Phenomena in glass
Nickel Sulphide Inclusion is a naturally occurring phenomenon in glass. Impurities can still be contained in the glass pane after its manufacture and toughening processes. Small particles of Nickel Sulphide can still be present in the glass at installation.
Visually, you will not able to see these tiny particles of metal but they can still be present in the glass, benign until they are aggravated.
Nickel Sulphide Inclusions have two main states, these are; stable at high temperatures and stable at lower temperatures. When glass is heat soaked, the heat converts the Nickel Sulphide Inclusion to the high temperature state, however the glass is cooled rapidly which doesn't allow the Nickel Sulphide Inclusion to change to the lower temperature state. The transformation to the lower temperature state can occur over time, therefore a glass breakage caused by a Nickel Sulphide Inclusion can happen if the inclusion is large enough and if it is located within the tensile (central) portion of the heat soaked glass.
A very simple way to determine whether a glass breakage has been caused by Nickel Sulphide Inclusion is to watch out for the 'Butterfly Effect' pattern on the glass. The implosion will centre around a singular point on the glass and will fan out in a butterfly wing formation.
Unfortunately, there is no way to totally remove the risk of Nickel Sulphide inclusion. In a standard pane of glass, the estimated risk of a Nickel Sulphide Inclusion is 1m2 in every 10,000m2 of glass (estimated by the GGF). But you can reduce the risk of an NSI breakage by putting the glass through a finishing process called Heat Soaking.
The Heat Soaking process includes thermally treating the glass further after completion, in large heat soaking ovens. The glass is heated to very high temperatures in an effort to force any panel with Nickel Sulphide impurities to shatter. The resulting glass that survives the testing therefore has a lower chance of containing a Nickel Sulphide Inclusion, reducing the risk of broken panels to the end user.
You should note that the Heat Soaking process will increase the cost of the glass and increase lead times but will reduce the risk of a Nickel Sulphide Implosion down to 1m2 in every 1 million m2 of glass.
Any glass unit used on a project can be specified as Heat Soaked by the architect. If you are worried about Nickel Sulphide Inclusion and implosion be sure that heat soaked glass panels have been specified.
NSI Breakages and Warranties
Nickel Sulphide Inclusions are a rare yet accepted anomaly within glass manufacturing and no glazier processors or suppliers are able to provide a warranty against breakages from this phenomena. This then means that IQ Glass are not able to pass any warranty onto our customers.
From Guardian Glass UK:
Guardian Industries UK Ltd constantly aim to reduce the potential for nickel contamination in the batch, however, it is impossible to eliminate all sources of contaminations, especially with raw materials. NiS within the float can occur in batches when a source of Nickel contamination is introduced into the furnace. This can lead to “outbreaks” of NiS induced failures.
Due to the nature of NiS inclusion, and the lack of available detection methods, Guardian, as a manufacturer, cannot provide a warranty against the possibility of NiS being present within the glass.
Specifying your glass units to be heat soaked will reduce the chance of a Nickel Sulphide breakage and we would recommend heat soaking on any project where you or the end client are worried about a Nickel Sulphide Breakage.
It would also be advisable to consider heat soaking on any element of glass that will be inaccessible once construction is complete, or pieces of glazing that will be very difficult to replace at a later stage.