The corridors are separated from the staircase by two doors in order to create a space (buffer space) whose walls and doors are fire-resistant. That space is ventilated through a ventilation duct that is always open (no mechanical ventilation system is foreseen). At the top the duct is naturally ventilated through a chimney.
Can the air in the ducts be considered as outdoor air, in order to consider those accesses as naturally ventilated?
If it cannot, shall those spaces be mechanically ventilated? No exception, since the provided air can go to the ventilation ducts and it is an energy waste? Additionally, if an air supply is required, this would have to be an extension of the corridor ducting and it would require a fire resistant dumper while crossing the wall between the corridor and this space, which are separate fire compartments.