From 9:59 until 10:28 A.M.

At 9:58:59, the South Tower collapsed in ten seconds, killing all civilians and emergency personnel inside, as well a number of individuals-both first responders and civilians-in the concourse, in the Marriott, and on neighboring streets. The building collapsed into itself, causing a ferocious windstorm and creating a massive debris cloud. The Marriott hotel suffered significant damage as a result of the collapse of the South Tower.¹⁵⁶

Civilian Response in the North Tower
The 911 calls placed from most locations in the North Tower grew increasingly desperate as time went on. As late as 10:28, people remained alive in some locations, including on the 92nd and 79th floors. Below the impact zone, it is likely that most civilians who were physically and emotionally capable of descending had exited the tower. The civilians who were nearing the bottom of stairwell C were assisted out of the building by NYPD, FDNY, and PAPD personnel. Others, who experienced difficulty evacuating, were being helped by first responders on lower floors.¹⁵⁷

FDNY Response Immediate Impact of the Collapse of the South Tower. The FDNY overall command post and posts in the North Tower lobby, the Marriott lobby, and the staging area on West Street south of Liberty all ceased to operate upon the collapse of the South Tower, as did EMS staging areas, because of their proximity to the building.¹⁵⁸

Those who had been in the North Tower lobby had no way of knowing that the South Tower had suffered a complete collapse. Chiefs who had fled from the overall command post on the west side of West Street took shelter in the underground parking garage at 2 World Financial Center and were not available to influence FDNY operations for the next ten minutes or so.¹⁵⁹

When the South Tower collapsed, firefighters on upper floors of the North Tower heard a violent roar, and many were knocked off their feet; they saw debris coming up the stairs and observed that the power was lost and emergency lights activated. Nevertheless, those firefighters not standing near windows facing south had no way of knowing that the South Tower had collapsed; many surmised that a bomb had exploded, or that the North Tower had suffered a partial collapse on its upper floors.¹⁶⁰

We do not know whether the repeater channel continued to function after 9:59.161

Initial Evacuation Instructions and Communications. The South Tower's total collapse was immediately communicated on the Manhattan dispatch channel by an FDNY boat on the Hudson River; but to our knowledge, no one at the site received this information, because every FDNY command post had been abandoned-including the overall command post, which included the Field