High-temperature behavior of fire-resistant glass

Many modern public buildings such as airports or offices use fire-resistant glass and special frames to create compartments and decrease the risk of fire spreading. Fire-resistant glass consists of layers of float glass with transparent silica gel between them. In fire conditions, due to high temperatures, the intumescent gel starts swelling creating an opaque, porous foam, that blocks the heat transfer to other compartments. Little is published in the literature regarding the fire-resistant glass behavior in a full-scale fire resistance test which is crucial for obtaining a product certification (i.e. EW and EI classes).
When subjected to fire, the fire-resistant glass undergoes a set of reactions that first include glass breakage due to thermal shock and free water vaporization in the silica gel (Fig. 2a) creating a visible white fog effect. Afterward, the bond water starts vaporizing creating bubbles inside the intumescent layer and causing its expansion, as well as glass breakage in case of mechanical restrain. When the foam is fully expanded, various chemical reactions happen depending on its chemical composition. Additionally, the most exposed float glass, due to its high temperature, starts softening and flowing down the furnace at the same time affecting the stability of the fire-resistant glass.
Various small, middle and full-scale tests were performed to understand the global and local behavior of fire-resistant glass. However, further investigation is needed to identify the chemical reactions in the intumescent layer and their influence on the heat transfer within the glass.