Heat-soak testing is an additional controlled heating process applied after toughening. It is intended to identify a high proportion of panes containing nickel-sulphide inclusions that could otherwise contribute to spontaneous breakage in service.
Why overhead glass is different
Toughened glass is strong and breaks into relatively small particles, but rare nickel-sulphide inclusions can lead to delayed breakage. Consequences are greater where glass is overhead or difficult to replace.
Overhead Glazing normally specifies heat-soak-tested toughened glass as part of its rooflight approach, together with a suitable laminated inner pane.
Risk reduction, not elimination
Heat-soak testing materially reduces the risk associated with nickel-sulphide inclusions, but it cannot prove that spontaneous breakage will never occur.
The complete safety strategy also considers lamination, glass retention, support, edge quality, installation and replacement access.
Project checklist
Heat-soak testing reduces a particular risk; it is not a warranty against every cause of glass breakage.
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