Section 4 Design for vertical escape – buildings other than flats

Design for vertical escape – buildings other than flats

  1. Introduction
    1. Number of escape stairs
      1. Mixed use buildings
        1. Single escape stairs
          1. Single escape stairs in small premises
          2. Provision of refuges
            1. Communication
              1. Evacuation lifts
                1. Width of escape stairs
                2. Calculation of minimum stair width
                  1. General
                    1. Discounting of stairs
                      1. Simultaneous evacuation
                        1. Phased evacuation
                        2. Protection of escape stairs
                          1. General
                            1. Enclosure of escape stairs
                              1. Small Premises
                                1. Access lobbies and corridors
                                  1. Separation of adjoining stairways
                                    1. Use of space within protected stairways
                                      1. External walls of protected stairways
                                        1. Gas service pipes in protected stairways
                                        2. Basement stairs
                                          1. External escape stairs


                                            4.1An important aspect of means of escape in multi-storey buildings is the availability of a sufficient number of adequately sized and protected escape stairs. This Section deals with escape stairs and includes measures necessary to protect them in all types of building.

                                            The limitation of distances of horizontal travel for means of escape purposes means that most people should be able independently to reach the safety of a protected escape route or final exit. However, some people, for example those who use wheelchairs, may not be able to use stairways without assistance. For them evacuation involving the use of refuges on escape routes and either assistance down (or up) stairways, or the use of suitable lifts, will be necessary.

                                            This Section should be read in conjunction with the general provisions in Section 5.

                                            Number of escape stairs

                                            4.2The number of escape stairs needed in a building (or part of a building) will be determined by:

                                            • athe constraints imposed in item 3 on the design of horizontal escape routes;
                                            • bwhether independent stairs are required in mixed occupancy buildings (see paragraph 4.4);
                                            • cwhether a single stair is acceptable (see paragraphs 4.5 and 4.6); and
                                            • dprovision of adequate width for escape (see paragraph 4.15) while allowing for the possibility that a stair may have to be discounted because of fire or smoke (see paragraph 4.20).

                                            4.3In larger buildings, provisions for access for the Fire and Rescue Service may apply, in which case, some escape stairs may also need to serve as firefighting stairs. The number of escape stairs may therefore be affected by provisions made in Section 17, paragraphs 17.8 and 17.9.

                                            Mixed use buildings

                                            4.4Where a building contains storeys (or parts of storeys) in different purpose groups, it is important to consider the effect of one risk on another. A fire in a shop, or unattended office, could have serious consequences on, for example, a residential or hotel use in the same building. It is therefore important to consider whether completely separate routes of escape should be provided from each different use within the building or whether other effective means to protect common escape routes can be provided.

                                            Single escape stairs

                                            4.5Provided that independent escape routes are not necessary from areas in different purpose groups in accordance with paragraph 2.50 or 4.4, the situations where a building (or part of a building) may be served by a single escape stair are:

                                            • afrom a basement which is allowed to have a single escape route in accordance with paragraph 3.5b and Table 2;
                                            • bfrom a building (other than small premises, see 4.5c) which has no storey with a floor level more than 11m above ground level and in which every storey is allowed to have a single escape route in accordance with paragraph 3.5b and Table 2;
                                            • cin the case of small premises (see paragraph 3.32), in situations where the guidance in paragraph 4.6 is followed.

                                            Single escape stairs in small premises

                                            4.6A single escape stair may be used from:

                                            • asmall premises as described in paragraph 3.33;
                                            • ban office building comprising not more than five storeys above the ground storey, provided that:
                                              • ithe travel distance from every point in each storey does not exceed that given in Table 2 for escape in one direction only; and
                                              • iievery storey at a height greater than 11m has an alternative means of escape;
                                            • ca factory comprising not more than:
                                              • itwo storeys above the ground storey (if the building, or part of the building, is of low risk); or
                                              • iione storey above the ground storey (if the building, or part of the building, is of normal risk); provided that the travel distance from every point on each storey does not exceed that given in Table 2 for escape in one direction only; or
                                            • dprocess plant buildings with an occupant capacity of not more than 10.

                                            Provision of refuges

                                            Diagram 20

                                            4.7Refuges are relatively safe waiting areas for short periods. They are not areas where disabled people should be left alone indefinitely until rescued by the fire and rescue service, or until the fire is extinguished.

                                            A refuge should be provided for each protected stairway affording egress from each storey, except storeys consisting exclusively of plant rooms.

                                            Notes:Whilst a refuge should be provided for each stairway, they need not necessarily be located within the stair enclosure but should enable direct access to the stair. The number of refuge spaces need not necessarily equal the sum of the number of wheelchair users who can be present in the building. Refuges form a part of the management plan and it may be that more than one disabled person will use a single refuge as they pass through as a part of the evacuation procedure.

