Water cascaded down the stairs and coursed down the elevator shafts of One World Trade center.
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It is one of the most meticulously designed and constructed buildings ever built.
"The first thing that came to my mind was why is there water inside the elevator and stair shafts. These are two particular locations where there shouldn't be any water force at all," said Glenn Corbett, professor at John Jay College.
Fire safety expert Corbett says he's never seen it.
Port Authority officials say a water main for the air conditioning system burst on the 88th floor, which flooded some stairways and stranded two elevators between the 69th and 70th floors, and also the 75th and 76th floors.
Here's a look from inside one of the elevators:
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"All of a sudden water started dripping out on the top, then the lights started flickering, and then the elevator slowed down and then everything just stopped dead," said Phil Pissutti, stranded in elevator.
Those trapped in the elevators were rescued by firefighters within 20 minutes.
Corbett suggests it could indicate a design flaw in the building.
Authorities, he says, need to investigate the incident thoroughly.
"These are locations where water shouldn't be in the first place, so how that water, that volume of water got from outside to inside these two shafts is a big question that I think going forward, this is a significant issue that the Port Authority needs to look into and find out exactly what happened," Corbett said.