In all well designed public buildings the emergency stairwells are actually isolated air-spaces (when the doors are shut). Their ventilation systems should draw from a location likely to be free of smoke and they should be at a higher pressure than every possible entry point so that they are positive pressure.

In such setups the /landings/ are life safety zones where those in wheel chairs can wait until rescue arrives to literally carry them down the stairwell (a stair sled might be a good for the rescuers).

It seems that internationally (recently the UK) laws and building codes are not as strict.