REDUCING URBAN INTERFACE ECOLOGICAL IMPACTS AND FIRE LOSSES THROUGH STRUCTURAL FIREBRAND PROTECTION

1. REDUCING URBAN INTERFACE ECOLOGICAL IMPACTS AND FIRE LOSSES THROUGH STRUCTURAL FIREBRAND PROTECTION Joseph W. Mitchell, Ph. D.M-bar Technologies and ConsultingRamona, Californiajwmitchell@mbartek.com 3rd International Fire Ecology and Management Congress

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? 3rd International Fire Ecology and Management Congress

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 3rd International Fire Ecology and Management Congress

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 . - Oct 2003: Cedar + others - 4,443 structures • Oct 1991: Oakland (Tunnel)– 2,886 structures • June 1990: Paint – 641 • Sept 1923: Berkeley - 624 • Nov 1961: Bel Air – 505 • Sept. 1970: Laguna – 382 3rd International Fire Ecology and Management Congress

5. 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 Structure ignition by firebrands 3rd International Fire Ecology and Management Congress

6. Idea: Separate the problem of radiant heat & flame protection(answer: distance from fuel) from the problem of firebrand protection… 3rd International Fire Ecology and Management Congress

7. Firebrand Protection • Protection from firebrand entryStructural 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 ignitionVegetation management / clearance adjacent to structure • Accumulation of litter & leaves in gutters, corners. • Ember extinguishingWater systems / gels • Subject to wind disruption • Roof protection adds no value to Class A roofs • Massive water use / undependable supplies • Gels require manual application 3rd International Fire Ecology and Management Congress

8. Wind-Enabled Ember Dousing (WEEDS) CONCEPT: ACHIEVE WIND-RESILIENT BRAND PROTECTION BY DIRECTING COARSE WATER SPRAY OUTWARD FROM THE STRUCTURE • The wind blows it backonto the structure • Spray accumulates where embers do • Low spray densities needed to protect from brands (as opposedto radiant heat) 3rd International Fire Ecology and Management Congress

9. 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 WEEDS Design Features 3rd International Fire Ecology and Management Congress

10. 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 Is it sufficient? 3rd International Fire Ecology and Management Congress

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. Wind speed = 20 km/hr 3rd International Fire Ecology and Management Congress

12. Testing of systemOctober 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. Not proof, but a case study (Fire Safety Journal, Sept. 06) 3rd International Fire Ecology and Management Congress

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! 3rd International Fire Ecology and Management Congress

14. Thank you 3rd International Fire Ecology and Management Congress

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