The 16 people who escaped the burning top floors of the World Trade Center's south tower owe their lives to an unlikely hero: a row of giant elevator machines that shielded one stairway from destruction. About 2,000 people were on or above the floors hit by two hijacked jets Sept. 11. USA TODAY has identified only 16 survivors from those floors. These survivors were all in the south tower. They all used the same stairway. And they all made it out because an enormous elevator machine room happened to be located on the 81st floor, where the nose of the jet hit.

The machine room contained a dozen 24-ton elevator hoists, which pulled high-speed express elevators from the lobby to the 78th floor. The Otis Elevator 339HT machines were the largest in the world when they were installed three decades ago during the towers' construction. Lined up like a row of soldiers in front of Stairway A, the machines helped protect the stairwell.

The elevator equipment room covered more than half the width of the 81st floor. Its size forced the tower's designers to route Stairway A around the machines. The detour moved Stairway A from the center of the building toward the northwest corner - away from the path the hijacked jet would take.

Stairway A

USA TODAY reported in December that Stairway A had remained open from top to bottom in the south tower, and about 15 people used it to escape from floors at or above the jet crash. Others went up the stairway in search of a helicopter rescue that never came.

But it was unclear why Stairway A had been spared. The other two stairwells in the south tower were wrecked by the explosion. In the north tower, even the stairwells on the two floors below the impact were destroyed, trapping dozens of people who survived the impact.

A close examination of architectural drawings, engineering plans and survivor stories reveals that the elevator equipment room played a key role in providing safe passage to those who took Stairway A.

In the north tower, the first to be hit, the jet slammed into the center of the building at the 94th through 98th floors - well above the north tower's 81st floor elevator machine room. The jet's impact cut off all three stairwells, which, from the 83rd floor up, were grouped in the building's center. Everyone above the 92nd floor died. On the 91st floor, two stairways were destroyed; the third survived, and everyone got out.

The second jet crashed at a sharp angle into the south tower 16 ½ minutes later, hitting the 78th through 84th floors and leaving only Stairway A for escape. The 16 survivors who went down Stairway A include:

	Ten people who were in the north side of the crowded 78th floor elevator lobby, where people transferred from local to express elevators. Many people, perhaps 200, lost their lives when the explosion ripped through the lobby. The area was "packed worse than lunch or rush hour," said Judy Wein, a survivor whose arm was shattered.
	Two people at Fuji Bank on the 81st floor. The elevator machine room was between these survivors and the crash.
	Four people who were on the 84th floor. Three worked at Euro Brokers, based on the 84th floor, and another worked at Fiduciary Trust on the 97th floor.

In the north tower, people just below the crash found themselves trapped because of damaged stairways. But in the south tower, Stairway A provided safe passage for 13 people on the 77th floor, just below the crash. "We tried the other two stairways, but they were gone," said Florence Jones of Baseline Financial.

Each tower had three stairways labeled A, B and C. On most floors, the stairways were about 30 feet apart in the core with the plumbing, elevators and other infrastructure. The building was 208 feet wide.

Stairway B went straight down, but stairways A and C left the core of the building twice to dodge elevator machine rooms: from the 76th through 82nd floors and the 42nd through 48th floors.

On the 82nd floor, Stairway A emptied into a 52-foot long corridor heading north, atop the elevator machine room on the floor below. The passage went through two doors, then headed west for 15 feet, where the stairwell resumed. The stairway ran down that north side of the building until the 76th floor, where another passageway led back to the center.

The detour around the 81st-floor elevator machine room proved to be a lifesaving coincidence when the jet struck the southeast side of the building. Nowhere in the tower was a stairway farther to the northwest than on the floors where it mattered most.

Safe Passage Down

Kelly Reyher, a lawyer who worked at AON Insurance, crawled out of a burning elevator on the 78th floor and over corpses to reach Stairway A. "There were no bodies or anything in the staircase," he said.

Several male survivors cleared heavy debris from Stairway A between the 77th and 78th floor. After detouring through a door and down a corridor, survivors picked up Stairway A again in the center of the 76th floor. There, the lights were on and the air was fresh.

Cut and bloodied by the jet's impact, Christine Sasser, who worked at Fuji Capital Markets, walked down Stairway A from the 78th floor with her badly injured colleague, Silvion Ramsundar. The 78th floor was dark, Sasser said, but the stairwell was lighted and the air quality fine. As a result, she had little idea of the extent of the death and damage on the floors above her. "You thought, 'This isn't that bad,' " she said.

Jake Pauls, an expert in high-rise evacuations, said the trend has been to pack fire stairs tightly into a building's core so stairs don't consume leasable floor space. "We may be relying too much on sprinklers and not enough on keeping evacuation routes separate," he said.

The elevator machine room also may have helped contain the upward force of the explosion, protecting Stairway A when it was in the building's center above the 82nd floor. To hold the 600,000-pound weight of the elevator hoists, the beams supporting the 81st floor were twice as big and four times as heavy as those on the 79th floor.

Even the collapse of the two towers did not destroy the massive Otis 339HT machines. The machines were 8 feet tall and 13-feet-by-8-feet wide. Some were found intact in the wreckage at Ground Zero, still bolted to the specially reinforced beams that held them. Investigators at first mistook them for jet engines.