Browsing by Subject "Fire"
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Item An analysis of terrain roughness: Generating a GIS application for prescribed burning(2008-05) Crawford, Matthew Allan; Fish, Ernest B.; Britton, Carlton M.; Mulligan, KevinPrescribed burning is a technique used to rejuvenate pastures by enhancing wildlife habitat, brush control, and removing old growth. The technique has become a science and has been in practice for decades to model naturally occurring fire regimes. Planning a prescribed burn is a detailed and careful formula that requires a great deal of time and preparation. This study presents a procedure that will greatly reduce the amount of time and money spent in planning a burn. Fire lines are typically located along pasture fences for prescribed burning in Texas. In rough, hilly terrain this results in fire lines traversing steep slopes and deep canyons that greatly increase expense and pose hazardous conditions for personnel. By combining the power of technology with the knowledge of a burn expert, an innovative approach to fire line location may possibly be developed, using existing programs to build a model that predicts the smoothest and most suitable path for fire lines. In order to accomplish this task, several steps were taken. First, an application was found that provides the desired algorithm to calculate a roughness surface from a digital elevation model. The roughness surface is then classified by a newly suggested classification index. An application has been developed to use the roughness surface to obtain isoline locations for the burn area. The Rocker Ranch which is located on the edge of the Llano Estacado escarpment in Borden County, Texas provided an excellent area for testing the model. The fire lines are based on the isolines which represent the smoothest route, within the designated area. This application will optimize the fire line planning process for prescribed burning by saving time and money.Item Analysis of thermally induced forces in steel columns subjected to fire(2010-08) Ho, Chung Thi Thu; Engelhardt, Michael D.; Helwig, Todd A.The effects that thermally induced forces and deformations have on the performance and safety of steel columns subjected to fire are not well understood and are not clearly treated in building codes and standards. This thesis investigates the behavior of steel columns subjected to fire, with an emphasis on studying the significance of thermally induced forces and deformations. The approach used in this research is to conduct a series of analyses of steel columns using the finite element computer program ABAQUS. Columns are modeled in ABAQUS using beam elements that include nonlinear geometry, nonlinear temperature dependent material properties, and initial geometric imperfections. Using the ABAQUS model, a series of analyses are conducted on the behavior of columns under axial compression for temperatures varying from room temperature up to 2400° F. A series of individual columns are analyzed with and without restraint to thermal expansion. A column that is part of a truss is also analyzed to study a simple case of a flexible restraint to thermal expansion. Finally, the behavior of columns that are part of multi-story steel moment frames are investigated. All of the analyses conducted in this research indicate that forces generated by restraint to thermal expansion can have a very large impact on the performance of a steel column in fire. When evaluating the safety of a column in a fire, it is important to recognize that the total axial force in the column is the sum of the force generated by external gravity load on the frame and the force generated by restraint to thermal expansion. The force generated by restrained thermal expansion can be very large, and neglecting this force can lead to unsafe designs.Item Behavior of the shear studs in composite beams at elevated temperatures(2015-12) Dara, Sepehr; Engelhardt, Michael D.; Helwig, Todd A; Williamson, Eric B; Ghannoum, Wassim M; Ezekoye, Ofodike AIn order to improve the fire safety and at the same time to provide more economical design of composite floors in fire, it is important to understand the behavior of these systems under fire exposure. An important step needed to reach this goal is to better understand the behavior of shear studs in composite beams at elevated temperatures, which was the focus of this research study. Typically, corrugated metal decks are used in construction of composite beams. These decks act as formwork and provide reinforcement for the concrete. For this study, however, the corrugated deck was not included. Rather, this study focused on cases where there is a solid concrete slab over the steel beam. The purpose of this limitation was to first gain a thorough understanding of shear stud behavior under fire exposure for this simpler configuration. This study on shear stud behavior at elevated temperature in solid slabs included both experiments and numerical simulations. The objective of the experimental test was to develop additional data on the load-slip behavior of shear studs in solid concrete slabs at elevated temperatures, and to compare the measured shear stud strength values with the limited test data and code provisions available in the literature. Two