LIVE FUEL MOISTURE S390-VG STAGE OF VEGETATIVE DEVELOPMENT ________________________________________ Fresh foliage, annuals developing early in growing cycle. Maturing foliage, still developing with full turgor. Mature foliage, new growth complete and comparable to older perennial foliage. Entering dormancy, coloration starting, some leaves may have dropped from stem. Completely cured. MOISTURE CONTENT Percent Less than 30, treat as a dead fuel.
PROBABILITY OF IGNITION S390-VG A rating of the probability that a glowing firebrand will cause a fire.
Wind 10 mi/h 20 mi/h 3 mi/h 20 mi/h S390-VG
Fuel exposure to wind Partly sheltered (patchy timber) Wind Unsheltered (no foliage, near clearings) Fully sheltered (under timber, flat or gentle slope, near base of steep mtn.) Partly sheltered (under timber midslope, wind on slope) Unsheltered(ridgetops) S390-VG
PERCENT SLOPE S390-VG % SLOPE = RISE IN FEET RUN IN FEET X 100 % RISE RUN
A MATHEMATICAL MODEL IS A SET OF EQUATIONS S390-VG
ASSUMPTIONS OF THE FIRE SPREAD MODEL S390-VG 1. Fire is spreading at the flame front. 2. Fire is free burning. 3. Fine fuels control rate of spread. 4. Uniform and continuous fuels. 5. Surface fire. 6. Uniform weather and topography.
RATE OF SPREAD DISTANCE/TIME S390-VG STARTING TIME ENDING TIME DISTANCE
FLAME LENGTH FEET S390-VG
POINT SOURCE S390-VG Point source model is designated for fires burning on flat ground or where the wind is blowing in the direction of the slope plus or minus 30°. upslope max slope ± 30º
SPREAD CALCULATION SD=PT X ROS SD = SPREAD DISTANCE PT= PROJECTION TIME ROS = RATE OF SPREAD S390-VG
SPREAD DIRECTION S390-VG WIND NO WIND WIND UP SLOPE UP SLOPE UP SLOPE WIND DOWN SLOPE DOWN SLOPE DOWN SLOPE
POINT SOURCE PREDICTION LIMITATIONS S390-VG Calculations with windspeeds less than 2.5 miles per hour are generally too low. Better predictions result with windspeeds greater than 2.5 miles per hour.
FIRE PERIMETER AND SHAPES S390-VG Fire perimeter and shapes are based on smooth ellipses - actual perimeter of the fire edge would likely be greater length and follow topographic relief.
APPROXIMATE FIRE SHAPES ASSOCIATED WITH MIDFLAME WINDSPEEDS OF… S390-VG Wind Direction Fire Start 2.5 mi/h 5 mi/h 7.5 mi/h 15 mi/h 10 mi/h
AREAS OF USE SUPPRESSION S390-VG Determination of locations to place crews, equipment, helicopters and fuel breaks. Development of the wildland fire situation analysis.
PRESCRIBED BURNING S390-VG Distance between spot fires to accomplish an objective. Calculating timing of ignition to take advantage of diurnal weather patterns. Managing wilderness fires. Development of escaped fire contingency planning.
EFFECTIVE WINDSPEED S390-VG The midflame adjusted for the effect of slope on uphill fire spread.
EXAMPLES OF EFFECTIVE WINDSPEED S390-VG EFFECTIVE WINDSPEED IS 5 mi/h 3 mi/h 60% 5 mi/h
MAXIMUM SPOTTING DISTANCE S390-VG When torching trees, piles or wind- driven surface fires loft firebrands, which are then carried by the prevailing wind.
SOURCES OF FIREBRAND S390-VG Torching trees Burning pile Spreading surface fire
FACTORS RELATING TO THE SPOTTING PROBLEM S390-VG Probability of production of firebrands. Windspeed. Fire intensity. Number of firebrands