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24.51.030 Wildfire Hazard Zone Map Adoption.

City Code Section
  1. A. Wildfire Hazard Zone Map adoption.
    1. 1. A Wildfire Hazard Zone Map (WHZM) has been developed for the City of Portland through a review of topography, weather, type vegetation and fuel density. This map is dated October 11, 2002.
    2. 2. The WHZM dated October 11, 2002, is adopted by this reference and incorporated into this ordinance.
    3. 3. The Chief will provide the City Administrator with a copy of the official map adopted in Subsection one of this Section. Copies of the map are available for review in the Development Services Center, First Floor 1900 SW 4th Avenue, Portland Oregon.
  2. B. Revisions to the Wildfire Hazard Zone Map.
    1. 1. The WHZM may be amended from time to time to either include or exclude properties as the facts may warrant.
    2. 2. The Chief may revise the Wildfire Hazard Zone Map.
    3. 3. All Wildfire Hazard Zone map revisions will be determined using the criteria set forth below. Any site having a cumulative hazard value of five (5) or more will be included in a wildfire hazard zone.
      1. a. Topography Hazard Factor Value. The topography hazard value will be calculated as follows:
        1. (1) Determine site slope using the appropriate 7.5 minute quadrangle map published by the U.S. Geological Survey, USDI.
        2. (2) Select appropriate hazard value using Table 1.
        3. TABLE 1
          APPROPRIATE TOPOGRAPHY
          HAZARD FACTOR VALUE

          1. Site Slope as determined by

            the 7.5 minute quadrangle map

            		Hazard Value
            Slopes 00 to < 03%0
            Slopes 03 to < 12%1
            Slopes 12 to < 20%2
            Slopes 20% or greater3
      2. b. Natural Vegetative Fuel Hazard Factor Value. The natural vegetative fuel hazard value is calculated as follows:
        1. (1) Divide the jurisdiction into geographic areas that best describe the natural vegetation expected to occupy sites for the next 10 to 15 years.
        2. (2) Select the appropriate hazard value from Table 2.
        3. TABLE 2
          NATURAL VEGETATIVE FUEL
          HAZARD FACTOR VALUE 
          1. Natural Vegetative Fuel Description 1Hazard Value 2
            LimitedLittle or no natural vegetative fuels are present.0
            GrassVery little shrub or timber is present, generally less than one-third of the area. Main fuel is generally less than two feet in height. Fires are surface fires that move rapidly through cured grass and associated material. (Fuel model 1)3
            GrassOpen shrub lands and pine stands or scrub oak stands that cover one-third to two-thirds of the area. Main fuel is generally less than two feet in height. Fires are surface fires that spread primarily through the fine herbaceous fuels, either curing or dead. (Fuel model 2)3
            GrassBeach grasses, prairie grasses, marshland grasses and wild or cultivated grains that have not been harvested. Main fuel is generally less than four feet in height, but considerable variation may occur. Fires are the most intense of the grass group and display high rates of spread under the influence of wind.(Fuel model 3)3
            ShrubsStands of mature shrubs have foliage known for its flammability, such as gorse, manzanita and snowberry. Main fuel is generally six feet or more tall. Fires burn with high intensity and spread very rapidly. (Fuel model 4)3
            ShrubsYoung shrubs with little dead material and having foliage not known for its flammability, such as laurel, vine maple and alders. Main fuel is generally three feet tall or less. Fires are generally carried in the surface fuels and are generally not very intense. (Fuel model 5)1
            ShrubsOlder shrubs with foliage having a flammability less than fuel model 4, but more than fuel model 5. Widely spaced juniper and sagebrush are represented by this group. Main fuel is generally less than six feet in height. Fires will drop to the ground at low wind speeds and in stand openings. (Fuel model 6)2
            TimberAreas of timber with little undergrowth and small amounts of litter buildup. Healthy stands of lodgepole pine, spruce, fir and larch are represented by this group. Fires will burn only under severe weather conditions involving high temperatures, low humidity and high winds. (Fuel model 8)1
            TimberAreas of timber with more surface litter than fuel model 8. Closed stands of healthy ponderosa pine and white oak are in this fuel model. Spread of fires will be aided by rolling or blowing leaves. (Fuel model 9)2
            TimberAreas of timber with heavy buildups of ground litter caused by over-maturity or natural events of wind throw or insect infestations. Fires are difficult to control due to large extent of ground fuel. (Fuel model 10)3
            1. Some areas may contain vegetative fuels other than those listed in Table 2.  Additional natural fuel hazard factors may be found in “Aids to Determining Fuel Models for Estimating Fire Behavior” published by the Forest Service, USDA Intermountain Forest and Ranger Experiment Station in 1982 as General Technical Report INT-122.  Vegetative fuel hazard factors determined using General Technical Report INT-122 must be used as alternative factors, for review under this chapter, as the facts warrant.
            2. Due to various factors, such as variations in local vegetation species or vegetation conditions, the fuel models used in Table 2 may not accurately portray wildfire behavior.  The Chief may make modifications to the hazard values as necessary to accurately reflect the following characteristics:

            (a)A hazard value of 1 describes vegetation that typically produces a flame length of up to 5 feet, a wildfire that exhibits very little spotting, torching, or crowning, and that results in a burned area that can normally be entered within 15 minutes.

            (b)A hazard value of 2 describes vegetation that typically produces a flame length of 5 to 8 feet, a wildfire that exhibits sporadic spotting, torching, or crowning, and that results in a burned area that can normally be entered within one hour.

            (c)A hazard value of 3 describes vegetation that typically produces a flame length of over 8 feet, a wildfire that exhibits frequent spotting, torching, or crowning, and that results in a burned area that normally cannot be entered for over one hour.

      3. c. Natural Vegetative Fuel Distribution Hazard Factor Value. To determine the natural vegetative fuel distribution hazard factor value:
        1. (1) Determine the percentage of each individual area that is covered by vegetation.
        2. (2) Using the calculated percentage, assign a value using Table 3.

          TABLE 3
          NATURAL VEGETATIVE FUEL
          DISTRIBUTION HAZARD FACTOR
    1. Natural Vegetative Fuel DistributionHazard Value
      0 to 10% of the area0
      10 to 25% of the area1
      25 to 40% of the area2

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