a. Internal exit staircase
E
Explanations & Illustrations
Clause 7.2.1a. : Provision
Section
Figure 7.2.1a. - 1
The above clause specifies that all internal staircases without provision for natural ventilation of building having more than 24m in habitable height, shall be provided with pressurisation notwithstanding that smoke-stop lobby is provided. Smoke-stop lobby, if mechanically ventilated, is to be provided with supply air of at least 10 air changes per hour during fire mode. There shall be no exhaust duct extracting air out from the smoke stop lobby.
The need of a dedicated pressurisation system (two fans are recommended, capacity of each fan shall be provided for 50% equipment) for each exit staircase is to prevent failure of one system affecting all exits. Air supply to the exit staircase must be obtained from outside the building to minimise the risk of contamination from smoke resulting from a fire in the building.
Ductwork associated with the discharge of air throughout the staircase may be located within the staircase itself, otherwise it must be protected in a masonry or fire rated shaft.
To achieve the required air flow velocity on any storey, air supplied by the system should be evenly distributed throughout the height of the staircase by ductwork with outlets located not more than two storeys apart. Relief air grilles (pressure relief dampers) could be used for pressure control thereby minimising periods of excessive force to open doors of the staircases. Variable speed fans with pressure relief damper can be accepted as alternative arrangement.
Section
Figure 7.2.1a. - 2
Internal exit staircase without adequate ventilation at lower part can be mechanically ventilated provided the lower part shall not exceed 24m in habitable height. Where the lower part exceed 24m, the internal exit staircase shall be pressurised.
Figure 7.2.1a. - 3
Exit staircase (A) is pressurised as it is located within the floor space where natural ventilation cannot be provided. Exit staircase, which is designed without provision for natural ventilation, is pressurised. Smoke-stop lobby is also required to be provided to staircase A.
Figure 7.2.1a. - 4
Exit staircase (B) is pressurised as it is located within the floor space where natural ventilation can not be provided. Exit staircase (C), which is designed without provision for natural ventilation, is pressurised.
Notwithstanding clause 2.2.13(c), smoke-stop lobby is required to be provided to all internal staircases, without provision for natural ventilation, serving building exceeding the habitable height of 24m.
Section
Figure 7.2.1a. - 5
Staircase A and transfer staircase A1 are considered as one single staircase sharing a common protected shaft. As staircase A is an internal staircase without openings for natural ventilation, exceeding a habitable height of 24m, it is required to be provided with MV and pressurisation. Since, staircase A1 is acting as a transfer staircase, it shall likewise be MV and pressurised notwithstanding the fact it can be naturally ventilated through external openings. The transfer exit passageway which connects staircases A and A1 should also be MV and pressurised. It is not acceptable to have partial pressurisation to staircase A by introducing a door across the transfer passageway, such that staircase A1 is separated for the provision of natural ventilation. The reason is that by providing a door across the transfer passageway, it would impede the movement of occupants moving towards staircase A1. In this way, the evacuation process within the whole shaft of staircase A would be slowed down.
In any building of which the habitable height exceeds 24m, any internal exit staircases without adequate provision for natural ventilation shall be pressurised to comply with the requirements in this Code. Where the upper part of the staircase is naturally
ventilated, its lower part can be provided with mechanical ventilation or pressurisation, whichever is appropriate, in accordance with Cl.2.3.3d.(9).
b. Basement
E
Explanations & Illustrations
Clause 7.2.1b. : Provision
Section
Figure 7.2.1b. - 1
In a building comprising more than 4 basement storeys, the exit staircase adjacent to the fire lift lobby shall be pressurised.
Section
Figure 7.2.1b. - 2
Owing to difference in ground levels, staircase B which is serving more than 4 basements shall be located adjacent to a fire lift lobby at each storey.
In a building comprising more than four basement storeys, exit staircases connected to a fire lift lobby in basement storeys shall be pressurised to comply with the requirements in this Code.
c. PG II occupancy
Effective Date: 01 Mar 2019
E
Explanations & Illustrations
Clause 7.2.1c. : Provision
Figure 7.2.1c.
Note:
a. Pure residential buildings are not required to be provided with manual fire alarm or automatic fire alarm system.
b. Where the stairs are not naturally ventilated and provided with mechanical ventilation or pressurisation system, there shall be a means to activate the mentioned system.
c. The manual call point provided at every entrance of exit staircase shall initiate the operation of mechanical ventilation or pressurisation system.
Amendment History
| 7.2.1c |
|
01 Mar 2019 |
Revised, formerly Cl.7.2.1(c) |
|
--- |
-
|
Where PG II building is provided with a mechanical ventilation system or pressurisation system for its staircase storey shelter, an automatic smoke detection system complying with SS 645 shall be installed. The smoke detector shall be located at the entrance of each exit staircase at every storey, including the non-residential floors. Activation of any smoke detector shall initiate the operation of the mechanical ventilation system or pressurisation system.
7.2.2 Pressurisation level
a. When in operation, the pressurisation system shall maintain a pressure differential of not less than 50 Pa between the pressurised exit staircase and the occupied area when all doors are closed.
E
Explanations & Illustrations
Clause 7.2.2a. : Pressurisation level
Section
Figure 7.2.2a. : Pressure differential between pressurised exit staircase and occupied space
b. Where a smoke-free lobby is also pressurised, the pressure at the exit staircase shall always be higher.
