At least two firefighters who were at the scene, Deputy Chief James Jackson and Battalion Chief Blaich, said that the southwest corner of the building near the fuel tank was severely damaged, possibly by falling debris, and that the tank might have been breached.
Mr. Jackson said that about an hour before the building's collapse, heavy black smoke, consistent with a fuel fire of some sort, was coming from that part of the building.
The Port Authority said it was unlikely the heavy masonry surrounding the tank could have been breached, and its officials have raised the possibility that the two diesel tanks buried just below the ground floor of the building might have contributed to the fire. They have also asserted that structural damage from falling debris is a more likely culprit in the collapse.