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Three main research topics are reported in this dissertation. This research project focused on estimating the burden of injury on large federal wildland fires and describing the injury characteristics and risk factors for severity of injury in a sample of injured federal wildland firefighters. Chapter 2 "Peak incident management level affects rates of injury on large federal wildland fires" reports estimates of rates of injury for large federal wildland fires and assesses the effect of peak incident management level (PIML) as a predictor of rate of injury. After adjusting for seasonal factors and fire characteristics, PIML was a predictor of both rate of injury and odds of any injury occurrence, but the effect was opposite. Fires with higher PIML demonstrated lower incidence rate ratios, but the odds of injury were increased. Chapter 3 "Wildland fire job assignment and burden of injury" describes the injury characteristics and severity associated with the firefighter's job assignment in fire-related injuries reported to the United States Department of Interior. Job assignment was significantly associated with cause and nature of injury, but not with the severity of injury as defined by days off work or job transfer. Chapter 4 "Cause, characteristics and severity of injuries in wildland firefighters" examines the relationship between the cause of injury and type of injury and the severity of injury. Injuries caused by slips, trips or falls were most frequently reported. Injuries caused by bites or stings and plants were less likely to be severe relative to injuries caused by slips, trips or falls. Together, these studies provide evidence that injuries may significantly impact the wildland fire community, but that better information is needed to fully evaluate risk factors and develop evidence-based interventions.

The wildland fire risk in Arizona is increasing due to shifting land uses, growing residential communities, and changing climate. As the fire hazard increases, land managers and fire educators are faced with educating wildland-urban interface residents about their risk to influence homeowner behavior. To determine how homeowners perceive their risk and what information they use to make decisions about risk and mitigation, this study surveyed residents in previously identified high risk areas in Arizona in three different vegetation types. Results show that ponderosa pine residents are more savvy about their risk and more active in mitigating that risk. Grassland and desert scrub residents consistently report a lower perceived risk to wildland fire than their forest counterparts and perform less mitigation. Results suggest that grassland and desert scrub communities may benefit from the production and dissemination of fire-related materials detailing risk specific to these areas.

Wildland fire is a natural part of the earth’s phenomenological pattern and like most natural phenomena has presented a challenge to human activity and engineering science. Wildfire presents Fire Safety Engineering with the task of developing fundamental research and designing analysis tools to address fire on a scale where interactions with atmospheric and terrestrial conditions dominate fire behavior. The research work presented in this thesis addresses a fundamental research issue involving transport processes in porous wildland fuel beds. This research project had the specific goal of developing an understanding of how transport processes affected the combustion of wildland fuels that were in the form of a porous bed. No detailed study could be found in the literature that specifically addressed how the fuel structure affected the combustion process in these types of fuels. To this end, a series of experiments were designed and carried out that approached the understanding of this problem using commonly available fire testing equipment, specifically the cone calorimeter and the FM Global Fire Propagation Apparatus. The goal of this research study and the basis for the novel and relevant contribution to the field of engineering was to conduct an experimental test series, analyze the data and examine the scalability of the results, to determine the effect of transport processes on the Heat Release Rate (HRR) of porous wildland fuels. The project concluded that flow dominates HRR in fires involving the wildland fuels tested. A dimensionless analysis of the fuel sample baskets showed consistency with well established mass transfer, fluid flow and chemical kinetic relationships. The dimensionless analysis also indicates that the experimental results should be scalable to similar configurations in larger fuel beds. One conclusion of this study was that wildland fire modeling efforts should invest in understanding flow conditions in fuel beds because this behavior dominates over the chemical kinetics of combustion for predicting HRR which is an important parameter in fire modeling.