                                            4.8The following are examples of satisfactory refuges:

                                            • a an enclosure such as a compartment (see Diagram 20), protected lobby, protected corridor or protected stairway (see Diagram 21); and
                                            • ban area in the open air such as a flat roof, balcony, podium or similar place which is sufficiently protected (or remote) from any fire risk and provided with its own means of escape.

                                            4.9Each refuge should provide an area accessible to a wheelchair of at least 900mm x 1400mm in which a wheelchair user can await assistance. Where a refuge is a protected stairway or protected lobby or protected corridor, the wheelchair space should not reduce the width of the escape route. Where the wheelchair space is within a protected stairway, access to the wheelchair space should not obstruct the flow of persons escaping.

                                            4.10Refuges and evacuation lifts should be clearly identified by appropriate fire safety signs. Where a refuge is in a lobby or stairway the sign should be accompanied by a blue mandatory sign worded “Refuge – keep clear”.


                                            4.11To facilitate the effective evacuation of people from refuges an emergency voice communication (EVC) system should be provided. It is essential that the occupants of each refuge are able to alert other people that they are in need of assistance and for them to be reassured that this assistance will be forthcoming.

                                            4.12The EVC system should comply with BS 5839-9:2003 and consist of Type B outstations which communicate with a master station located in the building control room (where one exists) or adjacent to the fire alarm panel.

                                            4.13In some buildings it may be more appropriate to use an alternative approach such as the use of wireless technology.

                                            Evacuation lifts

                                            4.14Guidance on the use of lifts when there is a fire is given in paragraph 5.39.

                                            Width of escape stairs

                                            Table 6

                                            4.15The width of escape stairs should:

                                            • abe not less than the width(s) required for any exit(s) affording access to them;
                                            • bconform with the minimum widths given in Table 6;
                                            • cnot exceed 1400mm if their vertical extent is more than 30m, unless it is provided with a central handrail (see Notes 1 and 2); and
                                            • dnot reduce in width at any point on the way to a final exit.
                                              Note: The 1400mm width has been given for stairs in tall buildings because research indicates that people prefer to stay within reach of a handrail when making a prolonged descent, so much so that the centre part of a wider stair is little used and could be hazardous. Thus additional stair(s) may be needed.
                                              Note: Where a stair wider than 1400mm is provided with a central handrail, then the stair width on each side of the central handrail needs to be considered separately for the purpose of assessing stair capacity.

                                            4.16If the resultant width of the stair is more than 1800mm, then for reasons of safety in use the guidance in Approved Document K Protection from falling, collision and impact is that, in public buildings, the stair should have a central handrail. In such a case see Note 2 to paragraph 4.15.

                                            4.17Where an exit route from a stair also forms the escape from the ground and/or basement storeys, the width may need to be increased accordingly. (See paragraph 3.23).

                                            Calculation of minimum stair width


                                            4.18Every escape stair should be wide enough to accommodate the number of persons needing to use it in an emergency. This width will depend on the number of stairs provided and whether the escape strategy for the building (or part of the building) is based on simultaneous evacuation see (paragraph 4.22) or phased evacuation see (paragraph 4.26).

                                            4.19As with the design of horizontal escape routes, where the maximum number of people needing to use the escape stairs is not known, the occupant capacity should be calculated on the basis of the appropriate floor space factors. Guidance for this is set out in Appendix C.

                                            Discounting of stairs

                                            p>4.20Whether phased or simultaneous evacuation is used, where two or more stairs are provided it should be assumed that one of them might not be available due to fire. It is therefore necessary to discount each stair in turn in order to ensure that the capacity of the remaining stair(s) is adequate for the number of persons needing to escape. The stair discounting rule applies to a building fitted with a sprinkler system.

                                            4.21Two exceptions to the above discounting rules are if the escape stairs:

                                            • aare protected by a smoke control system designed in accordance with BS EN 12101-6:2005.
                                            • bare approached on each storey through a protected lobby (a protected lobby need not be provided on the topmost storey for the exception still to apply).

                                            Notes:Paragraph 4.34 identifies several cases where stairs need lobby protection. In such cases the likelihood of a stair not being available is significantly reduced and it is not necessary to discount a stair. However, a storey exit still needs to be discounted, see paragraph 3.21. See also paragraph 4.27 for additional guidance on the potential need to discount stairs in tall buildings utilising phased evacuation.

                                            Simultaneous evacuation

                                            Table 7

                                            4.22In a building designed for simultaneous evacuation, the escape stairs (in conjunction with the rest of the means of escape) should have the capacity to allow all floors to be evacuated simultaneously. In calculating the width of the stairs account is taken of the number of people temporarily housed in the stairways during the evacuation.

