1	Firebrand Protection as the Key Design Element for Structure Survival during Catastrophic Wildland Fires Joseph W. Mitchell & Oren Patashnik
2	Firebrands & structures Historical data & analyses: Firebrands as leading cause of ignition Water spray as an effective countermeasure Cedar Fire, 2003 Curved-tile roofs: Some “good” roofs not so good Wind-Enabled Ember Dousing – a wind-resilient spray concept
3	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
4	Structure ignition by firebrands Firebrands are the leading cause of structure loss G.C. Ramsay, 1987 – study of 1148 structures Ethan Foote, Paint Fire analysis, 1993 Chen & McAneney, 2004 – 50% structure ignition at 45 m or more (satellite analysis) Cohen analyses of structure ignition potential Plus others… (but no comprehensive 2003 data published!) As determined by: Structures too far from fire front Observed ignition points (roof, attic, decks, fences) Civilian protection highly effective Observed density of brands Forensic evidence
5	Another entry mechanism: Curved-tile roofs
6	Data on roof type & structure survival from the Cedar Fire Collected in November 2003, Scripps Ranch, San Diego by Amy & Oren Patashnik Types included wood-shake, curved tile, flat tile, and stone-covered steel Divided into a portion with initial firefighter protection (“front loop”) and without (“back loop”)
7	Structure ignition data
8	Statistical significance
9	Idea: Separate the problem of radiant heat & flame protection (answer: distance from fuel) from the problem of firebrand protection…
10	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 fire-resistive roofs Massive water use / undependable supplies Gels require manual application
11	Water-spray systems Sufficient spray density to affect ignition Sufficient lifetime to protect during/after fire front Resilient against wind disruption
12	Re-evaluation of Paint Fire data Ethan Foote thesis results on water spray
13	Water-spray protection If spray density is high enough, brands can be directly extinguished. Water accumulates on surfaces and around structures, creating a “moat”. Spray & vapor can hydrate light fuels. Sensitive to wind disruption
14	Wind-Enabled Ember Dousing (WEEDS) CONCEPT: ACHIEVE WIND-RESILIENT BRAND PROTECTION BY DIRECTING COARSE WATER SPRAY OUTWARD FROM THE STRUCTURE
15	WEEDS design features Low flow rate (~120 l/min) Agricultural spray nozzles 5000 US gl water tank (plus municipal supply) 12 kW generator (propane) 1.5 kW pump 3-4+ hour protection window Potential improvements: gravity feed, 10k gal tank, automated or remote triggering
16	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 Achieves extinguishment zone around the structure at nominal design
17	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
18	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
19	Summary Prevent firebrand ignitions and you prevent the majority of structure ignitions in wildland fire. Approach radiant heat and firebrands as separate problems. Low-volume water spray systems are effective, and can be used to supplement vegetation management. Water spray systems must operate DURING and AFTER fire-front passage. Watch for curved tile as a potential avenue for brand entry. Better data is needed – lack of organized data collection in 2003 was a tragedy. Structures can withstand extreme wildfire conditions without professional intervention. Design for WIND!
20	Thank You Slides available from: M-bar Technologies and Consulting Ramona, California www.mbartek.com jwmitchell@mbartek.com
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