The LWF Blog
Fire Safety for Facilities Management Personnel – Means of Escape – Part 117
September 27, 2021 11:23 amLawrence 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 116, LWF talked about design codes for means of escape, how they are applied and alternatives to prescriptive codes. In part 117, we consider the principal aspects of design when planning means of escape, or assessing the adequacy of such in an existing building.
The three major elements in planning Means of Escape are:
- Travel distances, or direct distances;
- Escape routes and exit capacities;
- The number of building occupants who will utilise means of escape provision.
Travel Distance
The travel distance can be described as the maximum distance needing to be travelled from any point in a building to the nearest final exit/door to protected stairway/door to external escape route.
The door to a protected stairway element relates to buildings with floors above and below ground level or entrance level. An external escape route may be an alleyway, balcony, bridge, walkway etc.
A final exit is that which leads of a place of safety, usually in the open air and that is relevant when discussing the ground level or entrance level of a building.
In essence, then, the travel distance is the maximum distance a person would have to walk to reach a place of relative or absolute safety, measured along the actual route they would walk, and not as a direct line between two points.
Limitation of travel distances is a way of minimising the potential for people being exposed to the effects of fire in the unprotected part of the escape route. The maximum travel distances referred to in prescriptive codes are not necessarily to be followed rigidly, although they should not be exceeded by any significant amount either.
A fire engineered solution may allow a different approach to evacuation and therefore, more flexibility on travel distances. This is commonly achieved through a cohesive approach including active and passive fire protection measures.
Direct Distance
When a building is at the design stage, it can be the case that the internal layout has not yet been finalised and furnishings placement has not been decided upon. This can mean that a virtual walkthrough is not possible, to establish the actual distance a person might travel to a place of relative or absolute safety. An attempt to do so might mean that the figures were incorrect, because of ultimate placement of machinery, or desks, partitions etc.
In these instances, direct distance may be used. Direct distance is defined as the shortest distance from any point on the floor area to the nearest storey exit, ignoring walls, partitions and fittings – other than the enclosing walls or partitions of protected stairways. Direct distances are typically 2/3rd’s of the permissible travel distance, to make an allowance for furniture and other obstructions.
In part 118 of this series, LWF will continue to look at the use of direct distance in designing means of escape, and travel distance in general. 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.