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Chapter 1: Fire geometry and smoke movement in buildings
Vestibules:
Stairwells can also be built with a vestibule
that may include an air handling system. The vestibule
may serve a pressurized stair or it can be in lieu of a
pressurized stair, operating under the same criteria as a
pressurized stairwell for smoke control. Even
nonpressurized vestibules have the advantage of putting
two doors between the building interior and a stairwell,
which can help to limit smoke migration into a stair.
Vestibule pressurization controls are addressed in much
the same manner as stair pressurization systems by the
smoke control system.
Elevator smoke control
Elevator smoke control systems are of two types. The
first focuses on providing tenability and survivability of
the elevator system in order that it can be used for
occupant evacuation. Figure 16 diagrams two design
alternatives. Exhaust of the fire floor, smoke-tight
elevator lobbies, and the closing of elevator doors after
automatic recall are other design alternatives which are
less often chosen. Elevators traditionally have not been
used for fire evacuation due to the "chimney effect" of
the shafts in a fire.
In the last decade, due in part to increased demands for
egress of mobility-impaired occupants and driven by the
Americans with Disabilities Act (ADA), elevators have
increasingly been looked upon as a possible avenue for
fire escape. First, Canada developed standards for
"hardened" elevators for egress and then in the US the
NFPA Life Safety Code included elevators as an
alternate egress component from areas of refuge.
Smoke control for elevators used as an egress system
components must provide tenability for the expected
time needed for evacuation.
The second type of elevator smoke control system is
intended to prevent or limit smoke flow to other floors by
way of the hoistway. Elevators without enclosed lobbies
must have a smoke control system that develops a
pressure difference within the hoistway that is greater
than the sum of the fire and other building effects. The
smoke control system designer will calculate pressures,
flow rates, and vent sizes for the elevator shaft to
determine fan size.
Elevator recall is based upon ASME/ANSI A17.1, Safety
Code for Elevators and Escalators. The standard
requires that elevator doors open and remain open after
elevators are recalled. This requirement results in a
16
large opening into the elevator hoistway, greatly
increasing airflow requirements for pressurization.
NFPA 80, Standard for Fire Doors and Other Opening
Protectives, permits closing of elevator doors after a
predetermined time when required by the AHJ. Local
requirements for the operation of pressurized shafts
should therefore be determined and incorporated into
the system design.
Table 8.11 of NFPA's Smoke Movement and Control in
High-rise Buildings contains both elevator shaft and
lobby pressurization system calculation formulas. John
M. Klote, who worked with the author of this NFPA
reference book, includes the same methodologies and
several examples, in his ASHRAE book, Design of
Smoke Management Systems.
Elevator recall systems return the elevators to the lobby
or an adjacent floor when smoke is detected in an
elevator lobby or when the fire alarm system is activated.
Elevator doors can open at the recall location and
remain open or revert to the closed position. The smoke
control system designer must adjust airflow for the door
position.
VM-1 Smoke Management Application Guide
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