Tempered glass is required by code in entryways,
doors, shower enclosures and other areas close to public access
where breakage could be dangerous. The code was introduced
in response to horrific injuries caused when people walked into
sliding glass doors and were lacerated by shards of broken glass.
When it breaks, tempered glass forms small "popcorn" fragments
(right) which are relatively harmless. Tempered glass is also
much stronger than regular glass. Intrepid 200lb glass artist
(right) demonstrates the strength of tempered glass.
For the technically minded:Tempered
glass is produced by heating annealed glass to 1200 degrees F at
which point it begins to soften. Its outer surfaces are then
quickly chilled. As the center of the glass slowly cools, high compression
is created in the surface layer. The strength 4 or 5 times that
of annealed glass. Tempering also imparts a unique safety characteristic:
when it breaks it fractures into relatively harmless fragments.
This phenomenon, also known as "dicing" significantly
reduces the likelihood of injury from broken glass because there
are no jagged edges or shards. Tempered glass also resists
breakage by moving objects that could break ordinary glass and resists
temperature differences of up to 350 degrees F which would cause
ordinary glass to crack.