BS 5588-4:1998
When an air intake is distant from the fan, air should be ducted from the intake to the fan. Where air intake is not at roof level a smoke detector should be provided in the intake duct or within the immediate vicinity of the supply ductwork in order to cause the automatic shut down of the pressure differential system if substantial quantities of smoke are present in the supply. An override switch to reopen the closed damper should be provided for fire brigade use in the positions stated in Clause 7. Sheet metal ductwork should be run either within the protected space, or in protected shafts. NOTE 1 Builders’ ducts may be used provided that such ducts are used solely for air distribution and the internal surface is rendered to limit air leakage, a sheet metal lining is used, or it is shown that the leakage is satisfactory. NOTE 2 Ductwork mounted on the external face of an external wall enclosing the protected space is deemed to be within the protected space.
The fitting of fire dampers in branch ducts is considered detrimental to the reliable operation of a pressure differential system, since the closing of a damper would seriously disrupt the pressure differentials. Fire dampers should not be used in pressure differential system supply ductwork. If such ductwork penetrates a fire-resisting compartment, the ductwork should be protected using the methods given in BS 5588-9:1989. Air supply grilles should not be located near any major leakage path from a pressurized zone. 11.2 !Plant location" The pressure differential equipment, i.e. fan, motor and control gear, should be !positioned": a) in an enclosure with a fire resistance of not less than 1 h, preferably in a plant room separate from other plant on or near the ground level and close to the air supply intakes; or b) at the roof level if the fire resistance separation between the plant !Text deleted" and the building below is not less than 1 h within 5 m measured horizontally of any part of the pressure differential system equipment/enclosure. Access doors to the enclosure should have a fire resistance of not less than 1 h and be self-closing. NOTE
Where the pressure differential system protects a firefighting shaft the level of fire resistance should be increased to 2 h.
11.3 Regulations and standards Attention is drawn to the following regulations and standards which are applicable to equipment specification and installation: a) ductwork: BS 8313 and BS 5588-9; b) fans: the Electrical Equipment (Safety) Regulations [4]; c) ventilation system: the Electrical Equipment (Safety) Regulations [4], BS 7346; d) fire alarms and detectors: BS 5839. e) electrical installations and supply: Building Standards (Scotland) Regulations [5], Electricity at Work Regulations 1989, 635/1989 [6]; f) general: BS 5720 and the Building Regulations 1991 Approved Document B [7]. 11.4 Commissioning of systems The procedures for commissioning a pressure differential system are similar to those for other air handling units, with the addition of the actuation and control system. The air handling side of the pressure differential system should be commissioned by reference to appropriate guidance such as the CIBSE Commissioning Code A [8], BSRIA Application Guide AG3/89.1 [9]. The actuation system should be commissioned in accordance with BS 5839-1.
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Š BSI 8 December 2004