Modern commercial building facades are using increasingly large amount of glazing within their designs to suit tenants needs for natural light and energy efficient buildings. Often, these systems are installed with toughened glass which is traditionally used due to increased strength properties and manner of fracture during glass breakage - generally shattering into small cubes.
In recent years, there have been a number of incidents whereby glass from high rise buildings has broken unexpectedly and fallen from height. This poses a significant risk to building tenants and the general public as well as Landlords who need to ensure health and safety risks are minimised.
There could be a number of reasons for glass breaking. The main reasons include -
When glass is installed within a glazing system, it is exposed to any expansion and contraction of the system components. The resulting movement can result in fracture should the glass not be sufficiently isolated. This can occur when the glazing is installed without correctly positioned setting/edge blocks, insufficient gasket compression or general poor positioning. These issues can cause direct glass-to-metal contact which can result in edge damage when the system is exposed to wind or temperature related movement.
When a glazed unit/panel is manufactured, the glazing is often cut to size from a larger stock sheet. These should be inspected as part of the QC procedure to invstigste if any of the edges are damaged or chipped as this can weaken the glass integrity. Once installed, the glass is exposed to changing temperature, weather and building movement. These factors can increase the stresses on the glazed units and ultimately result in the glass breaking.
When glass is exposed to a sudden impact or load it can result in damage or fracture. Often stones dropped by birds or vandalism can cause this type of fracture.
Changes in temperature can result in spontaneous glass breakage. It is caused by the differences in temperature of the centre of the glass and its edge, with the centre being hotter. This can lead to additional stress to the edge of the glazing which can result in fracture if it exceeds the limits.
A leading cause of fractures in toughened glass is the presence of impurities / inclusions within the glass itself. Essentially, over time these inclusions can increase in size- this localised stress can cause the surrounding glass to fracture. Inclusions related fractures can often be identified by a "butterfly" fracture pattern where the failure takes place. Additional laboratory testing can be provided to test for inclusions to confirm as the cause of damage.
To reduce the risk of nickle sulphide inclusions, toughened glass can be heat soaked - a process of putting the glass through a heat cycle to encourage fracture during manufacture if it is at risk of inclusions. The HST toughened glass that remains will then have a significantly lower risk of inclusion related fracture in future.
At Sky Access, all toughened glass we install is heat soak treated as a company policy.
In the event of glass fracturing at height, we would recommend an initial assessment of the fracture by a suitably qualified professional and the isolation of the area below. If required, an emergency glazing contractor should be instructed to make the glass safe via the removal, boarding up or filming of the defective glazing. At this early juncture, the decision on whether to test for nickle sulphide inclusions can be made - it is important to decide this before removal as the point of impact must be carefully secured and removed whole in order to allow for testing.
Once the glazing has been suitably assessed and made safe, we would recommend appointing a contractor specialising in high level glass replacements such as Sky Access UK.