A few months too late, but I know the answer to this one!!
If it is the same as my piccy!
I have seen lots of these buildings in London.
There is a lobby to the stair and a lobby outside the four flats. Flats are within 4.5m of the stair lobby.
Permananet ventilation in the lobby to the stair was provided as per the original design. A horizontal permanent ventilation plenum also ran above this lobby to provide permanent ventilation to the lobby outside the flat (although it is very small: 0.3m2 at most!) COupled with the natural shaft in the flat lobby, this gives cross ventilation. However the shaft is open to all floor levels.
I am only concerned with life safety, so the mechanical fan on the roof; i don't care about, it will only be activated by fire fighters using their key.
In the 60s, the natural smoke shaft was thought to work as smoke is hot and bouyant. SInce then; BRE research has shown that smoke cools and falls. Hence why we only have AOVs to shafts nowadays. So the natural shaft compromises horizontal compartmentation and will aid smoke spread to floors above. I appreciate that the shaft was part of the original design intent, but we know now that it does not work. The shaft is also a convienient place to run a gas main, as I have seen in some of these designs!!
The landlord has two options:
1. Maintain permanent ventilation in the stair lobby; as per the original design or fit AOVs in the stair lobby. Then this building will comply with AD B 2006, figure 7a. (we are obviously not trying to comply with current standards, I am just refering to an accepted standard.)
The shaft will need stopping up at each level in this case to stop smoke spread.
2. Provide AOVs to the shaft to stop smoke spread to upper floor levels. Then we have a situation where we have a design similar to AD B 2002 Diagram 12a.
Stinky
