Heat soaking is an additional process that can be done to thermally toughened glass to reduce the risk of breakage in service from inclusions in the glass. The process puts the glass through a heat cycle to encourage the glass break under test if it is at risk from nickel sulphide inclusions. The result is a pane with a much lower risk of fracture from such inclusions than ‘ordinary’ thermally toughened glass.

There are a number of applications in which Pilkington generally recommends that toughened glass should be heat soaked. These are safety critical areas such as sloping or horizontal overhead applications where Pilkington Toughened Glass is used as single glazing or as the lower pane of an insulating glass unit and applications where Pilkington Toughened Glass is used as a protective barrier.

In the Pilkington Planar™ bolted structural glazing system, toughened glass is heat soaked as standard.

For less critical areas e.g. internal partitions, ‘ordinary’ vertical windows, etc. heat soaking is not specifically recommended, although it can be considered if required. Locations where the cost of re-glazing is relatively high may also make heat soaking an economic consideration by reducing the risk of breakage overall.

The standard for heat soaked thermally toughened glass is BS EN 14179-1 and -2.