The LWF Blog

Fire Safety Engineering for Design – Means of Escape Design – Part 101

October 3, 2022 10:32 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 100, LWF looked at travel distances and how escape routes are protected with fire protection measures. In part 101, we continue to discuss the fire protection measures necessary for escape routes, starting with protected lobbies.

It was established in part 100 of this series that escape stairs should be enclosed with fire-resisting construction to prevent the ingress of fire and fire products such as smoke. Additional protection to the stairway can be provided through the addition of a protected lobby and, where appropriate, pressurisation of the stair enclosure.

UK guidance contains recommendations as to when a protected lobby for staircases is required, as in the following cases:

• Where only one escape stairway is provided, it is important that they are protected from fire and smoke products to ensure a safe escape for building occupants.
• Where more than one stairway is provided, but the escape capacity of one of the stairs is not discounted. It is usual for buildings with more than one stairway to discount the exit capacity of one stairway in case it is impassable due to fire. In circumstances where this is impractical (i.e. the occupant capacity of the building requires use of all stairways to effectively evacuate the persons within) the stairways should be provided with a protected lobby.
• The height of the top storey is greater than 18 metres.
• The building is designed for phased evacuation – where the floor of fire origin and adjacent floors are evacuated before other storeys of the building and tenability must therefore be maintained in the stairways.
• The stair is designed as a firefighting stair – the stairway conditions should remain tenable to allow the Fire Service to attend, use the stairways and the protected lobbies to set up their equipment.
• The stairway serves basement levels.

It should be noted that where firefighting lifts are installed, these require the addition of protected lobbies and therefore, it is common to have the firefighting lift and stairway within adjacent enclosures opening into the same protected lobbies.

In part 102 of LWF’s series on fire engineering, we will continue discussing protected lobbies for stairways in line with NFPA guidance. 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.