How 18 People Escaped Above the 9/11 Impact Zone

At 9:03 a.m. on September 11, 2001, United Airlines Flight 175 struck the South Tower of the World Trade Center between the 77th and 85th floors. The impact killed hundreds instantly. It severed two of the tower’s three stairwells through the crash zone, trapping everyone above with no obvious way down.

But one stairwell survived. Stairwell A, in the northwest corner of the building’s core, remained marginally passable through the impact region. Eighteen people found it, descended through the damage, and made it out before the tower collapsed 56 minutes later.

This is the story of how they got out, and why almost no one else above the impact zone could.

Three Stairwells

The World Trade Center towers each had three stairwells running through the central core: A, B, and C. They were not spread across the floor plan the way modern building codes would later require. All three ran through the building’s core, relatively close together.

When Flight 175 struck the South Tower, it came in from the south at an angle, banking left. The aircraft’s trajectory carried it through the southeast portion of the core, directly through stairwells B and C. Both were obliterated across the impact floors. Concrete walls were shattered. Steel was twisted and displaced. Anyone trying to descend through those stairwells hit impassable wreckage.

Stairwell A sat in the northwest corner of the core, the farthest point from the plane’s path. The impact damaged it. Walls were cracked. Drywall was knocked loose. Debris littered the landings. But the stairwell’s structural integrity held. A narrow path remained.

Finding the Way Down

In the minutes after the impact, the floors above the crash zone were chaos. The building swayed. Smoke poured up through elevator shafts and ventilation systems. Communications were unreliable. Some people called 911 and were told to stay put and wait for rescue. Others tried to reach the roof, only to find the doors locked.

The eighteen who survived made a series of decisions, each one narrowing the gap between life and death. Some had been heading down immediately after the North Tower was struck at 8:46 a.m., seventeen minutes earlier. Others began descending only after their own building was hit.

On the 84th floor, Brian Clark, a fire warden for Euro Brokers, started down Stairwell A. A few floors below, he heard banging and calls for help. Stanley Praimnath, who worked for Fuji Bank on the 81st floor, had been at his desk when the plane’s wing tore through his office. He was trapped behind a wall of debris. Clark climbed over the wreckage and pulled him free. The two men descended together.

Others found Stairwell A through a combination of instinct, knowledge of the building, and luck. Some had worked in the towers for years and knew the floor plan. Others simply tried every door they could find until one opened onto a passable route.

Through the Impact Zone

The descent through the damaged floors was not a simple walk down the stairs. Between roughly the 78th and 84th floors, the stairwell was wrecked. Walls were cracked open. Sections of the path were partially blocked by rubble. In places, survivors could see through the walls into the burning wreckage of the floors around them. The air was thick with smoke and dust, and the heat was intense.

The survivors had to pick their way through, stepping over debris, squeezing past collapsed sections, sometimes crawling. There was no lighting. Some used the glow from fires burning on the surrounding floors to navigate.

Below the impact zone, conditions improved. The stairwell was intact, though smoky. The descent was still slow, sometimes painfully so, as they merged with streams of people evacuating from lower floors. But the path was clear.

Every one of the eighteen made it to the lobby and out of the building. The South Tower collapsed at 9:59 a.m., less than an hour after the plane hit.

Why Stairwell A Survived

The National Institute of Standards and Technology (NIST) investigated the collapse of the World Trade Center towers in detail. Their findings on the South Tower’s stairwells revealed how narrow the margin of survival was.

Flight 175’s angle of entry was the critical factor. The plane banked left as it approached, striking the south face and traveling through the southeast portion of the core. Stairwells B and C were directly in the path. Stairwell A was not.

But “survived” overstates the condition of Stairwell A. It was damaged enough that many people who reached it turned back, believing it was impassable. Others never found it at all. The door markings on many floors were obscured by dust and damage. In the confusion and darkness, navigating from one side of the core to the other, through offices full of debris and smoke, was extraordinarily difficult.

Of the roughly 600 people estimated to have been above the impact zone when the plane struck, only eighteen made it down through Stairwell A. The rest could not find it, could not reach it, or reached it and judged the damage too severe to pass through.

The 78th Floor Sky Lobby

The 78th floor was the South Tower’s sky lobby, a transfer point where workers switched from express elevators to local ones for the upper floors. When Flight 175 hit, dozens of people were waiting there for elevators.

The impact zone began at the 77th floor. The sky lobby took catastrophic damage. Many people were killed instantly. Survivors on the 78th floor faced some of the worst conditions in the building: structural collapse, fire, and the destruction of the elevator banks they had planned to use for evacuation.

Some survivors from the sky lobby managed to descend, but they were escaping from the edge of the impact zone itself, not from above it. The eighteen who came from higher floors had to pass through this devastation on their way down.

Building Safety Lessons

The investigation into the World Trade Center attacks led to significant changes in building codes across the United States. Many of these changes addressed the exact vulnerabilities that trapped people in the South Tower.

Stairwell separation. The concentration of all three stairwells within the building’s central core meant a single event could compromise all of them. Updated codes for tall buildings began requiring greater physical separation of egress routes, so that damage to one area of the building would be less likely to cut off every escape path simultaneously.

Stairwell hardening. Post-9/11 codes called for increased impact resistance in stairwell enclosures in high-rise buildings. The goal was to ensure that stairwells could withstand greater structural damage while remaining passable.

Roof access. The locked rooftop doors in the South Tower prevented anyone from reaching the roof for potential helicopter rescue. While helicopter evacuation from a burning skyscraper is extremely difficult and was not viable on September 11, the locked doors eliminated even the possibility. Subsequent discussions focused on whether roof access should be maintained as an emergency option in certain building types.

Communication systems. Many people above the impact zone called 911 and received instructions to remain in place. The information available to dispatchers did not reflect the conditions inside the building. Improvements to emergency communication systems in high-rises, including dedicated channels for building-specific information, followed.

Luminescent markings. The dark, smoke-filled stairwells made navigation nearly impossible. New codes required photoluminescent markings on stairwell steps, handrails, and door frames, so occupants could find and follow the exit path without electrical lighting.

Fifty-Six Minutes

The South Tower stood for 56 minutes after being struck. In that window, the eighteen survivors above the impact zone found Stairwell A, picked their way through the wreckage, and descended roughly 80 floors to the street.

Their survival was not guaranteed by the stairwell’s existence. It required finding it, judging that the damage was passable, and committing to the descent through conditions that would have turned most people back. Several of the eighteen later said they were not sure the stairwell would hold. They went anyway.

The story of Stairwell A is not a story about luck, though luck played a role. It is a story about how buildings are designed, how escape routes are planned, and how thin the margin between survival and catastrophe can be. One stairwell, in one corner, damaged but not destroyed. Eighteen people, out of hundreds, who found it in time.

The building codes that changed after September 11 exist because of what the South Tower revealed: that the difference between a building that lets people escape and one that traps them can come down to the placement of a single stairwell.