Heat Soaked Safety Glass

During float glass manufacture, impurities in the glass batch can result in inclusions in the finished product. These inclusions are so small that they are normally invisible to the naked eye and yet they can cause spontaneous breakage in Toughened Safety Glass.

The most notorious of these inclusions is nickel sulphide (NiS) crystals (stones), which can be contained in the raw material during the production of the glass.

The glass toughening process requires the glass to be heated to just below its softening point and then rapidly cooled. Because this heating and rapid cooling process induces substantial tension in the glass, nickel sulphide stone inclusions in the tension core can cause spontaneous breakage, as they are known to change phase (expand) some time after the toughening process.

Heat soak testing is a secondary process that can be applied to the Toughened units after initial processing. Heat soaking reduces the incidence of Toughened Safety Glass breaking spontaneously after installation by triggering prone panels before they are installed, meaning only the lower risk units ever make it to site. This therefore reduces the associated replacement, maintenance and disruption costs and the risk of the building being classified as unsafe.