There are two main types of heat treated glass, fully tempered and heat strengthened.
Usually just called tempered glass, fully tempered glass is a safety glass used in many applications where the possibility of human contact is high. This glass is 4-5 times stronger than non-tempered glass and breaks into very small pieces when fractured.
Heat strengthened glass is twice as strong as non-tempered glass. Fracture characteristics of heat strengthened glass vary widely from much like annealed glass to similar to fully tempered glass. For this reason, heat strengthened glass does not qualify as a safety glass.
Fully tempered glass and laminated glass are classified as safety glass.
Laminated glass consists of two or more panes of glass with a tough plastic interlayer, bonded together under heat and pressure. Laminated glass is also used as an effective sound control product. Laminated glass is commonly used in airports, sound studios, schools and in houses near freeways to keep away unwanted noise from airplanes, heavy machinery and traffic.
Anywhere glass is more prone to human contact such as doors, windows close to the floor, stair landings and tub/shower enclosures. Check your local building code for details or more specific locations.
Tempered glass must first be cut to the finished size, since it cannot be cut or modified after it is tempered. Then the edges are belt seamed or sanded to remove any sharp edges. Next it is washed to remove all fabricating debris. Finally, it is heated to almost 1200°F and then quick cooled, which produces the temper.
All tempered glass windows must have a permanent tempering stamp applied to each piece of glass to signify it is tempered.
Twice per year, beginning of spring & beginning of fall.
Is there a standard for washing glass before tempering?
No. But, it is highly advised that all glass be washed prior to tempering to remove all fabricating debris.