, some knowledge has been gained on specific vulnerabilities and the effectiveness of mitigation strategies, but a quantitative framework has not yet been established. On a community level, the layout of structures and the space between them has been shown to be incredibly important in mitigating wildfire risk. More locally, defensible space around homes has been effective in mitigating exposure from both radiation and direct flame contact. Firebrands still remain a challenge; however, many design recommendations have been proposed to harden structures against firebrand exposures. Recommendations for future research and development are also presented.     

Geographic information systems: Providing information for wildland fire planning

Controlling wildfires within the wildland/urban interface has proven to be the most complex challenge facing wildland fire agencies. Although program improvements to increase the efficiency of interface suppression efforts have been suggested, the availability of information about the wildfire environment remains a critical resource for wildland fire planning. Geographic Information Systems (GISs) can provide the technology to store, manipulate, analyze, and display spatially oriented information in a form necessary for efficient fire planning and incident decision making. Complex map and attribute information, including vegetation types, fuels models, weather patterns, topography, fire suppression environment, landuse characteristics, and microenvironmental features, can be rapidly summarized and integrated. This integrated information can be used to create unique polygons useful in predicting fire behavior, allocating fire suppression resources, and as an aid in planning land use. Simplified user interfaces and the portability of new hardware systems will allow GISs to be used at every level of wildland fire planning.     

Review of Pathways for Building Fire Spread in the Wildland Urban Interface Part I: Exposure Conditions

While the wildland–urban interface (WUI) is not a new concept, fires in WUI communities have rapidly expanded in frequency and severity over the past few decades. The number of structures lost per year has increased significantly, due in part to increased development in rural areas, fuel management policies, and climate change, all of which are projected to increase in the future. This two-part review presents an overview of research on the pathways for fire spread in the WUI. Recent involvement of the fire science community in WUI fire research has led to some great advances in knowledge; however, much work is left to be done. While the general pathways for fire spread in the WUI (radiative, flame, and ember exposure) are known, the exposure conditions generated by surrounding wildland fuels, nearby structures or other system-wide factors, and the subsequent response of WUI structures and communities are not well known or well understood. This first part of the review covers the current state of the WUI and existing knowledge on exposure conditions. Recommendations for future research and development are also presented for each part of the review.     

The effect of flow and geometry on concurrent flame spread

Flame spread is an important parameter used in the evaluation of hazards for fire safety applications. The problem of understanding and modeling flame spread has been approached before, however new developments continue to challenge our current view of the subject, necessitating future research efforts in the field. In this review, the problem of flame spread will be revisited, with a particular emphasis on the effect of flow and geometry on concurrent flame spread over solid fuels. The majority of this research is based on that of the senior author, who has worked on wind-driven flame spread, inclined fire spread, flame spread through discrete fuels and the particular problem of wildland fires, where all of the above scenarios play an important role. Recent developments in these areas have improved our understanding of flame-spread processes and will be reviewed, and areas for future research will be highlighted.     

Wildland fire modeling with an Eulerian level set method and automated calibration

This paper presents the mathematical development of a geospatial model for simulating wildland fire spread. The Eulerian level set method (LSM), a mathematical technique that tracks interfaces between separate regions on a regular grid, is applied here to track the interface between burned (or burning) areas and green areas. Model physics include surface fire spread rate and direction, transition from surface fire to passive or active crown fire, ember lofting, trajectory tracking, and spot fire formation, acceleration from point ignitions, and modifications to fuel strata attributed to suppression activities. A novel aspect of this work involves application of a stochastic optimization algorithm to automatically calibrate baseline model inputs by comparing calculated fire perimeters to observed (target) fire perimeters. The wildland fire model and associated automated calibration technique are assessed by simulating the first 22 h of progression of the 2007 Moonlight Fire in Northern California. Fuels and topography inputs are obtained from the Landfire project while wind and weather inputs are obtained from high resolution numerical weather prediction. Fire areas simulated with the calibrated model agree well with target perimeters.     

