Case Study #3: WTC 1 & WTC 2 Terrorist Attack, New York City (2001)
On the morning of 11 September 2001, in a coordinated terrorist attack, two commercial airliners, both Boeing 767s, were hijacked and subsequently flown into the 110-storey WTC 1 and WTC 2 towers. Over 3,000 people were killed in the attack including some 343 emergency responders.xiv
According to a report produced jointly by the Federal Emergency Management Agency (FEMA), the Structural Engineering Institute of the American Society of Civil Engineers (SEI/ASCE), the city of New York, and several other Federal agencies and professional organizations, it was the fire produced by the initial impact explosion that eventually induced complete structural failure in the two buildings:
"As each tower was struck, extensive structural damage, including localized collapse, occurred at the several floor levels directly impacted by the aircraft. Despite this massive localized damage, each structure remained standing. However, as each aircraft impacted a building, jet fuel on board ignited. Part of this fuel immediately burned off in the large fireballs that erupted at the impact floors. Remaining fuel flowed across the floors and down elevator and utility shafts, igniting intense fires throughout upper portions of the buildings. As these fires spread, they further weakened the steel-framed structures, eventually leading to total collapse."14
With the buildings? primary means of egress, stairways and elevators, blocked by raging fires and suffocating smoke, the prospect of safe egress for the two buildings? occupants was effectively nil. As a result, some occupants opted to jump from their office windows and plunge to their death rather than to suffocate or be burned alive.
Because it is impossible to protect high-rise buildings from such catastrophic events like those witnessed on 9/11, the lesson to heed from the tragedy is that high-rise buildings should be equipped with some form of secondary means of egress in case the primary means, stairways and elevators, fail or are compromised.
In today?s volatile times, reliance upon the primary methods of evacuation in high-rise buildings, stairways and elevators, is foolhardy and dangerous for occupants and costly, in terms of litigation, insurance, and loss of business continuity for companies.
It is much too risky to stake one?s life or a company?s human capital on the effectiveness of a building?s stairways and elevators during a crisis ? especially when considering the threats that high-rise buildings face, their inherent design vulnerabilities, and the severe inadequacies of their primary means of egress.
The current focus of the dialogue surrounding high-rise safety issues is on how best to augment and harden the structural aspects and redundancy of buildings. This is insufficient and impractical. Enacting various measures that structurally harden stairwells, elevator shafts, critical junctures, and other vulnerable parts of high-rise buildings may indeed grant occupants extra time to evacuate in the event of fire; however, such resilience techniques do not provide occupants with a secondary evacuation method when the primary means of egress, stairways and elevators, are compromised or unusable. The primary concern of every high-rise occupant, including companies, should be how to get out in an emergency. The most pragmatic solution lies not in structural strengthening but in the widespread adoption of secondary evacuation devices.
Cutting-edge secondary evacuation systems such as automatic harness-based lowering devices, mass-evacuation carriages that deploy from a buildings rooftop, and even inflatable slides that deploy from points on each floor to the ground, provide occupants and companies with a fail-safe should the unthinkable happen, once again, to a high-rise building.
More than just architectural gems, today?s high-rise buildings are symbols of power, prestige, wealth, success, and national pride. Unfortunately, these very same qualities make them the perfect targets for terrorists and wrongdoers. If we are to continue building towards the sky, we must take every possible precaution to make our buildings, and their occupants, as safe and secure as possible.