External escape stairs

Any external escape stair should meet all of the following conditions (Diagram 2.7).
a. Doors to the stair should be fire resisting (minimum E 30), except for a single exit door from the building to the top landing of a downward-leading external stair.
b. Fire resisting construction (minimum RE 30) is required for the building envelope within the following zones, measured from the flights and landings of the external stair.
i. 1800mm horizontally.
ii. 9m vertically below.
iii. 1100mm above the top landing of the stair (except where the stair leads from basement to ground level).
c. Fire resisting construction (minimum RE 30) should be provided for any part of the building (including doors) within 1800mm of the escape route from the foot of the stair to a place of safety. This does not apply if there are alternative escape routes from the foot of the external escape stair.
d. Stairs more than 6m in height should be protected from adverse weather. Protection should prevent the build-up of snow or ice but does not require full enclosure.
e. Glazing in areas of fire resisting construction should be fixed shut and fire resisting (in terms of integrity, but not insulation) (minimum E 30).