Thermal breakage can be influenced by a number of factors. A critical factor to consider in the early stages of glass selection is whether or not the glass will be shaded. When glass is partially shaded by building overhangs or extensions, it becomes cooler at the edges, and stress in the glass may occur, which can result in thermal breakage.
In areas where thermal breakage may be of concern, a thermal breakage analysis must be completed to determine if heat-treating (heat strengthening or tempering) may be needed.
Heat treating may also be necessary due to high wind loads or safety glass code requirements. The degree to which the central area of the glass becomes hot is largely dependent on the solar absorption of the glass, which varies among different types of glass. Some additional factors that may influence thermal breakage are listed below:
- Glass framing that is in direct contact with concrete or other materials that may contribute to the cooling of the glass edge
- Excessive coverage of the glass edge by the frame
- Heat-absorbing films attached to the glass after installation
- The use of internal shading devices such as curtains, drapes or venetian blinds—If shading devices are used, they must be placed away from the glass to allow for a free flow of air at the glass surface
- The airflow from room cooling or heating vents must be directed away from the glass
- Buildings not heated during the construction phase may experience an increase in thermal breakage
- Generally speaking, the greater the glass edge area, the greater the risk of thermal breakage
The potential risk can be estimated by a computer-aided thermal stress analysis.
Contact regional ASM for assistance with thermal stress analysis.