BS 9991 and Approved Document B list the situations in which external fire resistant doors and windows are necessary, including;
Flats with a balcony or deck or interconnected balconies where the means of escape would require occupants to escape past a door or window of a flat which may be on fire.
Windows looking out onto external escape stairs or landing within 1800mm of the floor level.
Windows or doorsets in close proximity to a boundary.
Flat entrance doorsets and glazed screens on internal protected escape corridors.
