Heat Soaked Glass is a process applied to tempered or toughened glass so that the spontaneous breakage of glass is avoided due to the presence of Nickel Sulphide (NIS).As a precaution the toughened glass is made to go through the process of heat soaking so that it can act as a safety glass.
Nickel Sulphide can be present in the glass as an impurity in raw materials during the glass manufacturing process. During the toughening process when the glass is heated from low temperature to high temperature in case there is any Nickel Sulphide it can expand and enlarge in size by 2% to 4% .In case the glass is rapidly cooled the Nickel sulphide cannot come to its original size which results in an internal stress in the glass causing it to break.
Heat Soaking is a process in which the glass is soaked in a heated chamber at 290 degree centigrade for around 2 hours. This process accelerates the expansion of Nickel in case here is any Nickel sulphide is present and causes the glass to break. For safety reasons it is better that the glass breaks in the factory than at site where the glass is installed.
Heat soaked glass is used in areas where there is high risk of human impact.