BS 5588-4:1998
9.4 Zoned smoke control systems 9.4.1 General During a fire, smoke and toxic gases can spread through construction gaps and service shafts to areas removed from the initial fire source. Whilst compartmentation should prevent fire spread between storeys it may also be desirable to provide smoke control to restrict the spread of smoke and hence to protect the following: — rooms that cannot be evacuated immediately in the event of a fire either because of other safety implications (e.g. air traffic control towers or process plant control rooms) or for practical reasons (e.g. hospital wards with bed-ridden patients or tall buildings where phased evacuation is being used); — rooms that house expensive or safety-related equipment that could be damaged or rendered inoperative by smoke contamination, e.g. computer suites. Zoned smoke control systems are intended to limit the spread of smoke from storey to storey (or zone to zone) within a building. The general approach is to divide the building up into a number of smoke control zones, the size and number of which vary according to the particular building circumstances. Typically each storey may be considered as a smoke control zone. The boundaries of the zones that limit the movement of smoke are the walls, floors, doors etc., within the building. Pressure differentials are produced by exhausting from the fire zone and supplying fresh air to the surrounding areas. 9.4.2 Features of a zoned smoke control system In many buildings the most convenient means of supplying air to and exhausting from the relevant smoke control zones is by adapting the HVAC system. Most HVAC systems are capable of providing in excess of three air changes per hour. This can be used to assist in restricting to some degree the spread of smoke from one zone to another. Ventilation systems intended for use in zoned smoke control applications should satisfy the following minimum recommendations. a) For systems serving multiple smoke control zones: 1) the common air supply should be capable of being selectively shut off from any zone by a remotely controlled smoke damper or, where the supply ductwork passes through the accommodation, by a combination fire/smoke damper; 2) the common exhaust should be capable of being selectively shut off from any of the covered zones by a remotely controlled smoke damper or a combination fire/smoke damper; 3) the HVAC system should be capable of fully closing off any return air by means of a remotely controlled damper, to prevent recirculation of smoke into the supply air. b) For systems serving only one smoke control zone: 1) the system should be capable of operating in a supply-only as well as an exhaust-only mode; 2) the HVAC system should be capable of fully closing off the return air by means of a remotely controlled damper, to prevent recirculation of smoke into the supply air. c) Duct materials should be selected and the ducts designed to handle smoke, withstand additional pressure (both positive and negative) by the supply and exhaust fans when operating in a smoke control mode, and to maintain their structural integrity during the period for which the system is designed to operate. 9.4.3 Choice of smoke control zones The choice of smoke control zones is likely to be dictated by the air conditioning zones. In some buildings it is likely that the zoning of the building for ventilation purposes will be different from that designated or desirable for smoke control purposes and this may preclude the use of a zoned smoke control system. There are no predefined limits for the size of smoke control zones. However, since the concentration of smoke in the smoke zone will go unchecked it is important that the occupants should be able to evacuate the zone quickly in the event of fire. It is also advisable that zones are kept as small as practicable so that the quantity of air required to pressurize the surrounding spaces is kept to a manageable level. Conversely, the smoke control zones should be large enough to ensure that the hot smoke and gases produced by the fire are sufficiently diluted with surrounding air to be cooled to a temperature that will not cause failure of the components of the smoke control system.
Š BSI 8 December 2004
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