Why does tempered glass break? Can it break on its own?
Tempered glass is the safety glass used in shower enclosures. It is far stronger than ordinary glass, but it is not unbreakable. Knowing why it can break lowers the risk, and explains why there is no need to panic if it ever does.
In short
- Tempered glass is about five times stronger than ordinary glass and breaks into small, blunt pieces.
- Impacts, point pressure, sudden temperature changes and badly adjusted doors raise the risk of breakage.
- Very rarely it can break with no visible cause; no glass maker can guarantee that it never will.
What is tempered glass?
Tempering means heating glass in a furnace to 600–700 °C and then cooling it suddenly. This puts the outer surfaces under compression and the core under tension. The result is glass about five times stronger than untreated glass.
Tempering has two goals: to make the glass far more resistant to impacts, and, if it does break for any reason, to make it crumble into small, blunt pieces instead of long, sharp shards. This all but removes the risk of serious, lasting injury when it breaks.
The stress inside the glass cannot be measured or photographed. Its quality is assured by tight control of production settings and by break tests.
Why does tempered glass break?
Glass can break when the force on it exceeds the stress it can carry. The most common causes are:
- Sudden or repeated point impacts, especially on the edges,
- Knocks from sharp or pointed objects,
- Sudden, large temperature changes,
- Mechanical strain from installation or door adjustment,
- Pressing too hard on the glass while cleaning.
The most common cause: a badly adjusted door
Rollers clogged with dirt and limescale stop doing their job, the door no longer runs smoothly on its rail, and we start forcing it. A door that does not close fully and force spread unevenly across the glass can lead to the panel cracking or breaking. Forcing the door without noticing this is one of the most basic causes of breakage. Our roller care article explains how to keep rollers in good shape.
Can tempered glass break on its own?
Rarely, yes. Glass can break even when none of the causes above are present. This does not always mean a fault in the glass or its production; factors that cannot be measured, such as buildings flexing naturally or swings between hot and cold weather, can play a part.
What matters is that the glass does not seriously harm anyone when it breaks, and that is exactly what tempered glass is designed for: there may be minor scratches, but serious injury is not expected. No glass maker can guarantee that tempered glass will never break once it is in use.
Where else is tempered glass used?
Besides shower enclosures, it is used wherever safety matters:
- Cars and home appliances (oven and fridge glass),
- Glass facades, glass balconies, balustrades and glass doors,
- Glass furniture, bus shelters and billboards,
- Busy places such as schools, offices and public buildings.
