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Fire Induced Thermal Fields in Window Glass I - Theory.


pdf icon Fire Induced Thermal Fields in Window Glass I - Theory. (1390 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.