Fire Safety

1. Smoke proof Enclosures
Definition: In building safety and construction, a smoke proof enclosure is a type of exit stairwell
that has been designed to keep out smoke in the event of a fire, so that building occupants may
more safely exit the building. Rather than entering the stairwell directly from the building interior,
one enters a smoke proof enclosure by means of an open-air balcony or alternatively, a so-called
open vestibule, and proceeds thence, to the stairwell itself.
 Enclosure fire rating: A smoke proof enclosure shall be enclosed from the highest point to the
lowest point by barriers having 2 hours fire resistance rating.

2. Smoke proof Enclosures
 Vestibules: Where a vestibule is used , it shall be within the 2 hour rated enclosure and shall be
considered as a part of smoke proof enclosure. The doorway into the vestibules shall be
protected with an appropriate fire door having 1.5 hour fire protection rating.
 Discharge: Every smoke proof enclosure shall discharge into a public way, into a yard or court
having direct access to a public way or into an exit passageway. The exit passageways shall be
separated from the remainder of the building by a 2 hour fire resistance rating.

3. Smoke proof Enclosures
 Design: A smoke proof enclosure shall be permitted to be created by using three methods. They
are:
1. Natural Ventilation.
2. Mechanical Ventilation.
3. Stair Pressurization System.

4. Smoke proof Enclosures
 Natural Ventilation:
1. Where access to the stair is by means of an open exterior balcony, the door assembly
to the stair shall have a 1.5 hour fire protection rating & shall be self closing by
actuation of a detector.
2. Every vestibule shall have a net area of not less than 16ft² of opening in an exterior
wall facing an exterior area not less than 20 ft in width.
3. Every vestibule shall have a minimum dimension of not less than the required width of
the corridor leading to it and a dimension of not less than 72 in. in the direction of
travel.

5. Smoke proof Enclosures
 Mechanical Ventilation:
1. Vestibules shall have a dimension of not less than 44 in. in width and not less than 72
in. in direction of travel.
2. The vestibules shall provided with not less than one air change per minute, and the
exhaust shall be 150% of the supply. Supply air shall enter and exhaust air shall
discharge from the vestibule through separate tightly constructed ducts used only for
those purposes.
3. To serve as a heat and smoke trap and to provide ab upward-moving air column, the
vestibule ceiling shall be not less than 20 in. higher than the door opening into the
vestibule.
4. The stair shall be provided with a dampened relief opening at the top and supplied
mechanically with sufficient air to discharge at least 2500 ft³/min through the relief
opening while maintaining a positive pressure of not less than 0.10 in. water column
(25 Pa) in the stair relative to the vestibule with all doors closed.

6. Smoke proof Enclosures
 Mechanical Ventilation:

7. Smoke proof Enclosures
 Stair Pressurization:
1. Smoke proof enclosures using stair pressurization shall use an approved engineered
system with a design pressure difference across the barrier of not less than 0.05 in.
water column (12.5 Pa) in sprinklered buildings and 0.10 in. water column in non
sprinklered buildings and shall be capable of maintaining these pressure diffrences
under likely condition of stack or wind effect.
2. Exterior to the building and directly connected to the stairway by ductwork enclosed in
noncombustible construction.
3. Within the stair a minimum 2 hour fire rating must be provided.
4. Within the building if separated from the remaining of the building, including other
mechanical equipment, a 2 hour fire rating.

8. Smoke proof Enclosures
 Stair Pressurization:

9. Smoke proof Enclosures
 Activation: For both Mechanical ventilation and Stair Pressurization systems, the activation of
the systems shall be initiated by a smoke detector installed in an approved location within 10 ft
of the entrance to the smoke proof enclosure. The required system can also be initiated by the
following, if provided:
1. Water flow signal from a complete automated sprinklered system.
2. General evacuation alarm signal.
 Door closers: The activation of an automatic device on any door in the smoke proof enclosure
shall activate all other automatic –closing devices on doors in the smoke proof enclosures.
 Standby Power: Standby Power for mechanical ventilation equipment shall be provided by an
approved generator set. The generator shall be located in a room having a minimum 1 hour fire
resistance rating from the remainder of the building.