With tempered glass, spontaneous breakage can occur occasionally resulting from inclusion of materials such as nickel sulfide. These inclusions are inherent to in the production process. When the window breaks, the tempered glass splinters into numerous pieces, which can fall out of the opening either wedged together or as individual pieces. Although the risk of spontaneous breakage is usually minimal, planners should take alternatives into consideration, where applicable. We recommend heat-strengthened glass, for which such cases of spontaneous breakage are unknown. In areas, for which tempered glass is mandatory, we can offer additional heat soak tests on the tempered glass. When nickel sulfide inclusions are heated, their volume canincrease. If this happens, small transverse forces can then lead to spontaneous breakage. Heat soaking accelerates this heat up and expansion process.