The South Tower and North Tower each collapsed in under a minute once the collapse began, but they stood burning for roughly an hour to nearly two hours before that.

Quick Scoop

How long did the actual collapses take?

When people ask ā€œhow long did it take for the Twin Towers to fall,ā€ they usually mean the duration of the visible collapse, from the first movement at the impact zone until the debris reached the ground. Structural analyses and video timing show:

  • The South Tower (WTC 2) collapse progression took on the order of about 10ā€“15 seconds from initiation to the bulk of the debris reaching the ground.
  • The North Tower (WTC 1) similarly took roughly 10ā€“15 seconds, with debris falling at close to, but not exactly, freeā€‘fall speed through much of the descent.

One engineering review notes that debris from the upper portion of a tower took about nine seconds to reach the ground from the top, very close to freeā€‘fall for that height.

How long were they standing after impact?

There is another, equally important ā€œhow longā€ question: how long the towers remained standing after they were hit.

  • North Tower (WTC 1): Hit at 8:46 a.m., collapsed at 10:28 a.m., so it stood for about 1 hour 42 minutes after impact.
  • South Tower (WTC 2): Hit at 9:03 a.m., collapsed at 9:59 a.m., so it stood for about 56 minutes after impact.

From the first impact (8:46) to the second collapse (10:28), it was about 102 minutes between the start of the attacks on the towers and the destruction of both.

Why did the collapses look so fast?

Engineers describe a ā€œpancakingā€ process: once the fireā€‘weakened structure at the impact and fire floors gave way, the mass of the stories above began to fall, overloading the floors beneath in rapid succession.

  • The upper part of each tower started descending.
  • Each lower floor was hit by far more load than it was designed to carry, failed in turn, and the process cascaded downward very quickly.

Analyses by groups such as NIST and independent structural engineers have emphasized that while some parts of the exterior dropped at near freeā€‘fall over a limited distance, the overall collapse time was still slightly longer than pure freeā€‘fall due to structural resistance.

TL;DR:

  • Each towerā€™s visible collapse took on the order of 10ā€“15 seconds.
  • The South Tower fell 56 minutes after impact; the North Tower fell 1 hour 42 minutes after impact, about 102 minutes total from the first impact until both were down.

Information gathered from public forums or data available on the internet and portrayed here.