By Robert Smilowitz, PhD, P.E., principal, Weidlinger Associates, Inc.
As the tallest building in the Western Hemisphere, One World Trade Center is both a landmark and a challenge to risk-takers.
It was to be expected that someone would eventually evade security guards and climb to the top of the tower. Last month’s apparent infiltration of 1 WTC security by a teenager has reignited a concern for security in tall buildings.
The precedent was set when Philippe Petit strung a tightrope between the Twin Towers in 1974 and successfully performed his high-wire act. In 2008, two people scaled the New York Times building, and two others have unsuccessfully attempted the same feat. And, according to a report in the New York Times, “a group of daredevils who parachuted off” WTC 1 last fall last week turned themselves in to officials.
What if their motives had been more far more sinister? Fortunately, the WTC towers are designed to unprecedented security standards, but what of all the other iconic buildings?
Security consultants dedicate considerable effort to devising effective operational and technical security measures, two of the three legs of the security triad, to deny access to all but authorized individuals and to screen all parcels entering protected buildings.
But sooner or later, no matter how fervent their good intentions, operational security becomes vulnerable to the human element.
Examples include innumerable personnel breaches and security lapses at airport screening stations across the country. Regardless of how unlikely the event, or how vigilant the security effort, errors are bound to happen.
This is why physical security, the third leg of the security triad, is so important. Structural hardening and debris mitigation measures are the silent sentinels built into the building’s fabric that protect the people and property when all else goes awry.
Blast consultants, schooled in the Cold War era, have converted methods for hardening military systems for use in commercial construction. The timeline of major terrorist activities has steered the transition of this technology. Starting with the bombing of the U.S. embassy and marine barracks in Beirut in 1983, the U.S. Department of State adopted stringent guidelines for the protective design of their overseas buildings.
The bombing of the World Trade Center in 1993 demonstrated that terrorist threats were a domestic concern, and building security became the focus of attention as a result. Following the collapse of the Alfred P. Murrah Federal Building in 1995, which killed 168 people, including 19 children, the General Services Administration adopted standards for the protective design of domestic government buildings.
In the years since the 2001 attacks against the World Trade Center and the Pentagon, the trend has moved to the commercial sector, as savvy developers of iconic properties have adapted similar protective-design methods for the protection of their tenants.
Engineers and physicists who studied blast effects through the Cold War era have applied these lessons to domestic commercial buildings.
Sophisticated analysis methods, including computational fluid dynamics and finite-element analysis, simulate the propagation of the blast wave and the distortion of building elements as building components respond to the effects of an explosion.
These advanced methods are the bread and butter of consultants who routinely research new protective measures and hone their skills, comparing analytical results to explosive tests that are primarily performed by U.S. government agencies. These experts are able to determine the most economical use of protective materials, and provide the desired level of protection with the least impact to form, function, or finance.
Engineers are bound to perform services only in their areas of competence, yet this obligation is increasingly ignored when it comes to protective design in the commercial world. The U.S. government is very judicious in its selection of design methods, requirements, and consultants when designing its most highly valued protected facilities.
Building developers have difficulty differentiating among various levels of expertise and criteria. Nondisclosure agreements and confidentiality limit the extent to which experts can educate potential clients.
Following September 11th, the New York City Building Code mandates structural integrity for tall buildings, but provides a watered-down alternative to alternate load path methods to resist progressive collapse.
There’s no telling when the next terrorist attack will occur and the form it might take.
The occupants of iconic commercial buildings deserve the same level of care as the occupants of the most valued U.S. government properties.
