Fully tempered glass is approximately four times stronger than annealed glass of the same thickness and configuration.
When broken, it will break into many relatively small fragments, which are less likely to cause serious injury. The typical process to produce tempered glass involves heating the glass to over 600 °C, then rapidly cooling to lock the glass surfaces in a state of compression and the core in a state of tension.
Tempered glass is referred to as “safety glass,” because it meets the requirements of the various code organizations. This type of glass is intended for general glazing, and safety glazing such as sliding doors, storm doors, building entrances, bath and shower enclosures, interior partitions, and other uses requiring superior strength and safety properties.
Tempered glass cannot be cut or drilled after tempering, and any alterations, such as edge grinding, sand blasting or acid etching, can cause premature failure.
The requirements on tempered glass and the properties are defined in the EN 12150.