This recommendation applies to atrium pressurization. 7) Where smoke exhaust is used to reduce the pressure in an atrium containing thermally-buoyant smoky gases, the design objective should be to raise the neutral pressure plane above the highest vulnerable leakage path, allowing for external wind pressures explicitly in the design calculation. This recommendation applies to atrium pressurization. 24.7 Smoke clearance As the provision of smoke clearance systems is primarily for the benefit of the fire service, appropriate recommendations are given in Clause 29. 24.8 Make-up air supply For smoke control, ventilation and smoke clearance systems, make-up air is essential.The following conditions should apply. a) It is essential that there should be sufficient provision of make-up air, with a velocity into the atria base not exceeding 2 msp1 for the proper functioning of any smoke ventilation, temperature control or smoke clearance system specified for the atrium. b) If not permanently open, all inlets should open simultaneously on activation of the smoke ventilation system that they serve. c) Powered inlets should only be used with powered exhaust fans where the objective is to design a smoke clearance system in accordance with 29.2. d) The maximum velocity of air passing through an escape route should be 5 msp1 and the smoke control system should be designed to avoid excessive pressures opposing the opening of escape doors located in the air flow [see 24.62)]. e) The inlets for replacement air should be located at a low level in the atrium, or alternatively at high or low level in other smoke control zones unaffected by the fire and communicating with the affected smoke control zone only at low level. 24.9 Smoke control equipment 24.9.1 Activation of smoke control systems a) With the exception of smoke clearance systems, any smoke control systems recommended in this code should be activated by an automatic smoke detection system designed and installed in accordance with BS 5839-1. b) All systems should be capable of manual override by fire service personnel, subject to the provisions of 29.2. c) Smoke clearance systems as detailed in 29.2 need only be provided with a manual switch limited to the use of security and fire service personnel. NOTE
For ventilation controls for the fire service, see 29.2.
24.9.2 HVAC ductwork HVAC ductwork used in conjunction with smoke and heat control systems inlet air and exhaust air should: a) be adequately protected against fire penetration and should be installed in accordance with the relevant recommendations of BS 5588-9; b) not be fitted with fusible link type fire dampers; c) be adequately constructed and braced to maintain the integrity of the ductwork at the high temperatures and pressures that may exist, and should be designed to accommodate thermal expansion without distortion or damage; and d) be designed to ensure that all materials associated with the system will continue to operate when any part is exposed to fire. Unless the design of the smoke/heat control system specifically does not allow the possibility, fire/smoke dampers that are operated by smoke detectors associated with the HVAC system(s) should all fail-safe to the correct position for the system(s) to work satisfactorily in the smoke exhaust ventilation mode.
ÂŠ BSI 8 December 2004