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Community-Scale Fire Spread.


pdf icon Community-Scale Fire Spread. (329 K)
Rehm, R. G.; Hamins, A.; Baum, H. R.; McGrattan, K. B.; Evans, D. D.

NISTIR 6891; 16 p. July 2002.
Order number: PB2002-107932

Keywords:

fire spread; wildland fires; large scale fire tests; wildland urban interface; mathematical models; computational fluid dynamics; fuel loads

Abstract:

This paper addresses community-scale fires, which have also been called urban/wildland interface or intermix fires. These fires arise when wildland fires invade the built environment and attack structures as well as wildland fuels. The prediction of the spread of wildland fires, such as those occurring out West this past summer, has been accomplished through "operational" mathematical models. These models are based on empirical correlations for wildland fuels and have generally performed well. They fail, however, when the fire spreads to the built environment where the empirical correlations no longer apply and where there is greatly increased potential for property damage, injury and death. The Oakland and Berkeley Hills fire of October 21, 1991, and the Los Alamos fires of May 2000 are examples of community-scale fires. The potential fuel loadings for various land uses demonstrates that structures generally provide much higher loadings than wildlands do. While this comparison is useful, it could also be misleading since generally, not all of the potential fuel in either the wildland or the built environment will burn. Furthermore, often the time scales for ignition and the heat release rates for the wildland fuel and the fuel in the structures will be widely disparate, and these differences will influence both the spread rate of the fire and its persistence. Although the NIST computational model known as the Fire Dynamic Simulator (FDS) was developed to study building fires, it is now being extended to study community-scale fires. These extensions require much higher resolution data on local topography, buildings, vegetation, and meteorological conditions. They also require additional research on the mechanisms by which fires spread in the built environment between discrete elements, such as structures or structures and trees.