Means of Escape Calculator

Maximum travel distance depends on the building type and whether escape is available in one direction only or in more than one direction. For offices and shops (AD B Vol 2 Table 2.1): 18m one direction, 45m more than one. For general assembly and recreation ("elsewhere" in Table 2.1): 18m and 45m — but where there is seating in rows it is 15m and 32m, and buildings primarily for disabled people 9m and 18m. For a block of flats, the common-area limit (flat entrance door to the common stair or stair lobby, AD B Vol 1 Table 3.1) is 7.5m one direction (4.5m in a small single-stair building) and 30m more than one direction; travel within the flat itself is limited separately to 9m. Distances are measured along the actual escape route from the furthest point to the nearest storey exit or final exit.

An inner room is a room from which escape is only possible by passing through another room (the access room). This is a fire safety concern because if a fire starts in the access room, the inner room becomes trapped. AD B Section 2 restricts inner rooms: they must not be bedrooms, the access room must not be a high fire risk, the inner room should have a vision panel or be within direct sight/sound of the access room, and an automatic fire detection system should be provided in the access room.

A protected stairway (fire-resisting enclosure around the stair) is required in most multi-storey buildings. For two-storey houses, it may not be required if alternative escape from the first floor is available. For all buildings of three or more storeys, a protected stair is needed. The enclosure must be fire-resisting with fire doorsets at all openings: FD30S self-closing doorsets in buildings other than dwellings and in the common parts of blocks of flats, but only E 20 (FD20) with no cold smoke seal and no self-closer where the stairway is inside a single-family dwellinghouse, including a loft conversion (AD B Vol 1 Table C1 item 11b and Appendix C5). The enclosure to a protected stairway has a baseline of REI 30 (30 minutes loadbearing capacity, integrity and insulation) under AD B Appendix B Table B1 item 9(a), and that item is expressly limited to an enclosure that does not form part of a compartment wall or a protected shaft. Where the enclosing wall is one of those, or is a loadbearing wall also described in another Table B1 item, item 2 directs you to the more onerous guidance and the period comes from Table B1 items 2, 6, 7 or 8, all of which read the period off Table B2 "Minimum periods of fire resistance". Table B2 sets the period by purpose group, by the height of the top floor above ground (banded up to 5m, up to 11m, up to 18m, up to 30m and more than 30m) and by whether the building is sprinklered, so there is no single universal figure: for example, an office without sprinklers is 30 minutes up to 5m, 60 minutes up to 18m, 90 minutes up to 30m, and is not permitted above 30m without a sprinkler system, whereas a sprinklered office is 30 minutes up to 18m, 60 minutes up to 30m and 120 minutes above 30m. Read the period for your specific purpose group, height band and sprinkler status from Table B2. The stair must discharge at ground level to a final exit.

Minimum escape-route (corridor) width is set by AD B Vol 2 Table 2.3 "Widths of escape routes and exits", based on the number of people served: up to 60 persons = 750mm, up to 110 = 850mm, up to 220 = 1050mm, and more than 220 = 5mm per person. Table 2.3 note 3 states widths below 1050mm should not be interpolated, and note 5 confirms the 5mm-per-person rule does not apply below 220 persons. These are clear widths excluding projections such as door handles and radiators, and Approved Document M may require greater widths for accessibility. All escape corridors must also have emergency lighting (BS 5266).

A dead end is a section of corridor from which escape is possible in one direction only. In buildings other than dwellings (AD B Vol 2) there is no single "maximum dead-end length": instead, para 2.28 requires a dead end of a corridor exceeding 4.5m to be separated from the rest of the corridor by self-closing fire doorsets, and the one-direction travel must stay within the Table 2.1 "one direction" limit for that use (for example 18m for an office). In the common areas of a block of flats (AD B Vol 1 Table 3.1) the one-direction limit is 7.5m, reduced to 4.5m in a small single-stair building. Beyond these limits you need a second escape direction or a layout change. Dead-end conditions are a common compliance failure and a significant life-safety risk.

AD B Vol 2 Table 2.2 sets the minimum number of escape routes and exits from a room, tier or storey by occupancy: up to 60 persons = 1, up to 600 = 2, more than 600 = 3. A single escape stair may serve a building only in the limited cases of para 3.3 (for example an office of up to five storeys above the ground storey with one-direction travel within Table 2.1 limits and alternative escape above 11m). Buildings with a storey floor level more than 18m above ground generally need at least two stairs with alternative escape. Each escape stair must be protected (fire-resisting enclosure with FD30S self-closing doors) and lead independently to a final exit, and its width must suit the number of occupants it serves (sized by capacity via Table 3.2 above 220 persons).