The US National Institute of Standards and Technology will soon be testing a controversial theory about the collapse of the World Trade Center towers.
According to an analysis by a leading fire-safety expert, had the fire-proofing insulation on the towers' steel structures been thicker, the towers would have survived longer and might even have remained standing after they were hit by the hijacked planes. The work is being seized on by lawyers representing victims' families and insurance companies.
If confirmed, it could also lead to changes in building codes. NIST is responsible for drawing up the final report on the towers' collapses and recommending if any changes are needed.
It is widely accepted that the collapses were caused by the failure of the buildings' steel structure as it was weakened by the heat of the fires. But Jim Quintiere of the University of Maryland, College Park, thinks the thickness of the surviving fire insulation, rather than the destruction of insulation during the impacts, explains why the towers collapsed when they did.
The south tower was the first to fall even though it was hit after the north tower. The insulation on its burning floors was only half as thick. According to Quintiere's calculations, if the insulation had matched that in the north tower, the south tower would have stayed standing longer.
No one doubts that the planes killed many people on impact and started the fires that led to the buildings' collapse, says Quintiere. But if both towers had had insulation over 50 millimetres thick, he says, they might not have collapsed at all. His analysis calls into question the safety of other buildings constructed to the same standards as the twin towers. However, the Port Authority of New York, the owner of the twin towers, rejects his theory.
Quintiere, whose previous work includes investigating the 1993 fire at the Branch Davidian compound in Waco, Texas, was struck by a statement in last year's preliminary report of the Federal Emergency Management Agency (FEMA). It noted that there was a discrepancy in the thickness of the fireproofing in the towers. On the floors of the south tower where the plane hit it was just 19 millimetres thick, half that on the floors struck in the north tower.
The diagonal rods in the trusses supporting the floors were particularly vulnerable, he says, since they were the thinnest structures and would heat up fastest. "The implications of these insulation differences are astounding," Quintiere says.
Together with Marino di Marzo, also at College Park, and Rachel Becker at the Technion, the Israel Institute of Technology in Haifa, Quintiere calculated how long it would take for the trusses to fail at the temperatures they were subjected to in the fires.
The results, presented in June 2002 at a meeting in New York organised by NIST, have now been published in Fire Safety Journal (vol 37, p 707). The team calculated that the south and north towers would collapse after 75 and 115 minutes respectively. In fact, they fell after 56 and 103 minutes. "It's the only calculation I've seen that has any correlation with events," Quintiere says.
Frank Lombardi, the Port Authority's chief engineer, insists that the thickness of the insulation is irrelevant. He says the impacts dislodged much of the fireproofing on the trusses. Without this protection, he says, it was inevitable that the heat would make them buckle.
This view is supported by Gene Corley, who led the FEMA's investigation last year. "I do not believe the insulation was substandard," he says. However, he concedes that if extra insulation had been applied and had remained in place after the planes hit, the buildings would have remained standing longer.
Quintiere is not convinced by Lombardi's account. He thinks that unprotected steel trusses would have given way after just 10 to 15 minutes. The fact the buildings stood as long as they did suggests the insulation remained intact on many structures, he says.
The FEMA report acknowledges that it is surprising the buildings stood for so long. "The fact that the structures were able to sustain this level of damage and remain standing for an extended period of time is remarkable," it states.
FEMA investigators should have looked more closely at this issue, Quintiere says. "We have a distorted, flawed and incomplete presentation to the public of why the WTC twin towers collapsed due to fire," he wrote in an email sent to fire-safety experts.
Quintiere acknowledges that further work is needed to prove or disprove his theory. But despite initial scepticism, it appears to be gaining ground. Shyam Sunder, the lead investigator at NIST, told New Scientist that his team will assess it. "We plan to conduct tests at NIST with different insulation thicknesses beginning in February and likely to end in March," he says. The results are unlikely to be revealed until the end of the investigation, which is due around September 2004.
If the NIST tests back Quintiere's theory, attention will turn to why the insulation was thinner in the south tower than the north tower. The New York City building code stipulates that the insulation on steel structures should be at least 38 millimetres thick. However, the Port Authority's special legal status means it does not have to comply with the code.
When the twin towers were built in the early 1970s, fire insulation just 19 millimetres thick was sprayed onto the trusses. But in 1996, Lombardi recommended the thickness be doubled. "I made the decision, since there was a question from a general contractor as to how much thickness is needed to provide a two-hour fire rating of the floor joists and floor assembly that would be in conformance with New York City building code," he says.
"Why would you be taking the dramatic measure of doubling the thickness if it wasn't for safety concerns?" says Brian Alexander, an attorney with Kreindler & Kreindler who is representing some of the families of victims. "They should have had double the building code requirements, given the size of the building and its design," he says. "The whole point of fireproofing in this building was to provide a certain amount of time for folks to get out." He will argue in court that they were not given this time.
Despite the recommendations by Lombardi, thicker insulation had been applied to fewer than a third of the trusses in the twin towers by 11 September. This, Lombardi says, was because it could only be done as floors became empty.
Six months before the attacks, the Port Authority received a copy of a report it commissioned from British consulting engineers Buro Happold to see if there was a more cost-effective alternative to applying thicker insulation. The authority declined to provide New Scientist with a copy of this report. But on being told of the report's existence, Alexander said he would be seeking a copy as part of legal proceedings.
Quintiere has also received the support of some of the families of those killed when the towers fell. Sally Regenhard, the founder of the Skyscraper Safety Campaign and the mother of one of the firefighters lost on 11 September, has said she would fund his research if NIST did not address the issue. "Right now we do not have the truth. We have people who have a vested interest in not knowing the truth," she says.