Let me make it clear. I’m talking here about systems providing smoke control, not just smoke clearance as recommended in Building Regulations. These systems are much more complex and costly than compliant smoke clearance systems, so why would anyone choose to use them?
Smoke clearance or smoke control?
As always it comes down to fire engineering. If your car park is fully compliant with Approved Document B (or its equivalents in Scotland and Ireland) then a simple smoke clearance system is all that is needed. However, if the design you are considering is non-compliant, a jet fan based smoke control system could be the way to achieve an equivalent level of safety.
When should you opt for a smoke control system?
The usual reasons for considering smoke control are:
- If you are not planning to provide a sprinkler system in those car parks where sprinklers are required, such as car parks attached to shopping centres or located in London Section 20 buildings.
- If the car park doesn’t meet prescriptive maximum travel distances for means of escape.
- If you are planning a stacker type car parking.
Smoke control systems can give more flexibility to your design, but they need to be used correctly.
Good design calculations are critical
The benefit of a smoke control system is that it keeps designated areas of the car parkeffectively smoke free, whereas a smoke clearance system may allow the whole car park to become smoke logged. BS 7346-7 provides guidance on the requirements for smoke control systems, but its scope does not include the necessary design calculations, which really do need to be backed up by CFD analysis.
The difference between smoke clearance and smoke control is clearly shown in two videos. The first test carried out at Avon Fire and Rescue Service showed how a smoke clearance system slowly clears a smoke logged car park. A second test carried out at BRE in Middlesbrough showed how impulse ventilation can limit the flow of smoke to a predefined area, ensuring good visibility is maintained throughout the car park, and how effective a properly executed CFD analysis can be in predicting smoke flows and temperatures. All the details of the test are available in a leaflet you can download at the bottom of this page.
Upgrading from smoke clearance to smoke control
It’s not a trivial task to upgrade from smoke clearance to smoke control in car parks. In all but the largest areas it is likely to require a significant increase in the ventilation rate with a concomitant increase in plant and duct space requirements. Location of extract plant also becomes more critical, as does the control strategy.
Smoke control systems are not a “get out of jail free” card but, used correctly, they can provide the additional design flexibility required on some projects.
Car park smoke control in practice: Liverpool One
The car park of the Liverpool One shopping centre provides a very good example of a situation where a smoke control system provided the most cost-efficient and effective solution. With more than 2,000 spaces split over a massive 56,000 m2 on four levels, the system is tasked with enabling occupants to escape and assisting fire-fighting crews. For details on the project as well as the CFD models and tests that were executed to show how the smoke control system would fulfil its mission in case of fire please visit the Liverpool One project page.
Webinar 10/06/16 - Car park ventilation
I will be hosting a live webinar on this topic, where I will explain this topic in more detail. This webinar will be CIBSE CPD accredited and will feature a Q&A at the end.
Whitepaper - Designing car park ventilation systems
For more detailed information on car park ventilation, you can read our Whitepaper.
Conor Logan is Associate Technical Director of Colt UK, Smoke and Climate Control Division. Conor designs innovative smoke control and HVAC systems and is also Chairman of the Smoke Control Association.