Tempered (safety) glass



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.

Broken tempered glass (left) - glass artist (right)

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.

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