Tempered glass is made from the normal annealed glass via a thermal tempering process in which the glass is subjected to heat till its softening point and then rapidly cools. This gives glass strength. A fully glass tempered glass is used in most modern glass façade, where glass strength is required. A fully tempered glass is recommended for windows that are on high floors or skylight.
A fully tempered glass as required in astm c 1048 is generally 4 to 5 times stronger than annealed glass and twice as strong as heat strengthened glass of similar thickness, size and type. When broken by impact, fully tempered glass immediately disintegrates into relatively small pieces thereby greatly reducing the likelihood of serious cutting or piercing injuries in comparison with ordinary annealed glass.
