The LWF Blog

Fire Safety Engineering for Design – Fire Growth – Part 89

July 12, 2022 9:23 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 88, LWF talked about smoke plume entrainment and the types of plume. In part 89, we look at spill plumes, otherwise known as flow from an opening.

The hot gases rising from a fire will be drawn to an opening in a compartment. They occur when gases rotate around and rise from the fire source through an opening into the adjacent area, which may be outside or another room/space within the building. The ascending spill plume entrains air as it rises.

The spill plume flow size is dependent on various factors, such as:

• the size of the opening
• the convective enthalpy of the gases
• whether there is a balcony, downstand or other construction element affecting flow
• the vertical height between the spill edge and the smoke layer interface in the adjacent area

Suggested equations to calculate flow from an opening can be found in CIBSE Guide E, although there are other accepted calculation methods available.

An adhered spill plume is one where there is a wall or solid construction directly above the spill edge, resulting in entrainment adhering to the wall. Adhered plumes can also be known as single-sided plumes, because the entrainment taking place above the spill edge occurs on one face only.

Where a balcony projects beyond the compartment opening and there is no wall or solid construction above the spill edge, a balcony spill plume may occur. Entrainment occurs from both sides of the rising plume. For this reason, balcony spill plumes are sometimes known as double-sided plumes, due to the entrainment above the spill edge taking place on both faces.

Channelling screens or side walls may be used below the level of the spill edge, they should extend from the compartment opening and can be used to reduce the lateral spread of the spill plume and, as a result, reduce the amount of entrainment above the spill edge.

CIBSE Guide E contains suggested equations for adhered spill plumes and balcony spill plumes. The guide also provides equations for smoke temperature, volume flow rate of smoke and ceiling flow.

In part 90 of LWF’s series on fire engineering, we will look at accumulated ceiling smoke layer. 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.