Type 3 Smoke Shafts
San Francisco, Calif.
— More correctly termed the interior exposure smoke-proof enclosure,
the Type 3 smoke shaft is often found in older high-rise buildings,
those constructed before the advent of more sophisticated heating,
ventilating, and air conditioning (HVAC) systems with a smoke
control mode.
With this type of smoke management system, the
occupant leaves the building through a door which leads out onto the
shaft. The occupant then accesses another door that leads into a
stairwell and out of the building.
A major contributor to smoke movement in tall
buildings is the vertical flow of air within it. This phenomenon is
called the Stack Effect. Stack Effect is a function of temperature
differential between the outside air and the inside air, the height
of the building, tightness of the exterior skin, and the amount of
air leakage between floors on the interior. The greater the degree
of any of these functions, the greater will be the stack effect.
Engineers incorporated this phenomenon into the design of smoke
management systems.
Tall shafts will
naturally draw products of combustion towards it. The Type 3 smoke
shaft is designed to draw smoke and products of combustion to it and
up and out of the building. The problem is that it cannot
differentiate between smoke and fire and will draw fire towards it.
This creates a potentially dangerous situation particularly when
standpipe risers are placed within the shaft. Firefighters leading a
line from the standpipe in a Type 3 smoke shaft onto the fire floor
will be confronted with a fire being pulled towards them. There is a
good possibility that the ferocity of the flame front will be more
than 2½-inch handlines can adequately handle. There have been
several well documented cases in New York City where lines led in
such a manner resulted in severe burn injuries and a failure to stop
the fire.
The photos below are
from the 55-story, Bank of America building in San Francisco. Photo
1 is a view from the occupied office space looking into the smoke
shaft. The door is normally self-closing but has been propped open
for the photo. Note the safety barrier installed to prevent
occupants from falling into the shaft. At one fire in New York City
where a line was led from the smoke shaft onto the fire floor, the
severity of the fire drawn towards the shaft melted the barrier. In
Photo 2, the view is looking up the shaft. There are two doors in
each vestibule, one leading from the occupied space and one leading
to the stair shaft. In Photo 3, the view is looking down the shaft
giving an excellent perspective of its height and that of the
standpipe. All photos by Ted Corporandy Questions or thoughts
about what you see?
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