Nickel Sulphide Inclusion
Nickel Sulphide Inclusion is the naturally occurring breakage of glass which still baffles the glass industry. Small particles of Nickel Sulphide present in glass can cause spontaneous breakage of glass which is near impossible to predict.
It is not visible, and the tiny inclusions cannot be seen by the human eye or even most modern technologies. Nickel Sulphide Inclusion is also incredibly rare; this phenomenon only occurs in approximately 1 pane in every 500.
Buildings that have experienced multiple instances of Nickel Sulphide Inclusion often have huge expanses of glass, automatically this increases the chances of obtaining an impure pane.
Microscopic imperfections in the glass, which are known as inclusions, are the cause of Nickel Sulphide Inclusion.
All glass contains these imperfections; there are approximately 50 different types of recognized impurities but almost all of them are completely harmless. However, Nickel Sulphide Inclusions can have a disastrous effect on tempered glass.
Common Causes of Nickel Sulphide Inclusion
Generally, the cause of Nickel Sulphide Inclusion is a rapid increase in temperature, whether that is from internal heating or from sunlight. When the glass is heated, the impurities are also heated.
The heated impurities increase in size and vibrate causing the glass structure to become unstable, weaken and fracture. Most panels containing the impurities break in the first 2 to 7 years after installation, usually after a change in internal or external temperature but this is not always the case.
It is easy to determine whether a piece of glass has broken due to a Nickel Sulphide Inclusion because of the unique ‘butterfly’ pattern made in the fractured glass.
The implosion will be centred around a single point in the glass and the glass will break from that point into small pieces.
Whilst with toughened, safety glass the risk of these small pieces do not pose a huge threat, as the glass pane will be able to stay intact, with float glass the small broken shards of glass can cause injury to inhabitants and the building itself.
Unfortunately, despite years of research, there is still no sure way to completely remove the risk of Nickel Sulphide Inclusion.
The risk can be greatly reduced through Heat Soak Testing which is a finishing process used by many manufacturers.
In the Heat Soaking process, the glass is heated and maintained at a very high temperature and then cooled; this causes most potential Nickel Sulphide impurities to vibrate and cause the glass to break.
The idea is that the glass will break during the process instead of years later. This reduces the risk to the end user.
This process will also have an uplift on the cost but it greatly reduces the risk of breakage – this is perfect for an end user with large or costly expanses of glass.
Another disadvantage of heat soak testing is that the secondary heating of the tempered glass can slightly reduce the strength of the glass; this is a concern to some designers who have specified structural glass.