Safety glass is actually a broad term for several different types of glass. One of these is tempered glass, which you will find in your car’s side windows and back window. It is also located in all glass doors of a residence and business that a whole human body normally passes through. It is four times more resistant to surface impact than regular plate (annealed) glass of the same thickness. When this safety glass breaks it shatters into small pebble to marble size pieces that, while they might still cut you a little, will not cause a mortal wound. There are plenty of videos on youtube of tempered glass being broken if you want to see it happen for yourself.
“Poly(methyl methacrylate) (PMMA) is a transparent thermoplastic, often used as a lightweight or shatter-resistant alternative to glass.” ~Wikipedia
Although it is not technically glass, PMMA (commonly called by the trademarked name “Plexiglas” or Acrylic) can be used in some cases where safety glass is required. There also is Polycarbonate which is usually known under the name of Lexan or other similar brand names. Acrylic is usually preferred because of its moderate properties, easy handling and processing, and low cost compared to polycarbonate. So whenever strength is not required acrylic is normally used.
Now, Since these are plastics and not actually glass, they are actually much easier to scratch and can end up with many micro scratches that may end up appearing as swirls in some cases from attempting to clean the surface with improper methods. At the same time these plastics can actually bend much further than glass. This helps them to absorb surface impacts and resist breaking. When the acrylic plastic finally does reach the breaking point it does so in large pieces but these pieces usually do not fall out, and even the broken pieces are flexible reducing the chance of injury.
Of course, these plastics are not as heat and fire resistant as glass. But they still open up many possibilities for different applications where glass might not be the most appropriate material. Case in point, most aircraft make use of these plastics for their cockpits during and since World War 2.
Another type of safety glass that is widely used is laminated glass. This type of glass is made up of two pieces of regular plate (annealed) glass that is joined together with a resin interlayer, normally polyvinyl butyral (PVB). The purpose of this interlayer is to keep the glass bonded together even after it breaks, and to keep the majority of it stuck together to prevent large shards from falling off and causing large amounts of injury.
You will find this type of safety glass in all American automobile windshields. It is also used in skylights. It is normally employed in places where Human body impact is possible or if the glass might fall down upon someone below. Also, due to the resin interlayer this glass functions very well as a sound dampener.
Since it is a safety glass, it can be used in many of the same places as tempered glass but not all places. Since it is two panes of glass stuck together, it is normally no thinner than 1/4″ thick. tempered glass can be as thin as 1/8″ which is half that thickness. So there are some applications where tempered glass is used instead of laminated.
Chicago tempered glass (we do glass)
Next week we’ll talk of a safety glass that most people do not normally think of as a “glass”. Until then! Thanks for tuning in! More interesting facts about glass will be posted in the future so keep coming on back! And if you need us to do any Chicago tempered glass or safety glass work for you please visit our website or give us a call!