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SECTION 909 SMOKE CONTROL SYSTEMS
909.20
Smoke proof enclosures. Where required by Section
1020.1.7, a smokeproof enclosure shall be constructed
in accordance with this section. A smokeproof enclosure
shall consist of an enclosed interior exit stairway that
conforms to Section 1020.1 and
an open exterior balcony or ventilated vestibule meeting
the requirements of this section. Where access to the roof
is required by the International Fire Code, such access
shall be from the smoke proof enclosure where a smoke proof
enclosure is required.
909.20.1
Access. Access to the stair shall be by way of a vestibule
or an open exterior balcony. The minimum dimension of
the vestibule shall not be less than the required width
of the corridor leading to the vestibule but shall not
have a width of less than 44 inches (1118 mm) and shall
not have a length of less than 72 inches (1829 mm) in
the direction of egress travel.
909.20.2
Construction. The smokeproof enclosure shall be separated
from the remainder of the building by not less than a
2- hour fire barrier without openings other than the required
means of egress doors. The vestibule shall be separated
from the stairway by not less than a 2- hour fire barrier.
The open exterior balcony shall be constructed in accordance
with the fire-resistance-rating requirements for floor
construction.
909.20.2.1
Door closers. Doors in a smokeproof enclosure shall
be self- or automatic closing by actuation of a smoke
detector installed at the floor-side entrance to the
smoke proof enclosure. The actuation of the smoke detector
on any door shall activate the closing devices on all
doors in the smokeproof enclosure at all levels. Smoke
detectors shall be installed in accordance with Section
907.10.
909.20.3
Natural ventilation alternative. The provisions of
Sections 909.20.3.1 through 909.20.3.3 shall apply to
ventilation of smoke proof enclosures by natural means.
909.20.3.1
Balcony doors. Where access to the stairway is by
way of an open exterior balcony, the door assembly into
the enclosure shall be a fire door assembly in accordance
with Section 715.4.
909.20.3.2
Vestibule doors. Where access to the stairway is
by way of a vestibule, the door assembly into the vestibule
shall be a fire door complying with Section
715.4. The door assembly from the vestibule to the
stairway shall have not less than a 20 minute fire
protection rating complying with Section
715.4.
909.20.3.3
Vestibule ventilation. Each vestibule shall have
a minimum net area of 16 square feet (1.5 m2)
of opening in a wall facing an outer court, yard or
public way that is at least 20 feet (6096 mm) in width.
909.20.4
Mechanical ventilation alternative. The provisions
of Sections 909.20.4.1 through 909.20.4.4 shall apply
to ventilation of smoke proof enclosures by mechanical
means.
909.20.4.1
Vestibule doors. The door assembly from the building
into the vestibule shall be a fire door assembly complying
with Section 715.4.3. The
door assembly from the vestibule to the stairway shall
not have less than a 20-minute fire protection rating
and meet the requirements for a smoke door assembly
in accordance with Section 715.4.3.
The door shall be installed in accordance with NFPA
105.
909.20.4.2
Vestibule ventilation. The vestibule shall be supplied
with not less than one air change per minute and the
exhaust shall not be less than 150 percent of supply.
Supply air shall enter and exhaust air shall discharge
from the vestibule through separate, tightly constructed
ducts used only for that purpose. Supply air shall enter
the vestibule within 6 inches (152 mm) of the floor
level. The top of the exhaust register shall be located
at the top of the smoke trap but not more than 6 inches
(152 mm) down from the top of the trap, and shall be
entirely within the smoke trap area. Doors in the open
position shall not obstruct duct openings. Duct openings
with controlling dampers are permitted where necessary
to meet the design requirements, but dampers are not
otherwise required.
909.20.4.2.1
Engineered ventilation system. Where a specially
engineered system is used, the system shall exhaust
a quantity of air equal to not less than 90 air changes
per hour from any vestibule in the emergency operation
mode and shall be sized to handle three vestibules
simultaneously. Smoke detectors shall be located at
the floor side entrance to each vestibule and shall
activate the system for the affected vestibule. Smoke
detectors shall be installed in accordance with Section
907.10.
909.20.4.3
Smoke trap. The vestibule ceiling shall be at least
20 inches (508 mm) higher than the door opening into
the vestibule to serve as a smoke and heat trap and
to provide an upward-moving air column. The height shall
not be decreased unless approved and justified by design
and test.
909.20.4.4
Stair shaft air movement system. The stair shaft
shall be provided with a dampered relief opening and
supplied with sufficient air to maintain a minimum positive
pressure of 0.10 inch of water (25 Pa) in the shaft
relative to the vestibule with all doors closed.
909.20.5 Stair pressurization
alternative. Where the building is equipped throughout
with an automatic sprinkler system in accordance with
Section 903.3.1.1, the vestibule
is not required, provided that interior exit stairways
are pressurized to a minimum of 0.15 inch of water (37
Pa) and a maximum of 0.35 inch of water (87 Pa) in the
shaft relative to the building measured with all stairway
doors closed under maximum anticipated stack pressures.
909.20.6 Ventilating equipment.
The activation of ventilating equipment required by the
alternatives in Sections 909.20.4 and 909.20.5 shall be
by smoke detectors installed at each floor level at an
approved location at the entrance to the smokeproof enclosure.
When the closing device for the stair shaft and vestibule
doors is activated by smoke detection or power failure,
the mechanical equipment shall activate and operate at
the required performance levels. Smoke detectors shall
be installed in accordance with Section
907.10.
909.20.6.1
Ventilation systems. Smokeproof enclosure ventilation
systems shall be independent of other building ventilation
systems. The equipment and ductwork shall comply with
one of the following:
1.
Equipment and ductwork shall be located exterior to
the building and directly connected to the smokeproof
enclosure or connected to the smokeproof enclosure
by ductwork enclosed by 2-hour fire barriers.
2.
Equipment and ductwork shall be located within the
smokeproof enclosure with intake or exhaust directly
from and to the outside or through ductwork enclosed
by 2-hour fire barriers.
3.
Equipment and ductwork shall be located within the
building if separated from the remainder of the building,
including other mechanical equipment, by 2-hour fire
barriers.
909.20.6.2
Standby power. Mechanical vestibule and stair shaft
ventilation systems and automatic fire detection systems
shall be powered by an approved standby power system
conforming to Section 403.10.1
and Chapter 27.
909.20.6.3
Acceptance and testing. Before the mechanical equipment
is approved, the system shall be tested in the presence
of the building official to confirm that the system
is operating in compliance with these requirements.
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