Tempered or toughened glass is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering puts the outer surfaces into compression and the interior into tension. Such stresses cause the glass, when broken, to shatter into small granular chunks instead of splintering into jagged shards as ordinary annealed glass does. The granular chunks are less likely to cause injury.
A vandalised telephone booth made with tempered glass
Tempered glass of car rear window. Variations in glass stress are clearly seen when the glass is photographed through a polarizing filter (bottom picture).
Safety approval markings on an automobile vent window made for a Chrysler car by PPG.
Police van with screen protector
Safety glass is glass with additional safety features that make it less likely to break, or less likely to pose a threat when broken. Common designs include toughened glass, laminated glass, and wire mesh glass. Toughened glass was invented in 1874 by Francois Barthelemy Alfred Royer de la Bastie. Wire mesh glass was invented in 1892 by Frank Shuman. Laminated glass was invented in 1903 by the French chemist Édouard Bénédictus (1878–1930).
Broken safety glass shows a characteristic circular "spider web" pattern
Broken tempered glass showing the shape of the granular chunks
Broken laminated safety glass, with the interlayer exposed at the top of the picture
Wire-mesh-reinforced glass in the Lloyd's Building
