Fire Induced Thermal Fields in Window Glass I - Theory.
Fire Induced Thermal Fields in Window Glass I - Theory.
(587 K)
Joshi, A. A.; Pagni, P. J.
NIST GCR 93-634; 34 p. December 1993.
Fire Safety Journal, Vol. 22, No. 1, 25-43, 1994.
Sponsor:
National Institute of Standards and Technology,
Gaithersburg, MD
Available from:
National Technical Information Service
Order number: PB94-139722
Keywords:
glass; windows; computer models; fire models;
mathematical models; radiation; thermal stresses; vents;
equations; temperature profiles; heat flux
Abstract:
Window glass breaking plays an important role in
compartment fire dynamics as the window acts as a wall
before breaking and as a vent after breaking. Previous
work suggested a model for the time to breakage of a
window glass exposed to a particular fire. In this
paper, the glass thermal fields obtained using that
model are examined in detail. The temperature field
dependence on heat transfer coefficients, radiative
decay length and flame radiation is explored. The
results show that the glass surface temperature
increases with a decrease in the decay length and
increases with an increase in flame radiation heat flux.
Early in the fire, the glass temperature may be higher
than the hot layer temperature due to direct impingement
of flame radiation. Later the glass temperature lags the
hot layer temperature. The variation of the time to
breakage as a function of the shading width and decay
length is also presented and the results indicate that
the breaking time decreases with an increase in the
shading width and decreases with a decrease in decay
length. Heat flux maps for typical conditions indicate
that most of the heat influx is stored in the glass,
increasing its temperature.
Building and Fire Research Laboratory
National Institute of Standards and Technology
Gaithersburg, MD 20899