NEW YORK, April 5 -- The hijacked airplanes that struck the World Trade Center hit with such force that the resulting explosions blew the fireproofing off the steel columns, accelerating heat buildup and weakening the structural core -- contributing to the towers' eventual collapse, according to a report issued Tuesday.
The process was hastened by fires outside that consumed the buildings' face and caused the exterior columns to bow in, according to the report.
Still, the study by the National Institute of Standards and Technology concluded that no amount of fireproofing could have saved the buildings.
Poor evacuation procedures, lack of communication and weak staircases cost the lives of civilians and emergency workers at the towers, as workers waited for directions and were slow to leave after the Sept. 11, 2001, attack, the report said.
Only two of the 198 elevators in the towers survived the initial explosions -- forcing most survivors to escape down emergency stairwells, which had suffered extensive damage. The report found that building codes lacked requirements sufficient to protect the structure of emergency stairwells.
Had such codes been in place, said S. Shyam Sunder, the lead investigator of the institute, "there would have been greater opportunity for people to evacuate."
Another federal report issued Tuesday found that the economic impact of the attacks was less than New York officials had originally estimated. After the attacks, state and city officials said the loss of tax revenue could approach $5.8 billion.
But the Government Accountability Office said the loss attributable to the attacks was closer to $2.9 billion and cited the city's recession, which had begun to take a toll before Sept. 11, for the rest of the loss.
The institute's report on the building collapse was long awaited by city officials. The institute based its analysis on extensive interviews with about 1,000 survivors, computer modeling, recovered steel and communications records.
The institute will use the findings in the 3,000-page report to formulate recommendations -- expected for release in September -- for changes in national building codes for office towers. A spokesman at the Port Authority of New York & New Jersey, which owned the World Trade Center, said local and state officials will review the recommendations and use them to guide reconstruction at Ground Zero.
"Whatever recommendations are adopted we will follow," said authority spokesman Steve Coleman. "Our engineering department has oversight over the buildings [and] will ensure the codes are followed."
In the past, city safety codes for office buildings often were a sort of informal compromise between safety and commercial imperatives. In 1968, New York City officials drastically reduced the number of required stairwells in skyscrapers, at the request of the real estate industry, to increase the amount of available rental space.
New York was, in fact, fortunate that the attacks took place in the morning, when most people had not yet reached their offices. If the building had been fully occupied, the report found, a full evacuation would have taken four hours and cost 14,000 lives.
The agency interviewed survivors and found that, although most had participated in a fire drill, nearly one-half had never used the stairwells in the buildings before the attacks. In fact, New York City prevents the use of stairwells during fire drills.
"I've never heard of another jurisdiction having such a prohibition," Sunder said.