Safety glass
Glass engineered to reduce breakage and injury risk.
Safety glass is designed to either resist breaking or reduce the danger if it does break. The three main types are toughened (or tempered) glass, laminated glass, and wire mesh (or wired) glass. These methods can be combined, so a single pane could be both toughened and laminated and include wire mesh, though combining wire mesh with other techniques is rare because it often undermines the benefits of each. In many developed countries, building regulations require safety glass to improve property safety.
Toughened glass is strengthened through controlled heating or chemical processes. When it breaks, the internal stresses cause it to crumble into small, rounded chunks rather than sharp, jagged shards, which reduces injury risk. Because of this strength and safety, it is used in car windows, shower doors, glass tables, refrigerator trays, bulletproof glass components, diving masks, and cookware. In the United States, federal law has required tempered glass in doors and tub or shower enclosures since 1977.
Laminated glass consists of layers of glass bonded to a plastic interlayer, usually polyvinyl butyral (PVB). When broken, the interlayer holds the glass pieces in place, producing a spider-web pattern of cracks instead of large, sharp fragments. It is commonly used where human impact is possible or where shattered glass could fall, such as skylights and car windshields. In hurricane-prone areas, it is used in storefronts and windows. The PVB layer also dampens sound and blocks most UV radiation—88% in windows and 97.4% in windshields.
Wire mesh glass has a metal grid embedded inside it. In the United States, it is valued for fire resistance, as it withstands heat and hose streams, and is used on service elevator shafts and in institutional buildings to prevent fire spread. The wire keeps the glass in place even when it cracks from heat. However, the wire actually weakens the glass compared to unwired glass, and the metal can make fractures more irregular, increasing injury risk. This has led to a decline in its use, especially in schools. Newer fire-rated and safety-rated materials have emerged, and the US International Building Code effectively banned wired glass in 2006. Canada still permits it but is reviewing its codes, with restrictions expected. Australia has no similar review underway.
- field
- Glass technology and building safety
- known_for
- Creating glass that is less likely to break or less hazardous when broken
Lore & Background
It is processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering creates balanced internal stresses which cause the glass sheet, when broken, to crumble into small granular chunks instead of splintering into jagged shards. It has a grid or mesh of thin metal wire embedded within the glass. Despite common belief, wired glass is actually weaker than unwired glass due to the incursions of the wire into the structure of the glass, and may cause heightened injury. It is composed of layers of glass and plastic held together by an interlayer, typically of polyvinyl butyral (PVB). When broken, it is held in place by the interlayer, producing a characteristic 'spider web' cracking pattern.
Reader's Guide
Safety glass has become essential in modern construction and transportation. Toughened glass is used in passenger vehicle windows, shower doors, architectural glass doors and tables, refrigerator trays, bulletproof glass, diving masks, and cookware. In the United States, federal law since 1977 has required safety glass located within doors and tub and shower enclosures. Laminated glass is normally used where human impact is possible or where glass could fall if shattered, such as skylight glazing and automobile windshields. It also provides higher sound insulation and blocks most UV radiation. Wire mesh glass is used in the US for its fire-resistant abilities, and is well-rated to withstand both heat and hose streams. However, its use has declined due to safety concerns. Canada's building codes still permit it but are being reviewed, while Australia has no similar review. New materials offering both fire-ratings and safety ratings have led to worldwide debate about the continued use of wired glass.
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