# The LWF Blog

## Fire Safety Engineering for Design – Fire Engineering Design Approaches – Part 119

February 13, 2023 12:02 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 118, LWF discussed pre-movement time distributions. In part 119, we begin to examine travel time and to look at how the different types of occupancy can affect travel time.

Once pre-movement time is over and the building occupant begins to move to exit the building, travel time has commenced. Travel time is the time between commencement of movement towards an exit and passing through an exit to a place of relative safety such as a protected stairway, or a place of ultimate safety outside the building.

The travel time of a building occupant, or the entire occupancy can be estimated based on the number and distribution of the occupants, the speed of travel towards an exit and the rate of flow through restrictions such as doorways, stairways etc.

This estimation can assist with providing indications as to the minimum time in which a building, floor, room etc. can be evacuated safely if the building occupants reacted immediately and began to evacuate when warned of a fire.

Depending upon the number of persons who must evacuate at once, the calculations undertaken may show that there are certain limiting factors on the escape route. This may be the distance to be travelled (where the ‘flow’ of evacuation is constant and uninhibited, so they are only restricted by the distance they must travel to safety) or there may be other constraints, such as the width of the escape route or final exit.

The number and distribution of occupants will usually be evaluated in a similar manner whether the fire safety design is based on design codes or a fire-engineered design.

In a low-occupancy building, such as a warehouse, it is likely that the overwhelming proportion of travel time is the distance to be travelled. In a large department store, with many customers and staff, it is likely that the high number of persons trying to evacuate at the same time will result in a bottleneck effect at exits and this will take up much of the travel time.

In part 120 of LWF’s series on fire engineering we will continue to look at travel time, in terms of time of travel to an exit. 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.