Wildland fire spot ignition by sparks and firebrands

Wildland and Wildland Urban Interface (WUI) fires are an important problem in many areas of the world and may have major consequences in terms of safety, air quality, and damage to buildings, infrastructure, and the ecosystem. It is expected that with climate changes the wildland fire and WUI fire problem will only intensify. The spot fire ignition of a wildland fire by hot (solid, molten or burning) metal fragments/sparks and firebrands (flaming or glowing embers) is an important fire ignition pathway by which wildfires, WUI fires, and fires in industrial settings are started and may propagate. There are numerous cases reported of wildfires started by hot metal particles from clashing power-lines, or generated by machines, grinding and welding. Once the wildfire or structural fire has been ignited and grows, it can spread rapidly through ember spotting, where pieces of burning material (e.g. branches, bark, building materials, etc.) are lofted by the plume of the fire and then transported forward by the wind landing where they can start spot fires downwind. The spot fire problem can be separated in several individual processes: the generation of the particles (metal or firebrand) and their thermochemical state; their flight by plume lofting and wind drag and the particle thermo-chemical change during the flight; the onset of ignition (smoldering or flaming) of the fuel after the particle lands on the fuel; and finally, the sustained ignition and burning of the combustible material. Here an attempt has been made to summarize the state of the art of the wildfire spotting problem by describing the distinct individual processes involved in the problem and by discussing their know-how status. Emphasis is given to those areas that the author is more familiar with, due to his work on the subject. By characterizing these distinct individual processes, it is possible to attain the required information to develop predictive, physics-base wildfire spotting models. Such spotting models, together with topographical maps and wind models, could be added to existing flame spread models to improve the predictive capabilities of landscape-scale wildland fire spread models. These enhanced wildland fire spread models would provide land managers and government agencies with better tools to prescribe preventive measures and fuels treatments before a fire, and allocate suppression resources and issue evacuation orders during a fire.     

Findings of the International Road Tunnel Fire Detection Research Project

Fire detection systems are essential fire protection elements for road tunnels to detect fires, activate safety systems and direct evacuation and firefighting. However, information on the performance of these systems is limited and guidelines for application of tunnel fire detection systems are not fully developed. The National Research Council of Canada and the Fire Protection Research Foundation, with support of government organizations, industries and private sector organizations, have completed a research project to investigate current fire detection technologies for road tunnel protection. The project included studies on the detection performance of current fire detection technologies with both laboratory and field fire tests combined with computer modelling studies. This paper provides an overview of the findings of the project. Fire detectors, fire scenarios and test protocols used in the test program are described. A summary of the research results of the series of full-scale fire tests conducted in a laboratory tunnel facility and in an operating road tunnel as well as of the computer modelling activities will be reported.     

Enticing Arsonists with Broken Windows and Social Disorder

In criminology, it is well understood that indicators of urban decay, such as abandoned buildings littered with broken windows, provide criminals with signals identifying neighborhoods with lower crime detection and apprehension rates than better maintained neighborhoods. Whether it is the resident population’s sense of apathy, lack of civic pride, or fear of confrontation that causes criminals to perceive an easy mark, it nevertheless emboldens them to strike. Previous research of wildland arson hints that broken windows (e.g., areas of criminal activity) are partly responsible for arson outbreaks within the wildland–urban interface. We model the incidence of wildland and non-wildland arson ignitions in Michigan from 2001 to 2005 as a function of constructed Broken Windows indices. Our results suggest that crime prevention and urban revitalization programs may be as valuable as fire suppression, fuels management, and law enforcement in limiting incidence and the damage from both wildland and non-wildland arson.     

A Wildland–Urban Interface Typology for Forest Fire Risk Management in Mediterranean Areas

The transitional areas that lie between wildlands and urbanized spaces, generally defined as wildland–urban interfaces (WUI), represent an increasing risk factor in Mediterranean areas; these define a new scenario in forest fire fighting and prevention. We have developed a methodological approach in order to assess the hazard and vulnerability of WUI which is based on landscape analysis, on the use of Geographic Information Systems (GIS) techniques and remote sensing. Unlike traditional approaches which are based on local scale characterization of WUI, we propose a progressive multi-scale approach. In order to reach an operative classification of the WUI the methodology was developed in three stages: a regional urban development model, a landscape character assessment and finally, a WUI typology. The last WUI typology has been based on the identification of different urban morphologies and their context within the type of landscape in which they occur.     

