When a bomb detonates, it produces gases at very high temperatures. This in turn leads to a rapid expansion of air and the creation of a shock wave travelling at supersonic speeds. The shock wave lasts only a few milliseconds and is then followed by an equally sudden but longer-lasting drop in pressure. It's the enormous impact of the shock wave and the subsequent suction that shatters the glass and distorts the framing.
Overall, blast injuries result in mortality ranging between 7.8% in open air to 49% in a confined space. A majority of victims (70%) will sustain soft tissue injury, and traumatic amputations will occur in approximately 11% of cases.
Most people killed or badly injured in a blast involving high-order explosives (HE) are affected by either primary or secondary blast injuries. Primary HE blast injuries are caused by high-pressure gases from the e4xplosion rapidly expanding to produce a supersonic blast wave. This has a devastating effect on human air-filled tissue, particularly the lungs and gastrointerstinal tract. Primary blast injuries are generally fatal.
Secondary blast injuries caused by flying objects, for example grass fragment are much more common than primary blast injuries and are the most usual cause of death for blast victims. The penetrating injuries occur most often in the exposed areas of the body such as the head, neck and extremities.
The Wrightstyle system's strength was achieved through a glazing technique that bonds the glass to its framing support, so that in an explosion the components work together to safely absorb the shock and retain the glazing elements.
In many instances, untested combinations of glass and frame are specified separately - despite the fact that, in a fire or blast situation, the glass will only be as good as its framing system, and vice versa. Wrightstyle's system, in comparison, is a compatible, complete and tested glass and steel framing system.
Although glass and glazing companies have been active for some years in developing safer systems, it was the attack in the USA on the Federal Building in Oklahoma City some fifteen years ago that focused research attention, the first major terrorist attack in an American city.
Amid that carnage, 200 victims suffered from glass injuries and glass fragments were found six miles from the detonation. In New York, on 9/11, 15,500 windows were damaged within a mile of Ground Zero – nearly 9,000 within half that distance.
In the independent test at an RAF base in the UK, the simulated lorry bomb attack was immediately followed by a simulated car bomb attack (100 kilos of TNT). The lorry bomb was detonated 75 metres from the test rig, while the car bomb was detonated at a distance of 20 metres to produce a higher pressure loading and shock on the façade – and was also successful.
"We may not have yet taken explosives from the hands of terrorists. But for the occupants of those buildings that incorporate the latest blast-resistant steel glazing systems, we have taken away an equally potent weapon: the glass itself," said Jane Embury, director, Wrightsyle.
"Also, and importantly, our system is aesthetically no different from a non-fire or blast system – giving architects the ability to once again design buildings using glass, glass and more glass," she said.
