Versatile glass: take the safe option

Glass is an invaluable and flexible design element in modern transport hubs, but also has to meet increasingly rigorous safety and security standards, says Sto’s Rob Freegard.

In today’s increasingly fluid world, the demand for easy and convenient travel continues to grow, which has seen increased funding allocated to new transport hubs such as rail and underground stations, and airports.

Consequently, architects and designers invest considerable effort into creating impressive transport projects that are distinctive and memorable.

Unfortunately, today’s increasingly uncertain world means that building designers have to factor in the risk of terrorist attacks, and this has influenced the way that our rail stations and airports are designed. So, it might seem strange that glass is proving to be increasingly popular in this type of infrastructure architecture.

Glass offers many advantages. It’s functional, versatile and it creates clean lines and well-defined spaces which can help manage the passenger flow through a transport hub. It can also flood a building with natural light, and be used both externally and internally to allow a design scheme to flow effortlessly into and out of a building.

As you’d expect, modern glass facades used in such public areas are subject to increased performance requirements, and one of the main areas where there may be a risk of an explosion occurring.

In this scenario, one of the biggest dangers comes from the debris hurled through the air, and often over long distances. Today’s security and safety glass products are designed to minimise this danger by creating as little debris as possible and so reducing the risk of injury.

Secret

The secret lies in the specially toughened glass panels used. Possessing their own inherent strength, these panels are fixed to carrier boards by a special adhesive. Although the glass itself may shatter, it’s designed to remain firmly fixed to the carrier board as far as possible, and so minimise flying debris.

The combined glass panel and carrier board structure is also manufactured so that it can flex and accommodate both the first explosive wave of positive pressure and then the following wave of negative pressure that can be just as destructive. It’s worth noting the best carrier board is itself typically made from 96 per cent recycled glass, underlining the environmentally friendly nature of glass as a construction material.

The level of safety is further increased by the grid sub structure to which the glass is fitted. Choosing the most appropriate grid and fixing system is essential for maximum safety, and a reputable glass manufacturer will be able to provide guidance here.

They will advise on the best substructure to allow the panels to flex and accommodate pressure change and so further minimise flying debris. Some manufacturers will also assist with such issues as wind loading calculations, standard design details, and onsite installation support, so it pays to choose your security glass supplier very carefully.

Rigorous testing

When specifying a glass system, safety is obviously a primary concern. Any glass used in construction must have undergone a rigorous testing regime, including extensive impact and blast testing to ensure, that is suitable for use in public locations such as rail stations. A standard BBA certification is a good starting point, as it confirms that the system in question has been properly assessed with regard to such things as mechanical resistance, durability and behaviour in a fire, but testing needs to go much further than this.

In an explosion there is always a risk that the blast wave itself will cause injury or damage within the immediately adjacent area. The testing of glass for this type of application revolves around assessing its potential to create flying debris which may cause injury to anyone beyond that immediate area. This is typically done by subjecting it to various blast sizes at distances of 6 m to 25 m away. This allows the different types of explosions to be simulated, and their likely effect beyond that to be calculated.

The glazing system also needs to pass many other tests with flying colours, including impacts by both hard and soft bodies. Pneumatic tyres, solid steel balls and canvas bags filled with lead shot are used for this purpose being dropped onto, or swung into, the glass from carefully specified distances. As well as ensuring that the glass meets a number of relevant British Standard requirements, this type of testing also provides reassurance that the glass can withstand the normal day-to-day treatment it will experience in the average railway station, airport or shopping centre.

Unlimited scope

While focusing on safety and security, it’s important to also remember that today’s glass materials can offer virtually unlimited design scope. Every glass system is a bespoke solution, so almost any design can be interpreted in glass, no matter whether it includes large surfaces, dramatic curved walls or unusual sizes and shapes.

Glass panels are available in the majority of RAL colours (with some manufacturers also offering custom options) and it’s possible to incorporate cut-outs or individual logos and designs onto the glass, so the creative possibilities on offer are virtually endless.

Rob Freegard is business development manager for glass specialists Sto Ltd