The term safety glass designates several families of glazing whose composition or treatment has been modified to reduce the risk of injury in the event of breakage. Unlike ordinary annealed glass, which shatters into sharp-edged fragments of varying sizes and shapes, safety glazing is designed either to break into small, relatively harmless pieces or to maintain its structural integrity after impact. This distinction is fundamental to understanding the compositional differences between the three main existing families.
Tempered Glass: A Thermal Treatment, Not a Different Composition
Tempered glass is produced by thermally treating standard float glass. The process consists of heating the glass to approximately 620–650 °C and then subjecting it to rapid, controlled cooling by air flow (quenching). This creates a stress gradient between the surface (placed under compression) and the core (placed under tension). The resulting mechanical resistance is approximately 4 to 5 times greater than that of annealed glass of the same thickness, in accordance with the requirements of standard EN 12150-1.
In the event of breakage, tempered glass shatters into a multitude of small pieces with blunt edges, limiting the risk of laceration. It cannot be cut after treatment: any dimensional modification must be carried out before tempering.
Its chemical composition remains identical to that of ordinary glass, primarily silicon dioxide (SiO₂), soda and lime. It is therefore the thermal treatment, and not the chemical formulation, that gives it its safety properties.
Laminated Glass: The PVB Interlayer at the Heart of the System
Laminated glass is the most widely used safety glazing when the primary requirement is to keep fragments in place after breakage. It is composed of at least two glass panes, annealed, tempered or heat-strengthened, assembled with one or more thermoplastic interlayers.
The most common interlayer material is PVB (polyvinyl butyral). This transparent polymer is heat-bonded between the glass panes under pressure and at high temperature in an autoclave. The standard thickness of a PVB layer is 0.38 mm; the most common configurations use interlayers of 0.76 mm or 1.52 mm depending on the required performance level.
Other interlayer materials are also used depending on the application:
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EVA (ethylene-vinyl acetate): preferred in certain decorative or non-autoclave laminated glazing;
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SGP: a high-performance interlayer whose stiffness is significantly greater than that of PVB, used in structural glazing, balustrades and advanced forced-entry resistant applications.
In the event of breakage, the interlayer holds the fragments together, forming a cracked but maintained surface. This property is required for overhead glazing, glass floors, glazed roofs and intrusion-protection glazing.
Wired Glass: An Older Technology with Recognised Limitations
Wired glass incorporates a mesh or network of metal wires into its mass, fused during manufacture. This reinforcement keeps the fragments in position after breakage, preventing their fall, which constituted its main advantage in glazed roofs and industrial buildings of the last century.
Its limitations are however significant: its mechanical resistance is lower than that of tempered glass, and the presence of metal makes it susceptible to corrosion in humid environments. Its compliance with current safety requirements, particularly standard EN 356 relating to resistance to manual attack, is generally insufficient. It is progressively being replaced in new construction by laminated glass.
Key European Standards: EN 12600 and EN 356
Two European standards structure the qualification of safety glazing:
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EN 12600: pendulum test for flat glass. It evaluates the behaviour of glazing under impact and classifies breakage according to the failure mode and the height of the pendulum drop (e.g.: classification 2B2);
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EN 356: resistance to manual attack. It defines protection classes ranging from P1A (resistance to repeated impacts) to P8B (resistance to burglary tools), allowing the appropriate level of protection to be specified for each context.
These standards apply to the glazing as a whole, regardless of its manufacturing method.
Limitations of Existing Glazing and the Contribution of Retrofit Security Film
Installing safety glazing during construction is the most robust solution, but it cannot be applied to glazing already in place in existing buildings. Yet a significant proportion of European building stock is still fitted with ordinary annealed glass, particularly in schools, retail premises and buildings open to the public.
For these configurations, security window film constitutes a retrofit reinforcement solution: applied directly to the existing glazing, it retains fragments in the event of breakage and slows forced-entry attempts, without structural works. This approach complies with the requirements of the PPMS decree (specific safety plan) applicable to schools and buildings open to the public.
The films in the Solar Screen anti-intrusion security film range are EN 12600 certified. Certain models achieve a tensile strength at break of 220 MPa for a thickness of 125 µm and present an EN 12600 classification of 2B2.
To understand the detailed operation of these solutions and their installation conditions, the Solar Screen article dedicated to anti-shatter films for building security presents the technical parameters and installation conditions.