Template:8:46 a.m. September 11, 2001: Flight 11

8:46 a.m. September 11, 2001: Flight 11 Hits the North Tower of the World Trade Center
Flight 11 slams into the WTC North Tower (Building 1). Seismic records pinpoint the crash at 26 seconds after 8:46 a.m.

The NIST report states the crash time to be 8:46:30. [NATIONAL INSTITUTE OF STANDARDS AND TECHNOLOGY, 9/2005, PP. 19 ] The 9/11 Commission Report states the crash time to be 8:46:40.

Investigators believe the plane still has about 10,000 gallons of fuel (see 8:57 a.m. September 11, 2001). [NEW YORK TIMES, 9/11/2002]

The plane strikes the 93rd through 99th floors in the 110-story building. No one above the crash line survives; approximately 1,360 people die. Below the crash line, approximately 72 die and more than 4,000 survive. Both towers are slightly less than half full at the time of the attack, with between 5,000 to 7,000 people in each tower. This number is lower than expected. Many office workers have not yet shown up to work, and tourists to the observation deck opening at 9:30 A.M. have yet to arrive.

The impact severs some columns on the north side of the North Tower. Each tower is designed as a “tube-in-tube” structure and the steel columns which support its weight are arranged around the perimeter and in the core. The plane, which weighs 283,600 lb and is traveling at an estimated speed of around 430 mph, severs 35 of the building’s 236 perimeter columns and damages another two. The damage to the South Tower’s perimeter will be similar.

The perimeter columns bear about half of the tower’s weight, so this damage reduces its ability to bear gravity loads by about 7.5 percent.

The actual damage to the 47 core columns is not known, as there are no photographs or videos of it, but there will be much speculation about this after 9/11. It will be suggested that some parts of the aircraft may have damaged the core even after crashing through the exterior wall. According to the National Institute of Standards and Technology (NIST): “Moving at 500 mph, an engine broke any exterior column it hit. If the engine missed the floor slab, the majority of the engine core remained intact and had enough residual momentum to sever a core column upon direct impact.” According to NIST’s base case computer model, three of the core columns are severed and another ten suffer some damage.

If this is accurate, it means that the impact damage to the core reduces the Tower’s strength by another approximately 7.5 percent, meaning that the building loses about 15 percent of its strength in total. This damage will be cited after 9/11 by NIST and others researchers as an event contributing to the building’s collapse. In addition, some of the fireproofing on the steel columns and trusses may be dislodged. The original fireproofing on the fire floors was mostly, but some of the fireproofing on the flooring has recently been upgraded to , which is about 20 percent denser and 20 percent more adhesive.

Photographs and videos of the towers will not show the state of fireproofing inside the buildings, but NIST will estimate the damage to it using a computer model. Its severe case model will predict that 43 of the 47 core columns are stripped of their fireproofing on one or more floors and that fireproofing is stripped from trusses covering 60,000 ft2 of floor area, the equivalent of about one and a half floors. NIST will say that the loss of fireproofing is a major cause of the collapse, and performs 15 tests on fireproofing samples. According to NIST, more fireproofing is stripped from the South Tower.