The LWF Blog

Fire Engineering for Healthcare Premises – Fire Growth – Part 35

May 17, 2021 10:42 am

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 34 of Fire Engineering for Healthcare Premises, LWF discussed the use of design fire specifications. In part 35, we will consider what information can be gained from calculating smoke movement and how it can then be used.

Once smoke movement has been calculated, using one of the methods given in the last blog, information is provided about the smoke which can be used to identify hazardous conditions at different locations within a building. The nature of the information provided is:

  • The mass flow rate of smoke
  • The temperature of smoke
  • The velocity of smoke and hot gases
  • The volume of smoke
  • The optical density of smoke (visibility by occupants)
  • The concentration of toxic gases

With the information gained, systems can be designed and put into place to remove and control the spread of smoke and avoid areas of particular danger with the aim of making conditions tenable for evacuation and Fire Service activities.

Barriers and screens may be used to contain the smoke in reservoirs. Exhaust systems can remove the smoke or pressurisation systems may be utilised to prevent smoke entering certain areas of the building. Collectively, such systems are known as smoke control systems.

The use of smoke control systems has a significant and positive affect on the available safe egress time (ASET) and should be considered at an early stage of the design process as many other building design decisions are made based on ASET and safe evacuation of occupants in a fire situation.

Innovative building concepts may require innovative smoke control systems in order to provide adequate ASET and the effectiveness can be proved using computerised simulations, calculation methods or hot smoke tests.

ASET is the time available between the fire starting and conditions becoming untenable for occupants. Untenability in terms of conditions includes a lack of breathable air and limited visibility, as well as radiant heat from hot smoke and gases.

ASET is used in comparison with required safe egress time (RSET) which is the time it will take for occupants to evacuate, or in the case of healthcare premises, for occupants to be moved to a place of safety.  The ASET value should always be greater than RSET.

In Part 36 of LWF’s blog series, LWF will continue to discuss ASET and RSET. 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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