Mapping areas at elevated risk of large-scale structure loss using Monte Carlo simulation and wildland fire modeling

This work presents, and demonstrates through application to California, a data-driven methodology that can be used to identify areas at elevated risk of experiencing wildland fires capable of causing large-scale structure loss. A 2D Eulerian level set fire spread model is used as the computational engine for Monte Carlo simulation with ignition points placed randomly across the landscape. For each randomly-placed ignition point, wind and weather conditions are also selected randomly from a 10-year climatology that has been developed by others using the Weather Research and Forecasting (WRF) mesoscale weather model at a resolution of 2 km. Fuel and topography inputs are obtained from LANDFIRE. Housing density is estimated from 2010 Census block data. For each randomly-selected combination of ignition location and wind/weather, fire progression is modeled so that fire area and number of impacted structures can be recorded. This is repeated for over 100 million discrete ignition points across California to generate “heat maps” of fire probability, fire consequence, and fire risk. In this work, fire volume (spatial integral of burned area and flame length) is used as a proxy for fire probability since quickly spreading fires with large flame lengths are most likely to escape initial attack and become extended attack fires. Fire consequence is taken as the number of impacted structures. Fire risk is then estimated as the product of probability and consequence. The methodology is assessed comparing the resultant fire risk raster with perimeters from California's 20 most damaging fires as tabulated by the California Department of Forestry and Fire Protection (CALFIRE). It is found that these historical perimeters from damaging fires correlate well with areas identified as high risk in the Monte Carlo simulation, suggesting that this methodology may be capable of identifying areas where similarly damaging fires may occur in the future.     

An integrated approach for tactical monitoring and data-driven spread forecasting of wildfires

In recent times there have been increasing efforts to integrate technology into wildfire management, especially in the fields of tactical monitoring and simulation. On the one hand, thermal infrared imaging (TIR) systems have been installed aboard surveillance aircraft including unmanned systems (UAS). On the other, there exists a variety of models and simulators able to forecast the fire spread. However, both fields currently present significant limitations. While relevant information is still extracted manually from aerial thermal imagery and is most times merely qualitative, simulators’ accuracy on fire spread prediction has proved insufficient. To solve these issues, this article presents a twofold methodology to couple meaningful automated wildfire monitoring with accurate fire spread forecasting. The main goals are to, firstly, automatically process aerial TIR imagery so that valuable information can be produced in real time during the event and, secondly, use this information to adjust a Rothermel-based simulator in order to improve its accuracy on-line. The fire perimeter location is tracked automatically through an unsupervised edge detector. Afterwards, an assimilation module uses the remotely sensed data to optimise the simulator's fuel and wind parameters, which are assumed to remain constant for a certain period of time. Subsequently, the optimum parameters’ values are used to issue a fire evolution forecast. All outputs are projected onto the corresponding Digital Terrain Model (DTM) and integrated into a Geographic Information System (GIS) for visualization. The global system was validated using two large-scale experiments. If these algorithms can be applied to a sufficiently rich and varied set of experimental data and further developed to cope with more complex scenarios, they could eventually be incorporated into a fire management decision support system.     

Fire Detection in Computer Facilities: 25 Years On

Computer centres have developed considerably over the past 25 years as data processing and use of information technology has transformed government, businesses and society. So-called data centres have become critical to business continuity. At the same time, new forms of smoke detection have been developed as part of an integrated approach to overall fire protection of these mission critical facilities. Research has provided the fire engineering tools and data to allow improved methods of determining smoke detector activation times, even for small fires in higher airflow environments. Nevertheless, there are further areas of research needed, particularly in the areas of modelling, specific materials data and more experimental results from large-scale computer facility fire tests.     

