Tempered Glass

This past Sunday, May 31, 2020, marks another day in United States history where peaceful demonstrations and orderly civil disobedience were highjacked by unlawful activity leading to property destruction and theft. The author’s Bixby Knolls, Long Beach, California neighborhood was thankfully sparred wide-spread damage.

This article is not about the political reasons for the nationwide demonstrations.  Instead it concentrates on something that television coverage and social media have not reported. Specifically, how advancement in glass safety has reduced the number of people being injured due to broken glass.In fact, we will never know how many of the looters and bystanders, including police and national guardsman, were able to escape what could have easily been a significant number of bodily injuries from glass shards and glass debris used as weapons.

In the television broadcasts viewed by this author none of the glass storefronts being damaged or destroyed showed human blood from cuts by broken glass.  This is due to the major change in building codes decades ago requiring all commercial glass to be either of the wire safety type or tempered.  Again, from television broadcasts the evidence indicates that all the broken glass shown was of the tempered type.

Here is a short tutorial regarding tempered glass:

Tempered glass is also referred to as toughened or sometimes as fully tempered glass.  The glass sheets are heated to around 1,148℉. They then undergo a high-pressure cooling process called quenching.  This process, which only lasts between 6 to 10 seconds, blasts cool air from various positioned nozzles onto the glass surfaces which cools the outer surfaces of the glass much quicker than the center. As the center cools down it tries to pull back from the outer surfaces resulting in the center remaining in tension while the outer surfaces go into compression which gives tempered glass its high strength. Tempering can also be achieved with chemical treatment but it is far more expensive than quenching and not widely used commercially.

When damaged tempered glass breaks into smaller granular pieces (as can be seen in the image taken of one of the targeted stores near the author’s home) as opposed to large jagged shards of non-tempered glass.  These smaller granular pieces are less likely to cause bodily harm.  The high strength of tempered glass and its high safety record is why you also see it being used in shower and tub glass enclosures, microwave ovens, refrigerator trays, glass table tops, and more.

We can all be thankful to the scientists, engineers, and the many manufacturers of glass products for making our communities safer.