Reducing the risk of spontaneous glass breakage from Viridian

Reducing the risk of spontaneous breakage of toughened glass

Some recent press attention has been attracted by the issue of glass failure in high-rise buildings, along with changes to building regulations aiming to combat the problem. This is not a new issue, or one which is unique to Australia.

Nickle Sulphide (NiS) is a substance which can very rarely form within glass during manufacture due to the presence of minute amounts of impurities in the batch ingredients or the manufacturing process. When present it can form invisibly small "inclusions" in the structure of the glass. This presents no issue to ordinary annealed glass. However, if that same glass is toughened to improve its strength in high load conditions, then the presence of NiS inclusions can create a problem. Under certain load and temperature conditions NiS particles can undergo a phase transformation, which if the particle is within the glass's tensile zone, may initiate a crack. In other words, an NiS particle can trigger a crack in the toughened glass causing the glass to shatter and fail at some point in the future.

Though no glass manufacturing process is immune from the possibility of NiS, manufacturers with good controls in place over their process and input materials are less at risk than others. Where you source your glass from therefore becomes important.

Though the risk of NiS failure is very small, there are steps that can be taken to mitigate this risk, and these may be warranted in some applications. These alternatives include heat soaking, using heat strengthened glass, or using custom laminated glass (incorporating heat strengthened or toughened glass).

Viridian is Australia's only manufacturer of float glass. Each year we make well over half of the float glass consumed by our local market here and in NZ, which we sell to glass processors, glaziers and window fabricators that service all sectors of the building market. The rest of the glass used in the Australian market is imported, mostly from Asia. In particular, many high-rise construction projects are of a scale where it is seen as being economically attractive to ship the glass (indeed, often the whole facade system) in from lower-cost overseas suppliers. Such glass may or may not have been heat-soaked or otherwise treated to mitigate the risk of NiS failure.

Even with our good process controls, Viridian still recommends heat soaking for all applications of its glass where the consequence of NiS failure, however slim, is seen as being hazardous.