An interim report by a federal agency investigating the collapse of the World Trade Center towers in the aftermath of the September 11, 2001 terrorist attack indicates inadequate fireproofing on the floors may have contributed to the disaster.

New York City fire codes call for fireproofing material on floors that can withstand two hours of fire. But the newly released interim report by the National Institute of Standards and Technology, NIST, shows that the fireproofing material on the steel floor supports in the towers of the World Trade Center was never tested to prove it could endure two hours of fire. The first of the two towers to fall collapsed one hour and forty-five minutes after terrorists first struck the buildings.

When the Trade Center was built it was exempted from New York City fire codes because it was owned by state agencies. After years of controversy, the buildings were upgraded to comply with New York City building codes. NIST has not been able to find documentation to prove the fireproofing material used on the floors was tested to meet the requirements. But Shyam Sunder, the agency's lead investigator, says it is too early to reach any conclusions. "I think what we are saying is we have this information in the interim report on the fireproofing of the floor system," he said. "That is what we are willing to report at this point. What that is saying is that we are not sure if, in fact, the two hour rating was met by the firefroofing that was provided to the buildings and how technically that selection was justified."

Two previous studies drew conflicting conclusions concerning the role floor supports played in the collapse of the buildings.

The agency is using computerized models, more than 250 piece of steel recovered from the World Trade Center site and over 6500 photographs and video clips in its investigation. But agency officials say some vital pieces of information are still needed, including tapes and transcripts of interviews from first responders, original project specifications for the two World Trade Center Towers and original design documents related to the ability of the towers to withstand aircraft crashes. Many of the documents were destroyed in the disaster

The agency's final report in due in August 2004.