different specimen heating scenarios were introduced. One was meant to result in a temperature gradient in the specimen to simulate a fire condition. The other scenario was meant to result in a uniform temperature throughout the specimen for comparison purposes with the other scenario. One of the conclusions was that the shear stud strength and initial stiffness in the shear stud load-slip behavior have strong correlations with bottom of stud temperature, regardless of the heating scenario. Therefore, choosing the bottom of stud temperature as a reference temperature in predicting the shear stud ultimate strength and initial stiffness is reasonable. The objective of the numerical simulations was to develop a finite element (FE) model which can predict the thermal and mechanical behavior of shear studs in solid concrete slabs at elevated temperatures, and to validate the model against the experimental data. Different aspects of modeling the specimen using the general purpose finite element software, Abaqus, were discussed. Results of the analyses were compared with the experimental results of this study. Temperatures resulting from the heat-transfer analysis were found to be in a good agreement with experimental results at some locations in the specimen. However, at some other locations the difference between the experimental and FE results were more than 100 ºC. The existing level of uncertainty in the input data highly contributes to the errors in the temperature results, and emphasizes the difficulty that exists in heat transfer modeling. The load-slip curves found from FE analysis were presented for all the tests. The ultimate strength and the initial stiffness of the specimens were predicted well by the FE analyses. However, the slip capacity did not match between the experiments and FE analyses. Several parametric studies using the finite element model were conducted to investigate the sensitivity of the analysis results to various model parameters, both for heat transfer analysis and structural response analysis. The studied parameters included thermal conductivity of concrete, convective heat transfer coefficient, resultant emissivity, thermal joint conductance coefficient, Concrete Damaged Plasticity model parameters, steel stress-strain curves recommended by two different code provisions, and concrete tensile strength. The current gaps in our knowledge about these parameters were discussed.Item Burning season effect on four southern Chihuahuan desert plants(Texas Tech University, 2009-05) Luna, Miguel; Britton, Carlton M.Use of prescribed fire to manage undesirable vegetation in the Chihuahuan Desert of Mexico, promises acceptable results, but information on plants responses to different weather conditions and fuel load availabilities is lacking in Mexico. This study investigated the effect of three burning seasons with two fuel load simulations and two plants size on plant mortality and changes in basal area of four native species of southern Chihuahuan Desert. The study was conducted in the Mexican High Plateau in Jalisco, Mexico during two consecutive years, 2005 and 2006, in a shortgrass prairie of blue grama (Bouteloua gracilis) with problematical populations of broomweed (Isocoma venetus), brickellbush (Brickellia spinulosa) and broomgrass (Muhlembergia rigida). Fire environment was simulated using a portable propane burner calibrated to simulate time-temperature reached with 1,700 and 2,800 kg/ha fine fuel load. Size of plant was determined by height and canopy diameter in shrubs, and indicial area diameter in grasses. Shrubs with a minimum height of 25 cm and canopy diameter of 31 cm were classed as large plants. Grasses with a basal area diameter of 10 cm were classed as large plants. Plants with measurements less than these were placed in the small plant group. For each species, 50 plants were randomly treated each season at each fuel load and plant size. Plants were identified with numbered tags to evaluate mortality and basal area changes in subsequent growing season. As control, 50 plant of each species and size received no fire treatment. Plants with no live tillers one year after treatment were assumed to be dead. Basal area change was estimated based in number of pixels/cm2, using vertical photos and the Adobe Photoshop Software. Statistical analysis was performed with the GLM procedure in SAS. Mortality of blue grama plants was affected significantly by season of burning, fuel load simulation, and plant size (P<0.05). Small blue grama plants were significantly (P<0.05) more affected than large plants, mainly after spring and summer burns. Mortality of broomgrass muhly was slightly affected by burning treatments in either evaluation year, with average mortality of 1% and 2% for 2005 and 2006. Brickellbush mortality was significantly affected by burning season (P<0.05), and plant size (P<0.05). Spring and winter burns were the most detrimental seasons for small brickellbush plants. Broomweed plants were severely affected (P<0.05) by all burn treatments, regardless of fuel load simulation and plant size, with 82% average mortality. Spring and summer burning with high fuel load simulations reduced basal area of large blue grama plants. However these changes were similar (P>0.05) to unburned plants that decreased 8%. Winter