The LWF Blog

Fire Safety for Facilities Management Personnel – Means of Escape – Part 118

October 4, 2021 11:55 am

Lawrence Webster Forrest (LWF) is a specialist fire engineering and fire risk management consultancy whose aim is to give information on best practice in fire safety for facilities management personnel through this blog series. In part 117, LWF considered the principal aspects of design when planning means of escape, or assessing existing adequacy. The three elements of design consideration – travel or direct distances; escape route and exit capacities; and the number of occupants for whom escape must be provided. In part 118, we continue discussing Direct Distance before looking at exit capacity.

 Direct Distance

When it is not possible to measure an escape route as it would be walked by a building occupant, due to unfinished layouts for instance, direct distance figures are used. Direct distance works as an ‘as the crow flies’ measurement, between the furthest point in the accommodation and the storey exit. Usually, if direct distance must be used, it is limited to two-thirds of the limit that will ultimately be imposed on travel distance. This allows the distance that a person may travel from the furthest point to a point of protection to be increased by 50 per cent as a result of partitioning and furnishings.

It should be noted that travel distance and direct distance are not parameters that should need to be imposed simultaneously. Travel distance is the measurement that actually matters, but direct distance is a useful concept that can be used until sufficient information on the interior layout is available.

The maximum permitted travel distance inside a building varies from one code to another. It is also very different depending upon if alternative means of escape is available, or escape is only possible in one direction (i.e. there is a dead end in the area).

Where there is only one escape route, the common maximum permitted travel distance is 18 metres. In circumstances requiring that prescriptive travel distances are to be used, the maximum travel distances for a particular type of occupancy should be sought from the relevant code.

In part 119 of this series, LWF will discuss the use of time rather than distance in limiting occupancy exposure to smoke, toxic gases and the effects of fire, as is usual in a fire safety engineered design. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact LWF on freephone 0800 410 1130.

Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 25 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.

While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.