Building Regulations glazing requirements state that glazing in certain areas of a build, known as Critical Glazing, is required to be a designated ‘safety glass’. This could be either laminated glass or fully tempered toughened glass.
Tempered glass is manufactured from standard annealed or ‘float glass’ under a thermal tempering process. Here the float glass is placed on a roller table and heated past its annealing point of around 720 C then rapidly cooled. This tempering process puts the external layers of the glass into compression and inner surfaces into tension.
As a result when a glass panel is broken it fractures into many small, blunt harmless pieces of glass and reduces the likelihood of human injury under impact. Toughened glass is tested under BS EN 12150 to ensure its safety under ‘accidental human impact’.
Toughened glass is also up to five times stronger than equivalent annealed glass panels so is able to be used in larger glass constructions and areas of structural glazing. It is also better suited for external applications of glazing as the toughening process increases the glass’s resistance to sudden temperature changes and differentials, reducing the risk of thermal shock.
Any holes, edging or shaping needed in a toughened panel of glass needs to be advised and implemented before the toughening process begins as toughened glass cannot be cut post tempering. As a rule of thumb required hole diameters should not be less than the thickness of the glass but please speak to LAG about any cut outs required.