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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.

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.

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.

Section

Figure 7.2.2a. : Pressure differential between pressurised exit staircase and occupied space

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.

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