H.6.1 WTC 1
It has already been mentioned that substantial fireballs formed on the north, east, and south faces
immediately following the plane strike. A brief period of intense burning from openings on these faces
was observed after the fireballs dissipated, but in a short period (on the order of 60 seconds) the fires
seemed to “damp down” and very little flame and only light smoke was evident from the outside. This
period of light burning lasted several minutes before fires began to reappear.
Rapid early fire growth was observed on the east side of the north face on floor 96 and floor 97, the center
of the east face on floor 94 and floor 97, and the western side of the south face on floor 96. Even though
relatively little initial damage was sustained by the west face, heavy smoke followed shortly by flame
appeared around window 97-437 at 8:55 a.m. After this time, a very rapid fire spread was observed
across the west face on this floor. Within a couple of minutes, over half of the windows were emitting
smoke, and flames were visible in many. Even though floor 92 was not directly struck by the airplane,
fire appeared on the east side of the tower on this floor shortly after 9:00 a.m.
Following the initial development of large fires, fire spread continued until WTC 1 collapsed around
10:28 a.m. At times the fires displayed the systematic, relatively slow spread expected for fire growth in
a typical building. For instance, after the initial rapid growth phase, fires on floors 92, 94, 96, and 97 on
the east face began to move deliberately toward the south. As they spread, the fires would burn intensely
at a given location for a while before dying down. As a result, these fires developed the appearance of a
wave moving slowly across the building.
There were also certain times and locations during which fire appeared to spread quite rapidly. Some of
these episodes were clearly connected with rapid fire growth and likely flashover in rooms. During the
first half hour, significant fires were observed toward the centers of floors 92, 94, 96, and 97 on the east
face that were spreading towards the north. Each of these fires eventually reached a certain point where
further fire spread was inhibited for many minutes. A review of building plans showed that walls of
offices or meeting rooms were presented at the locations where fire spread was inhibited.
Apparently, these walls served as effective fire breaks that protected against further fire spread. However,
for each of these floors fire and smoke eventually appeared at one of the windows beyond the walls, and
after one of these windows was broken fire growth was extremely rapid and robust across the remaining
windows. These observations are consistent with the occurrence of flashover within an enclosed space.
At other times, unusually rapid fire growth apparently occurred in areas that are believed to have been
relatively open and not constrained by walls. One of these episodes occurred around 9:54 a.m. on the
north face. Fire suddenly appeared on floor 96, a location to the west of the damage inflicted by the
airplane. Within a very short period of time, fire could be seen in roughly 10 windows covering a
distance of more than 30 ft.
Another example of very rapid fire growth appeared to take place on floor 98. In the early period of the
fire, this floor did not appear to be heavily involved, and this remained true for quite a while. However,
after 9:30 a.m., fire began to appear on this floor and by 10:00 a.m., fires were observed over significant
lengths on all four faces of the tower.
One of the more unusual fire spread episodes in WTC 1 occurred just after the collapse of WTC 2 around
9:59 a.m. Within a couple of minutes, a large intense fire suddenly appeared on the south side of the west
face on floor 104 in an area well above any other apparent fire. This unusual jump in fire location is
difficult to explain, but is likely associated with vertical shafts located in the core of the tower.
For most of the time following the plane strike, no fire was observed on any of the floors on the south
face over lengths extending from the eastern edge of the tower to near the center of the face. Fires were
not observed in this region of the building until around 10:00 a.m. By the time this tower collapsed
roughly 25 minutes later, intense fires extending over significant lengths of the originally uninvolved area
were burning on floor 94 to floor 98 in this area.
A final example of rapid fire spread and growth in WTC 1 was described previously in the May 2003
Progress Report for the Investigation (NIST 2003). In this case, a line of smoke appeared suddenly over
a significant length of floor 92 on the north face of WTC 1 at 10:18:48 a.m., or roughly 9 minutes before
the collapse of the tower. Puffs of smoke were observed simultaneously on the north face from floors 94,
95, and 97. More isolated puffs were seen at the same time from floor 92 and floor 95 on the west face
and from floor 92 on the south face. Very shortly (seconds) after the appearance of the smoke, a localized
fire on floor 95 to the west of the plane strike location grew very rapidly and flames erupted from
windows. Following the smoke release, a large fire began to spread rapidly across the western side of
floor 92 on the north face. Previous to the appearance of the smoke, only small fires were evident on this
floor. By the time the tower collapsed, this fire had spread across most of the floor and had reached the
western wall. This fire was responsible for the large burst of flame from the north face observed when
this tower collapsed.
I have seen the 3. program now.. good job Mackey!
