Individual cuttings from eight plant species native to California chaparral or Utah were burned in a well-controlled, well-instrumented facility. Gas temperatures above a flat-flame burner were controlled at 987 i 12°C and 10 * 0.5 mol% OZ, resulting in a heat flux at the leaf surface varying from 80-140 kw/m2. High moisture leaves were observed to burst due to the rapid escape of vapor from the leaf interior. Bubbles in or on the leaf surface were observed for leaves with moderate moisture contents. A large number of leaf temperature measurements were made, along with measurements of the ignition time and temperature, flame height, and flame duration. Average ignition temperatures were species dependent, ranging from 227°C to 453"C, with a large degree of scatter from leaf to leaf. Correlations of time to ignition and ignition temperature were made, but showed only a weak dependence on leaf thickness and almost no dependence on mass of moisture in the leaf. Leaf samples with similar mass showed that Utah juniper took longer to burn than the other species, and that the Utah broadleaf species burned more rapidly than all the other species.

Individual samples of high moisture fuels from the western and southern United States and humidified aspen excelsior were burned over a flat-flame burner at 987° ± 12°C and 10 ± 0.5 mol% O2. Time-dependent mass and temperature profiles of these samples were obtained and analysed. It was observed that significant amounts of moisture remained in the individual samples after ignition occurred. Temperature histories showed a plateau at 200°–300°C at the leaf perimeter rather than at 100°C, with a plateau of 140°C for the leaf interior. Implications are that classical combustion models should be altered to reflect the behaviour of moisture in high moisture (live) samples. Mass release rates were determined at ignition and maximum flame height; these appeared to vary due to surface area and perimeter, but no significant correlation was found for all species.

Combustion experiments were performed over a flat-flame burner that provided the heat source for multiple leaf samples. Interactions of the combustion behavior between two leaf samples were studied. Two leaves were placed in the path of the flat-flame burner, with the top leaf 2.5 cm above the bottom leaf. Local gas and particle temperatures, as well as local oxygen concentrations, were measured along with burning characteristics of both leaves. Results showed that the time to ignition of the upper leaf was not significantly affected by the presence of the lower leaf. The major difference observed was that the time of flame duration of the upper leaf was significantly affected by the presence of the lower leaf. Causes for the prolonged flame were found to be the consumption of oxygen by the burning lower leaf and the obstruction provided by the lower leaf, causing a wake effect, thus altering the combustion behavior of the upper leaf.

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