Tempered or fired glass is a type of safety glass that has undergone controlled heat or chemical treatments increasing its strength compared to normal glass. The hardening leads the outer surface of the glass pane to compressive stress and the inner surface to increased tensile forces. When the tempered glass breaks, these forces are released, causing it to shatter into small granular pieces instead of jagged fragments like ordinary unfired glass. Granular pieces are less likely to cause injury.