The LWF Blog

Fire Safety Engineering for Design – Fire Detection & Alarm Systems – Part 139

July 3, 2023 10:30 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 138, LWF looked at the classification of fire alarm systems as per BSI and NFPA. In part 139, we continue discussing the different types of property protection as per NFPA 72, before beginning to cover systems for life protection.

NFPA 72 splits the classification of fire alarm systems into different types of coverage. In the last blog we covered total or complete coverage.

Partial Coverage:

The areas to be covered as per the NFPA 72 guidance, once this is ascertained as required by the designer, are as follows;

  • All common areas,
  • All work spaces,
  • Areas such as corridors, lobbies, storage rooms,
  • Other spaces without tenants.

Selective Coverage:

Detection to be provided as required, where local codes, standards or legislation require the protection of selected areas.

No Required Coverage:

Some buildings may require coverage because the client wishes it, despite there being no requirement through codes, laws or standards.

Fire Detection Systems for Life Protection

BS 5839-1 Fire detection and fire alarm systems for buildings – Code of practice for design, installation, commissioning and maintenance of systems in non-domestic premises provides guidance on appropriate systems and coverage designed for life protection purposes – that is those systems installed in building to detect fire and provide warning to building occupants so that they may evacuate in a safe and timely manner.

It should be noted that, as per property protection systems, the NFPA do not provide guidance on the level of coverage required, but rely on designers to use their own judgement in deciding what is appropriate.

Category L systems laid out in BS 5839-1 are as follows:

L1 Fire Detection and Alarm Systems:

Detectors are required in all areas, with a few exceptions. Exceptions may include some voids of less than 800 mm in height, unless fire spread between rooms could take place, small cupboards less than 1 m2, toilets, bathrooms, some small lobbies. Floor voids in data processing rooms are to be protected, irrespective of depth. This is classed as comprehensive coverage and is as per a category P1 system.

In part 140 of LWF’s series on fire engineering, we will continue looking at the life safety system guidance contained within BS 5839-1. 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 since 1986 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.

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