Designing effective smoke ventilation in car parks
Enclosed or underground car parks normally require ventilation systems. Smoke ventilation is needed to provide a means of clearing smoke from the car park during and after a fire. This will limit smoke temperatures and structural damage and inhibit smoke spread between floors. Smoke ventilation systems may be designed in addition to provide clear smoke-free access for fire fighters to tackle the seat of the fire or to protect means of escape from the car park. These systems are more complex and exceed the requirements of the Building Regulations; they are generally used as compensating features when other requirements of the regulations are not met.
Day-to-day ventilation is also needed to control build-up of vehicle exhaust fumes or spilled fuel when the facility is in general use. Acceptable day-to-day air quality is maintained by removing exhaust gases produced by vehicles and by ensuring that there are no pockets of stagnant air. Invariably, smoke and fume ventilation are facilitated by the same dual-purpose system.
The two main system design approaches to smoke control in car parks
- Smoke Clearance Systems
- Smoke Control Systems
Smoke Clearance Systems
Smoke Clearance systems are used to help aid the removal of smoke from the car park after the fire has been dealt with and offer no protections or help with escape to anyone who may be in the car park when the fire breaks out. They meet the requirements of Approved Document B and allow fire fighters to clear smoke from an enclosed car park once the fire has been tackled.
- There are no prescribed objectives - just an air change rate for mechanical systems, or natural openings based on a percentage of the floor area, taking no account of potential fire size or fire location.
- Does NOT aid escape
- Does NOT compensate for extended escape distances
- Where mechanical extract is employed, it is usually sized to provide 6 ACH to all levels for fume control and 10 ACH to the largest level for smoke clearance – to be drawing from the fire affected floor only
- Ducted systems can be used to distribute extract across the whole of the car park area, with extract points at high or low level
- Alternatively, jet fans (aka impulse or induction fans) can be used in lieu of ducting - these are generally located over roadways and laid out to ensure no stagnant areas.
- Where jet fans are used, the Car Park is usually modelled using Computational Fluid Dynamics (CFD) to confirm good air movement throughout the space and that there are no stagnant areas. Systems based on air change rates can only offer smoke clearance.
Smoke Control Systems
As the name suggests, these systems are designed with a specific objective of controlling the movement and extract of smoke in mind. They offer added protection to anyone in the car park at the time of the fire and may be designed to aid in escape. They usually require additional extract over and above the basic clearance requirement.
These systems can be designed to:
- Aid escape and therefore extend safe escape distances
- Assist firefighting
- Control smoke as an alternative to compartmentation
- Trade-off against lobby ventilation in basement levels
In the UK, sprinklers are generally not required in car parks, except in certain applications, such as shopping centres or larger projects in London and Scotland – unless specifically specified in a fire engineering strategy.
Smoke ventilation and control regulation in the UK
Throughout the UK there is legislation covering the ventilation requirements in new and refurbished car parks which needs to be satisfied.
The requirements vary slightly from country to country and are detailed in the documents mentioned below:
England and Wales: Approved Document B to the Building Regulations;
Scotland: Scottish Buildings Standards Technical Handbooks;
Northern Ireland: Technical Booklet E.
Day to day fume ventilation:
England and Wales: Approved Document F – Ventilation;
Scotland: Scottish Technical handbook - Non domestic. 2013 section 3.14
Northern Ireland: Technical Booklet K - Ventilation. 2012
Guidance is based upon English Building Regulations. Additional guidance is given in:
BS 7346-7: 2013 - “Components for Smoke and Heat Control Systems. Code of practice on functional recommendations and calculation methods for smoke and heat control systems for covered car parks”. This covers natural ventilation, ducted mechanical ventilation and impulse ventilation, and summarises the requirements of the Buildings Regulations for both smoke ventilation and ventilation air indoor air quality.
BS 9999:2008 – “Code of practice for fire safety in the design, management and use of buildings” BR 368 “Design Methodologies for Smoke and Heat Exhaust Ventilation” (BRE, 1999) SCA Guide “Design of Smoke Ventilation Systems for Loading Bays and Coach Parks - a guide for system designers” (FETA, 2010).
SCA Guide “CFD Modelling for Car Park Ventilation Systems – a guide for designers and regulators” (FETA, 2007). The guidance makes it easier for designers to validate their designs and for building control bodies to sanction them.