The LWF Blog

Fire Safety Engineering for Design – Fire Engineering Design Approaches – Part 112

December 19, 2022 12:48 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 111, LWF looked at the tenability limits for smoke, before discussing the tenability limits for heat from a fire. In part 112, we will discuss pre-movement time, which is the time between the fire alarm sounding and people beginning to move to evacuate a building.

It seems like whenever a fire in a building is depicted in fiction, people panic and chaos ensues. However, studies of human behaviour in real fire situations show that most people do not panic or behave in an irrational manner.

The fact still remains that not all people act in the way the designer of the fire protection measures intended, not because they are acting irrationally, but because they are acting in a way that seems entirely logical to them in the circumstances.

The actions taken by an individual upon the fire alarm being sounded may involve a delay before they begin to move to evacuate the building.

Where possible, the fire safety design should address potential delays and consider behavioural tendencies, as follows:

• When deaths have occurred in large fires and were attributed to the building occupants panicking, it is more likely that there was a delay in those people receiving information about the fire.
• A traditional fire alarm sounder may not always be sufficient to spur people to move immediately to evacuate.
• The period of time known as pre-movement time can be a more important factor than the time it takes to physically reach an exit once movement has begun.
• People may be inclined to investigate the fire, or make further enquiries before beginning to exit the building.
• People are inclined to seek out a familiar route to leave a building, even when a different route provided as a fire escape is faster.
• Individuals will seek out and stay with those people to whom they feel an emotional attachment.
• Fire exit signs are not always noticed or remembered when they are needed and may not always provide the help they are intended to in a complex building.
• Building occupants are often prepared to try to move through smoke-filled areas despite the dangers posed.
• The ability of an individual to move towards an exit can vary considerably, depending upon their age and physical condition.
• People may be forced to retrace their steps if they have, unknowingly, been moving towards the source of the fire.

In part 113 of LWF’s series on fire engineering we will look at the types of occupancy which should be taken into account in a building’s fire safety design. 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.