What occurs to ordinary window glass when exposed to heat?

When ordinary window glass is exposed to heat, it typically undergoes thermal stress due to the uneven expansion of the material. If heated rapidly or unevenly, the glass can crack or shatter. This phenomenon can happen suddenly, creating a loud popping or cracking sound as the glass breaks apart. The material does not melt completely under normal fire conditions; instead, it becomes weakened and brittle, which increases the likelihood of breaking.

In contrast, melted glass does not turn into tempered glass, as the tempering process involves a specific heating and cooling method that increases its strength. Window glass also does not become more resistant to heat; it generally becomes less stable, making it more prone to failure under thermal stress.