Wildland fires are a type of vegetation fire that burn in a rural or wild landscape and affect many countries worldwide. They are an important mechanism in ecosystem maintenance, although in certain cases wildland fires can adversely affect both people and the environment. A wildland fire can interact with the surrounding topography, vegetation and weather in a complex manner, which makes microscale prediction of wildland fire behaviour difficult in many situations. This thesis focused on the application of the Weather Research and Forecast (WRF) numerical weather prediction (NWP) and WRF-Fire coupled atmosphere-fire models to investigating aspects of atmospheric interactions with wildland fire. The research covered a wide range of atmospheric scales, from a seasonal mesoscale analysis of fire weather conditions across New Zealand to a microscale analysis of complex atmosphere-fire interactions over idealised terrain. The first study investigated the suitability of WRF modelling of fire weather conditions for the 2009/10 wildland fire season in New Zealand. The WRF model horizontal grid spacing was 8 km and the model output was directly compared with near-surface fire weather conditions meaured and derived at 23 weather stations located throughout New Zealand. The analysis considered the air temperature, relative humidity, wind conditions, rainfall and the New Zealand Fire Weather Index (FWI) and Continuous Haines Index (CHI) on observed high-end fire weather days. WRF typically underpredicted the air temperatures and relative humidities, whereas it typically overpredicted the wind speeds, CHI and the number of high-end fire weather days. WRF was assessed to be unsuitable for accurately modelling particular aspects of fire weather, such as the wind speed and direction, in mountainous terrain and near complex coastlines. Further research is needed to investigate how varying the horizontal resolution in WRF affects the assessed accuracy of modelled fire weather conditions. The second study investigated the behaviour of the Haines Index (HI), CHI and FWI, and their associated atmospheric properties for the 2009/10 wildland fire season in New Zealand. The analysis demonstrated that there was a large degree of spatial variability in fire weather conditions throughout New Zealand, particularly in or near mountainous terrain. The fire weather severity was highest in the eastern South Island and appeared to be closely associated with mesoscale atmospheric processes over mountainous terrain, although the relationship between these atmospheric processes and fire weather condi- tions requires further investigation. The HI and CHI were both limited in their utility at measuring aloft fire weather conditions in high altitude regions. Finally, the fire weather conditions associated with the 36 largest wildland fires of the fire season were evaluated, although no statistical relationships were found between the wildland fire size and either the CHI or FWI. The third study investigated the fire weather conditions across the South Island associated with an extreme foehn event on 6 February 2011. Mountain waves developed in the northwesterly synoptic flow over the Southern Alps and were found to directly influence the fire weather conditions near the surface and aloft in the lee of the mountains. A hydraulic jump along the foothills of the Canterbury Plains resulted in a downslope windstorm with wind speeds exceeding 80 km/h. Further south, large amplitude mountain lee waves directly influenced the near-surface wind speeds and atmospheric stability aloft. The foehn winds were associated with peak air temperatures over 35˚C in the eastern South Island, which are significantly higher than the climatological average. The FWI indicated widespread extreme near-surface fire weather conditions in the lee of the mountains. The subsequent passge of a cold front on 7 February brought a marked reduction in fire weather severity across the South Island. The fourth study investigated atypical wildland fire behaviour on steep leeward slopes through a series of idealised WRF-Fire simulations. The analysis considered both the leeward flow characteristics over a triangular ridge line and the fire spread from an ignition point at the base of the leeward slope. The fire spread was modelled for two different fuel types and with two-way atmosphere-fire coupling both enabled and disabled. The modelled fire spread in the heavy fuel type with coupling enabled closely resembled the fire channelling wildland fire behaviour phenomenon. The initial fire spread was initially dominated by upslope fire spread to the mountain ridge line at an average rate of around 2.0 km/h. This was followed by a phase of intermittent rapid lateral fire spread close to the ridge line at a maximum rate of around 3.6 km/h. The intermittent rapid lateral fire spread was driven by strongly circulating horizontal near-surface winds that were associated with updraft-downdraft interfaces. These updraft-downdraft interfaces formed due to an interaction between the strong pyro-convection and terrain-modified winds. The presented research collectively demonstrated the versatility and effectiveness of NWP and coupled atmosphere-fire modelling for studying various aspects of atmospheric interactions with wildland fire. The research further highlighted the effects of atmospheric processes over complex terrain on fire weather conditions and wildland fire behaviour. Although three of the studies in the thesis had a regional focus on New Zealand, the research outcomes should benefit end users in fire management worldwide.

