Technical Advice | Glazing Technologies
What Is Heat Soaking and Where Should I Specify It?
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We do not make up topics just to get clicks. Our topics come from the questions people really ask us. Architects ask us when they plan a building. Builders ask us on-site. Homeowners ask us when they plan their project. If the same question keeps coming up, we write about it.
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The first draft is written by someone who works with that glazing system. This might be a technical advisor, a designer, or a product expert.
They write using three things, in this order. First, our own finished projects and what we learned from them. Second, the building rules and the glass standards that apply. Third, the maker's technical data for the system we supply. When we give a number or a limit, we say where it comes from. We name the rule or standard and link to the official source so you can check it yourself.
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Heat soaking is a testing process carried out in the manufacturing stage of glass, used to reduce the risk of spontaneous breakage in architectural glazing. Imagine investing in a stunning glass façade or skylight, only to face a sudden crack or fracture that interrupts daily operations and hits your budget hard. One of the major culprits behind these unexpected failures is the presence of nickel sulphide inclusions.
It is often advised that heat soaked glass be specified on high level, inaccessible or difficult to fit installations due to these installations of architectural glazing being harder to access and replace if required in the future. Minimising the risk of having to replace glass in the future reduces future cost and disruption to a client or building. It is always recommended that a glass replacement plan is put in place for extensive glass installations.
A nickel sulphide inclusion is a naturally occurring phenomenon within toughened glass in which small particles of nickel sulphide may be present in glass after the manufacturing and toughening process.
Although the inclusions are not visible, these particles can cause spontaneous glass breakages if the glass is aggravated by sudden or extreme temperature changes.
You can read more about the science behind these inclusions in our technical article: Nickel Sulphide Inclusions.

Heat soaking is a destructive test treatment that takes place after any toughening and laminating process’. The finished glass is placed into a large heat soaking oven and heated to extreme temperatures.
After being heated to around 290 +- 10 degrees Celsius and held at that temperature for approximately 2 hours, it is removed from the oven facility. During this thermal treatment, any glass containing nickel sulphide is forced to shatter, leaving behind only the panes with a reduced risk.
The risk of spontaneous breakage for heat soaked glass drops dramatically from 1m2 in every 10,000m2 to just 1m2 in every 1 million m2.

Heat Soaked Glass can be specified for any installation of architectural glazing. However, it has more value in glass installations that may be difficult to access or replace once construction is completed.
Some areas where Heat Soaked Glass can add value are:
Another note for specification would be that heat soaking is only really necessary for glass panes 6mm thick and over.
The general consensus within the glass industry is that 4mm toughened glass isn’t thick enough to support a Nickel Sulphide inclusion and that it would automatically break during the toughening process. So heat soaking glass of that thickness would not provide any further reduction in the likelihood of a NSI.

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Structural Glass & Structural Glazing – What is it?

Our experienced team of glass experts are on hand to answer any of your questions, including questions about whether heat soaked glass would be suitable for your project. Just get in touch with us by calling 01494 722 880 or visit our contact page for other ways to get in touch. We look forward to speaking with you soon.