How long did it take the Twin Towers to collapse?
The South Tower collapsed 56 minutes after being hit, and the
North Tower 102 minutes after being hit. Once the buildings began
to fall, each took less than 30 seconds to fully collapse. The
South Tower, though hit second, collapsed first.
Parts of the South Tower reached the ground about 9 seconds
after its collapse began at 9:59 AM EDT, approximately 56 minutes
after being hit. The central core of the lower 40 floors caved in
within 25 seconds thereafter. Debris flattened or filled the seven
basement levels within a few seconds.
The TV mast and roof from the North Tower struck the ground
about 11 seconds after the descent began, at 10:28 AM EDT, 102
minutes after being hit. The central core of the lower 60 floors
completely collapsed within 10 to 15 seconds after being bypassed
by the falling upper floors.
Most of the interior collapse was hidden by dust and debris,
which also spread over the surrounding buildings and streets.