The LWF Blog

Fire Safety for Facilities Management Personnel – Fire Detection & Fire Alarms – Part 203

May 30, 2023 10:44 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 202, LWF began to look at the reasons for and impact of false fire alarms. In part 203, we continue to discuss false alarms, in terms of how many false alarms can be considered ‘acceptable’.

False alarms from a fire alarm system are a nuisance, however often they occur. The impact of a malfunctioning or badly-calibrated fire alarm system can be catastrophic, however, if the building’s occupants begin to assume the sound of the fire alarm is a false alarm and do not react as expected in safely evacuating and reaching a place of safety.

BS 5839-1 provides benchmarks which indicate whether the number of false alarms experienced may be regarded as ‘acceptable’.

The environment in which the false alarms are occurring is important when considering how many false alarms may be acceptable. The standard suggests that in an environment which is relatively clean (no dust, fumes or insects) and where there is a good standard of building management, one false alarm per 100 detectors per annum is possible, even where there are very many smoke detectors in place.

On an industrial site with shift working, that figure increases to one false alarm per 75 detectors per annum as a more realistic expectation.

In most ‘normal’ circumstances, a false alarm rate of one false alarm per 50 detectors per annum should be achievable.

It should be noted that a fire alarm system incorporating mainly heat detectors rather than smoke detectors will produce fewer false alarms. However, this does not indicate that all fire alarm systems should use heat detectors, because the correct choice of detector depends upon the environment and processes that take place within the building.

For a system of 40 detectors or more, if the false alarm rate exceeds one false alarm per 20 detectors, per annum, BS 5839-1 recommends an in-depth investigation by suitable specialists. This also applies if there are three or more false alarms initiated by a single manual call point or detector.

Where a system has 40 detectors or less, the same investigation should be instigated if in a 12-month period, three or more false alarms occur.

In part 204 of this series, LWF will talk about the proper maintenance and servicing of fire alarm systems in the light of false alarms. 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.

Share this post