The behavior of live fuels is clearly different from that of dead fuels in wildfire conditions. Fire spread is sustainable at higher fuel moisture contents in live fuels than in dead fuels, but the fundamental reasons for this difference are not understood. Studies have examined the ignition times, rates of fire spread, moistures of extinction, and the fuel temperature histories of both dead and live fuels in a variety of conditions. However, a study of the temperature distribution and mass history of single live and dead leaves of the same moisture content in a wildfire condition has not previously been performed. Live and dead manzanita leaves (Arctostaphylos glandulosa) were conditioned to roughly 30% moisture content (dry basis) and burned over a flat flame burner. A base case of manzanita leaves at 4% moisture content was also burned. Each leaf had its mass logged by a cantilever balance and its face temperature recorded by an infrared camera. The temperature distribution of each leaf was tracked from the start of preheating to burnout and was analyzed as a whole leaf and in sections. Live leaves had a strong temperature plateau indicative of evaporation although it occurred well above the normal boiling point of water. In contrast, the conditioned and unconditioned dead leaves showed little if any temperature plateau. Using the dry, dead set, the average temperature of each section was used as the temperature input for a devolatilization model to predict the mass release of the leaf over time. This was compared to the measured mass release, showing good agreement. A theory to describe water release in moist leaves was developed to account for the difference in temperature distributions and histories of the dead and live leaves, especially with regards to the temperature plateau observed for live leaves. While the liquid in a dead leaf quickly diffuses out of a leaf as it locally reaches its boiling point, plant cells have been documented to hold pressures of between 30 atm and 100 atm (based on 50% bursting), depending on the species. These pressures correspond to water boiling temperatures of 235°C and 312°C which is similar to the temperature range of the live leaf temperature plateaus. This explanation was used to develop evaporation models which differentiate live and dead fuels and were coupled with a devolatilization model to predict a mass release curve which was compared to the measured history.
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