Wildfires pose a growing threat for communities along the wildland-urban interface (WUI) around the world driven by a changing climate and expanding urban areas. One of the primary mechanisms by which fires can spread in the WUI are firebrands, airborne embers capable of acting as ignition sources carried in the airstream. Many studies have been conducted on the generation and transport of firebrands, but limited work has been conducted to quantify the heat transfer of firebrand piles to surfaces. A series of three studies are presented here exploring the heat transfer, burning, and material ignition of firebrands. In the first study, the differences between firebrands from structure and vegetation sources was compared. It was found that an ash layer in the vegetation firebrands reduced the heat and mass transfer. In the second study, impact of the surface geometries that firebrands accumulate on was explored. It was found that wall and corner configurations reduced the heat transfer the most and caused piles to burn from the wall surfaces outwards. Flat plate and decking configurations had the highest heat flux due to the lack of flow obstruction. In the final study, a framework was developed for predicting the material ignition resistance reliability exposed to a smoldering firebrand pile. The exposure was based on empirical relations for the heat flux from piles as a function of pile height, porosity, and wind speed. Cone calorimeter data was used to generate material thermal and ignition properties. With these inputs, the framework was used to predict the potential for material ignition thus circumventing the need for costly firebrand tests. This collection of studies provides evidence of the factors that drive firebrand burning behavior and heat transfer and links those aspects to the potential for ignition of construction materials. / Doctor of Philosophy / Wildland-urban interface (WUI) fires pose a growing threat for communities around the world driven by a changing climate and expanding urban areas. A particularly dangerous way that fires can spread long distances is via firebrands, burning particles that splinter off of trees or buildings that can be blown long distances by the wind. These firebrands can land onto surfaces like buildings and ignite those surfaces, causing new fires called spot fires. The science behind how firebrands ignite new surfaces is not well-developed, and there is no broad tool that can be used to predict whether a material or a building will ignite given certain conditions. The research presented here aims to address that lack of understanding by approaching the problem systematically, breaking down the individual driving elements of firebrand burning. First, the difference in heat transfer and burning behavior between firebrands from structures and from vegetation was explored. Second, the impact of various surface geometries was explored. The surface geometry of where the firebrands accumulate also influences the heat transfer of the firebrands. Finally, a framework for predicting the material reliability of materials to firebrand exposure is presented. Experimental correlations for firebrand burning based on pile parameters were generated and used to predict the heat fluxes from piles. The framework used material ignition data from cone calorimeter experiments to predict how materials would respond under thermal exposure. The framework compares the predicted exposure with the material ignition data to calculate the reliability. This collection of studies provides insight on the many factors that drive firebrand burning behavior and heat transfer and links those aspects to the ignition of materials.

Wildfire can be an extremely destructive force, especially when it reaches our nation's ever-increasing wildland-urban interface (WUI) area. To address this issue, state and federal agencies and cooperative education programs have begun to promote homeowner responsibility and wildfire vulnerability minimization practices as a means for WUI residents to take a proactive approach to protecting their homes from wildfire. This research provides resource managers with a new understanding of the processes through which WUI residents receive, interpret, and reconstruct wildfire messages, which will allow them to better assess their wildfire education programs. Results from this study suggest that WUI residents negotiate meanings for wildfire messages by externalizing and/or internalizing the hazard and its solution, and that these interpretations are strongly related to residents' behavioral response. This study also reveals significant discrepancies between WUI residents' central values and program goals; whereas fire programs generally highlight risk to homes and structures in the WUI, residents were typically far more concerned with their homes' contents and the environments within which their homes are situated. The insights provided by this study will increase program managers' ability to remedy these discrepancies and improve the effectiveness of wildfire vulnerability minimization programs and messages. / Master of Science

