The LWF Blog

Fire Safety for Facilities Management Personnel – Fire Detection & Fire Alarms – Part 199

May 2, 2023 11:16 am

Lawrence Webster Forrest (LWF) is a specialist fire engineering and fire risk management consultancy whose aim is to give information on best practice in fire safety for facilities management personnel through this blog series. In part 198, LWF looked at radio-linked fire alarm systems. In part 199, we look at the types of fire detection and fire alarm systems.

There are two main types of fire detection and fire alarm system – addressable or non-addressable/conventional. A conventional fire alarm system will detect fire in an area and send a signal to the control and indicating equipment (CIE), but because it is non-addressable, it will not inform the CIE which detector sent the signal precisely, only giving an indication of the detection zone. The detection zone is basically which circuit the detector is linked to.

In order to assist firefighters and building occupants with ascertaining where the fire has started, the detection zone area should be limited in size, as per the restrictions given in 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.

An addressable system sends signals from each detection device to the CIE and that is shown on the CIE as the exact identity and location of the initiating detector.

A detection zone indication will also be sent, but this type of zone is not related to the circuit on which the detector is linked, but rather is designated by the software provided with the system. The ‘addresses’ of the detectors are grouped into detection zones by the software (or the installer).

The area of a detection zone is still limited by BS 5839-1, but a circuit on an addressable system can serve many zones. It is usually possible to connect more devices on a single pair of conductors than would be possible on a non-addressable system.

Addressable systems can be further sub-categorised depending upon the type of detector. They may be two state, multi-state or analogue.

Two state detectors are not commonly seen, but they are no different in principle to the two state detectors seen in non-addressable systems, but with the addition of sending their individual identity to the CIE to pinpoint the location of the signal.

Most addressable systems are analogue.

In part 200 of this series, LWF will discuss analogue addressable fire alarm systems and multi-state addressable fire alarm systems. In the meantime, if you have any queries about your own facilities or wish to discuss this blog series, please contact LWF on freephone 0800 410 1130.


Lawrence Webster Forrest is a fire engineering consultancy based in Surrey with over 35 years’ experience, which provides a wide range of consultancy services to professionals involved in the design, development and construction and operation of buildings.


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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