Fire Growth and Spread Models. (Model for Opposed Flow Flame Spread Over Charring Materials.) (Abstract/Presentation/Visuals)
Fire Growth and Spread Models. (Model for Opposed Flow
Flame Spread Over Charring Materials.)
(Abstract/Presentation/Visuals)
(252 K)
Atreya, A.; Baum, H. R.
NIST SP 998; May 2003.
Keywords:
fire growth; fire spread; pyrolysis; flame spread;
charring; fire models; temperature
Abstract:
Opposed-flow flame spread over the surface of a
semi-infinite solid has been a subject of much
investigation in the past. Several elegant analytical
flame spread models have also appeared in the
literature. It is indeed fascinating to note how the
authors of these and other previous studies reduced the
complex flame spread problem with novel approximations
to obtain analytical flame spread formulas. It is even
more fascinating to see how well these formulas agree
with the experimental measurements for materials for
which they were designed. Previous studies, however,
have focused primarily on the gas phase part of the
problem and the solid was assumed to "vaporize" at a
known fixed temperature. Yet, a large number of natural
and synthetic polymers do not simply "vaporize" -
instead, they undergo a complex thermal decomposition
process which results in an insulating layer of char on
the surface. This char layer thickens with time and
gives rise to a two-phase moving boundary problem in the
solid. Due to this difficulty, the understanding of
flame spread over these solids is lacking (a noteworthy
contribution toward developing a model of wind-aided
flame spread over charring materials was made by
Carrier, et. a. Also, to obtain an analytical solution,
it was often necessary to simplify the gas-phase
momentum and continuity equations by using a uniform
Oseen velocity 'Ug' and the constant pressure condition.
Thus, the objective of the present study is to extend
the previous work on "vaporizing" solids to charring
materials like wood and provide a more realistic
description of the gas phase.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899