Open Space Advisory Board Agenda and Packet 2012 03 14

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FIRE BEHAVIOR OUTPUTS The light, flashy grass (fuels) found on all of the open space properties in Louisville are likely to exhibit similar fire behavior, as there arerelatively minimal changes in elevation or steep slopes throughout most of the properties. Grass fuels respond quickly to environmental conditions such as changing temperatures, relative humidity, and wind. The combination of the homogenous fuel layer and flat topography could result in a fast-moving, wind-driven wildfire, especially given high wind speeds and/or high temperatures. Under high to extreme fire weather conditions (described in the Fire Behavior Technical Reference), rates of spread could be 4-6 miles/hour. Considering how small many of the open space parcels are, fire would likely encroach on private property boundaries very quickly. Fires under these conditions cannot be directly fought by an individual without additional mechanical equipment, such as brush trucks. Throughout the majority of the year wind speeds are not as high, leading to lower rates of spread and flame lengths. During these times a wildfire could readily be extinguished by the fire department. Although high and extreme weather conditions occur with less frequency, it is important to plan and strategize for the worst-case scenarios, especially when simple actions can easily mitigate many of the concerns. METHODOLOGY A detailed description of the fuel models, weather parameters, and fire behavior outputs can be found in the Fire Behavior Technical Reference. The appendix details the inputs used to model fire behavior, including topography, fuel loading and type, and fuel moistures. The appendix also details how and why specific weather parameters were chosen. The rating for the properties was based on a 100 point scale. Fire behavior modeling, specifically fire line intensity was responsible for 75% of the rating. Fireline intensity, measured in BTU/ft/sec, is broken down into four categories and weighted accordingly. The additional 25 points are a combination of wildland urban interface (WUI) density and other hazards that may be specific to the property, including proximity to transmission lines, communication towers, and railroads. More points were assigned to properties surrounded by high density housing, compared to areas with few or no adjacent homes or commercial buildings. Totals between 0-40 were given a low hazard rating, 41-60 a moderate hazard, and 61-100 a high hazard. 3