The LWF Blog

Fire Safety Engineering for Design – Fire Engineering Design Approaches – Part 114

January 9, 2023 12:06 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 113, LWF looked at the types of occupancy and how it may affect the time required to evacuate a building. In part 114, we begin to evaluate the pre-movement time in a fire situation.

Pre-movement time is made up of two elements – recognition time and response time. It is important to understand and minimise the duration of pre-movement time and it can be just as important as the time taken to evacuate once movement towards the exit begins.

For each person, pre-movement time is the time taken from first recognising the presence of fire in the building (through an alarm signal or someone passing the information, or through seeing the fire themselves) to the start of movement towards an exit.

The amount of pre-movement time can be influenced by various factors, such as:

• The location of the occupant in the building
• The location of the fire and pattern of fire growth
• If the fire is visible to the occupant (people who can see the fire are more likely to respond quickly)
• The type of cue or warning received, e.g. voice alarm, alarm sounder, smell of smoke.

Recognition Time

Recognition time is the time period between an individual hearing an alarm or being alerted to fire in another way, but before they begin to respond by moving towards an exit.

During the recognition time, a person might continue doing their job, for instance, they may be on the phone and finish the call. They may be in the bathroom and wash their hands. It is important to note that the activities continued or finished during this period are in no way considered the correct use of time when each person should immediately cease what they are doing and begin evacuating.

The length of the recognition period can vary widely depending on factors such as the type of building, nature of the occupants and the adequacy of fire training in preparing them for the situation.

The recognition time ends when the occupant accepts they need to respond and they take some action, such as putting on a coat or picking up a bag.

In part 115 of LWF’s series on fire engineering we will continue looking at pre-movement time by discussing response time. 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.