Bombs away

Yet many organisations need bomb-proof older buildings. Governments like their embassies to be located in city centres in grand classical buildings rather than in anonymous bunkers on the edge of town. Government ministries enjoy pomp and circumstance too – Whitehall is an obvious example. Also, many private companies are housed in old buildings and are not prepared to go to all the hassle of moving for an event that probably will never happen. So if an organisation wants to stay where it is, but in a more secure environment, what should it do?

One person who can help is Stephen Ward. He spent 24 years in the army as a civil engineer specialising in construction, and part of his work involved advising on making buildings more resistant to terrorist attack, particularly in Northern Ireland. He even has an MSc in weapons effects on structures. In late 1999, he left the army to run Blastec, the new blast protection arm of building reinforcement specialist Cintec.

Cintec specialises in reinforcing existing masonry structures. For example, it will reinforce weak structures that have deteriorated or become damaged, or protect buildings against structural collapse in earthquake zones. The system is very simple in principle (see "The Cintec system", right) and consists of drilling along the length or height of masonry walls and inserting steel reinforcing bars. The anchors are also ideal for stopping old walls caving in under the blast pressure from a bomb.

Ward is no salesman for the system and takes a refreshingly detached view of how to protect older buildings against blast. He says there are essentially two approaches to protecting a building's occupants against terrorist bombs: "The first question to ask is, do you mitigate the effects of blast or harden your building?" Mitigating the effects of bombs is best done by making sure there is a large area of "stand-off"; Buckingham Palace is a good example of this, with a huge empty space between the palace and public areas where a bomb might be placed. This is fine for the Queen, but most buildings are in spitting distance of a road or other public area.

If a building owner wants to make a building more bomb-proof, the first task is decide on the likely level of attack. "The problem is nobody knows the size of the bomb and where it is going to be planted so you argue for the worst-case scenario from the engineering point of view," says Ward. In practice this could turn out to be prohibitively expensive, so Cintec prepares a number of possible scenarios based on bombs varying in size and how close they are likely to be placed to the building. The security services and police also offer advice on likely scenarios. From this, the owner can decide on the appropriate level of protection for the perceived risk.

"Windows are the first thing you look at," says Ward. "Flying glass kills people." One approach is to stick film over the glass to hold it together in one piece, and to install bomb-proof net curtains behind the glass as a secondary measure to catch the glass in case it is blasted out in one piece. However, the curtains prevent occupants from seeing out of the window, and the film only lasts 10 years. "After two cycles, it would probably have been no more expensive to use bomb-proof windows in the first place," concludes Ward.

If you don’t allow the windows to break, you need more wall reinforcement as the force of the blast isn’t dissipated

Stephen Ward, Cintec

The window frame has to be securely fixed to the structure so that the whole lot doesn't get blown out as a unit. Conventional anchors are normally used for this job. At this point Ward puts on his salesman's hat and extols the virtues of the Cintec system for anchoring windows. "Cintec anchors can be engineered to be stronger than conventional window bolts so their number can be significantly reduced. And because they are much longer they also reinforce the surrounding masonry at the same time."

In any event, building owners may be forced to reinforce walls when installing blast-proof windows. "If you don't allow the windows to break you need more reinforcement in the walls as the force of the blast isn't dissipated," cautions Ward. He claims that if Cintec anchors are being installed to hold the windows into the structure, strengthening all the walls may not cost a lot more as much of the work is being done anyway during window installation.

As one of Ward's roles is as Blastec's research and development man, he has come up with two new ideas to prevent a blast reaching the building in the first place. The first idea is to use "water walls" – giant plastic bags filled with water to absorb the blast energy. Water also reduces the effectiveness of the explosive and its heat. The bags are small enough to fit into the boot of a car and are filled and emptied in situ, removing the need for heavy lifting equipment. The idea is not as crazy as it sounds; the Labour party used the bags at its last conference to protect delegates against potential bomb attacks.

Empty water bags could be hidden in pavements and activated when needed. They would rise up as a solid, water-filled wall up to 3 m high. This would be particularly useful for organisations that don't want to clutter their surroundings with huge lumps of concrete. A water wall could offer a discreet solution; if a security guard spotted a suspect vehicle they could deploy the water walls at the push of a button. These could provide full protection up to first-floor level and a lesser level of protection for higher floors.

The latest idea dreamed up by the eternally inventive Ward is "permeable blast walls". These are like gabion cages filled with rocks and the idea is to make the blast wave travel around all the rocks to dissipate its energy. The same principle is employed in a car exhaust by making the exhaust gases travel much further in the silencer to reduce the roar of the engine to a gentle purr. A water-filled core in the wall would perform the same job as the plastic water walls.

Ward has high hopes for the permeable blast wall. He says small-scale studies show it is 90% effective. "In the USA they are screaming out for this for airport car parks," he says." The Federal Aviation Authority regulations demand the introduction of increased stand-off, which means closing the lucrative car parking facilities near airport terminals." The permeable blast walls would surround the car park to contain any blast from a large vehicle bomb. "The rock-filled gabions are environmentally attractive," claims Ward. "It is possible to grow plants in them to offset their intrusiveness."

Unfortunately for British workers, most of Cintec's blast mitigation work is abroad. All the company's blast protection work in the UK is geared to preventing accidental blast damage. Most of Cintec's deliberate-blast protection work is in the USA and for American government properties in Europe. Ward says this is because UK organisations are very reluctant to spend money on blast protection. "The building owner will do the absolute minimum unless legislation forces them too do something," he says.