08 April 2005 -- Ineffective fireproofing and a shortage of staircases were the main reasons for the collapse of the World Trade Center, according to a report released Tuesday and led by Dr. Shyam Sunder, Acting Deputy Director of the Building and Fire Research Laboratory (BFRL) at the National Institute of Standards and Technology (NIST).
Dr Sunder's study is likely to have a significant effect on the future design of skyscrapers and on building regulations in the US.
The NIST report concludes that a combination of factors caused both buildings to collapse shortly after terrorists flew hijacked commercial airliners into them on 11 September 2001. Computer simulations have been used to help piece together the chain of events that unfolded between impact and the collapse of each structure.
The report says the initial collisions severely damaged several of the columns at the core of each building. Critically, they are also thought to have dislodged fireproofing on both the columns and the floors - the floors linked the inner columns to the supports on the outer structure.
"While the buildings were able to withstand the initial impact of the aircraft, the resulting fires that spread through the towers weakened support columns and floors that had fireproofing dislodged by the impacts," says Sunder, who led the NIST investigation. "This eventually led to collapse as the perimeter columns were pulled inward by the sagging floors and [became] buckled."
"The reason the towers collapsed is because the fireproofing was dislodged," according to Sunder. If the fireproofing had remained in place, Sunder said, the fires would have burned out and moved on without weakening key elements to the point of structural collapse.
At a news conference Sunder drew an analogy with the 2003 Columbia space shuttle disaster when the absence of a small piece of insulation foam - knocked off during launch - allowed fire to seep into the shuttle's entire wing span during re-entry with catastrophic results.New alternatives to traditional fireproofing should be explored, Sunder said, citing a paint-like substance which, if applied in sufficient layers, would stick "even if a plane hit it".
Nearly 3 000 people were killed in the attack on the World Trade Centre. Roughly 17 000 people were in the skyscrapers at the time of the attack, and Nist estimated that the death toll would have been closer to 14 000 if the two towers had been filled to their 50 000-person capacity.
Photographs show that the walls of the north tower to have deformed by as much as 140 centimetres just a few minutes before collapse and the walls of the south tower to have arched by 50 cm.
Sunder told a press conference that newly developed fireproofing could perhaps have sustained the structure for longer. "Even with the aeroplane impact and jet-fuel-ignited multi-floor fires - which are not normal building fires - the buildings would likely not have collapsed had it not been for the fireproofing that had been dislodged," he says.
The report further concludes that more lives might have been saved if both structures had been built with more than just three staircases. And the stairs were also surrounded by lightweight drywall that was immediately destroyed upon impact. Reinforced surrounding walls "might have provided greater opportunities for escape", Sunder says.
The complete report is comprised of more than 10,000 pages, the preliminary 3400 pages of which were released on Tuesday. The remainder of the study is planned for release in July 2005, when the institute will also make recommendations concerning building design and construction.
BFRL’s mission is to meet the measurements and standards needs of the building and fire safety communities by serving as the source of critical tools - metrics, models, and knowledge - used to increase productivity, facilitate trade and enhance public safety through technical innovations and improved codes, standards, and practices.
In his current position, Dr. Sunder also: • serves as the lead investigator for the federal building and fire safety investigation into the World Trade Center disaster; • leads NIST activities related to the National Earthquake Hazards Reduction Program (NEHRP); • oversees NIST activities related to the National Construction Safety Team Act; • guides effective implementation of the NIST strategic plan within BFRL and the four BFRL goals: Homeland Security, Fire Loss Reduction, Enhanced Building Performance, and High-Performance Construction Materials and Systems; • chairs, as designated by the NIST Director, the Interagency Committee on Seismic Safety in Construction (ICSSC) - a group that recommends policies and practices to its 32 member-agencies on improving the seismic safety of federal buildings nationwide; and • serves as the U.S.-side chair of the Wind and Seismic Effects Panel established under the U.S.-Japan Cooperative Program on Natural Resources (UJNR).
Prior to joining NIST, Dr. Sunder held a succession of positions at the Massachusetts Institute of Technology (MIT) beginning in 1980: instructor, assistant professor, associate professor, principal research scientist, and senior research scientist.
Dr. Sunder’s awards include the Gilbert W. Winslow Career Development Chair (1985-87) and the Doherty Professorship in Ocean Utilization (1987-89) from MIT, the Walter L. Huber Civil Engineering Research Prize (1991) from the American Society of Civil Engineers, and the Equal Employment Opportunity Award (1997) from NIST.Dr. Sunder holds a Bachelor of Technology (Honors) degree in civil engineering from the Indian Institute of Technology, Delhi (1977), a Master of Science degree in civil engineering from MIT (1979), and a Doctor of Science degree in structural engineering from MIT (1981).