Toughened glass is extremely strong, and the evidence to support this is found in the increasing abundance of walk-on glass structures used in places where safety is of the most vital importance.
The ultimate test of toughened glass is the skywalk, a glass-bottomed bridge which provides a view of the ground below, often several hundred metres in the air. It is a breathtaking attraction, even if it is one that people with vertigo should give it a miss.
Probably the most famous skywalk was the Zhangjiajie Glass Bridge, which measures 430m (1410 feet) and is suspended over 300 metres above the ground. So confident were the architects and builders of its strength that an SUV rather famously drove over it.
The secret to this strength is that instead of being one very thick sheet of glass, it consists of three layers of tempered glass, each over two inches thick.
However, it is not the longest-ever glass-bottomed bridge, nor is it even the longest that an SUV has driven over.
The Guinness World Records website claims that a 526m bridge in Guangdong is the longest, and also had an SUV by manufacturer Trumpchi drive over it to showcase its strength in what had seemingly become a tradition in a country that had over 2300 glass bridges at one point.
What is quite surprising, however, is that the longest glass skywalk is not actually in China but in neighbouring Vietnam, and its strength was tested, once again, by another SUV driving along it.
The Bach Long (White Dragon) bridge in Son La is 632m long, designed using the same three-layer tempered glass panel approach and towers over a thick jungle underneath. There is also a glass-bottomed cliff-side path providing similarly staggering views.
It was constructed to connect tourists to Happy Land, a mountain resort popular in the region of Moc Chao and provides breathtaking natural views.
It was designed to support up to 450 people, with guards stationed to ensure that traffic only flows in one direction. This is unlikely to be necessary, but it highlights the incredible technical accomplishment in place and how it contrasts with many people’s expectations of glass.
A good example of why it is important to comfort and keep people safe whilst traversing skywalk bridges can be found at the East Taihang Glasswalk in Hebei, China.
It became infamous after its initial opening in 2017 for a rather mean-spirited prank where the glass would project an illusion of cracking, complete with sound effects. There were a lot of viral videos of people terrified of the illusion, people complained and a rather forced apology ensued.
It became particularly distasteful when 32 glass bridges in the region were shut down after several accidents and incidents were reported in China, including two deaths due to rainfall affecting the friction of glass slides. It must be noted that the glass itself was not to blame in these cases.
Glass bridges are an incredible test of strengthened glass and with the technology only improving the White Dragon bridge’s record might not last as long as one might expect.