Due to the nature of the toughening process, glass will not be as flat as annealed glass and distortion is possible, including the following for horizontally toughened glass:
Overall bow - deformation of the whole pane of toughened glass caused by the heating and cooling process
Roller wave distortion – distortion produced in horizontally toughened glass as a result of the glass process being in contact with the rollers during the toughening process
Edge lift – distortion produced at the leading and trailing edge of the plate
EN 12150-1 sets requirements for distortion in toughened glass.
For more specific details, please refer to the standard, BS EN 12150-1: 2015: Glass in building – Thermally toughened soda lime silicate safety glass. (www.bsigroup.com )