Modelling of two-dimensional flame spread across a sloping fuel bed

A significant contributing factor to wildland fire development is the slope effect which causes the fire spread rate to increase considerably as compared to horizontal spread. This leads to difficulties in determining the development of the fires hence in coordinating forest fighting efforts. In the present study, a two-dimensional non-stationary model for a fire spreading across a sloping fuel bed made up of Pinus pinaster litter is described. Based on a series of hypotheses, we first defined a medium equivalent to the pine needle litter for which we provided a thermal balance. By coupling this balance to a diffusion flame model we obtained the fire spread model numerically solved by means of the SIMPLEC procedure. The fire spread rates given by the simulations were then compared to experimental results generated by small-scale laboratory fires for a range of slope values. Predicted flow field structure, and temperature field are also discussed.     

Parametric study of urban fire spread using an urban fire simulation model with fire department suppression

Although urban conflagrations are rare now, the threat still exists in two situations—following an earthquake and when a wildland fire reaches an urban area. In this paper, we first extend a previously developed urban fire simulation model to include fire department suppression, making it a complete, integrated ignition-spread-suppression model that can now better estimate urban fire risk and help understand the effectiveness of fire department efforts. We then apply this Urban Fire Simulation model (UFS2) to a case study area in California and conduct a parametric study to examine the key factors that influence fire spread and the interactions among them. The results suggest that urban fire spread is highly variable and under the right combination of unlucky but possible circumstances—many ignitions, high wind speeds, and limited water availability—the losses can be very high, much higher than observed in recent earthquakes. In addition to the three factors mentioned, the locations of the ignitions (relative to wind direction and fire breaks), number of engines, and engine arrival times are shown to be important. Strong interactions are evident between wind speed and number of ignitions, and between water availability and number of engines.     

Instrumentation of wildland fire: Characterisation of a fire spreading through a Mediterranean shrub

Although considerable progress has been made recently in the modelling of the spreading of a forest fire, there remains a lack of reliable field measurements of thermodynamic quantities. We propose in this paper a method and a set of measuring structures built in order to improve the knowledge of the fundamental physical mechanisms that control the propagation of wildland fires. These experimental devices are designed to determine: the fire front shape, its rate of spread, the amount of energy impinging ahead of it, the vertical distribution of the temperature within the fire plume as well as the wind velocity and direction. The methodology proposed was applied to a fire spreading across the Corsican scrub on a test site. The recorded data allowed us to reconstruct the fire behaviour and provide its main properties. Wind and vegetation effects on fire behaviour were particularly addressed.     

A Method for Assessing the Risk of Zebra Mussel Dreissena Polymorpha Infestation in Industrial Fire Protection Systems

Though zebra mussels, first discovered in the Great Lakes in 1988, have frequently been detected in fire protection systems, the potential for large-scale infestations and blockage has not been established. It is clear, however, that even small numbers of mussels can cause problems in areas with small-diameter piping or in sprinkler system spray heads or nozzles. A method developed to determine the risk of mussel infestation within fire protection systems was implemented without interfering with system operation. The complexity of fire protection systems makes it useful to determine low-risk areas where remediation is not necessary, as well as high-risk areas where infestation is likely, allowing treatment at a greatly reduced effort, cost, and impairment of these protection systems.A method was developed to sample representative oxygen levels in fire protection water systems in areas within Niagara Mohawk's Dunkirk Steam Station, while maintaining system pressure and operability. The systems were then assessed in terms of low risk (0 to 2 ppm), medium risk (2 to 4 ppm), and high risk (more than 4 ppm) based on criteria previously developed in the laboratory. Based on the findings presented in this paper, specific high-risk areas within Dunkirk Steam Station were later treated experimentally, and long-term strategies to eliminate and control mussels in the fire protection water were established. These methodologies may be useful in assessing other sites.     

A DIY Thermocouple Datalogger is Suitably Comparable to a Commercial System for Wildland Fire Research

Fire Technology - Thermocouple probes have long been standard equipment for wildland fire scientists. But despite substantial advancements in the electronic datalogger technology necessary to read...     

