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
A diving mask is an item of diving equipment that allows underwater divers, including scuba divers, free-divers, and snorkelers, to see clearly underwater. Surface supplied divers usually use a full face mask or diving helmet, but in some systems the half mask may be used. When the human eye is in direct contact with water as opposed to air, its normal environment, light entering the eye is refracted by a different angle and the eye is unable to focus the light on the retina. By providing an air space in front of the eyes, the eye is able to focus nearly normally. The shape of the air space in the mask slightly affects the ability to focus. Corrective lenses can be fitted to the inside surface of the viewport or contact lenses may be worn inside the mask to allow normal vision for people with focusing defects.
Snorkeler wearing a clear silicone diving mask
Views through a flat mask, above and below water
Disassembled components of a single-window, low-volume dive mask
Assembled diving half-mask showing the retaining strap