“Two weeks from now you will weep.”
That was the ominous warning posted on an al-Shebaab website, warning Kenya of a forthcoming attack on skyscrapers and other large buildings.
“Something big is coming,” the web site warned. “Watch your towers come down.”
The warnings, which follow an April 28 bomb attack in Kenya’s capital of Nairobi highlight what Kenyan intelligence authorities say is an increasing likelihood of attacks by the Islamic militant group. Towers most likely to be targeted include housing hostels and offices of government, media and prominent corporations.
Obviously, there is not much builders or engineers can do to stop a terrorist attack from happening.
Still, the Kenyan warnings highlight an important question that has relevance not just in North Africa, the Middle East and other hot spots but in virtually every part of the world: How can buildings and infrastructure be designed and constructed to best minimise the impact of any attack which occurs?
In its publication Primer for Design of Commercial Buildings to Mitigate Terrorist Attacks, the US Department of Homeland Security sets out a framework for basic concepts behind design considerations from a security perspective.
First, given the severity of extreme terrorist incidents, along with the unpredictability of the form of attack – explosive, airborne, chemical/biological, radiological or otherwise – and budgetary and other constraints, absolute and full protection of most commercial buildings is not feasible. With regard to explosive attacks, for example, the focus revolves around damage limitation and mitigation as opposed to a blast-resistant approach.
In addition, security concerns need to be balanced against other considerations, such as accessibility, natural hazards and mitigation, fire protection and energy efficiency and aesthetics. Security measures should be part of an overall, multi-hazard approach.
Given the relatively low likelihood of a major terrorism incident in many buildings, security measures should not interfere with the building’s ability to withstand more likely hazards such as fires, earthquakes and hurricanes. Wherever possible, security measures should also not unduly interfere with everyday operations of the building and its occupants.
That said, given the consequences of a significant attack, reasonable measures should be undertaken so as to save lives and also to minimise business disruption in the event that a terrorism incident does occur.
What can be done?
The aforementioned limitations notwithstanding, plenty can be done.
For starters, urban landscaping or barrier methods can be used to secure the perimeter against vehicular intrusion. Buildings should be placed as far away from the secured perimeter as practical. Any unsecured areas should be placed outside of the main structure or in the exterior bay.
Within the building, itself, vulnerable spots such as entry and delivery areas can be physically isolated from the rest of the structure by using floor-to floor walls in these areas. Lightweight, non-structural elements can be used for the building’s exterior and interior. Air intakes should be as far above the ground as is practical. Exterior window systems and cladding can be designed so that the framing, connections, and supporting structure have a lateral-load-resistance that is equal to or higher than the transparency or panel.
Finally, measures can be enacted to resist progressive collapse – whereby the failure of one structural element of the building results in a disproportionate level of flow-on damage to other structural elements – and indeed, the building as a whole – through a domino-type effect.
Architects, engineers and others involved in the design and construction of large buildings cannot stop terrorist attacks, but a few fundamental basic steps just might save hundreds or even thousands of lives if an attack does occur.