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Smoke control of exits is an essential aspect of fire safety design in buildings. It is critical to ensure that smoke does not hinder occupants from safely evacuating a building during a fire emergency.
1) Smoke control of exits
- In building design, compartmentation plays a vital part in limiting the spread of fire and smoke.
- The design should ensure avoidance of spread of smoke to adjacent spaces through the various leakage openings in the compartment enclosure, such as cracks, openings around pipes ducts, airflow grills and doors.
- In the absence of proper sealing of all these openings, smoke and toxic gases will obstruct the free movement of occupants of the building through the exits.
- Pressurization of staircases is of great importance for the exclusion of smoke and toxic gases from the protected exit.
- Pressurization is a method adopted for protecting the exits from ingress of smoke, especially in high-rise buildings.
- In pressurization, air is injected into the staircases, lobbies, etc., as applicable, to raise their pressure slightly above the pressure in adjacent parts of the building.
- As a result, ingress of smoke or toxic gases into the exits will be prevented.
- The pressurization of staircases and lift lobbies shall be adopted as given in Table below.
- The natural ventilation requirement of the staircase shall be, achieved through opening at each landing, of an area 0.5 m2 in the external wall. A cross ventilated staircase shall have 2 such openings in opposite/adjacent walls or the same shall be cross ventilated through the corridor.
- Enclosed staircase leading to more than one basement shall be pressurized.
- Lift lobby with fire doors (120 min) at all levels with pressurization of 25-30 Pa is required.
- However, if lift lobby cannot be provided at any of the levels in air conditioned buildings or in internal spaces where funnel/flue effect may be created, lift hoistway shall be pressurized at 50 Pa. For building greater than 30 m, multiple point injection air inlets to maintain desired pressurization level shall be provided.
- If the lift lobby, lift and staircase are part of firefighting shaft, lift lobby necessarily has to be pressurized in such case, unless naturally ventilated.
- The pressure difference for staircases shall be 50 Pa.
- Pressure differences for lobbies (or corridors) shall be between 25 Pa and 30 Pa.
- Further, the pressure differential for enclosed staircase adjacent to such lobby (or corridors) shall be 50 Pa.
- For enclosed staircases adjacent to non-pressurized lobby (or corridors), the pressure differential shall be 50 Pa.
- Equipment and ductwork for staircase pressurization shall be in accordance with one of the following.
- Directly connected to the stairway by ductwork enclosed in non-combustible construction.
- If ducts used to pressurize the system are passed through shafts and grills are provided at each level, it shall be ensured that hot gases and smoke from the building cannot ingress into the staircases under any circumstances.
- The normal air conditioning system and the pressurization system shall be designed and interfaced to meet the requirements of emergency services. When the emergency pressurization is brought into action, the following changes in the normal air conditioning system shall be effected.
- Any re-circulation of air shall be stopped and all exhaust air vented to atmosphere.
- Any air supply to the spaces/areas other than exits shall be stopped.
- The exhaust system may be continued provided,
- the positions of the extraction grills permit a general air flow away from the means of egress;
- the construction of the ductwork and fans is such that, it will not be rendered inoperable by hot gases and smoke; and
- there is no danger of spread of smoke to other floors by the path of the extraction system which can be ensured by keeping the extraction fans running.
- For pressurized stair enclosure systems, the activation of the systems shall be initiated by signalling from fire alarm panel.
- Pressurization system shall be integrated and supervised with the automatic/manual fire alarm system for actuation.
- Wherever pressurized staircase is to be connected to unpressurized area, the two areas shall be segregated by 120 min fire resistant wall.
- Fresh air intake for pressurization shall be away (at least 4 m) from any of the exhaust outlets/grille.
By following these guidelines, building owners and designers can ensure that the occupants of a building are protected during a fire emergency by preventing smoke from hindering their ability to evacuate the building safely.