Modeling wildfire potential in residential parcels: A case study of the north-central Colorado Front Range

This study evaluated if present-day wildfire potential (i.e. potential fireline intensity and percentage crown fire) differs for residential parcels developed at different time periods in the north–central Colorado Front Range. To answer this question, a model of wildfire potential was built based on 2001 fuels and vegetation and compared the output to actual fire severity of the 2002 Hayman and 2004 Picnic Rock fires (measured by satellite imagery). Except for low-load fuel types such as grass, the modeled wildfire potential corresponded well to observed fire severity. Wildfire potential was then evaluated within 7 classes: developed (1880–1944, 1945–1959, 1960–1974, 1975–1989, 1990–2005) and undeveloped (either zoned or not zoned for development). The results suggest that there is one class characterized by relatively low wildfire potential (developed 1880–1944) and three classes characterized by relatively high wildfire potential (developed 1960–1974 and the two undeveloped parcel classes). These results hold both for 99th percentile (extreme) and 50th percentile (average) fuel conditions. The results suggest that under current zoning regulations, future structures are likely to be built on parcels that, on average, have somewhat higher potential fireline intensity and higher percentage of crown fire compared to currently developed parcels. However, the location of future development may be influenced by forest changes, such as the visual degradation and perceived fire hazard of trees killed by the continuing mountain pine beetle outbreak. Overall, this study introduces an improved method for quantifying wildfire potential in the rapidly developing wildland–urban interface that could be applied to other areas.     

Ignition of Combustible Fuel Beds by Hot Particles: An Experimental and Theoretical Study

The process of spotting occurs in wildland fires when fire-lofted embers or hot particles land downwind, leading to ignition of new, discrete fires. This common mechanism of wildland fire propagation can result in rapid spread of the fire, potentially causing property damage and increased risk to life safety of both fire fighters and civilians. Despite the increasing frequency and losses in wildland fires, there has been relatively little research on ignition of fuel beds by embers and hot particles. In this work, an experimental and theoretical study of ignition of homogeneous cellulose fuel beds by hot metal particles is undertaken. This type of well-characterized laboratory fuel provides a more controllable fuel bed than natural fuels, and the use of hot metal particles simplifies interpretation of the experiments by reducing uncertainty due to unknown effects of the ember combustion reaction. Spherical steel particles with diameters in the range from 0.8 mm to 19.1 mm heated to temperatures between 500°C and 1300°C are used in the experiments. A relationship between the size of the particle and temperature required for flaming or smoldering ignition is found. These results are used to assess a simplified analysis based on hot-spot ignition theory to determine the particle size-temperature relationship required for ignition of a cellulose fuel bed.     

Protecting Lives and Property in the Wildland–Urban Interface: Communities in Montana and Southern California Adopt Australian Paradigm

Threats to people and property in the wildland–urban interface have taken on global proportions. It is becoming increasingly rare to have a wildland fire incident that does not involve people and their homes. In addition to Australia and North America, people have died in interface fires in Europe, Africa, and Asia, including 212 people who died in the devastating forest fires in northeastern China in May 1987. The prevailing interface model is one that attempts to evacuate people away from fire areas to get them out of harm’s way. This traditional approach in the U.S. has been preferred by law enforcement agencies and fire services. The problem with this model is that evacuation warnings are often late to non-existent, leading to the deaths of interface residents entrapped by fires on highways as they try to escape. For example, 16 people suffered lethal burns when the 2003 Cedar and Paradise Fires in California overran them as they were trying to evacuate. Two communities in the United States have adopted variations of the Australian model of Prepare, Go Early, or Stay and Defend (P/GE/SD). Officials in the Painted Rocks Fire District, Montana, and Rancho Santa Fe, California, were interviewed to determine how the Australian model was being implemented. Two of the authors have firsthand experience with these two case examples. P/GE/SD has been tested successfully at both locations. The Australian model, however, is under review following the Black Saturday fires of February 2009 in Victoria, Australia. The objective of this paper is to present specific ideas that can be used to reform and improve fire policy, planning, and performance in the Wildland–Urban Interface in the United States.