BSEE SMOKE CONTROL
Preventing the spread of smoke through buildings is of critical importance but clear guidance on best practice can be hard to come by. Conor Logan, Chairman of the Smoke Control Association (SCA), looks at a few of the different systems on the market and offers advice on relevant legislation, standards and best practice.
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SMOKE CONTROL SYSTEMS What you should consider
n the event of a fire, a properly designed and implemented smoke control system can be a life-saver, keeping vital access and escape routes almost completely free of smoke.
I Dealing with smoke ‘
When designing and planning a smoke control system, particularly in commercial properties and apartment blocks, a key
consideration has to be the protection of the staircases and common circulation areas within the building. By keeping primary escape routes clear of smoke the chances of survival can be significantly improved.
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uThe designer will need to carefully consider all interactions between the smoke control system and other building systems.
32 BUILDING SERVICES & ENVIRONMENTAL ENGINEER APRIL 2017
Most fire fatalities are not caused by the fire itself but by smoke inhalation. Smoke can build up extremely quickly and often incapacitates so rapidly that victims are not able to locate or access a suitable exit. A building fire is capable of filling a 10,000m2 area full of smoke within minutes and just a few breaths of toxic fumes can have fatal consequences for the unfortunate occupant. As well as saving lives, a smoke control system can protect property and help to minimise damage to the building. When designing and planning a smoke control system, particularly in commercial properties and apartment blocks, a key consideration has to be the protection of the staircases and common circulation areas within the building. By keeping primary escape routes clear of smoke the chances of survival can be significantly improved in the event of a major fire. Not only does this provide occupants with a clear and unobstructed escape route, it often allows the fire services to gain access to the blaze.
There are a number of different methods used to reduce the spread of smoke through a building but three of the most common solutions are as follows:
Natural smoke control systems
Natural ventilation is a simple, reliable, low noise and low energy method of smoke control and works by harnessing the power of the wind and thermal buoyancy to drive flow through the ventilator. The most significant drawback to this method is its sensitivity to very high winds. In
order to operate effectively, a source of inlet air and an exhaust opening needs to be provided. For a wall mounted vent, the vent generally provides both an inlet at the base of the vent and an exhaust at the top.
When designing a smoke control system, serious consideration should go into the ‘free’ open area of windows and smoke shaft doors when they are actuated to allow smoke to escape. The greater the opening, the greater the area available to allow smoke to leave the building. Measurement of the free area of a vent is clearly defined in Appendix C of Approved Document B – the building regulation that covers fire safety matters within and around buildings.
Mechanical smoke ventilation systems
With specified extraction rates, low wind sensitivity, a known capability to overcome system resistances and reduced shaft cross sections, mechanical smoke ventilations systems can be used as an effective alternative to natural ventilation systems. These systems generally utilise a mechanical extract shaft that serves a common corridor or lobby. In order to guarantee
performance, a mechanical system requires a maintained power supply, fire resistant wiring, temperature classified equipment and a standby fan. A suitable air inlet will also be needed in order to prevent damage to the system and to ensure that excessive pressurisation or depressurisation of the ventilated area does not occur. This will make sure that excess smoke is not drawn from the origin of the fire and that escape doors are not rendered inoperable.
Pressure differential system
The pressure differential system works by establishing a pressure gradient with the protected escape stairs at the highest pressure and the pressure
gradually decreasing through lobbies and corridors.
Air naturally tries to move from an area of high pressure to an area of low pressure. If the pressure in protected areas is increased above that in areas where a fire is more likely to occur, it is possible to prevent the spread of smoke to escape routes.
By introducing the required pressure differential, the building owner/operator can be almost certain that smoke from a fire will not enter the stairwell under normal conditions.
Installation
To ensure that the chosen smoke control system operates in the manner intended, it is vital that the design, installation, commissioning and maintenance phases are all carried out by competent and experienced professionals, trained to recognise the individual requirements of each building. From the very outset, the designer will need to carefully consider all interactions between the smoke control system and other building systems. Modern buildings are often equipped with building management systems and these can vary significantly when it comes to function and complexity. In the event of a fire, the building management system should not compromise the effectiveness of the smoke control system and other fire protection systems should work in harmony with the selected smoke control system.
Effective fire strategy
It is important to remember that smoke control systems represent one single element of an effective fire strategy and the proposed system should complement the overall approach to dealing with emergency situations. Guidance on equipment selection and installation can be found in Approved Document B as well as in the standards BS8519, BS9999, BS9991 and BS7346.
uA properly designed and implemented smoke control system can be a life‐saver.
Testing
Once the installation in complete it is imperative that the smoke control system is fully tested by the installer and then offered for witness testing to the authority having jurisdiction (AHJ) to prove compliance with project specification.
When handed over to the end user, the smoke control system documentation should ideally include: uDesign information detailing the performance criteria for the system and a description of the system
uA control philosophy or cause and effect diagram
uAs installed drawings uRelevant CE marking or test certificates
uInstallation and commissioning certificates
uWitness testing certificates uOperation, maintenance and testing instructions
uInstructions for fire service use Best practice
Smoke control can be achieved through a number of different methods and there are a great many factors to consider, including performance criteria, system type and legislation.
By seeking and following advice and guidance from all relevant parties throughout the planning, design, installation and testing phases, the end user will be left with a truly effective smoke control system with the capacity to save lives.
For more information visit the Smoke Control Association pages on the FETA website:
www.feta.co.uk VISIT OUR WEBSITE:
www.bsee.co.uk
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