Jane Embury reminds us that some threats haven’t gone away
We’re slowly emerging from one national threat and, maybe, forgetting about another.
That’s hardly surprising, because it’s easy to forget about terrorism when Covid-19 has been uppermost in our minds.
But as we redouble efforts to build for the future, it’s worth remembering the past. Home Secretary Priti Pastel has said that “terrorism remains one of the most direct and immediate risks to our national security.”
The UK’s threat level remains at “substantial” which still means that an attack on the UK is likely.
As architects and specifiers start reconfiguring and constructing the future, we should maybe bear in mind that old threats have not gone away.
While recent attacks have been in France and Austria, there have been almost 100 terrorist-related deaths in the UK since 2001.
Between 1971 and 2001 in the UK, there were 430 UK terrorist-related deaths, the highest in western Europe.
Building in strategies for social distancing in the new normal isn’t therefor the only risk that architects should be considering.
It’s an aspect of the built environment in which we are expert, although we wish that we didn’t have to be.
We have many years of experience, here and internationally, in helping to make buildings safe from extremist threats.
That expertise starts with precisely calculating the level of safety required. That means calculating the likely blast loading from various levels of attack at different stand-off distances.
That in turn means having a comprehensive understanding of blast dynamics and how different glazing systems react to blast pressures.
Simply, when a bomb detonates, it produces gases at very high temperatures which causes rapid air expansion.
The immediate result is the creation of a shock wave travelling at up to twenty times the speed of sound.
While that shock wave lasts only a few millionths of a second, it’s then followed by an equally sudden but longer-lasting drop in pressure.
Those enormous pressures are what shatters glass, allowing the bomb blast to penetrate inside a building.
We developed our first advanced system over ten years ago. But we didn’t rely on computational models to bring it to market.
We live tested it at a specialist test site in Northumberland, subjecting the structurally-glazed system to the equivalent of 500 kilos of TNT. That’s generally agreed to be the explosive impact of a lorry bomb.
The system’s successful test was down to several factors, not least a high-specification structural glazing technique that bonds the glass to the framing support system.
In an explosion, the components work together to safely absorb the thermal shock of the explosion.
But we didn’t stop there. After the lorry bomb test, we subjected the same system to another blast test involving 100 kilos of TNT-equivalent explosive. That equates to a car bomb.
While the amount of TNT might have been smaller, so too was the stand-off distance – making the blast impulse greater.
Our task is to calculate everything from laminate thicknesses to mullion depths. We also take into consideration such variables as likely blast impulse and stand-off distances.
We’re all more aware of personal safety in our day-to-day lives, whether at busy railway stations or at our places of work.
But personal safety isn’t just about airborne threats. Personal safety can be about the architecture around us, and its effectiveness in preserving people’s lives.
Photo: Our system being live tested against a lorry bomb.