WIDTH OF escape stairs
E4.1 a. The width of an escape stair must be at least the width required for any escape route giving access to it,
except -
i. where the number of people using the escape route is not more than 225 it may be reduced to not less than 1100mm, and
ii. where the number of people using the escape route is not more than 100 it may be reduced to not less than 1000mm
b. In stairs or ramps the minimum width is the width clear of handrails or other obstructions.
except -
stringers and newel posts, each of which may project not more than 30mm into the width.
E4.2 Where the escape routes from a storey consist solely of escape stairs, and the storey requires 2 or more escape stairs, the width of any escape stair in mm from that storey must be at least 5.3 x the appropriate capacity (see E4.4) divided by the number of such stairs, less one, except -
a. where there is a protected lobby between each escape stair enclosure and any part of the building at any storey from which there is access to the escape stair, other than the topmost storey, the provision as to less one escape stair does not apply; and
b. where the topmost storey contains plant and it is not accessible for a purpose other than the maintenance of the plant the width of any escape stair from this storey to the storey immediately below needs to comply only with the requirements of Part S for industrial stairs and fixed ladders.
c. Where escape routes from a storey consist of a combination of escape stairs and other escape routes (see diagram to this standard) the width of any escape stair from that storey may be designed to take into account that proportion of the number of occupants on that storey who may escape by way of the other escape routes.
DIAGRAM TO E4.2c.: WIDTH OF escape stairS
Diagram
E4.3 Where the escape route from an escape stair is also the escape route from the ground and/or basement storey its width shall be increased to take account of that proportion of the occupancy capacity of the ground and/or basement storey served by the escape route, and unless access to the escape route on the ground storey is by way of a protected lobby one escape route from the ground storey into an enclosure serving an escape stair must be discounted.
CALCULATION OF APPROPRIATE CAPACITY
E4.4* The appropriate capacity in relation to a suitable escape stair at any storey above or below the place of safety is -
a. the occupancy capacity of the part of the storey or space served by the escape stair, provided the escape stair does not also serve the next storey or space above or in the case of a basement storey, the next storey below; or
b. if the escape stair serves 2 or more storeys including any space in a building, or part of a building, which is not divided by compartment floors, the occupancy capacity of the part of each storey, including any space, served at and above or below as the case may be, by the escape stair less 20% (20% represents standing capacity within the escape stair enclosure). At each storey level the appropriate capacities must be accumulated in respect of those storeys which at that level have been served by the escape stair. The total appropriate capacity for all the storeys served by the escape stair must be taken into account at the storey level where the escape route leads to a place of safety; or
c. in a building, or part of a building, which is divided by one or more compartment floors, the total occupancy capacity, less 20%, of -
i. each of the 2 adjacent upper storeys, one or both of which may be a space, served by the escape stair, or in the case of an escape stair serving a basement storey the 2 adjacent basement storeys served by that escape stair, having in either case the greatest combined occupancy capacity, or
ii. the compartment either above or below ground level served by the escape stair having the greatest occupancy capacity, discounting the occupancy capacity of any storey within the compartment which is not served by the escape stair,
whichever is the greater according to i. or ii. above.
DIAGRAM TO E4.4: CALCULATION OF APPROPRIATE CAPACITY
Diagram