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Spontaneous Glass Breakage

3M External Safety Window Films

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Used for spontaneous glass breakage, human impact and accidental damage.
The 3M External Safety Film range has been rigorously tested to ensure they hold the glass safely in place during its life. This provides enough time to replace the broken window should it be broken or act as a sacrificial layer against accidental or intentional damage.

What is spontaneous glass breakage?

Spontaneous glass breakage [SGB] is a phenomenon by which toughened glass (or tempered) may spontaneously break without any apparent reason. Some common causes are:

  • Minor damage during installation such as nicked or chipped edges later developing into larger breaks
  • The binding of the glass in the frame, causing stresses to develop as the glass expands and contracts due to thermal changes or deflects due to wind
  • Thermal stresses in the glass
  • Inadequate glass thickness to resist wind load
  • Internal defects within the glass such as nickel sulphide inclusions

Any breakage problem has more severe consequences where the glass is installed overhead or in public areas (such as in high-rise buildings). A safety window film can be applied to the tempered panes of glass to protect from its falling.

Internal defects within the glass

Nickel sulfide inclusions [NSI] (“stones”) can be present in the glass. The most common cause of these inclusions is the use of stainless-steel machinery in the glassmaking and handling process. Small shavings of stainless steel containing nickel change structure over time and grow, creating internal stresses in the glass. Breakage results when these stresses exceed the strength of the glass. This type of breakage is almost always found in tempered glass and is indicated by a distinctive “figure eight” pattern, with each “loop” of the figure eight approx. 30mm in diameter.
Alternatively, small pieces of refractory brick can be eroded by the molten glass from the internal walls of the furnace during processing and become embedded in the finished glass. These are also known as “stones”, and can also break the glass when the glass is heated, as they create thermal anomalies.

3M Safety Window Film

Any breakage problem has more severe consequences where the glass is installed overhead or in public areas (such as in high-rise buildings). Safety window films can be applied to the tempered panes of glass as they use a strong adhesive acrylic to hold the fragments together, which protects from its falling.
3M™ Safety Window Films are composed of a transparent and weather stable polyester film, scratch resistant surface and a strong acrylic adhesive. The films high tensile strength and elongation at break increases resistance of the glazing system to impact and pressure. The films also significantly reduce the transmission of UVA and UVB rays which are the main cause of fading.
3M™ Safety Window Films are designed for use on the exterior surface of windows, but can also be used for interior applications.
In the case of Spontaneous Glass Breakage of toughened glass which can occur due to the expansion of nickel sulphide inclusions present in the glass, 3M’s Safety Exterior Product Family provides protection to pedestrians by retaining the shattered glass in the frame.

Product Features

  • Shard retention in window frame after SGB or building stress movement, wind-borne debris, seismic or other extreme weather (may require anchorage, covered later)
  • Shard retention after human or natural impact Protecting the outside from (low force) internal impact
  • Anti-scratch as sacrificial layer
  • Anti-graffiti as sacrificial layer

The video shows testing by one of our clients to ensure 3M External Safety Film is up to the job. The glass was broken and held in the frame for a week keeping the broken glass safe and the weather on the outside. The broken window was then tested to see whether it could physically be pulled out of the frame. The filmed glass was eventually cut out ready for the replacement window pane.

Product Applications

Anti-shatter and retention of toughened glass:

  • Windows, skylights, atriums, spandrel glass, balconies, balustrades, glass walls, 2nd skin facades or anywhere where glass has cracked in the past
  • Constructions with inferior toughened glass and glazing system safety specifications
  • Exterior application, although S40 Ext/ S70 Ext or S40/S70 may also be needed on the inside if anti spall is required (unless overhead toughened glass then interior only is necessary), attachment may be required

No Edge Sealant Required

Most external films including safety films require edge sealing. 3M External Safety Film is different. 3M Safety Films require no edge sealing unless there is a risk of water pooling on the film. It is important to note that Edge Sealant can be a point of failure and may not be aesthetically pleasing.

A 3M attachment may occasionally be required in double glazed units for:

  • Extreme wind load locations
  • Very heavy toughened panes
  • Overhead toughened glazing (although this is illegal)
  • Spider clamp/ planar fittings
  • Simply when the customer needs the extra piece of mind
  • Response times (to address SGB) longer than 24 hours
  • For toughened single glazed windows, the attachment is essential. If you can get to the inside, S40/S70 (interior) with attachment is likely to be preferable (from a cost and access perspective).


3M External Safety Films are available in extra wide rolls of 1819mm, which minimises the number of joins required. The film will make glass safe even if a join is required on a pane where both the width and height are greater than 1819mm.
The film is optically clear like glass so if joins are required then they will not be very noticeable. There is no requirement for a sealant spanning the centre of the pane which can distort light and be noticeable.


A vertical application of 3M interior safety film comes with a class-leading manufacturer-backed limited product warranty of 10 years.


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