                                            4.23Escape based on simultaneous evacuation should be used for:

                                            • aall stairs serving basements;
                                            • ball stairs serving buildings with open spatial planning; and
                                            • call stairs serving Other Residential or Assembly and Recreation buildings.

                                            Notes:BS 5588-7:1997 includes designs based on simultaneous evacuation.

                                            4.24Where simultaneous evacuation is to be used, the capacity of stairs of widths from 1000 to 1800mm is given in Table 7.

                                            4.25As an alternative to using Table 7, the capacity of stairs 1100mm or wider (for simultaneous evacuation) can be derived from the formula:

                                            P = 200w + 50 (w – 0.3)(n – 1), or

                                            w = P + 15n – 15

                                            150 + 50n


                                            (P) is the number of people that can be served;

                                            (w) is the width of the stair, in metres; and (n) is the number of storeys served.

                                            Notes:Stairs with a rise of more than 30m should not be wider than 1400mm unless provided with a central handrail (see paragraph 4.15).
                                            Separate calculations should be made for stairs/flights serving basement storeys and those serving upper storeys.
                                            The population ‘P’ should be divided by the number of available stairs.
                                            The formula is particularly useful when determining the width of stairs serving a building (or part of a building) where the occupants are not distributed evenly – either within a storey or between storeys.
                                            In the formula, the first part [200w] represents the number of persons estimated to have left the stair after 2.5 minutes of evacuation. The second part [50(w-0.3)(n-1)] represents the number of persons estimated to be accommodated on the stair after this time.

                                            Phased evacuation

                                            Table 8

                                            4.26Where it is appropriate to do so, it may be advantageous to design stairs in high buildings on the basis of phased evacuation. In phased evacuation the first people to be evacuated are all those of reduced mobility and those on the storey most immediately affected by the fire. Subsequently, if there is a need to evacuate more people, it is done two floors at a time. It is a method which cannot be used in every type of building and it depends on the provision (and maintenance) of certain supporting facilities such as fire alarms. It does however enable narrower stairs to be incorporated than would be the case if simultaneous evacuation were used and has the practical advantage of reducing disruption in large buildings.

                                            4.27In tall buildings over 30m in height, where phased evacuation is adopted, there is a potential that persons attempting to escape could be impeded by firefighters entering and operating within the building. This potential varies with the height of the building and with the number of escape stairs that are available. Generally, this can be addressed by incorporating special management procedures into the evacuation strategy in consultation with Fire and Rescue Service. However, in some very tall buildings, typically those over 45m in height, physical measures may need to be incorporated into the building (e.g. by discounting a stair or by some other suitable means).

                                            4.28Phased evacuation may be used for any building provided it is not identified in paragraph 4.23 as needing simultaneous evacuation.

                                            4.29The following criteria should be satisfied in a building (or part of a building) that is designed on the basis of phased evacuation:

                                            • athe stairways should be approached through a protected lobby or protected corridor at each storey, except a top storey;
                                            • bthe lifts should be approached through a protected lobby at each storey (see paragraph 5.42);
                                            • cevery floor should be a compartment floor;
                                            • dif the building has a storey with a floor over 30m above ground level, the building should be protected throughout by an automatic sprinkler system in accordance with paragraph 0.16.
                                            • ethe building should be fitted with an appropriate fire warning system, conforming to at least the L3 standard given in BS 5839-1:2002; and
                                            • fan internal speech communication system should be provided to permit conversation between a control point at fire and rescue service access level and a fire warden on every storey. In addition, the recommendations relating to phased evacuation provided in BS 5839-1 should be followed. Where it is deemed appropriate to install a voice alarm, this should be in accordance with BS 5839-8:1998.

                                            4.30The minimum width of stair needed when phased evacuation is used is given in Table 8. This table assumes a phased evacuation of the fire floor first followed by evacuation of not more than two floors at a time.

                                            Protection of escape stairs

                                            Diagram 22


                                            4.31Escape stairs need to have a satisfactory standard of fire protection if they are to fulfil their role as areas of relative safety during a fire evacuation. The guidance in paragraphs 4.32 to paragraph 4.33 should be followed to achieve this.

                                            Enclosure of escape stairs

                                            4.32Every internal escape stair should be a protected stairway (i.e. it should be within a fire-resisting enclosure).

                                            However an unprotected stair (e.g. an accommodation stair) may form part of an internal route to a storey exit or final exit, provided that the distance of travel and the number of people involved are very limited. For example, small premises (described in paragraph 3.32, 4.6 and 4.33) and raised storage areas (see paragraphs 7.7 and 7.8).

