Fire Department officials warned the city and the Port Authority of New York and New Jersey in 1998 and 1999 that a giant diesel fuel tank for the mayor's $13 million command bunker in 7 World Trade Center, a 47-story high-rise that burned and collapsed on Sept. 11, posed a hazard and was not consistent with city fire codes.
The 6,000-gallon tank was positioned about 15 feet above the ground floor and near several lobby elevators and was meant to fuel generators that would supply electricity to the 23rd-floor bunker in the event of a power failure. Although the city made some design changes to address the concerns -- moving a fuel pipe that would have run from the tank up an elevator shaft, for example -- it left the tank in place.
But the Fire Department repeatedly warned that a tank in that position could spread fumes throughout the building if it leaked, or, if it caught fire, could produce what one Fire Department memorandum called ''disaster.''
Putting a tank underground typically protects it from falling debris, and impedes leaks or tank fires from spreading throughout the building.
Engineering experts have spent three months trying to determine why 7 World Trade Center, part of the downtown complex that included the 110-story towers, collapsed about seven hours after being damaged and set on fire by debris from the damaged landmark buildings.
Some of the experts, who said that no major skyscraper had ever collapsed simply because of fire damage, have recently been examining whether the diesel tanks -- there were others beneath ground level -- played an important role in the building's stunning demise.
The Port Authority, which owns the land on which the building stood and issued the building permit for the tank and its fireproof enclosure, said yesterday that it believed the structure had in fact met the terms of the city's fire code. Though the tank was on a tall fireproof pedestal, it was still effectively on the lowest floor of the building, as the code requires, said Frank Lombardi, the Port Authority's chief engineer.
The authority also worked with Fire Department officials to eliminate the department's original objections, Mr. Lombardi said.
''We made sure that it was in agreement with the code,'' Mr. Lombardi said, adding that the tank was placed in an eight-inch-thick masonry enclosure.
A spokesman for the Fire Department said yesterday that he could not authoritatively say whether all the concerns of its officials had been addressed by the Port Authority. But when reached yesterday, the department official who wrote several of the warning memorandums said he regarded the Port Authority's interpretation of the code to be ''a stretch.'' The official, Battalion Chief William P. Blaich, said he still considered the tank's placement to have been unsafe.
The Port Authority has long held that, as a matter of law, it does not have to abide by city fire codes. But after the 1993 bombing of the towers, the Port Authority signed a memorandum of understanding with the city pledging to not only meet the city's fire codes, but also to often take additional precautions.
A spokesman for the city's office of emergency management, Francis E. McCarton, said the city accepted the Port Authority's determination that the tank and its placement were properly safe. He said it was essential that the mayor's command center have a backup energy source and placing it on ground floor was unacceptable because the area was deemed to be susceptible to floods.
''We put it in the area where we needed to put it,'' Mr. McCarton said. Any suggestion that the tank's position was a factor in the collapse of the building was ''pure speculation,'' he said.
He added that the tank had fire extinguishers and was surrounded by the thick, fire-resistant containment system, and that the fiery collapse of the towers could never have been anticipated in the city's planning.
No one is believed to have died in the collapse of 7 World Trade Center. But its collapse did further complicate the rescue and recovery efforts under way at the scene.