TV Program Description
Original PBS Broadcast Date: September 5, 2006
Following up its Emmy Award-winning documentary, "Why the Towers Fell," NOVA
probes the conclusions of the government's engineering investigation into the
World Trade Center's collapse on 9/11, with updated analysis of the devastating
attack and how subsequent knowledge gained will shape skyscrapers of the
future. Yet is it practical or even possible to construct invincible buildings?
"Building on Ground Zero" features candid interviews with leading construction
and safety experts, investigators, architects, and engineers—including
Leslie Robertson, lead structural engineer of the original World Trade Center
and Shanghai's new World Financial Center, and Jake Pauls, occupants advocate
and evacuation specialist. From the hallways of the newly erected World Trade
Center 7 in New York, to China, where the world's tallest building is midway to
completion, NOVA explores the complex challenges of building tall buildings in
the wake of 9/11.
Previously, it was natural threats to the safety of tall
buildings—earthquakes, hurricanes, and the relentless force of the
wind—that had driven structural engineering codes. But with the threat of
terrorism, determined attackers have targeted even the most secure structures,
forcing engineers and architects to consider what was once unimaginable.
In the months after 9/11, NOVA followed a team of engineers tasked by FEMA to
study the Twin Towers' collapse. Preliminary conclusions originally reported in
"Why the Towers Fell" determined that the floors of the buildings may have
"pancaked" down upon one another as their trusses failed. Now, with the benefit
of years of additional investigation, the National Institute of Standards and
Technology (NIST) has revealed that no structural element was to blame for the
Using vivid computer animations, NOVA takes viewers through a simulation of
what the buildings endured in the 9/11 attacks. It turns out that fireproofing
on the floor trusses was blown off by the impact of the jets, exposing the
trusses to severe fire temperature. This caused the trusses to bow and eventually
break the buildings' supporting columns, which then triggered the immediate
collapse of the buildings. (See an audio slide show narrated by the chief
Forensic engineer Eugene Corley also details the chilling results of another
critical engineering investigation, that of the bombing and destruction of the
Alfred P. Murrah Federal Building in Oklahoma City. Unlike the World Trade
Center towers, which stood for 56 minutes (South Tower) and one hour 42 minutes
(North Tower), the Murrah Building crumbled in a mere three seconds. In this
worst-case scenario, known as a progressive collapse, there was simply no time
for anyone to escape.
By standing as long as they did, the Twin Towers gave most people a chance to
escape. (Hear one survivor's remarkable tale of escape from high in the South
Tower.) So structurally they were very sound. But their ultimate collapse
revealed fatal weaknesses that many tall buildings share. These include
stairways that are too few and too narrow to accommodate crowds of evacuees,
fireproofing materials that are easily dislodged and could leave steel exposed
to dangerous levels of heat, and insufficient means by which firemen and other
First Responders can reach the upper floors of a building in an emergency.
These issues and more have been addressed by NIST in a comprehensive report
that recommends 30 safety revisions to American building codes. But as NOVA
learns, these recommendations are not without controversy among builders or
even among those in the emergency planning community. Code changes often come with
significant added costs, swift evacuations of giant structures may not be
possible, and the probability of future terrorism is difficult to quantify.
Most experts concede that protecting buildings from airplane attacks like those
that took down the Twin Towers is simply not practical. But many improvements
can be made to a building's design, structural integrity, and evacuation
systems that would better protect it from major fire or even some terrorist
threats, and NOVA details the ways this can be done.
"Building on Ground Zero" takes viewers to two structures that exemplify bold
advances in skyscraper safety and construction. In New York City, World Trade
Center 7 has risen from the ashes as one of America's safest and "greenest"
tall buildings. And in China, NOVA gets a tour from Leslie Robertson as he
guides the construction of Shanghai's new World Financial Center, which upon
completion will be the tallest building in the world. (Hear Robertson describe its unique design and safety
Exclusive footage shows off the skyscraper's massive structural shell, "refuge
floors" with extra fire protection, and additional elevators designed for use
by emergency personnel. While Robertson is relieved that the NIST investigation
found no flaw in his engineering of the World Trade Center, the horror of what
happened to the Towers still haunts him to this day. In Shanghai, he is doing
what many argue we all must do: take the lessons from Ground Zero, endorse
innovation, and continue to reach for the sky.