Rethinking the Response of Fuels to Changes in Atmospheric Moisture

The current framework for categorizing fuels in the United States uses bulk fuel moisture based on moisture content of the entire 1, 10, etc. hour time-lag fuel element. However, combustion is largely a fuel surface process, with much of the interior of fuels unengaged. We propose that the fraction of total fuel complex available for combustion at any moment in time is better represented by fuel surface area. Surface area is also more directly engaged in moisture exchange and so better represents the sensitivity of the fuel complex to rapid changes in atmospheric moisture. We discuss the implications of looking at surface area instead of mass in matters of fuel characterization, fire behavior, and fire danger.