In one of my project, I have come across the requirement to shut off the stair pressurisation fan when the stair smoke detector detects the smoke.
Suppose there is case of 25 story tower, where the smoke has entered the stair from 22nd floor fire due and the stair door was slightly open. Now the stair if not shut off then the fan will try to push the smoke away rather than accumulating when the fan is off. In this case the whole stair well will be full of smoke which hampers the evacuation. Is this correct strategy?
I would like to have another solution to this problem. When the habitable storey is more than say 10 floors with smoke detection in stair well, then we need to have by-pass fan for stair pressurisation to extract the smoke from the same stair pressurization duct so that the stair can be used for evacuation. What do you say?