Spontaneous Glass Breakage
This is an issue we are often asked about, and tagged in for answers on various online forums. There is an abundance of information out there on this topic but for the purpose of this blog I’ll try to keep it short, sweet and relevant.
There are many safety glazing options available; and manufacturers are always developing and improving methods to make glass stronger and safer. However, it is important to recognise that glass is an inherently fragile building material and always has the potential to break. For design and construction professionals, as well as the end user, understanding how and why glass breaks can be key to prevention.
Minor edge damage during glass handling, a scratch or nick during installation, a design flaw, or natural imperfection in the glass could all result in spontaneous breakage – the seemingly unprompted shattering of glass.
Handling Damage:
The most common cause of glass breakage comes from edge or surface damage during handling - chips, and even the slightest nick in the glass during packaging, shipping, or installation. The natural expansion and contraction of glass through temperature changes and building movement, cause stress around the imperfection leading to breakage.
Frame and fixings related breakage:
Glass is carefully installed to frames using different methods of cushioning, such as rubber blocks to protect against glass-to-metal stress. Environmental conditions including temperature changes and wind, contribute to glass-to-metal stress. There must also be adequate space within the top and sides of the frame, to allow for thermal expansion and building movement.
Thermal stress breakage:
Thermal stress breakage is not caused by a fault in the glass but by the many conditions the glass is exposed to. The thermal stress is caused by uneven heating/cooling of the glass – from external or internal sources. For example, if one half of the glass is in shade and the other half is in direct sunlight – the area in direct sunlight will expand and the shaded area will resist, causing a thermal stress breakage.
High performance glass can carry a higher risk of thermal breakage, and due to strict energy codes and requirements, is increasingly being specified in new buildings and renovations. Basically, the high performance glass absorbs the solar heat, reducing the passage of radiant flow to improve energy efficiency. This results in higher glass temperatures and increases the risk of thermal stress.
Even signwriting to areas of glass, such as on shopfronts can cause uneven heating of the glass and increase the risk of thermal breakage!
Inclusion breakage:
Nickel sulfide inclusions, otherwise referred to as ‘stones’ can make their way into the glass from the machinery used in the manufacturing process. Very small shavings of stainless steel containing nickel change structure over time and grow, causing internal stresses in the glass. Another type of manufacturing inclusion comes from the internal brick walls of the furnace during processing – also known as ‘stones’. The brick inclusions create thermal anomalies, increasing risk of breakage.
Inadequate glass thickness:
An improperly engineered piece of glass that is too large or thin can be damaged by weather factors on the site, such as wind loads.
Imported products:
There has been recent media attention surrounding the dangers of substandard building products being imported from overseas. Please see the linked article by Aisha Dow, The Age which includes expert comments from the Australian Window Association, Housing Industry Association and The Department of Immigration and Border Protection.
Sources:
Spontaneous Glass Breakage: Why it happens and what to do about it, Construction Specifier, December 2013
Technical Document TD-138: Heat Treated Glass for Architectural Glazing, PPG Glass
Thermal Stress Glass Breakage: Technical Fact Sheet, AGGA, October 2011
Nickel Sulfide Inclusions: Important Issues for the Designer, 2003