Earlier this month the Commerce Department's National Institute of Standards and Technology (NIST) released its analysis about how the World Trade Center (WTC) towers collapsed after two aircrafts were flown into them on Sept. 11, 2001. Tall buildings remain popular for TV transmission (Sears Tower and the Empire State Building, for example) and for ENG receive sites. The NIST analysis is valuable because it not only analyzes where the towers failed, but also describes what parts of the design that enhanced building structural performance and suggests specific changes that could be made in skyscraper design to improve resistance to terrorist acts.
The NIST news release describing the analysis includes a fact sheet listing four future practices and technologies that potentially could have improved building structural performance on Sept. 11, 2001:
- Fireproofing not dislodged or only minimally dislodged by aircraft impact.
- Perimeter columns and floor framing with greater mass to enhance thermal and buckling performance.
- Other passive and active fire protection features (e.g., compartmentation to retard spread of building fires; thermally resistant window assemblies to limit air supply and retard the spread of fires; fire-protected and structurally hardened elevators for firefighter access with continuous, redundant water supply for standpipes).
- Steels with improved high-temperature properties (e.g., yield strength and stiffness) and creep behavior.
In listing these items, NIST point out, "There is far greater knowledge of how fires influence structures in 2005 than was the case in the 1960s. The analysis tools available to calculate the response of structures to fires also are far better now than they were when the WTC towers were built."
The NIST fact sheet also lists some future practices and technologies that could have improved life safety on September 11, 2001:
- Improved performance to delay or prevent building collapse.
- Improved stairwell integrity via increased remoteness of stairwells and/or enhanced structural integrity of stairwell enclosures.
- Better communications to occupants and among first responders via improved systems and timely information sharing.
- Better command and control for large-scale incident management (e.g., location of command posts and physical assets; interagency coordination).
- Better evacuation training (e.g., practice stairwell evacuation, roof rescue not presently feasible as a standard option, existence of transfer hallways).
- Other life safety features (e.g., fire protected and structurally hardened elevators available for occupant use during emergencies; vibration-protected elevators such as those used in seismic regions; self-evacuation capability for mobility impaired occupants.
While broadcasters have little control over the buildings in which their facilities are located, one improvement should be able to be implemented easily - better evacuation training.
The NIST news release Latest Findings from NIST World Trade Center Investigation Released - Probable Collapse Sequences for Both Towers Finalized; Reports Issued for Three Projects has much more information on the WTC tower collapse including computer simulations of the impact of the aircraft on the towers.