burning with high fuel load had a positive effect (P<0.05) on basal area of large blue grama plants, with an increase of 37%. Small blue grama plants had a positive response to all burning treatments regardless of fuel load simulations, with average increases of 80%, 41%, and 31% for spring, summer, and winter burns respectively. Nevertheless, these changes were similar (P>0.05) with unburned plants that showed increased basal area of 41%. Basal area of muhly plants was generally reduced by all burn treatments. Basal area of large muhly plants had average reductions of 24% and 48% with summer and winter burns, while spring, summer, and winter burns reduced average basal area of small muhly plants by 2%, 4%, and 47% respectively.Item Experimental and computational characterization of strong vent flow enclosure fires(2011-08) Weinschenk, Craig George; Ezekoye, Ofodike A.; da Silva, Alexandre K.; Engelhardt, Michael D.; Howell, John R.; Raman, Venkatramanan; Nicks, RobertFirefighters often arrive at structures in which the state of fire progression can be described as ventilation-controlled or under-ventilated. This means that inside the enclosure the pyrolyzed fuel has consumed most, if not all of the available oxygen, resulting in incomplete combustion. Under-ventilated (fuel rich) combustion is particularly dangerous to occupants because of the high yield of toxins such as carbon monoxide and to firefighters because once firefighters enter the structure and introduce oxidizer, the environment can rapidly change into a very dangerous, fast burning condition. The fuel load in many compartment fires would support a several megawatt fire if the fire were not ventilation controlled. In the process of making entrance to the fire compartment, firefighters will likely provide additional ventilation paths for the fire and may initiate firefighting tactics like positive pressure ventilation to push the hot flammable combustion products out of the attack pathway. Forced ventilation creates a strongly mixed flow within the fire compartment. Ventilation creates a complex fluid mechanics and combustion environment that is generally not analyzed on the scale of compartment fires. To better understand the complex coupling of these phenomena, compartment scale non-reacting and reacting experiments were conducted. The experiments, which were conducted at The University of Texas at Austin’s fire research facility, were designed to gain insight into the effects of ventilation on compartment thermal characteristics. Computational models (low and high order) were used to augment the non-reacting and reacting experimental results. Though computationally expensive, computational fluid dynamics models provided significant detail into the coupling of buoyantly driven fire products with externally applied wind or fan flow. A partially stirred reactor model was used to describe strongly driven fire compartment combustion processes because previously there was not an appropriate low dimensional computational tool applicable to this type of problem. This dissertation will focus on the experimental and computational characterization of strong vent flows on single room enclosure fires.Item The joint effects of fire and herbivory on hardwood regeneration on the eastern Edwards Plateau(2012-05) Doyle, Kevin Francis; Fowler, Norma L.; Gilbert, LawrenceThe failure of regeneration of oak (Quercus spp.) and other hardwood species has been noted throughout eastern North America as well as on the eastern Edwards Plateau of central Texas. Previous research has suggested that two factors—prolonged periods of fire suppression and high densities of white-tailed deer—may be particularly influential in preventing seedlings of certain species from reaching the adult size class. It is also possible that these two factors interact, and the success of reintroducing fire to promote hardwood regeneration may depend on local deer density. This study, composed of observational and experimental components, first compared browsing frequency on woody plants in burned and unburned plots at six sites in central Texas. We found that although fire history did not affect browsing frequency, browsing frequency varied significantly among sites (likely due to differences in local deer densities) and among species. In our experimental study, we used cages to protect woody plants from deer herbivory in burned and unburned areas and compared growth after one year to plants of similar size and species that were exposed to herbivory. Plants in burned areas were significantly more likely to increase in height than plants in unburned areas. Similarly, plants protected from herbivory were more likely to increase in height after one year than plants that were browsed. There were no significant differences in the amount of growth woody plants in burned and unburned areas or plants that were caged or uncaged put on during one year. This is likely due to the extreme hot and dry weather that occurred across central Texas during the course of this study. These results support previous research showing that deer are currently limiting hardwood growth of multiple species on the eastern Edwards Plateau. Further, although it appears that fire can be used to stimulate hardwood growth (particularly during a non-drought