E
Explanations & Illustrations
Clause 7.2.2b. : Pressurisation level
Section
Figure 7.2.2b. : Pressure gradient
Where the smoke-stop lobby is pressurised, the pressure gradient shall be such that the pressure at the exit staircase is always higher.
c. The force required to open any door against the combined resistance of the pressurising air and the automatic door closing mechanism shall not exceed 110N at the door handle.
E
Explanations & Illustrations
Clause 7.2.2c. : Pressurisation level
Figure 7.2.2c.: Maximum force required to open door
Measurement of the force required to open a stair door can be simply carried out by using a force-measuring in the push or pull mode e.g. a spring balance. The maximum force permitted to open a door in accordance with this Code is 110N. This equates to a force of 11.2kg.
Lever operated latch sets are probably the easiest to measure. Simply hook the spring balance over the lever handle and depress same to unlatch the door, whilst taking care not to exert any push/pull force in doing so. To take a reading, slowly and steadily pull the spring balance and read the scale as the door just starts to open.
7.2.3 Egress velocity
E
Explanations & Illustrations
Clause 7.2.3 : Egress velocity
Figure 7.2.3 - 1
Air flow velocity of at least 1.0 m/s through open doors is required to prevent smoke from entering into the pressurised staircase.
Figure 7.2.3 - 2
The air flow velocity measurement through an open door of a pressurised staircase is taken from the entrance of any of two successive doors held open together with its exiting door at the 1st storey. The resulting value of its airflow velocity through the open door shall not be less than 1m/s.
Tests conducted by the Commonwealth Scientific and Industrial Research Organization (CSIRO) have demonstrated that air flows in excess of 0.8m/s through a door will minimise the spread of smoke against the direction of flow. A minimum air flow rate of 1m/s has therefore been adopted. This air flow must be maintained across the doorway providing egress from the fire-affected storey into the staircase during a fire. Initially, building occupants from both the fire floor and the floor above the fire floor will evacuate the building and, depending on the fire situation, this may be simultaneous operation.
The requirement for two floor doors and the 1st storey door (opening into the exterior) to be open the same time has two applications:
(i) When the fire fighters arrive and use the staircase for fire fighting operations, hose connection to the landing valves located on a floor would be carried out. Initially hose will be run from the floor below up the staircase and onto the fire floor hence a minimum opening of two doors is involved.
(ii) All required exit staircases must be usable at the same time as either fire fighters or evacuating occupants will be using any of them to exit at the 1st storey door to the street or external safe open area. Thus the final exit door would remain in the open position at all times.
a. When in operation, the pressurisation system shall maintain an airflow of sufficient velocity through open doors to prevent smoke from entering into the pressurised area.
b. The flow velocity shall be attained when a combination of two doors from any two successive storeys and the main discharge door are fully open.
c. The velocity averaged over the full area of each door opening shall not be less than 1.0 m/s.
7.2.4 Leakages
E
Explanations & Illustrations
Clause 7.2.4 : Leakages
Figure 7.2.4
Pressurised air could leak through areas such as gaps around doors, windows, other ventilation openings and other places where air will escape.
In the above figure, pressurised air from the exit staircase leaks into the smoke-stop lobby (A1) and occupancy areas (A2 & A3).
To avoid a pressure built-up in the occupancy area, adequate measures shall be taken to allow air leakage, e.g. through windows A4 to A7. A pressure build-up would create difficulty in opening the doors to the occupancy area.
The following are possible ways in which the escape of pressurising air can be achieved:
(a) by window leakage, or
(b) by specially provided vents at the building periphery, or
(c) by the provision of vertical shaft, or
(d) by mechanically operated extraction.
a. The rate of supply of pressurised air to the pressurised areas shall be sufficient to make up for loss through leakages into the unpressurised surroundings.
b. Adequate relief of leaked air out of the occupied area shall be provided to avoid a pressure build-up in this area. The relief can be in the form of perimeter leakages or purpose built extraction systems.
7.2.5 Distribution of pressurising air
E
Explanations & Illustrations
Clause 7.2.5 : Distribution of pressurising air
Section
Figure 7.2.5
The above installation is not acceptable as over pressurisation would occur at the upper portion of the staircase. Supply air to the staircase should be well distributed by a vertical supply duct, preferably serving all the levels of the staircase.
An example of an arrangement showing good distribution of supply air can be seen in Figure 7.2.6.
a. The number and distribution of injection points for supply of pressurising air to the exit staircase should ensure an even pressure profile complying with Cl.7.2.2.
b. The arrangement of the injection points and the control of the pressurisation system shall be such that when the opening of doors or other factors cause significant variations in pressure difference, the condition in Cl.7.2.2 shall be restored as soon as practicable.
7.2.6 Pressurisation equipment and controls
E
Explanations & Illustrations
Clause 7.2.6 : Pressurisation equipment & controls
Section
Figure 7.2.6
The “start-stop” switch is required to be provided in the FCC, or at the main fire alarm panel where there is no FCC. The rationale is to provide the firefighters greater ease and better control in operating the supply air fan to the staircase.
This arrangement facilitate the supply air fan to be shut from the designated remote “start-stop" location. The supply air fan can then be restarted anytime when required.
a. All the equipment and the relevant controls associated with the pressurisation system shall be designed and installed to ensure satisfactory operation in the event of a fire.
b. Supply air for the pressurisation system shall be drawn directly from the external space and its intake shall not be less than 5m from any exhaust discharge openings.
c. The pressurisation system shall be automatically activated by the building fire alarm system. In addition, a remote manual start-stop switch shall be made available to firefighters at the FCC, or at the fire alarm panel where there is no FCC. Visual indication of the operation status of the pressurisation system shall be provided.
