The LWF Blog

Fire Engineering for Healthcare Premises – Smoke spread and control – Part 16

January 4, 2021 12:52 pm

In LWF’s blog series for healthcare professionals, our aim is to give information on best practice of fire safety in hospitals and other healthcare premises. In part 15 of Fire Engineering for Healthcare Premises, LWF discussed smoke curtains and smoke venting as per HTM 05-03. In part 16, we continue looking at smoke spread and control through replacement air systems and pressurisation.

When a smoke extraction system removes air (and smoke) from an environment, there must be an adequate supply of replacement air. It is necessary to confirm the provision of and routes for replacement air (sometimes known as make-up or inlet air).

In circumstances where the building’s occupants are expected to use the route for replacement air, the velocity of the airflow should be less than 3 m/s.

One possible solution is a mechanical double reversible push-pull system. This is commonly used in stairways, where the stair is at the centre of a common corridor and has smoke shafts at each end. Double reversible fans may then be provided at the head of each shaft and smoke detectors are present at each end of the corridor. When a smoke detector is activated, the fan closest to that detector will automatically begin to remove air and smoke from the area.

The fan at the other end of the corridor will, in turn, begin to replace the air. Because of the need to stop smoke spreading to other areas of the corridor, it is important that the fans are set with a supply/extract rate.

Upon the Fire Service’s arrival, this system has the advantage of both fans being able to switch to extract, with supply air being provided from the top and bottom of the stair from a roof vent and the stairs door at the bottom. To prevent negative pressures, the vent which is placed at the head of the stairs will open automatically when the system begins operation.

When looking at pressurisation, the effects of stack effect, wind and fire pressure must be considered.  A pressurisation system relies on the presence of building leakage paths.

In Part 17 of LWF’s blog series, LWF will discuss smoke spread and control in healthcare environments through depressurisation and hot-smoke tests. 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 LWF on freephone 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.

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