The LWF Blog

Fire Engineering for Healthcare Premises – Smoke spread and control – Part 17

January 11, 2021 12:41 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 16 of Fire Engineering for Healthcare Premises, LWF looked at smoke spread and control through replacement air systems and pressurisation. In part 17, we consider smoke spread and control in healthcare environments through depressurisation.

In an atrium, depressurisation can be used to provide replacement air for a ventilation system through areas of a building that must be kept smoke-free for the safety of building occupants and firefighters.

The smoke-free environment is achieved by ensuring the neutral plane is above the highest level to be protected.

Depressurisation is not commonly seen in use in the UK. The system works to remove air and smoke from the area of the building where the fire is contained, which reduces the pressure in the space to a lower level than in adjacent areas of the building.

The pressure difference means smoke cannot move into the original area. In some cases, adjacent areas are pressurised, to further enhance the effect.

Depressurisation systems are most effective in situations where the fire-affected part of the building is adjacent to a large space and depressurisation can be carried out through use of the air handling/conditioning systems in the building. If a fire occurred, the air handling system would switch to ‘extract only’ on the floor of fire origin and to supply mode on the other floors. For systems such as this to work effectively, the potential for leakage must be relatively small, but the benefit to owners of a suitable building is that the air system is already in place.

In addition to the standard equipment, depressurisation systems may need fire-rated fans and fire-resistant ductwork to be installed, although these requirements and others will be based upon scenarios such as potential size of the fire, heat loss and smoke dilution within the duct system.

A fire strategy using a computational fluid dynamics (CFD) analysis, using a system such as FDS or JASMINE, to demonstrate the effectiveness of depressurisation should be subject to a third-party review.

In Part 18 of LWF’s blog series, LWF will discuss smoke control in the context of hot-smoke tests before moving on to look at structural fire protection. 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.