Combustion Models for Wooden Brands.
Combustion Models for Wooden Brands.
(1413 K)
Woycheese, J. P.; Pagni, P. J.
International Conference on Fire Research and
Engineering (ICFRE3), Third (3rd). Proceedings. Society
of Fire Protection Engineers (SFPE), National Institute
of Standards and Technology (NIST) and International
Association of Fire Safety Science (IAFSS). October
4-8, 1999, Chicago, IL, Society of Fire Protection
Engineers, Boston, MA, 53-71 pp, 1999.
Sponsor:
National Institute of Standards and Technology,
Gaithersburg, MD
Keywords:
fire research; fire protection engineering; combustion
models; wood; earthquakes; wildland urban interface;
equations; fire plumes
Abstract:
Eight combustion models for burning brands are reviewed.
An averaged stagnation-point burning model, using the
chemical properties of wood, is used here. Maximum
propagation distances are calculated for disk-shaped
brands lofted in large fires, such as occur after
earthquakes or at urban/wildland interfaces. Lofting in
the fire plume and propagation downwind are approximated
here with distinct flow fields: a Baum and McCaffrey
model for the plume and a constant horizontal velocity
driving downwind propagation. In the plume, the brands
rise with maximum drag and no lift. During propagation,
both lift and drag act on the brand. It is assumed to
have a fixed angle of attack, 35 deg < alpha < 90 deg,
with respect to the relative velocity vector. For these
alpha, the disk lift and drag coefficients are C1 =
1.17cos(alhpa) and Cd = 1.17sin(alpha), so that lift
increases with decreasing alpha. Analytical expressions
for dimensionless propagation distance, height, and
brand size are developed in terms of four dimensionless
parameters: initial lofting height; constant horizontal
wind; angle of attack; and dimensionless burning
parameter.
