The LWF Blog

Fire Safety Engineering for Design – Fire Engineering Design Approaches – Part 122

March 6, 2023 12:08 pm

LWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 121, LWF discussed time of travel to an exit during a total or partial building evacuation. In part 122, we will look at what can be done when the route to the exit for evacuation purposes is unavoidably complex.

In some buildings, especially older buildings, it may be the case that the route to an exit from most points within the building is unavoidably complex. A good wayfinding system is one way of assisting building occupants to evacuate, and the inclusion in that system of illuminated floor tracks can be helpful, especially in reduced visibility conditions.

If there is the potential to add more exits than would be provided in large open-plan spaces, this can also be helpful in evacuating occupants in a fire situation.

The travel time of building occupants will be impacted if they need to use stairs prior to reaching a storey exit and allowances must be made for this, including the effect on any disabled people, wheelchair-users or mobility-limited people.

A fire can start anywhere in a building and when planning escape provision, it should be borne in mind that a fire could start very near one of the building exits. It should be assumed, therefore, that one of the exits will be out of provision in a fire situation and the remaining exits should be sufficient and suitable to evacuate all people inside the building. It also means that distances travelled (and estimates of travel times) need to be measured in a different manner to that stipulated in design codes, which always measure travel distance to the nearest exit.

A fire engineered assessment of travel time would take into account the potential for building occupants to set off from a given point heading for the nearest exit and find it obstructed by fire and then have to divert their route to the next nearest (safe) exit. In other words, the first route to be traced to the point where a fire might become visible and then re-trace along the route and divert off to the next available exit.

The measurement of travel distance or calculation of travel times should either be based on worst-case scenario, or take account of all possible occupant locations.

In part 123 of LWF’s series on fire engineering we will begin to look at exit widths. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.

Lawrence Webster Forrest has been working with their clients since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.

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.