Fire Protection Engineering
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Item COMPARISON OF IGNITION AND COMBUSTION CHARACTERISTICS OF PRESSURE TREATED WOOD AND TREX EXPOSED TO THERMALLY CHARACTERIZED GLOWING FIREBRAND PILES(2023) Lauterbach, Alec; Stoliarov, Stanislov I; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In recent decades, the intensity of wildfires worldwide has escalated, leading to a rise in the destruction of structures and loss of lives within the Wildland-Urban Interface (WUI). Firebrands are small fragments of ignited vegetation or structural material that are carried by the plume of a wildfire, traveling in advance of the main fire front. Firebrand exposure has been recognized as the primary mechanism for the propagation of wildfires as well as a source of ignition of structural elements. However, this complex ignition process of structural elements in the WUI has yet to be fully understood. The ignition and combustion characteristics of a thermoplastic-wood composite (Trex) and Pressure Treated Wood (PTW), two frequently used WUI decking materials, when exposed to glowing firebrand piles were studied using a bench scale wind tunnel. An inert insulation material, ii Kaowool PM, was also used as a deposition substrate to quantify the heat feedback and combustion characteristics of solely the firebrand pile. Firebrand pile densities of 0.16 g cm-2 and 0.06 g cm-2 were deposited on each substrate in rectangular 10 cm x 5 cm orientations and exposed to air flow velocities of 0.9 m s-1, 1.4 m s-1, 2.4 m s-1, and 2.7 m s-1. Infrared camera measurements were used to determine the back surface temperatures of Kaowool PM tests. Using DSLR cameras, surface ignitions of the decking material in front of the firebrand pile (preleading zone ignition events), ignitions on top of the firebrand pile (pile ignition events), and surface ignitions of the decking material behind the firebrand pile (downstream ignition events) were visually quantified via their probability of ignition, time to ignition, and burn duration at each testing condition. A gas analyzer was used to compare combustion characteristics of Trex, PTW, and Kaowool PM tests through heat release rate (HRR) and modified combustion efficiency (MCE). Peak back surface temperatures of the firebrand pile were found to increase with increased air flow up to 2.4 m s-1, and then plateau. The same trend was observed for the ignition probabilities of preleading zone and pile ignition events. The probability of downstream ignition events increased with increasing air flow velocity. Peak HRR increased with increasing air flow velocity. Trex exhibited significantly less smoldering combustion than PTW yet was prone to more intense flaming combustion. When the rectangular 5 cm x 10 cm firebrand pile (10 cm edge facing the airflow), of which the majority of tests were conducted on, was rotated 90 degrees so that the 5 cm edge faced the airflow, the result was a significant decrease in the probability of ignition for both Trex and PTW, along with notable reductions in their HRR and MCE profiles.Item Firebrand Pile Thermal Characterization and Ignition Study of Firebrand Exposed Western Red Cedar(2021) Alascio, Joseph Anthony; Stoliarov, Stanislav I; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Over the past several decades, the severity of wildfires across the world has grown, resulting in increased number of structures in the Wildland–Urban Interface being destroyed, and lives lost. An ignition pathway that has been identified to contribute to most structures destroyed during a wildland fire is that of firebrand ignition. Firebrands are small burning pieces of vegetative material that are lofted ahead of the fire front. This study seeks to quantify thermal conditions experienced by building materials exposed to accumulated firebrands and to identify conditions that lead to ignition of these materials. A bench scale wind tunnel was used to house a decking material, western red cedar, on which the firebrands were deposited, which allowed for testing at different air flow velocities, while simultaneously analyzing the temperature of the solid substrate and gaseous exhaust flow constituents to identify trends in flaming and smoldering combustion. Higher peak temperatures and larger heating rates were found with the exposure of a higher air flow velocity. An increased air flow velocity also allowed for quicker, more frequent, and longer sustained flaming of the firebrand pile. A Modified Combustion Efficiency (MCE) value of 0.81 ± 0.02 for the firebrand pile across all testing conditions was quantified, which is indicative of a hybrid–smoldering/flaming combustion mode.Item Thermal Characterization of Firebrand Piles(2017) Hakes, Raquel Sara Pilar; Gollner, Michael J; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Over the past several decades, the severity of wildland-urban interface (WUI) fires has increased drastically, resulting in thousands of structures lost globally each year. The cause of the majority of structure losses is ignition via firebrands, small pieces of burning material which are generated from burning vegetation and structures. In this thesis, a methodology for studying the heating to recipient fuels by firebrands is developed. Small-scale experiments designed to capture heating from firebrand piles and the process of ignition were conducted using laboratory-fabricated cylindrical wooden firebrands. The methodology compares two heat flux measurement methods. Experimental results compare the effects of varying firebrand diameter, pile mass, and wind speed. An ignition condition is described using temperature and heat flux.