Fire Behavior and Fuels
What the exam tests
Fire Behavior and Fuels tests your ability to combine the fire triangle, fuel model, topography, and weather into a forecast of rate of spread, intensity, spotting, and probability of ignition. Expect questions on extreme fire behavior indicators and weather changes.
Core rules
- The fire triangle requires heat, oxygen, and fuel; suppression removes one leg, but weather and topography can overwhelm it.
- Fuel models describe fuel bed characteristics; grass models cure and carry fast surface fire, brush models can produce tall flame lengths, and timber litter models carry smoldering and torching.
- Watch for extreme indicators: crown fire, long-range spotting, convection column collapse, rapid wind shift, rolling embers, and fire behavior inconsistent with fuels and weather.
- Low relative humidity, strong or shifting wind, instability, and thunderstorm outflow increase spread; cold fronts can produce abrupt wind shifts.
Worked example
A grass fuel model with 4% 10-hour fuel moisture, 12% relative humidity, 20 mph wind, and 30% slope is not a low-risk edge because grass is fine fuel. The fine fuel, wind, and slope align to produce high rate of spread and easy spotting; a direct head attack would expose crews. The reasoning is to identify the limiting factor-fine fuel and wind-and choose an anchor-and-flank approach or indirect line.
Traps
Using only the fuel model name; ignoring live fuel moisture; assuming a green fuel break stops crown fire; missing outflow wind.