Glass Glossary

Tempered Glass

Last Updated: November 23, 2023

Tempered glass is a type of safety glass that has been thermally treated to significantly increase its strength compared to standard annealed glass. This process involves heating the glass to a high temperature and then rapidly cooling it to induce surface compression. As a result, tempered glass is at least four times stronger than annealed glass of the same thickness in resisting windload.

In the event of breakage, tempered glass shatters into very small particles, which usually evacuate the opening. However, these small fragments can pose a risk of damage or injury to people below. Therefore, tempered glass should be used judiciously in commercial construction.

Figure: Tempered glass break pattern

Cardinal advises the use of tempered glass primarily for specific applications where safety glazing codes are mandated. Such applications include door assemblies, sidelights, and certain window varieties. Tempered glass possesses a strength approximately four times greater against windload, making it an ideal choice for large windows to fulfill design specifications. Additionally, it is apt for fire knockout panels, wherein the glass serves as a protective barrier but can be readily shattered to allow emergency access. In situations where there’s minimal risk of glass fallout, tempered glass may also be deemed suitable.