Know your glass!
Annealed Glass – This is the most basic form of untreated glass and should never be used on a piece of machinery. When annealed glass breaks, it creates large, sharp shards and daggers that are likely to severely injure anyone who interacts with it.
Tempered Glass – Tempered glass, sometimes referred to as toughened glass, starts out as annealed glass. Annealed glass goes through an intense heating process which is immediately followed by a rapid cooling process. The tempering process forces the surface of the glass into compression and the interior into tension which is what gives it such great durability and strength. When tempered glass breaks it forms small granular chunks that are much safer and less likely to injure anyone who interacts with it. For reference, tempered glass is usually what is used on the side and rear windows of automobiles.
Laminated Glass – Laminated glass is basically two pieces of annealed glass bonded together by a thin polymer layer. When laminated glass breaks it does not form the dangerous shards that annealed glass produces but rather it creates a “spider web” cracking pattern and the glass is held together by the polymer interlayer. For reference, laminated glass is what is used on the windshield of automobiles.
Polycarbonate – Polycarbonate, often referred to by the trade marked brand names Lexan and Plexiglass, is not glass at all. It is a type of plastic. Polycarbonate doesn’t break like glass. It typically doesn’t break at all. While polycarbonate has incredible impact resistance, it scratches easily and can discolor from prolonged UV exposure. It is usually replaced because of reduced visibility. Polycarbonate is used on faceguards for motorcycle helmets, riot shields, boats, race cars, and select heavy equipment applications where impact resistance is crucial like in forestry applications or on machines with mulching/grinding implements that are sending hard chunks of debris back at the operator at the speed of a bullet.
Safety Glass – Tempered glass, laminated glass, and polycarbonate all fall under the definition of “safety glass” as far as MSHA and OSHA requirements are concerned. When it comes to heavy equipment that is not designed to be driven on roads and highways (but are often found there when working on roads and highways) there really aren’t any laws, rules, or regulations that govern what type of materials the windows are supposed to be made out of.
Tempered glass vs. Laminated glass.
So what’s better Tempered Glass or Laminated Glass ? Polycarbonate is not included in this comparison because it should be used sparingly. Since polycarbonate is virtually unbreakable, image yourself in a machine and every window is polycarbonate. The machine has tipped over onto its door side and is on fire or the cab is filling with water. How are you going to escape? We understand how frustrating, time consuming, and expensive it can be to replace glass on equipment so we can see the desire to replace every window with polycarbonate. But between the scratching, the discoloration, and the scenarios described above we do not recommend it.
- Strength – Tempered wins. Tempered can take a harder hit than laminated glass before breaking. Tempered glass can also bend and flex without breaking whereas laminated glass is rigid and has no give. When laminated glass gets in a bind, it just breaks while tempered glass can bend and flex a little bit without breaking.
- Security – Laminated wins. Since Laminated glass stays together when damaged it is harder for force entry from the outside
- Safety – Tempered wins. While laminated glass is good at keeping outside forces from entering, it can also trap someone inside who needs to get out. If you need to leave a machine in a hurry and the door is no longer an option, you don’t want to risk time, effort, and injury trying to kick out a piece of laminated glass. With the right tools and knowledge, tempered glass is the easiest to break to clear a path for emergency egress. Another safety factor to consider is visibility. When laminated glass takes damage, while it stays in place, usually the spider web cracking pattern makes it practically impossible to see out of which means you need to remove the window entirely to keep operating your machine. Tempered glass, however, will crumble leaving you with a mess at your feet but an otherwise uninterrupted view of the working environment. Laminated glass is safer than tempered glass at high speeds, though. At highway speeds you want outside things to stay outside and inside things to stay inside. But since heavy equipment doesn’t operate at those speeds, that point is moot.
- Acoustics and insulation – Laminated glass wins. The polymer interlayer in laminated glass can have properties that help with UV resistance as well as muffling sounds outside of the machine. Tempered glass can have films and coating applied to help with these features, though.