The following information on toughened safety glass breakage is offered from AFG Industries, Inc. This information is intended to provide the basis for a better understanding of the unusual characteristics of toughened safety glass, not to shrug off any serious problems.

1. There is frequently a misconception that toughened safety glass is 'unbreakable' or 'nearly unbreakable'. This is NOT true. Toughened safety glass is definitely breakable and some of the things that can break annealed glass can also break toughened safety glass.
   
2. Fully toughened safety glass as supplied for shower doors, patio doors, etc., is four to five times as strong as annealed glass of the same type and thickness and can meet CPSC break-safe requirements for Category I or II safety glazing.
   
3. Fully toughened safety glass, when broken, fractures into hundreds of small blunt particles. This is by design and is excellent proof of a well toughened safety product, not of a defective product. It is this fail-safe characteristic of toughened safety glass that makes it an excellent product for safety glazing applications.
   
4. Breakage of annealed glass is usually a simple one or two line fracture attracting little attention or comment (unless the glass has been smashed by a severe impact). Cracked lites of annealed glass have been seen by almost everyone a number of times and cause no great surprise. Conversely, breakage of fully toughened safety glass is spectacular, infrequently seen or experienced by the public, and attracts considerable surprise, attention, comment and question.
   
5. Annealed glass is easily broken by mechanical stress, impact and moderate thermal stress. Fully toughened safety glass will withstand much greater stresses than annealed glass before failure. However, it is the nature of fully toughened safety glass that it CANNOT break in the simple fashion of annealed glass, but the individual lite must release entirely into small fragments, even for a very small initial fracture.
   
6. Another characteristic of toughened safety glass is that occasionally a lite will not release immediately at the time of damage, but at some time, perhaps weeks, later. This adds to the surprise and amazement of bystanders since no apparent cause is immediately evident. This type of behavior is one of the factors leading to the so-called “spontaneous breakage” of toughened safety glass.
   
7. Spontaneous breakage or delayed release can occur if the lite has been damaged during its manufacture, shipping, subsequent installation handling, or use, or there is an inherent weak spot or stress concentration within the glass body. Most damaged lites or lites with inclusions that cause excessive stress concentrations will not survive the thermal rigors of the tempering operation. Of those few that do survive, most will release within a day or so, leaving a small portion of unexplained breakage.
   
8. Although some spontaneous breakage will occur as noted in #6 and #7 above, much breakage is erroneously called 'spontaneous' only because there was no easily visible cause. Frequently, inspection of the surround will reveal damage done to the framing through installation or abuse so that the glass is stressed near its breaking point and a subsequent movement, or temperature change forces the glass to yield.
   
9. Accidental or deliberate vandalism is another cause of unexplained breakage.