AIR CONDITIONING 2 CAR PARKS
with CFD modelling is as close as one is likely to get without setting a vehicle on fire.
Fire conditions The current requirements for compliance with the Building Regulations and BS7346: Part 7 for the activation of smoke ventilation systems serving car parks is very simple, even allowing manual activation by the fire service when they eventually arrive at the site of the incident (see boxes on this and the previous page). The options available for a smoke clearance system are smoke detection; rapid rate of rise heat detection; multi-criteria fire detection; sprinkler flow switch; and fire service override switch. Automatic activation of the ventilation
system will help earlier identification of a fire incident, limit the temperature level, reduce fire spread and potentially aid quicker access to the fire service. The adoption of limiting activation of the smoke ventilation system by the fire service manual activation as they arrive at the premises can lead to excessive smoke logging, higher temperatures and delayed identification of the fire.
Components: Continuous performance is key
It is critical that in any car park, heat and smoke control/ ventilation systems, ductwork, fans, silencers, fixings and all components such as smoke control dampers and automatic opening vents perform continuously – at least for as long a time period as the fans when there is a fire. One area of particular concern is the construction of the attenuators associated with smoke extract fans; another is the application of smoke control dampers (and fire dampers) mounted within ductwork. To address both areas, designers and installers of car park ventilation systems should
46 CIBSE Journal July 2012
buy and read the relevant sections of British Standard 7346: Pt 7: 2006; the following extracts are particularly relevant: n Ductwork and fixings including silencers within the car park should be constructed of materials capable of surviving exposure to gases that have temperatures at or above 8000C and should maintain their stability and integrity under fire conditions. n Where ductwork penetrates through a fire compartment wall or slab, the ductwork should have a fire resistance at least equal to that required for the compartment, or be in an enclosure with a fire resistance at least equal to that required for
the compartment. n A smoke control damper construction should not contain a device that is able to change the position of the damper once the safety position has been reached, i.e. the damper should not change position unless required by direct instruction from a control system. n It is assumed that power is maintained throughout the car park where the system is installed. Consequently smoke control damper assemblies should have no thermal devices to cause uncontrolled operation, and no automatic return mechanisms that might, for instance, operate on loss of power.
Main extract fans The installation of the main smoke extract fans within the car park itself is fairly common practice, mainly due to the fact that the extract fans are temperature rated for either 300C or 400C). However, some people have misinterpreted the term Temperature Rated to be the same as Fire Rated, which can lead to potentially hazardous situations, with temperature rated extract fans being installed within compartments external to the car park. A fire rated component means that the
item is specifically constructed in such a way that it will resist the breakout of fire from within, or the penetration of fire from without – for example, fire rated ductwork – whereas temperature rated product is only constructed in a way that will enable its component parts to withstand a specific temperature for a limited period, for example, a smoke extract fan rated for 300C for 60 minutes. If smoke extract fans are located within a compartment separate to the one they are serving (in this case the car park), those fans should be enclosed in a properly fire resistant enclosure providing the equivalent fire rating as the compartment within which they are located. CJ
Richard Brooks is general manager at Advanced Smoke Group. Keith Elves is a fire engineering systems consultant
www.cibsejournal.com
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