The LWF Blog

Fire Safety Engineering for Design – Means of Escape Design – Part 99

September 20, 2022 10:07 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 98, LWF discussed stair capacities and with simultaneous evacuation. In part 99, we will consider the design and provision of alternative exits for means of escape based on criteria such as distance to be travelled and predicted occupancy.

The basis on which means of escape design is based involves there being an escape route available in two directions, as a minimum. The only real exception to this rule is where the escape route is very short, i.e. between 6 metres and 30 metres depending on building use, level of fire protection and jurisdiction, and where the occupancy numbers are limited to a maximum of 50 to 60 people in the affected area.

The fire safety premise behind a choice of escape routes is that you can turn away from an area where there is a fire or a route that is filling with smoke and choose the alternative, safer route. For this reason, escape routes should be separated to avoid the potential for both to be obstructed by fire at the same time.

In the U.K., guidance illustrates that alternative escape routes should be provided at least 45 degrees apart, or must be separated by fire-resisting construction.

The U.S. codes contain a recommendation that alternative exits should be separated by a distance equal to at least one-half the diagonal drawn across the room, or one-third in buildings fitted with sprinkler systems.

Occupancy can also affect the design of means of escape and alternative escape routes. British guidance states that where more than 600 people will be occupying a room or storey, at least three adequately separated exits must be provided.

NFPA 101 requires a minimum of three exits for occupancies between 500 and 1000 and a minimum of four exits where the potential occupancy is above 1000 persons.

Codes and guidance published by British government are used in many places across the world, as is NFPA 101 from the United States. Local requirements and standards must always be adhered to where they differ in the jurisdiction to which they apply.

In part 100 of LWF’s series on fire engineering, we will discuss travel distances for means of escape. 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 for over 25 years 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.