Tempered glass is one of two kinds of safety glass regularly used in applications in which standard glass could pose a potential danger. Tempered glass is four to five times stronger than standard glass and does not break into sharp shards when it fails. Tempered glass is manufactured through a process of extreme heating and rapid cooling, making it harder than normal glass.
The brittle nature of tempered glass causes it to shatter into small oval-shaped pebbles when broken. This eliminates the danger of sharp edges. Due to this property, along with its strength, tempered glass is often referred to as safety glass.
The thermal process that cures tempered glass also makes it heat resistant. Tempered glass is used to make the carafes in automatic coffee makers and the windows in ovens. Computer screens, skylights, door windows, tub enclosures and shower doors are more examples of places you will find tempered glass. Building codes also require the windows of many public structures to be made of tempered glass.
Automobiles use a different type of safety glass for the windshield and tempered glass for the back and side windows. Windshields are made from laminated glass, which sandwiches a sheet of plastic between two panels of glass. When the windshield breaks, the glass panels stick to the plastic film, rather than falling away to possibly injure the driver or other passengers.
Tempered glass breaks in a unique way. If any part of the glass fails, the entire panel shatters at once. This distinguishes it from normal glass, which might experience a small crack or localized breakage from an isolated impact. Tempered glass might also fail long after the event that caused the failure. Stresses continue to play until the defect erupts, triggering breakage of the entire panel.
In recent years, acrylic has replaced tempered glass in many applications in which heat is not a factor. Acrylic is 20 times more impact resistant than glass and does not shatter like tempered glass. Instead, acrylic dents if the impact is strong enough. If the force is sufficient to cause acrylic to fail, it will crack without shattering.
Acrylic is also half the weight of glass and has many other advantages. However, it is flammable. Therefore, you won’t find an acrylic coffee carafe or oven door.