Causes of Spontaneous Glass Breakage and How to Prevent It

Spontaneous glass breakage is an extremely rare occurrence, however it is a possibility. There are a few reasons that glass would break without impact and the two main ones are nickel sulphide inclusions or thermal shock (also known and thermal stress).

This is a topic not often spoken about and can come as a shock to homeowners when two years after installation their glazing suddenly shatters.

It is important to know what can cause spontaneous glass breakage, when it should be a concern and what can be done to prevent it.

shattered structural glazing caused by nickel sulphide inclusion in toughened glass

Causes of Spontaneous Glass Breakage

Thermal Shock

When there is a significant temperature differentiation across the surface of a glass pane, this can put the glazing under what is known as ‘thermal shock’, also known as ‘thermal stress’.

This can occur in different ways such as there being a drastic difference between the edge and the centre of the pane.

Changes in temperature cause glass to expand and contract, and when this is done at different severities across the glass with the edges and centres changing in opposite directions, the pane is put under stress which can cause it to break.


Nicked Sulphide Inclusions

During glass production, small nickel sulphide stones can form within the glass, there is no specific cause for this it is a random but rare occurrence. This small impurity, known as a nickel sulphide inclusion, can sit dormant for weeks or even years after manufacturing and installation.

These inclusions will contract while the glass cools and become enclosed within the glass, remaining in their contracted state. Over time these inclusions will try to expand back to their original state, and occasionally they will succeed causing the glass to shatter ‘spontaneously’.

The pane shatters if these stresses exceed the strength of the glass, causing it to break. Nickel sulphide inclusions breakages are often characterised by a distinctive pattern that resembles a butterfly or figure of eight.

glass wall spontaneously shattered in a structural glass box
glass spontaneously shattered due to thermal shock and stress

How to Prevent Spontaneous Glass Breakage


Toughened Glass

Using toughened glass in a glazing system reduces the risk of spontaneous glass breakage from thermal shock. The rapid heating and cooling process eliminates weak panes leaving glazing that is up to five times stronger than standard float glass.

The toughening process can also reduce the already very low risk of nickel sulphide breakages. This is due to the nickel contaminants in the glass reacting with sulphur during the heating process.


Heat Soaked Glass

Heat soaking is an extra step that can be included in the glass manufacturing process. It involves a controlled heating cycle that accelerates and nickel sulphide expansion that would occur over time resulting in any weak panes that would have been at risk of a nickel sulphide shattering.

This process eliminates about 95% of problem panes, however no process can eliminate 100% of nickel sulphide inclusions.

Sieger used toughened glass as standard to ensure our glazing systems surpass requirements and keep our customers safe. Heat soaking incurs additional costs and it not always necessary however there are some applications where we may recommend it.

Heat soaking may be necessary for installations located in hard to reach places, as replacing the glass would be difficult and possibly costly. It can also be useful for decorative glazing that has intricate designs that would be difficult to replicate.


Again, spontaneous glass breakage is extremely rare and should not be a concern in majority of cases. If you have any questions don’t hesitate to get in touch with the team who will be happy to help.

Call 01494 722 882 or email [email protected]


thermal shock causing glazing to spontaneously shatter

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