LFI Site Inspections and In-Situ Testing Technology

Glazing failures are more common than may be perceived, particularly with modern developments using increasing volumes of glass to create eye catching structures, and can cause a major headache for Developer’s and Insurer’s alike due to the complexity in understanding the causes of failure and where ultimate liability lies for recovering costs. Often manufacturing-related defects such as Nickel Sulphide Inclusions are excluded from Insurance policies so understanding the risk of failure can be invaluable.

At LFI we are instructed regularly for glazing failures. If the glazing remains in-tact we offer a service to visit site at the earliest opportunity and obtain the failed pane for analysis in order to identify the fracture origin and ultimately the cause of the failure. However, often when the failure has occurred the glass shatters and with it much of the opportunity for identifying whether or not the cause was Nickel Sulphide (NiS) is lost. Although we do have methods of gathering the fragmented glass and can identify the cause from these, more often than not the fracture origin is lost.

Although the failure rate in toughened glass is estimated to be around 1 in 4 - 6 tonnes of glass, if a Nickel Sulphide is present then there is an increased likelihood that other panes made from the same batch may also contain Nickel Sulphide particles. The technology we have developed enables us to survey the panes of glass that are in tact, with or without known failures.

Using this In-Situ testing allows us to survey glazing panels on-site to identify and quantify the numbers and sizes of NiS present in in-tact glazing and therefore the likelihood of more failures occurring.

This is a clear image that was taken In-Situ of a Nickel Sulphide inclusion within an in-tact pane of glass using our proprietary technology.

What are Nickel Sulphide Inclusions (NiS)?

Nickel Sulphide Inclusions (NiS) are impurities that can cause spontaneous failures of toughened/tempered glass.

During the glass production process, many tons of raw ingredients are fed into a furnace and melted down to create the glass of the correct composition. Contamination of these ingredients, as well as contamination from steel furnace heating elements and components, can introduce Nickel into the molten glass. Sulphur contamination can also arise from the furnace fuels and additives to the glass. When combined these chemicals can create the compound Nickel Sulphide (NiS), which can then reside as small intermetallic particles of ‘inclusions’ within the glass and are generally so small that they are not normally visible to the eye.

After manufacture, Nickel Sulphide inclusions can be in an ‘unstable’ physical form within the glass. Over time, heat energy (e.g. from the sun) can cause the Nickel Sulphide inclusions to transform to a more stable state, which also causes them to expand in size. In toughened glass, this expansion can cause the glass to spontaneously, and rapidly, fracture. Often this type of failure is accompanied by a ‘loud bang’.

In order to reduce the risk of this happening, toughened glass can be passed through a separate procedure called Heat Soak Testing (HST). In this process, the glass is heated in an oven to accelerate the transformation (and expansion) of the Nickel Sulphide to encourage the growth changes to happen during the testing process rather than at a later date following installation.

Is Nickel Sulphide still an issue if the glass has been Heat Soak Tested?

As with all processes, things can still go wrong. We have undertaken numerous investigations where we have identified Nickel Sulphide Inclusions in Heat Soak tested glass. The process may not have been carried out fully to industry standards and, even if it has, it is not a fail safe that 100% guarantees Nickel Sulphide induced failures cannot occur.

Identifying a Nickel Sulphide Inclusion (NiS)

Nickel Sulphide (NiS) characteristics

Nickel Sulphide (NiS) failures are usually characterised by their Butterfly-like appearance with cracks in the glass fanning out from a singular point, or fracture origin.

However, the butterfly appearance alone is not enough to determine the cause of the failure. Other failure modes such as impact damage or other types of inclusion can also have a similar visual appearance.

Microscopic Analysis

Nickel Sulphide inclusions are often extremely small and not visible to the naked eye.

To identify the cause of failure is Nickel Sulphide requires expert microscopic investigation. At LFI, we have the facilities and expertise to carry out this microscopic analysis and produce comprehensive reports on the findings, providing a complete service in-house.

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