Glass is made by fusing silica together with sodium carbonate and calcium oxide at high temperatures. Normal glass or annealed glass tends to break into large pieces. This glass is used to produce more advanced glasses called safety glass. Very strong annealed glass is capable of releasing huge amounts of energy while breaking. This may cause major injury or severe damage. In order to prevent this, various techniques have been developed to design glass that breaks more safely. Such glasses are called safety glasses and are widely used in commercial, industrial, military, medical and household applications.
Modern safety glasses come in different forms – laminated glass and tempered glass. A combination of tempered and laminated glass could be used in making bullet proof glass. We see laminated glasses in windshields of the car. This glass is made by sandwiching a layer of plastic between two layers of glass. This bonding plastic is PVB (polyvinyl butyral). When the glass breaks, the broken pieces stick to PVB. The PVB layer does not allow the broken glass to shatter. We would be able to see a spider web of broken pieces or whole part comes out in one piece. In any case, the risk of being hit by shattered pieces is significantly reduced.
Toughened or tempered glass is used in shower and bathtub enclosures, refrigerator trays, sliding doors, furniture and side and rear windows in automobiles. The glass gets strong as it undergoes a special heating and cooling process. Resulting glass is capable of withstanding nearly four times the amount of force needed to break the normal glass. Tempered glass shatters into tiny chunks instead of breaking into large pieces reducing the damage.