                                            There may be additional measures if the protected stairway is also a protected shaft (where it penetrates one or more compartment floors, see Section 8) or if it is a firefighting shaft (see Section 17).

                                            Small Premises

                                            4.33A stair in a small premises, which is not a bar or restaurant, may be open if it does not connect more than two storeys and delivers into the ground storey not more than 3m from the final exit (see Diagrams 22 and 23) and either :

                                            • athe storey is also served by a protected stairway; or
                                            • bit is a single stair in a small premises with the floor area in any storey not exceeding 90m2 and, if the premises contains three storeys, the stair serving either the top or bottom storey is enclosed with fire-resisting construction at the ground storey level and discharges to a final exit independent of the ground storey (see Diagram 23).

                                            Access lobbies and corridors

                                            4.34There are situations where an escape stair needs the added protection of a protected lobby or protected corridor. These are:

                                            • awhere the stair is the only one serving a building (or part of a building) which has more than one storey above or below the ground storey (except for small premises covered in paragraph 4.6a); or
                                            • bwhere the stair serves any storey at a height greater than 18m; or
                                            • cwhere the building is designed for phased evacuation (see paragraph 4.29a).
                                            • dwhere the stair is a firefighting stair.

                                            Lobbies are also needed where the option in paragraph 4.21(b) has been used so as not to discount one stairway when calculating stair widths.

                                            An alternative that may be considered in (a) to (c) above is to use a smoke control system as described in paragraph 4.21(a).

                                            4.35A protected lobby should be also provided between an escape stairway and a place of special fire hazard. In this case, the lobby should have not less than 0.4m2 permanent ventilation, or be protected from the ingress of smoke by a mechanical smoke control system.

                                            4.36 Every protected stairway should discharge:

                                            • adirectly to a final exit; or
                                            • b by way of a protected exit passageway to a final exit.

                                            Notes:: Any such protected exit passageway should have the same standard of fire resistance and lobby protection as the stairway it serves. The exit from a protected stairway should meet the provisions in paragraphs 5.30 to 5.34.

                                            Separation of adjoining stairways

                                            4.37Where two protected stairways are adjacent, they and any protected exit passageways linking them to final exits, should be separated by an imperforate enclosure.

                                            Use of space within protected stairways

                                            4.38A protected stairway needs to be free of potential sources of fire. Consequently, facilities that may be incorporated in a protected stairway are limited to the following:

                                            • asanitary accommodation or washrooms, so long as the accommodation is not used as a cloakroom. A gas water heater or sanitary towel incinerator may be installed in the accommodation but not any other gas appliance;
                                            • b a lift well may be included in a protected stairway, if it is not a firefighting stair;
                                            • ca reception desk or enquiry office area at ground or access level, if it is not in the only stair serving the building or part of the building. The reception or enquiry office area should not be more than 10m2 in area; and/or
                                            • dcupboards enclosed with fire-resisting construction, if it is not in the only stair serving the building or part of the building.

                                            External walls of protected stairways

                                            4.39The external enclosures to protected stairways should meet the provisions in paragraph 5.24.

                                            Gas service pipes in protected stairways

                                            4.40Gas service and installation pipes or associated meters should not be incorporated within a protected stairway unless the gas installation is in accordance with the requirements for installation and connection set out in the Pipelines Safety Regulations 1996, SI 1996 No 825 and the Gas Safety (Installation and Use) Regulations 1998 SI 1998 No 2451. (See also paragraph 8.40.)

                                            Basement stairs

                                            4.41Because of their situation, basement stairways are more likely to be filled with smoke and heat than stairs in ground and upper storeys. Special measures are therefore needed in order to prevent a basement fire endangering upper storeys.

                                            These are set out in the following two paragraphs.

                                            4.42If an escape stair forms part of the only escape route from an upper storey of a building (or part of a building) it should not be continued down to serve any basement storey. The basement should be served by a separate stair.

                                            4.43If there is more than one escape stair from an upper storey of a building (or part of a building), only one of the stairs serving the upper storeys of the building (or part) need be terminated at ground level. Other stairs may connect with the basement storey(s) if there is a protected lobby, or a protected corridor between the stair(s) and accommodation at each basement level.

                                            External escape stairs

                                            Diagram 24

                                            4.44If more than one escape route is available from a storey (or part of a building), some of the escape routes from that storey or part of the building may be by way of an external escape stair, provided that:

                                            • athere is at least one internal escape stair from every part of each storey (excluding plant areas);
                                            • bin the case of an Assembly and Recreation building, the route is not intended for use by members of the public; or
                                            • cin the case of an Institutional building, the route serves only office or residential staff accommodation.

                                            4.45Where external stairs are acceptable as forming part of an escape route, they should meet the provisions in paragraph 5.25.