year) successful hardwood regeneration is unlikely at current deer densities.Item Novel suppression methods in fire protection(2013-12) Cabrera, Jan-Michael; Ezekoye, Ofodike A.The onset of fire within a compartment can pose a hazard to the occupants and the structure containing the compartment. Fire suppression systems aim to either extinguish or suppress an incipient fire before loss of life or damage to the structure can occur. The geometry and use of the compartment as well as the fuel packages within must be taken into account when choosing an appropriate fire suppression system. This thesis explores novel suppression methods inside of compartments. Los Alamos National Laboratories came to the University of Texas Fire Research Group (UTFRG) to characterize and investigate the fire danger inside of nuclear gloveboxes. The first suppression method discussed explores activation tests of a commercial automatic fire suppression system (Fire Foe [superscript TM]) containing heptaflouropropane (FE-36) fire suppressant conducted within a glovebox at the UTFRG's burn structure. Temperature and time to activation data of ten tests at four different fire sizes, three 13 kW, one 20 kW, three 25 kW, and three 50 kW, was taken. Gas temperatures from experiments were compared against NIST's Fire Dynamics Simulator (FDS) gas temperatures with good agreement. The time and spatially averaged net heat flux on a virtual Fire Foe [superscript TM] tube from the FDS simulations were passed to a thermo-physical, semi-empirical, sub-model to predict activation with poor agreement from experimental activation times. A Bayesian parameter inference was later run on the sub-model. While the Bayesian inference approach is able to match sub-model temperatures to experimental temperatures, some non-physical values for heat transfer coefficients and view factors were observed at the lower heat release rate fires. Micro combustion calorimetry (MCC) was used to determine heat of combustion of glovebox glove material and cone calorimetry tests were run to find ignition time versus incident heat flux. Using standard ignition time models, effective model parameters were calibrated. Thermal characterization of the glove material showed that the heat of combustion found from MCC was within the range of heats of combustion for other non-halogenated materials found in the literature. Analysis of the time to ignition tests showed that the glove material should be modeled as thermally thick when one would expect thin behavior. This behavior was attributed to possible heat losses from the back of the glove material. Dry water is expected to have similar suppression characteristics as water mist systems because the dry water particle sizes are on the order of water mist droplet sizes. The major benefit with dry water is the low pressures needed to drive the aerosol. An issue encountered with the dry water was flowing it in the way one would flow normal water. It was found that at low normal and shear stresses, the dry water clathrates would release the water held inside. A possible low shear delivery mechanism was discussed that avoids the ratholing effect. A continuous dry water production system was also designed. Filter loading tests were conducted to determine the quality of the dry water collected from the batch and continuous cases. It was observed that the ratio of water to silica for the continuous case reaches the batch value and is similar to results found in the literature. For the batch dry water it was observed that the particle size of the dried clathrates does vary with rotational speed of the blender and is independent of the type of water used (tap or deionized).Item Simulating Historic Landscape Patterns of Fire in the Southern Appalachian Mountains: Implications for Fire History and Management(2014-05-21) Gass, Ellen RFire suppression policies implemented in the early 20th century led to a decrease in fire-associated species and ecosystems in the southern Appalachian Mountains. As managers work towards restoration, a greater understanding of the pre-suppression fire regime is needed. Fire frequency and seasonality can be determined from physical fire records, such as fire scars, but fire size, fire cycle, ignition density, and ignition source are more difficult to ascertain. Using FARSITE, a spatially explicit fire model, I predicted past fire spread in the western Great Smoky Mountains National Park (GSMNP). Results showed a mean pre-suppression fire size of over an order of magnitude larger than fires on current landscape conditions (567 ha vs. 45 ha). Large fire sizes would have encouraged fire-associated vegetation and continuous flammable fuelbeds. In addition, the current lightning ignition rate within the study area resulted in a 120-135 year pre-suppression lightning fire cycle, which indicates that natural fires were influential on the landscape. This fire cycle is shorter than the lightning fire cycle experienced today (approx. 