Heat-strengthened glass is twice as strong as annealed glass of the same thickness, size and type. If broken, heat-strengthened glass will break into large shards similar to annealed glass. Because of this, the tendency for the glass to vacate the opening is reduced.
The surface compression of heat-strengthened glass with thicknesses of 1/4″ (6mm) and less is 4,000 – 7,000 psi. Surface compression for 5/16″ (8mm) and 3/8″ (10mm) heat-strengthened glass is 5,000 – 8,000 psi. (Because of reader repeatability and instrument tolerances, Viracon’s tolerance for heat-strengthened glass surface compression is +/- 1,000 psi.)
While improving the strength and resistance to thermal shock and stress, heat-strengthened glass does not meet safety glazing requirements as outlined by the American National Standards Institute (ANSI) Z97.1 or the federal safety standard Consumer Products Safety Commission (CPSC) 16 CFR 1201, and therefore should not be used in these situations.