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Full-Scale Experimental Investigation to Quantify Building Component Ignition Vulnerability from Mulch Beds Attacked by Firebrand Showers

Published

Author(s)

Samuel L. Manzello, Sayaka Suzuki, Daisaku Nii

Abstract

Detailed, systematic experiments that demonstrate if certain mulch types may ignite building elements have not been demonstrated. To this end, this paper outlines a series of experiments conducted with various mulch types placed adjacent to realistic-scale re- entrant corners. Mulch beds are a useful surrogate for various fuels that may be located near structures during the outbreak of large outdoor fires, such as Wildland-Urban Interface (WUI) fires and urban fires. In the first series of experiments, 1.2 m by 1.2 m, 51 mm in depth, mulch beds of were placed adjacent to a re-entrant corner 1.2 m by 1.2 m by 2.44 in height constructed with wood studs and lined with oriented strand board (OSB) as the sheathing. The premise behind conducting experiments with no siding treatments applied was predicated on the notion that bare OSB mulch contact would be a worst-case scenario, and therefore, a wall assembly in the most vulnerable state to mulch ignition. Three different common mulch types were used: shredded hardwood mulch (0.25 g/cm3), Japanese cypress woodchips (0.14 g/cm3), and pine bark nuggets (0.17 g/cm3). In all experiments, the mulch beds were oven-dried. It was observed that firebrands produced smoldering ignition in the mulch beds, this transitioned to flaming ignition, and the re-entrant corner assembly was ignited by the flaming mulch beds. Flaming ignition was observed to propagate to the back side of re-entrant corner assembly. These observations occurred under applied wind speeds of 6 m/s to 8 m/s. In the second series of experiments, siding treatments were applied to the re-entrant corner assemblies (wood studs/OSB/moisture barrier/siding), and the influence of vertical separation distance on wall ignition from adjacent mulch beds was determined. Vinyl siding was used, and the vertical separation distance from the mulch bed to base of siding used varied from 102 mm to 203 mm. For a given siding treatment, the mulch type, vertical separation d
Citation
Fire Technology

Keywords

WUI fires, Firebrands
Created October 8, 2015, Updated November 10, 2018