“Toughened” or “tempered” or simply “safety” glass is, as these names suggest, much more resistant to knocks and bumps than regular glass. It is manufactured by way of a slower cooling process, and as a result, is considerably more robust than standard panes of glass.
For applications where safety or security is paramount – such as public buildings – safety glass has become a must-have for many property developers, facilities managers and local authorities. It is used in applications as diverse as aquariums and shop fronts, as well as in protective eyewear for those dangerous operating machinery or involved in recreational activities – such as diving.
But how would you determine whether a pane of glass is “regular” or tempered safety glass?
Of course, the “proof is in the pudding”, in that, if you smash it, it will fracture into thousands of tiny pieces and remain, as far as possible, in the shape of the pane. But this is not a practical or advisable way of answering this quandary. So how else can you tell
Safety mark
This is the most straightforward way of working out if a pane is made of safety glass or not. The manufacturer’s logo and name should be present, alongside reference to the relevant product standard. In the UK, these standards are:
BS EN 12150 – to identify toughened glass
BS EN 14449 – to identify laminated glass
BS EN 14179 – to identify heat soaked, thermally toughened glass.
A developer or building owner may request that the safety glass marking is not present – perhaps for aesthetic reasons. However, some panes of the glass must be toughened under Building Control rules. If Building Control finds such a pane of glass does not carry the right mark, it can demand the glass is replaced.
Look and feel the edges
If a safety glass mark is not present, there are other ways to check. If the edges of the pane in question are exposed, softly and carefully run your finger along the border. If the edge is smooth and rounded, it is very likely to be tempered glass.
Examine the pane for imperfections
Look closely at the pane and try to spot dimples, warping or bending. Such imperfections strongly suggest the glass is of the toughened safety variety, and occur during the heating process: Due to the very high temperatures required in the manufacturing process, tongs are used. These tongs leave marks on the glass.
You might also spot tiny scratches on the glass. These may well have been caused by small particles present on the machine rollers; these melt and fuse to the glass surface.
Look at the pane with polarised lenses
Viewing the glass through a pair of polarised sunglasses may reveal dark patches or lines. This is a dead giveaway that the glass is tempered safety glass.
Score the glass
This should only be done if you plan to cut the glass! If the glass is tempered safety glass, it will result in an uneven, wavy line – because it is very, very strong.