SHANNON McCAFFREY
Associated Press Writer
WASHINGTON (AP) -- The World Trade Center's superior construction allowed it to withstand the initial impact of two jetliners and remain standing long enough for thousands to escape, according to a government analysis.
The Federal Emergency Management Agency's report, which The Associated Press obtained Tuesday from a government official, offers suggestions for improving building construction but concludes it may never be possible to build a structure that could survive a catastrophic event like Sept. 11.
``Reliably designing a building to survive the impact of the largest aircraft available now or in the future may not be possible,'' said the report, which will be released at a House Science Committee hearing on Wednesday.
The first jetliner hit the trade center's north tower between the 94th and 99th floors shortly before 9 a.m. The second plane slammed into the south tower about 11 minutes later, striking between the 78th and 84th floors. The south tower fell 56 minutes, 10 seconds after impact; the north tower about six minutes later.
The attack left 2,823 people dead or missing, though many thousands more escaped. Most of the victims were trapped in the floors above where the jetliners struck.
The report confirmed the emerging consensus that the twin towers could have withstood the impact of the hijacked airliners but eventually succumbed to the inferno that weakened the buildings' steel framework. Heat from the fire was comparable to the energy produced by a large commercial power-generating plant, the report said.
A large quantity of the approximately 10,000 gallons of fuel in each plane was quickly consumed in massive fireballs that caused limited structural damage. But the rest of the fuel quickly snaked across floors and down elevator shafts, setting ablaze furniture, computers, paper files and the planes' cargo.
The temperatures of the fire reached an estimated 2,000 degrees, melting the steel support system and causing the upper floors to collapse onto lower floors, which could not withstand the weight.
``The fact that the structures were able to sustain this level of damage and remain standing for an extended period of time is remarkable and is the reason that most building occupants were able to evacuate safely,'' the report said.
The ``building performance study'' was a collaborative effort by FEMA and the American Society of Civil Engineers. Architects, engineers and other experts reviewed the collapse to see whether flaws in the building were responsible.
The report suggests studying ways to improve fireproofing, enhance structural supports and strengthen walls around stairwells. In theory, the team said, occupants in the floors above the impact could have escaped had the stairwells withstood the impact.
The National Institutes of Standards and Technology is expected to take over the study after Wednesday's hearings and will be responsible for creating broad recommendations to improve building and fire codes.
