Double Strength Glass

double strength glass

Double strength glass, such as toughened glass is sometimes used for break glass because it is safer than glass when it breaks.  It can therefore overcome the safety concerns associated with glass.

As the name suggests, it is difficult to break.  We would not recommend using toughened or tempered glass for break glass use as it may to too difficult to break in an emergency.

Toughened or tempered glass is produced by heating normal float glass in a special ‘oven’. The heat puts the molecules under pressure and this makes the glass much stronger.

It does, however, have a weakness. When struck with a sharp instrument it causes the glass to be ‘notched’. This notching can have a chain reaction over the entire pane which suddenly breaks completely and forms cubes. These cubes will fall away if there is nothing to support them.

When used as break glass, the double strength glass will shatter into tiny cubes which then fall away leaving the emergency equipment exposed.


  • Tough – The glass is much stronger than real glass making it more durable and suitable for other uses.
  • Safer – When compared with glass, it is much safer when it breaks because cubes are formed rather than large shards.


  • Difficult to break in an emergency therefore limited break glass use.
  • Limited design – confined to simple shapes.
  • Minimum thickness is 4mm making it unsuitable for some uses.

Toughened or tempered glass can be used for break glass but it is very difficult to break. However, when it breaks, it forms cubes which are safer than the shards produced by real glass. It is often used on buses because it can withstand accidental knocks and bumps but is not recommended for break glass use.

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