Back in the days of the late 1990s and early 2000s, I remembered seeing many school bus side passenger windows that were made by the company “Guardian,” with the distinctive “G” logo on them. “Those windows aren’t safety glass” I knew, as I thought we’ve talked this through before… car windows are safety glass, school bus front and rear windows are safety glass, but school bus side windows are not safety glass. And by safety glass, I mean the glass-plastic-glass sandwich.
Well, we can hold that thought about safety glass, even on car windows. So, I was looking at one of the old 1970s or so era large glass back door windows in my house, and I noticed that it also had the distinctive Guardian “G” logo on it. So, I looked closer at the markings and read “Guardian tempered safety glass.” Interesting, so I looked that up on the Internet, and this is what I found out about it…
20190309/DuckDuckGo guardian tempered safety glass
20190309/https://www.guardianglass.com/GuardianGlass/glassproducts/TemperedGlass/index.htm
Guardian tempered safety glass is 5 times stronger than annealed glass, so it is less likely to break. But, if it does break, it shatters into very small pieces that are less likely to cause injury than larger shards. Now, about the side windows on cars. For many car models, those windows too are designed to shatter into many small pieces, and only the front and rear car windows are truly made of the glass-polycarbonate-glass sandwich.
Guardian is a pretty old company… and float glass is a surprisingly young technology. Not until the 1960/1970s did it gain commercial scale.
20190309/https://en.wikipedia.org/wiki/Guardian_Industries
20190309/https://en.wikipedia.org/wiki/Float_glass