1	REDUCING URBAN INTERFACE ECOLOGICAL IMPACTS AND FIRE LOSSES THROUGH STRUCTURAL FIREBRAND PROTECTION Joseph W. Mitchell, Ph. D. M-bar Technologies and Consulting Ramona, California jwmitchell@mbartek.com
2	What if the WUI didn’t matter? What if wildland firefighters & foresters could manage wildland fires, rather than engaging in structure protection, because the structures protected themselves? What if insurers estimated coverage and costs based on survivability rather than “brush clearance”? What if homeowners in the WUI took responsibility for protecting their structures, and had the means to do so?
3	Reliance on defensible space California “Hollingsworth Bill” – SB 841. Clearance to 300 ft. for some facilities “Preferred insurers” require 250’ to 500’ distance from fuels. [Insurance Journal, 2004] General perception of wildland as enemy
4	Wildland fire losses in California are driven by catastrophic wind-driven events Intense winds Rapid spread Firefighter intervention improbable. High density of brands Extreme fire behavior .
5	Structure ignition by firebrands Firebrands are the leading cause of structure loss G.C Ramsay, 1987 – study of 1148 structures Chen & McAneney, 2004 – 50% structure ignition at 45 m or more (satellite analysis) Cohen analyses of structure ignition potential Plus many others… As determined by: Structures too far from fire front Observed ignitions (roof, attic, decks, fences) Civilian protection highly effective Observed density of brands Forensic evidence
6	Idea: Separate the problem of radiant heat & flame protection (answer: distance from fuel) from the problem of firebrand protection…
7	Firebrand Protection Protection from firebrand entry Structural characteristics (Australian building codes; Ramsay & Rudolph; CA SFM Interface Fire Building Standards) Only as good as the weakest point / maintenance Not good for existing at-risk structures Protection from secondary ignition Vegetation management / clearance adjacent to structure Accumulation of litter & leaves in gutters, corners. Ember extinguishing Water systems / gels Subject to wind disruption Roof protection adds no value to Class A roofs Massive water use / undependable supplies Gels require manual application
8	Wind-Enabled Ember Dousing (WEEDS) CONCEPT: ACHIEVE WIND-RESILIENT BRAND PROTECTION BY DIRECTING COARSE WATER SPRAY OUTWARD FROM THE STRUCTURE
9	WEEDS Design Features Low flow rate (~120 l/min) Agricultural spray nozzles 5000 US gl water tank (plus municipal supply) 12kW generator (propane) 1.5 kW pump 3-4+ hour protection window Potential improvements: gravity feed, 10k gal tank, automated or remote triggering
10	Is it sufficient? Crib experiments suggest 1.5-4.0 gm/m²sec is sufficient to extinguish cribs (reviews: Novozhilov et al., Grant et al.) Simulation of droplet in wind Used similar nozzle for droplet size distribution Able to achieve extinguishment zone around the structure at nominal design
11	Wind resilience of spray Results conservative – don’t take airflow into account. Overlap of spray patterns to 50 km/hr 40% of spray onto roof / eaves at high wind speed.
12	Testing of system October 26, 2003 Cedar Fire Nominal operation Apparent success Structures lost on all adjacent properties. 60-70% loss rate / no professional fire protection Forensic evidence of brands on property.
13	Summary Low volume water spray systems that compensate for wind can be effective. Structures can withstand extreme wildfire conditions without professional intervention Approach radiant heat and firebrands as separate problems Design for WIND!
14	Thank you
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