Smoke Control for Car Parks Made Simple - FREE Carparkulator Available

With fire safety a key consideration in the design of a car park, sophisticated smoke control systems are increasingly being used as a method of protection. Here Lee Hewings of Smoke Control Services outlines the various systems available.

In 2002 116 fires occurred in car park buildings in the UK. Of those, 60 fires started in vehicles and of those cases, one spread to nine other vehicles and one spread to one other. Approximately 50 per cent of fires were started deliberately and at least two fires happened in car park buildings of 14 floors. (To be updated with more recent statistics if possible)

The need to protect car parks from fire and the resulting risk not only to car park structures but to the lives of those using them is evident.

Between 2000 and 2002 Jet fan type ventilation systems were introduced into the UK and have since become the preferred method of ventilating car parks.

For many years now Jet fan type smoke clearance systems have been incorporated into the fire safety design of buildings to protect structures ranging from multi-storey apartment and public buildings to large retail and commercial developments.

Jet fan type smoke clearance systems are incorporated in basement and enclosed car parks to remove carbon monoxide produced by vehicles when a car park is in general use, and also to ensure there are no pockets of stagnant air. They are also intended to aid the fire service in clearing smoke from the car park in the event of the fire.

Basement and Enclosed Car Park Systems

Approved Documents B and F set out the primary requirements for ventilation of enclosed car parks. Approved Document B applies to fire safety and Approved Document F relates to day-to-day ventilation.

Design guidance is given in BS 7346-7:2006. This defines three types of mechanical smoke ventilation systems which can be used, (1) Impulse ventilation to achieve smoke clearance. (2) Impulse ventilation to assist fire-fighting access. (3) Impulse ventilation to protect means of escape, all of which meet the requirements of Approved Documents B and F.

The Approved Document B describes three methods of ventilation for car parks.

Open-sided car parks

Natural ventilation is achieved if the car park is above ground level providing ventilation openings that are at least equal to five per cent of the floor area and these openings are located as described in Approved Document F. This is considered sufficient to provide ventilation for clearance of both smoke and vehicle exhausts fumes.

Naturally ventilated car parks

These have permanent openings on each level, equal to 2.5 per cent of the plan area, these should be arranged to provide cross flow ventilation and located as described in Approved Document B. This is sufficient ventilation for smoke clearance, but in addition a mechanical extract system providing three air changes per hour is needed to remove fumes.

Mechanically ventilated car parks

Where natural ventilation is not possible a mechanical system should be used. For mechanically ventilated car parks the basic requirements are that there should be a mechanical ventilation system that will limit the concentration of carbon monoxide to not more than 30 parts per million averaged over an 8 hour period for general ventilation on all levels and at least 10ac/hr on the fire floor in the event of a fire. The system should be capable of operating at temperatures of up to 300˚C for 60 minutes, ductwork and fixings should be made from materials that have a melting point of above 800˚C. The system should have at least two extract fans, each providing 50 per cent of the extract duty, with a secondary power supply to operate in the event of a mains power failure.

Jet Fan Systems

In recent years jet fan technology has established itself as the new standard of car park ventilation.

Naturally ventilated car parks

The use of Jet fans only may be possible if the car park has 2.5 per cent of the floor area provided as natural ventilation openings and there are sufficiently sized horizontal openings through which contaminated air may be discharged.

If there are insufficiently sized horizontal openings an additional extract facility to limit the concentration of carbon monoxide to below 30 parts per million averaged over an eight hour period are required.

Mechanically ventilated car parks

Slim and powerful ceiling-mounted jet fans located around the car park entrain fresh air from inlet positions and the bulk movement of fresh air direct fumes and smoke to collection points, where they are extracted by high temperature fans.

When controlled via carbon monoxide detection the system will be set to standby when the pollutant load is low and will only begin operation at low speed when a predetermined level of contamination is exceeded, if the contamination continues to rise the system will operate at a higher duty until levels fall below the first predetermined level of contamination.

This technology is an alternative to ducted mechanical systems and can overcome many of the problems associated with such systems.

Ductwork runs underneath the ceiling, reducing the already restricted height normally available. For traditional mechanical systems low level extract points are required, often needing protective barriers to surround them and these take up valuable floor space.

Jet fan ventilation technology eliminates the need for costly and bulky sheet metal ductwork. This provides more headroom and space for parking bays, a less cluttered environment and improved CCTV coverage. Jet fan systems are also easier and quicker to install than traditional systems and have been scientifically proven to be more effective than conventional ducted systems in full scale fire tests.

It is important to distinguish between smoke control and smoke clearance systems. Smoke clearance systems meet with all the requirements set out in Approved Documents B and F and will assist fire fighters by providing smoke clearance.

The alternative approach is to use a smoke control system to control smoke movement in order to assist fire fighting access and means of escape. This method is generally a more complicated option requiring complex controls and CFD modeling.

Protecting your car park

There are a number of specialist companies that supply smoke control systems for car parks. Look for systems with LANTAC-type approval which are automatically accepted by Local Authority Building Control organisations and consequently ‘fast tracked’ through the planning process.

The first step is to decide what level of protection you need. If you’re unsure there is a free and simple flowchart at www.smokecontrol.co.uk that can help you decide. Next calculate the floor area of your car park and contact your supplier for a quote.

By Lee Hewings, Project Manager

Date posted:

27-10-2008

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