Thermal and stress analysis of glazing systems under fire conditions

The cracking and subsequent fallout of glazing could significantly affect the dynamics of fires in compartments. The sudden venting resulting from the fallout of a window glass may result in backdraft or flashover depending on the development stage of the fire. The need for research on glazing behaviour in fires was first identified by Emmons [1]. There are two main physical processes involved when a glass pane is subjected to fire in a compartment: (i) heat transfer from the fire source and combustion gases to the glass and (ii) mechanical stress distribution and glass fracture. Pagni [2] suggested a glass breaking criterion based on the glass temperature rise, and subsequently developed a theoretical model for heat transfer and glass breakage which was implemented in the Break1 code [3]. Existing heat transfer models for glazing applications have been reviewed by Cuzzillo and Pagni [4]. The simplest heat transfer model treats the glass as a lumped mass and uses constant heat transfer coefficient. Another approach treats the glass as a distributed mass that absorbs radiation through its thickness with non-linear radiative boundary conditions [4]. Sincaglia and Barnett [5] developed a glass fracture model with emphasis on radiation wavelength dependence; this approach was implemented in the zone type BRANZFire computer code by Parry et al. [6]. All these studies were mainly concerned with heat transfer modelling, prediction of the time to first crack occurrence and the temperature distribution in the glass pane. However they did not provide more detailed information on the stress distribution in the glass which may be useful for a better understanding of the breakage mechanism.