Fire behavior in chaparral–Evaluating flame models with laboratory data

Abstract

Flame and mass loss data for chaparral, a mixture of shrub plants from the Mediterranean climate zone of southwestern North America, from five previously reported experiments were used to evaluate several published models relating flame characteristics to mass loss and heat release rates. These data are unique with fuel moisture content ranging from 0.36 to 0.94 (dry basis); the study used mass loss rates which included water loss. Fit of the data to Froude number correlations developed by Albini, Byram, Nelson and Thomas and heat release rate—flame length correlations by Heskestad, Zukoski, and Yuan/Cox for axisymmetric and line fires were examined.Chaparral fuels configured as circular cribs and burned in this fashion behaved similarly to other “pool fire” configurations. Scaled flame lengths generally agreed with heat release correlations developed for other fuel types; however, limited agreement for line fire data indicated potential for improvements that can be made. A strong relationship between mass loss rate and flame length in these live fuel beds extends this well-established relationship to these fuel types. The fitted exponent lends support to Byram's derivation that flame length is related to Fr0.5 and not Thomas’ derivation of Fr2/3. Live foliage particles still retain significant moisture at the time of ignition suggesting that moisture content may be an important parameter to include in these correlations if they are to be applied to live wildland fuels.