Fully tempered glass is a safety glass, generally four times stronger than the same thickness of ordinary annealed glass. Taking ordinary glass to a tempered state involves heating the glass in a special furnace to approximately 1260° Fahrenheit, then setting a permanent tension between the glass “core” and surfaces by rapidly cooling the glass in a high-pressure quench.. When fully tempered glass is broken, the release of tension between these surfaces initiates a cascade of much smaller glass fragments than ordinary annealed glass. While a person can still get cut by this safety glass, the objective is to eliminate as much of the dangerously long shards of glass raining down within the broken debris as possible.