Glass Expert discusses Why Tempered Glass Is Safety Glass

Tempered glass is safety glass because it breaks into small cubes. The edges of these cubes are still sharp. They are not "rounded". From a glass expert point of view, the safety aspect comes strictly from the small size, which is a function of the temper stress. If these pieces are interlocked, they can behave in a manner similar to a larger piece broken from an annealed piece of glass.

Video of Tempered Glass Failure

Read Consulting glass failure experts filmed in real-time the failure of a 7' x 1' u-shaped piece of tempered glass. The objective was to demonstrate how rapidly the glass falls apart and to assess the danger to one standing underneath a failed piece of tempered glass.

Tempered glass self destructs once its compressive layer has been penetrated by a defect. In the case as shown by the attached videos, a center punch was used to create a defect which penetrates into the tensile portion of the glass.

Once in the tensile region, the speed of the actual defect (crack) is in excess of 8,000MPH. To the normal eye, the glass piece fails almost instantly. Basically, it self destructs into thousands of small diced pieces as intended. Therefore, one would expect the failed glass to be safe. However, as one can by the videos, these pieces can remain interlocked and can fall as large interlocked "chunks." Naturally these chunks have the potential to injure anyone underneath.

Thus, in this configuration, tempered glass cannot be considered "safety-glass." Showing that there is risk involved with having tempered glass elevated above public access walkways, etc.