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Terrorist attack


In the wake of the World Trade Center disaster unions concerned about the safety of their members who are expected to work in what might become terrorist targets have been demanding major safety improvements. This week we ask: Does the public have a right to expect that landmark buildings are designed to resist terrorist attack?


Dr Graham Owens director, Steel Construction Institute 'Safe as houses' is an emotive phrase that very effectively encapsulates UK society's attitude for safety in our built environment. Of course, attitudes are different in other regions of the world. Areas subject to major seismic action are conditioned by those extreme events; some other countries hold life more cheaply than we do.

Although our building regulations and codes and standards are under the expert custodianship of civil and structural engineers, we are inevitably sensitive to society's attitudes when defining the underlying performance criteria. There is no doubt in my mind that our response to the disproportionate collapse of Ronan Point in 1968 was partially conditioned by the widespread, and fully justifiable, public concern at the accident.

As a result, our requirements for structural integrity are the most effective in the world.

There are widely held views that, if the WTC had been designed and detailed to our current regulations, these collapses would have been less catastrophic. It is most instructive to note the extensive structural damage to the Murrah Federal Building in Oklahoma City, bombed by Timothy McVeigh, and compare it with what happened in the IRA blast in London's Docklands, where the primary effect was shattered glazing.

We certainly have the tools to meet society's expectations.

Risk assessment is now established practice in sensitive situations - good examples are offshore structures (following the Piper Alpha disaster).

So, society undoubtedly has the right to expect engineers and the construction industry to respond effectively to their requirements for buildings to resist terrorist attack. However, before too extreme a reaction to September 11 becomes established in practice, there are two important cautions.

First, such construction will cost more and it may be much more effective to spend those resources reducing the risks at their source. Secondly, as we become more concerned about sustainability, construction will have to 'tread more lightly on the earth.' High rise bomb shelters would be impossible to demolish economically. They would remain as very forlorn testaments to our society's frailties long after they had outlived their usefulness.


James Bennett divisional director, Connell Mott MacDonald Clearly this answer is dependent on the extent to which engineers are to design for terrorist attacks.

Engineers cannot be expected to decide what is an appropriate type of terrorist attack to design for - several years ago it was a car bomb outside a building, then it was a bomb inside the building. Now it is airliners hitting the building. Next year it will be à who knows? This responsibility should not be placed on the engineer.

The client is the one to have the most say in this issue. A rational discussion with the design team is required. Even designing for reasonably predictable events/risks could lead to long term problems.

Imagine the situation where a client announces that his building has been designed to resist the effects of an internal bomb blast on any one floor, the bomb being typical of similar devices used by terrorists in the past. In terms of such an event the building is safe.

This creates a perception that it is safe full stop. Imagine then four bombs (far bigger than allowed for) exploding on four separate floors - and the building collapses.

Who is at fault?

Designing sensibly for something that is unknown and unpredictable is unrealistic and creates false perceptions.

The cost to the client will obviously increase while the net lettable area is very likely to decrease.

The return on investment is inevitably going to be hit. Projects become unviable. There becomes less work for all the industries associated with construction. Unemployment is affected. A vicious downward spiral.

To say the public has a right to expect that buildings be designed for terrorist attacks is far too big a call for my liking.

What it needs is rational consideration and 'appropriate' action.

The facts lMajor structural collapse after terrorist attack is extremely rare. During the IRA's 30 year bombing campaign, often employing very large car and truck bombs, only older structures suffered damage so severe they had to be demolished.

Major fires are also uncommon, unless deliberately started by incendiary devices.

lDisproportionate collapse is where a relatively minor event, such as a gas cylinder explosion or the impact of a road vehicle, causes major collapse or damage. What occurred in Manhattan on 11 September is arguably not disproportionate collapse.

lFollowing the spate of terrorist attacks in the UK in the 1990s, the Steel Construction Institute was commissioned to prepare guidance which appeared in publication P244, Protection of Buildings Against Explosions.

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