Community-Scale Fire Spread

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 during the summer of 2000, 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. This paper appeared as pp 126-139 in: Blonski, K.S., M.E. Morales and T.J. Morales, 2002. Proceedings of the California’s 2001 Wildfire Conference: Ten Years After the 1991 East Bay Hills Fire, 10-12 October 2001, Oakland California Technical Report 35.01.462. Richmond CA; University of California Forest Products Laboratory. Published by: University of California Agriculture & Natural Resources, Forest Products Laboratory, 1301 South 46th Street, Richmond CA 94804, www.ucfpl.ucop.edu. Proceedings of the California’s 2001 Wildfire Conference:10 Years After the 1991 East Bay Hills Fire 1 COMMUNITY-SCALE FIRE SPREAD R.G. Rehm, A. Hamins, H.R. Baum, K.B. Mcgrattan and D.D. Evans, Building and Fire Research Laboratory, National Institute of Standards & Technology, Gaithersburg, MD 28099 Email: Ronald.Rehm@nist.gov 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 during the summer of 2000, 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.