Heat Strengthened Glass is utilized when additional strength is required. By heat strengthening glass, it adds resistance to thermal, mechanical and deflection stresses. Heat treated glass can be measured to have compression between 3500 - 7500 Psi, and is twice as strong as annealed glass of the same size and thickness. Heat treated glass tends to fracture similar to annealed glass but typically stays in an opening. HEAT TREATED GLASS IS NOT SAFETY GLASS. RIG fabricates its heat treated glass to meet ASTM 1048 specifications.