The Spontaneous Breakage of Tempered Glass
WHY DOES GLASS “EXPLODE” WHEN BROKEN?
When used as safety glazing and in its resistance to being broken by human impact loads, tempered glazing behaves robustly in protecting building occupants. If ordinary, non-safety glass were to be specified and installed in hazardous locations, building occupant life safety would be gravely compromised. Catastrophic injuries and/or death are commonplace when humans impact non-safety glazing. The robust performance of tempered glass as a safety glazing material is due to the heat-treating process it undergoes during its manufacturing.
Tempered glazing starts out as basic, ordinary, non-safety glass called annealed glass. The tempering process transforms annealed glass into fully tempered glass. The process, called quenching, involves uniformly heating annealed glass to more than 1100 degrees Fahrenheit and then rapidly cooling it with relatively much cooler high-pressure air blown across its exposed surfaces from a precisely engineered grid of nozzles. This application of cool air to the outer surface of the glass cools the surface of the glass much more rapidly than the central core. The central core remains at a relatively much higher temperatures until it also eventually cools additional time and exposure to ambient temperatures.