An Experimental Investigation of Glass Breakage in Compartment Fires

An experimental investigation has been completed which examined the breaking of window glass by fire. The experiments were carried out in a compartment designed to achieve a two-layer fire environment characteristic of normal building fires. The experi mental data was collected from two test groups: the first for windows with their edges insulated from the fire (edge-protected) as occurs in normal window installations and the second for windows uniformly heated by the fire (edge-unprotected).

The results of the edge-protected window tests indicated that the glass breakage was caused by a critical temperature difference between the central heated portion of the pane and the glass edge. The experimental work showed the critical value to be approximately 90°C. After the material properties of the glass were determined, the theoretical findings of Keski-Rahkonen were used to obtain a value of 70°C; the difference attributed to radia tive heating of the glass surface thermocouple. The test results also demonstrated a dis tinctive loss of integrity by the windows. When breakage occurred, the cracks spread throughout the glass, joined together and caused catastrophic collapse of the pane.

The results from the edge-unprotected window tests were quite different. Relatively few cracks developed and almost no propagation across the glass was observed. Consequently, there was no window collapse in any of these cases. The breakage did ini tiate at a consistent glass temperature of 197°C, much higher than that observed for the edge-protected case.