25-30,000 years). Using the mean fire return interval from previous research, I determined the potential contribution of lightning and anthropogenic ignitions to the fire cycle. This contributes to the debate on the importance of lightning versus anthropogenic ignitions to the pre-suppression fire regime. Most importantly, the estimation of mean fire size, fire cycle, and ignition density for lightning and anthropogenically ignited fires may aid federal resource managers as they use lightning ignitions and prescribed burns to restore fire-associated ecosystems in the GSMNP and other areas of the southern Appalachians.Item The effects of fire on Kuenzler's hedgehog cactus(Texas Tech University, 2006-08) May, Benjamin C.; Britton, Carlton M.; Wester, David B.; Thorvilson, Harlan G.Echinocereus kuenzleri is a threatened and endangered species in the mountains of south-central New Mexico. E. kuenzleri grows in the pinyon-juniper grasslands between 1,500 and 2,000 m in elevation. Little is known about E. kuenzleri. Currently, land management practices to control woody species distribution, especially juniper, avoid E. kuenzleri habitat to reduce possible negative effects on the species. One of the more common management practices in this area is prescribed fire. To study the effects of prescribed fire on E. kuenzleri, 109 cacti were burned and 109 cacti were monitored as control plants. Macro- and micro-habitat characteristics were described in detail to help understand the effects of fire on E. kuenzleri. Burning was conducted in 2004 and 2005. Cacti were monitored for 1 to 2 years after treatment. Prescribed fire had no effect on the mortality of E. kuenzleri in the conditions of this study. Furthermore, prescribed fire had no effects on the frequency of flowering of cacti or on the number of flowers and fruits per cacti. These results suggest that prescribed fire would not have a detrimental effect on the population of E. kuenzleri 1 to 2 years after burning under the conditions of this study.Item Time out : organizational training for improvisation in lifesaving critial teams(2012-08) Ishak, Andrew Waguih, 1982-; Browning, Larry D.; Ballard, Dawna I.; Stephens, Keri K.; Maxwell, Madeline M.; Ziegler, Jennifer A.Exemplified by fire crews, SWAT teams, and emergency surgical units, critical teams are a subset of action teams whose work is marked by finality, pressure, and potentially fatal outcomes (Ishak & Ballard, 2012). Using communicative and temporal lenses, this study investigates how organizations prime and prepare their embedded critical teams to deal with improvisation. This study explicates how organizations both encourage and discourage improvisation for their embedded critical teams. Throughout the training process, organizations implement a structured yet flexible “roadmap”-type approach to critical team work, an approach that is encapsulated through three training goals. The first goal is to make events routine to members. The second goal is to help members deal with non-routine events. The third goal is to help members understand how to differentiate between what is routine and non-routine. The grounded theory analysis in this study also surfaced three tools that are used within the parameters of the roadmap approach: experience, communicative decision making, and sensemaking. Using Dewey’s (1939, 1958) theory of experience, I introduce a middle-range adapted theory of critical team experience. In this theory, experience and sensemaking are synthesized through communicative decision making to produce decisions, actions, and outcomes in time-limited, specialized, stressful environments. Critical teams have unique temporal patterns that must be considered in any study of their work. Partially based on the nested phase model (Ishak & Ballard, 2012), I also identify three phases of critical team process as critical-interactive, meaning that they are specific to action/critical teams, and they are engaged in by critical teams for the expressed purpose of interaction. These phases are simulation, adaptation, and debriefing. These tools and phases are then placed in the Critical-Action-Response Training Outcomes Grid (CARTOG) to create nine interactions that are useful in implementing a structured yet flexible approach to improvisation in the work of critical teams. Data collection consisted of field observations, semi-structured interviews, and impromptu interviews at work sites. In total, I engaged in 55 hours of field observations at 10 sites. I conducted 31 semi-structured interviews with members of wildland and urban fire crews; emergency medical teams; and tactical teams, including SWAT teams and a bomb squad. I also offer practical implications and future directions for research on the temporal and communicative aspects of critical teams, their parent organizations, and considerations of improvisation in their work.Item UT Fire, a preprocessor for SAFIR2007, for analysis of heat transfer for structural members exposed to fire(2009-12) Jennings, Timothy Mark; Engelhardt, Michael D.; Helwig, Todd A.This thesis describes the development of the computer program UT Fire, which serves as a preprocessor for the computer program SAFIR2007. SAFIR2007, developed at the University of Liege in Belgium, conducts heat transfer analysis and structural response analysis for structures subjected to fire. The preprocessor UT Fire was developed to allow a simplified graphical interface for input to the heat transfer portion of SAFIR 2007. This thesis provides step by step instructions on the use of UT Fire and illustrates its use through a series of detailed examples.