Due to continued outward expansion of industry and community development into the wildland-urban interface (WUI), the threat to life safety and property from wildland fires has become a significant problem. Such fire scenarios can be better understood through the use of computation fluid dynamics based fire-spread models. However, current physical fire models must be specifically adapted to handle the phenomena associated with WUI fires. Only then can they be reliably used as research and decision making tools to help mitigate the problem. In this research, the current standard in wildland fire modeling for representing the effect on wind flow from a porous vegetative medium is examined. The technique used employs basic correlations for object drag, and its validity with respect to real vegetation has yet to be examined in detail by the scientific community. The modeling of vegetation is studied within the framework of the existing Wildland-Urban Interface Fire Dynamics Simulator (WFDS), and the potential need for continued development is assessed. Comparisons are made to both experimental and numerical studies. Additionally, the validity of the model is considered at both the scale of an individual tree, as well as that of a whole forest canopy. Results show that as a first approximation the model is able to perform well in the latter case. At the scale of an individual tree, however, the behavior is governed by theoretical constants. The assumption of cylindrical vegetation elements performs slightly better than the commonly used spherical case, but neither adequately captures experimental tendencies. Accurate flow representation for single trees is crucial to modeling the key driving factors of fire behavior (such as combustion and heat transfer) in small scale WUI scenarios. Ultimately, this study illustrates the need for well-designed experiments, specifically to generate empirical constants which will improve the behavior of the simplified theory.

"The Wildland/Urban Interface, in which homes are intermingled with forested areas, presents unique challenges to fire protection and fire prediction, owing to the different fuel loads, conditions, and terrain. Computer models that predict fire spread through such an area require data for multiple scales, from crown fire spread to the heat release rates and ignition conditions for individual trees, as well as an understanding of fire behavior and spread. This discussion investigates a means by which fire behavior for Douglas-fir trees can be determined from quantifiable characteristics, such as height and moisture content. Mass, flame height, peak heat release rate, and total energy can be estimated from these simple measurements. A time scale of 60 seconds, combined with a peak heat release rate estimated from tree size characteristics, provides an approximation of total energy that is within 11% of measured values. Pre-heating of trees with a low (2.5 kW/m2) radiant heat flux did not have a noticeable impact on the resulting heat release rate. In addition, fire spread between trees was highly dependent on the presence of ambient wind; in the absence of wind or wind-borne embers, the trees were very resistant to ignition even when in close proximity (3 spacing). With the addition of wind, the fire would spread, although the heat release rates were dramatically reduced for trees of sufficiently high moisture content (< 70%)."

Ecological sites and state-transition models (STMs) have become the preferred means of summarizing plant community dynamics on distinctive types of rangeland. Ecological sites classify rangeland types based on soil-geomorphic and climatic conditions capable of producing a known plant community, while a STM depicts the vegetation dynamics of an ecological site. STMs are usually based on expert opinion rather than site-specific data; however, if they are to gain credibility, STMs must accurately describe the processes that drive plant community dynamics. This study examined three ways of developing process-based STMs using three levels of commonly collected field data. We began by taking field inventories of three ecological sites already mapped in northwestern Utah: Loamy Bottom, Mountain Gravelly Loam, and Upland Loam. The Loamy Bottom site was ideal for developing a data-rich, process-based STM because 1) the site concepts were well-defined, 2) the site was easy to recognize, 3) potential states and transitions had already been hypothesized, and 4) the site was easily accessible. The Loamy Bottom study was designed to link plant community structural indicators to measurable indicators of ecological process. Principal components analysis and cluster analysis were used to classify 14 study plots into four distinct states. Simple linear regression showed relationships between perennial grass cover, perennial canopy gaps, and soil organic carbon. Analysis of variance (ANOVA) linked four general vegetation classes to soil stability measurements. The resulting STM describes the structure and function of four alternative states. The other two STMs, developed for the Mountain Gravelly Loam and Upland Loam ecological sites, used less-intensive data collection methods. Rangeland health assessments, used for the Upland Loam STM, are useful for refining initial ecological site and STM concepts, documenting states, hypothesizing transitions, and locating study locations for future research. Quantitative production and cover estimates, used for the Mountain Gravelly Loam STM, are useful for describing the structure of states, but structural indicators must be coupled with process measurements, as with the Loamy Bottom STM to understand the drivers of state change. A coordinated data collection effort is needed to produce STMs that accurately depict the plant community dynamics of ecological sites.