Interstate Bank Building Fire;
THE FIRE
The fire originated in an open-plan office area in
the southeast quadrant of the 12th floor. (See Appendix
A.) The area of origin contained modular office furniture
with numerous personal computers and terminals used
by securities trading personnel. The cause is thought
to be electrical in origin, but the precise source
of ignition was not determined. The fire extended
to the entire open area and several office enclosures
to fully involve the 12th floor, except for the passenger
elevator lobby, which was protected by automatic closing
fire doors.
The fire extended to floors above, primarily via
the outer walls of the building; windows broke and
flames penetrated behind the spandrel panels around
the ends of the floor slabs. The curtain wall construction
creates separations between the end of the floor slab
and the exterior curtain wall. (For a discussion of
this type of fire spread see NFPA Fire Journal, May/June
1988, pages 75-84.)
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There was heavy exposure of flames to the windows on successive
floors as the fire extended upward from the 12th to 16th floors.
The flames were estimated to be lapping 30 feet up the face
of the building. The curtain walls, including windows, spandrel
panels, and mullions, were almost completely destroyed by
the fire. There were no "eyebrows" to stop the exterior vertical
spread, and fireground commanders were concerned about the
possibility of the fire "lapping" higher to involve additional
floors.
Minor fire extension
also occurred via poke-through penetrations for electricity
and communications, via HVAC shafts, and via heat conduction
through the floor slabs. A minor fire occurred in a storeroom
on the 27th floor, ignited by fire products escaping from
an HVAC shaft that originated on the 12th floor. This fire
self-extinguished due to oxygen deficiency, but could have
greatly complicated the situation if it had continued to
burn. The secondary extensions were minor compared to the
perimeter fire spread at the curtain walls.
The fire extended
at a rate estimated at 45 minutes per floor and burned intensely
for approximately 90 minutes on each level. This resulted
in two floors being heavily involved at any point during
the fire. The upward extension was stopped at the 16th floor
level, after completely destroying four and one-half floors
of the building. |
