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Fire Safety for Facilities Management Personnel – Fire Detection & Fire Alarms – Part 201

May 15, 2023 11:15 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 200, LWF discussed analogue addressable fire alarm systems. In part 201, we continue talking about analogue fire detection and alarm systems.

There are certain advantages to the user of an analogue fire alarm system. The pre-warning signal at the control and indicating equipment (CIE) allows the investigation of potential incipient fires without alerting the full occupancy with an alarm. They have the ability to request information of each sensor at the CIE to gain data on its present signal level, which can be used by maintenance engineers to identify sensors which need to be cleaned.

On some systems, it is possible to vary the sensitivity of the detectors so that higher sensitivity is present when the premises are empty. This also helps to avoid false alarms by using slightly less sensitive settings during working hours.

Some recent fire detection and alarm systems are fitted with multi-sensor fire detectors. This means simply that they can be used to detect smoke and heat, because each detector is capable of collecting readings of both. They work in the same way as analogue systems in that the decision making is undertaken at the control and indicating equipment based on the readings received from each detector head.

This can assist with filtering out false alarms. For example, if the smoke detector is triggered but the heat detector isn’t, then it’s possible something else is happening in that area. An optical detector may be triggered by a source of steam in that area, but a heat or ionization chamber is less likely to be triggered by the same set of circumstances.

Evidence so far on multi-sensor fire alarm systems has been positive in terms of reducing instances of false alarms and so in buildings or areas where these are a problem, it would certainly be likely to help. BS 5839-1 recommends the use of multi-sensor systems for systems incorporating more than 1000 fire detector units.

In part 202 of this series, LWF will begin to talk about false alarms from fire detection and alarm systems in more detail. 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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