The purpose of smoke shaft systems is to ventilate lobbies and corridors in the case of fire allowing an easier escape or more effective fire fighting due to reduced smoke levels. It is therefore necessary to provide a ventilator at each level of the building leading into the smoke shaft and to be positive that in an emergency each part of the solution will work as intended.
When such systems were initially applied there was a lack of guidance on how to design them. Some suppliers took the short cut of providing a cheap flap held closed with a magnet that opens on loss of power, as opposed to a motorised ventilator, which drives open and closed with no fail safe open position.
The issue with magnets
If a magnet fails or opens through loss of power on a floor which is not the fire floor, smoke – or even fire – can spread easily into other levels.
Approved Document B (ADB) has recently tightened up the regulations regarding design of smoke shafts. In residential buildings there is now a requirement for all shaft ventilators to be 30 minutes fire rated and smoke sealed, and for all ventilators on non-fire floors to remain closed.
What to do with old systems using magnets
One would have imagined that this would have outlawed any magnet systems but they do still exist on older schemes.
So if you have a building which uses ventilators held closed with magnets, or any other system where the shaft ventilators could fail to an open position, we would suggest that you consider upgrading them to a safer system.
Guidance is available
For further information please refer to “Guidance on smoke control to common escape routes in apartment buildings” published by HEVAC Smoke Control Association and available from FETA. Alternatively if you want to contact me I will be happy to answer any questions you have on the subject.
Paul is a Technical Director for Colt, experienced in smoke control, HVAC, solar shading and louvre systems.