The LWF Blog
Fire Safety Engineering for Design – Fire Engineering Design Approaches – Part 121February 27, 2023 11:47 am
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 120, LWF discussed time of travel to an exit during a total or partial building evacuation. In part 121, we will continue to talk about time of travel to an exit during evacuation.
Time of travel to an exit during evacuation will vary depending on various factors, one of which is where the individual is location when the fire starts.
Buildings with high occupant density will have occupants spread throughout the area occupied. Some people will already be near the exit and so their evacuation time will be very short. Others will have to cover more distance to reach the exit and so will take longer.
If every building occupant is able to reach the final exit from the building within the notional evacuation time (usually around 2.5 minutes) then it is possible there will be a queue at the exit doorway. Unless excessive, the travel distance is unlikely to have a significant effect on the overall travel time. 150 metres can be travelled in about 2 minutes at a speed of 1.2 metres per second. A slower travelling speed of 0.6 metres per second still means that 70 metres can be travelled in 2 minutes.
Where a building has low occupant density, the distance to be travelled to the exit will have more of a bearing on the overall evacuation time, as there will be no queuing at the exits and the longest travel distance will likely determine the total evacuation time. This does not mean that travel distances should be unrestricted. The location of the exit(s) must be easily identified and traversable by those who are not able to move quickly in a reasonable amount of time.
Where buildings are above a certain height and floor area, provisions made for firefighter access and facilities may dictate the maximum distance between stairways.
In larger open-plan areas, travel distances in excess of those specified in fire safety design codes may be acceptable, provided that the exits are clearly visible and accessible.
In part 122 of LWF’s series on fire engineering we will look at what can be done when the route to the exit is unavoidably complex. 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.