Travel distance calculator (Approved Document B)
Enter the purpose group, whether escape is possible in one direction only or in more than one direction, and the measured travel distance. The calculator returns the limit from Approved Document B and the margin you have left.
Travel distance is measured along the actual route a person would walk (around fixed obstructions and furniture layouts, not as a straight line) from any point in a room or storey to the nearest storey exit or final exit. Direct distance is measured in a straight line and, where a layout is not fixed, Approved Document B allows two-thirds of the travel distance to be used instead.
Travel distance is a prescriptive limit rather than a time. Where a fire engineered case has to show that people are out before conditions turn, that argument is made on time instead. See the ASET and RSET evacuation timeline calculator.
Within the Approved Document B limit
You have 15 m of margin. Record the measured route on the fire strategy drawing so the reviewer can follow the same line.
Working
| Step | Value |
|---|---|
| Tabulated limitOffice, escape in more than one directionApproved Document B, Volume 2, Table 2.1 | 45 m |
| Margin45 m limit − 30 m measured | +15 m |
Sources
- Approved Document B, Volume 2, Table 2.1Limitations on travel distance, by purpose group and number of escape directions.
- Approved Document B, Volume 1, Table 3.1Maximum travel distance in the common parts of a block of flats, from a flat entrance door to a storey exit or stair lobby.
- Approved Document B, Volume 2, Table 2.1 note 1Where the internal layout of partitions and fittings is not known, direct distances should be assessed instead, and the direct distance should be assumed to be two-thirds of the actual travel distance. This is a note to the table, not a numbered paragraph.
- Approved Document B, Volume 1, paragraphs 3.18b(i) and 3.24The 9 m layout limit within a single-storey flat, and the 18 m limit for live/work units.
- BS 9999:2017, Table 6Alternative, risk-based travel distances by risk profile. A sprinkler system reduces the risk profile by one level under BS 9999 clause 6.5.
This is an engineering aid, not engineering advice. The result above is produced from the inputs you gave and the guidance cited. It does not account for everything a competent fire engineer would consider on a real building, and it is not a substitute for reading the current published standard. Check every number before it goes into a design.
Questions people ask
What is the maximum travel distance in an office under Approved Document B?
18 m where escape is possible in one direction only, and 45 m where escape is possible in more than one direction. Those figures are from Approved Document B Volume 2, Table 2.1, and are measured along the actual route of travel.
Is travel distance measured in a straight line?
No. Travel distance is measured along the route a person would actually walk, around fixed obstructions and any fixed furniture or fittings. Direct distance is the straight-line measurement, and Approved Document B only allows it where the internal layout is not known, in which case the limit becomes two-thirds of the tabulated travel distance.
Do sprinklers increase the permitted travel distance?
Not under Approved Document B: its Table 2.1 figures do not change if you fit sprinklers. Under BS 9999 they can, because a sprinkler system meeting BS EN 12845 or BS 9251 lets you reduce the risk profile by one level (clause 6.5), and the travel distances in Table 6 are set by risk profile. Moving from Approved Document B to BS 9999 is a change of design code, not a relaxation you can apply selectively.
What is the travel distance limit in the common corridor of a block of flats?
7.5 m from a flat entrance door where escape is possible in one direction only, and 30 m where escape is possible in more than one direction, from Approved Document B Volume 1 Table 3.1. Note 2 to that table reduces the 7.5 m to 4.5 m in a small single stair building built to Diagram 3.9. The distance is measured to a storey exit or stair lobby, and where it is measured to a lobby, that lobby must not give direct access to a storage room, a flat, or any other space containing a fire hazard. BS 9991:2024 sets out an alternative approach.
Is there a 9 m travel distance limit inside a flat?
Only if you are relying on it. Paragraph 3.18 of Volume 1 gives three alternative ways to plan a single-storey flat: provide a protected entrance hall to at least REI 30 serving all habitable rooms, plan the flat so travel distance from the entrance door to any point in any habitable room is no more than 9 m with cooking facilities remote from that door, or provide an alternative exit. The 9 m figure belongs to the second option; it is not a limit that applies to every flat.
How is travel distance measured in an open-plan area with no fixed layout?
Use direct distance. Approved Document B allows a straight-line measurement where the layout is not fixed, but the permitted figure drops to two-thirds of the tabulated travel distance, so 45 m becomes 30 m, and 18 m becomes 12 m.
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