Fire Protection Engineering
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Item COMPARISON OF IGNITION AND COMBUSTION CHARACTERISTICS OF WESTERN RED CEDAR AND ORIENTED STRAND BOARD EXPOSED TO FIREBRAND PILE DEPOSITION(2022) Dietz, Emily; Stoliarov, Stanislav I; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Some of the most devastating consequences of the increasing occurrence of large wildfires throughout the world are the acres of land burned and the number of structures lost. Firebrand exposure has been identified as one of the main mechanisms of how wildfires spread as well as an ignition source for structural components. A bench-scale experimental procedure was developed to study the ignition process of Western Red Cedar (WRC) and Oriented Strand Board (OSB), two common materials used in the construction of outdoor decks. To study the combustion process of these materials, they were loaded into a wind tunnel and exposed to a constant wind velocity of 1.4 m s-1, 2.4 m s-1, or 2.7 m s-1 and a glowing firebrand pile coverage density of either 0.06 g cm-2 or 0.16 g cm-2. All tests were also conducted using Kaowool PM, an inert ceramic fiberboard, in order to quantify the heat feedback of the isolated firebrand pile as well as differentiate the contributions of WRC and OSB to the combustion process from that of the firebrand pile. Surface ignitions on the combustible materials were determined visually and characterized by time to ignition after deposition, burn duration, and location of ignition events. Back surface temperature profiles were collected using an infrared camera. Results from gas analyzer measurements were used to compare the combustion characteristics of the WRC, OSB, and Kaowool PM under the same conditions through heat release rate (HRR) and modified combustion efficiency (MCE) profiles. Additional tests were conducted under a single airflow of 2.4 m s-1 and firebrand pile coverage density of 0.16 g cm-2 yet rotated the orientation of firebrand deposition onto the board by 90 degrees, doubling the leading edge length of the firebrand pile. A series of tests also varied the airflow in the tunnel for a comparison between the surface ignition characteristics and the temperature profiles of the firebrand pile between continuous and intermittent wind exposure for a 2.7 m s-1 airflow and a 0.16 g cm-2 firebrand pile coverage density. Results included a higher probability of ignition on WRC than OSB under all continuous wind conditions, higher peak temperatures achieved with an increasing airflow up to 2.4 m s-1, and combination smoldering-flaming mode of combustion for the system, whether that be the firebrand pile alone or the firebrand pile deposited onto WRC or OSB. It was also found that changing the firebrand pile deposition orientation leading edge length by a factor of two doubled the number of surface ignitions observed on both WRC and OSB. Compared to the continuous wind condition, gusting the airflow velocity caused an increase in the number of ignitions by a factor of 14 on WRC and 19 on OSB, yet each saw a decrease in the burn duration by a factor of at least 4.Item Laboratory Studies on the Generation of Firebrands from Cylindrical Wooden Dowels(2016) Caton, Sara; Gollner, Michael J; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Wildland urban interface (WUI) fires are increasing in size and severity in the United States. These fires are a major concern because they spread into communities and ignite thousands of homes every year. The main source of home ignitions is not through direct flame contact or radiation; rather, firebrands are the primary pathway for fire to spread into WUI communities. Firebrands are pieces of a burning material that break off and then can be lofted and carried large distances to ignite subsequent fires. The purpose of this thesis is to study the breakage process to better understand how firebrands are produced. Cylindrical wooden dowels are used to represent vegetative fuels in WUI fires. The dowels were exposed to various heating conditions and then three-point bending tests were performed on each dowel to study the effect of combustion on strength properties. It has been found that there are two distinct regimes that describe the breakage. The size of the dowel and the final density of the dowel both control the transition between regimes. A scaling analysis was performed to show that the two regimes and transition point are the same for all species. Predictions of wind velocities needed to produce the measured critical stresses were calculated, because a connection needs to be drawn between the combustion and the wind to fully understand firebrand generation.