The LWF Blog

Fire Safety Engineering for Design – Fire Detection & Alarm Systems – Part 134

May 30, 2023 10:22 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 133, LWF discussed the use of fire detection and fire alarm systems and how they integrate with other fire protection systems. In part 134, we talk about the different types of fire alarm system.

BS 5839-1 splits fire alarms into two main categories and allocates each a letter. ‘P’ systems are those fire alarms which are designed to protect property. ‘L’ systems are primarily for the protection of life. A category P system is more likely to be found in a building containing valuable contents, but which is seldom occupied. Such systems may also be employed in buildings of historical significance. A category L system is intended for use in populated buildings, such as offices or hotels.

The standard goes further in categorising fire alarm systems, by allocating numbers alongside the P and L indicator. It is usual to see a P1 or P2 system, or L1-5.

Deciding which fire alarm system is the most appropriate choice for a current project or building is a process of the utmost importance. The fire detection and alarm requirements for the majority of buildings are covered by national and local legislation and any supporting codes and guidance. Consultation with any approving authority on relevant and applicable legislation for particular premises is advisable.

All stakeholder requirements should be considered before a final decision is taken. These may include (but are not limited to):

  • The owner of the building
  • The building’s occupier or tenant
  • Any authority having jurisdiction (e.g. building control, Fire Service)
  • Any architectural and engineering consultants
  • The building’s insurers
  • Installers of the system
  • Government health and safety departments
  • Government heritage departments, where the building may have historic value

Where the fire alarm design may be a part of a fire engineered solution for the building, it is important that there is a method of checking the operation in all known conditions, as the inter-relationship with other systems can be critical if there is a fire.

A table or chart, designed to cross-reference each set of known events with the expected outcome (or consequences). This is useful during design and installation, to ensure nothing is missed, but also afterwards as a tool for building managers. It should include reasonably foreseeable fault events over the life of the system and all potential eventualities, highlighting any single points of failure and linked operations.
In part 135 of LWF’s series on fire engineering, we will look at how to manage false alarms. 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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