Spontaneous glass breakage

 

Spontaneous glass breakage

Image courtesy of Wikimedia Commons

In an attempt to understand what may have caused Tuesday’s excitement, I did a little research. My thanks to Andrew and Willie for their input.

According to some sources spontaneous glass breakage is an extremely rare occurrence, but there is no guarantee that it will not occur in any installation and no indication of when it might happen. There are two main causes: thermal shock or stress, and nickel sulphide inclusions.

Thermal shock: Glass expands and contracts in response to changes in temperature. If there is a significant difference in temperature across the surface, for example, between the edge and the centre of a glass pane, and the parts expand or contract in opposite directions, the glass is placed under thermal stress and can shatter.

Sulphide inclusions: small nickel sulphide stones form during glass manufacture. Formation is random and probably caused by the use of stainless steel machinery in the glass-making process. Nickel sulphide inclusions can remain dormant for years after production and installation. There is no technology at present to eliminate the formation of nickel sulphides. The inclusions contract while the glass cools during the manufacturing process. Over time the sulphide inclusions will try to expand to their original size and sometimes they succeed, causing ‘spontaneous’ shattering.

Another possible inclusion is minute pieces of brick which are eroded from the furnace wall by the molten glass and become embedded in the finished product. These are also known as ‘stones’ and create thermal anomalies when the glass is heated, causing breakage.

Other reasons for later ‘spontaneous breakage’ may include nicked or clipped edges during installation which eventually develop into later breaks, or the securing of the glass in the frame using a sealant or adhesive. If expansion and contraction of the glass occurs and the stresses are stronger than the glass, it can break. A preventive measure, though not guaranteed, is to set the glass on resilient blocks at the bottom, with space for expansion at the other edges.

This post refers only to the particular circumstances of my conservatory in southern England. Other factors will be involved in tall glass buildings and in different climates.

The glazier who came today, who has decades of experience, said that he is seeing more such breakages recently than he has seen in the past. He thought they could be due to extreme heat in this part of the world. Our extreme heat is not comparable to the heat experienced in other parts of the world.

There are still pieces of glass dropping sporadically. I always have to sweep up flies from the conservatory floor – now I have to add glass fragments to the daily chore.

 A third glazier is due to visit tomorrow. I wonder what he will say.