The glass industry has been heat treating architectural glass to increase its strength since about 1930. The process of heat- treating glass involves uniformly heating glass close to its softening temperature and then rapidly, and uniformly, cooling it. This process results in the development of surface compressive stresses, thus increasing the strength of the glass. Heat-treated glass is used in many of today's architectural glazing applications where increased strength to resist glass breakage is desired. Vision and spandrel areas of buildings as well as building entrances, glass railings and balustrades, and other applications where public safety is a priority, are common examples. This document was published in January 2014 and updated in May 2019.